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/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
101 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
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 node 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 at most IIDMargin below beta.
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, 0)][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);
237 // Last seconds noise filtering (LSN)
238 const bool UseLSNFiltering = true;
239 const int LSNTime = 4000; // In milliseconds
240 const Value LSNValue = value_from_centipawns(200);
241 bool loseOnTime = false;
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
261 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
262 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
263 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode>
288 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
293 template <NodeType PvNode>
294 void sp_search(SplitPoint* sp, int threadID);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 void init_node(SearchStack ss[], int ply, int threadID);
300 void update_pv(SearchStack ss[], int ply);
301 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
302 bool connected_moves(const Position& pos, Move m1, Move m2);
303 bool value_is_mate(Value value);
304 bool move_is_killer(Move m, const SearchStack& ss);
305 bool ok_to_do_nullmove(const Position& pos);
306 bool ok_to_prune(const Position& pos, Move m, Move threat);
307 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
309 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
310 void update_killers(Move m, SearchStack& ss);
311 void update_gains(const Position& pos, Move move, Value before, Value after);
313 int current_search_time();
317 void wait_for_stop_or_ponderhit();
318 void init_ss_array(SearchStack ss[]);
319 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
321 #if !defined(_MSC_VER)
322 void *init_thread(void *threadID);
324 DWORD WINAPI init_thread(LPVOID threadID);
334 /// init_threads(), exit_threads() and nodes_searched() are helpers to
335 /// give accessibility to some TM methods from outside of current file.
337 void init_threads() { TM.init_threads(); }
338 void exit_threads() { TM.exit_threads(); }
339 int64_t nodes_searched() { return TM.nodes_searched(); }
342 /// perft() is our utility to verify move generation is bug free. All the legal
343 /// moves up to given depth are generated and counted and the sum returned.
345 int perft(Position& pos, Depth depth)
350 MovePicker mp(pos, MOVE_NONE, depth, H);
352 // If we are at the last ply we don't need to do and undo
353 // the moves, just to count them.
354 if (depth <= OnePly) // Replace with '<' to test also qsearch
356 while (mp.get_next_move()) sum++;
360 // Loop through all legal moves
362 while ((move = mp.get_next_move()) != MOVE_NONE)
364 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
365 sum += perft(pos, depth - OnePly);
372 /// think() is the external interface to Stockfish's search, and is called when
373 /// the program receives the UCI 'go' command. It initializes various
374 /// search-related global variables, and calls root_search(). It returns false
375 /// when a quit command is received during the search.
377 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
378 int time[], int increment[], int movesToGo, int maxDepth,
379 int maxNodes, int maxTime, Move searchMoves[]) {
381 // Initialize global search variables
382 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
383 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
385 TM.resetNodeCounters();
386 SearchStartTime = get_system_time();
387 ExactMaxTime = maxTime;
390 InfiniteSearch = infinite;
391 PonderSearch = ponder;
392 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
394 // Look for a book move, only during games, not tests
395 if (UseTimeManagement && get_option_value_bool("OwnBook"))
397 if (get_option_value_string("Book File") != OpeningBook.file_name())
398 OpeningBook.open(get_option_value_string("Book File"));
400 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
401 if (bookMove != MOVE_NONE)
404 wait_for_stop_or_ponderhit();
406 cout << "bestmove " << bookMove << endl;
411 // Reset loseOnTime flag at the beginning of a new game
412 if (button_was_pressed("New Game"))
415 // Read UCI option values
416 TT.set_size(get_option_value_int("Hash"));
417 if (button_was_pressed("Clear Hash"))
420 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
421 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
422 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
423 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
424 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
425 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
426 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
427 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
428 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
429 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
430 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
431 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
433 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
434 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
435 MultiPV = get_option_value_int("MultiPV");
436 Chess960 = get_option_value_bool("UCI_Chess960");
437 UseLogFile = get_option_value_bool("Use Search Log");
440 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
442 read_weights(pos.side_to_move());
444 // Set the number of active threads
445 int newActiveThreads = get_option_value_int("Threads");
446 if (newActiveThreads != TM.active_threads())
448 TM.set_active_threads(newActiveThreads);
449 init_eval(TM.active_threads());
452 // Wake up sleeping threads
453 TM.wake_sleeping_threads();
456 int myTime = time[side_to_move];
457 int myIncrement = increment[side_to_move];
458 if (UseTimeManagement)
460 if (!movesToGo) // Sudden death time control
464 MaxSearchTime = myTime / 30 + myIncrement;
465 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
467 else // Blitz game without increment
469 MaxSearchTime = myTime / 30;
470 AbsoluteMaxSearchTime = myTime / 8;
473 else // (x moves) / (y minutes)
477 MaxSearchTime = myTime / 2;
478 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
482 MaxSearchTime = myTime / Min(movesToGo, 20);
483 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
487 if (get_option_value_bool("Ponder"))
489 MaxSearchTime += MaxSearchTime / 4;
490 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
494 // Set best NodesBetweenPolls interval to avoid lagging under
495 // heavy time pressure.
497 NodesBetweenPolls = Min(MaxNodes, 30000);
498 else if (myTime && myTime < 1000)
499 NodesBetweenPolls = 1000;
500 else if (myTime && myTime < 5000)
501 NodesBetweenPolls = 5000;
503 NodesBetweenPolls = 30000;
505 // Write search information to log file
507 LogFile << "Searching: " << pos.to_fen() << endl
508 << "infinite: " << infinite
509 << " ponder: " << ponder
510 << " time: " << myTime
511 << " increment: " << myIncrement
512 << " moves to go: " << movesToGo << endl;
514 // LSN filtering. Used only for developing purposes, disabled by default
518 // Step 2. If after last move we decided to lose on time, do it now!
519 while (SearchStartTime + myTime + 1000 > get_system_time())
523 // We're ready to start thinking. Call the iterative deepening loop function
524 Value v = id_loop(pos, searchMoves);
528 // Step 1. If this is sudden death game and our position is hopeless,
529 // decide to lose on time.
530 if ( !loseOnTime // If we already lost on time, go to step 3.
540 // Step 3. Now after stepping over the time limit, reset flag for next match.
548 TM.put_threads_to_sleep();
554 /// init_search() is called during startup. It initializes various lookup tables
558 // Init our reduction lookup tables
559 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
560 for (int j = 1; j < 64; j++) // j == moveNumber
562 double pvRed = log(double(i)) * log(double(j)) / 3.0;
563 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
564 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
565 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
568 // Init futility margins array
569 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
570 for (int j = 0; j < 64; j++) // j == moveNumber
572 // FIXME: test using log instead of BSR
573 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
576 // Init futility move count array
577 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
578 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
582 // SearchStack::init() initializes a search stack. Used at the beginning of a
583 // new search from the root.
