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/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime, IterationTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
86 MovesStats Countermoves, Followupmoves;
88 template <NodeType NT>
89 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
91 template <NodeType NT, bool InCheck>
92 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
94 void id_loop(Position& pos);
95 Value value_to_tt(Value v, int ply);
96 Value value_from_tt(Value v, int ply);
97 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
98 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
101 Skill(int l) : level(l), best(MOVE_NONE) {}
103 if (enabled()) // Swap best PV line with the sub-optimal one
104 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
105 RootMoves.end(), best ? best : pick_move()));
108 bool enabled() const { return level < 20; }
109 bool time_to_pick(int depth) const { return depth == 1 + level; }
119 /// Search::init() is called during startup to initialize various lookup tables
121 void Search::init() {
123 int d; // depth (ONE_PLY == 2)
124 int hd; // half depth (ONE_PLY == 1)
127 // Init reductions array
128 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
130 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
131 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
132 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
133 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
135 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
136 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
138 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
139 Reductions[0][0][hd][mc] += ONE_PLY;
141 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
142 Reductions[0][0][hd][mc] += ONE_PLY / 2;
145 // Init futility move count array
146 for (d = 0; d < 32; ++d)
148 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
149 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
154 /// Search::perft() is our utility to verify move generation. All the leaf nodes
155 /// up to the given depth are generated and counted and the sum returned.
157 static size_t perft(Position& pos, Depth depth) {
162 const bool leaf = depth == 2 * ONE_PLY;
164 for (MoveList<LEGAL> it(pos); *it; ++it)
166 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
167 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
173 size_t Search::perft(Position& pos, Depth depth) {
174 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
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 static PolyglotBook book; // Defined static to initialize the PRNG only once
185 RootColor = RootPos.side_to_move();
186 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
188 if (RootMoves.empty())
190 RootMoves.push_back(MOVE_NONE);
191 sync_cout << "info depth 0 score "
192 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
198 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
200 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
202 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
204 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
209 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
211 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
212 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
213 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
214 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
217 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
219 if (Options["Write Search Log"])
221 Log log(Options["Search Log Filename"]);
222 log << "\nSearching: " << RootPos.fen()
223 << "\ninfinite: " << Limits.infinite
224 << " ponder: " << Limits.ponder
225 << " time: " << Limits.time[RootColor]
226 << " increment: " << Limits.inc[RootColor]
227 << " moves to go: " << Limits.movestogo
231 // Reset the threads, still sleeping: will wake up at split time
232 for (size_t i = 0; i < Threads.size(); ++i)
233 Threads[i]->maxPly = 0;
235 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
236 Threads.timer->run = true;
237 Threads.timer->notify_one(); // Wake up the recurring timer
239 id_loop(RootPos); // Let's start searching !
241 Threads.timer->run = false; // Stop the timer
242 Threads.sleepWhileIdle = true; // Send idle threads to sleep
244 if (Options["Write Search Log"])
246 Time::point elapsed = Time::now() - SearchTime + 1;
248 Log log(Options["Search Log Filename"]);
249 log << "Nodes: " << RootPos.nodes_searched()
250 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
251 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
254 RootPos.do_move(RootMoves[0].pv[0], st);
255 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
256 RootPos.undo_move(RootMoves[0].pv[0]);
261 // When search is stopped this info is not printed
262 sync_cout << "info nodes " << RootPos.nodes_searched()
263 << " time " << Time::now() - SearchTime + 1 << sync_endl;
265 // When we reach the maximum depth, we can arrive here without a raise of
266 // Signals.stop. However, if we are pondering or in an infinite search,
267 // the UCI protocol states that we shouldn't print the best move before the
268 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
269 // until the GUI sends one of those commands (which also raises Signals.stop).
270 if (!Signals.stop && (Limits.ponder || Limits.infinite))
272 Signals.stopOnPonderhit = true;
273 RootPos.this_thread()->wait_for(Signals.stop);
276 // Best move could be MOVE_NONE when searching on a stalemate position
277 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
278 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
285 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
286 // with increasing depth until the allocated thinking time has been consumed,
287 // user stops the search, or the maximum search depth is reached.
