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;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // This is the minimum interval in msec between two check_time() calls
59 const int TimerResolution = 5;
61 // Different node types, used as template parameter
62 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
64 // Lookup table to check if a Piece is a slider and its access function
65 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
66 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
68 // Dynamic razoring margin based on depth
69 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
71 // Futility lookup tables (initialized at startup) and their access functions
72 Value FutilityMargins[16][64]; // [depth][moveNumber]
73 int FutilityMoveCounts[32]; // [depth]
75 inline Value futility_margin(Depth d, int mn) {
77 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
81 // Reduction lookup tables (initialized at startup) and their access function
82 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
84 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
86 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
89 size_t MultiPV, UCIMultiPV, PVIdx;
93 bool SkillLevelEnabled, Chess960;
96 template <NodeType NT>
97 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
99 template <NodeType NT>
100 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
102 void id_loop(Position& pos);
103 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
104 bool connected_moves(const Position& pos, Move m1, Move m2);
105 Value value_to_tt(Value v, int ply);
106 Value value_from_tt(Value v, int ply);
107 bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);
108 bool connected_threat(const Position& pos, Move m, Move threat);
109 Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
110 Move do_skill_level();
111 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
113 // is_dangerous() checks whether a move belongs to some classes of known
114 // 'dangerous' moves so that we avoid to prune it.
115 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
118 if (type_of(m) == CASTLE)
122 if ( type_of(pos.piece_moved(m)) == PAWN
123 && pos.pawn_is_passed(pos.side_to_move(), to_sq(m)))
126 // Entering a pawn endgame?
127 if ( captureOrPromotion
128 && type_of(pos.piece_on(to_sq(m))) != PAWN
129 && type_of(m) == NORMAL
130 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
131 - PieceValue[Mg][pos.piece_on(to_sq(m))] == VALUE_ZERO))
140 /// Search::init() is called during startup to initialize various lookup tables
142 void Search::init() {
144 int d; // depth (ONE_PLY == 2)
145 int hd; // half depth (ONE_PLY == 1)
148 // Init reductions array
149 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
151 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
152 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
153 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
154 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
157 // Init futility margins array
158 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
159 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
161 // Init futility move count array
162 for (d = 0; d < 32; d++)
163 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
167 /// Search::perft() is our utility to verify move generation. All the leaf nodes
168 /// up to the given depth are generated and counted and the sum returned.
170 size_t Search::perft(Position& pos, Depth depth) {
172 // At the last ply just return the number of legal moves (leaf nodes)
173 if (depth == ONE_PLY)
174 return MoveList<LEGAL>(pos).size();
180 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
182 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
183 cnt += perft(pos, depth - ONE_PLY);
184 pos.undo_move(ml.move());
191 /// Search::think() is the external interface to Stockfish's search, and is
192 /// called by the main thread when the program receives the UCI 'go' command. It
193 /// searches from RootPosition and at the end prints the "bestmove" to output.
195 void Search::think() {
197 static PolyglotBook book; // Defined static to initialize the PRNG only once
199 Position& pos = RootPosition;
200 Chess960 = pos.is_chess960();
201 Eval::RootColor = pos.side_to_move();
202 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
206 if (RootMoves.empty())
208 sync_cout << "info depth 0 score "
209 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
211 RootMoves.push_back(MOVE_NONE);
215 if (Options["OwnBook"] && !Limits.infinite)
217 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
219 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
221 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
226 UCIMultiPV = Options["MultiPV"];
227 SkillLevel = Options["Skill Level"];
229 // Do we have to play with skill handicap? In this case enable MultiPV that
230 // we will use behind the scenes to retrieve a set of possible moves.
231 SkillLevelEnabled = (SkillLevel < 20);
232 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
234 if (Options["Use Search Log"])
236 Log log(Options["Search Log Filename"]);
237 log << "\nSearching: " << pos.to_fen()
238 << "\ninfinite: " << Limits.infinite
239 << " ponder: " << Limits.ponder
240 << " time: " << Limits.time[pos.side_to_move()]
241 << " increment: " << Limits.inc[pos.side_to_move()]
242 << " moves to go: " << Limits.movestogo
248 // Set best timer interval to avoid lagging under time pressure. Timer is
249 // used to check for remaining available thinking time.
250 if (Limits.use_time_management())
251 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
252 else if (Limits.nodes)
253 Threads.set_timer(2 * TimerResolution);
255 Threads.set_timer(100);
257 // We're ready to start searching. Call the iterative deepening loop function
260 Threads.set_timer(0); // Stop timer
263 if (Options["Use Search Log"])
265 Time::point elapsed = Time::now() - SearchTime + 1;
267 Log log(Options["Search Log Filename"]);
268 log << "Nodes: " << pos.nodes_searched()
269 << "\nNodes/second: " << pos.nodes_searched() * 1000 / elapsed
270 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
273 pos.do_move(RootMoves[0].pv[0], st);
274 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << std::endl;
275 pos.undo_move(RootMoves[0].pv[0]);
280 // When we reach max depth we arrive here even without Signals.stop is raised,
281 // but if we are pondering or in infinite search, we shouldn't print the best
282 // move before we are told to do so.
