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);
116 /// Search::init() is called during startup to initialize various lookup tables
118 void Search::init() {
120 int d; // depth (ONE_PLY == 2)
121 int hd; // half depth (ONE_PLY == 1)
124 // Init reductions array
125 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
127 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
128 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
129 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
130 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
133 // Init futility margins array
134 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
135 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
137 // Init futility move count array
138 for (d = 0; d < 32; d++)
139 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
143 /// Search::perft() is our utility to verify move generation. All the leaf nodes
144 /// up to the given depth are generated and counted and the sum returned.
146 size_t Search::perft(Position& pos, Depth depth) {
148 // At the last ply just return the number of legal moves (leaf nodes)
149 if (depth == ONE_PLY)
150 return MoveList<LEGAL>(pos).size();
156 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
158 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
159 cnt += perft(pos, depth - ONE_PLY);
160 pos.undo_move(ml.move());
167 /// Search::think() is the external interface to Stockfish's search, and is
168 /// called by the main thread when the program receives the UCI 'go' command. It
169 /// searches from RootPosition and at the end prints the "bestmove" to output.
171 void Search::think() {
173 static PolyglotBook book; // Defined static to initialize the PRNG only once
175 Position& pos = RootPosition;
176 Chess960 = pos.is_chess960();
177 Eval::RootColor = pos.side_to_move();
178 int scaledCF = Eval::ContemptFactor * MaterialTable::game_phase(pos) / PHASE_MIDGAME;
179 Eval::ValueDraw[ Eval::RootColor] = VALUE_DRAW - Value(scaledCF);
180 Eval::ValueDraw[~Eval::RootColor] = VALUE_DRAW + Value(scaledCF);
181 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
185 if (RootMoves.empty())
187 sync_cout << "info depth 0 score "
188 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
190 RootMoves.push_back(MOVE_NONE);
194 if (Options["OwnBook"] && !Limits.infinite)
196 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
198 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
200 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
205 UCIMultiPV = Options["MultiPV"];
206 SkillLevel = Options["Skill Level"];
208 // Do we have to play with skill handicap? In this case enable MultiPV that
209 // we will use behind the scenes to retrieve a set of possible moves.
210 SkillLevelEnabled = (SkillLevel < 20);
211 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
213 if (Options["Use Search Log"])
215 Log log(Options["Search Log Filename"]);
216 log << "\nSearching: " << pos.to_fen()
217 << "\ninfinite: " << Limits.infinite
218 << " ponder: " << Limits.ponder
219 << " time: " << Limits.time[pos.side_to_move()]
220 << " increment: " << Limits.inc[pos.side_to_move()]
221 << " moves to go: " << Limits.movestogo
227 // Set best timer interval to avoid lagging under time pressure. Timer is
228 // used to check for remaining available thinking time.
229 if (Limits.use_time_management())
230 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
231 else if (Limits.nodes)
232 Threads.set_timer(2 * TimerResolution);
234 Threads.set_timer(100);
236 // We're ready to start searching. Call the iterative deepening loop function
239 Threads.set_timer(0); // Stop timer
242 if (Options["Use Search Log"])
244 Time::point elapsed = Time::now() - SearchTime + 1;
246 Log log(Options["Search Log Filename"]);
247 log << "Nodes: " << pos.nodes_searched()
248 << "\nNodes/second: " << pos.nodes_searched() * 1000 / elapsed
249 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
252 pos.do_move(RootMoves[0].pv[0], st);
253 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << std::endl;
254 pos.undo_move(RootMoves[0].pv[0]);
259 // When we reach max depth we arrive here even without Signals.stop is raised,
260 // but if we are pondering or in infinite search, we shouldn't print the best
261 // move before we are told to do so.
262 if (!Signals.stop && (Limits.ponder || Limits.infinite))
263 pos.this_thread()->wait_for_stop_or_ponderhit();
265 // Best move could be MOVE_NONE when searching on a stalemate position
266 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
267 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << sync_endl;
273 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
274 // with increasing depth until the allocated thinking time has been consumed,
275 // user stops the search, or the maximum search depth is reached.
277 void id_loop(Position& pos) {
279 Stack ss[MAX_PLY_PLUS_2];
280 int depth, prevBestMoveChanges;
281 Value bestValue, alpha, beta, delta;
282 bool bestMoveNeverChanged = true;
283 Move skillBest = MOVE_NONE;
285 memset(ss, 0, 4 * sizeof(Stack));
286 depth = BestMoveChanges = 0;
287 bestValue = delta = -VALUE_INFINITE;
288 ss->currentMove = MOVE_NULL; // Hack to skip update gains
290 // Iterative deepening loop until requested to stop or target depth reached
291 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
293 // Save last iteration's scores before first PV line is searched and all
294 // the move scores but the (new) PV are set to -VALUE_INFINITE.
