mirror of
https://github.com/sockspls/badfish
synced 2025-04-30 16:53:09 +00:00
4bef7aa5cd
This patch is a combinaison of two parameters tweaks patches which have failed as strong yellows at LTC recently, by Alain Savard (Rocky640) and Fabian Fichter (ianfab): http://tests.stockfishchess.org/tests/view/5b8a71e60ebc592cf2749b1d http://tests.stockfishchess.org/tests/view/5b81ce3b0ebc5902bdbb6585 Passed STC: LLR: 2.95 (-2.94,2.94) [0.00,4.00] Total: 57200 W: 12392 L: 12008 D: 32800 http://tests.stockfishchess.org/tests/view/5b8d0a5a0ebc592cf274c48f And LTC: LLR: 2.96 (-2.94,2.94) [0.00,4.00] Total: 37215 W: 6233 L: 5962 D: 25020 http://tests.stockfishchess.org/tests/view/5b8d56090ebc592cf274cb53 Closes https://github.com/official-stockfish/Stockfish/pull/1764 Bench: 4136116 --------------- How to continue from there? The null move reduction formula in line 769 of search.cpp is quite convoluted and full of mysterious magic constants at the moment, it would certainly be nice to simplify it and/or gain more Elo from it: ``` Depth R = ( (823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY; ```
1709 lines
60 KiB
C++
1709 lines
60 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
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Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#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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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 };
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// Sizes and phases of the skip-blocks, used for distributing search depths across the threads
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constexpr int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
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constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
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// Razor and futility margins
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constexpr int RazorMargin = 600;
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Value futility_margin(Depth d, bool improving) {
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return Value((175 - 50 * improving) * d / ONE_PLY);
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}
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// Futility and reductions lookup tables, initialized at startup
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int FutilityMoveCounts[2][16]; // [improving][depth]
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int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
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template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
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return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
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}
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// History and stats update bonus, based on depth
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int stat_bonus(Depth depth) {
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int d = depth / ONE_PLY;
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return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
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}
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// Skill structure is used to implement strength limit
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struct Skill {
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explicit Skill(int l) : level(l) {}
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bool enabled() const { return level < 20; }
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bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
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Move pick_best(size_t multiPV);
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int level;
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Move best = MOVE_NONE;
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};
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template <NodeType NT>
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Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
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template <NodeType NT>
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Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
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Value value_to_tt(Value v, int ply);
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Value value_from_tt(Value v, int ply);
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void update_pv(Move* pv, Move move, 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, Move* quiets, int quietsCnt, int bonus);
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void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus);
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inline bool gives_check(const Position& pos, Move move) {
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Color us = pos.side_to_move();
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return type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us))
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? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
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: pos.gives_check(move);
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}
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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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uint64_t cnt, nodes = 0;
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const bool leaf = (depth == 2 * ONE_PLY);
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for (const auto& m : MoveList<LEGAL>(pos))
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{
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if (Root && depth <= ONE_PLY)
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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 - ONE_PLY);
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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 imp = 0; imp <= 1; ++imp)
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for (int d = 1; d < 64; ++d)
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for (int mc = 1; mc < 64; ++mc)
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{
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double r = log(d) * log(mc) / 1.95;
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Reductions[NonPV][imp][d][mc] = int(std::round(r));
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Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
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// Increase reduction for non-PV nodes when eval is not improving
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if (!imp && r > 1.0)
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Reductions[NonPV][imp][d][mc]++;
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}
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for (int d = 0; d < 16; ++d)
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{
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FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
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FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
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}
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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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}
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/// MainThread::search() is called by the main thread when the program receives
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/// the UCI 'go' 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 * ONE_PLY);
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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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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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for (Thread* th : Threads)
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if (th != this)
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th->start_searching();
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Thread::search(); // Let's 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 (which also raises Threads.stop).
