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, but I can see no good reason for this, FIXME)
808 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
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 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
819 // Step 6. Razoring (omitted at root)
820 // Step 7. Static null move pruning (omitted at root)
821 // Step 8. Null move search with verification search (omitted at root)
822 // Step 9. Internal iterative deepening (omitted at root)
824 // Step extra. Fail low loop
825 // We start with small aspiration window and in case of fail low, we research
826 // with bigger window until we are not failing low anymore.
829 // Sort the moves before to (re)search
832 // Step 10. Loop through all moves in the root move list
833 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
835 // This is used by time management
836 FirstRootMove = (i == 0);
838 // Save the current node count before the move is searched
839 nodes = TM.nodes_searched();
841 // Reset beta cut-off counters
842 TM.resetBetaCounters();
844 // Pick the next root move, and print the move and the move number to
845 // the standard output.
846 move = ss[0].currentMove = rml.get_move(i);
848 if (current_search_time() >= 1000)
849 cout << "info currmove " << move
850 << " currmovenumber " << i + 1 << endl;
852 moveIsCheck = pos.move_is_check(move);
853 captureOrPromotion = pos.move_is_capture_or_promotion(move);
855 // Step 11. Decide the new search depth
856 depth = (Iteration - 2) * OnePly + InitialDepth;
857 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
858 newDepth = depth + ext;
860 // Step 12. Futility pruning (omitted at root)
862 // Step extra. Fail high loop
863 // If move fails high, we research with bigger window until we are not failing
865 value = - VALUE_INFINITE;
869 // Step 13. Make the move
870 pos.do_move(move, st, ci, moveIsCheck);
872 // Step extra. pv search
873 // We do pv search for first moves (i < MultiPV)
874 // and for fail high research (value > alpha)
875 if (i < MultiPV || value > alpha)
877 // Aspiration window is disabled in multi-pv case
879 alpha = -VALUE_INFINITE;
881 // Full depth PV search, done on first move or after a fail high
882 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
886 // Step 14. Reduced search
887 // if the move fails high will be re-searched at full depth
888 bool doFullDepthSearch = true;
890 if ( depth >= 3 * OnePly
892 && !captureOrPromotion
893 && !move_is_castle(move))
895 ss[0].reduction = reduction<PV>(depth, i - MultiPV + 2);
898 // Reduced depth non-pv search using alpha as upperbound
899 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
900 doFullDepthSearch = (value > alpha);
904 // Step 15. Full depth search
905 if (doFullDepthSearch)
907 // Full depth non-pv search using alpha as upperbound
908 ss[0].reduction = Depth(0);
909 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
911 // If we are above alpha then research at same depth but as PV
912 // to get a correct score or eventually a fail high above beta.
914 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
918 // Step 16. Undo move
921 // Can we exit fail high loop ?
922 if (AbortSearch || value < beta)
925 // We are failing high and going to do a research. It's important to update
926 // the score before research in case we run out of time while researching.
927 rml.set_move_score(i, value);
929 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
930 rml.set_move_pv(i, ss[0].pv);
932 // Print information to the standard output
933 print_pv_info(pos, ss, alpha, beta, value);
935 // Prepare for a research after a fail high, each time with a wider window
936 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
939 } // End of fail high loop
941 // Finished searching the move. If AbortSearch is true, the search
942 // was aborted because the user interrupted the search or because we
943 // ran out of time. In this case, the return value of the search cannot
944 // be trusted, and we break out of the loop without updating the best
949 // Remember beta-cutoff and searched nodes counts for this move. The
950 // info is used to sort the root moves for the next iteration.
952 TM.get_beta_counters(pos.side_to_move(), our, their);
953 rml.set_beta_counters(i, our, their);
954 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
956 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
957 assert(value < beta);
959 // Step 17. Check for new best move
960 if (value <= alpha && i >= MultiPV)
961 rml.set_move_score(i, -VALUE_INFINITE);
964 // PV move or new best move!
967 rml.set_move_score(i, value);
969 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
970 rml.set_move_pv(i, ss[0].pv);
974 // We record how often the best move has been changed in each
975 // iteration. This information is used for time managment: When
976 // the best move changes frequently, we allocate some more time.
978 BestMoveChangesByIteration[Iteration]++;
980 // Print information to the standard output
981 print_pv_info(pos, ss, alpha, beta, value);
983 // Raise alpha to setup proper non-pv search upper bound
990 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
992 cout << "info multipv " << j + 1
993 << " score " << value_to_string(rml.get_move_score(j))
994 << " depth " << (j <= i ? Iteration : Iteration - 1)
995 << " time " << current_search_time()
996 << " nodes " << TM.nodes_searched()
1000 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1001 cout << rml.get_move_pv(j, k) << " ";
1005 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1007 } // PV move or new best move
1009 assert(alpha >= *alphaPtr);
1011 AspirationFailLow = (alpha == *alphaPtr);
1013 if (AspirationFailLow && StopOnPonderhit)
1014 StopOnPonderhit = false;
1017 // Can we exit fail low loop ?
