2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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;
44 Position RootPosition;
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 // This is the minimum interval in msec between two check_time() calls
60 const int TimerResolution = 5;
62 // Different node types, used as template parameter
63 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
65 // Lookup table to check if a Piece is a slider and its access function
66 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
67 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
69 // Dynamic razoring margin based on depth
70 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
72 // Futility lookup tables (initialized at startup) and their access functions
73 Value FutilityMargins[16][64]; // [depth][moveNumber]
74 int FutilityMoveCounts[32]; // [depth]
76 inline Value futility_margin(Depth d, int mn) {
78 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
82 // Reduction lookup tables (initialized at startup) and their access function
83 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
85 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
87 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
90 size_t MultiPV, UCIMultiPV, PVIdx;
95 bool SkillLevelEnabled, Chess960;
96 Value DrawValue[COLOR_NB];
99 template <NodeType NT>
100 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
102 template <NodeType NT>
103 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
105 void id_loop(Position& pos);
106 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
107 bool connected_moves(const Position& pos, Move m1, Move m2);
108 Value value_to_tt(Value v, int ply);
109 Value value_from_tt(Value v, int ply);
110 bool connected_threat(const Position& pos, Move m, Move threat);
111 Move do_skill_level();
112 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
117 /// Search::init() is called during startup to initialize various lookup tables
119 void Search::init() {
121 int d; // depth (ONE_PLY == 2)
122 int hd; // half depth (ONE_PLY == 1)
125 // Init reductions array
126 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
128 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
129 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
130 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
131 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
134 // Init futility margins array
135 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
136 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
138 // Init futility move count array
139 for (d = 0; d < 32; d++)
140 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(double(d), 2.0));
144 /// Search::perft() is our utility to verify move generation. All the leaf nodes
145 /// up to the given depth are generated and counted and the sum returned.
147 size_t Search::perft(Position& pos, Depth depth) {
149 // At the last ply just return the number of legal moves (leaf nodes)
150 if (depth == ONE_PLY)
151 return MoveList<LEGAL>(pos).size();
157 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
159 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
160 cnt += perft(pos, depth - ONE_PLY);
161 pos.undo_move(ml.move());
168 /// Search::think() is the external interface to Stockfish's search, and is
169 /// called by the main thread when the program receives the UCI 'go' command. It
170 /// searches from RootPosition and at the end prints the "bestmove" to output.
172 void Search::think() {
174 static PolyglotBook book; // Defined static to initialize the PRNG only once
176 Position& pos = RootPosition;
177 Chess960 = pos.is_chess960();
178 RootColor = pos.side_to_move();
179 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
183 if (RootMoves.empty())
185 sync_cout << "info depth 0 score "
186 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
188 RootMoves.push_back(MOVE_NONE);
192 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
194 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // In centipawns
195 cf = cf * MaterialTable::game_phase(pos) / PHASE_MIDGAME; // Scale down with phase
196 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
197 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
200 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
202 if (Options["OwnBook"] && !Limits.infinite)
204 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
206 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
208 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
213 UCIMultiPV = Options["MultiPV"];
214 SkillLevel = Options["Skill Level"];
216 // Do we have to play with skill handicap? In this case enable MultiPV that
217 // we will use behind the scenes to retrieve a set of possible moves.
218 SkillLevelEnabled = (SkillLevel < 20);
219 skillBest = MOVE_NONE;
220 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
222 if (Options["Use Search Log"])
224 Log log(Options["Search Log Filename"]);
225 log << "\nSearching: " << pos.to_fen()
226 << "\ninfinite: " << Limits.infinite
227 << " ponder: " << Limits.ponder
228 << " time: " << Limits.time[pos.side_to_move()]
229 << " increment: " << Limits.inc[pos.side_to_move()]
230 << " moves to go: " << Limits.movestogo
236 // Set best timer interval to avoid lagging under time pressure. Timer is
237 // used to check for remaining available thinking time.
238 if (Limits.use_time_management())
239 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
240 else if (Limits.nodes)
241 Threads.set_timer(2 * TimerResolution);
243 Threads.set_timer(100);
245 // We're ready to start searching. Call the iterative deepening loop function
248 Threads.set_timer(0); // Stop timer
251 // When using skills swap best PV line with the sub-optimal one
252 if (SkillLevelEnabled)
254 if (skillBest == MOVE_NONE) // Still unassigned ?
255 skillBest = do_skill_level();
257 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
260 if (Options["Use Search Log"])
262 Time::point elapsed = Time::now() - SearchTime + 1;
264 Log log(Options["Search Log Filename"]);
265 log << "Nodes: " << pos.nodes_searched()
266 << "\nNodes/second: " << pos.nodes_searched() * 1000 / elapsed
267 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
270 pos.do_move(RootMoves[0].pv[0], st);
271 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << std::endl;
272 pos.undo_move(RootMoves[0].pv[0]);
277 // When we reach max depth we arrive here even without Signals.stop is raised,
278 // but if we are pondering or in infinite search, we shouldn't print the best
279 // move before we are told to do so.
