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] = { 7 * 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, OptimumSearchTime;
255 int MaximumSearchTime, ExtraSearchTime, ExactMaxTime;
256 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
257 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
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() { TM.init_threads(); }
333 void exit_threads() { TM.exit_threads(); }
334 int64_t nodes_searched() { return TM.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)
372 MovePicker mp(pos, MOVE_NONE, depth, H);
374 // If we are at the last ply we don't need to do and undo
375 // the moves, just to count them.
376 if (depth <= OnePly) // Replace with '<' to test also qsearch
378 while (mp.get_next_move()) sum++;
382 // Loop through all legal moves
384 while ((move = mp.get_next_move()) != MOVE_NONE)
386 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
387 sum += perft(pos, depth - OnePly);
394 /// think() is the external interface to Stockfish's search, and is called when
395 /// the program receives the UCI 'go' command. It initializes various
396 /// search-related global variables, and calls root_search(). It returns false
397 /// when a quit command is received during the search.
399 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
400 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
402 // Initialize global search variables
403 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
404 OptimumSearchTime = MaximumSearchTime = ExtraSearchTime = 0;
406 TM.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 != TM.active_threads())
465 TM.set_active_threads(newActiveThreads);
466 init_eval(TM.active_threads());
469 // Wake up sleeping threads
470 TM.wake_sleeping_threads();
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
477 get_search_times(myTime, myIncrement, movesToGo, pos.startpos_ply_counter(),
478 &OptimumSearchTime, &MaximumSearchTime);
480 if (get_option_value_bool("Ponder"))
482 OptimumSearchTime += OptimumSearchTime / 4;
483 OptimumSearchTime = Min(OptimumSearchTime, MaximumSearchTime);
487 // Set best NodesBetweenPolls interval to avoid lagging under
488 // heavy time pressure.
490 NodesBetweenPolls = Min(MaxNodes, 30000);
491 else if (myTime && myTime < 1000)
492 NodesBetweenPolls = 1000;
493 else if (myTime && myTime < 5000)
494 NodesBetweenPolls = 5000;
496 NodesBetweenPolls = 30000;
498 // Write search information to log file
500 LogFile << "Searching: " << pos.to_fen() << endl
501 << "infinite: " << infinite
502 << " ponder: " << ponder
503 << " time: " << myTime
504 << " increment: " << myIncrement
505 << " moves to go: " << movesToGo << endl;
507 // We're ready to start thinking. Call the iterative deepening loop function
508 id_loop(pos, searchMoves);
513 TM.put_threads_to_sleep();
521 // id_loop() is the main iterative deepening loop. It calls root_search
522 // repeatedly with increasing depth until the allocated thinking time has
523 // been consumed, the user stops the search, or the maximum search depth is
526 Value id_loop(const Position& pos, Move searchMoves[]) {
528 Position p(pos, pos.thread());
529 SearchStack ss[PLY_MAX_PLUS_2];
530 Move pv[PLY_MAX_PLUS_2];
531 Move EasyMove = MOVE_NONE;
532 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
534 // Moves to search are verified, copied, scored and sorted
535 RootMoveList rml(p, searchMoves);
537 // Handle special case of searching on a mate/stale position
538 if (rml.move_count() == 0)
541 wait_for_stop_or_ponderhit();
543 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
546 // Print RootMoveList startup scoring to the standard output,
547 // so to output information also for iteration 1.
548 cout << "info depth " << 1
549 << "\ninfo depth " << 1
550 << " score " << value_to_uci(rml.get_move_score(0))
551 << " time " << current_search_time()
552 << " nodes " << TM.nodes_searched()
554 << " pv " << rml.get_move(0) << "\n";
559 init_ss_array(ss, PLY_MAX_PLUS_2);
560 pv[0] = pv[1] = MOVE_NONE;
561 ValueByIteration[1] = rml.get_move_score(0);
564 // Is one move significantly better than others after initial scoring ?
565 if ( rml.move_count() == 1
566 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
567 EasyMove = rml.get_move(0);
569 // Iterative deepening loop
570 while (Iteration < PLY_MAX)
572 // Initialize iteration
574 BestMoveChangesByIteration[Iteration] = 0;
576 cout << "info depth " << Iteration << endl;
578 // Calculate dynamic aspiration window based on previous iterations
579 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
581 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
582 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
584 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
585 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
587 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
588 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
591 // Search to the current depth, rml is updated and sorted, alpha and beta could change
592 value = root_search(p, ss, pv, rml, &alpha, &beta);
594 // Write PV to transposition table, in case the relevant entries have
595 // been overwritten during the search.
596 insert_pv_in_tt(p, pv);
599 break; // Value cannot be trusted. Break out immediately!
601 //Save info about search result
602 ValueByIteration[Iteration] = value;
604 // Drop the easy move if differs from the new best move
605 if (pv[0] != EasyMove)
606 EasyMove = MOVE_NONE;
608 if (UseTimeManagement)
611 bool stopSearch = false;
613 // Stop search early if there is only a single legal move,
614 // we search up to Iteration 6 anyway to get a proper score.
615 if (Iteration >= 6 && rml.move_count() == 1)
618 // Stop search early when the last two iterations returned a mate score
620 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
621 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
624 // Stop search early if one move seems to be much better than the others
625 int64_t nodes = TM.nodes_searched();
628 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
629 && current_search_time() > OptimumSearchTime / 16)
630 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
631 && current_search_time() > OptimumSearchTime / 32)))
634 // Add some extra time if the best move has changed during the last two iterations
635 if (Iteration > 5 && Iteration <= 50)
636 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (OptimumSearchTime / 2)
637 + BestMoveChangesByIteration[Iteration-1] * (OptimumSearchTime / 3);
639 // Stop search if most of MaxSearchTime is consumed at the end of the
640 // iteration. We probably don't have enough time to search the first
641 // move at the next iteration anyway.
642 if (current_search_time() > ((OptimumSearchTime + ExtraSearchTime) * 80) / 128)
648 StopOnPonderhit = true;
654 if (MaxDepth && Iteration >= MaxDepth)
658 // If we are pondering or in infinite search, we shouldn't print the
659 // best move before we are told to do so.
660 if (!AbortSearch && (PonderSearch || InfiniteSearch))
661 wait_for_stop_or_ponderhit();
663 // Print final search statistics
664 cout << "info nodes " << TM.nodes_searched()
666 << " time " << current_search_time() << endl;
668 // Print the best move and the ponder move to the standard output
669 if (pv[0] == MOVE_NONE)
671 pv[0] = rml.get_move(0);
675 assert(pv[0] != MOVE_NONE);
677 cout << "bestmove " << pv[0];
679 if (pv[1] != MOVE_NONE)
680 cout << " ponder " << pv[1];
687 dbg_print_mean(LogFile);
689 if (dbg_show_hit_rate)
690 dbg_print_hit_rate(LogFile);
692 LogFile << "\nNodes: " << TM.nodes_searched()
693 << "\nNodes/second: " << nps()
694 << "\nBest move: " << move_to_san(p, pv[0]);
697 p.do_move(pv[0], st);
698 LogFile << "\nPonder move: "
699 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
702 return rml.get_move_score(0);
706 // root_search() is the function which searches the root node. It is
707 // similar to search_pv except that it uses a different move ordering
708 // scheme, prints some information to the standard output and handles
709 // the fail low/high loops.
