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Subject: Re: Efficient hash algorithm?

Author: Dave Gomboc

Date: 19:20:48 09/22/98

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On September 22, 1998 at 12:17:03, Pat King wrote:

>Well, upon pondering the problem I made a refined estimate (but
>still only an estimate) of 2^32 or about 4.3 e+09 nodes, which
>works out to 20.2 plies instead of 19.something. Is the 2^32
>figure for P(lookup error)=.5 for a 32 bit key a coincidence? I
>suspect not. If not, then you can easily decide on how much error
>you're willing to tolerate.  Based on this analysis, 64 bits
>certainly seems like overkill to me.
>
>Pat

We know from experimentation that 32-bit hash keys are not enough to prevent a
fatally high number of collisions in a 3-minute search.  The next logical number
ot use is 64 bits, simply because it is the next higher power of two.  Sure,
maybe you could try it with 48 bits or 56 bits, but why bother?  It's going to
cost you more time than it is worth for the extra space that you save in the
hash table.

Dave Gomboc



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