2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
80 size_t MultiPV, PVIdx;
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
86 MovesStats Countermoves, Followupmoves;
88 template <NodeType NT>
89 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
91 template <NodeType NT, bool InCheck>
92 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
94 void id_loop(Position& pos);
95 Value value_to_tt(Value v, int ply);
96 Value value_from_tt(Value v, int ply);
97 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
98 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
101 Skill(int l) : level(l), best(MOVE_NONE) {}
103 if (enabled()) // Swap best PV line with the sub-optimal one
104 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
105 RootMoves.end(), best ? best : pick_move()));
108 bool enabled() const { return level < 20; }
109 bool time_to_pick(int depth) const { return depth == 1 + level; }
119 /// Search::init() is called during startup to initialize various lookup tables
121 void Search::init() {
123 int d; // depth (ONE_PLY == 2)
124 int hd; // half depth (ONE_PLY == 1)
127 // Init reductions array
128 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
130 double pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
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 + 0.00, 1.8));
149 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * 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 uint64_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 uint64_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 // Dynamic draw value: try to avoid repetition draws at early midgame
189 int cf = std::max(70 - RootPos.game_ply(), 0);
190 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
191 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
193 if (RootMoves.empty())
195 RootMoves.push_back(MOVE_NONE);
196 sync_cout << "info depth 0 score "
197 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
203 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
205 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
207 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
209 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
214 if (Options["Write Search Log"])
216 Log log(Options["Search Log Filename"]);
217 log << "\nSearching: " << RootPos.fen()
218 << "\ninfinite: " << Limits.infinite
219 << " ponder: " << Limits.ponder
220 << " time: " << Limits.time[RootColor]
221 << " increment: " << Limits.inc[RootColor]
222 << " moves to go: " << Limits.movestogo
226 // Reset the threads, still sleeping: will wake up at split time
227 for (size_t i = 0; i < Threads.size(); ++i)
228 Threads[i]->maxPly = 0;
230 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
231 Threads.timer->run = true;
232 Threads.timer->notify_one(); // Wake up the recurring timer
234 id_loop(RootPos); // Let's start searching !
236 Threads.timer->run = false; // Stop the timer
237 Threads.sleepWhileIdle = true; // Send idle threads to sleep
239 if (Options["Write Search Log"])
241 Time::point elapsed = Time::now() - SearchTime + 1;
243 Log log(Options["Search Log Filename"]);
244 log << "Nodes: " << RootPos.nodes_searched()
245 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
246 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
249 RootPos.do_move(RootMoves[0].pv[0], st);
250 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
251 RootPos.undo_move(RootMoves[0].pv[0]);
256 // When search is stopped this info is not printed
257 sync_cout << "info nodes " << RootPos.nodes_searched()
258 << " time " << Time::now() - SearchTime + 1 << sync_endl;
260 // When we reach the maximum depth, we can arrive here without a raise of
261 // Signals.stop. However, if we are pondering or in an infinite search,
262 // the UCI protocol states that we shouldn't print the best move before the
263 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
264 // until the GUI sends one of those commands (which also raises Signals.stop).
265 if (!Signals.stop && (Limits.ponder || Limits.infinite))
267 Signals.stopOnPonderhit = true;
268 RootPos.this_thread()->wait_for(Signals.stop);
271 // Best move could be MOVE_NONE when searching on a stalemate position
272 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
273 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
280 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
281 // with increasing depth until the allocated thinking time has been consumed,
282 // user stops the search, or the maximum search depth is reached.
284 void id_loop(Position& pos) {
286 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
288 Value bestValue, alpha, beta, delta;
290 std::memset(ss-2, 0, 5 * sizeof(Stack));
291 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
295 bestValue = delta = alpha = -VALUE_INFINITE;
296 beta = VALUE_INFINITE;
301 Countermoves.clear();
302 Followupmoves.clear();
304 MultiPV = Options["MultiPV"];
305 Skill skill(Options["Skill Level"]);
307 // Do we have to play with skill handicap? In this case enable MultiPV search
308 // that we will use behind the scenes to retrieve a set of possible moves.
