diff --git a/java/res/xml/key_f1.xml b/java/res/xml/key_f1.xml
index 455f9ef..72e38cb 100644
--- a/java/res/xml/key_f1.xml
+++ b/java/res/xml/key_f1.xml
@@ -47,7 +47,7 @@
             <Key
                 latin:keyLabel="!text/keylabel_for_comma"
                 latin:keyLabelFlags="hasPopupHint"
-                latin:additionalMoreKeys="!text/more_keys_for_comma"
+                latin:additionalMoreKeys="!text/more_keys_for_comma,!text/shortcut_as_more_key"
                 latin:keyStyle="f1MoreKeysStyle" />
         </default>
     </switch>
diff --git a/java/res/xml/row_dvorak4.xml b/java/res/xml/row_dvorak4.xml
index 02a95ac..b78872f 100644
--- a/java/res/xml/row_dvorak4.xml
+++ b/java/res/xml/row_dvorak4.xml
@@ -27,42 +27,11 @@
         <Key
             latin:keyStyle="toSymbolKeyStyle"
             latin:keyWidth="15%p" />
-        <switch>
-            <case
-                latin:hasShortcutKey="true"
-                latin:keyboardLayoutSetElement="alphabet"
-            >
-                <Key
-                    latin:keyLabel="q"
-                    latin:backgroundType="normal"
-                    latin:additionalMoreKeys="!text/shortcut_as_more_key"
-                    latin:keyStyle="f1MoreKeysStyle" />
-            </case>
-            <case
-                latin:hasShortcutKey="true"
-            >
-                <Key
-                    latin:keyLabel="Q"
-                    latin:backgroundType="normal"
-                    latin:additionalMoreKeys="!text/shortcut_as_more_key"
-                    latin:keyStyle="f1MoreKeysStyle" />
-            </case>
-            <!-- latin:hasShortcutKey="false" -->
-            <case
-                latin:keyboardLayoutSetElement="alphabet"
-            >
-                <Key
-                    latin:keyLabel="q"
-                    latin:backgroundType="normal"
-                    latin:keyStyle="f1MoreKeysStyle" />
-            </case>
-            <default>
-                <Key
-                    latin:keyLabel="Q"
-                    latin:backgroundType="normal"
-                    latin:keyStyle="f1MoreKeysStyle" />
-            </default>
-        </switch>
+        <Key
+            latin:keyLabel="q"
+            latin:backgroundType="normal"
+            latin:additionalMoreKeys="!text/shortcut_as_more_key"
+            latin:keyStyle="f1MoreKeysStyle" />
         <include
             latin:keyXPos="25%p"
             latin:keyboardLayout="@xml/key_space_5kw" />
diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index a5757fd..b61a66c 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -68,12 +68,14 @@
     suggest/core/policy/weighting.cpp \
     suggest/core/session/dic_traverse_session.cpp \
     $(addprefix suggest/policyimpl/dictionary/, \
-        bigram/bigram_list_read_write_utils.cpp \
-        bigram/dynamic_bigram_list_policy.cpp \
         header/header_policy.cpp \
         header/header_read_write_utils.cpp \
         shortcut/shortcut_list_reading_utils.cpp \
         structure/dictionary_structure_with_buffer_policy_factory.cpp) \
+    $(addprefix suggest/policyimpl/dictionary/bigram/, \
+        bigram_list_read_write_utils.cpp \
+        dynamic_bigram_list_policy.cpp \
+        ver4_bigram_list_policy.cpp) \
     $(addprefix suggest/policyimpl/dictionary/structure/v2/, \
         patricia_trie_policy.cpp \
         patricia_trie_reading_utils.cpp) \
@@ -88,6 +90,7 @@
         dynamic_patricia_trie_writing_helper.cpp \
         dynamic_patricia_trie_writing_utils.cpp) \
     $(addprefix suggest/policyimpl/dictionary/structure/v4/, \
+        content/bigram_dict_content.cpp \
         ver4_dict_constants.cpp \
         ver4_patricia_trie_node_reader.cpp \
         ver4_patricia_trie_node_writer.cpp \
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp
new file mode 100644
index 0000000..0280781
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp
@@ -0,0 +1,115 @@
+/*
+ * 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.
+ */
+
+#include "suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h"
+
+#include "suggest/policyimpl/dictionary/bigram/bigram_list_read_write_utils.h"
