pa[0] = (struct bst_node *) root;
da[0] = 0;
k = 1;
for (p = *root; p != NULL; p = p->bst_link[da[k - 1]])
  {
    int cmp = tree->bst_compare (n->bst_data, p->bst_data, tree->bst_param);
    assert (cmp != 0);

    if (k >= BST_MAX_HEIGHT)
      return 0;

    pa[k] = p;
    da[k++] = cmp > 0;
  }

