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 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, 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 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1287 // but fixing this made program slightly weaker.
1288 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1289 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1290 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1292 if (futilityValueScaled < beta)
1294 if (futilityValueScaled > bestValue)
1295 bestValue = futilityValueScaled;
1300 // Step 13. Make the move
1301 pos.do_move(move, st, ci, moveIsCheck);
1303 // Step extra. pv search (only in PV nodes)
1304 // The first move in list is the expected PV
1305 if (PvNode && moveCount == 1)
1306 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1309 // Step 14. Reduced search
1310 // if the move fails high will be re-searched at full depth.
1311 bool doFullDepthSearch = true;
1313 if ( depth >= 3 * OnePly
1315 && !captureOrPromotion
1316 && !move_is_castle(move)
1317 && !move_is_killer(move, ss[ply]))
1319 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1320 if (ss[ply].reduction)
1322 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1323 doFullDepthSearch = (value > alpha);
1327 // Step 15. Full depth search
1328 if (doFullDepthSearch)
1330 ss[ply].reduction = Depth(0);
1331 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1333 // Step extra. pv search (only in PV nodes)
1334 // Search only for possible new PV nodes, if instead value >= beta then
1335 // parent node fails low with value <= alpha and tries another move.
1336 if (PvNode && value > alpha && value < beta)
1337 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1341 // Step 16. Undo move
1342 pos.undo_move(move);
1344 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1346 // Step 17. Check for new best move
1347 if (value > bestValue)
1352 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1357 if (value == value_mate_in(ply + 1))
1358 ss[ply].mateKiller = move;
1362 // Step 18. Check for split
1363 if ( TM.active_threads() > 1
1365 && depth >= MinimumSplitDepth
1367 && TM.available_thread_exists(threadID)
1369 && !TM.thread_should_stop(threadID))
1370 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1371 mateThreat, &moveCount, &mp, threadID, PvNode);
1374 // Step 19. Check for mate and stalemate
1375 // All legal moves have been searched and if there are
1376 // no legal moves, it must be mate or stalemate.
1377 // If one move was excluded return fail low score.
1379 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1381 // Step 20. Update tables
1382 // If the search is not aborted, update the transposition table,
1383 // history counters, and killer moves.
1384 if (AbortSearch || TM.thread_should_stop(threadID))
1387 if (bestValue <= oldAlpha)
1388 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1390 else if (bestValue >= beta)
1392 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1393 move = ss[ply].pv[ply];
1394 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1395 if (!pos.move_is_capture_or_promotion(move))
1397 update_history(pos, move, depth, movesSearched, moveCount);
1398 update_killers(move, ss[ply]);
1402 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1404 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1410 // qsearch() is the quiescence search function, which is called by the main
1411 // search function when the remaining depth is zero (or, to be more precise,
1412 // less than OnePly).
1414 template <NodeType PvNode>
1415 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1416 Depth depth, int ply, int threadID) {
1418 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1419 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1420 assert(PvNode || alpha == beta - 1);
1422 assert(ply >= 0 && ply < PLY_MAX);
1423 assert(threadID >= 0 && threadID < TM.active_threads());
1428 Value staticValue, bestValue, value, futilityBase, futilityValue;
1429 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1430 const TTEntry* tte = NULL;
1432 Value oldAlpha = alpha;
1434 // Initialize, and make an early exit in case of an aborted search,
1435 // an instant draw, maximum ply reached, etc.
1436 init_node(ss, ply, threadID);
1438 // After init_node() that calls poll()
1439 if (AbortSearch || TM.thread_should_stop(threadID))
1442 if (pos.is_draw() || ply >= PLY_MAX - 1)
1445 // Transposition table lookup. At PV nodes, we don't use the TT for
1446 // pruning, but only for move ordering.
1447 tte = TT.retrieve(pos.get_key());
1448 ttMove = (tte ? tte->move() : MOVE_NONE);
1450 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1452 assert(tte->type() != VALUE_TYPE_EVAL);
1454 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1455 return value_from_tt(tte->value(), ply);
1458 isCheck = pos.is_check();
1460 // Evaluate the position statically
1462 staticValue = -VALUE_INFINITE;
1463 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1464 staticValue = value_from_tt(tte->value(), ply);
1466 staticValue = evaluate(pos, ei, threadID);
1470 ss[ply].eval = staticValue;
1471 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1474 // Initialize "stand pat score", and return it immediately if it is
1476 bestValue = staticValue;
1478 if (bestValue >= beta)
1480 // Store the score to avoid a future costly evaluation() call
1481 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1482 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1487 if (bestValue > alpha)
1490 // If we are near beta then try to get a cutoff pushing checks a bit further
1491 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1493 // Initialize a MovePicker object for the current position, and prepare
1494 // to search the moves. Because the depth is <= 0 here, only captures,
1495 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1496 // and we are near beta) will be generated.
