factorial.asm

BITS 32

segment .text

global _factorial
_factorial:
	push ebp
	mov ebp, esp
	push ebx
	mov ebx, [ebp+8]
	cmp ebx, 0
	jnz .l1
	mov eax, 1
	pop ebx
	pop ebp
	ret
.l1:
	mov eax, ebx
	dec eax
	push eax
	call _factorial
	add esp, 4
	imul eax, ebx
	pop ebx
	pop ebp
	ret

makefile

testfact.exe: testfact.obj factorial.obj
	link testfact.obj factorial.obj

testfact.obj: testfact.c
	cl /c testfact.c

factorial.obj: factorial.asm
	nasm -f win32 factorial.asm

testfact.c

#include <stdio.h>
int factorial(int n);

int main()
{
	printf("%d\n", factorial(10));
	return 0;
}