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<bool SpNode, bool Root> 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<true, false> : public MovePicker {
110 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
111 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
113 Move get_next_move() { return mp->get_next_move(); }
115 RootMoveList::iterator rm; // Dummy, needed to compile
119 // In case of a Root node we use RootMoveList as moves source
120 template<> struct MovePickerExt<false, true> : public MovePicker {
122 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
123 Move get_next_move();
125 RootMoveList::iterator rm;
132 // Lookup table to check if a Piece is a slider and its access function
133 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
134 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
138 // Maximum depth for razoring
139 const Depth RazorDepth = 4 * ONE_PLY;
141 // Dynamic razoring margin based on depth
142 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
144 // Maximum depth for use of dynamic threat detection when null move fails low
145 const Depth ThreatDepth = 5 * ONE_PLY;
147 // Step 9. Internal iterative deepening
149 // Minimum depth for use of internal iterative deepening
150 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
152 // At Non-PV nodes we do an internal iterative deepening search
153 // when the static evaluation is bigger then beta - IIDMargin.
154 const Value IIDMargin = Value(0x100);
156 // Step 11. Decide the new search depth
158 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
159 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
160 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
161 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
162 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
164 // Minimum depth for use of singular extension
165 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
167 // Step 12. Futility pruning
169 // Futility margin for quiescence search
170 const Value FutilityMarginQS = Value(0x80);
172 // Futility lookup tables (initialized at startup) and their access functions
173 Value FutilityMargins[16][64]; // [depth][moveNumber]
174 int FutilityMoveCounts[32]; // [depth]
176 inline Value futility_margin(Depth d, int mn) {
178 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
179 : 2 * VALUE_INFINITE;
182 inline int futility_move_count(Depth d) {
184 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
187 // Step 14. Reduced search
189 // Reduction lookup tables (initialized at startup) and their access function
190 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
192 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
194 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
197 // Easy move margin. An easy move candidate must be at least this much
198 // better than the second best move.
199 const Value EasyMoveMargin = Value(0x200);
202 /// Namespace variables
208 int MultiPV, UCIMultiPV;
210 // Time management variables
211 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
216 std::ofstream LogFile;
218 // Skill level adjustment
220 bool SkillLevelEnabled;
222 // Node counters, used only by thread[0] but try to keep in different cache
223 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
224 bool SendSearchedNodes;
226 int NodesBetweenPolls = 30000;
234 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
236 template <NodeType NT>
237 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
239 template <NodeType NT>
240 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
242 template <bool PvNode>
243 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
245 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
246 bool connected_moves(const Position& pos, Move m1, Move m2);
247 Value value_to_tt(Value v, int ply);
248 Value value_from_tt(Value v, int ply);
249 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
250 bool connected_threat(const Position& pos, Move m, Move threat);
251 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
252 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
253 void update_gains(const Position& pos, Move move, Value before, Value after);
254 void do_skill_level(Move* best, Move* ponder);
256 int current_search_time(int set = 0);
257 std::string value_to_uci(Value v);
258 std::string speed_to_uci(int64_t nodes);
259 void poll(const Position& pos);
260 void wait_for_stop_or_ponderhit();
262 // Overload operator<<() to make it easier to print moves in a coordinate
263 // notation compatible with UCI protocol.
264 std::ostream& operator<<(std::ostream& os, Move m) {
266 bool chess960 = (os.iword(0) != 0); // See set960()
267 return os << move_to_uci(m, chess960);
270 // When formatting a move for std::cout we must know if we are in Chess960
271 // or not. To keep using the handy operator<<() on the move the trick is to
272 // embed this flag in the stream itself. Function-like named enum set960 is
273 // used as a custom manipulator and the stream internal general-purpose array,
274 // accessed through ios_base::iword(), is used to pass the flag to the move's
275 // operator<<() that will read it to properly format castling moves.
278 std::ostream& operator<< (std::ostream& os, const set960& f) {
280 os.iword(0) = int(f);
287 /// init_search() is called during startup to initialize various lookup tables
291 int d; // depth (ONE_PLY == 2)
292 int hd; // half depth (ONE_PLY == 1)
295 // Init reductions array
296 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
298 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
299 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
300 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
301 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
304 // Init futility margins array
305 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
306 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
308 // Init futility move count array
309 for (d = 0; d < 32; d++)
310 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
314 /// perft() is our utility to verify move generation. All the leaf nodes up to
315 /// the given depth are generated and counted and the sum returned.
317 int64_t perft(Position& pos, Depth depth) {
319 MoveStack mlist[MAX_MOVES];
324 // Generate all legal moves
325 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
327 // If we are at the last ply we don't need to do and undo
328 // the moves, just to count them.
329 if (depth <= ONE_PLY)
330 return int(last - mlist);
332 // Loop through all legal moves
334 for (MoveStack* cur = mlist; cur != last; cur++)
337 pos.do_move(m, st, ci, pos.move_gives_check(m, ci));
338 sum += perft(pos, depth - ONE_PLY);
345 /// think() is the external interface to Stockfish's search, and is called when
346 /// the program receives the UCI 'go' command. It initializes various global
347 /// variables, and calls id_loop(). It returns false when a "quit" command is
348 /// received during the search.
350 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
354 // Initialize global search-related variables
355 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
357 current_search_time(get_system_time());
359 TimeMgr.init(Limits, pos.startpos_ply_counter());
361 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
363 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
364 else if (Limits.time && Limits.time < 1000)
365 NodesBetweenPolls = 1000;
366 else if (Limits.time && Limits.time < 5000)
367 NodesBetweenPolls = 5000;
369 NodesBetweenPolls = 30000;
371 // Look for a book move
372 if (Options["OwnBook"].value<bool>())
374 if (Options["Book File"].value<std::string>() != book.name())
375 book.open(Options["Book File"].value<std::string>());
377 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
378 if (bookMove != MOVE_NONE)
381 wait_for_stop_or_ponderhit();
383 cout << "bestmove " << bookMove << endl;
389 UCIMultiPV = Options["MultiPV"].value<int>();
390 SkillLevel = Options["Skill Level"].value<int>();
392 read_evaluation_uci_options(pos.side_to_move());
393 Threads.read_uci_options();
395 // If needed allocate pawn and material hash tables and adjust TT size
396 Threads.init_hash_tables();
397 TT.set_size(Options["Hash"].value<int>());
399 if (Options["Clear Hash"].value<bool>())
401 Options["Clear Hash"].set_value("false");
405 // Do we have to play with skill handicap? In this case enable MultiPV that
406 // we will use behind the scenes to retrieve a set of possible moves.
