1/*
2 * Copyright (C) 2010 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#include "ABitReader.h"
18
19#include <media/stagefright/foundation/ADebug.h>
20
21namespace android {
22
23ABitReader::ABitReader(const uint8_t *data, size_t size)
24    : mData(data),
25      mSize(size),
26      mReservoir(0),
27      mNumBitsLeft(0) {
28}
29
30void ABitReader::fillReservoir() {
31    CHECK_GT(mSize, 0u);
32
33    mReservoir = 0;
34    size_t i;
35    for (i = 0; mSize > 0 && i < 4; ++i) {
36        mReservoir = (mReservoir << 8) | *mData;
37
38        ++mData;
39        --mSize;
40    }
41
42    mNumBitsLeft = 8 * i;
43    mReservoir <<= 32 - mNumBitsLeft;
44}
45
46uint32_t ABitReader::getBits(size_t n) {
47    CHECK_LE(n, 32u);
48
49    uint32_t result = 0;
50    while (n > 0) {
51        if (mNumBitsLeft == 0) {
52            fillReservoir();
53        }
54
55        size_t m = n;
56        if (m > mNumBitsLeft) {
57            m = mNumBitsLeft;
58        }
59
60        result = (result << m) | (mReservoir >> (32 - m));
61        mReservoir <<= m;
62        mNumBitsLeft -= m;
63
64        n -= m;
65    }
66
67    return result;
68}
69
70void ABitReader::skipBits(size_t n) {
71    while (n > 32) {
72        getBits(32);
73        n -= 32;
74    }
75
76    if (n > 0) {
77        getBits(n);
78    }
79}
80
81void ABitReader::putBits(uint32_t x, size_t n) {
82    CHECK_LE(n, 32u);
83
84    while (mNumBitsLeft + n > 32) {
85        mNumBitsLeft -= 8;
86        --mData;
87        ++mSize;
88    }
89
90    mReservoir = (mReservoir >> n) | (x << (32 - n));
91    mNumBitsLeft += n;
92}
93
94size_t ABitReader::numBitsLeft() const {
95    return mSize * 8 + mNumBitsLeft;
96}
97
98const uint8_t *ABitReader::data() const {
99    return mData - (mNumBitsLeft + 7) / 8;
100}
101
102}  // namespace android
103