mirror of
https://github.com/sockspls/badfish
synced 2025-04-30 00:33:09 +00:00
3f4191392c
Based on machinery introduced by vondele. Logic behind patch if relatively simple - if we reduce less with high hit rate of transposition table somewhat logical is to reduce more with low hit rate. For example enable all captures for LMR. Threshold 0.375 is arbitrary and can be tweaked :) STC http://tests.stockfishchess.org/tests/view/5dd4d51df531e81cf278eaac LLR: 2.97 (-2.94,2.94) [-1.50,4.50] Total: 16495 W: 3591 L: 3434 D: 9470 LTC http://tests.stockfishchess.org/tests/view/5dd52265f531e81cf278eace LLR: 2.96 (-2.94,2.94) [0.00,3.50] Total: 23598 W: 3956 L: 3716 D: 15926 Closes https://github.com/official-stockfish/Stockfish/pull/2420 Bench: 5067870
1839 lines
65 KiB
C++
1839 lines
65 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) 2015-2019 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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constexpr uint64_t ttHitAverageWindow = 4096;
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constexpr uint64_t ttHitAverageResolution = 1024;
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// Razor and futility margins
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constexpr int RazorMargin = 661;
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Value futility_margin(Depth d, bool improving) {
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return Value(198 * (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) {
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int r = Reductions[d] * Reductions[mn];
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return (r + 520) / 1024 + (!i && r > 999);
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}
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constexpr int futility_move_count(bool improving, Depth depth) {
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return (5 + depth * depth) * (1 + improving) / 2 - 1;
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}
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// History and stats update bonus, based on depth
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int stat_bonus(Depth d) {
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return d > 17 ? -8 : 22 * d * d + 151 * d - 140;
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}
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// Add a small random component to draw evaluations to avoid 3fold-blindness
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Value value_draw(Thread* thisThread) {
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return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
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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 == 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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// Breadcrumbs are used to mark nodes as being searched by a given thread
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struct Breadcrumb {
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std::atomic<Thread*> thread;
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std::atomic<Key> key;
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};
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std::array<Breadcrumb, 1024> breadcrumbs;
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// ThreadHolding structure keeps track of which thread left breadcrumbs at the given
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// node for potential reductions. A free node will be marked upon entering the moves
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// loop by the constructor, and unmarked upon leaving that loop by the destructor.
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struct ThreadHolding {
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explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) {
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location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr;
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otherThread = false;
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owning = false;
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if (location)
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{
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// See if another already marked this location, if not, mark it ourselves
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Thread* tmp = (*location).thread.load(std::memory_order_relaxed);
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if (tmp == nullptr)
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{
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(*location).thread.store(thisThread, std::memory_order_relaxed);
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(*location).key.store(posKey, std::memory_order_relaxed);
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owning = true;
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}
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else if ( tmp != thisThread
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&& (*location).key.load(std::memory_order_relaxed) == posKey)
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otherThread = true;
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}
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}
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~ThreadHolding() {
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if (owning) // Free the marked location
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(*location).thread.store(nullptr, std::memory_order_relaxed);
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}
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bool marked() { return otherThread; }
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private:
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Breadcrumb* location;
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bool otherThread, owning;
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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 = 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, 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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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((23.4 + 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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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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{
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th->bestMoveChanges = 0;
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if (th != this)
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th->start_searching();
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}
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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.
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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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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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Thread* bestThread = this;
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// Check if there are threads with a better score than main thread
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if ( Options["MultiPV"] == 1
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&& !Limits.depth
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&& !(Skill(Options["Skill Level"]).enabled() || Options["UCI_LimitStrength"])
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&& rootMoves[0].pv[0] != MOVE_NONE)
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{
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std::map<Move, int64_t> votes;
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Value minScore = this->rootMoves[0].score;
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// Find out minimum score
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for (Thread* th: Threads)
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minScore = std::min(minScore, th->rootMoves[0].score);
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// Vote according to score and depth, and select the best thread
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for (Thread* th : Threads)
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{
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votes[th->rootMoves[0].pv[0]] +=
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(th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
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if (bestThread->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY)
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{
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// Make sure we pick the shortest mate
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if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
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bestThread = th;
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}
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else if ( th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY
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|| votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]])
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bestThread = th;
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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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// 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 statScores 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 bestValue, 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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std::memset(ss-7, 0, 10 * sizeof(Stack));
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for (int i = 7; i > 0; i--)
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(ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
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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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size_t multiPV = Options["MultiPV"];
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// Pick integer skill levels, but non-deterministically round up or down
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// such that the average integer skill corresponds to the input floating point one.