584 void SearchStack::init(int ply) {
586 pv[ply] = pv[ply + 1] = MOVE_NONE;
587 currentMove = threatMove = MOVE_NONE;
588 reduction = Depth(0);
592 void SearchStack::initKillers() {
594 mateKiller = MOVE_NONE;
595 for (int i = 0; i < KILLER_MAX; i++)
596 killers[i] = MOVE_NONE;
601 // id_loop() is the main iterative deepening loop. It calls root_search
602 // repeatedly with increasing depth until the allocated thinking time has
603 // been consumed, the user stops the search, or the maximum search depth is
606 Value id_loop(const Position& pos, Move searchMoves[]) {
609 SearchStack ss[PLY_MAX_PLUS_2];
610 Move EasyMove = MOVE_NONE;
611 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
613 // Moves to search are verified, copied, scored and sorted
614 RootMoveList rml(p, searchMoves);
616 // Handle special case of searching on a mate/stale position
617 if (rml.move_count() == 0)
620 wait_for_stop_or_ponderhit();
622 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
625 // Print RootMoveList startup scoring to the standard output,
626 // so to output information also for iteration 1.
627 cout << "info depth " << 1
628 << "\ninfo depth " << 1
629 << " score " << value_to_string(rml.get_move_score(0))
630 << " time " << current_search_time()
631 << " nodes " << TM.nodes_searched()
633 << " pv " << rml.get_move(0) << "\n";
639 ValueByIteration[1] = rml.get_move_score(0);
642 // Is one move significantly better than others after initial scoring ?
643 if ( rml.move_count() == 1
644 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
645 EasyMove = rml.get_move(0);
647 // Iterative deepening loop
648 while (Iteration < PLY_MAX)
650 // Initialize iteration
652 BestMoveChangesByIteration[Iteration] = 0;
654 cout << "info depth " << Iteration << endl;
656 // Calculate dynamic aspiration window based on previous iterations
657 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
659 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
660 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
662 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
663 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
665 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
666 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
669 // Search to the current depth, rml is updated and sorted, alpha and beta could change
670 value = root_search(p, ss, rml, &alpha, &beta);
672 // Write PV to transposition table, in case the relevant entries have
673 // been overwritten during the search.
674 TT.insert_pv(p, ss[0].pv);
677 break; // Value cannot be trusted. Break out immediately!
679 //Save info about search result
680 ValueByIteration[Iteration] = value;
682 // Drop the easy move if differs from the new best move
683 if (ss[0].pv[0] != EasyMove)
684 EasyMove = MOVE_NONE;
686 if (UseTimeManagement)
689 bool stopSearch = false;
691 // Stop search early if there is only a single legal move,
692 // we search up to Iteration 6 anyway to get a proper score.
693 if (Iteration >= 6 && rml.move_count() == 1)
696 // Stop search early when the last two iterations returned a mate score
698 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
699 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
702 // Stop search early if one move seems to be much better than the others
703 int64_t nodes = TM.nodes_searched();
705 && EasyMove == ss[0].pv[0]
706 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
707 && current_search_time() > MaxSearchTime / 16)
708 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
709 && current_search_time() > MaxSearchTime / 32)))
712 // Add some extra time if the best move has changed during the last two iterations
713 if (Iteration > 5 && Iteration <= 50)
714 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
715 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
717 // Stop search if most of MaxSearchTime is consumed at the end of the
718 // iteration. We probably don't have enough time to search the first
719 // move at the next iteration anyway.
720 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
726 StopOnPonderhit = true;
732 if (MaxDepth && Iteration >= MaxDepth)
736 // If we are pondering or in infinite search, we shouldn't print the
737 // best move before we are told to do so.
738 if (!AbortSearch && (PonderSearch || InfiniteSearch))
739 wait_for_stop_or_ponderhit();
741 // Print final search statistics
742 cout << "info nodes " << TM.nodes_searched()
744 << " time " << current_search_time()
745 << " hashfull " << TT.full() << endl;
747 // Print the best move and the ponder move to the standard output
748 if (ss[0].pv[0] == MOVE_NONE)
750 ss[0].pv[0] = rml.get_move(0);
751 ss[0].pv[1] = MOVE_NONE;
754 assert(ss[0].pv[0] != MOVE_NONE);
756 cout << "bestmove " << ss[0].pv[0];
758 if (ss[0].pv[1] != MOVE_NONE)
759 cout << " ponder " << ss[0].pv[1];
766 dbg_print_mean(LogFile);
768 if (dbg_show_hit_rate)
769 dbg_print_hit_rate(LogFile);
771 LogFile << "\nNodes: " << TM.nodes_searched()
772 << "\nNodes/second: " << nps()
773 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
776 p.do_move(ss[0].pv[0], st);
777 LogFile << "\nPonder move: "
778 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
781 return rml.get_move_score(0);
785 // root_search() is the function which searches the root node. It is
786 // similar to search_pv except that it uses a different move ordering
787 // scheme, prints some information to the standard output and handles
788 // the fail low/high loops.
790 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
797 Depth depth, ext, newDepth;
798 Value value, alpha, beta;
799 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
800 int researchCountFH, researchCountFL;
802 researchCountFH = researchCountFL = 0;
805 isCheck = pos.is_check();
807 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
808 // Step 2. Check for aborted search (omitted at root)
809 // Step 3. Mate distance pruning (omitted at root)
810 // Step 4. Transposition table lookup (omitted at root)
812 // Step 5. Evaluate the position statically
813 // At root we do this only to get reference value for child nodes
815 ss[0].eval = evaluate(pos, ei, 0);
817 // Step 6. Razoring (omitted at root)
818 // Step 7. Static null move pruning (omitted at root)
819 // Step 8. Null move search with verification search (omitted at root)
820 // Step 9. Internal iterative deepening (omitted at root)
822 // Step extra. Fail low loop
823 // We start with small aspiration window and in case of fail low, we research
824 // with bigger window until we are not failing low anymore.
827 // Sort the moves before to (re)search
830 // Step 10. Loop through all moves in the root move list
831 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
833 // This is used by time management
834 FirstRootMove = (i == 0);
836 // Save the current node count before the move is searched
837 nodes = TM.nodes_searched();
839 // Reset beta cut-off counters
840 TM.resetBetaCounters();
842 // Pick the next root move, and print the move and the move number to
843 // the standard output.
844 move = ss[0].currentMove = rml.get_move(i);
846 if (current_search_time() >= 1000)
847 cout << "info currmove " << move
848 << " currmovenumber " << i + 1 << endl;
850 moveIsCheck = pos.move_is_check(move);
851 captureOrPromotion = pos.move_is_capture_or_promotion(move);
853 // Step 11. Decide the new search depth
854 depth = (Iteration - 2) * OnePly + InitialDepth;
855 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
856 newDepth = depth + ext;
858 // Step 12. Futility pruning (omitted at root)
860 // Step extra. Fail high loop
861 // If move fails high, we research with bigger window until we are not failing
863 value = - VALUE_INFINITE;
867 // Step 13. Make the move
868 pos.do_move(move, st, ci, moveIsCheck);
870 // Step extra. pv search
871 // We do pv search for first moves (i < MultiPV)
872 // and for fail high research (value > alpha)
873 if (i < MultiPV || value > alpha)
875 // Aspiration window is disabled in multi-pv case
877 alpha = -VALUE_INFINITE;
879 // Full depth PV search, done on first move or after a fail high
880 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
884 // Step 14. Reduced search
885 // if the move fails high will be re-searched at full depth
886 bool doFullDepthSearch = true;
888 if ( depth >= 3 * OnePly
890 && !captureOrPromotion
891 && !move_is_castle(move))
893 ss[0].reduction = reduction<PV>(depth, i - MultiPV + 2);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
898 doFullDepthSearch = (value > alpha);
902 // Step 15. Full depth search
903 if (doFullDepthSearch)
905 // Full depth non-pv search using alpha as upperbound
906 ss[0].reduction = Depth(0);
907 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
909 // If we are above alpha then research at same depth but as PV
910 // to get a correct score or eventually a fail high above beta.