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Threads.stopOnPonderhit = true;
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while (!Threads.stop && (Threads.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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for (Thread* th : Threads)
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if (th != this)
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th->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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// Check if there are threads with a better score than main thread
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Thread* bestThread = this;
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if ( Options["MultiPV"] == 1
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&& !Limits.depth
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&& !Skill(Options["Skill Level"]).enabled()
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&& rootMoves[0].pv[0] != MOVE_NONE)
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{
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std::map<Move, int> votes;
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Value minScore = this->rootMoves[0].score;
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// Find out minimum score and reset votes for moves which can be voted
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for (Thread* th: Threads)
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{
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minScore = std::min(minScore, th->rootMoves[0].score);
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votes[th->rootMoves[0].pv[0]] = 0;
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}
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// Vote according to score and depth
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for (Thread* th : Threads)
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votes[th->rootMoves[0].pv[0]] += int(th->rootMoves[0].score - minScore)
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+ int(th->completedDepth);
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// Select best thread
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int bestVote = votes[this->rootMoves[0].pv[0]];
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for (Thread* th : Threads)
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{
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if (votes[th->rootMoves[0].pv[0]] > bestVote)
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{
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bestVote = votes[th->rootMoves[0].pv[0]];
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bestThread = th;
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}
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}
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}
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previousScore = bestThread->rootMoves[0].score;
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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, -VALUE_INFINITE, VALUE_INFINITE) << 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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Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2)
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Value bestValue, alpha, beta, delta;
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Move lastBestMove = MOVE_NONE;
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Depth lastBestMoveDepth = DEPTH_ZERO;
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MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
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double timeReduction = 1.0;
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Color us = rootPos.side_to_move();
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bool failedLow;
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std::memset(ss-4, 0, 7 * sizeof(Stack));
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for (int i = 4; i > 0; i--)
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(ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
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bestValue = delta = alpha = -VALUE_INFINITE;
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beta = VALUE_INFINITE;
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if (mainThread)
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mainThread->bestMoveChanges = 0, failedLow = false;
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size_t multiPV = Options["MultiPV"];
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Skill skill(Options["Skill Level"]);
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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 ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns
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// In analysis mode, adjust contempt in accordance with user preference
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if (Limits.infinite || Options["UCI_AnalyseMode"])
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ct = Options["Analysis Contempt"] == "Off" ? 0
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: Options["Analysis Contempt"] == "Both" ? ct
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: Options["Analysis Contempt"] == "White" && us == BLACK ? -ct
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: Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
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: ct;
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// In evaluate.cpp the evaluation is from the white point of view
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contempt = (us == WHITE ? make_score(ct, ct / 2)
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: -make_score(ct, ct / 2));
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// Iterative deepening loop until requested to stop or the target depth is reached
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while ( (rootDepth += ONE_PLY) < DEPTH_MAX
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&& !Threads.stop
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&& !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
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{
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// Distribute search depths across the helper threads
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if (idx > 0)
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{
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int i = (idx - 1) % 20;
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if (((rootDepth / ONE_PLY + SkipPhase[i]) / SkipSize[i]) % 2)
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continue; // Retry with an incremented rootDepth
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}
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// Age out PV variability metric
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if (mainThread)
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mainThread->bestMoveChanges *= 0.517, failedLow = false;
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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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// 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 >= 5 * ONE_PLY)
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{
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Value previousScore = rootMoves[pvIdx].previousScore;
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delta = Value(18);
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alpha = std::max(previousScore - delta,-VALUE_INFINITE);
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beta = std::min(previousScore + delta, VALUE_INFINITE);
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// Adjust contempt based on root move's previousScore (dynamic contempt)
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int dct = ct + 88 * previousScore / (abs(previousScore) + 200);
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contempt = (us == WHITE ? make_score(dct, dct / 2)
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: -make_score(dct, dct / 2));
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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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while (true)
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{
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bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, 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, alpha, beta) << 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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if (mainThread)
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{
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failedLow = true;
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Threads.stopOnPonderhit = false;
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}
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}
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else if (bestValue >= beta)
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beta = std::min(bestValue + delta, VALUE_INFINITE);
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else
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break;
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delta += delta / 4 + 5;
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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, alpha, beta) << 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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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
|
|
&& bestValue >= VALUE_MATE_IN_MAX_PLY
|
|
&& VALUE_MATE - bestValue <= 2 * Limits.mate)
|
|
Threads.stop = true;
|
|
|
|
if (!mainThread)
|
|
continue;
|
|
|
|
// If skill level is enabled and time is up, pick a sub-optimal best move
|
|
if (skill.enabled() && skill.time_to_pick(rootDepth))
|
|
skill.pick_best(multiPV);
|
|
|
|
// Do we have time for the next iteration? Can we stop searching now?
|
|
if ( Limits.use_time_management()
|
|
&& !Threads.stop
|
|
&& !Threads.stopOnPonderhit)
|
|
{
|
|
const int F[] = { failedLow,
|
|
bestValue - mainThread->previousScore };
|
|
|
|
int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1]));
|
|
|
|
// If the bestMove is stable over several iterations, reduce time accordingly
|
|
timeReduction = 1.0;
|
|
for (int i : {3, 4, 5})
|
|
if (lastBestMoveDepth * i < completedDepth)
|
|
timeReduction *= 1.25;
|
|
|
|
// Use part of the gained time from a previous stable move for the current move
|
|
double bestMoveInstability = 1.0 + mainThread->bestMoveChanges;
|
|
bestMoveInstability *= std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
|
|
|
|
// Stop the search if we have only one legal move, or if available time elapsed
|
|
if ( rootMoves.size() == 1
|
|
|| Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581)
|
|
{
|
|
// If we are allowed to ponder do not stop the search now but
|
|
// keep pondering until the GUI sends "ponderhit" or "stop".
