/// 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);
}
/// KB and one or more pawns vs K. It checks for draws with rook pawns and
/// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
/// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
/// will be used.
public ScaleFactor KBPsK(Position pos)
{
Debug.Assert(pos.non_pawn_material(strongSide) == ValueS.BishopValueMg);
Debug.Assert(pos.count(strongSide, PieceTypeS.PAWN) >= 1);
// No assertions about the material of weakSide, because we want draws to
// be detected even when the weaker side has some pawns.
Bitboard pawns = pos.pieces_color_piecetype(strongSide, PieceTypeS.PAWN);
File pawnFile = Types.file_of(pos.list(strongSide, PieceTypeS.PAWN)[0]);
// All pawns are on a single rook file ?
if ((pawnFile == FileS.FILE_A || pawnFile == FileS.FILE_H) &&
0 == (pawns & ~BitBoard.file_bb_file(pawnFile)))
{
Square bishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
Square queeningSq = Types.relative_square(strongSide, Types.make_square(pawnFile, RankS.RANK_8));
Square kingSq = pos.king_square(weakSide);
if (Types.opposite_colors(queeningSq, bishopSq) &&
BitBoard.square_distance(queeningSq, kingSq) <= 1)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
}
// If all the pawns are on the same B or G file, then it's potentially a draw
if ((pawnFile == FileS.FILE_B || pawnFile == FileS.FILE_G) &&
0 == (pos.pieces_piecetype(PieceTypeS.PAWN) & ~BitBoard.file_bb_file(pawnFile)) &&
pos.non_pawn_material(weakSide) == 0 &&
pos.count(weakSide, PieceTypeS.PAWN) >= 1)
{
// Get weakSide pawn that is closest to the home rank
Square weakPawnSq = BitBoard.backmost_sq(weakSide, pos.pieces_color_piecetype(weakSide, PieceTypeS.PAWN));
Square strongKingSq = pos.king_square(strongSide);
Square weakKingSq = pos.king_square(weakSide);
Square bishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
// There's potential for a draw if our pawn is blocked on the 7th rank,
// the bishop cannot attack it or they only have one pawn left
if (Types.relative_rank_square(strongSide, weakPawnSq) == RankS.RANK_7 &&
(pos.pieces_color_piecetype(strongSide, PieceTypeS.PAWN) & BitBoard.SquareBB[(weakPawnSq + Types.pawn_push(weakSide))]) != 0 &&
(Types.opposite_colors(bishopSq, weakPawnSq) || pos.count(strongSide, PieceTypeS.PAWN) == 1))
{
int strongKingDist = BitBoard.square_distance(weakPawnSq, strongKingSq);
int weakKingDist = BitBoard.square_distance(weakPawnSq, weakKingSq);
// It's a draw if the weak king is on its back two ranks, within 2
// squares of the blocking pawn and the strong king is not
// closer. (I think this rule only fails in practically
// unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
// and positions where qsearch will immediately correct the
// problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
if (Types.relative_rank_square(strongSide, weakKingSq) >= RankS.RANK_7 &&
weakKingDist <= 2 &&
weakKingDist <= strongKingDist)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
}
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