1018 if (AbortSearch || !AspirationFailLow)
1021 // Prepare for a research after a fail low, each time with a wider window
1022 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1027 // Sort the moves before to return
1034 // search<>() is the main search function for both PV and non-PV nodes
1036 template <NodeType PvNode>
1037 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth,
1038 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1040 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1041 assert(beta > alpha && beta <= VALUE_INFINITE);
1042 assert(PvNode || alpha == beta - 1);
1043 assert(ply >= 0 && ply < PLY_MAX);
1044 assert(threadID >= 0 && threadID < TM.active_threads());
1046 Move movesSearched[256];
1051 Depth ext, newDepth;
1052 Value bestValue, value, oldAlpha;
1053 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1054 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1055 bool mateThreat = false;
1057 refinedValue = bestValue = value = -VALUE_INFINITE;
1061 return qsearch<PvNode>(pos, ss, alpha, beta, Depth(0), ply, threadID);
1063 // Step 1. Initialize node and poll
1064 // Polling can abort search.
1065 init_node(ss, ply, threadID);
1067 // Step 2. Check for aborted search and immediate draw
1068 if (AbortSearch || TM.thread_should_stop(threadID))
1071 if (pos.is_draw() || ply >= PLY_MAX - 1)
1074 // Step 3. Mate distance pruning
1075 alpha = Max(value_mated_in(ply), alpha);
1076 beta = Min(value_mate_in(ply+1), beta);
1080 // Step 4. Transposition table lookup
1082 // We don't want the score of a partial search to overwrite a previous full search
1083 // TT value, so we use a different position key in case of an excluded move exists.
1084 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1086 tte = TT.retrieve(posKey);
1087 ttMove = (tte ? tte->move() : MOVE_NONE);
1089 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1090 // This is to avoid problems in the following areas:
1092 // * Repetition draw detection
1093 // * Fifty move rule detection
1094 // * Searching for a mate
1095 // * Printing of full PV line
1097 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1099 // Refresh tte entry to avoid aging
1100 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1102 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1103 return value_from_tt(tte->value(), ply);
1106 // Step 5. Evaluate the position statically
1107 // At PV nodes we do this only to update gain statistics
1108 isCheck = pos.is_check();
1111 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1112 ss[ply].eval = value_from_tt(tte->value(), ply);
1114 ss[ply].eval = evaluate(pos, ei, threadID);
1116 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1117 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1120 // Step 6. Razoring (is omitted in PV nodes)
1122 && refinedValue < beta - razor_margin(depth)
1123 && ttMove == MOVE_NONE
1124 && ss[ply - 1].currentMove != MOVE_NULL
1125 && depth < RazorDepth
1127 && !value_is_mate(beta)
1128 && !pos.has_pawn_on_7th(pos.side_to_move()))
1130 Value rbeta = beta - razor_margin(depth);
1131 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1133 // Logically we should return (v + razor_margin(depth)), but
1134 // surprisingly this did slightly weaker in tests.
1138 // Step 7. Static null move pruning (is omitted in PV nodes)
1139 // We're betting that the opponent doesn't have a move that will reduce
1140 // the score by more than futility_margin(depth) if we do a null move.
1143 && depth < RazorDepth
1145 && !value_is_mate(beta)
1146 && ok_to_do_nullmove(pos)
1147 && refinedValue >= beta + futility_margin(depth, 0))
1148 return refinedValue - futility_margin(depth, 0);
1150 // Step 8. Null move search with verification search (is omitted in PV nodes)
1151 // When we jump directly to qsearch() we do a null move only if static value is
1152 // at least beta. Otherwise we do a null move if static value is not more than
1153 // NullMoveMargin under beta.
1158 && !value_is_mate(beta)
1159 && ok_to_do_nullmove(pos)
1160 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1162 ss[ply].currentMove = MOVE_NULL;
1164 // Null move dynamic reduction based on depth
1165 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1167 // Null move dynamic reduction based on value
1168 if (refinedValue - beta > PawnValueMidgame)
1171 pos.do_null_move(st);
1173 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1175 pos.undo_null_move();
1177 if (nullValue >= beta)
1179 // Do not return unproven mate scores
1180 if (nullValue >= value_mate_in(PLY_MAX))
1183 if (depth < 6 * OnePly)
1186 // Do zugzwang verification search
1187 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1191 // The null move failed low, which means that we may be faced with
1192 // some kind of threat. If the previous move was reduced, check if
1193 // the move that refuted the null move was somehow connected to the
1194 // move which was reduced. If a connection is found, return a fail
1195 // low score (which will cause the reduced move to fail high in the
1196 // parent node, which will trigger a re-search with full depth).
