void swap(long* p, long* q)
{
  long t = *p;
  *p = *q;
  *q = t;
}

void swap_a(long *xp, long *yp) {
  volatile long loc[2];
  loc[0] = *xp;
  loc[1] = *yp;
  *xp = loc[1];
  *yp = loc[0];
}