/// <summary>
/// Returns whether the given move puts the opponent in check.
/// </summary>
/// <param name="move">The move to test for check.</param>
/// <returns>Whether the given move puts the opponent in check.</returns>
public Boolean CausesCheck(Int32 move)
{
UInt64 fromBitboard = 1UL << Move.From(move);
UInt64 toBitboard = 1UL << Move.To(move);
Int32 piece = Move.Piece(move);
Int32 special = Move.Special(move);
UInt64 occupiedBitboardCopy = OccupiedBitboard;
Boolean value = false;
switch (special & Piece.Mask)
{
// Consider normal move.
case Piece.Empty:
Bitboard[piece] ^= fromBitboard | toBitboard;
OccupiedBitboard ^= fromBitboard;
OccupiedBitboard |= toBitboard;
value = InCheck(1 - SideToMove);
Bitboard[piece] ^= fromBitboard | toBitboard;
OccupiedBitboard = occupiedBitboardCopy;
break;
// Consider castling.
case Piece.King:
UInt64 rookToBitboard = 1UL << ((toBitboard < fromBitboard ? 3 : 5) + Rank(Move.To(move)) * 8);
Bitboard[SideToMove | Piece.Rook] ^= rookToBitboard;
OccupiedBitboard ^= fromBitboard;
value = InCheck(1 - SideToMove);
Bitboard[SideToMove | Piece.Rook] ^= rookToBitboard;
OccupiedBitboard = occupiedBitboardCopy;
break;
// Consider en passant.
case Piece.Pawn:
UInt64 enPassantPawnBitboard = Move.Pawn(EnPassantSquare, 1 - SideToMove);
Bitboard[piece] ^= fromBitboard | toBitboard;
OccupiedBitboard ^= fromBitboard | toBitboard | enPassantPawnBitboard;
value = InCheck(1 - SideToMove);
Bitboard[piece] ^= fromBitboard | toBitboard;
OccupiedBitboard = occupiedBitboardCopy;
break;
// Consider pawn promotion.
default:
Bitboard[SideToMove | Piece.Pawn] ^= fromBitboard;
Bitboard[special] ^= toBitboard;
OccupiedBitboard ^= fromBitboard;
OccupiedBitboard |= toBitboard;
value = InCheck(1 - SideToMove);
Bitboard[SideToMove | Piece.Pawn] ^= fromBitboard;
Bitboard[special] ^= toBitboard;
OccupiedBitboard = occupiedBitboardCopy;
break;
}
return(value);
}
/// <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);
}
