/// <summary>
/// Executes the parsing.
/// </summary>
public static void Run()
{
Restrictions.Output = OutputType.UCI;
Engine engine = new Engine();
Position position = Position.Create(Position.StartingFEN);
String command;
while ((command = Console.ReadLine()) != null)
{
List <String> terms = new List <String>(command.Split(' '));
switch (terms[0])
{
default:
Terminal.WriteLine("Unknown command: {0}", terms[0]);
Terminal.WriteLine("Enter \"help\" for assistance.");
break;
case "uci":
Terminal.WriteLine("id name " + engine.Name);
Terminal.WriteLine("id author Zong Zheng Li");
Terminal.WriteLine("option name Hash type spin default " + Engine.DefaultHashAllocation + " min 1 max 2047");
Terminal.WriteLine("uciok");
break;
case "ucinewgame":
engine.Reset();
break;
case "setoption":
if (terms.Contains("Hash"))
{
engine.HashAllocation = Int32.Parse(terms[terms.IndexOf("value") + 1]);
}
break;
case "position":
String fen = Position.StartingFEN;
if (terms[1] != "startpos")
{
fen = command.Substring(command.IndexOf("fen") + 4);
}
position = Position.Create(fen);
Int32 movesIndex = terms.IndexOf("moves");
if (movesIndex >= 0)
{
for (Int32 i = movesIndex + 1; i < terms.Count; i++)
{
position.Make(Move.Create(position, terms[i]));
}
}
break;
case "go":
Restrictions.Reset();
for (Int32 i = 1; i < terms.Count; i++)
{
switch (terms[i])
{
default:
case "infinite":
break;
case "depth":
Restrictions.Depth = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = false;
break;
case "movetime":
Restrictions.MoveTime = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = false;
break;
case "wtime":
Restrictions.TimeControl[Colour.White] = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = true;
break;
case "btime":
Restrictions.TimeControl[Colour.Black] = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = true;
break;
case "winc":
Restrictions.TimeIncrement[Colour.White] = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = true;
break;
case "binc":
Restrictions.TimeIncrement[Colour.Black] = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = true;
break;
case "nodes":
Restrictions.Nodes = Int32.Parse(terms[i + 1]);
Restrictions.UseTimeControls = false;
break;
case "ponder":
// TODO: implement command.
break;
case "mate":
// TODO: implement command.
break;
case "movestogo":
// TODO: implement command.
break;
}
}
new Thread(new ThreadStart(() => {
Int32 bestMove = engine.GetMove(position);
Terminal.WriteLine("bestmove " + Stringify.Move(bestMove));
}))
{
IsBackground = true
}.Start();
break;
case "stop":
engine.Stop();
break;
case "isready":
Terminal.WriteLine("readyok");
break;
case "quit":
return;
case "perft":
Perft.Iterate(position, Int32.Parse(terms[1]));
break;
case "divide":
Perft.Divide(position, Int32.Parse(terms[1]));
break;
case "draw":
Terminal.WriteLine(position);
break;
case "fen":
Terminal.WriteLine(position.GetFEN());
break;
case "ponderhit":
// TODO: implement command.
break;
case "register":
// TODO: implement command.
break;
case "help":
Terminal.WriteLine("Command Function");
Terminal.WriteLine("-----------------------------------------------------------------------");
Terminal.WriteLine("position [fen] Sets the current position to the position denoted");
Terminal.WriteLine(" by the given FEN. \"startpos\" is accepted for the");
Terminal.WriteLine(" starting position");
Terminal.WriteLine("go [type] [number] Searches the current position. Search types include");
Terminal.WriteLine(" \"movetime\", \"depth\", \"nodes\", \"wtime\", \"btime\",");
Terminal.WriteLine(" \"winc\", and \"binc\"");
Terminal.WriteLine("perft [number] Runs perft() on the current position to the given");
Terminal.WriteLine(" depth");
Terminal.WriteLine("divide [number] Runs divide() on the current position for the given");
Terminal.WriteLine(" depth");
Terminal.WriteLine("fen Prints the FEN of the current position.");
Terminal.WriteLine("draw Draws the current position");
Terminal.WriteLine("stop Stops an ongoing search");
Terminal.WriteLine("quit Exits the application");
Terminal.WriteLine("-----------------------------------------------------------------------");
break;
}
}
}
/// <summary>
/// Returns the dynamic value of the position as determined by a recursive
/// search that terminates upon reaching a quiescent position.
/// </summary>
/// <param name="position">The position to search on.</param>
/// <param name="ply">The number of plies from the root position.</param>
/// <param name="alpha">The lower bound on the value of the best move.</param>
/// <param name="beta">The upper bound on the value of the best move.</param>
/// <returns>The value of the termination position given optimal play.</returns>
private Int32 Quiescence(Position position, Int32 ply, Int32 alpha, Int32 beta)
{
_totalNodes++;
_quiescenceNodes++;
// Evaluate the position statically. Check for upper bound cutoff and lower
// bound improvement.
