GCD.asm

SECTION .data

    msg1:       db "Enter the first number: ", 0
    msg2:       db "Enter the second number: ", 0
    options:    db "Options:", 0xA, \
                   "    1. Command line input",        0xA, \
                   "    2. File input (specify name)", 0xA, \
                                                       0xA, \
                   "Please enter your choice: ", 0
    filechoice: db "Enter your filename: ", 0
    formatin:   db "%d\n", 0
    filenamein: db "%s", 0
    formatout:  db "The GCD of %d and %d is %d.",  0xA, 0
    readmode:   db "r", 0
    errormsg:   db "Reached the end of the file.", 0xA, 0
    num1:       times 4 db 0
    num2:       times 4 db 0
    choice:     times 4 db 0
    filename:   times 100 db 0
    isfilemode: times 4 db 0

SECTION .text

    global main
    extern scanf
    extern fscanf
    extern printf
    extern fopen

main:

    push options
    call printf

    push choice
    push formatin
    call scanf

    cmp dword [choice], 2
    jne cmdline

;

    mov dword [isfilemode], 1

    push filechoice
    call printf

    push filename
    push filenamein
    call scanf

    push readmode
    push filename
    call fopen
    add esp, 8
    mov esi, eax

fileinput:

    mov dword [num1], 0
    mov dword [num2], 0

    push num1
    push formatin
    push esi
    call fscanf
    add esp, 12

    push num2
    push formatin
    push esi
    call fscanf
    add esp, 12

    jmp calculate

cmdline:

    push msg1
    call printf

    push num1
    push formatin
    call scanf

    push msg2
    call printf

    push num2
    push formatin
    call scanf

calculate:

    mov eax, dword [num1]
    mov ebx, dword [num2]

    test eax, eax
    jz error
    test ebx, ebx
    jz error

gcd0:

    xor edx, edx
    div ebx
    mov eax, ebx
    mov ebx, edx
    test ebx, ebx
    jnz gcd0

end:

    push eax
    push dword [num2]
    push dword [num1]
    push formatout
    call printf

    cmp dword [isfilemode], 0
    jne fileinput

    jmp exit

error:

    push errormsg
    call printf

exit:

    mov eax, 1
    mov ebx, 0
    int 0x80