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
262 // Multi-threads manager object
263 ThreadsManager ThreadsMgr;
265 // Node counters, used only by thread[0] but try to keep in different cache
266 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
267 bool SendSearchedNodes;
269 int NodesBetweenPolls = 30000;
276 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
278 template <NodeType PvNode, bool SpNode, bool Root>
279 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
281 template <NodeType PvNode>
282 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
287 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
288 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
291 template <NodeType PvNode>
292 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
294 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
295 bool connected_moves(const Position& pos, Move m1, Move m2);
296 bool value_is_mate(Value value);
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);
305 int current_search_time();
306 std::string value_to_uci(Value v);
307 std::string speed_to_uci(int64_t nodes);
308 void poll(const Position& pos);
309 void wait_for_stop_or_ponderhit();
311 #if !defined(_MSC_VER)
312 void* init_thread(void* threadID);
314 DWORD WINAPI init_thread(LPVOID threadID);
318 // MovePickerExt is an extended MovePicker used to choose at compile time
319 // the proper move source according to the type of node.
320 template<bool SpNode, bool Root> struct MovePickerExt;
322 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
323 // before to search them.
324 template<> struct MovePickerExt<false, true> : public MovePicker {
326 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
327 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
329 Value score = VALUE_ZERO;
331 // Score root moves using the standard way used in main search, the moves
332 // are scored according to the order in which they are returned by MovePicker.
333 // This is the second order score that is used to compare the moves when
334 // the first order pv scores of both moves are equal.
335 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
336 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
337 if (rm->pv[0] == move)
339 rm->non_pv_score = score--;
347 Move get_next_move() {
354 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
357 RootMoveList::iterator rm;
361 // In SpNodes use split point's shared MovePicker object as move source
362 template<> struct MovePickerExt<true, false> : public MovePicker {
364 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
365 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
368 Move get_next_move() { return mp->get_next_move(); }
370 RootMoveList::iterator rm; // Dummy, needed to compile
374 // Default case, create and use a MovePicker object as source
375 template<> struct MovePickerExt<false, false> : public MovePicker {
377 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
378 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
380 RootMoveList::iterator rm; // Dummy, needed to compile
390 /// init_threads(), exit_threads() and nodes_searched() are helpers to
391 /// give accessibility to some TM methods from outside of current file.
393 void init_threads() { ThreadsMgr.init_threads(); }
394 void exit_threads() { ThreadsMgr.exit_threads(); }
397 /// init_search() is called during startup. It initializes various lookup tables
401 int d; // depth (ONE_PLY == 2)
402 int hd; // half depth (ONE_PLY == 1)
405 // Init reductions array
406 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
408 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
409 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
410 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
411 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
414 // Init futility margins array
415 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
416 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
418 // Init futility move count array
419 for (d = 0; d < 32; d++)
420 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
424 /// perft() is our utility to verify move generation is bug free. All the legal
425 /// moves up to given depth are generated and counted and the sum returned.
427 int64_t perft(Position& pos, Depth depth)
429 MoveStack mlist[MOVES_MAX];
434 // Generate all legal moves
435 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
437 // If we are at the last ply we don't need to do and undo
438 // the moves, just to count them.
439 if (depth <= ONE_PLY)
440 return int(last - mlist);
442 // Loop through all legal moves
444 for (MoveStack* cur = mlist; cur != last; cur++)
447 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
448 sum += perft(pos, depth - ONE_PLY);
455 /// think() is the external interface to Stockfish's search, and is called when
456 /// the program receives the UCI 'go' command. It initializes various
457 /// search-related global variables, and calls id_loop(). It returns false
458 /// when a quit command is received during the search.
460 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
461 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
463 // Initialize global search variables
464 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
466 SearchStartTime = get_system_time();
467 ExactMaxTime = maxTime;
470 InfiniteSearch = infinite;
472 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
474 // Look for a book move, only during games, not tests
475 if (UseTimeManagement && Options["OwnBook"].value<bool>())
477 if (Options["Book File"].value<std::string>() != OpeningBook.name())
478 OpeningBook.open(Options["Book File"].value<std::string>());
480 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
481 if (bookMove != MOVE_NONE)
484 wait_for_stop_or_ponderhit();
486 cout << "bestmove " << bookMove << endl;
491 // Read UCI option values
492 TT.set_size(Options["Hash"].value<int>());
493 if (Options["Clear Hash"].value<bool>())
495 Options["Clear Hash"].set_value("false");
499 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
500 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
501 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
502 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
503 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
504 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
505 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
506 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
507 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
508 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
509 UCIMultiPV = Options["MultiPV"].value<int>();
510 SkillLevel = Options["Skill level"].value<int>();
511 UseLogFile = Options["Use Search Log"].value<bool>();
513 read_evaluation_uci_options(pos.side_to_move());
515 // Do we have to play with skill handicap? In this case enable MultiPV that
516 // we will use behind the scenes to retrieve a set of possible moves.
517 MultiPV = (SkillLevel < 20 ? Max(UCIMultiPV, 4) : UCIMultiPV);
519 // Set the number of active threads
520 ThreadsMgr.read_uci_options();
521 init_eval(ThreadsMgr.active_threads());
523 // Wake up needed threads
524 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
525 ThreadsMgr.wake_sleeping_thread(i);
528 int myTime = time[pos.side_to_move()];
529 int myIncrement = increment[pos.side_to_move()];
530 if (UseTimeManagement)
531 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
533 // Set best NodesBetweenPolls interval to avoid lagging under
534 // heavy time pressure.
536 NodesBetweenPolls = Min(MaxNodes, 30000);
537 else if (myTime && myTime < 1000)
538 NodesBetweenPolls = 1000;
539 else if (myTime && myTime < 5000)
540 NodesBetweenPolls = 5000;
542 NodesBetweenPolls = 30000;
544 // Write search information to log file
547 std::string name = Options["Search Log Filename"].value<std::string>();
548 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
550 LogFile << "\nSearching: " << pos.to_fen()
551 << "\ninfinite: " << infinite
552 << " ponder: " << ponder
553 << " time: " << myTime
554 << " increment: " << myIncrement
555 << " moves to go: " << movesToGo
559 // We're ready to start thinking. Call the iterative deepening loop function
560 Move ponderMove = MOVE_NONE;
561 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
563 // Print final search statistics
564 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
568 int t = current_search_time();
570 LogFile << "Nodes: " << pos.nodes_searched()
571 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
572 << "\nBest move: " << move_to_san(pos, bestMove);
575 pos.do_move(bestMove, st);
576 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
577 pos.undo_move(bestMove); // Return from think() with unchanged position
581 // This makes all the threads to go to sleep
582 ThreadsMgr.set_active_threads(1);
584 // If we are pondering or in infinite search, we shouldn't print the
585 // best move before we are told to do so.
