2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
24 #include <cstring> // For std::memset
38 #include "syzygy/tbprobe.h"
46 namespace Tablebases {
55 namespace TB = Tablebases;
59 using namespace Search;
63 // Different node types, used as a template parameter
64 enum NodeType { NonPV, PV };
66 // Razoring and futility margin based on depth
67 const int razor_margin[4] = { 483, 570, 603, 554 };
68 Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
70 // Futility and reductions lookup tables, initialized at startup
71 int FutilityMoveCounts[2][16]; // [improving][depth]
72 int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
74 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
75 return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
78 // History and stats update bonus, based on depth
79 Value stat_bonus(Depth depth) {
80 int d = depth / ONE_PLY ;
81 return Value(d * d + 2 * d - 2);
84 // Skill structure is used to implement strength limit
86 Skill(int l) : level(l) {}
87 bool enabled() const { return level < 20; }
88 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
89 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
90 Move pick_best(size_t multiPV);
93 Move best = MOVE_NONE;
96 // EasyMoveManager structure is used to detect an 'easy move'. When the PV is
97 // stable across multiple search iterations, we can quickly return the best move.
98 struct EasyMoveManager {
103 pv[0] = pv[1] = pv[2] = MOVE_NONE;
106 Move get(Key key) const {
107 return expectedPosKey == key ? pv[2] : MOVE_NONE;
110 void update(Position& pos, const std::vector<Move>& newPv) {
112 assert(newPv.size() >= 3);
114 // Keep track of how many times in a row the 3rd ply remains stable
115 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
117 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
119 std::copy(newPv.begin(), newPv.begin() + 3, pv);
122 pos.do_move(newPv[0], st[0]);
123 pos.do_move(newPv[1], st[1]);
124 expectedPosKey = pos.key();
125 pos.undo_move(newPv[1]);
126 pos.undo_move(newPv[0]);
135 // Set of rows with half bits set to 1 and half to 0. It is used to allocate
136 // the search depths across the threads.
137 typedef std::vector<int> Row;
139 const Row HalfDensity[] = {
152 {0, 0, 0, 0, 1, 1, 1, 1},
153 {0, 0, 0, 1, 1, 1, 1, 0},
154 {0, 0, 1, 1, 1, 1, 0 ,0},
155 {0, 1, 1, 1, 1, 0, 0 ,0},
156 {1, 1, 1, 1, 0, 0, 0 ,0},
157 {1, 1, 1, 0, 0, 0, 0 ,1},
158 {1, 1, 0, 0, 0, 0, 1 ,1},
159 {1, 0, 0, 0, 0, 1, 1 ,1},
162 const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
164 EasyMoveManager EasyMove;
165 Value DrawValue[COLOR_NB];
167 template <NodeType NT>
168 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
170 template <NodeType NT, bool InCheck>
171 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
173 Value value_to_tt(Value v, int ply);
174 Value value_from_tt(Value v, int ply);
175 void update_pv(Move* pv, Move move, Move* childPv);
176 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus);
177 void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
183 /// Search::init() is called during startup to initialize various lookup tables
185 void Search::init() {
187 for (int imp = 0; imp <= 1; ++imp)
188 for (int d = 1; d < 64; ++d)
189 for (int mc = 1; mc < 64; ++mc)
191 double r = log(d) * log(mc) / 2;
193 Reductions[NonPV][imp][d][mc] = int(std::round(r));
194 Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
196 // Increase reduction for non-PV nodes when eval is not improving
197 if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
198 Reductions[NonPV][imp][d][mc]++;
201 for (int d = 0; d < 16; ++d)
203 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
204 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
209 /// Search::clear() resets search state to zero, to obtain reproducible results
211 void Search::clear() {
215 for (Thread* th : Threads)
217 th->counterMoves.clear();
219 th->counterMoveHistory.clear();
220 th->resetCalls = true;
223 Threads.main()->previousScore = VALUE_INFINITE;
227 /// Search::perft() is our utility to verify move generation. All the leaf nodes
228 /// up to the given depth are generated and counted, and the sum is returned.
