mirror of
https://github.com/sockspls/badfish
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1938 lines
76 KiB
C++
1938 lines
76 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2024 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 "search.h"
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#include <algorithm>
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#include <array>
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#include <atomic>
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#include <cassert>
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#include <cmath>
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#include <cstdlib>
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#include <initializer_list>
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#include <iostream>
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#include <utility>
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#include <sstream>
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#include "evaluate.h"
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#include "misc.h"
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#include "movegen.h"
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#include "movepick.h"
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#include "nnue/evaluate_nnue.h"
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#include "nnue/nnue_common.h"
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#include "position.h"
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#include "syzygy/tbprobe.h"
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#include "thread.h"
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#include "timeman.h"
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#include "tt.h"
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#include "uci.h"
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#include "ucioption.h"
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namespace Stockfish {
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namespace TB = Tablebases;
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using Eval::evaluate;
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using namespace Search;
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namespace {
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// Futility margin
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Value futility_margin(Depth d, bool noTtCutNode, bool improving) {
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Value futilityMult = 116 - 47 * noTtCutNode;
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return (futilityMult * d - 3 * futilityMult / 2 * improving);
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}
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constexpr int futility_move_count(bool improving, Depth depth) {
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return improving ? (3 + depth * depth) : (3 + depth * depth) / 2;
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}
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// Add correctionHistory value to raw staticEval and guarantee evaluation does not hit the tablebase range
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Value to_corrected_static_eval(Value v, const Worker& w, const Position& pos) {
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auto cv = w.correctionHistory[pos.side_to_move()][pawn_structure_index<Correction>(pos)];
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v += cv * std::abs(cv) / 12890;
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return std::clamp(v, VALUE_TB_LOSS_IN_MAX_PLY + 1, VALUE_TB_WIN_IN_MAX_PLY - 1);
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}
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// History and stats update bonus, based on depth
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int stat_bonus(Depth d) { return std::min(253 * d - 356, 1117); }
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// History and stats update malus, based on depth
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int stat_malus(Depth d) { return std::min(517 * d - 308, 1206); }
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// Add a small random component to draw evaluations to avoid 3-fold blindness
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Value value_draw(size_t nodes) { return VALUE_DRAW - 1 + Value(nodes & 0x2); }
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// Skill structure is used to implement strength limit. If we have a UCI_Elo,
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// we convert it to an appropriate skill level, anchored to the Stash engine.
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// This method is based on a fit of the Elo results for games played between
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// Stockfish at various skill levels and various versions of the Stash engine.
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// Skill 0 .. 19 now covers CCRL Blitz Elo from 1320 to 3190, approximately
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// Reference: https://github.com/vondele/Stockfish/commit/a08b8d4e9711c2
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struct Skill {
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Skill(int skill_level, int uci_elo) {
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if (uci_elo)
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{
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double e = double(uci_elo - 1320) / (3190 - 1320);
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level = std::clamp((((37.2473 * e - 40.8525) * e + 22.2943) * e - 0.311438), 0.0, 19.0);
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}
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else
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level = double(skill_level);
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}
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bool enabled() const { return level < 20.0; }
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bool time_to_pick(Depth depth) const { return depth == 1 + int(level); }
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Move pick_best(const RootMoves&, size_t multiPV);
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double level;
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Move best = Move::none();
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};
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Value value_to_tt(Value v, int ply);
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Value value_from_tt(Value v, int ply, int r50c);
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void update_pv(Move* pv, Move move, const Move* childPv);
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void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
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void update_quiet_stats(
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const Position& pos, Stack* ss, Search::Worker& workerThread, Move move, int bonus);
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void update_all_stats(const Position& pos,
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Stack* ss,
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Search::Worker& workerThread,
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Move bestMove,
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Value bestValue,
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Value beta,
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Square prevSq,
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Move* quietsSearched,
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int quietCount,
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Move* capturesSearched,
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int captureCount,
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Depth depth);
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} // namespace
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Search::Worker::Worker(SharedState& sharedState,
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std::unique_ptr<ISearchManager> sm,
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size_t thread_id) :
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// Unpack the SharedState struct into member variables
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thread_idx(thread_id),
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manager(std::move(sm)),
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options(sharedState.options),
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threads(sharedState.threads),
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tt(sharedState.tt) {
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clear();
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}
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void Search::Worker::start_searching() {
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// Non-main threads go directly to iterative_deepening()
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if (!is_mainthread())
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{
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iterative_deepening();
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return;
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}
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main_manager()->tm.init(limits, rootPos.side_to_move(), rootPos.game_ply(), options);
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tt.new_search();
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if (rootMoves.empty())
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{
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rootMoves.emplace_back(Move::none());
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sync_cout << "info depth 0 score "
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<< UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
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}
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else
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{
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threads.start_searching(); // start non-main threads
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iterative_deepening(); // main thread start searching
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}
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// When we reach the maximum depth, we can arrive here without a raise of
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// threads.stop. However, if we are pondering or in an infinite search,
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// the UCI protocol states that we shouldn't print the best move before the
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// GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
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// until the GUI sends one of those commands.
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while (!threads.stop && (main_manager()->ponder || limits.infinite))
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{} // Busy wait for a stop or a ponder reset
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// Stop the threads if not already stopped (also raise the stop if
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// "ponderhit" just reset threads.ponder).
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threads.stop = true;
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// Wait until all threads have finished
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threads.wait_for_search_finished();
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// When playing in 'nodes as time' mode, subtract the searched nodes from
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// the available ones before exiting.
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if (limits.npmsec)
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main_manager()->tm.advance_nodes_time(limits.inc[rootPos.side_to_move()]
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- threads.nodes_searched());
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Worker* bestThread = this;
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Skill skill =
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Skill(options["Skill Level"], options["UCI_LimitStrength"] ? int(options["UCI_Elo"]) : 0);
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if (int(options["MultiPV"]) == 1 && !limits.depth && !skill.enabled()
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&& rootMoves[0].pv[0] != Move::none())
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bestThread = threads.get_best_thread()->worker.get();
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main_manager()->bestPreviousScore = bestThread->rootMoves[0].score;
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main_manager()->bestPreviousAverageScore = bestThread->rootMoves[0].averageScore;
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// Send again PV info if we have a new best thread
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if (bestThread != this)
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sync_cout << main_manager()->pv(*bestThread, threads, tt, bestThread->completedDepth)
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<< sync_endl;
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sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
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if (bestThread->rootMoves[0].pv.size() > 1
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|| bestThread->rootMoves[0].extract_ponder_from_tt(tt, rootPos))
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std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
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std::cout << sync_endl;
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}
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// Main iterative deepening loop. It calls search()
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// repeatedly with increasing depth until the allocated thinking time has been
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// consumed, the user stops the search, or the maximum search depth is reached.
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void Search::Worker::iterative_deepening() {
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SearchManager* mainThread = (thread_idx == 0 ? main_manager() : nullptr);
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Move pv[MAX_PLY + 1];
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Depth lastBestMoveDepth = 0;
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Value lastBestScore = -VALUE_INFINITE;
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auto lastBestPV = std::vector{Move::none()};
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Value alpha, beta;
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Value bestValue = -VALUE_INFINITE;
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Color us = rootPos.side_to_move();
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double timeReduction = 1, totBestMoveChanges = 0;
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int delta, iterIdx = 0;
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// Allocate stack with extra size to allow access from (ss - 7) to (ss + 2):
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// (ss - 7) is needed for update_continuation_histories(ss - 1) which accesses (ss - 6),
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// (ss + 2) is needed for initialization of cutOffCnt and killers.
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Stack stack[MAX_PLY + 10] = {};
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Stack* ss = stack + 7;
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for (int i = 7; i > 0; --i)
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{
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(ss - i)->continuationHistory =
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&this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
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(ss - i)->staticEval = VALUE_NONE;
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}
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for (int i = 0; i <= MAX_PLY + 2; ++i)
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(ss + i)->ply = i;
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ss->pv = pv;
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if (mainThread)
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{
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if (mainThread->bestPreviousScore == VALUE_INFINITE)
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mainThread->iterValue.fill(VALUE_ZERO);
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else
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mainThread->iterValue.fill(mainThread->bestPreviousScore);
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}
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size_t multiPV = size_t(options["MultiPV"]);
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Skill skill(options["Skill Level"], options["UCI_LimitStrength"] ? int(options["UCI_Elo"]) : 0);
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// When playing with strength handicap enable MultiPV search that we will
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// use behind-the-scenes to retrieve a set of possible moves.
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if (skill.enabled())
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multiPV = std::max(multiPV, size_t(4));
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multiPV = std::min(multiPV, rootMoves.size());
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int searchAgainCounter = 0;
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// Iterative deepening loop until requested to stop or the target depth is reached
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while (++rootDepth < MAX_PLY && !threads.stop
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&& !(limits.depth && mainThread && rootDepth > limits.depth))
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{
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// Age out PV variability metric
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if (mainThread)
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totBestMoveChanges /= 2;
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// Save the last iteration's scores before the first PV line is searched and
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// all the move scores except the (new) PV are set to -VALUE_INFINITE.
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for (RootMove& rm : rootMoves)
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rm.previousScore = rm.score;
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size_t pvFirst = 0;
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pvLast = 0;
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if (!threads.increaseDepth)
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searchAgainCounter++;
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// MultiPV loop. We perform a full root search for each PV line
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for (pvIdx = 0; pvIdx < multiPV && !threads.stop; ++pvIdx)
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{
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if (pvIdx == pvLast)
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{
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pvFirst = pvLast;
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for (pvLast++; pvLast < rootMoves.size(); pvLast++)
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if (rootMoves[pvLast].tbRank != rootMoves[pvFirst].tbRank)
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break;
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}
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// Reset UCI info selDepth for each depth and each PV line
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selDepth = 0;
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// Reset aspiration window starting size
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Value avg = rootMoves[pvIdx].averageScore;
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delta = 9 + avg * avg / 12480;
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alpha = std::max(avg - delta, -VALUE_INFINITE);
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beta = std::min(avg + delta, VALUE_INFINITE);
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// Adjust optimism based on root move's averageScore (~4 Elo)
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optimism[us] = 131 * avg / (std::abs(avg) + 95);
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optimism[~us] = -optimism[us];
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// Start with a small aspiration window and, in the case of a fail
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// high/low, re-search with a bigger window until we don't fail
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// high/low anymore.