586 if (!StopRequest && (Pondering || InfiniteSearch))
587 wait_for_stop_or_ponderhit();
589 // Could be MOVE_NONE when searching on a stalemate position
590 cout << "bestmove " << bestMove;
592 // UCI protol is not clear on allowing sending an empty ponder move, instead
593 // it is clear that ponder move is optional. So skip it if empty.
594 if (ponderMove != MOVE_NONE)
595 cout << " ponder " << ponderMove;
605 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
606 // with increasing depth until the allocated thinking time has been consumed,
607 // user stops the search, or the maximum search depth is reached.
609 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
611 SearchStack ss[PLY_MAX_PLUS_2];
612 Value bestValues[PLY_MAX_PLUS_2];
613 int bestMoveChanges[PLY_MAX_PLUS_2];
614 int depth, aspirationDelta;
615 Value value, alpha, beta;
616 Move bestMove, easyMove;
618 // Initialize stuff before a new search
619 memset(ss, 0, 4 * sizeof(SearchStack));
622 *ponderMove = bestMove = easyMove = MOVE_NONE;
623 depth = aspirationDelta = 0;
624 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
625 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
627 // Moves to search are verified and copied
628 Rml.init(pos, searchMoves);
630 // Handle special case of searching on a mate/stalemate position
633 cout << "info depth 0 score "
634 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
640 // Iterative deepening loop
641 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
643 Rml.bestMoveChanges = 0;
644 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
646 // Calculate dynamic aspiration window based on previous iterations
647 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
649 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
650 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
652 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
653 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
655 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
656 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
659 // Start with a small aspiration window and, in case of fail high/low,
660 // research with bigger window until not failing high/low anymore.
662 // Search starting from ss+1 to allow calling update_gains()
663 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
665 // Write PV back to transposition table in case the relevant entries
666 // have been overwritten during the search.
667 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
668 Rml[i].insert_pv_in_tt(pos);
670 // Value cannot be trusted. Break out immediately!
674 assert(value >= alpha);
676 // In case of failing high/low increase aspiration window and research,
677 // otherwise exit the fail high/low loop.
680 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
681 aspirationDelta += aspirationDelta / 2;
683 else if (value <= alpha)
685 AspirationFailLow = true;
686 StopOnPonderhit = false;
688 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
689 aspirationDelta += aspirationDelta / 2;
694 } while (abs(value) < VALUE_KNOWN_WIN);
696 // Collect info about search result
697 bestMove = Rml[0].pv[0];
698 *ponderMove = Rml[0].pv[1];
699 bestValues[depth] = value;
700 bestMoveChanges[depth] = Rml.bestMoveChanges;
702 // Send PV line to GUI and to log file
703 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
704 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
707 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
709 // Init easyMove after first iteration or drop if differs from the best move
710 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
712 else if (bestMove != easyMove)
713 easyMove = MOVE_NONE;
715 if (UseTimeManagement && !StopRequest)
718 bool noMoreTime = false;
720 // Stop search early when the last two iterations returned a mate score
722 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
723 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
726 // Stop search early if one move seems to be much better than the
727 // others or if there is only a single legal move. In this latter
728 // case we search up to Iteration 8 anyway to get a proper score.
730 && easyMove == bestMove
732 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
733 && current_search_time() > TimeMgr.available_time() / 16)
734 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
735 && current_search_time() > TimeMgr.available_time() / 32)))
738 // Add some extra time if the best move has changed during the last two iterations
739 if (depth > 4 && depth < 50)
740 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
742 // Stop search if most of MaxSearchTime is consumed at the end of the
743 // iteration. We probably don't have enough time to search the first
744 // move at the next iteration anyway.
745 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
751 StopOnPonderhit = true;
758 // When playing with strength handicap choose best move among the MultiPV set
759 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
764 // Rml list is already sorted by pv_score in descending order
766 int max_s = -VALUE_INFINITE;
767 int size = Min(MultiPV, (int)Rml.size());
768 int max = Rml[0].pv_score;
769 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
770 int wk = 120 - 2 * SkillLevel;
772 // PRNG sequence should be non deterministic
773 for (int i = abs(get_system_time() % 50); i > 0; i--)
776 // Choose best move. For each move's score we add two terms both dependent
777 // on wk, one deterministic and bigger for weaker moves, and one random,
778 // then we choose the move with the resulting highest score.
779 for (int i = 0; i < size; i++)
783 // Don't allow crazy blunders even at very low skills
784 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
787 // This is our magical formula
788 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
793 bestMove = Rml[i].pv[0];
794 *ponderMove = Rml[i].pv[1];
803 // search<>() is the main search function for both PV and non-PV nodes and for
804 // normal and SplitPoint nodes. When called just after a split point the search
805 // is simpler because we have already probed the hash table, done a null move
806 // search, and searched the first move before splitting, we don't have to repeat
807 // all this work again. We also don't need to store anything to the hash table
808 // here: This is taken care of after we return from the split point.
810 template <NodeType PvNode, bool SpNode, bool Root>
811 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
813 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
814 assert(beta > alpha && beta <= VALUE_INFINITE);
815 assert(PvNode || alpha == beta - 1);
816 assert((Root || ply > 0) && ply < PLY_MAX);
817 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
819 Move movesSearched[MOVES_MAX];
824 Move ttMove, move, excludedMove, threatMove;
827 Value bestValue, value, oldAlpha;
828 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
829 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
830 bool mateThreat = false;
831 int moveCount = 0, playedMoveCount = 0;
832 int threadID = pos.thread();
833 SplitPoint* sp = NULL;
835 refinedValue = bestValue = value = -VALUE_INFINITE;
837 isCheck = pos.is_check();
843 ttMove = excludedMove = MOVE_NONE;
844 threatMove = sp->threatMove;
845 mateThreat = sp->mateThreat;
846 goto split_point_start;
851 // Step 1. Initialize node and poll. Polling can abort search
852 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
853 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
854 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
856 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
862 // Step 2. Check for aborted search and immediate draw
864 || ThreadsMgr.cutoff_at_splitpoint(threadID)
866 || ply >= PLY_MAX - 1) && !Root)
869 // Step 3. Mate distance pruning
870 alpha = Max(value_mated_in(ply), alpha);
871 beta = Min(value_mate_in(ply+1), beta);
875 // Step 4. Transposition table lookup
876 // We don't want the score of a partial search to overwrite a previous full search
877 // TT value, so we use a different position key in case of an excluded move.
878 excludedMove = ss->excludedMove;
879 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
881 tte = TT.retrieve(posKey);
882 ttMove = tte ? tte->move() : MOVE_NONE;
884 // At PV nodes we check for exact scores, while at non-PV nodes we check for
885 // and return a fail high/low. Biggest advantage at probing at PV nodes is
886 // to have a smooth experience in analysis mode.
