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 // Different node types, used as template parameter
56 enum NodeType { Root, PV, NonPV };
58 // Dynamic razoring margin based on depth
59 inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
61 // Futility lookup tables (initialized at startup) and their access functions
62 int FutilityMoveCounts[2][32]; // [improving][depth]
64 inline Value futility_margin(Depth d) {
65 return Value(100 * d);
68 // Reduction lookup tables (initialized at startup) and their access function
69 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
71 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
73 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
78 double BestMoveChanges;
79 Value DrawValue[COLOR_NB];
82 MovesStats Countermoves, Followupmoves;
84 template <NodeType NT, bool SpNode>
85 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
87 template <NodeType NT, bool InCheck>
88 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
90 void id_loop(Position& pos);
91 Value value_to_tt(Value v, int ply);
92 Value value_from_tt(Value v, int ply);
93 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
94 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
97 Skill(int l, size_t rootSize) : level(l),
98 candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
101 if (candidates) // Swap best PV line with the sub-optimal one
102 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
103 RootMoves.end(), best ? best : pick_move()));
106 size_t candidates_size() const { return candidates; }
107 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 size_t multiPV = Options["MultiPV"];
286 Skill skill(Options["Skill Level"], RootMoves.size());
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 multiPV = std::max(multiPV, skill.candidates_size());
292 // Iterative deepening loop until requested to stop or target depth reached
293 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
295 // Age out PV variability metric
296 BestMoveChanges *= 0.5;
298 // Save the last iteration's scores before first PV line is searched and
299 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
300 for (size_t i = 0; i < RootMoves.size(); ++i)
301 RootMoves[i].prevScore = RootMoves[i].score;
303 // MultiPV loop. We perform a full root search for each PV line
304 for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
306 // Reset aspiration window starting size
310 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
311 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
314 // Start with a small aspiration window and, in the case of a fail
315 // high/low, re-search with a bigger window until we're not failing
319 bestValue = search<Root, false>(pos, ss, alpha, beta, depth * ONE_PLY, false);
321 // Bring the best move to the front. It is critical that sorting
322 // is done with a stable algorithm because all the values but the
323 // first and eventually the new best one are set to -VALUE_INFINITE
324 // and we want to keep the same order for all the moves except the
325 // new PV that goes to the front. Note that in case of MultiPV
326 // search the already searched PV lines are preserved.
327 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
329 // Write PV back to transposition table in case the relevant
330 // entries have been overwritten during the search.
331 for (size_t i = 0; i <= PVIdx; ++i)
332 RootMoves[i].insert_pv_in_tt(pos);
334 // If search has been stopped break immediately. Sorting and
335 // writing PV back to TT is safe because RootMoves is still
336 // valid, although it refers to previous iteration.
340 // When failing high/low give some update (without cluttering
341 // the UI) before a re-search.
342 if ( (bestValue <= alpha || bestValue >= beta)
343 && Time::now() - SearchTime > 3000)
344 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
346 // In case of failing low/high increase aspiration window and
347 // re-search, otherwise exit the loop.
348 if (bestValue <= alpha)
350 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
352 Signals.failedLowAtRoot = true;
353 Signals.stopOnPonderhit = false;
355 else if (bestValue >= beta)
356 beta = std::min(bestValue + delta, VALUE_INFINITE);
361 delta += 3 * delta / 8;
363 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
366 // Sort the PV lines searched so far and update the GUI
367 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
369 if (PVIdx + 1 == std::min(multiPV, RootMoves.size()) || Time::now() - SearchTime > 3000)
370 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
373 // If skill levels are enabled and time is up, pick a sub-optimal best move
374 if (skill.candidates_size() && skill.time_to_pick(depth))
377 if (Options["Write Search Log"])
379 RootMove& rm = RootMoves[0];
380 if (skill.best != MOVE_NONE)
381 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
383 Log log(Options["Search Log Filename"]);
384 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
388 // Have we found a "mate in x"?
390 && bestValue >= VALUE_MATE_IN_MAX_PLY
391 && VALUE_MATE - bestValue <= 2 * Limits.mate)
394 // Do we have time for the next iteration? Can we stop searching now?
