/// <summary>
/// Returns whether the given side is attacked on the given square.
/// </summary>
/// <param name="colour">The side to test for being attacked.</param>
/// <param name="square">The square to test for attacks.</param>
/// <returns>Whether the given side is attacked on the given square</returns>
public Boolean IsAttacked(Int32 colour, Int32 square)
{
Int32 enemy = 1 - colour;
if ((Bitboard[enemy | Piece.Knight] & Attack.Knight(square)) != 0 ||
(Bitboard[enemy | Piece.Pawn] & Attack.Pawn(square, colour)) != 0 ||
(Bitboard[enemy | Piece.King] & Attack.King(square)) != 0)
{
return(true);
}
UInt64 bishopQueenBitboard = Bitboard[enemy | Piece.Bishop] | Bitboard[enemy | Piece.Queen];
if ((bishopQueenBitboard & Bit.Diagonals[square]) != 0 &&
(bishopQueenBitboard & Attack.Bishop(square, OccupiedBitboard)) != 0)
{
return(true);
}
UInt64 rookQueenBitboard = Bitboard[enemy | Piece.Rook] | Bitboard[enemy | Piece.Queen];
if ((rookQueenBitboard & Bit.Axes[square]) != 0 &&
(rookQueenBitboard & Attack.Rook(square, OccupiedBitboard)) != 0)
{
return(true);
}
return(false);
}
/// <summary>
/// Populates the given array with the pseudo-legal capturing and queen
/// promotion moves for the position and returns the number of moves.
/// </summary>
/// <param name="moves">The array to populate with the pseudo-legal moves.</param>
/// <returns>The number of moves generated for the position.</returns>
public Int32 PseudoQuiescenceMoves(Int32[] moves)
{
UInt64 targetBitboard = Bitboard[(1 - SideToMove)];
Int32 index = 0;
// Consider king moves.
UInt64 pieceBitboard = Bitboard[SideToMove | Piece.King];
Int32 from = Bit.Read(pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.King(from);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
// Consider queen moves.
pieceBitboard = Bitboard[SideToMove | Piece.Queen];
while (pieceBitboard != 0)
{
from = Bit.Pop(ref pieceBitboard);
moveBitboard = targetBitboard & Attack.Queen(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider rook moves.
pieceBitboard = Bitboard[SideToMove | Piece.Rook];
while (pieceBitboard != 0)
{
from = Bit.Pop(ref pieceBitboard);
moveBitboard = targetBitboard & Attack.Rook(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider knight moves.
pieceBitboard = Bitboard[SideToMove | Piece.Knight];
while (pieceBitboard != 0)
{
from = Bit.Pop(ref pieceBitboard);
moveBitboard = targetBitboard & Attack.Knight(from);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider bishop moves.
pieceBitboard = Bitboard[SideToMove | Piece.Bishop];
while (pieceBitboard != 0)
{
from = Bit.Pop(ref pieceBitboard);
moveBitboard = targetBitboard & Attack.Bishop(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider pawn moves.
pieceBitboard = Bitboard[SideToMove | Piece.Pawn];
while (pieceBitboard != 0)
{
from = Bit.Pop(ref pieceBitboard);
moveBitboard = targetBitboard & Attack.Pawn(from, SideToMove);
Int32 to = from + 16 * SideToMove - 8;
Boolean promotion = (to - 8) * (to - 55) > 0;
if (promotion)
{
moveBitboard |= ~OccupiedBitboard & (1UL << to);
}
while (moveBitboard != 0)
{
to = Bit.Pop(ref moveBitboard);
if (promotion)
{
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Queen);
}
else
{
moves[index++] = Move.Create(this, from, to);
}
}
}
return(index);
}
/// <summary>
/// Populates the given array with the legal moves for the position and
/// returns the number of legal moves.
/// </summary>
/// <param name="moves">The array to populate with the legal moves.</param>
/// <returns>The number of legal moves for the position.</returns>
public Int32 LegalMoves(Int32[] moves)
{
// Initialize bitboards and squares that describe the position.
Int32 enemy = 1 - SideToMove;
Int32 kingSquare = Bit.Read(Bitboard[SideToMove | Piece.King]);
UInt64 selfBitboard = Bitboard[SideToMove];
UInt64 enemyBitboard = Bitboard[enemy];
UInt64 targetBitboard = ~selfBitboard;
UInt64 enemyBishopQueenBitboard = Bitboard[enemy | Piece.Bishop] | Bitboard[enemy | Piece.Queen];
UInt64 enemyRookQueenBitboard = Bitboard[enemy | Piece.Rook] | Bitboard[enemy | Piece.Queen];
// Initialize variables for move generation.
