linux-kernel - Re: [PATCH 1/6] firewire: handling of cards, buses, nodes

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Message-ID: <4638E379.4050401@s5r6.in-berlin.de>
Date:	Wed, 02 May 2007 21:16:09 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	linux-kernel@...r.kernel.org, Kristian H??gsberg <krh@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux1394-devel <linux1394-devel@...ts.sourceforge.net>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 1/6] firewire: handling of cards, buses, nodes

Pekka Enberg wrote:
> On 5/2/07, Stefan Richter <stefanr@...6.in-berlin.de> wrote:
>> +/* The lib/crc16.c implementation uses the standard (0x8005)
>> + * polynomial, but we need the ITU-T (or CCITT) polynomial (0x1021).
>> + * The implementation below works on an array of host-endian u32
>> + * words, assuming they'll be transmited msb first. */
>> +u16
>> +crc16_itu_t(const u32 *buffer, size_t length)
>> +{
> 
> [snip]
> 
> So put it in lib/crc-itu-t.c? Btw, there's apparently another ITU-T
> implementation floating around by Ivo van Doorn.

I looked around a bit with grep -R and a few search terms but didn't
find something definite.  Is there any other user of a crc16_itu_t or
crc_ccitt or whatever which operates on a (CPU byte ordered) u32[]
instead of on a (network byte ordered) u8[]?

The only value in having a shared implementation would be a potentially
smaller kernel.  Sharing it to ensure correctness is not an issue;
fw-topology.c::crc16_itu_t is simply the one in IEEE 1212 table 5.
Performance is also not an issue (if better algorithms exist) because
the FireWire stack uses it only infrequently on a moderate amount of data.
-- 
Stefan Richter
-=====-=-=== -=-= ---=-
http://arcgraph.de/sr/
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