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 // Different node types, used as template parameter
47 enum NodeType { NonPV, PV };
49 // Set to true to force running with one thread. Used for debugging.
50 const bool FakeSplit = false;
52 // Lookup table to check if a Piece is a slider and its access function
53 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
54 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
56 // RootMove struct is used for moves at the root of the tree. For each root
57 // move, we store two scores, a node count, and a PV (really a refutation
58 // in the case of moves which fail low). Value pv_score is normally set at
59 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
60 // according to the order in which moves are returned by MovePicker.
65 RootMove(const RootMove& rm) { *this = rm; }
66 RootMove& operator=(const RootMove& rm);
68 // RootMove::operator<() is the comparison function used when
69 // sorting the moves. A move m1 is considered to be better
70 // than a move m2 if it has an higher pv_score, or if it has
71 // equal pv_score but m1 has the higher non_pv_score. In this way
72 // we are guaranteed that PV moves are always sorted as first.
73 bool operator<(const RootMove& m) const {
74 return pv_score != m.pv_score ? pv_score < m.pv_score
75 : non_pv_score < m.non_pv_score;
78 void extract_pv_from_tt(Position& pos);
79 void insert_pv_in_tt(Position& pos);
80 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
81 Value alpha, Value beta, int pvIdx);
85 Move pv[PLY_MAX_PLUS_2];
89 // RootMoveList struct is just a vector of RootMove objects,
90 // with an handful of methods above the standard ones.
92 struct RootMoveList : public std::vector<RootMove> {
94 typedef std::vector<RootMove> Base;
96 void init(Position& pos, Move searchMoves[]);
97 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
98 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
104 // Overload operator<<() to make it easier to print moves in a coordinate
105 // notation compatible with UCI protocol.
106 std::ostream& operator<<(std::ostream& os, Move m) {
108 bool chess960 = (os.iword(0) != 0); // See set960()
109 return os << move_to_uci(m, chess960);
113 // When formatting a move for std::cout we must know if we are in Chess960
114 // or not. To keep using the handy operator<<() on the move the trick is to
115 // embed this flag in the stream itself. Function-like named enum set960 is
116 // used as a custom manipulator and the stream internal general-purpose array,
117 // accessed through ios_base::iword(), is used to pass the flag to the move's
118 // operator<<() that will read it to properly format castling moves.
121 std::ostream& operator<< (std::ostream& os, const set960& f) {
123 os.iword(0) = int(f);
132 // Maximum depth for razoring
133 const Depth RazorDepth = 4 * ONE_PLY;
135 // Dynamic razoring margin based on depth
136 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
138 // Maximum depth for use of dynamic threat detection when null move fails low
139 const Depth ThreatDepth = 5 * ONE_PLY;
141 // Step 9. Internal iterative deepening
143 // Minimum depth for use of internal iterative deepening
144 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
146 // At Non-PV nodes we do an internal iterative deepening search
147 // when the static evaluation is bigger then beta - IIDMargin.
148 const Value IIDMargin = Value(0x100);
150 // Step 11. Decide the new search depth
152 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
153 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
154 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
155 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
156 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
158 // Minimum depth for use of singular extension
159 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
161 // Step 12. Futility pruning
163 // Futility margin for quiescence search
164 const Value FutilityMarginQS = Value(0x80);
166 // Futility lookup tables (initialized at startup) and their access functions
167 Value FutilityMargins[16][64]; // [depth][moveNumber]
168 int FutilityMoveCounts[32]; // [depth]
170 inline Value futility_margin(Depth d, int mn) {
172 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
173 : 2 * VALUE_INFINITE;
176 inline int futility_move_count(Depth d) {
178 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
181 // Step 14. Reduced search
183 // Reduction lookup tables (initialized at startup) and their access function
184 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
186 template <NodeType PV> inline Depth reduction(Depth d, int mn) {
188 return (Depth) Reductions[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)];
191 // Easy move margin. An easy move candidate must be at least this much
192 // better than the second best move.
193 const Value EasyMoveMargin = Value(0x200);
196 /// Namespace variables
205 int MultiPV, UCIMultiPV;
207 // Time management variables
208 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
213 std::ofstream LogFile;
215 // Skill level adjustment
217 bool SkillLevelEnabled;
220 // Node counters, used only by thread[0] but try to keep in different cache
221 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
222 bool SendSearchedNodes;
224 int NodesBetweenPolls = 30000;
232 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
234 template <NodeType PvNode, bool SpNode, bool Root>
235 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
237 template <NodeType PvNode>
238 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
240 template <NodeType PvNode>
241 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
243 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
244 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
247 template <NodeType PvNode>
248 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
250 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
251 bool connected_moves(const Position& pos, Move m1, Move m2);
252 Value value_to_tt(Value v, int ply);
253 Value value_from_tt(Value v, int ply);
254 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
255 bool connected_threat(const Position& pos, Move m, Move threat);
256 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
257 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
258 void update_gains(const Position& pos, Move move, Value before, Value after);
259 void do_skill_level(Move* best, Move* ponder);
261 int current_search_time(int set = 0);
262 std::string value_to_uci(Value v);
263 std::string speed_to_uci(int64_t nodes);
264 void poll(const Position& pos);
265 void wait_for_stop_or_ponderhit();
268 // MovePickerExt is an extended MovePicker class used to choose at compile time
269 // the proper move source according to the type of node.
270 template<bool SpNode, bool Root> struct MovePickerExt;
272 // In Root nodes use RootMoveList as source. Score and sort the root moves
273 // before to search them.
274 template<> struct MovePickerExt<false, true> : public MovePicker {
276 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
277 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
279 Value score = VALUE_ZERO;
281 // Score root moves using standard ordering used in main search, the moves
282 // are scored according to the order in which they are returned by MovePicker.
283 // This is the second order score that is used to compare the moves when
284 // the first orders pv_score of both moves are equal.
