2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
39 volatile SignalsType Signals;
41 std::vector<RootMove> RootMoves;
43 Time::point SearchTime;
44 StateStackPtr SetupStates;
49 using namespace Search;
53 // Different node types, used as template parameter
54 enum NodeType { Root, PV, NonPV };
56 // Dynamic razoring margin based on depth
57 inline Value razor_margin(Depth d) { return Value(512 + 32 * d); }
59 // Futility lookup tables (initialized at startup) and their access functions
60 int FutilityMoveCounts[2][16]; // [improving][depth]
62 inline Value futility_margin(Depth d) {
63 return Value(200 * d);
66 // Reduction lookup tables (initialized at startup) and their access function
67 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
69 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
70 return (Depth) Reductions[PvNode][i][std::min(int(d), 63)][std::min(mn, 63)];
75 double BestMoveChanges;
76 Value DrawValue[COLOR_NB];
79 MovesStats Countermoves, Followupmoves;
81 template <NodeType NT, bool SpNode>
82 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
84 template <NodeType NT, bool InCheck>
85 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
87 void id_loop(Position& pos);
88 Value value_to_tt(Value v, int ply);
89 Value value_from_tt(Value v, int ply);
90 void update_pv(Move* pv, Move move, Move* childPv);
91 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
92 string uci_pv(const Position& pos, Depth depth, Value alpha, Value beta);
95 Skill(int l, size_t rootSize) : level(l),
96 candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
99 if (candidates) // Swap best PV line with the sub-optimal one
100 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
101 RootMoves.end(), best ? best : pick_move()));
104 size_t candidates_size() const { return candidates; }
105 bool time_to_pick(Depth depth) const { return depth == 1 + level; }
116 /// Search::init() is called during startup to initialize various lookup tables
118 void Search::init() {
120 // Init reductions array
121 for (int d = 1; d < 64; ++d)
122 for (int mc = 1; mc < 64; ++mc)
124 double pvRed = 0.00 + log(double(d)) * log(double(mc)) / 3.00;
125 double nonPVRed = 0.33 + log(double(d)) * log(double(mc)) / 2.25;
127 Reductions[1][1][d][mc] = int8_t( pvRed >= 1.0 ? pvRed + 0.5: 0);
128 Reductions[0][1][d][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed + 0.5: 0);
130 Reductions[1][0][d][mc] = Reductions[1][1][d][mc];
131 Reductions[0][0][d][mc] = Reductions[0][1][d][mc];
133 // Increase reduction when eval is not improving
134 if (Reductions[0][0][d][mc] >= 2)
135 Reductions[0][0][d][mc] += 1;
138 // Init futility move count array
139 for (int d = 0; d < 16; ++d)
141 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
142 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
147 /// Search::perft() is our utility to verify move generation. All the leaf nodes
148 /// up to the given depth are generated and counted and the sum returned.
150 uint64_t Search::perft(Position& pos, Depth depth) {
153 uint64_t cnt, nodes = 0;
155 const bool leaf = (depth == 2 * ONE_PLY);
157 for (MoveList<LEGAL> it(pos); *it; ++it)
159 if (Root && depth <= ONE_PLY)
163 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
164 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
169 sync_cout << UCI::format_move(*it, pos.is_chess960()) << ": " << cnt << sync_endl;
174 template uint64_t Search::perft<true>(Position& pos, Depth depth);
177 /// Search::think() is the external interface to Stockfish's search, and is
178 /// called by the main thread when the program receives the UCI 'go' command. It
179 /// searches from RootPos and at the end prints the "bestmove" to output.
181 void Search::think() {
183 TimeMgr.init(Limits, RootPos.game_ply(), RootPos.side_to_move());
185 int cf = Options["Contempt"] * PawnValueEg / 100; // From centipawns
186 DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(cf);
187 DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(cf);
189 if (RootMoves.empty())
191 RootMoves.push_back(MOVE_NONE);
192 sync_cout << "info depth 0 score "
193 << UCI::format_value(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
198 for (size_t i = 0; i < Threads.size(); ++i)
199 Threads[i]->maxPly = 0;
201 Threads.timer->run = true;
202 Threads.timer->notify_one(); // Wake up the recurring timer
204 id_loop(RootPos); // Let's start searching !
206 Threads.timer->run = false;
209 // When we reach the maximum depth, we can arrive here without a raise of
210 // Signals.stop. However, if we are pondering or in an infinite search,
211 // the UCI protocol states that we shouldn't print the best move before the
212 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
213 // until the GUI sends one of those commands (which also raises Signals.stop).
