2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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;
44 Position RootPosition;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // Different node types, used as template parameter
59 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
61 // Lookup table to check if a Piece is a slider and its access function
62 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
63 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
65 // Dynamic razoring margin based on depth
66 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
68 // Futility lookup tables (initialized at startup) and their access functions
69 Value FutilityMargins[16][64]; // [depth][moveNumber]
70 int FutilityMoveCounts[32]; // [depth]
72 inline Value futility_margin(Depth d, int mn) {
74 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
78 inline int futility_move_count(Depth d) {
80 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
83 // Reduction lookup tables (initialized at startup) and their access function
84 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
86 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
88 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
91 // This is the minimum interval in msec between two check_time() calls
92 const int TimerResolution = 5;
95 size_t MultiPV, UCIMultiPV, PVIdx;
99 bool SkillLevelEnabled, Chess960;
103 template <NodeType NT>
104 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
106 template <NodeType NT>
107 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
109 void id_loop(Position& pos);
110 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
111 bool connected_moves(const Position& pos, Move m1, Move m2);
112 Value value_to_tt(Value v, int ply);
113 Value value_from_tt(Value v, int ply);
114 bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);
115 bool connected_threat(const Position& pos, Move m, Move threat);
116 Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
117 Move do_skill_level();
118 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
120 // is_dangerous() checks whether a move belongs to some classes of known
121 // 'dangerous' moves so that we avoid to prune it.
122 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
125 if (type_of(m) == CASTLE)
129 if ( type_of(pos.piece_moved(m)) == PAWN
130 && pos.pawn_is_passed(pos.side_to_move(), to_sq(m)))
133 // Entering a pawn endgame?
134 if ( captureOrPromotion
135 && type_of(pos.piece_on(to_sq(m))) != PAWN
136 && type_of(m) == NORMAL
137 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
138 - PieceValue[Mg][pos.piece_on(to_sq(m))] == VALUE_ZERO))
147 /// Search::init() is called during startup to initialize various lookup tables
149 void Search::init() {
151 int d; // depth (ONE_PLY == 2)
152 int hd; // half depth (ONE_PLY == 1)
155 // Init reductions array
156 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
158 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
159 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
160 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
161 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
164 // Init futility margins array
165 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
166 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
168 // Init futility move count array
169 for (d = 0; d < 32; d++)
170 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
174 /// Search::perft() is our utility to verify move generation. All the leaf nodes
175 /// up to the given depth are generated and counted and the sum returned.
177 size_t Search::perft(Position& pos, Depth depth) {
179 // At the last ply just return the number of legal moves (leaf nodes)
180 if (depth == ONE_PLY)
181 return MoveList<LEGAL>(pos).size();
187 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
189 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
190 cnt += perft(pos, depth - ONE_PLY);
191 pos.undo_move(ml.move());
198 /// Search::think() is the external interface to Stockfish's search, and is
199 /// called by the main thread when the program receives the UCI 'go' command. It
200 /// searches from RootPosition and at the end prints the "bestmove" to output.
202 void Search::think() {
204 static PolyglotBook book; // Defined static to initialize the PRNG only once
206 Position& pos = RootPosition;
207 Chess960 = pos.is_chess960();
208 Eval::RootColor = pos.side_to_move();
209 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
213 if (RootMoves.empty())
215 sync_cout << "info depth 0 score "
216 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
218 RootMoves.push_back(MOVE_NONE);
222 if (Options["OwnBook"] && !Limits.infinite)
224 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
226 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
228 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
233 UCIMultiPV = Options["MultiPV"];
234 SkillLevel = Options["Skill Level"];
236 // Do we have to play with skill handicap? In this case enable MultiPV that
237 // we will use behind the scenes to retrieve a set of possible moves.
238 SkillLevelEnabled = (SkillLevel < 20);
239 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
241 if (Options["Use Search Log"])
243 Log log(Options["Search Log Filename"]);
244 log << "\nSearching: " << pos.to_fen()
245 << "\ninfinite: " << Limits.infinite
246 << " ponder: " << Limits.ponder
247 << " time: " << Limits.time[pos.side_to_move()]
248 << " increment: " << Limits.inc[pos.side_to_move()]
249 << " moves to go: " << Limits.movestogo
255 // Set best timer interval to avoid lagging under time pressure. Timer is
256 // used to check for remaining available thinking time.
257 if (Limits.use_time_management())
258 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
259 else if (Limits.nodes)
260 Threads.set_timer(2 * TimerResolution);
262 Threads.set_timer(100);
264 // We're ready to start searching. Call the iterative deepening loop function
267 Threads.set_timer(0); // Stop timer
270 if (Options["Use Search Log"])
272 Time::point elapsed = Time::now() - SearchTime + 1;
274 Log log(Options["Search Log Filename"]);
275 log << "Nodes: " << pos.nodes_searched()
276 << "\nNodes/second: " << pos.nodes_searched() * 1000 / elapsed
277 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
280 pos.do_move(RootMoves[0].pv[0], st);
281 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << std::endl;
282 pos.undo_move(RootMoves[0].pv[0]);
287 // When we reach max depth we arrive here even without Signals.stop is raised,
288 // but if we are pondering or in infinite search, we shouldn't print the best
289 // move before we are told to do so.
