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/***************************************************************************
* Copyright (C) 2009 by Stefan Bühler *
* stbuehler@web.de *
* *
* This program 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 of the License, or *
* (at your option) any later version. *
* *
* This program 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 this program; if not, write to the *
* Free Software Foundation, Inc., *
* 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *
***************************************************************************/
#include "ai.h"
namespace toruschess {
// NOPIECE = 0, PAWN = 1, KNIGHT = 2, BISHOP = 3, ROOK = 4, QUEEN = 5, KING = 6
static int piece_value[] = {
0, 1, 3, 3, 5, 9, 10
};
static const int MAXVAL = 10000;
static const int NOMOVE = -MAXVAL - 1;
static const int DRAWVAL = -7;
/* standard minimax search; saves the best move in *move if move != NULL;
* balance is the current "heuristic value" of a state (mult with curp to get the
* rating for a specifig player)
*/
static int minimax(Field &field, int bal, Player curp, unsigned int depth, Move *move) {
if (depth == 0) return curp * bal;
int mx = NOMOVE;
for (int x = 0; x < 8; x++)
for (int y = 0; y < 8; y++) {
Pos p(x, y);
if (field.player(p) != curp) continue;
int cbal = bal;
QList<Move> moves = field.validMoves(p);
foreach(Move m, moves) {
field.move_unchecked(m);
cbal -= m.prevTo();
int val = -minimax(field, cbal, Player(-curp), depth-1, NULL);
if (val > mx) {
mx = val;
if (move) *move = m;
}
field.undo_unchecked(m);
if (mx == MAXVAL) return mx;
}
}
if (mx == NOMOVE) {
if (field.inCheck(curp)) return -MAXVAL;
return curp * DRAWVAL;
}
return mx;
}
Move ai::getMove(Field &field, Player curp, int depth) {
int balance = 0;
for (int x = 0; x < 8; x++)
for (int y = 0; y < 8; y++) {
Pos p(x,y);
balance += field.player(p) * piece_value[field.piece(p)];
}
Move move;
minimax(field, balance, curp, depth, &move);
return move;
}
}