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/>.
45 #include "ucioption.h"
51 //// Local definitions
57 enum NodeType { NonPV, PV };
59 // Set to true to force running with one thread.
60 // Used for debugging SMP code.
61 const bool FakeSplit = false;
63 // Fast lookup table of sliding pieces indexed by Piece
64 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
65 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
67 // ThreadsManager class is used to handle all the threads related stuff in search,
68 // init, starting, parking and, the most important, launching a slave thread at a
69 // split point are what this class does. All the access to shared thread data is
70 // done through this class, so that we avoid using global variables instead.
72 class ThreadsManager {
73 /* As long as the single ThreadsManager object is defined as a global we don't
74 need to explicitly initialize to zero its data members because variables with
75 static storage duration are automatically set to zero before enter main()
81 int min_split_depth() const { return minimumSplitDepth; }
82 int active_threads() const { return activeThreads; }
83 void set_active_threads(int cnt) { activeThreads = cnt; }
85 void read_uci_options();
86 bool available_thread_exists(int master) const;
87 bool thread_is_available(int slave, int master) const;
88 bool cutoff_at_splitpoint(int threadID) const;
89 void wake_sleeping_thread(int threadID);
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 Depth minimumSplitDepth;
98 int maxThreadsPerSplitPoint;
99 bool useSleepingThreads;
101 volatile bool allThreadsShouldExit;
102 Thread threads[MAX_THREADS];
103 Lock mpLock, sleepLock[MAX_THREADS];
104 WaitCondition sleepCond[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each root
109 // move, we store two scores, a node count, and a PV (really a refutation
110 // in the case of moves which fail low). Value pv_score is normally set at
111 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
112 // according to the order in which moves are returned by MovePicker.
117 RootMove(const RootMove& rm) { *this = rm; }
118 RootMove& operator=(const RootMove& rm);
120 // RootMove::operator<() is the comparison function used when
121 // sorting the moves. A move m1 is considered to be better
122 // than a move m2 if it has an higher pv_score, or if it has
123 // equal pv_score but m1 has the higher non_pv_score. In this
124 // way we are guaranteed that PV moves are always sorted as first.
125 bool operator<(const RootMove& m) const {
126 return pv_score != m.pv_score ? pv_score < m.pv_score
127 : non_pv_score < m.non_pv_score;
130 void extract_pv_from_tt(Position& pos);
131 void insert_pv_in_tt(Position& pos);
132 std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 void init(Position& pos, Move searchMoves[]);
149 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
150 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
156 // When formatting a move for std::cout we must know if we are in Chess960
157 // or not. To keep using the handy operator<<() on the move the trick is to
158 // embed this flag in the stream itself. Function-like named enum set960 is
159 // used as a custom manipulator and the stream internal general-purpose array,
160 // accessed through ios_base::iword(), is used to pass the flag to the move's
161 // operator<<() that will use it to properly format castling moves.
164 std::ostream& operator<< (std::ostream& os, const set960& f) {
166 os.iword(0) = int(f);
171 // Overload operator << for moves to make it easier to print moves in
172 // coordinate notation compatible with UCI protocol.
173 std::ostream& operator<<(std::ostream& os, Move m) {
175 bool chess960 = (os.iword(0) != 0); // See set960()
176 return os << move_to_uci(m, chess960);
184 // Maximum depth for razoring
185 const Depth RazorDepth = 4 * ONE_PLY;
187 // Dynamic razoring margin based on depth
188 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
190 // Maximum depth for use of dynamic threat detection when null move fails low
191 const Depth ThreatDepth = 5 * ONE_PLY;
193 // Step 9. Internal iterative deepening
195 // Minimum depth for use of internal iterative deepening
196 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
198 // At Non-PV nodes we do an internal iterative deepening search
199 // when the static evaluation is bigger then beta - IIDMargin.
200 const Value IIDMargin = Value(0x100);
202 // Step 11. Decide the new search depth
204 // Extensions. Configurable UCI options
205 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
206 Depth CheckExtension[2], PawnPushTo7thExtension[2], PassedPawnExtension[2];
207 Depth PawnEndgameExtension[2], MateThreatExtension[2];
209 // Minimum depth for use of singular extension
210 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
212 // Step 12. Futility pruning
214 // Futility margin for quiescence search
215 const Value FutilityMarginQS = Value(0x80);
217 // Futility lookup tables (initialized at startup) and their getter functions
218 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
219 int FutilityMoveCountArray[32]; // [depth]
221 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
222 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
224 // Step 14. Reduced search
226 // Reduction lookup tables (initialized at startup) and their getter functions
227 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
229 template <NodeType PV>
230 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
237 /// Namespace variables
246 int MultiPV, UCIMultiPV;
248 // Time management variables
249 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
250 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
251 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
256 std::ofstream LogFile;
258 // Skill level adjustment
260 bool SkillLevelEnabled;
263 // Multi-threads manager object
264 ThreadsManager ThreadsMgr;
266 // Node counters, used only by thread[0] but try to keep in different cache
267 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
268 bool SendSearchedNodes;
270 int NodesBetweenPolls = 30000;
277 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
279 template <NodeType PvNode, bool SpNode, bool Root>
280 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
282 template <NodeType PvNode>
283 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
285 template <NodeType PvNode>
286 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
288 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
289 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
292 template <NodeType PvNode>
293 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
295 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
296 bool connected_moves(const Position& pos, Move m1, Move m2);
297 Value value_to_tt(Value v, int ply);
298 Value value_from_tt(Value v, int ply);
299 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
300 bool connected_threat(const Position& pos, Move m, Move threat);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_gains(const Position& pos, Move move, Value before, Value after);
304 void do_skill_level(Move* best, Move* ponder);
306 int current_search_time();
307 std::string value_to_uci(Value v);
308 std::string speed_to_uci(int64_t nodes);
309 void poll(const Position& pos);
310 void wait_for_stop_or_ponderhit();
312 #if !defined(_MSC_VER)
313 void* init_thread(void* threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
319 // MovePickerExt is an extended MovePicker used to choose at compile time
320 // the proper move source according to the type of node.
321 template<bool SpNode, bool Root> struct MovePickerExt;
323 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
324 // before to search them.
325 template<> struct MovePickerExt<false, true> : public MovePicker {
327 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
328 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
330 Value score = VALUE_ZERO;
332 // Score root moves using the standard way used in main search, the moves
333 // are scored according to the order in which they are returned by MovePicker.
334 // This is the second order score that is used to compare the moves when
335 // the first order pv scores of both moves are equal.
336 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
337 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
338 if (rm->pv[0] == move)
340 rm->non_pv_score = score--;
348 Move get_next_move() {
355 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
358 RootMoveList::iterator rm;
362 // In SpNodes use split point's shared MovePicker object as move source
363 template<> struct MovePickerExt<true, false> : public MovePicker {
365 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
366 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
369 Move get_next_move() { return mp->get_next_move(); }
371 RootMoveList::iterator rm; // Dummy, needed to compile
375 // Default case, create and use a MovePicker object as source
376 template<> struct MovePickerExt<false, false> : public MovePicker {
378 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
379 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
381 RootMoveList::iterator rm; // Dummy, needed to compile
391 /// init_threads(), exit_threads() and nodes_searched() are helpers to
392 /// give accessibility to some TM methods from outside of current file.
