mirror of
https://github.com/sockspls/badfish
synced 2025-04-30 08:43:09 +00:00
7a9f67747f
Reduce the number of overloads for pieces() by using a more general template implementation. Secondly simplify some code in search.cpp using the new general functionality. TC https://tests.stockfishchess.org/tests/view/642ce27877ff3301150dc193 LLR: 2.94 (-2.94,2.94) <-1.75,0.25> Total: 269640 W: 71775 L: 71809 D: 126056 Ptnml(0-2): 687, 27294, 78885, 27274, 680 closes https://github.com/official-stockfish/Stockfish/pull/4501 No functional change.
2019 lines
73 KiB
C++
2019 lines
73 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2023 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 <algorithm>
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#include <cassert>
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#include <cmath>
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#include <cstring> // For std::memset
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#include <iostream>
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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 "position.h"
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#include "search.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 "syzygy/tbprobe.h"
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#include "nnue/evaluate_nnue.h"
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namespace Stockfish {
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namespace Search {
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LimitsType Limits;
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}
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namespace Tablebases {
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int Cardinality;
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bool RootInTB;
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bool UseRule50;
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Depth ProbeDepth;
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}
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namespace TB = Tablebases;
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using std::string;
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using Eval::evaluate;
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using namespace Search;
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namespace {
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// Different node types, used as a template parameter
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enum NodeType { NonPV, PV, Root };
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// Futility margin
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Value futility_margin(Depth d, bool improving) {
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return Value(154 * (d - improving));
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}
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// Reductions lookup table, initialized at startup
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int Reductions[MAX_MOVES]; // [depth or moveNumber]
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Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
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int r = Reductions[d] * Reductions[mn];
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return (r + 1449 - int(delta) * 937 / int(rootDelta)) / 1024 + (!i && r > 941);
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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)
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: (3 + depth * depth) / 2;
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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) {
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return std::min(341 * d - 470, 1710);
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}
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// Add a small random component to draw evaluations to avoid 3-fold blindness
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Value value_draw(const Thread* thisThread) {
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return VALUE_DRAW - 1 + Value(thisThread->nodes & 0x2);
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}
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// Skill structure is used to implement strength limit. If we have an uci_elo then
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// we convert it to a suitable fractional skill level using anchoring to CCRL Elo
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// (goldfish 1.13 = 2000) and a fit through Ordo derived Elo for match (TC 60+0.6)
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// results spanning a wide range of k values.
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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(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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template <NodeType nodeType>
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Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
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template <NodeType nodeType>
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Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
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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(const Position& pos, Stack* ss, Move move, int bonus);
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void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
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Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth);
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// perft() is our utility to verify move generation. All the leaf nodes up
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// to the given depth are generated and counted, and the sum is returned.
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template<bool Root>
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uint64_t perft(Position& pos, Depth depth) {
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StateInfo st;
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ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
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uint64_t cnt, nodes = 0;
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const bool leaf = (depth == 2);
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for (const auto& m : MoveList<LEGAL>(pos))
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{
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if (Root && depth <= 1)
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cnt = 1, nodes++;
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else
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{
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pos.do_move(m, st);
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cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - 1);
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nodes += cnt;
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pos.undo_move(m);
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}
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if (Root)
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sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
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}
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return nodes;
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}
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} // namespace
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/// Search::init() is called at startup to initialize various lookup tables
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void Search::init() {
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for (int i = 1; i < MAX_MOVES; ++i)
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Reductions[i] = int((19.47 + std::log(Threads.size()) / 2) * std::log(i));
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}
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/// Search::clear() resets search state to its initial value
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void Search::clear() {
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Threads.main()->wait_for_search_finished();
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Time.availableNodes = 0;
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TT.clear();
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Threads.clear();
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Tablebases::init(Options["SyzygyPath"]); // Free mapped files
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}
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/// MainThread::search() is started when the program receives the UCI 'go'
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/// command. It searches from the root position and outputs the "bestmove".
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void MainThread::search() {
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if (Limits.perft)
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{
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nodes = perft<true>(rootPos, Limits.perft);
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sync_cout << "\nNodes searched: " << nodes << "\n" << sync_endl;
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return;
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}
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Color us = rootPos.side_to_move();
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Time.init(Limits, us, rootPos.game_ply());
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TT.new_search();
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Eval::NNUE::verify();
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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)
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<< 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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Thread::search(); // 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 && (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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Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
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Thread* bestThread = this;
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Skill skill = Skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0);
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if ( int(Options["MultiPV"]) == 1
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&& !Limits.depth
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&& !skill.enabled()
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&& rootMoves[0].pv[0] != MOVE_NONE)
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bestThread = Threads.get_best_thread();
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bestPreviousScore = bestThread->rootMoves[0].score;
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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 << UCI::pv(bestThread->rootPos, bestThread->completedDepth) << 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 || bestThread->rootMoves[0].extract_ponder_from_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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/// Thread::search() is the 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 Thread::search() {
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// To allow access to (ss-7) up to (ss+2), the stack must be oversized.
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// The former is needed to allow update_continuation_histories(ss-1, ...),
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// which accesses its argument at ss-6, also near the root.
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// The latter is needed for statScore and killer initialization.