395 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
397 // Take some extra time if the best move has changed
398 if (depth > 4 && multiPV == 1)
399 TimeMgr.pv_instability(BestMoveChanges);
401 // Stop the search if only one legal move is available or all
402 // of the available time has been used.
403 if ( RootMoves.size() == 1
404 || Time::now() - SearchTime > TimeMgr.available_time())
406 // If we are allowed to ponder do not stop the search now but
407 // keep pondering until the GUI sends "ponderhit" or "stop".
409 Signals.stopOnPonderhit = true;
418 // search<>() is the main search function for both PV and non-PV nodes and for
419 // normal and SplitPoint nodes. When called just after a split point the search
420 // is simpler because we have already probed the hash table, done a null move
421 // search, and searched the first move before splitting, so we don't have to
422 // repeat all this work again. We also don't need to store anything to the hash
423 // table here: This is taken care of after we return from the split point.
425 template <NodeType NT, bool SpNode>
426 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
428 const bool RootNode = NT == Root;
429 const bool PvNode = NT == PV || NT == Root;
431 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
432 assert(PvNode || (alpha == beta - 1));
433 assert(depth > DEPTH_ZERO);
435 Move quietsSearched[64];
438 SplitPoint* splitPoint;
440 Move ttMove, move, excludedMove, bestMove;
441 Depth ext, newDepth, predictedDepth;
442 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
443 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
444 bool captureOrPromotion, dangerous, doFullDepthSearch;
445 int moveCount, quietCount;
447 // Step 1. Initialize node
448 Thread* thisThread = pos.this_thread();
449 inCheck = pos.checkers();
453 splitPoint = ss->splitPoint;
454 bestMove = splitPoint->bestMove;
455 bestValue = splitPoint->bestValue;
457 ttMove = excludedMove = MOVE_NONE;
458 ttValue = VALUE_NONE;
460 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
465 moveCount = quietCount = 0;
466 bestValue = -VALUE_INFINITE;
467 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
468 ss->ply = (ss-1)->ply + 1;
469 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
470 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
472 // Used to send selDepth info to GUI
473 if (PvNode && thisThread->maxPly < ss->ply)
474 thisThread->maxPly = ss->ply;
478 // Step 2. Check for aborted search and immediate draw
479 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
480 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
482 // Step 3. Mate distance pruning. Even if we mate at the next move our score
483 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
484 // a shorter mate was found upward in the tree then there is no need to search
485 // because we will never beat the current alpha. Same logic but with reversed
486 // signs applies also in the opposite condition of being mated instead of giving
487 // mate. In this case return a fail-high score.
488 alpha = std::max(mated_in(ss->ply), alpha);
489 beta = std::min(mate_in(ss->ply+1), beta);
494 // Step 4. Transposition table lookup
495 // We don't want the score of a partial search to overwrite a previous full search
496 // TT value, so we use a different position key in case of an excluded move.
497 excludedMove = ss->excludedMove;
498 posKey = excludedMove ? pos.exclusion_key() : pos.key();
499 tte = TT.probe(posKey);
500 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
501 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
503 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
504 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
505 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
506 // we should also update RootMoveList to avoid bogus output.
509 && tte->depth() >= depth
510 && ttValue != VALUE_NONE // Only in case of TT access race
511 && ( PvNode ? tte->bound() == BOUND_EXACT
512 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
513 : (tte->bound() & BOUND_UPPER)))
515 ss->currentMove = ttMove; // Can be MOVE_NONE
517 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
518 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
519 update_stats(pos, ss, ttMove, depth, NULL, 0);
524 // Step 5. Evaluate the position statically and update parent's gain statistics
527 ss->staticEval = eval = VALUE_NONE;
533 // Never assume anything on values stored in TT
534 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
535 eval = ss->staticEval = evaluate(pos);
537 // Can ttValue be used as a better position evaluation?