230 uint64_t Search::perft(Position& pos, Depth depth) {
233 uint64_t cnt, nodes = 0;
234 const bool leaf = (depth == 2 * ONE_PLY);
236 for (const auto& m : MoveList<LEGAL>(pos))
238 if (Root && depth <= ONE_PLY)
243 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
248 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
253 template uint64_t Search::perft<true>(Position&, Depth);
256 /// MainThread::search() is called by the main thread when the program receives
257 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
259 void MainThread::search() {
261 Color us = rootPos.side_to_move();
262 Time.init(Limits, us, rootPos.game_ply());
264 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
265 DrawValue[ us] = VALUE_DRAW - Value(contempt);
266 DrawValue[~us] = VALUE_DRAW + Value(contempt);
268 if (rootMoves.empty())
270 rootMoves.push_back(RootMove(MOVE_NONE));
271 sync_cout << "info depth 0 score "
272 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
277 for (Thread* th : Threads)
279 th->start_searching();
281 Thread::search(); // Let's start searching!
284 // When playing in 'nodes as time' mode, subtract the searched nodes from
285 // the available ones before exiting.
287 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
289 // When we reach the maximum depth, we can arrive here without a raise of
290 // Signals.stop. However, if we are pondering or in an infinite search,
291 // the UCI protocol states that we shouldn't print the best move before the
292 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
293 // until the GUI sends one of those commands (which also raises Signals.stop).
294 if (!Signals.stop && (Limits.ponder || Limits.infinite))
296 Signals.stopOnPonderhit = true;
300 // Stop the threads if not already stopped
303 // Wait until all threads have finished
304 for (Thread* th : Threads)
306 th->wait_for_search_finished();
308 // Check if there are threads with a better score than main thread
309 Thread* bestThread = this;
310 if ( !this->easyMovePlayed
311 && Options["MultiPV"] == 1
313 && !Skill(Options["Skill Level"]).enabled()
314 && rootMoves[0].pv[0] != MOVE_NONE)
316 for (Thread* th : Threads)
318 Depth depthDiff = th->completedDepth - bestThread->completedDepth;
319 Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
321 if (scoreDiff > 0 && depthDiff >= 0)
326 previousScore = bestThread->rootMoves[0].score;
328 // Send new PV when needed
329 if (bestThread != this)
330 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
332 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
334 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
335 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
337 std::cout << sync_endl;
341 // Thread::search() is the main iterative deepening loop. It calls search()
342 // repeatedly with increasing depth until the allocated thinking time has been
343 // consumed, the user stops the search, or the maximum search depth is reached.
345 void Thread::search() {
347 Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
348 Value bestValue, alpha, beta, delta;
349 Move easyMove = MOVE_NONE;
350 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
352 std::memset(ss-4, 0, 7 * sizeof(Stack));
354 bestValue = delta = alpha = -VALUE_INFINITE;
355 beta = VALUE_INFINITE;
356 completedDepth = DEPTH_ZERO;
360 easyMove = EasyMove.get(rootPos.key());
362 mainThread->easyMovePlayed = mainThread->failedLow = false;
363 mainThread->bestMoveChanges = 0;
367 size_t multiPV = Options["MultiPV"];
368 Skill skill(Options["Skill Level"]);
370 // When playing with strength handicap enable MultiPV search that we will
371 // use behind the scenes to retrieve a set of possible moves.
373 multiPV = std::max(multiPV, (size_t)4);
375 multiPV = std::min(multiPV, rootMoves.size());
377 // Iterative deepening loop until requested to stop or the target depth is reached
378 while ( (rootDepth += ONE_PLY) < DEPTH_MAX
380 && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
382 // Set up the new depths for the helper threads skipping on average every
383 // 2nd ply (using a half-density matrix).
386 const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
387 if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()])
391 // Age out PV variability metric
393 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
395 // Save the last iteration's scores before first PV line is searched and
396 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
397 for (RootMove& rm : rootMoves)
398 rm.previousScore = rm.score;
400 // MultiPV loop. We perform a full root search for each PV line
401 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
403 // Reset aspiration window starting size
404 if (rootDepth >= 5 * ONE_PLY)
407 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
408 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
411 // Start with a small aspiration window and, in the case of a fail
412 // high/low, re-search with a bigger window until we're not failing
416 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
418 // Bring the best move to the front. It is critical that sorting
419 // is done with a stable algorithm because all the values but the
420 // first and eventually the new best one are set to -VALUE_INFINITE
421 // and we want to keep the same order for all the moves except the
422 // new PV that goes to the front. Note that in case of MultiPV
423 // search the already searched PV lines are preserved.
424 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
426 // If search has been stopped, break immediately. Sorting and
427 // writing PV back to TT is safe because RootMoves is still
428 // valid, although it refers to the previous iteration.
432 // When failing high/low give some update (without cluttering
433 // the UI) before a re-search.
436 && (bestValue <= alpha || bestValue >= beta)
437 && Time.elapsed() > 3000)
438 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
440 // In case of failing low/high increase aspiration window and
441 // re-search, otherwise exit the loop.
