2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
40 #include "ucioption.h"
47 // Different node types, used as template parameter
48 enum NodeType { NonPV, PV };
50 // Set to true to force running with one thread. Used for debugging.
51 const bool FakeSplit = false;
53 // Lookup table to check if a Piece is a slider and its access function
54 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
55 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
57 // ThreadsManager class is used to handle all the threads related stuff like init,
58 // starting, parking and, the most important, launching a slave thread at a split
59 // point. All the access to shared thread data is done through this class.
61 class ThreadsManager {
62 /* As long as the single ThreadsManager object is defined as a global we don't
63 need to explicitly initialize to zero its data members because variables with
64 static storage duration are automatically set to zero before enter main()
70 int min_split_depth() const { return minimumSplitDepth; }
71 int active_threads() const { return activeThreads; }
72 void set_active_threads(int cnt) { activeThreads = cnt; }
74 void read_uci_options();
75 bool available_thread_exists(int master) const;
76 bool thread_is_available(int slave, int master) const;
77 bool cutoff_at_splitpoint(int threadID) const;
78 void wake_sleeping_thread(int threadID);
79 void idle_loop(int threadID, SplitPoint* sp);
82 void split(Position& pos, SearchStack* ss, Value* alpha, const Value beta, Value* bestValue,
83 Depth depth, Move threatMove, int moveCount, MovePicker* mp, bool pvNode);
87 Depth minimumSplitDepth;
88 int maxThreadsPerSplitPoint;
89 bool useSleepingThreads;
91 volatile bool allThreadsShouldExit;
92 Thread threads[MAX_THREADS];
96 // RootMove struct is used for moves at the root of the tree. For each root
97 // move, we store two scores, a node count, and a PV (really a refutation
98 // in the case of moves which fail low). Value pv_score is normally set at
99 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
100 // according to the order in which moves are returned by MovePicker.
105 RootMove(const RootMove& rm) { *this = rm; }
106 RootMove& operator=(const RootMove& rm);
108 // RootMove::operator<() is the comparison function used when
109 // sorting the moves. A move m1 is considered to be better
110 // than a move m2 if it has an higher pv_score, or if it has
111 // equal pv_score but m1 has the higher non_pv_score. In this way
112 // we are guaranteed that PV moves are always sorted as first.
113 bool operator<(const RootMove& m) const {
114 return pv_score != m.pv_score ? pv_score < m.pv_score
115 : non_pv_score < m.non_pv_score;
118 void extract_pv_from_tt(Position& pos);
119 void insert_pv_in_tt(Position& pos);
120 std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvIdx);
125 Move pv[PLY_MAX_PLUS_2];
129 // RootMoveList struct is just a std::vector<> of RootMove objects,
130 // with an handful of methods above the standard ones.
132 struct RootMoveList : public std::vector<RootMove> {
134 typedef std::vector<RootMove> Base;
136 void init(Position& pos, Move searchMoves[]);
137 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
138 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
144 // Overload operator<<() to make it easier to print moves in a coordinate
145 // notation compatible with UCI protocol.
146 std::ostream& operator<<(std::ostream& os, Move m) {
148 bool chess960 = (os.iword(0) != 0); // See set960()
149 return os << move_to_uci(m, chess960);
153 // When formatting a move for std::cout we must know if we are in Chess960
154 // or not. To keep using the handy operator<<() on the move the trick is to
155 // embed this flag in the stream itself. Function-like named enum set960 is
156 // used as a custom manipulator and the stream internal general-purpose array,
157 // accessed through ios_base::iword(), is used to pass the flag to the move's
158 // operator<<() that will read it to properly format castling moves.
161 std::ostream& operator<< (std::ostream& os, const set960& f) {
163 os.iword(0) = int(f);
172 // Maximum depth for razoring
173 const Depth RazorDepth = 4 * ONE_PLY;
175 // Dynamic razoring margin based on depth
176 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
178 // Maximum depth for use of dynamic threat detection when null move fails low
179 const Depth ThreatDepth = 5 * ONE_PLY;
181 // Step 9. Internal iterative deepening
183 // Minimum depth for use of internal iterative deepening
184 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
186 // At Non-PV nodes we do an internal iterative deepening search
187 // when the static evaluation is bigger then beta - IIDMargin.
188 const Value IIDMargin = Value(0x100);
190 // Step 11. Decide the new search depth
192 // Extensions. Configurable UCI options
193 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
194 Depth CheckExtension[2], PawnPushTo7thExtension[2];
195 Depth PassedPawnExtension[2], PawnEndgameExtension[2];
197 // Minimum depth for use of singular extension
198 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
200 // Step 12. Futility pruning
202 // Futility margin for quiescence search
203 const Value FutilityMarginQS = Value(0x80);
205 // Futility lookup tables (initialized at startup) and their access functions
206 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
207 int FutilityMoveCountArray[32]; // [depth]
209 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
210 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
212 // Step 14. Reduced search
214 // Reduction lookup tables (initialized at startup) and their getter functions
215 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
217 template <NodeType PV>
218 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)]; }
220 // Easy move margin. An easy move candidate must be at least this much
221 // better than the second best move.
222 const Value EasyMoveMargin = Value(0x200);
225 /// Namespace variables
234 int MultiPV, UCIMultiPV;
236 // Time management variables
237 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
238 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
239 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
244 std::ofstream LogFile;
246 // Skill level adjustment
248 bool SkillLevelEnabled;
251 // Multi-threads manager
252 ThreadsManager ThreadsMgr;
254 // Node counters, used only by thread[0] but try to keep in different cache
255 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
256 bool SendSearchedNodes;
258 int NodesBetweenPolls = 30000;
266 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
268 template <NodeType PvNode, bool SpNode, bool Root>
269 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
271 template <NodeType PvNode>
272 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
274 template <NodeType PvNode>
275 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
277 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
278 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
281 template <NodeType PvNode>
282 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
284 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
285 bool connected_moves(const Position& pos, Move m1, Move m2);
286 Value value_to_tt(Value v, int ply);
287 Value value_from_tt(Value v, int ply);
288 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
289 bool connected_threat(const Position& pos, Move m, Move threat);
290 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
291 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
292 void update_gains(const Position& pos, Move move, Value before, Value after);
293 void do_skill_level(Move* best, Move* ponder);
295 int current_search_time();
296 std::string value_to_uci(Value v);
297 std::string speed_to_uci(int64_t nodes);
298 void poll(const Position& pos);
299 void wait_for_stop_or_ponderhit();
301 #if !defined(_MSC_VER)
302 void* init_thread(void* threadID);
304 DWORD WINAPI init_thread(LPVOID threadID);
308 // MovePickerExt is an extended MovePicker used to choose at compile time
309 // the proper move source according to the type of node.
310 template<bool SpNode, bool Root> struct MovePickerExt;
312 // In Root nodes use RootMoveList as source. Score and sort the root moves
313 // before to search them.
314 template<> struct MovePickerExt<false, true> : public MovePicker {
316 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
317 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
319 Value score = VALUE_ZERO;
321 // Score root moves using standard ordering used in main search, the moves
322 // are scored according to the order in which they are returned by MovePicker.
323 // This is the second order score that is used to compare the moves when
324 // the first orders pv_score of both moves are equal.