214 if (!Signals.stop && (Limits.ponder || Limits.infinite))
216 Signals.stopOnPonderhit = true;
217 RootPos.this_thread()->wait_for(Signals.stop);
220 sync_cout << "bestmove " << UCI::format_move(RootMoves[0].pv[0], RootPos.is_chess960());
222 if (RootMoves[0].pv.size() > 1)
223 std::cout << " ponder " << UCI::format_move(RootMoves[0].pv[1], RootPos.is_chess960());
225 std::cout << sync_endl;
231 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
232 // with increasing depth until the allocated thinking time has been consumed,
233 // user stops the search, or the maximum search depth is reached.
235 void id_loop(Position& pos) {
237 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
239 Value bestValue, alpha, beta, delta;
241 std::memset(ss-2, 0, 5 * sizeof(Stack));
245 bestValue = delta = alpha = -VALUE_INFINITE;
246 beta = VALUE_INFINITE;
251 Countermoves.clear();
252 Followupmoves.clear();
254 size_t multiPV = Options["MultiPV"];
255 Skill skill(Options["Skill Level"], RootMoves.size());
257 // Do we have to play with skill handicap? In this case enable MultiPV search
258 // that we will use behind the scenes to retrieve a set of possible moves.
259 multiPV = std::max(multiPV, skill.candidates_size());
261 // Iterative deepening loop until requested to stop or target depth reached
262 while (++depth < DEPTH_MAX && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
264 // Age out PV variability metric
265 BestMoveChanges *= 0.5;
267 // Save the last iteration's scores before first PV line is searched and
268 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
269 for (size_t i = 0; i < RootMoves.size(); ++i)
270 RootMoves[i].prevScore = RootMoves[i].score;
272 // MultiPV loop. We perform a full root search for each PV line
273 for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
275 // Reset aspiration window starting size
276 if (depth >= 5 * ONE_PLY)
279 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
280 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
283 // Start with a small aspiration window and, in the case of a fail
284 // high/low, re-search with a bigger window until we're not failing
288 bestValue = search<Root, false>(pos, ss, alpha, beta, depth, false);
290 // Bring the best move to the front. It is critical that sorting
291 // is done with a stable algorithm because all the values but the
292 // first and eventually the new best one are set to -VALUE_INFINITE
293 // and we want to keep the same order for all the moves except the
294 // new PV that goes to the front. Note that in case of MultiPV
295 // search the already searched PV lines are preserved.
296 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
298 // Write PV back to transposition table in case the relevant
299 // entries have been overwritten during the search.
300 for (size_t i = 0; i <= PVIdx; ++i)
301 RootMoves[i].insert_pv_in_tt(pos);
303 // If search has been stopped break immediately. Sorting and
304 // writing PV back to TT is safe because RootMoves is still
305 // valid, although it refers to previous iteration.
309 // When failing high/low give some update (without cluttering
310 // the UI) before a re-search.
311 if ( (bestValue <= alpha || bestValue >= beta)
312 && Time::now() - SearchTime > 3000)
313 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
315 // In case of failing low/high increase aspiration window and
316 // re-search, otherwise exit the loop.
317 if (bestValue <= alpha)
319 beta = (alpha + beta) / 2;
320 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
322 Signals.failedLowAtRoot = true;
323 Signals.stopOnPonderhit = false;
325 else if (bestValue >= beta)
327 alpha = (alpha + beta) / 2;
328 beta = std::min(bestValue + delta, VALUE_INFINITE);
335 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
338 // Sort the PV lines searched so far and update the GUI
339 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
342 sync_cout << "info nodes " << RootPos.nodes_searched()
343 << " time " << Time::now() - SearchTime << sync_endl;
345 else if ( PVIdx + 1 == std::min(multiPV, RootMoves.size())
346 || Time::now() - SearchTime > 3000)
347 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
350 // If skill levels are enabled and time is up, pick a sub-optimal best move
351 if (skill.candidates_size() && skill.time_to_pick(depth))
354 // Have we found a "mate in x"?
356 && bestValue >= VALUE_MATE_IN_MAX_PLY
357 && VALUE_MATE - bestValue <= 2 * Limits.mate)
360 // Do we have time for the next iteration? Can we stop searching now?
361 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
363 // Take some extra time if the best move has changed
364 if (depth > 4 * ONE_PLY && multiPV == 1)
365 TimeMgr.pv_instability(BestMoveChanges);
367 // Stop the search if only one legal move is available or all
368 // of the available time has been used.
