2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime, IterationTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
86 CountermovesStats Countermoves;
88 template <NodeType NT>
89 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
91 template <NodeType NT, bool InCheck>
92 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
94 void id_loop(Position& pos);
95 Value value_to_tt(Value v, int ply);
96 Value value_from_tt(Value v, int ply);
97 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
98 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
101 Skill(int l) : level(l), best(MOVE_NONE) {}
103 if (enabled()) // Swap best PV line with the sub-optimal one
104 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
105 RootMoves.end(), best ? best : pick_move()));
108 bool enabled() const { return level < 20; }
109 bool time_to_pick(int depth) const { return depth == 1 + level; }
119 /// Search::init() is called during startup to initialize various lookup tables
121 void Search::init() {
123 int d; // depth (ONE_PLY == 2)
124 int hd; // half depth (ONE_PLY == 1)
127 // Init reductions array
128 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
130 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
131 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
132 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
133 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
135 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
136 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
138 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
139 Reductions[0][0][hd][mc] += ONE_PLY;
141 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
142 Reductions[0][0][hd][mc] += ONE_PLY / 2;
145 // Init futility move count array
146 for (d = 0; d < 32; ++d)
148 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
149 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
154 /// Search::perft() is our utility to verify move generation. All the leaf nodes
155 /// up to the given depth are generated and counted and the sum returned.
157 static size_t perft(Position& pos, Depth depth) {
162 const bool leaf = depth == 2 * ONE_PLY;
164 for (MoveList<LEGAL> it(pos); *it; ++it)
166 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
167 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
173 size_t Search::perft(Position& pos, Depth depth) {
174 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
177 /// Search::think() is the external interface to Stockfish's search, and is
178 /// called by the main thread when the program receives the UCI 'go' command. It
179 /// searches from RootPos and at the end prints the "bestmove" to output.
181 void Search::think() {
183 static PolyglotBook book; // Defined static to initialize the PRNG only once
185 RootColor = RootPos.side_to_move();
186 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
188 if (RootMoves.empty())
190 RootMoves.push_back(MOVE_NONE);
191 sync_cout << "info depth 0 score "
192 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
198 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
200 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
202 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
204 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
209 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
211 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
212 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
213 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
214 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
217 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
219 if (Options["Write Search Log"])
221 Log log(Options["Search Log Filename"]);
222 log << "\nSearching: " << RootPos.fen()
223 << "\ninfinite: " << Limits.infinite
224 << " ponder: " << Limits.ponder
225 << " time: " << Limits.time[RootColor]
226 << " increment: " << Limits.inc[RootColor]
227 << " moves to go: " << Limits.movestogo
231 // Reset the threads, still sleeping: will wake up at split time
232 for (size_t i = 0; i < Threads.size(); ++i)
233 Threads[i]->maxPly = 0;
235 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
236 Threads.timer->run = true;
237 Threads.timer->notify_one(); // Wake up the recurring timer
239 id_loop(RootPos); // Let's start searching !
241 Threads.timer->run = false; // Stop the timer
242 Threads.sleepWhileIdle = true; // Send idle threads to sleep
244 if (Options["Write Search Log"])
246 Time::point elapsed = Time::now() - SearchTime + 1;
248 Log log(Options["Search Log Filename"]);
249 log << "Nodes: " << RootPos.nodes_searched()
250 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
251 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
254 RootPos.do_move(RootMoves[0].pv[0], st);
255 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
256 RootPos.undo_move(RootMoves[0].pv[0]);
261 // When search is stopped this info is not printed
262 sync_cout << "info nodes " << RootPos.nodes_searched()
263 << " time " << Time::now() - SearchTime + 1 << sync_endl;
265 // When we reach the maximum depth, we can arrive here without a raise of
266 // Signals.stop. However, if we are pondering or in an infinite search,
267 // the UCI protocol states that we shouldn't print the best move before the
268 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
269 // until the GUI sends one of those commands (which also raises Signals.stop).
270 if (!Signals.stop && (Limits.ponder || Limits.infinite))
272 Signals.stopOnPonderhit = true;
273 RootPos.this_thread()->wait_for(Signals.stop);
276 // Best move could be MOVE_NONE when searching on a stalemate position
277 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
278 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
285 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
286 // with increasing depth until the allocated thinking time has been consumed,
287 // user stops the search, or the maximum search depth is reached.
