2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
80 size_t MultiPV, PVIdx;
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
86 MovesStats Countermoves, Followupmoves;
88 template <NodeType NT>
89 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
91 template <NodeType NT, bool InCheck>
92 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
94 void id_loop(Position& pos);
95 Value value_to_tt(Value v, int ply);
96 Value value_from_tt(Value v, int ply);
97 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
98 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
101 Skill(int l) : level(l), best(MOVE_NONE) {}
103 if (enabled()) // Swap best PV line with the sub-optimal one
104 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
105 RootMoves.end(), best ? best : pick_move()));
108 bool enabled() const { return level < 20; }
109 bool time_to_pick(int depth) const { return depth == 1 + level; }
119 /// Search::init() is called during startup to initialize various lookup tables
121 void Search::init() {
123 int d; // depth (ONE_PLY == 2)
124 int hd; // half depth (ONE_PLY == 1)
127 // Init reductions array
128 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
130 double pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
131 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
132 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
133 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
135 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
136 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
138 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
139 Reductions[0][0][hd][mc] += ONE_PLY;
141 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
142 Reductions[0][0][hd][mc] += ONE_PLY / 2;
145 // Init futility move count array
146 for (d = 0; d < 32; ++d)
148 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.00, 1.8));
149 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * pow(d + 0.98, 1.8));
154 /// Search::perft() is our utility to verify move generation. All the leaf nodes
155 /// up to the given depth are generated and counted and the sum returned.
157 static uint64_t perft(Position& pos, Depth depth) {
162 const bool leaf = depth == 2 * ONE_PLY;
164 for (MoveList<LEGAL> it(pos); *it; ++it)
166 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
167 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
173 uint64_t Search::perft(Position& pos, Depth depth) {
174 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
177 /// Search::think() is the external interface to Stockfish's search, and is
178 /// called by the main thread when the program receives the UCI 'go' command. It
179 /// searches from RootPos and at the end prints the "bestmove" to output.
181 void Search::think() {
183 static PolyglotBook book; // Defined static to initialize the PRNG only once
185 RootColor = RootPos.side_to_move();
186 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
188 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
189 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
190 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
192 if (RootMoves.empty())
194 RootMoves.push_back(MOVE_NONE);
195 sync_cout << "info depth 0 score "
196 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
202 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
204 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
206 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
208 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
213 if (Options["Write Search Log"])
215 Log log(Options["Search Log Filename"]);
216 log << "\nSearching: " << RootPos.fen()
217 << "\ninfinite: " << Limits.infinite
218 << " ponder: " << Limits.ponder
219 << " time: " << Limits.time[RootColor]
220 << " increment: " << Limits.inc[RootColor]
221 << " moves to go: " << Limits.movestogo
225 // Reset the threads, still sleeping: will wake up at split time
226 for (size_t i = 0; i < Threads.size(); ++i)
227 Threads[i]->maxPly = 0;
229 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
230 Threads.timer->run = true;
231 Threads.timer->notify_one(); // Wake up the recurring timer
233 id_loop(RootPos); // Let's start searching !
235 Threads.timer->run = false; // Stop the timer
236 Threads.sleepWhileIdle = true; // Send idle threads to sleep
238 if (Options["Write Search Log"])
240 Time::point elapsed = Time::now() - SearchTime + 1;
242 Log log(Options["Search Log Filename"]);
243 log << "Nodes: " << RootPos.nodes_searched()
244 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
245 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
248 RootPos.do_move(RootMoves[0].pv[0], st);
249 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
250 RootPos.undo_move(RootMoves[0].pv[0]);
255 // When search is stopped this info is not printed
256 sync_cout << "info nodes " << RootPos.nodes_searched()
257 << " time " << Time::now() - SearchTime + 1 << sync_endl;
259 // When we reach the maximum depth, we can arrive here without a raise of
260 // Signals.stop. However, if we are pondering or in an infinite search,
261 // the UCI protocol states that we shouldn't print the best move before the
262 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
263 // until the GUI sends one of those commands (which also raises Signals.stop).
