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*To*: [email protected]*Subject*: Re: Random numbers*From*: [email protected] (Don Bellenger)*Date*: Fri, 27 Nov 92 17:07:00 PST*Cc*: [email protected] (Don Bellenger)

> > > > It has lately been discussed different ways to construct pure > > random number generators by means of radiactive decay. I must admit > > that this is a very good way to produce such numbers, but for a > > number of reasons it is impractical to use such a device. (High > > radiation levels are needed too produce a significant amount of data.) > > > The way to make good random numbers is to take about 20 stages of flops > and feedback 2 or three terms. Clock the thing as fast as you can, Say > 50 mhz, and asychronously to your main processor clock. The shift register > needs its own crystal. The selection of feedback points is based on > Linear Congruential Method of Pseudo random numbers generated by most > machines. > > The numbers generated are very, very uniform. > > The way to test random number generators for randomness is to generate > the numbers in pairs and plot them on a scatter plot. This simple > cross check will show up many poor generators. Checking for uniform > density in higher dimensions will uncover even more subtle variations > from uniformity. There is an enormous literature on this topic. Obviously > you can screw it up, but it isnt that hard to get right either. There > is an excellent book just out on simulations that covers this. If > anyone wants the reference, I can dig it up. > > Bottom line is that you don't need anything exotic. But the 8 or simple 16 > bit methods on the small processors are no good. > > Don Bellenger > [email protected] > > > > > > --

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