2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // Different node types, used as template parameter
59 enum NodeType { Root, PV, NonPV };
61 // Dynamic razoring margin based on depth
62 inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
64 // Futility lookup tables (initialized at startup) and their access functions
65 int FutilityMoveCounts[2][32]; // [improving][depth]
67 inline Value futility_margin(Depth d) {
68 return Value(100 * d);
71 // Reduction lookup tables (initialized at startup) and their access function
72 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
74 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
76 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
79 size_t MultiPV, PVIdx;
81 double BestMoveChanges;
82 Value DrawValue[COLOR_NB];
85 MovesStats Countermoves, Followupmoves;
87 template <NodeType NT, bool SpNode>
88 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
90 template <NodeType NT, bool InCheck>
91 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
93 void id_loop(Position& pos);
94 Value value_to_tt(Value v, int ply);
95 Value value_from_tt(Value v, int ply);
96 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
97 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
100 Skill(int l) : level(l), best(MOVE_NONE) {}
102 if (enabled()) // Swap best PV line with the sub-optimal one
103 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
104 RootMoves.end(), best ? best : pick_move()));
107 bool enabled() const { return level < 20; }
108 bool time_to_pick(int depth) const { return depth == 1 + level; }
118 /// Search::init() is called during startup to initialize various lookup tables
120 void Search::init() {
122 int d; // depth (ONE_PLY == 2)
123 int hd; // half depth (ONE_PLY == 1)
126 // Init reductions array
127 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
129 double pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
130 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
131 Reductions[1][1][hd][mc] = int8_t( pvRed >= 1.0 ? pvRed * int(ONE_PLY) : 0);
132 Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed * int(ONE_PLY) : 0);
134 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
135 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
137 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
138 Reductions[0][0][hd][mc] += ONE_PLY;
140 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
141 Reductions[0][0][hd][mc] += ONE_PLY / 2;
144 // Init futility move count array
145 for (d = 0; d < 32; ++d)
147 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.00, 1.8));
148 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * pow(d + 0.98, 1.8));
153 /// Search::perft() is our utility to verify move generation. All the leaf nodes
154 /// up to the given depth are generated and counted and the sum returned.
156 static uint64_t perft(Position& pos, Depth depth) {
161 const bool leaf = depth == 2 * ONE_PLY;
163 for (MoveList<LEGAL> it(pos); *it; ++it)
165 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
166 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
172 uint64_t Search::perft(Position& pos, Depth depth) {
173 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
176 /// Search::think() is the external interface to Stockfish's search, and is
177 /// called by the main thread when the program receives the UCI 'go' command. It
178 /// searches from RootPos and at the end prints the "bestmove" to output.
180 void Search::think() {
182 TimeMgr.init(Limits, RootPos.game_ply(), RootPos.side_to_move());
184 int cf = Options["Contempt Factor"] * PawnValueEg / 100; // From centipawns
185 DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(cf);
186 DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(cf);
188 if (RootMoves.empty())
190 RootMoves.push_back(MOVE_NONE);
191 sync_cout << "info depth 0 score "
192 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
198 if (Options["Write Search Log"])
200 Log log(Options["Search Log Filename"]);
201 log << "\nSearching: " << RootPos.fen()
202 << "\ninfinite: " << Limits.infinite
203 << " ponder: " << Limits.ponder
204 << " time: " << Limits.time[RootPos.side_to_move()]
205 << " increment: " << Limits.inc[RootPos.side_to_move()]
206 << " moves to go: " << Limits.movestogo
207 << "\n" << std::endl;
210 // Reset the threads, still sleeping: will wake up at split time
211 for (size_t i = 0; i < Threads.size(); ++i)
212 Threads[i]->maxPly = 0;
214 Threads.timer->run = true;
215 Threads.timer->notify_one(); // Wake up the recurring timer
217 id_loop(RootPos); // Let's start searching !
