; assemble and link using the commnads below
; arm-elf-as --gdwarf2 -marm7tdmi -o fact.o fact.s
; arm-elf-ld -o fact.elf fact.o
; Next use arm-elf-insight to debug.

fact:
	mov	ip, sp
	stmfd	sp!, {v1, fp, ip, lr}
        sub     fp, ip, #4

	mov	v1, a1 		; keep a copy of n for mul operation 
	cmp	v1, #1		; n==1
	sub	a1, a1, #1	; n -1 for fact(n-1)
	mov	a2, v1 		; return value if n=1	
	beq	fin		; return 
	bl	fact		; recursion with n-1
	mul	a2, a1, v1 	; n*fact(n-1) 
fin:
	mov	a1, a2 		; return 1 or n*fact(n-1)	
	ldmea	fp, {v1, fp, sp, pc}
main:
	b	fact