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SubjectRe: [PATCH] s390 (7/13): gcc 3.3 adaptions.
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.

Jörn

--
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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