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      */
RingBufferIndices(int capacity)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      */
add()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      */
clear()59     public void clear() {
60         mStart = 0;
61         mSize = 0;
62     }
63 
64     /**
65      * Return the current size of the ring buffer.
66      */
size()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      */
indexOf(int pos)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