diff --git a/java/res/layout/emoji_keyboard_page.xml b/java/res/layout/emoji_keyboard_page.xml
index 9afad36..0d10861 100644
--- a/java/res/layout/emoji_keyboard_page.xml
+++ b/java/res/layout/emoji_keyboard_page.xml
@@ -18,7 +18,7 @@
 */
 -->
 
-<com.android.inputmethod.keyboard.internal.EmojiPageKeyboardView
+<com.android.inputmethod.keyboard.emoji.EmojiPageKeyboardView
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/emoji_keyboard_page"
     android:layoutDirection="ltr"
diff --git a/java/res/layout/emoji_palettes_view.xml b/java/res/layout/emoji_palettes_view.xml
index 552a474..7618871 100644
--- a/java/res/layout/emoji_palettes_view.xml
+++ b/java/res/layout/emoji_palettes_view.xml
@@ -18,7 +18,7 @@
 */
 -->
 
-<com.android.inputmethod.keyboard.EmojiPalettesView
+<com.android.inputmethod.keyboard.emoji.EmojiPalettesView
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/emoji_keyboard_view"
     android:orientation="vertical"
@@ -78,7 +78,7 @@
         android:id="@+id/emoji_keyboard_pager"
         android:layout_width="match_parent"
         android:layout_height="wrap_content" />
-    <com.android.inputmethod.keyboard.EmojiCategoryPageIndicatorView
+    <com.android.inputmethod.keyboard.emoji.EmojiCategoryPageIndicatorView
         android:id="@+id/emoji_category_page_id_view"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
@@ -109,4 +109,4 @@
             android:gravity="center"
             android:layout_height="match_parent" />
     </LinearLayout>
-</com.android.inputmethod.keyboard.EmojiPalettesView>
+</com.android.inputmethod.keyboard.emoji.EmojiPalettesView>
diff --git a/java/src/com/android/inputmethod/keyboard/KeyboardSwitcher.java b/java/src/com/android/inputmethod/keyboard/KeyboardSwitcher.java
index ad8fc73..fc9faa6 100644
--- a/java/src/com/android/inputmethod/keyboard/KeyboardSwitcher.java
+++ b/java/src/com/android/inputmethod/keyboard/KeyboardSwitcher.java
@@ -28,6 +28,7 @@
 
 import com.android.inputmethod.compat.InputMethodServiceCompatUtils;
 import com.android.inputmethod.keyboard.KeyboardLayoutSet.KeyboardLayoutSetException;
+import com.android.inputmethod.keyboard.emoji.EmojiPalettesView;
 import com.android.inputmethod.keyboard.internal.KeyboardState;
 import com.android.inputmethod.keyboard.internal.KeyboardTextsSet;
 import com.android.inputmethod.latin.InputView;
diff --git a/java/src/com/android/inputmethod/keyboard/internal/DynamicGridKeyboard.java b/java/src/com/android/inputmethod/keyboard/emoji/DynamicGridKeyboard.java
similarity index 97%
rename from java/src/com/android/inputmethod/keyboard/internal/DynamicGridKeyboard.java
rename to java/src/com/android/inputmethod/keyboard/emoji/DynamicGridKeyboard.java
index a4879b8..c7a9025 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/DynamicGridKeyboard.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/DynamicGridKeyboard.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard.internal;
+package com.android.inputmethod.keyboard.emoji;
 
 import android.content.SharedPreferences;
 import android.text.TextUtils;
@@ -35,8 +35,7 @@
 /**
  * This is a Keyboard class where you can add keys dynamically shown in a grid layout
  */
-// TODO: Move this class to com.android.inputmethod.emoji package.
-public class DynamicGridKeyboard extends Keyboard {
+final class DynamicGridKeyboard extends Keyboard {
     private static final String TAG = DynamicGridKeyboard.class.getSimpleName();
     private static final int TEMPLATE_KEY_CODE_0 = 0x30;
     private static final int TEMPLATE_KEY_CODE_1 = 0x31;
diff --git a/java/src/com/android/inputmethod/keyboard/internal/EmojiCategory.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiCategory.java
similarity index 98%
rename from java/src/com/android/inputmethod/keyboard/internal/EmojiCategory.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiCategory.java
index 10bd621..dd0e3e8 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/EmojiCategory.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiCategory.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard.internal;
+package com.android.inputmethod.keyboard.emoji;
 
 import android.content.SharedPreferences;
 import android.content.res.Resources;
@@ -39,8 +39,7 @@
 import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 
-// TODO: Move this class to com.android.inputmethod.emoji package.
-public final class EmojiCategory {
+final class EmojiCategory {
     private final String TAG = EmojiCategory.class.getSimpleName();
 
     private static final int ID_UNSPECIFIED = -1;
diff --git a/java/src/com/android/inputmethod/keyboard/EmojiCategoryPageIndicatorView.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiCategoryPageIndicatorView.java
similarity index 95%
rename from java/src/com/android/inputmethod/keyboard/EmojiCategoryPageIndicatorView.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiCategoryPageIndicatorView.java
index 9922f90..74cfd9b 100644
--- a/java/src/com/android/inputmethod/keyboard/EmojiCategoryPageIndicatorView.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiCategoryPageIndicatorView.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard;
+package com.android.inputmethod.keyboard.emoji;
 
 import com.android.inputmethod.latin.R;
 
@@ -24,7 +24,6 @@
 import android.util.AttributeSet;
 import android.widget.LinearLayout;
 
-//TODO: Move this class to com.android.inputmethod.emoji package.
 public final class EmojiCategoryPageIndicatorView extends LinearLayout {
     private static final float BOTTOM_MARGIN_RATIO = 1.0f;
     private final Paint mPaint = new Paint();
diff --git a/java/src/com/android/inputmethod/keyboard/internal/EmojiLayoutParams.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiLayoutParams.java
similarity index 95%
rename from java/src/com/android/inputmethod/keyboard/internal/EmojiLayoutParams.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiLayoutParams.java
index 78af66b..77c183a 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/EmojiLayoutParams.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiLayoutParams.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard.internal;
+package com.android.inputmethod.keyboard.emoji;
 
 import com.android.inputmethod.latin.R;
 import com.android.inputmethod.latin.utils.ResourceUtils;
@@ -24,8 +24,7 @@
 import android.widget.ImageView;
 import android.widget.LinearLayout;
 
-//TODO: Move this class to com.android.inputmethod.emoji package.
-public final class EmojiLayoutParams {
+final class EmojiLayoutParams {
     private static final int DEFAULT_KEYBOARD_ROWS = 4;
 
     public final int mEmojiPagerHeight;
diff --git a/java/src/com/android/inputmethod/keyboard/internal/EmojiPageKeyboardView.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPageKeyboardView.java
similarity index 94%
rename from java/src/com/android/inputmethod/keyboard/internal/EmojiPageKeyboardView.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiPageKeyboardView.java
index 2f67d19..d14ffee 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/EmojiPageKeyboardView.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPageKeyboardView.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard.internal;
+package com.android.inputmethod.keyboard.emoji;
 
 import android.content.Context;
 import android.os.Handler;
@@ -26,16 +26,14 @@
 import com.android.inputmethod.keyboard.KeyDetector;
 import com.android.inputmethod.keyboard.Keyboard;
 import com.android.inputmethod.keyboard.KeyboardView;
-import com.android.inputmethod.keyboard.PointerTracker;
 import com.android.inputmethod.latin.R;
 
 /**
  * This is an extended {@link KeyboardView} class that hosts an emoji page keyboard.
- * Multi-touch unsupported. No {@link PointerTracker}s. No gesture support.
+ * Multi-touch unsupported. No gesture support.
  */
-// TODO: Move this class to com.android.inputmethod.emoji package.
 // TODO: Implement key popup preview.
-public final class EmojiPageKeyboardView extends KeyboardView implements
+final class EmojiPageKeyboardView extends KeyboardView implements
         GestureDetector.OnGestureListener {
     private static final long KEY_PRESS_DELAY_TIME = 250;  // msec
     private static final long KEY_RELEASE_DELAY_TIME = 30;  // msec
diff --git a/java/src/com/android/inputmethod/keyboard/internal/EmojiPalettesAdapter.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesAdapter.java
similarity index 96%
rename from java/src/com/android/inputmethod/keyboard/internal/EmojiPalettesAdapter.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesAdapter.java
index a44d134..52a4dde 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/EmojiPalettesAdapter.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesAdapter.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard.internal;
+package com.android.inputmethod.keyboard.emoji;
 
 import android.support.v4.view.PagerAdapter;
 import android.util.Log;
@@ -29,8 +29,7 @@
 import com.android.inputmethod.latin.R;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 
-// TODO: Move this class to com.android.inputmethod.emoji package.
-public final class EmojiPalettesAdapter extends PagerAdapter {
+final class EmojiPalettesAdapter extends PagerAdapter {
     private static final String TAG = EmojiPalettesAdapter.class.getSimpleName();
     private static final boolean DEBUG_PAGER = false;
 
diff --git a/java/src/com/android/inputmethod/keyboard/EmojiPalettesView.java b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesView.java
similarity index 97%
rename from java/src/com/android/inputmethod/keyboard/EmojiPalettesView.java
rename to java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesView.java
index 55e8071..3813c57 100644
--- a/java/src/com/android/inputmethod/keyboard/EmojiPalettesView.java
+++ b/java/src/com/android/inputmethod/keyboard/emoji/EmojiPalettesView.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.android.inputmethod.keyboard;
+package com.android.inputmethod.keyboard.emoji;
 
 import static com.android.inputmethod.latin.Constants.NOT_A_COORDINATE;
 
@@ -40,10 +40,10 @@
 import android.widget.TabHost.OnTabChangeListener;
 import android.widget.TextView;
 
-import com.android.inputmethod.keyboard.internal.EmojiCategory;
-import com.android.inputmethod.keyboard.internal.EmojiLayoutParams;
-import com.android.inputmethod.keyboard.internal.EmojiPageKeyboardView;
-import com.android.inputmethod.keyboard.internal.EmojiPalettesAdapter;
+import com.android.inputmethod.keyboard.Key;
+import com.android.inputmethod.keyboard.KeyboardActionListener;
+import com.android.inputmethod.keyboard.KeyboardLayoutSet;
+import com.android.inputmethod.keyboard.KeyboardView;
 import com.android.inputmethod.keyboard.internal.KeyDrawParams;
 import com.android.inputmethod.keyboard.internal.KeyVisualAttributes;
 import com.android.inputmethod.keyboard.internal.KeyboardIconsSet;
@@ -65,7 +65,6 @@
  * </ol>
  * Because of the above reasons, this class doesn't extend {@link KeyboardView}.
  */
-// TODO: Move this class to com.android.inputmethod.emoji package.
 public final class EmojiPalettesView extends LinearLayout implements OnTabChangeListener,
         ViewPager.OnPageChangeListener, View.OnClickListener, View.OnTouchListener,
         EmojiPageKeyboardView.OnKeyEventListener {
@@ -317,7 +316,7 @@
 
     /**
      * Called from {@link EmojiPageKeyboardView} through
-     * {@link com.android.inputmethod.keyboard.internal.EmojiPageKeyboardView.OnKeyEventListener}
+     * {@link com.android.inputmethod.keyboard.emoji.EmojiPageKeyboardView.OnKeyEventListener}
      * interface to handle touch events from non-View-based elements such as Emoji buttons.
      */
     @Override
@@ -328,7 +327,7 @@
 
     /**
      * Called from {@link EmojiPageKeyboardView} through
-     * {@link com.android.inputmethod.keyboard.internal.EmojiPageKeyboardView.OnKeyEventListener}
+     * {@link com.android.inputmethod.keyboard.emoji.EmojiPageKeyboardView.OnKeyEventListener}
      * interface to handle touch events from non-View-based elements such as Emoji buttons.
      */
     @Override
diff --git a/native/jni/CleanupNativeFileList.mk b/native/jni/CleanupNativeFileList.mk
index 1738f8c..eed6f1e 100644
--- a/native/jni/CleanupNativeFileList.mk
+++ b/native/jni/CleanupNativeFileList.mk
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 LATIN_IME_CORE_SRC_FILES :=
+LATIN_IME_CORE_SRC_FILES_BACKWARD_V401 :=
 LATIN_IME_CORE_TEST_FILES :=
 LATIN_IME_JNI_SRC_FILES :=
 LATIN_IME_SRC_DIR :=
diff --git a/native/jni/NativeFileList.mk b/native/jni/NativeFileList.mk
index f418f6e..cb337e6 100644
--- a/native/jni/NativeFileList.mk
+++ b/native/jni/NativeFileList.mk
@@ -99,6 +99,27 @@
         log_utils.cpp \
         time_keeper.cpp)
 
