From 636dd2b7def5c9c72551b51d4d516a65c269de08 Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Wed, 11 Jan 2006 22:43:24 +0100 Subject: [PATCH] [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: Stephen Hemminger Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- include/asm-x86_64/bitops.h | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/include/asm-x86_64/bitops.h b/include/asm-x86_64/bitops.h index 3638ffff87fd..eb4df23e1e41 100644 --- a/include/asm-x86_64/bitops.h +++ b/include/asm-x86_64/bitops.h @@ -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 */ -- 2.20.1