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,
120 Value alpha, Value beta, int pvIdx);
124 Move pv[PLY_MAX_PLUS_2];
128 // RootMoveList struct is just a 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. Array index 0 is used at
192 // 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 access function
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 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
242 std::ofstream LogFile;
244 // Skill level adjustment
246 bool SkillLevelEnabled;
249 // Multi-threads manager
250 ThreadsManager ThreadsMgr;
252 // Node counters, used only by thread[0] but try to keep in different cache
253 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
254 bool SendSearchedNodes;
256 int NodesBetweenPolls = 30000;
264 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
266 template <NodeType PvNode, bool SpNode, bool Root>
267 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
269 template <NodeType PvNode>
270 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
272 template <NodeType PvNode>
273 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
275 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
276 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
279 template <NodeType PvNode>
280 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
282 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
283 bool connected_moves(const Position& pos, Move m1, Move m2);
284 Value value_to_tt(Value v, int ply);
285 Value value_from_tt(Value v, int ply);
286 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
287 bool connected_threat(const Position& pos, Move m, Move threat);
288 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
289 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
290 void update_gains(const Position& pos, Move move, Value before, Value after);
291 void do_skill_level(Move* best, Move* ponder);
293 int current_search_time(int set = 0);
294 std::string value_to_uci(Value v);
295 std::string speed_to_uci(int64_t nodes);
296 void poll(const Position& pos);
297 void wait_for_stop_or_ponderhit();
299 #if !defined(_MSC_VER)
300 void* init_thread(void* threadID);
302 DWORD WINAPI init_thread(LPVOID threadID);
306 // MovePickerExt is an extended MovePicker class used to choose at compile time
307 // the proper move source according to the type of node.
308 template<bool SpNode, bool Root> struct MovePickerExt;
310 // In Root nodes use RootMoveList as source. Score and sort the root moves
311 // before to search them.
312 template<> struct MovePickerExt<false, true> : public MovePicker {
314 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
315 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
317 Value score = VALUE_ZERO;
319 // Score root moves using standard ordering used in main search, the moves
320 // are scored according to the order in which they are returned by MovePicker.
321 // This is the second order score that is used to compare the moves when
322 // the first orders pv_score of both moves are equal.
323 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
324 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
325 if (rm->pv[0] == move)
327 rm->non_pv_score = score--;
335 Move get_next_move() {
342 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
345 RootMoveList::iterator rm;
349 // In SpNodes use split point's shared MovePicker object as move source
350 template<> struct MovePickerExt<true, false> : public MovePicker {
352 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
353 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
355 Move get_next_move() { return mp->get_next_move(); }
357 RootMoveList::iterator rm; // Dummy, needed to compile
361 // Default case, create and use a MovePicker object as source
362 template<> struct MovePickerExt<false, false> : public MovePicker {
364 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
365 : MovePicker(p, ttm, d, h, ss, b) {}
367 RootMoveList::iterator rm; // Dummy, needed to compile
373 /// init_threads() is called during startup. It initializes various lookup tables
374 /// and creates and launches search threads.
376 void init_threads() {
378 int d; // depth (ONE_PLY == 2)
379 int hd; // half depth (ONE_PLY == 1)
382 // Init reductions array
383 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
385 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
386 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
387 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
388 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
391 // Init futility margins array
392 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
393 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
395 // Init futility move count array
396 for (d = 0; d < 32; d++)
397 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
399 // Create and startup threads
400 ThreadsMgr.init_threads();
404 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
405 void exit_threads() { ThreadsMgr.exit_threads(); }
408 /// perft() is our utility to verify move generation. All the legal moves up to
409 /// given depth are generated and counted and the sum returned.
411 int64_t perft(Position& pos, Depth depth) {
413 MoveStack mlist[MOVES_MAX];
418 // Generate all legal moves
419 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
421 // If we are at the last ply we don't need to do and undo
422 // the moves, just to count them.
423 if (depth <= ONE_PLY)
424 return int(last - mlist);
426 // Loop through all legal moves
428 for (MoveStack* cur = mlist; cur != last; cur++)
431 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
432 sum += perft(pos, depth - ONE_PLY);
439 /// think() is the external interface to Stockfish's search, and is called when
440 /// the program receives the UCI 'go' command. It initializes various global
441 /// variables, and calls id_loop(). It returns false when a "quit" command is
442 /// received during the search.
