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;
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 CountermovesStats Countermoves;
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();
308 PVSize = Options["MultiPV"];
309 Skill skill(Options["Skill Level"]);
311 // Do we have to play with skill handicap? In this case enable MultiPV search
312 // that we will use behind the scenes to retrieve a set of possible moves.
313 if (skill.enabled() && PVSize < 4)
316 PVSize = std::min(PVSize, RootMoves.size());
318 // Iterative deepening loop until requested to stop or target depth reached
319 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
321 // Age out PV variability metric
322 BestMoveChanges *= 0.8;
324 // Save the last iteration's scores before first PV line is searched and
325 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
326 for (size_t i = 0; i < RootMoves.size(); ++i)
327 RootMoves[i].prevScore = RootMoves[i].score;
329 // MultiPV loop. We perform a full root search for each PV line
330 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
332 // Reset aspiration window starting size
336 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
337 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
340 // Start with a small aspiration window and, in the case of a fail
341 // high/low, re-search with a bigger window until we're not failing
345 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
347 // Bring the best move to the front. It is critical that sorting
348 // is done with a stable algorithm because all the values but the
349 // first and eventually the new best one are set to -VALUE_INFINITE
350 // and we want to keep the same order for all the moves except the
351 // new PV that goes to the front. Note that in case of MultiPV
352 // search the already searched PV lines are preserved.
353 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
355 // Write PV back to transposition table in case the relevant
356 // entries have been overwritten during the search.
357 for (size_t i = 0; i <= PVIdx; ++i)
358 RootMoves[i].insert_pv_in_tt(pos);
360 // If search has been stopped break immediately. Sorting and
361 // writing PV back to TT is safe because RootMoves is still
362 // valid, although it refers to previous iteration.
366 // When failing high/low give some update (without cluttering
367 // the UI) before a re-search.
368 if ( (bestValue <= alpha || bestValue >= beta)
369 && Time::now() - SearchTime > 3000)
370 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
372 // In case of failing low/high increase aspiration window and
373 // re-search, otherwise exit the loop.
374 if (bestValue <= alpha)
376 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
378 Signals.failedLowAtRoot = true;
379 Signals.stopOnPonderhit = false;
381 else if (bestValue >= beta)
382 beta = std::min(bestValue + delta, VALUE_INFINITE);
389 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
392 // Sort the PV lines searched so far and update the GUI
393 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
395 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
396 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
399 // If skill levels are enabled and time is up, pick a sub-optimal best move
400 if (skill.enabled() && skill.time_to_pick(depth))
403 if (Options["Write Search Log"])
405 RootMove& rm = RootMoves[0];
406 if (skill.best != MOVE_NONE)
407 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
409 Log log(Options["Search Log Filename"]);
410 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
414 // Have we found a "mate in x"?
416 && bestValue >= VALUE_MATE_IN_MAX_PLY
417 && VALUE_MATE - bestValue <= 2 * Limits.mate)
420 // Do we have time for the next iteration? Can we stop searching now?
421 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
423 bool stop = false; // Local variable, not the volatile Signals.stop
425 // Take some extra time if the best move has changed
426 if (depth > 4 && depth < 50 && PVSize == 1)
427 TimeMgr.pv_instability(BestMoveChanges);
429 // Stop the search if most of the available time has been used. We
430 // probably don't have enough time to search the first move at the
431 // next iteration anyway.
432 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
435 // Stop the search early if one move seems to be much better than others
437 && BestMoveChanges <= DBL_EPSILON
440 && bestValue > VALUE_MATED_IN_MAX_PLY
441 && ( RootMoves.size() == 1
442 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
444 Value rBeta = bestValue - 2 * PawnValueMg;
445 ss->excludedMove = RootMoves[0].pv[0];
446 ss->skipNullMove = true;
447 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
448 ss->skipNullMove = false;
449 ss->excludedMove = MOVE_NONE;
457 // If we are allowed to ponder do not stop the search now but
458 // keep pondering until the GUI sends "ponderhit" or "stop".
460 Signals.stopOnPonderhit = true;
469 // search<>() is the main search function for both PV and non-PV nodes and for
470 // normal and SplitPoint nodes. When called just after a split point the search
471 // is simpler because we have already probed the hash table, done a null move
472 // search, and searched the first move before splitting, so we don't have to
473 // repeat all this work again. We also don't need to store anything to the hash
474 // table here: This is taken care of after we return from the split point.
