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()
67 Thread& operator[](int threadID) { return threads[threadID]; }
71 int min_split_depth() const { return minimumSplitDepth; }
72 int active_threads() const { return activeThreads; }
73 void set_active_threads(int cnt) { activeThreads = cnt; }
75 void read_uci_options();
76 bool available_thread_exists(int master) const;
77 bool thread_is_available(int slave, int master) const;
78 bool cutoff_at_splitpoint(int threadID) const;
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);
86 Depth minimumSplitDepth;
87 int maxThreadsPerSplitPoint;
88 bool useSleepingThreads;
90 volatile bool allThreadsShouldExit;
91 Thread threads[MAX_THREADS];
95 // RootMove struct is used for moves at the root of the tree. For each root
96 // move, we store two scores, a node count, and a PV (really a refutation
97 // in the case of moves which fail low). Value pv_score is normally set at
98 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
99 // according to the order in which moves are returned by MovePicker.
104 RootMove(const RootMove& rm) { *this = rm; }
105 RootMove& operator=(const RootMove& rm);
107 // RootMove::operator<() is the comparison function used when
108 // sorting the moves. A move m1 is considered to be better
109 // than a move m2 if it has an higher pv_score, or if it has
110 // equal pv_score but m1 has the higher non_pv_score. In this way
111 // we are guaranteed that PV moves are always sorted as first.
112 bool operator<(const RootMove& m) const {
113 return pv_score != m.pv_score ? pv_score < m.pv_score
114 : non_pv_score < m.non_pv_score;
117 void extract_pv_from_tt(Position& pos);
118 void insert_pv_in_tt(Position& pos);
119 std::string pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha, Value beta, int pvIdx);
124 Move pv[PLY_MAX_PLUS_2];
128 // RootMoveList struct is just a std::vector<> of RootMove objects,
129 // with an handful of methods above the standard ones.
131 struct RootMoveList : public std::vector<RootMove> {
133 typedef std::vector<RootMove> Base;
135 void init(Position& pos, Move searchMoves[]);
136 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
137 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
143 // Overload operator<<() to make it easier to print moves in a coordinate
144 // notation compatible with UCI protocol.
145 std::ostream& operator<<(std::ostream& os, Move m) {
147 bool chess960 = (os.iword(0) != 0); // See set960()
148 return os << move_to_uci(m, chess960);
152 // When formatting a move for std::cout we must know if we are in Chess960
153 // or not. To keep using the handy operator<<() on the move the trick is to
154 // embed this flag in the stream itself. Function-like named enum set960 is
155 // used as a custom manipulator and the stream internal general-purpose array,
156 // accessed through ios_base::iword(), is used to pass the flag to the move's
157 // operator<<() that will read it to properly format castling moves.
160 std::ostream& operator<< (std::ostream& os, const set960& f) {
162 os.iword(0) = int(f);
171 // Maximum depth for razoring
172 const Depth RazorDepth = 4 * ONE_PLY;
174 // Dynamic razoring margin based on depth
175 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
177 // Maximum depth for use of dynamic threat detection when null move fails low
178 const Depth ThreatDepth = 5 * ONE_PLY;
180 // Step 9. Internal iterative deepening
182 // Minimum depth for use of internal iterative deepening
183 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is bigger then beta - IIDMargin.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options
192 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
199 // Step 12. Futility pruning
201 // Futility margin for quiescence search
202 const Value FutilityMarginQS = Value(0x80);
204 // Futility lookup tables (initialized at startup) and their access functions
205 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
206 int FutilityMoveCountArray[32]; // [depth]
208 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
209 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
211 // Step 14. Reduced search
213 // Reduction lookup tables (initialized at startup) and their getter functions
214 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
216 template <NodeType PV>
217 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)]; }
219 // Easy move margin. An easy move candidate must be at least this much
220 // better than the second best move.
221 const Value EasyMoveMargin = Value(0x200);
224 /// Namespace variables
233 int MultiPV, UCIMultiPV;
235 // Time management variables
236 int MaxNodes, MaxDepth, ExactMaxTime;
237 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
238 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
243 std::ofstream LogFile;
245 // Skill level adjustment
247 bool SkillLevelEnabled;
250 // Multi-threads manager
251 ThreadsManager ThreadsMgr;
253 // Node counters, used only by thread[0] but try to keep in different cache
254 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
255 bool SendSearchedNodes;
257 int NodesBetweenPolls = 30000;
265 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
267 template <NodeType PvNode, bool SpNode, bool Root>
268 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
270 template <NodeType PvNode>
271 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
273 template <NodeType PvNode>
274 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
276 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
277 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
280 template <NodeType PvNode>
281 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
283 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
284 bool connected_moves(const Position& pos, Move m1, Move m2);
285 Value value_to_tt(Value v, int ply);
286 Value value_from_tt(Value v, int ply);
287 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
288 bool connected_threat(const Position& pos, Move m, Move threat);
289 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
290 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
291 void update_gains(const Position& pos, Move move, Value before, Value after);
292 void do_skill_level(Move* best, Move* ponder);
294 int current_search_time(int set = 0);
295 std::string value_to_uci(Value v);
296 std::string speed_to_uci(int64_t nodes);
297 void poll(const Position& pos);
298 void wait_for_stop_or_ponderhit();
300 #if !defined(_MSC_VER)
301 void* init_thread(void* threadID);
303 DWORD WINAPI init_thread(LPVOID threadID);
307 // MovePickerExt is an extended MovePicker used to choose at compile time
308 // the proper move source according to the type of node.
309 template<bool SpNode, bool Root> struct MovePickerExt;
311 // In Root nodes use RootMoveList as source. Score and sort the root moves
312 // before to search them.
313 template<> struct MovePickerExt<false, true> : public MovePicker {
315 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
316 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
318 Value score = VALUE_ZERO;
320 // Score root moves using standard ordering used in main search, the moves
321 // are scored according to the order in which they are returned by MovePicker.
322 // This is the second order score that is used to compare the moves when
323 // the first orders pv_score of both moves are equal.
324 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
325 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
326 if (rm->pv[0] == move)
328 rm->non_pv_score = score--;
336 Move get_next_move() {
343 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
346 RootMoveList::iterator rm;
350 // In SpNodes use split point's shared MovePicker object as move source
351 template<> struct MovePickerExt<true, false> : public MovePicker {
353 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
354 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
356 Move get_next_move() { return mp->get_next_move(); }
358 RootMoveList::iterator rm; // Dummy, needed to compile
362 // Default case, create and use a MovePicker object as source
363 template<> struct MovePickerExt<false, false> : public MovePicker {
365 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
366 : MovePicker(p, ttm, d, h, ss, b) {}
368 RootMoveList::iterator rm; // Dummy, needed to compile
374 /// init_threads() is called during startup. It initializes various lookup tables
375 /// and creates and launches search threads.
377 void init_threads() {
379 int d; // depth (ONE_PLY == 2)
380 int hd; // half depth (ONE_PLY == 1)
383 // Init reductions array
384 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
386 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
387 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
388 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
389 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
392 // Init futility margins array
393 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
394 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
396 // Init futility move count array
397 for (d = 0; d < 32; d++)
398 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
400 // Create and startup threads
401 ThreadsMgr.init_threads();
405 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
406 void exit_threads() { ThreadsMgr.exit_threads(); }
409 /// perft() is our utility to verify move generation. All the legal moves up to
410 /// given depth are generated and counted and the sum returned.
