UserHistoryForgettingCurveUtils.java revision 607a9244861ee22c25aaea6ffdfa19fccf497b0b 
1/*
2 * Copyright (C) 2012 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
17package com.android.inputmethod.latin;
18
19public class UserHistoryForgettingCurveUtils {
20    private static final int FC_FREQ_MAX = 127;
21    /* package */ static final int COUNT_MAX = 3;
22    private static final int FC_LEVEL_MAX = 3;
23    /* package */ static final int ELAPSED_TIME_MAX = 15;
24    private static final int ELAPSED_TIME_INTERVAL_HOURS = 6;
25    private static final int HALF_LIFE_HOURS = 48;
26
27    /* package */ static  int fcToElapsedTime(byte fc) {
28        return fc & 0x0F;
29    }
30
31    /* package */ static int fcToCount(byte fc) {
32        return (fc >> 4) & 0x03;
33    }
34
35    /* package */ static int fcToLevel(byte fc) {
36        return (fc >> 6) & 0x03;
37    }
38
39    private static int calcFreq(int elapsedTime, int count, int level) {
40        if (level <= 0) {
41            // Reserved words, just return 0
42            return 0;
43        }
44        if (count == COUNT_MAX) {
45            // Temporary promote because it's frequently typed recently
46            ++level;
47        }
48        final int et = Math.min(FC_FREQ_MAX, Math.max(0, elapsedTime));
49        final int l = Math.min(FC_LEVEL_MAX, Math.max(0, level));
50        return MathUtils.SCORE_TABLE[l - 1][et];
51    }
52
53    /* pakcage */ static byte calcFc(int elapsedTime, int count, int level) {
54        final int et = Math.min(FC_FREQ_MAX, Math.max(0, elapsedTime));
55        final int c = Math.min(COUNT_MAX, Math.max(0, count));
56        final int l = Math.min(FC_LEVEL_MAX, Math.max(0, level));
57        return (byte)(et | (c << 4) | (l << 6));
58    }
59
60    public static int fcToFreq(byte fc) {
61        final int elapsedTime = fcToElapsedTime(fc);
62        final int count = fcToCount(fc);
63        final int level = fcToLevel(fc);
64        return calcFreq(elapsedTime, count, level);
65    }
66
67    public static byte pushElapsedTime(byte fc) {
68        int elapsedTime = fcToElapsedTime(fc);
69        int count = fcToCount(fc);
70        int level = fcToLevel(fc);
71        if (elapsedTime >= ELAPSED_TIME_MAX) {
72            // Downgrade level
73            elapsedTime = 0;
74            count = COUNT_MAX;
75            --level;
76        } else {
77            ++elapsedTime;
78        }
79        return calcFc(elapsedTime, count, level);
80    }
81
82    public static byte pushCount(byte fc, boolean isValid) {
83        final int elapsedTime = fcToElapsedTime(fc);
84        int count = fcToCount(fc);
85        int level = fcToLevel(fc);
86        if ((elapsedTime == 0 && count >= COUNT_MAX) || (isValid && level == 0)) {
87            // Upgrade level
88            ++level;
89            count = 0;
90        } else {
91            ++count;
92        }
93        return calcFc(0, count, level);
94    }
95
96    private static class MathUtils {
97        public static final int[][] SCORE_TABLE = new int[FC_LEVEL_MAX][ELAPSED_TIME_MAX + 1];
98        static {
99            for (int i = 0; i < FC_LEVEL_MAX; ++i) {
100                final double initialFreq;
101                if (i >= 2) {
102                    initialFreq = (double)FC_FREQ_MAX;
103                } else if (i == 1) {
104                    initialFreq = (double)FC_FREQ_MAX / 2;
105                } else if (i == 0) {
106                    initialFreq = (double)FC_FREQ_MAX / 4;
107                } else {
108                    continue;
109                }
110                for (int j = 0; j < ELAPSED_TIME_MAX; ++j) {
111                    final double elapsedHour = j * ELAPSED_TIME_INTERVAL_HOURS;
112                    final double freq =
113                            initialFreq * Math.pow(initialFreq, elapsedHour / HALF_LIFE_HOURS);
114                    final int intFreq = Math.min(FC_FREQ_MAX, Math.max(0, (int)freq));
115                    SCORE_TABLE[i][j] = intFreq;
116                }
117            }
118        }
119    }
120}
121