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Date: Mon, 24 Feb 2003 23:21:44 +0100
From: =?iso-8859-1?Q?J=F6rn?= Engel <joern@wohnheim.fh-wedel.de>
To: Andreas Schwab <schwab@suse.de>
Cc: Jeff Garzik <jgarzik@pobox.com>, Linus Torvalds <torvalds@transmeta.com>,
       "Richard B. Johnson" <root@chaos.analogic.com>,
       Martin Schwidefsky <schwidefsky@de.ibm.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] s390 (7/13): gcc 3.3 adaptions.
Message-ID: <20030224222144.GA27579@wohnheim.fh-wedel.de>
References: <Pine.LNX.4.44.0302241259320.13406-100000@penguin.transmeta.com> <jeznol5plv.fsf@sykes.suse.de> <20030224215335.GA24975@gtf.org> <jeu1et5o4i.fsf@sykes.suse.de>
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On Mon, 24 February 2003 23:07:25 +0100, Andreas Schwab wrote:
> 
> Jeff Garzik <jgarzik@pobox.com> writes:
> 
> |> On Mon, Feb 24, 2003 at 10:35:24PM +0100, Andreas Schwab wrote:
> |> > Linus Torvalds <torvalds@transmeta.com> writes:
> |> > 
> |> > |> Does gcc still warn about things like
> |> > |> 
> |> > |> 	#define COUNT (sizeof(array)/sizeof(element))
> |> > |> 
> |> > |> 	int i;
> |> > |> 	for (i = 0; i < COUNT; i++)
> |> > |> 		...
> |> > |> 
> |> > |> where COUNT is obviously unsigned (because sizeof is size_t and thus 
> |> > |> unsigned)?
> |> > |> 
> |> > |> Gcc used to complain about things like that, which is a FUCKING DISASTER. 
> |> > 
> |> > How can you distinguish that from other occurrences of (int)<(size_t)?
> |> 
> |> The bounds are obviously constant and unsigned at compile time.
> 
> But that's not the point.  It's the runtime value of i that gets converted
> (to unsigned), not the compile time value of COUNT.  Thus if i ever gets
> negative you have a problem.

COUNT is constant and COUNT < INT_MAX. gcc can cast the constant bound
to the variable's type to fix this problem.
Or, gcc can see that i starts with 0, it's value monotonously
increases and will never wrap around due to COUNT < INT_MAX. Not a
cheap test, but still possible.

J?rn

-- 
My second remark is that our intellectual powers are rather geared to
master static relations and that our powers to visualize processes
evolving in time are relatively poorly developed.
-- Edsger W. Dijkstra
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