From: Joe Buck <Joe.Buck@synopsys.COM>
To: Dave Korn <dk@artimi.com>
Cc: "'Nick Ing-Simmons'" <nick@ing-simmons.net>,
jamie@shareable.org, gcc@gcc.gnu.org,
"'Morten Welinder'" <terra@gnome.org>
Subject: Re: signed vs unsigned pointer warning
Date: Fri, 08 Oct 2004 18:22:00 -0000 [thread overview]
Message-ID: <20041008102014.A2364@synopsys.com> (raw)
In-Reply-To: <NUTMEGmiU2mdk9tEee90000033d@NUTMEG.CAM.ARTIMI.COM>; from dk@artimi.com on Fri, Oct 08, 2004 at 06:12:09PM +0100
I wrote:
> > Here's a bug fix:
> >
> > table_lookup[1U+(unsigned)(c)]
> >
> > Now EOF goes into slot 0.
On Fri, Oct 08, 2004 at 06:12:09PM +0100, Dave Korn wrote:
> Hmm, but only by virtue of integer maths overflow. Wouldn't it be better
> to just leave out the cast in this case and do the sum in signed math?
No. The C standard guarantees that unsigned arithmetic obeys the rules
of arithmetic modulo 2**N, where N is the number of bits. The overflow is
well-defined and is required to yield zero.
Signed math would mishandle the original case, where the original argument
was a signed char with 8th bit set.
next prev parent reply other threads:[~2004-10-08 17:20 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-22 16:43 Morten Welinder
2004-09-22 17:17 ` Paul Koning
2004-09-22 17:27 ` Morten Welinder
2004-09-22 17:49 ` Dave Korn
2004-09-22 17:20 ` Dave Korn
2004-09-23 1:31 ` Andreas Schwab
2004-09-23 12:29 ` Dave Korn
2004-09-23 18:57 ` Joe Buck
2004-09-23 19:38 ` Dave Korn
2004-09-27 2:04 ` Jamie Lokier
2004-10-08 13:29 ` Nick Ing-Simmons
2004-10-08 13:32 ` Dave Korn
2004-10-08 17:20 ` Joe Buck
2004-10-08 17:28 ` Paul Jarc
2004-10-08 17:59 ` Joe Buck
2004-10-08 18:15 ` Dave Korn
2004-10-08 18:22 ` Joe Buck [this message]
2004-10-08 18:24 ` Jamie Lokier
2004-10-08 19:57 ` Paul Jarc
2004-10-09 7:05 ` Jamie Lokier
2004-10-09 8:48 ` Paul Jarc
2004-10-11 16:34 ` Richard Earnshaw
2004-10-08 18:57 ` Morten Welinder
2004-10-08 20:59 ` Matthias B.
2004-10-08 22:34 ` Paul Koning
2004-10-10 2:03 ` Matthias B.
2004-10-09 1:39 ` Andreas Schwab
2004-10-11 0:11 ` Kai Henningsen
-- strict thread matches above, loose matches on Subject: below --
2004-09-21 20:52 Richard Henderson
2004-09-21 22:36 ` Linus Torvalds
2004-09-22 14:35 ` Dave Korn
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