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;
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 // Lookup table to check if a Piece is a slider and its access function
63 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
64 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
66 // Maximum depth for razoring
67 const Depth RazorDepth = 4 * ONE_PLY;
69 // Dynamic razoring margin based on depth
70 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
72 // Maximum depth for use of dynamic threat detection when null move fails low
73 const Depth ThreatDepth = 5 * ONE_PLY;
75 // Minimum depth for use of internal iterative deepening
76 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
78 // At Non-PV nodes we do an internal iterative deepening search
79 // when the static evaluation is bigger then beta - IIDMargin.
80 const Value IIDMargin = Value(256);
82 // Minimum depth for use of singular extension
83 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
85 // Futility margin for quiescence search
86 const Value FutilityMarginQS = Value(128);
88 // Futility lookup tables (initialized at startup) and their access functions
89 Value FutilityMargins[16][64]; // [depth][moveNumber]
90 int FutilityMoveCounts[32]; // [depth]
92 inline Value futility_margin(Depth d, int mn) {
94 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
98 inline int futility_move_count(Depth d) {
100 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
103 // Reduction lookup tables (initialized at startup) and their access function
104 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
106 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
108 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
111 // Easy move margin. An easy move candidate must be at least this much better
112 // than the second best move.
113 const Value EasyMoveMargin = Value(0x150);
115 // This is the minimum interval in msec between two check_time() calls
116 const int TimerResolution = 5;
119 size_t MultiPV, UCIMultiPV, PVIdx;
123 bool SkillLevelEnabled, Chess960;
127 template <NodeType NT>
128 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
130 template <NodeType NT>
131 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
133 void id_loop(Position& pos);
134 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
135 bool connected_moves(const Position& pos, Move m1, Move m2);
136 Value value_to_tt(Value v, int ply);
137 Value value_from_tt(Value v, int ply);
138 bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);
139 bool connected_threat(const Position& pos, Move m, Move threat);
140 Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
141 Move do_skill_level();
142 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
144 // is_dangerous() checks whether a move belongs to some classes of known
145 // 'dangerous' moves so that we avoid to prune it.
146 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
149 if (type_of(m) == CASTLE)
153 if ( type_of(pos.piece_moved(m)) == PAWN
154 && pos.pawn_is_passed(pos.side_to_move(), to_sq(m)))
157 // Entering a pawn endgame?
158 if ( captureOrPromotion
159 && type_of(pos.piece_on(to_sq(m))) != PAWN
160 && type_of(m) == NORMAL
161 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
162 - PieceValue[Mg][pos.piece_on(to_sq(m))] == VALUE_ZERO))
171 /// Search::init() is called during startup to initialize various lookup tables
173 void Search::init() {
175 int d; // depth (ONE_PLY == 2)
176 int hd; // half depth (ONE_PLY == 1)
179 // Init reductions array
180 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
182 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
183 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
184 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
185 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
188 // Init futility margins array
189 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
190 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
192 // Init futility move count array
193 for (d = 0; d < 32; d++)
194 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
198 /// Search::perft() is our utility to verify move generation. All the leaf nodes
199 /// up to the given depth are generated and counted and the sum returned.
201 size_t Search::perft(Position& pos, Depth depth) {
203 // At the last ply just return the number of legal moves (leaf nodes)
204 if (depth == ONE_PLY)
205 return MoveList<LEGAL>(pos).size();
211 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
213 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
214 cnt += perft(pos, depth - ONE_PLY);
215 pos.undo_move(ml.move());
222 /// Search::think() is the external interface to Stockfish's search, and is
223 /// called by the main thread when the program receives the UCI 'go' command. It
224 /// searches from RootPosition and at the end prints the "bestmove" to output.
226 void Search::think() {
228 static Book book; // Defined static to initialize the PRNG only once
230 Position& pos = RootPosition;
231 Chess960 = pos.is_chess960();
232 Eval::RootColor = pos.side_to_move();
233 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
237 if (RootMoves.empty())
239 cout << "info depth 0 score "
240 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << endl;
242 RootMoves.push_back(MOVE_NONE);
246 if (Options["OwnBook"] && !Limits.infinite)
248 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
250 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
252 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
257 UCIMultiPV = Options["MultiPV"];
258 SkillLevel = Options["Skill Level"];
260 // Do we have to play with skill handicap? In this case enable MultiPV that
261 // we will use behind the scenes to retrieve a set of possible moves.
262 SkillLevelEnabled = (SkillLevel < 20);
263 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
265 if (Options["Use Search Log"])
267 Log log(Options["Search Log Filename"]);
268 log << "\nSearching: " << pos.to_fen()
269 << "\ninfinite: " << Limits.infinite
270 << " ponder: " << Limits.ponder
271 << " time: " << Limits.time[pos.side_to_move()]
272 << " increment: " << Limits.inc[pos.side_to_move()]
273 << " moves to go: " << Limits.movestogo
279 // Set best timer interval to avoid lagging under time pressure. Timer is
280 // used to check for remaining available thinking time.
