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 * int(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 * int(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 Contempt[0] = Options["Contempt Factor"] * PawnValueEg / 100; // From centipawns
190 Contempt[1] = (Options["Contempt Factor"] + 12) * PawnValueEg / 100;
192 if (RootMoves.empty())
194 RootMoves.push_back(MOVE_NONE);
195 sync_cout << "info depth 0 score "
196 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
202 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
204 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
206 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
208 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
213 if (Options["Write Search Log"])
215 Log log(Options["Search Log Filename"]);
216 log << "\nSearching: " << RootPos.fen()
217 << "\ninfinite: " << Limits.infinite
218 << " ponder: " << Limits.ponder
219 << " time: " << Limits.time[RootColor]
220 << " increment: " << Limits.inc[RootColor]
221 << " moves to go: " << Limits.movestogo
222 << "\n" << std::endl;
225 // Reset the threads, still sleeping: will wake up at split time
226 for (size_t i = 0; i < Threads.size(); ++i)
227 Threads[i]->maxPly = 0;
229 Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
230 Threads.timer->run = true;
231 Threads.timer->notify_one(); // Wake up the recurring timer
233 id_loop(RootPos); // Let's start searching !
235 Threads.timer->run = false; // Stop the timer
236 Threads.sleepWhileIdle = true; // Send idle threads to sleep
238 if (Options["Write Search Log"])
240 Time::point elapsed = Time::now() - SearchTime + 1;
242 Log log(Options["Search Log Filename"]);
243 log << "Nodes: " << RootPos.nodes_searched()
244 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
245 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
248 RootPos.do_move(RootMoves[0].pv[0], st);
249 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
250 RootPos.undo_move(RootMoves[0].pv[0]);
255 // When search is stopped this info is not printed
256 sync_cout << "info nodes " << RootPos.nodes_searched()
257 << " time " << Time::now() - SearchTime + 1 << sync_endl;
259 // When we reach the maximum depth, we can arrive here without a raise of
260 // Signals.stop. However, if we are pondering or in an infinite search,
261 // the UCI protocol states that we shouldn't print the best move before the
262 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
263 // until the GUI sends one of those commands (which also raises Signals.stop).
264 if (!Signals.stop && (Limits.ponder || Limits.infinite))
266 Signals.stopOnPonderhit = true;
267 RootPos.this_thread()->wait_for(Signals.stop);
270 // Best move could be MOVE_NONE when searching on a stalemate position
271 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
272 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
279 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
280 // with increasing depth until the allocated thinking time has been consumed,
281 // user stops the search, or the maximum search depth is reached.
283 void id_loop(Position& pos) {
285 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
287 Value bestValue, alpha, beta, delta;
289 std::memset(ss-2, 0, 5 * sizeof(Stack));
290 (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
294 bestValue = delta = alpha = -VALUE_INFINITE;
295 beta = VALUE_INFINITE;
300 Countermoves.clear();
301 Followupmoves.clear();
303 MultiPV = Options["MultiPV"];
304 Skill skill(Options["Skill Level"]);
306 // Do we have to play with skill handicap? In this case enable MultiPV search
307 // that we will use behind the scenes to retrieve a set of possible moves.
308 if (skill.enabled() && MultiPV < 4)
311 MultiPV = std::min(MultiPV, RootMoves.size());
313 // Iterative deepening loop until requested to stop or target depth reached
314 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
316 // Age out PV variability metric
317 BestMoveChanges *= 0.5;
319 // Save the last iteration's scores before first PV line is searched and
320 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
321 for (size_t i = 0; i < RootMoves.size(); ++i)
322 RootMoves[i].prevScore = RootMoves[i].score;
324 // MultiPV loop. We perform a full root search for each PV line
325 for (PVIdx = 0; PVIdx < MultiPV && !Signals.stop; ++PVIdx)
327 // Reset aspiration window starting size
331 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
332 beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
335 // Start with a small aspiration window and, in the case of a fail
336 // high/low, re-search with a bigger window until we're not failing
340 bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
342 DrawValue[ RootColor] = VALUE_DRAW - Contempt[bestValue > VALUE_DRAW];
343 DrawValue[~RootColor] = VALUE_DRAW + Contempt[bestValue > VALUE_DRAW];
345 // Bring the best move to the front. It is critical that sorting
346 // is done with a stable algorithm because all the values but the
347 // first and eventually the new best one are set to -VALUE_INFINITE
348 // and we want to keep the same order for all the moves except the
349 // new PV that goes to the front. Note that in case of MultiPV
350 // search the already searched PV lines are preserved.
