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// 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;
}