1197 if (nullValue == value_mated_in(ply + 2))
1200 ss[ply].threatMove = ss[ply + 1].currentMove;
1201 if ( depth < ThreatDepth
1202 && ss[ply - 1].reduction
1203 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1208 // Step 9. Internal iterative deepening
1209 if ( depth >= IIDDepth[PvNode]
1210 && ttMove == MOVE_NONE
1211 && (PvNode || (!isCheck && ss[ply].eval >= beta - IIDMargin)))
1213 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1214 search<PvNode>(pos, ss, alpha, beta, d, ply, false, threadID);
1215 ttMove = ss[ply].pv[ply];
1216 tte = TT.retrieve(posKey);
1219 // Expensive mate threat detection (only for PV nodes)
1221 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1223 // Initialize a MovePicker object for the current position
1224 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1227 // Step 10. Loop through moves
1228 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1229 while ( bestValue < beta
1230 && (move = mp.get_next_move()) != MOVE_NONE
1231 && !TM.thread_should_stop(threadID))
1233 assert(move_is_ok(move));
1235 if (move == excludedMove)
1238 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1239 moveIsCheck = pos.move_is_check(move, ci);
1240 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1242 // Step 11. Decide the new search depth
1243 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1245 // Singular extension search. We extend the TT move if its value is much better than
1246 // its siblings. To verify this we do a reduced search on all the other moves but the
1247 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1248 if ( depth >= SingularExtensionDepth[PvNode]
1250 && move == tte->move()
1251 && !excludedMove // Do not allow recursive singular extension search
1253 && is_lower_bound(tte->type())
1254 && tte->depth() >= depth - 3 * OnePly)
1256 Value ttValue = value_from_tt(tte->value(), ply);
1258 if (abs(ttValue) < VALUE_KNOWN_WIN)
1260 Value b = ttValue - SingularExtensionMargin;
1261 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply, false, threadID, move);
1263 if (v < ttValue - SingularExtensionMargin)
1268 newDepth = depth - OnePly + ext;
1270 // Update current move (this must be done after singular extension search)
1271 movesSearched[moveCount++] = ss[ply].currentMove = move;
1273 // Step 12. Futility pruning (is omitted in PV nodes)
1277 && !captureOrPromotion
1278 && !move_is_castle(move)
1281 // Move count based pruning
1282 if ( moveCount >= futility_move_count(depth)
1283 && ok_to_prune(pos, move, ss[ply].threatMove)
1284 && bestValue > value_mated_in(PLY_MAX))
1287 // Value based pruning
1288 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount); // FIXME We illogically ignore reduction condition depth >= 3*OnePly
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
1356 if (value == value_mate_in(ply + 1))
1357 ss[ply].mateKiller = move;
1361 // Step 18. Check for split
1362 if ( TM.active_threads() > 1
1364 && depth >= MinimumSplitDepth
1366 && TM.available_thread_exists(threadID)
1368 && !TM.thread_should_stop(threadID)
1369 && TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1370 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 && !TM.thread_should_stop(threadID)
1635 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1637 moveCount = ++sp->moves;
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 && !TM.thread_should_stop(threadID));
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 && !TM.thread_should_stop(threadID))
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);
1737 if (PvNode && value == value_mate_in(sp->ply + 1))
1738 ss[sp->ply].mateKiller = move;
1743 /* Here we have the lock still grabbed */
1745 sp->slaves[threadID] = 0;
1748 lock_release(&(sp->lock));
1751 // init_node() is called at the beginning of all the search functions
1752 // (search() qsearch(), and so on) and initializes the
1753 // search stack object corresponding to the current node. Once every
1754 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1755 // for user input and checks whether it is time to stop the search.
1757 void init_node(SearchStack ss[], int ply, int threadID) {
1759 assert(ply >= 0 && ply < PLY_MAX);
1760 assert(threadID >= 0 && threadID < TM.active_threads());
1762 TM.incrementNodeCounter(threadID);
1767 if (NodesSincePoll >= NodesBetweenPolls)
1774 ss[ply + 2].initKillers();
1777 // update_pv() is called whenever a search returns a value > alpha.
1778 // It updates the PV in the SearchStack object corresponding to the
1781 void update_pv(SearchStack ss[], int ply) {
1783 assert(ply >= 0 && ply < PLY_MAX);
1787 ss[ply].pv[ply] = ss[ply].currentMove;
1789 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1790 ss[ply].pv[p] = ss[ply + 1].pv[p];
1792 ss[ply].pv[p] = MOVE_NONE;
1796 // sp_update_pv() is a variant of update_pv for use at split points. The
1797 // difference between the two functions is that sp_update_pv also updates
1798 // the PV at the parent node.
1800 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1802 assert(ply >= 0 && ply < PLY_MAX);
1806 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1808 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1809 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1811 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1815 // connected_moves() tests whether two moves are 'connected' in the sense
1816 // that the first move somehow made the second move possible (for instance
1817 // if the moving piece is the same in both moves). The first move is assumed
1818 // to be the move that was made to reach the current position, while the
1819 // second move is assumed to be a move from the current position.
