/// 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);
}
public static Score evaluate(Position pos, Pawns.Entry e, Color Us)
{
Color Them = (Us == ColorS.WHITE ? ColorS.BLACK : ColorS.WHITE);
Square Up = (Us == ColorS.WHITE ? SquareS.DELTA_N : SquareS.DELTA_S);
Square Right = (Us == ColorS.WHITE ? SquareS.DELTA_NE : SquareS.DELTA_SW);
Square Left = (Us == ColorS.WHITE ? SquareS.DELTA_NW : SquareS.DELTA_SE);
Bitboard b, p, doubled;
Square s;
File f;
Rank r;
bool passed, isolated, opposed, connected, backward, candidate, unsupported;
Score value = ScoreS.SCORE_ZERO;
Square[] pl = pos.list(Us, PieceTypeS.PAWN);
int plPos = 0;
Bitboard ourPawns = pos.pieces_color_piecetype(Us, PieceTypeS.PAWN);
Bitboard theirPawns = pos.pieces_color_piecetype(Them, PieceTypeS.PAWN);
e.passedPawns[Us] = e.candidatePawns[Us] = 0;
e.kingSquares[Us] = SquareS.SQ_NONE;
e.semiopenFiles[Us] = 0xFF;
e.pawnAttacks[Us] = BitBoard.shift_bb(ourPawns, Right) | BitBoard.shift_bb(ourPawns, Left);
e.pawnsOnSquares[Us][ColorS.BLACK] = Bitcount.popcount_Max15(ourPawns & BitBoard.DarkSquares);
e.pawnsOnSquares[Us][ColorS.WHITE] = pos.count(Us, PieceTypeS.PAWN) - e.pawnsOnSquares[Us][ColorS.BLACK];
// Loop through all pawns of the current color and score each pawn
while ((s = pl[plPos++]) != SquareS.SQ_NONE)
{
Debug.Assert(pos.piece_on(s) == Types.make_piece(Us, PieceTypeS.PAWN));
f = Types.file_of(s);
// This file cannot be semi-open
e.semiopenFiles[Us] &= ~(1 << f);
// Previous rank
p = BitBoard.rank_bb_square(s - Types.pawn_push(Us));
// Our rank plus previous one
b = BitBoard.rank_bb_square(s) | p;
// Flag the pawn as passed, isolated, doubled,
// unsupported or connected (but not the backward one).
connected = (ourPawns & BitBoard.adjacent_files_bb(f) & b) != 0;
unsupported = (0 == (ourPawns & BitBoard.adjacent_files_bb(f) & p));
isolated = (0 == (ourPawns & BitBoard.adjacent_files_bb(f)));
doubled = ourPawns & BitBoard.forward_bb(Us, s);
opposed = (theirPawns & BitBoard.forward_bb(Us, s)) != 0;
passed = (0 == (theirPawns & BitBoard.passed_pawn_mask(Us, s)));
// Test for backward pawn.
// If the pawn is passed, isolated, or connected it cannot be
// backward. If there are friendly pawns behind on adjacent files
// or if it can capture an enemy pawn it cannot be backward either.
if ((passed | isolated | connected) ||
(ourPawns & BitBoard.pawn_attack_span(Them, s)) != 0 ||
(pos.attacks_from_pawn(s, Us) & theirPawns) != 0)
{
backward = false;
}
else
{
// We now know that there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
// files, and picking the closest pawn there.
b = BitBoard.pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = BitBoard.pawn_attack_span(Us, s) & BitBoard.rank_bb_square(BitBoard.backmost_sq(Us, b));
// If we have an enemy pawn in the same or next rank, the pawn is
// backward because it cannot advance without being captured.
backward = ((b | BitBoard.shift_bb(b, Up)) & theirPawns) != 0;
}
Debug.Assert(opposed | passed | (BitBoard.pawn_attack_span(Us, s) & theirPawns) != 0);
// A not-passed pawn is a candidate to become passed, if it is free to
// advance and if the number of friendly pawns beside or behind this
// pawn on adjacent files is higher than or equal to the number of
// enemy pawns in the forward direction on the adjacent files.
candidate = !(opposed | passed | backward | isolated) &&
(b = BitBoard.pawn_attack_span(Them, s + Types.pawn_push(Us)) & ourPawns) != 0 &&
Bitcount.popcount_Max15(b) >= Bitcount.popcount_Max15(BitBoard.pawn_attack_span(Us, s) & theirPawns);
// Passed pawns will be properly scored in evaluation because we need
// full attack info to evaluate passed pawns. Only the frontmost passed
// pawn on each file is considered a true passed pawn.
if (passed && 0 == doubled)
{
e.passedPawns[Us] |= BitBoard.SquareBB[s];
}
// Score this pawn
if (isolated)
{
value -= Isolated[opposed ? 1 : 0][f];
}
if (unsupported && !isolated)
{
value -= UnsupportedPawnPenalty;
}
if (doubled != 0)
{
value -= Types.divScore(Doubled[f], BitBoard.rank_distance(s, BitBoard.lsb(doubled)));
}
if (backward)
{
value -= Backward[opposed ? 1 : 0][f];
}
if (connected)
{
value += Connected[f][Types.relative_rank_square(Us, s)];
}
if (candidate)
{
value += CandidatePassed[Types.relative_rank_square(Us, s)];
if (0 == doubled)
{
e.candidatePawns[Us] |= BitBoard.SquareBB[s];
}
}
}
// In endgame it's better to have pawns on both wings. So give a bonus according
// to file distance between left and right outermost pawns.
if (pos.count(Us, PieceTypeS.PAWN) > 1)
{
b = (Bitboard)(e.semiopenFiles[Us] ^ 0xFF);
value += PawnsFileSpan * (BitBoard.msb(b) - BitBoard.lsb(b));
}
return(value);
}
/// 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);
}