Author: Tord Romstad
Date: 06:17:49 02/16/04
Go up one level in this thread
On February 16, 2004 at 07:34:07, Matthias Gemuh wrote:
>>
>>But on a somewhat related note, there is one little piece of information
>>on your BigLion page which I have always found really weird: You write
>>that you store the pseudo-legal move list in your hash table. I have
>>never tried anything like this myself, but I find it hard to believe
>>that it is really a good idea. Doesn't this make your hash table
>>entries insanely big? Does it really give you a sufficiently big
>>performance effect that it is worth the price?
>>
>
>
>
>The move list hashing code is still in BigLion but presently deactivated.
>If I switch it on, it consumes about 50% of total hash, with thick entries
>typedef struct {
> BITBOARD HashKey;
> unsigned short nMoveCount, nKingSq;
> CHESSMOVE Move[MOVECOUNTMAX]; // 230 moves
>} MOVEHASH;
>typedef struct {
> BITBOARD HashKey;
> unsigned short nMoveCount, nKingSq;
> CHESSMOVE Move[QMOVECOUNTMAX]; // 36 moves
>} QMOVEHASH;
>
It looks like you have separate hash tables for the move lists, rather
than storing move lists in the main hash table, as I thought? Separate
hash tables are probably not quite as bad, but I still don't believe in
the idea (and, because it is currently deactivated, I guess we agree
about that).
>Already at this point, it is clear that BigLion is just a strange toy,
>not really a chess engine.
Perhaps, but at least it does its job as a toy very well. It is a much
better toy than most of the stronger programs, including the top commercial
engines!
:-)
>Hit rates lie between 35%...65% in test suites, if I remember well.
>I shall test again and tell you. Speedup and gain were 0% approx.
>I experimented with generating and hashing only legal moves to reduce
>entry size and eliminate legality checking in search. No improvement.
>I tried sorting before hashing to save sorting time, but move ordering wept.
>I did release versions of BigLion with move list hashing.
>
>
>>
>>I am not sure this
>>is the right time to experiment with new pruning tricks. I have the
>>impression that you still suffer from a few serious bugs in your search,
>>and you should probably try to fix them before you make your search more
>>complicated.
>>
>
>
>This is the type of advice I like. It is naked truth.
But you should try to view it from a positive angle: You have already
done most of the hard work to create a really strong engine. It is
possible that a couple of bug fixes is all you need in order to get a
huge leap in playing strength.
The advice is of a general kind, of course. It is most often a good
idea to keep things as simple as possible until you are sure that no
bugs remain. I wish I were better at following this advice myself. :-(
Tord
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