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/>.
39 #include "ucioption.h"
46 // Set to true to force running with one thread. Used for debugging
47 const bool FakeSplit = false;
49 // Different node types, used as template parameter
50 enum NodeType { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
52 // RootMove struct is used for moves at the root of the tree. For each root
53 // move, we store two scores, a node count, and a PV (really a refutation
54 // in the case of moves which fail low). Value pv_score is normally set at
55 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
56 // according to the order in which moves are returned by MovePicker.
60 RootMove(const RootMove& rm) { *this = rm; }
61 RootMove& operator=(const RootMove& rm);
63 // RootMove::operator<() is the comparison function used when
64 // sorting the moves. A move m1 is considered to be better
65 // than a move m2 if it has an higher pv_score, or if it has
66 // equal pv_score but m1 has the higher non_pv_score. In this way
67 // we are guaranteed that PV moves are always sorted as first.
68 bool operator<(const RootMove& m) const {
69 return pv_score != m.pv_score ? pv_score < m.pv_score
70 : non_pv_score < m.non_pv_score;
73 void extract_pv_from_tt(Position& pos);
74 void insert_pv_in_tt(Position& pos);
75 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
76 Value alpha, Value beta, int pvIdx);
80 Move pv[PLY_MAX_PLUS_2];
83 // RootMoveList struct is just a vector of RootMove objects,
84 // with an handful of methods above the standard ones.
85 struct RootMoveList : public std::vector<RootMove> {
87 typedef std::vector<RootMove> Base;
89 void init(Position& pos, Move searchMoves[]);
90 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
91 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
96 // MovePickerExt template class extends MovePicker and allows to choose at compile
97 // time the proper moves source according to the type of node. In the default case
98 // we simply create and use a standard MovePicker object.
99 template<NodeType> struct MovePickerExt : public MovePicker {
101 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
102 : MovePicker(p, ttm, d, h, ss, b) {}
104 RootMoveList::iterator rm; // Dummy, needed to compile
107 // In case of a SpNode we use split point's shared MovePicker object as moves source
108 template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
110 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
111 : MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
113 Move get_next_move() { return mp->get_next_move(); }
117 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
119 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
120 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
123 // In case of a Root node we use RootMoveList as moves source
124 template<> struct MovePickerExt<Root> : public MovePicker {
126 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
127 Move get_next_move();
129 RootMoveList::iterator rm;
136 // Lookup table to check if a Piece is a slider and its access function
137 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
138 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
142 // Maximum depth for razoring
143 const Depth RazorDepth = 4 * ONE_PLY;
145 // Dynamic razoring margin based on depth
146 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
148 // Maximum depth for use of dynamic threat detection when null move fails low
149 const Depth ThreatDepth = 5 * ONE_PLY;
151 // Step 9. Internal iterative deepening
153 // Minimum depth for use of internal iterative deepening
154 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
156 // At Non-PV nodes we do an internal iterative deepening search
157 // when the static evaluation is bigger then beta - IIDMargin.
158 const Value IIDMargin = Value(0x100);
160 // Step 11. Decide the new search depth
162 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
163 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
164 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
165 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
166 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
168 // Minimum depth for use of singular extension
169 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
171 // Step 12. Futility pruning
173 // Futility margin for quiescence search
174 const Value FutilityMarginQS = Value(0x80);
176 // Futility lookup tables (initialized at startup) and their access functions
177 Value FutilityMargins[16][64]; // [depth][moveNumber]
178 int FutilityMoveCounts[32]; // [depth]
180 inline Value futility_margin(Depth d, int mn) {
182 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
183 : 2 * VALUE_INFINITE;
186 inline int futility_move_count(Depth d) {
188 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
191 // Step 14. Reduced search
193 // Reduction lookup tables (initialized at startup) and their access function
194 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
196 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
198 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
201 // Easy move margin. An easy move candidate must be at least this much
202 // better than the second best move.
203 const Value EasyMoveMargin = Value(0x200);
206 /// Namespace variables
212 int MultiPV, UCIMultiPV;
214 // Time management variables
215 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
220 std::ofstream LogFile;
222 // Skill level adjustment
224 bool SkillLevelEnabled;
226 // Node counters, used only by thread[0] but try to keep in different cache
227 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
228 bool SendSearchedNodes;
230 int NodesBetweenPolls = 30000;
238 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
240 template <NodeType NT>
241 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
243 template <NodeType NT>
244 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
246 template <bool PvNode>
247 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
249 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
250 bool connected_moves(const Position& pos, Move m1, Move m2);
251 Value value_to_tt(Value v, int ply);
252 Value value_from_tt(Value v, int ply);
253 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
254 bool connected_threat(const Position& pos, Move m, Move threat);
255 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
256 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
257 void update_gains(const Position& pos, Move move, Value before, Value after);
258 void do_skill_level(Move* best, Move* ponder);
260 int current_search_time(int set = 0);
261 std::string value_to_uci(Value v);
262 std::string speed_to_uci(int64_t nodes);
263 void poll(const Position& pos);
264 void wait_for_stop_or_ponderhit();
266 // Overload operator<<() to make it easier to print moves in a coordinate
267 // notation compatible with UCI protocol.
268 std::ostream& operator<<(std::ostream& os, Move m) {
270 bool chess960 = (os.iword(0) != 0); // See set960()
271 return os << move_to_uci(m, chess960);
274 // When formatting a move for std::cout we must know if we are in Chess960
275 // or not. To keep using the handy operator<<() on the move the trick is to
276 // embed this flag in the stream itself. Function-like named enum set960 is
277 // used as a custom manipulator and the stream internal general-purpose array,
278 // accessed through ios_base::iword(), is used to pass the flag to the move's
279 // operator<<() that will read it to properly format castling moves.
282 std::ostream& operator<< (std::ostream& os, const set960& f) {
284 os.iword(0) = int(f);
291 /// init_search() is called during startup to initialize various lookup tables
295 int d; // depth (ONE_PLY == 2)
296 int hd; // half depth (ONE_PLY == 1)
299 // Init reductions array
300 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
302 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
303 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
304 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
305 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
308 // Init futility margins array
309 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
310 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
312 // Init futility move count array
313 for (d = 0; d < 32; d++)
314 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
318 /// perft() is our utility to verify move generation. All the leaf nodes up to
319 /// the given depth are generated and counted and the sum returned.
