mirror of
https://github.com/sockspls/badfish
synced 2025-04-30 08:43:09 +00:00
3cb0200459
the nodes, tbHits, rootDepth and lastInfoTime variables are read by multiple threads, but not declared atomic, leading to data races as found by -fsanitize=thread. This patch fixes this issue. It is based on top of the CI-threading branch (PR #1129), and should fix the corresponding CI error messages. The patch passed an STC check for no regression: http://tests.stockfishchess.org/tests/view/5925d5590ebc59035df34b9f LLR: 2.96 (-2.94,2.94) [-3.00,1.00] Total: 169597 W: 29938 L: 30066 D: 109593 Whereas rootDepth and lastInfoTime are not performance critical, nodes and tbHits are. Indeed, an earlier version using relaxed atomic updates on the latter two variables failed STC testing (http://tests.stockfishchess.org/tests/view/592001700ebc59035df34924), which can be shown to be due to x86-32 (http://tests.stockfishchess.org/tests/view/592330ac0ebc59035df34a89). Indeed, the latter have no instruction to atomically update a 64bit variable. The proposed solution thus uses a variable in Position that is accessed only by one thread, which is copied every few thousand nodes to the shared variable in Thread. No functional change. Closes #1130 Closes #1129
1629 lines
56 KiB
C++
1629 lines
56 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) 2015-2017 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 "timeman.h"
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#include "thread.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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SignalsType Signals;
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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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Value Score;
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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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const 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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const 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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// Razoring and futility margin based on depth
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// razor_margin[0] is unused as long as depth >= ONE_PLY in search
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const int razor_margin[] = { 0, 570, 603, 554 };
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Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
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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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// Threshold used for countermoves based pruning
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const int CounterMovePruneThreshold = 0;
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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 : d * d + 2 * d - 2;
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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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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 best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
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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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// EasyMoveManager structure is used to detect an 'easy move'. When the PV is stable
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// across multiple search iterations, we can quickly return the best move.
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struct EasyMoveManager {
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void clear() {
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stableCnt = 0;
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expectedPosKey = 0;
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pv[0] = pv[1] = pv[2] = MOVE_NONE;
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}
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Move get(Key key) const {
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return expectedPosKey == key ? pv[2] : MOVE_NONE;
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}
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void update(Position& pos, const std::vector<Move>& newPv) {
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assert(newPv.size() >= 3);
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// Keep track of how many times in a row the 3rd ply remains stable
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stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
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if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
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{
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std::copy(newPv.begin(), newPv.begin() + 3, pv);
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StateInfo st[2];
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pos.do_move(newPv[0], st[0]);
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pos.do_move(newPv[1], st[1]);
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expectedPosKey = pos.key();
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pos.undo_move(newPv[1]);
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pos.undo_move(newPv[0]);
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}
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}
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int stableCnt;
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Key expectedPosKey;
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Move pv[3];
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};
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EasyMoveManager EasyMove;
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Value DrawValue[COLOR_NB];
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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, bool skipEarlyPruning);
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template <NodeType NT, bool InCheck>
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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_cm_stats(Stack* ss, Piece pc, Square s, int bonus);
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void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
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void check_time();
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} // namespace
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/// Search::init() is called during 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 && Reductions[NonPV][imp][d][mc] >= 2)
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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, to obtain reproducible results
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void Search::clear() {
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TT.clear();
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for (Thread* th : Threads)
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{
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th->resetCalls = true;
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th->counterMoves.fill(MOVE_NONE);
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th->history.fill(0);
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for (auto& to : th->counterMoveHistory)
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for (auto& h : to)
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h.fill(0);
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th->counterMoveHistory[NO_PIECE][0].fill(CounterMovePruneThreshold - 1);
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}
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Threads.main()->previousScore = VALUE_INFINITE;
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}
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/// Search::perft() is our utility to verify move generation. All the leaf nodes
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/// up 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 Search::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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template uint64_t Search::perft<true>(Position&, Depth);
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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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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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int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
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DrawValue[ us] = VALUE_DRAW - Value(contempt);
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DrawValue[~us] = VALUE_DRAW + Value(contempt);
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if (rootMoves.empty())
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{
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rootMoves.push_back(RootMove(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 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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// When we reach the maximum depth, we can arrive here without a raise of
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// Signals.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 Signals.stop).