912 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
916 // Step 16. Undo move
919 // Can we exit fail high loop ?
920 if (AbortSearch || value < beta)
923 // We are failing high and going to do a research. It's important to update
924 // the score before research in case we run out of time while researching.
925 rml.set_move_score(i, value);
927 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
928 rml.set_move_pv(i, ss[0].pv);
930 // Print information to the standard output
931 print_pv_info(pos, ss, alpha, beta, value);
933 // Prepare for a research after a fail high, each time with a wider window
934 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
937 } // End of fail high loop
939 // Finished searching the move. If AbortSearch is true, the search
940 // was aborted because the user interrupted the search or because we
941 // ran out of time. In this case, the return value of the search cannot
942 // be trusted, and we break out of the loop without updating the best
947 // Remember beta-cutoff and searched nodes counts for this move. The
948 // info is used to sort the root moves for the next iteration.
950 TM.get_beta_counters(pos.side_to_move(), our, their);
951 rml.set_beta_counters(i, our, their);
952 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
954 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
955 assert(value < beta);
957 // Step 17. Check for new best move
958 if (value <= alpha && i >= MultiPV)
959 rml.set_move_score(i, -VALUE_INFINITE);
962 // PV move or new best move!
965 rml.set_move_score(i, value);
967 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
968 rml.set_move_pv(i, ss[0].pv);
972 // We record how often the best move has been changed in each
973 // iteration. This information is used for time managment: When
974 // the best move changes frequently, we allocate some more time.
976 BestMoveChangesByIteration[Iteration]++;
978 // Print information to the standard output
979 print_pv_info(pos, ss, alpha, beta, value);
981 // Raise alpha to setup proper non-pv search upper bound
988 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
990 cout << "info multipv " << j + 1
991 << " score " << value_to_string(rml.get_move_score(j))
992 << " depth " << (j <= i ? Iteration : Iteration - 1)
993 << " time " << current_search_time()
994 << " nodes " << TM.nodes_searched()
998 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
999 cout << rml.get_move_pv(j, k) << " ";
1003 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1005 } // PV move or new best move
1007 assert(alpha >= *alphaPtr);
1009 AspirationFailLow = (alpha == *alphaPtr);
1011 if (AspirationFailLow && StopOnPonderhit)
1012 StopOnPonderhit = false;
1015 // Can we exit fail low loop ?
1016 if (AbortSearch || !AspirationFailLow)
1019 // Prepare for a research after a fail low, each time with a wider window
1020 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1025 // Sort the moves before to return
1032 // search<>() is the main search function for both PV and non-PV nodes
1034 template <NodeType PvNode>
1035 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth,
1036 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1038 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1039 assert(beta > alpha && beta <= VALUE_INFINITE);
1040 assert(PvNode || alpha == beta - 1);
1041 assert(ply >= 0 && ply < PLY_MAX);
1042 assert(threadID >= 0 && threadID < TM.active_threads());
1044 Move movesSearched[256];
1049 Depth ext, newDepth;
1050 Value bestValue, value, oldAlpha;
1051 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1052 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1053 bool mateThreat = false;
1055 refinedValue = bestValue = value = -VALUE_INFINITE;
1059 return qsearch<PvNode>(pos, ss, alpha, beta, Depth(0), ply, threadID);
1061 // Step 1. Initialize node and poll
1062 // Polling can abort search.
1063 init_node(ss, ply, threadID);
1065 // Step 2. Check for aborted search and immediate draw
1066 if (AbortSearch || TM.thread_should_stop(threadID))
1069 if (pos.is_draw() || ply >= PLY_MAX - 1)
1072 // Step 3. Mate distance pruning
1073 alpha = Max(value_mated_in(ply), alpha);
1074 beta = Min(value_mate_in(ply+1), beta);
1078 // Step 4. Transposition table lookup
1080 // We don't want the score of a partial search to overwrite a previous full search
1081 // TT value, so we use a different position key in case of an excluded move exists.
1082 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1084 tte = TT.retrieve(posKey);
1085 ttMove = (tte ? tte->move() : MOVE_NONE);
1087 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1088 // This is to avoid problems in the following areas:
1090 // * Repetition draw detection
1091 // * Fifty move rule detection
1092 // * Searching for a mate
1093 // * Printing of full PV line
1095 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1097 // Refresh tte entry to avoid aging
1098 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1100 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1101 return value_from_tt(tte->value(), ply);
1104 // Step 5. Evaluate the position statically
1105 // At PV nodes we do this only to update gain statistics
1106 isCheck = pos.is_check();
1109 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1110 ss[ply].eval = value_from_tt(tte->value(), ply);
1112 ss[ply].eval = evaluate(pos, ei, threadID);
1114 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1115 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1118 // Step 6. Razoring (is omitted in PV nodes)
1120 && refinedValue < beta - razor_margin(depth)
1121 && ttMove == MOVE_NONE
1122 && ss[ply - 1].currentMove != MOVE_NULL
1123 && depth < RazorDepth
1125 && !value_is_mate(beta)
1126 && !pos.has_pawn_on_7th(pos.side_to_move()))
1128 Value rbeta = beta - razor_margin(depth);
1129 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1131 // Logically we should return (v + razor_margin(depth)), but
1132 // surprisingly this did slightly weaker in tests.
1136 // Step 7. Static null move pruning (is omitted in PV nodes)
1137 // We're betting that the opponent doesn't have a move that will reduce
1138 // the score by more than futility_margin(depth) if we do a null move.
1141 && depth < RazorDepth
1143 && !value_is_mate(beta)
1144 && ok_to_do_nullmove(pos)
1145 && refinedValue >= beta + futility_margin(depth, 0))
1146 return refinedValue - futility_margin(depth, 0);
1148 // Step 8. Null move search with verification search (is omitted in PV nodes)
1149 // When we jump directly to qsearch() we do a null move only if static value is
1150 // at least beta. Otherwise we do a null move if static value is not more than
1151 // NullMoveMargin under beta.
1156 && !value_is_mate(beta)
1157 && ok_to_do_nullmove(pos)
1158 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1160 ss[ply].currentMove = MOVE_NULL;
1162 // Null move dynamic reduction based on depth
1163 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1165 // Null move dynamic reduction based on value
1166 if (refinedValue - beta > PawnValueMidgame)
1169 pos.do_null_move(st);
1171 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1173 pos.undo_null_move();
1175 if (nullValue >= beta)
1177 // Do not return unproven mate scores
1178 if (nullValue >= value_mate_in(PLY_MAX))
1181 if (depth < 6 * OnePly)
1184 // Do zugzwang verification search
1185 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1189 // The null move failed low, which means that we may be faced with
1190 // some kind of threat. If the previous move was reduced, check if
1191 // the move that refuted the null move was somehow connected to the
1192 // move which was reduced. If a connection is found, return a fail
1193 // low score (which will cause the reduced move to fail high in the
1194 // parent node, which will trigger a re-search with full depth).