289 void id_loop(Position& pos) {
291 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
293 Value bestValue, alpha, beta, delta;
295 std::memset(ss-2, 0, 5 * sizeof(Stack));
296 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
300 bestValue = delta = alpha = -VALUE_INFINITE;
301 beta = VALUE_INFINITE;
306 Countermoves.clear();
308 PVSize = Options["MultiPV"];
309 Skill skill(Options["Skill Level"]);
311 // Do we have to play with skill handicap? In this case enable MultiPV search
312 // that we will use behind the scenes to retrieve a set of possible moves.
313 if (skill.enabled() && PVSize < 4)
316 PVSize = std::min(PVSize, RootMoves.size());
318 // Iterative deepening loop until requested to stop or target depth reached
319 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
321 // Age out PV variability metric
322 BestMoveChanges *= 0.8;
324 // Save the last iteration's scores before first PV line is searched and
325 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
326 for (size_t i = 0; i < RootMoves.size(); ++i)
327 RootMoves[i].prevScore = RootMoves[i].score;
329 // MultiPV loop. We perform a full root search for each PV line
330 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
332 // Reset aspiration window starting size
336 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
337 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
340 // Start with a small aspiration window and, in the case of a fail
341 // high/low, re-search with a bigger window until we're not failing
345 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
347 // Bring the best move to the front. It is critical that sorting
348 // is done with a stable algorithm because all the values but the
349 // first and eventually the new best one are set to -VALUE_INFINITE
350 // and we want to keep the same order for all the moves except the
351 // new PV that goes to the front. Note that in case of MultiPV
352 // search the already searched PV lines are preserved.
353 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
355 // Write PV back to transposition table in case the relevant
356 // entries have been overwritten during the search.
357 for (size_t i = 0; i <= PVIdx; ++i)
358 RootMoves[i].insert_pv_in_tt(pos);
360 // If search has been stopped break immediately. Sorting and
361 // writing PV back to TT is safe because RootMoves is still
362 // valid, although it refers to previous iteration.
366 // When failing high/low give some update (without cluttering
367 // the UI) before a re-search.
368 if ( (bestValue <= alpha || bestValue >= beta)
369 && Time::now() - SearchTime > 3000)
370 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
372 // In case of failing low/high increase aspiration window and
373 // re-search, otherwise exit the loop.
374 if (bestValue <= alpha)
376 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
378 Signals.failedLowAtRoot = true;
379 Signals.stopOnPonderhit = false;
381 else if (bestValue >= beta)
382 beta = std::min(bestValue + delta, VALUE_INFINITE);
389 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
392 // Sort the PV lines searched so far and update the GUI
393 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
395 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
396 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
399 IterationTime = Time::now() - SearchTime;
401 // If skill levels are enabled and time is up, pick a sub-optimal best move
402 if (skill.enabled() && skill.time_to_pick(depth))
405 if (Options["Write Search Log"])
407 RootMove& rm = RootMoves[0];
408 if (skill.best != MOVE_NONE)
409 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
411 Log log(Options["Search Log Filename"]);
412 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
416 // Have we found a "mate in x"?
418 && bestValue >= VALUE_MATE_IN_MAX_PLY
419 && VALUE_MATE - bestValue <= 2 * Limits.mate)
422 // Do we have time for the next iteration? Can we stop searching now?
423 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
425 bool stop = false; // Local variable, not the volatile Signals.stop
427 // Take some extra time if the best move has changed
428 if (depth > 4 && depth < 50 && PVSize == 1)
429 TimeMgr.pv_instability(BestMoveChanges);
431 // Stop the search if most of the available time has been used. We
432 // probably don't have enough time to search the first move at the
433 // next iteration anyway.
434 if (IterationTime > (TimeMgr.available_time() * 62) / 100)
437 // Stop the search early if one move seems to be much better than others
439 && BestMoveChanges <= DBL_EPSILON
442 && bestValue > VALUE_MATED_IN_MAX_PLY
443 && ( RootMoves.size() == 1
444 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
446 Value rBeta = bestValue - 2 * PawnValueMg;
447 ss->excludedMove = RootMoves[0].pv[0];
448 ss->skipNullMove = true;
449 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
450 ss->skipNullMove = false;
451 ss->excludedMove = MOVE_NONE;
459 // If we are allowed to ponder do not stop the search now but
460 // keep pondering until the GUI sends "ponderhit" or "stop".
