assembly/pgcd.asm at main · qamro/assembly · GitHub

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%include "asm_io.asm"
global main

segment .data
    msg_a db "Enter a: ", 0
    msg_b db "Enter b: ", 0
    msg_res db "GCD = ", 0

segment .bss
    a resd 1
    b resd 1

segment .text
main:
    mov eax, msg_a
    call print_string
    call read_int
    mov [a], eax

    mov eax, msg_b
    call print_string
    call read_int
    mov [b], eax

    call gcd

    mov ecx, eax
    mov eax, msg_res
    call print_string
    mov eax, ecx
    call print_int
    call print_nl

    mov eax, 1
    mov ebx, 0
    int 0x80

; gcd — reads directly from [a] and [b], returns result in eax
gcd:
    mov eax, [a]
    mov ebx, [b]

.loop:
    cmp ebx, 0
    je .done
    mov edx, 0
    div ebx ; eax = eax / ebx, edx = eax % ebx
    mov eax, ebx ; a = b
    mov ebx, edx ; b = remainder
    jmp .loop

.done:
    ret