/* Returns the next data item in inorder
   within the tree being traversed with |trav|,
   or if there are no more data items returns |NULL|. */
void *
rtbst_t_next (struct rtbst_traverser *trav)
{
  assert (trav != NULL);

  if (trav->rtbst_node == NULL)
    return rtbst_t_first (trav, trav->rtbst_table);
  else if (trav->rtbst_node->rtbst_rtag == RTBST_THREAD)
    {
      trav->rtbst_node = trav->rtbst_node->rtbst_link[1];
      return trav->rtbst_node != NULL ? trav->rtbst_node->rtbst_data : NULL;
    }
  else
    {
      trav->rtbst_node = trav->rtbst_node->rtbst_link[1];
      while (trav->rtbst_node->rtbst_link[0] != NULL)
        trav->rtbst_node = trav->rtbst_node->rtbst_link[0];
      return trav->rtbst_node->rtbst_data;
    }
}