netdev - Re: ipv4: Simplify ARP hash function.

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Message-Id: <20110710.120732.419322076297775729.davem@davemloft.net>
Date:	Sun, 10 Jul 2011 12:07:32 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	roland@...estorage.com
Cc:	johnwheffner@...il.com, mj@....cz, netdev@...r.kernel.org
Subject: Re: ipv4: Simplify ARP hash function.

From: Roland Dreier <roland@...estorage.com>
Date: Fri, 8 Jul 2011 16:11:00 -0700

> Maybe * of hash key with a random odd value is good enough?

Yes, from what I've read over the past few days it should
be.  More precisely:

	(key * hash_rnd) >> (32 - hash_table_size_log2)

where "hash_rnd" is odd.

The reason we want the top bits is because multiplies intrinsically
work such that bits in the inputs can only effect the same or higher
bits in the result.
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