2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
85 CountermovesStats Countermoves;
87 template <NodeType NT>
88 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
90 template <NodeType NT, bool InCheck>
91 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
93 void id_loop(Position& pos);
94 Value value_to_tt(Value v, int ply);
95 Value value_from_tt(Value v, int ply);
96 bool allows(const Position& pos, Move first, Move second);
97 bool refutes(const Position& pos, Move first, Move second);
98 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
101 Skill(int l) : level(l), best(MOVE_NONE) {}
103 if (enabled()) // Swap best PV line with the sub-optimal one
104 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
105 RootMoves.end(), best ? best : pick_move()));
108 bool enabled() const { return level < 20; }
109 bool time_to_pick(int depth) const { return depth == 1 + level; }
119 /// Search::init() is called during startup to initialize various lookup tables
121 void Search::init() {
123 int d; // depth (ONE_PLY == 2)
124 int hd; // half depth (ONE_PLY == 1)
127 // Init reductions array
128 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
130 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
131 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
132 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
133 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
135 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
136 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
138 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
139 Reductions[0][0][hd][mc] += ONE_PLY;
141 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
142 Reductions[0][0][hd][mc] += ONE_PLY / 2;
145 // Init futility move count array
146 for (d = 0; d < 32; ++d)
148 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
149 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
154 /// Search::perft() is our utility to verify move generation. All the leaf nodes
155 /// up to the given depth are generated and counted and the sum returned.
157 static size_t perft(Position& pos, Depth depth) {
162 const bool leaf = depth == 2 * ONE_PLY;
164 for (MoveList<LEGAL> it(pos); *it; ++it)
166 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
167 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
173 size_t Search::perft(Position& pos, Depth depth) {
174 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
177 /// Search::think() is the external interface to Stockfish's search, and is
178 /// called by the main thread when the program receives the UCI 'go' command. It
179 /// searches from RootPos and at the end prints the "bestmove" to output.
181 void Search::think() {
183 static PolyglotBook book; // Defined static to initialize the PRNG only once
185 RootColor = RootPos.side_to_move();
186 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
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["OwnBook"] && !Limits.infinite && !Limits.mate)
200 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
202 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
204 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
209 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
211 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
212 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
213 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
214 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
217 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
219 if (Options["Write Search Log"])
221 Log log(Options["Search Log Filename"]);
222 log << "\nSearching: " << RootPos.fen()
223 << "\ninfinite: " << Limits.infinite
224 << " ponder: " << Limits.ponder
225 << " time: " << Limits.time[RootColor]
226 << " increment: " << Limits.inc[RootColor]
227 << " moves to go: " << Limits.movestogo
231 // Reset the threads, still sleeping: will be wake up at split time
232 for (size_t i = 0; i < Threads.size(); ++i)
233 Threads[i]->maxPly = 0;
235 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
236 Threads.timer->run = true;
237 Threads.timer->notify_one(); // Wake up the recurring timer
239 id_loop(RootPos); // Let's start searching !
241 Threads.timer->run = false; // Stop the timer
242 Threads.sleepWhileIdle = true; // Send idle threads to sleep
244 if (Options["Write Search Log"])
246 Time::point elapsed = Time::now() - SearchTime + 1;
248 Log log(Options["Search Log Filename"]);
249 log << "Nodes: " << RootPos.nodes_searched()
250 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
251 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
254 RootPos.do_move(RootMoves[0].pv[0], st);
255 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
256 RootPos.undo_move(RootMoves[0].pv[0]);
261 // When search is stopped this info is not printed
262 sync_cout << "info nodes " << RootPos.nodes_searched()
263 << " time " << Time::now() - SearchTime + 1 << sync_endl;
265 // When we reach max depth we arrive here even without Signals.stop is raised,
266 // but if we are pondering or in infinite search, according to UCI protocol,
267 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
268 // command. We simply wait here until GUI sends one of those commands (that
269 // raise Signals.stop).
270 if (!Signals.stop && (Limits.ponder || Limits.infinite))
272 Signals.stopOnPonderhit = true;
273 RootPos.this_thread()->wait_for(Signals.stop);
276 // Best move could be MOVE_NONE when searching on a stalemate position
277 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
278 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
285 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
286 // with increasing depth until the allocated thinking time has been consumed,
287 // user stops the search, or the maximum search depth is reached.
289 void id_loop(Position& pos) {
291 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
293 Value bestValue, alpha, beta, delta;
295 std::memset(ss-2, 0, 5 * sizeof(Stack));
299 bestValue = delta = alpha = -VALUE_INFINITE;
300 beta = VALUE_INFINITE;
304 Countermoves.clear();
306 PVSize = Options["MultiPV"];
307 Skill skill(Options["Skill Level"]);
309 // Do we have to play with skill handicap? In this case enable MultiPV search
310 // that we will use behind the scenes to retrieve a set of possible moves.