|
|
if (Threads.ponder)
|
|
Threads.stopOnPonderhit = true;
|
|
else
|
|
Threads.stop = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
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 NT>
|
|
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
|
|
|
|
constexpr bool PvNode = NT == PV;
|
|
const bool rootNode = PvNode && ss->ply == 0;
|
|
|
|
// Check if we have an upcoming move which draws by repetition, or
|
|
// if the opponent had an alternative move earlier to this position.
|
|
if ( pos.rule50_count() >= 3
|
|
&& alpha < VALUE_DRAW
|
|
&& !rootNode
|
|
&& pos.has_game_cycle(ss->ply))
|
|
{
|
|
alpha = VALUE_DRAW;
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
|
|
// Dive into quiescence search when the depth reaches zero
|
|
if (depth < ONE_PLY)
|
|
return qsearch<NT>(pos, ss, alpha, beta);
|
|
|
|
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
|
|
assert(PvNode || (alpha == beta - 1));
|
|
assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
|
|
assert(!(PvNode && cutNode));
|
|
assert(depth / ONE_PLY * ONE_PLY == depth);
|
|
|
|
Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
|
|
StateInfo st;
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, excludedMove, bestMove;
|
|
Depth extension, newDepth;
|
|
Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
|
|
bool ttHit, inCheck, givesCheck, improving;
|
|
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
|
|
Piece movedPiece;
|
|
int moveCount, captureCount, quietCount;
|
|
|
|
// Step 1. Initialize node
|
|
Thread* thisThread = pos.this_thread();
|
|
inCheck = pos.checkers();
|
|
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 && !inCheck) ? evaluate(pos) - 10 * ((ss-1)->statScore > 0)
|
|
: VALUE_DRAW;
|
|
|
|
// 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;
|
|
}
|
|
|
|
assert(0 <= ss->ply && ss->ply < MAX_PLY);
|
|
|
|
(ss+1)->ply = ss->ply + 1;
|
|
ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
|
|
ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
|
|
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
|
|
Square prevSq = to_sq((ss-1)->currentMove);
|
|
|
|
// Initialize statScore to zero for the grandchildren of the current position.
|
|
// So statScore is shared between all grandchildren and only the first grandchild
|
|
// starts with statScore = 0. Later grandchildren start with the last calculated
|
|
// statScore of the previous grandchild. This influences the reduction rules in
|
|
// LMR which are based on the statScore of parent position.
|
|
(ss+2)->statScore = 0;
|
|
|
|
// Step 4. Transposition table lookup. We don't want the score of a partial
|
|
// search to overwrite a previous full search TT value, so we use a different
|
|
// position key in case of an excluded move.
|
|
excludedMove = ss->excludedMove;
|
|
posKey = pos.key() ^ Key(excludedMove << 16); // Isn't a very good hash
|
|
tte = TT.probe(posKey, ttHit);
|
|
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
|
|
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
|
|
: ttHit ? tte->move() : MOVE_NONE;
|
|
|
|
// At non-PV nodes we check for an early TT cutoff
|
|
if ( !PvNode
|
|
&& ttHit
|
|
&& tte->depth() >= depth
|
|
&& ttValue != VALUE_NONE // Possible in case of TT access race
|
|
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
|
|
: (tte->bound() & BOUND_UPPER)))
|
|
{
|
|
// If ttMove is quiet, update move sorting heuristics on TT hit
|
|
if (ttMove)
|
|
{
|
|
if (ttValue >= beta)
|
|
{
|
|
if (!pos.capture_or_promotion(ttMove))
|
|
update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
|
|
|
|
// Extra penalty for a quiet TT move in previous ply when it gets refuted
|
|
if ((ss-1)->moveCount == 1 && !pos.captured_piece())
|
|
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
|
|
}
|
|
// Penalty for a quiet ttMove that fails low
|
|
else if (!pos.capture_or_promotion(ttMove))
|
|
{
|
|
int penalty = -stat_bonus(depth);
|
|
thisThread->mainHistory[us][from_to(ttMove)] << penalty;
|
|
update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
|
|
}
|
|
}
|
|
return ttValue;
|
|
}
|
|
|
|
// Step 5. Tablebases probe
|
|
if (!rootNode && 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);
|
|
|
|
if (err != TB::ProbeState::FAIL)
|
|
{
|
|
thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
|
|
|
|
int drawScore = TB::UseRule50 ? 1 : 0;
|
|
|
|
value = wdl < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1
|
|
: wdl > drawScore ? VALUE_MATE - 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), b,
|
|
std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
|
|
MOVE_NONE, VALUE_NONE);
|
|
|
|
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
|
|
if (inCheck)
|
|
{
|
|
ss->staticEval = eval = pureStaticEval = VALUE_NONE;
|
|
improving = false;
|
|
goto moves_loop; // Skip early pruning when in check
|
|
}
|
|
else if (ttHit)
|
|
{
|
|
// Never assume anything on values stored in TT
|
|
ss->staticEval = eval = pureStaticEval = tte->eval();
|
|
if (eval == VALUE_NONE)
|
|
ss->staticEval = eval = pureStaticEval = evaluate(pos);
|
|
|
|
// Can ttValue be used as a better position evaluation?
