2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
46 Time::point SearchTime;
47 StateStackPtr SetupStates;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // Dynamic razoring margin based on depth
63 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
65 // Futility lookup tables (initialized at startup) and their access functions
66 int FutilityMoveCounts[2][32]; // [improving][depth]
68 inline Value futility_margin(Depth d) {
69 return Value(100 * int(d));
72 // Reduction lookup tables (initialized at startup) and their access function
73 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
75 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
77 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
82 double BestMoveChanges;
83 Value DrawValue[COLOR_NB];
86 CountermovesStats Countermoves;
88 template <NodeType NT>
89 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
91 template <NodeType NT, bool InCheck>
92 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
94 void id_loop(Position& pos);
95 Value value_to_tt(Value v, int ply);
96 Value value_from_tt(Value v, int ply);
97 bool allows(const Position& pos, Move first, Move second);
98 bool refutes(const Position& pos, Move first, Move second);
99 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
102 Skill(int l) : level(l), best(MOVE_NONE) {}
104 if (enabled()) // Swap best PV line with the sub-optimal one
105 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
106 RootMoves.end(), best ? best : pick_move()));
109 bool enabled() const { return level < 20; }
110 bool time_to_pick(int depth) const { return depth == 1 + level; }
120 /// Search::init() is called during startup to initialize various lookup tables
122 void Search::init() {
124 int d; // depth (ONE_PLY == 2)
125 int hd; // half depth (ONE_PLY == 1)
128 // Init reductions array
129 for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
131 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
132 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
133 Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
134 Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
136 Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
137 Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
139 if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
140 Reductions[0][0][hd][mc] += ONE_PLY;
142 else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
143 Reductions[0][0][hd][mc] += ONE_PLY / 2;
146 // Init futility move count array
147 for (d = 0; d < 32; ++d)
149 FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.0, 1.8));
150 FutilityMoveCounts[1][d] = int(3.0 + 0.3 * pow(d + 0.98, 1.8));
155 /// Search::perft() is our utility to verify move generation. All the leaf nodes
156 /// up to the given depth are generated and counted and the sum returned.
158 static size_t perft(Position& pos, Depth depth) {
163 const bool leaf = depth == 2 * ONE_PLY;
165 for (MoveList<LEGAL> it(pos); *it; ++it)
167 pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
168 cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
174 size_t Search::perft(Position& pos, Depth depth) {
175 return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
178 /// Search::think() is the external interface to Stockfish's search, and is
179 /// called by the main thread when the program receives the UCI 'go' command. It
180 /// searches from RootPos and at the end prints the "bestmove" to output.
182 void Search::think() {
184 static PolyglotBook book; // Defined static to initialize the PRNG only once
186 RootColor = RootPos.side_to_move();
187 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
189 if (RootMoves.empty())
191 RootMoves.push_back(MOVE_NONE);
192 sync_cout << "info depth 0 score "
193 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
199 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
201 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
203 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
205 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
210 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
212 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
213 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
214 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
215 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
218 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
220 if (Options["Write Search Log"])
222 Log log(Options["Search Log Filename"]);
223 log << "\nSearching: " << RootPos.fen()
224 << "\ninfinite: " << Limits.infinite
225 << " ponder: " << Limits.ponder
226 << " time: " << Limits.time[RootColor]
227 << " increment: " << Limits.inc[RootColor]
228 << " moves to go: " << Limits.movestogo
232 // Reset the threads, still sleeping: will be wake up at split time
233 for (size_t i = 0; i < Threads.size(); ++i)
234 Threads[i]->maxPly = 0;
236 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
237 Threads.timer->run = true;
238 Threads.timer->notify_one(); // Wake up the recurring timer
240 id_loop(RootPos); // Let's start searching !
242 Threads.timer->run = false; // Stop the timer
243 Threads.sleepWhileIdle = true; // Send idle threads to sleep
245 if (Options["Write Search Log"])
247 Time::point elapsed = Time::now() - SearchTime + 1;
249 Log log(Options["Search Log Filename"]);
250 log << "Nodes: " << RootPos.nodes_searched()
251 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
252 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
255 RootPos.do_move(RootMoves[0].pv[0], st);
256 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
257 RootPos.undo_move(RootMoves[0].pv[0]);
262 // When search is stopped this info is not printed
263 sync_cout << "info nodes " << RootPos.nodes_searched()
264 << " time " << Time::now() - SearchTime + 1 << sync_endl;
266 // When we reach max depth we arrive here even without Signals.stop is raised,
267 // but if we are pondering or in infinite search, according to UCI protocol,
268 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
269 // command. We simply wait here until GUI sends one of those commands (that
270 // raise Signals.stop).
271 if (!Signals.stop && (Limits.ponder || Limits.infinite))
273 Signals.stopOnPonderhit = true;
274 RootPos.this_thread()->wait_for(Signals.stop);
277 // Best move could be MOVE_NONE when searching on a stalemate position
278 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
279 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
286 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
287 // with increasing depth until the allocated thinking time has been consumed,
288 // user stops the search, or the maximum search depth is reached.