1497 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1499 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1500 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1502 // Loop through the moves until no moves remain or a beta cutoff occurs
1503 while ( alpha < beta
1504 && (move = mp.get_next_move()) != MOVE_NONE)
1506 assert(move_is_ok(move));
1508 moveIsCheck = pos.move_is_check(move, ci);
1510 // Update current move
1512 ss[ply].currentMove = move;
1520 && !move_is_promotion(move)
1521 && !pos.move_is_passed_pawn_push(move))
1523 futilityValue = futilityBase
1524 + pos.endgame_value_of_piece_on(move_to(move))
1525 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1527 if (futilityValue < alpha)
1529 if (futilityValue > bestValue)
1530 bestValue = futilityValue;
1535 // Detect blocking evasions that are candidate to be pruned
1536 evasionPrunable = isCheck
1537 && bestValue > value_mated_in(PLY_MAX)
1538 && !pos.move_is_capture(move)
1539 && pos.type_of_piece_on(move_from(move)) != KING
1540 && !pos.can_castle(pos.side_to_move());
1542 // Don't search moves with negative SEE values
1544 && (!isCheck || evasionPrunable)
1546 && !move_is_promotion(move)
1547 && pos.see_sign(move) < 0)
1550 // Make and search the move
1551 pos.do_move(move, st, ci, moveIsCheck);
1552 value = -qsearch<PvNode>(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1553 pos.undo_move(move);
1555 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1558 if (value > bestValue)
1569 // All legal moves have been searched. A special case: If we're in check
1570 // and no legal moves were found, it is checkmate.
1571 if (!moveCount && isCheck) // Mate!
1572 return value_mated_in(ply);
1574 // Update transposition table
1575 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1576 if (bestValue <= oldAlpha)
1578 // If bestValue isn't changed it means it is still the static evaluation
1579 // of the node, so keep this info to avoid a future evaluation() call.
1580 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1581 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1583 else if (bestValue >= beta)
1585 move = ss[ply].pv[ply];
1586 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1588 // Update killers only for good checking moves
1589 if (!pos.move_is_capture_or_promotion(move))
1590 update_killers(move, ss[ply]);
1593 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1595 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1601 // sp_search() is used to search from a split point. This function is called
1602 // by each thread working at the split point. It is similar to the normal
1603 // search() function, but simpler. Because we have already probed the hash
1604 // table, done a null move search, and searched the first move before
1605 // splitting, we don't have to repeat all this work in sp_search(). We
1606 // also don't need to store anything to the hash table here: This is taken
1607 // care of after we return from the split point.
1609 template <NodeType PvNode>
1610 void sp_search(SplitPoint* sp, int threadID) {
1612 assert(threadID >= 0 && threadID < TM.active_threads());
1613 assert(TM.active_threads() > 1);
1617 Depth ext, newDepth;
1619 Value futilityValueScaled; // NonPV specific
1620 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1622 value = -VALUE_INFINITE;
1624 Position pos(*sp->pos);
1626 SearchStack* ss = sp->sstack[threadID];
1627 isCheck = pos.is_check();
1629 // Step 10. Loop through moves
1630 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1631 lock_grab(&(sp->lock));
1633 while ( sp->bestValue < sp->beta
1634 && (move = sp->mp->get_next_move()) != MOVE_NONE
1635 && !TM.thread_should_stop(threadID))
1637 moveCount = ++sp->moveCount;
1638 lock_release(&(sp->lock));
1640 assert(move_is_ok(move));
1642 moveIsCheck = pos.move_is_check(move, ci);
1643 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1645 // Step 11. Decide the new search depth
1646 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1647 newDepth = sp->depth - OnePly + ext;
1649 // Update current move
1650 ss[sp->ply].currentMove = move;
1652 // Step 12. Futility pruning (is omitted in PV nodes)
1656 && !captureOrPromotion
1657 && !move_is_castle(move))
1659 // Move count based pruning
1660 if ( moveCount >= futility_move_count(sp->depth)
1661 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1662 && sp->bestValue > value_mated_in(PLY_MAX))
1664 lock_grab(&(sp->lock));
1668 // Value based pruning
1669 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1670 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1671 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1673 if (futilityValueScaled < sp->beta)
1675 lock_grab(&(sp->lock));
1677 if (futilityValueScaled > sp->bestValue)
1678 sp->bestValue = futilityValueScaled;
1683 // Step 13. Make the move
1684 pos.do_move(move, st, ci, moveIsCheck);
1686 // Step 14. Reduced search
1687 // if the move fails high will be re-searched at full depth.
