зеркало из https://github.com/mozilla/gecko-dev.git
58 строки
1.4 KiB
C++
58 строки
1.4 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "mp4_demuxer/bit_reader.h"
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#include <algorithm>
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namespace mp4_demuxer {
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BitReader::BitReader(const uint8_t* data, off_t size)
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: data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) {
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DCHECK(data_ != nullptr && bytes_left_ > 0);
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UpdateCurrByte();
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}
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BitReader::~BitReader() {}
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int BitReader::bits_available() const {
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return 8 * bytes_left_ + num_remaining_bits_in_curr_byte_;
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}
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bool BitReader::ReadBitsInternal(int num_bits, uint64_t* out) {
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DCHECK_LE(num_bits, 64);
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*out = 0;
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while (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) {
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int bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits);
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*out <<= bits_to_take;
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*out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take);
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num_bits -= bits_to_take;
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num_remaining_bits_in_curr_byte_ -= bits_to_take;
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curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1;
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if (num_remaining_bits_in_curr_byte_ == 0)
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UpdateCurrByte();
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}
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return num_bits == 0;
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}
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void BitReader::UpdateCurrByte() {
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DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);
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if (bytes_left_ == 0)
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return;
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// Load a new byte and advance pointers.
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curr_byte_ = *data_;
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++data_;
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--bytes_left_;
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num_remaining_bits_in_curr_byte_ = 8;
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}
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} // namespace mp4_demuxer
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