; ***********************************************************************
; *									*
; *   Compare Two Signed Integer Numbers (Assembly Language Version)    *
; *									*
; ***********************************************************************

; Authors:  Saeid Nooshabadi and John Zaitseff
; Date:     5th May, 2003
; Version:  1.3

; This very simple program compares two numbers together and returns the
; greater value.  The whole point of this program is to illustrate the
; concept of signed integers as used in assembly language programs.
;
; Note the use of the signed-integer variant of the branch instruction:
; "bgt" is "branch if greater than", and implies the previous comparison
; instruction was with signed numbers.
;
; This program is essentially the equivalent of cmp-c-s.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

main:	ldr	r3, =a		; Load the address of a into R3

	ldr	r0, [r3]	; R0 = 0xE0001234
	ldr	r1, [r3, #4]	; R1 = 0x00004567 (NB: this assumes that
				; R3 + 4 = address of b; in general,
				; you should never make such assumptions!

	cmp	r0, r1		; Compare a and b (a - b)

	bgt	exit		; Return a (a > b)  [Signed branch]
	mov	r0, r1		; Return b (a =< b)

exit:	mov	pc, lr		; Stop the program (and return to OS)
				; R0 contains the exit code (return value)


; -----------------------------------------------------------------------
; Program variables (stored together with the code)

a:	.word	0xE0001234	; Variable "a"
b:	.word	0x00004567	; Variable "b"


; -----------------------------------------------------------------------

	.end