Colin Plumb has an amusing quote in the bignum library, where another
algorithm is used that has a failure probability:
"The chances that another Dinosaur Killer asteroid will land today is
about 10^-11 or 2^-36, so it would be better to spend your time worrying
This is assuming that such asteroids hit Earth every billion years or so.
It also assumes that they aren't detectable in advance, which according to
a documentary I saw recently about the late Dr. Gene Shoemaker, is