369 if ( RootMoves.size() == 1
370 || Time::now() - SearchTime > TimeMgr.available_time())
372 // If we are allowed to ponder do not stop the search now but
373 // keep pondering until the GUI sends "ponderhit" or "stop".
375 Signals.stopOnPonderhit = true;
384 // search<>() is the main search function for both PV and non-PV nodes and for
385 // normal and SplitPoint nodes. When called just after a split point the search
386 // is simpler because we have already probed the hash table, done a null move
387 // search, and searched the first move before splitting, so we don't have to
388 // repeat all this work again. We also don't need to store anything to the hash
389 // table here: This is taken care of after we return from the split point.
391 template <NodeType NT, bool SpNode>
392 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
394 const bool RootNode = NT == Root;
395 const bool PvNode = NT == PV || NT == Root;
397 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
398 assert(PvNode || (alpha == beta - 1));
399 assert(depth > DEPTH_ZERO);
401 Move pv[MAX_PLY+1], quietsSearched[64];
404 SplitPoint* splitPoint;
406 Move ttMove, move, excludedMove, bestMove;
407 Depth ext, newDepth, predictedDepth;
408 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
409 bool inCheck, givesCheck, singularExtensionNode, improving;
410 bool captureOrPromotion, dangerous, doFullDepthSearch;
411 int moveCount, quietCount;
413 // Step 1. Initialize node
414 Thread* thisThread = pos.this_thread();
415 inCheck = pos.checkers();
419 splitPoint = ss->splitPoint;
420 bestMove = splitPoint->bestMove;
421 bestValue = splitPoint->bestValue;
423 ttMove = excludedMove = MOVE_NONE;
424 ttValue = VALUE_NONE;
426 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
431 moveCount = quietCount = 0;
432 bestValue = -VALUE_INFINITE;
433 ss->ply = (ss-1)->ply + 1;
435 // Used to send selDepth info to GUI
436 if (PvNode && thisThread->maxPly < ss->ply)
437 thisThread->maxPly = ss->ply;
441 // Step 2. Check for aborted search and immediate draw
442 if (Signals.stop || pos.is_draw() || ss->ply >= MAX_PLY)
443 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
445 // Step 3. Mate distance pruning. Even if we mate at the next move our score
446 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
447 // a shorter mate was found upward in the tree then there is no need to search
448 // because we will never beat the current alpha. Same logic but with reversed
449 // signs applies also in the opposite condition of being mated instead of giving
450 // mate. In this case return a fail-high score.
451 alpha = std::max(mated_in(ss->ply), alpha);
452 beta = std::min(mate_in(ss->ply+1), beta);
457 assert(0 <= ss->ply && ss->ply < MAX_PLY);
459 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
460 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
461 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
463 // Step 4. Transposition table lookup
464 // We don't want the score of a partial search to overwrite a previous full search
465 // TT value, so we use a different position key in case of an excluded move.
466 excludedMove = ss->excludedMove;
467 posKey = excludedMove ? pos.exclusion_key() : pos.key();
468 tte = TT.probe(posKey);
469 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
470 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
472 // At non-PV nodes we check for a fail high/low. We don't probe at PV nodes
475 && tte->depth() >= depth
476 && ttValue != VALUE_NONE // Only in case of TT access race
477 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
478 : (tte->bound() & BOUND_UPPER)))
480 ss->currentMove = ttMove; // Can be MOVE_NONE
482 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
483 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
484 update_stats(pos, ss, ttMove, depth, NULL, 0);
489 // Step 5. Evaluate the position statically and update parent's gain statistics
492 ss->staticEval = eval = VALUE_NONE;
498 // Never assume anything on values stored in TT
499 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
500 eval = ss->staticEval = evaluate(pos);
502 // Can ttValue be used as a better position evaluation?