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if (!Signals.stop && (Limits.ponder || Limits.infinite))
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{
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Signals.stopOnPonderhit = true;
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wait(Signals.stop);
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}
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// Stop the threads if not already stopped
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Signals.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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// Check if there are threads with a better score than main thread
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Thread* bestThread = this;
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if ( !this->easyMovePlayed
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&& 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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for (Thread* th : Threads)
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{
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Depth depthDiff = th->completedDepth - bestThread->completedDepth;
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Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
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if (scoreDiff > 0 && depthDiff >= 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 new PV when needed
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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 allow referencing (ss-4) and (ss+2)
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Value bestValue, alpha, beta, delta;
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Move easyMove = MOVE_NONE;
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MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
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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)->history = &this->counterMoveHistory[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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completedDepth = DEPTH_ZERO;
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if (mainThread)
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{
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easyMove = EasyMove.get(rootPos.key());
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EasyMove.clear();
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mainThread->easyMovePlayed = mainThread->failedLow = false;
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mainThread->bestMoveChanges = 0;
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}
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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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// Iterative deepening loop until requested to stop or the target depth is reached
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while ( (rootDepth = rootDepth + ONE_PLY) < DEPTH_MAX
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&& !Signals.stop
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&& (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
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{
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// Distribute search depths across the threads
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if (idx)
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{
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int i = (idx - 1) % 20;
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if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2)
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continue;
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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 *= 0.505, mainThread->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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// MultiPV loop. We perform a full root search for each PV line
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for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
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{
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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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delta = Value(18);
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alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
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beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
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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're not failing
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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, false);
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this->tbHits = rootPos.tb_hits();
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this->nodes = rootPos.nodes_searched();
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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.end());
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// If search has been stopped, we break immediately. Sorting and
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// writing PV back to TT is safe because RootMoves is still
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// valid, although it refers to the previous iteration.
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if (Signals.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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mainThread->failedLow = true;
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Signals.stopOnPonderhit = false;
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}
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}
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else if (bestValue >= beta)
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{
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alpha = (alpha + beta) / 2;
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beta = std::min(bestValue + delta, VALUE_INFINITE);
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}
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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(), rootMoves.begin() + PVIdx + 1);
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if (!mainThread)
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continue;
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if (Signals.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 (!Signals.stop)
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completedDepth = rootDepth;
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if (!mainThread)
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continue;
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// If skill level is enabled and time is up, pick a sub-optimal best move
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if (skill.enabled() && skill.time_to_pick(rootDepth))
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skill.pick_best(multiPV);
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// Have we found a "mate in x"?
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if ( Limits.mate
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&& bestValue >= VALUE_MATE_IN_MAX_PLY
|
|
&& VALUE_MATE - bestValue <= 2 * Limits.mate)
|
|
Signals.stop = true;
|
|
|
|
// Do we have time for the next iteration? Can we stop searching now?
|
|
if (Limits.use_time_management())
|
|
{
|
|
if (!Signals.stop && !Signals.stopOnPonderhit)
|
|
{
|
|
// Stop the search if only one legal move is available, or if all
|
|
// of the available time has been used, or if we matched an easyMove
|
|
// from the previous search and just did a fast verification.
|
|
const int F[] = { mainThread->failedLow,
|
|
bestValue - mainThread->previousScore };
|
|
|
|
int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
|
|
double unstablePvFactor = 1 + mainThread->bestMoveChanges;
|
|
|
|
bool doEasyMove = rootMoves[0].pv[0] == easyMove
|
|
&& mainThread->bestMoveChanges < 0.03
|
|
&& Time.elapsed() > Time.optimum() * 5 / 44;
|
|
|
|
if ( rootMoves.size() == 1
|
|
|| Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
|
|
|| (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
|
|
{
|
|
// If we are allowed to ponder do not stop the search now but
|
|
// keep pondering until the GUI sends "ponderhit" or "stop".
|
|
if (Limits.ponder)
|
|
Signals.stopOnPonderhit = true;
|
|
else
|
|
Signals.stop = true;
|
|
}
|
|
}
|
|
|
|
if (rootMoves[0].pv.size() >= 3)
|
|
EasyMove.update(rootPos, rootMoves[0].pv);
|
|
else
|
|
EasyMove.clear();
|
|
}
|
|
}
|
|
|
|
if (!mainThread)
|
|
return;
|
|
|
|
// Clear any candidate easy move that wasn't stable for the last search
|
|
// iterations; the second condition prevents consecutive fast moves.