+LATIN_IME_CORE_SRC_FILES_BACKWARD_V401 := \
+    $(addprefix suggest/policyimpl/dictionary/structure/backward/v401/, \
+        ver4_dict_buffers.cpp \
+        ver4_dict_constants.cpp \
+        ver4_patricia_trie_node_reader.cpp \
+        ver4_patricia_trie_node_writer.cpp \
+        ver4_patricia_trie_policy.cpp \
+        ver4_patricia_trie_reading_utils.cpp \
+        ver4_patricia_trie_writing_helper.cpp \
+        ver4_pt_node_array_reader.cpp) \
+    $(addprefix suggest/policyimpl/dictionary/structure/backward/v401/content/, \
+        bigram_dict_content.cpp \
+        probability_dict_content.cpp \
+        shortcut_dict_content.cpp \
+        sparse_table_dict_content.cpp \
+        terminal_position_lookup_table.cpp) \
+    $(addprefix suggest/policyimpl/dictionary/structure/backward/v401/bigram/, \
+        ver4_bigram_list_policy.cpp)
+
+LATIN_IME_CORE_SRC_FILES += $(LATIN_IME_CORE_SRC_FILES_BACKWARD_V401)
+
 LATIN_IME_CORE_TEST_FILES := \
     defines_test.cpp \
     suggest/core/layout/normal_distribution_2d_test.cpp \
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/Readme.txt b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/Readme.txt
new file mode 100644
index 0000000..9e29e83
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/Readme.txt
@@ -0,0 +1 @@
+Files under this directory have been auto generated.
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.cpp
new file mode 100644
index 0000000..7ad072f
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.cpp
@@ -0,0 +1,290 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT CHANGE THE LOGIC IN THIS FILE !!!!!
+ * Do not edit this file other than updating policy's interface.
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/bigram/ver4_bigram_list_policy.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h"
+
+#include "suggest/core/dictionary/property/bigram_property.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/bigram/bigram_list_read_write_utils.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+void Ver4BigramListPolicy::getNextBigram(int *const outBigramPos, int *const outProbability,
+        bool *const outHasNext, int *const bigramEntryPos) const {
+    const BigramEntry bigramEntry =
+            mBigramDictContent->getBigramEntryAndAdvancePosition(bigramEntryPos);
+    if (outBigramPos) {
+        // Lookup target PtNode position.
+        *outBigramPos = mTerminalPositionLookupTable->getTerminalPtNodePosition(
+                bigramEntry.getTargetTerminalId());
+    }
+    if (outProbability) {
+        if (bigramEntry.hasHistoricalInfo()) {
+            *outProbability =
+                    ForgettingCurveUtils::decodeProbability(bigramEntry.getHistoricalInfo(),
+                            mHeaderPolicy);
+        } else {
+            *outProbability = bigramEntry.getProbability();
+        }
+    }
+    if (outHasNext) {
+        *outHasNext = bigramEntry.hasNext();
+    }
+}
+
+bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTargetTerminalId,
+        const BigramProperty *const bigramProperty, bool *const outAddedNewEntry) {
+    // 1. The word has no bigrams yet.
+    // 2. The word has bigrams, and there is the target in the list.
+    // 3. The word has bigrams, and there is an invalid entry that can be reclaimed.
+    // 4. The word has bigrams. We have to append new bigram entry to the list.
+    // 5. Same as 4, but the list is the last entry of the content file.
+    if (outAddedNewEntry) {
+        *outAddedNewEntry = false;
+    }
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Case 1. PtNode that doesn't have a bigram list.
+        // Create new bigram list.
+        if (!mBigramDictContent->createNewBigramList(terminalId)) {
+            return false;
+        }
+        const BigramEntry newBigramEntry(false /* hasNext */, NOT_A_PROBABILITY,
+                newTargetTerminalId);
+        const BigramEntry bigramEntryToWrite = createUpdatedBigramEntryFrom(&newBigramEntry,
+                bigramProperty);
+        // Write an entry.
+        const int writingPos =  mBigramDictContent->getBigramListHeadPos(terminalId);
+        if (!mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, writingPos)) {
+            return false;
+        }
+        if (outAddedNewEntry) {
+            *outAddedNewEntry = true;
+        }
+        return true;
+    }
+
+    int tailEntryPos = NOT_A_DICT_POS;
+    const int entryPosToUpdate = getEntryPosToUpdate(newTargetTerminalId, bigramListPos,
+            &tailEntryPos);
+    if (tailEntryPos != NOT_A_DICT_POS || entryPosToUpdate == NOT_A_DICT_POS) {
+        // Case 4, 5.
+        // Add new entry to the bigram list.
+        if (tailEntryPos == NOT_A_DICT_POS) {
+            // Case 4. Create new bigram list.
+            if (!mBigramDictContent->createNewBigramList(terminalId)) {
+                return false;
+            }
+            const int destPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+            // Copy existing bigram list.
+            if (!mBigramDictContent->copyBigramList(bigramListPos, destPos, &tailEntryPos)) {
+                return false;
+            }
+        }
+        // Write new entry at the tail position of the bigram content.
+        const BigramEntry newBigramEntry(false /* hasNext */, NOT_A_PROBABILITY,
+                newTargetTerminalId);
+        const BigramEntry bigramEntryToWrite = createUpdatedBigramEntryFrom(
+                &newBigramEntry, bigramProperty);
+        if (!mBigramDictContent->writeBigramEntryAtTail(&bigramEntryToWrite)) {
+            return false;
+        }
+        // Update has next flag of the tail entry.
+        if (!updateHasNextFlag(true /* hasNext */, tailEntryPos)) {
+            return false;
+        }
+        if (outAddedNewEntry) {
+            *outAddedNewEntry = true;
+        }
+        return true;
+    }
+
+    // Case 2. Overwrite the existing entry. Case 3. Reclaim and reuse the existing invalid entry.
+    const BigramEntry originalBigramEntry = mBigramDictContent->getBigramEntry(entryPosToUpdate);
+    if (!originalBigramEntry.isValid()) {
+        // Case 3. Reuse the existing invalid entry. outAddedNewEntry is false when an existing
+        // entry is updated.
+        if (outAddedNewEntry) {
+            *outAddedNewEntry = true;
+        }
+    }
+    const BigramEntry updatedBigramEntry =
+            originalBigramEntry.updateTargetTerminalIdAndGetEntry(newTargetTerminalId);
+    const BigramEntry bigramEntryToWrite = createUpdatedBigramEntryFrom(
+            &updatedBigramEntry, bigramProperty);
+    return mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, entryPosToUpdate);
+}
+
+bool Ver4BigramListPolicy::removeEntry(const int terminalId, const int targetTerminalId) {
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Bigram list doesn't exist.
+        return false;
+    }
+    const int entryPosToUpdate = getEntryPosToUpdate(targetTerminalId, bigramListPos,
+            nullptr /* outTailEntryPos */);
+    if (entryPosToUpdate == NOT_A_DICT_POS) {
+        // Bigram entry doesn't exist.
+        return false;
+    }
+    const BigramEntry bigramEntry = mBigramDictContent->getBigramEntry(entryPosToUpdate);
+    if (targetTerminalId != bigramEntry.getTargetTerminalId()) {
+        // Bigram entry doesn't exist.
+        return false;
+    }
+    // Remove bigram entry by marking it as invalid entry and overwriting the original entry.
+    const BigramEntry updatedBigramEntry = bigramEntry.getInvalidatedEntry();
+    return mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPosToUpdate);
+}
+
+bool Ver4BigramListPolicy::updateAllBigramEntriesAndDeleteUselessEntries(const int terminalId,
+        int *const outBigramCount) {
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Bigram list doesn't exist.
+        return true;
+    }
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    while (hasNext) {
+        const int entryPos = readingPos;
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (!bigramEntry.isValid()) {
+            continue;
+        }
+        const int targetPtNodePos = mTerminalPositionLookupTable->getTerminalPtNodePosition(
+                bigramEntry.getTargetTerminalId());
+        if (targetPtNodePos == NOT_A_DICT_POS) {
+            // Invalidate bigram entry.
+            const BigramEntry updatedBigramEntry = bigramEntry.getInvalidatedEntry();
+            if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
+                return false;
+            }
+        } else if (bigramEntry.hasHistoricalInfo()) {
+            const HistoricalInfo historicalInfo = ForgettingCurveUtils::createHistoricalInfoToSave(
+                    bigramEntry.getHistoricalInfo(), mHeaderPolicy);
+            if (ForgettingCurveUtils::needsToKeep(&historicalInfo, mHeaderPolicy)) {
+                const BigramEntry updatedBigramEntry =
+                        bigramEntry.updateHistoricalInfoAndGetEntry(&historicalInfo);
+                if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
+                    return false;
+                }
+                *outBigramCount += 1;
+            } else {
+                // Remove entry.
+                const BigramEntry updatedBigramEntry = bigramEntry.getInvalidatedEntry();
+                if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
+                    return false;
+                }
+            }
+        } else {
+            *outBigramCount += 1;
+        }
+    }
+    return true;
+}
+
+int Ver4BigramListPolicy::getBigramEntryConut(const int terminalId) {
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Bigram list doesn't exist.
+        return 0;
+    }
+    int bigramCount = 0;
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    while (hasNext) {
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (bigramEntry.isValid()) {
+            bigramCount++;
+        }
+    }
+    return bigramCount;
+}
+
+int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
+        const int bigramListPos, int *const outTailEntryPos) const {
+    if (outTailEntryPos) {
+        *outTailEntryPos = NOT_A_DICT_POS;
+    }
+    bool hasNext = true;
+    int invalidEntryPos = NOT_A_DICT_POS;
+    int readingPos = bigramListPos;
+    while (hasNext) {
+        const int entryPos = readingPos;
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (bigramEntry.getTargetTerminalId() == targetTerminalIdToFind) {
+            // Entry with same target is found.
+            return entryPos;
+        } else if (!bigramEntry.isValid()) {
+            // Invalid entry that can be reused is found.
+            invalidEntryPos = entryPos;
+        }
+        if (!hasNext && mBigramDictContent->isContentTailPos(readingPos)) {
+            if (outTailEntryPos) {
+                *outTailEntryPos = entryPos;
+            }
+        }
+    }
+    return invalidEntryPos;
+}
+
+const BigramEntry Ver4BigramListPolicy::createUpdatedBigramEntryFrom(
+        const BigramEntry *const originalBigramEntry,
+        const BigramProperty *const bigramProperty) const {
+    // TODO: Consolidate historical info and probability.
+    if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
+        const HistoricalInfo historicalInfoForUpdate(bigramProperty->getTimestamp(),
+                bigramProperty->getLevel(), bigramProperty->getCount());
+        const HistoricalInfo updatedHistoricalInfo =
+                ForgettingCurveUtils::createUpdatedHistoricalInfo(
+                        originalBigramEntry->getHistoricalInfo(), bigramProperty->getProbability(),
+                        &historicalInfoForUpdate, mHeaderPolicy);
+        return originalBigramEntry->updateHistoricalInfoAndGetEntry(&updatedHistoricalInfo);
+    } else {
+        return originalBigramEntry->updateProbabilityAndGetEntry(bigramProperty->getProbability());
+    }
+}
+
+bool Ver4BigramListPolicy::updateHasNextFlag(const bool hasNext, const int bigramEntryPos) {
+    const BigramEntry bigramEntry = mBigramDictContent->getBigramEntry(bigramEntryPos);
+    const BigramEntry updatedBigramEntry = bigramEntry.updateHasNextAndGetEntry(hasNext);
+    return mBigramDictContent->writeBigramEntry(&updatedBigramEntry, bigramEntryPos);
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h
new file mode 100644
index 0000000..adf687b
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT CHANGE THE LOGIC IN THIS FILE !!!!!
+ * Do not edit this file other than updating policy's interface.
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/bigram/ver4_bigram_list_policy.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_BIGRAM_LIST_POLICY_H
+#define LATINIME_BACKWARD_V401_VER4_BIGRAM_LIST_POLICY_H
+
+#include "defines.h"
+#include "suggest/core/policy/dictionary_bigrams_structure_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_entry.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class BigramDictContent;
+} // namespace v401
+} // namespace backward
+class BigramProperty;
+namespace backward {
+namespace v401 {
+} // namespace v401
+} // namespace backward
+class HeaderPolicy;
+namespace backward {
+namespace v401 {
+class TerminalPositionLookupTable;
+
+class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
+ public:
+    Ver4BigramListPolicy(BigramDictContent *const bigramDictContent,
+            const TerminalPositionLookupTable *const terminalPositionLookupTable,
+            const HeaderPolicy *const headerPolicy)
+            : mBigramDictContent(bigramDictContent),
+              mTerminalPositionLookupTable(terminalPositionLookupTable),
+              mHeaderPolicy(headerPolicy) {}
+
+    void getNextBigram(int *const outBigramPos, int *const outProbability,
+            bool *const outHasNext, int *const bigramEntryPos) const;
+
+    void skipAllBigrams(int *const pos) const {
+        // Do nothing because we don't need to skip bigram lists in ver4 dictionaries.
+    }
+
+    bool addNewEntry(const int terminalId, const int newTargetTerminalId,
+            const BigramProperty *const bigramProperty, bool *const outAddedNewEntry);
+
+    bool removeEntry(const int terminalId, const int targetTerminalId);
+
+    bool updateAllBigramEntriesAndDeleteUselessEntries(const int terminalId,
+            int *const outBigramCount);
+
+    int getBigramEntryConut(const int terminalId);
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4BigramListPolicy);
+
+    int getEntryPosToUpdate(const int targetTerminalIdToFind, const int bigramListPos,
+            int *const outTailEntryPos) const;
+
+    const BigramEntry createUpdatedBigramEntryFrom(const BigramEntry *const originalBigramEntry,
+            const BigramProperty *const bigramProperty) const;
+
+    bool updateHasNextFlag(const bool hasNext, const int bigramEntryPos);
+
+    BigramDictContent *const mBigramDictContent;
+    const TerminalPositionLookupTable *const mTerminalPositionLookupTable;
+    const HeaderPolicy *const mHeaderPolicy;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_BIGRAM_LIST_POLICY_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.cpp
new file mode 100644
index 0000000..1e53ff9
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.cpp
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h"
+
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+const BigramEntry BigramDictContent::getBigramEntryAndAdvancePosition(
+        int *const bigramEntryPos) const {
+    const BufferWithExtendableBuffer *const bigramListBuffer = getContentBuffer();
+    if (*bigramEntryPos < 0 || *bigramEntryPos >=  bigramListBuffer->getTailPosition()) {
+        AKLOGE("Invalid bigram entry position. bigramEntryPos: %d, bufSize: %d",
+                *bigramEntryPos, bigramListBuffer->getTailPosition());
+        ASSERT(false);
+        return BigramEntry(false /* hasNext */, NOT_A_PROBABILITY,
+                Ver4DictConstants::NOT_A_TERMINAL_ID);
+    }
+    const int bigramFlags = bigramListBuffer->readUintAndAdvancePosition(
+            Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE, bigramEntryPos);
+    const bool hasNext = (bigramFlags & Ver4DictConstants::BIGRAM_HAS_NEXT_MASK) != 0;
+    int probability = NOT_A_PROBABILITY;
+    int timestamp = NOT_A_TIMESTAMP;
+    int level = 0;
+    int count = 0;
+    if (mHasHistoricalInfo) {
+        probability = bigramListBuffer->readUintAndAdvancePosition(
+                Ver4DictConstants::PROBABILITY_SIZE, bigramEntryPos);
+        timestamp = bigramListBuffer->readUintAndAdvancePosition(
+                Ver4DictConstants::TIME_STAMP_FIELD_SIZE, bigramEntryPos);
+        level = bigramListBuffer->readUintAndAdvancePosition(
+                Ver4DictConstants::WORD_LEVEL_FIELD_SIZE, bigramEntryPos);
+        count = bigramListBuffer->readUintAndAdvancePosition(
+                Ver4DictConstants::WORD_COUNT_FIELD_SIZE, bigramEntryPos);
+    } else {
+        probability = bigramFlags & Ver4DictConstants::BIGRAM_PROBABILITY_MASK;
+    }
+    const int encodedTargetTerminalId = bigramListBuffer->readUintAndAdvancePosition(
+            Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, bigramEntryPos);
+    const int targetTerminalId =
+            (encodedTargetTerminalId == Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID) ?
+                    Ver4DictConstants::NOT_A_TERMINAL_ID : encodedTargetTerminalId;
+    if (mHasHistoricalInfo) {
+        const HistoricalInfo historicalInfo(timestamp, level, count);
+        return BigramEntry(hasNext, probability, &historicalInfo, targetTerminalId);
+    } else {
+        return BigramEntry(hasNext, probability, targetTerminalId);
+    }
+}
+
+bool BigramDictContent::writeBigramEntryAndAdvancePosition(
+        const BigramEntry *const bigramEntryToWrite, int *const entryWritingPos) {
+    BufferWithExtendableBuffer *const bigramListBuffer = getWritableContentBuffer();
+    const int bigramFlags = createAndGetBigramFlags(
+            mHasHistoricalInfo ? 0 : bigramEntryToWrite->getProbability(),
+            bigramEntryToWrite->hasNext());
+    if (!bigramListBuffer->writeUintAndAdvancePosition(bigramFlags,
+            Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE, entryWritingPos)) {
+        AKLOGE("Cannot write bigram flags. pos: %d, flags: %x", *entryWritingPos, bigramFlags);
+        return false;
+    }
+    if (mHasHistoricalInfo) {
+        if (!bigramListBuffer->writeUintAndAdvancePosition(bigramEntryToWrite->getProbability(),
+                Ver4DictConstants::PROBABILITY_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram probability. pos: %d, probability: %d", *entryWritingPos,
+                    bigramEntryToWrite->getProbability());
+            return false;
+        }
+        const HistoricalInfo *const historicalInfo = bigramEntryToWrite->getHistoricalInfo();
+        if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getTimeStamp(),
+                Ver4DictConstants::TIME_STAMP_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram timestamps. pos: %d, timestamp: %d", *entryWritingPos,
+                    historicalInfo->getTimeStamp());
+            return false;
+        }
+        if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getLevel(),
+                Ver4DictConstants::WORD_LEVEL_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram level. pos: %d, level: %d", *entryWritingPos,
+                    historicalInfo->getLevel());
+            return false;
+        }
+        if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getCount(),
+                Ver4DictConstants::WORD_COUNT_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram count. pos: %d, count: %d", *entryWritingPos,
+                    historicalInfo->getCount());
+            return false;
+        }
+    }
+    const int targetTerminalIdToWrite =
+            (bigramEntryToWrite->getTargetTerminalId() == Ver4DictConstants::NOT_A_TERMINAL_ID) ?
+                    Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID :
+                            bigramEntryToWrite->getTargetTerminalId();
+    if (!bigramListBuffer->writeUintAndAdvancePosition(targetTerminalIdToWrite,
+            Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, entryWritingPos)) {
+        AKLOGE("Cannot write bigram target terminal id. pos: %d, target terminal id: %d",
+                *entryWritingPos, bigramEntryToWrite->getTargetTerminalId());
+        return false;
+    }
+    return true;
+}
+
+bool BigramDictContent::copyBigramList(const int bigramListPos, const int toPos,
+        int *const outTailEntryPos) {
+    int readingPos = bigramListPos;
+    int writingPos = toPos;
+    bool hasNext = true;
+    while (hasNext) {
+        const BigramEntry bigramEntry = getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (!hasNext) {
+            *outTailEntryPos = writingPos;
+        }
+        if (!writeBigramEntryAndAdvancePosition(&bigramEntry, &writingPos)) {
+            AKLOGE("Cannot write bigram entry to copy. pos: %d", writingPos);
+            return false;
+        }
+    }
+    return true;
+}
+
+bool BigramDictContent::runGC(const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+        const BigramDictContent *const originalBigramDictContent,
+        int *const outBigramEntryCount) {
+    for (TerminalPositionLookupTable::TerminalIdMap::const_iterator it = terminalIdMap->begin();
+            it != terminalIdMap->end(); ++it) {
+        const int originalBigramListPos =
+                originalBigramDictContent->getBigramListHeadPos(it->first);
+        if (originalBigramListPos == NOT_A_DICT_POS) {
+            // This terminal does not have a bigram list.
+            continue;
+        }
+        const int bigramListPos = getContentBuffer()->getTailPosition();
+        int bigramEntryCount = 0;
+        // Copy bigram list with GC from original content.
+        if (!runGCBigramList(originalBigramListPos, originalBigramDictContent, bigramListPos,
+                terminalIdMap, &bigramEntryCount)) {
+            AKLOGE("Cannot complete GC for the bigram list. original pos: %d, pos: %d",
+                    originalBigramListPos, bigramListPos);
+            return false;
+        }
+        if (bigramEntryCount == 0) {
+            // All bigram entries are useless. This terminal does not have a bigram list.
+            continue;
+        }
+        *outBigramEntryCount += bigramEntryCount;
+        // Set bigram list position to the lookup table.
+        if (!getUpdatableAddressLookupTable()->set(it->second, bigramListPos)) {
+            AKLOGE("Cannot set bigram list position. terminal id: %d, pos: %d",
+                    it->second, bigramListPos);
+            return false;
+        }
+    }
+    return true;
+}
+
+// Returns whether GC for the bigram list was succeeded or not.
+bool BigramDictContent::runGCBigramList(const int bigramListPos,
+        const BigramDictContent *const sourceBigramDictContent, const int toPos,
+        const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+        int *const outEntrycount) {
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    int writingPos = toPos;
+    int lastEntryPos = NOT_A_DICT_POS;
+    while (hasNext) {
+        const BigramEntry originalBigramEntry =
+                sourceBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = originalBigramEntry.hasNext();
+        if (originalBigramEntry.getTargetTerminalId() == Ver4DictConstants::NOT_A_TERMINAL_ID) {
+            continue;
+        }
+        TerminalPositionLookupTable::TerminalIdMap::const_iterator it =
+                terminalIdMap->find(originalBigramEntry.getTargetTerminalId());
+        if (it == terminalIdMap->end()) {
+            // Target word has been removed.
+            continue;
+        }
+        lastEntryPos = hasNext ? writingPos : NOT_A_DICT_POS;
+        const BigramEntry updatedBigramEntry =
+                originalBigramEntry.updateTargetTerminalIdAndGetEntry(it->second);
+        if (!writeBigramEntryAndAdvancePosition(&updatedBigramEntry, &writingPos)) {
+            AKLOGE("Cannot write bigram entry to run GC. pos: %d", writingPos);
+            return false;
+        }
+        *outEntrycount += 1;
+    }
+    if (lastEntryPos != NOT_A_DICT_POS) {
+        // Update has next flag in the last written entry.
