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.
getProbabilityBiasForNgram(const int n)50     static int getProbabilityBiasForNgram(const int n) {
51         return (n - 1) * MULTIPLIER_TWO_IN_PROBABILITY_SCALE;
52     }
53 
getEntryCountHardLimit(const int maxEntryCount)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 
getProbability(const int tableId,const int level,const int elapsedTimeStepCount)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