/// generate<EVASIONS> generates all pseudo-legal check evasions when the side
/// to move is in check. Returns a pointer to the end of the move list.
public static int generate_evasions(Position pos, ExtMove[] mlist, int mPos)
{
Debug.Assert(pos.checkers() != 0);
Color us = pos.side_to_move();
Square ksq = pos.king_square(us);
Bitboard sliderAttacks = 0;
Bitboard sliders = pos.checkers() & ~pos.pieces_piecetype(PieceTypeS.KNIGHT, PieceTypeS.PAWN);
// Find all the squares attacked by slider checkers. We will remove them from
// the king evasions in order to skip known illegal moves, which avoids any
// useless legality checks later on.
while (sliders != 0)
{
Square checksq = BitBoard.pop_lsb(ref sliders);
sliderAttacks |= BitBoard.LineBB[checksq][ksq] ^ BitBoard.SquareBB[checksq];
}
// Generate evasions for king, capture and non capture moves
Bitboard b = pos.attacks_from_square_piecetype(ksq, PieceTypeS.KING) & ~pos.pieces_color(us) & ~sliderAttacks;
while (b != 0)
{
mlist[mPos++].move = Types.make_move(ksq, BitBoard.pop_lsb(ref b));
}
if (BitBoard.more_than_one(pos.checkers()))
{
return(mPos); // Double check, only a king move can save the day
}
// Generate blocking evasions or captures of the checking piece
Square checksq2 = BitBoard.lsb(pos.checkers());
Bitboard target = BitBoard.between_bb(checksq2, ksq) | BitBoard.SquareBB[checksq2];
return(us == ColorS.WHITE ? generate_all(pos, mlist, mPos, target, ColorS.WHITE, GenTypeS.EVASIONS) :
generate_all(pos, mlist, mPos, target, ColorS.BLACK, GenTypeS.EVASIONS));
}