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// UCI_Elo is converted to a suitable fractional skill level, using anchoring
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// to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo
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// for match (TC 60+0.6) results spanning a wide range of k values.
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PRNG rng(now());
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double floatLevel = Options["UCI_LimitStrength"] ?
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clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
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double(Options["Skill Level"]);
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int intLevel = int(floatLevel) +
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((floatLevel - int(floatLevel)) * 1024 > rng.rand<unsigned>() % 1024 ? 1 : 0);
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Skill skill(intLevel);
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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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ttHitAverage = ttHitAverageWindow * ttHitAverageResolution / 2;
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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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// Evaluation score 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 < 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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// 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 previousScore = rootMoves[pvIdx].previousScore;
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delta = Value(21 + abs(previousScore) / 128);
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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 + (111 - ct / 2) * previousScore / (abs(previousScore) + 176);
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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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int failedHighCnt = 0;
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while (true)
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{
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Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt);
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bestValue = ::search<PV>(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, 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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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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|
{
|
|
beta = std::min(bestValue + delta, VALUE_INFINITE);
|
|
++failedHighCnt;
|
|
}
|
|
else
|
|
{
|
|
++rootMoves[pvIdx].bestMoveCount;
|
|
break;
|
|
}
|
|
|
|
delta += delta / 4 + 5;
|
|
|
|
assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
|
|
}
|
|
|
|
// Sort the PV lines searched so far and update the GUI
|
|
std::stable_sort(rootMoves.begin() + pvFirst, rootMoves.begin() + pvIdx + 1);
|
|
|
|
if ( mainThread
|
|
&& (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000))
|
|
sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
|
|
}
|
|
|
|
if (!Threads.stop)
|
|
completedDepth = rootDepth;
|
|
|
|
if (rootMoves[0].pv[0] != lastBestMove) {
|
|
lastBestMove = rootMoves[0].pv[0];
|
|
lastBestMoveDepth = rootDepth;
|
|
}
|
|
|
|
// Have we found a "mate in x"?
|
|
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
|
|
&& !mainThread->stopOnPonderhit)
|
|
{
|
|
double fallingEval = (354 + 10 * (mainThread->previousScore - bestValue)) / 692.0;
|
|
fallingEval = clamp(fallingEval, 0.5, 1.5);
|
|
|
|
// If the bestMove is stable over several iterations, reduce time accordingly
|
|
timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.97 : 0.98;
|
|
double reduction = (1.36 + mainThread->previousTimeReduction) / (2.29 * timeReduction);
|
|
|
|
// Use part of the gained time from a previous stable move for the current move
|
|
for (Thread* th : Threads)
|
|
{
|
|
totBestMoveChanges += th->bestMoveChanges;
|
|
th->bestMoveChanges = 0;
|
|
}
|
|
double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
|
|
|
|
// Stop the search if we have only one legal move, or if available time elapsed
|
|
if ( rootMoves.size() == 1
|
|
|| Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability)
|
|
{
|
|
// 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;
|
|
}
|
|
}
|
|
}
|
|
|
|
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(pos.this_thread());
|
|
if (alpha >= beta)
|
|
return alpha;
|
|
}
|
|
|
|
// Dive into quiescence search when the depth reaches zero
|
|
if (depth <= 0)
|
|
return qsearch<NT>(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;
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, excludedMove, bestMove;
|
|
Depth extension, newDepth;
|
|
Value bestValue, value, ttValue, eval, maxValue;
|
|
bool ttHit, ttPv, inCheck, givesCheck, improving, didLMR, priorCapture;
|
|
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture, singularLMR;
|
|
Piece movedPiece;
|
|
int moveCount, captureCount, quietCount;
|
|
|
|
// Step 1. Initialize node
|
|
Thread* thisThread = pos.this_thread();
|
|
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 && !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;
|
|
}
|
|
|
|
assert(0 <= ss->ply && ss->ply < MAX_PLY);
|
|
|
|
(ss+1)->ply = ss->ply + 1;
|
|
(ss+1)->excludedMove = bestMove = MOVE_NONE;
|
|
(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.