476 template <NodeType NT>
477 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
479 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
480 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
481 const bool RootNode = (NT == Root || NT == SplitPointRoot);
483 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
484 assert(PvNode || (alpha == beta - 1));
485 assert(depth > DEPTH_ZERO);
487 Move quietsSearched[64];
490 SplitPoint* splitPoint;
492 Move ttMove, move, excludedMove, bestMove;
493 Depth ext, newDepth, predictedDepth;
494 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
495 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
496 bool captureOrPromotion, dangerous, doFullDepthSearch;
497 int moveCount, quietCount;
499 // Step 1. Initialize node
500 Thread* thisThread = pos.this_thread();
501 inCheck = pos.checkers();
505 splitPoint = ss->splitPoint;
506 bestMove = splitPoint->bestMove;
507 bestValue = splitPoint->bestValue;
509 ttMove = excludedMove = MOVE_NONE;
510 ttValue = VALUE_NONE;
512 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
517 moveCount = quietCount = 0;
518 bestValue = -VALUE_INFINITE;
519 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
520 ss->ply = (ss-1)->ply + 1;
521 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
522 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
524 // Used to send selDepth info to GUI
525 if (PvNode && thisThread->maxPly < ss->ply)
526 thisThread->maxPly = ss->ply;
530 // Step 2. Check for aborted search and immediate draw
531 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
532 return DrawValue[pos.side_to_move()];
534 // Step 3. Mate distance pruning. Even if we mate at the next move our score
535 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
536 // a shorter mate was found upward in the tree then there is no need to search
537 // because we will never beat the current alpha. Same logic but with reversed
538 // signs applies also in the opposite condition of being mated instead of giving
539 // mate. In this case return a fail-high score.
540 alpha = std::max(mated_in(ss->ply), alpha);
541 beta = std::min(mate_in(ss->ply+1), beta);
546 // Step 4. Transposition table lookup
547 // We don't want the score of a partial search to overwrite a previous full search
548 // TT value, so we use a different position key in case of an excluded move.
549 excludedMove = ss->excludedMove;
550 posKey = excludedMove ? pos.exclusion_key() : pos.key();
551 tte = TT.probe(posKey);
552 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
553 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
555 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
556 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
557 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
558 // we should also update RootMoveList to avoid bogus output.
561 && tte->depth() >= depth
562 && ttValue != VALUE_NONE // Only in case of TT access race
563 && ( PvNode ? tte->bound() == BOUND_EXACT
564 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
565 : (tte->bound() & BOUND_UPPER)))
568 ss->currentMove = ttMove; // Can be MOVE_NONE
570 // If ttMove is quiet, update killers, history, and counter move on TT hit
571 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
572 update_stats(pos, ss, ttMove, depth, NULL, 0);
577 // Step 5. Evaluate the position statically and update parent's gain statistics
580 ss->staticEval = eval = VALUE_NONE;
586 // Never assume anything on values stored in TT
587 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
588 eval = ss->staticEval = evaluate(pos);
590 // Can ttValue be used as a better position evaluation?
591 if (ttValue != VALUE_NONE)
592 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
597 eval = ss->staticEval = evaluate(pos);
598 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
601 if ( !pos.captured_piece_type()
602 && ss->staticEval != VALUE_NONE
603 && (ss-1)->staticEval != VALUE_NONE
604 && (move = (ss-1)->currentMove) != MOVE_NULL
605 && type_of(move) == NORMAL)
607 Square to = to_sq(move);
608 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
611 // Step 6. Razoring (skipped when in check)
613 && depth < 4 * ONE_PLY
614 && eval + razor_margin(depth) < beta
615 && ttMove == MOVE_NONE
616 && abs(beta) < VALUE_MATE_IN_MAX_PLY
617 && !pos.pawn_on_7th(pos.side_to_move()))
619 Value rbeta = beta - razor_margin(depth);
620 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
622 // Logically we should return (v + razor_margin(depth)), but
623 // surprisingly this performed slightly weaker in tests.
