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From: Marek Lindner <lindner_marek@yahoo.de>
Date: Sat, 4 May 2013 20:12:22 +0800
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Subject: Re: [B.A.T.M.A.N.] [PATCH 2/7] batman-adv: use vid when computing
	local and global TT CRC
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To: The list for a Better Approach To Mobile Ad-hoc Networking <b.a.t.m.a.n@lists.open-mesh.org>

On Wednesday, April 24, 2013 04:04:34 Antonio Quartulli wrote:
> On Wed, Apr 24, 2013 at 03:58:56AM +0800, Marek Lindner wrote:
> > On Tuesday, April 23, 2013 22:34:30 Antonio Quartulli wrote:
> > > @@ -1535,7 +1535,9 @@ static uint32_t batadv_tt_global_crc(struct
> > > batadv_priv *bat_priv, orig_node)) continue;
> > > 
> > > -                       crc ^= crc32c(0, tt_common->addr, ETH_ALEN);
> > > +                       crc_tmp = crc32c(0, &tt_common->vid,
> > > +                                        sizeof(tt_common->vid));
> > > +                       crc ^= crc32c(crc_tmp, tt_common->addr,
> > > ETH_ALEN);
> > > 
> > >                 }
> > >                 rcu_read_unlock();
> > 
> > Is it necessary to define another variable ?
> 
> yes
> 
> > Why not:
> > 
> > crc = crc32c(0, &tt_common->vid, sizeof(tt_common->vid));
> > crc ^= crc32c(crc, tt_common->addr, ETH_ALEN);
> 
> because crc_tmp is the result of the CRC operation on the VID and the MAC
> address (so one per client), while crc is the container of all the crc_tmp
> xor'ed together..

As we discussed on IRC please add a big comment here explaining why we do 
things this way and not differently.

Cheers,
Marek