264 if (!Signals.stop && (Limits.ponder || Limits.infinite))
266 Signals.stopOnPonderhit = true;
267 RootPos.this_thread()->wait_for(Signals.stop);
270 // Best move could be MOVE_NONE when searching on a stalemate position
271 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
272 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
279 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
280 // with increasing depth until the allocated thinking time has been consumed,
281 // user stops the search, or the maximum search depth is reached.
283 void id_loop(Position& pos) {
285 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
287 Value bestValue, alpha, beta, delta;
289 std::memset(ss-2, 0, 5 * sizeof(Stack));
290 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
294 bestValue = delta = alpha = -VALUE_INFINITE;
295 beta = VALUE_INFINITE;
300 Countermoves.clear();
301 Followupmoves.clear();
303 MultiPV = Options["MultiPV"];
304 Skill skill(Options["Skill Level"]);
306 // Do we have to play with skill handicap? In this case enable MultiPV search
307 // that we will use behind the scenes to retrieve a set of possible moves.
308 if (skill.enabled() && MultiPV < 4)
311 MultiPV = std::min(MultiPV, RootMoves.size());
313 // Iterative deepening loop until requested to stop or target depth reached
314 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
316 // Age out PV variability metric
317 BestMoveChanges *= 0.5;
319 // Save the last iteration's scores before first PV line is searched and
320 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
321 for (size_t i = 0; i < RootMoves.size(); ++i)
322 RootMoves[i].prevScore = RootMoves[i].score;
324 // MultiPV loop. We perform a full root search for each PV line
325 for (PVIdx = 0; PVIdx < MultiPV && !Signals.stop; ++PVIdx)
327 // Reset aspiration window starting size
331 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
332 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
335 // Start with a small aspiration window and, in the case of a fail
336 // high/low, re-search with a bigger window until we're not failing
340 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
342 // Bring the best move to the front. It is critical that sorting
343 // is done with a stable algorithm because all the values but the
344 // first and eventually the new best one are set to -VALUE_INFINITE
345 // and we want to keep the same order for all the moves except the
346 // new PV that goes to the front. Note that in case of MultiPV
347 // search the already searched PV lines are preserved.
348 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
350 // Write PV back to transposition table in case the relevant
351 // entries have been overwritten during the search.
352 for (size_t i = 0; i <= PVIdx; ++i)
353 RootMoves[i].insert_pv_in_tt(pos);
355 // If search has been stopped break immediately. Sorting and
356 // writing PV back to TT is safe because RootMoves is still
357 // valid, although it refers to previous iteration.
361 // When failing high/low give some update (without cluttering
362 // the UI) before a re-search.
363 if ( (bestValue <= alpha || bestValue >= beta)
364 && Time::now() - SearchTime > 3000)
365 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
367 // In case of failing low/high increase aspiration window and
368 // re-search, otherwise exit the loop.
369 if (bestValue <= alpha)
371 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
373 Signals.failedLowAtRoot = true;
374 Signals.stopOnPonderhit = false;
376 else if (bestValue >= beta)
377 beta = std::min(bestValue + delta, VALUE_INFINITE);
384 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
387 // Sort the PV lines searched so far and update the GUI
388 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
390 if (PVIdx + 1 == MultiPV || Time::now() - SearchTime > 3000)
391 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
394 Time::point iterationTime = Time::now() - SearchTime;
396 // If skill levels are enabled and time is up, pick a sub-optimal best move
397 if (skill.enabled() && skill.time_to_pick(depth))
400 if (Options["Write Search Log"])
402 RootMove& rm = RootMoves[0];
403 if (skill.best != MOVE_NONE)
404 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
406 Log log(Options["Search Log Filename"]);
407 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
411 // Have we found a "mate in x"?
413 && bestValue >= VALUE_MATE_IN_MAX_PLY
414 && VALUE_MATE - bestValue <= 2 * Limits.mate)
417 // Do we have time for the next iteration? Can we stop searching now?
418 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
420 bool stop = false; // Local variable, not the volatile Signals.stop
422 // Take some extra time if the best move has changed
423 if (depth > 4 && depth < 50 && MultiPV == 1)
424 TimeMgr.pv_instability(BestMoveChanges);
426 // Stop the search if only one legal move is available or all
427 // of the available time has been used.
