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/>.
36 #include "ucioption.h"
40 volatile SignalsType Signals;
42 std::vector<RootMove> RootMoves;
44 Time::point SearchTime;
45 StateStackPtr SetupStates;
50 using namespace Search;
54 // Different node types, used as template parameter
55 enum NodeType { Root, PV, NonPV };
57 // Dynamic razoring margin based on depth
58 inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
60 // Futility lookup tables (initialized at startup) and their access functions
61 int FutilityMoveCounts[2][32]; // [improving][depth]
63 inline Value futility_margin(Depth d) {
64 return Value(100 * d);
67 // Reduction lookup tables (initialized at startup) and their access function
68 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
70 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
72 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
77 double BestMoveChanges;
78 Value DrawValue[COLOR_NB];
81 MovesStats Countermoves, Followupmoves;
83 template <NodeType NT, bool SpNode>
84 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
86 template <NodeType NT, bool InCheck>
87 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
89 void id_loop(Position& pos);
90 Value value_to_tt(Value v, int ply);
91 Value value_from_tt(Value v, int ply);
92 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
93 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
96 Skill(int l, size_t rootSize) : level(l),
97 candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
100 if (candidates) // Swap best PV line with the sub-optimal one
101 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
102 RootMoves.end(), best ? best : pick_move()));
105 size_t candidates_size() const { return candidates; }
106 bool time_to_pick(int depth) const { return depth == 1 + level; }
117 /// Search::init() is called during startup to initialize various lookup tables
119 void Search::init() {
121 int d; // depth (ONE_PLY == 2)
122 int hd; // half depth (ONE_PLY == 1)
125 // Init reductions array
126 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
128 double pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
129 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
130 Reductions[1][1][hd][mc] = int8_t( pvRed >= 1.0 ? pvRed * int(ONE_PLY) : 0);
131 Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed * int(ONE_PLY) : 0);
133 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
134 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
136 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
137 Reductions[0][0][hd][mc] += ONE_PLY;
139 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
140 Reductions[0][0][hd][mc] += ONE_PLY / 2;
143 // Init futility move count array
144 for (d = 0; d < 32; ++d)
146 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.00, 1.8));
147 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * pow(d + 0.98, 1.8));
152 /// Search::perft() is our utility to verify move generation. All the leaf nodes
153 /// up to the given depth are generated and counted and the sum returned.
155 uint64_t Search::perft(Position& pos, Depth depth) {
158 uint64_t cnt, nodes = 0;
160 const bool leaf = depth == 2 * ONE_PLY;
162 for (MoveList<LEGAL> it(pos); *it; ++it)
164 if (Root && depth <= ONE_PLY)
168 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
169 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
174 sync_cout << move_to_uci(*it, pos.is_chess960()) << ": " << cnt << sync_endl;
179 template uint64_t Search::perft<true>(Position& pos, Depth depth);
182 /// Search::think() is the external interface to Stockfish's search, and is
183 /// called by the main thread when the program receives the UCI 'go' command. It
184 /// searches from RootPos and at the end prints the "bestmove" to output.
186 void Search::think() {
188 TimeMgr.init(Limits, RootPos.game_ply(), RootPos.side_to_move());
190 int cf = Options["Contempt Factor"] * PawnValueEg / 100; // From centipawns
191 DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(cf);
192 DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(cf);
194 if (RootMoves.empty())
196 RootMoves.push_back(MOVE_NONE);
197 sync_cout << "info depth 0 score "
198 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
204 // Reset the threads, still sleeping: will wake up at split time
205 for (size_t i = 0; i < Threads.size(); ++i)
206 Threads[i]->maxPly = 0;
208 Threads.timer->run = true;
209 Threads.timer->notify_one(); // Wake up the recurring timer
211 id_loop(RootPos); // Let's start searching !
213 Threads.timer->run = false; // Stop the timer
217 // When search is stopped this info is not printed
218 sync_cout << "info nodes " << RootPos.nodes_searched()
219 << " time " << Time::now() - SearchTime + 1 << sync_endl;
221 // When we reach the maximum depth, we can arrive here without a raise of
222 // Signals.stop. However, if we are pondering or in an infinite search,
223 // the UCI protocol states that we shouldn't print the best move before the
224 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
225 // until the GUI sends one of those commands (which also raises Signals.stop).
226 if (!Signals.stop && (Limits.ponder || Limits.infinite))
228 Signals.stopOnPonderhit = true;
229 RootPos.this_thread()->wait_for(Signals.stop);
232 // Best move could be MOVE_NONE when searching on a stalemate position
233 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
234 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
241 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
242 // with increasing depth until the allocated thinking time has been consumed,
243 // user stops the search, or the maximum search depth is reached.