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Stack stack[MAX_PLY+10], *ss = stack+7;
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Move pv[MAX_PLY+1];
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Value alpha, beta, delta;
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Move lastBestMove = MOVE_NONE;
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Depth lastBestMoveDepth = 0;
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MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
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double timeReduction = 1, totBestMoveChanges = 0;
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Color us = rootPos.side_to_move();
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int iterIdx = 0;
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std::memset(ss-7, 0, 10 * sizeof(Stack));
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for (int i = 7; i > 0; --i)
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{
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(ss-i)->continuationHistory = &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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bestValue = delta = alpha = -VALUE_INFINITE;
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beta = VALUE_INFINITE;
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optimism[WHITE] = optimism[BLACK] = VALUE_ZERO;
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if (mainThread)
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{
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if (!rootPos.checkers())
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{
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int rootComplexity;
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Eval::evaluate(rootPos, &rootComplexity);
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mainThread->complexity = std::min(1.03 + (rootComplexity - 241) / 1552.0, 1.45);
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}
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if (mainThread->bestPreviousScore == VALUE_INFINITE)
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for (int i = 0; i < 4; ++i)
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mainThread->iterValue[i] = VALUE_ZERO;
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else
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for (int i = 0; i < 4; ++i)
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mainThread->iterValue[i] = 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
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&& !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 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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if (rootDepth >= 4)
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{
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Value prev = rootMoves[pvIdx].averageScore;
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delta = Value(10) + int(prev) * prev / 16502;
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alpha = std::max(prev - delta,-VALUE_INFINITE);
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beta = std::min(prev + delta, VALUE_INFINITE);
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// Adjust optimism based on root move's previousScore
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int opt = 120 * prev / (std::abs(prev) + 161);
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optimism[ us] = Value(opt);
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optimism[~us] = -optimism[us];
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}
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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 ensuring at least one effective increment for every
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// four searchAgain steps (see issue #2717).
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Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
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bestValue = Stockfish::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 are 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 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
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&& multiPV == 1
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&& (bestValue <= alpha || bestValue >= beta)
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&& Time.elapsed() > 3000)
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sync_cout << UCI::pv(rootPos, 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 / 4 + 2;
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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 || Time.elapsed() > 3000))
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sync_cout << UCI::pv(rootPos, rootDepth) << sync_endl;
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}
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if (!Threads.stop)
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completedDepth = rootDepth;
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if (rootMoves[0].pv[0] != lastBestMove)
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{
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lastBestMove = rootMoves[0].pv[0];
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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
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&& 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 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(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->bestMoveChanges;
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th->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()
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&& !Threads.stop
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&& !mainThread->stopOnPonderhit)
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{
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double fallingEval = (69 + 13 * (mainThread->bestPreviousAverageScore - bestValue)
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+ 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 619.6;
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fallingEval = std::clamp(fallingEval, 0.5, 1.5);
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// If the bestMove is stable over several iterations, reduce time accordingly
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timeReduction = lastBestMoveDepth + 8 < completedDepth ? 1.57 : 0.65;
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double reduction = (1.4 + mainThread->previousTimeReduction) / (2.08 * timeReduction);
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double bestMoveInstability = 1 + 1.8 * totBestMoveChanges / Threads.size();
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double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * mainThread->complexity;
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// Cap used time in case of a single legal move for a better viewer experience in tournaments
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// yielding correct scores and sufficiently fast moves.
|
|
if (rootMoves.size() == 1)
|
|
totalTime = std::min(500.0, totalTime);
|
|
|
|
// Stop the search if we have exceeded the totalTime
|
|
if (Time.elapsed() > totalTime)
|
|
{
|
|
// If we are allowed to ponder do not stop the search now but
|
|
// keep pondering until the GUI sends "ponderhit" or "stop".
|
|
if (mainThread->ponder)
|
|
mainThread->stopOnPonderhit = true;
|
|
else
|
|
Threads.stop = true;
|
|
}
|
|
else if ( !mainThread->ponder
|
|
&& Time.elapsed() > totalTime * 0.50)
|
|
Threads.increaseDepth = false;
|
|
else
|
|
Threads.increaseDepth = true;
|
|
}
|
|
|
|
mainThread->iterValue[iterIdx] = bestValue;
|
|
iterIdx = (iterIdx + 1) & 3;
|
|
}
|
|
|
|
if (!mainThread)
|
|
return;
|
|
|
|
mainThread->previousTimeReduction = timeReduction;
|
|
|
|
// If skill level is enabled, swap best PV line with the sub-optimal one
|
|
if (skill.enabled())
|
|
std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(),
|
|
skill.best ? skill.best : skill.pick_best(multiPV)));
|
|
}
|
|
|
|
|
|
namespace {
|
|
|
|
// search<>() is the main search function for both PV and non-PV nodes
|
|
|
|
template <NodeType nodeType>
|
|
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
|
|
|
|
constexpr bool PvNode = nodeType != NonPV;
|
|
constexpr bool rootNode = nodeType == Root;
|
|
|
|
// Check if we have an upcoming move which draws by repetition, or
|
|
// if the opponent had an alternative move earlier to this position.