351 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
353 // Write PV back to transposition table in case the relevant
354 // entries have been overwritten during the search.
355 for (size_t i = 0; i <= PVIdx; ++i)
356 RootMoves[i].insert_pv_in_tt(pos);
358 // If search has been stopped break immediately. Sorting and
359 // writing PV back to TT is safe because RootMoves is still
360 // valid, although it refers to previous iteration.
364 // When failing high/low give some update (without cluttering
365 // the UI) before a re-search.
366 if ( (bestValue <= alpha || bestValue >= beta)
367 && Time::now() - SearchTime > 3000)
368 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
370 // In case of failing low/high increase aspiration window and
371 // re-search, otherwise exit the loop.
372 if (bestValue <= alpha)
374 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
376 Signals.failedLowAtRoot = true;
377 Signals.stopOnPonderhit = false;
379 else if (bestValue >= beta)
380 beta = std::min(bestValue + delta, VALUE_INFINITE);
387 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
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 == MultiPV || Time::now() - SearchTime > 3000)
394 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
397 // If skill levels are enabled and time is up, pick a sub-optimal best move
398 if (skill.enabled() && skill.time_to_pick(depth))
401 if (Options["Write 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 // Have we 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.stop && !Signals.stopOnPonderhit)
421 // Take some extra time if the best move has changed
422 if (depth > 4 && depth < 50 && MultiPV == 1)
423 TimeMgr.pv_instability(BestMoveChanges);
425 // Stop the search if only one legal move is available or all
426 // of the available time has been used.
427 if ( RootMoves.size() == 1
428 || Time::now() - SearchTime > TimeMgr.available_time())
430 // If we are allowed to ponder do not stop the search now but
431 // keep pondering until the GUI sends "ponderhit" or "stop".
433 Signals.stopOnPonderhit = true;
442 // search<>() is the main search function for both PV and non-PV nodes and for
443 // normal and SplitPoint nodes. When called just after a split point the search
444 // is simpler because we have already probed the hash table, done a null move
445 // search, and searched the first move before splitting, so we don't have to
446 // repeat all this work again. We also don't need to store anything to the hash
447 // table here: This is taken care of after we return from the split point.
449 template <NodeType NT>
450 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
452 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
453 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
454 const bool RootNode = (NT == Root || NT == SplitPointRoot);
456 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
457 assert(PvNode || (alpha == beta - 1));
458 assert(depth > DEPTH_ZERO);
460 Move quietsSearched[64];
463 SplitPoint* splitPoint;
465 Move ttMove, move, excludedMove, bestMove;
466 Depth ext, newDepth, predictedDepth;
467 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
468 bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
469 bool captureOrPromotion, dangerous, doFullDepthSearch;
470 int moveCount, quietCount;
472 // Step 1. Initialize node
473 Thread* thisThread = pos.this_thread();
474 inCheck = pos.checkers();
478 splitPoint = ss->splitPoint;
479 bestMove = splitPoint->bestMove;
480 bestValue = splitPoint->bestValue;
482 ttMove = excludedMove = MOVE_NONE;
483 ttValue = VALUE_NONE;
485 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
490 moveCount = quietCount = 0;
491 bestValue = -VALUE_INFINITE;
492 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
493 ss->ply = (ss-1)->ply + 1;
494 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
495 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
497 // Used to send selDepth info to GUI
498 if (PvNode && thisThread->maxPly < ss->ply)
499 thisThread->maxPly = ss->ply;
503 // Step 2. Check for aborted search and immediate draw
504 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
505 return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
507 // Step 3. Mate distance pruning. Even if we mate at the next move our score
508 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
509 // a shorter mate was found upward in the tree then there is no need to search
510 // because we will never beat the current alpha. Same logic but with reversed
511 // signs applies also in the opposite condition of being mated instead of giving
512 // mate. In this case return a fail-high score.
513 alpha = std::max(mated_in(ss->ply), alpha);
514 beta = std::min(mate_in(ss->ply+1), beta);
519 // Step 4. Transposition table lookup
520 // We don't want the score of a partial search to overwrite a previous full search
521 // TT value, so we use a different position key in case of an excluded move.
