Add header attributes for evaluation.

Bug: 13197276
Change-Id: Ib5247da691ff24a73e13485288237ccc51bb54f0

10 files changed, 119 insertions, 48 deletions

diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index b18951500..26545acbd 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -64,6 +64,9 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
     private static final int TIMEOUT_FOR_READ_OPS_IN_MILLISECONDS = 100;
     private static final int TIMEOUT_FOR_READ_OPS_FOR_TESTS_IN_MILLISECONDS = 10000;
 
+    private static final int DEFAULT_MAX_UNIGRAM_COUNT = 10000;
+    private static final int DEFAULT_MAX_BIGRAM_COUNT = 10000;
+
     /**
      * The maximum length of a word in this dictionary.
      */
@@ -207,6 +210,10 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
         attributeMap.put(DictionaryHeader.DICTIONARY_LOCALE_KEY, mLocale.toString());
         attributeMap.put(DictionaryHeader.DICTIONARY_VERSION_KEY,
                 String.valueOf(TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis())));
+        attributeMap.put(DictionaryHeader.MAX_UNIGRAM_COUNT_KEY,
+                String.valueOf(DEFAULT_MAX_UNIGRAM_COUNT));
+        attributeMap.put(DictionaryHeader.MAX_BIGRAM_COUNT_KEY,
+                String.valueOf(DEFAULT_MAX_BIGRAM_COUNT));
         return attributeMap;
     }
 
diff --git a/java/src/com/android/inputmethod/latin/makedict/DictionaryHeader.java b/java/src/com/android/inputmethod/latin/makedict/DictionaryHeader.java
index ed9c39602..b32eb9195 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DictionaryHeader.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DictionaryHeader.java
@@ -42,6 +42,10 @@ public final class DictionaryHeader {
             "FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP";
     public static final String FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID_KEY =
             "FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID";
+    public static final String FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS_KEY =
+            "FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS";
+    public static final String MAX_UNIGRAM_COUNT_KEY = "MAX_UNIGRAM_COUNT";
+    public static final String MAX_BIGRAM_COUNT_KEY = "MAX_BIGRAM_COUNT";
     public static final String ATTRIBUTE_VALUE_TRUE = "1";
 
     public DictionaryHeader(final int headerSize, final DictionaryOptions dictionaryOptions,
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 7f916677a..5df2096a4 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
@@ -162,7 +162,7 @@ bool Ver4BigramListPolicy::updateAllBigramEntriesAndDeleteUselessEntries(const i
         } else if (bigramEntry.hasHistoricalInfo()) {
             const HistoricalInfo historicalInfo = ForgettingCurveUtils::createHistoricalInfoToSave(
                     bigramEntry.getHistoricalInfo(), mHeaderPolicy);
-            if (ForgettingCurveUtils::needsToKeep(&historicalInfo)) {
+            if (ForgettingCurveUtils::needsToKeep(&historicalInfo, mHeaderPolicy)) {
                 const BigramEntry updatedBigramEntry =
                         bigramEntry.updateHistoricalInfoAndGetEntry(&historicalInfo);
                 if (!mBigramDictContent->writeBigramEntry(&updatedBigramEntry, entryPos)) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
index 2ac417b33..7c7b05ca8 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
@@ -37,11 +37,22 @@ const char *const HeaderPolicy::FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP_KEY =
         "FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP";
 const char *const HeaderPolicy::FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID_KEY =
         "FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID";
+const char *const HeaderPolicy::FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS_KEY =
+        "FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS";
+
+const char *const HeaderPolicy::MAX_UNIGRAM_COUNT_KEY = "MAX_UNIGRAM_COUNT";
+const char *const HeaderPolicy::MAX_BIGRAM_COUNT_KEY = "MAX_BIGRAM_COUNT";
 
 const int HeaderPolicy::DEFAULT_MULTIPLE_WORDS_DEMOTION_RATE = 100;
 const float HeaderPolicy::MULTIPLE_WORD_COST_MULTIPLIER_SCALE = 100.0f;
 const int HeaderPolicy::DEFAULT_FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP = 4;
 const int HeaderPolicy::DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID = 0;
+// 4 days
+const int HeaderPolicy::DEFAULT_FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS =
+        4 * 24 * 60 * 60;
+
+const int HeaderPolicy::DEFAULT_MAX_UNIGRAM_COUNT = 10000;
+const int HeaderPolicy::DEFAULT_MAX_BIGRAM_COUNT = 10000;
 