289 void id_loop(Position& pos) {
291 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
293 Value bestValue, alpha, beta, delta;
295 std::memset(ss-2, 0, 5 * sizeof(Stack));
296 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
300 bestValue = delta = alpha = -VALUE_INFINITE;
301 beta = VALUE_INFINITE;
306 Countermoves.clear();
307 Followupmoves.clear();
309 PVSize = Options["MultiPV"];
310 Skill skill(Options["Skill Level"]);
312 // Do we have to play with skill handicap? In this case enable MultiPV search
313 // that we will use behind the scenes to retrieve a set of possible moves.
314 if (skill.enabled() && PVSize < 4)
317 PVSize = std::min(PVSize, RootMoves.size());
319 // Iterative deepening loop until requested to stop or target depth reached
320 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
322 // Age out PV variability metric
323 BestMoveChanges *= 0.8;
325 // Save the last iteration's scores before first PV line is searched and
326 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
327 for (size_t i = 0; i < RootMoves.size(); ++i)
328 RootMoves[i].prevScore = RootMoves[i].score;
330 // MultiPV loop. We perform a full root search for each PV line
331 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
333 // Reset aspiration window starting size
337 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
338 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
341 // Start with a small aspiration window and, in the case of a fail
342 // high/low, re-search with a bigger window until we're not failing
346 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
348 // Bring the best move to the front. It is critical that sorting
349 // is done with a stable algorithm because all the values but the
350 // first and eventually the new best one are set to -VALUE_INFINITE
351 // and we want to keep the same order for all the moves except the
352 // new PV that goes to the front. Note that in case of MultiPV
353 // search the already searched PV lines are preserved.
354 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
356 // Write PV back to transposition table in case the relevant
357 // entries have been overwritten during the search.
358 for (size_t i = 0; i <= PVIdx; ++i)
359 RootMoves[i].insert_pv_in_tt(pos);
361 // If search has been stopped break immediately. Sorting and
362 // writing PV back to TT is safe because RootMoves is still
363 // valid, although it refers to previous iteration.
367 // When failing high/low give some update (without cluttering
368 // the UI) before a re-search.
369 if ( (bestValue <= alpha || bestValue >= beta)
370 && Time::now() - SearchTime > 3000)
371 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
373 // In case of failing low/high increase aspiration window and
374 // re-search, otherwise exit the loop.
375 if (bestValue <= alpha)
377 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
379 Signals.failedLowAtRoot = true;
380 Signals.stopOnPonderhit = false;
382 else if (bestValue >= beta)
383 beta = std::min(bestValue + delta, VALUE_INFINITE);
390 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
393 // Sort the PV lines searched so far and update the GUI
394 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
396 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
397 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
400 IterationTime = Time::now() - SearchTime;
402 // If skill levels are enabled and time is up, pick a sub-optimal best move
403 if (skill.enabled() && skill.time_to_pick(depth))
406 if (Options["Write Search Log"])
408 RootMove& rm = RootMoves[0];
409 if (skill.best != MOVE_NONE)
410 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
412 Log log(Options["Search Log Filename"]);
413 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
417 // Have we found a "mate in x"?
419 && bestValue >= VALUE_MATE_IN_MAX_PLY
420 && VALUE_MATE - bestValue <= 2 * Limits.mate)
423 // Do we have time for the next iteration? Can we stop searching now?
424 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
426 bool stop = false; // Local variable, not the volatile Signals.stop
428 // Take some extra time if the best move has changed
429 if (depth > 4 && depth < 50 && PVSize == 1)
430 TimeMgr.pv_instability(BestMoveChanges);
432 // Stop the search if only one legal move is available or most
433 // of the available time has been used. We probably don't have
434 // enough time to search the first move at the next iteration anyway.
435 if ( RootMoves.size() == 1
436 || IterationTime > (TimeMgr.available_time() * 62) / 100)
441 // If we are allowed to ponder do not stop the search now but
442 // keep pondering until the GUI sends "ponderhit" or "stop".
444 Signals.stopOnPonderhit = true;
453 // search<>() is the main search function for both PV and non-PV nodes and for
454 // normal and SplitPoint nodes. When called just after a split point the search
455 // is simpler because we have already probed the hash table, done a null move
456 // search, and searched the first move before splitting, so we don't have to
457 // repeat all this work again. We also don't need to store anything to the hash
458 // table here: This is taken care of after we return from the split point.
