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;
54 // Fast wrapper for common case of pos.gives_check()
55 #define FAST_GIVES_CHECK(pos, m, ci) \
56 ((type_of(m) == NORMAL && ci.dcCandidates == 0) \
57 ? (ci.checkSq[type_of(pos.piece_on(from_sq(m)))] & to_sq(m)) \
58 : pos.gives_check(m, ci))
62 // Set to true to force running with one thread. Used for debugging
63 const bool FakeSplit = false;
65 // Different node types, used as template parameter
66 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
68 // Dynamic razoring margin based on depth
69 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
71 // Futility lookup tables (initialized at startup) and their access functions
72 int FutilityMoveCounts[2][32]; // [improving][depth]
74 inline Value futility_margin(Depth d) {
75 return Value(100 * int(d));
78 // Reduction lookup tables (initialized at startup) and their access function
79 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
81 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
83 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
88 double BestMoveChanges;
89 Value DrawValue[COLOR_NB];
92 MovesStats Countermoves, Followupmoves;
94 template <NodeType NT>
95 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
97 template <NodeType NT, bool InCheck>
98 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
100 void id_loop(Position& pos);
101 Value value_to_tt(Value v, int ply);
102 Value value_from_tt(Value v, int ply);
103 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
104 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
107 Skill(int l) : level(l), best(MOVE_NONE) {}
109 if (enabled()) // Swap best PV line with the sub-optimal one
110 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
111 RootMoves.end(), best ? best : pick_move()));
114 bool enabled() const { return level < 20; }
115 bool time_to_pick(int depth) const { return depth == 1 + level; }
125 /// Search::init() is called during startup to initialize various lookup tables
127 void Search::init() {
129 int d; // depth (ONE_PLY == 2)
130 int hd; // half depth (ONE_PLY == 1)
133 // Init reductions array
134 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
136 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
137 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
138 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
139 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
141 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
142 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
144 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
145 Reductions[0][0][hd][mc] += ONE_PLY;
147 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
148 Reductions[0][0][hd][mc] += ONE_PLY / 2;
151 // Init futility move count array
152 for (d = 0; d < 32; ++d)
154 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
155 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
160 /// Search::perft() is our utility to verify move generation. All the leaf nodes
161 /// up to the given depth are generated and counted and the sum returned.
163 static size_t perft(Position& pos, Depth depth) {
168 const bool leaf = depth == 2 * ONE_PLY;
170 for (MoveList<LEGAL> it(pos); *it; ++it)
172 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
173 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
179 size_t Search::perft(Position& pos, Depth depth) {
180 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
183 /// Search::think() is the external interface to Stockfish's search, and is
184 /// called by the main thread when the program receives the UCI 'go' command. It
185 /// searches from RootPos and at the end prints the "bestmove" to output.
187 void Search::think() {
189 static PolyglotBook book; // Defined static to initialize the PRNG only once
191 RootColor = RootPos.side_to_move();
192 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
194 if (RootMoves.empty())
196 RootMoves.push_back(MOVE_NONE);
197 sync_cout << "info depth 0 score "
198 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
204 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
206 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
208 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
210 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
215 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
217 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
218 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
219 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
220 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
223 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
225 if (Options["Write Search Log"])
227 Log log(Options["Search Log Filename"]);
228 log << "\nSearching: " << RootPos.fen()
229 << "\ninfinite: " << Limits.infinite
230 << " ponder: " << Limits.ponder
231 << " time: " << Limits.time[RootColor]
232 << " increment: " << Limits.inc[RootColor]
233 << " moves to go: " << Limits.movestogo
237 // Reset the threads, still sleeping: will wake up at split time
238 for (size_t i = 0; i < Threads.size(); ++i)
239 Threads[i]->maxPly = 0;
241 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
242 Threads.timer->run = true;
243 Threads.timer->notify_one(); // Wake up the recurring timer
245 id_loop(RootPos); // Let's start searching !
247 Threads.timer->run = false; // Stop the timer
248 Threads.sleepWhileIdle = true; // Send idle threads to sleep
250 if (Options["Write Search Log"])
252 Time::point elapsed = Time::now() - SearchTime + 1;
254 Log log(Options["Search Log Filename"]);
255 log << "Nodes: " << RootPos.nodes_searched()
256 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
257 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
260 RootPos.do_move(RootMoves[0].pv[0], st);
261 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
262 RootPos.undo_move(RootMoves[0].pv[0]);
267 // When search is stopped this info is not printed
268 sync_cout << "info nodes " << RootPos.nodes_searched()
269 << " time " << Time::now() - SearchTime + 1 << sync_endl;
271 // When we reach the maximum depth, we can arrive here without a raise of
272 // Signals.stop. However, if we are pondering or in an infinite search,
273 // the UCI protocol states that we shouldn't print the best move before the
274 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
275 // until the GUI sends one of those commands (which also raises Signals.stop).
