if (tree->tbst_root != NULL)
  for (p = tree->tbst_root; ; p = p->tbst_link[dir])
    {
      int cmp = tree->tbst_compare (item, p->tbst_data, tree->tbst_param);
      if (cmp == 0)
        return &p->tbst_data;
      dir = cmp > 0;

      if (p->tbst_tag[dir] == TBST_THREAD)
        break;
    }
else
  {
    p = (struct tbst_node *) &tree->tbst_root;
    dir = 0;
  }