1195 if (nullValue == value_mated_in(ply + 2))
1198 ss[ply].threatMove = ss[ply + 1].currentMove;
1199 if ( depth < ThreatDepth
1200 && ss[ply - 1].reduction
1201 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1206 // Step 9. Internal iterative deepening
1207 if ( depth >= IIDDepth[PvNode]
1208 && ttMove == MOVE_NONE
1209 && (PvNode || (!isCheck && ss[ply].eval >= beta - IIDMargin)))
1211 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1212 search<PvNode>(pos, ss, alpha, beta, d, ply, false, threadID);
1213 ttMove = ss[ply].pv[ply];
1214 tte = TT.retrieve(posKey);
1217 // Expensive mate threat detection (only for PV nodes)
1219 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1221 // Initialize a MovePicker object for the current position
1222 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1225 // Step 10. Loop through moves
1226 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1227 while ( bestValue < beta
1228 && (move = mp.get_next_move()) != MOVE_NONE
1229 && !TM.thread_should_stop(threadID))
1231 assert(move_is_ok(move));
1233 if (move == excludedMove)
1236 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1237 moveIsCheck = pos.move_is_check(move, ci);
1238 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1240 // Step 11. Decide the new search depth
1241 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1243 // Singular extension search. We extend the TT move if its value is much better than
1244 // its siblings. To verify this we do a reduced search on all the other moves but the
1245 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1246 if ( depth >= SingularExtensionDepth[PvNode]
1248 && move == tte->move()
1249 && !excludedMove // Do not allow recursive singular extension search
1251 && is_lower_bound(tte->type())
1252 && tte->depth() >= depth - 3 * OnePly)
1254 Value ttValue = value_from_tt(tte->value(), ply);
1256 if (abs(ttValue) < VALUE_KNOWN_WIN)
1258 Value b = ttValue - SingularExtensionMargin;
1259 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply, false, threadID, move);
1261 if (v < ttValue - SingularExtensionMargin)
1266 newDepth = depth - OnePly + ext;
1268 // Update current move (this must be done after singular extension search)
1269 movesSearched[moveCount++] = ss[ply].currentMove = move;
1271 // Step 12. Futility pruning (is omitted in PV nodes)
1275 && !captureOrPromotion
1276 && !move_is_castle(move)
1279 // Move count based pruning
1280 if ( moveCount >= futility_move_count(depth)
1281 && ok_to_prune(pos, move, ss[ply].threatMove)
1282 && bestValue > value_mated_in(PLY_MAX))
1285 // Value based pruning
1286 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount); // FIXME We illogically ignore reduction condition depth >= 3*OnePly
1287 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1288 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1290 if (futilityValueScaled < beta)
1292 if (futilityValueScaled > bestValue)
1293 bestValue = futilityValueScaled;
1298 // Step 13. Make the move
1299 pos.do_move(move, st, ci, moveIsCheck);
1301 // Step extra. pv search (only in PV nodes)
1302 // The first move in list is the expected PV
1303 if (PvNode && moveCount == 1)
1304 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1307 // Step 14. Reduced search
1308 // if the move fails high will be re-searched at full depth.
1309 bool doFullDepthSearch = true;
1311 if ( depth >= 3 * OnePly
1313 && !captureOrPromotion
1314 && !move_is_castle(move)
1315 && !move_is_killer(move, ss[ply]))
1317 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1318 if (ss[ply].reduction)
1320 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1321 doFullDepthSearch = (value > alpha);
1325 // Step 15. Full depth search
1326 if (doFullDepthSearch)
1328 ss[ply].reduction = Depth(0);
1329 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1331 // Step extra. pv search (only in PV nodes)
1332 // Search only for possible new PV nodes, if instead value >= beta then
1333 // parent node fails low with value <= alpha and tries another move.
1334 if (PvNode && value > alpha && value < beta)
1335 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1339 // Step 16. Undo move
1340 pos.undo_move(move);
1342 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1344 // Step 17. Check for new best move
1345 if (value > bestValue)
1350 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1355 if (value == value_mate_in(ply + 1))
1356 ss[ply].mateKiller = move;
1360 // Step 18. Check for split
1361 if ( TM.active_threads() > 1
1363 && depth >= MinimumSplitDepth
1365 && TM.available_thread_exists(threadID)
1367 && !TM.thread_should_stop(threadID)
1368 && TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1369 mateThreat, &moveCount, &mp, threadID, PvNode))
1373 // Step 19. Check for mate and stalemate
1374 // All legal moves have been searched and if there are
1375 // no legal moves, it must be mate or stalemate.
1376 // If one move was excluded return fail low score.
1378 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1380 // Step 20. Update tables
1381 // If the search is not aborted, update the transposition table,
1382 // history counters, and killer moves.
1383 if (AbortSearch || TM.thread_should_stop(threadID))
1386 if (bestValue <= oldAlpha)
1387 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1389 else if (bestValue >= beta)
1391 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1392 move = ss[ply].pv[ply];
1393 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1394 if (!pos.move_is_capture_or_promotion(move))
1396 update_history(pos, move, depth, movesSearched, moveCount);
1397 update_killers(move, ss[ply]);
1401 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1403 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1409 // qsearch() is the quiescence search function, which is called by the main
1410 // search function when the remaining depth is zero (or, to be more precise,
1411 // less than OnePly).
1413 template <NodeType PvNode>
1414 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1415 Depth depth, int ply, int threadID) {
1417 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1418 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1419 assert(PvNode || alpha == beta - 1);
1421 assert(ply >= 0 && ply < PLY_MAX);
1422 assert(threadID >= 0 && threadID < TM.active_threads());
1427 Value staticValue, bestValue, value, futilityBase, futilityValue;
1428 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1429 const TTEntry* tte = NULL;
1431 Value oldAlpha = alpha;
1433 // Initialize, and make an early exit in case of an aborted search,
1434 // an instant draw, maximum ply reached, etc.
1435 init_node(ss, ply, threadID);
1437 // After init_node() that calls poll()
1438 if (AbortSearch || TM.thread_should_stop(threadID))
1441 if (pos.is_draw() || ply >= PLY_MAX - 1)
1444 // Transposition table lookup. At PV nodes, we don't use the TT for
1445 // pruning, but only for move ordering.
1446 tte = TT.retrieve(pos.get_key());
1447 ttMove = (tte ? tte->move() : MOVE_NONE);
1449 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1451 assert(tte->type() != VALUE_TYPE_EVAL);
1453 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1454 return value_from_tt(tte->value(), ply);
1457 isCheck = pos.is_check();
1459 // Evaluate the position statically
1461 staticValue = -VALUE_INFINITE;
1462 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1463 staticValue = value_from_tt(tte->value(), ply);
1465 staticValue = evaluate(pos, ei, threadID);
1469 ss[ply].eval = staticValue;
1470 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1473 // Initialize "stand pat score", and return it immediately if it is
1475 bestValue = staticValue;
1477 if (bestValue >= beta)
1479 // Store the score to avoid a future costly evaluation() call
1480 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1481 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1486 if (bestValue > alpha)
1489 // If we are near beta then try to get a cutoff pushing checks a bit further
1490 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1492 // Initialize a MovePicker object for the current position, and prepare
1493 // to search the moves. Because the depth is <= 0 here, only captures,
1494 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1495 // and we are near beta) will be generated.