276 if (!Signals.stop && (Limits.ponder || Limits.infinite))
278 Signals.stopOnPonderhit = true;
279 RootPos.this_thread()->wait_for(Signals.stop);
282 // Best move could be MOVE_NONE when searching on a stalemate position
283 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
284 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
291 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
292 // with increasing depth until the allocated thinking time has been consumed,
293 // user stops the search, or the maximum search depth is reached.
295 void id_loop(Position& pos) {
297 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
299 Value bestValue, alpha, beta, delta;
301 std::memset(ss-2, 0, 5 * sizeof(Stack));
302 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
306 bestValue = delta = alpha = -VALUE_INFINITE;
307 beta = VALUE_INFINITE;
312 Countermoves.clear();
313 Followupmoves.clear();
315 PVSize = Options["MultiPV"];
316 Skill skill(Options["Skill Level"]);
318 // Do we have to play with skill handicap? In this case enable MultiPV search
319 // that we will use behind the scenes to retrieve a set of possible moves.
320 if (skill.enabled() && PVSize < 4)
323 PVSize = std::min(PVSize, RootMoves.size());
325 // Iterative deepening loop until requested to stop or target depth reached
326 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
328 // Age out PV variability metric
329 BestMoveChanges *= 0.8;
331 // Save the last iteration's scores before first PV line is searched and
332 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
333 for (size_t i = 0; i < RootMoves.size(); ++i)
334 RootMoves[i].prevScore = RootMoves[i].score;
336 // MultiPV loop. We perform a full root search for each PV line
337 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
339 // Reset aspiration window starting size
343 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
344 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
347 // Start with a small aspiration window and, in the case of a fail
348 // high/low, re-search with a bigger window until we're not failing
352 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
354 // Bring the best move to the front. It is critical that sorting
355 // is done with a stable algorithm because all the values but the
356 // first and eventually the new best one are set to -VALUE_INFINITE
357 // and we want to keep the same order for all the moves except the
358 // new PV that goes to the front. Note that in case of MultiPV
359 // search the already searched PV lines are preserved.
360 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
362 // Write PV back to transposition table in case the relevant
363 // entries have been overwritten during the search.
364 for (size_t i = 0; i <= PVIdx; ++i)
365 RootMoves[i].insert_pv_in_tt(pos);
367 // If search has been stopped break immediately. Sorting and
368 // writing PV back to TT is safe because RootMoves is still
369 // valid, although it refers to previous iteration.
373 // When failing high/low give some update (without cluttering
374 // the UI) before a re-search.
375 if ( (bestValue <= alpha || bestValue >= beta)
376 && Time::now() - SearchTime > 3000)
377 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
379 // In case of failing low/high increase aspiration window and
380 // re-search, otherwise exit the loop.
381 if (bestValue <= alpha)
383 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
385 Signals.failedLowAtRoot = true;
386 Signals.stopOnPonderhit = false;
388 else if (bestValue >= beta)
389 beta = std::min(bestValue + delta, VALUE_INFINITE);
396 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
399 // Sort the PV lines searched so far and update the GUI
400 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
402 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
403 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
406 IterationTime = Time::now() - SearchTime;
408 // If skill levels are enabled and time is up, pick a sub-optimal best move
409 if (skill.enabled() && skill.time_to_pick(depth))
412 if (Options["Write Search Log"])
414 RootMove& rm = RootMoves[0];
415 if (skill.best != MOVE_NONE)
416 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
418 Log log(Options["Search Log Filename"]);
419 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
423 // Have we found a "mate in x"?
425 && bestValue >= VALUE_MATE_IN_MAX_PLY
426 && VALUE_MATE - bestValue <= 2 * Limits.mate)
429 // Do we have time for the next iteration? Can we stop searching now?
430 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
432 bool stop = false; // Local variable, not the volatile Signals.stop
434 // Take some extra time if the best move has changed
435 if (depth > 4 && depth < 50 && PVSize == 1)
436 TimeMgr.pv_instability(BestMoveChanges);
438 // Stop the search if only one legal move is available or most
439 // of the available time has been used. We probably don't have
440 // enough time to search the first move at the next iteration anyway.
