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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // Fast lookup table of sliding pieces indexed by Piece
63 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
64 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
66 // ThreadsManager class is used to handle all the threads related stuff in search,
67 // init, starting, parking and, the most important, launching a slave thread at a
68 // split point are what this class does. All the access to shared thread data is
69 // done through this class, so that we avoid using global variables instead.
71 class ThreadsManager {
72 /* As long as the single ThreadsManager object is defined as a global we don't
73 need to explicitly initialize to zero its data members because variables with
74 static storage duration are automatically set to zero before enter main()
80 int active_threads() const { return ActiveThreads; }
81 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
83 bool available_thread_exists(int master) const;
84 bool thread_is_available(int slave, int master) const;
85 bool thread_should_stop(int threadID) const;
86 void wake_sleeping_thread(int threadID);
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
95 volatile bool AllThreadsShouldExit;
96 Thread threads[MAX_THREADS];
98 WaitCondition WaitCond[MAX_THREADS];
102 // RootMove struct is used for moves at the root at the tree. For each
103 // root move, we store a score, a node count, and a PV (really a refutation
104 // in the case of moves which fail low).
108 RootMove() : mp_score(0), nodes(0) {}
110 // RootMove::operator<() is the comparison function used when
111 // sorting the moves. A move m1 is considered to be better
112 // than a move m2 if it has a higher score, or if the moves
113 // have equal score but m1 has the higher beta cut-off count.
114 bool operator<(const RootMove& m) const {
116 return score != m.score ? score < m.score : mp_score <= m.mp_score;
123 Move pv[PLY_MAX_PLUS_2];
127 // The RootMoveList class is essentially an array of RootMove objects, with
128 // a handful of methods for accessing the data in the individual moves.
133 RootMoveList(Position& pos, Move searchMoves[]);
135 Move move(int moveNum) const { return moves[moveNum].move; }
136 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
137 int move_count() const { return count; }
138 Value move_score(int moveNum) const { return moves[moveNum].score; }
139 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
140 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
141 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
143 void set_move_pv(int moveNum, const Move pv[]);
144 void score_moves(const Position& pos);
146 void sort_multipv(int n);
149 RootMove moves[MOVES_MAX];
154 // When formatting a move for std::cout we must know if we are in Chess960
155 // or not. To keep using the handy operator<<() on the move the trick is to
156 // embed this flag in the stream itself. Function-like named enum set960 is
157 // used as a custom manipulator and the stream internal general-purpose array,
158 // accessed through ios_base::iword(), is used to pass the flag to the move's
159 // operator<<() that will use it to properly format castling moves.
162 std::ostream& operator<< (std::ostream& os, const set960& m) {
164 os.iword(0) = int(m);
173 // Maximum depth for razoring
174 const Depth RazorDepth = 4 * ONE_PLY;
176 // Dynamic razoring margin based on depth
177 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
179 // Maximum depth for use of dynamic threat detection when null move fails low
180 const Depth ThreatDepth = 5 * ONE_PLY;
182 // Step 9. Internal iterative deepening
184 // Minimum depth for use of internal iterative deepening
185 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
187 // At Non-PV nodes we do an internal iterative deepening search
188 // when the static evaluation is bigger then beta - IIDMargin.
189 const Value IIDMargin = Value(0x100);
191 // Step 11. Decide the new search depth
193 // Extensions. Configurable UCI options
194 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
195 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
196 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
198 // Minimum depth for use of singular extension
199 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
201 // If the TT move is at least SingularExtensionMargin better then the
202 // remaining ones we will extend it.
203 const Value SingularExtensionMargin = Value(0x20);
205 // Step 12. Futility pruning
207 // Futility margin for quiescence search
208 const Value FutilityMarginQS = Value(0x80);
210 // Futility lookup tables (initialized at startup) and their getter functions
211 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
212 int FutilityMoveCountArray[32]; // [depth]
214 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
215 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
217 // Step 14. Reduced search
219 // Reduction lookup tables (initialized at startup) and their getter functions
220 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
222 template <NodeType PV>
223 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = ONE_PLY;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
235 /// Namespace variables
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
266 bool UseSleepingMaster;
267 ThreadsManager ThreadsMgr;
269 // Node counters, used only by thread[0] but try to keep in different cache
270 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
272 int NodesBetweenPolls = 30000;
279 Value id_loop(Position& pos, Move searchMoves[]);
280 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
282 template <NodeType PvNode, bool SpNode>
283 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
285 template <NodeType PvNode>
286 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
288 template <NodeType PvNode>
289 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
291 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
292 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 Value value_to_tt(Value v, int ply);
301 Value value_from_tt(Value v, int ply);
302 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
303 bool connected_threat(const Position& pos, Move m, Move threat);
304 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
305 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
306 void update_killers(Move m, SearchStack* ss);
307 void update_gains(const Position& pos, Move move, Value before, Value after);
309 int current_search_time();
310 std::string value_to_uci(Value v);
311 int nps(const Position& pos);
312 void poll(const Position& pos);
314 void wait_for_stop_or_ponderhit();
315 void init_ss_array(SearchStack* ss, int size);
316 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
317 void insert_pv_in_tt(const Position& pos, Move pv[]);
318 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
320 #if !defined(_MSC_VER)
321 void* init_thread(void* threadID);
323 DWORD WINAPI init_thread(LPVOID threadID);
333 /// init_threads(), exit_threads() and nodes_searched() are helpers to
334 /// give accessibility to some TM methods from outside of current file.
336 void init_threads() { ThreadsMgr.init_threads(); }
337 void exit_threads() { ThreadsMgr.exit_threads(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (ONE_PLY == 2)
345 int hd; // half depth (ONE_PLY == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
352 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
357 // Init futility margins array
358 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
367 /// perft() is our utility to verify move generation is bug free. All the legal
368 /// moves up to given depth are generated and counted and the sum returned.
370 int perft(Position& pos, Depth depth)
372 MoveStack mlist[MOVES_MAX];
377 // Generate all legal moves
378 MoveStack* last = generate_moves(pos, mlist);
380 // If we are at the last ply we don't need to do and undo
381 // the moves, just to count them.
382 if (depth <= ONE_PLY)
383 return int(last - mlist);
385 // Loop through all legal moves
387 for (MoveStack* cur = mlist; cur != last; cur++)
390 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
391 sum += perft(pos, depth - ONE_PLY);
398 /// think() is the external interface to Stockfish's search, and is called when
399 /// the program receives the UCI 'go' command. It initializes various
400 /// search-related global variables, and calls root_search(). It returns false
401 /// when a quit command is received during the search.
403 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
404 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
406 // Initialize global search variables
407 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
409 SearchStartTime = get_system_time();
410 ExactMaxTime = maxTime;
413 InfiniteSearch = infinite;
414 PonderSearch = ponder;
415 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
417 // Look for a book move, only during games, not tests
418 if (UseTimeManagement && Options["OwnBook"].value<bool>())
420 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
421 OpeningBook.open(Options["Book File"].value<std::string>());
423 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
434 // Read UCI option values
435 TT.set_size(Options["Hash"].value<int>());
436 if (Options["Clear Hash"].value<bool>())
438 Options["Clear Hash"].set_value("false");
442 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
443 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
444 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
445 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
446 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
447 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
448 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
449 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
450 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
451 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
452 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
453 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
455 MinimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
456 MaxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
457 MultiPV = Options["MultiPV"].value<int>();
458 UseLogFile = Options["Use Search Log"].value<bool>();
459 UseSleepingMaster = Options["Use Sleeping Master"].value<bool>();
462 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
464 read_weights(pos.side_to_move());
466 // Set the number of active threads
467 int newActiveThreads = Options["Threads"].value<int>();
468 if (newActiveThreads != ThreadsMgr.active_threads())
470 ThreadsMgr.set_active_threads(newActiveThreads);
471 init_eval(ThreadsMgr.active_threads());
475 int myTime = time[pos.side_to_move()];
476 int myIncrement = increment[pos.side_to_move()];
477 if (UseTimeManagement)
478 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
480 // Set best NodesBetweenPolls interval to avoid lagging under
481 // heavy time pressure.