219 Threads.timer->run = false; // Stop the timer
221 if (Options["Write Search Log"])
223 Time::point elapsed = Time::now() - SearchTime + 1;
225 Log log(Options["Search Log Filename"]);
226 log << "Nodes: " << RootPos.nodes_searched()
227 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
228 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
231 RootPos.do_move(RootMoves[0].pv[0], st);
232 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
233 RootPos.undo_move(RootMoves[0].pv[0]);
238 // When search is stopped this info is not printed
239 sync_cout << "info nodes " << RootPos.nodes_searched()
240 << " time " << Time::now() - SearchTime + 1 << sync_endl;
242 // When we reach the maximum depth, we can arrive here without a raise of
243 // Signals.stop. However, if we are pondering or in an infinite search,
244 // the UCI protocol states that we shouldn't print the best move before the
245 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
246 // until the GUI sends one of those commands (which also raises Signals.stop).
247 if (!Signals.stop && (Limits.ponder || Limits.infinite))
249 Signals.stopOnPonderhit = true;
250 RootPos.this_thread()->wait_for(Signals.stop);
253 // Best move could be MOVE_NONE when searching on a stalemate position
254 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
255 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
262 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
263 // with increasing depth until the allocated thinking time has been consumed,
264 // user stops the search, or the maximum search depth is reached.
266 void id_loop(Position& pos) {
268 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
270 Value bestValue, alpha, beta, delta;
272 std::memset(ss-2, 0, 5 * sizeof(Stack));
276 bestValue = delta = alpha = -VALUE_INFINITE;
277 beta = VALUE_INFINITE;
282 Countermoves.clear();
283 Followupmoves.clear();
285 MultiPV = Options["MultiPV"];
286 Skill skill(Options["Skill Level"]);
288 // Do we have to play with skill handicap? In this case enable MultiPV search
289 // that we will use behind the scenes to retrieve a set of possible moves.
290 if (skill.enabled() && MultiPV < 4)
293 MultiPV = std::min(MultiPV, RootMoves.size());
295 // Iterative deepening loop until requested to stop or target depth reached
296 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
298 // Age out PV variability metric
299 BestMoveChanges *= 0.5;
301 // Save the last iteration's scores before first PV line is searched and
302 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
303 for (size_t i = 0; i < RootMoves.size(); ++i)
304 RootMoves[i].prevScore = RootMoves[i].score;
306 // MultiPV loop. We perform a full root search for each PV line
307 for (PVIdx = 0; PVIdx < MultiPV && !Signals.stop; ++PVIdx)
309 // Reset aspiration window starting size
313 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
314 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
317 // Start with a small aspiration window and, in the case of a fail
318 // high/low, re-search with a bigger window until we're not failing
322 bestValue = search<Root, false>(pos, ss, alpha, beta, depth * ONE_PLY, false);
324 // Bring the best move to the front. It is critical that sorting
325 // is done with a stable algorithm because all the values but the
326 // first and eventually the new best one are set to -VALUE_INFINITE
327 // and we want to keep the same order for all the moves except the
328 // new PV that goes to the front. Note that in case of MultiPV
329 // search the already searched PV lines are preserved.
330 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
332 // Write PV back to transposition table in case the relevant
333 // entries have been overwritten during the search.
334 for (size_t i = 0; i <= PVIdx; ++i)
335 RootMoves[i].insert_pv_in_tt(pos);
337 // If search has been stopped break immediately. Sorting and
338 // writing PV back to TT is safe because RootMoves is still
339 // valid, although it refers to previous iteration.
343 // When failing high/low give some update (without cluttering
344 // the UI) before a re-search.
345 if ( (bestValue <= alpha || bestValue >= beta)
346 && Time::now() - SearchTime > 3000)
347 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
349 // In case of failing low/high increase aspiration window and
350 // re-search, otherwise exit the loop.
351 if (bestValue <= alpha)
353 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
355 Signals.failedLowAtRoot = true;
356 Signals.stopOnPonderhit = false;
358 else if (bestValue >= beta)
359 beta = std::min(bestValue + delta, VALUE_INFINITE);
366 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
369 // Sort the PV lines searched so far and update the GUI
370 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
372 if (PVIdx + 1 == MultiPV || Time::now() - SearchTime > 3000)
373 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
376 // If skill levels are enabled and time is up, pick a sub-optimal best move
377 if (skill.enabled() && skill.time_to_pick(depth))
380 if (Options["Write Search Log"])
382 RootMove& rm = RootMoves[0];
383 if (skill.best != MOVE_NONE)
384 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
386 Log log(Options["Search Log Filename"]);
387 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
391 // Have we found a "mate in x"?
