1 /* 2 * Copyright (C) 2016 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 17 package com.android.internal.util; 18 19 /** 20 * Helper class for implementing a ring buffer. This supplies the indices, you supply 21 * the array(s). 22 */ 23 public class RingBufferIndices { 24 private final int mCapacity; 25 26 // The first valid element and the next open slot. 27 private int mStart; 28 private int mSize; 29 30 /** 31 * Create ring buffer of the given capacity. 32 */ 33 public RingBufferIndices(int capacity) { 34 mCapacity = capacity; 35 } 36 37 /** 38 * Add a new item to the ring buffer. If the ring buffer is full, this 39 * replaces the oldest item. 40 * @return Returns the index at which the new item appears, for placing in your array. 41 */ 42 public int add() { 43 if (mSize < mCapacity) { 44 final int pos = mSize; 45 mSize++; 46 return pos; 47 } 48 int pos = mStart; 49 mStart++; 50 if (mStart == mCapacity) { 51 mStart = 0; 52 } 53 return pos; 54 } 55 56 /** 57 * Clear the ring buffer. 58 */ 59 public void clear() { 60 mStart = 0; 61 mSize = 0; 62 } 63 64 /** 65 * Return the current size of the ring buffer. 66 */ 67 public int size() { 68 return mSize; 69 } 70 71 /** 72 * Convert a position in the ring buffer that is [0..size()] to an offset 73 * in the array(s) containing the ring buffer items. 74 */ 75 public int indexOf(int pos) { 76 int index = mStart + pos; 77 if (index >= mCapacity) { 78 index -= mCapacity; 79 } 80 return index; 81 } 82 } 83