|
|
if (rootNode)
|
|
(ss+4)->statScore = 0;
|
|
else
|
|
(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, pos.rule50_count()) : VALUE_NONE;
|
|
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
|
|
: ttHit ? tte->move() : MOVE_NONE;
|
|
ttPv = PvNode || (ttHit && tte->is_pv());
|
|
// thisThread->ttHitAverage can be used to approximate the running average of ttHit
|
|
thisThread->ttHitAverage = (ttHitAverageWindow - 1) * thisThread->ttHitAverage / ttHitAverageWindow
|
|
+ ttHitAverageResolution * ttHit;
|
|
|
|
// 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, stat_bonus(depth));
|
|
|
|
// Extra penalty for early quiet moves of the previous ply
|
|
if ((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
|
|
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);
|
|
|
|
// 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;
|
|
|
|
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), 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;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Step 6. Static evaluation of the position
|
|
if (inCheck)
|
|
{
|
|
ss->staticEval = eval = VALUE_NONE;
|
|
improving = false;
|
|
goto moves_loop; // Skip early pruning when in check
|
|
}
|
|
else if (ttHit)
|
|
{
|
|
// Never assume anything about values stored in TT
|
|
ss->staticEval = eval = tte->eval();
|
|
if (eval == VALUE_NONE)
|
|
ss->staticEval = eval = evaluate(pos);
|
|
|
|
if (eval == VALUE_DRAW)
|
|
eval = value_draw(thisThread);
|
|
|
|
// 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 bonus = -(ss-1)->statScore / 512;
|
|
|
|
ss->staticEval = eval = evaluate(pos) + bonus;
|
|
}
|
|
else
|
|
ss->staticEval = eval = -(ss-1)->staticEval + 2 * Eval::Tempo;
|
|
|
|
tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
|
|
}
|
|
|
|
// Step 7. Razoring (~2 Elo)
|
|
if ( !rootNode // The required rootNode PV handling is not available in qsearch
|
|
&& depth < 2
|
|
&& 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 ( !PvNode
|
|
&& depth < 7
|
|
&& 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 < 22661
|
|
&& eval >= beta
|
|
&& eval >= ss->staticEval
|
|
&& ss->staticEval >= beta - 33 * depth + 299 - improving * 30
|
|
&& !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 = (835 + 70 * depth) / 256 + std::min(int(eval - beta) / 185, 3);
|
|
|
|
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 scores
|
|
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
|
|
nullValue = beta;
|
|
|
|
if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13))
|
|
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
|
|
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
|
|
{
|
|
Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
|
|
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
|
|
int probCutCount = 0;
|
|
|
|
while ( (move = mp.next_move()) != MOVE_NONE
|
|
&& probCutCount < 2 + 2 * cutNode)
|
|
if (move != excludedMove && pos.legal(move))
|
|
{
|
|
assert(pos.capture_or_promotion(move));
|
|
assert(depth >= 5);
|
|
|
|
captureOrPromotion = true;
|
|
probCutCount++;
|
|
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[inCheck]
|
|
[captureOrPromotion]
|
|
[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, -raisedBeta, -raisedBeta+1);
|
|
|
|
// If the qsearch held, perform the regular search
|
|
if (value >= raisedBeta)
|
|
value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4, !cutNode);
|
|
|
|
pos.undo_move(move);
|
|
|
|
if (value >= raisedBeta)
|
|
return value;
|
|
}
|
|
}
|
|
|
|
// Step 11. Internal iterative deepening (~2 Elo)
|
|
if (depth >= 7 && !ttMove)
|
|
{
|
|
search<NT>(pos, ss, alpha, beta, depth - 7, cutNode);
|
|
|
|
tte = TT.probe(posKey, ttHit);
|
|
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : 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,
|
|
nullptr , (ss-6)->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;
|
|
singularLMR = moveCountPruning = false;
|
|
ttCapture = ttMove && pos.capture_or_promotion(ttMove);
|
|
|
|
// Mark this node as being searched
|
|
ThreadHolding th(thisThread, posKey, ss->ply);
|
|
|
|
// Step 12. 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;
|
|
|
|
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;
|
|
captureOrPromotion = pos.capture_or_promotion(move);
|
|
movedPiece = pos.moved_piece(move);
|
|
givesCheck = pos.gives_check(move);
|
|
|
|
// Calculate new depth for this move
|
|
newDepth = depth - 1;
|
|
|
|
// Step 13. Pruning at shallow depth (~170 Elo)
|
|
if ( !rootNode
|
|
&& pos.non_pawn_material(us)
|
|
&& bestValue > VALUE_MATED_IN_MAX_PLY)
|
|
{
|
|
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
|
|
moveCountPruning = moveCount >= futility_move_count(improving, depth);
|
|
|
|
if ( !captureOrPromotion
|
|
&& !givesCheck)
|
|
{
|
|
// Reduced depth of the next LMR search
|
|
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
|
|
|
|
// Countermoves based pruning (~20 Elo)
