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;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Different node types, used as template parameter
56 enum NodeType { Root, PV, NonPV };
58 // Dynamic razoring margin based on depth
59 inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
61 // Futility lookup tables (initialized at startup) and their access functions
62 int FutilityMoveCounts[2][32]; // [improving][depth]
64 inline Value futility_margin(Depth d) {
65 return Value(100 * d);
68 // Reduction lookup tables (initialized at startup) and their access function
69 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
71 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
73 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
78 double BestMoveChanges;
79 Value DrawValue[COLOR_NB];
82 MovesStats Countermoves, Followupmoves;
84 template <NodeType NT, bool SpNode>
85 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
87 template <NodeType NT, bool InCheck>
88 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
90 void id_loop(Position& pos);
91 Value value_to_tt(Value v, int ply);
92 Value value_from_tt(Value v, int ply);
93 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
94 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
97 Skill(int l, size_t rootSize) : level(l),
98 candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
101 if (candidates) // Swap best PV line with the sub-optimal one
102 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
103 RootMoves.end(), best ? best : pick_move()));
106 size_t candidates_size() const { return candidates; }
107 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 = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
130 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
131 Reductions[1][1][hd][mc] = int8_t( pvRed >= 1.0 ? pvRed * int(ONE_PLY) : 0);
132 Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? 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 + 0.00, 1.8));
148 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * 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 uint64_t Search::perft(Position& pos, Depth depth) {
159 uint64_t cnt, nodes = 0;
161 const bool leaf = depth == 2 * ONE_PLY;
163 for (MoveList<LEGAL> it(pos); *it; ++it)
165 if (Root && depth <= ONE_PLY)
169 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
170 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
175 sync_cout << move_to_uci(*it, pos.is_chess960()) << ": " << cnt << sync_endl;
180 template uint64_t Search::perft<true>(Position& pos, Depth depth);
183 /// Search::think() is the external interface to Stockfish's search, and is
184 /// called by the main thread when the program receives the UCI 'go' command. It
185 /// searches from RootPos and at the end prints the "bestmove" to output.
187 void Search::think() {
189 TimeMgr.init(Limits, RootPos.game_ply(), RootPos.side_to_move());
191 int cf = Options["Contempt Factor"] * PawnValueEg / 100; // From centipawns
192 DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(cf);
193 DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(cf);
195 if (RootMoves.empty())
197 RootMoves.push_back(MOVE_NONE);
198 sync_cout << "info depth 0 score "
199 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
205 if (Options["Write Search Log"])
207 Log log(Options["Search Log Filename"]);
208 log << "\nSearching: " << RootPos.fen()
209 << "\ninfinite: " << Limits.infinite
210 << " ponder: " << Limits.ponder
211 << " time: " << Limits.time[RootPos.side_to_move()]
212 << " increment: " << Limits.inc[RootPos.side_to_move()]
213 << " moves to go: " << Limits.movestogo
214 << "\n" << std::endl;
217 // Reset the threads, still sleeping: will wake up at split time
218 for (size_t i = 0; i < Threads.size(); ++i)
219 Threads[i]->maxPly = 0;
221 Threads.timer->run = true;
222 Threads.timer->notify_one(); // Wake up the recurring timer
224 id_loop(RootPos); // Let's start searching !
226 Threads.timer->run = false; // Stop the timer
228 if (Options["Write Search Log"])
230 Time::point elapsed = Time::now() - SearchTime + 1;
232 Log log(Options["Search Log Filename"]);
233 log << "Nodes: " << RootPos.nodes_searched()
234 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
235 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
238 RootPos.do_move(RootMoves[0].pv[0], st);
239 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
240 RootPos.undo_move(RootMoves[0].pv[0]);
245 // When search is stopped this info is not printed
246 sync_cout << "info nodes " << RootPos.nodes_searched()
247 << " time " << Time::now() - SearchTime + 1 << sync_endl;
249 // When we reach the maximum depth, we can arrive here without a raise of
250 // Signals.stop. However, if we are pondering or in an infinite search,
251 // the UCI protocol states that we shouldn't print the best move before the
252 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
253 // until the GUI sends one of those commands (which also raises Signals.stop).
254 if (!Signals.stop && (Limits.ponder || Limits.infinite))
256 Signals.stopOnPonderhit = true;
257 RootPos.this_thread()->wait_for(Signals.stop);
260 // Best move could be MOVE_NONE when searching on a stalemate position
261 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
262 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
269 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
270 // with increasing depth until the allocated thinking time has been consumed,
271 // user stops the search, or the maximum search depth is reached.
