anchor.diff:  (defun wrap-byte (val)
     "Wrap the given value to ensure it conforms to (typep val '(unsigned-byte 8)),
   i.e. a Stack Pointer or general purpose register."
  -  (logand val 255))
  +  (logand val #xff))
   
   (defun wrap-word (val)
     "Wrap the given value to ensure it conforms to (typep val '(unsigned-byte 16)),
   i.e. a Program Counter address."
  -  (logand val 65535))
  +  (logand val #xffff))
   
   (defmethod wrap-stack ((cpu cpu))
     "Wrap the stack pointer."
  
positive.code:     result))
  
  (defmethod branch-relative ((cpu cpu))
    (let ((addr (zero-page cpu)))
      (if (zerop (status-bit 1))
          (wrap-word (if (zerop (logand addr 128))
                         (- (cpu-pc cpu) (logxor addr 255))
                         (+ (cpu-pc cpu) addr)))
          (wrap-word (1+ (cpu-pc cpu))))))
  
negative.code:   "Pop the value pointed to by the SP and increment the SP."
    (incf (cpu-sp *cpu*))
    (wrap-stack *cpu*)
    (get-byte (+ (cpu-sp *cpu*) #xff)))
  
  (defun stack-pop-word ()
    "Pop a 16-bit word off the stack."
  