321 int64_t perft(Position& pos, Depth depth) {
323 MoveStack mlist[MAX_MOVES];
328 // Generate all legal moves
329 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
331 // If we are at the last ply we don't need to do and undo
332 // the moves, just to count them.
333 if (depth <= ONE_PLY)
334 return int(last - mlist);
336 // Loop through all legal moves
338 for (MoveStack* cur = mlist; cur != last; cur++)
341 pos.do_move(m, st, ci, pos.move_gives_check(m, ci));
342 sum += perft(pos, depth - ONE_PLY);
349 /// think() is the external interface to Stockfish's search, and is called when
350 /// the program receives the UCI 'go' command. It initializes various global
351 /// variables, and calls id_loop(). It returns false when a "quit" command is
352 /// received during the search.
354 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
358 // Initialize global search-related variables
359 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
361 current_search_time(get_system_time());
363 TimeMgr.init(Limits, pos.startpos_ply_counter());
365 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
367 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
368 else if (Limits.time && Limits.time < 1000)
369 NodesBetweenPolls = 1000;
370 else if (Limits.time && Limits.time < 5000)
371 NodesBetweenPolls = 5000;
373 NodesBetweenPolls = 30000;
375 // Look for a book move
376 if (Options["OwnBook"].value<bool>())
378 if (Options["Book File"].value<std::string>() != book.name())
379 book.open(Options["Book File"].value<std::string>());
381 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
382 if (bookMove != MOVE_NONE)
385 wait_for_stop_or_ponderhit();
387 cout << "bestmove " << bookMove << endl;
393 UCIMultiPV = Options["MultiPV"].value<int>();
394 SkillLevel = Options["Skill Level"].value<int>();
396 read_evaluation_uci_options(pos.side_to_move());
397 Threads.read_uci_options();
399 // If needed allocate pawn and material hash tables and adjust TT size
400 Threads.init_hash_tables();
401 TT.set_size(Options["Hash"].value<int>());
403 if (Options["Clear Hash"].value<bool>())
405 Options["Clear Hash"].set_value("false");
409 // Do we have to play with skill handicap? In this case enable MultiPV that
410 // we will use behind the scenes to retrieve a set of possible moves.
411 SkillLevelEnabled = (SkillLevel < 20);
412 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
414 // Wake up needed threads and reset maxPly counter
415 for (int i = 0; i < Threads.size(); i++)
417 Threads[i].wake_up();
418 Threads[i].maxPly = 0;
421 // Write to log file and keep it open to be accessed during the search
422 if (Options["Use Search Log"].value<bool>())
424 std::string name = Options["Search Log Filename"].value<std::string>();
425 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
427 if (LogFile.is_open())
428 LogFile << "\nSearching: " << pos.to_fen()
429 << "\ninfinite: " << Limits.infinite
430 << " ponder: " << Limits.ponder
431 << " time: " << Limits.time
432 << " increment: " << Limits.increment
433 << " moves to go: " << Limits.movesToGo
437 // We're ready to start thinking. Call the iterative deepening loop function
438 Move ponderMove = MOVE_NONE;
439 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
441 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
443 // Write final search statistics and close log file
444 if (LogFile.is_open())
446 int t = current_search_time();
448 LogFile << "Nodes: " << pos.nodes_searched()
449 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
450 << "\nBest move: " << move_to_san(pos, bestMove);
453 pos.do_move(bestMove, st);
454 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
455 pos.undo_move(bestMove); // Return from think() with unchanged position
459 // This makes all the threads to go to sleep
462 // If we are pondering or in infinite search, we shouldn't print the
463 // best move before we are told to do so.
464 if (!StopRequest && (Limits.ponder || Limits.infinite))
465 wait_for_stop_or_ponderhit();
467 // Could be MOVE_NONE when searching on a stalemate position
468 cout << "bestmove " << bestMove;
470 // UCI protol is not clear on allowing sending an empty ponder move, instead
471 // it is clear that ponder move is optional. So skip it if empty.
472 if (ponderMove != MOVE_NONE)
473 cout << " ponder " << ponderMove;
483 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
484 // with increasing depth until the allocated thinking time has been consumed,
485 // user stops the search, or the maximum search depth is reached.
487 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
489 SearchStack ss[PLY_MAX_PLUS_2];
490 Value bestValues[PLY_MAX_PLUS_2];
491 int bestMoveChanges[PLY_MAX_PLUS_2];
492 int depth, selDepth, aspirationDelta;
493 Value value, alpha, beta;
494 Move bestMove, easyMove, skillBest, skillPonder;
496 // Initialize stuff before a new search
497 memset(ss, 0, 4 * sizeof(SearchStack));
500 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
501 depth = aspirationDelta = 0;
502 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
503 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
505 // Moves to search are verified and copied
506 Rml.init(pos, searchMoves);
508 // Handle special case of searching on a mate/stalemate position
511 cout << "info depth 0 score "
512 << value_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW)
518 // Iterative deepening loop until requested to stop or target depth reached
519 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
521 Rml.bestMoveChanges = 0;
522 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
524 // Calculate dynamic aspiration window based on previous iterations
525 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
527 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
528 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
530 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
531 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
533 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
534 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
537 // Start with a small aspiration window and, in case of fail high/low,
538 // research with bigger window until not failing high/low anymore.
540 // Search starting from ss+1 to allow calling update_gains()
541 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
543 // Write PV back to transposition table in case the relevant entries
544 // have been overwritten during the search.
545 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
546 Rml[i].insert_pv_in_tt(pos);
548 // Value cannot be trusted. Break out immediately!
552 assert(value >= alpha);
554 // In case of failing high/low increase aspiration window and research,
555 // otherwise exit the fail high/low loop.
558 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
559 aspirationDelta += aspirationDelta / 2;
561 else if (value <= alpha)
563 AspirationFailLow = true;
564 StopOnPonderhit = false;
566 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
567 aspirationDelta += aspirationDelta / 2;
572 } while (abs(value) < VALUE_KNOWN_WIN);
574 // Collect info about search result
575 bestMove = Rml[0].pv[0];
576 *ponderMove = Rml[0].pv[1];
577 bestValues[depth] = value;
578 bestMoveChanges[depth] = Rml.bestMoveChanges;
580 // Do we need to pick now the best and the ponder moves ?
