Merge "Extend bigram probability field to support historical info."

9 files changed, 291 insertions, 121 deletions

diff --git a/native/jni/src/defines.h b/native/jni/src/defines.h
index fbcd612b7..564811560 100644
--- a/native/jni/src/defines.h
+++ b/native/jni/src/defines.h
@@ -341,12 +341,21 @@ template<typename T> AK_FORCE_INLINE const T &max(const T &a, const T &b) { retu
 #define INPUTLENGTH_FOR_DEBUG (-1)
 #define MIN_OUTPUT_INDEX_FOR_DEBUG (-1)
 
-#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
-  TypeName(const TypeName&);               \
+#define DISALLOW_DEFAULT_CONSTRUCTOR(TypeName) \
+  TypeName()
+
+#define DISALLOW_COPY_CONSTRUCTOR(TypeName) \
+  TypeName(const TypeName&)
+
+#define DISALLOW_ASSIGNMENT_OPERATOR(TypeName) \
   void operator=(const TypeName&)
 
+#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
+  DISALLOW_COPY_CONSTRUCTOR(TypeName);     \
+  DISALLOW_ASSIGNMENT_OPERATOR(TypeName)
+
 #define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
-  TypeName();                                    \
+  DISALLOW_DEFAULT_CONSTRUCTOR(TypeName);        \
   DISALLOW_COPY_AND_ASSIGN(TypeName)
 
 // Used as a return value for character comparison
diff --git a/native/jni/src/suggest/core/dictionary/bloom_filter.h b/native/jni/src/suggest/core/dictionary/bloom_filter.h
index 5205456a8..5f9700486 100644
--- a/native/jni/src/suggest/core/dictionary/bloom_filter.h
+++ b/native/jni/src/suggest/core/dictionary/bloom_filter.h
@@ -50,6 +50,8 @@ class BloomFilter {
     }
 
  private:
+    DISALLOW_ASSIGNMENT_OPERATOR(BloomFilter);
+
     // Size, in bytes, of the bloom filter index for bigrams
     // 128 gives us 1024 buckets. The probability of false positive is (1 - e ** (-kn/m))**k,
     // where k is the number of hash functions, n the number of bigrams, and m the number of
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
index 7160f6f48..48ddb2ff4 100644
--- 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
@@ -26,12 +26,18 @@ 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);
+    const BigramEntry bigramEntry =
+            mBigramDictContent->getBigramEntryAndAdvancePosition(bigramEntryPos);
     if (outBigramPos) {
         // Lookup target PtNode position.
-        *outBigramPos = mTerminalPositionLookupTable->getTerminalPtNodePosition(targetTerminalId);
+        *outBigramPos = mTerminalPositionLookupTable->getTerminalPtNodePosition(
+                bigramEntry.getTargetTerminalId());
+    }
+    if (outProbability) {
+        *outProbability = bigramEntry.getProbability();
+    }
+    if (outHasNext) {
+        *outHasNext = bigramEntry.hasNext();
     }
 }
 
@@ -47,12 +53,13 @@ bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTarget
         if (!mBigramDictContent->createNewBigramList(terminalId)) {
             return false;
         }
-        const int probabilityToWrite = getUpdatedProbability(
-                NOT_A_PROBABILITY /* originalProbability */, newProbability);
+        const BigramEntry newBigramEntry(false /* hasNext */, NOT_A_PROBABILITY,
+                newTargetTerminalId);
+        const BigramEntry bigramEntryToWrite = getUpdatedBigramEntry(&newBigramEntry,
+                newProbability, timestamp);
         // Write an entry.
         const int writingPos =  mBigramDictContent->getBigramListHeadPos(terminalId);
-        if (!mBigramDictContent->writeBigramEntry(probabilityToWrite, false /* hasNext */,
-                newTargetTerminalId, writingPos)) {
+        if (!mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, writingPos)) {
             return false;
         }
         if (outAddedNewEntry) {
@@ -64,18 +71,19 @@ bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTarget
     const int entryPosToUpdate = getEntryPosToUpdate(newTargetTerminalId, bigramListPos);
     if (entryPosToUpdate != NOT_A_DICT_POS) {
         // Overwrite existing entry.
-        bool hasNext = false;
-        int probability = NOT_A_PROBABILITY;
-        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-        mBigramDictContent->getBigramEntry(&probability, &hasNext, &targetTerminalId,
-                entryPosToUpdate);
-        const int probabilityToWrite = getUpdatedProbability(probability, newProbability);
-        if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID && outAddedNewEntry) {
+        const BigramEntry originalBigramEntry =
+                mBigramDictContent->getBigramEntry(entryPosToUpdate);
+        if (!originalBigramEntry.isValid()) {
             // Reuse invalid entry.
-            *outAddedNewEntry = true;
+            if (outAddedNewEntry) {
+                *outAddedNewEntry = true;
+            }
         }
-        return mBigramDictContent->writeBigramEntry(probabilityToWrite, hasNext,
-                newTargetTerminalId, entryPosToUpdate);
+        const BigramEntry updatedBigramEntry =
+                originalBigramEntry.updateTargetTerminalIdAndGetEntry(newTargetTerminalId);
+        const BigramEntry bigramEntryToWrite = getUpdatedBigramEntry(
+                &updatedBigramEntry, newProbability, timestamp);
+        return mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, entryPosToUpdate);
     }
 