441 if ( RootMoves.size() == 1
442 || IterationTime > (TimeMgr.available_time() * 62) / 100)
447 // If we are allowed to ponder do not stop the search now but
448 // keep pondering until the GUI sends "ponderhit" or "stop".
450 Signals.stopOnPonderhit = true;
459 // search<>() is the main search function for both PV and non-PV nodes and for
460 // normal and SplitPoint nodes. When called just after a split point the search
461 // is simpler because we have already probed the hash table, done a null move
462 // search, and searched the first move before splitting, so we don't have to
463 // repeat all this work again. We also don't need to store anything to the hash
464 // table here: This is taken care of after we return from the split point.
466 template <NodeType NT>
467 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
469 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
470 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
471 const bool RootNode = (NT == Root || NT == SplitPointRoot);
473 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
474 assert(PvNode || (alpha == beta - 1));
475 assert(depth > DEPTH_ZERO);
477 Move quietsSearched[64];
480 SplitPoint* splitPoint;
482 Move ttMove, move, excludedMove, bestMove;
483 Depth ext, newDepth, predictedDepth;
484 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
485 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
486 bool captureOrPromotion, dangerous, doFullDepthSearch;
487 int moveCount, quietCount;
489 // Step 1. Initialize node
490 Thread* thisThread = pos.this_thread();
491 inCheck = pos.checkers();
495 splitPoint = ss->splitPoint;
496 bestMove = splitPoint->bestMove;
497 bestValue = splitPoint->bestValue;
499 ttMove = excludedMove = MOVE_NONE;
500 ttValue = VALUE_NONE;
502 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
507 moveCount = quietCount = 0;
508 bestValue = -VALUE_INFINITE;
509 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
510 ss->ply = (ss-1)->ply + 1;
511 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
512 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
514 // Used to send selDepth info to GUI
515 if (PvNode && thisThread->maxPly < ss->ply)
516 thisThread->maxPly = ss->ply;
520 // Step 2. Check for aborted search and immediate draw
521 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
522 return DrawValue[pos.side_to_move()];
524 // Step 3. Mate distance pruning. Even if we mate at the next move our score
525 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
526 // a shorter mate was found upward in the tree then there is no need to search
527 // because we will never beat the current alpha. Same logic but with reversed
528 // signs applies also in the opposite condition of being mated instead of giving
529 // mate. In this case return a fail-high score.
530 alpha = std::max(mated_in(ss->ply), alpha);
531 beta = std::min(mate_in(ss->ply+1), beta);
536 // Step 4. Transposition table lookup
537 // We don't want the score of a partial search to overwrite a previous full search
538 // TT value, so we use a different position key in case of an excluded move.
539 excludedMove = ss->excludedMove;
540 posKey = excludedMove ? pos.exclusion_key() : pos.key();
541 tte = TT.probe(posKey);
542 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
543 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
545 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
546 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
547 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
548 // we should also update RootMoveList to avoid bogus output.
551 && tte->depth() >= depth
552 && ttValue != VALUE_NONE // Only in case of TT access race
553 && ( PvNode ? tte->bound() == BOUND_EXACT
554 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
555 : (tte->bound() & BOUND_UPPER)))
558 ss->currentMove = ttMove; // Can be MOVE_NONE
560 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
561 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
562 update_stats(pos, ss, ttMove, depth, NULL, 0);
567 // Step 5. Evaluate the position statically and update parent's gain statistics
570 ss->staticEval = eval = VALUE_NONE;
576 // Never assume anything on values stored in TT
577 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
578 eval = ss->staticEval = evaluate(pos);
580 // Can ttValue be used as a better position evaluation?
