int Minimax::Quiescence(Board *board, GameInfo *gameInfo, int depth, int alpha, int beta) {
// Evaluate the node in its current state. If it causes a beta-cutoff, assume that there will be no move further down the
//game tree that will result in a better evaluation. Otherwise, set it as the lower bound, alpha.
int nodeEvaluation = Eval(board, gameInfo);
if (nodeEvaluation >= beta) return beta;
if (nodeEvaluation > alpha) alpha = nodeEvaluation;
MoveList moveList;
// If the node is in check, consider every move. Otherwise, just consider captures/promotions.
moveList.generate(gameInfo->turn, board, gameInfo, !MoveList::InCheck(gameInfo->turn, board));
moveList.prune((Piece::Color)!gameInfo->turn, board);
for (MoveList::iterator moveItr = moveList.begin(); moveItr != moveList.end(); moveItr++) {
Move move = *moveItr;
board->executeMove(move);
// Save any irreversible game info before making a move.
GameInfo::Irreversible irreversible(gameInfo);
gameInfo->executeMove(move);
int childEval = 0;
// If we are at depth 0, just get the score of the board (The score is negated as it is measured relative to the opposite color).
if (depth == 0) childEval = -Eval(board, gameInfo);
else childEval = -Quiescence(board, gameInfo, depth - 1, -beta, -alpha);
board->reverseMove(move);
gameInfo->reverseMove(irreversible);
if (childEval >= beta) return beta;
if (childEval > alpha) alpha = childEval;
}
return alpha;
}
int Minimax::AlphaBeta(Board *board, GameInfo *gameInfo, Move &move, int depth, const int quiescenceDepth, int alpha, int beta) {
// If we are at the end of the normal alpha beta search, perform a quiescence search with the given quiescence depth.
if (depth == 0) return Quiescence(board, gameInfo, quiescenceDepth, alpha, beta);
MoveList moveList;
// Generate move list and check game state.
GameInfo::State state = gameInfo->updateState(board, moveList);
switch (state) {
case GameInfo::STALEMATE:
case GameInfo::FIFTY_MOVE_RULE:
// Returns a score which will always be disregarded.
return LARGEST_NUM + 1;
case GameInfo::CHECKMATE:
// Return arbitrarily large negative score (But not -LARGEST_NUM, as it would be cut off).
return -LARGE_NUM;
}
MoveList::iterator bestMoveItr = moveList.begin();
for (MoveList::iterator moveItr = moveList.begin(); moveItr != moveList.end(); moveItr++) {
Move childMove = *moveItr;
board->executeMove(childMove);
// Save any irreversible game info before making a move.
GameInfo::Irreversible irreversible(gameInfo);
gameInfo->executeMove(childMove);
// Here, the child's evaluation is taken to be the negation of its return value, so that seperate if statements for maximising and minimising
//aren't required.
int childEval = -AlphaBeta(board, gameInfo, move, depth - 1, quiescenceDepth, -beta, -alpha);
board->reverseMove(childMove);
gameInfo->reverseMove(irreversible);
// If the child evaluates to a score greater than or equal to beta, there is a beta cutoff. This means that there is no further point exploring this
// node's moves, as it is known that this node will at least be as bad if not worse than another node elsewhere in the game tree.
if (childEval >= beta) {
// If a non-capture move caused a beta-cutoff, increase its history weighting. The depth squared is added to the heuristic so that moves near
//the leaf nodes don't dominate the heuristic (Leaf node score would be 0 * 0).
if (!move.isCapture()) Move::HistoryHeuristic[move.subject_from][move.subject_to] += depth * depth;
move = *bestMoveItr;
return beta;
}
// If the child's evaluation is greater than alpha, this is the best move at the moment.
if (childEval > alpha) {
alpha = childEval;
bestMoveItr = moveItr;
}
}
move = *bestMoveItr;
return alpha;
}
// Algorithme de recherche MinMax avec des coupes Alpha-Beta.