245 void id_loop(Position& pos) {
247 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
249 Value bestValue, alpha, beta, delta;
251 std::memset(ss-2, 0, 5 * sizeof(Stack));
255 bestValue = delta = alpha = -VALUE_INFINITE;
256 beta = VALUE_INFINITE;
261 Countermoves.clear();
262 Followupmoves.clear();
264 size_t multiPV = Options["MultiPV"];
265 Skill skill(Options["Skill Level"], RootMoves.size());
267 // Do we have to play with skill handicap? In this case enable MultiPV search
268 // that we will use behind the scenes to retrieve a set of possible moves.
269 multiPV = std::max(multiPV, skill.candidates_size());
271 // Iterative deepening loop until requested to stop or target depth reached
272 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
274 // Age out PV variability metric
275 BestMoveChanges *= 0.5;
277 // Save the last iteration's scores before first PV line is searched and
278 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
279 for (size_t i = 0; i < RootMoves.size(); ++i)
280 RootMoves[i].prevScore = RootMoves[i].score;
282 // MultiPV loop. We perform a full root search for each PV line
283 for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
285 // Reset aspiration window starting size
289 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
290 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
293 // Start with a small aspiration window and, in the case of a fail
294 // high/low, re-search with a bigger window until we're not failing
298 bestValue = search<Root, false>(pos, ss, alpha, beta, depth * ONE_PLY, false);
300 // Bring the best move to the front. It is critical that sorting
301 // is done with a stable algorithm because all the values but the
302 // first and eventually the new best one are set to -VALUE_INFINITE
303 // and we want to keep the same order for all the moves except the
304 // new PV that goes to the front. Note that in case of MultiPV
305 // search the already searched PV lines are preserved.
306 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
308 // Write PV back to transposition table in case the relevant
309 // entries have been overwritten during the search.
310 for (size_t i = 0; i <= PVIdx; ++i)
311 RootMoves[i].insert_pv_in_tt(pos);
313 // If search has been stopped break immediately. Sorting and
314 // writing PV back to TT is safe because RootMoves is still
315 // valid, although it refers to previous iteration.
319 // When failing high/low give some update (without cluttering
320 // the UI) before a re-search.
321 if ( (bestValue <= alpha || bestValue >= beta)
322 && Time::now() - SearchTime > 3000)
323 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
325 // In case of failing low/high increase aspiration window and
326 // re-search, otherwise exit the loop.
327 if (bestValue <= alpha)
329 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
331 Signals.failedLowAtRoot = true;
332 Signals.stopOnPonderhit = false;
334 else if (bestValue >= beta)
335 beta = std::min(bestValue + delta, VALUE_INFINITE);
340 delta += 3 * delta / 8;
342 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
345 // Sort the PV lines searched so far and update the GUI
346 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
348 if (PVIdx + 1 == std::min(multiPV, RootMoves.size()) || Time::now() - SearchTime > 3000)
349 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
352 // If skill levels are enabled and time is up, pick a sub-optimal best move
353 if (skill.candidates_size() && skill.time_to_pick(depth))
356 // Have we found a "mate in x"?
358 && bestValue >= VALUE_MATE_IN_MAX_PLY
359 && VALUE_MATE - bestValue <= 2 * Limits.mate)
362 // Do we have time for the next iteration? Can we stop searching now?
363 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
365 // Take some extra time if the best move has changed
366 if (depth > 4 && multiPV == 1)
367 TimeMgr.pv_instability(BestMoveChanges);
369 // Stop the search if only one legal move is available or all
370 // of the available time has been used.
371 if ( RootMoves.size() == 1
372 || Time::now() - SearchTime > TimeMgr.available_time())
374 // If we are allowed to ponder do not stop the search now but
375 // keep pondering until the GUI sends "ponderhit" or "stop".
377 Signals.stopOnPonderhit = true;
386 // search<>() is the main search function for both PV and non-PV nodes and for
387 // normal and SplitPoint nodes. When called just after a split point the search
388 // is simpler because we have already probed the hash table, done a null move
389 // search, and searched the first move before splitting, so we don't have to
390 // repeat all this work again. We also don't need to store anything to the hash
391 // table here: This is taken care of after we return from the split point.
