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/>.
36 #include "ucioption.h"
40 volatile SignalsType Signals;
42 std::vector<RootMove> RootMoves;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // This is the minimum interval in msec between two check_time() calls
59 const int TimerResolution = 5;
61 // Different node types, used as template parameter
62 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
64 // Dynamic razoring margin based on depth
65 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
67 // Futility lookup tables (initialized at startup) and their access functions
68 Value FutilityMargins[16][64]; // [depth][moveNumber]
69 int FutilityMoveCounts[32]; // [depth]
71 inline Value futility_margin(Depth d, int mn) {
73 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
77 // Reduction lookup tables (initialized at startup) and their access function
78 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
80 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
82 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
88 Value DrawValue[COLOR_NB];
91 CountermovesStats Countermoves;
93 template <NodeType NT>
94 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
96 template <NodeType NT, bool InCheck>
97 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
99 void id_loop(Position& pos);
100 Value value_to_tt(Value v, int ply);
101 Value value_from_tt(Value v, int ply);
102 bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
103 bool refutes(const Position& pos, Move first, Move second);
104 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
107 Skill(int l) : level(l), best(MOVE_NONE) {}
109 if (enabled()) // Swap best PV line with the sub-optimal one
110 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
111 RootMoves.end(), best ? best : pick_move()));
114 bool enabled() const { return level < 20; }
115 bool time_to_pick(int depth) const { return depth == 1 + level; }
125 /// Search::init() is called during startup to initialize various lookup tables
127 void Search::init() {
129 int d; // depth (ONE_PLY == 2)
130 int hd; // half depth (ONE_PLY == 1)
133 // Init reductions array
134 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
136 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
137 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
138 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
139 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
142 // Init futility margins array
143 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
144 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
146 // Init futility move count array
147 for (d = 0; d < 32; d++)
148 FutilityMoveCounts[d] = int(3.001 + 0.3 * pow(double(d), 1.8));
152 /// Search::perft() is our utility to verify move generation. All the leaf nodes
153 /// up to the given depth are generated and counted and the sum returned.
155 size_t Search::perft(Position& pos, Depth depth) {
160 const bool leaf = depth == 2 * ONE_PLY;
162 for (MoveList<LEGAL> it(pos); *it; ++it)
164 pos.do_move(*it, st, ci, pos.move_gives_check(*it, ci));
165 cnt += leaf ? MoveList<LEGAL>(pos).size() : perft(pos, depth - ONE_PLY);
172 /// Search::think() is the external interface to Stockfish's search, and is
173 /// called by the main thread when the program receives the UCI 'go' command. It
174 /// searches from RootPos and at the end prints the "bestmove" to output.
176 void Search::think() {
178 static PolyglotBook book; // Defined static to initialize the PRNG only once
180 RootColor = RootPos.side_to_move();
181 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
183 if (RootMoves.empty())
185 RootMoves.push_back(MOVE_NONE);
186 sync_cout << "info depth 0 score "
187 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
193 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
195 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
197 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
199 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
204 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
206 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
207 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
208 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
209 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
212 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
214 if (Options["Use Search Log"])
216 Log log(Options["Search Log Filename"]);
217 log << "\nSearching: " << RootPos.fen()
218 << "\ninfinite: " << Limits.infinite
219 << " ponder: " << Limits.ponder
220 << " time: " << Limits.time[RootColor]
221 << " increment: " << Limits.inc[RootColor]
222 << " moves to go: " << Limits.movestogo
226 // Reset the threads, still sleeping: will be wake up at split time
227 for (size_t i = 0; i < Threads.size(); i++)
228 Threads[i]->maxPly = 0;
230 Threads.sleepWhileIdle = Options["Use Sleeping Threads"];
232 // Set best timer interval to avoid lagging under time pressure. Timer is
233 // used to check for remaining available thinking time.
234 Threads.timer->msec =
235 Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
236 Limits.nodes ? 2 * TimerResolution
239 Threads.timer->notify_one(); // Wake up the recurring timer
241 id_loop(RootPos); // Let's start searching !
243 Threads.timer->msec = 0; // Stop the timer
244 Threads.sleepWhileIdle = true; // Send idle threads to sleep
246 if (Options["Use Search Log"])
248 Time::point elapsed = Time::now() - SearchTime + 1;
250 Log log(Options["Search Log Filename"]);
251 log << "Nodes: " << RootPos.nodes_searched()
252 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
253 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
256 RootPos.do_move(RootMoves[0].pv[0], st);
257 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
258 RootPos.undo_move(RootMoves[0].pv[0]);
263 // When search is stopped this info is not printed
264 sync_cout << "info nodes " << RootPos.nodes_searched()
265 << " time " << Time::now() - SearchTime + 1 << sync_endl;
267 // When we reach max depth we arrive here even without Signals.stop is raised,
268 // but if we are pondering or in infinite search, according to UCI protocol,
269 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
270 // command. We simply wait here until GUI sends one of those commands (that
271 // raise Signals.stop).