+        const BigramEntry bigramEntry = getBigramEntry(lastEntryPos).updateHasNextAndGetEntry(
+                false /* hasNext */);
+        if (!writeBigramEntry(&bigramEntry, lastEntryPos)) {
+            AKLOGE("Cannot write bigram entry to set hasNext flag after GC. pos: %d", writingPos);
+            return false;
+        }
+    }
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h
new file mode 100644
index 0000000..f9c474b
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_BIGRAM_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_BIGRAM_DICT_CONTENT_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_entry.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class BigramDictContent : public SparseTableDictContent {
+ public:
+    BigramDictContent(const char *const dictPath, const bool hasHistoricalInfo,
+            const bool isUpdatable)
+            : SparseTableDictContent(dictPath,
+                      Ver4DictConstants::BIGRAM_LOOKUP_TABLE_FILE_EXTENSION,
+                      Ver4DictConstants::BIGRAM_CONTENT_TABLE_FILE_EXTENSION,
+                      Ver4DictConstants::BIGRAM_FILE_EXTENSION, isUpdatable,
+                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE,
+                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE),
+              mHasHistoricalInfo(hasHistoricalInfo) {}
+
+    BigramDictContent(const bool hasHistoricalInfo)
+            : SparseTableDictContent(Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE,
+                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE),
+              mHasHistoricalInfo(hasHistoricalInfo) {}
+
+    const BigramEntry getBigramEntry(const int bigramEntryPos) const {
+        int readingPos = bigramEntryPos;
+        return getBigramEntryAndAdvancePosition(&readingPos);
+    }
+
+    const BigramEntry getBigramEntryAndAdvancePosition(int *const bigramEntryPos) const;
+
+    // Returns head position of bigram list for a PtNode specified by terminalId.
+    int getBigramListHeadPos(const int terminalId) const {
+        const SparseTable *const addressLookupTable = getAddressLookupTable();
+        if (!addressLookupTable->contains(terminalId)) {
+            return NOT_A_DICT_POS;
+        }
+        return addressLookupTable->get(terminalId);
+    }
+
+    bool writeBigramEntryAtTail(const BigramEntry *const bigramEntryToWrite) {
+        int writingPos = getContentBuffer()->getTailPosition();
+        return writeBigramEntryAndAdvancePosition(bigramEntryToWrite, &writingPos);
+    }
+
+    bool writeBigramEntry(const BigramEntry *const bigramEntryToWrite, const int entryWritingPos) {
+        int writingPos = entryWritingPos;
+        return writeBigramEntryAndAdvancePosition(bigramEntryToWrite, &writingPos);
+    }
+
+    bool writeBigramEntryAndAdvancePosition(const BigramEntry *const bigramEntryToWrite,
+            int *const entryWritingPos);
+
+    bool createNewBigramList(const int terminalId) {
+        const int bigramListPos = getContentBuffer()->getTailPosition();
+        return getUpdatableAddressLookupTable()->set(terminalId, bigramListPos);
+    }
+
+    bool copyBigramList(const int bigramListPos, const int toPos, int *const outTailEntryPos);
+
+    bool flushToFile(const char *const dictPath) const {
+        return flush(dictPath, Ver4DictConstants::BIGRAM_LOOKUP_TABLE_FILE_EXTENSION,
+                Ver4DictConstants::BIGRAM_CONTENT_TABLE_FILE_EXTENSION,
+                Ver4DictConstants::BIGRAM_FILE_EXTENSION);
+    }
+
+    bool runGC(const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+            const BigramDictContent *const originalBigramDictContent,
+            int *const outBigramEntryCount);
+
+    bool isContentTailPos(const int pos) const {
+        return pos == getContentBuffer()->getTailPosition();
+    }
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(BigramDictContent);
+
+    int createAndGetBigramFlags(const int probability, const bool hasNext) const {
+        return (probability & Ver4DictConstants::BIGRAM_PROBABILITY_MASK)
+                | (hasNext ? Ver4DictConstants::BIGRAM_HAS_NEXT_MASK : 0);
+    }
+
+    bool runGCBigramList(const int bigramListPos,
+            const BigramDictContent *const sourceBigramDictContent, const int toPos,
+            const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+            int *const outEntryCount);
+
+    bool mHasHistoricalInfo;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_BIGRAM_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_entry.h
new file mode 100644
index 0000000..82c4b53
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_entry.h
@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_BIGRAM_ENTRY_H
+#define LATINIME_BACKWARD_V401_BIGRAM_ENTRY_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/historical_info.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class BigramEntry {
+ public:
+    BigramEntry(const BigramEntry& bigramEntry)
+            : mHasNext(bigramEntry.mHasNext), mProbability(bigramEntry.mProbability),
+              mHistoricalInfo(), mTargetTerminalId(bigramEntry.mTargetTerminalId) {}
+
+    // Entry with historical information.
+    BigramEntry(const bool hasNext, const int probability, const int targetTerminalId)
+            : mHasNext(hasNext), mProbability(probability), mHistoricalInfo(),
+              mTargetTerminalId(targetTerminalId) {}
+
+    // Entry with historical information.
+    BigramEntry(const bool hasNext, const int probability,
+            const HistoricalInfo *const historicalInfo, const int targetTerminalId)
+            : mHasNext(hasNext), mProbability(probability), mHistoricalInfo(*historicalInfo),
+              mTargetTerminalId(targetTerminalId) {}
+
+    const BigramEntry getInvalidatedEntry() const {
+        return updateTargetTerminalIdAndGetEntry(Ver4DictConstants::NOT_A_TERMINAL_ID);
+    }
+
+    const BigramEntry updateHasNextAndGetEntry(const bool hasNext) const {
+        return BigramEntry(hasNext, mProbability, &mHistoricalInfo, mTargetTerminalId);
+    }
+
+    const BigramEntry updateTargetTerminalIdAndGetEntry(const int newTargetTerminalId) const {
+        return BigramEntry(mHasNext, mProbability, &mHistoricalInfo, newTargetTerminalId);
+    }
+
+    const BigramEntry updateProbabilityAndGetEntry(const int probability) const {
+        return BigramEntry(mHasNext, probability, &mHistoricalInfo, mTargetTerminalId);
+    }
+
+    const BigramEntry updateHistoricalInfoAndGetEntry(
+            const HistoricalInfo *const historicalInfo) const {
+        return BigramEntry(mHasNext, mProbability, historicalInfo, mTargetTerminalId);
+    }
+
+    bool isValid() const {
+        return mTargetTerminalId != Ver4DictConstants::NOT_A_TERMINAL_ID;
+    }
+
+    bool hasNext() const {
+        return mHasNext;
+    }
+
+    int getProbability() const {
+        return mProbability;
+    }
+
+    bool hasHistoricalInfo() const {
+        return mHistoricalInfo.isValid();
+    }
+
+    const HistoricalInfo *getHistoricalInfo() const {
+        return &mHistoricalInfo;
+    }
+
+    int getTargetTerminalId() const {
+        return mTargetTerminalId;
+    }
+
+ private:
+    // Copy constructor is public to use this class as a type of return value.
+    DISALLOW_DEFAULT_CONSTRUCTOR(BigramEntry);
+    DISALLOW_ASSIGNMENT_OPERATOR(BigramEntry);
+
+    const bool mHasNext;
+    const int mProbability;
+    const HistoricalInfo mHistoricalInfo;
+    const int mTargetTerminalId;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_BIGRAM_ENTRY_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/dict_content.h
new file mode 100644
index 0000000..39e2900
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/dict_content.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_DICT_CONTENT_H
+
+#include "defines.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class DictContent {
+ public:
+    virtual ~DictContent() {}
+    virtual bool isValid() const = 0;
+
+ protected:
+    DictContent() {}
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(DictContent);
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.cpp
new file mode 100644
index 0000000..337b97c
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.cpp
@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/probability_dict_content.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h"
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+const ProbabilityEntry ProbabilityDictContent::getProbabilityEntry(const int terminalId) const {
+    if (terminalId < 0 || terminalId >= mSize) {
+        // This method can be called with invalid terminal id during GC.
+        return ProbabilityEntry(0 /* flags */, NOT_A_PROBABILITY);
+    }
+    const BufferWithExtendableBuffer *const buffer = getBuffer();
+    int entryPos = getEntryPos(terminalId);
+    const int flags = buffer->readUintAndAdvancePosition(
+            Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE, &entryPos);
+    const int probability = buffer->readUintAndAdvancePosition(
+            Ver4DictConstants::PROBABILITY_SIZE, &entryPos);
+    if (mHasHistoricalInfo) {
+        const int timestamp = buffer->readUintAndAdvancePosition(
+                Ver4DictConstants::TIME_STAMP_FIELD_SIZE, &entryPos);
+        const int level = buffer->readUintAndAdvancePosition(
+                Ver4DictConstants::WORD_LEVEL_FIELD_SIZE, &entryPos);
+        const int count = buffer->readUintAndAdvancePosition(
+                Ver4DictConstants::WORD_COUNT_FIELD_SIZE, &entryPos);
+        const HistoricalInfo historicalInfo(timestamp, level, count);
+        return ProbabilityEntry(flags, probability, &historicalInfo);
+    } else {
+        return ProbabilityEntry(flags, probability);
+    }
+}
+
+bool ProbabilityDictContent::setProbabilityEntry(const int terminalId,
+        const ProbabilityEntry *const probabilityEntry) {
+    if (terminalId < 0) {
+        return false;
+    }
+    const int entryPos = getEntryPos(terminalId);
+    if (terminalId >= mSize) {
+        ProbabilityEntry dummyEntry;
+        // Write new entry.
+        int writingPos = getBuffer()->getTailPosition();
+        while (writingPos <= entryPos) {
+            // Fulfilling with dummy entries until writingPos.
+            if (!writeEntry(&dummyEntry, writingPos)) {
+                AKLOGE("Cannot write dummy entry. pos: %d, mSize: %d", writingPos, mSize);
+                return false;
+            }
+            writingPos += getEntrySize();
+            mSize++;
+        }
+    }
+    return writeEntry(probabilityEntry, entryPos);
+}
+
+bool ProbabilityDictContent::flushToFile(const char *const dictPath) const {
+    if (getEntryPos(mSize) < getBuffer()->getTailPosition()) {
+        ProbabilityDictContent probabilityDictContentToWrite(mHasHistoricalInfo);
+        for (int i = 0; i < mSize; ++i) {
+            const ProbabilityEntry probabilityEntry = getProbabilityEntry(i);
+            if (!probabilityDictContentToWrite.setProbabilityEntry(i, &probabilityEntry)) {
+                AKLOGE("Cannot set probability entry in flushToFile. terminalId: %d", i);
+                return false;
+            }
+        }
+        return probabilityDictContentToWrite.flush(dictPath,
+                Ver4DictConstants::FREQ_FILE_EXTENSION);
+    } else {
+        return flush(dictPath, Ver4DictConstants::FREQ_FILE_EXTENSION);
+    }
+}
+
+bool ProbabilityDictContent::runGC(
+        const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+        const ProbabilityDictContent *const originalProbabilityDictContent) {
+    mSize = 0;
+    for (TerminalPositionLookupTable::TerminalIdMap::const_iterator it = terminalIdMap->begin();
+            it != terminalIdMap->end(); ++it) {
+        const ProbabilityEntry probabilityEntry =
+                originalProbabilityDictContent->getProbabilityEntry(it->first);
+        if (!setProbabilityEntry(it->second, &probabilityEntry)) {
+            AKLOGE("Cannot set probability entry in runGC. terminalId: %d", it->second);
+            return false;
+        }
+        mSize++;
+    }
+    return true;
+}
+
+int ProbabilityDictContent::getEntrySize() const {
+    if (mHasHistoricalInfo) {
+        return Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE
+                + Ver4DictConstants::PROBABILITY_SIZE
+                + Ver4DictConstants::TIME_STAMP_FIELD_SIZE
+                + Ver4DictConstants::WORD_LEVEL_FIELD_SIZE
+                + Ver4DictConstants::WORD_COUNT_FIELD_SIZE;
+    } else {
+        return Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE
+                + Ver4DictConstants::PROBABILITY_SIZE;
+    }
+}
+
+int ProbabilityDictContent::getEntryPos(const int terminalId) const {
+    return terminalId * getEntrySize();
+}
+
+bool ProbabilityDictContent::writeEntry(const ProbabilityEntry *const probabilityEntry,
+        const int entryPos) {
+    BufferWithExtendableBuffer *const bufferToWrite = getWritableBuffer();
+    int writingPos = entryPos;
+    if (!bufferToWrite->writeUintAndAdvancePosition(probabilityEntry->getFlags(),
+            Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE, &writingPos)) {
+        AKLOGE("Cannot write flags in probability dict content. pos: %d", writingPos);
+        return false;
+    }
+    if (!bufferToWrite->writeUintAndAdvancePosition(probabilityEntry->getProbability(),
+            Ver4DictConstants::PROBABILITY_SIZE, &writingPos)) {
+        AKLOGE("Cannot write probability in probability dict content. pos: %d", writingPos);
+        return false;
+    }
+    if (mHasHistoricalInfo) {
+        const HistoricalInfo *const historicalInfo = probabilityEntry->getHistoricalInfo();
+        if (!bufferToWrite->writeUintAndAdvancePosition(historicalInfo->getTimeStamp(),
+                Ver4DictConstants::TIME_STAMP_FIELD_SIZE, &writingPos)) {
+            AKLOGE("Cannot write timestamp in probability dict content. pos: %d", writingPos);
+            return false;
+        }
+        if (!bufferToWrite->writeUintAndAdvancePosition(historicalInfo->getLevel(),
+                Ver4DictConstants::WORD_LEVEL_FIELD_SIZE, &writingPos)) {
+            AKLOGE("Cannot write level in probability dict content. pos: %d", writingPos);
+            return false;
+        }
+        if (!bufferToWrite->writeUintAndAdvancePosition(historicalInfo->getCount(),
+                Ver4DictConstants::WORD_COUNT_FIELD_SIZE, &writingPos)) {
+            AKLOGE("Cannot write count in probability dict content. pos: %d", writingPos);
+            return false;
+        }
+    }
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h
new file mode 100644
index 0000000..db30709
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/probability_dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_PROBABILITY_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_PROBABILITY_DICT_CONTENT_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/single_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class ProbabilityEntry;
+
+class ProbabilityDictContent : public SingleDictContent {
+ public:
+    ProbabilityDictContent(const char *const dictPath, const bool hasHistoricalInfo,
+            const bool isUpdatable)
+            : SingleDictContent(dictPath, Ver4DictConstants::FREQ_FILE_EXTENSION, isUpdatable),
+              mHasHistoricalInfo(hasHistoricalInfo),
+              mSize(getBuffer()->getTailPosition() / getEntrySize()) {}
+
+    ProbabilityDictContent(const bool hasHistoricalInfo)
+            : mHasHistoricalInfo(hasHistoricalInfo), mSize(0) {}
+
+    const ProbabilityEntry getProbabilityEntry(const int terminalId) const;
+
+    bool setProbabilityEntry(const int terminalId, const ProbabilityEntry *const probabilityEntry);
+
+    bool flushToFile(const char *const dictPath) const;
+
+    bool runGC(const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+            const ProbabilityDictContent *const originalProbabilityDictContent);
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(ProbabilityDictContent);
+
+    int getEntrySize() const;
+
+    int getEntryPos(const int terminalId) const;
+
+    bool writeEntry(const ProbabilityEntry *const probabilityEntry, const int entryPos);
+
+    bool mHasHistoricalInfo;
+    int mSize;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_PROBABILITY_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h
new file mode 100644
index 0000000..d341e7b
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_PROBABILITY_ENTRY_H
+#define LATINIME_BACKWARD_V401_PROBABILITY_ENTRY_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/historical_info.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class ProbabilityEntry {
+ public:
+    ProbabilityEntry(const ProbabilityEntry &probabilityEntry)
+            : mFlags(probabilityEntry.mFlags), mProbability(probabilityEntry.mProbability),
+              mHistoricalInfo(probabilityEntry.mHistoricalInfo) {}
+
+    // Dummy entry
+    ProbabilityEntry()
+            : mFlags(0), mProbability(NOT_A_PROBABILITY), mHistoricalInfo() {}
+
+    // Entry without historical information
+    ProbabilityEntry(const int flags, const int probability)
+            : mFlags(flags), mProbability(probability), mHistoricalInfo() {}
+
+    // Entry with historical information.
+    ProbabilityEntry(const int flags, const int probability,
+            const HistoricalInfo *const historicalInfo)
+            : mFlags(flags), mProbability(probability), mHistoricalInfo(*historicalInfo) {}
+
+    const ProbabilityEntry createEntryWithUpdatedProbability(const int probability) const {
+        return ProbabilityEntry(mFlags, probability, &mHistoricalInfo);
+    }
+
+    const ProbabilityEntry createEntryWithUpdatedHistoricalInfo(
+            const HistoricalInfo *const historicalInfo) const {
+        return ProbabilityEntry(mFlags, mProbability, historicalInfo);
+    }
+
+    bool hasHistoricalInfo() const {
+        return mHistoricalInfo.isValid();
+    }
+
+    int getFlags() const {
+        return mFlags;
+    }
+
+    int getProbability() const {
+        return mProbability;
+    }
+
+    const HistoricalInfo *getHistoricalInfo() const {
+        return &mHistoricalInfo;
+    }
+
+ private:
+    // Copy constructor is public to use this class as a type of return value.
+    DISALLOW_ASSIGNMENT_OPERATOR(ProbabilityEntry);
+
+    const int mFlags;
+    const int mProbability;
+    const HistoricalInfo mHistoricalInfo;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_PROBABILITY_ENTRY_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.cpp
new file mode 100644
index 0000000..3214807
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.cpp
@@ -0,0 +1,199 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/shortcut_dict_content.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h"
+
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+void ShortcutDictContent::getShortcutEntryAndAdvancePosition(const int maxCodePointCount,
+        int *const outCodePoint, int *const outCodePointCount, int *const outProbability,
+        bool *const outhasNext, int *const shortcutEntryPos) const {
+    const BufferWithExtendableBuffer *const shortcutListBuffer = getContentBuffer();
+    if (*shortcutEntryPos < 0 || *shortcutEntryPos >=  shortcutListBuffer->getTailPosition()) {
+        AKLOGE("Invalid shortcut entry position. shortcutEntryPos: %d, bufSize: %d",
+                *shortcutEntryPos, shortcutListBuffer->getTailPosition());
+        ASSERT(false);
+        if (outhasNext) {
+            *outhasNext = false;
+        }
+        if (outCodePointCount) {
+            *outCodePointCount = 0;
+        }
+        return;
+    }
+
+    const int shortcutFlags = shortcutListBuffer->readUintAndAdvancePosition(
+            Ver4DictConstants::SHORTCUT_FLAGS_FIELD_SIZE, shortcutEntryPos);
+    if (outProbability) {
+        *outProbability = shortcutFlags & Ver4DictConstants::SHORTCUT_PROBABILITY_MASK;
+    }
+    if (outhasNext) {
+        *outhasNext = shortcutFlags & Ver4DictConstants::SHORTCUT_HAS_NEXT_MASK;
+    }
+    if (outCodePoint && outCodePointCount) {
+        shortcutListBuffer->readCodePointsAndAdvancePosition(
+                maxCodePointCount, outCodePoint, outCodePointCount, shortcutEntryPos);
+    }
+}
+
+int ShortcutDictContent::getShortcutListHeadPos(const int terminalId) const {
+    const SparseTable *const addressLookupTable = getAddressLookupTable();
+    if (!addressLookupTable->contains(terminalId)) {
+        return NOT_A_DICT_POS;
+    }
+    return addressLookupTable->get(terminalId);
+}
+
+bool ShortcutDictContent::flushToFile(const char *const dictPath) const {
+    return flush(dictPath, Ver4DictConstants::SHORTCUT_LOOKUP_TABLE_FILE_EXTENSION,
+            Ver4DictConstants::SHORTCUT_CONTENT_TABLE_FILE_EXTENSION,
+            Ver4DictConstants::SHORTCUT_FILE_EXTENSION);
+}
+
+bool ShortcutDictContent::runGC(
+        const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+        const ShortcutDictContent *const originalShortcutDictContent) {
+   for (TerminalPositionLookupTable::TerminalIdMap::const_iterator it = terminalIdMap->begin();
+           it != terminalIdMap->end(); ++it) {
+       const int originalShortcutListPos =
+               originalShortcutDictContent->getShortcutListHeadPos(it->first);
+       if (originalShortcutListPos == NOT_A_DICT_POS) {
+           continue;
+       }
+       const int shortcutListPos = getContentBuffer()->getTailPosition();
+       // Copy shortcut list from original content.
+       if (!copyShortcutListFromDictContent(originalShortcutListPos, originalShortcutDictContent,
+               shortcutListPos)) {
+           AKLOGE("Cannot copy shortcut list during GC. original pos: %d, pos: %d",
+                   originalShortcutListPos, shortcutListPos);
+           return false;
+       }
+       // Set shortcut list position to the lookup table.
+       if (!getUpdatableAddressLookupTable()->set(it->second, shortcutListPos)) {
+           AKLOGE("Cannot set shortcut list position. terminal id: %d, pos: %d",
+                   it->second, shortcutListPos);
+           return false;
+       }
+   }
+   return true;
+}
+
+bool ShortcutDictContent::createNewShortcutList(const int terminalId) {
+    const int shortcutListListPos = getContentBuffer()->getTailPosition();
+    return getUpdatableAddressLookupTable()->set(terminalId, shortcutListListPos);
+}
+
+bool ShortcutDictContent::copyShortcutList(const int shortcutListPos, const int toPos) {
+    return copyShortcutListFromDictContent(shortcutListPos, this, toPos);
+}
+
+bool ShortcutDictContent::copyShortcutListFromDictContent(const int shortcutListPos,
+        const ShortcutDictContent *const sourceShortcutDictContent, const int toPos) {
+    bool hasNext = true;
+    int readingPos = shortcutListPos;
+    int writingPos = toPos;
+    int codePoints[MAX_WORD_LENGTH];
+    while (hasNext) {
+        int probability = 0;
+        int codePointCount = 0;
+        sourceShortcutDictContent->getShortcutEntryAndAdvancePosition(MAX_WORD_LENGTH,
+                codePoints, &codePointCount, &probability, &hasNext, &readingPos);
+        if (!writeShortcutEntryAndAdvancePosition(codePoints, codePointCount, probability,
+                hasNext, &writingPos)) {
+            AKLOGE("Cannot write shortcut entry to copy. pos: %d", writingPos);
+            return false;
+        }
+    }
+    return true;
+}
+
+bool ShortcutDictContent::setProbability(const int probability, const int shortcutEntryPos) {
+    BufferWithExtendableBuffer *const shortcutListBuffer = getWritableContentBuffer();
+    const int shortcutFlags = shortcutListBuffer->readUint(
+            Ver4DictConstants::SHORTCUT_FLAGS_FIELD_SIZE, shortcutEntryPos);
+    const bool hasNext = shortcutFlags & Ver4DictConstants::SHORTCUT_HAS_NEXT_MASK;
+    const int shortcutFlagsToWrite = createAndGetShortcutFlags(probability, hasNext);
+    return shortcutListBuffer->writeUint(shortcutFlagsToWrite,
+            Ver4DictConstants::SHORTCUT_FLAGS_FIELD_SIZE, shortcutEntryPos);
+}
+
+bool ShortcutDictContent::writeShortcutEntryAndAdvancePosition(const int *const codePoint,
+        const int codePointCount, const int probability, const bool hasNext,
+        int *const shortcutEntryPos) {
+    BufferWithExtendableBuffer *const shortcutListBuffer = getWritableContentBuffer();