522 excludedMove = ss->excludedMove;
523 posKey = excludedMove ? pos.exclusion_key() : pos.key();
524 tte = TT.probe(posKey);
525 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
526 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
528 // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
529 // a fail high/low. The biggest advantage to probing at PV nodes is to have a
530 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
531 // we should also update RootMoveList to avoid bogus output.
534 && tte->depth() >= depth
535 && ttValue != VALUE_NONE // Only in case of TT access race
536 && ( PvNode ? tte->bound() == BOUND_EXACT
537 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
538 : (tte->bound() & BOUND_UPPER)))
540 ss->currentMove = ttMove; // Can be MOVE_NONE
542 // If ttMove is quiet, update killers, history, counter move and followup move on TT hit
543 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove) && !inCheck)
544 update_stats(pos, ss, ttMove, depth, NULL, 0);
549 // Step 5. Evaluate the position statically and update parent's gain statistics
552 ss->staticEval = eval = VALUE_NONE;
558 // Never assume anything on values stored in TT
559 if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
560 eval = ss->staticEval = evaluate(pos);
562 // Can ttValue be used as a better position evaluation?
563 if (ttValue != VALUE_NONE)
564 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
569 eval = ss->staticEval = evaluate(pos);
570 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
573 if ( !pos.captured_piece_type()
574 && ss->staticEval != VALUE_NONE
575 && (ss-1)->staticEval != VALUE_NONE
576 && (move = (ss-1)->currentMove) != MOVE_NULL
577 && type_of(move) == NORMAL)
579 Square to = to_sq(move);
580 Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
583 // Step 6. Razoring (skipped when in check)
585 && depth < 4 * ONE_PLY
586 && eval + razor_margin(depth) <= alpha
587 && ttMove == MOVE_NONE
588 && abs(beta) < VALUE_MATE_IN_MAX_PLY
589 && !pos.pawn_on_7th(pos.side_to_move()))
591 Value ralpha = alpha - razor_margin(depth);
592 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
597 // Step 7. Futility pruning: child node (skipped when in check)
600 && depth < 7 * ONE_PLY
601 && eval - futility_margin(depth) >= beta
602 && abs(beta) < VALUE_MATE_IN_MAX_PLY
603 && abs(eval) < VALUE_KNOWN_WIN
604 && pos.non_pawn_material(pos.side_to_move()))
605 return eval - futility_margin(depth);
607 // Step 8. Null move search with verification search (is omitted in PV nodes)
610 && depth >= 2 * ONE_PLY
612 && abs(beta) < VALUE_MATE_IN_MAX_PLY
613 && pos.non_pawn_material(pos.side_to_move()))
615 ss->currentMove = MOVE_NULL;
617 assert(eval - beta >= 0);
619 // Null move dynamic reduction based on depth and value
620 Depth R = 3 * ONE_PLY
622 + int(eval - beta) / PawnValueMg * ONE_PLY;
624 pos.do_null_move(st);
625 (ss+1)->skipNullMove = true;
626 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
627 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
628 (ss+1)->skipNullMove = false;
629 pos.undo_null_move();
631 if (nullValue >= beta)
633 // Do not return unproven mate scores
634 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
637 if (depth < 12 * ONE_PLY)
640 // Do verification search at high depths
641 ss->skipNullMove = true;
642 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
643 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
644 ss->skipNullMove = false;
651 // Step 9. ProbCut (skipped when in check)
652 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
653 // and a reduced search returns a value much above beta, we can (almost) safely
654 // prune the previous move.
