/* GNU Chess 5.0 - hash.c - hash function code
   Copyright (c) 1999-2002 Free Software Foundation, Inc.

   GNU Chess is based on the two research programs 
   Cobalt by Chua Kong-Sian and Gazebo by Stuart Cracraft.

   GNU Chess is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   GNU Chess is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GNU Chess; see the file COPYING.  If not, write to
   the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.

   Contact Info: 
     bug-gnu-chess@gnu.org
     cracraft@ai.mit.edu, cracraft@stanfordalumni.org, cracraft@earthlink.net
*/

#include "common.h"


void CalcHashKey (void)
/***************************************************************************
 *
 *  Calculates the hashkey for the current board position.  We sometimes
 *  need to do this especially when loading an EPD  position.
 *  Note:  The hashkey is a 64 bit unsigned integer number.  
 *  Added in pawnhashkey calculation.
 *
 ***************************************************************************/
{
   int sq, piece, color;
   BitBoard b;

   PawnHashKey = HashKey = (HashType) 0;
   for (color = white; color <= black; color++)
   {
      for (piece = pawn; piece <= king; piece++)
      {
	 b = board.b[color][piece];
	 while (b)
	 {
		BitBoard h;
	    sq = leadz (b);
  	    CLEARBIT (b, sq);
		h=hashcode[color][piece][sq];
	    HashKey ^= h;
	    if (piece == pawn)
	       PawnHashKey ^= h;
	 }
      }
   }

   /* Take into account castling status & en passant */
   if (board.ep > -1)
      HashKey ^= ephash[board.ep];
   if (board.flag & WKINGCASTLE)
      HashKey ^= WKCastlehash;
   if (board.flag & WQUEENCASTLE)
      HashKey ^= WQCastlehash;
   if (board.flag & BKINGCASTLE)
      HashKey ^= BKCastlehash;
   if (board.flag & BQUEENCASTLE)
      HashKey ^= BQCastlehash;

   /* Take into account side to move */
   if (board.side == black)
      HashKey ^= Sidehash;

}