Increasing offset whilst reading/writing

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andyz74

Joined: 26 Nov 2007
Posts: 36
Location: Germany

andyz74 17 Oct 2010, 16:27

Hello, it's me again, the noob. :-/

I tried to copy content bitwise from one "array" to another, by increasing the offset of the array, but i got no working version. Sad

As an example, I have...

Code:

  sub [zeugs],18h
     sub [zeugs+1],18h
   sub [zeugs+2],18h
   sub [zeugs+3],18h
   sub [zeugs+4],18h
   sub [zeugs+5],18h
   sub [zeugs+6],18h
   sub [zeugs+7],18h
   sub [zeugs+8],18h
   sub [zeugs+9],18h
   sub [zeugs+10],18h

...where U can see, that the increasing of the offset was done by hand ( +1 +2 +3) and so on...
If I do sth like

Code:

    sub [zeugs+cl],18h

with "cl" being increased automatically, i get some error by the compiler.

So how can I get a workaround for this problem? Anybody could help me please with this?

17 Oct 2010, 16:27

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 17 Oct 2010, 17:05

Since you posted in Linux, you need 32-bit addresses, therefore you need to use ECX instead of just CL (lower 8 bits of ECX).

For your first code you could do this:

Code:

mov ecx, 0

.loop:
  mov byte [zeugs+ecx], 18h
  inc ecx
  cmp ecx, 10
  jbe .loop

And to copy one array into another:

Code:

mov ecx, 0
mov edi, dstArray
mov esi, srcArray
.loop:
  mov al, [srcArray+ecx]
  mov [dstArray+ecx], al
  inc ecx
  cmp ecx, srcArraySize
  jb .loop

Or just:

Code:

mov ecx, srcArraySize
mov edi, dstArray
mov esi, srcArray
rep movs byte[edi], byte[esi]

In all cases I'm been working with byte arrays.

17 Oct 2010, 17:05

andyz74

Joined: 26 Nov 2007
Posts: 36
Location: Germany

andyz74 17 Oct 2010, 18:04

OK, this seems to work with the 32-bit-registers. No more compilation-errors.

Many thanks for the fast help! Smile

17 Oct 2010, 18:04

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