311 if (skill.enabled() && PVSize < 4)
314 PVSize = std::min(PVSize, RootMoves.size());
316 // Iterative deepening loop until requested to stop or target depth reached
317 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
319 // Age out PV variability metric
320 BestMoveChanges *= 0.8;
322 // Save last iteration's scores before first PV line is searched and all
323 // the move scores but the (new) PV are set to -VALUE_INFINITE.
324 for (size_t i = 0; i < RootMoves.size(); ++i)
325 RootMoves[i].prevScore = RootMoves[i].score;
327 // MultiPV loop. We perform a full root search for each PV line
328 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
330 // Reset aspiration window starting size
334 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
335 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
338 // Start with a small aspiration window and, in case of fail high/low,
339 // research with bigger window until not failing high/low anymore.
342 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
344 // Bring to front the best move. It is critical that sorting is
345 // done with a stable algorithm because all the values but the first
346 // and eventually the new best one are set to -VALUE_INFINITE and
347 // we want to keep the same order for all the moves but the new
348 // PV that goes to the front. Note that in case of MultiPV search
349 // the already searched PV lines are preserved.
350 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
352 // Write PV back to transposition table in case the relevant
353 // entries have been overwritten during the search.
354 for (size_t i = 0; i <= PVIdx; ++i)
355 RootMoves[i].insert_pv_in_tt(pos);
357 // If search has been stopped break immediately. Sorting and
358 // writing PV back to TT is safe becuase RootMoves is still
359 // valid, although refers to previous iteration.
363 // When failing high/low give some update (without cluttering
364 // the UI) before to research.
365 if ( (bestValue <= alpha || bestValue >= beta)
366 && Time::now() - SearchTime > 3000)
367 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
369 // In case of failing low/high increase aspiration window and
370 // research, otherwise exit the loop.
371 if (bestValue <= alpha)
373 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
375 Signals.failedLowAtRoot = true;
376 Signals.stopOnPonderhit = false;
378 else if (bestValue >= beta)
379 beta = std::min(bestValue + delta, VALUE_INFINITE);
386 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
389 // Sort the PV lines searched so far and update the GUI
390 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
392 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
393 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
396 // Do we need to pick now the sub-optimal best move ?
397 if (skill.enabled() && skill.time_to_pick(depth))
400 if (Options["Write Search Log"])
402 RootMove& rm = RootMoves[0];
403 if (skill.best != MOVE_NONE)
404 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
406 Log log(Options["Search Log Filename"]);
407 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
411 // Do we have found a "mate in x"?
413 && bestValue >= VALUE_MATE_IN_MAX_PLY
414 && VALUE_MATE - bestValue <= 2 * Limits.mate)
417 // Do we have time for the next iteration? Can we stop searching now?
418 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
420 bool stop = false; // Local variable, not the volatile Signals.stop
422 // Take in account some extra time if the best move has changed
423 if (depth > 4 && depth < 50 && PVSize == 1)
424 TimeMgr.pv_instability(BestMoveChanges);
426 // Stop search if most of available time is already consumed. We
427 // probably don't have enough time to search the first move at the
428 // next iteration anyway.
429 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
432 // Stop search early if one move seems to be much better than others
434 && BestMoveChanges <= DBL_EPSILON
437 && bestValue > VALUE_MATED_IN_MAX_PLY
438 && ( RootMoves.size() == 1
439 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
441 Value rBeta = bestValue - 2 * PawnValueMg;
442 ss->excludedMove = RootMoves[0].pv[0];
443 ss->skipNullMove = true;
444 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
445 ss->skipNullMove = false;
446 ss->excludedMove = MOVE_NONE;
454 // If we are allowed to ponder do not stop the search now but
455 // keep pondering until GUI sends "ponderhit" or "stop".
457 Signals.stopOnPonderhit = true;
466 // search<>() is the main search function for both PV and non-PV nodes and for
467 // normal and SplitPoint nodes. When called just after a split point the search
468 // is simpler because we have already probed the hash table, done a null move
469 // search, and searched the first move before splitting, we don't have to repeat
470 // all this work again. We also don't need to store anything to the hash table
471 // here: This is taken care of after we return from the split point.
