The Tor Browser: content/media/fmp4/demuxer/bit

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

     1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.

     2 // Use of this source code is governed by a BSD-style license that can be

     3 // found in the LICENSE file.

     5 #include "mp4_demuxer/bit_reader.h"

     6 #include <algorithm>

     8 namespace mp4_demuxer {

    10 BitReader::BitReader(const uint8_t* data, off_t size)

    11     : data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) {

    12   DCHECK(data_ != nullptr && bytes_left_ > 0);

    14   UpdateCurrByte();

    15 }

    17 BitReader::~BitReader() {}

    19 int BitReader::bits_available() const {

    20   return 8 * bytes_left_ + num_remaining_bits_in_curr_byte_;

    21 }

    23 bool BitReader::ReadBitsInternal(int num_bits, uint64_t* out) {

    24   DCHECK_LE(num_bits, 64);

    26   *out = 0;

    28   while (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) {

    29     int bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits);

    31     *out <<= bits_to_take;

    32     *out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take);

    33     num_bits -= bits_to_take;

    34     num_remaining_bits_in_curr_byte_ -= bits_to_take;

    35     curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1;

    37     if (num_remaining_bits_in_curr_byte_ == 0)

    38       UpdateCurrByte();

    39   }

    41   return num_bits == 0;

    42 }

    44 void BitReader::UpdateCurrByte() {

    45   DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);

    47   if (bytes_left_ == 0)

    48     return;

    50   // Load a new byte and advance pointers.

    51   curr_byte_ = *data_;

    52   ++data_;

    53   --bytes_left_;

    54   num_remaining_bits_in_curr_byte_ = 8;

    55 }

    57 }  // namespace mp4_demuxer

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