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From: thyssen@batserver.cs.uq.oz.au (Anthony Thyssen)
Newsgroups: comp.sys.amiga
Subject: Re: Lattice Random Numbers
Message-ID: <4980@uqcspe.cs.uq.oz.au>
Date: 24 Sep 90 00:16:44 GMT
References: <4604@crash.cts.com>
Sender: news@uqcspe.cs.uq.oz.au
Reply-To: thyssen@batserver.cs.uq.oz.au
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acota@pro-realm.cts.com (Arnold Cota) writes:
>How do I generate a random number in the range of 1 to 54 in Lattice C?

  I recently had the same problem as you - random numbers in a certian range

To solve this I used the lattice C random number generators

              srand((long)time(NULL));     /* seed random with current time */
              ULONG  r = rand();           /* get a random number */

Note that the seeding is done once at the begining of your program only.
the result is a number in the rand   0..2^31   IE a positive long number.
(Of 31 bit length). 

    I large number of people will then tell you to then mod (`%' in C)
this over the range. - This is wrong and on larger ranges makes the
random number generator tend to produce more low numbers in the range than
higher ones. The solution is a little more complicated. The folloing
is my macro definition to produce a number over a range (inclusive)

#define RandInt(lo,hi) (int)\
    ((lo)+((((long)((hi)-(lo)+1)*(long)(rand()&0x7fff))>>15) & 0x7fff))

Then to get a number over range 1 to 54 inclusive you do
        number = RandInt(1,54)

The macro definition spreads the numbers produced equally over the whole
range.

  Anthony Thyssen - (Dragon Computing!)         thyssen@batserver.cs.uq.oz.au
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   It has been proved, beyond a shadow of a doubt, that million-to-one
       chances, occur nine times out of ten!         ---   Terry Pratchet
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