444 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
446 // Initialize global search-related variables
447 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
449 current_search_time(get_system_time());
451 TimeMgr.init(Limits, pos.startpos_ply_counter());
453 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
455 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
456 else if (Limits.time && Limits.time < 1000)
457 NodesBetweenPolls = 1000;
458 else if (Limits.time && Limits.time < 5000)
459 NodesBetweenPolls = 5000;
461 NodesBetweenPolls = 30000;
463 // Look for a book move, only during games, not tests
464 if (Limits.useTimeManagement() && Options["OwnBook"].value<bool>())
466 if (Options["Book File"].value<std::string>() != OpeningBook.name())
467 OpeningBook.open(Options["Book File"].value<std::string>());
469 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
470 if (bookMove != MOVE_NONE)
473 wait_for_stop_or_ponderhit();
475 cout << "bestmove " << bookMove << endl;
481 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
482 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
483 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
484 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
485 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
486 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
487 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
488 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
489 UCIMultiPV = Options["MultiPV"].value<int>();
490 SkillLevel = Options["Skill level"].value<int>();
491 UseLogFile = Options["Use Search Log"].value<bool>();
493 read_evaluation_uci_options(pos.side_to_move());
495 if (Options["Clear Hash"].value<bool>())
497 Options["Clear Hash"].set_value("false");
500 TT.set_size(Options["Hash"].value<int>());
502 // Do we have to play with skill handicap? In this case enable MultiPV that
503 // we will use behind the scenes to retrieve a set of possible moves.
504 SkillLevelEnabled = (SkillLevel < 20);
505 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
507 // Set the number of active threads
508 ThreadsMgr.read_uci_options();
509 init_eval(ThreadsMgr.active_threads());
511 // Wake up needed threads and reset maxPly counter
512 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
514 ThreadsMgr[i].wake_up();
515 ThreadsMgr[i].maxPly = 0;
518 // Write to log file and keep it open to be accessed during the search
521 std::string name = Options["Search Log Filename"].value<std::string>();
522 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
524 LogFile << "\nSearching: " << pos.to_fen()
525 << "\ninfinite: " << Limits.infinite
526 << " ponder: " << Limits.ponder
527 << " time: " << Limits.time
528 << " increment: " << Limits.increment
529 << " moves to go: " << Limits.movesToGo
533 // We're ready to start thinking. Call the iterative deepening loop function
534 Move ponderMove = MOVE_NONE;
535 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
537 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
539 // Write final search statistics and close log file
542 int t = current_search_time();
544 LogFile << "Nodes: " << pos.nodes_searched()
545 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
546 << "\nBest move: " << move_to_san(pos, bestMove);
549 pos.do_move(bestMove, st);
550 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
551 pos.undo_move(bestMove); // Return from think() with unchanged position
555 // This makes all the threads to go to sleep
556 ThreadsMgr.set_active_threads(1);
558 // If we are pondering or in infinite search, we shouldn't print the
559 // best move before we are told to do so.
560 if (!StopRequest && (Limits.ponder || Limits.infinite))
561 wait_for_stop_or_ponderhit();
563 // Could be MOVE_NONE when searching on a stalemate position
564 cout << "bestmove " << bestMove;
566 // UCI protol is not clear on allowing sending an empty ponder move, instead
567 // it is clear that ponder move is optional. So skip it if empty.
568 if (ponderMove != MOVE_NONE)
569 cout << " ponder " << ponderMove;
579 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
580 // with increasing depth until the allocated thinking time has been consumed,
581 // user stops the search, or the maximum search depth is reached.
