Guy Harris schrieb:
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?
To be honest I just don't have a clue.
I did some experiments to use the existing CRC algorithms (trial and
error based), but this is really no indication if it's possible or not ;-)
If you would like to do some "more educated" experiments on this I could
send you a capture file with some valid CRCs in PM.
Regards, ULFL