290 void id_loop(Position& pos) {
292 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
294 Value bestValue, alpha, beta, delta;
296 std::memset(ss-2, 0, 5 * sizeof(Stack));
297 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
301 bestValue = delta = alpha = -VALUE_INFINITE;
302 beta = VALUE_INFINITE;
307 Countermoves.clear();
309 PVSize = Options["MultiPV"];
310 Skill skill(Options["Skill Level"]);
312 // Do we have to play with skill handicap? In this case enable MultiPV search
313 // that we will use behind the scenes to retrieve a set of possible moves.
314 if (skill.enabled() && PVSize < 4)
317 PVSize = std::min(PVSize, RootMoves.size());
319 // Iterative deepening loop until requested to stop or target depth reached
320 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
322 // Age out PV variability metric
323 BestMoveChanges *= 0.8;
325 // Save last iteration's scores before first PV line is searched and all
326 // the move scores but the (new) PV are set to -VALUE_INFINITE.
327 for (size_t i = 0; i < RootMoves.size(); ++i)
328 RootMoves[i].prevScore = RootMoves[i].score;
330 // MultiPV loop. We perform a full root search for each PV line
331 for (PVIdx = 0; PVIdx < PVSize && !Signals.stop; ++PVIdx)
333 // Reset aspiration window starting size
337 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
338 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
341 // Start with a small aspiration window and, in case of fail high/low,
342 // research with bigger window until not failing high/low anymore.
345 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
347 // Bring to front the best move. It is critical that sorting is
348 // done with a stable algorithm because all the values but the first
349 // and eventually the new best one are set to -VALUE_INFINITE and
350 // we want to keep the same order for all the moves but the new
351 // PV that goes to the front. Note that in case of MultiPV search
352 // the already searched PV lines are preserved.
353 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
355 // Write PV back to transposition table in case the relevant
356 // entries have been overwritten during the search.
357 for (size_t i = 0; i <= PVIdx; ++i)
358 RootMoves[i].insert_pv_in_tt(pos);
360 // If search has been stopped break immediately. Sorting and
361 // writing PV back to TT is safe becuase RootMoves is still
362 // valid, although refers to previous iteration.
366 // When failing high/low give some update (without cluttering
367 // the UI) before to research.
368 if ( (bestValue <= alpha || bestValue >= beta)
369 && Time::now() - SearchTime > 3000)
370 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
372 // In case of failing low/high increase aspiration window and
373 // research, otherwise exit the loop.
374 if (bestValue <= alpha)
376 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
378 Signals.failedLowAtRoot = true;
379 Signals.stopOnPonderhit = false;
381 else if (bestValue >= beta)
382 beta = std::min(bestValue + delta, VALUE_INFINITE);
389 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
392 // Sort the PV lines searched so far and update the GUI
393 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
395 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
396 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
399 // Do we need to pick now the sub-optimal best move ?
400 if (skill.enabled() && skill.time_to_pick(depth))
403 if (Options["Write Search Log"])
405 RootMove& rm = RootMoves[0];
406 if (skill.best != MOVE_NONE)
407 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
409 Log log(Options["Search Log Filename"]);
410 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
414 // Do we have found a "mate in x"?
416 && bestValue >= VALUE_MATE_IN_MAX_PLY
417 && VALUE_MATE - bestValue <= 2 * Limits.mate)
420 // Do we have time for the next iteration? Can we stop searching now?
421 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
423 bool stop = false; // Local variable, not the volatile Signals.stop
425 // Take in account some extra time if the best move has changed
426 if (depth > 4 && depth < 50 && PVSize == 1)
427 TimeMgr.pv_instability(BestMoveChanges);
429 // Stop search if most of available time is already consumed. We
430 // probably don't have enough time to search the first move at the
431 // next iteration anyway.
432 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
435 // Stop search early if one move seems to be much better than others
437 && BestMoveChanges <= DBL_EPSILON
440 && bestValue > VALUE_MATED_IN_MAX_PLY
441 && ( RootMoves.size() == 1
442 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
444 Value rBeta = bestValue - 2 * PawnValueMg;
445 ss->excludedMove = RootMoves[0].pv[0];
446 ss->skipNullMove = true;
447 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
448 ss->skipNullMove = false;
449 ss->excludedMove = MOVE_NONE;
457 // If we are allowed to ponder do not stop the search now but
458 // keep pondering until GUI sends "ponderhit" or "stop".
460 Signals.stopOnPonderhit = true;
469 // search<>() is the main search function for both PV and non-PV nodes and for
470 // normal and SplitPoint nodes. When called just after a split point the search
471 // is simpler because we have already probed the hash table, done a null move
472 // search, and searched the first move before splitting, we don't have to repeat
473 // all this work again. We also don't need to store anything to the hash table
474 // here: This is taken care of after we return from the split point.