|
|
if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
|
|
EasyMove.clear();
|
|
|
|
// 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_move(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, bool skipEarlyPruning) {
|
|
|
|
const bool PvNode = NT == PV;
|
|
const bool rootNode = PvNode && (ss-1)->ply == 0;
|
|
|
|
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], quietsSearched[64];
|
|
StateInfo st;
|
|
TTEntry* tte;
|
|
Key posKey;
|
|
Move ttMove, move, excludedMove, bestMove;
|
|
Depth extension, newDepth;
|
|
Value bestValue, value, ttValue, eval;
|
|
bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
|
|
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets;
|
|
Piece moved_piece;
|
|
int moveCount, quietCount;
|
|
|
|
// Step 1. Initialize node
|
|
Thread* thisThread = pos.this_thread();
|
|
inCheck = pos.checkers();
|
|
moveCount = quietCount = ss->moveCount = 0;
|
|
ss->statScore = 0;
|
|
bestValue = -VALUE_INFINITE;
|
|
ss->ply = (ss-1)->ply + 1;
|
|
|
|
// Check for the available remaining time
|
|
if (thisThread->resetCalls.load(std::memory_order_relaxed))
|
|
{
|
|
thisThread->resetCalls = false;
|
|
|
|
thisThread->tbHits = pos.tb_hits();
|
|
thisThread->nodes = pos.nodes_searched();
|
|
|
|
// At low node count increase the checking rate to about 0.1% of nodes
|
|
// otherwise use a default value.
|
|
thisThread->callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024))
|
|
: 4096;
|
|
}
|
|
|
|
if (--thisThread->callsCnt <= 0)
|
|
{
|
|
for (Thread* th : Threads)
|
|
th->resetCalls = true;
|
|
|
|
check_time();
|
|
}
|
|
|
|
// Used to send selDepth info to GUI
|
|
if (PvNode && thisThread->maxPly < ss->ply)
|
|
thisThread->maxPly = ss->ply;
|
|
|
|
if (!rootNode)
|
|
{
|
|
// Step 2. Check for aborted search and immediate draw
|
|
if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
|
|
return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
|
|
: DrawValue[pos.side_to_move()];
|
|
|
|
// 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->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
|
|
ss->history = &thisThread->counterMoveHistory[NO_PIECE][0];
|
|
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
|
|
Square prevSq = to_sq((ss-1)->currentMove);
|
|
|
|
// 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);
|
|
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_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_cm_stats(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->history.update(pos.side_to_move(), ttMove, penalty);
|
|
update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
|
|
}
|
|
}
|
|
return ttValue;
|
|
}
|
|
|
|
// Step 4a. Tablebase 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 v = Tablebases::probe_wdl(pos, &err);
|
|
|
|
if (err != TB::ProbeState::FAIL)
|
|
{
|
|
pos.increment_tbHits();
|
|
|
|
int drawScore = TB::UseRule50 ? 1 : 0;
|
|
|
|
value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
|
|
: v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
|
|
: VALUE_DRAW + 2 * v * drawScore;
|
|
|
|
tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
|
|
std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
|
|
MOVE_NONE, VALUE_NONE, TT.generation());
|
|
|
|
return value;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Step 5. Evaluate the position statically
|
|
if (inCheck)
|
|
{
|
|
ss->staticEval = eval = VALUE_NONE;
|
|
goto moves_loop;
|
|
}
|
|
|
|
else if (ttHit)
|
|
{
|
|
// Never assume anything on values stored in TT
|
|
if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
|
|
eval = ss->staticEval = evaluate(pos);
|
|
|
|
// Can ttValue be used as a better position evaluation?
