2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
40 #include "ucioption.h"
48 // Set to true to force running with one thread. Used for debugging
49 const bool FakeSplit = false;
51 // Different node types, used as template parameter
52 enum NodeType { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
54 // RootMove struct is used for moves at the root of the tree. For each root
55 // move, we store a pv_score, a node count, and a PV (really a refutation
56 // in the case of moves which fail low). Value pv_score is normally set at
57 // -VALUE_INFINITE for all non-pv moves.
60 // RootMove::operator<() is the comparison function used when
61 // sorting the moves. A move m1 is considered to be better
62 // than a move m2 if it has an higher pv_score
63 bool operator<(const RootMove& m) const { return pv_score < m.pv_score; }
65 void extract_pv_from_tt(Position& pos);
66 void insert_pv_in_tt(Position& pos);
73 // RootMoveList struct is mainly a std::vector of RootMove objects
74 struct RootMoveList : public std::vector<RootMove> {
76 void init(Position& pos, Move searchMoves[]);
77 RootMove* find(const Move& m, int startIndex = 0);
85 // Lookup table to check if a Piece is a slider and its access function
86 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
87 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
91 // Maximum depth for razoring
92 const Depth RazorDepth = 4 * ONE_PLY;
94 // Dynamic razoring margin based on depth
95 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
97 // Maximum depth for use of dynamic threat detection when null move fails low
98 const Depth ThreatDepth = 5 * ONE_PLY;
100 // Step 9. Internal iterative deepening
102 // Minimum depth for use of internal iterative deepening
103 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
105 // At Non-PV nodes we do an internal iterative deepening search
106 // when the static evaluation is bigger then beta - IIDMargin.
107 const Value IIDMargin = Value(0x100);
109 // Step 11. Decide the new search depth
111 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
112 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
113 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
114 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
115 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
117 // Minimum depth for use of singular extension
118 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
120 // Step 12. Futility pruning
122 // Futility margin for quiescence search
123 const Value FutilityMarginQS = Value(0x80);
125 // Futility lookup tables (initialized at startup) and their access functions
126 Value FutilityMargins[16][64]; // [depth][moveNumber]
127 int FutilityMoveCounts[32]; // [depth]
129 inline Value futility_margin(Depth d, int mn) {
131 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
132 : 2 * VALUE_INFINITE;
135 inline int futility_move_count(Depth d) {
137 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
140 // Step 14. Reduced search
142 // Reduction lookup tables (initialized at startup) and their access function
143 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
145 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
147 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
150 // Easy move margin. An easy move candidate must be at least this much
151 // better than the second best move.
152 const Value EasyMoveMargin = Value(0x200);
155 /// Namespace variables
161 int MultiPV, UCIMultiPV, MultiPVIteration;
163 // Time management variables
164 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
169 std::ofstream LogFile;
171 // Skill level adjustment
173 bool SkillLevelEnabled;
175 // Node counters, used only by thread[0] but try to keep in different cache
176 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
177 bool SendSearchedNodes;
179 int NodesBetweenPolls = 30000;
187 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
189 template <NodeType NT>
190 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
192 template <NodeType NT>
193 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
195 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
196 bool connected_moves(const Position& pos, Move m1, Move m2);
197 Value value_to_tt(Value v, int ply);
198 Value value_from_tt(Value v, int ply);
199 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
200 bool connected_threat(const Position& pos, Move m, Move threat);
201 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
202 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
203 void update_gains(const Position& pos, Move move, Value before, Value after);
204 void do_skill_level(Move* best, Move* ponder);
206 int current_search_time(int set = 0);
207 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
208 string speed_to_uci(int64_t nodes);
209 string pv_to_uci(const Move pv[], int pvNum, bool chess960);
210 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
211 string depth_to_uci(Depth depth);
212 void poll(const Position& pos);
213 void wait_for_stop_or_ponderhit();
215 // MovePickerExt template class extends MovePicker and allows to choose at compile
216 // time the proper moves source according to the type of node. In the default case
217 // we simply create and use a standard MovePicker object.
218 template<NodeType> struct MovePickerExt : public MovePicker {
220 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
221 : MovePicker(p, ttm, d, h, ss, b) {}
224 // In case of a SpNode we use split point's shared MovePicker object as moves source
225 template<> struct MovePickerExt<SplitPointNonPV> : public MovePicker {
227 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
228 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
230 Move get_next_move() { return mp->get_next_move(); }
234 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
236 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
237 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
240 // Overload operator<<() to make it easier to print moves in a coordinate
241 // notation compatible with UCI protocol.
242 std::ostream& operator<<(std::ostream& os, Move m) {
244 bool chess960 = (os.iword(0) != 0); // See set960()
245 return os << move_to_uci(m, chess960);
248 // When formatting a move for std::cout we must know if we are in Chess960
249 // or not. To keep using the handy operator<<() on the move the trick is to
250 // embed this flag in the stream itself. Function-like named enum set960 is
251 // used as a custom manipulator and the stream internal general-purpose array,
252 // accessed through ios_base::iword(), is used to pass the flag to the move's
253 // operator<<() that will read it to properly format castling moves.
256 std::ostream& operator<< (std::ostream& os, const set960& f) {
258 os.iword(0) = int(f);
262 // extension() decides whether a move should be searched with normal depth,
263 // or with extended depth. Certain classes of moves (checking moves, in
264 // particular) are searched with bigger depth than ordinary moves and in
265 // any case are marked as 'dangerous'. Note that also if a move is not
266 // extended, as example because the corresponding UCI option is set to zero,
267 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
268 template <bool PvNode>
269 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
270 bool moveIsCheck, bool* dangerous) {
271 assert(m != MOVE_NONE);
273 Depth result = DEPTH_ZERO;
274 *dangerous = moveIsCheck;
276 if (moveIsCheck && pos.see_sign(m) >= 0)
277 result += CheckExtension[PvNode];
279 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
281 Color c = pos.side_to_move();
282 if (relative_rank(c, move_to(m)) == RANK_7)
284 result += PawnPushTo7thExtension[PvNode];
287 if (pos.pawn_is_passed(c, move_to(m)))
289 result += PassedPawnExtension[PvNode];
294 if ( captureOrPromotion
295 && piece_type(pos.piece_on(move_to(m))) != PAWN
296 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
297 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
298 && !move_is_special(m))
300 result += PawnEndgameExtension[PvNode];
304 return Min(result, ONE_PLY);
310 /// init_search() is called during startup to initialize various lookup tables
314 int d; // depth (ONE_PLY == 2)
315 int hd; // half depth (ONE_PLY == 1)
318 // Init reductions array
319 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
321 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
322 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
323 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
324 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
327 // Init futility margins array
328 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
329 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
331 // Init futility move count array
332 for (d = 0; d < 32; d++)
333 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
337 /// perft() is our utility to verify move generation. All the leaf nodes up to
338 /// the given depth are generated and counted and the sum returned.
