primo

; 3.  A prime number is an integer that is divisible only by 1 and by itself.
;
;  3.0   Write a program that takes a number m as input, and prints back 1 to the
;        console if m is a prime number. Otherwise, it prints 0.
;
;           ANSWER:
;
;               Take m, and divide it by all previous numbers. When one of the
;               divisions returns no remainder, it is not a prime, else it is.

format PE console

include 'C:\fasm\INCLUDE\win32a.inc'

; ===============================================
section '.text' code readable executable

_main:
    mov ebp, esp; for correct debugging
    call    read_hex
    ; eax = input()

    mov     ecx, eax                        ; use a counter
    ; ecx = eax

    mov     ebx, eax                        ; original user input in ebx, because we are gonna use eax in division
    ; ebx = eax

_do_division:
    dec     ecx
    ; ecx = ecx - 1

    mov     esi, ecx                        ; when we reach ecx=1, do not divide, but print 1
    ; esi = ecx

    sub     esi, 1
    ; esi = esi - 1
    jz      _set_eax_1
    ; if esi = 0 then return 1 (jump to set_eax_1)

    cmp     ecx, 0                          ; never divide by 0, so check if we have ecx = 0 here
    jz      _set_eax_1
    ; if ecx = 0 then return 1 (jump to set_eax_1)

    mov     edx, 0                          ; clear edx for division
    ; edx = 0
    mov     eax, ebx
    ; eax = ebx

    div     ecx                             ; edx:eax / ecx, result is stored in edx:eax (remainder:quotient)
    ; edx = eax  / ecx

    cmp     edx, 0                          ; set the flags
    jnz     _do_division
    ; if edx = 0 then jump to do_division

    jmp     _set_eax_0
    ; return 0 (jump to set_eax_1)

_set_eax_1:
    mov     eax, 1
    jmp     _print

_set_eax_0:
    mov     eax, 0
    jmp     _print

_print:
    call    print_eax

    ; Exit the process:
    push    0
    call    [ExitProcess]

        ret

include 'C:\fasm\INCLUDE\training.inc'