285 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
286 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
287 if (rm->pv[0] == move)
289 rm->non_pv_score = score--;
297 Move get_next_move() {
304 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
307 RootMoveList::iterator rm;
311 // In SpNodes use split point's shared MovePicker object as move source
312 template<> struct MovePickerExt<true, false> : public MovePicker {
314 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
315 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
317 Move get_next_move() { return mp->get_next_move(); }
319 RootMoveList::iterator rm; // Dummy, needed to compile
323 // Default case, create and use a MovePicker object as source
324 template<> struct MovePickerExt<false, false> : public MovePicker {
326 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
327 : MovePicker(p, ttm, d, h, ss, b) {}
329 RootMoveList::iterator rm; // Dummy, needed to compile
335 /// init_search() is called during startup to initialize various lookup tables
339 int d; // depth (ONE_PLY == 2)
340 int hd; // half depth (ONE_PLY == 1)
343 // Init reductions array
344 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
346 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
347 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
348 Reductions[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
349 Reductions[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
352 // Init futility margins array
353 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
354 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
356 // Init futility move count array
357 for (d = 0; d < 32; d++)
358 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
362 /// perft() is our utility to verify move generation. All the legal moves up to
363 /// given depth are generated and counted and the sum returned.
365 int64_t perft(Position& pos, Depth depth) {
367 MoveStack mlist[MAX_MOVES];
372 // Generate all legal moves
373 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
375 // If we are at the last ply we don't need to do and undo
376 // the moves, just to count them.
377 if (depth <= ONE_PLY)
378 return int(last - mlist);
380 // Loop through all legal moves
382 for (MoveStack* cur = mlist; cur != last; cur++)
385 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
386 sum += perft(pos, depth - ONE_PLY);
393 /// think() is the external interface to Stockfish's search, and is called when
394 /// the program receives the UCI 'go' command. It initializes various global
395 /// variables, and calls id_loop(). It returns false when a "quit" command is
396 /// received during the search.
398 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
400 // Initialize global search-related variables
401 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
403 current_search_time(get_system_time());
405 TimeMgr.init(Limits, pos.startpos_ply_counter());
407 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
409 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
410 else if (Limits.time && Limits.time < 1000)
411 NodesBetweenPolls = 1000;
412 else if (Limits.time && Limits.time < 5000)
413 NodesBetweenPolls = 5000;
415 NodesBetweenPolls = 30000;
417 // Look for a book move, only during games, not tests
418 if (Limits.useTimeManagement() && Options["OwnBook"].value<bool>())
420 if (Options["Book File"].value<std::string>() != OpeningBook.name())
421 OpeningBook.open(Options["Book File"].value<std::string>());
423 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
435 UCIMultiPV = Options["MultiPV"].value<int>();
436 SkillLevel = Options["Skill level"].value<int>();
438 ThreadsMgr.read_uci_options();
439 read_evaluation_uci_options(pos.side_to_move());
441 if (Options["Clear Hash"].value<bool>())
443 Options["Clear Hash"].set_value("false");
446 TT.set_size(Options["Hash"].value<int>());
448 // Do we have to play with skill handicap? In this case enable MultiPV that
449 // we will use behind the scenes to retrieve a set of possible moves.
450 SkillLevelEnabled = (SkillLevel < 20);
451 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
453 // Wake up needed threads and reset maxPly counter
454 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
456 ThreadsMgr[i].wake_up();
457 ThreadsMgr[i].maxPly = 0;
460 // Write to log file and keep it open to be accessed during the search
461 if (Options["Use Search Log"].value<bool>())
463 std::string name = Options["Search Log Filename"].value<std::string>();
464 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
466 if (LogFile.is_open())
467 LogFile << "\nSearching: " << pos.to_fen()
468 << "\ninfinite: " << Limits.infinite
469 << " ponder: " << Limits.ponder
470 << " time: " << Limits.time
471 << " increment: " << Limits.increment
472 << " moves to go: " << Limits.movesToGo
476 // We're ready to start thinking. Call the iterative deepening loop function
477 Move ponderMove = MOVE_NONE;
478 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
480 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
482 // Write final search statistics and close log file
483 if (LogFile.is_open())
485 int t = current_search_time();
487 LogFile << "Nodes: " << pos.nodes_searched()
488 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
489 << "\nBest move: " << move_to_san(pos, bestMove);
492 pos.do_move(bestMove, st);
493 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
494 pos.undo_move(bestMove); // Return from think() with unchanged position
498 // This makes all the threads to go to sleep
499 ThreadsMgr.set_active_threads(1);
501 // If we are pondering or in infinite search, we shouldn't print the
502 // best move before we are told to do so.
503 if (!StopRequest && (Limits.ponder || Limits.infinite))
504 wait_for_stop_or_ponderhit();
506 // Could be MOVE_NONE when searching on a stalemate position
507 cout << "bestmove " << bestMove;
509 // UCI protol is not clear on allowing sending an empty ponder move, instead
510 // it is clear that ponder move is optional. So skip it if empty.
511 if (ponderMove != MOVE_NONE)
512 cout << " ponder " << ponderMove;
522 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
523 // with increasing depth until the allocated thinking time has been consumed,
524 // user stops the search, or the maximum search depth is reached.
526 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
528 SearchStack ss[PLY_MAX_PLUS_2];
529 Value bestValues[PLY_MAX_PLUS_2];
530 int bestMoveChanges[PLY_MAX_PLUS_2];
531 int depth, selDepth, aspirationDelta;
532 Value value, alpha, beta;
533 Move bestMove, easyMove, skillBest, skillPonder;
535 // Initialize stuff before a new search
536 memset(ss, 0, 4 * sizeof(SearchStack));
539 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
540 depth = aspirationDelta = 0;
541 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
542 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
544 // Moves to search are verified and copied
545 Rml.init(pos, searchMoves);
547 // Handle special case of searching on a mate/stalemate position
550 cout << "info depth 0 score "
551 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
557 // Iterative deepening loop until requested to stop or target depth reached
558 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
560 Rml.bestMoveChanges = 0;
561 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
563 // Calculate dynamic aspiration window based on previous iterations
564 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
566 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
567 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
569 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
570 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
572 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
573 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
576 // Start with a small aspiration window and, in case of fail high/low,
577 // research with bigger window until not failing high/low anymore.