325 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
326 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
327 if (rm->pv[0] == move)
329 rm->non_pv_score = score--;
337 Move get_next_move() {
344 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
347 RootMoveList::iterator rm;
351 // In SpNodes use split point's shared MovePicker object as move source
352 template<> struct MovePickerExt<true, false> : public MovePicker {
354 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
355 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
357 Move get_next_move() { return mp->get_next_move(); }
359 RootMoveList::iterator rm; // Dummy, needed to compile
363 // Default case, create and use a MovePicker object as source
364 template<> struct MovePickerExt<false, false> : public MovePicker {
366 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
367 : MovePicker(p, ttm, d, h, ss, b) {}
369 RootMoveList::iterator rm; // Dummy, needed to compile
375 /// init_threads() is called during startup. It initializes various lookup tables
376 /// and creates and launches search threads.
378 void init_threads() {
380 int d; // depth (ONE_PLY == 2)
381 int hd; // half depth (ONE_PLY == 1)
384 // Init reductions array
385 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
387 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
388 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
389 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
390 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
393 // Init futility margins array
394 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
395 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
397 // Init futility move count array
398 for (d = 0; d < 32; d++)
399 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
401 // Create and startup threads
402 ThreadsMgr.init_threads();
406 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
407 void exit_threads() { ThreadsMgr.exit_threads(); }
410 /// perft() is our utility to verify move generation. All the legal moves up to
411 /// given depth are generated and counted and the sum returned.
413 int64_t perft(Position& pos, Depth depth) {
415 MoveStack mlist[MOVES_MAX];
420 // Generate all legal moves
421 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
423 // If we are at the last ply we don't need to do and undo
424 // the moves, just to count them.
425 if (depth <= ONE_PLY)
426 return int(last - mlist);
428 // Loop through all legal moves
430 for (MoveStack* cur = mlist; cur != last; cur++)
433 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
434 sum += perft(pos, depth - ONE_PLY);
441 /// think() is the external interface to Stockfish's search, and is called when
442 /// the program receives the UCI 'go' command. It initializes various global
443 /// variables, and calls id_loop(). It returns false when a quit command is
444 /// received during the search.
446 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
447 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
449 // Initialize global search-related variables
450 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
452 SearchStartTime = get_system_time();
453 ExactMaxTime = maxTime;
456 InfiniteSearch = infinite;
458 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
460 // Look for a book move, only during games, not tests
461 if (UseTimeManagement && Options["OwnBook"].value<bool>())
463 if (Options["Book File"].value<std::string>() != OpeningBook.name())
464 OpeningBook.open(Options["Book File"].value<std::string>());
466 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
467 if (bookMove != MOVE_NONE)
470 wait_for_stop_or_ponderhit();
472 cout << "bestmove " << bookMove << endl;
478 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
479 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
480 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
481 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
482 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
483 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
484 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
485 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
486 UCIMultiPV = Options["MultiPV"].value<int>();
487 SkillLevel = Options["Skill level"].value<int>();
488 UseLogFile = Options["Use Search Log"].value<bool>();
490 read_evaluation_uci_options(pos.side_to_move());
492 if (Options["Clear Hash"].value<bool>())
494 Options["Clear Hash"].set_value("false");
497 TT.set_size(Options["Hash"].value<int>());
499 // Do we have to play with skill handicap? In this case enable MultiPV that
500 // we will use behind the scenes to retrieve a set of possible moves.
501 SkillLevelEnabled = (SkillLevel < 20);
502 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
504 // Set the number of active threads
505 ThreadsMgr.read_uci_options();
506 init_eval(ThreadsMgr.active_threads());
508 // Wake up needed threads. Main thread, with threadID == 0, is always active
509 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
510 ThreadsMgr.wake_sleeping_thread(i);
513 int myTime = time[pos.side_to_move()];
514 int myIncrement = increment[pos.side_to_move()];
515 if (UseTimeManagement)
516 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
518 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
520 NodesBetweenPolls = Min(MaxNodes, 30000);
521 else if (myTime && myTime < 1000)
522 NodesBetweenPolls = 1000;
523 else if (myTime && myTime < 5000)
524 NodesBetweenPolls = 5000;
526 NodesBetweenPolls = 30000;
528 // Write search information to log file
531 std::string name = Options["Search Log Filename"].value<std::string>();
532 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
534 LogFile << "\nSearching: " << pos.to_fen()
535 << "\ninfinite: " << infinite
536 << " ponder: " << ponder
537 << " time: " << myTime
538 << " increment: " << myIncrement
539 << " moves to go: " << movesToGo
543 // We're ready to start thinking. Call the iterative deepening loop function
544 Move ponderMove = MOVE_NONE;
545 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
547 // Print final search statistics
548 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
552 int t = current_search_time();
554 LogFile << "Nodes: " << pos.nodes_searched()
555 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
556 << "\nBest move: " << move_to_san(pos, bestMove);
559 pos.do_move(bestMove, st);
560 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
561 pos.undo_move(bestMove); // Return from think() with unchanged position
565 // This makes all the threads to go to sleep
566 ThreadsMgr.set_active_threads(1);
568 // If we are pondering or in infinite search, we shouldn't print the
569 // best move before we are told to do so.
570 if (!StopRequest && (Pondering || InfiniteSearch))
571 wait_for_stop_or_ponderhit();
573 // Could be MOVE_NONE when searching on a stalemate position
574 cout << "bestmove " << bestMove;
576 // UCI protol is not clear on allowing sending an empty ponder move, instead
577 // it is clear that ponder move is optional. So skip it if empty.
578 if (ponderMove != MOVE_NONE)
579 cout << " ponder " << ponderMove;
589 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
590 // with increasing depth until the allocated thinking time has been consumed,
591 // user stops the search, or the maximum search depth is reached.
593 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
595 SearchStack ss[PLY_MAX_PLUS_2];
596 Value bestValues[PLY_MAX_PLUS_2];
597 int bestMoveChanges[PLY_MAX_PLUS_2];
598 int depth, aspirationDelta;
599 Value value, alpha, beta;
600 Move bestMove, easyMove, skillBest, skillPonder;
602 // Initialize stuff before a new search
603 memset(ss, 0, 4 * sizeof(SearchStack));
606 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
607 depth = aspirationDelta = 0;
608 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
609 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
611 // Moves to search are verified and copied
612 Rml.init(pos, searchMoves);
614 // Handle special case of searching on a mate/stalemate position
617 cout << "info depth 0 score "
618 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
624 // Iterative deepening loop
625 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
627 Rml.bestMoveChanges = 0;
628 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
630 // Calculate dynamic aspiration window based on previous iterations
631 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
633 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
634 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
636 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
637 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
639 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
640 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
643 // Start with a small aspiration window and, in case of fail high/low,
644 // research with bigger window until not failing high/low anymore.
646 // Search starting from ss+1 to allow calling update_gains()
647 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
649 // Write PV back to transposition table in case the relevant entries
650 // have been overwritten during the search.
651 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
652 Rml[i].insert_pv_in_tt(pos);
654 // Value cannot be trusted. Break out immediately!
658 assert(value >= alpha);
660 // In case of failing high/low increase aspiration window and research,
661 // otherwise exit the fail high/low loop.
664 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
665 aspirationDelta += aspirationDelta / 2;
667 else if (value <= alpha)
669 AspirationFailLow = true;
670 StopOnPonderhit = false;
672 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
673 aspirationDelta += aspirationDelta / 2;
678 } while (abs(value) < VALUE_KNOWN_WIN);
680 // Collect info about search result
681 bestMove = Rml[0].pv[0];
682 *ponderMove = Rml[0].pv[1];
683 bestValues[depth] = value;
684 bestMoveChanges[depth] = Rml.bestMoveChanges;
686 // Do we need to pick now the best and the ponder moves ?
