2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 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 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
100 Skill(int l) : level(l), best(MOVE_NONE) {}
102 if (enabled()) // Swap best PV line with the sub-optimal one
103 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
104 RootMoves.end(), best ? best : pick_move()));
107 bool enabled() const { return level < 20; }
108 bool time_to_pick(int depth) const { return depth == 1 + level; }
118 /// Search::init() is called during startup to initialize various lookup tables
120 void Search::init() {
122 int d; // depth (ONE_PLY == 2)
123 int hd; // half depth (ONE_PLY == 1)
126 // Init reductions array
127 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
129 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
130 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
131 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
132 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
134 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
135 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
137 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
138 Reductions[0][0][hd][mc] += ONE_PLY;
140 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
141 Reductions[0][0][hd][mc] += ONE_PLY / 2;
144 // Init futility move count array
145 for (d = 0; d < 32; ++d)
147 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
148 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
153 /// Search::perft() is our utility to verify move generation. All the leaf nodes
154 /// up to the given depth are generated and counted and the sum returned.
156 static size_t perft(Position& pos, Depth depth) {
161 const bool leaf = depth == 2 * ONE_PLY;
163 for (MoveList<LEGAL> it(pos); *it; ++it)
165 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
166 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
172 size_t Search::perft(Position& pos, Depth depth) {
173 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
176 /// Search::think() is the external interface to Stockfish's search, and is
177 /// called by the main thread when the program receives the UCI 'go' command. It
178 /// searches from RootPos and at the end prints the "bestmove" to output.
180 void Search::think() {
182 static PolyglotBook book; // Defined static to initialize the PRNG only once
184 RootColor = RootPos.side_to_move();
185 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
187 if (RootMoves.empty())
189 RootMoves.push_back(MOVE_NONE);
190 sync_cout << "info depth 0 score "
191 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
197 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
199 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
201 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
203 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
208 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
210 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
211 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
212 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
213 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
216 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
218 if (Options["Write Search Log"])
220 Log log(Options["Search Log Filename"]);
221 log << "\nSearching: " << RootPos.fen()
222 << "\ninfinite: " << Limits.infinite
223 << " ponder: " << Limits.ponder
224 << " time: " << Limits.time[RootColor]
225 << " increment: " << Limits.inc[RootColor]
226 << " moves to go: " << Limits.movestogo
230 // Reset the threads, still sleeping: will wake up at split time
231 for (size_t i = 0; i < Threads.size(); ++i)
232 Threads[i]->maxPly = 0;
234 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
235 Threads.timer->run = true;
236 Threads.timer->notify_one(); // Wake up the recurring timer
238 id_loop(RootPos); // Let's start searching !
240 Threads.timer->run = false; // Stop the timer
241 Threads.sleepWhileIdle = true; // Send idle threads to sleep
243 if (Options["Write Search Log"])
245 Time::point elapsed = Time::now() - SearchTime + 1;
247 Log log(Options["Search Log Filename"]);
248 log << "Nodes: " << RootPos.nodes_searched()
249 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
250 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
253 RootPos.do_move(RootMoves[0].pv[0], st);
254 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
255 RootPos.undo_move(RootMoves[0].pv[0]);
260 // When search is stopped this info is not printed
261 sync_cout << "info nodes " << RootPos.nodes_searched()
262 << " time " << Time::now() - SearchTime + 1 << sync_endl;
264 // When we reach the maximum depth, we can arrive here without a raise of
265 // Signals.stop. However, if we are pondering or in an infinite search,
266 // the UCI protocol states that we shouldn't print the best move before the
267 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
268 // until the GUI sends one of those commands (which also raises Signals.stop).
269 if (!Signals.stop && (Limits.ponder || Limits.infinite))
271 Signals.stopOnPonderhit = true;
272 RootPos.this_thread()->wait_for(Signals.stop);
275 // Best move could be MOVE_NONE when searching on a stalemate position
276 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
277 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
284 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
285 // with increasing depth until the allocated thinking time has been consumed,
286 // user stops the search, or the maximum search depth is reached.
288 void id_loop(Position& pos) {
290 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
292 Value bestValue, alpha, beta, delta;
294 std::memset(ss-2, 0, 5 * sizeof(Stack));
295 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
299 bestValue = delta = alpha = -VALUE_INFINITE;
300 beta = VALUE_INFINITE;
305 Countermoves.clear();
307 PVSize = Options["MultiPV"];
308 Skill skill(Options["Skill Level"]);
310 // Do we have to play with skill handicap? In this case enable MultiPV search
311 // that we will use behind the scenes to retrieve a set of possible moves.