|
|
if ( ttValue != VALUE_NONE
|
|
&& (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
|
|
eval = ttValue;
|
|
}
|
|
else
|
|
{
|
|
if ((ss-1)->currentMove != MOVE_NULL)
|
|
{
|
|
int p = (ss-1)->statScore;
|
|
int bonus = p > 0 ? (-p - 2500) / 512 :
|
|
p < 0 ? (-p + 2500) / 512 : 0;
|
|
|
|
pureStaticEval = evaluate(pos);
|
|
ss->staticEval = eval = pureStaticEval + bonus;
|
|
}
|
|
else
|
|
ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
|
|
|
|
tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
|
|
}
|
|
|
|
// Step 7. Razoring (~2 Elo)
|
|
if ( depth < 2 * ONE_PLY
|
|
&& eval <= alpha - RazorMargin)
|
|
return qsearch<NT>(pos, ss, alpha, beta);
|
|
|
|
improving = ss->staticEval >= (ss-2)->staticEval
|
|
|| (ss-2)->staticEval == VALUE_NONE;
|
|
|
|
// Step 8. Futility pruning: child node (~30 Elo)
|
|
if ( !rootNode
|
|
&& depth < 7 * ONE_PLY
|
|
&& eval - futility_margin(depth, improving) >= beta
|
|
&& eval < VALUE_KNOWN_WIN) // Do not return unproven wins
|
|
return eval;
|
|
|
|
// Step 9. Null move search with verification search (~40 Elo)
|
|
if ( !PvNode
|
|
&& (ss-1)->currentMove != MOVE_NULL
|
|
&& (ss-1)->statScore < 23200
|
|
&& eval >= beta
|
|
&& ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
|
|
&& !excludedMove
|
|
&& pos.non_pawn_material(us)
|
|
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
|
|
{
|
|
assert(eval - beta >= 0);
|
|
|
|
// Null move dynamic reduction based on depth and value
|
|
Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY;
|
|
|
|
ss->currentMove = MOVE_NULL;
|
|
ss->continuationHistory = &thisThread->continuationHistory[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 scores
|
|
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
|
|
nullValue = beta;
|
|
|
|
if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY))
|
|
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;
|
|
}
|
|
}
|
|
|
|
// Step 10. ProbCut (~10 Elo)
|
|
// If we have a good enough capture and a reduced search returns a value
|
|
// much above beta, we can (almost) safely prune the previous move.
|
|
if ( !PvNode
|
|
&& depth >= 5 * ONE_PLY
|
|
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
|
|
{
|
|
Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
|
|
MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
|
|
int probCutCount = 0;
|
|
|
|
while ( (move = mp.next_move()) != MOVE_NONE
|
|
&& probCutCount < 3)
|
|
if (move != excludedMove && pos.legal(move))
|
|
{
|
|
probCutCount++;
|
|
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
|
|
|
|
assert(depth >= 5 * ONE_PLY);
|
|
|
|
pos.do_move(move, st);
|
|
|
|
// Perform a preliminary qsearch to verify that the move holds
|
|
value = -qsearch<NonPV>(pos, ss+1, -rbeta, -rbeta+1);
|
|
|
|
// If the qsearch held perform the regular search
|
|
if (value >= rbeta)
|
|
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode);
|
|
|
|
pos.undo_move(move);
|
|
|
|
if (value >= rbeta)
|
|
return value;
|
|
}
|
|
}
|
|
|
|
// Step 11. Internal iterative deepening (~2 Elo)
|
|
if ( depth >= 8 * ONE_PLY
|
|
&& !ttMove)
|
|
{
|
|
search<NT>(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
|
|
|
|
tte = TT.probe(posKey, ttHit);
|
|
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
|
|
ttMove = ttHit ? tte->move() : MOVE_NONE;
|
|
}
|
|
|
|
moves_loop: // When in check, search starts from here
|
|
|
|
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
|
|
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
|
|
|
|
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
|
|
&thisThread->captureHistory,
|
|
contHist,
|
|
countermove,
|
|
ss->killers);
|
|
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
|
|
|
|
skipQuiets = false;
|
|
ttCapture = false;
|
|
pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
|
|
|
|
// Step 12. Loop through all pseudo-legal moves until no moves remain
|
|
// or a beta cutoff occurs.
