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| /* | |
| Stockfish, a UCI chess playing engine derived from Glaurung 2.1 | |
| Copyright (C) 2004-2008 Tord Romstad (Glaurung author) | |
| Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad | |
| Stockfish is free software: you can redistribute it and/or modify | |
| it under the terms of the GNU General Public License as published by | |
| the Free Software Foundation, either version 3 of the License, or | |
| (at your option) any later version. | |
| Stockfish is distributed in the hope that it will be useful, | |
| but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| GNU General Public License for more details. | |
| You should have received a copy of the GNU General Public License | |
| along with this program. If not, see <http://www.gnu.org/licenses/>. | |
| */ | |
| namespace { | |
| // Doubled pawn penalty by opposed flag and file | |
| const Score Doubled[2][FILE_NB] = { | |
| { S(13, 43), S(20, 48), S(23, 48), S(23, 48), | |
| S(23, 48), S(23, 48), S(20, 48), S(13, 43) }, | |
| { S(13, 43), S(20, 48), S(23, 48), S(23, 48), | |
| S(23, 48), S(23, 48), S(20, 48), S(13, 43) }}; | |
| // Isolated pawn penalty by opposed flag and file | |
| const Score Isolated[2][FILE_NB] = { | |
| { S(37, 45), S(54, 52), S(60, 52), S(60, 52), | |
| S(60, 52), S(60, 52), S(54, 52), S(37, 45) }, | |
| { S(25, 30), S(36, 35), S(40, 35), S(40, 35), | |
| S(40, 35), S(40, 35), S(36, 35), S(25, 30) }}; | |
| // Backward pawn penalty by opposed flag and file | |
| const Score Backward[2][FILE_NB] = { | |
| { S(30, 42), S(43, 46), S(49, 46), S(49, 46), | |
| S(49, 46), S(49, 46), S(43, 46), S(30, 42) }, | |
| { S(20, 28), S(29, 31), S(33, 31), S(33, 31), | |
| S(33, 31), S(33, 31), S(29, 31), S(20, 28) }}; | |
| // Pawn chain membership bonus by file | |
| const Score ChainMember[FILE_NB] = { | |
| S(11,-1), S(13,-1), S(13,-1), S(14,-1), | |
| S(14,-1), S(13,-1), S(13,-1), S(11,-1) | |
| }; | |
| // Candidate passed pawn bonus by rank | |
| const Score CandidatePassed[RANK_NB] = { | |
| S( 0, 0), S( 6, 13), S(6,13), S(14,29), | |
| S(34,68), S(83,166), S(0, 0), S( 0, 0) | |
| }; | |
| // Weakness of our pawn shelter in front of the king indexed by [rank] | |
| const Value ShelterWeakness[RANK_NB] = | |
| { V(100), V(0), V(27), V(73), V(92), V(101), V(101) }; | |
| // Danger of enemy pawns moving toward our king indexed by | |
| // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn] | |
| const Value StormDanger[3][RANK_NB] = { | |
| { V( 0), V(64), V(128), V(51), V(26) }, | |
| { V(26), V(32), V( 96), V(38), V(20) }, | |
| { V( 0), 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); | |
| template<Color Us> | |
| Score evaluate(const Position& pos, Pawns::Entry* e) { | |
| const Color Them = (Us == WHITE ? BLACK : WHITE); | |
| const Square Up = (Us == WHITE ? DELTA_N : DELTA_S); | |
| const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW); | |
| const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE); | |
| Bitboard b; | |
| Square s; | |
| File f; | |
| Rank r; | |
| bool passed, isolated, doubled, opposed, chain, backward, candidate; | |
| Score value = SCORE_ZERO; | |
| const Square* pl = pos.list<PAWN>(Us); | |
| Bitboard ourPawns = pos.pieces(Us, PAWN); | |
| Bitboard theirPawns = pos.pieces(Them, PAWN); | |
| e->passedPawns[Us] = 0; | |
| e->kingSquares[Us] = SQ_NONE; | |
| e->semiopenFiles[Us] = 0xFF; | |
| e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns); | |
| e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares); | |
| e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK]; | |
| // Loop through all pawns of the current color and score each pawn | |
| while ((s = *pl++) != SQ_NONE) | |
| { | |
| assert(pos.piece_on(s) == make_piece(Us, PAWN)); | |
| f = file_of(s); | |
| r = rank_of(s); | |
| // This file cannot be semi-open | |
| e->semiopenFiles[Us] &= ~(1 << f); | |
| // Our rank plus previous one. Used for chain detection | |
| b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1)); | |
| // Flag the pawn as passed, isolated, doubled or member of a pawn | |
| // chain (but not the backward one). | |
| chain = ourPawns & adjacent_files_bb(f) & b; | |
| isolated = !(ourPawns & adjacent_files_bb(f)); | |
| doubled = ourPawns & forward_bb(Us, s); | |
| opposed = theirPawns & forward_bb(Us, s); | |
| passed = !(theirPawns & passed_pawn_mask(Us, s)); | |
| // Test for backward pawn | |
| backward = false; | |
