Function crc32_16bytes

ogsr_engine/xrCore/crc32.cpp:332–375

compute CRC32 (Slicing-by-16 algorithm)

#ifdef CRC32_USE_LOOKUP_TABLE_SLICING_BY_16
/// compute CRC32 (Slicing-by-16 algorithm)
uint32_t crc32_16bytes(const void* data, size_t length, uint32_t previousCrc32)
{
    uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
    const uint32_t* current = (const uint32_t*)data;

    // enabling optimization (at least -O2) automatically unrolls the inner for-loop
    const size_t Unroll = 4;
    const size_t BytesAtOnce = 16 * Unroll;

    while (length >= BytesAtOnce)
    {
        for (size_t unrolling = 0; unrolling < Unroll; unrolling++)
        {
#if __BYTE_ORDER == __BIG_ENDIAN
            uint32_t one = *current++ ^ swap(crc);
            uint32_t two = *current++;
            uint32_t three = *current++;
            uint32_t four = *current++;
            crc = Crc32Lookup[0][four & 0xFF] ^ Crc32Lookup[1][(four >> 8) & 0xFF] ^ Crc32Lookup[2][(four >> 16) & 0xFF] ^ Crc32Lookup[3][(four >> 24) & 0xFF] ^
                Crc32Lookup[4][three & 0xFF] ^ Crc32Lookup[5][(three >> 8) & 0xFF] ^ Crc32Lookup[6][(three >> 16) & 0xFF] ^ Crc32Lookup[7][(three >> 24) & 0xFF] ^
                Crc32Lookup[8][two & 0xFF] ^ Crc32Lookup[9][(two >> 8) & 0xFF] ^ Crc32Lookup[10][(two >> 16) & 0xFF] ^ Crc32Lookup[11][(two >> 24) & 0xFF] ^
                Crc32Lookup[12][one & 0xFF] ^ Crc32Lookup[13][(one >> 8) & 0xFF] ^ Crc32Lookup[14][(one >> 16) & 0xFF] ^ Crc32Lookup[15][(one >> 24) & 0xFF];
#else
            uint32_t one = *current++ ^ crc;
            uint32_t two = *current++;
            uint32_t three = *current++;
            uint32_t four = *current++;
            crc = Crc32Lookup[0][(four >> 24) & 0xFF] ^ Crc32Lookup[1][(four >> 16) & 0xFF] ^ Crc32Lookup[2][(four >> 8) & 0xFF] ^ Crc32Lookup[3][four & 0xFF] ^
                Crc32Lookup[4][(three >> 24) & 0xFF] ^ Crc32Lookup[5][(three >> 16) & 0xFF] ^ Crc32Lookup[6][(three >> 8) & 0xFF] ^ Crc32Lookup[7][three & 0xFF] ^
                Crc32Lookup[8][(two >> 24) & 0xFF] ^ Crc32Lookup[9][(two >> 16) & 0xFF] ^ Crc32Lookup[10][(two >> 8) & 0xFF] ^ Crc32Lookup[11][two & 0xFF] ^
                Crc32Lookup[12][(one >> 24) & 0xFF] ^ Crc32Lookup[13][(one >> 16) & 0xFF] ^ Crc32Lookup[14][(one >> 8) & 0xFF] ^ Crc32Lookup[15][one & 0xFF];
#endif
        }

        length -= BytesAtOnce;
    }

    const uint8_t* currentChar = (const uint8_t*)current;
    // remaining 1 to 63 bytes (standard algorithm)
    while (length-- != 0)
        crc = (crc >> 8) ^ Crc32Lookup[0][(crc & 0xFF) ^ *currentChar++];

    return ~crc; // same as crc ^ 0xFFFFFFFF
}

/// compute CRC32 (Slicing-by-16 algorithm, prefetch upcoming data blocks)
uint32_t crc32_16bytes_prefetch(const void* data, size_t length, uint32_t previousCrc32, size_t prefetchAhead)