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int failedHighCnt = 0;
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while (true)
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{
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// Adjust the effective depth searched, but ensure at least one effective increment
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// for every four searchAgain steps (see issue #2717).
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Depth adjustedDepth =
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std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
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bestValue = search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
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// Bring the best move to the front. It is critical that sorting
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// is done with a stable algorithm because all the values but the
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// first and eventually the new best one is set to -VALUE_INFINITE
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// and we want to keep the same order for all the moves except the
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// new PV that goes to the front. Note that in the case of MultiPV
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// search the already searched PV lines are preserved.
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std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast);
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// If search has been stopped, we break immediately. Sorting is
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// safe because RootMoves is still valid, although it refers to
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// the previous iteration.
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if (threads.stop)
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break;
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// When failing high/low give some update (without cluttering
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// the UI) before a re-search.
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if (mainThread && multiPV == 1 && (bestValue <= alpha || bestValue >= beta)
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&& mainThread->tm.elapsed(threads.nodes_searched()) > 3000)
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sync_cout << main_manager()->pv(*this, threads, tt, rootDepth) << sync_endl;
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// In case of failing low/high increase aspiration window and
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// re-search, otherwise exit the loop.
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if (bestValue <= alpha)
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{
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beta = (alpha + beta) / 2;
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alpha = std::max(bestValue - delta, -VALUE_INFINITE);
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failedHighCnt = 0;
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if (mainThread)
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mainThread->stopOnPonderhit = false;
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}
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else if (bestValue >= beta)
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{
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beta = std::min(bestValue + delta, VALUE_INFINITE);
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++failedHighCnt;
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}
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else
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break;
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delta += delta / 3;
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assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
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}
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// Sort the PV lines searched so far and update the GUI
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std::stable_sort(rootMoves.begin() + pvFirst, rootMoves.begin() + pvIdx + 1);
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if (mainThread
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&& (threads.stop || pvIdx + 1 == multiPV
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|| mainThread->tm.elapsed(threads.nodes_searched()) > 3000)
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// A thread that aborted search can have mated-in/TB-loss PV and score
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// that cannot be trusted, i.e. it can be delayed or refuted if we would have
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// had time to fully search other root-moves. Thus we suppress this output and
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// below pick a proven score/PV for this thread (from the previous iteration).
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&& !(threads.abortedSearch && rootMoves[0].uciScore <= VALUE_TB_LOSS_IN_MAX_PLY))
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sync_cout << main_manager()->pv(*this, threads, tt, rootDepth) << sync_endl;
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}
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if (!threads.stop)
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completedDepth = rootDepth;
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// We make sure not to pick an unproven mated-in score,
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// in case this thread prematurely stopped search (aborted-search).
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if (threads.abortedSearch && rootMoves[0].score != -VALUE_INFINITE
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&& rootMoves[0].score <= VALUE_TB_LOSS_IN_MAX_PLY)
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{
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// Bring the last best move to the front for best thread selection.
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Utility::move_to_front(rootMoves, [&lastBestPV = std::as_const(lastBestPV)](
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const auto& rm) { return rm == lastBestPV[0]; });
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rootMoves[0].pv = lastBestPV;
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rootMoves[0].score = rootMoves[0].uciScore = lastBestScore;
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}
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else if (rootMoves[0].pv[0] != lastBestPV[0])
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{
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lastBestPV = rootMoves[0].pv;
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lastBestScore = rootMoves[0].score;
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lastBestMoveDepth = rootDepth;
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}
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// Have we found a "mate in x"?
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if (limits.mate && bestValue >= VALUE_MATE_IN_MAX_PLY
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&& VALUE_MATE - bestValue <= 2 * limits.mate)
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threads.stop = true;
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if (!mainThread)
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continue;
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// If the skill level is enabled and time is up, pick a sub-optimal best move
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if (skill.enabled() && skill.time_to_pick(rootDepth))
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skill.pick_best(rootMoves, multiPV);
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// Use part of the gained time from a previous stable move for the current move
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for (Thread* th : threads)
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{
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totBestMoveChanges += th->worker->bestMoveChanges;
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th->worker->bestMoveChanges = 0;
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}
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// Do we have time for the next iteration? Can we stop searching now?
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if (limits.use_time_management() && !threads.stop && !mainThread->stopOnPonderhit)
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{
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double fallingEval = (66 + 14 * (mainThread->bestPreviousAverageScore - bestValue)
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+ 6 * (mainThread->iterValue[iterIdx] - bestValue))
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/ 616.6;
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fallingEval = std::clamp(fallingEval, 0.51, 1.51);
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// If the bestMove is stable over several iterations, reduce time accordingly
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timeReduction = lastBestMoveDepth + 8 < completedDepth ? 1.56 : 0.69;
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double reduction = (1.4 + mainThread->previousTimeReduction) / (2.17 * timeReduction);
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double bestMoveInstability = 1 + 1.79 * totBestMoveChanges / threads.size();
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double totalTime =
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mainThread->tm.optimum() * fallingEval * reduction * bestMoveInstability;
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// Cap used time in case of a single legal move for a better viewer experience
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if (rootMoves.size() == 1)
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totalTime = std::min(500.0, totalTime);
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// Stop the search if we have exceeded the totalTime
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if (mainThread->tm.elapsed(threads.nodes_searched()) > totalTime)
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{
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// If we are allowed to ponder do not stop the search now but
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// keep pondering until the GUI sends "ponderhit" or "stop".
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if (mainThread->ponder)
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mainThread->stopOnPonderhit = true;
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else
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threads.stop = true;
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}
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else if (!mainThread->ponder
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&& mainThread->tm.elapsed(threads.nodes_searched()) > totalTime * 0.50)
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threads.increaseDepth = false;
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else
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threads.increaseDepth = true;
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}
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mainThread->iterValue[iterIdx] = bestValue;
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iterIdx = (iterIdx + 1) & 3;
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}
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if (!mainThread)
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return;
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mainThread->previousTimeReduction = timeReduction;
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// If the skill level is enabled, swap the best PV line with the sub-optimal one
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if (skill.enabled())
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std::swap(rootMoves[0],
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*std::find(rootMoves.begin(), rootMoves.end(),
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skill.best ? skill.best : skill.pick_best(rootMoves, multiPV)));
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}
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void Search::Worker::clear() {
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counterMoves.fill(Move::none());
|
|
mainHistory.fill(0);
|
|
captureHistory.fill(0);
|
|
pawnHistory.fill(0);
|
|
correctionHistory.fill(0);
|
|
|
|
for (bool inCheck : {false, true})
|
|
for (StatsType c : {NoCaptures, Captures})
|
|
for (auto& to : continuationHistory[inCheck][c])
|
|
for (auto& h : to)
|
|
h->fill(-71);
|
|
|
|
for (size_t i = 1; i < reductions.size(); ++i)
|
|
reductions[i] = int((20.37 + std::log(size_t(options["Threads"])) / 2) * std::log(i));
|
|
}
|
|
|
|
|
|
// Main search function for both PV and non-PV nodes.
|
|
template<NodeType nodeType>
|
|
Value Search::Worker::search(
|
|
Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
|
|
|
|
constexpr bool PvNode = nodeType != NonPV;
|
|
constexpr bool rootNode = nodeType == Root;
|
|
|
|
// Dive into quiescence search when the depth reaches zero
|
|
if (depth <= 0)
|
|
return qsearch < PvNode ? PV : NonPV > (pos, ss, alpha, beta);
|
|
|
|
// Check if we have an upcoming move that draws by repetition, or
|
|
// if the opponent had an alternative move earlier to this position.
|
|
if (!rootNode && alpha < VALUE_DRAW && pos.has_game_cycle(ss->ply))
|
|
{
|
|
alpha = value_draw(this->nodes);
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
|
|
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
|
|
assert(PvNode || (alpha == beta - 1));
|
|
assert(0 < depth && depth < MAX_PLY);
|
|
assert(!(PvNode && cutNode));
|
|
|
|
Move pv[MAX_PLY + 1], capturesSearched[32], quietsSearched[32];
|
|
StateInfo st;
|
|
ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
|
|
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, excludedMove, bestMove;
|
|
Depth extension, newDepth;
|
|
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
|
|
bool givesCheck, improving, priorCapture;
|
|
bool capture, moveCountPruning, ttCapture;
|
|
Piece movedPiece;
|
|
int moveCount, captureCount, quietCount;
|
|
|
|
// Step 1. Initialize node
|
|
Worker* thisThread = this;
|
|
ss->inCheck = pos.checkers();
|
|
priorCapture = pos.captured_piece();
|
|
Color us = pos.side_to_move();
|
|
moveCount = captureCount = quietCount = ss->moveCount = 0;
|
|
bestValue = -VALUE_INFINITE;
|
|
maxValue = VALUE_INFINITE;
|
|
|
|
// Check for the available remaining time
|
|
if (is_mainthread())
|
|
main_manager()->check_time(*thisThread);
|
|
|
|
// Used to send selDepth info to GUI (selDepth counts from 1, ply from 0)
|
|
if (PvNode && thisThread->selDepth < ss->ply + 1)
|
|
thisThread->selDepth = ss->ply + 1;
|
|
|
|
if (!rootNode)
|
|
{
|
|
// Step 2. Check for aborted search and immediate draw
|
|
if (threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply)
|
|
|| ss->ply >= MAX_PLY)
|
|
return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos, thisThread->optimism[us])
|
|
: value_draw(thisThread->nodes);
|
|
|
|
// Step 3. Mate distance pruning. Even if we mate at the next move our score
|
|
// would be at best mate_in(ss->ply + 1), but if alpha is already bigger because
|
|
// a shorter mate was found upward in the tree then there is no need to search
|
|
// because we will never beat the current alpha. Same logic but with reversed
|
|
// signs apply also in the opposite condition of being mated instead of giving
|
|
// mate. In this case, return a fail-high score.