281 if (Limits.use_time_management())
282 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
284 Threads.set_timer(100);
286 // We're ready to start searching. Call the iterative deepening loop function
289 Threads.set_timer(0); // Stop timer
292 if (Options["Use Search Log"])
294 int e = SearchTime.elapsed();
296 Log log(Options["Search Log Filename"]);
297 log << "Nodes: " << pos.nodes_searched()
298 << "\nNodes/second: " << (e > 0 ? pos.nodes_searched() * 1000 / e : 0)
299 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
302 pos.do_move(RootMoves[0].pv[0], st);
303 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << endl;
304 pos.undo_move(RootMoves[0].pv[0]);
309 // When we reach max depth we arrive here even without Signals.stop is raised,
310 // but if we are pondering or in infinite search, we shouldn't print the best
311 // move before we are told to do so.
312 if (!Signals.stop && (Limits.ponder || Limits.infinite))
313 pos.this_thread()->wait_for_stop_or_ponderhit();
315 // Best move could be MOVE_NONE when searching on a stalemate position
316 cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
317 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << endl;
323 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
324 // with increasing depth until the allocated thinking time has been consumed,
325 // user stops the search, or the maximum search depth is reached.
327 void id_loop(Position& pos) {
329 Stack ss[MAX_PLY_PLUS_2];
330 int depth, prevBestMoveChanges;
331 Value bestValue, alpha, beta, delta;
332 bool bestMoveNeverChanged = true;
333 Move skillBest = MOVE_NONE;
335 memset(ss, 0, 4 * sizeof(Stack));
336 depth = BestMoveChanges = 0;
337 bestValue = delta = -VALUE_INFINITE;
338 ss->currentMove = MOVE_NULL; // Hack to skip update gains
340 // Iterative deepening loop until requested to stop or target depth reached
341 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
343 // Save last iteration's scores before first PV line is searched and all
344 // the move scores but the (new) PV are set to -VALUE_INFINITE.
345 for (size_t i = 0; i < RootMoves.size(); i++)
346 RootMoves[i].prevScore = RootMoves[i].score;
348 prevBestMoveChanges = BestMoveChanges;
351 // MultiPV loop. We perform a full root search for each PV line
352 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
354 // Set aspiration window default width
355 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
358 alpha = RootMoves[PVIdx].prevScore - delta;
359 beta = RootMoves[PVIdx].prevScore + delta;
363 alpha = -VALUE_INFINITE;
364 beta = VALUE_INFINITE;
367 // Start with a small aspiration window and, in case of fail high/low,
368 // research with bigger window until not failing high/low anymore.
370 // Search starts from ss+1 to allow referencing (ss-1). This is
371 // needed by update gains and ss copy when splitting at Root.
372 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
374 // Bring to front the best move. It is critical that sorting is
375 // done with a stable algorithm because all the values but the first
376 // and eventually the new best one are set to -VALUE_INFINITE and
377 // we want to keep the same order for all the moves but the new
378 // PV that goes to the front. Note that in case of MultiPV search
379 // the already searched PV lines are preserved.
380 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
382 // In case we have found an exact score and we are going to leave
383 // the fail high/low loop then reorder the PV moves, otherwise
384 // leave the last PV move in its position so to be searched again.
385 // Of course this is needed only in MultiPV search.
386 if (PVIdx && bestValue > alpha && bestValue < beta)
387 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
389 // Write PV back to transposition table in case the relevant
390 // entries have been overwritten during the search.
391 for (size_t i = 0; i <= PVIdx; i++)
392 RootMoves[i].insert_pv_in_tt(pos);
394 // If search has been stopped exit the aspiration window loop.
395 // Sorting and writing PV back to TT is safe becuase RootMoves
396 // is still valid, although refers to previous iteration.
400 // Send full PV info to GUI if we are going to leave the loop or
401 // if we have a fail high/low and we are deep in the search.
402 if ((bestValue > alpha && bestValue < beta) || SearchTime.elapsed() > 2000)
403 cout << uci_pv(pos, depth, alpha, beta) << endl;
405 // In case of failing high/low increase aspiration window and
406 // research, otherwise exit the fail high/low loop.
407 if (bestValue >= beta)
412 else if (bestValue <= alpha)
414 Signals.failedLowAtRoot = true;
415 Signals.stopOnPonderhit = false;
423 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
425 } while (abs(bestValue) < VALUE_KNOWN_WIN);
428 // Skills: Do we need to pick now the best move ?
429 if (SkillLevelEnabled && depth == 1 + SkillLevel)
430 skillBest = do_skill_level();
432 if (!Signals.stop && Options["Use Search Log"])
434 Log log(Options["Search Log Filename"]);
435 log << pretty_pv(pos, depth, bestValue, SearchTime.elapsed(), &RootMoves[0].pv[0])
439 // Filter out startup noise when monitoring best move stability
440 if (depth > 2 && BestMoveChanges)
441 bestMoveNeverChanged = false;
443 // Do we have time for the next iteration? Can we stop searching now?
444 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
446 bool stop = false; // Local variable, not the volatile Signals.stop
448 // Take in account some extra time if the best move has changed
449 if (depth > 4 && depth < 50)
450 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
452 // Stop search if most of available time is already consumed. We
453 // probably don't have enough time to search the first move at the
454 // next iteration anyway.
