;; This program reads in a number n
;; and computes 1 + 2 + 3 + ... + n
;;
;; Date Written: 2008/02/15
;; Author: SS

  allocate-registers n, acc                    ; input registers
  allocate-registers zero, one                 ; constant registers
  allocate-registers cont, done, iter, back    ; label registers
  allocate-registers test                      ; temporary register

  li zero 0
  li one 1
  li done Ldone
  li iter Liter
  li back Lback

  read n
  li acc 0
  li cont Lback
  j iter
Lback:
  write acc
  halt

Liter:
  sgt test n zero
  jeqz test done
  add acc acc n
  sub n n one
  j iter
Ldone:
  j cont