581 if (ttValue != VALUE_NONE)
582 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
587 eval = ss->staticEval = evaluate(pos);
588 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
591 if ( !pos.captured_piece_type()
592 && ss->staticEval != VALUE_NONE
593 && (ss-1)->staticEval != VALUE_NONE
594 && (move = (ss-1)->currentMove) != MOVE_NULL
595 && type_of(move) == NORMAL)
597 Square to = to_sq(move);
598 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
601 // Step 6. Razoring (skipped when in check)
603 && depth < 4 * ONE_PLY
604 && eval + razor_margin(depth) <= alpha
605 && ttMove == MOVE_NONE
606 && abs(beta) < VALUE_MATE_IN_MAX_PLY
607 && !pos.pawn_on_7th(pos.side_to_move()))
609 Value ralpha = alpha - razor_margin(depth);
610 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
615 // Step 7. Futility pruning: child node (skipped when in check)
618 && depth < 7 * ONE_PLY
619 && eval - futility_margin(depth) >= beta
620 && abs(beta) < VALUE_MATE_IN_MAX_PLY
621 && abs(eval) < VALUE_KNOWN_WIN
622 && pos.non_pawn_material(pos.side_to_move()))
623 return eval - futility_margin(depth);
625 // Step 8. Null move search with verification search (is omitted in PV nodes)
628 && depth >= 2 * ONE_PLY
630 && abs(beta) < VALUE_MATE_IN_MAX_PLY
631 && pos.non_pawn_material(pos.side_to_move()))
633 ss->currentMove = MOVE_NULL;
635 assert(eval - beta >= 0);
637 // Null move dynamic reduction based on depth and value
638 Depth R = 3 * ONE_PLY
640 + int(eval - beta) / PawnValueMg * ONE_PLY;
642 pos.do_null_move(st);
643 (ss+1)->skipNullMove = true;
644 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
645 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
646 (ss+1)->skipNullMove = false;
647 pos.undo_null_move();
649 if (nullValue >= beta) // Do not return unproven mate scores
650 return nullValue >= VALUE_MATE_IN_MAX_PLY ? beta : nullValue;
653 // Step 9. ProbCut (skipped when in check)
654 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
655 // and a reduced search returns a value much above beta, we can (almost) safely
656 // prune the previous move.
658 && depth >= 5 * ONE_PLY
660 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
662 Value rbeta = beta + 200;
663 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
665 assert(rdepth >= ONE_PLY);
666 assert((ss-1)->currentMove != MOVE_NONE);
667 assert((ss-1)->currentMove != MOVE_NULL);
669 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
672 while ((move = mp.next_move<false>()) != MOVE_NONE)
673 if (pos.legal(move, ci.pinned))
675 ss->currentMove = move;
676 pos.do_move(move, st, ci, pos.gives_check(move, ci));
677 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
684 // Step 10. Internal iterative deepening (skipped when in check)
685 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
686 && ttMove == MOVE_NONE
687 && (PvNode || ss->staticEval + Value(256) >= beta))
689 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
691 ss->skipNullMove = true;
692 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
693 ss->skipNullMove = false;
695 tte = TT.probe(posKey);
696 ttMove = tte ? tte->move() : MOVE_NONE;
699 moves_loop: // When in check and at SpNode search starts from here
701 Square prevMoveSq = to_sq((ss-1)->currentMove);
702 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
703 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
705 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
706 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
707 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
709 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
711 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
712 improving = ss->staticEval >= (ss-2)->staticEval
713 || ss->staticEval == VALUE_NONE
714 ||(ss-2)->staticEval == VALUE_NONE;
716 singularExtensionNode = !RootNode
718 && depth >= 8 * ONE_PLY
719 && ttMove != MOVE_NONE
720 && !excludedMove // Recursive singular search is not allowed
721 && (tte->bound() & BOUND_LOWER)
722 && tte->depth() >= depth - 3 * ONE_PLY;
724 // Step 11. Loop through moves
725 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
726 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
730 if (move == excludedMove)
733 // At root obey the "searchmoves" option and skip moves not listed in Root
734 // Move List. As a consequence any illegal move is also skipped. In MultiPV
735 // mode we also skip PV moves which have been already searched.
736 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
741 // Shared counter cannot be decremented later if the move turns out to be illegal
742 if (!pos.legal(move, ci.pinned))
745 moveCount = ++splitPoint->moveCount;
746 splitPoint->mutex.unlock();
753 Signals.firstRootMove = (moveCount == 1);
755 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
756 sync_cout << "info depth " << depth / ONE_PLY
757 << " currmove " << move_to_uci(move, pos.is_chess960())
758 << " currmovenumber " << moveCount + PVIdx << sync_endl;
762 captureOrPromotion = pos.capture_or_promotion(move);
763 givesCheck = FAST_GIVES_CHECK(pos, move, ci);
764 dangerous = givesCheck
765 || type_of(move) != NORMAL
766 || pos.advanced_pawn_push(move);
768 // Step 12. Extend checks
769 if (givesCheck && pos.see_sign(move) >= 0)
772 // Singular extension search. If all moves but one fail low on a search of
773 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
774 // is singular and should be extended. To verify this we do a reduced search
775 // on all the other moves but the ttMove and if the result is lower than
776 // ttValue minus a margin then we extend the ttMove.