295 for (size_t i = 0; i < RootMoves.size(); i++)
296 RootMoves[i].prevScore = RootMoves[i].score;
298 prevBestMoveChanges = BestMoveChanges;
301 // MultiPV loop. We perform a full root search for each PV line
302 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
304 // Set aspiration window default width
305 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
308 alpha = RootMoves[PVIdx].prevScore - delta;
309 beta = RootMoves[PVIdx].prevScore + delta;
313 alpha = -VALUE_INFINITE;
314 beta = VALUE_INFINITE;
317 // Start with a small aspiration window and, in case of fail high/low,
318 // research with bigger window until not failing high/low anymore.
321 // Search starts from ss+1 to allow referencing (ss-1). This is
322 // needed by update gains and ss copy when splitting at Root.
323 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
325 // Bring to front the best move. It is critical that sorting is
326 // done with a stable algorithm because all the values but the first
327 // and eventually the new best one are set to -VALUE_INFINITE and
328 // we want to keep the same order for all the moves but the new
329 // PV that goes to the front. Note that in case of MultiPV search
330 // the already searched PV lines are preserved.
331 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
333 // In case we have found an exact score and we are going to leave
334 // the fail high/low loop then reorder the PV moves, otherwise
335 // leave the last PV move in its position so to be searched again.
336 // Of course this is needed only in MultiPV search.
337 if (PVIdx && bestValue > alpha && bestValue < beta)
338 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
340 // Write PV back to transposition table in case the relevant
341 // entries have been overwritten during the search.
342 for (size_t i = 0; i <= PVIdx; i++)
343 RootMoves[i].insert_pv_in_tt(pos);
345 // If search has been stopped exit the aspiration window loop.
346 // Sorting and writing PV back to TT is safe becuase RootMoves
347 // is still valid, although refers to previous iteration.
351 // Send full PV info to GUI if we are going to leave the loop or
352 // if we have a fail high/low and we are deep in the search.
353 if ((bestValue > alpha && bestValue < beta) || Time::now() - SearchTime > 2000)
354 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
356 // In case of failing high/low increase aspiration window and
357 // research, otherwise exit the fail high/low loop.
358 if (bestValue >= beta)
363 else if (bestValue <= alpha)
365 Signals.failedLowAtRoot = true;
366 Signals.stopOnPonderhit = false;
374 // Search with full window in case we have a win/mate score
375 if (abs(bestValue) >= VALUE_KNOWN_WIN)
377 alpha = -VALUE_INFINITE;
378 beta = VALUE_INFINITE;
381 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
385 // Skills: Do we need to pick now the best move ?
386 if (SkillLevelEnabled && depth == 1 + SkillLevel)
387 skillBest = do_skill_level();
389 if (!Signals.stop && Options["Use Search Log"])
391 Log log(Options["Search Log Filename"]);
392 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
396 // Filter out startup noise when monitoring best move stability
397 if (depth > 2 && BestMoveChanges)
398 bestMoveNeverChanged = false;
400 // Do we have time for the next iteration? Can we stop searching now?
401 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
403 bool stop = false; // Local variable, not the volatile Signals.stop
405 // Take in account some extra time if the best move has changed
406 if (depth > 4 && depth < 50)
407 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
409 // Stop search if most of available time is already consumed. We
410 // probably don't have enough time to search the first move at the
411 // next iteration anyway.
412 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
415 // Stop search early if one move seems to be much better than others
418 && ( (bestMoveNeverChanged && pos.captured_piece_type())
419 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
421 Value rBeta = bestValue - 2 * PawnValueMg;
422 (ss+1)->excludedMove = RootMoves[0].pv[0];
423 (ss+1)->skipNullMove = true;
424 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
425 (ss+1)->skipNullMove = false;
426 (ss+1)->excludedMove = MOVE_NONE;
434 // If we are allowed to ponder do not stop the search now but
435 // keep pondering until GUI sends "ponderhit" or "stop".
437 Signals.stopOnPonderhit = true;
444 // When using skills swap best PV line with the sub-optimal one
445 if (SkillLevelEnabled)
447 if (skillBest == MOVE_NONE) // Still unassigned ?
448 skillBest = do_skill_level();
450 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
455 // search<>() is the main search function for both PV and non-PV nodes and for
456 // normal and SplitPoint nodes. When called just after a split point the search
457 // is simpler because we have already probed the hash table, done a null move
458 // search, and searched the first move before splitting, we don't have to repeat
459 // all this work again. We also don't need to store anything to the hash table
460 // here: This is taken care of after we return from the split point.