412 int64_t perft(Position& pos, Depth depth) {
414 MoveStack mlist[MOVES_MAX];
419 // Generate all legal moves
420 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
422 // If we are at the last ply we don't need to do and undo
423 // the moves, just to count them.
424 if (depth <= ONE_PLY)
425 return int(last - mlist);
427 // Loop through all legal moves
429 for (MoveStack* cur = mlist; cur != last; cur++)
432 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
433 sum += perft(pos, depth - ONE_PLY);
440 /// think() is the external interface to Stockfish's search, and is called when
441 /// the program receives the UCI 'go' command. It initializes various global
442 /// variables, and calls id_loop(). It returns false when a quit command is
443 /// received during the search.
445 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
446 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
448 // Initialize global search-related variables
449 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
451 current_search_time(get_system_time());
452 ExactMaxTime = maxTime;
455 InfiniteSearch = infinite;
457 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
459 // Look for a book move, only during games, not tests
460 if (UseTimeManagement && Options["OwnBook"].value<bool>())
462 if (Options["Book File"].value<std::string>() != OpeningBook.name())
463 OpeningBook.open(Options["Book File"].value<std::string>());
465 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
466 if (bookMove != MOVE_NONE)
469 wait_for_stop_or_ponderhit();
471 cout << "bestmove " << bookMove << endl;
477 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
478 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
479 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
480 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
481 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
482 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
483 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
484 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
485 UCIMultiPV = Options["MultiPV"].value<int>();
486 SkillLevel = Options["Skill level"].value<int>();
487 UseLogFile = Options["Use Search Log"].value<bool>();
489 read_evaluation_uci_options(pos.side_to_move());
491 if (Options["Clear Hash"].value<bool>())
493 Options["Clear Hash"].set_value("false");
496 TT.set_size(Options["Hash"].value<int>());
498 // Do we have to play with skill handicap? In this case enable MultiPV that
499 // we will use behind the scenes to retrieve a set of possible moves.
500 SkillLevelEnabled = (SkillLevel < 20);
501 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
503 // Set the number of active threads
504 ThreadsMgr.read_uci_options();
505 init_eval(ThreadsMgr.active_threads());
507 // Wake up needed threads and reset maxPly counter
508 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
510 ThreadsMgr[i].wake_up();
511 ThreadsMgr[i].maxPly = 0;
515 int myTime = time[pos.side_to_move()];
516 int myIncrement = increment[pos.side_to_move()];
517 if (UseTimeManagement)
518 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
520 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
522 NodesBetweenPolls = Min(MaxNodes, 30000);
523 else if (myTime && myTime < 1000)
524 NodesBetweenPolls = 1000;
525 else if (myTime && myTime < 5000)
526 NodesBetweenPolls = 5000;
528 NodesBetweenPolls = 30000;
530 // Write search information to log file
533 std::string name = Options["Search Log Filename"].value<std::string>();
534 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
536 LogFile << "\nSearching: " << pos.to_fen()
537 << "\ninfinite: " << infinite
538 << " ponder: " << ponder
539 << " time: " << myTime
540 << " increment: " << myIncrement
541 << " moves to go: " << movesToGo
545 // We're ready to start thinking. Call the iterative deepening loop function
546 Move ponderMove = MOVE_NONE;
547 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
549 // Print final search statistics
550 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
554 int t = current_search_time();
556 LogFile << "Nodes: " << pos.nodes_searched()
557 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
558 << "\nBest move: " << move_to_san(pos, bestMove);
561 pos.do_move(bestMove, st);
562 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
563 pos.undo_move(bestMove); // Return from think() with unchanged position
567 // This makes all the threads to go to sleep
568 ThreadsMgr.set_active_threads(1);
570 // If we are pondering or in infinite search, we shouldn't print the
571 // best move before we are told to do so.
572 if (!StopRequest && (Pondering || InfiniteSearch))
573 wait_for_stop_or_ponderhit();
575 // Could be MOVE_NONE when searching on a stalemate position
576 cout << "bestmove " << bestMove;
578 // UCI protol is not clear on allowing sending an empty ponder move, instead
579 // it is clear that ponder move is optional. So skip it if empty.
580 if (ponderMove != MOVE_NONE)
581 cout << " ponder " << ponderMove;
591 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
592 // with increasing depth until the allocated thinking time has been consumed,
593 // user stops the search, or the maximum search depth is reached.
595 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
597 SearchStack ss[PLY_MAX_PLUS_2];
598 Value bestValues[PLY_MAX_PLUS_2];
599 int bestMoveChanges[PLY_MAX_PLUS_2];
600 int depth, selDepth, aspirationDelta;
601 Value value, alpha, beta;
602 Move bestMove, easyMove, skillBest, skillPonder;
604 // Initialize stuff before a new search
605 memset(ss, 0, 4 * sizeof(SearchStack));
608 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
609 depth = aspirationDelta = 0;
610 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
611 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
613 // Moves to search are verified and copied
614 Rml.init(pos, searchMoves);
616 // Handle special case of searching on a mate/stalemate position
619 cout << "info depth 0 score "
620 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
626 // Iterative deepening loop
627 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
629 Rml.bestMoveChanges = 0;
630 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
632 // Calculate dynamic aspiration window based on previous iterations
633 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
635 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
636 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
638 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
639 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
641 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
642 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
645 // Start with a small aspiration window and, in case of fail high/low,
646 // research with bigger window until not failing high/low anymore.
648 // Search starting from ss+1 to allow calling update_gains()
649 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
651 // Write PV back to transposition table in case the relevant entries
652 // have been overwritten during the search.
653 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
654 Rml[i].insert_pv_in_tt(pos);
656 // Value cannot be trusted. Break out immediately!
660 assert(value >= alpha);
662 // In case of failing high/low increase aspiration window and research,
663 // otherwise exit the fail high/low loop.
666 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
667 aspirationDelta += aspirationDelta / 2;
669 else if (value <= alpha)
671 AspirationFailLow = true;
672 StopOnPonderhit = false;
674 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
675 aspirationDelta += aspirationDelta / 2;
680 } while (abs(value) < VALUE_KNOWN_WIN);
682 // Collect info about search result
683 bestMove = Rml[0].pv[0];
684 *ponderMove = Rml[0].pv[1];
685 bestValues[depth] = value;
686 bestMoveChanges[depth] = Rml.bestMoveChanges;
688 // Do we need to pick now the best and the ponder moves ?
689 if (SkillLevelEnabled && depth == 1 + SkillLevel)
690 do_skill_level(&skillBest, &skillPonder);
692 // Retrieve max searched depth among threads
694 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
695 if (ThreadsMgr[i].maxPly > selDepth)
696 selDepth = ThreadsMgr[i].maxPly;
698 // Send PV line to GUI and to log file
699 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
700 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
703 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
705 // Init easyMove after first iteration or drop if differs from the best move
706 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
708 else if (bestMove != easyMove)
709 easyMove = MOVE_NONE;
711 if (UseTimeManagement && !StopRequest)
714 bool noMoreTime = false;
716 // Stop search early when the last two iterations returned a mate score
718 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
719 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
722 // Stop search early if one move seems to be much better than the
723 // others or if there is only a single legal move. In this latter
724 // case we search up to Iteration 8 anyway to get a proper score.