|
|
while ((move = mp.next_move(skipQuiets)) != 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;
|
|
|
|
ss->moveCount = ++moveCount;
|
|
|
|
if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
|
|
sync_cout << "info depth " << depth / ONE_PLY
|
|
<< " currmove " << UCI::move(move, pos.is_chess960())
|
|
<< " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
|
|
if (PvNode)
|
|
(ss+1)->pv = nullptr;
|
|
|
|
extension = DEPTH_ZERO;
|
|
captureOrPromotion = pos.capture_or_promotion(move);
|
|
movedPiece = pos.moved_piece(move);
|
|
givesCheck = gives_check(pos, move);
|
|
|
|
moveCountPruning = depth < 16 * ONE_PLY
|
|
&& moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
|
|
|
|
// Step 13. Extensions (~70 Elo)
|
|
|
|
// Singular extension search (~60 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 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 ( depth >= 8 * ONE_PLY
|
|
&& move == ttMove
|
|
&& !rootNode
|
|
&& !excludedMove // Recursive singular search is not allowed
|
|
&& ttValue != VALUE_NONE
|
|
&& (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 3 * ONE_PLY
|
|
&& pos.legal(move))
|
|
{
|
|
Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
|
|
ss->excludedMove = move;
|
|
value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
|
|
ss->excludedMove = MOVE_NONE;
|
|
|
|
if (value < rBeta)
|
|
extension = ONE_PLY;
|
|
}
|
|
else if ( givesCheck // Check extension (~2 Elo)
|
|
&& !moveCountPruning
|
|
&& pos.see_ge(move))
|
|
extension = ONE_PLY;
|
|
|
|
// Calculate new depth for this move
|
|
newDepth = depth - ONE_PLY + extension;
|
|
|
|
// Step 14. Pruning at shallow depth (~170 Elo)
|
|
if ( !rootNode
|
|
&& pos.non_pawn_material(us)
|
|
&& bestValue > VALUE_MATED_IN_MAX_PLY)
|
|
{
|
|
if ( !captureOrPromotion
|
|
&& !givesCheck
|
|
&& (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
|
|
{
|
|
// Move count based pruning (~30 Elo)
|
|
if (moveCountPruning)
|
|
{
|
|
skipQuiets = true;
|
|
continue;
|
|
}
|
|
|
|
// Reduced depth of the next LMR search
|
|
int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
|
|
|
|
// Countermoves based pruning (~20 Elo)
|
|
if ( lmrDepth < 3 + ((ss-1)->statScore > 0)
|
|
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
|
|
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
|
|
continue;
|
|
|
|
// Futility pruning: parent node (~2 Elo)
|
|
if ( lmrDepth < 7
|
|
&& !inCheck
|
|
&& ss->staticEval + 256 + 200 * lmrDepth <= alpha)
|
|
continue;
|
|
|
|
// Prune moves with negative SEE (~10 Elo)
|
|
if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
|
|
continue;
|
|
}
|
|
else if ( !extension // (~20 Elo)
|
|
&& !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
|
|
continue;
|
|
}
|
|
|
|
// Speculative prefetch as early as possible
|
|
prefetch(TT.first_entry(pos.key_after(move)));
|
|
|
|
// Check for legality just before making the move
|
|
if (!rootNode && !pos.legal(move))
|
|
{
|
|
ss->moveCount = --moveCount;
|
|
continue;
|
|
}
|
|
|
|
if (move == ttMove && captureOrPromotion)
|
|
ttCapture = true;
|
|
|
|
// Update the current move (this must be done after singular extension search)
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)];
|
|
|
|
// Step 15. Make the move
|
|
pos.do_move(move, st, givesCheck);
|
|
|
|
// Step 16. Reduced depth search (LMR). If the move fails high it will be
|
|
// re-searched at full depth.
|
|
if ( depth >= 3 * ONE_PLY
|
|
&& moveCount > 1
|
|
&& (!captureOrPromotion || moveCountPruning))
|
|
{
|
|
Depth r = reduction<PvNode>(improving, depth, moveCount);
|
|
|
|
// Decrease reduction if opponent's move count is high (~10 Elo)
|
|
if ((ss-1)->moveCount > 15)
|
|
r -= ONE_PLY;
|
|
|
|
if (!captureOrPromotion)
|
|
{
|
|
// Decrease reduction for exact PV nodes (~0 Elo)
|
|
if (pvExact)
|
|
r -= ONE_PLY;
|
|
|
|
// Increase reduction if ttMove is a capture (~0 Elo)
|
|
if (ttCapture)
|
|
r += ONE_PLY;
|
|
|
|
// Increase reduction for cut nodes (~5 Elo)
|
|
if (cutNode)
|
|
r += 2 * ONE_PLY;
|
|
|
|
// Decrease reduction for moves that escape a capture. Filter out
|
|
// castling moves, because they are coded as "king captures rook" and
|
|
// hence break make_move(). (~5 Elo)
|
|
else if ( type_of(move) == NORMAL
|
|
&& !pos.see_ge(make_move(to_sq(move), from_sq(move))))
|
|
r -= 2 * ONE_PLY;
|
|
|
|
ss->statScore = thisThread->mainHistory[us][from_to(move)]
|
|
+ (*contHist[0])[movedPiece][to_sq(move)]
|
|
+ (*contHist[1])[movedPiece][to_sq(move)]
|
|
+ (*contHist[3])[movedPiece][to_sq(move)]
|
|
- 4000;
|
|
|
|
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
|
|
if (ss->statScore >= 0 && (ss-1)->statScore < 0)
|
|
r -= ONE_PLY;
|
|
|
|
else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
|
|
r += ONE_PLY;
|
|
|
|
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
|
|
r -= ss->statScore / 20000 * ONE_PLY;
|
|
}
|
|
|
|
Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
|
|
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
|
|
|
|
doFullDepthSearch = (value > alpha && d != newDepth);
|
|
}
|
|
else
|
|
doFullDepthSearch = !PvNode || moveCount > 1;
|
|
|
|
// Step 17. Full depth search when LMR is skipped or fails high
|
|
if (doFullDepthSearch)
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !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);
|
|
}
|
|
|
|
// Step 18. Undo move
|
|
pos.undo_move(move);
|
|
|
|
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
|
|
|
|
// Step 19. 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);
|
|
|
|
// PV move or new best move?
