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/>.
39 volatile SignalsType Signals;
41 std::vector<RootMove> RootMoves;
43 Time::point SearchTime;
44 StateStackPtr SetupStates;
49 using namespace Search;
53 // Different node types, used as template parameter
54 enum NodeType { Root, PV, NonPV };
56 // Dynamic razoring margin based on depth
57 inline Value razor_margin(Depth d) { return Value(512 + 32 * d); }
59 // Futility lookup tables (initialized at startup) and their access functions
60 int FutilityMoveCounts[2][32]; // [improving][depth]
62 inline Value futility_margin(Depth d) {
63 return Value(200 * d);
66 // Reduction lookup tables (initialized at startup) and their access function
67 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
69 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
70 return (Depth) Reductions[PvNode][i][std::min(int(d), 63)][std::min(mn, 63)];
75 double BestMoveChanges;
76 Value DrawValue[COLOR_NB];
79 MovesStats Countermoves, Followupmoves;
81 template <NodeType NT, bool SpNode>
82 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
84 template <NodeType NT, bool InCheck>
85 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
87 void id_loop(Position& pos);
88 Value value_to_tt(Value v, int ply);
89 Value value_from_tt(Value v, int ply);
90 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
91 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
94 Skill(int l, size_t rootSize) : level(l),
95 candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
98 if (candidates) // Swap best PV line with the sub-optimal one
99 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
100 RootMoves.end(), best ? best : pick_move()));
103 size_t candidates_size() const { return candidates; }
104 bool time_to_pick(int depth) const { return depth == 1 + level; }
115 /// Search::init() is called during startup to initialize various lookup tables
117 void Search::init() {
119 int d; // depth (ONE_PLY == 2)
120 int hd; // half depth (ONE_PLY == 1)
123 // Init reductions array
124 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
126 double pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
127 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
129 Reductions[1][1][hd][mc] = int8_t( pvRed >= 1.0 ? pvRed + 0.5: 0);
130 Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed + 0.5: 0);
132 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
133 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
135 if (Reductions[0][0][hd][mc] >= 2)
136 Reductions[0][0][hd][mc] += 1;
139 // Init futility move count array
140 for (d = 0; d < 32; ++d)
142 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
143 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
148 /// Search::perft() is our utility to verify move generation. All the leaf nodes
149 /// up to the given depth are generated and counted and the sum returned.
151 uint64_t Search::perft(Position& pos, Depth depth) {
154 uint64_t cnt, nodes = 0;
156 const bool leaf = (depth == 2 * ONE_PLY);
158 for (MoveList<LEGAL> it(pos); *it; ++it)
160 if (Root && depth <= ONE_PLY)
164 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
165 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
170 sync_cout << UCI::format_move(*it, pos.is_chess960()) << ": " << cnt << sync_endl;
175 template uint64_t Search::perft<true>(Position& pos, Depth depth);
178 /// Search::think() is the external interface to Stockfish's search, and is
179 /// called by the main thread when the program receives the UCI 'go' command. It
180 /// searches from RootPos and at the end prints the "bestmove" to output.
182 void Search::think() {
184 TimeMgr.init(Limits, RootPos.game_ply(), RootPos.side_to_move());
186 int cf = Options["Contempt"] * PawnValueEg / 100; // From centipawns
187 DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(cf);
188 DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(cf);
190 if (RootMoves.empty())
192 RootMoves.push_back(MOVE_NONE);
193 sync_cout << "info depth 0 score "
194 << UCI::format_value(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
200 // Reset the threads, still sleeping: will wake up at split time
201 for (size_t i = 0; i < Threads.size(); ++i)
202 Threads[i]->maxPly = 0;
204 Threads.timer->run = true;
205 Threads.timer->notify_one(); // Wake up the recurring timer
207 id_loop(RootPos); // Let's start searching !
209 Threads.timer->run = false; // Stop the timer
213 // When search is stopped this info is not printed
214 sync_cout << "info nodes " << RootPos.nodes_searched()
215 << " time " << Time::now() - SearchTime + 1 << sync_endl;
217 // When we reach the maximum depth, we can arrive here without a raise of
218 // Signals.stop. However, if we are pondering or in an infinite search,
219 // the UCI protocol states that we shouldn't print the best move before the
220 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
221 // until the GUI sends one of those commands (which also raises Signals.stop).