309 if (skill.enabled() && MultiPV < 4)
312 MultiPV = std::min(MultiPV, RootMoves.size());
314 // Iterative deepening loop until requested to stop or target depth reached
315 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
317 // Age out PV variability metric
318 BestMoveChanges *= 0.5;
320 // Save the last iteration's scores before first PV line is searched and
321 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
322 for (size_t i = 0; i < RootMoves.size(); ++i)
323 RootMoves[i].prevScore = RootMoves[i].score;
325 // MultiPV loop. We perform a full root search for each PV line
326 for (PVIdx = 0; PVIdx < MultiPV && !Signals.stop; ++PVIdx)
328 // Reset aspiration window starting size
332 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
333 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
336 // Start with a small aspiration window and, in the case of a fail
337 // high/low, re-search with a bigger window until we're not failing
341 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
343 // Bring the best move to the front. It is critical that sorting
344 // is done with a stable algorithm because all the values but the
345 // first and eventually the new best one are set to -VALUE_INFINITE
346 // and we want to keep the same order for all the moves except the
347 // new PV that goes to the front. Note that in case of MultiPV
348 // search the already searched PV lines are preserved.
349 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
351 // Write PV back to transposition table in case the relevant
352 // entries have been overwritten during the search.
353 for (size_t i = 0; i <= PVIdx; ++i)
354 RootMoves[i].insert_pv_in_tt(pos);
356 // If search has been stopped break immediately. Sorting and
357 // writing PV back to TT is safe because RootMoves is still
358 // valid, although it refers to previous iteration.
362 // When failing high/low give some update (without cluttering
363 // the UI) before a re-search.
364 if ( (bestValue <= alpha || bestValue >= beta)
365 && Time::now() - SearchTime > 3000)
366 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
368 // In case of failing low/high increase aspiration window and
369 // re-search, otherwise exit the loop.
370 if (bestValue <= alpha)
372 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
374 Signals.failedLowAtRoot = true;
375 Signals.stopOnPonderhit = false;
377 else if (bestValue >= beta)
378 beta = std::min(bestValue + delta, VALUE_INFINITE);
385 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
388 // Sort the PV lines searched so far and update the GUI
389 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
391 if (PVIdx + 1 == MultiPV || Time::now() - SearchTime > 3000)
392 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
395 Time::point iterationTime = Time::now() - SearchTime;
397 // If skill levels are enabled and time is up, pick a sub-optimal best move
398 if (skill.enabled() && skill.time_to_pick(depth))
401 if (Options["Write Search Log"])
403 RootMove& rm = RootMoves[0];
404 if (skill.best != MOVE_NONE)
405 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
407 Log log(Options["Search Log Filename"]);
408 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
412 // Have we found a "mate in x"?
414 && bestValue >= VALUE_MATE_IN_MAX_PLY
415 && VALUE_MATE - bestValue <= 2 * Limits.mate)
418 // Do we have time for the next iteration? Can we stop searching now?
419 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
421 bool stop = false; // Local variable, not the volatile Signals.stop
423 // Take some extra time if the best move has changed
424 if (depth > 4 && depth < 50 && MultiPV == 1)
425 TimeMgr.pv_instability(BestMoveChanges);
427 // Stop the search if only one legal move is available or all
428 // of the available time has been used.
429 if ( RootMoves.size() == 1
430 || iterationTime > TimeMgr.available_time() )
435 // If we are allowed to ponder do not stop the search now but
436 // keep pondering until the GUI sends "ponderhit" or "stop".
438 Signals.stopOnPonderhit = true;
447 // search<>() is the main search function for both PV and non-PV nodes and for
448 // normal and SplitPoint nodes. When called just after a split point the search
449 // is simpler because we have already probed the hash table, done a null move
450 // search, and searched the first move before splitting, so we don't have to
451 // repeat all this work again. We also don't need to store anything to the hash
452 // table here: This is taken care of after we return from the split point.