312 if (skill.enabled() && PVSize < 4)
315 PVSize = std::min(PVSize, RootMoves.size());
317 // Iterative deepening loop until requested to stop or target depth reached
318 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
320 // Age out PV variability metric
321 BestMoveChanges *= 0.8;
323 // Save the last iteration's scores before first PV line is searched and
324 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
325 for (size_t i = 0; i < RootMoves.size(); ++i)
326 RootMoves[i].prevScore = RootMoves[i].score;
328 // MultiPV loop. We perform a full root search for each PV line
329 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
331 // Reset aspiration window starting size
335 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
336 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
339 // Start with a small aspiration window and, in the case of a fail
340 // high/low, re-search with a bigger window until we're not failing
344 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
346 // Bring the best move to the front. It is critical that sorting
347 // is done with a stable algorithm because all the values but the
348 // first and eventually the new best one are set to -VALUE_INFINITE
349 // and we want to keep the same order for all the moves except the
350 // new PV that goes to the front. Note that in case of MultiPV
351 // search the already searched PV lines are preserved.
352 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
354 // Write PV back to transposition table in case the relevant
355 // entries have been overwritten during the search.
356 for (size_t i = 0; i <= PVIdx; ++i)
357 RootMoves[i].insert_pv_in_tt(pos);
359 // If search has been stopped break immediately. Sorting and
360 // writing PV back to TT is safe because RootMoves is still
361 // valid, although it refers to previous iteration.
365 // When failing high/low give some update (without cluttering
366 // the UI) before a re-search.
367 if ( (bestValue <= alpha || bestValue >= beta)
368 && Time::now() - SearchTime > 3000)
369 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
371 // In case of failing low/high increase aspiration window and
372 // re-search, otherwise exit the loop.
373 if (bestValue <= alpha)
375 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
377 Signals.failedLowAtRoot = true;
378 Signals.stopOnPonderhit = false;
380 else if (bestValue >= beta)
381 beta = std::min(bestValue + delta, VALUE_INFINITE);
388 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
391 // Sort the PV lines searched so far and update the GUI
392 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
394 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
395 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
398 // If skill levels are enabled and time is up, pick a sub-optimal best move
399 if (skill.enabled() && skill.time_to_pick(depth))
402 if (Options["Write Search Log"])
404 RootMove& rm = RootMoves[0];
405 if (skill.best != MOVE_NONE)
406 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
408 Log log(Options["Search Log Filename"]);
409 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
413 // Have we found a "mate in x"?
415 && bestValue >= VALUE_MATE_IN_MAX_PLY
416 && VALUE_MATE - bestValue <= 2 * Limits.mate)
419 // Do we have time for the next iteration? Can we stop searching now?
420 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
422 bool stop = false; // Local variable, not the volatile Signals.stop
424 // Take some extra time if the best move has changed
425 if (depth > 4 && depth < 50 && PVSize == 1)
426 TimeMgr.pv_instability(BestMoveChanges);
428 // Stop the search if most of the available time has been used. We
429 // probably don't have enough time to search the first move at the
430 // next iteration anyway.
431 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
434 // Stop the search early if one move seems to be much better than others
436 && BestMoveChanges <= DBL_EPSILON
439 && bestValue > VALUE_MATED_IN_MAX_PLY
440 && ( RootMoves.size() == 1
441 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
443 Value rBeta = bestValue - 2 * PawnValueMg;
444 ss->excludedMove = RootMoves[0].pv[0];
445 ss->skipNullMove = true;
446 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
447 ss->skipNullMove = false;
448 ss->excludedMove = MOVE_NONE;
456 // If we are allowed to ponder do not stop the search now but
457 // keep pondering until the GUI sends "ponderhit" or "stop".
459 Signals.stopOnPonderhit = true;
468 // search<>() is the main search function for both PV and non-PV nodes and for
469 // normal and SplitPoint nodes. When called just after a split point the search
470 // is simpler because we have already probed the hash table, done a null move
471 // search, and searched the first move before splitting, so we don't have to
472 // repeat all this work again. We also don't need to store anything to the hash
473 // table here: This is taken care of after we return from the split point.