462 Signals.stopOnPonderhit = true;
471 // search<>() is the main search function for both PV and non-PV nodes and for
472 // normal and SplitPoint nodes. When called just after a split point the search
473 // is simpler because we have already probed the hash table, done a null move
474 // search, and searched the first move before splitting, so we don't have to
475 // repeat all this work again. We also don't need to store anything to the hash
476 // table here: This is taken care of after we return from the split point.
478 template <NodeType NT>
479 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
481 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
482 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
483 const bool RootNode = (NT == Root || NT == SplitPointRoot);
485 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
486 assert(PvNode || (alpha == beta - 1));
487 assert(depth > DEPTH_ZERO);
489 Move quietsSearched[64];
492 SplitPoint* splitPoint;
494 Move ttMove, move, excludedMove, bestMove;
495 Depth ext, newDepth, predictedDepth;
496 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
497 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
498 bool captureOrPromotion, dangerous, doFullDepthSearch;
499 int moveCount, quietCount;
501 // Step 1. Initialize node
502 Thread* thisThread = pos.this_thread();
503 inCheck = pos.checkers();
507 splitPoint = ss->splitPoint;
508 bestMove = splitPoint->bestMove;
509 bestValue = splitPoint->bestValue;
511 ttMove = excludedMove = MOVE_NONE;
512 ttValue = VALUE_NONE;
514 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
519 moveCount = quietCount = 0;
520 bestValue = -VALUE_INFINITE;
521 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
522 ss->ply = (ss-1)->ply + 1;
523 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
524 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
526 // Used to send selDepth info to GUI
527 if (PvNode && thisThread->maxPly < ss->ply)
528 thisThread->maxPly = ss->ply;
532 // Step 2. Check for aborted search and immediate draw
533 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
534 return DrawValue[pos.side_to_move()];
536 // Step 3. Mate distance pruning. Even if we mate at the next move our score
537 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
538 // a shorter mate was found upward in the tree then there is no need to search
539 // because we will never beat the current alpha. Same logic but with reversed
540 // signs applies also in the opposite condition of being mated instead of giving
541 // mate. In this case return a fail-high score.
542 alpha = std::max(mated_in(ss->ply), alpha);
543 beta = std::min(mate_in(ss->ply+1), beta);
548 // Step 4. Transposition table lookup
549 // We don't want the score of a partial search to overwrite a previous full search
550 // TT value, so we use a different position key in case of an excluded move.
551 excludedMove = ss->excludedMove;
552 posKey = excludedMove ? pos.exclusion_key() : pos.key();
553 tte = TT.probe(posKey);
554 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
555 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
557 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
558 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
559 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
560 // we should also update RootMoveList to avoid bogus output.
563 && tte->depth() >= depth
564 && ttValue != VALUE_NONE // Only in case of TT access race
565 && ( PvNode ? tte->bound() == BOUND_EXACT
566 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
567 : (tte->bound() & BOUND_UPPER)))
570 ss->currentMove = ttMove; // Can be MOVE_NONE
572 // If ttMove is quiet, update killers, history, and counter move on TT hit
573 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
574 update_stats(pos, ss, ttMove, depth, NULL, 0);
579 // Step 5. Evaluate the position statically and update parent's gain statistics
582 ss->staticEval = eval = VALUE_NONE;
588 // Never assume anything on values stored in TT
589 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
590 eval = ss->staticEval = evaluate(pos);
592 // Can ttValue be used as a better position evaluation?
593 if (ttValue != VALUE_NONE)
594 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
599 eval = ss->staticEval = evaluate(pos);
600 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
603 if ( !pos.captured_piece_type()
604 && ss->staticEval != VALUE_NONE
605 && (ss-1)->staticEval != VALUE_NONE
606 && (move = (ss-1)->currentMove) != MOVE_NULL
607 && type_of(move) == NORMAL)
609 Square to = to_sq(move);
610 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
613 // Step 6. Razoring (skipped when in check)
615 && depth < 4 * ONE_PLY
616 && eval + razor_margin(depth) < beta
617 && ttMove == MOVE_NONE
618 && abs(beta) < VALUE_MATE_IN_MAX_PLY
619 && !pos.pawn_on_7th(pos.side_to_move()))
621 Value rbeta = beta - razor_margin(depth);
622 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
624 // Logically we should return (v + razor_margin(depth)), but
625 // surprisingly this performed slightly weaker in tests.