273 void id_loop(Position& pos) {
275 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
277 Value bestValue, alpha, beta, delta;
279 std::memset(ss-2, 0, 5 * sizeof(Stack));
283 bestValue = delta = alpha = -VALUE_INFINITE;
284 beta = VALUE_INFINITE;
289 Countermoves.clear();
290 Followupmoves.clear();
292 size_t multiPV = Options["MultiPV"];
293 Skill skill(Options["Skill Level"], RootMoves.size());
295 // Do we have to play with skill handicap? In this case enable MultiPV search
296 // that we will use behind the scenes to retrieve a set of possible moves.
297 multiPV = std::max(multiPV, skill.candidates_size());
299 // Iterative deepening loop until requested to stop or target depth reached
300 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
302 // Age out PV variability metric
303 BestMoveChanges *= 0.5;
305 // Save the last iteration's scores before first PV line is searched and
306 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
307 for (size_t i = 0; i < RootMoves.size(); ++i)
308 RootMoves[i].prevScore = RootMoves[i].score;
310 // MultiPV loop. We perform a full root search for each PV line
311 for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
313 // Reset aspiration window starting size
317 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
318 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
321 // Start with a small aspiration window and, in the case of a fail
322 // high/low, re-search with a bigger window until we're not failing
326 bestValue = search<Root, false>(pos, ss, alpha, beta, depth * ONE_PLY, false);
328 // Bring the best move to the front. It is critical that sorting
329 // is done with a stable algorithm because all the values but the
330 // first and eventually the new best one are set to -VALUE_INFINITE
331 // and we want to keep the same order for all the moves except the
332 // new PV that goes to the front. Note that in case of MultiPV
333 // search the already searched PV lines are preserved.
334 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
336 // Write PV back to transposition table in case the relevant
337 // entries have been overwritten during the search.
338 for (size_t i = 0; i <= PVIdx; ++i)
339 RootMoves[i].insert_pv_in_tt(pos);
341 // If search has been stopped break immediately. Sorting and
342 // writing PV back to TT is safe because RootMoves is still
343 // valid, although it refers to previous iteration.
347 // When failing high/low give some update (without cluttering
348 // the UI) before a re-search.
349 if ( (bestValue <= alpha || bestValue >= beta)
350 && Time::now() - SearchTime > 3000)
351 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
353 // In case of failing low/high increase aspiration window and
354 // re-search, otherwise exit the loop.
355 if (bestValue <= alpha)
357 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
359 Signals.failedLowAtRoot = true;
360 Signals.stopOnPonderhit = false;
362 else if (bestValue >= beta)
363 beta = std::min(bestValue + delta, VALUE_INFINITE);
368 delta += 3 * delta / 8;
370 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
373 // Sort the PV lines searched so far and update the GUI
374 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
376 if (PVIdx + 1 == std::min(multiPV, RootMoves.size()) || Time::now() - SearchTime > 3000)
377 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
380 // If skill levels are enabled and time is up, pick a sub-optimal best move
381 if (skill.candidates_size() && skill.time_to_pick(depth))
384 if (Options["Write Search Log"])
386 RootMove& rm = RootMoves[0];
387 if (skill.best != MOVE_NONE)
388 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
390 Log log(Options["Search Log Filename"]);
391 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
395 // Have we found a "mate in x"?
397 && bestValue >= VALUE_MATE_IN_MAX_PLY
398 && VALUE_MATE - bestValue <= 2 * Limits.mate)
401 // Do we have time for the next iteration? Can we stop searching now?
402 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
404 // Take some extra time if the best move has changed
405 if (depth > 4 && multiPV == 1)
406 TimeMgr.pv_instability(BestMoveChanges);
408 // Stop the search if only one legal move is available or all
409 // of the available time has been used.
410 if ( RootMoves.size() == 1
411 || Time::now() - SearchTime > TimeMgr.available_time())
413 // If we are allowed to ponder do not stop the search now but
414 // keep pondering until the GUI sends "ponderhit" or "stop".
416 Signals.stopOnPonderhit = true;
425 // search<>() is the main search function for both PV and non-PV nodes and for
426 // normal and SplitPoint nodes. When called just after a split point the search
427 // is simpler because we have already probed the hash table, done a null move
428 // search, and searched the first move before splitting, so we don't have to
429 // repeat all this work again. We also don't need to store anything to the hash
430 // table here: This is taken care of after we return from the split point.