280 if (!Signals.stop && (Limits.ponder || Limits.infinite))
281 pos.this_thread()->wait_for_stop_or_ponderhit();
283 // Best move could be MOVE_NONE when searching on a stalemate position
284 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
285 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << sync_endl;
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 ss[MAX_PLY_PLUS_2];
298 int depth, prevBestMoveChanges;
299 Value bestValue, alpha, beta, delta;
300 bool bestMoveNeverChanged = true;
302 memset(ss, 0, 4 * sizeof(Stack));
303 depth = BestMoveChanges = 0;
304 bestValue = delta = -VALUE_INFINITE;
305 ss->currentMove = MOVE_NULL; // Hack to skip update gains
307 // Iterative deepening loop until requested to stop or target depth reached
308 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
310 // Save last iteration's scores before first PV line is searched and all
311 // the move scores but the (new) PV are set to -VALUE_INFINITE.
312 for (size_t i = 0; i < RootMoves.size(); i++)
313 RootMoves[i].prevScore = RootMoves[i].score;
315 prevBestMoveChanges = BestMoveChanges;
318 // MultiPV loop. We perform a full root search for each PV line
319 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
321 // Set aspiration window default width
322 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
325 alpha = RootMoves[PVIdx].prevScore - delta;
326 beta = RootMoves[PVIdx].prevScore + delta;
330 alpha = -VALUE_INFINITE;
331 beta = VALUE_INFINITE;
334 // Start with a small aspiration window and, in case of fail high/low,
335 // research with bigger window until not failing high/low anymore.
338 // Search starts from ss+1 to allow referencing (ss-1). This is
339 // needed by update gains and ss copy when splitting at Root.
340 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
342 // Bring to front the best move. It is critical that sorting is
343 // done with a stable algorithm because all the values but the first
344 // and eventually the new best one are set to -VALUE_INFINITE and
345 // we want to keep the same order for all the moves but the new
346 // PV that goes to the front. Note that in case of MultiPV search
347 // the already searched PV lines are preserved.
348 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
350 // Write PV back to transposition table in case the relevant
351 // entries have been overwritten during the search.
352 for (size_t i = 0; i <= PVIdx; i++)
353 RootMoves[i].insert_pv_in_tt(pos);
355 // If search has been stopped return immediately. Sorting and
356 // writing PV back to TT is safe becuase RootMoves is still
357 // valid, although refers to previous iteration.
361 // In case of failing high/low increase aspiration window and
362 // research, otherwise sort multi-PV lines and exit the loop.
363 if (bestValue > alpha && bestValue < beta)
365 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
366 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
370 // Give some update (without cluttering the UI) before to research
371 if (Time::now() - SearchTime > 3000)
372 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
374 if (abs(bestValue) >= VALUE_KNOWN_WIN)
376 alpha = -VALUE_INFINITE;
377 beta = VALUE_INFINITE;
379 else if (bestValue >= beta)
386 Signals.failedLowAtRoot = true;
387 Signals.stopOnPonderhit = false;
393 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
397 // Skills: Do we need to pick now the best move ?
398 if (SkillLevelEnabled && depth == 1 + SkillLevel)
399 skillBest = do_skill_level();
401 if (Options["Use Search Log"])
403 Log log(Options["Search Log Filename"]);
404 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
408 // Filter out startup noise when monitoring best move stability
409 if (depth > 2 && BestMoveChanges)
410 bestMoveNeverChanged = false;
412 // Do we have time for the next iteration? Can we stop searching now?
413 if (Limits.use_time_management() && !Signals.stopOnPonderhit)
415 bool stop = false; // Local variable, not the volatile Signals.stop
417 // Take in account some extra time if the best move has changed
418 if (depth > 4 && depth < 50)
419 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
421 // Stop search if most of available time is already consumed. We
422 // probably don't have enough time to search the first move at the
423 // next iteration anyway.
424 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
427 // Stop search early if one move seems to be much better than others
430 && ( (bestMoveNeverChanged && pos.captured_piece_type())
431 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
433 Value rBeta = bestValue - 2 * PawnValueMg;
434 (ss+1)->excludedMove = RootMoves[0].pv[0];
435 (ss+1)->skipNullMove = true;
436 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
437 (ss+1)->skipNullMove = false;
438 (ss+1)->excludedMove = MOVE_NONE;
446 // If we are allowed to ponder do not stop the search now but
447 // keep pondering until GUI sends "ponderhit" or "stop".
449 Signals.stopOnPonderhit = true;
458 // search<>() is the main search function for both PV and non-PV nodes and for
459 // normal and SplitPoint nodes. When called just after a split point the search
460 // is simpler because we have already probed the hash table, done a null move
461 // search, and searched the first move before splitting, we don't have to repeat
462 // all this work again. We also don't need to store anything to the hash table
463 // here: This is taken care of after we return from the split point.
