private readonly unsafe PooledList <Move> LoadCaptures()
{
var opposingSide = _activeSide.Flip();
Bitboard occupied = _bbs.Occupies[0] | _bbs.Occupies[1];
var result = PooledList <Move> .Get(16);
// Loop over all pieces that can be captured, from most to least valuable
for (var victimKind = PieceKind.Queen; victimKind >= PieceKind.Pawn; victimKind--)
{
var victim = new Piece(opposingSide, victimKind);
for (Bitboard ds = _bbs.PiecePlacement[victim.ToIndex()]; !ds.IsZero; ds = ds.ClearNext())
{
var destination = ds.NextLocation();
Debug.Assert(_board[destination].HasPiece && _board[destination].Piece == victim);
// Loop over all pieces that can capture at `destination`, from least to most valuable
Bitboard activeAttacks = _bbs.Attacks[(int)_activeSide];
if (activeAttacks[destination])
{
for (var aggKind = PieceKind.Pawn; aggKind <= PieceKind.King; aggKind++)
{
var agg = new Piece(_activeSide, aggKind);
for (Bitboard ss = _bbs.PiecePlacement[agg.ToIndex()]; !ss.IsZero; ss = ss.ClearNext())
{
var source = ss.NextLocation();
Debug.Assert(_board[source].HasPiece && _board[source].Piece == agg);
var sourceAttacks = GetAttackBitboard(_board[source].Piece, source, occupied);
if (sourceAttacks[destination])
{
bool isPromotion = (aggKind == PieceKind.Pawn && source.Rank == SeventhRank(_activeSide));
if (isPromotion)
{
result.Add(new Move(source, destination, promotionKind: PieceKind.Queen));
result.Add(new Move(source, destination, promotionKind: PieceKind.Knight));
result.Add(new Move(source, destination, promotionKind: PieceKind.Rook));
result.Add(new Move(source, destination, promotionKind: PieceKind.Bishop));
}
else
{
result.Add(new Move(source, destination));
}
}
}
}
}
// En passant captures need to be handled specially
if (_enPassantTarget is Location epTarget)
{
bool canBeCapturedEp = (destination == epTarget.Up(ForwardStep(opposingSide)));
if (canBeCapturedEp)
{
Debug.Assert(victimKind == PieceKind.Pawn);
Bitboard pawnPlacement = _bbs.PiecePlacement[new Piece(_activeSide, PieceKind.Pawn).ToIndex()];
if (destination.File > File.FileA && pawnPlacement[destination.Left(1)])
{
result.Add(new Move(destination.Left(1), epTarget));
}
if (destination.File < File.FileH && pawnPlacement[destination.Right(1)])
{
result.Add(new Move(destination.Right(1), epTarget));
}
}
}
}
}
return(result);
}
