2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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;
48 Value Contempt[2]; // [bestValue > VALUE_DRAW]
53 using namespace Search;
57 // Set to true to force running with one thread. Used for debugging
58 const bool FakeSplit = false;
60 // Different node types, used as template parameter
61 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
63 // Dynamic razoring margin based on depth
64 inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
66 // Futility lookup tables (initialized at startup) and their access functions
67 int FutilityMoveCounts[2][32]; // [improving][depth]
69 inline Value futility_margin(Depth d) {
70 return Value(100 * d);
73 // Reduction lookup tables (initialized at startup) and their access function
74 int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
76 template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
78 return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
81 size_t MultiPV, PVIdx;
83 double BestMoveChanges;
84 Value DrawValue[COLOR_NB];
87 MovesStats Countermoves, Followupmoves;
89 template <NodeType NT>
90 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
92 template <NodeType NT, bool InCheck>
93 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
95 void id_loop(Position& pos);
96 Value value_to_tt(Value v, int ply);
97 Value value_from_tt(Value v, int ply);
98 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
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 = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
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 + 0.00, 1.8));
150 FutilityMoveCounts[1][d] = int(3.0 + 0.300 * 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 uint64_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 uint64_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 DrawValue[0] = DrawValue[1] = VALUE_DRAW;
190 Contempt[0] = Options["Contempt Factor"] * PawnValueEg / 100; // From centipawns
191 Contempt[1] = (Options["Contempt Factor"] + 12) * PawnValueEg / 100;
193 if (RootMoves.empty())
195 RootMoves.push_back(MOVE_NONE);
196 sync_cout << "info depth 0 score "
197 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
203 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
205 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
207 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
209 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
214 if (Options["Write 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
223 << "\n" << std::endl;
226 // Reset the threads, still sleeping: will wake up at split time
227 for (size_t i = 0; i < Threads.size(); ++i)
228 Threads[i]->maxPly = 0;
230 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
231 Threads.timer->run = true;
232 Threads.timer->notify_one(); // Wake up the recurring timer
234 id_loop(RootPos); // Let's start searching !
236 Threads.timer->run = false; // Stop the timer
237 Threads.sleepWhileIdle = true; // Send idle threads to sleep
239 if (Options["Write Search Log"])
241 Time::point elapsed = Time::now() - SearchTime + 1;
243 Log log(Options["Search Log Filename"]);
244 log << "Nodes: " << RootPos.nodes_searched()
245 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
246 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
249 RootPos.do_move(RootMoves[0].pv[0], st);
250 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
251 RootPos.undo_move(RootMoves[0].pv[0]);
256 // When search is stopped this info is not printed
257 sync_cout << "info nodes " << RootPos.nodes_searched()
258 << " time " << Time::now() - SearchTime + 1 << sync_endl;
260 // When we reach the maximum depth, we can arrive here without a raise of
261 // Signals.stop. However, if we are pondering or in an infinite search,
262 // the UCI protocol states that we shouldn't print the best move before the
263 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
264 // until the GUI sends one of those commands (which also raises Signals.stop).
265 if (!Signals.stop && (Limits.ponder || Limits.infinite))
267 Signals.stopOnPonderhit = true;
268 RootPos.this_thread()->wait_for(Signals.stop);
271 // Best move could be MOVE_NONE when searching on a stalemate position
272 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
273 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
280 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
281 // with increasing depth until the allocated thinking time has been consumed,
282 // user stops the search, or the maximum search depth is reached.
284 void id_loop(Position& pos) {
286 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
288 Value bestValue, alpha, beta, delta;
290 std::memset(ss-2, 0, 5 * sizeof(Stack));
291 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
295 bestValue = delta = alpha = -VALUE_INFINITE;
296 beta = VALUE_INFINITE;
301 Countermoves.clear();
302 Followupmoves.clear();
304 MultiPV = Options["MultiPV"];
305 Skill skill(Options["Skill Level"]);
307 // Do we have to play with skill handicap? In this case enable MultiPV search
308 // that we will use behind the scenes to retrieve a set of possible moves.
