mirror of
https://github.com/melonDS-emu/melonDS.git
synced 2024-11-14 13:27:41 -07:00
68 lines
1.6 KiB
C++
68 lines
1.6 KiB
C++
/*
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Copyright 2016-2024 melonDS team
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This file is part of melonDS.
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melonDS is free software: you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation, either version 3 of the License, or (at your option)
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any later version.
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melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with melonDS. If not, see http://www.gnu.org/licenses/.
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*/
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#include "CRC32.h"
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// http://www.codeproject.com/KB/recipes/crc32_large.aspx
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namespace melonDS
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{
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constexpr u32 _reflect(u32 refl, char ch)
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{
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u32 value = 0;
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for(int i = 1; i < (ch + 1); i++)
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{
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if (refl & 1)
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value |= 1 << (ch - i);
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refl >>= 1;
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}
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return value;
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}
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constexpr auto GetCRC32Table()
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{
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std::array<u32, 256> Crc32Table { 0 };
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u32 polynomial = 0x04C11DB7;
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for (int i = 0; i < 0x100; i++)
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{
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Crc32Table[i] = _reflect(i, 8) << 24;
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for (int j = 0; j < 8; j++)
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Crc32Table[i] = (Crc32Table[i] << 1) ^ (Crc32Table[i] & (1 << 31) ? polynomial : 0);
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Crc32Table[i] = _reflect(Crc32Table[i], 32);
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}
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return Crc32Table;
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}
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u32 CRC32(const u8 *data, int len, u32 start)
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{
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auto Crc32Table = GetCRC32Table();
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u32 crc = start ^ 0xFFFFFFFF;
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while (len--)
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crc = (crc >> 8) ^ Crc32Table[(crc & 0xFF) ^ *data++];
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return (crc ^ 0xFFFFFFFF);
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}
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} |