393 template <NodeType NT, bool SpNode>
394 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
396 const bool RootNode = NT == Root;
397 const bool PvNode = NT == PV || NT == Root;
399 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
400 assert(PvNode || (alpha == beta - 1));
401 assert(depth > DEPTH_ZERO);
403 Move quietsSearched[64];
406 SplitPoint* splitPoint;
408 Move ttMove, move, excludedMove, bestMove;
409 Depth ext, newDepth, predictedDepth;
410 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
411 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
412 bool captureOrPromotion, dangerous, doFullDepthSearch;
413 int moveCount, quietCount;
415 // Step 1. Initialize node
416 Thread* thisThread = pos.this_thread();
417 inCheck = pos.checkers();
421 splitPoint = ss->splitPoint;
422 bestMove = splitPoint->bestMove;
423 bestValue = splitPoint->bestValue;
425 ttMove = excludedMove = MOVE_NONE;
426 ttValue = VALUE_NONE;
428 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
433 moveCount = quietCount = 0;
434 bestValue = -VALUE_INFINITE;
435 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
436 ss->ply = (ss-1)->ply + 1;
437 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
438 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
440 // Used to send selDepth info to GUI
441 if (PvNode && thisThread->maxPly < ss->ply)
442 thisThread->maxPly = ss->ply;
446 // Step 2. Check for aborted search and immediate draw
447 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
448 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
450 // Step 3. Mate distance pruning. Even if we mate at the next move our score
451 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
452 // a shorter mate was found upward in the tree then there is no need to search
453 // because we will never beat the current alpha. Same logic but with reversed
454 // signs applies also in the opposite condition of being mated instead of giving
455 // mate. In this case return a fail-high score.
456 alpha = std::max(mated_in(ss->ply), alpha);
457 beta = std::min(mate_in(ss->ply+1), beta);
462 // Step 4. Transposition table lookup
463 // We don't want the score of a partial search to overwrite a previous full search
464 // TT value, so we use a different position key in case of an excluded move.
465 excludedMove = ss->excludedMove;
466 posKey = excludedMove ? pos.exclusion_key() : pos.key();
467 tte = TT.probe(posKey);
468 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
469 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
471 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
472 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
473 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
474 // we should also update RootMoveList to avoid bogus output.
477 && tte->depth() >= depth
478 && ttValue != VALUE_NONE // Only in case of TT access race
479 && ( PvNode ? tte->bound() == BOUND_EXACT
480 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
481 : (tte->bound() & BOUND_UPPER)))
483 ss->currentMove = ttMove; // Can be MOVE_NONE
485 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
486 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
487 update_stats(pos, ss, ttMove, depth, NULL, 0);
492 // Step 5. Evaluate the position statically and update parent's gain statistics
495 ss->staticEval = eval = VALUE_NONE;
501 // Never assume anything on values stored in TT
502 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
503 eval = ss->staticEval = evaluate(pos);
505 // Can ttValue be used as a better position evaluation?
506 if (ttValue != VALUE_NONE)
507 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
512 eval = ss->staticEval =
513 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
515 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
518 if ( !pos.captured_piece_type()
519 && ss->staticEval != VALUE_NONE
520 && (ss-1)->staticEval != VALUE_NONE
521 && (move = (ss-1)->currentMove) != MOVE_NULL
523 && type_of(move) == NORMAL)
525 Square to = to_sq(move);
526 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
529 // Step 6. Razoring (skipped when in check)
531 && depth < 4 * ONE_PLY
532 && eval + razor_margin(depth) <= alpha
533 && ttMove == MOVE_NONE
534 && !pos.pawn_on_7th(pos.side_to_move()))
536 if ( depth <= ONE_PLY
537 && eval + razor_margin(3 * ONE_PLY) <= alpha)
538 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
540 Value ralpha = alpha - razor_margin(depth);
541 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
546 // Step 7. Futility pruning: child node (skipped when in check)
549 && depth < 7 * ONE_PLY
550 && eval - futility_margin(depth) >= beta
551 && abs(beta) < VALUE_MATE_IN_MAX_PLY
552 && abs(eval) < VALUE_KNOWN_WIN
553 && pos.non_pawn_material(pos.side_to_move()))
554 return eval - futility_margin(depth);
556 // Step 8. Null move search with verification search (is omitted in PV nodes)
559 && depth >= 2 * ONE_PLY
561 && pos.non_pawn_material(pos.side_to_move()))
563 ss->currentMove = MOVE_NULL;
565 assert(eval - beta >= 0);
567 // Null move dynamic reduction based on depth and value
568 Depth R = 3 * ONE_PLY
570 + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
573 pos.do_null_move(st);
574 (ss+1)->skipNullMove = true;
575 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
576 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
577 (ss+1)->skipNullMove = false;
578 pos.undo_null_move();
580 if (nullValue >= beta)
582 // Do not return unproven mate scores
583 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
586 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
589 // Do verification search at high depths
590 ss->skipNullMove = true;
591 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
592 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
593 ss->skipNullMove = false;
600 // Step 9. ProbCut (skipped when in check)
601 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
602 // and a reduced search returns a value much above beta, we can (almost) safely
603 // prune the previous move.
