From 570b6b5a7a4509cf659b38ff032eeedb58923db2 Mon Sep 17 00:00:00 2001 From: Daan Date: Tue, 21 Jan 2025 20:53:16 -0800 Subject: [PATCH] slightly better bsf --- include/mimalloc/bits.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/include/mimalloc/bits.h b/include/mimalloc/bits.h index 5b847f4b..64875e9d 100644 --- a/include/mimalloc/bits.h +++ b/include/mimalloc/bits.h @@ -205,9 +205,8 @@ static inline size_t mi_ctz(size_t x) { #elif mi_has_builtinz(ctz) return (x!=0 ? (size_t)mi_builtinz(ctz)(x) : MI_SIZE_BITS); #elif defined(__GNUC__) && (MI_ARCH_X64 || MI_ARCH_X86) - if (x==0) return MI_SIZE_BITS; - size_t r; - __asm ("bsf\t%1, %0" : "=r"(r) : "r"(x) : "cc"); + size_t r = MI_SIZE_BITS; // bsf leaves destination unmodified if the argument is 0 (see ) + __asm ("bsf\t%1, %0" : "+r"(r) : "r"(x) : "cc"); return r; #elif MI_HAS_FAST_POPCOUNT return (x!=0 ? (mi_popcount(x^(x-1))-1) : MI_SIZE_BITS);