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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI: reference for CRC32C?"KRUEGER,MARJORIE (HP-Roseville,ex1)" wrote: > > Looking thru the current draft I can't find any doc. reference for the > definition of CRC32C. Does the text in sec 11.1 suffice, or is there some > other document that fully defines the algorithm for CRC32C? If so, > shouldn't it be referenced in the bibliography? If I read your sentence correctly ``other document that fully defines the algorithm for CRC32C'', yes, there is: http://www.haifa.il.ibm.com/satran/ips/Vince-Luben-crc32c-01.pdf It fully ``defines the algorithm for CRC32C''. It also quotes: (i) Castagnoli et al. which don't talk about algoritms but analysis of the CRC space, probabilites etc and (ii) a paper by Williams which shows C code. This is from the abstract: ``The CRC32C (aka CRC32/4) digest from iSCSI is presented in a rigorous algebraic manner, the why and how it works and the origin of its verifier constant. The most commonly used CRC digest computation algorithm in iSCSI and Ethernet, the Simultaneous Multiply and Divide (SMD), is derived from the long division algorithm. Sample implementations are provided of both algorithms.'' At the end, a pseudo code implementation is given of SMD, which is what you'll find in actual implementations, including OS networking layer code, network interface device driver source code and hardware. The jump to SMD with table lookup (a great speed up) is trivial and is also mentioned. BTW, this exact question I've seen several times on IPS, ever since that paper appeared, but no one has quoted it yet. The irony is that, unbeknownst to me until last week, if you search for iSCSI on google.com, on most of the cites that will come up, you'll see several white paper references on iSCSI and one of them will be ``the definitive guide to iSCSI CRC <<link to this paper on Julian's web site or a local copy>>'', yet no one ever mentions it on IPS... -- Luben P.S. Perhaps a Linux outlook on how science is conducted by big companies is the only salvation. Yes, I know its new and has never existed but in philosophy, only until recently, but is more productive and fruitful. OTOH, everything I've seen so far is exactly as History of Science would tell us.
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