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slightly better bsf

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Daan 2025-01-21 20:53:16 -08:00
parent 3f6d286a08
commit 570b6b5a7a
1 changed files with 2 additions and 3 deletions
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5
include/mimalloc/bits.h
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@ -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 <https://github.com/llvm/llvm-project/pull/102885>)
__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);