290 if (!Signals.stop && (Limits.ponder || Limits.infinite))
291 pos.this_thread()->wait_for_stop_or_ponderhit();
293 // Best move could be MOVE_NONE when searching on a stalemate position
294 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
295 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << sync_endl;
301 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
302 // with increasing depth until the allocated thinking time has been consumed,
303 // user stops the search, or the maximum search depth is reached.
305 void id_loop(Position& pos) {
307 Stack ss[MAX_PLY_PLUS_2];
308 int depth, prevBestMoveChanges;
309 Value bestValue, alpha, beta, delta;
310 bool bestMoveNeverChanged = true;
311 Move skillBest = MOVE_NONE;
313 memset(ss, 0, 4 * sizeof(Stack));
314 depth = BestMoveChanges = 0;
315 bestValue = delta = -VALUE_INFINITE;
316 ss->currentMove = MOVE_NULL; // Hack to skip update gains
318 // Iterative deepening loop until requested to stop or target depth reached
319 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
321 // Save last iteration's scores before first PV line is searched and all
322 // the move scores but the (new) PV are set to -VALUE_INFINITE.
323 for (size_t i = 0; i < RootMoves.size(); i++)
324 RootMoves[i].prevScore = RootMoves[i].score;
326 prevBestMoveChanges = BestMoveChanges;
329 // MultiPV loop. We perform a full root search for each PV line
330 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
332 // Set aspiration window default width
333 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
336 alpha = RootMoves[PVIdx].prevScore - delta;
337 beta = RootMoves[PVIdx].prevScore + delta;
341 alpha = -VALUE_INFINITE;
342 beta = VALUE_INFINITE;
345 // Start with a small aspiration window and, in case of fail high/low,
346 // research with bigger window until not failing high/low anymore.
349 // Search starts from ss+1 to allow referencing (ss-1). This is
350 // needed by update gains and ss copy when splitting at Root.
351 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
353 // Bring to front the best move. It is critical that sorting is
354 // done with a stable algorithm because all the values but the first
355 // and eventually the new best one are set to -VALUE_INFINITE and
356 // we want to keep the same order for all the moves but the new
357 // PV that goes to the front. Note that in case of MultiPV search
358 // the already searched PV lines are preserved.
359 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
361 // In case we have found an exact score and we are going to leave
362 // the fail high/low loop then reorder the PV moves, otherwise
363 // leave the last PV move in its position so to be searched again.
364 // Of course this is needed only in MultiPV search.
365 if (PVIdx && bestValue > alpha && bestValue < beta)
366 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
368 // Write PV back to transposition table in case the relevant
369 // entries have been overwritten during the search.
370 for (size_t i = 0; i <= PVIdx; i++)
371 RootMoves[i].insert_pv_in_tt(pos);
373 // If search has been stopped exit the aspiration window loop.
374 // Sorting and writing PV back to TT is safe becuase RootMoves
375 // is still valid, although refers to previous iteration.
379 // Send full PV info to GUI if we are going to leave the loop or
380 // if we have a fail high/low and we are deep in the search.
381 if ((bestValue > alpha && bestValue < beta) || Time::now() - SearchTime > 2000)
382 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
384 // In case of failing high/low increase aspiration window and
385 // research, otherwise exit the fail high/low loop.
386 if (bestValue >= beta)
391 else if (bestValue <= alpha)
393 Signals.failedLowAtRoot = true;
394 Signals.stopOnPonderhit = false;
402 // Search with full window in case we have a win/mate score
403 if (abs(bestValue) >= VALUE_KNOWN_WIN)
405 alpha = -VALUE_INFINITE;
406 beta = VALUE_INFINITE;
409 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
413 // Skills: Do we need to pick now the best move ?
414 if (SkillLevelEnabled && depth == 1 + SkillLevel)
415 skillBest = do_skill_level();
417 if (!Signals.stop && Options["Use Search Log"])
419 Log log(Options["Search Log Filename"]);
420 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
424 // Filter out startup noise when monitoring best move stability
425 if (depth > 2 && BestMoveChanges)
426 bestMoveNeverChanged = false;
428 // Do we have time for the next iteration? Can we stop searching now?
429 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
431 bool stop = false; // Local variable, not the volatile Signals.stop
433 // Take in account some extra time if the best move has changed
434 if (depth > 4 && depth < 50)
435 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
437 // Stop search if most of available time is already consumed. We
438 // probably don't have enough time to search the first move at the
439 // next iteration anyway.
440 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
443 // Stop search early if one move seems to be much better than others
446 && ( (bestMoveNeverChanged && pos.captured_piece_type())
447 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
449 Value rBeta = bestValue - 2 * PawnValueMg;
450 (ss+1)->excludedMove = RootMoves[0].pv[0];
451 (ss+1)->skipNullMove = true;
452 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
453 (ss+1)->skipNullMove = false;
454 (ss+1)->excludedMove = MOVE_NONE;
462 // If we are allowed to ponder do not stop the search now but
463 // keep pondering until GUI sends "ponderhit" or "stop".
