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 // Maximum depth for razoring
66 const Depth RazorDepth = 4 * ONE_PLY;
68 // Dynamic razoring margin based on depth
69 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
71 // Maximum depth for use of dynamic threat detection when null move fails low
72 const Depth ThreatDepth = 5 * ONE_PLY;
74 // Minimum depth for use of internal iterative deepening
75 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
77 // At Non-PV nodes we do an internal iterative deepening search
78 // when the static evaluation is bigger then beta - IIDMargin.
79 const Value IIDMargin = Value(256);
81 // Minimum depth for use of singular extension
82 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
84 // Futility margin for quiescence search
85 const Value FutilityMarginQS = Value(128);
87 // Futility lookup tables (initialized at startup) and their access functions
88 Value FutilityMargins[16][64]; // [depth][moveNumber]
89 int FutilityMoveCounts[32]; // [depth]
91 inline Value futility_margin(Depth d, int mn) {
93 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
97 inline int futility_move_count(Depth d) {
99 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
102 // Reduction lookup tables (initialized at startup) and their access function
103 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
105 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
107 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
110 // Easy move margin. An easy move candidate must be at least this much better
111 // than the second best move.
112 const Value EasyMoveMargin = Value(0x150);
114 // This is the minimum interval in msec between two check_time() calls
115 const int TimerResolution = 5;
118 size_t MultiPV, UCIMultiPV, PVIdx;
122 bool SkillLevelEnabled, Chess960;
126 template <NodeType NT>
127 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
129 template <NodeType NT>
130 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
132 void id_loop(Position& pos);
133 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
134 bool connected_moves(const Position& pos, Move m1, Move m2);
135 Value value_to_tt(Value v, int ply);
136 Value value_from_tt(Value v, int ply);
137 bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);
138 bool connected_threat(const Position& pos, Move m, Move threat);
139 Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
140 Move do_skill_level();
141 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
143 // is_dangerous() checks whether a move belongs to some classes of known
144 // 'dangerous' moves so that we avoid to prune it.
145 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
148 if (type_of(m) == CASTLE)
152 if ( type_of(pos.piece_moved(m)) == PAWN
153 && pos.pawn_is_passed(pos.side_to_move(), to_sq(m)))
156 // Entering a pawn endgame?
157 if ( captureOrPromotion
158 && type_of(pos.piece_on(to_sq(m))) != PAWN
159 && type_of(m) == NORMAL
160 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
161 - PieceValue[Mg][pos.piece_on(to_sq(m))] == VALUE_ZERO))
170 /// Search::init() is called during startup to initialize various lookup tables
172 void Search::init() {
174 int d; // depth (ONE_PLY == 2)
175 int hd; // half depth (ONE_PLY == 1)
178 // Init reductions array
179 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
181 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
182 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
183 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
184 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
187 // Init futility margins array
188 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
189 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
191 // Init futility move count array
192 for (d = 0; d < 32; d++)
193 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
197 /// Search::perft() is our utility to verify move generation. All the leaf nodes
198 /// up to the given depth are generated and counted and the sum returned.
200 size_t Search::perft(Position& pos, Depth depth) {
202 // At the last ply just return the number of legal moves (leaf nodes)
203 if (depth == ONE_PLY)
204 return MoveList<LEGAL>(pos).size();
210 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
212 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
213 cnt += perft(pos, depth - ONE_PLY);
214 pos.undo_move(ml.move());
221 /// Search::think() is the external interface to Stockfish's search, and is
222 /// called by the main thread when the program receives the UCI 'go' command. It
223 /// searches from RootPosition and at the end prints the "bestmove" to output.
225 void Search::think() {
227 static PolyglotBook book; // Defined static to initialize the PRNG only once
229 Position& pos = RootPosition;
230 Chess960 = pos.is_chess960();
231 Eval::RootColor = pos.side_to_move();
232 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
236 if (RootMoves.empty())
238 sync_cout << "info depth 0 score "
239 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << sync_endl;
241 RootMoves.push_back(MOVE_NONE);
245 if (Options["OwnBook"] && !Limits.infinite)
247 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
249 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
251 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
256 UCIMultiPV = Options["MultiPV"];
257 SkillLevel = Options["Skill Level"];
259 // Do we have to play with skill handicap? In this case enable MultiPV that
260 // we will use behind the scenes to retrieve a set of possible moves.
261 SkillLevelEnabled = (SkillLevel < 20);
262 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
264 if (Options["Use Search Log"])
266 Log log(Options["Search Log Filename"]);
267 log << "\nSearching: " << pos.to_fen()
268 << "\ninfinite: " << Limits.infinite
269 << " ponder: " << Limits.ponder
270 << " time: " << Limits.time[pos.side_to_move()]
271 << " increment: " << Limits.inc[pos.side_to_move()]
272 << " moves to go: " << Limits.movestogo
278 // Set best timer interval to avoid lagging under time pressure. Timer is
279 // used to check for remaining available thinking time.