432 template <NodeType NT, bool SpNode>
433 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
435 const bool RootNode = NT == Root;
436 const bool PvNode = NT == PV || NT == Root;
438 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
439 assert(PvNode || (alpha == beta - 1));
440 assert(depth > DEPTH_ZERO);
442 Move quietsSearched[64];
445 SplitPoint* splitPoint;
447 Move ttMove, move, excludedMove, bestMove;
448 Depth ext, newDepth, predictedDepth;
449 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
450 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
451 bool captureOrPromotion, dangerous, doFullDepthSearch;
452 int moveCount, quietCount;
454 // Step 1. Initialize node
455 Thread* thisThread = pos.this_thread();
456 inCheck = pos.checkers();
460 splitPoint = ss->splitPoint;
461 bestMove = splitPoint->bestMove;
462 bestValue = splitPoint->bestValue;
464 ttMove = excludedMove = MOVE_NONE;
465 ttValue = VALUE_NONE;
467 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
472 moveCount = quietCount = 0;
473 bestValue = -VALUE_INFINITE;
474 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
475 ss->ply = (ss-1)->ply + 1;
476 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
477 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
479 // Used to send selDepth info to GUI
480 if (PvNode && thisThread->maxPly < ss->ply)
481 thisThread->maxPly = ss->ply;
485 // Step 2. Check for aborted search and immediate draw
486 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
487 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
489 // Step 3. Mate distance pruning. Even if we mate at the next move our score
490 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
491 // a shorter mate was found upward in the tree then there is no need to search
492 // because we will never beat the current alpha. Same logic but with reversed
493 // signs applies also in the opposite condition of being mated instead of giving
494 // mate. In this case return a fail-high score.
495 alpha = std::max(mated_in(ss->ply), alpha);
496 beta = std::min(mate_in(ss->ply+1), beta);
501 // Step 4. Transposition table lookup
502 // We don't want the score of a partial search to overwrite a previous full search
503 // TT value, so we use a different position key in case of an excluded move.
504 excludedMove = ss->excludedMove;
505 posKey = excludedMove ? pos.exclusion_key() : pos.key();
506 tte = TT.probe(posKey);
507 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
508 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
510 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
511 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
512 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
513 // we should also update RootMoveList to avoid bogus output.
516 && tte->depth() >= depth
517 && ttValue != VALUE_NONE // Only in case of TT access race
518 && ( PvNode ? tte->bound() == BOUND_EXACT
519 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
520 : (tte->bound() & BOUND_UPPER)))
522 ss->currentMove = ttMove; // Can be MOVE_NONE
524 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
525 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
526 update_stats(pos, ss, ttMove, depth, NULL, 0);
531 // Step 5. Evaluate the position statically and update parent's gain statistics
534 ss->staticEval = eval = VALUE_NONE;
540 // Never assume anything on values stored in TT
541 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
542 eval = ss->staticEval = evaluate(pos);
544 // Can ttValue be used as a better position evaluation?
545 if (ttValue != VALUE_NONE)
546 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
551 eval = ss->staticEval =
552 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
554 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
557 if ( !pos.captured_piece_type()
558 && ss->staticEval != VALUE_NONE
559 && (ss-1)->staticEval != VALUE_NONE
560 && (move = (ss-1)->currentMove) != MOVE_NULL
562 && type_of(move) == NORMAL)
564 Square to = to_sq(move);
565 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
568 // Step 6. Razoring (skipped when in check)
570 && depth < 4 * ONE_PLY
571 && eval + razor_margin(depth) <= alpha
572 && ttMove == MOVE_NONE
573 && !pos.pawn_on_7th(pos.side_to_move()))
575 if ( depth <= ONE_PLY
576 && eval + razor_margin(3 * ONE_PLY) <= alpha)
577 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
579 Value ralpha = alpha - razor_margin(depth);
580 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
585 // Step 7. Futility pruning: child node (skipped when in check)
588 && depth < 7 * ONE_PLY
589 && eval - futility_margin(depth) >= beta
590 && abs(beta) < VALUE_MATE_IN_MAX_PLY
591 && abs(eval) < VALUE_KNOWN_WIN
592 && pos.non_pawn_material(pos.side_to_move()))
593 return eval - futility_margin(depth);
595 // Step 8. Null move search with verification search (is omitted in PV nodes)
598 && depth >= 2 * ONE_PLY
600 && pos.non_pawn_material(pos.side_to_move()))
602 ss->currentMove = MOVE_NULL;
604 assert(eval - beta >= 0);
606 // Null move dynamic reduction based on depth and value
607 Depth R = 3 * ONE_PLY
609 + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
612 pos.do_null_move(st);
613 (ss+1)->skipNullMove = true;
614 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
615 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
616 (ss+1)->skipNullMove = false;
617 pos.undo_null_move();
619 if (nullValue >= beta)
621 // Do not return unproven mate scores
622 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
625 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
628 // Do verification search at high depths
629 ss->skipNullMove = true;
630 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
631 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
632 ss->skipNullMove = false;
639 // Step 9. ProbCut (skipped when in check)
640 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
641 // and a reduced search returns a value much above beta, we can (almost) safely
642 // prune the previous move.