475 template <NodeType NT>
476 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
478 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
479 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
480 const bool RootNode = (NT == Root || NT == SplitPointRoot);
482 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
483 assert(PvNode || (alpha == beta - 1));
484 assert(depth > DEPTH_ZERO);
486 Move quietsSearched[64];
489 SplitPoint* splitPoint;
491 Move ttMove, move, excludedMove, bestMove;
492 Depth ext, newDepth, predictedDepth;
493 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
494 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
495 bool captureOrPromotion, dangerous, doFullDepthSearch;
496 int moveCount, quietCount;
498 // Step 1. Initialize node
499 Thread* thisThread = pos.this_thread();
500 inCheck = pos.checkers();
504 splitPoint = ss->splitPoint;
505 bestMove = splitPoint->bestMove;
506 bestValue = splitPoint->bestValue;
508 ttMove = excludedMove = MOVE_NONE;
509 ttValue = VALUE_NONE;
511 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
516 moveCount = quietCount = 0;
517 bestValue = -VALUE_INFINITE;
518 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
519 ss->ply = (ss-1)->ply + 1;
520 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
521 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
523 // Used to send selDepth info to GUI
524 if (PvNode && thisThread->maxPly < ss->ply)
525 thisThread->maxPly = ss->ply;
529 // Step 2. Check for aborted search and immediate draw
530 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
531 return DrawValue[pos.side_to_move()];
533 // Step 3. Mate distance pruning. Even if we mate at the next move our score
534 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
535 // a shorter mate was found upward in the tree then there is no need to search
536 // because we will never beat the current alpha. Same logic but with reversed
537 // signs applies also in the opposite condition of being mated instead of giving
538 // mate. In this case return a fail-high score.
539 alpha = std::max(mated_in(ss->ply), alpha);
540 beta = std::min(mate_in(ss->ply+1), beta);
545 // Step 4. Transposition table lookup
546 // We don't want the score of a partial search to overwrite a previous full search
547 // TT value, so we use a different position key in case of an excluded move.
548 excludedMove = ss->excludedMove;
549 posKey = excludedMove ? pos.exclusion_key() : pos.key();
550 tte = TT.probe(posKey);
551 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
552 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
554 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
555 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
556 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
557 // we should also update RootMoveList to avoid bogus output.
560 && tte->depth() >= depth
561 && ttValue != VALUE_NONE // Only in case of TT access race
562 && ( PvNode ? tte->bound() == BOUND_EXACT
563 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
564 : (tte->bound() & BOUND_UPPER)))
567 ss->currentMove = ttMove; // Can be MOVE_NONE
569 // Update killers, history, and counter move on TT hit
572 && !pos.capture_or_promotion(ttMove)
575 if (ss->killers[0] != ttMove)
577 ss->killers[1] = ss->killers[0];
578 ss->killers[0] = ttMove;
581 Value bonus = Value(int(depth) * int(depth));
582 History.update(pos.moved_piece(ttMove), to_sq(ttMove), bonus);
584 if (is_ok((ss-1)->currentMove))
586 Square prevMoveSq = to_sq((ss-1)->currentMove);
587 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, ttMove);
593 // Step 5. Evaluate the position statically and update parent's gain statistics
596 ss->staticEval = eval = VALUE_NONE;
602 // Never assume anything on values stored in TT
603 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
604 eval = ss->staticEval = evaluate(pos);
606 // Can ttValue be used as a better position evaluation?
607 if (ttValue != VALUE_NONE)
608 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
613 eval = ss->staticEval = evaluate(pos);
614 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
617 if ( !pos.captured_piece_type()
618 && ss->staticEval != VALUE_NONE
619 && (ss-1)->staticEval != VALUE_NONE
620 && (move = (ss-1)->currentMove) != MOVE_NULL
621 && type_of(move) == NORMAL)
623 Square to = to_sq(move);
624 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
627 // Step 6. Razoring (skipped when in check)
629 && depth < 4 * ONE_PLY
630 && eval + razor_margin(depth) < beta
631 && ttMove == MOVE_NONE
632 && abs(beta) < VALUE_MATE_IN_MAX_PLY
633 && !pos.pawn_on_7th(pos.side_to_move()))
635 Value rbeta = beta - razor_margin(depth);
636 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
638 // Logically we should return (v + razor_margin(depth)), but
639 // surprisingly this performed slightly weaker in tests.