454 template <NodeType NT>
455 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
457 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
458 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
459 const bool RootNode = (NT == Root || NT == SplitPointRoot);
461 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
462 assert(PvNode || (alpha == beta - 1));
463 assert(depth > DEPTH_ZERO);
465 Move quietsSearched[64];
468 SplitPoint* splitPoint;
470 Move ttMove, move, excludedMove, bestMove;
471 Depth ext, newDepth, predictedDepth;
472 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
473 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
474 bool captureOrPromotion, dangerous, doFullDepthSearch;
475 int moveCount, quietCount;
477 // Step 1. Initialize node
478 Thread* thisThread = pos.this_thread();
479 inCheck = pos.checkers();
483 splitPoint = ss->splitPoint;
484 bestMove = splitPoint->bestMove;
485 bestValue = splitPoint->bestValue;
487 ttMove = excludedMove = MOVE_NONE;
488 ttValue = VALUE_NONE;
490 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
495 moveCount = quietCount = 0;
496 bestValue = -VALUE_INFINITE;
497 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
498 ss->ply = (ss-1)->ply + 1;
499 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
500 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
502 // Used to send selDepth info to GUI
503 if (PvNode && thisThread->maxPly < ss->ply)
504 thisThread->maxPly = ss->ply;
508 // Step 2. Check for aborted search and immediate draw
509 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
510 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
512 // Step 3. Mate distance pruning. Even if we mate at the next move our score
513 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
514 // a shorter mate was found upward in the tree then there is no need to search
515 // because we will never beat the current alpha. Same logic but with reversed
516 // signs applies also in the opposite condition of being mated instead of giving
517 // mate. In this case return a fail-high score.
518 alpha = std::max(mated_in(ss->ply), alpha);
519 beta = std::min(mate_in(ss->ply+1), beta);
524 // Step 4. Transposition table lookup
525 // We don't want the score of a partial search to overwrite a previous full search
526 // TT value, so we use a different position key in case of an excluded move.
527 excludedMove = ss->excludedMove;
528 posKey = excludedMove ? pos.exclusion_key() : pos.key();
529 tte = TT.probe(posKey);
530 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
531 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
533 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
534 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
535 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
536 // we should also update RootMoveList to avoid bogus output.
539 && tte->depth() >= depth
540 && ttValue != VALUE_NONE // Only in case of TT access race
541 && ( PvNode ? tte->bound() == BOUND_EXACT
542 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
543 : (tte->bound() & BOUND_UPPER)))
546 ss->currentMove = ttMove; // Can be MOVE_NONE
548 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
549 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
550 update_stats(pos, ss, ttMove, depth, NULL, 0);
555 // Step 5. Evaluate the position statically and update parent's gain statistics
558 ss->staticEval = eval = VALUE_NONE;
564 // Never assume anything on values stored in TT
565 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
566 eval = ss->staticEval = evaluate(pos);
568 // Can ttValue be used as a better position evaluation?
569 if (ttValue != VALUE_NONE)
570 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
575 eval = ss->staticEval = evaluate(pos);
576 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
579 if ( !pos.captured_piece_type()
580 && ss->staticEval != VALUE_NONE
581 && (ss-1)->staticEval != VALUE_NONE
582 && (move = (ss-1)->currentMove) != MOVE_NULL
583 && type_of(move) == NORMAL)
585 Square to = to_sq(move);
586 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
589 // Step 6. Razoring (skipped when in check)
591 && depth < 4 * ONE_PLY
592 && eval + razor_margin(depth) <= alpha
593 && ttMove == MOVE_NONE
594 && abs(beta) < VALUE_MATE_IN_MAX_PLY
595 && !pos.pawn_on_7th(pos.side_to_move()))
597 Value ralpha = alpha - razor_margin(depth);
598 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
603 // Step 7. Futility pruning: child node (skipped when in check)
606 && depth < 7 * ONE_PLY
607 && eval - futility_margin(depth) >= beta
608 && abs(beta) < VALUE_MATE_IN_MAX_PLY
609 && abs(eval) < VALUE_KNOWN_WIN
610 && pos.non_pawn_material(pos.side_to_move()))
611 return eval - futility_margin(depth);
613 // Step 8. Null move search with verification search (is omitted in PV nodes)
616 && depth >= 2 * ONE_PLY
618 && abs(beta) < VALUE_MATE_IN_MAX_PLY
619 && pos.non_pawn_material(pos.side_to_move()))
621 ss->currentMove = MOVE_NULL;
623 assert(eval - beta >= 0);
625 // Null move dynamic reduction based on depth and value
626 Depth R = 3 * ONE_PLY
628 + int(eval - beta) / PawnValueMg * ONE_PLY;
630 pos.do_null_move(st);
631 (ss+1)->skipNullMove = true;
632 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
633 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
634 (ss+1)->skipNullMove = false;
635 pos.undo_null_move();
637 if (nullValue >= beta)
639 // Do not return unproven mate scores
640 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
643 if (depth < 12 * ONE_PLY)
646 // Do verification search at high depths
647 ss->skipNullMove = true;
648 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
649 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
650 ss->skipNullMove = false;
657 // Step 9. ProbCut (skipped when in check)
658 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
659 // and a reduced search returns a value much above beta, we can (almost) safely
660 // prune the previous move.