283 if (!Signals.stop && (Limits.ponder || Limits.infinite))
284 pos.this_thread()->wait_for_stop_or_ponderhit();
286 // Best move could be MOVE_NONE when searching on a stalemate position
287 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
288 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << sync_endl;
294 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
295 // with increasing depth until the allocated thinking time has been consumed,
296 // user stops the search, or the maximum search depth is reached.
298 void id_loop(Position& pos) {
300 Stack ss[MAX_PLY_PLUS_2];
301 int depth, prevBestMoveChanges;
302 Value bestValue, alpha, beta, delta;
303 bool bestMoveNeverChanged = true;
304 Move skillBest = MOVE_NONE;
306 memset(ss, 0, 4 * sizeof(Stack));
307 depth = BestMoveChanges = 0;
308 bestValue = delta = -VALUE_INFINITE;
309 ss->currentMove = MOVE_NULL; // Hack to skip update gains
311 // Iterative deepening loop until requested to stop or target depth reached
312 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
314 // Save last iteration's scores before first PV line is searched and all
315 // the move scores but the (new) PV are set to -VALUE_INFINITE.
316 for (size_t i = 0; i < RootMoves.size(); i++)
317 RootMoves[i].prevScore = RootMoves[i].score;
319 prevBestMoveChanges = BestMoveChanges;
322 // MultiPV loop. We perform a full root search for each PV line
323 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
325 // Set aspiration window default width
326 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
329 alpha = RootMoves[PVIdx].prevScore - delta;
330 beta = RootMoves[PVIdx].prevScore + delta;
334 alpha = -VALUE_INFINITE;
335 beta = VALUE_INFINITE;
338 // Start with a small aspiration window and, in case of fail high/low,
339 // research with bigger window until not failing high/low anymore.
342 // Search starts from ss+1 to allow referencing (ss-1). This is
343 // needed by update gains and ss copy when splitting at Root.
344 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
346 // Bring to front the best move. It is critical that sorting is
347 // done with a stable algorithm because all the values but the first
348 // and eventually the new best one are set to -VALUE_INFINITE and
349 // we want to keep the same order for all the moves but the new
350 // PV that goes to the front. Note that in case of MultiPV search
351 // the already searched PV lines are preserved.
352 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
354 // In case we have found an exact score and we are going to leave
355 // the fail high/low loop then reorder the PV moves, otherwise
356 // leave the last PV move in its position so to be searched again.
357 // Of course this is needed only in MultiPV search.
358 if (PVIdx && bestValue > alpha && bestValue < beta)
359 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
361 // Write PV back to transposition table in case the relevant
362 // entries have been overwritten during the search.
363 for (size_t i = 0; i <= PVIdx; i++)
364 RootMoves[i].insert_pv_in_tt(pos);
366 // If search has been stopped exit the aspiration window loop.
367 // Sorting and writing PV back to TT is safe becuase RootMoves
368 // is still valid, although refers to previous iteration.
372 // Send full PV info to GUI if we are going to leave the loop or
373 // if we have a fail high/low and we are deep in the search.
374 if ((bestValue > alpha && bestValue < beta) || Time::now() - SearchTime > 2000)
375 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
377 // In case of failing high/low increase aspiration window and
378 // research, otherwise exit the fail high/low loop.
379 if (bestValue >= beta)
384 else if (bestValue <= alpha)
386 Signals.failedLowAtRoot = true;
387 Signals.stopOnPonderhit = false;
395 // Search with full window in case we have a win/mate score
396 if (abs(bestValue) >= VALUE_KNOWN_WIN)
398 alpha = -VALUE_INFINITE;
399 beta = VALUE_INFINITE;
402 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
406 // Skills: Do we need to pick now the best move ?
407 if (SkillLevelEnabled && depth == 1 + SkillLevel)
408 skillBest = do_skill_level();
410 if (!Signals.stop && Options["Use Search Log"])
412 Log log(Options["Search Log Filename"]);
413 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
417 // Filter out startup noise when monitoring best move stability
418 if (depth > 2 && BestMoveChanges)
419 bestMoveNeverChanged = false;
421 // Do we have time for the next iteration? Can we stop searching now?
422 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
424 bool stop = false; // Local variable, not the volatile Signals.stop
426 // Take in account some extra time if the best move has changed
427 if (depth > 4 && depth < 50)
428 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
430 // Stop search if most of available time is already consumed. We
431 // probably don't have enough time to search the first move at the
432 // next iteration anyway.
433 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
436 // Stop search early if one move seems to be much better than others
439 && ( (bestMoveNeverChanged && pos.captured_piece_type())
440 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
442 Value rBeta = bestValue - 2 * PawnValueMg;
443 (ss+1)->excludedMove = RootMoves[0].pv[0];
444 (ss+1)->skipNullMove = true;
445 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
446 (ss+1)->skipNullMove = false;
447 (ss+1)->excludedMove = MOVE_NONE;
455 // If we are allowed to ponder do not stop the search now but
456 // keep pondering until GUI sends "ponderhit" or "stop".