579 // Search starting from ss+1 to allow calling update_gains()
580 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
582 // Write PV back to transposition table in case the relevant entries
583 // have been overwritten during the search.
584 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
585 Rml[i].insert_pv_in_tt(pos);
587 // Value cannot be trusted. Break out immediately!
591 assert(value >= alpha);
593 // In case of failing high/low increase aspiration window and research,
594 // otherwise exit the fail high/low loop.
597 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
598 aspirationDelta += aspirationDelta / 2;
600 else if (value <= alpha)
602 AspirationFailLow = true;
603 StopOnPonderhit = false;
605 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
606 aspirationDelta += aspirationDelta / 2;
611 } while (abs(value) < VALUE_KNOWN_WIN);
613 // Collect info about search result
614 bestMove = Rml[0].pv[0];
615 *ponderMove = Rml[0].pv[1];
616 bestValues[depth] = value;
617 bestMoveChanges[depth] = Rml.bestMoveChanges;
619 // Do we need to pick now the best and the ponder moves ?
620 if (SkillLevelEnabled && depth == 1 + SkillLevel)
621 do_skill_level(&skillBest, &skillPonder);
623 // Retrieve max searched depth among threads
625 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
626 if (ThreadsMgr[i].maxPly > selDepth)
627 selDepth = ThreadsMgr[i].maxPly;
629 // Send PV line to GUI and to log file
630 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
631 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
633 if (LogFile.is_open())
634 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
636 // Init easyMove after first iteration or drop if differs from the best move
637 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
639 else if (bestMove != easyMove)
640 easyMove = MOVE_NONE;
642 // Check for some early stop condition
643 if (!StopRequest && Limits.useTimeManagement())
645 // Stop search early when the last two iterations returned a mate score
647 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
648 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
651 // Stop search early if one move seems to be much better than the
652 // others or if there is only a single legal move. Also in the latter
653 // case we search up to some depth anyway to get a proper score.
655 && easyMove == bestMove
657 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
658 && current_search_time() > TimeMgr.available_time() / 16)
659 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
660 && current_search_time() > TimeMgr.available_time() / 32)))
663 // Take in account some extra time if the best move has changed
664 if (depth > 4 && depth < 50)
665 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
667 // Stop search if most of available time is already consumed. We probably don't
668 // have enough time to search the first move at the next iteration anyway.
669 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
672 // If we are allowed to ponder do not stop the search now but keep pondering
673 if (StopRequest && Limits.ponder)
676 StopOnPonderhit = true;
681 // When using skills overwrite best and ponder moves with the sub-optimal ones
682 if (SkillLevelEnabled)
684 if (skillBest == MOVE_NONE) // Still unassigned ?
685 do_skill_level(&skillBest, &skillPonder);
687 bestMove = skillBest;
688 *ponderMove = skillPonder;
695 // search<>() is the main search function for both PV and non-PV nodes and for
696 // normal and SplitPoint nodes. When called just after a split point the search
697 // is simpler because we have already probed the hash table, done a null move
698 // search, and searched the first move before splitting, we don't have to repeat
699 // all this work again. We also don't need to store anything to the hash table
700 // here: This is taken care of after we return from the split point.
702 template <NodeType PvNode, bool SpNode, bool Root>
703 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
705 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
706 assert(beta > alpha && beta <= VALUE_INFINITE);
707 assert(PvNode || alpha == beta - 1);
708 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
710 Move movesSearched[MAX_MOVES];
715 Move ttMove, move, excludedMove, threatMove;
718 Value bestValue, value, oldAlpha;
719 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
720 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
721 int moveCount = 0, playedMoveCount = 0;
722 int threadID = pos.thread();
723 SplitPoint* sp = NULL;
725 refinedValue = bestValue = value = -VALUE_INFINITE;
727 isCheck = pos.is_check();
728 ss->ply = (ss-1)->ply + 1;
730 // Used to send selDepth info to GUI
731 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
732 ThreadsMgr[threadID].maxPly = ss->ply;
738 ttMove = excludedMove = MOVE_NONE;
739 threatMove = sp->threatMove;
740 goto split_point_start;
745 // Step 1. Initialize node and poll. Polling can abort search
746 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
747 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
748 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
750 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
756 // Step 2. Check for aborted search and immediate draw
758 || ThreadsMgr.cutoff_at_splitpoint(threadID)
760 || ss->ply > PLY_MAX) && !Root)
763 // Step 3. Mate distance pruning
764 alpha = Max(value_mated_in(ss->ply), alpha);
765 beta = Min(value_mate_in(ss->ply+1), beta);
769 // Step 4. Transposition table lookup
770 // We don't want the score of a partial search to overwrite a previous full search
771 // TT value, so we use a different position key in case of an excluded move.
772 excludedMove = ss->excludedMove;
773 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
775 tte = TT.retrieve(posKey);
776 ttMove = tte ? tte->move() : MOVE_NONE;
778 // At PV nodes we check for exact scores, while at non-PV nodes we check for
779 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
780 // smooth experience in analysis mode.
783 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
784 : ok_to_use_TT(tte, depth, beta, ss->ply)))
787 ss->bestMove = ttMove; // Can be MOVE_NONE
788 return value_from_tt(tte->value(), ss->ply);
791 // Step 5. Evaluate the position statically and update parent's gain statistics
793 ss->eval = ss->evalMargin = VALUE_NONE;
796 assert(tte->static_value() != VALUE_NONE);
798 ss->eval = tte->static_value();
799 ss->evalMargin = tte->static_value_margin();
800 refinedValue = refine_eval(tte, ss->eval, ss->ply);
804 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
805 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
808 // Save gain for the parent non-capture move
809 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
811 // Step 6. Razoring (is omitted in PV nodes)
813 && depth < RazorDepth
815 && refinedValue + razor_margin(depth) < beta
816 && ttMove == MOVE_NONE
817 && abs(beta) < VALUE_MATE_IN_PLY_MAX
818 && !pos.has_pawn_on_7th(pos.side_to_move()))
820 Value rbeta = beta - razor_margin(depth);
821 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
823 // Logically we should return (v + razor_margin(depth)), but
824 // surprisingly this did slightly weaker in tests.