442 if (bestValue <= alpha)
444 beta = (alpha + beta) / 2;
445 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
449 mainThread->failedLow = true;
450 Signals.stopOnPonderhit = false;
453 else if (bestValue >= beta)
455 alpha = (alpha + beta) / 2;
456 beta = std::min(bestValue + delta, VALUE_INFINITE);
461 delta += delta / 4 + 5;
463 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
466 // Sort the PV lines searched so far and update the GUI
467 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
472 if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
473 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
477 completedDepth = rootDepth;
482 // If skill level is enabled and time is up, pick a sub-optimal best move
483 if (skill.enabled() && skill.time_to_pick(rootDepth))
484 skill.pick_best(multiPV);
486 // Have we found a "mate in x"?
488 && bestValue >= VALUE_MATE_IN_MAX_PLY
489 && VALUE_MATE - bestValue <= 2 * Limits.mate)
492 // Do we have time for the next iteration? Can we stop searching now?
493 if (Limits.use_time_management())
495 if (!Signals.stop && !Signals.stopOnPonderhit)
497 // Stop the search if only one legal move is available, or if all
498 // of the available time has been used, or if we matched an easyMove
499 // from the previous search and just did a fast verification.
500 const int F[] = { mainThread->failedLow,
501 bestValue - mainThread->previousScore };
503 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
504 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
506 bool doEasyMove = rootMoves[0].pv[0] == easyMove
507 && mainThread->bestMoveChanges < 0.03
508 && Time.elapsed() > Time.optimum() * 5 / 44;
510 if ( rootMoves.size() == 1
511 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
512 || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
514 // If we are allowed to ponder do not stop the search now but
515 // keep pondering until the GUI sends "ponderhit" or "stop".
517 Signals.stopOnPonderhit = true;
523 if (rootMoves[0].pv.size() >= 3)
524 EasyMove.update(rootPos, rootMoves[0].pv);
533 // Clear any candidate easy move that wasn't stable for the last search
534 // iterations; the second condition prevents consecutive fast moves.
535 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
538 // If skill level is enabled, swap best PV line with the sub-optimal one
540 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
541 rootMoves.end(), skill.best_move(multiPV)));
547 // search<>() is the main search function for both PV and non-PV nodes
549 template <NodeType NT>
550 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
552 const bool PvNode = NT == PV;
553 const bool rootNode = PvNode && (ss-1)->ply == 0;
555 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
556 assert(PvNode || (alpha == beta - 1));
557 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
558 assert(!(PvNode && cutNode));
559 assert(depth / ONE_PLY * ONE_PLY == depth);
561 Move pv[MAX_PLY+1], quietsSearched[64];
565 Move ttMove, move, excludedMove, bestMove;
566 Depth extension, newDepth;
567 Value bestValue, value, ttValue, eval, nullValue;
568 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
569 bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
571 int moveCount, quietCount;
573 // Step 1. Initialize node
574 Thread* thisThread = pos.this_thread();
575 inCheck = pos.checkers();
576 moveCount = quietCount = ss->moveCount = 0;
577 ss->history = VALUE_ZERO;
578 bestValue = -VALUE_INFINITE;
579 ss->ply = (ss-1)->ply + 1;
581 // Check for the available remaining time
582 if (thisThread->resetCalls.load(std::memory_order_relaxed))
584 thisThread->resetCalls = false;
585 // At low node count increase the checking rate to about 0.1% of nodes
586 // otherwise use a default value.
587 thisThread->callsCnt = Limits.nodes ? std::min((int64_t)4096, Limits.nodes / 1024)
591 if (--thisThread->callsCnt <= 0)
593 for (Thread* th : Threads)
594 th->resetCalls = true;
599 // Used to send selDepth info to GUI
600 if (PvNode && thisThread->maxPly < ss->ply)
601 thisThread->maxPly = ss->ply;
605 // Step 2. Check for aborted search and immediate draw
606 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
607 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
608 : DrawValue[pos.side_to_move()];
610 // Step 3. Mate distance pruning. Even if we mate at the next move our score
611 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
612 // a shorter mate was found upward in the tree then there is no need to search
613 // because we will never beat the current alpha. Same logic but with reversed
614 // signs applies also in the opposite condition of being mated instead of giving
615 // mate. In this case return a fail-high score.
616 alpha = std::max(mated_in(ss->ply), alpha);
617 beta = std::min(mate_in(ss->ply+1), beta);
622 assert(0 <= ss->ply && ss->ply < MAX_PLY);
624 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
625 ss->counterMoves = nullptr;
626 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
627 Square prevSq = to_sq((ss-1)->currentMove);
629 // Step 4. Transposition table lookup. We don't want the score of a partial
630 // search to overwrite a previous full search TT value, so we use a different
631 // position key in case of an excluded move.
