anchor.diff:       (#xc4 3 2 zero-page)
        (#xcc 4 3 absolute))
     (let ((result (- (cpu-yr cpu) (funcall mode cpu))))
  -    (set-flags-if cpu :carry (< result #x100))
  +    (set-flags-if cpu :carry (not (minusp result)))
       (set-flags-nz cpu result)))
   
   (defopcode dec (:docs "Decrement Memory")
  
positive.code:      (#xe4 3 2 zero-page)
       (#xec 4 3 absolute))
    (let ((result (- (cpu-xr cpu) (funcall mode cpu))))
      (set-flags-if cpu :carry (< result #x100))
      (set-flags-nz cpu result)))
  
  (defopcode cpy (:docs "Compare Memory with Y register")
  
negative.code:      (#xd9 4 3 absolute-y)
       (#xdd 4 3 absolute-x))
    (let ((result (- (cpu-ar cpu) (funcall mode cpu))))
      (set-flags-if cpu :carry (not (minusp result)))
      (set-flags-nz cpu result)))
  
  (defopcode cpx (:docs "Compare Memory with X register")
  