|
|
if ( !rootNode
|
|
&& pos.rule50_count() >= 3
|
|
&& alpha < VALUE_DRAW
|
|
&& pos.has_game_cycle(ss->ply))
|
|
{
|
|
alpha = value_draw(pos.this_thread());
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
|
|
// Dive into quiescence search when the depth reaches zero
|
|
if (depth <= 0)
|
|
return qsearch<PvNode ? PV : NonPV>(pos, ss, alpha, beta);
|
|
|
|
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[64];
|
|
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, singularQuietLMR;
|
|
bool capture, moveCountPruning, ttCapture;
|
|
Piece movedPiece;
|
|
int moveCount, captureCount, quietCount, improvement, complexity;
|
|
|
|
// Step 1. Initialize node
|
|
Thread* thisThread = pos.this_thread();
|
|
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 (thisThread == Threads.main())
|
|
static_cast<MainThread*>(thisThread)->check_time();
|
|
|
|
// 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)
|
|
: value_draw(pos.this_thread());
|
|
|
|
// 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 applies 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->doubleExtensions = (ss-1)->doubleExtensions;
|
|
Square prevSq = is_ok((ss-1)->currentMove) ? to_sq((ss-1)->currentMove) : 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
|
|
&& ss->ttHit
|
|
&& !excludedMove
|
|
&& tte->depth() > depth - (tte->bound() == BOUND_EXACT)
|
|
&& ttValue != VALUE_NONE // Possible in case of TT access race
|
|
&& (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, 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_bonus(depth + 1));
|
|
}
|
|
// Penalty for a quiet ttMove that fails low (~1 Elo)
|
|
else if (!ttCapture)
|
|
{
|
|
int penalty = -stat_bonus(depth);
|
|
thisThread->mainHistory[us][from_to(ttMove)] << penalty;
|
|
update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), 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;
|
|
}
|
|
|
|
// Step 5. Tablebases probe
|
|
if (!rootNode && !excludedMove && TB::Cardinality)
|
|
{
|
|
int piecesCount = pos.count<ALL_PIECES>();
|
|
|
|
if ( piecesCount <= TB::Cardinality
|
|
&& (piecesCount < TB::Cardinality || depth >= TB::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 (thisThread == Threads.main())
|
|
static_cast<MainThread*>(thisThread)->callsCnt = 0;
|
|
|
|
if (err != TB::ProbeState::FAIL)
|
|
{
|
|
thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
|
|
|
|
int drawScore = TB::UseRule50 ? 1 : 0;
|
|
|
|
// use the range VALUE_MATE_IN_MAX_PLY to VALUE_TB_WIN_IN_MAX_PLY to score
|
|
value = wdl < -drawScore ? VALUE_MATED_IN_MAX_PLY + ss->ply + 1
|
|
: wdl > drawScore ? VALUE_MATE_IN_MAX_PLY - ss->ply - 1
|
|
: 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);
|
|
|
|
return value;
|
|
}
|
|
|
|
if (PvNode)
|
|
{
|
|
if (b == BOUND_LOWER)
|
|
bestValue = value, alpha = std::max(alpha, bestValue);
|
|
else
|
|
maxValue = value;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
CapturePieceToHistory& captureHistory = thisThread->captureHistory;
|
|
|
|
// Step 6. Static evaluation of the position
|
|
if (ss->inCheck)
|
|
{
|
|
// Skip early pruning when in check
|
|
ss->staticEval = eval = VALUE_NONE;
|
|
improving = false;
|
|
improvement = 0;
|
|
complexity = 0;
|
|
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);
|
|
eval = ss->staticEval;
|
|
complexity = abs(ss->staticEval - pos.psq_eg_stm());
|
|
}
|
|
else if (ss->ttHit)
|
|
{
|
|
// Never assume anything about values stored in TT
|
|
ss->staticEval = eval = tte->eval();
|
|
if (eval == VALUE_NONE)
|
|
ss->staticEval = eval = evaluate(pos, &complexity);
|
|
else // Fall back to (semi)classical complexity for TT hits, the NNUE complexity is lost
|
|
{
|
|
complexity = abs(ss->staticEval - pos.psq_eg_stm());
|
|
if (PvNode)
|
|
Eval::NNUE::hint_common_parent_position(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
|
|
{
|
|
ss->staticEval = eval = evaluate(pos, &complexity);
|
|
// Save static evaluation into transposition table
|
|
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
|
|
}
|
|
|
|
// Use static evaluation difference to improve quiet move ordering (~4 Elo)
|
|
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
|
|
{
|
|
int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1920, 1920);
|
|
thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
|
|
}
|
|
|
|
// Set up the improvement variable, which is the difference between the current
|
|
// static evaluation and the previous static evaluation at our turn (if we were
|
|
// in check at our previous move we look at the move prior to it). The improvement
|
|
// margin and the improving flag are used in various pruning heuristics.
|
|
improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
|
|
: (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
|
|
: 156;
|
|
improving = improvement > 0;
|
|
|
|
// 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.
|
|
if (eval < alpha - 426 - 256 * 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 < 9
|
|
&& eval - futility_margin(depth, improving) - (ss-1)->statScore / 280 >= beta
|
|
&& eval >= beta
|
|
&& eval < 25128) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
|
|
return eval;
|
|
|
|
// Step 9. Null move search with verification search (~35 Elo)
|
|
if ( !PvNode
|
|
&& (ss-1)->currentMove != MOVE_NULL
|
|
&& (ss-1)->statScore < 18755
|
|
&& eval >= beta
|
|
&& eval >= ss->staticEval
|
|
&& ss->staticEval >= beta - 20 * depth - improvement / 13 + 253 + complexity / 25
|
|
&& !excludedMove
|
|
&& pos.non_pawn_material(us)
|
|
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
|
|
{
|
|
assert(eval - beta >= 0);
|
|
|
|
// Null move dynamic reduction based on depth, eval and complexity of position
|
|
Depth R = std::min(int(eval - beta) / 172, 6) + depth / 3 + 4 - (complexity > 825);
|
|
|
|
ss->currentMove = MOVE_NULL;
|
|
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
|
|
|
|
pos.do_null_move(st);
|
|
|
|
Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
|
|
|
|
pos.undo_null_move();
|
|
|
|
if (nullValue >= beta)
|
|
{
|
|
// Do not return unproven mate or TB scores
|
|
if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY)
|
|
nullValue = beta;
|
|
|
|
if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 14))
|
|
return nullValue;
|
|
|
|
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
|
|
|
|
// Do verification search at high depths, with null move pruning disabled
|
|
// for us, until ply exceeds nmpMinPly.
