;;; tested with NASM version 2.16.01

section .text

;; entry point
main:
    mov ax, 1
    call _addition_test
    ret

;; adding tests
_add_cx:
    mov cx, 25
    add ax, cx
    ret
_add_dx:
    mov dx, 50
    add ax, dx
    ret
_add_bx:
    mov bx, 100
    add ax, bx
    ret

;; subtracting tests
_sub_cx:
    sub ax, cx
    ret
_sub_dx:
    sub ax, dx
    ret
_sub_bx:
    sub ax, bx
    ret

;; test function for call stack test
_addition_test:
    call _add_cx
    call _add_dx
    call _add_bx
    
    call _sub_cx
    call _sub_dx
    call _sub_bx

    inc ax
    dec dx
    ret ; result should be 2