777 if ( singularExtensionNode
780 && pos.legal(move, ci.pinned)
781 && abs(ttValue) < VALUE_KNOWN_WIN)
783 assert(ttValue != VALUE_NONE);
785 Value rBeta = ttValue - int(depth);
786 ss->excludedMove = move;
787 ss->skipNullMove = true;
788 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
789 ss->skipNullMove = false;
790 ss->excludedMove = MOVE_NONE;
796 // Update the current move (this must be done after singular extension search)
797 newDepth = depth - ONE_PLY + ext;
799 // Step 13. Pruning at shallow depth (exclude PV nodes)
801 && !captureOrPromotion
804 /* && move != ttMove Already implicit in the next condition */
805 && bestValue > VALUE_MATED_IN_MAX_PLY)
807 // Move count based pruning
808 if ( depth < 16 * ONE_PLY
809 && moveCount >= FutilityMoveCounts[improving][depth] )
812 splitPoint->mutex.lock();
817 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
819 // Futility pruning: parent node
820 if (predictedDepth < 7 * ONE_PLY)
822 futilityValue = ss->staticEval + futility_margin(predictedDepth)
823 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
825 if (futilityValue <= alpha)
827 bestValue = std::max(bestValue, futilityValue);
831 splitPoint->mutex.lock();
832 if (bestValue > splitPoint->bestValue)
833 splitPoint->bestValue = bestValue;
839 // Prune moves with negative SEE at low depths
840 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
843 splitPoint->mutex.lock();
849 // Check for legality just before making the move
850 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
856 pvMove = PvNode && moveCount == 1;
857 ss->currentMove = move;
858 if (!SpNode && !captureOrPromotion && quietCount < 64)
859 quietsSearched[quietCount++] = move;
861 // Step 14. Make the move
862 pos.do_move(move, st, ci, givesCheck);
864 // Step 15. Reduced depth search (LMR). If the move fails high it will be
865 // re-searched at full depth.
866 if ( depth >= 3 * ONE_PLY
868 && !captureOrPromotion
870 && move != ss->killers[0]
871 && move != ss->killers[1])
873 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
875 if (!PvNode && cutNode)
876 ss->reduction += ONE_PLY;
878 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
879 ss->reduction += ONE_PLY / 2;
881 if (move == countermoves[0] || move == countermoves[1])
882 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
884 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
886 alpha = splitPoint->alpha;
888 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
890 // Research at intermediate depth if reduction is very high
891 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
893 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
894 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
897 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
898 ss->reduction = DEPTH_ZERO;
901 doFullDepthSearch = !pvMove;
903 // Step 16. Full depth search, when LMR is skipped or fails high
904 if (doFullDepthSearch)
907 alpha = splitPoint->alpha;
909 value = newDepth < ONE_PLY ?
910 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
911 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
912 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
915 // For PV nodes only, do a full PV search on the first move or after a fail
916 // high (in the latter case search only if value < beta), otherwise let the
917 // parent node fail low with value <= alpha and to try another move.
918 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
919 value = newDepth < ONE_PLY ?
920 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
921 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
922 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
923 // Step 17. Undo move
926 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
928 // Step 18. Check for new best move
931 splitPoint->mutex.lock();
932 bestValue = splitPoint->bestValue;
933 alpha = splitPoint->alpha;
936 // Finished searching the move. If Signals.stop is true, the search
937 // was aborted because the user interrupted the search or because we
938 // ran out of time. In this case, the return value of the search cannot
939 // be trusted, and we don't update the best move and/or PV.
940 if (Signals.stop || thisThread->cutoff_occurred())
941 return value; // To avoid returning VALUE_INFINITE
945 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
947 // PV move or new best move ?
948 if (pvMove || value > alpha)
951 rm.extract_pv_from_tt(pos);
953 // We record how often the best move has been changed in each
954 // iteration. This information is used for time management: When
955 // the best move changes frequently, we allocate some more time.
960 // All other moves but the PV are set to the lowest value: this is
961 // not a problem when sorting because the sort is stable and the
962 // move position in the list is preserved - just the PV is pushed up.
