1 files changed, 112 insertions, 0 deletions
diff --git a/native/jni/src/dictionary/utils/forgetting_curve_utils.h b/native/jni/src/dictionary/utils/forgetting_curve_utils.h
new file mode 100644
index 000000000..ddaac7e3b
--- /dev/null
+++ b/native/jni/src/dictionary/utils/forgetting_curve_utils.h
@@ -0,0 +1,112 @@
+/*
+ * 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_FORGETTING_CURVE_UTILS_H
+#define LATINIME_FORGETTING_CURVE_UTILS_H
+
+#include <vector>
+
+#include "defines.h"
+#include "dictionary/property/historical_info.h"
+#include "dictionary/utils/entry_counters.h"
+
+namespace latinime {
+
+class HeaderPolicy;
+
+class ForgettingCurveUtils {
+ public:
+    static const HistoricalInfo createUpdatedHistoricalInfo(
+            const HistoricalInfo *const originalHistoricalInfo, const int newProbability,
+            const HistoricalInfo *const newHistoricalInfo, const HeaderPolicy *const headerPolicy);
+
+    static const HistoricalInfo createHistoricalInfoToSave(
+            const HistoricalInfo *const originalHistoricalInfo,
+            const HeaderPolicy *const headerPolicy);
+
+    static int decodeProbability(const HistoricalInfo *const historicalInfo,
+            const HeaderPolicy *const headerPolicy);
+
+    static bool needsToKeep(const HistoricalInfo *const historicalInfo,
+            const HeaderPolicy *const headerPolicy);
+
+    static bool needsToDecay(const bool mindsBlockByDecay, const EntryCounts &entryCounters,
+            const HeaderPolicy *const headerPolicy);
+
+    // TODO: Improve probability computation method and remove this.
+    static int getProbabilityBiasForNgram(const int n) {
+        return (n - 1) * MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
+    }
+
+    AK_FORCE_INLINE static int getEntryCountHardLimit(const int maxEntryCount) {
+        return static_cast<int>(static_cast<float>(maxEntryCount)
+                * ENTRY_COUNT_HARD_LIMIT_WEIGHT);
+    }
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(ForgettingCurveUtils);
+
+    class ProbabilityTable {
+     public:
+        ProbabilityTable();
+
+        int getProbability(const int tableId, const int level,
+                const int elapsedTimeStepCount) const {
+            return mTables[tableId][level][elapsedTimeStepCount];
+        }
+
+     private:
+        DISALLOW_COPY_AND_ASSIGN(ProbabilityTable);
+
+        static const int PROBABILITY_TABLE_COUNT;
+        static const int WEAK_PROBABILITY_TABLE_ID;
+        static const int MODEST_PROBABILITY_TABLE_ID;
+        static const int STRONG_PROBABILITY_TABLE_ID;
+        static const int AGGRESSIVE_PROBABILITY_TABLE_ID;
+
+        static const int WEAK_MAX_PROBABILITY;
+        static const int MODEST_BASE_PROBABILITY;
+        static const int STRONG_BASE_PROBABILITY;
+        static const int AGGRESSIVE_BASE_PROBABILITY;
+
+        std::vector<std::vector<std::vector<int>>> mTables;
+
+        static int getBaseProbabilityForLevel(const int tableId, const int level);
+    };
+
+    static const int MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
+    static const int DECAY_INTERVAL_SECONDS;
+
+    static const int MAX_LEVEL;
+    static const int MIN_VISIBLE_LEVEL;
+    static const int MAX_ELAPSED_TIME_STEP_COUNT;
+    static const int DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
+    static const int OCCURRENCES_TO_RAISE_THE_LEVEL;
+    static const int DURATION_TO_LOWER_THE_LEVEL_IN_SECONDS;
+
+    static const float ENTRY_COUNT_HARD_LIMIT_WEIGHT;
+
+    static const ProbabilityTable sProbabilityTable;
+
+    static int backoff(const int unigramProbability);
+    static int getElapsedTimeStepCount(const int timestamp, const int durationToLevelDown);
+    static int clampToVisibleEntryLevelRange(const int level);
+    static int clampToValidLevelRange(const int level);
+    static int clampToValidCountRange(const int count, const HeaderPolicy *const headerPolicy);
+    static int clampToValidTimeStepCountRange(const int timeStepCount);
+};
+} // namespace latinime
+#endif /* LATINIME_FORGETTING_CURVE_UTILS_H */