393 && bestValue >= VALUE_MATE_IN_MAX_PLY
394 && VALUE_MATE - bestValue <= 2 * Limits.mate)
397 // Do we have time for the next iteration? Can we stop searching now?
398 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
400 // Take some extra time if the best move has changed
401 if (depth > 4 && depth < 50 && MultiPV == 1)
402 TimeMgr.pv_instability(BestMoveChanges);
404 // Stop the search if only one legal move is available or all
405 // of the available time has been used.
406 if ( RootMoves.size() == 1
407 || Time::now() - SearchTime > TimeMgr.available_time())
409 // If we are allowed to ponder do not stop the search now but
410 // keep pondering until the GUI sends "ponderhit" or "stop".
412 Signals.stopOnPonderhit = true;
421 // search<>() is the main search function for both PV and non-PV nodes and for
422 // normal and SplitPoint nodes. When called just after a split point the search
423 // is simpler because we have already probed the hash table, done a null move
424 // search, and searched the first move before splitting, so we don't have to
425 // repeat all this work again. We also don't need to store anything to the hash
426 // table here: This is taken care of after we return from the split point.
428 template <NodeType NT, bool SpNode>
429 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
431 const bool RootNode = NT == Root;
432 const bool PvNode = NT == PV || NT == Root;
434 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
435 assert(PvNode || (alpha == beta - 1));
436 assert(depth > DEPTH_ZERO);
438 Move quietsSearched[64];
441 SplitPoint* splitPoint;
443 Move ttMove, move, excludedMove, bestMove;
444 Depth ext, newDepth, predictedDepth;
445 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
446 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
447 bool captureOrPromotion, dangerous, doFullDepthSearch;
448 int moveCount, quietCount;
450 // Step 1. Initialize node
451 Thread* thisThread = pos.this_thread();
452 inCheck = pos.checkers();
456 splitPoint = ss->splitPoint;
457 bestMove = splitPoint->bestMove;
458 bestValue = splitPoint->bestValue;
460 ttMove = excludedMove = MOVE_NONE;
461 ttValue = VALUE_NONE;
463 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
468 moveCount = quietCount = 0;
469 bestValue = -VALUE_INFINITE;
470 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
471 ss->ply = (ss-1)->ply + 1;
472 (ss+1)->skipNullMove = (ss+1)->nullChild = false; (ss+1)->reduction = DEPTH_ZERO;
473 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
475 // Used to send selDepth info to GUI
476 if (PvNode && thisThread->maxPly < ss->ply)
477 thisThread->maxPly = ss->ply;
481 // Step 2. Check for aborted search and immediate draw
482 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
483 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
485 // Step 3. Mate distance pruning. Even if we mate at the next move our score
486 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
487 // a shorter mate was found upward in the tree then there is no need to search
488 // because we will never beat the current alpha. Same logic but with reversed
489 // signs applies also in the opposite condition of being mated instead of giving
490 // mate. In this case return a fail-high score.
491 alpha = std::max(mated_in(ss->ply), alpha);
492 beta = std::min(mate_in(ss->ply+1), beta);
497 // Step 4. Transposition table lookup
498 // We don't want the score of a partial search to overwrite a previous full search
499 // TT value, so we use a different position key in case of an excluded move.
500 excludedMove = ss->excludedMove;
501 posKey = excludedMove ? pos.exclusion_key() : pos.key();
502 tte = TT.probe(posKey);
503 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
504 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
506 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
507 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
508 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
509 // we should also update RootMoveList to avoid bogus output.