656 && depth >= 5 * ONE_PLY
658 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
660 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
661 Depth rdepth = depth - 4 * ONE_PLY;
663 assert(rdepth >= ONE_PLY);
664 assert((ss-1)->currentMove != MOVE_NONE);
665 assert((ss-1)->currentMove != MOVE_NULL);
667 MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
670 while ((move = mp.next_move<false>()) != MOVE_NONE)
671 if (pos.legal(move, ci.pinned))
673 ss->currentMove = move;
674 pos.do_move(move, st, ci, pos.gives_check(move, ci));
675 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
682 // Step 10. Internal iterative deepening (skipped when in check)
683 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
685 && (PvNode || ss->staticEval + Value(256) >= beta))
687 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
689 ss->skipNullMove = true;
690 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
691 ss->skipNullMove = false;
693 tte = TT.probe(posKey);
694 ttMove = tte ? tte->move() : MOVE_NONE;
697 moves_loop: // When in check and at SpNode search starts from here
699 Square prevMoveSq = to_sq((ss-1)->currentMove);
700 Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
701 Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
703 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
704 Move followupmoves[] = { Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].first,
705 Followupmoves[pos.piece_on(prevOwnMoveSq)][prevOwnMoveSq].second };
707 MovePicker mp(pos, ttMove, depth, History, countermoves, followupmoves, ss);
709 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
710 improving = ss->staticEval >= (ss-2)->staticEval
711 || ss->staticEval == VALUE_NONE
712 ||(ss-2)->staticEval == VALUE_NONE;
714 singularExtensionNode = !RootNode
716 && depth >= 8 * ONE_PLY
717 && ttMove != MOVE_NONE
718 && !excludedMove // Recursive singular search is not allowed
719 && (tte->bound() & BOUND_LOWER)
720 && tte->depth() >= depth - 3 * ONE_PLY;
722 // Step 11. Loop through moves
723 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
724 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
728 if (move == excludedMove)
731 // At root obey the "searchmoves" option and skip moves not listed in Root
732 // Move List. As a consequence any illegal move is also skipped. In MultiPV
733 // mode we also skip PV moves which have been already searched.
734 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
739 // Shared counter cannot be decremented later if the move turns out to be illegal
740 if (!pos.legal(move, ci.pinned))
743 moveCount = ++splitPoint->moveCount;
744 splitPoint->mutex.unlock();
751 Signals.firstRootMove = (moveCount == 1);
753 if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
754 sync_cout << "info depth " << depth / ONE_PLY
755 << " currmove " << move_to_uci(move, pos.is_chess960())
756 << " currmovenumber " << moveCount + PVIdx << sync_endl;
760 captureOrPromotion = pos.capture_or_promotion(move);
762 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
763 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
764 : pos.gives_check(move, ci);
766 dangerous = givesCheck
767 || type_of(move) != NORMAL
768 || pos.advanced_pawn_push(move);
770 // Step 12. Extend checks
771 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
774 // Singular extension search. If all moves but one fail low on a search of
775 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
776 // is singular and should be extended. To verify this we do a reduced search
777 // on all the other moves but the ttMove and if the result is lower than
778 // ttValue minus a margin then we extend the ttMove.
779 if ( singularExtensionNode
782 && pos.legal(move, ci.pinned)
783 && abs(ttValue) < VALUE_KNOWN_WIN)
785 assert(ttValue != VALUE_NONE);
787 Value rBeta = ttValue - int(depth);
788 ss->excludedMove = move;
789 ss->skipNullMove = true;
790 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
791 ss->skipNullMove = false;
792 ss->excludedMove = MOVE_NONE;
798 // Update the current move (this must be done after singular extension search)
799 newDepth = depth - ONE_PLY + ext;
801 // Step 13. Pruning at shallow depth (exclude PV nodes)
803 && !captureOrPromotion
806 /* && move != ttMove Already implicit in the next condition */
807 && bestValue > VALUE_MATED_IN_MAX_PLY)
809 // Move count based pruning
810 if ( depth < 16 * ONE_PLY
811 && moveCount >= FutilityMoveCounts[improving][depth] )
814 splitPoint->mutex.lock();
819 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
821 // Futility pruning: parent node
822 if (predictedDepth < 7 * ONE_PLY)
824 futilityValue = ss->staticEval + futility_margin(predictedDepth)
825 + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
827 if (futilityValue <= alpha)
829 bestValue = std::max(bestValue, futilityValue);
833 splitPoint->mutex.lock();
834 if (bestValue > splitPoint->bestValue)
835 splitPoint->bestValue = bestValue;
841 // Prune moves with negative SEE at low depths
842 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
845 splitPoint->mutex.lock();
851 // Check for legality just before making the move
852 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
858 pvMove = PvNode && moveCount == 1;
859 ss->currentMove = move;
860 if (!SpNode && !captureOrPromotion && quietCount < 64)
861 quietsSearched[quietCount++] = move;
863 // Step 14. Make the move
864 pos.do_move(move, st, ci, givesCheck);
866 // Step 15. Reduced depth search (LMR). If the move fails high it will be
867 // re-searched at full depth.
