void list_ins_aft ( node_t *old ,node_t *new )
{

  if ( old->next != NULL )
  {
    old->next->prev = new;
  }
  new->next = old->next;
  new->prev = old ;

  old->next = new ;
}

void list_detach( node_t *n , dlist_t *nlst)
{

  if (n->prev == NULL)
  {
    nlst->head = n->next;
  }
  else
  {
    n->prev->next = n->next;
  }

  if(n->next == NULL )
  {
    nlst->tail = n->prev;
  }
  else
  {
    n->next->prev = n->prev;
  }
}


void qsort_segment ( node_t *t1 , node_t *t2 , dlist_t *lst)
{

  /* skip 0 or 1 lengh segment */
  if ( t1 == t2 || t1->next == t2 )
    return;
  /*define pivot and make sure its the first element
   * so put the less before pivot and bigger after pivot
   * */
  node_t *piv;
  piv = t1->next;
  node_t *s,*b,*temp = piv , *x  = t2 ? t2->next : NULL ;

  for ( s = piv->next ; s != x ; s = b )
  {

    b = s->next ;

    list_detach ( s ,lst ) ;

    if ( s->value < piv->value )
    {
      list_ins_aft(t1 , s );
    }
    else
    {
      list_ins_aft ( piv , temp == piv ? ( temp = s ) : s );
    }
  }

  /* now sort new segments on right and left sides of pivot the same way */
  qsort_segment ( piv , temp ,lst );
  qsort_segment ( t1 , piv->prev , lst);

}

/*define pivot and make sure its the first element
* so put the less before pivot and bigger after pivot
* */
node_t *piv;
piv = t1->next;

if ( s->value < piv->value )
    {
      list_ins_aft(t1 , s );
    }