309 if (skill.enabled() && MultiPV < 4)
312 MultiPV = std::min(MultiPV, RootMoves.size());
314 // Iterative deepening loop until requested to stop or target depth reached
315 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
317 // Age out PV variability metric
318 BestMoveChanges *= 0.5;
320 // Save the last iteration's scores before first PV line is searched and
321 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
322 for (size_t i = 0; i < RootMoves.size(); ++i)
323 RootMoves[i].prevScore = RootMoves[i].score;
325 // MultiPV loop. We perform a full root search for each PV line
326 for (PVIdx = 0; PVIdx < MultiPV && !Signals.stop; ++PVIdx)
328 // Reset aspiration window starting size
332 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
333 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
336 // Start with a small aspiration window and, in the case of a fail
337 // high/low, re-search with a bigger window until we're not failing
341 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
343 DrawValue[ RootColor] = VALUE_DRAW - Contempt[bestValue > VALUE_DRAW];
344 DrawValue[~RootColor] = VALUE_DRAW + Contempt[bestValue > VALUE_DRAW];
346 // Bring the best move to the front. It is critical that sorting
347 // is done with a stable algorithm because all the values but the
348 // first and eventually the new best one are set to -VALUE_INFINITE
349 // and we want to keep the same order for all the moves except the
350 // new PV that goes to the front. Note that in case of MultiPV
351 // search the already searched PV lines are preserved.
352 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
354 // Write PV back to transposition table in case the relevant
355 // entries have been overwritten during the search.
356 for (size_t i = 0; i <= PVIdx; ++i)
357 RootMoves[i].insert_pv_in_tt(pos);
359 // If search has been stopped break immediately. Sorting and
360 // writing PV back to TT is safe because RootMoves is still
361 // valid, although it refers to previous iteration.
365 // When failing high/low give some update (without cluttering
366 // the UI) before a re-search.
367 if ( (bestValue <= alpha || bestValue >= beta)
368 && Time::now() - SearchTime > 3000)
369 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
371 // In case of failing low/high increase aspiration window and
372 // re-search, otherwise exit the loop.
373 if (bestValue <= alpha)
375 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
377 Signals.failedLowAtRoot = true;
378 Signals.stopOnPonderhit = false;
380 else if (bestValue >= beta)
381 beta = std::min(bestValue + delta, VALUE_INFINITE);
388 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
391 // Sort the PV lines searched so far and update the GUI
392 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
394 if (PVIdx + 1 == MultiPV || Time::now() - SearchTime > 3000)
395 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
398 // If skill levels are enabled and time is up, pick a sub-optimal best move
399 if (skill.enabled() && skill.time_to_pick(depth))
402 if (Options["Write Search Log"])
404 RootMove& rm = RootMoves[0];
405 if (skill.best != MOVE_NONE)
406 rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
408 Log log(Options["Search Log Filename"]);
409 log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
413 // Have we found a "mate in x"?
415 && bestValue >= VALUE_MATE_IN_MAX_PLY
416 && VALUE_MATE - bestValue <= 2 * Limits.mate)
419 // Do we have time for the next iteration? Can we stop searching now?
420 if (Limits.use_time_management() && !Signals.stop && !Signals.stopOnPonderhit)
422 // Take some extra time if the best move has changed
423 if (depth > 4 && depth < 50 && MultiPV == 1)
424 TimeMgr.pv_instability(BestMoveChanges);
426 // Stop the search if only one legal move is available or all
427 // of the available time has been used.
428 if ( RootMoves.size() == 1
429 || Time::now() - SearchTime > TimeMgr.available_time())
431 // If we are allowed to ponder do not stop the search now but
432 // keep pondering until the GUI sends "ponderhit" or "stop".
434 Signals.stopOnPonderhit = true;
443 // search<>() is the main search function for both PV and non-PV nodes and for
444 // normal and SplitPoint nodes. When called just after a split point the search
445 // is simpler because we have already probed the hash table, done a null move
446 // search, and searched the first move before splitting, so we don't have to
447 // repeat all this work again. We also don't need to store anything to the hash
448 // table here: This is taken care of after we return from the split point.