512 && tte->depth() >= depth
513 && ttValue != VALUE_NONE // Only in case of TT access race
514 && ( PvNode ? tte->bound() == BOUND_EXACT
515 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
516 : (tte->bound() & BOUND_UPPER)))
518 ss->currentMove = ttMove; // Can be MOVE_NONE
520 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
521 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
522 update_stats(pos, ss, ttMove, depth, NULL, 0);
527 // Step 5. Evaluate the position statically and update parent's gain statistics
530 ss->staticEval = eval = VALUE_NONE;
536 // Never assume anything on values stored in TT
537 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
538 eval = ss->staticEval = evaluate(pos);
540 // Can ttValue be used as a better position evaluation?
541 if (ttValue != VALUE_NONE)
542 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
547 eval = ss->staticEval = ss->nullChild ? -(ss-1)->staticEval + 2 * Eval::Tempo : evaluate(pos);
548 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
551 if ( !pos.captured_piece_type()
552 && ss->staticEval != VALUE_NONE
553 && (ss-1)->staticEval != VALUE_NONE
554 && (move = (ss-1)->currentMove) != MOVE_NULL
556 && type_of(move) == NORMAL)
558 Square to = to_sq(move);
559 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
562 // Step 6. Razoring (skipped when in check)
564 && depth < 4 * ONE_PLY
565 && eval + razor_margin(depth) <= alpha
566 && ttMove == MOVE_NONE
567 && abs(beta) < VALUE_MATE_IN_MAX_PLY
568 && !pos.pawn_on_7th(pos.side_to_move()))
570 if ( depth <= ONE_PLY
571 && eval + razor_margin(3 * ONE_PLY) <= alpha)
572 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
574 Value ralpha = alpha - razor_margin(depth);
575 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
580 // Step 7. Futility pruning: child node (skipped when in check)
583 && depth < 7 * ONE_PLY
584 && eval - futility_margin(depth) >= beta
585 && abs(beta) < VALUE_MATE_IN_MAX_PLY
586 && abs(eval) < VALUE_KNOWN_WIN
587 && pos.non_pawn_material(pos.side_to_move()))
588 return eval - futility_margin(depth);
590 // Step 8. Null move search with verification search (is omitted in PV nodes)
593 && depth >= 2 * ONE_PLY
595 && abs(beta) < VALUE_MATE_IN_MAX_PLY
596 && pos.non_pawn_material(pos.side_to_move()))
598 ss->currentMove = MOVE_NULL;
600 assert(eval - beta >= 0);
602 // Null move dynamic reduction based on depth and value
603 Depth R = 3 * ONE_PLY
605 + int(eval - beta) / PawnValueMg * ONE_PLY;
607 pos.do_null_move(st);
608 (ss+1)->skipNullMove = (ss+1)->nullChild = true;
609 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
610 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
611 (ss+1)->skipNullMove = (ss+1)->nullChild = false;
612 pos.undo_null_move();
614 if (nullValue >= beta)
616 // Do not return unproven mate scores
617 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
620 if (depth < 12 * ONE_PLY)
623 // Do verification search at high depths
624 ss->skipNullMove = true;
625 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
626 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
627 ss->skipNullMove = false;
634 // Step 9. ProbCut (skipped when in check)
635 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
636 // and a reduced search returns a value much above beta, we can (almost) safely
637 // prune the previous move.
639 && depth >= 5 * ONE_PLY
641 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
643 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
644 Depth rdepth = depth - 4 * ONE_PLY;
646 assert(rdepth >= ONE_PLY);
647 assert((ss-1)->currentMove != MOVE_NONE);
648 assert((ss-1)->currentMove != MOVE_NULL);
650 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
653 while ((move = mp.next_move<false>()) != MOVE_NONE)
654 if (pos.legal(move, ci.pinned))
656 ss->currentMove = move;
657 pos.do_move(move, st, ci, pos.gives_check(move, ci));
658 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
665 // Step 10. Internal iterative deepening (skipped when in check)
666 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
668 && (PvNode || ss->staticEval + 256 >= beta))
670 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
672 ss->skipNullMove = true;
673 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
674 ss->skipNullMove = false;
676 tte = TT.probe(posKey);
677 ttMove = tte ? tte->move() : MOVE_NONE;
680 moves_loop: // When in check and at SpNode search starts from here
682 Square prevMoveSq = to_sq((ss-1)->currentMove);
683 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
684 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
686 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
687 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
688 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
690 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
692 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
693 improving = ss->staticEval >= (ss-2)->staticEval
694 || ss->staticEval == VALUE_NONE
695 ||(ss-2)->staticEval == VALUE_NONE;
697 singularExtensionNode = !RootNode
699 && depth >= 8 * ONE_PLY
700 && ttMove != MOVE_NONE
701 && !excludedMove // Recursive singular search is not allowed
702 && (tte->bound() & BOUND_LOWER)
703 && tte->depth() >= depth - 3 * ONE_PLY;
705 // Step 11. Loop through moves
706 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
707 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
711 if (move == excludedMove)
714 // At root obey the "searchmoves" option and skip moves not listed in Root
715 // Move List. As a consequence any illegal move is also skipped. In MultiPV
716 // mode we also skip PV moves which have been already searched.