     // Add new entry to the bigram list.
@@ -85,10 +93,10 @@ bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTarget
     }
     // Write new entry at a head position of the bigram list.
     int writingPos = mBigramDictContent->getBigramListHeadPos(terminalId);
-    const int probabilityToWrite = getUpdatedProbability(
-            NOT_A_PROBABILITY /* originalProbability */, newProbability);
-    if (!mBigramDictContent->writeBigramEntryAndAdvancePosition(probabilityToWrite,
-            true /* hasNext */, newTargetTerminalId, &writingPos)) {
+    const BigramEntry newBigramEntry(true /* hasNext */, NOT_A_PROBABILITY, newTargetTerminalId);
+    const BigramEntry bigramEntryToWrite = getUpdatedBigramEntry(
+            &newBigramEntry, newProbability, timestamp);
+    if (!mBigramDictContent->writeBigramEntryAndAdvancePosition(&bigramEntryToWrite, &writingPos)) {
         return false;
     }
     if (outAddedNewEntry) {
@@ -109,18 +117,14 @@ bool Ver4BigramListPolicy::removeEntry(const int terminalId, const int targetTer
         // Bigram entry doesn't exist.
         return false;
     }
-    bool hasNext = false;
-    int probability = NOT_A_PROBABILITY;
-    int originalTargetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-    mBigramDictContent->getBigramEntry(&probability, &hasNext, &originalTargetTerminalId,
-            entryPosToUpdate);
-    if (targetTerminalId != originalTargetTerminalId) {
+    const BigramEntry bigramEntry = mBigramDictContent->getBigramEntry(entryPosToUpdate);
+    if (targetTerminalId != bigramEntry.getTargetTerminalId()) {
         // Bigram entry doesn't exist.
         return false;
     }
-    // Remove bigram entry by overwriting target terminal Id.
-    return mBigramDictContent->writeBigramEntry(probability, hasNext,
-            Ver4DictConstants::NOT_A_TERMINAL_ID /* targetTerminalId */, entryPosToUpdate);
+    // 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,
@@ -134,34 +138,35 @@ bool Ver4BigramListPolicy::updateAllBigramEntriesAndDeleteUselessEntries(const i
     int readingPos = bigramListPos;
     while (hasNext) {
         const int entryPos = readingPos;
-        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) {
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (!bigramEntry.isValid()) {
             continue;
         }
         const int targetPtNodePos = mTerminalPositionLookupTable->getTerminalPtNodePosition(
-                targetTerminalId);
+                bigramEntry.getTargetTerminalId());
         if (targetPtNodePos == NOT_A_DICT_POS) {
             // Invalidate bigram entry.
-            if (!mBigramDictContent->writeBigramEntry(probability, hasNext,
-                    Ver4DictConstants::NOT_A_TERMINAL_ID /* targetTerminalId */, entryPos)) {
+            const BigramEntry updatedBigramEntry = bigramEntry.getInvalidatedEntry();
+            if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
                 return false;
             }
         } else if (mNeedsToDecayWhenUpdating) {
-            probability = ForgettingCurveUtils::getEncodedProbabilityToSave(
-                    probability, mHeaderPolicy);
+            // TODO: Quit decaying probability during GC.
+            const int probability = ForgettingCurveUtils::getEncodedProbabilityToSave(
+                    bigramEntry.getProbability(), mHeaderPolicy);
             if (ForgettingCurveUtils::isValidEncodedProbability(probability)) {
-                if (!mBigramDictContent->writeBigramEntry(probability, hasNext, targetTerminalId,
-                        entryPos)) {
+                const BigramEntry updatedBigramEntry =
+                        bigramEntry.updateProbabilityAndGetEntry(probability);
+                if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
                     return false;
                 }
                 *outBigramCount += 1;
             } else {
                 // Remove entry.
-                if (!mBigramDictContent->writeBigramEntry(probability, hasNext,
-                        Ver4DictConstants::NOT_A_TERMINAL_ID /* targetTerminalId */, entryPos)) {
+                const BigramEntry updatedBigramEntry = bigramEntry.getInvalidatedEntry();
+                if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
                     return false;
                 }
             }
@@ -182,10 +187,10 @@ int Ver4BigramListPolicy::getBigramEntryConut(const int terminalId) {
     bool hasNext = true;
     int readingPos = bigramListPos;
     while (hasNext) {
-        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-        mBigramDictContent->getBigramEntryAndAdvancePosition(0 /* probability */, &hasNext,
-                &targetTerminalId, &readingPos);
-        if (targetTerminalId != Ver4DictConstants::NOT_A_TERMINAL_ID) {
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (bigramEntry.isValid()) {
             bigramCount++;
         }
     }
@@ -199,13 +204,13 @@ int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
     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) {
+        const BigramEntry bigramEntry =
+                mBigramDictContent->getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (bigramEntry.getTargetTerminalId() == targetTerminalIdToFind) {
             // Entry with same target is found.
             return entryPos;
-        } else if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID) {
+        } else if (!bigramEntry.isValid()) {
             // Invalid entry that can be reused is found.
             invalidEntryPos = entryPos;
         }
@@ -213,13 +218,16 @@ int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
     return invalidEntryPos;
 }
 