 // Used for logging. Question mark is used to indicate that the key is not found.
 void HeaderPolicy::readHeaderValueOrQuestionMark(const char *const key, int *outValue,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
index 8fa7e168c..66824245e 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
@@ -58,7 +58,14 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
                       DEFAULT_FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP)),
               mForgettingCurveProbabilityValuesTableId(HeaderReadWriteUtils::readIntAttributeValue(
                       &mAttributeMap, FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID_KEY,
-                      DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID)) {}
+                      DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID)),
+              mForgettingCurveDurationToLevelDown(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS_KEY,
+                      DEFAULT_FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS)),
+              mMaxUnigramCount(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, MAX_UNIGRAM_COUNT_KEY, DEFAULT_MAX_UNIGRAM_COUNT)),
+              mMaxBigramCount(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, MAX_BIGRAM_COUNT_KEY, DEFAULT_MAX_BIGRAM_COUNT)) {}
 
     // Constructs header information using an attribute map.
     HeaderPolicy(const FormatUtils::FORMAT_VERSION dictFormatVersion,
@@ -83,7 +90,14 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
                       DEFAULT_FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP)),
               mForgettingCurveProbabilityValuesTableId(HeaderReadWriteUtils::readIntAttributeValue(
                       &mAttributeMap, FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID_KEY,
-                      DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID)) {}
+                      DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID)),
+              mForgettingCurveDurationToLevelDown(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS_KEY,
+                      DEFAULT_FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS)),
+              mMaxUnigramCount(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, MAX_UNIGRAM_COUNT_KEY, DEFAULT_MAX_UNIGRAM_COUNT)),
+              mMaxBigramCount(HeaderReadWriteUtils::readIntAttributeValue(
+                      &mAttributeMap, MAX_BIGRAM_COUNT_KEY, DEFAULT_MAX_BIGRAM_COUNT)) {}
 
     // Temporary dummy header.
     HeaderPolicy()
@@ -92,7 +106,8 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
               mRequiresGermanUmlautProcessing(false), mIsDecayingDict(false),
               mDate(0), mLastDecayedTime(0), mUnigramCount(0), mBigramCount(0),
               mExtendedRegionSize(0), mHasHistoricalInfoOfWords(false),
-              mForgettingCurveOccurrencesToLevelUp(0), mForgettingCurveProbabilityValuesTableId(0) {}
+              mForgettingCurveOccurrencesToLevelUp(0), mForgettingCurveProbabilityValuesTableId(0),
+              mForgettingCurveDurationToLevelDown(0), mMaxUnigramCount(0), mMaxBigramCount(0) {}
 
     ~HeaderPolicy() {}
 
@@ -179,6 +194,18 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
         return mForgettingCurveProbabilityValuesTableId;
     }
 
+    AK_FORCE_INLINE int getForgettingCurveDurationToLevelDown() const {
+        return mForgettingCurveDurationToLevelDown;
+    }
+
+    AK_FORCE_INLINE int getMaxUnigramCount() const {
+        return mMaxUnigramCount;
+    }
+
+    AK_FORCE_INLINE int getMaxBigramCount() const {
+        return mMaxBigramCount;
+    }
+
     void readHeaderValueOrQuestionMark(const char *const key,
             int *outValue, int outValueSize) const;
 
@@ -205,10 +232,16 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
     static const char *const LOCALE_KEY;
     static const char *const FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP_KEY;
     static const char *const FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID_KEY;
+    static const char *const FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS_KEY;
+    static const char *const MAX_UNIGRAM_COUNT_KEY;
+    static const char *const MAX_BIGRAM_COUNT_KEY;
     static const int DEFAULT_MULTIPLE_WORDS_DEMOTION_RATE;
     static const float MULTIPLE_WORD_COST_MULTIPLIER_SCALE;
     static const int DEFAULT_FORGETTING_CURVE_OCCURRENCES_TO_LEVEL_UP;
     static const int DEFAULT_FORGETTING_CURVE_PROBABILITY_VALUES_TABLE_ID;
+    static const int DEFAULT_FORGETTING_CURVE_DURATION_TO_LEVEL_DOWN_IN_SECONDS;
+    static const int DEFAULT_MAX_UNIGRAM_COUNT;
+    static const int DEFAULT_MAX_BIGRAM_COUNT;
 
