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 Value FutilityMargins[14][64]; // [depth][moveNumber]
67 int FutilityMoveCounts[2][32]; // [improving][depth]
69 inline Value futility_margin(Depth d, int mn) {
70 assert(DEPTH_ZERO <= d && d < 7 * ONE_PLY);
71 return FutilityMargins[d][std::min(mn, 63)];
74 // Reduction lookup tables (initialized at startup) and their access function
75 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
77 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
79 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
84 double BestMoveChanges;
85 Value DrawValue[COLOR_NB];
87 CountermovesStats Countermoves;
89 template <NodeType NT>
90 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
92 template <NodeType NT, bool InCheck>
93 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
95 void id_loop(Position& pos);
96 Value value_to_tt(Value v, int ply);
97 Value value_from_tt(Value v, int ply);
98 bool allows(const Position& pos, Move first, Move second);
99 bool refutes(const Position& pos, Move first, Move second);
100 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
103 Skill(int l) : level(l), best(MOVE_NONE) {}
105 if (enabled()) // Swap best PV line with the sub-optimal one
106 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
107 RootMoves.end(), best ? best : pick_move()));
110 bool enabled() const { return level < 20; }
111 bool time_to_pick(int depth) const { return depth == 1 + level; }
121 /// Search::init() is called during startup to initialize various lookup tables
123 void Search::init() {
125 int d; // depth (ONE_PLY == 2)
126 int hd; // half depth (ONE_PLY == 1)
129 // Init reductions array
130 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
132 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
133 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
134 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
135 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
137 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
138 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
140 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
141 Reductions[0][0][hd][mc] += ONE_PLY;
143 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
144 Reductions[0][0][hd][mc] += ONE_PLY / 2;
147 // Init futility margins array
148 for (d = 0; d < 14; ++d) for (mc = 0; mc < 64; ++mc)
149 FutilityMargins[d][mc] = Value(112 * int(2.9 * log(d >= 1 ? double(d) : 1.0)) - 8 * mc + 45);
151 // Init futility move count array
152 for (d = 0; d < 32; ++d)
154 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
155 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
160 /// Search::perft() is our utility to verify move generation. All the leaf nodes
161 /// up to the given depth are generated and counted and the sum returned.
163 static size_t perft(Position& pos, Depth depth) {
168 const bool leaf = depth == 2 * ONE_PLY;
170 for (MoveList<LEGAL> it(pos); *it; ++it)
172 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
173 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
179 size_t Search::perft(Position& pos, Depth depth) {
180 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
183 /// Search::think() is the external interface to Stockfish's search, and is
184 /// called by the main thread when the program receives the UCI 'go' command. It
185 /// searches from RootPos and at the end prints the "bestmove" to output.
187 void Search::think() {
189 static PolyglotBook book; // Defined static to initialize the PRNG only once
191 RootColor = RootPos.side_to_move();
192 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
194 if (RootMoves.empty())
196 RootMoves.push_back(MOVE_NONE);
197 sync_cout << "info depth 0 score "
198 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
204 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
206 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
208 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
210 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
215 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
217 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
218 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
219 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
220 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
223 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
225 if (Options["Write Search Log"])
227 Log log(Options["Search Log Filename"]);
228 log << "\nSearching: " << RootPos.fen()
229 << "\ninfinite: " << Limits.infinite
230 << " ponder: " << Limits.ponder
231 << " time: " << Limits.time[RootColor]
232 << " increment: " << Limits.inc[RootColor]
233 << " moves to go: " << Limits.movestogo
237 // Reset the threads, still sleeping: will be wake up at split time
238 for (size_t i = 0; i < Threads.size(); ++i)
239 Threads[i]->maxPly = 0;
241 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
242 Threads.timer->run = true;
243 Threads.timer->notify_one(); // Wake up the recurring timer
245 id_loop(RootPos); // Let's start searching !
247 Threads.timer->run = false; // Stop the timer
248 Threads.sleepWhileIdle = true; // Send idle threads to sleep
250 if (Options["Write Search Log"])
252 Time::point elapsed = Time::now() - SearchTime + 1;
254 Log log(Options["Search Log Filename"]);
255 log << "Nodes: " << RootPos.nodes_searched()
256 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
257 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
260 RootPos.do_move(RootMoves[0].pv[0], st);
261 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
262 RootPos.undo_move(RootMoves[0].pv[0]);
267 // When search is stopped this info is not printed
268 sync_cout << "info nodes " << RootPos.nodes_searched()
269 << " time " << Time::now() - SearchTime + 1 << sync_endl;
271 // When we reach max depth we arrive here even without Signals.stop is raised,
272 // but if we are pondering or in infinite search, according to UCI protocol,
273 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
274 // command. We simply wait here until GUI sends one of those commands (that
275 // raise Signals.stop).