394 void init_threads() { ThreadsMgr.init_threads(); }
395 void exit_threads() { ThreadsMgr.exit_threads(); }
398 /// init_search() is called during startup. It initializes various lookup tables
402 int d; // depth (ONE_PLY == 2)
403 int hd; // half depth (ONE_PLY == 1)
406 // Init reductions array
407 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
409 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
410 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
411 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
412 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
415 // Init futility margins array
416 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
417 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
419 // Init futility move count array
420 for (d = 0; d < 32; d++)
421 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
425 /// perft() is our utility to verify move generation is bug free. All the legal
426 /// moves up to given depth are generated and counted and the sum returned.
428 int64_t perft(Position& pos, Depth depth)
430 MoveStack mlist[MOVES_MAX];
435 // Generate all legal moves
436 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
438 // If we are at the last ply we don't need to do and undo
439 // the moves, just to count them.
440 if (depth <= ONE_PLY)
441 return int(last - mlist);
443 // Loop through all legal moves
445 for (MoveStack* cur = mlist; cur != last; cur++)
448 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
449 sum += perft(pos, depth - ONE_PLY);
456 /// think() is the external interface to Stockfish's search, and is called when
457 /// the program receives the UCI 'go' command. It initializes various
458 /// search-related global variables, and calls id_loop(). It returns false
459 /// when a quit command is received during the search.
461 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
462 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
464 // Initialize global search variables
465 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
467 SearchStartTime = get_system_time();
468 ExactMaxTime = maxTime;
471 InfiniteSearch = infinite;
473 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
475 // Look for a book move, only during games, not tests
476 if (UseTimeManagement && Options["OwnBook"].value<bool>())
478 if (Options["Book File"].value<std::string>() != OpeningBook.name())
479 OpeningBook.open(Options["Book File"].value<std::string>());
481 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
482 if (bookMove != MOVE_NONE)
485 wait_for_stop_or_ponderhit();
487 cout << "bestmove " << bookMove << endl;
492 // Read UCI option values
493 TT.set_size(Options["Hash"].value<int>());
494 if (Options["Clear Hash"].value<bool>())
496 Options["Clear Hash"].set_value("false");
500 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
501 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
502 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
503 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
504 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
505 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
506 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
507 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
508 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
509 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
510 UCIMultiPV = Options["MultiPV"].value<int>();
511 SkillLevel = Options["Skill level"].value<int>();
512 UseLogFile = Options["Use Search Log"].value<bool>();
514 read_evaluation_uci_options(pos.side_to_move());
516 // Do we have to play with skill handicap? In this case enable MultiPV that
517 // we will use behind the scenes to retrieve a set of possible moves.
518 SkillLevelEnabled = (SkillLevel < 20);
519 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
521 // Set the number of active threads
522 ThreadsMgr.read_uci_options();
523 init_eval(ThreadsMgr.active_threads());
525 // Wake up needed threads
526 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
527 ThreadsMgr.wake_sleeping_thread(i);
530 int myTime = time[pos.side_to_move()];
531 int myIncrement = increment[pos.side_to_move()];
532 if (UseTimeManagement)
533 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
535 // Set best NodesBetweenPolls interval to avoid lagging under
536 // heavy time pressure.
538 NodesBetweenPolls = Min(MaxNodes, 30000);
539 else if (myTime && myTime < 1000)
540 NodesBetweenPolls = 1000;
541 else if (myTime && myTime < 5000)
542 NodesBetweenPolls = 5000;
544 NodesBetweenPolls = 30000;
546 // Write search information to log file
549 std::string name = Options["Search Log Filename"].value<std::string>();
550 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
552 LogFile << "\nSearching: " << pos.to_fen()
553 << "\ninfinite: " << infinite
554 << " ponder: " << ponder
555 << " time: " << myTime
556 << " increment: " << myIncrement
557 << " moves to go: " << movesToGo
561 // We're ready to start thinking. Call the iterative deepening loop function
562 Move ponderMove = MOVE_NONE;
563 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
565 // Print final search statistics
566 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
570 int t = current_search_time();
572 LogFile << "Nodes: " << pos.nodes_searched()
573 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
574 << "\nBest move: " << move_to_san(pos, bestMove);
577 pos.do_move(bestMove, st);
578 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
579 pos.undo_move(bestMove); // Return from think() with unchanged position
583 // This makes all the threads to go to sleep
584 ThreadsMgr.set_active_threads(1);
586 // If we are pondering or in infinite search, we shouldn't print the
587 // best move before we are told to do so.
588 if (!StopRequest && (Pondering || InfiniteSearch))
589 wait_for_stop_or_ponderhit();
591 // Could be MOVE_NONE when searching on a stalemate position
592 cout << "bestmove " << bestMove;
594 // UCI protol is not clear on allowing sending an empty ponder move, instead
595 // it is clear that ponder move is optional. So skip it if empty.
596 if (ponderMove != MOVE_NONE)
597 cout << " ponder " << ponderMove;
607 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
608 // with increasing depth until the allocated thinking time has been consumed,
609 // user stops the search, or the maximum search depth is reached.
611 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
613 SearchStack ss[PLY_MAX_PLUS_2];
614 Value bestValues[PLY_MAX_PLUS_2];
615 int bestMoveChanges[PLY_MAX_PLUS_2];
616 int depth, aspirationDelta, skillSamplingDepth;
617 Value value, alpha, beta;
618 Move bestMove, easyMove, skillBest, skillPonder;
620 // Initialize stuff before a new search
621 memset(ss, 0, 4 * sizeof(SearchStack));
624 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
625 depth = aspirationDelta = skillSamplingDepth = 0;
626 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
627 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
629 // Moves to search are verified and copied
630 Rml.init(pos, searchMoves);
632 // Handle special case of searching on a mate/stalemate position
635 cout << "info depth 0 score "
636 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
642 // Choose a random sampling depth according to SkillLevel so that at low
643 // skills there is an higher risk to pick up a blunder.
644 if (SkillLevelEnabled)
645 skillSamplingDepth = 4 + SkillLevel + (RK.rand<unsigned>() % 4);
647 // Iterative deepening loop
648 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
650 Rml.bestMoveChanges = 0;
651 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
653 // Calculate dynamic aspiration window based on previous iterations
654 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
656 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
657 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
659 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
660 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
662 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
663 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
666 // Start with a small aspiration window and, in case of fail high/low,
667 // research with bigger window until not failing high/low anymore.
669 // Search starting from ss+1 to allow calling update_gains()
670 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
672 // Write PV back to transposition table in case the relevant entries
673 // have been overwritten during the search.
674 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
675 Rml[i].insert_pv_in_tt(pos);
677 // Value cannot be trusted. Break out immediately!
681 assert(value >= alpha);
683 // In case of failing high/low increase aspiration window and research,
684 // otherwise exit the fail high/low loop.
687 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
688 aspirationDelta += aspirationDelta / 2;
690 else if (value <= alpha)
692 AspirationFailLow = true;
693 StopOnPonderhit = false;
695 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
696 aspirationDelta += aspirationDelta / 2;
701 } while (abs(value) < VALUE_KNOWN_WIN);
703 // Collect info about search result
704 bestMove = Rml[0].pv[0];
705 *ponderMove = Rml[0].pv[1];
706 bestValues[depth] = value;
707 bestMoveChanges[depth] = Rml.bestMoveChanges;
709 // Do we need to pick now the best and the ponder moves ?
710 if (SkillLevelEnabled && depth == skillSamplingDepth)
711 do_skill_level(&skillBest, &skillPonder);
713 // Send PV line to GUI and to log file
714 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
715 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
718 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
720 // Init easyMove after first iteration or drop if differs from the best move
721 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
723 else if (bestMove != easyMove)
724 easyMove = MOVE_NONE;
726 if (UseTimeManagement && !StopRequest)
729 bool noMoreTime = false;
731 // Stop search early when the last two iterations returned a mate score
733 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
734 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
737 // Stop search early if one move seems to be much better than the
738 // others or if there is only a single legal move. In this latter
739 // case we search up to Iteration 8 anyway to get a proper score.
