/* Initializes |trav| for use with |tree|
   and selects the null node. */
void
tbst_t_init (struct tbst_traverser *trav, struct tbst_table *tree)
{
  trav->tbst_table = tree;
  trav->tbst_node = NULL;
}

/* Initializes |trav| for |tree|.
   Returns data item in |tree| with the least value,
   or |NULL| if |tree| is empty. */
void *
tbst_t_first (struct tbst_traverser *trav, struct tbst_table *tree)
{
  assert (tree != NULL && trav != NULL);

  trav->tbst_table = tree;
  trav->tbst_node = tree->tbst_root;
  if (trav->tbst_node != NULL)
    {
      while (trav->tbst_node->tbst_tag[0] == TBST_CHILD)
        trav->tbst_node = trav->tbst_node->tbst_link[0];
      return trav->tbst_node->tbst_data;
    }
  else
    return NULL;
}

/* Initializes |trav| for |tree|.
   Returns data item in |tree| with the greatest value,
   or |NULL| if |tree| is empty. */
void *
tbst_t_last (struct tbst_traverser *trav, struct tbst_table *tree)
{
  assert (tree != NULL && trav != NULL);

  trav->tbst_table = tree;
  trav->tbst_node = tree->tbst_root;
  if (trav->tbst_node != NULL)
    {
      while (trav->tbst_node->tbst_tag[1] == TBST_CHILD)
        trav->tbst_node = trav->tbst_node->tbst_link[1];
      return trav->tbst_node->tbst_data;
    }
  else
    return NULL;
}

/* Searches for |item| in |tree|.
   If found, initializes |trav| to the item found and returns the item
   as well.
   If there is no matching item, initializes |trav| to the null item
   and returns |NULL|. */
void *
tbst_t_find (struct tbst_traverser *trav, struct tbst_table *tree, void *item)
{
  struct tbst_node *p;

  assert (trav != NULL && tree != NULL && item != NULL);

  trav->tbst_table = tree;
  trav->tbst_node = NULL;

  p = tree->tbst_root;
  if (p == NULL)
    return NULL;

  for (;;)
    {
      int cmp, dir;

      cmp = tree->tbst_compare (item, p->tbst_data, tree->tbst_param);
      if (cmp == 0)
        {
          trav->tbst_node = p;
          return p->tbst_data;
        }

      dir = cmp > 0;
      if (p->tbst_tag[dir] == TBST_CHILD)
        p = p->tbst_link[dir];
      else
        return NULL;
    }
}

/* Attempts to insert |item| into |tree|.
   If |item| is inserted successfully, it is returned and |trav| is
   initialized to its location.
   If a duplicate is found, it is returned and |trav| is initialized to
   its location.  No replacement of the item occurs.
   If a memory allocation failure occurs, |NULL| is returned and |trav|
   is initialized to the null item. */
void *
tbst_t_insert (struct tbst_traverser *trav,
               struct tbst_table *tree, void *item)
{
  void **p;

  assert (trav != NULL && tree != NULL && item != NULL);

  p = tbst_probe (tree, item);
  if (p != NULL)
    {
      trav->tbst_table = tree;
      trav->tbst_node =
        ((struct tbst_node *)
         ((char *) p - offsetof (struct tbst_node, tbst_data)));
      return *p;
    }
  else
    {
      tbst_t_init (trav, tree);
      return NULL;
    }
}

/* Initializes |trav| to have the same current node as |src|. */
void *
tbst_t_copy (struct tbst_traverser *trav, const struct tbst_traverser *src)
{
  assert (trav != NULL && src != NULL);

  trav->tbst_table = src->tbst_table;
  trav->tbst_node = src->tbst_node;

  return trav->tbst_node != NULL ? trav->tbst_node->tbst_data : NULL;
}

/* 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 *
tbst_t_next (struct tbst_traverser *trav)
{
  assert (trav != NULL);

  if (trav->tbst_node == NULL)
    return tbst_t_first (trav, trav->tbst_table);
  else if (trav->tbst_node->tbst_tag[1] == TBST_THREAD)
    {
      trav->tbst_node = trav->tbst_node->tbst_link[1];
      return trav->tbst_node != NULL ? trav->tbst_node->tbst_data : NULL;
    }
  else
    {
      trav->tbst_node = trav->tbst_node->tbst_link[1];
      while (trav->tbst_node->tbst_tag[0] == TBST_CHILD)
        trav->tbst_node = trav->tbst_node->tbst_link[0];
      return trav->tbst_node->tbst_data;
    }
}

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

  if (trav->tbst_node == NULL)
    return tbst_t_last (trav, trav->tbst_table);
  else if (trav->tbst_node->tbst_tag[0] == TBST_THREAD)
    {
      trav->tbst_node = trav->tbst_node->tbst_link[0];
      return trav->tbst_node != NULL ? trav->tbst_node->tbst_data : NULL;
    }
  else
    {
      trav->tbst_node = trav->tbst_node->tbst_link[0];
      while (trav->tbst_node->tbst_tag[1] == TBST_CHILD)
        trav->tbst_node = trav->tbst_node->tbst_link[1];
      return trav->tbst_node->tbst_data;
    }
}

/* Returns |trav|'s current item. */
void *
tbst_t_cur (struct tbst_traverser *trav)
{
  assert (trav != NULL);

  return trav->tbst_node != NULL ? trav->tbst_node->tbst_data : NULL;
}

/* Replaces the current item in |trav| by |new| and returns the item replaced.
   |trav| must not have the null item selected.
   The new item must not upset the ordering of the tree. */
void *
tbst_t_replace (struct tbst_traverser *trav, void *new)
{
  void *old;

  assert (trav != NULL && trav->tbst_node != NULL && new != NULL);
  old = trav->tbst_node->tbst_data;
  trav->tbst_node->tbst_data = new;
  return old;
}