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Path: utzoo!dciem!dms
From: dms@dciem.UUCP (Dave Sweeney)
Newsgroups: net.micro.cpm
Subject: Re: Random Numbers
Message-ID: <1523@dciem.UUCP>
Date: Wed, 10-Apr-85 11:42:38 EST
Article-I.D.: dciem.1523
Posted: Wed Apr 10 11:42:38 1985
Date-Received: Wed, 10-Apr-85 13:56:11 EST
References: <9787@brl-tgr.ARPA>
Organization: D.C.I.E.M., Toronto, Canada
Lines: 28

Nick Cuccia writes:
> 
> 
> function Random(var x: integer): real;
> 
> const
> 	A = 2047;		(* = 2^11 - 1, a prime number *)
> 	M = 524287;		(* = 2^19 - 1, a prime number *)
> 
> begin (* random *)
>     x := (A*x) mod M;		(* finding new seed value *)
>     Random := x / M;		(* finding next number in series *)
> end; (* function random *)

While A (= 2047) and M (= 524287) are mutually prime (HCF = 1), which
is all that is required for the algorithm, A is not a prime number:

	2047 = 23 * 89

which will hopefully discourage 16-bit-machine users from using it
for M (which must be prime for the series to have full period).
Here at DCIEM we use an implementation of the generator described
on p. 464 of Knuth's vol. 2, with k = 55, j = 31.  As no multiplications
or divisions are involved, it is reasonably fast.
-- 
	Dave Sweeney, DCIEM
	{allegra,ubc-vision,linus,ihnp4,uw-beaver,floyd}!utcsrgv!dciem!dms
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