Re: Subtracting unsigned entities

On May 12, 11:18=A0pm, fred.l.kleinschm...@[EMAIL PROTECTED]
 wrote:
> If one knows that x and y are unsigned integers (of unknown size -
> they may be short, int, long, long long), what is the most ****table
> way to determine their difference?


Let's take an example:

    unsigned x, y;

    x =3D 65530u;
    y =3D 655u;

The difference between these two is 64875.

If you do (x-y), you'll get 64875u. However if you do (y-x), you'll
get an implementation-defined value which depends on the value of
UINT_MAX (because when you go past zero you'll start counting backward
from UINT_MAX).


> If x is smaller than y, then x-y is negative.
>
> A naive approach is
> =A0 =A0if ( x > y ) {
> =A0 =A0 =A0 ...
> =A0 =A0}
>
> but a compiler may code (x>y) as =A0(x-y > 0)


The if method is the only one that comes to mind.