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
17package 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 */
23public 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