483 NodesBetweenPolls = Min(MaxNodes, 30000);
484 else if (myTime && myTime < 1000)
485 NodesBetweenPolls = 1000;
486 else if (myTime && myTime < 5000)
487 NodesBetweenPolls = 5000;
489 NodesBetweenPolls = 30000;
491 // Write search information to log file
493 LogFile << "Searching: " << pos.to_fen() << endl
494 << "infinite: " << infinite
495 << " ponder: " << ponder
496 << " time: " << myTime
497 << " increment: " << myIncrement
498 << " moves to go: " << movesToGo << endl;
500 // We're ready to start thinking. Call the iterative deepening loop function
501 id_loop(pos, searchMoves);
512 // id_loop() is the main iterative deepening loop. It calls root_search
513 // repeatedly with increasing depth until the allocated thinking time has
514 // been consumed, the user stops the search, or the maximum search depth is
517 Value id_loop(Position& pos, Move searchMoves[]) {
519 SearchStack ss[PLY_MAX_PLUS_2];
520 Move pv[PLY_MAX_PLUS_2];
521 Move EasyMove = MOVE_NONE;
522 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
524 // Moves to search are verified, copied, scored and sorted
525 RootMoveList rml(pos, searchMoves);
527 // Handle special case of searching on a mate/stale position
528 if (rml.move_count() == 0)
531 wait_for_stop_or_ponderhit();
533 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
536 // Print RootMoveList startup scoring to the standard output,
537 // so to output information also for iteration 1.
538 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
539 << "info depth " << 1
540 << "\ninfo depth " << 1
541 << " score " << value_to_uci(rml.move_score(0))
542 << " time " << current_search_time()
543 << " nodes " << pos.nodes_searched()
544 << " nps " << nps(pos)
545 << " pv " << rml.move(0) << "\n";
550 init_ss_array(ss, PLY_MAX_PLUS_2);
551 pv[0] = pv[1] = MOVE_NONE;
552 ValueByIteration[1] = rml.move_score(0);
555 // Is one move significantly better than others after initial scoring ?
556 if ( rml.move_count() == 1
557 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
558 EasyMove = rml.move(0);
560 // Iterative deepening loop
561 while (Iteration < PLY_MAX)
563 // Initialize iteration
565 BestMoveChangesByIteration[Iteration] = 0;
567 cout << "info depth " << Iteration << endl;
569 // Calculate dynamic aspiration window based on previous iterations
570 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
572 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
573 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
575 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
576 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
578 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
579 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
582 // Search to the current depth, rml is updated and sorted, alpha and beta could change
583 value = root_search(pos, ss, pv, rml, &alpha, &beta);
585 // Write PV to transposition table, in case the relevant entries have
586 // been overwritten during the search.
587 insert_pv_in_tt(pos, pv);
590 break; // Value cannot be trusted. Break out immediately!
592 //Save info about search result
593 ValueByIteration[Iteration] = value;
595 // Drop the easy move if differs from the new best move
596 if (pv[0] != EasyMove)
597 EasyMove = MOVE_NONE;
599 if (UseTimeManagement)
602 bool stopSearch = false;
604 // Stop search early if there is only a single legal move,
605 // we search up to Iteration 6 anyway to get a proper score.
606 if (Iteration >= 6 && rml.move_count() == 1)
609 // Stop search early when the last two iterations returned a mate score
611 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
612 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
615 // Stop search early if one move seems to be much better than the others
618 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
619 && current_search_time() > TimeMgr.available_time() / 16)
620 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
621 && current_search_time() > TimeMgr.available_time() / 32)))
624 // Add some extra time if the best move has changed during the last two iterations
625 if (Iteration > 5 && Iteration <= 50)
626 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
627 BestMoveChangesByIteration[Iteration-1]);
629 // Stop search if most of MaxSearchTime is consumed at the end of the
630 // iteration. We probably don't have enough time to search the first
631 // move at the next iteration anyway.
632 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
638 StopOnPonderhit = true;
644 if (MaxDepth && Iteration >= MaxDepth)
648 // If we are pondering or in infinite search, we shouldn't print the
649 // best move before we are told to do so.
650 if (!AbortSearch && (PonderSearch || InfiniteSearch))
651 wait_for_stop_or_ponderhit();
653 // Print final search statistics
654 cout << "info nodes " << pos.nodes_searched()
655 << " nps " << nps(pos)
656 << " time " << current_search_time() << endl;
658 // Print the best move and the ponder move to the standard output
659 if (pv[0] == MOVE_NONE)
665 assert(pv[0] != MOVE_NONE);
667 cout << "bestmove " << pv[0];
669 if (pv[1] != MOVE_NONE)
670 cout << " ponder " << pv[1];
677 dbg_print_mean(LogFile);
679 if (dbg_show_hit_rate)
680 dbg_print_hit_rate(LogFile);
682 LogFile << "\nNodes: " << pos.nodes_searched()
683 << "\nNodes/second: " << nps(pos)
684 << "\nBest move: " << move_to_san(pos, pv[0]);
687 pos.do_move(pv[0], st);
688 LogFile << "\nPonder move: "
689 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
692 return rml.move_score(0);
696 // root_search() is the function which searches the root node. It is
697 // similar to search_pv except that it uses a different move ordering
698 // scheme, prints some information to the standard output and handles
699 // the fail low/high loops.
701 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
707 Depth depth, ext, newDepth;
708 Value value, alpha, beta;
709 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
710 int researchCountFH, researchCountFL;
712 researchCountFH = researchCountFL = 0;
715 isCheck = pos.is_check();
716 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
718 // Step 1. Initialize node (polling is omitted at root)
719 ss->currentMove = ss->bestMove = MOVE_NONE;
721 // Step 2. Check for aborted search (omitted at root)
722 // Step 3. Mate distance pruning (omitted at root)
723 // Step 4. Transposition table lookup (omitted at root)
725 // Step 5. Evaluate the position statically
726 // At root we do this only to get reference value for child nodes
727 ss->evalMargin = VALUE_NONE;
728 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
730 // Step 6. Razoring (omitted at root)
731 // Step 7. Static null move pruning (omitted at root)
732 // Step 8. Null move search with verification search (omitted at root)
733 // Step 9. Internal iterative deepening (omitted at root)
735 // Step extra. Fail low loop
736 // We start with small aspiration window and in case of fail low, we research
737 // with bigger window until we are not failing low anymore.
740 // Sort the moves before to (re)search
741 rml.score_moves(pos);
744 // Step 10. Loop through all moves in the root move list
745 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
747 // This is used by time management
748 FirstRootMove = (i == 0);
750 // Save the current node count before the move is searched
751 nodes = pos.nodes_searched();
753 // Pick the next root move, and print the move and the move number to
754 // the standard output.
