anchor.diff:    (if (minusp n)
         (scroll-down (- n))
         (dotimes (_ n t)
  -        (when (and (= (window-cursor-y-if-wrapping (current-window))
  +        (when (and (= (window-cursor-y (current-window))
                         (- (window-height) 2))
                      (/= 1 (window-vtop-linum)))
             (unless (forward-line (- n))
  
positive.code:   (- (window-current-linum window)
       (window-vtop-linum window)))
  
  (defun window-cursor-y-if-wrapping (window)
    (+ (window-cursor-y-not-wrapping window)
       (window-wrapping-offset window)))
  
  
negative.code:                  (window-vtop-linum window))
                (< 0 (window-vtop-charpos window)))
           -1)
          ((let ((n (- (window-cursor-y window)
                       (- (window-height window) 2))))
             (when (< 0 n) n)))
          (t
  