583 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
585 SearchStack ss[PLY_MAX_PLUS_2];
586 Value bestValues[PLY_MAX_PLUS_2];
587 int bestMoveChanges[PLY_MAX_PLUS_2];
588 int depth, selDepth, aspirationDelta;
589 Value value, alpha, beta;
590 Move bestMove, easyMove, skillBest, skillPonder;
592 // Initialize stuff before a new search
593 memset(ss, 0, 4 * sizeof(SearchStack));
596 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
597 depth = aspirationDelta = 0;
598 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
599 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
601 // Moves to search are verified and copied
602 Rml.init(pos, searchMoves);
604 // Handle special case of searching on a mate/stalemate position
607 cout << "info depth 0 score "
608 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
614 // Iterative deepening loop
615 while (++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth) && !StopRequest)
617 Rml.bestMoveChanges = 0;
618 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
620 // Calculate dynamic aspiration window based on previous iterations
621 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
623 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
624 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
626 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
627 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
629 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
630 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
633 // Start with a small aspiration window and, in case of fail high/low,
634 // research with bigger window until not failing high/low anymore.
636 // Search starting from ss+1 to allow calling update_gains()
637 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
639 // Write PV back to transposition table in case the relevant entries
640 // have been overwritten during the search.
641 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
642 Rml[i].insert_pv_in_tt(pos);
644 // Value cannot be trusted. Break out immediately!
648 assert(value >= alpha);
650 // In case of failing high/low increase aspiration window and research,
651 // otherwise exit the fail high/low loop.
654 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
655 aspirationDelta += aspirationDelta / 2;
657 else if (value <= alpha)
659 AspirationFailLow = true;
660 StopOnPonderhit = false;
662 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
663 aspirationDelta += aspirationDelta / 2;
668 } while (abs(value) < VALUE_KNOWN_WIN);
670 // Collect info about search result
671 bestMove = Rml[0].pv[0];
672 *ponderMove = Rml[0].pv[1];
673 bestValues[depth] = value;
674 bestMoveChanges[depth] = Rml.bestMoveChanges;
676 // Do we need to pick now the best and the ponder moves ?
677 if (SkillLevelEnabled && depth == 1 + SkillLevel)
678 do_skill_level(&skillBest, &skillPonder);
680 // Retrieve max searched depth among threads
682 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
683 if (ThreadsMgr[i].maxPly > selDepth)
684 selDepth = ThreadsMgr[i].maxPly;
686 // Send PV line to GUI and to log file
687 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
688 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
691 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
693 // Init easyMove after first iteration or drop if differs from the best move
694 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
696 else if (bestMove != easyMove)
697 easyMove = MOVE_NONE;
699 if (Limits.useTimeManagement() && !StopRequest)
702 bool noMoreTime = false;
704 // Stop search early when the last two iterations returned a mate score
706 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
707 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
710 // Stop search early if one move seems to be much better than the
711 // others or if there is only a single legal move. In this latter
712 // case we search up to Iteration 8 anyway to get a proper score.
714 && easyMove == bestMove
716 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
717 && current_search_time() > TimeMgr.available_time() / 16)
718 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
719 && current_search_time() > TimeMgr.available_time() / 32)))
722 // Add some extra time if the best move has changed during the last two iterations
723 if (depth > 4 && depth < 50)
724 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
726 // Stop search if most of MaxSearchTime is consumed at the end of the
727 // iteration. We probably don't have enough time to search the first
728 // move at the next iteration anyway.
729 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
735 StopOnPonderhit = true;
742 // When using skills fake best and ponder moves with the sub-optimal ones
743 if (SkillLevelEnabled)
745 if (skillBest == MOVE_NONE) // Still unassigned ?
746 do_skill_level(&skillBest, &skillPonder);
748 bestMove = skillBest;
749 *ponderMove = skillPonder;
756 // search<>() is the main search function for both PV and non-PV nodes and for
757 // normal and SplitPoint nodes. When called just after a split point the search
758 // is simpler because we have already probed the hash table, done a null move
759 // search, and searched the first move before splitting, we don't have to repeat
760 // all this work again. We also don't need to store anything to the hash table
761 // here: This is taken care of after we return from the split point.
763 template <NodeType PvNode, bool SpNode, bool Root>
764 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
766 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
767 assert(beta > alpha && beta <= VALUE_INFINITE);
768 assert(PvNode || alpha == beta - 1);
769 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
771 Move movesSearched[MOVES_MAX];
776 Move ttMove, move, excludedMove, threatMove;
779 Value bestValue, value, oldAlpha;
780 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
781 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
782 int moveCount = 0, playedMoveCount = 0;
783 int threadID = pos.thread();
784 SplitPoint* sp = NULL;
786 refinedValue = bestValue = value = -VALUE_INFINITE;
788 isCheck = pos.is_check();
789 ss->ply = (ss-1)->ply + 1;
791 // Used to send selDepth info to GUI
792 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
793 ThreadsMgr[threadID].maxPly = ss->ply;
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_special(m))
1713 result += PawnEndgameExtension[PvNode];
1717 return Min(result, ONE_PLY);
1721 // connected_threat() tests whether it is safe to forward prune a move or if
1722 // is somehow connected to the threat move returned by null search.