828 // Step 7. Static null move pruning (is omitted in PV nodes)
829 // We're betting that the opponent doesn't have a move that will reduce
830 // the score by more than futility_margin(depth) if we do a null move.
833 && depth < RazorDepth
835 && refinedValue - futility_margin(depth, 0) >= beta
836 && abs(beta) < VALUE_MATE_IN_PLY_MAX
837 && pos.non_pawn_material(pos.side_to_move()))
838 return refinedValue - futility_margin(depth, 0);
840 // Step 8. Null move search with verification search (is omitted in PV nodes)
845 && refinedValue >= beta
846 && abs(beta) < VALUE_MATE_IN_PLY_MAX
847 && pos.non_pawn_material(pos.side_to_move()))
849 ss->currentMove = MOVE_NULL;
851 // Null move dynamic reduction based on depth
852 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
854 // Null move dynamic reduction based on value
855 if (refinedValue - PawnValueMidgame > beta)
858 pos.do_null_move(st);
859 (ss+1)->skipNullMove = true;
860 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
861 (ss+1)->skipNullMove = false;
862 pos.undo_null_move();
864 if (nullValue >= beta)
866 // Do not return unproven mate scores
867 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
870 if (depth < 6 * ONE_PLY)
873 // Do verification search at high depths
874 ss->skipNullMove = true;
875 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
876 ss->skipNullMove = false;
883 // The null move failed low, which means that we may be faced with
884 // some kind of threat. If the previous move was reduced, check if
885 // the move that refuted the null move was somehow connected to the
886 // move which was reduced. If a connection is found, return a fail
887 // low score (which will cause the reduced move to fail high in the
888 // parent node, which will trigger a re-search with full depth).
889 threatMove = (ss+1)->bestMove;
891 if ( depth < ThreatDepth
893 && threatMove != MOVE_NONE
894 && connected_moves(pos, (ss-1)->currentMove, threatMove))
899 // Step 9. Internal iterative deepening
900 if ( depth >= IIDDepth[PvNode]
901 && ttMove == MOVE_NONE
902 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
904 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
906 ss->skipNullMove = true;
907 search<PvNode>(pos, ss, alpha, beta, d);
908 ss->skipNullMove = false;
910 ttMove = ss->bestMove;
911 tte = TT.retrieve(posKey);
914 split_point_start: // At split points actual search starts from here
916 // Initialize a MovePicker object for the current position
917 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
919 ss->bestMove = MOVE_NONE;
920 futilityBase = ss->eval + ss->evalMargin;
921 singularExtensionNode = !Root
923 && depth >= SingularExtensionDepth[PvNode]
926 && !excludedMove // Do not allow recursive singular extension search
927 && (tte->type() & VALUE_TYPE_LOWER)
928 && tte->depth() >= depth - 3 * ONE_PLY;
931 lock_grab(&(sp->lock));
932 bestValue = sp->bestValue;
935 // Step 10. Loop through moves
936 // Loop through all legal moves until no moves remain or a beta cutoff occurs
937 while ( bestValue < beta
938 && (move = mp.get_next_move()) != MOVE_NONE
939 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
941 assert(move_is_ok(move));
945 moveCount = ++sp->moveCount;
946 lock_release(&(sp->lock));
948 else if (move == excludedMove)
955 // This is used by time management
956 FirstRootMove = (moveCount == 1);
958 // Save the current node count before the move is searched
959 nodes = pos.nodes_searched();
961 // If it's time to send nodes info, do it here where we have the
962 // correct accumulated node counts searched by each thread.
963 if (SendSearchedNodes)
965 SendSearchedNodes = false;
966 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
969 if (current_search_time() > 2000)
970 cout << "info currmove " << move
971 << " currmovenumber " << moveCount << endl;
974 // At Root and at first iteration do a PV search on all the moves to score root moves
975 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
976 moveIsCheck = pos.move_is_check(move, ci);
977 captureOrPromotion = pos.move_is_capture_or_promotion(move);
979 // Step 11. Decide the new search depth
980 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
982 // Singular extension search. If all moves but one fail low on a search of
983 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
984 // is singular and should be extended. To verify this we do a reduced search
985 // on all the other moves but the ttMove, if result is lower than ttValue minus
986 // a margin then we extend ttMove.
987 if ( singularExtensionNode
988 && move == tte->move()
991 Value ttValue = value_from_tt(tte->value(), ss->ply);
993 if (abs(ttValue) < VALUE_KNOWN_WIN)
995 Value rBeta = ttValue - int(depth);
996 ss->excludedMove = move;
997 ss->skipNullMove = true;
998 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
999 ss->skipNullMove = false;
1000 ss->excludedMove = MOVE_NONE;
1001 ss->bestMove = MOVE_NONE;
1007 // Update current move (this must be done after singular extension search)
1008 ss->currentMove = move;
1009 newDepth = depth - ONE_PLY + ext;
1011 // Step 12. Futility pruning (is omitted in PV nodes)
1013 && !captureOrPromotion
1017 && !move_is_castle(move))
1019 // Move count based pruning
1020 if ( moveCount >= futility_move_count(depth)
1021 && (!threatMove || !connected_threat(pos, move, threatMove))
1022 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1025 lock_grab(&(sp->lock));
1030 // Value based pruning
1031 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1032 // but fixing this made program slightly weaker.