455 if (SearchTime.elapsed() > (TimeMgr.available_time() * 62) / 100)
458 // Stop search early if one move seems to be much better than others
461 && ( (bestMoveNeverChanged && pos.captured_piece_type())
462 || SearchTime.elapsed() > (TimeMgr.available_time() * 40) / 100))
464 Value rBeta = bestValue - EasyMoveMargin;
465 (ss+1)->excludedMove = RootMoves[0].pv[0];
466 (ss+1)->skipNullMove = true;
467 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
468 (ss+1)->skipNullMove = false;
469 (ss+1)->excludedMove = MOVE_NONE;
477 // If we are allowed to ponder do not stop the search now but
478 // keep pondering until GUI sends "ponderhit" or "stop".
480 Signals.stopOnPonderhit = true;
487 // When using skills swap best PV line with the sub-optimal one
488 if (SkillLevelEnabled)
490 if (skillBest == MOVE_NONE) // Still unassigned ?
491 skillBest = do_skill_level();
493 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
498 // search<>() is the main search function for both PV and non-PV nodes and for
499 // normal and SplitPoint nodes. When called just after a split point the search
500 // is simpler because we have already probed the hash table, done a null move
501 // search, and searched the first move before splitting, we don't have to repeat
502 // all this work again. We also don't need to store anything to the hash table
503 // here: This is taken care of after we return from the split point.
505 template <NodeType NT>
506 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
508 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
509 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
510 const bool RootNode = (NT == Root || NT == SplitPointRoot);
512 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
513 assert((alpha == beta - 1) || PvNode);
514 assert(depth > DEPTH_ZERO);
516 Move movesSearched[64];
520 Move ttMove, move, excludedMove, bestMove, threatMove;
523 Value bestValue, value, oldAlpha, ttValue;
524 Value refinedValue, nullValue, futilityBase, futilityValue;
525 bool isPvMove, inCheck, singularExtensionNode, givesCheck;
526 bool captureOrPromotion, dangerous, doFullDepthSearch;
527 int moveCount = 0, playedMoveCount = 0;
528 Thread* thisThread = pos.this_thread();
529 SplitPoint* sp = NULL;
531 refinedValue = bestValue = value = -VALUE_INFINITE;
533 inCheck = pos.in_check();
534 ss->ply = (ss-1)->ply + 1;
536 // Used to send selDepth info to GUI
537 if (PvNode && thisThread->maxPly < ss->ply)
538 thisThread->maxPly = ss->ply;
540 // Step 1. Initialize node
544 ttMove = excludedMove = MOVE_NONE;
545 ttValue = VALUE_ZERO;
547 bestMove = sp->bestMove;
548 threatMove = sp->threatMove;
549 bestValue = sp->bestValue;
550 moveCount = sp->moveCount; // Lock must be held here
552 assert(bestValue > -VALUE_INFINITE && moveCount > 0);
554 goto split_point_start;
558 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
559 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
560 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
564 // Step 2. Check for aborted search and immediate draw
565 // Enforce node limit here. FIXME: This only works with 1 search thread.
566 if (Limits.nodes && pos.nodes_searched() >= Limits.nodes)
570 || pos.is_draw<false>()
571 || ss->ply > MAX_PLY) && !RootNode)
574 // Step 3. Mate distance pruning. Even if we mate at the next move our score
575 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
576 // a shorter mate was found upward in the tree then there is no need to search
577 // further, we will never beat current alpha. Same logic but with reversed signs
578 // applies also in the opposite condition of being mated instead of giving mate,
579 // in this case return a fail-high score.
582 alpha = std::max(mated_in(ss->ply), alpha);
583 beta = std::min(mate_in(ss->ply+1), beta);
588 // Step 4. Transposition table lookup
589 // We don't want the score of a partial search to overwrite a previous full search
590 // TT value, so we use a different position key in case of an excluded move.
591 excludedMove = ss->excludedMove;
592 posKey = excludedMove ? pos.exclusion_key() : pos.key();
593 tte = TT.probe(posKey);
594 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
595 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_ZERO;
597 // At PV nodes we check for exact scores, while at non-PV nodes we check for
598 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
599 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
600 // we should also update RootMoveList to avoid bogus output.
601 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
602 : can_return_tt(tte, depth, ttValue, beta)))
605 ss->currentMove = ttMove; // Can be MOVE_NONE
609 && !pos.is_capture_or_promotion(ttMove)
610 && ttMove != ss->killers[0])
612 ss->killers[1] = ss->killers[0];
613 ss->killers[0] = ttMove;
618 // Step 5. Evaluate the position statically and update parent's gain statistics
620 ss->eval = ss->evalMargin = VALUE_NONE;
623 assert(tte->static_value() != VALUE_NONE);
625 ss->eval = tte->static_value();
626 ss->evalMargin = tte->static_value_margin();
627 refinedValue = refine_eval(tte, ttValue, ss->eval);
631 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
632 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
635 // Update gain for the parent non-capture move given the static position
636 // evaluation before and after the move.
