Re: How can Emacs get a unique ID per Linux reboot?

G. Allen Morris III (gam3@ixlabs.com)
Thu, 03 Jun 1999 10:43:55 -0700

>>>Tim Smith said:
> On Tue, 1 Jun 1999, G. Allen Morris III wrote:
> > How about generating a 32bit random number at boot time. There
> > is a 1 in 2**32 of getting the same number after a reboot, but
> > that should not be a large problem.
>
> That 1 in 2**32 is the chance of duplicating any specific number in the
> sequence. The chances of *some* member of the sequence being a duplicate
> is much higher. This is called the "birthday paradox" because if you
> pick ~30 people at random, it is highly likely that two of them will
> have the same birthday.

There is no `birthday paradox' in this case. There would be a birthday
paradox if the question was what is the chance of having two random numbers
that are the same after picking _n_ random numbers. In this case instead
of have a n/2**32 chance of a collision there would be an
(n(n-1)/2)/2**32 chance of a collision. But in this case we have
a single random number, and we want to know if it is the same as a
single previous random number, so the odds of a collision are 1/2**32.

Allen

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