276 if (!Signals.stop && (Limits.ponder || Limits.infinite))
278 Signals.stopOnPonderhit = true;
279 RootPos.this_thread()->wait_for(Signals.stop);
282 // Best move could be MOVE_NONE when searching on a stalemate position
283 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
284 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
291 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
292 // with increasing depth until the allocated thinking time has been consumed,
293 // user stops the search, or the maximum search depth is reached.
295 void id_loop(Position& pos) {
297 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
299 Value bestValue, alpha, beta, delta;
301 std::memset(ss-2, 0, 5 * sizeof(Stack));
305 bestValue = delta = alpha = -VALUE_INFINITE;
306 beta = VALUE_INFINITE;
310 Countermoves.clear();
312 PVSize = Options["MultiPV"];
313 Skill skill(Options["Skill Level"]);
315 // Do we have to play with skill handicap? In this case enable MultiPV search
316 // that we will use behind the scenes to retrieve a set of possible moves.
317 if (skill.enabled() && PVSize < 4)
320 PVSize = std::min(PVSize, RootMoves.size());
322 // Iterative deepening loop until requested to stop or target depth reached
323 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
325 // Age out PV variability metric
326 BestMoveChanges *= 0.8;
328 // Save last iteration's scores before first PV line is searched and all
329 // the move scores but the (new) PV are set to -VALUE_INFINITE.
330 for (size_t i = 0; i < RootMoves.size(); ++i)
331 RootMoves[i].prevScore = RootMoves[i].score;
333 // MultiPV loop. We perform a full root search for each PV line
334 for (PVIdx = 0; PVIdx < PVSize; ++PVIdx)
336 // Reset aspiration window starting size
340 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
341 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
344 // Start with a small aspiration window and, in case of fail high/low,
345 // research with bigger window until not failing high/low anymore.
348 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
350 // Bring to front the best move. It is critical that sorting is
351 // done with a stable algorithm because all the values but the first
352 // and eventually the new best one are set to -VALUE_INFINITE and
353 // we want to keep the same order for all the moves but the new
354 // PV that goes to the front. Note that in case of MultiPV search
355 // the already searched PV lines are preserved.
356 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
358 // Write PV back to transposition table in case the relevant
359 // entries have been overwritten during the search.
360 for (size_t i = 0; i <= PVIdx; ++i)
361 RootMoves[i].insert_pv_in_tt(pos);
363 // If search has been stopped return immediately. Sorting and
364 // writing PV back to TT is safe becuase RootMoves is still
365 // valid, although refers to previous iteration.
369 // When failing high/low give some update (without cluttering
370 // the UI) before to research.
371 if ( (bestValue <= alpha || bestValue >= beta)
372 && Time::now() - SearchTime > 3000)
373 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
375 // In case of failing low/high increase aspiration window and
376 // research, otherwise exit the loop.
377 if (bestValue <= alpha)
379 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
381 Signals.failedLowAtRoot = true;
382 Signals.stopOnPonderhit = false;
384 else if (bestValue >= beta)
385 beta = std::min(bestValue + delta, VALUE_INFINITE);
392 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
395 // Sort the PV lines searched so far and update the GUI
396 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
398 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
399 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
402 // Do we need to pick now the sub-optimal best move ?
403 if (skill.enabled() && skill.time_to_pick(depth))
406 if (Options["Write Search Log"])
408 RootMove& rm = RootMoves[0];
409 if (skill.best != MOVE_NONE)
410 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
412 Log log(Options["Search Log Filename"]);
413 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
417 // Do we have found a "mate in x"?
419 && bestValue >= VALUE_MATE_IN_MAX_PLY
420 && VALUE_MATE - bestValue <= 2 * Limits.mate)
423 // Do we have time for the next iteration? Can we stop searching now?
424 if (Limits.use_time_management() && !Signals.stopOnPonderhit)
426 bool stop = false; // Local variable, not the volatile Signals.stop
428 // Take in account some extra time if the best move has changed
429 if (depth > 4 && depth < 50 && PVSize == 1)
430 TimeMgr.pv_instability(BestMoveChanges);
432 // Stop search if most of available time is already consumed. We
433 // probably don't have enough time to search the first move at the
434 // next iteration anyway.
435 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
438 // Stop search early if one move seems to be much better than others
440 && BestMoveChanges <= DBL_EPSILON
443 && bestValue > VALUE_MATED_IN_MAX_PLY
444 && ( RootMoves.size() == 1
445 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
447 Value rBeta = bestValue - 2 * PawnValueMg;
448 ss->excludedMove = RootMoves[0].pv[0];
449 ss->skipNullMove = true;
450 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
451 ss->skipNullMove = false;
452 ss->excludedMove = MOVE_NONE;
460 // If we are allowed to ponder do not stop the search now but
461 // keep pondering until GUI sends "ponderhit" or "stop".