460 template <NodeType NT>
461 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
463 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
464 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
465 const bool RootNode = (NT == Root || NT == SplitPointRoot);
467 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
468 assert(PvNode || (alpha == beta - 1));
469 assert(depth > DEPTH_ZERO);
471 Move quietsSearched[64];
474 SplitPoint* splitPoint;
476 Move ttMove, move, excludedMove, bestMove;
477 Depth ext, newDepth, predictedDepth;
478 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
479 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
480 bool captureOrPromotion, dangerous, doFullDepthSearch;
481 int moveCount, quietCount;
483 // Step 1. Initialize node
484 Thread* thisThread = pos.this_thread();
485 inCheck = pos.checkers();
489 splitPoint = ss->splitPoint;
490 bestMove = splitPoint->bestMove;
491 bestValue = splitPoint->bestValue;
493 ttMove = excludedMove = MOVE_NONE;
494 ttValue = VALUE_NONE;
496 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
501 moveCount = quietCount = 0;
502 bestValue = -VALUE_INFINITE;
503 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
504 ss->ply = (ss-1)->ply + 1;
505 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
506 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
508 // Used to send selDepth info to GUI
509 if (PvNode && thisThread->maxPly < ss->ply)
510 thisThread->maxPly = ss->ply;
514 // Step 2. Check for aborted search and immediate draw
515 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
516 return DrawValue[pos.side_to_move()];
518 // Step 3. Mate distance pruning. Even if we mate at the next move our score
519 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
520 // a shorter mate was found upward in the tree then there is no need to search
521 // because we will never beat the current alpha. Same logic but with reversed
522 // signs applies also in the opposite condition of being mated instead of giving
523 // mate. In this case return a fail-high score.
524 alpha = std::max(mated_in(ss->ply), alpha);
525 beta = std::min(mate_in(ss->ply+1), beta);
530 // Step 4. Transposition table lookup
531 // We don't want the score of a partial search to overwrite a previous full search
532 // TT value, so we use a different position key in case of an excluded move.
533 excludedMove = ss->excludedMove;
534 posKey = excludedMove ? pos.exclusion_key() : pos.key();
535 tte = TT.probe(posKey);
536 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
537 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
539 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
540 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
541 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
542 // we should also update RootMoveList to avoid bogus output.
545 && tte->depth() >= depth
546 && ttValue != VALUE_NONE // Only in case of TT access race
547 && ( PvNode ? tte->bound() == BOUND_EXACT
548 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
549 : (tte->bound() & BOUND_UPPER)))
552 ss->currentMove = ttMove; // Can be MOVE_NONE
554 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
555 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
556 update_stats(pos, ss, ttMove, depth, NULL, 0);
561 // Step 5. Evaluate the position statically and update parent's gain statistics
564 ss->staticEval = eval = VALUE_NONE;
570 // Never assume anything on values stored in TT
571 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
572 eval = ss->staticEval = evaluate(pos);
574 // Can ttValue be used as a better position evaluation?
575 if (ttValue != VALUE_NONE)
576 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
581 eval = ss->staticEval = evaluate(pos);
582 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
585 if ( !pos.captured_piece_type()
586 && ss->staticEval != VALUE_NONE
587 && (ss-1)->staticEval != VALUE_NONE
588 && (move = (ss-1)->currentMove) != MOVE_NULL
589 && type_of(move) == NORMAL)
591 Square to = to_sq(move);
592 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
595 // Step 6. Razoring (skipped when in check)
597 && depth < 4 * ONE_PLY
598 && eval + razor_margin(depth) < beta
599 && ttMove == MOVE_NONE
600 && abs(beta) < VALUE_MATE_IN_MAX_PLY
601 && !pos.pawn_on_7th(pos.side_to_move()))
603 Value rbeta = beta - razor_margin(depth);
604 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
606 // Logically we should return (v + razor_margin(depth)), but
607 // surprisingly this performed slightly weaker in tests.
