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"
45 namespace Tablebases {
54 namespace TB = Tablebases;
58 using namespace Search;
62 // Different node types, used as a template parameter
63 enum NodeType { NonPV, PV };
65 // Sizes and phases of the skip-blocks, used for distributing search depths across the threads
66 const int skipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
67 const int skipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
69 // Razoring and futility margin based on depth
70 // razor_margin[0] is unused as long as depth >= ONE_PLY in search
71 const int razor_margin[] = { 0, 570, 603, 554 };
72 Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
74 // Futility and reductions lookup tables, initialized at startup
75 int FutilityMoveCounts[2][16]; // [improving][depth]
76 int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
78 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
79 return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
82 // History and stats update bonus, based on depth
83 int stat_bonus(Depth depth) {
84 int d = depth / ONE_PLY;
85 return d > 17 ? 0 : d * d + 2 * d - 2;
88 // Skill structure is used to implement strength limit
90 explicit Skill(int l) : level(l) {}
91 bool enabled() const { return level < 20; }
92 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
93 Move pick_best(size_t multiPV);
96 Move best = MOVE_NONE;
99 // EasyMoveManager structure is used to detect an 'easy move'. When the PV is stable
100 // across multiple search iterations, we can quickly return the best move.
101 struct EasyMoveManager {
106 pv[0] = pv[1] = pv[2] = MOVE_NONE;
109 Move get(Key key) const {
110 return expectedPosKey == key ? pv[2] : MOVE_NONE;
113 void update(Position& pos, const std::vector<Move>& newPv) {
115 assert(newPv.size() >= 3);
117 // Keep track of how many times in a row the 3rd ply remains stable
118 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
120 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
122 std::copy(newPv.begin(), newPv.begin() + 3, pv);
125 pos.do_move(newPv[0], st[0]);
126 pos.do_move(newPv[1], st[1]);
127 expectedPosKey = pos.key();
128 pos.undo_move(newPv[1]);
129 pos.undo_move(newPv[0]);
138 EasyMoveManager EasyMove;
139 Value DrawValue[COLOR_NB];
141 template <NodeType NT>
142 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
144 template <NodeType NT, bool InCheck>
145 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
147 Value value_to_tt(Value v, int ply);
148 Value value_from_tt(Value v, int ply);
149 void update_pv(Move* pv, Move move, Move* childPv);
150 void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
151 void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
153 // perft() is our utility to verify move generation. All the leaf nodes up
154 // to the given depth are generated and counted, and the sum is returned.
156 uint64_t perft(Position& pos, Depth depth) {
159 uint64_t cnt, nodes = 0;
160 const bool leaf = (depth == 2 * ONE_PLY);
162 for (const auto& m : MoveList<LEGAL>(pos))
164 if (Root && depth <= ONE_PLY)
169 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
174 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
182 /// Search::init() is called during startup to initialize various lookup tables
184 void Search::init() {
186 for (int imp = 0; imp <= 1; ++imp)
187 for (int d = 1; d < 64; ++d)
188 for (int mc = 1; mc < 64; ++mc)
190 double r = log(d) * log(mc) / 1.95;
192 Reductions[NonPV][imp][d][mc] = int(std::round(r));
193 Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
195 // Increase reduction for non-PV nodes when eval is not improving
196 if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
197 Reductions[NonPV][imp][d][mc]++;
200 for (int d = 0; d < 16; ++d)
202 FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
203 FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
208 /// Search::clear() resets search state to its initial value
210 void Search::clear() {
212 Threads.main()->wait_for_search_finished();
214 Time.availableNodes = 0;
217 for (Thread* th : Threads)
220 Threads.main()->callsCnt = 0;
221 Threads.main()->previousScore = VALUE_INFINITE;
225 /// MainThread::search() is called by the main thread when the program receives
226 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
228 void MainThread::search() {
232 nodes = perft<true>(rootPos, Limits.perft * ONE_PLY);
233 sync_cout << "\nNodes searched: " << nodes << "\n" << sync_endl;
237 Color us = rootPos.side_to_move();
238 Time.init(Limits, us, rootPos.game_ply());
241 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
242 DrawValue[ us] = VALUE_DRAW - Value(contempt);
243 DrawValue[~us] = VALUE_DRAW + Value(contempt);
245 if (rootMoves.empty())
247 rootMoves.emplace_back(MOVE_NONE);
248 sync_cout << "info depth 0 score "
249 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
254 for (Thread* th : Threads)
256 th->start_searching();
258 Thread::search(); // Let's start searching!
261 // When we reach the maximum depth, we can arrive here without a raise of
262 // Threads.stop. However, if we are pondering or in an infinite search,
263 // the UCI protocol states that we shouldn't print the best move before the
264 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
265 // until the GUI sends one of those commands (which also raises Threads.stop).
