de Bruijn CTZ with proper handling of 0

ctz.c

// you faggots probably know the de bruijn trick to count trailing zeros:

inline int ctz32_retarded(uint32_t x)
{
    static const unsigned char debruijn_ctz32[32] = {
        0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
        31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
    };
    return debruijn_ctz32[((x & -x) * 0x077CB531) >> 27];
}

// explanation:
//
// * x&-x clears all bits except the least significant non-zero bit, i.e., we
//   obtain 2^n for some 0<=n<=31 and our goal is to determine n
// * 0x077CB531(0) is a de bruijn sequence containing all of the 32 distinct
//   5-bit strings (and exactly once)
// * multiplication by 2^n shifts the sequence to the left by n bits
// * thus, the 5 most significant bits of the product are unique for each n
// * the debruijn_ctz32 lookup table maps the unique 5 bits to n
//
// however, this yields an incorrect result for x=0
//
//  debruijn_ctz32[((0 & -0) * 0x077CB531) >> 27] = debruin_ctz32[0] = 0
//
// some may argue that this isn't incorrect because CTZ is undefined for 0.
// these people are retarded since ctz32(1)=0=ctz32(0) is just fucking stupid.
//
// so let me propose a relatively clean workaround to get ctz32(0)=32

inline int ctz32(uint32_t x)
{
    static const unsigned char debruijn_ctz32[32] = {
        31, 0, 27, 1, 28, 13, 23, 2, 29, 21, 19, 14, 24, 16, 3, 7,
        30, 26, 12, 22, 20, 18, 15, 6, 25, 11, 17, 5, 10, 4, 9, 8 
    };
    return !x + debruijn_ctz32[((x & -x) * 0x0EF96A62) >> 27];
}

// here we use a de bruijn sequence that multiplied by 2^31 sets the 5 most
// significant bits to 0 so that debruijn_ctz32[0] = 31, and therefore
//
//  !0 + debruijn_ctz32[((0 & -0) * 0x0EF96A62) >> 27] = 1 + 31 = 32

// 64-bit versions:

inline int ctz64_retarded(uint64_t x) {
    static const unsigned char debruijn_ctz64[64] = {
        0, 1, 2, 53, 3, 7, 54, 27, 4, 38, 41, 8, 34, 55, 48, 28,
        62, 5, 39, 46, 44, 42, 22, 9, 24, 35, 59, 56, 49, 18, 29, 11,
        63, 52, 6, 26, 37, 40, 33, 47, 61, 45, 43, 21, 23, 58, 17, 10,
        51, 25, 36, 32, 60, 20, 57, 16, 50, 31, 19, 15, 30, 14, 13, 12
    };
    return debruijn_ctz64[((x & -x) * 0x022FDD63CC95386D) >> 58];
}

inline int ctz64(uint64_t x) {
    static const unsigned char debruijn_ctz64[64] = {
        63, 0, 1, 52, 2, 6, 53, 26, 3, 37, 40, 7, 33, 54, 47, 27,
        61, 4, 38, 45, 43, 41, 21, 8, 23, 34, 58, 55, 48, 17, 28, 10,
        62, 51, 5, 25, 36, 39, 32, 46, 60, 44, 42, 20, 22, 57, 16, 9,
        50, 24, 35, 31, 59, 19, 56, 15, 49, 30, 18, 14, 29, 13, 12, 11
    };
    return !x + debruijn_ctz64[((x & -x) * 0x045FBAC7992A70DA) >> 58];
}