717 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
722 // Shared counter cannot be decremented later if the move turns out to be illegal
723 if (!pos.legal(move, ci.pinned))
726 moveCount = ++splitPoint->moveCount;
727 splitPoint->mutex.unlock();
734 Signals.firstRootMove = (moveCount == 1);
736 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
737 sync_cout << "info depth " << depth / ONE_PLY
738 << " currmove " << move_to_uci(move, pos.is_chess960())
739 << " currmovenumber " << moveCount + PVIdx << sync_endl;
743 captureOrPromotion = pos.capture_or_promotion(move);
745 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
746 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
747 : pos.gives_check(move, ci);
749 dangerous = givesCheck
750 || type_of(move) != NORMAL
751 || pos.advanced_pawn_push(move);
753 // Step 12. Extend checks
754 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
757 // Singular extension search. If all moves but one fail low on a search of
758 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
759 // is singular and should be extended. To verify this we do a reduced search
760 // on all the other moves but the ttMove and if the result is lower than
761 // ttValue minus a margin then we extend the ttMove.
762 if ( singularExtensionNode
765 && pos.legal(move, ci.pinned)
766 && abs(ttValue) < VALUE_KNOWN_WIN)
768 assert(ttValue != VALUE_NONE);
770 Value rBeta = ttValue - int(depth);
771 ss->excludedMove = move;
772 ss->skipNullMove = true;
773 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
774 ss->skipNullMove = false;
775 ss->excludedMove = MOVE_NONE;
781 // Update the current move (this must be done after singular extension search)
782 newDepth = depth - ONE_PLY + ext;
784 // Step 13. Pruning at shallow depth (exclude PV nodes)
786 && !captureOrPromotion
789 /* && move != ttMove Already implicit in the next condition */
790 && bestValue > VALUE_MATED_IN_MAX_PLY)
792 // Move count based pruning
793 if ( depth < 16 * ONE_PLY
794 && moveCount >= FutilityMoveCounts[improving][depth] )
797 splitPoint->mutex.lock();
802 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
804 // Futility pruning: parent node
805 if (predictedDepth < 7 * ONE_PLY)
807 futilityValue = ss->staticEval + futility_margin(predictedDepth)
808 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
810 if (futilityValue <= alpha)
812 bestValue = std::max(bestValue, futilityValue);
816 splitPoint->mutex.lock();
817 if (bestValue > splitPoint->bestValue)
818 splitPoint->bestValue = bestValue;
824 // Prune moves with negative SEE at low depths
825 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
828 splitPoint->mutex.lock();
834 // Check for legality just before making the move
835 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
841 pvMove = PvNode && moveCount == 1;
842 ss->currentMove = move;
843 if (!SpNode && !captureOrPromotion && quietCount < 64)
844 quietsSearched[quietCount++] = move;
846 // Step 14. Make the move
847 pos.do_move(move, st, ci, givesCheck);
849 // Step 15. Reduced depth search (LMR). If the move fails high it will be
850 // re-searched at full depth.