889 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
890 : ok_to_use_TT(tte, depth, beta, ply)))
893 ss->bestMove = ttMove; // Can be MOVE_NONE
894 return value_from_tt(tte->value(), ply);
897 // Step 5. Evaluate the position statically and
898 // update gain statistics of parent move.
900 ss->eval = ss->evalMargin = VALUE_NONE;
903 assert(tte->static_value() != VALUE_NONE);
905 ss->eval = tte->static_value();
906 ss->evalMargin = tte->static_value_margin();
907 refinedValue = refine_eval(tte, ss->eval, ply);
911 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
912 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
915 // Save gain for the parent non-capture move
916 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
918 // Step 6. Razoring (is omitted in PV nodes)
920 && depth < RazorDepth
922 && refinedValue < beta - razor_margin(depth)
923 && ttMove == MOVE_NONE
924 && !value_is_mate(beta)
925 && !pos.has_pawn_on_7th(pos.side_to_move()))
927 Value rbeta = beta - razor_margin(depth);
928 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
930 // Logically we should return (v + razor_margin(depth)), but
931 // surprisingly this did slightly weaker in tests.
935 // Step 7. Static null move pruning (is omitted in PV nodes)
936 // We're betting that the opponent doesn't have a move that will reduce
937 // the score by more than futility_margin(depth) if we do a null move.
940 && depth < RazorDepth
942 && refinedValue >= beta + futility_margin(depth, 0)
943 && !value_is_mate(beta)
944 && pos.non_pawn_material(pos.side_to_move()))
945 return refinedValue - futility_margin(depth, 0);
947 // Step 8. Null move search with verification search (is omitted in PV nodes)
952 && refinedValue >= beta
953 && !value_is_mate(beta)
954 && pos.non_pawn_material(pos.side_to_move()))
956 ss->currentMove = MOVE_NULL;
958 // Null move dynamic reduction based on depth
959 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
961 // Null move dynamic reduction based on value
962 if (refinedValue - beta > PawnValueMidgame)
965 pos.do_null_move(st);
966 (ss+1)->skipNullMove = true;
967 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
968 (ss+1)->skipNullMove = false;
969 pos.undo_null_move();
971 if (nullValue >= beta)
973 // Do not return unproven mate scores
974 if (nullValue >= value_mate_in(PLY_MAX))
977 if (depth < 6 * ONE_PLY)
980 // Do verification search at high depths
981 ss->skipNullMove = true;
982 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
983 ss->skipNullMove = false;
990 // The null move failed low, which means that we may be faced with
991 // some kind of threat. If the previous move was reduced, check if
992 // the move that refuted the null move was somehow connected to the
993 // move which was reduced. If a connection is found, return a fail
994 // low score (which will cause the reduced move to fail high in the
995 // parent node, which will trigger a re-search with full depth).
996 if (nullValue == value_mated_in(ply + 2))
999 threatMove = (ss+1)->bestMove;
1000 if ( depth < ThreatDepth
1001 && (ss-1)->reduction
1002 && threatMove != MOVE_NONE
1003 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1008 // Step 9. Internal iterative deepening
1009 if ( depth >= IIDDepth[PvNode]
1010 && ttMove == MOVE_NONE
1011 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1013 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1015 ss->skipNullMove = true;
1016 search<PvNode>(pos, ss, alpha, beta, d, ply);
1017 ss->skipNullMove = false;
1019 ttMove = ss->bestMove;
1020 tte = TT.retrieve(posKey);
1023 // Expensive mate threat detection (only for PV nodes)
1025 mateThreat = pos.has_mate_threat();
1027 split_point_start: // At split points actual search starts from here
1029 // Initialize a MovePicker object for the current position
1030 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1032 ss->bestMove = MOVE_NONE;
1033 futilityBase = ss->eval + ss->evalMargin;
1034 singularExtensionNode = !Root
1036 && depth >= SingularExtensionDepth[PvNode]
1039 && !excludedMove // Do not allow recursive singular extension search
1040 && (tte->type() & VALUE_TYPE_LOWER)
1041 && tte->depth() >= depth - 3 * ONE_PLY;
1044 lock_grab(&(sp->lock));
1045 bestValue = sp->bestValue;
1048 // Step 10. Loop through moves
1049 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1050 while ( bestValue < beta
1051 && (move = mp.get_next_move()) != MOVE_NONE
1052 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1054 assert(move_is_ok(move));
1058 moveCount = ++sp->moveCount;
1059 lock_release(&(sp->lock));
1061 else if (move == excludedMove)
1068 // This is used by time management
1069 FirstRootMove = (moveCount == 1);
1071 // Save the current node count before the move is searched
1072 nodes = pos.nodes_searched();
1074 // If it's time to send nodes info, do it here where we have the
1075 // correct accumulated node counts searched by each thread.
1076 if (SendSearchedNodes)
1078 SendSearchedNodes = false;
1079 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1082 if (current_search_time() >= 1000)
1083 cout << "info currmove " << move
1084 << " currmovenumber " << moveCount << endl;
1087 // At Root and at first iteration do a PV search on all the moves
1088 // to score root moves. Otherwise only the first one is the PV.
1089 isPvMove = (PvNode && moveCount <= (Root ? MultiPV + 1000 * (depth <= ONE_PLY) : 1));
1090 moveIsCheck = pos.move_is_check(move, ci);
1091 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1093 // Step 11. Decide the new search depth
1094 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
1096 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1097 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1098 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1099 // lower than ttValue minus a margin then we extend ttMove.
1100 if ( singularExtensionNode
1101 && move == tte->move()
1104 Value ttValue = value_from_tt(tte->value(), ply);
1106 if (abs(ttValue) < VALUE_KNOWN_WIN)
1108 Value b = ttValue - int(depth);
1109 ss->excludedMove = move;
1110 ss->skipNullMove = true;
1111 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1112 ss->skipNullMove = false;
1113 ss->excludedMove = MOVE_NONE;
1114 ss->bestMove = MOVE_NONE;
1120 // Update current move (this must be done after singular extension search)
1121 ss->currentMove = move;
1122 newDepth = depth - ONE_PLY + ext;
1124 // Step 12. Futility pruning (is omitted in PV nodes)
1126 && !captureOrPromotion
1130 && !move_is_castle(move))
1132 // Move count based pruning
1133 if ( moveCount >= futility_move_count(depth)
1134 && !(threatMove && connected_threat(pos, move, threatMove))
1135 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1138 lock_grab(&(sp->lock));
1143 // Value based pruning
1144 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1145 // but fixing this made program slightly weaker.
