gcd of 2 digits

section .data
    result_msg db "GCD is: ", 0
    result_len equ $ - result_msg
    newline db 0xA

section .bss
    num1 resb 2       ; 1 digit + newline
    num2 resb 2

section .text
    global _start

_start:

    ; Read first digit
    mov rax, 0
    mov rdi, 0
    mov rsi, num1
    mov rdx, 2        ; 1 digit + newline
    syscall

    ; Read second digit
    mov rax, 0
    mov rdi, 0
    mov rsi, num2
    mov rdx, 2
    syscall

    ; Convert ASCII to numbers
    movzx rax, byte [num1]   ; First number
    sub rax, '0'             ; Convert from ASCII

    movzx rbx, byte [num2]   ; Second number
    sub rbx, '0'             ; Convert from ASCII

    ; Calculate GCD using repeated subtractions
gcd_loop:
    cmp rax, rbx        ; Compare numbers
    je gcd_done         ; If equal, we found GCD
    jl smaller          ; If RAX < RBX, swap
    sub rax, rbx        ; Subtract smaller from larger
    jmp gcd_loop

smaller:
    sub rbx, rax        ; RBX is larger, subtract RAX from it
    jmp gcd_loop

gcd_done:
    ; Print result message
    push rax            ; Save result
    mov rax, 1
    mov rdi, 1
    mov rsi, result_msg
    mov rdx, result_len
    syscall
    pop rax             ; Restore result

    ; Convert result to ASCII
    add rax, '0'        ; Convert to ASCII

    ; Print result digit
    push rax
    mov rax, 1
    mov rdi, 1
    mov rsi, rsp        ; Print from stack
    mov rdx, 1
    syscall
    pop rax

    ; Print newline
    mov rax, 1
    mov rdi, 1
    mov rsi, newline
    mov rdx, 1
    syscall

    ; Exit
    mov rax, 60
    mov rdi, 0
    syscall