reversed_sum.asm

%include 'functions.asm'


section .data           ;Uninitialized data
   num_1 db '123' ,0h
   num_2 db '2' ,0h
section .bss
   num1 resb LEN
   num2 resb LEN
section .text


reverse:
    push    ebx             ; preserve ebx on the stack to be restored after function runs
    push    ecx             ; preserve ecx on the stack to be restored after function runs
    push    edx             ; preserve edx on the stack to be restored after function runs
    push    esi

    mov     esi, eax        ; move pointer in eax into esi (our number to convert)
    call    slen            ; initialise eax with decimal value 0
    mov     ecx, eax
    dec     ecx             ; initialise ecx with decimal value 0
    mov     eax, 0

.multiplyLoop:
    xor     ebx, ebx        ; resets both lower and uppper bytes of ebx to be 0
    mov     bl, [esi+ecx]   ; move a single byte into ebx register's lower half

    sub     bl, 48          ; convert ebx register's lower half to decimal representation of ascii value
    add     eax, ebx        ; add ebx to our interger value in eax
    mov     ebx, 10         ; move decimal value 10 into ebx
    mul     ebx


    dec     ecx
    cmp     ecx, -1         ; compare ebx register's lower half value against ascii value 48 (char value 0)
    je      .finished       ; jump if less than to label finished
    jmp     .multiplyLoop   ; continue multiply loop

.finished:
    cmp     ecx, 0          ; compare ecx register's value against decimal 0 (our counter register)
    je      .restore        ; jump if equal to 0 (no integer arguments were passed to atoi)
    mov     ebx, 10         ; move decimal value 10 into ebx
    div     ebx             ; divide eax by value in ebx (in this case 10)

.restore:
    pop     esi             ; restore esi from the value we pushed onto the stack at the start
    pop     edx             ; restore edx from the value we pushed onto the stack at the start
    pop     ecx             ; restore ecx from the value we pushed onto the stack at the start
    pop     ebx             ; restore ebx from the value we pushed onto the stack at the start
    ret


global  _start
_start:



    ;mov eax,3
    ;mov ebx,2
    ;mov ecx,num1
    ;mov edx,LEN
    ;int 80h

    ;mov byte [num1+LEN-1], 0h
    mov eax,num_1

    call reverse  ;reverse first number
    push eax      ;push result to stack
    call iprintLF


    ;mov eax,3
    ;mov ebx,2
    ;mov ecx,num2
    ;mov edx,LEN
    ;int 80h

    ;mov byte [num2+LEN-1], 0h
    mov eax,num_2  ;move second number to eax

    call reverse   ;reverse second number
    call iprintLF

    pop ebx        ;pop first reversed number
    add eax,ebx    ;add them up


    call iprintLF


    ; below code section is for reverse the sum
    ; we can't use reverse function beacuse it accepts string but we have decimal value


     mov    ebx,    10  ;move 10 to ebx as divident to get remainder
     xor    ecx,    ecx ;clear ecx for

  godivide:
    xor edx,    edx ; clear remainder
    div ebx     ; divide eax by 10
        cmp     edx ,   0
        je      godivide        ;skip the zero
        add     edx,   '0'      ;convert digit to ascii char
        push    eax             ;reserve
        push    ebx             ;reserve
    push    edx             ;reserve


        mov ecx,esp             ;get the adress of first digit from stack(remainder edx)
        mov edx,1
        mov ebx,STDOUT
        mov eax,SYS_WRITE
        int 80h

        pop edx                  ;restore
        pop ebx                  ;restore
        pop eax                  ;restore

    cmp eax,    0   ; if eax
    jne godivide    ; is not equal to zero, divide again



    call quit