222 if (!Signals.stop && (Limits.ponder || Limits.infinite))
224 Signals.stopOnPonderhit = true;
225 RootPos.this_thread()->wait_for(Signals.stop);
228 // Best move could be MOVE_NONE when searching on a stalemate position
229 sync_cout << "bestmove " << UCI::format_move(RootMoves[0].pv[0], RootPos.is_chess960())
230 << " ponder " << UCI::format_move(RootMoves[0].pv[1], RootPos.is_chess960())
237 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
238 // with increasing depth until the allocated thinking time has been consumed,
239 // user stops the search, or the maximum search depth is reached.
241 void id_loop(Position& pos) {
243 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
245 Value bestValue, alpha, beta, delta;
247 std::memset(ss-2, 0, 5 * sizeof(Stack));
251 bestValue = delta = alpha = -VALUE_INFINITE;
252 beta = VALUE_INFINITE;
257 Countermoves.clear();
258 Followupmoves.clear();
260 size_t multiPV = Options["MultiPV"];
261 Skill skill(Options["Skill Level"], RootMoves.size());
263 // Do we have to play with skill handicap? In this case enable MultiPV search
264 // that we will use behind the scenes to retrieve a set of possible moves.
265 multiPV = std::max(multiPV, skill.candidates_size());
267 // Iterative deepening loop until requested to stop or target depth reached
268 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
270 // Age out PV variability metric
271 BestMoveChanges *= 0.5;
273 // Save the last iteration's scores before first PV line is searched and
274 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
275 for (size_t i = 0; i < RootMoves.size(); ++i)
276 RootMoves[i].prevScore = RootMoves[i].score;
278 // MultiPV loop. We perform a full root search for each PV line
279 for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
281 // Reset aspiration window starting size
285 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
286 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
289 // Start with a small aspiration window and, in the case of a fail
290 // high/low, re-search with a bigger window until we're not failing
294 bestValue = search<Root, false>(pos, ss, alpha, beta, depth * ONE_PLY, false);
296 // Bring the best move to the front. It is critical that sorting
297 // is done with a stable algorithm because all the values but the
298 // first and eventually the new best one are set to -VALUE_INFINITE
299 // and we want to keep the same order for all the moves except the
300 // new PV that goes to the front. Note that in case of MultiPV
301 // search the already searched PV lines are preserved.
302 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
304 // Write PV back to transposition table in case the relevant
305 // entries have been overwritten during the search.
306 for (size_t i = 0; i <= PVIdx; ++i)
307 RootMoves[i].insert_pv_in_tt(pos);
309 // If search has been stopped break immediately. Sorting and
310 // writing PV back to TT is safe because RootMoves is still
311 // valid, although it refers to previous iteration.
315 // When failing high/low give some update (without cluttering
316 // the UI) before a re-search.
317 if ( (bestValue <= alpha || bestValue >= beta)
318 && Time::now() - SearchTime > 3000)
319 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
321 // In case of failing low/high increase aspiration window and
322 // re-search, otherwise exit the loop.
323 if (bestValue <= alpha)
325 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
327 Signals.failedLowAtRoot = true;
328 Signals.stopOnPonderhit = false;
330 else if (bestValue >= beta)
331 beta = std::min(bestValue + delta, VALUE_INFINITE);
336 delta += 3 * delta / 8;
338 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
341 // Sort the PV lines searched so far and update the GUI
342 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
345 && ( PVIdx + 1 == std::min(multiPV, RootMoves.size())
346 || Time::now() - SearchTime > 3000))
347 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
350 // If skill levels are enabled and time is up, pick a sub-optimal best move
351 if (skill.candidates_size() && skill.time_to_pick(depth))
354 // Have we found a "mate in x"?
356 && bestValue >= VALUE_MATE_IN_MAX_PLY
357 && VALUE_MATE - bestValue <= 2 * Limits.mate)
360 // Do we have time for the next iteration? Can we stop searching now?
361 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
363 // Take some extra time if the best move has changed
364 if (depth > 4 && multiPV == 1)
365 TimeMgr.pv_instability(BestMoveChanges);
367 // Stop the search if only one legal move is available or all
368 // of the available time has been used.
369 if ( RootMoves.size() == 1
370 || Time::now() - SearchTime > TimeMgr.available_time())
372 // If we are allowed to ponder do not stop the search now but
373 // keep pondering until the GUI sends "ponderhit" or "stop".
375 Signals.stopOnPonderhit = true;
384 // search<>() is the main search function for both PV and non-PV nodes and for
385 // normal and SplitPoint nodes. When called just after a split point the search
386 // is simpler because we have already probed the hash table, done a null move
387 // search, and searched the first move before splitting, so we don't have to
388 // repeat all this work again. We also don't need to store anything to the hash
389 // table here: This is taken care of after we return from the split point.