726 && easyMove == bestMove
728 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
729 && current_search_time() > TimeMgr.available_time() / 16)
730 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
731 && current_search_time() > TimeMgr.available_time() / 32)))
734 // Add some extra time if the best move has changed during the last two iterations
735 if (depth > 4 && depth < 50)
736 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
738 // Stop search if most of MaxSearchTime is consumed at the end of the
739 // iteration. We probably don't have enough time to search the first
740 // move at the next iteration anyway.
741 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
747 StopOnPonderhit = true;
754 // When using skills fake best and ponder moves with the sub-optimal ones
755 if (SkillLevelEnabled)
757 if (skillBest == MOVE_NONE) // Still unassigned ?
758 do_skill_level(&skillBest, &skillPonder);
760 bestMove = skillBest;
761 *ponderMove = skillPonder;
768 // search<>() is the main search function for both PV and non-PV nodes and for
769 // normal and SplitPoint nodes. When called just after a split point the search
770 // is simpler because we have already probed the hash table, done a null move
771 // search, and searched the first move before splitting, we don't have to repeat
772 // all this work again. We also don't need to store anything to the hash table
773 // here: This is taken care of after we return from the split point.
775 template <NodeType PvNode, bool SpNode, bool Root>
776 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
778 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
779 assert(beta > alpha && beta <= VALUE_INFINITE);
780 assert(PvNode || alpha == beta - 1);
781 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
783 Move movesSearched[MOVES_MAX];
788 Move ttMove, move, excludedMove, threatMove;
791 Value bestValue, value, oldAlpha;
792 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
793 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
794 int moveCount = 0, playedMoveCount = 0;
795 int threadID = pos.thread();
796 SplitPoint* sp = NULL;
798 refinedValue = bestValue = value = -VALUE_INFINITE;
800 isCheck = pos.is_check();
801 ss->ply = (ss-1)->ply + 1;
803 // Used to send selDepth info to GUI
804 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
805 ThreadsMgr[threadID].maxPly = ss->ply;
811 ttMove = excludedMove = MOVE_NONE;
812 threatMove = sp->threatMove;
813 goto split_point_start;
818 // Step 1. Initialize node and poll. Polling can abort search
819 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
820 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
821 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
823 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
829 // Step 2. Check for aborted search and immediate draw
831 || ThreadsMgr.cutoff_at_splitpoint(threadID)
833 || ss->ply > PLY_MAX) && !Root)
836 // Step 3. Mate distance pruning
837 alpha = Max(value_mated_in(ss->ply), alpha);
838 beta = Min(value_mate_in(ss->ply+1), beta);
842 // Step 4. Transposition table lookup
843 // We don't want the score of a partial search to overwrite a previous full search
844 // TT value, so we use a different position key in case of an excluded move.
845 excludedMove = ss->excludedMove;
846 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
848 tte = TT.retrieve(posKey);
849 ttMove = tte ? tte->move() : MOVE_NONE;
851 // At PV nodes we check for exact scores, while at non-PV nodes we check for
852 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
853 // smooth experience in analysis mode.
856 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
857 : ok_to_use_TT(tte, depth, beta, ss->ply)))
860 ss->bestMove = ttMove; // Can be MOVE_NONE
861 return value_from_tt(tte->value(), ss->ply);
864 // Step 5. Evaluate the position statically and update parent's gain statistics
866 ss->eval = ss->evalMargin = VALUE_NONE;
869 assert(tte->static_value() != VALUE_NONE);
871 ss->eval = tte->static_value();
872 ss->evalMargin = tte->static_value_margin();
873 refinedValue = refine_eval(tte, ss->eval, ss->ply);
877 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
878 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
881 // Save gain for the parent non-capture move
882 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
884 // Step 6. Razoring (is omitted in PV nodes)
886 && depth < RazorDepth
888 && refinedValue + razor_margin(depth) < beta
889 && ttMove == MOVE_NONE
890 && abs(beta) < VALUE_MATE_IN_PLY_MAX
891 && !pos.has_pawn_on_7th(pos.side_to_move()))
893 Value rbeta = beta - razor_margin(depth);
894 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
896 // Logically we should return (v + razor_margin(depth)), but
897 // surprisingly this did slightly weaker in tests.
901 // Step 7. Static null move pruning (is omitted in PV nodes)
902 // We're betting that the opponent doesn't have a move that will reduce
903 // the score by more than futility_margin(depth) if we do a null move.
906 && depth < RazorDepth
908 && refinedValue - futility_margin(depth, 0) >= beta
909 && abs(beta) < VALUE_MATE_IN_PLY_MAX
910 && pos.non_pawn_material(pos.side_to_move()))
911 return refinedValue - futility_margin(depth, 0);
913 // Step 8. Null move search with verification search (is omitted in PV nodes)
918 && refinedValue >= beta
919 && abs(beta) < VALUE_MATE_IN_PLY_MAX
920 && pos.non_pawn_material(pos.side_to_move()))
922 ss->currentMove = MOVE_NULL;
924 // Null move dynamic reduction based on depth
925 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
927 // Null move dynamic reduction based on value
928 if (refinedValue - PawnValueMidgame > beta)
931 pos.do_null_move(st);
932 (ss+1)->skipNullMove = true;
933 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
934 (ss+1)->skipNullMove = false;
935 pos.undo_null_move();
937 if (nullValue >= beta)
939 // Do not return unproven mate scores
940 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
943 if (depth < 6 * ONE_PLY)
946 // Do verification search at high depths
947 ss->skipNullMove = true;
948 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
949 ss->skipNullMove = false;
956 // The null move failed low, which means that we may be faced with
957 // some kind of threat. If the previous move was reduced, check if
958 // the move that refuted the null move was somehow connected to the
959 // move which was reduced. If a connection is found, return a fail
960 // low score (which will cause the reduced move to fail high in the
961 // parent node, which will trigger a re-search with full depth).
962 threatMove = (ss+1)->bestMove;
964 if ( depth < ThreatDepth
966 && threatMove != MOVE_NONE
967 && connected_moves(pos, (ss-1)->currentMove, threatMove))
972 // Step 9. Internal iterative deepening
973 if ( depth >= IIDDepth[PvNode]
974 && ttMove == MOVE_NONE
975 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
977 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
979 ss->skipNullMove = true;
980 search<PvNode>(pos, ss, alpha, beta, d);
981 ss->skipNullMove = false;
983 ttMove = ss->bestMove;
984 tte = TT.retrieve(posKey);
987 split_point_start: // At split points actual search starts from here
989 // Initialize a MovePicker object for the current position
990 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
992 ss->bestMove = MOVE_NONE;
993 futilityBase = ss->eval + ss->evalMargin;
994 singularExtensionNode = !Root
996 && depth >= SingularExtensionDepth[PvNode]
999 && !excludedMove // Do not allow recursive singular extension search
1000 && (tte->type() & VALUE_TYPE_LOWER)
1001 && tte->depth() >= depth - 3 * ONE_PLY;
1004 lock_grab(&(sp->lock));
1005 bestValue = sp->bestValue;
1008 // Step 10. Loop through moves
1009 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1010 while ( bestValue < beta
1011 && (move = mp.get_next_move()) != MOVE_NONE
1012 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1014 assert(move_is_ok(move));
1018 moveCount = ++sp->moveCount;
1019 lock_release(&(sp->lock));
1021 else if (move == excludedMove)
1028 // This is used by time management
1029 FirstRootMove = (moveCount == 1);
1031 // Save the current node count before the move is searched
1032 nodes = pos.nodes_searched();
1034 // If it's time to send nodes info, do it here where we have the
1035 // correct accumulated node counts searched by each thread.