458 Signals.stopOnPonderhit = true;
465 // When using skills swap best PV line with the sub-optimal one
466 if (SkillLevelEnabled)
468 if (skillBest == MOVE_NONE) // Still unassigned ?
469 skillBest = do_skill_level();
471 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
476 // search<>() is the main search function for both PV and non-PV nodes and for
477 // normal and SplitPoint nodes. When called just after a split point the search
478 // is simpler because we have already probed the hash table, done a null move
479 // search, and searched the first move before splitting, we don't have to repeat
480 // all this work again. We also don't need to store anything to the hash table
481 // here: This is taken care of after we return from the split point.
483 template <NodeType NT>
484 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
486 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
487 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
488 const bool RootNode = (NT == Root || NT == SplitPointRoot);
490 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
491 assert(PvNode || (alpha == beta - 1));
492 assert(depth > DEPTH_ZERO);
494 Move movesSearched[64];
499 Move ttMove, move, excludedMove, bestMove, threatMove;
501 Value bestValue, value, ttValue;
502 Value refinedValue, nullValue, futilityValue;
503 bool pvMove, inCheck, singularExtensionNode, givesCheck;
504 bool captureOrPromotion, dangerous, doFullDepthSearch;
505 int moveCount, playedMoveCount;
507 // Step 1. Initialize node
508 Thread* thisThread = pos.this_thread();
509 moveCount = playedMoveCount = 0;
510 inCheck = pos.in_check();
515 bestMove = sp->bestMove;
516 threatMove = sp->threatMove;
517 bestValue = sp->bestValue;
519 ttMove = excludedMove = MOVE_NONE;
520 ttValue = VALUE_NONE;
522 assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);
524 goto split_point_start;
527 bestValue = -VALUE_INFINITE;
528 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
529 ss->ply = (ss-1)->ply + 1;
530 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
531 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
533 // Used to send selDepth info to GUI
534 if (PvNode && thisThread->maxPly < ss->ply)
535 thisThread->maxPly = ss->ply;
539 // Step 2. Check for aborted search and immediate draw
540 if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
541 return Eval::ValueDrawContempt;
543 // Step 3. Mate distance pruning. Even if we mate at the next move our score
544 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
545 // a shorter mate was found upward in the tree then there is no need to search
546 // further, we will never beat current alpha. Same logic but with reversed signs
547 // applies also in the opposite condition of being mated instead of giving mate,
548 // in this case return a fail-high score.
549 alpha = std::max(mated_in(ss->ply), alpha);
550 beta = std::min(mate_in(ss->ply+1), beta);
555 // Step 4. Transposition table lookup
556 // We don't want the score of a partial search to overwrite a previous full search
557 // TT value, so we use a different position key in case of an excluded move.
558 excludedMove = ss->excludedMove;
559 posKey = excludedMove ? pos.exclusion_key() : pos.key();
560 tte = TT.probe(posKey);
561 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
562 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
564 // At PV nodes we check for exact scores, while at non-PV nodes we check for
565 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
566 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
567 // we should also update RootMoveList to avoid bogus output.
568 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
569 : can_return_tt(tte, depth, ttValue, beta)))
572 ss->currentMove = ttMove; // Can be MOVE_NONE
576 && !pos.is_capture_or_promotion(ttMove)
577 && ttMove != ss->killers[0])
579 ss->killers[1] = ss->killers[0];
580 ss->killers[0] = ttMove;
585 // Step 5. Evaluate the position statically and update parent's gain statistics
587 ss->eval = ss->evalMargin = refinedValue = VALUE_NONE;
590 assert(tte->static_value() != VALUE_NONE);
592 ss->eval = tte->static_value();
593 ss->evalMargin = tte->static_value_margin();
594 refinedValue = refine_eval(tte, ttValue, ss->eval);
598 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
599 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
602 // Update gain for the parent non-capture move given the static position
603 // evaluation before and after the move.
604 if ( (move = (ss-1)->currentMove) != MOVE_NULL
605 && (ss-1)->eval != VALUE_NONE
606 && ss->eval != VALUE_NONE
607 && !pos.captured_piece_type()
608 && type_of(move) == NORMAL)
610 Square to = to_sq(move);
611 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
614 // Step 6. Razoring (is omitted in PV nodes)
616 && depth < 4 * ONE_PLY
618 && refinedValue + razor_margin(depth) < beta
619 && ttMove == MOVE_NONE
620 && abs(beta) < VALUE_MATE_IN_MAX_PLY
621 && !pos.pawn_on_7th(pos.side_to_move()))
623 Value rbeta = beta - razor_margin(depth);
624 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
626 // Logically we should return (v + razor_margin(depth)), but
627 // surprisingly this did slightly weaker in tests.
631 // Step 7. Static null move pruning (is omitted in PV nodes)
632 // We're betting that the opponent doesn't have a move that will reduce
633 // the score by more than futility_margin(depth) if we do a null move.
