Re: Lockless file readingu

[jlnance@unity.ncsu.edu]

On Fri, Aug 29, 2003 at 12:44:00AM +0100, root@mauve.demon.co.uk wrote:

> Of course it dowesn't.
> The probability gets rather smaller as numbers go down, and bigger as
> they go up.
> With 2^128 bits, the chance of a a collision between 2^64 randomly chosen 
> pictures is 50%.
> At 2^54 pictures, it's about one in a million, and at 2^34 (enough for
> several pictures of everyone alive) one in a billion billion.
> At more common numbers of pictures (say 2^14) it becomes vanishingly
> unlikely for anyone to have two matching pictures (even with several billion
> archives)

Be careful.  I remember discussing in probability class the liklyhood that
two people in a room with N people have the same birthday.  N does not have
to be anywhere close to 365 for your probability of a collision to be greater
than 50%.  I forget what the exact number is but its less than 30.  The
image problem sounds similar, depending on exactly how you phrase it.

Thanks,

Jim