Integer arithmetic operations in x86 MASM

.586
.MODEL FLAT, C

.DATA
advOper DB 1 ;Set to 0 if addition or subtraction, 1 if multiplication and division
oper DB 1 ;Set to 0 if addition or multiplication, 1 if subtraction or division
a DWORD 25
b DWORD 5

.CODE

MAIN PROC
    mov ebx, 1 ;move 0 to EBX register for counter
    mov eax, a

    cmp advOper, 0
    je simpCall
    jmp advCall

    simpCall:
        cmp oper, 0
        je additionCall
        jmp subtractionCall

    advCall:
        cmp oper, 0
        je multiplyCall
        jmp divideCall

    additionCall:
        call ADDITION
        jmp endSect

    subtractionCall:
        call SUBTRACTION
        jmp endSect

    multiplyCall:
        call MULTIPLY
        jmp endSect

    divideCall:
        call DIVIDE
        jmp endSect

    endSect:
        mov eax, eax
MAIN ENDP

ADDITION PROC
    mov eax, a
    add eax, b
    ret
ADDITION ENDP

SUBTRACTION PROC
    mov eax, a
    sub eax, b
    ret
SUBTRACTION ENDP

MULTIPLY PROC
    multi:
        add eax, a
        inc ebx
        cmp ebx, b
        jl multi
        ret
MULTIPLY ENDP

DIVIDE PROC
    divi:
        sub eax, b
        inc ebx
        cmp eax, 1
        jg divi
        mov eax, ebx
        dec eax
        ret
DIVIDE ENDP

END