636 && depth < 4 * ONE_PLY
638 && refinedValue - FutilityMargins[depth][0] >= beta
639 && abs(beta) < VALUE_MATE_IN_MAX_PLY
640 && pos.non_pawn_material(pos.side_to_move()))
641 return refinedValue - FutilityMargins[depth][0];
643 // Step 8. Null move search with verification search (is omitted in PV nodes)
648 && refinedValue >= beta
649 && abs(beta) < VALUE_MATE_IN_MAX_PLY
650 && pos.non_pawn_material(pos.side_to_move()))
652 ss->currentMove = MOVE_NULL;
654 // Null move dynamic reduction based on depth
655 Depth R = 3 * ONE_PLY + depth / 4;
657 // Null move dynamic reduction based on value
658 if (refinedValue - PawnValueMg > beta)
661 pos.do_null_move<true>(st);
662 (ss+1)->skipNullMove = true;
663 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
664 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
665 (ss+1)->skipNullMove = false;
666 pos.do_null_move<false>(st);
668 if (nullValue >= beta)
670 // Do not return unproven mate scores
671 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
674 if (depth < 6 * ONE_PLY)
677 // Do verification search at high depths
678 ss->skipNullMove = true;
679 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
680 ss->skipNullMove = false;
687 // The null move failed low, which means that we may be faced with
688 // some kind of threat. If the previous move was reduced, check if
689 // the move that refuted the null move was somehow connected to the
690 // move which was reduced. If a connection is found, return a fail
691 // low score (which will cause the reduced move to fail high in the
692 // parent node, which will trigger a re-search with full depth).
693 threatMove = (ss+1)->currentMove;
695 if ( depth < 5 * ONE_PLY
697 && threatMove != MOVE_NONE
698 && connected_moves(pos, (ss-1)->currentMove, threatMove))
703 // Step 9. ProbCut (is omitted in PV nodes)
704 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
705 // and a reduced search returns a value much above beta, we can (almost) safely
706 // prune the previous move.
708 && depth >= 5 * ONE_PLY
711 && excludedMove == MOVE_NONE
712 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
714 Value rbeta = beta + 200;
715 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
717 assert(rdepth >= ONE_PLY);
718 assert((ss-1)->currentMove != MOVE_NONE);
719 assert((ss-1)->currentMove != MOVE_NULL);
721 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
724 while ((move = mp.next_move<false>()) != MOVE_NONE)
725 if (pos.pl_move_is_legal(move, ci.pinned))
727 ss->currentMove = move;
728 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
729 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
736 // Step 10. Internal iterative deepening
737 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
738 && ttMove == MOVE_NONE
739 && (PvNode || (!inCheck && ss->eval + Value(256) >= beta)))
741 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
743 ss->skipNullMove = true;
744 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
745 ss->skipNullMove = false;
747 tte = TT.probe(posKey);
748 ttMove = tte ? tte->move() : MOVE_NONE;
751 split_point_start: // At split points actual search starts from here
753 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
755 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
756 singularExtensionNode = !RootNode
758 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
759 && ttMove != MOVE_NONE
760 && !excludedMove // Recursive singular search is not allowed
761 && (tte->type() & BOUND_LOWER)
762 && tte->depth() >= depth - 3 * ONE_PLY;
764 // Step 11. Loop through moves
765 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
766 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
770 if (move == excludedMove)
773 // At root obey the "searchmoves" option and skip moves not listed in Root
774 // Move List, as a consequence any illegal move is also skipped. In MultiPV
775 // mode we also skip PV moves which have been already searched.
776 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
781 // Shared counter cannot be decremented later if move turns out to be illegal
782 if (!pos.pl_move_is_legal(move, ci.pinned))
785 moveCount = ++sp->moveCount;
793 Signals.firstRootMove = (moveCount == 1);
795 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
796 sync_cout << "info depth " << depth / ONE_PLY
797 << " currmove " << move_to_uci(move, Chess960)
798 << " currmovenumber " << moveCount + PVIdx << sync_endl;
801 captureOrPromotion = pos.is_capture_or_promotion(move);
802 givesCheck = pos.move_gives_check(move, ci);
803 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
806 // Step 12. Extend checks and, in PV nodes, also dangerous moves
807 if (PvNode && dangerous)
810 else if (givesCheck && pos.see_sign(move) >= 0)
813 // Singular extension search. If all moves but one fail low on a search of
814 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
815 // is singular and should be extended. To verify this we do a reduced search
816 // on all the other moves but the ttMove, if result is lower than ttValue minus
817 // a margin then we extend ttMove.
818 if ( singularExtensionNode
821 && pos.pl_move_is_legal(move, ci.pinned)
822 && abs(ttValue) < VALUE_KNOWN_WIN)
824 Value rBeta = ttValue - int(depth);
825 ss->excludedMove = move;
826 ss->skipNullMove = true;
827 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
828 ss->skipNullMove = false;
829 ss->excludedMove = MOVE_NONE;
832 ext = rBeta >= beta ? ONE_PLY + ONE_PLY / 2 : ONE_PLY;
835 // Update current move (this must be done after singular extension search)
836 newDepth = depth - ONE_PLY + ext;
838 // Step 13. Futility pruning (is omitted in PV nodes)
840 && !captureOrPromotion
844 && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
846 // Move count based pruning
847 if ( depth < 16 * ONE_PLY
848 && moveCount >= FutilityMoveCounts[depth]
849 && (!threatMove || !connected_threat(pos, move, threatMove)))
857 // Value based pruning
858 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
859 // but fixing this made program slightly weaker.