741 && easyMove == bestMove
743 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
744 && current_search_time() > TimeMgr.available_time() / 16)
745 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
746 && current_search_time() > TimeMgr.available_time() / 32)))
749 // Add some extra time if the best move has changed during the last two iterations
750 if (depth > 4 && depth < 50)
751 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
753 // Stop search if most of MaxSearchTime is consumed at the end of the
754 // iteration. We probably don't have enough time to search the first
755 // move at the next iteration anyway.
756 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
762 StopOnPonderhit = true;
769 // When using skills fake best and ponder moves with the sub-optimal ones
770 if (SkillLevelEnabled)
772 if (skillBest == MOVE_NONE) // Still unassigned ?
773 do_skill_level(&skillBest, &skillPonder);
775 bestMove = skillBest;
776 *ponderMove = skillPonder;
783 // search<>() is the main search function for both PV and non-PV nodes and for
784 // normal and SplitPoint nodes. When called just after a split point the search
785 // is simpler because we have already probed the hash table, done a null move
786 // search, and searched the first move before splitting, we don't have to repeat
787 // all this work again. We also don't need to store anything to the hash table
788 // here: This is taken care of after we return from the split point.
790 template <NodeType PvNode, bool SpNode, bool Root>
791 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
793 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
794 assert(beta > alpha && beta <= VALUE_INFINITE);
795 assert(PvNode || alpha == beta - 1);
796 assert((Root || ply > 0) && ply < PLY_MAX);
797 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
799 Move movesSearched[MOVES_MAX];
804 Move ttMove, move, excludedMove, threatMove;
807 Value bestValue, value, oldAlpha;
808 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
809 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
810 bool mateThreat = false;
811 int moveCount = 0, playedMoveCount = 0;
812 int threadID = pos.thread();
813 SplitPoint* sp = NULL;
815 refinedValue = bestValue = value = -VALUE_INFINITE;
817 isCheck = pos.is_check();
823 ttMove = excludedMove = MOVE_NONE;
824 threatMove = sp->threatMove;
825 mateThreat = sp->mateThreat;
826 goto split_point_start;
831 // Step 1. Initialize node and poll. Polling can abort search
832 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
833 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
834 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
836 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
842 // Step 2. Check for aborted search and immediate draw
844 || ThreadsMgr.cutoff_at_splitpoint(threadID)
846 || ply >= PLY_MAX - 1) && !Root)
849 // Step 3. Mate distance pruning
850 alpha = Max(value_mated_in(ply), alpha);
851 beta = Min(value_mate_in(ply+1), beta);
855 // Step 4. Transposition table lookup
856 // We don't want the score of a partial search to overwrite a previous full search
857 // TT value, so we use a different position key in case of an excluded move.
858 excludedMove = ss->excludedMove;
859 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
861 tte = TT.retrieve(posKey);
862 ttMove = tte ? tte->move() : MOVE_NONE;
864 // At PV nodes we check for exact scores, while at non-PV nodes we check for
865 // and return a fail high/low. Biggest advantage at probing at PV nodes is
866 // to have a smooth experience in analysis mode.
869 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
870 : ok_to_use_TT(tte, depth, beta, ply)))
873 ss->bestMove = ttMove; // Can be MOVE_NONE
874 return value_from_tt(tte->value(), ply);
877 // Step 5. Evaluate the position statically and
878 // update gain statistics of parent move.
880 ss->eval = ss->evalMargin = VALUE_NONE;
883 assert(tte->static_value() != VALUE_NONE);
885 ss->eval = tte->static_value();
886 ss->evalMargin = tte->static_value_margin();
887 refinedValue = refine_eval(tte, ss->eval, ply);
891 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
892 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
895 // Save gain for the parent non-capture move
896 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
898 // Step 6. Razoring (is omitted in PV nodes)
900 && depth < RazorDepth
902 && refinedValue < beta - razor_margin(depth)
903 && ttMove == MOVE_NONE
904 && abs(beta) < VALUE_MATE_IN_PLY_MAX
905 && !pos.has_pawn_on_7th(pos.side_to_move()))
907 Value rbeta = beta - razor_margin(depth);
908 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
910 // Logically we should return (v + razor_margin(depth)), but
911 // surprisingly this did slightly weaker in tests.
915 // Step 7. Static null move pruning (is omitted in PV nodes)
916 // We're betting that the opponent doesn't have a move that will reduce
917 // the score by more than futility_margin(depth) if we do a null move.
920 && depth < RazorDepth
922 && refinedValue >= beta + futility_margin(depth, 0)
923 && abs(beta) < VALUE_MATE_IN_PLY_MAX
924 && pos.non_pawn_material(pos.side_to_move()))
925 return refinedValue - futility_margin(depth, 0);
927 // Step 8. Null move search with verification search (is omitted in PV nodes)
932 && refinedValue >= beta
933 && abs(beta) < VALUE_MATE_IN_PLY_MAX
934 && pos.non_pawn_material(pos.side_to_move()))
936 ss->currentMove = MOVE_NULL;
938 // Null move dynamic reduction based on depth
939 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
941 // Null move dynamic reduction based on value
942 if (refinedValue - beta > PawnValueMidgame)
945 pos.do_null_move(st);
946 (ss+1)->skipNullMove = true;
947 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
948 (ss+1)->skipNullMove = false;
949 pos.undo_null_move();
951 if (nullValue >= beta)
953 // Do not return unproven mate scores
954 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
957 if (depth < 6 * ONE_PLY)
960 // Do verification search at high depths
961 ss->skipNullMove = true;
962 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
963 ss->skipNullMove = false;
970 // The null move failed low, which means that we may be faced with
971 // some kind of threat. If the previous move was reduced, check if
972 // the move that refuted the null move was somehow connected to the
973 // move which was reduced. If a connection is found, return a fail
974 // low score (which will cause the reduced move to fail high in the
975 // parent node, which will trigger a re-search with full depth).
976 if (nullValue == value_mated_in(ply + 2))
979 threatMove = (ss+1)->bestMove;
980 if ( depth < ThreatDepth
982 && threatMove != MOVE_NONE
983 && connected_moves(pos, (ss-1)->currentMove, threatMove))
988 // Step 9. Internal iterative deepening
989 if ( depth >= IIDDepth[PvNode]
990 && ttMove == MOVE_NONE
991 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
993 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
995 ss->skipNullMove = true;
996 search<PvNode>(pos, ss, alpha, beta, d, ply);
997 ss->skipNullMove = false;
999 ttMove = ss->bestMove;
1000 tte = TT.retrieve(posKey);
1003 // Expensive mate threat detection (only for PV nodes)
1005 mateThreat = pos.has_mate_threat();
1007 split_point_start: // At split points actual search starts from here
1009 // Initialize a MovePicker object for the current position
1010 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1012 ss->bestMove = MOVE_NONE;
1013 futilityBase = ss->eval + ss->evalMargin;
1014 singularExtensionNode = !Root
1016 && depth >= SingularExtensionDepth[PvNode]
1019 && !excludedMove // Do not allow recursive singular extension search
1020 && (tte->type() & VALUE_TYPE_LOWER)
1021 && tte->depth() >= depth - 3 * ONE_PLY;
1024 lock_grab(&(sp->lock));
1025 bestValue = sp->bestValue;
1028 // Step 10. Loop through moves
1029 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1030 while ( bestValue < beta
1031 && (move = mp.get_next_move()) != MOVE_NONE
1032 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1034 assert(move_is_ok(move));
1038 moveCount = ++sp->moveCount;
1039 lock_release(&(sp->lock));
1041 else if (move == excludedMove)
1048 // This is used by time management
1049 FirstRootMove = (moveCount == 1);
1051 // Save the current node count before the move is searched
1052 nodes = pos.nodes_searched();
1054 // If it's time to send nodes info, do it here where we have the
1055 // correct accumulated node counts searched by each thread.
