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 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 IterationTime = Time::now() - SearchTime;
401 // If skill levels are enabled and time is up, pick a sub-optimal best move
402 if (skill.enabled() && skill.time_to_pick(depth))
405 if (Options["Write Search Log"])
407 RootMove& rm = RootMoves[0];
408 if (skill.best != MOVE_NONE)
409 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
411 Log log(Options["Search Log Filename"]);
412 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
416 // Have we found a "mate in x"?
418 && bestValue >= VALUE_MATE_IN_MAX_PLY
419 && VALUE_MATE - bestValue <= 2 * Limits.mate)
422 // Do we have time for the next iteration? Can we stop searching now?
423 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
425 bool stop = false; // Local variable, not the volatile Signals.stop
427 // Take some extra time if the best move has changed
428 if (depth > 4 && depth < 50 && PVSize == 1)
429 TimeMgr.pv_instability(BestMoveChanges);
431 // Stop the search if only one legal move is available or most
432 // of the available time has been used. We probably don't have
433 // enough time to search the first move at the next iteration anyway.
434 if ( RootMoves.size() == 1
435 || IterationTime > (TimeMgr.available_time() * 62) / 100)
440 // If we are allowed to ponder do not stop the search now but
441 // keep pondering until the GUI sends "ponderhit" or "stop".
443 Signals.stopOnPonderhit = true;
452 // search<>() is the main search function for both PV and non-PV nodes and for
453 // normal and SplitPoint nodes. When called just after a split point the search
454 // is simpler because we have already probed the hash table, done a null move
455 // search, and searched the first move before splitting, so we don't have to
456 // repeat all this work again. We also don't need to store anything to the hash
457 // table here: This is taken care of after we return from the split point.
459 template <NodeType NT>
460 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
462 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
463 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
464 const bool RootNode = (NT == Root || NT == SplitPointRoot);
466 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
467 assert(PvNode || (alpha == beta - 1));
468 assert(depth > DEPTH_ZERO);
470 Move quietsSearched[64];
473 SplitPoint* splitPoint;
475 Move ttMove, move, excludedMove, bestMove;
476 Depth ext, newDepth, predictedDepth;
477 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
478 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
479 bool captureOrPromotion, dangerous, doFullDepthSearch;
480 int moveCount, quietCount;
482 // Step 1. Initialize node
483 Thread* thisThread = pos.this_thread();
484 inCheck = pos.checkers();
488 splitPoint = ss->splitPoint;
489 bestMove = splitPoint->bestMove;
490 bestValue = splitPoint->bestValue;
492 ttMove = excludedMove = MOVE_NONE;
493 ttValue = VALUE_NONE;
495 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
500 moveCount = quietCount = 0;
501 bestValue = -VALUE_INFINITE;
502 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
503 ss->ply = (ss-1)->ply + 1;
504 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
505 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
507 // Used to send selDepth info to GUI
508 if (PvNode && thisThread->maxPly < ss->ply)
509 thisThread->maxPly = ss->ply;
513 // Step 2. Check for aborted search and immediate draw
514 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
515 return DrawValue[pos.side_to_move()];
517 // Step 3. Mate distance pruning. Even if we mate at the next move our score
518 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
519 // a shorter mate was found upward in the tree then there is no need to search
520 // because we will never beat the current alpha. Same logic but with reversed
521 // signs applies also in the opposite condition of being mated instead of giving
522 // mate. In this case return a fail-high score.
523 alpha = std::max(mated_in(ss->ply), alpha);
524 beta = std::min(mate_in(ss->ply+1), beta);
529 // Step 4. Transposition table lookup
530 // We don't want the score of a partial search to overwrite a previous full search
531 // TT value, so we use a different position key in case of an excluded move.
532 excludedMove = ss->excludedMove;
533 posKey = excludedMove ? pos.exclusion_key() : pos.key();
534 tte = TT.probe(posKey);
535 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
536 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
538 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
539 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
540 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
541 // we should also update RootMoveList to avoid bogus output.
