/* Performs a compression transformation |count| times,
   starting at |root|. */
static void
compress (struct rtbst_node *root,
          unsigned long nonthread, unsigned long thread)
{
  assert (root != NULL);

  while (nonthread--)
    {
      struct rtbst_node *red = root->rtbst_link[0];
      struct rtbst_node *black = red->rtbst_link[0];

      root->rtbst_link[0] = black;
      red->rtbst_link[0] = black->rtbst_link[1];
      black->rtbst_link[1] = red;
      root = black;
    }

  while (thread--)
    {
      struct rtbst_node *red = root->rtbst_link[0];
      struct rtbst_node *black = red->rtbst_link[0];

      root->rtbst_link[0] = black;
      red->rtbst_link[0] = NULL;
      black->rtbst_rtag = RTBST_CHILD;
      root = black;
    }
}