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 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
79 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
81 void resetNodeCounters();
82 void resetBetaCounters();
83 int64_t nodes_searched() const;
84 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const 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);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is bigger then beta - IIDMargin.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
218 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
220 // Step 14. Reduced search
222 // Reduction lookup tables (initialized at startup) and their getter functions
223 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
225 template <NodeType PV>
226 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
228 // Common adjustments
230 // Search depth at iteration 1
231 const Depth InitialDepth = OnePly;
233 // Easy move margin. An easy move candidate must be at least this much
234 // better than the second best move.
235 const Value EasyMoveMargin = Value(0x200);
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 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(const Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 void sp_search(SplitPoint* sp, int threadID);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool move_is_killer(Move m, SearchStack* ss);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 bool connected_threat(const Position& pos, Move m, Move threat);
300 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
301 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
302 void update_killers(Move m, SearchStack* ss);
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);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack* ss, int size);
312 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 void insert_pv_in_tt(const Position& pos, Move pv[]);
314 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
329 /// init_threads(), exit_threads() and nodes_searched() are helpers to
330 /// give accessibility to some TM methods from outside of current file.
332 void init_threads() { ThreadsMgr.init_threads(); }
333 void exit_threads() { ThreadsMgr.exit_threads(); }
334 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (OnePly == 2)
342 int hd; // half depth (OnePly == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
369 MoveStack mlist[256];
374 // Generate all legal moves
375 MoveStack* last = generate_moves(pos, mlist);
377 // If we are at the last ply we don't need to do and undo
378 // the moves, just to count them.
380 return int(last - mlist);
382 // Loop through all legal moves
384 for (MoveStack* cur = mlist; cur != last; cur++)
387 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
388 sum += perft(pos, depth - OnePly);
395 /// think() is the external interface to Stockfish's search, and is called when
396 /// the program receives the UCI 'go' command. It initializes various
397 /// search-related global variables, and calls root_search(). It returns false
398 /// when a quit command is received during the search.
400 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
401 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
403 // Initialize global search variables
404 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
406 ThreadsMgr.resetNodeCounters();
407 SearchStartTime = get_system_time();
408 ExactMaxTime = maxTime;
411 InfiniteSearch = infinite;
412 PonderSearch = ponder;
413 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
415 // Look for a book move, only during games, not tests
416 if (UseTimeManagement && get_option_value_bool("OwnBook"))
418 if (get_option_value_string("Book File") != OpeningBook.file_name())
419 OpeningBook.open(get_option_value_string("Book File"));
421 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
422 if (bookMove != MOVE_NONE)
425 wait_for_stop_or_ponderhit();
427 cout << "bestmove " << bookMove << endl;
432 // Read UCI option values
433 TT.set_size(get_option_value_int("Hash"));
434 if (button_was_pressed("Clear Hash"))
437 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
438 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
439 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
440 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
441 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
442 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
443 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
444 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
445 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
446 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
447 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
448 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
450 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
451 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
452 MultiPV = get_option_value_int("MultiPV");
453 Chess960 = get_option_value_bool("UCI_Chess960");
454 UseLogFile = get_option_value_bool("Use Search Log");
457 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
459 read_weights(pos.side_to_move());
461 // Set the number of active threads
462 int newActiveThreads = get_option_value_int("Threads");
463 if (newActiveThreads != ThreadsMgr.active_threads())
465 ThreadsMgr.set_active_threads(newActiveThreads);
466 init_eval(ThreadsMgr.active_threads());
469 // Wake up sleeping threads
470 ThreadsMgr.wake_sleeping_threads();
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
476 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
478 // Set best NodesBetweenPolls interval to avoid lagging under
479 // heavy time pressure.
481 NodesBetweenPolls = Min(MaxNodes, 30000);
482 else if (myTime && myTime < 1000)
483 NodesBetweenPolls = 1000;
484 else if (myTime && myTime < 5000)
485 NodesBetweenPolls = 5000;
487 NodesBetweenPolls = 30000;
489 // Write search information to log file
491 LogFile << "Searching: " << pos.to_fen() << endl
492 << "infinite: " << infinite
493 << " ponder: " << ponder
494 << " time: " << myTime
495 << " increment: " << myIncrement
496 << " moves to go: " << movesToGo << endl;
498 // We're ready to start thinking. Call the iterative deepening loop function
499 id_loop(pos, searchMoves);
504 ThreadsMgr.put_threads_to_sleep();
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(const Position& pos, Move searchMoves[]) {
519 Position p(pos, pos.thread());
520 SearchStack ss[PLY_MAX_PLUS_2];
521 Move pv[PLY_MAX_PLUS_2];
522 Move EasyMove = MOVE_NONE;
523 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
525 // Moves to search are verified, copied, scored and sorted
526 RootMoveList rml(p, searchMoves);
528 // Handle special case of searching on a mate/stale position
529 if (rml.move_count() == 0)
532 wait_for_stop_or_ponderhit();
534 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
537 // Print RootMoveList startup scoring to the standard output,
538 // so to output information also for iteration 1.
539 cout << "info depth " << 1
540 << "\ninfo depth " << 1
541 << " score " << value_to_uci(rml.get_move_score(0))
542 << " time " << current_search_time()
543 << " nodes " << ThreadsMgr.nodes_searched()
545 << " pv " << rml.get_move(0) << "\n";
550 init_ss_array(ss, PLY_MAX_PLUS_2);
551 pv[0] = pv[1] = MOVE_NONE;
552 ValueByIteration[1] = rml.get_move_score(0);
555 // Is one move significantly better than others after initial scoring ?
556 if ( rml.move_count() == 1
557 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
558 EasyMove = rml.get_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(p, 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(p, 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
616 int64_t nodes = ThreadsMgr.nodes_searched();
619 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
620 && current_search_time() > TimeMgr.available_time() / 16)
621 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
622 && current_search_time() > TimeMgr.available_time() / 32)))
625 // Add some extra time if the best move has changed during the last two iterations
626 if (Iteration > 5 && Iteration <= 50)
627 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
628 BestMoveChangesByIteration[Iteration-1]);
630 // Stop search if most of MaxSearchTime is consumed at the end of the
631 // iteration. We probably don't have enough time to search the first
632 // move at the next iteration anyway.
633 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
639 StopOnPonderhit = true;
645 if (MaxDepth && Iteration >= MaxDepth)
649 // If we are pondering or in infinite search, we shouldn't print the
650 // best move before we are told to do so.
651 if (!AbortSearch && (PonderSearch || InfiniteSearch))
652 wait_for_stop_or_ponderhit();
654 // Print final search statistics
655 cout << "info nodes " << ThreadsMgr.nodes_searched()
657 << " time " << current_search_time() << endl;
659 // Print the best move and the ponder move to the standard output
660 if (pv[0] == MOVE_NONE)
662 pv[0] = rml.get_move(0);
666 assert(pv[0] != MOVE_NONE);
668 cout << "bestmove " << pv[0];
670 if (pv[1] != MOVE_NONE)
671 cout << " ponder " << pv[1];
678 dbg_print_mean(LogFile);
680 if (dbg_show_hit_rate)
681 dbg_print_hit_rate(LogFile);
683 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
684 << "\nNodes/second: " << nps()
685 << "\nBest move: " << move_to_san(p, pv[0]);
688 p.do_move(pv[0], st);
689 LogFile << "\nPonder move: "
690 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
693 return rml.get_move_score(0);
697 // root_search() is the function which searches the root node. It is
698 // similar to search_pv except that it uses a different move ordering
699 // scheme, prints some information to the standard output and handles
700 // the fail low/high loops.