860 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
861 futilityValue = ss->eval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
862 + H.gain(pos.piece_moved(move), to_sq(move));
864 if (futilityValue < beta)
872 // Prune moves with negative SEE at low depths
873 if ( predictedDepth < 2 * ONE_PLY
874 && pos.see_sign(move) < 0)
883 // Check for legality only before to do the move
884 if (!pos.pl_move_is_legal(move, ci.pinned))
890 pvMove = PvNode ? moveCount == 1 : false;
891 ss->currentMove = move;
892 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
893 movesSearched[playedMoveCount++] = move;
895 // Step 14. Make the move
896 pos.do_move(move, st, ci, givesCheck);
898 // Step 15. Reduced depth search (LMR). If the move fails high will be
899 // re-searched at full depth.
900 if ( depth > 3 * ONE_PLY
902 && !captureOrPromotion
904 && ss->killers[0] != move
905 && ss->killers[1] != move)
907 ss->reduction = reduction<PvNode>(depth, moveCount);
908 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
909 alpha = SpNode ? sp->alpha : alpha;
911 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
913 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
914 ss->reduction = DEPTH_ZERO;
917 doFullDepthSearch = !pvMove;
919 // Step 16. Full depth search, when LMR is skipped or fails high
920 if (doFullDepthSearch)
922 alpha = SpNode ? sp->alpha : alpha;
923 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
924 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
927 // Only for PV nodes do a full PV search on the first move or after a fail
928 // high, in the latter case search only if value < beta, otherwise let the
929 // parent node to fail low with value <= alpha and to try another move.
930 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
931 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
932 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
934 // Step 17. Undo move
937 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
939 // Step 18. Check for new best move
943 bestValue = sp->bestValue;
947 // Finished searching the move. If Signals.stop is true, the search
948 // was aborted because the user interrupted the search or because we
949 // ran out of time. In this case, the return value of the search cannot
950 // be trusted, and we don't update the best move and/or PV.
951 if (Signals.stop || thisThread->cutoff_occurred())
956 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
958 // PV move or new best move ?
959 if (pvMove || value > alpha)
962 rm.extract_pv_from_tt(pos);
964 // We record how often the best move has been changed in each
965 // iteration. This information is used for time management: When
966 // the best move changes frequently, we allocate some more time.
967 if (!pvMove && MultiPV == 1)
971 // All other moves but the PV are set to the lowest value, this
972 // is not a problem when sorting becuase sort is stable and move
973 // position in the list is preserved, just the PV is pushed up.
974 rm.score = -VALUE_INFINITE;
977 if (value > bestValue)
980 if (SpNode) sp->bestValue = value;
985 if (SpNode) sp->bestMove = move;
987 if (PvNode && value < beta)
989 alpha = value; // Update alpha here! Always alpha < beta
990 if (SpNode) sp->alpha = alpha;
994 if (SpNode) sp->cutoff = true;
1000 // Step 19. Check for splitting the search
1002 && depth >= Threads.min_split_depth()
1004 && Threads.available_slave_exists(thisThread))
1006 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1007 depth, threatMove, moveCount, mp, NT);
1015 // Step 20. Check for mate and stalemate
1016 // All legal moves have been searched and if there are no legal moves, it
1017 // must be mate or stalemate. Note that we can have a false positive in
1018 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1019 // harmless because return value is discarded anyhow in the parent nodes.
1020 // If we are in a singular extension search then return a fail low score.
1021 // A split node has at least one move, the one tried before to be splitted.
1023 return excludedMove ? alpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1025 // If we have pruned all the moves without searching return a fail-low score
1026 if (bestValue == -VALUE_INFINITE)
1028 assert(!playedMoveCount);
1033 if (bestValue >= beta) // Failed high
1035 TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
1036 bestMove, ss->eval, ss->evalMargin);
1038 if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
1040 if (bestMove != ss->killers[0])
1042 ss->killers[1] = ss->killers[0];
1043 ss->killers[0] = bestMove;
1046 // Increase history value of the cut-off move
1047 Value bonus = Value(int(depth) * int(depth));
1048 H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1050 // Decrease history of all the other played non-capture moves
1051 for (int i = 0; i < playedMoveCount - 1; i++)
1053 Move m = movesSearched[i];
1054 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1058 else // Failed low or PV search
1059 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1060 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1061 depth, bestMove, ss->eval, ss->evalMargin);
1063 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1069 // qsearch() is the quiescence search function, which is called by the main
1070 // search function when the remaining depth is zero (or, to be more precise,
1071 // less than ONE_PLY).