// Ici on considere seulement les prises.
int Quiescence(int ply, int wtm, int alpha, int beta )
{
register int Valeur, AlphaInitiale;
if ( ply >= MAXPLY-1 )
return beta;
iNodes++;
if ( wtm ) {
Valeur = Eval(ply, wtm, alpha, beta);
}
else {
Valeur = -Eval(ply, wtm, alpha, beta);
}
// Remplace si le score est egal au score pour la NULLE.
if ( Valeur == DRAWSCORE )
Valeur = DRAWSCORE+1;
AlphaInitiale = alpha;
if ( Valeur > alpha ) {
if ( Valeur >= beta ) return Valeur;
alpha = Valeur;
pv_length[ply] = ply-1;
}
// On genere toutes les prises.
cb.MoveList[ply].nbmove = 0;
GenMoveAttaque(ply, wtm, cb.MoveList[ply]);
int keep = -1;
// Le materiel.
int iScoreMateriel = cb.ScoreMaterielBlanc-cb.ScoreMaterielNoir;
iScoreMateriel = wtm?iScoreMateriel:-iScoreMateriel;
int delta = alpha-100-iScoreMateriel;
int iScoreGain;
for( int i=0; i<cb.MoveList[ply].nbmove; i++ ) {
// Garder le coup.
bool bGarde = false;
// On cherche seulement les coups qui ramene le materiel proche de alpha.
// ex. Si celui qui jouent vient de se faire prendre une dame et que alpha
// dit que le meilleur score est la perte d'un pion et bien ignorer tout
// les captures qui ramene pas au moins la dame.
if ( ValeurPiece[cb.MoveList[ply].moves[i].Capture] >= delta ) {
if (cb.MoveList[ply].moves[i].Capture == ROI) return beta;
#ifdef USE_SEE
int iScoreCapture = ValeurPiece[cb.MoveList[ply].moves[i].Capture];
iScoreGain = iScoreCapture-ValeurPiece[cb.MoveList[ply].moves[i].Piece];
if ( iScoreGain > 0 ||
iScoreGain >= 0 &&
delta <= 0 ) {
bGarde = true;
}
else {
iScoreGain = Echange(cb.MoveList[ply].moves[i].From, cb.MoveList[ply].moves[i].To, wtm );
if ( iScoreGain >= 0 ) {
bGarde = true;
}
}
#else
bGarde = true;
#endif
}
if ( bGarde ) {
keep++;
cb.MoveList[ply].moves[i].Score = iScoreGain;
memcpy( &cb.MoveList[ply].moves[keep],
&cb.MoveList[ply].moves[i],
sizeof( TMove ) );
}
}
cb.MoveList[ply].nbmove = keep+1;
cb.MoveList[ply].currmove = -1;
cb.MoveList[ply].Tri();
Phase[ply] = CAPTURE_MOVES;
// Maintenant, evaluer chaque coup.
while( NextMove( cb, ply, wtm ) ) {
// On execute le coup.
MakeMove(ply, cb.MoveList[ply].CurrentMove(), wtm);
// Mettre le coup dans le chemin actuel.
cb.CurrentPath.moves[ply] = cb.MoveList[ply].moves[cb.MoveList[ply].currmove];
if (!Check(wtm))
Valeur = -Quiescence(ply+1, !wtm, -beta, -alpha);
cb.MoveList[ply].CurrentMove().Score = Valeur;
// On defait le coup.
UnmakeMove(ply, cb.MoveList[ply].CurrentMove(), wtm);
// Est-il meileur que notre valeur actuelle?
if ( Valeur > alpha ) {
if ( Valeur >= beta ) return Valeur;
pv_length[ply] = pv_length[ply+1];
pv[ply][ply] = cb.CurrentPath.moves[ply];
memcpy(&pv[ply][ply+1], &pv[ply+1][ply], sizeof(TMove)*(pv_length[ply]-ply));
alpha = Valeur;
}
#ifdef DEBUG
Consistence( cb, cb.MoveList[ply].CurrentMove() );
#endif
}
return alpha;
}