629 // Step 7. Futility pruning: child node (skipped when in check)
632 && depth < 7 * ONE_PLY
633 && eval - futility_margin(depth) >= beta
634 && abs(beta) < VALUE_MATE_IN_MAX_PLY
635 && abs(eval) < VALUE_KNOWN_WIN
636 && pos.non_pawn_material(pos.side_to_move()))
637 return eval - futility_margin(depth);
639 // Step 8. Null move search with verification search (is omitted in PV nodes)
642 && depth >= 2 * ONE_PLY
644 && abs(beta) < VALUE_MATE_IN_MAX_PLY
645 && pos.non_pawn_material(pos.side_to_move()))
647 ss->currentMove = MOVE_NULL;
649 // Null move dynamic reduction based on depth
650 Depth R = 3 * ONE_PLY + depth / 4;
652 // Null move dynamic reduction based on value
653 if (eval - PawnValueMg > beta)
656 pos.do_null_move(st);
657 (ss+1)->skipNullMove = true;
658 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
659 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
660 (ss+1)->skipNullMove = false;
661 pos.undo_null_move();
663 if (nullValue >= beta)
665 // Do not return unproven mate scores
666 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
669 if (depth < 12 * ONE_PLY)
672 // Do verification search at high depths
673 ss->skipNullMove = true;
674 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
675 ss->skipNullMove = false;
682 // Step 9. ProbCut (skipped when in check)
683 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
684 // and a reduced search returns a value much above beta, we can (almost) safely
685 // prune the previous move.
687 && depth >= 5 * ONE_PLY
689 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
691 Value rbeta = beta + 200;
692 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
694 assert(rdepth >= ONE_PLY);
695 assert((ss-1)->currentMove != MOVE_NONE);
696 assert((ss-1)->currentMove != MOVE_NULL);
698 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
701 while ((move = mp.next_move<false>()) != MOVE_NONE)
702 if (pos.legal(move, ci.pinned))
704 ss->currentMove = move;
705 pos.do_move(move, st, ci, pos.gives_check(move, ci));
706 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
713 // Step 10. Internal iterative deepening (skipped when in check)
714 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
715 && ttMove == MOVE_NONE
716 && (PvNode || ss->staticEval + Value(256) >= beta))
718 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
720 ss->skipNullMove = true;
721 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
722 ss->skipNullMove = false;
724 tte = TT.probe(posKey);
725 ttMove = tte ? tte->move() : MOVE_NONE;
728 moves_loop: // When in check and at SpNode search starts from here
730 Square prevMoveSq = to_sq((ss-1)->currentMove);
731 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
732 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
734 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
736 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
737 improving = ss->staticEval >= (ss-2)->staticEval
738 || ss->staticEval == VALUE_NONE
739 ||(ss-2)->staticEval == VALUE_NONE;
741 singularExtensionNode = !RootNode
743 && depth >= 8 * ONE_PLY
744 && ttMove != MOVE_NONE
745 && !excludedMove // Recursive singular search is not allowed
746 && (tte->bound() & BOUND_LOWER)
747 && tte->depth() >= depth - 3 * ONE_PLY;
749 // Step 11. Loop through moves
750 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
751 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
755 if (move == excludedMove)
758 // At root obey the "searchmoves" option and skip moves not listed in Root
759 // Move List. As a consequence any illegal move is also skipped. In MultiPV
760 // mode we also skip PV moves which have been already searched.
761 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
766 // Shared counter cannot be decremented later if the move turns out to be illegal
767 if (!pos.legal(move, ci.pinned))
770 moveCount = ++splitPoint->moveCount;
771 splitPoint->mutex.unlock();
778 Signals.firstRootMove = (moveCount == 1);
780 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
781 sync_cout << "info depth " << depth / ONE_PLY
782 << " currmove " << move_to_uci(move, pos.is_chess960())
783 << " currmovenumber " << moveCount + PVIdx << sync_endl;
787 captureOrPromotion = pos.capture_or_promotion(move);
788 givesCheck = pos.gives_check(move, ci);
789 dangerous = givesCheck
790 || type_of(move) != NORMAL
791 || pos.advanced_pawn_push(move);
793 // Step 12. Extend checks
794 if (givesCheck && pos.see_sign(move) >= 0)
797 // Singular extension search. If all moves but one fail low on a search of
798 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
799 // is singular and should be extended. To verify this we do a reduced search
800 // on all the other moves but the ttMove and if the result is lower than
801 // ttValue minus a margin then we extend the ttMove.
