blob: 2ddb8d4f45d72ac8e3a3c8c86e96320230b9ce1a (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
// 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 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::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
|
