On Tue, May 08, 2007, Esben Nielsen wrote:
This is contrary to C99 standeard annex H2.2
(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf):
"An implementation that defines signed integer types as also being modulo
need
not detect integer overflow, in which case, only integer divide-by-zero need
be detected."
So if it doesn't properly defines wrapping it has to detect integer
overflow, right?
No. Annex H (informative!) only talks about LIA-1 conformance.
C99 isn't LIA-1 conformant. H2.2 describes what an implementation
might do to make signed integers LIA-1 compatible.
, which is
what gcc does with -fwarpv or -ftrapv.
At least that's how I understand it, the C99 standard
seems to have been written with the "it was hard to
write, so it should be hard to read" mindset. :-/
I still don't know _why_ signed integer overflow behaviour
isn't defined in C. It just goes against everyones expectation
and thus causes bugs.
-
Johannes