am 2fdb62a6: Start using historical info for decaying.

* commit '2fdb62a6a28d769435fe5d48d8b997c3e9a083d5':
  Start using historical info for decaying.

native/jni/src/suggest/core/dictionary/bigram_dictionary.cpp

@@ -163,7 +163,8 @@ int BigramDictionary::getBigramProbability(const int *word0, int length0, const
             mDictionaryStructurePolicy->getBigramsStructurePolicy(), pos);
     while (bigramsIt.hasNext()) {
         bigramsIt.next();
-        if (bigramsIt.getBigramPos() == nextWordPos) {
+        if (bigramsIt.getBigramPos() == nextWordPos
+                && bigramsIt.getProbability() != NOT_A_PROBABILITY) {
             return mDictionaryStructurePolicy->getProbability(
                     mDictionaryStructurePolicy->getUnigramProbabilityOfPtNode(nextWordPos),
                     bigramsIt.getProbability());

native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp

@@ -17,6 +17,7 @@
 #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/header/header_policy.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"
@@ -34,7 +35,12 @@ void Ver4BigramListPolicy::getNextBigram(int *const outBigramPos, int *const out
                 bigramEntry.getTargetTerminalId());
     }
     if (outProbability) {
-        *outProbability = bigramEntry.getProbability();
+        if (bigramEntry.hasHistoricalInfo()) {
+            *outProbability =
+                    ForgettingCurveUtils::decodeProbability(bigramEntry.getHistoricalInfo());
+        } else {
+            *outProbability = bigramEntry.getProbability();
+        }
     }
     if (outHasNext) {
         *outHasNext = bigramEntry.hasNext();
@@ -152,17 +158,12 @@ bool Ver4BigramListPolicy::updateAllBigramEntriesAndDeleteUselessEntries(const i
             if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
                 return false;
             }
-        } else if (mNeedsToDecayWhenUpdating) {
+        } else if (bigramEntry.hasHistoricalInfo()) {
-            const int probability = ForgettingCurveUtils::getEncodedProbabilityToSave(
+            const HistoricalInfo historicalInfo = ForgettingCurveUtils::createHistoricalInfoToSave(
-                    bigramEntry.getProbability(), mHeaderPolicy);
+                    bigramEntry.getHistoricalInfo());
-            const HistoricalInfo historicalInfo =
+            if (ForgettingCurveUtils::needsToKeep(&historicalInfo)) {
-                    ForgettingCurveUtils::createHistoricalInfoToSave(
-                            bigramEntry.getHistoricalInfo());
-            // TODO: Use ForgettingCurveUtils::needsToKeep(&historicalInfo).
-            if (ForgettingCurveUtils::isValidEncodedProbability(probability)) {
                 const BigramEntry updatedBigramEntry =
-                        bigramEntry.updateProbabilityAndGetEntry(probability)
+                        bigramEntry.updateHistoricalInfoAndGetEntry(&historicalInfo);
-                                .updateHistoricalInfoAndGetEntry(&historicalInfo);
                 if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
                     return false;
                 }
@@ -225,14 +226,12 @@ int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
 const BigramEntry Ver4BigramListPolicy::createUpdatedBigramEntryFrom(
         const BigramEntry *const originalBigramEntry, const int newProbability,
         const int timestamp) const {
-    if (mNeedsToDecayWhenUpdating) {
+    // TODO: Consolidate historical info and probability.
-        const int probability = ForgettingCurveUtils::getUpdatedEncodedProbability(
+    if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
-                originalBigramEntry->getProbability(), newProbability);
         const HistoricalInfo updatedHistoricalInfo =
                 ForgettingCurveUtils::createUpdatedHistoricalInfo(
                         originalBigramEntry->getHistoricalInfo(), newProbability, timestamp);
-        return originalBigramEntry->updateProbabilityAndGetEntry(probability)
+        return originalBigramEntry->updateHistoricalInfoAndGetEntry(&updatedHistoricalInfo);
-                .updateHistoricalInfoAndGetEntry(&updatedHistoricalInfo);
     } else {
         return originalBigramEntry->updateProbabilityAndGetEntry(newProbability);
     }

native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h

@@ -24,18 +24,17 @@
 namespace latinime {
 
 class BigramDictContent;
-class DictionaryHeaderStructurePolicy;
+class HeaderPolicy;
 class TerminalPositionLookupTable;
 
 class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
  public:
     Ver4BigramListPolicy(BigramDictContent *const bigramDictContent,
             const TerminalPositionLookupTable *const terminalPositionLookupTable,
-            const DictionaryHeaderStructurePolicy *const headerPolicy,
+            const HeaderPolicy *const headerPolicy)
-            const bool needsToDecayWhenUpdating)
             : mBigramDictContent(bigramDictContent),
               mTerminalPositionLookupTable(terminalPositionLookupTable),
-              mHeaderPolicy(headerPolicy), mNeedsToDecayWhenUpdating(needsToDecayWhenUpdating) {}
+              mHeaderPolicy(headerPolicy) {}
 
     void getNextBigram(int *const outBigramPos, int *const outProbability,
             bool *const outHasNext, int *const bigramEntryPos) const;
@@ -64,8 +63,7 @@ class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
 
     BigramDictContent *const mBigramDictContent;
     const TerminalPositionLookupTable *const mTerminalPositionLookupTable;
-    const DictionaryHeaderStructurePolicy *const mHeaderPolicy;
+    const HeaderPolicy *const mHeaderPolicy;
-    const bool mNeedsToDecayWhenUpdating;
 };
 } // namespace latinime
 #endif /* LATINIME_VER4_BIGRAM_LIST_POLICY_H */

native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h

@@ -93,6 +93,18 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
         }
     }
 
+    AK_FORCE_INLINE bool isValid() const {
+        // Decaying dictionary must have historical information.
+        if (!mIsDecayingDict) {
+            return true;
+        }
+        if (mHasHistoricalInfoOfWords) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
     AK_FORCE_INLINE int getSize() const {
         return mSize;
     }
@@ -137,7 +149,7 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
         return mExtendedRegionSize;
     }
 
-    AK_FORCE_INLINE bool hasHistricalInfoOfWords() const {
+    AK_FORCE_INLINE bool hasHistoricalInfoOfWords() const {
         return mHasHistoricalInfoOfWords;
     }
 

native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_gc_event_listeners.cpp

@@ -20,7 +20,6 @@
 #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/v3/dynamic_patricia_trie_writing_utils.h"
-#include "suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h"
 
 namespace latinime {
 
@@ -30,8 +29,7 @@ bool DynamicPatriciaTrieGcEventListeners
     // PtNode is useless when the PtNode is not a terminal and doesn't have any not useless
     // children.
     bool isUselessPtNode = !ptNodeParams->isTerminal();
-    // TODO: Quit checking mNeedsToDecayWhenUpdating.
+    if (ptNodeParams->isTerminal()) {
-    if (ptNodeParams->isTerminal() && mNeedsToDecayWhenUpdating) {
         bool needsToKeepPtNode = true;
         if (!mPtNodeWriter->updatePtNodeProbabilityAndGetNeedsToKeepPtNodeAfterGC(ptNodeParams,
                 &needsToKeepPtNode)) {

native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_gc_event_listeners.h

@@ -27,8 +27,6 @@
 
 namespace latinime {
 
-class DictionaryHeaderStructurePolicy;
-class PtNodeWriter;
 class PtNodeParams;
 
 // TODO: Move to pt_common.
@@ -41,12 +39,9 @@ class DynamicPatriciaTrieGcEventListeners {
         : public DynamicPatriciaTrieReadingHelper::TraversingEventListener {
      public:
         TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
-                const DictionaryHeaderStructurePolicy *const headerPolicy,
+                PtNodeWriter *const ptNodeWriter)
-                PtNodeWriter *const ptNodeWriter, BufferWithExtendableBuffer *const buffer,
+                : mPtNodeWriter(ptNodeWriter), mValueStack(), mChildrenValue(0),
-                const bool needsToDecayWhenUpdating)
+                  mValidUnigramCount(0) {}
-                : mHeaderPolicy(headerPolicy), mPtNodeWriter(ptNodeWriter), mBuffer(buffer),
-                  mNeedsToDecayWhenUpdating(needsToDecayWhenUpdating), mValueStack(),
-                  mChildrenValue(0), mValidUnigramCount(0) {}
 
         ~TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted() {};
 
@@ -77,10 +72,7 @@ class DynamicPatriciaTrieGcEventListeners {
         DISALLOW_IMPLICIT_CONSTRUCTORS(
                 TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted);
 
-        const DictionaryHeaderStructurePolicy *const mHeaderPolicy;
         PtNodeWriter *const mPtNodeWriter;
-        BufferWithExtendableBuffer *const mBuffer;
-        const bool mNeedsToDecayWhenUpdating;
         std::vector<int> mValueStack;
         int mChildrenValue;
         int mValidUnigramCount;

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_entry.h

@@ -73,6 +73,10 @@ class BigramEntry {
         return mProbability;
     }
 
+    bool hasHistoricalInfo() const {
+        return mHistoricalInfo.isValid();
+    }
+
     const HistoricalInfo *getHistoricalInfo() const {
         return &mHistoricalInfo;
     }

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h

@@ -51,6 +51,10 @@ class ProbabilityEntry {
         return ProbabilityEntry(mFlags, mProbability, historicalInfo);
     }
 
+    bool hasHistoricalInfo() const {
+        return mHistoricalInfo.isValid();
+    }
+
     int getFlags() const {
         return mFlags;
     }

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h

@@ -45,9 +45,9 @@ class Ver4DictBuffers {
     }
 
     AK_FORCE_INLINE bool isValid() const {
-        return mDictBuffer.get() != 0 && mProbabilityDictContent.isValid()
+        return mDictBuffer.get() != 0 && mHeaderPolicy.isValid()
-                && mTerminalPositionLookupTable.isValid() && mBigramDictContent.isValid()
+                && mProbabilityDictContent.isValid() && mTerminalPositionLookupTable.isValid()
-                && mShortcutDictContent.isValid();
+                && mBigramDictContent.isValid() && mShortcutDictContent.isValid();
     }
 
     AK_FORCE_INLINE bool isNearSizeLimit() const {
@@ -131,9 +131,10 @@ class Ver4DictBuffers {
                       BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
               // TODO: Quit using header size.
               mTerminalPositionLookupTable(dictDirPath, isUpdatable, mHeaderPolicy.getSize()),
-              mProbabilityDictContent(dictDirPath, mHeaderPolicy.hasHistricalInfoOfWords(),
+              mProbabilityDictContent(dictDirPath, mHeaderPolicy.hasHistoricalInfoOfWords(),
+                      isUpdatable),
+              mBigramDictContent(dictDirPath, mHeaderPolicy.hasHistoricalInfoOfWords(),
                       isUpdatable),
-              mBigramDictContent(dictDirPath, mHeaderPolicy.hasHistricalInfoOfWords(), isUpdatable),
               mShortcutDictContent(dictDirPath, isUpdatable),
               mIsUpdatable(isUpdatable) {}
 
@@ -142,8 +143,8 @@ class Ver4DictBuffers {
               mExpandableHeaderBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
               mExpandableTrieBuffer(Ver4DictConstants::MAX_DICTIONARY_SIZE),
               mTerminalPositionLookupTable(),
-              mProbabilityDictContent(headerPolicy->hasHistricalInfoOfWords()),
+              mProbabilityDictContent(headerPolicy->hasHistoricalInfoOfWords()),
-              mBigramDictContent(headerPolicy->hasHistricalInfoOfWords()), mShortcutDictContent(),
+              mBigramDictContent(headerPolicy->hasHistoricalInfoOfWords()), mShortcutDictContent(),
               mIsUpdatable(true) {}
 
     const MmappedBuffer::MmappedBufferPtr mDictBuffer;

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_reader.cpp

@@ -22,6 +22,7 @@
 #include "suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h"
 #include "suggest/policyimpl/dictionary/structure/v4/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 {
 
@@ -62,7 +63,12 @@ const PtNodeParams Ver4PatriciaTrieNodeReader::fetchPtNodeInfoFromBufferAndProce
         terminalId = Ver4PatriciaTrieReadingUtils::getTerminalIdAndAdvancePosition(dictBuf, &pos);
         const ProbabilityEntry probabilityEntry =
                 mProbabilityDictContent->getProbabilityEntry(terminalId);
-        probability = probabilityEntry.getProbability();
+        if (probabilityEntry.hasHistoricalInfo()) {
+            probability = ForgettingCurveUtils::decodeProbability(
+                    probabilityEntry.getHistoricalInfo());
+        } else {
+            probability = probabilityEntry.getProbability();
+        }
     }
     int childrenPosFieldPos = pos;
     if (usesAdditionalBuffer) {

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp

@@ -17,6 +17,7 @@
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h"
 