851 if ( depth >= 3 * ONE_PLY
853 && !captureOrPromotion
855 && move != ss->killers[0]
856 && move != ss->killers[1])
858 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
860 if (!PvNode && cutNode)
861 ss->reduction += ONE_PLY;
863 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
864 ss->reduction += ONE_PLY / 2;
866 if (move == countermoves[0] || move == countermoves[1])
867 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
869 // Decrease reduction for moves that escape a capture
871 && type_of(move) == NORMAL
872 && type_of(pos.piece_on(to_sq(move))) != PAWN
873 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
874 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
876 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
878 alpha = splitPoint->alpha;
880 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
882 // Re-search at intermediate depth if reduction is very high
883 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
885 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
886 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
889 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
890 ss->reduction = DEPTH_ZERO;
893 doFullDepthSearch = !pvMove;
895 // Step 16. Full depth search, when LMR is skipped or fails high
896 if (doFullDepthSearch)
899 alpha = splitPoint->alpha;
901 value = newDepth < ONE_PLY ?
902 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
903 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
904 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
907 // For PV nodes only, do a full PV search on the first move or after a fail
908 // high (in the latter case search only if value < beta), otherwise let the
909 // parent node fail low with value <= alpha and to try another move.
910 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
911 value = newDepth < ONE_PLY ?
912 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
913 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
914 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
915 // Step 17. Undo move
918 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
920 // Step 18. Check for new best move
923 splitPoint->mutex.lock();
924 bestValue = splitPoint->bestValue;
925 alpha = splitPoint->alpha;
928 // Finished searching the move. If a stop or a cutoff occurred, the return
929 // value of the search cannot be trusted, and we return immediately without
930 // updating best move, PV and TT.
931 if (Signals.stop || thisThread->cutoff_occurred())
936 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
938 // PV move or new best move ?
939 if (pvMove || value > alpha)
942 rm.extract_pv_from_tt(pos);
944 // We record how often the best move has been changed in each
945 // iteration. This information is used for time management: When
946 // the best move changes frequently, we allocate some more time.
951 // All other moves but the PV are set to the lowest value: this is
952 // not a problem when sorting because the sort is stable and the
953 // move position in the list is preserved - just the PV is pushed up.
954 rm.score = -VALUE_INFINITE;
957 if (value > bestValue)
959 bestValue = SpNode ? splitPoint->bestValue = value : value;
963 bestMove = SpNode ? splitPoint->bestMove = move : move;
965 if (PvNode && value < beta) // Update alpha! Always alpha < beta
966 alpha = SpNode ? splitPoint->alpha = value : value;
969 assert(value >= beta); // Fail high
972 splitPoint->cutoff = true;
979 // Step 19. Check for splitting the search
981 && Threads.size() >= 2
982 && depth >= Threads.minimumSplitDepth
983 && ( !thisThread->activeSplitPoint
984 || !thisThread->activeSplitPoint->allSlavesSearching)
985 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
987 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
989 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
990 depth, moveCount, &mp, NT, cutNode);
992 if (Signals.stop || thisThread->cutoff_occurred())
995 if (bestValue >= beta)
1003 // Following condition would detect a stop or a cutoff set only after move
1004 // loop has been completed. But in this case bestValue is valid because we
1005 // have fully searched our subtree, and we can anyhow save the result in TT.
1007 if (Signals.stop || thisThread->cutoff_occurred())
1011 // Step 20. Check for mate and stalemate
1012 // All legal moves have been searched and if there are no legal moves, it
1013 // must be mate or stalemate. If we are in a singular extension search then
1014 // return a fail low score.
1016 bestValue = excludedMove ? alpha
1017 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1019 // Quiet best move: update killers, history, countermoves and followupmoves
1020 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1021 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1023 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1024 bestValue >= beta ? BOUND_LOWER :
1025 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1026 depth, bestMove, ss->staticEval);
1028 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1034 // qsearch() is the quiescence search function, which is called by the main
1035 // search function when the remaining depth is zero (or, to be more precise,
1036 // less than ONE_PLY).