463 Signals.stopOnPonderhit = true;
472 // search<>() is the main search function for both PV and non-PV nodes and for
473 // normal and SplitPoint nodes. When called just after a split point the search
474 // is simpler because we have already probed the hash table, done a null move
475 // search, and searched the first move before splitting, we don't have to repeat
476 // all this work again. We also don't need to store anything to the hash table
477 // here: This is taken care of after we return from the split point.
479 template <NodeType NT>
480 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
482 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
483 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
484 const bool RootNode = (NT == Root || NT == SplitPointRoot);
486 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
487 assert(PvNode || (alpha == beta - 1));
488 assert(depth > DEPTH_ZERO);
490 Move quietsSearched[64];
493 SplitPoint* splitPoint;
495 Move ttMove, move, excludedMove, bestMove, threatMove;
497 Value bestValue, value, ttValue;
498 Value eval, nullValue;
499 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
500 bool captureOrPromotion, dangerous, doFullDepthSearch;
501 int moveCount, quietCount;
503 // Step 1. Initialize node
504 Thread* thisThread = pos.this_thread();
505 inCheck = pos.checkers();
509 splitPoint = ss->splitPoint;
510 bestMove = splitPoint->bestMove;
511 threatMove = splitPoint->threatMove;
512 bestValue = splitPoint->bestValue;
514 ttMove = excludedMove = MOVE_NONE;
515 ttValue = VALUE_NONE;
517 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
522 moveCount = quietCount = 0;
523 bestValue = -VALUE_INFINITE;
524 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
525 ss->ply = (ss-1)->ply + 1;
526 ss->futilityMoveCount = 0;
527 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
528 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
530 // Used to send selDepth info to GUI
531 if (PvNode && thisThread->maxPly < ss->ply)
532 thisThread->maxPly = ss->ply;
536 // Step 2. Check for aborted search and immediate draw
537 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
538 return DrawValue[pos.side_to_move()];
540 // Step 3. Mate distance pruning. Even if we mate at the next move our score
541 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
542 // a shorter mate was found upward in the tree then there is no need to search
543 // further, we will never beat current alpha. Same logic but with reversed signs
544 // applies also in the opposite condition of being mated instead of giving mate,
545 // in this case return a fail-high score.
546 alpha = std::max(mated_in(ss->ply), alpha);
547 beta = std::min(mate_in(ss->ply+1), beta);
552 // Step 4. Transposition table lookup
553 // We don't want the score of a partial search to overwrite a previous full search
554 // TT value, so we use a different position key in case of an excluded move.
555 excludedMove = ss->excludedMove;
556 posKey = excludedMove ? pos.exclusion_key() : pos.key();
557 tte = TT.probe(posKey);
558 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
559 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
561 // At PV nodes we check for exact scores, while at non-PV nodes we check for
562 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
563 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
564 // we should also update RootMoveList to avoid bogus output.
567 && tte->depth() >= depth
568 && ttValue != VALUE_NONE // Only in case of TT access race
569 && ( PvNode ? tte->bound() == BOUND_EXACT
570 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
571 : (tte->bound() & BOUND_UPPER)))
574 ss->currentMove = ttMove; // Can be MOVE_NONE
578 && !pos.capture_or_promotion(ttMove)
579 && ttMove != ss->killers[0])
581 ss->killers[1] = ss->killers[0];
582 ss->killers[0] = ttMove;
587 // Step 5. Evaluate the position statically and update parent's gain statistics
590 ss->staticEval = eval = VALUE_NONE;
596 // Never assume anything on values stored in TT
597 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
598 eval = ss->staticEval = evaluate(pos);
600 // Can ttValue be used as a better position evaluation?
601 if (ttValue != VALUE_NONE)
602 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
607 eval = ss->staticEval = evaluate(pos);
608 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
611 // Step 6. Razoring (skipped when in check)
613 && depth < 4 * ONE_PLY
614 && eval + razor_margin(depth) < beta
615 && ttMove == MOVE_NONE
616 && abs(beta) < VALUE_MATE_IN_MAX_PLY
617 && !pos.pawn_on_7th(pos.side_to_move()))
619 Value rbeta = beta - razor_margin(depth);
620 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
622 // Logically we should return (v + razor_margin(depth)), but
623 // surprisingly this did slightly weaker in tests.