-int Ver4BigramListPolicy::getUpdatedProbability(const int originalProbability,
-        const int newProbability) const {
+const BigramEntry Ver4BigramListPolicy::getUpdatedBigramEntry(
+        const BigramEntry *const originalBigramEntry, const int newProbability,
+        const int timestamp) const {
     if (mNeedsToDecayWhenUpdating) {
-        return ForgettingCurveUtils::getUpdatedEncodedProbability(originalProbability,
-                newProbability);
+        // TODO: Update historical information.
+        const int probability = ForgettingCurveUtils::getUpdatedEncodedProbability(
+                originalBigramEntry->getProbability(), newProbability);
+        return originalBigramEntry->updateProbabilityAndGetEntry(probability);
     } else {
-        return newProbability;
+        return originalBigramEntry->updateProbabilityAndGetEntry(newProbability);
     }
 }
 
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 c0959118e..e718645b4 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
@@ -19,6 +19,7 @@
 
 #include "defines.h"
 #include "suggest/core/policy/dictionary_bigrams_structure_policy.h"
+#include "suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h"
 
 namespace latinime {
 
@@ -58,7 +59,8 @@ class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
 
     int getEntryPosToUpdate(const int targetTerminalIdToFind, const int bigramListPos) const;
 
-    int getUpdatedProbability(const int originalProbability, const int newProbability) const;
+    const BigramEntry getUpdatedBigramEntry(const BigramEntry *const originalBigramEntry,
+            const int newProbability, const int timestamp) const;
 
     BigramDictContent *const mBigramDictContent;
     const TerminalPositionLookupTable *const mTerminalPositionLookupTable;
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
index 431f342ae..2a783543a 100644
--- 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
@@ -20,53 +20,98 @@
 
 namespace latinime {
 
-void BigramDictContent::getBigramEntryAndAdvancePosition(int *const outProbability,
-        bool *const outHasNext, int *const outTargetTerminalId, int *const bigramEntryPos) const {
+const BigramEntry BigramDictContent::getBigramEntryAndAdvancePosition(
+        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;
+    const int hasNext = (bigramFlags & Ver4DictConstants::BIGRAM_HAS_NEXT_MASK) != 0;
+    int probability = NOT_A_PROBABILITY;
+    int timestamp = Ver4DictConstants::NOT_A_TIME_STAMP;
+    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;
     }
-    if (outHasNext) {
-        *outHasNext = (bigramFlags & Ver4DictConstants::BIGRAM_HAS_NEXT_MASK) != 0;
-    }
-    const int targetTerminalId = bigramListBuffer->readUintAndAdvancePosition(
+    const int encodedTargetTerminalId = bigramListBuffer->readUintAndAdvancePosition(
             Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, bigramEntryPos);
-    if (outTargetTerminalId) {
-        *outTargetTerminalId =
-                (targetTerminalId == Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID) ?
-                        Ver4DictConstants::NOT_A_TERMINAL_ID : targetTerminalId;
+    const int targetTerminalId =
+            (encodedTargetTerminalId == Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID) ?
+                    Ver4DictConstants::NOT_A_TERMINAL_ID : encodedTargetTerminalId;
+    if (mHasHistoricalInfo) {
+        return BigramEntry(hasNext, probability, timestamp, level, count, targetTerminalId);
+    } else {
+        return BigramEntry(hasNext, probability, targetTerminalId);
     }
 }
 