+    const int shortcutFlags = createAndGetShortcutFlags(probability, hasNext);
+    if (!shortcutListBuffer->writeUintAndAdvancePosition(shortcutFlags,
+            Ver4DictConstants::SHORTCUT_FLAGS_FIELD_SIZE, shortcutEntryPos)) {
+        AKLOGE("Cannot write shortcut flags. flags; %x, pos: %d", shortcutFlags, *shortcutEntryPos);
+        return false;
+    }
+    if (!shortcutListBuffer->writeCodePointsAndAdvancePosition(codePoint, codePointCount,
+            true /* writesTerminator */, shortcutEntryPos)) {
+        AKLOGE("Cannot write shortcut target code points. pos: %d", *shortcutEntryPos);
+        return false;
+    }
+    return true;
+}
+
+// Find a shortcut entry that has specified target and return its position.
+int ShortcutDictContent::findShortcutEntryAndGetPos(const int shortcutListPos,
+        const int *const targetCodePointsToFind, const int codePointCount) const {
+    bool hasNext = true;
+    int readingPos = shortcutListPos;
+    int targetCodePoints[MAX_WORD_LENGTH];
+    while (hasNext) {
+        const int entryPos = readingPos;
+        int probability = 0;
+        int targetCodePointCount = 0;
+        getShortcutEntryAndAdvancePosition(MAX_WORD_LENGTH, targetCodePoints, &targetCodePointCount,
+                &probability, &hasNext, &readingPos);
+        if (targetCodePointCount != codePointCount) {
+            continue;
+        }
+        bool matched = true;
+        for (int i = 0; i < codePointCount; ++i) {
+            if (targetCodePointsToFind[i] != targetCodePoints[i]) {
+                matched = false;
+                break;
+            }
+        }
+        if (matched) {
+            return entryPos;
+        }
+    }
+    return NOT_A_DICT_POS;
+}
+
+int ShortcutDictContent::createAndGetShortcutFlags(const int probability,
+        const bool hasNext) const {
+    return (probability & Ver4DictConstants::SHORTCUT_PROBABILITY_MASK)
+            | (hasNext ? Ver4DictConstants::SHORTCUT_HAS_NEXT_MASK : 0);
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h
new file mode 100644
index 0000000..75fd4f3
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h
@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/shortcut_dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_SHORTCUT_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_SHORTCUT_DICT_CONTENT_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class ShortcutDictContent : public SparseTableDictContent {
+ public:
+    ShortcutDictContent(const char *const dictPath, const bool isUpdatable)
+            : SparseTableDictContent(dictPath,
+                      Ver4DictConstants::SHORTCUT_LOOKUP_TABLE_FILE_EXTENSION,
+                      Ver4DictConstants::SHORTCUT_CONTENT_TABLE_FILE_EXTENSION,
+                      Ver4DictConstants::SHORTCUT_FILE_EXTENSION, isUpdatable,
+                      Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_BLOCK_SIZE,
+                      Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_DATA_SIZE) {}
+
+    ShortcutDictContent()
+            : SparseTableDictContent(Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_BLOCK_SIZE,
+                      Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_DATA_SIZE) {}
+
+    void getShortcutEntry(const int maxCodePointCount, int *const outCodePoint,
+            int *const outCodePointCount, int *const outProbability, bool *const outhasNext,
+            const int shortcutEntryPos) {
+        int readingPos = shortcutEntryPos;
+        return getShortcutEntryAndAdvancePosition(maxCodePointCount, outCodePoint,
+                outCodePointCount, outProbability, outhasNext, &readingPos);
+    }
+
+    void getShortcutEntryAndAdvancePosition(const int maxCodePointCount,
+            int *const outCodePoint, int *const outCodePointCount, int *const outProbability,
+            bool *const outhasNext, int *const shortcutEntryPos) const;
+
+   // Returns head position of shortcut list for a PtNode specified by terminalId.
+   int getShortcutListHeadPos(const int terminalId) const;
+
+   bool flushToFile(const char *const dictPath) const;
+
+   bool runGC(const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
+           const ShortcutDictContent *const originalShortcutDictContent);
+
+   bool createNewShortcutList(const int terminalId);
+
+   bool copyShortcutList(const int shortcutListPos, const int toPos);
+
+   bool setProbability(const int probability, const int shortcutEntryPos);
+
+   bool writeShortcutEntry(const int *const codePoint, const int codePointCount,
+           const int probability, const bool hasNext, const int shortcutEntryPos) {
+       int writingPos = shortcutEntryPos;
+       return writeShortcutEntryAndAdvancePosition(codePoint, codePointCount, probability,
+               hasNext, &writingPos);
+   }
+
+   bool writeShortcutEntryAndAdvancePosition(const int *const codePoint,
+           const int codePointCount, const int probability, const bool hasNext,
+           int *const shortcutEntryPos);
+
+   int findShortcutEntryAndGetPos(const int shortcutListPos,
+           const int *const targetCodePointsToFind, const int codePointCount) const;
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(ShortcutDictContent);
+
+    bool copyShortcutListFromDictContent(const int shortcutListPos,
+            const ShortcutDictContent *const sourceShortcutDictContent, const int toPos);
+
+    int createAndGetShortcutFlags(const int probability, const bool hasNext) const;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_SHORTCUT_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/single_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/single_dict_content.h
new file mode 100644
index 0000000..a519cd8
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/single_dict_content.h
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/single_dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_SINGLE_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_SINGLE_DICT_CONTENT_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h"
+#include "suggest/policyimpl/dictionary/utils/mmapped_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class SingleDictContent : public DictContent {
+ public:
+    SingleDictContent(const char *const dictPath, const char *const contentFileName,
+            const bool isUpdatable)
+            : mMmappedBuffer(MmappedBuffer::openBuffer(dictPath, contentFileName, isUpdatable)),
+              mExpandableContentBuffer(mMmappedBuffer ? mMmappedBuffer->getBuffer() : nullptr,
+                      mMmappedBuffer ? mMmappedBuffer->getBufferSize() : 0,
+                      BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+              mIsValid(mMmappedBuffer) {}
+
+    SingleDictContent()
+            : mMmappedBuffer(nullptr),
+              mExpandableContentBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE), mIsValid(true) {}
+
+    virtual ~SingleDictContent() {}
+
+    virtual bool isValid() const {
+        return mIsValid;
+    }
+
+    bool isNearSizeLimit() const {
+        return mExpandableContentBuffer.isNearSizeLimit();
+    }
+
+ protected:
+    BufferWithExtendableBuffer *getWritableBuffer() {
+        return &mExpandableContentBuffer;
+    }
+
+    const BufferWithExtendableBuffer *getBuffer() const {
+        return &mExpandableContentBuffer;
+    }
+
+    bool flush(const char *const dictPath, const char *const contentFileNameSuffix) const {
+        return DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath,
+                contentFileNameSuffix, &mExpandableContentBuffer);
+    }
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(SingleDictContent);
+
+    const MmappedBuffer::MmappedBufferPtr mMmappedBuffer;
+    BufferWithExtendableBuffer mExpandableContentBuffer;
+    const bool mIsValid;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_SINGLE_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.cpp
new file mode 100644
index 0000000..638132c
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.cpp
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+bool SparseTableDictContent::flush(const char *const dictPath,
+        const char *const lookupTableFileNameSuffix, const char *const addressTableFileNameSuffix,
+        const char *const contentFileNameSuffix) const {
+    if (!DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath, lookupTableFileNameSuffix,
+            &mExpandableLookupTableBuffer)){
+        return false;
+    }
+    if (!DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath, addressTableFileNameSuffix,
+            &mExpandableAddressTableBuffer)) {
+        return false;
+    }
+    if (!DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath, contentFileNameSuffix,
+            &mExpandableContentBuffer)) {
+        return false;
+    }
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h
new file mode 100644
index 0000000..b95de2e
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/sparse_table_dict_content.h
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_SPARSE_TABLE_DICT_CONTENT_H
+#define LATINIME_BACKWARD_V401_SPARSE_TABLE_DICT_CONTENT_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h"
+#include "suggest/policyimpl/dictionary/utils/mmapped_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/sparse_table.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+// TODO: Support multiple contents.
+class SparseTableDictContent : public DictContent {
+ public:
+    AK_FORCE_INLINE SparseTableDictContent(const char *const dictPath,
+            const char *const lookupTableFileName, const char *const addressTableFileName,
+            const char *const contentFileName, const bool isUpdatable,
+            const int sparseTableBlockSize, const int sparseTableDataSize)
+            : mLookupTableBuffer(
+                      MmappedBuffer::openBuffer(dictPath, lookupTableFileName, isUpdatable)),
+              mAddressTableBuffer(
+                      MmappedBuffer::openBuffer(dictPath, addressTableFileName, isUpdatable)),
+              mContentBuffer(
+                      MmappedBuffer::openBuffer(dictPath, contentFileName, isUpdatable)),
+              mExpandableLookupTableBuffer(
+                      mLookupTableBuffer ? mLookupTableBuffer->getBuffer() : nullptr,
+                      mLookupTableBuffer ? mLookupTableBuffer->getBufferSize() : 0,
+                      BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+              mExpandableAddressTableBuffer(
+                      mAddressTableBuffer ? mAddressTableBuffer->getBuffer() : nullptr,
+                      mAddressTableBuffer ? mAddressTableBuffer->getBufferSize() : 0,
+                      BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+              mExpandableContentBuffer(mContentBuffer ? mContentBuffer->getBuffer() : nullptr,
+                      mContentBuffer ? mContentBuffer->getBufferSize() : 0,
+                      BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+              mAddressLookupTable(&mExpandableLookupTableBuffer, &mExpandableAddressTableBuffer,
+                      sparseTableBlockSize, sparseTableDataSize),
+              mIsValid(mLookupTableBuffer && mAddressTableBuffer && mContentBuffer) {}
+
+    SparseTableDictContent(const int sparseTableBlockSize, const int sparseTableDataSize)
+            : mLookupTableBuffer(), mAddressTableBuffer(), mContentBuffer(),
+              mExpandableLookupTableBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
+              mExpandableAddressTableBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
+              mExpandableContentBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
+              mAddressLookupTable(&mExpandableLookupTableBuffer, &mExpandableAddressTableBuffer,
+                      sparseTableBlockSize, sparseTableDataSize), mIsValid(true) {}
+
+    virtual ~SparseTableDictContent() {}
+
+    virtual bool isValid() const {
+        return mIsValid;
+    }
+
+    bool isNearSizeLimit() const {
+        return mExpandableLookupTableBuffer.isNearSizeLimit()
+                || mExpandableAddressTableBuffer.isNearSizeLimit()
+                || mExpandableContentBuffer.isNearSizeLimit();
+    }
+
+ protected:
+    SparseTable *getUpdatableAddressLookupTable() {
+        return &mAddressLookupTable;
+    }
+
+    const SparseTable *getAddressLookupTable() const {
+        return &mAddressLookupTable;
+    }
+
+    BufferWithExtendableBuffer *getWritableContentBuffer() {
+        return &mExpandableContentBuffer;
+    }
+
+    const BufferWithExtendableBuffer *getContentBuffer() const {
+        return &mExpandableContentBuffer;
+    }
+
+    bool flush(const char *const dictDirPath, const char *const lookupTableFileName,
+            const char *const addressTableFileName, const char *const contentFileName) const;
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(SparseTableDictContent);
+
+    const MmappedBuffer::MmappedBufferPtr mLookupTableBuffer;
+    const MmappedBuffer::MmappedBufferPtr mAddressTableBuffer;
+    const MmappedBuffer::MmappedBufferPtr mContentBuffer;
+    BufferWithExtendableBuffer mExpandableLookupTableBuffer;
+    BufferWithExtendableBuffer mExpandableAddressTableBuffer;
+    BufferWithExtendableBuffer mExpandableContentBuffer;
+    SparseTable mAddressLookupTable;
+    const bool mIsValid;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_SPARSE_TABLE_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.cpp
new file mode 100644
index 0000000..ab8a3ae
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.cpp
@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/terminal_position_lookup_table.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+int TerminalPositionLookupTable::getTerminalPtNodePosition(const int terminalId) const {
+    if (terminalId < 0 || terminalId >= mSize) {
+        return NOT_A_DICT_POS;
+    }
+    const int terminalPos = getBuffer()->readUint(
+            Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, getEntryPos(terminalId));
+    return (terminalPos == Ver4DictConstants::NOT_A_TERMINAL_ADDRESS) ?
+            NOT_A_DICT_POS : terminalPos;
+}
+
+bool TerminalPositionLookupTable::setTerminalPtNodePosition(
+        const int terminalId, const int terminalPtNodePos) {
+    if (terminalId < 0) {
+        return NOT_A_DICT_POS;
+    }
+    while (terminalId >= mSize) {
+        // Write new entry.
+        if (!getWritableBuffer()->writeUint(Ver4DictConstants::NOT_A_TERMINAL_ADDRESS,
+                Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, getEntryPos(mSize))) {
+            return false;
+        }
+        mSize++;
+    }
+    const int terminalPos = (terminalPtNodePos != NOT_A_DICT_POS) ?
+            terminalPtNodePos : Ver4DictConstants::NOT_A_TERMINAL_ADDRESS;
+    return getWritableBuffer()->writeUint(terminalPos,
+            Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, getEntryPos(terminalId));
+}
+
+bool TerminalPositionLookupTable::flushToFile(const char *const dictPath) const {
+    // If the used buffer size is smaller than the actual buffer size, regenerate the lookup
+    // table and write the new table to the file.
+    if (getEntryPos(mSize) < getBuffer()->getTailPosition()) {
+        TerminalPositionLookupTable lookupTableToWrite;
+        for (int i = 0; i < mSize; ++i) {
+            const int terminalPtNodePosition = getTerminalPtNodePosition(i);
+            if (!lookupTableToWrite.setTerminalPtNodePosition(i, terminalPtNodePosition)) {
+                AKLOGE("Cannot set terminal position to lookupTableToWrite."
+                        " terminalId: %d, position: %d", i, terminalPtNodePosition);
+                return false;
+            }
+        }
+        return lookupTableToWrite.flush(dictPath,
+                Ver4DictConstants::TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
+    } else {
+        // We can simply use this lookup table because the buffer size has not been
+        // changed.
+        return flush(dictPath, Ver4DictConstants::TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
+    }
+}
+
+bool TerminalPositionLookupTable::runGCTerminalIds(TerminalIdMap *const terminalIdMap) {
+    int removedEntryCount = 0;
+    int nextNewTerminalId = 0;
+    for (int i = 0; i < mSize; ++i) {
+        const int terminalPos = getBuffer()->readUint(
+                Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, getEntryPos(i));
+        if (terminalPos == Ver4DictConstants::NOT_A_TERMINAL_ADDRESS) {
+            // This entry is a garbage.
+            removedEntryCount++;
+        } else {
+            // Give a new terminal id to the entry.
+            if (!getWritableBuffer()->writeUint(terminalPos,
+                    Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE,
+                    getEntryPos(nextNewTerminalId))) {
+                return false;
+            }
+            // Memorize the mapping to the old terminal id to the new terminal id.
+            terminalIdMap->insert(TerminalIdMap::value_type(i, nextNewTerminalId));
+            nextNewTerminalId++;
+        }
+    }
+    mSize = nextNewTerminalId;
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h
new file mode 100644
index 0000000..dbf0e60
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/content/terminal_position_lookup_table.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_TERMINAL_POSITION_LOOKUP_TABLE_H
+#define LATINIME_BACKWARD_V401_TERMINAL_POSITION_LOOKUP_TABLE_H
+
+#include <unordered_map>
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/single_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class TerminalPositionLookupTable : public SingleDictContent {
+ public:
+    typedef std::unordered_map<int, int> TerminalIdMap;
+
+    TerminalPositionLookupTable(const char *const dictPath, const bool isUpdatable)
+            : SingleDictContent(dictPath,
+                      Ver4DictConstants::TERMINAL_ADDRESS_TABLE_FILE_EXTENSION, isUpdatable),
+              mSize(getBuffer()->getTailPosition()
+                      / Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE) {}
+
+    TerminalPositionLookupTable() : mSize(0) {}
+
+    int getTerminalPtNodePosition(const int terminalId) const;
+
+    bool setTerminalPtNodePosition(const int terminalId, const int terminalPtNodePos);
+
+    int getNextTerminalId() const {
+        return mSize;
+    }
+
+    bool flushToFile(const char *const dictPath) const;
+
+    bool runGCTerminalIds(TerminalIdMap *const terminalIdMap);
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(TerminalPositionLookupTable);
+
+    int getEntryPos(const int terminalId) const {
+        return terminalId * Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
+    }
+
+    int mSize;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif // LATINIME_BACKWARD_V401_TERMINAL_POSITION_LOOKUP_TABLE_H
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h
new file mode 100644
index 0000000..6a4e83c
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT CHANGE THE LOGIC IN THIS FILE !!!!!
+ * Do not edit this file other than updating policy's interface.
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/shortcut/ver4_shortcut_list_policy.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_SHORTCUT_LIST_POLICY_H
+#define LATINIME_BACKWARD_V401_VER4_SHORTCUT_LIST_POLICY_H
+
+#include "defines.h"
+#include "suggest/core/policy/dictionary_shortcuts_structure_policy.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/shortcut/shortcut_list_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class Ver4ShortcutListPolicy : public DictionaryShortcutsStructurePolicy {
+ public:
+    Ver4ShortcutListPolicy(ShortcutDictContent *const shortcutDictContent,
+            const TerminalPositionLookupTable *const terminalPositionLookupTable)
+            : mShortcutDictContent(shortcutDictContent) {}
+
+    ~Ver4ShortcutListPolicy() {}
+
+    int getStartPos(const int pos) const {
+        // The first shortcut entry is located at the head position of the shortcut list.
+        return pos;
+    }
+
+    void getNextShortcut(const int maxCodePointCount, int *const outCodePoint,
+            int *const outCodePointCount, bool *const outIsWhitelist, bool *const outHasNext,
+            int *const pos) const {
+        int probability = 0;
+        mShortcutDictContent->getShortcutEntryAndAdvancePosition(maxCodePointCount,
+                outCodePoint, outCodePointCount, &probability, outHasNext, pos);
+        if (outIsWhitelist) {
+            *outIsWhitelist = ShortcutListReadingUtils::isWhitelist(probability);
+        }
+    }
+
+    void skipAllShortcuts(int *const pos) const {
+        // Do nothing because we don't need to skip shortcut lists in ver4 dictionaries.
+    }
+
+    bool addNewShortcut(const int terminalId, const int *const codePoints, const int codePointCount,
+            const int probability) {
+        const int shortcutListPos = mShortcutDictContent->getShortcutListHeadPos(terminalId);
+        if (shortcutListPos == NOT_A_DICT_POS) {
+            // Create shortcut list.
+            if (!mShortcutDictContent->createNewShortcutList(terminalId)) {
+                AKLOGE("Cannot create new shortcut list. terminal id: %d", terminalId);
+                return false;
+            }
+            const int writingPos =  mShortcutDictContent->getShortcutListHeadPos(terminalId);
+            return mShortcutDictContent->writeShortcutEntry(codePoints, codePointCount, probability,
+                    false /* hasNext */, writingPos);
+        }
+        const int entryPos = mShortcutDictContent->findShortcutEntryAndGetPos(shortcutListPos,
+                codePoints, codePointCount);
+        if (entryPos == NOT_A_DICT_POS) {
+            // Add new entry to the shortcut list.
+            // Create new shortcut list.
+            if (!mShortcutDictContent->createNewShortcutList(terminalId)) {
+                AKLOGE("Cannot create new shortcut list. terminal id: %d", terminalId);
+                return false;
+            }
+            int writingPos =  mShortcutDictContent->getShortcutListHeadPos(terminalId);
+            if (!mShortcutDictContent->writeShortcutEntryAndAdvancePosition(codePoints,
+                    codePointCount, probability, true /* hasNext */, &writingPos)) {
+                AKLOGE("Cannot write shortcut entry. terminal id: %d, pos: %d", terminalId,
+                        writingPos);
+                return false;
+            }
+            return mShortcutDictContent->copyShortcutList(shortcutListPos, writingPos);
+        }
+        // Overwrite existing entry.
+        bool hasNext = false;
+        mShortcutDictContent->getShortcutEntry(MAX_WORD_LENGTH, 0 /* outCodePoint */,
+                0 /* outCodePointCount */ , 0 /* probability */, &hasNext, entryPos);
+        if (!mShortcutDictContent->writeShortcutEntry(codePoints,
+                codePointCount, probability, hasNext, entryPos)) {
+            AKLOGE("Cannot overwrite shortcut entry. terminal id: %d, pos: %d", terminalId,
+                    entryPos);
+            return false;
+        }
+        return true;
+    }
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4ShortcutListPolicy);
+
+    ShortcutDictContent *const mShortcutDictContent;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif // LATINIME_BACKWARD_V401_VER4_SHORTCUT_LIST_POLICY_H
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.cpp
new file mode 100644
index 0000000..55ead01
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.cpp
@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h"
+
+#include <cerrno>
+#include <cstring>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include "suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h"
+#include "suggest/policyimpl/dictionary/utils/file_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+/* static */ Ver4DictBuffers::Ver4DictBuffersPtr Ver4DictBuffers::openVer4DictBuffers(
+        const char *const dictPath, MmappedBuffer::MmappedBufferPtr headerBuffer,
+        const FormatUtils::FORMAT_VERSION formatVersion) {
+    if (!headerBuffer) {
+        ASSERT(false);
+        AKLOGE("The header buffer must be valid to open ver4 dict buffers.");
+        return Ver4DictBuffersPtr(nullptr);
+    }