581 if (SkillLevelEnabled && depth == 1 + SkillLevel)
582 do_skill_level(&skillBest, &skillPonder);
584 // Retrieve max searched depth among threads
586 for (int i = 0; i < Threads.size(); i++)
587 if (Threads[i].maxPly > selDepth)
588 selDepth = Threads[i].maxPly;
590 // Send PV line to GUI and to log file
591 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
592 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
594 if (LogFile.is_open())
595 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
597 // Init easyMove after first iteration or drop if differs from the best move
598 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
600 else if (bestMove != easyMove)
601 easyMove = MOVE_NONE;
603 // Check for some early stop condition
604 if (!StopRequest && Limits.useTimeManagement())
606 // Stop search early when the last two iterations returned a mate score
608 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
609 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
612 // Stop search early if one move seems to be much better than the
613 // others or if there is only a single legal move. Also in the latter
614 // case we search up to some depth anyway to get a proper score.
616 && easyMove == bestMove
618 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
619 && current_search_time() > TimeMgr.available_time() / 16)
620 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
621 && current_search_time() > TimeMgr.available_time() / 32)))
624 // Take in account some extra time if the best move has changed
625 if (depth > 4 && depth < 50)
626 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
628 // Stop search if most of available time is already consumed. We probably don't
629 // have enough time to search the first move at the next iteration anyway.
630 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
633 // If we are allowed to ponder do not stop the search now but keep pondering
634 if (StopRequest && Limits.ponder)
637 StopOnPonderhit = true;
642 // When using skills overwrite best and ponder moves with the sub-optimal ones
643 if (SkillLevelEnabled)
645 if (skillBest == MOVE_NONE) // Still unassigned ?
646 do_skill_level(&skillBest, &skillPonder);
648 bestMove = skillBest;
649 *ponderMove = skillPonder;
656 // search<>() is the main search function for both PV and non-PV nodes and for
657 // normal and SplitPoint nodes. When called just after a split point the search
658 // is simpler because we have already probed the hash table, done a null move
659 // search, and searched the first move before splitting, we don't have to repeat
660 // all this work again. We also don't need to store anything to the hash table
661 // here: This is taken care of after we return from the split point.
663 template <NodeType NT>
664 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
666 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
667 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
668 const bool RootNode = (NT == Root);
670 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
671 assert(beta > alpha && beta <= VALUE_INFINITE);
672 assert(PvNode || alpha == beta - 1);
673 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
675 Move movesSearched[MAX_MOVES];
681 Move ttMove, move, excludedMove, threatMove;
684 Value bestValue, value, oldAlpha;
685 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
686 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
687 int moveCount = 0, playedMoveCount = 0;
688 int threadID = pos.thread();
689 SplitPoint* sp = NULL;
691 refinedValue = bestValue = value = -VALUE_INFINITE;
693 inCheck = pos.in_check();
694 ss->ply = (ss-1)->ply + 1;
696 // Used to send selDepth info to GUI
697 if (PvNode && Threads[threadID].maxPly < ss->ply)
698 Threads[threadID].maxPly = ss->ply;
704 ttMove = excludedMove = MOVE_NONE;
705 threatMove = sp->threatMove;
706 goto split_point_start;
711 // Step 1. Initialize node and poll. Polling can abort search
712 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
713 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
714 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
716 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
722 // Step 2. Check for aborted search and immediate draw
724 || Threads[threadID].cutoff_occurred()
726 || ss->ply > PLY_MAX) && !RootNode)
729 // Step 3. Mate distance pruning
730 alpha = Max(value_mated_in(ss->ply), alpha);
731 beta = Min(value_mate_in(ss->ply+1), beta);
735 // Step 4. Transposition table lookup
736 // We don't want the score of a partial search to overwrite a previous full search
737 // TT value, so we use a different position key in case of an excluded move.
738 excludedMove = ss->excludedMove;
739 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
741 tte = TT.probe(posKey);
742 ttMove = tte ? tte->move() : MOVE_NONE;
744 // At PV nodes we check for exact scores, while at non-PV nodes we check for
745 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
746 // smooth experience in analysis mode.
749 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
750 : ok_to_use_TT(tte, depth, beta, ss->ply)))
753 ss->bestMove = ttMove; // Can be MOVE_NONE
754 return value_from_tt(tte->value(), ss->ply);
757 // Step 5. Evaluate the position statically and update parent's gain statistics
759 ss->eval = ss->evalMargin = VALUE_NONE;
762 assert(tte->static_value() != VALUE_NONE);
764 ss->eval = tte->static_value();
765 ss->evalMargin = tte->static_value_margin();
766 refinedValue = refine_eval(tte, ss->eval, ss->ply);
770 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
771 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
774 // Save gain for the parent non-capture move
775 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
777 // Step 6. Razoring (is omitted in PV nodes)
779 && depth < RazorDepth
781 && refinedValue + razor_margin(depth) < beta
782 && ttMove == MOVE_NONE
783 && abs(beta) < VALUE_MATE_IN_PLY_MAX
784 && !pos.has_pawn_on_7th(pos.side_to_move()))
786 Value rbeta = beta - razor_margin(depth);
787 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
789 // Logically we should return (v + razor_margin(depth)), but
790 // surprisingly this did slightly weaker in tests.
794 // Step 7. Static null move pruning (is omitted in PV nodes)
795 // We're betting that the opponent doesn't have a move that will reduce
796 // the score by more than futility_margin(depth) if we do a null move.
799 && depth < RazorDepth
801 && refinedValue - futility_margin(depth, 0) >= beta
802 && abs(beta) < VALUE_MATE_IN_PLY_MAX
803 && pos.non_pawn_material(pos.side_to_move()))
804 return refinedValue - futility_margin(depth, 0);
806 // Step 8. Null move search with verification search (is omitted in PV nodes)
811 && refinedValue >= beta
812 && abs(beta) < VALUE_MATE_IN_PLY_MAX
813 && pos.non_pawn_material(pos.side_to_move()))
815 ss->currentMove = MOVE_NULL;
817 // Null move dynamic reduction based on depth
818 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
820 // Null move dynamic reduction based on value
821 if (refinedValue - PawnValueMidgame > beta)
824 pos.do_null_move(st);
825 (ss+1)->skipNullMove = true;
826 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
827 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
828 (ss+1)->skipNullMove = false;
829 pos.undo_null_move();
831 if (nullValue >= beta)
833 // Do not return unproven mate scores
834 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
837 if (depth < 6 * ONE_PLY)
840 // Do verification search at high depths
841 ss->skipNullMove = true;
842 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
843 ss->skipNullMove = false;
850 // The null move failed low, which means that we may be faced with
851 // some kind of threat. If the previous move was reduced, check if
852 // the move that refuted the null move was somehow connected to the
853 // move which was reduced. If a connection is found, return a fail
854 // low score (which will cause the reduced move to fail high in the
855 // parent node, which will trigger a re-search with full depth).