627 // Step 7. Futility pruning: child node (skipped when in check)
630 && depth < 7 * ONE_PLY
631 && eval - futility_margin(depth) >= beta
632 && abs(beta) < VALUE_MATE_IN_MAX_PLY
633 && abs(eval) < VALUE_KNOWN_WIN
634 && pos.non_pawn_material(pos.side_to_move()))
635 return eval - futility_margin(depth);
637 // Step 8. Null move search with verification search (is omitted in PV nodes)
640 && depth >= 2 * ONE_PLY
642 && abs(beta) < VALUE_MATE_IN_MAX_PLY
643 && pos.non_pawn_material(pos.side_to_move()))
645 ss->currentMove = MOVE_NULL;
647 // Null move dynamic reduction based on depth
648 Depth R = 3 * ONE_PLY + depth / 4;
650 // Null move dynamic reduction based on value
651 if (eval - PawnValueMg > beta)
654 pos.do_null_move(st);
655 (ss+1)->skipNullMove = true;
656 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
657 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
658 (ss+1)->skipNullMove = false;
659 pos.undo_null_move();
661 if (nullValue >= beta)
663 // Do not return unproven mate scores
664 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
667 if (depth < 12 * ONE_PLY)
670 // Do verification search at high depths
671 ss->skipNullMove = true;
672 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
673 ss->skipNullMove = false;
680 // Step 9. ProbCut (skipped when in check)
681 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
682 // and a reduced search returns a value much above beta, we can (almost) safely
683 // prune the previous move.
685 && depth >= 5 * ONE_PLY
687 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
689 Value rbeta = beta + 200;
690 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
692 assert(rdepth >= ONE_PLY);
693 assert((ss-1)->currentMove != MOVE_NONE);
694 assert((ss-1)->currentMove != MOVE_NULL);
696 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
699 while ((move = mp.next_move<false>()) != MOVE_NONE)
700 if (pos.legal(move, ci.pinned))
702 ss->currentMove = move;
703 pos.do_move(move, st, ci, pos.gives_check(move, ci));
704 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
711 // Step 10. Internal iterative deepening (skipped when in check)
712 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
713 && ttMove == MOVE_NONE
714 && (PvNode || ss->staticEval + Value(256) >= beta))
716 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
718 ss->skipNullMove = true;
719 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
720 ss->skipNullMove = false;
722 tte = TT.probe(posKey);
723 ttMove = tte ? tte->move() : MOVE_NONE;
726 moves_loop: // When in check and at SpNode search starts from here
728 Square prevMoveSq = to_sq((ss-1)->currentMove);
729 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
730 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
732 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
734 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
735 improving = ss->staticEval >= (ss-2)->staticEval
736 || ss->staticEval == VALUE_NONE
737 ||(ss-2)->staticEval == VALUE_NONE;
739 singularExtensionNode = !RootNode
741 && depth >= 8 * ONE_PLY
742 && ttMove != MOVE_NONE
743 && !excludedMove // Recursive singular search is not allowed
744 && (tte->bound() & BOUND_LOWER)
745 && tte->depth() >= depth - 3 * ONE_PLY;
747 // Step 11. Loop through moves
748 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
749 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
753 if (move == excludedMove)
756 // At root obey the "searchmoves" option and skip moves not listed in Root
757 // Move List. As a consequence any illegal move is also skipped. In MultiPV
758 // mode we also skip PV moves which have been already searched.
759 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
764 // Shared counter cannot be decremented later if the move turns out to be illegal
765 if (!pos.legal(move, ci.pinned))
768 moveCount = ++splitPoint->moveCount;
769 splitPoint->mutex.unlock();
776 Signals.firstRootMove = (moveCount == 1);
778 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
779 sync_cout << "info depth " << depth / ONE_PLY
780 << " currmove " << move_to_uci(move, pos.is_chess960())
781 << " currmovenumber " << moveCount + PVIdx << sync_endl;
785 captureOrPromotion = pos.capture_or_promotion(move);
786 givesCheck = pos.gives_check(move, ci);
787 dangerous = givesCheck
788 || type_of(move) != NORMAL
789 || pos.advanced_pawn_push(move);
791 // Step 12. Extend checks
792 if (givesCheck && pos.see_sign(move) >= 0)
795 // Singular extension search. If all moves but one fail low on a search of
796 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
797 // is singular and should be extended. To verify this we do a reduced search
798 // on all the other moves but the ttMove and if the result is lower than
799 // ttValue minus a margin then we extend the ttMove.