802 if ( singularExtensionNode
805 && pos.legal(move, ci.pinned)
806 && abs(ttValue) < VALUE_KNOWN_WIN)
808 assert(ttValue != VALUE_NONE);
810 Value rBeta = ttValue - int(depth);
811 ss->excludedMove = move;
812 ss->skipNullMove = true;
813 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
814 ss->skipNullMove = false;
815 ss->excludedMove = MOVE_NONE;
821 // Update the current move (this must be done after singular extension search)
822 newDepth = depth - ONE_PLY + ext;
824 // Step 13. Pruning at shallow depth (exclude PV nodes)
826 && !captureOrPromotion
829 /* && move != ttMove Already implicit in the next condition */
830 && bestValue > VALUE_MATED_IN_MAX_PLY)
832 // Move count based pruning
833 if ( depth < 16 * ONE_PLY
834 && moveCount >= FutilityMoveCounts[improving][depth] )
837 splitPoint->mutex.lock();
842 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
844 // Futility pruning: parent node
845 if (predictedDepth < 7 * ONE_PLY)
847 futilityValue = ss->staticEval + futility_margin(predictedDepth)
848 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
850 if (futilityValue <= alpha)
852 bestValue = std::max(bestValue, futilityValue);
856 splitPoint->mutex.lock();
857 if (bestValue > splitPoint->bestValue)
858 splitPoint->bestValue = bestValue;
864 // Prune moves with negative SEE at low depths
865 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
868 splitPoint->mutex.lock();
874 // Check for legality just before making the move
875 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
881 pvMove = PvNode && moveCount == 1;
882 ss->currentMove = move;
883 if (!SpNode && !captureOrPromotion && quietCount < 64)
884 quietsSearched[quietCount++] = move;
886 // Step 14. Make the move
887 pos.do_move(move, st, ci, givesCheck);
889 // Step 15. Reduced depth search (LMR). If the move fails high it will be
890 // re-searched at full depth.
891 if ( depth >= 3 * ONE_PLY
893 && !captureOrPromotion
895 && move != ss->killers[0]
896 && move != ss->killers[1])
898 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
900 if (!PvNode && cutNode)
901 ss->reduction += ONE_PLY;
903 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
904 ss->reduction += ONE_PLY / 2;
906 if (move == countermoves[0] || move == countermoves[1])
907 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
909 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
911 alpha = splitPoint->alpha;
913 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
915 // Research at intermediate depth if reduction is very high
916 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
918 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
919 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
922 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
923 ss->reduction = DEPTH_ZERO;
926 doFullDepthSearch = !pvMove;
928 // Step 16. Full depth search, when LMR is skipped or fails high
929 if (doFullDepthSearch)
932 alpha = splitPoint->alpha;
934 value = newDepth < ONE_PLY ?
935 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
936 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
937 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
940 // For PV nodes only, do a full PV search on the first move or after a fail
941 // high (in the latter case search only if value < beta), otherwise let the
942 // parent node fail low with value <= alpha and to try another move.
943 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
944 value = newDepth < ONE_PLY ?
945 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
946 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
947 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
948 // Step 17. Undo move
951 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
953 // Step 18. Check for new best move
956 splitPoint->mutex.lock();
957 bestValue = splitPoint->bestValue;
958 alpha = splitPoint->alpha;
961 // Finished searching the move. If Signals.stop is true, the search
962 // was aborted because the user interrupted the search or because we
963 // ran out of time. In this case, the return value of the search cannot
964 // be trusted, and we don't update the best move and/or PV.
965 if (Signals.stop || thisThread->cutoff_occurred())
966 return value; // To avoid returning VALUE_INFINITE
970 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
972 // PV move or new best move ?
973 if (pvMove || value > alpha)
976 rm.extract_pv_from_tt(pos);
978 // We record how often the best move has been changed in each
979 // iteration. This information is used for time management: When
980 // the best move changes frequently, we allocate some more time.
985 // All other moves but the PV are set to the lowest value: this is
986 // not a problem when sorting because the sort is stable and the
987 // move position in the list is preserved - just the PV is pushed up.
