Outputting registers to the console with MASM

Question

I'm one day into learning ASM and I've done a few tutorials, and even successfully modified the tutorial content to use jmp and cmp, etc instead of the MASM .if and .while macros.

I've decided to try and write something very, very simple to begin with before I continue with more advanced tutorials. I'm writing a Fibonacci number generator. Here is the source I have so far:

.386
.model flat, stdcall

option casemap :none

include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
include \masm32\include\masm32.inc

includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\masm32.lib

.code
start:

  mov eax, 1
  mov ecx, 1

  _a:

    push eax
    add  eax, ecx
    pop  ecx

    ; Jump to _b if there is an overflow on eax

    ; Print Values Here

  jmp _a

  _b:

  push 0
  call ExitProcess

end start

I intend to check for overflows on eax/ecx but right now I'm just interested in displaying the values of eax/ecx on the screen.

I know how to push the address of a constant string from .data and call StdOut which was the first example in the hello world tutorial, but this appears to be quite different (?).

Answer 1

There is this code provided by Microsoft itself

http://support.microsoft.com/kb/85068

Note that this code outputs AX register on 16 bit systems. But you can get the idea, you just need to convert AX value into ASCII characters by looping through each character. Skip the interrupts part and use your StdOut function.

 mov dx, 4          ; Loop will print out 4 hex characters.
nexthex:
          push dx            ; Save the loop counter.
          mov cl, 4          ; Rotate register 4 bits.
          rol ax, cl
          push ax            ; Save current value in AX.

          and al, 0Fh        ; Mask off all but 4 lowest bits.
          cmp al, 10         ; Check to see if digit is 0-9.
          jl decimal         ; Digit is 0-9.
          add al, 7          ; Add 7 for Digits A-F.
decimal:
          add al, 30h        ; Add 30h to get ASCII character.

          mov dl, al
          ;Use StdOut to print value of dl
           ;mov ah, 02h        ; Prepare for interrupt.
          ;int 21h            ; Do MS-DOS call to print out value.

          pop ax             ; Restore value to AX.
          pop dx             ; Restore the loop counter.
          dec dx             ; Decrement loop counter.
          jnz nexthex        ; Loop back if there is another character
                             ; to print.

See here as well:

http://www.masm32.com/board/index.php?PHPSESSID=fa4590ba57dbaad4bc44088172af0b49&action=printpage;topic=14410.0