662 && depth >= 5 * ONE_PLY
664 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
666 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
667 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
669 assert(rdepth >= ONE_PLY);
670 assert((ss-1)->currentMove != MOVE_NONE);
671 assert((ss-1)->currentMove != MOVE_NULL);
673 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
676 while ((move = mp.next_move<false>()) != MOVE_NONE)
677 if (pos.legal(move, ci.pinned))
679 ss->currentMove = move;
680 pos.do_move(move, st, ci, pos.gives_check(move, ci));
681 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
688 // Step 10. Internal iterative deepening (skipped when in check)
689 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
691 && (PvNode || ss->staticEval + Value(256) >= beta))
693 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
695 ss->skipNullMove = true;
696 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
697 ss->skipNullMove = false;
699 tte = TT.probe(posKey);
700 ttMove = tte ? tte->move() : MOVE_NONE;
703 moves_loop: // When in check and at SpNode search starts from here
705 Square prevMoveSq = to_sq((ss-1)->currentMove);
706 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
707 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
709 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
710 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
711 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
713 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
715 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
716 improving = ss->staticEval >= (ss-2)->staticEval
717 || ss->staticEval == VALUE_NONE
718 ||(ss-2)->staticEval == VALUE_NONE;
720 singularExtensionNode = !RootNode
722 && depth >= 8 * ONE_PLY
723 && ttMove != MOVE_NONE
724 && !excludedMove // Recursive singular search is not allowed
725 && (tte->bound() & BOUND_LOWER)
726 && tte->depth() >= depth - 3 * ONE_PLY;
728 // Step 11. Loop through moves
729 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
730 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
734 if (move == excludedMove)
737 // At root obey the "searchmoves" option and skip moves not listed in Root
738 // Move List. As a consequence any illegal move is also skipped. In MultiPV
739 // mode we also skip PV moves which have been already searched.
740 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
745 // Shared counter cannot be decremented later if the move turns out to be illegal
746 if (!pos.legal(move, ci.pinned))
749 moveCount = ++splitPoint->moveCount;
750 splitPoint->mutex.unlock();
757 Signals.firstRootMove = (moveCount == 1);
759 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
760 sync_cout << "info depth " << depth / ONE_PLY
761 << " currmove " << move_to_uci(move, pos.is_chess960())
762 << " currmovenumber " << moveCount + PVIdx << sync_endl;
766 captureOrPromotion = pos.capture_or_promotion(move);
768 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
769 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
770 : pos.gives_check(move, ci);
772 dangerous = givesCheck
773 || type_of(move) != NORMAL
774 || pos.advanced_pawn_push(move);
776 // Step 12. Extend checks
777 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
780 // Singular extension search. If all moves but one fail low on a search of
781 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
782 // is singular and should be extended. To verify this we do a reduced search
783 // on all the other moves but the ttMove and if the result is lower than
784 // ttValue minus a margin then we extend the ttMove.
