Re: The randomfunction

From: Darrell Grainger (darrell_at_NOMORESPAMcs.utoronto.ca.com)
Date: 11/29/03 

Date: 29 Nov 2003 01:51:24 GMT

On Fri, 28 Nov 2003, Espen Amundsen wrote:

> Hi
>
> Ive ofte used the randomfunction in different languages but Ive never
> understood how it works. As I see it, truly randomness should be impossible;
> so I just have to know how the randomfx works. Does anyone have the
> sourcecode(any language) or can tell me how thats done?

You are correct that truly random number generators would be impossible in
a programming language. Most languages will use a mathematical formula to
generate a sequence of numbers. Most will use a linear congruent method.
For example:

        x' = (a*x + c) % m

where x is the previous number in the sequence, x' is the next number in
the sequence, a, c and m are set values. The idea is that if you choose a
and c wisely, the sequence will be the maximum length before repeating.
For example, if x is an 8 bit char then the sequence will repeat after all
256 numbers are use. 

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