UInt64 checkingBitboard = 0;
UInt64 pinningBitboard = 0;
Int32 index = 0;
// Consider knight and pawn checks.
checkingBitboard |= Bitboard[enemy | Piece.Knight] & Attack.Knight(kingSquare);
checkingBitboard |= Bitboard[enemy | Piece.Pawn] & Attack.Pawn(kingSquare, SideToMove);
// Consider bishop and queen checks and pins.
if ((enemyBishopQueenBitboard & Bit.Diagonals[kingSquare]) != 0)
{
checkingBitboard |= enemyBishopQueenBitboard & Attack.Bishop(kingSquare, OccupiedBitboard);
// Determine pinning pieces by removing the first line of defence around the
// the king, then seeing which pieces are able to attack.
UInt64 defenceRemovedBitboard = OccupiedBitboard;
UInt64 defenceBitboard = Bit.RayNE[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.IsolateReverse(defenceBitboard);
}
defenceBitboard = Bit.RayNW[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.IsolateReverse(defenceBitboard);
}
defenceBitboard = Bit.RaySE[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.Isolate(defenceBitboard);
}
defenceBitboard = Bit.RaySW[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.Isolate(defenceBitboard);
}
if (defenceRemovedBitboard != OccupiedBitboard)
{
pinningBitboard |= enemyBishopQueenBitboard & Attack.Bishop(kingSquare, defenceRemovedBitboard);
}
}
// Consider rook and queen checks and pins.
if ((enemyRookQueenBitboard & Bit.Axes[kingSquare]) != 0)
{
checkingBitboard |= enemyRookQueenBitboard & Attack.Rook(kingSquare, OccupiedBitboard);
// Determine pinning pieces by removing the first line of defence around the
// the king, then seeing which pieces are able to attack.
UInt64 defenceRemovedBitboard = OccupiedBitboard;
UInt64 defenceBitboard = Bit.RayN[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.IsolateReverse(defenceBitboard);
}
defenceBitboard = Bit.RayE[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.Isolate(defenceBitboard);
}
defenceBitboard = Bit.RayS[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.Isolate(defenceBitboard);
}
defenceBitboard = Bit.RayW[kingSquare] & selfBitboard;
if (defenceBitboard != 0)
{
defenceRemovedBitboard ^= Bit.IsolateReverse(defenceBitboard);
}
if (defenceRemovedBitboard != OccupiedBitboard)
{
pinningBitboard |= enemyRookQueenBitboard & Attack.Rook(kingSquare, defenceRemovedBitboard);
}
}
// Consider castling. This is always fully tested for legality.
if (checkingBitboard == 0)
{
Int32 rank = -56 * SideToMove + 56;
if (CastleQueenside[SideToMove] > 0 && (Square[1 + rank] | Square[2 + rank] | Square[3 + rank]) == Piece.Empty)
{
if (!IsAttacked(SideToMove, 3 + rank) && !IsAttacked(SideToMove, 2 + rank))
{
moves[index++] = Move.Create(this, kingSquare, 2 + rank, SideToMove | Piece.King);
}
}
if (CastleKingside[SideToMove] > 0 && (Square[5 + rank] | Square[6 + rank]) == Piece.Empty)
{
if (!IsAttacked(SideToMove, 5 + rank) && !IsAttacked(SideToMove, 6 + rank))
{
moves[index++] = Move.Create(this, kingSquare, 6 + rank, SideToMove | Piece.King);
}
}
}
// Consider en passant. This is always fully tested for legality.
if (EnPassantSquare != InvalidSquare)
{
UInt64 enPassantPawnBitboard = Bitboard[SideToMove | Piece.Pawn] & Attack.Pawn(EnPassantSquare, enemy);
UInt64 enPassantVictimBitboard = Move.Pawn(EnPassantSquare, enemy);
while (enPassantPawnBitboard != 0)
{
// Perform minimal state changes to mimick en passant and check for
// legality.