711 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
718 Depth depth, ext, newDepth;
719 Value value, alpha, beta;
720 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
721 int researchCountFH, researchCountFL;
723 researchCountFH = researchCountFL = 0;
726 isCheck = pos.is_check();
728 // Step 1. Initialize node (polling is omitted at root)
729 ss->currentMove = ss->bestMove = MOVE_NONE;
731 // Step 2. Check for aborted search (omitted at root)
732 // Step 3. Mate distance pruning (omitted at root)
733 // Step 4. Transposition table lookup (omitted at root)
735 // Step 5. Evaluate the position statically
736 // At root we do this only to get reference value for child nodes
737 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
739 // Step 6. Razoring (omitted at root)
740 // Step 7. Static null move pruning (omitted at root)
741 // Step 8. Null move search with verification search (omitted at root)
742 // Step 9. Internal iterative deepening (omitted at root)
744 // Step extra. Fail low loop
745 // We start with small aspiration window and in case of fail low, we research
746 // with bigger window until we are not failing low anymore.
749 // Sort the moves before to (re)search
752 // Step 10. Loop through all moves in the root move list
753 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
755 // This is used by time management
756 FirstRootMove = (i == 0);
758 // Save the current node count before the move is searched
759 nodes = TM.nodes_searched();
761 // Reset beta cut-off counters
762 TM.resetBetaCounters();
764 // Pick the next root move, and print the move and the move number to
765 // the standard output.
766 move = ss->currentMove = rml.get_move(i);
768 if (current_search_time() >= 1000)
769 cout << "info currmove " << move
770 << " currmovenumber " << i + 1 << endl;
772 moveIsCheck = pos.move_is_check(move);
773 captureOrPromotion = pos.move_is_capture_or_promotion(move);
775 // Step 11. Decide the new search depth
776 depth = (Iteration - 2) * OnePly + InitialDepth;
777 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
778 newDepth = depth + ext;
780 // Step 12. Futility pruning (omitted at root)
782 // Step extra. Fail high loop
783 // If move fails high, we research with bigger window until we are not failing
785 value = - VALUE_INFINITE;
789 // Step 13. Make the move
790 pos.do_move(move, st, ci, moveIsCheck);
792 // Step extra. pv search
793 // We do pv search for first moves (i < MultiPV)
794 // and for fail high research (value > alpha)
795 if (i < MultiPV || value > alpha)
797 // Aspiration window is disabled in multi-pv case
799 alpha = -VALUE_INFINITE;
801 // Full depth PV search, done on first move or after a fail high
802 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
806 // Step 14. Reduced search
807 // if the move fails high will be re-searched at full depth
808 bool doFullDepthSearch = true;
810 if ( depth >= 3 * OnePly
812 && !captureOrPromotion
813 && !move_is_castle(move))
815 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
818 assert(newDepth-ss->reduction >= OnePly);
820 // Reduced depth non-pv search using alpha as upperbound
821 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
822 doFullDepthSearch = (value > alpha);
825 // The move failed high, but if reduction is very big we could
826 // face a false positive, retry with a less aggressive reduction,
827 // if the move fails high again then go with full depth search.
828 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
830 assert(newDepth - OnePly >= OnePly);
832 ss->reduction = OnePly;
833 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
834 doFullDepthSearch = (value > alpha);
836 ss->reduction = Depth(0); // Restore original reduction
839 // Step 15. Full depth search
840 if (doFullDepthSearch)
842 // Full depth non-pv search using alpha as upperbound
843 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
845 // If we are above alpha then research at same depth but as PV
846 // to get a correct score or eventually a fail high above beta.
848 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
852 // Step 16. Undo move
855 // Can we exit fail high loop ?
856 if (AbortSearch || value < beta)
859 // We are failing high and going to do a research. It's important to update
860 // the score before research in case we run out of time while researching.
861 rml.set_move_score(i, value);
863 extract_pv_from_tt(pos, move, pv);
864 rml.set_move_pv(i, pv);
866 // Print information to the standard output
867 print_pv_info(pos, pv, alpha, beta, value);
869 // Prepare for a research after a fail high, each time with a wider window
870 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
873 } // End of fail high loop
875 // Finished searching the move. If AbortSearch is true, the search
876 // was aborted because the user interrupted the search or because we
877 // ran out of time. In this case, the return value of the search cannot
878 // be trusted, and we break out of the loop without updating the best
883 // Remember beta-cutoff and searched nodes counts for this move. The
884 // info is used to sort the root moves for the next iteration.
886 TM.get_beta_counters(pos.side_to_move(), our, their);
887 rml.set_beta_counters(i, our, their);
888 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
890 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
891 assert(value < beta);
893 // Step 17. Check for new best move
894 if (value <= alpha && i >= MultiPV)
895 rml.set_move_score(i, -VALUE_INFINITE);
898 // PV move or new best move!
901 rml.set_move_score(i, value);
903 extract_pv_from_tt(pos, move, pv);
904 rml.set_move_pv(i, pv);
908 // We record how often the best move has been changed in each
909 // iteration. This information is used for time managment: When
910 // the best move changes frequently, we allocate some more time.
912 BestMoveChangesByIteration[Iteration]++;
914 // Print information to the standard output
915 print_pv_info(pos, pv, alpha, beta, value);
917 // Raise alpha to setup proper non-pv search upper bound
924 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
926 cout << "info multipv " << j + 1
927 << " score " << value_to_uci(rml.get_move_score(j))
928 << " depth " << (j <= i ? Iteration : Iteration - 1)
929 << " time " << current_search_time()
930 << " nodes " << TM.nodes_searched()
934 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
935 cout << rml.get_move_pv(j, k) << " ";
939 alpha = rml.get_move_score(Min(i, MultiPV - 1));
941 } // PV move or new best move
943 assert(alpha >= *alphaPtr);
945 AspirationFailLow = (alpha == *alphaPtr);
947 if (AspirationFailLow && StopOnPonderhit)
948 StopOnPonderhit = false;
951 // Can we exit fail low loop ?
952 if (AbortSearch || !AspirationFailLow)
955 // Prepare for a research after a fail low, each time with a wider window
956 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
961 // Sort the moves before to return
968 // search<>() is the main search function for both PV and non-PV nodes
970 template <NodeType PvNode>
971 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
973 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
974 assert(beta > alpha && beta <= VALUE_INFINITE);
975 assert(PvNode || alpha == beta - 1);
976 assert(ply > 0 && ply < PLY_MAX);
977 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
979 Move movesSearched[256];
984 Move ttMove, move, excludedMove, threatMove;
986 Value bestValue, value, oldAlpha;
987 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
988 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
989 bool mateThreat = false;
991 int threadID = pos.thread();
992 refinedValue = bestValue = value = -VALUE_INFINITE;
995 // Step 1. Initialize node and poll. Polling can abort search
996 TM.incrementNodeCounter(threadID);
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 || TM.thread_should_stop(threadID))
1010 if (pos.is_draw() || ply >= PLY_MAX - 1)
1013 // Step 3. Mate distance pruning
1014 alpha = Max(value_mated_in(ply), alpha);
1015 beta = Min(value_mate_in(ply+1), beta);
1019 // Step 4. Transposition table lookup
1021 // We don't want the score of a partial search to overwrite a previous full search
1022 // TT value, so we use a different position key in case of an excluded move exists.