632 excludedMove = ss->excludedMove;
633 posKey = pos.key() ^ Key(excludedMove);
634 tte = TT.probe(posKey, ttHit);
635 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
636 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
637 : ttHit ? tte->move() : MOVE_NONE;
639 // At non-PV nodes we check for an early TT cutoff
642 && tte->depth() >= depth
643 && ttValue != VALUE_NONE // Possible in case of TT access race
644 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
645 : (tte->bound() & BOUND_UPPER)))
647 // If ttMove is quiet, update move sorting heuristics on TT hit
652 if (!pos.capture_or_promotion(ttMove))
653 update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
655 // Extra penalty for a quiet TT move in previous ply when it gets refuted
656 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
657 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
659 // Penalty for a quiet ttMove that fails low
660 else if (!pos.capture_or_promotion(ttMove))
662 Value penalty = -stat_bonus(depth + ONE_PLY);
663 thisThread->history.update(pos.side_to_move(), ttMove, penalty);
664 update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
670 // Step 4a. Tablebase probe
671 if (!rootNode && TB::Cardinality)
673 int piecesCount = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
675 if ( piecesCount <= TB::Cardinality
676 && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
677 && pos.rule50_count() == 0
678 && !pos.can_castle(ANY_CASTLING))
681 TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
683 if (err != TB::ProbeState::FAIL)
685 thisThread->tbHits++;
687 int drawScore = TB::UseRule50 ? 1 : 0;
689 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
690 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
691 : VALUE_DRAW + 2 * v * drawScore;
693 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
694 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
695 MOVE_NONE, VALUE_NONE, TT.generation());
702 // Step 5. Evaluate the position statically
705 ss->staticEval = eval = VALUE_NONE;
711 // Never assume anything on values stored in TT
712 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
713 eval = ss->staticEval = evaluate(pos);
715 // Can ttValue be used as a better position evaluation?
716 if (ttValue != VALUE_NONE)
717 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
722 eval = ss->staticEval =
723 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
724 : -(ss-1)->staticEval + 2 * Eval::Tempo;
726 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
727 ss->staticEval, TT.generation());
730 if (skipEarlyPruning)
733 // Step 6. Razoring (skipped when in check)
735 && depth < 4 * ONE_PLY
736 && ttMove == MOVE_NONE
737 && eval + razor_margin[depth / ONE_PLY] <= alpha)
739 if (depth <= ONE_PLY)
740 return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
742 Value ralpha = alpha - razor_margin[depth / ONE_PLY];
743 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
748 // Step 7. Futility pruning: child node (skipped when in check)
750 && depth < 7 * ONE_PLY
751 && eval - futility_margin(depth) >= beta
752 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
753 && pos.non_pawn_material(pos.side_to_move()))
756 // Step 8. Null move search with verification search (is omitted in PV nodes)
759 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
760 && pos.non_pawn_material(pos.side_to_move()))
762 ss->currentMove = MOVE_NULL;
763 ss->counterMoves = nullptr;
765 assert(eval - beta >= 0);
767 // Null move dynamic reduction based on depth and value
768 Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
770 pos.do_null_move(st);
771 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
772 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
773 pos.undo_null_move();
775 if (nullValue >= beta)
777 // Do not return unproven mate scores
778 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
781 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
784 // Do verification search at high depths
785 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
786 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
793 // Step 9. ProbCut (skipped when in check)
794 // If we have a good enough capture and a reduced search returns a value
795 // much above beta, we can (almost) safely prune the previous move.