 #include "suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
 #include "suggest/policyimpl/dictionary/shortcut/ver4_shortcut_list_policy.h"
 #include "suggest/policyimpl/dictionary/structure/v2/patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h"
@@ -147,27 +148,21 @@ bool Ver4PatriciaTrieNodeWriter::updatePtNodeProbabilityAndGetNeedsToKeepPtNodeA
         AKLOGE("updatePtNodeProbabilityAndGetNeedsToSaveForGC is called for non-terminal PtNode.");
         return false;
     }
-    if (mBuffers->getHeaderPolicy()->isDecayingDict()) {
+    const ProbabilityEntry originalProbabilityEntry =
-        const ProbabilityEntry originalProbabilityEntry =
+            mBuffers->getProbabilityDictContent()->getProbabilityEntry(
-                mBuffers->getProbabilityDictContent()->getProbabilityEntry(
+                    toBeUpdatedPtNodeParams->getTerminalId());
-                        toBeUpdatedPtNodeParams->getTerminalId());
+    if (originalProbabilityEntry.hasHistoricalInfo()) {
-        // TODO: Remove.
+        const HistoricalInfo historicalInfo = ForgettingCurveUtils::createHistoricalInfoToSave(
-        const int newProbability = ForgettingCurveUtils::getEncodedProbabilityToSave(
+                originalProbabilityEntry.getHistoricalInfo());
-                originalProbabilityEntry.getProbability(), mBuffers->getHeaderPolicy());
-        const HistoricalInfo historicalInfo =
-                ForgettingCurveUtils::createHistoricalInfoToSave(
-                        originalProbabilityEntry.getHistoricalInfo());
         const ProbabilityEntry probabilityEntry =
-                originalProbabilityEntry.createEntryWithUpdatedProbability(newProbability)
+                originalProbabilityEntry.createEntryWithUpdatedHistoricalInfo(&historicalInfo);
-                        .createEntryWithUpdatedHistoricalInfo(&historicalInfo);
         if (!mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(
                 toBeUpdatedPtNodeParams->getTerminalId(), &probabilityEntry)) {
             AKLOGE("Cannot write updated probability entry. terminalId: %d",
                     toBeUpdatedPtNodeParams->getTerminalId());
             return false;
         }
-        // TODO: Use ForgettingCurveUtils::needsToKeep(&historicalInfo).
+        const bool isValid = ForgettingCurveUtils::needsToKeep(&historicalInfo);
-        const bool isValid = ForgettingCurveUtils::isValidEncodedProbability(newProbability);
         if (!isValid) {
             if (!markPtNodeAsWillBecomeNonTerminal(toBeUpdatedPtNodeParams)) {
                 AKLOGE("Cannot mark PtNode as willBecomeNonTerminal.");
@@ -380,14 +375,13 @@ bool Ver4PatriciaTrieNodeWriter::writePtNodeAndGetTerminalIdAndAdvancePosition(
 const ProbabilityEntry Ver4PatriciaTrieNodeWriter::createUpdatedEntryFrom(
         const ProbabilityEntry *const originalProbabilityEntry, const int newProbability,
         const int timestamp) const {
-    if (mNeedsToDecayWhenUpdating) {
+    // TODO: Consolidate historical info and probability.
-        const int updatedProbability = ForgettingCurveUtils::getUpdatedEncodedProbability(
+    if (mBuffers->getHeaderPolicy()->hasHistoricalInfoOfWords()) {
-                originalProbabilityEntry->getProbability(), newProbability);
         const HistoricalInfo updatedHistoricalInfo =
                 ForgettingCurveUtils::createUpdatedHistoricalInfo(
                         originalProbabilityEntry->getHistoricalInfo(), newProbability, timestamp);
-        return originalProbabilityEntry->createEntryWithUpdatedProbability(updatedProbability)
+        return originalProbabilityEntry->createEntryWithUpdatedHistoricalInfo(
-                .createEntryWithUpdatedHistoricalInfo(&updatedHistoricalInfo);
+                &updatedHistoricalInfo);
     } else {
         return originalProbabilityEntry->createEntryWithUpdatedProbability(newProbability);
     }

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h

@@ -40,12 +40,10 @@ class Ver4PatriciaTrieNodeWriter : public PtNodeWriter {
  public:
     Ver4PatriciaTrieNodeWriter(BufferWithExtendableBuffer *const trieBuffer,
             Ver4DictBuffers *const buffers, const Ver4PatriciaTrieNodeReader *const ptNodeReader,
-            Ver4BigramListPolicy *const bigramPolicy, Ver4ShortcutListPolicy *const shortcutPolicy,
+            Ver4BigramListPolicy *const bigramPolicy, Ver4ShortcutListPolicy *const shortcutPolicy)
-            const bool needsToDecayWhenUpdating)
             : mTrieBuffer(trieBuffer), mBuffers(buffers), mPtNodeReader(ptNodeReader),
               mReadingHelper(mTrieBuffer, mPtNodeReader),
-              mBigramPolicy(bigramPolicy), mShortcutPolicy(shortcutPolicy),
+              mBigramPolicy(bigramPolicy), mShortcutPolicy(shortcutPolicy) {}
-              mNeedsToDecayWhenUpdating(needsToDecayWhenUpdating) {}
 
     virtual ~Ver4PatriciaTrieNodeWriter() {}
 
@@ -120,7 +118,6 @@ class Ver4PatriciaTrieNodeWriter : public PtNodeWriter {
     DynamicPatriciaTrieReadingHelper mReadingHelper;
     Ver4BigramListPolicy *const mBigramPolicy;
     Ver4ShortcutListPolicy *const mShortcutPolicy;
-    const bool mNeedsToDecayWhenUpdating;
 };
 } // namespace latinime
 #endif /* LATINIME_VER4_PATRICIA_TRIE_NODE_WRITER_H */

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp

@@ -34,8 +34,6 @@ 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 char *const Ver4PatriciaTriePolicy::SET_NEEDS_TO_DECAY_FOR_TESTING_QUERY =
-        "SET_NEEDS_TO_DECAY_FOR_TESTING";
 const char *const Ver4PatriciaTriePolicy::SET_CURRENT_TIME_FOR_TESTING_QUERY_FORMAT =
         "SET_CURRENT_TIME_FOR_TESTING:%d";
 const char *const Ver4PatriciaTriePolicy::GET_CURRENT_TIME_QUERY = "GET_CURRENT_TIME";
@@ -62,8 +60,7 @@ void Ver4PatriciaTriePolicy::createAndGetAllChildDicNodes(const DicNode *const d
             // 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 = getProbability(ptNodeParams.getProbability(), NOT_A_PROBABILITY)
+            isTerminal = ptNodeParams.getProbability() != NOT_A_PROBABILITY;
-                    != NOT_A_PROBABILITY;
         }
         childDicNodes->pushLeavingChild(dicNode, ptNodeParams.getHeadPos(),
                 ptNodeParams.getChildrenPos(), ptNodeParams.getProbability(), isTerminal,
@@ -262,11 +259,7 @@ void Ver4PatriciaTriePolicy::flushWithGC(const char *const filePath) {
         AKLOGI("Warning: flushWithGC() is called for non-updatable dictionary.");
         return;
     }
-    const bool needsToDecay = mHeaderPolicy->isDecayingDict()
+    mWritingHelper.writeToDictFileWithGC(getRootPosition(), filePath);
-            && (mNeedsToDecayForTesting || ForgettingCurveUtils::needsToDecay(
-                    false /* mindsBlockByDecay */, mUnigramCount, mBigramCount, mHeaderPolicy));
-    mWritingHelper.writeToDictFileWithGC(getRootPosition(), filePath, needsToDecay);
-    mNeedsToDecayForTesting = false;
 }
 