644 && depth >= 5 * ONE_PLY
646 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
648 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
649 Depth rdepth = depth - 4 * ONE_PLY;
651 assert(rdepth >= ONE_PLY);
652 assert((ss-1)->currentMove != MOVE_NONE);
653 assert((ss-1)->currentMove != MOVE_NULL);
655 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
658 while ((move = mp.next_move<false>()) != MOVE_NONE)
659 if (pos.legal(move, ci.pinned))
661 ss->currentMove = move;
662 pos.do_move(move, st, ci, pos.gives_check(move, ci));
663 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
670 // Step 10. Internal iterative deepening (skipped when in check)
671 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
673 && (PvNode || ss->staticEval + 256 >= beta))
675 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
677 ss->skipNullMove = true;
678 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
679 ss->skipNullMove = false;
681 tte = TT.probe(posKey);
682 ttMove = tte ? tte->move() : MOVE_NONE;
685 moves_loop: // When in check and at SpNode search starts from here
687 Square prevMoveSq = to_sq((ss-1)->currentMove);
688 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
689 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
691 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
692 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
693 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
695 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
697 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
698 improving = ss->staticEval >= (ss-2)->staticEval
699 || ss->staticEval == VALUE_NONE
700 ||(ss-2)->staticEval == VALUE_NONE;
702 singularExtensionNode = !RootNode
704 && depth >= 8 * ONE_PLY
705 && abs(beta) < VALUE_KNOWN_WIN
706 && ttMove != MOVE_NONE
707 /* && ttValue != VALUE_NONE Already implicit in the next condition */
708 && abs(ttValue) < VALUE_KNOWN_WIN
709 && !excludedMove // Recursive singular search is not allowed
710 && (tte->bound() & BOUND_LOWER)
711 && tte->depth() >= depth - 3 * ONE_PLY;
713 // Step 11. Loop through moves
714 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
715 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
719 if (move == excludedMove)
722 // At root obey the "searchmoves" option and skip moves not listed in Root
723 // Move List. As a consequence any illegal move is also skipped. In MultiPV
724 // mode we also skip PV moves which have been already searched.
725 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
730 // Shared counter cannot be decremented later if the move turns out to be illegal
731 if (!pos.legal(move, ci.pinned))
734 moveCount = ++splitPoint->moveCount;
735 splitPoint->mutex.unlock();
742 Signals.firstRootMove = (moveCount == 1);
744 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
745 sync_cout << "info depth " << depth / ONE_PLY
746 << " currmove " << move_to_uci(move, pos.is_chess960())
747 << " currmovenumber " << moveCount + PVIdx << sync_endl;
751 captureOrPromotion = pos.capture_or_promotion(move);
753 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
754 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
755 : pos.gives_check(move, ci);
757 dangerous = givesCheck
758 || type_of(move) != NORMAL
759 || pos.advanced_pawn_push(move);
761 // Step 12. Extend checks
762 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
765 // Singular extension search. If all moves but one fail low on a search of
766 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
767 // is singular and should be extended. To verify this we do a reduced search
768 // on all the other moves but the ttMove and if the result is lower than
769 // ttValue minus a margin then we extend the ttMove.