988 rm.score = -VALUE_INFINITE;
991 if (value > bestValue)
993 bestValue = SpNode ? splitPoint->bestValue = value : value;
997 bestMove = SpNode ? splitPoint->bestMove = move : move;
999 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1000 alpha = SpNode ? splitPoint->alpha = value : value;
1003 assert(value >= beta); // Fail high
1006 splitPoint->cutoff = true;
1013 // Step 19. Check for splitting the search
1015 && depth >= Threads.minimumSplitDepth
1016 && Threads.available_slave(thisThread)
1017 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1019 assert(bestValue < beta);
1021 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1022 depth, moveCount, &mp, NT, cutNode);
1023 if (bestValue >= beta)
1031 // Step 20. Check for mate and stalemate
1032 // All legal moves have been searched and if there are no legal moves, it
1033 // must be mate or stalemate. Note that we can have a false positive in
1034 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1035 // harmless because return value is discarded anyhow in the parent nodes.
1036 // If we are in a singular extension search then return a fail low score.
1037 // A split node has at least one move - the one tried before to be splitted.
1039 return excludedMove ? alpha
1040 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1042 // If we have pruned all the moves without searching return a fail-low score
1043 if (bestValue == -VALUE_INFINITE)
1046 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1047 bestValue >= beta ? BOUND_LOWER :
1048 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1049 depth, bestMove, ss->staticEval);
1051 // Quiet best move: update killers, history and countermoves
1052 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1053 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1055 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1061 // qsearch() is the quiescence search function, which is called by the main
1062 // search function when the remaining depth is zero (or, to be more precise,
1063 // less than ONE_PLY).
1065 template <NodeType NT, bool InCheck>
1066 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1068 const bool PvNode = (NT == PV);
1070 assert(NT == PV || NT == NonPV);
1071 assert(InCheck == !!pos.checkers());
1072 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1073 assert(PvNode || (alpha == beta - 1));
1074 assert(depth <= DEPTH_ZERO);
1079 Move ttMove, move, bestMove;
1080 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1081 bool givesCheck, evasionPrunable;
1084 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1088 ss->currentMove = bestMove = MOVE_NONE;
1089 ss->ply = (ss-1)->ply + 1;
1091 // Check for an instant draw or if the maximum ply has been reached
1092 if (pos.is_draw() || ss->ply > MAX_PLY)
1093 return DrawValue[pos.side_to_move()];
1095 // Decide whether or not to include checks: this fixes also the type of
1096 // TT entry depth that we are going to use. Note that in qsearch we use
1097 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1098 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1099 : DEPTH_QS_NO_CHECKS;
1101 // Transposition table lookup
1103 tte = TT.probe(posKey);
1104 ttMove = tte ? tte->move() : MOVE_NONE;
1105 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1108 && tte->depth() >= ttDepth
1109 && ttValue != VALUE_NONE // Only in case of TT access race
1110 && ( PvNode ? tte->bound() == BOUND_EXACT
1111 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1112 : (tte->bound() & BOUND_UPPER)))
1114 ss->currentMove = ttMove; // Can be MOVE_NONE
1118 // Evaluate the position statically
1121 ss->staticEval = VALUE_NONE;
1122 bestValue = futilityBase = -VALUE_INFINITE;
1128 // Never assume anything on values stored in TT
1129 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1130 ss->staticEval = bestValue = evaluate(pos);
1132 // Can ttValue be used as a better position evaluation?
1133 if (ttValue != VALUE_NONE)
1134 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1135 bestValue = ttValue;
1138 ss->staticEval = bestValue = evaluate(pos);
1140 // Stand pat. Return immediately if static value is at least beta
1141 if (bestValue >= beta)
1144 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1145 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1150 if (PvNode && bestValue > alpha)
1153 futilityBase = bestValue + Value(128);
1156 // Initialize a MovePicker object for the current position, and prepare
1157 // to search the moves. Because the depth is <= 0 here, only captures,
1158 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1160 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1163 // Loop through the moves until no moves remain or a beta cutoff occurs
1164 while ((move = mp.next_move<false>()) != MOVE_NONE)
1166 assert(is_ok(move));
1168 givesCheck = pos.gives_check(move, ci);
1175 && futilityBase > -VALUE_KNOWN_WIN
1176 && !pos.advanced_pawn_push(move))
1178 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1180 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1182 if (futilityValue < beta)
1184 bestValue = std::max(bestValue, futilityValue);
1188 if (futilityBase < beta && pos.see(move) <= 0)
1190 bestValue = std::max(bestValue, futilityBase);
1195 // Detect non-capture evasions that are candidates to be pruned
1196 evasionPrunable = InCheck
1197 && bestValue > VALUE_MATED_IN_MAX_PLY
1198 && !pos.capture(move)
1199 && !pos.can_castle(pos.side_to_move());
1201 // Don't search moves with negative SEE values
1203 && (!InCheck || evasionPrunable)
1205 && type_of(move) != PROMOTION
1206 && pos.see_sign(move) < 0)
1209 // Check for legality just before making the move
1210 if (!pos.legal(move, ci.pinned))
1213 ss->currentMove = move;
1215 // Make and search the move
1216 pos.do_move(move, st, ci, givesCheck);
1217 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1218 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1219 pos.undo_move(move);
1221 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1223 // Check for new best move
1224 if (value > bestValue)
1230 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1237 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1238 ttDepth, move, ss->staticEval);
1246 // All legal moves have been searched. A special case: If we're in check
1247 // and no legal moves were found, it is checkmate.
