diff --git a/native/jni/NativeFileList.mk b/native/jni/NativeFileList.mk
index b896f38..7299ed3 100644
--- a/native/jni/NativeFileList.mk
+++ b/native/jni/NativeFileList.mk
@@ -40,6 +40,7 @@
         proximity_info_state_utils.cpp) \
     suggest/core/policy/weighting.cpp \
     suggest/core/session/dic_traverse_session.cpp \
+    suggest/core/session/ngram_context.cpp \
     $(addprefix suggest/core/result/, \
         suggestion_results.cpp \
         suggestions_output_utils.cpp) \
@@ -55,7 +56,7 @@
         dynamic_pt_updating_helper.cpp \
         dynamic_pt_writing_utils.cpp \
         patricia_trie_reading_utils.cpp \
-        shortcut/shortcut_list_reading_utils.cpp ) \
+        shortcut/shortcut_list_reading_utils.cpp) \
     $(addprefix suggest/policyimpl/dictionary/structure/v2/, \
         patricia_trie_policy.cpp \
         ver2_patricia_trie_node_reader.cpp \
diff --git a/native/jni/src/suggest/core/session/ngram_context.cpp b/native/jni/src/suggest/core/session/ngram_context.cpp
new file mode 100644
index 0000000..17ef9ae
--- /dev/null
+++ b/native/jni/src/suggest/core/session/ngram_context.cpp
@@ -0,0 +1,123 @@
+/*
+ * 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.
+ */
+
+#include "suggest/core/session/ngram_context.h"
+
+#include "suggest/core/policy/dictionary_structure_with_buffer_policy.h"
+#include "utils/char_utils.h"
+
+namespace latinime {
+
+NgramContext::NgramContext() : mPrevWordCount(0) {}
+
+NgramContext::NgramContext(const NgramContext &ngramContext)
+        : mPrevWordCount(ngramContext.mPrevWordCount) {
+    for (size_t i = 0; i < mPrevWordCount; ++i) {
+        mPrevWordCodePointCount[i] = ngramContext.mPrevWordCodePointCount[i];
+        memmove(mPrevWordCodePoints[i], ngramContext.mPrevWordCodePoints[i],
+                sizeof(mPrevWordCodePoints[i][0]) * mPrevWordCodePointCount[i]);
+        mIsBeginningOfSentence[i] = ngramContext.mIsBeginningOfSentence[i];
+    }
+}
+
+NgramContext::NgramContext(const int prevWordCodePoints[][MAX_WORD_LENGTH],
+        const int *const prevWordCodePointCount, const bool *const isBeginningOfSentence,
+        const size_t prevWordCount)
+        : mPrevWordCount(std::min(NELEMS(mPrevWordCodePoints), prevWordCount)) {
+    clear();
+    for (size_t i = 0; i < mPrevWordCount; ++i) {
+        if (prevWordCodePointCount[i] < 0 || prevWordCodePointCount[i] > MAX_WORD_LENGTH) {
+            continue;
+        }
+        memmove(mPrevWordCodePoints[i], prevWordCodePoints[i],
+                sizeof(mPrevWordCodePoints[i][0]) * prevWordCodePointCount[i]);
+        mPrevWordCodePointCount[i] = prevWordCodePointCount[i];
+        mIsBeginningOfSentence[i] = isBeginningOfSentence[i];
+    }
+}
+
+NgramContext::NgramContext(const int *const prevWordCodePoints, const int prevWordCodePointCount,
+        const bool isBeginningOfSentence) : mPrevWordCount(1) {
+    clear();
+    if (prevWordCodePointCount > MAX_WORD_LENGTH || !prevWordCodePoints) {
+        return;
+    }
+    memmove(mPrevWordCodePoints[0], prevWordCodePoints,
+            sizeof(mPrevWordCodePoints[0][0]) * prevWordCodePointCount);
+    mPrevWordCodePointCount[0] = prevWordCodePointCount;
+    mIsBeginningOfSentence[0] = isBeginningOfSentence;
+}
+
+bool NgramContext::isValid() const {
+    if (mPrevWordCodePointCount[0] > 0) {
+        return true;
+    }
+    if (mIsBeginningOfSentence[0]) {
+        return true;
+    }
+    return false;
+}
+
+const CodePointArrayView NgramContext::getNthPrevWordCodePoints(const size_t n) const {
+    if (n <= 0 || n > mPrevWordCount) {
+        return CodePointArrayView();
+    }
+    return CodePointArrayView(mPrevWordCodePoints[n - 1], mPrevWordCodePointCount[n - 1]);
+}
+
+bool NgramContext::isNthPrevWordBeginningOfSentence(const size_t n) const {
+    if (n <= 0 || n > mPrevWordCount) {
+        return false;
+    }
+    return mIsBeginningOfSentence[n - 1];
+}
+
+/* static */ int NgramContext::getWordId(
+        const DictionaryStructureWithBufferPolicy *const dictStructurePolicy,
+        const int *const wordCodePoints, const int wordCodePointCount,
+        const bool isBeginningOfSentence, const bool tryLowerCaseSearch) {
+    if (!dictStructurePolicy || !wordCodePoints || wordCodePointCount > MAX_WORD_LENGTH) {
+        return NOT_A_WORD_ID;
+    }
+    int codePoints[MAX_WORD_LENGTH];
+    int codePointCount = wordCodePointCount;
+    memmove(codePoints, wordCodePoints, sizeof(int) * codePointCount);
+    if (isBeginningOfSentence) {
+        codePointCount = CharUtils::attachBeginningOfSentenceMarker(codePoints, codePointCount,
+                MAX_WORD_LENGTH);
+        if (codePointCount <= 0) {
+            return NOT_A_WORD_ID;
+        }
+    }
+    const CodePointArrayView codePointArrayView(codePoints, codePointCount);
+    const int wordId = dictStructurePolicy->getWordId(codePointArrayView,
+            false /* forceLowerCaseSearch */);
+    if (wordId != NOT_A_WORD_ID || !tryLowerCaseSearch) {
+        // Return the id when when the word was found or doesn't try lower case search.
+        return wordId;
+    }
+    // Check bigrams for lower-cased previous word if original was not found. Useful for
+    // auto-capitalized words like "The [current_word]".
+    return dictStructurePolicy->getWordId(codePointArrayView, true /* forceLowerCaseSearch */);
+}
+
+void NgramContext::clear() {
+    for (size_t i = 0; i < NELEMS(mPrevWordCodePoints); ++i) {
+        mPrevWordCodePointCount[i] = 0;
+        mIsBeginningOfSentence[i] = false;
+    }
+}
+} // namespace latinime
diff --git a/native/jni/src/suggest/core/session/ngram_context.h b/native/jni/src/suggest/core/session/ngram_context.h
index 64c7141..9b36199 100644
--- a/native/jni/src/suggest/core/session/ngram_context.h
+++ b/native/jni/src/suggest/core/session/ngram_context.h
@@ -20,145 +20,54 @@
 #include <array>
 
