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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 "suggest/policyimpl/dictionary/utils/historical_info.h"
     24 
     25 namespace latinime {
     26 
     27 class HeaderPolicy;
     28 
     29 class ForgettingCurveUtils {
     30  public:
     31     static const HistoricalInfo createUpdatedHistoricalInfo(
     32             const HistoricalInfo *const originalHistoricalInfo, const int newProbability,
     33             const HistoricalInfo *const newHistoricalInfo, const HeaderPolicy *const headerPolicy);
     34 
     35     static const HistoricalInfo createHistoricalInfoToSave(
     36             const HistoricalInfo *const originalHistoricalInfo,
     37             const HeaderPolicy *const headerPolicy);
     38 
     39     static int decodeProbability(const HistoricalInfo *const historicalInfo,
     40             const HeaderPolicy *const headerPolicy);
     41 
     42     static int getProbability(const int encodedUnigramProbability,
     43             const int encodedBigramProbability);
     44 
     45     static bool needsToKeep(const HistoricalInfo *const historicalInfo,
     46             const HeaderPolicy *const headerPolicy);
     47 
     48     static bool needsToDecay(const bool mindsBlockByDecay, const int unigramCount,
     49             const int bigramCount, const HeaderPolicy *const headerPolicy);
     50 
     51     AK_FORCE_INLINE static int getUnigramCountHardLimit(const int maxUnigramCount) {
     52         return static_cast<int>(static_cast<float>(maxUnigramCount)
     53                 * UNIGRAM_COUNT_HARD_LIMIT_WEIGHT);
     54     }
     55 
     56     AK_FORCE_INLINE static int getBigramCountHardLimit(const int maxBigramCount) {
     57         return static_cast<int>(static_cast<float>(maxBigramCount)
     58                 * BIGRAM_COUNT_HARD_LIMIT_WEIGHT);
     59     }
     60 
     61  private:
     62     DISALLOW_IMPLICIT_CONSTRUCTORS(ForgettingCurveUtils);
     63 
     64     class ProbabilityTable {
     65      public:
     66         ProbabilityTable();
     67 
     68         int getProbability(const int tableId, const int level,
     69                 const int elapsedTimeStepCount) const {
     70             return mTables[tableId][level][elapsedTimeStepCount];
     71         }
     72 
     73      private:
     74         DISALLOW_COPY_AND_ASSIGN(ProbabilityTable);
     75 
     76         static const int PROBABILITY_TABLE_COUNT;
     77         static const int WEAK_PROBABILITY_TABLE_ID;
     78         static const int MODEST_PROBABILITY_TABLE_ID;
     79         static const int STRONG_PROBABILITY_TABLE_ID;
     80         static const int AGGRESSIVE_PROBABILITY_TABLE_ID;
     81 
     82         static const int WEAK_MAX_PROBABILITY;
     83         static const int MODEST_BASE_PROBABILITY;
     84         static const int STRONG_BASE_PROBABILITY;
     85         static const int AGGRESSIVE_BASE_PROBABILITY;
     86 
     87         std::vector<std::vector<std::vector<int>>> mTables;
     88 
     89         static int getBaseProbabilityForLevel(const int tableId, const int level);
     90     };
     91 
     92     static const int MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
     93     static const int DECAY_INTERVAL_SECONDS;
     94 
     95     static const int MAX_LEVEL;
     96     static const int MIN_VISIBLE_LEVEL;
     97     static const int MAX_ELAPSED_TIME_STEP_COUNT;
     98     static const int DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
     99 
    100     static const float UNIGRAM_COUNT_HARD_LIMIT_WEIGHT;
    101     static const float BIGRAM_COUNT_HARD_LIMIT_WEIGHT;
    102 
    103     static const ProbabilityTable sProbabilityTable;
    104 
    105     static int backoff(const int unigramProbability);
    106     static int getElapsedTimeStepCount(const int timestamp, const int durationToLevelDown);
    107     static int clampToVisibleEntryLevelRange(const int level);
    108     static int clampToValidLevelRange(const int level);
    109     static int clampToValidCountRange(const int count, const HeaderPolicy *const headerPolicy);
    110     static int clampToValidTimeStepCountRange(const int timeStepCount);
    111 };
    112 } // namespace latinime
    113 #endif /* LATINIME_FORGETTING_CURVE_UTILS_H */
    114