anchor.diff:        (make-instance 'tiff-image
                        :length image-length
                        :width image-width
  +                     :bits-per-sample bits-per-sample
                        :samples-per-pixel samples-per-pixel
                        :data data))))
   
  
positive.code: 
  (defun read-field-shorts (stream count)
    (if (<= count 2)
        (loop for i below 2
           for short = (read-int-16 stream)
           when (< i count)
           collect short)
        (let ((offset (read-int-32 stream))
              (field-pos (file-position stream)))
          (file-position stream offset)
  
negative.code:   (dotimes (i (length array))
      (write-int-32 stream (aref array i))))
  
  (defun write-int-32-sequence (stream values)
    (if (atom values)
        (write-int-32 stream values)
        (write-int-32-array stream (vectorize values))))
  
  (defun read-rational (stream)
    (/ (read-int-32 stream) (read-int-32 stream)))
  
  