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/*
* Copyright (C) 2012 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.
*/
package com.android.inputmethod.latin;
public class UserHistoryForgettingCurveUtils {
private static final int FC_FREQ_MAX = 127;
/* package */ static final int COUNT_MAX = 3;
private static final int FC_LEVEL_MAX = 3;
/* package */ static final int ELAPSED_TIME_MAX = 15;
private static final int ELAPSED_TIME_INTERVAL_HOURS = 6;
private static final int HALF_LIFE_HOURS = 48;
/* package */ static int fcToElapsedTime(byte fc) {
return fc & 0x0F;
}
/* package */ static int fcToCount(byte fc) {
return (fc >> 4) & 0x03;
}
/* package */ static int fcToLevel(byte fc) {
return (fc >> 6) & 0x03;
}
private static int calcFreq(int elapsedTime, int count, int level) {
if (level <= 0) {
// Reserved words, just return 0
return 0;
}
if (count == COUNT_MAX) {
// Temporary promote because it's frequently typed recently
++level;
}
final int et = Math.min(FC_FREQ_MAX, Math.max(0, elapsedTime));
final int l = Math.min(FC_LEVEL_MAX, Math.max(0, level));
return MathUtils.SCORE_TABLE[l - 1][et];
}
/* pakcage */ static byte calcFc(int elapsedTime, int count, int level) {
final int et = Math.min(FC_FREQ_MAX, Math.max(0, elapsedTime));
final int c = Math.min(COUNT_MAX, Math.max(0, count));
final int l = Math.min(FC_LEVEL_MAX, Math.max(0, level));
return (byte)(et | (c << 4) | (l << 6));
}
public static int fcToFreq(byte fc) {
final int elapsedTime = fcToElapsedTime(fc);
final int count = fcToCount(fc);
final int level = fcToLevel(fc);
return calcFreq(elapsedTime, count, level);
}
public static byte pushElapsedTime(byte fc) {
int elapsedTime = fcToElapsedTime(fc);
int count = fcToCount(fc);
int level = fcToLevel(fc);
if (elapsedTime >= ELAPSED_TIME_MAX) {
// Downgrade level
elapsedTime = 0;
count = COUNT_MAX;
--level;
} else {
++elapsedTime;
}
return calcFc(elapsedTime, count, level);
}
public static byte pushCount(byte fc, boolean isValid) {
final int elapsedTime = fcToElapsedTime(fc);
int count = fcToCount(fc);
int level = fcToLevel(fc);
if ((elapsedTime == 0 && count >= COUNT_MAX) || (isValid && level == 0)) {
// Upgrade level
++level;
count = 0;
} else {
++count;
}
return calcFc(0, count, level);
}
private static class MathUtils {
public static final int[][] SCORE_TABLE = new int[FC_LEVEL_MAX][ELAPSED_TIME_MAX + 1];
static {
for (int i = 0; i < FC_LEVEL_MAX; ++i) {
final double initialFreq;
if (i >= 2) {
initialFreq = (double)FC_FREQ_MAX;
} else if (i == 1) {
initialFreq = (double)FC_FREQ_MAX / 2;
} else if (i == 0) {
initialFreq = (double)FC_FREQ_MAX / 4;
} else {
continue;
}
for (int j = 0; j < ELAPSED_TIME_MAX; ++j) {
final double elapsedHour = j * ELAPSED_TIME_INTERVAL_HOURS;
final double freq =
initialFreq * Math.pow(initialFreq, elapsedHour / HALF_LIFE_HOURS);
final int intFreq = Math.min(FC_FREQ_MAX, Math.max(0, (int)freq));
SCORE_TABLE[i][j] = intFreq;
}
}
}
}
}
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