797 && depth >= 5 * ONE_PLY
798 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
800 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
801 Depth rdepth = depth - 4 * ONE_PLY;
803 assert(rdepth >= ONE_PLY);
804 assert((ss-1)->currentMove != MOVE_NONE);
805 assert((ss-1)->currentMove != MOVE_NULL);
807 MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
809 while ((move = mp.next_move()) != MOVE_NONE)
812 ss->currentMove = move;
813 ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
814 pos.do_move(move, st);
815 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
822 // Step 10. Internal iterative deepening (skipped when in check)
823 if ( depth >= 6 * ONE_PLY
825 && (PvNode || ss->staticEval + 256 >= beta))
827 Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
828 search<NT>(pos, ss, alpha, beta, d, cutNode, true);
830 tte = TT.probe(posKey, ttHit);
831 ttMove = ttHit ? tte->move() : MOVE_NONE;
834 moves_loop: // When in check search starts from here
836 const CounterMoveStats* cmh = (ss-1)->counterMoves;
837 const CounterMoveStats* fmh = (ss-2)->counterMoves;
838 const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
840 MovePicker mp(pos, ttMove, depth, ss);
841 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
842 improving = ss->staticEval >= (ss-2)->staticEval
843 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
844 ||(ss-2)->staticEval == VALUE_NONE;
846 singularExtensionNode = !rootNode
847 && depth >= 8 * ONE_PLY
848 && ttMove != MOVE_NONE
849 && ttValue != VALUE_NONE
850 && !excludedMove // Recursive singular search is not allowed
851 && (tte->bound() & BOUND_LOWER)
852 && tte->depth() >= depth - 3 * ONE_PLY;
854 // Step 11. Loop through moves
855 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
856 while ((move = mp.next_move()) != MOVE_NONE)
860 if (move == excludedMove)
863 // At root obey the "searchmoves" option and skip moves not listed in Root
864 // Move List. As a consequence any illegal move is also skipped. In MultiPV
865 // mode we also skip PV moves which have been already searched.
866 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
867 thisThread->rootMoves.end(), move))
870 ss->moveCount = ++moveCount;
872 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
873 sync_cout << "info depth " << depth / ONE_PLY
874 << " currmove " << UCI::move(move, pos.is_chess960())
875 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
878 (ss+1)->pv = nullptr;
880 extension = DEPTH_ZERO;
881 captureOrPromotion = pos.capture_or_promotion(move);
882 moved_piece = pos.moved_piece(move);
884 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
885 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
886 : pos.gives_check(move);
888 moveCountPruning = depth < 16 * ONE_PLY
889 && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
891 // Step 12. Extensions
895 && pos.see_ge(move, VALUE_ZERO))
898 // Singular extension search. If all moves but one fail low on a search of
899 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
900 // is singular and should be extended. To verify this we do a reduced search
901 // on all the other moves but the ttMove and if the result is lower than
902 // ttValue minus a margin then we extend the ttMove.
903 if ( singularExtensionNode
908 Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
909 Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
910 ss->excludedMove = move;
911 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
912 ss->excludedMove = MOVE_NONE;
918 // Calculate new depth for this move
919 newDepth = depth - ONE_PLY + extension;
921 // Step 13. Pruning at shallow depth
923 && bestValue > VALUE_MATED_IN_MAX_PLY)
925 if ( !captureOrPromotion
927 && !pos.advanced_pawn_push(move))
929 // Move count based pruning
930 if (moveCountPruning)
933 // Reduced depth of the next LMR search
934 int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
936 // Countermoves based pruning
938 && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
939 && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
940 && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
943 // Futility pruning: parent node
946 && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
949 // Prune moves with negative SEE
951 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
954 else if ( depth < 7 * ONE_PLY
956 && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
960 // Speculative prefetch as early as possible
961 prefetch(TT.first_entry(pos.key_after(move)));
963 // Check for legality just before making the move
964 if (!rootNode && !pos.legal(move))
966 ss->moveCount = --moveCount;
970 // Update the current move (this must be done after singular extension search)
971 ss->currentMove = move;
972 ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
974 // Step 14. Make the move
975 pos.do_move(move, st, givesCheck);
977 // Step 15. Reduced depth search (LMR). If the move fails high it will be
978 // re-searched at full depth.
979 if ( depth >= 3 * ONE_PLY
981 && (!captureOrPromotion || moveCountPruning))
983 Depth r = reduction<PvNode>(improving, depth, moveCount);
985 if (captureOrPromotion)
986 r -= r ? ONE_PLY : DEPTH_ZERO;
989 // Increase reduction for cut nodes
993 // Decrease reduction for moves that escape a capture. Filter out
994 // castling moves, because they are coded as "king captures rook" and
995 // hence break make_move().
996 else if ( type_of(move) == NORMAL
997 && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO))
1000 ss->history = (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
1001 + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
1002 + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
1003 + thisThread->history.get(~pos.side_to_move(), move)
1004 - 4000; // Correction factor
1006 // Decrease/increase reduction by comparing opponent's stat score
1007 if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO)
1010 else if (ss->history < VALUE_ZERO && (ss-1)->history > VALUE_ZERO)
1013 // Decrease/increase reduction for moves with a good/bad history
1014 r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
1017 Depth d = std::max(newDepth - r, ONE_PLY);
1019 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
1021 doFullDepthSearch = (value > alpha && d != newDepth);
1024 doFullDepthSearch = !PvNode || moveCount > 1;
1026 // Step 16. Full depth search when LMR is skipped or fails high
1027 if (doFullDepthSearch)
1028 value = newDepth < ONE_PLY ?
