Problem in Loop

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Ianis

Joined: 06 Jan 2011
Posts: 10

Ianis 17 Mar 2012, 19:40

Code:

format PE GUI 4.0
entry EntryPoint

EntryPoint:      
    xor eax, eax
        xor ebx, ebx
        mov ecx, 0FFFFh
     bloop:
          mov al, 7Ah
         sub al, 80h
         mov bx, 0FFh
                idiv bx
     loop bloop
  ret

Hello I would like to know why the code doesn't loop and get stuck on idiv bx.
Thank you.

17 Mar 2012, 19:40

cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 17 Mar 2012, 20:48

The division is applied to dx:ax, so if dx:ax/bx cannot fit inside ax #DE exception will occur; to fix this zero dx before each idiv (after idiv the remainder is put in dx)

17 Mar 2012, 20:48

Ianis

Joined: 06 Jan 2011
Posts: 10

Ianis 18 Mar 2012, 15:43

Thank you a lot cod3b453.
I didn't know it works like that.

18 Mar 2012, 15:43

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