namespace {
+ #define V Value
#define S(mg, eg) make_score(mg, eg)
// Doubled pawn penalty by opposed flag and file
const Score PawnStructureWeight = S(233, 201);
+ // Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
+ const Value ShelterWeakness[2][8] =
+ { { V(141), V(0), V(38), V(102), V(128), V(141), V(141) },
+ { V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61) } };
+
+ // Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
+ const Value StormDanger[2][8] =
+ { { V(26), V(0), V(128), V(51), V(26) },
+ { V(13), V(0), V( 64), V(25), V(13) } };
+
+ // Max bonus for king safety. Corresponds to start position with all the pawns
+ // in front of the king and no enemy pawn on the horizont.
+ const Value MaxSafetyBonus = V(263);
+
#undef S
+ #undef V
inline Score apply_weight(Score v, Score w) {
return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
}
-/// PawnInfo::updateShelter() calculates and caches king shelter. It is called
-/// only when king square changes, about 20% of total king_shelter() calls.
+/// PawnInfo::shelter_storm() calculates shelter and storm penalties for the file
+/// the king is on, as well as the two adjacent files.
+
template<Color Us>
-Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
+Value PawnInfo::shelter_storm(const Position& pos, Square ksq) {
+
+ const Color Them = (Us == WHITE ? BLACK : WHITE);
- const int Shift = (Us == WHITE ? 8 : -8);
+ Value safety = MaxSafetyBonus;
+ Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | rank_bb(ksq));
+ Bitboard ourPawns = b & pos.pieces(Us) & ~rank_bb(ksq);
+ Bitboard theirPawns = b & pos.pieces(Them);
+ Rank rkUs, rkThem;
+ File kf = file_of(ksq);
- Bitboard pawns;
- int r, shelter = 0;
+ kf = (kf == FILE_A) ? kf++ : (kf == FILE_H) ? kf-- : kf;
- if (relative_rank(Us, ksq) <= RANK_4)
+ for (int f = kf - 1; f <= kf + 1; f++)
{
- pawns = pos.pieces(PAWN, Us) & this_and_adjacent_files_bb(file_of(ksq));
- r = ksq & (7 << 3);
- for (int i = 0; i < 3; i++)
- {
- r += Shift;
- shelter += BitCount8Bit[(pawns >> r) & 0xFF] << (6 - i);
- }
+ // Shelter penalty is higher for the pawn in front of the king
+ b = ourPawns & FileBB[f];
+ rkUs = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+ safety -= ShelterWeakness[f != kf][rkUs];
+
+ // Storm danger is smaller if enemy pawn is blocked
+ b = theirPawns & FileBB[f];
+ rkThem = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+ safety -= StormDanger[rkThem == rkUs + 1][rkThem];
}
+
+ return safety;
+}
+
+
+/// PawnInfo::update_safety() calculates and caches a bonus for king safety. It is
+/// called only when king square changes, about 20% of total king_safety() calls.
+
+template<Color Us>
+Score PawnInfo::update_safety(const Position& pos, Square ksq) {
+
kingSquares[Us] = ksq;
- kingShelters[Us] = make_score(shelter, 0);
- return kingShelters[Us];
+
+ if (relative_rank(Us, ksq) > RANK_4)
+ return kingShelters[Us] = SCORE_ZERO;
+
+ Value bonus = shelter_storm<Us>(pos, ksq);
+
+ // If we can castle use the bonus after the castle if is bigger
+ if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
+ bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
+
+ if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
+ bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
+
+ return kingShelters[Us] = make_score(bonus, 0);
}
// Explicit template instantiation
-template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
-template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);
+template Score PawnInfo::update_safety<WHITE>(const Position& pos, Square ksq);
+template Score PawnInfo::update_safety<BLACK>(const Position& pos, Square ksq);