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Date: 7 Dec 2014 05:02:52 -0500 From: "George Spelvin" <linux@...izon.com> To: herbert@...dor.apana.org.au, linux@...izon.com Cc: dborkman@...hat.com, hannes@...essinduktion.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, tgraf@...g.ch Subject: Re: Where exactly will arch_fast_hash be used > For a start why don't you print out the hashes of 1-255 and then > find out how easy it is to deduce the last bit of the hash result. They're available in lib/crc32table.h, as crc32ctable_le[0]. As a CRC is a linear function, every bit is the XOR of some selected bits of the input, i.e. the parity of the input and some bit-specific mask sequence. Furthermore, CRCs are cyclic, so the mask sequences for adjacent bits are shifts of each other. The lsbit of the CRC32c of x is the parity of x & 0x1f. This is because the LFSR sequence generated by the polynomial starts 0001111110010001110010101111011000111000011011110010110000100101... The first bit corresponds to the msbit of the last byte. How does this implicate the low bits specifically? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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