1724 bool connected_threat(const Position& pos, Move m, Move threat) {
1726 assert(move_is_ok(m));
1727 assert(threat && move_is_ok(threat));
1728 assert(!pos.move_is_check(m));
1729 assert(!pos.move_is_capture_or_promotion(m));
1730 assert(!pos.move_is_passed_pawn_push(m));
1732 Square mfrom, mto, tfrom, tto;
1734 mfrom = move_from(m);
1736 tfrom = move_from(threat);
1737 tto = move_to(threat);
1739 // Case 1: Don't prune moves which move the threatened piece
1743 // Case 2: If the threatened piece has value less than or equal to the
1744 // value of the threatening piece, don't prune moves which defend it.
1745 if ( pos.move_is_capture(threat)
1746 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1747 || pos.type_of_piece_on(tfrom) == KING)
1748 && pos.move_attacks_square(m, tto))
1751 // Case 3: If the moving piece in the threatened move is a slider, don't
1752 // prune safe moves which block its ray.
1753 if ( piece_is_slider(pos.piece_on(tfrom))
1754 && bit_is_set(squares_between(tfrom, tto), mto)
1755 && pos.see_sign(m) >= 0)
1762 // ok_to_use_TT() returns true if a transposition table score
1763 // can be used at a given point in search.
1765 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1767 Value v = value_from_tt(tte->value(), ply);
1769 return ( tte->depth() >= depth
1770 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1771 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1773 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1774 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1778 // refine_eval() returns the transposition table score if
1779 // possible otherwise falls back on static position evaluation.
1781 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1785 Value v = value_from_tt(tte->value(), ply);
1787 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1788 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1795 // update_history() registers a good move that produced a beta-cutoff
1796 // in history and marks as failures all the other moves of that ply.
1798 void update_history(const Position& pos, Move move, Depth depth,
1799 Move movesSearched[], int moveCount) {
1801 Value bonus = Value(int(depth) * int(depth));
1803 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1805 for (int i = 0; i < moveCount - 1; i++)
1807 m = movesSearched[i];
1811 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1816 // update_gains() updates the gains table of a non-capture move given
1817 // the static position evaluation before and after the move.
1819 void update_gains(const Position& pos, Move m, Value before, Value after) {
1822 && before != VALUE_NONE
1823 && after != VALUE_NONE
1824 && pos.captured_piece_type() == PIECE_TYPE_NONE
1825 && !move_is_special(m))
1826 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1830 // current_search_time() returns the number of milliseconds which have passed
1831 // since the beginning of the current search.
1833 int current_search_time(int set) {
1835 static int searchStartTime;
1838 searchStartTime = set;
1840 return get_system_time() - searchStartTime;
1844 // value_to_uci() converts a value to a string suitable for use with the UCI
1845 // protocol specifications:
1847 // cp <x> The score from the engine's point of view in centipawns.
1848 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1849 // use negative values for y.
1851 std::string value_to_uci(Value v) {
1853 std::stringstream s;
1855 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1856 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1858 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1864 // speed_to_uci() returns a string with time stats of current search suitable
1865 // to be sent to UCI gui.
1867 std::string speed_to_uci(int64_t nodes) {
1869 std::stringstream s;
1870 int t = current_search_time();
1872 s << " nodes " << nodes
1873 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1880 // poll() performs two different functions: It polls for user input, and it
1881 // looks at the time consumed so far and decides if it's time to abort the
1884 void poll(const Position& pos) {
1886 static int lastInfoTime;
1887 int t = current_search_time();
1890 if (input_available())
1892 // We are line oriented, don't read single chars
1893 std::string command;
1895 if (!std::getline(std::cin, command) || command == "quit")
1897 // Quit the program as soon as possible
1898 Limits.ponder = false;
1899 QuitRequest = StopRequest = true;
1902 else if (command == "stop")
1904 // Stop calculating as soon as possible, but still send the "bestmove"
1905 // and possibly the "ponder" token when finishing the search.
