anchor.diff:                 `(for (,n (i start)
                            ,@(and window `((j window-start))))
                     (setf (aref vec i) (%scale
  -                                      (%window (* (aref vec i)
  -                                               (aref window j))
  +                                      (%window (aref vec i)
                                                  ,window
                                                  ,(if window 'j 0))
                                         ,scale))))
  
positive.code:              (gen (n)
                 (cond
                   ((= n 16)
                    (gen 4)
                    (gen 8)
                    (push
                     `(dif/16 (start)
  
negative.code:                   (aref vec (+ start 2)) (- s0-s2 s1-s3)
                    (aref vec (+ start 3)) (+ s0-s2 s1-s3)))
            nil)
          ;; I think this one is worse than split-radix
          `(dif/8 (start)
            (declare (type index start))
            (let* ((s0 (aref vec start))
  