280 if (Limits.use_time_management())
281 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
283 Threads.set_timer(100);
285 // We're ready to start searching. Call the iterative deepening loop function
288 Threads.set_timer(0); // Stop timer
291 if (Options["Use Search Log"])
293 Time::point elapsed = Time::now() - SearchTime + 1;
295 Log log(Options["Search Log Filename"]);
296 log << "Nodes: " << pos.nodes_searched()
297 << "\nNodes/second: " << pos.nodes_searched() * 1000 / elapsed
298 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
301 pos.do_move(RootMoves[0].pv[0], st);
302 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << std::endl;
303 pos.undo_move(RootMoves[0].pv[0]);
308 // When we reach max depth we arrive here even without Signals.stop is raised,
309 // but if we are pondering or in infinite search, we shouldn't print the best
310 // move before we are told to do so.
311 if (!Signals.stop && (Limits.ponder || Limits.infinite))
312 pos.this_thread()->wait_for_stop_or_ponderhit();
314 // Best move could be MOVE_NONE when searching on a stalemate position
315 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
316 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << sync_endl;
322 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
323 // with increasing depth until the allocated thinking time has been consumed,
324 // user stops the search, or the maximum search depth is reached.
326 void id_loop(Position& pos) {
328 Stack ss[MAX_PLY_PLUS_2];
329 int depth, prevBestMoveChanges;
330 Value bestValue, alpha, beta, delta;
331 bool bestMoveNeverChanged = true;
332 Move skillBest = MOVE_NONE;
334 memset(ss, 0, 4 * sizeof(Stack));
335 depth = BestMoveChanges = 0;
336 bestValue = delta = -VALUE_INFINITE;
337 ss->currentMove = MOVE_NULL; // Hack to skip update gains
339 // Iterative deepening loop until requested to stop or target depth reached
340 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
342 // Save last iteration's scores before first PV line is searched and all
343 // the move scores but the (new) PV are set to -VALUE_INFINITE.
344 for (size_t i = 0; i < RootMoves.size(); i++)
345 RootMoves[i].prevScore = RootMoves[i].score;
347 prevBestMoveChanges = BestMoveChanges;
350 // MultiPV loop. We perform a full root search for each PV line
351 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
353 // Set aspiration window default width
354 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
357 alpha = RootMoves[PVIdx].prevScore - delta;
358 beta = RootMoves[PVIdx].prevScore + delta;
362 alpha = -VALUE_INFINITE;
363 beta = VALUE_INFINITE;
366 // Start with a small aspiration window and, in case of fail high/low,
367 // research with bigger window until not failing high/low anymore.
370 // Search starts from ss+1 to allow referencing (ss-1). This is
371 // needed by update gains and ss copy when splitting at Root.
372 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
374 // Bring to front the best move. It is critical that sorting is
375 // done with a stable algorithm because all the values but the first
376 // and eventually the new best one are set to -VALUE_INFINITE and
377 // we want to keep the same order for all the moves but the new
378 // PV that goes to the front. Note that in case of MultiPV search
379 // the already searched PV lines are preserved.
380 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
382 // In case we have found an exact score and we are going to leave
383 // the fail high/low loop then reorder the PV moves, otherwise
384 // leave the last PV move in its position so to be searched again.
385 // Of course this is needed only in MultiPV search.
386 if (PVIdx && bestValue > alpha && bestValue < beta)
387 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
389 // Write PV back to transposition table in case the relevant
390 // entries have been overwritten during the search.
391 for (size_t i = 0; i <= PVIdx; i++)
392 RootMoves[i].insert_pv_in_tt(pos);
394 // If search has been stopped exit the aspiration window loop.
395 // Sorting and writing PV back to TT is safe becuase RootMoves
396 // is still valid, although refers to previous iteration.
400 // Send full PV info to GUI if we are going to leave the loop or
401 // if we have a fail high/low and we are deep in the search.
402 if ((bestValue > alpha && bestValue < beta) || Time::now() - SearchTime > 2000)
403 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
405 // In case of failing high/low increase aspiration window and
406 // research, otherwise exit the fail high/low loop.
407 if (bestValue >= beta)
412 else if (bestValue <= alpha)
414 Signals.failedLowAtRoot = true;
415 Signals.stopOnPonderhit = false;
423 // Search with full window in case we have a win/mate score
424 if (abs(bestValue) >= VALUE_KNOWN_WIN)
426 alpha = -VALUE_INFINITE;
427 beta = VALUE_INFINITE;
430 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
434 // Skills: Do we need to pick now the best move ?
435 if (SkillLevelEnabled && depth == 1 + SkillLevel)
436 skillBest = do_skill_level();
438 if (!Signals.stop && Options["Use Search Log"])
440 Log log(Options["Search Log Filename"]);
441 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
445 // Filter out startup noise when monitoring best move stability
446 if (depth > 2 && BestMoveChanges)
447 bestMoveNeverChanged = false;
449 // Do we have time for the next iteration? Can we stop searching now?
450 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
452 bool stop = false; // Local variable, not the volatile Signals.stop
454 // Take in account some extra time if the best move has changed
455 if (depth > 4 && depth < 50)
456 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
458 // Stop search if most of available time is already consumed. We
459 // probably don't have enough time to search the first move at the
460 // next iteration anyway.