785 if ( singularExtensionNode
788 && pos.legal(move, ci.pinned)
789 && abs(ttValue) < VALUE_KNOWN_WIN)
791 assert(ttValue != VALUE_NONE);
793 Value rBeta = ttValue - int(depth);
794 ss->excludedMove = move;
795 ss->skipNullMove = true;
796 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
797 ss->skipNullMove = false;
798 ss->excludedMove = MOVE_NONE;
804 // Update the current move (this must be done after singular extension search)
805 newDepth = depth - ONE_PLY + ext;
807 // Step 13. Pruning at shallow depth (exclude PV nodes)
809 && !captureOrPromotion
812 /* && move != ttMove Already implicit in the next condition */
813 && bestValue > VALUE_MATED_IN_MAX_PLY)
815 // Move count based pruning
816 if ( depth < 16 * ONE_PLY
817 && moveCount >= FutilityMoveCounts[improving][depth] )
820 splitPoint->mutex.lock();
825 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
827 // Futility pruning: parent node
828 if (predictedDepth < 7 * ONE_PLY)
830 futilityValue = ss->staticEval + futility_margin(predictedDepth)
831 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
833 if (futilityValue <= alpha)
835 bestValue = std::max(bestValue, futilityValue);
839 splitPoint->mutex.lock();
840 if (bestValue > splitPoint->bestValue)
841 splitPoint->bestValue = bestValue;
847 // Prune moves with negative SEE at low depths
848 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
851 splitPoint->mutex.lock();
857 // Check for legality just before making the move
858 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
864 pvMove = PvNode && moveCount == 1;
865 ss->currentMove = move;
866 if (!SpNode && !captureOrPromotion && quietCount < 64)
867 quietsSearched[quietCount++] = move;
869 // Step 14. Make the move
870 pos.do_move(move, st, ci, givesCheck);
872 // Step 15. Reduced depth search (LMR). If the move fails high it will be
873 // re-searched at full depth.
874 if ( depth >= 3 * ONE_PLY
876 && !captureOrPromotion
878 && move != ss->killers[0]
879 && move != ss->killers[1])
881 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
883 if (!PvNode && cutNode)
884 ss->reduction += ONE_PLY;
886 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
887 ss->reduction += ONE_PLY / 2;
889 if (move == countermoves[0] || move == countermoves[1])
890 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
892 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
894 alpha = splitPoint->alpha;
896 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
898 // Research at intermediate depth if reduction is very high
899 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
901 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
902 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
905 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
906 ss->reduction = DEPTH_ZERO;
909 doFullDepthSearch = !pvMove;
911 // Step 16. Full depth search, when LMR is skipped or fails high
912 if (doFullDepthSearch)
915 alpha = splitPoint->alpha;
917 value = newDepth < ONE_PLY ?
918 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
919 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
920 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
923 // For PV nodes only, do a full PV search on the first move or after a fail
924 // high (in the latter case search only if value < beta), otherwise let the
925 // parent node fail low with value <= alpha and to try another move.
926 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
927 value = newDepth < ONE_PLY ?
928 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
929 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
930 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
931 // Step 17. Undo move
934 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
936 // Step 18. Check for new best move
939 splitPoint->mutex.lock();
940 bestValue = splitPoint->bestValue;
941 alpha = splitPoint->alpha;
944 // Finished searching the move. If Signals.stop is true, the search
945 // was aborted because the user interrupted the search or because we
946 // ran out of time. In this case, the return value of the search cannot
947 // be trusted, and we don't update the best move and/or PV.
948 if (Signals.stop || thisThread->cutoff_occurred())
949 return value; // To avoid returning VALUE_INFINITE
953 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
955 // PV move or new best move ?
956 if (pvMove || value > alpha)
959 rm.extract_pv_from_tt(pos);
961 // We record how often the best move has been changed in each
962 // iteration. This information is used for time management: When
963 // the best move changes frequently, we allocate some more time.
968 // All other moves but the PV are set to the lowest value: this is
969 // not a problem when sorting because the sort is stable and the
970 // move position in the list is preserved - just the PV is pushed up.
971 rm.score = -VALUE_INFINITE;
974 if (value > bestValue)
976 bestValue = SpNode ? splitPoint->bestValue = value : value;
980 bestMove = SpNode ? splitPoint->bestMove = move : move;
982 if (PvNode && value < beta) // Update alpha! Always alpha < beta
983 alpha = SpNode ? splitPoint->alpha = value : value;
986 assert(value >= beta); // Fail high
989 splitPoint->cutoff = true;
996 // Step 19. Check for splitting the search
998 && depth >= Threads.minimumSplitDepth
999 && Threads.available_slave(thisThread)
1000 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1002 assert(bestValue < beta);
1004 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1005 depth, moveCount, &mp, NT, cutNode);
1006 if (bestValue >= beta)
1014 // Step 20. Check for mate and stalemate
1015 // All legal moves have been searched and if there are no legal moves, it
1016 // must be mate or stalemate. Note that we can have a false positive in
1017 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1018 // harmless because return value is discarded anyhow in the parent nodes.
