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// 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
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