266 Threads.stopOnPonderhit = true;
268 while (!Threads.stop && (Threads.ponder || Limits.infinite))
269 {} // Busy wait for a stop or a ponder reset
271 // Stop the threads if not already stopped (also raise the stop if
272 // "ponderhit" just reset Threads.ponder).
275 // Wait until all threads have finished
276 for (Thread* th : Threads)
278 th->wait_for_search_finished();
280 // When playing in 'nodes as time' mode, subtract the searched nodes from
281 // the available ones before exiting.
283 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
285 // Check if there are threads with a better score than main thread
286 Thread* bestThread = this;
287 if ( !this->easyMovePlayed
288 && Options["MultiPV"] == 1
290 && !Skill(Options["Skill Level"]).enabled()
291 && rootMoves[0].pv[0] != MOVE_NONE)
293 for (Thread* th : Threads)
295 Depth depthDiff = th->completedDepth - bestThread->completedDepth;
296 Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
298 // Select the thread with the best score, always if it is a mate
300 && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
305 previousScore = bestThread->rootMoves[0].score;
307 // Send new PV when needed
308 if (bestThread != this)
309 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
311 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
313 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
314 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
316 std::cout << sync_endl;
320 /// Thread::search() is the main iterative deepening loop. It calls search()
321 /// repeatedly with increasing depth until the allocated thinking time has been
322 /// consumed, the user stops the search, or the maximum search depth is reached.
324 void Thread::search() {
326 Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2)
327 Value bestValue, alpha, beta, delta;
328 Move easyMove = MOVE_NONE;
329 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
331 std::memset(ss-4, 0, 7 * sizeof(Stack));
332 for (int i = 4; i > 0; i--)
333 (ss-i)->contHistory = &this->contHistory[NO_PIECE][0]; // Use as sentinel
335 bestValue = delta = alpha = -VALUE_INFINITE;
336 beta = VALUE_INFINITE;
340 easyMove = EasyMove.get(rootPos.key());
342 mainThread->easyMovePlayed = mainThread->failedLow = false;
343 mainThread->bestMoveChanges = 0;
346 size_t multiPV = Options["MultiPV"];
347 Skill skill(Options["Skill Level"]);
349 // When playing with strength handicap enable MultiPV search that we will
350 // use behind the scenes to retrieve a set of possible moves.
352 multiPV = std::max(multiPV, (size_t)4);
354 multiPV = std::min(multiPV, rootMoves.size());
356 // Iterative deepening loop until requested to stop or the target depth is reached
357 while ( (rootDepth += ONE_PLY) < DEPTH_MAX
359 && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
361 // Distribute search depths across the threads
364 int i = (idx - 1) % 20;
365 if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2)
369 // Age out PV variability metric
371 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
373 // Save the last iteration's scores before first PV line is searched and
374 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
375 for (RootMove& rm : rootMoves)
376 rm.previousScore = rm.score;
378 // MultiPV loop. We perform a full root search for each PV line
379 for (PVIdx = 0; PVIdx < multiPV && !Threads.stop; ++PVIdx)
381 // Reset UCI info selDepth for each depth and each PV line
384 // Reset aspiration window starting size
385 if (rootDepth >= 5 * ONE_PLY)
388 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
389 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
392 // Start with a small aspiration window and, in the case of a fail
393 // high/low, re-search with a bigger window until we're not failing
397 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
399 // Bring the best move to the front. It is critical that sorting
400 // is done with a stable algorithm because all the values but the
401 // first and eventually the new best one are set to -VALUE_INFINITE
402 // and we want to keep the same order for all the moves except the
403 // new PV that goes to the front. Note that in case of MultiPV
404 // search the already searched PV lines are preserved.
405 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
407 // If search has been stopped, we break immediately. Sorting and
408 // writing PV back to TT is safe because RootMoves is still
409 // valid, although it refers to the previous iteration.
413 // When failing high/low give some update (without cluttering
414 // the UI) before a re-search.
417 && (bestValue <= alpha || bestValue >= beta)
418 && Time.elapsed() > 3000)
419 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
421 // In case of failing low/high increase aspiration window and
422 // re-search, otherwise exit the loop.
