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Subject: DarkThought: keeps all 3/4-piece endgame databases in RAM

Author: Wylie Garvin

Date: 02:49:24 11/16/01


Hi all,

  I'm a newcomer here who got interested in chess programming a while back and
have been pretty gusto about it over the last two months.  There seem to be
several past threads about shrinking endgame databases.  In my research I came
across Heinz's excellent publications about DarkThought.  There don't seem to be
any posts about this style of endgame-database use, so I thought I'd post one!

  +Brief+ summary: DarkThought uses knowledgable encoding to shrink >150MBs of
databases to 15.1MB.  It loads them into RAM and consults them everywhere in the
search.  It uses interior node recognition to efficiently classify positions and
apply specialized scoring to them (in this case, database lookups tempered with
weighted scoring functions).  The loss of optimal play is a small disadvantage,
but consulting the databases at every potentially recognizable position (even
20+ ply deep in quiescence!) is a big advantage.  DT searches smoothly from
late-middlegame positions into the endgame databases and then plays those
endgames solidly.

  And those 15.1MB of "bit-bases" are not even compressed!  My own idea is to
store them in RAM in a compressed format that still allows efficient random
access (i.e. 2-3 loads and a few simple insns).  I have not tested this out yet;
I am working on two chess engines of my own but I have a bunch of other stuff I
better do before I go back to fooling around with endgame databases...but I have
a wild and totally untested theory that I can adapt the sparse-table compression
algorithms used e.g. in parser generators (compiler toolkits) to this purpose.
I have good reasons to believe this will not affect performance at all--it will
just (hopefully) shrink the RAM consumption a bunch so I can afford to do the
same thing with some 5-piece subgames (e.g. all 5-piece endgames with rammed
pawns??) and load them into RAM too!  Muahahahaha.

Anyway, here are the links:

Knowledgeable Encoding of Endgame Databases
http://supertech.lcs.mit.edu/~heinz/ps/know_edb.ps.gz

Efficient Interior-Node Recognition
http://supertech.lcs.mit.edu/~heinz/ps/node_rcg.ps.gz
http://supertech.lcs.mit.edu/~heinz/dt/node33.html

How DarkThought Plays Chess:
http://supertech.lcs.mit.edu/~heinz/dt/

Cheers,
Wylie



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