Function MostSignificantBit

layers/utils/math_utils.h:77–91

Returns the 0-based index of the MSB, like the x86 bit scan reverse (bsr) instruction Note: an input mask of 0 yields -1

// Returns the 0-based index of the MSB, like the x86 bit scan reverse (bsr) instruction
// Note: an input mask of 0 yields -1
[[maybe_unused]] static inline int MostSignificantBit(uint32_t mask) {
#if defined __GNUC__
    return mask ? __builtin_clz(mask) ^ 31 : -1;
#elif defined _MSC_VER
    unsigned long bit_pos;
    return _BitScanReverse(&bit_pos, mask) ? int(bit_pos) : -1;
#else
    for (int k = 31; k >= 0; --k) {
        if (((mask >> k) & 1) != 0) {
            return k;
        }
    }
    return -1;
#endif
}

static inline int u_ffs(int val) {
#ifdef WIN32