627 // Step 7. post-Futility pruning (skipped when in check)
630 && depth < 7 * ONE_PLY
631 && eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
632 && abs(beta) < VALUE_MATE_IN_MAX_PLY
633 && abs(eval) < VALUE_KNOWN_WIN
634 && pos.non_pawn_material(pos.side_to_move()))
635 return eval - futility_margin(depth, (ss-1)->futilityMoveCount);
637 // Step 8. Null move search with verification search (is omitted in PV nodes)
640 && depth >= 2 * ONE_PLY
642 && abs(beta) < VALUE_MATE_IN_MAX_PLY
643 && pos.non_pawn_material(pos.side_to_move()))
645 ss->currentMove = MOVE_NULL;
647 // Null move dynamic reduction based on depth
648 Depth R = 3 * ONE_PLY + depth / 4;
650 // Null move dynamic reduction based on value
651 if (eval - PawnValueMg > beta)
654 pos.do_null_move(st);
655 (ss+1)->skipNullMove = true;
656 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
657 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
658 (ss+1)->skipNullMove = false;
659 pos.undo_null_move();
661 if (nullValue >= beta)
663 // Do not return unproven mate scores
664 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
667 if (depth < 12 * ONE_PLY)
670 // Do verification search at high depths
671 ss->skipNullMove = true;
672 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
673 ss->skipNullMove = false;
680 // The null move failed low, which means that we may be faced with
681 // some kind of threat. If the previous move was reduced, check if
682 // the move that refuted the null move was somehow connected to the
683 // move which was reduced. If a connection is found, return a fail
684 // low score (which will cause the reduced move to fail high in the
685 // parent node, which will trigger a re-search with full depth).
686 threatMove = (ss+1)->currentMove;
688 if ( depth < 5 * ONE_PLY
690 && threatMove != MOVE_NONE
691 && allows(pos, (ss-1)->currentMove, threatMove))
696 // Step 9. ProbCut (skipped when in check)
697 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
698 // and a reduced search returns a value much above beta, we can (almost) safely
699 // prune the previous move.
701 && depth >= 5 * ONE_PLY
703 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
705 Value rbeta = beta + 200;
706 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
708 assert(rdepth >= ONE_PLY);
709 assert((ss-1)->currentMove != MOVE_NONE);
710 assert((ss-1)->currentMove != MOVE_NULL);
712 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
715 while ((move = mp.next_move<false>()) != MOVE_NONE)
716 if (pos.legal(move, ci.pinned))
718 ss->currentMove = move;
719 pos.do_move(move, st, ci, pos.gives_check(move, ci));
720 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
727 // Step 10. Internal iterative deepening (skipped when in check)
728 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
729 && ttMove == MOVE_NONE
730 && (PvNode || ss->staticEval + Value(256) >= beta))
732 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
734 ss->skipNullMove = true;
735 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
736 ss->skipNullMove = false;
738 tte = TT.probe(posKey);
739 ttMove = tte ? tte->move() : MOVE_NONE;
742 moves_loop: // When in check and at SpNode search starts from here
744 Square prevMoveSq = to_sq((ss-1)->currentMove);
745 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
746 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
748 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
750 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
751 improving = ss->staticEval >= (ss-2)->staticEval
752 || ss->staticEval == VALUE_NONE
753 ||(ss-2)->staticEval == VALUE_NONE;
755 singularExtensionNode = !RootNode
757 && depth >= 8 * ONE_PLY
758 && ttMove != MOVE_NONE
759 && !excludedMove // Recursive singular search is not allowed
760 && (tte->bound() & BOUND_LOWER)
761 && tte->depth() >= depth - 3 * ONE_PLY;
763 // Step 11. Loop through moves
764 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
765 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
769 if (move == excludedMove)
772 // At root obey the "searchmoves" option and skip moves not listed in Root
773 // Move List, as a consequence any illegal move is also skipped. In MultiPV
774 // mode we also skip PV moves which have been already searched.
775 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
780 // Shared counter cannot be decremented later if move turns out to be illegal
781 if (!pos.legal(move, ci.pinned))
784 moveCount = ++splitPoint->moveCount;
785 splitPoint->mutex.unlock();
792 Signals.firstRootMove = (moveCount == 1);
794 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
795 sync_cout << "info depth " << depth / ONE_PLY
796 << " currmove " << move_to_uci(move, pos.is_chess960())
797 << " currmovenumber " << moveCount + PVIdx << sync_endl;
801 captureOrPromotion = pos.capture_or_promotion(move);
802 givesCheck = pos.gives_check(move, ci);
803 dangerous = givesCheck
804 || pos.passed_pawn_push(move)
805 || type_of(move) == CASTLE;
807 // Step 12. Extend checks
808 if (givesCheck && pos.see_sign(move) >= 0)
811 // Singular extension search. If all moves but one fail low on a search of
812 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
813 // is singular and should be extended. To verify this we do a reduced search
814 // on all the other moves but the ttMove, if result is lower than ttValue minus
815 // a margin then we extend ttMove.
816 if ( singularExtensionNode
819 && pos.legal(move, ci.pinned)
820 && abs(ttValue) < VALUE_KNOWN_WIN)
822 assert(ttValue != VALUE_NONE);
824 Value rBeta = ttValue - int(depth);
825 ss->excludedMove = move;
826 ss->skipNullMove = true;
827 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
828 ss->skipNullMove = false;
829 ss->excludedMove = MOVE_NONE;
835 // Update current move (this must be done after singular extension search)
836 newDepth = depth - ONE_PLY + ext;
837 Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
839 // Step 13. Futility pruning (is omitted in PV nodes)
841 && !captureOrPromotion
844 && bestValue > VALUE_MATED_IN_MAX_PLY)
846 // Move count based pruning
847 if ( depth < 16 * ONE_PLY
848 && moveCount >= FutilityMoveCounts[improving][depth]
849 && (!threatMove || !refutes(pos, move, threatMove)))
852 splitPoint->mutex.lock();
857 // Prune moves with negative SEE at low depths
858 if ( predictedDepth < 4 * ONE_PLY
859 && pos.see_sign(move) < 0)
862 splitPoint->mutex.lock();
867 // We have not pruned the move that will be searched, but remember how
868 // far in the move list we are to be more aggressive in the child node.