|
|
if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
|
|
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
|
|
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
|
|
continue;
|
|
|
|
// Futility pruning: parent node (~2 Elo)
|
|
if ( lmrDepth < 6
|
|
&& !inCheck
|
|
&& ss->staticEval + 250 + 211 * lmrDepth <= alpha)
|
|
continue;
|
|
|
|
// Prune moves with negative SEE (~10 Elo)
|
|
if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
|
|
continue;
|
|
}
|
|
else if (!pos.see_ge(move, Value(-199) * depth)) // (~20 Elo)
|
|
continue;
|
|
}
|
|
|
|
// Step 14. 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 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 >= 6
|
|
&& move == ttMove
|
|
&& !rootNode
|
|
&& !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
|
|
&& pos.legal(move))
|
|
{
|
|
Value singularBeta = ttValue - 2 * depth;
|
|
Depth halfDepth = depth / 2;
|
|
ss->excludedMove = move;
|
|
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
|
|
ss->excludedMove = MOVE_NONE;
|
|
|
|
if (value < singularBeta)
|
|
{
|
|
extension = 1;
|
|
singularLMR = true;
|
|
}
|
|
|
|
// 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 ( eval >= beta
|
|
&& singularBeta >= beta)
|
|
return singularBeta;
|
|
}
|
|
|
|
// Check extension (~2 Elo)
|
|
else if ( givesCheck
|
|
&& (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
|
|
extension = 1;
|
|
|
|
// Passed pawn extension
|
|
else if ( move == ss->killers[0]
|
|
&& pos.advanced_pawn_push(move)
|
|
&& pos.pawn_passed(us, to_sq(move)))
|
|
extension = 1;
|
|
|
|
// Castling extension
|
|
if (type_of(move) == CASTLING)
|
|
extension = 1;
|
|
|
|
// Add extension to new depth
|
|
newDepth += extension;
|
|
|
|
// 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;
|
|
}
|
|
|
|
// Update the current move (this must be done after singular extension search)
|
|
ss->currentMove = move;
|
|
ss->continuationHistory = &thisThread->continuationHistory[inCheck]
|
|
[captureOrPromotion]
|
|
[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
|
|
&& moveCount > 1 + 2 * rootNode
|
|
&& (!rootNode || thisThread->best_move_count(move) == 0)
|
|
&& ( !captureOrPromotion
|
|
|| moveCountPruning
|
|
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
|
|
|| cutNode
|
|
|| thisThread->ttHitAverage < 384 * ttHitAverageResolution * ttHitAverageWindow / 1024))
|
|
{
|
|
Depth r = reduction(improving, depth, moveCount);
|
|
|
|
// Decrease reduction if the ttHit running average is large
|
|
if (thisThread->ttHitAverage > 544 * ttHitAverageResolution * ttHitAverageWindow / 1024)
|
|
r--;
|
|
|
|
// Reduction if other threads are searching this position.
|
|
if (th.marked())
|
|
r++;
|
|
|
|
// Decrease reduction if position is or has been on the PV
|
|
if (ttPv)
|
|
r -= 2;
|
|
|
|
// Decrease reduction if opponent's move count is high (~10 Elo)
|
|
if ((ss-1)->moveCount > 15)
|
|
r--;
|
|
|
|
// Decrease reduction if ttMove has been singularly extended
|
|
if (singularLMR)
|
|
r -= 2;
|
|
|
|
if (!captureOrPromotion)
|
|
{
|
|
// Increase reduction if ttMove is a capture (~0 Elo)
|
|
if (ttCapture)
|
|
r++;
|
|
|
|
// Increase reduction for cut nodes (~5 Elo)
|
|
if (cutNode)
|
|
r += 2;
|
|
|
|
// 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(reverse_move(move)))
|
|
r -= 2;
|
|
|
|
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)]
|
|
- 4729;
|
|
|
|
// Reset statScore to zero if negative and most stats shows >= 0
|
|
if ( ss->statScore < 0
|
|
&& (*contHist[0])[movedPiece][to_sq(move)] >= 0
|
|
&& (*contHist[1])[movedPiece][to_sq(move)] >= 0
|
|
&& thisThread->mainHistory[us][from_to(move)] >= 0)
|
|
ss->statScore = 0;
|
|
|
|
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
|
|
if (ss->statScore >= -99 && (ss-1)->statScore < -116)
|
|
r--;
|
|
|
|
else if ((ss-1)->statScore >= -117 && ss->statScore < -144)
|
|
r++;
|
|
|
|
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
|
|
r -= ss->statScore / 16384;
|
|
}
|
|
|
|
Depth d = clamp(newDepth - r, 1, newDepth);
|
|
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
|
|
|
|
doFullDepthSearch = (value > alpha && d != newDepth), didLMR = true;
|
|
}
|
|
else
|
|
doFullDepthSearch = !PvNode || moveCount > 1, didLMR = false;
|
|
|
|
// 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);
|
|
|
|
if (didLMR && !captureOrPromotion)
|
|
{
|
|
int bonus = value > alpha ? stat_bonus(newDepth)
|
|
: -stat_bonus(newDepth);
|
|
|
|
if (move == ss->killers[0])
|
|
bonus += bonus / 4;
|
|
|
|
update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
|
|
}
|
|
}
|
|
|
|
// 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->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)
|
|
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 ( (depth >= 3 || PvNode)
|
|
&& !priorCapture)
|
|
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), 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.