770 if ( singularExtensionNode
773 && pos.legal(move, ci.pinned))
775 Value rBeta = ttValue - int(depth);
776 ss->excludedMove = move;
777 ss->skipNullMove = true;
778 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
779 ss->skipNullMove = false;
780 ss->excludedMove = MOVE_NONE;
786 // Update the current move (this must be done after singular extension search)
787 newDepth = depth - ONE_PLY + ext;
789 // Step 13. Pruning at shallow depth (exclude PV nodes)
791 && !captureOrPromotion
794 /* && move != ttMove Already implicit in the next condition */
795 && bestValue > VALUE_MATED_IN_MAX_PLY)
797 // Move count based pruning
798 if ( depth < 16 * ONE_PLY
799 && moveCount >= FutilityMoveCounts[improving][depth] )
802 splitPoint->mutex.lock();
807 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
809 // Futility pruning: parent node
810 if (predictedDepth < 7 * ONE_PLY)
812 futilityValue = ss->staticEval + futility_margin(predictedDepth)
813 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
815 if (futilityValue <= alpha)
817 bestValue = std::max(bestValue, futilityValue);
821 splitPoint->mutex.lock();
822 if (bestValue > splitPoint->bestValue)
823 splitPoint->bestValue = bestValue;
829 // Prune moves with negative SEE at low depths
830 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
833 splitPoint->mutex.lock();
839 // Check for legality just before making the move
840 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
846 pvMove = PvNode && moveCount == 1;
847 ss->currentMove = move;
848 if (!SpNode && !captureOrPromotion && quietCount < 64)
849 quietsSearched[quietCount++] = move;
851 // Step 14. Make the move
852 pos.do_move(move, st, ci, givesCheck);
854 // Step 15. Reduced depth search (LMR). If the move fails high it will be
855 // re-searched at full depth.
856 if ( depth >= 3 * ONE_PLY
858 && !captureOrPromotion
860 && move != ss->killers[0]
861 && move != ss->killers[1])
863 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
865 if (!PvNode && cutNode)
866 ss->reduction += ONE_PLY;
868 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
869 ss->reduction += ONE_PLY / 2;
871 if (move == countermoves[0] || move == countermoves[1])
872 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
874 // Decrease reduction for moves that escape a capture
876 && type_of(move) == NORMAL
877 && type_of(pos.piece_on(to_sq(move))) != PAWN
878 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
879 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
881 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
883 alpha = splitPoint->alpha;
885 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
887 // Re-search at intermediate depth if reduction is very high
888 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
890 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
891 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
894 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
895 ss->reduction = DEPTH_ZERO;
898 doFullDepthSearch = !pvMove;
900 // Step 16. Full depth search, when LMR is skipped or fails high
901 if (doFullDepthSearch)
904 alpha = splitPoint->alpha;
906 value = newDepth < ONE_PLY ?
907 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
908 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
909 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
912 // For PV nodes only, do a full PV search on the first move or after a fail
913 // high (in the latter case search only if value < beta), otherwise let the
914 // parent node fail low with value <= alpha and to try another move.
915 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
916 value = newDepth < ONE_PLY ?
917 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
918 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
919 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
920 // Step 17. Undo move
923 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
925 // Step 18. Check for new best move
928 splitPoint->mutex.lock();
929 bestValue = splitPoint->bestValue;
930 alpha = splitPoint->alpha;
933 // Finished searching the move. If a stop or a cutoff occurred, the return
934 // value of the search cannot be trusted, and we return immediately without
935 // updating best move, PV and TT.
936 if (Signals.stop || thisThread->cutoff_occurred())
941 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
943 // PV move or new best move ?
944 if (pvMove || value > alpha)
947 rm.extract_pv_from_tt(pos);
949 // We record how often the best move has been changed in each
950 // iteration. This information is used for time management: When
951 // the best move changes frequently, we allocate some more time.
956 // All other moves but the PV are set to the lowest value: this is
957 // not a problem when sorting because the sort is stable and the
958 // move position in the list is preserved - just the PV is pushed up.
959 rm.score = -VALUE_INFINITE;
962 if (value > bestValue)
964 bestValue = SpNode ? splitPoint->bestValue = value : value;
968 bestMove = SpNode ? splitPoint->bestMove = move : move;
970 if (PvNode && value < beta) // Update alpha! Always alpha < beta
971 alpha = SpNode ? splitPoint->alpha = value : value;
974 assert(value >= beta); // Fail high
977 splitPoint->cutoff = true;
984 // Step 19. Check for splitting the search
986 && Threads.size() >= 2
987 && depth >= Threads.minimumSplitDepth
988 && ( !thisThread->activeSplitPoint
989 || !thisThread->activeSplitPoint->allSlavesSearching)
990 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
992 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
994 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
995 depth, moveCount, &mp, NT, cutNode);
997 if (Signals.stop || thisThread->cutoff_occurred())
1000 if (bestValue >= beta)
1008 // Following condition would detect a stop or a cutoff set only after move
1009 // loop has been completed. But in this case bestValue is valid because we
1010 // have fully searched our subtree, and we can anyhow save the result in TT.
1012 if (Signals.stop || thisThread->cutoff_occurred())
1016 // Step 20. Check for mate and stalemate
1017 // All legal moves have been searched and if there are no legal moves, it
1018 // must be mate or stalemate. If we are in a singular extension search then
1019 // return a fail low score.