407 SkillLevelEnabled = (SkillLevel < 20);
408 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
410 // Wake up needed threads and reset maxPly counter
411 for (int i = 0; i < Threads.size(); i++)
413 Threads[i].wake_up();
414 Threads[i].maxPly = 0;
417 // Write to log file and keep it open to be accessed during the search
418 if (Options["Use Search Log"].value<bool>())
420 std::string name = Options["Search Log Filename"].value<std::string>();
421 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
423 if (LogFile.is_open())
424 LogFile << "\nSearching: " << pos.to_fen()
425 << "\ninfinite: " << Limits.infinite
426 << " ponder: " << Limits.ponder
427 << " time: " << Limits.time
428 << " increment: " << Limits.increment
429 << " moves to go: " << Limits.movesToGo
433 // We're ready to start thinking. Call the iterative deepening loop function
434 Move ponderMove = MOVE_NONE;
435 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
437 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
439 // Write final search statistics and close log file
440 if (LogFile.is_open())
442 int t = current_search_time();
444 LogFile << "Nodes: " << pos.nodes_searched()
445 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
446 << "\nBest move: " << move_to_san(pos, bestMove);
449 pos.do_move(bestMove, st);
450 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
451 pos.undo_move(bestMove); // Return from think() with unchanged position
455 // This makes all the threads to go to sleep
458 // If we are pondering or in infinite search, we shouldn't print the
459 // best move before we are told to do so.
460 if (!StopRequest && (Limits.ponder || Limits.infinite))
461 wait_for_stop_or_ponderhit();
463 // Could be MOVE_NONE when searching on a stalemate position
464 cout << "bestmove " << bestMove;
466 // UCI protol is not clear on allowing sending an empty ponder move, instead
467 // it is clear that ponder move is optional. So skip it if empty.
468 if (ponderMove != MOVE_NONE)
469 cout << " ponder " << ponderMove;
479 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
480 // with increasing depth until the allocated thinking time has been consumed,
481 // user stops the search, or the maximum search depth is reached.
483 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
485 SearchStack ss[PLY_MAX_PLUS_2];
486 Value bestValues[PLY_MAX_PLUS_2];
487 int bestMoveChanges[PLY_MAX_PLUS_2];
488 int depth, selDepth, aspirationDelta;
489 Value value, alpha, beta;
490 Move bestMove, easyMove, skillBest, skillPonder;
492 // Initialize stuff before a new search
493 memset(ss, 0, 4 * sizeof(SearchStack));
496 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
497 depth = aspirationDelta = 0;
498 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
499 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
501 // Moves to search are verified and copied
502 Rml.init(pos, searchMoves);
504 // Handle special case of searching on a mate/stalemate position
507 cout << "info depth 0 score "
508 << value_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW)
514 // Iterative deepening loop until requested to stop or target depth reached
515 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
517 Rml.bestMoveChanges = 0;
518 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
520 // Calculate dynamic aspiration window based on previous iterations
521 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
523 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
524 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
526 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
527 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
529 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
530 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
533 // Start with a small aspiration window and, in case of fail high/low,
534 // research with bigger window until not failing high/low anymore.
536 // Search starting from ss+1 to allow calling update_gains()
537 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
539 // Write PV back to transposition table in case the relevant entries
540 // have been overwritten during the search.
541 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
542 Rml[i].insert_pv_in_tt(pos);
544 // Value cannot be trusted. Break out immediately!
548 assert(value >= alpha);
550 // In case of failing high/low increase aspiration window and research,
551 // otherwise exit the fail high/low loop.
554 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
555 aspirationDelta += aspirationDelta / 2;
557 else if (value <= alpha)
559 AspirationFailLow = true;
560 StopOnPonderhit = false;
562 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
563 aspirationDelta += aspirationDelta / 2;
568 } while (abs(value) < VALUE_KNOWN_WIN);
570 // Collect info about search result
571 bestMove = Rml[0].pv[0];
572 *ponderMove = Rml[0].pv[1];
573 bestValues[depth] = value;
574 bestMoveChanges[depth] = Rml.bestMoveChanges;
576 // Do we need to pick now the best and the ponder moves ?
577 if (SkillLevelEnabled && depth == 1 + SkillLevel)
578 do_skill_level(&skillBest, &skillPonder);
580 // Retrieve max searched depth among threads
582 for (int i = 0; i < Threads.size(); i++)
583 if (Threads[i].maxPly > selDepth)
584 selDepth = Threads[i].maxPly;
586 // Send PV line to GUI and to log file
587 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
588 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
590 if (LogFile.is_open())
591 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
593 // Init easyMove after first iteration or drop if differs from the best move
594 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
596 else if (bestMove != easyMove)
597 easyMove = MOVE_NONE;
599 // Check for some early stop condition
600 if (!StopRequest && Limits.useTimeManagement())
602 // Stop search early when the last two iterations returned a mate score
604 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
605 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
608 // Stop search early if one move seems to be much better than the
609 // others or if there is only a single legal move. Also in the latter
610 // case we search up to some depth anyway to get a proper score.
612 && easyMove == bestMove
614 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
615 && current_search_time() > TimeMgr.available_time() / 16)
616 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
617 && current_search_time() > TimeMgr.available_time() / 32)))
620 // Take in account some extra time if the best move has changed
621 if (depth > 4 && depth < 50)
622 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
624 // Stop search if most of available time is already consumed. We probably don't
625 // have enough time to search the first move at the next iteration anyway.
626 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
629 // If we are allowed to ponder do not stop the search now but keep pondering
630 if (StopRequest && Limits.ponder)
633 StopOnPonderhit = true;
638 // When using skills overwrite best and ponder moves with the sub-optimal ones
639 if (SkillLevelEnabled)
641 if (skillBest == MOVE_NONE) // Still unassigned ?