461 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
464 // Stop search early if one move seems to be much better than others
467 && ( (bestMoveNeverChanged && pos.captured_piece_type())
468 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
470 Value rBeta = bestValue - EasyMoveMargin;
471 (ss+1)->excludedMove = RootMoves[0].pv[0];
472 (ss+1)->skipNullMove = true;
473 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
474 (ss+1)->skipNullMove = false;
475 (ss+1)->excludedMove = MOVE_NONE;
483 // If we are allowed to ponder do not stop the search now but
484 // keep pondering until GUI sends "ponderhit" or "stop".
486 Signals.stopOnPonderhit = true;
493 // When using skills swap best PV line with the sub-optimal one
494 if (SkillLevelEnabled)
496 if (skillBest == MOVE_NONE) // Still unassigned ?
497 skillBest = do_skill_level();
499 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), skillBest));
504 // search<>() is the main search function for both PV and non-PV nodes and for
505 // normal and SplitPoint nodes. When called just after a split point the search
506 // is simpler because we have already probed the hash table, done a null move
507 // search, and searched the first move before splitting, we don't have to repeat
508 // all this work again. We also don't need to store anything to the hash table
509 // here: This is taken care of after we return from the split point.
511 template <NodeType NT>
512 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
514 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
515 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
516 const bool RootNode = (NT == Root || NT == SplitPointRoot);
518 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
519 assert((alpha == beta - 1) || PvNode);
520 assert(depth > DEPTH_ZERO);
522 Move movesSearched[64];
526 Move ttMove, move, excludedMove, bestMove, threatMove;
529 Value bestValue, value, oldAlpha, ttValue;
530 Value refinedValue, nullValue, futilityBase, futilityValue;
531 bool isPvMove, inCheck, singularExtensionNode, givesCheck;
532 bool captureOrPromotion, dangerous, doFullDepthSearch;
533 int moveCount = 0, playedMoveCount = 0;
534 Thread* thisThread = pos.this_thread();
535 SplitPoint* sp = NULL;
537 refinedValue = bestValue = value = -VALUE_INFINITE;
539 inCheck = pos.in_check();
540 ss->ply = (ss-1)->ply + 1;
542 // Used to send selDepth info to GUI
543 if (PvNode && thisThread->maxPly < ss->ply)
544 thisThread->maxPly = ss->ply;
546 // Step 1. Initialize node
550 ttMove = excludedMove = MOVE_NONE;
551 ttValue = VALUE_ZERO;
553 bestMove = sp->bestMove;
554 threatMove = sp->threatMove;
555 bestValue = sp->bestValue;
556 moveCount = sp->moveCount; // Lock must be held here
558 assert(bestValue > -VALUE_INFINITE && moveCount > 0);
560 goto split_point_start;
564 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
565 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
566 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
570 // Step 2. Check for aborted search and immediate draw
571 // Enforce node limit here. FIXME: This only works with 1 search thread.
572 if (Limits.nodes && pos.nodes_searched() >= Limits.nodes)
576 || pos.is_draw<false>()
577 || ss->ply > MAX_PLY) && !RootNode)
580 // Step 3. Mate distance pruning. Even if we mate at the next move our score
581 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
582 // a shorter mate was found upward in the tree then there is no need to search
583 // further, we will never beat current alpha. Same logic but with reversed signs
584 // applies also in the opposite condition of being mated instead of giving mate,
585 // in this case return a fail-high score.
588 alpha = std::max(mated_in(ss->ply), alpha);
589 beta = std::min(mate_in(ss->ply+1), beta);
594 // Step 4. Transposition table lookup
595 // We don't want the score of a partial search to overwrite a previous full search
596 // TT value, so we use a different position key in case of an excluded move.
597 excludedMove = ss->excludedMove;
598 posKey = excludedMove ? pos.exclusion_key() : pos.key();
599 tte = TT.probe(posKey);
600 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
601 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_ZERO;
603 // At PV nodes we check for exact scores, while at non-PV nodes we check for
604 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
605 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
606 // we should also update RootMoveList to avoid bogus output.
607 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
608 : can_return_tt(tte, depth, ttValue, beta)))
611 ss->currentMove = ttMove; // Can be MOVE_NONE
615 && !pos.is_capture_or_promotion(ttMove)
616 && ttMove != ss->killers[0])
618 ss->killers[1] = ss->killers[0];
619 ss->killers[0] = ttMove;
624 // Step 5. Evaluate the position statically and update parent's gain statistics
626 ss->eval = ss->evalMargin = VALUE_NONE;
629 assert(tte->static_value() != VALUE_NONE);
631 ss->eval = tte->static_value();
632 ss->evalMargin = tte->static_value_margin();
633 refinedValue = refine_eval(tte, ttValue, ss->eval);
637 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
638 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
641 // Update gain for the parent non-capture move given the static position
642 // evaluation before and after the move.
