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syzygy1
108f0da4d7
This patch corrects both MultiPV behaviour and "go searchmoves" behaviour for tablebases. We change the logic of table base probing at root positions from filtering to ranking. The ranking code is much more straightforward than the current filtering code (this is a simplification), and also more versatile. If the root is a TB position, each root move is probed and assigned a TB score and a TB rank. The TB score is the Value to be displayed to the user for that move (unless the search finds a mate score), while the TB rank determines which moves should appear higher in a multi-pv search. In game play, the engine will always pick a move with the highest rank. Ranks run from -1000 to +1000: 901 to 1000 : TB win 900 : normally a TB win, in rare cases this could be a draw 1 to 899 : cursed TB wins 0 : draw -1 to -899 : blessed TB losses -900 : normally a TB loss, in rare cases this could be a draw -901 to -1000 : TB loss Normally all winning moves get rank 1000 (to let the search pick the best among them). The exception is if there has been a first repetition. In that case, moves are ranked strictly by DTZ so that the engine will play a move that lowers DTZ (and therefore cannot repeat the position a second time). Losing moves get rank -1000 unless they have relatively high DTZ, meaning they have some drawing chances. Those get ranks towards -901 (when they cross -900 the draw is certain). Closes https://github.com/official-stockfish/Stockfish/pull/1467 No functional change (without tablebases).
109 lines
3.1 KiB
C++
109 lines
3.1 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) 2015-2018 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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#ifndef SEARCH_H_INCLUDED
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#define SEARCH_H_INCLUDED
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#include <vector>
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#include "misc.h"
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#include "movepick.h"
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#include "types.h"
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class Position;
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namespace Search {
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/// Threshold used for countermoves based pruning
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constexpr int CounterMovePruneThreshold = 0;
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/// Stack struct keeps track of the information we need to remember from nodes
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/// shallower and deeper in the tree during the search. Each search thread has
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/// its own array of Stack objects, indexed by the current ply.
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struct Stack {
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Move* pv;
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PieceToHistory* contHistory;
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int ply;
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Move currentMove;
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Move excludedMove;
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Move killers[2];
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Value staticEval;
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int statScore;
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int moveCount;
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};
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/// RootMove struct is used for moves at the root of the tree. For each root move
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/// we store a score and a PV (really a refutation in the case of moves which
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/// fail low). Score is normally set at -VALUE_INFINITE for all non-pv moves.
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struct RootMove {
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explicit RootMove(Move m) : pv(1, m) {}
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bool extract_ponder_from_tt(Position& pos);
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bool operator==(const Move& m) const { return pv[0] == m; }
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bool operator<(const RootMove& m) const { // Sort in descending order
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return m.score != score ? m.score < score
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: m.previousScore < previousScore;
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}
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Value score = -VALUE_INFINITE;
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Value previousScore = -VALUE_INFINITE;
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int selDepth = 0;
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int TBRank;
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Value TBScore;
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std::vector<Move> pv;
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};
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typedef std::vector<RootMove> RootMoves;
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/// LimitsType struct stores information sent by GUI about available time to
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/// search the current move, maximum depth/time, or if we are in analysis mode.
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struct LimitsType {
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LimitsType() { // Init explicitly due to broken value-initialization of non POD in MSVC
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time[WHITE] = time[BLACK] = inc[WHITE] = inc[BLACK] = npmsec = movetime = TimePoint(0);
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movestogo = depth = mate = perft = infinite = 0;
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nodes = 0;
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}
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bool use_time_management() const {
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return !(mate | movetime | depth | nodes | perft | infinite);
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}
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std::vector<Move> searchmoves;
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TimePoint time[COLOR_NB], inc[COLOR_NB], npmsec, movetime, startTime;
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int movestogo, depth, mate, perft, infinite;
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int64_t nodes;
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};
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extern LimitsType Limits;
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void init();
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void clear();
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} // namespace Search
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#endif // #ifndef SEARCH_H_INCLUDED
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