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309 lines
11 KiB
C++
309 lines
11 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
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Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <algorithm>
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#include <cassert>
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#include "bitboard.h"
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#include "pawns.h"
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#include "position.h"
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#include "thread.h"
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namespace {
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#define V Value
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#define S(mg, eg) make_score(mg, eg)
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// Isolated pawn penalty by opposed flag
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const Score Isolated[] = { S(27, 30), S(13, 18) };
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// Backward pawn penalty by opposed flag
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const Score Backward[] = { S(40, 26), S(24, 12) };
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// Connected pawn bonus by opposed, phalanx, #support and rank
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Score Connected[2][2][3][RANK_NB];
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// Doubled pawn penalty
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const Score Doubled = S(18, 38);
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// Lever bonus by rank
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const Score Lever[RANK_NB] = {
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S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
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S(17, 16), S(33, 32), S(0, 0), S(0, 0)
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};
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// Weakness of our pawn shelter in front of the king by [isKingFile][distance from edge][rank].
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// RANK_1 = 0 is used for files where we have no pawns or our pawn is behind our king.
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const Value ShelterWeakness[][int(FILE_NB) / 2][RANK_NB] = {
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{ { V( 97), V(17), V( 9), V(44), V( 84), V( 87), V( 99) }, // Not On King file
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{ V(106), V( 6), V(33), V(86), V( 87), V(104), V(112) },
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{ V(101), V( 2), V(65), V(98), V( 58), V( 89), V(115) },
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{ V( 73), V( 7), V(54), V(73), V( 84), V( 83), V(111) } },
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{ { V(104), V(20), V( 6), V(27), V( 86), V( 93), V( 82) }, // On King file
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{ V(123), V( 9), V(34), V(96), V(112), V( 88), V( 75) },
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{ V(120), V(25), V(65), V(91), V( 66), V( 78), V(117) },
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{ V( 81), V( 2), V(47), V(63), V( 94), V( 93), V(104) } }
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};
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// Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
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// For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
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// no pawn on the given file, or their pawn is behind our king.
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const Value StormDanger[][4][RANK_NB] = {
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{ { V( 0), V(-290), V(-274), V(57), V(41) }, // BlockedByKing
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{ V( 0), V( 60), V( 144), V(39), V(13) },
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{ V( 0), V( 65), V( 141), V(41), V(34) },
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{ V( 0), V( 53), V( 127), V(56), V(14) } },
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{ { V( 4), V( 73), V( 132), V(46), V(31) }, // Unopposed
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{ V( 1), V( 64), V( 143), V(26), V(13) },
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{ V( 1), V( 47), V( 110), V(44), V(24) },
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{ V( 0), V( 72), V( 127), V(50), V(31) } },
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{ { V( 0), V( 0), V( 79), V(23), V( 1) }, // BlockedByPawn
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{ V( 0), V( 0), V( 148), V(27), V( 2) },
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{ V( 0), V( 0), V( 161), V(16), V( 1) },
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{ V( 0), V( 0), V( 171), V(22), V(15) } },
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{ { V(22), V( 45), V( 104), V(62), V( 6) }, // Unblocked
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{ V(31), V( 30), V( 99), V(39), V(19) },
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{ V(23), V( 29), V( 96), V(41), V(15) },
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{ V(21), V( 23), V( 116), V(41), V(15) } }
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};
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// Max bonus for king safety. Corresponds to start position with all the pawns
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// in front of the king and no enemy pawn on the horizon.
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const Value MaxSafetyBonus = V(258);
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#undef S
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#undef V
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template<Color Us>
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Score evaluate(const Position& pos, Pawns::Entry* e) {
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const Color Them = (Us == WHITE ? BLACK : WHITE);
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const Square Up = (Us == WHITE ? NORTH : SOUTH);
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const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
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const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
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Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
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Bitboard lever, leverPush;
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Square s;
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bool opposed, backward;
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Score score = SCORE_ZERO;
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const Square* pl = pos.squares<PAWN>(Us);
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Bitboard ourPawns = pos.pieces( Us, PAWN);
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Bitboard theirPawns = pos.pieces(Them, PAWN);
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e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
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e->semiopenFiles[Us] = 0xFF;
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e->kingSquares[Us] = SQ_NONE;
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e->pawnAttacks[Us] = shift<Right>(ourPawns) | shift<Left>(ourPawns);
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e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
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e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
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// Loop through all pawns of the current color and score each pawn
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while ((s = *pl++) != SQ_NONE)
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{
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assert(pos.piece_on(s) == make_piece(Us, PAWN));
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File f = file_of(s);
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e->semiopenFiles[Us] &= ~(1 << f);
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e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
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// Flag the pawn
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opposed = theirPawns & forward_file_bb(Us, s);
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stoppers = theirPawns & passed_pawn_mask(Us, s);
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lever = theirPawns & PawnAttacks[Us][s];
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leverPush = theirPawns & PawnAttacks[Us][s + Up];
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doubled = ourPawns & (s - Up);
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neighbours = ourPawns & adjacent_files_bb(f);
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phalanx = neighbours & rank_bb(s);
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supported = neighbours & rank_bb(s - Up);
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// A pawn is backward when it is behind all pawns of the same color on the
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// adjacent files and cannot be safely advanced.
