public static string ToMoveString(Move move, BoardState board, AttackState attackState)
{
// Algo: Move from end, adding tokens in order
// - Check if move is promotion, add tokens if so
// - Add end square
// - Check if move is capture, output 'x' if so
// - Then check if multiple pieces of same type can move to end square, then output first rank or file of moved piece
// - Then output piece notation if piece is not a pawn
//
// - Now that the move string is built, splice to only used tokens
var startSquareBit = BitTranslator.TranslateToBit(move.StartFile, move.StartRank);
var endSquareBit = BitTranslator.TranslateToBit(move.EndFile, move.EndRank);
var movedPiece = board.GetSquareContents(startSquareBit) & ~SquareContents.Colours;
Span <char> buffer = stackalloc char[8];
var lastIdx = buffer.Length - 1;
if (attackState != AttackState.None)
{
// Check if move ended in attack
var notation = GetAttackStateMoveNotation(attackState);
if (notation != 0)
{
buffer[lastIdx--] = notation;
}
}
if (movedPiece == SquareContents.King)
{
// Check for castling
var squareDiff = (decimal)startSquareBit / endSquareBit;
var castleNotation = "";
if (squareDiff == 4) // King has moved 2 squares horizontally towards queenside
{
castleNotation = "0-0-0";
}
else if (squareDiff == 0.25M) // King has moved 2 squares horizontally towards kingside
{
castleNotation = "0-0";
}
if (!string.IsNullOrEmpty(castleNotation))
{
var copyIdx = lastIdx - castleNotation.Length + 1;
var notationBuffer = buffer.Slice(copyIdx, castleNotation.Length);
castleNotation.AsSpan().CopyTo(notationBuffer);
lastIdx -= castleNotation.Length;
var copyLocation = buffer.Slice(lastIdx + 1);
return(copyLocation.ToString());
}
}
if (move.PromotedPiece != SquareContents.Empty)
{
var pieceType = move.PromotedPiece & ~SquareContents.Colours;
buffer[lastIdx--] = PiecesAsLetters[pieceType];
buffer[lastIdx--] = '=';
}
buffer[lastIdx--] = (char)(move.EndRank + '0');
buffer[lastIdx--] = move.EndFile;
var isCapture = (endSquareBit & board.AllPieces) != 0;
if (!isCapture && movedPiece == SquareContents.Pawn)
{
// Capture pattern for pawn is diagonal movement
// Explicitly checking will account for capture by en passant where end square is empty
var diff = Math.Max(startSquareBit, endSquareBit) / Math.Min(startSquareBit, endSquareBit);
isCapture = diff == 1 << 7 || diff == 1 << 9;
}
if (isCapture)
{
buffer[lastIdx--] = 'x';
}
if (movedPiece == SquareContents.Pawn)
{
if (isCapture)
{
buffer[lastIdx--] = move.StartFile;
}
}
else
{
if (movedPiece != SquareContents.King)
{
// Check for disambiguation
var colorMask = (startSquareBit & board.WhitePieces) != 0 ? board.WhitePieces : board.BlackPieces;
var pieceMask = 0UL;
if (movedPiece == SquareContents.Knight)
{
pieceMask = board.Knights;
}
else if (movedPiece == SquareContents.Bishop)
{
pieceMask = board.Bishops;
}
else if (movedPiece == SquareContents.Rook)
{
pieceMask = board.Rooks;
}
else if (movedPiece == SquareContents.Queen)
{
pieceMask = board.Queens;
}
pieceMask = pieceMask & colorMask & ~startSquareBit;
var otherPossibleStartSquares = new List <Square>();
for (var i = 0; i < 64; i++)
{
var mask = pieceMask & (1UL << i);
if (mask != 0)
{
var moves = MoveGenerator.GenerateStatelessMovesForPiece(board, mask);
if ((moves & endSquareBit) != 0)
{
otherPossibleStartSquares.Add(BitTranslator.TranslateToSquare(mask));
}
}
}
// There may be multiple possible start squares to disambiguate from
var disambiguateByRank = false;
var disambiguateByFile = false;
foreach (var otherSquare in otherPossibleStartSquares)
{
disambiguateByRank = disambiguateByRank || (otherSquare.File == move.StartFile);
disambiguateByFile = disambiguateByFile || (otherSquare.Rank == move.StartRank);
}
// Need to disambiguate, but both rank + file are different. Default to by file.
