netdev - Re: [RESEND][PATCH 1/3] PPPoE: improved hashing routine

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Message-Id: <20070731.012609.41193630.davem@davemloft.net>
Date:	Tue, 31 Jul 2007 01:26:09 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	florz@...rz.de
Cc:	mostrows@...thlink.net, netdev@...r.kernel.org
Subject: Re: [RESEND][PATCH 1/3] PPPoE: improved hashing routine

From: Florian Zumbiehl <florz@...rz.de>
Date: Tue, 31 Jul 2007 10:07:19 +0200

> Erm, I'd say this not only produces different results than the old
> version, but it also produces "wrong" results, in that it ignores quite
> a bit of the data that's supposed to be hashed. If I didn't overlook
> something, it only considers addr&0x0f0f0f0f0f00 and sid&0x0f0f, given
> the right endianness of addr and that PPPOE_HASH_SIZE stays 16.

You're right, I need to fix the shifts up.  How does this version
look?

	hash ^= (hash >> 4) ^ (hash >> 12) ^ (hash >> 20);
	return (head ^ (hash >> 8) ^ (hash >> 24)) &
		(PPPOE_HASH_SIZE - 1);

Actually it might be simpler and more efficient to just make
PPPOE_HASH_SHIFT be 8.
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