 bool Ver4PatriciaTriePolicy::needsToRunGC(const bool mindsBlockByGC) const {
@@ -286,8 +279,8 @@ bool Ver4PatriciaTriePolicy::needsToRunGC(const bool mindsBlockByGC) const {
         // Needs to reduce dictionary size.
         return true;
     } else if (mHeaderPolicy->isDecayingDict()) {
-        return mNeedsToDecayForTesting || ForgettingCurveUtils::needsToDecay(
+        return ForgettingCurveUtils::needsToDecay(mindsBlockByGC, mUnigramCount, mBigramCount,
-                mindsBlockByGC, mUnigramCount, mBigramCount, mHeaderPolicy);
+                mHeaderPolicy);
     }
     return false;
 }
@@ -308,8 +301,6 @@ void Ver4PatriciaTriePolicy::getProperty(const char *const query, const int quer
         snprintf(outResult, maxResultLength, "%d",
                 mHeaderPolicy->isDecayingDict() ? ForgettingCurveUtils::MAX_BIGRAM_COUNT :
                         static_cast<int>(Ver4DictConstants::MAX_DICTIONARY_SIZE));
-    } else if (strncmp(query, SET_NEEDS_TO_DECAY_FOR_TESTING_QUERY, compareLength) == 0) {
-        mNeedsToDecayForTesting = true;
     } else if (sscanf(query, SET_CURRENT_TIME_FOR_TESTING_QUERY_FORMAT, &timestamp) == 1) {
         TimeKeeper::startTestModeWithForceCurrentTime(timestamp);
     } else if (strncmp(query, GET_CURRENT_TIME_QUERY, compareLength) == 0) {

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h

@@ -41,17 +41,16 @@ class Ver4PatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
             : mBuffers(buffers), mHeaderPolicy(mBuffers.get()->getHeaderPolicy()),
               mDictBuffer(mBuffers.get()->getWritableTrieBuffer()),
               mBigramPolicy(mBuffers.get()->getMutableBigramDictContent(),
-                      mBuffers.get()->getTerminalPositionLookupTable(), mHeaderPolicy,
+                      mBuffers.get()->getTerminalPositionLookupTable(), mHeaderPolicy),
-                      mHeaderPolicy->isDecayingDict()),
               mShortcutPolicy(mBuffers.get()->getMutableShortcutDictContent(),
                       mBuffers.get()->getTerminalPositionLookupTable()),
               mNodeReader(mDictBuffer, mBuffers.get()->getProbabilityDictContent()),
               mNodeWriter(mDictBuffer, mBuffers.get(), &mNodeReader, &mBigramPolicy,
-                      &mShortcutPolicy, mHeaderPolicy->isDecayingDict()),
+                      &mShortcutPolicy),
               mUpdatingHelper(mDictBuffer, &mNodeReader, &mNodeWriter),
               mWritingHelper(mBuffers.get()),
               mUnigramCount(mHeaderPolicy->getUnigramCount()),
-              mBigramCount(mHeaderPolicy->getBigramCount()), mNeedsToDecayForTesting(false) {};
+              mBigramCount(mHeaderPolicy->getBigramCount()) {};
 
     AK_FORCE_INLINE int getRootPosition() const {
         return 0;
@@ -117,7 +116,6 @@ class Ver4PatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
     static const char *const BIGRAM_COUNT_QUERY;
     static const char *const MAX_UNIGRAM_COUNT_QUERY;
     static const char *const MAX_BIGRAM_COUNT_QUERY;
-    static const char *const SET_NEEDS_TO_DECAY_FOR_TESTING_QUERY;
     static const char *const SET_CURRENT_TIME_FOR_TESTING_QUERY_FORMAT;
     static const char *const GET_CURRENT_TIME_QUERY;
     static const char *const QUIT_TIMEKEEPER_TEST_MODE_QUERY;
@@ -137,7 +135,6 @@ class Ver4PatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
     Ver4PatriciaTrieWritingHelper mWritingHelper;
     int mUnigramCount;
     int mBigramCount;
-    bool mNeedsToDecayForTesting;
 };
 } // namespace latinime
 #endif // LATINIME_VER4_PATRICIA_TRIE_POLICY_H

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp

@@ -53,20 +53,20 @@ void Ver4PatriciaTrieWritingHelper::writeToDictFile(const char *const trieFilePa
 }
 
 void Ver4PatriciaTrieWritingHelper::writeToDictFileWithGC(const int rootPtNodeArrayPos,
-        const char *const trieFilePath, const bool needsToDecay) {
+        const char *const trieFilePath) {
     const HeaderPolicy *const headerPolicy = mBuffers->getHeaderPolicy();
     Ver4DictBuffers::Ver4DictBuffersPtr dictBuffers(
             Ver4DictBuffers::createVer4DictBuffers(headerPolicy));
     int unigramCount = 0;
     int bigramCount = 0;
-    if (!runGC(rootPtNodeArrayPos, headerPolicy, dictBuffers.get(), &unigramCount, &bigramCount,
+    if (!runGC(rootPtNodeArrayPos, headerPolicy, dictBuffers.get(), &unigramCount, &bigramCount)) {
-            needsToDecay)) {
         return;
     }
     BufferWithExtendableBuffer headerBuffer(
             BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE);
     if (!headerPolicy->writeHeaderToBuffer(&headerBuffer, true /* updatesLastUpdatedTime */,
-            needsToDecay, unigramCount, bigramCount, 0 /* extendedRegionSize */)) {
+            true /* updatesLastDecayedTime */, unigramCount, bigramCount,
+            0 /* extendedRegionSize */)) {
         return;
     }
     const int dirPathBufSize = strlen(trieFilePath) + 1 /* terminator */;
@@ -77,30 +77,29 @@ void Ver4PatriciaTrieWritingHelper::writeToDictFileWithGC(const int rootPtNodeAr
 
 bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
         const HeaderPolicy *const headerPolicy, Ver4DictBuffers *const buffersToWrite,
-        int *const outUnigramCount, int *const outBigramCount, const bool needsToDecay) {
+        int *const outUnigramCount, int *const outBigramCount) {
     Ver4PatriciaTrieNodeReader ptNodeReader(mBuffers->getTrieBuffer(),
             mBuffers->getProbabilityDictContent());
     Ver4BigramListPolicy bigramPolicy(mBuffers->getMutableBigramDictContent(),
-            mBuffers->getTerminalPositionLookupTable(), headerPolicy, needsToDecay);
+            mBuffers->getTerminalPositionLookupTable(), headerPolicy);
     Ver4ShortcutListPolicy shortcutPolicy(mBuffers->getMutableShortcutDictContent(),
             mBuffers->getTerminalPositionLookupTable());
     Ver4PatriciaTrieNodeWriter ptNodeWriter(mBuffers->getWritableTrieBuffer(),
-            mBuffers, &ptNodeReader, &bigramPolicy, &shortcutPolicy,
+            mBuffers, &ptNodeReader, &bigramPolicy, &shortcutPolicy);
-            false /* needsToDecayWhenUpdating */);
 
     DynamicPatriciaTrieReadingHelper readingHelper(mBuffers->getTrieBuffer(), &ptNodeReader);
     readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
     DynamicPatriciaTrieGcEventListeners
             ::TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
                     traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
-                            headerPolicy, &ptNodeWriter, mBuffers->getWritableTrieBuffer(),
+                            &ptNodeWriter);
-                            needsToDecay);
     if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
             &traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted)) {
         return false;
     }
-    if (needsToDecay && traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+    if (headerPolicy->isDecayingDict()
-            .getValidUnigramCount() > ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC) {
+            && traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+                    .getValidUnigramCount() > ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC) {
         // TODO: Remove more unigrams.
     }
 
@@ -111,8 +110,9 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
             &traversePolicyToUpdateBigramProbability)) {
         return false;
     }
-    if (needsToDecay && traversePolicyToUpdateBigramProbability.getValidBigramEntryCount()
+    if (headerPolicy->isDecayingDict()
-            > ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC) {
+            && traversePolicyToUpdateBigramProbability.getValidBigramEntryCount()
+                    > ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC) {
         // TODO: Remove more bigrams.
     }
 
@@ -120,8 +120,7 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
     PtNodeWriter::DictPositionRelocationMap dictPositionRelocationMap;
     readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
     Ver4PatriciaTrieNodeWriter ptNodeWriterForNewBuffers(buffersToWrite->getWritableTrieBuffer(),
-            buffersToWrite, &ptNodeReader, &bigramPolicy, &shortcutPolicy,
+            buffersToWrite, &ptNodeReader, &bigramPolicy, &shortcutPolicy);
-            false /* needsToDecayWhenUpdating */);
     DynamicPatriciaTrieGcEventListeners::TraversePolicyToPlaceAndWriteValidPtNodesToBuffer
             traversePolicyToPlaceAndWriteValidPtNodesToBuffer(&ptNodeWriterForNewBuffers,
                     buffersToWrite->getWritableTrieBuffer(), &dictPositionRelocationMap);
@@ -134,13 +133,11 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
     Ver4PatriciaTrieNodeReader newPtNodeReader(buffersToWrite->getTrieBuffer(),
             buffersToWrite->getProbabilityDictContent());
     Ver4BigramListPolicy newBigramPolicy(buffersToWrite->getMutableBigramDictContent(),
-            buffersToWrite->getTerminalPositionLookupTable(), headerPolicy,
+            buffersToWrite->getTerminalPositionLookupTable(), headerPolicy);
-            false /* needsToDecay */);
     Ver4ShortcutListPolicy newShortcutPolicy(buffersToWrite->getMutableShortcutDictContent(),
             buffersToWrite->getTerminalPositionLookupTable());
     Ver4PatriciaTrieNodeWriter newPtNodeWriter(buffersToWrite->getWritableTrieBuffer(),
-            buffersToWrite, &newPtNodeReader, &newBigramPolicy, &newShortcutPolicy,
+            buffersToWrite, &newPtNodeReader, &newBigramPolicy, &newShortcutPolicy);
-            false /* needsToDecayWhenUpdating */);
     // Re-assign terminal IDs for valid terminal PtNodes.
     TerminalPositionLookupTable::TerminalIdMap terminalIdMap;
     if(!buffersToWrite->getMutableTerminalPositionLookupTable()->runGCTerminalIds(

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.h

@@ -36,7 +36,7 @@ class Ver4PatriciaTrieWritingHelper {
             const int bigramCount) const;
 
     void writeToDictFileWithGC(const int rootPtNodeArrayPos,
-            const char *const trieFilePath, const bool needsToDecay);
+            const char *const trieFilePath);
 
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4PatriciaTrieWritingHelper);
@@ -66,7 +66,7 @@ class Ver4PatriciaTrieWritingHelper {
 
     bool runGC(const int rootPtNodeArrayPos, const HeaderPolicy *const headerPolicy,
             Ver4DictBuffers *const buffersToWrite, int *const outUnigramCount,
-            int *const outBigramCount, const bool needsToDecay);
+            int *const outBigramCount);
 
     Ver4DictBuffers *const mBuffers;
 };

native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp

@@ -31,12 +31,6 @@ const int ForgettingCurveUtils::MAX_BIGRAM_COUNT = 12000;
 const int ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC = 10000;
 
 const int ForgettingCurveUtils::MAX_COMPUTED_PROBABILITY = 127;
-const int ForgettingCurveUtils::MAX_ENCODED_PROBABILITY = 15;
-const int ForgettingCurveUtils::MIN_VALID_ENCODED_PROBABILITY = 3;
-const int ForgettingCurveUtils::ENCODED_PROBABILITY_STEP = 1;
-// Currently, we try to decay each uni/bigram once every 2 hours. Accordingly, the expected
-// duration of the decay is approximately 66hours.
-const float ForgettingCurveUtils::MIN_PROBABILITY_TO_DECAY = 0.03f;
 const int ForgettingCurveUtils::DECAY_INTERVAL_SECONDS = 2 * 60 * 60;
 
 const int ForgettingCurveUtils::MAX_LEVEL = 3;
@@ -53,9 +47,9 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
         const int newProbability, const int timestamp) {
     if (newProbability != NOT_A_PROBABILITY && originalHistoricalInfo->getLevel() == 0) {
         return HistoricalInfo(timestamp, MIN_VALID_LEVEL /* level */, 0 /* count */);
-    } else if (originalHistoricalInfo->getTimeStamp() == NOT_A_TIMESTAMP) {
+    } else if (!originalHistoricalInfo->isValid()) {
         // Initial information.
-        return HistoricalInfo(timestamp, 0 /* level */, 0 /* count */);
+        return HistoricalInfo(timestamp, 0 /* level */, 1 /* count */);
     } else {
         const int updatedCount = originalHistoricalInfo->getCount() + 1;
         if (updatedCount > MAX_COUNT) {
@@ -75,85 +69,46 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     }
 }
 