1019 // If we are in a singular extension search then return a fail low score.
1020 // A split node has at least one move - the one tried before to be splitted.
1022 return excludedMove ? alpha
1023 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1025 // If we have pruned all the moves without searching return a fail-low score
1026 if (bestValue == -VALUE_INFINITE)
1029 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1030 bestValue >= beta ? BOUND_LOWER :
1031 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1032 depth, bestMove, ss->staticEval);
1034 // Quiet best move: update killers, history, countermoves and followupmoves
1035 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1036 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1038 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1044 // qsearch() is the quiescence search function, which is called by the main
1045 // search function when the remaining depth is zero (or, to be more precise,
1046 // less than ONE_PLY).
1048 template <NodeType NT, bool InCheck>
1049 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1051 const bool PvNode = (NT == PV);
1053 assert(NT == PV || NT == NonPV);
1054 assert(InCheck == !!pos.checkers());
1055 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1056 assert(PvNode || (alpha == beta - 1));
1057 assert(depth <= DEPTH_ZERO);
1062 Move ttMove, move, bestMove;
1063 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1064 bool givesCheck, evasionPrunable;
1067 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1071 ss->currentMove = bestMove = MOVE_NONE;
1072 ss->ply = (ss-1)->ply + 1;
1074 // Check for an instant draw or if the maximum ply has been reached
1075 if (pos.is_draw() || ss->ply > MAX_PLY)
1076 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1078 // Decide whether or not to include checks: this fixes also the type of
1079 // TT entry depth that we are going to use. Note that in qsearch we use
1080 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1081 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1082 : DEPTH_QS_NO_CHECKS;
1084 // Transposition table lookup
1086 tte = TT.probe(posKey);
1087 ttMove = tte ? tte->move() : MOVE_NONE;
1088 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1091 && tte->depth() >= ttDepth
1092 && ttValue != VALUE_NONE // Only in case of TT access race
1093 && ( PvNode ? tte->bound() == BOUND_EXACT
1094 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1095 : (tte->bound() & BOUND_UPPER)))
1097 ss->currentMove = ttMove; // Can be MOVE_NONE
1101 // Evaluate the position statically
1104 ss->staticEval = VALUE_NONE;
1105 bestValue = futilityBase = -VALUE_INFINITE;
1111 // Never assume anything on values stored in TT
1112 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1113 ss->staticEval = bestValue = evaluate(pos);
1115 // Can ttValue be used as a better position evaluation?
1116 if (ttValue != VALUE_NONE)
1117 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1118 bestValue = ttValue;
1121 ss->staticEval = bestValue = evaluate(pos);
1123 // Stand pat. Return immediately if static value is at least beta
1124 if (bestValue >= beta)
1127 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1128 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1133 if (PvNode && bestValue > alpha)
1136 futilityBase = bestValue + Value(128);
1139 // Initialize a MovePicker object for the current position, and prepare
1140 // to search the moves. Because the depth is <= 0 here, only captures,
1141 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1143 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1146 // Loop through the moves until no moves remain or a beta cutoff occurs
1147 while ((move = mp.next_move<false>()) != MOVE_NONE)
1149 assert(is_ok(move));
1151 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1152 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1153 : pos.gives_check(move, ci);
1160 && futilityBase > -VALUE_KNOWN_WIN
1161 && !pos.advanced_pawn_push(move))
1163 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1165 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1167 if (futilityValue < beta)
1169 bestValue = std::max(bestValue, futilityValue);
1173 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1175 bestValue = std::max(bestValue, futilityBase);
1180 // Detect non-capture evasions that are candidates to be pruned
1181 evasionPrunable = InCheck
1182 && bestValue > VALUE_MATED_IN_MAX_PLY
1183 && !pos.capture(move)
1184 && !pos.can_castle(pos.side_to_move());
1186 // Don't search moves with negative SEE values
1188 && (!InCheck || evasionPrunable)
1190 && type_of(move) != PROMOTION
1191 && pos.see_sign(move) < VALUE_ZERO)
1194 // Check for legality just before making the move
1195 if (!pos.legal(move, ci.pinned))
1198 ss->currentMove = move;
1200 // Make and search the move
1201 pos.do_move(move, st, ci, givesCheck);
1202 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1203 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1204 pos.undo_move(move);
1206 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1208 // Check for new best move
1209 if (value > bestValue)
1215 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1222 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1223 ttDepth, move, ss->staticEval);
1231 // All legal moves have been searched. A special case: If we're in check
1232 // and no legal moves were found, it is checkmate.