|
|
if (ttValue != VALUE_NONE)
|
|
if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
|
|
eval = ttValue;
|
|
}
|
|
else
|
|
{
|
|
eval = ss->staticEval =
|
|
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
|
|
: -(ss-1)->staticEval + 2 * Eval::Tempo;
|
|
|
|
tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
|
|
ss->staticEval, TT.generation());
|
|
}
|
|
|
|
if (skipEarlyPruning)
|
|
goto moves_loop;
|
|
|
|
// Step 6. Razoring (skipped when in check)
|
|
if ( !PvNode
|
|
&& depth < 4 * ONE_PLY
|
|
&& eval + razor_margin[depth / ONE_PLY] <= alpha)
|
|
{
|
|
if (depth <= ONE_PLY)
|
|
return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
|
|
|
|
Value ralpha = alpha - razor_margin[depth / ONE_PLY];
|
|
Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
|
|
if (v <= ralpha)
|
|
return v;
|
|
}
|
|
|
|
// Step 7. Futility pruning: child node (skipped when in check)
|
|
if ( !rootNode
|
|
&& depth < 7 * ONE_PLY
|
|
&& eval - futility_margin(depth) >= beta
|
|
&& eval < VALUE_KNOWN_WIN // Do not return unproven wins
|
|
&& pos.non_pawn_material(pos.side_to_move()))
|
|
return eval;
|
|
|
|
// Step 8. Null move search with verification search (is omitted in PV nodes)
|
|
if ( !PvNode
|
|
&& eval >= beta
|
|
&& (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
|
|
&& pos.non_pawn_material(pos.side_to_move()))
|
|
{
|
|
|
|
assert(eval - beta >= 0);
|
|
|
|
// Null move dynamic reduction based on depth and value
|
|
Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
|
|
|
|
ss->currentMove = MOVE_NULL;
|
|
ss->history = &thisThread->counterMoveHistory[NO_PIECE][0];
|
|
|
|
pos.do_null_move(st);
|
|
Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
|
|
: - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
|
|
pos.undo_null_move();
|
|
|
|
if (nullValue >= beta)
|
|
{
|
|
// Do not return unproven mate scores
|
|
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
|
|
nullValue = beta;
|
|
|
|
if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
|
|
return nullValue;
|
|
|
|
// Do verification search at high depths
|
|
Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
|
|
: search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
|
|
|
|
if (v >= beta)
|
|
return nullValue;
|
|
}
|
|
}
|
|
|
|
// Step 9. ProbCut (skipped when in check)
|
|
// 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 + 200, VALUE_INFINITE);
|
|
|
|
assert(is_ok((ss-1)->currentMove));
|
|
|
|
MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
|
|
|
|
while ((move = mp.next_move()) != MOVE_NONE)
|
|
if (pos.legal(move))
|
|
{
|
|
ss->currentMove = move;
|
|
ss->history = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
|
|
|
|
assert(depth >= 5 * ONE_PLY);
|
|
pos.do_move(move, st);
|
|
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
|
|
pos.undo_move(move);
|
|
if (value >= rbeta)
|
|
return value;
|
|
}
|
|
}
|
|
|
|
// Step 10. Internal iterative deepening (skipped when in check)
|
|
if ( depth >= 6 * ONE_PLY
|
|
&& !ttMove
|
|
&& (PvNode || ss->staticEval + 256 >= beta))
|
|
{
|
|
Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
|
|
search<NT>(pos, ss, alpha, beta, d, cutNode, true);
|
|
|
|
tte = TT.probe(posKey, ttHit);
|
|
ttMove = ttHit ? tte->move() : MOVE_NONE;
|
|
}
|
|
|
|
moves_loop: // When in check search starts from here
|
|
|
|
const PieceToHistory& cmh = *(ss-1)->history;
|
|
const PieceToHistory& fmh = *(ss-2)->history;
|
|
const PieceToHistory& fm2 = *(ss-4)->history;
|
|
|
|
MovePicker mp(pos, ttMove, depth, ss);
|
|
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
|
|
improving = ss->staticEval >= (ss-2)->staticEval
|
|
/* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
|
|
||(ss-2)->staticEval == VALUE_NONE;
|
|
|
|
singularExtensionNode = !rootNode
|
|
&& depth >= 8 * ONE_PLY
|
|
&& ttMove != MOVE_NONE
|
|
&& ttValue != VALUE_NONE
|
|
&& !excludedMove // Recursive singular search is not allowed
|
|
&& (tte->bound() & BOUND_LOWER)
|
|
&& tte->depth() >= depth - 3 * ONE_PLY;
|
|
skipQuiets = false;
|
|
|
|
// Step 11. Loop through moves
|
|
// 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.