1029 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
1030 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
1031 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
1033 // For PV nodes only, do a full PV search on the first move or after a fail
1034 // high (in the latter case search only if value < beta), otherwise let the
1035 // parent node fail low with value <= alpha and try another move.
1036 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1039 (ss+1)->pv[0] = MOVE_NONE;
1041 value = newDepth < ONE_PLY ?
1042 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
1043 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
1044 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
1047 // Step 17. Undo move
1048 pos.undo_move(move);
1050 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1052 // Step 18. Check for a new best move
1053 // Finished searching the move. If a stop occurred, the return value of
1054 // the search cannot be trusted, and we return immediately without
1055 // updating best move, PV and TT.
1056 if (Signals.stop.load(std::memory_order_relaxed))
1061 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1062 thisThread->rootMoves.end(), move);
1064 // PV move or new best move ?
1065 if (moveCount == 1 || value > alpha)
1072 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1073 rm.pv.push_back(*m);
1075 // We record how often the best move has been changed in each
1076 // iteration. This information is used for time management: When
1077 // the best move changes frequently, we allocate some more time.
1078 if (moveCount > 1 && thisThread == Threads.main())
1079 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1082 // All other moves but the PV are set to the lowest value: this is
1083 // not a problem when sorting because the sort is stable and the
1084 // move position in the list is preserved - just the PV is pushed up.
1085 rm.score = -VALUE_INFINITE;
1088 if (value > bestValue)
1096 if (PvNode && !rootNode) // Update pv even in fail-high case
1097 update_pv(ss->pv, move, (ss+1)->pv);
1099 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1103 assert(value >= beta); // Fail high
1109 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1110 quietsSearched[quietCount++] = move;
1113 // The following condition would detect a stop only after move loop has been
1114 // completed. But in this case bestValue is valid because we have fully
1115 // searched our subtree, and we can anyhow save the result in TT.
1121 // Step 20. Check for mate and stalemate
1122 // All legal moves have been searched and if there are no legal moves, it
1123 // must be a mate or a stalemate. If we are in a singular extension search then
1124 // return a fail low score.
1126 assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
1129 bestValue = excludedMove ? alpha
1130 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1134 // Quiet best move: update move sorting heuristics
1135 if (!pos.capture_or_promotion(bestMove))
1136 update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
1138 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1139 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
1140 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
1142 // Bonus for prior countermove that caused the fail low
1143 else if ( depth >= 3 * ONE_PLY
1144 && !pos.captured_piece()
1145 && is_ok((ss-1)->currentMove))
1146 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
1148 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1149 bestValue >= beta ? BOUND_LOWER :
1150 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1151 depth, bestMove, ss->staticEval, TT.generation());
1153 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1159 // qsearch() is the quiescence search function, which is called by the main
1160 // search function with depth zero, or recursively with depth less than ONE_PLY.
1162 template <NodeType NT, bool InCheck>
1163 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1165 const bool PvNode = NT == PV;
1167 assert(InCheck == !!pos.checkers());
1168 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1169 assert(PvNode || (alpha == beta - 1));
1170 assert(depth <= DEPTH_ZERO);
1171 assert(depth / ONE_PLY * ONE_PLY == depth);
1177 Move ttMove, move, bestMove;
1178 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1179 bool ttHit, givesCheck, evasionPrunable;
1184 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1186 ss->pv[0] = MOVE_NONE;
1189 ss->currentMove = bestMove = MOVE_NONE;
1190 ss->ply = (ss-1)->ply + 1;
1192 // Check for an instant draw or if the maximum ply has been reached
1193 if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
1194 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1195 : DrawValue[pos.side_to_move()];
1197 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1199 // Decide whether or not to include checks: this fixes also the type of
1200 // TT entry depth that we are going to use. Note that in qsearch we use
1201 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1202 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1203 : DEPTH_QS_NO_CHECKS;
1205 // Transposition table lookup
1207 tte = TT.probe(posKey, ttHit);
1208 ttMove = ttHit ? tte->move() : MOVE_NONE;
1209 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1213 && tte->depth() >= ttDepth
1214 && ttValue != VALUE_NONE // Only in case of TT access race
1215 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1216 : (tte->bound() & BOUND_UPPER)))
1219 // Evaluate the position statically
1222 ss->staticEval = VALUE_NONE;
1223 bestValue = futilityBase = -VALUE_INFINITE;
1229 // Never assume anything on values stored in TT
1230 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1231 ss->staticEval = bestValue = evaluate(pos);
1233 // Can ttValue be used as a better position evaluation?