687 if (SkillLevelEnabled && depth == 1 + SkillLevel)
688 do_skill_level(&skillBest, &skillPonder);
690 // Send PV line to GUI and to log file
691 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
692 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
695 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
697 // Init easyMove after first iteration or drop if differs from the best move
698 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
700 else if (bestMove != easyMove)
701 easyMove = MOVE_NONE;
703 if (UseTimeManagement && !StopRequest)
706 bool noMoreTime = false;
708 // Stop search early when the last two iterations returned a mate score
710 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
711 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
714 // Stop search early if one move seems to be much better than the
715 // others or if there is only a single legal move. In this latter
716 // case we search up to Iteration 8 anyway to get a proper score.
718 && easyMove == bestMove
720 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
721 && current_search_time() > TimeMgr.available_time() / 16)
722 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
723 && current_search_time() > TimeMgr.available_time() / 32)))
726 // Add some extra time if the best move has changed during the last two iterations
727 if (depth > 4 && depth < 50)
728 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
730 // Stop search if most of MaxSearchTime is consumed at the end of the
731 // iteration. We probably don't have enough time to search the first
732 // move at the next iteration anyway.
733 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
739 StopOnPonderhit = true;
746 // When using skills fake best and ponder moves with the sub-optimal ones
747 if (SkillLevelEnabled)
749 if (skillBest == MOVE_NONE) // Still unassigned ?
750 do_skill_level(&skillBest, &skillPonder);
752 bestMove = skillBest;
753 *ponderMove = skillPonder;
760 // search<>() is the main search function for both PV and non-PV nodes and for
761 // normal and SplitPoint nodes. When called just after a split point the search
762 // is simpler because we have already probed the hash table, done a null move
763 // search, and searched the first move before splitting, we don't have to repeat
764 // all this work again. We also don't need to store anything to the hash table
765 // here: This is taken care of after we return from the split point.
767 template <NodeType PvNode, bool SpNode, bool Root>
768 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
770 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
771 assert(beta > alpha && beta <= VALUE_INFINITE);
772 assert(PvNode || alpha == beta - 1);
773 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
775 Move movesSearched[MOVES_MAX];
780 Move ttMove, move, excludedMove, threatMove;
783 Value bestValue, value, oldAlpha;
784 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
785 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
786 int moveCount = 0, playedMoveCount = 0;
787 int threadID = pos.thread();
788 SplitPoint* sp = NULL;
790 refinedValue = bestValue = value = -VALUE_INFINITE;
792 isCheck = pos.is_check();
793 ss->ply = (ss-1)->ply + 1;
799 ttMove = excludedMove = MOVE_NONE;
800 threatMove = sp->threatMove;
801 goto split_point_start;
806 // Step 1. Initialize node and poll. Polling can abort search
807 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
808 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
809 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
811 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
817 // Step 2. Check for aborted search and immediate draw
819 || ThreadsMgr.cutoff_at_splitpoint(threadID)
821 || ss->ply > PLY_MAX) && !Root)
824 // Step 3. Mate distance pruning
825 alpha = Max(value_mated_in(ss->ply), alpha);
826 beta = Min(value_mate_in(ss->ply+1), beta);
830 // Step 4. Transposition table lookup
831 // We don't want the score of a partial search to overwrite a previous full search
832 // TT value, so we use a different position key in case of an excluded move.
833 excludedMove = ss->excludedMove;
834 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
836 tte = TT.retrieve(posKey);
837 ttMove = tte ? tte->move() : MOVE_NONE;
839 // At PV nodes we check for exact scores, while at non-PV nodes we check for
840 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
841 // smooth experience in analysis mode.
844 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
845 : ok_to_use_TT(tte, depth, beta, ss->ply)))
848 ss->bestMove = ttMove; // Can be MOVE_NONE
849 return value_from_tt(tte->value(), ss->ply);
852 // Step 5. Evaluate the position statically and update parent's gain statistics
854 ss->eval = ss->evalMargin = VALUE_NONE;
857 assert(tte->static_value() != VALUE_NONE);
859 ss->eval = tte->static_value();
860 ss->evalMargin = tte->static_value_margin();
861 refinedValue = refine_eval(tte, ss->eval, ss->ply);
865 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
866 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
869 // Save gain for the parent non-capture move
870 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
872 // Step 6. Razoring (is omitted in PV nodes)
874 && depth < RazorDepth
876 && refinedValue + razor_margin(depth) < beta
877 && ttMove == MOVE_NONE
878 && abs(beta) < VALUE_MATE_IN_PLY_MAX
879 && !pos.has_pawn_on_7th(pos.side_to_move()))
881 Value rbeta = beta - razor_margin(depth);
882 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
884 // Logically we should return (v + razor_margin(depth)), but
885 // surprisingly this did slightly weaker in tests.
889 // Step 7. Static null move pruning (is omitted in PV nodes)
890 // We're betting that the opponent doesn't have a move that will reduce
891 // the score by more than futility_margin(depth) if we do a null move.
894 && depth < RazorDepth
896 && refinedValue - futility_margin(depth, 0) >= beta
897 && abs(beta) < VALUE_MATE_IN_PLY_MAX
898 && pos.non_pawn_material(pos.side_to_move()))
899 return refinedValue - futility_margin(depth, 0);
901 // Step 8. Null move search with verification search (is omitted in PV nodes)
906 && refinedValue >= beta
907 && abs(beta) < VALUE_MATE_IN_PLY_MAX
908 && pos.non_pawn_material(pos.side_to_move()))
910 ss->currentMove = MOVE_NULL;
912 // Null move dynamic reduction based on depth
913 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
915 // Null move dynamic reduction based on value
916 if (refinedValue - PawnValueMidgame > beta)
919 pos.do_null_move(st);
920 (ss+1)->skipNullMove = true;
921 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
922 (ss+1)->skipNullMove = false;
923 pos.undo_null_move();
925 if (nullValue >= beta)
927 // Do not return unproven mate scores
928 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
931 if (depth < 6 * ONE_PLY)
934 // Do verification search at high depths
935 ss->skipNullMove = true;
936 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
937 ss->skipNullMove = false;
944 // The null move failed low, which means that we may be faced with
945 // some kind of threat. If the previous move was reduced, check if
946 // the move that refuted the null move was somehow connected to the
947 // move which was reduced. If a connection is found, return a fail
948 // low score (which will cause the reduced move to fail high in the
949 // parent node, which will trigger a re-search with full depth).
950 threatMove = (ss+1)->bestMove;
952 if ( depth < ThreatDepth
954 && threatMove != MOVE_NONE
955 && connected_moves(pos, (ss-1)->currentMove, threatMove))
960 // Step 9. Internal iterative deepening
961 if ( depth >= IIDDepth[PvNode]
962 && ttMove == MOVE_NONE
963 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
965 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
967 ss->skipNullMove = true;
968 search<PvNode>(pos, ss, alpha, beta, d);
969 ss->skipNullMove = false;
971 ttMove = ss->bestMove;
972 tte = TT.retrieve(posKey);
975 split_point_start: // At split points actual search starts from here
977 // Initialize a MovePicker object for the current position
978 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
980 ss->bestMove = MOVE_NONE;
981 futilityBase = ss->eval + ss->evalMargin;
982 singularExtensionNode = !Root
984 && depth >= SingularExtensionDepth[PvNode]
987 && !excludedMove // Do not allow recursive singular extension search
988 && (tte->type() & VALUE_TYPE_LOWER)
989 && tte->depth() >= depth - 3 * ONE_PLY;
992 lock_grab(&(sp->lock));
993 bestValue = sp->bestValue;
996 // Step 10. Loop through moves
997 // Loop through all legal moves until no moves remain or a beta cutoff occurs
998 while ( bestValue < beta
999 && (move = mp.get_next_move()) != MOVE_NONE
1000 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1002 assert(move_is_ok(move));
1006 moveCount = ++sp->moveCount;
1007 lock_release(&(sp->lock));
1009 else if (move == excludedMove)
1016 // This is used by time management
1017 FirstRootMove = (moveCount == 1);
1019 // Save the current node count before the move is searched
1020 nodes = pos.nodes_searched();
1022 // If it's time to send nodes info, do it here where we have the
1023 // correct accumulated node counts searched by each thread.
