CSC231 Recursion with Factorials

--D. Thiebaut 10:32, 16 November 2012 (EST)

---

;;; factorial.asm
;;;
;;; demo of the recursive factorial program
;;; uses the stack to pass parameters.
	
%include	"dumpRegs.asm"
	
	section	.data
n	dd	5		;n
factN	dd	0		;we'll put n! here

	section	.text
	global	_start

_start:	push	eax		;make room in stack for resut
	push	dword[n]	;pass n
	call	fact
	pop	eax		;put result in eax
	mov	dword[factN],eax ;and in global
	
	call	dumpRegs

;;; exit
	mov	eax, 1
	mov	ebx, 0
	int	0x80

;;; --------------------------------------------------------
;;; fact: computes the factorial of n, where n is passed in
;;; 	  eax.  Returns the result in edx
;;; --------------------------------------------------------
fact:	push	ebp
	mov	ebp, esp

	pushad

	mov	eax, [ebp+8]	;get n
	cmp	eax, 1
	jne	.recurse

	mov	dword[ebp+12], 1 ;set result to 1
	
	popad
	pop	ebx
	ret	1*4		;get rid of n param

.recurse:

	dec	eax
	push	eax		;make room for result
	push	eax		;pass n-1
	call	fact
	pop	eax		;get fact(n-1)
	mul	dword[ebp+8]	;mult by n
	mov	dword[ebp+12],eax
				;pass result back

	popad
	pop	ebp
	ret	1*4