423 if (bestValue <= alpha)
425 beta = (alpha + beta) / 2;
426 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
430 mainThread->failedLow = true;
431 Threads.stopOnPonderhit = false;
434 else if (bestValue >= beta)
435 beta = std::min(bestValue + delta, VALUE_INFINITE);
439 delta += delta / 4 + 5;
441 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
444 // Sort the PV lines searched so far and update the GUI
445 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
448 && (Threads.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000))
449 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
453 completedDepth = rootDepth;
455 // Have we found a "mate in x"?
457 && bestValue >= VALUE_MATE_IN_MAX_PLY
458 && VALUE_MATE - bestValue <= 2 * Limits.mate)
464 // If skill level is enabled and time is up, pick a sub-optimal best move
465 if (skill.enabled() && skill.time_to_pick(rootDepth))
466 skill.pick_best(multiPV);
468 // Do we have time for the next iteration? Can we stop searching now?
469 if (Limits.use_time_management())
471 if (!Threads.stop && !Threads.stopOnPonderhit)
473 // Stop the search if only one legal move is available, or if all
474 // of the available time has been used, or if we matched an easyMove
475 // from the previous search and just did a fast verification.
476 const int F[] = { mainThread->failedLow,
477 bestValue - mainThread->previousScore };
479 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
480 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
482 bool doEasyMove = rootMoves[0].pv[0] == easyMove
483 && mainThread->bestMoveChanges < 0.03
484 && Time.elapsed() > Time.optimum() * 5 / 44;
486 if ( rootMoves.size() == 1
487 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
488 || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
490 // If we are allowed to ponder do not stop the search now but
491 // keep pondering until the GUI sends "ponderhit" or "stop".
493 Threads.stopOnPonderhit = true;
499 if (rootMoves[0].pv.size() >= 3)
500 EasyMove.update(rootPos, rootMoves[0].pv);
509 // Clear any candidate easy move that wasn't stable for the last search
510 // iterations; the second condition prevents consecutive fast moves.
511 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
514 // If skill level is enabled, swap best PV line with the sub-optimal one
516 std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(),
517 skill.best ? skill.best : skill.pick_best(multiPV)));
523 // search<>() is the main search function for both PV and non-PV nodes
525 template <NodeType NT>
526 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
528 const bool PvNode = NT == PV;
529 const bool rootNode = PvNode && ss->ply == 0;
531 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
532 assert(PvNode || (alpha == beta - 1));
533 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
534 assert(!(PvNode && cutNode));
535 assert(depth / ONE_PLY * ONE_PLY == depth);
537 Move pv[MAX_PLY+1], quietsSearched[64];
541 Move ttMove, move, excludedMove, bestMove;
542 Depth extension, newDepth;
543 Value bestValue, value, ttValue, eval;
544 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
545 bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
547 int moveCount, quietCount;
549 // Step 1. Initialize node
550 Thread* thisThread = pos.this_thread();
551 inCheck = pos.checkers();
552 moveCount = quietCount = ss->moveCount = 0;
554 bestValue = -VALUE_INFINITE;
556 // Check for the available remaining time
557 if (thisThread == Threads.main())
558 static_cast<MainThread*>(thisThread)->check_time();
560 // Used to send selDepth info to GUI (selDepth counts from 1, ply from 0)
561 if (PvNode && thisThread->selDepth < ss->ply + 1)
562 thisThread->selDepth = ss->ply + 1;
566 // Step 2. Check for aborted search and immediate draw
567 if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
568 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
569 : DrawValue[pos.side_to_move()];
571 // Step 3. Mate distance pruning. Even if we mate at the next move our score
572 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
573 // a shorter mate was found upward in the tree then there is no need to search
574 // because we will never beat the current alpha. Same logic but with reversed
575 // signs applies also in the opposite condition of being mated instead of giving
576 // mate. In this case return a fail-high score.
577 alpha = std::max(mated_in(ss->ply), alpha);
578 beta = std::min(mate_in(ss->ply+1), beta);
583 assert(0 <= ss->ply && ss->ply < MAX_PLY);
585 (ss+1)->ply = ss->ply + 1;
586 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
587 ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
588 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
589 Square prevSq = to_sq((ss-1)->currentMove);
591 // Step 4. Transposition table lookup. We don't want the score of a partial
592 // search to overwrite a previous full search TT value, so we use a different
593 // position key in case of an excluded move.
