84 lines
2.4 KiB
C++
84 lines
2.4 KiB
C++
// 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"
|
|
|
|
namespace edash_packager {
|
|
namespace media {
|
|
|
|
BitReader::BitReader(const uint8_t* 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);
|
|
DLOG_IF(INFO, 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_t 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_t* 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
|
|
} // namespace edash_packager
|