450 template <NodeType NT>
451 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
453 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
454 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
455 const bool RootNode = (NT == Root || NT == SplitPointRoot);
457 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
458 assert(PvNode || (alpha == beta - 1));
459 assert(depth > DEPTH_ZERO);
461 Move quietsSearched[64];
464 SplitPoint* splitPoint;
466 Move ttMove, move, excludedMove, bestMove;
467 Depth ext, newDepth, predictedDepth;
468 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
469 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
470 bool captureOrPromotion, dangerous, doFullDepthSearch;
471 int moveCount, quietCount;
473 // Step 1. Initialize node
474 Thread* thisThread = pos.this_thread();
475 inCheck = pos.checkers();
479 splitPoint = ss->splitPoint;
480 bestMove = splitPoint->bestMove;
481 bestValue = splitPoint->bestValue;
483 ttMove = excludedMove = MOVE_NONE;
484 ttValue = VALUE_NONE;
486 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
491 moveCount = quietCount = 0;
492 bestValue = -VALUE_INFINITE;
493 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
494 ss->ply = (ss-1)->ply + 1;
495 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
496 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
498 // Used to send selDepth info to GUI
499 if (PvNode && thisThread->maxPly < ss->ply)
500 thisThread->maxPly = ss->ply;
504 // Step 2. Check for aborted search and immediate draw
505 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
506 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
508 // Step 3. Mate distance pruning. Even if we mate at the next move our score
509 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
510 // a shorter mate was found upward in the tree then there is no need to search
511 // because we will never beat the current alpha. Same logic but with reversed
512 // signs applies also in the opposite condition of being mated instead of giving
513 // mate. In this case return a fail-high score.
514 alpha = std::max(mated_in(ss->ply), alpha);
515 beta = std::min(mate_in(ss->ply+1), beta);
520 // Step 4. Transposition table lookup
521 // We don't want the score of a partial search to overwrite a previous full search
522 // TT value, so we use a different position key in case of an excluded move.
523 excludedMove = ss->excludedMove;
524 posKey = excludedMove ? pos.exclusion_key() : pos.key();
525 tte = TT.probe(posKey);
526 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
527 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
529 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
530 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
531 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
532 // we should also update RootMoveList to avoid bogus output.
535 && tte->depth() >= depth
536 && ttValue != VALUE_NONE // Only in case of TT access race
537 && ( PvNode ? tte->bound() == BOUND_EXACT
538 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
539 : (tte->bound() & BOUND_UPPER)))
541 ss->currentMove = ttMove; // Can be MOVE_NONE
543 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
544 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
545 update_stats(pos, ss, ttMove, depth, NULL, 0);
550 // Step 5. Evaluate the position statically and update parent's gain statistics
553 ss->staticEval = eval = VALUE_NONE;
559 // Never assume anything on values stored in TT
560 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
561 eval = ss->staticEval = evaluate(pos);
563 // Can ttValue be used as a better position evaluation?
564 if (ttValue != VALUE_NONE)
565 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
570 eval = ss->staticEval = evaluate(pos);
571 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
574 if ( !pos.captured_piece_type()
575 && ss->staticEval != VALUE_NONE
576 && (ss-1)->staticEval != VALUE_NONE
577 && (move = (ss-1)->currentMove) != MOVE_NULL
578 && type_of(move) == NORMAL)
580 Square to = to_sq(move);
581 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
584 // Step 6. Razoring (skipped when in check)
586 && depth < 4 * ONE_PLY
587 && eval + razor_margin(depth) <= alpha
588 && ttMove == MOVE_NONE
589 && abs(beta) < VALUE_MATE_IN_MAX_PLY
590 && !pos.pawn_on_7th(pos.side_to_move()))
592 Value ralpha = alpha - razor_margin(depth);
593 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
598 // Step 7. Futility pruning: child node (skipped when in check)
601 && depth < 7 * ONE_PLY
602 && eval - futility_margin(depth) >= beta
603 && abs(beta) < VALUE_MATE_IN_MAX_PLY
604 && abs(eval) < VALUE_KNOWN_WIN
605 && pos.non_pawn_material(pos.side_to_move()))
606 return eval - futility_margin(depth);
608 // Step 8. Null move search with verification search (is omitted in PV nodes)
611 && depth >= 2 * ONE_PLY
613 && abs(beta) < VALUE_MATE_IN_MAX_PLY
614 && pos.non_pawn_material(pos.side_to_move()))
616 ss->currentMove = MOVE_NULL;
618 assert(eval - beta >= 0);
620 // Null move dynamic reduction based on depth and value
621 Depth R = 3 * ONE_PLY
623 + int(eval - beta) / PawnValueMg * ONE_PLY;
625 pos.do_null_move(st);
626 (ss+1)->skipNullMove = true;
627 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
628 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
629 (ss+1)->skipNullMove = false;
630 pos.undo_null_move();
632 if (nullValue >= beta)
634 // Do not return unproven mate scores
635 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
638 if (depth < 12 * ONE_PLY)
641 // Do verification search at high depths
642 ss->skipNullMove = true;
643 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
644 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
645 ss->skipNullMove = false;
652 // Step 9. ProbCut (skipped when in check)
653 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
654 // and a reduced search returns a value much above beta, we can (almost) safely
655 // prune the previous move.