1023 excludedMove = ss->excludedMove;
1024 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1026 tte = TT.retrieve(posKey);
1027 ttMove = (tte ? tte->move() : MOVE_NONE);
1029 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1030 // This is to avoid problems in the following areas:
1032 // * Repetition draw detection
1033 // * Fifty move rule detection
1034 // * Searching for a mate
1035 // * Printing of full PV line
1037 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1039 // Refresh tte entry to avoid aging
1040 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1042 ss->bestMove = ttMove; // Can be MOVE_NONE
1043 return value_from_tt(tte->value(), ply);
1046 // Step 5. Evaluate the position statically
1047 // At PV nodes we do this only to update gain statistics
1048 isCheck = pos.is_check();
1053 assert(tte->static_value() != VALUE_NONE);
1054 ss->eval = tte->static_value();
1055 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1059 ss->eval = evaluate(pos, ei);
1060 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1063 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1064 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1067 ss->eval = VALUE_NONE;
1069 // Step 6. Razoring (is omitted in PV nodes)
1071 && depth < RazorDepth
1073 && refinedValue < beta - razor_margin(depth)
1074 && ttMove == MOVE_NONE
1075 && (ss-1)->currentMove != MOVE_NULL
1076 && !value_is_mate(beta)
1077 && !pos.has_pawn_on_7th(pos.side_to_move()))
1079 Value rbeta = beta - razor_margin(depth);
1080 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1082 // Logically we should return (v + razor_margin(depth)), but
1083 // surprisingly this did slightly weaker in tests.
1087 // Step 7. Static null move pruning (is omitted in PV nodes)
1088 // We're betting that the opponent doesn't have a move that will reduce
1089 // the score by more than futility_margin(depth) if we do a null move.
1091 && !ss->skipNullMove
1092 && depth < RazorDepth
1093 && refinedValue >= beta + futility_margin(depth, 0)
1095 && !value_is_mate(beta)
1096 && pos.non_pawn_material(pos.side_to_move()))
1097 return refinedValue - futility_margin(depth, 0);
1099 // Step 8. Null move search with verification search (is omitted in PV nodes)
1100 // When we jump directly to qsearch() we do a null move only if static value is
1101 // at least beta. Otherwise we do a null move if static value is not more than
1102 // NullMoveMargin under beta.
1104 && !ss->skipNullMove
1106 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1108 && !value_is_mate(beta)
1109 && pos.non_pawn_material(pos.side_to_move()))
1111 ss->currentMove = MOVE_NULL;
1113 // Null move dynamic reduction based on depth
1114 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1116 // Null move dynamic reduction based on value
1117 if (refinedValue - beta > PawnValueMidgame)
1120 pos.do_null_move(st);
1121 (ss+1)->skipNullMove = true;
1123 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1124 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1125 (ss+1)->skipNullMove = false;
1126 pos.undo_null_move();
1128 if (nullValue >= beta)
1130 // Do not return unproven mate scores
1131 if (nullValue >= value_mate_in(PLY_MAX))
1134 if (depth < 6 * OnePly)
1137 // Do verification search at high depths
1138 ss->skipNullMove = true;
1139 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1140 ss->skipNullMove = false;
1147 // The null move failed low, which means that we may be faced with
1148 // some kind of threat. If the previous move was reduced, check if
1149 // the move that refuted the null move was somehow connected to the
1150 // move which was reduced. If a connection is found, return a fail
1151 // low score (which will cause the reduced move to fail high in the
1152 // parent node, which will trigger a re-search with full depth).
1153 if (nullValue == value_mated_in(ply + 2))
1156 threatMove = (ss+1)->bestMove;
1157 if ( depth < ThreatDepth
1158 && (ss-1)->reduction
1159 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1164 // Step 9. Internal iterative deepening
1165 if ( depth >= IIDDepth[PvNode]
1166 && ttMove == MOVE_NONE
1167 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1169 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1171 ss->skipNullMove = true;
1172 search<PvNode>(pos, ss, alpha, beta, d, ply);
1173 ss->skipNullMove = false;
1175 ttMove = ss->bestMove;
1176 tte = TT.retrieve(posKey);
1179 // Expensive mate threat detection (only for PV nodes)
1181 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1183 // Initialize a MovePicker object for the current position
1184 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1186 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1187 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1188 && tte && tte->move()
1189 && !excludedMove // Do not allow recursive singular extension search
1190 && is_lower_bound(tte->type())
1191 && tte->depth() >= depth - 3 * OnePly;
1193 // Avoid to do an expensive singular extension search on nodes where
1194 // such search had already failed in the past.
1196 && singularExtensionNode
1197 && depth < SingularExtensionDepth[PvNode] + 5 * OnePly)
1199 TTEntry* ttx = TT.retrieve(pos.get_exclusion_key());
1200 if (ttx && is_lower_bound(ttx->type()))
1201 singularExtensionNode = false;
1204 // Step 10. Loop through moves
1205 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1206 while ( bestValue < beta
1207 && (move = mp.get_next_move()) != MOVE_NONE
1208 && !TM.thread_should_stop(threadID))
1210 assert(move_is_ok(move));
1212 if (move == excludedMove)
1215 moveIsCheck = pos.move_is_check(move, ci);
1216 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1218 // Step 11. Decide the new search depth
1219 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1221 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1222 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1223 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1224 // lower then ttValue minus a margin then we extend ttMove.
1225 if ( singularExtensionNode
1226 && move == tte->move()
1229 Value ttValue = value_from_tt(tte->value(), ply);
1231 if (abs(ttValue) < VALUE_KNOWN_WIN)
1233 Value b = ttValue - SingularExtensionMargin;
1234 ss->excludedMove = move;
1235 ss->skipNullMove = true;
1236 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1237 ss->skipNullMove = false;
1238 ss->excludedMove = MOVE_NONE;
1244 newDepth = depth - OnePly + ext;
1246 // Update current move (this must be done after singular extension search)
1247 movesSearched[moveCount++] = ss->currentMove = move;
1249 // Step 12. Futility pruning (is omitted in PV nodes)
1251 && !captureOrPromotion
1255 && !move_is_castle(move))
1257 // Move count based pruning
1258 if ( moveCount >= futility_move_count(depth)
1259 && !(threatMove && connected_threat(pos, move, threatMove))
1260 && bestValue > value_mated_in(PLY_MAX))
1263 // Value based pruning
1264 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1265 // but fixing this made program slightly weaker.
1266 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1267 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1268 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1270 if (futilityValueScaled < beta)
1272 if (futilityValueScaled > bestValue)
1273 bestValue = futilityValueScaled;
1278 // Step 13. Make the move
1279 pos.do_move(move, st, ci, moveIsCheck);
1281 // Step extra. pv search (only in PV nodes)
1282 // The first move in list is the expected PV
1283 if (PvNode && moveCount == 1)
1284 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1285 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1288 // Step 14. Reduced depth search
1289 // If the move fails high will be re-searched at full depth.
