Use clz ^ 31 instead of 31 - clz; better codegen for GCC

2019-09-23 21:23:09 +02:00
parent 7451c6578c
commit 1f7228c040
8 changed files with 8 additions and 8 deletions
@@ -530,7 +530,7 @@ MEM_STATIC unsigned BITv07_highbit32 (U32 val)
    _BitScanReverse ( &r, val );
    return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   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;