1036 if (SendSearchedNodes)
1038 SendSearchedNodes = false;
1039 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1042 if (current_search_time() > 2000)
1043 cout << "info currmove " << move
1044 << " currmovenumber " << moveCount << endl;
1047 // At Root and at first iteration do a PV search on all the moves to score root moves
1048 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
1049 moveIsCheck = pos.move_is_check(move, ci);
1050 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1052 // Step 11. Decide the new search depth
1053 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
1055 // Singular extension search. If all moves but one fail low on a search of
1056 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1057 // is singular and should be extended. To verify this we do a reduced search
1058 // on all the other moves but the ttMove, if result is lower than ttValue minus
1059 // a margin then we extend ttMove.
1060 if ( singularExtensionNode
1061 && move == tte->move()
1064 Value ttValue = value_from_tt(tte->value(), ss->ply);
1066 if (abs(ttValue) < VALUE_KNOWN_WIN)
1068 Value rBeta = ttValue - int(depth);
1069 ss->excludedMove = move;
1070 ss->skipNullMove = true;
1071 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1072 ss->skipNullMove = false;
1073 ss->excludedMove = MOVE_NONE;
1074 ss->bestMove = MOVE_NONE;
1080 // Update current move (this must be done after singular extension search)
1081 ss->currentMove = move;
1082 newDepth = depth - ONE_PLY + ext;
1084 // Step 12. Futility pruning (is omitted in PV nodes)
1086 && !captureOrPromotion
1090 && !move_is_castle(move))
1092 // Move count based pruning
1093 if ( moveCount >= futility_move_count(depth)
1094 && (!threatMove || !connected_threat(pos, move, threatMove))
1095 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1098 lock_grab(&(sp->lock));
1103 // Value based pruning
1104 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1105 // but fixing this made program slightly weaker.
1106 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1107 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1108 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1110 if (futilityValueScaled < beta)
1114 lock_grab(&(sp->lock));
1115 if (futilityValueScaled > sp->bestValue)
1116 sp->bestValue = bestValue = futilityValueScaled;
1118 else if (futilityValueScaled > bestValue)
1119 bestValue = futilityValueScaled;
1124 // Prune moves with negative SEE at low depths
1125 if ( predictedDepth < 2 * ONE_PLY
1126 && bestValue > VALUE_MATED_IN_PLY_MAX
1127 && pos.see_sign(move) < 0)
1130 lock_grab(&(sp->lock));
1136 // Bad capture detection. Will be used by prob-cut search
1137 isBadCap = depth >= 3 * ONE_PLY
1138 && depth < 8 * ONE_PLY
1139 && captureOrPromotion
1142 && !move_is_promotion(move)
1143 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1144 && pos.see_sign(move) < 0;
1146 // Step 13. Make the move
1147 pos.do_move(move, st, ci, moveIsCheck);
1149 if (!SpNode && !captureOrPromotion)
1150 movesSearched[playedMoveCount++] = move;
1152 // Step extra. pv search (only in PV nodes)
1153 // The first move in list is the expected PV
1156 // Aspiration window is disabled in multi-pv case
1157 if (Root && MultiPV > 1)
1158 alpha = -VALUE_INFINITE;
1160 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1164 // Step 14. Reduced depth search
1165 // If the move fails high will be re-searched at full depth.
1166 bool doFullDepthSearch = true;
1167 alpha = SpNode ? sp->alpha : alpha;
1169 if ( depth >= 3 * ONE_PLY
1170 && !captureOrPromotion
1172 && !move_is_castle(move)
1173 && ss->killers[0] != move
1174 && ss->killers[1] != move)
1176 ss->reduction = reduction<PvNode>(depth, moveCount);
1179 alpha = SpNode ? sp->alpha : alpha;
1180 Depth d = newDepth - ss->reduction;
1181 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1183 doFullDepthSearch = (value > alpha);
1185 ss->reduction = DEPTH_ZERO; // Restore original reduction
1188 // Probcut search for bad captures. If a reduced search returns a value
1189 // very below beta then we can (almost) safely prune the bad capture.
1192 ss->reduction = 3 * ONE_PLY;
1193 Value rAlpha = alpha - 300;
1194 Depth d = newDepth - ss->reduction;
1195 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1196 doFullDepthSearch = (value > rAlpha);
1197 ss->reduction = DEPTH_ZERO; // Restore original reduction
1200 // Step 15. Full depth search
1201 if (doFullDepthSearch)
1203 alpha = SpNode ? sp->alpha : alpha;
1204 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1206 // Step extra. pv search (only in PV nodes)
1207 // Search only for possible new PV nodes, if instead value >= beta then
1208 // parent node fails low with value <= alpha and tries another move.
1209 if (PvNode && value > alpha && (Root || value < beta))
1210 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1214 // Step 16. Undo move
1215 pos.undo_move(move);
1217 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1219 // Step 17. Check for new best move
1222 lock_grab(&(sp->lock));
1223 bestValue = sp->bestValue;
1227 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1232 sp->bestValue = value;
1234 if (!Root && value > alpha)
1236 if (PvNode && value < beta) // We want always alpha < beta
1244 sp->betaCutoff = true;
1246 if (value == value_mate_in(ss->ply + 1))
1247 ss->mateKiller = move;
1249 ss->bestMove = move;
1252 sp->ss->bestMove = move;
1258 // Finished searching the move. If StopRequest is true, the search
1259 // was aborted because the user interrupted the search or because we
1260 // ran out of time. In this case, the return value of the search cannot
1261 // be trusted, and we break out of the loop without updating the best
1266 // Remember searched nodes counts for this move
1267 mp.rm->nodes += pos.nodes_searched() - nodes;
1269 // PV move or new best move ?
1270 if (isPvMove || value > alpha)
1273 ss->bestMove = move;
1274 mp.rm->pv_score = value;
1275 mp.rm->extract_pv_from_tt(pos);
1277 // We record how often the best move has been changed in each
1278 // iteration. This information is used for time management: When
1279 // the best move changes frequently, we allocate some more time.
1280 if (!isPvMove && MultiPV == 1)
1281 Rml.bestMoveChanges++;
1283 Rml.sort_multipv(moveCount);
1285 // Update alpha. In multi-pv we don't use aspiration window, so
1286 // set alpha equal to minimum score among the PV lines.
1288 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1289 else if (value > alpha)
1293 mp.rm->pv_score = -VALUE_INFINITE;
1297 // Step 18. Check for split
1300 && depth >= ThreadsMgr.min_split_depth()
1301 && ThreadsMgr.active_threads() > 1
1303 && ThreadsMgr.available_thread_exists(threadID)
1305 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1306 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1307 threatMove, moveCount, &mp, PvNode);
1310 // Step 19. Check for mate and stalemate
1311 // All legal moves have been searched and if there are
1312 // no legal moves, it must be mate or stalemate.
1313 // If one move was excluded return fail low score.
1314 if (!SpNode && !moveCount)
1315 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1317 // Step 20. Update tables
1318 // If the search is not aborted, update the transposition table,
1319 // history counters, and killer moves.