|
|
if (moveCount == 1 || value > alpha)
|
|
{
|
|
rm.score = value;
|
|
rm.selDepth = thisThread->selDepth;
|
|
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: When
|
|
// the best move changes frequently, we allocate some more time.
|
|
if (moveCount > 1 && thisThread == Threads.main())
|
|
++static_cast<MainThread*>(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
|
|
alpha = value;
|
|
else
|
|
{
|
|
assert(value >= beta); // Fail high
|
|
ss->statScore = 0;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (move != bestMove)
|
|
{
|
|
if (captureOrPromotion && captureCount < 32)
|
|
capturesSearched[captureCount++] = move;
|
|
|
|
else if (!captureOrPromotion && 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 20. 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 || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
|
|
|
|
if (!moveCount)
|
|
bestValue = excludedMove ? alpha
|
|
: inCheck ? mated_in(ss->ply) : VALUE_DRAW;
|
|
else if (bestMove)
|
|
{
|
|
// Quiet best move: update move sorting heuristics
|
|
if (!pos.capture_or_promotion(bestMove))
|
|
update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount,
|
|
stat_bonus(depth + (bestValue > beta + PawnValueMg ? ONE_PLY : DEPTH_ZERO)));
|
|
|
|
update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
|
|
|
|
// Extra penalty for a quiet TT move in previous ply when it gets refuted
|
|
if ((ss-1)->moveCount == 1 && !pos.captured_piece())
|
|
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
|
|
}
|
|
// Bonus for prior countermove that caused the fail low
|
|
else if ( (depth >= 3 * ONE_PLY || PvNode)
|
|
&& !pos.captured_piece()
|
|
&& is_ok((ss-1)->currentMove))
|
|
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
|
|
|
|
if (PvNode)
|
|
bestValue = std::min(bestValue, maxValue);
|
|
|
|
if (!excludedMove)
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply),
|
|
bestValue >= beta ? BOUND_LOWER :
|
|
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
|
|
depth, bestMove, pureStaticEval);
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
|
|
// qsearch() is the quiescence search function, which is called by the main
|
|
// search function with depth zero, or recursively with depth less than ONE_PLY.
|
|
template <NodeType NT>
|
|
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
|
|
|
|
constexpr bool PvNode = NT == PV;
|
|
|
|
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
|
|
assert(PvNode || (alpha == beta - 1));
|
|
assert(depth <= DEPTH_ZERO);
|
|
assert(depth / ONE_PLY * ONE_PLY == depth);
|
|
|
|
Move pv[MAX_PLY+1];
|
|
StateInfo st;
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, bestMove;
|
|
Depth ttDepth;
|
|
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
|
|
bool ttHit, inCheck, givesCheck, evasionPrunable;
|
|
int moveCount;
|
|
|
|
if (PvNode)
|
|
{
|
|
oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
|
|
(ss+1)->pv = pv;
|
|
ss->pv[0] = MOVE_NONE;
|
|
}
|
|
|
|
Thread* thisThread = pos.this_thread();
|
|
(ss+1)->ply = ss->ply + 1;
|
|
ss->currentMove = bestMove = MOVE_NONE;
|
|
ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
|
|
inCheck = pos.checkers();
|
|
moveCount = 0;
|
|
|
|
// Check for an immediate draw or maximum ply reached
|
|
if ( pos.is_draw(ss->ply)
|
|
|| ss->ply >= MAX_PLY)
|
|
return (ss->ply >= MAX_PLY && !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 = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
|
|
: DEPTH_QS_NO_CHECKS;
|
|
// Transposition table lookup
|
|
posKey = pos.key();
|
|
tte = TT.probe(posKey, ttHit);
|
|
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
|
|
ttMove = ttHit ? tte->move() : MOVE_NONE;
|
|
|
|
if ( !PvNode
|
|
&& ttHit
|
|
&& tte->depth() >= ttDepth
|
|
&& ttValue != VALUE_NONE // Only in case of TT access race
|
|
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
|
|
: (tte->bound() & BOUND_UPPER)))
|
|
return ttValue;
|
|
|
|
// Evaluate the position statically
|
|
if (inCheck)
|
|
{
|
|
ss->staticEval = VALUE_NONE;
|
|
bestValue = futilityBase = -VALUE_INFINITE;
|
|
}
|
|
else
|
|
{
|
|
if (ttHit)
|
|
{
|
|
// Never assume anything on values stored in TT
|
|
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
|
|
ss->staticEval = bestValue = evaluate(pos);
|
|
|
|
// Can ttValue be used as a better position evaluation?
