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

  if (a == NULL || b == NULL)
    {
      if (a != NULL || b != NULL)
        {
          printf (" a=%d b=%d\n",
                  a ? *(int *) a->tbst_data : -1,
                  b ? *(int *) b->tbst_data : -1);
          assert (0);
        }
      return 1;
    }
  assert (a != b);

  if (*(int *) a->tbst_data != *(int *) b->tbst_data
      || a->tbst_tag[0] != b->tbst_tag[0]
      || a->tbst_tag[1] != b->tbst_tag[1])
    {
      printf (" Copied nodes differ: a=%d b=%d a:",
              *(int *) a->tbst_data, *(int *) b->tbst_data);

      if (a->tbst_tag[0] == TBST_CHILD)
        printf ("l");
      if (a->tbst_tag[1] == TBST_CHILD)
        printf ("r");

      printf (" b:");
      if (b->tbst_tag[0] == TBST_CHILD)
        printf ("l");
      if (b->tbst_tag[1] == TBST_CHILD)
        printf ("r");

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

  if (a->tbst_tag[0] == TBST_THREAD)
    assert ((a->tbst_link[0] == NULL) != (a->tbst_link[0] != b->tbst_link[0]));
  if (a->tbst_tag[1] == TBST_THREAD)
    assert ((a->tbst_link[1] == NULL) != (a->tbst_link[1] != b->tbst_link[1]));

  okay = 1;
  if (a->tbst_tag[0] == TBST_CHILD)
    okay &= compare_trees (a->tbst_link[0], b->tbst_link[0]);
  if (a->tbst_tag[1] == TBST_CHILD)
    okay &= compare_trees (a->tbst_link[1], b->tbst_link[1]);
  return okay;
}