Update:

I just checked the docs - I'm only allowed *one* variable - the pointer. That doesn't invalidate the method below, it just makes it a lot more complicated. Just shuttle the pointer between the two variables as needed.

Are you sure you want to do this in a programming language that has less instructions than a RISC processor?

The only conditional operation you have is in the while, so in crappy-meta-language (I'm assuming a while (0) is false, just like in perl):

Put your values into *X and *Y somehow


while (*X) {
*X--
*Y--
}

#if Y was greater than X it will still be postive
while (*Y) {
  while (*Y) {
   #Empty Y so we can get out of the  
  #surrounding loop
   *Y--
 }
#Do your thing here
}
[download]

Of course, this will fail if while (-1) evaluates as true, but at least you can see where I'm going here.

____________________
Jeremy
I didn't believe in evil until I dated it.