657 && depth >= 5 * ONE_PLY
659 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
661 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
662 Depth rdepth = depth - 4 * ONE_PLY;
664 assert(rdepth >= ONE_PLY);
665 assert((ss-1)->currentMove != MOVE_NONE);
666 assert((ss-1)->currentMove != MOVE_NULL);
668 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
671 while ((move = mp.next_move<false>()) != MOVE_NONE)
672 if (pos.legal(move, ci.pinned))
674 ss->currentMove = move;
675 pos.do_move(move, st, ci, pos.gives_check(move, ci));
676 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
683 // Step 10. Internal iterative deepening (skipped when in check)
684 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
686 && (PvNode || ss->staticEval + 256 >= beta))
688 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
690 ss->skipNullMove = true;
691 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
692 ss->skipNullMove = false;
694 tte = TT.probe(posKey);
695 ttMove = tte ? tte->move() : MOVE_NONE;
698 moves_loop: // When in check and at SpNode search starts from here
700 Square prevMoveSq = to_sq((ss-1)->currentMove);
701 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
702 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
704 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
705 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
706 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
708 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
710 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
711 improving = ss->staticEval >= (ss-2)->staticEval
712 || ss->staticEval == VALUE_NONE
713 ||(ss-2)->staticEval == VALUE_NONE;
715 singularExtensionNode = !RootNode
717 && depth >= 8 * ONE_PLY
718 && ttMove != MOVE_NONE
719 && !excludedMove // Recursive singular search is not allowed
720 && (tte->bound() & BOUND_LOWER)
721 && tte->depth() >= depth - 3 * ONE_PLY;
723 // Step 11. Loop through moves
724 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
725 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
729 if (move == excludedMove)
732 // At root obey the "searchmoves" option and skip moves not listed in Root
733 // Move List. As a consequence any illegal move is also skipped. In MultiPV
734 // mode we also skip PV moves which have been already searched.
735 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
740 // Shared counter cannot be decremented later if the move turns out to be illegal
741 if (!pos.legal(move, ci.pinned))
744 moveCount = ++splitPoint->moveCount;
745 splitPoint->mutex.unlock();
752 Signals.firstRootMove = (moveCount == 1);
754 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
755 sync_cout << "info depth " << depth / ONE_PLY
756 << " currmove " << move_to_uci(move, pos.is_chess960())
757 << " currmovenumber " << moveCount + PVIdx << sync_endl;
761 captureOrPromotion = pos.capture_or_promotion(move);
763 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
764 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
765 : pos.gives_check(move, ci);
767 dangerous = givesCheck
768 || type_of(move) != NORMAL
769 || pos.advanced_pawn_push(move);
771 // Step 12. Extend checks
772 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
775 // Singular extension search. If all moves but one fail low on a search of
776 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
777 // is singular and should be extended. To verify this we do a reduced search
778 // on all the other moves but the ttMove and if the result is lower than
779 // ttValue minus a margin then we extend the ttMove.
