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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.
+
+
+#include <qapplication.h>
+
+#include "Engine.h"
+
+
+// ================================================================
+// Class ULONG64
+
+
+#if !defined(__GNUC__)
+
+
+ULONG64::ULONG64() : QBitArray(64)
+{
+ fill(0);
+}
+
+
+// Initialize an ULONG64 from a 32 bit value.
+//
+
+ULONG64::ULONG64( unsigned int value ) : QBitArray(64)
+{
+ fill(0);
+ for(int i = 0; i < 32; i++) {
+ setBit(i, (bool)(value & 1));
+ value >>= 1;
+ }
+}
+
+
+// Shift an ULONG64 left one bit.
+//
+
+void ULONG64::shl()
+{
+ for(int i = 63; i > 0; i--)
+ setBit(i, testBit(i - 1));
+ setBit(0, 0);
+}
+
+#endif
+
+
+// ================================================================
+// Classes SquareStackEntry and SquareStack
+
+
+// A SquareStack is used to store changes to the squares on the board
+// during search.
+
+
+inline void SquareStackEntry::setXY(int x, int y) {
+ m_x = x;
+ m_y = y;
+}
+
+
+SquareStackEntry::SquareStackEntry()
+{
+ setXY(0,0);
+}
+
+
+// ----------------------------------------------------------------
+
+
+SquareStack::SquareStack() {
+ init(0);
+}
+
+
+SquareStack::SquareStack(int size) {
+ init(size);
+}
+
+
+void SquareStack::resize(int size)
+{
+ m_squarestack.resize(size);
+}
+
+
+// (Re)initialize the stack so that is empty, and at the same time
+// resize it to 'size'.
+//
+
+void SquareStack::init(int size)
+{
+ resize(size);
+
+ m_top = 0;
+ for (int i = 0; i < size; i++)
+ m_squarestack[i].setXY(0,0);
+}
+
+
+
+inline SquareStackEntry SquareStack::Pop()
+{
+ return m_squarestack[--m_top];
+}
+
+
+inline void SquareStack::Push(int x, int y)
+{
+ m_squarestack[m_top].m_x = x;
+ m_squarestack[m_top++].m_y = y;
+}
+
+
+// ================================================================
+// Class MoveAndValue
+
+
+// Class MoveAndValue aggregates a move with its value.
+//
+
+
+inline void MoveAndValue::setXYV(int x, int y, int value)
+{
+ m_x = x;
+ m_y = y;
+ m_value = value;
+}
+
+
+MoveAndValue::MoveAndValue()
+{
+ setXYV(0,0,0);
+}
+
+
+MoveAndValue::MoveAndValue(int x, int y, int value)
+{
+ setXYV(x, y, value);
+}
+
+
+// ================================================================
+// The Engine itself
+
+
+// Some special values used in the search.
+const int Engine::LARGEINT = 99999;
+const int Engine::ILLEGAL_VALUE = 8888888;
+const int Engine::BC_WEIGHT = 3;
+
+
+Engine::Engine(int st, int sd) : SuperEngine(st, sd)
+{
+ SetupBcBoard();
+ SetupBits();
+}
+
+
+Engine::Engine(int st) : SuperEngine(st)
+{
+ SetupBcBoard();
+ SetupBits();
+}
+
+
+Engine::Engine() : SuperEngine(1)
+{
+ SetupBcBoard();
+ SetupBits();
+}
+
+
+// keep GUI alive
+void Engine::yield()
+{
+ qApp->processEvents();
+}
+
+
+// Calculate the best move from the current position, and return it.
+
+Move Engine::computeMove(Game *game, bool competitive)
+{
+ Color color;
+
+ // A competitive game is one where we try our damnedest to make the
+ // best move. The opposite is a casual game where the engine might
+ // make "a mistake". The idea behind this is not to scare away
+ // newbies. The member m_competitive is used during search for this
+ // very move.