476 template <NodeType NT>
477 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
479 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
480 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
481 const bool RootNode = (NT == Root || NT == SplitPointRoot);
483 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
484 assert(PvNode || (alpha == beta - 1));
485 assert(depth > DEPTH_ZERO);
487 Move quietsSearched[64];
490 SplitPoint* splitPoint;
492 Move ttMove, move, excludedMove, bestMove, threatMove;
493 Depth ext, newDepth, predictedDepth;
494 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
495 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
496 bool captureOrPromotion, dangerous, doFullDepthSearch;
497 int moveCount, quietCount;
499 // Step 1. Initialize node
500 Thread* thisThread = pos.this_thread();
501 inCheck = pos.checkers();
505 splitPoint = ss->splitPoint;
506 bestMove = splitPoint->bestMove;
507 threatMove = splitPoint->threatMove;
508 bestValue = splitPoint->bestValue;
510 ttMove = excludedMove = MOVE_NONE;
511 ttValue = VALUE_NONE;
513 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
518 moveCount = quietCount = 0;
519 bestValue = -VALUE_INFINITE;
520 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
521 ss->ply = (ss-1)->ply + 1;
522 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
523 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
525 // Used to send selDepth info to GUI
526 if (PvNode && thisThread->maxPly < ss->ply)
527 thisThread->maxPly = ss->ply;
531 // Step 2. Check for aborted search and immediate draw
532 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
533 return DrawValue[pos.side_to_move()];
535 // Step 3. Mate distance pruning. Even if we mate at the next move our score
536 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
537 // a shorter mate was found upward in the tree then there is no need to search
538 // further, we will never beat current alpha. Same logic but with reversed signs
539 // applies also in the opposite condition of being mated instead of giving mate,
540 // in this case return a fail-high score.
541 alpha = std::max(mated_in(ss->ply), alpha);
542 beta = std::min(mate_in(ss->ply+1), beta);
547 // Step 4. Transposition table lookup
548 // We don't want the score of a partial search to overwrite a previous full search
549 // TT value, so we use a different position key in case of an excluded move.
550 excludedMove = ss->excludedMove;
551 posKey = excludedMove ? pos.exclusion_key() : pos.key();
552 tte = TT.probe(posKey);
553 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
554 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
556 // At PV nodes we check for exact scores, while at non-PV nodes we check for
557 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
558 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
559 // we should also update RootMoveList to avoid bogus output.
562 && tte->depth() >= depth
563 && ttValue != VALUE_NONE // Only in case of TT access race
564 && ( PvNode ? tte->bound() == BOUND_EXACT
565 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
566 : (tte->bound() & BOUND_UPPER)))
569 ss->currentMove = ttMove; // Can be MOVE_NONE
573 && !pos.capture_or_promotion(ttMove)
574 && ttMove != ss->killers[0])
576 ss->killers[1] = ss->killers[0];
577 ss->killers[0] = ttMove;
582 // Step 5. Evaluate the position statically and update parent's gain statistics
585 ss->staticEval = eval = VALUE_NONE;
591 // Never assume anything on values stored in TT
592 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
593 eval = ss->staticEval = evaluate(pos);
595 // Can ttValue be used as a better position evaluation?
596 if (ttValue != VALUE_NONE)
597 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
602 eval = ss->staticEval = evaluate(pos);
603 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
606 if ( !pos.captured_piece_type()
607 && ss->staticEval != VALUE_NONE
608 && (ss-1)->staticEval != VALUE_NONE
609 && (move = (ss-1)->currentMove) != MOVE_NULL
610 && type_of(move) == NORMAL)
612 Square to = to_sq(move);
613 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
616 // Step 6. Razoring (skipped when in check)
618 && depth < 4 * ONE_PLY
619 && eval + razor_margin(depth) < beta
620 && ttMove == MOVE_NONE
621 && abs(beta) < VALUE_MATE_IN_MAX_PLY
622 && !pos.pawn_on_7th(pos.side_to_move()))
624 Value rbeta = beta - razor_margin(depth);
625 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
627 // Logically we should return (v + razor_margin(depth)), but
628 // surprisingly this did slightly weaker in tests.