780 if ( singularExtensionNode
783 && pos.legal(move, ci.pinned)
784 && abs(ttValue) < VALUE_KNOWN_WIN)
786 assert(ttValue != VALUE_NONE);
788 Value rBeta = ttValue - int(depth);
789 ss->excludedMove = move;
790 ss->skipNullMove = true;
791 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
792 ss->skipNullMove = false;
793 ss->excludedMove = MOVE_NONE;
799 // Update the current move (this must be done after singular extension search)
800 newDepth = depth - ONE_PLY + ext;
802 // Step 13. Pruning at shallow depth (exclude PV nodes)
804 && !captureOrPromotion
807 /* && move != ttMove Already implicit in the next condition */
808 && bestValue > VALUE_MATED_IN_MAX_PLY)
810 // Move count based pruning
811 if ( depth < 16 * ONE_PLY
812 && moveCount >= FutilityMoveCounts[improving][depth] )
815 splitPoint->mutex.lock();
820 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
822 // Futility pruning: parent node
823 if (predictedDepth < 7 * ONE_PLY)
825 futilityValue = ss->staticEval + futility_margin(predictedDepth)
826 + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
828 if (futilityValue <= alpha)
830 bestValue = std::max(bestValue, futilityValue);
834 splitPoint->mutex.lock();
835 if (bestValue > splitPoint->bestValue)
836 splitPoint->bestValue = bestValue;
842 // Prune moves with negative SEE at low depths
843 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
846 splitPoint->mutex.lock();
852 // Check for legality just before making the move
853 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
859 pvMove = PvNode && moveCount == 1;
860 ss->currentMove = move;
861 if (!SpNode && !captureOrPromotion && quietCount < 64)
862 quietsSearched[quietCount++] = move;
864 // Step 14. Make the move
865 pos.do_move(move, st, ci, givesCheck);
867 // Step 15. Reduced depth search (LMR). If the move fails high it will be
868 // re-searched at full depth.
869 if ( depth >= 3 * ONE_PLY
871 && !captureOrPromotion
873 && move != ss->killers[0]
874 && move != ss->killers[1])
876 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
878 if (!PvNode && cutNode)
879 ss->reduction += ONE_PLY;
881 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
882 ss->reduction += ONE_PLY / 2;
884 if (move == countermoves[0] || move == countermoves[1])
885 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
887 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
889 alpha = splitPoint->alpha;
891 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
893 // Research at intermediate depth if reduction is very high
894 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
896 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
897 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
900 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
901 ss->reduction = DEPTH_ZERO;
904 doFullDepthSearch = !pvMove;
906 // Step 16. Full depth search, when LMR is skipped or fails high
907 if (doFullDepthSearch)
910 alpha = splitPoint->alpha;
912 value = newDepth < ONE_PLY ?
913 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
914 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
915 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
918 // For PV nodes only, do a full PV search on the first move or after a fail
919 // high (in the latter case search only if value < beta), otherwise let the
920 // parent node fail low with value <= alpha and to try another move.
921 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
922 value = newDepth < ONE_PLY ?
923 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
924 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
925 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
926 // Step 17. Undo move
929 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
931 // Step 18. Check for new best move
934 splitPoint->mutex.lock();
935 bestValue = splitPoint->bestValue;
936 alpha = splitPoint->alpha;
939 // Finished searching the move. If Signals.stop is true, the search
940 // was aborted because the user interrupted the search or because we
941 // ran out of time. In this case, the return value of the search cannot
942 // be trusted, and we don't update the best move and/or PV.
943 if (Signals.stop || thisThread->cutoff_occurred())
944 return value; // To avoid returning VALUE_INFINITE
948 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
950 // PV move or new best move ?
951 if (pvMove || value > alpha)
954 rm.extract_pv_from_tt(pos);
956 // We record how often the best move has been changed in each
957 // iteration. This information is used for time management: When
958 // the best move changes frequently, we allocate some more time.
963 // All other moves but the PV are set to the lowest value: this is
964 // not a problem when sorting because the sort is stable and the
965 // move position in the list is preserved - just the PV is pushed up.
966 rm.score = -VALUE_INFINITE;
969 if (value > bestValue)
971 bestValue = SpNode ? splitPoint->bestValue = value : value;
975 bestMove = SpNode ? splitPoint->bestMove = move : move;
977 if (PvNode && value < beta) // Update alpha! Always alpha < beta
978 alpha = SpNode ? splitPoint->alpha = value : value;
981 assert(value >= beta); // Fail high
984 splitPoint->cutoff = true;
991 // Step 19. Check for splitting the search
993 && depth >= Threads.minimumSplitDepth
994 && Threads.available_slave(thisThread)
995 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
997 assert(bestValue < beta);
999 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1000 depth, moveCount, &mp, NT, cutNode);
1001 if (bestValue >= beta)
1009 // Step 20. Check for mate and stalemate
1010 // All legal moves have been searched and if there are no legal moves, it
1011 // must be mate or stalemate. Note that we can have a false positive in
1012 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1013 // harmless because return value is discarded anyhow in the parent nodes.