1146 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1147 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1148 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1150 if (futilityValueScaled < beta)
1154 lock_grab(&(sp->lock));
1155 if (futilityValueScaled > sp->bestValue)
1156 sp->bestValue = bestValue = futilityValueScaled;
1158 else if (futilityValueScaled > bestValue)
1159 bestValue = futilityValueScaled;
1164 // Prune moves with negative SEE at low depths
1165 if ( predictedDepth < 2 * ONE_PLY
1166 && bestValue > value_mated_in(PLY_MAX)
1167 && pos.see_sign(move) < 0)
1170 lock_grab(&(sp->lock));
1176 // Step 13. Make the move
1177 pos.do_move(move, st, ci, moveIsCheck);
1179 if (!SpNode && !captureOrPromotion)
1180 movesSearched[playedMoveCount++] = move;
1182 // Step extra. pv search (only in PV nodes)
1183 // The first move in list is the expected PV
1186 // Aspiration window is disabled in multi-pv case
1187 if (Root && MultiPV > 1)
1188 alpha = -VALUE_INFINITE;
1190 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1194 // Step 14. Reduced depth search
1195 // If the move fails high will be re-searched at full depth.
1196 bool doFullDepthSearch = true;
1198 if ( depth >= 3 * ONE_PLY
1199 && !captureOrPromotion
1201 && !move_is_castle(move)
1202 && ss->killers[0] != move
1203 && ss->killers[1] != move)
1205 ss->reduction = reduction<PvNode>(depth, moveCount);
1208 alpha = SpNode ? sp->alpha : alpha;
1209 Depth d = newDepth - ss->reduction;
1210 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1212 doFullDepthSearch = (value > alpha);
1214 ss->reduction = DEPTH_ZERO; // Restore original reduction
1217 // Step 15. Full depth search
1218 if (doFullDepthSearch)
1220 alpha = SpNode ? sp->alpha : alpha;
1221 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1223 // Step extra. pv search (only in PV nodes)
1224 // Search only for possible new PV nodes, if instead value >= beta then
1225 // parent node fails low with value <= alpha and tries another move.
1226 if (PvNode && value > alpha && (Root || value < beta))
1227 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1231 // Step 16. Undo move
1232 pos.undo_move(move);
1234 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1236 // Step 17. Check for new best move
1239 lock_grab(&(sp->lock));
1240 bestValue = sp->bestValue;
1244 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1249 sp->bestValue = value;
1251 if (!Root && value > alpha)
1253 if (PvNode && value < beta) // We want always alpha < beta
1261 sp->betaCutoff = true;
1263 if (value == value_mate_in(ply + 1))
1264 ss->mateKiller = move;
1266 ss->bestMove = move;
1269 sp->ss->bestMove = move;
1275 // Finished searching the move. If StopRequest is true, the search
1276 // was aborted because the user interrupted the search or because we
1277 // ran out of time. In this case, the return value of the search cannot
1278 // be trusted, and we break out of the loop without updating the best
1283 // Remember searched nodes counts for this move
1284 mp.rm->nodes += pos.nodes_searched() - nodes;
1286 // PV move or new best move ?
1287 if (isPvMove || value > alpha)
1290 ss->bestMove = move;
1291 mp.rm->pv_score = value;
1292 mp.rm->extract_pv_from_tt(pos);
1294 // We record how often the best move has been changed in each
1295 // iteration. This information is used for time management: When
1296 // the best move changes frequently, we allocate some more time.
1297 if (!isPvMove && MultiPV == 1)
1298 Rml.bestMoveChanges++;
1300 Rml.sort_multipv(moveCount);
1302 // Update alpha. In multi-pv we don't use aspiration window, so
1303 // set alpha equal to minimum score among the PV lines.
1305 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1306 else if (value > alpha)
1310 mp.rm->pv_score = -VALUE_INFINITE;
1314 // Step 18. Check for split
1317 && depth >= ThreadsMgr.min_split_depth()
1318 && ThreadsMgr.active_threads() > 1
1320 && ThreadsMgr.available_thread_exists(threadID)
1322 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1323 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1324 threatMove, mateThreat, moveCount, &mp, PvNode);
1327 // Step 19. Check for mate and stalemate
1328 // All legal moves have been searched and if there are
1329 // no legal moves, it must be mate or stalemate.
1330 // If one move was excluded return fail low score.
1331 if (!SpNode && !moveCount)
1332 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1334 // Step 20. Update tables
1335 // If the search is not aborted, update the transposition table,
1336 // history counters, and killer moves.
1337 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1339 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1340 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1341 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1343 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1345 // Update killers and history only for non capture moves that fails high
1346 if ( bestValue >= beta
1347 && !pos.move_is_capture_or_promotion(move))
1349 if (move != ss->killers[0])
1351 ss->killers[1] = ss->killers[0];
1352 ss->killers[0] = move;
1354 update_history(pos, move, depth, movesSearched, playedMoveCount);
1360 // Here we have the lock still grabbed
1361 sp->slaves[threadID] = 0;
1362 sp->nodes += pos.nodes_searched();
1363 lock_release(&(sp->lock));
1366 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1371 // qsearch() is the quiescence search function, which is called by the main
1372 // search function when the remaining depth is zero (or, to be more precise,
1373 // less than ONE_PLY).
1375 template <NodeType PvNode>
1376 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1378 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1379 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1380 assert(PvNode || alpha == beta - 1);
1382 assert(ply > 0 && ply < PLY_MAX);
1383 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1387 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1388 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1391 Value oldAlpha = alpha;
1393 ss->bestMove = ss->currentMove = MOVE_NONE;
1395 // Check for an instant draw or maximum ply reached
1396 if (pos.is_draw() || ply >= PLY_MAX - 1)
1399 // Decide whether or not to include checks, this fixes also the type of
1400 // TT entry depth that we are going to use. Note that in qsearch we use
1401 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1402 isCheck = pos.is_check();
1403 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1405 // Transposition table lookup. At PV nodes, we don't use the TT for
1406 // pruning, but only for move ordering.