856 threatMove = (ss+1)->bestMove;
858 if ( depth < ThreatDepth
860 && threatMove != MOVE_NONE
861 && connected_moves(pos, (ss-1)->currentMove, threatMove))
866 // Step 9. ProbCut (is omitted in PV nodes)
867 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
868 // and a reduced search returns a value much above beta, we can (almost) safely
869 // prune the previous move.
871 && depth >= RazorDepth + ONE_PLY
874 && excludedMove == MOVE_NONE
875 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
877 Value rbeta = beta + 200;
878 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
880 assert(rdepth >= ONE_PLY);
882 MovePicker mp(pos, ttMove, H, Position::see_value(pos.captured_piece_type()));
883 pinned = pos.pinned_pieces(pos.side_to_move());
885 while ((move = mp.get_next_move()) != MOVE_NONE)
886 if (pos.pl_move_is_legal(move, pinned))
888 pos.do_move(move, st);
889 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
896 // Step 10. Internal iterative deepening
897 if ( depth >= IIDDepth[PvNode]
898 && ttMove == MOVE_NONE
899 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
901 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
903 ss->skipNullMove = true;
904 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
905 ss->skipNullMove = false;
907 tte = TT.probe(posKey);
908 ttMove = tte ? tte->move() : MOVE_NONE;
911 split_point_start: // At split points actual search starts from here
913 // Initialize a MovePicker object for the current position
914 MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
916 pinned = pos.pinned_pieces(pos.side_to_move());
917 ss->bestMove = MOVE_NONE;
918 futilityBase = ss->eval + ss->evalMargin;
919 singularExtensionNode = !RootNode
921 && depth >= SingularExtensionDepth[PvNode]
922 && ttMove != MOVE_NONE
923 && !excludedMove // Do not allow recursive singular extension search
924 && (tte->type() & VALUE_TYPE_LOWER)
925 && tte->depth() >= depth - 3 * ONE_PLY;
928 lock_grab(&(sp->lock));
929 bestValue = sp->bestValue;
932 // Step 11. Loop through moves
933 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
934 while ( bestValue < beta
935 && (move = mp.get_next_move()) != MOVE_NONE
936 && !Threads[threadID].cutoff_occurred())
938 assert(move_is_ok(move));
940 if (move == excludedMove)
943 // At PV and SpNode nodes we want the moves to be legal
944 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, pinned))
949 moveCount = ++sp->moveCount;
950 lock_release(&(sp->lock));
957 // This is used by time management
958 FirstRootMove = (moveCount == 1);
960 // Save the current node count before the move is searched
961 nodes = pos.nodes_searched();
963 // If it's time to send nodes info, do it here where we have the
964 // correct accumulated node counts searched by each thread.
965 if (SendSearchedNodes)
967 SendSearchedNodes = false;
968 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
971 if (current_search_time() > 2000)
972 cout << "info currmove " << move
973 << " currmovenumber " << moveCount << endl;
976 // At Root and at first iteration do a PV search on all the moves to score root moves
977 isPvMove = (PvNode && moveCount <= (RootNode ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
978 givesCheck = pos.move_gives_check(move, ci);
979 captureOrPromotion = pos.move_is_capture(move) || move_is_promotion(move);
981 // Step 12. Decide the new search depth
982 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
984 // Singular extension search. If all moves but one fail low on a search of
985 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
986 // is singular and should be extended. To verify this we do a reduced search
987 // on all the other moves but the ttMove, if result is lower than ttValue minus
988 // a margin then we extend ttMove.
989 if ( singularExtensionNode
991 && pos.pl_move_is_legal(move, pinned)
994 Value ttValue = value_from_tt(tte->value(), ss->ply);
996 if (abs(ttValue) < VALUE_KNOWN_WIN)
998 Value rBeta = ttValue - int(depth);
999 ss->excludedMove = move;
1000 ss->skipNullMove = true;
1001 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1002 ss->skipNullMove = false;
1003 ss->excludedMove = MOVE_NONE;
1004 ss->bestMove = MOVE_NONE;
1010 // Update current move (this must be done after singular extension search)
1011 newDepth = depth - ONE_PLY + ext;
1013 // Step 13. Futility pruning (is omitted in PV nodes)
1015 && !captureOrPromotion
1019 && !move_is_castle(move))
1021 // Move count based pruning
1022 if ( moveCount >= futility_move_count(depth)
1023 && (!threatMove || !connected_threat(pos, move, threatMove))
1024 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1027 lock_grab(&(sp->lock));
1032 // Value based pruning
1033 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1034 // but fixing this made program slightly weaker.
1035 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1036 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1037 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1039 if (futilityValueScaled < beta)
1043 lock_grab(&(sp->lock));
1044 if (futilityValueScaled > sp->bestValue)
1045 sp->bestValue = bestValue = futilityValueScaled;
1047 else if (futilityValueScaled > bestValue)
1048 bestValue = futilityValueScaled;
1053 // Prune moves with negative SEE at low depths
1054 if ( predictedDepth < 2 * ONE_PLY
1055 && bestValue > VALUE_MATED_IN_PLY_MAX
1056 && pos.see_sign(move) < 0)
1059 lock_grab(&(sp->lock));
1065 // Check for legality only before to do the move
1066 if (!pos.pl_move_is_legal(move, pinned))
1072 ss->currentMove = move;
1074 // Step 14. Make the move
1075 pos.do_move(move, st, ci, givesCheck);
1077 if (!SpNode && !captureOrPromotion)
1078 movesSearched[playedMoveCount++] = move;
1080 // Step extra. pv search (only in PV nodes)
1081 // The first move in list is the expected PV
1084 // Aspiration window is disabled in multi-pv case
1085 if (RootNode && MultiPV > 1)
1086 alpha = -VALUE_INFINITE;
1088 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1089 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1093 // Step 15. Reduced depth search
1094 // If the move fails high will be re-searched at full depth.