632 // Step 7. Futility pruning: child node (skipped when in check)
635 && depth < 7 * ONE_PLY
636 && eval - futility_margin(depth) >= beta
637 && abs(beta) < VALUE_MATE_IN_MAX_PLY
638 && abs(eval) < VALUE_KNOWN_WIN
639 && pos.non_pawn_material(pos.side_to_move()))
640 return eval - futility_margin(depth);
642 // Step 8. Null move search with verification search (is omitted in PV nodes)
645 && depth >= 2 * ONE_PLY
647 && abs(beta) < VALUE_MATE_IN_MAX_PLY
648 && pos.non_pawn_material(pos.side_to_move()))
650 ss->currentMove = MOVE_NULL;
652 // Null move dynamic reduction based on depth
653 Depth R = 3 * ONE_PLY + depth / 4;
655 // Null move dynamic reduction based on value
656 if (eval - PawnValueMg > beta)
659 pos.do_null_move(st);
660 (ss+1)->skipNullMove = true;
661 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
662 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
663 (ss+1)->skipNullMove = false;
664 pos.undo_null_move();
666 if (nullValue >= beta)
668 // Do not return unproven mate scores
669 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
672 if (depth < 12 * ONE_PLY)
675 // Do verification search at high depths
676 ss->skipNullMove = true;
677 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
678 ss->skipNullMove = false;
685 // The null move failed low, which means that we may be faced with
686 // some kind of threat. If the previous move was reduced, check if
687 // the move that refuted the null move was somehow connected to the
688 // move which was reduced. If a connection is found, return a fail
689 // low score (which will cause the reduced move to fail high in the
690 // parent node, which will trigger a re-search with full depth).
691 threatMove = (ss+1)->currentMove;
693 if ( depth < 5 * ONE_PLY
695 && threatMove != MOVE_NONE
696 && allows(pos, (ss-1)->currentMove, threatMove))
701 // Step 9. ProbCut (skipped when in check)
702 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
703 // and a reduced search returns a value much above beta, we can (almost) safely
704 // prune the previous move.
706 && depth >= 5 * ONE_PLY
708 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
710 Value rbeta = beta + 200;
711 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
713 assert(rdepth >= ONE_PLY);
714 assert((ss-1)->currentMove != MOVE_NONE);
715 assert((ss-1)->currentMove != MOVE_NULL);
717 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
720 while ((move = mp.next_move<false>()) != MOVE_NONE)
721 if (pos.legal(move, ci.pinned))
723 ss->currentMove = move;
724 pos.do_move(move, st, ci, pos.gives_check(move, ci));
725 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
732 // Step 10. Internal iterative deepening (skipped when in check)
733 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
734 && ttMove == MOVE_NONE
735 && (PvNode || ss->staticEval + Value(256) >= beta))
737 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
739 ss->skipNullMove = true;
740 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
741 ss->skipNullMove = false;
743 tte = TT.probe(posKey);
744 ttMove = tte ? tte->move() : MOVE_NONE;
747 moves_loop: // When in check and at SpNode search starts from here
749 Square prevMoveSq = to_sq((ss-1)->currentMove);
750 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
751 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
753 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
755 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
756 improving = ss->staticEval >= (ss-2)->staticEval
757 || ss->staticEval == VALUE_NONE
758 ||(ss-2)->staticEval == VALUE_NONE;
760 singularExtensionNode = !RootNode
762 && depth >= 8 * ONE_PLY
763 && ttMove != MOVE_NONE
764 && !excludedMove // Recursive singular search is not allowed
765 && (tte->bound() & BOUND_LOWER)
766 && tte->depth() >= depth - 3 * ONE_PLY;
768 // Step 11. Loop through moves
769 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
770 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
774 if (move == excludedMove)
777 // At root obey the "searchmoves" option and skip moves not listed in Root
778 // Move List, as a consequence any illegal move is also skipped. In MultiPV
779 // mode we also skip PV moves which have been already searched.
780 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
785 // Shared counter cannot be decremented later if move turns out to be illegal
786 if (!pos.legal(move, ci.pinned))
789 moveCount = ++splitPoint->moveCount;
790 splitPoint->mutex.unlock();
797 Signals.firstRootMove = (moveCount == 1);
799 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
800 sync_cout << "info depth " << depth / ONE_PLY
801 << " currmove " << move_to_uci(move, pos.is_chess960())
802 << " currmovenumber " << moveCount + PVIdx << sync_endl;
806 captureOrPromotion = pos.capture_or_promotion(move);
807 givesCheck = pos.gives_check(move, ci);
808 dangerous = givesCheck
809 || pos.passed_pawn_push(move)
810 || type_of(move) == CASTLE;
812 // Step 12. Extend checks
813 if (givesCheck && pos.see_sign(move) >= 0)
816 // Singular extension search. If all moves but one fail low on a search of
817 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
818 // is singular and should be extended. To verify this we do a reduced search
819 // on all the other moves but the ttMove, if result is lower than ttValue minus
820 // a margin then we extend ttMove.