538 if (ttValue != VALUE_NONE)
539 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
544 eval = ss->staticEval =
545 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
547 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
550 if ( !pos.captured_piece_type()
551 && ss->staticEval != VALUE_NONE
552 && (ss-1)->staticEval != VALUE_NONE
553 && (move = (ss-1)->currentMove) != MOVE_NULL
555 && type_of(move) == NORMAL)
557 Square to = to_sq(move);
558 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
561 // Step 6. Razoring (skipped when in check)
563 && depth < 4 * ONE_PLY
564 && eval + razor_margin(depth) <= alpha
565 && ttMove == MOVE_NONE
566 && !pos.pawn_on_7th(pos.side_to_move()))
568 if ( depth <= ONE_PLY
569 && eval + razor_margin(3 * ONE_PLY) <= alpha)
570 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
572 Value ralpha = alpha - razor_margin(depth);
573 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
578 // Step 7. Futility pruning: child node (skipped when in check)
581 && depth < 7 * ONE_PLY
582 && eval - futility_margin(depth) >= beta
583 && abs(beta) < VALUE_MATE_IN_MAX_PLY
584 && abs(eval) < VALUE_KNOWN_WIN
585 && pos.non_pawn_material(pos.side_to_move()))
586 return eval - futility_margin(depth);
588 // Step 8. Null move search with verification search (is omitted in PV nodes)
591 && depth >= 2 * ONE_PLY
593 && pos.non_pawn_material(pos.side_to_move()))
595 ss->currentMove = MOVE_NULL;
597 assert(eval - beta >= 0);
599 // Null move dynamic reduction based on depth and value
600 Depth R = 3 * ONE_PLY
602 + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
605 pos.do_null_move(st);
606 (ss+1)->skipNullMove = true;
607 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
608 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
609 (ss+1)->skipNullMove = false;
610 pos.undo_null_move();
612 if (nullValue >= beta)
614 // Do not return unproven mate scores
615 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
618 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
621 // Do verification search at high depths
622 ss->skipNullMove = true;
623 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
624 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
625 ss->skipNullMove = false;
632 // Step 9. ProbCut (skipped when in check)
633 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
634 // and a reduced search returns a value much above beta, we can (almost) safely
635 // prune the previous move.
637 && depth >= 5 * ONE_PLY
639 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
641 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
642 Depth rdepth = depth - 4 * ONE_PLY;
644 assert(rdepth >= ONE_PLY);
645 assert((ss-1)->currentMove != MOVE_NONE);
646 assert((ss-1)->currentMove != MOVE_NULL);
648 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
651 while ((move = mp.next_move<false>()) != MOVE_NONE)
652 if (pos.legal(move, ci.pinned))
654 ss->currentMove = move;
655 pos.do_move(move, st, ci, pos.gives_check(move, ci));
656 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
663 // Step 10. Internal iterative deepening (skipped when in check)
664 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
666 && (PvNode || ss->staticEval + 256 >= beta))
668 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
670 ss->skipNullMove = true;
671 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
672 ss->skipNullMove = false;
674 tte = TT.probe(posKey);
675 ttMove = tte ? tte->move() : MOVE_NONE;
678 moves_loop: // When in check and at SpNode search starts from here
680 Square prevMoveSq = to_sq((ss-1)->currentMove);
681 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
682 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
684 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
685 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
686 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
688 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
690 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
691 improving = ss->staticEval >= (ss-2)->staticEval
692 || ss->staticEval == VALUE_NONE
693 ||(ss-2)->staticEval == VALUE_NONE;
695 singularExtensionNode = !RootNode
697 && depth >= 8 * ONE_PLY
698 && abs(beta) < VALUE_KNOWN_WIN
699 && ttMove != MOVE_NONE
700 /* && ttValue != VALUE_NONE Already implicit in the next condition */
701 && abs(ttValue) < VALUE_KNOWN_WIN
702 && !excludedMove // Recursive singular search is not allowed
703 && (tte->bound() & BOUND_LOWER)
704 && tte->depth() >= depth - 3 * ONE_PLY;
706 // Step 11. Loop through moves
707 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
708 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
712 if (move == excludedMove)
715 // At root obey the "searchmoves" option and skip moves not listed in Root
716 // Move List. As a consequence any illegal move is also skipped. In MultiPV
717 // mode we also skip PV moves which have been already searched.