1821 bool connected_moves(const Position& pos, Move m1, Move m2) {
1823 Square f1, t1, f2, t2;
1826 assert(move_is_ok(m1));
1827 assert(move_is_ok(m2));
1829 if (m2 == MOVE_NONE)
1832 // Case 1: The moving piece is the same in both moves
1838 // Case 2: The destination square for m2 was vacated by m1
1844 // Case 3: Moving through the vacated square
1845 if ( piece_is_slider(pos.piece_on(f2))
1846 && bit_is_set(squares_between(f2, t2), f1))
1849 // Case 4: The destination square for m2 is defended by the moving piece in m1
1850 p = pos.piece_on(t1);
1851 if (bit_is_set(pos.attacks_from(p, t1), t2))
1854 // Case 5: Discovered check, checking piece is the piece moved in m1
1855 if ( piece_is_slider(p)
1856 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1857 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1859 // discovered_check_candidates() works also if the Position's side to
1860 // move is the opposite of the checking piece.
1861 Color them = opposite_color(pos.side_to_move());
1862 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1864 if (bit_is_set(dcCandidates, f2))
1871 // value_is_mate() checks if the given value is a mate one
1872 // eventually compensated for the ply.
1874 bool value_is_mate(Value value) {
1876 assert(abs(value) <= VALUE_INFINITE);
1878 return value <= value_mated_in(PLY_MAX)
1879 || value >= value_mate_in(PLY_MAX);
1883 // move_is_killer() checks if the given move is among the
1884 // killer moves of that ply.
1886 bool move_is_killer(Move m, const SearchStack& ss) {
1888 const Move* k = ss.killers;
1889 for (int i = 0; i < KILLER_MAX; i++, k++)
1897 // extension() decides whether a move should be searched with normal depth,
1898 // or with extended depth. Certain classes of moves (checking moves, in
1899 // particular) are searched with bigger depth than ordinary moves and in
1900 // any case are marked as 'dangerous'. Note that also if a move is not
1901 // extended, as example because the corresponding UCI option is set to zero,
1902 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1903 template <NodeType PvNode>
1904 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1905 bool singleEvasion, bool mateThreat, bool* dangerous) {
1907 assert(m != MOVE_NONE);
1909 Depth result = Depth(0);
1910 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1915 result += CheckExtension[PvNode];
1918 result += SingleEvasionExtension[PvNode];
1921 result += MateThreatExtension[PvNode];
1924 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1926 Color c = pos.side_to_move();
1927 if (relative_rank(c, move_to(m)) == RANK_7)
1929 result += PawnPushTo7thExtension[PvNode];
1932 if (pos.pawn_is_passed(c, move_to(m)))
1934 result += PassedPawnExtension[PvNode];
1939 if ( captureOrPromotion
1940 && pos.type_of_piece_on(move_to(m)) != PAWN
1941 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1942 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1943 && !move_is_promotion(m)
1946 result += PawnEndgameExtension[PvNode];
1951 && captureOrPromotion
1952 && pos.type_of_piece_on(move_to(m)) != PAWN
1953 && pos.see_sign(m) >= 0)
1959 return Min(result, OnePly);
1963 // ok_to_do_nullmove() looks at the current position and decides whether
1964 // doing a 'null move' should be allowed. In order to avoid zugzwang
1965 // problems, null moves are not allowed when the side to move has very
1966 // little material left. Currently, the test is a bit too simple: Null
1967 // moves are avoided only when the side to move has only pawns left.
1968 // It's probably a good idea to avoid null moves in at least some more
1969 // complicated endgames, e.g. KQ vs KR. FIXME
1971 bool ok_to_do_nullmove(const Position& pos) {
1973 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1977 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1978 // non-tactical moves late in the move list close to the leaves are
1979 // candidates for pruning.
1981 bool ok_to_prune(const Position& pos, Move m, Move threat) {
1983 assert(move_is_ok(m));
1984 assert(threat == MOVE_NONE || move_is_ok(threat));
1985 assert(!pos.move_is_check(m));
1986 assert(!pos.move_is_capture_or_promotion(m));
1987 assert(!pos.move_is_passed_pawn_push(m));
1989 Square mfrom, mto, tfrom, tto;
1991 // Prune if there isn't any threat move
1992 if (threat == MOVE_NONE)
1995 mfrom = move_from(m);
1997 tfrom = move_from(threat);
1998 tto = move_to(threat);
2000 // Case 1: Don't prune moves which move the threatened piece
2004 // Case 2: If the threatened piece has value less than or equal to the
2005 // value of the threatening piece, don't prune move which defend it.
2006 if ( pos.move_is_capture(threat)
2007 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2008 || pos.type_of_piece_on(tfrom) == KING)
2009 && pos.move_attacks_square(m, tto))
2012 // Case 3: If the moving piece in the threatened move is a slider, don't
2013 // prune safe moves which block its ray.