1248 if (InCheck && bestValue == -VALUE_INFINITE)
1249 return mated_in(ss->ply); // Plies to mate from the root
1251 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1252 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1253 ttDepth, bestMove, ss->staticEval);
1255 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1261 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1262 // "plies to mate from the current position". Non-mate scores are unchanged.
1263 // The function is called before storing a value in the transposition table.
1265 Value value_to_tt(Value v, int ply) {
1267 assert(v != VALUE_NONE);
1269 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1270 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1274 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1275 // from the transposition table (which refers to the plies to mate/be mated
1276 // from current position) to "plies to mate/be mated from the root".
1278 Value value_from_tt(Value v, int ply) {
1280 return v == VALUE_NONE ? VALUE_NONE
1281 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1282 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1286 // update_stats() updates killers, history and countermoves stats after a fail-high
1289 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1291 if (ss->killers[0] != move)
1293 ss->killers[1] = ss->killers[0];
1294 ss->killers[0] = move;
1297 // Increase history value of the cut-off move and decrease all the other
1298 // played quiet moves.
1299 Value bonus = Value(int(depth) * int(depth));
1300 History.update(pos.moved_piece(move), to_sq(move), bonus);
1301 for (int i = 0; i < quietsCnt; ++i)
1304 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1307 if (is_ok((ss-1)->currentMove))
1309 Square prevMoveSq = to_sq((ss-1)->currentMove);
1310 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1315 // When playing with a strength handicap, choose best move among the MultiPV
1316 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1318 Move Skill::pick_move() {
1322 // PRNG sequence should be not deterministic
1323 for (int i = Time::now() % 50; i > 0; --i)
1324 rk.rand<unsigned>();
1326 // RootMoves are already sorted by score in descending order
1327 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1328 int weakness = 120 - 2 * level;
1329 int max_s = -VALUE_INFINITE;
1332 // Choose best move. For each move score we add two terms both dependent on
1333 // weakness. One deterministic and bigger for weaker moves, and one random,
1334 // then we choose the move with the resulting highest score.
1335 for (size_t i = 0; i < PVSize; ++i)
1337 int s = RootMoves[i].score;
1339 // Don't allow crazy blunders even at very low skills
1340 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1343 // This is our magic formula
1344 s += ( weakness * int(RootMoves[0].score - s)
1345 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1350 best = RootMoves[i].pv[0];
1357 // uci_pv() formats PV information according to the UCI protocol. UCI
1358 // requires that all (if any) unsearched PV lines are sent using a previous
1361 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1363 std::stringstream s;
1364 Time::point elapsed = Time::now() - SearchTime + 1;
1365 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1368 for (size_t i = 0; i < Threads.size(); ++i)
1369 if (Threads[i]->maxPly > selDepth)
1370 selDepth = Threads[i]->maxPly;
1372 for (size_t i = 0; i < uciPVSize; ++i)
1374 bool updated = (i <= PVIdx);
1376 if (depth == 1 && !updated)
1379 int d = updated ? depth : depth - 1;
1380 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1382 if (s.rdbuf()->in_avail()) // Not at first line
1385 s << "info depth " << d
1386 << " seldepth " << selDepth
1387 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1388 << " nodes " << pos.nodes_searched()
1389 << " nps " << pos.nodes_searched() * 1000 / elapsed
1390 << " time " << elapsed
1391 << " multipv " << i + 1
1394 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1395 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1404 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1405 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1406 /// ensure that we have a ponder move even when we fail high at root. This
1407 /// results in a long PV to print that is important for position analysis.
1409 void RootMove::extract_pv_from_tt(Position& pos) {
1411 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1421 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1423 pos.do_move(pv[ply++], *st++);
1424 tte = TT.probe(pos.key());
1427 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1428 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1430 && (!pos.is_draw() || ply < 2));
1432 pv.push_back(MOVE_NONE); // Must be zero-terminating
1434 while (ply) pos.undo_move(pv[--ply]);
1438 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1439 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1440 /// first, even if the old TT entries have been overwritten.