642 do_skill_level(&skillBest, &skillPonder);
644 bestMove = skillBest;
645 *ponderMove = skillPonder;
652 // search<>() is the main search function for both PV and non-PV nodes and for
653 // normal and SplitPoint nodes. When called just after a split point the search
654 // is simpler because we have already probed the hash table, done a null move
655 // search, and searched the first move before splitting, we don't have to repeat
656 // all this work again. We also don't need to store anything to the hash table
657 // here: This is taken care of after we return from the split point.
659 template <NodeType NT>
660 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
662 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
663 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
664 const bool RootNode = (NT == Root);
666 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
667 assert(beta > alpha && beta <= VALUE_INFINITE);
668 assert(PvNode || alpha == beta - 1);
669 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
671 Move movesSearched[MAX_MOVES];
676 Move ttMove, move, excludedMove, threatMove;
679 Value bestValue, value, oldAlpha;
680 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
681 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
682 int moveCount = 0, playedMoveCount = 0;
683 int threadID = pos.thread();
684 SplitPoint* sp = NULL;
686 refinedValue = bestValue = value = -VALUE_INFINITE;
688 inCheck = pos.in_check();
689 ss->ply = (ss-1)->ply + 1;
691 // Used to send selDepth info to GUI
692 if (PvNode && Threads[threadID].maxPly < ss->ply)
693 Threads[threadID].maxPly = ss->ply;
699 ttMove = excludedMove = MOVE_NONE;
700 threatMove = sp->threatMove;
701 goto split_point_start;
706 // Step 1. Initialize node and poll. Polling can abort search
707 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
708 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
709 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
711 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
717 // Step 2. Check for aborted search and immediate draw
719 || Threads[threadID].cutoff_occurred()
721 || ss->ply > PLY_MAX) && !RootNode)
724 // Step 3. Mate distance pruning
725 alpha = Max(value_mated_in(ss->ply), alpha);
726 beta = Min(value_mate_in(ss->ply+1), beta);
730 // Step 4. Transposition table lookup
731 // We don't want the score of a partial search to overwrite a previous full search
732 // TT value, so we use a different position key in case of an excluded move.
733 excludedMove = ss->excludedMove;
734 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
736 tte = TT.probe(posKey);
737 ttMove = tte ? tte->move() : MOVE_NONE;
739 // At PV nodes we check for exact scores, while at non-PV nodes we check for
740 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
741 // smooth experience in analysis mode.
744 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
745 : ok_to_use_TT(tte, depth, beta, ss->ply)))
748 ss->bestMove = ttMove; // Can be MOVE_NONE
749 return value_from_tt(tte->value(), ss->ply);
752 // Step 5. Evaluate the position statically and update parent's gain statistics
754 ss->eval = ss->evalMargin = VALUE_NONE;
757 assert(tte->static_value() != VALUE_NONE);
759 ss->eval = tte->static_value();
760 ss->evalMargin = tte->static_value_margin();
761 refinedValue = refine_eval(tte, ss->eval, ss->ply);
765 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
766 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
769 // Save gain for the parent non-capture move
770 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
772 // Step 6. Razoring (is omitted in PV nodes)
774 && depth < RazorDepth
776 && refinedValue + razor_margin(depth) < beta
777 && ttMove == MOVE_NONE
778 && abs(beta) < VALUE_MATE_IN_PLY_MAX
779 && !pos.has_pawn_on_7th(pos.side_to_move()))
781 Value rbeta = beta - razor_margin(depth);
782 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
784 // Logically we should return (v + razor_margin(depth)), but
785 // surprisingly this did slightly weaker in tests.
789 // Step 7. Static null move pruning (is omitted in PV nodes)
790 // We're betting that the opponent doesn't have a move that will reduce
791 // the score by more than futility_margin(depth) if we do a null move.
794 && depth < RazorDepth
796 && refinedValue - futility_margin(depth, 0) >= beta
797 && abs(beta) < VALUE_MATE_IN_PLY_MAX
798 && pos.non_pawn_material(pos.side_to_move()))
799 return refinedValue - futility_margin(depth, 0);
801 // Step 8. Null move search with verification search (is omitted in PV nodes)
806 && refinedValue >= beta
807 && abs(beta) < VALUE_MATE_IN_PLY_MAX
808 && pos.non_pawn_material(pos.side_to_move()))
810 ss->currentMove = MOVE_NULL;
812 // Null move dynamic reduction based on depth
813 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
815 // Null move dynamic reduction based on value
816 if (refinedValue - PawnValueMidgame > beta)
819 pos.do_null_move(st);
820 (ss+1)->skipNullMove = true;
821 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
822 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
823 (ss+1)->skipNullMove = false;
824 pos.undo_null_move();
826 if (nullValue >= beta)
828 // Do not return unproven mate scores
829 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
832 if (depth < 6 * ONE_PLY)
835 // Do verification search at high depths
836 ss->skipNullMove = true;
837 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
838 ss->skipNullMove = false;
845 // The null move failed low, which means that we may be faced with
846 // some kind of threat. If the previous move was reduced, check if
847 // the move that refuted the null move was somehow connected to the
848 // move which was reduced. If a connection is found, return a fail
849 // low score (which will cause the reduced move to fail high in the
850 // parent node, which will trigger a re-search with full depth).
851 threatMove = (ss+1)->bestMove;
853 if ( depth < ThreatDepth
855 && threatMove != MOVE_NONE
856 && connected_moves(pos, (ss-1)->currentMove, threatMove))
861 // Step 9. Internal iterative deepening
862 if ( depth >= IIDDepth[PvNode]
863 && ttMove == MOVE_NONE
864 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
866 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
868 ss->skipNullMove = true;
869 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
870 ss->skipNullMove = false;
872 tte = TT.probe(posKey);
873 ttMove = tte ? tte->move() : MOVE_NONE;
876 split_point_start: // At split points actual search starts from here
878 // Initialize a MovePicker object for the current position
879 MovePickerExt<SpNode, RootNode> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
881 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
882 ss->bestMove = MOVE_NONE;
883 futilityBase = ss->eval + ss->evalMargin;
884 singularExtensionNode = !RootNode
886 && depth >= SingularExtensionDepth[PvNode]
887 && ttMove != MOVE_NONE
888 && !excludedMove // Do not allow recursive singular extension search
889 && (tte->type() & VALUE_TYPE_LOWER)
890 && tte->depth() >= depth - 3 * ONE_PLY;
893 lock_grab(&(sp->lock));
894 bestValue = sp->bestValue;
897 // Step 10. Loop through moves
898 // Loop through all legal moves until no moves remain or a beta cutoff occurs
899 while ( bestValue < beta
900 && (move = mp.get_next_move()) != MOVE_NONE
901 && !Threads[threadID].cutoff_occurred())
903 assert(move_is_ok(move));
905 if (move == excludedMove)
908 // At PV and SpNode nodes we want the moves to be legal
909 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, pinned))
914 moveCount = ++sp->moveCount;
915 lock_release(&(sp->lock));
922 // This is used by time management
923 FirstRootMove = (moveCount == 1);
925 // Save the current node count before the move is searched
926 nodes = pos.nodes_searched();
928 // If it's time to send nodes info, do it here where we have the
929 // correct accumulated node counts searched by each thread.