1021 bestValue = excludedMove ? alpha
1022 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1024 // Quiet best move: update killers, history, countermoves and followupmoves
1025 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1026 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1028 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1029 bestValue >= beta ? BOUND_LOWER :
1030 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1031 depth, bestMove, ss->staticEval);
1033 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1039 // qsearch() is the quiescence search function, which is called by the main
1040 // search function when the remaining depth is zero (or, to be more precise,
1041 // less than ONE_PLY).
1043 template <NodeType NT, bool InCheck>
1044 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1046 const bool PvNode = NT == PV;
1048 assert(NT == PV || NT == NonPV);
1049 assert(InCheck == !!pos.checkers());
1050 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1051 assert(PvNode || (alpha == beta - 1));
1052 assert(depth <= DEPTH_ZERO);
1057 Move ttMove, move, bestMove;
1058 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1059 bool givesCheck, evasionPrunable;
1062 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1066 ss->currentMove = bestMove = MOVE_NONE;
1067 ss->ply = (ss-1)->ply + 1;
1069 // Check for an instant draw or if the maximum ply has been reached
1070 if (pos.is_draw() || ss->ply > MAX_PLY)
1071 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1073 // Decide whether or not to include checks: this fixes also the type of
1074 // TT entry depth that we are going to use. Note that in qsearch we use
1075 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1076 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1077 : DEPTH_QS_NO_CHECKS;
1079 // Transposition table lookup
1081 tte = TT.probe(posKey);
1082 ttMove = tte ? tte->move() : MOVE_NONE;
1083 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1086 && tte->depth() >= ttDepth
1087 && ttValue != VALUE_NONE // Only in case of TT access race
1088 && ( PvNode ? tte->bound() == BOUND_EXACT
1089 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1090 : (tte->bound() & BOUND_UPPER)))
1092 ss->currentMove = ttMove; // Can be MOVE_NONE
1096 // Evaluate the position statically
1099 ss->staticEval = VALUE_NONE;
1100 bestValue = futilityBase = -VALUE_INFINITE;
1106 // Never assume anything on values stored in TT
1107 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1108 ss->staticEval = bestValue = evaluate(pos);
1110 // Can ttValue be used as a better position evaluation?
1111 if (ttValue != VALUE_NONE)
1112 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1113 bestValue = ttValue;
1116 ss->staticEval = bestValue =
1117 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1119 // Stand pat. Return immediately if static value is at least beta
1120 if (bestValue >= beta)
1123 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1124 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1129 if (PvNode && bestValue > alpha)
1132 futilityBase = bestValue + 128;
1135 // Initialize a MovePicker object for the current position, and prepare
1136 // to search the moves. Because the depth is <= 0 here, only captures,
1137 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1139 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1142 // Loop through the moves until no moves remain or a beta cutoff occurs
1143 while ((move = mp.next_move<false>()) != MOVE_NONE)
1145 assert(is_ok(move));
1147 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1148 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1149 : pos.gives_check(move, ci);
1156 && futilityBase > -VALUE_KNOWN_WIN
1157 && !pos.advanced_pawn_push(move))
1159 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1161 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1163 if (futilityValue < beta)
1165 bestValue = std::max(bestValue, futilityValue);
1169 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1171 bestValue = std::max(bestValue, futilityBase);
1176 // Detect non-capture evasions that are candidates to be pruned
1177 evasionPrunable = InCheck
1178 && bestValue > VALUE_MATED_IN_MAX_PLY
1179 && !pos.capture(move)
1180 && !pos.can_castle(pos.side_to_move());
1182 // Don't search moves with negative SEE values
1184 && (!InCheck || evasionPrunable)
1186 && type_of(move) != PROMOTION
1187 && pos.see_sign(move) < VALUE_ZERO)
1190 // Check for legality just before making the move
1191 if (!pos.legal(move, ci.pinned))
1194 ss->currentMove = move;
1196 // Make and search the move
1197 pos.do_move(move, st, ci, givesCheck);
1198 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1199 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1200 pos.undo_move(move);
1202 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1204 // Check for new best move
1205 if (value > bestValue)
1211 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1218 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1219 ttDepth, move, ss->staticEval);
1227 // All legal moves have been searched. A special case: If we're in check
1228 // and no legal moves were found, it is checkmate.
1229 if (InCheck && bestValue == -VALUE_INFINITE)
1230 return mated_in(ss->ply); // Plies to mate from the root
1232 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1233 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1234 ttDepth, bestMove, ss->staticEval);
1236 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1242 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1243 // "plies to mate from the current position". Non-mate scores are unchanged.
