From: root@mauve.demon.co.uk
Message-Id: <200308282344.AAA26603@mauve.demon.co.uk>
Subject: Re: Lockless file readingu
To: ecki@calista.eckenfels.6bone.ka-ip.net (Bernd Eckenfels)
Date: Fri, 29 Aug 2003 00:44:00 +0100 (BST)
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <E19sUna-0003Zq-00@calista.inka.de> from "Bernd Eckenfels" at Aug 28, 2003 11:59:22 PM
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> 
> In article <200308281726.SAA24033@mauve.demon.co.uk> you wrote:
> > I'd be really surprised if there were that many pictures in the world.
> 
> Well, this is about probabilty. It does not mean that you need 2^64
> pictures, neighter does it mean you have a collision within 2^64 pictures.

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)

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