1024 if (SendSearchedNodes)
1026 SendSearchedNodes = false;
1027 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1030 if (current_search_time() > 2000)
1031 cout << "info currmove " << move
1032 << " currmovenumber " << moveCount << endl;
1035 // At Root and at first iteration do a PV search on all the moves to score root moves
1036 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
1037 moveIsCheck = pos.move_is_check(move, ci);
1038 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1040 // Step 11. Decide the new search depth
1041 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
1043 // Singular extension search. If all moves but one fail low on a search of
1044 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1045 // is singular and should be extended. To verify this we do a reduced search
1046 // on all the other moves but the ttMove, if result is lower than ttValue minus
1047 // a margin then we extend ttMove.
1048 if ( singularExtensionNode
1049 && move == tte->move()
1052 Value ttValue = value_from_tt(tte->value(), ss->ply);
1054 if (abs(ttValue) < VALUE_KNOWN_WIN)
1056 Value rBeta = ttValue - int(depth);
1057 ss->excludedMove = move;
1058 ss->skipNullMove = true;
1059 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1060 ss->skipNullMove = false;
1061 ss->excludedMove = MOVE_NONE;
1062 ss->bestMove = MOVE_NONE;
1068 // Update current move (this must be done after singular extension search)
1069 ss->currentMove = move;
1070 newDepth = depth - ONE_PLY + ext;
1072 // Step 12. Futility pruning (is omitted in PV nodes)
1074 && !captureOrPromotion
1078 && !move_is_castle(move))
1080 // Move count based pruning
1081 if ( moveCount >= futility_move_count(depth)
1082 && (!threatMove || !connected_threat(pos, move, threatMove))
1083 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1086 lock_grab(&(sp->lock));
1091 // Value based pruning
1092 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1093 // but fixing this made program slightly weaker.
1094 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1095 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1096 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1098 if (futilityValueScaled < beta)
1102 lock_grab(&(sp->lock));
1103 if (futilityValueScaled > sp->bestValue)
1104 sp->bestValue = bestValue = futilityValueScaled;
1106 else if (futilityValueScaled > bestValue)
1107 bestValue = futilityValueScaled;
1112 // Prune moves with negative SEE at low depths
1113 if ( predictedDepth < 2 * ONE_PLY
1114 && bestValue > VALUE_MATED_IN_PLY_MAX
1115 && pos.see_sign(move) < 0)
1118 lock_grab(&(sp->lock));
1124 // Bad capture detection. Will be used by prob-cut search
1125 isBadCap = depth >= 3 * ONE_PLY
1126 && depth < 8 * ONE_PLY
1127 && captureOrPromotion
1130 && !move_is_promotion(move)
1131 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1132 && pos.see_sign(move) < 0;
1134 // Step 13. Make the move
1135 pos.do_move(move, st, ci, moveIsCheck);
1137 if (!SpNode && !captureOrPromotion)
1138 movesSearched[playedMoveCount++] = move;
1140 // Step extra. pv search (only in PV nodes)
1141 // The first move in list is the expected PV
1144 // Aspiration window is disabled in multi-pv case
1145 if (Root && MultiPV > 1)
1146 alpha = -VALUE_INFINITE;
1148 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1152 // Step 14. Reduced depth search
1153 // If the move fails high will be re-searched at full depth.
1154 bool doFullDepthSearch = true;
1155 alpha = SpNode ? sp->alpha : alpha;
1157 if ( depth >= 3 * ONE_PLY
1158 && !captureOrPromotion
1160 && !move_is_castle(move)
1161 && ss->killers[0] != move
1162 && ss->killers[1] != move)
1164 ss->reduction = reduction<PvNode>(depth, moveCount);
1167 alpha = SpNode ? sp->alpha : alpha;
1168 Depth d = newDepth - ss->reduction;
1169 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1171 doFullDepthSearch = (value > alpha);
1173 ss->reduction = DEPTH_ZERO; // Restore original reduction
1176 // Probcut search for bad captures. If a reduced search returns a value
1177 // very below beta then we can (almost) safely prune the bad capture.
1180 ss->reduction = 3 * ONE_PLY;
1181 Value rAlpha = alpha - 300;
1182 Depth d = newDepth - ss->reduction;
1183 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1184 doFullDepthSearch = (value > rAlpha);
1185 ss->reduction = DEPTH_ZERO; // Restore original reduction
1188 // Step 15. Full depth search
1189 if (doFullDepthSearch)
1191 alpha = SpNode ? sp->alpha : alpha;
1192 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1194 // Step extra. pv search (only in PV nodes)
1195 // Search only for possible new PV nodes, if instead value >= beta then
1196 // parent node fails low with value <= alpha and tries another move.
1197 if (PvNode && value > alpha && (Root || value < beta))
1198 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1202 // Step 16. Undo move
1203 pos.undo_move(move);
1205 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1207 // Step 17. Check for new best move
1210 lock_grab(&(sp->lock));
1211 bestValue = sp->bestValue;
1215 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1220 sp->bestValue = value;
1222 if (!Root && value > alpha)
1224 if (PvNode && value < beta) // We want always alpha < beta
1232 sp->betaCutoff = true;
1234 if (value == value_mate_in(ss->ply + 1))
1235 ss->mateKiller = move;
1237 ss->bestMove = move;
1240 sp->ss->bestMove = move;
1246 // Finished searching the move. If StopRequest is true, the search
1247 // was aborted because the user interrupted the search or because we
1248 // ran out of time. In this case, the return value of the search cannot
1249 // be trusted, and we break out of the loop without updating the best
1254 // Remember searched nodes counts for this move
1255 mp.rm->nodes += pos.nodes_searched() - nodes;
1257 // PV move or new best move ?
1258 if (isPvMove || value > alpha)
1261 ss->bestMove = move;
1262 mp.rm->pv_score = value;
1263 mp.rm->extract_pv_from_tt(pos);
1265 // We record how often the best move has been changed in each
1266 // iteration. This information is used for time management: When
1267 // the best move changes frequently, we allocate some more time.
1268 if (!isPvMove && MultiPV == 1)
1269 Rml.bestMoveChanges++;
1271 Rml.sort_multipv(moveCount);
1273 // Update alpha. In multi-pv we don't use aspiration window, so
1274 // set alpha equal to minimum score among the PV lines.
1276 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1277 else if (value > alpha)
1281 mp.rm->pv_score = -VALUE_INFINITE;
1285 // Step 18. Check for split
1288 && depth >= ThreadsMgr.min_split_depth()
1289 && ThreadsMgr.active_threads() > 1
1291 && ThreadsMgr.available_thread_exists(threadID)
1293 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1294 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1295 threatMove, moveCount, &mp, PvNode);
1298 // Step 19. Check for mate and stalemate
1299 // All legal moves have been searched and if there are
1300 // no legal moves, it must be mate or stalemate.
