;; This program reads in a number n and prints out
;; the sum of its digits, calculated recursively
;; like in the following scheme procedure.
;;
;;(define sod
;;  (lambda (n)
;;    (if (< n 10)
;;        n
;;        (+ (sod (quotient n 10))
;;           (remainder n 10)))))
;;
;; Date Written: 2008/02/20
;; Author: Peter Dierauer

allocate-registers sod, n, base-case, result, sp, zero, one, ten, cont, compare, remainder

  li sod Lsod
  li base-case Lbase-case
  li sp 0
  li zero 0
  li one 1
  li ten 10
  
  read n
  li cont Lhere
  j sod
Lhere:
  write result
  halt

Lsod:
  sge compare n ten
  jeqz compare base-case

;; save my context
  st n sp
  add sp sp one
  st cont sp
  add sp sp one

;; make recursive call
  li cont Lback
  quo n n ten
  j sod

Lback:
;; retrieve my context
  sub sp sp one
  ld cont sp
  sub sp sp one
  ld n sp

  rem remainder n ten
  add result result remainder
  j cont

Lbase-case:
  add result n zero
  j cont