800 if ( singularExtensionNode
803 && pos.legal(move, ci.pinned)
804 && abs(ttValue) < VALUE_KNOWN_WIN)
806 assert(ttValue != VALUE_NONE);
808 Value rBeta = ttValue - int(depth);
809 ss->excludedMove = move;
810 ss->skipNullMove = true;
811 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
812 ss->skipNullMove = false;
813 ss->excludedMove = MOVE_NONE;
819 // Update the current move (this must be done after singular extension search)
820 newDepth = depth - ONE_PLY + ext;
822 // Step 13. Pruning at shallow depth (exclude PV nodes)
824 && !captureOrPromotion
827 /* && move != ttMove Already implicit in the next condition */
828 && bestValue > VALUE_MATED_IN_MAX_PLY)
830 // Move count based pruning
831 if ( depth < 16 * ONE_PLY
832 && moveCount >= FutilityMoveCounts[improving][depth] )
835 splitPoint->mutex.lock();
840 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
842 // Futility pruning: parent node
843 if (predictedDepth < 7 * ONE_PLY)
845 futilityValue = ss->staticEval + futility_margin(predictedDepth)
846 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
848 if (futilityValue <= alpha)
850 bestValue = std::max(bestValue, futilityValue);
854 splitPoint->mutex.lock();
855 if (bestValue > splitPoint->bestValue)
856 splitPoint->bestValue = bestValue;
862 // Prune moves with negative SEE at low depths
863 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
866 splitPoint->mutex.lock();
872 // Check for legality just before making the move
873 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
879 pvMove = PvNode && moveCount == 1;
880 ss->currentMove = move;
881 if (!SpNode && !captureOrPromotion && quietCount < 64)
882 quietsSearched[quietCount++] = move;
884 // Step 14. Make the move
885 pos.do_move(move, st, ci, givesCheck);
887 // Step 15. Reduced depth search (LMR). If the move fails high it will be
888 // re-searched at full depth.
889 if ( depth >= 3 * ONE_PLY
891 && !captureOrPromotion
893 && move != ss->killers[0]
894 && move != ss->killers[1])
896 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
898 if (!PvNode && cutNode)
899 ss->reduction += ONE_PLY;
901 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
902 ss->reduction += ONE_PLY / 2;
904 if (move == countermoves[0] || move == countermoves[1])
905 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
907 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
909 alpha = splitPoint->alpha;
911 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
913 // Research at intermediate depth if reduction is very high
914 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
916 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
917 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
920 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
921 ss->reduction = DEPTH_ZERO;
924 doFullDepthSearch = !pvMove;
926 // Step 16. Full depth search, when LMR is skipped or fails high
927 if (doFullDepthSearch)
930 alpha = splitPoint->alpha;
932 value = newDepth < ONE_PLY ?
933 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
934 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
935 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
938 // For PV nodes only, do a full PV search on the first move or after a fail
939 // high (in the latter case search only if value < beta), otherwise let the
940 // parent node fail low with value <= alpha and to try another move.
941 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
942 value = newDepth < ONE_PLY ?
943 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
944 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
945 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
946 // Step 17. Undo move
949 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
951 // Step 18. Check for new best move
954 splitPoint->mutex.lock();
955 bestValue = splitPoint->bestValue;
956 alpha = splitPoint->alpha;
959 // Finished searching the move. If Signals.stop is true, the search
960 // was aborted because the user interrupted the search or because we
961 // ran out of time. In this case, the return value of the search cannot
962 // be trusted, and we don't update the best move and/or PV.
963 if (Signals.stop || thisThread->cutoff_occurred())
964 return value; // To avoid returning VALUE_INFINITE
968 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
970 // PV move or new best move ?
971 if (pvMove || value > alpha)
974 rm.extract_pv_from_tt(pos);
976 // We record how often the best move has been changed in each
977 // iteration. This information is used for time management: When
978 // the best move changes frequently, we allocate some more time.
983 // All other moves but the PV are set to the lowest value: this is
984 // not a problem when sorting because the sort is stable and the
985 // move position in the list is preserved - just the PV is pushed up.
986 rm.score = -VALUE_INFINITE;
989 if (value > bestValue)
991 bestValue = SpNode ? splitPoint->bestValue = value : value;
995 bestMove = SpNode ? splitPoint->bestMove = move : move;
997 if (PvNode && value < beta) // Update alpha! Always alpha < beta
998 alpha = SpNode ? splitPoint->alpha = value : value;
1001 assert(value >= beta); // Fail high
1004 splitPoint->cutoff = true;
1011 // Step 19. Check for splitting the search
1013 && depth >= Threads.minimumSplitDepth
1014 && Threads.available_slave(thisThread)
1015 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1017 assert(bestValue < beta);
1019 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1020 depth, moveCount, &mp, NT, cutNode);
1021 if (bestValue >= beta)
1029 // Step 20. Check for mate and stalemate
1030 // All legal moves have been searched and if there are no legal moves, it
1031 // must be mate or stalemate. Note that we can have a false positive in
1032 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1033 // harmless because return value is discarded anyhow in the parent nodes.