503 if (ttValue != VALUE_NONE)
504 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
509 eval = ss->staticEval =
510 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
512 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
515 if ( !pos.captured_piece_type()
516 && ss->staticEval != VALUE_NONE
517 && (ss-1)->staticEval != VALUE_NONE
518 && (move = (ss-1)->currentMove) != MOVE_NULL
520 && type_of(move) == NORMAL)
522 Square to = to_sq(move);
523 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
526 // Step 6. Razoring (skipped when in check)
528 && depth < 4 * ONE_PLY
529 && eval + razor_margin(depth) <= alpha
530 && ttMove == MOVE_NONE
531 && !pos.pawn_on_7th(pos.side_to_move()))
533 if ( depth <= ONE_PLY
534 && eval + razor_margin(3 * ONE_PLY) <= alpha)
535 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
537 Value ralpha = alpha - razor_margin(depth);
538 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
543 // Step 7. Futility pruning: child node (skipped when in check)
546 && depth < 7 * ONE_PLY
547 && eval - futility_margin(depth) >= beta
548 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
549 && pos.non_pawn_material(pos.side_to_move()))
550 return eval - futility_margin(depth);
552 // Step 8. Null move search with verification search (is omitted in PV nodes)
555 && depth >= 2 * ONE_PLY
557 && pos.non_pawn_material(pos.side_to_move()))
559 ss->currentMove = MOVE_NULL;
561 assert(eval - beta >= 0);
563 // Null move dynamic reduction based on depth and value
564 Depth R = (3 + depth / 4 + std::min(int(eval - beta) / PawnValueMg, 3)) * ONE_PLY;
566 pos.do_null_move(st);
567 (ss+1)->skipNullMove = true;
568 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
569 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
570 (ss+1)->skipNullMove = false;
571 pos.undo_null_move();
573 if (nullValue >= beta)
575 // Do not return unproven mate scores
576 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
579 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
582 // Do verification search at high depths
583 ss->skipNullMove = true;
584 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
585 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
586 ss->skipNullMove = false;
593 // Step 9. ProbCut (skipped when in check)
594 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
595 // and a reduced search returns a value much above beta, we can (almost) safely
596 // prune the previous move.
598 && depth >= 5 * ONE_PLY
600 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
602 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
603 Depth rdepth = depth - 4 * ONE_PLY;
605 assert(rdepth >= ONE_PLY);
606 assert((ss-1)->currentMove != MOVE_NONE);
607 assert((ss-1)->currentMove != MOVE_NULL);
609 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
612 while ((move = mp.next_move<false>()) != MOVE_NONE)
613 if (pos.legal(move, ci.pinned))
615 ss->currentMove = move;
616 pos.do_move(move, st, ci, pos.gives_check(move, ci));
617 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
624 // Step 10. Internal iterative deepening (skipped when in check)
625 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
627 && (PvNode || ss->staticEval + 256 >= beta))
629 Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
630 ss->skipNullMove = true;
631 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
632 ss->skipNullMove = false;
634 tte = TT.probe(posKey);
635 ttMove = tte ? tte->move() : MOVE_NONE;
638 moves_loop: // When in check and at SpNode search starts from here
640 Square prevMoveSq = to_sq((ss-1)->currentMove);
641 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
642 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
644 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
645 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
646 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
648 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
650 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
651 improving = ss->staticEval >= (ss-2)->staticEval
652 || ss->staticEval == VALUE_NONE
653 ||(ss-2)->staticEval == VALUE_NONE;
655 singularExtensionNode = !RootNode
657 && depth >= 8 * ONE_PLY
658 && ttMove != MOVE_NONE
659 /* && ttValue != VALUE_NONE Already implicit in the next condition */
660 && abs(ttValue) < VALUE_KNOWN_WIN
661 && !excludedMove // Recursive singular search is not allowed
662 && (tte->bound() & BOUND_LOWER)
663 && tte->depth() >= depth - 3 * ONE_PLY;
665 // Step 11. Loop through moves
666 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
667 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
671 if (move == excludedMove)
674 // At root obey the "searchmoves" option and skip moves not listed in Root
675 // Move List. As a consequence any illegal move is also skipped. In MultiPV
676 // mode we also skip PV moves which have been already searched.
677 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
682 // Shared counter cannot be decremented later if the move turns out to be illegal
683 if (!pos.legal(move, ci.pinned))
686 moveCount = ++splitPoint->moveCount;
687 splitPoint->mutex.unlock();
694 Signals.firstRootMove = (moveCount == 1);
696 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
697 sync_cout << "info depth " << depth
698 << " currmove " << UCI::format_move(move, pos.is_chess960())
699 << " currmovenumber " << moveCount + PVIdx << sync_endl;
706 captureOrPromotion = pos.capture_or_promotion(move);
708 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
709 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
710 : pos.gives_check(move, ci);
712 dangerous = givesCheck
713 || type_of(move) != NORMAL
714 || pos.advanced_pawn_push(move);
716 // Step 12. Extend checks
717 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
720 // Singular extension search. If all moves but one fail low on a search of
721 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
722 // is singular and should be extended. To verify this we do a reduced search
723 // on all the other moves but the ttMove and if the result is lower than
724 // ttValue minus a margin then we extend the ttMove.
