private static int DoAlphaBetaPruning(int depth, int alpha, int beta)
{
VisitedNodes++;
List <Move> availableMoves = MoveGenerator.GetAvailableMoves(position);
position.PieceActivity = availableMoves.Count;
int gameStateScore = GetGameStateScore(position, availableMoves.Count, depth);
if (gameStateScore != 9999)
{
return(gameStateScore);
}
MoveSorter.SortMoves(position, availableMoves, killerMoves, depth);
for (int moveIndex = 0; moveIndex < availableMoves.Count; moveIndex++)
{
Move currentMove = availableMoves[moveIndex];
position.MakeMove(currentMove);
long zobristKey = ZobristHasher.GetZobristHash(position);
if (!position.GameHistory.ContainsKey(zobristKey))
{
position.GameHistory.Add(zobristKey, 1);
}
else
{
position.GameHistory[zobristKey]++;
}
int score =
(position.TranspositionTable.ContainsKey(zobristKey) &&
position.TranspositionTable[zobristKey].Depth >= depth) ?
position.TranspositionTable[zobristKey].Score :
DoAlphaBetaPruning(depth + 1, alpha, beta);
position.UndoMove(currentMove);
position.GameHistory.Remove(zobristKey);
if (position.SideToMove == maximizingSide)
{
if (score >= beta)
{
TryAddKillerMove(currentMove, depth);
return(beta);
}
if (score > alpha)
{
alpha = score;
if (depth == 0)
{
position.MaximizingSideBestMove = currentMove;
}
UpdatePrincipalVariation(depth, currentMove);
TryAddTableEntry(zobristKey, score, depth, currentMove);
}
}
else
{
if (score <= alpha)
{
return(alpha);
}
if (score <= beta)
{
beta = score;
UpdatePrincipalVariation(depth, currentMove);
}
}
}
return((position.SideToMove == maximizingSide) ? alpha : beta);
}