272 if (!Signals.stop && (Limits.ponder || Limits.infinite))
274 Signals.stopOnPonderhit = true;
275 RootPos.this_thread()->wait_for(Signals.stop);
278 // Best move could be MOVE_NONE when searching on a stalemate position
279 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
280 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
287 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
288 // with increasing depth until the allocated thinking time has been consumed,
289 // user stops the search, or the maximum search depth is reached.
291 void id_loop(Position& pos) {
293 Stack stack[MAX_PLY_PLUS_2], *ss = stack+1; // To allow referencing (ss-1)
294 int depth, prevBestMoveChanges;
295 Value bestValue, alpha, beta, delta;
297 memset(ss-1, 0, 4 * sizeof(Stack));
298 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
300 depth = BestMoveChanges = 0;
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 // Save last iteration's scores before first PV line is searched and all
323 // the move scores but the (new) PV are set to -VALUE_INFINITE.
324 for (size_t i = 0; i < RootMoves.size(); i++)
325 RootMoves[i].prevScore = RootMoves[i].score;
327 prevBestMoveChanges = BestMoveChanges; // Only sensible when PVSize == 1
330 // MultiPV loop. We perform a full root search for each PV line
331 for (PVIdx = 0; PVIdx < PVSize; 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 return immediately. Sorting and
361 // writing PV back to TT is safe becuase RootMoves is still
362 // valid, although refers to previous iteration.
366 // In case of failing low/high increase aspiration window and
367 // research, otherwise exit the loop.
368 if (bestValue <= alpha)
370 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
372 Signals.failedLowAtRoot = true;
373 Signals.stopOnPonderhit = false;
375 else if (bestValue >= beta)
376 beta = std::min(bestValue + delta, VALUE_INFINITE);
383 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
385 // Give some update (without cluttering the UI) before to research
386 if (Time::now() - SearchTime > 3000)
387 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
390 // Sort the PV lines searched so far and update the GUI
391 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
393 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
394 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
397 // Do we need to pick now the sub-optimal best move ?
398 if (skill.enabled() && skill.time_to_pick(depth))
401 if (Options["Use Search Log"])
403 RootMove& rm = RootMoves[0];
404 if (skill.best != MOVE_NONE)
405 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
407 Log log(Options["Search Log Filename"]);
408 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
412 // Do we have found a "mate in x"?
414 && bestValue >= VALUE_MATE_IN_MAX_PLY
415 && VALUE_MATE - bestValue <= 2 * Limits.mate)
418 // Do we have time for the next iteration? Can we stop searching now?
419 if (Limits.use_time_management() && !Signals.stopOnPonderhit)
421 bool stop = false; // Local variable, not the volatile Signals.stop
423 // Take in account some extra time if the best move has changed
424 if (depth > 4 && depth < 50 && PVSize == 1)
425 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
427 // Stop search if most of available time is already consumed. We
428 // probably don't have enough time to search the first move at the
429 // next iteration anyway.
430 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
433 // Stop search early if one move seems to be much better than others
437 && bestValue > VALUE_MATED_IN_MAX_PLY
438 && ( RootMoves.size() == 1
439 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
441 Value rBeta = bestValue - 2 * PawnValueMg;
442 ss->excludedMove = RootMoves[0].pv[0];
443 ss->skipNullMove = true;
444 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
445 ss->skipNullMove = false;
446 ss->excludedMove = MOVE_NONE;
454 // If we are allowed to ponder do not stop the search now but
455 // keep pondering until GUI sends "ponderhit" or "stop".
457 Signals.stopOnPonderhit = true;
466 // search<>() is the main search function for both PV and non-PV nodes and for
467 // normal and SplitPoint nodes. When called just after a split point the search
468 // is simpler because we have already probed the hash table, done a null move
469 // search, and searched the first move before splitting, we don't have to repeat
470 // all this work again. We also don't need to store anything to the hash table
471 // here: This is taken care of after we return from the split point.