465 template <NodeType NT>
466 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
468 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
469 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
470 const bool RootNode = (NT == Root || NT == SplitPointRoot);
472 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
473 assert(PvNode || (alpha == beta - 1));
474 assert(depth > DEPTH_ZERO);
476 Move movesSearched[64];
481 Move ttMove, move, excludedMove, bestMove, threatMove;
483 Value bestValue, value, ttValue;
484 Value eval, nullValue, futilityValue;
485 bool inCheck, givesCheck, pvMove, singularExtensionNode;
486 bool captureOrPromotion, dangerous, doFullDepthSearch;
487 int moveCount, playedMoveCount;
489 // Step 1. Initialize node
490 Thread* thisThread = pos.this_thread();
491 moveCount = playedMoveCount = 0;
492 inCheck = pos.in_check();
497 bestMove = sp->bestMove;
498 threatMove = sp->threatMove;
499 bestValue = sp->bestValue;
501 ttMove = excludedMove = MOVE_NONE;
502 ttValue = VALUE_NONE;
504 assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);
506 goto split_point_start;
509 bestValue = -VALUE_INFINITE;
510 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
511 ss->ply = (ss-1)->ply + 1;
512 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
513 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
515 // Used to send selDepth info to GUI
516 if (PvNode && thisThread->maxPly < ss->ply)
517 thisThread->maxPly = ss->ply;
521 // Step 2. Check for aborted search and immediate draw
522 if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
523 return DrawValue[pos.side_to_move()];
525 // Step 3. Mate distance pruning. Even if we mate at the next move our score
526 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
527 // a shorter mate was found upward in the tree then there is no need to search
528 // further, we will never beat current alpha. Same logic but with reversed signs
529 // applies also in the opposite condition of being mated instead of giving mate,
530 // in this case return a fail-high score.
531 alpha = std::max(mated_in(ss->ply), alpha);
532 beta = std::min(mate_in(ss->ply+1), beta);
537 // Step 4. Transposition table lookup
538 // We don't want the score of a partial search to overwrite a previous full search
539 // TT value, so we use a different position key in case of an excluded move.
540 excludedMove = ss->excludedMove;
541 posKey = excludedMove ? pos.exclusion_key() : pos.key();
542 tte = TT.probe(posKey);
543 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
544 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
546 // At PV nodes we check for exact scores, while at non-PV nodes we check for
547 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
548 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
549 // we should also update RootMoveList to avoid bogus output.
551 && tte && tte->depth() >= depth
552 && ( PvNode ? tte->type() == BOUND_EXACT
553 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
554 : (tte->type() & BOUND_UPPER)))
556 assert(ttValue != VALUE_NONE); // Due to depth > DEPTH_NONE
559 ss->currentMove = ttMove; // Can be MOVE_NONE
563 && !pos.is_capture_or_promotion(ttMove)
564 && ttMove != ss->killers[0])
566 ss->killers[1] = ss->killers[0];
567 ss->killers[0] = ttMove;
572 // Step 5. Evaluate the position statically and update parent's gain statistics
574 ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
578 assert(tte->static_value() != VALUE_NONE);
579 assert(ttValue != VALUE_NONE || tte->type() == BOUND_NONE);
581 ss->staticEval = eval = tte->static_value();
582 ss->evalMargin = tte->static_value_margin();
584 // Can ttValue be used as a better position evaluation?
585 if ( ((tte->type() & BOUND_LOWER) && ttValue > eval)
586 || ((tte->type() & BOUND_UPPER) && ttValue < eval))
591 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
592 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
593 ss->staticEval, ss->evalMargin);
596 // Update gain for the parent non-capture move given the static position
597 // evaluation before and after the move.
598 if ( (move = (ss-1)->currentMove) != MOVE_NULL
599 && (ss-1)->staticEval != VALUE_NONE
600 && ss->staticEval != VALUE_NONE
601 && !pos.captured_piece_type()
602 && type_of(move) == NORMAL)
604 Square to = to_sq(move);
605 H.update_gain(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
608 // Step 6. Razoring (is omitted in PV nodes)
610 && depth < 4 * ONE_PLY
612 && eval + razor_margin(depth) < beta
613 && ttMove == MOVE_NONE
614 && abs(beta) < VALUE_MATE_IN_MAX_PLY
615 && !pos.pawn_on_7th(pos.side_to_move()))
617 Value rbeta = beta - razor_margin(depth);
618 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
620 // Logically we should return (v + razor_margin(depth)), but
621 // surprisingly this did slightly weaker in tests.
625 // Step 7. Static null move pruning (is omitted in PV nodes)
626 // We're betting that the opponent doesn't have a move that will reduce
627 // the score by more than futility_margin(depth) if we do a null move.