|
|
alpha = std::max(mated_in(ss->ply), alpha);
|
|
beta = std::min(mate_in(ss->ply + 1), beta);
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
else
|
|
thisThread->rootDelta = beta - alpha;
|
|
|
|
assert(0 <= ss->ply && ss->ply < MAX_PLY);
|
|
|
|
(ss + 1)->excludedMove = bestMove = Move::none();
|
|
(ss + 2)->killers[0] = (ss + 2)->killers[1] = Move::none();
|
|
(ss + 2)->cutoffCnt = 0;
|
|
ss->multipleExtensions = (ss - 1)->multipleExtensions;
|
|
Square prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
|
|
ss->statScore = 0;
|
|
|
|
// Step 4. Transposition table lookup.
|
|
excludedMove = ss->excludedMove;
|
|
posKey = pos.key();
|
|
tte = tt.probe(posKey, ss->ttHit);
|
|
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
|
|
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
|
|
: ss->ttHit ? tte->move()
|
|
: Move::none();
|
|
ttCapture = ttMove && pos.capture_stage(ttMove);
|
|
|
|
// At this point, if excluded, skip straight to step 6, static eval. However,
|
|
// to save indentation, we list the condition in all code between here and there.
|
|
if (!excludedMove)
|
|
ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
|
|
|
|
// At non-PV nodes we check for an early TT cutoff
|
|
if (!PvNode && !excludedMove && tte->depth() > depth
|
|
&& ttValue != VALUE_NONE // Possible in case of TT access race or if !ttHit
|
|
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
|
|
{
|
|
// If ttMove is quiet, update move sorting heuristics on TT hit (~2 Elo)
|
|
if (ttMove)
|
|
{
|
|
if (ttValue >= beta)
|
|
{
|
|
// Bonus for a quiet ttMove that fails high (~2 Elo)
|
|
if (!ttCapture)
|
|
update_quiet_stats(pos, ss, *this, ttMove, stat_bonus(depth));
|
|
|
|
// Extra penalty for early quiet moves of
|
|
// the previous ply (~0 Elo on STC, ~2 Elo on LTC).
|
|
if (prevSq != SQ_NONE && (ss - 1)->moveCount <= 2 && !priorCapture)
|
|
update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
|
|
-stat_malus(depth + 1));
|
|
}
|
|
// Penalty for a quiet ttMove that fails low (~1 Elo)
|
|
else if (!ttCapture)
|
|
{
|
|
int penalty = -stat_malus(depth);
|
|
thisThread->mainHistory[us][ttMove.from_to()] << penalty;
|
|
update_continuation_histories(ss, pos.moved_piece(ttMove), ttMove.to_sq(), penalty);
|
|
}
|
|
}
|
|
|
|
// Partial workaround for the graph history interaction problem
|
|
// For high rule50 counts don't produce transposition table cutoffs.
|
|
if (pos.rule50_count() < 90)
|
|
return ttValue >= beta && std::abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY
|
|
? (ttValue * 3 + beta) / 4
|
|
: ttValue;
|
|
}
|
|
|
|
// Step 5. Tablebases probe
|
|
if (!rootNode && !excludedMove && tbConfig.cardinality)
|
|
{
|
|
int piecesCount = pos.count<ALL_PIECES>();
|
|
|
|
if (piecesCount <= tbConfig.cardinality
|
|
&& (piecesCount < tbConfig.cardinality || depth >= tbConfig.probeDepth)
|
|
&& pos.rule50_count() == 0 && !pos.can_castle(ANY_CASTLING))
|
|
{
|
|
TB::ProbeState err;
|
|
TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err);
|
|
|
|
// Force check of time on the next occasion
|
|
if (is_mainthread())
|
|
main_manager()->callsCnt = 0;
|
|
|
|
if (err != TB::ProbeState::FAIL)
|
|
{
|
|
thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
|
|
|
|
int drawScore = tbConfig.useRule50 ? 1 : 0;
|
|
|
|
Value tbValue = VALUE_TB - ss->ply;
|
|
|
|
// use the range VALUE_TB to VALUE_TB_WIN_IN_MAX_PLY to score
|
|
value = wdl < -drawScore ? -tbValue
|
|
: wdl > drawScore ? tbValue
|
|
: VALUE_DRAW + 2 * wdl * drawScore;
|
|
|
|
Bound b = wdl < -drawScore ? BOUND_UPPER
|
|
: wdl > drawScore ? BOUND_LOWER
|
|
: BOUND_EXACT;
|
|
|
|
if (b == BOUND_EXACT || (b == BOUND_LOWER ? value >= beta : value <= alpha))
|
|
{
|
|
tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, b,
|
|
std::min(MAX_PLY - 1, depth + 6), Move::none(), VALUE_NONE,
|
|
tt.generation());
|
|
|
|
return value;
|
|
}
|
|
|
|
if (PvNode)
|
|
{
|
|
if (b == BOUND_LOWER)
|
|
bestValue = value, alpha = std::max(alpha, bestValue);
|
|
else
|
|
maxValue = value;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Step 6. Static evaluation of the position
|
|
Value unadjustedStaticEval = VALUE_NONE;
|
|
if (ss->inCheck)
|
|
{
|
|
// Skip early pruning when in check
|
|
ss->staticEval = eval = VALUE_NONE;
|
|
improving = false;
|
|
goto moves_loop;
|
|
}
|
|
else if (excludedMove)
|
|
{
|
|
// Providing the hint that this node's accumulator will be used often
|
|
// brings significant Elo gain (~13 Elo).
|
|
Eval::NNUE::hint_common_parent_position(pos);
|
|
unadjustedStaticEval = eval = ss->staticEval;
|
|
}
|
|
else if (ss->ttHit)
|
|
{
|
|
// Never assume anything about values stored in TT
|
|
unadjustedStaticEval = tte->eval();
|
|
if (unadjustedStaticEval == VALUE_NONE)
|
|
unadjustedStaticEval = evaluate(pos, thisThread->optimism[us]);
|
|
else if (PvNode)
|
|
Eval::NNUE::hint_common_parent_position(pos);
|
|
|
|
ss->staticEval = eval = to_corrected_static_eval(unadjustedStaticEval, *thisThread, pos);
|
|
|
|
// ttValue can be used as a better position evaluation (~7 Elo)
|
|
if (ttValue != VALUE_NONE && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
|
|
eval = ttValue;
|
|
}
|
|
else
|
|
{
|
|
unadjustedStaticEval = evaluate(pos, thisThread->optimism[us]);
|
|
ss->staticEval = eval = to_corrected_static_eval(unadjustedStaticEval, *thisThread, pos);
|
|
|
|
// Static evaluation is saved as it was before adjustment by correction history
|
|
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, Move::none(),
|
|
unadjustedStaticEval, tt.generation());
|
|
}
|
|
|
|
// Use static evaluation difference to improve quiet move ordering (~9 Elo)
|
|
if (((ss - 1)->currentMove).is_ok() && !(ss - 1)->inCheck && !priorCapture)
|
|
{
|
|
int bonus = std::clamp(-14 * int((ss - 1)->staticEval + ss->staticEval), -1661, 1495);
|
|
bonus = bonus > 0 ? 2 * bonus : bonus / 2;
|
|
thisThread->mainHistory[~us][((ss - 1)->currentMove).from_to()] << bonus;
|
|
if (type_of(pos.piece_on(prevSq)) != PAWN && ((ss - 1)->currentMove).type_of() != PROMOTION)
|
|
thisThread->pawnHistory[pawn_structure_index(pos)][pos.piece_on(prevSq)][prevSq]
|
|
<< bonus / 4;
|
|
}
|
|
|
|
// Set up the improving flag, which is true if current static evaluation is
|
|
// bigger than the previous static evaluation at our turn (if we were in
|
|
// check at our previous move we look at static evaluation at move prior to it
|
|
// and if we were in check at move prior to it flag is set to true) and is
|
|
// false otherwise. The improving flag is used in various pruning heuristics.
|
|
improving = (ss - 2)->staticEval != VALUE_NONE
|
|
? ss->staticEval > (ss - 2)->staticEval
|
|
: (ss - 4)->staticEval != VALUE_NONE && ss->staticEval > (ss - 4)->staticEval;
|
|
|
|
// Step 7. Razoring (~1 Elo)
|
|
// If eval is really low check with qsearch if it can exceed alpha, if it can't,
|
|
// return a fail low.
|
|
// Adjust razor margin according to cutoffCnt. (~1 Elo)
|
|
if (eval < alpha - 450 - (332 - 160 * ((ss + 1)->cutoffCnt > 3)) * depth * depth)
|
|
{
|
|
value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
|
|
if (value < alpha)
|
|
return value;
|
|
}
|
|
|
|
// Step 8. Futility pruning: child node (~40 Elo)
|
|
// The depth condition is important for mate finding.
