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Commit 1edfbb41 authored by Jan Beulich's avatar Jan Beulich Committed by Ingo Molnar
Browse files

x86/64: Adjust types of temporaries used by ffs()/fls()/fls64() 



The 64-bit special cases of the former two (the thrird one is
64-bit only anyway) don't need to use "long" temporaries, as the
result will always fit in a 32-bit variable, and the functions
return plain "int". This avoids a few REX prefixes, i.e.
minimally reduces code size.

Signed-off-by: default avatarJan Beulich <jbeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/504DE550020000780009A258@nat28.tlf.novell.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 6eebdda3

arch/x86/include/asm/bitops.h

+4 −6
Original line number Diff line number Diff line
@@ -417,10 +417,9 @@ static inline int ffs(int x) 
	 * We cannot do this on 32 bits because at the very least some

	 * 486 CPUs did not behave this way.

	 */

	long tmp = -1;

	asm("bsfl %1,%0"

	    : "=r" (r)

	    : "rm" (x), "0" (tmp));

	    : "rm" (x), "0" (-1));

#elif defined(CONFIG_X86_CMOV)

	asm("bsfl %1,%0\n\t"

	    "cmovzl %2,%0"
@@ -459,10 +458,9 @@ static inline int fls(int x) 
	 * We cannot do this on 32 bits because at the very least some

	 * 486 CPUs did not behave this way.

	 */

	long tmp = -1;

	asm("bsrl %1,%0"

	    : "=r" (r)

	    : "rm" (x), "0" (tmp));

	    : "rm" (x), "0" (-1));

#elif defined(CONFIG_X86_CMOV)

	asm("bsrl %1,%0\n\t"

	    "cmovzl %2,%0"
@@ -490,13 +488,13 @@ static inline int fls(int x) 
#ifdef CONFIG_X86_64

static __always_inline int fls64(__u64 x)

{

	long bitpos = -1;

	int bitpos = -1;

	/*

	 * AMD64 says BSRQ won't clobber the dest reg if x==0; Intel64 says the

	 * dest reg is undefined if x==0, but their CPU architect says its

	 * value is written to set it to the same as before.

	 */

	asm("bsrq %1,%0"

	asm("bsrq %1,%q0"

	    : "+r" (bitpos)

	    : "rm" (x));

	return bitpos + 1;