594 excludedMove = ss->excludedMove;
595 posKey = pos.key() ^ Key(excludedMove);
596 tte = TT.probe(posKey, ttHit);
597 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
598 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
599 : ttHit ? tte->move() : MOVE_NONE;
601 // At non-PV nodes we check for an early TT cutoff
604 && tte->depth() >= depth
605 && ttValue != VALUE_NONE // Possible in case of TT access race
606 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
607 : (tte->bound() & BOUND_UPPER)))
609 // If ttMove is quiet, update move sorting heuristics on TT hit
614 if (!pos.capture_or_promotion(ttMove))
615 update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
617 // Extra penalty for a quiet TT move in previous ply when it gets refuted
618 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
619 update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
621 // Penalty for a quiet ttMove that fails low
622 else if (!pos.capture_or_promotion(ttMove))
624 int penalty = -stat_bonus(depth);
625 thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty);
626 update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
632 // Step 4a. Tablebase probe
633 if (!rootNode && TB::Cardinality)
635 int piecesCount = pos.count<ALL_PIECES>();
637 if ( piecesCount <= TB::Cardinality
638 && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
639 && pos.rule50_count() == 0
640 && !pos.can_castle(ANY_CASTLING))
643 TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
645 if (err != TB::ProbeState::FAIL)
647 thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
649 int drawScore = TB::UseRule50 ? 1 : 0;
651 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1
652 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1
653 : VALUE_DRAW + 2 * v * drawScore;
655 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
656 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
657 MOVE_NONE, VALUE_NONE, TT.generation());
664 // Step 5. Evaluate the position statically
667 ss->staticEval = eval = VALUE_NONE;
673 // Never assume anything on values stored in TT
674 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
675 eval = ss->staticEval = evaluate(pos);
677 // Can ttValue be used as a better position evaluation?
678 if ( ttValue != VALUE_NONE
679 && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
684 eval = ss->staticEval =
685 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
686 : -(ss-1)->staticEval + 2 * Eval::Tempo;
688 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
689 ss->staticEval, TT.generation());
692 if (skipEarlyPruning)
695 // Step 6. Razoring (skipped when in check)
697 && depth < 4 * ONE_PLY
698 && eval + razor_margin[depth / ONE_PLY] <= alpha)
700 if (depth <= ONE_PLY)
701 return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
703 Value ralpha = alpha - razor_margin[depth / ONE_PLY];
704 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
709 // Step 7. Futility pruning: child node (skipped when in check)
711 && depth < 7 * ONE_PLY
712 && eval - futility_margin(depth) >= beta
713 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
714 && pos.non_pawn_material(pos.side_to_move()))
717 // Step 8. Null move search with verification search (is omitted in PV nodes)
720 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
721 && pos.non_pawn_material(pos.side_to_move()))
724 assert(eval - beta >= 0);
726 // Null move dynamic reduction based on depth and value
727 Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
729 ss->currentMove = MOVE_NULL;
730 ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
732 pos.do_null_move(st);
733 Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
734 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
735 pos.undo_null_move();
737 if (nullValue >= beta)
739 // Do not return unproven mate scores
740 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
743 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
746 // Do verification search at high depths
747 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
748 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
755 // Step 9. ProbCut (skipped when in check)
756 // If we have a good enough capture and a reduced search returns a value
757 // much above beta, we can (almost) safely prune the previous move.
759 && depth >= 5 * ONE_PLY
760 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
762 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
764 assert(is_ok((ss-1)->currentMove));
766 MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
768 while ((move = mp.next_move()) != MOVE_NONE)
771 ss->currentMove = move;
772 ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)];
774 assert(depth >= 5 * ONE_PLY);
775 pos.do_move(move, st);
776 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
783 // Step 10. Internal iterative deepening (skipped when in check)
784 if ( depth >= 6 * ONE_PLY
786 && (PvNode || ss->staticEval + 256 >= beta))
788 Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
789 search<NT>(pos, ss, alpha, beta, d, cutNode, true);
791 tte = TT.probe(posKey, ttHit);
792 ttMove = ttHit ? tte->move() : MOVE_NONE;
795 moves_loop: // When in check search starts from here
797 const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
798 Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
800 MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, contHist, countermove, ss->killers);
801 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
802 improving = ss->staticEval >= (ss-2)->staticEval
803 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
804 ||(ss-2)->staticEval == VALUE_NONE;
806 singularExtensionNode = !rootNode
807 && depth >= 8 * ONE_PLY
808 && ttMove != MOVE_NONE
809 && ttValue != VALUE_NONE
810 && !excludedMove // Recursive singular search is not allowed
811 && (tte->bound() & BOUND_LOWER)
812 && tte->depth() >= depth - 3 * ONE_PLY;
815 pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
817 // Step 11. Loop through moves
818 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
819 while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
823 if (move == excludedMove)
826 // At root obey the "searchmoves" option and skip moves not listed in Root
827 // Move List. As a consequence any illegal move is also skipped. In MultiPV
828 // mode we also skip PV moves which have been already searched.