428 if ( RootMoves.size() == 1
429 || iterationTime > TimeMgr.available_time() )
434 // If we are allowed to ponder do not stop the search now but
435 // keep pondering until the GUI sends "ponderhit" or "stop".
437 Signals.stopOnPonderhit = true;
446 // search<>() is the main search function for both PV and non-PV nodes and for
447 // normal and SplitPoint nodes. When called just after a split point the search
448 // is simpler because we have already probed the hash table, done a null move
449 // search, and searched the first move before splitting, so we don't have to
450 // repeat all this work again. We also don't need to store anything to the hash
451 // table here: This is taken care of after we return from the split point.
453 template <NodeType NT>
454 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
456 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
457 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
458 const bool RootNode = (NT == Root || NT == SplitPointRoot);
460 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
461 assert(PvNode || (alpha == beta - 1));
462 assert(depth > DEPTH_ZERO);
464 Move quietsSearched[64];
467 SplitPoint* splitPoint;
469 Move ttMove, move, excludedMove, bestMove;
470 Depth ext, newDepth, predictedDepth;
471 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
472 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
473 bool captureOrPromotion, dangerous, doFullDepthSearch;
474 int moveCount, quietCount;
476 // Step 1. Initialize node
477 Thread* thisThread = pos.this_thread();
478 inCheck = pos.checkers();
482 splitPoint = ss->splitPoint;
483 bestMove = splitPoint->bestMove;
484 bestValue = splitPoint->bestValue;
486 ttMove = excludedMove = MOVE_NONE;
487 ttValue = VALUE_NONE;
489 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
494 moveCount = quietCount = 0;
495 bestValue = -VALUE_INFINITE;
496 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
497 ss->ply = (ss-1)->ply + 1;
498 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
499 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
501 // Used to send selDepth info to GUI
502 if (PvNode && thisThread->maxPly < ss->ply)
503 thisThread->maxPly = ss->ply;
507 // Step 2. Check for aborted search and immediate draw
508 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
509 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
511 // Step 3. Mate distance pruning. Even if we mate at the next move our score
512 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
513 // a shorter mate was found upward in the tree then there is no need to search
514 // because we will never beat the current alpha. Same logic but with reversed
515 // signs applies also in the opposite condition of being mated instead of giving
516 // mate. In this case return a fail-high score.
517 alpha = std::max(mated_in(ss->ply), alpha);
518 beta = std::min(mate_in(ss->ply+1), beta);
523 // Step 4. Transposition table lookup
524 // We don't want the score of a partial search to overwrite a previous full search
525 // TT value, so we use a different position key in case of an excluded move.
526 excludedMove = ss->excludedMove;
527 posKey = excludedMove ? pos.exclusion_key() : pos.key();
528 tte = TT.probe(posKey);
529 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
530 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
532 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
533 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
534 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
535 // we should also update RootMoveList to avoid bogus output.
538 && tte->depth() >= depth
539 && ttValue != VALUE_NONE // Only in case of TT access race
540 && ( PvNode ? tte->bound() == BOUND_EXACT
541 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
542 : (tte->bound() & BOUND_UPPER)))
545 ss->currentMove = ttMove; // Can be MOVE_NONE
547 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
548 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
549 update_stats(pos, ss, ttMove, depth, NULL, 0);
554 // Step 5. Evaluate the position statically and update parent's gain statistics
557 ss->staticEval = eval = VALUE_NONE;
563 // Never assume anything on values stored in TT
564 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
565 eval = ss->staticEval = evaluate(pos);
567 // Can ttValue be used as a better position evaluation?
