1// Copyright 2017 PDFium 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.
4
5// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
6
7#include "core/fxcrt/cfx_bitstream.h"
8
9#include <limits>
10
11#include "core/fxcrt/fx_system.h"
12
13CFX_BitStream::CFX_BitStream(const uint8_t* pData, uint32_t dwSize)
14    : m_BitPos(0), m_BitSize(dwSize * 8), m_pData(pData) {
15  ASSERT(dwSize <= std::numeric_limits<uint32_t>::max() / 8);
16}
17
18CFX_BitStream::~CFX_BitStream() {}
19
20void CFX_BitStream::ByteAlign() {
21  m_BitPos = (m_BitPos + 7) & ~7;
22}
23
24uint32_t CFX_BitStream::GetBits(uint32_t nBits) {
25  if (nBits > m_BitSize || m_BitPos + nBits > m_BitSize)
26    return 0;
27
28  const uint8_t* data = m_pData.Get();
29
30  if (nBits == 1) {
31    int bit = (data[m_BitPos / 8] & (1 << (7 - m_BitPos % 8))) ? 1 : 0;
32    m_BitPos++;
33    return bit;
34  }
35
36  uint32_t byte_pos = m_BitPos / 8;
37  uint32_t bit_pos = m_BitPos % 8;
38  uint32_t bit_left = nBits;
39  uint32_t result = 0;
40  if (bit_pos) {
41    if (8 - bit_pos >= bit_left) {
42      result = (data[byte_pos] & (0xff >> bit_pos)) >> (8 - bit_pos - bit_left);
43      m_BitPos += bit_left;
44      return result;
45    }
46    bit_left -= 8 - bit_pos;
47    result = (data[byte_pos++] & ((1 << (8 - bit_pos)) - 1)) << bit_left;
48  }
49  while (bit_left >= 8) {
50    bit_left -= 8;
51    result |= data[byte_pos++] << bit_left;
52  }
53  if (bit_left)
54    result |= data[byte_pos] >> (8 - bit_left);
55  m_BitPos += nBits;
56  return result;
57}
58