630 && depth < 4 * ONE_PLY
632 && eval - FutilityMargins[depth][0] >= beta
633 && abs(beta) < VALUE_MATE_IN_MAX_PLY
634 && pos.non_pawn_material(pos.side_to_move()))
635 return eval - FutilityMargins[depth][0];
637 // Step 8. Null move search with verification search (is omitted in PV nodes)
643 && abs(beta) < VALUE_MATE_IN_MAX_PLY
644 && pos.non_pawn_material(pos.side_to_move()))
646 ss->currentMove = MOVE_NULL;
648 // Null move dynamic reduction based on depth
649 Depth R = 3 * ONE_PLY + depth / 4;
651 // Null move dynamic reduction based on value
652 if (eval - PawnValueMg > beta)
655 pos.do_null_move<true>(st);
656 (ss+1)->skipNullMove = true;
657 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
658 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
659 (ss+1)->skipNullMove = false;
660 pos.do_null_move<false>(st);
662 if (nullValue >= beta)
664 // Do not return unproven mate scores
665 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
668 if (depth < 6 * ONE_PLY)
671 // Do verification search at high depths
672 ss->skipNullMove = true;
673 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
674 ss->skipNullMove = false;
681 // The null move failed low, which means that we may be faced with
682 // some kind of threat. If the previous move was reduced, check if
683 // the move that refuted the null move was somehow connected to the
684 // move which was reduced. If a connection is found, return a fail
685 // low score (which will cause the reduced move to fail high in the
686 // parent node, which will trigger a re-search with full depth).
687 threatMove = (ss+1)->currentMove;
689 if ( depth < 5 * ONE_PLY
691 && threatMove != MOVE_NONE
692 && connected_moves(pos, (ss-1)->currentMove, threatMove))
697 // Step 9. ProbCut (is omitted in PV nodes)
698 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
699 // and a reduced search returns a value much above beta, we can (almost) safely
700 // prune the previous move.
702 && depth >= 5 * ONE_PLY
705 && excludedMove == MOVE_NONE
706 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
708 Value rbeta = beta + 200;
709 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
711 assert(rdepth >= ONE_PLY);
712 assert((ss-1)->currentMove != MOVE_NONE);
713 assert((ss-1)->currentMove != MOVE_NULL);
715 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
718 while ((move = mp.next_move<false>()) != MOVE_NONE)
719 if (pos.pl_move_is_legal(move, ci.pinned))
721 ss->currentMove = move;
722 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
723 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
730 // Step 10. Internal iterative deepening
731 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
732 && ttMove == MOVE_NONE
733 && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
735 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
737 ss->skipNullMove = true;
738 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
739 ss->skipNullMove = false;
741 tte = TT.probe(posKey);
742 ttMove = tte ? tte->move() : MOVE_NONE;
745 split_point_start: // At split points actual search starts from here
747 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
749 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
750 singularExtensionNode = !RootNode
752 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
753 && ttMove != MOVE_NONE
754 && !excludedMove // Recursive singular search is not allowed
755 && (tte->type() & BOUND_LOWER)
756 && tte->depth() >= depth - 3 * ONE_PLY;
758 // Step 11. Loop through moves
759 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
760 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
764 if (move == excludedMove)
767 // At root obey the "searchmoves" option and skip moves not listed in Root
768 // Move List, as a consequence any illegal move is also skipped. In MultiPV
769 // mode we also skip PV moves which have been already searched.
770 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
775 // Shared counter cannot be decremented later if move turns out to be illegal
776 if (!pos.pl_move_is_legal(move, ci.pinned))
779 moveCount = ++sp->moveCount;
787 Signals.firstRootMove = (moveCount == 1);
789 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
790 sync_cout << "info depth " << depth / ONE_PLY
791 << " currmove " << move_to_uci(move, Chess960)
792 << " currmovenumber " << moveCount + PVIdx << sync_endl;
796 captureOrPromotion = pos.is_capture_or_promotion(move);
797 givesCheck = pos.move_gives_check(move, ci);
798 dangerous = givesCheck
799 || pos.is_passed_pawn_push(move)
800 || type_of(move) == CASTLE
801 || ( captureOrPromotion // Entering a pawn endgame?
802 && type_of(pos.piece_on(to_sq(move))) != PAWN
803 && type_of(move) == NORMAL
804 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
805 - PieceValue[MG][pos.piece_on(to_sq(move))] == VALUE_ZERO));
807 // Step 12. Extend checks and, in PV nodes, also dangerous moves
808 if (PvNode && dangerous)
811 else if (givesCheck && pos.see_sign(move) >= 0)
814 // Singular extension search. If all moves but one fail low on a search of
815 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
816 // is singular and should be extended. To verify this we do a reduced search
817 // on all the other moves but the ttMove, if result is lower than ttValue minus
818 // a margin then we extend ttMove.
819 if ( singularExtensionNode
822 && pos.pl_move_is_legal(move, ci.pinned)
823 && abs(ttValue) < VALUE_KNOWN_WIN)
825 assert(ttValue != VALUE_NONE);
827 Value rBeta = ttValue - int(depth);
828 ss->excludedMove = move;
829 ss->skipNullMove = true;
830 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
831 ss->skipNullMove = false;
832 ss->excludedMove = MOVE_NONE;
835 ext = rBeta >= beta ? ONE_PLY + ONE_PLY / 2 : ONE_PLY;
838 // Update current move (this must be done after singular extension search)
839 newDepth = depth - ONE_PLY + ext;
841 // Step 13. Futility pruning (is omitted in PV nodes)
843 && !captureOrPromotion
847 && (bestValue > VALUE_MATED_IN_MAX_PLY || ( bestValue == -VALUE_INFINITE
848 && alpha > VALUE_MATED_IN_MAX_PLY)))
850 // Move count based pruning
851 if ( depth < 16 * ONE_PLY
852 && moveCount >= FutilityMoveCounts[depth]
853 && (!threatMove || !connected_threat(pos, move, threatMove)))
861 // Value based pruning
862 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
863 // but fixing this made program slightly weaker.