if (!disambiguateByFile && !disambiguateByRank && otherPossibleStartSquares.Count > 0)
{
disambiguateByFile = true;
}
if (disambiguateByRank)
{
buffer[lastIdx--] = (char)(move.StartRank + '0');
}
if (disambiguateByFile)
{
buffer[lastIdx--] = move.StartFile;
}
}
buffer[lastIdx--] = PiecesAsLetters[movedPiece];
}
var segment = buffer.Slice(lastIdx + 1);
return(segment.ToString());
}
private static bool TryInferStartSquare(BoardState state, ulong piecesOnCurrentSide, bool isWhiteMove, bool isCapture, char pieceDesignation, ref ParsedMoveState result)
{
var endBit = BitTranslator.TranslateToBit(result.EndFile, result.EndRank);
var disambiguityMask = BuildDisambiguityMask(result);
switch (pieceDesignation)
{
case Constants.PieceNotation.King:
{
var possibleStartBits = MoveGenerator.GetKingMovements(endBit);
var existingOfPiece = state.Kings & piecesOnCurrentSide;
var actualStartPiece = possibleStartBits & existingOfPiece;
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
case Constants.PieceNotation.Knight:
{
var possibleStartBits = MoveGenerator.GetKnightMovements(endBit);
var existingOfPiece = state.Knights & piecesOnCurrentSide;
var actualStartPiece = possibleStartBits & existingOfPiece;
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
case Constants.PieceNotation.Queen:
{
var possibleStartBits = MoveGenerator.GetQueenMovements(endBit, state);
var existingOfPiece = state.Queens & piecesOnCurrentSide;
var actualStartPiece = possibleStartBits & existingOfPiece;
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
case Constants.PieceNotation.Rook:
{
var possibleStartBits = MoveGenerator.GetRookMovements(endBit, state);
var existingOfPiece = state.Rooks & piecesOnCurrentSide;
var actualStartPiece = possibleStartBits & existingOfPiece;
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
case Constants.PieceNotation.Bishop:
{
var possibleStartBits = MoveGenerator.GetBishopMovements(endBit, state);
var existingOfPiece = state.Bishops & piecesOnCurrentSide;
var actualStartPiece = possibleStartBits & existingOfPiece;
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
case Constants.PieceNotation.Pawn:
{
ulong actualStartPiece;
if (isWhiteMove)
{
var possibleMoves = endBit >> 8 | endBit >> 16;
var possibleAttacks = (endBit >> 7 & (~MoveGenerator.Rank8)) | (endBit >> 9 & (~MoveGenerator.Rank1));
var possibleStart = isCapture ? possibleAttacks : possibleMoves;
var pawns = state.Pawns & state.WhitePieces;
actualStartPiece = pawns & possibleStart;
}
else
{
var possibleMoves = endBit << 8 | endBit << 16;
var possibleAttacks = (endBit << 7 & (~MoveGenerator.Rank1)) | (endBit << 9 & (~MoveGenerator.Rank8));
var possibleStart = isCapture ? possibleAttacks : possibleMoves;
var pawns = state.Pawns & state.BlackPieces;
actualStartPiece = pawns & possibleStart;
}
if (disambiguityMask != 0)
{
actualStartPiece &= disambiguityMask;
}
if (actualStartPiece == 0)
{
return(false);
}
var startSquare = BitTranslator.TranslateToSquare(actualStartPiece);
result.StartFile = startSquare.File;
result.StartRank = startSquare.Rank;
return(true);
}
default:
return(false);
}
}
private static GameState AnalyzeAndApplyState(GameState newState, ulong endSquare, ulong opponentPieces)
{
// All state detections
// ✔ Account for piece promotions
// ✔ Detect checks
// ✔ Detect checkmate
// ✔ Detect stalemate
// ✔ Detect draw by repetition
// ✔ Detect draw by inactivity (50 moves without a capture)
var newBoard = newState.Board;
var didBlackMove = ((endSquare & newBoard.BlackPieces) != 0) ? 1 : 0;
var whiteAttack = MoveGenerator.GenerateSquaresAttackedBy(newState, newBoard.WhitePieces);
var blackAttack = MoveGenerator.GenerateSquaresAttackedBy(newState, newBoard.BlackPieces);
var squaresAttackedBy = new IndexedTuple <ulong>(whiteAttack, blackAttack);
var ownMovements = squaresAttackedBy.Get(didBlackMove);
var opponentMovements = MoveGenerator.GenerateValidMoves(newState, opponentPieces, ownMovements);
var opponentKingUnderAttack = (opponentPieces & newBoard.Kings & ownMovements) != 0;
var opponentCanMove = opponentMovements != 0;
var attackState = AttackState.None;
if (opponentKingUnderAttack)
{
attackState = opponentCanMove ? AttackState.Check : AttackState.Checkmate;
}
else if (!opponentCanMove)
{
attackState = AttackState.Stalemate;
}
else
{
var count = 0;
var duplicateCount = 0;
var newStateUnmovedCastlingPieces = (newState.PiecesOnStartSquares & MoveGenerator.StartingKingsAndRooks);
foreach (var state in newState.PossibleRepeatedHistory)
{
count++;
if (BoardState.Equals(state.Item1, newBoard) && state.Item2 == newStateUnmovedCastlingPieces)
{
duplicateCount++;
}
}
if (count == Constants.MoveLimits.InactivityLimit)
{
attackState = AttackState.DrawByInactivity;
}
else if (duplicateCount >= Constants.MoveLimits.RepetitionLimit)
{
attackState = AttackState.DrawByRepetition;
}
}
return(newState.SetAttackState(attackState, squaresAttackedBy));
}