1095 bool doFullDepthSearch = true;
1096 alpha = SpNode ? sp->alpha : alpha;
1098 if ( depth >= 3 * ONE_PLY
1099 && !captureOrPromotion
1101 && !move_is_castle(move)
1102 && ss->killers[0] != move
1103 && ss->killers[1] != move)
1105 ss->reduction = reduction<PvNode>(depth, moveCount);
1108 Depth d = newDepth - ss->reduction;
1109 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1110 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1111 doFullDepthSearch = (value > alpha);
1113 ss->reduction = DEPTH_ZERO; // Restore original reduction
1116 // Step 16. Full depth search
1117 if (doFullDepthSearch)
1119 alpha = SpNode ? sp->alpha : alpha;
1120 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1121 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1123 // Step extra. pv search (only in PV nodes)
1124 // Search only for possible new PV nodes, if instead value >= beta then
1125 // parent node fails low with value <= alpha and tries another move.
1126 if (PvNode && value > alpha && (RootNode || value < beta))
1127 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1128 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1132 // Step 17. Undo move
1133 pos.undo_move(move);
1135 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1137 // Step 18. Check for new best move
1140 lock_grab(&(sp->lock));
1141 bestValue = sp->bestValue;
1145 if (value > bestValue && !(SpNode && Threads[threadID].cutoff_occurred()))
1150 sp->bestValue = value;
1152 if (!RootNode && value > alpha)
1154 if (PvNode && value < beta) // We want always alpha < beta
1162 sp->is_betaCutoff = true;
1164 ss->bestMove = move;
1167 sp->ss->bestMove = move;
1173 // Finished searching the move. If StopRequest is true, the search
1174 // was aborted because the user interrupted the search or because we
1175 // ran out of time. In this case, the return value of the search cannot
1176 // be trusted, and we break out of the loop without updating the best
1181 // Remember searched nodes counts for this move
1182 mp.rm->nodes += pos.nodes_searched() - nodes;
1184 // PV move or new best move ?
1185 if (isPvMove || value > alpha)
1188 ss->bestMove = move;
1189 mp.rm->pv_score = value;
1190 mp.rm->extract_pv_from_tt(pos);
1192 // We record how often the best move has been changed in each
1193 // iteration. This information is used for time management: When
1194 // the best move changes frequently, we allocate some more time.
1195 if (!isPvMove && MultiPV == 1)
1196 Rml.bestMoveChanges++;
1198 Rml.sort_multipv(moveCount);
1200 // Update alpha. In multi-pv we don't use aspiration window, so
1201 // set alpha equal to minimum score among the PV lines.
1203 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1204 else if (value > alpha)
1208 mp.rm->pv_score = -VALUE_INFINITE;
1212 // Step 19. Check for split
1215 && depth >= Threads.min_split_depth()
1217 && Threads.available_slave_exists(threadID)
1219 && !Threads[threadID].cutoff_occurred())
1220 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1221 threatMove, moveCount, &mp, PvNode);
1224 // Step 20. Check for mate and stalemate
1225 // All legal moves have been searched and if there are
1226 // no legal moves, it must be mate or stalemate.
1227 // If one move was excluded return fail low score.
1228 if (!SpNode && !moveCount)
1229 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1231 // Step 21. Update tables
1232 // If the search is not aborted, update the transposition table,
1233 // history counters, and killer moves.
1234 if (!SpNode && !StopRequest && !Threads[threadID].cutoff_occurred())
1236 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1237 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1238 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1240 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1242 // Update killers and history only for non capture moves that fails high
1243 if ( bestValue >= beta
1244 && !pos.move_is_capture(move)
1245 && !move_is_promotion(move))
1247 if (move != ss->killers[0])
1249 ss->killers[1] = ss->killers[0];
1250 ss->killers[0] = move;
1252 update_history(pos, move, depth, movesSearched, playedMoveCount);
1258 // Here we have the lock still grabbed
1259 sp->is_slave[threadID] = false;
1260 sp->nodes += pos.nodes_searched();
1261 lock_release(&(sp->lock));
1264 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1269 // qsearch() is the quiescence search function, which is called by the main
1270 // search function when the remaining depth is zero (or, to be more precise,
1271 // less than ONE_PLY).
1273 template <NodeType NT>
1274 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1276 const bool PvNode = (NT == PV);
1278 assert(NT == PV || NT == NonPV);
1279 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1280 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1281 assert(PvNode || alpha == beta - 1);
1283 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1287 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1288 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1291 Value oldAlpha = alpha;
1293 ss->bestMove = ss->currentMove = MOVE_NONE;
1294 ss->ply = (ss-1)->ply + 1;
1296 // Check for an instant draw or maximum ply reached
1297 if (ss->ply > PLY_MAX || pos.is_draw())
1300 // Decide whether or not to include checks, this fixes also the type of
1301 // TT entry depth that we are going to use. Note that in qsearch we use
1302 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1303 inCheck = pos.in_check();
1304 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1306 // Transposition table lookup. At PV nodes, we don't use the TT for
1307 // pruning, but only for move ordering.
1308 tte = TT.probe(pos.get_key());
1309 ttMove = (tte ? tte->move() : MOVE_NONE);
1311 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1313 ss->bestMove = ttMove; // Can be MOVE_NONE
1314 return value_from_tt(tte->value(), ss->ply);
1317 // Evaluate the position statically
1320 bestValue = futilityBase = -VALUE_INFINITE;
1321 ss->eval = evalMargin = VALUE_NONE;
1322 enoughMaterial = false;
1328 assert(tte->static_value() != VALUE_NONE);
1330 evalMargin = tte->static_value_margin();
1331 ss->eval = bestValue = tte->static_value();
1334 ss->eval = bestValue = evaluate(pos, evalMargin);
1336 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1338 // Stand pat. Return immediately if static value is at least beta
1339 if (bestValue >= beta)
1342 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1347 if (PvNode && bestValue > alpha)
1350 // Futility pruning parameters, not needed when in check
1351 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1352 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1355 // Initialize a MovePicker object for the current position, and prepare
1356 // to search the moves. Because the depth is <= 0 here, only captures,
1357 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1359 MovePicker mp(pos, ttMove, depth, H);
1361 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
1363 // Loop through the moves until no moves remain or a beta cutoff occurs
1364 while ( alpha < beta
1365 && (move = mp.get_next_move()) != MOVE_NONE)
1367 assert(move_is_ok(move));
1369 givesCheck = pos.move_gives_check(move, ci);
1377 && !move_is_promotion(move)
1378 && !pos.move_is_passed_pawn_push(move))
1380 futilityValue = futilityBase
1381 + pos.endgame_value_of_piece_on(move_to(move))
1382 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1384 if (futilityValue < alpha)
1386 if (futilityValue > bestValue)
1387 bestValue = futilityValue;
1391 // Prune moves with negative or equal SEE
1392 if ( futilityBase < beta
1393 && depth < DEPTH_ZERO
1394 && pos.see(move) <= 0)
1398 // Detect non-capture evasions that are candidate to be pruned
1399 evasionPrunable = !PvNode
1401 && bestValue > VALUE_MATED_IN_PLY_MAX
1402 && !pos.move_is_capture(move)
1403 && !pos.can_castle(pos.side_to_move());
1405 // Don't search moves with negative SEE values
1407 && (!inCheck || evasionPrunable)
1409 && !move_is_promotion(move)
1410 && pos.see_sign(move) < 0)
1413 // Don't search useless checks
1418 && !pos.move_is_capture(move)
1419 && !move_is_promotion(move)
1420 && ss->eval + PawnValueMidgame / 4 < beta
1421 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1423 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1424 bestValue = ss->eval + PawnValueMidgame / 4;
1429 // Check for legality only before to do the move
1430 if (!pos.pl_move_is_legal(move, pinned))
1433 // Update current move
1434 ss->currentMove = move;
1436 // Make and search the move
1437 pos.do_move(move, st, ci, givesCheck);
1438 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1439 pos.undo_move(move);
1441 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1444 if (value > bestValue)
1450 ss->bestMove = move;
1455 // All legal moves have been searched. A special case: If we're in check
1456 // and no legal moves were found, it is checkmate.
