Re: [RFC][PATCH] Faster generic_fls

From: Falk Hueffner (falk.hueffner@student.uni-tuebingen.de)
Date: Wed Apr 30 2003 - 16:59:09 EST

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Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> On Mer, 2003-04-30 at 17:16, Linus Torvalds wrote:
> > Clearly you're not going to make _one_ load to get fls, since having a
> > 4GB lookup array for a 32-bit fls would be "somewhat" wasteful.
>
> It ought to be basically the same as ffs because if I remember rightly
>
> ffs(x^(x-1)) == fls(x)

I don't think so. Maybe you are thinking of ffs(x) == fls(x & -x). So
you can calculate ffs with fls, but not easily the other way round.

-- 
	Falk
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