anchor.diff:  (defun reader-length (reader)
     "Returns length of stream in octets or zero
      if the value is unknown"
  -  (declare (type reader reader))
     (let ((len (file-length (reader-stream reader))))
       (if len len 0)))
   
  
positive.code:         
          (reader-crc-start reader) 0)
  
    (setf (reader-end reader)
          (read-sequence (reader-buffer reader)
                         (reader-stream reader)))
    
  
negative.code: (declaim (inline fill-buffer))
  (defun fill-buffer (reader)
    "Fills internal buffer of READER"
    #+easy-audio-check-crc
    (setf (reader-crc reader)
          (funcall (reader-crc-fun reader)
  