1457 if (inCheck && bestValue == -VALUE_INFINITE)
1458 return value_mated_in(ss->ply);
1460 // Update transposition table
1461 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1462 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1464 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1470 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1471 // bestValue is updated only when returning false because in that case move
1474 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1476 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1477 Square from, to, ksq, victimSq;
1480 Value futilityValue, bv = *bestValue;
1482 from = move_from(move);
1484 them = opposite_color(pos.side_to_move());
1485 ksq = pos.king_square(them);
1486 kingAtt = pos.attacks_from<KING>(ksq);
1487 pc = pos.piece_on(from);
1489 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1490 oldAtt = pos.attacks_from(pc, from, occ);
1491 newAtt = pos.attacks_from(pc, to, occ);
1493 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1494 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1496 if (!(b && (b & (b - 1))))
1499 // Rule 2. Queen contact check is very dangerous
1500 if ( type_of_piece(pc) == QUEEN
1501 && bit_is_set(kingAtt, to))
1504 // Rule 3. Creating new double threats with checks
1505 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1509 victimSq = pop_1st_bit(&b);
1510 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1512 // Note that here we generate illegal "double move"!
1513 if ( futilityValue >= beta
1514 && pos.see_sign(make_move(from, victimSq)) >= 0)
1517 if (futilityValue > bv)
1521 // Update bestValue only if check is not dangerous (because we will prune the move)
1527 // connected_moves() tests whether two moves are 'connected' in the sense
1528 // that the first move somehow made the second move possible (for instance
1529 // if the moving piece is the same in both moves). The first move is assumed
1530 // to be the move that was made to reach the current position, while the
1531 // second move is assumed to be a move from the current position.
1533 bool connected_moves(const Position& pos, Move m1, Move m2) {
1535 Square f1, t1, f2, t2;
1538 assert(m1 && move_is_ok(m1));
1539 assert(m2 && move_is_ok(m2));
1541 // Case 1: The moving piece is the same in both moves
1547 // Case 2: The destination square for m2 was vacated by m1
1553 // Case 3: Moving through the vacated square
1554 if ( piece_is_slider(pos.piece_on(f2))
1555 && bit_is_set(squares_between(f2, t2), f1))
1558 // Case 4: The destination square for m2 is defended by the moving piece in m1
1559 p = pos.piece_on(t1);
1560 if (bit_is_set(pos.attacks_from(p, t1), t2))
1563 // Case 5: Discovered check, checking piece is the piece moved in m1
1564 if ( piece_is_slider(p)
1565 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1566 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1568 // discovered_check_candidates() works also if the Position's side to
1569 // move is the opposite of the checking piece.
1570 Color them = opposite_color(pos.side_to_move());
1571 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1573 if (bit_is_set(dcCandidates, f2))
1580 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1581 // "plies to mate from the current ply". Non-mate scores are unchanged.
1582 // The function is called before storing a value to the transposition table.
1584 Value value_to_tt(Value v, int ply) {
1586 if (v >= VALUE_MATE_IN_PLY_MAX)
1589 if (v <= VALUE_MATED_IN_PLY_MAX)
1596 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1597 // the transposition table to a mate score corrected for the current ply.
1599 Value value_from_tt(Value v, int ply) {
1601 if (v >= VALUE_MATE_IN_PLY_MAX)
1604 if (v <= VALUE_MATED_IN_PLY_MAX)
1611 // extension() decides whether a move should be searched with normal depth,
1612 // or with extended depth. Certain classes of moves (checking moves, in
1613 // particular) are searched with bigger depth than ordinary moves and in
1614 // any case are marked as 'dangerous'. Note that also if a move is not
1615 // extended, as example because the corresponding UCI option is set to zero,
1616 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1617 template <bool PvNode>
1618 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1619 bool moveIsCheck, bool* dangerous) {
1621 assert(m != MOVE_NONE);
1623 Depth result = DEPTH_ZERO;
1624 *dangerous = moveIsCheck;
1626 if (moveIsCheck && pos.see_sign(m) >= 0)
1627 result += CheckExtension[PvNode];
1629 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1631 Color c = pos.side_to_move();
1632 if (relative_rank(c, move_to(m)) == RANK_7)
1634 result += PawnPushTo7thExtension[PvNode];
1637 if (pos.pawn_is_passed(c, move_to(m)))
1639 result += PassedPawnExtension[PvNode];
1644 if ( captureOrPromotion
1645 && pos.type_of_piece_on(move_to(m)) != PAWN
1646 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1647 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1648 && !move_is_special(m))
1650 result += PawnEndgameExtension[PvNode];
1654 return Min(result, ONE_PLY);
1658 // connected_threat() tests whether it is safe to forward prune a move or if
1659 // is somehow connected to the threat move returned by null search.