+ m_competitive = competitive;
+
+ // Suppose that we should give a heuristic evaluation. If we are
+ // close to the end of the game we can make an exhaustive search,
+ // but that case is determined further down.
+ m_exhaustive = false;
+
+ // Get the color to calculate the move for.
+ color = game->toMove();
+ if (color == Nobody)
+ return Move(Nobody, -1, -1);
+
+ // Figure out the current score
+ m_score.set(White, game->score(White));
+ m_score.set(Black, game->score(Black));
+
+ // Treat the first move as a special case (we can basically just
+ // pick a move at random).
+ if (m_score.score(White) + m_score.score(Black) == 4)
+ return ComputeFirstMove(game);
+
+ // Let there be room for 3000 changes during the recursive search.
+ // This is more than will ever be needed.
+ m_squarestack.init(3000);
+
+ // Get the search depth. If we are close to the end of the game,
+ // the number of possible moves goes down, so we can search deeper
+ // without using more time.
+ m_depth = m_strength;
+ if (m_score.score(White) + m_score.score(Black) + m_depth + 3 >= 64)
+ m_depth = 64 - m_score.score(White) - m_score.score(Black);
+ else if (m_score.score(White) + m_score.score(Black) + m_depth + 4 >= 64)
+ m_depth += 2;
+ else if (m_score.score(White) + m_score.score(Black) + m_depth + 5 >= 64)
+ m_depth++;
+
+ // If we are very close to the end, we can even make the search
+ // exhaustive.
+ if (m_score.score(White) + m_score.score(Black) + m_depth >= 64)
+ m_exhaustive = true;
+
+ // The evaluation is a linear combination of the score (number of
+ // pieces) and the sum of the scores for the squares (given by
+ // m_bc_score). The earlier in the game, the more we use the square
+ // values and the later in the game the more we use the number of
+ // pieces.
+ m_coeff = 100 - (100*
+ (m_score.score(White) + m_score.score(Black)
+ + m_depth - 4)) / 60;
+
+ // Initialize the board that we use for the search.
+ for (uint x = 0; x < 10; x++)
+ for (uint y = 0; y < 10; y++) {
+ if (1 <= x && x <= 8
+ && 1 <= y && y <= 8)
+ m_board[x][y] = game->color(x, y);
+ else
+ m_board[x][y] = Nobody;
+ }
+
+ // Initialize a lot of stuff that we will use in the search.
+
+ // Initialize m_bc_score to the current bc score. This is kept
+ // up-to-date incrementally so that way we won't have to calculate
+ // it from scratch for each evaluation.
+ m_bc_score.set(White, CalcBcScore(White));
+ m_bc_score.set(Black, CalcBcScore(Black));
+
+ ULONG64 colorbits = ComputeOccupiedBits(color);
+ ULONG64 opponentbits = ComputeOccupiedBits(opponent(color));
+
+ int maxval = -LARGEINT;
+ int max_x = 0;
+ int max_y = 0;
+
+ MoveAndValue moves[60];
+ int number_of_moves = 0;
+ int number_of_maxval = 0;
+
+ setInterrupt(false);
+
+ ULONG64 null_bits;
+ null_bits = 0;
+
+ // The main search loop. Step through all possible moves and keep
+ // track of the most valuable one. This move is stored in
+ // (max_x, max_y) and the value is stored in maxval.
+ m_nodes_searched = 0;
+ for (int x = 1; x < 9; x++) {
+ for (int y = 1; y < 9; y++) {
+ // Don't bother with non-empty squares and squares that aren't
+ // neighbors to opponent pieces.
+ if (m_board[x][y] != Nobody
+ || (m_neighbor_bits[x][y] & opponentbits) == null_bits)
+ continue;
+
+
+ int val = ComputeMove2(x, y, color, 1, maxval,
+ colorbits, opponentbits);
+
+ if (val != ILLEGAL_VALUE) {
+ moves[number_of_moves++].setXYV(x, y, val);
+
+ // If the move is better than all previous moves, then record
+ // this fact...
