anchor.diff:  
   3. A reader function named {NAME}-{SLOT-NAME} for each slot.
   
  +In addition to these functions, NAME is defined as a suitable subtype
  +of (and unsigned-byte fixnum).
  +
   Currently this macro supports boolean, unsigned-byte and signed-byte slots.
   
    Example:
  
positive.code:                                collect
                                 `(,(bitfield-slot-name slot)
                                   (,(bitfield-slot-reader slot) ,name))))
           (declare (type (unsigned-byte ,*bitfield-position*) ,name))
           (logior
            ,@(loop for slot in slots
                    collect
  
negative.code:                    (symbol-package name))))
      (assert (<= *bitfield-position* +bitfield-max-bits+))
      `(progn
         (deftype ,name () '(unsigned-byte ,*bitfield-position*))
         ;; Define all slot readers.
         ,@(loop for slot in slots
                 collect
                 `(declaim (inline ,(bitfield-slot-reader slot)))
                 collect
                 `(defun ,(bitfield-slot-reader slot) (,name)
                    (declare (,name ,name))
                    ,(bitfield-slot-unpack
                      slot
                      `(ldb (byte ,(bitfield-slot-size slot)
  