+    // TODO: take only dictDirPath, and open both header and trie files in the constructor below
+    const bool isUpdatable = headerBuffer->isUpdatable();
+    return Ver4DictBuffersPtr(new Ver4DictBuffers(dictPath, std::move(headerBuffer), isUpdatable,
+            formatVersion));
+}
+
+bool Ver4DictBuffers::flushHeaderAndDictBuffers(const char *const dictDirPath,
+        const BufferWithExtendableBuffer *const headerBuffer) const {
+    // Create temporary directory.
+    const int tmpDirPathBufSize = FileUtils::getFilePathWithSuffixBufSize(dictDirPath,
+            DictFileWritingUtils::TEMP_FILE_SUFFIX_FOR_WRITING_DICT_FILE);
+    char tmpDirPath[tmpDirPathBufSize];
+    FileUtils::getFilePathWithSuffix(dictDirPath,
+            DictFileWritingUtils::TEMP_FILE_SUFFIX_FOR_WRITING_DICT_FILE, tmpDirPathBufSize,
+            tmpDirPath);
+    if (FileUtils::existsDir(tmpDirPath)) {
+        if (!FileUtils::removeDirAndFiles(tmpDirPath)) {
+            AKLOGE("Existing directory %s cannot be removed.", tmpDirPath);
+            ASSERT(false);
+            return false;
+        }
+    }
+    if (mkdir(tmpDirPath, S_IRWXU) == -1) {
+        AKLOGE("Cannot create directory: %s. errno: %d.", tmpDirPath, errno);
+        return false;
+    }
+    // Get dictionary base path.
+    const int dictNameBufSize = strlen(dictDirPath) + 1 /* terminator */;
+    char dictName[dictNameBufSize];
+    FileUtils::getBasename(dictDirPath, dictNameBufSize, dictName);
+    const int dictPathBufSize = FileUtils::getFilePathBufSize(tmpDirPath, dictName);
+    char dictPath[dictPathBufSize];
+    FileUtils::getFilePath(tmpDirPath, dictName, dictPathBufSize, dictPath);
+
+    // Write header file.
+    if (!DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath,
+            Ver4DictConstants::HEADER_FILE_EXTENSION, headerBuffer)) {
+        AKLOGE("Dictionary header file %s%s cannot be written.", tmpDirPath,
+                Ver4DictConstants::HEADER_FILE_EXTENSION);
+        return false;
+    }
+    // Write trie file.
+    if (!DictFileWritingUtils::flushBufferToFileWithSuffix(dictPath,
+            Ver4DictConstants::TRIE_FILE_EXTENSION, &mExpandableTrieBuffer)) {
+        AKLOGE("Dictionary trie file %s%s cannot be written.", tmpDirPath,
+                Ver4DictConstants::TRIE_FILE_EXTENSION);
+        return false;
+    }
+    // Write dictionary contents.
+    if (!mTerminalPositionLookupTable.flushToFile(dictPath)) {
+        AKLOGE("Terminal position lookup table cannot be written. %s", tmpDirPath);
+        return false;
+    }
+    if (!mProbabilityDictContent.flushToFile(dictPath)) {
+        AKLOGE("Probability dict content cannot be written. %s", tmpDirPath);
+        return false;
+    }
+    if (!mBigramDictContent.flushToFile(dictPath)) {
+        AKLOGE("Bigram dict content cannot be written. %s", tmpDirPath);
+        return false;
+    }
+    if (!mShortcutDictContent.flushToFile(dictPath)) {
+        AKLOGE("Shortcut dict content cannot be written. %s", tmpDirPath);
+        return false;
+    }
+    // Remove existing dictionary.
+    if (!FileUtils::removeDirAndFiles(dictDirPath)) {
+        AKLOGE("Existing directory %s cannot be removed.", dictDirPath);
+        ASSERT(false);
+        return false;
+    }
+    // Rename temporary directory.
+    if (rename(tmpDirPath, dictDirPath) != 0) {
+        AKLOGE("%s cannot be renamed to %s", tmpDirPath, dictDirPath);
+        ASSERT(false);
+        return false;
+    }
+    return true;
+}
+
+Ver4DictBuffers::Ver4DictBuffers(const char *const dictPath,
+        MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable,
+        const FormatUtils::FORMAT_VERSION formatVersion)
+        : mHeaderBuffer(std::move(headerBuffer)),
+          mDictBuffer(MmappedBuffer::openBuffer(dictPath,
+                  Ver4DictConstants::TRIE_FILE_EXTENSION, isUpdatable)),
+          mHeaderPolicy(mHeaderBuffer->getBuffer(), formatVersion),
+          mExpandableHeaderBuffer(mHeaderBuffer ? mHeaderBuffer->getBuffer() : nullptr,
+                  mHeaderPolicy.getSize(),
+                  BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+          mExpandableTrieBuffer(mDictBuffer ? mDictBuffer->getBuffer() : nullptr,
+                  mDictBuffer ? mDictBuffer->getBufferSize() : 0,
+                  BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
+          mTerminalPositionLookupTable(dictPath, isUpdatable),
+          mProbabilityDictContent(dictPath, mHeaderPolicy.hasHistoricalInfoOfWords(), isUpdatable),
+          mBigramDictContent(dictPath, mHeaderPolicy.hasHistoricalInfoOfWords(), isUpdatable),
+          mShortcutDictContent(dictPath, isUpdatable),
+          mIsUpdatable(isUpdatable) {}
+
+Ver4DictBuffers::Ver4DictBuffers(const HeaderPolicy *const headerPolicy, const int maxTrieSize)
+        : mHeaderBuffer(nullptr), mDictBuffer(nullptr), mHeaderPolicy(headerPolicy),
+          mExpandableHeaderBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
+          mExpandableTrieBuffer(maxTrieSize), mTerminalPositionLookupTable(),
+          mProbabilityDictContent(headerPolicy->hasHistoricalInfoOfWords()),
+          mBigramDictContent(headerPolicy->hasHistoricalInfoOfWords()), mShortcutDictContent(),
+          mIsUpdatable(true) {}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h
new file mode 100644
index 0000000..716ed93
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_DICT_BUFFER_H
+#define LATINIME_BACKWARD_V401_VER4_DICT_BUFFER_H
+
+#include <memory>
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/bigram_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/shortcut_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/mmapped_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+class Ver4DictBuffers {
+ public:
+    typedef std::unique_ptr<Ver4DictBuffers> Ver4DictBuffersPtr;
+
+    static Ver4DictBuffersPtr openVer4DictBuffers(const char *const dictDirPath,
+            MmappedBuffer::MmappedBufferPtr headerBuffer,
+            const FormatUtils::FORMAT_VERSION formatVersion);
+
+    static AK_FORCE_INLINE Ver4DictBuffersPtr createVer4DictBuffers(
+            const HeaderPolicy *const headerPolicy, const int maxTrieSize) {
+        return Ver4DictBuffersPtr(new Ver4DictBuffers(headerPolicy, maxTrieSize));
+    }
+
+    AK_FORCE_INLINE bool isValid() const {
+        return mHeaderBuffer && mDictBuffer && mHeaderPolicy.isValid()
+                && mProbabilityDictContent.isValid() && mTerminalPositionLookupTable.isValid()
+                && mBigramDictContent.isValid() && mShortcutDictContent.isValid();
+    }
+
+    AK_FORCE_INLINE bool isNearSizeLimit() const {
+        return mExpandableTrieBuffer.isNearSizeLimit()
+                || mTerminalPositionLookupTable.isNearSizeLimit()
+                || mProbabilityDictContent.isNearSizeLimit()
+                || mBigramDictContent.isNearSizeLimit()
+                || mShortcutDictContent.isNearSizeLimit();
+    }
+
+    AK_FORCE_INLINE const HeaderPolicy *getHeaderPolicy() const {
+        return &mHeaderPolicy;
+    }
+
+    AK_FORCE_INLINE BufferWithExtendableBuffer *getWritableHeaderBuffer() {
+        return &mExpandableHeaderBuffer;
+    }
+
+    AK_FORCE_INLINE BufferWithExtendableBuffer *getWritableTrieBuffer() {
+        return &mExpandableTrieBuffer;
+    }
+
+    AK_FORCE_INLINE const BufferWithExtendableBuffer *getTrieBuffer() const {
+        return &mExpandableTrieBuffer;
+    }
+
+    AK_FORCE_INLINE TerminalPositionLookupTable *getMutableTerminalPositionLookupTable() {
+        return &mTerminalPositionLookupTable;
+    }
+
+    AK_FORCE_INLINE const TerminalPositionLookupTable *getTerminalPositionLookupTable() const {
+        return &mTerminalPositionLookupTable;
+    }
+
+    AK_FORCE_INLINE ProbabilityDictContent *getMutableProbabilityDictContent() {
+        return &mProbabilityDictContent;
+    }
+
+    AK_FORCE_INLINE const ProbabilityDictContent *getProbabilityDictContent() const {
+        return &mProbabilityDictContent;
+    }
+
+    AK_FORCE_INLINE BigramDictContent *getMutableBigramDictContent() {
+        return &mBigramDictContent;
+    }
+
+    AK_FORCE_INLINE const BigramDictContent *getBigramDictContent() const {
+        return &mBigramDictContent;
+    }
+
+    AK_FORCE_INLINE ShortcutDictContent *getMutableShortcutDictContent() {
+        return &mShortcutDictContent;
+    }
+
+    AK_FORCE_INLINE const ShortcutDictContent *getShortcutDictContent() const {
+        return &mShortcutDictContent;
+    }
+
+    AK_FORCE_INLINE bool isUpdatable() const {
+        return mIsUpdatable;
+    }
+
+    bool flush(const char *const dictDirPath) const {
+        return flushHeaderAndDictBuffers(dictDirPath, &mExpandableHeaderBuffer);
+    }
+
+    bool flushHeaderAndDictBuffers(const char *const dictDirPath,
+            const BufferWithExtendableBuffer *const headerBuffer) const;
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(Ver4DictBuffers);
+
+    Ver4DictBuffers(const char *const dictDirPath,
+            const MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable,
+            const FormatUtils::FORMAT_VERSION formatVersion);
+
+    Ver4DictBuffers(const HeaderPolicy *const headerPolicy, const int maxTrieSize);
+
+    const MmappedBuffer::MmappedBufferPtr mHeaderBuffer;
+    const MmappedBuffer::MmappedBufferPtr mDictBuffer;
+    const HeaderPolicy mHeaderPolicy;
+    BufferWithExtendableBuffer mExpandableHeaderBuffer;
+    BufferWithExtendableBuffer mExpandableTrieBuffer;
+    TerminalPositionLookupTable mTerminalPositionLookupTable;
+    ProbabilityDictContent mProbabilityDictContent;
+    BigramDictContent mBigramDictContent;
+    ShortcutDictContent mShortcutDictContent;
+    const int mIsUpdatable;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_DICT_BUFFER_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.cpp
new file mode 100644
index 0000000..793b44e
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.cpp
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+// These values MUST match the definitions in FormatSpec.java.
+const char *const Ver4DictConstants::TRIE_FILE_EXTENSION = ".trie";
+const char *const Ver4DictConstants::HEADER_FILE_EXTENSION = ".header";
+const char *const Ver4DictConstants::FREQ_FILE_EXTENSION = ".freq";
+// tat = Terminal Address Table
+const char *const Ver4DictConstants::TERMINAL_ADDRESS_TABLE_FILE_EXTENSION = ".tat";
+const char *const Ver4DictConstants::BIGRAM_FILE_EXTENSION = ".bigram_freq";
+const char *const Ver4DictConstants::BIGRAM_LOOKUP_TABLE_FILE_EXTENSION = ".bigram_lookup";
+const char *const Ver4DictConstants::BIGRAM_CONTENT_TABLE_FILE_EXTENSION = ".bigram_index_freq";
+const char *const Ver4DictConstants::SHORTCUT_FILE_EXTENSION = ".shortcut_shortcut";
+const char *const Ver4DictConstants::SHORTCUT_LOOKUP_TABLE_FILE_EXTENSION = ".shortcut_lookup";
+const char *const Ver4DictConstants::SHORTCUT_CONTENT_TABLE_FILE_EXTENSION =
+        ".shortcut_index_shortcut";
+
+// Version 4 dictionary size is implicitly limited to 8MB due to 3-byte offsets.
+const int Ver4DictConstants::MAX_DICTIONARY_SIZE = 8 * 1024 * 1024;
+// Extended region size, which is not GCed region size in dict file + additional buffer size, is
+// limited to 1MB to prevent from inefficient traversing.
+const int Ver4DictConstants::MAX_DICT_EXTENDED_REGION_SIZE = 1 * 1024 * 1024;
+
+const int Ver4DictConstants::NOT_A_TERMINAL_ID = -1;
+const int Ver4DictConstants::PROBABILITY_SIZE = 1;
+const int Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE = 1;
+const int Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE = 3;
+const int Ver4DictConstants::NOT_A_TERMINAL_ADDRESS = 0;
+const int Ver4DictConstants::TERMINAL_ID_FIELD_SIZE = 4;
+const int Ver4DictConstants::TIME_STAMP_FIELD_SIZE = 4;
+const int Ver4DictConstants::WORD_LEVEL_FIELD_SIZE = 1;
+const int Ver4DictConstants::WORD_COUNT_FIELD_SIZE = 1;
+
+const int Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE = 16;
+const int Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE = 4;
+const int Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_BLOCK_SIZE = 64;
+const int Ver4DictConstants::SHORTCUT_ADDRESS_TABLE_DATA_SIZE = 4;
+
+const int Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE = 3;
+// Unsigned int max value of BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE-byte is used for representing
+// invalid terminal ID in bigram lists.
+const int Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID =
+        (1 << (BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE * 8)) - 1;
+const int Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE = 1;
+const int Ver4DictConstants::BIGRAM_PROBABILITY_MASK = 0x0F;
+const int Ver4DictConstants::BIGRAM_HAS_NEXT_MASK = 0x80;
+const int Ver4DictConstants::BIGRAM_LARGE_PROBABILITY_FIELD_SIZE = 1;
+
+const int Ver4DictConstants::SHORTCUT_FLAGS_FIELD_SIZE = 1;
+const int Ver4DictConstants::SHORTCUT_PROBABILITY_MASK = 0x0F;
+const int Ver4DictConstants::SHORTCUT_HAS_NEXT_MASK = 0x80;
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h
new file mode 100644
index 0000000..17afeb1
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h
@@ -0,0 +1,84 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_DICT_CONSTANTS_H
+#define LATINIME_BACKWARD_V401_VER4_DICT_CONSTANTS_H
+
+#include "defines.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+// TODO: Create PtConstants under the pt_common and move some constant values there.
+// Note that there are corresponding definitions in FormatSpec.java.
+class Ver4DictConstants {
+ public:
+    static const char *const TRIE_FILE_EXTENSION;
+    static const char *const HEADER_FILE_EXTENSION;
+    static const char *const FREQ_FILE_EXTENSION;
+    static const char *const TERMINAL_ADDRESS_TABLE_FILE_EXTENSION;
+    static const char *const BIGRAM_FILE_EXTENSION;
+    static const char *const BIGRAM_LOOKUP_TABLE_FILE_EXTENSION;
+    static const char *const BIGRAM_CONTENT_TABLE_FILE_EXTENSION;
+    static const char *const SHORTCUT_FILE_EXTENSION;
+    static const char *const SHORTCUT_LOOKUP_TABLE_FILE_EXTENSION;
+    static const char *const SHORTCUT_CONTENT_TABLE_FILE_EXTENSION;
+
+    static const int MAX_DICTIONARY_SIZE;
+    static const int MAX_DICT_EXTENDED_REGION_SIZE;
+
+    static const int NOT_A_TERMINAL_ID;
+    static const int PROBABILITY_SIZE;
+    static const int FLAGS_IN_PROBABILITY_FILE_SIZE;
+    static const int TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
+    static const int NOT_A_TERMINAL_ADDRESS;
+    static const int TERMINAL_ID_FIELD_SIZE;
+    static const int TIME_STAMP_FIELD_SIZE;
+    static const int WORD_LEVEL_FIELD_SIZE;
+    static const int WORD_COUNT_FIELD_SIZE;
+
+    static const int BIGRAM_ADDRESS_TABLE_BLOCK_SIZE;
+    static const int BIGRAM_ADDRESS_TABLE_DATA_SIZE;
+    static const int SHORTCUT_ADDRESS_TABLE_BLOCK_SIZE;
+    static const int SHORTCUT_ADDRESS_TABLE_DATA_SIZE;
+
+    static const int BIGRAM_FLAGS_FIELD_SIZE;
+    static const int BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE;
+    static const int INVALID_BIGRAM_TARGET_TERMINAL_ID;
+    static const int BIGRAM_PROBABILITY_MASK;
+    static const int BIGRAM_HAS_NEXT_MASK;
+    // Used when bigram list has time stamp.
+    static const int BIGRAM_LARGE_PROBABILITY_FIELD_SIZE;
+
+    static const int SHORTCUT_FLAGS_FIELD_SIZE;
+    static const int SHORTCUT_PROBABILITY_MASK;
+    static const int SHORTCUT_HAS_NEXT_MASK;
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4DictConstants);
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_DICT_CONSTANTS_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.cpp
new file mode 100644
index 0000000..80b51b2
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.cpp
@@ -0,0 +1,109 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_reader.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h"
+
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+const PtNodeParams Ver4PatriciaTrieNodeReader::fetchPtNodeInfoFromBufferAndProcessMovedPtNode(
+        const int ptNodePos, const int siblingNodePos) const {
+    if (ptNodePos < 0 || ptNodePos >= mBuffer->getTailPosition()) {
+        // Reading invalid position because of bug or broken dictionary.
+        AKLOGE("Fetching PtNode info from invalid dictionary position: %d, dictionary size: %d",
+                ptNodePos, mBuffer->getTailPosition());
+        ASSERT(false);
+        return PtNodeParams();
+    }
+    const bool usesAdditionalBuffer = mBuffer->isInAdditionalBuffer(ptNodePos);
+    const uint8_t *const dictBuf = mBuffer->getBuffer(usesAdditionalBuffer);
+    int pos = ptNodePos;
+    const int headPos = ptNodePos;
+    if (usesAdditionalBuffer) {
+        pos -= mBuffer->getOriginalBufferSize();
+    }
+    const PatriciaTrieReadingUtils::NodeFlags flags =
+            PatriciaTrieReadingUtils::getFlagsAndAdvancePosition(dictBuf, &pos);
+    const int parentPosOffset =
+            DynamicPtReadingUtils::getParentPtNodePosOffsetAndAdvancePosition(
+                    dictBuf, &pos);
+    const int parentPos =
+            DynamicPtReadingUtils::getParentPtNodePos(parentPosOffset, headPos);
+    int codePoints[MAX_WORD_LENGTH];
+    const int codePonitCount = PatriciaTrieReadingUtils::getCharsAndAdvancePosition(
+            dictBuf, flags, MAX_WORD_LENGTH, codePoints, &pos);
+    int terminalIdFieldPos = NOT_A_DICT_POS;
+    int terminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+    int probability = NOT_A_PROBABILITY;
+    if (PatriciaTrieReadingUtils::isTerminal(flags)) {
+        terminalIdFieldPos = pos;
+        if (usesAdditionalBuffer) {
+            terminalIdFieldPos += mBuffer->getOriginalBufferSize();
+        }
+        terminalId = Ver4PatriciaTrieReadingUtils::getTerminalIdAndAdvancePosition(dictBuf, &pos);
+        const ProbabilityEntry probabilityEntry =
+                mProbabilityDictContent->getProbabilityEntry(terminalId);
+        if (probabilityEntry.hasHistoricalInfo()) {
+            probability = ForgettingCurveUtils::decodeProbability(
+                    probabilityEntry.getHistoricalInfo(), mHeaderPolicy);
+        } else {
+            probability = probabilityEntry.getProbability();
+        }
+    }
+    int childrenPosFieldPos = pos;
+    if (usesAdditionalBuffer) {
+        childrenPosFieldPos += mBuffer->getOriginalBufferSize();
+    }
+    int childrenPos = DynamicPtReadingUtils::readChildrenPositionAndAdvancePosition(
+            dictBuf, &pos);
+    if (usesAdditionalBuffer && childrenPos != NOT_A_DICT_POS) {
+        childrenPos += mBuffer->getOriginalBufferSize();
+    }
+    if (usesAdditionalBuffer) {
+        pos += mBuffer->getOriginalBufferSize();
+    }
+    // Sibling position is the tail position of original PtNode.
+    int newSiblingNodePos = (siblingNodePos == NOT_A_DICT_POS) ? pos : siblingNodePos;
+    // Read destination node if the read node is a moved node.
+    if (DynamicPtReadingUtils::isMoved(flags)) {
+        // The destination position is stored at the same place as the parent position.
+        return fetchPtNodeInfoFromBufferAndProcessMovedPtNode(parentPos, newSiblingNodePos);
+    } else {
+        return PtNodeParams(headPos, flags, parentPos, codePonitCount, codePoints,
+                terminalIdFieldPos, terminalId, probability, childrenPosFieldPos, childrenPos,
+                newSiblingNodePos);
+    }
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h
new file mode 100644
index 0000000..0531b0a
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h
@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_reader.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_READER_H
+#define LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_READER_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/pt_node_params.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/pt_node_reader.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class BufferWithExtendableBuffer;
+namespace backward {
+namespace v401 {
+} // namespace v401
+} // namespace backward
+class HeaderPolicy;
+namespace backward {
+namespace v401 {
+class ProbabilityDictContent;
+
+/*
+ * This class is used for helping to read nodes of ver4 patricia trie. This class handles moved
+ * node and reads node attributes including probability form probabilityBuffer.
+ */
+class Ver4PatriciaTrieNodeReader : public PtNodeReader {
+ public:
+    Ver4PatriciaTrieNodeReader(const BufferWithExtendableBuffer *const buffer,
+            const ProbabilityDictContent *const probabilityDictContent,
+            const HeaderPolicy *const headerPolicy)
+            : mBuffer(buffer), mProbabilityDictContent(probabilityDictContent),
+              mHeaderPolicy(headerPolicy) {}
+
+    ~Ver4PatriciaTrieNodeReader() {}
+
+    virtual const PtNodeParams fetchNodeInfoInBufferFromPtNodePos(const int ptNodePos) const {
+        return fetchPtNodeInfoFromBufferAndProcessMovedPtNode(ptNodePos,
+                NOT_A_DICT_POS /* siblingNodePos */);
+    }
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(Ver4PatriciaTrieNodeReader);
+
+    const BufferWithExtendableBuffer *const mBuffer;
+    const ProbabilityDictContent *const mProbabilityDictContent;
+    const HeaderPolicy *const mHeaderPolicy;
+
+    const PtNodeParams fetchPtNodeInfoFromBufferAndProcessMovedPtNode(const int ptNodePos,
+            const int siblingNodePos) const;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_READER_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.cpp
new file mode 100644
index 0000000..8de6bac
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.cpp
@@ -0,0 +1,429 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h"
+
+#include "suggest/core/dictionary/property/unigram_property.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_writing_utils.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+const int Ver4PatriciaTrieNodeWriter::CHILDREN_POSITION_FIELD_SIZE = 3;
+
+bool Ver4PatriciaTrieNodeWriter::markPtNodeAsDeleted(
+        const PtNodeParams *const toBeUpdatedPtNodeParams) {
+    int pos = toBeUpdatedPtNodeParams->getHeadPos();
+    const bool usesAdditionalBuffer = mTrieBuffer->isInAdditionalBuffer(pos);
+    const uint8_t *const dictBuf = mTrieBuffer->getBuffer(usesAdditionalBuffer);
+    if (usesAdditionalBuffer) {
+        pos -= mTrieBuffer->getOriginalBufferSize();
+    }
+    // Read original flags
+    const PatriciaTrieReadingUtils::NodeFlags originalFlags =
+            PatriciaTrieReadingUtils::getFlagsAndAdvancePosition(dictBuf, &pos);
+    const PatriciaTrieReadingUtils::NodeFlags updatedFlags =
+            DynamicPtReadingUtils::updateAndGetFlags(originalFlags, false /* isMoved */,
+                    true /* isDeleted */, false /* willBecomeNonTerminal */);
+    int writingPos = toBeUpdatedPtNodeParams->getHeadPos();
+    // Update flags.
+    if (!DynamicPtWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer, updatedFlags,
+            &writingPos)) {
+        return false;
+    }
+    if (toBeUpdatedPtNodeParams->isTerminal()) {
+        // The PtNode is a terminal. Delete entry from the terminal position lookup table.
+        return mBuffers->getMutableTerminalPositionLookupTable()->setTerminalPtNodePosition(
+                toBeUpdatedPtNodeParams->getTerminalId(), NOT_A_DICT_POS /* ptNodePos */);
+    } else {
+        return true;
+    }
+}
+
+bool Ver4PatriciaTrieNodeWriter::markPtNodeAsMoved(
+        const PtNodeParams *const toBeUpdatedPtNodeParams,
+        const int movedPos, const int bigramLinkedNodePos) {
+    int pos = toBeUpdatedPtNodeParams->getHeadPos();
+    const bool usesAdditionalBuffer = mTrieBuffer->isInAdditionalBuffer(pos);
+    const uint8_t *const dictBuf = mTrieBuffer->getBuffer(usesAdditionalBuffer);
+    if (usesAdditionalBuffer) {
+        pos -= mTrieBuffer->getOriginalBufferSize();
+    }
+    // Read original flags
+    const PatriciaTrieReadingUtils::NodeFlags originalFlags =
+            PatriciaTrieReadingUtils::getFlagsAndAdvancePosition(dictBuf, &pos);
+    const PatriciaTrieReadingUtils::NodeFlags updatedFlags =
+            DynamicPtReadingUtils::updateAndGetFlags(originalFlags, true /* isMoved */,
+                    false /* isDeleted */, false /* willBecomeNonTerminal */);
+    int writingPos = toBeUpdatedPtNodeParams->getHeadPos();
+    // Update flags.