473 template <NodeType NT>
474 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
476 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
477 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
478 const bool RootNode = (NT == Root || NT == SplitPointRoot);
480 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
481 assert(PvNode || (alpha == beta - 1));
482 assert(depth > DEPTH_ZERO);
484 Move quietsSearched[64];
487 SplitPoint* splitPoint;
489 Move ttMove, move, excludedMove, bestMove, threatMove;
491 Value bestValue, value, ttValue;
492 Value eval, nullValue;
493 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
494 bool captureOrPromotion, dangerous, doFullDepthSearch;
495 int moveCount, quietCount;
497 // Step 1. Initialize node
498 Thread* thisThread = pos.this_thread();
499 inCheck = pos.checkers();
503 splitPoint = ss->splitPoint;
504 bestMove = splitPoint->bestMove;
505 threatMove = splitPoint->threatMove;
506 bestValue = splitPoint->bestValue;
508 ttMove = excludedMove = MOVE_NONE;
509 ttValue = VALUE_NONE;
511 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
516 moveCount = quietCount = 0;
517 bestValue = -VALUE_INFINITE;
518 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
519 ss->ply = (ss-1)->ply + 1;
520 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
521 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
523 // Used to send selDepth info to GUI
524 if (PvNode && thisThread->maxPly < ss->ply)
525 thisThread->maxPly = ss->ply;
529 // Step 2. Check for aborted search and immediate draw
530 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
531 return DrawValue[pos.side_to_move()];
533 // Step 3. Mate distance pruning. Even if we mate at the next move our score
534 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
535 // a shorter mate was found upward in the tree then there is no need to search
536 // further, we will never beat current alpha. Same logic but with reversed signs
537 // applies also in the opposite condition of being mated instead of giving mate,
538 // in this case return a fail-high score.
539 alpha = std::max(mated_in(ss->ply), alpha);
540 beta = std::min(mate_in(ss->ply+1), beta);
545 // Step 4. Transposition table lookup
546 // We don't want the score of a partial search to overwrite a previous full search
547 // TT value, so we use a different position key in case of an excluded move.
548 excludedMove = ss->excludedMove;
549 posKey = excludedMove ? pos.exclusion_key() : pos.key();
550 tte = TT.probe(posKey);
551 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
552 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
554 // At PV nodes we check for exact scores, while at non-PV nodes we check for
555 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
556 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
557 // we should also update RootMoveList to avoid bogus output.
560 && tte->depth() >= depth
561 && ttValue != VALUE_NONE // Only in case of TT access race
562 && ( PvNode ? tte->bound() == BOUND_EXACT
563 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
564 : (tte->bound() & BOUND_UPPER)))
567 ss->currentMove = ttMove; // Can be MOVE_NONE
571 && !pos.capture_or_promotion(ttMove)
572 && ttMove != ss->killers[0])
574 ss->killers[1] = ss->killers[0];
575 ss->killers[0] = ttMove;
580 // Step 5. Evaluate the position statically and update parent's gain statistics
583 ss->staticEval = eval = VALUE_NONE;
589 // Never assume anything on values stored in TT
590 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
591 eval = ss->staticEval = evaluate(pos);
593 // Can ttValue be used as a better position evaluation?
594 if (ttValue != VALUE_NONE)
595 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
600 eval = ss->staticEval = evaluate(pos);
601 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
604 // Step 6. Razoring (skipped when in check)
606 && depth < 4 * ONE_PLY
607 && eval + razor_margin(depth) < beta
608 && ttMove == MOVE_NONE
609 && abs(beta) < VALUE_MATE_IN_MAX_PLY
610 && !pos.pawn_on_7th(pos.side_to_move()))
612 Value rbeta = beta - razor_margin(depth);
613 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
615 // Logically we should return (v + razor_margin(depth)), but
616 // surprisingly this did slightly weaker in tests.
620 // Step 7. Futility pruning: child node (skipped when in check)
623 && depth < 7 * ONE_PLY
624 && eval - futility_margin(depth) >= beta
625 && abs(beta) < VALUE_MATE_IN_MAX_PLY
626 && abs(eval) < VALUE_KNOWN_WIN
627 && pos.non_pawn_material(pos.side_to_move()))
628 return eval - futility_margin(depth);
630 // Step 8. Null move search with verification search (is omitted in PV nodes)
633 && depth >= 2 * ONE_PLY
635 && abs(beta) < VALUE_MATE_IN_MAX_PLY
636 && pos.non_pawn_material(pos.side_to_move()))
638 ss->currentMove = MOVE_NULL;
640 // Null move dynamic reduction based on depth
641 Depth R = 3 * ONE_PLY + depth / 4;
643 // Null move dynamic reduction based on value
644 if (eval - PawnValueMg > beta)
647 pos.do_null_move(st);
648 (ss+1)->skipNullMove = true;
649 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
650 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
651 (ss+1)->skipNullMove = false;
652 pos.undo_null_move();
654 if (nullValue >= beta)
656 // Do not return unproven mate scores
657 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
660 if (depth < 12 * ONE_PLY)
663 // Do verification search at high depths
664 ss->skipNullMove = true;
665 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
666 ss->skipNullMove = false;
673 // The null move failed low, which means that we may be faced with
674 // some kind of threat. If the previous move was reduced, check if
675 // the move that refuted the null move was somehow connected to the
676 // move which was reduced. If a connection is found, return a fail
677 // low score (which will cause the reduced move to fail high in the
678 // parent node, which will trigger a re-search with full depth).