+#include "suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h"
+#include "suggest/policyimpl/dictionary/structure/v4/content/terminal_position_lookup_table.h"
+#include "suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h"
+
+namespace latinime {
+
+void Ver4BigramListPolicy::getNextBigram(int *const outBigramPos, int *const outProbability,
+        bool *const outHasNext, int *const bigramEntryPos) const {
+    int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+    mBigramDictContent->getBigramEntryAndAdvancePosition(outProbability, outHasNext,
+            &targetTerminalId, bigramEntryPos);
+    if (outBigramPos) {
+        // Lookup target PtNode position.
+        *outBigramPos = mTerminalPositionLookupTable->getTerminalPtNodePosition(targetTerminalId);
+    }
+}
+
+bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTargetTerminalId,
+        const int newProbability, bool *const outAddedNewEntry) {
+    if (outAddedNewEntry) {
+        *outAddedNewEntry = false;
+    }
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Updating PtNode doesn't have a bigram list.
+        // Create new bigram list.
+        if (!mBigramDictContent->createNewBigramList(terminalId)) {
+            return false;
+        }
+        // Write an entry.
+        int writingPos =  mBigramDictContent->getBigramListHeadPos(terminalId);
+        if (!mBigramDictContent->writeBigramEntryAndAdvancePosition(newProbability,
+                false /* hasNext */, newTargetTerminalId, &writingPos)) {
+            return false;
+        }
+        return true;
+    }
+
+    const int entryPosToUpdate = getEntryPosToUpdate(newTargetTerminalId, bigramListPos);
+    if (entryPosToUpdate != NOT_A_DICT_POS) {
+        // Overwrite existing entry.
+        int readingPos = entryPosToUpdate;
+        bool hasNext = false;
+        int probability = NOT_A_PROBABILITY;
+        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+        mBigramDictContent->getBigramEntryAndAdvancePosition(&probability, &hasNext,
+                &targetTerminalId, &readingPos);
+        if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID && outAddedNewEntry) {
+            // Reuse invalid entry.
+            *outAddedNewEntry = true;
+        }
+        int writingPos = entryPosToUpdate;
+        return mBigramDictContent->writeBigramEntryAndAdvancePosition(newProbability, hasNext,
+                newTargetTerminalId, &writingPos);
+    }
+
+    // Add new entry to the bigram list.
+    // Create new bigram list.
+    if (!mBigramDictContent->createNewBigramList(terminalId)) {
+        return false;
+    }
+    // Write new entry at a head position of the bigram list.
+    int writingPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (!mBigramDictContent->writeBigramEntryAndAdvancePosition(newProbability,
+            true /* hasNext */, newTargetTerminalId, &writingPos)) {
+        return false;
+    }
+    if (outAddedNewEntry) {
+        *outAddedNewEntry = true;
+    }
+    // Append existing entries by copying.
+    return mBigramDictContent->copyBigramList(bigramListPos, writingPos);
+}
+
+int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
+        const int bigramListPos) const {
+    bool hasNext = true;
+    int invalidEntryPos = NOT_A_DICT_POS;
+    int readingPos = bigramListPos;
+    while(hasNext) {
+        const int entryPos = readingPos;
+        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+        mBigramDictContent->getBigramEntryAndAdvancePosition(0 /* probability */, &hasNext,
+                &targetTerminalId, &readingPos);
+        if (targetTerminalId == targetTerminalIdToFind) {
+            // Entry with same target is found.
+            return entryPos;
+        } else if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID) {
+            // Invalid entry that can be reused is found.
+            invalidEntryPos = entryPos;
+        }
+    }
+    return invalidEntryPos;
+}
+
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
index 875a0ff..e599a2c 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
@@ -19,46 +19,35 @@
 