963 rm.score = -VALUE_INFINITE;
966 if (value > bestValue)
968 bestValue = SpNode ? splitPoint->bestValue = value : value;
972 bestMove = SpNode ? splitPoint->bestMove = move : move;
974 if (PvNode && value < beta) // Update alpha! Always alpha < beta
975 alpha = SpNode ? splitPoint->alpha = value : value;
978 assert(value >= beta); // Fail high
981 splitPoint->cutoff = true;
988 // Step 19. Check for splitting the search
990 && depth >= Threads.minimumSplitDepth
991 && Threads.available_slave(thisThread)
992 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
994 assert(bestValue < beta);
996 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
997 depth, moveCount, &mp, NT, cutNode);
998 if (bestValue >= beta)
1006 // Step 20. Check for mate and stalemate
1007 // All legal moves have been searched and if there are no legal moves, it
1008 // must be mate or stalemate. Note that we can have a false positive in
1009 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1010 // harmless because return value is discarded anyhow in the parent nodes.
1011 // If we are in a singular extension search then return a fail low score.
1012 // A split node has at least one move - the one tried before to be splitted.
1014 return excludedMove ? alpha
1015 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1017 // If we have pruned all the moves without searching return a fail-low score
1018 if (bestValue == -VALUE_INFINITE)
1021 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1022 bestValue >= beta ? BOUND_LOWER :
1023 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1024 depth, bestMove, ss->staticEval);
1026 // Quiet best move: update killers, history, countermoves and followupmoves
1027 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1028 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1030 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1036 // qsearch() is the quiescence search function, which is called by the main
1037 // search function when the remaining depth is zero (or, to be more precise,
1038 // less than ONE_PLY).
1040 template <NodeType NT, bool InCheck>
1041 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1043 const bool PvNode = (NT == PV);
1045 assert(NT == PV || NT == NonPV);
1046 assert(InCheck == !!pos.checkers());
1047 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1048 assert(PvNode || (alpha == beta - 1));
1049 assert(depth <= DEPTH_ZERO);
1054 Move ttMove, move, bestMove;
1055 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1056 bool givesCheck, evasionPrunable;
1059 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1063 ss->currentMove = bestMove = MOVE_NONE;
1064 ss->ply = (ss-1)->ply + 1;
1066 // Check for an instant draw or if the maximum ply has been reached
1067 if (pos.is_draw() || ss->ply > MAX_PLY)
1068 return DrawValue[pos.side_to_move()];
1070 // Decide whether or not to include checks: this fixes also the type of
1071 // TT entry depth that we are going to use. Note that in qsearch we use
1072 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1073 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1074 : DEPTH_QS_NO_CHECKS;
1076 // Transposition table lookup
1078 tte = TT.probe(posKey);
1079 ttMove = tte ? tte->move() : MOVE_NONE;
1080 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1083 && tte->depth() >= ttDepth
1084 && ttValue != VALUE_NONE // Only in case of TT access race
1085 && ( PvNode ? tte->bound() == BOUND_EXACT
1086 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1087 : (tte->bound() & BOUND_UPPER)))
1089 ss->currentMove = ttMove; // Can be MOVE_NONE
1093 // Evaluate the position statically
1096 ss->staticEval = VALUE_NONE;
1097 bestValue = futilityBase = -VALUE_INFINITE;
1103 // Never assume anything on values stored in TT
1104 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1105 ss->staticEval = bestValue = evaluate(pos);
1107 // Can ttValue be used as a better position evaluation?
1108 if (ttValue != VALUE_NONE)
1109 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1110 bestValue = ttValue;
1113 ss->staticEval = bestValue = evaluate(pos);
1115 // Stand pat. Return immediately if static value is at least beta
1116 if (bestValue >= beta)
1119 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1120 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1125 if (PvNode && bestValue > alpha)
1128 futilityBase = bestValue + Value(128);
1131 // Initialize a MovePicker object for the current position, and prepare
1132 // to search the moves. Because the depth is <= 0 here, only captures,
1133 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1135 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1138 // Loop through the moves until no moves remain or a beta cutoff occurs
1139 while ((move = mp.next_move<false>()) != MOVE_NONE)
1141 assert(is_ok(move));
1143 givesCheck = FAST_GIVES_CHECK(pos, move, ci);
1150 && futilityBase > -VALUE_KNOWN_WIN
1151 && !pos.advanced_pawn_push(move))
1153 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1155 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1157 if (futilityValue < beta)
1159 bestValue = std::max(bestValue, futilityValue);
1163 if (futilityBase < beta && pos.see(move) <= 0)
1165 bestValue = std::max(bestValue, futilityBase);
1170 // Detect non-capture evasions that are candidates to be pruned
1171 evasionPrunable = InCheck
1172 && bestValue > VALUE_MATED_IN_MAX_PLY
1173 && !pos.capture(move)
1174 && !pos.can_castle(pos.side_to_move());
1176 // Don't search moves with negative SEE values
1178 && (!InCheck || evasionPrunable)
1180 && type_of(move) != PROMOTION
1181 && pos.see_sign(move) < 0)
1184 // Check for legality just before making the move
1185 if (!pos.legal(move, ci.pinned))
1188 ss->currentMove = move;
1190 // Make and search the move
1191 pos.do_move(move, st, ci, givesCheck);
1192 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1193 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1194 pos.undo_move(move);
1196 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1198 // Check for new best move
1199 if (value > bestValue)
1205 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1212 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1213 ttDepth, move, ss->staticEval);
1221 // All legal moves have been searched. A special case: If we're in check
1222 // and no legal moves were found, it is checkmate.