869 ss->futilityMoveCount = moveCount;
872 ss->futilityMoveCount = 0;
874 // Check for legality only before to do the move
875 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
881 pvMove = PvNode && moveCount == 1;
882 ss->currentMove = move;
883 if (!SpNode && !captureOrPromotion && quietCount < 64)
884 quietsSearched[quietCount++] = move;
886 // Step 14. Make the move
887 pos.do_move(move, st, ci, givesCheck);
889 // Step 15. Reduced depth search (LMR). If the move fails high will be
890 // re-searched at full depth.
891 if ( depth >= 3 * ONE_PLY
893 && !captureOrPromotion
895 && move != ss->killers[0]
896 && move != ss->killers[1])
898 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
900 if (!PvNode && cutNode)
901 ss->reduction += ONE_PLY;
903 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
904 ss->reduction += ONE_PLY / 2;
906 if (move == countermoves[0] || move == countermoves[1])
907 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
909 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
911 alpha = splitPoint->alpha;
913 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
915 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
916 ss->reduction = DEPTH_ZERO;
919 doFullDepthSearch = !pvMove;
921 // Step 16. Full depth search, when LMR is skipped or fails high
922 if (doFullDepthSearch)
925 alpha = splitPoint->alpha;
927 value = newDepth < ONE_PLY ?
928 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
929 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
930 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
933 // Only for PV nodes do a full PV search on the first move or after a fail
934 // high, in the latter case search only if value < beta, otherwise let the
935 // parent node to fail low with value <= alpha and to try another move.
936 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
937 value = newDepth < ONE_PLY ?
938 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
939 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
940 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
941 // Step 17. Undo move
944 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
946 // Step 18. Check for new best move
949 splitPoint->mutex.lock();
950 bestValue = splitPoint->bestValue;
951 alpha = splitPoint->alpha;
954 // Finished searching the move. If Signals.stop is true, the search
955 // was aborted because the user interrupted the search or because we
956 // ran out of time. In this case, the return value of the search cannot
957 // be trusted, and we don't update the best move and/or PV.
958 if (Signals.stop || thisThread->cutoff_occurred())
959 return value; // To avoid returning VALUE_INFINITE
963 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
965 // PV move or new best move ?
966 if (pvMove || value > alpha)
969 rm.extract_pv_from_tt(pos);
971 // We record how often the best move has been changed in each
972 // iteration. This information is used for time management: When
973 // the best move changes frequently, we allocate some more time.
978 // All other moves but the PV are set to the lowest value, this
979 // is not a problem when sorting becuase sort is stable and move
980 // position in the list is preserved, just the PV is pushed up.
981 rm.score = -VALUE_INFINITE;
984 if (value > bestValue)
986 bestValue = SpNode ? splitPoint->bestValue = value : value;
990 bestMove = SpNode ? splitPoint->bestMove = move : move;
992 if (PvNode && value < beta) // Update alpha! Always alpha < beta
993 alpha = SpNode ? splitPoint->alpha = value : value;
996 assert(value >= beta); // Fail high
999 splitPoint->cutoff = true;
1006 // Step 19. Check for splitting the search
1008 && depth >= Threads.minimumSplitDepth
1009 && Threads.available_slave(thisThread)
1010 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1012 assert(bestValue < beta);
1014 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1015 depth, threatMove, moveCount, &mp, NT, cutNode);
1016 if (bestValue >= beta)
1024 // Step 20. Check for mate and stalemate
1025 // All legal moves have been searched and if there are no legal moves, it
1026 // must be mate or stalemate. Note that we can have a false positive in
1027 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1028 // harmless because return value is discarded anyhow in the parent nodes.
1029 // If we are in a singular extension search then return a fail low score.
1030 // A split node has at least one move, the one tried before to be splitted.
1032 return excludedMove ? alpha
1033 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1035 // If we have pruned all the moves without searching return a fail-low score
1036 if (bestValue == -VALUE_INFINITE)
1039 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1040 bestValue >= beta ? BOUND_LOWER :
1041 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1042 depth, bestMove, ss->staticEval);
1044 // Quiet best move: update killers, history and countermoves
1045 if ( bestValue >= beta
1046 && !pos.capture_or_promotion(bestMove)
1049 if (ss->killers[0] != bestMove)
1051 ss->killers[1] = ss->killers[0];
1052 ss->killers[0] = bestMove;
1055 // Increase history value of the cut-off move and decrease all the other
1056 // played non-capture moves.
