Re: [PATCH] Update jhash.h with the new version of Jenkins' hash

[Kyle Moffett <kyle@moffetthome.net>]

On Thu, Feb 12, 2009 at 4:11 AM, Jozsef Kadlecsik
<kadlec@blackhole.kfki.hu> wrote:
> The current jhash.h implements the lookup2() hash function by Bob Jenkins.
> However, lookup2() is outdated as Bob wrote a new hash function called
> lookup3(). The new hash function
>
> - mixes better than lookup2(): it passes the check that every input bit
>  changes every output bit 50% of the time, while lookup2() failed it.
> - performs better: compiled with -O2 on Core2 Duo, lookup3() 20-40% faster
>  than lookup2() depending on the key length.

Well, there's another question which is not addressed by Bob Jenkins'
design docs:

Kernel code usually runs cache-cold, whereas Bob Jenkins did most of
his testing cache-hot in tight loops.  If you compile both lookup2 and
lookup3 with -Os and run them in a loop with a cache flush, how well
do they compare then?

Cheers,
Kyle Moffett