611 // Step 7. Futility pruning: child node (skipped when in check)
614 && depth < 7 * ONE_PLY
615 && eval - futility_margin(depth) >= beta
616 && abs(beta) < VALUE_MATE_IN_MAX_PLY
617 && abs(eval) < VALUE_KNOWN_WIN
618 && pos.non_pawn_material(pos.side_to_move()))
619 return eval - futility_margin(depth);
621 // Step 8. Null move search with verification search (is omitted in PV nodes)
624 && depth >= 2 * ONE_PLY
626 && abs(beta) < VALUE_MATE_IN_MAX_PLY
627 && pos.non_pawn_material(pos.side_to_move()))
629 ss->currentMove = MOVE_NULL;
631 assert(eval - beta >= 0);
633 // Null move dynamic reduction based on depth and value
634 Depth R = 3 * ONE_PLY
635 + depth / (2 * ONE_PLY)
636 + int(eval - beta) / PawnValueMg * ONE_PLY;
638 pos.do_null_move(st);
639 (ss+1)->skipNullMove = true;
640 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
641 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
642 (ss+1)->skipNullMove = false;
643 pos.undo_null_move();
645 if (nullValue >= beta)
647 // Do not return unproven mate scores
648 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
651 if (depth < 12 * ONE_PLY)
654 // Do verification search at high depths
655 ss->skipNullMove = true;
656 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO)
657 : search<NonPV>(pos, ss, alpha, beta, depth-R, false);
658 ss->skipNullMove = false;
665 // Step 9. ProbCut (skipped when in check)
666 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
667 // and a reduced search returns a value much above beta, we can (almost) safely
668 // prune the previous move.
670 && depth >= 5 * ONE_PLY
672 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
674 Value rbeta = beta + 200;
675 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
677 assert(rdepth >= ONE_PLY);
678 assert((ss-1)->currentMove != MOVE_NONE);
679 assert((ss-1)->currentMove != MOVE_NULL);
681 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
684 while ((move = mp.next_move<false>()) != MOVE_NONE)
685 if (pos.legal(move, ci.pinned))
687 ss->currentMove = move;
688 pos.do_move(move, st, ci, pos.gives_check(move, ci));
689 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
696 // Step 10. Internal iterative deepening (skipped when in check)
697 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
698 && ttMove == MOVE_NONE
699 && (PvNode || ss->staticEval + Value(256) >= beta))
701 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
703 ss->skipNullMove = true;
704 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
705 ss->skipNullMove = false;
707 tte = TT.probe(posKey);
708 ttMove = tte ? tte->move() : MOVE_NONE;
711 moves_loop: // When in check and at SpNode search starts from here
713 Square prevMoveSq = to_sq((ss-1)->currentMove);
714 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
715 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
717 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
718 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
719 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
721 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
723 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
724 improving = ss->staticEval >= (ss-2)->staticEval
725 || ss->staticEval == VALUE_NONE
726 ||(ss-2)->staticEval == VALUE_NONE;
728 singularExtensionNode = !RootNode
730 && depth >= 8 * ONE_PLY
731 && ttMove != MOVE_NONE
732 && !excludedMove // Recursive singular search is not allowed
733 && (tte->bound() & BOUND_LOWER)
734 && tte->depth() >= depth - 3 * ONE_PLY;
736 // Step 11. Loop through moves
737 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
738 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
742 if (move == excludedMove)
745 // At root obey the "searchmoves" option and skip moves not listed in Root
746 // Move List. As a consequence any illegal move is also skipped. In MultiPV
747 // mode we also skip PV moves which have been already searched.
748 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
753 // Shared counter cannot be decremented later if the move turns out to be illegal
754 if (!pos.legal(move, ci.pinned))
757 moveCount = ++splitPoint->moveCount;
758 splitPoint->mutex.unlock();
765 Signals.firstRootMove = (moveCount == 1);
767 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
768 sync_cout << "info depth " << depth / ONE_PLY
769 << " currmove " << move_to_uci(move, pos.is_chess960())
770 << " currmovenumber " << moveCount + PVIdx << sync_endl;
774 captureOrPromotion = pos.capture_or_promotion(move);
775 givesCheck = pos.gives_check(move, ci);
776 dangerous = givesCheck
777 || type_of(move) != NORMAL
778 || pos.advanced_pawn_push(move);
780 // Step 12. Extend checks
781 if (givesCheck && pos.see_sign(move) >= 0)
784 // Singular extension search. If all moves but one fail low on a search of
785 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
786 // is singular and should be extended. To verify this we do a reduced search
787 // on all the other moves but the ttMove and if the result is lower than
788 // ttValue minus a margin then we extend the ttMove.