702 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
709 Depth depth, ext, newDepth;
710 Value value, alpha, beta;
711 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
712 int researchCountFH, researchCountFL;
714 researchCountFH = researchCountFL = 0;
717 isCheck = pos.is_check();
718 depth = (Iteration - 2) * OnePly + InitialDepth;
720 // Step 1. Initialize node (polling is omitted at root)
721 ss->currentMove = ss->bestMove = MOVE_NONE;
723 // Step 2. Check for aborted search (omitted at root)
724 // Step 3. Mate distance pruning (omitted at root)
725 // Step 4. Transposition table lookup (omitted at root)
727 // Step 5. Evaluate the position statically
728 // At root we do this only to get reference value for child nodes
729 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
731 // Step 6. Razoring (omitted at root)
732 // Step 7. Static null move pruning (omitted at root)
733 // Step 8. Null move search with verification search (omitted at root)
734 // Step 9. Internal iterative deepening (omitted at root)
736 // Step extra. Fail low loop
737 // We start with small aspiration window and in case of fail low, we research
738 // with bigger window until we are not failing low anymore.
741 // Sort the moves before to (re)search
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 = ThreadsMgr.nodes_searched();
753 // Reset beta cut-off counters
754 ThreadsMgr.resetBetaCounters();
756 // Pick the next root move, and print the move and the move number to
757 // the standard output.
758 move = ss->currentMove = rml.get_move(i);
760 if (current_search_time() >= 1000)
761 cout << "info currmove " << move
762 << " currmovenumber " << i + 1 << endl;
764 moveIsCheck = pos.move_is_check(move);
765 captureOrPromotion = pos.move_is_capture_or_promotion(move);
767 // Step 11. Decide the new search depth
768 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
769 newDepth = depth + ext;
771 // Step 12. Futility pruning (omitted at root)
773 // Step extra. Fail high loop
774 // If move fails high, we research with bigger window until we are not failing
776 value = - VALUE_INFINITE;
780 // Step 13. Make the move
781 pos.do_move(move, st, ci, moveIsCheck);
783 // Step extra. pv search
784 // We do pv search for first moves (i < MultiPV)
785 // and for fail high research (value > alpha)
786 if (i < MultiPV || value > alpha)
788 // Aspiration window is disabled in multi-pv case
790 alpha = -VALUE_INFINITE;
792 // Full depth PV search, done on first move or after a fail high
793 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
797 // Step 14. Reduced search
798 // if the move fails high will be re-searched at full depth
799 bool doFullDepthSearch = true;
801 if ( depth >= 3 * OnePly
803 && !captureOrPromotion
804 && !move_is_castle(move))
806 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
809 assert(newDepth-ss->reduction >= OnePly);
811 // Reduced depth non-pv search using alpha as upperbound
812 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
813 doFullDepthSearch = (value > alpha);
816 // The move failed high, but if reduction is very big we could
817 // face a false positive, retry with a less aggressive reduction,
818 // if the move fails high again then go with full depth search.
819 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
821 assert(newDepth - OnePly >= OnePly);
823 ss->reduction = OnePly;
824 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
825 doFullDepthSearch = (value > alpha);
827 ss->reduction = Depth(0); // Restore original reduction
830 // Step 15. Full depth search
831 if (doFullDepthSearch)
833 // Full depth non-pv search using alpha as upperbound
834 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
836 // If we are above alpha then research at same depth but as PV
837 // to get a correct score or eventually a fail high above beta.
839 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
843 // Step 16. Undo move
846 // Can we exit fail high loop ?
847 if (AbortSearch || value < beta)
850 // We are failing high and going to do a research. It's important to update
851 // the score before research in case we run out of time while researching.
852 rml.set_move_score(i, value);
854 extract_pv_from_tt(pos, move, pv);
855 rml.set_move_pv(i, pv);
857 // Print information to the standard output
858 print_pv_info(pos, pv, alpha, beta, value);
860 // Prepare for a research after a fail high, each time with a wider window
861 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
864 } // End of fail high loop
866 // Finished searching the move. If AbortSearch is true, the search
867 // was aborted because the user interrupted the search or because we
868 // ran out of time. In this case, the return value of the search cannot
869 // be trusted, and we break out of the loop without updating the best
874 // Remember beta-cutoff and searched nodes counts for this move. The
875 // info is used to sort the root moves for the next iteration.
877 ThreadsMgr.get_beta_counters(pos.side_to_move(), our, their);
878 rml.set_beta_counters(i, our, their);
879 rml.set_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
881 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
882 assert(value < beta);
884 // Step 17. Check for new best move
885 if (value <= alpha && i >= MultiPV)
886 rml.set_move_score(i, -VALUE_INFINITE);
889 // PV move or new best move!
892 rml.set_move_score(i, value);
894 extract_pv_from_tt(pos, move, pv);
895 rml.set_move_pv(i, pv);
899 // We record how often the best move has been changed in each
900 // iteration. This information is used for time managment: When
901 // the best move changes frequently, we allocate some more time.
903 BestMoveChangesByIteration[Iteration]++;
905 // Print information to the standard output
906 print_pv_info(pos, pv, alpha, beta, value);
908 // Raise alpha to setup proper non-pv search upper bound
915 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
917 cout << "info multipv " << j + 1
918 << " score " << value_to_uci(rml.get_move_score(j))
919 << " depth " << (j <= i ? Iteration : Iteration - 1)
920 << " time " << current_search_time()
921 << " nodes " << ThreadsMgr.nodes_searched()
925 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
926 cout << rml.get_move_pv(j, k) << " ";
930 alpha = rml.get_move_score(Min(i, MultiPV - 1));
932 } // PV move or new best move
934 assert(alpha >= *alphaPtr);
936 AspirationFailLow = (alpha == *alphaPtr);
938 if (AspirationFailLow && StopOnPonderhit)
939 StopOnPonderhit = false;
942 // Can we exit fail low loop ?
943 if (AbortSearch || !AspirationFailLow)
946 // Prepare for a research after a fail low, each time with a wider window
947 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
952 // Sort the moves before to return
959 // search<>() is the main search function for both PV and non-PV nodes
961 template <NodeType PvNode>
962 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
964 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
965 assert(beta > alpha && beta <= VALUE_INFINITE);
966 assert(PvNode || alpha == beta - 1);
967 assert(ply > 0 && ply < PLY_MAX);
968 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
970 Move movesSearched[256];
975 Move ttMove, move, excludedMove, threatMove;
977 Value bestValue, value, oldAlpha;
978 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
979 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
980 bool mateThreat = false;
982 int threadID = pos.thread();
983 refinedValue = bestValue = value = -VALUE_INFINITE;
986 // Step 1. Initialize node and poll. Polling can abort search
987 ThreadsMgr.incrementNodeCounter(threadID);
988 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
989 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
991 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
997 // Step 2. Check for aborted search and immediate draw
998 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1001 if (pos.is_draw() || ply >= PLY_MAX - 1)
1004 // Step 3. Mate distance pruning
1005 alpha = Max(value_mated_in(ply), alpha);
1006 beta = Min(value_mate_in(ply+1), beta);
1010 // Step 4. Transposition table lookup
1012 // We don't want the score of a partial search to overwrite a previous full search
1013 // TT value, so we use a different position key in case of an excluded move exists.
1014 excludedMove = ss->excludedMove;
1015 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1017 tte = TT.retrieve(posKey);
1018 ttMove = (tte ? tte->move() : MOVE_NONE);
1020 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1021 // This is to avoid problems in the following areas:
1023 // * Repetition draw detection
1024 // * Fifty move rule detection
1025 // * Searching for a mate
1026 // * Printing of full PV line
1028 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1030 // Refresh tte entry to avoid aging
1031 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1033 ss->bestMove = ttMove; // Can be MOVE_NONE
1034 return value_from_tt(tte->value(), ply);
1037 // Step 5. Evaluate the position statically and
1038 // update gain statistics of parent move.
1039 isCheck = pos.is_check();
1041 ss->eval = VALUE_NONE;
1044 assert(tte->static_value() != VALUE_NONE);
1046 ss->eval = tte->static_value();
1047 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1048 refinedValue = refine_eval(tte, ss->eval, ply);
1052 refinedValue = ss->eval = evaluate(pos, ei);
1053 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1056 // Save gain for the parent non-capture move
1057 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1059 // Step 6. Razoring (is omitted in PV nodes)
1061 && depth < RazorDepth
1063 && refinedValue < beta - razor_margin(depth)
1064 && ttMove == MOVE_NONE
1065 && (ss-1)->currentMove != MOVE_NULL
1066 && !value_is_mate(beta)
1067 && !pos.has_pawn_on_7th(pos.side_to_move()))
1069 Value rbeta = beta - razor_margin(depth);
1070 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1072 // Logically we should return (v + razor_margin(depth)), but
1073 // surprisingly this did slightly weaker in tests.
1077 // Step 7. Static null move pruning (is omitted in PV nodes)
1078 // We're betting that the opponent doesn't have a move that will reduce
1079 // the score by more than futility_margin(depth) if we do a null move.
1081 && !ss->skipNullMove
1082 && depth < RazorDepth
1084 && refinedValue >= beta + futility_margin(depth, 0)
1085 && !value_is_mate(beta)
1086 && pos.non_pawn_material(pos.side_to_move()))
1087 return refinedValue - futility_margin(depth, 0);
1089 // Step 8. Null move search with verification search (is omitted in PV nodes)
1090 // When we jump directly to qsearch() we do a null move only if static value is
1091 // at least beta. Otherwise we do a null move if static value is not more than
1092 // NullMoveMargin under beta.
1094 && !ss->skipNullMove
1097 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
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 * OnePly ? 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;
1113 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1114 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * OnePly)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1154 // Step 9. Internal iterative deepening
1155 if ( depth >= IIDDepth[PvNode]
1156 && ttMove == MOVE_NONE
1157 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1159 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1161 ss->skipNullMove = true;
1162 search<PvNode>(pos, ss, alpha, beta, d, ply);
1163 ss->skipNullMove = false;
1165 ttMove = ss->bestMove;
1166 tte = TT.retrieve(posKey);
1169 // Expensive mate threat detection (only for PV nodes)
1171 mateThreat = pos.has_mate_threat();
1173 // Initialize a MovePicker object for the current position
1174 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1176 ss->bestMove = MOVE_NONE;
1177 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1178 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1181 && !excludedMove // Do not allow recursive singular extension search
1182 && is_lower_bound(tte->type())
1183 && tte->depth() >= depth - 3 * OnePly;
1185 // Step 10. Loop through moves
1186 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1187 while ( bestValue < beta
1188 && (move = mp.get_next_move()) != MOVE_NONE
1189 && !ThreadsMgr.thread_should_stop(threadID))
1191 assert(move_is_ok(move));
1193 if (move == excludedMove)
1196 moveIsCheck = pos.move_is_check(move, ci);
1197 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1199 // Step 11. Decide the new search depth
1200 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1202 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1203 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1204 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1205 // lower then ttValue minus a margin then we extend ttMove.
1206 if ( singularExtensionNode
1207 && move == tte->move()
1210 Value ttValue = value_from_tt(tte->value(), ply);
1212 if (abs(ttValue) < VALUE_KNOWN_WIN)
1214 Value b = ttValue - SingularExtensionMargin;
1215 ss->excludedMove = move;
1216 ss->skipNullMove = true;
1217 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1218 ss->skipNullMove = false;
1219 ss->excludedMove = MOVE_NONE;
1220 ss->bestMove = MOVE_NONE;
1226 newDepth = depth - OnePly + ext;
1228 // Update current move (this must be done after singular extension search)
1229 movesSearched[moveCount++] = ss->currentMove = move;
1231 // Step 12. Futility pruning (is omitted in PV nodes)
1233 && !captureOrPromotion
1237 && !move_is_castle(move))
1239 // Move count based pruning
1240 if ( moveCount >= futility_move_count(depth)
1241 && !(threatMove && connected_threat(pos, move, threatMove))
1242 && bestValue > value_mated_in(PLY_MAX))
1245 // Value based pruning
1246 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1247 // but fixing this made program slightly weaker.
1248 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1249 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1250 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1252 if (futilityValueScaled < beta)
1254 if (futilityValueScaled > bestValue)
1255 bestValue = futilityValueScaled;
1260 // Step 13. Make the move
1261 pos.do_move(move, st, ci, moveIsCheck);
1263 // Step extra. pv search (only in PV nodes)
1264 // The first move in list is the expected PV
1265 if (PvNode && moveCount == 1)
1266 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1267 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1270 // Step 14. Reduced depth search
1271 // If the move fails high will be re-searched at full depth.
1272 bool doFullDepthSearch = true;
1274 if ( depth >= 3 * OnePly
1275 && !captureOrPromotion
1277 && !move_is_castle(move)
1278 && !move_is_killer(move, ss))
1280 ss->reduction = reduction<PvNode>(depth, moveCount);
1283 Depth d = newDepth - ss->reduction;
1284 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1285 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1287 doFullDepthSearch = (value > alpha);
1290 // The move failed high, but if reduction is very big we could
1291 // face a false positive, retry with a less aggressive reduction,
1292 // if the move fails high again then go with full depth search.