637 if ( (move = (ss-1)->currentMove) != MOVE_NULL
638 && (ss-1)->eval != VALUE_NONE
639 && ss->eval != VALUE_NONE
640 && !pos.captured_piece_type()
641 && type_of(move) == NORMAL)
643 Square to = to_sq(move);
644 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
647 // Step 6. Razoring (is omitted in PV nodes)
649 && depth < RazorDepth
651 && refinedValue + razor_margin(depth) < beta
652 && ttMove == MOVE_NONE
653 && abs(beta) < VALUE_MATE_IN_MAX_PLY
654 && !pos.pawn_on_7th(pos.side_to_move()))
656 Value rbeta = beta - razor_margin(depth);
657 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
659 // Logically we should return (v + razor_margin(depth)), but
660 // surprisingly this did slightly weaker in tests.
664 // Step 7. Static null move pruning (is omitted in PV nodes)
665 // We're betting that the opponent doesn't have a move that will reduce
666 // the score by more than futility_margin(depth) if we do a null move.
669 && depth < RazorDepth
671 && refinedValue - futility_margin(depth, 0) >= beta
672 && abs(beta) < VALUE_MATE_IN_MAX_PLY
673 && pos.non_pawn_material(pos.side_to_move()))
674 return refinedValue - futility_margin(depth, 0);
676 // Step 8. Null move search with verification search (is omitted in PV nodes)
681 && refinedValue >= beta
682 && abs(beta) < VALUE_MATE_IN_MAX_PLY
683 && pos.non_pawn_material(pos.side_to_move()))
685 ss->currentMove = MOVE_NULL;
687 // Null move dynamic reduction based on depth
688 Depth R = 3 * ONE_PLY + depth / 4;
690 // Null move dynamic reduction based on value
691 if (refinedValue - PawnValueMg > beta)
694 pos.do_null_move<true>(st);
695 (ss+1)->skipNullMove = true;
696 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
697 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
698 (ss+1)->skipNullMove = false;
699 pos.do_null_move<false>(st);
701 if (nullValue >= beta)
703 // Do not return unproven mate scores
704 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
707 if (depth < 6 * ONE_PLY)
710 // Do verification search at high depths
711 ss->skipNullMove = true;
712 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
713 ss->skipNullMove = false;
720 // The null move failed low, which means that we may be faced with
721 // some kind of threat. If the previous move was reduced, check if
722 // the move that refuted the null move was somehow connected to the
723 // move which was reduced. If a connection is found, return a fail
724 // low score (which will cause the reduced move to fail high in the
725 // parent node, which will trigger a re-search with full depth).
726 threatMove = (ss+1)->currentMove;
728 if ( depth < ThreatDepth
730 && threatMove != MOVE_NONE
731 && connected_moves(pos, (ss-1)->currentMove, threatMove))
736 // Step 9. ProbCut (is omitted in PV nodes)
737 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
738 // and a reduced search returns a value much above beta, we can (almost) safely
739 // prune the previous move.
741 && depth >= RazorDepth + ONE_PLY
744 && excludedMove == MOVE_NONE
745 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
747 Value rbeta = beta + 200;
748 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
750 assert(rdepth >= ONE_PLY);
751 assert((ss-1)->currentMove != MOVE_NONE);
752 assert((ss-1)->currentMove != MOVE_NULL);
754 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
757 while ((move = mp.next_move<false>()) != MOVE_NONE)
758 if (pos.pl_move_is_legal(move, ci.pinned))
760 ss->currentMove = move;
761 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
762 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
769 // Step 10. Internal iterative deepening
770 if ( depth >= IIDDepth[PvNode]
771 && ttMove == MOVE_NONE
772 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
774 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
776 ss->skipNullMove = true;
777 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
778 ss->skipNullMove = false;
780 tte = TT.probe(posKey);
781 ttMove = tte ? tte->move() : MOVE_NONE;
784 split_point_start: // At split points actual search starts from here
786 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
788 futilityBase = ss->eval + ss->evalMargin;
789 singularExtensionNode = !RootNode
791 && depth >= SingularExtensionDepth[PvNode]
792 && ttMove != MOVE_NONE
793 && !excludedMove // Recursive singular search is not allowed
794 && (tte->type() & BOUND_LOWER)
795 && tte->depth() >= depth - 3 * ONE_PLY;
797 // Step 11. Loop through moves
798 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
799 while ( bestValue < beta
800 && (move = mp.next_move<SpNode>()) != MOVE_NONE
801 && !thisThread->cutoff_occurred()
806 if (move == excludedMove)
809 // At root obey the "searchmoves" option and skip moves not listed in Root
810 // Move List, as a consequence any illegal move is also skipped. In MultiPV
811 // mode we also skip PV moves which have been already searched.
812 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
815 // At PV and SpNode nodes we want all moves to be legal since the beginning
816 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
821 moveCount = ++sp->moveCount;
829 Signals.firstRootMove = (moveCount == 1);
831 if (thisThread == Threads.main_thread() && SearchTime.elapsed() > 2000)
832 cout << "info depth " << depth / ONE_PLY
833 << " currmove " << move_to_uci(move, Chess960)
834 << " currmovenumber " << moveCount + PVIdx << endl;
837 isPvMove = (PvNode && moveCount <= 1);
838 captureOrPromotion = pos.is_capture_or_promotion(move);
839 givesCheck = pos.move_gives_check(move, ci);
840 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
843 // Step 12. Extend checks and, in PV nodes, also dangerous moves
844 if (PvNode && dangerous)
847 else if (givesCheck && pos.see_sign(move) >= 0)
850 // Singular extension search. If all moves but one fail low on a search of
851 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
852 // is singular and should be extended. To verify this we do a reduced search
853 // on all the other moves but the ttMove, if result is lower than ttValue minus
854 // a margin then we extend ttMove.
