; sub.asm include file
bits 32

%define arg1 [ebp+8]
%define arg2 [ebp+12]

push ebp
mov ebp,esp

mov eax,arg1
mov ebx,arg2

mov edx,_overflow
xor ecx,ecx
mov word cx,[edx]
shl cx,1

%ifdef bits32
    sub eax,ebx
%endif

%ifdef bits16
    sub ax,bx
%endif

%ifdef bits8
    sub al,bl
%endif

jc .overflowed
jmp .end

.overflowed:
    or cx,1

.end:
    mov word [edx],cx
    mov esp,ebp
    pop ebp
    ret