755 move = ss->currentMove = rml.move(i);
757 if (current_search_time() >= 1000)
758 cout << "info currmove " << move
759 << " currmovenumber " << i + 1 << endl;
761 moveIsCheck = pos.move_is_check(move);
762 captureOrPromotion = pos.move_is_capture_or_promotion(move);
764 // Step 11. Decide the new search depth
765 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
766 newDepth = depth + ext;
768 // Step 12. Futility pruning (omitted at root)
770 // Step extra. Fail high loop
771 // If move fails high, we research with bigger window until we are not failing
773 value = - VALUE_INFINITE;
777 // Step 13. Make the move
778 pos.do_move(move, st, ci, moveIsCheck);
780 // Step extra. pv search
781 // We do pv search for first moves (i < MultiPV)
782 // and for fail high research (value > alpha)
783 if (i < MultiPV || value > alpha)
785 // Aspiration window is disabled in multi-pv case
787 alpha = -VALUE_INFINITE;
789 // Full depth PV search, done on first move or after a fail high
790 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
794 // Step 14. Reduced search
795 // if the move fails high will be re-searched at full depth
796 bool doFullDepthSearch = true;
798 if ( depth >= 3 * ONE_PLY
800 && !captureOrPromotion
801 && !move_is_castle(move))
803 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
806 assert(newDepth-ss->reduction >= ONE_PLY);
808 // Reduced depth non-pv search using alpha as upperbound
809 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
810 doFullDepthSearch = (value > alpha);
813 // The move failed high, but if reduction is very big we could
814 // face a false positive, retry with a less aggressive reduction,
815 // if the move fails high again then go with full depth search.
816 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
818 assert(newDepth - ONE_PLY >= ONE_PLY);
820 ss->reduction = ONE_PLY;
821 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
822 doFullDepthSearch = (value > alpha);
824 ss->reduction = DEPTH_ZERO; // Restore original reduction
827 // Step 15. Full depth search
828 if (doFullDepthSearch)
830 // Full depth non-pv search using alpha as upperbound
831 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
833 // If we are above alpha then research at same depth but as PV
834 // to get a correct score or eventually a fail high above beta.
836 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
840 // Step 16. Undo move
843 // Can we exit fail high loop ?
844 if (AbortSearch || value < beta)
847 // We are failing high and going to do a research. It's important to update
848 // the score before research in case we run out of time while researching.
849 rml.set_move_score(i, value);
851 extract_pv_from_tt(pos, move, pv);
852 rml.set_move_pv(i, pv);
854 // Print information to the standard output
855 print_pv_info(pos, pv, alpha, beta, value);
857 // Prepare for a research after a fail high, each time with a wider window
858 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
861 } // End of fail high loop
863 // Finished searching the move. If AbortSearch is true, the search
864 // was aborted because the user interrupted the search or because we
865 // ran out of time. In this case, the return value of the search cannot
866 // be trusted, and we break out of the loop without updating the best
871 // Remember searched nodes counts for this move
872 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
874 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
875 assert(value < beta);
877 // Step 17. Check for new best move
878 if (value <= alpha && i >= MultiPV)
879 rml.set_move_score(i, -VALUE_INFINITE);
882 // PV move or new best move!
885 rml.set_move_score(i, value);
887 extract_pv_from_tt(pos, move, pv);
888 rml.set_move_pv(i, pv);
892 // We record how often the best move has been changed in each
893 // iteration. This information is used for time managment: When
894 // the best move changes frequently, we allocate some more time.
896 BestMoveChangesByIteration[Iteration]++;
898 // Print information to the standard output
899 print_pv_info(pos, pv, alpha, beta, value);
901 // Raise alpha to setup proper non-pv search upper bound
908 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
910 cout << "info multipv " << j + 1
911 << " score " << value_to_uci(rml.move_score(j))
912 << " depth " << (j <= i ? Iteration : Iteration - 1)
913 << " time " << current_search_time()
914 << " nodes " << pos.nodes_searched()
915 << " nps " << nps(pos)
918 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
919 cout << rml.move_pv(j, k) << " ";
923 alpha = rml.move_score(Min(i, MultiPV - 1));
925 } // PV move or new best move
927 assert(alpha >= *alphaPtr);
929 AspirationFailLow = (alpha == *alphaPtr);
931 if (AspirationFailLow && StopOnPonderhit)
932 StopOnPonderhit = false;
935 // Can we exit fail low loop ?
936 if (AbortSearch || !AspirationFailLow)
939 // Prepare for a research after a fail low, each time with a wider window
940 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
945 // Sort the moves before to return
952 // search<>() is the main search function for both PV and non-PV nodes and for
953 // normal and SplitPoint nodes. When called just after a split point the search
954 // is simpler because we have already probed the hash table, done a null move
955 // search, and searched the first move before splitting, we don't have to repeat
956 // all this work again. We also don't need to store anything to the hash table
957 // here: This is taken care of after we return from the split point.
959 template <NodeType PvNode, bool SpNode>
960 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
962 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
963 assert(beta > alpha && beta <= VALUE_INFINITE);
964 assert(PvNode || alpha == beta - 1);
965 assert(ply > 0 && ply < PLY_MAX);
966 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
968 Move movesSearched[MOVES_MAX];
972 Move ttMove, move, excludedMove, threatMove;
975 Value bestValue, value, oldAlpha;
976 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
977 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
978 bool mateThreat = false;
980 int threadID = pos.thread();
981 SplitPoint* sp = NULL;
982 refinedValue = bestValue = value = -VALUE_INFINITE;
984 isCheck = pos.is_check();
990 ttMove = excludedMove = MOVE_NONE;
991 threatMove = sp->threatMove;
992 mateThreat = sp->mateThreat;
993 goto split_point_start;
994 } else {} // Hack to fix icc's "statement is unreachable" warning
996 // Step 1. Initialize node and poll. Polling can abort search
997 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
998 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1000 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1006 // Step 2. Check for aborted search and immediate draw
1007 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1008 || pos.is_draw() || ply >= PLY_MAX - 1)
1011 // Step 3. Mate distance pruning
1012 alpha = Max(value_mated_in(ply), alpha);
1013 beta = Min(value_mate_in(ply+1), beta);
1017 // Step 4. Transposition table lookup
1019 // We don't want the score of a partial search to overwrite a previous full search
1020 // TT value, so we use a different position key in case of an excluded move exists.
1021 excludedMove = ss->excludedMove;
1022 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1024 tte = TT.retrieve(posKey);
1025 ttMove = tte ? tte->move() : MOVE_NONE;
1027 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1028 // This is to avoid problems in the following areas:
1030 // * Repetition draw detection
1031 // * Fifty move rule detection
1032 // * Searching for a mate
1033 // * Printing of full PV line
1034 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1037 ss->bestMove = ttMove; // Can be MOVE_NONE
1038 return value_from_tt(tte->value(), ply);
1041 // Step 5. Evaluate the position statically and
1042 // update gain statistics of parent move.
1044 ss->eval = ss->evalMargin = VALUE_NONE;
1047 assert(tte->static_value() != VALUE_NONE);
1049 ss->eval = tte->static_value();
1050 ss->evalMargin = tte->static_value_margin();
1051 refinedValue = refine_eval(tte, ss->eval, ply);
1055 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1056 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1059 // Save gain for the parent non-capture move
1060 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1062 // Step 6. Razoring (is omitted in PV nodes)
1064 && depth < RazorDepth
1066 && refinedValue < beta - razor_margin(depth)
1067 && ttMove == MOVE_NONE
1068 && (ss-1)->currentMove != MOVE_NULL
1069 && !value_is_mate(beta)
1070 && !pos.has_pawn_on_7th(pos.side_to_move()))
1072 Value rbeta = beta - razor_margin(depth);
1073 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1075 // Logically we should return (v + razor_margin(depth)), but
1076 // surprisingly this did slightly weaker in tests.