1057 Value bonus = Value(int(depth) * int(depth));
1058 History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
1059 for (int i = 0; i < quietCount - 1; ++i)
1061 Move m = quietsSearched[i];
1062 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1065 if (is_ok((ss-1)->currentMove))
1066 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1069 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1075 // qsearch() is the quiescence search function, which is called by the main
1076 // search function when the remaining depth is zero (or, to be more precise,
1077 // less than ONE_PLY).
1079 template <NodeType NT, bool InCheck>
1080 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1082 const bool PvNode = (NT == PV);
1084 assert(NT == PV || NT == NonPV);
1085 assert(InCheck == !!pos.checkers());
1086 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1087 assert(PvNode || (alpha == beta - 1));
1088 assert(depth <= DEPTH_ZERO);
1093 Move ttMove, move, bestMove;
1094 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1095 bool givesCheck, evasionPrunable;
1098 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1102 ss->currentMove = bestMove = MOVE_NONE;
1103 ss->ply = (ss-1)->ply + 1;
1105 // Check for an instant draw or maximum ply reached
1106 if (pos.is_draw() || ss->ply > MAX_PLY)
1107 return DrawValue[pos.side_to_move()];
1109 // Decide whether or not to include checks, this fixes also the type of
1110 // TT entry depth that we are going to use. Note that in qsearch we use
1111 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1112 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1113 : DEPTH_QS_NO_CHECKS;
1115 // Transposition table lookup
1117 tte = TT.probe(posKey);
1118 ttMove = tte ? tte->move() : MOVE_NONE;
1119 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1122 && tte->depth() >= ttDepth
1123 && ttValue != VALUE_NONE // Only in case of TT access race
1124 && ( PvNode ? tte->bound() == BOUND_EXACT
1125 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1126 : (tte->bound() & BOUND_UPPER)))
1128 ss->currentMove = ttMove; // Can be MOVE_NONE
1132 // Evaluate the position statically
1135 ss->staticEval = VALUE_NONE;
1136 bestValue = futilityBase = -VALUE_INFINITE;
1142 // Never assume anything on values stored in TT
1143 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1144 ss->staticEval = bestValue = evaluate(pos);
1146 // Can ttValue be used as a better position evaluation?
1147 if (ttValue != VALUE_NONE)
1148 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1149 bestValue = ttValue;
1152 ss->staticEval = bestValue = evaluate(pos);
1154 // Stand pat. Return immediately if static value is at least beta
1155 if (bestValue >= beta)
1158 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1159 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1164 if (PvNode && bestValue > alpha)
1167 futilityBase = bestValue + Value(128);
1170 // Initialize a MovePicker object for the current position, and prepare
1171 // to search the moves. Because the depth is <= 0 here, only captures,
1172 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1174 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1177 // Loop through the moves until no moves remain or a beta cutoff occurs
1178 while ((move = mp.next_move<false>()) != MOVE_NONE)
1180 assert(is_ok(move));
1182 givesCheck = pos.gives_check(move, ci);
1189 && type_of(move) != PROMOTION
1190 && futilityBase > -VALUE_KNOWN_WIN
1191 && !pos.passed_pawn_push(move))
1193 futilityValue = futilityBase
1194 + PieceValue[EG][pos.piece_on(to_sq(move))]
1195 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1197 if (futilityValue < beta)
1199 bestValue = std::max(bestValue, futilityValue);
1203 // Prune moves with negative or equal SEE and also moves with positive
1204 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1205 if ( futilityBase < beta
1206 && pos.see(move, beta - futilityBase) <= 0)
1208 bestValue = std::max(bestValue, futilityBase);
1213 // Detect non-capture evasions that are candidate to be pruned
1214 evasionPrunable = InCheck
1215 && bestValue > VALUE_MATED_IN_MAX_PLY
1216 && !pos.capture(move)
1217 && !pos.can_castle(pos.side_to_move());
1219 // Don't search moves with negative SEE values
1221 && (!InCheck || evasionPrunable)
1223 && type_of(move) != PROMOTION
1224 && pos.see_sign(move) < 0)
1227 // Check for legality only before to do the move
1228 if (!pos.legal(move, ci.pinned))
1231 ss->currentMove = move;
1233 // Make and search the move
1234 pos.do_move(move, st, ci, givesCheck);
1235 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1236 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1237 pos.undo_move(move);
1239 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1241 // Check for new best move
1242 if (value > bestValue)
1248 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1255 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1256 ttDepth, move, ss->staticEval);
1264 // All legal moves have been searched. A special case: If we're in check
1265 // and no legal moves were found, it is checkmate.