1233 if (InCheck && bestValue == -VALUE_INFINITE)
1234 return mated_in(ss->ply); // Plies to mate from the root
1236 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1237 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1238 ttDepth, bestMove, ss->staticEval);
1240 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1246 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1247 // "plies to mate from the current position". Non-mate scores are unchanged.
1248 // The function is called before storing a value in the transposition table.
1250 Value value_to_tt(Value v, int ply) {
1252 assert(v != VALUE_NONE);
1254 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1255 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1259 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1260 // from the transposition table (which refers to the plies to mate/be mated
1261 // from current position) to "plies to mate/be mated from the root".
1263 Value value_from_tt(Value v, int ply) {
1265 return v == VALUE_NONE ? VALUE_NONE
1266 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1267 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1271 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1274 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1276 if (ss->killers[0] != move)
1278 ss->killers[1] = ss->killers[0];
1279 ss->killers[0] = move;
1282 // Increase history value of the cut-off move and decrease all the other
1283 // played quiet moves.
1284 Value bonus = Value(int(depth) * int(depth));
1285 History.update(pos.moved_piece(move), to_sq(move), bonus);
1286 for (int i = 0; i < quietsCnt; ++i)
1289 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1292 if (is_ok((ss-1)->currentMove))
1294 Square prevMoveSq = to_sq((ss-1)->currentMove);
1295 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1298 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1300 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1301 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1306 // When playing with a strength handicap, choose best move among the MultiPV
1307 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1309 Move Skill::pick_move() {
1313 // PRNG sequence should be not deterministic
1314 for (int i = Time::now() % 50; i > 0; --i)
1315 rk.rand<unsigned>();
1317 // RootMoves are already sorted by score in descending order
1318 int variance = std::min(RootMoves[0].score - RootMoves[MultiPV - 1].score, PawnValueMg);
1319 int weakness = 120 - 2 * level;
1320 int max_s = -VALUE_INFINITE;
1323 // Choose best move. For each move score we add two terms both dependent on
1324 // weakness. One deterministic and bigger for weaker moves, and one random,
1325 // then we choose the move with the resulting highest score.
1326 for (size_t i = 0; i < MultiPV; ++i)
1328 int s = RootMoves[i].score;
1330 // Don't allow crazy blunders even at very low skills
1331 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1334 // This is our magic formula
1335 s += ( weakness * int(RootMoves[0].score - s)
1336 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1341 best = RootMoves[i].pv[0];
1348 // uci_pv() formats PV information according to the UCI protocol. UCI
1349 // requires that all (if any) unsearched PV lines are sent using a previous
1352 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1354 std::stringstream s;
1355 Time::point elapsed = Time::now() - SearchTime + 1;
1356 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1359 for (size_t i = 0; i < Threads.size(); ++i)
1360 if (Threads[i]->maxPly > selDepth)
1361 selDepth = Threads[i]->maxPly;
1363 for (size_t i = 0; i < uciPVSize; ++i)
1365 bool updated = (i <= PVIdx);
1367 if (depth == 1 && !updated)
1370 int d = updated ? depth : depth - 1;
1371 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1373 if (s.rdbuf()->in_avail()) // Not at first line
1376 s << "info depth " << d
1377 << " seldepth " << selDepth
1378 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1379 << " nodes " << pos.nodes_searched()
1380 << " nps " << pos.nodes_searched() * 1000 / elapsed
1381 << " time " << elapsed
1382 << " multipv " << i + 1
1385 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1386 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1395 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1396 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1397 /// ensure that we have a ponder move even when we fail high at root. This
1398 /// results in a long PV to print that is important for position analysis.
1400 void RootMove::extract_pv_from_tt(Position& pos) {
1402 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1412 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1414 pos.do_move(pv[ply++], *st++);
1415 tte = TT.probe(pos.key());
1418 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1419 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1421 && (!pos.is_draw() || ply < 2));
1423 pv.push_back(MOVE_NONE); // Must be zero-terminating
1425 while (ply) pos.undo_move(pv[--ply]);
1429 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1430 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1431 /// first, even if the old TT entries have been overwritten.