1080 // Step 7. Static null move pruning (is omitted in PV nodes)
1081 // We're betting that the opponent doesn't have a move that will reduce
1082 // the score by more than futility_margin(depth) if we do a null move.
1084 && !ss->skipNullMove
1085 && depth < RazorDepth
1087 && refinedValue >= beta + futility_margin(depth, 0)
1088 && !value_is_mate(beta)
1089 && pos.non_pawn_material(pos.side_to_move()))
1090 return refinedValue - futility_margin(depth, 0);
1092 // Step 8. Null move search with verification search (is omitted in PV nodes)
1094 && !ss->skipNullMove
1097 && refinedValue >= beta
1098 && !value_is_mate(beta)
1099 && pos.non_pawn_material(pos.side_to_move()))
1101 ss->currentMove = MOVE_NULL;
1103 // Null move dynamic reduction based on depth
1104 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1106 // Null move dynamic reduction based on value
1107 if (refinedValue - beta > PawnValueMidgame)
1110 pos.do_null_move(st);
1111 (ss+1)->skipNullMove = true;
1112 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1113 (ss+1)->skipNullMove = false;
1114 pos.undo_null_move();
1116 if (nullValue >= beta)
1118 // Do not return unproven mate scores
1119 if (nullValue >= value_mate_in(PLY_MAX))
1122 if (depth < 6 * ONE_PLY)
1125 // Do verification search at high depths
1126 ss->skipNullMove = true;
1127 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1128 ss->skipNullMove = false;
1135 // The null move failed low, which means that we may be faced with
1136 // some kind of threat. If the previous move was reduced, check if
1137 // the move that refuted the null move was somehow connected to the
1138 // move which was reduced. If a connection is found, return a fail
1139 // low score (which will cause the reduced move to fail high in the
1140 // parent node, which will trigger a re-search with full depth).
1141 if (nullValue == value_mated_in(ply + 2))
1144 threatMove = (ss+1)->bestMove;
1145 if ( depth < ThreatDepth
1146 && (ss-1)->reduction
1147 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1152 // Step 9. Internal iterative deepening
1153 if ( depth >= IIDDepth[PvNode]
1154 && ttMove == MOVE_NONE
1155 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1157 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1159 ss->skipNullMove = true;
1160 search<PvNode>(pos, ss, alpha, beta, d, ply);
1161 ss->skipNullMove = false;
1163 ttMove = ss->bestMove;
1164 tte = TT.retrieve(posKey);
1167 // Expensive mate threat detection (only for PV nodes)
1169 mateThreat = pos.has_mate_threat();
1171 split_point_start: // At split points actual search starts from here
1173 // Initialize a MovePicker object for the current position
1174 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1175 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1176 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1178 ss->bestMove = MOVE_NONE;
1179 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1180 futilityBase = ss->eval + ss->evalMargin;
1181 singularExtensionNode = !SpNode
1182 && depth >= SingularExtensionDepth[PvNode]
1185 && !excludedMove // Do not allow recursive singular extension search
1186 && (tte->type() & VALUE_TYPE_LOWER)
1187 && tte->depth() >= depth - 3 * ONE_PLY;
1190 lock_grab(&(sp->lock));
1191 bestValue = sp->bestValue;
1194 // Step 10. Loop through moves
1195 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1196 while ( bestValue < beta
1197 && (move = mp.get_next_move()) != MOVE_NONE
1198 && !ThreadsMgr.thread_should_stop(threadID))
1200 assert(move_is_ok(move));
1204 moveCount = ++sp->moveCount;
1205 lock_release(&(sp->lock));
1207 else if (move == excludedMove)
1210 movesSearched[moveCount++] = move;
1212 moveIsCheck = pos.move_is_check(move, ci);
1213 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1215 // Step 11. Decide the new search depth
1216 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1218 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1219 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1220 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1221 // lower then ttValue minus a margin then we extend ttMove.
1222 if ( singularExtensionNode
1223 && move == tte->move()
1226 Value ttValue = value_from_tt(tte->value(), ply);
1228 if (abs(ttValue) < VALUE_KNOWN_WIN)
1230 Value b = ttValue - SingularExtensionMargin;
1231 ss->excludedMove = move;
1232 ss->skipNullMove = true;
1233 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1234 ss->skipNullMove = false;
1235 ss->excludedMove = MOVE_NONE;
1236 ss->bestMove = MOVE_NONE;
1242 // Update current move (this must be done after singular extension search)
1243 ss->currentMove = move;
1244 newDepth = depth - ONE_PLY + ext;
1246 // Step 12. Futility pruning (is omitted in PV nodes)
1248 && !captureOrPromotion
1252 && !move_is_castle(move))
1254 // Move count based pruning
1255 if ( moveCount >= futility_move_count(depth)
1256 && !(threatMove && connected_threat(pos, move, threatMove))
1257 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1260 lock_grab(&(sp->lock));
1265 // Value based pruning
1266 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1267 // but fixing this made program slightly weaker.
1268 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1269 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1270 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1272 if (futilityValueScaled < beta)
1276 lock_grab(&(sp->lock));
1277 if (futilityValueScaled > sp->bestValue)
1278 sp->bestValue = bestValue = futilityValueScaled;
1280 else if (futilityValueScaled > bestValue)
1281 bestValue = futilityValueScaled;
1287 // Step 13. Make the move
1288 pos.do_move(move, st, ci, moveIsCheck);
1290 // Step extra. pv search (only in PV nodes)
1291 // The first move in list is the expected PV
1292 if (!SpNode && PvNode && moveCount == 1)
1293 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1296 // Step 14. Reduced depth search
1297 // If the move fails high will be re-searched at full depth.
1298 bool doFullDepthSearch = true;
1300 if ( depth >= 3 * ONE_PLY
1301 && !captureOrPromotion
1303 && !move_is_castle(move)
1304 && !(ss->killers[0] == move || ss->killers[1] == move))
1306 ss->reduction = reduction<PvNode>(depth, moveCount);
1309 alpha = SpNode ? sp->alpha : alpha;
1310 Depth d = newDepth - ss->reduction;
1311 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1313 doFullDepthSearch = (value > alpha);
1316 // The move failed high, but if reduction is very big we could
1317 // face a false positive, retry with a less aggressive reduction,
1318 // if the move fails high again then go with full depth search.
1319 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1321 assert(newDepth - ONE_PLY >= ONE_PLY);
1323 ss->reduction = ONE_PLY;
1324 alpha = SpNode ? sp->alpha : alpha;
1325 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1326 doFullDepthSearch = (value > alpha);
1328 ss->reduction = DEPTH_ZERO; // Restore original reduction
1331 // Step 15. Full depth search
1332 if (doFullDepthSearch)
1334 alpha = SpNode ? sp->alpha : alpha;
1335 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1337 // Step extra. pv search (only in PV nodes)
1338 // Search only for possible new PV nodes, if instead value >= beta then
1339 // parent node fails low with value <= alpha and tries another move.