1033 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1034 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1035 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1037 if (futilityValueScaled < beta)
1041 lock_grab(&(sp->lock));
1042 if (futilityValueScaled > sp->bestValue)
1043 sp->bestValue = bestValue = futilityValueScaled;
1045 else if (futilityValueScaled > bestValue)
1046 bestValue = futilityValueScaled;
1051 // Prune moves with negative SEE at low depths
1052 if ( predictedDepth < 2 * ONE_PLY
1053 && bestValue > VALUE_MATED_IN_PLY_MAX
1054 && pos.see_sign(move) < 0)
1057 lock_grab(&(sp->lock));
1063 // Bad capture detection. Will be used by prob-cut search
1064 isBadCap = depth >= 3 * ONE_PLY
1065 && depth < 8 * ONE_PLY
1066 && captureOrPromotion
1069 && !move_is_promotion(move)
1070 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1071 && pos.see_sign(move) < 0;
1073 // Step 13. Make the move
1074 pos.do_move(move, st, ci, moveIsCheck);
1076 if (!SpNode && !captureOrPromotion)
1077 movesSearched[playedMoveCount++] = move;
1079 // Step extra. pv search (only in PV nodes)
1080 // The first move in list is the expected PV
1083 // Aspiration window is disabled in multi-pv case
1084 if (Root && MultiPV > 1)
1085 alpha = -VALUE_INFINITE;
1087 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1091 // Step 14. Reduced depth search
1092 // If the move fails high will be re-searched at full depth.
1093 bool doFullDepthSearch = true;
1094 alpha = SpNode ? sp->alpha : alpha;
1096 if ( depth >= 3 * ONE_PLY
1097 && !captureOrPromotion
1099 && !move_is_castle(move)
1100 && ss->killers[0] != move
1101 && ss->killers[1] != move)
1103 ss->reduction = reduction<PvNode>(depth, moveCount);
1106 alpha = SpNode ? sp->alpha : alpha;
1107 Depth d = newDepth - ss->reduction;
1108 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1110 doFullDepthSearch = (value > alpha);
1112 ss->reduction = DEPTH_ZERO; // Restore original reduction
1115 // Probcut search for bad captures. If a reduced search returns a value
1116 // very below beta then we can (almost) safely prune the bad capture.
1119 ss->reduction = 3 * ONE_PLY;
1120 Value rAlpha = alpha - 300;
1121 Depth d = newDepth - ss->reduction;
1122 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1123 doFullDepthSearch = (value > rAlpha);
1124 ss->reduction = DEPTH_ZERO; // Restore original reduction
1127 // Step 15. Full depth search
1128 if (doFullDepthSearch)
1130 alpha = SpNode ? sp->alpha : alpha;
1131 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1133 // Step extra. pv search (only in PV nodes)
1134 // Search only for possible new PV nodes, if instead value >= beta then
1135 // parent node fails low with value <= alpha and tries another move.
1136 if (PvNode && value > alpha && (Root || value < beta))
1137 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1141 // Step 16. Undo move
1142 pos.undo_move(move);
1144 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1146 // Step 17. Check for new best move
1149 lock_grab(&(sp->lock));
1150 bestValue = sp->bestValue;
1154 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1159 sp->bestValue = value;
1161 if (!Root && value > alpha)
1163 if (PvNode && value < beta) // We want always alpha < beta
1171 sp->betaCutoff = true;
1173 if (value == value_mate_in(ss->ply + 1))
1174 ss->mateKiller = move;
1176 ss->bestMove = move;
1179 sp->ss->bestMove = move;
1185 // Finished searching the move. If StopRequest is true, the search
1186 // was aborted because the user interrupted the search or because we
1187 // ran out of time. In this case, the return value of the search cannot
1188 // be trusted, and we break out of the loop without updating the best
1193 // Remember searched nodes counts for this move
1194 mp.rm->nodes += pos.nodes_searched() - nodes;
1196 // PV move or new best move ?
1197 if (isPvMove || value > alpha)
1200 ss->bestMove = move;
1201 mp.rm->pv_score = value;
1202 mp.rm->extract_pv_from_tt(pos);
1204 // We record how often the best move has been changed in each
1205 // iteration. This information is used for time management: When
1206 // the best move changes frequently, we allocate some more time.
1207 if (!isPvMove && MultiPV == 1)
1208 Rml.bestMoveChanges++;
1210 Rml.sort_multipv(moveCount);
1212 // Update alpha. In multi-pv we don't use aspiration window, so
1213 // set alpha equal to minimum score among the PV lines.
1215 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1216 else if (value > alpha)
1220 mp.rm->pv_score = -VALUE_INFINITE;
1224 // Step 18. Check for split
1227 && depth >= ThreadsMgr.min_split_depth()
1228 && ThreadsMgr.active_threads() > 1
1230 && ThreadsMgr.available_thread_exists(threadID)
1232 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1233 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1234 threatMove, moveCount, &mp, PvNode);
1237 // Step 19. Check for mate and stalemate
1238 // All legal moves have been searched and if there are
1239 // no legal moves, it must be mate or stalemate.
1240 // If one move was excluded return fail low score.
1241 if (!SpNode && !moveCount)
1242 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1244 // Step 20. Update tables
1245 // If the search is not aborted, update the transposition table,
1246 // history counters, and killer moves.
1247 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1249 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1250 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1251 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1253 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1255 // Update killers and history only for non capture moves that fails high
1256 if ( bestValue >= beta
1257 && !pos.move_is_capture_or_promotion(move))
1259 if (move != ss->killers[0])
1261 ss->killers[1] = ss->killers[0];
1262 ss->killers[0] = move;
1264 update_history(pos, move, depth, movesSearched, playedMoveCount);
1270 // Here we have the lock still grabbed
1271 sp->slaves[threadID] = 0;
1272 sp->nodes += pos.nodes_searched();
1273 lock_release(&(sp->lock));
1276 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1281 // qsearch() is the quiescence search function, which is called by the main
1282 // search function when the remaining depth is zero (or, to be more precise,
1283 // less than ONE_PLY).
1285 template <NodeType PvNode>
1286 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1288 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1289 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1290 assert(PvNode || alpha == beta - 1);
1292 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1296 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1297 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1300 Value oldAlpha = alpha;
1302 ss->bestMove = ss->currentMove = MOVE_NONE;
1303 ss->ply = (ss-1)->ply + 1;
1305 // Check for an instant draw or maximum ply reached
1306 if (ss->ply > PLY_MAX || pos.is_draw())
1309 // Decide whether or not to include checks, this fixes also the type of
1310 // TT entry depth that we are going to use. Note that in qsearch we use
1311 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1312 isCheck = pos.is_check();
1313 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1315 // Transposition table lookup. At PV nodes, we don't use the TT for
1316 // pruning, but only for move ordering.
