Re: Direct computation of integer limits in K&R2?

Harald van D?k wrote:
CBFalconer wrote:
Harald van D?k wrote:

.... snip ...

#include <stdio.h>
int main(void) {
unsigned u = -1;
int i;
while ((i = u) < 0 || i != u)
u = u >> 1;
printf("INT_MAX == %u\n", u);
}

This is not guaranteed to work in C99, where the conversion of
an out-of- range integer may raise a signal, but it's valid C90,
since the result of the conversion must be a valid int, and
therefore between INT_MIN and INT_MAX.

This CAN'T work everywhere.

Yes, it can.

The u = -1 statement is legal, and results in UINT_MAX value.
However the first i = u statement always overruns the INT_MAX
value for i, unless the system has INT_MAX defined to be equal
to UINT_MAX. Very rare. So the result of that statement is
implementation defined.

Of course. And any of the permissible implementation-defined
values of i will result in the intended behaviour.

I think you have a misinterpretation of 'implementaion-defined'.
This means that the action, on a particular implementation, is
defined. However that may well be "*** ABORT in line nnn, integer
overflow ***".

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.



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