/// Entry::shelter_storm() calculates shelter and storm penalties for the file
/// the king is on, as well as the two adjacent files.
public Value shelter_storm(Position pos, Square ksq, Color Us)
{
Color Them = (Us == ColorS.WHITE ? ColorS.BLACK : ColorS.WHITE);
Value safety = Pawns.MaxSafetyBonus;
Bitboard b = pos.pieces_piecetype(PieceTypeS.PAWN) & (BitBoard.in_front_bb(Us, Types.rank_of(ksq)) | BitBoard.rank_bb_square(ksq));
Bitboard ourPawns = b & pos.pieces_color(Us);
Bitboard theirPawns = b & pos.pieces_color(Them);
Rank rkUs, rkThem;
File kf = Math.Max(FileS.FILE_B, Math.Min(FileS.FILE_G, Types.file_of(ksq)));
for (File f = kf - 1; f <= kf + 1; ++f)
{
b = ourPawns & BitBoard.file_bb_file(f);
rkUs = b != 0 ? Types.relative_rank_square(Us, BitBoard.backmost_sq(Us, b)) : RankS.RANK_1;
b = theirPawns & BitBoard.file_bb_file(f);
rkThem = b != 0 ? Types.relative_rank_square(Us, BitBoard.frontmost_sq(Them, b)) : RankS.RANK_1;
if ((MiddleEdges & BitBoard.SquareBB[Types.make_square(f, rkThem)]) != 0 &&
Types.file_of(ksq) == f &&
Types.relative_rank_square(Us, ksq) == rkThem - 1)
{
safety += 200;
}
else
{
safety -= ShelterWeakness[rkUs]
+ StormDanger[rkUs == RankS.RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
}
}
return(safety);
}
/// K and two or more pawns vs K. There is just a single rule here: If all pawns
/// are on the same rook file and are blocked by the defending king, it's a draw.
public ScaleFactor KPsK(Position pos)
{
Debug.Assert(pos.non_pawn_material(strongSide) == ValueS.VALUE_ZERO);
Debug.Assert(pos.count(strongSide, PieceTypeS.PAWN) >= 2);
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 0));
Square ksq = pos.king_square(weakSide);
Bitboard pawns = pos.pieces_color_piecetype(strongSide, PieceTypeS.PAWN);
Square psq = pos.list(strongSide, PieceTypeS.PAWN)[0];
// If all pawns are ahead of the king, on a single rook file and
// the king is within one file of the pawns, it's a draw.
if (0 == (pawns & ~BitBoard.in_front_bb(weakSide, Types.rank_of(ksq))) &&
!((pawns & ~BitBoard.FileABB) != 0 && (pawns & ~BitBoard.FileHBB) != 0) &&
BitBoard.file_distance(ksq, psq) <= 1)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}