-bool BigramDictContent::writeBigramEntryAndAdvancePosition(const int probability, const int hasNext,
-        const int targetTerminalId, int *const entryWritingPos) {
+bool BigramDictContent::writeBigramEntryAndAdvancePosition(
+        const BigramEntry *const bigramEntryToWrite, int *const entryWritingPos) {
     BufferWithExtendableBuffer *const bigramListBuffer = getWritableContentBuffer();
-    const int bigramFlags = createAndGetBigramFlags(probability, hasNext);
+    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;
+        }
+        if (!bigramListBuffer->writeUintAndAdvancePosition(bigramEntryToWrite->getTimeStamp(),
+                Ver4DictConstants::TIME_STAMP_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram timestamps. pos: %d, timestamp: %d", *entryWritingPos,
+                    bigramEntryToWrite->getTimeStamp());
+            return false;
+        }
+        if (!bigramListBuffer->writeUintAndAdvancePosition(bigramEntryToWrite->getLevel(),
+                Ver4DictConstants::WORD_LEVEL_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram level. pos: %d, level: %d", *entryWritingPos,
+                    bigramEntryToWrite->getLevel());
+            return false;
+        }
+        if (!bigramListBuffer->writeUintAndAdvancePosition(bigramEntryToWrite->getCount(),
+                Ver4DictConstants::WORD_COUNT_FIELD_SIZE, entryWritingPos)) {
+            AKLOGE("Cannot write bigram count. pos: %d, count: %d", *entryWritingPos,
+                    bigramEntryToWrite->getCount());
+            return false;
+        }
+    }
     const int targetTerminalIdToWrite =
-            (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID) ?
-                    Ver4DictConstants::INVALID_BIGRAM_TARGET_TERMINAL_ID : targetTerminalId;
-    return bigramListBuffer->writeUintAndAdvancePosition(targetTerminalIdToWrite,
-            Ver4DictConstants::BIGRAM_TARGET_TERMINAL_ID_FIELD_SIZE, entryWritingPos);
+            (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) {
-    bool hasNext = true;
     int readingPos = bigramListPos;
     int writingPos = toPos;
+    bool hasNext = true;
     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)) {
+        const BigramEntry bigramEntry = getBigramEntryAndAdvancePosition(&readingPos);
+        hasNext = bigramEntry.hasNext();
+        if (!writeBigramEntryAndAdvancePosition(&bigramEntry, &writingPos)) {
             AKLOGE("Cannot write bigram entry to copy. pos: %d", writingPos);
             return false;
         }
@@ -119,22 +164,22 @@ bool BigramDictContent::runGCBigramList(const int bigramListPos,
     int writingPos = toPos;
     int lastEntryPos = NOT_A_DICT_POS;
     while (hasNext) {
-        int probability = NOT_A_PROBABILITY;
-        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-        sourceBigramDictContent->getBigramEntryAndAdvancePosition(&probability, &hasNext,
-                &targetTerminalId, &readingPos);
-        if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID) {
+        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(targetTerminalId);
+                terminalIdMap->find(originalBigramEntry.getTargetTerminalId());
         if (it == terminalIdMap->end()) {
             // Target word has been removed.
             continue;
         }
         lastEntryPos = hasNext ? writingPos : NOT_A_DICT_POS;
-        if (!writeBigramEntryAndAdvancePosition(probability, hasNext, it->second,
-                &writingPos)) {
+        const BigramEntry updatedBigramEntry =
+                originalBigramEntry.updateTargetTerminalIdAndGetEntry(it->second);
+        if (!writeBigramEntryAndAdvancePosition(&updatedBigramEntry, &writingPos)) {
             AKLOGE("Cannot write bigram entry to run GC. pos: %d", writingPos);
             return false;
         }
@@ -142,10 +187,9 @@ bool BigramDictContent::runGCBigramList(const int bigramListPos,
     }
     if (lastEntryPos != NOT_A_DICT_POS) {
         // Update has next flag in the last written entry.
-        int probability = NOT_A_PROBABILITY;
-        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
-        getBigramEntry(&probability, 0 /* outHasNext */, &targetTerminalId, lastEntryPos);
-        if (!writeBigramEntry(probability, false /* hasNext */, targetTerminalId, writingPos)) {
+        const BigramEntry bigramEntry = getBigramEntry(lastEntryPos).updateHasNextAndGetEntry(
+                false /* hasNext */);
+        if (!writeBigramEntry(&bigramEntry, writingPos)) {
             AKLOGE("Cannot write bigram entry to set hasNext flag after GC. pos: %d", writingPos);
             return false;
         }
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 cf380f403..ac05b215b 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
@@ -18,6 +18,7 @@
 #define LATINIME_BIGRAM_DICT_CONTENT_H
 