725 if ( singularExtensionNode
728 && pos.legal(move, ci.pinned))
730 Value rBeta = ttValue - int(2 * depth);
731 ss->excludedMove = move;
732 ss->skipNullMove = true;
733 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
734 ss->skipNullMove = false;
735 ss->excludedMove = MOVE_NONE;
741 // Update the current move (this must be done after singular extension search)
742 newDepth = depth - ONE_PLY + ext;
744 // Step 13. Pruning at shallow depth (exclude PV nodes)
746 && !captureOrPromotion
749 && bestValue > VALUE_MATED_IN_MAX_PLY)
751 // Move count based pruning
752 if ( depth < 16 * ONE_PLY
753 && moveCount >= FutilityMoveCounts[improving][depth])
756 splitPoint->mutex.lock();
761 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
763 // Futility pruning: parent node
764 if (predictedDepth < 7 * ONE_PLY)
766 futilityValue = ss->staticEval + futility_margin(predictedDepth)
767 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
769 if (futilityValue <= alpha)
771 bestValue = std::max(bestValue, futilityValue);
775 splitPoint->mutex.lock();
776 if (bestValue > splitPoint->bestValue)
777 splitPoint->bestValue = bestValue;
783 // Prune moves with negative SEE at low depths
784 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
787 splitPoint->mutex.lock();
793 // Speculative prefetch as early as possible
794 prefetch((char*)TT.first_entry(pos.key_after(move)));
796 // Check for legality just before making the move
797 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
803 ss->currentMove = move;
804 if (!SpNode && !captureOrPromotion && quietCount < 64)
805 quietsSearched[quietCount++] = move;
807 // Step 14. Make the move
808 pos.do_move(move, st, ci, givesCheck);
810 // Step 15. Reduced depth search (LMR). If the move fails high it will be
811 // re-searched at full depth.
812 if ( depth >= 3 * ONE_PLY
814 && !captureOrPromotion
815 && move != ss->killers[0]
816 && move != ss->killers[1])
818 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
820 if ( (!PvNode && cutNode)
821 || History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
822 ss->reduction += ONE_PLY;
824 if (move == countermoves[0] || move == countermoves[1])
825 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
827 // Decrease reduction for moves that escape a capture
829 && type_of(move) == NORMAL
830 && type_of(pos.piece_on(to_sq(move))) != PAWN
831 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
832 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
834 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
836 alpha = splitPoint->alpha;
838 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
840 // Re-search at intermediate depth if reduction is very high
841 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
843 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
844 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
847 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
848 ss->reduction = DEPTH_ZERO;
851 doFullDepthSearch = !PvNode || moveCount > 1;
853 // Step 16. Full depth search, when LMR is skipped or fails high
854 if (doFullDepthSearch)
857 alpha = splitPoint->alpha;
859 value = newDepth < ONE_PLY ?
860 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
861 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
862 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
865 // For PV nodes only, do a full PV search on the first move or after a fail
866 // high (in the latter case search only if value < beta), otherwise let the
867 // parent node fail low with value <= alpha and to try another move.
868 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
871 (ss+1)->pv[0] = MOVE_NONE;
873 value = newDepth < ONE_PLY ?
874 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
875 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
876 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
879 // Step 17. Undo move
882 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
884 // Step 18. Check for new best move
887 splitPoint->mutex.lock();
888 bestValue = splitPoint->bestValue;
889 alpha = splitPoint->alpha;
892 // Finished searching the move. If a stop or a cutoff occurred, the return
893 // value of the search cannot be trusted, and we return immediately without
894 // updating best move, PV and TT.
895 if (Signals.stop || thisThread->cutoff_occurred())
900 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
902 // PV move or new best move ?
903 if (moveCount == 1 || value > alpha)
910 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
913 // We record how often the best move has been changed in each
914 // iteration. This information is used for time management: When
915 // the best move changes frequently, we allocate some more time.
920 // All other moves but the PV are set to the lowest value: this is
921 // not a problem when sorting because the sort is stable and the
922 // move position in the list is preserved - just the PV is pushed up.
923 rm.score = -VALUE_INFINITE;
926 if (value > bestValue)
928 bestValue = SpNode ? splitPoint->bestValue = value : value;
932 bestMove = SpNode ? splitPoint->bestMove = move : move;
934 if (PvNode && !RootNode) // Update pv even in fail-high case
935 update_pv(SpNode ? splitPoint->ss->pv : ss->pv, move, (ss+1)->pv);
937 if (PvNode && value < beta) // Update alpha! Always alpha < beta
938 alpha = SpNode ? splitPoint->alpha = value : value;
941 assert(value >= beta); // Fail high
944 splitPoint->cutoff = true;
951 // Step 19. Check for splitting the search
953 && Threads.size() >= 2
954 && depth >= Threads.minimumSplitDepth
955 && ( !thisThread->activeSplitPoint
956 || !thisThread->activeSplitPoint->allSlavesSearching)
957 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
959 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
961 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
962 depth, moveCount, &mp, NT, cutNode);
964 if (Signals.stop || thisThread->cutoff_occurred())
967 if (bestValue >= beta)
975 // Following condition would detect a stop or a cutoff set only after move
976 // loop has been completed. But in this case bestValue is valid because we
977 // have fully searched our subtree, and we can anyhow save the result in TT.
