Question

I just started playing around with MASM styled assembly and after playing around long enough managed to make a sort of loop. This is just from tinkering so I was wondering if anybody could give me any insight and explanation on if this code is inefficient or how it can be improved.

.386
.model flat, stdcall
option casemap:none
include \masm32\include\windows.inc
include \masm32\include\masm32.inc
include \masm32\include\user32.inc
includelib \masm32\lib\masm32.lib
includelib \masm32\lib\user32.lib

.data
MsgBxTitle db "Loop Step", NULL

.data?
Buff dd ?
MsgBxBody dd ?

.code
start:
XOR eax,eax
MOV Buff, eax 
lp:
invoke dw2hex, Buff, addr MsgBxBody
invoke MessageBox, NULL, addr MsgBxBody, addr MsgBxTitle, MB_OKCANCEL
.IF eax==IDCANCEL
RET
.ENDIF
INC Buff
CMP Buff,10
JL lp
RET
end lp
invoke ExitProcess, NULL
end start

Answer 1

You can shave 16 bytes off the code this way. Zero a register and push that for zero. Use a register for you dword buffer. Using registers Assemble to smaller opcodes and are “faster” than memory (labels).

I personally don’t like/use the high level stuff.

start:
    xor     edi, edi
    xor     esi, esi
    mov     ebx, 10
lp:
    push    offset MsgBxBody
    push    edi
    call    dw2hex

    push    MB_OKCANCEL
    push    offset MsgBxTitle
    push    offset MsgBxBody
    push    esi
    call    MessageBox
    test    eax, IDCANCEL
    jnz     Done

    inc     edi
    dec     ebx
    jns     lp

Done:
    push    esi
    call    ExitProcess
end start