1688 bool doFullDepthSearch = true;
1691 && !captureOrPromotion
1692 && !move_is_castle(move)
1693 && !move_is_killer(move, ss[sp->ply]))
1695 ss[sp->ply].reduction = reduction<PvNode>(sp->depth, moveCount);
1696 if (ss[sp->ply].reduction)
1698 Value localAlpha = sp->alpha;
1699 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1700 doFullDepthSearch = (value > localAlpha);
1704 // Step 15. Full depth search
1705 if (doFullDepthSearch)
1707 ss[sp->ply].reduction = Depth(0);
1708 Value localAlpha = sp->alpha;
1709 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1711 if (PvNode && value > localAlpha && value < sp->beta)
1712 value = -search<PV>(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, false, threadID);
1715 // Step 16. Undo move
1716 pos.undo_move(move);
1718 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1720 // Step 17. Check for new best move
1721 lock_grab(&(sp->lock));
1723 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1725 sp->bestValue = value;
1727 if (sp->bestValue > sp->alpha)
1729 if (!PvNode || value >= sp->beta)
1730 sp->stopRequest = true;
1732 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1735 sp_update_pv(sp->parentSstack, ss, sp->ply);
1740 /* Here we have the lock still grabbed */
1742 sp->slaves[threadID] = 0;
1744 lock_release(&(sp->lock));
1747 // init_node() is called at the beginning of all the search functions
1748 // (search() qsearch(), and so on) and initializes the
1749 // search stack object corresponding to the current node. Once every
1750 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1751 // for user input and checks whether it is time to stop the search.
1753 void init_node(SearchStack ss[], int ply, int threadID) {
1755 assert(ply >= 0 && ply < PLY_MAX);
1756 assert(threadID >= 0 && threadID < TM.active_threads());
1758 TM.incrementNodeCounter(threadID);
1763 if (NodesSincePoll >= NodesBetweenPolls)
1770 ss[ply + 2].initKillers();
1773 // update_pv() is called whenever a search returns a value > alpha.
1774 // It updates the PV in the SearchStack object corresponding to the
1777 void update_pv(SearchStack ss[], int ply) {
1779 assert(ply >= 0 && ply < PLY_MAX);
1783 ss[ply].pv[ply] = ss[ply].currentMove;
1785 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1786 ss[ply].pv[p] = ss[ply + 1].pv[p];
1788 ss[ply].pv[p] = MOVE_NONE;
1792 // sp_update_pv() is a variant of update_pv for use at split points. The
1793 // difference between the two functions is that sp_update_pv also updates
1794 // the PV at the parent node.
1796 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1798 assert(ply >= 0 && ply < PLY_MAX);
1802 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1804 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1805 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1807 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1811 // connected_moves() tests whether two moves are 'connected' in the sense
1812 // that the first move somehow made the second move possible (for instance
1813 // if the moving piece is the same in both moves). The first move is assumed
1814 // to be the move that was made to reach the current position, while the
1815 // second move is assumed to be a move from the current position.
1817 bool connected_moves(const Position& pos, Move m1, Move m2) {
1819 Square f1, t1, f2, t2;
1822 assert(move_is_ok(m1));
1823 assert(move_is_ok(m2));
1825 if (m2 == MOVE_NONE)
1828 // Case 1: The moving piece is the same in both moves
1834 // Case 2: The destination square for m2 was vacated by m1
1840 // Case 3: Moving through the vacated square
1841 if ( piece_is_slider(pos.piece_on(f2))
1842 && bit_is_set(squares_between(f2, t2), f1))
1845 // Case 4: The destination square for m2 is defended by the moving piece in m1
1846 p = pos.piece_on(t1);
1847 if (bit_is_set(pos.attacks_from(p, t1), t2))
1850 // Case 5: Discovered check, checking piece is the piece moved in m1
1851 if ( piece_is_slider(p)
1852 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1853 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1855 // discovered_check_candidates() works also if the Position's side to
1856 // move is the opposite of the checking piece.
1857 Color them = opposite_color(pos.side_to_move());
1858 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1860 if (bit_is_set(dcCandidates, f2))
1867 // value_is_mate() checks if the given value is a mate one
1868 // eventually compensated for the ply.