1290 bool doFullDepthSearch = true;
1292 if ( depth >= 3 * OnePly
1293 && !captureOrPromotion
1295 && !move_is_castle(move)
1296 && !move_is_killer(move, ss))
1298 ss->reduction = reduction<PvNode>(depth, moveCount);
1301 Depth d = newDepth - ss->reduction;
1302 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1303 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1305 doFullDepthSearch = (value > alpha);
1308 // The move failed high, but if reduction is very big we could
1309 // face a false positive, retry with a less aggressive reduction,
1310 // if the move fails high again then go with full depth search.
1311 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1313 assert(newDepth - OnePly >= OnePly);
1315 ss->reduction = OnePly;
1316 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1317 doFullDepthSearch = (value > alpha);
1319 ss->reduction = Depth(0); // Restore original reduction
1322 // Step 15. Full depth search
1323 if (doFullDepthSearch)
1325 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1326 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1328 // Step extra. pv search (only in PV nodes)
1329 // Search only for possible new PV nodes, if instead value >= beta then
1330 // parent node fails low with value <= alpha and tries another move.
1331 if (PvNode && value > alpha && value < beta)
1332 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1333 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1337 // Step 16. Undo move
1338 pos.undo_move(move);
1340 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1342 // Step 17. Check for new best move
1343 if (value > bestValue)
1348 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1351 if (value == value_mate_in(ply + 1))
1352 ss->mateKiller = move;
1354 ss->bestMove = move;
1358 // Step 18. Check for split
1359 if ( depth >= MinimumSplitDepth
1360 && TM.active_threads() > 1
1362 && TM.available_thread_exists(threadID)
1364 && !TM.thread_should_stop(threadID)
1366 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1367 threatMove, mateThreat, &moveCount, &mp, PvNode);
1370 // Step 19. Check for mate and stalemate
1371 // All legal moves have been searched and if there are
1372 // no legal moves, it must be mate or stalemate.
1373 // If one move was excluded return fail low score.
1375 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1377 // Step 20. Update tables
1378 // If the search is not aborted, update the transposition table,
1379 // history counters, and killer moves.
1380 if (AbortSearch || TM.thread_should_stop(threadID))
1383 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1384 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1385 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1387 // Update killers and history only for non capture moves that fails high
1388 if (bestValue >= beta)
1390 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1391 if (!pos.move_is_capture_or_promotion(move))
1393 update_history(pos, move, depth, movesSearched, moveCount);
1394 update_killers(move, ss);
1398 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1404 // qsearch() is the quiescence search function, which is called by the main
1405 // search function when the remaining depth is zero (or, to be more precise,
1406 // less than OnePly).
1408 template <NodeType PvNode>
1409 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1411 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1412 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1413 assert(PvNode || alpha == beta - 1);
1415 assert(ply > 0 && ply < PLY_MAX);
1416 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1421 Value bestValue, value, futilityValue, futilityBase;
1422 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1424 Value oldAlpha = alpha;
1426 TM.incrementNodeCounter(pos.thread());
1427 ss->bestMove = ss->currentMove = MOVE_NONE;
1429 // Check for an instant draw or maximum ply reached
1430 if (pos.is_draw() || ply >= PLY_MAX - 1)
1433 // Transposition table lookup. At PV nodes, we don't use the TT for
1434 // pruning, but only for move ordering.
1435 tte = TT.retrieve(pos.get_key());
1436 ttMove = (tte ? tte->move() : MOVE_NONE);
1438 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1440 ss->bestMove = ttMove; // Can be MOVE_NONE
1441 return value_from_tt(tte->value(), ply);
1444 isCheck = pos.is_check();
1446 // Evaluate the position statically
1449 bestValue = futilityBase = -VALUE_INFINITE;
1450 ss->eval = VALUE_NONE;
1451 deepChecks = enoughMaterial = false;
1457 assert(tte->static_value() != VALUE_NONE);
1458 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1459 bestValue = tte->static_value();
1462 bestValue = evaluate(pos, ei);
1464 ss->eval = bestValue;
1465 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1467 // Stand pat. Return immediately if static value is at least beta
1468 if (bestValue >= beta)
1471 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()]);
1476 if (PvNode && bestValue > alpha)
1479 // If we are near beta then try to get a cutoff pushing checks a bit further
1480 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1482 // Futility pruning parameters, not needed when in check
1483 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1484 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1487 // Initialize a MovePicker object for the current position, and prepare
1488 // to search the moves. Because the depth is <= 0 here, only captures,
1489 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1490 // and we are near beta) will be generated.
1491 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1494 // Loop through the moves until no moves remain or a beta cutoff occurs
1495 while ( alpha < beta
1496 && (move = mp.get_next_move()) != MOVE_NONE)
1498 assert(move_is_ok(move));
1500 moveIsCheck = pos.move_is_check(move, ci);
1508 && !move_is_promotion(move)
1509 && !pos.move_is_passed_pawn_push(move))
1511 futilityValue = futilityBase
1512 + pos.endgame_value_of_piece_on(move_to(move))
1513 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1515 if (futilityValue < alpha)
1517 if (futilityValue > bestValue)
1518 bestValue = futilityValue;
1523 // Detect blocking evasions that are candidate to be pruned
1524 evasionPrunable = isCheck
1525 && bestValue > value_mated_in(PLY_MAX)
1526 && !pos.move_is_capture(move)
1527 && pos.type_of_piece_on(move_from(move)) != KING
1528 && !pos.can_castle(pos.side_to_move());
1530 // Don't search moves with negative SEE values
1532 && (!isCheck || evasionPrunable)
1534 && !move_is_promotion(move)
1535 && pos.see_sign(move) < 0)
1538 // Update current move
1539 ss->currentMove = move;
1541 // Make and search the move
1542 pos.do_move(move, st, ci, moveIsCheck);
1543 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1544 pos.undo_move(move);
1546 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1549 if (value > bestValue)
1555 ss->bestMove = move;
1560 // All legal moves have been searched. A special case: If we're in check
1561 // and no legal moves were found, it is checkmate.
1562 if (isCheck && bestValue == -VALUE_INFINITE)
1563 return value_mated_in(ply);
1565 // Update transposition table
1566 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1567 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1568 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1570 // Update killers only for checking moves that fails high
1571 if ( bestValue >= beta
1572 && !pos.move_is_capture_or_promotion(ss->bestMove))
1573 update_killers(ss->bestMove, ss);
1575 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1581 // sp_search() is used to search from a split point. This function is called
1582 // by each thread working at the split point. It is similar to the normal
1583 // search() function, but simpler. Because we have already probed the hash
1584 // table, done a null move search, and searched the first move before
1585 // splitting, we don't have to repeat all this work in sp_search(). We
1586 // also don't need to store anything to the hash table here: This is taken
1587 // care of after we return from the split point.
1589 template <NodeType PvNode>
1590 void sp_search(SplitPoint* sp, int threadID) {
1592 assert(threadID >= 0 && threadID < TM.active_threads());
1593 assert(TM.active_threads() > 1);
1597 Depth ext, newDepth;
1599 Value futilityValueScaled; // NonPV specific
1600 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1602 value = -VALUE_INFINITE;
1604 Position pos(*sp->pos, threadID);
1606 SearchStack* ss = sp->sstack[threadID] + 1;
1607 isCheck = pos.is_check();
1609 // Step 10. Loop through moves
1610 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1611 lock_grab(&(sp->lock));
1613 while ( sp->bestValue < sp->beta
1614 && (move = sp->mp->get_next_move()) != MOVE_NONE
1615 && !TM.thread_should_stop(threadID))
1617 moveCount = ++sp->moveCount;
1618 lock_release(&(sp->lock));
1620 assert(move_is_ok(move));
1622 moveIsCheck = pos.move_is_check(move, ci);
1623 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1625 // Step 11. Decide the new search depth
1626 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1627 newDepth = sp->depth - OnePly + ext;
1629 // Update current move
1630 ss->currentMove = move;
1632 // Step 12. Futility pruning (is omitted in PV nodes)
1634 && !captureOrPromotion
1637 && !move_is_castle(move))
1639 // Move count based pruning
1640 if ( moveCount >= futility_move_count(sp->depth)
1641 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1642 && sp->bestValue > value_mated_in(PLY_MAX))
1644 lock_grab(&(sp->lock));
1648 // Value based pruning
1649 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1650 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1651 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1653 if (futilityValueScaled < sp->beta)
1655 lock_grab(&(sp->lock));
1657 if (futilityValueScaled > sp->bestValue)
1658 sp->bestValue = futilityValueScaled;
1663 // Step 13. Make the move
1664 pos.do_move(move, st, ci, moveIsCheck);
1666 // Step 14. Reduced search
1667 // If the move fails high will be re-searched at full depth.
1668 bool doFullDepthSearch = true;
1670 if ( !captureOrPromotion
1672 && !move_is_castle(move)
1673 && !move_is_killer(move, ss))
1675 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1678 Value localAlpha = sp->alpha;
1679 Depth d = newDepth - ss->reduction;
1680 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1681 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1683 doFullDepthSearch = (value > localAlpha);
1686 // The move failed high, but if reduction is very big we could
1687 // face a false positive, retry with a less aggressive reduction,
1688 // if the move fails high again then go with full depth search.
1689 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1691 assert(newDepth - OnePly >= OnePly);
1693 ss->reduction = OnePly;
1694 Value localAlpha = sp->alpha;
1695 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1696 doFullDepthSearch = (value > localAlpha);
1698 ss->reduction = Depth(0); // Restore original reduction
1701 // Step 15. Full depth search
1702 if (doFullDepthSearch)
1704 Value localAlpha = sp->alpha;
1705 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1706 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1708 // Step extra. pv search (only in PV nodes)
1709 // Search only for possible new PV nodes, if instead value >= beta then
1710 // parent node fails low with value <= alpha and tries another move.
1711 if (PvNode && value > localAlpha && value < sp->beta)
1712 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1713 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1716 // Step 16. Undo move
1717 pos.undo_move(move);
1719 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1721 // Step 17. Check for new best move
1722 lock_grab(&(sp->lock));
1724 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1726 sp->bestValue = value;
1728 if (sp->bestValue > sp->alpha)
1730 if (!PvNode || value >= sp->beta)
1731 sp->stopRequest = true;
1733 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1736 sp->parentSstack->bestMove = ss->bestMove = move;
1741 /* Here we have the lock still grabbed */
1743 sp->slaves[threadID] = 0;
1745 lock_release(&(sp->lock));
1749 // connected_moves() tests whether two moves are 'connected' in the sense
1750 // that the first move somehow made the second move possible (for instance
1751 // if the moving piece is the same in both moves). The first move is assumed
1752 // to be the move that was made to reach the current position, while the
1753 // second move is assumed to be a move from the current position.
1755 bool connected_moves(const Position& pos, Move m1, Move m2) {
1757 Square f1, t1, f2, t2;
1760 assert(move_is_ok(m1));
1761 assert(move_is_ok(m2));
1763 if (m2 == MOVE_NONE)
1766 // Case 1: The moving piece is the same in both moves
1772 // Case 2: The destination square for m2 was vacated by m1
1778 // Case 3: Moving through the vacated square
1779 if ( piece_is_slider(pos.piece_on(f2))
1780 && bit_is_set(squares_between(f2, t2), f1))
1783 // Case 4: The destination square for m2 is defended by the moving piece in m1
1784 p = pos.piece_on(t1);
1785 if (bit_is_set(pos.attacks_from(p, t1), t2))
1788 // Case 5: Discovered check, checking piece is the piece moved in m1
1789 if ( piece_is_slider(p)
1790 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1791 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1793 // discovered_check_candidates() works also if the Position's side to
1794 // move is the opposite of the checking piece.
1795 Color them = opposite_color(pos.side_to_move());
1796 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1798 if (bit_is_set(dcCandidates, f2))
1805 // value_is_mate() checks if the given value is a mate one eventually
1806 // compensated for the ply.
1808 bool value_is_mate(Value value) {
1810 assert(abs(value) <= VALUE_INFINITE);
1812 return value <= value_mated_in(PLY_MAX)
1813 || value >= value_mate_in(PLY_MAX);
1817 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1818 // "plies to mate from the current ply". Non-mate scores are unchanged.
1819 // The function is called before storing a value to the transposition table.
1821 Value value_to_tt(Value v, int ply) {
1823 if (v >= value_mate_in(PLY_MAX))
1826 if (v <= value_mated_in(PLY_MAX))
1833 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1834 // the transposition table to a mate score corrected for the current ply.
1836 Value value_from_tt(Value v, int ply) {
1838 if (v >= value_mate_in(PLY_MAX))
1841 if (v <= value_mated_in(PLY_MAX))
1848 // move_is_killer() checks if the given move is among the killer moves
1850 bool move_is_killer(Move m, SearchStack* ss) {
1852 if (ss->killers[0] == m || ss->killers[1] == m)
1859 // extension() decides whether a move should be searched with normal depth,
1860 // or with extended depth. Certain classes of moves (checking moves, in
1861 // particular) are searched with bigger depth than ordinary moves and in
1862 // any case are marked as 'dangerous'. Note that also if a move is not
1863 // extended, as example because the corresponding UCI option is set to zero,
1864 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1865 template <NodeType PvNode>
1866 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1867 bool singleEvasion, bool mateThreat, bool* dangerous) {
1869 assert(m != MOVE_NONE);
1871 Depth result = Depth(0);
1872 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1876 if (moveIsCheck && pos.see_sign(m) >= 0)
1877 result += CheckExtension[PvNode];
1880 result += SingleEvasionExtension[PvNode];
1883 result += MateThreatExtension[PvNode];
1886 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1888 Color c = pos.side_to_move();
1889 if (relative_rank(c, move_to(m)) == RANK_7)
1891 result += PawnPushTo7thExtension[PvNode];
1894 if (pos.pawn_is_passed(c, move_to(m)))
1896 result += PassedPawnExtension[PvNode];
1901 if ( captureOrPromotion
1902 && pos.type_of_piece_on(move_to(m)) != PAWN
1903 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1904 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1905 && !move_is_promotion(m)
1908 result += PawnEndgameExtension[PvNode];
1913 && captureOrPromotion
1914 && pos.type_of_piece_on(move_to(m)) != PAWN
1915 && pos.see_sign(m) >= 0)
1921 return Min(result, OnePly);
1925 // connected_threat() tests whether it is safe to forward prune a move or if
1926 // is somehow coonected to the threat move returned by null search.
