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);
489 SplitPoint* splitPoint;
491 Move ttMove, move, excludedMove, bestMove, threatMove;
492 Depth ext, newDepth, predictedDepth;
493 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
494 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
495 bool captureOrPromotion, dangerous, doFullDepthSearch;
498 // Step 1. Initialize node
499 Thread* thisThread = pos.this_thread();
500 inCheck = pos.checkers();
504 splitPoint = ss->splitPoint;
505 bestMove = splitPoint->bestMove;
506 threatMove = splitPoint->threatMove;
507 bestValue = splitPoint->bestValue;
509 ttMove = excludedMove = MOVE_NONE;
510 ttValue = VALUE_NONE;
512 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
518 bestValue = -VALUE_INFINITE;
519 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
520 ss->ply = (ss-1)->ply + 1;
521 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
522 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
524 // Used to send selDepth info to GUI
525 if (PvNode && thisThread->maxPly < ss->ply)
526 thisThread->maxPly = ss->ply;
530 // Step 2. Check for aborted search and immediate draw
531 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
532 return DrawValue[pos.side_to_move()];
534 // Step 3. Mate distance pruning. Even if we mate at the next move our score
535 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
536 // a shorter mate was found upward in the tree then there is no need to search
537 // further, we will never beat current alpha. Same logic but with reversed signs
538 // applies also in the opposite condition of being mated instead of giving mate,
539 // in this case return a fail-high score.
540 alpha = std::max(mated_in(ss->ply), alpha);
541 beta = std::min(mate_in(ss->ply+1), beta);
546 // Step 4. Transposition table lookup
547 // We don't want the score of a partial search to overwrite a previous full search
548 // TT value, so we use a different position key in case of an excluded move.
549 excludedMove = ss->excludedMove;
550 posKey = excludedMove ? pos.exclusion_key() : pos.key();
551 tte = TT.probe(posKey);
552 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
553 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
555 // At PV nodes we check for exact scores, while at non-PV nodes we check for
556 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
557 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
558 // we should also update RootMoveList to avoid bogus output.
561 && tte->depth() >= depth
562 && ttValue != VALUE_NONE // Only in case of TT access race
563 && ( PvNode ? tte->bound() == BOUND_EXACT
564 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
565 : (tte->bound() & BOUND_UPPER)))
568 ss->currentMove = ttMove; // Can be MOVE_NONE
572 && !pos.capture_or_promotion(ttMove)
573 && ttMove != ss->killers[0])
575 ss->killers[1] = ss->killers[0];
576 ss->killers[0] = ttMove;
581 // Step 5. Evaluate the position statically and update parent's gain statistics
584 ss->staticEval = eval = VALUE_NONE;
590 // Never assume anything on values stored in TT
591 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
592 eval = ss->staticEval = evaluate(pos);
594 // Can ttValue be used as a better position evaluation?
595 if (ttValue != VALUE_NONE)
596 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
601 eval = ss->staticEval = evaluate(pos);
602 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
605 if ( !pos.captured_piece_type()
606 && ss->staticEval != VALUE_NONE
607 && (ss-1)->staticEval != VALUE_NONE
608 && (move = (ss-1)->currentMove) != MOVE_NULL
609 && type_of(move) == NORMAL)
611 Square to = to_sq(move);
612 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
615 // Step 6. Razoring (skipped when in check)
617 && depth < 4 * ONE_PLY
618 && eval + razor_margin(depth) < beta
619 && ttMove == MOVE_NONE
620 && abs(beta) < VALUE_MATE_IN_MAX_PLY
621 && !pos.pawn_on_7th(pos.side_to_move()))
623 Value rbeta = beta - razor_margin(depth);
624 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
626 // Logically we should return (v + razor_margin(depth)), but
627 // surprisingly this did slightly weaker in tests.