1407 tte = TT.retrieve(pos.get_key());
1408 ttMove = (tte ? tte->move() : MOVE_NONE);
1410 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1412 ss->bestMove = ttMove; // Can be MOVE_NONE
1413 return value_from_tt(tte->value(), ply);
1416 // Evaluate the position statically
1419 bestValue = futilityBase = -VALUE_INFINITE;
1420 ss->eval = evalMargin = VALUE_NONE;
1421 enoughMaterial = false;
1427 assert(tte->static_value() != VALUE_NONE);
1429 evalMargin = tte->static_value_margin();
1430 ss->eval = bestValue = tte->static_value();
1433 ss->eval = bestValue = evaluate(pos, evalMargin);
1435 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1437 // Stand pat. Return immediately if static value is at least beta
1438 if (bestValue >= beta)
1441 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1446 if (PvNode && bestValue > alpha)
1449 // Futility pruning parameters, not needed when in check
1450 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1451 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1454 // Initialize a MovePicker object for the current position, and prepare
1455 // to search the moves. Because the depth is <= 0 here, only captures,
1456 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1458 MovePicker mp(pos, ttMove, depth, H);
1461 // Loop through the moves until no moves remain or a beta cutoff occurs
1462 while ( alpha < beta
1463 && (move = mp.get_next_move()) != MOVE_NONE)
1465 assert(move_is_ok(move));
1467 moveIsCheck = pos.move_is_check(move, ci);
1475 && !move_is_promotion(move)
1476 && !pos.move_is_passed_pawn_push(move))
1478 futilityValue = futilityBase
1479 + pos.endgame_value_of_piece_on(move_to(move))
1480 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1482 if (futilityValue < alpha)
1484 if (futilityValue > bestValue)
1485 bestValue = futilityValue;
1489 // Prune moves with negative or equal SEE
1490 if ( futilityBase < beta
1491 && depth < DEPTH_ZERO
1492 && pos.see(move) <= 0)
1496 // Detect non-capture evasions that are candidate to be pruned
1497 evasionPrunable = isCheck
1498 && bestValue > value_mated_in(PLY_MAX)
1499 && !pos.move_is_capture(move)
1500 && !pos.can_castle(pos.side_to_move());
1502 // Don't search moves with negative SEE values
1504 && (!isCheck || evasionPrunable)
1506 && !move_is_promotion(move)
1507 && pos.see_sign(move) < 0)
1510 // Don't search useless checks
1515 && !pos.move_is_capture_or_promotion(move)
1516 && ss->eval + PawnValueMidgame / 4 < beta
1517 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1519 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1520 bestValue = ss->eval + PawnValueMidgame / 4;
1525 // Update current move
1526 ss->currentMove = move;
1528 // Make and search the move
1529 pos.do_move(move, st, ci, moveIsCheck);
1530 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1531 pos.undo_move(move);
1533 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1536 if (value > bestValue)
1542 ss->bestMove = move;
1547 // All legal moves have been searched. A special case: If we're in check
1548 // and no legal moves were found, it is checkmate.
1549 if (isCheck && bestValue == -VALUE_INFINITE)
1550 return value_mated_in(ply);
1552 // Update transposition table
1553 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1554 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1556 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1562 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1563 // bestValue is updated only when returning false because in that case move
1566 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1568 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1569 Square from, to, ksq, victimSq;
1572 Value futilityValue, bv = *bestValue;
1574 from = move_from(move);
1576 them = opposite_color(pos.side_to_move());
1577 ksq = pos.king_square(them);
1578 kingAtt = pos.attacks_from<KING>(ksq);
1579 pc = pos.piece_on(from);
1581 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1582 oldAtt = pos.attacks_from(pc, from, occ);
1583 newAtt = pos.attacks_from(pc, to, occ);
1585 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1586 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1588 if (!(b && (b & (b - 1))))
1591 // Rule 2. Queen contact check is very dangerous
1592 if ( type_of_piece(pc) == QUEEN
1593 && bit_is_set(kingAtt, to))
1596 // Rule 3. Creating new double threats with checks
1597 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1601 victimSq = pop_1st_bit(&b);
1602 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1604 // Note that here we generate illegal "double move"!
1605 if ( futilityValue >= beta
1606 && pos.see_sign(make_move(from, victimSq)) >= 0)
1609 if (futilityValue > bv)
1613 // Update bestValue only if check is not dangerous (because we will prune the move)
1619 // connected_moves() tests whether two moves are 'connected' in the sense
1620 // that the first move somehow made the second move possible (for instance
1621 // if the moving piece is the same in both moves). The first move is assumed
1622 // to be the move that was made to reach the current position, while the
1623 // second move is assumed to be a move from the current position.
1625 bool connected_moves(const Position& pos, Move m1, Move m2) {
1627 Square f1, t1, f2, t2;
1630 assert(m1 && move_is_ok(m1));
1631 assert(m2 && move_is_ok(m2));
1633 // Case 1: The moving piece is the same in both moves
1639 // Case 2: The destination square for m2 was vacated by m1
1645 // Case 3: Moving through the vacated square
1646 if ( piece_is_slider(pos.piece_on(f2))
1647 && bit_is_set(squares_between(f2, t2), f1))
1650 // Case 4: The destination square for m2 is defended by the moving piece in m1
1651 p = pos.piece_on(t1);
1652 if (bit_is_set(pos.attacks_from(p, t1), t2))
1655 // Case 5: Discovered check, checking piece is the piece moved in m1
1656 if ( piece_is_slider(p)
1657 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1658 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1660 // discovered_check_candidates() works also if the Position's side to
1661 // move is the opposite of the checking piece.
1662 Color them = opposite_color(pos.side_to_move());
1663 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1665 if (bit_is_set(dcCandidates, f2))
1672 // value_is_mate() checks if the given value is a mate one eventually
1673 // compensated for the ply.
1675 bool value_is_mate(Value value) {
1677 assert(abs(value) <= VALUE_INFINITE);
1679 return value <= value_mated_in(PLY_MAX)
1680 || value >= value_mate_in(PLY_MAX);
1684 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1685 // "plies to mate from the current ply". Non-mate scores are unchanged.
1686 // The function is called before storing a value to the transposition table.
1688 Value value_to_tt(Value v, int ply) {
1690 if (v >= value_mate_in(PLY_MAX))
1693 if (v <= value_mated_in(PLY_MAX))
1700 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1701 // the transposition table to a mate score corrected for the current ply.
1703 Value value_from_tt(Value v, int ply) {
1705 if (v >= value_mate_in(PLY_MAX))
1708 if (v <= value_mated_in(PLY_MAX))
1715 // extension() decides whether a move should be searched with normal depth,
1716 // or with extended depth. Certain classes of moves (checking moves, in
1717 // particular) are searched with bigger depth than ordinary moves and in
1718 // any case are marked as 'dangerous'. Note that also if a move is not
1719 // extended, as example because the corresponding UCI option is set to zero,
1720 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1721 template <NodeType PvNode>
1722 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1723 bool moveIsCheck, bool mateThreat, bool* dangerous) {
1725 assert(m != MOVE_NONE);
1727 Depth result = DEPTH_ZERO;
1728 *dangerous = moveIsCheck | mateThreat;
1732 if (moveIsCheck && pos.see_sign(m) >= 0)
1733 result += CheckExtension[PvNode];
1736 result += MateThreatExtension[PvNode];
1739 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1741 Color c = pos.side_to_move();
1742 if (relative_rank(c, move_to(m)) == RANK_7)
1744 result += PawnPushTo7thExtension[PvNode];
1747 if (pos.pawn_is_passed(c, move_to(m)))
1749 result += PassedPawnExtension[PvNode];
1754 if ( captureOrPromotion
1755 && pos.type_of_piece_on(move_to(m)) != PAWN
1756 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1757 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1758 && !move_is_promotion(m)
1761 result += PawnEndgameExtension[PvNode];
1766 && captureOrPromotion
1767 && pos.type_of_piece_on(move_to(m)) != PAWN
1768 && pos.see_sign(m) >= 0)
1770 result += ONE_PLY / 2;
1774 return Min(result, ONE_PLY);
1778 // connected_threat() tests whether it is safe to forward prune a move or if
1779 // is somehow connected to the threat move returned by null search.