643 // Step 7. Futility pruning: child node (skipped when in check)
646 && depth < 7 * ONE_PLY
647 && eval - futility_margin(depth) >= beta
648 && abs(beta) < VALUE_MATE_IN_MAX_PLY
649 && abs(eval) < VALUE_KNOWN_WIN
650 && pos.non_pawn_material(pos.side_to_move()))
651 return eval - futility_margin(depth);
653 // Step 8. Null move search with verification search (is omitted in PV nodes)
656 && depth >= 2 * ONE_PLY
658 && abs(beta) < VALUE_MATE_IN_MAX_PLY
659 && pos.non_pawn_material(pos.side_to_move()))
661 ss->currentMove = MOVE_NULL;
663 // Null move dynamic reduction based on depth
664 Depth R = 3 * ONE_PLY + depth / 4;
666 // Null move dynamic reduction based on value
667 if (eval - PawnValueMg > beta)
670 pos.do_null_move(st);
671 (ss+1)->skipNullMove = true;
672 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
673 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
674 (ss+1)->skipNullMove = false;
675 pos.undo_null_move();
677 if (nullValue >= beta)
679 // Do not return unproven mate scores
680 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
683 if (depth < 12 * ONE_PLY)
686 // Do verification search at high depths
687 ss->skipNullMove = true;
688 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
689 ss->skipNullMove = false;
696 // Step 9. ProbCut (skipped when in check)
697 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
698 // and a reduced search returns a value much above beta, we can (almost) safely
699 // prune the previous move.
701 && depth >= 5 * ONE_PLY
703 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
705 Value rbeta = beta + 200;
706 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
708 assert(rdepth >= ONE_PLY);
709 assert((ss-1)->currentMove != MOVE_NONE);
710 assert((ss-1)->currentMove != MOVE_NULL);
712 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
715 while ((move = mp.next_move<false>()) != MOVE_NONE)
716 if (pos.legal(move, ci.pinned))
718 ss->currentMove = move;
719 pos.do_move(move, st, ci, pos.gives_check(move, ci));
720 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
727 // Step 10. Internal iterative deepening (skipped when in check)
728 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
729 && ttMove == MOVE_NONE
730 && (PvNode || ss->staticEval + Value(256) >= beta))
732 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
734 ss->skipNullMove = true;
735 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
736 ss->skipNullMove = false;
738 tte = TT.probe(posKey);
739 ttMove = tte ? tte->move() : MOVE_NONE;
742 moves_loop: // When in check and at SpNode search starts from here
744 Square prevMoveSq = to_sq((ss-1)->currentMove);
745 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
746 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
748 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
750 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
751 improving = ss->staticEval >= (ss-2)->staticEval
752 || ss->staticEval == VALUE_NONE
753 ||(ss-2)->staticEval == VALUE_NONE;
755 singularExtensionNode = !RootNode
757 && depth >= 8 * ONE_PLY
758 && ttMove != MOVE_NONE
759 && !excludedMove // Recursive singular search is not allowed
760 && (tte->bound() & BOUND_LOWER)
761 && tte->depth() >= depth - 3 * ONE_PLY;
763 // Step 11. Loop through moves
764 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
765 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
769 if (move == excludedMove)
772 // At root obey the "searchmoves" option and skip moves not listed in Root
773 // Move List. As a consequence any illegal move is also skipped. In MultiPV
774 // mode we also skip PV moves which have been already searched.
775 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
780 // Shared counter cannot be decremented later if the move turns out to be illegal
781 if (!pos.legal(move, ci.pinned))
784 moveCount = ++splitPoint->moveCount;
785 splitPoint->mutex.unlock();
792 Signals.firstRootMove = (moveCount == 1);
794 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
795 sync_cout << "info depth " << depth / ONE_PLY
796 << " currmove " << move_to_uci(move, pos.is_chess960())
797 << " currmovenumber " << moveCount + PVIdx << sync_endl;
801 captureOrPromotion = pos.capture_or_promotion(move);
802 givesCheck = pos.gives_check(move, ci);
803 dangerous = givesCheck
804 || type_of(move) != NORMAL
805 || pos.advanced_pawn_push(move);
807 // Step 12. Extend checks
808 if (givesCheck && pos.see_sign(move) >= 0)
811 // Singular extension search. If all moves but one fail low on a search of
812 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
813 // is singular and should be extended. To verify this we do a reduced search
814 // on all the other moves but the ttMove and if the result is lower than
815 // ttValue minus a margin then we extend the ttMove.