1293 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1295 assert(newDepth - OnePly >= OnePly);
1297 ss->reduction = OnePly;
1298 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1299 doFullDepthSearch = (value > alpha);
1301 ss->reduction = Depth(0); // Restore original reduction
1304 // Step 15. Full depth search
1305 if (doFullDepthSearch)
1307 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1308 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1310 // Step extra. pv search (only in PV nodes)
1311 // Search only for possible new PV nodes, if instead value >= beta then
1312 // parent node fails low with value <= alpha and tries another move.
1313 if (PvNode && value > alpha && value < beta)
1314 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1315 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1319 // Step 16. Undo move
1320 pos.undo_move(move);
1322 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1324 // Step 17. Check for new best move
1325 if (value > bestValue)
1330 if (PvNode && value < beta) // We want always alpha < beta
1333 if (value == value_mate_in(ply + 1))
1334 ss->mateKiller = move;
1336 ss->bestMove = move;
1340 // Step 18. Check for split
1341 if ( depth >= MinimumSplitDepth
1342 && ThreadsMgr.active_threads() > 1
1344 && ThreadsMgr.available_thread_exists(threadID)
1346 && !ThreadsMgr.thread_should_stop(threadID)
1348 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1349 threatMove, mateThreat, &moveCount, &mp, PvNode);
1352 // Step 19. Check for mate and stalemate
1353 // All legal moves have been searched and if there are
1354 // no legal moves, it must be mate or stalemate.
1355 // If one move was excluded return fail low score.
1357 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1359 // Step 20. Update tables
1360 // If the search is not aborted, update the transposition table,
1361 // history counters, and killer moves.
1362 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1365 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1366 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1367 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1369 // Update killers and history only for non capture moves that fails high
1370 if (bestValue >= beta)
1372 ThreadsMgr.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1373 if (!pos.move_is_capture_or_promotion(move))
1375 update_history(pos, move, depth, movesSearched, moveCount);
1376 update_killers(move, ss);
1380 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1386 // qsearch() is the quiescence search function, which is called by the main
1387 // search function when the remaining depth is zero (or, to be more precise,
1388 // less than OnePly).
1390 template <NodeType PvNode>
1391 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1393 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1394 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1395 assert(PvNode || alpha == beta - 1);
1397 assert(ply > 0 && ply < PLY_MAX);
1398 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1403 Value bestValue, value, futilityValue, futilityBase;
1404 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1406 Value oldAlpha = alpha;
1408 ThreadsMgr.incrementNodeCounter(pos.thread());
1409 ss->bestMove = ss->currentMove = MOVE_NONE;
1411 // Check for an instant draw or maximum ply reached
1412 if (pos.is_draw() || ply >= PLY_MAX - 1)
1415 // Transposition table lookup. At PV nodes, we don't use the TT for
1416 // pruning, but only for move ordering.
1417 tte = TT.retrieve(pos.get_key());
1418 ttMove = (tte ? tte->move() : MOVE_NONE);
1420 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1422 ss->bestMove = ttMove; // Can be MOVE_NONE
1423 return value_from_tt(tte->value(), ply);
1426 isCheck = pos.is_check();
1428 // Evaluate the position statically
1431 bestValue = futilityBase = -VALUE_INFINITE;
1432 ss->eval = VALUE_NONE;
1433 deepChecks = enoughMaterial = false;
1439 assert(tte->static_value() != VALUE_NONE);
1441 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1442 bestValue = tte->static_value();
1445 bestValue = evaluate(pos, ei);
1447 ss->eval = bestValue;
1448 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1450 // Stand pat. Return immediately if static value is at least beta
1451 if (bestValue >= beta)
1454 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1459 if (PvNode && bestValue > alpha)
1462 // If we are near beta then try to get a cutoff pushing checks a bit further
1463 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1465 // Futility pruning parameters, not needed when in check
1466 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1467 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1470 // Initialize a MovePicker object for the current position, and prepare
1471 // to search the moves. Because the depth is <= 0 here, only captures,
1472 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1473 // and we are near beta) will be generated.
1474 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1477 // Loop through the moves until no moves remain or a beta cutoff occurs
1478 while ( alpha < beta
1479 && (move = mp.get_next_move()) != MOVE_NONE)
1481 assert(move_is_ok(move));
1483 moveIsCheck = pos.move_is_check(move, ci);
1491 && !move_is_promotion(move)
1492 && !pos.move_is_passed_pawn_push(move))
1494 futilityValue = futilityBase
1495 + pos.endgame_value_of_piece_on(move_to(move))
1496 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1498 if (futilityValue < alpha)
1500 if (futilityValue > bestValue)
1501 bestValue = futilityValue;
1506 // Detect blocking evasions that are candidate to be pruned
1507 evasionPrunable = isCheck
1508 && bestValue > value_mated_in(PLY_MAX)
1509 && !pos.move_is_capture(move)
1510 && pos.type_of_piece_on(move_from(move)) != KING
1511 && !pos.can_castle(pos.side_to_move());
1513 // Don't search moves with negative SEE values
1515 && (!isCheck || evasionPrunable)
1517 && !move_is_promotion(move)
1518 && pos.see_sign(move) < 0)
1521 // Update current move
1522 ss->currentMove = move;
1524 // Make and search the move
1525 pos.do_move(move, st, ci, moveIsCheck);
1526 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1527 pos.undo_move(move);
1529 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1532 if (value > bestValue)
1538 ss->bestMove = move;
1543 // All legal moves have been searched. A special case: If we're in check
1544 // and no legal moves were found, it is checkmate.
1545 if (isCheck && bestValue == -VALUE_INFINITE)
1546 return value_mated_in(ply);
1548 // Update transposition table
1549 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1550 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1551 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1553 // Update killers only for checking moves that fails high
1554 if ( bestValue >= beta
1555 && !pos.move_is_capture_or_promotion(ss->bestMove))
1556 update_killers(ss->bestMove, ss);
1558 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1564 // sp_search() is used to search from a split point. This function is called
1565 // by each thread working at the split point. It is similar to the normal
1566 // search() function, but simpler. Because we have already probed the hash
1567 // table, done a null move search, and searched the first move before
1568 // splitting, we don't have to repeat all this work in sp_search(). We
1569 // also don't need to store anything to the hash table here: This is taken
1570 // care of after we return from the split point.