864 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
865 futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
866 + H.gain(pos.piece_moved(move), to_sq(move));
868 if (futilityValue < beta)
876 // Prune moves with negative SEE at low depths
877 if ( predictedDepth < 2 * ONE_PLY
878 && pos.see_sign(move) < 0)
887 // Check for legality only before to do the move
888 if (!pos.pl_move_is_legal(move, ci.pinned))
894 pvMove = PvNode ? moveCount == 1 : false;
895 ss->currentMove = move;
896 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
897 movesSearched[playedMoveCount++] = move;
899 // Step 14. Make the move
900 pos.do_move(move, st, ci, givesCheck);
902 // Step 15. Reduced depth search (LMR). If the move fails high will be
903 // re-searched at full depth.
904 if ( depth > 3 * ONE_PLY
906 && !captureOrPromotion
908 && ss->killers[0] != move
909 && ss->killers[1] != move)
911 ss->reduction = reduction<PvNode>(depth, moveCount);
912 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
913 alpha = SpNode ? sp->alpha : alpha;
915 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
917 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
918 ss->reduction = DEPTH_ZERO;
921 doFullDepthSearch = !pvMove;
923 // Step 16. Full depth search, when LMR is skipped or fails high
924 if (doFullDepthSearch)
926 alpha = SpNode ? sp->alpha : alpha;
927 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
928 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
931 // Only for PV nodes do a full PV search on the first move or after a fail
932 // high, in the latter case search only if value < beta, otherwise let the
933 // parent node to fail low with value <= alpha and to try another move.
934 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
935 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
936 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
938 // Step 17. Undo move
941 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
943 // Step 18. Check for new best move
947 bestValue = sp->bestValue;
951 // Finished searching the move. If Signals.stop is true, the search
952 // was aborted because the user interrupted the search or because we
953 // ran out of time. In this case, the return value of the search cannot
954 // be trusted, and we don't update the best move and/or PV.
955 if (Signals.stop || thisThread->cutoff_occurred())
960 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
962 // PV move or new best move ?
963 if (pvMove || value > alpha)
966 rm.extract_pv_from_tt(pos);
968 // We record how often the best move has been changed in each
969 // iteration. This information is used for time management: When
970 // the best move changes frequently, we allocate some more time.
971 if (!pvMove && MultiPV == 1)
975 // All other moves but the PV are set to the lowest value, this
976 // is not a problem when sorting becuase sort is stable and move
977 // position in the list is preserved, just the PV is pushed up.
978 rm.score = -VALUE_INFINITE;
981 if (value > bestValue)
984 if (SpNode) sp->bestValue = value;
989 if (SpNode) sp->bestMove = move;
991 if (PvNode && value < beta)
993 alpha = value; // Update alpha here! Always alpha < beta
994 if (SpNode) sp->alpha = value;
998 if (SpNode) sp->cutoff = true;
1004 // Step 19. Check for splitting the search
1006 && depth >= Threads.min_split_depth()
1008 && Threads.available_slave_exists(thisThread))
1010 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1011 depth, threatMove, moveCount, mp, NT);
1019 // Step 20. Check for mate and stalemate
1020 // All legal moves have been searched and if there are no legal moves, it
1021 // must be mate or stalemate. Note that we can have a false positive in
1022 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1023 // harmless because return value is discarded anyhow in the parent nodes.
1024 // If we are in a singular extension search then return a fail low score.
1025 // A split node has at least one move, the one tried before to be splitted.
1027 return excludedMove ? alpha
1028 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1030 // If we have pruned all the moves without searching return a fail-low score
1031 if (bestValue == -VALUE_INFINITE)
1033 assert(!playedMoveCount);
1038 if (bestValue >= beta) // Failed high
1040 TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
1041 bestMove, ss->staticEval, ss->evalMargin);
1043 if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
1045 if (bestMove != ss->killers[0])
1047 ss->killers[1] = ss->killers[0];
1048 ss->killers[0] = bestMove;
1051 // Increase history value of the cut-off move
1052 Value bonus = Value(int(depth) * int(depth));
1053 H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1055 // Decrease history of all the other played non-capture moves
1056 for (int i = 0; i < playedMoveCount - 1; i++)
1058 Move m = movesSearched[i];
1059 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1063 else // Failed low or PV search
1064 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1065 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1066 depth, bestMove, ss->staticEval, ss->evalMargin);
1068 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1074 // qsearch() is the quiescence search function, which is called by the main
1075 // search function when the remaining depth is zero (or, to be more precise,
1076 // less than ONE_PLY).