391 template <NodeType NT, bool SpNode>
392 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
394 const bool RootNode = NT == Root;
395 const bool PvNode = NT == PV || NT == Root;
397 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
398 assert(PvNode || (alpha == beta - 1));
399 assert(depth > DEPTH_ZERO);
401 Move quietsSearched[64];
404 SplitPoint* splitPoint;
406 Move ttMove, move, excludedMove, bestMove;
407 Depth ext, newDepth, predictedDepth;
408 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
409 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
410 bool captureOrPromotion, dangerous, doFullDepthSearch;
411 int moveCount, quietCount;
413 // Step 1. Initialize node
414 Thread* thisThread = pos.this_thread();
415 inCheck = pos.checkers();
419 splitPoint = ss->splitPoint;
420 bestMove = splitPoint->bestMove;
421 bestValue = splitPoint->bestValue;
423 ttMove = excludedMove = MOVE_NONE;
424 ttValue = VALUE_NONE;
426 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
431 moveCount = quietCount = 0;
432 bestValue = -VALUE_INFINITE;
433 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
434 ss->ply = (ss-1)->ply + 1;
435 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
436 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
438 // Used to send selDepth info to GUI
439 if (PvNode && thisThread->maxPly < ss->ply)
440 thisThread->maxPly = ss->ply;
444 // Step 2. Check for aborted search and immediate draw
445 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
446 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
448 // Step 3. Mate distance pruning. Even if we mate at the next move our score
449 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
450 // a shorter mate was found upward in the tree then there is no need to search
451 // because we will never beat the current alpha. Same logic but with reversed
452 // signs applies also in the opposite condition of being mated instead of giving
453 // mate. In this case return a fail-high score.
454 alpha = std::max(mated_in(ss->ply), alpha);
455 beta = std::min(mate_in(ss->ply+1), beta);
460 // Step 4. Transposition table lookup
461 // We don't want the score of a partial search to overwrite a previous full search
462 // TT value, so we use a different position key in case of an excluded move.
463 excludedMove = ss->excludedMove;
464 posKey = excludedMove ? pos.exclusion_key() : pos.key();
465 tte = TT.probe(posKey);
466 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
467 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
469 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
470 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
471 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
472 // we should also update RootMoveList to avoid bogus output.
475 && tte->depth() >= depth
476 && ttValue != VALUE_NONE // Only in case of TT access race
477 && ( PvNode ? tte->bound() == BOUND_EXACT
478 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
479 : (tte->bound() & BOUND_UPPER)))
481 ss->currentMove = ttMove; // Can be MOVE_NONE
483 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
484 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
485 update_stats(pos, ss, ttMove, depth, NULL, 0);
490 // Step 5. Evaluate the position statically and update parent's gain statistics
493 ss->staticEval = eval = VALUE_NONE;
499 // Never assume anything on values stored in TT
500 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
501 eval = ss->staticEval = evaluate(pos);
503 // Can ttValue be used as a better position evaluation?
504 if (ttValue != VALUE_NONE)
505 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
510 eval = ss->staticEval =
511 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
513 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
516 if ( !pos.captured_piece_type()
517 && ss->staticEval != VALUE_NONE
518 && (ss-1)->staticEval != VALUE_NONE
519 && (move = (ss-1)->currentMove) != MOVE_NULL
521 && type_of(move) == NORMAL)
523 Square to = to_sq(move);
524 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
527 // Step 6. Razoring (skipped when in check)
529 && depth < 4 * ONE_PLY
530 && eval + razor_margin(depth) <= alpha
531 && ttMove == MOVE_NONE
532 && !pos.pawn_on_7th(pos.side_to_move()))
534 if ( depth <= ONE_PLY
535 && eval + razor_margin(3 * ONE_PLY) <= alpha)
536 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
538 Value ralpha = alpha - razor_margin(depth);
539 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
544 // Step 7. Futility pruning: child node (skipped when in check)
547 && depth < 7 * ONE_PLY
548 && eval - futility_margin(depth) >= beta
549 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
550 && pos.non_pawn_material(pos.side_to_move()))
551 return eval - futility_margin(depth);
553 // Step 8. Null move search with verification search (is omitted in PV nodes)
556 && depth >= 2 * ONE_PLY
558 && pos.non_pawn_material(pos.side_to_move()))
560 ss->currentMove = MOVE_NULL;
562 assert(eval - beta >= 0);
564 // Null move dynamic reduction based on depth and value
565 Depth R = (3 + depth / 4 + std::min(int(eval - beta) / PawnValueMg, 3)) * ONE_PLY;
567 pos.do_null_move(st);
568 (ss+1)->skipNullMove = true;
569 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
570 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
571 (ss+1)->skipNullMove = false;
572 pos.undo_null_move();
574 if (nullValue >= beta)
576 // Do not return unproven mate scores
577 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
580 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
583 // Do verification search at high depths
584 ss->skipNullMove = true;
585 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
586 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
587 ss->skipNullMove = false;
594 // Step 9. ProbCut (skipped when in check)
595 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
596 // and a reduced search returns a value much above beta, we can (almost) safely
597 // prune the previous move.