 #include "defines.h"
-#include "suggest/core/policy/dictionary_structure_with_buffer_policy.h"
-#include "utils/char_utils.h"
 #include "utils/int_array_view.h"
 
 namespace latinime {
 
-// Rename to NgramContext.
+class DictionaryStructureWithBufferPolicy;
+
 class NgramContext {
  public:
     // No prev word information.
-    NgramContext() : mPrevWordCount(0) {
-        clear();
-    }
-
-    NgramContext(const NgramContext &ngramContext)
-            : mPrevWordCount(ngramContext.mPrevWordCount) {
-        for (size_t i = 0; i < mPrevWordCount; ++i) {
-            mPrevWordCodePointCount[i] = ngramContext.mPrevWordCodePointCount[i];
-            memmove(mPrevWordCodePoints[i], ngramContext.mPrevWordCodePoints[i],
-                    sizeof(mPrevWordCodePoints[i][0]) * mPrevWordCodePointCount[i]);
-            mIsBeginningOfSentence[i] = ngramContext.mIsBeginningOfSentence[i];
-        }
-    }
-
+    NgramContext();
+    // Copy constructor to use this class with std::vector and use this class as a return value.
+    NgramContext(const NgramContext &ngramContext);
     // Construct from previous words.
     NgramContext(const int prevWordCodePoints[][MAX_WORD_LENGTH],
             const int *const prevWordCodePointCount, const bool *const isBeginningOfSentence,
-            const size_t prevWordCount)
-            : mPrevWordCount(std::min(NELEMS(mPrevWordCodePoints), prevWordCount)) {
-        clear();
-        for (size_t i = 0; i < mPrevWordCount; ++i) {
-            if (prevWordCodePointCount[i] < 0 || prevWordCodePointCount[i] > MAX_WORD_LENGTH) {
-                continue;
-            }
-            memmove(mPrevWordCodePoints[i], prevWordCodePoints[i],
-                    sizeof(mPrevWordCodePoints[i][0]) * prevWordCodePointCount[i]);
-            mPrevWordCodePointCount[i] = prevWordCodePointCount[i];
-            mIsBeginningOfSentence[i] = isBeginningOfSentence[i];
-        }
-    }
-
+            const size_t prevWordCount);
     // Construct from a previous word.
     NgramContext(const int *const prevWordCodePoints, const int prevWordCodePointCount,
-            const bool isBeginningOfSentence) : mPrevWordCount(1) {
-        clear();
-        if (prevWordCodePointCount > MAX_WORD_LENGTH || !prevWordCodePoints) {
-            return;
-        }
-        memmove(mPrevWordCodePoints[0], prevWordCodePoints,
-                sizeof(mPrevWordCodePoints[0][0]) * prevWordCodePointCount);
-        mPrevWordCodePointCount[0] = prevWordCodePointCount;
-        mIsBeginningOfSentence[0] = isBeginningOfSentence;
-    }
+            const bool isBeginningOfSentence);
 