568 if (ttValue != VALUE_NONE)
569 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
574 eval = ss->staticEval = evaluate(pos);
575 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
578 if ( !pos.captured_piece_type()
579 && ss->staticEval != VALUE_NONE
580 && (ss-1)->staticEval != VALUE_NONE
581 && (move = (ss-1)->currentMove) != MOVE_NULL
582 && type_of(move) == NORMAL)
584 Square to = to_sq(move);
585 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
588 // Step 6. Razoring (skipped when in check)
590 && depth < 4 * ONE_PLY
591 && eval + razor_margin(depth) <= alpha
592 && ttMove == MOVE_NONE
593 && abs(beta) < VALUE_MATE_IN_MAX_PLY
594 && !pos.pawn_on_7th(pos.side_to_move()))
596 Value ralpha = alpha - razor_margin(depth);
597 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
602 // Step 7. Futility pruning: child node (skipped when in check)
605 && depth < 7 * ONE_PLY
606 && eval - futility_margin(depth) >= beta
607 && abs(beta) < VALUE_MATE_IN_MAX_PLY
608 && abs(eval) < VALUE_KNOWN_WIN
609 && pos.non_pawn_material(pos.side_to_move()))
610 return eval - futility_margin(depth);
612 // Step 8. Null move search with verification search (is omitted in PV nodes)
615 && depth >= 2 * ONE_PLY
617 && abs(beta) < VALUE_MATE_IN_MAX_PLY
618 && pos.non_pawn_material(pos.side_to_move()))
620 ss->currentMove = MOVE_NULL;
622 assert(eval - beta >= 0);
624 // Null move dynamic reduction based on depth and value
625 Depth R = 3 * ONE_PLY
627 + int(eval - beta) / PawnValueMg * ONE_PLY;
629 pos.do_null_move(st);
630 (ss+1)->skipNullMove = true;
631 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
632 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
633 (ss+1)->skipNullMove = false;
634 pos.undo_null_move();
636 if (nullValue >= beta)
638 // Do not return unproven mate scores
639 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
642 if (depth < 12 * ONE_PLY)
645 // Do verification search at high depths
646 ss->skipNullMove = true;
647 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
648 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
649 ss->skipNullMove = false;
656 // Step 9. ProbCut (skipped when in check)
657 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
658 // and a reduced search returns a value much above beta, we can (almost) safely
659 // prune the previous move.
661 && depth >= 5 * ONE_PLY
663 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
665 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
666 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
668 assert(rdepth >= ONE_PLY);
669 assert((ss-1)->currentMove != MOVE_NONE);
670 assert((ss-1)->currentMove != MOVE_NULL);
672 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
675 while ((move = mp.next_move<false>()) != MOVE_NONE)
676 if (pos.legal(move, ci.pinned))
678 ss->currentMove = move;
679 pos.do_move(move, st, ci, pos.gives_check(move, ci));
680 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
687 // Step 10. Internal iterative deepening (skipped when in check)
688 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
690 && (PvNode || ss->staticEval + Value(256) >= beta))
692 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
694 ss->skipNullMove = true;
695 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
696 ss->skipNullMove = false;
698 tte = TT.probe(posKey);
699 ttMove = tte ? tte->move() : MOVE_NONE;
702 moves_loop: // When in check and at SpNode search starts from here
704 Square prevMoveSq = to_sq((ss-1)->currentMove);
705 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
706 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
708 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
709 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
710 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
712 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
714 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
715 improving = ss->staticEval >= (ss-2)->staticEval
716 || ss->staticEval == VALUE_NONE
717 ||(ss-2)->staticEval == VALUE_NONE;
719 singularExtensionNode = !RootNode
721 && depth >= 8 * ONE_PLY
722 && ttMove != MOVE_NONE
723 && !excludedMove // Recursive singular search is not allowed
724 && (tte->bound() & BOUND_LOWER)
725 && tte->depth() >= depth - 3 * ONE_PLY;
727 // Step 11. Loop through moves
728 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
729 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
733 if (move == excludedMove)
736 // At root obey the "searchmoves" option and skip moves not listed in Root
737 // Move List. As a consequence any illegal move is also skipped. In MultiPV
738 // mode we also skip PV moves which have been already searched.
739 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
744 // Shared counter cannot be decremented later if the move turns out to be illegal
745 if (!pos.legal(move, ci.pinned))
748 moveCount = ++splitPoint->moveCount;
749 splitPoint->mutex.unlock();
756 Signals.firstRootMove = (moveCount == 1);
758 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
759 sync_cout << "info depth " << depth / ONE_PLY
760 << " currmove " << move_to_uci(move, pos.is_chess960())
761 << " currmovenumber " << moveCount + PVIdx << sync_endl;
765 captureOrPromotion = pos.capture_or_promotion(move);
767 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
768 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
769 : pos.gives_check(move, ci);
771 dangerous = givesCheck
772 || type_of(move) != NORMAL
773 || pos.advanced_pawn_push(move);
775 // Step 12. Extend checks
776 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
779 // Singular extension search. If all moves but one fail low on a search of
780 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
781 // is singular and should be extended. To verify this we do a reduced search
782 // on all the other moves but the ttMove and if the result is lower than
783 // ttValue minus a margin then we extend the ttMove.
784 if ( singularExtensionNode
787 && pos.legal(move, ci.pinned)
788 && abs(ttValue) < VALUE_KNOWN_WIN)
790 assert(ttValue != VALUE_NONE);
792 Value rBeta = ttValue - int(depth);
793 ss->excludedMove = move;
794 ss->skipNullMove = true;
795 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
796 ss->skipNullMove = false;
797 ss->excludedMove = MOVE_NONE;
803 // Update the current move (this must be done after singular extension search)
804 newDepth = depth - ONE_PLY + ext;
806 // Step 13. Pruning at shallow depth (exclude PV nodes)
808 && !captureOrPromotion
811 /* && move != ttMove Already implicit in the next condition */
812 && bestValue > VALUE_MATED_IN_MAX_PLY)
814 // Move count based pruning
815 if ( depth < 16 * ONE_PLY
816 && moveCount >= FutilityMoveCounts[improving][depth] )
819 splitPoint->mutex.lock();
824 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
826 // Futility pruning: parent node
827 if (predictedDepth < 7 * ONE_PLY)
829 futilityValue = ss->staticEval + futility_margin(predictedDepth)
830 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
832 if (futilityValue <= alpha)
834 bestValue = std::max(bestValue, futilityValue);
838 splitPoint->mutex.lock();
839 if (bestValue > splitPoint->bestValue)
840 splitPoint->bestValue = bestValue;
846 // Prune moves with negative SEE at low depths
847 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
850 splitPoint->mutex.lock();
856 // Check for legality just before making the move
857 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
863 pvMove = PvNode && moveCount == 1;
864 ss->currentMove = move;
865 if (!SpNode && !captureOrPromotion && quietCount < 64)
866 quietsSearched[quietCount++] = move;
868 // Step 14. Make the move
869 pos.do_move(move, st, ci, givesCheck);
871 // Step 15. Reduced depth search (LMR). If the move fails high it will be
872 // re-searched at full depth.
873 if ( depth >= 3 * ONE_PLY
875 && !captureOrPromotion
877 && move != ss->killers[0]
878 && move != ss->killers[1])
880 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
882 if (!PvNode && cutNode)
883 ss->reduction += ONE_PLY;
885 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
886 ss->reduction += ONE_PLY / 2;
888 if (move == countermoves[0] || move == countermoves[1])
889 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
891 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
893 alpha = splitPoint->alpha;
895 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
897 // Research at intermediate depth if reduction is very high
898 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
900 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
901 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
904 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
905 ss->reduction = DEPTH_ZERO;
908 doFullDepthSearch = !pvMove;
910 // Step 16. Full depth search, when LMR is skipped or fails high
911 if (doFullDepthSearch)
914 alpha = splitPoint->alpha;
916 value = newDepth < ONE_PLY ?
917 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
918 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
919 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
922 // For PV nodes only, do a full PV search on the first move or after a fail
923 // high (in the latter case search only if value < beta), otherwise let the
924 // parent node fail low with value <= alpha and to try another move.
925 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
926 value = newDepth < ONE_PLY ?
927 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
928 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
929 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
930 // Step 17. Undo move
933 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
935 // Step 18. Check for new best move
938 splitPoint->mutex.lock();
939 bestValue = splitPoint->bestValue;
940 alpha = splitPoint->alpha;
943 // Finished searching the move. If Signals.stop is true, the search
944 // was aborted because the user interrupted the search or because we
945 // ran out of time. In this case, the return value of the search cannot
946 // be trusted, and we don't update the best move and/or PV.
947 if (Signals.stop || thisThread->cutoff_occurred())
948 return value; // To avoid returning VALUE_INFINITE
952 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
954 // PV move or new best move ?