 #include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h"
 #include "suggest/policyimpl/dictionary/structure/v4/content/sparse_table_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"
@@ -26,27 +27,27 @@ namespace latinime {
 
 class BigramDictContent : public SparseTableDictContent {
  public:
-    BigramDictContent(const char *const dictDirPath, const bool isUpdatable)
+    BigramDictContent(const char *const dictDirPath, const bool hasHistoricalInfo,
+            const bool isUpdatable)
             : SparseTableDictContent(dictDirPath,
                       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) {}
+                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE),
+              mHasHistoricalInfo(hasHistoricalInfo) {}
 
-    BigramDictContent()
+    BigramDictContent(const bool hasHistoricalInfo)
             : SparseTableDictContent(Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE,
-                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE) {}
+                      Ver4DictConstants::BIGRAM_ADDRESS_TABLE_DATA_SIZE),
+              mHasHistoricalInfo(hasHistoricalInfo) {}
 
-    void getBigramEntry(int *const outProbability, bool *const outHasNext,
-            int *const outTargetTerminalId, const int bigramEntryPos) const {
+    const BigramEntry getBigramEntry(const int bigramEntryPos) const {
         int readingPos = bigramEntryPos;
-        getBigramEntryAndAdvancePosition(outProbability, outHasNext, outTargetTerminalId,
-                &readingPos);
+        return getBigramEntryAndAdvancePosition(&readingPos);
     }
 
-    void getBigramEntryAndAdvancePosition(int *const outProbability, bool *const outHasNext,
-            int *const outTargetTerminalId, int *const bigramEntryPos) const;
+    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 {
@@ -57,15 +58,13 @@ class BigramDictContent : public SparseTableDictContent {
         return addressLookupTable->get(terminalId);
     }
 
-    bool writeBigramEntry(const int probability, const int hasNext, const int targetTerminalId,
-            const int entryWritingPos) {
+    bool writeBigramEntry(const BigramEntry *const bigramEntryToWrite, const int entryWritingPos) {
         int writingPos = entryWritingPos;
-        return writeBigramEntryAndAdvancePosition(probability, hasNext, targetTerminalId,
-                &writingPos);
+        return writeBigramEntryAndAdvancePosition(bigramEntryToWrite, &writingPos);
     }
 
-    bool writeBigramEntryAndAdvancePosition(const int probability, const int hasNext,
-            const int targetTerminalId, int *const entryWritingPos);
+    bool writeBigramEntryAndAdvancePosition(const BigramEntry *const bigramEntryToWrite,
+            int *const entryWritingPos);
 