544 && tte->depth() >= depth
545 && ttValue != VALUE_NONE // Only in case of TT access race
546 && ( PvNode ? tte->bound() == BOUND_EXACT
547 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
548 : (tte->bound() & BOUND_UPPER)))
551 ss->currentMove = ttMove; // Can be MOVE_NONE
553 // If ttMove is quiet, update killers, history, and counter move on TT hit
554 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
555 update_stats(pos, ss, ttMove, depth, NULL, 0);
560 // Step 5. Evaluate the position statically and update parent's gain statistics
563 ss->staticEval = eval = VALUE_NONE;
569 // Never assume anything on values stored in TT
570 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
571 eval = ss->staticEval = evaluate(pos);
573 // Can ttValue be used as a better position evaluation?
574 if (ttValue != VALUE_NONE)
575 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
580 eval = ss->staticEval = evaluate(pos);
581 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
584 if ( !pos.captured_piece_type()
585 && ss->staticEval != VALUE_NONE
586 && (ss-1)->staticEval != VALUE_NONE
587 && (move = (ss-1)->currentMove) != MOVE_NULL
588 && type_of(move) == NORMAL)
590 Square to = to_sq(move);
591 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
594 // Step 6. Razoring (skipped when in check)
596 && depth < 4 * ONE_PLY
597 && eval + razor_margin(depth) < beta
598 && ttMove == MOVE_NONE
599 && abs(beta) < VALUE_MATE_IN_MAX_PLY
600 && !pos.pawn_on_7th(pos.side_to_move()))
602 Value rbeta = beta - razor_margin(depth);
603 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
605 // Logically we should return (v + razor_margin(depth)), but
606 // surprisingly this performed slightly weaker in tests.
610 // Step 7. Futility pruning: child node (skipped when in check)
613 && depth < 7 * ONE_PLY
614 && eval - futility_margin(depth) >= beta
615 && abs(beta) < VALUE_MATE_IN_MAX_PLY
616 && abs(eval) < VALUE_KNOWN_WIN
617 && pos.non_pawn_material(pos.side_to_move()))
618 return eval - futility_margin(depth);
620 // Step 8. Null move search with verification search (is omitted in PV nodes)
623 && depth >= 2 * ONE_PLY
625 && abs(beta) < VALUE_MATE_IN_MAX_PLY
626 && pos.non_pawn_material(pos.side_to_move()))
628 ss->currentMove = MOVE_NULL;
630 // Null move dynamic reduction based on depth
631 Depth R = 3 * ONE_PLY + depth / 4;
633 // Null move dynamic reduction based on value
634 if (eval - PawnValueMg > beta)
637 pos.do_null_move(st);
638 (ss+1)->skipNullMove = true;
639 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
640 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
641 (ss+1)->skipNullMove = false;
642 pos.undo_null_move();
644 if (nullValue >= beta)
646 // Do not return unproven mate scores
647 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
650 if (depth < 12 * ONE_PLY)
653 // Do verification search at high depths
654 ss->skipNullMove = true;
655 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
656 ss->skipNullMove = false;
663 // Step 9. ProbCut (skipped when in check)
664 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
665 // and a reduced search returns a value much above beta, we can (almost) safely
666 // prune the previous move.