1906 Limits.ponder = false;
1909 else if (command == "ponderhit")
1911 // The opponent has played the expected move. GUI sends "ponderhit" if
1912 // we were told to ponder on the same move the opponent has played. We
1913 // should continue searching but switching from pondering to normal search.
1914 Limits.ponder = false;
1916 if (StopOnPonderhit)
1921 // Print search information
1925 else if (lastInfoTime > t)
1926 // HACK: Must be a new search where we searched less than
1927 // NodesBetweenPolls nodes during the first second of search.
1930 else if (t - lastInfoTime >= 1000)
1935 dbg_print_hit_rate();
1937 // Send info on searched nodes as soon as we return to root
1938 SendSearchedNodes = true;
1941 // Should we stop the search?
1945 bool stillAtFirstMove = FirstRootMove
1946 && !AspirationFailLow
1947 && t > TimeMgr.available_time();
1949 bool noMoreTime = t > TimeMgr.maximum_time()
1950 || stillAtFirstMove;
1952 if ( (Limits.useTimeManagement() && noMoreTime)
1953 || (Limits.maxTime && t >= Limits.maxTime)
1954 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1959 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1960 // while the program is pondering. The point is to work around a wrinkle in
1961 // the UCI protocol: When pondering, the engine is not allowed to give a
1962 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1963 // We simply wait here until one of these commands is sent, and return,
1964 // after which the bestmove and pondermove will be printed.
1966 void wait_for_stop_or_ponderhit() {
1968 std::string command;
1970 // Wait for a command from stdin
1971 while ( std::getline(std::cin, command)
1972 && command != "ponderhit" && command != "stop" && command != "quit") {};
1974 if (command != "ponderhit" && command != "stop")
1975 QuitRequest = true; // Must be "quit" or getline() returned false
1979 // init_thread() is the function which is called when a new thread is
1980 // launched. It simply calls the idle_loop() function with the supplied
1981 // threadID. There are two versions of this function; one for POSIX
1982 // threads and one for Windows threads.
1984 #if !defined(_MSC_VER)
1986 void* init_thread(void* threadID) {
1988 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
1994 DWORD WINAPI init_thread(LPVOID threadID) {
1996 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2003 /// The ThreadsManager class
2006 // read_uci_options() updates number of active threads and other internal
2007 // parameters according to the UCI options values. It is called before
2008 // to start a new search.
2010 void ThreadsManager::read_uci_options() {
2012 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2013 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2014 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2015 activeThreads = Options["Threads"].value<int>();
2019 // idle_loop() is where the threads are parked when they have no work to do.
2020 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2021 // object for which the current thread is the master.
2023 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2025 assert(threadID >= 0 && threadID < MAX_THREADS);
2032 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2033 // master should exit as last one.
2034 if (allThreadsShouldExit)
2037 threads[threadID].state = THREAD_TERMINATED;
2041 // If we are not thinking, wait for a condition to be signaled
2042 // instead of wasting CPU time polling for work.
2043 while ( threadID >= activeThreads
2044 || threads[threadID].state == THREAD_INITIALIZING
2045 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2047 assert(!sp || useSleepingThreads);
2048 assert(threadID != 0 || useSleepingThreads);
2050 if (threads[threadID].state == THREAD_INITIALIZING)
2051 threads[threadID].state = THREAD_AVAILABLE;
2053 // Grab the lock to avoid races with Thread::wake_up()
2054 lock_grab(&threads[threadID].sleepLock);
2056 // If we are master and all slaves have finished do not go to sleep
2057 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2058 allFinished = (i == activeThreads);
2060 if (allFinished || allThreadsShouldExit)
2062 lock_release(&threads[threadID].sleepLock);
2066 // Do sleep here after retesting sleep conditions
2067 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2068 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2070 lock_release(&threads[threadID].sleepLock);
2073 // If this thread has been assigned work, launch a search
2074 if (threads[threadID].state == THREAD_WORKISWAITING)
2076 assert(!allThreadsShouldExit);
2078 threads[threadID].state = THREAD_SEARCHING;
2080 // Copy split point position and search stack and call search()
2081 // with SplitPoint template parameter set to true.