1301 // If one move was excluded return fail low score.
1302 if (!SpNode && !moveCount)
1303 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1305 // Step 20. Update tables
1306 // If the search is not aborted, update the transposition table,
1307 // history counters, and killer moves.
1308 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1310 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1311 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1312 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1314 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1316 // Update killers and history only for non capture moves that fails high
1317 if ( bestValue >= beta
1318 && !pos.move_is_capture_or_promotion(move))
1320 if (move != ss->killers[0])
1322 ss->killers[1] = ss->killers[0];
1323 ss->killers[0] = move;
1325 update_history(pos, move, depth, movesSearched, playedMoveCount);
1331 // Here we have the lock still grabbed
1332 sp->slaves[threadID] = 0;
1333 sp->nodes += pos.nodes_searched();
1334 lock_release(&(sp->lock));
1337 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1342 // qsearch() is the quiescence search function, which is called by the main
1343 // search function when the remaining depth is zero (or, to be more precise,
1344 // less than ONE_PLY).
1346 template <NodeType PvNode>
1347 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1349 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1350 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1351 assert(PvNode || alpha == beta - 1);
1353 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1357 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1358 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1361 Value oldAlpha = alpha;
1363 ss->bestMove = ss->currentMove = MOVE_NONE;
1364 ss->ply = (ss-1)->ply + 1;
1366 // Check for an instant draw or maximum ply reached
1367 if (ss->ply > PLY_MAX || pos.is_draw())
1370 // Decide whether or not to include checks, this fixes also the type of
1371 // TT entry depth that we are going to use. Note that in qsearch we use
1372 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1373 isCheck = pos.is_check();
1374 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1376 // Transposition table lookup. At PV nodes, we don't use the TT for
1377 // pruning, but only for move ordering.
1378 tte = TT.retrieve(pos.get_key());
1379 ttMove = (tte ? tte->move() : MOVE_NONE);
1381 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1383 ss->bestMove = ttMove; // Can be MOVE_NONE
1384 return value_from_tt(tte->value(), ss->ply);
1387 // Evaluate the position statically
1390 bestValue = futilityBase = -VALUE_INFINITE;
1391 ss->eval = evalMargin = VALUE_NONE;
1392 enoughMaterial = false;
1398 assert(tte->static_value() != VALUE_NONE);
1400 evalMargin = tte->static_value_margin();
1401 ss->eval = bestValue = tte->static_value();
1404 ss->eval = bestValue = evaluate(pos, evalMargin);
1406 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1408 // Stand pat. Return immediately if static value is at least beta
1409 if (bestValue >= beta)
1412 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1417 if (PvNode && bestValue > alpha)
1420 // Futility pruning parameters, not needed when in check
1421 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1422 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1425 // Initialize a MovePicker object for the current position, and prepare
1426 // to search the moves. Because the depth is <= 0 here, only captures,
1427 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1429 MovePicker mp(pos, ttMove, depth, H);
1432 // Loop through the moves until no moves remain or a beta cutoff occurs
1433 while ( alpha < beta
1434 && (move = mp.get_next_move()) != MOVE_NONE)
1436 assert(move_is_ok(move));
1438 moveIsCheck = pos.move_is_check(move, ci);
1446 && !move_is_promotion(move)
1447 && !pos.move_is_passed_pawn_push(move))
1449 futilityValue = futilityBase
1450 + pos.endgame_value_of_piece_on(move_to(move))
1451 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1453 if (futilityValue < alpha)
1455 if (futilityValue > bestValue)
1456 bestValue = futilityValue;
1460 // Prune moves with negative or equal SEE
1461 if ( futilityBase < beta
1462 && depth < DEPTH_ZERO
1463 && pos.see(move) <= 0)
1467 // Detect non-capture evasions that are candidate to be pruned
1468 evasionPrunable = isCheck
1469 && bestValue > VALUE_MATED_IN_PLY_MAX
1470 && !pos.move_is_capture(move)
1471 && !pos.can_castle(pos.side_to_move());
1473 // Don't search moves with negative SEE values
1475 && (!isCheck || evasionPrunable)
1477 && !move_is_promotion(move)
1478 && pos.see_sign(move) < 0)
1481 // Don't search useless checks
1486 && !pos.move_is_capture_or_promotion(move)
1487 && ss->eval + PawnValueMidgame / 4 < beta
1488 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1490 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1491 bestValue = ss->eval + PawnValueMidgame / 4;
1496 // Update current move
1497 ss->currentMove = move;
1499 // Make and search the move
1500 pos.do_move(move, st, ci, moveIsCheck);
1501 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1502 pos.undo_move(move);
1504 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1507 if (value > bestValue)
1513 ss->bestMove = move;
1518 // All legal moves have been searched. A special case: If we're in check
1519 // and no legal moves were found, it is checkmate.
1520 if (isCheck && bestValue == -VALUE_INFINITE)
1521 return value_mated_in(ss->ply);
1523 // Update transposition table
1524 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1525 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1527 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1533 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1534 // bestValue is updated only when returning false because in that case move
1537 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1539 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1540 Square from, to, ksq, victimSq;
1543 Value futilityValue, bv = *bestValue;
1545 from = move_from(move);
1547 them = opposite_color(pos.side_to_move());
1548 ksq = pos.king_square(them);
1549 kingAtt = pos.attacks_from<KING>(ksq);
1550 pc = pos.piece_on(from);
1552 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1553 oldAtt = pos.attacks_from(pc, from, occ);
1554 newAtt = pos.attacks_from(pc, to, occ);
1556 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1557 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1559 if (!(b && (b & (b - 1))))
1562 // Rule 2. Queen contact check is very dangerous
1563 if ( type_of_piece(pc) == QUEEN
1564 && bit_is_set(kingAtt, to))
1567 // Rule 3. Creating new double threats with checks
1568 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1572 victimSq = pop_1st_bit(&b);
1573 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1575 // Note that here we generate illegal "double move"!
1576 if ( futilityValue >= beta
1577 && pos.see_sign(make_move(from, victimSq)) >= 0)
1580 if (futilityValue > bv)
1584 // Update bestValue only if check is not dangerous (because we will prune the move)
1590 // connected_moves() tests whether two moves are 'connected' in the sense
1591 // that the first move somehow made the second move possible (for instance
1592 // if the moving piece is the same in both moves). The first move is assumed
1593 // to be the move that was made to reach the current position, while the
1594 // second move is assumed to be a move from the current position.
1596 bool connected_moves(const Position& pos, Move m1, Move m2) {
1598 Square f1, t1, f2, t2;
1601 assert(m1 && move_is_ok(m1));
1602 assert(m2 && move_is_ok(m2));
1604 // Case 1: The moving piece is the same in both moves
1610 // Case 2: The destination square for m2 was vacated by m1
1616 // Case 3: Moving through the vacated square
1617 if ( piece_is_slider(pos.piece_on(f2))
1618 && bit_is_set(squares_between(f2, t2), f1))
1621 // Case 4: The destination square for m2 is defended by the moving piece in m1
1622 p = pos.piece_on(t1);
1623 if (bit_is_set(pos.attacks_from(p, t1), t2))
1626 // Case 5: Discovered check, checking piece is the piece moved in m1
1627 if ( piece_is_slider(p)
1628 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1629 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1631 // discovered_check_candidates() works also if the Position's side to
1632 // move is the opposite of the checking piece.
1633 Color them = opposite_color(pos.side_to_move());
1634 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1636 if (bit_is_set(dcCandidates, f2))
1643 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1644 // "plies to mate from the current ply". Non-mate scores are unchanged.