1038 template <NodeType NT, bool InCheck>
1039 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1041 const bool PvNode = NT == PV;
1043 assert(NT == PV || NT == NonPV);
1044 assert(InCheck == !!pos.checkers());
1045 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1046 assert(PvNode || (alpha == beta - 1));
1047 assert(depth <= DEPTH_ZERO);
1052 Move ttMove, move, bestMove;
1053 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1054 bool givesCheck, evasionPrunable;
1057 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1061 ss->currentMove = bestMove = MOVE_NONE;
1062 ss->ply = (ss-1)->ply + 1;
1064 // Check for an instant draw or if the maximum ply has been reached
1065 if (pos.is_draw() || ss->ply > MAX_PLY)
1066 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1068 // Decide whether or not to include checks: this fixes also the type of
1069 // TT entry depth that we are going to use. Note that in qsearch we use
1070 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1071 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1072 : DEPTH_QS_NO_CHECKS;
1074 // Transposition table lookup
1076 tte = TT.probe(posKey);
1077 ttMove = tte ? tte->move() : MOVE_NONE;
1078 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1081 && tte->depth() >= ttDepth
1082 && ttValue != VALUE_NONE // Only in case of TT access race
1083 && ( PvNode ? tte->bound() == BOUND_EXACT
1084 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1085 : (tte->bound() & BOUND_UPPER)))
1087 ss->currentMove = ttMove; // Can be MOVE_NONE
1091 // Evaluate the position statically
1094 ss->staticEval = VALUE_NONE;
1095 bestValue = futilityBase = -VALUE_INFINITE;
1101 // Never assume anything on values stored in TT
1102 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1103 ss->staticEval = bestValue = evaluate(pos);
1105 // Can ttValue be used as a better position evaluation?
1106 if (ttValue != VALUE_NONE)
1107 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1108 bestValue = ttValue;
1111 ss->staticEval = bestValue = ss->nullChild ? -(ss-1)->staticEval + 2 * Eval::Tempo : evaluate(pos);
1113 // Stand pat. Return immediately if static value is at least beta
1114 if (bestValue >= beta)
1117 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1118 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1123 if (PvNode && bestValue > alpha)
1126 futilityBase = bestValue + 128;
1129 // Initialize a MovePicker object for the current position, and prepare
1130 // to search the moves. Because the depth is <= 0 here, only captures,
1131 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1133 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1136 // Loop through the moves until no moves remain or a beta cutoff occurs
1137 while ((move = mp.next_move<false>()) != MOVE_NONE)
1139 assert(is_ok(move));
1141 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1142 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1143 : pos.gives_check(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) <= VALUE_ZERO)
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) < VALUE_ZERO)
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(const 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[MultiPV - 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 < MultiPV; ++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 ss;
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 (ss.rdbuf()->in_avail()) // Not at first line
1366 ss << "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 ss << " " << 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;
1394 int ply = 1; // At root ply is 1...
1395 Move m = pv[0]; // ...instead pv[] array starts from 0
1396 Value expectedScore = score;
1403 assert(MoveList<LEGAL>(pos).contains(pv[ply - 1]));
1405 pos.do_move(pv[ply++ - 1], *st++);
1406 tte = TT.probe(pos.key());
1407 expectedScore = -expectedScore;
1410 && expectedScore == value_from_tt(tte->value(), ply)
1411 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1412 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1414 && (!pos.is_draw() || ply <= 2));
1416 pv.push_back(MOVE_NONE); // Must be zero-terminating
1418 while (--ply) pos.undo_move(pv[ply - 1]);
1422 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1423 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1424 /// first, even if the old TT entries have been overwritten.
1426 void RootMove::insert_pv_in_tt(Position& pos) {
1428 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1430 int idx = 0; // Ply starts from 1, we need to start from 0
1433 tte = TT.probe(pos.key());
1435 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1436 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1438 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1440 pos.do_move(pv[idx++], *st++);
1442 } while (pv[idx] != MOVE_NONE);
1444 while (idx) pos.undo_move(pv[--idx]);
1448 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1450 void Thread::idle_loop() {
1452 // Pointer 'this_sp' is not null only if we are called from split(), and not
1453 // at the thread creation. This means we are the split point's master.
1454 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1456 assert(!this_sp || (this_sp->masterThread == this && searching));
1460 // If we are not searching, wait for a condition to be signaled instead of
1461 // wasting CPU time polling for work.