1340 if (PvNode && value > alpha && value < beta)
1341 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1345 // Step 16. Undo move
1346 pos.undo_move(move);
1348 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1350 // Step 17. Check for new best move
1353 lock_grab(&(sp->lock));
1354 bestValue = sp->bestValue;
1358 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1363 sp->bestValue = value;
1367 if (SpNode && (!PvNode || value >= beta))
1368 sp->stopRequest = true;
1370 if (PvNode && value < beta) // We want always alpha < beta
1377 if (value == value_mate_in(ply + 1))
1378 ss->mateKiller = move;
1380 ss->bestMove = move;
1383 sp->parentSstack->bestMove = move;
1387 // Step 18. Check for split
1389 && depth >= MinimumSplitDepth
1390 && ThreadsMgr.active_threads() > 1
1392 && ThreadsMgr.available_thread_exists(threadID)
1394 && !ThreadsMgr.thread_should_stop(threadID)
1396 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1397 threatMove, mateThreat, moveCount, &mp, PvNode);
1400 // Step 19. Check for mate and stalemate
1401 // All legal moves have been searched and if there are
1402 // no legal moves, it must be mate or stalemate.
1403 // If one move was excluded return fail low score.
1404 if (!SpNode && !moveCount)
1405 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1407 // Step 20. Update tables
1408 // If the search is not aborted, update the transposition table,
1409 // history counters, and killer moves.
1410 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1412 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1413 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1414 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1416 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1418 // Update killers and history only for non capture moves that fails high
1419 if ( bestValue >= beta
1420 && !pos.move_is_capture_or_promotion(move))
1422 update_history(pos, move, depth, movesSearched, moveCount);
1423 update_killers(move, ss);
1429 // Here we have the lock still grabbed
1430 sp->slaves[threadID] = 0;
1431 sp->nodes += pos.nodes_searched();
1432 lock_release(&(sp->lock));
1435 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1441 // qsearch() is the quiescence search function, which is called by the main
1442 // search function when the remaining depth is zero (or, to be more precise,
1443 // less than ONE_PLY).
1445 template <NodeType PvNode>
1446 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1448 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1449 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1450 assert(PvNode || alpha == beta - 1);
1452 assert(ply > 0 && ply < PLY_MAX);
1453 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1457 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1458 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1460 Value oldAlpha = alpha;
1462 ss->bestMove = ss->currentMove = MOVE_NONE;
1464 // Check for an instant draw or maximum ply reached
1465 if (pos.is_draw() || ply >= PLY_MAX - 1)
1468 // Transposition table lookup. At PV nodes, we don't use the TT for
1469 // pruning, but only for move ordering.
1470 tte = TT.retrieve(pos.get_key());
1471 ttMove = (tte ? tte->move() : MOVE_NONE);
1473 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1475 ss->bestMove = ttMove; // Can be MOVE_NONE
1476 return value_from_tt(tte->value(), ply);
1479 isCheck = pos.is_check();
1481 // Evaluate the position statically
1484 bestValue = futilityBase = -VALUE_INFINITE;
1485 ss->eval = evalMargin = VALUE_NONE;
1486 deepChecks = enoughMaterial = false;
1492 assert(tte->static_value() != VALUE_NONE);
1494 evalMargin = tte->static_value_margin();
1495 ss->eval = bestValue = tte->static_value();
1498 ss->eval = bestValue = evaluate(pos, evalMargin);
1500 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1502 // Stand pat. Return immediately if static value is at least beta
1503 if (bestValue >= beta)
1506 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1511 if (PvNode && bestValue > alpha)
1514 // If we are near beta then try to get a cutoff pushing checks a bit further
1515 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1517 // Futility pruning parameters, not needed when in check
1518 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1519 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1522 // Initialize a MovePicker object for the current position, and prepare
1523 // to search the moves. Because the depth is <= 0 here, only captures,
1524 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1525 // and we are near beta) will be generated.
1526 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1529 // Loop through the moves until no moves remain or a beta cutoff occurs
1530 while ( alpha < beta
1531 && (move = mp.get_next_move()) != MOVE_NONE)
1533 assert(move_is_ok(move));
1535 moveIsCheck = pos.move_is_check(move, ci);
1543 && !move_is_promotion(move)
1544 && !pos.move_is_passed_pawn_push(move))
1546 futilityValue = futilityBase
1547 + pos.endgame_value_of_piece_on(move_to(move))
1548 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1550 if (futilityValue < alpha)
1552 if (futilityValue > bestValue)
1553 bestValue = futilityValue;
1558 // Detect non-capture evasions that are candidate to be pruned
1559 evasionPrunable = isCheck
1560 && bestValue > value_mated_in(PLY_MAX)
1561 && !pos.move_is_capture(move)
1562 && !pos.can_castle(pos.side_to_move());
1564 // Don't search moves with negative SEE values
1566 && (!isCheck || evasionPrunable)
1568 && !move_is_promotion(move)
1569 && pos.see_sign(move) < 0)
1572 // Update current move
1573 ss->currentMove = move;
1575 // Make and search the move
1576 pos.do_move(move, st, ci, moveIsCheck);
1577 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1578 pos.undo_move(move);
1580 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1583 if (value > bestValue)
1589 ss->bestMove = move;
1594 // All legal moves have been searched. A special case: If we're in check
1595 // and no legal moves were found, it is checkmate.
1596 if (isCheck && bestValue == -VALUE_INFINITE)
1597 return value_mated_in(ply);
1599 // Update transposition table
1600 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1601 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1602 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1604 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1610 // connected_moves() tests whether two moves are 'connected' in the sense
1611 // that the first move somehow made the second move possible (for instance
1612 // if the moving piece is the same in both moves). The first move is assumed
1613 // to be the move that was made to reach the current position, while the
1614 // second move is assumed to be a move from the current position.
1616 bool connected_moves(const Position& pos, Move m1, Move m2) {
1618 Square f1, t1, f2, t2;
1621 assert(move_is_ok(m1));
1622 assert(move_is_ok(m2));
1624 if (m2 == MOVE_NONE)
1627 // Case 1: The moving piece is the same in both moves
1633 // Case 2: The destination square for m2 was vacated by m1
1639 // Case 3: Moving through the vacated square
1640 if ( piece_is_slider(pos.piece_on(f2))
1641 && bit_is_set(squares_between(f2, t2), f1))
1644 // Case 4: The destination square for m2 is defended by the moving piece in m1
1645 p = pos.piece_on(t1);
1646 if (bit_is_set(pos.attacks_from(p, t1), t2))
1649 // Case 5: Discovered check, checking piece is the piece moved in m1
1650 if ( piece_is_slider(p)
1651 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1652 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1654 // discovered_check_candidates() works also if the Position's side to
1655 // move is the opposite of the checking piece.
1656 Color them = opposite_color(pos.side_to_move());
1657 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1659 if (bit_is_set(dcCandidates, f2))
1666 // value_is_mate() checks if the given value is a mate one eventually
1667 // compensated for the ply.
1669 bool value_is_mate(Value value) {
1671 assert(abs(value) <= VALUE_INFINITE);
1673 return value <= value_mated_in(PLY_MAX)
1674 || value >= value_mate_in(PLY_MAX);
1678 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1679 // "plies to mate from the current ply". Non-mate scores are unchanged.
1680 // The function is called before storing a value to the transposition table.
1682 Value value_to_tt(Value v, int ply) {
1684 if (v >= value_mate_in(PLY_MAX))
1687 if (v <= value_mated_in(PLY_MAX))
1694 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1695 // the transposition table to a mate score corrected for the current ply.