631 // Step 7. Futility pruning: child node (skipped when in check)
634 && depth < 7 * ONE_PLY
635 && eval - futility_margin(depth) >= beta
636 && abs(beta) < VALUE_MATE_IN_MAX_PLY
637 && abs(eval) < VALUE_KNOWN_WIN
638 && pos.non_pawn_material(pos.side_to_move()))
639 return eval - futility_margin(depth);
641 // Step 8. Null move search with verification search (is omitted in PV nodes)
644 && depth >= 2 * ONE_PLY
646 && abs(beta) < VALUE_MATE_IN_MAX_PLY
647 && pos.non_pawn_material(pos.side_to_move()))
649 ss->currentMove = MOVE_NULL;
651 // Null move dynamic reduction based on depth
652 Depth R = 3 * ONE_PLY + depth / 4;
654 // Null move dynamic reduction based on value
655 if (eval - PawnValueMg > beta)
658 pos.do_null_move(st);
659 (ss+1)->skipNullMove = true;
660 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
661 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
662 (ss+1)->skipNullMove = false;
663 pos.undo_null_move();
665 if (nullValue >= beta)
667 // Do not return unproven mate scores
668 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
671 if (depth < 12 * ONE_PLY)
674 // Do verification search at high depths
675 ss->skipNullMove = true;
676 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
677 ss->skipNullMove = false;
684 // The null move failed low, which means that we may be faced with
685 // some kind of threat. If the previous move was reduced, check if
686 // the move that refuted the null move was somehow connected to the
687 // move which was reduced. If a connection is found, return a fail
688 // low score (which will cause the reduced move to fail high in the
689 // parent node, which will trigger a re-search with full depth).
690 threatMove = (ss+1)->currentMove;
692 if ( depth < 5 * ONE_PLY
694 && threatMove != MOVE_NONE
695 && allows(pos, (ss-1)->currentMove, threatMove))
700 // Step 9. ProbCut (skipped when in check)
701 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
702 // and a reduced search returns a value much above beta, we can (almost) safely
703 // prune the previous move.
705 && depth >= 5 * ONE_PLY
707 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
709 Value rbeta = beta + 200;
710 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
712 assert(rdepth >= ONE_PLY);
713 assert((ss-1)->currentMove != MOVE_NONE);
714 assert((ss-1)->currentMove != MOVE_NULL);
716 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
719 while ((move = mp.next_move<false>()) != MOVE_NONE)
720 if (pos.legal(move, ci.pinned))
722 ss->currentMove = move;
723 pos.do_move(move, st, ci, pos.gives_check(move, ci));
724 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
731 // Step 10. Internal iterative deepening (skipped when in check)
732 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
733 && ttMove == MOVE_NONE
734 && (PvNode || ss->staticEval + Value(256) >= beta))
736 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
738 ss->skipNullMove = true;
739 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
740 ss->skipNullMove = false;
742 tte = TT.probe(posKey);
743 ttMove = tte ? tte->move() : MOVE_NONE;
746 moves_loop: // When in check and at SpNode search starts from here
748 Square prevMoveSq = to_sq((ss-1)->currentMove);
749 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
750 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
752 MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
754 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
755 improving = ss->staticEval >= (ss-2)->staticEval
756 || ss->staticEval == VALUE_NONE
757 ||(ss-2)->staticEval == VALUE_NONE;
759 singularExtensionNode = !RootNode
761 && depth >= 8 * ONE_PLY
762 && ttMove != MOVE_NONE
763 && !excludedMove // Recursive singular search is not allowed
764 && (tte->bound() & BOUND_LOWER)
765 && tte->depth() >= depth - 3 * ONE_PLY;
767 // Step 11. Loop through moves
768 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
769 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
773 if (move == excludedMove)
776 // At root obey the "searchmoves" option and skip moves not listed in Root
777 // Move List, as a consequence any illegal move is also skipped. In MultiPV
778 // mode we also skip PV moves which have been already searched.
779 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
784 // Shared counter cannot be decremented later if move turns out to be illegal
785 if (!pos.legal(move, ci.pinned))
788 moveCount = ++splitPoint->moveCount;
789 splitPoint->mutex.unlock();
796 Signals.firstRootMove = (moveCount == 1);
798 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
799 sync_cout << "info depth " << depth / ONE_PLY
800 << " currmove " << move_to_uci(move, pos.is_chess960())
801 << " currmovenumber " << moveCount + PVIdx << sync_endl;
805 captureOrPromotion = pos.capture_or_promotion(move);
806 givesCheck = pos.gives_check(move, ci);
807 dangerous = givesCheck
808 || pos.passed_pawn_push(move)
809 || type_of(move) == CASTLE;
811 // Step 12. Extend checks
812 if (givesCheck && pos.see_sign(move) >= 0)
815 // Singular extension search. If all moves but one fail low on a search of
816 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
817 // is singular and should be extended. To verify this we do a reduced search
818 // on all the other moves but the ttMove, if result is lower than ttValue minus
819 // a margin then we extend ttMove.