-/* static */ int ForgettingCurveUtils::getProbability(const int encodedUnigramProbability,
+/* static */ int ForgettingCurveUtils::decodeProbability(
-        const int encodedBigramProbability) {
+        const HistoricalInfo *const historicalInfo) {
-    if (encodedUnigramProbability == NOT_A_PROBABILITY) {
+    const int elapsedTimeStepCount = getElapsedTimeStepCount(historicalInfo->getTimeStamp());
+    return sProbabilityTable.getProbability(historicalInfo->getLevel(),
+            min(max(elapsedTimeStepCount, 0), MAX_ELAPSED_TIME_STEP_COUNT));
+}
+
+/* static */ int ForgettingCurveUtils::getProbability(const int unigramProbability,
+        const int bigramProbability) {
+    if (unigramProbability == NOT_A_PROBABILITY) {
         return NOT_A_PROBABILITY;
-    } else if (encodedBigramProbability == NOT_A_PROBABILITY) {
+    } else if (bigramProbability == NOT_A_PROBABILITY) {
-        return backoff(decodeProbability(encodedUnigramProbability));
+        return min(backoff(unigramProbability), MAX_COMPUTED_PROBABILITY);
     } else {
-        const int unigramProbability = decodeProbability(encodedUnigramProbability);
-        const int bigramProbability = decodeProbability(encodedBigramProbability);
         return min(max(unigramProbability, bigramProbability), MAX_COMPUTED_PROBABILITY);
     }
 }
 
-// Caveat: Unlike getProbability(), this method doesn't assume special bigram probability encoding
-// (i.e. unigram probability + bigram probability delta).
-/* static */ int ForgettingCurveUtils::getUpdatedEncodedProbability(
-        const int originalEncodedProbability, const int newProbability) {
-    if (originalEncodedProbability == NOT_A_PROBABILITY) {
-        // The bigram relation is not in this dictionary.
-        if (newProbability == NOT_A_PROBABILITY) {
-            // The bigram target is not in other dictionaries.
-            return 0;
-        } else {
-            return MIN_VALID_ENCODED_PROBABILITY;
-        }
-    } else {
-        if (newProbability != NOT_A_PROBABILITY
-                && originalEncodedProbability < MIN_VALID_ENCODED_PROBABILITY) {
-            return MIN_VALID_ENCODED_PROBABILITY;
-        }
-        return min(originalEncodedProbability + ENCODED_PROBABILITY_STEP, MAX_ENCODED_PROBABILITY);
-    }
-}
-
-/* static */ int ForgettingCurveUtils::isValidEncodedProbability(const int encodedProbability) {
-    return encodedProbability >= MIN_VALID_ENCODED_PROBABILITY;
-}
-
 /* static */ bool ForgettingCurveUtils::needsToKeep(const HistoricalInfo *const historicalInfo) {
     return historicalInfo->getLevel() > 0
             || getElapsedTimeStepCount(historicalInfo->getTimeStamp())
                     < DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
 }
 
-/* static */ int ForgettingCurveUtils::getEncodedProbabilityToSave(const int encodedProbability,
-        const DictionaryHeaderStructurePolicy *const headerPolicy) {
-    const int elapsedTime = TimeKeeper::peekCurrentTime() - headerPolicy->getLastDecayedTime();
-    const int decayIterationCount = max(elapsedTime / DECAY_INTERVAL_SECONDS, 1);
-    int currentEncodedProbability = max(min(encodedProbability, MAX_ENCODED_PROBABILITY), 0);
-    // TODO: Implement the decay in more proper way.
-    for (int i = 0; i < decayIterationCount; ++i) {
-        const float currentRate = static_cast<float>(currentEncodedProbability)
-                / static_cast<float>(MAX_ENCODED_PROBABILITY);
-        const float thresholdToDecay = (1.0f - MIN_PROBABILITY_TO_DECAY) * currentRate;
-        const float randValue = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
-        if (thresholdToDecay < randValue) {
-            currentEncodedProbability = max(currentEncodedProbability - ENCODED_PROBABILITY_STEP,
-                    0);
-        }
-    }
-    return currentEncodedProbability;
-}
-
 /* static */ const HistoricalInfo ForgettingCurveUtils::createHistoricalInfoToSave(
         const HistoricalInfo *const originalHistoricalInfo) {
     if (originalHistoricalInfo->getTimeStamp() == NOT_A_TIMESTAMP) {
         return HistoricalInfo();
     }
     const int elapsedTimeStep = getElapsedTimeStepCount(originalHistoricalInfo->getTimeStamp());
-    if (elapsedTimeStep < MAX_ELAPSED_TIME_STEP_COUNT) {
+    if (elapsedTimeStep <= MAX_ELAPSED_TIME_STEP_COUNT) {
         // No need to update historical info.
         return *originalHistoricalInfo;
     }
     // Level down.
-    const int maxLevelDownAmonut = elapsedTimeStep / MAX_ELAPSED_TIME_STEP_COUNT;
+    const int maxLevelDownAmonut = elapsedTimeStep / (MAX_ELAPSED_TIME_STEP_COUNT + 1);
     const int levelDownAmount = (maxLevelDownAmonut >= originalHistoricalInfo->getLevel()) ?
             originalHistoricalInfo->getLevel() : maxLevelDownAmonut;
     const int adjustedTimestamp = originalHistoricalInfo->getTimeStamp() +
-            levelDownAmount * MAX_ELAPSED_TIME_STEP_COUNT * TIME_STEP_DURATION_IN_SECONDS;
+            levelDownAmount * (MAX_ELAPSED_TIME_STEP_COUNT + 1) * TIME_STEP_DURATION_IN_SECONDS;
     return HistoricalInfo(adjustedTimestamp,
             originalHistoricalInfo->getLevel() - levelDownAmount, 0 /* count */);
 }
@@ -179,14 +134,6 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     return false;
 }
 
-/* static */ int ForgettingCurveUtils::decodeProbability(const int encodedProbability) {
-    if (encodedProbability < MIN_VALID_ENCODED_PROBABILITY) {
-        return NOT_A_PROBABILITY;
-    } else {
-        return min(sProbabilityTable.getProbability(encodedProbability), MAX_ENCODED_PROBABILITY);
-    }
-}
-
 // See comments in ProbabilityUtils::backoff().
 /* static */ int ForgettingCurveUtils::backoff(const int unigramProbability) {
     if (unigramProbability == NOT_A_PROBABILITY) {
@@ -201,14 +148,24 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
 }
 