462 template <NodeType NT>
463 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
465 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
466 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
467 const bool RootNode = (NT == Root || NT == SplitPointRoot);
469 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
470 assert(PvNode || (alpha == beta - 1));
471 assert(depth > DEPTH_ZERO);
473 Move movesSearched[64];
478 Move ttMove, move, excludedMove, bestMove, threatMove;
480 Value bestValue, value, ttValue;
481 Value refinedValue, nullValue, futilityValue;
482 bool inCheck, givesCheck, pvMove, singularExtensionNode;
483 bool captureOrPromotion, dangerous, doFullDepthSearch;
484 int moveCount, playedMoveCount;
486 // Step 1. Initialize node
487 Thread* thisThread = pos.this_thread();
488 moveCount = playedMoveCount = 0;
489 inCheck = pos.in_check();
494 bestMove = sp->bestMove;
495 threatMove = sp->threatMove;
496 bestValue = sp->bestValue;
498 ttMove = excludedMove = MOVE_NONE;
499 ttValue = VALUE_NONE;
501 assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);
503 goto split_point_start;
506 bestValue = -VALUE_INFINITE;
507 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
508 ss->ply = (ss-1)->ply + 1;
509 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
510 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
512 // Used to send selDepth info to GUI
513 if (PvNode && thisThread->maxPly < ss->ply)
514 thisThread->maxPly = ss->ply;
518 // Step 2. Check for aborted search and immediate draw
519 if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
520 return Eval::ValueDraw[pos.side_to_move()];
522 // Step 3. Mate distance pruning. Even if we mate at the next move our score
523 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
524 // a shorter mate was found upward in the tree then there is no need to search
525 // further, we will never beat current alpha. Same logic but with reversed signs
526 // applies also in the opposite condition of being mated instead of giving mate,
527 // in this case return a fail-high score.
528 alpha = std::max(mated_in(ss->ply), alpha);
529 beta = std::min(mate_in(ss->ply+1), beta);
534 // Step 4. Transposition table lookup
535 // We don't want the score of a partial search to overwrite a previous full search
536 // TT value, so we use a different position key in case of an excluded move.
537 excludedMove = ss->excludedMove;
538 posKey = excludedMove ? pos.exclusion_key() : pos.key();
539 tte = TT.probe(posKey);
540 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
541 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
543 // At PV nodes we check for exact scores, while at non-PV nodes we check for
544 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
545 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
546 // we should also update RootMoveList to avoid bogus output.
547 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
548 : can_return_tt(tte, depth, ttValue, beta)))
551 ss->currentMove = ttMove; // Can be MOVE_NONE
555 && !pos.is_capture_or_promotion(ttMove)
556 && ttMove != ss->killers[0])
558 ss->killers[1] = ss->killers[0];
559 ss->killers[0] = ttMove;
564 // Step 5. Evaluate the position statically and update parent's gain statistics
566 ss->eval = ss->evalMargin = refinedValue = VALUE_NONE;
569 assert(tte->static_value() != VALUE_NONE);
571 ss->eval = tte->static_value();
572 ss->evalMargin = tte->static_value_margin();
573 refinedValue = refine_eval(tte, ttValue, ss->eval);
577 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
578 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
581 // Update gain for the parent non-capture move given the static position
582 // evaluation before and after the move.
583 if ( (move = (ss-1)->currentMove) != MOVE_NULL
584 && (ss-1)->eval != VALUE_NONE
585 && ss->eval != VALUE_NONE
586 && !pos.captured_piece_type()
587 && type_of(move) == NORMAL)
589 Square to = to_sq(move);
590 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
593 // Step 6. Razoring (is omitted in PV nodes)
595 && depth < 4 * ONE_PLY
597 && refinedValue + razor_margin(depth) < beta
598 && ttMove == MOVE_NONE
599 && abs(beta) < VALUE_MATE_IN_MAX_PLY
600 && !pos.pawn_on_7th(pos.side_to_move()))
602 Value rbeta = beta - razor_margin(depth);
603 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
605 // Logically we should return (v + razor_margin(depth)), but
606 // surprisingly this did slightly weaker in tests.
610 // Step 7. Static null move pruning (is omitted in PV nodes)
611 // We're betting that the opponent doesn't have a move that will reduce
612 // the score by more than futility_margin(depth) if we do a null move.
615 && depth < 4 * ONE_PLY
617 && refinedValue - FutilityMargins[depth][0] >= beta
618 && abs(beta) < VALUE_MATE_IN_MAX_PLY
619 && pos.non_pawn_material(pos.side_to_move()))
620 return refinedValue - FutilityMargins[depth][0];
622 // Step 8. Null move search with verification search (is omitted in PV nodes)
627 && refinedValue >= beta
628 && abs(beta) < VALUE_MATE_IN_MAX_PLY
629 && pos.non_pawn_material(pos.side_to_move()))
631 ss->currentMove = MOVE_NULL;
633 // Null move dynamic reduction based on depth
634 Depth R = 3 * ONE_PLY + depth / 4;
636 // Null move dynamic reduction based on value
637 if (refinedValue - PawnValueMg > beta)
640 pos.do_null_move<true>(st);
641 (ss+1)->skipNullMove = true;
642 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
643 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
644 (ss+1)->skipNullMove = false;
645 pos.do_null_move<false>(st);
647 if (nullValue >= beta)
649 // Do not return unproven mate scores
650 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
653 if (depth < 6 * ONE_PLY)
656 // Do verification search at high depths
657 ss->skipNullMove = true;
658 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
659 ss->skipNullMove = false;
666 // The null move failed low, which means that we may be faced with
667 // some kind of threat. If the previous move was reduced, check if
668 // the move that refuted the null move was somehow connected to the
669 // move which was reduced. If a connection is found, return a fail
670 // low score (which will cause the reduced move to fail high in the
671 // parent node, which will trigger a re-search with full depth).