1317 tte = TT.retrieve(pos.get_key());
1318 ttMove = (tte ? tte->move() : MOVE_NONE);
1320 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1322 ss->bestMove = ttMove; // Can be MOVE_NONE
1323 return value_from_tt(tte->value(), ss->ply);
1326 // Evaluate the position statically
1329 bestValue = futilityBase = -VALUE_INFINITE;
1330 ss->eval = evalMargin = VALUE_NONE;
1331 enoughMaterial = false;
1337 assert(tte->static_value() != VALUE_NONE);
1339 evalMargin = tte->static_value_margin();
1340 ss->eval = bestValue = tte->static_value();
1343 ss->eval = bestValue = evaluate(pos, evalMargin);
1345 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1347 // Stand pat. Return immediately if static value is at least beta
1348 if (bestValue >= beta)
1351 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1356 if (PvNode && bestValue > alpha)
1359 // Futility pruning parameters, not needed when in check
1360 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1361 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1364 // Initialize a MovePicker object for the current position, and prepare
1365 // to search the moves. Because the depth is <= 0 here, only captures,
1366 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1368 MovePicker mp(pos, ttMove, depth, H);
1371 // Loop through the moves until no moves remain or a beta cutoff occurs
1372 while ( alpha < beta
1373 && (move = mp.get_next_move()) != MOVE_NONE)
1375 assert(move_is_ok(move));
1377 moveIsCheck = pos.move_is_check(move, ci);
1385 && !move_is_promotion(move)
1386 && !pos.move_is_passed_pawn_push(move))
1388 futilityValue = futilityBase
1389 + pos.endgame_value_of_piece_on(move_to(move))
1390 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1392 if (futilityValue < alpha)
1394 if (futilityValue > bestValue)
1395 bestValue = futilityValue;
1399 // Prune moves with negative or equal SEE
1400 if ( futilityBase < beta
1401 && depth < DEPTH_ZERO
1402 && pos.see(move) <= 0)
1406 // Detect non-capture evasions that are candidate to be pruned
1407 evasionPrunable = isCheck
1408 && bestValue > VALUE_MATED_IN_PLY_MAX
1409 && !pos.move_is_capture(move)
1410 && !pos.can_castle(pos.side_to_move());
1412 // Don't search moves with negative SEE values
1414 && (!isCheck || evasionPrunable)
1416 && !move_is_promotion(move)
1417 && pos.see_sign(move) < 0)
1420 // Don't search useless checks
1425 && !pos.move_is_capture_or_promotion(move)
1426 && ss->eval + PawnValueMidgame / 4 < beta
1427 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1429 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1430 bestValue = ss->eval + PawnValueMidgame / 4;
1435 // Update current move
1436 ss->currentMove = move;
1438 // Make and search the move
1439 pos.do_move(move, st, ci, moveIsCheck);
1440 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1441 pos.undo_move(move);
1443 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1446 if (value > bestValue)
1452 ss->bestMove = move;
1457 // All legal moves have been searched. A special case: If we're in check
1458 // and no legal moves were found, it is checkmate.
1459 if (isCheck && bestValue == -VALUE_INFINITE)
1460 return value_mated_in(ss->ply);
1462 // Update transposition table
1463 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1464 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1466 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1472 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1473 // bestValue is updated only when returning false because in that case move
1476 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1478 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1479 Square from, to, ksq, victimSq;
1482 Value futilityValue, bv = *bestValue;
1484 from = move_from(move);
1486 them = opposite_color(pos.side_to_move());
1487 ksq = pos.king_square(them);
1488 kingAtt = pos.attacks_from<KING>(ksq);
1489 pc = pos.piece_on(from);
1491 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1492 oldAtt = pos.attacks_from(pc, from, occ);
1493 newAtt = pos.attacks_from(pc, to, occ);
1495 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1496 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1498 if (!(b && (b & (b - 1))))
1501 // Rule 2. Queen contact check is very dangerous
1502 if ( type_of_piece(pc) == QUEEN
1503 && bit_is_set(kingAtt, to))
1506 // Rule 3. Creating new double threats with checks
1507 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1511 victimSq = pop_1st_bit(&b);
1512 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1514 // Note that here we generate illegal "double move"!
1515 if ( futilityValue >= beta
1516 && pos.see_sign(make_move(from, victimSq)) >= 0)
1519 if (futilityValue > bv)
1523 // Update bestValue only if check is not dangerous (because we will prune the move)
1529 // connected_moves() tests whether two moves are 'connected' in the sense
1530 // that the first move somehow made the second move possible (for instance
1531 // if the moving piece is the same in both moves). The first move is assumed
1532 // to be the move that was made to reach the current position, while the
1533 // second move is assumed to be a move from the current position.
1535 bool connected_moves(const Position& pos, Move m1, Move m2) {
1537 Square f1, t1, f2, t2;
1540 assert(m1 && move_is_ok(m1));
1541 assert(m2 && move_is_ok(m2));
1543 // Case 1: The moving piece is the same in both moves
1549 // Case 2: The destination square for m2 was vacated by m1
1555 // Case 3: Moving through the vacated square
1556 if ( piece_is_slider(pos.piece_on(f2))
1557 && bit_is_set(squares_between(f2, t2), f1))
1560 // Case 4: The destination square for m2 is defended by the moving piece in m1
1561 p = pos.piece_on(t1);
1562 if (bit_is_set(pos.attacks_from(p, t1), t2))
1565 // Case 5: Discovered check, checking piece is the piece moved in m1
1566 if ( piece_is_slider(p)
1567 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1568 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1570 // discovered_check_candidates() works also if the Position's side to
1571 // move is the opposite of the checking piece.
1572 Color them = opposite_color(pos.side_to_move());
1573 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1575 if (bit_is_set(dcCandidates, f2))
1582 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1583 // "plies to mate from the current ply". Non-mate scores are unchanged.
1584 // The function is called before storing a value to the transposition table.