     size_t getPrevWordCount() const {
         return mPrevWordCount;
     }
-
-    // TODO: Remove.
-    const NgramContext getTrimmedNgramContext(const size_t maxPrevWordCount) const {
-        return NgramContext(mPrevWordCodePoints, mPrevWordCodePointCount, mIsBeginningOfSentence,
-                std::min(mPrevWordCount, maxPrevWordCount));
-    }
-
-    bool isValid() const {
-        if (mPrevWordCodePointCount[0] > 0) {
-            return true;
-        }
-        if (mIsBeginningOfSentence[0]) {
-            return true;
-        }
-        return false;
-    }
+    bool isValid() const;
 
     template<size_t N>
     const WordIdArrayView getPrevWordIds(
             const DictionaryStructureWithBufferPolicy *const dictStructurePolicy,
-            std::array<int, N> *const prevWordIdBuffer, const bool tryLowerCaseSearch) const {
+            WordIdArray<N> *const prevWordIdBuffer, const bool tryLowerCaseSearch) const {
         for (size_t i = 0; i < std::min(mPrevWordCount, N); ++i) {
-            prevWordIdBuffer->at(i) = getWordId(dictStructurePolicy,
-                    mPrevWordCodePoints[i], mPrevWordCodePointCount[i],
-                    mIsBeginningOfSentence[i], tryLowerCaseSearch);
+            prevWordIdBuffer->at(i) = getWordId(dictStructurePolicy, mPrevWordCodePoints[i],
+                    mPrevWordCodePointCount[i], mIsBeginningOfSentence[i], tryLowerCaseSearch);
         }
         return WordIdArrayView::fromArray(*prevWordIdBuffer).limit(mPrevWordCount);
     }
 
     // n is 1-indexed.
-    const CodePointArrayView getNthPrevWordCodePoints(const size_t n) const {
-        if (n <= 0 || n > mPrevWordCount) {
-            return CodePointArrayView();
-        }
-        return CodePointArrayView(mPrevWordCodePoints[n - 1], mPrevWordCodePointCount[n - 1]);
-    }
-
+    const CodePointArrayView getNthPrevWordCodePoints(const size_t n) const;
     // n is 1-indexed.
-    bool isNthPrevWordBeginningOfSentence(const size_t n) const {
-        if (n <= 0 || n > mPrevWordCount) {
-            return false;
-        }
-        return mIsBeginningOfSentence[n - 1];
-    }
+    bool isNthPrevWordBeginningOfSentence(const size_t n) const;
 
  private:
     DISALLOW_ASSIGNMENT_OPERATOR(NgramContext);
 
     static int getWordId(const DictionaryStructureWithBufferPolicy *const dictStructurePolicy,
             const int *const wordCodePoints, const int wordCodePointCount,
-            const bool isBeginningOfSentence, const bool tryLowerCaseSearch) {
-        if (!dictStructurePolicy || !wordCodePoints || wordCodePointCount > MAX_WORD_LENGTH) {
-            return NOT_A_WORD_ID;
-        }
-        int codePoints[MAX_WORD_LENGTH];
-        int codePointCount = wordCodePointCount;
-        memmove(codePoints, wordCodePoints, sizeof(int) * codePointCount);
-        if (isBeginningOfSentence) {
-            codePointCount = CharUtils::attachBeginningOfSentenceMarker(codePoints,
-                    codePointCount, MAX_WORD_LENGTH);
-            if (codePointCount <= 0) {
-                return NOT_A_WORD_ID;
-            }
-        }
-        const CodePointArrayView codePointArrayView(codePoints, codePointCount);
-        const int wordId = dictStructurePolicy->getWordId(
-                codePointArrayView, false /* forceLowerCaseSearch */);
-        if (wordId != NOT_A_WORD_ID || !tryLowerCaseSearch) {
-            // Return the id when when the word was found or doesn't try lower case search.
-            return wordId;
-        }
-        // Check bigrams for lower-cased previous word if original was not found. Useful for
-        // auto-capitalized words like "The [current_word]".
-        return dictStructurePolicy->getWordId(codePointArrayView, true /* forceLowerCaseSearch */);
-    }
-
-    void clear() {
-        for (size_t i = 0; i < NELEMS(mPrevWordCodePoints); ++i) {
-            mPrevWordCodePointCount[i] = 0;
-            mIsBeginningOfSentence[i] = false;
-        }
-    }
+            const bool isBeginningOfSentence, const bool tryLowerCaseSearch);
+    void clear();
 
     const size_t mPrevWordCount;
     int mPrevWordCodePoints[MAX_PREV_WORD_COUNT_FOR_N_GRAM][MAX_WORD_LENGTH];