Re: Where exactly will arch_fast_hash be used

From: George Spelvin
Date: Mon Dec 08 2014 - 11:20:10 EST

>>> In case of openvswitch it shows a performance improvment. The seed
>>> parameter could be used as an initial biasing of the crc32 function, but
>>> in case of openvswitch it is only set to 0.

>> NACK. [...]

> Sorry for being unclear, I understood that and didn't bother patching
> that '0' with a random seed exactly because of this.

And I'm sorry for delivering a long lecture on a subject you already
understood perfectly well.

I'd just been thinking about it because of Herbert's comments, so it was
conveniently at hand. :-)

Out of curiousity, what *were* you referring to when you talked
about biasing the crc32 function? "Biasing" is a good term becuase
it just applies an offset, but what do you gain from doing that?

There are nifty things one can do with the CRC32 instruction, however.
A lot of ciphers these days use an ARX (add, rotate, XOR) kernel.
A crc32 instruction, although linear, does some very powerful rotate &
xor operations, and could replace the XOR and rotate.
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