1928 bool connected_threat(const Position& pos, Move m, Move threat) {
1930 assert(move_is_ok(m));
1931 assert(threat && move_is_ok(threat));
1932 assert(!pos.move_is_check(m));
1933 assert(!pos.move_is_capture_or_promotion(m));
1934 assert(!pos.move_is_passed_pawn_push(m));
1936 Square mfrom, mto, tfrom, tto;
1938 mfrom = move_from(m);
1940 tfrom = move_from(threat);
1941 tto = move_to(threat);
1943 // Case 1: Don't prune moves which move the threatened piece
1947 // Case 2: If the threatened piece has value less than or equal to the
1948 // value of the threatening piece, don't prune move which defend it.
1949 if ( pos.move_is_capture(threat)
1950 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1951 || pos.type_of_piece_on(tfrom) == KING)
1952 && pos.move_attacks_square(m, tto))
1955 // Case 3: If the moving piece in the threatened move is a slider, don't
1956 // prune safe moves which block its ray.
1957 if ( piece_is_slider(pos.piece_on(tfrom))
1958 && bit_is_set(squares_between(tfrom, tto), mto)
1959 && pos.see_sign(m) >= 0)
1966 // ok_to_use_TT() returns true if a transposition table score
1967 // can be used at a given point in search.
1969 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1971 Value v = value_from_tt(tte->value(), ply);
1973 return ( tte->depth() >= depth
1974 || v >= Max(value_mate_in(PLY_MAX), beta)
1975 || v < Min(value_mated_in(PLY_MAX), beta))
1977 && ( (is_lower_bound(tte->type()) && v >= beta)
1978 || (is_upper_bound(tte->type()) && v < beta));
1982 // refine_eval() returns the transposition table score if
1983 // possible otherwise falls back on static position evaluation.
1985 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1990 Value v = value_from_tt(tte->value(), ply);
1992 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1993 || (is_upper_bound(tte->type()) && v < defaultEval))
2000 // update_history() registers a good move that produced a beta-cutoff
2001 // in history and marks as failures all the other moves of that ply.
2003 void update_history(const Position& pos, Move move, Depth depth,
2004 Move movesSearched[], int moveCount) {
2008 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2010 for (int i = 0; i < moveCount - 1; i++)
2012 m = movesSearched[i];
2016 if (!pos.move_is_capture_or_promotion(m))
2017 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2022 // update_killers() add a good move that produced a beta-cutoff
2023 // among the killer moves of that ply.
2025 void update_killers(Move m, SearchStack* ss) {
2027 if (m == ss->killers[0])
2030 ss->killers[1] = ss->killers[0];
2035 // update_gains() updates the gains table of a non-capture move given
2036 // the static position evaluation before and after the move.
2038 void update_gains(const Position& pos, Move m, Value before, Value after) {
2041 && before != VALUE_NONE
2042 && after != VALUE_NONE
2043 && pos.captured_piece() == NO_PIECE_TYPE
2044 && !move_is_castle(m)
2045 && !move_is_promotion(m))
2046 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2050 // current_search_time() returns the number of milliseconds which have passed
2051 // since the beginning of the current search.
2053 int current_search_time() {
2055 return get_system_time() - SearchStartTime;
2059 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2061 std::string value_to_uci(Value v) {
2063 std::stringstream s;
2065 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2066 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2068 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2073 // nps() computes the current nodes/second count.
2077 int t = current_search_time();
2078 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2082 // poll() performs two different functions: It polls for user input, and it
2083 // looks at the time consumed so far and decides if it's time to abort the
2088 static int lastInfoTime;
2089 int t = current_search_time();
2094 // We are line oriented, don't read single chars
2095 std::string command;
2097 if (!std::getline(std::cin, command))
2100 if (command == "quit")
2103 PonderSearch = false;
2107 else if (command == "stop")
2110 PonderSearch = false;
2112 else if (command == "ponderhit")
2116 // Print search information
2120 else if (lastInfoTime > t)
2121 // HACK: Must be a new search where we searched less than
2122 // NodesBetweenPolls nodes during the first second of search.
2125 else if (t - lastInfoTime >= 1000)
2132 if (dbg_show_hit_rate)
2133 dbg_print_hit_rate();
2135 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2136 << " time " << t << endl;
2139 // Should we stop the search?
2143 bool stillAtFirstMove = FirstRootMove
2144 && !AspirationFailLow
2145 && t > OptimumSearchTime + ExtraSearchTime;
2147 bool noMoreTime = t > MaximumSearchTime
2148 || stillAtFirstMove;
2150 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2151 || (ExactMaxTime && t >= ExactMaxTime)
2152 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2157 // ponderhit() is called when the program is pondering (i.e. thinking while
2158 // it's the opponent's turn to move) in order to let the engine know that
2159 // it correctly predicted the opponent's move.
2163 int t = current_search_time();
2164 PonderSearch = false;
2166 bool stillAtFirstMove = FirstRootMove
2167 && !AspirationFailLow
2168 && t > OptimumSearchTime + ExtraSearchTime;
2170 bool noMoreTime = t > MaximumSearchTime
2171 || stillAtFirstMove;
2173 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2178 // init_ss_array() does a fast reset of the first entries of a SearchStack
2179 // array and of all the excludedMove and skipNullMove entries.
2181 void init_ss_array(SearchStack* ss, int size) {
2183 for (int i = 0; i < size; i++, ss++)
2185 ss->excludedMove = MOVE_NONE;
2186 ss->skipNullMove = false;
2187 ss->reduction = Depth(0);
2190 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2195 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2196 // while the program is pondering. The point is to work around a wrinkle in
2197 // the UCI protocol: When pondering, the engine is not allowed to give a
2198 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2199 // We simply wait here until one of these commands is sent, and return,
2200 // after which the bestmove and pondermove will be printed (in id_loop()).
2202 void wait_for_stop_or_ponderhit() {
2204 std::string command;
2208 if (!std::getline(std::cin, command))
2211 if (command == "quit")
2216 else if (command == "ponderhit" || command == "stop")
2222 // print_pv_info() prints to standard output and eventually to log file information on
2223 // the current PV line. It is called at each iteration or after a new pv is found.
2225 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2227 cout << "info depth " << Iteration
2228 << " score " << value_to_uci(value)
2229 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2230 << " time " << current_search_time()
2231 << " nodes " << TM.nodes_searched()
2235 for (Move* m = pv; *m != MOVE_NONE; m++)
2242 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2243 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2245 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2246 TM.nodes_searched(), value, t, pv) << endl;
2251 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2252 // the PV back into the TT. This makes sure the old PV moves are searched
2253 // first, even if the old TT entries have been overwritten.
2255 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2259 Position p(pos, pos.thread());
2263 for (int i = 0; pv[i] != MOVE_NONE; i++)
2265 tte = TT.retrieve(p.get_key());
2266 if (!tte || tte->move() != pv[i])
2268 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2269 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2271 p.do_move(pv[i], st);
2276 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2277 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2278 // allow to always have a ponder move even when we fail high at root and also a
2279 // long PV to print that is important for position analysis.