2014 if ( piece_is_slider(pos.piece_on(tfrom))
2015 && bit_is_set(squares_between(tfrom, tto), mto)
2016 && pos.see_sign(m) >= 0)
2023 // ok_to_use_TT() returns true if a transposition table score
2024 // can be used at a given point in search.
2026 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2028 Value v = value_from_tt(tte->value(), ply);
2030 return ( tte->depth() >= depth
2031 || v >= Max(value_mate_in(PLY_MAX), beta)
2032 || v < Min(value_mated_in(PLY_MAX), beta))
2034 && ( (is_lower_bound(tte->type()) && v >= beta)
2035 || (is_upper_bound(tte->type()) && v < beta));
2039 // refine_eval() returns the transposition table score if
2040 // possible otherwise falls back on static position evaluation.
2042 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2047 Value v = value_from_tt(tte->value(), ply);
2049 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2050 || (is_upper_bound(tte->type()) && v < defaultEval))
2057 // update_history() registers a good move that produced a beta-cutoff
2058 // in history and marks as failures all the other moves of that ply.
2060 void update_history(const Position& pos, Move move, Depth depth,
2061 Move movesSearched[], int moveCount) {
2065 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2067 for (int i = 0; i < moveCount - 1; i++)
2069 m = movesSearched[i];
2073 if (!pos.move_is_capture_or_promotion(m))
2074 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2079 // update_killers() add a good move that produced a beta-cutoff
2080 // among the killer moves of that ply.
2082 void update_killers(Move m, SearchStack& ss) {
2084 if (m == ss.killers[0])
2087 for (int i = KILLER_MAX - 1; i > 0; i--)
2088 ss.killers[i] = ss.killers[i - 1];
2094 // update_gains() updates the gains table of a non-capture move given
2095 // the static position evaluation before and after the move.
2097 void update_gains(const Position& pos, Move m, Value before, Value after) {
2100 && before != VALUE_NONE
2101 && after != VALUE_NONE
2102 && pos.captured_piece() == NO_PIECE_TYPE
2103 && !move_is_castle(m)
2104 && !move_is_promotion(m))
2105 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2109 // current_search_time() returns the number of milliseconds which have passed
2110 // since the beginning of the current search.
2112 int current_search_time() {
2114 return get_system_time() - SearchStartTime;
2118 // nps() computes the current nodes/second count.
2122 int t = current_search_time();
2123 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2127 // poll() performs two different functions: It polls for user input, and it
2128 // looks at the time consumed so far and decides if it's time to abort the
2133 static int lastInfoTime;
2134 int t = current_search_time();
2139 // We are line oriented, don't read single chars
2140 std::string command;
2142 if (!std::getline(std::cin, command))
2145 if (command == "quit")
2148 PonderSearch = false;
2152 else if (command == "stop")
2155 PonderSearch = false;
2157 else if (command == "ponderhit")
2161 // Print search information
2165 else if (lastInfoTime > t)
2166 // HACK: Must be a new search where we searched less than
2167 // NodesBetweenPolls nodes during the first second of search.
2170 else if (t - lastInfoTime >= 1000)
2177 if (dbg_show_hit_rate)
2178 dbg_print_hit_rate();
2180 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2181 << " time " << t << " hashfull " << TT.full() << endl;
2184 // Should we stop the search?
2188 bool stillAtFirstMove = FirstRootMove
2189 && !AspirationFailLow
2190 && t > MaxSearchTime + ExtraSearchTime;
2192 bool noMoreTime = t > AbsoluteMaxSearchTime
2193 || stillAtFirstMove;
2195 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2196 || (ExactMaxTime && t >= ExactMaxTime)
2197 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2202 // ponderhit() is called when the program is pondering (i.e. thinking while
2203 // it's the opponent's turn to move) in order to let the engine know that
2204 // it correctly predicted the opponent's move.
2208 int t = current_search_time();
2209 PonderSearch = false;
2211 bool stillAtFirstMove = FirstRootMove
2212 && !AspirationFailLow
2213 && t > MaxSearchTime + ExtraSearchTime;
2215 bool noMoreTime = t > AbsoluteMaxSearchTime
2216 || stillAtFirstMove;
2218 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2223 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2225 void init_ss_array(SearchStack ss[]) {
2227 for (int i = 0; i < 3; i++)
2230 ss[i].initKillers();
2235 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2236 // while the program is pondering. The point is to work around a wrinkle in
2237 // the UCI protocol: When pondering, the engine is not allowed to give a
2238 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2239 // We simply wait here until one of these commands is sent, and return,
2240 // after which the bestmove and pondermove will be printed (in id_loop()).
2242 void wait_for_stop_or_ponderhit() {
2244 std::string command;
2248 if (!std::getline(std::cin, command))
2251 if (command == "quit")
2256 else if (command == "ponderhit" || command == "stop")
2262 // print_pv_info() prints to standard output and eventually to log file information on
2263 // the current PV line. It is called at each iteration or after a new pv is found.