1572 template <NodeType PvNode>
1573 void sp_search(SplitPoint* sp, int threadID) {
1575 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1576 assert(ThreadsMgr.active_threads() > 1);
1580 Depth ext, newDepth;
1582 Value futilityValueScaled; // NonPV specific
1583 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1585 value = -VALUE_INFINITE;
1587 Position pos(*sp->pos, threadID);
1589 SearchStack* ss = sp->sstack[threadID] + 1;
1590 isCheck = pos.is_check();
1592 // Step 10. Loop through moves
1593 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1594 lock_grab(&(sp->lock));
1596 while ( sp->bestValue < sp->beta
1597 && (move = sp->mp->get_next_move()) != MOVE_NONE
1598 && !ThreadsMgr.thread_should_stop(threadID))
1600 moveCount = ++sp->moveCount;
1601 lock_release(&(sp->lock));
1603 assert(move_is_ok(move));
1605 moveIsCheck = pos.move_is_check(move, ci);
1606 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1608 // Step 11. Decide the new search depth
1609 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1610 newDepth = sp->depth - OnePly + ext;
1612 // Update current move
1613 ss->currentMove = move;
1615 // Step 12. Futility pruning (is omitted in PV nodes)
1617 && !captureOrPromotion
1620 && !move_is_castle(move))
1622 // Move count based pruning
1623 if ( moveCount >= futility_move_count(sp->depth)
1624 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1625 && sp->bestValue > value_mated_in(PLY_MAX))
1627 lock_grab(&(sp->lock));
1631 // Value based pruning
1632 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1633 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1634 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1636 if (futilityValueScaled < sp->beta)
1638 lock_grab(&(sp->lock));
1640 if (futilityValueScaled > sp->bestValue)
1641 sp->bestValue = futilityValueScaled;
1646 // Step 13. Make the move
1647 pos.do_move(move, st, ci, moveIsCheck);
1649 // Step 14. Reduced search
1650 // If the move fails high will be re-searched at full depth.
1651 bool doFullDepthSearch = true;
1653 if ( !captureOrPromotion
1655 && !move_is_castle(move)
1656 && !move_is_killer(move, ss))
1658 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1661 Value localAlpha = sp->alpha;
1662 Depth d = newDepth - ss->reduction;
1663 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1664 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1666 doFullDepthSearch = (value > localAlpha);
1669 // The move failed high, but if reduction is very big we could
1670 // face a false positive, retry with a less aggressive reduction,
1671 // if the move fails high again then go with full depth search.
1672 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1674 assert(newDepth - OnePly >= OnePly);
1676 ss->reduction = OnePly;
1677 Value localAlpha = sp->alpha;
1678 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1679 doFullDepthSearch = (value > localAlpha);
1681 ss->reduction = Depth(0); // Restore original reduction
1684 // Step 15. Full depth search
1685 if (doFullDepthSearch)
1687 Value localAlpha = sp->alpha;
1688 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1689 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1691 // Step extra. pv search (only in PV nodes)
1692 // Search only for possible new PV nodes, if instead value >= beta then
1693 // parent node fails low with value <= alpha and tries another move.
1694 if (PvNode && value > localAlpha && value < sp->beta)
1695 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1696 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1699 // Step 16. Undo move
1700 pos.undo_move(move);
1702 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1704 // Step 17. Check for new best move
1705 lock_grab(&(sp->lock));
1707 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1709 sp->bestValue = value;
1711 if (sp->bestValue > sp->alpha)
1713 if (!PvNode || value >= sp->beta)
1714 sp->stopRequest = true;
1716 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1719 sp->parentSstack->bestMove = ss->bestMove = move;
1724 /* Here we have the lock still grabbed */
1726 sp->slaves[threadID] = 0;
1728 lock_release(&(sp->lock));
1732 // connected_moves() tests whether two moves are 'connected' in the sense
1733 // that the first move somehow made the second move possible (for instance
1734 // if the moving piece is the same in both moves). The first move is assumed
1735 // to be the move that was made to reach the current position, while the
1736 // second move is assumed to be a move from the current position.
1738 bool connected_moves(const Position& pos, Move m1, Move m2) {
1740 Square f1, t1, f2, t2;
1743 assert(move_is_ok(m1));
1744 assert(move_is_ok(m2));
1746 if (m2 == MOVE_NONE)
1749 // Case 1: The moving piece is the same in both moves
1755 // Case 2: The destination square for m2 was vacated by m1
1761 // Case 3: Moving through the vacated square
1762 if ( piece_is_slider(pos.piece_on(f2))
1763 && bit_is_set(squares_between(f2, t2), f1))
1766 // Case 4: The destination square for m2 is defended by the moving piece in m1
1767 p = pos.piece_on(t1);
1768 if (bit_is_set(pos.attacks_from(p, t1), t2))
1771 // Case 5: Discovered check, checking piece is the piece moved in m1
1772 if ( piece_is_slider(p)
1773 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1774 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1776 // discovered_check_candidates() works also if the Position's side to
1777 // move is the opposite of the checking piece.
1778 Color them = opposite_color(pos.side_to_move());
1779 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1781 if (bit_is_set(dcCandidates, f2))
1788 // value_is_mate() checks if the given value is a mate one eventually
1789 // compensated for the ply.
1791 bool value_is_mate(Value value) {
1793 assert(abs(value) <= VALUE_INFINITE);
1795 return value <= value_mated_in(PLY_MAX)
1796 || value >= value_mate_in(PLY_MAX);
1800 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1801 // "plies to mate from the current ply". Non-mate scores are unchanged.
1802 // The function is called before storing a value to the transposition table.
1804 Value value_to_tt(Value v, int ply) {
1806 if (v >= value_mate_in(PLY_MAX))
1809 if (v <= value_mated_in(PLY_MAX))
1816 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1817 // the transposition table to a mate score corrected for the current ply.
1819 Value value_from_tt(Value v, int ply) {
1821 if (v >= value_mate_in(PLY_MAX))
1824 if (v <= value_mated_in(PLY_MAX))
1831 // move_is_killer() checks if the given move is among the killer moves
1833 bool move_is_killer(Move m, SearchStack* ss) {
1835 if (ss->killers[0] == m || ss->killers[1] == m)
1842 // extension() decides whether a move should be searched with normal depth,
1843 // or with extended depth. Certain classes of moves (checking moves, in
1844 // particular) are searched with bigger depth than ordinary moves and in
1845 // any case are marked as 'dangerous'. Note that also if a move is not
1846 // extended, as example because the corresponding UCI option is set to zero,
1847 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1848 template <NodeType PvNode>
1849 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1850 bool singleEvasion, bool mateThreat, bool* dangerous) {
1852 assert(m != MOVE_NONE);
1854 Depth result = Depth(0);
1855 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1859 if (moveIsCheck && pos.see_sign(m) >= 0)
1860 result += CheckExtension[PvNode];
1863 result += SingleEvasionExtension[PvNode];
1866 result += MateThreatExtension[PvNode];
1869 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1871 Color c = pos.side_to_move();
1872 if (relative_rank(c, move_to(m)) == RANK_7)
1874 result += PawnPushTo7thExtension[PvNode];
1877 if (pos.pawn_is_passed(c, move_to(m)))
1879 result += PassedPawnExtension[PvNode];
1884 if ( captureOrPromotion
1885 && pos.type_of_piece_on(move_to(m)) != PAWN
1886 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1887 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1888 && !move_is_promotion(m)
1891 result += PawnEndgameExtension[PvNode];
1896 && captureOrPromotion
1897 && pos.type_of_piece_on(move_to(m)) != PAWN
1898 && pos.see_sign(m) >= 0)
1904 return Min(result, OnePly);
1908 // connected_threat() tests whether it is safe to forward prune a move or if
1909 // is somehow coonected to the threat move returned by null search.