816 if ( singularExtensionNode
819 && pos.legal(move, ci.pinned)
820 && abs(ttValue) < VALUE_KNOWN_WIN)
822 assert(ttValue != VALUE_NONE);
824 Value rBeta = ttValue - int(depth);
825 ss->excludedMove = move;
826 ss->skipNullMove = true;
827 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
828 ss->skipNullMove = false;
829 ss->excludedMove = MOVE_NONE;
835 // Update the current move (this must be done after singular extension search)
836 newDepth = depth - ONE_PLY + ext;
838 // Step 13. Pruning at shallow depth (exclude PV nodes)
840 && !captureOrPromotion
843 /* && move != ttMove Already implicit in the next condition */
844 && bestValue > VALUE_MATED_IN_MAX_PLY)
846 // Move count based pruning
847 if ( depth < 16 * ONE_PLY
848 && moveCount >= FutilityMoveCounts[improving][depth] )
851 splitPoint->mutex.lock();
856 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
858 // Futility pruning: parent node
859 if (predictedDepth < 7 * ONE_PLY)
861 futilityValue = ss->staticEval + futility_margin(predictedDepth)
862 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
864 if (futilityValue <= alpha)
866 bestValue = std::max(bestValue, futilityValue);
870 splitPoint->mutex.lock();
871 if (bestValue > splitPoint->bestValue)
872 splitPoint->bestValue = bestValue;
878 // Prune moves with negative SEE at low depths
879 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
882 splitPoint->mutex.lock();
888 // Check for legality just before making the move
889 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
895 pvMove = PvNode && moveCount == 1;
896 ss->currentMove = move;
897 if (!SpNode && !captureOrPromotion && quietCount < 64)
898 quietsSearched[quietCount++] = move;
900 // Step 14. Make the move
901 pos.do_move(move, st, ci, givesCheck);
903 // Step 15. Reduced depth search (LMR). If the move fails high it will be
904 // re-searched at full depth.
905 if ( depth >= 3 * ONE_PLY
907 && !captureOrPromotion
909 && move != ss->killers[0]
910 && move != ss->killers[1])
912 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
914 if (!PvNode && cutNode)
915 ss->reduction += ONE_PLY;
917 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
918 ss->reduction += ONE_PLY / 2;
920 if (move == countermoves[0] || move == countermoves[1])
921 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
923 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
925 alpha = splitPoint->alpha;
927 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
929 // Research at intermediate depth if reduction is very high
930 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
932 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
933 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
936 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
937 ss->reduction = DEPTH_ZERO;
940 doFullDepthSearch = !pvMove;
942 // Step 16. Full depth search, when LMR is skipped or fails high
943 if (doFullDepthSearch)
946 alpha = splitPoint->alpha;
948 value = newDepth < ONE_PLY ?
949 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
950 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
951 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
954 // For PV nodes only, do a full PV search on the first move or after a fail
955 // high (in the latter case search only if value < beta), otherwise let the
956 // parent node fail low with value <= alpha and to try another move.
957 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
958 value = newDepth < ONE_PLY ?
959 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
960 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
961 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
962 // Step 17. Undo move
965 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
967 // Step 18. Check for new best move
970 splitPoint->mutex.lock();
971 bestValue = splitPoint->bestValue;
972 alpha = splitPoint->alpha;
975 // Finished searching the move. If Signals.stop is true, the search
976 // was aborted because the user interrupted the search or because we
977 // ran out of time. In this case, the return value of the search cannot
978 // be trusted, and we don't update the best move and/or PV.
979 if (Signals.stop || thisThread->cutoff_occurred())
980 return value; // To avoid returning VALUE_INFINITE
984 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
986 // PV move or new best move ?
987 if (pvMove || value > alpha)
990 rm.extract_pv_from_tt(pos);
992 // We record how often the best move has been changed in each
993 // iteration. This information is used for time management: When
994 // the best move changes frequently, we allocate some more time.
999 // All other moves but the PV are set to the lowest value: this is
1000 // not a problem when sorting because the sort is stable and the
1001 // move position in the list is preserved - just the PV is pushed up.