Int32 from = Bit.Pop(ref enPassantPawnBitboard);
Bitboard[enemy | Piece.Pawn] ^= enPassantVictimBitboard;
OccupiedBitboard ^= enPassantVictimBitboard;
OccupiedBitboard ^= (1UL << from) | (1UL << EnPassantSquare);
// Check for legality and add move.
if (!IsAttacked(SideToMove, kingSquare))
{
moves[index++] = Move.Create(this, from, EnPassantSquare, enemy | Piece.Pawn);
}
// Revert state changes.
Bitboard[enemy | Piece.Pawn] ^= enPassantVictimBitboard;
OccupiedBitboard ^= enPassantVictimBitboard;
OccupiedBitboard ^= (1UL << from) | (1UL << EnPassantSquare);
}
}
// Consider king moves. This is always fully tested for legality.
{
Int32 from = kingSquare;
UInt64 moveBitboard = targetBitboard & Attack.King(from);
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
Int32 to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add move.
if (!IsAttacked(SideToMove, to))
{
moves[index++] = Move.Create(this, from, to);
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
// Case 1. If we are not in check and there are no pinned pieces, we don't
// need to test normal moves for legality.
if (checkingBitboard == 0 & pinningBitboard == 0)
{
// Consider normal pawn moves.
UInt64 pieceBitboard = Bitboard[SideToMove | Piece.Pawn];
while (pieceBitboard != 0)
{
// Consider single square advance.
Int32 from = Bit.Pop(ref pieceBitboard);
Int32 to = from + 16 * SideToMove - 8;
UInt64 moveBitboard = ~OccupiedBitboard & (1UL << to);
// Consider two square advance.
if (moveBitboard != 0 && (from - 16) * (from - 47) > 0 && (to - 8) * (to - 55) < 0)
{
moveBitboard |= ~OccupiedBitboard & (1UL << (from + 32 * SideToMove - 16));
}
// Consider captures.
UInt64 attackBitboard = Attack.Pawn(from, SideToMove);
moveBitboard |= enemyBitboard & attackBitboard;
// Populate pawn moves.
while (moveBitboard != 0)
{
to = Bit.Pop(ref moveBitboard);
if ((to - 8) * (to - 55) > 0)
{
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Queen);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Knight);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Rook);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Bishop);
}
else
{
moves[index++] = Move.Create(this, from, to);
}
}
}
// Consider knight moves.
pieceBitboard = Bitboard[SideToMove | Piece.Knight];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Knight(from);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider bishop moves.
pieceBitboard = Bitboard[SideToMove | Piece.Bishop];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Bishop(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider queen moves.
pieceBitboard = Bitboard[SideToMove | Piece.Queen];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Queen(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
// Consider rook moves.
pieceBitboard = Bitboard[SideToMove | Piece.Rook];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Rook(from, OccupiedBitboard);
while (moveBitboard != 0)
{
Int32 to = Bit.Pop(ref moveBitboard);
moves[index++] = Move.Create(this, from, to);
}
}
}
// Case 2. There are pinned pieces or a single check. We can still move but
// all moves are tested for legality.
else if ((checkingBitboard & (checkingBitboard - 1)) == 0)
{
// Consider pawn moves.
UInt64 pieceBitboard = Bitboard[SideToMove | Piece.Pawn];
while (pieceBitboard != 0)
{
// Consider single square advance.
Int32 from = Bit.Pop(ref pieceBitboard);
Int32 to = from + 16 * SideToMove - 8;
UInt64 moveBitboard = ~OccupiedBitboard & (1UL << to);
// Consider two square advance.
if (moveBitboard != 0 && (from - 16) * (from - 47) > 0 && (to - 8) * (to - 55) < 0)
{
moveBitboard |= ~OccupiedBitboard & (1UL << (from + 32 * SideToMove - 16));
}
// Consider captures.
UInt64 attackBitboard = Attack.Pawn(from, SideToMove);
moveBitboard |= enemyBitboard & attackBitboard;
// Populate pawn moves.