668 && depth >= 5 * ONE_PLY
670 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
672 Value rbeta = beta + 200;
673 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
675 assert(rdepth >= ONE_PLY);
676 assert((ss-1)->currentMove != MOVE_NONE);
677 assert((ss-1)->currentMove != MOVE_NULL);
679 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
682 while ((move = mp.next_move<false>()) != MOVE_NONE)
683 if (pos.legal(move, ci.pinned))
685 ss->currentMove = move;
686 pos.do_move(move, st, ci, pos.gives_check(move, ci));
687 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
694 // Step 10. Internal iterative deepening (skipped when in check)
695 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
696 && ttMove == MOVE_NONE
697 && (PvNode || ss->staticEval + Value(256) >= beta))
699 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
701 ss->skipNullMove = true;
702 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
703 ss->skipNullMove = false;
705 tte = TT.probe(posKey);
706 ttMove = tte ? tte->move() : MOVE_NONE;
709 moves_loop: // When in check and at SpNode search starts from here
711 Square prevMoveSq = to_sq((ss-1)->currentMove);
712 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
713 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
715 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
717 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
718 improving = ss->staticEval >= (ss-2)->staticEval
719 || ss->staticEval == VALUE_NONE
720 ||(ss-2)->staticEval == VALUE_NONE;
722 singularExtensionNode = !RootNode
724 && depth >= 8 * ONE_PLY
725 && ttMove != MOVE_NONE
726 && !excludedMove // Recursive singular search is not allowed
727 && (tte->bound() & BOUND_LOWER)
728 && tte->depth() >= depth - 3 * ONE_PLY;
730 // Step 11. Loop through moves
731 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
732 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
736 if (move == excludedMove)
739 // At root obey the "searchmoves" option and skip moves not listed in Root
740 // Move List. As a consequence any illegal move is also skipped. In MultiPV
741 // mode we also skip PV moves which have been already searched.
742 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
747 // Shared counter cannot be decremented later if the move turns out to be illegal
748 if (!pos.legal(move, ci.pinned))
751 moveCount = ++splitPoint->moveCount;
752 splitPoint->mutex.unlock();
759 Signals.firstRootMove = (moveCount == 1);
761 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
762 sync_cout << "info depth " << depth / ONE_PLY
763 << " currmove " << move_to_uci(move, pos.is_chess960())
764 << " currmovenumber " << moveCount + PVIdx << sync_endl;
768 captureOrPromotion = pos.capture_or_promotion(move);
769 givesCheck = pos.gives_check(move, ci);
770 dangerous = givesCheck
771 || type_of(move) != NORMAL
772 || pos.advanced_pawn_push(move);
774 // Step 12. Extend checks
775 if (givesCheck && pos.see_sign(move) >= 0)
778 // Singular extension search. If all moves but one fail low on a search of
779 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
780 // is singular and should be extended. To verify this we do a reduced search
781 // on all the other moves but the ttMove and if the result is lower than
782 // ttValue minus a margin then we extend the ttMove.
783 if ( singularExtensionNode
786 && pos.legal(move, ci.pinned)
787 && abs(ttValue) < VALUE_KNOWN_WIN)
789 assert(ttValue != VALUE_NONE);
791 Value rBeta = ttValue - int(depth);
792 ss->excludedMove = move;
793 ss->skipNullMove = true;
794 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
795 ss->skipNullMove = false;
796 ss->excludedMove = MOVE_NONE;
802 // Update the current move (this must be done after singular extension search)
803 newDepth = depth - ONE_PLY + ext;
805 // Step 13. Pruning at shallow depth (exclude PV nodes)
807 && !captureOrPromotion
810 /* && move != ttMove Already implicit in the next condition */
811 && bestValue > VALUE_MATED_IN_MAX_PLY)
813 // Move count based pruning
814 if ( depth < 16 * ONE_PLY
815 && moveCount >= FutilityMoveCounts[improving][depth] )
818 splitPoint->mutex.lock();
823 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
825 // Futility pruning: parent node
826 if (predictedDepth < 7 * ONE_PLY)
828 futilityValue = ss->staticEval + futility_margin(predictedDepth)
829 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
831 if (futilityValue <= alpha)
833 bestValue = std::max(bestValue, futilityValue);
837 splitPoint->mutex.lock();
838 if (bestValue > splitPoint->bestValue)
839 splitPoint->bestValue = bestValue;
845 // Prune moves with negative SEE at low depths
846 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
849 splitPoint->mutex.lock();
855 // Check for legality just before making the move
856 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
862 pvMove = PvNode && moveCount == 1;
863 ss->currentMove = move;
864 if (!SpNode && !captureOrPromotion && quietCount < 64)
865 quietsSearched[quietCount++] = move;
867 // Step 14. Make the move
868 pos.do_move(move, st, ci, givesCheck);
870 // Step 15. Reduced depth search (LMR). If the move fails high it will be
871 // re-searched at full depth.