979 if (Signals.stop || thisThread->cutoff_occurred())
983 // Step 20. Check for mate and stalemate
984 // All legal moves have been searched and if there are no legal moves, it
985 // must be mate or stalemate. If we are in a singular extension search then
986 // return a fail low score.
988 bestValue = excludedMove ? alpha
989 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
991 // Quiet best move: update killers, history, countermoves and followupmoves
992 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
993 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
995 TT.store(posKey, value_to_tt(bestValue, ss->ply),
996 bestValue >= beta ? BOUND_LOWER :
997 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
998 depth, bestMove, ss->staticEval);
1000 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1006 // qsearch() is the quiescence search function, which is called by the main
1007 // search function when the remaining depth is zero (or, to be more precise,
1008 // less than ONE_PLY).
1010 template <NodeType NT, bool InCheck>
1011 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1013 const bool PvNode = NT == PV;
1015 assert(NT == PV || NT == NonPV);
1016 assert(InCheck == !!pos.checkers());
1017 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1018 assert(PvNode || (alpha == beta - 1));
1019 assert(depth <= DEPTH_ZERO);
1025 Move ttMove, move, bestMove;
1026 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1027 bool givesCheck, evasionPrunable;
1032 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1034 ss->pv[0] = MOVE_NONE;
1037 ss->currentMove = bestMove = MOVE_NONE;
1038 ss->ply = (ss-1)->ply + 1;
1040 // Check for an instant draw or if the maximum ply has been reached
1041 if (pos.is_draw() || ss->ply >= MAX_PLY)
1042 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1044 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1046 // Decide whether or not to include checks: this fixes also the type of
1047 // TT entry depth that we are going to use. Note that in qsearch we use
1048 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1049 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1050 : DEPTH_QS_NO_CHECKS;
1052 // Transposition table lookup
1054 tte = TT.probe(posKey);
1055 ttMove = tte ? tte->move() : MOVE_NONE;
1056 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1060 && tte->depth() >= ttDepth
1061 && ttValue != VALUE_NONE // Only in case of TT access race
1062 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1063 : (tte->bound() & BOUND_UPPER)))
1065 ss->currentMove = ttMove; // Can be MOVE_NONE
1069 // Evaluate the position statically
1072 ss->staticEval = VALUE_NONE;
1073 bestValue = futilityBase = -VALUE_INFINITE;
1079 // Never assume anything on values stored in TT
1080 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1081 ss->staticEval = bestValue = evaluate(pos);
1083 // Can ttValue be used as a better position evaluation?
1084 if (ttValue != VALUE_NONE)
1085 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1086 bestValue = ttValue;
1089 ss->staticEval = bestValue =
1090 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1092 // Stand pat. Return immediately if static value is at least beta
1093 if (bestValue >= beta)
1096 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1097 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1102 if (PvNode && bestValue > alpha)
1105 futilityBase = bestValue + 128;
1108 // Initialize a MovePicker object for the current position, and prepare
1109 // to search the moves. Because the depth is <= 0 here, only captures,
1110 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1112 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1115 // Loop through the moves until no moves remain or a beta cutoff occurs
1116 while ((move = mp.next_move<false>()) != MOVE_NONE)
1118 assert(is_ok(move));
1120 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1121 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1122 : pos.gives_check(move, ci);
1128 && futilityBase > -VALUE_KNOWN_WIN
1129 && !pos.advanced_pawn_push(move))
1131 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1133 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1135 if (futilityValue < beta)
1137 bestValue = std::max(bestValue, futilityValue);
1141 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1143 bestValue = std::max(bestValue, futilityBase);
1148 // Detect non-capture evasions that are candidates to be pruned
1149 evasionPrunable = InCheck
1150 && bestValue > VALUE_MATED_IN_MAX_PLY
1151 && !pos.capture(move)
1152 && !pos.can_castle(pos.side_to_move());
1154 // Don't search moves with negative SEE values
1156 && (!InCheck || evasionPrunable)
1157 && type_of(move) != PROMOTION
1158 && pos.see_sign(move) < VALUE_ZERO)
1161 // Speculative prefetch as early as possible
1162 prefetch((char*)TT.first_entry(pos.key_after(move)));
1164 // Check for legality just before making the move
1165 if (!pos.legal(move, ci.pinned))
1168 ss->currentMove = move;
1170 // Make and search the move
1171 pos.do_move(move, st, ci, givesCheck);
1172 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1173 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1174 pos.undo_move(move);
1176 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1178 // Check for new best move
1179 if (value > bestValue)
1185 if (PvNode) // Update pv even in fail-high case
1186 update_pv(ss->pv, move, (ss+1)->pv);
1188 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1195 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1196 ttDepth, move, ss->staticEval);
1204 // All legal moves have been searched. A special case: If we're in check
1205 // and no legal moves were found, it is checkmate.