605 && depth >= 5 * ONE_PLY
607 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
609 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
610 Depth rdepth = depth - 4 * ONE_PLY;
612 assert(rdepth >= ONE_PLY);
613 assert((ss-1)->currentMove != MOVE_NONE);
614 assert((ss-1)->currentMove != MOVE_NULL);
616 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
619 while ((move = mp.next_move<false>()) != MOVE_NONE)
620 if (pos.legal(move, ci.pinned))
622 ss->currentMove = move;
623 pos.do_move(move, st, ci, pos.gives_check(move, ci));
624 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
631 // Step 10. Internal iterative deepening (skipped when in check)
632 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
634 && (PvNode || ss->staticEval + 256 >= beta))
636 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
638 ss->skipNullMove = true;
639 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
640 ss->skipNullMove = false;
642 tte = TT.probe(posKey);
643 ttMove = tte ? tte->move() : MOVE_NONE;
646 moves_loop: // When in check and at SpNode search starts from here
648 Square prevMoveSq = to_sq((ss-1)->currentMove);
649 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
650 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
652 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
653 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
654 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
656 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
658 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
659 improving = ss->staticEval >= (ss-2)->staticEval
660 || ss->staticEval == VALUE_NONE
661 ||(ss-2)->staticEval == VALUE_NONE;
663 singularExtensionNode = !RootNode
665 && depth >= 8 * ONE_PLY
666 && abs(beta) < VALUE_KNOWN_WIN
667 && ttMove != MOVE_NONE
668 /* && ttValue != VALUE_NONE Already implicit in the next condition */
669 && abs(ttValue) < VALUE_KNOWN_WIN
670 && !excludedMove // Recursive singular search is not allowed
671 && (tte->bound() & BOUND_LOWER)
672 && tte->depth() >= depth - 3 * ONE_PLY;
674 // Step 11. Loop through moves
675 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
676 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
680 if (move == excludedMove)
683 // At root obey the "searchmoves" option and skip moves not listed in Root
684 // Move List. As a consequence any illegal move is also skipped. In MultiPV
685 // mode we also skip PV moves which have been already searched.
686 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
691 // Shared counter cannot be decremented later if the move turns out to be illegal
692 if (!pos.legal(move, ci.pinned))
695 moveCount = ++splitPoint->moveCount;
696 splitPoint->mutex.unlock();
703 Signals.firstRootMove = (moveCount == 1);
705 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
706 sync_cout << "info depth " << depth / ONE_PLY
707 << " currmove " << move_to_uci(move, pos.is_chess960())
708 << " currmovenumber " << moveCount + PVIdx << sync_endl;
712 captureOrPromotion = pos.capture_or_promotion(move);
714 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
715 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
716 : pos.gives_check(move, ci);
718 dangerous = givesCheck
719 || type_of(move) != NORMAL
720 || pos.advanced_pawn_push(move);
722 // Step 12. Extend checks
723 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
726 // Singular extension search. If all moves but one fail low on a search of
727 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
728 // is singular and should be extended. To verify this we do a reduced search
729 // on all the other moves but the ttMove and if the result is lower than
730 // ttValue minus a margin then we extend the ttMove.