1496 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1498 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1499 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1501 // Loop through the moves until no moves remain or a beta cutoff occurs
1502 while ( alpha < beta
1503 && (move = mp.get_next_move()) != MOVE_NONE)
1505 assert(move_is_ok(move));
1507 moveIsCheck = pos.move_is_check(move, ci);
1509 // Update current move
1511 ss[ply].currentMove = move;
1519 && !move_is_promotion(move)
1520 && !pos.move_is_passed_pawn_push(move))
1522 futilityValue = futilityBase
1523 + pos.endgame_value_of_piece_on(move_to(move))
1524 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1526 if (futilityValue < alpha)
1528 if (futilityValue > bestValue)
1529 bestValue = futilityValue;
1534 // Detect blocking evasions that are candidate to be pruned
1535 evasionPrunable = isCheck
1536 && bestValue > value_mated_in(PLY_MAX)
1537 && !pos.move_is_capture(move)
1538 && pos.type_of_piece_on(move_from(move)) != KING
1539 && !pos.can_castle(pos.side_to_move());
1541 // Don't search moves with negative SEE values
1543 && (!isCheck || evasionPrunable)
1545 && !move_is_promotion(move)
1546 && pos.see_sign(move) < 0)
1549 // Make and search the move
1550 pos.do_move(move, st, ci, moveIsCheck);
1551 value = -qsearch<PvNode>(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1552 pos.undo_move(move);
1554 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1557 if (value > bestValue)
1568 // All legal moves have been searched. A special case: If we're in check
1569 // and no legal moves were found, it is checkmate.
1570 if (!moveCount && isCheck) // Mate!
1571 return value_mated_in(ply);
1573 // Update transposition table
1574 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1575 if (bestValue <= oldAlpha)
1577 // If bestValue isn't changed it means it is still the static evaluation
1578 // of the node, so keep this info to avoid a future evaluation() call.
1579 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1580 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1582 else if (bestValue >= beta)
1584 move = ss[ply].pv[ply];
1585 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1587 // Update killers only for good checking moves
1588 if (!pos.move_is_capture_or_promotion(move))
1589 update_killers(move, ss[ply]);
1592 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1594 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1600 // sp_search() is used to search from a split point. This function is called
1601 // by each thread working at the split point. It is similar to the normal
1602 // search() function, but simpler. Because we have already probed the hash
1603 // table, done a null move search, and searched the first move before
1604 // splitting, we don't have to repeat all this work in sp_search(). We
1605 // also don't need to store anything to the hash table here: This is taken
1606 // care of after we return from the split point.
1608 template <NodeType PvNode>
1609 void sp_search(SplitPoint* sp, int threadID) {
1611 assert(threadID >= 0 && threadID < TM.active_threads());
1612 assert(TM.active_threads() > 1);
1616 Depth ext, newDepth;
1618 Value futilityValueScaled; // NonPV specific
1619 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1621 value = -VALUE_INFINITE;
1623 Position pos(*sp->pos);
1625 SearchStack* ss = sp->sstack[threadID];
1626 isCheck = pos.is_check();
1628 // Step 10. Loop through moves
1629 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1630 lock_grab(&(sp->lock));
1632 while ( sp->bestValue < sp->beta
1633 && (move = sp->mp->get_next_move()) != MOVE_NONE
1634 && !TM.thread_should_stop(threadID))
1636 moveCount = ++sp->moves;
1637 lock_release(&(sp->lock));
1639 assert(move_is_ok(move));
1641 moveIsCheck = pos.move_is_check(move, ci);
1642 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1644 // Step 11. Decide the new search depth
1645 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1646 newDepth = sp->depth - OnePly + ext;
1648 // Update current move
1649 ss[sp->ply].currentMove = move;
1651 // Step 12. Futility pruning (is omitted in PV nodes)
1655 && !captureOrPromotion
1656 && !move_is_castle(move))
1658 // Move count based pruning
1659 if ( moveCount >= futility_move_count(sp->depth)
1660 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1661 && sp->bestValue > value_mated_in(PLY_MAX))
1663 lock_grab(&(sp->lock));
1667 // Value based pruning
1668 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1669 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1670 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1672 if (futilityValueScaled < sp->beta)
1674 lock_grab(&(sp->lock));
1676 if (futilityValueScaled > sp->bestValue)
1677 sp->bestValue = futilityValueScaled;
1682 // Step 13. Make the move
1683 pos.do_move(move, st, ci, moveIsCheck);
1685 // Step 14. Reduced search
1686 // if the move fails high will be re-searched at full depth.
1687 bool doFullDepthSearch = true;
1690 && !captureOrPromotion
1691 && !move_is_castle(move)
1692 && !move_is_killer(move, ss[sp->ply]))
1694 ss[sp->ply].reduction = reduction<PvNode>(sp->depth, moveCount);
1695 if (ss[sp->ply].reduction)
1697 Value localAlpha = sp->alpha;
1698 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1699 doFullDepthSearch = (value > localAlpha);
1703 // Step 15. Full depth search
1704 if (doFullDepthSearch)
1706 ss[sp->ply].reduction = Depth(0);
1707 Value localAlpha = sp->alpha;
1708 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1710 if (PvNode && value > localAlpha && value < sp->beta)
1711 value = -search<PV>(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, false, threadID);
1714 // Step 16. Undo move
1715 pos.undo_move(move);
1717 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1719 // Step 17. Check for new best move
1720 lock_grab(&(sp->lock));
1722 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1724 sp->bestValue = value;
1726 if (sp->bestValue > sp->alpha)
1728 if (!PvNode || value >= sp->beta)
1729 sp->stopRequest = true;
1731 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1734 sp_update_pv(sp->parentSstack, ss, sp->ply);
1739 /* Here we have the lock still grabbed */
1741 sp->slaves[threadID] = 0;
1743 lock_release(&(sp->lock));
1746 // init_node() is called at the beginning of all the search functions
1747 // (search() qsearch(), and so on) and initializes the
1748 // search stack object corresponding to the current node. Once every
1749 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1750 // for user input and checks whether it is time to stop the search.
1752 void init_node(SearchStack ss[], int ply, int threadID) {
1754 assert(ply >= 0 && ply < PLY_MAX);
1755 assert(threadID >= 0 && threadID < TM.active_threads());
1757 TM.incrementNodeCounter(threadID);
1762 if (NodesSincePoll >= NodesBetweenPolls)
1769 ss[ply + 2].initKillers();
1772 // update_pv() is called whenever a search returns a value > alpha.