643 if ( (move = (ss-1)->currentMove) != MOVE_NULL
644 && (ss-1)->eval != VALUE_NONE
645 && ss->eval != VALUE_NONE
646 && !pos.captured_piece_type()
647 && type_of(move) == NORMAL)
649 Square to = to_sq(move);
650 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
653 // Step 6. Razoring (is omitted in PV nodes)
655 && depth < RazorDepth
657 && refinedValue + razor_margin(depth) < beta
658 && ttMove == MOVE_NONE
659 && abs(beta) < VALUE_MATE_IN_MAX_PLY
660 && !pos.pawn_on_7th(pos.side_to_move()))
662 Value rbeta = beta - razor_margin(depth);
663 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
665 // Logically we should return (v + razor_margin(depth)), but
666 // surprisingly this did slightly weaker in tests.
670 // Step 7. Static null move pruning (is omitted in PV nodes)
671 // We're betting that the opponent doesn't have a move that will reduce
672 // the score by more than futility_margin(depth) if we do a null move.
675 && depth < RazorDepth
677 && refinedValue - futility_margin(depth, 0) >= beta
678 && abs(beta) < VALUE_MATE_IN_MAX_PLY
679 && pos.non_pawn_material(pos.side_to_move()))
680 return refinedValue - futility_margin(depth, 0);
682 // Step 8. Null move search with verification search (is omitted in PV nodes)
687 && refinedValue >= beta
688 && abs(beta) < VALUE_MATE_IN_MAX_PLY
689 && pos.non_pawn_material(pos.side_to_move()))
691 ss->currentMove = MOVE_NULL;
693 // Null move dynamic reduction based on depth
694 Depth R = 3 * ONE_PLY + depth / 4;
696 // Null move dynamic reduction based on value
697 if (refinedValue - PawnValueMg > beta)
700 pos.do_null_move<true>(st);
701 (ss+1)->skipNullMove = true;
702 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
703 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
704 (ss+1)->skipNullMove = false;
705 pos.do_null_move<false>(st);
707 if (nullValue >= beta)
709 // Do not return unproven mate scores
710 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
713 if (depth < 6 * ONE_PLY)
716 // Do verification search at high depths
717 ss->skipNullMove = true;
718 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
719 ss->skipNullMove = false;
726 // The null move failed low, which means that we may be faced with
727 // some kind of threat. If the previous move was reduced, check if
728 // the move that refuted the null move was somehow connected to the
729 // move which was reduced. If a connection is found, return a fail
730 // low score (which will cause the reduced move to fail high in the
731 // parent node, which will trigger a re-search with full depth).
732 threatMove = (ss+1)->currentMove;
734 if ( depth < ThreatDepth
736 && threatMove != MOVE_NONE
737 && connected_moves(pos, (ss-1)->currentMove, threatMove))
742 // Step 9. ProbCut (is omitted in PV nodes)
743 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
744 // and a reduced search returns a value much above beta, we can (almost) safely
745 // prune the previous move.
747 && depth >= RazorDepth + ONE_PLY
750 && excludedMove == MOVE_NONE
751 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
753 Value rbeta = beta + 200;
754 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
756 assert(rdepth >= ONE_PLY);
757 assert((ss-1)->currentMove != MOVE_NONE);
758 assert((ss-1)->currentMove != MOVE_NULL);
760 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
763 while ((move = mp.next_move<false>()) != MOVE_NONE)
764 if (pos.pl_move_is_legal(move, ci.pinned))
766 ss->currentMove = move;
767 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
768 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
775 // Step 10. Internal iterative deepening
776 if ( depth >= IIDDepth[PvNode]
777 && ttMove == MOVE_NONE
778 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
780 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
782 ss->skipNullMove = true;
783 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
784 ss->skipNullMove = false;
786 tte = TT.probe(posKey);
787 ttMove = tte ? tte->move() : MOVE_NONE;
790 split_point_start: // At split points actual search starts from here
792 MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
794 futilityBase = ss->eval + ss->evalMargin;
795 singularExtensionNode = !RootNode
797 && depth >= SingularExtensionDepth[PvNode]
798 && ttMove != MOVE_NONE
799 && !excludedMove // Recursive singular search is not allowed
800 && (tte->type() & BOUND_LOWER)
801 && tte->depth() >= depth - 3 * ONE_PLY;
803 // Step 11. Loop through moves
804 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
805 while ( bestValue < beta
806 && (move = mp.next_move<SpNode>()) != MOVE_NONE
807 && !thisThread->cutoff_occurred()
812 if (move == excludedMove)
815 // At root obey the "searchmoves" option and skip moves not listed in Root
816 // Move List, as a consequence any illegal move is also skipped. In MultiPV
817 // mode we also skip PV moves which have been already searched.
818 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
821 // At PV and SpNode nodes we want all moves to be legal since the beginning
822 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
827 moveCount = ++sp->moveCount;
835 Signals.firstRootMove = (moveCount == 1);
837 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
838 sync_cout << "info depth " << depth / ONE_PLY
839 << " currmove " << move_to_uci(move, Chess960)
840 << " currmovenumber " << moveCount + PVIdx << sync_endl;
843 isPvMove = (PvNode && moveCount <= 1);
844 captureOrPromotion = pos.is_capture_or_promotion(move);
845 givesCheck = pos.move_gives_check(move, ci);
846 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
849 // Step 12. Extend checks and, in PV nodes, also dangerous moves
850 if (PvNode && dangerous)
853 else if (givesCheck && pos.see_sign(move) >= 0)
856 // Singular extension search. If all moves but one fail low on a search of
857 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
858 // is singular and should be extended. To verify this we do a reduced search
859 // on all the other moves but the ttMove, if result is lower than ttValue minus
860 // a margin then we extend ttMove.