930 if (SendSearchedNodes)
932 SendSearchedNodes = false;
933 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
936 if (current_search_time() > 2000)
937 cout << "info currmove " << move
938 << " currmovenumber " << moveCount << endl;
941 // At Root and at first iteration do a PV search on all the moves to score root moves
942 isPvMove = (PvNode && moveCount <= (RootNode ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
943 givesCheck = pos.move_gives_check(move, ci);
944 captureOrPromotion = pos.move_is_capture(move) || move_is_promotion(move);
946 // Step 11. Decide the new search depth
947 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
949 // Singular extension search. If all moves but one fail low on a search of
950 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
951 // is singular and should be extended. To verify this we do a reduced search
952 // on all the other moves but the ttMove, if result is lower than ttValue minus
953 // a margin then we extend ttMove.
954 if ( singularExtensionNode
956 && pos.pl_move_is_legal(move, pinned)
959 Value ttValue = value_from_tt(tte->value(), ss->ply);
961 if (abs(ttValue) < VALUE_KNOWN_WIN)
963 Value rBeta = ttValue - int(depth);
964 ss->excludedMove = move;
965 ss->skipNullMove = true;
966 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
967 ss->skipNullMove = false;
968 ss->excludedMove = MOVE_NONE;
969 ss->bestMove = MOVE_NONE;
975 // Update current move (this must be done after singular extension search)
976 newDepth = depth - ONE_PLY + ext;
978 // Step 12. Futility pruning (is omitted in PV nodes)
980 && !captureOrPromotion
984 && !move_is_castle(move))
986 // Move count based pruning
987 if ( moveCount >= futility_move_count(depth)
988 && (!threatMove || !connected_threat(pos, move, threatMove))
989 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
992 lock_grab(&(sp->lock));
997 // Value based pruning
998 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
999 // but fixing this made program slightly weaker.
1000 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1001 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1002 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1004 if (futilityValueScaled < beta)
1008 lock_grab(&(sp->lock));
1009 if (futilityValueScaled > sp->bestValue)
1010 sp->bestValue = bestValue = futilityValueScaled;
1012 else if (futilityValueScaled > bestValue)
1013 bestValue = futilityValueScaled;
1018 // Prune moves with negative SEE at low depths
1019 if ( predictedDepth < 2 * ONE_PLY
1020 && bestValue > VALUE_MATED_IN_PLY_MAX
1021 && pos.see_sign(move) < 0)
1024 lock_grab(&(sp->lock));
1030 // Check for legality only before to do the move
1031 if (!pos.pl_move_is_legal(move, pinned))
1037 ss->currentMove = move;
1039 // Step 13. Make the move
1040 pos.do_move(move, st, ci, givesCheck);
1042 if (!SpNode && !captureOrPromotion)
1043 movesSearched[playedMoveCount++] = move;
1045 // Step extra. pv search (only in PV nodes)
1046 // The first move in list is the expected PV
1049 // Aspiration window is disabled in multi-pv case
1050 if (RootNode && MultiPV > 1)
1051 alpha = -VALUE_INFINITE;
1053 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1054 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1058 // Step 14. Reduced depth search
1059 // If the move fails high will be re-searched at full depth.
1060 bool doFullDepthSearch = true;
1061 alpha = SpNode ? sp->alpha : alpha;
1063 if ( depth >= 3 * ONE_PLY
1064 && !captureOrPromotion
1066 && !move_is_castle(move)
1067 && ss->killers[0] != move
1068 && ss->killers[1] != move)
1070 ss->reduction = reduction<PvNode>(depth, moveCount);
1073 Depth d = newDepth - ss->reduction;
1074 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1075 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1076 doFullDepthSearch = (value > alpha);
1078 ss->reduction = DEPTH_ZERO; // Restore original reduction
1081 // Probcut search for bad captures. If a reduced search returns a value
1082 // very below beta then we can (almost) safely prune the bad capture.
1083 if ( depth >= 3 * ONE_PLY
1084 && depth < 8 * ONE_PLY
1085 && mp.isBadCapture()
1088 && !move_is_promotion(move)
1089 && abs(alpha) < VALUE_MATE_IN_PLY_MAX)
1091 ss->reduction = 3 * ONE_PLY;
1092 Value rAlpha = alpha - 300;
1093 Depth d = newDepth - ss->reduction;
1094 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, DEPTH_ZERO)
1095 : - search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1096 doFullDepthSearch = (value > rAlpha);
1097 ss->reduction = DEPTH_ZERO; // Restore original reduction
1100 // Step 15. Full depth search
1101 if (doFullDepthSearch)
1103 alpha = SpNode ? sp->alpha : alpha;
1104 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1105 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1107 // Step extra. pv search (only in PV nodes)
1108 // Search only for possible new PV nodes, if instead value >= beta then
1109 // parent node fails low with value <= alpha and tries another move.