1206 if (InCheck && bestValue == -VALUE_INFINITE)
1207 return mated_in(ss->ply); // Plies to mate from the root
1209 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1210 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1211 ttDepth, bestMove, ss->staticEval);
1213 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1219 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1220 // "plies to mate from the current position". Non-mate scores are unchanged.
1221 // The function is called before storing a value in the transposition table.
1223 Value value_to_tt(Value v, int ply) {
1225 assert(v != VALUE_NONE);
1227 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1228 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1232 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1233 // from the transposition table (which refers to the plies to mate/be mated
1234 // from current position) to "plies to mate/be mated from the root".
1236 Value value_from_tt(Value v, int ply) {
1238 return v == VALUE_NONE ? VALUE_NONE
1239 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1240 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1244 // update_pv() adds current move and appends child pv[]
1246 void update_pv(Move* pv, Move move, Move* childPv) {
1248 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1253 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1256 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1258 if (ss->killers[0] != move)
1260 ss->killers[1] = ss->killers[0];
1261 ss->killers[0] = move;
1264 // Increase history value of the cut-off move and decrease all the other
1265 // played quiet moves.
1266 Value bonus = Value(int(depth) * int(depth));
1267 History.update(pos.moved_piece(move), to_sq(move), bonus);
1268 for (int i = 0; i < quietsCnt; ++i)
1271 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1274 if (is_ok((ss-1)->currentMove))
1276 Square prevMoveSq = to_sq((ss-1)->currentMove);
1277 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1280 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1282 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1283 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1288 // When playing with a strength handicap, choose best move among the first 'candidates'
1289 // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1291 Move Skill::pick_move() {
1295 // PRNG sequence should be not deterministic
1296 for (int i = Time::now() % 50; i > 0; --i)
1297 rk.rand<unsigned>();
1299 // RootMoves are already sorted by score in descending order
1300 int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
1301 int weakness = 120 - 2 * level;
1302 int max_s = -VALUE_INFINITE;
1305 // Choose best move. For each move score we add two terms both dependent on
1306 // weakness. One deterministic and bigger for weaker moves, and one random,
1307 // then we choose the move with the resulting highest score.
1308 for (size_t i = 0; i < candidates; ++i)
1310 int s = RootMoves[i].score;
1312 // Don't allow crazy blunders even at very low skills
1313 if (i > 0 && RootMoves[i - 1].score > s + 2 * PawnValueMg)
1316 // This is our magic formula
1317 s += ( weakness * int(RootMoves[0].score - s)
1318 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1323 best = RootMoves[i].pv[0];
1330 // uci_pv() formats PV information according to the UCI protocol. UCI
1331 // requires that all (if any) unsearched PV lines are sent using a previous
1334 string uci_pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1336 std::stringstream ss;
1337 Time::point elapsed = Time::now() - SearchTime + 1;
1338 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1341 for (size_t i = 0; i < Threads.size(); ++i)
1342 if (Threads[i]->maxPly > selDepth)
1343 selDepth = Threads[i]->maxPly;
1345 for (size_t i = 0; i < uciPVSize; ++i)
1347 bool updated = (i <= PVIdx);
1349 if (depth == 1 && !updated)
1352 Depth d = updated ? depth : depth - ONE_PLY;
1353 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1355 if (ss.rdbuf()->in_avail()) // Not at first line
1358 ss << "info depth " << d / ONE_PLY
1359 << " seldepth " << selDepth
1360 << " multipv " << i + 1
1361 << " score " << (i == PVIdx ? UCI::format_value(v, alpha, beta) : UCI::format_value(v))
1362 << " nodes " << pos.nodes_searched()
1363 << " nps " << pos.nodes_searched() * 1000 / elapsed
1364 << " time " << elapsed
1367 for (size_t j = 0; j < RootMoves[i].pv.size(); ++j)
1368 ss << " " << UCI::format_move(RootMoves[i].pv[j], pos.is_chess960());
1377 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1378 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1379 /// first, even if the old TT entries have been overwritten.