1645 // The function is called before storing a value to the transposition table.
1647 Value value_to_tt(Value v, int ply) {
1649 if (v >= VALUE_MATE_IN_PLY_MAX)
1652 if (v <= VALUE_MATED_IN_PLY_MAX)
1659 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1660 // the transposition table to a mate score corrected for the current ply.
1662 Value value_from_tt(Value v, int ply) {
1664 if (v >= VALUE_MATE_IN_PLY_MAX)
1667 if (v <= VALUE_MATED_IN_PLY_MAX)
1674 // extension() decides whether a move should be searched with normal depth,
1675 // or with extended depth. Certain classes of moves (checking moves, in
1676 // particular) are searched with bigger depth than ordinary moves and in
1677 // any case are marked as 'dangerous'. Note that also if a move is not
1678 // extended, as example because the corresponding UCI option is set to zero,
1679 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1680 template <NodeType PvNode>
1681 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1682 bool moveIsCheck, bool* dangerous) {
1684 assert(m != MOVE_NONE);
1686 Depth result = DEPTH_ZERO;
1687 *dangerous = moveIsCheck;
1689 if (moveIsCheck && pos.see_sign(m) >= 0)
1690 result += CheckExtension[PvNode];
1692 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1694 Color c = pos.side_to_move();
1695 if (relative_rank(c, move_to(m)) == RANK_7)
1697 result += PawnPushTo7thExtension[PvNode];
1700 if (pos.pawn_is_passed(c, move_to(m)))
1702 result += PassedPawnExtension[PvNode];
1707 if ( captureOrPromotion
1708 && pos.type_of_piece_on(move_to(m)) != PAWN
1709 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1710 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1711 && !move_is_promotion(m)
1714 result += PawnEndgameExtension[PvNode];
1718 return Min(result, ONE_PLY);
1722 // connected_threat() tests whether it is safe to forward prune a move or if
1723 // is somehow connected to the threat move returned by null search.
1725 bool connected_threat(const Position& pos, Move m, Move threat) {
1727 assert(move_is_ok(m));
1728 assert(threat && move_is_ok(threat));
1729 assert(!pos.move_is_check(m));
1730 assert(!pos.move_is_capture_or_promotion(m));
1731 assert(!pos.move_is_passed_pawn_push(m));
1733 Square mfrom, mto, tfrom, tto;
1735 mfrom = move_from(m);
1737 tfrom = move_from(threat);
1738 tto = move_to(threat);
1740 // Case 1: Don't prune moves which move the threatened piece
1744 // Case 2: If the threatened piece has value less than or equal to the
1745 // value of the threatening piece, don't prune moves which defend it.
1746 if ( pos.move_is_capture(threat)
1747 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1748 || pos.type_of_piece_on(tfrom) == KING)
1749 && pos.move_attacks_square(m, tto))
1752 // Case 3: If the moving piece in the threatened move is a slider, don't
1753 // prune safe moves which block its ray.
1754 if ( piece_is_slider(pos.piece_on(tfrom))
1755 && bit_is_set(squares_between(tfrom, tto), mto)
1756 && pos.see_sign(m) >= 0)
1763 // ok_to_use_TT() returns true if a transposition table score
1764 // can be used at a given point in search.
1766 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1768 Value v = value_from_tt(tte->value(), ply);
1770 return ( tte->depth() >= depth
1771 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1772 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1774 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1775 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1779 // refine_eval() returns the transposition table score if
1780 // possible otherwise falls back on static position evaluation.
1782 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1786 Value v = value_from_tt(tte->value(), ply);
1788 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1789 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1796 // update_history() registers a good move that produced a beta-cutoff
1797 // in history and marks as failures all the other moves of that ply.
1799 void update_history(const Position& pos, Move move, Depth depth,
1800 Move movesSearched[], int moveCount) {
1802 Value bonus = Value(int(depth) * int(depth));
1804 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1806 for (int i = 0; i < moveCount - 1; i++)
1808 m = movesSearched[i];
1812 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1817 // update_gains() updates the gains table of a non-capture move given
1818 // the static position evaluation before and after the move.
1820 void update_gains(const Position& pos, Move m, Value before, Value after) {
1823 && before != VALUE_NONE
1824 && after != VALUE_NONE
1825 && pos.captured_piece_type() == PIECE_TYPE_NONE
1826 && !move_is_special(m))
1827 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1831 // current_search_time() returns the number of milliseconds which have passed
1832 // since the beginning of the current search.
1834 int current_search_time() {
1836 return get_system_time() - SearchStartTime;
1840 // value_to_uci() converts a value to a string suitable for use with the UCI
1841 // protocol specifications:
1843 // cp <x> The score from the engine's point of view in centipawns.
1844 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1845 // use negative values for y.
1847 std::string value_to_uci(Value v) {
1849 std::stringstream s;
1851 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1852 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1854 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1860 // speed_to_uci() returns a string with time stats of current search suitable
1861 // to be sent to UCI gui.
1863 std::string speed_to_uci(int64_t nodes) {
1865 std::stringstream s;
1866 int t = current_search_time();
1868 s << " nodes " << nodes
1869 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1876 // poll() performs two different functions: It polls for user input, and it
1877 // looks at the time consumed so far and decides if it's time to abort the
1880 void poll(const Position& pos) {
1882 static int lastInfoTime;
1883 int t = current_search_time();
1886 if (input_available())
1888 // We are line oriented, don't read single chars
1889 std::string command;
1891 if (!std::getline(std::cin, command) || command == "quit")
1893 // Quit the program as soon as possible
1895 QuitRequest = StopRequest = true;
1898 else if (command == "stop")
1900 // Stop calculating as soon as possible, but still send the "bestmove"
1901 // and possibly the "ponder" token when finishing the search.
1905 else if (command == "ponderhit")
1907 // The opponent has played the expected move. GUI sends "ponderhit" if
1908 // we were told to ponder on the same move the opponent has played. We
1909 // should continue searching but switching from pondering to normal search.
1912 if (StopOnPonderhit)
1917 // Print search information
1921 else if (lastInfoTime > t)
1922 // HACK: Must be a new search where we searched less than
1923 // NodesBetweenPolls nodes during the first second of search.
1926 else if (t - lastInfoTime >= 1000)
1931 dbg_print_hit_rate();
1933 // Send info on searched nodes as soon as we return to root
1934 SendSearchedNodes = true;
1937 // Should we stop the search?
1941 bool stillAtFirstMove = FirstRootMove
1942 && !AspirationFailLow
1943 && t > TimeMgr.available_time();
1945 bool noMoreTime = t > TimeMgr.maximum_time()
1946 || stillAtFirstMove;
1948 if ( (UseTimeManagement && noMoreTime)
1949 || (ExactMaxTime && t >= ExactMaxTime)
1950 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1955 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1956 // while the program is pondering. The point is to work around a wrinkle in
1957 // the UCI protocol: When pondering, the engine is not allowed to give a
1958 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1959 // We simply wait here until one of these commands is sent, and return,
1960 // after which the bestmove and pondermove will be printed.
1962 void wait_for_stop_or_ponderhit() {
1964 std::string command;
1966 // Wait for a command from stdin
1967 while ( std::getline(std::cin, command)
1968 && command != "ponderhit" && command != "stop" && command != "quit") {};
1970 if (command != "ponderhit" && command != "stop")
1971 QuitRequest = true; // Must be "quit" or getline() returned false
1975 // init_thread() is the function which is called when a new thread is
1976 // launched. It simply calls the idle_loop() function with the supplied
1977 // threadID. There are two versions of this function; one for POSIX
1978 // threads and one for Windows threads.