1073 template <NodeType NT>
1074 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1076 const bool PvNode = (NT == PV);
1078 assert(NT == PV || NT == NonPV);
1079 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1080 assert((alpha == beta - 1) || PvNode);
1081 assert(depth <= DEPTH_ZERO);
1084 Move ttMove, move, bestMove;
1085 Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
1086 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1090 Value oldAlpha = alpha;
1092 ss->currentMove = bestMove = MOVE_NONE;
1093 ss->ply = (ss-1)->ply + 1;
1095 // Check for an instant draw or maximum ply reached
1096 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1097 return Eval::ValueDrawContempt;
1099 // Decide whether or not to include checks, this fixes also the type of
1100 // TT entry depth that we are going to use. Note that in qsearch we use
1101 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1102 inCheck = pos.in_check();
1103 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1105 // Transposition table lookup. At PV nodes, we don't use the TT for
1106 // pruning, but only for move ordering.
1107 tte = TT.probe(pos.key());
1108 ttMove = (tte ? tte->move() : MOVE_NONE);
1109 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
1111 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1113 ss->currentMove = ttMove; // Can be MOVE_NONE
1117 // Evaluate the position statically
1120 bestValue = futilityBase = -VALUE_INFINITE;
1121 ss->eval = evalMargin = VALUE_NONE;
1122 enoughMaterial = false;
1128 assert(tte->static_value() != VALUE_NONE);
1130 evalMargin = tte->static_value_margin();
1131 ss->eval = bestValue = tte->static_value();
1134 ss->eval = bestValue = evaluate(pos, evalMargin);
1136 // Stand pat. Return immediately if static value is at least beta
1137 if (bestValue >= beta)
1140 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1145 if (PvNode && bestValue > alpha)
1148 futilityBase = ss->eval + evalMargin + Value(128);
1149 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1152 // Initialize a MovePicker object for the current position, and prepare
1153 // to search the moves. Because the depth is <= 0 here, only captures,
1154 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1156 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1159 // Loop through the moves until no moves remain or a beta cutoff occurs
1160 while ( bestValue < beta
1161 && (move = mp.next_move<false>()) != MOVE_NONE)
1163 assert(is_ok(move));
1165 givesCheck = pos.move_gives_check(move, ci);
1173 && type_of(move) != PROMOTION
1174 && !pos.is_passed_pawn_push(move))
1176 futilityValue = futilityBase
1177 + PieceValue[Eg][pos.piece_on(to_sq(move))]
1178 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1180 if (futilityValue < beta)
1182 if (futilityValue > bestValue)
1183 bestValue = futilityValue;
1188 // Prune moves with negative or equal SEE
1189 if ( futilityBase < beta
1190 && depth < DEPTH_ZERO
1191 && pos.see(move) <= 0)
1195 // Detect non-capture evasions that are candidate to be pruned
1196 evasionPrunable = !PvNode
1198 && bestValue > VALUE_MATED_IN_MAX_PLY
1199 && !pos.is_capture(move)
1200 && !pos.can_castle(pos.side_to_move());
1202 // Don't search moves with negative SEE values
1204 && (!inCheck || evasionPrunable)
1206 && type_of(move) != PROMOTION
1207 && pos.see_sign(move) < 0)
1210 // Don't search useless checks
1215 && !pos.is_capture_or_promotion(move)
1216 && ss->eval + PawnValueMg / 4 < beta
1217 && !check_is_dangerous(pos, move, futilityBase, beta))
1220 // Check for legality only before to do the move
1221 if (!pos.pl_move_is_legal(move, ci.pinned))
1224 ss->currentMove = move;
1226 // Make and search the move
1227 pos.do_move(move, st, ci, givesCheck);
1228 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1229 pos.undo_move(move);
1231 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1234 if (value > bestValue)
1241 && value < beta) // We want always alpha < beta
1246 // All legal moves have been searched. A special case: If we're in check
1247 // and no legal moves were found, it is checkmate.
1248 if (inCheck && bestValue == -VALUE_INFINITE)
1249 return mated_in(ss->ply); // Plies to mate from the root
1251 // Update transposition table
1252 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1253 bt = bestValue <= oldAlpha ? BOUND_UPPER
1254 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1256 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
1258 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1264 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1265 // bestValue is updated only when returning false because in that case move
1268 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1270 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1271 Square from, to, ksq;
1275 from = from_sq(move);
1277 them = ~pos.side_to_move();
1278 ksq = pos.king_square(them);
1279 kingAtt = pos.attacks_from<KING>(ksq);
1280 pc = pos.piece_moved(move);
1282 occ = pos.pieces() ^ from ^ ksq;
1283 oldAtt = pos.attacks_from(pc, from, occ);
1284 newAtt = pos.attacks_from(pc, to, occ);
1286 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1287 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1289 if (!more_than_one(b))
1292 // Rule 2. Queen contact check is very dangerous
1293 if (type_of(pc) == QUEEN && (kingAtt & to))
1296 // Rule 3. Creating new double threats with checks
1297 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1300 // Note that here we generate illegal "double move"!
1301 if (futilityBase + PieceValue[Eg][pos.piece_on(pop_lsb(&b))] >= beta)
1309 // connected_moves() tests whether two moves are 'connected' in the sense
1310 // that the first move somehow made the second move possible (for instance
1311 // if the moving piece is the same in both moves). The first move is assumed
1312 // to be the move that was made to reach the current position, while the
1313 // second move is assumed to be a move from the current position.