1002 rm.score = -VALUE_INFINITE;
1005 if (value > bestValue)
1007 bestValue = SpNode ? splitPoint->bestValue = value : value;
1011 bestMove = SpNode ? splitPoint->bestMove = move : move;
1013 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1014 alpha = SpNode ? splitPoint->alpha = value : value;
1017 assert(value >= beta); // Fail high
1020 splitPoint->cutoff = true;
1027 // Step 19. Check for splitting the search
1029 && depth >= Threads.minimumSplitDepth
1030 && Threads.available_slave(thisThread)
1031 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1033 assert(bestValue < beta);
1035 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1036 depth, moveCount, &mp, NT, cutNode);
1037 if (bestValue >= beta)
1045 // Step 20. Check for mate and stalemate
1046 // All legal moves have been searched and if there are no legal moves, it
1047 // must be mate or stalemate. Note that we can have a false positive in
1048 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1049 // harmless because return value is discarded anyhow in the parent nodes.
1050 // If we are in a singular extension search then return a fail low score.
1051 // A split node has at least one move - the one tried before to be splitted.
1053 return excludedMove ? alpha
1054 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1056 // If we have pruned all the moves without searching return a fail-low score
1057 if (bestValue == -VALUE_INFINITE)
1060 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1061 bestValue >= beta ? BOUND_LOWER :
1062 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1063 depth, bestMove, ss->staticEval);
1065 // Quiet best move: update killers, history and countermoves
1066 if ( bestValue >= beta
1067 && !pos.capture_or_promotion(bestMove)
1070 if (ss->killers[0] != bestMove)
1072 ss->killers[1] = ss->killers[0];
1073 ss->killers[0] = bestMove;
1076 // Increase history value of the cut-off move and decrease all the other
1077 // played non-capture moves.
1078 Value bonus = Value(int(depth) * int(depth));
1079 History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
1080 for (int i = 0; i < quietCount - 1; ++i)
1082 Move m = quietsSearched[i];
1083 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1086 if (is_ok((ss-1)->currentMove))
1087 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1090 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1096 // qsearch() is the quiescence search function, which is called by the main
1097 // search function when the remaining depth is zero (or, to be more precise,
1098 // less than ONE_PLY).
1100 template <NodeType NT, bool InCheck>
1101 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1103 const bool PvNode = (NT == PV);
1105 assert(NT == PV || NT == NonPV);
1106 assert(InCheck == !!pos.checkers());
1107 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1108 assert(PvNode || (alpha == beta - 1));
1109 assert(depth <= DEPTH_ZERO);
1114 Move ttMove, move, bestMove;
1115 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1116 bool givesCheck, evasionPrunable;
1119 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1123 ss->currentMove = bestMove = MOVE_NONE;
1124 ss->ply = (ss-1)->ply + 1;
1126 // Check for an instant draw or if the maximum ply has been reached
1127 if (pos.is_draw() || ss->ply > MAX_PLY)
1128 return DrawValue[pos.side_to_move()];
1130 // Decide whether or not to include checks: this fixes also the type of
1131 // TT entry depth that we are going to use. Note that in qsearch we use
1132 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1133 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1134 : DEPTH_QS_NO_CHECKS;
1136 // Transposition table lookup
1138 tte = TT.probe(posKey);
1139 ttMove = tte ? tte->move() : MOVE_NONE;
1140 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1143 && tte->depth() >= ttDepth
1144 && ttValue != VALUE_NONE // Only in case of TT access race
1145 && ( PvNode ? tte->bound() == BOUND_EXACT
1146 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1147 : (tte->bound() & BOUND_UPPER)))
1149 ss->currentMove = ttMove; // Can be MOVE_NONE
1153 // Evaluate the position statically
1156 ss->staticEval = VALUE_NONE;
1157 bestValue = futilityBase = -VALUE_INFINITE;
1163 // Never assume anything on values stored in TT
1164 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1165 ss->staticEval = bestValue = evaluate(pos);
1167 // Can ttValue be used as a better position evaluation?