465 Signals.stopOnPonderhit = true;
472 // When using skills swap best PV line with the sub-optimal one
473 if (SkillLevelEnabled)
475 if (skillBest == MOVE_NONE) // Still unassigned ?
476 skillBest = do_skill_level();
478 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
483 // search<>() is the main search function for both PV and non-PV nodes and for
484 // normal and SplitPoint nodes. When called just after a split point the search
485 // is simpler because we have already probed the hash table, done a null move
486 // search, and searched the first move before splitting, we don't have to repeat
487 // all this work again. We also don't need to store anything to the hash table
488 // here: This is taken care of after we return from the split point.
490 template <NodeType NT>
491 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
493 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
494 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
495 const bool RootNode = (NT == Root || NT == SplitPointRoot);
497 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
498 assert(PvNode || (alpha == beta - 1));
499 assert(depth > DEPTH_ZERO);
501 Move movesSearched[64];
506 Move ttMove, move, excludedMove, bestMove, threatMove;
508 Value bestValue, value, oldAlpha, ttValue;
509 Value refinedValue, nullValue, futilityValue;
510 bool pvMove, inCheck, singularExtensionNode, givesCheck;
511 bool captureOrPromotion, dangerous, doFullDepthSearch;
512 int moveCount, playedMoveCount;
514 // Step 1. Initialize node
515 Thread* thisThread = pos.this_thread();
516 moveCount = playedMoveCount = 0;
518 inCheck = pos.in_check();
523 bestMove = sp->bestMove;
524 threatMove = sp->threatMove;
525 bestValue = sp->bestValue;
527 ttMove = excludedMove = MOVE_NONE;
528 ttValue = VALUE_NONE;
530 assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);
532 goto split_point_start;
535 bestValue = -VALUE_INFINITE;
536 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
537 ss->ply = (ss-1)->ply + 1;
538 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
539 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
541 // Used to send selDepth info to GUI
542 if (PvNode && thisThread->maxPly < ss->ply)
543 thisThread->maxPly = ss->ply;
547 // Step 2. Check for aborted search and immediate draw
548 if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
549 return Eval::ValueDrawContempt;
551 // Step 3. Mate distance pruning. Even if we mate at the next move our score
552 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
553 // a shorter mate was found upward in the tree then there is no need to search
554 // further, we will never beat current alpha. Same logic but with reversed signs
555 // applies also in the opposite condition of being mated instead of giving mate,
556 // in this case return a fail-high score.
557 alpha = std::max(mated_in(ss->ply), alpha);
558 beta = std::min(mate_in(ss->ply+1), beta);
563 // Step 4. Transposition table lookup
564 // We don't want the score of a partial search to overwrite a previous full search
565 // TT value, so we use a different position key in case of an excluded move.
566 excludedMove = ss->excludedMove;
567 posKey = excludedMove ? pos.exclusion_key() : pos.key();
568 tte = TT.probe(posKey);
569 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
570 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
572 // At PV nodes we check for exact scores, while at non-PV nodes we check for
573 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
574 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
575 // we should also update RootMoveList to avoid bogus output.
576 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
577 : can_return_tt(tte, depth, ttValue, beta)))
580 ss->currentMove = ttMove; // Can be MOVE_NONE
584 && !pos.is_capture_or_promotion(ttMove)
585 && ttMove != ss->killers[0])
587 ss->killers[1] = ss->killers[0];
588 ss->killers[0] = ttMove;
593 // Step 5. Evaluate the position statically and update parent's gain statistics
595 ss->eval = ss->evalMargin = refinedValue = VALUE_NONE;
598 assert(tte->static_value() != VALUE_NONE);
600 ss->eval = tte->static_value();
601 ss->evalMargin = tte->static_value_margin();
602 refinedValue = refine_eval(tte, ttValue, ss->eval);
606 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
607 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
610 // Update gain for the parent non-capture move given the static position
611 // evaluation before and after the move.
612 if ( (move = (ss-1)->currentMove) != MOVE_NULL
613 && (ss-1)->eval != VALUE_NONE
614 && ss->eval != VALUE_NONE
615 && !pos.captured_piece_type()
616 && type_of(move) == NORMAL)
618 Square to = to_sq(move);
619 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
622 // Step 6. Razoring (is omitted in PV nodes)
624 && depth < 4 * ONE_PLY
626 && refinedValue + razor_margin(depth) < beta
627 && ttMove == MOVE_NONE
628 && abs(beta) < VALUE_MATE_IN_MAX_PLY
629 && !pos.pawn_on_7th(pos.side_to_move()))
631 Value rbeta = beta - razor_margin(depth);
632 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
634 // Logically we should return (v + razor_margin(depth)), but
635 // surprisingly this did slightly weaker in tests.
639 // Step 7. Static null move pruning (is omitted in PV nodes)
640 // We're betting that the opponent doesn't have a move that will reduce
641 // the score by more than futility_margin(depth) if we do a null move.
