From: Andreas Schwab <schwab@suse.de>
To: Gabriel Paubert <paubert@iram.es>
Cc: Steven Rostedt <rostedt@goodmis.org>, paulus@samba.org,
       LKML <linux-kernel@vger.kernel.org>, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] add strncmp to PowerPC
References: <1204301097.14759.6.camel@localhost.localdomain>
	<1204340690.15052.457.camel@pasglop>
	<Pine.LNX.4.58.0802292250490.21555@gandalf.stny.rr.com>
	<20080303095443.GB27105@iram.es>
Date: Mon, 03 Mar 2008 11:10:27 +0100
In-Reply-To: <20080303095443.GB27105@iram.es> (Gabriel Paubert's message of
	"Mon\, 3 Mar 2008 10\:54\:43 +0100")
Message-ID: <je4pbow224.fsf@sykes.suse.de>
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Gabriel Paubert <paubert@iram.es> writes:

> Now that I think a bit more about it, I believe that the C version is
> incorrect: the clrldi/extsb dance takes a value between -255 and +255
> and collapses it into the -128 to 127 range, meaning that the return
> value may be wrong if we rely on the sign of the result. So unless I
> miss something, the problem is much more serious than just stupid code
> (I had just a look at the libc version in C and characters are cast to
> unsigned char before the comparison).

The latter is explicitly required by the C standard.  Ie. even if your
characters are signed they are always compared as unsigned by
strcmp/strncmp/memcmp.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstra?e 5, 90409 N?rnberg, Germany
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"And now for something completely different."
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