1870 bool value_is_mate(Value value) {
1872 assert(abs(value) <= VALUE_INFINITE);
1874 return value <= value_mated_in(PLY_MAX)
1875 || value >= value_mate_in(PLY_MAX);
1879 // move_is_killer() checks if the given move is among the
1880 // killer moves of that ply.
1882 bool move_is_killer(Move m, const SearchStack& ss) {
1884 const Move* k = ss.killers;
1885 for (int i = 0; i < KILLER_MAX; i++, k++)
1893 // extension() decides whether a move should be searched with normal depth,
1894 // or with extended depth. Certain classes of moves (checking moves, in
1895 // particular) are searched with bigger depth than ordinary moves and in
1896 // any case are marked as 'dangerous'. Note that also if a move is not
1897 // extended, as example because the corresponding UCI option is set to zero,
1898 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1899 template <NodeType PvNode>
1900 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1901 bool singleEvasion, bool mateThreat, bool* dangerous) {
1903 assert(m != MOVE_NONE);
1905 Depth result = Depth(0);
1906 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1911 result += CheckExtension[PvNode];
1914 result += SingleEvasionExtension[PvNode];
1917 result += MateThreatExtension[PvNode];
1920 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1922 Color c = pos.side_to_move();
1923 if (relative_rank(c, move_to(m)) == RANK_7)
1925 result += PawnPushTo7thExtension[PvNode];
1928 if (pos.pawn_is_passed(c, move_to(m)))
1930 result += PassedPawnExtension[PvNode];
1935 if ( captureOrPromotion
1936 && pos.type_of_piece_on(move_to(m)) != PAWN
1937 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1938 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1939 && !move_is_promotion(m)
1942 result += PawnEndgameExtension[PvNode];
1947 && captureOrPromotion
1948 && pos.type_of_piece_on(move_to(m)) != PAWN
1949 && pos.see_sign(m) >= 0)
1955 return Min(result, OnePly);
1959 // ok_to_do_nullmove() looks at the current position and decides whether
1960 // doing a 'null move' should be allowed. In order to avoid zugzwang
1961 // problems, null moves are not allowed when the side to move has very
1962 // little material left. Currently, the test is a bit too simple: Null
1963 // moves are avoided only when the side to move has only pawns left.
1964 // It's probably a good idea to avoid null moves in at least some more
1965 // complicated endgames, e.g. KQ vs KR. FIXME
1967 bool ok_to_do_nullmove(const Position& pos) {
1969 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1973 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1974 // non-tactical moves late in the move list close to the leaves are
1975 // candidates for pruning.
1977 bool ok_to_prune(const Position& pos, Move m, Move threat) {
1979 assert(move_is_ok(m));
1980 assert(threat == MOVE_NONE || move_is_ok(threat));
1981 assert(!pos.move_is_check(m));
1982 assert(!pos.move_is_capture_or_promotion(m));
1983 assert(!pos.move_is_passed_pawn_push(m));
1985 Square mfrom, mto, tfrom, tto;
1987 // Prune if there isn't any threat move
1988 if (threat == MOVE_NONE)
1991 mfrom = move_from(m);
1993 tfrom = move_from(threat);
1994 tto = move_to(threat);
1996 // Case 1: Don't prune moves which move the threatened piece
2000 // Case 2: If the threatened piece has value less than or equal to the
2001 // value of the threatening piece, don't prune move which defend it.
2002 if ( pos.move_is_capture(threat)
2003 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2004 || pos.type_of_piece_on(tfrom) == KING)
2005 && pos.move_attacks_square(m, tto))
2008 // Case 3: If the moving piece in the threatened move is a slider, don't
2009 // prune safe moves which block its ray.
2010 if ( piece_is_slider(pos.piece_on(tfrom))
2011 && bit_is_set(squares_between(tfrom, tto), mto)
2012 && pos.see_sign(m) >= 0)
2019 // ok_to_use_TT() returns true if a transposition table score
2020 // can be used at a given point in search.
2022 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2024 Value v = value_from_tt(tte->value(), ply);
2026 return ( tte->depth() >= depth
2027 || v >= Max(value_mate_in(PLY_MAX), beta)
2028 || v < Min(value_mated_in(PLY_MAX), beta))
2030 && ( (is_lower_bound(tte->type()) && v >= beta)
2031 || (is_upper_bound(tte->type()) && v < beta));
2035 // refine_eval() returns the transposition table score if
2036 // possible otherwise falls back on static position evaluation.