718 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
723 // Shared counter cannot be decremented later if the move turns out to be illegal
724 if (!pos.legal(move, ci.pinned))
727 moveCount = ++splitPoint->moveCount;
728 splitPoint->mutex.unlock();
735 Signals.firstRootMove = (moveCount == 1);
737 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
738 sync_cout << "info depth " << depth / ONE_PLY
739 << " currmove " << move_to_uci(move, pos.is_chess960())
740 << " currmovenumber " << moveCount + PVIdx << sync_endl;
744 captureOrPromotion = pos.capture_or_promotion(move);
746 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
747 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
748 : pos.gives_check(move, ci);
750 dangerous = givesCheck
751 || type_of(move) != NORMAL
752 || pos.advanced_pawn_push(move);
754 // Step 12. Extend checks
755 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
758 // Singular extension search. If all moves but one fail low on a search of
759 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
760 // is singular and should be extended. To verify this we do a reduced search
761 // on all the other moves but the ttMove and if the result is lower than
762 // ttValue minus a margin then we extend the ttMove.
763 if ( singularExtensionNode
766 && pos.legal(move, ci.pinned))
768 Value rBeta = ttValue - int(depth);
769 ss->excludedMove = move;
770 ss->skipNullMove = true;
771 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
772 ss->skipNullMove = false;
773 ss->excludedMove = MOVE_NONE;
779 // Update the current move (this must be done after singular extension search)
780 newDepth = depth - ONE_PLY + ext;
782 // Step 13. Pruning at shallow depth (exclude PV nodes)
784 && !captureOrPromotion
787 /* && move != ttMove Already implicit in the next condition */
788 && bestValue > VALUE_MATED_IN_MAX_PLY)
790 // Move count based pruning
791 if ( depth < 16 * ONE_PLY
792 && moveCount >= FutilityMoveCounts[improving][depth] )
795 splitPoint->mutex.lock();
800 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
802 // Futility pruning: parent node
803 if (predictedDepth < 7 * ONE_PLY)
805 futilityValue = ss->staticEval + futility_margin(predictedDepth)
806 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
808 if (futilityValue <= alpha)
810 bestValue = std::max(bestValue, futilityValue);
814 splitPoint->mutex.lock();
815 if (bestValue > splitPoint->bestValue)
816 splitPoint->bestValue = bestValue;
822 // Prune moves with negative SEE at low depths
823 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
826 splitPoint->mutex.lock();
832 // Check for legality just before making the move
833 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
839 pvMove = PvNode && moveCount == 1;
840 ss->currentMove = move;
841 if (!SpNode && !captureOrPromotion && quietCount < 64)
842 quietsSearched[quietCount++] = move;
844 // Step 14. Make the move
845 pos.do_move(move, st, ci, givesCheck);
847 // Step 15. Reduced depth search (LMR). If the move fails high it will be
848 // re-searched at full depth.
849 if ( depth >= 3 * ONE_PLY
851 && !captureOrPromotion
853 && move != ss->killers[0]
854 && move != ss->killers[1])
856 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
858 if (!PvNode && cutNode)
859 ss->reduction += ONE_PLY;
861 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
862 ss->reduction += ONE_PLY / 2;
864 if (move == countermoves[0] || move == countermoves[1])
865 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
867 // Decrease reduction for moves that escape a capture
869 && type_of(move) == NORMAL
870 && type_of(pos.piece_on(to_sq(move))) != PAWN
871 && pos.see(make_move(to_sq(move), from_sq(move))) < 0)
872 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
874 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
876 alpha = splitPoint->alpha;
878 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
880 // Re-search at intermediate depth if reduction is very high
881 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
883 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
884 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
887 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
888 ss->reduction = DEPTH_ZERO;
891 doFullDepthSearch = !pvMove;
893 // Step 16. Full depth search, when LMR is skipped or fails high
894 if (doFullDepthSearch)
897 alpha = splitPoint->alpha;
899 value = newDepth < ONE_PLY ?
