(load "5.13.scm")

(define expt-recur
  (make-machine
  (list (list '= =) (list '- -) (list '* *))
  '(   (assign continue (label expt-done))
     expt-loop
       (test (op =) (reg n) (const 0))
       (branch (label return-one))
       (save continue)
       (assign continue (label got-result))
       (assign n (op -) (reg n) (const 1))
       (goto (label expt-loop))
     got-result
       (restore continue)
       (assign val (op *) (reg b) (reg val))
       (goto (reg continue))
     return-one
       (assign val (const 1))
       (goto (reg continue))
     expt-done)))

(define (test-expt-recur)
  (set-register-contents! expt-recur 'b 7)
  (set-register-contents! expt-recur 'n 3)
  (start expt-recur)
  (get-register-contents expt-recur 'val))

(define expt-iter
  (make-machine
  (list (list '= =) (list '- -) (list '* *))
  '(    (assign val (const 1))
      loop
        (test (op =) (reg n) (const 0))
        (branch (label end))
        (assign val (op *) (reg val) (reg b))
        (assign n (op -) (reg n) (const 1))
        (goto (label loop))
      end)))

(define (test-expt-iter)
  (set-register-contents! expt-iter 'b 7)
  (set-register-contents! expt-iter 'n 3)
  (start expt-iter)
  (get-register-contents expt-iter 'val))