|
|
if (!ss->ttPv && depth < 11
|
|
&& eval - futility_margin(depth, cutNode && !ss->ttHit, improving)
|
|
- (ss - 1)->statScore / 327
|
|
>= beta
|
|
&& eval >= beta && eval < 28702 // smaller than TB wins
|
|
&& (!ttMove || ttCapture))
|
|
return beta > VALUE_TB_LOSS_IN_MAX_PLY ? (eval + beta) / 2 : eval;
|
|
|
|
// Step 9. Null move search with verification search (~35 Elo)
|
|
if (!PvNode && (ss - 1)->currentMove != Move::null() && (ss - 1)->statScore < 17379
|
|
&& eval >= beta && eval >= ss->staticEval && ss->staticEval >= beta - 21 * depth + 329
|
|
&& !excludedMove && pos.non_pawn_material(us) && ss->ply >= thisThread->nmpMinPly
|
|
&& beta > VALUE_TB_LOSS_IN_MAX_PLY)
|
|
{
|
|
assert(eval - beta >= 0);
|
|
|
|
// Null move dynamic reduction based on depth and eval
|
|
Depth R = std::min(int(eval - beta) / 148, 6) + depth / 3 + 4;
|
|
|
|
ss->currentMove = Move::null();
|
|
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
|
|
|
|
pos.do_null_move(st, tt);
|
|
|
|
Value nullValue = -search<NonPV>(pos, ss + 1, -beta, -beta + 1, depth - R, !cutNode);
|
|
|
|
pos.undo_null_move();
|
|
|
|
// Do not return unproven mate or TB scores
|
|
if (nullValue >= beta && nullValue < VALUE_TB_WIN_IN_MAX_PLY)
|
|
{
|
|
if (thisThread->nmpMinPly || depth < 16)
|
|
return nullValue;
|
|
|
|
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
|
|
|
|
// Do verification search at high depths, with null move pruning disabled
|
|
// until ply exceeds nmpMinPly.
|
|
thisThread->nmpMinPly = ss->ply + 3 * (depth - R) / 4;
|
|
|
|
Value v = search<NonPV>(pos, ss, beta - 1, beta, depth - R, false);
|
|
|
|
thisThread->nmpMinPly = 0;
|
|
|
|
if (v >= beta)
|
|
return nullValue;
|
|
}
|
|
}
|
|
|
|
// Step 10. Internal iterative reductions (~9 Elo)
|
|
// For PV nodes without a ttMove, we decrease depth by 2,
|
|
// or by 4 if the current position is present in the TT and
|
|
// the stored depth is greater than or equal to the current depth.
|
|
// Use qsearch if depth <= 0.
|
|
if (PvNode && !ttMove)
|
|
depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
|
|
|
|
if (depth <= 0)
|
|
return qsearch<PV>(pos, ss, alpha, beta);
|
|
|
|
// For cutNodes without a ttMove, we decrease depth by 2 if depth is high enough.
|
|
if (cutNode && depth >= 8 && !ttMove)
|
|
depth -= 2;
|
|
|
|
// Step 11. ProbCut (~10 Elo)
|
|
// If we have a good enough capture (or queen promotion) and a reduced search returns a value
|
|
// much above beta, we can (almost) safely prune the previous move.
|
|
probCutBeta = beta + 182 - 68 * improving;
|
|
if (
|
|
!PvNode && depth > 3
|
|
&& std::abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
|
|
// If value from transposition table is lower than probCutBeta, don't attempt probCut
|
|
// there and in further interactions with transposition table cutoff depth is set to depth - 3
|
|
// because probCut search has depth set to depth - 4 but we also do a move before it
|
|
// So effective depth is equal to depth - 3
|
|
&& !(tte->depth() >= depth - 3 && ttValue != VALUE_NONE && ttValue < probCutBeta))
|
|
{
|
|
assert(probCutBeta < VALUE_INFINITE && probCutBeta > beta);
|
|
|
|
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &thisThread->captureHistory);
|
|
|
|
while ((move = mp.next_move()) != Move::none())
|
|
if (move != excludedMove && pos.legal(move))
|
|
{
|
|
assert(pos.capture_stage(move));
|
|
|
|
// Prefetch the TT entry for the resulting position
|
|
prefetch(tt.first_entry(pos.key_after(move)));
|
|
|
|
ss->currentMove = move;
|
|
ss->continuationHistory =
|
|
&this
|
|
->continuationHistory[ss->inCheck][true][pos.moved_piece(move)][move.to_sq()];
|
|
|
|
thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
|
|
pos.do_move(move, st);
|
|
|
|
// Perform a preliminary qsearch to verify that the move holds
|
|
value = -qsearch<NonPV>(pos, ss + 1, -probCutBeta, -probCutBeta + 1);
|
|
|
|
// If the qsearch held, perform the regular search
|
|
if (value >= probCutBeta)
|
|
value = -search<NonPV>(pos, ss + 1, -probCutBeta, -probCutBeta + 1, depth - 4,
|
|
!cutNode);
|
|
|
|
pos.undo_move(move);
|
|
|
|
if (value >= probCutBeta)
|
|
{
|
|
// Save ProbCut data into transposition table
|
|
tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, BOUND_LOWER, depth - 3,
|
|
move, unadjustedStaticEval, tt.generation());
|
|
return std::abs(value) < VALUE_TB_WIN_IN_MAX_PLY ? value - (probCutBeta - beta)
|
|
: value;
|
|
}
|
|
}
|
|
|
|
Eval::NNUE::hint_common_parent_position(pos);
|
|
}
|
|
|
|
moves_loop: // When in check, search starts here
|
|
|
|
// Step 12. A small Probcut idea, when we are in check (~4 Elo)
|
|
probCutBeta = beta + 446;
|
|
if (ss->inCheck && !PvNode && ttCapture && (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 4 && ttValue >= probCutBeta
|
|
&& std::abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY && std::abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
|
|
return probCutBeta;
|
|
|
|
const PieceToHistory* contHist[] = {(ss - 1)->continuationHistory,
|
|
(ss - 2)->continuationHistory,
|
|
(ss - 3)->continuationHistory,
|
|
(ss - 4)->continuationHistory,
|
|
nullptr,
|
|
(ss - 6)->continuationHistory};
|
|
|
|
Move countermove =
|
|
prevSq != SQ_NONE ? thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] : Move::none();
|
|
|
|
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory,
|
|
contHist, &thisThread->pawnHistory, countermove, ss->killers);
|
|
|
|
value = bestValue;
|
|
moveCountPruning = false;
|
|
|
|
// Step 13. Loop through all pseudo-legal moves until no moves remain
|
|
// or a beta cutoff occurs.
|
|
while ((move = mp.next_move(moveCountPruning)) != Move::none())
|
|
{
|
|
assert(move.is_ok());
|
|
|
|
if (move == excludedMove)
|
|
continue;
|
|
|
|
// Check for legality
|
|
if (!pos.legal(move))
|
|
continue;
|
|
|
|
// At root obey the "searchmoves" option and skip moves not listed in Root
|
|
// Move List. In MultiPV mode we also skip PV moves that have been already
|
|
// searched and those of lower "TB rank" if we are in a TB root position.
|
|
if (rootNode
|
|
&& !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx,
|
|
thisThread->rootMoves.begin() + thisThread->pvLast, move))
|
|
continue;
|
|
|
|
ss->moveCount = ++moveCount;
|
|
|
|
if (rootNode && is_mainthread()
|
|
&& main_manager()->tm.elapsed(threads.nodes_searched()) > 3000)
|
|
sync_cout << "info depth " << depth << " currmove "
|
|
<< UCI::move(move, pos.is_chess960()) << " currmovenumber "
|
|
<< moveCount + thisThread->pvIdx << sync_endl;
|
|
if (PvNode)
|
|
(ss + 1)->pv = nullptr;
|
|
|
|
extension = 0;
|
|
capture = pos.capture_stage(move);
|
|
movedPiece = pos.moved_piece(move);
|
|
givesCheck = pos.gives_check(move);
|
|
|
|
// Calculate new depth for this move
|
|
newDepth = depth - 1;
|
|
|
|
int delta = beta - alpha;
|
|
|
|
Depth r = reduction(improving, depth, moveCount, delta);
|
|
|
|
// Step 14. Pruning at shallow depth (~120 Elo).
|
|
// Depth conditions are important for mate finding.
|
|
if (!rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
|
|
{
|
|
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~8 Elo)
|
|
if (!moveCountPruning)
|
|
moveCountPruning = moveCount >= futility_move_count(improving, depth);
|
|
|
|
// Reduced depth of the next LMR search
|
|
int lmrDepth = newDepth - r;
|
|
|
|
if (capture || givesCheck)
|
|
{
|
|
// Futility pruning for captures (~2 Elo)
|
|
if (!givesCheck && lmrDepth < 7 && !ss->inCheck)
|
|
{
|
|
Piece capturedPiece = pos.piece_on(move.to_sq());
|
|
int futilityEval =
|
|
ss->staticEval + 279 + 295 * lmrDepth + PieceValue[capturedPiece]
|
|
+ thisThread->captureHistory[movedPiece][move.to_sq()][type_of(capturedPiece)]
|
|
/ 7;
|
|
if (futilityEval < alpha)
|
|
continue;
|
|
}
|
|
|
|
// SEE based pruning for captures and checks (~11 Elo)
|
|
if (!pos.see_ge(move, -204 * depth))
|
|
continue;
|
|
}
|
|
else
|
|
{
|
|
int history =
|
|
(*contHist[0])[movedPiece][move.to_sq()]
|
|
+ (*contHist[1])[movedPiece][move.to_sq()]
|
|
+ (*contHist[3])[movedPiece][move.to_sq()]
|
|
+ thisThread->pawnHistory[pawn_structure_index(pos)][movedPiece][move.to_sq()];
|
|
|
|
// Continuation history based pruning (~2 Elo)
|
|
if (lmrDepth < 6 && history < -4215 * depth)
|
|
continue;
|
|
|
|
history += 2 * thisThread->mainHistory[us][move.from_to()];
|
|
|
|
lmrDepth += history / 6658;
|
|
|
|
// Futility pruning: parent node (~13 Elo)
|
|
if (!ss->inCheck && lmrDepth < 15
|
|
&& ss->staticEval + (bestValue < ss->staticEval - 58 ? 139 : 55)
|
|
+ 121 * lmrDepth
|
|
<= alpha)
|
|
continue;
|
|
|
|
lmrDepth = std::max(lmrDepth, 0);
|
|
|
|
// Prune moves with negative SEE (~4 Elo)
|
|
if (!pos.see_ge(move, -26 * lmrDepth * lmrDepth))
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Step 15. Extensions (~100 Elo)
|
|
// We take care to not overdo to avoid search getting stuck.