1315 bool connected_moves(const Position& pos, Move m1, Move m2) {
1317 Square f1, t1, f2, t2;
1324 // Case 1: The moving piece is the same in both moves
1330 // Case 2: The destination square for m2 was vacated by m1
1336 // Case 3: Moving through the vacated square
1337 p2 = pos.piece_on(f2);
1338 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1341 // Case 4: The destination square for m2 is defended by the moving piece in m1
1342 p1 = pos.piece_on(t1);
1343 if (pos.attacks_from(p1, t1) & t2)
1346 // Case 5: Discovered check, checking piece is the piece moved in m1
1347 ksq = pos.king_square(pos.side_to_move());
1348 if ( piece_is_slider(p1)
1349 && (between_bb(t1, ksq) & f2)
1350 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1357 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1358 // "plies to mate from the current position". Non-mate scores are unchanged.
1359 // The function is called before storing a value to the transposition table.
1361 Value value_to_tt(Value v, int ply) {
1363 if (v >= VALUE_MATE_IN_MAX_PLY)
1366 if (v <= VALUE_MATED_IN_MAX_PLY)
1373 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1374 // from the transposition table (where refers to the plies to mate/be mated
1375 // from current position) to "plies to mate/be mated from the root".
1377 Value value_from_tt(Value v, int ply) {
1379 if (v >= VALUE_MATE_IN_MAX_PLY)
1382 if (v <= VALUE_MATED_IN_MAX_PLY)
1389 // connected_threat() tests whether it is safe to forward prune a move or if
1390 // is somehow connected to the threat move returned by null search.
1392 bool connected_threat(const Position& pos, Move m, Move threat) {
1395 assert(is_ok(threat));
1396 assert(!pos.is_capture_or_promotion(m));
1397 assert(!pos.is_passed_pawn_push(m));
1399 Square mfrom, mto, tfrom, tto;
1403 tfrom = from_sq(threat);
1404 tto = to_sq(threat);
1406 // Case 1: Don't prune moves which move the threatened piece
1410 // Case 2: If the threatened piece has value less than or equal to the
1411 // value of the threatening piece, don't prune moves which defend it.
1412 if ( pos.is_capture(threat)
1413 && ( PieceValue[Mg][pos.piece_on(tfrom)] >= PieceValue[Mg][pos.piece_on(tto)]
1414 || type_of(pos.piece_on(tfrom)) == KING)
1415 && pos.move_attacks_square(m, tto))
1418 // Case 3: If the moving piece in the threatened move is a slider, don't
1419 // prune safe moves which block its ray.
1420 if ( piece_is_slider(pos.piece_on(tfrom))
1421 && (between_bb(tfrom, tto) & mto)
1422 && pos.see_sign(m) >= 0)
1429 // can_return_tt() returns true if a transposition table score can be used to
1430 // cut-off at a given point in search.
1432 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1434 return ( tte->depth() >= depth
1435 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1436 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1438 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1439 || ((tte->type() & BOUND_UPPER) && v < beta));
1443 // refine_eval() returns the transposition table score if possible, otherwise
1444 // falls back on static position evaluation.
1446 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1450 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1451 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1458 // When playing with strength handicap choose best move among the MultiPV set
1459 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1461 Move do_skill_level() {
1463 assert(MultiPV > 1);
1467 // PRNG sequence should be not deterministic
1468 for (int i = Time::now() % 50; i > 0; i--)
1469 rk.rand<unsigned>();
1471 // RootMoves are already sorted by score in descending order
1472 size_t size = std::min(MultiPV, RootMoves.size());
1473 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1474 int weakness = 120 - 2 * SkillLevel;
1475 int max_s = -VALUE_INFINITE;
1476 Move best = MOVE_NONE;
1478 // Choose best move. For each move score we add two terms both dependent on
1479 // weakness, one deterministic and bigger for weaker moves, and one random,
1480 // then we choose the move with the resulting highest score.
1481 for (size_t i = 0; i < size; i++)
1483 int s = RootMoves[i].score;
1485 // Don't allow crazy blunders even at very low skills
1486 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1489 // This is our magic formula
1490 s += ( weakness * int(RootMoves[0].score - s)
1491 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1496 best = RootMoves[i].pv[0];
1503 // uci_pv() formats PV information according to UCI protocol. UCI requires
1504 // to send all the PV lines also if are still to be searched and so refer to
1505 // the previous search score.
1507 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1509 std::stringstream s;
1510 Time::point elaspsed = Time::now() - SearchTime + 1;
1513 for (size_t i = 0; i < Threads.size(); i++)
1514 if (Threads[i].maxPly > selDepth)
1515 selDepth = Threads[i].maxPly;
1517 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1519 bool updated = (i <= PVIdx);
1521 if (depth == 1 && !updated)
1524 int d = (updated ? depth : depth - 1);
1525 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1527 if (s.rdbuf()->in_avail())
1530 s << "info depth " << d
1531 << " seldepth " << selDepth
1532 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1533 << " nodes " << pos.nodes_searched()
1534 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1535 << " time " << elaspsed
1536 << " multipv " << i + 1
1539 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1540 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1549 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1550 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1551 /// allow to always have a ponder move even when we fail high at root, and a
1552 /// long PV to print that is important for position analysis.
