43 lines
1.1 KiB
C++
43 lines
1.1 KiB
C++
// Copyright © 2008-2021 Pioneer Developers. See AUTHORS.txt for details
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// Licensed under the terms of the GPL v3. See licenses/GPL-3.txt
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#include "CRC32.h"
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const Uint32 CRC32::s_polynomial = 0x04c11db7;
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bool CRC32::s_lookupTableGenerated;
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Uint32 CRC32::s_lookupTable[256];
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static Uint32 crc32_reflect(Uint32 v, const int bits)
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{
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Uint32 r = 0;
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for (int i = 1; i <= bits; i++) {
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if (v & 1)
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r = r | (1 << (bits - i));
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v >>= 1;
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}
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return r;
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}
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CRC32::CRC32() :
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m_checksum(0xffffffff)
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{
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if (!s_lookupTableGenerated) {
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for (int i = 0; i <= 0xff; i++) {
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s_lookupTable[i] = crc32_reflect(i, 8) << 24;
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for (int j = 0; j < 8; j++)
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s_lookupTable[i] = (s_lookupTable[i] << 1) ^ (s_lookupTable[i] & (1 << 31) ? s_polynomial : 0);
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s_lookupTable[i] = crc32_reflect(s_lookupTable[i], 32);
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}
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s_lookupTableGenerated = true;
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}
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}
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void CRC32::AddData(const char *data, int length)
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{
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const unsigned char *buf = reinterpret_cast<const unsigned char *>(data);
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while (length--)
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m_checksum = (m_checksum >> 8) ^ s_lookupTable[(m_checksum & 0xff) ^ *buf++];
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}
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