1697 Value value_from_tt(Value v, int ply) {
1699 if (v >= value_mate_in(PLY_MAX))
1702 if (v <= value_mated_in(PLY_MAX))
1709 // extension() decides whether a move should be searched with normal depth,
1710 // or with extended depth. Certain classes of moves (checking moves, in
1711 // particular) are searched with bigger depth than ordinary moves and in
1712 // any case are marked as 'dangerous'. Note that also if a move is not
1713 // extended, as example because the corresponding UCI option is set to zero,
1714 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1715 template <NodeType PvNode>
1716 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1717 bool singleEvasion, bool mateThreat, bool* dangerous) {
1719 assert(m != MOVE_NONE);
1721 Depth result = DEPTH_ZERO;
1722 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1726 if (moveIsCheck && pos.see_sign(m) >= 0)
1727 result += CheckExtension[PvNode];
1730 result += SingleEvasionExtension[PvNode];
1733 result += MateThreatExtension[PvNode];
1736 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1738 Color c = pos.side_to_move();
1739 if (relative_rank(c, move_to(m)) == RANK_7)
1741 result += PawnPushTo7thExtension[PvNode];
1744 if (pos.pawn_is_passed(c, move_to(m)))
1746 result += PassedPawnExtension[PvNode];
1751 if ( captureOrPromotion
1752 && pos.type_of_piece_on(move_to(m)) != PAWN
1753 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1754 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1755 && !move_is_promotion(m)
1758 result += PawnEndgameExtension[PvNode];
1763 && captureOrPromotion
1764 && pos.type_of_piece_on(move_to(m)) != PAWN
1765 && pos.see_sign(m) >= 0)
1767 result += ONE_PLY / 2;
1771 return Min(result, ONE_PLY);
1775 // connected_threat() tests whether it is safe to forward prune a move or if
1776 // is somehow coonected to the threat move returned by null search.
1778 bool connected_threat(const Position& pos, Move m, Move threat) {
1780 assert(move_is_ok(m));
1781 assert(threat && move_is_ok(threat));
1782 assert(!pos.move_is_check(m));
1783 assert(!pos.move_is_capture_or_promotion(m));
1784 assert(!pos.move_is_passed_pawn_push(m));
1786 Square mfrom, mto, tfrom, tto;
1788 mfrom = move_from(m);
1790 tfrom = move_from(threat);
1791 tto = move_to(threat);
1793 // Case 1: Don't prune moves which move the threatened piece
1797 // Case 2: If the threatened piece has value less than or equal to the
1798 // value of the threatening piece, don't prune move which defend it.
1799 if ( pos.move_is_capture(threat)
1800 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1801 || pos.type_of_piece_on(tfrom) == KING)
1802 && pos.move_attacks_square(m, tto))
1805 // Case 3: If the moving piece in the threatened move is a slider, don't
1806 // prune safe moves which block its ray.
1807 if ( piece_is_slider(pos.piece_on(tfrom))
1808 && bit_is_set(squares_between(tfrom, tto), mto)
1809 && pos.see_sign(m) >= 0)
1816 // ok_to_use_TT() returns true if a transposition table score
1817 // can be used at a given point in search.
1819 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1821 Value v = value_from_tt(tte->value(), ply);
1823 return ( tte->depth() >= depth
1824 || v >= Max(value_mate_in(PLY_MAX), beta)
1825 || v < Min(value_mated_in(PLY_MAX), beta))
1827 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1828 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1832 // refine_eval() returns the transposition table score if
1833 // possible otherwise falls back on static position evaluation.
1835 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1839 Value v = value_from_tt(tte->value(), ply);
1841 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1842 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1849 // update_history() registers a good move that produced a beta-cutoff
1850 // in history and marks as failures all the other moves of that ply.
1852 void update_history(const Position& pos, Move move, Depth depth,
1853 Move movesSearched[], int moveCount) {
1856 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1858 for (int i = 0; i < moveCount - 1; i++)
1860 m = movesSearched[i];
1864 if (!pos.move_is_capture_or_promotion(m))
1865 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1870 // update_killers() add a good move that produced a beta-cutoff
1871 // among the killer moves of that ply.
1873 void update_killers(Move m, SearchStack* ss) {
1875 if (m == ss->killers[0])
1878 ss->killers[1] = ss->killers[0];
1883 // update_gains() updates the gains table of a non-capture move given
1884 // the static position evaluation before and after the move.
1886 void update_gains(const Position& pos, Move m, Value before, Value after) {
1889 && before != VALUE_NONE
1890 && after != VALUE_NONE
1891 && pos.captured_piece_type() == PIECE_TYPE_NONE
1892 && !move_is_special(m))
1893 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1897 // current_search_time() returns the number of milliseconds which have passed
1898 // since the beginning of the current search.
1900 int current_search_time() {
1902 return get_system_time() - SearchStartTime;
1906 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1908 std::string value_to_uci(Value v) {
1910 std::stringstream s;
1912 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1913 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1915 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1920 // nps() computes the current nodes/second count.
1922 int nps(const Position& pos) {
1924 int t = current_search_time();
1925 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1929 // poll() performs two different functions: It polls for user input, and it
1930 // looks at the time consumed so far and decides if it's time to abort the
1933 void poll(const Position& pos) {
1935 static int lastInfoTime;
1936 int t = current_search_time();
1939 if (data_available())
1941 // We are line oriented, don't read single chars
1942 std::string command;
1944 if (!std::getline(std::cin, command))
1947 if (command == "quit")
1950 PonderSearch = false;
1954 else if (command == "stop")
1957 PonderSearch = false;
1959 else if (command == "ponderhit")
1963 // Print search information
1967 else if (lastInfoTime > t)
1968 // HACK: Must be a new search where we searched less than
1969 // NodesBetweenPolls nodes during the first second of search.
1972 else if (t - lastInfoTime >= 1000)
1979 if (dbg_show_hit_rate)
1980 dbg_print_hit_rate();
1982 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1983 << " time " << t << endl;
1986 // Should we stop the search?
1990 bool stillAtFirstMove = FirstRootMove
1991 && !AspirationFailLow
1992 && t > TimeMgr.available_time();
1994 bool noMoreTime = t > TimeMgr.maximum_time()
1995 || stillAtFirstMove;
1997 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1998 || (ExactMaxTime && t >= ExactMaxTime)
1999 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2004 // ponderhit() is called when the program is pondering (i.e. thinking while
2005 // it's the opponent's turn to move) in order to let the engine know that
2006 // it correctly predicted the opponent's move.
2010 int t = current_search_time();
2011 PonderSearch = false;
2013 bool stillAtFirstMove = FirstRootMove
2014 && !AspirationFailLow
2015 && t > TimeMgr.available_time();
2017 bool noMoreTime = t > TimeMgr.maximum_time()
2018 || stillAtFirstMove;
2020 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2025 // init_ss_array() does a fast reset of the first entries of a SearchStack
2026 // array and of all the excludedMove and skipNullMove entries.
2028 void init_ss_array(SearchStack* ss, int size) {
2030 for (int i = 0; i < size; i++, ss++)
2032 ss->excludedMove = MOVE_NONE;
2033 ss->skipNullMove = false;
2034 ss->reduction = DEPTH_ZERO;
2038 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2043 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2044 // while the program is pondering. The point is to work around a wrinkle in
2045 // the UCI protocol: When pondering, the engine is not allowed to give a
2046 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2047 // We simply wait here until one of these commands is sent, and return,
2048 // after which the bestmove and pondermove will be printed (in id_loop()).