829 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
830 thisThread->rootMoves.end(), move))
833 ss->moveCount = ++moveCount;
835 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
836 sync_cout << "info depth " << depth / ONE_PLY
837 << " currmove " << UCI::move(move, pos.is_chess960())
838 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
841 (ss+1)->pv = nullptr;
843 extension = DEPTH_ZERO;
844 captureOrPromotion = pos.capture_or_promotion(move);
845 movedPiece = pos.moved_piece(move);
847 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
848 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
849 : pos.gives_check(move);
851 moveCountPruning = depth < 16 * ONE_PLY
852 && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
854 // Step 12. Singular and Gives Check Extensions
856 // Singular extension search. If all moves but one fail low on a search of
857 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
858 // is singular and should be extended. To verify this we do a reduced search
859 // on all the other moves but the ttMove and if the result is lower than
860 // ttValue minus a margin then we will extend the ttMove.
861 if ( singularExtensionNode
865 Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
866 Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
867 ss->excludedMove = move;
868 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
869 ss->excludedMove = MOVE_NONE;
879 // Calculate new depth for this move
880 newDepth = depth - ONE_PLY + extension;
882 // Step 13. Pruning at shallow depth
884 && pos.non_pawn_material(pos.side_to_move())
885 && bestValue > VALUE_MATED_IN_MAX_PLY)
887 if ( !captureOrPromotion
889 && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
891 // Move count based pruning
892 if (moveCountPruning)
898 // Reduced depth of the next LMR search
899 int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
901 // Countermoves based pruning
903 && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
904 && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
907 // Futility pruning: parent node
910 && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
913 // Prune moves with negative SEE
915 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
918 else if ( depth < 7 * ONE_PLY
920 && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
924 // Speculative prefetch as early as possible
925 prefetch(TT.first_entry(pos.key_after(move)));
927 // Check for legality just before making the move
928 if (!rootNode && !pos.legal(move))
930 ss->moveCount = --moveCount;
934 if (move == ttMove && captureOrPromotion)
937 // Update the current move (this must be done after singular extension search)
938 ss->currentMove = move;
939 ss->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)];
941 // Step 14. Make the move
942 pos.do_move(move, st, givesCheck);
944 // Step 15. Reduced depth search (LMR). If the move fails high it will be
945 // re-searched at full depth.
946 if ( depth >= 3 * ONE_PLY
948 && (!captureOrPromotion || moveCountPruning))
950 Depth r = reduction<PvNode>(improving, depth, moveCount);
952 if (captureOrPromotion)
953 r -= r ? ONE_PLY : DEPTH_ZERO;
956 // Decrease reduction if opponent's move count is high
957 if ((ss-1)->moveCount > 15)
960 // Decrease reduction for exact PV nodes
964 // Increase reduction if ttMove is a capture
968 // Increase reduction for cut nodes
972 // Decrease reduction for moves that escape a capture. Filter out
973 // castling moves, because they are coded as "king captures rook" and
974 // hence break make_move().
975 else if ( type_of(move) == NORMAL
976 && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
979 ss->statScore = thisThread->mainHistory[~pos.side_to_move()][from_to(move)]
980 + (*contHist[0])[movedPiece][to_sq(move)]
981 + (*contHist[1])[movedPiece][to_sq(move)]
982 + (*contHist[3])[movedPiece][to_sq(move)]
985 // Decrease/increase reduction by comparing opponent's stat score
986 if (ss->statScore >= 0 && (ss-1)->statScore < 0)
989 else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
992 // Decrease/increase reduction for moves with a good/bad history
993 r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
996 Depth d = std::max(newDepth - r, ONE_PLY);
998 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
1000 doFullDepthSearch = (value > alpha && d != newDepth);
1003 doFullDepthSearch = !PvNode || moveCount > 1;
1005 // Step 16. Full depth search when LMR is skipped or fails high
1006 if (doFullDepthSearch)
1007 value = newDepth < ONE_PLY ?
1008 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
1009 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
1010 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
1012 // For PV nodes only, do a full PV search on the first move or after a fail
1013 // high (in the latter case search only if value < beta), otherwise let the
1014 // parent node fail low with value <= alpha and try another move.
1015 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1018 (ss+1)->pv[0] = MOVE_NONE;
1020 value = newDepth < ONE_PLY ?
