;; ggT in Scheme

(define (gcd a b)
  (if (= b 0)
      a
      (gcd b (remainder a b))))

;; ggT-Maschine

(data-paths
 (a
  (a<-b (register b)))
 (b
  (b<-t (register t)))
 (t
  (t<-r (operation rem)))
 (flags
  (=0 (operation =0))))

(operations
 (rem (a b))
 (=0  (b)))

(controller
 test
   (=0)
   (branch gcd-done)
   (t<-r)
   (a<-b)
   (b<-t)
   (goto test)
 gcd-one)

;; ggT im Drei-Adreß-Format

(registers a b t)
(operations rem =)
(controller
  test
    (test (op =) (reg b) (const 0))
    (branch (label gcd-done))
    (assign t (op rem) (reg a) (reg b))
    (assign a (reg b))
    (assign b (reg t))
    (goto (label test))
   gcd-done)

;; Divisionsrest in Scheme

(define (remainder n d)
  (if (< n d)
      n
      (remainder (- n d) d)))

;; ggT-Maschine mit ausprogrammiertem Divisionsrest

(registers a b t)
(operations = < -)
(controller
 test
   (test (op =) (reg b) (const 0))
   (branch (label gcd-done))
   (assign t (reg a))
 rem-loop
   (test (op <) (reg t) (reg b))
   (branch (label rem-done))
   (assign t (op -) (reg t) (reg b))
   (goto (label rem-loop))
 rem-done
   (assign a (reg b))
   (assign b (reg t))
   (goto (label test))
 gcd-done)