public void UnMake()
{
if (!MoveHistory.Any())
{
throw new Exception("No move to unmake");
}
int MoveToUnmake = MoveHistory.Pop();
int ColorMadeMove = 1 - ColorToMove;
int fromSquare = Move.FromSquare(MoveToUnmake);
int toSquare = Move.ToSquare(MoveToUnmake);
int fromPiece = Move.FromPiece(MoveToUnmake);
int toPiece = Move.ToPiece(MoveToUnmake);
MovesFiftyHistory.Pop();
//Moving Back And Cancelling Capturing
SquarePiece[toSquare] = toPiece;
SquarePiece[fromSquare] = fromPiece;
PieceBitboard[fromPiece] ^= 1UL << fromSquare; //no changes
PieceBitboard[fromPiece] ^= 1UL << toSquare; //no changes
PieceBitboard[fromPiece & Color.Mask] ^= 1UL << fromSquare; //no changes
PieceBitboard[fromPiece & Color.Mask] ^= 1UL << toSquare; //no changes
OccupiedBB ^= 1UL << fromSquare; //no changes
if (toPiece != 0)
{
PieceBitboard[toPiece] ^= 1UL << toSquare;
PieceBitboard[toPiece & Color.Mask] ^= 1UL << toSquare;
int EnemyLeftRookIndex = 56 * ColorMadeMove;
if (toSquare == EnemyLeftRookIndex && toPiece == Piece.Rook && CastleShortIndex[1 - ColorMadeMove] <= 0)
{
CastleShortIndex[1 - ColorMadeMove]++;
}
else if (toSquare == EnemyLeftRookIndex + 7 && toPiece == Piece.Rook && CastleLongIndex[1 - ColorMadeMove] <= 0)
{
CastleShortIndex[1 - ColorMadeMove]++;
}
}
else
{
OccupiedBB ^= 1UL << toSquare;
}
if (CastleShortIndex[ColorMadeMove] <= 0)
{
CastleShortIndex[ColorMadeMove]++;
}
if (CastleLongIndex[ColorMadeMove] <= 0)
{
CastleLongIndex[ColorMadeMove]++;
}
if (CastleShortIndex[1 - ColorMadeMove] <= 0)
{
CastleShortIndex[1 - ColorMadeMove]++;
}
if (CastleLongIndex[1 - ColorMadeMove] <= 0)
{
CastleLongIndex[1 - ColorMadeMove]++;
}
//Castling Back
if (Move.Castling(MoveToUnmake))
{
int sidePreIndex = 56 * ColorMadeMove;
int rookSquare, rookToSquare;
//Short castling (getting rook position)
if (File(toSquare) == 6)
{
rookSquare = sidePreIndex + 7;
rookToSquare = fromSquare + 1;
}
//Long castling (getting rook position)
else
{
rookSquare = sidePreIndex;
rookToSquare = fromSquare - 1;
}
//Moving the rook back
SquarePiece[rookSquare] = SquarePiece[rookToSquare];
SquarePiece[rookToSquare] = 0;
OccupiedBB ^= 1UL << rookSquare;
OccupiedBB ^= 1UL << rookToSquare;
PieceBitboard[Piece.Rook | ColorMadeMove] ^= 1UL << rookSquare;
PieceBitboard[Piece.Rook | ColorMadeMove] ^= 1UL << rookToSquare;
PieceBitboard[ColorMadeMove] ^= 1UL << rookSquare;
PieceBitboard[ColorMadeMove] ^= 1UL << rookToSquare;
}
//Promotion
if (Move.Promotion(MoveToUnmake))
{
int PromotedTo = Move.PromotionPiece(MoveToUnmake); //Either queen, knight, bishop or rook
//SquarePiece[toSquare] = PromotedTo;
//If we are here, we've just set the PieceBitboard[fromPiece] to 1 at the toSquare thinking of doing the opposite, so we need to cancel that
PieceBitboard[fromPiece] ^= 1UL << toSquare;
PieceBitboard[PromotedTo] ^= 1UL << toSquare;
//Color maps do not change, as well as occupied (we're just replacing the piece)
}
//Enpassant
if (Move.EnPassant(MoveToUnmake))
{
//Restoring the pawn
int EnPassantVictimSquare = toSquare + 16 * ColorMadeMove - 8;
UInt64 enPassantVictimBitboard = 1UL << EnPassantVictimSquare;
OccupiedBB ^= enPassantVictimBitboard;
PieceBitboard[Piece.Pawn | ColorToMove] ^= enPassantVictimBitboard;
PieceBitboard[ColorToMove] ^= enPassantVictimBitboard;
SquarePiece[EnPassantVictimSquare] = Piece.Pawn | ColorToMove;
}
ColorToMove = ColorMadeMove;
EnPassantHistory.Pop();
}