2038 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2043 Value v = value_from_tt(tte->value(), ply);
2045 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2046 || (is_upper_bound(tte->type()) && v < defaultEval))
2053 // update_history() registers a good move that produced a beta-cutoff
2054 // in history and marks as failures all the other moves of that ply.
2056 void update_history(const Position& pos, Move move, Depth depth,
2057 Move movesSearched[], int moveCount) {
2061 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2063 for (int i = 0; i < moveCount - 1; i++)
2065 m = movesSearched[i];
2069 if (!pos.move_is_capture_or_promotion(m))
2070 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2075 // update_killers() add a good move that produced a beta-cutoff
2076 // among the killer moves of that ply.
2078 void update_killers(Move m, SearchStack& ss) {
2080 if (m == ss.killers[0])
2083 for (int i = KILLER_MAX - 1; i > 0; i--)
2084 ss.killers[i] = ss.killers[i - 1];
2090 // update_gains() updates the gains table of a non-capture move given
2091 // the static position evaluation before and after the move.
2093 void update_gains(const Position& pos, Move m, Value before, Value after) {
2096 && before != VALUE_NONE
2097 && after != VALUE_NONE
2098 && pos.captured_piece() == NO_PIECE_TYPE
2099 && !move_is_castle(m)
2100 && !move_is_promotion(m))
2101 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2105 // current_search_time() returns the number of milliseconds which have passed
2106 // since the beginning of the current search.
2108 int current_search_time() {
2110 return get_system_time() - SearchStartTime;
2114 // nps() computes the current nodes/second count.
2118 int t = current_search_time();
2119 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2123 // poll() performs two different functions: It polls for user input, and it
2124 // looks at the time consumed so far and decides if it's time to abort the
2129 static int lastInfoTime;
2130 int t = current_search_time();
2135 // We are line oriented, don't read single chars
2136 std::string command;
2138 if (!std::getline(std::cin, command))
2141 if (command == "quit")
2144 PonderSearch = false;
2148 else if (command == "stop")
2151 PonderSearch = false;
2153 else if (command == "ponderhit")
2157 // Print search information
2161 else if (lastInfoTime > t)
2162 // HACK: Must be a new search where we searched less than
2163 // NodesBetweenPolls nodes during the first second of search.
2166 else if (t - lastInfoTime >= 1000)
2173 if (dbg_show_hit_rate)
2174 dbg_print_hit_rate();
2176 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2177 << " time " << t << " hashfull " << TT.full() << endl;
2180 // Should we stop the search?
2184 bool stillAtFirstMove = FirstRootMove
2185 && !AspirationFailLow
2186 && t > MaxSearchTime + ExtraSearchTime;
2188 bool noMoreTime = t > AbsoluteMaxSearchTime
2189 || stillAtFirstMove;
2191 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2192 || (ExactMaxTime && t >= ExactMaxTime)
2193 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2198 // ponderhit() is called when the program is pondering (i.e. thinking while
2199 // it's the opponent's turn to move) in order to let the engine know that
2200 // it correctly predicted the opponent's move.
2204 int t = current_search_time();
2205 PonderSearch = false;
2207 bool stillAtFirstMove = FirstRootMove
2208 && !AspirationFailLow
2209 && t > MaxSearchTime + ExtraSearchTime;
2211 bool noMoreTime = t > AbsoluteMaxSearchTime
2212 || stillAtFirstMove;
2214 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2219 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2221 void init_ss_array(SearchStack ss[]) {
2223 for (int i = 0; i < 3; i++)
2226 ss[i].initKillers();
2231 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2232 // while the program is pondering. The point is to work around a wrinkle in
2233 // the UCI protocol: When pondering, the engine is not allowed to give a
2234 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2235 // We simply wait here until one of these commands is sent, and return,
2236 // after which the bestmove and pondermove will be printed (in id_loop()).
2238 void wait_for_stop_or_ponderhit() {
2240 std::string command;
2244 if (!std::getline(std::cin, command))
2247 if (command == "quit")
2252 else if (command == "ponderhit" || command == "stop")
2258 // print_pv_info() prints to standard output and eventually to log file information on
2259 // the current PV line. It is called at each iteration or after a new pv is found.
2261 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2263 cout << "info depth " << Iteration
2264 << " score " << value_to_string(value)
2265 << ((value >= beta) ? " lowerbound" :
2266 ((value <= alpha)? " upperbound" : ""))
2267 << " time " << current_search_time()
2268 << " nodes " << TM.nodes_searched()
2272 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2273 cout << ss[0].pv[j] << " ";
2279 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2280 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2282 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2283 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2288 // init_thread() is the function which is called when a new thread is
2289 // launched. It simply calls the idle_loop() function with the supplied
2290 // threadID. There are two versions of this function; one for POSIX
2291 // threads and one for Windows threads.
