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      1 /*
      2  * Copyright (C) 2013, The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *     http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef LATINIME_FORGETTING_CURVE_UTILS_H
     18 #define LATINIME_FORGETTING_CURVE_UTILS_H
     19 
     20 #include <vector>
     21 
     22 #include "defines.h"
     23 #include "dictionary/property/historical_info.h"
     24 #include "dictionary/utils/entry_counters.h"
     25 
     26 namespace latinime {
     27 
     28 class HeaderPolicy;
     29 
     30 class ForgettingCurveUtils {
     31  public:
     32     static const HistoricalInfo createUpdatedHistoricalInfo(
     33             const HistoricalInfo *const originalHistoricalInfo, const int newProbability,
     34             const HistoricalInfo *const newHistoricalInfo, const HeaderPolicy *const headerPolicy);
     35 
     36     static const HistoricalInfo createHistoricalInfoToSave(
     37             const HistoricalInfo *const originalHistoricalInfo,
     38             const HeaderPolicy *const headerPolicy);
     39 
     40     static int decodeProbability(const HistoricalInfo *const historicalInfo,
     41             const HeaderPolicy *const headerPolicy);
     42 
     43     static bool needsToKeep(const HistoricalInfo *const historicalInfo,
     44             const HeaderPolicy *const headerPolicy);
     45 
     46     static bool needsToDecay(const bool mindsBlockByDecay, const EntryCounts &entryCounters,
     47             const HeaderPolicy *const headerPolicy);
     48 
     49     // TODO: Improve probability computation method and remove this.
     50     static int getProbabilityBiasForNgram(const int n) {
     51         return (n - 1) * MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
     52     }
     53 
     54     AK_FORCE_INLINE static int getEntryCountHardLimit(const int maxEntryCount) {
     55         return static_cast<int>(static_cast<float>(maxEntryCount)
     56                 * ENTRY_COUNT_HARD_LIMIT_WEIGHT);
     57     }
     58 
     59  private:
     60     DISALLOW_IMPLICIT_CONSTRUCTORS(ForgettingCurveUtils);
     61 
     62     class ProbabilityTable {
     63      public:
     64         ProbabilityTable();
     65 
     66         int getProbability(const int tableId, const int level,
     67                 const int elapsedTimeStepCount) const {
     68             return mTables[tableId][level][elapsedTimeStepCount];
     69         }
     70 
     71      private:
     72         DISALLOW_COPY_AND_ASSIGN(ProbabilityTable);
     73 
     74         static const int PROBABILITY_TABLE_COUNT;
     75         static const int WEAK_PROBABILITY_TABLE_ID;
     76         static const int MODEST_PROBABILITY_TABLE_ID;
     77         static const int STRONG_PROBABILITY_TABLE_ID;
     78         static const int AGGRESSIVE_PROBABILITY_TABLE_ID;
     79 
     80         static const int WEAK_MAX_PROBABILITY;
     81         static const int MODEST_BASE_PROBABILITY;
     82         static const int STRONG_BASE_PROBABILITY;
     83         static const int AGGRESSIVE_BASE_PROBABILITY;
     84 
     85         std::vector<std::vector<std::vector<int>>> mTables;
     86 
     87         static int getBaseProbabilityForLevel(const int tableId, const int level);
     88     };
     89 
     90     static const int MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
     91     static const int DECAY_INTERVAL_SECONDS;
     92 
     93     static const int MAX_LEVEL;
     94     static const int MIN_VISIBLE_LEVEL;
     95     static const int MAX_ELAPSED_TIME_STEP_COUNT;
     96     static const int DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
     97     static const int OCCURRENCES_TO_RAISE_THE_LEVEL;
     98     static const int DURATION_TO_LOWER_THE_LEVEL_IN_SECONDS;
     99 
    100     static const float ENTRY_COUNT_HARD_LIMIT_WEIGHT;
    101 
    102     static const ProbabilityTable sProbabilityTable;
    103 
    104     static int backoff(const int unigramProbability);
    105     static int getElapsedTimeStepCount(const int timestamp, const int durationToLevelDown);
    106     static int clampToVisibleEntryLevelRange(const int level);
    107     static int clampToValidLevelRange(const int level);
    108     static int clampToValidCountRange(const int count, const HeaderPolicy *const headerPolicy);
    109     static int clampToValidTimeStepCountRange(const int timeStepCount);
    110 };
    111 } // namespace latinime
    112 #endif /* LATINIME_FORGETTING_CURVE_UTILS_H */
    113