679 threatMove = (ss+1)->currentMove;
681 if ( depth < 5 * ONE_PLY
683 && threatMove != MOVE_NONE
684 && allows(pos, (ss-1)->currentMove, threatMove))
689 // Step 9. ProbCut (skipped when in check)
690 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
691 // and a reduced search returns a value much above beta, we can (almost) safely
692 // prune the previous move.
694 && depth >= 5 * ONE_PLY
696 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
698 Value rbeta = beta + 200;
699 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
701 assert(rdepth >= ONE_PLY);
702 assert((ss-1)->currentMove != MOVE_NONE);
703 assert((ss-1)->currentMove != MOVE_NULL);
705 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
708 while ((move = mp.next_move<false>()) != MOVE_NONE)
709 if (pos.legal(move, ci.pinned))
711 ss->currentMove = move;
712 pos.do_move(move, st, ci, pos.gives_check(move, ci));
713 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
720 // Step 10. Internal iterative deepening (skipped when in check)
721 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
722 && ttMove == MOVE_NONE
723 && (PvNode || ss->staticEval + Value(256) >= beta))
725 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
727 ss->skipNullMove = true;
728 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
729 ss->skipNullMove = false;
731 tte = TT.probe(posKey);
732 ttMove = tte ? tte->move() : MOVE_NONE;
735 moves_loop: // When in check and at SpNode search starts from here
737 Square prevMoveSq = to_sq((ss-1)->currentMove);
738 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
739 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
741 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
743 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
744 improving = ss->staticEval >= (ss-2)->staticEval
745 || ss->staticEval == VALUE_NONE
746 ||(ss-2)->staticEval == VALUE_NONE;
748 singularExtensionNode = !RootNode
750 && depth >= 8 * ONE_PLY
751 && ttMove != MOVE_NONE
752 && !excludedMove // Recursive singular search is not allowed
753 && (tte->bound() & BOUND_LOWER)
754 && tte->depth() >= depth - 3 * ONE_PLY;
756 // Step 11. Loop through moves
757 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
758 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
762 if (move == excludedMove)
765 // At root obey the "searchmoves" option and skip moves not listed in Root
766 // Move List, as a consequence any illegal move is also skipped. In MultiPV
767 // mode we also skip PV moves which have been already searched.
768 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
773 // Shared counter cannot be decremented later if move turns out to be illegal
774 if (!pos.legal(move, ci.pinned))
777 moveCount = ++splitPoint->moveCount;
778 splitPoint->mutex.unlock();
785 Signals.firstRootMove = (moveCount == 1);
787 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
788 sync_cout << "info depth " << depth / ONE_PLY
789 << " currmove " << move_to_uci(move, pos.is_chess960())
790 << " currmovenumber " << moveCount + PVIdx << sync_endl;
794 captureOrPromotion = pos.capture_or_promotion(move);
795 givesCheck = pos.gives_check(move, ci);
796 dangerous = givesCheck
797 || pos.passed_pawn_push(move)
798 || type_of(move) == CASTLE;
800 // Step 12. Extend checks
801 if (givesCheck && pos.see_sign(move) >= 0)
804 // Singular extension search. If all moves but one fail low on a search of
805 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
806 // is singular and should be extended. To verify this we do a reduced search
807 // on all the other moves but the ttMove, if result is lower than ttValue minus
808 // a margin then we extend ttMove.
809 if ( singularExtensionNode
812 && pos.legal(move, ci.pinned)
813 && abs(ttValue) < VALUE_KNOWN_WIN)
815 assert(ttValue != VALUE_NONE);
817 Value rBeta = ttValue - int(depth);
818 ss->excludedMove = move;
819 ss->skipNullMove = true;
820 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
821 ss->skipNullMove = false;
822 ss->excludedMove = MOVE_NONE;
828 // Update current move (this must be done after singular extension search)
829 newDepth = depth - ONE_PLY + ext;
831 // Step 13. Pruning at shallow depth (exclude PV nodes)
833 && !captureOrPromotion
836 /* && move != ttMove Already implicit in the next condition */
837 && bestValue > VALUE_MATED_IN_MAX_PLY)
839 // Move count based pruning
840 if ( depth < 16 * ONE_PLY
841 && moveCount >= FutilityMoveCounts[improving][depth]
842 && (!threatMove || !refutes(pos, move, threatMove)))
845 splitPoint->mutex.lock();
850 Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
852 // Futility pruning: parent node
853 if (predictedDepth < 7 * ONE_PLY)
855 Value futilityValue = ss->staticEval + futility_margin(predictedDepth) + Value(128);
857 if (futilityValue <= alpha)
859 bestValue = std::max(bestValue, futilityValue);
863 splitPoint->mutex.lock();
864 if (bestValue > splitPoint->bestValue)
865 splitPoint->bestValue = bestValue;
871 // Prune moves with negative SEE at low depths
872 if ( predictedDepth < 4 * ONE_PLY
873 && pos.see_sign(move) < 0)
876 splitPoint->mutex.lock();
883 // Check for legality only before to do the move
884 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
890 pvMove = PvNode && moveCount == 1;
891 ss->currentMove = move;
892 if (!SpNode && !captureOrPromotion && quietCount < 64)
893 quietsSearched[quietCount++] = move;
895 // Step 14. Make the move
896 pos.do_move(move, st, ci, givesCheck);
898 // Step 15. Reduced depth search (LMR). If the move fails high will be
899 // re-searched at full depth.