|
|
if (ss->ply < thisThread->rootDepth * 2)
|
|
{
|
|
// Singular extension search (~94 Elo). If all moves but one fail low on a
|
|
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
|
|
// then that move is singular and should be extended. To verify this we do
|
|
// a reduced search on the position excluding the ttMove and if the result
|
|
// is lower than ttValue minus a margin, then we will extend the ttMove.
|
|
|
|
// Note: the depth margin and singularBeta margin are known for having non-linear
|
|
// scaling. Their values are optimized to time controls of 180+1.8 and longer
|
|
// so changing them requires tests at these types of time controls.
|
|
// Recursive singular search is avoided.
|
|
if (!rootNode && move == ttMove && !excludedMove
|
|
&& depth >= 4 - (thisThread->completedDepth > 29) + ss->ttPv
|
|
&& std::abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY && (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 3)
|
|
{
|
|
Value singularBeta = ttValue - (62 + 52 * (ss->ttPv && !PvNode)) * depth / 64;
|
|
Depth singularDepth = newDepth / 2;
|
|
|
|
ss->excludedMove = move;
|
|
value =
|
|
search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
|
|
ss->excludedMove = Move::none();
|
|
|
|
if (value < singularBeta)
|
|
{
|
|
extension = 1;
|
|
|
|
// We make sure to limit the extensions in some way to avoid a search explosion
|
|
if (!PvNode && ss->multipleExtensions <= 16)
|
|
{
|
|
extension = 2 + (value < singularBeta - 78 && !ttCapture);
|
|
depth += depth < 16;
|
|
}
|
|
}
|
|
|
|
// Multi-cut pruning
|
|
// Our ttMove is assumed to fail high based on the bound of the TT entry,
|
|
// and if after excluding the ttMove with a reduced search we fail high over the original beta,
|
|
// we assume this expected cut-node is not singular (multiple moves fail high),
|
|
// and we can prune the whole subtree by returning a softbound.
|
|
else if (singularBeta >= beta)
|
|
return singularBeta;
|
|
|
|
// Negative extensions
|
|
// If other moves failed high over (ttValue - margin) without the ttMove on a reduced search,
|
|
// but we cannot do multi-cut because (ttValue - margin) is lower than the original beta,
|
|
// we do not know if the ttMove is singular or can do a multi-cut,
|
|
// so we reduce the ttMove in favor of other moves based on some conditions:
|
|
|
|
// If the ttMove is assumed to fail high over current beta (~7 Elo)
|
|
else if (ttValue >= beta)
|
|
extension = -2 - !PvNode;
|
|
|
|
// If we are on a cutNode but the ttMove is not assumed to fail high over current beta (~1 Elo)
|
|
else if (cutNode)
|
|
extension = -2;
|
|
|
|
// If the ttMove is assumed to fail low over the value of the reduced search (~1 Elo)
|
|
else if (ttValue <= value)
|
|
extension = -1;
|
|
}
|
|
|
|
// Recapture extensions (~1 Elo)
|
|
else if (PvNode && move == ttMove && move.to_sq() == prevSq
|
|
&& thisThread->captureHistory[movedPiece][move.to_sq()]
|
|
[type_of(pos.piece_on(move.to_sq()))]
|
|
> 4356)
|
|
extension = 1;
|
|
}
|
|
|
|
// Add extension to new depth
|
|
newDepth += extension;
|
|
ss->multipleExtensions = (ss - 1)->multipleExtensions + (extension >= 2);
|
|
|
|
// Speculative prefetch as early as possible
|
|
prefetch(tt.first_entry(pos.key_after(move)));
|
|
|
|
// Update the current move (this must be done after singular extension search)
|
|
ss->currentMove = move;
|
|
ss->continuationHistory =
|
|
&thisThread->continuationHistory[ss->inCheck][capture][movedPiece][move.to_sq()];
|
|
|
|
// Step 16. Make the move
|
|
thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
|
|
pos.do_move(move, st, givesCheck);
|
|
|
|
// Decrease reduction if position is or has been on the PV (~5 Elo)
|
|
if (ss->ttPv)
|
|
r -= 1 + (ttValue > alpha) + (ttValue > beta && tte->depth() >= depth);
|
|
|
|
// Increase reduction for cut nodes (~4 Elo)
|
|
if (cutNode)
|
|
r += 2 - (tte->depth() >= depth && ss->ttPv);
|
|
|
|
// Increase reduction if ttMove is a capture (~3 Elo)
|
|
if (ttCapture)
|
|
r++;
|
|
|
|
// Decrease reduction for PvNodes (~3 Elo)
|
|
if (PvNode && tte->bound() != BOUND_UPPER)
|
|
r--;
|
|
|
|
// Increase reduction on repetition (~1 Elo)
|
|
if (move == (ss - 4)->currentMove && pos.has_repeated())
|
|
r += 2;
|
|
|
|
// Increase reduction if next ply has a lot of fail high (~5 Elo)
|
|
if ((ss + 1)->cutoffCnt > 3)
|
|
r++;
|
|
|
|
// Set reduction to 0 for first picked move (ttMove) (~2 Elo)
|
|
// Nullifies all previous reduction adjustments to ttMove and leaves only history to do them
|
|
else if (move == ttMove)
|
|
r = 0;
|
|
|
|
ss->statScore = 2 * thisThread->mainHistory[us][move.from_to()]
|
|
+ (*contHist[0])[movedPiece][move.to_sq()]
|
|
+ (*contHist[1])[movedPiece][move.to_sq()]
|
|
+ (*contHist[3])[movedPiece][move.to_sq()] - 4409;
|
|
|
|
// Decrease/increase reduction for moves with a good/bad history (~8 Elo)
|
|
r -= ss->statScore / 14894;
|
|
|
|
// Step 17. Late moves reduction / extension (LMR, ~117 Elo)
|
|
if (depth >= 2 && moveCount > 1 + rootNode)
|
|
{
|
|
// In general we want to cap the LMR depth search at newDepth, but when
|
|
// reduction is negative, we allow this move a limited search extension
|
|
// beyond the first move depth. This may lead to hidden multiple extensions.
|
|
// To prevent problems when the max value is less than the min value,
|
|
// std::clamp has been replaced by a more robust implementation.
|
|
Depth d = std::max(1, std::min(newDepth - r, newDepth + 1));
|
|
|
|
value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, d, true);
|
|
|
|
// Do a full-depth search when reduced LMR search fails high
|
|
if (value > alpha && d < newDepth)
|
|
{
|
|
// Adjust full-depth search based on LMR results - if the result
|
|
// was good enough search deeper, if it was bad enough search shallower.
|
|
const bool doDeeperSearch = value > (bestValue + 49 + 2 * newDepth); // (~1 Elo)
|
|
const bool doShallowerSearch = value < bestValue + newDepth; // (~2 Elo)
|
|
|
|
newDepth += doDeeperSearch - doShallowerSearch;
|
|
|
|
if (newDepth > d)
|
|
value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth, !cutNode);
|
|
|
|
// Post LMR continuation history updates (~1 Elo)
|
|
int bonus = value <= alpha ? -stat_malus(newDepth)
|
|
: value >= beta ? stat_bonus(newDepth)
|
|
: 0;
|
|
|
|
update_continuation_histories(ss, movedPiece, move.to_sq(), bonus);
|
|
}
|
|
}
|
|
|
|
// Step 18. Full-depth search when LMR is skipped
|
|
else if (!PvNode || moveCount > 1)
|
|
{
|
|
// Increase reduction if ttMove is not present (~1 Elo)
|
|
if (!ttMove)
|
|
r += 2;
|
|
|
|
// Note that if expected reduction is high, we reduce search depth by 1 here (~9 Elo)
|
|
value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth - (r > 3), !cutNode);
|
|
}
|
|
|
|
// For PV nodes only, do a full PV search on the first move or after a fail high,
|
|
// otherwise let the parent node fail low with value <= alpha and try another move.
|
|
if (PvNode && (moveCount == 1 || value > alpha))
|
|
{
|
|
(ss + 1)->pv = pv;
|
|
(ss + 1)->pv[0] = Move::none();
|
|
|
|
value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, false);
|
|
}
|
|
|
|
// Step 19. Undo move
|
|
pos.undo_move(move);
|
|
|
|
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
|
|
|
|
// Step 20. Check for a new best move
|
|
// Finished searching the move. If a stop occurred, the return value of
|
|
// the search cannot be trusted, and we return immediately without
|
|
// updating best move, PV and TT.
|
|
if (threads.stop.load(std::memory_order_relaxed))
|
|
return VALUE_ZERO;
|
|
|
|
if (rootNode)
|
|
{
|
|
RootMove& rm =
|
|
*std::find(thisThread->rootMoves.begin(), thisThread->rootMoves.end(), move);
|
|
|
|
rm.averageScore =
|
|
rm.averageScore != -VALUE_INFINITE ? (2 * value + rm.averageScore) / 3 : value;
|
|
|
|
// PV move or new best move?