672 threatMove = (ss+1)->currentMove;
674 if ( depth < 5 * ONE_PLY
676 && threatMove != MOVE_NONE
677 && connected_moves(pos, (ss-1)->currentMove, threatMove))
682 // Step 9. ProbCut (is omitted in PV nodes)
683 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
684 // and a reduced search returns a value much above beta, we can (almost) safely
685 // prune the previous move.
687 && depth >= 5 * ONE_PLY
690 && excludedMove == MOVE_NONE
691 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
693 Value rbeta = beta + 200;
694 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
696 assert(rdepth >= ONE_PLY);
697 assert((ss-1)->currentMove != MOVE_NONE);
698 assert((ss-1)->currentMove != MOVE_NULL);
700 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
703 while ((move = mp.next_move<false>()) != MOVE_NONE)
704 if (pos.pl_move_is_legal(move, ci.pinned))
706 ss->currentMove = move;
707 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
708 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
715 // Step 10. Internal iterative deepening
716 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
717 && ttMove == MOVE_NONE
718 && (PvNode || (!inCheck && ss->eval + Value(256) >= beta)))
720 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
722 ss->skipNullMove = true;
723 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
724 ss->skipNullMove = false;
726 tte = TT.probe(posKey);
727 ttMove = tte ? tte->move() : MOVE_NONE;
730 split_point_start: // At split points actual search starts from here
732 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
734 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
735 singularExtensionNode = !RootNode
737 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
738 && ttMove != MOVE_NONE
739 && !excludedMove // Recursive singular search is not allowed
740 && (tte->type() & BOUND_LOWER)
741 && tte->depth() >= depth - 3 * ONE_PLY;
743 // Step 11. Loop through moves
744 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
745 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
749 if (move == excludedMove)
752 // At root obey the "searchmoves" option and skip moves not listed in Root
753 // Move List, as a consequence any illegal move is also skipped. In MultiPV
754 // mode we also skip PV moves which have been already searched.
755 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
760 // Shared counter cannot be decremented later if move turns out to be illegal
761 if (!pos.pl_move_is_legal(move, ci.pinned))
764 moveCount = ++sp->moveCount;
772 Signals.firstRootMove = (moveCount == 1);
774 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
775 sync_cout << "info depth " << depth / ONE_PLY
776 << " currmove " << move_to_uci(move, Chess960)
777 << " currmovenumber " << moveCount + PVIdx << sync_endl;
781 captureOrPromotion = pos.is_capture_or_promotion(move);
782 givesCheck = pos.move_gives_check(move, ci);
783 dangerous = givesCheck
784 || pos.is_passed_pawn_push(move)
785 || type_of(move) == CASTLE
786 || ( captureOrPromotion // Entering a pawn endgame?
787 && type_of(pos.piece_on(to_sq(move))) != PAWN
788 && type_of(move) == NORMAL
789 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
790 - PieceValue[Mg][pos.piece_on(to_sq(move))] == VALUE_ZERO));
792 // Step 12. Extend checks and, in PV nodes, also dangerous moves
793 if (PvNode && dangerous)
796 else if (givesCheck && pos.see_sign(move) >= 0)
799 // Singular extension search. If all moves but one fail low on a search of
800 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
801 // is singular and should be extended. To verify this we do a reduced search
802 // on all the other moves but the ttMove, if result is lower than ttValue minus
803 // a margin then we extend ttMove.
804 if ( singularExtensionNode
807 && pos.pl_move_is_legal(move, ci.pinned)
808 && abs(ttValue) < VALUE_KNOWN_WIN)
810 Value rBeta = ttValue - int(depth);
811 ss->excludedMove = move;
812 ss->skipNullMove = true;
813 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
814 ss->skipNullMove = false;
815 ss->excludedMove = MOVE_NONE;
818 ext = rBeta >= beta ? ONE_PLY + ONE_PLY / 2 : ONE_PLY;
821 // Update current move (this must be done after singular extension search)
822 newDepth = depth - ONE_PLY + ext;
824 // Step 13. Futility pruning (is omitted in PV nodes)
826 && !captureOrPromotion
830 && (bestValue > VALUE_MATED_IN_MAX_PLY || ( bestValue == -VALUE_INFINITE
831 && alpha > VALUE_MATED_IN_MAX_PLY)))
833 // Move count based pruning
834 if ( depth < 16 * ONE_PLY
835 && moveCount >= FutilityMoveCounts[depth]
836 && (!threatMove || !connected_threat(pos, move, threatMove)))
844 // Value based pruning
845 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
846 // but fixing this made program slightly weaker.