1110 if (PvNode && value > alpha && (RootNode || value < beta))
1111 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1112 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1116 // Step 16. Undo move
1117 pos.undo_move(move);
1119 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1121 // Step 17. Check for new best move
1124 lock_grab(&(sp->lock));
1125 bestValue = sp->bestValue;
1129 if (value > bestValue && !(SpNode && Threads[threadID].cutoff_occurred()))
1134 sp->bestValue = value;
1136 if (!RootNode && value > alpha)
1138 if (PvNode && value < beta) // We want always alpha < beta
1146 sp->is_betaCutoff = true;
1148 if (value == value_mate_in(ss->ply + 1))
1149 ss->mateKiller = move;
1151 ss->bestMove = move;
1154 sp->ss->bestMove = move;
1160 // Finished searching the move. If StopRequest is true, the search
1161 // was aborted because the user interrupted the search or because we
1162 // ran out of time. In this case, the return value of the search cannot
1163 // be trusted, and we break out of the loop without updating the best
1168 // Remember searched nodes counts for this move
1169 mp.rm->nodes += pos.nodes_searched() - nodes;
1171 // PV move or new best move ?
1172 if (isPvMove || value > alpha)
1175 ss->bestMove = move;
1176 mp.rm->pv_score = value;
1177 mp.rm->extract_pv_from_tt(pos);
1179 // We record how often the best move has been changed in each
1180 // iteration. This information is used for time management: When
1181 // the best move changes frequently, we allocate some more time.
1182 if (!isPvMove && MultiPV == 1)
1183 Rml.bestMoveChanges++;
1185 Rml.sort_multipv(moveCount);
1187 // Update alpha. In multi-pv we don't use aspiration window, so
1188 // set alpha equal to minimum score among the PV lines.
1190 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1191 else if (value > alpha)
1195 mp.rm->pv_score = -VALUE_INFINITE;
1199 // Step 18. Check for split
1202 && depth >= Threads.min_split_depth()
1204 && Threads.available_slave_exists(threadID)
1206 && !Threads[threadID].cutoff_occurred())
1207 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1208 threatMove, moveCount, &mp, PvNode);
1211 // Step 19. Check for mate and stalemate
1212 // All legal moves have been searched and if there are
1213 // no legal moves, it must be mate or stalemate.
1214 // If one move was excluded return fail low score.
1215 if (!SpNode && !moveCount)
1216 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1218 // Step 20. Update tables
1219 // If the search is not aborted, update the transposition table,
1220 // history counters, and killer moves.
1221 if (!SpNode && !StopRequest && !Threads[threadID].cutoff_occurred())
1223 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1224 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1225 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1227 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1229 // Update killers and history only for non capture moves that fails high
1230 if ( bestValue >= beta
1231 && !pos.move_is_capture(move)
1232 && !move_is_promotion(move))
1234 if (move != ss->killers[0])
1236 ss->killers[1] = ss->killers[0];
1237 ss->killers[0] = move;
1239 update_history(pos, move, depth, movesSearched, playedMoveCount);
1245 // Here we have the lock still grabbed
1246 sp->is_slave[threadID] = false;
1247 sp->nodes += pos.nodes_searched();
1248 lock_release(&(sp->lock));
1251 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1256 // qsearch() is the quiescence search function, which is called by the main
1257 // search function when the remaining depth is zero (or, to be more precise,
1258 // less than ONE_PLY).
1260 template <NodeType NT>
1261 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1263 const bool PvNode = (NT == PV);
1265 assert(NT == PV || NT == NonPV);
1266 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1267 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1268 assert(PvNode || alpha == beta - 1);
1270 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1274 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1275 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1278 Value oldAlpha = alpha;
1280 ss->bestMove = ss->currentMove = MOVE_NONE;
1281 ss->ply = (ss-1)->ply + 1;
1283 // Check for an instant draw or maximum ply reached
1284 if (ss->ply > PLY_MAX || pos.is_draw())
1287 // Decide whether or not to include checks, this fixes also the type of
1288 // TT entry depth that we are going to use. Note that in qsearch we use
1289 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1290 inCheck = pos.in_check();
1291 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1293 // Transposition table lookup. At PV nodes, we don't use the TT for
1294 // pruning, but only for move ordering.
1295 tte = TT.probe(pos.get_key());
1296 ttMove = (tte ? tte->move() : MOVE_NONE);
1298 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1300 ss->bestMove = ttMove; // Can be MOVE_NONE
1301 return value_from_tt(tte->value(), ss->ply);
1304 // Evaluate the position statically
1307 bestValue = futilityBase = -VALUE_INFINITE;
1308 ss->eval = evalMargin = VALUE_NONE;
1309 enoughMaterial = false;
1315 assert(tte->static_value() != VALUE_NONE);
1317 evalMargin = tte->static_value_margin();
1318 ss->eval = bestValue = tte->static_value();
1321 ss->eval = bestValue = evaluate(pos, evalMargin);
1323 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1325 // Stand pat. Return immediately if static value is at least beta
1326 if (bestValue >= beta)
1329 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1334 if (PvNode && bestValue > alpha)
1337 // Futility pruning parameters, not needed when in check
1338 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1339 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1342 // Initialize a MovePicker object for the current position, and prepare
1343 // to search the moves. Because the depth is <= 0 here, only captures,
1344 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1346 MovePicker mp(pos, ttMove, depth, H);
1348 Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
1350 // Loop through the moves until no moves remain or a beta cutoff occurs
1351 while ( alpha < beta
1352 && (move = mp.get_next_move()) != MOVE_NONE)
1354 assert(move_is_ok(move));
1356 givesCheck = pos.move_gives_check(move, ci);
1364 && !move_is_promotion(move)
1365 && !pos.move_is_passed_pawn_push(move))
1367 futilityValue = futilityBase
1368 + pos.endgame_value_of_piece_on(move_to(move))
1369 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1371 if (futilityValue < alpha)
1373 if (futilityValue > bestValue)
1374 bestValue = futilityValue;
1378 // Prune moves with negative or equal SEE
1379 if ( futilityBase < beta
1380 && depth < DEPTH_ZERO
1381 && pos.see(move) <= 0)
1385 // Detect non-capture evasions that are candidate to be pruned
1386 evasionPrunable = !PvNode
1388 && bestValue > VALUE_MATED_IN_PLY_MAX
1389 && !pos.move_is_capture(move)
1390 && !pos.can_castle(pos.side_to_move());
1392 // Don't search moves with negative SEE values
1394 && (!inCheck || evasionPrunable)
1396 && !move_is_promotion(move)
1397 && pos.see_sign(move) < 0)
1400 // Don't search useless checks
1405 && !pos.move_is_capture(move)
1406 && !move_is_promotion(move)
1407 && ss->eval + PawnValueMidgame / 4 < beta
1408 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1410 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1411 bestValue = ss->eval + PawnValueMidgame / 4;
1416 // Check for legality only before to do the move
1417 if (!pos.pl_move_is_legal(move, pinned))
1420 // Update current move
1421 ss->currentMove = move;
1423 // Make and search the move
1424 pos.do_move(move, st, ci, givesCheck);
1425 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1426 pos.undo_move(move);
1428 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1431 if (value > bestValue)
1437 ss->bestMove = move;
1442 // All legal moves have been searched. A special case: If we're in check
1443 // and no legal moves were found, it is checkmate.
