Autzoo.1633
net.bugs.v7
utzoo!henry
Tue May 4 22:02:15 1982
overflow in C revisited
Very entertaining things can happen with integer overflow in C. This
isn't really a bug, except that (as reported some months ago) the
manual should say the effects of overflow are "undefined" instead of
saying that it is "ignored". Consider the following:
-----
/*
* Arithmetic in the presence of overflow is context-dependent in
* very strange ways.
*/
unsigned int compile = (56*1024)/64;
main()
{
printf("%u == %u\n", compile, (56*1024)/64);
printf("%u == %u == %u (!!)\n", compile, 57734/64, (56*1024)/64);
}
-----
Can you guess what this prints? Like this:
65408 == 65408
65408 == 0 == 902 (!!)
Yes, friends, it's context-dependent!
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