955 if (pvMove || value > alpha)
958 rm.extract_pv_from_tt(pos);
960 // We record how often the best move has been changed in each
961 // iteration. This information is used for time management: When
962 // the best move changes frequently, we allocate some more time.
967 // All other moves but the PV are set to the lowest value: this is
968 // not a problem when sorting because the sort is stable and the
969 // move position in the list is preserved - just the PV is pushed up.
970 rm.score = -VALUE_INFINITE;
973 if (value > bestValue)
975 bestValue = SpNode ? splitPoint->bestValue = value : value;
979 bestMove = SpNode ? splitPoint->bestMove = move : move;
981 if (PvNode && value < beta) // Update alpha! Always alpha < beta
982 alpha = SpNode ? splitPoint->alpha = value : value;
985 assert(value >= beta); // Fail high
988 splitPoint->cutoff = true;
995 // Step 19. Check for splitting the search
997 && depth >= Threads.minimumSplitDepth
998 && Threads.available_slave(thisThread)
999 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1001 assert(bestValue < beta);
1003 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1004 depth, moveCount, &mp, NT, cutNode);
1005 if (bestValue >= beta)
1013 // Step 20. Check for mate and stalemate
1014 // All legal moves have been searched and if there are no legal moves, it
1015 // must be mate or stalemate. Note that we can have a false positive in
1016 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1017 // harmless because return value is discarded anyhow in the parent nodes.
1018 // If we are in a singular extension search then return a fail low score.
1019 // A split node has at least one move - the one tried before to be splitted.
1021 return excludedMove ? alpha
1022 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1024 // If we have pruned all the moves without searching return a fail-low score
1025 if (bestValue == -VALUE_INFINITE)
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 // Quiet best move: update killers, history, countermoves and followupmoves
1034 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1035 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1037 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1043 // qsearch() is the quiescence search function, which is called by the main
1044 // search function when the remaining depth is zero (or, to be more precise,
1045 // less than ONE_PLY).
1047 template <NodeType NT, bool InCheck>
1048 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1050 const bool PvNode = (NT == PV);
1052 assert(NT == PV || NT == NonPV);
1053 assert(InCheck == !!pos.checkers());
1054 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1055 assert(PvNode || (alpha == beta - 1));
1056 assert(depth <= DEPTH_ZERO);
1061 Move ttMove, move, bestMove;
1062 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1063 bool givesCheck, evasionPrunable;
1066 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1070 ss->currentMove = bestMove = MOVE_NONE;
1071 ss->ply = (ss-1)->ply + 1;
1073 // Check for an instant draw or if the maximum ply has been reached
1074 if (pos.is_draw() || ss->ply > MAX_PLY)
1075 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1077 // Decide whether or not to include checks: this fixes also the type of
1078 // TT entry depth that we are going to use. Note that in qsearch we use
1079 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1080 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1081 : DEPTH_QS_NO_CHECKS;
1083 // Transposition table lookup
1085 tte = TT.probe(posKey);
1086 ttMove = tte ? tte->move() : MOVE_NONE;
1087 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1090 && tte->depth() >= ttDepth
1091 && ttValue != VALUE_NONE // Only in case of TT access race
1092 && ( PvNode ? tte->bound() == BOUND_EXACT
1093 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1094 : (tte->bound() & BOUND_UPPER)))
1096 ss->currentMove = ttMove; // Can be MOVE_NONE
1100 // Evaluate the position statically
1103 ss->staticEval = VALUE_NONE;
1104 bestValue = futilityBase = -VALUE_INFINITE;
1110 // Never assume anything on values stored in TT
1111 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1112 ss->staticEval = bestValue = evaluate(pos);
1114 // Can ttValue be used as a better position evaluation?