1266 if (InCheck && bestValue == -VALUE_INFINITE)
1267 return mated_in(ss->ply); // Plies to mate from the root
1269 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1270 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1271 ttDepth, bestMove, ss->staticEval);
1273 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1279 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1280 // "plies to mate from the current position". Non-mate scores are unchanged.
1281 // The function is called before storing a value to the transposition table.
1283 Value value_to_tt(Value v, int ply) {
1285 assert(v != VALUE_NONE);
1287 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1288 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1292 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1293 // from the transposition table (where refers to the plies to mate/be mated
1294 // from current position) to "plies to mate/be mated from the root".
1296 Value value_from_tt(Value v, int ply) {
1298 return v == VALUE_NONE ? VALUE_NONE
1299 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1300 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1304 // allows() tests whether the 'first' move at previous ply somehow makes the
1305 // 'second' move possible, for instance if the moving piece is the same in
1306 // both moves. Normally the second move is the threat (the best move returned
1307 // from a null search that fails low).
1309 bool allows(const Position& pos, Move first, Move second) {
1311 assert(is_ok(first));
1312 assert(is_ok(second));
1313 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1314 assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1316 Square m1from = from_sq(first);
1317 Square m2from = from_sq(second);
1318 Square m1to = to_sq(first);
1319 Square m2to = to_sq(second);
1321 // The piece is the same or second's destination was vacated by the first move
1322 // We exclude the trivial case where a sliding piece does in two moves what
1323 // it could do in one move: eg. Ra1a2, Ra2a3.
1325 || (m1to == m2from && !squares_aligned(m1from, m2from, m2to)))
1328 // Second one moves through the square vacated by first one
1329 if (between_bb(m2from, m2to) & m1from)
1332 // Second's destination is defended by the first move's piece
1333 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1337 // Second move gives a discovered check through the first's checking piece
1338 if (m1att & pos.king_square(pos.side_to_move()))
1340 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1348 // refutes() tests whether a 'first' move is able to defend against a 'second'
1349 // opponent's move. In this case will not be pruned. Normally the second move
1350 // is the threat (the best move returned from a null search that fails low).
1352 bool refutes(const Position& pos, Move first, Move second) {
1354 assert(is_ok(first));
1355 assert(is_ok(second));
1357 Square m1from = from_sq(first);
1358 Square m2from = from_sq(second);
1359 Square m1to = to_sq(first);
1360 Square m2to = to_sq(second);
1362 // Don't prune moves of the threatened piece
1366 // If the threatened piece has value less than or equal to the value of the
1367 // threat piece, don't prune moves which defend it.
1368 if ( pos.capture(second)
1369 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1370 || type_of(pos.piece_on(m2from)) == KING))
1372 // Update occupancy as if the piece and the threat are moving
1373 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1374 Piece pc = pos.piece_on(m1from);
1376 // The moved piece attacks the square 'tto' ?
1377 if (pos.attacks_from(pc, m1to, occ) & m2to)
1380 // Scan for possible X-ray attackers behind the moved piece
1381 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
1382 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
1384 // Verify attackers are triggered by our move and not already existing
1385 if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
1389 // Don't prune safe moves which block the threat path
1390 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1397 // When playing with strength handicap choose best move among the MultiPV set
1398 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1400 Move Skill::pick_move() {
1404 // PRNG sequence should be not deterministic
1405 for (int i = Time::now() % 50; i > 0; --i)
1406 rk.rand<unsigned>();
1408 // RootMoves are already sorted by score in descending order
1409 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1410 int weakness = 120 - 2 * level;
1411 int max_s = -VALUE_INFINITE;
1414 // Choose best move. For each move score we add two terms both dependent on
1415 // weakness, one deterministic and bigger for weaker moves, and one random,
1416 // then we choose the move with the resulting highest score.
1417 for (size_t i = 0; i < PVSize; ++i)
1419 int s = RootMoves[i].score;
1421 // Don't allow crazy blunders even at very low skills
1422 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1425 // This is our magic formula
1426 s += ( weakness * int(RootMoves[0].score - s)
1427 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1432 best = RootMoves[i].pv[0];
1439 // uci_pv() formats PV information according to UCI protocol. UCI requires
1440 // to send all the PV lines also if are still to be searched and so refer to
1441 // the previous search score.
1443 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1445 std::stringstream s;
1446 Time::point elapsed = Time::now() - SearchTime + 1;
1447 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1450 for (size_t i = 0; i < Threads.size(); ++i)
1451 if (Threads[i]->maxPly > selDepth)
1452 selDepth = Threads[i]->maxPly;
1454 for (size_t i = 0; i < uciPVSize; ++i)
1456 bool updated = (i <= PVIdx);
1458 if (depth == 1 && !updated)
1461 int d = updated ? depth : depth - 1;
1462 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1464 if (s.rdbuf()->in_avail()) // Not at first line
1467 s << "info depth " << d
1468 << " seldepth " << selDepth
1469 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1470 << " nodes " << pos.nodes_searched()
1471 << " nps " << pos.nodes_searched() * 1000 / elapsed
1472 << " time " << elapsed
1473 << " multipv " << i + 1
1476 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1477 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1486 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1487 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1488 /// allow to always have a ponder move even when we fail high at root, and a
1489 /// long PV to print that is important for position analysis.