820 if ( singularExtensionNode
823 && pos.legal(move, ci.pinned)
824 && abs(ttValue) < VALUE_KNOWN_WIN)
826 assert(ttValue != VALUE_NONE);
828 Value rBeta = ttValue - int(depth);
829 ss->excludedMove = move;
830 ss->skipNullMove = true;
831 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
832 ss->skipNullMove = false;
833 ss->excludedMove = MOVE_NONE;
839 // Update current move (this must be done after singular extension search)
840 newDepth = depth - ONE_PLY + ext;
842 // Step 13. Pruning at shallow depth (exclude PV nodes)
844 && !captureOrPromotion
847 /* && move != ttMove Already implicit in the next condition */
848 && bestValue > VALUE_MATED_IN_MAX_PLY)
850 // Move count based pruning
851 if ( depth < 16 * ONE_PLY
852 && moveCount >= FutilityMoveCounts[improving][depth]
853 && (!threatMove || !refutes(pos, move, threatMove)))
856 splitPoint->mutex.lock();
861 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
863 // Futility pruning: parent node
864 if (predictedDepth < 7 * ONE_PLY)
866 futilityValue = ss->staticEval + futility_margin(predictedDepth)
867 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
869 if (futilityValue <= alpha)
871 bestValue = std::max(bestValue, futilityValue);
875 splitPoint->mutex.lock();
876 if (bestValue > splitPoint->bestValue)
877 splitPoint->bestValue = bestValue;
883 // Prune moves with negative SEE at low depths
884 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
887 splitPoint->mutex.lock();
894 // Check for legality only before to do the move
895 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
901 pvMove = PvNode && moveCount == 1;
902 ss->currentMove = move;
904 // Step 14. Make the move
905 pos.do_move(move, st, ci, givesCheck);
907 // Step 15. Reduced depth search (LMR). If the move fails high will be
908 // re-searched at full depth.
909 if ( depth >= 3 * ONE_PLY
911 && !captureOrPromotion
913 && move != ss->killers[0]
914 && move != ss->killers[1])
916 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
918 if (!PvNode && cutNode)
919 ss->reduction += ONE_PLY;
921 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
922 ss->reduction += ONE_PLY / 2;
924 if (move == countermoves[0] || move == countermoves[1])
925 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
927 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
929 alpha = splitPoint->alpha;
931 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
933 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
934 ss->reduction = DEPTH_ZERO;
937 doFullDepthSearch = !pvMove;
939 // Step 16. Full depth search, when LMR is skipped or fails high
940 if (doFullDepthSearch)
943 alpha = splitPoint->alpha;
945 value = newDepth < ONE_PLY ?
946 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
947 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
948 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
951 // Only for PV nodes do a full PV search on the first move or after a fail
952 // high, in the latter case search only if value < beta, otherwise let the
953 // parent node to fail low with value <= alpha and to try another move.
954 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
955 value = newDepth < ONE_PLY ?
956 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
957 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
958 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
959 // Step 17. Undo move
962 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
964 // Step 18. Check for new best move
967 splitPoint->mutex.lock();
968 bestValue = splitPoint->bestValue;
969 alpha = splitPoint->alpha;
972 // Finished searching the move. If Signals.stop is true, the search
973 // was aborted because the user interrupted the search or because we
974 // ran out of time. In this case, the return value of the search cannot
975 // be trusted, and we don't update the best move and/or PV.
976 if (Signals.stop || thisThread->cutoff_occurred())
977 return value; // To avoid returning VALUE_INFINITE
981 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
983 // PV move or new best move ?
984 if (pvMove || value > alpha)
987 rm.extract_pv_from_tt(pos);
989 // We record how often the best move has been changed in each
990 // iteration. This information is used for time management: When
991 // the best move changes frequently, we allocate some more time.