1021 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
1022 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
1023 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
1026 // Step 17. Undo move
1027 pos.undo_move(move);
1029 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1031 // Step 18. Check for a new best move
1032 // Finished searching the move. If a stop occurred, the return value of
1033 // the search cannot be trusted, and we return immediately without
1034 // updating best move, PV and TT.
1035 if (Threads.stop.load(std::memory_order_relaxed))
1040 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1041 thisThread->rootMoves.end(), move);
1043 // PV move or new best move ?
1044 if (moveCount == 1 || value > alpha)
1047 rm.selDepth = thisThread->selDepth;
1052 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1053 rm.pv.push_back(*m);
1055 // We record how often the best move has been changed in each
1056 // iteration. This information is used for time management: When
1057 // the best move changes frequently, we allocate some more time.
1058 if (moveCount > 1 && thisThread == Threads.main())
1059 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1062 // All other moves but the PV are set to the lowest value: this
1063 // is not a problem when sorting because the sort is stable and the
1064 // move position in the list is preserved - just the PV is pushed up.
1065 rm.score = -VALUE_INFINITE;
1068 if (value > bestValue)
1076 if (PvNode && !rootNode) // Update pv even in fail-high case
1077 update_pv(ss->pv, move, (ss+1)->pv);
1079 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1083 assert(value >= beta); // Fail high
1089 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1090 quietsSearched[quietCount++] = move;
1093 // The following condition would detect a stop only after move loop has been
1094 // completed. But in this case bestValue is valid because we have fully
1095 // searched our subtree, and we can anyhow save the result in TT.
1101 // Step 20. Check for mate and stalemate
1102 // All legal moves have been searched and if there are no legal moves, it
1103 // must be a mate or a stalemate. If we are in a singular extension search then
1104 // return a fail low score.
1106 assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
1109 bestValue = excludedMove ? alpha
1110 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1113 // Quiet best move: update move sorting heuristics
1114 if (!pos.capture_or_promotion(bestMove))
1115 update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
1117 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1118 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
1119 update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
1121 // Bonus for prior countermove that caused the fail low
1122 else if ( depth >= 3 * ONE_PLY
1123 && !pos.captured_piece()
1124 && is_ok((ss-1)->currentMove))
1125 update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
1128 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1129 bestValue >= beta ? BOUND_LOWER :
1130 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1131 depth, bestMove, ss->staticEval, TT.generation());
1133 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1139 // qsearch() is the quiescence search function, which is called by the main
1140 // search function with depth zero, or recursively with depth less than ONE_PLY.
1142 template <NodeType NT, bool InCheck>
1143 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1145 const bool PvNode = NT == PV;
1147 assert(InCheck == !!pos.checkers());
1148 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1149 assert(PvNode || (alpha == beta - 1));
1150 assert(depth <= DEPTH_ZERO);
1151 assert(depth / ONE_PLY * ONE_PLY == depth);
1157 Move ttMove, move, bestMove;
1158 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1159 bool ttHit, givesCheck, evasionPrunable;
1165 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1167 ss->pv[0] = MOVE_NONE;
1170 ss->currentMove = bestMove = MOVE_NONE;
1171 (ss+1)->ply = ss->ply + 1;
1174 // Check for an instant draw or if the maximum ply has been reached
1175 if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
1176 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1177 : DrawValue[pos.side_to_move()];
1179 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1181 // Decide whether or not to include checks: this fixes also the type of
1182 // TT entry depth that we are going to use. Note that in qsearch we use
1183 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1184 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1185 : DEPTH_QS_NO_CHECKS;
1186 // Transposition table lookup
1188 tte = TT.probe(posKey, ttHit);
1189 ttMove = ttHit ? tte->move() : MOVE_NONE;
1190 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1194 && tte->depth() >= ttDepth
1195 && ttValue != VALUE_NONE // Only in case of TT access race
1196 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1197 : (tte->bound() & BOUND_UPPER)))
1200 // Evaluate the position statically
1203 ss->staticEval = VALUE_NONE;
1204 bestValue = futilityBase = -VALUE_INFINITE;
1210 // Never assume anything on values stored in TT
1211 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1212 ss->staticEval = bestValue = evaluate(pos);
1214 // Can ttValue be used as a better position evaluation?
