| // Copyright 2017 PDFium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com |
| |
| #include "core/fxcrt/cfx_bitstream.h" |
| |
| #include <limits> |
| |
| #include "core/fxcrt/fx_memory.h" |
| #include "core/fxcrt/fx_system.h" |
| |
| CFX_BitStream::CFX_BitStream(pdfium::span<const uint8_t> pData) |
| : m_BitPos(0), m_BitSize(pData.size() * 8), m_pData(pData.data()) { |
| ASSERT(pData.size() <= std::numeric_limits<uint32_t>::max() / 8); |
| } |
| |
| CFX_BitStream::~CFX_BitStream() = default; |
| |
| void CFX_BitStream::ByteAlign() { |
| m_BitPos = FxAlignToBoundary<8>(m_BitPos); |
| } |
| |
| uint32_t CFX_BitStream::GetBits(uint32_t nBits) { |
| ASSERT(nBits > 0); |
| ASSERT(nBits <= 32); |
| if (nBits > m_BitSize || m_BitPos > m_BitSize - nBits) |
| return 0; |
| |
| const uint32_t bit_pos = m_BitPos % 8; |
| uint32_t byte_pos = m_BitPos / 8; |
| const uint8_t* data = m_pData.Get(); |
| uint8_t current_byte = data[byte_pos]; |
| |
| if (nBits == 1) { |
| int bit = (current_byte & (1 << (7 - bit_pos))) ? 1 : 0; |
| m_BitPos++; |
| return bit; |
| } |
| |
| uint32_t bit_left = nBits; |
| uint32_t result = 0; |
| if (bit_pos) { |
| uint32_t bits_readable = 8 - bit_pos; |
| if (bits_readable >= bit_left) { |
| result = (current_byte & (0xff >> bit_pos)) >> (bits_readable - bit_left); |
| m_BitPos += bit_left; |
| return result; |
| } |
| bit_left -= bits_readable; |
| result = (current_byte & ((1 << bits_readable) - 1)) << bit_left; |
| ++byte_pos; |
| } |
| while (bit_left >= 8) { |
| bit_left -= 8; |
| result |= data[byte_pos++] << bit_left; |
| } |
| if (bit_left) |
| result |= data[byte_pos] >> (8 - bit_left); |
| m_BitPos += nBits; |
| return result; |
| } |