1773 // It updates the PV in the SearchStack object corresponding to the
1776 void update_pv(SearchStack ss[], int ply) {
1778 assert(ply >= 0 && ply < PLY_MAX);
1782 ss[ply].pv[ply] = ss[ply].currentMove;
1784 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1785 ss[ply].pv[p] = ss[ply + 1].pv[p];
1787 ss[ply].pv[p] = MOVE_NONE;
1791 // sp_update_pv() is a variant of update_pv for use at split points. The
1792 // difference between the two functions is that sp_update_pv also updates
1793 // the PV at the parent node.
1795 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1797 assert(ply >= 0 && ply < PLY_MAX);
1801 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1803 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1804 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1806 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1810 // connected_moves() tests whether two moves are 'connected' in the sense
1811 // that the first move somehow made the second move possible (for instance
1812 // if the moving piece is the same in both moves). The first move is assumed
1813 // to be the move that was made to reach the current position, while the
1814 // second move is assumed to be a move from the current position.
1816 bool connected_moves(const Position& pos, Move m1, Move m2) {
1818 Square f1, t1, f2, t2;
1821 assert(move_is_ok(m1));
1822 assert(move_is_ok(m2));
1824 if (m2 == MOVE_NONE)
1827 // Case 1: The moving piece is the same in both moves
1833 // Case 2: The destination square for m2 was vacated by m1
1839 // Case 3: Moving through the vacated square
1840 if ( piece_is_slider(pos.piece_on(f2))
1841 && bit_is_set(squares_between(f2, t2), f1))
1844 // Case 4: The destination square for m2 is defended by the moving piece in m1
1845 p = pos.piece_on(t1);
1846 if (bit_is_set(pos.attacks_from(p, t1), t2))
1849 // Case 5: Discovered check, checking piece is the piece moved in m1
1850 if ( piece_is_slider(p)
1851 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1852 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1854 // discovered_check_candidates() works also if the Position's side to
1855 // move is the opposite of the checking piece.
1856 Color them = opposite_color(pos.side_to_move());
1857 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1859 if (bit_is_set(dcCandidates, f2))
1866 // value_is_mate() checks if the given value is a mate one
1867 // eventually compensated for the ply.
1869 bool value_is_mate(Value value) {
1871 assert(abs(value) <= VALUE_INFINITE);
1873 return value <= value_mated_in(PLY_MAX)
1874 || value >= value_mate_in(PLY_MAX);
1878 // move_is_killer() checks if the given move is among the
1879 // killer moves of that ply.
1881 bool move_is_killer(Move m, const SearchStack& ss) {
1883 const Move* k = ss.killers;
1884 for (int i = 0; i < KILLER_MAX; i++, k++)
1892 // extension() decides whether a move should be searched with normal depth,
1893 // or with extended depth. Certain classes of moves (checking moves, in
1894 // particular) are searched with bigger depth than ordinary moves and in
1895 // any case are marked as 'dangerous'. Note that also if a move is not
1896 // extended, as example because the corresponding UCI option is set to zero,
1897 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1898 template <NodeType PvNode>
1899 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1900 bool singleEvasion, bool mateThreat, bool* dangerous) {
1902 assert(m != MOVE_NONE);
1904 Depth result = Depth(0);
1905 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1910 result += CheckExtension[PvNode];
1913 result += SingleEvasionExtension[PvNode];
1916 result += MateThreatExtension[PvNode];
1919 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1921 Color c = pos.side_to_move();
1922 if (relative_rank(c, move_to(m)) == RANK_7)
1924 result += PawnPushTo7thExtension[PvNode];
1927 if (pos.pawn_is_passed(c, move_to(m)))
1929 result += PassedPawnExtension[PvNode];
1934 if ( captureOrPromotion
1935 && pos.type_of_piece_on(move_to(m)) != PAWN
1936 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1937 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1938 && !move_is_promotion(m)
1941 result += PawnEndgameExtension[PvNode];
1946 && captureOrPromotion
1947 && pos.type_of_piece_on(move_to(m)) != PAWN
1948 && pos.see_sign(m) >= 0)
1954 return Min(result, OnePly);
1958 // ok_to_do_nullmove() looks at the current position and decides whether
1959 // doing a 'null move' should be allowed. In order to avoid zugzwang
1960 // problems, null moves are not allowed when the side to move has very
1961 // little material left. Currently, the test is a bit too simple: Null
1962 // moves are avoided only when the side to move has only pawns left.
1963 // It's probably a good idea to avoid null moves in at least some more
1964 // complicated endgames, e.g. KQ vs KR. FIXME
1966 bool ok_to_do_nullmove(const Position& pos) {
1968 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1972 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1973 // non-tactical moves late in the move list close to the leaves are
1974 // candidates for pruning.
1976 bool ok_to_prune(const Position& pos, Move m, Move threat) {
1978 assert(move_is_ok(m));
1979 assert(threat == MOVE_NONE || move_is_ok(threat));
1980 assert(!pos.move_is_check(m));
1981 assert(!pos.move_is_capture_or_promotion(m));
1982 assert(!pos.move_is_passed_pawn_push(m));
1984 Square mfrom, mto, tfrom, tto;
1986 // Prune if there isn't any threat move
1987 if (threat == MOVE_NONE)
1990 mfrom = move_from(m);
1992 tfrom = move_from(threat);
1993 tto = move_to(threat);
1995 // Case 1: Don't prune moves which move the threatened piece
1999 // Case 2: If the threatened piece has value less than or equal to the
2000 // value of the threatening piece, don't prune move which defend it.
2001 if ( pos.move_is_capture(threat)
2002 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2003 || pos.type_of_piece_on(tfrom) == KING)
2004 && pos.move_attacks_square(m, tto))
2007 // Case 3: If the moving piece in the threatened move is a slider, don't
2008 // prune safe moves which block its ray.
2009 if ( piece_is_slider(pos.piece_on(tfrom))
2010 && bit_is_set(squares_between(tfrom, tto), mto)
2011 && pos.see_sign(m) >= 0)
2018 // ok_to_use_TT() returns true if a transposition table score
2019 // can be used at a given point in search.
2021 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2023 Value v = value_from_tt(tte->value(), ply);
2025 return ( tte->depth() >= depth
2026 || v >= Max(value_mate_in(PLY_MAX), beta)
2027 || v < Min(value_mated_in(PLY_MAX), beta))
2029 && ( (is_lower_bound(tte->type()) && v >= beta)
2030 || (is_upper_bound(tte->type()) && v < beta));
2034 // refine_eval() returns the transposition table score if
2035 // possible otherwise falls back on static position evaluation.
2037 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2042 Value v = value_from_tt(tte->value(), ply);
2044 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2045 || (is_upper_bound(tte->type()) && v < defaultEval))
2052 // update_history() registers a good move that produced a beta-cutoff
2053 // in history and marks as failures all the other moves of that ply.
2055 void update_history(const Position& pos, Move move, Depth depth,
2056 Move movesSearched[], int moveCount) {
2060 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2062 for (int i = 0; i < moveCount - 1; i++)
2064 m = movesSearched[i];
2068 if (!pos.move_is_capture_or_promotion(m))
2069 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2074 // update_killers() add a good move that produced a beta-cutoff
2075 // among the killer moves of that ply.