644 && depth < 4 * ONE_PLY
646 && refinedValue - futility_margin(depth, 0) >= beta
647 && abs(beta) < VALUE_MATE_IN_MAX_PLY
648 && pos.non_pawn_material(pos.side_to_move()))
649 return refinedValue - futility_margin(depth, 0);
651 // Step 8. Null move search with verification search (is omitted in PV nodes)
656 && refinedValue >= beta
657 && abs(beta) < VALUE_MATE_IN_MAX_PLY
658 && pos.non_pawn_material(pos.side_to_move()))
660 ss->currentMove = MOVE_NULL;
662 // Null move dynamic reduction based on depth
663 Depth R = 3 * ONE_PLY + depth / 4;
665 // Null move dynamic reduction based on value
666 if (refinedValue - PawnValueMg > beta)
669 pos.do_null_move<true>(st);
670 (ss+1)->skipNullMove = true;
671 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
672 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
673 (ss+1)->skipNullMove = false;
674 pos.do_null_move<false>(st);
676 if (nullValue >= beta)
678 // Do not return unproven mate scores
679 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
682 if (depth < 6 * ONE_PLY)
685 // Do verification search at high depths
686 ss->skipNullMove = true;
687 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
688 ss->skipNullMove = false;
695 // The null move failed low, which means that we may be faced with
696 // some kind of threat. If the previous move was reduced, check if
697 // the move that refuted the null move was somehow connected to the
698 // move which was reduced. If a connection is found, return a fail
699 // low score (which will cause the reduced move to fail high in the
700 // parent node, which will trigger a re-search with full depth).
701 threatMove = (ss+1)->currentMove;
703 if ( depth < 5 * ONE_PLY
705 && threatMove != MOVE_NONE
706 && connected_moves(pos, (ss-1)->currentMove, threatMove))
711 // Step 9. ProbCut (is omitted in PV nodes)
712 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
713 // and a reduced search returns a value much above beta, we can (almost) safely
714 // prune the previous move.
716 && depth >= 5 * ONE_PLY
719 && excludedMove == MOVE_NONE
720 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
722 Value rbeta = beta + 200;
723 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
725 assert(rdepth >= ONE_PLY);
726 assert((ss-1)->currentMove != MOVE_NONE);
727 assert((ss-1)->currentMove != MOVE_NULL);
729 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
732 while ((move = mp.next_move<false>()) != MOVE_NONE)
733 if (pos.pl_move_is_legal(move, ci.pinned))
735 ss->currentMove = move;
736 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
737 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
744 // Step 10. Internal iterative deepening
745 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
746 && ttMove == MOVE_NONE
747 && (PvNode || (!inCheck && ss->eval + Value(256) >= beta)))
749 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
751 ss->skipNullMove = true;
752 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
753 ss->skipNullMove = false;
755 tte = TT.probe(posKey);
756 ttMove = tte ? tte->move() : MOVE_NONE;
759 split_point_start: // At split points actual search starts from here
761 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
763 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
764 singularExtensionNode = !RootNode
766 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
767 && ttMove != MOVE_NONE
768 && !excludedMove // Recursive singular search is not allowed
769 && (tte->type() & BOUND_LOWER)
770 && tte->depth() >= depth - 3 * ONE_PLY;
772 // Step 11. Loop through moves
773 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
774 while ( bestValue < beta
775 && (move = mp.next_move<SpNode>()) != MOVE_NONE
776 && !thisThread->cutoff_occurred()
781 if (move == excludedMove)
784 // At root obey the "searchmoves" option and skip moves not listed in Root
785 // Move List, as a consequence any illegal move is also skipped. In MultiPV
786 // mode we also skip PV moves which have been already searched.
787 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
792 // Shared counter cannot be decremented later if move turns out to be illegal
793 if (!pos.pl_move_is_legal(move, ci.pinned))
796 moveCount = ++sp->moveCount;
804 Signals.firstRootMove = (moveCount == 1);
806 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
807 sync_cout << "info depth " << depth / ONE_PLY
808 << " currmove " << move_to_uci(move, Chess960)
809 << " currmovenumber " << moveCount + PVIdx << sync_endl;
812 captureOrPromotion = pos.is_capture_or_promotion(move);
813 givesCheck = pos.move_gives_check(move, ci);
814 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
817 // Step 12. Extend checks and, in PV nodes, also dangerous moves
818 if (PvNode && dangerous)
821 else if (givesCheck && pos.see_sign(move) >= 0)
824 // Singular extension search. If all moves but one fail low on a search of
825 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
826 // is singular and should be extended. To verify this we do a reduced search
827 // on all the other moves but the ttMove, if result is lower than ttValue minus
828 // a margin then we extend ttMove.
829 if ( singularExtensionNode
832 && pos.pl_move_is_legal(move, ci.pinned)
833 && abs(ttValue) < VALUE_KNOWN_WIN)
835 Value rBeta = ttValue - int(depth);
836 ss->excludedMove = move;
837 ss->skipNullMove = true;
838 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
839 ss->skipNullMove = false;
840 ss->excludedMove = MOVE_NONE;
843 ext = rBeta >= beta ? ONE_PLY + ONE_PLY / 2 : ONE_PLY;
846 // Update current move (this must be done after singular extension search)
847 newDepth = depth - ONE_PLY + ext;
849 // Step 13. Futility pruning (is omitted in PV nodes)
851 && !captureOrPromotion
855 && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
857 // Move count based pruning
858 if ( moveCount >= futility_move_count(depth)
859 && (!threatMove || !connected_threat(pos, move, threatMove)))
867 // Value based pruning
868 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
869 // but fixing this made program slightly weaker.