 ForgettingCurveUtils::ProbabilityTable::ProbabilityTable() : mTable() {
-    // Table entry is as follows:
+    mTable.resize(MAX_LEVEL + 1);
-    // 1, 1, 1, 2, 3, 5, 6, 9, 13, 18, 25, 34, 48, 66, 91, 127.
+    for (int level = 0; level <= MAX_LEVEL; ++level) {
-    // Note that first MIN_VALID_ENCODED_PROBABILITY values are not used.
+        mTable[level].resize(MAX_ELAPSED_TIME_STEP_COUNT + 1);
-    mTable.resize(MAX_ENCODED_PROBABILITY + 1);
+        const float initialProbability =
-    for (int i = 0; i <= MAX_ENCODED_PROBABILITY; ++i) {
+                static_cast<float>(MAX_COMPUTED_PROBABILITY / (1 << (MAX_LEVEL - level)));
-        const int probability = static_cast<int>(powf(static_cast<float>(MAX_COMPUTED_PROBABILITY),
+        for (int timeStepCount = 0; timeStepCount <= MAX_ELAPSED_TIME_STEP_COUNT; ++timeStepCount) {
-                static_cast<float>(i) / static_cast<float>(MAX_ENCODED_PROBABILITY)));
+            if (level == 0) {
-         mTable[i] = min(MAX_COMPUTED_PROBABILITY, max(0, probability));
+                mTable[level][timeStepCount] = NOT_A_PROBABILITY;
+                continue;
+            }
+            const int elapsedTime = timeStepCount * TIME_STEP_DURATION_IN_SECONDS;
+            const float probability = initialProbability
+                    * powf(2.0f, -1.0f * static_cast<float>(elapsedTime)
+                            / static_cast<float>(TIME_STEP_DURATION_IN_SECONDS
+                                    * (MAX_ELAPSED_TIME_STEP_COUNT + 1)));
+            mTable[level][timeStepCount] =
+                    min(max(static_cast<int>(probability), 1), MAX_COMPUTED_PROBABILITY);
+        }
     }
 }
 

native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h

@@ -26,8 +26,6 @@ namespace latinime {
 
 class DictionaryHeaderStructurePolicy;
 
-// TODO: Check the elapsed time and decrease the probability depending on the time. Time field is
-// required to introduced to each terminal PtNode and bigram entry.
 // TODO: Quit using bigram probability to indicate the delta.
 class ForgettingCurveUtils {
  public:
@@ -43,22 +41,13 @@ class ForgettingCurveUtils {
     static const HistoricalInfo createHistoricalInfoToSave(
             const HistoricalInfo *const originalHistoricalInfo);
 
+    static int decodeProbability(const HistoricalInfo *const historicalInfo);
+
     static int getProbability(const int encodedUnigramProbability,
             const int encodedBigramProbability);
 
-    // TODO: Remove.
-    static int getUpdatedEncodedProbability(const int originalEncodedProbability,
-            const int newProbability);
-
-    // TODO: Remove.
-    static int isValidEncodedProbability(const int encodedProbability);
-
     static bool needsToKeep(const HistoricalInfo *const historicalInfo);
 
-    // TODO: Remove.
-    static int getEncodedProbabilityToSave(const int encodedProbability,
-            const DictionaryHeaderStructurePolicy *const headerPolicy);
-
     static bool needsToDecay(const bool mindsBlockByDecay, const int unigramCount,
             const int bigramCount, const DictionaryHeaderStructurePolicy *const headerPolicy);
 
@@ -69,24 +58,17 @@ class ForgettingCurveUtils {
      public:
         ProbabilityTable();
 
-        int getProbability(const int encodedProbability) const {
+        int getProbability(const int level, const int elapsedTimeStepCount) const {
-            if (encodedProbability < 0 || encodedProbability > static_cast<int>(mTable.size())) {
+            return mTable[level][elapsedTimeStepCount];
-                return NOT_A_PROBABILITY;
-            }
-            return mTable[encodedProbability];
         }
 
      private:
         DISALLOW_COPY_AND_ASSIGN(ProbabilityTable);
 
-        std::vector<int> mTable;
+        std::vector<std::vector<int> > mTable;
     };
 
     static const int MAX_COMPUTED_PROBABILITY;
-    static const int MAX_ENCODED_PROBABILITY;
-    static const int MIN_VALID_ENCODED_PROBABILITY;
-    static const int ENCODED_PROBABILITY_STEP;
-    static const float MIN_PROBABILITY_TO_DECAY;
     static const int DECAY_INTERVAL_SECONDS;
 
     static const int MAX_LEVEL;
@@ -95,11 +77,10 @@ class ForgettingCurveUtils {
     static const int TIME_STEP_DURATION_IN_SECONDS;
     static const int MAX_ELAPSED_TIME_STEP_COUNT;
     static const int DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
+    static const int HALF_LIFE_TIME_IN_SECONDS;
 
     static const ProbabilityTable sProbabilityTable;
 
-    static int decodeProbability(const int encodedProbability);
-
     static int backoff(const int unigramProbability);
 
     static int getElapsedTimeStepCount(const int timestamp);

native/jni/src/suggest/policyimpl/dictionary/utils/historical_info.h

@@ -30,6 +30,10 @@ class HistoricalInfo {
     HistoricalInfo(const int timestamp, const int level, const int count)
             : mTimestamp(timestamp), mLevel(level), mCount(count) {}
 
+    bool isValid() const {
+        return mTimestamp != NOT_A_TIMESTAMP;
+    }
+
     int getTimeStamp() const {
         return mTimestamp;
     }

tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java

@@ -30,6 +30,7 @@ import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Random;
+import java.util.concurrent.TimeUnit;
 
 @LargeTest
 public class BinaryDictionaryDecayingTests extends AndroidTestCase {
@@ -38,8 +39,6 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
 
     // Note that these are corresponding definitions in native code in
     // latinime::Ver4PatriciaTriePolicy.
-    private static final String SET_NEEDS_TO_DECAY_FOR_TESTING_KEY =
-            "SET_NEEDS_TO_DECAY_FOR_TESTING";
     private static final String SET_CURRENT_TIME_FOR_TESTING_QUERY =
             "SET_CURRENT_TIME_FOR_TESTING";
     private static final String GET_CURRENT_TIME_QUERY = "GET_CURRENT_TIME";
@@ -47,14 +46,28 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
 
     private static final int DUMMY_PROBABILITY = 0;
 
+    private int mCurrentTime = 0;
+
     @Override
     protected void setUp() throws Exception {
         super.setUp();
+        mCurrentTime = 0;
     }
 
