Messages in this thread | | | Date | Fri, 16 Apr 1999 13:31:58 -0400 (EDT) | From | Chuck Lever <> | Subject | Re: random table-driven hash benchmarked |
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On Fri, 16 Apr 1999, Andrea Arcangeli wrote: > >/* this is 40499 * 65543 - both are prime; the result is ~0.68*(2^32) */ > >#define MULTIPLIER 2654425957UL > > > >#define _hashfn(dev,block) \ > > ((((unsigned long) (block) * MULTIPLIER) >> 11) & bh_hash_mask) > > Personally I like this mul hashfn. But your implementation doesn't use dev > information. Is that intentional?
yes. i reasoned that the dev parameter isn't really adding any useful randomness, so i left it out of my original function. i've done a few benchmarks to test the hypothesis, and, by-and-large, the hash functions without "dev" seemed to work a little better.
if you want to add it back, i suggest this:
((((unsigned long) (minor(dev) + (block)) * MULTIPLIER) >> 11) & bh_hash_mask)
- Chuck Lever -- corporate: <chuckl@netscape.com> personal: <chucklever@netscape.net> or <cel@monkey.org>
The Linux Scalability project: http://www.citi.umich.edu/projects/citi-netscape/
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