1442 void RootMove::insert_pv_in_tt(Position& pos) {
1444 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1449 tte = TT.probe(pos.key());
1451 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1452 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1454 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1456 pos.do_move(pv[ply++], *st++);
1458 } while (pv[ply] != MOVE_NONE);
1460 while (ply) pos.undo_move(pv[--ply]);
1464 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1466 void Thread::idle_loop() {
1468 // Pointer 'this_sp' is not null only if we are called from split(), and not
1469 // at the thread creation. This means we are the split point's master.
1470 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1472 assert(!this_sp || (this_sp->masterThread == this && searching));
1476 // If we are not searching, wait for a condition to be signaled instead of
1477 // wasting CPU time polling for work.
1478 while ((!searching && Threads.sleepWhileIdle) || exit)
1486 // Grab the lock to avoid races with Thread::notify_one()
1489 // If we are master and all slaves have finished then exit idle_loop
1490 if (this_sp && !this_sp->slavesMask)
1496 // Do sleep after retesting sleep conditions under lock protection. In
1497 // particular we need to avoid a deadlock in case a master thread has,
1498 // in the meanwhile, allocated us and sent the notify_one() call before
1499 // we had the chance to grab the lock.
1500 if (!searching && !exit)
1501 sleepCondition.wait(mutex);
1506 // If this thread has been assigned work, launch a search
1511 Threads.mutex.lock();
1514 assert(activeSplitPoint);
1515 SplitPoint* sp = activeSplitPoint;
1517 Threads.mutex.unlock();
1519 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1520 Position pos(*sp->pos, this);
1522 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1523 ss->splitPoint = sp;
1527 assert(activePosition == NULL);
1529 activePosition = &pos;
1531 switch (sp->nodeType) {
1533 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1536 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1539 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1548 activePosition = NULL;
1549 sp->slavesMask &= ~(1ULL << idx);
1550 sp->nodes += pos.nodes_searched();
1552 // Wake up the master thread so to allow it to return from the idle
1553 // loop in case we are the last slave of the split point.
1554 if ( Threads.sleepWhileIdle
1555 && this != sp->masterThread
1558 assert(!sp->masterThread->searching);
1559 sp->masterThread->notify_one();
1562 // After releasing the lock we can't access any SplitPoint related data
1563 // in a safe way because it could have been released under our feet by
1564 // the sp master. Also accessing other Thread objects is unsafe because
1565 // if we are exiting there is a chance that they are already freed.
1569 // If this thread is the master of a split point and all slaves have finished
1570 // their work at this split point, return from the idle loop.
1571 if (this_sp && !this_sp->slavesMask)
1573 this_sp->mutex.lock();
1574 bool finished = !this_sp->slavesMask; // Retest under lock protection
1575 this_sp->mutex.unlock();
1583 /// check_time() is called by the timer thread when the timer triggers. It is
1584 /// used to print debug info and, more importantly, to detect when we are out of
1585 /// available time and thus stop the search.
1589 static Time::point lastInfoTime = Time::now();
1590 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1592 if (Time::now() - lastInfoTime >= 1000)
1594 lastInfoTime = Time::now();
1603 Threads.mutex.lock();
1605 nodes = RootPos.nodes_searched();
1607 // Loop across all split points and sum accumulated SplitPoint nodes plus
1608 // all the currently active positions nodes.
1609 for (size_t i = 0; i < Threads.size(); ++i)
1610 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1612 SplitPoint& sp = Threads[i]->splitPoints[j];
1617 Bitboard sm = sp.slavesMask;
1620 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1622 nodes += pos->nodes_searched();
1628 Threads.mutex.unlock();
1631 Time::point elapsed = Time::now() - SearchTime;
1632 bool stillAtFirstMove = Signals.firstRootMove
1633 && !Signals.failedLowAtRoot
1634 && elapsed > (TimeMgr.available_time() * 62) / 100
1635 && elapsed > IterationTime * 1.4;
1637 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1638 || stillAtFirstMove;
1640 if ( (Limits.use_time_management() && noMoreTime)
1641 || (Limits.movetime && elapsed >= Limits.movetime)
1642 || (Limits.nodes && nodes >= Limits.nodes))
1643 Signals.stop = true;