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320 lines
12 KiB
C++
320 lines
12 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) 2015-2016 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 "bitcount.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 and file
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const Score Isolated[2][FILE_NB] = {
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{ S(37, 45), S(54, 52), S(60, 52), S(60, 52),
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S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
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{ S(25, 30), S(36, 35), S(40, 35), S(40, 35),
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S(40, 35), S(40, 35), S(36, 35), S(25, 30) } };
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// Backward pawn penalty by opposed flag
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const Score Backward[2] = { S(67, 42), S(49, 24) };
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// Unsupported pawn penalty, for pawns which are neither isolated or backward
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const Score Unsupported = S(20, 10);
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// Connected pawn bonus by opposed, phalanx, twice supported and rank
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Score Connected[2][2][2][RANK_NB];
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// Doubled pawn penalty by file
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const Score Doubled[FILE_NB] = {
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S(13, 43), S(20, 48), S(23, 48), S(23, 48),
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S(23, 48), S(23, 48), S(20, 48), S(13, 43) };
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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(20, 20), S(40, 40), S(0, 0), S(0, 0) };
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// Center bind bonus, when two pawns controls the same central square
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const Score CenterBind = S(16, 0);
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// Weakness of our pawn shelter in front of the king by [distance from edge][rank]
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const Value ShelterWeakness[][RANK_NB] = {
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{ V( 97), V(21), V(26), V(51), V(87), V( 89), V( 99) },
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{ V(120), V( 0), V(28), V(76), V(88), V(103), V(104) },
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{ V(101), V( 7), V(54), V(78), V(77), V( 92), V(101) },
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{ V( 80), V(11), V(44), V(68), V(87), V( 90), V(119) } };
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// Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
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const Value StormDanger[][4][RANK_NB] = {
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{ { V( 0), V( 67), V( 134), V(38), V(32) },
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{ V( 0), V( 57), V( 139), V(37), V(22) },
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{ V( 0), V( 43), V( 115), V(43), V(27) },
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{ V( 0), V( 68), V( 124), V(57), V(32) } },
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{ { V(20), V( 43), V( 100), V(56), V(20) },
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{ V(23), V( 20), V( 98), V(40), V(15) },
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{ V(23), V( 39), V( 103), V(36), V(18) },
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{ V(28), V( 19), V( 108), V(42), V(26) } },
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{ { V( 0), V( 0), V( 75), V(14), V( 2) },
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{ V( 0), V( 0), V( 150), V(30), V( 4) },
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{ V( 0), V( 0), V( 160), V(22), V( 5) },
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{ V( 0), V( 0), V( 166), V(24), V(13) } },
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{ { V( 0), V(-283), V(-281), V(57), V(31) },
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{ V( 0), V( 58), V( 141), V(39), V(18) },
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{ V( 0), V( 65), V( 142), V(48), V(32) },
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{ V( 0), V( 60), V( 126), V(51), V(19) } } };
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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 ? DELTA_N : DELTA_S);
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const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
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const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
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const Bitboard CenterBindMask =
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Us == WHITE ? (FileDBB | FileEBB) & (Rank5BB | Rank6BB | Rank7BB)
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: (FileDBB | FileEBB) & (Rank4BB | Rank3BB | Rank2BB);
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Bitboard b, neighbours, doubled, supported, phalanx;
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Square s;
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bool passed, isolated, opposed, backward, lever, connected;
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Score score = SCORE_ZERO;
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const Square* pl = pos.squares<PAWN>(Us);
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const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
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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->kingSquares[Us] = SQ_NONE;
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e->semiopenFiles[Us] = 0xFF;
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e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
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e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(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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neighbours = ourPawns & adjacent_files_bb(f);
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doubled = ourPawns & forward_bb(Us, s);
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opposed = theirPawns & forward_bb(Us, s);
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passed = !(theirPawns & passed_pawn_mask(Us, s));
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lever = theirPawns & pawnAttacksBB[s];
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phalanx = neighbours & rank_bb(s);
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supported = neighbours & rank_bb(s - Up);
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connected = supported | phalanx;
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isolated = !neighbours;
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// Test for backward pawn.
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// If the pawn is passed, isolated, lever or connected it cannot be
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// backward. If there are friendly pawns behind on adjacent files
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// or if it is sufficiently advanced, it cannot be backward either.
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if ( (passed | isolated | lever | connected)
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|| (ourPawns & pawn_attack_span(Them, s))
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|| (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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// We now know there are no friendly pawns beside or behind this
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// pawn on adjacent files. We now check whether the pawn is
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// backward by looking in the forward direction on the adjacent
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// files, and picking the closest pawn there.
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b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
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b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
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// If we have an enemy pawn in the same or next rank, the pawn is
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// backward because it cannot advance without being captured.
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backward = (b | shift_bb<Up>(b)) & theirPawns;
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}
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assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
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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. Only the frontmost passed
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// pawn on each file is considered a true passed pawn.
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if (passed && !doubled)
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e->passedPawns[Us] |= s;
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// Score this pawn
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if (isolated)
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score -= Isolated[opposed][f];
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else if (backward)
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score -= Backward[opposed];
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else if (!supported)
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score -= Unsupported;
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if (connected)
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score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
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if (doubled)
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score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, 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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b = e->semiopenFiles[Us] ^ 0xFF;
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e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
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b = shift_bb<Right>(ourPawns) & shift_bb<Left>(ourPawns) & CenterBindMask;
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score += CenterBind * popcount<Max15>(b);
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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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{
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static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
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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 apex = 0; apex <= 1; ++apex)
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for (Rank r = RANK_2; r < RANK_8; ++r)
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{
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int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
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v += (apex ? v / 2 : 0);
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Connected[opposed][phalanx][apex][r] = make_score(3 * v / 2, v);
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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<Max15>(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 adjacent 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 { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
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Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(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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safety -= ShelterWeakness[std::min(f, FILE_H - f)][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 ? NoFriendlyPawn :
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rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
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[std::min(f, FILE_H - f)][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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if (relative_rank(Us, ksq) > RANK_4)
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return make_score(0, -16 * minKingPawnDistance);
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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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