1034 // If we are in a singular extension search then return a fail low score.
1035 // A split node has at least one move - the one tried before to be splitted.
1037 return excludedMove ? alpha
1038 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1040 // If we have pruned all the moves without searching return a fail-low score
1041 if (bestValue == -VALUE_INFINITE)
1044 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1045 bestValue >= beta ? BOUND_LOWER :
1046 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1047 depth, bestMove, ss->staticEval);
1049 // Quiet best move: update killers, history and countermoves
1050 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1051 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1053 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1059 // qsearch() is the quiescence search function, which is called by the main
1060 // search function when the remaining depth is zero (or, to be more precise,
1061 // less than ONE_PLY).
1063 template <NodeType NT, bool InCheck>
1064 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1066 const bool PvNode = (NT == PV);
1068 assert(NT == PV || NT == NonPV);
1069 assert(InCheck == !!pos.checkers());
1070 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1071 assert(PvNode || (alpha == beta - 1));
1072 assert(depth <= DEPTH_ZERO);
1077 Move ttMove, move, bestMove;
1078 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1079 bool givesCheck, evasionPrunable;
1082 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1086 ss->currentMove = bestMove = MOVE_NONE;
1087 ss->ply = (ss-1)->ply + 1;
1089 // Check for an instant draw or if the maximum ply has been reached
1090 if (pos.is_draw() || ss->ply > MAX_PLY)
1091 return DrawValue[pos.side_to_move()];
1093 // Decide whether or not to include checks: this fixes also the type of
1094 // TT entry depth that we are going to use. Note that in qsearch we use
1095 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1096 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1097 : DEPTH_QS_NO_CHECKS;
1099 // Transposition table lookup
1101 tte = TT.probe(posKey);
1102 ttMove = tte ? tte->move() : MOVE_NONE;
1103 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1106 && tte->depth() >= ttDepth
1107 && ttValue != VALUE_NONE // Only in case of TT access race
1108 && ( PvNode ? tte->bound() == BOUND_EXACT
1109 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1110 : (tte->bound() & BOUND_UPPER)))
1112 ss->currentMove = ttMove; // Can be MOVE_NONE
1116 // Evaluate the position statically
1119 ss->staticEval = VALUE_NONE;
1120 bestValue = futilityBase = -VALUE_INFINITE;
1126 // Never assume anything on values stored in TT
1127 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1128 ss->staticEval = bestValue = evaluate(pos);
1130 // Can ttValue be used as a better position evaluation?
1131 if (ttValue != VALUE_NONE)
1132 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1133 bestValue = ttValue;
1136 ss->staticEval = bestValue = evaluate(pos);
1138 // Stand pat. Return immediately if static value is at least beta
1139 if (bestValue >= beta)
1142 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1143 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1148 if (PvNode && bestValue > alpha)
1151 futilityBase = bestValue + Value(128);
1154 // Initialize a MovePicker object for the current position, and prepare
1155 // to search the moves. Because the depth is <= 0 here, only captures,
1156 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1158 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1161 // Loop through the moves until no moves remain or a beta cutoff occurs
1162 while ((move = mp.next_move<false>()) != MOVE_NONE)
1164 assert(is_ok(move));
1166 givesCheck = pos.gives_check(move, ci);
1173 && futilityBase > -VALUE_KNOWN_WIN
1174 && !pos.advanced_pawn_push(move))
1176 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1178 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1180 if (futilityValue < beta)
1182 bestValue = std::max(bestValue, futilityValue);
1186 if (futilityBase < beta && pos.see(move) <= 0)
1188 bestValue = std::max(bestValue, futilityBase);
1193 // Detect non-capture evasions that are candidates to be pruned
1194 evasionPrunable = InCheck
1195 && bestValue > VALUE_MATED_IN_MAX_PLY
1196 && !pos.capture(move)
1197 && !pos.can_castle(pos.side_to_move());
1199 // Don't search moves with negative SEE values
1201 && (!InCheck || evasionPrunable)
1203 && type_of(move) != PROMOTION
1204 && pos.see_sign(move) < 0)
1207 // Check for legality just before making the move
1208 if (!pos.legal(move, ci.pinned))
1211 ss->currentMove = move;
1213 // Make and search the move
1214 pos.do_move(move, st, ci, givesCheck);
1215 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1216 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1217 pos.undo_move(move);
1219 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1221 // Check for new best move
1222 if (value > bestValue)
1228 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1235 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1236 ttDepth, move, ss->staticEval);
1244 // All legal moves have been searched. A special case: If we're in check
1245 // and no legal moves were found, it is checkmate.