1320 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1322 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1323 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1324 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1326 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1328 // Update killers and history only for non capture moves that fails high
1329 if ( bestValue >= beta
1330 && !pos.move_is_capture_or_promotion(move))
1332 if (move != ss->killers[0])
1334 ss->killers[1] = ss->killers[0];
1335 ss->killers[0] = move;
1337 update_history(pos, move, depth, movesSearched, playedMoveCount);
1343 // Here we have the lock still grabbed
1344 sp->slaves[threadID] = 0;
1345 sp->nodes += pos.nodes_searched();
1346 lock_release(&(sp->lock));
1349 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1354 // qsearch() is the quiescence search function, which is called by the main
1355 // search function when the remaining depth is zero (or, to be more precise,
1356 // less than ONE_PLY).
1358 template <NodeType PvNode>
1359 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1361 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1362 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1363 assert(PvNode || alpha == beta - 1);
1365 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1369 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1370 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1373 Value oldAlpha = alpha;
1375 ss->bestMove = ss->currentMove = MOVE_NONE;
1376 ss->ply = (ss-1)->ply + 1;
1378 // Check for an instant draw or maximum ply reached
1379 if (ss->ply > PLY_MAX || pos.is_draw())
1382 // Decide whether or not to include checks, this fixes also the type of
1383 // TT entry depth that we are going to use. Note that in qsearch we use
1384 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1385 isCheck = pos.is_check();
1386 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1388 // Transposition table lookup. At PV nodes, we don't use the TT for
1389 // pruning, but only for move ordering.
1390 tte = TT.retrieve(pos.get_key());
1391 ttMove = (tte ? tte->move() : MOVE_NONE);
1393 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1395 ss->bestMove = ttMove; // Can be MOVE_NONE
1396 return value_from_tt(tte->value(), ss->ply);
1399 // Evaluate the position statically
1402 bestValue = futilityBase = -VALUE_INFINITE;
1403 ss->eval = evalMargin = VALUE_NONE;
1404 enoughMaterial = false;
1410 assert(tte->static_value() != VALUE_NONE);
1412 evalMargin = tte->static_value_margin();
1413 ss->eval = bestValue = tte->static_value();
1416 ss->eval = bestValue = evaluate(pos, evalMargin);
1418 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1420 // Stand pat. Return immediately if static value is at least beta
1421 if (bestValue >= beta)
1424 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1429 if (PvNode && bestValue > alpha)
1432 // Futility pruning parameters, not needed when in check
1433 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1434 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1437 // Initialize a MovePicker object for the current position, and prepare
1438 // to search the moves. Because the depth is <= 0 here, only captures,
1439 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1441 MovePicker mp(pos, ttMove, depth, H);
1444 // Loop through the moves until no moves remain or a beta cutoff occurs
1445 while ( alpha < beta
1446 && (move = mp.get_next_move()) != MOVE_NONE)
1448 assert(move_is_ok(move));
1450 moveIsCheck = pos.move_is_check(move, ci);
1458 && !move_is_promotion(move)
1459 && !pos.move_is_passed_pawn_push(move))
1461 futilityValue = futilityBase
1462 + pos.endgame_value_of_piece_on(move_to(move))
1463 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1465 if (futilityValue < alpha)
1467 if (futilityValue > bestValue)
1468 bestValue = futilityValue;
1472 // Prune moves with negative or equal SEE
1473 if ( futilityBase < beta
1474 && depth < DEPTH_ZERO
1475 && pos.see(move) <= 0)
1479 // Detect non-capture evasions that are candidate to be pruned
1480 evasionPrunable = isCheck
1481 && bestValue > VALUE_MATED_IN_PLY_MAX
1482 && !pos.move_is_capture(move)
1483 && !pos.can_castle(pos.side_to_move());
1485 // Don't search moves with negative SEE values
1487 && (!isCheck || evasionPrunable)
1489 && !move_is_promotion(move)
1490 && pos.see_sign(move) < 0)
1493 // Don't search useless checks
1498 && !pos.move_is_capture_or_promotion(move)
1499 && ss->eval + PawnValueMidgame / 4 < beta
1500 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1502 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1503 bestValue = ss->eval + PawnValueMidgame / 4;
1508 // Update current move
1509 ss->currentMove = move;
1511 // Make and search the move
1512 pos.do_move(move, st, ci, moveIsCheck);
1513 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1514 pos.undo_move(move);
1516 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1519 if (value > bestValue)
1525 ss->bestMove = move;
1530 // All legal moves have been searched. A special case: If we're in check
1531 // and no legal moves were found, it is checkmate.
1532 if (isCheck && bestValue == -VALUE_INFINITE)
1533 return value_mated_in(ss->ply);
1535 // Update transposition table
1536 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1537 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1539 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1545 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1546 // bestValue is updated only when returning false because in that case move
1549 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1551 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1552 Square from, to, ksq, victimSq;
1555 Value futilityValue, bv = *bestValue;
1557 from = move_from(move);
1559 them = opposite_color(pos.side_to_move());
1560 ksq = pos.king_square(them);
1561 kingAtt = pos.attacks_from<KING>(ksq);
1562 pc = pos.piece_on(from);
1564 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1565 oldAtt = pos.attacks_from(pc, from, occ);
1566 newAtt = pos.attacks_from(pc, to, occ);
1568 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1569 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1571 if (!(b && (b & (b - 1))))
1574 // Rule 2. Queen contact check is very dangerous
1575 if ( type_of_piece(pc) == QUEEN
1576 && bit_is_set(kingAtt, to))
1579 // Rule 3. Creating new double threats with checks
1580 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1584 victimSq = pop_1st_bit(&b);
1585 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1587 // Note that here we generate illegal "double move"!
1588 if ( futilityValue >= beta
1589 && pos.see_sign(make_move(from, victimSq)) >= 0)
1592 if (futilityValue > bv)
1596 // Update bestValue only if check is not dangerous (because we will prune the move)
1602 // connected_moves() tests whether two moves are 'connected' in the sense
1603 // that the first move somehow made the second move possible (for instance
1604 // if the moving piece is the same in both moves). The first move is assumed
1605 // to be the move that was made to reach the current position, while the
1606 // second move is assumed to be a move from the current position.
1608 bool connected_moves(const Position& pos, Move m1, Move m2) {
1610 Square f1, t1, f2, t2;
1613 assert(m1 && move_is_ok(m1));
1614 assert(m2 && move_is_ok(m2));
1616 // Case 1: The moving piece is the same in both moves
1622 // Case 2: The destination square for m2 was vacated by m1
1628 // Case 3: Moving through the vacated square
1629 if ( piece_is_slider(pos.piece_on(f2))
1630 && bit_is_set(squares_between(f2, t2), f1))
1633 // Case 4: The destination square for m2 is defended by the moving piece in m1
1634 p = pos.piece_on(t1);
1635 if (bit_is_set(pos.attacks_from(p, t1), t2))
1638 // Case 5: Discovered check, checking piece is the piece moved in m1
1639 if ( piece_is_slider(p)
1640 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1641 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1643 // discovered_check_candidates() works also if the Position's side to
1644 // move is the opposite of the checking piece.
1645 Color them = opposite_color(pos.side_to_move());
1646 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1648 if (bit_is_set(dcCandidates, f2))
1655 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1656 // "plies to mate from the current ply". Non-mate scores are unchanged.
1657 // The function is called before storing a value to the transposition table.