1056 if (SendSearchedNodes)
1058 SendSearchedNodes = false;
1059 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1062 if (current_search_time() >= 1000)
1063 cout << "info currmove " << move
1064 << " currmovenumber " << moveCount << endl;
1067 // At Root and at first iteration do a PV search on all the moves
1068 // to score root moves. Otherwise only the first one is the PV.
1069 isPvMove = (PvNode && moveCount <= (Root ? MultiPV + 1000 * (depth <= ONE_PLY) : 1));
1070 moveIsCheck = pos.move_is_check(move, ci);
1071 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1073 // Step 11. Decide the new search depth
1074 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
1076 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1077 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1078 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1079 // lower than ttValue minus a margin then we extend ttMove.
1080 if ( singularExtensionNode
1081 && move == tte->move()
1084 Value ttValue = value_from_tt(tte->value(), ply);
1086 if (abs(ttValue) < VALUE_KNOWN_WIN)
1088 Value b = ttValue - int(depth);
1089 ss->excludedMove = move;
1090 ss->skipNullMove = true;
1091 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1092 ss->skipNullMove = false;
1093 ss->excludedMove = MOVE_NONE;
1094 ss->bestMove = MOVE_NONE;
1100 // Update current move (this must be done after singular extension search)
1101 ss->currentMove = move;
1102 newDepth = depth - ONE_PLY + ext;
1104 // Step 12. Futility pruning (is omitted in PV nodes)
1106 && !captureOrPromotion
1110 && !move_is_castle(move))
1112 // Move count based pruning
1113 if ( moveCount >= futility_move_count(depth)
1114 && !(threatMove && connected_threat(pos, move, threatMove))
1115 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1118 lock_grab(&(sp->lock));
1123 // Value based pruning
1124 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1125 // but fixing this made program slightly weaker.
1126 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1127 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1128 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1130 if (futilityValueScaled < beta)
1134 lock_grab(&(sp->lock));
1135 if (futilityValueScaled > sp->bestValue)
1136 sp->bestValue = bestValue = futilityValueScaled;
1138 else if (futilityValueScaled > bestValue)
1139 bestValue = futilityValueScaled;
1144 // Prune moves with negative SEE at low depths
1145 if ( predictedDepth < 2 * ONE_PLY
1146 && bestValue > VALUE_MATED_IN_PLY_MAX
1147 && pos.see_sign(move) < 0)
1150 lock_grab(&(sp->lock));
1156 // Bad capture detection. Will be used by prob-cut search
1157 isBadCap = depth >= 3 * ONE_PLY
1158 && depth < 8 * ONE_PLY
1159 && captureOrPromotion
1162 && !move_is_promotion(move)
1163 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1164 && pos.see_sign(move) < 0;
1166 // Step 13. Make the move
1167 pos.do_move(move, st, ci, moveIsCheck);
1169 if (!SpNode && !captureOrPromotion)
1170 movesSearched[playedMoveCount++] = move;
1172 // Step extra. pv search (only in PV nodes)
1173 // The first move in list is the expected PV
1176 // Aspiration window is disabled in multi-pv case
1177 if (Root && MultiPV > 1)
1178 alpha = -VALUE_INFINITE;
1180 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1184 // Step 14. Reduced depth search
1185 // If the move fails high will be re-searched at full depth.
1186 bool doFullDepthSearch = true;
1187 alpha = SpNode ? sp->alpha : alpha;
1189 if ( depth >= 3 * ONE_PLY
1190 && !captureOrPromotion
1192 && !move_is_castle(move)
1193 && ss->killers[0] != move
1194 && ss->killers[1] != move)
1196 ss->reduction = reduction<PvNode>(depth, moveCount);
1199 alpha = SpNode ? sp->alpha : alpha;
1200 Depth d = newDepth - ss->reduction;
1201 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1203 doFullDepthSearch = (value > alpha);
1205 ss->reduction = DEPTH_ZERO; // Restore original reduction
1208 // Probcut search for bad captures. If a reduced search returns a value
1209 // very below beta then we can (almost) safely prune the bad capture.
1212 ss->reduction = 3 * ONE_PLY;
1213 Value redAlpha = alpha - 300;
1214 Depth d = newDepth - ss->reduction;
1215 value = -search<NonPV>(pos, ss+1, -(redAlpha+1), -redAlpha, d, ply+1);
1216 doFullDepthSearch = (value > redAlpha);
1217 ss->reduction = DEPTH_ZERO; // Restore original reduction
1220 // Step 15. Full depth search
1221 if (doFullDepthSearch)
1223 alpha = SpNode ? sp->alpha : alpha;
1224 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1226 // Step extra. pv search (only in PV nodes)
1227 // Search only for possible new PV nodes, if instead value >= beta then
1228 // parent node fails low with value <= alpha and tries another move.
1229 if (PvNode && value > alpha && (Root || value < beta))
1230 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1234 // Step 16. Undo move
1235 pos.undo_move(move);
1237 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1239 // Step 17. Check for new best move
1242 lock_grab(&(sp->lock));
1243 bestValue = sp->bestValue;
1247 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1252 sp->bestValue = value;
1254 if (!Root && value > alpha)
1256 if (PvNode && value < beta) // We want always alpha < beta
1264 sp->betaCutoff = true;
1266 if (value == value_mate_in(ply + 1))
1267 ss->mateKiller = move;
1269 ss->bestMove = move;
1272 sp->ss->bestMove = move;
1278 // Finished searching the move. If StopRequest is true, the search
1279 // was aborted because the user interrupted the search or because we
1280 // ran out of time. In this case, the return value of the search cannot
1281 // be trusted, and we break out of the loop without updating the best
1286 // Remember searched nodes counts for this move
1287 mp.rm->nodes += pos.nodes_searched() - nodes;
1289 // PV move or new best move ?
1290 if (isPvMove || value > alpha)
1293 ss->bestMove = move;
1294 mp.rm->pv_score = value;
1295 mp.rm->extract_pv_from_tt(pos);
1297 // We record how often the best move has been changed in each
1298 // iteration. This information is used for time management: When
1299 // the best move changes frequently, we allocate some more time.
1300 if (!isPvMove && MultiPV == 1)
1301 Rml.bestMoveChanges++;
1303 Rml.sort_multipv(moveCount);
1305 // Update alpha. In multi-pv we don't use aspiration window, so
1306 // set alpha equal to minimum score among the PV lines.
1308 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1309 else if (value > alpha)
1313 mp.rm->pv_score = -VALUE_INFINITE;
1317 // Step 18. Check for split
1320 && depth >= ThreadsMgr.min_split_depth()
1321 && ThreadsMgr.active_threads() > 1
1323 && ThreadsMgr.available_thread_exists(threadID)
1325 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1326 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1327 threatMove, mateThreat, moveCount, &mp, PvNode);
1330 // Step 19. Check for mate and stalemate
1331 // All legal moves have been searched and if there are
1332 // no legal moves, it must be mate or stalemate.
1333 // If one move was excluded return fail low score.
