🚀 go-pugleaf

In article <3AF40FEC.447D89D9@wretched.demon.co.uk>, 
Simon@wretched.demon.co.uk wrote:
> 
> Since GNU chess uses the same pseudo random hash codes
> everytime it is run, you can make the pawn hash table
> permanent by saving it to disk. Alas the other hash table is
> cleared between moves, but simply stopping the reset seems
> to cause problems I never completely understood.

Saving a permanent pawn hash on disk would work if the pawn hash table 
is large enough to hold every possible pawn configuration. Or if the 
pawn evaluation is complex enough that a disk access is faster, the pawn 
evaluations could be precomputed on disk and cached in ram. I don't 
think either of these conditions hold so we will typically have a subset 
of pawn configurations evaluated in the pawn hash table and recompute 
new configurations as needed.

In the later versions of Gnu Chess 4.0 I had implemented transposition 
aging so that the transposition table did not need to be cleared between 
moves. Without aging, the hash table would eventually be filled with 
unreachable positions from previous moves making hash hits less likely 
and the damage from hash collisions more severe. Aging has not been 
carried into Gnu Chess 5 yet.

If you use short time controls you may want to limit the size of the 
hash table since the time to clear the table before each move can be 
significant.

-- Dan Oetting