/* Initializes |trav| for use with |tree|
   and selects the null node. */
void
pavl_t_init (struct pavl_traverser *trav, struct pavl_table *tree)
{
  trav->pavl_table = tree;
  trav->pavl_node = NULL;
}

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

  trav->pavl_table = tree;
  trav->pavl_node = tree->pavl_root;
  if (trav->pavl_node != NULL)
    {
      while (trav->pavl_node->pavl_link[0] != NULL)
        trav->pavl_node = trav->pavl_node->pavl_link[0];
      return trav->pavl_node->pavl_data;
    }
  else
    return NULL;
}

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

  trav->pavl_table = tree;
  trav->pavl_node = tree->pavl_root;
  if (trav->pavl_node != NULL)
    {
      while (trav->pavl_node->pavl_link[1] != NULL)
        trav->pavl_node = trav->pavl_node->pavl_link[1];
      return trav->pavl_node->pavl_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 *
pavl_t_find (struct pavl_traverser *trav, struct pavl_table *tree, void *item)
{
  struct pavl_node *p;
  int dir;

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

  trav->pavl_table = tree;
  for (p = tree->pavl_root; p != NULL; p = p->pavl_link[dir])
    {
      int cmp = tree->pavl_compare (item, p->pavl_data, tree->pavl_param);
      if (cmp == 0)
        {
          trav->pavl_node = p;
          return p->pavl_data;
        }

      dir = cmp > 0;
    }

  trav->pavl_node = NULL;
  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 *
pavl_t_insert (struct pavl_traverser *trav,
               struct pavl_table *tree, void *item)
{
  void **p;

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

  p = pavl_probe (tree, item);
  if (p != NULL)
    {
      trav->pavl_table = tree;
      trav->pavl_node =
        ((struct pavl_node *)
         ((char *) p - offsetof (struct pavl_node, pavl_data)));
      return *p;
    }
  else
    {
      pavl_t_init (trav, tree);
      return NULL;
    }
}

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

  trav->pavl_table = src->pavl_table;
  trav->pavl_node = src->pavl_node;

  return trav->pavl_node != NULL ? trav->pavl_node->pavl_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 *
pavl_t_next (struct pavl_traverser *trav)
{
  assert (trav != NULL);

  if (trav->pavl_node == NULL)
    return pavl_t_first (trav, trav->pavl_table);
  else if (trav->pavl_node->pavl_link[1] == NULL)
    {
      struct pavl_node *q, *p; /* Current node and its child. */
      for (p = trav->pavl_node, q = p->pavl_parent; ;
           p = q, q = q->pavl_parent)
        if (q == NULL || p == q->pavl_link[0])
          {
            trav->pavl_node = q;
            return trav->pavl_node != NULL ? trav->pavl_node->pavl_data : NULL;
          }
    }
  else
    {
      trav->pavl_node = trav->pavl_node->pavl_link[1];
      while (trav->pavl_node->pavl_link[0] != NULL)
        trav->pavl_node = trav->pavl_node->pavl_link[0];
      return trav->pavl_node->pavl_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 *
pavl_t_prev (struct pavl_traverser *trav)
{
  assert (trav != NULL);

  if (trav->pavl_node == NULL)
    return pavl_t_last (trav, trav->pavl_table);
  else if (trav->pavl_node->pavl_link[0] == NULL)
    {
      struct pavl_node *q, *p; /* Current node and its child. */
      for (p = trav->pavl_node, q = p->pavl_parent; ;
           p = q, q = q->pavl_parent)
        if (q == NULL || p == q->pavl_link[1])
          {
            trav->pavl_node = q;
            return trav->pavl_node != NULL ? trav->pavl_node->pavl_data : NULL;
          }
    }
  else
    {
      trav->pavl_node = trav->pavl_node->pavl_link[0];
      while (trav->pavl_node->pavl_link[1] != NULL)
        trav->pavl_node = trav->pavl_node->pavl_link[1];
      return trav->pavl_node->pavl_data;
    }
}

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

  return trav->pavl_node != NULL ? trav->pavl_node->pavl_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 *
pavl_t_replace (struct pavl_traverser *trav, void *new)
{
  void *old;

  assert (trav != NULL && trav->pavl_node != NULL && new != NULL);
  old = trav->pavl_node->pavl_data;
  trav->pavl_node->pavl_data = new;
  return old;
}