473 template <NodeType NT>
474 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
476 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
477 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
478 const bool RootNode = (NT == Root || NT == SplitPointRoot);
480 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
481 assert(PvNode || (alpha == beta - 1));
482 assert(depth > DEPTH_ZERO);
484 Move quietsSearched[64];
487 SplitPoint* splitPoint;
489 Move ttMove, move, excludedMove, bestMove, threatMove;
491 Value bestValue, value, ttValue;
492 Value eval, nullValue, futilityValue;
493 bool inCheck, givesCheck, pvMove, singularExtensionNode;
494 bool captureOrPromotion, dangerous, doFullDepthSearch;
495 int moveCount, quietCount;
497 // Step 1. Initialize node
498 Thread* thisThread = pos.this_thread();
499 moveCount = quietCount = 0;
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);
514 goto split_point_start;
517 bestValue = -VALUE_INFINITE;
518 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
519 ss->ply = (ss-1)->ply + 1;
520 ss->futilityMoveCount = 0;
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.is_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 = ss->evalMargin = eval = VALUE_NONE;
590 // Never assume anything on values stored in TT
591 if ( (ss->staticEval = eval = tte->eval_value()) == VALUE_NONE
592 ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
593 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
595 // Can ttValue be used as a better position evaluation?
596 if (ttValue != VALUE_NONE)
597 if ( ((tte->bound() & BOUND_LOWER) && ttValue > eval)
598 || ((tte->bound() & BOUND_UPPER) && ttValue < eval))
603 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
604 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
605 ss->staticEval, ss->evalMargin);
608 // Update gain for the parent non-capture move given the static position
609 // evaluation before and after the move.
610 if ( !pos.captured_piece_type()
611 && ss->staticEval != VALUE_NONE
612 && (ss-1)->staticEval != VALUE_NONE
613 && (move = (ss-1)->currentMove) != MOVE_NULL
614 && type_of(move) == NORMAL)
616 Square to = to_sq(move);
617 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
620 // Step 6. Razoring (is omitted in PV nodes)
622 && depth < 4 * ONE_PLY
623 && eval + razor_margin(depth) < beta
624 && ttMove == MOVE_NONE
625 && abs(beta) < VALUE_MATE_IN_MAX_PLY
626 && !pos.pawn_on_7th(pos.side_to_move()))
628 Value rbeta = beta - razor_margin(depth);
629 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
631 // Logically we should return (v + razor_margin(depth)), but
632 // surprisingly this did slightly weaker in tests.
636 // Step 7. Static null move pruning (is omitted in PV nodes)
637 // We're betting that the opponent doesn't have a move that will reduce
638 // the score by more than futility_margin(depth) if we do a null move.
641 && depth < 4 * ONE_PLY
642 && eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
643 && abs(beta) < VALUE_MATE_IN_MAX_PLY
644 && abs(eval) < VALUE_KNOWN_WIN
645 && pos.non_pawn_material(pos.side_to_move()))
646 return eval - futility_margin(depth, (ss-1)->futilityMoveCount);
648 // Step 8. Null move search with verification search (is omitted in PV nodes)
653 && abs(beta) < VALUE_MATE_IN_MAX_PLY
654 && pos.non_pawn_material(pos.side_to_move()))
656 ss->currentMove = MOVE_NULL;
658 // Null move dynamic reduction based on depth
659 Depth R = 3 * ONE_PLY + depth / 4;
661 // Null move dynamic reduction based on value
662 if (eval - PawnValueMg > beta)
665 pos.do_null_move(st);
666 (ss+1)->skipNullMove = true;
667 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
668 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
669 (ss+1)->skipNullMove = false;
670 pos.undo_null_move();
672 if (nullValue >= beta)
674 // Do not return unproven mate scores
675 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
678 if (depth < 12 * ONE_PLY)
681 // Do verification search at high depths
682 ss->skipNullMove = true;
683 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
684 ss->skipNullMove = false;
691 // The null move failed low, which means that we may be faced with
692 // some kind of threat. If the previous move was reduced return a fail
693 // low score (which will cause the reduced move to fail high in the
694 // parent node, which will trigger a re-search with full depth).
695 if ( depth < 5 * ONE_PLY
697 && nullValue < beta - Value(128))
700 threatMove = (ss+1)->currentMove;
704 // Step 9. ProbCut (is omitted in PV nodes)
705 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
706 // and a reduced search returns a value much above beta, we can (almost) safely
707 // prune the previous move.