1781 bool connected_threat(const Position& pos, Move m, Move threat) {
1783 assert(move_is_ok(m));
1784 assert(threat && move_is_ok(threat));
1785 assert(!pos.move_is_check(m));
1786 assert(!pos.move_is_capture_or_promotion(m));
1787 assert(!pos.move_is_passed_pawn_push(m));
1789 Square mfrom, mto, tfrom, tto;
1791 mfrom = move_from(m);
1793 tfrom = move_from(threat);
1794 tto = move_to(threat);
1796 // Case 1: Don't prune moves which move the threatened piece
1800 // Case 2: If the threatened piece has value less than or equal to the
1801 // value of the threatening piece, don't prune moves which defend it.
1802 if ( pos.move_is_capture(threat)
1803 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1804 || pos.type_of_piece_on(tfrom) == KING)
1805 && pos.move_attacks_square(m, tto))
1808 // Case 3: If the moving piece in the threatened move is a slider, don't
1809 // prune safe moves which block its ray.
1810 if ( piece_is_slider(pos.piece_on(tfrom))
1811 && bit_is_set(squares_between(tfrom, tto), mto)
1812 && pos.see_sign(m) >= 0)
1819 // ok_to_use_TT() returns true if a transposition table score
1820 // can be used at a given point in search.
1822 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1824 Value v = value_from_tt(tte->value(), ply);
1826 return ( tte->depth() >= depth
1827 || v >= Max(value_mate_in(PLY_MAX), beta)
1828 || v < Min(value_mated_in(PLY_MAX), beta))
1830 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1831 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1835 // refine_eval() returns the transposition table score if
1836 // possible otherwise falls back on static position evaluation.
1838 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1842 Value v = value_from_tt(tte->value(), ply);
1844 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1845 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1852 // update_history() registers a good move that produced a beta-cutoff
1853 // in history and marks as failures all the other moves of that ply.
1855 void update_history(const Position& pos, Move move, Depth depth,
1856 Move movesSearched[], int moveCount) {
1858 Value bonus = Value(int(depth) * int(depth));
1860 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1862 for (int i = 0; i < moveCount - 1; i++)
1864 m = movesSearched[i];
1868 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1873 // update_gains() updates the gains table of a non-capture move given
1874 // the static position evaluation before and after the move.
1876 void update_gains(const Position& pos, Move m, Value before, Value after) {
1879 && before != VALUE_NONE
1880 && after != VALUE_NONE
1881 && pos.captured_piece_type() == PIECE_TYPE_NONE
1882 && !move_is_special(m))
1883 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1887 // current_search_time() returns the number of milliseconds which have passed
1888 // since the beginning of the current search.
1890 int current_search_time() {
1892 return get_system_time() - SearchStartTime;
1896 // value_to_uci() converts a value to a string suitable for use with the UCI
1897 // protocol specifications:
1899 // cp <x> The score from the engine's point of view in centipawns.
1900 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1901 // use negative values for y.
1903 std::string value_to_uci(Value v) {
1905 std::stringstream s;
1907 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1908 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1910 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2);
1916 // speed_to_uci() returns a string with time stats of current search suitable
1917 // to be sent to UCI gui.
1919 std::string speed_to_uci(int64_t nodes) {
1921 std::stringstream s;
1922 int t = current_search_time();
1924 s << " nodes " << nodes
1925 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1932 // poll() performs two different functions: It polls for user input, and it
1933 // looks at the time consumed so far and decides if it's time to abort the
1936 void poll(const Position& pos) {
1938 static int lastInfoTime;
1939 int t = current_search_time();
1942 if (input_available())
1944 // We are line oriented, don't read single chars
1945 std::string command;
1947 if (!std::getline(std::cin, command) || command == "quit")
1949 // Quit the program as soon as possible
1951 QuitRequest = StopRequest = true;
1954 else if (command == "stop")
1956 // Stop calculating as soon as possible, but still send the "bestmove"
1957 // and possibly the "ponder" token when finishing the search.
1961 else if (command == "ponderhit")
1963 // The opponent has played the expected move. GUI sends "ponderhit" if
1964 // we were told to ponder on the same move the opponent has played. We
1965 // should continue searching but switching from pondering to normal search.
1968 if (StopOnPonderhit)
1973 // Print search information
1977 else if (lastInfoTime > t)
1978 // HACK: Must be a new search where we searched less than
1979 // NodesBetweenPolls nodes during the first second of search.
1982 else if (t - lastInfoTime >= 1000)
1989 if (dbg_show_hit_rate)
1990 dbg_print_hit_rate();
1992 // Send info on searched nodes as soon as we return to root
1993 SendSearchedNodes = true;
1996 // Should we stop the search?
2000 bool stillAtFirstMove = FirstRootMove
2001 && !AspirationFailLow
2002 && t > TimeMgr.available_time();
2004 bool noMoreTime = t > TimeMgr.maximum_time()
2005 || stillAtFirstMove;
2007 if ( (UseTimeManagement && noMoreTime)
2008 || (ExactMaxTime && t >= ExactMaxTime)
2009 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2014 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2015 // while the program is pondering. The point is to work around a wrinkle in
2016 // the UCI protocol: When pondering, the engine is not allowed to give a
2017 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2018 // We simply wait here until one of these commands is sent, and return,
2019 // after which the bestmove and pondermove will be printed.
2021 void wait_for_stop_or_ponderhit() {
2023 std::string command;
2025 // Wait for a command from stdin
2026 while ( std::getline(std::cin, command)
2027 && command != "ponderhit" && command != "stop" && command != "quit") {};
2029 if (command != "ponderhit" && command != "stop")
2030 QuitRequest = true; // Must be "quit" or getline() returned false
2034 // init_thread() is the function which is called when a new thread is
2035 // launched. It simply calls the idle_loop() function with the supplied
2036 // threadID. There are two versions of this function; one for POSIX
2037 // threads and one for Windows threads.
2039 #if !defined(_MSC_VER)
2041 void* init_thread(void* threadID) {
2043 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2049 DWORD WINAPI init_thread(LPVOID threadID) {
2051 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2058 /// The ThreadsManager class
2061 // read_uci_options() updates number of active threads and other internal
2062 // parameters according to the UCI options values. It is called before
2063 // to start a new search.