1078 template <NodeType NT>
1079 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1081 const bool PvNode = (NT == PV);
1083 assert(NT == PV || NT == NonPV);
1084 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1085 assert(PvNode || (alpha == beta - 1));
1086 assert(depth <= DEPTH_ZERO);
1091 Move ttMove, move, bestMove;
1092 Value bestValue, value, ttValue, futilityValue, futilityBase;
1093 bool inCheck, givesCheck, enoughMaterial, evasionPrunable;
1096 inCheck = pos.in_check();
1097 ss->currentMove = bestMove = MOVE_NONE;
1098 ss->ply = (ss-1)->ply + 1;
1100 // Check for an instant draw or maximum ply reached
1101 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1102 return DrawValue[pos.side_to_move()];
1104 // Transposition table lookup. At PV nodes, we don't use the TT for
1105 // pruning, but only for move ordering.
1107 tte = TT.probe(posKey);
1108 ttMove = tte ? tte->move() : MOVE_NONE;
1109 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1111 // Decide whether or not to include checks, this fixes also the type of
1112 // TT entry depth that we are going to use. Note that in qsearch we use
1113 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1114 ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1115 : DEPTH_QS_NO_CHECKS;
1116 if ( tte && tte->depth() >= ttDepth
1117 && ( PvNode ? tte->type() == BOUND_EXACT
1118 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
1119 : (tte->type() & BOUND_UPPER)))
1121 assert(ttValue != VALUE_NONE); // Due to ttDepth > DEPTH_NONE
1123 ss->currentMove = ttMove; // Can be MOVE_NONE
1127 // Evaluate the position statically
1130 ss->staticEval = ss->evalMargin = VALUE_NONE;
1131 bestValue = futilityBase = -VALUE_INFINITE;
1132 enoughMaterial = false;
1138 assert(tte->static_value() != VALUE_NONE);
1140 ss->staticEval = bestValue = tte->static_value();
1141 ss->evalMargin = tte->static_value_margin();
1144 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1146 // Stand pat. Return immediately if static value is at least beta
1147 if (bestValue >= beta)
1150 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1151 DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
1156 if (PvNode && bestValue > alpha)
1159 futilityBase = ss->staticEval + ss->evalMargin + Value(128);
1160 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1163 // Initialize a MovePicker object for the current position, and prepare
1164 // to search the moves. Because the depth is <= 0 here, only captures,
1165 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1167 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1170 // Loop through the moves until no moves remain or a beta cutoff occurs
1171 while ((move = mp.next_move<false>()) != MOVE_NONE)
1173 assert(is_ok(move));
1175 givesCheck = pos.move_gives_check(move, ci);
1183 && type_of(move) != PROMOTION
1184 && !pos.is_passed_pawn_push(move))
1186 futilityValue = futilityBase
1187 + PieceValue[EG][pos.piece_on(to_sq(move))]
1188 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1190 if (futilityValue < beta)
1192 if (futilityValue > bestValue)
1193 bestValue = futilityValue;
1198 // Prune moves with negative or equal SEE
1199 if ( futilityBase < beta
1200 && depth < DEPTH_ZERO
1201 && pos.see(move) <= 0)
1205 // Detect non-capture evasions that are candidate to be pruned
1206 evasionPrunable = !PvNode
1208 && bestValue > VALUE_MATED_IN_MAX_PLY
1209 && !pos.is_capture(move)
1210 && !pos.can_castle(pos.side_to_move());
1212 // Don't search moves with negative SEE values
1214 && (!inCheck || evasionPrunable)
1216 && type_of(move) != PROMOTION
1217 && pos.see_sign(move) < 0)
1220 // Don't search useless checks
1225 && !pos.is_capture_or_promotion(move)
1226 && ss->staticEval + PawnValueMg / 4 < beta
1227 && !check_is_dangerous(pos, move, futilityBase, beta))
1230 // Check for legality only before to do the move
1231 if (!pos.pl_move_is_legal(move, ci.pinned))
1234 ss->currentMove = move;
1236 // Make and search the move
1237 pos.do_move(move, st, ci, givesCheck);
1238 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1239 pos.undo_move(move);
1241 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1243 // Check for new best move
1244 if (value > bestValue)
1250 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1257 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1258 ttDepth, move, ss->staticEval, ss->evalMargin);
1266 // All legal moves have been searched. A special case: If we're in check
1267 // and no legal moves were found, it is checkmate.
1268 if (inCheck && bestValue == -VALUE_INFINITE)
1269 return mated_in(ss->ply); // Plies to mate from the root
1271 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1272 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1273 ttDepth, bestMove, ss->staticEval, ss->evalMargin);
1275 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1281 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1282 // bestValue is updated only when returning false because in that case move
1285 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1287 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1288 Square from, to, ksq;
1292 from = from_sq(move);
1294 them = ~pos.side_to_move();
1295 ksq = pos.king_square(them);
1296 kingAtt = pos.attacks_from<KING>(ksq);
1297 pc = pos.piece_moved(move);
1299 occ = pos.pieces() ^ from ^ ksq;
1300 oldAtt = pos.attacks_from(pc, from, occ);
1301 newAtt = pos.attacks_from(pc, to, occ);
1303 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1304 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1306 if (!more_than_one(b))
1309 // Rule 2. Queen contact check is very dangerous
1310 if (type_of(pc) == QUEEN && (kingAtt & to))
1313 // Rule 3. Creating new double threats with checks
1314 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1317 // Note that here we generate illegal "double move"!