1661 bool connected_threat(const Position& pos, Move m, Move threat) {
1663 assert(move_is_ok(m));
1664 assert(threat && move_is_ok(threat));
1665 assert(!pos.move_gives_check(m));
1666 assert(!pos.move_is_capture(m) && !move_is_promotion(m));
1667 assert(!pos.move_is_passed_pawn_push(m));
1669 Square mfrom, mto, tfrom, tto;
1671 mfrom = move_from(m);
1673 tfrom = move_from(threat);
1674 tto = move_to(threat);
1676 // Case 1: Don't prune moves which move the threatened piece
1680 // Case 2: If the threatened piece has value less than or equal to the
1681 // value of the threatening piece, don't prune moves which defend it.
1682 if ( pos.move_is_capture(threat)
1683 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1684 || pos.type_of_piece_on(tfrom) == KING)
1685 && pos.move_attacks_square(m, tto))
1688 // Case 3: If the moving piece in the threatened move is a slider, don't
1689 // prune safe moves which block its ray.
1690 if ( piece_is_slider(pos.piece_on(tfrom))
1691 && bit_is_set(squares_between(tfrom, tto), mto)
1692 && pos.see_sign(m) >= 0)
1699 // ok_to_use_TT() returns true if a transposition table score
1700 // can be used at a given point in search.
1702 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1704 Value v = value_from_tt(tte->value(), ply);
1706 return ( tte->depth() >= depth
1707 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1708 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1710 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1711 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1715 // refine_eval() returns the transposition table score if
1716 // possible otherwise falls back on static position evaluation.
1718 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1722 Value v = value_from_tt(tte->value(), ply);
1724 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1725 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1732 // update_history() registers a good move that produced a beta-cutoff
1733 // in history and marks as failures all the other moves of that ply.
1735 void update_history(const Position& pos, Move move, Depth depth,
1736 Move movesSearched[], int moveCount) {
1738 Value bonus = Value(int(depth) * int(depth));
1740 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1742 for (int i = 0; i < moveCount - 1; i++)
1744 m = movesSearched[i];
1748 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1753 // update_gains() updates the gains table of a non-capture move given
1754 // the static position evaluation before and after the move.
1756 void update_gains(const Position& pos, Move m, Value before, Value after) {
1759 && before != VALUE_NONE
1760 && after != VALUE_NONE
1761 && pos.captured_piece_type() == PIECE_TYPE_NONE
1762 && !move_is_special(m))
1763 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1767 // current_search_time() returns the number of milliseconds which have passed
1768 // since the beginning of the current search.
1770 int current_search_time(int set) {
1772 static int searchStartTime;
1775 searchStartTime = set;
1777 return get_system_time() - searchStartTime;
1781 // value_to_uci() converts a value to a string suitable for use with the UCI
1782 // protocol specifications:
1784 // cp <x> The score from the engine's point of view in centipawns.
1785 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1786 // use negative values for y.
1788 std::string value_to_uci(Value v) {
1790 std::stringstream s;
1792 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1793 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1795 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1801 // speed_to_uci() returns a string with time stats of current search suitable
1802 // to be sent to UCI gui.
1804 std::string speed_to_uci(int64_t nodes) {
1806 std::stringstream s;
1807 int t = current_search_time();
1809 s << " nodes " << nodes
1810 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1817 // poll() performs two different functions: It polls for user input, and it
1818 // looks at the time consumed so far and decides if it's time to abort the
1821 void poll(const Position& pos) {
1823 static int lastInfoTime;
1824 int t = current_search_time();
1827 if (input_available())
1829 // We are line oriented, don't read single chars
1830 std::string command;
1832 if (!std::getline(std::cin, command) || command == "quit")
1834 // Quit the program as soon as possible
1835 Limits.ponder = false;
1836 QuitRequest = StopRequest = true;
1839 else if (command == "stop")
1841 // Stop calculating as soon as possible, but still send the "bestmove"
1842 // and possibly the "ponder" token when finishing the search.
1843 Limits.ponder = false;
1846 else if (command == "ponderhit")
1848 // The opponent has played the expected move. GUI sends "ponderhit" if
1849 // we were told to ponder on the same move the opponent has played. We
1850 // should continue searching but switching from pondering to normal search.
1851 Limits.ponder = false;
1853 if (StopOnPonderhit)
1858 // Print search information
1862 else if (lastInfoTime > t)
1863 // HACK: Must be a new search where we searched less than
1864 // NodesBetweenPolls nodes during the first second of search.
1867 else if (t - lastInfoTime >= 1000)
1872 dbg_print_hit_rate();
1874 // Send info on searched nodes as soon as we return to root
1875 SendSearchedNodes = true;
1878 // Should we stop the search?
1882 bool stillAtFirstMove = FirstRootMove
1883 && !AspirationFailLow
1884 && t > TimeMgr.available_time();
1886 bool noMoreTime = t > TimeMgr.maximum_time()
1887 || stillAtFirstMove;
1889 if ( (Limits.useTimeManagement() && noMoreTime)
1890 || (Limits.maxTime && t >= Limits.maxTime)
1891 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1896 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1897 // while the program is pondering. The point is to work around a wrinkle in
1898 // the UCI protocol: When pondering, the engine is not allowed to give a
1899 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1900 // We simply wait here until one of these commands is sent, and return,
1901 // after which the bestmove and pondermove will be printed.
1903 void wait_for_stop_or_ponderhit() {
1905 std::string command;
1907 // Wait for a command from stdin
1908 while ( std::getline(std::cin, command)
1909 && command != "ponderhit" && command != "stop" && command != "quit") {};
1911 if (command != "ponderhit" && command != "stop")
1912 QuitRequest = true; // Must be "quit" or getline() returned false
1916 // When playing with strength handicap choose best move among the MultiPV set
1917 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1918 void do_skill_level(Move* best, Move* ponder) {
1920 assert(MultiPV > 1);
1924 // Rml list is already sorted by pv_score in descending order
1926 int max_s = -VALUE_INFINITE;
1927 int size = Min(MultiPV, (int)Rml.size());
1928 int max = Rml[0].pv_score;
1929 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1930 int wk = 120 - 2 * SkillLevel;
1932 // PRNG sequence should be non deterministic
1933 for (int i = abs(get_system_time() % 50); i > 0; i--)
1934 rk.rand<unsigned>();
1936 // Choose best move. For each move's score we add two terms both dependent
1937 // on wk, one deterministic and bigger for weaker moves, and one random,
1938 // then we choose the move with the resulting highest score.
