Author: Daniel Clausen
Date: 15:01:44 02/28/00
Go up one level in this thread
Hi On February 28, 2000 at 17:04:13, William Bryant wrote: >I am curious, >do you hash a different constant for each of the 16 possible ep squares, or >simply a single constant if ep is possible. Although I'm not really the one the question was directed to, I'll answer. Hope you don't mind. :) You should use more than just a constant if EP is possible, since you can't always conclude WHAT ep-move is possible from the position alone. EP to the left or to the right may be possible so you need to store more than just a single constant. I have a random[64] array I xor to the hash-value if EP on a certain square is possible. I think this solves this pretty nice. [Don't forget to reset the EP-flag and update the hash-value accordingly.] >I have sixteen different values that are XOR'ed into the hash signature >depending on which square is the ep square. Now that you mention 16 I realize that my 64 are a bit overkill.. oh well. It's easier in a bitboard engine. >It is intersting that Bruce made a comment about this a while back. He noted >that the same opening position reached by a different order of moves will >produce a different hash signature doing ep squares in this way. Therefore it >does create a degree of inefficiency because (except for the ep move) the rest >of the position may have already been evaluated and in the hash table. Not sure if we have the same discussion in mind. What I remember is the following. Bruce suggested to set the EP-flag after a double-step move of a pawn ONLY if the opponent has pawns adjacent to it which ALLOW him to make an EP search. Consider the initial position after the moves E2-E4, E7-E5. There's no sense in setting the EP-flag because there's no white pawn on D5 of F5 which could possibly capture E5 en passant. Now consider the initial position and the moves E2-E3, E7-E6, E3-E4, E6-E5. Again the same position appears. If you stored the first position with the EP-flag set you won't have the same hash-value here now, and therefore won't get a hash-hit. Kind regards, -sargon
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.