868 if ( depth >= 3 * ONE_PLY
870 && !captureOrPromotion
872 && move != ss->killers[0]
873 && move != ss->killers[1])
875 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
877 if (!PvNode && cutNode)
878 ss->reduction += ONE_PLY;
880 else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
881 ss->reduction += ONE_PLY / 2;
883 if (move == countermoves[0] || move == countermoves[1])
884 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
886 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
888 alpha = splitPoint->alpha;
890 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
892 // Research at intermediate depth if reduction is very high
893 if (value > alpha && ss->reduction >= 4 * ONE_PLY)
895 Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
896 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
899 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
900 ss->reduction = DEPTH_ZERO;
903 doFullDepthSearch = !pvMove;
905 // Step 16. Full depth search, when LMR is skipped or fails high
906 if (doFullDepthSearch)
909 alpha = splitPoint->alpha;
911 value = newDepth < ONE_PLY ?
912 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
913 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
914 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
917 // For PV nodes only, do a full PV search on the first move or after a fail
918 // high (in the latter case search only if value < beta), otherwise let the
919 // parent node fail low with value <= alpha and to try another move.
920 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
921 value = newDepth < ONE_PLY ?
922 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
923 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
924 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
925 // Step 17. Undo move
928 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
930 // Step 18. Check for new best move
933 splitPoint->mutex.lock();
934 bestValue = splitPoint->bestValue;
935 alpha = splitPoint->alpha;
938 // Finished searching the move. If Signals.stop is true, the search
939 // was aborted because the user interrupted the search or because we
940 // ran out of time. In this case, the return value of the search cannot
941 // be trusted, and we don't update the best move and/or PV.
942 if (Signals.stop || thisThread->cutoff_occurred())
943 return value; // To avoid returning VALUE_INFINITE
947 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
949 // PV move or new best move ?
950 if (pvMove || value > alpha)
953 rm.extract_pv_from_tt(pos);
955 // We record how often the best move has been changed in each
956 // iteration. This information is used for time management: When
957 // the best move changes frequently, we allocate some more time.
962 // All other moves but the PV are set to the lowest value: this is
963 // not a problem when sorting because the sort is stable and the
964 // move position in the list is preserved - just the PV is pushed up.
965 rm.score = -VALUE_INFINITE;
968 if (value > bestValue)
970 bestValue = SpNode ? splitPoint->bestValue = value : value;
974 bestMove = SpNode ? splitPoint->bestMove = move : move;
976 if (PvNode && value < beta) // Update alpha! Always alpha < beta
977 alpha = SpNode ? splitPoint->alpha = value : value;
980 assert(value >= beta); // Fail high
983 splitPoint->cutoff = true;
990 // Step 19. Check for splitting the search
992 && depth >= Threads.minimumSplitDepth
993 && Threads.available_slave(thisThread)
994 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
996 assert(bestValue < beta);
998 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
999 depth, moveCount, &mp, NT, cutNode);
1000 if (bestValue >= beta)
1008 // Step 20. Check for mate and stalemate
1009 // All legal moves have been searched and if there are no legal moves, it
1010 // must be mate or stalemate. Note that we can have a false positive in
1011 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1012 // harmless because return value is discarded anyhow in the parent nodes.
1013 // If we are in a singular extension search then return a fail low score.
1014 // A split node has at least one move - the one tried before to be split.
1016 return excludedMove ? alpha
1017 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1019 // If we have pruned all the moves without searching return a fail-low score
1020 if (bestValue == -VALUE_INFINITE)
1023 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1024 bestValue >= beta ? BOUND_LOWER :
1025 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1026 depth, bestMove, ss->staticEval);
1028 // Quiet best move: update killers, history, countermoves and followupmoves
1029 if (bestValue >= beta && !pos.capture_or_promotion(bestMove) && !inCheck)
1030 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount - 1);
1032 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1038 // qsearch() is the quiescence search function, which is called by the main
1039 // search function when the remaining depth is zero (or, to be more precise,
1040 // less than ONE_PLY).
