Subject: Re: [PATCH] add strncmp to PowerPC

From: Andreas Schwab <[email-masked]>
Date: Mon, 03 Mar 2008 11:10:27 +0100

Gabriel Paubert <[email-masked]> 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, [email-masked]
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."