2082 SearchStack ss[PLY_MAX_PLUS_2];
2083 SplitPoint* tsp = threads[threadID].splitPoint;
2084 Position pos(*tsp->pos, threadID);
2086 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2090 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2092 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2094 assert(threads[threadID].state == THREAD_SEARCHING);
2096 threads[threadID].state = THREAD_AVAILABLE;
2098 // Wake up master thread so to allow it to return from the idle loop in
2099 // case we are the last slave of the split point.
2100 if ( useSleepingThreads
2101 && threadID != tsp->master
2102 && threads[tsp->master].state == THREAD_AVAILABLE)
2103 threads[tsp->master].wake_up();
2106 // If this thread is the master of a split point and all slaves have
2107 // finished their work at this split point, return from the idle loop.
2108 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2109 allFinished = (i == activeThreads);
2113 // Because sp->slaves[] is reset under lock protection,
2114 // be sure sp->lock has been released before to return.
2115 lock_grab(&(sp->lock));
2116 lock_release(&(sp->lock));
2118 // In helpful master concept a master can help only a sub-tree, and
2119 // because here is all finished is not possible master is booked.
2120 assert(threads[threadID].state == THREAD_AVAILABLE);
2122 threads[threadID].state = THREAD_SEARCHING;
2129 // init_threads() is called during startup. Initializes locks and condition
2130 // variables and launches all threads sending them immediately to sleep.
2132 void ThreadsManager::init_threads() {
2134 int i, arg[MAX_THREADS];
2137 // This flag is needed to properly end the threads when program exits
2138 allThreadsShouldExit = false;
2140 // Threads will sent to sleep as soon as created, only main thread is kept alive
2145 for (i = 0; i < MAX_THREADS; i++)
2147 // Initialize thread and split point locks
2148 lock_init(&threads[i].sleepLock);
2149 cond_init(&threads[i].sleepCond);
2151 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2152 lock_init(&(threads[i].splitPoints[j].lock));
2154 // All threads but first should be set to THREAD_INITIALIZING
2155 threads[i].state = (i == 0 ? THREAD_SEARCHING : THREAD_INITIALIZING);
2158 // Create and startup the threads
2159 for (i = 1; i < MAX_THREADS; i++)
2163 #if !defined(_MSC_VER)
2164 pthread_t pthread[1];
2165 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2166 pthread_detach(pthread[0]);
2168 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2172 cout << "Failed to create thread number " << i << endl;
2176 // Wait until the thread has finished launching and is gone to sleep
2177 while (threads[i].state == THREAD_INITIALIZING) {}
2182 // exit_threads() is called when the program exits. It makes all the
2183 // helper threads exit cleanly.
2185 void ThreadsManager::exit_threads() {
2187 // Force the woken up threads to exit idle_loop() and hence terminate
2188 allThreadsShouldExit = true;
2190 for (int i = 0; i < MAX_THREADS; i++)
2192 // Wake up all the threads and waits for termination
2195 threads[i].wake_up();
2196 while (threads[i].state != THREAD_TERMINATED) {}
2199 // Now we can safely destroy the locks and wait conditions
2200 lock_destroy(&threads[i].sleepLock);
2201 cond_destroy(&threads[i].sleepCond);
2203 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2204 lock_destroy(&(threads[i].splitPoints[j].lock));
2207 lock_destroy(&mpLock);
2211 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2212 // the thread's currently active split point, or in some ancestor of
2213 // the current split point.
2215 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2217 assert(threadID >= 0 && threadID < activeThreads);
2219 SplitPoint* sp = threads[threadID].splitPoint;
2221 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2226 // thread_is_available() checks whether the thread with threadID "slave" is
2227 // available to help the thread with threadID "master" at a split point. An
2228 // obvious requirement is that "slave" must be idle. With more than two
2229 // threads, this is not by itself sufficient: If "slave" is the master of
2230 // some active split point, it is only available as a slave to the other
2231 // threads which are busy searching the split point at the top of "slave"'s
2232 // split point stack (the "helpful master concept" in YBWC terminology).