|
|
thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
|
|
thisThread->nmpColor = us;
|
|
|
|
Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
|
|
|
|
thisThread->nmpMinPly = 0;
|
|
|
|
if (v >= beta)
|
|
return nullValue;
|
|
}
|
|
}
|
|
|
|
probCutBeta = beta + 186 - 54 * improving;
|
|
|
|
// Step 10. 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.
|
|
if ( !PvNode
|
|
&& depth > 4
|
|
&& 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
|
|
&& !( ss->ttHit
|
|
&& tte->depth() >= depth - 3
|
|
&& ttValue != VALUE_NONE
|
|
&& ttValue < probCutBeta))
|
|
{
|
|
assert(probCutBeta < VALUE_INFINITE);
|
|
|
|
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
|
|
|
|
while ((move = mp.next_move()) != MOVE_NONE)
|
|
if (move != excludedMove && pos.legal(move))
|
|
{
|
|
assert(pos.capture_stage(move));
|
|
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
|
|
[true]
|
|
[pos.moved_piece(move)]
|
|
[to_sq(move)];
|
|
|
|
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, ss->staticEval);
|
|
return value;
|
|
}
|
|
}
|
|
|
|
Eval::NNUE::hint_common_parent_position(pos);
|
|
}
|
|
|
|
// Step 11. If the position is not in TT, decrease depth by 2 (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
|
|
// Use qsearch if depth is equal or below zero (~9 Elo)
|
|
if ( PvNode
|
|
&& !ttMove)
|
|
depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
|
|
|
|
if (depth <= 0)
|
|
return qsearch<PV>(pos, ss, alpha, beta);
|
|
|
|
if ( cutNode
|
|
&& depth >= 7
|
|
&& !ttMove)
|
|
depth -= 2;
|
|
|
|
moves_loop: // When in check, search starts here
|
|
|
|
// Step 12. A small Probcut idea, when we are in check (~4 Elo)
|
|
probCutBeta = beta + 391;
|
|
if ( ss->inCheck
|
|
&& !PvNode
|
|
&& depth >= 2
|
|
&& ttCapture
|
|
&& (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 3
|
|
&& ttValue >= probCutBeta
|
|
&& abs(ttValue) <= VALUE_KNOWN_WIN
|
|
&& abs(beta) <= VALUE_KNOWN_WIN)
|
|
return probCutBeta;
|
|
|
|
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
|
|
nullptr , (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,
|
|
&captureHistory,
|
|
contHist,
|
|
countermove,
|
|
ss->killers);
|
|
|
|
value = bestValue;
|
|
moveCountPruning = singularQuietLMR = false;
|
|
|
|
// Indicate PvNodes that will probably fail low if the node was searched
|
|
// at a depth equal or greater than the current depth, and the result of this search was a fail low.
|
|
bool likelyFailLow = PvNode
|
|
&& ttMove
|
|
&& (tte->bound() & BOUND_UPPER)
|
|
&& tte->depth() >= depth;
|
|
|
|
// 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(is_ok(move));
|
|
|
|
if (move == excludedMove)
|
|
continue;
|
|
|
|
// At root obey the "searchmoves" option and skip moves not listed in Root
|
|
// Move List. As a consequence any illegal move is also skipped. In MultiPV
|
|
// mode we also skip PV moves which 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;
|
|
|
|
// Check for legality
|
|
if (!rootNode && !pos.legal(move))
|
|
continue;
|
|
|
|
ss->moveCount = ++moveCount;
|
|
|
|
if (rootNode && thisThread == Threads.main() && Time.elapsed() > 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;
|
|
|
|
Value delta = beta - alpha;
|
|
|
|
Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
|
|
|
|
// 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)
|
|
moveCountPruning = moveCount >= futility_move_count(improving, depth);
|
|
|
|
// Reduced depth of the next LMR search
|
|
int lmrDepth = std::max(newDepth - r, 0);
|
|
|
|
if ( capture
|
|
|| givesCheck)
|
|
{
|
|
// Futility pruning for captures (~2 Elo)
|
|
if ( !givesCheck
|
|
&& lmrDepth < 6
|
|
&& !ss->inCheck
|
|
&& ss->staticEval + 182 + 230 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
|
|
+ captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
|
|
continue;
|
|
|
|
Bitboard occupied;
|
|
// SEE based pruning (~11 Elo)
|
|
if (!pos.see_ge(move, occupied, Value(-206) * depth))
|
|
{
|
|
if (depth < 2 - capture)
|
|
continue;
|
|
// Don't prune the move if opp. King/Queen/Rook is attacked by a slider after the exchanges.
|
|
// Since in see_ge we don't update occupied when the king recaptures, we also don't prune the
|
|
// move when the opp. King gets a discovered slider attack DURING the exchanges.
|
|
Bitboard leftEnemies = pos.pieces(~us, ROOK, QUEEN, KING) & occupied;
|
|
Bitboard attacks = 0;
|
|
occupied |= to_sq(move);
|
|
while (leftEnemies && !attacks)
|
|
{
|
|
Square sq = pop_lsb(leftEnemies);
|
|
attacks = pos.attackers_to(sq, occupied) & pos.pieces(us) & occupied;
|
|
// Exclude Queen/Rook(s) which were already threatened before SEE
|
|
if (attacks && sq != pos.square<KING>(~us) && (pos.attackers_to(sq, pos.pieces()) & pos.pieces(us)))
|
|
attacks = 0;
|
|
}
|
|
if (!attacks)
|
|
continue;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
int history = (*contHist[0])[movedPiece][to_sq(move)]
|
|
+ (*contHist[1])[movedPiece][to_sq(move)]
|
|
+ (*contHist[3])[movedPiece][to_sq(move)];
|
|
|
|
// Continuation history based pruning (~2 Elo)
|
|
if ( lmrDepth < 5
|
|
&& history < -4405 * (depth - 1))
|
|
continue;
|
|
|
|
history += 2 * thisThread->mainHistory[us][from_to(move)];
|
|
|
|
lmrDepth += history / 7278;
|
|
lmrDepth = std::max(lmrDepth, -2);
|
|
|
|
// Futility pruning: parent node (~13 Elo)
|
|
if ( !ss->inCheck
|
|
&& lmrDepth < 13
|
|
&& ss->staticEval + 103 + 138 * lmrDepth <= alpha)
|
|
continue;
|
|
|
|
lmrDepth = std::max(lmrDepth, 0);
|
|
|
|
// Prune moves with negative SEE (~4 Elo)
|
|
if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 16 * 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 all the other moves but the ttMove and if the
|
|
// result is lower than ttValue minus a margin, then we will extend the ttMove.