996 // All other moves but the PV are set to the lowest value, this
997 // is not a problem when sorting becuase sort is stable and move
998 // position in the list is preserved, just the PV is pushed up.
999 rm.score = -VALUE_INFINITE;
1002 if (value > bestValue)
1004 bestValue = SpNode ? splitPoint->bestValue = value : value;
1008 bestMove = SpNode ? splitPoint->bestMove = move : move;
1010 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1011 alpha = SpNode ? splitPoint->alpha = value : value;
1014 assert(value >= beta); // Fail high
1017 splitPoint->cutoff = true;
1024 // Step 19. Check for splitting the search
1026 && depth >= Threads.minimumSplitDepth
1027 && Threads.available_slave(thisThread)
1028 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1030 assert(bestValue < beta);
1032 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1033 depth, threatMove, moveCount, &mp, NT, cutNode);
1034 if (bestValue >= beta)
1042 // Step 20. Check for mate and stalemate
1043 // All legal moves have been searched and if there are no legal moves, it
1044 // must be mate or stalemate. Note that we can have a false positive in
1045 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1046 // harmless because return value is discarded anyhow in the parent nodes.
1047 // If we are in a singular extension search then return a fail low score.
1048 // A split node has at least one move, the one tried before to be splitted.
1050 return excludedMove ? alpha
1051 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1053 // If we have pruned all the moves without searching return a fail-low score
1054 if (bestValue == -VALUE_INFINITE)
1057 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1058 bestValue >= beta ? BOUND_LOWER :
1059 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1060 depth, bestMove, ss->staticEval);
1062 // Quiet best move: update killers, history and countermoves
1063 if ( bestValue >= beta
1064 && !pos.capture_or_promotion(bestMove)
1067 if (ss->killers[0] != bestMove)
1069 ss->killers[1] = ss->killers[0];
1070 ss->killers[0] = bestMove;
1073 // Increase history value of the cut-off move and decrease all the other
1074 // played non-capture moves.
1075 Value bonus = Value(int(depth) * int(depth));
1076 History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
1078 for (const ExtMove* em = mp.quiet_moves(); em && em->move != bestMove; ++em)
1079 History.update(pos.moved_piece(em->move), to_sq(em->move), -bonus);
1081 if (is_ok((ss-1)->currentMove))
1082 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1085 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1091 // qsearch() is the quiescence search function, which is called by the main
1092 // search function when the remaining depth is zero (or, to be more precise,
1093 // less than ONE_PLY).
1095 template <NodeType NT, bool InCheck>
1096 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1098 const bool PvNode = (NT == PV);
1100 assert(NT == PV || NT == NonPV);
1101 assert(InCheck == !!pos.checkers());
1102 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1103 assert(PvNode || (alpha == beta - 1));
1104 assert(depth <= DEPTH_ZERO);
1109 Move ttMove, move, bestMove;
1110 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1111 bool givesCheck, evasionPrunable;
1114 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1118 ss->currentMove = bestMove = MOVE_NONE;
1119 ss->ply = (ss-1)->ply + 1;
1121 // Check for an instant draw or maximum ply reached
1122 if (pos.is_draw() || ss->ply > MAX_PLY)
1123 return DrawValue[pos.side_to_move()];
1125 // Decide whether or not to include checks, this fixes also the type of
1126 // TT entry depth that we are going to use. Note that in qsearch we use
1127 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1128 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1129 : DEPTH_QS_NO_CHECKS;
1131 // Transposition table lookup
1133 tte = TT.probe(posKey);
1134 ttMove = tte ? tte->move() : MOVE_NONE;
1135 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1138 && tte->depth() >= ttDepth
1139 && ttValue != VALUE_NONE // Only in case of TT access race
1140 && ( PvNode ? tte->bound() == BOUND_EXACT
1141 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1142 : (tte->bound() & BOUND_UPPER)))
1144 ss->currentMove = ttMove; // Can be MOVE_NONE
1148 // Evaluate the position statically
1151 ss->staticEval = VALUE_NONE;
1152 bestValue = futilityBase = -VALUE_INFINITE;
1158 // Never assume anything on values stored in TT
1159 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1160 ss->staticEval = bestValue = evaluate(pos);
1162 // Can ttValue be used as a better position evaluation?