2293 #if !defined(_MSC_VER)
2295 void* init_thread(void *threadID) {
2297 TM.idle_loop(*(int*)threadID, NULL);
2303 DWORD WINAPI init_thread(LPVOID threadID) {
2305 TM.idle_loop(*(int*)threadID, NULL);
2312 /// The ThreadsManager class
2314 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2315 // get_beta_counters() are getters/setters for the per thread
2316 // counters used to sort the moves at root.
2318 void ThreadsManager::resetNodeCounters() {
2320 for (int i = 0; i < MAX_THREADS; i++)
2321 threads[i].nodes = 0ULL;
2324 void ThreadsManager::resetBetaCounters() {
2326 for (int i = 0; i < MAX_THREADS; i++)
2327 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2330 int64_t ThreadsManager::nodes_searched() const {
2332 int64_t result = 0ULL;
2333 for (int i = 0; i < ActiveThreads; i++)
2334 result += threads[i].nodes;
2339 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2342 for (int i = 0; i < MAX_THREADS; i++)
2344 our += threads[i].betaCutOffs[us];
2345 their += threads[i].betaCutOffs[opposite_color(us)];
2350 // idle_loop() is where the threads are parked when they have no work to do.
2351 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2352 // object for which the current thread is the master.
2354 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2356 assert(threadID >= 0 && threadID < MAX_THREADS);
2360 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2361 // master should exit as last one.
2362 if (AllThreadsShouldExit)
2365 threads[threadID].state = THREAD_TERMINATED;
2369 // If we are not thinking, wait for a condition to be signaled
2370 // instead of wasting CPU time polling for work.
2371 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2374 assert(threadID != 0);
2375 threads[threadID].state = THREAD_SLEEPING;
2377 #if !defined(_MSC_VER)
2378 lock_grab(&WaitLock);
2379 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2380 pthread_cond_wait(&WaitCond, &WaitLock);
2381 lock_release(&WaitLock);
2383 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2387 // If thread has just woken up, mark it as available
2388 if (threads[threadID].state == THREAD_SLEEPING)
2389 threads[threadID].state = THREAD_AVAILABLE;
2391 // If this thread has been assigned work, launch a search
2392 if (threads[threadID].state == THREAD_WORKISWAITING)
2394 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2396 threads[threadID].state = THREAD_SEARCHING;
2398 if (threads[threadID].splitPoint->pvNode)
2399 sp_search<PV>(threads[threadID].splitPoint, threadID);
2401 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2403 assert(threads[threadID].state == THREAD_SEARCHING);
2405 threads[threadID].state = THREAD_AVAILABLE;
2408 // If this thread is the master of a split point and all slaves have
2409 // finished their work at this split point, return from the idle loop.
2411 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2413 if (i == ActiveThreads)
2415 // Because sp->slaves[] is reset under lock protection,
2416 // be sure sp->lock has been released before to return.
2417 lock_grab(&(sp->lock));
2418 lock_release(&(sp->lock));
2420 assert(threads[threadID].state == THREAD_AVAILABLE);
2422 threads[threadID].state = THREAD_SEARCHING;
2429 // init_threads() is called during startup. It launches all helper threads,
2430 // and initializes the split point stack and the global locks and condition
2433 void ThreadsManager::init_threads() {
2438 #if !defined(_MSC_VER)
2439 pthread_t pthread[1];
2442 // Initialize global locks
2443 lock_init(&MPLock, NULL);
2444 lock_init(&WaitLock, NULL);
2446 #if !defined(_MSC_VER)
2447 pthread_cond_init(&WaitCond, NULL);
2449 for (i = 0; i < MAX_THREADS; i++)
2450 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2453 // Initialize SplitPointStack locks
2454 for (i = 0; i < MAX_THREADS; i++)
2455 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2457 SplitPointStack[i][j].parent = NULL;
2458 lock_init(&(SplitPointStack[i][j].lock), NULL);
2461 // Will be set just before program exits to properly end the threads
2462 AllThreadsShouldExit = false;
2464 // Threads will be put to sleep as soon as created
2465 AllThreadsShouldSleep = true;
2467 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2469 threads[0].state = THREAD_SEARCHING;
2470 for (i = 1; i < MAX_THREADS; i++)
2471 threads[i].state = THREAD_AVAILABLE;
2473 // Launch the helper threads
2474 for (i = 1; i < MAX_THREADS; i++)
2477 #if !defined(_MSC_VER)
2478 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2480 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2485 cout << "Failed to create thread number " << i << endl;
2486 Application::exit_with_failure();
2489 // Wait until the thread has finished launching and is gone to sleep
2490 while (threads[i].state != THREAD_SLEEPING) {}
2495 // exit_threads() is called when the program exits. It makes all the
2496 // helper threads exit cleanly.