Int32 value = Evaluate(position);
if (value >= beta)
{
return(value);
}
if (value > alpha)
{
alpha = value;
}
// Initialize variables and generate the pseudo-legal moves to be
// considered. Perform basic move ordering and sort the moves.
Int32 colour = position.SideToMove;
Int32[] moves = _generatedMoves[ply];
Int32 movesCount = position.PseudoQuiescenceMoves(moves);
for (Int32 i = 0; i < movesCount; i++)
{
_moveValues[i] = MoveOrderingValue(moves[i]);
}
Sort(moves, _moveValues, movesCount);
// Go through the move list.
for (Int32 i = 0; i < movesCount; i++)
{
_movesSearched++;
Int32 move = moves[i];
// Consider the move only if it doesn't immediately lose material. This
// improves efficiency.
if ((Move.Piece(move) & Piece.Mask) <= (Move.Capture(move) & Piece.Mask) || EvaluateStaticExchange(position, move) >= 0)
{
// Make the move.
position.Make(move);
// Search the move if it is legal. This is equivalent to not leaving the
// king in check.
if (!position.InCheck(colour))
{
value = -Quiescence(position, ply + 1, -beta, -alpha);
// Check for upper bound cutoff and lower bound improvement.
if (value >= beta)
{
position.Unmake(move);
return(value);
}
if (value > alpha)
{
alpha = value;
}
}
// Unmake the move.
position.Unmake(move);
}
}
return(alpha);
}
/// <summary>
/// Returns whether the given move is a dangerous pawn advance. A dangerous
/// pawn advance is a pawn move that results in the pawn being in a position
/// in which no enemy pawns can threaten or block it.
/// </summary>
/// <param name="move">The move to consider.</param>
/// <param name="passedPawnPreventionBitboard">A bitboard giving the long term attack possibilities of the enemy pawns.</param>
/// <returns>Whether the given move is a dangerous pawn advance.</returns>
private Boolean IsDangerousPawnAdvance(Int32 move, UInt64 passedPawnPreventionBitboard)
{
return(Move.IsPawnAdvance(move) && ((1UL << Move.To(move)) & passedPawnPreventionBitboard) == 0);
}
/// <summary>
/// Returns the dynamic value of the position as determined by a recursive
/// search to the given depth. This implements the main search algorithm.
/// </summary>
/// <param name="position">The position to search on.</param>
/// <param name="depth">The depth to search to.</param>
/// <param name="ply">The number of plies from the root position.</param>
/// <param name="alpha">The lower bound on the value of the best move.</param>
/// <param name="beta">The upper bound on the value of the best move.</param>
/// <param name="inCheck">Whether the side to play is in check.</param>
/// <param name="allowNull">Whether a null move is permitted.</param>
/// <returns>The value of the termination position given optimal play.</returns>
private Int32 Search(Position position, Int32 depth, Int32 ply, Int32 alpha, Int32 beta, Boolean inCheck, Boolean allowNull = true)
{
// Check whether to enter quiescence search and initialize pv length.
_pvLength[ply] = 0;
if (depth <= 0 && !inCheck)
{
return(Quiescence(position, ply, alpha, beta));
}
// Check for time extension and search termination. This is done once for
// every given number of nodes for efficency.
if (++_totalNodes > _referenceNodes)
{
_referenceNodes += NodeResolution;
// Apply loss time extension. The value of the best move for the current
// root position is compared with the value of the previous root position.
// If there is a large loss, a time extension is given.
Int32 loss = _finalAlpha - _rootAlpha;
if (loss >= TimeControlsLossResolution)
{
Int32 index = Math.Min(loss / TimeControlsLossResolution, TimeControlsLossExtension.Length - 1);
TryTimeExtension(TimeControlsLossThreshold, TimeControlsLossExtension[index]);
}
if (_stopwatch.ElapsedMilliseconds >= _timeLimit + _timeExtension || _totalNodes >= Restrictions.Nodes)
{
_abortSearch = true;
}
}
if (_abortSearch)
{
return(Infinity);
}
// Perform draw detection.
Int32 drawValue = ((ply & 1) == 0) ? DrawValue : -DrawValue;
Int32 drawRepetitions = (ply > 2) ? 2 : 3;
if (position.FiftyMovesClock >= 100 || position.InsufficientMaterial() || position.HasRepeated(drawRepetitions))
{
return(drawValue);
}
// Perform mate distance pruning.
Int32 mateAlpha = Math.Max(alpha, -(CheckmateValue - ply));
Int32 mateBeta = Math.Min(beta, CheckmateValue - (ply + 1));
if (mateAlpha >= mateBeta)
{
return(mateAlpha);
}
// Perform hash probe.