731 if ( singularExtensionNode
734 && pos.legal(move, ci.pinned))
736 Value rBeta = ttValue - int(depth);
737 ss->excludedMove = move;
738 ss->skipNullMove = true;
739 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
740 ss->skipNullMove = false;
741 ss->excludedMove = MOVE_NONE;
747 // Update the current move (this must be done after singular extension search)
748 newDepth = depth - ONE_PLY + ext;
750 // Step 13. Pruning at shallow depth (exclude PV nodes)
752 && !captureOrPromotion
755 /* && move != ttMove Already implicit in the next condition */
756 && bestValue > VALUE_MATED_IN_MAX_PLY)
758 // Move count based pruning
759 if ( depth < 16 * ONE_PLY
760 && moveCount >= FutilityMoveCounts[improving][depth] )
763 splitPoint->mutex.lock();
768 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
770 // Futility pruning: parent node
771 if (predictedDepth < 7 * ONE_PLY)
773 futilityValue = ss->staticEval + futility_margin(predictedDepth)
774 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
776 if (futilityValue <= alpha)
778 bestValue = std::max(bestValue, futilityValue);
782 splitPoint->mutex.lock();
783 if (bestValue > splitPoint->bestValue)
784 splitPoint->bestValue = bestValue;
790 // Prune moves with negative SEE at low depths
791 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
794 splitPoint->mutex.lock();
800 // Check for legality just before making the move
801 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
807 pvMove = PvNode && moveCount == 1;
808 ss->currentMove = move;
809 if (!SpNode && !captureOrPromotion && quietCount < 64)
810 quietsSearched[quietCount++] = move;
812 // Step 14. Make the move
813 pos.do_move(move, st, ci, givesCheck);
815 // Step 15. Reduced depth search (LMR). If the move fails high it will be
816 // re-searched at full depth.
817 if ( depth >= 3 * ONE_PLY
819 && !captureOrPromotion
821 && move != ss->killers[0]
822 && move != ss->killers[1])
824 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
826 if (!PvNode && cutNode)
827 ss->reduction += ONE_PLY;
829 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
830 ss->reduction += ONE_PLY / 2;
832 if (move == countermoves[0] || move == countermoves[1])
833 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
835 // Decrease reduction for moves that escape a capture
837 && type_of(move) == NORMAL
838 && type_of(pos.piece_on(to_sq(move))) != PAWN
839 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
840 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
842 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
844 alpha = splitPoint->alpha;
846 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
848 // Re-search at intermediate depth if reduction is very high
849 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
851 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
852 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
855 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
856 ss->reduction = DEPTH_ZERO;
859 doFullDepthSearch = !pvMove;
861 // Step 16. Full depth search, when LMR is skipped or fails high
862 if (doFullDepthSearch)
865 alpha = splitPoint->alpha;
867 value = newDepth < ONE_PLY ?
868 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
869 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
870 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
873 // For PV nodes only, do a full PV search on the first move or after a fail
874 // high (in the latter case search only if value < beta), otherwise let the
875 // parent node fail low with value <= alpha and to try another move.
876 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
877 value = newDepth < ONE_PLY ?
878 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
879 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
880 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
881 // Step 17. Undo move
884 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
886 // Step 18. Check for new best move
889 splitPoint->mutex.lock();
890 bestValue = splitPoint->bestValue;
891 alpha = splitPoint->alpha;
894 // Finished searching the move. If a stop or a cutoff occurred, the return
895 // value of the search cannot be trusted, and we return immediately without
896 // updating best move, PV and TT.
897 if (Signals.stop || thisThread->cutoff_occurred())
902 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
904 // PV move or new best move ?
905 if (pvMove || value > alpha)
908 rm.extract_pv_from_tt(pos);
910 // We record how often the best move has been changed in each
911 // iteration. This information is used for time management: When
912 // the best move changes frequently, we allocate some more time.
917 // All other moves but the PV are set to the lowest value: this is
918 // not a problem when sorting because the sort is stable and the
919 // move position in the list is preserved - just the PV is pushed up.
920 rm.score = -VALUE_INFINITE;
923 if (value > bestValue)
925 bestValue = SpNode ? splitPoint->bestValue = value : value;
929 bestMove = SpNode ? splitPoint->bestMove = move : move;
931 if (PvNode && value < beta) // Update alpha! Always alpha < beta
932 alpha = SpNode ? splitPoint->alpha = value : value;
935 assert(value >= beta); // Fail high
938 splitPoint->cutoff = true;
945 // Step 19. Check for splitting the search
947 && Threads.size() >= 2
948 && depth >= Threads.minimumSplitDepth
949 && ( !thisThread->activeSplitPoint
950 || !thisThread->activeSplitPoint->allSlavesSearching)
951 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
953 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
955 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
956 depth, moveCount, &mp, NT, cutNode);
958 if (Signals.stop || thisThread->cutoff_occurred())
961 if (bestValue >= beta)
969 // Following condition would detect a stop or a cutoff set only after move
970 // loop has been completed. But in this case bestValue is valid because we
971 // have fully searched our subtree, and we can anyhow save the result in TT.
973 if (Signals.stop || thisThread->cutoff_occurred())
977 // Step 20. Check for mate and stalemate
978 // All legal moves have been searched and if there are no legal moves, it
979 // must be mate or stalemate. If we are in a singular extension search then
980 // return a fail low score.
