; ----------------------------------------------------------------------------
; fib.asm
;
; This is a Win32 console program that writes the first 40 Fibonacci numbers.
; It needs to be linked with a C library.
; ----------------------------------------------------------------------------

        global  _main
        extern  _printf

        section .text
_main:
        push    ebx                     ; we have to save this since we use it

        mov     ecx, 40                 ; ecx will countdown from 40 to 0
        xor     eax, eax                ; eax will hold the current number
        xor     ebx, ebx                ; ebx will hold the next number
        inc     ebx                     ; ebx is originally 1
print:
        ; We need to call printf, but we are using eax, ebx, and ecx.  printf
        ; may destroy eax and ecx so we will save these before the call and
        ; restore them afterwards.

        push    eax
        push    ecx

        push    eax
        push    format
        call    _printf
        add     esp, 8

        pop     ecx
        pop     eax

        mov     edx, eax                ; save the current number
        mov     eax, ebx                ; next number is now current
        add     ebx, edx                ; get the new next number
        dec     ecx                     ; count down
        jnz     print                   ; if not done counting, do some more

        pop     ebx                     ; restore ebx before returning
        ret
format:
        db      '%d', 0x0a