linux-kernel - Re: [PATCH] add strncmp to PowerPC

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Date:	Mon, 03 Mar 2008 11:10:27 +0100
From:	Andreas Schwab <schwab@...e.de>
To:	Gabriel Paubert <paubert@...m.es>
Cc:	Steven Rostedt <rostedt@...dmis.org>, paulus@...ba.org,
	LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...abs.org
Subject: Re: [PATCH] add strncmp to PowerPC

Gabriel Paubert <paubert@...m.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@...e.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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