1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
/*
* Copyright (c) 2010, The WebM Project authors. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* * Neither the name of Google, nor the WebM Project, nor the names
* of its contributors may be used to endorse or promote products
* derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
// This file is modified from the dboolhuff.{c,h} from the WebM's libvpx
// project. (http://www.webmproject.org/code)
// It is used to decode bits from a vp8 stream.
#include <limits.h>
#include <algorithm>
#include "base/numerics/safe_conversions.h"
#include "media/filters/vp8_bool_decoder.h"
namespace media {
#define VP8_BD_VALUE_BIT \
static_cast<int>(sizeof(Vp8BoolDecoder::value_) * CHAR_BIT)
static const int kDefaultProbability = 0x80; // 0x80 / 256 = 0.5
// This is meant to be a large, positive constant that can still be efficiently
// loaded as an immediate (on platforms like ARM, for example). Even relatively
// modest values like 100 would work fine.
#define VP8_LOTS_OF_BITS (0x40000000)
// The number of leading zeros.
static const unsigned char kVp8Norm[256] = {
0, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
Vp8BoolDecoder::Vp8BoolDecoder()
: user_buffer_(NULL),
user_buffer_end_(NULL),
value_(0),
count_(-8),
range_(255) {
}
bool Vp8BoolDecoder::Initialize(const uint8_t* data, size_t size) {
if (data == NULL || size == 0)
return false;
user_buffer_start_ = data;
user_buffer_ = data;
user_buffer_end_ = data + size;
value_ = 0;
count_ = -8;
range_ = 255;
return true;
}
void Vp8BoolDecoder::FillDecoder() {
DCHECK(user_buffer_ != NULL);
int shift = VP8_BD_VALUE_BIT - CHAR_BIT - (count_ + CHAR_BIT);
size_t bytes_left = user_buffer_end_ - user_buffer_;
size_t bits_left = bytes_left * CHAR_BIT;
int x = static_cast<int>(shift + CHAR_BIT - bits_left);
int loop_end = 0;
if (x >= 0) {
count_ += VP8_LOTS_OF_BITS;
loop_end = x;
}
if (x < 0 || bits_left) {
while (shift >= loop_end) {
count_ += CHAR_BIT;
value_ |= static_cast<size_t>(*user_buffer_) << shift;
++user_buffer_;
shift -= CHAR_BIT;
}
}
}
int Vp8BoolDecoder::ReadBit(int probability) {
int bit = 0;
size_t split = 1 + (((range_ - 1) * probability) >> 8);
if (count_ < 0)
FillDecoder();
size_t bigsplit = static_cast<size_t>(split) << (VP8_BD_VALUE_BIT - 8);
if (value_ >= bigsplit) {
range_ -= split;
value_ -= bigsplit;
bit = 1;
} else {
range_ = split;
}
size_t shift = kVp8Norm[range_];
range_ <<= shift;
value_ <<= shift;
count_ -= shift;
DCHECK_EQ(1U, (range_ >> 7)); // In the range [128, 255].
return bit;
}
bool Vp8BoolDecoder::ReadLiteral(size_t num_bits, int* out) {
DCHECK_LE(num_bits, sizeof(int) * CHAR_BIT);
*out = 0;
for (; num_bits > 0; --num_bits)
*out = (*out << 1) | ReadBit(kDefaultProbability);
return !OutOfBuffer();
}
bool Vp8BoolDecoder::ReadBool(bool* out, uint8_t probability) {
*out = !!ReadBit(probability);
return !OutOfBuffer();
}
bool Vp8BoolDecoder::ReadBool(bool* out) {
return ReadBool(out, kDefaultProbability);
}
bool Vp8BoolDecoder::ReadLiteralWithSign(size_t num_bits, int* out) {
ReadLiteral(num_bits, out);
// Read sign.
if (ReadBit(kDefaultProbability))
*out = -*out;
return !OutOfBuffer();
}
size_t Vp8BoolDecoder::BitOffset() {
int bit_count = count_ + 8;
if (bit_count > VP8_BD_VALUE_BIT)
// Capped at 0 to ignore buffer underrun.
bit_count = std::max(0, bit_count - VP8_LOTS_OF_BITS);
return (user_buffer_ - user_buffer_start_) * 8 - bit_count;
}
uint8_t Vp8BoolDecoder::GetRange() {
return base::checked_cast<uint8_t>(range_);
}
uint8_t Vp8BoolDecoder::GetBottom() {
if (count_ < 0)
FillDecoder();
return static_cast<uint8_t>(value_ >> (VP8_BD_VALUE_BIT - 8));
}
inline bool Vp8BoolDecoder::OutOfBuffer() {
// Check if we have reached the end of the buffer.
//
// Variable |count_| stores the number of bits in the |value_| buffer, minus
// 8. The top byte is part of the algorithm and the remainder is buffered to
// be shifted into it. So, if |count_| == 8, the top 16 bits of |value_| are
// occupied, 8 for the algorithm and 8 in the buffer.
//
// When reading a byte from the user's buffer, |count_| is filled with 8 and
// one byte is filled into the |value_| buffer. When we reach the end of the
// data, |count_| is additionally filled with VP8_LOTS_OF_BITS. So when
// |count_| == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
return (count_ > VP8_BD_VALUE_BIT) && (count_ < VP8_LOTS_OF_BITS);
}
} // namespace media
|