1444 if (inCheck && bestValue == -VALUE_INFINITE)
1445 return value_mated_in(ss->ply);
1447 // Update transposition table
1448 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1449 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1451 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1457 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1458 // bestValue is updated only when returning false because in that case move
1461 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1463 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1464 Square from, to, ksq, victimSq;
1467 Value futilityValue, bv = *bestValue;
1469 from = move_from(move);
1471 them = opposite_color(pos.side_to_move());
1472 ksq = pos.king_square(them);
1473 kingAtt = pos.attacks_from<KING>(ksq);
1474 pc = pos.piece_on(from);
1476 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1477 oldAtt = pos.attacks_from(pc, from, occ);
1478 newAtt = pos.attacks_from(pc, to, occ);
1480 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1481 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1483 if (!(b && (b & (b - 1))))
1486 // Rule 2. Queen contact check is very dangerous
1487 if ( type_of_piece(pc) == QUEEN
1488 && bit_is_set(kingAtt, to))
1491 // Rule 3. Creating new double threats with checks
1492 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1496 victimSq = pop_1st_bit(&b);
1497 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1499 // Note that here we generate illegal "double move"!
1500 if ( futilityValue >= beta
1501 && pos.see_sign(make_move(from, victimSq)) >= 0)
1504 if (futilityValue > bv)
1508 // Update bestValue only if check is not dangerous (because we will prune the move)
1514 // connected_moves() tests whether two moves are 'connected' in the sense
1515 // that the first move somehow made the second move possible (for instance
1516 // if the moving piece is the same in both moves). The first move is assumed
1517 // to be the move that was made to reach the current position, while the
1518 // second move is assumed to be a move from the current position.
1520 bool connected_moves(const Position& pos, Move m1, Move m2) {
1522 Square f1, t1, f2, t2;
1525 assert(m1 && move_is_ok(m1));
1526 assert(m2 && move_is_ok(m2));
1528 // Case 1: The moving piece is the same in both moves
1534 // Case 2: The destination square for m2 was vacated by m1
1540 // Case 3: Moving through the vacated square
1541 if ( piece_is_slider(pos.piece_on(f2))
1542 && bit_is_set(squares_between(f2, t2), f1))
1545 // Case 4: The destination square for m2 is defended by the moving piece in m1
1546 p = pos.piece_on(t1);
1547 if (bit_is_set(pos.attacks_from(p, t1), t2))
1550 // Case 5: Discovered check, checking piece is the piece moved in m1
1551 if ( piece_is_slider(p)
1552 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1553 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1555 // discovered_check_candidates() works also if the Position's side to
1556 // move is the opposite of the checking piece.
1557 Color them = opposite_color(pos.side_to_move());
1558 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1560 if (bit_is_set(dcCandidates, f2))
1567 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1568 // "plies to mate from the current ply". Non-mate scores are unchanged.
1569 // The function is called before storing a value to the transposition table.
1571 Value value_to_tt(Value v, int ply) {
1573 if (v >= VALUE_MATE_IN_PLY_MAX)
1576 if (v <= VALUE_MATED_IN_PLY_MAX)
1583 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1584 // the transposition table to a mate score corrected for the current ply.
1586 Value value_from_tt(Value v, int ply) {
1588 if (v >= VALUE_MATE_IN_PLY_MAX)
1591 if (v <= VALUE_MATED_IN_PLY_MAX)
1598 // extension() decides whether a move should be searched with normal depth,
1599 // or with extended depth. Certain classes of moves (checking moves, in
1600 // particular) are searched with bigger depth than ordinary moves and in
1601 // any case are marked as 'dangerous'. Note that also if a move is not
1602 // extended, as example because the corresponding UCI option is set to zero,
1603 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1604 template <bool PvNode>
1605 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1606 bool moveIsCheck, bool* dangerous) {
1608 assert(m != MOVE_NONE);
1610 Depth result = DEPTH_ZERO;
1611 *dangerous = moveIsCheck;
1613 if (moveIsCheck && pos.see_sign(m) >= 0)
1614 result += CheckExtension[PvNode];
1616 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1618 Color c = pos.side_to_move();
1619 if (relative_rank(c, move_to(m)) == RANK_7)
1621 result += PawnPushTo7thExtension[PvNode];
1624 if (pos.pawn_is_passed(c, move_to(m)))
1626 result += PassedPawnExtension[PvNode];
1631 if ( captureOrPromotion
1632 && pos.type_of_piece_on(move_to(m)) != PAWN
1633 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1634 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1635 && !move_is_special(m))
1637 result += PawnEndgameExtension[PvNode];
1641 return Min(result, ONE_PLY);
1645 // connected_threat() tests whether it is safe to forward prune a move or if
1646 // is somehow connected to the threat move returned by null search.
1648 bool connected_threat(const Position& pos, Move m, Move threat) {
1650 assert(move_is_ok(m));
1651 assert(threat && move_is_ok(threat));
1652 assert(!pos.move_gives_check(m));
1653 assert(!pos.move_is_capture(m) && !move_is_promotion(m));
1654 assert(!pos.move_is_passed_pawn_push(m));
1656 Square mfrom, mto, tfrom, tto;
1658 mfrom = move_from(m);
1660 tfrom = move_from(threat);
1661 tto = move_to(threat);
1663 // Case 1: Don't prune moves which move the threatened piece
1667 // Case 2: If the threatened piece has value less than or equal to the
1668 // value of the threatening piece, don't prune moves which defend it.