 #include "defines.h"
 #include "suggest/core/policy/dictionary_bigrams_structure_policy.h"
-#include "suggest/policyimpl/dictionary/bigram/bigram_list_read_write_utils.h"
-#include "suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h"
-#include "suggest/policyimpl/dictionary/structure/v4/content/terminal_position_lookup_table.h"
 
 namespace latinime {
 
+class BigramDictContent;
+class TerminalPositionLookupTable;
+
 class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
  public:
-    Ver4BigramListPolicy(const BigramDictContent *const bigramDictContent,
+    Ver4BigramListPolicy(BigramDictContent *const bigramDictContent,
             const TerminalPositionLookupTable *const terminalPositionLookupTable)
             : mBigramDictContent(bigramDictContent),
               mTerminalPositionLookupTable(terminalPositionLookupTable) {}
 
     void getNextBigram(int *const outBigramPos, int *const outProbability,
-            bool *const outHasNext, int *const bigramEntryPos) const {
-        int bigramFlags = 0;
-        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-        mBigramDictContent->getBigramEntryAndAdvancePosition(&bigramFlags, &targetTerminalId,
-                bigramEntryPos);
-        if (outProbability) {
-            *outProbability = BigramListReadWriteUtils::getProbabilityFromFlags(bigramFlags);
-        }
-        if (outHasNext) {
-            *outHasNext = BigramListReadWriteUtils::hasNext(bigramFlags);
-        }
-        if (outBigramPos) {
-            // Lookup target PtNode position.
-            *outBigramPos =
-                    mTerminalPositionLookupTable->getTerminalPtNodePosition(targetTerminalId);
-        }
-    }
+            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 int newProbability,
+            bool *const outAddedNewEntry);
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4BigramListPolicy);
 
-    const BigramDictContent *const mBigramDictContent;
+    int getEntryPosToUpdate(const int targetTerminalIdToFind, const int bigramListPos) const;
+
+    BigramDictContent *const mBigramDictContent;
     const TerminalPositionLookupTable *const mTerminalPositionLookupTable;
 };
 } // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_reading_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_reading_helper.cpp
index c3fe03d..b3fdbeb 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_reading_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_reading_helper.cpp
@@ -238,6 +238,9 @@
         }
         // All characters are matched.
         if (length == getTotalCodePointCount(ptNodeParams)) {
+            if (!ptNodeParams.isTerminal()) {
+                return NOT_A_DICT_POS;
+            }
             // Terminal position is found.
             return ptNodeParams.getHeadPos();
         }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.cpp
new file mode 100644
index 0000000..f02f145
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.cpp
@@ -0,0 +1,69 @@
+/*
+ * 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.
+ */
+
+#include "suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h"
+
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+
+namespace latinime {
+
+void BigramDictContent::getBigramEntryAndAdvancePosition(int *const outProbability,
+        bool *const outHasNext, int *const outTargetTerminalId, int *const bigramEntryPos) const {
+    const BufferWithExtendableBuffer *const bigramListBuffer = getContentBuffer();
+    const int bigramFlags = bigramListBuffer->readUintAndAdvancePosition(
+            Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE, bigramEntryPos);
+    if (outProbability) {
+        *outProbability = bigramFlags & Ver4DictConstants::BIGRAM_PROBABILITY_MASK;
+    }
+    if (outHasNext) {
+        *outHasNext = (bigramFlags & Ver4DictConstants::BIGRAM_HAS_NEXT_MASK) != 0;
+    }
+    if (outTargetTerminalId) {
+        *outTargetTerminalId = bigramListBuffer->readUintAndAdvancePosition(
+                Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, bigramEntryPos);
+    }
+}
+
+bool BigramDictContent::writeBigramEntryAndAdvancePosition(const int probability, const int hasNext,
+        const int targetTerminalId, int *const entryWritingPos) {
+    BufferWithExtendableBuffer *const bigramListBuffer = getWritableContentBuffer();
+    const int bigramFlags = createAndGetBigramFlags(probability, hasNext);
+    if (!bigramListBuffer->writeUintAndAdvancePosition(bigramFlags,
+            Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE, entryWritingPos)) {
+        return false;
+    }
+    return bigramListBuffer->writeUintAndAdvancePosition(targetTerminalId,
+            Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, entryWritingPos);
+}
+
+bool BigramDictContent::copyBigramList(const int bigramListPos, const int toPos) {
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    int writingPos = toPos;
+    while(hasNext) {
+        int probability = NOT_A_PROBABILITY;
+        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+        getBigramEntryAndAdvancePosition(&probability, &hasNext, &targetTerminalId,
+                &readingPos);
+        if (!writeBigramEntryAndAdvancePosition(probability, hasNext, targetTerminalId,
+                &writingPos)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
index 5eed13e..a112667 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
@@ -33,21 +33,11 @@
                       Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE,
                       Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE) {}
 
-    void getBigramEntryAndAdvancePosition(int *const outBigramFlags,
-            int *const outTargetTerminalId, int *const bigramEntryPos) const {
-        const BufferWithExtendableBuffer *const bigramListBuffer = getContentBuffer();
-        if (outBigramFlags) {
-            *outBigramFlags = bigramListBuffer->readUintAndAdvancePosition(
-                    Ver4DictConstants::BIGRAM_FLAGS_FIELD_SIZE, bigramEntryPos);
-        }
-        if (outTargetTerminalId) {
-            *outTargetTerminalId = bigramListBuffer->readUintAndAdvancePosition(
-                    Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, bigramEntryPos);
-        }
-    }
+    void getBigramEntryAndAdvancePosition(int *const outProbability, bool *const outHasNext,
+            int *const outTargetTerminalId, int *const bigramEntryPos) const;
 