|
|
if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
|
|
thisThread->rootMoves.end(), 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);
|
|
moved_piece = pos.moved_piece(move);
|
|
|
|
givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
|
|
? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
|
|
: pos.gives_check(move);
|
|
|
|
moveCountPruning = depth < 16 * ONE_PLY
|
|
&& moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
|
|
|
|
// Step 12. Singular and Gives Check Extensions
|
|
|
|
// Singular extension search. 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 ( singularExtensionNode
|
|
&& move == ttMove
|
|
&& pos.legal(move))
|
|
{
|
|
Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
|
|
Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
|
|
ss->excludedMove = move;
|
|
value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
|
|
ss->excludedMove = MOVE_NONE;
|
|
|
|
if (value < rBeta)
|
|
extension = ONE_PLY;
|
|
}
|
|
else if ( givesCheck
|
|
&& !moveCountPruning
|
|
&& pos.see_ge(move))
|
|
extension = ONE_PLY;
|
|
|
|
// Calculate new depth for this move
|
|
newDepth = depth - ONE_PLY + extension;
|
|
|
|
// Step 13. Pruning at shallow depth
|
|
if ( !rootNode
|
|
&& pos.non_pawn_material(pos.side_to_move())
|
|
&& bestValue > VALUE_MATED_IN_MAX_PLY)
|
|
{
|
|
if ( !captureOrPromotion
|
|
&& !givesCheck
|
|
&& (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
|
|
{
|
|
// Move count based pruning
|
|
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
|
|
if ( lmrDepth < 3
|
|
&& (cmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold)
|
|
&& (fmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold))
|
|
continue;
|
|
|
|
// Futility pruning: parent node
|
|
if ( lmrDepth < 7
|
|
&& !inCheck
|
|
&& ss->staticEval + 256 + 200 * lmrDepth <= alpha)
|
|
continue;
|
|
|
|
// Prune moves with negative SEE
|
|
if ( lmrDepth < 8
|
|
&& !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
|
|
continue;
|
|
}
|
|
else if ( depth < 7 * ONE_PLY
|
|
&& !extension
|
|
&& !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;
|
|
}
|
|
|
|
// Update the current move (this must be done after singular extension search)
|
|
ss->currentMove = move;
|
|
ss->history = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
|
|
|
|
// Step 14. Make the move
|
|
pos.do_move(move, st, givesCheck);
|
|
|
|
// Step 15. 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);
|
|
|
|
if (captureOrPromotion)
|
|
r -= r ? ONE_PLY : DEPTH_ZERO;
|
|
else
|
|
{
|
|
// Increase reduction for cut nodes
|
|
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().
|
|
else if ( type_of(move) == NORMAL
|
|
&& !pos.see_ge(make_move(to_sq(move), from_sq(move))))
|
|
r -= 2 * ONE_PLY;
|
|
|
|
ss->statScore = cmh[moved_piece][to_sq(move)]
|
|
+ fmh[moved_piece][to_sq(move)]
|
|
+ fm2[moved_piece][to_sq(move)]
|
|
+ thisThread->history[~pos.side_to_move()][from_to(move)]
|
|
- 4000; // Correction factor
|
|
|
|
// Decrease/increase reduction by comparing opponent's stat score
|
|
if (ss->statScore > 0 && (ss-1)->statScore < 0)
|
|
r -= ONE_PLY;
|
|
|
|
else if (ss->statScore < 0 && (ss-1)->statScore > 0)
|
|
r += ONE_PLY;
|
|
|
|
// Decrease/increase reduction for moves with a good/bad history
|
|
r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
|
|
}
|
|
|
|
Depth d = std::max(newDepth - r, ONE_PLY);
|
|
|
|
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
|
|
|
|
doFullDepthSearch = (value > alpha && d != newDepth);
|
|
}
|
|
else
|
|
doFullDepthSearch = !PvNode || moveCount > 1;
|
|
|
|
// Step 16. Full depth search when LMR is skipped or fails high
|
|
if (doFullDepthSearch)
|
|
value = newDepth < ONE_PLY ?