900 if ( depth >= 3 * ONE_PLY
902 && !captureOrPromotion
904 && move != ss->killers[0]
905 && move != ss->killers[1])
907 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
909 if (!PvNode && cutNode)
910 ss->reduction += ONE_PLY;
912 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
913 ss->reduction += ONE_PLY / 2;
915 if (move == countermoves[0] || move == countermoves[1])
916 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
918 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
920 alpha = splitPoint->alpha;
922 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
924 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
925 ss->reduction = DEPTH_ZERO;
928 doFullDepthSearch = !pvMove;
930 // Step 16. Full depth search, when LMR is skipped or fails high
931 if (doFullDepthSearch)
934 alpha = splitPoint->alpha;
936 value = newDepth < ONE_PLY ?
937 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
938 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
939 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
942 // Only for PV nodes do a full PV search on the first move or after a fail
943 // high, in the latter case search only if value < beta, otherwise let the
944 // parent node to fail low with value <= alpha and to try another move.
945 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
946 value = newDepth < ONE_PLY ?
947 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
948 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
949 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
950 // Step 17. Undo move
953 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
955 // Step 18. Check for new best move
958 splitPoint->mutex.lock();
959 bestValue = splitPoint->bestValue;
960 alpha = splitPoint->alpha;
963 // Finished searching the move. If Signals.stop is true, the search
964 // was aborted because the user interrupted the search or because we
965 // ran out of time. In this case, the return value of the search cannot
966 // be trusted, and we don't update the best move and/or PV.
967 if (Signals.stop || thisThread->cutoff_occurred())
968 return value; // To avoid returning VALUE_INFINITE
972 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
974 // PV move or new best move ?
975 if (pvMove || value > alpha)
978 rm.extract_pv_from_tt(pos);
980 // We record how often the best move has been changed in each
981 // iteration. This information is used for time management: When
982 // the best move changes frequently, we allocate some more time.
987 // All other moves but the PV are set to the lowest value, this
988 // is not a problem when sorting becuase sort is stable and move
989 // position in the list is preserved, just the PV is pushed up.
990 rm.score = -VALUE_INFINITE;
993 if (value > bestValue)
995 bestValue = SpNode ? splitPoint->bestValue = value : value;
999 bestMove = SpNode ? splitPoint->bestMove = move : move;
1001 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1002 alpha = SpNode ? splitPoint->alpha = value : value;
1005 assert(value >= beta); // Fail high
1008 splitPoint->cutoff = true;
1015 // Step 19. Check for splitting the search
1017 && depth >= Threads.minimumSplitDepth
1018 && Threads.available_slave(thisThread)
1019 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1021 assert(bestValue < beta);
1023 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1024 depth, threatMove, moveCount, &mp, NT, cutNode);
1025 if (bestValue >= beta)
1033 // Step 20. Check for mate and stalemate
1034 // All legal moves have been searched and if there are no legal moves, it
1035 // must be mate or stalemate. Note that we can have a false positive in
1036 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1037 // harmless because return value is discarded anyhow in the parent nodes.
1038 // If we are in a singular extension search then return a fail low score.
1039 // A split node has at least one move, the one tried before to be splitted.
1041 return excludedMove ? alpha
1042 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1044 // If we have pruned all the moves without searching return a fail-low score
1045 if (bestValue == -VALUE_INFINITE)
1048 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1049 bestValue >= beta ? BOUND_LOWER :
1050 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1051 depth, bestMove, ss->staticEval);
1053 // Quiet best move: update killers, history and countermoves
1054 if ( bestValue >= beta
1055 && !pos.capture_or_promotion(bestMove)
1058 if (ss->killers[0] != bestMove)
1060 ss->killers[1] = ss->killers[0];
1061 ss->killers[0] = bestMove;
1064 // Increase history value of the cut-off move and decrease all the other
1065 // played non-capture moves.