+    if (!DynamicPtWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer, updatedFlags,
+            &writingPos)) {
+        return false;
+    }
+    // Update moved position, which is stored in the parent offset field.
+    if (!DynamicPtWritingUtils::writeParentPosOffsetAndAdvancePosition(
+            mTrieBuffer, movedPos, toBeUpdatedPtNodeParams->getHeadPos(), &writingPos)) {
+        return false;
+    }
+    if (toBeUpdatedPtNodeParams->hasChildren()) {
+        // Update children's parent position.
+        mReadingHelper.initWithPtNodeArrayPos(toBeUpdatedPtNodeParams->getChildrenPos());
+        while (!mReadingHelper.isEnd()) {
+            const PtNodeParams childPtNodeParams(mReadingHelper.getPtNodeParams());
+            int parentOffsetFieldPos = childPtNodeParams.getHeadPos()
+                    + DynamicPtWritingUtils::NODE_FLAG_FIELD_SIZE;
+            if (!DynamicPtWritingUtils::writeParentPosOffsetAndAdvancePosition(
+                    mTrieBuffer, bigramLinkedNodePos, childPtNodeParams.getHeadPos(),
+                    &parentOffsetFieldPos)) {
+                // Parent offset cannot be written because of a bug or a broken dictionary; thus,
+                // we give up to update dictionary.
+                return false;
+            }
+            mReadingHelper.readNextSiblingNode(childPtNodeParams);
+        }
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieNodeWriter::markPtNodeAsWillBecomeNonTerminal(
+        const PtNodeParams *const toBeUpdatedPtNodeParams) {
+    int pos = toBeUpdatedPtNodeParams->getHeadPos();
+    const bool usesAdditionalBuffer = mTrieBuffer->isInAdditionalBuffer(pos);
+    const uint8_t *const dictBuf = mTrieBuffer->getBuffer(usesAdditionalBuffer);
+    if (usesAdditionalBuffer) {
+        pos -= mTrieBuffer->getOriginalBufferSize();
+    }
+    // Read original flags
+    const PatriciaTrieReadingUtils::NodeFlags originalFlags =
+            PatriciaTrieReadingUtils::getFlagsAndAdvancePosition(dictBuf, &pos);
+    const PatriciaTrieReadingUtils::NodeFlags updatedFlags =
+            DynamicPtReadingUtils::updateAndGetFlags(originalFlags, false /* isMoved */,
+                    false /* isDeleted */, true /* willBecomeNonTerminal */);
+    if (!mBuffers->getMutableTerminalPositionLookupTable()->setTerminalPtNodePosition(
+            toBeUpdatedPtNodeParams->getTerminalId(), NOT_A_DICT_POS /* ptNodePos */)) {
+        AKLOGE("Cannot update terminal position lookup table. terminal id: %d",
+                toBeUpdatedPtNodeParams->getTerminalId());
+        return false;
+    }
+    // Update flags.
+    int writingPos = toBeUpdatedPtNodeParams->getHeadPos();
+    return DynamicPtWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer, updatedFlags,
+            &writingPos);
+}
+
+bool Ver4PatriciaTrieNodeWriter::updatePtNodeUnigramProperty(
+        const PtNodeParams *const toBeUpdatedPtNodeParams,
+        const UnigramProperty *const unigramProperty) {
+    // Update probability and historical information.
+    // TODO: Update other information in the unigram property.
+    if (!toBeUpdatedPtNodeParams->isTerminal()) {
+        return false;
+    }
+    const ProbabilityEntry originalProbabilityEntry =
+            mBuffers->getProbabilityDictContent()->getProbabilityEntry(
+                    toBeUpdatedPtNodeParams->getTerminalId());
+    const ProbabilityEntry probabilityEntry = createUpdatedEntryFrom(&originalProbabilityEntry,
+            unigramProperty);
+    return mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(
+            toBeUpdatedPtNodeParams->getTerminalId(), &probabilityEntry);
+}
+
+bool Ver4PatriciaTrieNodeWriter::updatePtNodeProbabilityAndGetNeedsToKeepPtNodeAfterGC(
+        const PtNodeParams *const toBeUpdatedPtNodeParams, bool *const outNeedsToKeepPtNode) {
+    if (!toBeUpdatedPtNodeParams->isTerminal()) {
+        AKLOGE("updatePtNodeProbabilityAndGetNeedsToSaveForGC is called for non-terminal PtNode.");
+        return false;
+    }
+    const ProbabilityEntry originalProbabilityEntry =
+            mBuffers->getProbabilityDictContent()->getProbabilityEntry(
+                    toBeUpdatedPtNodeParams->getTerminalId());
+    if (originalProbabilityEntry.hasHistoricalInfo()) {
+        const HistoricalInfo historicalInfo = ForgettingCurveUtils::createHistoricalInfoToSave(
+                originalProbabilityEntry.getHistoricalInfo(), mHeaderPolicy);
+        const ProbabilityEntry probabilityEntry =
+                originalProbabilityEntry.createEntryWithUpdatedHistoricalInfo(&historicalInfo);
+        if (!mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(
+                toBeUpdatedPtNodeParams->getTerminalId(), &probabilityEntry)) {
+            AKLOGE("Cannot write updated probability entry. terminalId: %d",
+                    toBeUpdatedPtNodeParams->getTerminalId());
+            return false;
+        }
+        const bool isValid = ForgettingCurveUtils::needsToKeep(&historicalInfo, mHeaderPolicy);
+        if (!isValid) {
+            if (!markPtNodeAsWillBecomeNonTerminal(toBeUpdatedPtNodeParams)) {
+                AKLOGE("Cannot mark PtNode as willBecomeNonTerminal.");
+                return false;
+            }
+        }
+        *outNeedsToKeepPtNode = isValid;
+    } else {
+        // No need to update probability.
+        *outNeedsToKeepPtNode = true;
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieNodeWriter::updateChildrenPosition(
+        const PtNodeParams *const toBeUpdatedPtNodeParams, const int newChildrenPosition) {
+    int childrenPosFieldPos = toBeUpdatedPtNodeParams->getChildrenPosFieldPos();
+    return DynamicPtWritingUtils::writeChildrenPositionAndAdvancePosition(mTrieBuffer,
+            newChildrenPosition, &childrenPosFieldPos);
+}
+
+bool Ver4PatriciaTrieNodeWriter::updateTerminalId(const PtNodeParams *const toBeUpdatedPtNodeParams,
+        const int newTerminalId) {
+    return mTrieBuffer->writeUint(newTerminalId, Ver4DictConstants::TERMINAL_ID_FIELD_SIZE,
+            toBeUpdatedPtNodeParams->getTerminalIdFieldPos());
+}
+
+bool Ver4PatriciaTrieNodeWriter::writePtNodeAndAdvancePosition(
+        const PtNodeParams *const ptNodeParams, int *const ptNodeWritingPos) {
+    return writePtNodeAndGetTerminalIdAndAdvancePosition(ptNodeParams, 0 /* outTerminalId */,
+            ptNodeWritingPos);
+}
+
+
+bool Ver4PatriciaTrieNodeWriter::writeNewTerminalPtNodeAndAdvancePosition(
+        const PtNodeParams *const ptNodeParams, const UnigramProperty *const unigramProperty,
+        int *const ptNodeWritingPos) {
+    int terminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+    if (!writePtNodeAndGetTerminalIdAndAdvancePosition(ptNodeParams, &terminalId,
+            ptNodeWritingPos)) {
+        return false;
+    }
+    // Write probability.
+    ProbabilityEntry newProbabilityEntry;
+    const ProbabilityEntry probabilityEntryToWrite = createUpdatedEntryFrom(
+            &newProbabilityEntry, unigramProperty);
+    return mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(terminalId,
+            &probabilityEntryToWrite);
+}
+
+bool Ver4PatriciaTrieNodeWriter::addNewBigramEntry(
+        const PtNodeParams *const sourcePtNodeParams, const PtNodeParams *const targetPtNodeParam,
+        const BigramProperty *const bigramProperty, bool *const outAddedNewBigram) {
+    if (!mBigramPolicy->addNewEntry(sourcePtNodeParams->getTerminalId(),
+            targetPtNodeParam->getTerminalId(), bigramProperty, outAddedNewBigram)) {
+        AKLOGE("Cannot add new bigram entry. terminalId: %d, targetTerminalId: %d",
+                sourcePtNodeParams->getTerminalId(), targetPtNodeParam->getTerminalId());
+        return false;
+    }
+    if (!sourcePtNodeParams->hasBigrams()) {
+        // Update has bigrams flag.
+        return updatePtNodeFlags(sourcePtNodeParams->getHeadPos(),
+                sourcePtNodeParams->isBlacklisted(), sourcePtNodeParams->isNotAWord(),
+                sourcePtNodeParams->isTerminal(), sourcePtNodeParams->hasShortcutTargets(),
+                true /* hasBigrams */,
+                sourcePtNodeParams->getCodePointCount() > 1 /* hasMultipleChars */);
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieNodeWriter::removeBigramEntry(
+        const PtNodeParams *const sourcePtNodeParams, const PtNodeParams *const targetPtNodeParam) {
+    return mBigramPolicy->removeEntry(sourcePtNodeParams->getTerminalId(),
+            targetPtNodeParam->getTerminalId());
+}
+
+bool Ver4PatriciaTrieNodeWriter::updateAllBigramEntriesAndDeleteUselessEntries(
+            const PtNodeParams *const sourcePtNodeParams, int *const outBigramEntryCount) {
+    return mBigramPolicy->updateAllBigramEntriesAndDeleteUselessEntries(
+            sourcePtNodeParams->getTerminalId(), outBigramEntryCount);
+}
+
+bool Ver4PatriciaTrieNodeWriter::updateAllPositionFields(
+        const PtNodeParams *const toBeUpdatedPtNodeParams,
+        const DictPositionRelocationMap *const dictPositionRelocationMap,
+        int *const outBigramEntryCount) {
+    int parentPos = toBeUpdatedPtNodeParams->getParentPos();
+    if (parentPos != NOT_A_DICT_POS) {
+        PtNodeWriter::PtNodePositionRelocationMap::const_iterator it =
+                dictPositionRelocationMap->mPtNodePositionRelocationMap.find(parentPos);
+        if (it != dictPositionRelocationMap->mPtNodePositionRelocationMap.end()) {
+            parentPos = it->second;
+        }
+    }
+    int writingPos = toBeUpdatedPtNodeParams->getHeadPos()
+            + DynamicPtWritingUtils::NODE_FLAG_FIELD_SIZE;
+    // Write updated parent offset.
+    if (!DynamicPtWritingUtils::writeParentPosOffsetAndAdvancePosition(mTrieBuffer,
+            parentPos, toBeUpdatedPtNodeParams->getHeadPos(), &writingPos)) {
+        return false;
+    }
+
+    // Updates children position.
+    int childrenPos = toBeUpdatedPtNodeParams->getChildrenPos();
+    if (childrenPos != NOT_A_DICT_POS) {
+        PtNodeWriter::PtNodeArrayPositionRelocationMap::const_iterator it =
+                dictPositionRelocationMap->mPtNodeArrayPositionRelocationMap.find(childrenPos);
+        if (it != dictPositionRelocationMap->mPtNodeArrayPositionRelocationMap.end()) {
+            childrenPos = it->second;
+        }
+    }
+    if (!updateChildrenPosition(toBeUpdatedPtNodeParams, childrenPos)) {
+        return false;
+    }
+
+    // Counts bigram entries.
+    if (outBigramEntryCount) {
+        *outBigramEntryCount = mBigramPolicy->getBigramEntryConut(
+                toBeUpdatedPtNodeParams->getTerminalId());
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieNodeWriter::addShortcutTarget(const PtNodeParams *const ptNodeParams,
+        const int *const targetCodePoints, const int targetCodePointCount,
+        const int shortcutProbability) {
+    if (!mShortcutPolicy->addNewShortcut(ptNodeParams->getTerminalId(),
+            targetCodePoints, targetCodePointCount, shortcutProbability)) {
+        AKLOGE("Cannot add new shortuct entry. terminalId: %d", ptNodeParams->getTerminalId());
+        return false;
+    }
+    if (!ptNodeParams->hasShortcutTargets()) {
+        // Update has shortcut targets flag.
+        return updatePtNodeFlags(ptNodeParams->getHeadPos(),
+                ptNodeParams->isBlacklisted(), ptNodeParams->isNotAWord(),
+                ptNodeParams->isTerminal(), true /* hasShortcutTargets */,
+                ptNodeParams->hasBigrams(),
+                ptNodeParams->getCodePointCount() > 1 /* hasMultipleChars */);
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieNodeWriter::updatePtNodeHasBigramsAndShortcutTargetsFlags(
+        const PtNodeParams *const ptNodeParams) {
+    const bool hasBigrams = mBuffers->getBigramDictContent()->getBigramListHeadPos(
+            ptNodeParams->getTerminalId()) != NOT_A_DICT_POS;
+    const bool hasShortcutTargets = mBuffers->getShortcutDictContent()->getShortcutListHeadPos(
+            ptNodeParams->getTerminalId()) != NOT_A_DICT_POS;
+    return updatePtNodeFlags(ptNodeParams->getHeadPos(), ptNodeParams->isBlacklisted(),
+            ptNodeParams->isNotAWord(), ptNodeParams->isTerminal(), hasShortcutTargets,
+            hasBigrams, ptNodeParams->getCodePointCount() > 1 /* hasMultipleChars */);
+}
+
+bool Ver4PatriciaTrieNodeWriter::writePtNodeAndGetTerminalIdAndAdvancePosition(
+        const PtNodeParams *const ptNodeParams, int *const outTerminalId,
+        int *const ptNodeWritingPos) {
+    const int nodePos = *ptNodeWritingPos;
+    // Write dummy flags. The Node flags are updated with appropriate flags at the last step of the
+    // PtNode writing.
+    if (!DynamicPtWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer,
+            0 /* nodeFlags */, ptNodeWritingPos)) {
+        return false;
+    }
+    // Calculate a parent offset and write the offset.
+    if (!DynamicPtWritingUtils::writeParentPosOffsetAndAdvancePosition(mTrieBuffer,
+            ptNodeParams->getParentPos(), nodePos, ptNodeWritingPos)) {
+        return false;
+    }
+    // Write code points
+    if (!DynamicPtWritingUtils::writeCodePointsAndAdvancePosition(mTrieBuffer,
+            ptNodeParams->getCodePoints(), ptNodeParams->getCodePointCount(), ptNodeWritingPos)) {
+        return false;
+    }
+    int terminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+    if (!ptNodeParams->willBecomeNonTerminal()) {
+        if (ptNodeParams->getTerminalId() != Ver4DictConstants::NOT_A_TERMINAL_ID) {
+            terminalId = ptNodeParams->getTerminalId();
+        } else if (ptNodeParams->isTerminal()) {
+            // Write terminal information using a new terminal id.
+            // Get a new unused terminal id.
+            terminalId = mBuffers->getTerminalPositionLookupTable()->getNextTerminalId();
+        }
+    }
+    const int isTerminal = terminalId != Ver4DictConstants::NOT_A_TERMINAL_ID;
+    if (isTerminal) {
+        // Update the lookup table.
+        if (!mBuffers->getMutableTerminalPositionLookupTable()->setTerminalPtNodePosition(
+                terminalId, nodePos)) {
+            return false;
+        }
+        // Write terminal Id.
+        if (!mTrieBuffer->writeUintAndAdvancePosition(terminalId,
+                Ver4DictConstants::TERMINAL_ID_FIELD_SIZE, ptNodeWritingPos)) {
+            return false;
+        }
+        if (outTerminalId) {
+            *outTerminalId = terminalId;
+        }
+    }
+    // Write children position
+    if (!DynamicPtWritingUtils::writeChildrenPositionAndAdvancePosition(mTrieBuffer,
+            ptNodeParams->getChildrenPos(), ptNodeWritingPos)) {
+        return false;
+    }
+    return updatePtNodeFlags(nodePos, ptNodeParams->isBlacklisted(), ptNodeParams->isNotAWord(),
+            isTerminal, ptNodeParams->hasShortcutTargets(), ptNodeParams->hasBigrams(),
+            ptNodeParams->getCodePointCount() > 1 /* hasMultipleChars */);
+}
+
+const ProbabilityEntry Ver4PatriciaTrieNodeWriter::createUpdatedEntryFrom(
+        const ProbabilityEntry *const originalProbabilityEntry,
+        const UnigramProperty *const unigramProperty) const {
+    // TODO: Consolidate historical info and probability.
+    if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
+        const HistoricalInfo historicalInfoForUpdate(unigramProperty->getTimestamp(),
+                unigramProperty->getLevel(), unigramProperty->getCount());
+        const HistoricalInfo updatedHistoricalInfo =
+                ForgettingCurveUtils::createUpdatedHistoricalInfo(
+                        originalProbabilityEntry->getHistoricalInfo(),
+                        unigramProperty->getProbability(), &historicalInfoForUpdate, mHeaderPolicy);
+        return originalProbabilityEntry->createEntryWithUpdatedHistoricalInfo(
+                &updatedHistoricalInfo);
+    } else {
+        return originalProbabilityEntry->createEntryWithUpdatedProbability(
+                unigramProperty->getProbability());
+    }
+}
+
+bool Ver4PatriciaTrieNodeWriter::updatePtNodeFlags(const int ptNodePos,
+        const bool isBlacklisted, const bool isNotAWord, const bool isTerminal,
+        const bool hasShortcutTargets, const bool hasBigrams, const bool hasMultipleChars) {
+    // Create node flags and write them.
+    PatriciaTrieReadingUtils::NodeFlags nodeFlags =
+            PatriciaTrieReadingUtils::createAndGetFlags(isBlacklisted, isNotAWord, isTerminal,
+                    hasShortcutTargets, hasBigrams, hasMultipleChars,
+                    CHILDREN_POSITION_FIELD_SIZE);
+    if (!DynamicPtWritingUtils::writeFlags(mTrieBuffer, nodeFlags, ptNodePos)) {
+        AKLOGE("Cannot write PtNode flags. flags: %x, pos: %d", nodeFlags, ptNodePos);
+        return false;
+    }
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h
new file mode 100644
index 0000000..7f1851d
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h
@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_WRITER_H
+#define LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_WRITER_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_helper.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/pt_node_params.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/pt_node_writer.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/probability_entry.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class BufferWithExtendableBuffer;
+namespace backward {
+namespace v401 {
+} // namespace v401
+} // namespace backward
+class HeaderPolicy;
+namespace backward {
+namespace v401 {
+class Ver4BigramListPolicy;
+class Ver4DictBuffers;
+class Ver4PatriciaTrieNodeReader;
+class Ver4PtNodeArrayReader;
+class Ver4ShortcutListPolicy;
+
+/*
+ * This class is used for helping to writes nodes of ver4 patricia trie.
+ */
+class Ver4PatriciaTrieNodeWriter : public PtNodeWriter {
+ public:
+    Ver4PatriciaTrieNodeWriter(BufferWithExtendableBuffer *const trieBuffer,
+            Ver4DictBuffers *const buffers, const HeaderPolicy *const headerPolicy,
+            const PtNodeReader *const ptNodeReader,
+            const PtNodeArrayReader *const ptNodeArrayReader,
+            Ver4BigramListPolicy *const bigramPolicy, Ver4ShortcutListPolicy *const shortcutPolicy)
+            : mTrieBuffer(trieBuffer), mBuffers(buffers), mHeaderPolicy(headerPolicy),
+              mReadingHelper(ptNodeReader, ptNodeArrayReader), mBigramPolicy(bigramPolicy),
+              mShortcutPolicy(shortcutPolicy) {}
+
+    virtual ~Ver4PatriciaTrieNodeWriter() {}
+
+    virtual bool markPtNodeAsDeleted(const PtNodeParams *const toBeUpdatedPtNodeParams);
+
+    virtual bool markPtNodeAsMoved(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const int movedPos, const int bigramLinkedNodePos);
+
+    virtual bool markPtNodeAsWillBecomeNonTerminal(
+            const PtNodeParams *const toBeUpdatedPtNodeParams);
+
+    virtual bool updatePtNodeUnigramProperty(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const UnigramProperty *const unigramProperty);
+
+    virtual bool updatePtNodeProbabilityAndGetNeedsToKeepPtNodeAfterGC(
+            const PtNodeParams *const toBeUpdatedPtNodeParams, bool *const outNeedsToKeepPtNode);
+
+    virtual bool updateChildrenPosition(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const int newChildrenPosition);
+
+    bool updateTerminalId(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const int newTerminalId);
+
+    virtual bool writePtNodeAndAdvancePosition(const PtNodeParams *const ptNodeParams,
+            int *const ptNodeWritingPos);
+
+    virtual bool writeNewTerminalPtNodeAndAdvancePosition(const PtNodeParams *const ptNodeParams,
+            const UnigramProperty *const unigramProperty, int *const ptNodeWritingPos);
+
+    virtual bool addNewBigramEntry(const PtNodeParams *const sourcePtNodeParams,
+            const PtNodeParams *const targetPtNodeParam, const BigramProperty *const bigramProperty,
+            bool *const outAddedNewBigram);
+
+    virtual bool removeBigramEntry(const PtNodeParams *const sourcePtNodeParams,
+            const PtNodeParams *const targetPtNodeParam);
+
+    virtual bool updateAllBigramEntriesAndDeleteUselessEntries(
+            const PtNodeParams *const sourcePtNodeParams, int *const outBigramEntryCount);
+
+    virtual bool updateAllPositionFields(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const DictPositionRelocationMap *const dictPositionRelocationMap,
+            int *const outBigramEntryCount);
+
+    virtual bool addShortcutTarget(const PtNodeParams *const ptNodeParams,
+            const int *const targetCodePoints, const int targetCodePointCount,
+            const int shortcutProbability);
+
+    bool updatePtNodeHasBigramsAndShortcutTargetsFlags(const PtNodeParams *const ptNodeParams);
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(Ver4PatriciaTrieNodeWriter);
+
+    bool writePtNodeAndGetTerminalIdAndAdvancePosition(
+            const PtNodeParams *const ptNodeParams, int *const outTerminalId,
+            int *const ptNodeWritingPos);
+
+    // Create updated probability entry using given unigram property. In addition to the
+    // probability, this method updates historical information if needed.
+    // TODO: Update flags belonging to the unigram property.
+    const ProbabilityEntry createUpdatedEntryFrom(
+            const ProbabilityEntry *const originalProbabilityEntry,
+            const UnigramProperty *const unigramProperty) const;
+
+    bool updatePtNodeFlags(const int ptNodePos, const bool isBlacklisted, const bool isNotAWord,
+            const bool isTerminal, const bool hasShortcutTargets, const bool hasBigrams,
+            const bool hasMultipleChars);
+
+    static const int CHILDREN_POSITION_FIELD_SIZE;
+
+    BufferWithExtendableBuffer *const mTrieBuffer;
+    Ver4DictBuffers *const mBuffers;
+    const HeaderPolicy *const mHeaderPolicy;
+    DynamicPtReadingHelper mReadingHelper;
+    Ver4BigramListPolicy *const mBigramPolicy;
+    Ver4ShortcutListPolicy *const mShortcutPolicy;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_NODE_WRITER_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.cpp
new file mode 100644
index 0000000..dde1af2
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.cpp
@@ -0,0 +1,475 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT CHANGE THE LOGIC IN THIS FILE !!!!!
+ * Do not edit this file other than updating policy's interface.
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.h"
+
+#include <vector>
+
+#include "suggest/core/dicnode/dic_node.h"
+#include "suggest/core/dicnode/dic_node_vector.h"
+#include "suggest/core/dictionary/property/bigram_property.h"
+#include "suggest/core/dictionary/property/unigram_property.h"
+#include "suggest/core/dictionary/property/word_property.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_helper.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h"
+#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
+#include "suggest/policyimpl/dictionary/utils/probability_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+// Note that there are corresponding definitions in Java side in BinaryDictionaryTests and
+// BinaryDictionaryDecayingTests.
+const char *const Ver4PatriciaTriePolicy::UNIGRAM_COUNT_QUERY = "UNIGRAM_COUNT";
+const char *const Ver4PatriciaTriePolicy::BIGRAM_COUNT_QUERY = "BIGRAM_COUNT";
+const char *const Ver4PatriciaTriePolicy::MAX_UNIGRAM_COUNT_QUERY = "MAX_UNIGRAM_COUNT";
+const char *const Ver4PatriciaTriePolicy::MAX_BIGRAM_COUNT_QUERY = "MAX_BIGRAM_COUNT";
+const int Ver4PatriciaTriePolicy::MARGIN_TO_REFUSE_DYNAMIC_OPERATIONS = 1024;
+const int Ver4PatriciaTriePolicy::MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS =
+        Ver4DictConstants::MAX_DICTIONARY_SIZE - MARGIN_TO_REFUSE_DYNAMIC_OPERATIONS;
+
+void Ver4PatriciaTriePolicy::createAndGetAllChildDicNodes(const DicNode *const dicNode,
+        DicNodeVector *const childDicNodes) const {
+    if (!dicNode->hasChildren()) {
+        return;
+    }
+    DynamicPtReadingHelper readingHelper(&mNodeReader, &mPtNodeArrayReader);
+    readingHelper.initWithPtNodeArrayPos(dicNode->getChildrenPtNodeArrayPos());
+    while (!readingHelper.isEnd()) {
+        const PtNodeParams ptNodeParams = readingHelper.getPtNodeParams();
+        if (!ptNodeParams.isValid()) {
+            break;
+        }
+        bool isTerminal = ptNodeParams.isTerminal() && !ptNodeParams.isDeleted();
+        if (isTerminal && mHeaderPolicy->isDecayingDict()) {
