%ifndef _FACTORIAL_ASM_ ; continue if _FACTORIAL_ASM_ is undefined
%define _FACTORIAL_ASM_ ; make sure that it is defined
                        ; otherwise, %include allows only one inclusion

;define the function
factorial: ; int _stdcall factorial(int n)
    mov eax, 1
    mov ecx, [esp + 4]
    
    repeat: 
        mul ecx
    loop repeat ; atention, the case ecx = 0 is not treated!

    ret 4 ; in this case, 4 represents the number of bytes that need to be cleared from the stack (the parameter of the function)

%endif