1042 template <NodeType NT, bool InCheck>
1043 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1045 const bool PvNode = (NT == PV);
1047 assert(NT == PV || NT == NonPV);
1048 assert(InCheck == !!pos.checkers());
1049 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1050 assert(PvNode || (alpha == beta - 1));
1051 assert(depth <= DEPTH_ZERO);
1056 Move ttMove, move, bestMove;
1057 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1058 bool givesCheck, evasionPrunable;
1061 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1065 ss->currentMove = bestMove = MOVE_NONE;
1066 ss->ply = (ss-1)->ply + 1;
1068 // Check for an instant draw or if the maximum ply has been reached
1069 if (pos.is_draw() || ss->ply > MAX_PLY)
1070 return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1072 // Decide whether or not to include checks: this fixes also the type of
1073 // TT entry depth that we are going to use. Note that in qsearch we use
1074 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1075 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1076 : DEPTH_QS_NO_CHECKS;
1078 // Transposition table lookup
1080 tte = TT.probe(posKey);
1081 ttMove = tte ? tte->move() : MOVE_NONE;
1082 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1085 && tte->depth() >= ttDepth
1086 && ttValue != VALUE_NONE // Only in case of TT access race
1087 && ( PvNode ? tte->bound() == BOUND_EXACT
1088 : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1089 : (tte->bound() & BOUND_UPPER)))
1091 ss->currentMove = ttMove; // Can be MOVE_NONE
1095 // Evaluate the position statically
1098 ss->staticEval = VALUE_NONE;
1099 bestValue = futilityBase = -VALUE_INFINITE;
1105 // Never assume anything on values stored in TT
1106 if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
1107 ss->staticEval = bestValue = evaluate(pos);
1109 // Can ttValue be used as a better position evaluation?
1110 if (ttValue != VALUE_NONE)
1111 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1112 bestValue = ttValue;
1115 ss->staticEval = bestValue = evaluate(pos);
1117 // Stand pat. Return immediately if static value is at least beta
1118 if (bestValue >= beta)
1121 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1122 DEPTH_NONE, MOVE_NONE, ss->staticEval);
1127 if (PvNode && bestValue > alpha)
1130 futilityBase = bestValue + Value(128);
1133 // Initialize a MovePicker object for the current position, and prepare
1134 // to search the moves. Because the depth is <= 0 here, only captures,
1135 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1137 MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
1140 // Loop through the moves until no moves remain or a beta cutoff occurs
1141 while ((move = mp.next_move<false>()) != MOVE_NONE)
1143 assert(is_ok(move));
1145 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1146 ? ci.checkSq[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1147 : pos.gives_check(move, ci);
1154 && futilityBase > -VALUE_KNOWN_WIN
1155 && !pos.advanced_pawn_push(move))
1157 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1159 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1161 if (futilityValue < beta)
1163 bestValue = std::max(bestValue, futilityValue);
1167 if (futilityBase < beta && pos.see(move) <= VALUE_ZERO)
1169 bestValue = std::max(bestValue, futilityBase);
1174 // Detect non-capture evasions that are candidates to be pruned
1175 evasionPrunable = InCheck
1176 && bestValue > VALUE_MATED_IN_MAX_PLY
1177 && !pos.capture(move)
1178 && !pos.can_castle(pos.side_to_move());
1180 // Don't search moves with negative SEE values
1182 && (!InCheck || evasionPrunable)
1184 && type_of(move) != PROMOTION
1185 && pos.see_sign(move) < VALUE_ZERO)
1188 // Check for legality just before making the move
1189 if (!pos.legal(move, ci.pinned))
1192 ss->currentMove = move;
1194 // Make and search the move
1195 pos.do_move(move, st, ci, givesCheck);
1196 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1197 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1198 pos.undo_move(move);
1200 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1202 // Check for new best move
1203 if (value > bestValue)
1209 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1216 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1217 ttDepth, move, ss->staticEval);
1225 // All legal moves have been searched. A special case: If we're in check
1226 // and no legal moves were found, it is checkmate.
1227 if (InCheck && bestValue == -VALUE_INFINITE)
1228 return mated_in(ss->ply); // Plies to mate from the root
1230 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1231 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1232 ttDepth, bestMove, ss->staticEval);
1234 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1240 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1241 // "plies to mate from the current position". Non-mate scores are unchanged.