847 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
848 futilityValue = ss->eval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
849 + H.gain(pos.piece_moved(move), to_sq(move));
851 if (futilityValue < beta)
859 // Prune moves with negative SEE at low depths
860 if ( predictedDepth < 2 * ONE_PLY
861 && pos.see_sign(move) < 0)
870 // Check for legality only before to do the move
871 if (!pos.pl_move_is_legal(move, ci.pinned))
877 pvMove = PvNode ? moveCount == 1 : false;
878 ss->currentMove = move;
879 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
880 movesSearched[playedMoveCount++] = move;
882 // Step 14. Make the move
883 pos.do_move(move, st, ci, givesCheck);
885 // Step 15. Reduced depth search (LMR). If the move fails high will be
886 // re-searched at full depth.
887 if ( depth > 3 * ONE_PLY
889 && !captureOrPromotion
891 && ss->killers[0] != move
892 && ss->killers[1] != move)
894 ss->reduction = reduction<PvNode>(depth, moveCount);
895 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
896 alpha = SpNode ? sp->alpha : alpha;
898 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
900 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
901 ss->reduction = DEPTH_ZERO;
904 doFullDepthSearch = !pvMove;
906 // Step 16. Full depth search, when LMR is skipped or fails high
907 if (doFullDepthSearch)
909 alpha = SpNode ? sp->alpha : alpha;
910 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
911 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
914 // Only for PV nodes do a full PV search on the first move or after a fail
915 // high, in the latter case search only if value < beta, otherwise let the
916 // parent node to fail low with value <= alpha and to try another move.
917 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
918 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
919 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
921 // Step 17. Undo move
924 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
926 // Step 18. Check for new best move
930 bestValue = sp->bestValue;
934 // Finished searching the move. If Signals.stop is true, the search
935 // was aborted because the user interrupted the search or because we
936 // ran out of time. In this case, the return value of the search cannot
937 // be trusted, and we don't update the best move and/or PV.
938 if (Signals.stop || thisThread->cutoff_occurred())
943 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
945 // PV move or new best move ?
946 if (pvMove || value > alpha)
949 rm.extract_pv_from_tt(pos);
951 // We record how often the best move has been changed in each
952 // iteration. This information is used for time management: When
953 // the best move changes frequently, we allocate some more time.
954 if (!pvMove && MultiPV == 1)
958 // All other moves but the PV are set to the lowest value, this
959 // is not a problem when sorting becuase sort is stable and move
960 // position in the list is preserved, just the PV is pushed up.
961 rm.score = -VALUE_INFINITE;
964 if (value > bestValue)
967 if (SpNode) sp->bestValue = value;
972 if (SpNode) sp->bestMove = move;
974 if (PvNode && value < beta)
976 alpha = value; // Update alpha here! Always alpha < beta
977 if (SpNode) sp->alpha = value;
981 if (SpNode) sp->cutoff = true;
987 // Step 19. Check for splitting the search
989 && depth >= Threads.min_split_depth()
991 && Threads.available_slave_exists(thisThread))
993 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
994 depth, threatMove, moveCount, mp, NT);
1002 // Step 20. Check for mate and stalemate
1003 // All legal moves have been searched and if there are no legal moves, it
1004 // must be mate or stalemate. Note that we can have a false positive in
1005 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1006 // harmless because return value is discarded anyhow in the parent nodes.
1007 // If we are in a singular extension search then return a fail low score.
1008 // A split node has at least one move, the one tried before to be splitted.
1010 return excludedMove ? alpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1012 // If we have pruned all the moves without searching return a fail-low score
1013 if (bestValue == -VALUE_INFINITE)
1015 assert(!playedMoveCount);
1020 if (bestValue >= beta) // Failed high
1022 TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
1023 bestMove, ss->eval, ss->evalMargin);
1025 if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
1027 if (bestMove != ss->killers[0])
1029 ss->killers[1] = ss->killers[0];
1030 ss->killers[0] = bestMove;
1033 // Increase history value of the cut-off move
1034 Value bonus = Value(int(depth) * int(depth));
1035 H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1037 // Decrease history of all the other played non-capture moves
1038 for (int i = 0; i < playedMoveCount - 1; i++)
1040 Move m = movesSearched[i];
1041 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1045 else // Failed low or PV search
1046 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1047 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1048 depth, bestMove, ss->eval, ss->evalMargin);
1050 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1056 // qsearch() is the quiescence search function, which is called by the main
1057 // search function when the remaining depth is zero (or, to be more precise,
1058 // less than ONE_PLY).
1060 template <NodeType NT>
1061 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1063 const bool PvNode = (NT == PV);
1065 assert(NT == PV || NT == NonPV);
1066 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1067 assert(PvNode || (alpha == beta - 1));
1068 assert(depth <= DEPTH_ZERO);
1073 Move ttMove, move, bestMove;
1074 Value bestValue, value, ttValue, futilityValue, futilityBase;
1075 bool inCheck, givesCheck, enoughMaterial, evasionPrunable;
1078 inCheck = pos.in_check();
1079 ss->currentMove = bestMove = MOVE_NONE;
1080 ss->ply = (ss-1)->ply + 1;
1082 // Check for an instant draw or maximum ply reached
1083 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1084 return Eval::ValueDraw[pos.side_to_move()];
1086 // Transposition table lookup. At PV nodes, we don't use the TT for
1087 // pruning, but only for move ordering.