+            // A DecayingDict may have a terminal PtNode that has a terminal DicNode whose
+            // probability is NOT_A_PROBABILITY. In such case, we don't want to treat it as a
+            // valid terminal DicNode.
+            isTerminal = ptNodeParams.getProbability() != NOT_A_PROBABILITY;
+        }
+        childDicNodes->pushLeavingChild(dicNode, ptNodeParams.getHeadPos(),
+                ptNodeParams.getChildrenPos(), ptNodeParams.getProbability(), isTerminal,
+                ptNodeParams.hasChildren(),
+                ptNodeParams.isBlacklisted()
+                        || ptNodeParams.isNotAWord() /* isBlacklistedOrNotAWord */,
+                ptNodeParams.getCodePointCount(), ptNodeParams.getCodePoints());
+        readingHelper.readNextSiblingNode(ptNodeParams);
+    }
+    if (readingHelper.isError()) {
+        mIsCorrupted = true;
+        AKLOGE("Dictionary reading error in createAndGetAllChildDicNodes().");
+    }
+}
+
+int Ver4PatriciaTriePolicy::getCodePointsAndProbabilityAndReturnCodePointCount(
+        const int ptNodePos, const int maxCodePointCount, int *const outCodePoints,
+        int *const outUnigramProbability) const {
+    DynamicPtReadingHelper readingHelper(&mNodeReader, &mPtNodeArrayReader);
+    readingHelper.initWithPtNodePos(ptNodePos);
+    const int codePointCount =  readingHelper.getCodePointsAndProbabilityAndReturnCodePointCount(
+            maxCodePointCount, outCodePoints, outUnigramProbability);
+    if (readingHelper.isError()) {
+        mIsCorrupted = true;
+        AKLOGE("Dictionary reading error in getCodePointsAndProbabilityAndReturnCodePointCount().");
+    }
+    return codePointCount;
+}
+
+int Ver4PatriciaTriePolicy::getTerminalPtNodePositionOfWord(const int *const inWord,
+        const int length, const bool forceLowerCaseSearch) const {
+    DynamicPtReadingHelper readingHelper(&mNodeReader, &mPtNodeArrayReader);
+    readingHelper.initWithPtNodeArrayPos(getRootPosition());
+    const int ptNodePos =
+            readingHelper.getTerminalPtNodePositionOfWord(inWord, length, forceLowerCaseSearch);
+    if (readingHelper.isError()) {
+        mIsCorrupted = true;
+        AKLOGE("Dictionary reading error in createAndGetAllChildDicNodes().");
+    }
+    return ptNodePos;
+}
+
+int Ver4PatriciaTriePolicy::getProbability(const int unigramProbability,
+        const int bigramProbability) const {
+    if (mHeaderPolicy->isDecayingDict()) {
+        // Both probabilities are encoded. Decode them and get probability.
+        return ForgettingCurveUtils::getProbability(unigramProbability, bigramProbability);
+    } else {
+        if (unigramProbability == NOT_A_PROBABILITY) {
+            return NOT_A_PROBABILITY;
+        } else if (bigramProbability == NOT_A_PROBABILITY) {
+            return ProbabilityUtils::backoff(unigramProbability);
+        } else {
+            // bigramProbability is a bigram probability delta.
+            return ProbabilityUtils::computeProbabilityForBigram(unigramProbability,
+                    bigramProbability);
+        }
+    }
+}
+
+int Ver4PatriciaTriePolicy::getUnigramProbabilityOfPtNode(const int ptNodePos) const {
+    if (ptNodePos == NOT_A_DICT_POS) {
+        return NOT_A_PROBABILITY;
+    }
+    const PtNodeParams ptNodeParams(mNodeReader.fetchNodeInfoInBufferFromPtNodePos(ptNodePos));
+    if (ptNodeParams.isDeleted() || ptNodeParams.isBlacklisted() || ptNodeParams.isNotAWord()) {
+        return NOT_A_PROBABILITY;
+    }
+    return getProbability(ptNodeParams.getProbability(), NOT_A_PROBABILITY);
+}
+
+int Ver4PatriciaTriePolicy::getShortcutPositionOfPtNode(const int ptNodePos) const {
+    if (ptNodePos == NOT_A_DICT_POS) {
+        return NOT_A_DICT_POS;
+    }
+    const PtNodeParams ptNodeParams(mNodeReader.fetchNodeInfoInBufferFromPtNodePos(ptNodePos));
+    if (ptNodeParams.isDeleted()) {
+        return NOT_A_DICT_POS;
+    }
+    return mBuffers->getShortcutDictContent()->getShortcutListHeadPos(
+            ptNodeParams.getTerminalId());
+}
+
+int Ver4PatriciaTriePolicy::getBigramsPositionOfPtNode(const int ptNodePos) const {
+    if (ptNodePos == NOT_A_DICT_POS) {
+        return NOT_A_DICT_POS;
+    }
+    const PtNodeParams ptNodeParams(mNodeReader.fetchNodeInfoInBufferFromPtNodePos(ptNodePos));
+    if (ptNodeParams.isDeleted()) {
+        return NOT_A_DICT_POS;
+    }
+    return mBuffers->getBigramDictContent()->getBigramListHeadPos(
+            ptNodeParams.getTerminalId());
+}
+
+bool Ver4PatriciaTriePolicy::addUnigramWord(const int *const word, const int length,
+        const UnigramProperty *const unigramProperty) {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: addUnigramWord() is called for non-updatable dictionary.");
+        return false;
+    }
+    if (mDictBuffer->getTailPosition() >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update. Dictionary size: %d",
+                mDictBuffer->getTailPosition());
+        return false;
+    }
+    if (length > MAX_WORD_LENGTH) {
+        AKLOGE("The word is too long to insert to the dictionary, length: %d", length);
+        return false;
+    }
+    for (const auto &shortcut : unigramProperty->getShortcuts()) {
+        if (shortcut.getTargetCodePoints()->size() > MAX_WORD_LENGTH) {
+            AKLOGE("One of shortcut targets is too long to insert to the dictionary, length: %d",
+                    shortcut.getTargetCodePoints()->size());
+            return false;
+        }
+    }
+    DynamicPtReadingHelper readingHelper(&mNodeReader, &mPtNodeArrayReader);
+    readingHelper.initWithPtNodeArrayPos(getRootPosition());
+    bool addedNewUnigram = false;
+    if (mUpdatingHelper.addUnigramWord(&readingHelper, word, length,
+            unigramProperty, &addedNewUnigram)) {
+        if (addedNewUnigram) {
+            mUnigramCount++;
+        }
+        if (unigramProperty->getShortcuts().size() > 0) {
+            // Add shortcut target.
+            const int wordPos = getTerminalPtNodePositionOfWord(word, length,
+                    false /* forceLowerCaseSearch */);
+            if (wordPos == NOT_A_DICT_POS) {
+                AKLOGE("Cannot find terminal PtNode position to add shortcut target.");
+                return false;
+            }
+            for (const auto &shortcut : unigramProperty->getShortcuts()) {
+                if (!mUpdatingHelper.addShortcutTarget(wordPos,
+                        shortcut.getTargetCodePoints()->data(),
+                        shortcut.getTargetCodePoints()->size(), shortcut.getProbability())) {
+                    AKLOGE("Cannot add new shortcut target. PtNodePos: %d, length: %d, "
+                            "probability: %d", wordPos, shortcut.getTargetCodePoints()->size(),
+                            shortcut.getProbability());
+                    return false;
+                }
+            }
+        }
+        return true;
+    } else {
+        return false;
+    }
+}
+
+bool Ver4PatriciaTriePolicy::addBigramWords(const int *const word0, const int length0,
+        const BigramProperty *const bigramProperty) {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: addBigramWords() is called for non-updatable dictionary.");
+        return false;
+    }
+    if (mDictBuffer->getTailPosition() >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update. Dictionary size: %d",
+                mDictBuffer->getTailPosition());
+        return false;
+    }
+    if (length0 > MAX_WORD_LENGTH
+            || bigramProperty->getTargetCodePoints()->size() > MAX_WORD_LENGTH) {
+        AKLOGE("Either src word or target word is too long to insert the bigram to the dictionary. "
+                "length0: %d, length1: %d", length0, bigramProperty->getTargetCodePoints()->size());
+        return false;
+    }
+    const int word0Pos = getTerminalPtNodePositionOfWord(word0, length0,
+            false /* forceLowerCaseSearch */);
+    if (word0Pos == NOT_A_DICT_POS) {
+        return false;
+    }
+    const int word1Pos = getTerminalPtNodePositionOfWord(
+            bigramProperty->getTargetCodePoints()->data(),
+            bigramProperty->getTargetCodePoints()->size(), false /* forceLowerCaseSearch */);
+    if (word1Pos == NOT_A_DICT_POS) {
+        return false;
+    }
+    bool addedNewBigram = false;
+    if (mUpdatingHelper.addBigramWords(word0Pos, word1Pos, bigramProperty, &addedNewBigram)) {
+        if (addedNewBigram) {
+            mBigramCount++;
+        }
+        return true;
+    } else {
+        return false;
+    }
+}
+
+bool Ver4PatriciaTriePolicy::removeBigramWords(const int *const word0, const int length0,
+        const int *const word1, const int length1) {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: addBigramWords() is called for non-updatable dictionary.");
+        return false;
+    }
+    if (mDictBuffer->getTailPosition() >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update. Dictionary size: %d",
+                mDictBuffer->getTailPosition());
+        return false;
+    }
+    if (length0 > MAX_WORD_LENGTH || length1 > MAX_WORD_LENGTH) {
+        AKLOGE("Either src word or target word is too long to remove the bigram to from the "
+                "dictionary. length0: %d, length1: %d", length0, length1);
+        return false;
+    }
+    const int word0Pos = getTerminalPtNodePositionOfWord(word0, length0,
+            false /* forceLowerCaseSearch */);
+    if (word0Pos == NOT_A_DICT_POS) {
+        return false;
+    }
+    const int word1Pos = getTerminalPtNodePositionOfWord(word1, length1,
+            false /* forceLowerCaseSearch */);
+    if (word1Pos == NOT_A_DICT_POS) {
+        return false;
+    }
+    if (mUpdatingHelper.removeBigramWords(word0Pos, word1Pos)) {
+        mBigramCount--;
+        return true;
+    } else {
+        return false;
+    }
+}
+
+void Ver4PatriciaTriePolicy::flush(const char *const filePath) {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: flush() is called for non-updatable dictionary. filePath: %s", filePath);
+        return;
+    }
+    if (!mWritingHelper.writeToDictFile(filePath, mUnigramCount, mBigramCount)) {
+        AKLOGE("Cannot flush the dictionary to file.");
+        mIsCorrupted = true;
+    }
+}
+
+void Ver4PatriciaTriePolicy::flushWithGC(const char *const filePath) {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: flushWithGC() is called for non-updatable dictionary.");
+        return;
+    }
+    if (!mWritingHelper.writeToDictFileWithGC(getRootPosition(), filePath)) {
+        AKLOGE("Cannot flush the dictionary to file with GC.");
+        mIsCorrupted = true;
+    }
+}
+
+bool Ver4PatriciaTriePolicy::needsToRunGC(const bool mindsBlockByGC) const {
+    if (!mBuffers->isUpdatable()) {
+        AKLOGI("Warning: needsToRunGC() is called for non-updatable dictionary.");
+        return false;
+    }
+    if (mBuffers->isNearSizeLimit()) {
+        // Additional buffer size is near the limit.
+        return true;
+    } else if (mHeaderPolicy->getExtendedRegionSize() + mDictBuffer->getUsedAdditionalBufferSize()
+            > Ver4DictConstants::MAX_DICT_EXTENDED_REGION_SIZE) {
+        // Total extended region size of the trie exceeds the limit.
+        return true;
+    } else if (mDictBuffer->getTailPosition() >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS
+            && mDictBuffer->getUsedAdditionalBufferSize() > 0) {
+        // Needs to reduce dictionary size.
+        return true;
+    } else if (mHeaderPolicy->isDecayingDict()) {
+        return ForgettingCurveUtils::needsToDecay(mindsBlockByGC, mUnigramCount, mBigramCount,
+                mHeaderPolicy);
+    }
+    return false;
+}
+
+void Ver4PatriciaTriePolicy::getProperty(const char *const query, const int queryLength,
+        char *const outResult, const int maxResultLength) {
+    const int compareLength = queryLength + 1 /* terminator */;
+    if (strncmp(query, UNIGRAM_COUNT_QUERY, compareLength) == 0) {
+        snprintf(outResult, maxResultLength, "%d", mUnigramCount);
+    } else if (strncmp(query, BIGRAM_COUNT_QUERY, compareLength) == 0) {
+        snprintf(outResult, maxResultLength, "%d", mBigramCount);
+    } else if (strncmp(query, MAX_UNIGRAM_COUNT_QUERY, compareLength) == 0) {
+        snprintf(outResult, maxResultLength, "%d",
+                mHeaderPolicy->isDecayingDict() ?
+                        ForgettingCurveUtils::getUnigramCountHardLimit(
+                                mHeaderPolicy->getMaxUnigramCount()) :
+                        static_cast<int>(Ver4DictConstants::MAX_DICTIONARY_SIZE));
+    } else if (strncmp(query, MAX_BIGRAM_COUNT_QUERY, compareLength) == 0) {
+        snprintf(outResult, maxResultLength, "%d",
+                mHeaderPolicy->isDecayingDict() ?
+                        ForgettingCurveUtils::getBigramCountHardLimit(
+                                mHeaderPolicy->getMaxBigramCount()) :
+                        static_cast<int>(Ver4DictConstants::MAX_DICTIONARY_SIZE));
+    }
+}
+
+const WordProperty Ver4PatriciaTriePolicy::getWordProperty(const int *const codePoints,
+        const int codePointCount) const {
+    const int ptNodePos = getTerminalPtNodePositionOfWord(codePoints, codePointCount,
+            false /* forceLowerCaseSearch */);
+    if (ptNodePos == NOT_A_DICT_POS) {
+        AKLOGE("getWordProperty is called for invalid word.");
+        return WordProperty();
+    }
+    const PtNodeParams ptNodeParams = mNodeReader.fetchNodeInfoInBufferFromPtNodePos(ptNodePos);
+    std::vector<int> codePointVector(ptNodeParams.getCodePoints(),
+            ptNodeParams.getCodePoints() + ptNodeParams.getCodePointCount());
+    const ProbabilityEntry probabilityEntry =
+            mBuffers->getProbabilityDictContent()->getProbabilityEntry(
+                    ptNodeParams.getTerminalId());
+    const HistoricalInfo *const historicalInfo = probabilityEntry.getHistoricalInfo();
+    // Fetch bigram information.
+    std::vector<BigramProperty> bigrams;
+    const int bigramListPos = getBigramsPositionOfPtNode(ptNodePos);
+    if (bigramListPos != NOT_A_DICT_POS) {
+        int bigramWord1CodePoints[MAX_WORD_LENGTH];
+        const BigramDictContent *const bigramDictContent = mBuffers->getBigramDictContent();
+        const TerminalPositionLookupTable *const terminalPositionLookupTable =
+                mBuffers->getTerminalPositionLookupTable();
+        bool hasNext = true;
+        int readingPos = bigramListPos;
+        while (hasNext) {
+            const BigramEntry bigramEntry =
+                    bigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+            hasNext = bigramEntry.hasNext();
+            const int word1TerminalId = bigramEntry.getTargetTerminalId();
+            const int word1TerminalPtNodePos =
+                    terminalPositionLookupTable->getTerminalPtNodePosition(word1TerminalId);
+            if (word1TerminalPtNodePos == NOT_A_DICT_POS) {
+                continue;
+            }
+            // Word (unigram) probability
+            int word1Probability = NOT_A_PROBABILITY;
+            const int codePointCount = getCodePointsAndProbabilityAndReturnCodePointCount(
+                    word1TerminalPtNodePos, MAX_WORD_LENGTH, bigramWord1CodePoints,
+                    &word1Probability);
+            const std::vector<int> word1(bigramWord1CodePoints,
+                    bigramWord1CodePoints + codePointCount);
+            const HistoricalInfo *const historicalInfo = bigramEntry.getHistoricalInfo();
+            const int probability = bigramEntry.hasHistoricalInfo() ?
+                    ForgettingCurveUtils::decodeProbability(
+                            bigramEntry.getHistoricalInfo(), mHeaderPolicy) :
+                    getProbability(word1Probability, bigramEntry.getProbability());
+            bigrams.emplace_back(&word1, probability,
+                    historicalInfo->getTimeStamp(), historicalInfo->getLevel(),
+                    historicalInfo->getCount());
+        }
+    }
+    // Fetch shortcut information.
+    std::vector<UnigramProperty::ShortcutProperty> shortcuts;
+    int shortcutPos = getShortcutPositionOfPtNode(ptNodePos);
+    if (shortcutPos != NOT_A_DICT_POS) {
+        int shortcutTarget[MAX_WORD_LENGTH];
+        const ShortcutDictContent *const shortcutDictContent =
+                mBuffers->getShortcutDictContent();
+        bool hasNext = true;
+        while (hasNext) {
+            int shortcutTargetLength = 0;
+            int shortcutProbability = NOT_A_PROBABILITY;
+            shortcutDictContent->getShortcutEntryAndAdvancePosition(MAX_WORD_LENGTH, shortcutTarget,
+                    &shortcutTargetLength, &shortcutProbability, &hasNext, &shortcutPos);
+            const std::vector<int> target(shortcutTarget, shortcutTarget + shortcutTargetLength);
+            shortcuts.emplace_back(&target, shortcutProbability);
+        }
+    }
+    const UnigramProperty unigramProperty(ptNodeParams.isNotAWord(),
+            ptNodeParams.isBlacklisted(), ptNodeParams.getProbability(),
+            historicalInfo->getTimeStamp(), historicalInfo->getLevel(),
+            historicalInfo->getCount(), &shortcuts);
+    return WordProperty(&codePointVector, &unigramProperty, &bigrams);
+}
+
+int Ver4PatriciaTriePolicy::getNextWordAndNextToken(const int token, int *const outCodePoints) {
+    // TODO: Return code point count like other methods.
+    // Null termination.
+    outCodePoints[0] = 0;
+    if (token == 0) {
+        mTerminalPtNodePositionsForIteratingWords.clear();
+        DynamicPtReadingHelper::TraversePolicyToGetAllTerminalPtNodePositions traversePolicy(
+                &mTerminalPtNodePositionsForIteratingWords);
+        DynamicPtReadingHelper readingHelper(&mNodeReader, &mPtNodeArrayReader);
+        readingHelper.initWithPtNodeArrayPos(getRootPosition());
+        readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(&traversePolicy);
+    }
+    const int terminalPtNodePositionsVectorSize =
+            static_cast<int>(mTerminalPtNodePositionsForIteratingWords.size());
+    if (token < 0 || token >= terminalPtNodePositionsVectorSize) {
+        AKLOGE("Given token %d is invalid.", token);
+        return 0;
+    }
+    const int terminalPtNodePos = mTerminalPtNodePositionsForIteratingWords[token];
+    int unigramProbability = NOT_A_PROBABILITY;
+    const int codePointCount = getCodePointsAndProbabilityAndReturnCodePointCount(
+            terminalPtNodePos, MAX_WORD_LENGTH, outCodePoints, &unigramProbability);
+    if (codePointCount < MAX_WORD_LENGTH) {
+        // Null termination. outCodePoints have to be null terminated or contain MAX_WORD_LENGTH
+        // code points.
+        outCodePoints[codePointCount] = 0;
+    }
+    const int nextToken = token + 1;
+    if (nextToken >= terminalPtNodePositionsVectorSize) {
+        // All words have been iterated.
+        mTerminalPtNodePositionsForIteratingWords.clear();
+        return 0;
+    }
+    return nextToken;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.h
new file mode 100644
index 0000000..2f8ad53
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_policy.h
@@ -0,0 +1,168 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT CHANGE THE LOGIC IN THIS FILE !!!!!
+ * Do not edit this file other than updating policy's interface.
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_POLICY_H
+#define LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_POLICY_H
+
+#include <vector>
+
+#include "defines.h"
+#include "suggest/core/policy/dictionary_structure_with_buffer_policy.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class DicNode;
+namespace backward {
+namespace v401 {
+} // namespace v401
+} // namespace backward
+class DicNodeVector;
+namespace backward {
+namespace v401 {
+
+class Ver4PatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
+ public:
+    Ver4PatriciaTriePolicy(Ver4DictBuffers::Ver4DictBuffersPtr buffers)
+            : mBuffers(std::move(buffers)), mHeaderPolicy(mBuffers->getHeaderPolicy()),
+              mDictBuffer(mBuffers->getWritableTrieBuffer()),
+              mBigramPolicy(mBuffers->getMutableBigramDictContent(),
+                      mBuffers->getTerminalPositionLookupTable(), mHeaderPolicy),
+              mShortcutPolicy(mBuffers->getMutableShortcutDictContent(),
+                      mBuffers->getTerminalPositionLookupTable()),
+              mNodeReader(mDictBuffer, mBuffers->getProbabilityDictContent(), mHeaderPolicy),
+              mPtNodeArrayReader(mDictBuffer),
+              mNodeWriter(mDictBuffer, mBuffers.get(), mHeaderPolicy, &mNodeReader,
+                      &mPtNodeArrayReader, &mBigramPolicy, &mShortcutPolicy),
+              mUpdatingHelper(mDictBuffer, &mNodeReader, &mNodeWriter),
+              mWritingHelper(mBuffers.get()),
+              mUnigramCount(mHeaderPolicy->getUnigramCount()),
+              mBigramCount(mHeaderPolicy->getBigramCount()),
+              mTerminalPtNodePositionsForIteratingWords(), mIsCorrupted(false) {};
+
+    AK_FORCE_INLINE int getRootPosition() const {
+        return 0;
+    }
+
+    void createAndGetAllChildDicNodes(const DicNode *const dicNode,
+            DicNodeVector *const childDicNodes) const;
+
+    int getCodePointsAndProbabilityAndReturnCodePointCount(
+            const int terminalPtNodePos, const int maxCodePointCount, int *const outCodePoints,
+            int *const outUnigramProbability) const;
+
+    int getTerminalPtNodePositionOfWord(const int *const inWord,
+            const int length, const bool forceLowerCaseSearch) const;
+
+    int getProbability(const int unigramProbability, const int bigramProbability) const;
+
+    int getUnigramProbabilityOfPtNode(const int ptNodePos) const;
+
+    int getShortcutPositionOfPtNode(const int ptNodePos) const;
+
+    int getBigramsPositionOfPtNode(const int ptNodePos) const;
+
+    const DictionaryHeaderStructurePolicy *getHeaderStructurePolicy() const {
+        return mHeaderPolicy;
+    }
+
+    const DictionaryBigramsStructurePolicy *getBigramsStructurePolicy() const {
+        return &mBigramPolicy;
+    }
+
+    const DictionaryShortcutsStructurePolicy *getShortcutsStructurePolicy() const {
+        return &mShortcutPolicy;
+    }
+
+    bool addUnigramWord(const int *const word, const int length,
+            const UnigramProperty *const unigramProperty);
+
+    bool addBigramWords(const int *const word0, const int length0,
+            const BigramProperty *const bigramProperty);
+
+    bool removeBigramWords(const int *const word0, const int length0, const int *const word1,
+            const int length1);
+
+    void flush(const char *const filePath);
+
+    void flushWithGC(const char *const filePath);
+
+    bool needsToRunGC(const bool mindsBlockByGC) const;
+
+    void getProperty(const char *const query, const int queryLength, char *const outResult,
+            const int maxResultLength);
+
+    const WordProperty getWordProperty(const int *const codePoints,
+            const int codePointCount) const;
+
+    int getNextWordAndNextToken(const int token, int *const outCodePoints);
+
+    bool isCorrupted() const {
+        return mIsCorrupted;
+    }
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4PatriciaTriePolicy);
+
+    static const char *const UNIGRAM_COUNT_QUERY;
+    static const char *const BIGRAM_COUNT_QUERY;
+    static const char *const MAX_UNIGRAM_COUNT_QUERY;
+    static const char *const MAX_BIGRAM_COUNT_QUERY;
+    // When the dictionary size is near the maximum size, we have to refuse dynamic operations to
+    // prevent the dictionary from overflowing.
+    static const int MARGIN_TO_REFUSE_DYNAMIC_OPERATIONS;
+    static const int MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS;
+
+    const Ver4DictBuffers::Ver4DictBuffersPtr mBuffers;
+    const HeaderPolicy *const mHeaderPolicy;
+    BufferWithExtendableBuffer *const mDictBuffer;
+    Ver4BigramListPolicy mBigramPolicy;
+    Ver4ShortcutListPolicy mShortcutPolicy;
+    Ver4PatriciaTrieNodeReader mNodeReader;
+    Ver4PtNodeArrayReader mPtNodeArrayReader;
+    Ver4PatriciaTrieNodeWriter mNodeWriter;
+    DynamicPtUpdatingHelper mUpdatingHelper;
+    Ver4PatriciaTrieWritingHelper mWritingHelper;
+    int mUnigramCount;
+    int mBigramCount;
+    std::vector<int> mTerminalPtNodePositionsForIteratingWords;