1669 if ( pos.move_is_capture(threat)
1670 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1671 || pos.type_of_piece_on(tfrom) == KING)
1672 && pos.move_attacks_square(m, tto))
1675 // Case 3: If the moving piece in the threatened move is a slider, don't
1676 // prune safe moves which block its ray.
1677 if ( piece_is_slider(pos.piece_on(tfrom))
1678 && bit_is_set(squares_between(tfrom, tto), mto)
1679 && pos.see_sign(m) >= 0)
1686 // ok_to_use_TT() returns true if a transposition table score
1687 // can be used at a given point in search.
1689 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1691 Value v = value_from_tt(tte->value(), ply);
1693 return ( tte->depth() >= depth
1694 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1695 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1697 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1698 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1702 // refine_eval() returns the transposition table score if
1703 // possible otherwise falls back on static position evaluation.
1705 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1709 Value v = value_from_tt(tte->value(), ply);
1711 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1712 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1719 // update_history() registers a good move that produced a beta-cutoff
1720 // in history and marks as failures all the other moves of that ply.
1722 void update_history(const Position& pos, Move move, Depth depth,
1723 Move movesSearched[], int moveCount) {
1725 Value bonus = Value(int(depth) * int(depth));
1727 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1729 for (int i = 0; i < moveCount - 1; i++)
1731 m = movesSearched[i];
1735 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1740 // update_gains() updates the gains table of a non-capture move given
1741 // the static position evaluation before and after the move.
1743 void update_gains(const Position& pos, Move m, Value before, Value after) {
1746 && before != VALUE_NONE
1747 && after != VALUE_NONE
1748 && pos.captured_piece_type() == PIECE_TYPE_NONE
1749 && !move_is_special(m))
1750 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1754 // current_search_time() returns the number of milliseconds which have passed
1755 // since the beginning of the current search.
1757 int current_search_time(int set) {
1759 static int searchStartTime;
1762 searchStartTime = set;
1764 return get_system_time() - searchStartTime;
1768 // value_to_uci() converts a value to a string suitable for use with the UCI
1769 // protocol specifications:
1771 // cp <x> The score from the engine's point of view in centipawns.
1772 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1773 // use negative values for y.
1775 std::string value_to_uci(Value v) {
1777 std::stringstream s;
1779 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1780 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1782 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1788 // speed_to_uci() returns a string with time stats of current search suitable
1789 // to be sent to UCI gui.
1791 std::string speed_to_uci(int64_t nodes) {
1793 std::stringstream s;
1794 int t = current_search_time();
1796 s << " nodes " << nodes
1797 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1804 // poll() performs two different functions: It polls for user input, and it
1805 // looks at the time consumed so far and decides if it's time to abort the
1808 void poll(const Position& pos) {
1810 static int lastInfoTime;
1811 int t = current_search_time();
1814 if (input_available())
1816 // We are line oriented, don't read single chars
1817 std::string command;
1819 if (!std::getline(std::cin, command) || command == "quit")
1821 // Quit the program as soon as possible
1822 Limits.ponder = false;
1823 QuitRequest = StopRequest = true;
1826 else if (command == "stop")
1828 // Stop calculating as soon as possible, but still send the "bestmove"
1829 // and possibly the "ponder" token when finishing the search.
1830 Limits.ponder = false;
1833 else if (command == "ponderhit")
1835 // The opponent has played the expected move. GUI sends "ponderhit" if
1836 // we were told to ponder on the same move the opponent has played. We
1837 // should continue searching but switching from pondering to normal search.
1838 Limits.ponder = false;
1840 if (StopOnPonderhit)
1845 // Print search information
1849 else if (lastInfoTime > t)
1850 // HACK: Must be a new search where we searched less than
1851 // NodesBetweenPolls nodes during the first second of search.
1854 else if (t - lastInfoTime >= 1000)
1859 dbg_print_hit_rate();
1861 // Send info on searched nodes as soon as we return to root
1862 SendSearchedNodes = true;
1865 // Should we stop the search?
1869 bool stillAtFirstMove = FirstRootMove
1870 && !AspirationFailLow
1871 && t > TimeMgr.available_time();
1873 bool noMoreTime = t > TimeMgr.maximum_time()
1874 || stillAtFirstMove;
1876 if ( (Limits.useTimeManagement() && noMoreTime)
1877 || (Limits.maxTime && t >= Limits.maxTime)
1878 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1883 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1884 // while the program is pondering. The point is to work around a wrinkle in
1885 // the UCI protocol: When pondering, the engine is not allowed to give a
1886 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1887 // We simply wait here until one of these commands is sent, and return,
1888 // after which the bestmove and pondermove will be printed.
1890 void wait_for_stop_or_ponderhit() {
1892 std::string command;
1894 // Wait for a command from stdin
1895 while ( std::getline(std::cin, command)
1896 && command != "ponderhit" && command != "stop" && command != "quit") {};
1898 if (command != "ponderhit" && command != "stop")
1899 QuitRequest = true; // Must be "quit" or getline() returned false
1903 // When playing with strength handicap choose best move among the MultiPV set
1904 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1905 void do_skill_level(Move* best, Move* ponder) {
1907 assert(MultiPV > 1);
1911 // Rml list is already sorted by pv_score in descending order
1913 int max_s = -VALUE_INFINITE;
1914 int size = Min(MultiPV, (int)Rml.size());
1915 int max = Rml[0].pv_score;
1916 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1917 int wk = 120 - 2 * SkillLevel;
1919 // PRNG sequence should be non deterministic
1920 for (int i = abs(get_system_time() % 50); i > 0; i--)
1921 rk.rand<unsigned>();
1923 // Choose best move. For each move's score we add two terms both dependent
1924 // on wk, one deterministic and bigger for weaker moves, and one random,
1925 // then we choose the move with the resulting highest score.