1014 // If we are in a singular extension search then return a fail low score.
1015 // A split node has at least one move - the one tried before to be split.
1017 return excludedMove ? alpha
1018 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1020 // If we have pruned all the moves without searching return a fail-low score
1021 if (bestValue == -VALUE_INFINITE)
1024 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1025 bestValue >= beta ? BOUND_LOWER :
1026 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1027 depth, bestMove, ss->staticEval);
1029 // Quiet best move: update killers, history, countermoves and followupmoves
1030 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1031 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1033 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1039 // qsearch() is the quiescence search function, which is called by the main
1040 // search function when the remaining depth is zero (or, to be more precise,
1041 // less than ONE_PLY).
1043 template <NodeType NT, bool InCheck>
1044 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1046 const bool PvNode = (NT == PV);
1048 assert(NT == PV || NT == NonPV);
1049 assert(InCheck == !!pos.checkers());
1050 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1051 assert(PvNode || (alpha == beta - 1));
1052 assert(depth <= DEPTH_ZERO);
1057 Move ttMove, move, bestMove;
1058 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1059 bool givesCheck, evasionPrunable;
1062 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1066 ss->currentMove = bestMove = MOVE_NONE;
1067 ss->ply = (ss-1)->ply + 1;
1069 // Check for an instant draw or if the maximum ply has been reached
1070 if (pos.is_draw() || ss->ply > MAX_PLY)
1071 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1073 // Decide whether or not to include checks: this fixes also the type of
1074 // TT entry depth that we are going to use. Note that in qsearch we use
1075 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1076 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1077 : DEPTH_QS_NO_CHECKS;
1079 // Transposition table lookup
1081 tte = TT.probe(posKey);
1082 ttMove = tte ? tte->move() : MOVE_NONE;
1083 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1086 && tte->depth() >= ttDepth
1087 && ttValue != VALUE_NONE // Only in case of TT access race
1088 && ( PvNode ? tte->bound() == BOUND_EXACT
1089 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1090 : (tte->bound() & BOUND_UPPER)))
1092 ss->currentMove = ttMove; // Can be MOVE_NONE
1096 // Evaluate the position statically
1099 ss->staticEval = VALUE_NONE;
1100 bestValue = futilityBase = -VALUE_INFINITE;
1106 // Never assume anything on values stored in TT
1107 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1108 ss->staticEval = bestValue = evaluate(pos);
1110 // Can ttValue be used as a better position evaluation?
1111 if (ttValue != VALUE_NONE)
1112 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1113 bestValue = ttValue;
1116 ss->staticEval = bestValue = evaluate(pos);
1118 // Stand pat. Return immediately if static value is at least beta
1119 if (bestValue >= beta)
1122 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1123 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1128 if (PvNode && bestValue > alpha)
1131 futilityBase = bestValue + 128;
1134 // Initialize a MovePicker object for the current position, and prepare
1135 // to search the moves. Because the depth is <= 0 here, only captures,
1136 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1138 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1141 // Loop through the moves until no moves remain or a beta cutoff occurs
1142 while ((move = mp.next_move<false>()) != MOVE_NONE)
1144 assert(is_ok(move));
1146 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1147 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1148 : pos.gives_check(move, ci);
1155 && futilityBase > -VALUE_KNOWN_WIN
1156 && !pos.advanced_pawn_push(move))
1158 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1160 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1162 if (futilityValue < beta)
1164 bestValue = std::max(bestValue, futilityValue);
1168 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1170 bestValue = std::max(bestValue, futilityBase);
1175 // Detect non-capture evasions that are candidates to be pruned
1176 evasionPrunable = InCheck
1177 && bestValue > VALUE_MATED_IN_MAX_PLY
1178 && !pos.capture(move)
1179 && !pos.can_castle(pos.side_to_move());
1181 // Don't search moves with negative SEE values
1183 && (!InCheck || evasionPrunable)
1185 && type_of(move) != PROMOTION
1186 && pos.see_sign(move) < VALUE_ZERO)
1189 // Check for legality just before making the move
1190 if (!pos.legal(move, ci.pinned))
1193 ss->currentMove = move;
1195 // Make and search the move
1196 pos.do_move(move, st, ci, givesCheck);
1197 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1198 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1199 pos.undo_move(move);
1201 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1203 // Check for new best move
1204 if (value > bestValue)
1210 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1217 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1218 ttDepth, move, ss->staticEval);
1226 // All legal moves have been searched. A special case: If we're in check
1227 // and no legal moves were found, it is checkmate.