| // If the pawn is passed, isolated, or member of a pawn chain it cannot | |
| // be backward. If there are friendly pawns behind on adjacent files | |
| // or if can capture an enemy pawn it cannot be backward either. | |
| if ( !(passed | isolated | chain) | |
| && !(ourPawns & pawn_attack_span(Them, s)) | |
| && !(pos.attacks_from<PAWN>(s, Us) & theirPawns)) | |
| { | |
| // 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 seeing whether we meet a friendly or an enemy pawn first. | |
| b = pos.attacks_from<PAWN>(s, Us); | |
| // Note that we are sure to find something because pawn is not passed | |
| // nor isolated, so loop is potentially infinite, but it isn't. | |
| while (!(b & (ourPawns | theirPawns))) | |
| b = shift_bb<Up>(b); | |
| // The friendly pawn needs to be at least two ranks closer than the | |
| // enemy pawn in order to help the potentially backward pawn advance. | |
| backward = (b | shift_bb<Up>(b)) & theirPawns; | |
| } | |
| assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns)); | |
| // 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 or equal than the number of | |
| // enemy pawns in the forward direction on the adjacent files. | |
| candidate = !(opposed | passed | backward | isolated) | |
| && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0 | |
| && popcount<Max15>(b) >= popcount<Max15>(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 && !doubled) | |
| e->passedPawns[Us] |= s; | |
| // Score this pawn | |
| if (isolated) | |
| value -= Isolated[opposed][f]; | |
| if (doubled) | |
| value -= Doubled[opposed][f]; | |
| if (backward) | |
| value -= Backward[opposed][f]; | |
| if (chain) | |
| value += ChainMember[f]; | |
| if (candidate) | |
| value += CandidatePassed[relative_rank(Us, s)]; | |
| } | |
| return value; | |
| } | |
| } // namespace | |
| namespace Pawns { | |
| /// probe() takes a position object as input, computes a Entry object, and returns | |
| /// a pointer to it. The result is also stored in a hash table, so we don't have | |
| /// to recompute everything when the same pawn structure occurs again. | |
| Entry* probe(const Position& pos, Table& entries) { | |
| Key key = pos.pawn_key(); | |
| Entry* e = entries[key]; | |
| if (e->key == key) | |
| return e; | |
| e->key = key; | |
| e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e); | |
| return e; | |
| } | |
| /// Entry::shelter_storm() calculates shelter and storm penalties for the file | |
| /// the king is on, as well as the two adjacent files. | |
| template<Color Us> | |
| Value Entry::shelter_storm(const Position& pos, Square ksq) { | |
| const Color Them = (Us == WHITE ? BLACK : WHITE); | |
| Value safety = MaxSafetyBonus; | |
| Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq)); | |
| Bitboard ourPawns = b & pos.pieces(Us); | |
| Bitboard theirPawns = b & pos.pieces(Them); | |
| Rank rkUs, rkThem; | |
| File kf = file_of(ksq); | |
| kf = (kf == FILE_A) ? FILE_B : (kf == FILE_H) ? FILE_G : kf; | |
| for (int f = kf - 1; f <= kf + 1; f++) | |
| { | |
| b = ourPawns & FileBB[f]; | |
| rkUs = b ? relative_rank(Us, Us == WHITE ? lsb(b) : msb(b)) : RANK_1; | |
| safety -= ShelterWeakness[rkUs]; | |
| b = theirPawns & FileBB[f]; | |
| rkThem = b ? relative_rank(Us, Us == WHITE ? lsb(b) : msb(b)) : RANK_1; | |
| safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem]; | |
| } | |
| return safety; | |
| } | |
| /// Entry::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 Entry::update_safety(const Position& pos, Square ksq) { | |
| kingSquares[Us] = ksq; | |
| castleRights[Us] = pos.can_castle(Us); | |
| minKPdistance[Us] = 0; | |
| Bitboard pawns = pos.pieces(Us, PAWN); | |
| if (pawns) | |
| while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {} | |
| if (relative_rank(Us, ksq) > RANK_4) | |
| return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]); | |
| Value bonus = shelter_storm<Us>(pos, ksq); | |
| // If we can castle use the bonus after the castle if is bigger | |
| if (pos.can_castle(make_castle_right(Us, KING_SIDE))) | |
| bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1))); | |
| if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE))) | |
| bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1))); | |
| return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]); | |
| } | |
| // Explicit template instantiation | |
| template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq); | |
| template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq); | |
| } // namespace Pawns | |