1215 if ( ttValue != VALUE_NONE
1216 && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
1217 bestValue = ttValue;
1220 ss->staticEval = bestValue =
1221 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1222 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1224 // Stand pat. Return immediately if static value is at least beta
1225 if (bestValue >= beta)
1228 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1229 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1234 if (PvNode && bestValue > alpha)
1237 futilityBase = bestValue + 128;
1240 // Initialize a MovePicker object for the current position, and prepare
1241 // to search the moves. Because the depth is <= 0 here, only captures,
1242 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1244 MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory, to_sq((ss-1)->currentMove));
1246 // Loop through the moves until no moves remain or a beta cutoff occurs
1247 while ((move = mp.next_move()) != MOVE_NONE)
1249 assert(is_ok(move));
1251 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
1252 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
1253 : pos.gives_check(move);
1260 && futilityBase > -VALUE_KNOWN_WIN
1261 && !pos.advanced_pawn_push(move))
1263 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1265 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1267 if (futilityValue <= alpha)
1269 bestValue = std::max(bestValue, futilityValue);
1273 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
1275 bestValue = std::max(bestValue, futilityBase);
1280 // Detect non-capture evasions that are candidates to be pruned
1281 evasionPrunable = InCheck
1282 && (depth != DEPTH_ZERO || moveCount > 2)
1283 && bestValue > VALUE_MATED_IN_MAX_PLY
1284 && !pos.capture(move);
1286 // Don't search moves with negative SEE values
1287 if ( (!InCheck || evasionPrunable)
1288 && type_of(move) != PROMOTION
1289 && !pos.see_ge(move))
1292 // Speculative prefetch as early as possible
1293 prefetch(TT.first_entry(pos.key_after(move)));
1295 // Check for legality just before making the move
1296 if (!pos.legal(move))
1302 ss->currentMove = move;
1304 // Make and search the move
1305 pos.do_move(move, st, givesCheck);
1306 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1307 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1308 pos.undo_move(move);
1310 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1312 // Check for a new best move
1313 if (value > bestValue)
1319 if (PvNode) // Update pv even in fail-high case
1320 update_pv(ss->pv, move, (ss+1)->pv);
1322 if (PvNode && value < beta) // Update alpha here!
1329 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1330 ttDepth, move, ss->staticEval, TT.generation());
1338 // All legal moves have been searched. A special case: If we're in check
1339 // and no legal moves were found, it is checkmate.
1340 if (InCheck && bestValue == -VALUE_INFINITE)
1341 return mated_in(ss->ply); // Plies to mate from the root
1343 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1344 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1345 ttDepth, bestMove, ss->staticEval, TT.generation());
1347 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1353 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1354 // "plies to mate from the current position". Non-mate scores are unchanged.
1355 // The function is called before storing a value in the transposition table.
1357 Value value_to_tt(Value v, int ply) {
1359 assert(v != VALUE_NONE);
1361 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1362 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1366 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1367 // from the transposition table (which refers to the plies to mate/be mated
1368 // from current position) to "plies to mate/be mated from the root".
1370 Value value_from_tt(Value v, int ply) {
1372 return v == VALUE_NONE ? VALUE_NONE
1373 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1374 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1378 // update_pv() adds current move and appends child pv[]
1380 void update_pv(Move* pv, Move move, Move* childPv) {
1382 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1388 // update_continuation_histories() updates histories of the move pairs formed
1389 // by moves at ply -1, -2, and -4 with current move.
1391 void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
1393 for (int i : {1, 2, 4})
1394 if (is_ok((ss-i)->currentMove))
1395 (ss-i)->contHistory->update(pc, to, bonus);
1399 // update_stats() updates move sorting heuristics when a new quiet best move is found
1401 void update_stats(const Position& pos, Stack* ss, Move move,
1402 Move* quiets, int quietsCnt, int bonus) {
1404 if (ss->killers[0] != move)
1406 ss->killers[1] = ss->killers[0];
1407 ss->killers[0] = move;
1410 Color c = pos.side_to_move();
1411 Thread* thisThread = pos.this_thread();
1412 thisThread->mainHistory.update(c, move, bonus);
1413 update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
1415 if (is_ok((ss-1)->currentMove))
1417 Square prevSq = to_sq((ss-1)->currentMove);
1418 thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
1421 // Decrease all the other played quiet moves
1422 for (int i = 0; i < quietsCnt; ++i)
1424 thisThread->mainHistory.update(c, quiets[i], -bonus);
1425 update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1430 // When playing with strength handicap, choose best move among a set of RootMoves
1431 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1433 Move Skill::pick_best(size_t multiPV) {
1435 const RootMoves& rootMoves = Threads.main()->rootMoves;
1436 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1438 // RootMoves are already sorted by score in descending order
1439 Value topScore = rootMoves[0].score;
1440 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1441 int weakness = 120 - 2 * level;
1442 int maxScore = -VALUE_INFINITE;
1444 // Choose best move. For each move score we add two terms, both dependent on
1445 // weakness. One is deterministic and bigger for weaker levels, and one is
1446 // random. Then we choose the move with the resulting highest score.