1980 #if !defined(_MSC_VER)
1982 void* init_thread(void* threadID) {
1984 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
1990 DWORD WINAPI init_thread(LPVOID threadID) {
1992 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
1999 /// The ThreadsManager class
2002 // read_uci_options() updates number of active threads and other internal
2003 // parameters according to the UCI options values. It is called before
2004 // to start a new search.
2006 void ThreadsManager::read_uci_options() {
2008 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2009 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2010 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2011 activeThreads = Options["Threads"].value<int>();
2015 // idle_loop() is where the threads are parked when they have no work to do.
2016 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2017 // object for which the current thread is the master.
2019 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2021 assert(threadID >= 0 && threadID < MAX_THREADS);
2024 bool allFinished = false;
2028 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2029 // master should exit as last one.
2030 if (allThreadsShouldExit)
2033 threads[threadID].state = THREAD_TERMINATED;
2037 // If we are not thinking, wait for a condition to be signaled
2038 // instead of wasting CPU time polling for work.
2039 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2040 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2042 assert(!sp || useSleepingThreads);
2043 assert(threadID != 0 || useSleepingThreads);
2045 if (threads[threadID].state == THREAD_INITIALIZING)
2046 threads[threadID].state = THREAD_AVAILABLE;
2048 // Grab the lock to avoid races with wake_sleeping_thread()
2049 lock_grab(&threads[threadID].sleepLock);
2051 // If we are master and all slaves have finished do not go to sleep
2052 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2053 allFinished = (i == activeThreads);
2055 if (allFinished || allThreadsShouldExit)
2057 lock_release(&threads[threadID].sleepLock);
2061 // Do sleep here after retesting sleep conditions
2062 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2063 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2065 lock_release(&threads[threadID].sleepLock);
2068 // If this thread has been assigned work, launch a search
2069 if (threads[threadID].state == THREAD_WORKISWAITING)
2071 assert(!allThreadsShouldExit);
2073 threads[threadID].state = THREAD_SEARCHING;
2075 // Copy SplitPoint position and search stack and call search()
2076 // with SplitPoint template parameter set to true.
2077 SearchStack ss[PLY_MAX_PLUS_2];
2078 SplitPoint* tsp = threads[threadID].splitPoint;
2079 Position pos(*tsp->pos, threadID);
2081 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2085 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2087 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2089 assert(threads[threadID].state == THREAD_SEARCHING);
2091 threads[threadID].state = THREAD_AVAILABLE;
2093 // Wake up master thread so to allow it to return from the idle loop in
2094 // case we are the last slave of the split point.
2095 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2096 wake_sleeping_thread(tsp->master);
2099 // If this thread is the master of a split point and all slaves have
2100 // finished their work at this split point, return from the idle loop.
2101 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2102 allFinished = (i == activeThreads);
2106 // Because sp->slaves[] is reset under lock protection,
2107 // be sure sp->lock has been released before to return.
2108 lock_grab(&(sp->lock));
2109 lock_release(&(sp->lock));
2111 // In helpful master concept a master can help only a sub-tree, and
2112 // because here is all finished is not possible master is booked.
2113 assert(threads[threadID].state == THREAD_AVAILABLE);
2115 threads[threadID].state = THREAD_SEARCHING;
2122 // init_threads() is called during startup. It launches all helper threads,
2123 // and initializes the split point stack and the global locks and condition
2126 void ThreadsManager::init_threads() {
2128 int i, arg[MAX_THREADS];
2131 // Initialize global locks
2134 for (i = 0; i < MAX_THREADS; i++)
2136 lock_init(&threads[i].sleepLock);
2137 cond_init(&threads[i].sleepCond);
2140 // Initialize splitPoints[] locks
2141 for (i = 0; i < MAX_THREADS; i++)
2142 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2143 lock_init(&(threads[i].splitPoints[j].lock));
2145 // Will be set just before program exits to properly end the threads
2146 allThreadsShouldExit = false;
2148 // Threads will be put all threads to sleep as soon as created
2151 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2152 threads[0].state = THREAD_SEARCHING;
2153 for (i = 1; i < MAX_THREADS; i++)
2154 threads[i].state = THREAD_INITIALIZING;
2156 // Launch the helper threads
2157 for (i = 1; i < MAX_THREADS; i++)
2161 #if !defined(_MSC_VER)
2162 pthread_t pthread[1];
2163 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2164 pthread_detach(pthread[0]);
2166 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2170 cout << "Failed to create thread number " << i << endl;
2174 // Wait until the thread has finished launching and is gone to sleep
2175 while (threads[i].state == THREAD_INITIALIZING) {}
2180 // exit_threads() is called when the program exits. It makes all the
2181 // helper threads exit cleanly.
2183 void ThreadsManager::exit_threads() {
2185 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2187 // Wake up all the threads and waits for termination
2188 for (int i = 1; i < MAX_THREADS; i++)
2190 wake_sleeping_thread(i);
2191 while (threads[i].state != THREAD_TERMINATED) {}
2194 // Now we can safely destroy the locks
2195 for (int i = 0; i < MAX_THREADS; i++)
2196 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2197 lock_destroy(&(threads[i].splitPoints[j].lock));
2199 lock_destroy(&mpLock);
2201 // Now we can safely destroy the wait conditions
2202 for (int i = 0; i < MAX_THREADS; i++)
2204 lock_destroy(&threads[i].sleepLock);
2205 cond_destroy(&threads[i].sleepCond);
2210 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2211 // the thread's currently active split point, or in some ancestor of
2212 // the current split point.
2214 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2216 assert(threadID >= 0 && threadID < activeThreads);
2218 SplitPoint* sp = threads[threadID].splitPoint;
2220 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2225 // thread_is_available() checks whether the thread with threadID "slave" is
2226 // available to help the thread with threadID "master" at a split point. An
2227 // obvious requirement is that "slave" must be idle. With more than two
2228 // threads, this is not by itself sufficient: If "slave" is the master of
2229 // some active split point, it is only available as a slave to the other
2230 // threads which are busy searching the split point at the top of "slave"'s
2231 // split point stack (the "helpful master concept" in YBWC terminology).
2233 bool ThreadsManager::thread_is_available(int slave, int master) const {
2235 assert(slave >= 0 && slave < activeThreads);
2236 assert(master >= 0 && master < activeThreads);
2237 assert(activeThreads > 1);
2239 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2242 // Make a local copy to be sure doesn't change under our feet
2243 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2245 // No active split points means that the thread is available as
2246 // a slave for any other thread.
2247 if (localActiveSplitPoints == 0 || activeThreads == 2)
2250 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2251 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2252 // could have been set to 0 by another thread leading to an out of bound access.
2253 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2260 // available_thread_exists() tries to find an idle thread which is available as
2261 // a slave for the thread with threadID "master".
2263 bool ThreadsManager::available_thread_exists(int master) const {
2265 assert(master >= 0 && master < activeThreads);
2266 assert(activeThreads > 1);
2268 for (int i = 0; i < activeThreads; i++)
2269 if (thread_is_available(i, master))
2276 // split() does the actual work of distributing the work at a node between
2277 // several available threads. If it does not succeed in splitting the
2278 // node (because no idle threads are available, or because we have no unused
2279 // split point objects), the function immediately returns. If splitting is
2280 // possible, a SplitPoint object is initialized with all the data that must be
2281 // copied to the helper threads and we tell our helper threads that they have
2282 // been assigned work. This will cause them to instantly leave their idle loops and
2283 // call search().When all threads have returned from search() then split() returns.
