/* Converts |tree| into a vine. */
static void
tree_to_vine (struct bst_table *tree)
{
  struct bst_node *q, *p;

  q = (struct bst_node *) &tree->bst_root;
  p = tree->bst_root;
  while (p != NULL)
    if (p->bst_link[1] == NULL)
      {
        q = p;
        p = p->bst_link[0];
      }
    else
      {
        struct bst_node *r = p->bst_link[1];
        p->bst_link[1] = r->bst_link[0];
        r->bst_link[0] = p;
        p = r;
        q->bst_link[0] = r;
      }
}