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 CFX_BitStream(const uint8_t * pData,uint32_t dwSize)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 ~CFX_BitStream()18CFX_BitStream::~CFX_BitStream() {} 19 ByteAlign()20void CFX_BitStream::ByteAlign() { 21 m_BitPos = (m_BitPos + 7) & ~7; 22 } 23 GetBits(uint32_t nBits)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