+ if (val > maxval) {
+
+ // ...except that we want to make the computer miss some
+ // good moves so that beginners can play against the program
+ // and not always lose. However, we only do this if the
+ // user wants a casual game, which is set in the settings
+ // dialog.
+ int randi = m_random.getLong(7);
+ if (maxval == -LARGEINT
+ || m_competitive
+ || randi < (int) m_strength) {
+ maxval = val;
+ max_x = x;
+ max_y = y;
+
+ number_of_maxval = 1;
+ }
+ }
+ else if (val == maxval)
+ number_of_maxval++;
+ }
+
+ // Jump out prematurely if interrupt is set.
+ if (interrupted())
+ break;
+ }
+ }
+
+ // long endtime = times(&tmsdummy);
+
+ // If there are more than one best move, the pick one randomly.
+ if (number_of_maxval > 1) {
+ int r = m_random.getLong(number_of_maxval) + 1;
+ int i;
+
+ for (i = 0; i < number_of_moves; i++) {
+ if (moves[i].m_value == maxval && --r <= 0)
+ break;
+ }
+
+ max_x = moves[i].m_x;
+ max_y = moves[i].m_y;
+ }
+
+ // Return a suitable move.
+ if (interrupted())
+ return Move(Nobody, -1, -1);
+ else if (maxval != -LARGEINT)
+ return Move(color, max_x, max_y);
+ else
+ return Move(Nobody, -1, -1);
+}
+
+
+// Get the first move. We can pick any move at random.
+//
+
+Move Engine::ComputeFirstMove(Game *game)
+{
+ int r;
+ Color color = game->toMove();
+
+ r = m_random.getLong(4) + 1;
+
+ if (color == White) {
+ if (r == 1) return Move(color, 3, 5);
+ else if (r == 2) return Move(color, 4, 6);
+ else if (r == 3) return Move(color, 5, 3);
+ else return Move(color, 6, 4);
+ }
+ else {
+ if (r == 1) return Move(color, 3, 4);
+ else if (r == 2) return Move(color, 5, 6);
+ else if (r == 3) return Move(color, 4, 3);
+ else return Move(color, 6, 5);
+ }
+}
+
+
+// Play a move at (xplay, yplay) and generate a value for it. If we
+// are at the maximum search depth, we get the value by calling
+// EvaluatePosition(), otherwise we get it by performing an alphabeta
+// search.
+//
+
+int Engine::ComputeMove2(int xplay, int yplay, Color color, int level,
+ int cutoffval, ULONG64 colorbits,
+ ULONG64 opponentbits)
+{
+ int number_of_turned = 0;
+ SquareStackEntry mse;
+ Color opponent = ::opponent(color);
+
+ m_nodes_searched++;
+
+ // Put the piece on the board and incrementally update scores and bitmaps.
+ m_board[xplay][yplay] = color;
+ colorbits |= m_coord_bit[xplay][yplay];
+ m_score.inc(color);
+ m_bc_score.add(color, m_bc_board[xplay][yplay]);
+
+ // Loop through all 8 directions and turn the pieces that can be turned.
+ for (int xinc = -1; xinc <= 1; xinc++)
+ for (int yinc = -1; yinc <= 1; yinc++) {
+ if (xinc == 0 && yinc == 0)
+ continue;
+
+ int x, y;
+
+ for (x = xplay + xinc, y = yplay + yinc; m_board[x][y] == opponent;
+ x += xinc, y += yinc)
+ ;
+
+ // If we found the end of a turnable row, then go back and turn
+ // all pieces on the way back. Also push the squares with
+ // turned pieces on the squarestack so that we can undo the move
+ // later.