1911 bool connected_threat(const Position& pos, Move m, Move threat) {
1913 assert(move_is_ok(m));
1914 assert(threat && move_is_ok(threat));
1915 assert(!pos.move_is_check(m));
1916 assert(!pos.move_is_capture_or_promotion(m));
1917 assert(!pos.move_is_passed_pawn_push(m));
1919 Square mfrom, mto, tfrom, tto;
1921 mfrom = move_from(m);
1923 tfrom = move_from(threat);
1924 tto = move_to(threat);
1926 // Case 1: Don't prune moves which move the threatened piece
1930 // Case 2: If the threatened piece has value less than or equal to the
1931 // value of the threatening piece, don't prune move which defend it.
1932 if ( pos.move_is_capture(threat)
1933 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1934 || pos.type_of_piece_on(tfrom) == KING)
1935 && pos.move_attacks_square(m, tto))
1938 // Case 3: If the moving piece in the threatened move is a slider, don't
1939 // prune safe moves which block its ray.
1940 if ( piece_is_slider(pos.piece_on(tfrom))
1941 && bit_is_set(squares_between(tfrom, tto), mto)
1942 && pos.see_sign(m) >= 0)
1949 // ok_to_use_TT() returns true if a transposition table score
1950 // can be used at a given point in search.
1952 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1954 Value v = value_from_tt(tte->value(), ply);
1956 return ( tte->depth() >= depth
1957 || v >= Max(value_mate_in(PLY_MAX), beta)
1958 || v < Min(value_mated_in(PLY_MAX), beta))
1960 && ( (is_lower_bound(tte->type()) && v >= beta)
1961 || (is_upper_bound(tte->type()) && v < beta));
1965 // refine_eval() returns the transposition table score if
1966 // possible otherwise falls back on static position evaluation.
1968 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1972 Value v = value_from_tt(tte->value(), ply);
1974 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1975 || (is_upper_bound(tte->type()) && v < defaultEval))
1982 // update_history() registers a good move that produced a beta-cutoff
1983 // in history and marks as failures all the other moves of that ply.
1985 void update_history(const Position& pos, Move move, Depth depth,
1986 Move movesSearched[], int moveCount) {
1990 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1992 for (int i = 0; i < moveCount - 1; i++)
1994 m = movesSearched[i];
1998 if (!pos.move_is_capture_or_promotion(m))
1999 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2004 // update_killers() add a good move that produced a beta-cutoff
2005 // among the killer moves of that ply.
2007 void update_killers(Move m, SearchStack* ss) {
2009 if (m == ss->killers[0])
2012 ss->killers[1] = ss->killers[0];
2017 // update_gains() updates the gains table of a non-capture move given
2018 // the static position evaluation before and after the move.
2020 void update_gains(const Position& pos, Move m, Value before, Value after) {
2023 && before != VALUE_NONE
2024 && after != VALUE_NONE
2025 && pos.captured_piece_type() == PIECE_TYPE_NONE
2026 && !move_is_special(m))
2027 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2031 // current_search_time() returns the number of milliseconds which have passed
2032 // since the beginning of the current search.
2034 int current_search_time() {
2036 return get_system_time() - SearchStartTime;
2040 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2042 std::string value_to_uci(Value v) {
2044 std::stringstream s;
2046 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2047 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2049 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2054 // nps() computes the current nodes/second count.
2058 int t = current_search_time();
2059 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2063 // poll() performs two different functions: It polls for user input, and it
2064 // looks at the time consumed so far and decides if it's time to abort the
2069 static int lastInfoTime;
2070 int t = current_search_time();
2075 // We are line oriented, don't read single chars
2076 std::string command;
2078 if (!std::getline(std::cin, command))
2081 if (command == "quit")
2084 PonderSearch = false;
2088 else if (command == "stop")
2091 PonderSearch = false;
2093 else if (command == "ponderhit")
2097 // Print search information
2101 else if (lastInfoTime > t)
2102 // HACK: Must be a new search where we searched less than
2103 // NodesBetweenPolls nodes during the first second of search.
2106 else if (t - lastInfoTime >= 1000)
2113 if (dbg_show_hit_rate)
2114 dbg_print_hit_rate();
2116 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2117 << " time " << t << endl;
2120 // Should we stop the search?
2124 bool stillAtFirstMove = FirstRootMove
2125 && !AspirationFailLow
2126 && t > TimeMgr.available_time();
2128 bool noMoreTime = t > TimeMgr.maximum_time()
2129 || stillAtFirstMove;
2131 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2132 || (ExactMaxTime && t >= ExactMaxTime)
2133 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2138 // ponderhit() is called when the program is pondering (i.e. thinking while
2139 // it's the opponent's turn to move) in order to let the engine know that
2140 // it correctly predicted the opponent's move.
2144 int t = current_search_time();
2145 PonderSearch = false;
2147 bool stillAtFirstMove = FirstRootMove
2148 && !AspirationFailLow
2149 && t > TimeMgr.available_time();
2151 bool noMoreTime = t > TimeMgr.maximum_time()
2152 || stillAtFirstMove;
2154 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2159 // init_ss_array() does a fast reset of the first entries of a SearchStack
2160 // array and of all the excludedMove and skipNullMove entries.
2162 void init_ss_array(SearchStack* ss, int size) {
2164 for (int i = 0; i < size; i++, ss++)
2166 ss->excludedMove = MOVE_NONE;
2167 ss->skipNullMove = false;
2168 ss->reduction = Depth(0);
2171 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2176 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2177 // while the program is pondering. The point is to work around a wrinkle in
2178 // the UCI protocol: When pondering, the engine is not allowed to give a
2179 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2180 // We simply wait here until one of these commands is sent, and return,
2181 // after which the bestmove and pondermove will be printed (in id_loop()).
2183 void wait_for_stop_or_ponderhit() {
2185 std::string command;
2189 if (!std::getline(std::cin, command))
2192 if (command == "quit")
2197 else if (command == "ponderhit" || command == "stop")
2203 // print_pv_info() prints to standard output and eventually to log file information on
2204 // the current PV line. It is called at each iteration or after a new pv is found.
2206 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2208 cout << "info depth " << Iteration
2209 << " score " << value_to_uci(value)
2210 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2211 << " time " << current_search_time()
2212 << " nodes " << ThreadsMgr.nodes_searched()
2216 for (Move* m = pv; *m != MOVE_NONE; m++)
2223 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2224 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2226 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2227 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2232 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2233 // the PV back into the TT. This makes sure the old PV moves are searched
2234 // first, even if the old TT entries have been overwritten.
2236 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2240 Position p(pos, pos.thread());
2244 for (int i = 0; pv[i] != MOVE_NONE; i++)
2246 tte = TT.retrieve(p.get_key());
2247 if (!tte || tte->move() != pv[i])
2249 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2250 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2252 p.do_move(pv[i], st);
2257 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2258 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2259 // allow to always have a ponder move even when we fail high at root and also a
2260 // long PV to print that is important for position analysis.
