Re: need POSIX cksum tables

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1 total messages Started by Randy Campbell Tue, 14 Aug 1990 23:18

#435

Author: Randy Campbell
Date: Tue, 14 Aug 1990 23:18

38 lines
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From:  Randy Campbell <randyc@hpfclj.hp.com>

>From:  andrew@alice.uucp (Andrew Hume)
>
>	i would hate to cause trouble but can anyone justify
>why cksum uses anything other than CRC-32 for its polynomial?
>(i am not 1000% sure it isn't but am fairly sure.)
>it really frosts my shorts when CCITT and other folks
>bust their chops developing and testing 32 bit CRCs, find a really good
>one and then posix picks some hokey thing whose only apparent recommendation
>is that pathalias uses it (not strictly the highest form of praise).
>
>
>Volume-Number: Volume 21, Number 23
>----------

Well, I had some part in developing the current (Draft 10) spec of cksum.
There was certainly no intention to "frost your shorts" (is this a 
reference to some kind of stone-washed jeans?).  

The Draft 9 spec for cksum (the one that was derived from pathalias)
had a problem in that it would too often yield identical results for
files that were different only near the beginning.

It may be that CRC-32 would be an adequate or even superior polynomial to
the one we used.  However, the polynomial selected is the one used by
Ethernet and is specified in a networking standard (ISO 8802-3), so we 
thought it would be appropriate to use.  In fact, finding a known,
standard polynomial to use was one of our criteria.  And it gave good 
empirical results on some filesets that had exposed weaknesses in other 
implementations.


	Randy Campbell



Volume-Number: Volume 21, Number 31

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