|
|
if ( !rootNode
|
|
&& depth >= 4 - (thisThread->completedDepth > 21) + 2 * (PvNode && tte->is_pv())
|
|
&& move == ttMove
|
|
&& !excludedMove // Avoid recursive singular search
|
|
/* && ttValue != VALUE_NONE Already implicit in the next condition */
|
|
&& abs(ttValue) < VALUE_KNOWN_WIN
|
|
&& (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 3)
|
|
{
|
|
Value singularBeta = ttValue - (3 + 2 * (ss->ttPv && !PvNode)) * depth / 2;
|
|
Depth singularDepth = (depth - 1) / 2;
|
|
|
|
ss->excludedMove = move;
|
|
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
|
|
ss->excludedMove = MOVE_NONE;
|
|
|
|
if (value < singularBeta)
|
|
{
|
|
extension = 1;
|
|
singularQuietLMR = !ttCapture;
|
|
|
|
// Avoid search explosion by limiting the number of double extensions
|
|
if ( !PvNode
|
|
&& value < singularBeta - 25
|
|
&& ss->doubleExtensions <= 10)
|
|
{
|
|
extension = 2;
|
|
depth += depth < 13;
|
|
}
|
|
}
|
|
|
|
// Multi-cut pruning
|
|
// Our ttMove is assumed to fail high, and now we failed high also on a reduced
|
|
// search without the ttMove. So we assume this expected Cut-node is not singular,
|
|
// that multiple moves fail high, and we can prune the whole subtree by returning
|
|
// a soft bound.
|
|
else if (singularBeta >= beta)
|
|
return singularBeta;
|
|
|
|
// If the eval of ttMove is greater than beta, we reduce it (negative extension) (~7 Elo)
|
|
else if (ttValue >= beta)
|
|
extension = -2 - !PvNode;
|
|
|
|
// If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
|
|
else if (ttValue <= value)
|
|
extension = -1;
|
|
|
|
// If the eval of ttMove is less than alpha, we reduce it (negative extension) (~1 Elo)
|
|
else if (ttValue <= alpha)
|
|
extension = -1;
|
|
}
|
|
|
|
// Check extensions (~1 Elo)
|
|
else if ( givesCheck
|
|
&& depth > 10
|
|
&& abs(ss->staticEval) > 88)
|
|
extension = 1;
|
|
|
|
// Quiet ttMove extensions (~1 Elo)
|
|
else if ( PvNode
|
|
&& move == ttMove
|
|
&& move == ss->killers[0]
|
|
&& (*contHist[0])[movedPiece][to_sq(move)] >= 5705)
|
|
extension = 1;
|
|
}
|
|
|
|
// Add extension to new depth
|
|
newDepth += extension;
|
|
ss->doubleExtensions = (ss-1)->doubleExtensions + (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]
|
|
[to_sq(move)];
|
|
|
|
// Step 16. Make the move
|
|
pos.do_move(move, st, givesCheck);
|
|
|
|
// Decrease reduction if position is or has been on the PV
|
|
// and node is not likely to fail low. (~3 Elo)
|
|
if ( ss->ttPv
|
|
&& !likelyFailLow)
|
|
r -= 2;
|
|
|
|
// Decrease reduction if opponent's move count is high (~1 Elo)
|
|
if ((ss-1)->moveCount > 7)
|
|
r--;
|
|
|
|
// Increase reduction for cut nodes (~3 Elo)
|
|
if (cutNode)
|
|
r += 2;
|
|
|
|
// Increase reduction if ttMove is a capture (~3 Elo)
|
|
if (ttCapture)
|
|
r++;
|
|
|
|
// Decrease reduction for PvNodes based on depth (~2 Elo)
|
|
if (PvNode)
|
|
r -= 1 + 12 / (3 + depth);
|
|
|
|
// Decrease reduction if ttMove has been singularly extended (~1 Elo)
|
|
if (singularQuietLMR)
|
|
r--;
|
|
|
|
// Increase reduction if next ply has a lot of fail high (~5 Elo)
|
|
if ((ss+1)->cutoffCnt > 3)
|
|
r++;
|
|
|
|
// Decrease reduction if move is a killer and we have a good history (~1 Elo)
|
|
if (move == ss->killers[0]
|
|
&& (*contHist[0])[movedPiece][to_sq(move)] >= 3722)
|
|
r--;
|
|
|
|
ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)]
|
|
+ (*contHist[0])[movedPiece][to_sq(move)]
|
|
+ (*contHist[1])[movedPiece][to_sq(move)]
|
|
+ (*contHist[3])[movedPiece][to_sq(move)]
|
|
- 4082;
|
|
|
|
// Decrease/increase reduction for moves with a good/bad history (~25 Elo)
|
|
r -= ss->statScore / (11079 + 4626 * (depth > 6 && depth < 19));
|
|
|
|
// Step 17. Late moves reduction / extension (LMR, ~117 Elo)
|
|
// We use various heuristics for the sons of a node after the first son has
|
|
// been searched. In general we would like to reduce them, but there are many
|
|
// cases where we extend a son if it has good chances to be "interesting".
