netdev - Re: bridge: faster compare for link local addresses

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Message-ID: <20070313130654.7addde2b@freekitty>
Date:	Tue, 13 Mar 2007 13:06:54 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, andi@...stfloor.org, rick.jones2@...com,
	netdev@...r.kernel.org
Subject: Re: bridge: faster compare for link local addresses

On Tue, 13 Mar 2007 12:39:54 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Tue, 13 Mar 2007 14:38:32 +0100
> 
> > But memcmp() has a strong semantic (in libc). memcmp(a, b, 6) should
> > do 6 byte compares and conditional branches, regardless of a/b
> > alignment.  Or use the x86 "rep cmpsb" instruction that basically
> > has the same cost.
> 
> Yep, that's the issue, gcc won't make the reductions necessary
> here to get it down to one comparison and one branch.

Also, for our usage we only care about equality, not greater/less than
return value.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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