982 bestValue = excludedMove ? alpha
983 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
985 // Quiet best move: update killers, history, countermoves and followupmoves
986 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
987 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
989 TT.store(posKey, value_to_tt(bestValue, ss->ply),
990 bestValue >= beta ? BOUND_LOWER :
991 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
992 depth, bestMove, ss->staticEval);
994 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1000 // qsearch() is the quiescence search function, which is called by the main
1001 // search function when the remaining depth is zero (or, to be more precise,
1002 // less than ONE_PLY).
1004 template <NodeType NT, bool InCheck>
1005 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1007 const bool PvNode = NT == PV;
1009 assert(NT == PV || NT == NonPV);
1010 assert(InCheck == !!pos.checkers());
1011 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1012 assert(PvNode || (alpha == beta - 1));
1013 assert(depth <= DEPTH_ZERO);
1018 Move ttMove, move, bestMove;
1019 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1020 bool givesCheck, evasionPrunable;
1023 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1027 ss->currentMove = bestMove = MOVE_NONE;
1028 ss->ply = (ss-1)->ply + 1;
1030 // Check for an instant draw or if the maximum ply has been reached
1031 if (pos.is_draw() || ss->ply > MAX_PLY)
1032 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1034 // Decide whether or not to include checks: this fixes also the type of
1035 // TT entry depth that we are going to use. Note that in qsearch we use
1036 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1037 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1038 : DEPTH_QS_NO_CHECKS;
1040 // Transposition table lookup
1042 tte = TT.probe(posKey);
1043 ttMove = tte ? tte->move() : MOVE_NONE;
1044 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1047 && tte->depth() >= ttDepth
1048 && ttValue != VALUE_NONE // Only in case of TT access race
1049 && ( PvNode ? tte->bound() == BOUND_EXACT
1050 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1051 : (tte->bound() & BOUND_UPPER)))
1053 ss->currentMove = ttMove; // Can be MOVE_NONE
1057 // Evaluate the position statically
1060 ss->staticEval = VALUE_NONE;
1061 bestValue = futilityBase = -VALUE_INFINITE;
1067 // Never assume anything on values stored in TT
1068 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1069 ss->staticEval = bestValue = evaluate(pos);
1071 // Can ttValue be used as a better position evaluation?
1072 if (ttValue != VALUE_NONE)
1073 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1074 bestValue = ttValue;
1077 ss->staticEval = bestValue =
1078 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1080 // Stand pat. Return immediately if static value is at least beta
1081 if (bestValue >= beta)
1084 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1085 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1090 if (PvNode && bestValue > alpha)
1093 futilityBase = bestValue + 128;
1096 // Initialize a MovePicker object for the current position, and prepare
1097 // to search the moves. Because the depth is <= 0 here, only captures,
1098 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1100 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1103 // Loop through the moves until no moves remain or a beta cutoff occurs
1104 while ((move = mp.next_move<false>()) != MOVE_NONE)
1106 assert(is_ok(move));
1108 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1109 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1110 : pos.gives_check(move, ci);
1117 && futilityBase > -VALUE_KNOWN_WIN
1118 && !pos.advanced_pawn_push(move))
1120 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1122 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1124 if (futilityValue < beta)
1126 bestValue = std::max(bestValue, futilityValue);
1130 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1132 bestValue = std::max(bestValue, futilityBase);
1137 // Detect non-capture evasions that are candidates to be pruned
1138 evasionPrunable = InCheck
1139 && bestValue > VALUE_MATED_IN_MAX_PLY
1140 && !pos.capture(move)
1141 && !pos.can_castle(pos.side_to_move());
1143 // Don't search moves with negative SEE values
1145 && (!InCheck || evasionPrunable)
1147 && type_of(move) != PROMOTION
1148 && pos.see_sign(move) < VALUE_ZERO)
1151 // Check for legality just before making the move
1152 if (!pos.legal(move, ci.pinned))
1155 ss->currentMove = move;
1157 // Make and search the move
1158 pos.do_move(move, st, ci, givesCheck);
1159 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1160 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1161 pos.undo_move(move);
1163 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1165 // Check for new best move
1166 if (value > bestValue)
1172 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1179 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1180 ttDepth, move, ss->staticEval);
1188 // All legal moves have been searched. A special case: If we're in check
1189 // and no legal moves were found, it is checkmate.
1190 if (InCheck && bestValue == -VALUE_INFINITE)
1191 return mated_in(ss->ply); // Plies to mate from the root
1193 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1194 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1195 ttDepth, bestMove, ss->staticEval);
1197 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1203 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1204 // "plies to mate from the current position". Non-mate scores are unchanged.