+    mutable bool mIsCorrupted;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif // LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_POLICY_H
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.cpp
new file mode 100644
index 0000000..6cc36fb
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.cpp
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_reading_utils.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h"
+
+#include "suggest/policyimpl/dictionary/utils/byte_array_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+/* static */ int Ver4PatriciaTrieReadingUtils::getTerminalIdAndAdvancePosition(
+        const uint8_t *const buffer, int *pos) {
+    return ByteArrayUtils::readUint32AndAdvancePosition(buffer, pos);
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h
new file mode 100644
index 0000000..7417c26
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_reading_utils.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_reading_utils.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_READING_UTILS_H
+#define LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_READING_UTILS_H
+
+#include <cstdint>
+
+#include "defines.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class BufferWithExtendableBuffer;
+namespace backward {
+namespace v401 {
+
+class Ver4PatriciaTrieReadingUtils {
+ public:
+    static int getTerminalIdAndAdvancePosition(const uint8_t *const buffer,
+            int *const pos);
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4PatriciaTrieReadingUtils);
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_READING_UTILS_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.cpp
new file mode 100644
index 0000000..10f27be
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.cpp
@@ -0,0 +1,301 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.h"
+
+#include <cstring>
+#include <queue>
+
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/bigram/ver4_bigram_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/shortcut/ver4_shortcut_list_policy.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_buffers.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_dict_constants.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_reader.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_node_writer.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/file_utils.h"
+#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+bool Ver4PatriciaTrieWritingHelper::writeToDictFile(const char *const dictDirPath,
+        const int unigramCount, const int bigramCount) const {
+    const HeaderPolicy *const headerPolicy = mBuffers->getHeaderPolicy();
+    BufferWithExtendableBuffer headerBuffer(
+            BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE);
+    const int extendedRegionSize = headerPolicy->getExtendedRegionSize()
+            + mBuffers->getTrieBuffer()->getUsedAdditionalBufferSize();
+    if (!headerPolicy->fillInAndWriteHeaderToBuffer(false /* updatesLastDecayedTime */,
+            unigramCount, bigramCount, extendedRegionSize, &headerBuffer)) {
+        AKLOGE("Cannot write header structure to buffer. "
+                "updatesLastDecayedTime: %d, unigramCount: %d, bigramCount: %d, "
+                "extendedRegionSize: %d", false, unigramCount, bigramCount,
+                extendedRegionSize);
+        return false;
+    }
+    return mBuffers->flushHeaderAndDictBuffers(dictDirPath, &headerBuffer);
+}
+
+bool Ver4PatriciaTrieWritingHelper::writeToDictFileWithGC(const int rootPtNodeArrayPos,
+        const char *const dictDirPath) {
+    const HeaderPolicy *const headerPolicy = mBuffers->getHeaderPolicy();
+    Ver4DictBuffers::Ver4DictBuffersPtr dictBuffers(
+            Ver4DictBuffers::createVer4DictBuffers(headerPolicy,
+                    Ver4DictConstants::MAX_DICTIONARY_SIZE));
+    int unigramCount = 0;
+    int bigramCount = 0;
+    if (!runGC(rootPtNodeArrayPos, headerPolicy, dictBuffers.get(), &unigramCount, &bigramCount)) {
+        return false;
+    }
+    BufferWithExtendableBuffer headerBuffer(
+            BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE);
+    if (!headerPolicy->fillInAndWriteHeaderToBuffer(true /* updatesLastDecayedTime */,
+            unigramCount, bigramCount, 0 /* extendedRegionSize */, &headerBuffer)) {
+        return false;
+    }
+    return dictBuffers->flushHeaderAndDictBuffers(dictDirPath, &headerBuffer);
+}
+
+bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
+        const HeaderPolicy *const headerPolicy, Ver4DictBuffers *const buffersToWrite,
+        int *const outUnigramCount, int *const outBigramCount) {
+    Ver4PatriciaTrieNodeReader ptNodeReader(mBuffers->getTrieBuffer(),
+            mBuffers->getProbabilityDictContent(), headerPolicy);
+    Ver4PtNodeArrayReader ptNodeArrayReader(mBuffers->getTrieBuffer());
+    Ver4BigramListPolicy bigramPolicy(mBuffers->getMutableBigramDictContent(),
+            mBuffers->getTerminalPositionLookupTable(), headerPolicy);
+    Ver4ShortcutListPolicy shortcutPolicy(mBuffers->getMutableShortcutDictContent(),
+            mBuffers->getTerminalPositionLookupTable());
+    Ver4PatriciaTrieNodeWriter ptNodeWriter(mBuffers->getWritableTrieBuffer(),
+            mBuffers, headerPolicy, &ptNodeReader, &ptNodeArrayReader, &bigramPolicy,
+            &shortcutPolicy);
+
+    DynamicPtReadingHelper readingHelper(&ptNodeReader, &ptNodeArrayReader);
+    readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPtGcEventListeners
+            ::TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+                    traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
+                            &ptNodeWriter);
+    if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
+            &traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted)) {
+        return false;
+    }
+    const int unigramCount = traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+            .getValidUnigramCount();
+    const int maxUnigramCount = headerPolicy->getMaxUnigramCount();
+    if (headerPolicy->isDecayingDict() && unigramCount > maxUnigramCount) {
+        if (!truncateUnigrams(&ptNodeReader, &ptNodeWriter, maxUnigramCount)) {
+            AKLOGE("Cannot remove unigrams. current: %d, max: %d", unigramCount,
+                    maxUnigramCount);
+            return false;
+        }
+    }
+
+    readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPtGcEventListeners::TraversePolicyToUpdateBigramProbability
+            traversePolicyToUpdateBigramProbability(&ptNodeWriter);
+    if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
+            &traversePolicyToUpdateBigramProbability)) {
+        return false;
+    }
+    const int bigramCount = traversePolicyToUpdateBigramProbability.getValidBigramEntryCount();
+    const int maxBigramCount = headerPolicy->getMaxBigramCount();
+    if (headerPolicy->isDecayingDict() && bigramCount > maxBigramCount) {
+        if (!truncateBigrams(maxBigramCount)) {
+            AKLOGE("Cannot remove bigrams. current: %d, max: %d", bigramCount, maxBigramCount);
+            return false;
+        }
+    }
+
+    // Mapping from positions in mBuffer to positions in bufferToWrite.
+    PtNodeWriter::DictPositionRelocationMap dictPositionRelocationMap;
+    readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    Ver4PatriciaTrieNodeWriter ptNodeWriterForNewBuffers(buffersToWrite->getWritableTrieBuffer(),
+            buffersToWrite, headerPolicy, &ptNodeReader, &ptNodeArrayReader, &bigramPolicy,
+            &shortcutPolicy);
+    DynamicPtGcEventListeners::TraversePolicyToPlaceAndWriteValidPtNodesToBuffer
+            traversePolicyToPlaceAndWriteValidPtNodesToBuffer(&ptNodeWriterForNewBuffers,
+                    buffersToWrite->getWritableTrieBuffer(), &dictPositionRelocationMap);
+    if (!readingHelper.traverseAllPtNodesInPtNodeArrayLevelPreorderDepthFirstManner(
+            &traversePolicyToPlaceAndWriteValidPtNodesToBuffer)) {
+        return false;
+    }
+
+    // Create policy instances for the GCed dictionary.
+    Ver4PatriciaTrieNodeReader newPtNodeReader(buffersToWrite->getTrieBuffer(),
+            buffersToWrite->getProbabilityDictContent(), headerPolicy);
+    Ver4PtNodeArrayReader newPtNodeArrayreader(buffersToWrite->getTrieBuffer());
+    Ver4BigramListPolicy newBigramPolicy(buffersToWrite->getMutableBigramDictContent(),
+            buffersToWrite->getTerminalPositionLookupTable(), headerPolicy);
+    Ver4ShortcutListPolicy newShortcutPolicy(buffersToWrite->getMutableShortcutDictContent(),
+            buffersToWrite->getTerminalPositionLookupTable());
+    Ver4PatriciaTrieNodeWriter newPtNodeWriter(buffersToWrite->getWritableTrieBuffer(),
+            buffersToWrite, headerPolicy, &newPtNodeReader, &newPtNodeArrayreader, &newBigramPolicy,
+            &newShortcutPolicy);
+    // Re-assign terminal IDs for valid terminal PtNodes.
+    TerminalPositionLookupTable::TerminalIdMap terminalIdMap;
+    if(!buffersToWrite->getMutableTerminalPositionLookupTable()->runGCTerminalIds(
+            &terminalIdMap)) {
+        return false;
+    }
+    // Run GC for probability dict content.
+    if (!buffersToWrite->getMutableProbabilityDictContent()->runGC(&terminalIdMap,
+            mBuffers->getProbabilityDictContent())) {
+        return false;
+    }
+    // Run GC for bigram dict content.
+    if(!buffersToWrite->getMutableBigramDictContent()->runGC(&terminalIdMap,
+            mBuffers->getBigramDictContent(), outBigramCount)) {
+        return false;
+    }
+    // Run GC for shortcut dict content.
+    if(!buffersToWrite->getMutableShortcutDictContent()->runGC(&terminalIdMap,
+            mBuffers->getShortcutDictContent())) {
+        return false;
+    }
+    DynamicPtReadingHelper newDictReadingHelper(&newPtNodeReader, &newPtNodeArrayreader);
+    newDictReadingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPtGcEventListeners::TraversePolicyToUpdateAllPositionFields
+            traversePolicyToUpdateAllPositionFields(&newPtNodeWriter, &dictPositionRelocationMap);
+    if (!newDictReadingHelper.traverseAllPtNodesInPtNodeArrayLevelPreorderDepthFirstManner(
+            &traversePolicyToUpdateAllPositionFields)) {
+        return false;
+    }
+    newDictReadingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    TraversePolicyToUpdateAllPtNodeFlagsAndTerminalIds
+            traversePolicyToUpdateAllPtNodeFlagsAndTerminalIds(&newPtNodeWriter, &terminalIdMap);
+    if (!newDictReadingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
+            &traversePolicyToUpdateAllPtNodeFlagsAndTerminalIds)) {
+        return false;
+    }
+    *outUnigramCount = traversePolicyToUpdateAllPositionFields.getUnigramCount();
+    return true;
+}
+
+bool Ver4PatriciaTrieWritingHelper::truncateUnigrams(
+        const Ver4PatriciaTrieNodeReader *const ptNodeReader,
+        Ver4PatriciaTrieNodeWriter *const ptNodeWriter, const int maxUnigramCount) {
+    const TerminalPositionLookupTable *const terminalPosLookupTable =
+            mBuffers->getTerminalPositionLookupTable();
+    const int nextTerminalId = terminalPosLookupTable->getNextTerminalId();
+    std::priority_queue<DictProbability, std::vector<DictProbability>, DictProbabilityComparator>
+            priorityQueue;
+    for (int i = 0; i < nextTerminalId; ++i) {
+        const int terminalPos = terminalPosLookupTable->getTerminalPtNodePosition(i);
+        if (terminalPos == NOT_A_DICT_POS) {
+            continue;
+        }
+        const ProbabilityEntry probabilityEntry =
+                mBuffers->getProbabilityDictContent()->getProbabilityEntry(i);
+        const int probability = probabilityEntry.hasHistoricalInfo() ?
+                ForgettingCurveUtils::decodeProbability(
+                        probabilityEntry.getHistoricalInfo(), mBuffers->getHeaderPolicy()) :
+                probabilityEntry.getProbability();
+        priorityQueue.push(DictProbability(terminalPos, probability,
+                probabilityEntry.getHistoricalInfo()->getTimeStamp()));
+    }
+
+    // Delete unigrams.
+    while (static_cast<int>(priorityQueue.size()) > maxUnigramCount) {
+        const int ptNodePos = priorityQueue.top().getDictPos();
+        const PtNodeParams ptNodeParams =
+                ptNodeReader->fetchNodeInfoInBufferFromPtNodePos(ptNodePos);
+        if (!ptNodeWriter->markPtNodeAsWillBecomeNonTerminal(&ptNodeParams)) {
+            AKLOGE("Cannot mark PtNode as willBecomeNonterminal. PtNode pos: %d", ptNodePos);
+            return false;
+        }
+        priorityQueue.pop();
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieWritingHelper::truncateBigrams(const int maxBigramCount) {
+    const TerminalPositionLookupTable *const terminalPosLookupTable =
+            mBuffers->getTerminalPositionLookupTable();
+    const int nextTerminalId = terminalPosLookupTable->getNextTerminalId();
+    std::priority_queue<DictProbability, std::vector<DictProbability>, DictProbabilityComparator>
+            priorityQueue;
+    BigramDictContent *const bigramDictContent = mBuffers->getMutableBigramDictContent();
+    for (int i = 0; i < nextTerminalId; ++i) {
+        const int bigramListPos = bigramDictContent->getBigramListHeadPos(i);
+        if (bigramListPos == NOT_A_DICT_POS) {
+            continue;
+        }
+        bool hasNext = true;
+        int readingPos = bigramListPos;
+        while (hasNext) {
+            const int entryPos = readingPos;
+            const BigramEntry bigramEntry =
+                    bigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+            hasNext = bigramEntry.hasNext();
+            if (!bigramEntry.isValid()) {
+                continue;
+            }
+            const int probability = bigramEntry.hasHistoricalInfo() ?
+                    ForgettingCurveUtils::decodeProbability(
+                            bigramEntry.getHistoricalInfo(), mBuffers->getHeaderPolicy()) :
+                    bigramEntry.getProbability();
+            priorityQueue.push(DictProbability(entryPos, probability,
+                    bigramEntry.getHistoricalInfo()->getTimeStamp()));
+        }
+    }
+
+    // Delete bigrams.
+    while (static_cast<int>(priorityQueue.size()) > maxBigramCount) {
+        const int entryPos = priorityQueue.top().getDictPos();
+        const BigramEntry bigramEntry = bigramDictContent->getBigramEntry(entryPos);
+        const BigramEntry invalidatedBigramEntry = bigramEntry.getInvalidatedEntry();
+        if (!bigramDictContent->writeBigramEntry(&invalidatedBigramEntry, entryPos)) {
+            AKLOGE("Cannot write bigram entry to remove. pos: %d", entryPos);
+            return false;
+        }
+        priorityQueue.pop();
+    }
+    return true;
+}
+
+bool Ver4PatriciaTrieWritingHelper::TraversePolicyToUpdateAllPtNodeFlagsAndTerminalIds
+        ::onVisitingPtNode(const PtNodeParams *const ptNodeParams) {
+    if (!ptNodeParams->isTerminal()) {
+        return true;
+    }
+    TerminalPositionLookupTable::TerminalIdMap::const_iterator it =
+            mTerminalIdMap->find(ptNodeParams->getTerminalId());
+    if (it == mTerminalIdMap->end()) {
+        AKLOGE("terminal Id %d is not in the terminal position map. map size: %zd",
+                ptNodeParams->getTerminalId(), mTerminalIdMap->size());
+        return false;
+    }
+    if (!mPtNodeWriter->updateTerminalId(ptNodeParams, it->second)) {
+        AKLOGE("Cannot update terminal id. %d -> %d", it->first, it->second);
+    }
+    return mPtNodeWriter->updatePtNodeHasBigramsAndShortcutTargetsFlags(ptNodeParams);
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.h
new file mode 100644
index 0000000..be44aaa
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_patricia_trie_writing_helper.h
@@ -0,0 +1,140 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_WRITING_HELPER_H
+#define LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_WRITING_HELPER_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_gc_event_listeners.h"
+#include "suggest/policyimpl/dictionary/structure/backward/v401/content/terminal_position_lookup_table.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class HeaderPolicy;
+namespace backward {
+namespace v401 {
+class Ver4DictBuffers;
+class Ver4PatriciaTrieNodeReader;
+class Ver4PatriciaTrieNodeWriter;
+
+class Ver4PatriciaTrieWritingHelper {
+ public:
+    Ver4PatriciaTrieWritingHelper(Ver4DictBuffers *const buffers)
+            : mBuffers(buffers) {}
+
+    bool writeToDictFile(const char *const dictDirPath, const int unigramCount,
+            const int bigramCount) const;
+
+    // This method cannot be const because the original dictionary buffer will be updated to detect
+    // useless PtNodes during GC.
+    bool writeToDictFileWithGC(const int rootPtNodeArrayPos, const char *const dictDirPath);
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4PatriciaTrieWritingHelper);
+
+    class TraversePolicyToUpdateAllPtNodeFlagsAndTerminalIds
+            : public DynamicPtReadingHelper::TraversingEventListener {
+     public:
+        TraversePolicyToUpdateAllPtNodeFlagsAndTerminalIds(
+                Ver4PatriciaTrieNodeWriter *const ptNodeWriter,
+                const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap)
+                : mPtNodeWriter(ptNodeWriter), mTerminalIdMap(terminalIdMap) {}
+
+        bool onAscend() { return true; }
+
+        bool onDescend(const int ptNodeArrayPos) { return true; }
+
+        bool onReadingPtNodeArrayTail() { return true; }
+
+        bool onVisitingPtNode(const PtNodeParams *const ptNodeParams);
+
+     private:
+        DISALLOW_IMPLICIT_CONSTRUCTORS(TraversePolicyToUpdateAllPtNodeFlagsAndTerminalIds);
+
+        Ver4PatriciaTrieNodeWriter *const mPtNodeWriter;
+        const TerminalPositionLookupTable::TerminalIdMap *const mTerminalIdMap;
+    };
+
+    // For truncateUnigrams() and truncateBigrams().
+    class DictProbability {
+     public:
+        DictProbability(const int dictPos, const int probability, const int timestamp)
+                : mDictPos(dictPos), mProbability(probability), mTimestamp(timestamp) {}
+
+        int getDictPos() const {
+            return mDictPos;
+        }
+
+        int getProbability() const {
+            return mProbability;
+        }
+
+        int getTimestamp() const {
+            return mTimestamp;
+        }
+
+     private:
+        DISALLOW_DEFAULT_CONSTRUCTOR(DictProbability);
+
+        int mDictPos;
+        int mProbability;
+        int mTimestamp;
+    };
+
+    // For truncateUnigrams() and truncateBigrams().
+    class DictProbabilityComparator {
+     public:
+        bool operator()(const DictProbability &left, const DictProbability &right) {
+            if (left.getProbability() != right.getProbability()) {
+                return left.getProbability() > right.getProbability();
+            }
+            if (left.getTimestamp() != right.getTimestamp()) {
+                return left.getTimestamp() < right.getTimestamp();
+            }
+            return left.getDictPos() > right.getDictPos();
+        }
+
+     private:
+        DISALLOW_ASSIGNMENT_OPERATOR(DictProbabilityComparator);
+    };
+
+    bool runGC(const int rootPtNodeArrayPos, const HeaderPolicy *const headerPolicy,
+            Ver4DictBuffers *const buffersToWrite, int *const outUnigramCount,
+            int *const outBigramCount);
+
+    bool truncateUnigrams(const Ver4PatriciaTrieNodeReader *const ptNodeReader,
+            Ver4PatriciaTrieNodeWriter *const ptNodeWriter, const int maxUnigramCount);
+
+    bool truncateBigrams(const int maxBigramCount);
+
+    Ver4DictBuffers *const mBuffers;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+
+#endif /* LATINIME_BACKWARD_V401_VER4_PATRICIA_TRIE_WRITING_HELPER_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.cpp
new file mode 100644
index 0000000..33e4e55
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.cpp
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2014, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_pt_node_array_reader.cpp
+ */
+
+#include "suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h"
+
+#include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_utils.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+bool Ver4PtNodeArrayReader::readPtNodeArrayInfoAndReturnIfValid(const int ptNodeArrayPos,
+        int *const outPtNodeCount, int *const outFirstPtNodePos) const {
+    if (ptNodeArrayPos < 0 || ptNodeArrayPos >= mBuffer->getTailPosition()) {
+        // Reading invalid position because of a bug or a broken dictionary.
+        AKLOGE("Reading PtNode array info from invalid dictionary position: %d, dict size: %d",
+                ptNodeArrayPos, mBuffer->getTailPosition());
+        ASSERT(false);
+        return false;
+    }
+    const bool usesAdditionalBuffer = mBuffer->isInAdditionalBuffer(ptNodeArrayPos);
+    const uint8_t *const dictBuf = mBuffer->getBuffer(usesAdditionalBuffer);
+    int readingPos = ptNodeArrayPos;
+    if (usesAdditionalBuffer) {
+        readingPos -= mBuffer->getOriginalBufferSize();
+    }
+    const int ptNodeCountInArray = PatriciaTrieReadingUtils::getPtNodeArraySizeAndAdvancePosition(
+            dictBuf, &readingPos);
+    if (usesAdditionalBuffer) {
+        readingPos += mBuffer->getOriginalBufferSize();
+    }
+    if (ptNodeCountInArray < 0) {
+        AKLOGE("Invalid PtNode count in an array: %d.", ptNodeCountInArray);
+        return false;
+    }
+    *outPtNodeCount = ptNodeCountInArray;
+    *outFirstPtNodePos = readingPos;
+    return true;
+}
+
+bool Ver4PtNodeArrayReader::readForwardLinkAndReturnIfValid(const int forwordLinkPos,
+        int *const outNextPtNodeArrayPos) const {
+    if (forwordLinkPos < 0 || forwordLinkPos >= mBuffer->getTailPosition()) {
+        // Reading invalid position because of bug or broken dictionary.
+        AKLOGE("Reading forward link from invalid dictionary position: %d, dict size: %d",
+                forwordLinkPos, mBuffer->getTailPosition());
+        ASSERT(false);
+        return false;
+    }
+    const bool usesAdditionalBuffer = mBuffer->isInAdditionalBuffer(forwordLinkPos);
+    const uint8_t *const dictBuf = mBuffer->getBuffer(usesAdditionalBuffer);
+    int readingPos = forwordLinkPos;
+    if (usesAdditionalBuffer) {
+        readingPos -= mBuffer->getOriginalBufferSize();
+    }
+    const int nextPtNodeArrayOffset =
+            DynamicPtReadingUtils::getForwardLinkPosition(dictBuf, readingPos);
+    if (DynamicPtReadingUtils::isValidForwardLinkPosition(nextPtNodeArrayOffset)) {
+        *outNextPtNodeArrayPos = forwordLinkPos + nextPtNodeArrayOffset;
+    } else {
+        *outNextPtNodeArrayPos = NOT_A_DICT_POS;
+    }
+    return true;
+}
+
+} // namespace v401
+} // namespace backward
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h
new file mode 100644
index 0000000..3a7eefa
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v401/ver4_pt_node_array_reader.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2014, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * !!!!! DO NOT EDIT THIS FILE !!!!!
+ *
+ * This file was generated from
+ *   suggest/policyimpl/dictionary/structure/v4/ver4_pt_node_array_reader.h
+ */
+
+#ifndef LATINIME_BACKWARD_V401_VER4_PT_NODE_ARRAY_READER_H
+#define LATINIME_BACKWARD_V401_VER4_PT_NODE_ARRAY_READER_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/pt_common/pt_node_array_reader.h"
+
+namespace latinime {
+namespace backward {
+namespace v401 {
+
+} // namespace v401
+} // namespace backward
+class BufferWithExtendableBuffer;
+namespace backward {
+namespace v401 {
+
+class Ver4PtNodeArrayReader : public PtNodeArrayReader {
+ public:
+    Ver4PtNodeArrayReader(const BufferWithExtendableBuffer *const buffer) : mBuffer(buffer) {};
+
+    virtual bool readPtNodeArrayInfoAndReturnIfValid(const int ptNodeArrayPos,
+            int *const outPtNodeCount, int *const outFirstPtNodePos) const;
+    virtual bool readForwardLinkAndReturnIfValid(const int forwordLinkPos,
+            int *const outNextPtNodeArrayPos) const;
+
+ private:
+    DISALLOW_COPY_AND_ASSIGN(Ver4PtNodeArrayReader);
+
+    const BufferWithExtendableBuffer *const mBuffer;
+};
+} // namespace v401
+} // namespace backward
+} // namespace latinime
+#endif /* LATINIME_BACKWARD_V401_VER4_PT_NODE_ARRAY_READER_H */