2285 template <bool Fake>
2286 void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
2287 Value* bestValue, Depth depth, Move threatMove,
2288 int moveCount, MovePicker* mp, bool pvNode) {
2289 assert(pos.is_ok());
2290 assert(*bestValue >= -VALUE_INFINITE);
2291 assert(*bestValue <= *alpha);
2292 assert(*alpha < beta);
2293 assert(beta <= VALUE_INFINITE);
2294 assert(depth > DEPTH_ZERO);
2295 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2296 assert(activeThreads > 1);
2298 int i, master = pos.thread();
2299 Thread& masterThread = threads[master];
2303 // If no other thread is available to help us, or if we have too many
2304 // active split points, don't split.
2305 if ( !available_thread_exists(master)
2306 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2308 lock_release(&mpLock);
2312 // Pick the next available split point object from the split point stack
2313 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2315 // Initialize the split point object
2316 splitPoint.parent = masterThread.splitPoint;
2317 splitPoint.master = master;
2318 splitPoint.betaCutoff = false;
2319 splitPoint.depth = depth;
2320 splitPoint.threatMove = threatMove;
2321 splitPoint.alpha = *alpha;
2322 splitPoint.beta = beta;
2323 splitPoint.pvNode = pvNode;
2324 splitPoint.bestValue = *bestValue;
2326 splitPoint.moveCount = moveCount;
2327 splitPoint.pos = &pos;
2328 splitPoint.nodes = 0;
2330 for (i = 0; i < activeThreads; i++)
2331 splitPoint.slaves[i] = 0;
2333 masterThread.splitPoint = &splitPoint;
2335 // If we are here it means we are not available
2336 assert(masterThread.state != THREAD_AVAILABLE);
2338 int workersCnt = 1; // At least the master is included
2340 // Allocate available threads setting state to THREAD_BOOKED
2341 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2342 if (thread_is_available(i, master))
2344 threads[i].state = THREAD_BOOKED;
2345 threads[i].splitPoint = &splitPoint;
2346 splitPoint.slaves[i] = 1;
2350 assert(Fake || workersCnt > 1);
2352 // We can release the lock because slave threads are already booked and master is not available
2353 lock_release(&mpLock);
2355 // Tell the threads that they have work to do. This will make them leave
2357 for (i = 0; i < activeThreads; i++)
2358 if (i == master || splitPoint.slaves[i])
2360 assert(i == master || threads[i].state == THREAD_BOOKED);
2362 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2364 if (useSleepingThreads && i != master)
2365 wake_sleeping_thread(i);
2368 // Everything is set up. The master thread enters the idle loop, from
2369 // which it will instantly launch a search, because its state is
2370 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2371 // idle loop, which means that the main thread will return from the idle
2372 // loop when all threads have finished their work at this split point.
2373 idle_loop(master, &splitPoint);
2375 // We have returned from the idle loop, which means that all threads are
2376 // finished. Update alpha and bestValue, and return.
2379 *alpha = splitPoint.alpha;
2380 *bestValue = splitPoint.bestValue;
2381 masterThread.activeSplitPoints--;
2382 masterThread.splitPoint = splitPoint.parent;
2383 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2385 lock_release(&mpLock);
2389 // wake_sleeping_thread() wakes up the thread with the given threadID
2390 // when it is time to start a new search.
2392 void ThreadsManager::wake_sleeping_thread(int threadID) {
2394 lock_grab(&threads[threadID].sleepLock);
2395 cond_signal(&threads[threadID].sleepCond);
2396 lock_release(&threads[threadID].sleepLock);
2400 /// RootMove and RootMoveList method's definitions
2402 RootMove::RootMove() {
2405 pv_score = non_pv_score = -VALUE_INFINITE;
2409 RootMove& RootMove::operator=(const RootMove& rm) {
2411 const Move* src = rm.pv;
2414 // Avoid a costly full rm.pv[] copy
2415 do *dst++ = *src; while (*src++ != MOVE_NONE);
2418 pv_score = rm.pv_score;
2419 non_pv_score = rm.non_pv_score;
2423 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2424 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2425 // allow to always have a ponder move even when we fail high at root and also a
2426 // long PV to print that is important for position analysis.
2428 void RootMove::extract_pv_from_tt(Position& pos) {
2430 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2434 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2436 pos.do_move(pv[0], *st++);
2438 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2439 && tte->move() != MOVE_NONE
2440 && pos.move_is_legal(tte->move())
2442 && (!pos.is_draw() || ply < 2))
2444 pv[ply] = tte->move();
2445 pos.do_move(pv[ply++], *st++);
2447 pv[ply] = MOVE_NONE;
2449 do pos.undo_move(pv[--ply]); while (ply);
2452 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2453 // the PV back into the TT. This makes sure the old PV moves are searched
2454 // first, even if the old TT entries have been overwritten.
2456 void RootMove::insert_pv_in_tt(Position& pos) {
2458 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2461 Value v, m = VALUE_NONE;
2464 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2468 tte = TT.retrieve(k);
2470 // Don't overwrite existing correct entries
2471 if (!tte || tte->move() != pv[ply])
2473 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2474 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2476 pos.do_move(pv[ply], *st++);
2478 } while (pv[++ply] != MOVE_NONE);
2480 do pos.undo_move(pv[--ply]); while (ply);
2483 // pv_info_to_uci() returns a string with information on the current PV line
2484 // formatted according to UCI specification.
2486 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha,
2487 Value beta, int pvIdx) {
2488 std::stringstream s, l;
2491 while (*m != MOVE_NONE)
2494 s << "info depth " << depth
2495 << " seldepth " << int(m - pv)
2496 << " multipv " << pvIdx + 1
2497 << " score " << value_to_uci(pv_score)
2498 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2499 << speed_to_uci(pos.nodes_searched())
2500 << " pv " << l.str();
2506 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2508 MoveStack mlist[MOVES_MAX];
2512 bestMoveChanges = 0;
2514 // Generate all legal moves and add them to RootMoveList
2515 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2516 for (MoveStack* cur = mlist; cur != last; cur++)
2518 // If we have a searchMoves[] list then verify cur->move
2519 // is in the list before to add it.
2520 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2522 if (searchMoves[0] && *sm != cur->move)
2526 rm.pv[0] = cur->move;
2527 rm.pv[1] = MOVE_NONE;
2528 rm.pv_score = -VALUE_INFINITE;
2534 // When playing with strength handicap choose best move among the MultiPV set
2535 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2536 void do_skill_level(Move* best, Move* ponder) {
2538 assert(MultiPV > 1);
2540 // Rml list is already sorted by pv_score in descending order
2542 int max_s = -VALUE_INFINITE;
2543 int size = Min(MultiPV, (int)Rml.size());
2544 int max = Rml[0].pv_score;
2545 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2546 int wk = 120 - 2 * SkillLevel;
2548 // PRNG sequence should be non deterministic
2549 for (int i = abs(get_system_time() % 50); i > 0; i--)
2550 RK.rand<unsigned>();
2552 // Choose best move. For each move's score we add two terms both dependent
2553 // on wk, one deterministic and bigger for weaker moves, and one random,
2554 // then we choose the move with the resulting highest score.
2555 for (int i = 0; i < size; i++)
2557 s = Rml[i].pv_score;
2559 // Don't allow crazy blunders even at very low skills
2560 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2563 // This is our magical formula
2564 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2569 *best = Rml[i].pv[0];
2570 *ponder = Rml[i].pv[1];