1066 Value bonus = Value(int(depth) * int(depth));
1067 History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
1068 for (int i = 0; i < quietCount - 1; ++i)
1070 Move m = quietsSearched[i];
1071 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1074 if (is_ok((ss-1)->currentMove))
1075 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1078 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1084 // qsearch() is the quiescence search function, which is called by the main
1085 // search function when the remaining depth is zero (or, to be more precise,
1086 // less than ONE_PLY).
1088 template <NodeType NT, bool InCheck>
1089 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1091 const bool PvNode = (NT == PV);
1093 assert(NT == PV || NT == NonPV);
1094 assert(InCheck == !!pos.checkers());
1095 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1096 assert(PvNode || (alpha == beta - 1));
1097 assert(depth <= DEPTH_ZERO);
1102 Move ttMove, move, bestMove;
1103 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1104 bool givesCheck, evasionPrunable;
1107 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1111 ss->currentMove = bestMove = MOVE_NONE;
1112 ss->ply = (ss-1)->ply + 1;
1114 // Check for an instant draw or maximum ply reached
1115 if (pos.is_draw() || ss->ply > MAX_PLY)
1116 return DrawValue[pos.side_to_move()];
1118 // Decide whether or not to include checks, this fixes also the type of
1119 // TT entry depth that we are going to use. Note that in qsearch we use
1120 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1121 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1122 : DEPTH_QS_NO_CHECKS;
1124 // Transposition table lookup
1126 tte = TT.probe(posKey);
1127 ttMove = tte ? tte->move() : MOVE_NONE;
1128 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1131 && tte->depth() >= ttDepth
1132 && ttValue != VALUE_NONE // Only in case of TT access race
1133 && ( PvNode ? tte->bound() == BOUND_EXACT
1134 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1135 : (tte->bound() & BOUND_UPPER)))
1137 ss->currentMove = ttMove; // Can be MOVE_NONE
1141 // Evaluate the position statically
1144 ss->staticEval = VALUE_NONE;
1145 bestValue = futilityBase = -VALUE_INFINITE;
1151 // Never assume anything on values stored in TT
1152 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1153 ss->staticEval = bestValue = evaluate(pos);
1155 // Can ttValue be used as a better position evaluation?
1156 if (ttValue != VALUE_NONE)
1157 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1158 bestValue = ttValue;
1161 ss->staticEval = bestValue = evaluate(pos);
1163 // Stand pat. Return immediately if static value is at least beta
1164 if (bestValue >= beta)
1167 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1168 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1173 if (PvNode && bestValue > alpha)
1176 futilityBase = bestValue + Value(128);
1179 // Initialize a MovePicker object for the current position, and prepare
1180 // to search the moves. Because the depth is <= 0 here, only captures,
1181 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1183 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1186 // Loop through the moves until no moves remain or a beta cutoff occurs
1187 while ((move = mp.next_move<false>()) != MOVE_NONE)
1189 assert(is_ok(move));
1191 givesCheck = pos.gives_check(move, ci);
1198 && type_of(move) != PROMOTION
1199 && futilityBase > -VALUE_KNOWN_WIN
1200 && !pos.passed_pawn_push(move))
1202 futilityValue = futilityBase
1203 + PieceValue[EG][pos.piece_on(to_sq(move))]
1204 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1206 if (futilityValue < beta)
1208 bestValue = std::max(bestValue, futilityValue);
1212 // Prune moves with negative or equal SEE and also moves with positive
1213 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1214 if ( futilityBase < beta
1215 && pos.see(move, beta - futilityBase) <= 0)
1217 bestValue = std::max(bestValue, futilityBase);
1222 // Detect non-capture evasions that are candidate to be pruned
1223 evasionPrunable = InCheck
1224 && bestValue > VALUE_MATED_IN_MAX_PLY
1225 && !pos.capture(move)
1226 && !pos.can_castle(pos.side_to_move());
1228 // Don't search moves with negative SEE values
1230 && (!InCheck || evasionPrunable)
1232 && type_of(move) != PROMOTION
1233 && pos.see_sign(move) < 0)
1236 // Check for legality only before to do the move
1237 if (!pos.legal(move, ci.pinned))
1240 ss->currentMove = move;
1242 // Make and search the move
1243 pos.do_move(move, st, ci, givesCheck);
1244 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1245 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1246 pos.undo_move(move);
1248 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1250 // Check for new best move
1251 if (value > bestValue)
1257 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1264 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1265 ttDepth, move, ss->staticEval);
1273 // All legal moves have been searched. A special case: If we're in check
1274 // and no legal moves were found, it is checkmate.
1275 if (InCheck && bestValue == -VALUE_INFINITE)
1276 return mated_in(ss->ply); // Plies to mate from the root
1278 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1279 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1280 ttDepth, bestMove, ss->staticEval);
1282 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1288 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1289 // "plies to mate from the current position". Non-mate scores are unchanged.
1290 // The function is called before storing a value to the transposition table.