     @Override
     protected void tearDown() throws Exception {
         super.tearDown();
+        try {
+            final File dictFile =
+                    createEmptyDictionaryAndGetFile("TestBinaryDictionary", FormatSpec.VERSION4);
+            final BinaryDictionary binaryDictionary =
+                    new BinaryDictionary(dictFile.getAbsolutePath(), 0 /* offset */,
+                            dictFile.length(), true /* useFullEditDistance */, Locale.getDefault(),
+                            TEST_LOCALE, true /* isUpdatable */);
+            binaryDictionary.getPropertyForTests(QUIT_TIMEKEEPER_TEST_MODE_QUERY);
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
     }
 
     private void addUnigramWord(final BinaryDictionary binaryDictionary, final String word,
@@ -62,32 +75,29 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
         binaryDictionary.addUnigramWord(word, probability, "" /* shortcutTarget */,
                 BinaryDictionary.NOT_A_PROBABILITY /* shortcutProbability */,
                 false /* isNotAWord */, false /* isBlacklisted */,
-                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+                mCurrentTime /* timestamp */);
     }
 
     private void addBigramWords(final BinaryDictionary binaryDictionary, final String word0,
             final String word1, final int probability) {
         binaryDictionary.addBigramWords(word0, word1, probability,
-                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+                mCurrentTime /* timestamp */);
     }
 
     private void forcePassingShortTime(final BinaryDictionary binaryDictionary) {
-        // Entries having low probability would be suppressed once in 3 GCs.
+        // 4 days.
-        final int count = 3;
+        final int timeToElapse = (int)TimeUnit.SECONDS.convert(4, TimeUnit.DAYS);
-        for (int i = 0; i < count; i++) {
+        mCurrentTime += timeToElapse;
-            binaryDictionary.getPropertyForTests(SET_NEEDS_TO_DECAY_FOR_TESTING_KEY);
+        setCurrentTime(binaryDictionary, mCurrentTime);
-            binaryDictionary.flushWithGC();
+        binaryDictionary.flushWithGC();
-        }
     }
 
     private void forcePassingLongTime(final BinaryDictionary binaryDictionary) {
-        // Currently, probabilities are decayed when GC is run. All entries that have never been
+        // 60 days.
-        // typed in 128 GCs would be removed.
+        final int timeToElapse = (int)TimeUnit.SECONDS.convert(60, TimeUnit.DAYS);
-        final int count = 128;
+        mCurrentTime += timeToElapse;
-        for (int i = 0; i < count; i++) {
+        setCurrentTime(binaryDictionary, mCurrentTime);
-            binaryDictionary.getPropertyForTests(SET_NEEDS_TO_DECAY_FOR_TESTING_KEY);
+        binaryDictionary.flushWithGC();
-            binaryDictionary.flushWithGC();
-        }
     }
 
     private File createEmptyDictionaryAndGetFile(final String dictId,
@@ -147,6 +157,7 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
         BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
                 0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
                 Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+        binaryDictionary.getPropertyForTests(QUIT_TIMEKEEPER_TEST_MODE_QUERY);
         final int startTime = getCurrentTime(binaryDictionary);
         for (int i = 0; i < TEST_COUNT; i++) {
             final int currentTime = random.nextInt(Integer.MAX_VALUE);
@@ -233,6 +244,8 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
         addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
         addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
         addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
+        addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidWord("a"));
         forcePassingShortTime(binaryDictionary);
         assertTrue(binaryDictionary.isValidWord("a"));
         forcePassingLongTime(binaryDictionary);
@@ -257,6 +270,9 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
         addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
         addUnigramWord(binaryDictionary, "b", DUMMY_PROBABILITY);
         addBigramWords(binaryDictionary, "a", "b", DUMMY_PROBABILITY);
+        addUnigramWord(binaryDictionary, "a", DUMMY_PROBABILITY);
+        addUnigramWord(binaryDictionary, "b", DUMMY_PROBABILITY);
+        addBigramWords(binaryDictionary, "a", "b", DUMMY_PROBABILITY);
         assertTrue(binaryDictionary.isValidBigram("a", "b"));
         forcePassingShortTime(binaryDictionary);
         assertTrue(binaryDictionary.isValidBigram("a", "b"));
@@ -307,8 +323,7 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
                         Integer.parseInt(binaryDictionary.getPropertyForTests(
                                 BinaryDictionary.UNIGRAM_COUNT_QUERY));
                 while (binaryDictionary.needsToRunGC(true /* mindsBlockByGC */)) {
-                    binaryDictionary.getPropertyForTests(SET_NEEDS_TO_DECAY_FOR_TESTING_KEY);
+                    forcePassingShortTime(binaryDictionary);
-                    binaryDictionary.flushWithGC();
                 }
                 final int unigramCountAfterGC =
                         Integer.parseInt(binaryDictionary.getPropertyForTests(
@@ -321,6 +336,10 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
                 BinaryDictionary.UNIGRAM_COUNT_QUERY)) > 0);
         assertTrue(Integer.parseInt(binaryDictionary.getPropertyForTests(
                 BinaryDictionary.UNIGRAM_COUNT_QUERY)) <= maxUnigramCount);
+        forcePassingLongTime(binaryDictionary);
+        assertEquals(0, Integer.parseInt(binaryDictionary.getPropertyForTests(
+                BinaryDictionary.UNIGRAM_COUNT_QUERY)));
+
     }
 
     public void testAddManyBigramsToDecayingDict() {
@@ -378,8 +397,7 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
                         Integer.parseInt(binaryDictionary.getPropertyForTests(
                                 BinaryDictionary.BIGRAM_COUNT_QUERY));
                 while (binaryDictionary.needsToRunGC(true /* mindsBlockByGC */)) {
-                    binaryDictionary.getPropertyForTests(SET_NEEDS_TO_DECAY_FOR_TESTING_KEY);
+                    forcePassingShortTime(binaryDictionary);
-                    binaryDictionary.flushWithGC();
                 }
                 final int bigramCountAfterGC =
                         Integer.parseInt(binaryDictionary.getPropertyForTests(
@@ -392,5 +410,8 @@ public class BinaryDictionaryDecayingTests extends AndroidTestCase {
                 BinaryDictionary.BIGRAM_COUNT_QUERY)) > 0);
         assertTrue(Integer.parseInt(binaryDictionary.getPropertyForTests(
                 BinaryDictionary.BIGRAM_COUNT_QUERY)) <= maxBigramCount);
+        forcePassingLongTime(binaryDictionary);
+        assertEquals(0, Integer.parseInt(binaryDictionary.getPropertyForTests(
+                BinaryDictionary.BIGRAM_COUNT_QUERY)));
     }
 }