900 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
901 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
902 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
905 // For PV nodes only, do a full PV search on the first move or after a fail
906 // high (in the latter case search only if value < beta), otherwise let the
907 // parent node fail low with value <= alpha and to try another move.
908 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
909 value = newDepth < ONE_PLY ?
910 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
911 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
912 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
913 // Step 17. Undo move
916 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
918 // Step 18. Check for new best move
921 splitPoint->mutex.lock();
922 bestValue = splitPoint->bestValue;
923 alpha = splitPoint->alpha;
926 // Finished searching the move. If a stop or a cutoff occurred, the return
927 // value of the search cannot be trusted, and we return immediately without
928 // updating best move, PV and TT.
929 if (Signals.stop || thisThread->cutoff_occurred())
934 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
936 // PV move or new best move ?
937 if (pvMove || value > alpha)
940 rm.extract_pv_from_tt(pos);
942 // We record how often the best move has been changed in each
943 // iteration. This information is used for time management: When
944 // the best move changes frequently, we allocate some more time.
949 // All other moves but the PV are set to the lowest value: this is
950 // not a problem when sorting because the sort is stable and the
951 // move position in the list is preserved - just the PV is pushed up.
952 rm.score = -VALUE_INFINITE;
955 if (value > bestValue)
957 bestValue = SpNode ? splitPoint->bestValue = value : value;
961 bestMove = SpNode ? splitPoint->bestMove = move : move;
963 if (PvNode && value < beta) // Update alpha! Always alpha < beta
964 alpha = SpNode ? splitPoint->alpha = value : value;
967 assert(value >= beta); // Fail high
970 splitPoint->cutoff = true;
977 // Step 19. Check for splitting the search
979 && Threads.size() >= 2
980 && depth >= Threads.minimumSplitDepth
981 && ( !thisThread->activeSplitPoint
982 || !thisThread->activeSplitPoint->allSlavesSearching)
983 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
985 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
987 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
988 depth, moveCount, &mp, NT, cutNode);
990 if (Signals.stop || thisThread->cutoff_occurred())
993 if (bestValue >= beta)
1001 // Following condition would detect a stop or a cutoff set only after move
1002 // loop has been completed. But in this case bestValue is valid because we
1003 // have fully searched our subtree, and we can anyhow save the result in TT.
1005 if (Signals.stop || thisThread->cutoff_occurred())
1009 // Step 20. Check for mate and stalemate
1010 // All legal moves have been searched and if there are no legal moves, it
1011 // must be mate or stalemate. If we are in a singular extension search then
1012 // return a fail low score.
1014 bestValue = excludedMove ? alpha
1015 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1017 // Quiet best move: update killers, history, countermoves and followupmoves
1018 else if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1019 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1021 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1022 bestValue >= beta ? BOUND_LOWER :
1023 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1024 depth, bestMove, ss->staticEval);
1026 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1032 // qsearch() is the quiescence search function, which is called by the main
1033 // search function when the remaining depth is zero (or, to be more precise,
1034 // less than ONE_PLY).
1036 template <NodeType NT, bool InCheck>
1037 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1039 const bool PvNode = NT == PV;
1041 assert(NT == PV || NT == NonPV);
1042 assert(InCheck == !!pos.checkers());
1043 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1044 assert(PvNode || (alpha == beta - 1));
1045 assert(depth <= DEPTH_ZERO);
1050 Move ttMove, move, bestMove;
1051 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1052 bool givesCheck, evasionPrunable;
1055 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1059 ss->currentMove = bestMove = MOVE_NONE;
1060 ss->ply = (ss-1)->ply + 1;
1062 // Check for an instant draw or if the maximum ply has been reached
1063 if (pos.is_draw() || ss->ply > MAX_PLY)
1064 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1066 // Decide whether or not to include checks: this fixes also the type of
1067 // TT entry depth that we are going to use. Note that in qsearch we use
1068 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1069 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1070 : DEPTH_QS_NO_CHECKS;
1072 // Transposition table lookup
1074 tte = TT.probe(posKey);
1075 ttMove = tte ? tte->move() : MOVE_NONE;
1076 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1079 && tte->depth() >= ttDepth
1080 && ttValue != VALUE_NONE // Only in case of TT access race
1081 && ( PvNode ? tte->bound() == BOUND_EXACT
1082 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1083 : (tte->bound() & BOUND_UPPER)))
1085 ss->currentMove = ttMove; // Can be MOVE_NONE
1089 // Evaluate the position statically
1092 ss->staticEval = VALUE_NONE;
1093 bestValue = futilityBase = -VALUE_INFINITE;
1099 // Never assume anything on values stored in TT
1100 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1101 ss->staticEval = bestValue = evaluate(pos);
1103 // Can ttValue be used as a better position evaluation?