     const FormatUtils::FORMAT_VERSION mDictFormatVersion;
     const HeaderReadWriteUtils::DictionaryFlags mDictionaryFlags;
@@ -226,6 +259,9 @@ class HeaderPolicy : public DictionaryHeaderStructurePolicy {
     const bool mHasHistoricalInfoOfWords;
     const int mForgettingCurveOccurrencesToLevelUp;
     const int mForgettingCurveProbabilityValuesTableId;
+    const int mForgettingCurveDurationToLevelDown;
+    const int mMaxUnigramCount;
+    const int mMaxBigramCount;
 
     const std::vector<int> readLocale() const;
     float readMultipleWordCostMultiplier() const;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
index 13ae9d923..f24c2e1af 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
@@ -168,7 +168,7 @@ bool Ver4PatriciaTrieNodeWriter::updatePtNodeProbabilityAndGetNeedsToKeepPtNodeA
                     toBeUpdatedPtNodeParams->getTerminalId());
             return false;
         }
-        const bool isValid = ForgettingCurveUtils::needsToKeep(&historicalInfo);
+        const bool isValid = ForgettingCurveUtils::needsToKeep(&historicalInfo, mHeaderPolicy);
         if (!isValid) {
             if (!markPtNodeAsWillBecomeNonTerminal(toBeUpdatedPtNodeParams)) {
                 AKLOGE("Cannot mark PtNode as willBecomeNonTerminal.");
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
index 197250ff3..4d1b0dadb 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
@@ -329,11 +329,15 @@ void Ver4PatriciaTriePolicy::getProperty(const char *const query, const int quer
         snprintf(outResult, maxResultLength, "%d", mBigramCount);
     } else if (strncmp(query, MAX_UNIGRAM_COUNT_QUERY, compareLength) == 0) {
         snprintf(outResult, maxResultLength, "%d",
-                mHeaderPolicy->isDecayingDict() ? ForgettingCurveUtils::MAX_UNIGRAM_COUNT :
+                mHeaderPolicy->isDecayingDict() ?
+                        ForgettingCurveUtils::getUnigramCountHardLimit(
+                                mHeaderPolicy->getMaxUnigramCount()) :
                         static_cast<int>(Ver4DictConstants::MAX_DICTIONARY_SIZE));
     } else if (strncmp(query, MAX_BIGRAM_COUNT_QUERY, compareLength) == 0) {
         snprintf(outResult, maxResultLength, "%d",
-                mHeaderPolicy->isDecayingDict() ? ForgettingCurveUtils::MAX_BIGRAM_COUNT :
+                mHeaderPolicy->isDecayingDict() ?
+                        ForgettingCurveUtils::getBigramCountHardLimit(
+                                mHeaderPolicy->getMaxBigramCount()) :
                         static_cast<int>(Ver4DictConstants::MAX_DICTIONARY_SIZE));
     }
 }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp
index 2da295054..3907c84a0 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp
@@ -96,12 +96,11 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
     }
     const int unigramCount = traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
             .getValidUnigramCount();
-    if (headerPolicy->isDecayingDict()
-            && unigramCount > ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC) {
-        if (!truncateUnigrams(&ptNodeReader, &ptNodeWriter,
-                ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC)) {
+    const int maxUnigramCount = headerPolicy->getMaxUnigramCount();
+    if (headerPolicy->isDecayingDict() && unigramCount > maxUnigramCount) {
+        if (!truncateUnigrams(&ptNodeReader, &ptNodeWriter, maxUnigramCount)) {
             AKLOGE("Cannot remove unigrams. current: %d, max: %d", unigramCount,
-                    ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC);
+                    maxUnigramCount);
             return false;
         }
     }
@@ -114,11 +113,10 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
         return false;
     }
     const int bigramCount = traversePolicyToUpdateBigramProbability.getValidBigramEntryCount();
-    if (headerPolicy->isDecayingDict()
-            && bigramCount > ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC) {
-        if (!truncateBigrams(ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC)) {
-            AKLOGE("Cannot remove bigrams. current: %d, max: %d", bigramCount,
-                    ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC);
+    const int maxBigramCount = headerPolicy->getMaxBigramCount();
+    if (headerPolicy->isDecayingDict() && bigramCount > maxBigramCount) {
+        if (!truncateBigrams(maxBigramCount)) {
+            AKLOGE("Cannot remove bigrams. current: %d, max: %d", bigramCount, maxBigramCount);
             return false;
         }
     }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
index 51b0eb23f..35e05d77a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
@@ -25,20 +25,17 @@
 
 namespace latinime {
 
-const int ForgettingCurveUtils::MAX_UNIGRAM_COUNT = 12000;
-const int ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC = 10000;
-const int ForgettingCurveUtils::MAX_BIGRAM_COUNT = 12000;
-const int ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC = 10000;
-
 const int ForgettingCurveUtils::MULTIPLIER_TWO_IN_PROBABILITY_SCALE = 8;
 const int ForgettingCurveUtils::DECAY_INTERVAL_SECONDS = 2 * 60 * 60;
 
 const int ForgettingCurveUtils::MAX_LEVEL = 3;
 const int ForgettingCurveUtils::MIN_VALID_LEVEL = 1;
-const int ForgettingCurveUtils::TIME_STEP_DURATION_IN_SECONDS = 6 * 60 * 60;
 const int ForgettingCurveUtils::MAX_ELAPSED_TIME_STEP_COUNT = 15;
 const int ForgettingCurveUtils::DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD = 14;
 