1228 if (InCheck && bestValue == -VALUE_INFINITE)
1229 return mated_in(ss->ply); // Plies to mate from the root
1231 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1232 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1233 ttDepth, bestMove, ss->staticEval);
1235 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1241 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1242 // "plies to mate from the current position". Non-mate scores are unchanged.
1243 // The function is called before storing a value in the transposition table.
1245 Value value_to_tt(Value v, int ply) {
1247 assert(v != VALUE_NONE);
1249 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1250 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1254 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1255 // from the transposition table (which refers to the plies to mate/be mated
1256 // from current position) to "plies to mate/be mated from the root".
1258 Value value_from_tt(Value v, int ply) {
1260 return v == VALUE_NONE ? VALUE_NONE
1261 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1262 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1266 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1269 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1271 if (ss->killers[0] != move)
1273 ss->killers[1] = ss->killers[0];
1274 ss->killers[0] = move;
1277 // Increase history value of the cut-off move and decrease all the other
1278 // played quiet moves.
1279 Value bonus = Value(int(depth) * int(depth));
1280 History.update(pos.moved_piece(move), to_sq(move), bonus);
1281 for (int i = 0; i < quietsCnt; ++i)
1284 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1287 if (is_ok((ss-1)->currentMove))
1289 Square prevMoveSq = to_sq((ss-1)->currentMove);
1290 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1293 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1295 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1296 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1301 // When playing with a strength handicap, choose best move among the MultiPV
1302 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1304 Move Skill::pick_move() {
1308 // PRNG sequence should be not deterministic
1309 for (int i = Time::now() % 50; i > 0; --i)
1310 rk.rand<unsigned>();
1312 // RootMoves are already sorted by score in descending order
1313 int variance = std::min(RootMoves[0].score - RootMoves[MultiPV - 1].score, PawnValueMg);
1314 int weakness = 120 - 2 * level;
1315 int max_s = -VALUE_INFINITE;
1318 // Choose best move. For each move score we add two terms both dependent on
1319 // weakness. One deterministic and bigger for weaker moves, and one random,
1320 // then we choose the move with the resulting highest score.
1321 for (size_t i = 0; i < MultiPV; ++i)
1323 int s = RootMoves[i].score;
1325 // Don't allow crazy blunders even at very low skills
1326 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1329 // This is our magic formula
1330 s += ( weakness * int(RootMoves[0].score - s)
1331 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1336 best = RootMoves[i].pv[0];
1343 // uci_pv() formats PV information according to the UCI protocol. UCI
1344 // requires that all (if any) unsearched PV lines are sent using a previous
1347 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1349 std::stringstream ss;
1350 Time::point elapsed = Time::now() - SearchTime + 1;
1351 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1354 for (size_t i = 0; i < Threads.size(); ++i)
1355 if (Threads[i]->maxPly > selDepth)
1356 selDepth = Threads[i]->maxPly;
1358 for (size_t i = 0; i < uciPVSize; ++i)
1360 bool updated = (i <= PVIdx);
1362 if (depth == 1 && !updated)
1365 int d = updated ? depth : depth - 1;
1366 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1368 if (ss.rdbuf()->in_avail()) // Not at first line
1371 ss << "info depth " << d
1372 << " seldepth " << selDepth
1373 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1374 << " nodes " << pos.nodes_searched()
1375 << " nps " << pos.nodes_searched() * 1000 / elapsed
1376 << " time " << elapsed
1377 << " multipv " << i + 1
1380 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1381 ss << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1390 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1391 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1392 /// ensure that we have a ponder move even when we fail high at root. This
1393 /// results in a long PV to print that is important for position analysis.
1395 void RootMove::extract_pv_from_tt(Position& pos) {
1397 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1407 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1409 pos.do_move(pv[ply++], *st++);
1410 tte = TT.probe(pos.key());
1413 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1414 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1416 && (!pos.is_draw() || ply < 2));
1418 pv.push_back(MOVE_NONE); // Must be zero-terminating
1420 while (ply) pos.undo_move(pv[--ply]);
1424 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1425 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1426 /// first, even if the old TT entries have been overwritten.