1334 if (!SpNode && !moveCount)
1335 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1337 // Step 20. Update tables
1338 // If the search is not aborted, update the transposition table,
1339 // history counters, and killer moves.
1340 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1342 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1343 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1344 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1346 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1348 // Update killers and history only for non capture moves that fails high
1349 if ( bestValue >= beta
1350 && !pos.move_is_capture_or_promotion(move))
1352 if (move != ss->killers[0])
1354 ss->killers[1] = ss->killers[0];
1355 ss->killers[0] = move;
1357 update_history(pos, move, depth, movesSearched, playedMoveCount);
1363 // Here we have the lock still grabbed
1364 sp->slaves[threadID] = 0;
1365 sp->nodes += pos.nodes_searched();
1366 lock_release(&(sp->lock));
1369 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1374 // qsearch() is the quiescence search function, which is called by the main
1375 // search function when the remaining depth is zero (or, to be more precise,
1376 // less than ONE_PLY).
1378 template <NodeType PvNode>
1379 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1381 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1382 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1383 assert(PvNode || alpha == beta - 1);
1385 assert(ply > 0 && ply < PLY_MAX);
1386 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1390 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1391 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1394 Value oldAlpha = alpha;
1396 ss->bestMove = ss->currentMove = MOVE_NONE;
1398 // Check for an instant draw or maximum ply reached
1399 if (pos.is_draw() || ply >= PLY_MAX - 1)
1402 // Decide whether or not to include checks, this fixes also the type of
1403 // TT entry depth that we are going to use. Note that in qsearch we use
1404 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1405 isCheck = pos.is_check();
1406 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1408 // Transposition table lookup. At PV nodes, we don't use the TT for
1409 // pruning, but only for move ordering.
1410 tte = TT.retrieve(pos.get_key());
1411 ttMove = (tte ? tte->move() : MOVE_NONE);
1413 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1415 ss->bestMove = ttMove; // Can be MOVE_NONE
1416 return value_from_tt(tte->value(), ply);
1419 // Evaluate the position statically
1422 bestValue = futilityBase = -VALUE_INFINITE;
1423 ss->eval = evalMargin = VALUE_NONE;
1424 enoughMaterial = false;
1430 assert(tte->static_value() != VALUE_NONE);
1432 evalMargin = tte->static_value_margin();
1433 ss->eval = bestValue = tte->static_value();
1436 ss->eval = bestValue = evaluate(pos, evalMargin);
1438 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1440 // Stand pat. Return immediately if static value is at least beta
1441 if (bestValue >= beta)
1444 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1449 if (PvNode && bestValue > alpha)
1452 // Futility pruning parameters, not needed when in check
1453 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1454 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1457 // Initialize a MovePicker object for the current position, and prepare
1458 // to search the moves. Because the depth is <= 0 here, only captures,
1459 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1461 MovePicker mp(pos, ttMove, depth, H);
1464 // Loop through the moves until no moves remain or a beta cutoff occurs
1465 while ( alpha < beta
1466 && (move = mp.get_next_move()) != MOVE_NONE)
1468 assert(move_is_ok(move));
1470 moveIsCheck = pos.move_is_check(move, ci);
1478 && !move_is_promotion(move)
1479 && !pos.move_is_passed_pawn_push(move))
1481 futilityValue = futilityBase
1482 + pos.endgame_value_of_piece_on(move_to(move))
1483 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1485 if (futilityValue < alpha)
1487 if (futilityValue > bestValue)
1488 bestValue = futilityValue;
1492 // Prune moves with negative or equal SEE
1493 if ( futilityBase < beta
1494 && depth < DEPTH_ZERO
1495 && pos.see(move) <= 0)
1499 // Detect non-capture evasions that are candidate to be pruned
1500 evasionPrunable = isCheck
1501 && bestValue > VALUE_MATED_IN_PLY_MAX
1502 && !pos.move_is_capture(move)
1503 && !pos.can_castle(pos.side_to_move());
1505 // Don't search moves with negative SEE values
1507 && (!isCheck || evasionPrunable)
1509 && !move_is_promotion(move)
1510 && pos.see_sign(move) < 0)
1513 // Don't search useless checks
1518 && !pos.move_is_capture_or_promotion(move)
1519 && ss->eval + PawnValueMidgame / 4 < beta
1520 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1522 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1523 bestValue = ss->eval + PawnValueMidgame / 4;
1528 // Update current move
1529 ss->currentMove = move;
1531 // Make and search the move
1532 pos.do_move(move, st, ci, moveIsCheck);
1533 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1534 pos.undo_move(move);
1536 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1539 if (value > bestValue)
1545 ss->bestMove = move;
1550 // All legal moves have been searched. A special case: If we're in check
1551 // and no legal moves were found, it is checkmate.
1552 if (isCheck && bestValue == -VALUE_INFINITE)
1553 return value_mated_in(ply);
1555 // Update transposition table
1556 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1557 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1559 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1565 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1566 // bestValue is updated only when returning false because in that case move
1569 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1571 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1572 Square from, to, ksq, victimSq;
1575 Value futilityValue, bv = *bestValue;
1577 from = move_from(move);
1579 them = opposite_color(pos.side_to_move());
1580 ksq = pos.king_square(them);
1581 kingAtt = pos.attacks_from<KING>(ksq);
1582 pc = pos.piece_on(from);
1584 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1585 oldAtt = pos.attacks_from(pc, from, occ);
1586 newAtt = pos.attacks_from(pc, to, occ);
1588 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1589 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1591 if (!(b && (b & (b - 1))))
1594 // Rule 2. Queen contact check is very dangerous
1595 if ( type_of_piece(pc) == QUEEN
1596 && bit_is_set(kingAtt, to))
1599 // Rule 3. Creating new double threats with checks
1600 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1604 victimSq = pop_1st_bit(&b);
1605 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1607 // Note that here we generate illegal "double move"!
1608 if ( futilityValue >= beta
1609 && pos.see_sign(make_move(from, victimSq)) >= 0)
1612 if (futilityValue > bv)
1616 // Update bestValue only if check is not dangerous (because we will prune the move)
1622 // connected_moves() tests whether two moves are 'connected' in the sense
1623 // that the first move somehow made the second move possible (for instance
1624 // if the moving piece is the same in both moves). The first move is assumed
1625 // to be the move that was made to reach the current position, while the
1626 // second move is assumed to be a move from the current position.
1628 bool connected_moves(const Position& pos, Move m1, Move m2) {
1630 Square f1, t1, f2, t2;
1633 assert(m1 && move_is_ok(m1));
1634 assert(m2 && move_is_ok(m2));
1636 // Case 1: The moving piece is the same in both moves
1642 // Case 2: The destination square for m2 was vacated by m1
1648 // Case 3: Moving through the vacated square
1649 if ( piece_is_slider(pos.piece_on(f2))
1650 && bit_is_set(squares_between(f2, t2), f1))
1653 // Case 4: The destination square for m2 is defended by the moving piece in m1
1654 p = pos.piece_on(t1);
1655 if (bit_is_set(pos.attacks_from(p, t1), t2))
1658 // Case 5: Discovered check, checking piece is the piece moved in m1
1659 if ( piece_is_slider(p)
1660 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1661 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1663 // discovered_check_candidates() works also if the Position's side to
1664 // move is the opposite of the checking piece.
1665 Color them = opposite_color(pos.side_to_move());
1666 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1668 if (bit_is_set(dcCandidates, f2))
1675 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1676 // "plies to mate from the current ply". Non-mate scores are unchanged.