872 if ( depth >= 3 * ONE_PLY
874 && !captureOrPromotion
876 && move != ss->killers[0]
877 && move != ss->killers[1])
879 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
881 if (!PvNode && cutNode)
882 ss->reduction += ONE_PLY;
884 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
885 ss->reduction += ONE_PLY / 2;
887 if (move == countermoves[0] || move == countermoves[1])
888 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
890 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
892 alpha = splitPoint->alpha;
894 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
896 // Research at intermediate depth if reduction is very high
897 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
899 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
900 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
903 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
904 ss->reduction = DEPTH_ZERO;
907 doFullDepthSearch = !pvMove;
909 // Step 16. Full depth search, when LMR is skipped or fails high
910 if (doFullDepthSearch)
913 alpha = splitPoint->alpha;
915 value = newDepth < ONE_PLY ?
916 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
917 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
918 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
921 // For PV nodes only, do a full PV search on the first move or after a fail
922 // high (in the latter case search only if value < beta), otherwise let the
923 // parent node fail low with value <= alpha and to try another move.
924 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
925 value = newDepth < ONE_PLY ?
926 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
927 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
928 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
929 // Step 17. Undo move
932 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
934 // Step 18. Check for new best move
937 splitPoint->mutex.lock();
938 bestValue = splitPoint->bestValue;
939 alpha = splitPoint->alpha;
942 // Finished searching the move. If Signals.stop is true, the search
943 // was aborted because the user interrupted the search or because we
944 // ran out of time. In this case, the return value of the search cannot
945 // be trusted, and we don't update the best move and/or PV.
946 if (Signals.stop || thisThread->cutoff_occurred())
947 return value; // To avoid returning VALUE_INFINITE
951 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
953 // PV move or new best move ?
954 if (pvMove || value > alpha)
957 rm.extract_pv_from_tt(pos);
959 // We record how often the best move has been changed in each
960 // iteration. This information is used for time management: When
961 // the best move changes frequently, we allocate some more time.
966 // All other moves but the PV are set to the lowest value: this is
967 // not a problem when sorting because the sort is stable and the
968 // move position in the list is preserved - just the PV is pushed up.
969 rm.score = -VALUE_INFINITE;
972 if (value > bestValue)
974 bestValue = SpNode ? splitPoint->bestValue = value : value;
978 bestMove = SpNode ? splitPoint->bestMove = move : move;
980 if (PvNode && value < beta) // Update alpha! Always alpha < beta
981 alpha = SpNode ? splitPoint->alpha = value : value;
984 assert(value >= beta); // Fail high
987 splitPoint->cutoff = true;
994 // Step 19. Check for splitting the search
996 && depth >= Threads.minimumSplitDepth
997 && Threads.available_slave(thisThread)
998 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1000 assert(bestValue < beta);
1002 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1003 depth, moveCount, &mp, NT, cutNode);
1004 if (bestValue >= beta)
1012 // Step 20. Check for mate and stalemate
1013 // All legal moves have been searched and if there are no legal moves, it
1014 // must be mate or stalemate. Note that we can have a false positive in
1015 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1016 // harmless because return value is discarded anyhow in the parent nodes.
1017 // If we are in a singular extension search then return a fail low score.
1018 // A split node has at least one move - the one tried before to be splitted.
1020 return excludedMove ? alpha
1021 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1023 // If we have pruned all the moves without searching return a fail-low score
1024 if (bestValue == -VALUE_INFINITE)
1027 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1028 bestValue >= beta ? BOUND_LOWER :
1029 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1030 depth, bestMove, ss->staticEval);
1032 // Quiet best move: update killers, history and countermoves
1033 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1034 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1036 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1042 // qsearch() is the quiescence search function, which is called by the main
1043 // search function when the remaining depth is zero (or, to be more precise,
1044 // less than ONE_PLY).
