Re: Integer Overflow

On 2010-12-30, Ian Collins <ian-news@xxxxxxxxxxx> wrote:
"What could possibly be a cheaper way to detect overflow than reading a
status register?"

Ahh, that's an interesting question. I'm not sure, actually; there's a lot
of ideas that might come to mind, but it's not obvious that any of them
are necessarily cheaper.

That said, there is almost certainly at least one implementation out there
where calculating-in-advance whether or not something will overflow would
be orders of magnitude cheaper than checking the status register. So, you
do your check of the form
if (INT_MAX - b < a)
...
and the resulting instructions execute faster than the equivalent of:
c = a + b;
if (_overflow())
...

Who knows? CPUs surprise us. When I was a kid, I was told to avoid floating
point math because it was so much slower than integer.

-s
--
Copyright 2010, all wrongs reversed. Peter Seebach / usenet-nospam@xxxxxxxxx
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