599 && depth >= 5 * ONE_PLY
601 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
603 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
604 Depth rdepth = depth - 4 * ONE_PLY;
606 assert(rdepth >= ONE_PLY);
607 assert((ss-1)->currentMove != MOVE_NONE);
608 assert((ss-1)->currentMove != MOVE_NULL);
610 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
613 while ((move = mp.next_move<false>()) != MOVE_NONE)
614 if (pos.legal(move, ci.pinned))
616 ss->currentMove = move;
617 pos.do_move(move, st, ci, pos.gives_check(move, ci));
618 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
625 // Step 10. Internal iterative deepening (skipped when in check)
626 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
628 && (PvNode || ss->staticEval + 256 >= beta))
630 Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
631 ss->skipNullMove = true;
632 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
633 ss->skipNullMove = false;
635 tte = TT.probe(posKey);
636 ttMove = tte ? tte->move() : MOVE_NONE;
639 moves_loop: // When in check and at SpNode search starts from here
641 Square prevMoveSq = to_sq((ss-1)->currentMove);
642 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
643 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
645 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
646 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
647 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
649 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
651 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
652 improving = ss->staticEval >= (ss-2)->staticEval
653 || ss->staticEval == VALUE_NONE
654 ||(ss-2)->staticEval == VALUE_NONE;
656 singularExtensionNode = !RootNode
658 && depth >= 8 * ONE_PLY
659 && ttMove != MOVE_NONE
660 /* && ttValue != VALUE_NONE Already implicit in the next condition */
661 && abs(ttValue) < VALUE_KNOWN_WIN
662 && !excludedMove // Recursive singular search is not allowed
663 && (tte->bound() & BOUND_LOWER)
664 && tte->depth() >= depth - 3 * ONE_PLY;
666 // Step 11. Loop through moves
667 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
668 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
672 if (move == excludedMove)
675 // At root obey the "searchmoves" option and skip moves not listed in Root
676 // Move List. As a consequence any illegal move is also skipped. In MultiPV
677 // mode we also skip PV moves which have been already searched.
678 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
683 // Shared counter cannot be decremented later if the move turns out to be illegal
684 if (!pos.legal(move, ci.pinned))
687 moveCount = ++splitPoint->moveCount;
688 splitPoint->mutex.unlock();
695 Signals.firstRootMove = (moveCount == 1);
697 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
698 sync_cout << "info depth " << depth
699 << " currmove " << UCI::format_move(move, pos.is_chess960())
700 << " currmovenumber " << moveCount + PVIdx << sync_endl;
704 captureOrPromotion = pos.capture_or_promotion(move);
706 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
707 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
708 : pos.gives_check(move, ci);
710 dangerous = givesCheck
711 || type_of(move) != NORMAL
712 || pos.advanced_pawn_push(move);
714 // Step 12. Extend checks
715 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
718 // Singular extension search. If all moves but one fail low on a search of
719 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
720 // is singular and should be extended. To verify this we do a reduced search
721 // on all the other moves but the ttMove and if the result is lower than
722 // ttValue minus a margin then we extend the ttMove.
