OpenChess

Posted: **Sat Jan 12, 2013 3:41 am**

Hello, time for yet another question (sorry if I have so many

). Basically I've just integrated transposition tables in and I'm having trouble figuring out a bug. My program is being written in java. Using transposition tables causes it to fail to see a mate in 5 ply even if it is evaluating to a deeper ply than that. In my code the transposition table is a HashMap of type <Long, int[] >.

Before the start of the cpu's turn, after the user has made their move, the table is cleared. Then I use the code like this:

Code: Select all

// inside the alphabeta search
tempHash = hashMove( move, currentHash ); // Hashes in the move to the current positional hash. Takes into account castling

int[] info = hashTable.get( new Long( tempHash ) ); // info, contains two ints, a value for the search and the depth it was searched to.
if ( info != null && info[0] >= currentDepth - depth ) // If we get a hit, and the depth for the value in the hashmap is large enough
     return info[1]; // Return the value stored in the hash table
}

// perform actual search of move...

if ( info == null ) {
     info = new int[2];
     info[0] = currentDepth - depth;
     info[1] = SCORE_OF_EVALUATED_MOVE;
     hashTable.put( new Long( tempHash ), info ); // Store the value and depth and hash
}

I am using a zobrist hash key. the zobrist hash function and move hashing function is working perfectly, I've verified that with extensive tests. Also, I very much doubt that I am getting a collision of hashes between new positions because I am analyzing maybe 1 million positions per move ( if i'm lucky) and I've also tried several different seeds for my RNG.

OpenChess

Transposition Tables

Transposition Tables