1318 if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
1326 // connected_moves() tests whether two moves are 'connected' in the sense
1327 // that the first move somehow made the second move possible (for instance
1328 // if the moving piece is the same in both moves). The first move is assumed
1329 // to be the move that was made to reach the current position, while the
1330 // second move is assumed to be a move from the current position.
1332 bool connected_moves(const Position& pos, Move m1, Move m2) {
1334 Square f1, t1, f2, t2;
1341 // Case 1: The moving piece is the same in both moves
1347 // Case 2: The destination square for m2 was vacated by m1
1353 // Case 3: Moving through the vacated square
1354 p2 = pos.piece_on(f2);
1355 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1358 // Case 4: The destination square for m2 is defended by the moving piece in m1
1359 p1 = pos.piece_on(t1);
1360 if (pos.attacks_from(p1, t1) & t2)
1363 // Case 5: Discovered check, checking piece is the piece moved in m1
1364 ksq = pos.king_square(pos.side_to_move());
1365 if ( piece_is_slider(p1)
1366 && (between_bb(t1, ksq) & f2)
1367 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1374 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1375 // "plies to mate from the current position". Non-mate scores are unchanged.
1376 // The function is called before storing a value to the transposition table.
1378 Value value_to_tt(Value v, int ply) {
1380 assert(v != VALUE_NONE);
1382 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1383 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1387 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1388 // from the transposition table (where refers to the plies to mate/be mated
1389 // from current position) to "plies to mate/be mated from the root".
1391 Value value_from_tt(Value v, int ply) {
1393 return v == VALUE_NONE ? VALUE_NONE
1394 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1395 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1399 // connected_threat() tests whether it is safe to forward prune a move or if
1400 // is somehow connected to the threat move returned by null search.
1402 bool connected_threat(const Position& pos, Move m, Move threat) {
1405 assert(is_ok(threat));
1406 assert(!pos.is_capture_or_promotion(m));
1407 assert(!pos.is_passed_pawn_push(m));
1409 Square mfrom, mto, tfrom, tto;
1413 tfrom = from_sq(threat);
1414 tto = to_sq(threat);
1416 // Case 1: Don't prune moves which move the threatened piece
1420 // Case 2: If the threatened piece has value less than or equal to the
1421 // value of the threatening piece, don't prune moves which defend it.
1422 if ( pos.is_capture(threat)
1423 && ( PieceValue[MG][pos.piece_on(tfrom)] >= PieceValue[MG][pos.piece_on(tto)]
1424 || type_of(pos.piece_on(tfrom)) == KING)
1425 && pos.move_attacks_square(m, tto))
1428 // Case 3: If the moving piece in the threatened move is a slider, don't
1429 // prune safe moves which block its ray.
1430 if ( piece_is_slider(pos.piece_on(tfrom))
1431 && (between_bb(tfrom, tto) & mto)
1432 && pos.see_sign(m) >= 0)
1439 // When playing with strength handicap choose best move among the MultiPV set
1440 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1442 Move do_skill_level() {
1444 assert(MultiPV > 1);
1448 // PRNG sequence should be not deterministic
1449 for (int i = Time::now() % 50; i > 0; i--)
1450 rk.rand<unsigned>();
1452 // RootMoves are already sorted by score in descending order
1453 size_t size = std::min(MultiPV, RootMoves.size());
1454 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1455 int weakness = 120 - 2 * SkillLevel;
1456 int max_s = -VALUE_INFINITE;
1457 Move best = MOVE_NONE;
1459 // Choose best move. For each move score we add two terms both dependent on
1460 // weakness, one deterministic and bigger for weaker moves, and one random,
1461 // then we choose the move with the resulting highest score.
1462 for (size_t i = 0; i < size; i++)
1464 int s = RootMoves[i].score;
1466 // Don't allow crazy blunders even at very low skills
1467 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1470 // This is our magic formula
1471 s += ( weakness * int(RootMoves[0].score - s)
1472 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1477 best = RootMoves[i].pv[0];
1484 // uci_pv() formats PV information according to UCI protocol. UCI requires
1485 // to send all the PV lines also if are still to be searched and so refer to
1486 // the previous search score.
1488 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1490 std::stringstream s;
1491 Time::point elaspsed = Time::now() - SearchTime + 1;
1494 for (size_t i = 0; i < Threads.size(); i++)
1495 if (Threads[i].maxPly > selDepth)
1496 selDepth = Threads[i].maxPly;
1498 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1500 bool updated = (i <= PVIdx);
1502 if (depth == 1 && !updated)
1505 int d = (updated ? depth : depth - 1);
1506 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1508 if (s.rdbuf()->in_avail())
1511 s << "info depth " << d
1512 << " seldepth " << selDepth
1513 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1514 << " nodes " << pos.nodes_searched()
1515 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1516 << " time " << elaspsed
1517 << " multipv " << i + 1
1520 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1521 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1530 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1531 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1532 /// allow to always have a ponder move even when we fail high at root, and a
1533 /// long PV to print that is important for position analysis.