723 if ( singularExtensionNode
726 && pos.legal(move, ci.pinned))
728 Value rBeta = ttValue - int(2 * depth);
729 ss->excludedMove = move;
730 ss->skipNullMove = true;
731 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
732 ss->skipNullMove = false;
733 ss->excludedMove = MOVE_NONE;
739 // Update the current move (this must be done after singular extension search)
740 newDepth = depth - ONE_PLY + ext;
742 // Step 13. Pruning at shallow depth (exclude PV nodes)
744 && !captureOrPromotion
747 /* && move != ttMove Already implicit in the next condition */
748 && bestValue > VALUE_MATED_IN_MAX_PLY)
750 // Move count based pruning
751 if ( depth < 16 * ONE_PLY
752 && moveCount >= FutilityMoveCounts[improving][depth])
755 splitPoint->mutex.lock();
760 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
762 // Futility pruning: parent node
763 if (predictedDepth < 7 * ONE_PLY)
765 futilityValue = ss->staticEval + futility_margin(predictedDepth)
766 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
768 if (futilityValue <= alpha)
770 bestValue = std::max(bestValue, futilityValue);
774 splitPoint->mutex.lock();
775 if (bestValue > splitPoint->bestValue)
776 splitPoint->bestValue = bestValue;
782 // Prune moves with negative SEE at low depths
783 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
786 splitPoint->mutex.lock();
792 // Speculative prefetch as early as possible
793 prefetch((char*)TT.first_entry(pos.key_after(move)));
795 // Check for legality just before making the move
796 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
802 pvMove = PvNode && moveCount == 1;
803 ss->currentMove = move;
804 if (!SpNode && !captureOrPromotion && quietCount < 64)
805 quietsSearched[quietCount++] = move;
807 // Step 14. Make the move
808 pos.do_move(move, st, ci, givesCheck);
810 // Step 15. Reduced depth search (LMR). If the move fails high it will be
811 // re-searched at full depth.
812 if ( depth >= 3 * ONE_PLY
814 && !captureOrPromotion
816 && move != ss->killers[0]
817 && move != ss->killers[1])
819 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
821 if ( (!PvNode && cutNode)
822 || History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
823 ss->reduction += ONE_PLY;
825 if (move == countermoves[0] || move == countermoves[1])
826 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
828 // Decrease reduction for moves that escape a capture
830 && type_of(move) == NORMAL
831 && type_of(pos.piece_on(to_sq(move))) != PAWN
832 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
833 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
835 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
837 alpha = splitPoint->alpha;
839 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
841 // Re-search at intermediate depth if reduction is very high
842 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
844 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
845 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
848 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
849 ss->reduction = DEPTH_ZERO;
852 doFullDepthSearch = !pvMove;
854 // Step 16. Full depth search, when LMR is skipped or fails high
855 if (doFullDepthSearch)
858 alpha = splitPoint->alpha;
860 value = newDepth < ONE_PLY ?
861 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
862 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
863 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
866 // For PV nodes only, do a full PV search on the first move or after a fail
867 // high (in the latter case search only if value < beta), otherwise let the
868 // parent node fail low with value <= alpha and to try another move.
869 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
870 value = newDepth < ONE_PLY ?
871 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
872 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
873 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
874 // Step 17. Undo move
877 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
879 // Step 18. Check for new best move
882 splitPoint->mutex.lock();
883 bestValue = splitPoint->bestValue;
884 alpha = splitPoint->alpha;
887 // Finished searching the move. If a stop or a cutoff occurred, the return
888 // value of the search cannot be trusted, and we return immediately without
889 // updating best move, PV and TT.
890 if (Signals.stop || thisThread->cutoff_occurred())
895 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
897 // PV move or new best move ?
898 if (pvMove || value > alpha)
901 rm.extract_pv_from_tt(pos);
903 // We record how often the best move has been changed in each
904 // iteration. This information is used for time management: When
905 // the best move changes frequently, we allocate some more time.
910 // All other moves but the PV are set to the lowest value: this is
911 // not a problem when sorting because the sort is stable and the
912 // move position in the list is preserved - just the PV is pushed up.
913 rm.score = -VALUE_INFINITE;
916 if (value > bestValue)
918 bestValue = SpNode ? splitPoint->bestValue = value : value;
922 bestMove = SpNode ? splitPoint->bestMove = move : move;
924 if (PvNode && value < beta) // Update alpha! Always alpha < beta
925 alpha = SpNode ? splitPoint->alpha = value : value;
928 assert(value >= beta); // Fail high
931 splitPoint->cutoff = true;
938 // Step 19. Check for splitting the search
940 && Threads.size() >= 2
941 && depth >= Threads.minimumSplitDepth
942 && ( !thisThread->activeSplitPoint
943 || !thisThread->activeSplitPoint->allSlavesSearching)
944 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
946 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
948 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
949 depth, moveCount, &mp, NT, cutNode);
951 if (Signals.stop || thisThread->cutoff_occurred())
954 if (bestValue >= beta)
962 // Following condition would detect a stop or a cutoff set only after move
963 // loop has been completed. But in this case bestValue is valid because we
964 // have fully searched our subtree, and we can anyhow save the result in TT.