861 if ( singularExtensionNode
864 && pos.pl_move_is_legal(move, ci.pinned)
865 && abs(ttValue) < VALUE_KNOWN_WIN)
867 Value rBeta = ttValue - int(depth);
868 ss->excludedMove = move;
869 ss->skipNullMove = true;
870 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
871 ss->skipNullMove = false;
872 ss->excludedMove = MOVE_NONE;
878 // Update current move (this must be done after singular extension search)
879 newDepth = depth - ONE_PLY + ext;
881 // Step 13. Futility pruning (is omitted in PV nodes)
883 && !captureOrPromotion
887 && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
889 // Move count based pruning
890 if ( moveCount >= futility_move_count(depth)
891 && (!threatMove || !connected_threat(pos, move, threatMove)))
899 // Value based pruning
900 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
901 // but fixing this made program slightly weaker.
902 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
903 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
904 + H.gain(pos.piece_moved(move), to_sq(move));
906 if (futilityValue < beta)
914 // Prune moves with negative SEE at low depths
915 if ( predictedDepth < 2 * ONE_PLY
916 && pos.see_sign(move) < 0)
925 // Check for legality only before to do the move
926 if (!pos.pl_move_is_legal(move, ci.pinned))
932 ss->currentMove = move;
933 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
934 movesSearched[playedMoveCount++] = move;
936 // Step 14. Make the move
937 pos.do_move(move, st, ci, givesCheck);
939 // Step 15. Reduced depth search (LMR). If the move fails high will be
940 // re-searched at full depth.
941 if ( depth > 3 * ONE_PLY
943 && !captureOrPromotion
945 && ss->killers[0] != move
946 && ss->killers[1] != move)
948 ss->reduction = reduction<PvNode>(depth, moveCount);
949 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
950 alpha = SpNode ? sp->alpha : alpha;
952 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
954 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
955 ss->reduction = DEPTH_ZERO;
958 doFullDepthSearch = !isPvMove;
960 // Step 16. Full depth search, when LMR is skipped or fails high
961 if (doFullDepthSearch)
963 alpha = SpNode ? sp->alpha : alpha;
964 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
965 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
968 // Only for PV nodes do a full PV search on the first move or after a fail
969 // high, in the latter case search only if value < beta, otherwise let the
970 // parent node to fail low with value <= alpha and to try another move.
971 if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
972 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
973 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
975 // Step 17. Undo move
978 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
980 // Step 18. Check for new best move
984 bestValue = sp->bestValue;
988 // Finished searching the move. If Signals.stop is true, the search
989 // was aborted because the user interrupted the search or because we
990 // ran out of time. In this case, the return value of the search cannot
991 // be trusted, and we don't update the best move and/or PV.
992 if (RootNode && !Signals.stop)
994 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
996 // PV move or new best move ?
997 if (isPvMove || value > alpha)
1000 rm.extract_pv_from_tt(pos);
1002 // We record how often the best move has been changed in each
1003 // iteration. This information is used for time management: When
1004 // the best move changes frequently, we allocate some more time.
1005 if (!isPvMove && MultiPV == 1)
1009 // All other moves but the PV are set to the lowest value, this
1010 // is not a problem when sorting becuase sort is stable and move
1011 // position in the list is preserved, just the PV is pushed up.
1012 rm.score = -VALUE_INFINITE;
1016 if (value > bestValue)
1023 && value < beta) // We want always alpha < beta
1026 if (SpNode && !thisThread->cutoff_occurred())
1028 sp->bestValue = value;
1029 sp->bestMove = move;
1037 // Step 19. Check for split
1039 && depth >= Threads.min_split_depth()
1041 && Threads.available_slave_exists(thisThread)
1043 && !thisThread->cutoff_occurred())
1044 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1045 depth, threatMove, moveCount, &mp, NT);
1048 // Step 20. Check for mate and stalemate
1049 // All legal moves have been searched and if there are no legal moves, it
1050 // must be mate or stalemate. Note that we can have a false positive in
1051 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1052 // harmless because return value is discarded anyhow in the parent nodes.
1053 // If we are in a singular extension search then return a fail low score.
1055 return excludedMove ? oldAlpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1057 // If we have pruned all the moves without searching return a fail-low score
1058 if (bestValue == -VALUE_INFINITE)
1060 assert(!playedMoveCount);
1062 bestValue = oldAlpha;
1065 // Step 21. Update tables
1066 // Update transposition table entry, killers and history
1067 if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
1069 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1070 bt = bestValue <= oldAlpha ? BOUND_UPPER
1071 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1073 TT.store(posKey, value_to_tt(bestValue, ss->ply), bt, depth, move, ss->eval, ss->evalMargin);
1075 // Update killers and history for non capture cut-off moves
1076 if ( bestValue >= beta
1077 && !pos.is_capture_or_promotion(move)
1080 if (move != ss->killers[0])
1082 ss->killers[1] = ss->killers[0];
1083 ss->killers[0] = move;
1086 // Increase history value of the cut-off move
1087 Value bonus = Value(int(depth) * int(depth));
1088 H.add(pos.piece_moved(move), to_sq(move), bonus);
1090 // Decrease history of all the other played non-capture moves
1091 for (int i = 0; i < playedMoveCount - 1; i++)
1093 Move m = movesSearched[i];
1094 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1099 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1105 // qsearch() is the quiescence search function, which is called by the main
1106 // search function when the remaining depth is zero (or, to be more precise,
1107 // less than ONE_PLY).