|
|
if ( depth >= 2
|
|
&& moveCount > 1 + (PvNode && ss->ply <= 1)
|
|
&& ( !ss->ttPv
|
|
|| !capture
|
|
|| (cutNode && (ss-1)->moveCount > 1)))
|
|
{
|
|
// 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 double extensions.
|
|
Depth d = std::clamp(newDepth - r, 1, newDepth + 1);
|
|
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
|
|
|
|
// Do full depth search when reduced LMR search fails high
|
|
if (value > alpha && d < newDepth)
|
|
{
|
|
// Adjust full depth search based on LMR results - if result
|
|
// was good enough search deeper, if it was bad enough search shallower
|
|
const bool doDeeperSearch = value > (alpha + 58 + 12 * (newDepth - d));
|
|
const bool doEvenDeeperSearch = value > alpha + 588 && ss->doubleExtensions <= 5;
|
|
const bool doShallowerSearch = value < bestValue + newDepth;
|
|
|
|
ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch;
|
|
|
|
newDepth += doDeeperSearch - doShallowerSearch + doEvenDeeperSearch;
|
|
|
|
if (newDepth > d)
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
|
|
|
|
int bonus = value > alpha ? stat_bonus(newDepth)
|
|
: -stat_bonus(newDepth);
|
|
|
|
update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
|
|
}
|
|
}
|
|
|
|
// Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
|
|
else if (!PvNode || moveCount > 1)
|
|
{
|
|
// Increase reduction for cut nodes and not ttMove (~1 Elo)
|
|
if (!ttMove && cutNode)
|
|
r += 2;
|
|
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode);
|
|
}
|
|
|
|
// For PV nodes only, do a full PV search on the first move or after a fail
|
|
// high (in the latter case search only if value < beta), otherwise let the
|
|
// parent node fail low with value <= alpha and try another move.
|
|
if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
|
|
{
|
|
(ss+1)->pv = pv;
|
|
(ss+1)->pv[0] = MOVE_NONE;
|
|
|
|
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
|
|
|
|
if (moveCount > 1 && newDepth >= depth && !capture)
|
|
update_continuation_histories(ss, movedPiece, to_sq(move), -stat_bonus(newDepth));
|
|
}
|
|
|
|
// 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 (PvNode && value < beta) // Update alpha! Always alpha < beta
|
|
{
|
|
// Reduce other moves if we have found at least one score improvement (~1 Elo)
|
|
if ( depth > 1
|
|
&& ( (improving && complexity > 971)
|
|
|| value < (5 * alpha + 75 * beta) / 87
|
|
|| depth < 6)
|
|
&& beta < 12535
|
|
&& value > -12535)
|
|
depth -= 1;
|
|
|
|
assert(depth > 0);
|
|
alpha = value;
|
|
}
|
|
else
|
|
{
|
|
ss->cutoffCnt++;
|
|
assert(value >= beta); // Fail high
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
// If the move is worse than some previously searched move, remember it to update its stats later
|
|
if (move != bestMove)
|
|
{
|
|
if (capture && captureCount < 32)
|
|
capturesSearched[captureCount++] = move;
|
|
|
|
else if (!capture && quietCount < 64)
|
|
quietsSearched[quietCount++] = move;
|
|
}
|
|
}
|
|
|
|
// The following condition would detect a stop only after move loop has been
|
|
// completed. But in this case bestValue is valid because we have fully
|
|
// searched our subtree, and we can anyhow save the result in TT.
|
|
/*
|
|
if (Threads.stop)
|
|
return VALUE_DRAW;
|
|
*/
|
|
|
|
// 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());
|
|
|
|
if (!moveCount)
|
|
bestValue = excludedMove ? alpha :
|
|
ss->inCheck ? mated_in(ss->ply)
|
|
: VALUE_DRAW;
|
|
|
|
// If there is a move which produces search value greater than alpha we update stats of searched moves
|
|
else if (bestMove)
|
|
update_all_stats(pos, ss, 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) + (bestValue < alpha - 97 * depth) + ((ss-1)->moveCount > 10);
|
|
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus);
|
|
}
|
|
|
|
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
|
|
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, ss->staticEval);
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
|
|
// qsearch() is the 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 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);
|
|
|
|
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;
|
|
|
|
// Step 1. Initialize node
|
|
if (PvNode)
|
|
{
|
|
(ss+1)->pv = pv;
|
|
ss->pv[0] = MOVE_NONE;
|
|
}
|
|
|
|
Thread* thisThread = pos.this_thread();
|
|
bestMove = MOVE_NONE;
|
|
ss->inCheck = pos.checkers();
|
|
moveCount = 0;
|
|
|
|
// 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) : VALUE_DRAW;
|
|
|
|
assert(0 <= ss->ply && ss->ply < MAX_PLY);
|
|
|
|
// Decide whether or not to include checks: this fixes also the type of
|
|
// TT entry depth that we are going to use. Note that in qsearch we use
|
|
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
|
|
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
|
|
&& ss->ttHit
|
|
&& tte->depth() >= ttDepth
|
|
&& ttValue != VALUE_NONE // Only in case of TT access race
|
|
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
|
|
return ttValue;
|
|
|
|
// Step 4. Static evaluation of the position
|
|
if (ss->inCheck)
|
|
{
|
|
ss->staticEval = VALUE_NONE;
|
|
bestValue = futilityBase = -VALUE_INFINITE;
|
|
}
|
|
else
|
|
{
|
|
if (ss->ttHit)
|
|
{
|
|
// Never assume anything about values stored in TT
