   0 ;; do 2^n
   0 ;; n = 3, a = 2
   0 ;; while n > 0
   0 ;;    a = a * a
   0 ;;    n = n - 1
   0 
   0 ;; let r1 = n, r2 = a
   0 .a 0
   0 .c
   0   ld r1 #3
   1   ld r2 #2
   2   jmp always label1
   3 :loop
   3   mul r2 r2 r2
   4   sub r1 r1 #1 
   5 :label1  
   5   sub r0 r1 r0
   6   jmp GT loop
   7   trap stop r0
   8 .e