1244 // The function is called before storing a value in the transposition table.
1246 Value value_to_tt(Value v, int ply) {
1248 assert(v != VALUE_NONE);
1250 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1251 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1255 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1256 // from the transposition table (which refers to the plies to mate/be mated
1257 // from current position) to "plies to mate/be mated from the root".
1259 Value value_from_tt(Value v, int ply) {
1261 return v == VALUE_NONE ? VALUE_NONE
1262 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1263 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1267 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1270 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1272 if (ss->killers[0] != move)
1274 ss->killers[1] = ss->killers[0];
1275 ss->killers[0] = move;
1278 // Increase history value of the cut-off move and decrease all the other
1279 // played quiet moves.
1280 Value bonus = Value(int(depth) * int(depth));
1281 History.update(pos.moved_piece(move), to_sq(move), bonus);
1282 for (int i = 0; i < quietsCnt; ++i)
1285 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1288 if (is_ok((ss-1)->currentMove))
1290 Square prevMoveSq = to_sq((ss-1)->currentMove);
1291 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1294 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1296 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1297 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1302 // When playing with a strength handicap, choose best move among the first 'candidates'
1303 // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1305 Move Skill::pick_move() {
1309 // PRNG sequence should be not deterministic
1310 for (int i = Time::now() % 50; i > 0; --i)
1311 rk.rand<unsigned>();
1313 // RootMoves are already sorted by score in descending order
1314 int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
1315 int weakness = 120 - 2 * level;
1316 int max_s = -VALUE_INFINITE;
1319 // Choose best move. For each move score we add two terms both dependent on
1320 // weakness. One deterministic and bigger for weaker moves, and one random,
1321 // then we choose the move with the resulting highest score.
1322 for (size_t i = 0; i < candidates; ++i)
1324 int s = RootMoves[i].score;
1326 // Don't allow crazy blunders even at very low skills
1327 if (i > 0 && RootMoves[i - 1].score > s + 2 * PawnValueMg)
1330 // This is our magic formula
1331 s += ( weakness * int(RootMoves[0].score - s)
1332 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1337 best = RootMoves[i].pv[0];
1344 // uci_pv() formats PV information according to the UCI protocol. UCI
1345 // requires that all (if any) unsearched PV lines are sent using a previous
1348 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1350 std::stringstream ss;
1351 Time::point elapsed = Time::now() - SearchTime + 1;
1352 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1355 for (size_t i = 0; i < Threads.size(); ++i)
1356 if (Threads[i]->maxPly > selDepth)
1357 selDepth = Threads[i]->maxPly;
1359 for (size_t i = 0; i < uciPVSize; ++i)
1361 bool updated = (i <= PVIdx);
1363 if (depth == 1 && !updated)
1366 int d = updated ? depth : depth - 1;
1367 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1369 if (ss.rdbuf()->in_avail()) // Not at first line
1372 ss << "info depth " << d
1373 << " seldepth " << selDepth
1374 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1375 << " nodes " << pos.nodes_searched()
1376 << " nps " << pos.nodes_searched() * 1000 / elapsed
1377 << " time " << elapsed
1378 << " multipv " << i + 1
1381 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1382 ss << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1391 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1392 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1393 /// ensure that we have a ponder move even when we fail high at root. This
1394 /// results in a long PV to print that is important for position analysis.
1396 void RootMove::extract_pv_from_tt(Position& pos) {
1398 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1400 int ply = 1; // At root ply is 1...
1401 Move m = pv[0]; // ...instead pv[] array starts from 0
1402 Value expectedScore = score;
1409 assert(MoveList<LEGAL>(pos).contains(pv[ply - 1]));
1411 pos.do_move(pv[ply++ - 1], *st++);
1412 tte = TT.probe(pos.key());
1413 expectedScore = -expectedScore;
1416 && expectedScore == value_from_tt(tte->value(), ply)
1417 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1418 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1420 && (!pos.is_draw() || ply <= 2));
1422 pv.push_back(MOVE_NONE); // Must be zero-terminating
1424 while (--ply) pos.undo_move(pv[ply - 1]);
1428 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1429 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1430 /// first, even if the old TT entries have been overwritten.
1432 void RootMove::insert_pv_in_tt(Position& pos) {
1434 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1436 int idx = 0; // Ply starts from 1, we need to start from 0
1439 tte = TT.probe(pos.key());
1441 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1442 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1444 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1446 pos.do_move(pv[idx++], *st++);
1448 } while (pv[idx] != MOVE_NONE);
1450 while (idx) pos.undo_move(pv[--idx]);
1454 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1456 void Thread::idle_loop() {
1458 // Pointer 'this_sp' is not null only if we are called from split(), and not
1459 // at the thread creation. This means we are the split point's master.