2265 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2267 cout << "info depth " << Iteration
2268 << " score " << value_to_string(value)
2269 << ((value >= beta) ? " lowerbound" :
2270 ((value <= alpha)? " upperbound" : ""))
2271 << " time " << current_search_time()
2272 << " nodes " << TM.nodes_searched()
2276 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2277 cout << ss[0].pv[j] << " ";
2283 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2284 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2286 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2287 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2292 // init_thread() is the function which is called when a new thread is
2293 // launched. It simply calls the idle_loop() function with the supplied
2294 // threadID. There are two versions of this function; one for POSIX
2295 // threads and one for Windows threads.
2297 #if !defined(_MSC_VER)
2299 void* init_thread(void *threadID) {
2301 TM.idle_loop(*(int*)threadID, NULL);
2307 DWORD WINAPI init_thread(LPVOID threadID) {
2309 TM.idle_loop(*(int*)threadID, NULL);
2316 /// The ThreadsManager class
2318 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2319 // get_beta_counters() are getters/setters for the per thread
2320 // counters used to sort the moves at root.
2322 void ThreadsManager::resetNodeCounters() {
2324 for (int i = 0; i < MAX_THREADS; i++)
2325 threads[i].nodes = 0ULL;
2328 void ThreadsManager::resetBetaCounters() {
2330 for (int i = 0; i < MAX_THREADS; i++)
2331 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2334 int64_t ThreadsManager::nodes_searched() const {
2336 int64_t result = 0ULL;
2337 for (int i = 0; i < ActiveThreads; i++)
2338 result += threads[i].nodes;
2343 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2346 for (int i = 0; i < MAX_THREADS; i++)
2348 our += threads[i].betaCutOffs[us];
2349 their += threads[i].betaCutOffs[opposite_color(us)];
2354 // idle_loop() is where the threads are parked when they have no work to do.
2355 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2356 // object for which the current thread is the master.
2358 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2360 assert(threadID >= 0 && threadID < MAX_THREADS);
2364 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2365 // master should exit as last one.
2366 if (AllThreadsShouldExit)
2369 threads[threadID].state = THREAD_TERMINATED;
2373 // If we are not thinking, wait for a condition to be signaled
2374 // instead of wasting CPU time polling for work.
2375 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2378 assert(threadID != 0);
2379 threads[threadID].state = THREAD_SLEEPING;
2381 #if !defined(_MSC_VER)
2382 lock_grab(&WaitLock);
2383 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2384 pthread_cond_wait(&WaitCond, &WaitLock);
2385 lock_release(&WaitLock);
2387 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2391 // If thread has just woken up, mark it as available
2392 if (threads[threadID].state == THREAD_SLEEPING)
2393 threads[threadID].state = THREAD_AVAILABLE;
2395 // If this thread has been assigned work, launch a search
2396 if (threads[threadID].state == THREAD_WORKISWAITING)
2398 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2400 threads[threadID].state = THREAD_SEARCHING;
2402 if (threads[threadID].splitPoint->pvNode)
2403 sp_search<PV>(threads[threadID].splitPoint, threadID);
2405 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2407 assert(threads[threadID].state == THREAD_SEARCHING);
2409 threads[threadID].state = THREAD_AVAILABLE;
2412 // If this thread is the master of a split point and all threads have
2413 // finished their work at this split point, return from the idle loop.
2414 if (sp && sp->cpus == 0)
2416 // Because sp->cpus is decremented under lock protection,
2417 // be sure sp->lock has been released before to proceed.
2418 lock_grab(&(sp->lock));
2419 lock_release(&(sp->lock));
2421 assert(threads[threadID].state == THREAD_AVAILABLE);
2423 threads[threadID].state = THREAD_SEARCHING;
2430 // init_threads() is called during startup. It launches all helper threads,
2431 // and initializes the split point stack and the global locks and condition
2434 void ThreadsManager::init_threads() {
2439 #if !defined(_MSC_VER)
2440 pthread_t pthread[1];
2443 // Initialize global locks
2444 lock_init(&MPLock, NULL);
2445 lock_init(&WaitLock, NULL);
2447 #if !defined(_MSC_VER)
2448 pthread_cond_init(&WaitCond, NULL);
2450 for (i = 0; i < MAX_THREADS; i++)
2451 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2454 // Initialize SplitPointStack locks
2455 for (i = 0; i < MAX_THREADS; i++)
2456 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2458 SplitPointStack[i][j].parent = NULL;
2459 lock_init(&(SplitPointStack[i][j].lock), NULL);
2462 // Will be set just before program exits to properly end the threads
2463 AllThreadsShouldExit = false;
2465 // Threads will be put to sleep as soon as created
2466 AllThreadsShouldSleep = true;
2468 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2470 threads[0].state = THREAD_SEARCHING;
2471 for (i = 1; i < MAX_THREADS; i++)
2472 threads[i].state = THREAD_AVAILABLE;
2474 // Launch the helper threads
2475 for (i = 1; i < MAX_THREADS; i++)
2478 #if !defined(_MSC_VER)
2479 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2481 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2486 cout << "Failed to create thread number " << i << endl;
2487 Application::exit_with_failure();
2490 // Wait until the thread has finished launching and is gone to sleep
2491 while (threads[i].state != THREAD_SLEEPING) {}
2496 // exit_threads() is called when the program exits. It makes all the
2497 // helper threads exit cleanly.