2498 void ThreadsManager::exit_threads() {
2500 ActiveThreads = MAX_THREADS; // HACK
2501 AllThreadsShouldSleep = true; // HACK
2502 wake_sleeping_threads();
2504 // This makes the threads to exit idle_loop()
2505 AllThreadsShouldExit = true;
2507 // Wait for thread termination
2508 for (int i = 1; i < MAX_THREADS; i++)
2509 while (threads[i].state != THREAD_TERMINATED);
2511 // Now we can safely destroy the locks
2512 for (int i = 0; i < MAX_THREADS; i++)
2513 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2514 lock_destroy(&(SplitPointStack[i][j].lock));
2516 lock_destroy(&WaitLock);
2517 lock_destroy(&MPLock);
2521 // thread_should_stop() checks whether the thread should stop its search.
2522 // This can happen if a beta cutoff has occurred in the thread's currently
2523 // active split point, or in some ancestor of the current split point.
2525 bool ThreadsManager::thread_should_stop(int threadID) const {
2527 assert(threadID >= 0 && threadID < ActiveThreads);
2531 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2536 // thread_is_available() checks whether the thread with threadID "slave" is
2537 // available to help the thread with threadID "master" at a split point. An
2538 // obvious requirement is that "slave" must be idle. With more than two
2539 // threads, this is not by itself sufficient: If "slave" is the master of
2540 // some active split point, it is only available as a slave to the other
2541 // threads which are busy searching the split point at the top of "slave"'s
2542 // split point stack (the "helpful master concept" in YBWC terminology).
2544 bool ThreadsManager::thread_is_available(int slave, int master) const {
2546 assert(slave >= 0 && slave < ActiveThreads);
2547 assert(master >= 0 && master < ActiveThreads);
2548 assert(ActiveThreads > 1);
2550 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2553 // Make a local copy to be sure doesn't change under our feet
2554 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2556 if (localActiveSplitPoints == 0)
2557 // No active split points means that the thread is available as
2558 // a slave for any other thread.
2561 if (ActiveThreads == 2)
2564 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2565 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2566 // could have been set to 0 by another thread leading to an out of bound access.
2567 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2574 // available_thread_exists() tries to find an idle thread which is available as
2575 // a slave for the thread with threadID "master".
2577 bool ThreadsManager::available_thread_exists(int master) const {
2579 assert(master >= 0 && master < ActiveThreads);
2580 assert(ActiveThreads > 1);
2582 for (int i = 0; i < ActiveThreads; i++)
2583 if (thread_is_available(i, master))
2590 // split() does the actual work of distributing the work at a node between
2591 // several available threads. If it does not succeed in splitting the
2592 // node (because no idle threads are available, or because we have no unused
2593 // split point objects), the function immediately returns. If splitting is
2594 // possible, a SplitPoint object is initialized with all the data that must be
2595 // copied to the helper threads and we tell our helper threads that they have
2596 // been assigned work. This will cause them to instantly leave their idle loops
2597 // and call sp_search(). When all threads have returned from sp_search() then
2600 template <bool Fake>
2601 void ThreadsManager::split(const Position& p, SearchStack* sstck, int ply, Value* alpha,
2602 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2603 int* moveCount, 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);
2617 // If no other thread is available to help us, or if we have too many
2618 // active split points, don't split.