855 if ( singularExtensionNode
858 && pos.pl_move_is_legal(move, ci.pinned)
859 && abs(ttValue) < VALUE_KNOWN_WIN)
861 Value rBeta = ttValue - int(depth);
862 ss->excludedMove = move;
863 ss->skipNullMove = true;
864 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
865 ss->skipNullMove = false;
866 ss->excludedMove = MOVE_NONE;
872 // Update current move (this must be done after singular extension search)
873 newDepth = depth - ONE_PLY + ext;
875 // Step 13. Futility pruning (is omitted in PV nodes)
877 && !captureOrPromotion
881 && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
883 // Move count based pruning
884 if ( moveCount >= futility_move_count(depth)
885 && (!threatMove || !connected_threat(pos, move, threatMove)))
893 // Value based pruning
894 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
895 // but fixing this made program slightly weaker.
896 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
897 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
898 + H.gain(pos.piece_moved(move), to_sq(move));
900 if (futilityValue < beta)
908 // Prune moves with negative SEE at low depths
909 if ( predictedDepth < 2 * ONE_PLY
910 && pos.see_sign(move) < 0)
919 // Check for legality only before to do the move
920 if (!pos.pl_move_is_legal(move, ci.pinned))
926 ss->currentMove = move;
927 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
928 movesSearched[playedMoveCount++] = move;
930 // Step 14. Make the move
931 pos.do_move(move, st, ci, givesCheck);
933 // Step 15. Reduced depth search (LMR). If the move fails high will be
934 // re-searched at full depth.
935 if ( depth > 3 * ONE_PLY
937 && !captureOrPromotion
939 && ss->killers[0] != move
940 && ss->killers[1] != move)
942 ss->reduction = reduction<PvNode>(depth, moveCount);
943 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
944 alpha = SpNode ? sp->alpha : alpha;
946 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
948 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
949 ss->reduction = DEPTH_ZERO;
952 doFullDepthSearch = !isPvMove;
954 // Step 16. Full depth search, when LMR is skipped or fails high
955 if (doFullDepthSearch)
957 alpha = SpNode ? sp->alpha : alpha;
958 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
959 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
962 // Only for PV nodes do a full PV search on the first move or after a fail
963 // high, in the latter case search only if value < beta, otherwise let the
964 // parent node to fail low with value <= alpha and to try another move.
965 if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
966 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
967 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
969 // Step 17. Undo move
972 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
974 // Step 18. Check for new best move
978 bestValue = sp->bestValue;
982 // Finished searching the move. If Signals.stop is true, the search
983 // was aborted because the user interrupted the search or because we
984 // ran out of time. In this case, the return value of the search cannot
985 // be trusted, and we don't update the best move and/or PV.
986 if (RootNode && !Signals.stop)
988 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
990 // PV move or new best move ?
991 if (isPvMove || value > alpha)
994 rm.extract_pv_from_tt(pos);
996 // We record how often the best move has been changed in each
997 // iteration. This information is used for time management: When
998 // the best move changes frequently, we allocate some more time.
999 if (!isPvMove && MultiPV == 1)
1003 // All other moves but the PV are set to the lowest value, this
1004 // is not a problem when sorting becuase sort is stable and move
1005 // position in the list is preserved, just the PV is pushed up.
1006 rm.score = -VALUE_INFINITE;
1010 if (value > bestValue)
1017 && value < beta) // We want always alpha < beta
1020 if (SpNode && !thisThread->cutoff_occurred())
1022 sp->bestValue = value;
1023 sp->bestMove = move;
1031 // Step 19. Check for split
1033 && depth >= Threads.min_split_depth()
1035 && Threads.available_slave_exists(thisThread)
1037 && !thisThread->cutoff_occurred())
1038 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1039 depth, threatMove, moveCount, &mp, NT);
1042 // Step 20. Check for mate and stalemate
1043 // All legal moves have been searched and if there are no legal moves, it
1044 // must be mate or stalemate. Note that we can have a false positive in
1045 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1046 // harmless because return value is discarded anyhow in the parent nodes.
1047 // If we are in a singular extension search then return a fail low score.
