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