709 && depth >= 5 * ONE_PLY
711 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
713 Value rbeta = beta + 200;
714 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
716 assert(rdepth >= ONE_PLY);
717 assert((ss-1)->currentMove != MOVE_NONE);
718 assert((ss-1)->currentMove != MOVE_NULL);
720 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
723 while ((move = mp.next_move<false>()) != MOVE_NONE)
724 if (pos.pl_move_is_legal(move, ci.pinned))
726 ss->currentMove = move;
727 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
728 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
735 iid_start: // When in check we skip early cut tests
737 // Step 10. Internal iterative deepening
738 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
739 && ttMove == MOVE_NONE
740 && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
742 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
744 ss->skipNullMove = true;
745 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
746 ss->skipNullMove = false;
748 tte = TT.probe(posKey);
749 ttMove = tte ? tte->move() : MOVE_NONE;
752 split_point_start: // At split points actual search starts from here
754 Square prevMoveSq = to_sq((ss-1)->currentMove);
755 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
756 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
758 MovePicker mp(pos, ttMove, depth, History, countermoves, ss, PvNode ? -VALUE_INFINITE : beta);
760 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
761 singularExtensionNode = !RootNode
763 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
764 && ttMove != MOVE_NONE
765 && !excludedMove // Recursive singular search is not allowed
766 && (tte->bound() & BOUND_LOWER)
767 && tte->depth() >= depth - 3 * ONE_PLY;
769 // Step 11. Loop through moves
770 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
771 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
775 if (move == excludedMove)
778 // At root obey the "searchmoves" option and skip moves not listed in Root
779 // Move List, as a consequence any illegal move is also skipped. In MultiPV
780 // mode we also skip PV moves which have been already searched.
781 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
786 // Shared counter cannot be decremented later if move turns out to be illegal
787 if (!pos.pl_move_is_legal(move, ci.pinned))
790 moveCount = ++splitPoint->moveCount;
791 splitPoint->mutex.unlock();
798 Signals.firstRootMove = (moveCount == 1);
800 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 3000)
801 sync_cout << "info depth " << depth / ONE_PLY
802 << " currmove " << move_to_uci(move, pos.is_chess960())
803 << " currmovenumber " << moveCount + PVIdx << sync_endl;
807 captureOrPromotion = pos.is_capture_or_promotion(move);
808 givesCheck = pos.move_gives_check(move, ci);
809 dangerous = givesCheck
810 || pos.is_passed_pawn_push(move)
811 || type_of(move) == CASTLE;
813 // Step 12. Extend checks and, in PV nodes, also dangerous moves
814 if (PvNode && dangerous)
817 else if (givesCheck && pos.see_sign(move) >= 0)
820 // Singular extension search. If all moves but one fail low on a search of
821 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
822 // is singular and should be extended. To verify this we do a reduced search
823 // on all the other moves but the ttMove, if result is lower than ttValue minus
824 // a margin then we extend ttMove.
825 if ( singularExtensionNode
828 && pos.pl_move_is_legal(move, ci.pinned)
829 && abs(ttValue) < VALUE_KNOWN_WIN)
831 assert(ttValue != VALUE_NONE);
833 Value rBeta = ttValue - int(depth);
834 ss->excludedMove = move;
835 ss->skipNullMove = true;
836 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
837 ss->skipNullMove = false;
838 ss->excludedMove = MOVE_NONE;
844 // Update current move (this must be done after singular extension search)
845 newDepth = depth - ONE_PLY + ext;
847 // Step 13. Futility pruning (is omitted in PV nodes)
849 && !captureOrPromotion
852 /* && move != ttMove Already implicit in the next condition */
853 && bestValue > VALUE_MATED_IN_MAX_PLY)
855 // Move count based pruning
856 if ( depth < 16 * ONE_PLY
857 && moveCount >= FutilityMoveCounts[depth]
858 && (!threatMove || !refutes(pos, move, threatMove)))
861 splitPoint->mutex.lock();
866 // Value based pruning
867 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
868 // but fixing this made program slightly weaker.
869 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
870 futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
871 + Gains[pos.piece_moved(move)][to_sq(move)];
873 if (futilityValue < beta)
875 bestValue = std::max(bestValue, futilityValue);
879 splitPoint->mutex.lock();
880 if (bestValue > splitPoint->bestValue)
881 splitPoint->bestValue = bestValue;
886 // Prune moves with negative SEE at low depths
887 if ( predictedDepth < 4 * ONE_PLY
888 && pos.see_sign(move) < 0)
891 splitPoint->mutex.lock();
896 // We have not pruned the move that will be searched, but remember how
897 // far in the move list we are to be more aggressive in the child node.
898 ss->futilityMoveCount = moveCount;
901 ss->futilityMoveCount = 0;
903 // Check for legality only before to do the move
904 if (!RootNode && !SpNode && !pos.pl_move_is_legal(move, ci.pinned))
910 pvMove = PvNode && moveCount == 1;
911 ss->currentMove = move;
912 if (!SpNode && !captureOrPromotion && quietCount < 64)
913 quietsSearched[quietCount++] = move;
915 // Step 14. Make the move
916 pos.do_move(move, st, ci, givesCheck);
918 // Step 15. Reduced depth search (LMR). If the move fails high will be
919 // re-searched at full depth.
