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From: radford@calgary.UUCP
Newsgroups: comp.arch
Subject: Re: random number generator in hardware
Message-ID: <516@vaxb.calgary.UUCP>
Date: Tue, 18-Nov-86 14:34:54 EST
Article-I.D.: vaxb.516
Posted: Tue Nov 18 14:34:54 1986
Date-Received: Thu, 20-Nov-86 22:44:12 EST
References: <317@zuring.mcvax.UUCP> <267@bath63.UUCP>, <2490@phri.UUCP> <7320@utzoo.UUCP>
Organization: U. of Calgary, Calgary, Ab.
Lines: 15
Summary: How about this scheme?

In article <7320@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> > ...  Why don't computers come with hardware random number generators?

> My understanding is that the problem is avoiding bias in the resulting
> numbers.  Building a noise generator isn't hard, but one would like the
> probability of a 0 to be roughly equal to the probability of a 1.  Getting
> this sort of balance, and *keeping* it, apparently is almost impossible
> without constant tweaking...

How about taking the exclusive-or of several such random bit generators?
This converges exponentially toward probability 1/2 as the number of
bits xor'ed increases.

    Radford Neal
    The University of Calgary