On Wed, 21 Dec 2005, Robert Dewar wrote:
> Gabriel Dos Reis wrote:
>
> >with no more qualifications (this definition is slightly different in
> >some nearby languages), it is slippery to found optimizations on
> >"pointer overflows."
> >
> >
> Well I think unfortunately the standard does allow such "optimizations", but
> that does
> not mean it is a good thing to take advantage of this.
Another example is
char a[2];
void foo(void)
{
char *p = &a[1];
if (p + 0xffffffff > p)
abort ();
}
where, on a 32bit arch, p + 0xffffffff will point to a[0] (does the std
say so?), but we still optimize the test to if (1) abort (); because
we say "pointer overflow" is undefined. Using p - 1 > p will work as
expected.
So the basic question remains - is pointer overflow defined?
Richard.