920 if ( depth > 3 * ONE_PLY
922 && !captureOrPromotion
925 && move != ss->killers[0]
926 && move != ss->killers[1])
928 ss->reduction = reduction<PvNode>(depth, moveCount);
930 if (!PvNode && cutNode)
931 ss->reduction += ONE_PLY;
933 if (move == countermoves[0] || move == countermoves[1])
934 ss->reduction = std::max(DEPTH_ZERO, ss->reduction-ONE_PLY);
936 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
938 alpha = splitPoint->alpha;
940 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
942 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
943 ss->reduction = DEPTH_ZERO;
946 doFullDepthSearch = !pvMove;
948 // Step 16. Full depth search, when LMR is skipped or fails high
949 if (doFullDepthSearch)
952 alpha = splitPoint->alpha;
954 value = newDepth < ONE_PLY ?
955 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
956 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
957 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
960 // Only for PV nodes do a full PV search on the first move or after a fail
961 // high, in the latter case search only if value < beta, otherwise let the
962 // parent node to fail low with value <= alpha and to try another move.
963 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
964 value = newDepth < ONE_PLY ?
965 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
966 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
967 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
968 // Step 17. Undo move
971 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
973 // Step 18. Check for new best move
976 splitPoint->mutex.lock();
977 bestValue = splitPoint->bestValue;
978 alpha = splitPoint->alpha;
981 // Finished searching the move. If Signals.stop is true, the search
982 // was aborted because the user interrupted the search or because we
983 // ran out of time. In this case, the return value of the search cannot
984 // be trusted, and we don't update the best move and/or PV.
985 if (Signals.stop || thisThread->cutoff_occurred())
986 return value; // To avoid returning VALUE_INFINITE
990 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
992 // PV move or new best move ?
993 if (pvMove || value > alpha)
996 rm.extract_pv_from_tt(pos);
998 // We record how often the best move has been changed in each
999 // iteration. This information is used for time management: When
1000 // the best move changes frequently, we allocate some more time.
1005 // All other moves but the PV are set to the lowest value, this
1006 // is not a problem when sorting becuase sort is stable and move
1007 // position in the list is preserved, just the PV is pushed up.
1008 rm.score = -VALUE_INFINITE;
1011 if (value > bestValue)
1013 bestValue = SpNode ? splitPoint->bestValue = value : value;
1017 bestMove = SpNode ? splitPoint->bestMove = move : move;
1019 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1020 alpha = SpNode ? splitPoint->alpha = value : value;
1023 assert(value >= beta); // Fail high
1026 splitPoint->cutoff = true;
1033 // Step 19. Check for splitting the search
1035 && depth >= Threads.minimumSplitDepth
1036 && Threads.available_slave(thisThread)
1037 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1039 assert(bestValue < beta);
1041 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1042 depth, threatMove, moveCount, &mp, NT, cutNode);
1043 if (bestValue >= beta)
1051 // Step 20. Check for mate and stalemate
1052 // All legal moves have been searched and if there are no legal moves, it
1053 // must be mate or stalemate. Note that we can have a false positive in
1054 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1055 // harmless because return value is discarded anyhow in the parent nodes.
1056 // If we are in a singular extension search then return a fail low score.
1057 // A split node has at least one move, the one tried before to be splitted.
1059 return excludedMove ? alpha
1060 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1062 // If we have pruned all the moves without searching return a fail-low score
1063 if (bestValue == -VALUE_INFINITE)
1066 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1067 bestValue >= beta ? BOUND_LOWER :
1068 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1069 depth, bestMove, ss->staticEval, ss->evalMargin);
1071 // Quiet best move: update killers, history and countermoves
1072 if ( bestValue >= beta
1073 && !pos.is_capture_or_promotion(bestMove)
1076 if (ss->killers[0] != bestMove)
1078 ss->killers[1] = ss->killers[0];
1079 ss->killers[0] = bestMove;
1082 // Increase history value of the cut-off move and decrease all the other
1083 // played non-capture moves.
1084 Value bonus = Value(int(depth) * int(depth));
1085 History.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1086 for (int i = 0; i < quietCount - 1; i++)
1088 Move m = quietsSearched[i];
1089 History.update(pos.piece_moved(m), to_sq(m), -bonus);
1092 if (is_ok((ss-1)->currentMove))
1093 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
1096 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1102 // qsearch() is the quiescence search function, which is called by the main
1103 // search function when the remaining depth is zero (or, to be more precise,
1104 // less than ONE_PLY).