+const float ForgettingCurveUtils::UNIGRAM_COUNT_HARD_LIMIT_WEIGHT = 1.2;
+const float ForgettingCurveUtils::BIGRAM_COUNT_HARD_LIMIT_WEIGHT = 1.2;
+
 const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityTable;
 
 // TODO: Revise the logic to decide the initial probability depending on the given probability.
@@ -71,7 +68,8 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
 
 /* static */ int ForgettingCurveUtils::decodeProbability(
         const HistoricalInfo *const historicalInfo, const HeaderPolicy *const headerPolicy) {
-    const int elapsedTimeStepCount = getElapsedTimeStepCount(historicalInfo->getTimeStamp());
+    const int elapsedTimeStepCount = getElapsedTimeStepCount(historicalInfo->getTimeStamp(),
+            headerPolicy->getForgettingCurveDurationToLevelDown());
     return sProbabilityTable.getProbability(
             headerPolicy->getForgettingCurveProbabilityValuesTableId(), historicalInfo->getLevel(),
             min(max(elapsedTimeStepCount, 0), MAX_ELAPSED_TIME_STEP_COUNT));
@@ -90,10 +88,12 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     }
 }
 
-/* static */ bool ForgettingCurveUtils::needsToKeep(const HistoricalInfo *const historicalInfo) {
+/* static */ bool ForgettingCurveUtils::needsToKeep(const HistoricalInfo *const historicalInfo,
+        const HeaderPolicy *const headerPolicy) {
     return historicalInfo->getLevel() > 0
-            || getElapsedTimeStepCount(historicalInfo->getTimeStamp())
-                    < DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
+            || getElapsedTimeStepCount(historicalInfo->getTimeStamp(),
+                    headerPolicy->getForgettingCurveDurationToLevelDown())
+                            < DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
 }
 
 /* static */ const HistoricalInfo ForgettingCurveUtils::createHistoricalInfoToSave(
@@ -102,7 +102,9 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     if (originalHistoricalInfo->getTimeStamp() == NOT_A_TIMESTAMP) {
         return HistoricalInfo();
     }
-    const int elapsedTimeStep = getElapsedTimeStepCount(originalHistoricalInfo->getTimeStamp());
+    const int durationToLevelDownInSeconds = headerPolicy->getForgettingCurveDurationToLevelDown();
+    const int elapsedTimeStep = getElapsedTimeStepCount(
+            originalHistoricalInfo->getTimeStamp(), durationToLevelDownInSeconds);
     if (elapsedTimeStep <= MAX_ELAPSED_TIME_STEP_COUNT) {
         // No need to update historical info.
         return *originalHistoricalInfo;
@@ -111,18 +113,18 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     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 + 1) * TIME_STEP_DURATION_IN_SECONDS;
-    return HistoricalInfo(adjustedTimestamp,
+    const int adjustedTimestampInSeconds = originalHistoricalInfo->getTimeStamp() +
+            levelDownAmount * durationToLevelDownInSeconds;
+    return HistoricalInfo(adjustedTimestampInSeconds,
             originalHistoricalInfo->getLevel() - levelDownAmount, 0 /* count */);
 }
 
 /* static */ bool ForgettingCurveUtils::needsToDecay(const bool mindsBlockByDecay,
         const int unigramCount, const int bigramCount, const HeaderPolicy *const headerPolicy) {
-    if (unigramCount >= ForgettingCurveUtils::MAX_UNIGRAM_COUNT) {
+    if (unigramCount >= getUnigramCountHardLimit(headerPolicy->getMaxUnigramCount())) {
         // Unigram count exceeds the limit.
         return true;
-    } else if (bigramCount >= ForgettingCurveUtils::MAX_BIGRAM_COUNT) {
+    } else if (bigramCount >= getBigramCountHardLimit(headerPolicy->getMaxBigramCount())) {
         // Bigram count exceeds the limit.
         return true;
     }
@@ -143,8 +145,12 @@ const ForgettingCurveUtils::ProbabilityTable ForgettingCurveUtils::sProbabilityT
     return unigramProbability;
 }
 