1234 if (ttValue != VALUE_NONE)
1235 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1236 bestValue = ttValue;
1239 ss->staticEval = bestValue =
1240 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1241 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1243 // Stand pat. Return immediately if static value is at least beta
1244 if (bestValue >= beta)
1247 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1248 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1253 if (PvNode && bestValue > alpha)
1256 futilityBase = bestValue + 128;
1259 // Initialize a MovePicker object for the current position, and prepare
1260 // to search the moves. Because the depth is <= 0 here, only captures,
1261 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1263 MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
1265 // Loop through the moves until no moves remain or a beta cutoff occurs
1266 while ((move = mp.next_move()) != MOVE_NONE)
1268 assert(is_ok(move));
1270 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
1271 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
1272 : pos.gives_check(move);
1277 && futilityBase > -VALUE_KNOWN_WIN
1278 && !pos.advanced_pawn_push(move))
1280 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1282 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1284 if (futilityValue <= alpha)
1286 bestValue = std::max(bestValue, futilityValue);
1290 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
1292 bestValue = std::max(bestValue, futilityBase);
1297 // Detect non-capture evasions that are candidates to be pruned
1298 evasionPrunable = InCheck
1299 && bestValue > VALUE_MATED_IN_MAX_PLY
1300 && !pos.capture(move);
1302 // Don't search moves with negative SEE values
1303 if ( (!InCheck || evasionPrunable)
1304 && type_of(move) != PROMOTION
1305 && !pos.see_ge(move, VALUE_ZERO))
1308 // Speculative prefetch as early as possible
1309 prefetch(TT.first_entry(pos.key_after(move)));
1311 // Check for legality just before making the move
1312 if (!pos.legal(move))
1315 ss->currentMove = move;
1317 // Make and search the move
1318 pos.do_move(move, st, givesCheck);
1319 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1320 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1321 pos.undo_move(move);
1323 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1325 // Check for a new best move
1326 if (value > bestValue)
1332 if (PvNode) // Update pv even in fail-high case
1333 update_pv(ss->pv, move, (ss+1)->pv);
1335 if (PvNode && value < beta) // Update alpha here!
1342 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1343 ttDepth, move, ss->staticEval, TT.generation());
1351 // All legal moves have been searched. A special case: If we're in check
1352 // and no legal moves were found, it is checkmate.
1353 if (InCheck && bestValue == -VALUE_INFINITE)
1354 return mated_in(ss->ply); // Plies to mate from the root
1356 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1357 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1358 ttDepth, bestMove, ss->staticEval, TT.generation());
1360 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1366 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1367 // "plies to mate from the current position". Non-mate scores are unchanged.
1368 // The function is called before storing a value in the transposition table.
1370 Value value_to_tt(Value v, int ply) {
1372 assert(v != VALUE_NONE);
1374 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1375 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1379 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1380 // from the transposition table (which refers to the plies to mate/be mated
1381 // from current position) to "plies to mate/be mated from the root".
1383 Value value_from_tt(Value v, int ply) {
1385 return v == VALUE_NONE ? VALUE_NONE
1386 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1387 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1391 // update_pv() adds current move and appends child pv[]
1393 void update_pv(Move* pv, Move move, Move* childPv) {
1395 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1401 // update_cm_stats() updates countermove and follow-up move history
1403 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
1405 CounterMoveStats* cmh = (ss-1)->counterMoves;
1406 CounterMoveStats* fmh1 = (ss-2)->counterMoves;
1407 CounterMoveStats* fmh2 = (ss-4)->counterMoves;
1410 cmh->update(pc, s, bonus);
1413 fmh1->update(pc, s, bonus);
1416 fmh2->update(pc, s, bonus);
1420 // update_stats() updates move sorting heuristics when a new quiet best move is found
1422 void update_stats(const Position& pos, Stack* ss, Move move,
1423 Move* quiets, int quietsCnt, Value bonus) {
1425 if (ss->killers[0] != move)
1427 ss->killers[1] = ss->killers[0];
1428 ss->killers[0] = move;
1431 Color c = pos.side_to_move();
1432 Thread* thisThread = pos.this_thread();
1433 thisThread->history.update(c, move, bonus);
1434 update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
1436 if ((ss-1)->counterMoves)
1438 Square prevSq = to_sq((ss-1)->currentMove);
1439 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1442 // Decrease all the other played quiet moves
1443 for (int i = 0; i < quietsCnt; ++i)
1445 thisThread->history.update(c, quiets[i], -bonus);
1446 update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1451 // When playing with strength handicap, choose best move among a set of RootMoves
1452 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1454 Move Skill::pick_best(size_t multiPV) {
1456 const RootMoves& rootMoves = Threads.main()->rootMoves;
1457 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1459 // RootMoves are already sorted by score in descending order
1460 Value topScore = rootMoves[0].score;
1461 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1462 int weakness = 120 - 2 * level;
1463 int maxScore = -VALUE_INFINITE;
1465 // Choose best move. For each move score we add two terms, both dependent on
1466 // weakness. One is deterministic and bigger for weaker levels, and one is
1467 // random. Then we choose the move with the resulting highest score.