1106 template <NodeType NT, bool InCheck>
1107 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1109 const bool PvNode = (NT == PV);
1111 assert(NT == PV || NT == NonPV);
1112 assert(InCheck == !!pos.checkers());
1113 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1114 assert(PvNode || (alpha == beta - 1));
1115 assert(depth <= DEPTH_ZERO);
1120 Move ttMove, move, bestMove;
1121 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1122 bool givesCheck, enoughMaterial, evasionPrunable;
1125 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1129 ss->currentMove = bestMove = MOVE_NONE;
1130 ss->ply = (ss-1)->ply + 1;
1132 // Check for an instant draw or maximum ply reached
1133 if (pos.is_draw() || ss->ply > MAX_PLY)
1134 return DrawValue[pos.side_to_move()];
1136 // Decide whether or not to include checks, this fixes also the type of
1137 // TT entry depth that we are going to use. Note that in qsearch we use
1138 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1139 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1140 : DEPTH_QS_NO_CHECKS;
1142 // Transposition table lookup
1144 tte = TT.probe(posKey);
1145 ttMove = tte ? tte->move() : MOVE_NONE;
1146 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1149 && tte->depth() >= ttDepth
1150 && ttValue != VALUE_NONE // Only in case of TT access race
1151 && ( PvNode ? tte->bound() == BOUND_EXACT
1152 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1153 : (tte->bound() & BOUND_UPPER)))
1155 ss->currentMove = ttMove; // Can be MOVE_NONE
1159 // Evaluate the position statically
1162 ss->staticEval = ss->evalMargin = VALUE_NONE;
1163 bestValue = futilityBase = -VALUE_INFINITE;
1164 enoughMaterial = false;
1170 // Never assume anything on values stored in TT
1171 if ( (ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE
1172 ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
1173 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1176 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1178 // Stand pat. Return immediately if static value is at least beta
1179 if (bestValue >= beta)
1182 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1183 DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
1188 if (PvNode && bestValue > alpha)
1191 futilityBase = ss->staticEval + ss->evalMargin + Value(128);
1192 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1195 // Initialize a MovePicker object for the current position, and prepare
1196 // to search the moves. Because the depth is <= 0 here, only captures,
1197 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1199 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1202 // Loop through the moves until no moves remain or a beta cutoff occurs
1203 while ((move = mp.next_move<false>()) != MOVE_NONE)
1205 assert(is_ok(move));
1207 givesCheck = pos.move_gives_check(move, ci);
1215 && type_of(move) != PROMOTION
1216 && !pos.is_passed_pawn_push(move))
1218 futilityValue = futilityBase
1219 + PieceValue[EG][pos.piece_on(to_sq(move))]
1220 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1222 if (futilityValue < beta)
1224 bestValue = std::max(bestValue, futilityValue);
1228 // Prune moves with negative or equal SEE and also moves with positive
1229 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1230 if ( futilityBase < beta
1231 && pos.see(move, beta - futilityBase) <= 0)
1233 bestValue = std::max(bestValue, futilityBase);
1238 // Detect non-capture evasions that are candidate to be pruned
1239 evasionPrunable = !PvNode
1241 && bestValue > VALUE_MATED_IN_MAX_PLY
1242 && !pos.is_capture(move)
1243 && !pos.can_castle(pos.side_to_move());
1245 // Don't search moves with negative SEE values
1247 && (!InCheck || evasionPrunable)
1249 && type_of(move) != PROMOTION
1250 && pos.see_sign(move) < 0)
1253 // Don't search useless checks
1258 && !pos.is_capture_or_promotion(move)
1259 && ss->staticEval + PawnValueMg / 4 < beta
1260 && !check_is_dangerous(pos, move, futilityBase, beta))
1263 // Check for legality only before to do the move
1264 if (!pos.pl_move_is_legal(move, ci.pinned))
1267 ss->currentMove = move;
1269 // Make and search the move
1270 pos.do_move(move, st, ci, givesCheck);
1271 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1272 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1273 pos.undo_move(move);
1275 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1277 // Check for new best move
1278 if (value > bestValue)
1284 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1291 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1292 ttDepth, move, ss->staticEval, ss->evalMargin);
1300 // All legal moves have been searched. A special case: If we're in check
1301 // and no legal moves were found, it is checkmate.
1302 if (InCheck && bestValue == -VALUE_INFINITE)
1303 return mated_in(ss->ply); // Plies to mate from the root
1305 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1306 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1307 ttDepth, bestMove, ss->staticEval, ss->evalMargin);
1309 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1315 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1316 // "plies to mate from the current position". Non-mate scores are unchanged.
1317 // The function is called before storing a value to the transposition table.
1319 Value value_to_tt(Value v, int ply) {
1321 assert(v != VALUE_NONE);
1323 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1324 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1328 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1329 // from the transposition table (where refers to the plies to mate/be mated
1330 // from current position) to "plies to mate/be mated from the root".