1205 // The function is called before storing a value in the transposition table.
1207 Value value_to_tt(Value v, int ply) {
1209 assert(v != VALUE_NONE);
1211 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1212 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1216 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1217 // from the transposition table (which refers to the plies to mate/be mated
1218 // from current position) to "plies to mate/be mated from the root".
1220 Value value_from_tt(Value v, int ply) {
1222 return v == VALUE_NONE ? VALUE_NONE
1223 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1224 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1228 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1231 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1233 if (ss->killers[0] != move)
1235 ss->killers[1] = ss->killers[0];
1236 ss->killers[0] = move;
1239 // Increase history value of the cut-off move and decrease all the other
1240 // played quiet moves.
1241 Value bonus = Value(int(depth) * int(depth));
1242 History.update(pos.moved_piece(move), to_sq(move), bonus);
1243 for (int i = 0; i < quietsCnt; ++i)
1246 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1249 if (is_ok((ss-1)->currentMove))
1251 Square prevMoveSq = to_sq((ss-1)->currentMove);
1252 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1255 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1257 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1258 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1263 // When playing with a strength handicap, choose best move among the first 'candidates'
1264 // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1266 Move Skill::pick_move() {
1270 // PRNG sequence should be not deterministic
1271 for (int i = Time::now() % 50; i > 0; --i)
1272 rk.rand<unsigned>();
1274 // RootMoves are already sorted by score in descending order
1275 int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
1276 int weakness = 120 - 2 * level;
1277 int max_s = -VALUE_INFINITE;
1280 // Choose best move. For each move score we add two terms both dependent on
1281 // weakness. One deterministic and bigger for weaker moves, and one random,
1282 // then we choose the move with the resulting highest score.
1283 for (size_t i = 0; i < candidates; ++i)
1285 int s = RootMoves[i].score;
1287 // Don't allow crazy blunders even at very low skills
1288 if (i > 0 && RootMoves[i - 1].score > s + 2 * PawnValueMg)
1291 // This is our magic formula
1292 s += ( weakness * int(RootMoves[0].score - s)
1293 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1298 best = RootMoves[i].pv[0];
1305 // uci_pv() formats PV information according to the UCI protocol. UCI
1306 // requires that all (if any) unsearched PV lines are sent using a previous
1309 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1311 std::stringstream ss;
1312 Time::point elapsed = Time::now() - SearchTime + 1;
1313 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1316 for (size_t i = 0; i < Threads.size(); ++i)
1317 if (Threads[i]->maxPly > selDepth)
1318 selDepth = Threads[i]->maxPly;
1320 for (size_t i = 0; i < uciPVSize; ++i)
1322 bool updated = (i <= PVIdx);
1324 if (depth == 1 && !updated)
1327 int d = updated ? depth : depth - 1;
1328 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1330 if (ss.rdbuf()->in_avail()) // Not at first line
1333 ss << "info depth " << d
1334 << " seldepth " << selDepth
1335 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1336 << " nodes " << pos.nodes_searched()
1337 << " nps " << pos.nodes_searched() * 1000 / elapsed
1338 << " time " << elapsed
1339 << " multipv " << i + 1
1342 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1343 ss << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1352 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1353 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1354 /// ensure that we have a ponder move even when we fail high at root. This
1355 /// results in a long PV to print that is important for position analysis.
1357 void RootMove::extract_pv_from_tt(Position& pos) {
1359 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1361 int ply = 1; // At root ply is 1...
1362 Move m = pv[0]; // ...instead pv[] array starts from 0
1363 Value expectedScore = score;
1370 assert(MoveList<LEGAL>(pos).contains(pv[ply - 1]));
1372 pos.do_move(pv[ply++ - 1], *st++);
1373 tte = TT.probe(pos.key());
1374 expectedScore = -expectedScore;
1377 && expectedScore == value_from_tt(tte->value(), ply)
1378 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1379 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1381 && (!pos.is_draw() || ply <= 2));
1383 pv.push_back(MOVE_NONE); // Must be zero-terminating
1385 while (--ply) pos.undo_move(pv[ply - 1]);
1389 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1390 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1391 /// first, even if the old TT entries have been overwritten.
1393 void RootMove::insert_pv_in_tt(Position& pos) {
1395 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1397 int idx = 0; // Ply starts from 1, we need to start from 0
1400 tte = TT.probe(pos.key());
1402 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1403 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1405 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1407 pos.do_move(pv[idx++], *st++);
1409 } while (pv[idx] != MOVE_NONE);
1411 while (idx) pos.undo_move(pv[--idx]);
1415 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1417 void Thread::idle_loop() {
1419 // Pointer 'this_sp' is not null only if we are called from split(), and not
1420 // at the thread creation. This means we are the split point's master.