821 if ( singularExtensionNode
824 && pos.legal(move, ci.pinned)
825 && abs(ttValue) < VALUE_KNOWN_WIN)
827 assert(ttValue != VALUE_NONE);
829 Value rBeta = ttValue - int(depth);
830 ss->excludedMove = move;
831 ss->skipNullMove = true;
832 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
833 ss->skipNullMove = false;
834 ss->excludedMove = MOVE_NONE;
840 // Update current move (this must be done after singular extension search)
841 newDepth = depth - ONE_PLY + ext;
843 // Step 13. Pruning at shallow depth (exclude PV nodes)
845 && !captureOrPromotion
848 /* && move != ttMove Already implicit in the next condition */
849 && bestValue > VALUE_MATED_IN_MAX_PLY)
851 // Move count based pruning
852 if ( depth < 16 * ONE_PLY
853 && moveCount >= FutilityMoveCounts[improving][depth]
854 && (!threatMove || !refutes(pos, move, threatMove)))
857 splitPoint->mutex.lock();
862 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
864 // Futility pruning: parent node
865 if (predictedDepth < 7 * ONE_PLY)
867 futilityValue = ss->staticEval + futility_margin(predictedDepth)
868 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
870 if (futilityValue <= alpha)
872 bestValue = std::max(bestValue, futilityValue);
876 splitPoint->mutex.lock();
877 if (bestValue > splitPoint->bestValue)
878 splitPoint->bestValue = bestValue;
884 // Prune moves with negative SEE at low depths
885 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
888 splitPoint->mutex.lock();
895 // Check for legality only before to do the move
896 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
902 pvMove = PvNode && moveCount == 1;
903 ss->currentMove = move;
904 if (!SpNode && !captureOrPromotion && quietCount < 64)
905 quietsSearched[quietCount++] = move;
907 // Step 14. Make the move
908 pos.do_move(move, st, ci, givesCheck);
910 // Step 15. Reduced depth search (LMR). If the move fails high will be
911 // re-searched at full depth.
912 if ( depth >= 3 * ONE_PLY
914 && !captureOrPromotion
916 && move != ss->killers[0]
917 && move != ss->killers[1])
919 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
921 if (!PvNode && cutNode)
922 ss->reduction += ONE_PLY;
924 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
925 ss->reduction += ONE_PLY / 2;
927 if (move == countermoves[0] || move == countermoves[1])
928 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
930 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
932 alpha = splitPoint->alpha;
934 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
936 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
937 ss->reduction = DEPTH_ZERO;
940 doFullDepthSearch = !pvMove;
942 // Step 16. Full depth search, when LMR is skipped or fails high
943 if (doFullDepthSearch)
946 alpha = splitPoint->alpha;
948 value = newDepth < ONE_PLY ?
949 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
950 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
951 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
954 // Only for PV nodes do a full PV search on the first move or after a fail
955 // high, in the latter case search only if value < beta, otherwise let the
956 // parent node to fail low with value <= alpha and to try another move.
957 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
958 value = newDepth < ONE_PLY ?
959 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
960 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
961 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
962 // Step 17. Undo move
965 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
967 // Step 18. Check for new best move
970 splitPoint->mutex.lock();
971 bestValue = splitPoint->bestValue;
972 alpha = splitPoint->alpha;
975 // Finished searching the move. If Signals.stop is true, the search
976 // was aborted because the user interrupted the search or because we
977 // ran out of time. In this case, the return value of the search cannot
978 // be trusted, and we don't update the best move and/or PV.
979 if (Signals.stop || thisThread->cutoff_occurred())
980 return value; // To avoid returning VALUE_INFINITE
984 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
986 // PV move or new best move ?
987 if (pvMove || value > alpha)
990 rm.extract_pv_from_tt(pos);
992 // We record how often the best move has been changed in each
993 // iteration. This information is used for time management: When
994 // the best move changes frequently, we allocate some more time.
999 // All other moves but the PV are set to the lowest value, this
1000 // is not a problem when sorting becuase sort is stable and move
1001 // position in the list is preserved, just the PV is pushed up.
1002 rm.score = -VALUE_INFINITE;
1005 if (value > bestValue)
1007 bestValue = SpNode ? splitPoint->bestValue = value : value;
1011 bestMove = SpNode ? splitPoint->bestMove = move : move;
1013 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1014 alpha = SpNode ? splitPoint->alpha = value : value;
1017 assert(value >= beta); // Fail high
1020 splitPoint->cutoff = true;
1027 // Step 19. Check for splitting the search
1029 && depth >= Threads.minimumSplitDepth
1030 && Threads.available_slave(thisThread)
1031 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1033 assert(bestValue < beta);
1035 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1036 depth, threatMove, moveCount, &mp, NT, cutNode);
1037 if (bestValue >= beta)
1045 // Step 20. Check for mate and stalemate
1046 // All legal moves have been searched and if there are no legal moves, it
1047 // must be mate or stalemate. Note that we can have a false positive in
1048 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1049 // harmless because return value is discarded anyhow in the parent nodes.
1050 // If we are in a singular extension search then return a fail low score.
1051 // A split node has at least one move, the one tried before to be splitted.
1053 return excludedMove ? alpha
1054 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1056 // If we have pruned all the moves without searching return a fail-low score
1057 if (bestValue == -VALUE_INFINITE)
1060 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1061 bestValue >= beta ? BOUND_LOWER :
1062 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1063 depth, bestMove, ss->staticEval);
1065 // Quiet best move: update killers, history and countermoves
1066 if ( bestValue >= beta
1067 && !pos.capture_or_promotion(bestMove)
1070 if (ss->killers[0] != bestMove)
1072 ss->killers[1] = ss->killers[0];
1073 ss->killers[0] = bestMove;
1076 // Increase history value of the cut-off move and decrease all the other
1077 // played non-capture moves.
