;; do 2^n
;; n = 3, a = 2
;; while n > 0
;;    a = a * a
;;    n = n - 1

;; let r1 = n, r2 = a
.a 0
.c
  ld r1 #3
  ld r2 #2
  jmp always label1
:loop
  mul r2 r2 r2
  sub r1 r1 #1 
:label1  
  sub r0 r1 r0
  jmp GT loop
  trap stop r0
.e