789 if ( singularExtensionNode
792 && pos.legal(move, ci.pinned)
793 && abs(ttValue) < VALUE_KNOWN_WIN)
795 assert(ttValue != VALUE_NONE);
797 Value rBeta = ttValue - int(depth);
798 ss->excludedMove = move;
799 ss->skipNullMove = true;
800 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
801 ss->skipNullMove = false;
802 ss->excludedMove = MOVE_NONE;
808 // Update the current move (this must be done after singular extension search)
809 newDepth = depth - ONE_PLY + ext;
811 // Step 13. Pruning at shallow depth (exclude PV nodes)
813 && !captureOrPromotion
816 /* && move != ttMove Already implicit in the next condition */
817 && bestValue > VALUE_MATED_IN_MAX_PLY)
819 // Move count based pruning
820 if ( depth < 16 * ONE_PLY
821 && moveCount >= FutilityMoveCounts[improving][depth] )
824 splitPoint->mutex.lock();
829 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
831 // Futility pruning: parent node
832 if (predictedDepth < 7 * ONE_PLY)
834 futilityValue = ss->staticEval + futility_margin(predictedDepth)
835 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
837 if (futilityValue <= alpha)
839 bestValue = std::max(bestValue, futilityValue);
843 splitPoint->mutex.lock();
844 if (bestValue > splitPoint->bestValue)
845 splitPoint->bestValue = bestValue;
851 // Prune moves with negative SEE at low depths
852 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
855 splitPoint->mutex.lock();
861 // Check for legality just before making the move
862 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
868 pvMove = PvNode && moveCount == 1;
869 ss->currentMove = move;
870 if (!SpNode && !captureOrPromotion && quietCount < 64)
871 quietsSearched[quietCount++] = move;
873 // Step 14. Make the move
874 pos.do_move(move, st, ci, givesCheck);
876 // Step 15. Reduced depth search (LMR). If the move fails high it will be
877 // re-searched at full depth.
878 if ( depth >= 3 * ONE_PLY
880 && !captureOrPromotion
882 && move != ss->killers[0]
883 && move != ss->killers[1])
885 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
887 if (!PvNode && cutNode)
888 ss->reduction += ONE_PLY;
890 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
891 ss->reduction += ONE_PLY / 2;
893 if (move == countermoves[0] || move == countermoves[1])
894 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
896 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
898 alpha = splitPoint->alpha;
900 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
902 // Research at intermediate depth if reduction is very high
903 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
905 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
906 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
909 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
910 ss->reduction = DEPTH_ZERO;
913 doFullDepthSearch = !pvMove;
915 // Step 16. Full depth search, when LMR is skipped or fails high
916 if (doFullDepthSearch)
919 alpha = splitPoint->alpha;
921 value = newDepth < ONE_PLY ?
922 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
923 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
924 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
927 // For PV nodes only, do a full PV search on the first move or after a fail
928 // high (in the latter case search only if value < beta), otherwise let the
929 // parent node fail low with value <= alpha and to try another move.
930 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
931 value = newDepth < ONE_PLY ?
932 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
933 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
934 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
935 // Step 17. Undo move
938 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
940 // Step 18. Check for new best move
943 splitPoint->mutex.lock();
944 bestValue = splitPoint->bestValue;
945 alpha = splitPoint->alpha;
948 // Finished searching the move. If Signals.stop is true, the search
949 // was aborted because the user interrupted the search or because we
950 // ran out of time. In this case, the return value of the search cannot
951 // be trusted, and we don't update the best move and/or PV.
952 if (Signals.stop || thisThread->cutoff_occurred())
953 return value; // To avoid returning VALUE_INFINITE
957 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
959 // PV move or new best move ?
960 if (pvMove || value > alpha)
963 rm.extract_pv_from_tt(pos);
965 // We record how often the best move has been changed in each
966 // iteration. This information is used for time management: When
967 // the best move changes frequently, we allocate some more time.
972 // All other moves but the PV are set to the lowest value: this is
973 // not a problem when sorting because the sort is stable and the
974 // move position in the list is preserved - just the PV is pushed up.
975 rm.score = -VALUE_INFINITE;
978 if (value > bestValue)
980 bestValue = SpNode ? splitPoint->bestValue = value : value;
984 bestMove = SpNode ? splitPoint->bestMove = move : move;
986 if (PvNode && value < beta) // Update alpha! Always alpha < beta
987 alpha = SpNode ? splitPoint->alpha = value : value;
990 assert(value >= beta); // Fail high
993 splitPoint->cutoff = true;
1000 // Step 19. Check for splitting the search
1002 && depth >= Threads.minimumSplitDepth
1003 && Threads.available_slave(thisThread)
1004 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1006 assert(bestValue < beta);
1008 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1009 depth, moveCount, &mp, NT, cutNode);
1010 if (bestValue >= beta)
1018 // Step 20. Check for mate and stalemate
1019 // All legal moves have been searched and if there are no legal moves, it
1020 // must be mate or stalemate. Note that we can have a false positive in
1021 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1022 // harmless because return value is discarded anyhow in the parent nodes.