1462 while (!searching || exit)
1470 // Grab the lock to avoid races with Thread::notify_one()
1473 // If we are master and all slaves have finished then exit idle_loop
1474 if (this_sp && this_sp->slavesMask.none())
1480 // Do sleep after retesting sleep conditions under lock protection. In
1481 // particular we need to avoid a deadlock in case a master thread has,
1482 // in the meanwhile, allocated us and sent the notify_one() call before
1483 // we had the chance to grab the lock.
1484 if (!searching && !exit)
1485 sleepCondition.wait(mutex);
1490 // If this thread has been assigned work, launch a search
1495 Threads.mutex.lock();
1498 assert(activeSplitPoint);
1499 SplitPoint* sp = activeSplitPoint;
1501 Threads.mutex.unlock();
1503 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1504 Position pos(*sp->pos, this);
1506 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1507 ss->splitPoint = sp;
1511 assert(activePosition == NULL);
1513 activePosition = &pos;
1515 if (sp->nodeType == NonPV)
1516 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1518 else if (sp->nodeType == PV)
1519 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1521 else if (sp->nodeType == Root)
1522 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1530 activePosition = NULL;
1531 sp->slavesMask.reset(idx);
1532 sp->allSlavesSearching = false;
1533 sp->nodes += pos.nodes_searched();
1535 // Wake up the master thread so to allow it to return from the idle
1536 // loop in case we are the last slave of the split point.
1537 if ( this != sp->masterThread
1538 && sp->slavesMask.none())
1540 assert(!sp->masterThread->searching);
1541 sp->masterThread->notify_one();
1544 // After releasing the lock we can't access any SplitPoint related data
1545 // in a safe way because it could have been released under our feet by
1549 // Try to late join to another split point if none of its slaves has
1550 // already finished.
1551 if (Threads.size() > 2)
1552 for (size_t i = 0; i < Threads.size(); ++i)
1554 const int size = Threads[i]->splitPointsSize; // Local copy
1555 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1558 && sp->allSlavesSearching
1559 && available_to(Threads[i]))
1561 // Recheck the conditions under lock protection
1562 Threads.mutex.lock();
1565 if ( sp->allSlavesSearching
1566 && available_to(Threads[i]))
1568 sp->slavesMask.set(idx);
1569 activeSplitPoint = sp;
1574 Threads.mutex.unlock();
1576 break; // Just a single attempt
1581 // If this thread is the master of a split point and all slaves have finished
1582 // their work at this split point, return from the idle loop.
1583 if (this_sp && this_sp->slavesMask.none())
1585 this_sp->mutex.lock();
1586 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1587 this_sp->mutex.unlock();
1595 /// check_time() is called by the timer thread when the timer triggers. It is
1596 /// used to print debug info and, more importantly, to detect when we are out of
1597 /// available time and thus stop the search.
1601 static Time::point lastInfoTime = Time::now();
1602 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1604 if (Time::now() - lastInfoTime >= 1000)
1606 lastInfoTime = Time::now();
1615 Threads.mutex.lock();
1617 nodes = RootPos.nodes_searched();
1619 // Loop across all split points and sum accumulated SplitPoint nodes plus
1620 // all the currently active positions nodes.
1621 for (size_t i = 0; i < Threads.size(); ++i)
1622 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1624 SplitPoint& sp = Threads[i]->splitPoints[j];
1630 for (size_t idx = 0; idx < Threads.size(); ++idx)
1631 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1632 nodes += Threads[idx]->activePosition->nodes_searched();
1637 Threads.mutex.unlock();
1640 Time::point elapsed = Time::now() - SearchTime;
1641 bool stillAtFirstMove = Signals.firstRootMove
1642 && !Signals.failedLowAtRoot
1643 && elapsed > TimeMgr.available_time() * 75 / 100;
1645 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1646 || stillAtFirstMove;
1648 if ( (Limits.use_time_management() && noMoreTime)
1649 || (Limits.movetime && elapsed >= Limits.movetime)
1650 || (Limits.nodes && nodes >= Limits.nodes))
1651 Signals.stop = true;