can fasm do this?

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tthsqe

Joined: 20 May 2009
Posts: 767

tthsqe 30 Oct 2009, 07:49

I know the irp macro can be used to loop over a given set of values, but it is possible to do something like this:

Code:

rept 10 i:0 {
 mov eax,[[table+4*i^2]]
}
table: dd 0,1,2,3,4,5,6,7,8,...

and have the code generated be:

Code:

 mov eax,0
 mov eax,1
 mov eax,4
 mov eax,9
...

Essentialy fasm need to find the value from the address and substitue it in instead of encoding it as a memory access.

30 Oct 2009, 07:49

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 30 Oct 2009, 08:09

Read up about the load directive.

Code:

table: dd 0,1,2,whatever,...
rept 10 i:0 {
  load x dword from table+4*i*i
  mov eax,x
}

30 Oct 2009, 08:09

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 30 Oct 2009, 08:12

But if all you want to do is generate squares then:

Code:

rept 10 i:0 {
  mov eax,i*i
}

30 Oct 2009, 08:12

tthsqe

Joined: 20 May 2009
Posts: 767

tthsqe 19 Nov 2009, 06:24

How about this one:
How can you get fasm to compile something like this:

Code:

.ifc
x1
.nz
y1
.elseif
x2
.nz
y2
.elseif
x3
.nz
y3
.else
y4
.endif

into:

Code:

x1
jnz .1
x2
jnz .2
x3
jnz .3
y4
jmp .end
.3:
y3
jmp .end
.2:
y2
jmp .end
.1:
y1
.end:

It essentially involves movinf the intruction blocks y1,y2,.. around but keeping the condition checking block x1,x2 in the same order.

19 Nov 2009, 06:24

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