2281 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2285 Position p(pos, pos.thread());
2288 assert(bestMove != MOVE_NONE);
2291 p.do_move(pv[ply++], st);
2293 while ( (tte = TT.retrieve(p.get_key())) != NULL
2294 && tte->move() != MOVE_NONE
2295 && move_is_legal(p, tte->move())
2297 && (!p.is_draw() || ply < 2))
2299 pv[ply] = tte->move();
2300 p.do_move(pv[ply++], st);
2302 pv[ply] = MOVE_NONE;
2306 // init_thread() is the function which is called when a new thread is
2307 // launched. It simply calls the idle_loop() function with the supplied
2308 // threadID. There are two versions of this function; one for POSIX
2309 // threads and one for Windows threads.
2311 #if !defined(_MSC_VER)
2313 void* init_thread(void *threadID) {
2315 TM.idle_loop(*(int*)threadID, NULL);
2321 DWORD WINAPI init_thread(LPVOID threadID) {
2323 TM.idle_loop(*(int*)threadID, NULL);
2330 /// The ThreadsManager class
2332 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2333 // get_beta_counters() are getters/setters for the per thread
2334 // counters used to sort the moves at root.
2336 void ThreadsManager::resetNodeCounters() {
2338 for (int i = 0; i < MAX_THREADS; i++)
2339 threads[i].nodes = 0ULL;
2342 void ThreadsManager::resetBetaCounters() {
2344 for (int i = 0; i < MAX_THREADS; i++)
2345 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2348 int64_t ThreadsManager::nodes_searched() const {
2350 int64_t result = 0ULL;
2351 for (int i = 0; i < ActiveThreads; i++)
2352 result += threads[i].nodes;
2357 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2360 for (int i = 0; i < MAX_THREADS; i++)
2362 our += threads[i].betaCutOffs[us];
2363 their += threads[i].betaCutOffs[opposite_color(us)];
2368 // idle_loop() is where the threads are parked when they have no work to do.
2369 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2370 // object for which the current thread is the master.
2372 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2374 assert(threadID >= 0 && threadID < MAX_THREADS);
2378 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2379 // master should exit as last one.
2380 if (AllThreadsShouldExit)
2383 threads[threadID].state = THREAD_TERMINATED;
2387 // If we are not thinking, wait for a condition to be signaled
2388 // instead of wasting CPU time polling for work.
2389 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2392 assert(threadID != 0);
2393 threads[threadID].state = THREAD_SLEEPING;
2395 #if !defined(_MSC_VER)
2396 lock_grab(&WaitLock);
2397 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2398 pthread_cond_wait(&WaitCond, &WaitLock);
2399 lock_release(&WaitLock);
2401 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2405 // If thread has just woken up, mark it as available
2406 if (threads[threadID].state == THREAD_SLEEPING)
2407 threads[threadID].state = THREAD_AVAILABLE;
2409 // If this thread has been assigned work, launch a search
2410 if (threads[threadID].state == THREAD_WORKISWAITING)
2412 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2414 threads[threadID].state = THREAD_SEARCHING;
2416 if (threads[threadID].splitPoint->pvNode)
2417 sp_search<PV>(threads[threadID].splitPoint, threadID);
2419 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2421 assert(threads[threadID].state == THREAD_SEARCHING);
2423 threads[threadID].state = THREAD_AVAILABLE;
2426 // If this thread is the master of a split point and all slaves have
2427 // finished their work at this split point, return from the idle loop.
2429 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2431 if (i == ActiveThreads)
2433 // Because sp->slaves[] is reset under lock protection,
2434 // be sure sp->lock has been released before to return.
2435 lock_grab(&(sp->lock));
2436 lock_release(&(sp->lock));
2438 assert(threads[threadID].state == THREAD_AVAILABLE);
2440 threads[threadID].state = THREAD_SEARCHING;
2447 // init_threads() is called during startup. It launches all helper threads,
2448 // and initializes the split point stack and the global locks and condition
2451 void ThreadsManager::init_threads() {
2456 #if !defined(_MSC_VER)
2457 pthread_t pthread[1];
2460 // Initialize global locks
2462 lock_init(&WaitLock);
2464 #if !defined(_MSC_VER)
2465 pthread_cond_init(&WaitCond, NULL);
2467 for (i = 0; i < MAX_THREADS; i++)
2468 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2471 // Initialize splitPoints[] locks
2472 for (i = 0; i < MAX_THREADS; i++)
2473 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2474 lock_init(&(threads[i].splitPoints[j].lock));
2476 // Will be set just before program exits to properly end the threads
2477 AllThreadsShouldExit = false;
2479 // Threads will be put to sleep as soon as created
2480 AllThreadsShouldSleep = true;
2482 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2484 threads[0].state = THREAD_SEARCHING;
2485 for (i = 1; i < MAX_THREADS; i++)
2486 threads[i].state = THREAD_AVAILABLE;
2488 // Launch the helper threads
2489 for (i = 1; i < MAX_THREADS; i++)
2492 #if !defined(_MSC_VER)
2493 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2495 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2500 cout << "Failed to create thread number " << i << endl;
2501 Application::exit_with_failure();
2504 // Wait until the thread has finished launching and is gone to sleep
2505 while (threads[i].state != THREAD_SLEEPING) {}
2510 // exit_threads() is called when the program exits. It makes all the
2511 // helper threads exit cleanly.
2513 void ThreadsManager::exit_threads() {
2515 ActiveThreads = MAX_THREADS; // HACK
2516 AllThreadsShouldSleep = true; // HACK
2517 wake_sleeping_threads();
2519 // This makes the threads to exit idle_loop()
2520 AllThreadsShouldExit = true;
2522 // Wait for thread termination
2523 for (int i = 1; i < MAX_THREADS; i++)
2524 while (threads[i].state != THREAD_TERMINATED) {}
2526 // Now we can safely destroy the locks
2527 for (int i = 0; i < MAX_THREADS; i++)
2528 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2529 lock_destroy(&(threads[i].splitPoints[j].lock));
2531 lock_destroy(&WaitLock);
2532 lock_destroy(&MPLock);
2536 // thread_should_stop() checks whether the thread should stop its search.
2537 // This can happen if a beta cutoff has occurred in the thread's currently
2538 // active split point, or in some ancestor of the current split point.
2540 bool ThreadsManager::thread_should_stop(int threadID) const {
2542 assert(threadID >= 0 && threadID < ActiveThreads);
2546 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2551 // thread_is_available() checks whether the thread with threadID "slave" is
2552 // available to help the thread with threadID "master" at a split point. An
2553 // obvious requirement is that "slave" must be idle. With more than two
2554 // threads, this is not by itself sufficient: If "slave" is the master of
2555 // some active split point, it is only available as a slave to the other
2556 // threads which are busy searching the split point at the top of "slave"'s
2557 // split point stack (the "helpful master concept" in YBWC terminology).
2559 bool ThreadsManager::thread_is_available(int slave, int master) const {
2561 assert(slave >= 0 && slave < ActiveThreads);
2562 assert(master >= 0 && master < ActiveThreads);
2563 assert(ActiveThreads > 1);
2565 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2568 // Make a local copy to be sure doesn't change under our feet
2569 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2571 if (localActiveSplitPoints == 0)
2572 // No active split points means that the thread is available as
2573 // a slave for any other thread.
