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To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] Faster generic_fls
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From: Andi Kleen <ak@suse.de>
Date: 01 May 2003 03:46:18 +0200
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Linus Torvalds <torvalds@transmeta.com> writes:

> Yeah, except if you want best code generation you should probably use
> 
> 	static inline int fls(int x)
> 	{
> 		int bit;
> 		/* Only well-defined for non-zero */
> 		asm("bsrl %1,%0":"=r" (bit):"rm" (x));

"g" should work for the second operand too and it'll give gcc
slightly more choices with possibly better code.

But the __builtin is probably preferable if gcc supports it because
a builtin can be scheduled, inline assembly can't.

-Andi