340 int64_t perft(Position& pos, Depth depth) {
345 // Generate all legal moves
346 MoveList<MV_LEGAL> ml(pos);
348 // If we are at the last ply we don't need to do and undo
349 // the moves, just to count them.
350 if (depth <= ONE_PLY)
353 // Loop through all legal moves
355 for ( ; !ml.end(); ++ml)
357 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
358 sum += perft(pos, depth - ONE_PLY);
359 pos.undo_move(ml.move());
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various global
367 /// variables, and calls id_loop(). It returns false when a "quit" command is
368 /// received during the search.
370 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
374 // Initialize global search-related variables
375 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
377 current_search_time(get_system_time());
379 TimeMgr.init(Limits, pos.startpos_ply_counter());
381 // Set output steram in normal or chess960 mode
382 cout << set960(pos.is_chess960());
384 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
386 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
387 else if (Limits.time && Limits.time < 1000)
388 NodesBetweenPolls = 1000;
389 else if (Limits.time && Limits.time < 5000)
390 NodesBetweenPolls = 5000;
392 NodesBetweenPolls = 30000;
394 // Look for a book move
395 if (Options["OwnBook"].value<bool>())
397 if (Options["Book File"].value<string>() != book.name())
398 book.open(Options["Book File"].value<string>());
400 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
401 if (bookMove != MOVE_NONE)
404 wait_for_stop_or_ponderhit();
406 cout << "bestmove " << bookMove << endl;
412 UCIMultiPV = Options["MultiPV"].value<int>();
413 SkillLevel = Options["Skill Level"].value<int>();
415 read_evaluation_uci_options(pos.side_to_move());
416 Threads.read_uci_options();
418 // If needed allocate pawn and material hash tables and adjust TT size
419 Threads.init_hash_tables();
420 TT.set_size(Options["Hash"].value<int>());
422 if (Options["Clear Hash"].value<bool>())
424 Options["Clear Hash"].set_value("false");
428 // Do we have to play with skill handicap? In this case enable MultiPV that
429 // we will use behind the scenes to retrieve a set of possible moves.
430 SkillLevelEnabled = (SkillLevel < 20);
431 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
433 // Wake up needed threads and reset maxPly counter
434 for (int i = 0; i < Threads.size(); i++)
436 Threads[i].wake_up();
437 Threads[i].maxPly = 0;
440 // Write to log file and keep it open to be accessed during the search
441 if (Options["Use Search Log"].value<bool>())
443 string name = Options["Search Log Filename"].value<string>();
444 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
446 if (LogFile.is_open())
447 LogFile << "\nSearching: " << pos.to_fen()
448 << "\ninfinite: " << Limits.infinite
449 << " ponder: " << Limits.ponder
450 << " time: " << Limits.time
451 << " increment: " << Limits.increment
452 << " moves to go: " << Limits.movesToGo
456 // We're ready to start thinking. Call the iterative deepening loop function
457 Move ponderMove = MOVE_NONE;
458 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
460 // Write final search statistics and close log file
461 if (LogFile.is_open())
463 int t = current_search_time();
465 LogFile << "Nodes: " << pos.nodes_searched()
466 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
467 << "\nBest move: " << move_to_san(pos, bestMove);
470 pos.do_move(bestMove, st);
471 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
472 pos.undo_move(bestMove); // Return from think() with unchanged position
476 // This makes all the threads to go to sleep
479 // If we are pondering or in infinite search, we shouldn't print the
480 // best move before we are told to do so.
481 if (!StopRequest && (Limits.ponder || Limits.infinite))
482 wait_for_stop_or_ponderhit();
484 // Could be MOVE_NONE when searching on a stalemate position
485 cout << "bestmove " << bestMove;
487 // UCI protol is not clear on allowing sending an empty ponder move, instead
488 // it is clear that ponder move is optional. So skip it if empty.
489 if (ponderMove != MOVE_NONE)
490 cout << " ponder " << ponderMove;
500 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
501 // with increasing depth until the allocated thinking time has been consumed,
502 // user stops the search, or the maximum search depth is reached.
504 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
506 SearchStack ss[PLY_MAX_PLUS_2];
507 Value bestValues[PLY_MAX_PLUS_2];
508 int bestMoveChanges[PLY_MAX_PLUS_2];
509 int depth, aspirationDelta;
510 Value value, alpha, beta;
511 Move bestMove, easyMove, skillBest, skillPonder;
513 // Initialize stuff before a new search
514 memset(ss, 0, 4 * sizeof(SearchStack));
517 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
518 depth = aspirationDelta = 0;
519 value = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
520 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
522 // Moves to search are verified and copied
523 Rml.init(pos, searchMoves);
525 // Handle special case of searching on a mate/stalemate position
528 cout << "info" << depth_to_uci(DEPTH_ZERO)
529 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
534 // Iterative deepening loop until requested to stop or target depth reached
535 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
537 // Remember best moves and values from previous iteration
538 RootMoveList prevRml = Rml;
540 Rml.bestMoveChanges = 0;
542 // MultiPV iteration loop
543 for (MultiPVIteration = 0; MultiPVIteration < Min(MultiPV, (int)Rml.size()); MultiPVIteration++)
545 // Calculate dynamic aspiration window based on previous iterations
546 if (depth >= 5 && abs(prevRml[MultiPVIteration].pv_score) < VALUE_KNOWN_WIN)
548 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
549 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
551 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
552 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
554 alpha = Max(prevRml[MultiPVIteration].pv_score - aspirationDelta, -VALUE_INFINITE);
555 beta = Min(prevRml[MultiPVIteration].pv_score + aspirationDelta, VALUE_INFINITE);
559 alpha = -VALUE_INFINITE;
560 beta = VALUE_INFINITE;
563 // Start with a small aspiration window and, in case of fail high/low,
564 // research with bigger window until not failing high/low anymore.
566 // Search starting from ss+1 to allow calling update_gains()
567 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
569 // It is critical that sorting is done with a stable algorithm
570 // because all the values but the first are usually set to
571 // -VALUE_INFINITE and we want to keep the same order for all
572 // the moves but the new PV that goes to head.
573 if (value > alpha && value < beta)
574 sort<RootMove>(Rml.begin(), Rml.end());
576 // In MultiPV mode, sort only the tail of the list
577 // until all fail-highs and fail-lows have been resolved
578 sort<RootMove>(Rml.begin() + MultiPVIteration, Rml.end());
580 // Write PV back to transposition table in case the relevant entries
581 // have been overwritten during the search.
582 for (int i = 0; i <= MultiPVIteration; i++)
583 Rml[i].insert_pv_in_tt(pos);
585 // Value cannot be trusted. Break out immediately!
589 // Send full PV info to GUI if we are going to leave the loop or
590 // if we have a fail high/low and we are deep in the search.
591 if ((value > alpha && value < beta) || current_search_time() > 2000)
592 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
594 bool updated = (i <= MultiPVIteration);
596 if (depth == 1 && !updated)
599 const RootMoveList& rml = (updated ? Rml : prevRml);
602 << depth_to_uci((updated ? depth : depth - 1) * ONE_PLY)
603 << (i == MultiPVIteration ? score_to_uci(rml[i].pv_score, alpha, beta)
604 : score_to_uci(rml[i].pv_score))
605 << speed_to_uci(pos.nodes_searched())
606 << pv_to_uci(&rml[i].pv[0], i + 1, pos.is_chess960())
610 // In case of failing high/low increase aspiration window and research,
611 // otherwise exit the fail high/low loop.
614 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
615 aspirationDelta += aspirationDelta / 2;
617 else if (value <= alpha)
619 AspirationFailLow = true;
620 StopOnPonderhit = false;
622 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
623 aspirationDelta += aspirationDelta / 2;
628 } while (abs(value) < VALUE_KNOWN_WIN);
631 // Collect info about search result
632 bestMove = Rml[0].pv[0];
633 *ponderMove = Rml[0].pv[1];
634 bestValues[depth] = value;
635 bestMoveChanges[depth] = Rml.bestMoveChanges;
637 // Do we need to pick now the best and the ponder moves ?
638 if (SkillLevelEnabled && depth == 1 + SkillLevel)
639 do_skill_level(&skillBest, &skillPonder);
641 if (LogFile.is_open())
642 LogFile << pretty_pv(pos, depth, value, current_search_time(), &Rml[0].pv[0]) << endl;
644 // Init easyMove after first iteration or drop if differs from the best move
645 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
647 else if (bestMove != easyMove)
648 easyMove = MOVE_NONE;
650 // Check for some early stop condition
651 if (!StopRequest && Limits.useTimeManagement())
653 // Stop search early if one move seems to be much better than the
654 // others or if there is only a single legal move. Also in the latter
655 // case we search up to some depth anyway to get a proper score.
657 && easyMove == bestMove
659 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
660 && current_search_time() > TimeMgr.available_time() / 16)
661 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
662 && current_search_time() > TimeMgr.available_time() / 32)))
665 // Take in account some extra time if the best move has changed
666 if (depth > 4 && depth < 50)
667 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
669 // Stop search if most of available time is already consumed. We probably don't
670 // have enough time to search the first move at the next iteration anyway.
671 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
674 // If we are allowed to ponder do not stop the search now but keep pondering
675 if (StopRequest && Limits.ponder)
678 StopOnPonderhit = true;
683 // When using skills overwrite best and ponder moves with the sub-optimal ones
684 if (SkillLevelEnabled)
686 if (skillBest == MOVE_NONE) // Still unassigned ?
687 do_skill_level(&skillBest, &skillPonder);
689 bestMove = skillBest;
690 *ponderMove = skillPonder;
697 // search<>() is the main search function for both PV and non-PV nodes and for
698 // normal and SplitPoint nodes. When called just after a split point the search
699 // is simpler because we have already probed the hash table, done a null move
700 // search, and searched the first move before splitting, we don't have to repeat
701 // all this work again. We also don't need to store anything to the hash table
702 // here: This is taken care of after we return from the split point.
704 template <NodeType NT>
705 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
707 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
708 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
709 const bool RootNode = (NT == Root);
711 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
712 assert(beta > alpha && beta <= VALUE_INFINITE);
713 assert(PvNode || alpha == beta - 1);
714 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
716 Move movesSearched[MAX_MOVES];
721 Move ttMove, move, excludedMove, threatMove;
724 Value bestValue, value, oldAlpha;
725 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
726 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
727 int moveCount = 0, playedMoveCount = 0;
728 Thread& thread = Threads[pos.thread()];
729 SplitPoint* sp = NULL;
731 refinedValue = bestValue = value = -VALUE_INFINITE;
733 inCheck = pos.in_check();
734 ss->ply = (ss-1)->ply + 1;
736 // Used to send selDepth info to GUI
737 if (PvNode && thread.maxPly < ss->ply)
738 thread.maxPly = ss->ply;
740 // Step 1. Initialize node and poll. Polling can abort search
743 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
744 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
745 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
751 ttMove = excludedMove = MOVE_NONE;
752 threatMove = sp->threatMove;
753 goto split_point_start;
756 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
762 // Step 2. Check for aborted search and immediate draw
764 || pos.is_draw<false>()
765 || ss->ply > PLY_MAX) && !RootNode)
768 // Step 3. Mate distance pruning
771 alpha = Max(value_mated_in(ss->ply), alpha);
772 beta = Min(value_mate_in(ss->ply+1), beta);
777 // Step 4. Transposition table lookup
778 // We don't want the score of a partial search to overwrite a previous full search
779 // TT value, so we use a different position key in case of an excluded move.
780 excludedMove = ss->excludedMove;
781 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
782 tte = TT.probe(posKey);
783 ttMove = tte ? tte->move() : MOVE_NONE;
785 // At PV nodes we check for exact scores, while at non-PV nodes we check for
786 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
787 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
788 // we should also update RootMoveList to avoid bogus output.
789 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
790 : ok_to_use_TT(tte, depth, beta, ss->ply)))
793 ss->bestMove = ttMove; // Can be MOVE_NONE
794 return value_from_tt(tte->value(), ss->ply);
797 // Step 5. Evaluate the position statically and update parent's gain statistics
799 ss->eval = ss->evalMargin = VALUE_NONE;
802 assert(tte->static_value() != VALUE_NONE);
804 ss->eval = tte->static_value();
805 ss->evalMargin = tte->static_value_margin();
806 refinedValue = refine_eval(tte, ss->eval, ss->ply);
810 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
811 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
814 // Save gain for the parent non-capture move
815 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
817 // Step 6. Razoring (is omitted in PV nodes)
819 && depth < RazorDepth
821 && refinedValue + razor_margin(depth) < beta
822 && ttMove == MOVE_NONE
823 && abs(beta) < VALUE_MATE_IN_PLY_MAX
824 && !pos.has_pawn_on_7th(pos.side_to_move()))
826 Value rbeta = beta - razor_margin(depth);
827 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
829 // Logically we should return (v + razor_margin(depth)), but
830 // surprisingly this did slightly weaker in tests.