870 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
871 futilityValue = ss->eval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
872 + H.gain(pos.piece_moved(move), to_sq(move));
874 if (futilityValue < beta)
882 // Prune moves with negative SEE at low depths
883 if ( predictedDepth < 2 * ONE_PLY
884 && pos.see_sign(move) < 0)
893 // Check for legality only before to do the move
894 if (!pos.pl_move_is_legal(move, ci.pinned))
900 pvMove = PvNode ? moveCount == 1 : false;
901 ss->currentMove = move;
902 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
903 movesSearched[playedMoveCount++] = move;
905 // Step 14. Make the move
906 pos.do_move(move, st, ci, givesCheck);
908 // Step 15. Reduced depth search (LMR). If the move fails high will be
909 // re-searched at full depth.
910 if ( depth > 3 * ONE_PLY
912 && !captureOrPromotion
914 && ss->killers[0] != move
915 && ss->killers[1] != move)
917 ss->reduction = reduction<PvNode>(depth, moveCount);
918 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
919 alpha = SpNode ? sp->alpha : alpha;
921 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
923 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
924 ss->reduction = DEPTH_ZERO;
927 doFullDepthSearch = !pvMove;
929 // Step 16. Full depth search, when LMR is skipped or fails high
930 if (doFullDepthSearch)
932 alpha = SpNode ? sp->alpha : alpha;
933 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
934 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
937 // Only for PV nodes do a full PV search on the first move or after a fail
938 // high, in the latter case search only if value < beta, otherwise let the
939 // parent node to fail low with value <= alpha and to try another move.
940 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
941 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
942 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
944 // Step 17. Undo move
947 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
949 // Step 18. Check for new best move
953 bestValue = sp->bestValue;
957 // Finished searching the move. If Signals.stop is true, the search
958 // was aborted because the user interrupted the search or because we
959 // ran out of time. In this case, the return value of the search cannot
960 // be trusted, and we don't update the best move and/or PV.
961 if (RootNode && !Signals.stop)
963 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
965 // PV move or new best move ?
966 if (pvMove || value > alpha)
969 rm.extract_pv_from_tt(pos);
971 // We record how often the best move has been changed in each
972 // iteration. This information is used for time management: When
973 // the best move changes frequently, we allocate some more time.
974 if (!pvMove && MultiPV == 1)
978 // All other moves but the PV are set to the lowest value, this
979 // is not a problem when sorting becuase sort is stable and move
980 // position in the list is preserved, just the PV is pushed up.
981 rm.score = -VALUE_INFINITE;
984 if (value > bestValue)
991 && value < beta) // We want always alpha < beta
993 alpha = bestValue; // Update alpha here!
996 if (SpNode && !thisThread->cutoff_occurred())
998 sp->bestValue = bestValue;
999 sp->bestMove = bestMove;
1002 if (bestValue >= beta)
1007 // Step 19. Check for split
1009 && depth >= Threads.min_split_depth()
1011 && Threads.available_slave_exists(thisThread)
1013 && !thisThread->cutoff_occurred())
1014 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1015 depth, threatMove, moveCount, mp, NT);
1018 // Step 20. Check for mate and stalemate
1019 // All legal moves have been searched and if there are no legal moves, it
1020 // must be mate or stalemate. Note that we can have a false positive in
1021 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1022 // harmless because return value is discarded anyhow in the parent nodes.
1023 // If we are in a singular extension search then return a fail low score.
1024 // A split node has at least one move, the one tried before to be splitted.
1025 if (!SpNode && !moveCount)
1026 return excludedMove ? alpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1028 // If we have pruned all the moves without searching return a fail-low score
1029 if (bestValue == -VALUE_INFINITE)
1031 assert(!playedMoveCount);
1036 // Step 21. Update tables
1037 // Update transposition table entry, killers and history
1038 if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
1040 Move ttm = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1041 Bound bt = bestValue <= oldAlpha ? BOUND_UPPER
1042 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1044 TT.store(posKey, value_to_tt(bestValue, ss->ply), bt, depth, ttm, ss->eval, ss->evalMargin);
1046 // Update killers and history for non capture cut-off moves
1047 if ( bestValue >= beta
1048 && !pos.is_capture_or_promotion(bestMove)
1051 if (bestMove != ss->killers[0])
1053 ss->killers[1] = ss->killers[0];
1054 ss->killers[0] = bestMove;
1057 // Increase history value of the cut-off move
1058 Value bonus = Value(int(depth) * int(depth));
1059 H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1061 // Decrease history of all the other played non-capture moves
1062 for (int i = 0; i < playedMoveCount - 1; i++)
1064 Move m = movesSearched[i];
1065 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1070 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1076 // qsearch() is the quiescence search function, which is called by the main
1077 // search function when the remaining depth is zero (or, to be more precise,
1078 // less than ONE_PLY).