1089 tte = TT.probe(posKey);
1090 ttMove = tte ? tte->move() : MOVE_NONE;
1091 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1093 // Decide whether or not to include checks, this fixes also the type of
1094 // TT entry depth that we are going to use. Note that in qsearch we use
1095 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1096 ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;
1098 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1100 ss->currentMove = ttMove; // Can be MOVE_NONE
1104 // Evaluate the position statically
1107 ss->eval = ss->evalMargin = VALUE_NONE;
1108 bestValue = futilityBase = -VALUE_INFINITE;
1109 enoughMaterial = false;
1115 assert(tte->static_value() != VALUE_NONE);
1117 ss->eval = bestValue = tte->static_value();
1118 ss->evalMargin = tte->static_value_margin();
1121 ss->eval = bestValue = evaluate(pos, ss->evalMargin);
1123 // Stand pat. Return immediately if static value is at least beta
1124 if (bestValue >= beta)
1127 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1132 if (PvNode && bestValue > alpha)
1135 futilityBase = ss->eval + ss->evalMargin + Value(128);
1136 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1139 // Initialize a MovePicker object for the current position, and prepare
1140 // to search the moves. Because the depth is <= 0 here, only captures,
1141 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1143 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1146 // Loop through the moves until no moves remain or a beta cutoff occurs
1147 while ((move = mp.next_move<false>()) != MOVE_NONE)
1149 assert(is_ok(move));
1151 givesCheck = pos.move_gives_check(move, ci);
1159 && type_of(move) != PROMOTION
1160 && !pos.is_passed_pawn_push(move))
1162 futilityValue = futilityBase
1163 + PieceValue[Eg][pos.piece_on(to_sq(move))]
1164 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1166 if (futilityValue < beta)
1168 if (futilityValue > bestValue)
1169 bestValue = futilityValue;
1174 // Prune moves with negative or equal SEE
1175 if ( futilityBase < beta
1176 && depth < DEPTH_ZERO
1177 && pos.see(move) <= 0)
1181 // Detect non-capture evasions that are candidate to be pruned
1182 evasionPrunable = !PvNode
1184 && bestValue > VALUE_MATED_IN_MAX_PLY
1185 && !pos.is_capture(move)
1186 && !pos.can_castle(pos.side_to_move());
1188 // Don't search moves with negative SEE values
1190 && (!inCheck || evasionPrunable)
1192 && type_of(move) != PROMOTION
1193 && pos.see_sign(move) < 0)
1196 // Don't search useless checks
1201 && !pos.is_capture_or_promotion(move)
1202 && ss->eval + PawnValueMg / 4 < beta
1203 && !check_is_dangerous(pos, move, futilityBase, beta))
1206 // Check for legality only before to do the move
1207 if (!pos.pl_move_is_legal(move, ci.pinned))
1210 ss->currentMove = move;
1212 // Make and search the move
1213 pos.do_move(move, st, ci, givesCheck);
1214 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1215 pos.undo_move(move);
1217 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1219 // Check for new best move
1220 if (value > bestValue)
1226 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1233 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1234 ttDepth, move, ss->eval, ss->evalMargin);
1242 // All legal moves have been searched. A special case: If we're in check
1243 // and no legal moves were found, it is checkmate.
1244 if (inCheck && bestValue == -VALUE_INFINITE)
1245 return mated_in(ss->ply); // Plies to mate from the root
1247 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1248 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1249 ttDepth, bestMove, ss->eval, ss->evalMargin);
1251 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1257 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1258 // bestValue is updated only when returning false because in that case move
1261 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1263 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1264 Square from, to, ksq;
1268 from = from_sq(move);
1270 them = ~pos.side_to_move();
1271 ksq = pos.king_square(them);
1272 kingAtt = pos.attacks_from<KING>(ksq);
1273 pc = pos.piece_moved(move);
1275 occ = pos.pieces() ^ from ^ ksq;
1276 oldAtt = pos.attacks_from(pc, from, occ);
1277 newAtt = pos.attacks_from(pc, to, occ);
1279 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1280 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1282 if (!more_than_one(b))
1285 // Rule 2. Queen contact check is very dangerous
1286 if (type_of(pc) == QUEEN && (kingAtt & to))
1289 // Rule 3. Creating new double threats with checks
1290 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1293 // Note that here we generate illegal "double move"!
1294 if (futilityBase + PieceValue[Eg][pos.piece_on(pop_lsb(&b))] >= beta)
1302 // connected_moves() tests whether two moves are 'connected' in the sense
1303 // that the first move somehow made the second move possible (for instance
1304 // if the moving piece is the same in both moves). The first move is assumed
1305 // to be the move that was made to reach the current position, while the
1306 // second move is assumed to be a move from the current position.