2234 bool ThreadsManager::thread_is_available(int slave, int master) const {
2236 assert(slave >= 0 && slave < activeThreads);
2237 assert(master >= 0 && master < activeThreads);
2238 assert(activeThreads > 1);
2240 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2243 // Make a local copy to be sure doesn't change under our feet
2244 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2246 // No active split points means that the thread is available as
2247 // a slave for any other thread.
2248 if (localActiveSplitPoints == 0 || activeThreads == 2)
2251 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2252 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2253 // could have been set to 0 by another thread leading to an out of bound access.
2254 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2261 // available_thread_exists() tries to find an idle thread which is available as
2262 // a slave for the thread with threadID "master".
2264 bool ThreadsManager::available_thread_exists(int master) const {
2266 assert(master >= 0 && master < activeThreads);
2267 assert(activeThreads > 1);
2269 for (int i = 0; i < activeThreads; i++)
2270 if (thread_is_available(i, master))
2277 // split() does the actual work of distributing the work at a node between
2278 // several available threads. If it does not succeed in splitting the
2279 // node (because no idle threads are available, or because we have no unused
2280 // split point objects), the function immediately returns. If splitting is
2281 // possible, a SplitPoint object is initialized with all the data that must be
2282 // copied to the helper threads and we tell our helper threads that they have
2283 // been assigned work. This will cause them to instantly leave their idle loops and
2284 // call search().When all threads have returned from search() then split() returns.
2286 template <bool Fake>
2287 void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
2288 Value* bestValue, Depth depth, Move threatMove,
2289 int moveCount, MovePicker* mp, bool pvNode) {
2290 assert(pos.is_ok());
2291 assert(*bestValue >= -VALUE_INFINITE);
2292 assert(*bestValue <= *alpha);
2293 assert(*alpha < beta);
2294 assert(beta <= VALUE_INFINITE);
2295 assert(depth > DEPTH_ZERO);
2296 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2297 assert(activeThreads > 1);
2299 int i, master = pos.thread();
2300 Thread& masterThread = threads[master];
2304 // If no other thread is available to help us, or if we have too many
2305 // active split points, don't split.
2306 if ( !available_thread_exists(master)
2307 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2309 lock_release(&mpLock);
2313 // Pick the next available split point object from the split point stack
2314 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2316 // Initialize the split point object
2317 splitPoint.parent = masterThread.splitPoint;
2318 splitPoint.master = master;
2319 splitPoint.betaCutoff = false;
2320 splitPoint.depth = depth;
2321 splitPoint.threatMove = threatMove;
2322 splitPoint.alpha = *alpha;
2323 splitPoint.beta = beta;
2324 splitPoint.pvNode = pvNode;
2325 splitPoint.bestValue = *bestValue;
2327 splitPoint.moveCount = moveCount;
2328 splitPoint.pos = &pos;
2329 splitPoint.nodes = 0;
2331 for (i = 0; i < activeThreads; i++)
2332 splitPoint.slaves[i] = 0;
2334 masterThread.splitPoint = &splitPoint;
2336 // If we are here it means we are not available
2337 assert(masterThread.state != THREAD_AVAILABLE);
2339 int workersCnt = 1; // At least the master is included
2341 // Allocate available threads setting state to THREAD_BOOKED
2342 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2343 if (thread_is_available(i, master))
2345 threads[i].state = THREAD_BOOKED;
2346 threads[i].splitPoint = &splitPoint;
2347 splitPoint.slaves[i] = 1;
2351 assert(Fake || workersCnt > 1);
2353 // We can release the lock because slave threads are already booked and master is not available
2354 lock_release(&mpLock);
2356 // Tell the threads that they have work to do. This will make them leave
2358 for (i = 0; i < activeThreads; i++)
2359 if (i == master || splitPoint.slaves[i])
2361 assert(i == master || threads[i].state == THREAD_BOOKED);
2363 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2365 if (useSleepingThreads && i != master)
2366 threads[i].wake_up();
2369 // Everything is set up. The master thread enters the idle loop, from
2370 // which it will instantly launch a search, because its state is
2371 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2372 // idle loop, which means that the main thread will return from the idle
2373 // loop when all threads have finished their work at this split point.
2374 idle_loop(master, &splitPoint);
2376 // We have returned from the idle loop, which means that all threads are
2377 // finished. Update alpha and bestValue, and return.