1046 template <NodeType NT, bool InCheck>
1047 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1049 const bool PvNode = (NT == PV);
1051 assert(NT == PV || NT == NonPV);
1052 assert(InCheck == !!pos.checkers());
1053 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1054 assert(PvNode || (alpha == beta - 1));
1055 assert(depth <= DEPTH_ZERO);
1060 Move ttMove, move, bestMove;
1061 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1062 bool givesCheck, evasionPrunable;
1065 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1069 ss->currentMove = bestMove = MOVE_NONE;
1070 ss->ply = (ss-1)->ply + 1;
1072 // Check for an instant draw or if the maximum ply has been reached
1073 if (pos.is_draw() || ss->ply > MAX_PLY)
1074 return DrawValue[pos.side_to_move()];
1076 // Decide whether or not to include checks: this fixes also the type of
1077 // TT entry depth that we are going to use. Note that in qsearch we use
1078 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1079 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1080 : DEPTH_QS_NO_CHECKS;
1082 // Transposition table lookup
1084 tte = TT.probe(posKey);
1085 ttMove = tte ? tte->move() : MOVE_NONE;
1086 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1089 && tte->depth() >= ttDepth
1090 && ttValue != VALUE_NONE // Only in case of TT access race
1091 && ( PvNode ? tte->bound() == BOUND_EXACT
1092 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1093 : (tte->bound() & BOUND_UPPER)))
1095 ss->currentMove = ttMove; // Can be MOVE_NONE
1099 // Evaluate the position statically
1102 ss->staticEval = VALUE_NONE;
1103 bestValue = futilityBase = -VALUE_INFINITE;
1109 // Never assume anything on values stored in TT
1110 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1111 ss->staticEval = bestValue = evaluate(pos);
1113 // Can ttValue be used as a better position evaluation?
1114 if (ttValue != VALUE_NONE)
1115 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1116 bestValue = ttValue;
1119 ss->staticEval = bestValue = evaluate(pos);
1121 // Stand pat. Return immediately if static value is at least beta
1122 if (bestValue >= beta)
1125 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1126 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1131 if (PvNode && bestValue > alpha)
1134 futilityBase = bestValue + Value(128);
1137 // Initialize a MovePicker object for the current position, and prepare
1138 // to search the moves. Because the depth is <= 0 here, only captures,
1139 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1141 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1144 // Loop through the moves until no moves remain or a beta cutoff occurs
1145 while ((move = mp.next_move<false>()) != MOVE_NONE)
1147 assert(is_ok(move));
1149 givesCheck = pos.gives_check(move, ci);
1156 && futilityBase > -VALUE_KNOWN_WIN
1157 && !pos.advanced_pawn_push(move))
1159 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1161 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1163 if (futilityValue < beta)
1165 bestValue = std::max(bestValue, futilityValue);
1169 if (futilityBase < beta && pos.see(move) <= 0)
1171 bestValue = std::max(bestValue, futilityBase);
1176 // Detect non-capture evasions that are candidates to be pruned
1177 evasionPrunable = InCheck
1178 && bestValue > VALUE_MATED_IN_MAX_PLY
1179 && !pos.capture(move)
1180 && !pos.can_castle(pos.side_to_move());
1182 // Don't search moves with negative SEE values
1184 && (!InCheck || evasionPrunable)
1186 && type_of(move) != PROMOTION
1187 && pos.see_sign(move) < 0)
1190 // Check for legality just before making the move
1191 if (!pos.legal(move, ci.pinned))
1194 ss->currentMove = move;
1196 // Make and search the move
1197 pos.do_move(move, st, ci, givesCheck);
1198 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1199 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1200 pos.undo_move(move);
1202 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1204 // Check for new best move
1205 if (value > bestValue)
1211 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1218 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1219 ttDepth, move, ss->staticEval);
1227 // All legal moves have been searched. A special case: If we're in check
1228 // and no legal moves were found, it is checkmate.
1229 if (InCheck && bestValue == -VALUE_INFINITE)
1230 return mated_in(ss->ply); // Plies to mate from the root
1232 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1233 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1234 ttDepth, bestMove, ss->staticEval);
1236 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1242 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1243 // "plies to mate from the current position". Non-mate scores are unchanged.