1659 Value value_to_tt(Value v, int ply) {
1661 if (v >= VALUE_MATE_IN_PLY_MAX)
1664 if (v <= VALUE_MATED_IN_PLY_MAX)
1671 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1672 // the transposition table to a mate score corrected for the current ply.
1674 Value value_from_tt(Value v, int ply) {
1676 if (v >= VALUE_MATE_IN_PLY_MAX)
1679 if (v <= VALUE_MATED_IN_PLY_MAX)
1686 // extension() decides whether a move should be searched with normal depth,
1687 // or with extended depth. Certain classes of moves (checking moves, in
1688 // particular) are searched with bigger depth than ordinary moves and in
1689 // any case are marked as 'dangerous'. Note that also if a move is not
1690 // extended, as example because the corresponding UCI option is set to zero,
1691 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1692 template <NodeType PvNode>
1693 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1694 bool moveIsCheck, bool* dangerous) {
1696 assert(m != MOVE_NONE);
1698 Depth result = DEPTH_ZERO;
1699 *dangerous = moveIsCheck;
1701 if (moveIsCheck && pos.see_sign(m) >= 0)
1702 result += CheckExtension[PvNode];
1704 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1706 Color c = pos.side_to_move();
1707 if (relative_rank(c, move_to(m)) == RANK_7)
1709 result += PawnPushTo7thExtension[PvNode];
1712 if (pos.pawn_is_passed(c, move_to(m)))
1714 result += PassedPawnExtension[PvNode];
1719 if ( captureOrPromotion
1720 && pos.type_of_piece_on(move_to(m)) != PAWN
1721 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1722 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1723 && !move_is_promotion(m)
1726 result += PawnEndgameExtension[PvNode];
1730 return Min(result, ONE_PLY);
1734 // connected_threat() tests whether it is safe to forward prune a move or if
1735 // is somehow connected to the threat move returned by null search.
1737 bool connected_threat(const Position& pos, Move m, Move threat) {
1739 assert(move_is_ok(m));
1740 assert(threat && move_is_ok(threat));
1741 assert(!pos.move_is_check(m));
1742 assert(!pos.move_is_capture_or_promotion(m));
1743 assert(!pos.move_is_passed_pawn_push(m));
1745 Square mfrom, mto, tfrom, tto;
1747 mfrom = move_from(m);
1749 tfrom = move_from(threat);
1750 tto = move_to(threat);
1752 // Case 1: Don't prune moves which move the threatened piece
1756 // Case 2: If the threatened piece has value less than or equal to the
1757 // value of the threatening piece, don't prune moves which defend it.
1758 if ( pos.move_is_capture(threat)
1759 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1760 || pos.type_of_piece_on(tfrom) == KING)
1761 && pos.move_attacks_square(m, tto))
1764 // Case 3: If the moving piece in the threatened move is a slider, don't
1765 // prune safe moves which block its ray.
1766 if ( piece_is_slider(pos.piece_on(tfrom))
1767 && bit_is_set(squares_between(tfrom, tto), mto)
1768 && pos.see_sign(m) >= 0)
1775 // ok_to_use_TT() returns true if a transposition table score
1776 // can be used at a given point in search.
1778 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1780 Value v = value_from_tt(tte->value(), ply);
1782 return ( tte->depth() >= depth
1783 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1784 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1786 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1787 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1791 // refine_eval() returns the transposition table score if
1792 // possible otherwise falls back on static position evaluation.
1794 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1798 Value v = value_from_tt(tte->value(), ply);
1800 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1801 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1808 // update_history() registers a good move that produced a beta-cutoff
1809 // in history and marks as failures all the other moves of that ply.
1811 void update_history(const Position& pos, Move move, Depth depth,
1812 Move movesSearched[], int moveCount) {
1814 Value bonus = Value(int(depth) * int(depth));
1816 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1818 for (int i = 0; i < moveCount - 1; i++)
1820 m = movesSearched[i];
1824 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1829 // update_gains() updates the gains table of a non-capture move given
1830 // the static position evaluation before and after the move.
1832 void update_gains(const Position& pos, Move m, Value before, Value after) {
1835 && before != VALUE_NONE
1836 && after != VALUE_NONE
1837 && pos.captured_piece_type() == PIECE_TYPE_NONE
1838 && !move_is_special(m))
1839 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1843 // current_search_time() returns the number of milliseconds which have passed
1844 // since the beginning of the current search.
1846 int current_search_time(int set) {
1848 static int searchStartTime;
1851 searchStartTime = set;
1853 return get_system_time() - searchStartTime;
1857 // value_to_uci() converts a value to a string suitable for use with the UCI
1858 // protocol specifications:
1860 // cp <x> The score from the engine's point of view in centipawns.
1861 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1862 // use negative values for y.
1864 std::string value_to_uci(Value v) {
1866 std::stringstream s;
1868 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1869 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1871 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1877 // speed_to_uci() returns a string with time stats of current search suitable
1878 // to be sent to UCI gui.
1880 std::string speed_to_uci(int64_t nodes) {
1882 std::stringstream s;
1883 int t = current_search_time();
1885 s << " nodes " << nodes
1886 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1893 // poll() performs two different functions: It polls for user input, and it
1894 // looks at the time consumed so far and decides if it's time to abort the
1897 void poll(const Position& pos) {
1899 static int lastInfoTime;
1900 int t = current_search_time();
1903 if (input_available())
1905 // We are line oriented, don't read single chars
1906 std::string command;
1908 if (!std::getline(std::cin, command) || command == "quit")
1910 // Quit the program as soon as possible
1912 QuitRequest = StopRequest = true;
1915 else if (command == "stop")
1917 // Stop calculating as soon as possible, but still send the "bestmove"
1918 // and possibly the "ponder" token when finishing the search.
1922 else if (command == "ponderhit")
1924 // The opponent has played the expected move. GUI sends "ponderhit" if
1925 // we were told to ponder on the same move the opponent has played. We
1926 // should continue searching but switching from pondering to normal search.
1929 if (StopOnPonderhit)
1934 // Print search information
1938 else if (lastInfoTime > t)
1939 // HACK: Must be a new search where we searched less than
1940 // NodesBetweenPolls nodes during the first second of search.
1943 else if (t - lastInfoTime >= 1000)
1948 dbg_print_hit_rate();
1950 // Send info on searched nodes as soon as we return to root
1951 SendSearchedNodes = true;
1954 // Should we stop the search?
1958 bool stillAtFirstMove = FirstRootMove
1959 && !AspirationFailLow
1960 && t > TimeMgr.available_time();
1962 bool noMoreTime = t > TimeMgr.maximum_time()
1963 || stillAtFirstMove;
1965 if ( (UseTimeManagement && noMoreTime)
1966 || (ExactMaxTime && t >= ExactMaxTime)
1967 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1972 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1973 // while the program is pondering. The point is to work around a wrinkle in
1974 // the UCI protocol: When pondering, the engine is not allowed to give a
1975 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1976 // We simply wait here until one of these commands is sent, and return,
1977 // after which the bestmove and pondermove will be printed.
1979 void wait_for_stop_or_ponderhit() {
1981 std::string command;
1983 // Wait for a command from stdin
1984 while ( std::getline(std::cin, command)
1985 && command != "ponderhit" && command != "stop" && command != "quit") {};
1987 if (command != "ponderhit" && command != "stop")
1988 QuitRequest = true; // Must be "quit" or getline() returned false
1992 // init_thread() is the function which is called when a new thread is
1993 // launched. It simply calls the idle_loop() function with the supplied
1994 // threadID. There are two versions of this function; one for POSIX
1995 // threads and one for Windows threads.
