1 files changed, 120 insertions, 0 deletions
diff --git a/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java b/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java
new file mode 100644
index 000000000..eb3881726
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java
@@ -0,0 +1,120 @@
+/*
+ * 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;
+                }
+            }
+        }
+    }
+}