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Subject: Re: Rehashing (was Re: Hash replacement question)

Author: Ernst A. Heinz

Date: 08:01:51 01/15/98

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On January 15, 1998 at 10:27:28, Stuart Cracraft wrote:

>Also, I think we need to discuss rehashing. Does somenoe
>have this implemented? It seems like rehashing for say
>8 slots based on nodes-recorded would be better than
>single-tier since quite a few collisions could be handled
>without replacing information already at that slot.
>
>Does anyone have some good algorithms for this? Let's say
>I hash to index X and find it is filled. What is a good
>algorithm to choose another index to try? And it seems like
>that algorithm would have to be deterministic because the
>next time into this entry, I'd want to go search those
>alternate indexes/slots in the same order to find where I'd
>stored it.
>
>--Stuart

We simply use linear rehashing. Citing from my article about
"How DarkThought plays chess" (ICCA Journal, Vol. 20, No. 3)
[online preprint available from
 URL = <http://wwwipd.ira.uka.de/Tichy/DarkThought>]:

``DarkThought performs multiple probes in the transposition table
  because experiments conducted by Peter W. Gillgasch in 1993
  showed the superiority thereof as compared to multiple tables
  (see [Beal and Smith] for an independent confirmation). The
  number of probes per access is a redefinable parameter normally
  set to 4.

  Beal, D.F. and Smith, M.C. (1996).
  Multiple probes of transposition tables.
  ICCA Journal, Vol. 19, No. 4, pp. 227-233.''

=Ernst=



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