1997 #if !defined(_MSC_VER)
1999 void* init_thread(void* threadID) {
2001 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2007 DWORD WINAPI init_thread(LPVOID threadID) {
2009 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2016 /// The ThreadsManager class
2019 // read_uci_options() updates number of active threads and other internal
2020 // parameters according to the UCI options values. It is called before
2021 // to start a new search.
2023 void ThreadsManager::read_uci_options() {
2025 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2026 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2027 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2028 activeThreads = Options["Threads"].value<int>();
2032 // idle_loop() is where the threads are parked when they have no work to do.
2033 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2034 // object for which the current thread is the master.
2036 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2038 assert(threadID >= 0 && threadID < MAX_THREADS);
2045 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2046 // master should exit as last one.
2047 if (allThreadsShouldExit)
2050 threads[threadID].state = THREAD_TERMINATED;
2054 // If we are not thinking, wait for a condition to be signaled
2055 // instead of wasting CPU time polling for work.
2056 while ( threadID >= activeThreads
2057 || threads[threadID].state == THREAD_INITIALIZING
2058 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2060 assert(!sp || useSleepingThreads);
2061 assert(threadID != 0 || useSleepingThreads);
2063 if (threads[threadID].state == THREAD_INITIALIZING)
2064 threads[threadID].state = THREAD_AVAILABLE;
2066 // Grab the lock to avoid races with Thread::wake_up()
2067 lock_grab(&threads[threadID].sleepLock);
2069 // If we are master and all slaves have finished do not go to sleep
2070 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2071 allFinished = (i == activeThreads);
2073 if (allFinished || allThreadsShouldExit)
2075 lock_release(&threads[threadID].sleepLock);
2079 // Do sleep here after retesting sleep conditions
2080 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2081 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2083 lock_release(&threads[threadID].sleepLock);
2086 // If this thread has been assigned work, launch a search
2087 if (threads[threadID].state == THREAD_WORKISWAITING)
2089 assert(!allThreadsShouldExit);
2091 threads[threadID].state = THREAD_SEARCHING;
2093 // Copy split point position and search stack and call search()
2094 // with SplitPoint template parameter set to true.
2095 SearchStack ss[PLY_MAX_PLUS_2];
2096 SplitPoint* tsp = threads[threadID].splitPoint;
2097 Position pos(*tsp->pos, threadID);
2099 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2103 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2105 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2107 assert(threads[threadID].state == THREAD_SEARCHING);
2109 threads[threadID].state = THREAD_AVAILABLE;
2111 // Wake up master thread so to allow it to return from the idle loop in
2112 // case we are the last slave of the split point.
2113 if ( useSleepingThreads
2114 && threadID != tsp->master
2115 && threads[tsp->master].state == THREAD_AVAILABLE)
2116 threads[tsp->master].wake_up();
2119 // If this thread is the master of a split point and all slaves have
2120 // finished their work at this split point, return from the idle loop.
2121 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2122 allFinished = (i == activeThreads);
2126 // Because sp->slaves[] is reset under lock protection,
2127 // be sure sp->lock has been released before to return.
2128 lock_grab(&(sp->lock));
2129 lock_release(&(sp->lock));
2131 // In helpful master concept a master can help only a sub-tree, and
2132 // because here is all finished is not possible master is booked.
2133 assert(threads[threadID].state == THREAD_AVAILABLE);
2135 threads[threadID].state = THREAD_SEARCHING;
2142 // init_threads() is called during startup. Initializes locks and condition
2143 // variables and launches all threads sending them immediately to sleep.
2145 void ThreadsManager::init_threads() {
2147 int i, arg[MAX_THREADS];
2150 // This flag is needed to properly end the threads when program exits
2151 allThreadsShouldExit = false;
2153 // Threads will sent to sleep as soon as created, only main thread is kept alive
2158 for (i = 0; i < MAX_THREADS; i++)
2160 // Initialize thread and split point locks
2161 lock_init(&threads[i].sleepLock);
2162 cond_init(&threads[i].sleepCond);
2164 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2165 lock_init(&(threads[i].splitPoints[j].lock));
2167 // All threads but first should be set to THREAD_INITIALIZING
2168 threads[i].state = (i == 0 ? THREAD_SEARCHING : THREAD_INITIALIZING);
2171 // Create and startup the threads
2172 for (i = 1; i < MAX_THREADS; i++)
2176 #if !defined(_MSC_VER)
2177 pthread_t pthread[1];
2178 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2179 pthread_detach(pthread[0]);
2181 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2185 cout << "Failed to create thread number " << i << endl;
2189 // Wait until the thread has finished launching and is gone to sleep
2190 while (threads[i].state == THREAD_INITIALIZING) {}
2195 // exit_threads() is called when the program exits. It makes all the
2196 // helper threads exit cleanly.
2198 void ThreadsManager::exit_threads() {
2200 // Force the woken up threads to exit idle_loop() and hence terminate
2201 allThreadsShouldExit = true;
2203 for (int i = 0; i < MAX_THREADS; i++)
2205 // Wake up all the threads and waits for termination
2208 threads[i].wake_up();
2209 while (threads[i].state != THREAD_TERMINATED) {}
2212 // Now we can safely destroy the locks and wait conditions
2213 lock_destroy(&threads[i].sleepLock);
2214 cond_destroy(&threads[i].sleepCond);
2216 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2217 lock_destroy(&(threads[i].splitPoints[j].lock));
2220 lock_destroy(&mpLock);
2224 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2225 // the thread's currently active split point, or in some ancestor of
2226 // the current split point.
2228 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2230 assert(threadID >= 0 && threadID < activeThreads);
2232 SplitPoint* sp = threads[threadID].splitPoint;
2234 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2239 // thread_is_available() checks whether the thread with threadID "slave" is
2240 // available to help the thread with threadID "master" at a split point. An
2241 // obvious requirement is that "slave" must be idle. With more than two
2242 // threads, this is not by itself sufficient: If "slave" is the master of
2243 // some active split point, it is only available as a slave to the other
2244 // threads which are busy searching the split point at the top of "slave"'s
2245 // split point stack (the "helpful master concept" in YBWC terminology).
2247 bool ThreadsManager::thread_is_available(int slave, int master) const {
2249 assert(slave >= 0 && slave < activeThreads);
2250 assert(master >= 0 && master < activeThreads);
2251 assert(activeThreads > 1);
2253 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2256 // Make a local copy to be sure doesn't change under our feet
2257 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2259 // No active split points means that the thread is available as
2260 // a slave for any other thread.
2261 if (localActiveSplitPoints == 0 || activeThreads == 2)
2264 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2265 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2266 // could have been set to 0 by another thread leading to an out of bound access.
2267 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2274 // available_thread_exists() tries to find an idle thread which is available as
2275 // a slave for the thread with threadID "master".
2277 bool ThreadsManager::available_thread_exists(int master) const {
2279 assert(master >= 0 && master < activeThreads);
2280 assert(activeThreads > 1);
2282 for (int i = 0; i < activeThreads; i++)
2283 if (thread_is_available(i, master))
2290 // split() does the actual work of distributing the work at a node between
2291 // several available threads. If it does not succeed in splitting the
2292 // node (because no idle threads are available, or because we have no unused
2293 // split point objects), the function immediately returns. If splitting is
2294 // possible, a SplitPoint object is initialized with all the data that must be
2295 // copied to the helper threads and we tell our helper threads that they have
2296 // been assigned work. This will cause them to instantly leave their idle loops and
2297 // call search().When all threads have returned from search() then split() returns.