2065 void ThreadsManager::read_uci_options() {
2067 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2068 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2069 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2070 activeThreads = Options["Threads"].value<int>();
2074 // idle_loop() is where the threads are parked when they have no work to do.
2075 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2076 // object for which the current thread is the master.
2078 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2080 assert(threadID >= 0 && threadID < MAX_THREADS);
2083 bool allFinished = false;
2087 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2088 // master should exit as last one.
2089 if (allThreadsShouldExit)
2092 threads[threadID].state = THREAD_TERMINATED;
2096 // If we are not thinking, wait for a condition to be signaled
2097 // instead of wasting CPU time polling for work.
2098 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2099 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2101 assert(!sp || useSleepingThreads);
2102 assert(threadID != 0 || useSleepingThreads);
2104 if (threads[threadID].state == THREAD_INITIALIZING)
2105 threads[threadID].state = THREAD_AVAILABLE;
2107 // Grab the lock to avoid races with wake_sleeping_thread()
2108 lock_grab(&sleepLock[threadID]);
2110 // If we are master and all slaves have finished do not go to sleep
2111 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2112 allFinished = (i == activeThreads);
2114 if (allFinished || allThreadsShouldExit)
2116 lock_release(&sleepLock[threadID]);
2120 // Do sleep here after retesting sleep conditions
2121 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2122 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2124 lock_release(&sleepLock[threadID]);
2127 // If this thread has been assigned work, launch a search
2128 if (threads[threadID].state == THREAD_WORKISWAITING)
2130 assert(!allThreadsShouldExit);
2132 threads[threadID].state = THREAD_SEARCHING;
2134 // Copy SplitPoint position and search stack and call search()
2135 // with SplitPoint template parameter set to true.
2136 SearchStack ss[PLY_MAX_PLUS_2];
2137 SplitPoint* tsp = threads[threadID].splitPoint;
2138 Position pos(*tsp->pos, threadID);
2140 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2144 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2146 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2148 assert(threads[threadID].state == THREAD_SEARCHING);
2150 threads[threadID].state = THREAD_AVAILABLE;
2152 // Wake up master thread so to allow it to return from the idle loop in
2153 // case we are the last slave of the split point.
2154 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2155 wake_sleeping_thread(tsp->master);
2158 // If this thread is the master of a split point and all slaves have
2159 // finished their work at this split point, return from the idle loop.
2160 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2161 allFinished = (i == activeThreads);
2165 // Because sp->slaves[] is reset under lock protection,
2166 // be sure sp->lock has been released before to return.
2167 lock_grab(&(sp->lock));
2168 lock_release(&(sp->lock));
2170 // In helpful master concept a master can help only a sub-tree, and
2171 // because here is all finished is not possible master is booked.
2172 assert(threads[threadID].state == THREAD_AVAILABLE);
2174 threads[threadID].state = THREAD_SEARCHING;
2181 // init_threads() is called during startup. It launches all helper threads,
2182 // and initializes the split point stack and the global locks and condition
2185 void ThreadsManager::init_threads() {
2187 int i, arg[MAX_THREADS];
2190 // Initialize global locks
2193 for (i = 0; i < MAX_THREADS; i++)
2195 lock_init(&sleepLock[i]);
2196 cond_init(&sleepCond[i]);
2199 // Initialize splitPoints[] locks
2200 for (i = 0; i < MAX_THREADS; i++)
2201 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2202 lock_init(&(threads[i].splitPoints[j].lock));
2204 // Will be set just before program exits to properly end the threads
2205 allThreadsShouldExit = false;
2207 // Threads will be put all threads to sleep as soon as created
2210 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2211 threads[0].state = THREAD_SEARCHING;
2212 for (i = 1; i < MAX_THREADS; i++)
2213 threads[i].state = THREAD_INITIALIZING;
2215 // Launch the helper threads
2216 for (i = 1; i < MAX_THREADS; i++)
2220 #if !defined(_MSC_VER)
2221 pthread_t pthread[1];
2222 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2223 pthread_detach(pthread[0]);
2225 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2229 cout << "Failed to create thread number " << i << endl;
2233 // Wait until the thread has finished launching and is gone to sleep
2234 while (threads[i].state == THREAD_INITIALIZING) {}
2239 // exit_threads() is called when the program exits. It makes all the
2240 // helper threads exit cleanly.
2242 void ThreadsManager::exit_threads() {
2244 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2246 // Wake up all the threads and waits for termination
2247 for (int i = 1; i < MAX_THREADS; i++)
2249 wake_sleeping_thread(i);
2250 while (threads[i].state != THREAD_TERMINATED) {}
2253 // Now we can safely destroy the locks
2254 for (int i = 0; i < MAX_THREADS; i++)
2255 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2256 lock_destroy(&(threads[i].splitPoints[j].lock));
2258 lock_destroy(&mpLock);
2260 // Now we can safely destroy the wait conditions
2261 for (int i = 0; i < MAX_THREADS; i++)
2263 lock_destroy(&sleepLock[i]);
2264 cond_destroy(&sleepCond[i]);
2269 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2270 // the thread's currently active split point, or in some ancestor of
2271 // the current split point.
2273 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2275 assert(threadID >= 0 && threadID < activeThreads);
2277 SplitPoint* sp = threads[threadID].splitPoint;
2279 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2284 // thread_is_available() checks whether the thread with threadID "slave" is
2285 // available to help the thread with threadID "master" at a split point. An
2286 // obvious requirement is that "slave" must be idle. With more than two
2287 // threads, this is not by itself sufficient: If "slave" is the master of
2288 // some active split point, it is only available as a slave to the other
2289 // threads which are busy searching the split point at the top of "slave"'s
2290 // split point stack (the "helpful master concept" in YBWC terminology).
2292 bool ThreadsManager::thread_is_available(int slave, int master) const {
2294 assert(slave >= 0 && slave < activeThreads);
2295 assert(master >= 0 && master < activeThreads);
2296 assert(activeThreads > 1);
2298 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2301 // Make a local copy to be sure doesn't change under our feet
2302 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2304 // No active split points means that the thread is available as
2305 // a slave for any other thread.
2306 if (localActiveSplitPoints == 0 || activeThreads == 2)
2309 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2310 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2311 // could have been set to 0 by another thread leading to an out of bound access.
2312 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2319 // available_thread_exists() tries to find an idle thread which is available as
2320 // a slave for the thread with threadID "master".
