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// CRC-32
#define CRCPOLY 0xEDB88320
#define CRCINIT 0xFFFFFFFF

UINT g_crc_precalc[4][256];

void CRC32Init() {
	for(UINT i = 0; i <= 0xFF; i++) {
		UINT x = i;
		for(UINT j = 0; j < 8; j++)
			x = (x>>1) ^ (CRCPOLY & (-(INT)(x & 1)));
		g_crc_precalc[0][i] = x;
	}

for(UINT i = 0; i <= 0xFF; i++) {
		UINT c = g_crc_precalc[0][i];
		for(UINT j = 1; j < 4; j++) {
			c = g_crc_precalc[0][c & 0xFF] ^ (c >> 8);
			g_crc_precalc[j][i] = c;
		}
	}
}

UINT CRC32(const CHAR* key, SIZE_T len) {
	UINT crc = CRCINIT;
	SIZE_T ndwords = len / sizeof(DWORD);
	for(; ndwords; ndwords--) {
		crc ^= *(DWORD*)key;
		crc =
			g_crc_precalc[3][(crc      ) & 0xFF] ^
			g_crc_precalc[2][(crc >>  8) & 0xFF] ^
			g_crc_precalc[1][(crc >> 16) & 0xFF] ^
			g_crc_precalc[0][(crc >> 24) & 0xFF];
		key += sizeof(DWORD);
	}
	if (len & sizeof(WORD)) {
		UINT c = crc ^ *(WORD*)key;
		crc = g_crc_precalc[1][(c     ) & 0xFF] ^
			  g_crc_precalc[0][(c >> 8) & 0xFF] ^ (crc >> 16);
		key += sizeof(WORD);
	}
	if (len & sizeof(BYTE))
		crc = g_crc_precalc[0][(crc ^ *key) & 0xFF] ^ (crc >> 8);
	return ~crc;
}

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