2299 template <bool Fake>
2300 void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
2301 Value* bestValue, Depth depth, Move threatMove,
2302 int moveCount, MovePicker* mp, bool pvNode) {
2303 assert(pos.is_ok());
2304 assert(*bestValue >= -VALUE_INFINITE);
2305 assert(*bestValue <= *alpha);
2306 assert(*alpha < beta);
2307 assert(beta <= VALUE_INFINITE);
2308 assert(depth > DEPTH_ZERO);
2309 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2310 assert(activeThreads > 1);
2312 int i, master = pos.thread();
2313 Thread& masterThread = threads[master];
2317 // If no other thread is available to help us, or if we have too many
2318 // active split points, don't split.
2319 if ( !available_thread_exists(master)
2320 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2322 lock_release(&mpLock);
2326 // Pick the next available split point object from the split point stack
2327 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2329 // Initialize the split point object
2330 splitPoint.parent = masterThread.splitPoint;
2331 splitPoint.master = master;
2332 splitPoint.betaCutoff = false;
2333 splitPoint.depth = depth;
2334 splitPoint.threatMove = threatMove;
2335 splitPoint.alpha = *alpha;
2336 splitPoint.beta = beta;
2337 splitPoint.pvNode = pvNode;
2338 splitPoint.bestValue = *bestValue;
2340 splitPoint.moveCount = moveCount;
2341 splitPoint.pos = &pos;
2342 splitPoint.nodes = 0;
2344 for (i = 0; i < activeThreads; i++)
2345 splitPoint.slaves[i] = 0;
2347 masterThread.splitPoint = &splitPoint;
2349 // If we are here it means we are not available
2350 assert(masterThread.state != THREAD_AVAILABLE);
2352 int workersCnt = 1; // At least the master is included
2354 // Allocate available threads setting state to THREAD_BOOKED
2355 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2356 if (thread_is_available(i, master))
2358 threads[i].state = THREAD_BOOKED;
2359 threads[i].splitPoint = &splitPoint;
2360 splitPoint.slaves[i] = 1;
2364 assert(Fake || workersCnt > 1);
2366 // We can release the lock because slave threads are already booked and master is not available
2367 lock_release(&mpLock);
2369 // Tell the threads that they have work to do. This will make them leave
2371 for (i = 0; i < activeThreads; i++)
2372 if (i == master || splitPoint.slaves[i])
2374 assert(i == master || threads[i].state == THREAD_BOOKED);
2376 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2378 if (useSleepingThreads && i != master)
2379 threads[i].wake_up();
2382 // Everything is set up. The master thread enters the idle loop, from
2383 // which it will instantly launch a search, because its state is
2384 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2385 // idle loop, which means that the main thread will return from the idle
2386 // loop when all threads have finished their work at this split point.
2387 idle_loop(master, &splitPoint);
2389 // We have returned from the idle loop, which means that all threads are
2390 // finished. Update alpha and bestValue, and return.
2393 *alpha = splitPoint.alpha;
2394 *bestValue = splitPoint.bestValue;
2395 masterThread.activeSplitPoints--;
2396 masterThread.splitPoint = splitPoint.parent;
2397 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2399 lock_release(&mpLock);
2403 /// RootMove and RootMoveList method's definitions
2405 RootMove::RootMove() {
2408 pv_score = non_pv_score = -VALUE_INFINITE;
2412 RootMove& RootMove::operator=(const RootMove& rm) {
2414 const Move* src = rm.pv;
2417 // Avoid a costly full rm.pv[] copy
2418 do *dst++ = *src; while (*src++ != MOVE_NONE);
2421 pv_score = rm.pv_score;
2422 non_pv_score = rm.non_pv_score;
2426 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2427 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2428 // allow to always have a ponder move even when we fail high at root and also a
2429 // long PV to print that is important for position analysis.
2431 void RootMove::extract_pv_from_tt(Position& pos) {
2433 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2437 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2439 pos.do_move(pv[0], *st++);
2441 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2442 && tte->move() != MOVE_NONE
2443 && pos.move_is_legal(tte->move())
2445 && (!pos.is_draw() || ply < 2))
2447 pv[ply] = tte->move();
2448 pos.do_move(pv[ply++], *st++);
2450 pv[ply] = MOVE_NONE;
2452 do pos.undo_move(pv[--ply]); while (ply);
2455 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2456 // the PV back into the TT. This makes sure the old PV moves are searched
2457 // first, even if the old TT entries have been overwritten.
2459 void RootMove::insert_pv_in_tt(Position& pos) {
2461 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2464 Value v, m = VALUE_NONE;
2467 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2471 tte = TT.retrieve(k);
2473 // Don't overwrite existing correct entries
2474 if (!tte || tte->move() != pv[ply])
2476 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2477 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2479 pos.do_move(pv[ply], *st++);
2481 } while (pv[++ply] != MOVE_NONE);
2483 do pos.undo_move(pv[--ply]); while (ply);
2486 // pv_info_to_uci() returns a string with information on the current PV line
2487 // formatted according to UCI specification.
2489 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2490 Value beta, int pvIdx) {
2491 std::stringstream s;
2493 s << "info depth " << depth
2494 << " seldepth " << selDepth
2495 << " multipv " << pvIdx + 1
2496 << " score " << value_to_uci(pv_score)
2497 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2498 << speed_to_uci(pos.nodes_searched())
2501 for (Move* m = pv; *m != MOVE_NONE; m++)
2508 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2510 MoveStack mlist[MOVES_MAX];
2514 bestMoveChanges = 0;
2516 // Generate all legal moves and add them to RootMoveList
2517 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2518 for (MoveStack* cur = mlist; cur != last; cur++)
2520 // If we have a searchMoves[] list then verify cur->move
2521 // is in the list before to add it.
2522 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2524 if (searchMoves[0] && *sm != cur->move)
2528 rm.pv[0] = cur->move;
2529 rm.pv[1] = MOVE_NONE;
2530 rm.pv_score = -VALUE_INFINITE;
2536 // When playing with strength handicap choose best move among the MultiPV set
2537 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2538 void do_skill_level(Move* best, Move* ponder) {
2540 assert(MultiPV > 1);
2542 // Rml list is already sorted by pv_score in descending order
2544 int max_s = -VALUE_INFINITE;
2545 int size = Min(MultiPV, (int)Rml.size());
2546 int max = Rml[0].pv_score;
2547 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2548 int wk = 120 - 2 * SkillLevel;
2550 // PRNG sequence should be non deterministic
2551 for (int i = abs(get_system_time() % 50); i > 0; i--)
2552 RK.rand<unsigned>();
2554 // Choose best move. For each move's score we add two terms both dependent
2555 // on wk, one deterministic and bigger for weaker moves, and one random,
2556 // then we choose the move with the resulting highest score.
2557 for (int i = 0; i < size; i++)
2559 s = Rml[i].pv_score;
2561 // Don't allow crazy blunders even at very low skills
2562 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2565 // This is our magical formula
2566 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2571 *best = Rml[i].pv[0];
2572 *ponder = Rml[i].pv[1];