1163 if (ttValue != VALUE_NONE)
1164 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1165 bestValue = ttValue;
1168 ss->staticEval = bestValue = evaluate(pos);
1170 // Stand pat. Return immediately if static value is at least beta
1171 if (bestValue >= beta)
1174 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1175 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1180 if (PvNode && bestValue > alpha)
1183 futilityBase = bestValue + Value(128);
1186 // Initialize a MovePicker object for the current position, and prepare
1187 // to search the moves. Because the depth is <= 0 here, only captures,
1188 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1190 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1193 // Loop through the moves until no moves remain or a beta cutoff occurs
1194 while ((move = mp.next_move<false>()) != MOVE_NONE)
1196 assert(is_ok(move));
1198 givesCheck = pos.gives_check(move, ci);
1205 && type_of(move) != PROMOTION
1206 && futilityBase > -VALUE_KNOWN_WIN
1207 && !pos.passed_pawn_push(move))
1209 futilityValue = futilityBase
1210 + PieceValue[EG][pos.piece_on(to_sq(move))]
1211 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1213 if (futilityValue < beta)
1215 bestValue = std::max(bestValue, futilityValue);
1219 // Prune moves with negative or equal SEE and also moves with positive
1220 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1221 if ( futilityBase < beta
1222 && pos.see(move, beta - futilityBase) <= 0)
1224 bestValue = std::max(bestValue, futilityBase);
1229 // Detect non-capture evasions that are candidate to be pruned
1230 evasionPrunable = InCheck
1231 && bestValue > VALUE_MATED_IN_MAX_PLY
1232 && !pos.capture(move)
1233 && !pos.can_castle(pos.side_to_move());
1235 // Don't search moves with negative SEE values
1237 && (!InCheck || evasionPrunable)
1239 && type_of(move) != PROMOTION
1240 && pos.see_sign(move) < 0)
1243 // Check for legality only before to do the move
1244 if (!pos.legal(move, ci.pinned))
1247 ss->currentMove = move;
1249 // Make and search the move
1250 pos.do_move(move, st, ci, givesCheck);
1251 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1252 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1253 pos.undo_move(move);
1255 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1257 // Check for new best move
1258 if (value > bestValue)
1264 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1271 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1272 ttDepth, move, ss->staticEval);
1280 // All legal moves have been searched. A special case: If we're in check
1281 // and no legal moves were found, it is checkmate.
1282 if (InCheck && bestValue == -VALUE_INFINITE)
1283 return mated_in(ss->ply); // Plies to mate from the root
1285 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1286 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1287 ttDepth, bestMove, ss->staticEval);
1289 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1295 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1296 // "plies to mate from the current position". Non-mate scores are unchanged.
1297 // The function is called before storing a value to the transposition table.
1299 Value value_to_tt(Value v, int ply) {
1301 assert(v != VALUE_NONE);
1303 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1304 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1308 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1309 // from the transposition table (where refers to the plies to mate/be mated
1310 // from current position) to "plies to mate/be mated from the root".
1312 Value value_from_tt(Value v, int ply) {
1314 return v == VALUE_NONE ? VALUE_NONE
1315 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1316 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1320 // allows() tests whether the 'first' move at previous ply somehow makes the
1321 // 'second' move possible, for instance if the moving piece is the same in
1322 // both moves. Normally the second move is the threat (the best move returned
1323 // from a null search that fails low).
1325 bool allows(const Position& pos, Move first, Move second) {
1327 assert(is_ok(first));
1328 assert(is_ok(second));
1329 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1330 assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1332 Square m1from = from_sq(first);
1333 Square m2from = from_sq(second);
1334 Square m1to = to_sq(first);
1335 Square m2to = to_sq(second);
1337 // The piece is the same or second's destination was vacated by the first move
1338 // We exclude the trivial case where a sliding piece does in two moves what
1339 // it could do in one move: eg. Ra1a2, Ra2a3.
