RollingStat.java

/*
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

package com.facebook.imagepipeline.animated.impl;

import android.os.SystemClock;

/**
 * Simple class to track a rolling stat efficiently.
 */
class RollingStat {

  private static final int WINDOWS = 60;

  private final short[] mStat;

  public RollingStat() {
    mStat = new short[WINDOWS];
  }

  void incrementStats(int toAdd) {
    long nowMs = SystemClock.uptimeMillis();
    long nowSeconds = nowMs / 1000;
    int statsIndex = (int) (nowSeconds % WINDOWS);
    int marker = (int) ((nowSeconds / WINDOWS) & 0xff);

    short bucketData = mStat[statsIndex];
    int prevCount = bucketData & 0xff;
    int prevMarker = (bucketData >> 8) & 0xff;

    int newCount;
    if (marker != prevMarker) {
      newCount = toAdd;
    } else {
      newCount = prevCount + toAdd;
    }

    int newData = (marker << 8) | newCount;
    mStat[statsIndex] = (short) newData;
  }

  int getSum(int previousSeconds) {
    long nowMs = SystemClock.uptimeMillis();
    long nowSeconds = nowMs / 1000;
    int statsIndexStart = (int) ((nowSeconds - previousSeconds) % WINDOWS);
    int currentMarker = (int) ((nowSeconds / WINDOWS) & 0xff);

    int sum = 0;
    for (int i = 0; i < previousSeconds; i++) {
      short bucketData = mStat[(statsIndexStart + i) % WINDOWS];
      int count = bucketData & 0xff;
      int marker = (bucketData >> 8) & 0xff;
      if (marker == currentMarker) {
        sum += count;
      }
    }
    return sum;
  }
}