Function BIT_highbit32

freebsd/contrib/openzfs/module/zstd/lib/zstd.c:1435–1460

-************************************************************** * Internal functions ****************************************************************/

*  Internal functions
****************************************************************/
MEM_STATIC unsigned BIT_highbit32 (U32 val)
{
    assert(val != 0);
    {
#   if defined(_MSC_VER)   /* Visual */
        unsigned long r=0;
        return _BitScanReverse ( &r, val ) ? (unsigned)r : 0;
#   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
        return __builtin_clz (val) ^ 31;
#   elif defined(__ICCARM__)    /* IAR Intrinsic */
        return 31 - __CLZ(val);
#   else   /* Software version */
        static const unsigned DeBruijnClz[32] = { 0,  9,  1, 10, 13, 21,  2, 29,
                                                 11, 14, 16, 18, 22, 25,  3, 30,
                                                  8, 12, 20, 28, 15, 17, 24,  7,
                                                 19, 27, 23,  6, 26,  5,  4, 31 };
        U32 v = val;
        v |= v >> 1;
        v |= v >> 2;
        v |= v >> 4;
        v |= v >> 8;
        v |= v >> 16;
        return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
#   endif
    }
}

/*=====    Local Constants   =====*/
static const unsigned BIT_mask[] = {