966 if (Signals.stop || thisThread->cutoff_occurred())
970 // Step 20. Check for mate and stalemate
971 // All legal moves have been searched and if there are no legal moves, it
972 // must be mate or stalemate. If we are in a singular extension search then
973 // return a fail low score.
975 bestValue = excludedMove ? alpha
976 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
978 // Quiet best move: update killers, history, countermoves and followupmoves
979 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
980 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
982 TT.store(posKey, value_to_tt(bestValue, ss->ply),
983 bestValue >= beta ? BOUND_LOWER :
984 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
985 depth, bestMove, ss->staticEval);
987 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
993 // qsearch() is the quiescence search function, which is called by the main
994 // search function when the remaining depth is zero (or, to be more precise,
995 // less than ONE_PLY).
997 template <NodeType NT, bool InCheck>
998 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1000 const bool PvNode = NT == PV;
1002 assert(NT == PV || NT == NonPV);
1003 assert(InCheck == !!pos.checkers());
1004 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1005 assert(PvNode || (alpha == beta - 1));
1006 assert(depth <= DEPTH_ZERO);
1011 Move ttMove, move, bestMove;
1012 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1013 bool givesCheck, evasionPrunable;
1016 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1020 ss->currentMove = bestMove = MOVE_NONE;
1021 ss->ply = (ss-1)->ply + 1;
1023 // Check for an instant draw or if the maximum ply has been reached
1024 if (pos.is_draw() || ss->ply > MAX_PLY)
1025 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1027 // Decide whether or not to include checks: this fixes also the type of
1028 // TT entry depth that we are going to use. Note that in qsearch we use
1029 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1030 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1031 : DEPTH_QS_NO_CHECKS;
1033 // Transposition table lookup
1035 tte = TT.probe(posKey);
1036 ttMove = tte ? tte->move() : MOVE_NONE;
1037 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1040 && tte->depth() >= ttDepth
1041 && ttValue != VALUE_NONE // Only in case of TT access race
1042 && ( PvNode ? tte->bound() == BOUND_EXACT
1043 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1044 : (tte->bound() & BOUND_UPPER)))
1046 ss->currentMove = ttMove; // Can be MOVE_NONE
1050 // Evaluate the position statically
1053 ss->staticEval = VALUE_NONE;
1054 bestValue = futilityBase = -VALUE_INFINITE;
1060 // Never assume anything on values stored in TT
1061 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1062 ss->staticEval = bestValue = evaluate(pos);
1064 // Can ttValue be used as a better position evaluation?
1065 if (ttValue != VALUE_NONE)
1066 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1067 bestValue = ttValue;
1070 ss->staticEval = bestValue =
1071 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1073 // Stand pat. Return immediately if static value is at least beta
1074 if (bestValue >= beta)
1077 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1078 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1083 if (PvNode && bestValue > alpha)
1086 futilityBase = bestValue + 128;
1089 // Initialize a MovePicker object for the current position, and prepare
1090 // to search the moves. Because the depth is <= 0 here, only captures,
1091 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1093 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1096 // Loop through the moves until no moves remain or a beta cutoff occurs
1097 while ((move = mp.next_move<false>()) != MOVE_NONE)
1099 assert(is_ok(move));
1101 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1102 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1103 : pos.gives_check(move, ci);
1110 && futilityBase > -VALUE_KNOWN_WIN
1111 && !pos.advanced_pawn_push(move))
1113 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1115 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1117 if (futilityValue < beta)
1119 bestValue = std::max(bestValue, futilityValue);
1123 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1125 bestValue = std::max(bestValue, futilityBase);
1130 // Detect non-capture evasions that are candidates to be pruned
1131 evasionPrunable = InCheck
1132 && bestValue > VALUE_MATED_IN_MAX_PLY
1133 && !pos.capture(move)
1134 && !pos.can_castle(pos.side_to_move());
1136 // Don't search moves with negative SEE values
1138 && (!InCheck || evasionPrunable)
1140 && type_of(move) != PROMOTION
1141 && pos.see_sign(move) < VALUE_ZERO)
1144 // Speculative prefetch as early as possible
1145 prefetch((char*)TT.first_entry(pos.key_after(move)));
1147 // Check for legality just before making the move
1148 if (!pos.legal(move, ci.pinned))
1151 ss->currentMove = move;
1153 // Make and search the move
1154 pos.do_move(move, st, ci, givesCheck);
1155 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1156 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1157 pos.undo_move(move);
1159 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1161 // Check for new best move
1162 if (value > bestValue)
1168 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1175 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1176 ttDepth, move, ss->staticEval);
1184 // All legal moves have been searched. A special case: If we're in check
1185 // and no legal moves were found, it is checkmate.