1115 if (ttValue != VALUE_NONE)
1116 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1117 bestValue = ttValue;
1120 ss->staticEval = bestValue = evaluate(pos);
1122 // Stand pat. Return immediately if static value is at least beta
1123 if (bestValue >= beta)
1126 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1127 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1132 if (PvNode && bestValue > alpha)
1135 futilityBase = bestValue + Value(128);
1138 // Initialize a MovePicker object for the current position, and prepare
1139 // to search the moves. Because the depth is <= 0 here, only captures,
1140 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1142 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1145 // Loop through the moves until no moves remain or a beta cutoff occurs
1146 while ((move = mp.next_move<false>()) != MOVE_NONE)
1148 assert(is_ok(move));
1150 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1151 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1152 : pos.gives_check(move, ci);
1159 && futilityBase > -VALUE_KNOWN_WIN
1160 && !pos.advanced_pawn_push(move))
1162 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1164 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1166 if (futilityValue < beta)
1168 bestValue = std::max(bestValue, futilityValue);
1172 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1174 bestValue = std::max(bestValue, futilityBase);
1179 // Detect non-capture evasions that are candidates to be pruned
1180 evasionPrunable = InCheck
1181 && bestValue > VALUE_MATED_IN_MAX_PLY
1182 && !pos.capture(move)
1183 && !pos.can_castle(pos.side_to_move());
1185 // Don't search moves with negative SEE values
1187 && (!InCheck || evasionPrunable)
1189 && type_of(move) != PROMOTION
1190 && pos.see_sign(move) < VALUE_ZERO)
1193 // Check for legality just before making the move
1194 if (!pos.legal(move, ci.pinned))
1197 ss->currentMove = move;
1199 // Make and search the move
1200 pos.do_move(move, st, ci, givesCheck);
1201 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1202 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1203 pos.undo_move(move);
1205 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1207 // Check for new best move
1208 if (value > bestValue)
1214 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1221 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1222 ttDepth, move, ss->staticEval);
1230 // All legal moves have been searched. A special case: If we're in check
1231 // and no legal moves were found, it is checkmate.
1232 if (InCheck && bestValue == -VALUE_INFINITE)
1233 return mated_in(ss->ply); // Plies to mate from the root
1235 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1236 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1237 ttDepth, bestMove, ss->staticEval);
1239 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1245 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1246 // "plies to mate from the current position". Non-mate scores are unchanged.
1247 // The function is called before storing a value in the transposition table.
1249 Value value_to_tt(Value v, int ply) {
1251 assert(v != VALUE_NONE);
1253 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1254 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1258 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1259 // from the transposition table (which refers to the plies to mate/be mated
1260 // from current position) to "plies to mate/be mated from the root".
1262 Value value_from_tt(Value v, int ply) {
1264 return v == VALUE_NONE ? VALUE_NONE
1265 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1266 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1270 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1273 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1275 if (ss->killers[0] != move)
1277 ss->killers[1] = ss->killers[0];
1278 ss->killers[0] = move;
1281 // Increase history value of the cut-off move and decrease all the other
1282 // played quiet moves.
1283 Value bonus = Value(int(depth) * int(depth));
1284 History.update(pos.moved_piece(move), to_sq(move), bonus);
1285 for (int i = 0; i < quietsCnt; ++i)
1288 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1291 if (is_ok((ss-1)->currentMove))
1293 Square prevMoveSq = to_sq((ss-1)->currentMove);
1294 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1297 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1299 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1300 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1305 // When playing with a strength handicap, choose best move among the MultiPV
1306 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1308 Move Skill::pick_move() {
1312 // PRNG sequence should be not deterministic
1313 for (int i = Time::now() % 50; i > 0; --i)
1314 rk.rand<unsigned>();
1316 // RootMoves are already sorted by score in descending order
1317 int variance = std::min(RootMoves[0].score - RootMoves[MultiPV - 1].score, PawnValueMg);
1318 int weakness = 120 - 2 * level;
1319 int max_s = -VALUE_INFINITE;
1322 // Choose best move. For each move score we add two terms both dependent on
1323 // weakness. One deterministic and bigger for weaker moves, and one random,
1324 // then we choose the move with the resulting highest score.