2077 void update_killers(Move m, SearchStack& ss) {
2079 if (m == ss.killers[0])
2082 for (int i = KILLER_MAX - 1; i > 0; i--)
2083 ss.killers[i] = ss.killers[i - 1];
2089 // update_gains() updates the gains table of a non-capture move given
2090 // the static position evaluation before and after the move.
2092 void update_gains(const Position& pos, Move m, Value before, Value after) {
2095 && before != VALUE_NONE
2096 && after != VALUE_NONE
2097 && pos.captured_piece() == NO_PIECE_TYPE
2098 && !move_is_castle(m)
2099 && !move_is_promotion(m))
2100 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2104 // current_search_time() returns the number of milliseconds which have passed
2105 // since the beginning of the current search.
2107 int current_search_time() {
2109 return get_system_time() - SearchStartTime;
2113 // nps() computes the current nodes/second count.
2117 int t = current_search_time();
2118 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2122 // poll() performs two different functions: It polls for user input, and it
2123 // looks at the time consumed so far and decides if it's time to abort the
2128 static int lastInfoTime;
2129 int t = current_search_time();
2134 // We are line oriented, don't read single chars
2135 std::string command;
2137 if (!std::getline(std::cin, command))
2140 if (command == "quit")
2143 PonderSearch = false;
2147 else if (command == "stop")
2150 PonderSearch = false;
2152 else if (command == "ponderhit")
2156 // Print search information
2160 else if (lastInfoTime > t)
2161 // HACK: Must be a new search where we searched less than
2162 // NodesBetweenPolls nodes during the first second of search.
2165 else if (t - lastInfoTime >= 1000)
2172 if (dbg_show_hit_rate)
2173 dbg_print_hit_rate();
2175 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2176 << " time " << t << " hashfull " << TT.full() << endl;
2179 // Should we stop the search?
2183 bool stillAtFirstMove = FirstRootMove
2184 && !AspirationFailLow
2185 && t > MaxSearchTime + ExtraSearchTime;
2187 bool noMoreTime = t > AbsoluteMaxSearchTime
2188 || stillAtFirstMove;
2190 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2191 || (ExactMaxTime && t >= ExactMaxTime)
2192 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2197 // ponderhit() is called when the program is pondering (i.e. thinking while
2198 // it's the opponent's turn to move) in order to let the engine know that
2199 // it correctly predicted the opponent's move.
2203 int t = current_search_time();
2204 PonderSearch = false;
2206 bool stillAtFirstMove = FirstRootMove
2207 && !AspirationFailLow
2208 && t > MaxSearchTime + ExtraSearchTime;
2210 bool noMoreTime = t > AbsoluteMaxSearchTime
2211 || stillAtFirstMove;
2213 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2218 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2220 void init_ss_array(SearchStack ss[]) {
2222 for (int i = 0; i < 3; i++)
2225 ss[i].initKillers();
2230 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2231 // while the program is pondering. The point is to work around a wrinkle in
2232 // the UCI protocol: When pondering, the engine is not allowed to give a
2233 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2234 // We simply wait here until one of these commands is sent, and return,
2235 // after which the bestmove and pondermove will be printed (in id_loop()).
2237 void wait_for_stop_or_ponderhit() {
2239 std::string command;
2243 if (!std::getline(std::cin, command))
2246 if (command == "quit")
2251 else if (command == "ponderhit" || command == "stop")
2257 // print_pv_info() prints to standard output and eventually to log file information on
2258 // the current PV line. It is called at each iteration or after a new pv is found.
2260 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2262 cout << "info depth " << Iteration
2263 << " score " << value_to_string(value)
2264 << ((value >= beta) ? " lowerbound" :
2265 ((value <= alpha)? " upperbound" : ""))
2266 << " time " << current_search_time()
2267 << " nodes " << TM.nodes_searched()
2271 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2272 cout << ss[0].pv[j] << " ";
2278 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2279 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2281 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2282 TM.nodes_searched(), value, type, ss[0].pv) << endl;
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 TM.idle_loop(*(int*)threadID, NULL);
2302 DWORD WINAPI init_thread(LPVOID threadID) {
2304 TM.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
2442 lock_init(&MPLock, NULL);
2443 lock_init(&WaitLock, NULL);
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 SplitPointStack locks
2453 for (i = 0; i < MAX_THREADS; i++)
2454 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2456 SplitPointStack[i][j].parent = NULL;
2457 lock_init(&(SplitPointStack[i][j].lock), NULL);
2460 // Will be set just before program exits to properly end the threads
2461 AllThreadsShouldExit = false;
2463 // Threads will be put to sleep as soon as created
2464 AllThreadsShouldSleep = true;
2466 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2468 threads[0].state = THREAD_SEARCHING;
2469 for (i = 1; i < MAX_THREADS; i++)
2470 threads[i].state = THREAD_AVAILABLE;
2472 // Launch the helper threads
2473 for (i = 1; i < MAX_THREADS; i++)
2476 #if !defined(_MSC_VER)
2477 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2479 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2484 cout << "Failed to create thread number " << i << endl;
2485 Application::exit_with_failure();
2488 // Wait until the thread has finished launching and is gone to sleep
2489 while (threads[i].state != THREAD_SLEEPING) {}
2494 // exit_threads() is called when the program exits. It makes all the
2495 // helper threads exit cleanly.
2497 void ThreadsManager::exit_threads() {
2499 ActiveThreads = MAX_THREADS; // HACK
2500 AllThreadsShouldSleep = true; // HACK
2501 wake_sleeping_threads();
2503 // This makes the threads to exit idle_loop()
2504 AllThreadsShouldExit = true;
2506 // Wait for thread termination
2507 for (int i = 1; i < MAX_THREADS; i++)
2508 while (threads[i].state != THREAD_TERMINATED);
2510 // Now we can safely destroy the locks
2511 for (int i = 0; i < MAX_THREADS; i++)
2512 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2513 lock_destroy(&(SplitPointStack[i][j].lock));
2515 lock_destroy(&WaitLock);
2516 lock_destroy(&MPLock);
2520 // thread_should_stop() checks whether the thread should stop its search.
2521 // This can happen if a beta cutoff has occurred in the thread's currently
2522 // active split point, or in some ancestor of the current split point.
2524 bool ThreadsManager::thread_should_stop(int threadID) const {
2526 assert(threadID >= 0 && threadID < ActiveThreads);
2530 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2535 // thread_is_available() checks whether the thread with threadID "slave" is
2536 // available to help the thread with threadID "master" at a split point. An
2537 // obvious requirement is that "slave" must be idle. With more than two
2538 // threads, this is not by itself sufficient: If "slave" is the master of
2539 // some active split point, it is only available as a slave to the other
2540 // threads which are busy searching the split point at the top of "slave"'s
2541 // split point stack (the "helpful master concept" in YBWC terminology).
2543 bool ThreadsManager::thread_is_available(int slave, int master) const {
2545 assert(slave >= 0 && slave < ActiveThreads);
2546 assert(master >= 0 && master < ActiveThreads);
2547 assert(ActiveThreads > 1);
2549 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2552 // Make a local copy to be sure doesn't change under our feet
2553 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2555 if (localActiveSplitPoints == 0)
2556 // No active split points means that the thread is available as
2557 // a slave for any other thread.