1186 if (InCheck && bestValue == -VALUE_INFINITE)
1187 return mated_in(ss->ply); // Plies to mate from the root
1189 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1190 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1191 ttDepth, bestMove, ss->staticEval);
1193 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1199 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1200 // "plies to mate from the current position". Non-mate scores are unchanged.
1201 // The function is called before storing a value in the transposition table.
1203 Value value_to_tt(Value v, int ply) {
1205 assert(v != VALUE_NONE);
1207 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1208 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1212 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1213 // from the transposition table (which refers to the plies to mate/be mated
1214 // from current position) to "plies to mate/be mated from the root".
1216 Value value_from_tt(Value v, int ply) {
1218 return v == VALUE_NONE ? VALUE_NONE
1219 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1220 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1224 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1227 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1229 if (ss->killers[0] != move)
1231 ss->killers[1] = ss->killers[0];
1232 ss->killers[0] = move;
1235 // Increase history value of the cut-off move and decrease all the other
1236 // played quiet moves.
1237 Value bonus = Value(4 * int(depth) * int(depth));
1238 History.update(pos.moved_piece(move), to_sq(move), bonus);
1239 for (int i = 0; i < quietsCnt; ++i)
1242 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1245 if (is_ok((ss-1)->currentMove))
1247 Square prevMoveSq = to_sq((ss-1)->currentMove);
1248 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1251 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1253 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1254 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1259 // When playing with a strength handicap, choose best move among the first 'candidates'
1260 // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1262 Move Skill::pick_move() {
1266 // PRNG sequence should be not deterministic
1267 for (int i = Time::now() % 50; i > 0; --i)
1268 rk.rand<unsigned>();
1270 // RootMoves are already sorted by score in descending order
1271 int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
1272 int weakness = 120 - 2 * level;
1273 int max_s = -VALUE_INFINITE;
1276 // Choose best move. For each move score we add two terms both dependent on
1277 // weakness. One deterministic and bigger for weaker moves, and one random,
1278 // then we choose the move with the resulting highest score.
1279 for (size_t i = 0; i < candidates; ++i)
1281 int s = RootMoves[i].score;
1283 // Don't allow crazy blunders even at very low skills
1284 if (i > 0 && RootMoves[i - 1].score > s + 2 * PawnValueMg)
1287 // This is our magic formula
1288 s += ( weakness * int(RootMoves[0].score - s)
1289 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1294 best = RootMoves[i].pv[0];
1301 // uci_pv() formats PV information according to the UCI protocol. UCI
1302 // requires that all (if any) unsearched PV lines are sent using a previous
1305 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1307 std::stringstream ss;
1308 Time::point elapsed = Time::now() - SearchTime + 1;
1309 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1312 for (size_t i = 0; i < Threads.size(); ++i)
1313 if (Threads[i]->maxPly > selDepth)
1314 selDepth = Threads[i]->maxPly;
1316 for (size_t i = 0; i < uciPVSize; ++i)
1318 bool updated = (i <= PVIdx);
1320 if (depth == 1 && !updated)
1323 int d = updated ? depth : depth - 1;
1324 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1326 if (ss.rdbuf()->in_avail()) // Not at first line
1329 ss << "info depth " << d
1330 << " seldepth " << selDepth
1331 << " multipv " << i + 1
1332 << " score " << (i == PVIdx ? UCI::format_value(v, alpha, beta) : UCI::format_value(v))
1333 << " nodes " << pos.nodes_searched()
1334 << " nps " << pos.nodes_searched() * 1000 / elapsed
1335 << " time " << elapsed
1338 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1339 ss << " " << UCI::format_move(RootMoves[i].pv[j], pos.is_chess960());
1348 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1349 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1350 /// ensure that we have a ponder move even when we fail high at root. This
1351 /// results in a long PV to print that is important for position analysis.
1353 void RootMove::extract_pv_from_tt(Position& pos) {
1355 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1357 int ply = 1; // At root ply is 1...
1358 Move m = pv[0]; // ...instead pv[] array starts from 0
1359 Value expectedScore = score;
1366 assert(MoveList<LEGAL>(pos).contains(pv[ply - 1]));
1368 pos.do_move(pv[ply++ - 1], *st++);
1369 tte = TT.probe(pos.key());
1370 expectedScore = -expectedScore;
1373 && expectedScore == value_from_tt(tte->value(), ply)
1374 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1375 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1377 && (!pos.is_draw() || ply <= 2));
1379 pv.push_back(MOVE_NONE); // Must be zero-terminating
1381 while (--ply) pos.undo_move(pv[ply - 1]);
1385 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1386 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1387 /// first, even if the old TT entries have been overwritten.