1049 return excludedMove ? oldAlpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1051 // If we have pruned all the moves without searching return a fail-low score
1052 if (bestValue == -VALUE_INFINITE)
1054 assert(!playedMoveCount);
1056 bestValue = oldAlpha;
1059 // Step 21. Update tables
1060 // Update transposition table entry, killers and history
1061 if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
1063 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1064 bt = bestValue <= oldAlpha ? BOUND_UPPER
1065 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1067 TT.store(posKey, value_to_tt(bestValue, ss->ply), bt, depth, move, ss->eval, ss->evalMargin);
1069 // Update killers and history for non capture cut-off moves
1070 if ( bestValue >= beta
1071 && !pos.is_capture_or_promotion(move)
1074 if (move != ss->killers[0])
1076 ss->killers[1] = ss->killers[0];
1077 ss->killers[0] = move;
1080 // Increase history value of the cut-off move
1081 Value bonus = Value(int(depth) * int(depth));
1082 H.add(pos.piece_moved(move), to_sq(move), bonus);
1084 // Decrease history of all the other played non-capture moves
1085 for (int i = 0; i < playedMoveCount - 1; i++)
1087 Move m = movesSearched[i];
1088 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1093 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1099 // qsearch() is the quiescence search function, which is called by the main
1100 // search function when the remaining depth is zero (or, to be more precise,
1101 // less than ONE_PLY).
1103 template <NodeType NT>
1104 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1106 const bool PvNode = (NT == PV);
1108 assert(NT == PV || NT == NonPV);
1109 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1110 assert((alpha == beta - 1) || PvNode);
1111 assert(depth <= DEPTH_ZERO);
1114 Move ttMove, move, bestMove;
1115 Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
1116 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1120 Value oldAlpha = alpha;
1122 ss->currentMove = bestMove = MOVE_NONE;
1123 ss->ply = (ss-1)->ply + 1;
1125 // Check for an instant draw or maximum ply reached
1126 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1129 // Decide whether or not to include checks, this fixes also the type of
1130 // TT entry depth that we are going to use. Note that in qsearch we use
1131 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1132 inCheck = pos.in_check();
1133 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1135 // Transposition table lookup. At PV nodes, we don't use the TT for
1136 // pruning, but only for move ordering.
1137 tte = TT.probe(pos.key());
1138 ttMove = (tte ? tte->move() : MOVE_NONE);
1139 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
1141 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1143 ss->currentMove = ttMove; // Can be MOVE_NONE
1147 // Evaluate the position statically
1150 bestValue = futilityBase = -VALUE_INFINITE;
1151 ss->eval = evalMargin = VALUE_NONE;
1152 enoughMaterial = false;
1158 assert(tte->static_value() != VALUE_NONE);
1160 evalMargin = tte->static_value_margin();
1161 ss->eval = bestValue = tte->static_value();
1164 ss->eval = bestValue = evaluate(pos, evalMargin);
1166 // Stand pat. Return immediately if static value is at least beta
1167 if (bestValue >= beta)
1170 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1175 if (PvNode && bestValue > alpha)
1178 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1179 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1182 // Initialize a MovePicker object for the current position, and prepare
1183 // to search the moves. Because the depth is <= 0 here, only captures,
1184 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1186 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1189 // Loop through the moves until no moves remain or a beta cutoff occurs
1190 while ( bestValue < beta
1191 && (move = mp.next_move<false>()) != MOVE_NONE)
1193 assert(is_ok(move));
1195 givesCheck = pos.move_gives_check(move, ci);
1203 && type_of(move) != PROMOTION
1204 && !pos.is_passed_pawn_push(move))
1206 futilityValue = futilityBase
1207 + PieceValue[Eg][pos.piece_on(to_sq(move))]
1208 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1210 if (futilityValue < beta)
1212 if (futilityValue > bestValue)
1213 bestValue = futilityValue;
1218 // Prune moves with negative or equal SEE
1219 if ( futilityBase < beta
1220 && depth < DEPTH_ZERO
1221 && pos.see(move) <= 0)
1225 // Detect non-capture evasions that are candidate to be pruned
1226 evasionPrunable = !PvNode
1228 && bestValue > VALUE_MATED_IN_MAX_PLY
1229 && !pos.is_capture(move)
1230 && !pos.can_castle(pos.side_to_move());
1232 // Don't search moves with negative SEE values
1234 && (!inCheck || evasionPrunable)
1236 && type_of(move) != PROMOTION
1237 && pos.see_sign(move) < 0)
1240 // Don't search useless checks
1245 && !pos.is_capture_or_promotion(move)
1246 && ss->eval + PawnValueMg / 4 < beta
1247 && !check_is_dangerous(pos, move, futilityBase, beta))
1250 // Check for legality only before to do the move
1251 if (!pos.pl_move_is_legal(move, ci.pinned))
1254 ss->currentMove = move;
1256 // Make and search the move
1257 pos.do_move(move, st, ci, givesCheck);
1258 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1259 pos.undo_move(move);
1261 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1264 if (value > bestValue)
1271 && value < beta) // We want always alpha < beta
1276 // All legal moves have been searched. A special case: If we're in check
1277 // and no legal moves were found, it is checkmate.
1278 if (inCheck && bestValue == -VALUE_INFINITE)
1279 return mated_in(ss->ply); // Plies to mate from the root
1281 // Update transposition table
1282 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1283 bt = bestValue <= oldAlpha ? BOUND_UPPER
1284 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1286 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
1288 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1294 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1295 // bestValue is updated only when returning false because in that case move
1298 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1300 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1301 Square from, to, ksq;
1305 from = from_sq(move);
1307 them = ~pos.side_to_move();
1308 ksq = pos.king_square(them);
1309 kingAtt = pos.attacks_from<KING>(ksq);
1310 pc = pos.piece_moved(move);
1312 occ = pos.pieces() ^ from ^ ksq;
1313 oldAtt = pos.attacks_from(pc, from, occ);
1314 newAtt = pos.attacks_from(pc, to, occ);
1316 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1317 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1319 if (!more_than_one(b))
1322 // Rule 2. Queen contact check is very dangerous
1323 if (type_of(pc) == QUEEN && (kingAtt & to))
1326 // Rule 3. Creating new double threats with checks
1327 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1330 // Note that here we generate illegal "double move"!