|
|
if ( ttValue != VALUE_NONE
|
|
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
|
|
bestValue = ttValue;
|
|
}
|
|
else
|
|
ss->staticEval = bestValue =
|
|
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
|
|
: -(ss-1)->staticEval + 2 * Eval::Tempo;
|
|
|
|
// Stand pat. Return immediately if static value is at least beta
|
|
if (bestValue >= beta)
|
|
{
|
|
if (!ttHit)
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER,
|
|
DEPTH_NONE, MOVE_NONE, ss->staticEval);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
if (PvNode && bestValue > alpha)
|
|
alpha = bestValue;
|
|
|
|
futilityBase = bestValue + 128;
|
|
}
|
|
|
|
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->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 checks (only if depth >= DEPTH_QS_CHECKS) will
|
|
// be generated.
|
|
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
|
|
&thisThread->captureHistory,
|
|
contHist,
|
|
to_sq((ss-1)->currentMove));
|
|
|
|
// Loop through the moves until no moves remain or a beta cutoff occurs
|
|
while ((move = mp.next_move()) != MOVE_NONE)
|
|
{
|
|
assert(is_ok(move));
|
|
|
|
givesCheck = gives_check(pos, move);
|
|
|
|
moveCount++;
|
|
|
|
// Futility pruning
|
|
if ( !inCheck
|
|
&& !givesCheck
|
|
&& futilityBase > -VALUE_KNOWN_WIN
|
|
&& !pos.advanced_pawn_push(move))
|
|
{
|
|
assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
|
|
|
|
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;
|
|
}
|
|
}
|
|
|
|
// Detect non-capture evasions that are candidates to be pruned
|
|
evasionPrunable = inCheck
|
|
&& (depth != DEPTH_ZERO || moveCount > 2)
|
|
&& bestValue > VALUE_MATED_IN_MAX_PLY
|
|
&& !pos.capture(move);
|
|
|
|
// Don't search moves with negative SEE values
|
|
if ( (!inCheck || evasionPrunable)
|
|
&& !pos.see_ge(move))
|
|
continue;
|
|
|
|
// Speculative prefetch as early as possible
|
|
prefetch(TT.first_entry(pos.key_after(move)));
|
|
|
|
// Check for legality just before making the move
|
|
if (!pos.legal(move))
|
|
{
|
|
moveCount--;
|
|
continue;
|
|
}
|
|
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
|
|
|
|
// Make and search the move
|
|
pos.do_move(move, st, givesCheck);
|
|
value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
|
|
pos.undo_move(move);
|
|
|
|
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
|
|
|
|
// Check for a new best move
|
|
if (value > bestValue)
|
|
{
|
|
bestValue = value;
|
|
|
|
if (value > alpha)
|
|
{
|
|
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;
|
|
bestMove = move;
|
|
}
|
|
else // Fail high
|
|
{
|
|
tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
|
|
ttDepth, move, ss->staticEval);
|
|
|
|
return value;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// All legal moves have been searched. A special case: If we're in check
|
|
// and no legal moves were found, it is checkmate.
|
|
if (inCheck && bestValue == -VALUE_INFINITE)
|
|
return mated_in(ss->ply); // Plies to mate from the root
|
|
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply),
|
|
PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
|
|
ttDepth, bestMove, ss->staticEval);
|
|
|
|
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
|
|
// value_to_tt() adjusts a mate score from "plies to mate from the root" to
|
|
// "plies to mate from the current position". Non-mate 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_MATE_IN_MAX_PLY ? v + ply
|
|
: v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
|
|
}
|
|
|
|
|
|
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
|
|
// from the transposition table (which refers to the plies to mate/be mated
|
|
// from current position) to "plies to mate/be mated from the root".
|
|
|
|
Value value_from_tt(Value v, int ply) {
|
|
|
|
return v == VALUE_NONE ? VALUE_NONE
|
|
: v >= VALUE_MATE_IN_MAX_PLY ? v - ply
|
|
: v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
|
|
}
|
|
|
|
|
|
// update_pv() adds current move and appends child pv[]
|
|
|
|
void update_pv(Move* pv, Move move, Move* childPv) {
|
|
|
|
for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
|
|
*pv++ = *childPv++;
|
|
*pv = MOVE_NONE;
|
|
}
|
|
|
|
|
|
// update_continuation_histories() updates histories of the move pairs formed
|
|
// by moves at ply -1, -2, and -4 with current move.
