Wireshark · Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] rev 27748: /trunk/plugins/profinet/ /trunk/plugins/profinet/

[Guy Harris <guy@xxxxxxxxxxxx>]

On Mar 16, 2009, at 3:45 PM, Joerg Mayer wrote:

> On Mon, Mar 16, 2009 at 09:40:03PM +0000, ulfl@xxxxxxxxxxxxx wrote:
> > http://anonsvn.wireshark.org/viewvc/viewvc.cgi? 
> > view=rev&revision=27748
> > crc16 algorithm copied from Linux sources (GPL V2 only!)
>
> So far the wireshark sources are v2 or later - so adding a gplv2  
> only file
> is not something that should be done without asking *first*, because  
> it
> has effects for all of Wireshark. Or maybe there already were files  
> that
> are v2 only and I missed that?

Is the only difference between the CRC16 in PROFINET and the ITU-T  
CRC16 implemented in epan/crc16.c the polynomial?  It looks as if the  
algorithm is the same in the PROFINET CRC16 and the "reflected" ITU-T  
CRC16:

	crc = initial value;
	for (all bytes in the buffer)
		crc = (crc >> 8) ^ table[(crc ^ byte from buffer) & 0xff];
	return crc;

so it might just be the table.  If so, could we just generate the  
appropriate table for the PROFINET polynomial, have epan/crc16.c  
export crc16_reflected(), and have the PROFINET CRC16 routine use  
crc16_reflected() and the appropriate table?