From: Andreas Schwab <schwab@suse.de>
To: Gabriel Paubert <paubert@iram.es>
Cc: linuxppc-dev@ozlabs.org, paulus@samba.org,
LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] add strncmp to PowerPC
Date: Mon, 03 Mar 2008 11:10:27 +0100 [thread overview]
Message-ID: <je4pbow224.fsf@sykes.suse.de> (raw)
In-Reply-To: <20080303095443.GB27105@iram.es> (Gabriel Paubert's message of "Mon\, 3 Mar 2008 10\:54\:43 +0100")
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, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
WARNING: multiple messages have this Message-ID (diff)
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
Date: Mon, 03 Mar 2008 11:10:27 +0100 [thread overview]
Message-ID: <je4pbow224.fsf@sykes.suse.de> (raw)
In-Reply-To: <20080303095443.GB27105@iram.es> (Gabriel Paubert's message of "Mon\, 3 Mar 2008 10\:54\:43 +0100")
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, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
next prev parent reply other threads:[~2008-03-03 10:10 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-29 16:04 [PATCH] add strncmp to PowerPC Steven Rostedt
2008-03-01 3:04 ` Benjamin Herrenschmidt
2008-03-01 3:04 ` Benjamin Herrenschmidt
2008-03-01 3:56 ` Steven Rostedt
2008-03-01 3:56 ` Steven Rostedt
2008-03-03 9:54 ` Gabriel Paubert
2008-03-03 9:54 ` Gabriel Paubert
2008-03-03 10:10 ` Andreas Schwab [this message]
2008-03-03 10:10 ` Andreas Schwab
2008-03-03 19:08 ` Segher Boessenkool
2008-03-03 19:08 ` Segher Boessenkool
2008-03-05 4:03 ` Paul Mackerras
2008-03-05 4:03 ` Paul Mackerras
2008-03-05 5:26 ` Segher Boessenkool
2008-03-05 5:26 ` Segher Boessenkool
2008-03-05 5:39 ` Paul Mackerras
2008-03-05 5:39 ` Paul Mackerras
2008-03-05 7:01 ` Segher Boessenkool
2008-03-05 7:01 ` Segher Boessenkool
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