swap(x,y)

[Jon Doran/60000]

In article <MYwDEFy00WB842JEUx at andrew.cmu.edu>, tg1e+ at andrew.cmu.edu (Timothy R. Gottschalk) writes:
> 
>        To swap two variables x,y in C without using a temporary variable:
> 
>        /* begin swap */
>        x += y;
>        y = x - y;
>        x -= y;
>        /* end swap */

I don't know about that, seems that overflow is a possibility...

Something that I've used (mainly in assembly code) is:
	x ^= y;
	y ^= x;
	x ^= y;

To verify that the above works (x and y must be the same size of a variable...)
choose appropriate values for x and y, represent these in binary on paper,
then perform the exclusive ors manually.  This is perhaps the best explaination.



Jon Doran
IBM AWD,  Austin TX