2499 void ThreadsManager::exit_threads() {
2501 ActiveThreads = MAX_THREADS; // HACK
2502 AllThreadsShouldSleep = true; // HACK
2503 wake_sleeping_threads();
2505 // This makes the threads to exit idle_loop()
2506 AllThreadsShouldExit = true;
2508 // Wait for thread termination
2509 for (int i = 1; i < MAX_THREADS; i++)
2510 while (threads[i].state != THREAD_TERMINATED);
2512 // Now we can safely destroy the locks
2513 for (int i = 0; i < MAX_THREADS; i++)
2514 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2515 lock_destroy(&(SplitPointStack[i][j].lock));
2517 lock_destroy(&WaitLock);
2518 lock_destroy(&MPLock);
2522 // thread_should_stop() checks whether the thread should stop its search.
2523 // This can happen if a beta cutoff has occurred in the thread's currently
2524 // active split point, or in some ancestor of the current split point.
2526 bool ThreadsManager::thread_should_stop(int threadID) const {
2528 assert(threadID >= 0 && threadID < ActiveThreads);
2532 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2537 // thread_is_available() checks whether the thread with threadID "slave" is
2538 // available to help the thread with threadID "master" at a split point. An
2539 // obvious requirement is that "slave" must be idle. With more than two
2540 // threads, this is not by itself sufficient: If "slave" is the master of
2541 // some active split point, it is only available as a slave to the other
2542 // threads which are busy searching the split point at the top of "slave"'s
2543 // split point stack (the "helpful master concept" in YBWC terminology).
2545 bool ThreadsManager::thread_is_available(int slave, int master) const {
2547 assert(slave >= 0 && slave < ActiveThreads);
2548 assert(master >= 0 && master < ActiveThreads);
2549 assert(ActiveThreads > 1);
2551 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2554 // Make a local copy to be sure doesn't change under our feet
2555 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2557 if (localActiveSplitPoints == 0)
2558 // No active split points means that the thread is available as
2559 // a slave for any other thread.
2562 if (ActiveThreads == 2)
2565 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2566 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2567 // could have been set to 0 by another thread leading to an out of bound access.
2568 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2575 // available_thread_exists() tries to find an idle thread which is available as
2576 // a slave for the thread with threadID "master".
2578 bool ThreadsManager::available_thread_exists(int master) const {
2580 assert(master >= 0 && master < ActiveThreads);
2581 assert(ActiveThreads > 1);
2583 for (int i = 0; i < ActiveThreads; i++)
2584 if (thread_is_available(i, master))
2591 // split() does the actual work of distributing the work at a node between
2592 // several threads at PV nodes. If it does not succeed in splitting the
2593 // node (because no idle threads are available, or because we have no unused
2594 // split point objects), the function immediately returns false. If
2595 // splitting is possible, a SplitPoint object is initialized with all the
2596 // data that must be copied to the helper threads (the current position and
2597 // search stack, alpha, beta, the search depth, etc.), and we tell our
2598 // helper threads that they have been assigned work. This will cause them
2599 // to instantly leave their idle loops and call sp_search_pv(). When all
2600 // threads have returned from sp_search_pv (or, equivalently, when
2601 // splitPoint->cpus becomes 0), split() returns true.
2603 template <bool Fake>
2604 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply, Value* alpha,
2605 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2606 int* moves, MovePicker* mp, int master, bool pvNode) {
2608 assert(sstck != NULL);
2609 assert(ply >= 0 && ply < PLY_MAX);
2610 assert(*bestValue >= -VALUE_INFINITE);
2611 assert(*bestValue <= *alpha);
2612 assert(*alpha < beta);
2613 assert(beta <= VALUE_INFINITE);
2614 assert(depth > Depth(0));
2615 assert(master >= 0 && master < ActiveThreads);
2616 assert(ActiveThreads > 1);
2618 SplitPoint* splitPoint;
2622 // If no other thread is available to help us, or if we have too many
2623 // active split points, don't split.
