Messages in this thread |  | | Date | Mon, 24 Feb 2003 23:21:44 +0100 | From | Jörn Engel <> | Subject | Re: [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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |