From: Segher Boessenkool <segher@kernel.crashing.org>
To: Gabriel Paubert <paubert@iram.es>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
wei.guo.simon@gmail.com, linux-kernel@vger.kernel.org,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v4 3/4] powerpc/lib: implement strlen() in assembly
Date: Fri, 8 Jun 2018 07:05:32 -0500 [thread overview]
Message-ID: <20180608120532.GD17342@gate.crashing.org> (raw)
In-Reply-To: <20180608114513.gtgg7o4ejcqrjiz4@lt-gp.iram.es>
On Fri, Jun 08, 2018 at 01:45:13PM +0200, Gabriel Paubert wrote:
> On Fri, Jun 08, 2018 at 10:20:41AM +0000, Christophe Leroy wrote:
> > + rlwinm. r8, r9, 0, 0xff000000
> > + beq 20f
> > + rlwinm. r8, r9, 0, 0x00ff0000
> > + beq 21f
> > + rlwinm. r8, r9, 0, 0x0000ff00
> > + beq 22f
> > +23: subf r3, r3, r10
>
> Actually these rlwinm. can likely be replaced by a single
> cntlzw /cntlzd; for 32 bit something like:
>
> cntlzw r8,r9
> subf r3,r3,r10
> srwi r8,r8,3
> add r3,r3,r8
> blr
The code is finding the first zero byte in the word, not how many leading
zero bytes there are.
Segher
next prev parent reply other threads:[~2018-06-08 12:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-08 10:20 [PATCH v4 1/4] selftests/powerpc: add test for 32 bits memcmp Christophe Leroy
2018-06-08 10:20 ` [PATCH v4 2/4] selftests/powerpc: Add test for strlen() Christophe Leroy
2018-06-08 10:20 ` [PATCH v4 3/4] powerpc/lib: implement strlen() in assembly Christophe Leroy
2018-06-08 11:45 ` Gabriel Paubert
2018-06-08 12:05 ` Segher Boessenkool [this message]
2018-06-08 10:20 ` [PATCH v4 4/4] selftests/powerpc: update strlen() test to test the new assembly function Christophe Leroy
2018-06-08 10:26 ` [PATCH v4 1/4] selftests/powerpc: add test for 32 bits memcmp Christophe Leroy
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