// Copyright (c) 2012 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. #include "media/base/bit_reader.h" #include namespace media { BitReader::BitReader(const uint8* data, off_t size) : data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) { DCHECK(data_ != NULL && bytes_left_ > 0); UpdateCurrByte(); } BitReader::~BitReader() {} bool BitReader::SkipBits(int num_bits) { DCHECK_GE(num_bits, 0); DVLOG_IF(0, num_bits > 100) << "BitReader::SkipBits inefficient for large skips"; // Skip any bits in the current byte waiting to be processed, then // process full bytes until less than 8 bits remaining. while (num_bits > 0 && num_bits > num_remaining_bits_in_curr_byte_) { num_bits -= num_remaining_bits_in_curr_byte_; num_remaining_bits_in_curr_byte_ = 0; UpdateCurrByte(); // If there is no more data remaining, only return true if we // skipped all that were requested. if (num_remaining_bits_in_curr_byte_ == 0) return (num_bits == 0); } // Less than 8 bits remaining to skip. Use ReadBitsInternal to verify // that the remaining bits we need exist, and adjust them as necessary // for subsequent operations. uint64 not_needed; return ReadBitsInternal(num_bits, ¬_needed); } int BitReader::bits_available() const { return 8 * bytes_left_ + num_remaining_bits_in_curr_byte_; } bool BitReader::ReadBitsInternal(int num_bits, uint64* out) { DCHECK_LE(num_bits, 64); *out = 0; while (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) { int bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits); *out <<= bits_to_take; *out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take); num_bits -= bits_to_take; num_remaining_bits_in_curr_byte_ -= bits_to_take; curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1; if (num_remaining_bits_in_curr_byte_ == 0) UpdateCurrByte(); } return num_bits == 0; } void BitReader::UpdateCurrByte() { DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0); if (bytes_left_ == 0) return; // Load a new byte and advance pointers. curr_byte_ = *data_; ++data_; --bytes_left_; num_remaining_bits_in_curr_byte_ = 8; } } // namespace media