def _combine64()

in oss2/crc64_combine.py [0:0]

• 35 lines of code
• 11 McCabe index (conditional complexity)

def _combine64(poly, initCrc, rev, xorOut, crc1, crc2, len2):
    if len2 == 0:
        return crc1

    even = [0] * GF2_DIM
    odd = [0] * GF2_DIM

    crc1 ^= initCrc ^ xorOut

    if (rev):
        # put operator for one zero bit in odd
        odd[0] = poly  # CRC-64 polynomial
        row = 1
        for n in xrange(1, GF2_DIM):
            odd[n] = row
            row <<= 1
    else:
        row = 2
        for n in xrange(0, GF2_DIM - 1):
            odd[n] = row
            row <<= 1
        odd[GF2_DIM - 1] = poly

    gf2_matrix_square(even, odd)

    gf2_matrix_square(odd, even)

    while True:
        gf2_matrix_square(even, odd)
        if len2 & long(1):
            crc1 = gf2_matrix_times(even, crc1)
        len2 >>= 1
        if len2 == 0:
            break

        gf2_matrix_square(odd, even)
        if len2 & long(1):
            crc1 = gf2_matrix_times(odd, crc1)
        len2 >>= 1

        if len2 == 0:
            break

    crc1 ^= crc2

    return crc1