2262 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2266 Position p(pos, pos.thread());
2269 assert(bestMove != MOVE_NONE);
2272 p.do_move(pv[ply++], st);
2274 while ( (tte = TT.retrieve(p.get_key())) != NULL
2275 && tte->move() != MOVE_NONE
2276 && move_is_legal(p, tte->move())
2278 && (!p.is_draw() || ply < 2))
2280 pv[ply] = tte->move();
2281 p.do_move(pv[ply++], st);
2283 pv[ply] = MOVE_NONE;
2287 // init_thread() is the function which is called when a new thread is
2288 // launched. It simply calls the idle_loop() function with the supplied
2289 // threadID. There are two versions of this function; one for POSIX
2290 // threads and one for Windows threads.
2292 #if !defined(_MSC_VER)
2294 void* init_thread(void *threadID) {
2296 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2302 DWORD WINAPI init_thread(LPVOID threadID) {
2304 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2311 /// The ThreadsManager class
2313 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2314 // get_beta_counters() are getters/setters for the per thread
2315 // counters used to sort the moves at root.
2317 void ThreadsManager::resetNodeCounters() {
2319 for (int i = 0; i < MAX_THREADS; i++)
2320 threads[i].nodes = 0ULL;
2323 void ThreadsManager::resetBetaCounters() {
2325 for (int i = 0; i < MAX_THREADS; i++)
2326 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2329 int64_t ThreadsManager::nodes_searched() const {
2331 int64_t result = 0ULL;
2332 for (int i = 0; i < ActiveThreads; i++)
2333 result += threads[i].nodes;
2338 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2341 for (int i = 0; i < MAX_THREADS; i++)
2343 our += threads[i].betaCutOffs[us];
2344 their += threads[i].betaCutOffs[opposite_color(us)];
2349 // idle_loop() is where the threads are parked when they have no work to do.
2350 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2351 // object for which the current thread is the master.
2353 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2355 assert(threadID >= 0 && threadID < MAX_THREADS);
2359 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2360 // master should exit as last one.
2361 if (AllThreadsShouldExit)
2364 threads[threadID].state = THREAD_TERMINATED;
2368 // If we are not thinking, wait for a condition to be signaled
2369 // instead of wasting CPU time polling for work.
2370 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2373 assert(threadID != 0);
2374 threads[threadID].state = THREAD_SLEEPING;
2376 #if !defined(_MSC_VER)
2377 lock_grab(&WaitLock);
2378 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2379 pthread_cond_wait(&WaitCond, &WaitLock);
2380 lock_release(&WaitLock);
2382 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2386 // If thread has just woken up, mark it as available
2387 if (threads[threadID].state == THREAD_SLEEPING)
2388 threads[threadID].state = THREAD_AVAILABLE;
2390 // If this thread has been assigned work, launch a search
2391 if (threads[threadID].state == THREAD_WORKISWAITING)
2393 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2395 threads[threadID].state = THREAD_SEARCHING;
2397 if (threads[threadID].splitPoint->pvNode)
2398 sp_search<PV>(threads[threadID].splitPoint, threadID);
2400 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2402 assert(threads[threadID].state == THREAD_SEARCHING);
2404 threads[threadID].state = THREAD_AVAILABLE;
2407 // If this thread is the master of a split point and all slaves have
2408 // finished their work at this split point, return from the idle loop.
2410 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2412 if (i == ActiveThreads)
2414 // Because sp->slaves[] is reset under lock protection,
2415 // be sure sp->lock has been released before to return.
2416 lock_grab(&(sp->lock));
2417 lock_release(&(sp->lock));
2419 assert(threads[threadID].state == THREAD_AVAILABLE);
2421 threads[threadID].state = THREAD_SEARCHING;
2428 // init_threads() is called during startup. It launches all helper threads,
2429 // and initializes the split point stack and the global locks and condition
2432 void ThreadsManager::init_threads() {
2437 #if !defined(_MSC_VER)
2438 pthread_t pthread[1];
2441 // Initialize global locks
2443 lock_init(&WaitLock);
2445 #if !defined(_MSC_VER)
2446 pthread_cond_init(&WaitCond, NULL);
2448 for (i = 0; i < MAX_THREADS; i++)
2449 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2452 // Initialize splitPoints[] locks
2453 for (i = 0; i < MAX_THREADS; i++)
2454 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2455 lock_init(&(threads[i].splitPoints[j].lock));
2457 // Will be set just before program exits to properly end the threads
2458 AllThreadsShouldExit = false;
2460 // Threads will be put to sleep as soon as created
2461 AllThreadsShouldSleep = true;
2463 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2465 threads[0].state = THREAD_SEARCHING;
2466 for (i = 1; i < MAX_THREADS; i++)
2467 threads[i].state = THREAD_AVAILABLE;
2469 // Launch the helper threads
2470 for (i = 1; i < MAX_THREADS; i++)
2473 #if !defined(_MSC_VER)
2474 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2476 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2481 cout << "Failed to create thread number " << i << endl;
2482 Application::exit_with_failure();
2485 // Wait until the thread has finished launching and is gone to sleep
2486 while (threads[i].state != THREAD_SLEEPING) {}
2491 // exit_threads() is called when the program exits. It makes all the
2492 // helper threads exit cleanly.
2494 void ThreadsManager::exit_threads() {
2496 ActiveThreads = MAX_THREADS; // HACK
2497 AllThreadsShouldSleep = true; // HACK
2498 wake_sleeping_threads();
2500 // This makes the threads to exit idle_loop()
2501 AllThreadsShouldExit = true;
2503 // Wait for thread termination
2504 for (int i = 1; i < MAX_THREADS; i++)
2505 while (threads[i].state != THREAD_TERMINATED) {}
2507 // Now we can safely destroy the locks
2508 for (int i = 0; i < MAX_THREADS; i++)
2509 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2510 lock_destroy(&(threads[i].splitPoints[j].lock));
2512 lock_destroy(&WaitLock);
2513 lock_destroy(&MPLock);
2517 // thread_should_stop() checks whether the thread should stop its search.
2518 // This can happen if a beta cutoff has occurred in the thread's currently
2519 // active split point, or in some ancestor of the current split point.
2521 bool ThreadsManager::thread_should_stop(int threadID) const {
2523 assert(threadID >= 0 && threadID < ActiveThreads);
2527 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2532 // thread_is_available() checks whether the thread with threadID "slave" is
2533 // available to help the thread with threadID "master" at a split point. An
2534 // obvious requirement is that "slave" must be idle. With more than two
2535 // threads, this is not by itself sufficient: If "slave" is the master of
2536 // some active split point, it is only available as a slave to the other
2537 // threads which are busy searching the split point at the top of "slave"'s
2538 // split point stack (the "helpful master concept" in YBWC terminology).
2540 bool ThreadsManager::thread_is_available(int slave, int master) const {
2542 assert(slave >= 0 && slave < ActiveThreads);
2543 assert(master >= 0 && master < ActiveThreads);
2544 assert(ActiveThreads > 1);
2546 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2549 // Make a local copy to be sure doesn't change under our feet
2550 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2552 if (localActiveSplitPoints == 0)
2553 // No active split points means that the thread is available as
2554 // a slave for any other thread.