1677 // The function is called before storing a value to the transposition table.
1679 Value value_to_tt(Value v, int ply) {
1681 if (v >= VALUE_MATE_IN_PLY_MAX)
1684 if (v <= VALUE_MATED_IN_PLY_MAX)
1691 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1692 // the transposition table to a mate score corrected for the current ply.
1694 Value value_from_tt(Value v, int ply) {
1696 if (v >= VALUE_MATE_IN_PLY_MAX)
1699 if (v <= VALUE_MATED_IN_PLY_MAX)
1706 // extension() decides whether a move should be searched with normal depth,
1707 // or with extended depth. Certain classes of moves (checking moves, in
1708 // particular) are searched with bigger depth than ordinary moves and in
1709 // any case are marked as 'dangerous'. Note that also if a move is not
1710 // extended, as example because the corresponding UCI option is set to zero,
1711 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1712 template <NodeType PvNode>
1713 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1714 bool moveIsCheck, bool mateThreat, bool* dangerous) {
1716 assert(m != MOVE_NONE);
1718 Depth result = DEPTH_ZERO;
1719 *dangerous = moveIsCheck | mateThreat;
1723 if (moveIsCheck && pos.see_sign(m) >= 0)
1724 result += CheckExtension[PvNode];
1727 result += MateThreatExtension[PvNode];
1730 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1732 Color c = pos.side_to_move();
1733 if (relative_rank(c, move_to(m)) == RANK_7)
1735 result += PawnPushTo7thExtension[PvNode];
1738 if (pos.pawn_is_passed(c, move_to(m)))
1740 result += PassedPawnExtension[PvNode];
1745 if ( captureOrPromotion
1746 && pos.type_of_piece_on(move_to(m)) != PAWN
1747 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1748 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1749 && !move_is_promotion(m)
1752 result += PawnEndgameExtension[PvNode];
1756 return Min(result, ONE_PLY);
1760 // connected_threat() tests whether it is safe to forward prune a move or if
1761 // is somehow connected to the threat move returned by null search.
1763 bool connected_threat(const Position& pos, Move m, Move threat) {
1765 assert(move_is_ok(m));
1766 assert(threat && move_is_ok(threat));
1767 assert(!pos.move_is_check(m));
1768 assert(!pos.move_is_capture_or_promotion(m));
1769 assert(!pos.move_is_passed_pawn_push(m));
1771 Square mfrom, mto, tfrom, tto;
1773 mfrom = move_from(m);
1775 tfrom = move_from(threat);
1776 tto = move_to(threat);
1778 // Case 1: Don't prune moves which move the threatened piece
1782 // Case 2: If the threatened piece has value less than or equal to the
1783 // value of the threatening piece, don't prune moves which defend it.
1784 if ( pos.move_is_capture(threat)
1785 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1786 || pos.type_of_piece_on(tfrom) == KING)
1787 && pos.move_attacks_square(m, tto))
1790 // Case 3: If the moving piece in the threatened move is a slider, don't
1791 // prune safe moves which block its ray.
1792 if ( piece_is_slider(pos.piece_on(tfrom))
1793 && bit_is_set(squares_between(tfrom, tto), mto)
1794 && pos.see_sign(m) >= 0)
1801 // ok_to_use_TT() returns true if a transposition table score
1802 // can be used at a given point in search.
1804 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1806 Value v = value_from_tt(tte->value(), ply);
1808 return ( tte->depth() >= depth
1809 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1810 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1812 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1813 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1817 // refine_eval() returns the transposition table score if
1818 // possible otherwise falls back on static position evaluation.
1820 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1824 Value v = value_from_tt(tte->value(), ply);
1826 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1827 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1834 // update_history() registers a good move that produced a beta-cutoff
1835 // in history and marks as failures all the other moves of that ply.
1837 void update_history(const Position& pos, Move move, Depth depth,
1838 Move movesSearched[], int moveCount) {
1840 Value bonus = Value(int(depth) * int(depth));
1842 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1844 for (int i = 0; i < moveCount - 1; i++)
1846 m = movesSearched[i];
1850 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1855 // update_gains() updates the gains table of a non-capture move given
1856 // the static position evaluation before and after the move.
1858 void update_gains(const Position& pos, Move m, Value before, Value after) {
1861 && before != VALUE_NONE
1862 && after != VALUE_NONE
1863 && pos.captured_piece_type() == PIECE_TYPE_NONE
1864 && !move_is_special(m))
1865 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1869 // current_search_time() returns the number of milliseconds which have passed
1870 // since the beginning of the current search.
1872 int current_search_time() {
1874 return get_system_time() - SearchStartTime;
1878 // value_to_uci() converts a value to a string suitable for use with the UCI
1879 // protocol specifications:
1881 // cp <x> The score from the engine's point of view in centipawns.
1882 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1883 // use negative values for y.
1885 std::string value_to_uci(Value v) {
1887 std::stringstream s;
1889 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1890 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1892 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1898 // speed_to_uci() returns a string with time stats of current search suitable
1899 // to be sent to UCI gui.
1901 std::string speed_to_uci(int64_t nodes) {
1903 std::stringstream s;
1904 int t = current_search_time();
1906 s << " nodes " << nodes
1907 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1914 // poll() performs two different functions: It polls for user input, and it
1915 // looks at the time consumed so far and decides if it's time to abort the
1918 void poll(const Position& pos) {
1920 static int lastInfoTime;
1921 int t = current_search_time();
1924 if (input_available())
1926 // We are line oriented, don't read single chars
1927 std::string command;
1929 if (!std::getline(std::cin, command) || command == "quit")
1931 // Quit the program as soon as possible
1933 QuitRequest = StopRequest = true;
1936 else if (command == "stop")
1938 // Stop calculating as soon as possible, but still send the "bestmove"
1939 // and possibly the "ponder" token when finishing the search.
1943 else if (command == "ponderhit")
1945 // The opponent has played the expected move. GUI sends "ponderhit" if
1946 // we were told to ponder on the same move the opponent has played. We
1947 // should continue searching but switching from pondering to normal search.
1950 if (StopOnPonderhit)
1955 // Print search information
1959 else if (lastInfoTime > t)
1960 // HACK: Must be a new search where we searched less than
1961 // NodesBetweenPolls nodes during the first second of search.
1964 else if (t - lastInfoTime >= 1000)
1971 if (dbg_show_hit_rate)
1972 dbg_print_hit_rate();
1974 // Send info on searched nodes as soon as we return to root
1975 SendSearchedNodes = true;
1978 // Should we stop the search?
1982 bool stillAtFirstMove = FirstRootMove
1983 && !AspirationFailLow
1984 && t > TimeMgr.available_time();
1986 bool noMoreTime = t > TimeMgr.maximum_time()
1987 || stillAtFirstMove;
1989 if ( (UseTimeManagement && noMoreTime)
1990 || (ExactMaxTime && t >= ExactMaxTime)
1991 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1996 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1997 // while the program is pondering. The point is to work around a wrinkle in
1998 // the UCI protocol: When pondering, the engine is not allowed to give a
1999 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2000 // We simply wait here until one of these commands is sent, and return,
2001 // after which the bestmove and pondermove will be printed.
2003 void wait_for_stop_or_ponderhit() {
2005 std::string command;
2007 // Wait for a command from stdin
2008 while ( std::getline(std::cin, command)
2009 && command != "ponderhit" && command != "stop" && command != "quit") {};
2011 if (command != "ponderhit" && command != "stop")
2012 QuitRequest = true; // Must be "quit" or getline() returned false
2016 // init_thread() is the function which is called when a new thread is
2017 // launched. It simply calls the idle_loop() function with the supplied
2018 // threadID. There are two versions of this function; one for POSIX
2019 // threads and one for Windows threads.