1246 if (InCheck && bestValue == -VALUE_INFINITE)
1247 return mated_in(ss->ply); // Plies to mate from the root
1249 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1250 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1251 ttDepth, bestMove, ss->staticEval);
1253 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1259 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1260 // "plies to mate from the current position". Non-mate scores are unchanged.
1261 // The function is called before storing a value in the transposition table.
1263 Value value_to_tt(Value v, int ply) {
1265 assert(v != VALUE_NONE);
1267 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1268 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1272 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1273 // from the transposition table (which refers to the plies to mate/be mated
1274 // from current position) to "plies to mate/be mated from the root".
1276 Value value_from_tt(Value v, int ply) {
1278 return v == VALUE_NONE ? VALUE_NONE
1279 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1280 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1284 // update_stats() updates killers, history and countermoves stats after a fail-high
1287 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1289 if (ss->killers[0] != move)
1291 ss->killers[1] = ss->killers[0];
1292 ss->killers[0] = move;
1295 // Increase history value of the cut-off move and decrease all the other
1296 // played quiet moves.
1297 Value bonus = Value(int(depth) * int(depth));
1298 History.update(pos.moved_piece(move), to_sq(move), bonus);
1299 for (int i = 0; i < quietsCnt; ++i)
1302 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1305 if (is_ok((ss-1)->currentMove))
1307 Square prevMoveSq = to_sq((ss-1)->currentMove);
1308 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1313 // When playing with a strength handicap, choose best move among the MultiPV
1314 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1316 Move Skill::pick_move() {
1320 // PRNG sequence should be not deterministic
1321 for (int i = Time::now() % 50; i > 0; --i)
1322 rk.rand<unsigned>();
1324 // RootMoves are already sorted by score in descending order
1325 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1326 int weakness = 120 - 2 * level;
1327 int max_s = -VALUE_INFINITE;
1330 // Choose best move. For each move score we add two terms both dependent on
1331 // weakness. One deterministic and bigger for weaker moves, and one random,
1332 // then we choose the move with the resulting highest score.
1333 for (size_t i = 0; i < PVSize; ++i)
1335 int s = RootMoves[i].score;
1337 // Don't allow crazy blunders even at very low skills
1338 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1341 // This is our magic formula
1342 s += ( weakness * int(RootMoves[0].score - s)
1343 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1348 best = RootMoves[i].pv[0];
1355 // uci_pv() formats PV information according to the UCI protocol. UCI
1356 // requires that all (if any) unsearched PV lines are sent using a previous
1359 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1361 std::stringstream s;
1362 Time::point elapsed = Time::now() - SearchTime + 1;
1363 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1366 for (size_t i = 0; i < Threads.size(); ++i)
1367 if (Threads[i]->maxPly > selDepth)
1368 selDepth = Threads[i]->maxPly;
1370 for (size_t i = 0; i < uciPVSize; ++i)
1372 bool updated = (i <= PVIdx);
1374 if (depth == 1 && !updated)
1377 int d = updated ? depth : depth - 1;
1378 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1380 if (s.rdbuf()->in_avail()) // Not at first line
1383 s << "info depth " << d
1384 << " seldepth " << selDepth
1385 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1386 << " nodes " << pos.nodes_searched()
1387 << " nps " << pos.nodes_searched() * 1000 / elapsed
1388 << " time " << elapsed
1389 << " multipv " << i + 1
1392 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1393 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1402 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1403 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1404 /// ensure that we have a ponder move even when we fail high at root. This
1405 /// results in a long PV to print that is important for position analysis.