1428 void RootMove::insert_pv_in_tt(Position& pos) {
1430 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1435 tte = TT.probe(pos.key());
1437 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1438 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1440 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1442 pos.do_move(pv[ply++], *st++);
1444 } while (pv[ply] != MOVE_NONE);
1446 while (ply) pos.undo_move(pv[--ply]);
1450 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1452 void Thread::idle_loop() {
1454 // Pointer 'this_sp' is not null only if we are called from split(), and not
1455 // at the thread creation. This means we are the split point's master.
1456 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1458 assert(!this_sp || (this_sp->masterThread == this && searching));
1462 // If we are not searching, wait for a condition to be signaled instead of
1463 // wasting CPU time polling for work.
1464 while ((!searching && Threads.sleepWhileIdle) || exit)
1472 // Grab the lock to avoid races with Thread::notify_one()
1475 // If we are master and all slaves have finished then exit idle_loop
1476 if (this_sp && this_sp->slavesMask.none())
1482 // Do sleep after retesting sleep conditions under lock protection. In
1483 // particular we need to avoid a deadlock in case a master thread has,
1484 // in the meanwhile, allocated us and sent the notify_one() call before
1485 // we had the chance to grab the lock.
1486 if (!searching && !exit)
1487 sleepCondition.wait(mutex);
1492 // If this thread has been assigned work, launch a search
1497 Threads.mutex.lock();
1500 assert(activeSplitPoint);
1501 SplitPoint* sp = activeSplitPoint;
1503 Threads.mutex.unlock();
1505 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1506 Position pos(*sp->pos, this);
1508 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1509 ss->splitPoint = sp;
1513 assert(activePosition == NULL);
1515 activePosition = &pos;
1517 switch (sp->nodeType) {
1519 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1522 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1525 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1534 activePosition = NULL;
1535 sp->slavesMask.reset(idx);
1536 sp->nodes += pos.nodes_searched();
1538 // Wake up the master thread so to allow it to return from the idle
1539 // loop in case we are the last slave of the split point.
1540 if ( Threads.sleepWhileIdle
1541 && this != sp->masterThread
1542 && sp->slavesMask.none())
1544 assert(!sp->masterThread->searching);
1545 sp->masterThread->notify_one();
1548 // After releasing the lock we can't access any SplitPoint related data
1549 // in a safe way because it could have been released under our feet by
1550 // the sp master. Also accessing other Thread objects is unsafe because
1551 // if we are exiting there is a chance that they are already freed.
1555 // If this thread is the master of a split point and all slaves have finished
1556 // their work at this split point, return from the idle loop.
1557 if (this_sp && this_sp->slavesMask.none())
1559 this_sp->mutex.lock();
1560 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1561 this_sp->mutex.unlock();
1569 /// check_time() is called by the timer thread when the timer triggers. It is
1570 /// used to print debug info and, more importantly, to detect when we are out of
1571 /// available time and thus stop the search.
1575 static Time::point lastInfoTime = Time::now();
1576 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1578 if (Time::now() - lastInfoTime >= 1000)
1580 lastInfoTime = Time::now();
1589 Threads.mutex.lock();
1591 nodes = RootPos.nodes_searched();
1593 // Loop across all split points and sum accumulated SplitPoint nodes plus
1594 // all the currently active positions nodes.
1595 for (size_t i = 0; i < Threads.size(); ++i)
1596 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1598 SplitPoint& sp = Threads[i]->splitPoints[j];
1604 for (size_t idx = 0; idx < Threads.size(); ++idx)
1605 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1606 nodes += Threads[idx]->activePosition->nodes_searched();
1611 Threads.mutex.unlock();
1614 Time::point elapsed = Time::now() - SearchTime;
1615 bool stillAtFirstMove = Signals.firstRootMove
1616 && !Signals.failedLowAtRoot
1617 && elapsed > TimeMgr.available_time() * 75 / 100;
1619 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1620 || stillAtFirstMove;
1622 if ( (Limits.use_time_management() && noMoreTime)
1623 || (Limits.movetime && elapsed >= Limits.movetime)
1624 || (Limits.nodes && nodes >= Limits.nodes))
1625 Signals.stop = true;