|
|
if (moveCount == 1 || value > alpha)
|
|
{
|
|
rm.score = rm.uciScore = value;
|
|
rm.selDepth = thisThread->selDepth;
|
|
rm.scoreLowerbound = rm.scoreUpperbound = false;
|
|
|
|
if (value >= beta)
|
|
{
|
|
rm.scoreLowerbound = true;
|
|
rm.uciScore = beta;
|
|
}
|
|
else if (value <= alpha)
|
|
{
|
|
rm.scoreUpperbound = true;
|
|
rm.uciScore = alpha;
|
|
}
|
|
|
|
rm.pv.resize(1);
|
|
|
|
assert((ss + 1)->pv);
|
|
|
|
for (Move* m = (ss + 1)->pv; *m != Move::none(); ++m)
|
|
rm.pv.push_back(*m);
|
|
|
|
// We record how often the best move has been changed in each iteration.
|
|
// This information is used for time management. In MultiPV mode,
|
|
// we must take care to only do this for the first PV line.
|
|
if (moveCount > 1 && !thisThread->pvIdx)
|
|
++thisThread->bestMoveChanges;
|
|
}
|
|
else
|
|
// All other moves but the PV, are set to the lowest value: this
|
|
// is not a problem when sorting because the sort is stable and the
|
|
// move position in the list is preserved - just the PV is pushed up.
|
|
rm.score = -VALUE_INFINITE;
|
|
}
|
|
|
|
if (value > bestValue)
|
|
{
|
|
bestValue = value;
|
|
|
|
if (value > alpha)
|
|
{
|
|
bestMove = move;
|
|
|
|
if (PvNode && !rootNode) // Update pv even in fail-high case
|
|
update_pv(ss->pv, move, (ss + 1)->pv);
|
|
|
|
if (value >= beta)
|
|
{
|
|
ss->cutoffCnt += 1 + !ttMove;
|
|
assert(value >= beta); // Fail high
|
|
break;
|
|
}
|
|
else
|
|
{
|
|
// Reduce other moves if we have found at least one score improvement (~2 Elo)
|
|
if (depth > 2 && depth < 13 && beta < 13710 && value > -12589)
|
|
depth -= 2;
|
|
|
|
assert(depth > 0);
|
|
alpha = value; // Update alpha! Always alpha < beta
|
|
}
|
|
}
|
|
}
|
|
|
|
// If the move is worse than some previously searched move,
|
|
// remember it, to update its stats later.
|
|
if (move != bestMove && moveCount <= 32)
|
|
{
|
|
if (capture)
|
|
capturesSearched[captureCount++] = move;
|
|
else
|
|
quietsSearched[quietCount++] = move;
|
|
}
|
|
}
|
|
|
|
// Step 21. Check for mate and stalemate
|
|
// All legal moves have been searched and if there are no legal moves, it
|
|
// must be a mate or a stalemate. If we are in a singular extension search then
|
|
// return a fail low score.
|
|
|
|
assert(moveCount || !ss->inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
|
|
|
|
// Adjust best value for fail high cases at non-pv nodes
|
|
if (!PvNode && bestValue >= beta && std::abs(bestValue) < VALUE_TB_WIN_IN_MAX_PLY
|
|
&& std::abs(beta) < VALUE_TB_WIN_IN_MAX_PLY && std::abs(alpha) < VALUE_TB_WIN_IN_MAX_PLY)
|
|
bestValue = (bestValue * (depth + 2) + beta) / (depth + 3);
|
|
|
|
if (!moveCount)
|
|
bestValue = excludedMove ? alpha : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
|
|
|
|
// If there is a move that produces search value greater than alpha we update the stats of searched moves
|
|
else if (bestMove)
|
|
update_all_stats(pos, ss, *this, bestMove, bestValue, beta, prevSq, quietsSearched,
|
|
quietCount, capturesSearched, captureCount, depth);
|
|
|
|
// Bonus for prior countermove that caused the fail low
|
|
else if (!priorCapture && prevSq != SQ_NONE)
|
|
{
|
|
int bonus = (depth > 5) + (PvNode || cutNode) + ((ss - 1)->statScore < -15401)
|
|
+ ((ss - 1)->moveCount > 11);
|
|
update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
|
|
stat_bonus(depth) * bonus);
|
|
thisThread->mainHistory[~us][((ss - 1)->currentMove).from_to()]
|
|
<< stat_bonus(depth) * bonus / 2;
|
|
}
|
|
|
|
if (PvNode)
|
|
bestValue = std::min(bestValue, maxValue);
|
|
|
|
// If no good move is found and the previous position was ttPv, then the previous
|
|
// opponent move is probably good and the new position is added to the search tree. (~7 Elo)
|
|
if (bestValue <= alpha)
|
|
ss->ttPv = ss->ttPv || ((ss - 1)->ttPv && depth > 3);
|
|
|
|
// Write gathered information in transposition table
|
|
// Static evaluation is saved as it was before correction history
|
|
if (!excludedMove && !(rootNode && thisThread->pvIdx))
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), ss->ttPv,
|
|
bestValue >= beta ? BOUND_LOWER
|
|
: PvNode && bestMove ? BOUND_EXACT
|
|
: BOUND_UPPER,
|
|
depth, bestMove, unadjustedStaticEval, tt.generation());
|
|
|
|
// Adjust correction history
|
|
if (!ss->inCheck && (!bestMove || !pos.capture(bestMove))
|
|
&& !(bestValue >= beta && bestValue <= ss->staticEval)
|
|
&& !(!bestMove && bestValue >= ss->staticEval))
|
|
{
|
|
auto bonus = std::clamp(int(bestValue - ss->staticEval) * depth / 8,
|
|
-CORRECTION_HISTORY_LIMIT / 4, CORRECTION_HISTORY_LIMIT / 4);
|
|
thisThread->correctionHistory[us][pawn_structure_index<Correction>(pos)] << bonus;
|
|
}
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
|
|
// Quiescence search function, which is called by the main search
|
|
// function with zero depth, or recursively with further decreasing depth per call.
|
|
// (~155 Elo)
|
|
template<NodeType nodeType>
|
|
Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
|
|
|
|
static_assert(nodeType != Root);
|
|
constexpr bool PvNode = nodeType == PV;
|
|
|
|
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
|
|
assert(PvNode || (alpha == beta - 1));
|
|
assert(depth <= 0);
|
|
|
|
// Check if we have an upcoming move that draws by repetition, or if
|
|
// the opponent had an alternative move earlier to this position. (~1 Elo)
|
|
if (alpha < VALUE_DRAW && pos.has_game_cycle(ss->ply))
|
|
{
|
|
alpha = value_draw(this->nodes);
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
|
|
Move pv[MAX_PLY + 1];
|
|
StateInfo st;
|
|
ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
|
|
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, bestMove;
|
|
Depth ttDepth;
|
|
Value bestValue, value, ttValue, futilityValue, futilityBase;
|
|
bool pvHit, givesCheck, capture;
|
|
int moveCount;
|
|
Color us = pos.side_to_move();
|
|
|
|
// Step 1. Initialize node
|
|
if (PvNode)
|
|
{
|
|
(ss + 1)->pv = pv;
|
|
ss->pv[0] = Move::none();
|
|
}
|
|
|
|
Worker* thisThread = this;
|
|
bestMove = Move::none();
|
|
ss->inCheck = pos.checkers();
|
|
moveCount = 0;
|
|
|
|
// Used to send selDepth info to GUI (selDepth counts from 1, ply from 0)
|
|
if (PvNode && thisThread->selDepth < ss->ply + 1)
|
|
thisThread->selDepth = ss->ply + 1;
|
|
|
|
// Step 2. Check for an immediate draw or maximum ply reached
|
|
if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
|
|
return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos, thisThread->optimism[us])
|
|
: VALUE_DRAW;
|
|
|
|
assert(0 <= ss->ply && ss->ply < MAX_PLY);
|
|
|
|
// Decide the replacement and cutoff priority of the qsearch TT entries
|
|
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;
|
|
|
|
// Step 3. Transposition table lookup
|
|
posKey = pos.key();
|
|
tte = tt.probe(posKey, ss->ttHit);
|
|
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
|
|
ttMove = ss->ttHit ? tte->move() : Move::none();
|
|
pvHit = ss->ttHit && tte->is_pv();
|
|
|
|
// At non-PV nodes we check for an early TT cutoff
|
|
if (!PvNode && tte->depth() >= ttDepth
|
|
&& ttValue != VALUE_NONE // Only in case of TT access race or if !ttHit
|
|
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
|
|
return ttValue;
|
|
|
|
// Step 4. Static evaluation of the position
|
|
Value unadjustedStaticEval = VALUE_NONE;
|
|
if (ss->inCheck)
|
|
bestValue = futilityBase = -VALUE_INFINITE;
|
|
else
|
|
{
|
|
if (ss->ttHit)
|
|
{
|
|
// Never assume anything about values stored in TT
|
|
unadjustedStaticEval = tte->eval();
|
|
if (unadjustedStaticEval == VALUE_NONE)
|
|
unadjustedStaticEval = evaluate(pos, thisThread->optimism[us]);
|
|
ss->staticEval = bestValue =
|
|
to_corrected_static_eval(unadjustedStaticEval, *thisThread, pos);
|
|
|
|
// ttValue can be used as a better position evaluation (~13 Elo)
|
|
if (ttValue != VALUE_NONE
|
|
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
|
|
bestValue = ttValue;
|
|
}
|
|
else
|
|
{
|
|
// In case of null move search, use previous static eval with a different sign
|
|
unadjustedStaticEval = (ss - 1)->currentMove != Move::null()
|
|
? evaluate(pos, thisThread->optimism[us])
|
|
: -(ss - 1)->staticEval;
|
|
ss->staticEval = bestValue =
|
|
to_corrected_static_eval(unadjustedStaticEval, *thisThread, pos);
|
|
}
|
|
|
|
// Stand pat. Return immediately if static value is at least beta
|
|
if (bestValue >= beta)
|
|
{
|
|
if (!ss->ttHit)
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER, DEPTH_NONE,
|
|
Move::none(), unadjustedStaticEval, tt.generation());
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
if (bestValue > alpha)
|
|
alpha = bestValue;
|
|
|
|
futilityBase = ss->staticEval + 204;
|
|
}
|
|
|
|
const PieceToHistory* contHist[] = {(ss - 1)->continuationHistory,
|
|
(ss - 2)->continuationHistory};
|
|
|
|
// Initialize a MovePicker object for the current position, and prepare
|
|
// to search the moves. Because the depth is <= 0 here, only captures,
|
|
// queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
|
|
// will be generated.