2021 #if !defined(_MSC_VER)
2023 void* init_thread(void* threadID) {
2025 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2031 DWORD WINAPI init_thread(LPVOID threadID) {
2033 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2040 /// The ThreadsManager class
2043 // read_uci_options() updates number of active threads and other internal
2044 // parameters according to the UCI options values. It is called before
2045 // to start a new search.
2047 void ThreadsManager::read_uci_options() {
2049 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2050 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2051 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2052 activeThreads = Options["Threads"].value<int>();
2056 // idle_loop() is where the threads are parked when they have no work to do.
2057 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2058 // object for which the current thread is the master.
2060 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2062 assert(threadID >= 0 && threadID < MAX_THREADS);
2065 bool allFinished = false;
2069 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2070 // master should exit as last one.
2071 if (allThreadsShouldExit)
2074 threads[threadID].state = THREAD_TERMINATED;
2078 // If we are not thinking, wait for a condition to be signaled
2079 // instead of wasting CPU time polling for work.
2080 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2081 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2083 assert(!sp || useSleepingThreads);
2084 assert(threadID != 0 || useSleepingThreads);
2086 if (threads[threadID].state == THREAD_INITIALIZING)
2087 threads[threadID].state = THREAD_AVAILABLE;
2089 // Grab the lock to avoid races with wake_sleeping_thread()
2090 lock_grab(&sleepLock[threadID]);
2092 // If we are master and all slaves have finished do not go to sleep
2093 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2094 allFinished = (i == activeThreads);
2096 if (allFinished || allThreadsShouldExit)
2098 lock_release(&sleepLock[threadID]);
2102 // Do sleep here after retesting sleep conditions
2103 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2104 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2106 lock_release(&sleepLock[threadID]);
2109 // If this thread has been assigned work, launch a search
2110 if (threads[threadID].state == THREAD_WORKISWAITING)
2112 assert(!allThreadsShouldExit);
2114 threads[threadID].state = THREAD_SEARCHING;
2116 // Copy SplitPoint position and search stack and call search()
2117 // with SplitPoint template parameter set to true.
2118 SearchStack ss[PLY_MAX_PLUS_2];
2119 SplitPoint* tsp = threads[threadID].splitPoint;
2120 Position pos(*tsp->pos, threadID);
2122 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2126 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2128 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2130 assert(threads[threadID].state == THREAD_SEARCHING);
2132 threads[threadID].state = THREAD_AVAILABLE;
2134 // Wake up master thread so to allow it to return from the idle loop in
2135 // case we are the last slave of the split point.
2136 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2137 wake_sleeping_thread(tsp->master);
2140 // If this thread is the master of a split point and all slaves have
2141 // finished their work at this split point, return from the idle loop.
2142 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2143 allFinished = (i == activeThreads);
2147 // Because sp->slaves[] is reset under lock protection,
2148 // be sure sp->lock has been released before to return.
2149 lock_grab(&(sp->lock));
2150 lock_release(&(sp->lock));
2152 // In helpful master concept a master can help only a sub-tree, and
2153 // because here is all finished is not possible master is booked.
2154 assert(threads[threadID].state == THREAD_AVAILABLE);
2156 threads[threadID].state = THREAD_SEARCHING;
2163 // init_threads() is called during startup. It launches all helper threads,
2164 // and initializes the split point stack and the global locks and condition
2167 void ThreadsManager::init_threads() {
2169 int i, arg[MAX_THREADS];
2172 // Initialize global locks
2175 for (i = 0; i < MAX_THREADS; i++)
2177 lock_init(&sleepLock[i]);
2178 cond_init(&sleepCond[i]);
2181 // Initialize splitPoints[] locks
2182 for (i = 0; i < MAX_THREADS; i++)
2183 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2184 lock_init(&(threads[i].splitPoints[j].lock));
2186 // Will be set just before program exits to properly end the threads
2187 allThreadsShouldExit = false;
2189 // Threads will be put all threads to sleep as soon as created
2192 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2193 threads[0].state = THREAD_SEARCHING;
2194 for (i = 1; i < MAX_THREADS; i++)
2195 threads[i].state = THREAD_INITIALIZING;
2197 // Launch the helper threads
2198 for (i = 1; i < MAX_THREADS; i++)
2202 #if !defined(_MSC_VER)
2203 pthread_t pthread[1];
2204 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2205 pthread_detach(pthread[0]);
2207 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2211 cout << "Failed to create thread number " << i << endl;
2215 // Wait until the thread has finished launching and is gone to sleep
2216 while (threads[i].state == THREAD_INITIALIZING) {}
2221 // exit_threads() is called when the program exits. It makes all the
2222 // helper threads exit cleanly.
2224 void ThreadsManager::exit_threads() {
2226 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2228 // Wake up all the threads and waits for termination
2229 for (int i = 1; i < MAX_THREADS; i++)
2231 wake_sleeping_thread(i);
2232 while (threads[i].state != THREAD_TERMINATED) {}
2235 // Now we can safely destroy the locks
2236 for (int i = 0; i < MAX_THREADS; i++)
2237 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2238 lock_destroy(&(threads[i].splitPoints[j].lock));
2240 lock_destroy(&mpLock);
2242 // Now we can safely destroy the wait conditions
2243 for (int i = 0; i < MAX_THREADS; i++)
2245 lock_destroy(&sleepLock[i]);
2246 cond_destroy(&sleepCond[i]);
2251 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2252 // the thread's currently active split point, or in some ancestor of
2253 // the current split point.
2255 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2257 assert(threadID >= 0 && threadID < activeThreads);
2259 SplitPoint* sp = threads[threadID].splitPoint;
2261 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2266 // thread_is_available() checks whether the thread with threadID "slave" is
2267 // available to help the thread with threadID "master" at a split point. An
2268 // obvious requirement is that "slave" must be idle. With more than two
2269 // threads, this is not by itself sufficient: If "slave" is the master of
2270 // some active split point, it is only available as a slave to the other
2271 // threads which are busy searching the split point at the top of "slave"'s
2272 // split point stack (the "helpful master concept" in YBWC terminology).
2274 bool ThreadsManager::thread_is_available(int slave, int master) const {
2276 assert(slave >= 0 && slave < activeThreads);
2277 assert(master >= 0 && master < activeThreads);
2278 assert(activeThreads > 1);
2280 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2283 // Make a local copy to be sure doesn't change under our feet
2284 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2286 // No active split points means that the thread is available as
2287 // a slave for any other thread.
2288 if (localActiveSplitPoints == 0 || activeThreads == 2)
2291 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2292 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2293 // could have been set to 0 by another thread leading to an out of bound access.
2294 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2301 // available_thread_exists() tries to find an idle thread which is available as
2302 // a slave for the thread with threadID "master".
2304 bool ThreadsManager::available_thread_exists(int master) const {
2306 assert(master >= 0 && master < activeThreads);
2307 assert(activeThreads > 1);
2309 for (int i = 0; i < activeThreads; i++)
2310 if (thread_is_available(i, master))
2317 // split() does the actual work of distributing the work at a node between
2318 // several available threads. If it does not succeed in splitting the
2319 // node (because no idle threads are available, or because we have no unused
2320 // split point objects), the function immediately returns. If splitting is
2321 // possible, a SplitPoint object is initialized with all the data that must be
2322 // copied to the helper threads and we tell our helper threads that they have
2323 // been assigned work. This will cause them to instantly leave their idle loops and
2324 // call search().When all threads have returned from search() then split() returns.