1080 template <NodeType NT>
1081 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1083 const bool PvNode = (NT == PV);
1085 assert(NT == PV || NT == NonPV);
1086 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1087 assert((alpha == beta - 1) || PvNode);
1088 assert(depth <= DEPTH_ZERO);
1091 Move ttMove, move, bestMove;
1092 Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
1093 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1097 Value oldAlpha = alpha;
1099 ss->currentMove = bestMove = MOVE_NONE;
1100 ss->ply = (ss-1)->ply + 1;
1102 // Check for an instant draw or maximum ply reached
1103 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1104 return Eval::ValueDrawContempt;
1106 // Decide whether or not to include checks, this fixes also the type of
1107 // TT entry depth that we are going to use. Note that in qsearch we use
1108 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1109 inCheck = pos.in_check();
1110 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1112 // Transposition table lookup. At PV nodes, we don't use the TT for
1113 // pruning, but only for move ordering.
1114 tte = TT.probe(pos.key());
1115 ttMove = (tte ? tte->move() : MOVE_NONE);
1116 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
1118 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1120 ss->currentMove = ttMove; // Can be MOVE_NONE
1124 // Evaluate the position statically
1127 bestValue = futilityBase = -VALUE_INFINITE;
1128 ss->eval = evalMargin = VALUE_NONE;
1129 enoughMaterial = false;
1135 assert(tte->static_value() != VALUE_NONE);
1137 evalMargin = tte->static_value_margin();
1138 ss->eval = bestValue = tte->static_value();
1141 ss->eval = bestValue = evaluate(pos, evalMargin);
1143 // Stand pat. Return immediately if static value is at least beta
1144 if (bestValue >= beta)
1147 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1152 if (PvNode && bestValue > alpha)
1155 futilityBase = ss->eval + evalMargin + Value(128);
1156 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1159 // Initialize a MovePicker object for the current position, and prepare
1160 // to search the moves. Because the depth is <= 0 here, only captures,
1161 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1163 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1166 // Loop through the moves until no moves remain or a beta cutoff occurs
1167 while ( bestValue < beta
1168 && (move = mp.next_move<false>()) != MOVE_NONE)
1170 assert(is_ok(move));
1172 givesCheck = pos.move_gives_check(move, ci);
1180 && type_of(move) != PROMOTION
1181 && !pos.is_passed_pawn_push(move))
1183 futilityValue = futilityBase
1184 + PieceValue[Eg][pos.piece_on(to_sq(move))]
1185 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1187 if (futilityValue < beta)
1189 if (futilityValue > bestValue)
1190 bestValue = futilityValue;
1195 // Prune moves with negative or equal SEE
1196 if ( futilityBase < beta
1197 && depth < DEPTH_ZERO
1198 && pos.see(move) <= 0)
1202 // Detect non-capture evasions that are candidate to be pruned
1203 evasionPrunable = !PvNode
1205 && bestValue > VALUE_MATED_IN_MAX_PLY
1206 && !pos.is_capture(move)
1207 && !pos.can_castle(pos.side_to_move());
1209 // Don't search moves with negative SEE values
1211 && (!inCheck || evasionPrunable)
1213 && type_of(move) != PROMOTION
1214 && pos.see_sign(move) < 0)
1217 // Don't search useless checks
1222 && !pos.is_capture_or_promotion(move)
1223 && ss->eval + PawnValueMg / 4 < beta
1224 && !check_is_dangerous(pos, move, futilityBase, beta))
1227 // Check for legality only before to do the move
1228 if (!pos.pl_move_is_legal(move, ci.pinned))
1231 ss->currentMove = move;
1233 // Make and search the move
1234 pos.do_move(move, st, ci, givesCheck);
1235 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1236 pos.undo_move(move);
1238 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1241 if (value > bestValue)
1248 && value < beta) // We want always alpha < beta
1253 // All legal moves have been searched. A special case: If we're in check
1254 // and no legal moves were found, it is checkmate.
1255 if (inCheck && bestValue == -VALUE_INFINITE)
1256 return mated_in(ss->ply); // Plies to mate from the root
1258 // Update transposition table
1259 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1260 bt = bestValue <= oldAlpha ? BOUND_UPPER
1261 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1263 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
1265 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1271 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1272 // bestValue is updated only when returning false because in that case move
1275 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1277 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1278 Square from, to, ksq;
1282 from = from_sq(move);
1284 them = ~pos.side_to_move();
1285 ksq = pos.king_square(them);
1286 kingAtt = pos.attacks_from<KING>(ksq);
1287 pc = pos.piece_moved(move);
1289 occ = pos.pieces() ^ from ^ ksq;
1290 oldAtt = pos.attacks_from(pc, from, occ);
1291 newAtt = pos.attacks_from(pc, to, occ);
1293 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1294 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1296 if (!more_than_one(b))
1299 // Rule 2. Queen contact check is very dangerous
1300 if (type_of(pc) == QUEEN && (kingAtt & to))
1303 // Rule 3. Creating new double threats with checks
1304 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1307 // Note that here we generate illegal "double move"!
1308 if (futilityBase + PieceValue[Eg][pos.piece_on(pop_lsb(&b))] >= beta)
1316 // connected_moves() tests whether two moves are 'connected' in the sense
1317 // that the first move somehow made the second move possible (for instance
1318 // if the moving piece is the same in both moves). The first move is assumed
1319 // to be the move that was made to reach the current position, while the
1320 // second move is assumed to be a move from the current position.