1407 void RootMove::extract_pv_from_tt(Position& pos) {
1409 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1419 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1421 pos.do_move(pv[ply++], *st++);
1422 tte = TT.probe(pos.key());
1425 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1426 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1428 && (!pos.is_draw() || ply < 2));
1430 pv.push_back(MOVE_NONE); // Must be zero-terminating
1432 while (ply) pos.undo_move(pv[--ply]);
1436 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1437 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1438 /// first, even if the old TT entries have been overwritten.
1440 void RootMove::insert_pv_in_tt(Position& pos) {
1442 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1447 tte = TT.probe(pos.key());
1449 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1450 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1452 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1454 pos.do_move(pv[ply++], *st++);
1456 } while (pv[ply] != MOVE_NONE);
1458 while (ply) pos.undo_move(pv[--ply]);
1462 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1464 void Thread::idle_loop() {
1466 // Pointer 'this_sp' is not null only if we are called from split(), and not
1467 // at the thread creation. This means we are the split point's master.
1468 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1470 assert(!this_sp || (this_sp->masterThread == this && searching));
1474 // If we are not searching, wait for a condition to be signaled instead of
1475 // wasting CPU time polling for work.
1476 while ((!searching && Threads.sleepWhileIdle) || exit)
1484 // Grab the lock to avoid races with Thread::notify_one()
1487 // If we are master and all slaves have finished then exit idle_loop
1488 if (this_sp && !this_sp->slavesMask)
1494 // Do sleep after retesting sleep conditions under lock protection. In
1495 // particular we need to avoid a deadlock in case a master thread has,
1496 // in the meanwhile, allocated us and sent the notify_one() call before
1497 // we had the chance to grab the lock.
1498 if (!searching && !exit)
1499 sleepCondition.wait(mutex);
1504 // If this thread has been assigned work, launch a search
1509 Threads.mutex.lock();
1512 assert(activeSplitPoint);
1513 SplitPoint* sp = activeSplitPoint;
1515 Threads.mutex.unlock();
1517 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1518 Position pos(*sp->pos, this);
1520 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1521 ss->splitPoint = sp;
1525 assert(activePosition == NULL);
1527 activePosition = &pos;
1529 switch (sp->nodeType) {
1531 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1534 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1537 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1546 activePosition = NULL;
1547 sp->slavesMask &= ~(1ULL << idx);
1548 sp->nodes += pos.nodes_searched();
1550 // Wake up the master thread so to allow it to return from the idle
1551 // loop in case we are the last slave of the split point.
1552 if ( Threads.sleepWhileIdle
1553 && this != sp->masterThread
1556 assert(!sp->masterThread->searching);
1557 sp->masterThread->notify_one();
1560 // After releasing the lock we can't access any SplitPoint related data
1561 // in a safe way because it could have been released under our feet by
1562 // the sp master. Also accessing other Thread objects is unsafe because
1563 // if we are exiting there is a chance that they are already freed.
1567 // If this thread is the master of a split point and all slaves have finished
1568 // their work at this split point, return from the idle loop.
1569 if (this_sp && !this_sp->slavesMask)
1571 this_sp->mutex.lock();
1572 bool finished = !this_sp->slavesMask; // Retest under lock protection
1573 this_sp->mutex.unlock();
1581 /// check_time() is called by the timer thread when the timer triggers. It is
1582 /// used to print debug info and, more importantly, to detect when we are out of
1583 /// available time and thus stop the search.
1587 static Time::point lastInfoTime = Time::now();
1588 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1590 if (Time::now() - lastInfoTime >= 1000)
1592 lastInfoTime = Time::now();
1601 Threads.mutex.lock();
1603 nodes = RootPos.nodes_searched();
1605 // Loop across all split points and sum accumulated SplitPoint nodes plus
1606 // all the currently active positions nodes.
1607 for (size_t i = 0; i < Threads.size(); ++i)
1608 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1610 SplitPoint& sp = Threads[i]->splitPoints[j];
1615 Bitboard sm = sp.slavesMask;
1618 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1620 nodes += pos->nodes_searched();
1626 Threads.mutex.unlock();
1629 Time::point elapsed = Time::now() - SearchTime;
1630 bool stillAtFirstMove = Signals.firstRootMove
1631 && !Signals.failedLowAtRoot
1632 && elapsed > TimeMgr.available_time();
1634 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1635 || stillAtFirstMove;
1637 if ( (Limits.use_time_management() && noMoreTime)
1638 || (Limits.movetime && elapsed >= Limits.movetime)
1639 || (Limits.nodes && nodes >= Limits.nodes))
1640 Signals.stop = true;