+ if (m_board[x][y] == color)
+ for (x -= xinc, y -= yinc; x != xplay || y != yplay;
+ x -= xinc, y -= yinc) {
+ m_board[x][y] = color;
+ colorbits |= m_coord_bit[x][y];
+ opponentbits &= ~m_coord_bit[x][y];
+
+ m_squarestack.Push(x, y);
+
+ m_bc_score.add(color, m_bc_board[x][y]);
+ m_bc_score.sub(opponent, m_bc_board[x][y]);
+ number_of_turned++;
+ }
+ }
+
+ int retval = -LARGEINT;
+
+ // If we managed to turn at least one piece, then (xplay, yplay) was
+ // a legal move. Now find out the value of the move.
+ if (number_of_turned > 0) {
+
+ // First adjust the number of pieces for each side.
+ m_score.add(color, number_of_turned);
+ m_score.sub(opponent, number_of_turned);
+
+ // If we are at the bottom of the search, get the evaluation.
+ if (level >= m_depth)
+ retval = EvaluatePosition(color); // Terminal node
+ else {
+ int maxval = TryAllMoves(opponent, level, cutoffval, opponentbits,
+ colorbits);
+
+ if (maxval != -LARGEINT)
+ retval = -maxval;
+ else {
+
+ // No possible move for the opponent, it is colors turn again:
+ retval = TryAllMoves(color, level, -LARGEINT, colorbits, opponentbits);
+
+ if (retval == -LARGEINT) {
+
+ // No possible move for anybody => end of game:
+ int finalscore = m_score.score(color) - m_score.score(opponent);
+
+ if (m_exhaustive)
+ retval = finalscore;
+ else {
+ // Take a sure win and avoid a sure loss (may not be optimal):
+
+ if (finalscore > 0)
+ retval = LARGEINT - 65 + finalscore;
+ else if (finalscore < 0)
+ retval = -(LARGEINT - 65 + finalscore);
+ else
+ retval = 0;
+ }
+ }
+ }
+ }
+
+ m_score.add(opponent, number_of_turned);
+ m_score.sub(color, number_of_turned);
+ }
+
+ // Undo the move. Start by unturning the turned pieces.
+ for (int i = number_of_turned; i > 0; i--) {
+ mse = m_squarestack.Pop();
+ m_bc_score.add(opponent, m_bc_board[mse.m_x][mse.m_y]);
+ m_bc_score.sub(color, m_bc_board[mse.m_x][mse.m_y]);
+ m_board[mse.m_x][mse.m_y] = opponent;
+ }
+
+ // Now remove the new piece that we put down.
+ m_board[xplay][yplay] = Nobody;
+ m_score.sub(color, 1);
+ m_bc_score.sub(color, m_bc_board[xplay][yplay]);
+
+ // Return a suitable value.
+ if (number_of_turned < 1 || interrupted())
+ return ILLEGAL_VALUE;
+ else
+ return retval;
+}
+
+
+// Generate all legal moves from the current position, and do a search
+// to see the value of them. This function returns the value of the
+// most valuable move, but not the move itself.
+//
+
+int Engine::TryAllMoves(Color opponent, int level, int cutoffval,
+ ULONG64 opponentbits, ULONG64 colorbits)
+{
+ int maxval = -LARGEINT;
+
+ // Keep GUI alive by calling the event loop.
+ yield();
+
+ ULONG64 null_bits;
+ null_bits = 0;
+
+ for (int x = 1; x < 9; x++) {
+ for (int y = 1; y < 9; y++) {
+ if (m_board[x][y] == Nobody
+ && (m_neighbor_bits[x][y] & colorbits) != null_bits) {
+ int val = ComputeMove2(x, y, opponent, level+1, maxval, opponentbits,
+ colorbits);
+
+ if (val != ILLEGAL_VALUE && val > maxval) {
+ maxval = val;
+ if (maxval > -cutoffval || interrupted())
+ break;
+ }
+ }
+ }
+
+ if (maxval > -cutoffval || interrupted())
+ break;
+ }
+
+ if (interrupted())
+ return -LARGEINT;
+
+ return maxval;
+}
+
+
+// Calculate a heuristic value for the current position. If we are at
+// the end of the game, do this by counting the pieces. Otherwise do
+// it by combining the score using the number of pieces, and the score
+// using the board control values.