1168 if (ttValue != VALUE_NONE)
1169 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1170 bestValue = ttValue;
1173 ss->staticEval = bestValue = evaluate(pos);
1175 // Stand pat. Return immediately if static value is at least beta
1176 if (bestValue >= beta)
1179 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1180 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1185 if (PvNode && bestValue > alpha)
1188 futilityBase = bestValue + Value(128);
1191 // Initialize a MovePicker object for the current position, and prepare
1192 // to search the moves. Because the depth is <= 0 here, only captures,
1193 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1195 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1198 // Loop through the moves until no moves remain or a beta cutoff occurs
1199 while ((move = mp.next_move<false>()) != MOVE_NONE)
1201 assert(is_ok(move));
1203 givesCheck = pos.gives_check(move, ci);
1210 && futilityBase > -VALUE_KNOWN_WIN
1211 && !pos.advanced_pawn_push(move))
1213 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1215 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1217 if (futilityValue < beta)
1219 bestValue = std::max(bestValue, futilityValue);
1223 if (futilityBase < beta && pos.see(move) <= 0)
1225 bestValue = std::max(bestValue, futilityBase);
1230 // Detect non-capture evasions that are candidates to be pruned
1231 evasionPrunable = InCheck
1232 && bestValue > VALUE_MATED_IN_MAX_PLY
1233 && !pos.capture(move)
1234 && !pos.can_castle(pos.side_to_move());
1236 // Don't search moves with negative SEE values
1238 && (!InCheck || evasionPrunable)
1240 && type_of(move) != PROMOTION
1241 && pos.see_sign(move) < 0)
1244 // Check for legality just before making the move
1245 if (!pos.legal(move, ci.pinned))
1248 ss->currentMove = move;
1250 // Make and search the move
1251 pos.do_move(move, st, ci, givesCheck);
1252 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1253 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1254 pos.undo_move(move);
1256 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1258 // Check for new best move
1259 if (value > bestValue)
1265 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1272 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1273 ttDepth, move, ss->staticEval);
1281 // All legal moves have been searched. A special case: If we're in check
1282 // and no legal moves were found, it is checkmate.
1283 if (InCheck && bestValue == -VALUE_INFINITE)
1284 return mated_in(ss->ply); // Plies to mate from the root
1286 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1287 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1288 ttDepth, bestMove, ss->staticEval);
1290 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1296 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1297 // "plies to mate from the current position". Non-mate scores are unchanged.
1298 // The function is called before storing a value in the transposition table.
1300 Value value_to_tt(Value v, int ply) {
1302 assert(v != VALUE_NONE);
1304 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1305 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1309 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1310 // from the transposition table (which refers to the plies to mate/be mated
1311 // from current position) to "plies to mate/be mated from the root".
1313 Value value_from_tt(Value v, int ply) {
1315 return v == VALUE_NONE ? VALUE_NONE
1316 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1317 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1321 // When playing with a strength handicap, choose best move among the MultiPV
1322 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1324 Move Skill::pick_move() {
1328 // PRNG sequence should be not deterministic
1329 for (int i = Time::now() % 50; i > 0; --i)
1330 rk.rand<unsigned>();
1332 // RootMoves are already sorted by score in descending order
1333 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1334 int weakness = 120 - 2 * level;
1335 int max_s = -VALUE_INFINITE;
1338 // Choose best move. For each move score we add two terms both dependent on
1339 // weakness. One deterministic and bigger for weaker moves, and one random,
1340 // then we choose the move with the resulting highest score.
1341 for (size_t i = 0; i < PVSize; ++i)
1343 int s = RootMoves[i].score;
1345 // Don't allow crazy blunders even at very low skills
1346 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1349 // This is our magic formula
1350 s += ( weakness * int(RootMoves[0].score - s)
1351 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1356 best = RootMoves[i].pv[0];
1363 // uci_pv() formats PV information according to the UCI protocol. UCI
1364 // requires that all (if any) unsearched PV lines are sent using a previous
1367 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1369 std::stringstream s;
1370 Time::point elapsed = Time::now() - SearchTime + 1;
1371 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1374 for (size_t i = 0; i < Threads.size(); ++i)
1375 if (Threads[i]->maxPly > selDepth)
1376 selDepth = Threads[i]->maxPly;
1378 for (size_t i = 0; i < uciPVSize; ++i)
1380 bool updated = (i <= PVIdx);
1382 if (depth == 1 && !updated)
1385 int d = updated ? depth : depth - 1;
1386 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1388 if (s.rdbuf()->in_avail()) // Not at first line
1391 s << "info depth " << d
1392 << " seldepth " << selDepth
1393 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1394 << " nodes " << pos.nodes_searched()
1395 << " nps " << pos.nodes_searched() * 1000 / elapsed
1396 << " time " << elapsed
1397 << " multipv " << i + 1
1400 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1401 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1410 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1411 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1412 /// ensure that we have a ponder move even when we fail high at root. This
1413 /// results in a long PV to print that is important for position analysis.
