Messages in this thread | ![/](/images/icornerl.gif) | | From | jlnance@unity ... | Date | Fri, 29 Aug 2003 06:00:11 -0400 | Subject | Re: Lockless file readingu |
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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,
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