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From: rhb@sc7.hgc.edu (Roger H. Brown)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Random number Generator wanted.
Keywords: Random number
Message-ID: <409@mstr.hgc.edu>
Date: 28 Jun 90 20:21:38 GMT
References: <152@asacsg.mh.nl>
Sender: news@mstr.hgc.edu
Reply-To: rhb@sc7.hgc.edu (Roger H. Brown)
Organization: The Hartford Graduate Center, Hartford CT.
Lines: 48

In article <152@asacsg.mh.nl> kr@asacsg.mh.nl (Koos Remigius) writes:
>
>What I need is a random number generator that gives me a random LongInt back.
>The random number I want must lis between 0 and 2097151.
>
>Koos Remigius.

If you can get your hands on a copy of the following article
you will get the full details of generating uniform random
integers between 1 and 2147483646 or up to maxInt = 2^31 -1.

See:
  S.K. Park and K.W. Miller, "Random Number Generators: Good
Ones are Hard To Find," Communications of the ACM, Vol.31,
No. 10, 1988.

Until then, you might want to play with the following code:

  var seed : integer

  function Random : real  
            (* Uses integer arith, yet returns a real between
                0.0 and 1.0  *)
  const
    a = 16807;
    m = 2147483647;
    q = 127773;   (* m div a *)
    r = 2836;     (* m mod a *)
  var
    lo, hi, test : integer;
  begin
    hi := seed div q;
    lo := seed mod q;
    test := a * lo - r * hi;
    if test > 0 then
      seed := test
    else
      seed := test + m;
    Random := seed / m
  end;


Regards

|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Roger H. Brown              GEnie: R.BROWN64     AOL: Roger48       |
| Sch. of Eng. & Science      rhb@mstr.hgc.edu   ...uupsi!mstr!rhb    |
|_____________________________________________________________________|