2322 bool ThreadsManager::available_thread_exists(int master) const {
2324 assert(master >= 0 && master < activeThreads);
2325 assert(activeThreads > 1);
2327 for (int i = 0; i < activeThreads; i++)
2328 if (thread_is_available(i, master))
2335 // split() does the actual work of distributing the work at a node between
2336 // several available threads. If it does not succeed in splitting the
2337 // node (because no idle threads are available, or because we have no unused
2338 // split point objects), the function immediately returns. If splitting is
2339 // possible, a SplitPoint object is initialized with all the data that must be
2340 // copied to the helper threads and we tell our helper threads that they have
2341 // been assigned work. This will cause them to instantly leave their idle loops and
2342 // call search().When all threads have returned from search() then split() returns.
2344 template <bool Fake>
2345 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2346 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2347 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2348 assert(pos.is_ok());
2349 assert(ply > 0 && ply < PLY_MAX);
2350 assert(*bestValue >= -VALUE_INFINITE);
2351 assert(*bestValue <= *alpha);
2352 assert(*alpha < beta);
2353 assert(beta <= VALUE_INFINITE);
2354 assert(depth > DEPTH_ZERO);
2355 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2356 assert(activeThreads > 1);
2358 int i, master = pos.thread();
2359 Thread& masterThread = threads[master];
2363 // If no other thread is available to help us, or if we have too many
2364 // active split points, don't split.
2365 if ( !available_thread_exists(master)
2366 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2368 lock_release(&mpLock);
2372 // Pick the next available split point object from the split point stack
2373 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2375 // Initialize the split point object
2376 splitPoint.parent = masterThread.splitPoint;
2377 splitPoint.master = master;
2378 splitPoint.betaCutoff = false;
2379 splitPoint.ply = ply;
2380 splitPoint.depth = depth;
2381 splitPoint.threatMove = threatMove;
2382 splitPoint.mateThreat = mateThreat;
2383 splitPoint.alpha = *alpha;
2384 splitPoint.beta = beta;
2385 splitPoint.pvNode = pvNode;
2386 splitPoint.bestValue = *bestValue;
2388 splitPoint.moveCount = moveCount;
2389 splitPoint.pos = &pos;
2390 splitPoint.nodes = 0;
2392 for (i = 0; i < activeThreads; i++)
2393 splitPoint.slaves[i] = 0;
2395 masterThread.splitPoint = &splitPoint;
2397 // If we are here it means we are not available
2398 assert(masterThread.state != THREAD_AVAILABLE);
2400 int workersCnt = 1; // At least the master is included
2402 // Allocate available threads setting state to THREAD_BOOKED
2403 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2404 if (thread_is_available(i, master))
2406 threads[i].state = THREAD_BOOKED;
2407 threads[i].splitPoint = &splitPoint;
2408 splitPoint.slaves[i] = 1;
2412 assert(Fake || workersCnt > 1);
2414 // We can release the lock because slave threads are already booked and master is not available
2415 lock_release(&mpLock);
2417 // Tell the threads that they have work to do. This will make them leave
2419 for (i = 0; i < activeThreads; i++)
2420 if (i == master || splitPoint.slaves[i])
2422 assert(i == master || threads[i].state == THREAD_BOOKED);
2424 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2426 if (useSleepingThreads && i != master)
2427 wake_sleeping_thread(i);
2430 // Everything is set up. The master thread enters the idle loop, from
2431 // which it will instantly launch a search, because its state is
2432 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2433 // idle loop, which means that the main thread will return from the idle
2434 // loop when all threads have finished their work at this split point.
2435 idle_loop(master, &splitPoint);
2437 // We have returned from the idle loop, which means that all threads are
2438 // finished. Update alpha and bestValue, and return.
2441 *alpha = splitPoint.alpha;
2442 *bestValue = splitPoint.bestValue;
2443 masterThread.activeSplitPoints--;
2444 masterThread.splitPoint = splitPoint.parent;
2445 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2447 lock_release(&mpLock);
2451 // wake_sleeping_thread() wakes up the thread with the given threadID
2452 // when it is time to start a new search.
2454 void ThreadsManager::wake_sleeping_thread(int threadID) {
2456 lock_grab(&sleepLock[threadID]);
2457 cond_signal(&sleepCond[threadID]);
2458 lock_release(&sleepLock[threadID]);
2462 /// RootMove and RootMoveList method's definitions
2464 RootMove::RootMove() {
2467 pv_score = non_pv_score = -VALUE_INFINITE;
2471 RootMove& RootMove::operator=(const RootMove& rm) {
2473 const Move* src = rm.pv;
2476 // Avoid a costly full rm.pv[] copy
2477 do *dst++ = *src; while (*src++ != MOVE_NONE);
2480 pv_score = rm.pv_score;
2481 non_pv_score = rm.non_pv_score;
2485 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2486 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2487 // allow to always have a ponder move even when we fail high at root and also a
2488 // long PV to print that is important for position analysis.
2490 void RootMove::extract_pv_from_tt(Position& pos) {
2492 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2496 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2498 pos.do_move(pv[0], *st++);
2500 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2501 && tte->move() != MOVE_NONE
2502 && move_is_legal(pos, tte->move())
2504 && (!pos.is_draw() || ply < 2))
2506 pv[ply] = tte->move();
2507 pos.do_move(pv[ply++], *st++);
2509 pv[ply] = MOVE_NONE;
2511 do pos.undo_move(pv[--ply]); while (ply);
2514 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2515 // the PV back into the TT. This makes sure the old PV moves are searched
2516 // first, even if the old TT entries have been overwritten.
2518 void RootMove::insert_pv_in_tt(Position& pos) {
2520 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2523 Value v, m = VALUE_NONE;
2526 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2530 tte = TT.retrieve(k);
2532 // Don't overwrite existing correct entries
2533 if (!tte || tte->move() != pv[ply])
2535 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2536 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2538 pos.do_move(pv[ply], *st++);
2540 } while (pv[++ply] != MOVE_NONE);
2542 do pos.undo_move(pv[--ply]); while (ply);
2545 // pv_info_to_uci() returns a string with information on the current PV line
2546 // formatted according to UCI specification. It is called at each iteration
2547 // or after a new pv is found.
2549 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
2551 std::stringstream s, l;
2554 while (*m != MOVE_NONE)
2557 s << "info depth " << depth
2558 << " seldepth " << int(m - pv)
2559 << " multipv " << pvLine + 1
2560 << " score " << value_to_uci(pv_score)
2561 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2562 << speed_to_uci(pos.nodes_searched())
2563 << " pv " << l.str();
2569 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2571 MoveStack mlist[MOVES_MAX];
2575 bestMoveChanges = 0;
2577 // Generate all legal moves and add them to RootMoveList
2578 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2579 for (MoveStack* cur = mlist; cur != last; cur++)
2581 // If we have a searchMoves[] list then verify cur->move
2582 // is in the list before to add it.
2583 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2585 if (searchMoves[0] && *sm != cur->move)
2589 rm.pv[0] = cur->move;
2590 rm.pv[1] = MOVE_NONE;
2591 rm.pv_score = -VALUE_INFINITE;