NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/comp/os/msdos/programm/8580

Internet Message Format | 1992-08-17 | 1.9 KB

Path: sparky!uunet!bonnie.concordia.ca!hobbit.ireq.hydro.qc.ca!beaurega
From: [e-mail] (Denis Beauregard)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Random numbers in assembly language
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Date: 17 Aug 92 18:45:50 GMT
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Organization: Institut de recherche d'Hydro-Quebec, Varennes, Canada
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I don't see how you could generate random numbers using a timer, except
for the 1st number ;-)

So, another solution :

From Electronics, May 27, 1976.

You will have to consider a word or a byte and a few bits (or taps) in it.
You shift the word and insert a value (i.e. carry) that is one or zero
depending on the added value of the taps (with a xor operator).

carry = A xor B xor C, when A, B and C etc. are taps.

For the longer sequence, with one byte, use:
bits 1 and 7 or 3 and 7 (i.e. carry depends on bits 1 and 7, then do a ROT).

For a word (15 bits in the example), you will get 32767 consecutive different
pseudo-random values from : 1 and 15, or 4 and 15 or 7 and 15.

For a double word (31 bits), taps are 3 and 31, 6 and 31, 7 and 31 or
13 and 31 (2,146,483,647 values).

For the exact programming, I leave it to the original poster!  After all,
you selected Assembly because it was too easy otherwise...

P.S.  I used taps because the original article is for an electronics device.
Taps are selected bits.

P.P.S.  You still select the initial value from a true random event like
the initial clock value, but don't use the 18.2 clock (not enough random).

--
  \_\    Denis Beauregard  *  internet:[e-mail]
 /   \   Genealogiste officiel : Beauregard/Jarret/Jarest/Vincent
J   __>  Barthelemy Jarret (1471) -> Andre Jarret, sieur de Beauregard (1665)
\_.-===   -> Denis Beauregard (1992)                  Opinions ? Et pis non !