834 // Step 7. Static null move pruning (is omitted in PV nodes)
835 // We're betting that the opponent doesn't have a move that will reduce
836 // the score by more than futility_margin(depth) if we do a null move.
839 && depth < RazorDepth
841 && refinedValue - futility_margin(depth, 0) >= beta
842 && abs(beta) < VALUE_MATE_IN_PLY_MAX
843 && pos.non_pawn_material(pos.side_to_move()))
844 return refinedValue - futility_margin(depth, 0);
846 // Step 8. Null move search with verification search (is omitted in PV nodes)
851 && refinedValue >= beta
852 && abs(beta) < VALUE_MATE_IN_PLY_MAX
853 && pos.non_pawn_material(pos.side_to_move()))
855 ss->currentMove = MOVE_NULL;
857 // Null move dynamic reduction based on depth
858 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
860 // Null move dynamic reduction based on value
861 if (refinedValue - PawnValueMidgame > beta)
864 pos.do_null_move(st);
865 (ss+1)->skipNullMove = true;
866 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
867 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
868 (ss+1)->skipNullMove = false;
869 pos.undo_null_move();
871 if (nullValue >= beta)
873 // Do not return unproven mate scores
874 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
877 if (depth < 6 * ONE_PLY)
880 // Do verification search at high depths
881 ss->skipNullMove = true;
882 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
883 ss->skipNullMove = false;
890 // The null move failed low, which means that we may be faced with
891 // some kind of threat. If the previous move was reduced, check if
892 // the move that refuted the null move was somehow connected to the
893 // move which was reduced. If a connection is found, return a fail
894 // low score (which will cause the reduced move to fail high in the
895 // parent node, which will trigger a re-search with full depth).
896 threatMove = (ss+1)->bestMove;
898 if ( depth < ThreatDepth
900 && threatMove != MOVE_NONE
901 && connected_moves(pos, (ss-1)->currentMove, threatMove))
906 // Step 9. ProbCut (is omitted in PV nodes)
907 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
908 // and a reduced search returns a value much above beta, we can (almost) safely
909 // prune the previous move.
911 && depth >= RazorDepth + ONE_PLY
914 && excludedMove == MOVE_NONE
915 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
917 Value rbeta = beta + 200;
918 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
920 assert(rdepth >= ONE_PLY);
922 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
925 while ((move = mp.get_next_move()) != MOVE_NONE)
926 if (pos.pl_move_is_legal(move, ci.pinned))
928 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
929 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
936 // Step 10. Internal iterative deepening
937 if ( depth >= IIDDepth[PvNode]
938 && ttMove == MOVE_NONE
939 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
941 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
943 ss->skipNullMove = true;
944 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
945 ss->skipNullMove = false;
947 tte = TT.probe(posKey);
948 ttMove = tte ? tte->move() : MOVE_NONE;
951 split_point_start: // At split points actual search starts from here
953 // Initialize a MovePicker object for the current position
954 MovePickerExt<NT> mp(pos, RootNode ? Rml[MultiPVIteration].pv[0] : ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
956 ss->bestMove = MOVE_NONE;
957 futilityBase = ss->eval + ss->evalMargin;
958 singularExtensionNode = !RootNode
960 && depth >= SingularExtensionDepth[PvNode]
961 && ttMove != MOVE_NONE
962 && !excludedMove // Do not allow recursive singular extension search
963 && (tte->type() & VALUE_TYPE_LOWER)
964 && tte->depth() >= depth - 3 * ONE_PLY;
967 lock_grab(&(sp->lock));
968 bestValue = sp->bestValue;
971 // Step 11. Loop through moves
972 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
973 while ( bestValue < beta
974 && (move = mp.get_next_move()) != MOVE_NONE
975 && !thread.cutoff_occurred())
977 assert(move_is_ok(move));
979 if (move == excludedMove)
982 // At root obey the "searchmoves" option and skip moves not listed in Root Move List.
983 // Also in MultiPV mode we skip moves which already have got an exact score
984 // in previous MultiPV Iteration.
985 if (RootNode && !Rml.find(move, MultiPVIteration))
988 // At PV and SpNode nodes we want all moves to be legal since the beginning
989 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
994 moveCount = ++sp->moveCount;
995 lock_release(&(sp->lock));
1002 // This is used by time management
1003 FirstRootMove = (moveCount == 1);
1005 // Save the current node count before the move is searched
1006 nodes = pos.nodes_searched();
1008 // If it's time to send nodes info, do it here where we have the
1009 // correct accumulated node counts searched by each thread.
1010 if (SendSearchedNodes)
1012 SendSearchedNodes = false;
1013 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1016 // For long searches send current move info to GUI
1017 if (current_search_time() > 2000)
1018 cout << "info" << depth_to_uci(depth)
1019 << " currmove " << move << " currmovenumber " << moveCount + MultiPVIteration << endl;
1022 // At Root and at first iteration do a PV search on all the moves to score root moves
1023 isPvMove = (PvNode && moveCount <= ((RootNode && depth <= ONE_PLY) ? MAX_MOVES : 1));
1024 givesCheck = pos.move_gives_check(move, ci);
1025 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1027 // Step 12. Decide the new search depth
1028 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1030 // Singular extension search. If all moves but one fail low on a search of
1031 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1032 // is singular and should be extended. To verify this we do a reduced search
1033 // on all the other moves but the ttMove, if result is lower than ttValue minus
1034 // a margin then we extend ttMove.
1035 if ( singularExtensionNode
1037 && pos.pl_move_is_legal(move, ci.pinned)
1040 Value ttValue = value_from_tt(tte->value(), ss->ply);
1042 if (abs(ttValue) < VALUE_KNOWN_WIN)
1044 Value rBeta = ttValue - int(depth);
1045 ss->excludedMove = move;
1046 ss->skipNullMove = true;
1047 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1048 ss->skipNullMove = false;
1049 ss->excludedMove = MOVE_NONE;
1050 ss->bestMove = MOVE_NONE;
1056 // Update current move (this must be done after singular extension search)
1057 newDepth = depth - ONE_PLY + ext;
1059 // Step 13. Futility pruning (is omitted in PV nodes)
1061 && !captureOrPromotion
1065 && !move_is_castle(move))
1067 // Move count based pruning
1068 if ( moveCount >= futility_move_count(depth)
1069 && (!threatMove || !connected_threat(pos, move, threatMove))
1070 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1073 lock_grab(&(sp->lock));
1078 // Value based pruning
1079 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1080 // but fixing this made program slightly weaker.
1081 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1082 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1083 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1085 if (futilityValueScaled < beta)
1089 lock_grab(&(sp->lock));
1090 if (futilityValueScaled > sp->bestValue)
1091 sp->bestValue = bestValue = futilityValueScaled;
1093 else if (futilityValueScaled > bestValue)
1094 bestValue = futilityValueScaled;
1099 // Prune moves with negative SEE at low depths
1100 if ( predictedDepth < 2 * ONE_PLY
1101 && bestValue > VALUE_MATED_IN_PLY_MAX
1102 && pos.see_sign(move) < 0)
1105 lock_grab(&(sp->lock));
1111 // Check for legality only before to do the move
1112 if (!pos.pl_move_is_legal(move, ci.pinned))
1118 ss->currentMove = move;
1119 if (!SpNode && !captureOrPromotion)
1120 movesSearched[playedMoveCount++] = move;
1122 // Step 14. Make the move
1123 pos.do_move(move, st, ci, givesCheck);
1125 // Step extra. pv search (only in PV nodes)
1126 // The first move in list is the expected PV
1128 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1129 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1132 // Step 15. Reduced depth search
1133 // If the move fails high will be re-searched at full depth.
1134 bool doFullDepthSearch = true;
1136 if ( depth > 3 * ONE_PLY
1137 && !captureOrPromotion
1139 && !move_is_castle(move)
1140 && ss->killers[0] != move
1141 && ss->killers[1] != move
1142 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1144 Depth d = newDepth - ss->reduction;
1145 alpha = SpNode ? sp->alpha : alpha;
1147 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1148 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1150 ss->reduction = DEPTH_ZERO;
1151 doFullDepthSearch = (value > alpha);
1154 // Step 16. Full depth search
1155 if (doFullDepthSearch)
1157 alpha = SpNode ? sp->alpha : alpha;
1158 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1159 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1161 // Step extra. pv search (only in PV nodes)
1162 // Search only for possible new PV nodes, if instead value >= beta then
1163 // parent node fails low with value <= alpha and tries another move.
1164 if (PvNode && value > alpha && (RootNode || value < beta))
1165 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1166 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1170 // Step 17. Undo move
1171 pos.undo_move(move);
1173 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1175 // Step 18. Check for new best move
1178 lock_grab(&(sp->lock));
1179 bestValue = sp->bestValue;
1183 if (value > bestValue)
1186 ss->bestMove = move;
1191 && value < beta) // We want always alpha < beta
1194 if (SpNode && !thread.cutoff_occurred())
1196 sp->bestValue = value;
1197 sp->ss->bestMove = move;
1199 sp->is_betaCutoff = (value >= beta);
1205 // Finished searching the move. If StopRequest is true, the search
1206 // was aborted because the user interrupted the search or because we
1207 // ran out of time. In this case, the return value of the search cannot
1208 // be trusted, and we break out of the loop without updating the best
1213 // Remember searched nodes counts for this move
1214 RootMove* rm = Rml.find(move);
1215 rm->nodes += pos.nodes_searched() - nodes;
1217 // PV move or new best move ?
1218 if (isPvMove || value > alpha)
1221 rm->pv_score = value;
1222 rm->extract_pv_from_tt(pos);
1224 // We record how often the best move has been changed in each
1225 // iteration. This information is used for time management: When
1226 // the best move changes frequently, we allocate some more time.
1227 if (!isPvMove && MultiPV == 1)
1228 Rml.bestMoveChanges++;
1235 // All other moves but the PV are set to the lowest value, this
1236 // is not a problem when sorting becuase sort is stable and move
1237 // position in the list is preserved, just the PV is pushed up.
1238 rm->pv_score = -VALUE_INFINITE;
1242 // Step 19. Check for split
1245 && depth >= Threads.min_split_depth()
1247 && Threads.available_slave_exists(pos.thread())
1249 && !thread.cutoff_occurred())
1250 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1251 threatMove, moveCount, &mp, PvNode);
1254 // Step 20. Check for mate and stalemate
1255 // All legal moves have been searched and if there are
1256 // no legal moves, it must be mate or stalemate.
1257 // If one move was excluded return fail low score.
1258 if (!SpNode && !moveCount)
1259 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1261 // Step 21. Update tables
1262 // If the search is not aborted, update the transposition table,
1263 // history counters, and killer moves.
1264 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1266 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1267 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1268 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1270 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1272 // Update killers and history only for non capture moves that fails high
1273 if ( bestValue >= beta
1274 && !pos.move_is_capture_or_promotion(move))
1276 if (move != ss->killers[0])
1278 ss->killers[1] = ss->killers[0];
1279 ss->killers[0] = move;
1281 update_history(pos, move, depth, movesSearched, playedMoveCount);
1287 // Here we have the lock still grabbed
1288 sp->is_slave[pos.thread()] = false;
1289 sp->nodes += pos.nodes_searched();
1290 lock_release(&(sp->lock));
1293 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1298 // qsearch() is the quiescence search function, which is called by the main
1299 // search function when the remaining depth is zero (or, to be more precise,
1300 // less than ONE_PLY).
1302 template <NodeType NT>
1303 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1305 const bool PvNode = (NT == PV);
1307 assert(NT == PV || NT == NonPV);
1308 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1309 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1310 assert(PvNode || alpha == beta - 1);
1312 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1316 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1317 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1320 Value oldAlpha = alpha;
1322 ss->bestMove = ss->currentMove = MOVE_NONE;
1323 ss->ply = (ss-1)->ply + 1;
1325 // Check for an instant draw or maximum ply reached
1326 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1329 // Decide whether or not to include checks, this fixes also the type of
1330 // TT entry depth that we are going to use. Note that in qsearch we use
1331 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1332 inCheck = pos.in_check();
1333 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1335 // Transposition table lookup. At PV nodes, we don't use the TT for
1336 // pruning, but only for move ordering.
1337 tte = TT.probe(pos.get_key());
1338 ttMove = (tte ? tte->move() : MOVE_NONE);
1340 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1342 ss->bestMove = ttMove; // Can be MOVE_NONE
1343 return value_from_tt(tte->value(), ss->ply);
1346 // Evaluate the position statically
1349 bestValue = futilityBase = -VALUE_INFINITE;
1350 ss->eval = evalMargin = VALUE_NONE;
1351 enoughMaterial = false;
1357 assert(tte->static_value() != VALUE_NONE);
1359 evalMargin = tte->static_value_margin();
1360 ss->eval = bestValue = tte->static_value();
1363 ss->eval = bestValue = evaluate(pos, evalMargin);
1365 // Stand pat. Return immediately if static value is at least beta
1366 if (bestValue >= beta)
1369 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1374 if (PvNode && bestValue > alpha)
1377 // Futility pruning parameters, not needed when in check
1378 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1379 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1382 // Initialize a MovePicker object for the current position, and prepare
1383 // to search the moves. Because the depth is <= 0 here, only captures,
1384 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1386 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1389 // Loop through the moves until no moves remain or a beta cutoff occurs
1390 while ( alpha < beta
1391 && (move = mp.get_next_move()) != MOVE_NONE)
1393 assert(move_is_ok(move));
1395 givesCheck = pos.move_gives_check(move, ci);
1403 && !move_is_promotion(move)
1404 && !pos.move_is_passed_pawn_push(move))
1406 futilityValue = futilityBase
1407 + piece_value_endgame(pos.piece_on(move_to(move)))
1408 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1410 if (futilityValue < alpha)
1412 if (futilityValue > bestValue)
1413 bestValue = futilityValue;
1417 // Prune moves with negative or equal SEE
1418 if ( futilityBase < beta
1419 && depth < DEPTH_ZERO
1420 && pos.see(move) <= 0)
1424 // Detect non-capture evasions that are candidate to be pruned
1425 evasionPrunable = !PvNode
1427 && bestValue > VALUE_MATED_IN_PLY_MAX
1428 && !pos.move_is_capture(move)
1429 && !pos.can_castle(pos.side_to_move());
1431 // Don't search moves with negative SEE values
1433 && (!inCheck || evasionPrunable)
1435 && !move_is_promotion(move)
1436 && pos.see_sign(move) < 0)
1439 // Don't search useless checks
1444 && !pos.move_is_capture_or_promotion(move)
1445 && ss->eval + PawnValueMidgame / 4 < beta
1446 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1448 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1449 bestValue = ss->eval + PawnValueMidgame / 4;
1454 // Check for legality only before to do the move
1455 if (!pos.pl_move_is_legal(move, ci.pinned))
1458 // Update current move
1459 ss->currentMove = move;
1461 // Make and search the move
1462 pos.do_move(move, st, ci, givesCheck);
1463 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1464 pos.undo_move(move);
1466 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1469 if (value > bestValue)
1475 ss->bestMove = move;
1480 // All legal moves have been searched. A special case: If we're in check
1481 // and no legal moves were found, it is checkmate.
1482 if (inCheck && bestValue == -VALUE_INFINITE)
1483 return value_mated_in(ss->ply);
1485 // Update transposition table
1486 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1487 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1489 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1495 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1496 // bestValue is updated only when returning false because in that case move
1499 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1501 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1502 Square from, to, ksq, victimSq;
1505 Value futilityValue, bv = *bestValue;
1507 from = move_from(move);
1509 them = opposite_color(pos.side_to_move());
1510 ksq = pos.king_square(them);
1511 kingAtt = pos.attacks_from<KING>(ksq);
1512 pc = pos.piece_on(from);
1514 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1515 oldAtt = pos.attacks_from(pc, from, occ);
1516 newAtt = pos.attacks_from(pc, to, occ);
1518 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1519 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1521 if (!(b && (b & (b - 1))))
1524 // Rule 2. Queen contact check is very dangerous
1525 if ( piece_type(pc) == QUEEN
1526 && bit_is_set(kingAtt, to))
1529 // Rule 3. Creating new double threats with checks
1530 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1534 victimSq = pop_1st_bit(&b);
1535 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1537 // Note that here we generate illegal "double move"!
1538 if ( futilityValue >= beta
1539 && pos.see_sign(make_move(from, victimSq)) >= 0)
1542 if (futilityValue > bv)
1546 // Update bestValue only if check is not dangerous (because we will prune the move)
1552 // connected_moves() tests whether two moves are 'connected' in the sense
1553 // that the first move somehow made the second move possible (for instance
1554 // if the moving piece is the same in both moves). The first move is assumed
1555 // to be the move that was made to reach the current position, while the
1556 // second move is assumed to be a move from the current position.
1558 bool connected_moves(const Position& pos, Move m1, Move m2) {
1560 Square f1, t1, f2, t2;
1564 assert(m1 && move_is_ok(m1));
1565 assert(m2 && move_is_ok(m2));
1567 // Case 1: The moving piece is the same in both moves
1573 // Case 2: The destination square for m2 was vacated by m1
1579 // Case 3: Moving through the vacated square
1580 p2 = pos.piece_on(f2);
1581 if ( piece_is_slider(p2)
1582 && bit_is_set(squares_between(f2, t2), f1))
1585 // Case 4: The destination square for m2 is defended by the moving piece in m1
1586 p1 = pos.piece_on(t1);
1587 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1590 // Case 5: Discovered check, checking piece is the piece moved in m1
1591 ksq = pos.king_square(pos.side_to_move());
1592 if ( piece_is_slider(p1)
1593 && bit_is_set(squares_between(t1, ksq), f2))
1595 Bitboard occ = pos.occupied_squares();
1596 clear_bit(&occ, f2);
1597 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1604 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1605 // "plies to mate from the current ply". Non-mate scores are unchanged.
1606 // The function is called before storing a value to the transposition table.
1608 Value value_to_tt(Value v, int ply) {
1610 if (v >= VALUE_MATE_IN_PLY_MAX)
1613 if (v <= VALUE_MATED_IN_PLY_MAX)
1620 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1621 // the transposition table to a mate score corrected for the current ply.
1623 Value value_from_tt(Value v, int ply) {
1625 if (v >= VALUE_MATE_IN_PLY_MAX)
1628 if (v <= VALUE_MATED_IN_PLY_MAX)
1635 // connected_threat() tests whether it is safe to forward prune a move or if
1636 // is somehow connected to the threat move returned by null search.
1638 bool connected_threat(const Position& pos, Move m, Move threat) {
1640 assert(move_is_ok(m));
1641 assert(threat && move_is_ok(threat));
1642 assert(!pos.move_is_capture_or_promotion(m));
1643 assert(!pos.move_is_passed_pawn_push(m));
1645 Square mfrom, mto, tfrom, tto;
1647 mfrom = move_from(m);
1649 tfrom = move_from(threat);
1650 tto = move_to(threat);
1652 // Case 1: Don't prune moves which move the threatened piece
1656 // Case 2: If the threatened piece has value less than or equal to the
1657 // value of the threatening piece, don't prune moves which defend it.
1658 if ( pos.move_is_capture(threat)
1659 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1660 || piece_type(pos.piece_on(tfrom)) == KING)
1661 && pos.move_attacks_square(m, tto))
1664 // Case 3: If the moving piece in the threatened move is a slider, don't
1665 // prune safe moves which block its ray.
1666 if ( piece_is_slider(pos.piece_on(tfrom))
1667 && bit_is_set(squares_between(tfrom, tto), mto)
1668 && pos.see_sign(m) >= 0)
1675 // ok_to_use_TT() returns true if a transposition table score
1676 // can be used at a given point in search.
1678 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1680 Value v = value_from_tt(tte->value(), ply);
1682 return ( tte->depth() >= depth
1683 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1684 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1686 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1687 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1691 // refine_eval() returns the transposition table score if
1692 // possible otherwise falls back on static position evaluation.
1694 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1698 Value v = value_from_tt(tte->value(), ply);
1700 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1701 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1708 // update_history() registers a good move that produced a beta-cutoff
1709 // in history and marks as failures all the other moves of that ply.
1711 void update_history(const Position& pos, Move move, Depth depth,
1712 Move movesSearched[], int moveCount) {
1714 Value bonus = Value(int(depth) * int(depth));
1716 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1718 for (int i = 0; i < moveCount - 1; i++)
1720 m = movesSearched[i];
1724 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1729 // update_gains() updates the gains table of a non-capture move given
1730 // the static position evaluation before and after the move.
1732 void update_gains(const Position& pos, Move m, Value before, Value after) {
1735 && before != VALUE_NONE
1736 && after != VALUE_NONE
1737 && pos.captured_piece_type() == PIECE_TYPE_NONE
1738 && !move_is_special(m))
1739 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1743 // current_search_time() returns the number of milliseconds which have passed
1744 // since the beginning of the current search.
1746 int current_search_time(int set) {
1748 static int searchStartTime;
1751 searchStartTime = set;
1753 return get_system_time() - searchStartTime;
1757 // score_to_uci() converts a value to a string suitable for use with the UCI
1758 // protocol specifications:
1760 // cp <x> The score from the engine's point of view in centipawns.
1761 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1762 // use negative values for y.
1764 string score_to_uci(Value v, Value alpha, Value beta) {
1766 std::stringstream s;
1768 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1769 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1771 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1773 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1779 // speed_to_uci() returns a string with time stats of current search suitable
1780 // to be sent to UCI gui.
1782 string speed_to_uci(int64_t nodes) {
1784 std::stringstream s;
1785 int t = current_search_time();
1787 s << " nodes " << nodes
1788 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1794 // pv_to_uci() returns a string with information on the current PV line
1795 // formatted according to UCI specification.
1797 string pv_to_uci(const Move pv[], int pvNum, bool chess960) {
1799 std::stringstream s;
1801 s << " multipv " << pvNum << " pv " << set960(chess960);
1803 for ( ; *pv != MOVE_NONE; pv++)
1809 // depth_to_uci() returns a string with information on the current depth and
1810 // seldepth formatted according to UCI specification.
1812 string depth_to_uci(Depth depth) {
1814 std::stringstream s;
1816 // Retrieve max searched depth among threads
1818 for (int i = 0; i < Threads.size(); i++)
1819 if (Threads[i].maxPly > selDepth)
1820 selDepth = Threads[i].maxPly;
1822 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1827 string time_to_string(int millisecs) {
1829 const int MSecMinute = 1000 * 60;
1830 const int MSecHour = 1000 * 60 * 60;
1832 int hours = millisecs / MSecHour;
1833 int minutes = (millisecs % MSecHour) / MSecMinute;
1834 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1836 std::stringstream s;
1841 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1845 string score_to_string(Value v) {
1847 std::stringstream s;
1849 if (v >= VALUE_MATE_IN_PLY_MAX)
1850 s << "#" << (VALUE_MATE - v + 1) / 2;
1851 else if (v <= VALUE_MATED_IN_PLY_MAX)
1852 s << "-#" << (VALUE_MATE + v) / 2;
1854 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1859 // pretty_pv() creates a human-readable string from a position and a PV.
1860 // It is used to write search information to the log file (which is created
1861 // when the UCI parameter "Use Search Log" is "true").
1863 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1865 const int64_t K = 1000;
1866 const int64_t M = 1000000;
1867 const int startColumn = 28;
1868 const size_t maxLength = 80 - startColumn;
1870 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1873 std::stringstream s;
1876 // First print depth, score, time and searched nodes...
1877 s << set960(pos.is_chess960())
1878 << std::setw(2) << depth
1879 << std::setw(8) << score_to_string(value)
1880 << std::setw(8) << time_to_string(time);
1882 if (pos.nodes_searched() < M)
1883 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1884 else if (pos.nodes_searched() < K * M)
1885 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1887 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1889 // ...then print the full PV line in short algebraic notation
1890 while (*m != MOVE_NONE)
1892 san = move_to_san(pos, *m);
1893 length += san.length() + 1;
1895 if (length > maxLength)
1897 length = san.length() + 1;
1898 s << "\n" + string(startColumn, ' ');
1902 pos.do_move(*m++, *st++);
1905 // Restore original position before to leave
1906 while (m != pv) pos.undo_move(*--m);
1911 // poll() performs two different functions: It polls for user input, and it
1912 // looks at the time consumed so far and decides if it's time to abort the
1915 void poll(const Position& pos) {
1917 static int lastInfoTime;
1918 int t = current_search_time();
1921 if (input_available())
1923 // We are line oriented, don't read single chars
1926 if (!std::getline(std::cin, command) || command == "quit")
1928 // Quit the program as soon as possible
1929 Limits.ponder = false;
1930 QuitRequest = StopRequest = true;
1933 else if (command == "stop")
1935 // Stop calculating as soon as possible, but still send the "bestmove"
1936 // and possibly the "ponder" token when finishing the search.
1937 Limits.ponder = false;
1940 else if (command == "ponderhit")
1942 // The opponent has played the expected move. GUI sends "ponderhit" if
1943 // we were told to ponder on the same move the opponent has played. We
1944 // should continue searching but switching from pondering to normal search.
1945 Limits.ponder = false;
1947 if (StopOnPonderhit)
1952 // Print search information
1956 else if (lastInfoTime > t)
1957 // HACK: Must be a new search where we searched less than
1958 // NodesBetweenPolls nodes during the first second of search.
1961 else if (t - lastInfoTime >= 1000)
1966 dbg_print_hit_rate();
1968 // Send info on searched nodes as soon as we return to root
1969 SendSearchedNodes = true;
1972 // Should we stop the search?