1926 for (int i = 0; i < size; i++)
1928 s = Rml[i].pv_score;
1930 // Don't allow crazy blunders even at very low skills
1931 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1934 // This is our magical formula
1935 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1940 *best = Rml[i].pv[0];
1941 *ponder = Rml[i].pv[1];
1947 /// RootMove and RootMoveList method's definitions
1949 RootMove::RootMove() {
1952 pv_score = non_pv_score = -VALUE_INFINITE;
1956 RootMove& RootMove::operator=(const RootMove& rm) {
1958 const Move* src = rm.pv;
1961 // Avoid a costly full rm.pv[] copy
1962 do *dst++ = *src; while (*src++ != MOVE_NONE);
1965 pv_score = rm.pv_score;
1966 non_pv_score = rm.non_pv_score;
1970 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1972 MoveStack mlist[MAX_MOVES];
1976 bestMoveChanges = 0;
1978 // Generate all legal moves and add them to RootMoveList
1979 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
1980 for (MoveStack* cur = mlist; cur != last; cur++)
1982 // If we have a searchMoves[] list then verify cur->move
1983 // is in the list before to add it.
1984 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
1986 if (searchMoves[0] && *sm != cur->move)
1990 rm.pv[0] = cur->move;
1991 rm.pv[1] = MOVE_NONE;
1992 rm.pv_score = -VALUE_INFINITE;
1997 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
1998 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
1999 // allow to always have a ponder move even when we fail high at root and also a
2000 // long PV to print that is important for position analysis.
2002 void RootMove::extract_pv_from_tt(Position& pos) {
2004 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2008 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2010 pos.do_move(pv[0], *st++);
2012 while ( (tte = TT.probe(pos.get_key())) != NULL
2013 && tte->move() != MOVE_NONE
2014 && pos.move_is_pl(tte->move())
2015 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces(pos.side_to_move()))
2017 && (!pos.is_draw() || ply < 2))
2019 pv[ply] = tte->move();
2020 pos.do_move(pv[ply++], *st++);
2022 pv[ply] = MOVE_NONE;
2024 do pos.undo_move(pv[--ply]); while (ply);
2027 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2028 // the PV back into the TT. This makes sure the old PV moves are searched
2029 // first, even if the old TT entries have been overwritten.
2031 void RootMove::insert_pv_in_tt(Position& pos) {
2033 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2036 Value v, m = VALUE_NONE;
2039 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2045 // Don't overwrite existing correct entries
2046 if (!tte || tte->move() != pv[ply])
2048 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2049 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2051 pos.do_move(pv[ply], *st++);
2053 } while (pv[++ply] != MOVE_NONE);
2055 do pos.undo_move(pv[--ply]); while (ply);
2058 // pv_info_to_uci() returns a string with information on the current PV line
2059 // formatted according to UCI specification.
2061 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2062 Value beta, int pvIdx) {
2063 std::stringstream s;
2065 s << "info depth " << depth
2066 << " seldepth " << selDepth
2067 << " multipv " << pvIdx + 1
2068 << " score " << value_to_uci(pv_score)
2069 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2070 << speed_to_uci(pos.nodes_searched())
2073 for (Move* m = pv; *m != MOVE_NONE; m++)
2079 // Specializations for MovePickerExt in case of Root node
2080 MovePickerExt<false, true>::MovePickerExt(const Position& p, Move ttm, Depth d,
2081 const History& h, SearchStack* ss, Value b)
2082 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
2084 Value score = VALUE_ZERO;
2086 // Score root moves using standard ordering used in main search, the moves
2087 // are scored according to the order in which they are returned by MovePicker.
2088 // This is the second order score that is used to compare the moves when
2089 // the first orders pv_score of both moves are equal.
2090 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2091 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
2092 if (rm->pv[0] == move)
2094 rm->non_pv_score = score--;
2102 Move MovePickerExt<false, true>::get_next_move() {
2109 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
2115 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2116 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2117 // object for which the current thread is the master.
2119 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2121 assert(threadID >= 0 && threadID < MAX_THREADS);
2128 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2129 // master should exit as last one.
2130 if (allThreadsShouldExit)
2133 threads[threadID].state = Thread::TERMINATED;
2137 // If we are not thinking, wait for a condition to be signaled
2138 // instead of wasting CPU time polling for work.
2139 while ( threadID >= activeThreads
2140 || threads[threadID].state == Thread::INITIALIZING
2141 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2143 assert(!sp || useSleepingThreads);
2144 assert(threadID != 0 || useSleepingThreads);
2146 if (threads[threadID].state == Thread::INITIALIZING)
2147 threads[threadID].state = Thread::AVAILABLE;
2149 // Grab the lock to avoid races with Thread::wake_up()
2150 lock_grab(&threads[threadID].sleepLock);
2152 // If we are master and all slaves have finished do not go to sleep
2153 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2154 allFinished = (i == activeThreads);
2156 if (allFinished || allThreadsShouldExit)
2158 lock_release(&threads[threadID].sleepLock);
2162 // Do sleep here after retesting sleep conditions
2163 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2164 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2166 lock_release(&threads[threadID].sleepLock);
2169 // If this thread has been assigned work, launch a search
2170 if (threads[threadID].state == Thread::WORKISWAITING)
2172 assert(!allThreadsShouldExit);
2174 threads[threadID].state = Thread::SEARCHING;
2176 // Copy split point position and search stack and call search()
2177 // with SplitPoint template parameter set to true.
2178 SearchStack ss[PLY_MAX_PLUS_2];
2179 SplitPoint* tsp = threads[threadID].splitPoint;
2180 Position pos(*tsp->pos, threadID);
2182 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2186 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2188 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2190 assert(threads[threadID].state == Thread::SEARCHING);
2192 threads[threadID].state = Thread::AVAILABLE;
2194 // Wake up master thread so to allow it to return from the idle loop in
2195 // case we are the last slave of the split point.
2196 if ( useSleepingThreads
2197 && threadID != tsp->master
2198 && threads[tsp->master].state == Thread::AVAILABLE)
2199 threads[tsp->master].wake_up();
2202 // If this thread is the master of a split point and all slaves have
2203 // finished their work at this split point, return from the idle loop.
2204 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2205 allFinished = (i == activeThreads);
2209 // Because sp->slaves[] is reset under lock protection,
2210 // be sure sp->lock has been released before to return.
2211 lock_grab(&(sp->lock));
2212 lock_release(&(sp->lock));
2214 // In helpful master concept a master can help only a sub-tree, and
2215 // because here is all finished is not possible master is booked.
2216 assert(threads[threadID].state == Thread::AVAILABLE);
2218 threads[threadID].state = Thread::SEARCHING;