|
|
|
|
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
|
|
|
|
for (int i : {1, 2, 4})
|
|
if (is_ok((ss-i)->currentMove))
|
|
(*(ss-i)->continuationHistory)[pc][to] << bonus;
|
|
}
|
|
|
|
|
|
// update_capture_stats() updates move sorting heuristics when a new capture best move is found
|
|
|
|
void update_capture_stats(const Position& pos, Move move,
|
|
Move* captures, int captureCnt, int bonus) {
|
|
|
|
CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
|
|
Piece moved_piece = pos.moved_piece(move);
|
|
PieceType captured = type_of(pos.piece_on(to_sq(move)));
|
|
|
|
if (pos.capture_or_promotion(move))
|
|
captureHistory[moved_piece][to_sq(move)][captured] << bonus;
|
|
|
|
// Decrease all the other played capture moves
|
|
for (int i = 0; i < captureCnt; ++i)
|
|
{
|
|
moved_piece = pos.moved_piece(captures[i]);
|
|
captured = type_of(pos.piece_on(to_sq(captures[i])));
|
|
captureHistory[moved_piece][to_sq(captures[i])][captured] << -bonus;
|
|
}
|
|
}
|
|
|
|
|
|
// update_quiet_stats() updates move sorting heuristics when a new quiet best move is found
|
|
|
|
void update_quiet_stats(const Position& pos, Stack* ss, Move move,
|
|
Move* quiets, int quietsCnt, int bonus) {
|
|
|
|
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);
|
|
|
|
if (is_ok((ss-1)->currentMove))
|
|
{
|
|
Square prevSq = to_sq((ss-1)->currentMove);
|
|
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
|
|
}
|
|
|
|
// Decrease all the other played quiet moves
|
|
for (int i = 0; i < quietsCnt; ++i)
|
|
{
|
|
thisThread->mainHistory[us][from_to(quiets[i])] << -bonus;
|
|
update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
|
|
}
|
|
}
|
|
|
|
// 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 weakness = 120 - 2 * level;
|
|
int maxScore = -VALUE_INFINITE;
|
|
|
|
// 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>() % 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 (Threads.ponder)
|
|
return;
|
|
|
|
if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
|
|
|| (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, Value alpha, Value beta) {
|
|
|
|
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 = (i <= pvIdx && rootMoves[i].score != -VALUE_INFINITE);
|
|
|
|
if (depth == ONE_PLY && !updated)
|
|
continue;
|
|
|
|
Depth d = updated ? depth : depth - ONE_PLY;
|
|
Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
|
|
|
|
bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
|
|
v = tb ? rootMoves[i].tbScore : v;
|
|
|
|
if (ss.rdbuf()->in_avail()) // Not at first line
|
|
ss << "\n";
|
|
|
|
ss << "info"
|
|
<< " depth " << d / ONE_PLY
|
|
<< " seldepth " << rootMoves[i].selDepth
|
|
<< " multipv " << i + 1
|
|
<< " score " << UCI::value(v);
|
|
|
|
if (!tb && i == pvIdx)
|
|
ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
|
|
|
|
ss << " nodes " << nodesSearched
|
|
<< " nps " << nodesSearched * 1000 / elapsed;
|
|
|
|
if (elapsed > 1000) // Earlier makes little sense
|
|
ss << " hashfull " << TT.hashfull();
|
|
|
|
ss << " tbhits " << tbHits
|
|
<< " time " << elapsed
|
|
<< " pv";
|
|
|
|
for (Move m : rootMoves[i].pv)
|
|
ss << " " << UCI::move(m, pos.is_chess960());
|
|
}
|
|
|
|
return ss.str();
|
|
}
|
|
|
|
|
|
/// RootMove::extract_ponder_from_tt() is 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 on.
|
|
|
|
bool RootMove::extract_ponder_from_tt(Position& pos) {
|
|
|
|
StateInfo st;
|
|
bool ttHit;
|
|
|
|
assert(pv.size() == 1);
|
|
|
|
if (!pv[0])
|
|
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;
|
|
}
|
|
|
|
void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
|
|
|
|
RootInTB = false;
|
|
UseRule50 = bool(Options["Syzygy50MoveRule"]);
|
|
ProbeDepth = int(Options["SyzygyProbeDepth"]) * ONE_PLY;
|
|
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 = DEPTH_ZERO;
|
|
}
|
|
|
|
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::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
|
|
{
|
|
// Assign the same rank to all moves
|
|
for (auto& m : rootMoves)
|
|
m.tbRank = 0;
|
|
}
|
|
}
|