1104 if (ttValue != VALUE_NONE)
1105 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1106 bestValue = ttValue;
1109 ss->staticEval = bestValue =
1110 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1112 // Stand pat. Return immediately if static value is at least beta
1113 if (bestValue >= beta)
1116 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1117 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1122 if (PvNode && bestValue > alpha)
1125 futilityBase = bestValue + 128;
1128 // Initialize a MovePicker object for the current position, and prepare
1129 // to search the moves. Because the depth is <= 0 here, only captures,
1130 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1132 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1135 // Loop through the moves until no moves remain or a beta cutoff occurs
1136 while ((move = mp.next_move<false>()) != MOVE_NONE)
1138 assert(is_ok(move));
1140 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1141 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1142 : pos.gives_check(move, ci);
1149 && futilityBase > -VALUE_KNOWN_WIN
1150 && !pos.advanced_pawn_push(move))
1152 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1154 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1156 if (futilityValue < beta)
1158 bestValue = std::max(bestValue, futilityValue);
1162 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1164 bestValue = std::max(bestValue, futilityBase);
1169 // Detect non-capture evasions that are candidates to be pruned
1170 evasionPrunable = InCheck
1171 && bestValue > VALUE_MATED_IN_MAX_PLY
1172 && !pos.capture(move)
1173 && !pos.can_castle(pos.side_to_move());
1175 // Don't search moves with negative SEE values
1177 && (!InCheck || evasionPrunable)
1179 && type_of(move) != PROMOTION
1180 && pos.see_sign(move) < VALUE_ZERO)
1183 // Check for legality just before making the move
1184 if (!pos.legal(move, ci.pinned))
1187 ss->currentMove = move;
1189 // Make and search the move
1190 pos.do_move(move, st, ci, givesCheck);
1191 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1192 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1193 pos.undo_move(move);
1195 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1197 // Check for new best move
1198 if (value > bestValue)
1204 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1211 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1212 ttDepth, move, ss->staticEval);
1220 // All legal moves have been searched. A special case: If we're in check
1221 // and no legal moves were found, it is checkmate.
1222 if (InCheck && bestValue == -VALUE_INFINITE)
1223 return mated_in(ss->ply); // Plies to mate from the root
1225 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1226 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1227 ttDepth, bestMove, ss->staticEval);
1229 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1235 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1236 // "plies to mate from the current position". Non-mate scores are unchanged.
1237 // The function is called before storing a value in the transposition table.
1239 Value value_to_tt(Value v, int ply) {
1241 assert(v != VALUE_NONE);
1243 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1244 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1248 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1249 // from the transposition table (which refers to the plies to mate/be mated
1250 // from current position) to "plies to mate/be mated from the root".
1252 Value value_from_tt(Value v, int ply) {
1254 return v == VALUE_NONE ? VALUE_NONE
1255 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1256 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1260 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1263 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1265 if (ss->killers[0] != move)
1267 ss->killers[1] = ss->killers[0];
1268 ss->killers[0] = move;
1271 // Increase history value of the cut-off move and decrease all the other
1272 // played quiet moves.