1308 bool connected_moves(const Position& pos, Move m1, Move m2) {
1310 Square f1, t1, f2, t2;
1317 // Case 1: The moving piece is the same in both moves
1323 // Case 2: The destination square for m2 was vacated by m1
1329 // Case 3: Moving through the vacated square
1330 p2 = pos.piece_on(f2);
1331 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1334 // Case 4: The destination square for m2 is defended by the moving piece in m1
1335 p1 = pos.piece_on(t1);
1336 if (pos.attacks_from(p1, t1) & t2)
1339 // Case 5: Discovered check, checking piece is the piece moved in m1
1340 ksq = pos.king_square(pos.side_to_move());
1341 if ( piece_is_slider(p1)
1342 && (between_bb(t1, ksq) & f2)
1343 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1350 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1351 // "plies to mate from the current position". Non-mate scores are unchanged.
1352 // The function is called before storing a value to the transposition table.
1354 Value value_to_tt(Value v, int ply) {
1356 if (v >= VALUE_MATE_IN_MAX_PLY)
1359 if (v <= VALUE_MATED_IN_MAX_PLY)
1366 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1367 // from the transposition table (where refers to the plies to mate/be mated
1368 // from current position) to "plies to mate/be mated from the root".
1370 Value value_from_tt(Value v, int ply) {
1372 if (v >= VALUE_MATE_IN_MAX_PLY)
1375 if (v <= VALUE_MATED_IN_MAX_PLY)
1382 // connected_threat() tests whether it is safe to forward prune a move or if
1383 // is somehow connected to the threat move returned by null search.
1385 bool connected_threat(const Position& pos, Move m, Move threat) {
1388 assert(is_ok(threat));
1389 assert(!pos.is_capture_or_promotion(m));
1390 assert(!pos.is_passed_pawn_push(m));
1392 Square mfrom, mto, tfrom, tto;
1396 tfrom = from_sq(threat);
1397 tto = to_sq(threat);
1399 // Case 1: Don't prune moves which move the threatened piece
1403 // Case 2: If the threatened piece has value less than or equal to the
1404 // value of the threatening piece, don't prune moves which defend it.
1405 if ( pos.is_capture(threat)
1406 && ( PieceValue[Mg][pos.piece_on(tfrom)] >= PieceValue[Mg][pos.piece_on(tto)]
1407 || type_of(pos.piece_on(tfrom)) == KING)
1408 && pos.move_attacks_square(m, tto))
1411 // Case 3: If the moving piece in the threatened move is a slider, don't
1412 // prune safe moves which block its ray.
1413 if ( piece_is_slider(pos.piece_on(tfrom))
1414 && (between_bb(tfrom, tto) & mto)
1415 && pos.see_sign(m) >= 0)
1422 // can_return_tt() returns true if a transposition table score can be used to
1423 // cut-off at a given point in search.
1425 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1427 return ( tte->depth() >= depth
1428 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1429 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1431 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1432 || ((tte->type() & BOUND_UPPER) && v < beta));
1436 // refine_eval() returns the transposition table score if possible, otherwise
1437 // falls back on static position evaluation.
1439 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1443 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1444 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1451 // When playing with strength handicap choose best move among the MultiPV set
1452 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1454 Move do_skill_level() {
1456 assert(MultiPV > 1);
1460 // PRNG sequence should be not deterministic
1461 for (int i = Time::now() % 50; i > 0; i--)
1462 rk.rand<unsigned>();
1464 // RootMoves are already sorted by score in descending order
1465 size_t size = std::min(MultiPV, RootMoves.size());
1466 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1467 int weakness = 120 - 2 * SkillLevel;
1468 int max_s = -VALUE_INFINITE;
1469 Move best = MOVE_NONE;
1471 // Choose best move. For each move score we add two terms both dependent on
1472 // weakness, one deterministic and bigger for weaker moves, and one random,
1473 // then we choose the move with the resulting highest score.
1474 for (size_t i = 0; i < size; i++)
1476 int s = RootMoves[i].score;
1478 // Don't allow crazy blunders even at very low skills
1479 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1482 // This is our magic formula
1483 s += ( weakness * int(RootMoves[0].score - s)
1484 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1489 best = RootMoves[i].pv[0];
1496 // uci_pv() formats PV information according to UCI protocol. UCI requires
1497 // to send all the PV lines also if are still to be searched and so refer to
1498 // the previous search score.
1500 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1502 std::stringstream s;
1503 Time::point elaspsed = Time::now() - SearchTime + 1;
1506 for (size_t i = 0; i < Threads.size(); i++)
1507 if (Threads[i].maxPly > selDepth)
1508 selDepth = Threads[i].maxPly;
1510 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1512 bool updated = (i <= PVIdx);
1514 if (depth == 1 && !updated)
1517 int d = (updated ? depth : depth - 1);
1518 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1520 if (s.rdbuf()->in_avail())
1523 s << "info depth " << d
1524 << " seldepth " << selDepth
1525 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1526 << " nodes " << pos.nodes_searched()
1527 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1528 << " time " << elaspsed
1529 << " multipv " << i + 1
1532 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1533 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1542 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1543 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1544 /// allow to always have a ponder move even when we fail high at root, and a
1545 /// long PV to print that is important for position analysis.