1292 Value value_to_tt(Value v, int ply) {
1294 assert(v != VALUE_NONE);
1296 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1297 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1301 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1302 // from the transposition table (where refers to the plies to mate/be mated
1303 // from current position) to "plies to mate/be mated from the root".
1305 Value value_from_tt(Value v, int ply) {
1307 return v == VALUE_NONE ? VALUE_NONE
1308 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1309 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1313 // allows() tests whether the 'first' move at previous ply somehow makes the
1314 // 'second' move possible, for instance if the moving piece is the same in
1315 // both moves. Normally the second move is the threat (the best move returned
1316 // from a null search that fails low).
1318 bool allows(const Position& pos, Move first, Move second) {
1320 assert(is_ok(first));
1321 assert(is_ok(second));
1322 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1323 assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1325 Square m1from = from_sq(first);
1326 Square m2from = from_sq(second);
1327 Square m1to = to_sq(first);
1328 Square m2to = to_sq(second);
1330 // The piece is the same or second's destination was vacated by the first move
1331 // We exclude the trivial case where a sliding piece does in two moves what
1332 // it could do in one move: eg. Ra1a2, Ra2a3.
1334 || (m1to == m2from && !squares_aligned(m1from, m2from, m2to)))
1337 // Second one moves through the square vacated by first one
1338 if (between_bb(m2from, m2to) & m1from)
1341 // Second's destination is defended by the first move's piece
1342 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1346 // Second move gives a discovered check through the first's checking piece
1347 if (m1att & pos.king_square(pos.side_to_move()))
1349 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1357 // refutes() tests whether a 'first' move is able to defend against a 'second'
1358 // opponent's move. In this case will not be pruned. Normally the second move
1359 // is the threat (the best move returned from a null search that fails low).
1361 bool refutes(const Position& pos, Move first, Move second) {
1363 assert(is_ok(first));
1364 assert(is_ok(second));
1366 Square m1from = from_sq(first);
1367 Square m2from = from_sq(second);
1368 Square m1to = to_sq(first);
1369 Square m2to = to_sq(second);
1371 // Don't prune moves of the threatened piece
1375 // If the threatened piece has value less than or equal to the value of the
1376 // threat piece, don't prune moves which defend it.
1377 if ( pos.capture(second)
1378 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1379 || type_of(pos.piece_on(m2from)) == KING))
1381 // Update occupancy as if the piece and the threat are moving
1382 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1383 Piece pc = pos.piece_on(m1from);
1385 // The moved piece attacks the square 'tto' ?
1386 if (pos.attacks_from(pc, m1to, occ) & m2to)
1389 // Scan for possible X-ray attackers behind the moved piece
1390 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
1391 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
1393 // Verify attackers are triggered by our move and not already existing
1394 if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
1398 // Don't prune safe moves which block the threat path
1399 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1406 // When playing with strength handicap choose best move among the MultiPV set
1407 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1409 Move Skill::pick_move() {
1413 // PRNG sequence should be not deterministic
1414 for (int i = Time::now() % 50; i > 0; --i)
1415 rk.rand<unsigned>();
1417 // RootMoves are already sorted by score in descending order
1418 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1419 int weakness = 120 - 2 * level;
1420 int max_s = -VALUE_INFINITE;
1423 // Choose best move. For each move score we add two terms both dependent on
1424 // weakness, one deterministic and bigger for weaker moves, and one random,
1425 // then we choose the move with the resulting highest score.
1426 for (size_t i = 0; i < PVSize; ++i)
1428 int s = RootMoves[i].score;
1430 // Don't allow crazy blunders even at very low skills
1431 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1434 // This is our magic formula
1435 s += ( weakness * int(RootMoves[0].score - s)
1436 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1441 best = RootMoves[i].pv[0];
1448 // uci_pv() formats PV information according to UCI protocol. UCI requires
1449 // to send all the PV lines also if are still to be searched and so refer to
1450 // the previous search score.
1452 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1454 std::stringstream s;
1455 Time::point elapsed = Time::now() - SearchTime + 1;
1456 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1459 for (size_t i = 0; i < Threads.size(); ++i)
1460 if (Threads[i]->maxPly > selDepth)
1461 selDepth = Threads[i]->maxPly;
1463 for (size_t i = 0; i < uciPVSize; ++i)
1465 bool updated = (i <= PVIdx);
1467 if (depth == 1 && !updated)
1470 int d = updated ? depth : depth - 1;
1471 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1473 if (s.rdbuf()->in_avail()) // Not at first line
1476 s << "info depth " << d
1477 << " seldepth " << selDepth
1478 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1479 << " nodes " << pos.nodes_searched()
1480 << " nps " << pos.nodes_searched() * 1000 / elapsed
1481 << " time " << elapsed
1482 << " multipv " << i + 1
1485 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1486 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1495 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1496 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1497 /// allow to always have a ponder move even when we fail high at root, and a
1498 /// long PV to print that is important for position analysis.