2619 if ( !available_thread_exists(master)
2620 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2622 lock_release(&MPLock);
2626 // Pick the next available split point object from the split point stack
2627 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2629 // Initialize the split point object
2630 splitPoint->parent = threads[master].splitPoint;
2631 splitPoint->stopRequest = false;
2632 splitPoint->ply = ply;
2633 splitPoint->depth = depth;
2634 splitPoint->mateThreat = mateThreat;
2635 splitPoint->alpha = *alpha;
2636 splitPoint->beta = beta;
2637 splitPoint->pvNode = pvNode;
2638 splitPoint->bestValue = *bestValue;
2639 splitPoint->mp = mp;
2640 splitPoint->moveCount = *moveCount;
2641 splitPoint->pos = &p;
2642 splitPoint->parentSstack = sstck;
2643 for (int i = 0; i < ActiveThreads; i++)
2644 splitPoint->slaves[i] = 0;
2646 threads[master].splitPoint = splitPoint;
2647 threads[master].activeSplitPoints++;
2649 // If we are here it means we are not available
2650 assert(threads[master].state != THREAD_AVAILABLE);
2652 int workersCnt = 1; // At least the master is included
2654 // Allocate available threads setting state to THREAD_BOOKED
2655 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2656 if (thread_is_available(i, master))
2658 threads[i].state = THREAD_BOOKED;
2659 threads[i].splitPoint = splitPoint;
2660 splitPoint->slaves[i] = 1;
2664 assert(Fake || workersCnt > 1);
2666 // We can release the lock because slave threads are already booked and master is not available
2667 lock_release(&MPLock);
2669 // Tell the threads that they have work to do. This will make them leave
2670 // their idle loop. But before copy search stack tail for each thread.
2671 for (int i = 0; i < ActiveThreads; i++)
2672 if (i == master || splitPoint->slaves[i])
2674 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2676 assert(i == master || threads[i].state == THREAD_BOOKED);
2678 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2681 // Everything is set up. The master thread enters the idle loop, from
2682 // which it will instantly launch a search, because its state is
2683 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2684 // idle loop, which means that the main thread will return from the idle
2685 // loop when all threads have finished their work at this split point.
2686 idle_loop(master, splitPoint);
2688 // We have returned from the idle loop, which means that all threads are
2689 // finished. Update alpha and bestValue, and return.
2692 *alpha = splitPoint->alpha;
2693 *bestValue = splitPoint->bestValue;
2694 threads[master].activeSplitPoints--;
2695 threads[master].splitPoint = splitPoint->parent;
2697 lock_release(&MPLock);
2701 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2702 // to start a new search from the root.
2704 void ThreadsManager::wake_sleeping_threads() {
2706 assert(AllThreadsShouldSleep);
2707 assert(ActiveThreads > 0);
2709 AllThreadsShouldSleep = false;
2711 if (ActiveThreads == 1)
2714 #if !defined(_MSC_VER)
2715 pthread_mutex_lock(&WaitLock);
2716 pthread_cond_broadcast(&WaitCond);
2717 pthread_mutex_unlock(&WaitLock);
2719 for (int i = 1; i < MAX_THREADS; i++)
2720 SetEvent(SitIdleEvent[i]);
2726 // put_threads_to_sleep() makes all the threads go to sleep just before
2727 // to leave think(), at the end of the search. Threads should have already
2728 // finished the job and should be idle.
2730 void ThreadsManager::put_threads_to_sleep() {
2732 assert(!AllThreadsShouldSleep);
2734 // This makes the threads to go to sleep
2735 AllThreadsShouldSleep = true;
2738 /// The RootMoveList class
2740 // RootMoveList c'tor
2742 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2744 SearchStack ss[PLY_MAX_PLUS_2];
2745 MoveStack mlist[MaxRootMoves];
2747 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2749 // Generate all legal moves
2750 MoveStack* last = generate_moves(pos, mlist);
2752 // Add each move to the moves[] array
2753 for (MoveStack* cur = mlist; cur != last; cur++)
2755 bool includeMove = includeAllMoves;
2757 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2758 includeMove = (searchMoves[k] == cur->move);
2763 // Find a quick score for the move
2765 pos.do_move(cur->move, st);
2766 moves[count].move = cur->move;
2767 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2768 moves[count].pv[0] = cur->move;
2769 moves[count].pv[1] = MOVE_NONE;
2770 pos.undo_move(cur->move);
2777 // RootMoveList simple methods definitions
2779 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2781 moves[moveNum].nodes = nodes;
2782 moves[moveNum].cumulativeNodes += nodes;
2785 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2787 moves[moveNum].ourBeta = our;
2788 moves[moveNum].theirBeta = their;
2791 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2795 for (j = 0; pv[j] != MOVE_NONE; j++)
2796 moves[moveNum].pv[j] = pv[j];
2798 moves[moveNum].pv[j] = MOVE_NONE;
2802 // RootMoveList::sort() sorts the root move list at the beginning of a new
2805 void RootMoveList::sort() {
2807 sort_multipv(count - 1); // Sort all items
2811 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2812 // list by their scores and depths. It is used to order the different PVs
2813 // correctly in MultiPV mode.
2815 void RootMoveList::sort_multipv(int n) {
2819 for (i = 1; i <= n; i++)
2821 RootMove rm = moves[i];
2822 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2823 moves[j] = moves[j - 1];