1273 Value bonus = Value(int(depth) * int(depth));
1274 History.update(pos.moved_piece(move), to_sq(move), bonus);
1275 for (int i = 0; i < quietsCnt; ++i)
1278 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1281 if (is_ok((ss-1)->currentMove))
1283 Square prevMoveSq = to_sq((ss-1)->currentMove);
1284 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1287 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1289 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1290 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1295 // When playing with a strength handicap, choose best move among the first 'candidates'
1296 // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1298 Move Skill::pick_move() {
1302 // PRNG sequence should be not deterministic
1303 for (int i = Time::now() % 50; i > 0; --i)
1304 rk.rand<unsigned>();
1306 // RootMoves are already sorted by score in descending order
1307 int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
1308 int weakness = 120 - 2 * level;
1309 int max_s = -VALUE_INFINITE;
1312 // Choose best move. For each move score we add two terms both dependent on
1313 // weakness. One deterministic and bigger for weaker moves, and one random,
1314 // then we choose the move with the resulting highest score.
1315 for (size_t i = 0; i < candidates; ++i)
1317 int s = RootMoves[i].score;
1319 // Don't allow crazy blunders even at very low skills
1320 if (i > 0 && RootMoves[i - 1].score > s + 2 * PawnValueMg)
1323 // This is our magic formula
1324 s += ( weakness * int(RootMoves[0].score - s)
1325 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1330 best = RootMoves[i].pv[0];
1337 // uci_pv() formats PV information according to the UCI protocol. UCI
1338 // requires that all (if any) unsearched PV lines are sent using a previous
1341 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1343 std::stringstream ss;
1344 Time::point elapsed = Time::now() - SearchTime + 1;
1345 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1348 for (size_t i = 0; i < Threads.size(); ++i)
1349 if (Threads[i]->maxPly > selDepth)
1350 selDepth = Threads[i]->maxPly;
1352 for (size_t i = 0; i < uciPVSize; ++i)
1354 bool updated = (i <= PVIdx);
1356 if (depth == 1 && !updated)
1359 int d = updated ? depth : depth - 1;
1360 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1362 if (ss.rdbuf()->in_avail()) // Not at first line
1365 ss << "info depth " << d
1366 << " seldepth " << selDepth
1367 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1368 << " nodes " << pos.nodes_searched()
1369 << " nps " << pos.nodes_searched() * 1000 / elapsed
1370 << " time " << elapsed
1371 << " multipv " << i + 1
1374 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1375 ss << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1384 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1385 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1386 /// ensure that we have a ponder move even when we fail high at root. This
1387 /// results in a long PV to print that is important for position analysis.
1389 void RootMove::extract_pv_from_tt(Position& pos) {
1391 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1393 int ply = 1; // At root ply is 1...
1394 Move m = pv[0]; // ...instead pv[] array starts from 0
1395 Value expectedScore = score;
1402 assert(MoveList<LEGAL>(pos).contains(pv[ply - 1]));
1404 pos.do_move(pv[ply++ - 1], *st++);
1405 tte = TT.probe(pos.key());
1406 expectedScore = -expectedScore;
1409 && expectedScore == value_from_tt(tte->value(), ply)
1410 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1411 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1413 && (!pos.is_draw() || ply <= 2));
1415 pv.push_back(MOVE_NONE); // Must be zero-terminating
1417 while (--ply) pos.undo_move(pv[ply - 1]);
1421 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1422 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1423 /// first, even if the old TT entries have been overwritten.
1425 void RootMove::insert_pv_in_tt(Position& pos) {
1427 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1429 int idx = 0; // Ply starts from 1, we need to start from 0
1432 tte = TT.probe(pos.key());
1434 if (!tte || tte->move() != pv[idx]) // Don't overwrite correct entries
1435 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[idx], VALUE_NONE);
1437 assert(MoveList<LEGAL>(pos).contains(pv[idx]));
1439 pos.do_move(pv[idx++], *st++);
1441 } while (pv[idx] != MOVE_NONE);
1443 while (idx) pos.undo_move(pv[--idx]);
1447 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1449 void Thread::idle_loop() {
1451 // Pointer 'this_sp' is not null only if we are called from split(), and not
1452 // at the thread creation. This means we are the split point's master.
1453 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1455 assert(!this_sp || (this_sp->masterThread == this && searching));
1459 // If we are not searching, wait for a condition to be signaled instead of
1460 // wasting CPU time polling for work.