1341 || (m1to == m2from && !aligned(m1from, m2from, m2to)))
1344 // Second one moves through the square vacated by first one
1345 if (between_bb(m2from, m2to) & m1from)
1348 // Second's destination is defended by the first move's piece
1349 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1353 // Second move gives a discovered check through the first's checking piece
1354 if (m1att & pos.king_square(pos.side_to_move()))
1356 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1364 // refutes() tests whether a 'first' move is able to defend against a 'second'
1365 // opponent's move. In this case will not be pruned. Normally the second move
1366 // is the threat (the best move returned from a null search that fails low).
1368 bool refutes(const Position& pos, Move first, Move second) {
1370 assert(is_ok(first));
1371 assert(is_ok(second));
1373 Square m1from = from_sq(first);
1374 Square m2from = from_sq(second);
1375 Square m1to = to_sq(first);
1376 Square m2to = to_sq(second);
1378 // Don't prune moves of the threatened piece
1382 // If the threatened piece has value less than or equal to the value of the
1383 // threat piece, don't prune moves which defend it.
1384 if ( pos.capture(second)
1385 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1386 || type_of(pos.piece_on(m2from)) == KING))
1388 // Update occupancy as if the piece and the threat are moving
1389 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1390 Piece pc = pos.piece_on(m1from);
1392 // The moved piece attacks the square 'tto' ?
1393 if (pos.attacks_from(pc, m1to, occ) & m2to)
1396 // Scan for possible X-ray attackers behind the moved piece
1397 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
1398 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
1400 // Verify attackers are triggered by our move and not already existing
1401 if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
1405 // Don't prune safe moves which block the threat path
1406 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1413 // When playing with strength handicap choose best move among the MultiPV set
1414 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1416 Move Skill::pick_move() {
1420 // PRNG sequence should be not deterministic
1421 for (int i = Time::now() % 50; i > 0; --i)
1422 rk.rand<unsigned>();
1424 // RootMoves are already sorted by score in descending order
1425 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1426 int weakness = 120 - 2 * level;
1427 int max_s = -VALUE_INFINITE;
1430 // Choose best move. For each move score we add two terms both dependent on
1431 // weakness, one deterministic and bigger for weaker moves, and one random,
1432 // then we choose the move with the resulting highest score.
1433 for (size_t i = 0; i < PVSize; ++i)
1435 int s = RootMoves[i].score;
1437 // Don't allow crazy blunders even at very low skills
1438 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1441 // This is our magic formula
1442 s += ( weakness * int(RootMoves[0].score - s)
1443 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1448 best = RootMoves[i].pv[0];
1455 // uci_pv() formats PV information according to UCI protocol. UCI requires
1456 // to send all the PV lines also if are still to be searched and so refer to
1457 // the previous search score.
1459 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1461 std::stringstream s;
1462 Time::point elapsed = Time::now() - SearchTime + 1;
1463 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1466 for (size_t i = 0; i < Threads.size(); ++i)
1467 if (Threads[i]->maxPly > selDepth)
1468 selDepth = Threads[i]->maxPly;
1470 for (size_t i = 0; i < uciPVSize; ++i)
1472 bool updated = (i <= PVIdx);
1474 if (depth == 1 && !updated)
1477 int d = updated ? depth : depth - 1;
1478 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1480 if (s.rdbuf()->in_avail()) // Not at first line
1483 s << "info depth " << d
1484 << " seldepth " << selDepth
1485 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1486 << " nodes " << pos.nodes_searched()
1487 << " nps " << pos.nodes_searched() * 1000 / elapsed
1488 << " time " << elapsed
1489 << " multipv " << i + 1
1492 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1493 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1502 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1503 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1504 /// allow to always have a ponder move even when we fail high at root, and a
1505 /// long PV to print that is important for position analysis.
1507 void RootMove::extract_pv_from_tt(Position& pos) {
1509 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1519 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1521 pos.do_move(pv[ply++], *st++);
1522 tte = TT.probe(pos.key());
1525 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1526 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1528 && (!pos.is_draw() || ply < 2));
1530 pv.push_back(MOVE_NONE); // Must be zero-terminating
1532 while (ply) pos.undo_move(pv[--ply]);
1536 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1537 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1538 /// first, even if the old TT entries have been overwritten.
