230 lines
8.7 KiB
C++
230 lines
8.7 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
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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 <cassert>
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#include <cstring> // For std::memset
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#include "material.h"
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#include "thread.h"
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using namespace std;
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namespace Stockfish {
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namespace {
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#define S(mg, eg) make_score(mg, eg)
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// Polynomial material imbalance parameters
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// One Score parameter for each pair (our piece, another of our pieces)
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constexpr Score QuadraticOurs[][PIECE_TYPE_NB] = {
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// OUR PIECE 2
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// bishop pair pawn knight bishop rook queen
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{S(1419, 1455) }, // Bishop pair
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{S( 101, 28), S( 37, 39) }, // Pawn
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{S( 57, 64), S(249, 187), S(-49, -62) }, // Knight OUR PIECE 1
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{S( 0, 0), S(118, 137), S( 10, 27), S( 0, 0) }, // Bishop
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{S( -63, -68), S( -5, 3), S(100, 81), S(132, 118), S(-246, -244) }, // Rook
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{S(-210, -211), S( 37, 14), S(147, 141), S(161, 105), S(-158, -174), S(-9,-31) } // Queen
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};
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// One Score parameter for each pair (our piece, their piece)
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constexpr Score QuadraticTheirs[][PIECE_TYPE_NB] = {
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// THEIR PIECE
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// bishop pair pawn knight bishop rook queen
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{ }, // Bishop pair
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{S( 33, 30) }, // Pawn
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{S( 46, 18), S(106, 84) }, // Knight OUR PIECE
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{S( 75, 35), S( 59, 44), S( 60, 15) }, // Bishop
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{S( 26, 35), S( 6, 22), S( 38, 39), S(-12, -2) }, // Rook
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{S( 97, 93), S(100, 163), S(-58, -91), S(112, 192), S(276, 225) } // Queen
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};
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#undef S
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// Endgame evaluation and scaling functions are accessed directly and not through
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// the function maps because they correspond to more than one material hash key.
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Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
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Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
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Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
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Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
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Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
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// Helper used to detect a given material distribution
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bool is_KXK(const Position& pos, Color us) {
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return !more_than_one(pos.pieces(~us))
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&& pos.non_pawn_material(us) >= RookValueMg;
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}
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bool is_KBPsK(const Position& pos, Color us) {
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return pos.non_pawn_material(us) == BishopValueMg
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&& pos.count<PAWN>(us) >= 1;
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}
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bool is_KQKRPs(const Position& pos, Color us) {
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return !pos.count<PAWN>(us)
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&& pos.non_pawn_material(us) == QueenValueMg
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&& pos.count<ROOK>(~us) == 1
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&& pos.count<PAWN>(~us) >= 1;
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}
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/// imbalance() calculates the imbalance by comparing the piece count of each
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/// piece type for both colors.
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template<Color Us>
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Score imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
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constexpr Color Them = ~Us;
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Score bonus = SCORE_ZERO;
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// Second-degree polynomial material imbalance, by Tord Romstad
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for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
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{
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if (!pieceCount[Us][pt1])
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continue;
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int v = QuadraticOurs[pt1][pt1] * pieceCount[Us][pt1];
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for (int pt2 = NO_PIECE_TYPE; pt2 < pt1; ++pt2)
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v += QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]
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+ QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];
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bonus += pieceCount[Us][pt1] * v;
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}
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return bonus;
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}
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} // namespace
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namespace Material {
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/// Material::probe() looks up the current position's material configuration in
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/// the material 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 material configuration occurs again.
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Entry* probe(const Position& pos) {
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Key key = pos.material_key();
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Entry* e = pos.this_thread()->materialTable[key];
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if (e->key == key)
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return e;
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std::memset(e, 0, sizeof(Entry));
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e->key = key;
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e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
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Value npm_w = pos.non_pawn_material(WHITE);
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Value npm_b = pos.non_pawn_material(BLACK);
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Value npm = std::clamp(npm_w + npm_b, EndgameLimit, MidgameLimit);
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// Map total non-pawn material into [PHASE_ENDGAME, PHASE_MIDGAME]
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e->gamePhase = Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
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// Let's look if we have a specialized evaluation function for this particular
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// material configuration. Firstly we look for a fixed configuration one, then
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// for a generic one if the previous search failed.
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if ((e->evaluationFunction = Endgames::probe<Value>(key)) != nullptr)
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return e;
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for (Color c : { WHITE, BLACK })
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if (is_KXK(pos, c))
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{
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e->evaluationFunction = &EvaluateKXK[c];
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return e;
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}
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// OK, we didn't find any special evaluation function for the current material
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// configuration. Is there a suitable specialized scaling function?
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const auto* sf = Endgames::probe<ScaleFactor>(key);
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if (sf)
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{
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e->scalingFunction[sf->strongSide] = sf; // Only strong color assigned
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return e;
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}
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// We didn't find any specialized scaling function, so fall back on generic
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// ones that refer to more than one material distribution. Note that in this
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// case we don't return after setting the function.
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for (Color c : { WHITE, BLACK })
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{
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if (is_KBPsK(pos, c))
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e->scalingFunction[c] = &ScaleKBPsK[c];
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else if (is_KQKRPs(pos, c))
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e->scalingFunction[c] = &ScaleKQKRPs[c];
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}
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if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
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{
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if (!pos.count<PAWN>(BLACK))
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{
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assert(pos.count<PAWN>(WHITE) >= 2);
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e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
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}
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else if (!pos.count<PAWN>(WHITE))
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{
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assert(pos.count<PAWN>(BLACK) >= 2);
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e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
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}
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else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
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{
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// This is a special case because we set scaling functions
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// for both colors instead of only one.
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e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
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e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
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}
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}
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// Zero or just one pawn makes it difficult to win, even with a small material
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// advantage. This catches some trivial draws like KK, KBK and KNK and gives a
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// drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
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if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
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e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
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npm_b <= BishopValueMg ? 4 : 14);
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if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
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e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
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npm_w <= BishopValueMg ? 4 : 14);
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// Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
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// for the bishop pair "extended piece", which allows us to be more flexible
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// in defining bishop pair bonuses.
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const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
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{ pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
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pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
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{ pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
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pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
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e->score = (imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16;
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return e;
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}
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} // namespace Material
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} // namespace Stockfish
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