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add moves.
if (!IsAttacked(SideToMove, kingSquare))
{
if ((to - 8) * (to - 55) > 0)
{
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Queen);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Knight);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Rook);
moves[index++] = Move.Create(this, from, to, SideToMove | Piece.Bishop);
}
else
{
moves[index++] = Move.Create(this, from, to);
}
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
// Consider knight moves.
pieceBitboard = Bitboard[SideToMove | Piece.Knight];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Knight(from);
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
Int32 to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add move.
if (!IsAttacked(SideToMove, kingSquare))
{
moves[index++] = Move.Create(this, from, to);
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
// Consider bishop moves.
pieceBitboard = Bitboard[SideToMove | Piece.Bishop];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Bishop(from, OccupiedBitboard);
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
Int32 to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add move.
if (!IsAttacked(SideToMove, kingSquare))
{
moves[index++] = Move.Create(this, from, to);
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
// Consider queen moves.
pieceBitboard = Bitboard[SideToMove | Piece.Queen];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Queen(from, OccupiedBitboard);
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
Int32 to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add move.
if (!IsAttacked(SideToMove, kingSquare))
{
moves[index++] = Move.Create(this, from, to);
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
// Consider rook moves.
pieceBitboard = Bitboard[SideToMove | Piece.Rook];
while (pieceBitboard != 0)
{
Int32 from = Bit.Pop(ref pieceBitboard);
UInt64 moveBitboard = targetBitboard & Attack.Rook(from, OccupiedBitboard);
while (moveBitboard != 0)
{
// Perform minimal state changes to mimick real move and check for legality.
Int32 to = Bit.Pop(ref moveBitboard);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Int32 capture = Square[to];
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard ^= 1UL << from;
OccupiedBitboard |= 1UL << to;
// Check for legality and add move.
if (!IsAttacked(SideToMove, kingSquare))
{
moves[index++] = Move.Create(this, from, to);
}
// Revert state changes.
Bitboard[capture] ^= 1UL << to;
OccupiedBitboard = occupiedBitboardCopy;
}
}
}
return(index);
}
/// <summary>
/// Returns the square of the piece with the lowest material value that can
/// move to the given square.
/// </summary>
/// <param name="position">The position to find the square for.</param>
/// <param name="colour">The side to find the square for.</param>
/// <param name="square">The square to move to.</param>
/// <returns>The square of the piece with the lowest material value that can move to the given square.</returns>
private static Int32 SmallestAttackerSquare(Position position, Int32 colour, Int32 square)
{
// Try pawns.
UInt64 sourceBitboard = position.Bitboard[colour | Piece.Pawn] & Attack.Pawn(square, 1 - colour);
if (sourceBitboard != 0)
{
return(Bit.Scan(sourceBitboard));
}
// Try knights.
sourceBitboard = position.Bitboard[colour | Piece.Knight] & Attack.Knight(square);
if (sourceBitboard != 0)
{
return(Bit.Scan(sourceBitboard));
}
// Try bishops.
UInt64 bishopAttackBitboard = UInt64.MaxValue;
if ((position.Bitboard[colour | Piece.Bishop] & Bit.Diagonals[square]) != 0)
{
bishopAttackBitboard = Attack.Bishop(square, position.OccupiedBitboard);
sourceBitboard = position.Bitboard[colour | Piece.Bishop] & bishopAttackBitboard;
if (sourceBitboard != 0)
{
return(Bit.Scan(sourceBitboard));
}
}
// Try rooks.
UInt64 rookAttackBitboard = UInt64.MaxValue;
if ((position.Bitboard[colour | Piece.Rook] & Bit.Axes[square]) != 0)
{
rookAttackBitboard = Attack.Rook(square, position.OccupiedBitboard);
sourceBitboard = position.Bitboard[colour | Piece.Rook] & rookAttackBitboard;
if (sourceBitboard != 0)
{
return(Bit.Scan(sourceBitboard));
}
}
// Try queens.
if ((position.Bitboard[colour | Piece.Queen] & (Bit.Diagonals[square] | Bit.Axes[square])) != 0)
{
if (bishopAttackBitboard == UInt64.MaxValue)
{
bishopAttackBitboard = Attack.Bishop(square, position.OccupiedBitboard);
}
if (rookAttackBitboard == UInt64.MaxValue)
{
rookAttackBitboard = Attack.Rook(square, position.OccupiedBitboard);
}
sourceBitboard = position.Bitboard[colour | Piece.Queen] & (bishopAttackBitboard | rookAttackBitboard);
if (sourceBitboard != 0)
{
return(Bit.Scan(sourceBitboard));
}
}
// Try king.
sourceBitboard = position.Bitboard[colour | Piece.King] & Attack.King(square);
if (sourceBitboard != 0)
{
return(Bit.Read(sourceBitboard));
}
return(Position.InvalidSquare);
}