Author: Andrew Williams
Date: 06:08:03 05/09/99
Go up one level in this thread
On May 09, 1999 at 07:32:28, Frank Phillips wrote:
>On May 09, 1999 at 06:50:17, Andrew Williams wrote:
>
>>On May 09, 1999 at 06:31:41, Frank Phillips wrote:
>>
>>>I have noticed that bugs in my program sometimes cause the onset of
>>>irrationality where I bang the keyboard randomly hoping that by magic (or
>>>perhaps the monkeys writing Shakespeare theory) the problem will go away.
>>>
>>>Up until now I have been calculating the hash code for a position in the
>>>ABSearch() from scratch by looping through the board and XORing the Random64
>>>[colour_of_piece][piece][square] combinations, followed by XORing for the
>>>enpassant square and castling rights. To speed things up I thought I would do
>>>this incrementally in the MakeMove() function by taking the last hash code
>>>(always stored as wtm), undoing the enpassant and castling effects, by XORing
>>>with same values to switch them off, then XORing to remove the piece from a
>>>square, put piece on square, remove captured piece, add promoted piece
>>>etc???.and then finally XORing the result for new enpassant square and castling
>>>rights.
>>>
>>>Everything works fine without hashing the enpassant square and castling rights,
>>>but not otherwise. By which I mean the new method gives the same hash code as
>>>that calculated from scratch in the same position by looping through the board,
>>>provided I do not hash for ep and castling. When I print out the moves, the
>>>offending move where it all goes wrong seems to be castling, but I cannot find
>>>the error.
>>>
>>>Should what I am doing work, so that there is still a bug in the incremental
>>>hash update I have not found yet, or can I not do it the way I am trying?
>>
>>What you describe here is exactly what I do, so it is possible to do it this
>>way. Do you also include the hashkey update for the Rook and King moving about
>>during castling? This question isn't meant to insult your intelligence; this
>>was one of the main problems I had when implementing incremental hashkey
>>updates.
>>
>>Andrew
>
>Thanks. Yes. I XOR king[E1]/king[G1]/rook[H1]/rook[F1] for example.
Well, I don't know if it will help much, but here is what PostModernist does
when updating the hashkey for castling moves:
void update_hashKey_castle(move mv) {
piece movedP;
move rookmv;
movedP = bd[mv.frsq];
/* This bit does the King movement */
currentHashKey = currentHashKey ^
random_bd[movedP.type][mv.frsq][movedP.colour];
currentHashKey = currentHashKey ^
random_bd[movedP.type][mv.tosq][movedP.colour];
/* This bit does the Rook movement */
switch(mv.tosq) {
case C1 : rookmv.frsq = A1; rookmv.tosq = D1; break;
case G1 : rookmv.frsq = H1; rookmv.tosq = F1; break;
case C8 : rookmv.frsq = A8; rookmv.tosq = D8; break;
case G8 : rookmv.frsq = H8; rookmv.tosq = F8; break;
}
movedP = bd[rookmv.frsq];
currentHashKey = currentHashKey ^
random_bd[movedP.type][rookmv.frsq][movedP.colour];
currentHashKey = currentHashKey ^
random_bd[movedP.type][rookmv.tosq][movedP.colour];
currentHashKey = currentHashKey ^ random_cstl[gamescore[halfMoves].cr];
currentHashKey = currentHashKey ^ random_cstl[castlerights];
currentHashKey = currentHashKey ^ random_epsq[gamescore[halfMoves].epsquare];
currentHashKey = currentHashKey ^ random_epsq[epsquare];
currentHashKey = currentHashKey ^ random_col[OTHERSIDE(whoseTurn)];
currentHashKey = currentHashKey ^ random_col[whoseTurn];
}
bd[] is the board array.
gamescore[halfMoves] is a record of various information from the previous
position: .cr is the castling rights; .epsquare is the ep square
castlerights and epsquare are the current values.
random_bd, random_cstl, random_col and random_epsq are my random number
tables.
Hope this makes some sense.
Andrew
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