1447 for (size_t i = 0; i < multiPV; ++i)
1449 // This is our magic formula
1450 int push = ( weakness * int(topScore - rootMoves[i].score)
1451 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1453 if (rootMoves[i].score + push >= maxScore)
1455 maxScore = rootMoves[i].score + push;
1456 best = rootMoves[i].pv[0];
1465 // check_time() is used to print debug info and, more importantly, to detect
1466 // when we are out of available time and thus stop the search.
1468 void MainThread::check_time() {
1473 // At low node count increase the checking rate to about 0.1% of nodes
1474 // otherwise use a default value.
1475 callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096;
1477 static TimePoint lastInfoTime = now();
1479 int elapsed = Time.elapsed();
1480 TimePoint tick = Limits.startTime + elapsed;
1482 if (tick - lastInfoTime >= 1000)
1484 lastInfoTime = tick;
1488 // An engine may not stop pondering until told so by the GUI
1492 if ( (Limits.use_time_management() && elapsed > Time.maximum())
1493 || (Limits.movetime && elapsed >= Limits.movetime)
1494 || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
1495 Threads.stop = true;
1499 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1500 /// that all (if any) unsearched PV lines are sent using a previous search score.
1502 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1504 std::stringstream ss;
1505 int elapsed = Time.elapsed() + 1;
1506 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1507 size_t PVIdx = pos.this_thread()->PVIdx;
1508 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1509 uint64_t nodesSearched = Threads.nodes_searched();
1510 uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
1512 for (size_t i = 0; i < multiPV; ++i)
1514 bool updated = (i <= PVIdx && rootMoves[i].score != -VALUE_INFINITE);
1516 if (depth == ONE_PLY && !updated)
1519 Depth d = updated ? depth : depth - ONE_PLY;
1520 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1522 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1523 v = tb ? TB::Score : v;
1525 if (ss.rdbuf()->in_avail()) // Not at first line
1529 << " depth " << d / ONE_PLY
1530 << " seldepth " << rootMoves[i].selDepth
1531 << " multipv " << i + 1
1532 << " score " << UCI::value(v);
1534 if (!tb && i == PVIdx)
1535 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1537 ss << " nodes " << nodesSearched
1538 << " nps " << nodesSearched * 1000 / elapsed;
1540 if (elapsed > 1000) // Earlier makes little sense
1541 ss << " hashfull " << TT.hashfull();
1543 ss << " tbhits " << tbHits
1544 << " time " << elapsed
1547 for (Move m : rootMoves[i].pv)
1548 ss << " " << UCI::move(m, pos.is_chess960());
1555 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1556 /// before exiting the search, for instance, in case we stop the search during a
1557 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1558 /// otherwise in case of 'ponder on' we have nothing to think on.
1560 bool RootMove::extract_ponder_from_tt(Position& pos) {
1565 assert(pv.size() == 1);
1570 pos.do_move(pv[0], st);
1571 TTEntry* tte = TT.probe(pos.key(), ttHit);
1575 Move m = tte->move(); // Local copy to be SMP safe
1576 if (MoveList<LEGAL>(pos).contains(m))
1580 pos.undo_move(pv[0]);
1581 return pv.size() > 1;
1584 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1587 UseRule50 = Options["Syzygy50MoveRule"];
1588 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1589 Cardinality = Options["SyzygyProbeLimit"];
1591 // Don't filter any moves if the user requested analysis on multiple
1592 if (Options["MultiPV"] != 1)
1595 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1596 if (Cardinality > MaxCardinality)
1598 Cardinality = MaxCardinality;
1599 ProbeDepth = DEPTH_ZERO;
1602 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1605 // If the current root position is in the tablebases, then RootMoves
1606 // contains only moves that preserve the draw or the win.
1607 RootInTB = root_probe(pos, rootMoves, TB::Score);
1610 Cardinality = 0; // Do not probe tablebases during the search
1612 else // If DTZ tables are missing, use WDL tables as a fallback
1614 // Filter out moves that do not preserve the draw or the win.
1615 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1617 // Only probe during search if winning
1618 if (RootInTB && TB::Score <= VALUE_DRAW)
1622 if (RootInTB && !UseRule50)
1623 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1624 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1