anchor.diff:  
   (eval-when (:compile-toplevel :load-toplevel :execute)
   ;;; For ease of reference
  -(defmacro dbref (data x y)
  +(defmacro u8ref (data x y)
     `(the uint8 (aref (the uint8-array (aref (the uint8-2d-array ,data) ,y)) ,x)))
  +
  +(defmacro s16ref (data x y)
  +  `(the sint16 (aref (the sint16-array (aref (the sint16-2d-array ,data) ,y)) ,x)))
   
   (defmacro fixref (data x y)
     `(the fixnum (aref (the fixnum-array (aref (the fixnum-2d-array ,data) ,y)) ,x)))
  
positive.code: 
  (defun quantize (block q-table)
    (declare #.*optimize*
  	   (type fixnum-2d-array block)
  	   (type uint8-2d-array q-table))
    (quantize-block))
  
  
negative.code:                 for cx fixnum = (minus xd dx)
                  for cy fixnum = (minus yd dy) do
                  (loop for i fixnum from 0 below ncomp do
                        (setf (u8ref (aref outbuf i) cx cy)
                              (minus (aref inbuf (plus pos i)) 128)))))
      (values xend yend)))
  
  