; ***********************************************************************
; *									*
; *   Computer 2^31 Using Multiplication (Assembly Language Version)	*
; *									*
; ***********************************************************************

; Authors:  Saeid Nooshabadi and John Zaitseff
; Date:	    20th June, 2003
; Version:  1.5

; This program calculates the value of 2^31 (two to the power of 31) using
; shift instructions.  It is essentially a hand-compiled (but not
; necessarilly optimised) version of exp-c.c.


; -----------------------------------------------------------------------
; Assembly-language preamble for the main module

	.text				; Executable code follows

_start: .global _start			; "_start" is required by the linker
	.global main			; "main" is our main program

	b	main			; Start running the main program


; -----------------------------------------------------------------------
; Start of the main program

; This program calculates 2^31 and returns this result in register R0.  It
; uses R2 as the temporary counter "k".


main:					; Entry to the function "main"

	mov	r0, #1			; Initial value of exp (R0)
	mov	r2, #0			; Initial value of k (R2)

exp_loop:
	mov	r0, r0, lsl #1		; exp = exp * 2 (shifting left by 1 bit
					; is the same as multiplying by 2)
	add	r2, r2, #1		; Increment k
	cmp	r2, #31			; and compare with 31
	bne	exp_loop		; Repeat the loop if k is less than 31

	mov	pc, lr			; Stop the program (return to the OS)

	.end