/* Compares binary trees rooted at |a| and |b|,
   making sure that they are identical. */
static int
compare_trees (struct prb_node *a, struct prb_node *b)
{
  int okay;

  if (a == NULL || b == NULL)
    {
      assert (a == NULL && b == NULL);
      return 1;
    }

  if (*(int *) a->prb_data != *(int *) b->prb_data
      || ((a->prb_link[0] != NULL) != (b->prb_link[0] != NULL))
      || ((a->prb_link[1] != NULL) != (b->prb_link[1] != NULL))
      || a->prb_color != b->prb_color)
    {
      printf (" Copied nodes differ: a=%d%c b=%d%c a:",
              *(int *) a->prb_data, a->prb_color == PRB_RED ? 'r' : 'b',
              *(int *) b->prb_data, b->prb_color == PRB_RED ? 'r' : 'b');

      if (a->prb_link[0] != NULL)
        printf ("l");
      if (a->prb_link[1] != NULL)
        printf ("r");

      printf (" b:");
      if (b->prb_link[0] != NULL)
        printf ("l");
      if (b->prb_link[1] != NULL)
        printf ("r");

      printf ("\n");
      return 0;
    }

  okay = 1;
  if (a->prb_link[0] != NULL)
    okay &= compare_trees (a->prb_link[0], b->prb_link[0]);
  if (a->prb_link[1] != NULL)
    okay &= compare_trees (a->prb_link[1], b->prb_link[1]);
  return okay;
}