-   // Returns head position of bigram list for a PtNode specified by terminalId.
-   int getBigramListHeadPos(const int terminalId) 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;
@@ -55,8 +45,23 @@
         return addressLookupTable->get(terminalId);
     }
 
+    bool writeBigramEntryAndAdvancePosition(const int probability, const int hasNext,
+            const int targetTerminalId, 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);
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(BigramDictContent);
+
+    int createAndGetBigramFlags(const int probability, const bool hasNext) const {
+        return (probability & Ver4DictConstants::BIGRAM_PROBABILITY_MASK)
+                | (hasNext ? Ver4DictConstants::BIGRAM_HAS_NEXT_MASK : 0);
+    }
 };
 } // namespace latinime
 #endif /* LATINIME_BIGRAM_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h
index 71868e9..fe9efe8 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h
@@ -59,10 +59,18 @@
     }
 
  protected:
+    SparseTable *getUpdatableAddressLookupTable() {
+        return &mAddressLookupTable;
+    }
+
     const SparseTable *getAddressLookupTable() const {
         return &mAddressLookupTable;
     }
 
+    BufferWithExtendableBuffer *getWritableContentBuffer() {
+        return &mExpandableContentBuffer;
+    }
+
     const BufferWithExtendableBuffer *getContentBuffer() const {
         return &mExpandableContentBuffer;
     }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
index 6476478..b9e56a2 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
@@ -70,6 +70,10 @@
         return &mProbabilityDictContent;
     }
 
+    AK_FORCE_INLINE BigramDictContent *getUpdatableBigramDictContent() {
+        return &mBigramDictContent;
+    }
+
     AK_FORCE_INLINE const BigramDictContent *getBigramDictContent() const {
         return &mBigramDictContent;
     }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp
index 941bcd5..2b113e3 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp
@@ -43,6 +43,8 @@
 
 const int Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE = 3;
 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::SHORTCUT_FLAGS_FIELD_SIZE = 1;
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h
index 7270d9e..a1830dd 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h
@@ -47,6 +47,8 @@
 
     static const int BIGRAM_FLAGS_FIELD_SIZE;
     static const int BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE;
+    static const int BIGRAM_PROBABILITY_MASK;
+    static const int BIGRAM_HAS_NEXT_MASK;
 
     static const int SHORTCUT_FLAGS_FIELD_SIZE;
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
index 8b0ea82..7c66a66 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
@@ -16,7 +16,7 @@
 
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h"
 
-#include "suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h"
+#include "suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h"
 #include "suggest/policyimpl/dictionary/shortcut/dynamic_shortcut_list_policy.h"
 #include "suggest/policyimpl/dictionary/structure/v2/patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_reader.h"
@@ -167,8 +167,6 @@
             ptNodeParams->getChildrenPos(), ptNodeWritingPos)) {
         return false;
     }
-    // TODO: Implement bigram and shortcut writing.
-
     // Create node flags and write them.
     PatriciaTrieReadingUtils::NodeFlags nodeFlags =
             PatriciaTrieReadingUtils::createAndGetFlags(ptNodeParams->isBlacklisted(),
@@ -188,8 +186,8 @@
         const PtNodeParams *const sourcePtNodeParams,
         const PtNodeParams *const targetPtNodeParam, const int probability,
         bool *const outAddedNewBigram) {
-    // TODO: Implement.
-    return false;
+    return mBigramPolicy->addNewEntry(sourcePtNodeParams->getTerminalId(),
+            targetPtNodeParam->getTerminalId(), probability, outAddedNewBigram);
 }
 
 bool Ver4PatriciaTrieNodeWriter::removeBigramEntry(
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
index 520ffc0..57201e4 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
@@ -135,9 +135,9 @@
         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.");
+    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;
     }
     DynamicPatriciaTrieReadingHelper readingHelper(&mDictBuffer, &mNodeReader);
@@ -156,8 +156,34 @@
 
