linux-kernel - Re: [PATCH V2 mmots] fs/hfsplus/wrapper.c: replace shift loop by fls

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Message-ID: <1400543405.19786.4.camel@joe-AO725>
Date:	Mon, 19 May 2014 16:50:05 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Fabian Frederick <fabf@...net.be>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 mmots] fs/hfsplus/wrapper.c: replace shift loop by fls

On Mon, 2014-05-19 at 16:40 -0700, Andrew Morton wrote:
> On Mon, 19 May 2014 16:22:28 -0700 Joe Perches <joe@...ches.com> wrote:
> 
> > On Mon, 2014-05-19 at 16:09 -0700, Andrew Morton wrote:
> > > On Fri, 16 May 2014 22:38:15 +0200 Fabian Frederick <fabf@...net.be> wrote:
> > > > Replace while blocksize;shift by fls -1
> > []
> > > fls() always makes my brain hurt.  ilog() is nicer?
> > Maybe take an aspirin?
> > ilog2(n) is effectively fls(n) - 1
> Precisely.  ilog2() means "integer log 2".  Whereas fls() is some weird
> low-level bit-scanning thing.

<shrug>  find-last[bit]-set is pretty obvious to me.
ilog2(n) makes me think just a little more.

> What we want at this callsite is "integer log 2".  So use it.

Same thing.  Same ratio of use too.

$ git grep -w fls | wc -l
457
$ git grep -w ilog2 | wc -l
391


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