4_MS.asm

Write an ALP to accept the 64 bit numbers from user, perform arithmetic operations on them, and display the 
result.i) Multiplication ii) Subtraction


%macro WRITE 2
    mov rax, 1
    mov rdi, 1
    mov rsi, %1
    mov rdx, %2
    syscall
%endmacro

%macro READ 2
    mov rax, 0
    mov rdi, 0
    mov rsi, %1
    mov rdx, %2
    syscall
%endmacro

%macro EXIT 0
    mov rax, 60
    xor rdi, rdi
    syscall
%endmacro

section .data
menu db "1. Multiplication",10
     db "2. Subtraction",10
     db "3. Exit",10
     db "Enter your choice: ",0
menulen equ $ - menu

prompt1 db "Enter first number: ",0
len_p1 equ $ - prompt1

prompt2 db "Enter second number: ",0
len_p2 equ $ - prompt2

msg_mul db "Multiplication is: ",0
len_mul equ $ - msg_mul

msg_sub db "Subtraction is: ",0
len_sub equ $ - msg_sub

msg_wrong db "Wrong choice. Try again.",10
len_wrong equ $ - msg_wrong

section .bss
a resq 1
b resq 1
c resq 1
choice resb 4
char_buf resb 64
disp_buf resb 64

section .text
global _start

_start:

main_loop:

    ; --- INPUT FIRST NUMBER ---
    WRITE prompt1, len_p1
    READ char_buf, 64
    call accept_decimal
    mov [a], rbx

    ; --- INPUT SECOND NUMBER ---
    WRITE prompt2, len_p2
    READ char_buf, 64
    call accept_decimal
    mov [b], rbx

menu_print:
    WRITE menu, menulen
    READ choice, 4

    mov al, [choice]

    cmp al, '1'
    je do_mul

    cmp al, '2'
    je do_sub

    cmp al, '3'
    je do_exit

    WRITE msg_wrong, len_wrong
    jmp menu_print

; ---------------- MULTIPLICATION ----------------
do_mul:
    mov rax, [a]
    mov rdx, 0
    mul qword [b]      ; rdx:rax = rax * [b], high bits ignored later
    mov [c], rax
    WRITE msg_mul, len_mul
    mov rbx, [c]
    call display_decimal
    jmp menu_print

; ---------------- SUBTRACTION ----------------
do_sub:
    mov rax, [a]
    sub rax, [b]
    mov [c], rax
    WRITE msg_sub, len_sub
    mov rbx, [c]
    call display_decimal
    jmp menu_print

do_exit:
    EXIT

; ---------- ACCEPT DECIMAL ----------
accept_decimal:
    mov rcx, rax
    xor rax, rax
    xor rbx, rbx
    mov rsi, char_buf

parse_loop:
    cmp rcx, 0
    je accept_done

    mov dl, [rsi]
    cmp dl, 10
    je accept_done

    cmp dl, '0'
    jb skip_ch
    cmp dl, '9'
    ja skip_ch

    sub dl, '0'
    imul rax, rax, 10
    movzx rdx, dl
    add rax, rdx

skip_ch:
    inc rsi
    dec rcx
    jmp parse_loop

accept_done:
    mov rbx, rax
    ret

; ---------- DISPLAY DECIMAL ----------
display_decimal:

    mov rax, rbx
    cmp rax, 0
    jne disp_conv

    mov byte [disp_buf], '0'
    mov byte [disp_buf+1], 10
    mov rdx, 2
    WRITE disp_buf, rdx
    ret

disp_conv:
    mov rcx, 0
    lea rdi, [disp_buf + 63]
    mov rax, rbx

conv_loop:
    xor rdx, rdx
    mov rbx, 10
    div rbx
    add dl, '0'
    mov [rdi], dl
    dec rdi
    inc rcx
    cmp rax, 0
    jne conv_loop

    lea rsi, [rdi + 1]

    mov rbx, rcx
    lea rdi, [rsi + rbx]
    mov byte [rdi], 10

    mov rdx, rbx
    inc rdx

    WRITE rsi, rdx
    ret