|
|
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 <= 0);
|
|
|
|
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, pvHit, inCheck, givesCheck, captureOrPromotion, 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;
|
|
bestMove = MOVE_NONE;
|
|
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, pos.rule50_count()) : VALUE_NONE;
|
|
ttMove = ttHit ? tte->move() : MOVE_NONE;
|
|
pvHit = ttHit && tte->is_pv();
|
|
|
|
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 about 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), pvHit, BOUND_LOWER,
|
|
DEPTH_NONE, MOVE_NONE, ss->staticEval);
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
if (PvNode && bestValue > alpha)
|
|
alpha = bestValue;
|
|
|
|
futilityBase = bestValue + 153;
|
|
}
|
|
|
|
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 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 = pos.gives_check(move);
|
|
captureOrPromotion = pos.capture_or_promotion(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 != 0 || moveCount > 2)
|
|
&& bestValue > VALUE_MATED_IN_MAX_PLY
|
|
&& !pos.capture(move);
|
|
|
|
// Don't search moves with negative SEE values
|
|
if ( (!inCheck || evasionPrunable)
|
|
&& !(givesCheck && pos.is_discovery_check_on_king(~pos.side_to_move(), move))
|
|
&& !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[inCheck]
|
|
[captureOrPromotion]
|
|
[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 - 1);
|
|
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)
|
|
{
|
|
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
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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), pvHit,
|
|
bestValue >= beta ? BOUND_LOWER :
|
|
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, int r50c) {
|
|
|
|
return v == VALUE_NONE ? VALUE_NONE
|
|
: v >= VALUE_MATE_IN_MAX_PLY ? VALUE_MATE - v > 99 - r50c ? VALUE_MATE_IN_MAX_PLY : v - ply
|
|
: v <= VALUE_MATED_IN_MAX_PLY ? VALUE_MATE + v > 99 - r50c ? 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_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) {
|
|
|
|
int bonus1, bonus2;
|
|
Color us = pos.side_to_move();
|
|
Thread* thisThread = pos.this_thread();
|
|
CapturePieceToHistory& captureHistory = thisThread->captureHistory;
|
|
Piece moved_piece = pos.moved_piece(bestMove);
|
|
PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
|
|
|
|
bonus1 = stat_bonus(depth + 1);
|
|
bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
|
|
: stat_bonus(depth); // smaller bonus
|
|
|
|
if (!pos.capture_or_promotion(bestMove))
|
|
{
|
|
update_quiet_stats(pos, ss, bestMove, bonus2);
|
|
|
|
// Decrease all the 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
|
|
captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
|
|
|
|
// Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
|
|
if ( ((ss-1)->moveCount == 1 || ((ss-1)->currentMove == (ss-1)->killers[0]))
|
|
&& !pos.captured_piece())
|
|
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1);
|
|
|
|
// Decrease all the 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, and -4 with current move.
|
|
|
|
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
|
|
|
|
for (int i : {1, 2, 4, 6})
|
|
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) {
|
|
|
|
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 (type_of(pos.moved_piece(move)) != PAWN)
|
|
thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
|
|
|
|
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 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 (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, 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 == 1 && !updated)
|
|
continue;
|
|
|
|
Depth d = updated ? depth : depth - 1;
|
|
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
|
|
<< " 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] == MOVE_NONE)
|
|
return false;
|
|
|
|
pos.do_move(pv[0], st);
|
|
TTEntry* tte = TT.probe(pos.key(), ttHit);
|
|
|
|
if (ttHit)
|
|
{
|
|
Move m = tte->move(); // Local copy to be SMP safe
|
|
if (MoveList<LEGAL>(pos).contains(m))
|
|
pv.push_back(m);
|
|
}
|
|
|
|
pos.undo_move(pv[0]);
|
|
return pv.size() > 1;
|
|
}
|
|
|
|
void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
|
|
|
|
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::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;
|
|
}
|
|
}
|