1223 if (InCheck && bestValue == -VALUE_INFINITE)
1224 return mated_in(ss->ply); // Plies to mate from the root
1226 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1227 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1228 ttDepth, bestMove, ss->staticEval);
1230 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1236 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1237 // "plies to mate from the current position". Non-mate scores are unchanged.
1238 // The function is called before storing a value in the transposition table.
1240 Value value_to_tt(Value v, int ply) {
1242 assert(v != VALUE_NONE);
1244 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1245 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1249 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1250 // from the transposition table (which refers to the plies to mate/be mated
1251 // from current position) to "plies to mate/be mated from the root".
1253 Value value_from_tt(Value v, int ply) {
1255 return v == VALUE_NONE ? VALUE_NONE
1256 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1257 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1261 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1264 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1266 if (ss->killers[0] != move)
1268 ss->killers[1] = ss->killers[0];
1269 ss->killers[0] = move;
1272 // Increase history value of the cut-off move and decrease all the other
1273 // played quiet moves.
1274 Value bonus = Value(int(depth) * int(depth));
1275 History.update(pos.moved_piece(move), to_sq(move), bonus);
1276 for (int i = 0; i < quietsCnt; ++i)
1279 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1282 if (is_ok((ss-1)->currentMove))
1284 Square prevMoveSq = to_sq((ss-1)->currentMove);
1285 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1288 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1290 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1291 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1296 // When playing with a strength handicap, choose best move among the MultiPV
1297 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1299 Move Skill::pick_move() {
1303 // PRNG sequence should be not deterministic
1304 for (int i = Time::now() % 50; i > 0; --i)
1305 rk.rand<unsigned>();
1307 // RootMoves are already sorted by score in descending order
1308 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1309 int weakness = 120 - 2 * level;
1310 int max_s = -VALUE_INFINITE;
1313 // Choose best move. For each move score we add two terms both dependent on
1314 // weakness. One deterministic and bigger for weaker moves, and one random,
1315 // then we choose the move with the resulting highest score.
1316 for (size_t i = 0; i < PVSize; ++i)
1318 int s = RootMoves[i].score;
1320 // Don't allow crazy blunders even at very low skills
1321 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1324 // This is our magic formula
1325 s += ( weakness * int(RootMoves[0].score - s)
1326 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1331 best = RootMoves[i].pv[0];
1338 // uci_pv() formats PV information according to the UCI protocol. UCI
1339 // requires that all (if any) unsearched PV lines are sent using a previous
1342 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1344 std::stringstream s;
1345 Time::point elapsed = Time::now() - SearchTime + 1;
1346 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1349 for (size_t i = 0; i < Threads.size(); ++i)
1350 if (Threads[i]->maxPly > selDepth)
1351 selDepth = Threads[i]->maxPly;
1353 for (size_t i = 0; i < uciPVSize; ++i)
1355 bool updated = (i <= PVIdx);
1357 if (depth == 1 && !updated)
1360 int d = updated ? depth : depth - 1;
1361 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1363 if (s.rdbuf()->in_avail()) // Not at first line
1366 s << "info depth " << d
1367 << " seldepth " << selDepth
1368 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1369 << " nodes " << pos.nodes_searched()
1370 << " nps " << pos.nodes_searched() * 1000 / elapsed
1371 << " time " << elapsed
1372 << " multipv " << i + 1
1375 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1376 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1385 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1386 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1387 /// ensure that we have a ponder move even when we fail high at root. This
1388 /// results in a long PV to print that is important for position analysis.
1390 void RootMove::extract_pv_from_tt(Position& pos) {
1392 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1402 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1404 pos.do_move(pv[ply++], *st++);
1405 tte = TT.probe(pos.key());
1408 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1409 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1411 && (!pos.is_draw() || ply < 2));
1413 pv.push_back(MOVE_NONE); // Must be zero-terminating
1415 while (ply) pos.undo_move(pv[--ply]);
1419 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1420 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1421 /// first, even if the old TT entries have been overwritten.