|
|
Square prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
|
|
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory,
|
|
contHist, &thisThread->pawnHistory);
|
|
|
|
int quietCheckEvasions = 0;
|
|
|
|
// Step 5. Loop through all pseudo-legal moves until no moves remain
|
|
// or a beta cutoff occurs.
|
|
while ((move = mp.next_move()) != Move::none())
|
|
{
|
|
assert(move.is_ok());
|
|
|
|
// Check for legality
|
|
if (!pos.legal(move))
|
|
continue;
|
|
|
|
givesCheck = pos.gives_check(move);
|
|
capture = pos.capture_stage(move);
|
|
|
|
moveCount++;
|
|
|
|
// Step 6. Pruning
|
|
if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY && pos.non_pawn_material(us))
|
|
{
|
|
// Futility pruning and moveCount pruning (~10 Elo)
|
|
if (!givesCheck && move.to_sq() != prevSq && futilityBase > VALUE_TB_LOSS_IN_MAX_PLY
|
|
&& move.type_of() != PROMOTION)
|
|
{
|
|
if (moveCount > 2)
|
|
continue;
|
|
|
|
futilityValue = futilityBase + PieceValue[pos.piece_on(move.to_sq())];
|
|
|
|
// If static eval + value of piece we are going to capture is much lower
|
|
// than alpha we can prune this move. (~2 Elo)
|
|
if (futilityValue <= alpha)
|
|
{
|
|
bestValue = std::max(bestValue, futilityValue);
|
|
continue;
|
|
}
|
|
|
|
// If static eval is much lower than alpha and move is not winning material
|
|
// we can prune this move. (~2 Elo)
|
|
if (futilityBase <= alpha && !pos.see_ge(move, 1))
|
|
{
|
|
bestValue = std::max(bestValue, futilityBase);
|
|
continue;
|
|
}
|
|
|
|
// If static exchange evaluation is much worse than what is needed to not
|
|
// fall below alpha we can prune this move.
|
|
if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
|
|
{
|
|
bestValue = alpha;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// We prune after the second quiet check evasion move, where being 'in check' is
|
|
// implicitly checked through the counter, and being a 'quiet move' apart from
|
|
// being a tt move is assumed after an increment because captures are pushed ahead.
|
|
if (quietCheckEvasions > 1)
|
|
break;
|
|
|
|
// Continuation history based pruning (~3 Elo)
|
|
if (!capture && (*contHist[0])[pos.moved_piece(move)][move.to_sq()] < 0
|
|
&& (*contHist[1])[pos.moved_piece(move)][move.to_sq()] < 0)
|
|
continue;
|
|
|
|
// Do not search moves with bad enough SEE values (~5 Elo)
|
|
if (!pos.see_ge(move, -75))
|
|
continue;
|
|
}
|
|
|
|
// Speculative prefetch as early as possible
|
|
prefetch(tt.first_entry(pos.key_after(move)));
|
|
|
|
// Update the current move
|
|
ss->currentMove = move;
|
|
ss->continuationHistory =
|
|
&thisThread
|
|
->continuationHistory[ss->inCheck][capture][pos.moved_piece(move)][move.to_sq()];
|
|
|
|
quietCheckEvasions += !capture && ss->inCheck;
|
|
|
|
// Step 7. Make and search the move
|
|
thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
|
|
pos.do_move(move, st, givesCheck);
|
|
value = -qsearch<nodeType>(pos, ss + 1, -beta, -alpha, depth - 1);
|
|
pos.undo_move(move);
|
|
|
|
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
|
|
|
|
// Step 8. Check for a new best move
|
|
if (value > bestValue)
|
|
{
|
|
bestValue = value;
|
|
|
|
if (value > alpha)
|
|
{
|
|
bestMove = move;
|
|
|
|
if (PvNode) // Update pv even in fail-high case
|
|
update_pv(ss->pv, move, (ss + 1)->pv);
|
|
|
|
if (value < beta) // Update alpha here!
|
|
alpha = value;
|
|
else
|
|
break; // Fail high
|
|
}
|
|
}
|
|
}
|
|
|
|
// Step 9. Check for mate
|
|
// All legal moves have been searched. A special case: if we're in check
|
|
// and no legal moves were found, it is checkmate.
|
|
if (ss->inCheck && bestValue == -VALUE_INFINITE)
|
|
{
|
|
assert(!MoveList<LEGAL>(pos).size());
|
|
return mated_in(ss->ply); // Plies to mate from the root
|
|
}
|
|
|
|
if (std::abs(bestValue) < VALUE_TB_WIN_IN_MAX_PLY && bestValue >= beta)
|
|
bestValue = (3 * bestValue + beta) / 4;
|
|
|
|
// Save gathered info in transposition table
|
|
// Static evaluation is saved as it was before adjustment by correction history
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
|
|
bestValue >= beta ? BOUND_LOWER : BOUND_UPPER, ttDepth, bestMove,
|
|
unadjustedStaticEval, tt.generation());
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
Depth Search::Worker::reduction(bool i, Depth d, int mn, int delta) {
|
|
int reductionScale = reductions[d] * reductions[mn];
|
|
return (reductionScale + 1177 - delta * 776 / rootDelta) / 1024 + (!i && reductionScale > 842);
|
|
}
|
|
|
|
namespace {
|
|
// Adjusts a mate or TB score from "plies to mate from the root"
|
|
// to "plies to mate from the current position". Standard scores are unchanged.
|
|
// The function is called before storing a value in the transposition table.
|
|
Value value_to_tt(Value v, int ply) {
|
|
|
|
assert(v != VALUE_NONE);
|
|
return v >= VALUE_TB_WIN_IN_MAX_PLY ? v + ply : v <= VALUE_TB_LOSS_IN_MAX_PLY ? v - ply : v;
|
|
}
|
|
|
|
|
|
// Inverse of value_to_tt(): it adjusts a mate or TB score
|
|
// from the transposition table (which refers to the plies to mate/be mated from
|
|
// current position) to "plies to mate/be mated (TB win/loss) from the root".
|
|
// However, to avoid potentially false mate or TB scores related to the 50 moves rule
|
|
// and the graph history interaction, we return the highest non-TB score instead.
|
|
Value value_from_tt(Value v, int ply, int r50c) {
|
|
|
|
if (v == VALUE_NONE)
|
|
return VALUE_NONE;
|
|
|
|
// handle TB win or better
|
|
if (v >= VALUE_TB_WIN_IN_MAX_PLY)
|
|
{
|
|
// Downgrade a potentially false mate score
|
|
if (v >= VALUE_MATE_IN_MAX_PLY && VALUE_MATE - v > 100 - r50c)
|
|
return VALUE_TB_WIN_IN_MAX_PLY - 1;
|
|
|
|
// Downgrade a potentially false TB score.
|
|
if (VALUE_TB - v > 100 - r50c)
|
|
return VALUE_TB_WIN_IN_MAX_PLY - 1;
|
|
|
|
return v - ply;
|
|
}
|
|
|
|
// handle TB loss or worse
|
|
if (v <= VALUE_TB_LOSS_IN_MAX_PLY)
|
|
{
|
|
// Downgrade a potentially false mate score.
|
|
if (v <= VALUE_MATED_IN_MAX_PLY && VALUE_MATE + v > 100 - r50c)
|
|
return VALUE_TB_LOSS_IN_MAX_PLY + 1;
|
|
|
|
// Downgrade a potentially false TB score.
|
|
if (VALUE_TB + v > 100 - r50c)
|
|
return VALUE_TB_LOSS_IN_MAX_PLY + 1;
|
|
|
|
return v + ply;
|
|
}
|
|
|
|
return v;
|
|
}
|
|
|
|
|
|
// Adds current move and appends child pv[]
|
|
void update_pv(Move* pv, Move move, const Move* childPv) {
|
|
|
|
for (*pv++ = move; childPv && *childPv != Move::none();)
|
|
*pv++ = *childPv++;
|
|
*pv = Move::none();
|
|
}
|
|
|
|
|
|
// Updates stats at the end of search() when a bestMove is found
|
|
void update_all_stats(const Position& pos,
|
|
Stack* ss,
|
|
Search::Worker& workerThread,
|
|
Move bestMove,
|
|
Value bestValue,
|
|
Value beta,
|
|
Square prevSq,
|
|
Move* quietsSearched,
|
|
int quietCount,
|
|
Move* capturesSearched,
|
|
int captureCount,
|
|
Depth depth) {
|
|
|
|
Color us = pos.side_to_move();
|
|
CapturePieceToHistory& captureHistory = workerThread.captureHistory;
|
|
Piece moved_piece = pos.moved_piece(bestMove);
|
|
PieceType captured;
|
|
|
|
int quietMoveBonus = stat_bonus(depth + 1);
|
|
int quietMoveMalus = stat_malus(depth);
|
|
|
|
if (!pos.capture_stage(bestMove))
|
|
{
|
|
int bestMoveBonus = bestValue > beta + 167 ? quietMoveBonus // larger bonus
|
|
: stat_bonus(depth); // smaller bonus
|
|
|
|
// Increase stats for the best move in case it was a quiet move
|
|
update_quiet_stats(pos, ss, workerThread, bestMove, bestMoveBonus);
|
|
|
|
int pIndex = pawn_structure_index(pos);
|
|
workerThread.pawnHistory[pIndex][moved_piece][bestMove.to_sq()] << quietMoveBonus;
|
|
|
|
// Decrease stats for all non-best quiet moves
|
|
for (int i = 0; i < quietCount; ++i)
|
|
{
|
|
workerThread
|
|
.pawnHistory[pIndex][pos.moved_piece(quietsSearched[i])][quietsSearched[i].to_sq()]
|
|
<< -quietMoveMalus;
|
|
|
|
workerThread.mainHistory[us][quietsSearched[i].from_to()] << -quietMoveMalus;
|
|
update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]),
|
|
quietsSearched[i].to_sq(), -quietMoveMalus);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
// Increase stats for the best move in case it was a capture move
|
|
captured = type_of(pos.piece_on(bestMove.to_sq()));
|
|
captureHistory[moved_piece][bestMove.to_sq()][captured] << quietMoveBonus;
|
|
}
|
|
|
|
// Extra penalty for a quiet early move that was not a TT move or
|
|
// main killer move in previous ply when it gets refuted.