1540 void RootMove::insert_pv_in_tt(Position& pos) {
1542 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1547 tte = TT.probe(pos.key());
1549 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1550 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1552 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1554 pos.do_move(pv[ply++], *st++);
1556 } while (pv[ply] != MOVE_NONE);
1558 while (ply) pos.undo_move(pv[--ply]);
1562 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1564 void Thread::idle_loop() {
1566 // Pointer 'this_sp' is not null only if we are called from split(), and not
1567 // at the thread creation. So it means we are the split point's master.
1568 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1570 assert(!this_sp || (this_sp->masterThread == this && searching));
1574 // If we are not searching, wait for a condition to be signaled instead of
1575 // wasting CPU time polling for work.
1576 while ((!searching && Threads.sleepWhileIdle) || exit)
1584 // Grab the lock to avoid races with Thread::notify_one()
1587 // If we are master and all slaves have finished then exit idle_loop
1588 if (this_sp && !this_sp->slavesMask)
1594 // Do sleep after retesting sleep conditions under lock protection, in
1595 // particular we need to avoid a deadlock in case a master thread has,
1596 // in the meanwhile, allocated us and sent the notify_one() call before
1597 // we had the chance to grab the lock.
1598 if (!searching && !exit)
1599 sleepCondition.wait(mutex);
1604 // If this thread has been assigned work, launch a search
1609 Threads.mutex.lock();
1612 assert(activeSplitPoint);
1613 SplitPoint* sp = activeSplitPoint;
1615 Threads.mutex.unlock();
1617 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1618 Position pos(*sp->pos, this);
1620 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1621 ss->splitPoint = sp;
1625 assert(activePosition == NULL);
1627 activePosition = &pos;
1629 switch (sp->nodeType) {
1631 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1634 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1637 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1646 activePosition = NULL;
1647 sp->slavesMask &= ~(1ULL << idx);
1648 sp->nodes += pos.nodes_searched();
1650 // Wake up master thread so to allow it to return from the idle loop
1651 // in case we are the last slave of the split point.
1652 if ( Threads.sleepWhileIdle
1653 && this != sp->masterThread
1656 assert(!sp->masterThread->searching);
1657 sp->masterThread->notify_one();
1660 // After releasing the lock we cannot access anymore any SplitPoint
1661 // related data in a safe way becuase it could have been released under
1662 // our feet by the sp master. Also accessing other Thread objects is
1663 // unsafe because if we are exiting there is a chance are already freed.
1667 // If this thread is the master of a split point and all slaves have finished
1668 // their work at this split point, return from the idle loop.
1669 if (this_sp && !this_sp->slavesMask)
1671 this_sp->mutex.lock();
1672 bool finished = !this_sp->slavesMask; // Retest under lock protection
1673 this_sp->mutex.unlock();
1681 /// check_time() is called by the timer thread when the timer triggers. It is
1682 /// used to print debug info and, more important, to detect when we are out of
1683 /// available time and so stop the search.
1687 static Time::point lastInfoTime = Time::now();
1688 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1690 if (Time::now() - lastInfoTime >= 1000)
1692 lastInfoTime = Time::now();
1701 Threads.mutex.lock();
1703 nodes = RootPos.nodes_searched();
1705 // Loop across all split points and sum accumulated SplitPoint nodes plus
1706 // all the currently active positions nodes.
1707 for (size_t i = 0; i < Threads.size(); ++i)
1708 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1710 SplitPoint& sp = Threads[i]->splitPoints[j];
1715 Bitboard sm = sp.slavesMask;
1718 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1720 nodes += pos->nodes_searched();
1726 Threads.mutex.unlock();
1729 Time::point elapsed = Time::now() - SearchTime;
1730 bool stillAtFirstMove = Signals.firstRootMove
1731 && !Signals.failedLowAtRoot
1732 && elapsed > TimeMgr.available_time();
1734 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1735 || stillAtFirstMove;
1737 if ( (Limits.use_time_management() && noMoreTime)
1738 || (Limits.movetime && elapsed >= Limits.movetime)
1739 || (Limits.nodes && nodes >= Limits.nodes))
1740 Signals.stop = true;