1423 void RootMove::insert_pv_in_tt(Position& pos) {
1425 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1430 tte = TT.probe(pos.key());
1432 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1433 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1435 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1437 pos.do_move(pv[ply++], *st++);
1439 } while (pv[ply] != MOVE_NONE);
1441 while (ply) pos.undo_move(pv[--ply]);
1445 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1447 void Thread::idle_loop() {
1449 // Pointer 'this_sp' is not null only if we are called from split(), and not
1450 // at the thread creation. This means we are the split point's master.
1451 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1453 assert(!this_sp || (this_sp->masterThread == this && searching));
1457 // If we are not searching, wait for a condition to be signaled instead of
1458 // wasting CPU time polling for work.
1459 while ((!searching && Threads.sleepWhileIdle) || exit)
1467 // Grab the lock to avoid races with Thread::notify_one()
1470 // If we are master and all slaves have finished then exit idle_loop
1471 if (this_sp && !this_sp->slavesMask)
1477 // Do sleep after retesting sleep conditions under lock protection. In
1478 // particular we need to avoid a deadlock in case a master thread has,
1479 // in the meanwhile, allocated us and sent the notify_one() call before
1480 // we had the chance to grab the lock.
1481 if (!searching && !exit)
1482 sleepCondition.wait(mutex);
1487 // If this thread has been assigned work, launch a search
1492 Threads.mutex.lock();
1495 assert(activeSplitPoint);
1496 SplitPoint* sp = activeSplitPoint;
1498 Threads.mutex.unlock();
1500 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1501 Position pos(*sp->pos, this);
1503 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1504 ss->splitPoint = sp;
1508 assert(activePosition == NULL);
1510 activePosition = &pos;
1512 switch (sp->nodeType) {
1514 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1517 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1520 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1529 activePosition = NULL;
1530 sp->slavesMask &= ~(1ULL << idx);
1531 sp->nodes += pos.nodes_searched();
1533 // Wake up the master thread so to allow it to return from the idle
1534 // loop in case we are the last slave of the split point.
1535 if ( Threads.sleepWhileIdle
1536 && this != sp->masterThread
1539 assert(!sp->masterThread->searching);
1540 sp->masterThread->notify_one();
1543 // After releasing the lock we can't access any SplitPoint related data
1544 // in a safe way because it could have been released under our feet by
1545 // the sp master. Also accessing other Thread objects is unsafe because
1546 // if we are exiting there is a chance that they are already freed.
1550 // If this thread is the master of a split point and all slaves have finished
1551 // their work at this split point, return from the idle loop.
1552 if (this_sp && !this_sp->slavesMask)
1554 this_sp->mutex.lock();
1555 bool finished = !this_sp->slavesMask; // Retest under lock protection
1556 this_sp->mutex.unlock();
1564 /// check_time() is called by the timer thread when the timer triggers. It is
1565 /// used to print debug info and, more importantly, to detect when we are out of
1566 /// available time and thus stop the search.
1570 static Time::point lastInfoTime = Time::now();
1571 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1573 if (Time::now() - lastInfoTime >= 1000)
1575 lastInfoTime = Time::now();
1584 Threads.mutex.lock();
1586 nodes = RootPos.nodes_searched();
1588 // Loop across all split points and sum accumulated SplitPoint nodes plus
1589 // all the currently active positions nodes.
1590 for (size_t i = 0; i < Threads.size(); ++i)
1591 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1593 SplitPoint& sp = Threads[i]->splitPoints[j];
1598 Bitboard sm = sp.slavesMask;
1601 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1603 nodes += pos->nodes_searched();
1609 Threads.mutex.unlock();
1612 Time::point elapsed = Time::now() - SearchTime;
1613 bool stillAtFirstMove = Signals.firstRootMove
1614 && !Signals.failedLowAtRoot
1615 && ( elapsed > TimeMgr.available_time()
1616 || ( elapsed > (TimeMgr.available_time() * 62) / 100
1617 && elapsed > IterationTime * 1.4));
1619 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1620 || stillAtFirstMove;
1622 if ( (Limits.use_time_management() && noMoreTime)
1623 || (Limits.movetime && elapsed >= Limits.movetime)
1624 || (Limits.nodes && nodes >= Limits.nodes))
1625 Signals.stop = true;