-/* static */ int ForgettingCurveUtils::getElapsedTimeStepCount(const int timestamp) {
-    return (TimeKeeper::peekCurrentTime() - timestamp) / TIME_STEP_DURATION_IN_SECONDS;
+/* static */ int ForgettingCurveUtils::getElapsedTimeStepCount(const int timestamp,
+        const int durationToLevelDownInSeconds) {
+    const int elapsedTimeInSeconds = TimeKeeper::peekCurrentTime() - timestamp;
+    const int timeStepDurationInSeconds =
+            durationToLevelDownInSeconds / (MAX_ELAPSED_TIME_STEP_COUNT + 1);
+    return elapsedTimeInSeconds / timeStepDurationInSeconds;
 }
 
 const int ForgettingCurveUtils::ProbabilityTable::PROBABILITY_TABLE_COUNT = 4;
@@ -172,12 +178,10 @@ ForgettingCurveUtils::ProbabilityTable::ProbabilityTable() : mTables() {
                     mTables[tableId][level][timeStepCount] = NOT_A_PROBABILITY;
                     continue;
                 }
-                const int elapsedTime = timeStepCount * TIME_STEP_DURATION_IN_SECONDS;
                 const float probability = initialProbability
                         * powf(initialProbability / endProbability,
-                                -1.0f * static_cast<float>(elapsedTime)
-                                        / static_cast<float>(TIME_STEP_DURATION_IN_SECONDS
-                                                * (MAX_ELAPSED_TIME_STEP_COUNT + 1)));
+                                -1.0f * static_cast<float>(timeStepCount)
+                                        / static_cast<float>(MAX_ELAPSED_TIME_STEP_COUNT + 1));
                 mTables[tableId][level][timeStepCount] =
                         min(max(static_cast<int>(probability), 1), MAX_PROBABILITY);
             }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
index 1a285e573..bb8690939 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
@@ -28,11 +28,6 @@ class HeaderPolicy;
 
 class ForgettingCurveUtils {
  public:
-    static const int MAX_UNIGRAM_COUNT;
-    static const int MAX_UNIGRAM_COUNT_AFTER_GC;
-    static const int MAX_BIGRAM_COUNT;
-    static const int MAX_BIGRAM_COUNT_AFTER_GC;
-
     static const HistoricalInfo createUpdatedHistoricalInfo(
             const HistoricalInfo *const originalHistoricalInfo, const int newProbability,
             const int timestamp, const HeaderPolicy *const headerPolicy);
@@ -47,11 +42,22 @@ class ForgettingCurveUtils {
     static int getProbability(const int encodedUnigramProbability,
             const int encodedBigramProbability);
 
-    static bool needsToKeep(const HistoricalInfo *const historicalInfo);
+    static bool needsToKeep(const HistoricalInfo *const historicalInfo,
+            const HeaderPolicy *const headerPolicy);
 
     static bool needsToDecay(const bool mindsBlockByDecay, const int unigramCount,
             const int bigramCount, const HeaderPolicy *const headerPolicy);
 
+    AK_FORCE_INLINE static int getUnigramCountHardLimit(const int maxUnigramCount) {
+        return static_cast<int>(static_cast<float>(maxUnigramCount)
+                * UNIGRAM_COUNT_HARD_LIMIT_WEIGHT);
+    }
+
+    AK_FORCE_INLINE static int getBigramCountHardLimit(const int maxBigramCount) {
+        return static_cast<int>(static_cast<float>(maxBigramCount)
+                * BIGRAM_COUNT_HARD_LIMIT_WEIGHT);
+    }
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(ForgettingCurveUtils);
 
@@ -88,16 +94,17 @@ class ForgettingCurveUtils {
 
     static const int MAX_LEVEL;
     static const int MIN_VALID_LEVEL;
-    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 float UNIGRAM_COUNT_HARD_LIMIT_WEIGHT;
+    static const float BIGRAM_COUNT_HARD_LIMIT_WEIGHT;
 
     static const ProbabilityTable sProbabilityTable;
 
     static int backoff(const int unigramProbability);
 
-    static int getElapsedTimeStepCount(const int timestamp);
+    static int getElapsedTimeStepCount(const int timestamp, const int durationToLevelDown);
 };
 } // namespace latinime
 #endif /* LATINIME_FORGETTING_CURVE_UTILS_H */