|
|
givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
|
|
: -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
|
|
: - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
|
|
|
|
// 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 = newDepth < ONE_PLY ?
|
|
givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
|
|
: -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
|
|
: - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
|
|
}
|
|
|
|
// Step 17. Undo move
|
|
pos.undo_move(move);
|
|
|
|
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
|
|
|
|
// Step 18. 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 (Signals.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.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
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (!captureOrPromotion && move != bestMove && 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 (Signals.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) : DrawValue[pos.side_to_move()];
|
|
else if (bestMove)
|
|
{
|
|
// Quiet best move: update move sorting heuristics
|
|
if (!pos.capture_or_promotion(bestMove))
|
|
update_stats(pos, ss, bestMove, quietsSearched, quietCount, 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_cm_stats(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
|
|
&& !pos.captured_piece()
|
|
&& is_ok((ss-1)->currentMove))
|
|
update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
|
|
|
|
if (!excludedMove)
|
|
tte->save(posKey, value_to_tt(bestValue, ss->ply),
|
|
bestValue >= beta ? BOUND_LOWER :
|
|
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
|
|
depth, bestMove, ss->staticEval, TT.generation());
|
|
|
|
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, bool InCheck>
|
|
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
|
|
|
|
const bool PvNode = NT == PV;
|
|
|
|
assert(InCheck == !!pos.checkers());
|
|
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;
|
|
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
|
|
bool ttHit, givesCheck, evasionPrunable;
|
|
Depth ttDepth;
|
|
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;
|
|
}
|
|
|
|
ss->currentMove = bestMove = MOVE_NONE;
|
|
ss->ply = (ss-1)->ply + 1;
|
|
moveCount = 0;
|
|
|
|
// Check for an instant draw or if the maximum ply has been reached
|
|
if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
|
|
return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
|
|
: DrawValue[pos.side_to_move()];
|
|
|
|
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);
|
|
ttMove = ttHit ? tte->move() : MOVE_NONE;
|
|
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_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)
|
|
if (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(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
|
|
DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
|
|
|
|
return bestValue;
|
|
}
|
|
|
|
if (PvNode && bestValue > alpha)
|
|
alpha = bestValue;
|
|
|
|
futilityBase = bestValue + 128;
|
|
}
|
|
|
|
// 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, 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));
|
|
|
|
// Speculative prefetch as early as possible
|
|
prefetch(TT.first_entry(pos.key_after(move)));
|
|
|
|
givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
|
|
? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
|
|
: pos.gives_check(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)
|
|
&& type_of(move) != PROMOTION
|
|
&& !pos.see_ge(move))
|
|
continue;
|
|
|
|
// Check for legality just before making the move
|
|
if (!pos.legal(move))
|
|
{
|
|
moveCount--;
|
|
continue;
|
|
}
|
|
|
|
ss->currentMove = move;
|
|
|
|
// Make and search the move
|
|
pos.do_move(move, st, givesCheck);
|
|
value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
|
|
: -qsearch<NT, false>(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, TT.generation());
|
|
|
|
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, TT.generation());
|
|
|
|
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_cm_stats() updates countermove and follow-up move history
|
|
|
|
void update_cm_stats(Stack* ss, Piece pc, Square s, int bonus) {
|
|
|
|
for (int i : {1, 2, 4})
|
|
if (is_ok((ss-i)->currentMove))
|
|
(ss-i)->history->update(pc, s, bonus);
|
|
}
|
|
|
|
|
|
// update_stats() updates move sorting heuristics when a new quiet best move is found
|
|
|
|
void update_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 c = pos.side_to_move();
|
|
Thread* thisThread = pos.this_thread();
|
|
thisThread->history.update(c, move, bonus);
|
|
update_cm_stats(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->history.update(c, quiets[i], -bonus);
|
|
update_cm_stats(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) {
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const RootMoves& rootMoves = Threads.main()->rootMoves;
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static PRNG rng(now()); // PRNG sequence should be non-deterministic
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// RootMoves are already sorted by score in descending order
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Value topScore = rootMoves[0].score;
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int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
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int weakness = 120 - 2 * level;
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int maxScore = -VALUE_INFINITE;
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// Choose best move. For each move score we add two terms, both dependent on
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// weakness. One is deterministic and bigger for weaker levels, and one is
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// random. Then we choose the move with the resulting highest score.
