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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).
80 lines
2.4 KiB
C++
80 lines
2.4 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (c) 2013 Ronald de Man
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Copyright (C) 2016-2018 Marco Costalba, Lucas Braesch
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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 TBPROBE_H
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#define TBPROBE_H
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#include <ostream>
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#include "../search.h"
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namespace Tablebases {
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enum WDLScore {
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WDLLoss = -2, // Loss
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WDLBlessedLoss = -1, // Loss, but draw under 50-move rule
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WDLDraw = 0, // Draw
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WDLCursedWin = 1, // Win, but draw under 50-move rule
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WDLWin = 2, // Win
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WDLScoreNone = -1000
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};
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// Possible states after a probing operation
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enum ProbeState {
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FAIL = 0, // Probe failed (missing file table)
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OK = 1, // Probe succesful
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CHANGE_STM = -1, // DTZ should check the other side
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ZEROING_BEST_MOVE = 2 // Best move zeroes DTZ (capture or pawn move)
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};
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extern int MaxCardinality;
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void init(const std::string& paths);
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WDLScore probe_wdl(Position& pos, ProbeState* result);
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int probe_dtz(Position& pos, ProbeState* result);
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bool root_probe(Position& pos, Search::RootMoves& rootMoves);
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bool root_probe_wdl(Position& pos, Search::RootMoves& rootMoves);
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void rank_root_moves(Position& pos, Search::RootMoves& rootMoves);
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inline std::ostream& operator<<(std::ostream& os, const WDLScore v) {
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os << (v == WDLLoss ? "Loss" :
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v == WDLBlessedLoss ? "Blessed loss" :
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v == WDLDraw ? "Draw" :
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v == WDLCursedWin ? "Cursed win" :
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v == WDLWin ? "Win" : "None");
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return os;
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}
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inline std::ostream& operator<<(std::ostream& os, const ProbeState v) {
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os << (v == FAIL ? "Failed" :
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v == OK ? "Success" :
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v == CHANGE_STM ? "Probed opponent side" :
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v == ZEROING_BEST_MOVE ? "Best move zeroes DTZ" : "None");
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return os;
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}
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}
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#endif
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