[solved] generate random data in macros?

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edfed

Joined: 20 Feb 2006
Posts: 4354
Location: Now

edfed 12 Jul 2019, 08:44

how can i generate random datas from a bunch of macro repetition?

for example something like

Code:

macro Random {
local p = random mod 4
repeat 4
 if % equ p
 db random ; here i want to make a random byte
 else 
 db 0xff
 end if
end repeat
}

repeat 4
Random
end random

as a result, i would get 4 packets of 4 bytes, with a random byte at a random position for each packet.

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12 Jul 2019, 08:44

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 12 Jul 2019, 09:21

It depends upon your definition of "random".

You can use %t to get the current time. It isn't really random but might serve for your purpose as a seed value.

Otherwise use an external file to grab some random bytes and insert those. If you have Linux then /dev/urandom could suffice.

12 Jul 2019, 09:21

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8406
Location: Kraków, Poland

Tomasz Grysztar 12 Jul 2019, 09:51

If pseudo-random numbers would be enough for you, my article about types of multi-pass assembly contains some Xorshift macros for fasmg that I used to generate randomized sources. You could make something similar for fasm 1, though you'd have to do it a bit differently to avoid overflows.

12 Jul 2019, 09:51

edfed

Joined: 20 Feb 2006
Posts: 4354
Location: Now

edfed 12 Jul 2019, 12:49

Code:

macro Random n{
p = ((%t mod n) mod 14) + 1
db n and 0xff
db p
repeat 14
 if % = p
 db (%t shr n) and 0xff ; here i want to make a random byte
 else 
 db 0xff
 end if
end repeat
}

repeat 256
Random %
end repeat

this code makes what i wanted. thanks Wink

12 Jul 2019, 12:49

edfed

Joined: 20 Feb 2006
Posts: 4354
Location: Now

edfed 18 Jul 2019, 15:04

this single line makes a good enough random source

Code:

RNDT equ ($ + %t)

18 Jul 2019, 15:04

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 18 Jul 2019, 16:10

Yeah, sometimes simple is all that is needed.

18 Jul 2019, 16:10

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