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if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
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backward = false;
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else
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{
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// Find the backmost rank with neighbours or stoppers
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b = rank_bb(backmost_sq(Us, neighbours | stoppers));
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// The pawn is backward when it cannot safely progress to that rank:
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// either there is a stopper in the way on this rank, or there is a
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// stopper on adjacent file which controls the way to that rank.
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backward = (b | shift<Up>(b & adjacent_files_bb(f))) & stoppers;
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assert(!(backward && (forward_ranks_bb(Them, s + Up) & neighbours)));
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}
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// Passed pawns will be properly scored in evaluation because we need
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// full attack info to evaluate them. Include also not passed pawns
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// which could become passed after one or two pawn pushes when are
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// not attacked more times than defended.
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if ( !(stoppers ^ lever ^ leverPush)
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&& !(ourPawns & forward_file_bb(Us, s))
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&& popcount(supported) >= popcount(lever)
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&& popcount(phalanx) >= popcount(leverPush))
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e->passedPawns[Us] |= s;
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else if ( stoppers == SquareBB[s + Up]
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&& relative_rank(Us, s) >= RANK_5)
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{
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b = shift<Up>(supported) & ~theirPawns;
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while (b)
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if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
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e->passedPawns[Us] |= s;
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}
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// Score this pawn
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if (supported | phalanx)
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score += Connected[opposed][!!phalanx][popcount(supported)][relative_rank(Us, s)];
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else if (!neighbours)
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score -= Isolated[opposed];
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else if (backward)
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score -= Backward[opposed];
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if (doubled && !supported)
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score -= Doubled;
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if (lever)
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score += Lever[relative_rank(Us, s)];
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}
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return score;
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}
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} // namespace
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namespace Pawns {
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/// Pawns::init() initializes some tables needed by evaluation. Instead of using
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/// hard-coded tables, when makes sense, we prefer to calculate them with a formula
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/// to reduce independent parameters and to allow easier tuning and better insight.
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void init() {
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static const int Seed[RANK_NB] = { 0, 13, 24, 18, 76, 100, 175, 330 };
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for (int opposed = 0; opposed <= 1; ++opposed)
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for (int phalanx = 0; phalanx <= 1; ++phalanx)
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for (int support = 0; support <= 2; ++support)
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for (Rank r = RANK_2; r < RANK_8; ++r)
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{
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int v = 17 * support;
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v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
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Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
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}
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}
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/// Pawns::probe() looks up the current position's pawns configuration in
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/// the pawns hash table. It returns a pointer to the Entry if the position
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/// is found. Otherwise a new Entry is computed and stored there, so we don't
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/// have to recompute all when the same pawns configuration occurs again.
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Entry* probe(const Position& pos) {
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Key key = pos.pawn_key();
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Entry* e = pos.this_thread()->pawnsTable[key];
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if (e->key == key)
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return e;
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e->key = key;
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e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
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e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
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e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
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return e;
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}
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/// Entry::shelter_storm() calculates shelter and storm penalties for the file
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/// the king is on, as well as the two closest files.
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template<Color Us>
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Value Entry::shelter_storm(const Position& pos, Square ksq) {
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const Color Them = (Us == WHITE ? BLACK : WHITE);
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enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
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Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
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Bitboard ourPawns = b & pos.pieces(Us);
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Bitboard theirPawns = b & pos.pieces(Them);
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Value safety = MaxSafetyBonus;
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File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
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for (File f = center - File(1); f <= center + File(1); ++f)
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{
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b = ourPawns & file_bb(f);
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Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
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b = theirPawns & file_bb(f);
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Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
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int d = std::min(f, FILE_H - f);
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safety -= ShelterWeakness[f == file_of(ksq)][d][rkUs]
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+ StormDanger
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[f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
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rkUs == RANK_1 ? Unopposed :
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rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
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[d][rkThem];
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}
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return safety;
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}
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/// Entry::do_king_safety() calculates a bonus for king safety. It is called only
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/// when king square changes, which is about 20% of total king_safety() calls.
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template<Color Us>
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Score Entry::do_king_safety(const Position& pos, Square ksq) {
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kingSquares[Us] = ksq;
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castlingRights[Us] = pos.can_castle(Us);
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int minKingPawnDistance = 0;
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Bitboard pawns = pos.pieces(Us, PAWN);
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if (pawns)
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while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
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Value bonus = shelter_storm<Us>(pos, ksq);
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// If we can castle use the bonus after the castling if it is bigger
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if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
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bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
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if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
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bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
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return make_score(bonus, -16 * minKingPawnDistance);
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}
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// Explicit template instantiation
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template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
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template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);
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} // namespace Pawns
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