1109 template <NodeType NT>
1110 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1112 const bool PvNode = (NT == PV);
1114 assert(NT == PV || NT == NonPV);
1115 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1116 assert((alpha == beta - 1) || PvNode);
1117 assert(depth <= DEPTH_ZERO);
1120 Move ttMove, move, bestMove;
1121 Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
1122 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1126 Value oldAlpha = alpha;
1128 ss->currentMove = bestMove = MOVE_NONE;
1129 ss->ply = (ss-1)->ply + 1;
1131 // Check for an instant draw or maximum ply reached
1132 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1135 // Decide whether or not to include checks, this fixes also the type of
1136 // TT entry depth that we are going to use. Note that in qsearch we use
1137 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1138 inCheck = pos.in_check();
1139 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1141 // Transposition table lookup. At PV nodes, we don't use the TT for
1142 // pruning, but only for move ordering.
1143 tte = TT.probe(pos.key());
1144 ttMove = (tte ? tte->move() : MOVE_NONE);
1145 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
1147 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1149 ss->currentMove = ttMove; // Can be MOVE_NONE
1153 // Evaluate the position statically
1156 bestValue = futilityBase = -VALUE_INFINITE;
1157 ss->eval = evalMargin = VALUE_NONE;
1158 enoughMaterial = false;
1164 assert(tte->static_value() != VALUE_NONE);
1166 evalMargin = tte->static_value_margin();
1167 ss->eval = bestValue = tte->static_value();
1170 ss->eval = bestValue = evaluate(pos, evalMargin);
1172 // Stand pat. Return immediately if static value is at least beta
1173 if (bestValue >= beta)
1176 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1181 if (PvNode && bestValue > alpha)
1184 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1185 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1188 // Initialize a MovePicker object for the current position, and prepare
1189 // to search the moves. Because the depth is <= 0 here, only captures,
1190 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1192 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1195 // Loop through the moves until no moves remain or a beta cutoff occurs
1196 while ( bestValue < beta
1197 && (move = mp.next_move<false>()) != MOVE_NONE)
1199 assert(is_ok(move));
1201 givesCheck = pos.move_gives_check(move, ci);
1209 && type_of(move) != PROMOTION
1210 && !pos.is_passed_pawn_push(move))
1212 futilityValue = futilityBase
1213 + PieceValue[Eg][pos.piece_on(to_sq(move))]
1214 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1216 if (futilityValue < beta)
1218 if (futilityValue > bestValue)
1219 bestValue = futilityValue;
1224 // Prune moves with negative or equal SEE
1225 if ( futilityBase < beta
1226 && depth < DEPTH_ZERO
1227 && pos.see(move) <= 0)
1231 // Detect non-capture evasions that are candidate to be pruned
1232 evasionPrunable = !PvNode
1234 && bestValue > VALUE_MATED_IN_MAX_PLY
1235 && !pos.is_capture(move)
1236 && !pos.can_castle(pos.side_to_move());
1238 // Don't search moves with negative SEE values
1240 && (!inCheck || evasionPrunable)
1242 && type_of(move) != PROMOTION
1243 && pos.see_sign(move) < 0)
1246 // Don't search useless checks
1251 && !pos.is_capture_or_promotion(move)
1252 && ss->eval + PawnValueMg / 4 < beta
1253 && !check_is_dangerous(pos, move, futilityBase, beta))
1256 // Check for legality only before to do the move
1257 if (!pos.pl_move_is_legal(move, ci.pinned))
1260 ss->currentMove = move;
1262 // Make and search the move
1263 pos.do_move(move, st, ci, givesCheck);
1264 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1265 pos.undo_move(move);
1267 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1270 if (value > bestValue)
1277 && value < beta) // We want always alpha < beta
1282 // All legal moves have been searched. A special case: If we're in check
1283 // and no legal moves were found, it is checkmate.
1284 if (inCheck && bestValue == -VALUE_INFINITE)
1285 return mated_in(ss->ply); // Plies to mate from the root
1287 // Update transposition table
1288 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1289 bt = bestValue <= oldAlpha ? BOUND_UPPER
1290 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1292 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
1294 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1300 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1301 // bestValue is updated only when returning false because in that case move
1304 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1306 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1307 Square from, to, ksq;
1311 from = from_sq(move);
1313 them = ~pos.side_to_move();
1314 ksq = pos.king_square(them);
1315 kingAtt = pos.attacks_from<KING>(ksq);
1316 pc = pos.piece_moved(move);
1318 occ = pos.pieces() ^ from ^ ksq;
1319 oldAtt = pos.attacks_from(pc, from, occ);
1320 newAtt = pos.attacks_from(pc, to, occ);
1322 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1323 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1325 if (!more_than_one(b))
1328 // Rule 2. Queen contact check is very dangerous
1329 if (type_of(pc) == QUEEN && (kingAtt & to))
1332 // Rule 3. Creating new double threats with checks
1333 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1336 // Note that here we generate illegal "double move"!