1242 // The function is called before storing a value in the transposition table.
1244 Value value_to_tt(Value v, int ply) {
1246 assert(v != VALUE_NONE);
1248 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1249 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1253 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1254 // from the transposition table (which refers to the plies to mate/be mated
1255 // from current position) to "plies to mate/be mated from the root".
1257 Value value_from_tt(Value v, int ply) {
1259 return v == VALUE_NONE ? VALUE_NONE
1260 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1261 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1265 // update_stats() updates killers, history, countermoves and followupmoves stats after a fail-high
1268 void update_stats(Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt) {
1270 if (ss->killers[0] != move)
1272 ss->killers[1] = ss->killers[0];
1273 ss->killers[0] = move;
1276 // Increase history value of the cut-off move and decrease all the other
1277 // played quiet moves.
1278 Value bonus = Value(int(depth) * int(depth));
1279 History.update(pos.moved_piece(move), to_sq(move), bonus);
1280 for (int i = 0; i < quietsCnt; ++i)
1283 History.update(pos.moved_piece(m), to_sq(m), -bonus);
1286 if (is_ok((ss-1)->currentMove))
1288 Square prevMoveSq = to_sq((ss-1)->currentMove);
1289 Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, move);
1292 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1294 Square prevOwnMoveSq = to_sq((ss-2)->currentMove);
1295 Followupmoves.update(pos.piece_on(prevOwnMoveSq), prevOwnMoveSq, move);
1300 // When playing with a strength handicap, choose best move among the MultiPV
1301 // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1303 Move Skill::pick_move() {
1307 // PRNG sequence should be not deterministic
1308 for (int i = Time::now() % 50; i > 0; --i)
1309 rk.rand<unsigned>();
1311 // RootMoves are already sorted by score in descending order
1312 int variance = std::min(RootMoves[0].score - RootMoves[MultiPV - 1].score, PawnValueMg);
1313 int weakness = 120 - 2 * level;
1314 int max_s = -VALUE_INFINITE;
1317 // Choose best move. For each move score we add two terms both dependent on
1318 // weakness. One deterministic and bigger for weaker moves, and one random,
1319 // then we choose the move with the resulting highest score.
1320 for (size_t i = 0; i < MultiPV; ++i)
1322 int s = RootMoves[i].score;
1324 // Don't allow crazy blunders even at very low skills
1325 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1328 // This is our magic formula
1329 s += ( weakness * int(RootMoves[0].score - s)
1330 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1335 best = RootMoves[i].pv[0];
1342 // uci_pv() formats PV information according to the UCI protocol. UCI
1343 // requires that all (if any) unsearched PV lines are sent using a previous
1346 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1348 std::stringstream ss;
1349 Time::point elapsed = Time::now() - SearchTime + 1;
1350 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1353 for (size_t i = 0; i < Threads.size(); ++i)
1354 if (Threads[i]->maxPly > selDepth)
1355 selDepth = Threads[i]->maxPly;
1357 for (size_t i = 0; i < uciPVSize; ++i)
1359 bool updated = (i <= PVIdx);
1361 if (depth == 1 && !updated)
1364 int d = updated ? depth : depth - 1;
1365 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1367 if (ss.rdbuf()->in_avail()) // Not at first line
1370 ss << "info depth " << d
1371 << " seldepth " << selDepth
1372 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1373 << " nodes " << pos.nodes_searched()
1374 << " nps " << pos.nodes_searched() * 1000 / elapsed
1375 << " time " << elapsed
1376 << " multipv " << i + 1
1379 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
1380 ss << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1389 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1390 /// We also consider both failing high nodes and BOUND_EXACT nodes here to
1391 /// ensure that we have a ponder move even when we fail high at root. This
1392 /// results in a long PV to print that is important for position analysis.
1394 void RootMove::extract_pv_from_tt(Position& pos) {
1396 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1406 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1408 pos.do_move(pv[ply++], *st++);
1409 tte = TT.probe(pos.key());
1412 && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
1413 && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
1415 && (!pos.is_draw() || ply < 2));
1417 pv.push_back(MOVE_NONE); // Must be zero-terminating
1419 while (ply) pos.undo_move(pv[--ply]);
1423 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1424 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1425 /// first, even if the old TT entries have been overwritten.