1389 void RootMove::insert_pv_in_tt(Position& pos) {
1391 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1393 int idx = 0; // Ply starts from 1, we need to start from 0
1396 tte = TT.probe(pos.key());
1398 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1399 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1401 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1403 pos.do_move(pv[idx++], *st++);
1405 } while (pv[idx] != MOVE_NONE);
1407 while (idx) pos.undo_move(pv[--idx]);
1411 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1413 void Thread::idle_loop() {
1415 // Pointer 'this_sp' is not null only if we are called from split(), and not
1416 // at the thread creation. This means we are the split point's master.
1417 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1419 assert(!this_sp || (this_sp->masterThread == this && searching));
1423 // If this thread has been assigned work, launch a search
1426 Threads.mutex.lock();
1428 assert(activeSplitPoint);
1429 SplitPoint* sp = activeSplitPoint;
1431 Threads.mutex.unlock();
1433 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1434 Position pos(*sp->pos, this);
1436 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1437 ss->splitPoint = sp;
1441 assert(activePosition == NULL);
1443 activePosition = &pos;
1445 if (sp->nodeType == NonPV)
1446 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1448 else if (sp->nodeType == PV)
1449 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1451 else if (sp->nodeType == Root)
1452 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1460 activePosition = NULL;
1461 sp->slavesMask.reset(idx);
1462 sp->allSlavesSearching = false;
1463 sp->nodes += pos.nodes_searched();
1465 // Wake up the master thread so to allow it to return from the idle
1466 // loop in case we are the last slave of the split point.
1467 if ( this != sp->masterThread
1468 && sp->slavesMask.none())
1470 assert(!sp->masterThread->searching);
1471 sp->masterThread->notify_one();
1474 // After releasing the lock we can't access any SplitPoint related data
1475 // in a safe way because it could have been released under our feet by
1479 // Try to late join to another split point if none of its slaves has
1480 // already finished.
1481 if (Threads.size() > 2)
1482 for (size_t i = 0; i < Threads.size(); ++i)
1484 const int size = Threads[i]->splitPointsSize; // Local copy
1485 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1488 && sp->allSlavesSearching
1489 && available_to(Threads[i]))
1491 // Recheck the conditions under lock protection
1492 Threads.mutex.lock();
1495 if ( sp->allSlavesSearching
1496 && available_to(Threads[i]))
1498 sp->slavesMask.set(idx);
1499 activeSplitPoint = sp;
1504 Threads.mutex.unlock();
1506 break; // Just a single attempt
1511 // Grab the lock to avoid races with Thread::notify_one()
1514 // If we are master and all slaves have finished then exit idle_loop
1515 if (this_sp && this_sp->slavesMask.none())
1522 // If we are not searching, wait for a condition to be signaled instead of
1523 // wasting CPU time polling for work.
1524 if (!searching && !exit)
1525 sleepCondition.wait(mutex);
1532 /// check_time() is called by the timer thread when the timer triggers. It is
1533 /// used to print debug info and, more importantly, to detect when we are out of
1534 /// available time and thus stop the search.
1538 static Time::point lastInfoTime = Time::now();
1539 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1541 if (Time::now() - lastInfoTime >= 1000)
1543 lastInfoTime = Time::now();
1552 Threads.mutex.lock();
1554 nodes = RootPos.nodes_searched();
1556 // Loop across all split points and sum accumulated SplitPoint nodes plus
1557 // all the currently active positions nodes.
1558 for (size_t i = 0; i < Threads.size(); ++i)
1559 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1561 SplitPoint& sp = Threads[i]->splitPoints[j];
1567 for (size_t idx = 0; idx < Threads.size(); ++idx)
1568 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1569 nodes += Threads[idx]->activePosition->nodes_searched();
1574 Threads.mutex.unlock();
1577 Time::point elapsed = Time::now() - SearchTime;
1578 bool stillAtFirstMove = Signals.firstRootMove
1579 && !Signals.failedLowAtRoot
1580 && elapsed > TimeMgr.available_time() * 75 / 100;
1582 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1583 || stillAtFirstMove;
1585 if ( (Limits.use_time_management() && noMoreTime)
1586 || (Limits.movetime && elapsed >= Limits.movetime)
1587 || (Limits.nodes && nodes >= Limits.nodes))
1588 Signals.stop = true;