Author: Robert Hyatt
Date: 08:12:37 06/24/02
Go up one level in this thread
On June 24, 2002 at 00:01:23, Pham Hong Nguyen wrote:
>>First, you probably don't want the king positions hashed into your pawn
>>structure hash signature.
>>
>>Second, all you can really hash is simple pawn structure information, plus
>>information that is expensive to compute (where are passed pawns, weak pawns,
>>and the like) so that you can use this elsewhere without having to compute it,
>>when you get a pawn hash hit...
>
>I think I had had wrong understanding about the content of pawn's hash table.
>Thanks for your exlaination. Some other questions:
>- How many bits do you use for that simple structure? (and what are they?)
I store the following:
typedef struct {
BITBOARD key;
short p_score;
unsigned char allb;
unsigned char black_defects_k;
unsigned char black_defects_q;
unsigned char passed_b;
unsigned char candidates_b;
unsigned char allw;
unsigned char white_defects_k;
unsigned char white_defects_q;
unsigned char passed_w;
unsigned char candidates_w;
unsigned char protected;
unsigned char outside;
unsigned char open_files;
} PAWN_HASH_ENTRY;
There are five values for black and five for white.
allb/w is an 8 bit mask, 1 bit per file, saying "there is a white or black
pawn on this file."
defects K/Q indicates the "pawn structure related 'defects'" for the kingside
and queenside pawns (used after determining which side the king is on after
castling.
passed is passed pawns, 1 bit per file, saying "the most advanced pawn on this
file is passed"
candidates is the same thing but for "candidate passers". IE black has a pawn
at a7, none on b or c files. White has pawns at a2 and b2. White has a
candidate passer on the b file.
the final 3 values include which side has a protected passed pawn on which file,
which side has an "outside passer" on which file
And finally which files are open, period.
>- Do you know how fast of that method (use hash table for simple pawn structure)
>is, comparing with method of updating pawn structure on the fly?
>
>Many thanks,
>PHN
It costs nothing, basically, to "hash". This means that whatever you do
in EvaluatePawns() will be free since you will compute it once and use it
every time you reach the same position.
>
>
>>
>>Note that the score you hash can _only_ depend on the positions of pawns. If
>>you do _anything_ else you will introduce a bug, since the signature will not
>>reflect the locations of anything but pawns...
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.