1415 void RootMove::extract_pv_from_tt(Position& pos) {
1417 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1427 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1429 pos.do_move(pv[ply++], *st++);
1430 tte = TT.probe(pos.key());
1433 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1434 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1436 && (!pos.is_draw() || ply < 2));
1438 pv.push_back(MOVE_NONE); // Must be zero-terminating
1440 while (ply) pos.undo_move(pv[--ply]);
1444 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1445 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1446 /// first, even if the old TT entries have been overwritten.
1448 void RootMove::insert_pv_in_tt(Position& pos) {
1450 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1455 tte = TT.probe(pos.key());
1457 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1458 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1460 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1462 pos.do_move(pv[ply++], *st++);
1464 } while (pv[ply] != MOVE_NONE);
1466 while (ply) pos.undo_move(pv[--ply]);
1470 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1472 void Thread::idle_loop() {
1474 // Pointer 'this_sp' is not null only if we are called from split(), and not
1475 // at the thread creation. This means we are the split point's master.
1476 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1478 assert(!this_sp || (this_sp->masterThread == this && searching));
1482 // If we are not searching, wait for a condition to be signaled instead of
1483 // wasting CPU time polling for work.
1484 while ((!searching && Threads.sleepWhileIdle) || exit)
1492 // Grab the lock to avoid races with Thread::notify_one()
1495 // If we are master and all slaves have finished then exit idle_loop
1496 if (this_sp && !this_sp->slavesMask)
1502 // Do sleep after retesting sleep conditions under lock protection. In
1503 // particular we need to avoid a deadlock in case a master thread has,
1504 // in the meanwhile, allocated us and sent the notify_one() call before
1505 // we had the chance to grab the lock.
1506 if (!searching && !exit)
1507 sleepCondition.wait(mutex);
1512 // If this thread has been assigned work, launch a search
1517 Threads.mutex.lock();
1520 assert(activeSplitPoint);
1521 SplitPoint* sp = activeSplitPoint;
1523 Threads.mutex.unlock();
1525 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1526 Position pos(*sp->pos, this);
1528 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1529 ss->splitPoint = sp;
1533 assert(activePosition == NULL);
1535 activePosition = &pos;
1537 switch (sp->nodeType) {
1539 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1542 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1545 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1554 activePosition = NULL;
1555 sp->slavesMask &= ~(1ULL << idx);
1556 sp->nodes += pos.nodes_searched();
1558 // Wake up the master thread so to allow it to return from the idle
1559 // loop in case we are the last slave of the split point.
1560 if ( Threads.sleepWhileIdle
1561 && this != sp->masterThread
1564 assert(!sp->masterThread->searching);
1565 sp->masterThread->notify_one();
1568 // After releasing the lock we can't access any SplitPoint related data
1569 // in a safe way because it could have been released under our feet by
1570 // the sp master. Also accessing other Thread objects is unsafe because
1571 // if we are exiting there is a chance that they are already freed.
1575 // If this thread is the master of a split point and all slaves have finished
1576 // their work at this split point, return from the idle loop.
1577 if (this_sp && !this_sp->slavesMask)
1579 this_sp->mutex.lock();
1580 bool finished = !this_sp->slavesMask; // Retest under lock protection
1581 this_sp->mutex.unlock();
1589 /// check_time() is called by the timer thread when the timer triggers. It is
1590 /// used to print debug info and, more importantly, to detect when we are out of
1591 /// available time and thus stop the search.
1595 static Time::point lastInfoTime = Time::now();
1596 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1598 if (Time::now() - lastInfoTime >= 1000)
1600 lastInfoTime = Time::now();
1609 Threads.mutex.lock();
1611 nodes = RootPos.nodes_searched();
1613 // Loop across all split points and sum accumulated SplitPoint nodes plus
1614 // all the currently active positions nodes.
1615 for (size_t i = 0; i < Threads.size(); ++i)
1616 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1618 SplitPoint& sp = Threads[i]->splitPoints[j];
1623 Bitboard sm = sp.slavesMask;
1626 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1628 nodes += pos->nodes_searched();
1634 Threads.mutex.unlock();
1637 Time::point elapsed = Time::now() - SearchTime;
1638 bool stillAtFirstMove = Signals.firstRootMove
1639 && !Signals.failedLowAtRoot
1640 && elapsed > TimeMgr.available_time();
1642 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1643 || stillAtFirstMove;
1645 if ( (Limits.use_time_management() && noMoreTime)
1646 || (Limits.movetime && elapsed >= Limits.movetime)
1647 || (Limits.nodes && nodes >= Limits.nodes))
1648 Signals.stop = true;