1337 if (futilityBase + PieceValue[Eg][pos.piece_on(pop_lsb(&b))] >= beta)
1345 // connected_moves() tests whether two moves are 'connected' in the sense
1346 // that the first move somehow made the second move possible (for instance
1347 // if the moving piece is the same in both moves). The first move is assumed
1348 // to be the move that was made to reach the current position, while the
1349 // second move is assumed to be a move from the current position.
1351 bool connected_moves(const Position& pos, Move m1, Move m2) {
1353 Square f1, t1, f2, t2;
1360 // Case 1: The moving piece is the same in both moves
1366 // Case 2: The destination square for m2 was vacated by m1
1372 // Case 3: Moving through the vacated square
1373 p2 = pos.piece_on(f2);
1374 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1377 // Case 4: The destination square for m2 is defended by the moving piece in m1
1378 p1 = pos.piece_on(t1);
1379 if (pos.attacks_from(p1, t1) & t2)
1382 // Case 5: Discovered check, checking piece is the piece moved in m1
1383 ksq = pos.king_square(pos.side_to_move());
1384 if ( piece_is_slider(p1)
1385 && (between_bb(t1, ksq) & f2)
1386 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1393 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1394 // "plies to mate from the current position". Non-mate scores are unchanged.
1395 // The function is called before storing a value to the transposition table.
1397 Value value_to_tt(Value v, int ply) {
1399 if (v >= VALUE_MATE_IN_MAX_PLY)
1402 if (v <= VALUE_MATED_IN_MAX_PLY)
1409 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1410 // from the transposition table (where refers to the plies to mate/be mated
1411 // from current position) to "plies to mate/be mated from the root".
1413 Value value_from_tt(Value v, int ply) {
1415 if (v >= VALUE_MATE_IN_MAX_PLY)
1418 if (v <= VALUE_MATED_IN_MAX_PLY)
1425 // connected_threat() tests whether it is safe to forward prune a move or if
1426 // is somehow connected to the threat move returned by null search.
1428 bool connected_threat(const Position& pos, Move m, Move threat) {
1431 assert(is_ok(threat));
1432 assert(!pos.is_capture_or_promotion(m));
1433 assert(!pos.is_passed_pawn_push(m));
1435 Square mfrom, mto, tfrom, tto;
1439 tfrom = from_sq(threat);
1440 tto = to_sq(threat);
1442 // Case 1: Don't prune moves which move the threatened piece
1446 // Case 2: If the threatened piece has value less than or equal to the
1447 // value of the threatening piece, don't prune moves which defend it.
1448 if ( pos.is_capture(threat)
1449 && ( PieceValue[Mg][pos.piece_on(tfrom)] >= PieceValue[Mg][pos.piece_on(tto)]
1450 || type_of(pos.piece_on(tfrom)) == KING)
1451 && pos.move_attacks_square(m, tto))
1454 // Case 3: If the moving piece in the threatened move is a slider, don't
1455 // prune safe moves which block its ray.
1456 if ( piece_is_slider(pos.piece_on(tfrom))
1457 && (between_bb(tfrom, tto) & mto)
1458 && pos.see_sign(m) >= 0)
1465 // can_return_tt() returns true if a transposition table score can be used to
1466 // cut-off at a given point in search.
1468 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1470 return ( tte->depth() >= depth
1471 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1472 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1474 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1475 || ((tte->type() & BOUND_UPPER) && v < beta));
1479 // refine_eval() returns the transposition table score if possible, otherwise
1480 // falls back on static position evaluation.
1482 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1486 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1487 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1494 // When playing with strength handicap choose best move among the MultiPV set
1495 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1497 Move do_skill_level() {
1499 assert(MultiPV > 1);
1503 // PRNG sequence should be not deterministic
1504 for (int i = Time::now() % 50; i > 0; i--)
1505 rk.rand<unsigned>();
1507 // RootMoves are already sorted by score in descending order
1508 size_t size = std::min(MultiPV, RootMoves.size());
1509 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMg);
1510 int weakness = 120 - 2 * SkillLevel;
1511 int max_s = -VALUE_INFINITE;
1512 Move best = MOVE_NONE;
1514 // Choose best move. For each move score we add two terms both dependent on
1515 // weakness, one deterministic and bigger for weaker moves, and one random,
1516 // then we choose the move with the resulting highest score.
1517 for (size_t i = 0; i < size; i++)
1519 int s = RootMoves[i].score;
1521 // Don't allow crazy blunders even at very low skills
1522 if (i > 0 && RootMoves[i-1].score > s + EasyMoveMargin)
1525 // This is our magic formula
1526 s += ( weakness * int(RootMoves[0].score - s)
1527 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1532 best = RootMoves[i].pv[0];
1539 // uci_pv() formats PV information according to UCI protocol. UCI requires
1540 // to send all the PV lines also if are still to be searched and so refer to
1541 // the previous search score.