+//
+
+int Engine::EvaluatePosition(Color color)
+{
+ int retval;
+
+ Color opponent = ::opponent(color);
+
+ int score_color = m_score.score(color);
+ int score_opponent = m_score.score(opponent);
+
+ if (m_exhaustive)
+ retval = score_color - score_opponent;
+ else {
+ retval = (100-m_coeff) *
+ (m_score.score(color) - m_score.score(opponent))
+ + m_coeff * BC_WEIGHT * (m_bc_score.score(color)
+ - m_bc_score.score(opponent));
+ }
+
+ return retval;
+}
+
+
+// Calculate bitmaps for each square, and also for neighbors of each
+// square.
+//
+
+void Engine::SetupBits()
+{
+ //m_coord_bit = new long[9][9];
+ //m_neighbor_bits = new long[9][9];
+
+ ULONG64 bits = 1;
+
+ // Store a 64 bit unsigned it with the corresponding bit set for
+ // each square.
+ for (int i=1; i < 9; i++)
+ for (int j=1; j < 9; j++) {
+ m_coord_bit[i][j] = bits;
+#if !defined(__GNUC__)
+ bits.shl();
+#else
+ bits *= 2;
+#endif
+ }
+
+ // Store a bitmap consisting of all neighbors for each square.
+ for (int i=1; i < 9; i++)
+ for (int j=1; j < 9; j++) {
+ m_neighbor_bits[i][j] = 0;
+
+ for (int xinc=-1; xinc<=1; xinc++)
+ for (int yinc=-1; yinc<=1; yinc++) {
+ if (xinc != 0 || yinc != 0)
+ if (i + xinc > 0 && i + xinc < 9 && j + yinc > 0 && j + yinc < 9)
+ m_neighbor_bits[i][j] |= m_coord_bit[i + xinc][j + yinc];
+ }
+ }
+}
+
+
+// Set up the board control values that will be used in evaluation of
+// the position.
+//
+
+void Engine::SetupBcBoard()
+{
+ // JAVA m_bc_board = new int[9][9];
+
+ for (int i=1; i < 9; i++)
+ for (int j=1; j < 9; j++) {
+ if (i == 2 || i == 7)
+ m_bc_board[i][j] = -1;
+ else
+ m_bc_board[i][j] = 0;
+
+ if (j == 2 || j == 7)
+ m_bc_board[i][j] -= 1;
+ }
+
+ m_bc_board[1][1] = 2;
+ m_bc_board[8][1] = 2;
+ m_bc_board[1][8] = 2;
+ m_bc_board[8][8] = 2;
+
+ m_bc_board[1][2] = -1;
+ m_bc_board[2][1] = -1;
+ m_bc_board[1][7] = -1;
+ m_bc_board[7][1] = -1;
+ m_bc_board[8][2] = -1;
+ m_bc_board[2][8] = -1;
+ m_bc_board[8][7] = -1;
+ m_bc_board[7][8] = -1;
+}
+
+
+// Calculate the board control score.
+//
+
+int Engine::CalcBcScore(Color color)
+{
+ int sum = 0;
+
+ for (int i=1; i < 9; i++)
+ for (int j=1; j < 9; j++)
+ if (m_board[i][j] == color)
+ sum += m_bc_board[i][j];
+
+ return sum;
+}
+
+
+// Calculate a bitmap of the occupied squares for a certain color.
+//
+
+ULONG64 Engine::ComputeOccupiedBits(Color color)
+{
+ ULONG64 retval = 0;
+
+ for (int i=1; i < 9; i++)
+ for (int j=1; j < 9; j++)
+ if (m_board[i][j] == color) retval |= m_coord_bit[i][j];
+
+ return retval;
+}
+
generated by cgit v1.2.1 (git 2.18.0) at 2024-11-10 14:10:13 +0000