1547 void RootMove::extract_pv_from_tt(Position& pos) {
1549 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1554 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1558 pos.do_move(m, *st++);
1560 while ( (tte = TT.probe(pos.key())) != NULL
1561 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1562 && pos.is_pseudo_legal(m)
1563 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1565 && (!pos.is_draw<false>() || ply < 2))
1568 pos.do_move(m, *st++);
1571 pv.push_back(MOVE_NONE);
1573 do pos.undo_move(pv[--ply]); while (ply);
1577 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1578 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1579 /// first, even if the old TT entries have been overwritten.
1581 void RootMove::insert_pv_in_tt(Position& pos) {
1583 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1586 Value v, m = VALUE_NONE;
1589 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1595 // Don't overwrite existing correct entries
1596 if (!tte || tte->move() != pv[ply])
1598 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1599 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1601 pos.do_move(pv[ply], *st++);
1603 } while (pv[++ply] != MOVE_NONE);
1605 do pos.undo_move(pv[--ply]); while (ply);
1609 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1611 void Thread::idle_loop() {
1613 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1614 // object for which the thread is the master.
1615 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1617 assert(!sp_master || (sp_master->master == this && is_searching));
1619 // If this thread is the master of a split point and all slaves have
1620 // finished their work at this split point, return from the idle loop.
1621 while (!sp_master || sp_master->slavesMask)
1623 // If we are not searching, wait for a condition to be signaled
1624 // instead of wasting CPU time polling for work.
1627 || (!is_searching && Threads.use_sleeping_threads()))
1635 // Grab the lock to avoid races with Thread::wake_up()
1638 // If we are master and all slaves have finished don't go to sleep
1639 if (sp_master && !sp_master->slavesMask)
1645 // Do sleep after retesting sleep conditions under lock protection, in
1646 // particular we need to avoid a deadlock in case a master thread has,
1647 // in the meanwhile, allocated us and sent the wake_up() call before we
1648 // had the chance to grab the lock.
1649 if (do_sleep || !is_searching)
1650 sleepCondition.wait(mutex);
1655 // If this thread has been assigned work, launch a search
1658 assert(!do_sleep && !do_exit);
1660 Threads.mutex.lock();
1662 assert(is_searching);
1663 SplitPoint* sp = curSplitPoint;
1665 Threads.mutex.unlock();
1667 Stack ss[MAX_PLY_PLUS_2];
1668 Position pos(*sp->pos, this);
1670 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1675 assert(sp->activePositions[idx] == NULL);
1677 sp->activePositions[idx] = &pos;
1679 if (sp->nodeType == Root)
1680 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1681 else if (sp->nodeType == PV)
1682 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1683 else if (sp->nodeType == NonPV)
1684 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1688 assert(is_searching);
1690 is_searching = false;
1691 sp->activePositions[idx] = NULL;
1692 sp->slavesMask &= ~(1ULL << idx);
1693 sp->nodes += pos.nodes_searched();
1695 // Wake up master thread so to allow it to return from the idle loop in
1696 // case we are the last slave of the split point.
1697 if ( Threads.use_sleeping_threads()
1698 && this != sp->master
1701 assert(!sp->master->is_searching);
1702 sp->master->wake_up();
1705 // After releasing the lock we cannot access anymore any SplitPoint
1706 // related data in a safe way becuase it could have been released under
1707 // our feet by the sp master. Also accessing other Thread objects is
1708 // unsafe because if we are exiting there is a chance are already freed.
1715 /// check_time() is called by the timer thread when the timer triggers. It is
1716 /// used to print debug info and, more important, to detect when we are out of
1717 /// available time and so stop the search.
1721 static Time::point lastInfoTime = Time::now();
1722 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1724 if (Time::now() - lastInfoTime >= 1000)
1726 lastInfoTime = Time::now();
1735 Threads.mutex.lock();
1737 nodes = RootPosition.nodes_searched();
1739 // Loop across all split points and sum accumulated SplitPoint nodes plus
1740 // all the currently active slaves positions.
1741 for (size_t i = 0; i < Threads.size(); i++)
1742 for (int j = 0; j < Threads[i].splitPointsCnt; j++)
1744 SplitPoint& sp = Threads[i].splitPoints[j];
1749 Bitboard sm = sp.slavesMask;
1752 Position* pos = sp.activePositions[pop_lsb(&sm)];
1753 nodes += pos ? pos->nodes_searched() : 0;
1759 Threads.mutex.unlock();
1762 Time::point elapsed = Time::now() - SearchTime;
1763 bool stillAtFirstMove = Signals.firstRootMove
1764 && !Signals.failedLowAtRoot
1765 && elapsed > TimeMgr.available_time();
1767 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1768 || stillAtFirstMove;
1770 if ( (Limits.use_time_management() && noMoreTime)
1771 || (Limits.movetime && elapsed >= Limits.movetime)
1772 || (Limits.nodes && nodes >= Limits.nodes))
1773 Signals.stop = true;