1433 void RootMove::insert_pv_in_tt(Position& pos) {
1435 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1440 tte = TT.probe(pos.key());
1442 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1443 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1445 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1447 pos.do_move(pv[ply++], *st++);
1449 } while (pv[ply] != MOVE_NONE);
1451 while (ply) pos.undo_move(pv[--ply]);
1455 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1457 void Thread::idle_loop() {
1459 // Pointer 'this_sp' is not null only if we are called from split(), and not
1460 // at the thread creation. This means we are the split point's master.
1461 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1463 assert(!this_sp || (this_sp->masterThread == this && searching));
1467 // If we are not searching, wait for a condition to be signaled instead of
1468 // wasting CPU time polling for work.
1469 while ((!searching && Threads.sleepWhileIdle) || exit)
1477 // Grab the lock to avoid races with Thread::notify_one()
1480 // If we are master and all slaves have finished then exit idle_loop
1481 if (this_sp && !this_sp->slavesMask)
1487 // Do sleep after retesting sleep conditions under lock protection. In
1488 // particular we need to avoid a deadlock in case a master thread has,
1489 // in the meanwhile, allocated us and sent the notify_one() call before
1490 // we had the chance to grab the lock.
1491 if (!searching && !exit)
1492 sleepCondition.wait(mutex);
1497 // If this thread has been assigned work, launch a search
1502 Threads.mutex.lock();
1505 assert(activeSplitPoint);
1506 SplitPoint* sp = activeSplitPoint;
1508 Threads.mutex.unlock();
1510 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1511 Position pos(*sp->pos, this);
1513 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1514 ss->splitPoint = sp;
1518 assert(activePosition == NULL);
1520 activePosition = &pos;
1522 switch (sp->nodeType) {
1524 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1527 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1530 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1539 activePosition = NULL;
1540 sp->slavesMask &= ~(1ULL << idx);
1541 sp->nodes += pos.nodes_searched();
1543 // Wake up the master thread so to allow it to return from the idle
1544 // loop in case we are the last slave of the split point.
1545 if ( Threads.sleepWhileIdle
1546 && this != sp->masterThread
1549 assert(!sp->masterThread->searching);
1550 sp->masterThread->notify_one();
1553 // After releasing the lock we can't access any SplitPoint related data
1554 // in a safe way because it could have been released under our feet by
1555 // the sp master. Also accessing other Thread objects is unsafe because
1556 // if we are exiting there is a chance that they are already freed.
1560 // If this thread is the master of a split point and all slaves have finished
1561 // their work at this split point, return from the idle loop.
1562 if (this_sp && !this_sp->slavesMask)
1564 this_sp->mutex.lock();
1565 bool finished = !this_sp->slavesMask; // Retest under lock protection
1566 this_sp->mutex.unlock();
1574 /// check_time() is called by the timer thread when the timer triggers. It is
1575 /// used to print debug info and, more importantly, to detect when we are out of
1576 /// available time and thus stop the search.
1580 static Time::point lastInfoTime = Time::now();
1581 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1583 if (Time::now() - lastInfoTime >= 1000)
1585 lastInfoTime = Time::now();
1594 Threads.mutex.lock();
1596 nodes = RootPos.nodes_searched();
1598 // Loop across all split points and sum accumulated SplitPoint nodes plus
1599 // all the currently active positions nodes.
1600 for (size_t i = 0; i < Threads.size(); ++i)
1601 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1603 SplitPoint& sp = Threads[i]->splitPoints[j];
1608 Bitboard sm = sp.slavesMask;
1611 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1613 nodes += pos->nodes_searched();
1619 Threads.mutex.unlock();
1622 Time::point elapsed = Time::now() - SearchTime;
1623 bool stillAtFirstMove = Signals.firstRootMove
1624 && !Signals.failedLowAtRoot
1625 && elapsed > TimeMgr.available_time() * 75 / 100;
1627 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1628 || stillAtFirstMove;
1630 if ( (Limits.use_time_management() && noMoreTime)
1631 || (Limits.movetime && elapsed >= Limits.movetime)
1632 || (Limits.nodes && nodes >= Limits.nodes))
1633 Signals.stop = true;