From: Joe Buck <Joe.Buck@synopsys.COM>
To: Dave Korn <dk@artimi.com>
Cc: "'Andreas Schwab'" <schwab@suse.de>,
"'Morten Welinder'" <terra@gnome.org>,
gcc@gcc.gnu.org
Subject: Re: signed vs unsigned pointer warning
Date: Thu, 23 Sep 2004 18:57:00 -0000 [thread overview]
Message-ID: <20040923091118.A2943@synopsys.com> (raw)
In-Reply-To: <NUTMEGL3tAkqzwUUAPk00000053@NUTMEG.CAM.ARTIMI.COM>; from dk@artimi.com on Thu, Sep 23, 2004 at 12:35:22PM +0100
On Thu, Sep 23, 2004 at 12:35:22PM +0100, Dave Korn wrote:
> > "Dave Korn" writes:
> >
> > > Which I don't think you can, since you can't store negative numbers
> > > in an unsigned type.
> >
> > Actually you can, due to the modulo behaviour of unsigned integers.
> >
> > Andreas.
>
> Well, yes, it is physically possible, but it's a kind of type-punning, it
> defies the aliasing rules, and we get into some very deeply
> language-lawyerly issues here, but it's not a valid representation IIUIC and
> therefore invokes undefined behaviour in many circumstances.
The C aliasing rules specifically bless accessing ints as unsigneds, and,
more generally, punning accesses between any type and the unsigned version
of that type.
next prev parent reply other threads:[~2004-09-23 16:11 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 [this message]
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
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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