     bool createNewBigramList(const int terminalId) {
         const int bigramListPos = getContentBuffer()->getTailPosition();
@@ -96,6 +95,8 @@ class BigramDictContent : public SparseTableDictContent {
             const BigramDictContent *const sourceBigramDictContent, const int toPos,
             const TerminalPositionLookupTable::TerminalIdMap *const terminalIdMap,
             int *const outEntryCount);
+
+    bool mHasHistoricalInfo;
 };
 } // namespace latinime
 #endif /* LATINIME_BIGRAM_DICT_CONTENT_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h
new file mode 100644
index 000000000..10b3ec8dc
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h
@@ -0,0 +1,104 @@
+/*
+ * 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.
+ */
+
+#ifndef LATINIME_BIGRAM_ENTRY_H
+#define LATINIME_BIGRAM_ENTRY_H
+
+#include "defines.h"
+#include "suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h"
+
+namespace latinime {
+
+class BigramEntry {
+ public:
+    BigramEntry(const BigramEntry& bigramEntry)
+            : mHasNext(bigramEntry.mHasNext), mProbability(bigramEntry.mProbability),
+              mTimestamp(bigramEntry.mTimestamp), mLevel(bigramEntry.mLevel),
+              mCount(bigramEntry.mCount), mTargetTerminalId(bigramEntry.mTargetTerminalId) {}
+
+    // Entry with historical information.
+    BigramEntry(const bool hasNext, const int probability, const int targetTerminalId)
+            : mHasNext(hasNext), mProbability(probability),
+              mTimestamp(Ver4DictConstants::NOT_A_TIME_STAMP), mLevel(0), mCount(0),
+              mTargetTerminalId(targetTerminalId) {}
+
+    // Entry with historical information.
+    BigramEntry(const bool hasNext, const int probability, const int timestamp, const int level,
+            const int count, const int targetTerminalId)
+            : mHasNext(hasNext), mProbability(probability), mTimestamp(timestamp),
+              mLevel(level), mCount(count), mTargetTerminalId(targetTerminalId) {}
+
+    const BigramEntry getInvalidatedEntry() const {
+        return updateTargetTerminalIdAndGetEntry(Ver4DictConstants::NOT_A_TERMINAL_ID);
+    }
+
+    const BigramEntry updateHasNextAndGetEntry(const bool hasNext) const {
+        return BigramEntry(hasNext, mProbability, mTimestamp, mLevel, mCount,
+                mTargetTerminalId);
+    }
+
+    const BigramEntry updateTargetTerminalIdAndGetEntry(const int newTargetTerminalId) const {
+        return BigramEntry(mHasNext, mProbability, mTimestamp, mLevel, mCount,
+                newTargetTerminalId);
+    }
+
+    const BigramEntry updateProbabilityAndGetEntry(const int probability) const {
+        return BigramEntry(mHasNext, probability, mTimestamp, mLevel, mCount,
+                mTargetTerminalId);
+    }
+
+    bool isValid() const {
+        return mTargetTerminalId != Ver4DictConstants::NOT_A_TERMINAL_ID;
+    }
+
+    bool hasNext() const {
+        return mHasNext;
+    }
+
+    int getProbability() const {
+        return mProbability;
+    }
+
+    int getTimeStamp() const {
+        return mTimestamp;
+    }
+
+    int getLevel() const {
+        return mLevel;
+    }
+
+    int getCount() const {
+        return mCount;
+    }
+
+    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 int mTimestamp;
+    const int mLevel;
+    const int mCount;
+    const int mTargetTerminalId;
+};
+} // namespace latinime
+#endif /* LATINIME_BIGRAM_ENTRY_H */
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 8fdbbedfe..07b8f181d 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
@@ -127,7 +127,7 @@ class Ver4DictBuffers {
               // TODO: Quit using header size.
               mTerminalPositionLookupTable(dictDirPath, isUpdatable, mHeaderSize),
               mProbabilityDictContent(dictDirPath, false /* hasHistoricalInfo */, isUpdatable),
-              mBigramDictContent(dictDirPath, isUpdatable),
+              mBigramDictContent(dictDirPath, false /* hasHistoricalInfo */, isUpdatable),
               mShortcutDictContent(dictDirPath, isUpdatable),
               mIsUpdatable(isUpdatable) {}
 
@@ -137,7 +137,8 @@ class Ver4DictBuffers {
               mExpandableTrieBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
               mTerminalPositionLookupTable(),
               mProbabilityDictContent(false /* hasHistoricalInfo */),
-              mBigramDictContent(), mShortcutDictContent(), mIsUpdatable(true) {}
+              mBigramDictContent(false /* hasHistoricalInfo */), mShortcutDictContent(),
+              mIsUpdatable(true) {}
 
     const MmappedBuffer::MmappedBufferPtr mDictBuffer;
     const int mHeaderSize;
diff --git a/native/jni/src/utils/exclusive_ownership_pointer.h b/native/jni/src/utils/exclusive_ownership_pointer.h
index 3cf78954a..6c67df28e 100644
--- a/native/jni/src/utils/exclusive_ownership_pointer.h
+++ b/native/jni/src/utils/exclusive_ownership_pointer.h
@@ -56,8 +56,7 @@ class ExclusiveOwnershipPointer {
  private:
     // This class allows to copy and assign and ensures only one instance has the ownership of the
     // managed pointer.
-
-    ExclusiveOwnershipPointer() : mPointer(0), mSharedOwnerPtr(0) {}
+    DISALLOW_DEFAULT_CONSTRUCTOR(ExclusiveOwnershipPointer);
 
     void transferOwnership(const ExclusiveOwnershipPointer<T> *const src) {
         if (*mSharedOwnerPtr != src) {