1381 void RootMove::insert_pv_in_tt(Position& pos) {
1383 StateInfo state[MAX_PLY], *st = state;
1387 for ( ; idx < pv.size(); ++idx)
1389 tte = TT.probe(pos.key());
1391 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1392 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1394 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1396 pos.do_move(pv[idx], *st++);
1399 while (idx) pos.undo_move(pv[--idx]);
1403 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1405 void Thread::idle_loop() {
1407 // Pointer 'this_sp' is not null only if we are called from split(), and not
1408 // at the thread creation. This means we are the split point's master.
1409 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1411 assert(!this_sp || (this_sp->masterThread == this && searching));
1415 // If this thread has been assigned work, launch a search
1418 Threads.mutex.lock();
1420 assert(activeSplitPoint);
1421 SplitPoint* sp = activeSplitPoint;
1423 Threads.mutex.unlock();
1425 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
1426 Position pos(*sp->pos, this);
1428 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1429 ss->splitPoint = sp;
1433 assert(activePosition == NULL);
1435 activePosition = &pos;
1437 if (sp->nodeType == NonPV)
1438 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1440 else if (sp->nodeType == PV)
1441 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1443 else if (sp->nodeType == Root)
1444 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1452 activePosition = NULL;
1453 sp->slavesMask.reset(idx);
1454 sp->allSlavesSearching = false;
1455 sp->nodes += pos.nodes_searched();
1457 // Wake up the master thread so to allow it to return from the idle
1458 // loop in case we are the last slave of the split point.
1459 if ( this != sp->masterThread
1460 && sp->slavesMask.none())
1462 assert(!sp->masterThread->searching);
1463 sp->masterThread->notify_one();
1466 // After releasing the lock we can't access any SplitPoint related data
1467 // in a safe way because it could have been released under our feet by
1471 // Try to late join to another split point if none of its slaves has
1472 // already finished.
1473 if (Threads.size() > 2)
1474 for (size_t i = 0; i < Threads.size(); ++i)
1476 const int size = Threads[i]->splitPointsSize; // Local copy
1477 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1480 && sp->allSlavesSearching
1481 && available_to(Threads[i]))
1483 // Recheck the conditions under lock protection
1484 Threads.mutex.lock();
1487 if ( sp->allSlavesSearching
1488 && available_to(Threads[i]))
1490 sp->slavesMask.set(idx);
1491 activeSplitPoint = sp;
1496 Threads.mutex.unlock();
1498 break; // Just a single attempt
1503 // Grab the lock to avoid races with Thread::notify_one()
1506 // If we are master and all slaves have finished then exit idle_loop
1507 if (this_sp && this_sp->slavesMask.none())
1514 // If we are not searching, wait for a condition to be signaled instead of
1515 // wasting CPU time polling for work.
1516 if (!searching && !exit)
1517 sleepCondition.wait(mutex);
1524 /// check_time() is called by the timer thread when the timer triggers. It is
1525 /// used to print debug info and, more importantly, to detect when we are out of
1526 /// available time and thus stop the search.
1530 static Time::point lastInfoTime = Time::now();
1531 Time::point elapsed = Time::now() - SearchTime;
1533 if (Time::now() - lastInfoTime >= 1000)
1535 lastInfoTime = Time::now();
1539 // An engine may not stop pondering until told so by the GUI
1543 if (Limits.use_time_management())
1545 bool stillAtFirstMove = Signals.firstRootMove
1546 && !Signals.failedLowAtRoot
1547 && elapsed > TimeMgr.available_time() * 75 / 100;
1549 if ( stillAtFirstMove
1550 || elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution)
1551 Signals.stop = true;
1553 else if (Limits.movetime && elapsed >= Limits.movetime)
1554 Signals.stop = true;
1556 else if (Limits.nodes)
1558 Threads.mutex.lock();
1560 int64_t nodes = RootPos.nodes_searched();
1562 // Loop across all split points and sum accumulated SplitPoint nodes plus
1563 // all the currently active positions nodes.
1564 for (size_t i = 0; i < Threads.size(); ++i)
1565 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1567 SplitPoint& sp = Threads[i]->splitPoints[j];
1573 for (size_t idx = 0; idx < Threads.size(); ++idx)
1574 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1575 nodes += Threads[idx]->activePosition->nodes_searched();
1580 Threads.mutex.unlock();
1582 if (nodes >= Limits.nodes)
1583 Signals.stop = true;