1535 void RootMove::extract_pv_from_tt(Position& pos) {
1537 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1542 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1546 pos.do_move(m, *st++);
1548 while ( (tte = TT.probe(pos.key())) != NULL
1549 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1550 && pos.is_pseudo_legal(m)
1551 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1553 && (!pos.is_draw<false>() || ply < 2))
1556 pos.do_move(m, *st++);
1559 pv.push_back(MOVE_NONE);
1561 do pos.undo_move(pv[--ply]); while (ply);
1565 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1566 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1567 /// first, even if the old TT entries have been overwritten.
1569 void RootMove::insert_pv_in_tt(Position& pos) {
1571 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1574 Value v, m = VALUE_NONE;
1577 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1583 // Don't overwrite existing correct entries
1584 if (!tte || tte->move() != pv[ply])
1586 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1587 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1589 pos.do_move(pv[ply], *st++);
1591 } while (pv[++ply] != MOVE_NONE);
1593 do pos.undo_move(pv[--ply]); while (ply);
1597 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1599 void Thread::idle_loop() {
1601 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1602 // object for which the thread is the master.
1603 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1605 assert(!sp_master || (sp_master->master == this && is_searching));
1607 // If this thread is the master of a split point and all slaves have
1608 // finished their work at this split point, return from the idle loop.
1609 while (!sp_master || sp_master->slavesMask)
1611 // If we are not searching, wait for a condition to be signaled
1612 // instead of wasting CPU time polling for work.
1615 || (!is_searching && Threads.use_sleeping_threads()))
1623 // Grab the lock to avoid races with Thread::wake_up()
1626 // If we are master and all slaves have finished don't go to sleep
1627 if (sp_master && !sp_master->slavesMask)
1633 // Do sleep after retesting sleep conditions under lock protection, in
1634 // particular we need to avoid a deadlock in case a master thread has,
1635 // in the meanwhile, allocated us and sent the wake_up() call before we
1636 // had the chance to grab the lock.
1637 if (do_sleep || !is_searching)
1638 sleepCondition.wait(mutex);
1643 // If this thread has been assigned work, launch a search
1646 assert(!do_sleep && !do_exit);
1648 Threads.mutex.lock();
1650 assert(is_searching);
1651 SplitPoint* sp = curSplitPoint;
1653 Threads.mutex.unlock();
1655 Stack ss[MAX_PLY_PLUS_2];
1656 Position pos(*sp->pos, this);
1658 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1663 assert(sp->activePositions[idx] == NULL);
1665 sp->activePositions[idx] = &pos;
1667 if (sp->nodeType == Root)
1668 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1669 else if (sp->nodeType == PV)
1670 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1671 else if (sp->nodeType == NonPV)
1672 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1676 assert(is_searching);
1678 is_searching = false;
1679 sp->activePositions[idx] = NULL;
1680 sp->slavesMask &= ~(1ULL << idx);
1681 sp->nodes += pos.nodes_searched();
1683 // Wake up master thread so to allow it to return from the idle loop in
1684 // case we are the last slave of the split point.
1685 if ( Threads.use_sleeping_threads()
1686 && this != sp->master
1689 assert(!sp->master->is_searching);
1690 sp->master->wake_up();
1693 // After releasing the lock we cannot access anymore any SplitPoint
1694 // related data in a safe way becuase it could have been released under
1695 // our feet by the sp master. Also accessing other Thread objects is
1696 // unsafe because if we are exiting there is a chance are already freed.
1703 /// check_time() is called by the timer thread when the timer triggers. It is
1704 /// used to print debug info and, more important, to detect when we are out of
1705 /// available time and so stop the search.
1709 static Time::point lastInfoTime = Time::now();
1710 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1712 if (Time::now() - lastInfoTime >= 1000)
1714 lastInfoTime = Time::now();
1723 Threads.mutex.lock();
1725 nodes = RootPosition.nodes_searched();
1727 // Loop across all split points and sum accumulated SplitPoint nodes plus
1728 // all the currently active slaves positions.
1729 for (size_t i = 0; i < Threads.size(); i++)
1730 for (int j = 0; j < Threads[i].splitPointsCnt; j++)
1732 SplitPoint& sp = Threads[i].splitPoints[j];
1737 Bitboard sm = sp.slavesMask;
1740 Position* pos = sp.activePositions[pop_lsb(&sm)];
1741 nodes += pos ? pos->nodes_searched() : 0;
1747 Threads.mutex.unlock();
1750 Time::point elapsed = Time::now() - SearchTime;
1751 bool stillAtFirstMove = Signals.firstRootMove
1752 && !Signals.failedLowAtRoot
1753 && elapsed > TimeMgr.available_time();
1755 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1756 || stillAtFirstMove;
1758 if ( (Limits.use_time_management() && noMoreTime)
1759 || (Limits.movetime && elapsed >= Limits.movetime)
1760 || (Limits.nodes && nodes >= Limits.nodes))
1761 Signals.stop = true;