1543 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1545 std::stringstream s;
1546 Time::point elaspsed = Time::now() - SearchTime + 1;
1549 for (size_t i = 0; i < Threads.size(); i++)
1550 if (Threads[i].maxPly > selDepth)
1551 selDepth = Threads[i].maxPly;
1553 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1555 bool updated = (i <= PVIdx);
1557 if (depth == 1 && !updated)
1560 int d = (updated ? depth : depth - 1);
1561 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1563 if (s.rdbuf()->in_avail())
1566 s << "info depth " << d
1567 << " seldepth " << selDepth
1568 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1569 << " nodes " << pos.nodes_searched()
1570 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1571 << " time " << elaspsed
1572 << " multipv " << i + 1
1575 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1576 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1585 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1586 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1587 /// allow to always have a ponder move even when we fail high at root, and a
1588 /// long PV to print that is important for position analysis.
1590 void RootMove::extract_pv_from_tt(Position& pos) {
1592 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1597 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1601 pos.do_move(m, *st++);
1603 while ( (tte = TT.probe(pos.key())) != NULL
1604 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1605 && pos.is_pseudo_legal(m)
1606 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1608 && (!pos.is_draw<false>() || ply < 2))
1611 pos.do_move(m, *st++);
1614 pv.push_back(MOVE_NONE);
1616 do pos.undo_move(pv[--ply]); while (ply);
1620 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1621 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1622 /// first, even if the old TT entries have been overwritten.
1624 void RootMove::insert_pv_in_tt(Position& pos) {
1626 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1629 Value v, m = VALUE_NONE;
1632 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1638 // Don't overwrite existing correct entries
1639 if (!tte || tte->move() != pv[ply])
1641 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1642 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1644 pos.do_move(pv[ply], *st++);
1646 } while (pv[++ply] != MOVE_NONE);
1648 do pos.undo_move(pv[--ply]); while (ply);
1652 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1654 void Thread::idle_loop() {
1656 // Pointer 'sp_master', if non-NULL, points to the active SplitPoint
1657 // object for which the thread is the master.
1658 const SplitPoint* sp_master = splitPointsCnt ? curSplitPoint : NULL;
1660 assert(!sp_master || (sp_master->master == this && is_searching));
1662 // If this thread is the master of a split point and all slaves have
1663 // finished their work at this split point, return from the idle loop.
1664 while (!sp_master || sp_master->slavesMask)
1666 // If we are not searching, wait for a condition to be signaled
1667 // instead of wasting CPU time polling for work.
1670 || (!is_searching && Threads.use_sleeping_threads()))
1678 // Grab the lock to avoid races with Thread::wake_up()
1681 // If we are master and all slaves have finished don't go to sleep
1682 if (sp_master && !sp_master->slavesMask)
1688 // Do sleep after retesting sleep conditions under lock protection, in
1689 // particular we need to avoid a deadlock in case a master thread has,
1690 // in the meanwhile, allocated us and sent the wake_up() call before we
1691 // had the chance to grab the lock.
1692 if (do_sleep || !is_searching)
1693 sleepCondition.wait(mutex);
1698 // If this thread has been assigned work, launch a search
1701 assert(!do_sleep && !do_exit);
1703 Threads.mutex.lock();
1705 assert(is_searching);
1706 SplitPoint* sp = curSplitPoint;
1708 Threads.mutex.unlock();
1710 Stack ss[MAX_PLY_PLUS_2];
1711 Position pos(*sp->pos, this);
1713 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1718 if (sp->nodeType == Root)
1719 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1720 else if (sp->nodeType == PV)
1721 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1722 else if (sp->nodeType == NonPV)
1723 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1727 assert(is_searching);
1729 is_searching = false;
1730 sp->slavesMask &= ~(1ULL << idx);
1731 sp->nodes += pos.nodes_searched();
1733 // Wake up master thread so to allow it to return from the idle loop in
1734 // case we are the last slave of the split point.
1735 if ( Threads.use_sleeping_threads()
1736 && this != sp->master
1739 assert(!sp->master->is_searching);
1740 sp->master->wake_up();
1743 // After releasing the lock we cannot access anymore any SplitPoint
1744 // related data in a safe way becuase it could have been released under
1745 // our feet by the sp master. Also accessing other Thread objects is
1746 // unsafe because if we are exiting there is a chance are already freed.
1753 /// check_time() is called by the timer thread when the timer triggers. It is
1754 /// used to print debug info and, more important, to detect when we are out of
1755 /// available time and so stop the search.
1759 static Time::point lastInfoTime = Time::now();
1761 if (Time::now() - lastInfoTime >= 1000)
1763 lastInfoTime = Time::now();
1770 Time::point elapsed = Time::now() - SearchTime;
1771 bool stillAtFirstMove = Signals.firstRootMove
1772 && !Signals.failedLowAtRoot
1773 && elapsed > TimeMgr.available_time();
1775 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1776 || stillAtFirstMove;
1778 if ( (Limits.use_time_management() && noMoreTime)
1779 || (Limits.movetime && elapsed >= Limits.movetime))
1780 Signals.stop = true;