1586 Value value_to_tt(Value v, int ply) {
1588 if (v >= VALUE_MATE_IN_PLY_MAX)
1591 if (v <= VALUE_MATED_IN_PLY_MAX)
1598 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1599 // the transposition table to a mate score corrected for the current ply.
1601 Value value_from_tt(Value v, int ply) {
1603 if (v >= VALUE_MATE_IN_PLY_MAX)
1606 if (v <= VALUE_MATED_IN_PLY_MAX)
1613 // extension() decides whether a move should be searched with normal depth,
1614 // or with extended depth. Certain classes of moves (checking moves, in
1615 // particular) are searched with bigger depth than ordinary moves and in
1616 // any case are marked as 'dangerous'. Note that also if a move is not
1617 // extended, as example because the corresponding UCI option is set to zero,
1618 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1619 template <NodeType PvNode>
1620 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1621 bool moveIsCheck, bool* dangerous) {
1623 assert(m != MOVE_NONE);
1625 Depth result = DEPTH_ZERO;
1626 *dangerous = moveIsCheck;
1628 if (moveIsCheck && pos.see_sign(m) >= 0)
1629 result += CheckExtension[PvNode];
1631 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1633 Color c = pos.side_to_move();
1634 if (relative_rank(c, move_to(m)) == RANK_7)
1636 result += PawnPushTo7thExtension[PvNode];
1639 if (pos.pawn_is_passed(c, move_to(m)))
1641 result += PassedPawnExtension[PvNode];
1646 if ( captureOrPromotion
1647 && pos.type_of_piece_on(move_to(m)) != PAWN
1648 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1649 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1650 && !move_is_special(m))
1652 result += PawnEndgameExtension[PvNode];
1656 return Min(result, ONE_PLY);
1660 // connected_threat() tests whether it is safe to forward prune a move or if
1661 // is somehow connected to the threat move returned by null search.
1663 bool connected_threat(const Position& pos, Move m, Move threat) {
1665 assert(move_is_ok(m));
1666 assert(threat && move_is_ok(threat));
1667 assert(!pos.move_is_check(m));
1668 assert(!pos.move_is_capture_or_promotion(m));
1669 assert(!pos.move_is_passed_pawn_push(m));
1671 Square mfrom, mto, tfrom, tto;
1673 mfrom = move_from(m);
1675 tfrom = move_from(threat);
1676 tto = move_to(threat);
1678 // Case 1: Don't prune moves which move the threatened piece
1682 // Case 2: If the threatened piece has value less than or equal to the
1683 // value of the threatening piece, don't prune moves which defend it.
1684 if ( pos.move_is_capture(threat)
1685 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1686 || pos.type_of_piece_on(tfrom) == KING)
1687 && pos.move_attacks_square(m, tto))
1690 // Case 3: If the moving piece in the threatened move is a slider, don't
1691 // prune safe moves which block its ray.
1692 if ( piece_is_slider(pos.piece_on(tfrom))
1693 && bit_is_set(squares_between(tfrom, tto), mto)
1694 && pos.see_sign(m) >= 0)
1701 // ok_to_use_TT() returns true if a transposition table score
1702 // can be used at a given point in search.
1704 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1706 Value v = value_from_tt(tte->value(), ply);
1708 return ( tte->depth() >= depth
1709 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1710 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1712 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1713 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1717 // refine_eval() returns the transposition table score if
1718 // possible otherwise falls back on static position evaluation.
1720 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1724 Value v = value_from_tt(tte->value(), ply);
1726 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1727 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1734 // update_history() registers a good move that produced a beta-cutoff
1735 // in history and marks as failures all the other moves of that ply.
1737 void update_history(const Position& pos, Move move, Depth depth,
1738 Move movesSearched[], int moveCount) {
1740 Value bonus = Value(int(depth) * int(depth));
1742 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1744 for (int i = 0; i < moveCount - 1; i++)
1746 m = movesSearched[i];
1750 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1755 // update_gains() updates the gains table of a non-capture move given
1756 // the static position evaluation before and after the move.
1758 void update_gains(const Position& pos, Move m, Value before, Value after) {
1761 && before != VALUE_NONE
1762 && after != VALUE_NONE
1763 && pos.captured_piece_type() == PIECE_TYPE_NONE
1764 && !move_is_special(m))
1765 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1769 // current_search_time() returns the number of milliseconds which have passed
1770 // since the beginning of the current search.
1772 int current_search_time(int set) {
1774 static int searchStartTime;
1777 searchStartTime = set;
1779 return get_system_time() - searchStartTime;
1783 // value_to_uci() converts a value to a string suitable for use with the UCI
1784 // protocol specifications:
1786 // cp <x> The score from the engine's point of view in centipawns.
1787 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1788 // use negative values for y.
1790 std::string value_to_uci(Value v) {
1792 std::stringstream s;
1794 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1795 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1797 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1803 // speed_to_uci() returns a string with time stats of current search suitable
1804 // to be sent to UCI gui.
1806 std::string speed_to_uci(int64_t nodes) {
1808 std::stringstream s;
1809 int t = current_search_time();
1811 s << " nodes " << nodes
1812 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1819 // poll() performs two different functions: It polls for user input, and it
1820 // looks at the time consumed so far and decides if it's time to abort the
1823 void poll(const Position& pos) {
1825 static int lastInfoTime;
1826 int t = current_search_time();
1829 if (input_available())
1831 // We are line oriented, don't read single chars
1832 std::string command;
1834 if (!std::getline(std::cin, command) || command == "quit")
1836 // Quit the program as soon as possible
1837 Limits.ponder = false;
1838 QuitRequest = StopRequest = true;
1841 else if (command == "stop")
1843 // Stop calculating as soon as possible, but still send the "bestmove"
1844 // and possibly the "ponder" token when finishing the search.
1845 Limits.ponder = false;
1848 else if (command == "ponderhit")
1850 // The opponent has played the expected move. GUI sends "ponderhit" if
1851 // we were told to ponder on the same move the opponent has played. We
1852 // should continue searching but switching from pondering to normal search.