1332 Value value_from_tt(Value v, int ply) {
1334 return v == VALUE_NONE ? VALUE_NONE
1335 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1336 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1340 // check_is_dangerous() tests if a checking move can be pruned in qsearch()
1342 bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta)
1344 Piece pc = pos.piece_moved(move);
1345 Square from = from_sq(move);
1346 Square to = to_sq(move);
1347 Color them = ~pos.side_to_move();
1348 Square ksq = pos.king_square(them);
1349 Bitboard enemies = pos.pieces(them);
1350 Bitboard kingAtt = pos.attacks_from<KING>(ksq);
1351 Bitboard occ = pos.pieces() ^ from ^ ksq;
1352 Bitboard oldAtt = pos.attacks_from(pc, from, occ);
1353 Bitboard newAtt = pos.attacks_from(pc, to, occ);
1355 // Checks which give opponent's king at most one escape square are dangerous
1356 if (!more_than_one(kingAtt & ~(enemies | newAtt | to)))
1359 // Queen contact check is very dangerous
1360 if (type_of(pc) == QUEEN && (kingAtt & to))
1363 // Creating new double threats with checks is dangerous
1364 Bitboard b = (enemies ^ ksq) & newAtt & ~oldAtt;
1367 // Note that here we generate illegal "double move"!
1368 if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
1376 // refutes() tests whether a 'first' move is able to defend against a 'second'
1377 // opponent's move. In this case will not be pruned. Normally the second move
1378 // is the threat (the best move returned from a null search that fails low).
1380 bool refutes(const Position& pos, Move first, Move second) {
1382 assert(is_ok(first));
1383 assert(is_ok(second));
1385 Square m1from = from_sq(first);
1386 Square m2from = from_sq(second);
1387 Square m1to = to_sq(first);
1388 Square m2to = to_sq(second);
1390 // Don't prune moves of the threatened piece
1394 // If the threatened piece has value less than or equal to the value of the
1395 // threat piece, don't prune moves which defend it.
1396 if ( pos.is_capture(second)
1397 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1398 || type_of(pos.piece_on(m2from)) == KING))
1400 // Update occupancy as if the piece and the threat are moving
1401 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1402 Piece pc = pos.piece_on(m1from);
1404 // The moved piece attacks the square 'tto' ?
1405 if (pos.attacks_from(pc, m1to, occ) & m2to)
1408 // Scan for possible X-ray attackers behind the moved piece
1409 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
1410 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
1412 // Verify attackers are triggered by our move and not already existing
1413 if (xray && (xray ^ (xray & pos.attacks_from<QUEEN>(m2to))))
1417 // Don't prune safe moves which block the threat path
1418 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1425 // When playing with strength handicap choose best move among the MultiPV set
1426 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1428 Move Skill::pick_move() {
1432 // PRNG sequence should be not deterministic
1433 for (int i = Time::now() % 50; i > 0; i--)
1434 rk.rand<unsigned>();
1436 // RootMoves are already sorted by score in descending order
1437 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1438 int weakness = 120 - 2 * level;
1439 int max_s = -VALUE_INFINITE;
1442 // Choose best move. For each move score we add two terms both dependent on
1443 // weakness, one deterministic and bigger for weaker moves, and one random,
1444 // then we choose the move with the resulting highest score.
1445 for (size_t i = 0; i < PVSize; i++)
1447 int s = RootMoves[i].score;
1449 // Don't allow crazy blunders even at very low skills
1450 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1453 // This is our magic formula
1454 s += ( weakness * int(RootMoves[0].score - s)
1455 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1460 best = RootMoves[i].pv[0];
1467 // uci_pv() formats PV information according to UCI protocol. UCI requires
1468 // to send all the PV lines also if are still to be searched and so refer to
1469 // the previous search score.
1471 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1473 std::stringstream s;
1474 Time::point elapsed = Time::now() - SearchTime + 1;
1475 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1478 for (size_t i = 0; i < Threads.size(); i++)
1479 if (Threads[i]->maxPly > selDepth)
1480 selDepth = Threads[i]->maxPly;
1482 for (size_t i = 0; i < uciPVSize; i++)
1484 bool updated = (i <= PVIdx);
1486 if (depth == 1 && !updated)
1489 int d = updated ? depth : depth - 1;
1490 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1492 if (s.rdbuf()->in_avail()) // Not at first line
1495 s << "info depth " << d
1496 << " seldepth " << selDepth
1497 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1498 << " nodes " << pos.nodes_searched()
1499 << " nps " << pos.nodes_searched() * 1000 / elapsed
1500 << " time " << elapsed
1501 << " multipv " << i + 1
1504 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1505 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1514 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1515 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1516 /// allow to always have a ponder move even when we fail high at root, and a
1517 /// long PV to print that is important for position analysis.