2576 if (ActiveThreads == 2)
2579 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2580 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2581 // could have been set to 0 by another thread leading to an out of bound access.
2582 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2589 // available_thread_exists() tries to find an idle thread which is available as
2590 // a slave for the thread with threadID "master".
2592 bool ThreadsManager::available_thread_exists(int master) const {
2594 assert(master >= 0 && master < ActiveThreads);
2595 assert(ActiveThreads > 1);
2597 for (int i = 0; i < ActiveThreads; i++)
2598 if (thread_is_available(i, master))
2605 // split() does the actual work of distributing the work at a node between
2606 // several available threads. If it does not succeed in splitting the
2607 // node (because no idle threads are available, or because we have no unused
2608 // split point objects), the function immediately returns. If splitting is
2609 // possible, a SplitPoint object is initialized with all the data that must be
2610 // copied to the helper threads and we tell our helper threads that they have
2611 // been assigned work. This will cause them to instantly leave their idle loops
2612 // and call sp_search(). When all threads have returned from sp_search() then
2615 template <bool Fake>
2616 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2617 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2618 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2620 assert(ply > 0 && ply < PLY_MAX);
2621 assert(*bestValue >= -VALUE_INFINITE);
2622 assert(*bestValue <= *alpha);
2623 assert(*alpha < beta);
2624 assert(beta <= VALUE_INFINITE);
2625 assert(depth > Depth(0));
2626 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2627 assert(ActiveThreads > 1);
2629 int i, master = p.thread();
2630 Thread& masterThread = threads[master];
2634 // If no other thread is available to help us, or if we have too many
2635 // active split points, don't split.
2636 if ( !available_thread_exists(master)
2637 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2639 lock_release(&MPLock);
2643 // Pick the next available split point object from the split point stack
2644 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2646 // Initialize the split point object
2647 splitPoint.parent = masterThread.splitPoint;
2648 splitPoint.stopRequest = false;
2649 splitPoint.ply = ply;
2650 splitPoint.depth = depth;
2651 splitPoint.threatMove = threatMove;
2652 splitPoint.mateThreat = mateThreat;
2653 splitPoint.alpha = *alpha;
2654 splitPoint.beta = beta;
2655 splitPoint.pvNode = pvNode;
2656 splitPoint.bestValue = *bestValue;
2658 splitPoint.moveCount = *moveCount;
2659 splitPoint.pos = &p;
2660 splitPoint.parentSstack = ss;
2661 for (i = 0; i < ActiveThreads; i++)
2662 splitPoint.slaves[i] = 0;
2664 masterThread.splitPoint = &splitPoint;
2666 // If we are here it means we are not available
2667 assert(masterThread.state != THREAD_AVAILABLE);
2669 int workersCnt = 1; // At least the master is included
2671 // Allocate available threads setting state to THREAD_BOOKED
2672 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2673 if (thread_is_available(i, master))
2675 threads[i].state = THREAD_BOOKED;
2676 threads[i].splitPoint = &splitPoint;
2677 splitPoint.slaves[i] = 1;
2681 assert(Fake || workersCnt > 1);
2683 // We can release the lock because slave threads are already booked and master is not available
2684 lock_release(&MPLock);
2686 // Tell the threads that they have work to do. This will make them leave
2687 // their idle loop. But before copy search stack tail for each thread.
2688 for (i = 0; i < ActiveThreads; i++)
2689 if (i == master || splitPoint.slaves[i])
2691 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2693 assert(i == master || threads[i].state == THREAD_BOOKED);
2695 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2698 // Everything is set up. The master thread enters the idle loop, from
2699 // which it will instantly launch a search, because its state is
2700 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2701 // idle loop, which means that the main thread will return from the idle
2702 // loop when all threads have finished their work at this split point.
2703 idle_loop(master, &splitPoint);
2705 // We have returned from the idle loop, which means that all threads are
2706 // finished. Update alpha and bestValue, and return.
2709 *alpha = splitPoint.alpha;
2710 *bestValue = splitPoint.bestValue;
2711 masterThread.activeSplitPoints--;
2712 masterThread.splitPoint = splitPoint.parent;
2714 lock_release(&MPLock);
2718 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2719 // to start a new search from the root.
2721 void ThreadsManager::wake_sleeping_threads() {
2723 assert(AllThreadsShouldSleep);
2724 assert(ActiveThreads > 0);
2726 AllThreadsShouldSleep = false;
2728 if (ActiveThreads == 1)
2731 #if !defined(_MSC_VER)
2732 pthread_mutex_lock(&WaitLock);
2733 pthread_cond_broadcast(&WaitCond);
2734 pthread_mutex_unlock(&WaitLock);
2736 for (int i = 1; i < MAX_THREADS; i++)
2737 SetEvent(SitIdleEvent[i]);
2743 // put_threads_to_sleep() makes all the threads go to sleep just before
2744 // to leave think(), at the end of the search. Threads should have already
2745 // finished the job and should be idle.
2747 void ThreadsManager::put_threads_to_sleep() {
2749 assert(!AllThreadsShouldSleep);
2751 // This makes the threads to go to sleep
2752 AllThreadsShouldSleep = true;
2755 /// The RootMoveList class
2757 // RootMoveList c'tor
2759 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2761 SearchStack ss[PLY_MAX_PLUS_2];
2762 MoveStack mlist[MaxRootMoves];
2764 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2766 // Initialize search stack
2767 init_ss_array(ss, PLY_MAX_PLUS_2);
2768 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2769 ss[0].eval = VALUE_NONE;
2771 // Generate all legal moves
2772 MoveStack* last = generate_moves(pos, mlist);
2774 // Add each move to the moves[] array
2775 for (MoveStack* cur = mlist; cur != last; cur++)
2777 bool includeMove = includeAllMoves;
2779 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2780 includeMove = (searchMoves[k] == cur->move);
2785 // Find a quick score for the move
2786 pos.do_move(cur->move, st);
2787 ss[0].currentMove = cur->move;
2788 moves[count].move = cur->move;
2789 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2790 moves[count].pv[0] = cur->move;
2791 moves[count].pv[1] = MOVE_NONE;
2792 pos.undo_move(cur->move);
2799 // RootMoveList simple methods definitions
2801 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2803 moves[moveNum].nodes = nodes;
2804 moves[moveNum].cumulativeNodes += nodes;
2807 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2809 moves[moveNum].ourBeta = our;
2810 moves[moveNum].theirBeta = their;
2813 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2817 for (j = 0; pv[j] != MOVE_NONE; j++)
2818 moves[moveNum].pv[j] = pv[j];
2820 moves[moveNum].pv[j] = MOVE_NONE;
2824 // RootMoveList::sort() sorts the root move list at the beginning of a new
2827 void RootMoveList::sort() {
2829 sort_multipv(count - 1); // Sort all items
2833 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2834 // list by their scores and depths. It is used to order the different PVs
2835 // correctly in MultiPV mode.
2837 void RootMoveList::sort_multipv(int n) {
2841 for (i = 1; i <= n; i++)
2843 RootMove rm = moves[i];
2844 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2845 moves[j] = moves[j - 1];