private int alphaBeta(int alpha, int beta, int depthleft) {
int ttAplha = alpha;
nodeCount++;
TableEntry tableEntry = transpositionTable.get(pos.key);
if (tableEntry != null) {
if (tableEntry.getDepth() >= depthleft) {
int type = tableEntry.getType();
int eval = tableEntry.getEval();
if (type == TableEntry.EXACT) {
return eval;
} else if (type == TableEntry.LOWER) {
alpha = Math.max(alpha, eval);
} else if (type == TableEntry.UPPER) {
beta = Math.min(beta, eval);
}
if (alpha >= beta) {
return eval;
}
}
}
if (depthleft == 0) {
return Evaluator.evaluate(pos);
}
Move[] moves = new Move[MAX_NUMBER_OF_MOVES];
int numberOfMoves = moveGen.findLegalMoves(pos, moves);
// orderMoves(moves, numberOfMoves);
int best = -10000;
Move bestMove = null;
for (int i = 0; i < numberOfMoves; i++) {
final byte result = moveGen.makeMove(pos, moves[i]);
if (!PerftStat.isLegalPosition(result)) {
moveGen.unMakeMove(pos, moves[i]);
return Integer.MIN_VALUE;
} else if (!PerftStat.isLegalMove(result)) {
moveGen.unMakeMove(pos, moves[i]);
continue;
}
int score = -alphaBeta(-beta, -alpha, depthleft - 1);
moveGen.unMakeMove(pos, moves[i]);
if (score > best) {
best = score;
bestMove = moves[i];
}
if (score > alpha) {
alpha = score;
}
if (alpha >= beta) {
break;
}
}
transpositionTable.store(pos.key, depthleft, best, ttAplha, beta, age, bestMove);
return best;
}