1322 bool connected_moves(const Position& pos, Move m1, Move m2) {
1324 Square f1, t1, f2, t2;
1331 // Case 1: The moving piece is the same in both moves
1337 // Case 2: The destination square for m2 was vacated by m1
1343 // Case 3: Moving through the vacated square
1344 p2 = pos.piece_on(f2);
1345 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1348 // Case 4: The destination square for m2 is defended by the moving piece in m1
1349 p1 = pos.piece_on(t1);
1350 if (pos.attacks_from(p1, t1) & t2)
1353 // Case 5: Discovered check, checking piece is the piece moved in m1
1354 ksq = pos.king_square(pos.side_to_move());
1355 if ( piece_is_slider(p1)
1356 && (between_bb(t1, ksq) & f2)
1357 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1364 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1365 // "plies to mate from the current position". Non-mate scores are unchanged.
1366 // The function is called before storing a value to the transposition table.
1368 Value value_to_tt(Value v, int ply) {
1370 if (v >= VALUE_MATE_IN_MAX_PLY)
1373 if (v <= VALUE_MATED_IN_MAX_PLY)
1380 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1381 // from the transposition table (where refers to the plies to mate/be mated
1382 // from current position) to "plies to mate/be mated from the root".
1384 Value value_from_tt(Value v, int ply) {
1386 if (v >= VALUE_MATE_IN_MAX_PLY)
1389 if (v <= VALUE_MATED_IN_MAX_PLY)
1396 // connected_threat() tests whether it is safe to forward prune a move or if
1397 // is somehow connected to the threat move returned by null search.
1399 bool connected_threat(const Position& pos, Move m, Move threat) {
1402 assert(is_ok(threat));
1403 assert(!pos.is_capture_or_promotion(m));
1404 assert(!pos.is_passed_pawn_push(m));
1406 Square mfrom, mto, tfrom, tto;
1410 tfrom = from_sq(threat);
1411 tto = to_sq(threat);
1413 // Case 1: Don't prune moves which move the threatened piece
1417 // Case 2: If the threatened piece has value less than or equal to the
1418 // value of the threatening piece, don't prune moves which defend it.
1419 if ( pos.is_capture(threat)
1420 && ( PieceValue[Mg][pos.piece_on(tfrom)] >= PieceValue[Mg][pos.piece_on(tto)]
1421 || type_of(pos.piece_on(tfrom)) == KING)
1422 && pos.move_attacks_square(m, tto))
1425 // Case 3: If the moving piece in the threatened move is a slider, don't
1426 // prune safe moves which block its ray.
1427 if ( piece_is_slider(pos.piece_on(tfrom))
1428 && (between_bb(tfrom, tto) & mto)
1429 && pos.see_sign(m) >= 0)
1436 // can_return_tt() returns true if a transposition table score can be used to
1437 // cut-off at a given point in search.
1439 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1441 return ( tte->depth() >= depth
1442 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1443 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1445 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1446 || ((tte->type() & BOUND_UPPER) && v < beta));
1450 // refine_eval() returns the transposition table score if possible, otherwise
1451 // falls back on static position evaluation.
1453 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1457 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1458 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1465 // When playing with strength handicap choose best move among the MultiPV set
1466 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1468 Move do_skill_level() {
1470 assert(MultiPV > 1);
1474 // PRNG sequence should be not deterministic
1475 for (int i = Time::now() % 50; i > 0; i--)
1476 rk.rand<unsigned>();
1478 // RootMoves are already sorted by score in descending order
1479 size_t size = std::min(MultiPV, RootMoves.size());
1480 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1481 int weakness = 120 - 2 * SkillLevel;
1482 int max_s = -VALUE_INFINITE;
1483 Move best = MOVE_NONE;
1485 // Choose best move. For each move score we add two terms both dependent on
1486 // weakness, one deterministic and bigger for weaker moves, and one random,
1487 // then we choose the move with the resulting highest score.
1488 for (size_t i = 0; i < size; i++)
1490 int s = RootMoves[i].score;
1492 // Don't allow crazy blunders even at very low skills
1493 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1496 // This is our magic formula
1497 s += ( weakness * int(RootMoves[0].score - s)
1498 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1503 best = RootMoves[i].pv[0];
1510 // uci_pv() formats PV information according to UCI protocol. UCI requires
1511 // to send all the PV lines also if are still to be searched and so refer to
1512 // the previous search score.
1514 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1516 std::stringstream s;
1517 Time::point elaspsed = Time::now() - SearchTime + 1;
1520 for (size_t i = 0; i < Threads.size(); i++)
1521 if (Threads[i].maxPly > selDepth)
1522 selDepth = Threads[i].maxPly;
1524 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1526 bool updated = (i <= PVIdx);
1528 if (depth == 1 && !updated)
1531 int d = (updated ? depth : depth - 1);
1532 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1534 if (s.rdbuf()->in_avail())
1537 s << "info depth " << d
1538 << " seldepth " << selDepth
1539 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1540 << " nodes " << pos.nodes_searched()
1541 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1542 << " time " << elaspsed
1543 << " multipv " << i + 1
1546 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1547 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1556 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1557 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1558 /// allow to always have a ponder move even when we fail high at root, and a
1559 /// long PV to print that is important for position analysis.