1461 while (!searching || exit)
1469 // Grab the lock to avoid races with Thread::notify_one()
1472 // If we are master and all slaves have finished then exit idle_loop
1473 if (this_sp && this_sp->slavesMask.none())
1479 // Do sleep after retesting sleep conditions under lock protection. In
1480 // particular we need to avoid a deadlock in case a master thread has,
1481 // in the meanwhile, allocated us and sent the notify_one() call before
1482 // we had the chance to grab the lock.
1483 if (!searching && !exit)
1484 sleepCondition.wait(mutex);
1489 // If this thread has been assigned work, launch a search
1494 Threads.mutex.lock();
1497 assert(activeSplitPoint);
1498 SplitPoint* sp = activeSplitPoint;
1500 Threads.mutex.unlock();
1502 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1503 Position pos(*sp->pos, this);
1505 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1506 ss->splitPoint = sp;
1510 assert(activePosition == NULL);
1512 activePosition = &pos;
1514 if (sp->nodeType == NonPV)
1515 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1517 else if (sp->nodeType == PV)
1518 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1520 else if (sp->nodeType == Root)
1521 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1529 activePosition = NULL;
1530 sp->slavesMask.reset(idx);
1531 sp->allSlavesSearching = false;
1532 sp->nodes += pos.nodes_searched();
1534 // Wake up the master thread so to allow it to return from the idle
1535 // loop in case we are the last slave of the split point.
1536 if ( this != sp->masterThread
1537 && sp->slavesMask.none())
1539 assert(!sp->masterThread->searching);
1540 sp->masterThread->notify_one();
1543 // After releasing the lock we can't access any SplitPoint related data
1544 // in a safe way because it could have been released under our feet by
1548 // Try to late join to another split point if none of its slaves has
1549 // already finished.
1550 if (Threads.size() > 2)
1551 for (size_t i = 0; i < Threads.size(); ++i)
1553 const int size = Threads[i]->splitPointsSize; // Local copy
1554 sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
1557 && sp->allSlavesSearching
1558 && available_to(Threads[i]))
1560 // Recheck the conditions under lock protection
1561 Threads.mutex.lock();
1564 if ( sp->allSlavesSearching
1565 && available_to(Threads[i]))
1567 sp->slavesMask.set(idx);
1568 activeSplitPoint = sp;
1573 Threads.mutex.unlock();
1575 break; // Just a single attempt
1580 // If this thread is the master of a split point and all slaves have finished
1581 // their work at this split point, return from the idle loop.
1582 if (this_sp && this_sp->slavesMask.none())
1584 this_sp->mutex.lock();
1585 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1586 this_sp->mutex.unlock();
1594 /// check_time() is called by the timer thread when the timer triggers. It is
1595 /// used to print debug info and, more importantly, to detect when we are out of
1596 /// available time and thus stop the search.
1600 static Time::point lastInfoTime = Time::now();
1601 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1603 if (Time::now() - lastInfoTime >= 1000)
1605 lastInfoTime = Time::now();
1614 Threads.mutex.lock();
1616 nodes = RootPos.nodes_searched();
1618 // Loop across all split points and sum accumulated SplitPoint nodes plus
1619 // all the currently active positions nodes.
1620 for (size_t i = 0; i < Threads.size(); ++i)
1621 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1623 SplitPoint& sp = Threads[i]->splitPoints[j];
1629 for (size_t idx = 0; idx < Threads.size(); ++idx)
1630 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1631 nodes += Threads[idx]->activePosition->nodes_searched();
1636 Threads.mutex.unlock();
1639 Time::point elapsed = Time::now() - SearchTime;
1640 bool stillAtFirstMove = Signals.firstRootMove
1641 && !Signals.failedLowAtRoot
1642 && elapsed > TimeMgr.available_time() * 75 / 100;
1644 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1645 || stillAtFirstMove;
1647 if ( (Limits.use_time_management() && noMoreTime)
1648 || (Limits.movetime && elapsed >= Limits.movetime)
1649 || (Limits.nodes && nodes >= Limits.nodes))
1650 Signals.stop = true;