1244 // The function is called before storing a value in the transposition table.
1246 Value value_to_tt(Value v, int ply) {
1248 assert(v != VALUE_NONE);
1250 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1251 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1255 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1256 // from the transposition table (which refers to the plies to mate/be mated
1257 // from current position) to "plies to mate/be mated from the root".
1259 Value value_from_tt(Value v, int ply) {
1261 return v == VALUE_NONE ? VALUE_NONE
1262 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1263 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1267 // update_stats() updates killers, history and countermoves stats after a fail-high
1270 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1272 if (ss->killers[0] != move)
1274 ss->killers[1] = ss->killers[0];
1275 ss->killers[0] = move;
1278 // Increase history value of the cut-off move and decrease all the other
1279 // played quiet moves.
1280 Value bonus = Value(int(depth) * int(depth));
1281 History.update(pos.moved_piece(move), to_sq(move), bonus);
1282 for (int i = 0; i < quietsCnt; ++i)
1285 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1288 if (is_ok((ss-1)->currentMove))
1290 Square prevMoveSq = to_sq((ss-1)->currentMove);
1291 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1296 // When playing with a strength handicap, choose best move among the MultiPV
1297 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1299 Move Skill::pick_move() {
1303 // PRNG sequence should be not deterministic
1304 for (int i = Time::now() % 50; i > 0; --i)
1305 rk.rand<unsigned>();
1307 // RootMoves are already sorted by score in descending order
1308 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1309 int weakness = 120 - 2 * level;
1310 int max_s = -VALUE_INFINITE;
1313 // Choose best move. For each move score we add two terms both dependent on
1314 // weakness. One deterministic and bigger for weaker moves, and one random,
1315 // then we choose the move with the resulting highest score.
1316 for (size_t i = 0; i < PVSize; ++i)
1318 int s = RootMoves[i].score;
1320 // Don't allow crazy blunders even at very low skills
1321 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1324 // This is our magic formula
1325 s += ( weakness * int(RootMoves[0].score - s)
1326 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1331 best = RootMoves[i].pv[0];
1338 // uci_pv() formats PV information according to the UCI protocol. UCI
1339 // requires that all (if any) unsearched PV lines are sent using a previous
1342 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1344 std::stringstream s;
1345 Time::point elapsed = Time::now() - SearchTime + 1;
1346 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1349 for (size_t i = 0; i < Threads.size(); ++i)
1350 if (Threads[i]->maxPly > selDepth)
1351 selDepth = Threads[i]->maxPly;
1353 for (size_t i = 0; i < uciPVSize; ++i)
1355 bool updated = (i <= PVIdx);
1357 if (depth == 1 && !updated)
1360 int d = updated ? depth : depth - 1;
1361 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1363 if (s.rdbuf()->in_avail()) // Not at first line
1366 s << "info depth " << d
1367 << " seldepth " << selDepth
1368 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1369 << " nodes " << pos.nodes_searched()
1370 << " nps " << pos.nodes_searched() * 1000 / elapsed
1371 << " time " << elapsed
1372 << " multipv " << i + 1
1375 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1376 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1385 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1386 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1387 /// ensure that we have a ponder move even when we fail high at root. This
1388 /// results in a long PV to print that is important for position analysis.
1390 void RootMove::extract_pv_from_tt(Position& pos) {
1392 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1402 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1404 pos.do_move(pv[ply++], *st++);
1405 tte = TT.probe(pos.key());
1408 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1409 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1411 && (!pos.is_draw() || ply < 2));
1413 pv.push_back(MOVE_NONE); // Must be zero-terminating
1415 while (ply) pos.undo_move(pv[--ply]);
1419 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1420 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1421 /// first, even if the old TT entries have been overwritten.