1500 void RootMove::extract_pv_from_tt(Position& pos) {
1502 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1512 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1514 pos.do_move(pv[ply++], *st++);
1515 tte = TT.probe(pos.key());
1518 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1519 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1521 && (!pos.is_draw() || ply < 2));
1523 pv.push_back(MOVE_NONE); // Must be zero-terminating
1525 while (ply) pos.undo_move(pv[--ply]);
1529 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1530 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1531 /// first, even if the old TT entries have been overwritten.
1533 void RootMove::insert_pv_in_tt(Position& pos) {
1535 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1540 tte = TT.probe(pos.key());
1542 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1543 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1545 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1547 pos.do_move(pv[ply++], *st++);
1549 } while (pv[ply] != MOVE_NONE);
1551 while (ply) pos.undo_move(pv[--ply]);
1555 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1557 void Thread::idle_loop() {
1559 // Pointer 'this_sp' is not null only if we are called from split(), and not
1560 // at the thread creation. So it means we are the split point's master.
1561 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1563 assert(!this_sp || (this_sp->masterThread == this && searching));
1567 // If we are not searching, wait for a condition to be signaled instead of
1568 // wasting CPU time polling for work.
1569 while ((!searching && Threads.sleepWhileIdle) || exit)
1577 // Grab the lock to avoid races with Thread::notify_one()
1580 // If we are master and all slaves have finished then exit idle_loop
1581 if (this_sp && !this_sp->slavesMask)
1587 // Do sleep after retesting sleep conditions under lock protection, in
1588 // particular we need to avoid a deadlock in case a master thread has,
1589 // in the meanwhile, allocated us and sent the notify_one() call before
1590 // we had the chance to grab the lock.
1591 if (!searching && !exit)
1592 sleepCondition.wait(mutex);
1597 // If this thread has been assigned work, launch a search
1602 Threads.mutex.lock();
1605 assert(activeSplitPoint);
1606 SplitPoint* sp = activeSplitPoint;
1608 Threads.mutex.unlock();
1610 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1611 Position pos(*sp->pos, this);
1613 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1614 ss->splitPoint = sp;
1618 assert(activePosition == NULL);
1620 activePosition = &pos;
1622 switch (sp->nodeType) {
1624 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1627 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1630 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1639 activePosition = NULL;
1640 sp->slavesMask &= ~(1ULL << idx);
1641 sp->nodes += pos.nodes_searched();
1643 // Wake up master thread so to allow it to return from the idle loop
1644 // in case we are the last slave of the split point.
1645 if ( Threads.sleepWhileIdle
1646 && this != sp->masterThread
1649 assert(!sp->masterThread->searching);
1650 sp->masterThread->notify_one();
1653 // After releasing the lock we cannot access anymore any SplitPoint
1654 // related data in a safe way becuase it could have been released under
1655 // our feet by the sp master. Also accessing other Thread objects is
1656 // unsafe because if we are exiting there is a chance are already freed.
1660 // If this thread is the master of a split point and all slaves have finished
1661 // their work at this split point, return from the idle loop.
1662 if (this_sp && !this_sp->slavesMask)
1664 this_sp->mutex.lock();
1665 bool finished = !this_sp->slavesMask; // Retest under lock protection
1666 this_sp->mutex.unlock();
1674 /// check_time() is called by the timer thread when the timer triggers. It is
1675 /// used to print debug info and, more important, to detect when we are out of
1676 /// available time and so stop the search.
1680 static Time::point lastInfoTime = Time::now();
1681 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1683 if (Time::now() - lastInfoTime >= 1000)
1685 lastInfoTime = Time::now();
1694 Threads.mutex.lock();
1696 nodes = RootPos.nodes_searched();
1698 // Loop across all split points and sum accumulated SplitPoint nodes plus
1699 // all the currently active positions nodes.
1700 for (size_t i = 0; i < Threads.size(); ++i)
1701 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1703 SplitPoint& sp = Threads[i]->splitPoints[j];
1708 Bitboard sm = sp.slavesMask;
1711 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1713 nodes += pos->nodes_searched();
1719 Threads.mutex.unlock();
1722 Time::point elapsed = Time::now() - SearchTime;
1723 bool stillAtFirstMove = Signals.firstRootMove
1724 && !Signals.failedLowAtRoot
1725 && elapsed > TimeMgr.available_time();
1727 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1728 || stillAtFirstMove;
1730 if ( (Limits.use_time_management() && noMoreTime)
1731 || (Limits.movetime && elapsed >= Limits.movetime)
1732 || (Limits.nodes && nodes >= Limits.nodes))
1733 Signals.stop = true;