1325 for (size_t i = 0; i < MultiPV; ++i)
1327 int s = RootMoves[i].score;
1329 // Don't allow crazy blunders even at very low skills
1330 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1333 // This is our magic formula
1334 s += ( weakness * int(RootMoves[0].score - s)
1335 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1340 best = RootMoves[i].pv[0];
1347 // uci_pv() formats PV information according to the UCI protocol. UCI
1348 // requires that all (if any) unsearched PV lines are sent using a previous
1351 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1353 std::stringstream s;
1354 Time::point elapsed = Time::now() - SearchTime + 1;
1355 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1358 for (size_t i = 0; i < Threads.size(); ++i)
1359 if (Threads[i]->maxPly > selDepth)
1360 selDepth = Threads[i]->maxPly;
1362 for (size_t i = 0; i < uciPVSize; ++i)
1364 bool updated = (i <= PVIdx);
1366 if (depth == 1 && !updated)
1369 int d = updated ? depth : depth - 1;
1370 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1372 if (s.rdbuf()->in_avail()) // Not at first line
1375 s << "info depth " << d
1376 << " seldepth " << selDepth
1377 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1378 << " nodes " << pos.nodes_searched()
1379 << " nps " << pos.nodes_searched() * 1000 / elapsed
1380 << " time " << elapsed
1381 << " multipv " << i + 1
1384 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1385 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1394 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1395 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1396 /// ensure that we have a ponder move even when we fail high at root. This
1397 /// results in a long PV to print that is important for position analysis.
1399 void RootMove::extract_pv_from_tt(Position& pos) {
1401 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1411 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1413 pos.do_move(pv[ply++], *st++);
1414 tte = TT.probe(pos.key());
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]);
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;
1439 tte = TT.probe(pos.key());
1441 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1442 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1444 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1446 pos.do_move(pv[ply++], *st++);
1448 } while (pv[ply] != MOVE_NONE);
1450 while (ply) pos.undo_move(pv[--ply]);
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 && Threads.sleepWhileIdle) || 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)
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 switch (sp->nodeType) {
1523 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1526 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1529 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1538 activePosition = NULL;
1539 sp->slavesMask &= ~(1ULL << idx);
1540 sp->nodes += pos.nodes_searched();
1542 // Wake up the master thread so to allow it to return from the idle
1543 // loop in case we are the last slave of the split point.
1544 if ( Threads.sleepWhileIdle
1545 && this != sp->masterThread
1548 assert(!sp->masterThread->searching);
1549 sp->masterThread->notify_one();
1552 // After releasing the lock we can't access any SplitPoint related data
1553 // in a safe way because it could have been released under our feet by
1554 // the sp master. Also accessing other Thread objects is unsafe because
1555 // if we are exiting there is a chance that they are already freed.
1559 // If this thread is the master of a split point and all slaves have finished
1560 // their work at this split point, return from the idle loop.
1561 if (this_sp && !this_sp->slavesMask)
1563 this_sp->mutex.lock();
1564 bool finished = !this_sp->slavesMask; // Retest under lock protection
1565 this_sp->mutex.unlock();
1573 /// check_time() is called by the timer thread when the timer triggers. It is
1574 /// used to print debug info and, more importantly, to detect when we are out of
1575 /// available time and thus stop the search.
1579 static Time::point lastInfoTime = Time::now();
1580 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1582 if (Time::now() - lastInfoTime >= 1000)
1584 lastInfoTime = Time::now();
1593 Threads.mutex.lock();
1595 nodes = RootPos.nodes_searched();
1597 // Loop across all split points and sum accumulated SplitPoint nodes plus
1598 // all the currently active positions nodes.
1599 for (size_t i = 0; i < Threads.size(); ++i)
1600 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1602 SplitPoint& sp = Threads[i]->splitPoints[j];
1607 Bitboard sm = sp.slavesMask;
1610 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1612 nodes += pos->nodes_searched();
1618 Threads.mutex.unlock();
1621 Time::point elapsed = Time::now() - SearchTime;
1622 bool stillAtFirstMove = Signals.firstRootMove
1623 && !Signals.failedLowAtRoot
1624 && elapsed > TimeMgr.available_time() * 75 / 100;
1626 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1627 || stillAtFirstMove;
1629 if ( (Limits.use_time_management() && noMoreTime)
1630 || (Limits.movetime && elapsed >= Limits.movetime)
1631 || (Limits.nodes && nodes >= Limits.nodes))
1632 Signals.stop = true;