doh array inversion

How do I get this function to work for arrays with an odd height?

Code:

---

int invert_array(int ptrarray[width][height],int width, int height)
{
  for (int down=0, up=height-1; down<=up; ++down,--up){
      for (int forward=0, reverse=width-1; forward < width; ++forward,--reverse){
        swap(&ptrarray[forward][down],&ptrarray[reverse][up]);
    }
  }
}

---

> down<=up
Presumably, on the last (middle) row, down == up

So perhaps
down<up
is the condition

Unless your swap function is so broken that you can't swap an element with itself.
You're not using some dumb xor-ing trick are you?