1023 // If we are in a singular extension search then return a fail low score.
1024 // A split node has at least one move - the one tried before to be splitted.
1026 return excludedMove ? alpha
1027 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1029 // If we have pruned all the moves without searching return a fail-low score
1030 if (bestValue == -VALUE_INFINITE)
1033 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1034 bestValue >= beta ? BOUND_LOWER :
1035 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1036 depth, bestMove, ss->staticEval);
1038 // Quiet best move: update killers, history, countermoves and followupmoves
1039 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1040 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1042 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1048 // qsearch() is the quiescence search function, which is called by the main
1049 // search function when the remaining depth is zero (or, to be more precise,
1050 // less than ONE_PLY).
1052 template <NodeType NT, bool InCheck>
1053 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1055 const bool PvNode = (NT == PV);
1057 assert(NT == PV || NT == NonPV);
1058 assert(InCheck == !!pos.checkers());
1059 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1060 assert(PvNode || (alpha == beta - 1));
1061 assert(depth <= DEPTH_ZERO);
1066 Move ttMove, move, bestMove;
1067 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1068 bool givesCheck, evasionPrunable;
1071 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1075 ss->currentMove = bestMove = MOVE_NONE;
1076 ss->ply = (ss-1)->ply + 1;
1078 // Check for an instant draw or if the maximum ply has been reached
1079 if (pos.is_draw() || ss->ply > MAX_PLY)
1080 return DrawValue[pos.side_to_move()];
1082 // Decide whether or not to include checks: this fixes also the type of
1083 // TT entry depth that we are going to use. Note that in qsearch we use
1084 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1085 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1086 : DEPTH_QS_NO_CHECKS;
1088 // Transposition table lookup
1090 tte = TT.probe(posKey);
1091 ttMove = tte ? tte->move() : MOVE_NONE;
1092 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1095 && tte->depth() >= ttDepth
1096 && ttValue != VALUE_NONE // Only in case of TT access race
1097 && ( PvNode ? tte->bound() == BOUND_EXACT
1098 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1099 : (tte->bound() & BOUND_UPPER)))
1101 ss->currentMove = ttMove; // Can be MOVE_NONE
1105 // Evaluate the position statically
1108 ss->staticEval = VALUE_NONE;
1109 bestValue = futilityBase = -VALUE_INFINITE;
1115 // Never assume anything on values stored in TT
1116 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1117 ss->staticEval = bestValue = evaluate(pos);
1119 // Can ttValue be used as a better position evaluation?
1120 if (ttValue != VALUE_NONE)
1121 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1122 bestValue = ttValue;
1125 ss->staticEval = bestValue = evaluate(pos);
1127 // Stand pat. Return immediately if static value is at least beta
1128 if (bestValue >= beta)
1131 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1132 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1137 if (PvNode && bestValue > alpha)
1140 futilityBase = bestValue + Value(128);
1143 // Initialize a MovePicker object for the current position, and prepare
1144 // to search the moves. Because the depth is <= 0 here, only captures,
1145 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1147 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1150 // Loop through the moves until no moves remain or a beta cutoff occurs
1151 while ((move = mp.next_move<false>()) != MOVE_NONE)
1153 assert(is_ok(move));
1155 givesCheck = pos.gives_check(move, ci);
1162 && futilityBase > -VALUE_KNOWN_WIN
1163 && !pos.advanced_pawn_push(move))
1165 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1167 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1169 if (futilityValue < beta)
1171 bestValue = std::max(bestValue, futilityValue);
1175 if (futilityBase < beta && pos.see(move) <= 0)
1177 bestValue = std::max(bestValue, futilityBase);
1182 // Detect non-capture evasions that are candidates to be pruned
1183 evasionPrunable = InCheck
1184 && bestValue > VALUE_MATED_IN_MAX_PLY
1185 && !pos.capture(move)
1186 && !pos.can_castle(pos.side_to_move());
1188 // Don't search moves with negative SEE values
1190 && (!InCheck || evasionPrunable)
1192 && type_of(move) != PROMOTION
1193 && pos.see_sign(move) < 0)
1196 // Check for legality just before making the move
1197 if (!pos.legal(move, ci.pinned))
1200 ss->currentMove = move;
1202 // Make and search the move
1203 pos.do_move(move, st, ci, givesCheck);
1204 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1205 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1206 pos.undo_move(move);
1208 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1210 // Check for new best move
1211 if (value > bestValue)
1217 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1224 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1225 ttDepth, move, ss->staticEval);
1233 // All legal moves have been searched. A special case: If we're in check
1234 // and no legal moves were found, it is checkmate.
