Pawn hash tables

[mageofmaple]

Hello all!

I'm interested in your thoughts on pawn hash tables. For one thing, a 32-bit hash key is not considered adequate for storing a full-board representation, but do you think that 32 bits would be enough if you are just hashing the pawn position?

Also, what information besides an evaluation is worth storing? A bitboard of passed pawns sounds useful, because you might try placing a move that pushes a passed pawn higher in the move ordering. Any other ideas?

Thanks,
Greg

[Gerd Isenberg]

Hello all!

I'm interested in your thoughts on pawn hash tables. For one thing, a 32-bit hash key is not considered adequate for storing a full-board representation, but do you think that 32 bits would be enough if you are just hashing the pawn position?

Also, what information besides an evaluation is worth storing? A bitboard of passed pawns sounds useful, because you might try placing a move that pushes a passed pawn higher in the move ordering. Any other ideas?

Thanks,
Greg

Hi Greg,

32-bit keys for pawn-hashing should be fine.

Storing king-safety related pawn-shield stuff for both wings and eventually center comes in mind. Some pure pawn related aggregated first order scores. What about arbitrary enumeration of pawn-structure of center and wings, where one can possibly index appropriate piece-square tables with?

I would not store bitboards of pawns with certain properties, since they are sparsly populated or often empty and take too much space and in average low information density. File sets only take one byte instead of eight.

Gerd

[jwes]

Hello all!

I'm interested in your thoughts on pawn hash tables. For one thing, a 32-bit hash key is not considered adequate for storing a full-board representation, but do you think that 32 bits would be enough if you are just hashing the pawn position?

Also, what information besides an evaluation is worth storing? A bitboard of passed pawns sounds useful, because you might try placing a move that pushes a passed pawn higher in the move ordering. Any other ideas?

Thanks,
Greg

Hi Greg,

32-bit keys for pawn-hashing should be fine.
Gerd

32-bit keys for pawn-hashing + the address bits should be enough, but if you take the address bits from the 32 bit key, leaving 10-18 effective hash bits, you will have false matches.