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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 "media/parsers/vp8_bool_decoder.h"
- #include <limits.h>
- #include <algorithm>
- #include "base/check_op.h"
- #include "base/numerics/safe_conversions.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_(nullptr),
- user_buffer_end_(nullptr),
- value_(0),
- count_(-8),
- range_(255) {}
- bool Vp8BoolDecoder::Initialize(const uint8_t* data, size_t size) {
- if (data == nullptr || 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_ != nullptr);
- 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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