1235 if (InCheck && bestValue == -VALUE_INFINITE)
1236 return mated_in(ss->ply); // Plies to mate from the root
1238 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1239 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1240 ttDepth, bestMove, ss->staticEval);
1242 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1248 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1249 // "plies to mate from the current position". Non-mate scores are unchanged.
1250 // The function is called before storing a value in the transposition table.
1252 Value value_to_tt(Value v, int ply) {
1254 assert(v != VALUE_NONE);
1256 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1257 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1261 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1262 // from the transposition table (which refers to the plies to mate/be mated
1263 // from current position) to "plies to mate/be mated from the root".
1265 Value value_from_tt(Value v, int ply) {
1267 return v == VALUE_NONE ? VALUE_NONE
1268 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1269 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1273 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1276 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1278 if (ss->killers[0] != move)
1280 ss->killers[1] = ss->killers[0];
1281 ss->killers[0] = move;
1284 // Increase history value of the cut-off move and decrease all the other
1285 // played quiet moves.
1286 Value bonus = Value(int(depth) * int(depth));
1287 History.update(pos.moved_piece(move), to_sq(move), bonus);
1288 for (int i = 0; i < quietsCnt; ++i)
1291 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1294 if (is_ok((ss-1)->currentMove))
1296 Square prevMoveSq = to_sq((ss-1)->currentMove);
1297 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1300 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1302 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1303 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1308 // When playing with a strength handicap, choose best move among the MultiPV
1309 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1311 Move Skill::pick_move() {
1315 // PRNG sequence should be not deterministic
1316 for (int i = Time::now() % 50; i > 0; --i)
1317 rk.rand<unsigned>();
1319 // RootMoves are already sorted by score in descending order
1320 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1321 int weakness = 120 - 2 * level;
1322 int max_s = -VALUE_INFINITE;
1325 // Choose best move. For each move score we add two terms both dependent on
1326 // weakness. One deterministic and bigger for weaker moves, and one random,
1327 // then we choose the move with the resulting highest score.
1328 for (size_t i = 0; i < PVSize; ++i)
1330 int s = RootMoves[i].score;
1332 // Don't allow crazy blunders even at very low skills
1333 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1336 // This is our magic formula
1337 s += ( weakness * int(RootMoves[0].score - s)
1338 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1343 best = RootMoves[i].pv[0];
1350 // uci_pv() formats PV information according to the UCI protocol. UCI
1351 // requires that all (if any) unsearched PV lines are sent using a previous
1354 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1356 std::stringstream s;
1357 Time::point elapsed = Time::now() - SearchTime + 1;
1358 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1361 for (size_t i = 0; i < Threads.size(); ++i)
1362 if (Threads[i]->maxPly > selDepth)
1363 selDepth = Threads[i]->maxPly;
1365 for (size_t i = 0; i < uciPVSize; ++i)
1367 bool updated = (i <= PVIdx);
1369 if (depth == 1 && !updated)
1372 int d = updated ? depth : depth - 1;
1373 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1375 if (s.rdbuf()->in_avail()) // Not at first line
1378 s << "info depth " << d
1379 << " seldepth " << selDepth
1380 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1381 << " nodes " << pos.nodes_searched()
1382 << " nps " << pos.nodes_searched() * 1000 / elapsed
1383 << " time " << elapsed
1384 << " multipv " << i + 1
1387 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1388 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1397 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1398 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1399 /// ensure that we have a ponder move even when we fail high at root. This
1400 /// results in a long PV to print that is important for position analysis.
1402 void RootMove::extract_pv_from_tt(Position& pos) {
1404 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1414 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1416 pos.do_move(pv[ply++], *st++);
1417 tte = TT.probe(pos.key());
1420 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1421 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1423 && (!pos.is_draw() || ply < 2));
1425 pv.push_back(MOVE_NONE); // Must be zero-terminating
1427 while (ply) pos.undo_move(pv[--ply]);
1431 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1432 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1433 /// first, even if the old TT entries have been overwritten.