|
|
if (prevSq != SQ_NONE
|
|
&& ((ss - 1)->moveCount == 1 + (ss - 1)->ttHit
|
|
|| ((ss - 1)->currentMove == (ss - 1)->killers[0]))
|
|
&& !pos.captured_piece())
|
|
update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq, -quietMoveMalus);
|
|
|
|
// Decrease stats for all non-best capture moves
|
|
for (int i = 0; i < captureCount; ++i)
|
|
{
|
|
moved_piece = pos.moved_piece(capturesSearched[i]);
|
|
captured = type_of(pos.piece_on(capturesSearched[i].to_sq()));
|
|
captureHistory[moved_piece][capturesSearched[i].to_sq()][captured] << -quietMoveMalus;
|
|
}
|
|
}
|
|
|
|
|
|
// Updates histories of the move pairs formed
|
|
// by moves at ply -1, -2, -3, -4, and -6 with current move.
|
|
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
|
|
|
|
for (int i : {1, 2, 3, 4, 6})
|
|
{
|
|
// Only update the first 2 continuation histories if we are in check
|
|
if (ss->inCheck && i > 2)
|
|
break;
|
|
if (((ss - i)->currentMove).is_ok())
|
|
(*(ss - i)->continuationHistory)[pc][to] << bonus / (1 + 3 * (i == 3));
|
|
}
|
|
}
|
|
|
|
|
|
// Updates move sorting heuristics
|
|
void update_quiet_stats(
|
|
const Position& pos, Stack* ss, Search::Worker& workerThread, Move move, int bonus) {
|
|
|
|
// Update killers
|
|
if (ss->killers[0] != move)
|
|
{
|
|
ss->killers[1] = ss->killers[0];
|
|
ss->killers[0] = move;
|
|
}
|
|
|
|
Color us = pos.side_to_move();
|
|
workerThread.mainHistory[us][move.from_to()] << bonus;
|
|
update_continuation_histories(ss, pos.moved_piece(move), move.to_sq(), bonus);
|
|
|
|
// Update countermove history
|
|
if (((ss - 1)->currentMove).is_ok())
|
|
{
|
|
Square prevSq = ((ss - 1)->currentMove).to_sq();
|
|
workerThread.counterMoves[pos.piece_on(prevSq)][prevSq] = move;
|
|
}
|
|
}
|
|
}
|
|
|
|
// When playing with strength handicap, choose the best move among a set of RootMoves
|
|
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
|
|
Move Skill::pick_best(const RootMoves& rootMoves, size_t multiPV) {
|
|
static PRNG rng(now()); // PRNG sequence should be non-deterministic
|
|
|
|
// RootMoves are already sorted by score in descending order
|
|
Value topScore = rootMoves[0].score;
|
|
int delta = std::min(topScore - rootMoves[multiPV - 1].score, int(PawnValue));
|
|
int maxScore = -VALUE_INFINITE;
|
|
double weakness = 120 - 2 * level;
|
|
|
|
// Choose best move. For each move score we add two terms, both dependent on
|
|
// weakness. One is deterministic and bigger for weaker levels, and one is
|
|
// random. Then we choose the move with the resulting highest score.
|
|
for (size_t i = 0; i < multiPV; ++i)
|
|
{
|
|
// This is our magic formula
|
|
int push = (weakness * int(topScore - rootMoves[i].score)
|
|
+ delta * (rng.rand<unsigned>() % int(weakness)))
|
|
/ 128;
|
|
|
|
if (rootMoves[i].score + push >= maxScore)
|
|
{
|
|
maxScore = rootMoves[i].score + push;
|
|
best = rootMoves[i].pv[0];
|
|
}
|
|
}
|
|
|
|
return best;
|
|
}
|
|
|
|
|
|
// Used to print debug info and, more importantly,
|
|
// to detect when we are out of available time and thus stop the search.
|
|
void SearchManager::check_time(Search::Worker& worker) {
|
|
if (--callsCnt > 0)
|
|
return;
|
|
|
|
// When using nodes, ensure checking rate is not lower than 0.1% of nodes
|
|
callsCnt = worker.limits.nodes ? std::min(512, int(worker.limits.nodes / 1024)) : 512;
|
|
|
|
static TimePoint lastInfoTime = now();
|
|
|
|
TimePoint elapsed = tm.elapsed(worker.threads.nodes_searched());
|
|
TimePoint tick = worker.limits.startTime + elapsed;
|
|
|
|
if (tick - lastInfoTime >= 1000)
|
|
{
|
|
lastInfoTime = tick;
|
|
dbg_print();
|
|
}
|
|
|
|
// We should not stop pondering until told so by the GUI
|
|
if (ponder)
|
|
return;
|
|
|
|
if (
|
|
// Later we rely on the fact that we can at least use the mainthread previous
|
|
// root-search score and PV in a multithreaded environment to prove mated-in scores.
|
|
worker.completedDepth >= 1
|
|
&& ((worker.limits.use_time_management() && (elapsed > tm.maximum() || stopOnPonderhit))
|
|
|| (worker.limits.movetime && elapsed >= worker.limits.movetime)
|
|
|| (worker.limits.nodes && worker.threads.nodes_searched() >= worker.limits.nodes)))
|
|
worker.threads.stop = worker.threads.abortedSearch = true;
|
|
}
|
|
|
|
std::string SearchManager::pv(const Search::Worker& worker,
|
|
const ThreadPool& threads,
|
|
const TranspositionTable& tt,
|
|
Depth depth) const {
|
|
std::stringstream ss;
|
|
|
|
const auto nodes = threads.nodes_searched();
|
|
const auto& rootMoves = worker.rootMoves;
|
|
const auto& pos = worker.rootPos;
|
|
size_t pvIdx = worker.pvIdx;
|
|
TimePoint time = tm.elapsed(nodes) + 1;
|
|
size_t multiPV = std::min(size_t(worker.options["MultiPV"]), rootMoves.size());
|
|
uint64_t tbHits = threads.tb_hits() + (worker.tbConfig.rootInTB ? rootMoves.size() : 0);
|
|
|
|
for (size_t i = 0; i < multiPV; ++i)
|
|
{
|
|
bool updated = rootMoves[i].score != -VALUE_INFINITE;
|
|
|
|
if (depth == 1 && !updated && i > 0)
|
|
continue;
|
|
|
|
Depth d = updated ? depth : std::max(1, depth - 1);
|
|
Value v = updated ? rootMoves[i].uciScore : rootMoves[i].previousScore;
|
|
|
|
if (v == -VALUE_INFINITE)
|
|
v = VALUE_ZERO;
|
|
|
|
bool tb = worker.tbConfig.rootInTB && std::abs(v) <= VALUE_TB;
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v = tb ? rootMoves[i].tbScore : v;
|
|
|
|
if (ss.rdbuf()->in_avail()) // Not at first line
|
|
ss << "\n";
|
|
|
|
ss << "info"
|
|
<< " depth " << d << " seldepth " << rootMoves[i].selDepth << " multipv " << i + 1
|
|
<< " score " << UCI::value(v);
|
|
|
|
if (worker.options["UCI_ShowWDL"])
|
|
ss << UCI::wdl(v, pos.game_ply());
|
|
|
|
if (i == pvIdx && !tb && updated) // tablebase- and previous-scores are exact
|
|
ss << (rootMoves[i].scoreLowerbound
|
|
? " lowerbound"
|
|
: (rootMoves[i].scoreUpperbound ? " upperbound" : ""));
|
|
|
|
ss << " nodes " << nodes << " nps " << nodes * 1000 / time << " hashfull " << tt.hashfull()
|
|
<< " tbhits " << tbHits << " time " << time << " pv";
|
|
|
|
for (Move m : rootMoves[i].pv)
|
|
ss << " " << UCI::move(m, pos.is_chess960());
|
|
}
|
|
|
|
return ss.str();
|
|
}
|
|
|
|
// Called in case we have no ponder move before exiting the search,
|
|
// for instance, in case we stop the search during a fail high at root.
|
|
// We try hard to have a ponder move to return to the GUI,
|
|
// otherwise in case of 'ponder on' we have nothing to think about.
|
|
bool RootMove::extract_ponder_from_tt(const TranspositionTable& tt, Position& pos) {
|
|
|
|
StateInfo st;
|
|
ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
|
|
|
|
bool ttHit;
|
|
|
|
assert(pv.size() == 1);
|
|
if (pv[0] == Move::none())
|
|
return false;
|
|
|
|
pos.do_move(pv[0], st);
|
|
TTEntry* tte = tt.probe(pos.key(), ttHit);
|
|
|
|
if (ttHit)
|
|
{
|
|
Move m = tte->move(); // Local copy to be SMP safe
|
|
if (MoveList<LEGAL>(pos).contains(m))
|
|
pv.push_back(m);
|
|
}
|
|
|
|
pos.undo_move(pv[0]);
|
|
return pv.size() > 1;
|
|
}
|
|
|
|
|
|
} // namespace Stockfish
|