1554 void RootMove::extract_pv_from_tt(Position& pos) {
1556 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1561 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1565 pos.do_move(m, *st++);
1567 while ( (tte = TT.probe(pos.key())) != NULL
1568 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1569 && pos.is_pseudo_legal(m)
1570 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1572 && (!pos.is_draw<false>() || ply < 2))
1575 pos.do_move(m, *st++);
1578 pv.push_back(MOVE_NONE);
1580 do pos.undo_move(pv[--ply]); while (ply);
1584 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1585 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1586 /// first, even if the old TT entries have been overwritten.
1588 void RootMove::insert_pv_in_tt(Position& pos) {
1590 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1593 Value v, m = VALUE_NONE;
1596 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1602 // Don't overwrite existing correct entries
1603 if (!tte || tte->move() != pv[ply])
1605 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1606 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1608 pos.do_move(pv[ply], *st++);
1610 } while (pv[++ply] != MOVE_NONE);
1612 do pos.undo_move(pv[--ply]); while (ply);
1616 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1618 void Thread::idle_loop() {
1620 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1621 // object for which the thread is the master.
1622 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1624 assert(!sp_master || (sp_master->master == this && is_searching));
1626 // If this thread is the master of a split point and all slaves have
1627 // finished their work at this split point, return from the idle loop.
1628 while (!sp_master || sp_master->slavesMask)
1630 // If we are not searching, wait for a condition to be signaled
1631 // instead of wasting CPU time polling for work.
1634 || (!is_searching && Threads.use_sleeping_threads()))
1642 // Grab the lock to avoid races with Thread::wake_up()
1645 // If we are master and all slaves have finished don't go to sleep
1646 if (sp_master && !sp_master->slavesMask)
1652 // Do sleep after retesting sleep conditions under lock protection, in
1653 // particular we need to avoid a deadlock in case a master thread has,
1654 // in the meanwhile, allocated us and sent the wake_up() call before we
1655 // had the chance to grab the lock.
1656 if (do_sleep || !is_searching)
1657 sleepCondition.wait(mutex);
1662 // If this thread has been assigned work, launch a search
1665 assert(!do_sleep && !do_exit);
1667 Threads.mutex.lock();
1669 assert(is_searching);
1670 SplitPoint* sp = curSplitPoint;
1672 Threads.mutex.unlock();
1674 Stack ss[MAX_PLY_PLUS_2];
1675 Position pos(*sp->pos, this);
1677 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1682 assert(sp->activePositions[idx] == NULL);
1684 sp->activePositions[idx] = &pos;
1686 if (sp->nodeType == Root)
1687 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1688 else if (sp->nodeType == PV)
1689 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1690 else if (sp->nodeType == NonPV)
1691 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1695 assert(is_searching);
1697 is_searching = false;
1698 sp->activePositions[idx] = NULL;
1699 sp->slavesMask &= ~(1ULL << idx);
1700 sp->nodes += pos.nodes_searched();
1702 // Wake up master thread so to allow it to return from the idle loop in
1703 // case we are the last slave of the split point.
1704 if ( Threads.use_sleeping_threads()
1705 && this != sp->master
1708 assert(!sp->master->is_searching);
1709 sp->master->wake_up();
1712 // After releasing the lock we cannot access anymore any SplitPoint
1713 // related data in a safe way becuase it could have been released under
1714 // our feet by the sp master. Also accessing other Thread objects is
1715 // unsafe because if we are exiting there is a chance are already freed.
1722 /// check_time() is called by the timer thread when the timer triggers. It is
1723 /// used to print debug info and, more important, to detect when we are out of
1724 /// available time and so stop the search.
1728 static Time::point lastInfoTime = Time::now();
1729 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1731 if (Time::now() - lastInfoTime >= 1000)
1733 lastInfoTime = Time::now();
1742 Threads.mutex.lock();
1744 nodes = RootPosition.nodes_searched();
1746 // Loop across all split points and sum accumulated SplitPoint nodes plus
1747 // all the currently active slaves positions.
1748 for (size_t i = 0; i < Threads.size(); i++)
1749 for (int j = 0; j < Threads[i].splitPointsCnt; j++)
1751 SplitPoint& sp = Threads[i].splitPoints[j];
1756 Bitboard sm = sp.slavesMask;
1759 Position* pos = sp.activePositions[pop_lsb(&sm)];
1760 nodes += pos ? pos->nodes_searched() : 0;
1766 Threads.mutex.unlock();
1769 Time::point elapsed = Time::now() - SearchTime;
1770 bool stillAtFirstMove = Signals.firstRootMove
1771 && !Signals.failedLowAtRoot
1772 && elapsed > TimeMgr.available_time();
1774 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1775 || stillAtFirstMove;
1777 if ( (Limits.use_time_management() && noMoreTime)
1778 || (Limits.movetime && elapsed >= Limits.movetime)
1779 || (Limits.nodes && nodes >= Limits.nodes))
1780 Signals.stop = true;