2557 if (ActiveThreads == 2)
2560 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2561 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2562 // could have been set to 0 by another thread leading to an out of bound access.
2563 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2570 // available_thread_exists() tries to find an idle thread which is available as
2571 // a slave for the thread with threadID "master".
2573 bool ThreadsManager::available_thread_exists(int master) const {
2575 assert(master >= 0 && master < ActiveThreads);
2576 assert(ActiveThreads > 1);
2578 for (int i = 0; i < ActiveThreads; i++)
2579 if (thread_is_available(i, master))
2586 // split() does the actual work of distributing the work at a node between
2587 // several available threads. If it does not succeed in splitting the
2588 // node (because no idle threads are available, or because we have no unused
2589 // split point objects), the function immediately returns. If splitting is
2590 // possible, a SplitPoint object is initialized with all the data that must be
2591 // copied to the helper threads and we tell our helper threads that they have
2592 // been assigned work. This will cause them to instantly leave their idle loops
2593 // and call sp_search(). When all threads have returned from sp_search() then
2596 template <bool Fake>
2597 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2598 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2599 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2601 assert(ply > 0 && ply < PLY_MAX);
2602 assert(*bestValue >= -VALUE_INFINITE);
2603 assert(*bestValue <= *alpha);
2604 assert(*alpha < beta);
2605 assert(beta <= VALUE_INFINITE);
2606 assert(depth > Depth(0));
2607 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2608 assert(ActiveThreads > 1);
2610 int i, master = p.thread();
2611 Thread& masterThread = threads[master];
2615 // If no other thread is available to help us, or if we have too many
2616 // active split points, don't split.
2617 if ( !available_thread_exists(master)
2618 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2620 lock_release(&MPLock);
2624 // Pick the next available split point object from the split point stack
2625 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2627 // Initialize the split point object
2628 splitPoint.parent = masterThread.splitPoint;
2629 splitPoint.stopRequest = false;
2630 splitPoint.ply = ply;
2631 splitPoint.depth = depth;
2632 splitPoint.threatMove = threatMove;
2633 splitPoint.mateThreat = mateThreat;
2634 splitPoint.alpha = *alpha;
2635 splitPoint.beta = beta;
2636 splitPoint.pvNode = pvNode;
2637 splitPoint.bestValue = *bestValue;
2639 splitPoint.moveCount = *moveCount;
2640 splitPoint.pos = &p;
2641 splitPoint.parentSstack = ss;
2642 for (i = 0; i < ActiveThreads; i++)
2643 splitPoint.slaves[i] = 0;
2645 masterThread.splitPoint = &splitPoint;
2647 // If we are here it means we are not available
2648 assert(masterThread.state != THREAD_AVAILABLE);
2650 int workersCnt = 1; // At least the master is included
2652 // Allocate available threads setting state to THREAD_BOOKED
2653 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2654 if (thread_is_available(i, master))
2656 threads[i].state = THREAD_BOOKED;
2657 threads[i].splitPoint = &splitPoint;
2658 splitPoint.slaves[i] = 1;
2662 assert(Fake || workersCnt > 1);
2664 // We can release the lock because slave threads are already booked and master is not available
2665 lock_release(&MPLock);
2667 // Tell the threads that they have work to do. This will make them leave
2668 // their idle loop. But before copy search stack tail for each thread.
2669 for (i = 0; i < ActiveThreads; i++)
2670 if (i == master || splitPoint.slaves[i])
2672 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2674 assert(i == master || threads[i].state == THREAD_BOOKED);
2676 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2679 // Everything is set up. The master thread enters the idle loop, from
2680 // which it will instantly launch a search, because its state is
2681 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2682 // idle loop, which means that the main thread will return from the idle
2683 // loop when all threads have finished their work at this split point.
2684 idle_loop(master, &splitPoint);
2686 // We have returned from the idle loop, which means that all threads are
2687 // finished. Update alpha and bestValue, and return.
2690 *alpha = splitPoint.alpha;
2691 *bestValue = splitPoint.bestValue;
2692 masterThread.activeSplitPoints--;
2693 masterThread.splitPoint = splitPoint.parent;
2695 lock_release(&MPLock);
2699 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2700 // to start a new search from the root.
2702 void ThreadsManager::wake_sleeping_threads() {
2704 assert(AllThreadsShouldSleep);
2705 assert(ActiveThreads > 0);
2707 AllThreadsShouldSleep = false;
2709 if (ActiveThreads == 1)
2712 #if !defined(_MSC_VER)
2713 pthread_mutex_lock(&WaitLock);
2714 pthread_cond_broadcast(&WaitCond);
2715 pthread_mutex_unlock(&WaitLock);
2717 for (int i = 1; i < MAX_THREADS; i++)
2718 SetEvent(SitIdleEvent[i]);
2724 // put_threads_to_sleep() makes all the threads go to sleep just before
2725 // to leave think(), at the end of the search. Threads should have already
2726 // finished the job and should be idle.
2728 void ThreadsManager::put_threads_to_sleep() {
2730 assert(!AllThreadsShouldSleep);
2732 // This makes the threads to go to sleep
2733 AllThreadsShouldSleep = true;
2736 /// The RootMoveList class
2738 // RootMoveList c'tor
2740 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2742 SearchStack ss[PLY_MAX_PLUS_2];
2743 MoveStack mlist[MaxRootMoves];
2745 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2747 // Initialize search stack
2748 init_ss_array(ss, PLY_MAX_PLUS_2);
2749 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2750 ss[0].eval = VALUE_NONE;
2752 // Generate all legal moves
2753 MoveStack* last = generate_moves(pos, mlist);
2755 // Add each move to the moves[] array
2756 for (MoveStack* cur = mlist; cur != last; cur++)
2758 bool includeMove = includeAllMoves;
2760 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2761 includeMove = (searchMoves[k] == cur->move);
2766 // Find a quick score for the move
2767 pos.do_move(cur->move, st);
2768 ss[0].currentMove = cur->move;
2769 moves[count].move = cur->move;
2770 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2771 moves[count].pv[0] = cur->move;
2772 moves[count].pv[1] = MOVE_NONE;
2773 pos.undo_move(cur->move);
2780 // RootMoveList simple methods definitions
2782 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2784 moves[moveNum].nodes = nodes;
2785 moves[moveNum].cumulativeNodes += nodes;
2788 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2790 moves[moveNum].ourBeta = our;
2791 moves[moveNum].theirBeta = their;
2794 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2798 for (j = 0; pv[j] != MOVE_NONE; j++)
2799 moves[moveNum].pv[j] = pv[j];
2801 moves[moveNum].pv[j] = MOVE_NONE;
2805 // RootMoveList::sort() sorts the root move list at the beginning of a new
2808 void RootMoveList::sort() {
2810 sort_multipv(count - 1); // Sort all items
2814 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2815 // list by their scores and depths. It is used to order the different PVs
2816 // correctly in MultiPV mode.
2818 void RootMoveList::sort_multipv(int n) {
2822 for (i = 1; i <= n; i++)
2824 RootMove rm = moves[i];
2825 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2826 moves[j] = moves[j - 1];