1939 for (int i = 0; i < size; i++)
1941 s = Rml[i].pv_score;
1943 // Don't allow crazy blunders even at very low skills
1944 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1947 // This is our magical formula
1948 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1953 *best = Rml[i].pv[0];
1954 *ponder = Rml[i].pv[1];
1960 /// RootMove and RootMoveList method's definitions
1962 RootMove::RootMove() {
1965 pv_score = non_pv_score = -VALUE_INFINITE;
1969 RootMove& RootMove::operator=(const RootMove& rm) {
1971 const Move* src = rm.pv;
1974 // Avoid a costly full rm.pv[] copy
1975 do *dst++ = *src; while (*src++ != MOVE_NONE);
1978 pv_score = rm.pv_score;
1979 non_pv_score = rm.non_pv_score;
1983 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1985 MoveStack mlist[MAX_MOVES];
1989 bestMoveChanges = 0;
1991 // Generate all legal moves and add them to RootMoveList
1992 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
1993 for (MoveStack* cur = mlist; cur != last; cur++)
1995 // If we have a searchMoves[] list then verify cur->move
1996 // is in the list before to add it.
1997 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
1999 if (searchMoves[0] && *sm != cur->move)
2003 rm.pv[0] = cur->move;
2004 rm.pv[1] = MOVE_NONE;
2005 rm.pv_score = -VALUE_INFINITE;
2010 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2011 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2012 // allow to always have a ponder move even when we fail high at root and also a
2013 // long PV to print that is important for position analysis.
2015 void RootMove::extract_pv_from_tt(Position& pos) {
2017 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2021 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2023 pos.do_move(pv[0], *st++);
2025 while ( (tte = TT.probe(pos.get_key())) != NULL
2026 && tte->move() != MOVE_NONE
2027 && pos.move_is_pl(tte->move())
2028 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces(pos.side_to_move()))
2030 && (!pos.is_draw() || ply < 2))
2032 pv[ply] = tte->move();
2033 pos.do_move(pv[ply++], *st++);
2035 pv[ply] = MOVE_NONE;
2037 do pos.undo_move(pv[--ply]); while (ply);
2040 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2041 // the PV back into the TT. This makes sure the old PV moves are searched
2042 // first, even if the old TT entries have been overwritten.
2044 void RootMove::insert_pv_in_tt(Position& pos) {
2046 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2049 Value v, m = VALUE_NONE;
2052 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2058 // Don't overwrite existing correct entries
2059 if (!tte || tte->move() != pv[ply])
2061 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2062 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2064 pos.do_move(pv[ply], *st++);
2066 } while (pv[++ply] != MOVE_NONE);
2068 do pos.undo_move(pv[--ply]); while (ply);
2071 // pv_info_to_uci() returns a string with information on the current PV line
2072 // formatted according to UCI specification.
2074 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2075 Value beta, int pvIdx) {
2076 std::stringstream s;
2078 s << "info depth " << depth
2079 << " seldepth " << selDepth
2080 << " multipv " << pvIdx + 1
2081 << " score " << value_to_uci(pv_score)
2082 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2083 << speed_to_uci(pos.nodes_searched())
2086 for (Move* m = pv; *m != MOVE_NONE; m++)
2092 // Specializations for MovePickerExt in case of Root node
2093 MovePickerExt<Root>::MovePickerExt(const Position& p, Move ttm, Depth d,
2094 const History& h, SearchStack* ss, Value b)
2095 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
2097 Value score = VALUE_ZERO;
2099 // Score root moves using standard ordering used in main search, the moves
2100 // are scored according to the order in which they are returned by MovePicker.
2101 // This is the second order score that is used to compare the moves when
2102 // the first orders pv_score of both moves are equal.
2103 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2104 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
2105 if (rm->pv[0] == move)
2107 rm->non_pv_score = score--;
2115 Move MovePickerExt<Root>::get_next_move() {
2122 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
2128 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2129 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2130 // object for which the current thread is the master.
2132 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2134 assert(threadID >= 0 && threadID < MAX_THREADS);
2141 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2142 // master should exit as last one.
2143 if (allThreadsShouldExit)
2146 threads[threadID].state = Thread::TERMINATED;
2150 // If we are not thinking, wait for a condition to be signaled
2151 // instead of wasting CPU time polling for work.
2152 while ( threadID >= activeThreads
2153 || threads[threadID].state == Thread::INITIALIZING
2154 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2156 assert(!sp || useSleepingThreads);
2157 assert(threadID != 0 || useSleepingThreads);
2159 if (threads[threadID].state == Thread::INITIALIZING)
2160 threads[threadID].state = Thread::AVAILABLE;
2162 // Grab the lock to avoid races with Thread::wake_up()
2163 lock_grab(&threads[threadID].sleepLock);
2165 // If we are master and all slaves have finished do not go to sleep
2166 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2167 allFinished = (i == activeThreads);
2169 if (allFinished || allThreadsShouldExit)
2171 lock_release(&threads[threadID].sleepLock);
2175 // Do sleep here after retesting sleep conditions
2176 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2177 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2179 lock_release(&threads[threadID].sleepLock);
2182 // If this thread has been assigned work, launch a search
2183 if (threads[threadID].state == Thread::WORKISWAITING)
2185 assert(!allThreadsShouldExit);
2187 threads[threadID].state = Thread::SEARCHING;
2189 // Copy split point position and search stack and call search()
2190 // with SplitPoint template parameter set to true.
2191 SearchStack ss[PLY_MAX_PLUS_2];
2192 SplitPoint* tsp = threads[threadID].splitPoint;
2193 Position pos(*tsp->pos, threadID);
2195 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2199 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2201 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2203 assert(threads[threadID].state == Thread::SEARCHING);
2205 threads[threadID].state = Thread::AVAILABLE;
2207 // Wake up master thread so to allow it to return from the idle loop in
2208 // case we are the last slave of the split point.
2209 if ( useSleepingThreads
2210 && threadID != tsp->master
2211 && threads[tsp->master].state == Thread::AVAILABLE)
2212 threads[tsp->master].wake_up();
2215 // If this thread is the master of a split point and all slaves have
2216 // finished their work at this split point, return from the idle loop.
2217 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2218 allFinished = (i == activeThreads);
2222 // Because sp->slaves[] is reset under lock protection,
2223 // be sure sp->lock has been released before to return.
2224 lock_grab(&(sp->lock));
2225 lock_release(&(sp->lock));
2227 // In helpful master concept a master can help only a sub-tree, and
2228 // because here is all finished is not possible master is booked.
2229 assert(threads[threadID].state == Thread::AVAILABLE);
2231 threads[threadID].state = Thread::SEARCHING;