2380 *alpha = splitPoint.alpha;
2381 *bestValue = splitPoint.bestValue;
2382 masterThread.activeSplitPoints--;
2383 masterThread.splitPoint = splitPoint.parent;
2384 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2386 lock_release(&mpLock);
2390 /// RootMove and RootMoveList method's definitions
2392 RootMove::RootMove() {
2395 pv_score = non_pv_score = -VALUE_INFINITE;
2399 RootMove& RootMove::operator=(const RootMove& rm) {
2401 const Move* src = rm.pv;
2404 // Avoid a costly full rm.pv[] copy
2405 do *dst++ = *src; while (*src++ != MOVE_NONE);
2408 pv_score = rm.pv_score;
2409 non_pv_score = rm.non_pv_score;
2413 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2414 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2415 // allow to always have a ponder move even when we fail high at root and also a
2416 // long PV to print that is important for position analysis.
2418 void RootMove::extract_pv_from_tt(Position& pos) {
2420 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2424 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2426 pos.do_move(pv[0], *st++);
2428 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2429 && tte->move() != MOVE_NONE
2430 && pos.move_is_legal(tte->move())
2432 && (!pos.is_draw() || ply < 2))
2434 pv[ply] = tte->move();
2435 pos.do_move(pv[ply++], *st++);
2437 pv[ply] = MOVE_NONE;
2439 do pos.undo_move(pv[--ply]); while (ply);
2442 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2443 // the PV back into the TT. This makes sure the old PV moves are searched
2444 // first, even if the old TT entries have been overwritten.
2446 void RootMove::insert_pv_in_tt(Position& pos) {
2448 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2451 Value v, m = VALUE_NONE;
2454 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2458 tte = TT.retrieve(k);
2460 // Don't overwrite existing correct entries
2461 if (!tte || tte->move() != pv[ply])
2463 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2464 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2466 pos.do_move(pv[ply], *st++);
2468 } while (pv[++ply] != MOVE_NONE);
2470 do pos.undo_move(pv[--ply]); while (ply);
2473 // pv_info_to_uci() returns a string with information on the current PV line
2474 // formatted according to UCI specification.
2476 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2477 Value beta, int pvIdx) {
2478 std::stringstream s;
2480 s << "info depth " << depth
2481 << " seldepth " << selDepth
2482 << " multipv " << pvIdx + 1
2483 << " score " << value_to_uci(pv_score)
2484 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2485 << speed_to_uci(pos.nodes_searched())
2488 for (Move* m = pv; *m != MOVE_NONE; m++)
2495 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2497 MoveStack mlist[MOVES_MAX];
2501 bestMoveChanges = 0;
2503 // Generate all legal moves and add them to RootMoveList
2504 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2505 for (MoveStack* cur = mlist; cur != last; cur++)
2507 // If we have a searchMoves[] list then verify cur->move
2508 // is in the list before to add it.
2509 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2511 if (searchMoves[0] && *sm != cur->move)
2515 rm.pv[0] = cur->move;
2516 rm.pv[1] = MOVE_NONE;
2517 rm.pv_score = -VALUE_INFINITE;
2523 // When playing with strength handicap choose best move among the MultiPV set
2524 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2525 void do_skill_level(Move* best, Move* ponder) {
2527 assert(MultiPV > 1);
2529 // Rml list is already sorted by pv_score in descending order
2531 int max_s = -VALUE_INFINITE;
2532 int size = Min(MultiPV, (int)Rml.size());
2533 int max = Rml[0].pv_score;
2534 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2535 int wk = 120 - 2 * SkillLevel;
2537 // PRNG sequence should be non deterministic
2538 for (int i = abs(get_system_time() % 50); i > 0; i--)
2539 RK.rand<unsigned>();
2541 // Choose best move. For each move's score we add two terms both dependent
2542 // on wk, one deterministic and bigger for weaker moves, and one random,
2543 // then we choose the move with the resulting highest score.
2544 for (int i = 0; i < size; i++)
2546 s = Rml[i].pv_score;
2548 // Don't allow crazy blunders even at very low skills
2549 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2552 // This is our magical formula
2553 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2558 *best = Rml[i].pv[0];
2559 *ponder = Rml[i].pv[1];