1468 for (size_t i = 0; i < multiPV; ++i)
1470 // This is our magic formula
1471 int push = ( weakness * int(topScore - rootMoves[i].score)
1472 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1474 if (rootMoves[i].score + push > maxScore)
1476 maxScore = rootMoves[i].score + push;
1477 best = rootMoves[i].pv[0];
1485 // check_time() is used to print debug info and, more importantly, to detect
1486 // when we are out of available time and thus stop the search.
1490 static TimePoint lastInfoTime = now();
1492 int elapsed = Time.elapsed();
1493 TimePoint tick = Limits.startTime + elapsed;
1495 if (tick - lastInfoTime >= 1000)
1497 lastInfoTime = tick;
1501 // An engine may not stop pondering until told so by the GUI
1505 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1506 || (Limits.movetime && elapsed >= Limits.movetime)
1507 || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
1508 Signals.stop = true;
1514 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1515 /// that all (if any) unsearched PV lines are sent using a previous search score.
1517 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1519 std::stringstream ss;
1520 int elapsed = Time.elapsed() + 1;
1521 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1522 size_t PVIdx = pos.this_thread()->PVIdx;
1523 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1524 uint64_t nodesSearched = Threads.nodes_searched();
1525 uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
1527 for (size_t i = 0; i < multiPV; ++i)
1529 bool updated = (i <= PVIdx);
1531 if (depth == ONE_PLY && !updated)
1534 Depth d = updated ? depth : depth - ONE_PLY;
1535 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1537 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1538 v = tb ? TB::Score : v;
1540 if (ss.rdbuf()->in_avail()) // Not at first line
1544 << " depth " << d / ONE_PLY
1545 << " seldepth " << pos.this_thread()->maxPly
1546 << " multipv " << i + 1
1547 << " score " << UCI::value(v);
1549 if (!tb && i == PVIdx)
1550 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1552 ss << " nodes " << nodesSearched
1553 << " nps " << nodesSearched * 1000 / elapsed;
1555 if (elapsed > 1000) // Earlier makes little sense
1556 ss << " hashfull " << TT.hashfull();
1558 ss << " tbhits " << tbHits
1559 << " time " << elapsed
1562 for (Move m : rootMoves[i].pv)
1563 ss << " " << UCI::move(m, pos.is_chess960());
1570 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1571 /// before exiting the search, for instance, in case we stop the search during a
1572 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1573 /// otherwise in case of 'ponder on' we have nothing to think on.
1575 bool RootMove::extract_ponder_from_tt(Position& pos) {
1580 assert(pv.size() == 1);
1585 pos.do_move(pv[0], st);
1586 TTEntry* tte = TT.probe(pos.key(), ttHit);
1590 Move m = tte->move(); // Local copy to be SMP safe
1591 if (MoveList<LEGAL>(pos).contains(m))
1595 pos.undo_move(pv[0]);
1596 return pv.size() > 1;
1599 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1602 UseRule50 = Options["Syzygy50MoveRule"];
1603 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1604 Cardinality = Options["SyzygyProbeLimit"];
1606 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1607 if (Cardinality > MaxCardinality)
1609 Cardinality = MaxCardinality;
1610 ProbeDepth = DEPTH_ZERO;
1613 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1616 // If the current root position is in the tablebases, then RootMoves
1617 // contains only moves that preserve the draw or the win.
1618 RootInTB = root_probe(pos, rootMoves, TB::Score);
1621 Cardinality = 0; // Do not probe tablebases during the search
1623 else // If DTZ tables are missing, use WDL tables as a fallback
1625 // Filter out moves that do not preserve the draw or the win.
1626 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1628 // Only probe during search if winning
1629 if (RootInTB && TB::Score <= VALUE_DRAW)
1633 if (RootInTB && !UseRule50)
1634 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1635 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1