Commit d832245d authored by Stephen Hemminger's avatar Stephen Hemminger Committed by Linus Torvalds
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[PATCH] x86: fls() in asm

There is a single instruction on i386 to find largest set bit; so it makes
sense to use it (like we use bfs for ffs()).
Signed-off-by: default avatarStephen Hemminger <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent e31b88ba
......@@ -367,11 +367,6 @@ static inline unsigned long ffz(unsigned long word)
return word;
* fls: find last bit set.
#define fls(x) generic_fls(x)
#define fls64(x) generic_fls64(x)
#ifdef __KERNEL__
......@@ -414,6 +409,23 @@ static inline int ffs(int x)
return r+1;
* fls - find last bit set
* @x: the word to search
* This is defined the same way as ffs.
static inline int fls(int x)
int r;
__asm__("bsrl %1,%0\n\t"
"jnz 1f\n\t"
"movl $-1,%0\n"
"1:" : "=r" (r) : "rm" (x));
return r+1;
* hweightN - returns the hamming weight of a N-bit word
* @x: the word to weigh
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