1853 Limits.ponder = false;
1855 if (StopOnPonderhit)
1860 // Print search information
1864 else if (lastInfoTime > t)
1865 // HACK: Must be a new search where we searched less than
1866 // NodesBetweenPolls nodes during the first second of search.
1869 else if (t - lastInfoTime >= 1000)
1874 dbg_print_hit_rate();
1876 // Send info on searched nodes as soon as we return to root
1877 SendSearchedNodes = true;
1880 // Should we stop the search?
1884 bool stillAtFirstMove = FirstRootMove
1885 && !AspirationFailLow
1886 && t > TimeMgr.available_time();
1888 bool noMoreTime = t > TimeMgr.maximum_time()
1889 || stillAtFirstMove;
1891 if ( (Limits.useTimeManagement() && noMoreTime)
1892 || (Limits.maxTime && t >= Limits.maxTime)
1893 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1898 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1899 // while the program is pondering. The point is to work around a wrinkle in
1900 // the UCI protocol: When pondering, the engine is not allowed to give a
1901 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1902 // We simply wait here until one of these commands is sent, and return,
1903 // after which the bestmove and pondermove will be printed.
1905 void wait_for_stop_or_ponderhit() {
1907 std::string command;
1909 // Wait for a command from stdin
1910 while ( std::getline(std::cin, command)
1911 && command != "ponderhit" && command != "stop" && command != "quit") {};
1913 if (command != "ponderhit" && command != "stop")
1914 QuitRequest = true; // Must be "quit" or getline() returned false
1918 // When playing with strength handicap choose best move among the MultiPV set
1919 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1920 void do_skill_level(Move* best, Move* ponder) {
1922 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_legal(pv[0]));
2023 pos.do_move(pv[0], *st++);
2025 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2026 && tte->move() != MOVE_NONE
2027 && pos.move_is_legal(tte->move())
2029 && (!pos.is_draw() || ply < 2))
2031 pv[ply] = tte->move();
2032 pos.do_move(pv[ply++], *st++);
2034 pv[ply] = MOVE_NONE;
2036 do pos.undo_move(pv[--ply]); while (ply);
2039 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2040 // the PV back into the TT. This makes sure the old PV moves are searched
2041 // first, even if the old TT entries have been overwritten.
2043 void RootMove::insert_pv_in_tt(Position& pos) {
2045 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2048 Value v, m = VALUE_NONE;
2051 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2055 tte = TT.retrieve(k);
2057 // Don't overwrite existing correct entries
2058 if (!tte || tte->move() != pv[ply])
2060 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2061 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2063 pos.do_move(pv[ply], *st++);
2065 } while (pv[++ply] != MOVE_NONE);
2067 do pos.undo_move(pv[--ply]); while (ply);
2070 // pv_info_to_uci() returns a string with information on the current PV line
2071 // formatted according to UCI specification.
2073 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2074 Value beta, int pvIdx) {
2075 std::stringstream s;
2077 s << "info depth " << depth
2078 << " seldepth " << selDepth
2079 << " multipv " << pvIdx + 1
2080 << " score " << value_to_uci(pv_score)
2081 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2082 << speed_to_uci(pos.nodes_searched())
2085 for (Move* m = pv; *m != MOVE_NONE; m++)
2094 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2095 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2096 // object for which the current thread is the master.
2098 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2100 assert(threadID >= 0 && threadID < MAX_THREADS);
2107 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2108 // master should exit as last one.
2109 if (allThreadsShouldExit)
2112 threads[threadID].state = THREAD_TERMINATED;
2116 // If we are not thinking, wait for a condition to be signaled
2117 // instead of wasting CPU time polling for work.
2118 while ( threadID >= activeThreads
2119 || threads[threadID].state == THREAD_INITIALIZING
2120 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2122 assert(!sp || useSleepingThreads);
2123 assert(threadID != 0 || useSleepingThreads);
2125 if (threads[threadID].state == THREAD_INITIALIZING)
2126 threads[threadID].state = THREAD_AVAILABLE;
2128 // Grab the lock to avoid races with Thread::wake_up()
2129 lock_grab(&threads[threadID].sleepLock);
2131 // If we are master and all slaves have finished do not go to sleep
2132 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2133 allFinished = (i == activeThreads);
2135 if (allFinished || allThreadsShouldExit)
2137 lock_release(&threads[threadID].sleepLock);
2141 // Do sleep here after retesting sleep conditions
2142 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2143 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2145 lock_release(&threads[threadID].sleepLock);
2148 // If this thread has been assigned work, launch a search
2149 if (threads[threadID].state == THREAD_WORKISWAITING)
2151 assert(!allThreadsShouldExit);
2153 threads[threadID].state = THREAD_SEARCHING;
2155 // Copy split point position and search stack and call search()
2156 // with SplitPoint template parameter set to true.
2157 SearchStack ss[PLY_MAX_PLUS_2];
2158 SplitPoint* tsp = threads[threadID].splitPoint;
2159 Position pos(*tsp->pos, threadID);
2161 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2165 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2167 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2169 assert(threads[threadID].state == THREAD_SEARCHING);
2171 threads[threadID].state = THREAD_AVAILABLE;
2173 // Wake up master thread so to allow it to return from the idle loop in
2174 // case we are the last slave of the split point.
2175 if ( useSleepingThreads
2176 && threadID != tsp->master
2177 && threads[tsp->master].state == THREAD_AVAILABLE)
2178 threads[tsp->master].wake_up();
2181 // If this thread is the master of a split point and all slaves have
2182 // finished their work at this split point, return from the idle loop.
2183 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2184 allFinished = (i == activeThreads);
2188 // Because sp->slaves[] is reset under lock protection,
2189 // be sure sp->lock has been released before to return.
2190 lock_grab(&(sp->lock));
2191 lock_release(&(sp->lock));
2193 // In helpful master concept a master can help only a sub-tree, and
2194 // because here is all finished is not possible master is booked.
2195 assert(threads[threadID].state == THREAD_AVAILABLE);
2197 threads[threadID].state = THREAD_SEARCHING;