1078 Value bonus = Value(int(depth) * int(depth));
1079 History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
1080 for (int i = 0; i < quietCount - 1; ++i)
1082 Move m = quietsSearched[i];
1083 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1086 if (is_ok((ss-1)->currentMove))
1087 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1090 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1096 // qsearch() is the quiescence search function, which is called by the main
1097 // search function when the remaining depth is zero (or, to be more precise,
1098 // less than ONE_PLY).
1100 template <NodeType NT, bool InCheck>
1101 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1103 const bool PvNode = (NT == PV);
1105 assert(NT == PV || NT == NonPV);
1106 assert(InCheck == !!pos.checkers());
1107 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1108 assert(PvNode || (alpha == beta - 1));
1109 assert(depth <= DEPTH_ZERO);
1114 Move ttMove, move, bestMove;
1115 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1116 bool givesCheck, evasionPrunable;
1119 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1123 ss->currentMove = bestMove = MOVE_NONE;
1124 ss->ply = (ss-1)->ply + 1;
1126 // Check for an instant draw or maximum ply reached
1127 if (pos.is_draw() || ss->ply > MAX_PLY)
1128 return DrawValue[pos.side_to_move()];
1130 // Decide whether or not to include checks, this fixes also the type of
1131 // TT entry depth that we are going to use. Note that in qsearch we use
1132 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1133 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1134 : DEPTH_QS_NO_CHECKS;
1136 // Transposition table lookup
1138 tte = TT.probe(posKey);
1139 ttMove = tte ? tte->move() : MOVE_NONE;
1140 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1143 && tte->depth() >= ttDepth
1144 && ttValue != VALUE_NONE // Only in case of TT access race
1145 && ( PvNode ? tte->bound() == BOUND_EXACT
1146 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1147 : (tte->bound() & BOUND_UPPER)))
1149 ss->currentMove = ttMove; // Can be MOVE_NONE
1153 // Evaluate the position statically
1156 ss->staticEval = VALUE_NONE;
1157 bestValue = futilityBase = -VALUE_INFINITE;
1163 // Never assume anything on values stored in TT
1164 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1165 ss->staticEval = bestValue = evaluate(pos);
1167 // Can ttValue be used as a better position evaluation?
1168 if (ttValue != VALUE_NONE)
1169 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1170 bestValue = ttValue;
1173 ss->staticEval = bestValue = evaluate(pos);
1175 // Stand pat. Return immediately if static value is at least beta
1176 if (bestValue >= beta)
1179 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1180 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1185 if (PvNode && bestValue > alpha)
1188 futilityBase = bestValue + Value(128);
1191 // Initialize a MovePicker object for the current position, and prepare
1192 // to search the moves. Because the depth is <= 0 here, only captures,
1193 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1195 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1198 // Loop through the moves until no moves remain or a beta cutoff occurs
1199 while ((move = mp.next_move<false>()) != MOVE_NONE)
1201 assert(is_ok(move));
1203 givesCheck = pos.gives_check(move, ci);
1210 && type_of(move) != PROMOTION
1211 && futilityBase > -VALUE_KNOWN_WIN
1212 && !pos.passed_pawn_push(move))
1214 futilityValue = futilityBase
1215 + PieceValue[EG][pos.piece_on(to_sq(move))]
1216 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1218 if (futilityValue < beta)
1220 bestValue = std::max(bestValue, futilityValue);
1224 // Prune moves with negative or equal SEE and also moves with positive
1225 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1226 if ( futilityBase < beta
1227 && pos.see(move, beta - futilityBase) <= 0)
1229 bestValue = std::max(bestValue, futilityBase);
1234 // Detect non-capture evasions that are candidate to be pruned
1235 evasionPrunable = InCheck
1236 && bestValue > VALUE_MATED_IN_MAX_PLY
1237 && !pos.capture(move)
1238 && !pos.can_castle(pos.side_to_move());
1240 // Don't search moves with negative SEE values
1242 && (!InCheck || evasionPrunable)
1244 && type_of(move) != PROMOTION
1245 && pos.see_sign(move) < 0)
1248 // Check for legality only before to do the move
1249 if (!pos.legal(move, ci.pinned))
1252 ss->currentMove = move;
1254 // Make and search the move
1255 pos.do_move(move, st, ci, givesCheck);
1256 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1257 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1258 pos.undo_move(move);
1260 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1262 // Check for new best move
1263 if (value > bestValue)
1269 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1276 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1277 ttDepth, move, ss->staticEval);
1285 // All legal moves have been searched. A special case: If we're in check
1286 // and no legal moves were found, it is checkmate.