1976 bool stillAtFirstMove = FirstRootMove
1977 && !AspirationFailLow
1978 && t > TimeMgr.available_time();
1980 bool noMoreTime = t > TimeMgr.maximum_time()
1981 || stillAtFirstMove;
1983 if ( (Limits.useTimeManagement() && noMoreTime)
1984 || (Limits.maxTime && t >= Limits.maxTime)
1985 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1990 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1991 // while the program is pondering. The point is to work around a wrinkle in
1992 // the UCI protocol: When pondering, the engine is not allowed to give a
1993 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1994 // We simply wait here until one of these commands is sent, and return,
1995 // after which the bestmove and pondermove will be printed.
1997 void wait_for_stop_or_ponderhit() {
2001 // Wait for a command from stdin
2002 while ( std::getline(std::cin, command)
2003 && command != "ponderhit" && command != "stop" && command != "quit") {};
2005 if (command != "ponderhit" && command != "stop")
2006 QuitRequest = true; // Must be "quit" or getline() returned false
2010 // When playing with strength handicap choose best move among the MultiPV set
2011 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2012 void do_skill_level(Move* best, Move* ponder) {
2014 assert(MultiPV > 1);
2018 // Rml list is already sorted by pv_score in descending order
2020 int max_s = -VALUE_INFINITE;
2021 int size = Min(MultiPV, (int)Rml.size());
2022 int max = Rml[0].pv_score;
2023 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2024 int wk = 120 - 2 * SkillLevel;
2026 // PRNG sequence should be non deterministic
2027 for (int i = abs(get_system_time() % 50); i > 0; i--)
2028 rk.rand<unsigned>();
2030 // Choose best move. For each move's score we add two terms both dependent
2031 // on wk, one deterministic and bigger for weaker moves, and one random,
2032 // then we choose the move with the resulting highest score.
2033 for (int i = 0; i < size; i++)
2035 s = Rml[i].pv_score;
2037 // Don't allow crazy blunders even at very low skills
2038 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2041 // This is our magical formula
2042 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
2047 *best = Rml[i].pv[0];
2048 *ponder = Rml[i].pv[1];
2054 /// RootMove and RootMoveList method's definitions
2056 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2059 bestMoveChanges = 0;
2062 // Generate all legal moves and add them to RootMoveList
2063 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2065 // If we have a searchMoves[] list then verify the move
2066 // is in the list before to add it.
2067 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2069 if (sm != searchMoves && *sm != ml.move())
2073 rm.pv.push_back(ml.move());
2074 rm.pv.push_back(MOVE_NONE);
2075 rm.pv_score = -VALUE_INFINITE;
2081 RootMove* RootMoveList::find(const Move& m, int startIndex) {
2083 for (size_t i = startIndex; i < size(); i++)
2084 if ((*this)[i].pv[0] == m)
2090 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2091 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2092 // allow to always have a ponder move even when we fail high at root and also a
2093 // long PV to print that is important for position analysis.
2095 void RootMove::extract_pv_from_tt(Position& pos) {
2097 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2102 assert(m != MOVE_NONE && pos.move_is_pl(m));
2106 pos.do_move(m, *st++);
2108 while ( (tte = TT.probe(pos.get_key())) != NULL
2109 && tte->move() != MOVE_NONE
2110 && pos.move_is_pl(tte->move())
2111 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2113 && (!pos.is_draw<false>() || ply < 2))
2115 pv.push_back(tte->move());
2116 pos.do_move(tte->move(), *st++);
2119 pv.push_back(MOVE_NONE);
2121 do pos.undo_move(pv[--ply]); while (ply);
2124 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2125 // the PV back into the TT. This makes sure the old PV moves are searched
2126 // first, even if the old TT entries have been overwritten.
2128 void RootMove::insert_pv_in_tt(Position& pos) {
2130 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2133 Value v, m = VALUE_NONE;
2136 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2142 // Don't overwrite existing correct entries
2143 if (!tte || tte->move() != pv[ply])
2145 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2146 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2148 pos.do_move(pv[ply], *st++);
2150 } while (pv[++ply] != MOVE_NONE);
2152 do pos.undo_move(pv[--ply]); while (ply);
2157 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2158 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2159 // object for which the current thread is the master.
2161 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2163 assert(threadID >= 0 && threadID < MAX_THREADS);
2170 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2171 // master should exit as last one.
2172 if (allThreadsShouldExit)
2175 threads[threadID].state = Thread::TERMINATED;
2179 // If we are not thinking, wait for a condition to be signaled
2180 // instead of wasting CPU time polling for work.
2181 while ( threadID >= activeThreads
2182 || threads[threadID].state == Thread::INITIALIZING
2183 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2185 assert(!sp || useSleepingThreads);
2186 assert(threadID != 0 || useSleepingThreads);
2188 if (threads[threadID].state == Thread::INITIALIZING)
2189 threads[threadID].state = Thread::AVAILABLE;
2191 // Grab the lock to avoid races with Thread::wake_up()
2192 lock_grab(&threads[threadID].sleepLock);
2194 // If we are master and all slaves have finished do not go to sleep
2195 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2196 allFinished = (i == activeThreads);
2198 if (allFinished || allThreadsShouldExit)
2200 lock_release(&threads[threadID].sleepLock);
2204 // Do sleep here after retesting sleep conditions
2205 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2206 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2208 lock_release(&threads[threadID].sleepLock);
2211 // If this thread has been assigned work, launch a search
2212 if (threads[threadID].state == Thread::WORKISWAITING)
2214 assert(!allThreadsShouldExit);
2216 threads[threadID].state = Thread::SEARCHING;
2218 // Copy split point position and search stack and call search()
2219 // with SplitPoint template parameter set to true.
2220 SearchStack ss[PLY_MAX_PLUS_2];
2221 SplitPoint* tsp = threads[threadID].splitPoint;
2222 Position pos(*tsp->pos, threadID);
2224 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2228 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2230 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2232 assert(threads[threadID].state == Thread::SEARCHING);
2234 threads[threadID].state = Thread::AVAILABLE;
2236 // Wake up master thread so to allow it to return from the idle loop in
2237 // case we are the last slave of the split point.
2238 if ( useSleepingThreads
2239 && threadID != tsp->master
2240 && threads[tsp->master].state == Thread::AVAILABLE)
2241 threads[tsp->master].wake_up();
2244 // If this thread is the master of a split point and all slaves have
2245 // finished their work at this split point, return from the idle loop.
2246 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2247 allFinished = (i == activeThreads);
2251 // Because sp->slaves[] is reset under lock protection,
2252 // be sure sp->lock has been released before to return.
2253 lock_grab(&(sp->lock));
2254 lock_release(&(sp->lock));
2256 // In helpful master concept a master can help only a sub-tree, and
2257 // because here is all finished is not possible master is booked.
2258 assert(threads[threadID].state == Thread::AVAILABLE);
2260 threads[threadID].state = Thread::SEARCHING;