Generating a unique identifier

[Paul Rubin]

Paul Rubin <http://phr.cx@NOSPAM.invalid> writes:
> the probability is about exp(-(2**60 / 2*2**160)) = 1/exp(2**101)

Bah.  Got that backwards and calculated wrong.  The probability of no
collisions is

    exp(-(2**60) / (2*2**160)) = exp(-(2**-101)) = approx (1 - 2**-101)

which is very close to 1.  The probability of collision is about
2**-101 which is close to 0.  Proofread first, then post.  I keep
getting that in the wrong order.