Re: [ProgSoc] Randomisation

[Peter Meric <pmeric@nospam.progsoc.uts.edu.au>]

On Mon, 1 Feb 1999, daedalus wrote:

> I've heard tell of generators which read the system things like space 
> between interrupts (keyboard etc) and small variations in the system 
> clock ticks to try to randomise the values a little more. I suggest a 
> quick look on the web for stuff on pseudo-random number generators and 
> check out how big their sequences are. 

Or measure the electrical noise from system components?

>               "If you want to generate a random integer between 1
>               and 10, you should always do it by
>  
>                      j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
>  
>               and never by anything resembling
>  
>                      j=1+((int) (1000000.0*rand()) % 10);
>  
>               (which uses lower-order bits)."

In both cases, depending on the RNG, you could overflow first. (But not
a problem with the standard unix rand().)

Peter

------------------------------------------------------------------------
Peter Meric                   pmeric@nospam.cs.usyd.edu.au
                              pmeric@nospam.progsoc.uts.edu.au
                              http://www.progsoc.uts.edu.au/~pmeric

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