1287 if (InCheck && bestValue == -VALUE_INFINITE)
1288 return mated_in(ss->ply); // Plies to mate from the root
1290 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1291 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1292 ttDepth, bestMove, ss->staticEval);
1294 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1300 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1301 // "plies to mate from the current position". Non-mate scores are unchanged.
1302 // The function is called before storing a value to the transposition table.
1304 Value value_to_tt(Value v, int ply) {
1306 assert(v != VALUE_NONE);
1308 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1309 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1313 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1314 // from the transposition table (where refers to the plies to mate/be mated
1315 // from current position) to "plies to mate/be mated from the root".
1317 Value value_from_tt(Value v, int ply) {
1319 return v == VALUE_NONE ? VALUE_NONE
1320 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1321 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1325 // allows() tests whether the 'first' move at previous ply somehow makes the
1326 // 'second' move possible, for instance if the moving piece is the same in
1327 // both moves. Normally the second move is the threat (the best move returned
1328 // from a null search that fails low).
1330 bool allows(const Position& pos, Move first, Move second) {
1332 assert(is_ok(first));
1333 assert(is_ok(second));
1334 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1335 assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1337 Square m1from = from_sq(first);
1338 Square m2from = from_sq(second);
1339 Square m1to = to_sq(first);
1340 Square m2to = to_sq(second);
1342 // The piece is the same or second's destination was vacated by the first move
1343 // We exclude the trivial case where a sliding piece does in two moves what
1344 // it could do in one move: eg. Ra1a2, Ra2a3.
1346 || (m1to == m2from && !aligned(m1from, m2from, m2to)))
1349 // Second one moves through the square vacated by first one
1350 if (between_bb(m2from, m2to) & m1from)
1353 // Second's destination is defended by the first move's piece
1354 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1358 // Second move gives a discovered check through the first's checking piece
1359 if (m1att & pos.king_square(pos.side_to_move()))
1361 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1369 // refutes() tests whether a 'first' move is able to defend against a 'second'
1370 // opponent's move. In this case will not be pruned. Normally the second move
1371 // is the threat (the best move returned from a null search that fails low).
1373 bool refutes(const Position& pos, Move first, Move second) {
1375 assert(is_ok(first));
1376 assert(is_ok(second));
1378 Square m1from = from_sq(first);
1379 Square m2from = from_sq(second);
1380 Square m1to = to_sq(first);
1381 Square m2to = to_sq(second);
1383 // Don't prune moves of the threatened piece
1387 // If the threatened piece has value less than or equal to the value of the
1388 // threat piece, don't prune moves which defend it.
1389 if ( pos.capture(second)
1390 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1391 || type_of(pos.piece_on(m2from)) == KING))
1393 // Update occupancy as if the piece and the threat are moving
1394 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1395 Piece pc = pos.piece_on(m1from);
1397 // The moved piece attacks the square 'tto' ?
1398 if (pos.attacks_from(pc, m1to, occ) & m2to)
1401 // Scan for possible X-ray attackers behind the moved piece
1402 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
1403 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
1405 // Verify attackers are triggered by our move and not already existing
1406 if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
1410 // Don't prune safe moves which block the threat path
1411 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1418 // When playing with strength handicap choose best move among the MultiPV set
1419 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1421 Move Skill::pick_move() {
1425 // PRNG sequence should be not deterministic
1426 for (int i = Time::now() % 50; i > 0; --i)
1427 rk.rand<unsigned>();
1429 // RootMoves are already sorted by score in descending order
1430 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1431 int weakness = 120 - 2 * level;
1432 int max_s = -VALUE_INFINITE;
1435 // Choose best move. For each move score we add two terms both dependent on
1436 // weakness, one deterministic and bigger for weaker moves, and one random,
1437 // then we choose the move with the resulting highest score.
1438 for (size_t i = 0; i < PVSize; ++i)
1440 int s = RootMoves[i].score;
1442 // Don't allow crazy blunders even at very low skills
1443 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1446 // This is our magic formula
1447 s += ( weakness * int(RootMoves[0].score - s)
1448 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1453 best = RootMoves[i].pv[0];
1460 // uci_pv() formats PV information according to UCI protocol. UCI requires
1461 // to send all the PV lines also if are still to be searched and so refer to
1462 // the previous search score.
1464 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1466 std::stringstream s;
1467 Time::point elapsed = Time::now() - SearchTime + 1;
1468 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1471 for (size_t i = 0; i < Threads.size(); ++i)
1472 if (Threads[i]->maxPly > selDepth)
1473 selDepth = Threads[i]->maxPly;
1475 for (size_t i = 0; i < uciPVSize; ++i)
1477 bool updated = (i <= PVIdx);
1479 if (depth == 1 && !updated)
1482 int d = updated ? depth : depth - 1;
1483 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1485 if (s.rdbuf()->in_avail()) // Not at first line
1488 s << "info depth " << d
1489 << " seldepth " << selDepth
1490 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1491 << " nodes " << pos.nodes_searched()
1492 << " nps " << pos.nodes_searched() * 1000 / elapsed
1493 << " time " << elapsed
1494 << " multipv " << i + 1
1497 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1498 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1507 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1508 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1509 /// allow to always have a ponder move even when we fail high at root, and a
1510 /// long PV to print that is important for position analysis.