|
|
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
|
|
ss->staticEval = bestValue = evaluate(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
|
|
ss->staticEval = bestValue =
|
|
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
|
|
: -(ss-1)->staticEval;
|
|
|
|
// Stand pat. Return immediately if static value is at least beta
|
|
if (bestValue >= beta)
|
|
{
|
|
// Save gathered info in transposition table
|
|
if (!ss->ttHit)
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
|
|
DEPTH_NONE, MOVE_NONE, ss->staticEval);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
if (PvNode && bestValue > alpha)
|
|
alpha = bestValue;
|
|
|
|
futilityBase = bestValue + 168;
|
|
}
|
|
|
|
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
|
|
nullptr , (ss-4)->continuationHistory,
|
|
nullptr , (ss-6)->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 != MOVE_NULL ? to_sq((ss-1)->currentMove) : SQ_NONE;
|
|
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
|
|
&thisThread->captureHistory,
|
|
contHist,
|
|
prevSq);
|
|
|
|
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(is_ok(move));
|
|
|
|
// 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)
|
|
{
|
|
// Futility pruning and moveCount pruning (~10 Elo)
|
|
if ( !givesCheck
|
|
&& to_sq(move) != prevSq
|
|
&& futilityBase > -VALUE_KNOWN_WIN
|
|
&& type_of(move) != PROMOTION)
|
|
{
|
|
if (moveCount > 2)
|
|
continue;
|
|
|
|
futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
|
|
|
|
if (futilityValue <= alpha)
|
|
{
|
|
bestValue = std::max(bestValue, futilityValue);
|
|
continue;
|
|
}
|
|
|
|
if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
|
|
{
|
|
bestValue = std::max(bestValue, futilityBase);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter
|
|
// and being a 'quiet' 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)][to_sq(move)] < 0
|
|
&& (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
|
|
continue;
|
|
|
|
// Do not search moves with bad enough SEE values (~5 Elo)
|
|
if (!pos.see_ge(move, Value(-110)))
|
|
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)]
|
|
[to_sq(move)];
|
|
|
|
quietCheckEvasions += !capture && ss->inCheck;
|
|
|
|
// Step 7. Make and search the move
|
|
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 (PvNode && 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
|
|
}
|
|
|
|
// Save gathered info in transposition table
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
|
|
bestValue >= beta ? BOUND_LOWER : BOUND_UPPER,
|
|
ttDepth, bestMove, ss->staticEval);
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
|
|
// value_to_tt() 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;
|
|
}
|
|
|
|
|
|
// value_from_tt() is the 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,
|
|
// for mate scores, to avoid potentially false mate scores related to the 50 moves rule
|
|
// and the graph history interaction, we return an optimal TB score instead.
|
|
|
|
Value value_from_tt(Value v, int ply, int r50c) {
|
|
|
|
if (v == VALUE_NONE)
|
|
return VALUE_NONE;
|
|
|
|
if (v >= VALUE_TB_WIN_IN_MAX_PLY) // TB win or better
|
|
{
|
|
if (v >= VALUE_MATE_IN_MAX_PLY && VALUE_MATE - v > 99 - r50c)
|
|
return VALUE_MATE_IN_MAX_PLY - 1; // do not return a potentially false mate score
|
|
|
|
return v - ply;
|
|
}
|
|
|
|
if (v <= VALUE_TB_LOSS_IN_MAX_PLY) // TB loss or worse
|
|
{
|
|
if (v <= VALUE_MATED_IN_MAX_PLY && VALUE_MATE + v > 99 - r50c)
|
|
return VALUE_MATED_IN_MAX_PLY + 1; // do not return a potentially false mate score
|
|
|
|
return v + ply;
|
|
}
|
|
|
|
return v;
|
|
}
|
|
|
|
|
|
// update_pv() 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;
|
|
}
|
|
|
|
|
|
// update_all_stats() updates stats at the end of search() when a bestMove is found
|
|
|
|
void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
|
|
Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth) {
|
|
|
|
Color us = pos.side_to_move();
|
|
Thread* thisThread = pos.this_thread();
|
|
CapturePieceToHistory& captureHistory = thisThread->captureHistory;
|
|
Piece moved_piece = pos.moved_piece(bestMove);
|
|
PieceType captured;
|
|
|
|
int bonus1 = stat_bonus(depth + 1);
|
|
|
|
if (!pos.capture_stage(bestMove))
|
|
{
|
|
int bonus2 = bestValue > beta + 153 ? bonus1 // 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, bestMove, bonus2);
|
|
|
|
// Decrease stats for all non-best quiet moves
|
|
for (int i = 0; i < quietCount; ++i)
|
|
{
|
|
thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2;
|
|
update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bonus2);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
// Increase stats for the best move in case it was a capture move
|
|
captured = type_of(pos.piece_on(to_sq(bestMove)));
|
|
captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
|
|
}
|
|
|
|
// 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, -bonus1);
|
|
|
|
// 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(to_sq(capturesSearched[i])));
|
|
captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -bonus1;
|
|
}
|
|
}
|
|
|
|
|
|
// update_continuation_histories() updates histories of the move pairs formed
|
|
// by moves at ply -1, -2, -4, and -6 with current move.