 bool Ver4PatriciaTriePolicy::addBigramWords(const int *const word0, const int length0,
         const int *const word1, const int length1, const int probability) {
-    // TODO: Implement.
-    return false;
+    if (!mBuffers.get()->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;
+    }
+    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;
+    }
+    bool addedNewBigram = false;
+    if (mUpdatingHelper.addBigramWords(word0Pos, word1Pos, probability, &addedNewBigram)) {
+        if (addedNewBigram) {
+            mBigramCount++;
+        }
+        return true;
+    } else {
+        return false;
+    }
 }
 
 bool Ver4PatriciaTriePolicy::removeBigramWords(const int *const word0, const int length0,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h
index fdb7ac6..93cc4b7 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h
@@ -42,7 +42,7 @@
               mDictBuffer(mBuffers.get()->getRawDictBuffer() + mHeaderPolicy.getSize(),
                       mBuffers.get()->getRawDictBufferSize() - mHeaderPolicy.getSize(),
                       BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
-              mBigramPolicy(mBuffers.get()->getBigramDictContent(),
+              mBigramPolicy(mBuffers.get()->getUpdatableBigramDictContent(),
                       mBuffers.get()->getTerminalPositionLookupTable()),
               mShortcutPolicy(mBuffers.get()->getShortcutDictContent(),
                       mBuffers.get()->getTerminalPositionLookupTable()),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp
index f17a0d1..26eafcd 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp
@@ -49,6 +49,11 @@
     }
 }
 
+bool BufferWithExtendableBuffer::writeUint(const uint32_t data, const int size, const int pos) {
+    int writingPos = pos;
+    return writeUintAndAdvancePosition(data, size, &writingPos);
+}
+
 bool BufferWithExtendableBuffer::writeUintAndAdvancePosition(const uint32_t data, const int size,
         int *const pos) {
     if (!(size >= 1 && size <= 4)) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
index 13dce9b..ee6107a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
@@ -93,6 +93,8 @@
      * Writing is allowed for original buffer, already written region of additional buffer and the
      * tail of additional buffer.
      */
+    bool writeUint(const uint32_t data, const int size, const int pos);
+
     bool writeUintAndAdvancePosition(const uint32_t data, const int size, int *const pos);
 
     bool writeCodePointsAndAdvancePosition(const int *const codePoints, const int codePointCount,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.cpp
index 2678b8c..9be3562 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.cpp
@@ -19,23 +19,68 @@
 namespace latinime {
 
 const int SparseTable::NOT_EXIST = -1;
+const int SparseTable::INDEX_SIZE = 4;
 
 bool SparseTable::contains(const int id) const {
-    const int readingPos = id / mBlockSize * mDataSize;
+    const int readingPos = getPosInIndexTable(id);
     if (id < 0 || mIndexTableBuffer->getTailPosition() <= readingPos) {
         return false;
     }
-    const int index = mIndexTableBuffer->readUint(mDataSize, readingPos);
+    const int index = mIndexTableBuffer->readUint(INDEX_SIZE, readingPos);
     return index != NOT_EXIST;
 }
 
 uint32_t SparseTable::get(const int id) const {
-    const int indexTableIndex = id / mBlockSize;
-    int readingPos = indexTableIndex * mDataSize;
-    const int index = mIndexTableBuffer->readUint(mDataSize, readingPos);
+    const int indexTableReadingPos = getPosInIndexTable(id);
+    const int index = mIndexTableBuffer->readUint(INDEX_SIZE, indexTableReadingPos);
+    const int contentTableReadingPos = getPosInContentTable(id, index);
+    return mContentTableBuffer->readUint(mDataSize, contentTableReadingPos);
+}
+
+bool SparseTable::set(const int id, const uint32_t value) {
+    const int posInIndexTable = getPosInIndexTable(id);
+    // Extends the index table if needed.
+    if (mIndexTableBuffer->getTailPosition() < posInIndexTable) {
+        int tailPos = mIndexTableBuffer->getTailPosition();
+        while(tailPos < posInIndexTable) {
+            if (!mIndexTableBuffer->writeUintAndAdvancePosition(NOT_EXIST, INDEX_SIZE, &tailPos)) {
+                return false;
+            }
+        }
+    }
+    if (contains(id)) {
+        // The entry is already in the content table.
+        const int index = mIndexTableBuffer->readUint(INDEX_SIZE, posInIndexTable);
+        return mContentTableBuffer->writeUint(value, mDataSize, getPosInContentTable(id, index));
+    }
+    // The entry is not in the content table.
+    // Create new entry in the content table.
+    const int index = getIndexFromContentTablePos(mContentTableBuffer->getTailPosition());
+    if (!mIndexTableBuffer->writeUint(index, INDEX_SIZE, posInIndexTable)) {
+        return false;
+    }
+    // Write a new block that containing the entry to be set.
+    int writingPos = getPosInContentTable(0 /* id */, index);
+    for (int i = 0; i < mBlockSize; ++i) {
+        if (!mContentTableBuffer->writeUintAndAdvancePosition(NOT_A_DICT_POS, mDataSize,
+                &writingPos)) {
+            return false;
+        }
+    }
+    return mContentTableBuffer->writeUint(value, mDataSize, getPosInContentTable(id, index));
+}
+
+int SparseTable::getIndexFromContentTablePos(const int contentTablePos) const {
+    return contentTablePos / mDataSize / mBlockSize;
+}
+
+int SparseTable::getPosInIndexTable(const int id) const {
+    return (id / mBlockSize) * INDEX_SIZE;
+}
+
+int SparseTable::getPosInContentTable(const int id, const int index) const {
     const int offset = id % mBlockSize;
-    readingPos = (index * mDataSize + offset) * mBlockSize;
-    return mContentTableBuffer->readUint(mDataSize, readingPos);
+    return (index * mDataSize + offset) * mBlockSize;
 }
 
 } // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.h b/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.h
index d71756c..21c1675 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/sparse_table.h
@@ -38,10 +38,19 @@
 
     uint32_t get(const int id) const;
 
+    bool set(const int id, const uint32_t value);
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(SparseTable);
 
+    int getIndexFromContentTablePos(const int contentTablePos) const;
+
+    int getPosInIndexTable(const int id) const;
+
+    int getPosInContentTable(const int id, const int index) const;
+
     static const int NOT_EXIST;
+    static const int INDEX_SIZE;
 
     BufferWithExtendableBuffer *const mIndexTableBuffer;
     BufferWithExtendableBuffer *const mContentTableBuffer;
diff --git a/tests/src/com/android/inputmethod/latin/Ver4BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/Ver4BinaryDictionaryTests.java
index 85e6243..b7cef73 100644
--- a/tests/src/com/android/inputmethod/latin/Ver4BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/Ver4BinaryDictionaryTests.java
@@ -206,4 +206,44 @@
         assertEquals(probability, binaryDictionary.getFrequency("y"));
     }
 
+    public void testWriteBigrams() {
+        final String dictVersion = Long.toString(System.currentTimeMillis());
+        final FusionDictionary dict = new FusionDictionary(new PtNodeArray(),
+                getDictionaryOptions(TEST_LOCALE, dictVersion));
+        final DictEncoder encoder = new Ver4DictEncoder(getContext().getCacheDir());
+        try {
+            encoder.writeDictionary(dict, FORMAT_OPTIONS);
+        } catch (IOException e) {
+            Log.e(TAG, "IOException while writing dictionary", e);
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "Unsupported format", e);
+        }
+        final File trieFile = getTrieFile(TEST_LOCALE, dictVersion);
+        final BinaryDictionary binaryDictionary = new BinaryDictionary(trieFile.getAbsolutePath(),
+                0 /* offset */, trieFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+        assertTrue(binaryDictionary.isValidDictionary());
+
+        final int unigramProbability = 100;
+        final int bigramProbability = 10;
+        final int updatedBigramProbability = 15;
+        binaryDictionary.addUnigramWord("aaa", unigramProbability);
+        binaryDictionary.addUnigramWord("abb", unigramProbability);
+        binaryDictionary.addUnigramWord("bcc", unigramProbability);
+        binaryDictionary.addBigramWords("aaa", "abb", bigramProbability);
+        binaryDictionary.addBigramWords("aaa", "bcc", bigramProbability);
+        binaryDictionary.addBigramWords("abb", "aaa", bigramProbability);
+        binaryDictionary.addBigramWords("abb", "bcc", bigramProbability);
+
+        final int probability = binaryDictionary.calculateProbability(unigramProbability,
+                bigramProbability);
+        assertEquals(true, binaryDictionary.isValidBigram("aaa", "abb"));
+        assertEquals(true, binaryDictionary.isValidBigram("aaa", "bcc"));
+        assertEquals(true, binaryDictionary.isValidBigram("abb", "aaa"));
+        assertEquals(true, binaryDictionary.isValidBigram("abb", "bcc"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("aaa", "abb"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("aaa", "bcc"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("abb", "aaa"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("abb", "bcc"));
+    }
 }