Multi-dimensional arrays...

flat assembler
Message board for the users of flat assembler.

Index > Main > Multi-dimensional arrays...

Author

Thread

Patrick_

Joined: 11 Mar 2006
Posts: 53
Location: 127.0.0.1

Patrick_ 13 Aug 2008, 23:39

Haven't ever had to use multi-dimensional arrays in assembly until now. What's the best way to do it? I tried:

Code:

mov     eax, 5
lea     ebx, dword [array+array_size*eax]
mov     ecx, dword [ebx+4*4]

array       dd 100
array_size = 100*4

This should be the equivalent of:

Code:

unsigned int array[10][10];
unsigned int temp = array[5][4];

but FASM gives me an 'out of range' error. Is there a simpler way to do it than having to do some multiplication instructions?

13 Aug 2008, 23:39

bitRAKE

Joined: 21 Jul 2003
Posts: 4043
Location: vpcmpistri

bitRAKE 14 Aug 2008, 01:42

One way...

Code:

ARRAY_WIDTH = 10
ARRAY_HEIGHT = 10

mov eax,[X]
imul ebx,[Y],4*ARRAY_WIDTH
mov ecx,[array+eax*4+ebx]

array rd ARRAY_WIDTH * ARRAY_HEIGHT

Note: addressing modes only support register multiples of 1,2,4, and 8 - Intel calls it the "scale".

Edit: thx, LocoDelAssembly

_________________
¯\(°_o)/¯ “languages are not safe - uses can be” Bjarne Stroustrup

Last edited by bitRAKE on 14 Aug 2008, 02:16; edited 1 time in total

14 Aug 2008, 01:42

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 14 Aug 2008, 01:58

dd must be rd

14 Aug 2008, 01:58

Patrick_

Joined: 11 Mar 2006
Posts: 53
Location: 127.0.0.1

Patrick_ 14 Aug 2008, 13:22

Yeah, that should've been an 'rd'. Smile

Thanks guys. For some reason I thought it wouldn't require an extra instruction but it does.

14 Aug 2008, 13:22

Azu

Joined: 16 Dec 2008
Posts: 1159

Azu 08 Jun 2009, 00:34

If you aligned the array on 4byte boundary shouldn't the lea way work then? Since it would be multiples of 4?

08 Jun 2009, 00:34

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum