;--------------------------------------------------------------------------------------;
Factorial_Recursive
	;this subrouinte returns the factorial of R0,
	;and writes it back into R0. 
	;this function is recursive
	CMP R0, #0      ; if argument n is 0, return 1
	BNE notzero
	MOV R0, #1
	PUSH{LR}
	B theRend
notzero
	PUSH{LR}
	PUSH{R0}      ; otherwise save argument n into R3
	SUB R0, R0, #1  ; and perform recursive call on R3 - 1
	BL Factorial_Recursive
	POP{R1}
	MUL R0, R1, R0  ; multiply returned value by n
theRend
	POP{PC}      	; and return
;--------------------------------------------------------------------------------------;