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/*
* Copyright (C) 2015 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.incallui.answer.impl.classifier;
import android.os.SystemClock;
import java.util.ArrayList;
/**
* Holds the evaluations for ended strokes and gestures. These values are decreased through time.
*/
class HistoryEvaluator {
private static final float INTERVAL = 50.0f;
private static final float HISTORY_FACTOR = 0.9f;
private static final float EPSILON = 1e-5f;
private final ArrayList<Data> strokes = new ArrayList<>();
private final ArrayList<Data> gestureWeights = new ArrayList<>();
private long lastUpdate;
public HistoryEvaluator() {
lastUpdate = SystemClock.elapsedRealtime();
}
public void addStroke(float evaluation) {
decayValue();
strokes.add(new Data(evaluation));
}
public void addGesture(float evaluation) {
decayValue();
gestureWeights.add(new Data(evaluation));
}
/** Calculates the weighted average of strokes and adds to it the weighted average of gestures */
public float getEvaluation() {
return weightedAverage(strokes) + weightedAverage(gestureWeights);
}
private float weightedAverage(ArrayList<Data> list) {
float sumValue = 0.0f;
float sumWeight = 0.0f;
int size = list.size();
for (int i = 0; i < size; i++) {
Data data = list.get(i);
sumValue += data.evaluation * data.weight;
sumWeight += data.weight;
}
if (sumWeight == 0.0f) {
return 0.0f;
}
return sumValue / sumWeight;
}
private void decayValue() {
long time = SystemClock.elapsedRealtime();
if (time <= lastUpdate) {
return;
}
// All weights are multiplied by HISTORY_FACTOR after each INTERVAL milliseconds.
float factor = (float) Math.pow(HISTORY_FACTOR, (time - lastUpdate) / INTERVAL);
decayValue(strokes, factor);
decayValue(gestureWeights, factor);
lastUpdate = time;
}
private void decayValue(ArrayList<Data> list, float factor) {
int size = list.size();
for (int i = 0; i < size; i++) {
list.get(i).weight *= factor;
}
// Removing evaluations with such small weights that they do not matter anymore
while (!list.isEmpty() && isZero(list.get(0).weight)) {
list.remove(0);
}
}
private boolean isZero(float x) {
return x <= EPSILON && x >= -EPSILON;
}
/**
* For each stroke it holds its initial value and the current weight. Initially the weight is set
* to 1.0
*/
private static class Data {
public float evaluation;
public float weight;
public Data(float evaluation) {
this.evaluation = evaluation;
weight = 1.0f;
}
}
}
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