2624 if ( !available_thread_exists(master)
2625 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2627 lock_release(&MPLock);
2631 // Pick the next available split point object from the split point stack
2632 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2634 // Initialize the split point object
2635 splitPoint->parent = threads[master].splitPoint;
2636 splitPoint->stopRequest = false;
2637 splitPoint->ply = ply;
2638 splitPoint->depth = depth;
2639 splitPoint->mateThreat = mateThreat;
2640 splitPoint->alpha = *alpha;
2641 splitPoint->beta = beta;
2642 splitPoint->pvNode = pvNode;
2643 splitPoint->bestValue = *bestValue;
2644 splitPoint->master = master;
2645 splitPoint->mp = mp;
2646 splitPoint->moves = *moves;
2647 splitPoint->cpus = 1;
2648 splitPoint->pos = &p;
2649 splitPoint->parentSstack = sstck;
2650 for (int i = 0; i < ActiveThreads; i++)
2651 splitPoint->slaves[i] = 0;
2653 threads[master].splitPoint = splitPoint;
2654 threads[master].activeSplitPoints++;
2656 // If we are here it means we are not available
2657 assert(threads[master].state != THREAD_AVAILABLE);
2659 // Allocate available threads setting state to THREAD_BOOKED
2660 for (int i = 0; !Fake && i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2661 if (thread_is_available(i, master))
2663 threads[i].state = THREAD_BOOKED;
2664 threads[i].splitPoint = splitPoint;
2665 splitPoint->slaves[i] = 1;
2669 assert(Fake || splitPoint->cpus > 1);
2671 // We can release the lock because slave threads are already booked and master is not available
2672 lock_release(&MPLock);
2674 // Tell the threads that they have work to do. This will make them leave
2675 // their idle loop. But before copy search stack tail for each thread.
2676 for (int i = 0; i < ActiveThreads; i++)
2677 if (i == master || splitPoint->slaves[i])
2679 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2681 assert(i == master || threads[i].state == THREAD_BOOKED);
2683 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2686 // Everything is set up. The master thread enters the idle loop, from
2687 // which it will instantly launch a search, because its state is
2688 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2689 // idle loop, which means that the main thread will return from the idle
2690 // loop when all threads have finished their work at this split point
2691 // (i.e. when splitPoint->cpus == 0).
2692 idle_loop(master, splitPoint);
2694 // We have returned from the idle loop, which means that all threads are
2695 // finished. Update alpha and bestValue, and return.
2698 *alpha = splitPoint->alpha;
2699 *bestValue = splitPoint->bestValue;
2700 threads[master].activeSplitPoints--;
2701 threads[master].splitPoint = splitPoint->parent;
2703 lock_release(&MPLock);
2708 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2709 // to start a new search from the root.
2711 void ThreadsManager::wake_sleeping_threads() {
2713 assert(AllThreadsShouldSleep);
2714 assert(ActiveThreads > 0);
2716 AllThreadsShouldSleep = false;
2718 if (ActiveThreads == 1)
2721 #if !defined(_MSC_VER)
2722 pthread_mutex_lock(&WaitLock);
2723 pthread_cond_broadcast(&WaitCond);
2724 pthread_mutex_unlock(&WaitLock);
2726 for (int i = 1; i < MAX_THREADS; i++)
2727 SetEvent(SitIdleEvent[i]);
2733 // put_threads_to_sleep() makes all the threads go to sleep just before
2734 // to leave think(), at the end of the search. Threads should have already
2735 // finished the job and should be idle.
2737 void ThreadsManager::put_threads_to_sleep() {
2739 assert(!AllThreadsShouldSleep);
2741 // This makes the threads to go to sleep
2742 AllThreadsShouldSleep = true;
2745 /// The RootMoveList class
2747 // RootMoveList c'tor
2749 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2751 SearchStack ss[PLY_MAX_PLUS_2];
2752 MoveStack mlist[MaxRootMoves];
2754 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2756 // Generate all legal moves
2757 MoveStack* last = generate_moves(pos, mlist);
2759 // Add each move to the moves[] array
2760 for (MoveStack* cur = mlist; cur != last; cur++)
2762 bool includeMove = includeAllMoves;
2764 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2765 includeMove = (searchMoves[k] == cur->move);
2770 // Find a quick score for the move
2772 pos.do_move(cur->move, st);
2773 moves[count].move = cur->move;
2774 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2775 moves[count].pv[0] = cur->move;
2776 moves[count].pv[1] = MOVE_NONE;
2777 pos.undo_move(cur->move);
2784 // RootMoveList simple methods definitions
2786 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2788 moves[moveNum].nodes = nodes;
2789 moves[moveNum].cumulativeNodes += nodes;
2792 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2794 moves[moveNum].ourBeta = our;
2795 moves[moveNum].theirBeta = their;
2798 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2802 for (j = 0; pv[j] != MOVE_NONE; j++)
2803 moves[moveNum].pv[j] = pv[j];
2805 moves[moveNum].pv[j] = MOVE_NONE;
2809 // RootMoveList::sort() sorts the root move list at the beginning of a new
2812 void RootMoveList::sort() {
2814 sort_multipv(count - 1); // Sort all items
2818 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2819 // list by their scores and depths. It is used to order the different PVs
2820 // correctly in MultiPV mode.
2822 void RootMoveList::sort_multipv(int n) {
2826 for (i = 1; i <= n; i++)
2828 RootMove rm = moves[i];
2829 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2830 moves[j] = moves[j - 1];