private int QuiesceneSearch(int alpha, int beta)
{
searchInfo.Nodes++;
searchInfo.QNodes++;
int currentEval = Evaluation.Evaluate(board);
if (currentEval >= beta)
{
searchInfo.BetaCutoffs++;
return(beta);
}
if (currentEval > alpha)
{
alpha = currentEval;
}
generator.Setup();
var moves = generator.GetMoves(true);
foreach (var move in moves.OrderByDescending(m => MoveImportance(m, -1, null)))
{
board.SubmitMove(move);
var eval = -QuiesceneSearch(-beta, -alpha);
board.UndoMove();
if (eval >= beta)
{
searchInfo.BetaCutoffs++;
return(beta);
}
if (eval > alpha)
{
alpha = eval;
}
}
return(alpha);
}
private int DeepEval(int depth, int alpha, int beta, bool nullMoveAllowed, Move[] pv, IDictionary <Move, int> orderedTopLevelMoves = null)
{
searchInfo.Nodes++;
if (transpositions.ContainsKey(board.positionKey))
{
searchInfo.Transpositions++;
var score = LookupEvaluation(alpha, beta);
if (score != LookupFailed)
{
return(score);
}
}
generator.Setup();
var moves = generator.GetMoves(false);
if (!moves.Any())
{
//When in Check: Checkmate:
if (generator.InCheck)
{
//Compute checkmate score:
var currentDepth = board.states.Count; //TODO add ply variable to board
return(-CHECKMATE + currentDepth);
}
else //Stalemate
{
return(DRAW);
}
}
else if (board.states.Any(s => s.positionKey == board.positionKey))
{
//Repetition
return(DRAW);
}
//TODO Add 50 moves rule
if (depth == 0)
{
return(QuiesceneSearch(alpha, beta));
}
if (depth == 1)
{
//Futility pruning
var currentEval = Evaluation.Evaluate(board);
if (currentEval + Evaluation.BishopValue < alpha)
{
searchInfo.FutilityPrunes++;
//Prune this node, i.e. go directly to QuiesceneSearch
return(QuiesceneSearch(alpha, beta));
}
}
if (nullMoveAllowed && !generator.InCheck && depth >= 1 + R)
{
searchInfo.NullMoves++;
//Null move pruning
var npv = new Move[depth]; //irellevant here
board.SubmitNullMove();
int eval = -DeepEval(depth - 1 - R, -beta, -beta + 1, false, npv);
board.UndoNullMove();
if (eval >= beta)
{
searchInfo.NullMovesSuccess++;
return(eval);
}
}
TranspositionEntryType ttType = TranspositionEntryType.UpperBound;
int movenumber = 1;
bool searchPV = true;
foreach (var move in moves.OrderByDescending(m => MoveImportance(m, depth, orderedTopLevelMoves)))
{
if (depth == searchInfo.Depth) //Upper level
{
Console.WriteLine($"info currmove {move.ToAlgebraicNotation()} currmovenumber {movenumber++} depth {depth}");
}
var npv = new Move[depth - 1];
board.SubmitMove(move);
int eval;
if (searchPV)
{
eval = -DeepEval(depth - 1, -beta, -alpha, true, npv);
}
else
{
searchInfo.Scouts++;
//Scout zw search
eval = -ZWSerach(depth - 1, -alpha);
if (eval > alpha)
{
eval = -DeepEval(depth - 1, -beta, -alpha, true, npv); // re-search
}
else
{
searchInfo.ScoutRemovals++;
}
}
board.UndoMove();
if (depth == searchInfo.Depth)
{
searchInfo.TopLevelMoveOrder.Add(move, eval);
}
if (eval >= beta)
{
searchInfo.BetaCutoffs++;
//transposition is an upper bound
StoreEvaluation(eval, TranspositionEntryType.LowerBound);
if (move.CapturedPiece == Piece.NONE)
{
KillerMoves[board.Ply][2] = KillerMoves[board.Ply][1];
KillerMoves[board.Ply][1] = KillerMoves[board.Ply][0];
KillerMoves[board.Ply][0] = move;
}
return(beta);
}
else if (eval > alpha)
{
alpha = eval;
searchPV = false;
pv[0] = move;
Array.Copy(npv, 0, pv, 1, npv.Length);
ttType = TranspositionEntryType.Exact;
}
}
StoreEvaluation(alpha, ttType);
return(alpha);
}
//ZW search with multicut
private int ZWSerach(int depth, int beta, bool cut = true, bool nullMoveAllowed = true)
{
searchInfo.Nodes++;
generator.Setup();
var moves = generator.GetMoves(false);
if (transpositions.ContainsKey(board.positionKey))
{
searchInfo.Transpositions++;
var score = LookupEvaluation(beta - 1, beta);
if (score != LookupFailed)
{
return(score);
}
}
if (!moves.Any())
{
//When in Check: Checkmate:
if (generator.InCheck)
{
return(beta - 1);
}
else //Stalemate
{
if (0 >= beta)
{
return(beta);
}
else
{
return(beta - 1);
}
}
}
else if (board.states.Any(s => s.positionKey == board.positionKey))
{
//Repetition
if (0 >= beta)
{
return(beta);
}
else
{
return(beta - 1);
}
}
if (depth <= 0)
{
return(QuiesceneSearch(beta - 1, beta));
}
if (depth == 1)
{
//Futility pruning
var currentEval = Evaluation.Evaluate(board);
if (currentEval + Evaluation.BishopValue < beta - 1)
{
searchInfo.FutilityPrunes++;
//Prune this node, i.e. go directly to QuiesceneSearch
return(QuiesceneSearch(beta - 1, beta));
}
}
if (nullMoveAllowed && !generator.InCheck && depth >= 1 + R)
{
searchInfo.NullMoves++;
//Null move pruning
board.SubmitNullMove();
int eval = -ZWSerach(depth - 1 - R, 1 - beta, cut, false);
board.UndoNullMove();
if (eval >= beta)
{
searchInfo.NullMovesSuccess++;
return(beta);
}
}
var orderedMoves = moves.OrderByDescending(m => MoveImportance(m, depth, null)).ToList();
var moveIndex = 0;
if (depth >= MC_R && cut)
{
int c = 0;
for (int m = 0; m < MC_M && moveIndex < orderedMoves.Count; m++)
{
board.SubmitMove(orderedMoves[moveIndex]);
int eval = -ZWSerach(depth - 1 - MC_R, 1 - beta, !cut, true);
board.UndoMove();
moveIndex++;
if (eval >= beta)
{
c++;
if (c == MC_C)
{
searchInfo.MCPrunes++;
return(beta); // mc-prune
}
}
}
}
for (moveIndex = 0; moveIndex < orderedMoves.Count; moveIndex++)
{
board.SubmitMove(orderedMoves[moveIndex]);
int eval = -ZWSerach(depth - 1, 1 - beta, !cut, true);
board.UndoMove();
if (eval >= beta)
{
return(beta);
}
}
return(beta - 1);
}