_hashProbes++;
Int32 hashMove = Move.Invalid;
HashEntry hashEntry;
if (_table.TryProbe(position.ZobristKey, out hashEntry))
{
hashMove = hashEntry.Move;
if (hashEntry.Depth >= depth)
{
Int32 hashType = hashEntry.Type;
Int32 hashValue = hashEntry.GetValue(ply);
if ((hashType == HashEntry.Beta && hashValue >= beta) || (hashType == HashEntry.Alpha && hashValue <= alpha))
{
_hashCutoffs++;
return(hashValue);
}
}
}
Int32 colour = position.SideToMove;
// Apply null move heuristic.
if (allowNull && !inCheck && position.Bitboard[colour] != (position.Bitboard[colour | Piece.King] | position.Bitboard[colour | Piece.Pawn]))
{
position.MakeNull();
Int32 reduction = NullMoveReduction + (depth >= NullMoveAggressiveDepth ? depth / NullMoveAggressiveDivisor : 0);
Int32 value = -Search(position, depth - 1 - reduction, ply + 1, -beta, -beta + 1, false, false);
position.UnmakeNull();
if (value >= beta)
{
return(value);
}
}
// Generate legal moves and perform basic move ordering.
Int32[] moves = _generatedMoves[ply];
Int32 movesCount = position.LegalMoves(moves);
if (movesCount == 0)
{
return(inCheck ? -(CheckmateValue - ply) : drawValue);
}
for (Int32 i = 0; i < movesCount; i++)
{
_moveValues[i] = MoveOrderingValue(moves[i]);
}
// Apply single reply and check extensions.
if (movesCount == 1 || inCheck)
{
depth++;
}
// Perform killer move ordering.
_killerMoveChecks++;
bool killerMoveFound = false;
for (Int32 slot = 0; slot < KillerMovesAllocation; slot++)
{
Int32 killerMove = _killerMoves[ply][slot];
for (Int32 i = 0; i < movesCount; i++)
{
if (moves[i] == killerMove)
{
_moveValues[i] = KillerMoveValue + slot * KillerMoveSlotValue;
if (!killerMoveFound)
{
_killerMoveMatches++;
}
killerMoveFound = true;
break;
}
}
}
// Perform hash move ordering.
_hashMoveChecks++;
if (hashMove != Move.Invalid)
{
for (Int32 i = 0; i < movesCount; i++)
{
if (moves[i] == hashMove)
{
_moveValues[i] = HashMoveValue;
_hashMoveMatches++;
break;
}
}
}
// Check for futility pruning activation.
Boolean futileNode = false;
Int32 futilityValue = 0;
if (depth < FutilityMargin.Length && !inCheck)
{
futilityValue = Evaluate(position) + FutilityMargin[depth];
futileNode = futilityValue <= alpha;
}
// Sort the moves based on their ordering values and initialize variables.
Sort(moves, _moveValues, movesCount);
Int32 irreducibleMoves = 1;
while (irreducibleMoves < movesCount && _moveValues[irreducibleMoves] > 0)
{
irreducibleMoves++;
}
UInt64 preventionBitboard = PassedPawnPreventionBitboard(position);
Int32 bestType = HashEntry.Alpha;
Int32 bestMove = moves[0];
// Go through the move list.
for (Int32 i = 0; i < movesCount; i++)
{
_movesSearched++;
Int32 move = moves[i];
Boolean causesCheck = position.CausesCheck(move);
Boolean dangerous = inCheck || causesCheck || alpha < -NearCheckmateValue || IsDangerousPawnAdvance(move, preventionBitboard);
Boolean reducible = i + 1 > irreducibleMoves;
// Perform futility pruning.
if (futileNode && !dangerous && futilityValue + PieceValue[Move.Capture(move)] <= alpha)
{
_futileMoves++;
continue;
}
// Make the move and initialize its value.
position.Make(move);
Int32 value = alpha + 1;
// Perform late move reductions.
if (reducible && !dangerous)
{
value = -Search(position, depth - 1 - LateMoveReduction, ply + 1, -alpha - 1, -alpha, causesCheck);
}
// Perform principal variation search.
else if (i > 0)
{
value = -Search(position, depth - 1, ply + 1, -alpha - 1, -alpha, causesCheck);
}
// Perform a full search.
if (value > alpha)
{
value = -Search(position, depth - 1, ply + 1, -beta, -alpha, causesCheck);
}
// Unmake the move and check for search termination.
position.Unmake(move);
if (_abortSearch)
{
return(Infinity);
}
// Check for upper bound cutoff.
if (value >= beta)
{
_table.Store(new HashEntry(position, depth, ply, move, value, HashEntry.Beta));
if (reducible)
{
for (Int32 j = _killerMoves[ply].Length - 2; j >= 0; j--)
{
_killerMoves[ply][j + 1] = _killerMoves[ply][j];
}
_killerMoves[ply][0] = move;
}
return(value);
}
// Check for lower bound improvement.
if (value > alpha)
{
alpha = value;
bestMove = move;
bestType = HashEntry.Exact;
// Collect the principal variation.
_pvMoves[ply][0] = move;
for (Int32 j = 0; j < _pvLength[ply + 1]; j++)
{
_pvMoves[ply][j + 1] = _pvMoves[ply + 1][j];
}
_pvLength[ply] = _pvLength[ply + 1] + 1;
}
}
// Store the results in the hash table and return the lower bound of the
// value of the position.
_table.Store(new HashEntry(position, depth, ply, bestMove, alpha, bestType));
return(alpha);
}