1421 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1423 assert(!this_sp || (this_sp->masterThread == this && searching));
1427 // If we are not searching, wait for a condition to be signaled instead of
1428 // wasting CPU time polling for work.
1429 while (!searching || exit)
1437 // Grab the lock to avoid races with Thread::notify_one()
1440 // If we are master and all slaves have finished then exit idle_loop
1441 if (this_sp && this_sp->slavesMask.none())
1447 // Do sleep after retesting sleep conditions under lock protection. In
1448 // particular we need to avoid a deadlock in case a master thread has,
1449 // in the meanwhile, allocated us and sent the notify_one() call before
1450 // we had the chance to grab the lock.
1451 if (!searching && !exit)
1452 sleepCondition.wait(mutex);
1457 // If this thread has been assigned work, launch a search
1462 Threads.mutex.lock();
1465 assert(activeSplitPoint);
1466 SplitPoint* sp = activeSplitPoint;
1468 Threads.mutex.unlock();
1470 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1471 Position pos(*sp->pos, this);
1473 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1474 ss->splitPoint = sp;
1478 assert(activePosition == NULL);
1480 activePosition = &pos;
1482 if (sp->nodeType == NonPV)
1483 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1485 else if (sp->nodeType == PV)
1486 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1488 else if (sp->nodeType == Root)
1489 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1497 activePosition = NULL;
1498 sp->slavesMask.reset(idx);
1499 sp->allSlavesSearching = false;
1500 sp->nodes += pos.nodes_searched();
1502 // Wake up the master thread so to allow it to return from the idle
1503 // loop in case we are the last slave of the split point.
1504 if ( this != sp->masterThread
1505 && sp->slavesMask.none())
1507 assert(!sp->masterThread->searching);
1508 sp->masterThread->notify_one();
1511 // After releasing the lock we can't access any SplitPoint related data
1512 // in a safe way because it could have been released under our feet by
1516 // Try to late join to another split point if none of its slaves has
1517 // already finished.
1518 if (Threads.size() > 2)
1519 for (size_t i = 0; i < Threads.size(); ++i)
1521 const int size = Threads[i]->splitPointsSize; // Local copy
1522 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1525 && sp->allSlavesSearching
1526 && available_to(Threads[i]))
1528 // Recheck the conditions under lock protection
1529 Threads.mutex.lock();
1532 if ( sp->allSlavesSearching
1533 && available_to(Threads[i]))
1535 sp->slavesMask.set(idx);
1536 activeSplitPoint = sp;
1541 Threads.mutex.unlock();
1543 break; // Just a single attempt
1548 // If this thread is the master of a split point and all slaves have finished
1549 // their work at this split point, return from the idle loop.
1550 if (this_sp && this_sp->slavesMask.none())
1552 this_sp->mutex.lock();
1553 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1554 this_sp->mutex.unlock();
1562 /// check_time() is called by the timer thread when the timer triggers. It is
1563 /// used to print debug info and, more importantly, to detect when we are out of
1564 /// available time and thus stop the search.
1568 static Time::point lastInfoTime = Time::now();
1569 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1571 if (Time::now() - lastInfoTime >= 1000)
1573 lastInfoTime = Time::now();
1582 Threads.mutex.lock();
1584 nodes = RootPos.nodes_searched();
1586 // Loop across all split points and sum accumulated SplitPoint nodes plus
1587 // all the currently active positions nodes.
1588 for (size_t i = 0; i < Threads.size(); ++i)
1589 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1591 SplitPoint& sp = Threads[i]->splitPoints[j];
1597 for (size_t idx = 0; idx < Threads.size(); ++idx)
1598 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1599 nodes += Threads[idx]->activePosition->nodes_searched();
1604 Threads.mutex.unlock();
1607 Time::point elapsed = Time::now() - SearchTime;
1608 bool stillAtFirstMove = Signals.firstRootMove
1609 && !Signals.failedLowAtRoot
1610 && elapsed > TimeMgr.available_time() * 75 / 100;
1612 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1613 || stillAtFirstMove;
1615 if ( (Limits.use_time_management() && noMoreTime)
1616 || (Limits.movetime && elapsed >= Limits.movetime)
1617 || (Limits.nodes && nodes >= Limits.nodes))
1618 Signals.stop = true;