1423 void RootMove::insert_pv_in_tt(Position& pos) {
1425 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1430 tte = TT.probe(pos.key());
1432 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1433 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1435 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1437 pos.do_move(pv[ply++], *st++);
1439 } while (pv[ply] != MOVE_NONE);
1441 while (ply) pos.undo_move(pv[--ply]);
1445 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1447 void Thread::idle_loop() {
1449 // Pointer 'this_sp' is not null only if we are called from split(), and not
1450 // at the thread creation. This means we are the split point's master.
1451 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1453 assert(!this_sp || (this_sp->masterThread == this && searching));
1457 // If we are not searching, wait for a condition to be signaled instead of
1458 // wasting CPU time polling for work.
1459 while ((!searching && Threads.sleepWhileIdle) || exit)
1467 // Grab the lock to avoid races with Thread::notify_one()
1470 // If we are master and all slaves have finished then exit idle_loop
1471 if (this_sp && !this_sp->slavesMask)
1477 // Do sleep after retesting sleep conditions under lock protection. In
1478 // particular we need to avoid a deadlock in case a master thread has,
1479 // in the meanwhile, allocated us and sent the notify_one() call before
1480 // we had the chance to grab the lock.
1481 if (!searching && !exit)
1482 sleepCondition.wait(mutex);
1487 // If this thread has been assigned work, launch a search
1492 Threads.mutex.lock();
1495 assert(activeSplitPoint);
1496 SplitPoint* sp = activeSplitPoint;
1498 Threads.mutex.unlock();
1500 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1501 Position pos(*sp->pos, this);
1503 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1504 ss->splitPoint = sp;
1508 assert(activePosition == NULL);
1510 activePosition = &pos;
1512 switch (sp->nodeType) {
1514 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1517 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1520 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1529 activePosition = NULL;
1530 sp->slavesMask &= ~(1ULL << idx);
1531 sp->nodes += pos.nodes_searched();
1533 // Wake up the master thread so to allow it to return from the idle
1534 // loop in case we are the last slave of the split point.
1535 if ( Threads.sleepWhileIdle
1536 && this != sp->masterThread
1539 assert(!sp->masterThread->searching);
1540 sp->masterThread->notify_one();
1543 // After releasing the lock we can't access any SplitPoint related data
1544 // in a safe way because it could have been released under our feet by
1545 // the sp master. Also accessing other Thread objects is unsafe because
1546 // if we are exiting there is a chance that they are already freed.
1550 // If this thread is the master of a split point and all slaves have finished
1551 // their work at this split point, return from the idle loop.
1552 if (this_sp && !this_sp->slavesMask)
1554 this_sp->mutex.lock();
1555 bool finished = !this_sp->slavesMask; // Retest under lock protection
1556 this_sp->mutex.unlock();
1564 /// check_time() is called by the timer thread when the timer triggers. It is
1565 /// used to print debug info and, more importantly, to detect when we are out of
1566 /// available time and thus stop the search.
1570 static Time::point lastInfoTime = Time::now();
1571 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1573 if (Time::now() - lastInfoTime >= 1000)
1575 lastInfoTime = Time::now();
1584 Threads.mutex.lock();
1586 nodes = RootPos.nodes_searched();
1588 // Loop across all split points and sum accumulated SplitPoint nodes plus
1589 // all the currently active positions nodes.
1590 for (size_t i = 0; i < Threads.size(); ++i)
1591 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1593 SplitPoint& sp = Threads[i]->splitPoints[j];
1598 Bitboard sm = sp.slavesMask;
1601 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1603 nodes += pos->nodes_searched();
1609 Threads.mutex.unlock();
1612 Time::point elapsed = Time::now() - SearchTime;
1613 bool stillAtFirstMove = Signals.firstRootMove
1614 && !Signals.failedLowAtRoot
1615 && ( elapsed > TimeMgr.available_time()
1616 || ( elapsed > (TimeMgr.available_time() * 62) / 100
1617 && elapsed > IterationTime * 1.4));
1619 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1620 || stillAtFirstMove;
1622 if ( (Limits.use_time_management() && noMoreTime)
1623 || (Limits.movetime && elapsed >= Limits.movetime)
1624 || (Limits.nodes && nodes >= Limits.nodes))
1625 Signals.stop = true;