|
|
|
|
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
|
|
|
|
for (int i : {1, 2, 4, 6})
|
|
{
|
|
// Only update first 2 continuation histories if we are in check
|
|
if (ss->inCheck && i > 2)
|
|
break;
|
|
if (is_ok((ss-i)->currentMove))
|
|
(*(ss-i)->continuationHistory)[pc][to] << bonus;
|
|
}
|
|
}
|
|
|
|
|
|
// update_quiet_stats() updates move sorting heuristics
|
|
|
|
void update_quiet_stats(const Position& pos, Stack* ss, 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();
|
|
Thread* thisThread = pos.this_thread();
|
|
thisThread->mainHistory[us][from_to(move)] << bonus;
|
|
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
|
|
|
|
// Update countermove history
|
|
if (is_ok((ss-1)->currentMove))
|
|
{
|
|
Square prevSq = to_sq((ss-1)->currentMove);
|
|
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
|
|
}
|
|
}
|
|
|
|
// When playing with strength handicap, choose best move among a set of RootMoves
|
|
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
|
|
|
|
Move Skill::pick_best(size_t multiPV) {
|
|
|
|
const RootMoves& rootMoves = Threads.main()->rootMoves;
|
|
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, PawnValueMg);
|
|
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 = int(( 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;
|
|
}
|
|
|
|
} // namespace
|
|
|
|
|
|
/// MainThread::check_time() is used to print debug info and, more importantly,
|
|
/// to detect when we are out of available time and thus stop the search.
|
|
|
|
void MainThread::check_time() {
|
|
|
|
if (--callsCnt > 0)
|
|
return;
|
|
|
|
// When using nodes, ensure checking rate is not lower than 0.1% of nodes
|
|
callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024;
|
|
|
|
static TimePoint lastInfoTime = now();
|
|
|
|
TimePoint elapsed = Time.elapsed();
|
|
TimePoint tick = 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 ( (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit))
|
|
|| (Limits.movetime && elapsed >= Limits.movetime)
|
|
|| (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
|
|
Threads.stop = true;
|
|
}
|
|
|
|
|
|
/// UCI::pv() formats PV information according to the UCI protocol. UCI requires
|
|
/// that all (if any) unsearched PV lines are sent using a previous search score.
|
|
|
|
string UCI::pv(const Position& pos, Depth depth) {
|
|
|
|
std::stringstream ss;
|
|
TimePoint elapsed = Time.elapsed() + 1;
|
|
const RootMoves& rootMoves = pos.this_thread()->rootMoves;
|
|
size_t pvIdx = pos.this_thread()->pvIdx;
|
|
size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
|
|
uint64_t nodesSearched = Threads.nodes_searched();
|
|
uint64_t tbHits = Threads.tb_hits() + (TB::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 = TB::RootInTB && abs(v) < VALUE_MATE_IN_MAX_PLY;
|
|
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 (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 " << nodesSearched
|
|
<< " nps " << nodesSearched * 1000 / elapsed
|
|
<< " hashfull " << TT.hashfull()
|
|
<< " tbhits " << tbHits
|
|
<< " time " << elapsed
|
|
<< " pv";
|
|
|
|
for (Move m : rootMoves[i].pv)
|
|
ss << " " << UCI::move(m, pos.is_chess960());
|
|
}
|
|
|
|
return ss.str();
|
|
}
|
|
|
|
|
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/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
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/// before exiting the search, for instance, in case we stop the search during a
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/// fail high at root. We try hard to have a ponder move to return to the GUI,
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/// otherwise in case of 'ponder on' we have nothing to think on.
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bool RootMove::extract_ponder_from_tt(Position& pos) {
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|
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StateInfo st;
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ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
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|
|
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bool ttHit;
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|
|
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assert(pv.size() == 1);
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|
|
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if (pv[0] == MOVE_NONE)
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return false;
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|
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pos.do_move(pv[0], st);
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TTEntry* tte = TT.probe(pos.key(), ttHit);
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|
|
|
if (ttHit)
|
|
{
|
|
Move m = tte->move(); // Local copy to be SMP safe
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if (MoveList<LEGAL>(pos).contains(m))
|
|
pv.push_back(m);
|
|
}
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|
|
|
pos.undo_move(pv[0]);
|
|
return pv.size() > 1;
|
|
}
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|
|
|
void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
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|
|
|
RootInTB = false;
|
|
UseRule50 = bool(Options["Syzygy50MoveRule"]);
|
|
ProbeDepth = int(Options["SyzygyProbeDepth"]);
|
|
Cardinality = int(Options["SyzygyProbeLimit"]);
|
|
bool dtz_available = true;
|
|
|
|
// Tables with fewer pieces than SyzygyProbeLimit are searched with
|
|
// ProbeDepth == DEPTH_ZERO
|
|
if (Cardinality > MaxCardinality)
|
|
{
|
|
Cardinality = MaxCardinality;
|
|
ProbeDepth = 0;
|
|
}
|
|
|
|
if (Cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING))
|
|
{
|
|
// Rank moves using DTZ tables
|
|
RootInTB = root_probe(pos, rootMoves);
|
|
|
|
if (!RootInTB)
|
|
{
|
|
// DTZ tables are missing; try to rank moves using WDL tables
|
|
dtz_available = false;
|
|
RootInTB = root_probe_wdl(pos, rootMoves);
|
|
}
|
|
}
|
|
|
|
if (RootInTB)
|
|
{
|
|
// Sort moves according to TB rank
|
|
std::stable_sort(rootMoves.begin(), rootMoves.end(),
|
|
[](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } );
|
|
|
|
// Probe during search only if DTZ is not available and we are winning
|
|
if (dtz_available || rootMoves[0].tbScore <= VALUE_DRAW)
|
|
Cardinality = 0;
|
|
}
|
|
else
|
|
{
|
|
// Clean up if root_probe() and root_probe_wdl() have failed
|
|
for (auto& m : rootMoves)
|
|
m.tbRank = 0;
|
|
}
|
|
}
|
|
|
|
} // namespace Stockfish
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