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tdegames/kreversi/Engine.h

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/* Yo Emacs, this -*- C++ -*-
*******************************************************************
*******************************************************************
*
*
* KREVERSI
*
*
*******************************************************************
*
* A Reversi (or sometimes called Othello) game
*
*******************************************************************
*
* Created 1997 by Mario Weilguni <mweilguni@sime.com>. This file
* is ported from Mats Luthman's <Mats.Luthman@sylog.se> JAVA applet.
* Many thanks to Mr. Luthman who has allowed me to put this port
* under the GNU GPL. Without his wonderful game engine kreversi
* would be just another of those Reversi programs a five year old
* child could beat easily. But with it it's a worthy opponent!
*
* If you are interested on the JAVA applet of Mr. Luthman take a
* look at http://www.sylog.se/~mats/
*
*******************************************************************
*
* This file is part of the KDE project "KREVERSI"
*
* KREVERSI 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.
*
* KREVERSI 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 KREVERSI; see the file COPYING. If not, write to
* the Free Software Foundation, 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*
*******************************************************************
*/
// The class Engine produces moves from a Game object through calls to the
// function ComputeMove().
//
// First of all: this is meant to be a simple example of a game playing
// program. Not everything is done in the most clever way, particularly not
// the way the moves are searched, but it is hopefully made in a way that makes
// it easy to understand. The function ComputeMove2() that does all the work
// is actually not much more than a hundred lines. Much could be done to
// make the search faster though, I'm perfectly aware of that. Feel free
// to experiment.
//
// The method used to generate the moves is called minimax tree search with
// alpha-beta pruning to a fixed depth. In short this means that all possible
// moves a predefined number of moves ahead are either searched or refuted
// with a method called alpha-beta pruning. A more thorough explanation of
// this method could be found at the world wide web at http:
// //yoda.cis.temple.edu:8080/UGAIWWW/lectures96/search/minimax/alpha-beta.html
// at the time this was written. Searching for "minimax" would also point
// you to information on this subject. It is probably possible to understand
// this method by reading the source code though, it is not that complicated.
//
// At every leaf node at the search tree, the resulting position is evaluated.
// Two things are considered when evaluating a position: the number of pieces
// of each color and at which squares the pieces are located. Pieces at the
// corners are valuable and give a high value, and having pieces at squares
// next to a corner is not very good and they give a lower value. In the
// beginning of a game it is more important to have pieces on "good" squares,
// but towards the end the total number of pieces of each color is given a
// higher weight. Other things, like how many legal moves that can be made in a
// position, and the number of pieces that can never be turned would probably
// make the program stronger if they were considered in evaluating a position,
// but that would make things more complicated (this was meant to be very
// simple example) and would also slow down computation (considerably?).
//
// The member m_board[10][10]) holds the current position during the
// computation. It is initiated at the start of ComputeMove() and
// every move that is made during the search is made on this board. It should
// be noted that 1 to 8 is used for the actual board, but 0 and 9 can be
// used too (they are always empty). This is practical when turning pieces
// when moves are made on the board. Every piece that is put on the board
// or turned is saved in the stack m_squarestack (see class SquareStack) so
// every move can easily be reversed after the search in a node is completed.
//
// The member m_bc_board[][] holds board control values for each square
// and is initiated by a call to the function private void SetupBcBoard()
// from Engines constructor. It is used in evaluation of positions except
// when the game tree is searched all the way to the end of the game.
//
// The two members m_coord_bit[9][9] and m_neighbor_bits[9][9] are used to
// speed up the tree search. This goes against the principle of keeping things
// simple, but to understand the program you do not need to understand them
// at all. They are there to make it possible to throw away moves where
// the piece that is played is not adjacent to a piece of opposite color
// at an early stage (because they could never be legal). It should be
// pointed out that not all moves that pass this test are legal, there will
// just be fewer moves that have to be tested in a more time consuming way.
//
// There are also two other members that should be mentioned: Score m_score
// and Score m_bc_score. They hold the number of pieces of each color and
// the sum of the board control values for each color during the search
// (this is faster than counting at every leaf node).
//
// The classes SquareStackEntry and SquareStack implement a
// stack that is used by Engine to store pieces that are turned during
// searching (see ComputeMove()).
//
// The class MoveAndValue is used by Engine to store all possible moves
// at the first level and the values that were calculated for them.
// This makes it possible to select a random move among those with equal
// or nearly equal value after the search is completed.
#ifndef __ENGINE__H__
#define __ENGINE__H__
#include "SuperEngine.h"
#include "Position.h"
#include "Game.h"
#include "Move.h"
#include "Score.h"
#include <qmemarray.h>
#include <sys/times.h>
#include <qbitarray.h>
// Class ULONG64 is used as a bitmap for the squares.
#if defined(__GNUC__)
#define ULONG64 unsigned long long int
#else
class ULONG64 : public QBitArray {
public:
ULONG64();
ULONG64( unsigned int );
void shl();
};
#endif
// SquareStackEntry and SquareStack are used during search to keep
// track of turned pieces.
class SquareStackEntry
{
public:
SquareStackEntry();
void setXY(int x, int y);
public:
int m_x;
int m_y;
};
class SquareStack
{
public:
SquareStack();
SquareStack(int size);
void resize(int size);
void init(int size);
SquareStackEntry Pop();
void Push(int x, int y);
private:
QMemArray<SquareStackEntry> m_squarestack;
int m_top;
};
// Connect a move with its value.
class MoveAndValue
{
public:
MoveAndValue();
MoveAndValue(int x, int y, int value);
void setXYV(int x, int y, int value);
public:
int m_x;
int m_y;
int m_value;
};
// The real beef of this program: the engine that finds good moves for
// the computer player.
//
class Engine : public SuperEngine {
public:
Engine(int st, int sd);
Engine(int st);
Engine();
Move computeMove(Game *game, bool competitive);
private:
Move ComputeFirstMove(Game *game);
int ComputeMove2(int xplay, int yplay, Color color, int level,
int cutoffval,
ULONG64 colorbits, ULONG64 opponentbits);
int TryAllMoves(Color opponent, int level, int cutoffval,
ULONG64 opponentbits, ULONG64 colorbits);
int EvaluatePosition(Color color);
void SetupBcBoard();
void SetupBits();
int CalcBcScore(Color color);
ULONG64 ComputeOccupiedBits(Color color);
void yield();
private:
static const int LARGEINT;
static const int ILLEGAL_VALUE;
static const int BC_WEIGHT;
Color m_board[10][10];
int m_bc_board[9][9];
Score m_score;
Score m_bc_score;
SquareStack m_squarestack;
int m_depth;
int m_coeff;
int m_nodes_searched;
bool m_exhaustive;
bool m_competitive;
ULONG64 m_coord_bit[9][9];
ULONG64 m_neighbor_bits[9][9];
};
#endif