1460 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1462 assert(!this_sp || (this_sp->masterThread == this && searching));
1466 // If we are not searching, wait for a condition to be signaled instead of
1467 // wasting CPU time polling for work.
1468 while (!searching || exit)
1476 // Grab the lock to avoid races with Thread::notify_one()
1479 // If we are master and all slaves have finished then exit idle_loop
1480 if (this_sp && this_sp->slavesMask.none())
1486 // Do sleep after retesting sleep conditions under lock protection. In
1487 // particular we need to avoid a deadlock in case a master thread has,
1488 // in the meanwhile, allocated us and sent the notify_one() call before
1489 // we had the chance to grab the lock.
1490 if (!searching && !exit)
1491 sleepCondition.wait(mutex);
1496 // If this thread has been assigned work, launch a search
1501 Threads.mutex.lock();
1504 assert(activeSplitPoint);
1505 SplitPoint* sp = activeSplitPoint;
1507 Threads.mutex.unlock();
1509 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1510 Position pos(*sp->pos, this);
1512 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1513 ss->splitPoint = sp;
1517 assert(activePosition == NULL);
1519 activePosition = &pos;
1521 if (sp->nodeType == NonPV)
1522 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1524 else if (sp->nodeType == PV)
1525 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1527 else if (sp->nodeType == Root)
1528 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1536 activePosition = NULL;
1537 sp->slavesMask.reset(idx);
1538 sp->allSlavesSearching = false;
1539 sp->nodes += pos.nodes_searched();
1541 // Wake up the master thread so to allow it to return from the idle
1542 // loop in case we are the last slave of the split point.
1543 if ( this != sp->masterThread
1544 && sp->slavesMask.none())
1546 assert(!sp->masterThread->searching);
1547 sp->masterThread->notify_one();
1550 // After releasing the lock we can't access any SplitPoint related data
1551 // in a safe way because it could have been released under our feet by
1555 // Try to late join to another split point if none of its slaves has
1556 // already finished.
1557 if (Threads.size() > 2)
1558 for (size_t i = 0; i < Threads.size(); ++i)
1560 const int size = Threads[i]->splitPointsSize; // Local copy
1561 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1564 && sp->allSlavesSearching
1565 && available_to(Threads[i]))
1567 // Recheck the conditions under lock protection
1568 Threads.mutex.lock();
1571 if ( sp->allSlavesSearching
1572 && available_to(Threads[i]))
1574 sp->slavesMask.set(idx);
1575 activeSplitPoint = sp;
1580 Threads.mutex.unlock();
1582 break; // Just a single attempt
1587 // If this thread is the master of a split point and all slaves have finished
1588 // their work at this split point, return from the idle loop.
1589 if (this_sp && this_sp->slavesMask.none())
1591 this_sp->mutex.lock();
1592 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1593 this_sp->mutex.unlock();
1601 /// check_time() is called by the timer thread when the timer triggers. It is
1602 /// used to print debug info and, more importantly, to detect when we are out of
1603 /// available time and thus stop the search.
1607 static Time::point lastInfoTime = Time::now();
1608 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1610 if (Time::now() - lastInfoTime >= 1000)
1612 lastInfoTime = Time::now();
1621 Threads.mutex.lock();
1623 nodes = RootPos.nodes_searched();
1625 // Loop across all split points and sum accumulated SplitPoint nodes plus
1626 // all the currently active positions nodes.
1627 for (size_t i = 0; i < Threads.size(); ++i)
1628 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1630 SplitPoint& sp = Threads[i]->splitPoints[j];
1636 for (size_t idx = 0; idx < Threads.size(); ++idx)
1637 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1638 nodes += Threads[idx]->activePosition->nodes_searched();
1643 Threads.mutex.unlock();
1646 Time::point elapsed = Time::now() - SearchTime;
1647 bool stillAtFirstMove = Signals.firstRootMove
1648 && !Signals.failedLowAtRoot
1649 && elapsed > TimeMgr.available_time() * 75 / 100;
1651 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1652 || stillAtFirstMove;
1654 if ( (Limits.use_time_management() && noMoreTime)
1655 || (Limits.movetime && elapsed >= Limits.movetime)
1656 || (Limits.nodes && nodes >= Limits.nodes))
1657 Signals.stop = true;