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Commit 636dd2b7 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by Linus Torvalds
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[PATCH] x86_64: fls in asm for x86_64 



Use single instruction for find largest set bit on x86_64.

[Updated by Jan Beulich to fix wrong asm constraints in original
patch -AK]

Cc: jbeulich@novell.com
Signed-off-by: default avatarStephen Hemminger <shemminger@osdl.org>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent bd9cb64d

include/asm-x86_64/bitops.h

+16 −3
Original line number Diff line number Diff line
@@ -396,6 +396,22 @@ static __inline__ int fls64(__u64 x) 
	return __fls(x) + 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"

		"cmovzl %2,%0"

		: "=&r" (r) : "rm" (x), "rm" (-1));

	return r+1;

}



/**

 * hweightN - returns the hamming weight of a N-bit word

 * @x: the word to weigh
@@ -434,9 +450,6 @@ static __inline__ int fls64(__u64 x) 
#define minix_find_first_zero_bit(addr,size) \

	find_first_zero_bit((void*)addr,size)



/* find last set bit */

#define fls(x) generic_fls(x)



#endif /* __KERNEL__ */



#endif /* _X86_64_BITOPS_H */