2560 if (ActiveThreads == 2)
2563 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2564 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2565 // could have been set to 0 by another thread leading to an out of bound access.
2566 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2573 // available_thread_exists() tries to find an idle thread which is available as
2574 // a slave for the thread with threadID "master".
2576 bool ThreadsManager::available_thread_exists(int master) const {
2578 assert(master >= 0 && master < ActiveThreads);
2579 assert(ActiveThreads > 1);
2581 for (int i = 0; i < ActiveThreads; i++)
2582 if (thread_is_available(i, master))
2589 // split() does the actual work of distributing the work at a node between
2590 // several threads at PV nodes. If it does not succeed in splitting the
2591 // node (because no idle threads are available, or because we have no unused
2592 // split point objects), the function immediately returns false. If
2593 // splitting is possible, a SplitPoint object is initialized with all the
2594 // data that must be copied to the helper threads (the current position and
2595 // search stack, alpha, beta, the search depth, etc.), and we tell our
2596 // helper threads that they have been assigned work. This will cause them
2597 // to instantly leave their idle loops and call sp_search(). When all
2598 // threads have returned from sp_search() then split() returns true.
2600 template <bool Fake>
2601 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply, Value* alpha,
2602 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2603 int* moves, MovePicker* mp, int master, bool pvNode) {
2605 assert(sstck != NULL);
2606 assert(ply >= 0 && ply < PLY_MAX);
2607 assert(*bestValue >= -VALUE_INFINITE);
2608 assert(*bestValue <= *alpha);
2609 assert(*alpha < beta);
2610 assert(beta <= VALUE_INFINITE);
2611 assert(depth > Depth(0));
2612 assert(master >= 0 && master < ActiveThreads);
2613 assert(ActiveThreads > 1);
2615 SplitPoint* splitPoint;
2619 // If no other thread is available to help us, or if we have too many
2620 // active split points, don't split.
2621 if ( !available_thread_exists(master)
2622 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2624 lock_release(&MPLock);
2628 // Pick the next available split point object from the split point stack
2629 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2631 // Initialize the split point object
2632 splitPoint->parent = threads[master].splitPoint;
2633 splitPoint->stopRequest = false;
2634 splitPoint->ply = ply;
2635 splitPoint->depth = depth;
2636 splitPoint->mateThreat = mateThreat;
2637 splitPoint->alpha = *alpha;
2638 splitPoint->beta = beta;
2639 splitPoint->pvNode = pvNode;
2640 splitPoint->bestValue = *bestValue;
2641 splitPoint->master = master;
2642 splitPoint->mp = mp;
2643 splitPoint->moves = *moves;
2644 splitPoint->pos = &p;
2645 splitPoint->parentSstack = sstck;
2646 for (int i = 0; i < ActiveThreads; i++)
2647 splitPoint->slaves[i] = 0;
2649 threads[master].splitPoint = splitPoint;
2650 threads[master].activeSplitPoints++;
2652 // If we are here it means we are not available
2653 assert(threads[master].state != THREAD_AVAILABLE);
2655 int workersCnt = 1; // At least the master is included
2657 // Allocate available threads setting state to THREAD_BOOKED
2658 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2659 if (thread_is_available(i, master))
2661 threads[i].state = THREAD_BOOKED;
2662 threads[i].splitPoint = splitPoint;
2663 splitPoint->slaves[i] = 1;
2667 assert(Fake || workersCnt > 1);
2669 // We can release the lock because slave threads are already booked and master is not available
2670 lock_release(&MPLock);
2672 // Tell the threads that they have work to do. This will make them leave
2673 // their idle loop. But before copy search stack tail for each thread.
2674 for (int i = 0; i < ActiveThreads; i++)
2675 if (i == master || splitPoint->slaves[i])
2677 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2679 assert(i == master || threads[i].state == THREAD_BOOKED);
2681 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2684 // Everything is set up. The master thread enters the idle loop, from
2685 // which it will instantly launch a search, because its state is
2686 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2687 // idle loop, which means that the main thread will return from the idle
2688 // loop when all threads have finished their work at this split point.
2689 idle_loop(master, splitPoint);
2691 // We have returned from the idle loop, which means that all threads are
2692 // finished. Update alpha and bestValue, and return.
2695 *alpha = splitPoint->alpha;
2696 *bestValue = splitPoint->bestValue;
2697 threads[master].activeSplitPoints--;
2698 threads[master].splitPoint = splitPoint->parent;
2700 lock_release(&MPLock);
2705 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2706 // to start a new search from the root.
2708 void ThreadsManager::wake_sleeping_threads() {
2710 assert(AllThreadsShouldSleep);
2711 assert(ActiveThreads > 0);
2713 AllThreadsShouldSleep = false;
2715 if (ActiveThreads == 1)
2718 #if !defined(_MSC_VER)
2719 pthread_mutex_lock(&WaitLock);
2720 pthread_cond_broadcast(&WaitCond);
2721 pthread_mutex_unlock(&WaitLock);
2723 for (int i = 1; i < MAX_THREADS; i++)
2724 SetEvent(SitIdleEvent[i]);
2730 // put_threads_to_sleep() makes all the threads go to sleep just before
2731 // to leave think(), at the end of the search. Threads should have already
2732 // finished the job and should be idle.
2734 void ThreadsManager::put_threads_to_sleep() {
2736 assert(!AllThreadsShouldSleep);
2738 // This makes the threads to go to sleep
2739 AllThreadsShouldSleep = true;
2742 /// The RootMoveList class
2744 // RootMoveList c'tor
2746 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2748 SearchStack ss[PLY_MAX_PLUS_2];
2749 MoveStack mlist[MaxRootMoves];
2751 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2753 // Generate all legal moves
2754 MoveStack* last = generate_moves(pos, mlist);
2756 // Add each move to the moves[] array
2757 for (MoveStack* cur = mlist; cur != last; cur++)
2759 bool includeMove = includeAllMoves;
2761 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2762 includeMove = (searchMoves[k] == cur->move);
2767 // Find a quick score for the move
2769 pos.do_move(cur->move, st);
2770 moves[count].move = cur->move;
2771 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2772 moves[count].pv[0] = cur->move;
2773 moves[count].pv[1] = MOVE_NONE;
2774 pos.undo_move(cur->move);
2781 // RootMoveList simple methods definitions
2783 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2785 moves[moveNum].nodes = nodes;
2786 moves[moveNum].cumulativeNodes += nodes;
2789 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2791 moves[moveNum].ourBeta = our;
2792 moves[moveNum].theirBeta = their;
2795 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2799 for (j = 0; pv[j] != MOVE_NONE; j++)
2800 moves[moveNum].pv[j] = pv[j];
2802 moves[moveNum].pv[j] = MOVE_NONE;
2806 // RootMoveList::sort() sorts the root move list at the beginning of a new
2809 void RootMoveList::sort() {
2811 sort_multipv(count - 1); // Sort all items
2815 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2816 // list by their scores and depths. It is used to order the different PVs
2817 // correctly in MultiPV mode.
2819 void RootMoveList::sort_multipv(int n) {
2823 for (i = 1; i <= n; i++)
2825 RootMove rm = moves[i];
2826 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2827 moves[j] = moves[j - 1];