anchor.diff:              (when (> required available)
                 (let ((new-capacity
                        (if (<= old-capacity (truncate array-dimension-limit 2))
  -                         #+nil (* old-capacity 2)
                            (ash old-capacity 1) ;; twice the size
                            array-dimension-limit)))
                   (reserve (<deque>) deque
  
positive.code:                                  (:back  extra-capacity)
                                   (t      (ash (ufixnum- new-capacity size) -1)))))
              (dotimes (i size)
                ;; this one is ignoring the resizable array in default cl --- performance comparison required?
                (setf (aref new-data (ufixnum+ i new-start))
                      (aref old-data (ufixnum+ i old-start))))
              (setf <qdata>  new-data
  
negative.code:              (asked-capacity (max new-capacity size))
               (extra-capacity (if (eq at :both)
                                   0
                                   (min (ash asked-capacity -2)
                                        (ufixnum- array-dimension-limit asked-capacity))))
               (new-capacity (ufixnum+ asked-capacity extra-capacity)))
              
  