1519 void RootMove::extract_pv_from_tt(Position& pos) {
1521 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1531 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1533 pos.do_move(pv[ply++], *st++);
1534 tte = TT.probe(pos.key());
1537 && pos.is_pseudo_legal(m = tte->move()) // Local copy, TT could change
1538 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1540 && (!pos.is_draw() || ply < 2));
1542 pv.push_back(MOVE_NONE); // Must be zero-terminating
1544 while (ply) pos.undo_move(pv[--ply]);
1548 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1549 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1550 /// first, even if the old TT entries have been overwritten.
1552 void RootMove::insert_pv_in_tt(Position& pos) {
1554 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1559 tte = TT.probe(pos.key());
1561 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1562 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE, VALUE_NONE);
1564 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1566 pos.do_move(pv[ply++], *st++);
1568 } while (pv[ply] != MOVE_NONE);
1570 while (ply) pos.undo_move(pv[--ply]);
1574 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1576 void Thread::idle_loop() {
1578 // Pointer 'this_sp' is not null only if we are called from split(), and not
1579 // at the thread creation. So it means we are the split point's master.
1580 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1582 assert(!this_sp || (this_sp->masterThread == this && searching));
1586 // If we are not searching, wait for a condition to be signaled instead of
1587 // wasting CPU time polling for work.
1588 while ((!searching && Threads.sleepWhileIdle) || exit)
1596 // Grab the lock to avoid races with Thread::notify_one()
1599 // If we are master and all slaves have finished then exit idle_loop
1600 if (this_sp && !this_sp->slavesMask)
1606 // Do sleep after retesting sleep conditions under lock protection, in
1607 // particular we need to avoid a deadlock in case a master thread has,
1608 // in the meanwhile, allocated us and sent the notify_one() call before
1609 // we had the chance to grab the lock.
1610 if (!searching && !exit)
1611 sleepCondition.wait(mutex);
1616 // If this thread has been assigned work, launch a search
1621 Threads.mutex.lock();
1624 SplitPoint* sp = activeSplitPoint;
1626 Threads.mutex.unlock();
1628 Stack stack[MAX_PLY_PLUS_2], *ss = stack+1; // To allow referencing (ss-1)
1629 Position pos(*sp->pos, this);
1631 memcpy(ss-1, sp->ss-1, 4 * sizeof(Stack));
1632 ss->splitPoint = sp;
1636 assert(activePosition == NULL);
1638 activePosition = &pos;
1640 switch (sp->nodeType) {
1642 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1645 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1648 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1657 activePosition = NULL;
1658 sp->slavesMask &= ~(1ULL << idx);
1659 sp->nodes += pos.nodes_searched();
1661 // Wake up master thread so to allow it to return from the idle loop
1662 // in case we are the last slave of the split point.
1663 if ( Threads.sleepWhileIdle
1664 && this != sp->masterThread
1667 assert(!sp->masterThread->searching);
1668 sp->masterThread->notify_one();
1671 // After releasing the lock we cannot access anymore any SplitPoint
1672 // related data in a safe way becuase it could have been released under
1673 // our feet by the sp master. Also accessing other Thread objects is
1674 // unsafe because if we are exiting there is a chance are already freed.
1678 // If this thread is the master of a split point and all slaves have finished
1679 // their work at this split point, return from the idle loop.
1680 if (this_sp && !this_sp->slavesMask)
1682 this_sp->mutex.lock();
1683 bool finished = !this_sp->slavesMask; // Retest under lock protection
1684 this_sp->mutex.unlock();
1692 /// check_time() is called by the timer thread when the timer triggers. It is
1693 /// used to print debug info and, more important, to detect when we are out of
1694 /// available time and so stop the search.
1698 static Time::point lastInfoTime = Time::now();
1699 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1701 if (Time::now() - lastInfoTime >= 1000)
1703 lastInfoTime = Time::now();
1712 Threads.mutex.lock();
1714 nodes = RootPos.nodes_searched();
1716 // Loop across all split points and sum accumulated SplitPoint nodes plus
1717 // all the currently active positions nodes.
1718 for (size_t i = 0; i < Threads.size(); i++)
1719 for (int j = 0; j < Threads[i]->splitPointsSize; j++)
1721 SplitPoint& sp = Threads[i]->splitPoints[j];
1726 Bitboard sm = sp.slavesMask;
1729 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1731 nodes += pos->nodes_searched();
1737 Threads.mutex.unlock();
1740 Time::point elapsed = Time::now() - SearchTime;
1741 bool stillAtFirstMove = Signals.firstRootMove
1742 && !Signals.failedLowAtRoot
1743 && elapsed > TimeMgr.available_time();
1745 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1746 || stillAtFirstMove;
1748 if ( (Limits.use_time_management() && noMoreTime)
1749 || (Limits.movetime && elapsed >= Limits.movetime)
1750 || (Limits.nodes && nodes >= Limits.nodes))
1751 Signals.stop = true;