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/*
Copyright 2016-2023 melonDS team
This file is part of melonDS.
melonDS is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option)
any later version.
melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with melonDS. If not, see http://www.gnu.org/licenses/.
*/
#include "CRC32.h"
// http://www.codeproject.com/KB/recipes/crc32_large.aspx
namespace melonDS
{
constexpr u32 _reflect(u32 refl, char ch)
{
u32 value = 0;
for(int i = 1; i < (ch + 1); i++)
{
if (refl & 1)
value |= 1 << (ch - i);
refl >>= 1;
}
return value;
}
constexpr auto GetCRC32Table()
{
std::array<u32, 256> Crc32Table { 0 };
u32 polynomial = 0x04C11DB7;
for (int i = 0; i < 0x100; i++)
{
Crc32Table[i] = _reflect(i, 8) << 24;
for (int j = 0; j < 8; j++)
Crc32Table[i] = (Crc32Table[i] << 1) ^ (Crc32Table[i] & (1 << 31) ? polynomial : 0);
Crc32Table[i] = _reflect(Crc32Table[i], 32);
}
return Crc32Table;
}
u32 CRC32(const u8 *data, int len, u32 start)
{
auto Crc32Table = GetCRC32Table();
u32 crc = start ^ 0xFFFFFFFF;
while (len--)
crc = (crc >> 8) ^ Crc32Table[(crc & 0xFF) ^ *data++];
return (crc ^ 0xFFFFFFFF);
}
}
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