1435 void RootMove::insert_pv_in_tt(Position& pos) {
1437 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1442 tte = TT.probe(pos.key());
1444 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1445 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1447 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1449 pos.do_move(pv[ply++], *st++);
1451 } while (pv[ply] != MOVE_NONE);
1453 while (ply) pos.undo_move(pv[--ply]);
1457 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1459 void Thread::idle_loop() {
1461 // Pointer 'this_sp' is not null only if we are called from split(), and not
1462 // at the thread creation. This means we are the split point's master.
1463 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1465 assert(!this_sp || (this_sp->masterThread == this && searching));
1469 // If we are not searching, wait for a condition to be signaled instead of
1470 // wasting CPU time polling for work.
1471 while ((!searching && Threads.sleepWhileIdle) || exit)
1479 // Grab the lock to avoid races with Thread::notify_one()
1482 // If we are master and all slaves have finished then exit idle_loop
1483 if (this_sp && !this_sp->slavesMask)
1489 // Do sleep after retesting sleep conditions under lock protection. In
1490 // particular we need to avoid a deadlock in case a master thread has,
1491 // in the meanwhile, allocated us and sent the notify_one() call before
1492 // we had the chance to grab the lock.
1493 if (!searching && !exit)
1494 sleepCondition.wait(mutex);
1499 // If this thread has been assigned work, launch a search
1504 Threads.mutex.lock();
1507 assert(activeSplitPoint);
1508 SplitPoint* sp = activeSplitPoint;
1510 Threads.mutex.unlock();
1512 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1513 Position pos(*sp->pos, this);
1515 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1516 ss->splitPoint = sp;
1520 assert(activePosition == NULL);
1522 activePosition = &pos;
1524 switch (sp->nodeType) {
1526 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1529 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1532 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1541 activePosition = NULL;
1542 sp->slavesMask &= ~(1ULL << idx);
1543 sp->nodes += pos.nodes_searched();
1545 // Wake up the master thread so to allow it to return from the idle
1546 // loop in case we are the last slave of the split point.
1547 if ( Threads.sleepWhileIdle
1548 && this != sp->masterThread
1551 assert(!sp->masterThread->searching);
1552 sp->masterThread->notify_one();
1555 // After releasing the lock we can't access any SplitPoint related data
1556 // in a safe way because it could have been released under our feet by
1557 // the sp master. Also accessing other Thread objects is unsafe because
1558 // if we are exiting there is a chance that they are already freed.
1562 // If this thread is the master of a split point and all slaves have finished
1563 // their work at this split point, return from the idle loop.
1564 if (this_sp && !this_sp->slavesMask)
1566 this_sp->mutex.lock();
1567 bool finished = !this_sp->slavesMask; // Retest under lock protection
1568 this_sp->mutex.unlock();
1576 /// check_time() is called by the timer thread when the timer triggers. It is
1577 /// used to print debug info and, more importantly, to detect when we are out of
1578 /// available time and thus stop the search.
1582 static Time::point lastInfoTime = Time::now();
1583 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1585 if (Time::now() - lastInfoTime >= 1000)
1587 lastInfoTime = Time::now();
1596 Threads.mutex.lock();
1598 nodes = RootPos.nodes_searched();
1600 // Loop across all split points and sum accumulated SplitPoint nodes plus
1601 // all the currently active positions nodes.
1602 for (size_t i = 0; i < Threads.size(); ++i)
1603 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1605 SplitPoint& sp = Threads[i]->splitPoints[j];
1610 Bitboard sm = sp.slavesMask;
1613 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1615 nodes += pos->nodes_searched();
1621 Threads.mutex.unlock();
1624 Time::point elapsed = Time::now() - SearchTime;
1625 bool stillAtFirstMove = Signals.firstRootMove
1626 && !Signals.failedLowAtRoot
1627 && ( elapsed > TimeMgr.available_time()
1628 || ( elapsed > (TimeMgr.available_time() * 62) / 100
1629 && elapsed > IterationTime * 1.4));
1631 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1632 || stillAtFirstMove;
1634 if ( (Limits.use_time_management() && noMoreTime)
1635 || (Limits.movetime && elapsed >= Limits.movetime)
1636 || (Limits.nodes && nodes >= Limits.nodes))
1637 Signals.stop = true;