1491 void RootMove::extract_pv_from_tt(Position& pos) {
1493 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1503 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1505 pos.do_move(pv[ply++], *st++);
1506 tte = TT.probe(pos.key());
1509 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1510 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1512 && (!pos.is_draw() || ply < 2));
1514 pv.push_back(MOVE_NONE); // Must be zero-terminating
1516 while (ply) pos.undo_move(pv[--ply]);
1520 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1521 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1522 /// first, even if the old TT entries have been overwritten.
1524 void RootMove::insert_pv_in_tt(Position& pos) {
1526 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1531 tte = TT.probe(pos.key());
1533 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1534 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1536 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1538 pos.do_move(pv[ply++], *st++);
1540 } while (pv[ply] != MOVE_NONE);
1542 while (ply) pos.undo_move(pv[--ply]);
1546 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1548 void Thread::idle_loop() {
1550 // Pointer 'this_sp' is not null only if we are called from split(), and not
1551 // at the thread creation. So it means we are the split point's master.
1552 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1554 assert(!this_sp || (this_sp->masterThread == this && searching));
1558 // If we are not searching, wait for a condition to be signaled instead of
1559 // wasting CPU time polling for work.
1560 while ((!searching && Threads.sleepWhileIdle) || exit)
1568 // Grab the lock to avoid races with Thread::notify_one()
1571 // If we are master and all slaves have finished then exit idle_loop
1572 if (this_sp && !this_sp->slavesMask)
1578 // Do sleep after retesting sleep conditions under lock protection, in
1579 // particular we need to avoid a deadlock in case a master thread has,
1580 // in the meanwhile, allocated us and sent the notify_one() call before
1581 // we had the chance to grab the lock.
1582 if (!searching && !exit)
1583 sleepCondition.wait(mutex);
1588 // If this thread has been assigned work, launch a search
1593 Threads.mutex.lock();
1596 assert(activeSplitPoint);
1597 SplitPoint* sp = activeSplitPoint;
1599 Threads.mutex.unlock();
1601 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1602 Position pos(*sp->pos, this);
1604 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1605 ss->splitPoint = sp;
1609 assert(activePosition == NULL);
1611 activePosition = &pos;
1613 switch (sp->nodeType) {
1615 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1618 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1621 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1630 activePosition = NULL;
1631 sp->slavesMask &= ~(1ULL << idx);
1632 sp->nodes += pos.nodes_searched();
1634 // Wake up master thread so to allow it to return from the idle loop
1635 // in case we are the last slave of the split point.
1636 if ( Threads.sleepWhileIdle
1637 && this != sp->masterThread
1640 assert(!sp->masterThread->searching);
1641 sp->masterThread->notify_one();
1644 // After releasing the lock we cannot access anymore any SplitPoint
1645 // related data in a safe way becuase it could have been released under
1646 // our feet by the sp master. Also accessing other Thread objects is
1647 // unsafe because if we are exiting there is a chance are already freed.
1651 // If this thread is the master of a split point and all slaves have finished
1652 // their work at this split point, return from the idle loop.
1653 if (this_sp && !this_sp->slavesMask)
1655 this_sp->mutex.lock();
1656 bool finished = !this_sp->slavesMask; // Retest under lock protection
1657 this_sp->mutex.unlock();
1665 /// check_time() is called by the timer thread when the timer triggers. It is
1666 /// used to print debug info and, more important, to detect when we are out of
1667 /// available time and so stop the search.
1671 static Time::point lastInfoTime = Time::now();
1672 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1674 if (Time::now() - lastInfoTime >= 1000)
1676 lastInfoTime = Time::now();
1685 Threads.mutex.lock();
1687 nodes = RootPos.nodes_searched();
1689 // Loop across all split points and sum accumulated SplitPoint nodes plus
1690 // all the currently active positions nodes.
1691 for (size_t i = 0; i < Threads.size(); ++i)
1692 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1694 SplitPoint& sp = Threads[i]->splitPoints[j];
1699 Bitboard sm = sp.slavesMask;
1702 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1704 nodes += pos->nodes_searched();
1710 Threads.mutex.unlock();
1713 Time::point elapsed = Time::now() - SearchTime;
1714 bool stillAtFirstMove = Signals.firstRootMove
1715 && !Signals.failedLowAtRoot
1716 && elapsed > TimeMgr.available_time();
1718 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1719 || stillAtFirstMove;
1721 if ( (Limits.use_time_management() && noMoreTime)
1722 || (Limits.movetime && elapsed >= Limits.movetime)
1723 || (Limits.nodes && nodes >= Limits.nodes))
1724 Signals.stop = true;