2050 void wait_for_stop_or_ponderhit() {
2052 std::string command;
2056 if (!std::getline(std::cin, command))
2059 if (command == "quit")
2064 else if (command == "ponderhit" || command == "stop")
2070 // print_pv_info() prints to standard output and eventually to log file information on
2071 // the current PV line. It is called at each iteration or after a new pv is found.
2073 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2075 cout << "info depth " << Iteration
2076 << " score " << value_to_uci(value)
2077 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2078 << " time " << current_search_time()
2079 << " nodes " << pos.nodes_searched()
2080 << " nps " << nps(pos)
2083 for (Move* m = pv; *m != MOVE_NONE; m++)
2090 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2091 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2093 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2098 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2099 // the PV back into the TT. This makes sure the old PV moves are searched
2100 // first, even if the old TT entries have been overwritten.
2102 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2106 Position p(pos, pos.thread());
2107 Value v, m = VALUE_NONE;
2109 for (int i = 0; pv[i] != MOVE_NONE; i++)
2111 tte = TT.retrieve(p.get_key());
2112 if (!tte || tte->move() != pv[i])
2114 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2115 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2117 p.do_move(pv[i], st);
2122 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2123 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2124 // allow to always have a ponder move even when we fail high at root and also a
2125 // long PV to print that is important for position analysis.
2127 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2131 Position p(pos, pos.thread());
2134 assert(bestMove != MOVE_NONE);
2137 p.do_move(pv[ply++], st);
2139 while ( (tte = TT.retrieve(p.get_key())) != NULL
2140 && tte->move() != MOVE_NONE
2141 && move_is_legal(p, tte->move())
2143 && (!p.is_draw() || ply < 2))
2145 pv[ply] = tte->move();
2146 p.do_move(pv[ply++], st);
2148 pv[ply] = MOVE_NONE;
2152 // init_thread() is the function which is called when a new thread is
2153 // launched. It simply calls the idle_loop() function with the supplied
2154 // threadID. There are two versions of this function; one for POSIX
2155 // threads and one for Windows threads.
2157 #if !defined(_MSC_VER)
2159 void* init_thread(void* threadID) {
2161 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2167 DWORD WINAPI init_thread(LPVOID threadID) {
2169 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2176 /// The ThreadsManager class
2179 // idle_loop() is where the threads are parked when they have no work to do.
2180 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2181 // object for which the current thread is the master.
2183 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2185 assert(threadID >= 0 && threadID < MAX_THREADS);
2188 bool allFinished = false;
2192 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2193 // master should exit as last one.
2194 if (AllThreadsShouldExit)
2197 threads[threadID].state = THREAD_TERMINATED;
2201 // If we are not thinking, wait for a condition to be signaled
2202 // instead of wasting CPU time polling for work.
2203 while ( threadID >= ActiveThreads
2204 || threads[threadID].state == THREAD_INITIALIZING
2205 || (threads[threadID].state == THREAD_AVAILABLE && (!sp || UseSleepingMaster)))
2209 // Test with lock held to avoid races with wake_sleeping_thread()
2210 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2211 allFinished = (i == ActiveThreads);
2213 // Retest sleep conditions under lock protection
2214 if ( AllThreadsShouldExit
2216 || !( threadID >= ActiveThreads
2217 || threads[threadID].state == THREAD_INITIALIZING
2218 || (threads[threadID].state == THREAD_AVAILABLE && (!sp || UseSleepingMaster))))
2220 lock_release(&MPLock);
2224 // Put thread to sleep
2225 threads[threadID].state = THREAD_AVAILABLE;
2226 cond_wait(&WaitCond[threadID], &MPLock);
2227 lock_release(&MPLock);
2230 // If this thread has been assigned work, launch a search
2231 if (threads[threadID].state == THREAD_WORKISWAITING)
2233 assert(!AllThreadsShouldExit);
2235 threads[threadID].state = THREAD_SEARCHING;
2237 // Here we call search() with SplitPoint template parameter set to true
2238 SplitPoint* tsp = threads[threadID].splitPoint;
2239 Position pos(*tsp->pos, threadID);
2240 SearchStack* ss = tsp->sstack[threadID] + 1;
2244 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2246 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2248 assert(threads[threadID].state == THREAD_SEARCHING);
2250 threads[threadID].state = THREAD_AVAILABLE;
2252 // Wake up master thread so to allow it to return from the idle loop in
2253 // case we are the last slave of the split point.
2254 if (UseSleepingMaster && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2255 wake_sleeping_thread(tsp->master);
2258 // If this thread is the master of a split point and all slaves have
2259 // finished their work at this split point, return from the idle loop.
2260 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2261 allFinished = (i == ActiveThreads);
2265 // Because sp->slaves[] is reset under lock protection,
2266 // be sure sp->lock has been released before to return.
2267 lock_grab(&(sp->lock));
2268 lock_release(&(sp->lock));
2270 // In helpful master concept a master can help only a sub-tree, and
2271 // because here is all finished is not possible master is booked.
2272 assert(threads[threadID].state == THREAD_AVAILABLE);
2274 threads[threadID].state = THREAD_SEARCHING;
2281 // init_threads() is called during startup. It launches all helper threads,
2282 // and initializes the split point stack and the global locks and condition
2285 void ThreadsManager::init_threads() {
2287 int i, arg[MAX_THREADS];
2290 // Initialize global locks
2293 for (i = 0; i < MAX_THREADS; i++)
2294 cond_init(&WaitCond[i]);
2296 // Initialize splitPoints[] locks
2297 for (i = 0; i < MAX_THREADS; i++)
2298 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2299 lock_init(&(threads[i].splitPoints[j].lock));
2301 // Will be set just before program exits to properly end the threads
2302 AllThreadsShouldExit = false;
2304 // Threads will be put all threads to sleep as soon as created
2307 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2308 threads[0].state = THREAD_SEARCHING;
2309 for (i = 1; i < MAX_THREADS; i++)
2310 threads[i].state = THREAD_INITIALIZING;
2312 // Launch the helper threads
2313 for (i = 1; i < MAX_THREADS; i++)
2317 #if !defined(_MSC_VER)
2318 pthread_t pthread[1];
2319 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2320 pthread_detach(pthread[0]);
2322 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2326 cout << "Failed to create thread number " << i << endl;
2327 Application::exit_with_failure();
2330 // Wait until the thread has finished launching and is gone to sleep
2331 while (threads[i].state == THREAD_INITIALIZING) {}
2336 // exit_threads() is called when the program exits. It makes all the
2337 // helper threads exit cleanly.
2339 void ThreadsManager::exit_threads() {
2341 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2343 // Wake up all the threads and waits for termination
2344 for (int i = 1; i < MAX_THREADS; i++)
2346 wake_sleeping_thread(i);
2347 while (threads[i].state != THREAD_TERMINATED) {}
2350 // Now we can safely destroy the locks
2351 for (int i = 0; i < MAX_THREADS; i++)
2352 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2353 lock_destroy(&(threads[i].splitPoints[j].lock));
2355 lock_destroy(&MPLock);
2357 // Now we can safely destroy the wait conditions
2358 for (int i = 0; i < MAX_THREADS; i++)
2359 cond_destroy(&WaitCond[i]);
2363 // thread_should_stop() checks whether the thread should stop its search.
2364 // This can happen if a beta cutoff has occurred in the thread's currently
2365 // active split point, or in some ancestor of the current split point.
