if (!overflow)
  {
    for (; k > 1; k--)
      {
        struct bst_node *q = pa[k - 1];

        if (da[k - 1] == 0)
          {
            q->bst_link[0] = n->bst_link[1];
            n->bst_link[1] = q;
          }
        else /* |da[k - 1] == 1| */
          {
            q->bst_link[1] = n->bst_link[0];
            n->bst_link[0] = q;
          }
        pa[k - 2]->bst_link[da[k - 2]] = n;
      }
  }
else
  {
    while (*root != n)
      {
        struct bst_node **r; /* Link to node to rotate. */
        struct bst_node *q;  /* Node to rotate. */
        int dir;

        for (r = root; ; r = &q->bst_link[dir])
          {
            q = *r;
            dir = 0 < tree->bst_compare (n->bst_data, q->bst_data,
                                         tree->bst_param);

            if (q->bst_link[dir] == n)
              break;
          }

        if (dir == 0)
          {
            q->bst_link[0] = n->bst_link[1];
            n->bst_link[1] = q;
          }
        else
          {
            q->bst_link[1] = n->bst_link[0];
            n->bst_link[0] = q;
          }
        *r = n;
      }
  }