1331 if (futilityBase + PieceValue[Eg][pos.piece_on(pop_lsb(&b))] >= beta)
1339 // connected_moves() tests whether two moves are 'connected' in the sense
1340 // that the first move somehow made the second move possible (for instance
1341 // if the moving piece is the same in both moves). The first move is assumed
1342 // to be the move that was made to reach the current position, while the
1343 // second move is assumed to be a move from the current position.
1345 bool connected_moves(const Position& pos, Move m1, Move m2) {
1347 Square f1, t1, f2, t2;
1354 // Case 1: The moving piece is the same in both moves
1360 // Case 2: The destination square for m2 was vacated by m1
1366 // Case 3: Moving through the vacated square
1367 p2 = pos.piece_on(f2);
1368 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1371 // Case 4: The destination square for m2 is defended by the moving piece in m1
1372 p1 = pos.piece_on(t1);
1373 if (pos.attacks_from(p1, t1) & t2)
1376 // Case 5: Discovered check, checking piece is the piece moved in m1
1377 ksq = pos.king_square(pos.side_to_move());
1378 if ( piece_is_slider(p1)
1379 && (between_bb(t1, ksq) & f2)
1380 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1387 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1388 // "plies to mate from the current position". Non-mate scores are unchanged.
1389 // The function is called before storing a value to the transposition table.
1391 Value value_to_tt(Value v, int ply) {
1393 if (v >= VALUE_MATE_IN_MAX_PLY)
1396 if (v <= VALUE_MATED_IN_MAX_PLY)
1403 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1404 // from the transposition table (where refers to the plies to mate/be mated
1405 // from current position) to "plies to mate/be mated from the root".
1407 Value value_from_tt(Value v, int ply) {
1409 if (v >= VALUE_MATE_IN_MAX_PLY)
1412 if (v <= VALUE_MATED_IN_MAX_PLY)
1419 // connected_threat() tests whether it is safe to forward prune a move or if
1420 // is somehow connected to the threat move returned by null search.
1422 bool connected_threat(const Position& pos, Move m, Move threat) {
1425 assert(is_ok(threat));
1426 assert(!pos.is_capture_or_promotion(m));
1427 assert(!pos.is_passed_pawn_push(m));
1429 Square mfrom, mto, tfrom, tto;
1433 tfrom = from_sq(threat);
1434 tto = to_sq(threat);
1436 // Case 1: Don't prune moves which move the threatened piece
1440 // Case 2: If the threatened piece has value less than or equal to the
1441 // value of the threatening piece, don't prune moves which defend it.
1442 if ( pos.is_capture(threat)
1443 && ( PieceValue[Mg][pos.piece_on(tfrom)] >= PieceValue[Mg][pos.piece_on(tto)]
1444 || type_of(pos.piece_on(tfrom)) == KING)
1445 && pos.move_attacks_square(m, tto))
1448 // Case 3: If the moving piece in the threatened move is a slider, don't
1449 // prune safe moves which block its ray.
1450 if ( piece_is_slider(pos.piece_on(tfrom))
1451 && (between_bb(tfrom, tto) & mto)
1452 && pos.see_sign(m) >= 0)
1459 // can_return_tt() returns true if a transposition table score can be used to
1460 // cut-off at a given point in search.
1462 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1464 return ( tte->depth() >= depth
1465 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1466 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1468 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1469 || ((tte->type() & BOUND_UPPER) && v < beta));
1473 // refine_eval() returns the transposition table score if possible, otherwise
1474 // falls back on static position evaluation.
1476 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1480 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1481 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1488 // When playing with strength handicap choose best move among the MultiPV set
1489 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1491 Move do_skill_level() {
1493 assert(MultiPV > 1);
1497 // PRNG sequence should be not deterministic
1498 for (int i = Time::current_time().msec() % 50; i > 0; i--)
1499 rk.rand<unsigned>();
1501 // RootMoves are already sorted by score in descending order
1502 size_t size = std::min(MultiPV, RootMoves.size());
1503 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1504 int weakness = 120 - 2 * SkillLevel;
1505 int max_s = -VALUE_INFINITE;
1506 Move best = MOVE_NONE;
1508 // Choose best move. For each move score we add two terms both dependent on
1509 // weakness, one deterministic and bigger for weaker moves, and one random,
1510 // then we choose the move with the resulting highest score.
1511 for (size_t i = 0; i < size; i++)
1513 int s = RootMoves[i].score;
1515 // Don't allow crazy blunders even at very low skills
1516 if (i > 0 && RootMoves[i-1].score > s + EasyMoveMargin)
1519 // This is our magic formula
1520 s += ( weakness * int(RootMoves[0].score - s)
1521 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1526 best = RootMoves[i].pv[0];
1533 // uci_pv() formats PV information according to UCI protocol. UCI requires
1534 // to send all the PV lines also if are still to be searched and so refer to
1535 // the previous search score.
