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uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
const uint8_t* current = (const uint8_t*) data;
while (length-- != 0)
{
crc ^= *current++;
for (int j = 0; j < 8; j++)
{
// branch-free
crc = (crc >> 1) ^ (-int32_t(crc & 1) & Polynomial);
// branching, much slower:
//if (crc & 1)
// crc = (crc >> 1) ^ Polynomial;
//else
// crc = crc >> 1;
}
}
return ~crc; // same as crc ^ 0xFFFFFFFF
}
*/
#if USE > 2
/// compute CRC32 (half-byte algoritm)
uint32_t crc32_halfbyte(const void* data, size_t length, uint32_t previousCrc32 = 0)
{
uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
const uint8_t* current = (const uint8_t*) data;
/// look-up table for half-byte, same as crc32Lookup[0][16*i]
static const uint32_t Crc32Lookup16[16] =
{
0x00000000,0x1DB71064,0x3B6E20C8,0x26D930AC,0x76DC4190,0x6B6B51F4,0x4DB26158,0x5005713C,
0xEDB88320,0xF00F9344,0xD6D6A3E8,0xCB61B38C,0x9B64C2B0,0x86D3D2D4,0xA00AE278,0xBDBDF21C
};
while (length-- != 0)
{
crc = Crc32Lookup16[(crc ^ *current ) & 0x0F] ^ (crc >> 4);
crc = Crc32Lookup16[(crc ^ (*current >> 4)) & 0x0F] ^ (crc >> 4);
current++;
}
return ~crc; // same as crc ^ 0xFFFFFFFF
}
/// compute CRC32 (standard algorithm)
uint32_t crc32_1byte(const void* data, size_t length, uint32_t previousCrc32 = 0)
{
uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
const uint8_t* current = (const uint8_t*) data;
while (length-- > 0)
crc = (crc >> 8) ^ Crc32Lookup[0][(crc & 0xFF) ^ *current++];
return ~crc; // same as crc ^ 0xFFFFFFFF
}
/// compute CRC32 (Slicing-by-4 algorithm)
uint32_t crc32_4bytes(const void* data, size_t length, uint32_t previousCrc32 = 0)
{
uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
const uint32_t* current = (const uint32_t*) data;
// process four bytes at once (Slicing-by-4)
while (length >= 4)
{
#if __BYTE_ORDER == __BIG_ENDIAN
uint32_t one = *current++ ^ swap(crc);
crc = Crc32Lookup[0][ one & 0xFF] ^
Crc32Lookup[1][(one>> 8) & 0xFF] ^
Crc32Lookup[2][(one>>16) & 0xFF] ^
Crc32Lookup[3][(one>>24) & 0xFF];
#else
uint32_t one = *current++ ^ crc;
crc = Crc32Lookup[0][(one>>24) & 0xFF] ^
Crc32Lookup[1][(one>>16) & 0xFF] ^
Crc32Lookup[2][(one>> 8) & 0xFF] ^
Crc32Lookup[3][ one & 0xFF];
#endif
length -= 4;
}
const uint8_t* currentChar = (const uint8_t*) current;
// remaining 1 to 3 bytes (standard algorithm)
while (length-- != 0)
crc = (crc >> 8) ^ Crc32Lookup[0][(crc & 0xFF) ^ *currentChar++];
return ~crc; // same as crc ^ 0xFFFFFFFF
}
/// compute CRC32 (Slicing-by-8 algorithm)
uint32_t crc32_8bytes(const void* data, size_t length, uint32_t previousCrc32 = 0)
{