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: (declaim (ftype (function (reader) (integer 0 1)) read-bit))
  (defun read-bit (reader)
    "Read a single bit from READER"
    (declare (type reader reader))
    (if (can-not-read reader) (fill-buffer reader))
  
    (prog1
  
negative.code:                0) :type function)
    stream)
  
  (declaim (inline move-forward))
  (defun move-forward (reader &optional (bits 1))
    "Moves position in READER bit reader in range [0; 8-ibit] BITS.
  