1537 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1539 std::stringstream s;
1540 int t = SearchTime.elapsed();
1543 for (size_t i = 0; i < Threads.size(); i++)
1544 if (Threads[i].maxPly > selDepth)
1545 selDepth = Threads[i].maxPly;
1547 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1549 bool updated = (i <= PVIdx);
1551 if (depth == 1 && !updated)
1554 int d = (updated ? depth : depth - 1);
1555 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1557 if (s.rdbuf()->in_avail())
1560 s << "info depth " << d
1561 << " seldepth " << selDepth
1562 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1563 << " nodes " << pos.nodes_searched()
1564 << " nps " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
1566 << " multipv " << i + 1
1569 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1570 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1579 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1580 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1581 /// allow to always have a ponder move even when we fail high at root, and a
1582 /// long PV to print that is important for position analysis.
1584 void RootMove::extract_pv_from_tt(Position& pos) {
1586 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1591 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1595 pos.do_move(m, *st++);
1597 while ( (tte = TT.probe(pos.key())) != NULL
1598 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1599 && pos.is_pseudo_legal(m)
1600 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1602 && (!pos.is_draw<false>() || ply < 2))
1605 pos.do_move(m, *st++);
1608 pv.push_back(MOVE_NONE);
1610 do pos.undo_move(pv[--ply]); while (ply);
1614 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1615 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1616 /// first, even if the old TT entries have been overwritten.
1618 void RootMove::insert_pv_in_tt(Position& pos) {
1620 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1623 Value v, m = VALUE_NONE;
1626 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1632 // Don't overwrite existing correct entries
1633 if (!tte || tte->move() != pv[ply])
1635 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1636 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1638 pos.do_move(pv[ply], *st++);
1640 } while (pv[++ply] != MOVE_NONE);
1642 do pos.undo_move(pv[--ply]); while (ply);
1646 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1648 void Thread::idle_loop() {
1650 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1651 // object for which the thread is the master.
1652 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1654 assert(!sp_master || (sp_master->master == this && is_searching));
1656 // If this thread is the master of a split point and all slaves have
1657 // finished their work at this split point, return from the idle loop.
1658 while (!sp_master || sp_master->slavesMask)
1660 // If we are not searching, wait for a condition to be signaled
1661 // instead of wasting CPU time polling for work.
1664 || (!is_searching && Threads.use_sleeping_threads()))
1672 // Grab the lock to avoid races with Thread::wake_up()
1675 // If we are master and all slaves have finished don't go to sleep
1676 if (sp_master && !sp_master->slavesMask)
1682 // Do sleep after retesting sleep conditions under lock protection, in
1683 // particular we need to avoid a deadlock in case a master thread has,
1684 // in the meanwhile, allocated us and sent the wake_up() call before we
1685 // had the chance to grab the lock.
1686 if (do_sleep || !is_searching)
1687 sleepCondition.wait(mutex);
1692 // If this thread has been assigned work, launch a search
1695 assert(!do_sleep && !do_exit);
1697 Threads.mutex.lock();
1699 assert(is_searching);
1700 SplitPoint* sp = curSplitPoint;
1702 Threads.mutex.unlock();
1704 Stack ss[MAX_PLY_PLUS_2];
1705 Position pos(*sp->pos, this);
1707 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1712 if (sp->nodeType == Root)
1713 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1714 else if (sp->nodeType == PV)
1715 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1716 else if (sp->nodeType == NonPV)
1717 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1721 assert(is_searching);
1723 is_searching = false;
1724 sp->slavesMask &= ~(1ULL << idx);
1725 sp->nodes += pos.nodes_searched();
1727 // Wake up master thread so to allow it to return from the idle loop in
1728 // case we are the last slave of the split point.
1729 if ( Threads.use_sleeping_threads()
1730 && this != sp->master
1733 assert(!sp->master->is_searching);
1734 sp->master->wake_up();
1737 // After releasing the lock we cannot access anymore any SplitPoint
1738 // related data in a safe way becuase it could have been released under
1739 // our feet by the sp master. Also accessing other Thread objects is
1740 // unsafe because if we are exiting there is a chance are already freed.
1747 /// check_time() is called by the timer thread when the timer triggers. It is
1748 /// used to print debug info and, more important, to detect when we are out of
1749 /// available time and so stop the search.
1753 static Time lastInfoTime = Time::current_time();
1755 if (lastInfoTime.elapsed() >= 1000)
1757 lastInfoTime.restart();
1764 int e = SearchTime.elapsed();
1765 bool stillAtFirstMove = Signals.firstRootMove
1766 && !Signals.failedLowAtRoot
1767 && e > TimeMgr.available_time();
1769 bool noMoreTime = e > TimeMgr.maximum_time() - 2 * TimerResolution
1770 || stillAtFirstMove;
1772 if ( (Limits.use_time_management() && noMoreTime)
1773 || (Limits.movetime && e >= Limits.movetime))
1774 Signals.stop = true;