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for (size_t i = 0; i < multiPV; ++i)
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{
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// This is our magic formula
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int push = ( weakness * int(topScore - rootMoves[i].score)
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+ delta * (rng.rand<unsigned>() % weakness)) / 128;
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if (rootMoves[i].score + push > maxScore)
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{
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maxScore = rootMoves[i].score + push;
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best = rootMoves[i].pv[0];
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}
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}
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return best;
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}
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// check_time() is used to print debug info and, more importantly, to detect
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// when we are out of available time and thus stop the search.
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void check_time() {
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static std::atomic<TimePoint> lastInfoTime = { now() };
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int elapsed = Time.elapsed();
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TimePoint tick = Limits.startTime + elapsed;
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if (tick - lastInfoTime >= 1000)
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{
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lastInfoTime = tick;
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dbg_print();
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}
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// An engine may not stop pondering until told so by the GUI
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if (Limits.ponder)
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return;
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if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
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|| (Limits.movetime && elapsed >= Limits.movetime)
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|| (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
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Signals.stop = true;
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}
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} // namespace
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/// UCI::pv() formats PV information according to the UCI protocol. UCI requires
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/// that all (if any) unsearched PV lines are sent using a previous search score.
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string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
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std::stringstream ss;
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int elapsed = Time.elapsed() + 1;
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const RootMoves& rootMoves = pos.this_thread()->rootMoves;
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size_t PVIdx = pos.this_thread()->PVIdx;
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size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
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uint64_t nodesSearched = Threads.nodes_searched();
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uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
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for (size_t i = 0; i < multiPV; ++i)
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{
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bool updated = (i <= PVIdx && rootMoves[i].score != -VALUE_INFINITE);
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if (depth == ONE_PLY && !updated)
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continue;
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Depth d = updated ? depth : depth - ONE_PLY;
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Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
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bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
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v = tb ? TB::Score : v;
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if (ss.rdbuf()->in_avail()) // Not at first line
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ss << "\n";
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ss << "info"
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<< " depth " << d / ONE_PLY
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<< " seldepth " << pos.this_thread()->maxPly
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<< " multipv " << i + 1
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<< " score " << UCI::value(v);
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if (!tb && i == PVIdx)
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ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
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ss << " nodes " << nodesSearched
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<< " nps " << nodesSearched * 1000 / elapsed;
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if (elapsed > 1000) // Earlier makes little sense
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ss << " hashfull " << TT.hashfull();
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|
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ss << " tbhits " << tbHits
|
|
<< " time " << elapsed
|
|
<< " pv";
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for (Move m : rootMoves[i].pv)
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ss << " " << UCI::move(m, pos.is_chess960());
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}
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return ss.str();
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}
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/// 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.
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|
|
bool RootMove::extract_ponder_from_tt(Position& pos) {
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|
|
StateInfo st;
|
|
bool ttHit;
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|
|
|
assert(pv.size() == 1);
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|
|
|
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::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
|
|
|
|
RootInTB = false;
|
|
UseRule50 = Options["Syzygy50MoveRule"];
|
|
ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
|
|
Cardinality = Options["SyzygyProbeLimit"];
|
|
|
|
// Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
|
|
if (Cardinality > MaxCardinality)
|
|
{
|
|
Cardinality = MaxCardinality;
|
|
ProbeDepth = DEPTH_ZERO;
|
|
}
|
|
|
|
if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
|
|
return;
|
|
|
|
// If the current root position is in the tablebases, then RootMoves
|
|
// contains only moves that preserve the draw or the win.
|
|
RootInTB = root_probe(pos, rootMoves, TB::Score);
|
|
|
|
if (RootInTB)
|
|
Cardinality = 0; // Do not probe tablebases during the search
|
|
|
|
else // If DTZ tables are missing, use WDL tables as a fallback
|
|
{
|
|
// Filter out moves that do not preserve the draw or the win.
|
|
RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
|
|
|
|
// Only probe during search if winning
|
|
if (RootInTB && TB::Score <= VALUE_DRAW)
|
|
Cardinality = 0;
|
|
}
|
|
|
|
if (RootInTB && !UseRule50)
|
|
TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
|
|
: TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
|
|
: VALUE_DRAW;
|
|
}
|