"M. Edward Wilborne III" <[EMAIL PROTECTED]> writes:
> The real question, is, IMHO, "Is there an overflow carry when A+B get
> added?"
>
> So, if you right shift by 1 bit a and b, (i.e. divide each by 2) and then
> add those divided numbers together, then the resulting answer will have the
> high order bit set if the numbers when added (unshifted) would have caused
> and "overflow".
>
> There's probably an easy way to test this using subtraction...
Simple algebra.
To avoid overflow, the following equation must hold:
a + b <= maxint
Rearranging terms:
a <= maxint - b
Therefore,
if (a <= maxint - b) {
// no overflow, safe to add
}
It gets a little more complicated if you're using signed ints.
--
Dave Carrigan ([EMAIL PROTECTED]) | Yow! Can you MAIL a BEAN CAKE?
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http://www.rudedog.org/ |
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