1427 void RootMove::insert_pv_in_tt(Position& pos) {
1429 StateInfo state[MAX_PLY_PLUS_6], *st = state;
1434 tte = TT.probe(pos.key());
1436 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1437 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
1439 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1441 pos.do_move(pv[ply++], *st++);
1443 } while (pv[ply] != MOVE_NONE);
1445 while (ply) pos.undo_move(pv[--ply]);
1449 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1451 void Thread::idle_loop() {
1453 // Pointer 'this_sp' is not null only if we are called from split(), and not
1454 // at the thread creation. This means we are the split point's master.
1455 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1457 assert(!this_sp || (this_sp->masterThread == this && searching));
1461 // If we are not searching, wait for a condition to be signaled instead of
1462 // wasting CPU time polling for work.
1463 while ((!searching && Threads.sleepWhileIdle) || exit)
1471 // Grab the lock to avoid races with Thread::notify_one()
1474 // If we are master and all slaves have finished then exit idle_loop
1475 if (this_sp && this_sp->slavesMask.none())
1481 // Do sleep after retesting sleep conditions under lock protection. In
1482 // particular we need to avoid a deadlock in case a master thread has,
1483 // in the meanwhile, allocated us and sent the notify_one() call before
1484 // we had the chance to grab the lock.
1485 if (!searching && !exit)
1486 sleepCondition.wait(mutex);
1491 // If this thread has been assigned work, launch a search
1496 Threads.mutex.lock();
1499 assert(activeSplitPoint);
1500 SplitPoint* sp = activeSplitPoint;
1502 Threads.mutex.unlock();
1504 Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
1505 Position pos(*sp->pos, this);
1507 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1508 ss->splitPoint = sp;
1512 assert(activePosition == NULL);
1514 activePosition = &pos;
1516 switch (sp->nodeType) {
1518 search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1521 search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1524 search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1533 activePosition = NULL;
1534 sp->slavesMask.reset(idx);
1535 sp->nodes += pos.nodes_searched();
1537 // Wake up the master thread so to allow it to return from the idle
1538 // loop in case we are the last slave of the split point.
1539 if ( Threads.sleepWhileIdle
1540 && this != sp->masterThread
1541 && sp->slavesMask.none())
1543 assert(!sp->masterThread->searching);
1544 sp->masterThread->notify_one();
1547 // After releasing the lock we can't access any SplitPoint related data
1548 // in a safe way because it could have been released under our feet by
1549 // the sp master. Also accessing other Thread objects is unsafe because
1550 // if we are exiting there is a chance that they are already freed.
1554 // If this thread is the master of a split point and all slaves have finished
1555 // their work at this split point, return from the idle loop.
1556 if (this_sp && this_sp->slavesMask.none())
1558 this_sp->mutex.lock();
1559 bool finished = this_sp->slavesMask.none(); // Retest under lock protection
1560 this_sp->mutex.unlock();
1568 /// check_time() is called by the timer thread when the timer triggers. It is
1569 /// used to print debug info and, more importantly, to detect when we are out of
1570 /// available time and thus stop the search.
1574 static Time::point lastInfoTime = Time::now();
1575 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1577 if (Time::now() - lastInfoTime >= 1000)
1579 lastInfoTime = Time::now();
1588 Threads.mutex.lock();
1590 nodes = RootPos.nodes_searched();
1592 // Loop across all split points and sum accumulated SplitPoint nodes plus
1593 // all the currently active positions nodes.
1594 for (size_t i = 0; i < Threads.size(); ++i)
1595 for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
1597 SplitPoint& sp = Threads[i]->splitPoints[j];
1603 for (size_t idx = 0; idx < Threads.size(); ++idx)
1604 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1605 nodes += Threads[idx]->activePosition->nodes_searched();
1610 Threads.mutex.unlock();
1613 Time::point elapsed = Time::now() - SearchTime;
1614 bool stillAtFirstMove = Signals.firstRootMove
1615 && !Signals.failedLowAtRoot
1616 && elapsed > TimeMgr.available_time() * 75 / 100;
1618 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
1619 || stillAtFirstMove;
1621 if ( (Limits.use_time_management() && noMoreTime)
1622 || (Limits.movetime && elapsed >= Limits.movetime)
1623 || (Limits.nodes && nodes >= Limits.nodes))
1624 Signals.stop = true;