linux-kernel - Re: If not readdir() then what?

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Message-ID: <Pine.LNX.4.63.0704111506040.28394@qynat.qvtvafvgr.pbz>
Date:	Wed, 11 Apr 2007 15:06:44 -0700 (PDT)
From:	David Lang <david.lang@...italinsight.com>
To:	Neil Brown <neilb@...e.de>
cc:	Theodore Tso <tytso@....edu>,
	Jörn Engel <joern@...ybastard.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ulrich Drepper <drepper@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: If not readdir() then what?

On Thu, 12 Apr 2007, Neil Brown wrote:

> For the second.
>  You say that you " would need at least 96 bits in order to make that
>  guarantee; 64 bits of hash, plus a 32-bit count value in the hash
>  collision chain".  I think 96 is a bit greedy.  Surely 48 bits of
>  hash and 16 bits of collision-chain-position would plenty.  You would
>  need 65537 entries before a collision was even possible, and
>  billions before it was at all likely. (How big does a set of 48bit
>  numbers have to get before the probability that "No subset of 65536
>  numbers are all the same" drops below 0.95?)

Neil,
   you can get a hash collision with two entries.

David Lang
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