1512 void RootMove::extract_pv_from_tt(Position& pos) {
1514 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1524 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1526 pos.do_move(pv[ply++], *st++);
1527 tte = TT.probe(pos.key());
1530 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1531 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1533 && (!pos.is_draw() || ply < 2));
1535 pv.push_back(MOVE_NONE); // Must be zero-terminating
1537 while (ply) pos.undo_move(pv[--ply]);
1541 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1542 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1543 /// first, even if the old TT entries have been overwritten.
1545 void RootMove::insert_pv_in_tt(Position& pos) {
1547 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1552 tte = TT.probe(pos.key());
1554 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1555 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1557 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1559 pos.do_move(pv[ply++], *st++);
1561 } while (pv[ply] != MOVE_NONE);
1563 while (ply) pos.undo_move(pv[--ply]);
1567 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1569 void Thread::idle_loop() {
1571 // Pointer 'this_sp' is not null only if we are called from split(), and not
1572 // at the thread creation. So it means we are the split point's master.
1573 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1575 assert(!this_sp || (this_sp->masterThread == this && searching));
1579 // If we are not searching, wait for a condition to be signaled instead of
1580 // wasting CPU time polling for work.
1581 while ((!searching && Threads.sleepWhileIdle) || exit)
1589 // Grab the lock to avoid races with Thread::notify_one()
1592 // If we are master and all slaves have finished then exit idle_loop
1593 if (this_sp && !this_sp->slavesMask)
1599 // Do sleep after retesting sleep conditions under lock protection, in
1600 // particular we need to avoid a deadlock in case a master thread has,
1601 // in the meanwhile, allocated us and sent the notify_one() call before
1602 // we had the chance to grab the lock.
1603 if (!searching && !exit)
1604 sleepCondition.wait(mutex);
1609 // If this thread has been assigned work, launch a search
1614 Threads.mutex.lock();
1617 assert(activeSplitPoint);
1618 SplitPoint* sp = activeSplitPoint;
1620 Threads.mutex.unlock();
1622 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1623 Position pos(*sp->pos, this);
1625 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1626 ss->splitPoint = sp;
1630 assert(activePosition == NULL);
1632 activePosition = &pos;
1634 switch (sp->nodeType) {
1636 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1639 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1642 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1651 activePosition = NULL;
1652 sp->slavesMask &= ~(1ULL << idx);
1653 sp->nodes += pos.nodes_searched();
1655 // Wake up master thread so to allow it to return from the idle loop
1656 // in case we are the last slave of the split point.
1657 if ( Threads.sleepWhileIdle
1658 && this != sp->masterThread
1661 assert(!sp->masterThread->searching);
1662 sp->masterThread->notify_one();
1665 // After releasing the lock we cannot access anymore any SplitPoint
1666 // related data in a safe way becuase it could have been released under
1667 // our feet by the sp master. Also accessing other Thread objects is
1668 // unsafe because if we are exiting there is a chance are already freed.
1672 // If this thread is the master of a split point and all slaves have finished
1673 // their work at this split point, return from the idle loop.
1674 if (this_sp && !this_sp->slavesMask)
1676 this_sp->mutex.lock();
1677 bool finished = !this_sp->slavesMask; // Retest under lock protection
1678 this_sp->mutex.unlock();
1686 /// check_time() is called by the timer thread when the timer triggers. It is
1687 /// used to print debug info and, more important, to detect when we are out of
1688 /// available time and so stop the search.
1692 static Time::point lastInfoTime = Time::now();
1693 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1695 if (Time::now() - lastInfoTime >= 1000)
1697 lastInfoTime = Time::now();
1706 Threads.mutex.lock();
1708 nodes = RootPos.nodes_searched();
1710 // Loop across all split points and sum accumulated SplitPoint nodes plus
1711 // all the currently active positions nodes.
1712 for (size_t i = 0; i < Threads.size(); ++i)
1713 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1715 SplitPoint& sp = Threads[i]->splitPoints[j];
1720 Bitboard sm = sp.slavesMask;
1723 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1725 nodes += pos->nodes_searched();
1731 Threads.mutex.unlock();
1734 Time::point elapsed = Time::now() - SearchTime;
1735 bool stillAtFirstMove = Signals.firstRootMove
1736 && !Signals.failedLowAtRoot
1737 && elapsed > TimeMgr.available_time();
1739 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1740 || stillAtFirstMove;
1742 if ( (Limits.use_time_management() && noMoreTime)
1743 || (Limits.movetime && elapsed >= Limits.movetime)
1744 || (Limits.nodes && nodes >= Limits.nodes))
1745 Signals.stop = true;