2326 template <bool Fake>
2327 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2328 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2329 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2330 assert(pos.is_ok());
2331 assert(ply > 0 && ply < PLY_MAX);
2332 assert(*bestValue >= -VALUE_INFINITE);
2333 assert(*bestValue <= *alpha);
2334 assert(*alpha < beta);
2335 assert(beta <= VALUE_INFINITE);
2336 assert(depth > DEPTH_ZERO);
2337 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2338 assert(activeThreads > 1);
2340 int i, master = pos.thread();
2341 Thread& masterThread = threads[master];
2345 // If no other thread is available to help us, or if we have too many
2346 // active split points, don't split.
2347 if ( !available_thread_exists(master)
2348 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2350 lock_release(&mpLock);
2354 // Pick the next available split point object from the split point stack
2355 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2357 // Initialize the split point object
2358 splitPoint.parent = masterThread.splitPoint;
2359 splitPoint.master = master;
2360 splitPoint.betaCutoff = false;
2361 splitPoint.ply = ply;
2362 splitPoint.depth = depth;
2363 splitPoint.threatMove = threatMove;
2364 splitPoint.mateThreat = mateThreat;
2365 splitPoint.alpha = *alpha;
2366 splitPoint.beta = beta;
2367 splitPoint.pvNode = pvNode;
2368 splitPoint.bestValue = *bestValue;
2370 splitPoint.moveCount = moveCount;
2371 splitPoint.pos = &pos;
2372 splitPoint.nodes = 0;
2374 for (i = 0; i < activeThreads; i++)
2375 splitPoint.slaves[i] = 0;
2377 masterThread.splitPoint = &splitPoint;
2379 // If we are here it means we are not available
2380 assert(masterThread.state != THREAD_AVAILABLE);
2382 int workersCnt = 1; // At least the master is included
2384 // Allocate available threads setting state to THREAD_BOOKED
2385 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2386 if (thread_is_available(i, master))
2388 threads[i].state = THREAD_BOOKED;
2389 threads[i].splitPoint = &splitPoint;
2390 splitPoint.slaves[i] = 1;
2394 assert(Fake || workersCnt > 1);
2396 // We can release the lock because slave threads are already booked and master is not available
2397 lock_release(&mpLock);
2399 // Tell the threads that they have work to do. This will make them leave
2401 for (i = 0; i < activeThreads; i++)
2402 if (i == master || splitPoint.slaves[i])
2404 assert(i == master || threads[i].state == THREAD_BOOKED);
2406 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2408 if (useSleepingThreads && i != master)
2409 wake_sleeping_thread(i);
2412 // Everything is set up. The master thread enters the idle loop, from
2413 // which it will instantly launch a search, because its state is
2414 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2415 // idle loop, which means that the main thread will return from the idle
2416 // loop when all threads have finished their work at this split point.
2417 idle_loop(master, &splitPoint);
2419 // We have returned from the idle loop, which means that all threads are
2420 // finished. Update alpha and bestValue, and return.
2423 *alpha = splitPoint.alpha;
2424 *bestValue = splitPoint.bestValue;
2425 masterThread.activeSplitPoints--;
2426 masterThread.splitPoint = splitPoint.parent;
2427 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2429 lock_release(&mpLock);
2433 // wake_sleeping_thread() wakes up the thread with the given threadID
2434 // when it is time to start a new search.
2436 void ThreadsManager::wake_sleeping_thread(int threadID) {
2438 lock_grab(&sleepLock[threadID]);
2439 cond_signal(&sleepCond[threadID]);
2440 lock_release(&sleepLock[threadID]);
2444 /// RootMove and RootMoveList method's definitions
2446 RootMove::RootMove() {
2449 pv_score = non_pv_score = -VALUE_INFINITE;
2453 RootMove& RootMove::operator=(const RootMove& rm) {
2455 const Move* src = rm.pv;
2458 // Avoid a costly full rm.pv[] copy
2459 do *dst++ = *src; while (*src++ != MOVE_NONE);
2462 pv_score = rm.pv_score;
2463 non_pv_score = rm.non_pv_score;
2467 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2468 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2469 // allow to always have a ponder move even when we fail high at root and also a
2470 // long PV to print that is important for position analysis.
2472 void RootMove::extract_pv_from_tt(Position& pos) {
2474 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2478 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2480 pos.do_move(pv[0], *st++);
2482 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2483 && tte->move() != MOVE_NONE
2484 && move_is_legal(pos, tte->move())
2486 && (!pos.is_draw() || ply < 2))
2488 pv[ply] = tte->move();
2489 pos.do_move(pv[ply++], *st++);
2491 pv[ply] = MOVE_NONE;
2493 do pos.undo_move(pv[--ply]); while (ply);
2496 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2497 // the PV back into the TT. This makes sure the old PV moves are searched
2498 // first, even if the old TT entries have been overwritten.
2500 void RootMove::insert_pv_in_tt(Position& pos) {
2502 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2505 Value v, m = VALUE_NONE;
2508 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2512 tte = TT.retrieve(k);
2514 // Don't overwrite existing correct entries
2515 if (!tte || tte->move() != pv[ply])
2517 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2518 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2520 pos.do_move(pv[ply], *st++);
2522 } while (pv[++ply] != MOVE_NONE);
2524 do pos.undo_move(pv[--ply]); while (ply);
2527 // pv_info_to_uci() returns a string with information on the current PV line
2528 // formatted according to UCI specification. It is called at each iteration
2529 // or after a new pv is found.
2531 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
2533 std::stringstream s, l;
2536 while (*m != MOVE_NONE)
2539 s << "info depth " << depth
2540 << " seldepth " << int(m - pv)
2541 << " multipv " << pvLine + 1
2542 << " score " << value_to_uci(pv_score)
2543 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2544 << speed_to_uci(pos.nodes_searched())
2545 << " pv " << l.str();
2551 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2553 MoveStack mlist[MOVES_MAX];
2557 bestMoveChanges = 0;
2559 // Generate all legal moves and add them to RootMoveList
2560 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2561 for (MoveStack* cur = mlist; cur != last; cur++)
2563 // If we have a searchMoves[] list then verify cur->move
2564 // is in the list before to add it.
2565 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2567 if (searchMoves[0] && *sm != cur->move)
2571 rm.pv[0] = cur->move;
2572 rm.pv[1] = MOVE_NONE;
2573 rm.pv_score = -VALUE_INFINITE;
2579 // When playing with strength handicap choose best move among the MultiPV set
2580 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2581 void do_skill_level(Move* best, Move* ponder) {
2583 assert(MultiPV > 1);
2585 // Rml list is already sorted by pv_score in descending order
2587 int max_s = -VALUE_INFINITE;
2588 int size = Min(MultiPV, (int)Rml.size());
2589 int max = Rml[0].pv_score;
2590 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2591 int wk = 120 - 2 * SkillLevel;
2593 // PRNG sequence should be non deterministic
2594 for (int i = abs(get_system_time() % 50); i > 0; i--)
2595 RK.rand<unsigned>();
2597 // Choose best move. For each move's score we add two terms both dependent
2598 // on wk, one deterministic and bigger for weaker moves, and one random,
2599 // then we choose the move with the resulting highest score.
2600 for (int i = 0; i < size; i++)
2602 s = Rml[i].pv_score;
2604 // Don't allow crazy blunders even at very low skills
2605 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2608 // This is our magical formula
2609 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2614 *best = Rml[i].pv[0];
2615 *ponder = Rml[i].pv[1];