2367 bool ThreadsManager::thread_should_stop(int threadID) const {
2369 assert(threadID >= 0 && threadID < ActiveThreads);
2371 SplitPoint* sp = threads[threadID].splitPoint;
2373 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2378 // thread_is_available() checks whether the thread with threadID "slave" is
2379 // available to help the thread with threadID "master" at a split point. An
2380 // obvious requirement is that "slave" must be idle. With more than two
2381 // threads, this is not by itself sufficient: If "slave" is the master of
2382 // some active split point, it is only available as a slave to the other
2383 // threads which are busy searching the split point at the top of "slave"'s
2384 // split point stack (the "helpful master concept" in YBWC terminology).
2386 bool ThreadsManager::thread_is_available(int slave, int master) const {
2388 assert(slave >= 0 && slave < ActiveThreads);
2389 assert(master >= 0 && master < ActiveThreads);
2390 assert(ActiveThreads > 1);
2392 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2395 // Make a local copy to be sure doesn't change under our feet
2396 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2398 // No active split points means that the thread is available as
2399 // a slave for any other thread.
2400 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2403 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2404 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2405 // could have been set to 0 by another thread leading to an out of bound access.
2406 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2413 // available_thread_exists() tries to find an idle thread which is available as
2414 // a slave for the thread with threadID "master".
2416 bool ThreadsManager::available_thread_exists(int master) const {
2418 assert(master >= 0 && master < ActiveThreads);
2419 assert(ActiveThreads > 1);
2421 for (int i = 0; i < ActiveThreads; i++)
2422 if (thread_is_available(i, master))
2429 // split() does the actual work of distributing the work at a node between
2430 // several available threads. If it does not succeed in splitting the
2431 // node (because no idle threads are available, or because we have no unused
2432 // split point objects), the function immediately returns. If splitting is
2433 // possible, a SplitPoint object is initialized with all the data that must be
2434 // copied to the helper threads and we tell our helper threads that they have
2435 // been assigned work. This will cause them to instantly leave their idle loops and
2436 // call search().When all threads have returned from search() then split() returns.
2438 template <bool Fake>
2439 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2440 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2441 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2442 assert(pos.is_ok());
2443 assert(ply > 0 && ply < PLY_MAX);
2444 assert(*bestValue >= -VALUE_INFINITE);
2445 assert(*bestValue <= *alpha);
2446 assert(*alpha < beta);
2447 assert(beta <= VALUE_INFINITE);
2448 assert(depth > DEPTH_ZERO);
2449 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2450 assert(ActiveThreads > 1);
2452 int i, master = pos.thread();
2453 Thread& masterThread = threads[master];
2457 // If no other thread is available to help us, or if we have too many
2458 // active split points, don't split.
2459 if ( !available_thread_exists(master)
2460 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2462 lock_release(&MPLock);
2466 // Pick the next available split point object from the split point stack
2467 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2469 // Initialize the split point object
2470 splitPoint.parent = masterThread.splitPoint;
2471 splitPoint.master = master;
2472 splitPoint.stopRequest = false;
2473 splitPoint.ply = ply;
2474 splitPoint.depth = depth;
2475 splitPoint.threatMove = threatMove;
2476 splitPoint.mateThreat = mateThreat;
2477 splitPoint.alpha = *alpha;
2478 splitPoint.beta = beta;
2479 splitPoint.pvNode = pvNode;
2480 splitPoint.bestValue = *bestValue;
2482 splitPoint.moveCount = moveCount;
2483 splitPoint.pos = &pos;
2484 splitPoint.nodes = 0;
2485 splitPoint.parentSstack = ss;
2486 for (i = 0; i < ActiveThreads; i++)
2487 splitPoint.slaves[i] = 0;
2489 masterThread.splitPoint = &splitPoint;
2491 // If we are here it means we are not available
2492 assert(masterThread.state != THREAD_AVAILABLE);
2494 int workersCnt = 1; // At least the master is included
2496 // Allocate available threads setting state to THREAD_BOOKED
2497 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2498 if (thread_is_available(i, master))
2500 threads[i].state = THREAD_BOOKED;
2501 threads[i].splitPoint = &splitPoint;
2502 splitPoint.slaves[i] = 1;
2506 assert(Fake || workersCnt > 1);
2508 // We can release the lock because slave threads are already booked and master is not available
2509 lock_release(&MPLock);
2511 // Tell the threads that they have work to do. This will make them leave
2512 // their idle loop. But before copy search stack tail for each thread.
2513 for (i = 0; i < ActiveThreads; i++)
2514 if (i == master || splitPoint.slaves[i])
2516 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2518 assert(i == master || threads[i].state == THREAD_BOOKED);
2520 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2522 wake_sleeping_thread(i);
2525 // Everything is set up. The master thread enters the idle loop, from
2526 // which it will instantly launch a search, because its state is
2527 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2528 // idle loop, which means that the main thread will return from the idle
2529 // loop when all threads have finished their work at this split point.
2530 idle_loop(master, &splitPoint);
2532 // We have returned from the idle loop, which means that all threads are
2533 // finished. Update alpha and bestValue, and return.
2536 *alpha = splitPoint.alpha;
2537 *bestValue = splitPoint.bestValue;
2538 masterThread.activeSplitPoints--;
2539 masterThread.splitPoint = splitPoint.parent;
2540 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2542 lock_release(&MPLock);
2546 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2547 // to start a new search from the root.
2549 void ThreadsManager::wake_sleeping_thread(int threadID) {
2552 cond_signal(&WaitCond[threadID]);
2553 lock_release(&MPLock);
2557 /// The RootMoveList class
2559 // RootMoveList c'tor
2561 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2563 SearchStack ss[PLY_MAX_PLUS_2];
2564 MoveStack mlist[MOVES_MAX];
2566 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2568 // Initialize search stack
2569 init_ss_array(ss, PLY_MAX_PLUS_2);
2570 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2573 // Generate all legal moves
2574 MoveStack* last = generate_moves(pos, mlist);
2576 // Add each move to the moves[] array
2577 for (MoveStack* cur = mlist; cur != last; cur++)
2579 bool includeMove = includeAllMoves;
2581 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2582 includeMove = (searchMoves[k] == cur->move);
2587 // Find a quick score for the move
2588 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2589 moves[count].pv[1] = MOVE_NONE;
2590 pos.do_move(cur->move, st);
2591 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2592 pos.undo_move(cur->move);
2598 // Score root moves using the standard way used in main search, the moves
2599 // are scored according to the order in which are returned by MovePicker.
2601 void RootMoveList::score_moves(const Position& pos)
2605 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2607 while ((move = mp.get_next_move()) != MOVE_NONE)
2608 for (int i = 0; i < count; i++)
2609 if (moves[i].move == move)
2611 moves[i].mp_score = score--;
2616 // RootMoveList simple methods definitions
2618 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2622 for (j = 0; pv[j] != MOVE_NONE; j++)
2623 moves[moveNum].pv[j] = pv[j];
2625 moves[moveNum].pv[j] = MOVE_NONE;
2629 // RootMoveList::sort() sorts the root move list at the beginning of a new
2632 void RootMoveList::sort() {
2634 sort_multipv(count - 1); // Sort all items
2638 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2639 // list by their scores and depths. It is used to order the different PVs
2640 // correctly in MultiPV mode.
2642 void RootMoveList::sort_multipv(int n) {
2646 for (i = 1; i <= n; i++)
2648 RootMove rm = moves[i];
2649 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2650 moves[j] = moves[j - 1];