1561 void RootMove::extract_pv_from_tt(Position& pos) {
1563 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1568 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1572 pos.do_move(m, *st++);
1574 while ( (tte = TT.probe(pos.key())) != NULL
1575 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1576 && pos.is_pseudo_legal(m)
1577 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1579 && (!pos.is_draw<false>() || ply < 2))
1582 pos.do_move(m, *st++);
1585 pv.push_back(MOVE_NONE);
1587 do pos.undo_move(pv[--ply]); while (ply);
1591 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1592 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1593 /// first, even if the old TT entries have been overwritten.
1595 void RootMove::insert_pv_in_tt(Position& pos) {
1597 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1600 Value v, m = VALUE_NONE;
1603 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1609 // Don't overwrite existing correct entries
1610 if (!tte || tte->move() != pv[ply])
1612 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1613 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1615 pos.do_move(pv[ply], *st++);
1617 } while (pv[++ply] != MOVE_NONE);
1619 do pos.undo_move(pv[--ply]); while (ply);
1623 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1625 void Thread::idle_loop() {
1627 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1628 // object for which the thread is the master.
1629 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1631 assert(!sp_master || (sp_master->master == this && is_searching));
1633 // If this thread is the master of a split point and all slaves have
1634 // finished their work at this split point, return from the idle loop.
1635 while (!sp_master || sp_master->slavesMask)
1637 // If we are not searching, wait for a condition to be signaled
1638 // instead of wasting CPU time polling for work.
1641 || (!is_searching && Threads.use_sleeping_threads()))
1649 // Grab the lock to avoid races with Thread::wake_up()
1652 // If we are master and all slaves have finished don't go to sleep
1653 if (sp_master && !sp_master->slavesMask)
1659 // Do sleep after retesting sleep conditions under lock protection, in
1660 // particular we need to avoid a deadlock in case a master thread has,
1661 // in the meanwhile, allocated us and sent the wake_up() call before we
1662 // had the chance to grab the lock.
1663 if (do_sleep || !is_searching)
1664 sleepCondition.wait(mutex);
1669 // If this thread has been assigned work, launch a search
1672 assert(!do_sleep && !do_exit);
1674 Threads.mutex.lock();
1676 assert(is_searching);
1677 SplitPoint* sp = curSplitPoint;
1679 Threads.mutex.unlock();
1681 Stack ss[MAX_PLY_PLUS_2];
1682 Position pos(*sp->pos, this);
1684 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1689 assert(sp->activePositions[idx] == NULL);
1691 sp->activePositions[idx] = &pos;
1693 if (sp->nodeType == Root)
1694 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1695 else if (sp->nodeType == PV)
1696 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1697 else if (sp->nodeType == NonPV)
1698 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1702 assert(is_searching);
1704 is_searching = false;
1705 sp->activePositions[idx] = NULL;
1706 sp->slavesMask &= ~(1ULL << idx);
1707 sp->nodes += pos.nodes_searched();
1709 // Wake up master thread so to allow it to return from the idle loop in
1710 // case we are the last slave of the split point.
1711 if ( Threads.use_sleeping_threads()
1712 && this != sp->master
1715 assert(!sp->master->is_searching);
1716 sp->master->wake_up();
1719 // After releasing the lock we cannot access anymore any SplitPoint
1720 // related data in a safe way becuase it could have been released under
1721 // our feet by the sp master. Also accessing other Thread objects is
1722 // unsafe because if we are exiting there is a chance are already freed.
1729 /// check_time() is called by the timer thread when the timer triggers. It is
1730 /// used to print debug info and, more important, to detect when we are out of
1731 /// available time and so stop the search.
1735 static Time::point lastInfoTime = Time::now();
1736 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1738 if (Time::now() - lastInfoTime >= 1000)
1740 lastInfoTime = Time::now();
1749 Threads.mutex.lock();
1751 nodes = RootPosition.nodes_searched();
1753 // Loop across all split points and sum accumulated SplitPoint nodes plus
1754 // all the currently active slaves positions.
1755 for (size_t i = 0; i < Threads.size(); i++)
1756 for (int j = 0; j < Threads[i].splitPointsCnt; j++)
1758 SplitPoint& sp = Threads[i].splitPoints[j];
1763 Bitboard sm = sp.slavesMask;
1766 Position* pos = sp.activePositions[pop_lsb(&sm)];
1767 nodes += pos ? pos->nodes_searched() : 0;
1773 Threads.mutex.unlock();
1776 Time::point elapsed = Time::now() - SearchTime;
1777 bool stillAtFirstMove = Signals.firstRootMove
1778 && !Signals.failedLowAtRoot
1779 && elapsed > TimeMgr.available_time();
1781 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1782 || stillAtFirstMove;
1784 if ( (Limits.use_time_management() && noMoreTime)
1785 || (Limits.movetime && elapsed >= Limits.movetime)
1786 || (Limits.nodes && nodes >= Limits.nodes))
1787 Signals.stop = true;