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, 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 beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is bigger then beta - IIDMargin.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 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, 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 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 update_pv(SearchStack* ss, int ply);
300 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 bool move_is_killer(Move m, SearchStack* ss);
304 bool ok_to_do_nullmove(const Position& pos);
305 bool ok_to_prune(const Position& pos, Move m, Move threat);
306 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
307 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
308 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
309 void update_killers(Move m, SearchStack* ss);
310 void update_gains(const Position& pos, Move move, Value before, Value after);
312 int current_search_time();
316 void wait_for_stop_or_ponderhit();
317 void init_ss_array(SearchStack* ss);
318 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value);
320 #if !defined(_MSC_VER)
321 void *init_thread(void *threadID);
323 DWORD WINAPI init_thread(LPVOID threadID);
333 /// init_threads(), exit_threads() and nodes_searched() are helpers to
334 /// give accessibility to some TM methods from outside of current file.
336 void init_threads() { TM.init_threads(); }
337 void exit_threads() { TM.exit_threads(); }
338 int64_t nodes_searched() { return TM.nodes_searched(); }
341 /// perft() is our utility to verify move generation is bug free. All the legal
342 /// moves up to given depth are generated and counted and the sum returned.
344 int perft(Position& pos, Depth depth)
349 MovePicker mp(pos, MOVE_NONE, depth, H);
351 // If we are at the last ply we don't need to do and undo
352 // the moves, just to count them.
353 if (depth <= OnePly) // Replace with '<' to test also qsearch
355 while (mp.get_next_move()) sum++;
359 // Loop through all legal moves
361 while ((move = mp.get_next_move()) != MOVE_NONE)
363 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
364 sum += perft(pos, depth - OnePly);
371 /// think() is the external interface to Stockfish's search, and is called when
372 /// the program receives the UCI 'go' command. It initializes various
373 /// search-related global variables, and calls root_search(). It returns false
374 /// when a quit command is received during the search.
376 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
377 int time[], int increment[], int movesToGo, int maxDepth,
378 int maxNodes, int maxTime, Move searchMoves[]) {
380 // Initialize global search variables
381 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
382 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
384 TM.resetNodeCounters();
385 SearchStartTime = get_system_time();
386 ExactMaxTime = maxTime;
389 InfiniteSearch = infinite;
390 PonderSearch = ponder;
391 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
393 // Look for a book move, only during games, not tests
394 if (UseTimeManagement && get_option_value_bool("OwnBook"))
396 if (get_option_value_string("Book File") != OpeningBook.file_name())
397 OpeningBook.open(get_option_value_string("Book File"));
399 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
400 if (bookMove != MOVE_NONE)
403 wait_for_stop_or_ponderhit();
405 cout << "bestmove " << bookMove << endl;
410 // Reset loseOnTime flag at the beginning of a new game
411 if (button_was_pressed("New Game"))
414 // Read UCI option values
415 TT.set_size(get_option_value_int("Hash"));
416 if (button_was_pressed("Clear Hash"))
419 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
420 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
421 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
422 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
423 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
424 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
425 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
426 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
427 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
428 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
429 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
430 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
432 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
433 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
434 MultiPV = get_option_value_int("MultiPV");
435 Chess960 = get_option_value_bool("UCI_Chess960");
436 UseLogFile = get_option_value_bool("Use Search Log");
439 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
441 read_weights(pos.side_to_move());
443 // Set the number of active threads
444 int newActiveThreads = get_option_value_int("Threads");
445 if (newActiveThreads != TM.active_threads())
447 TM.set_active_threads(newActiveThreads);
448 init_eval(TM.active_threads());
451 // Wake up sleeping threads
452 TM.wake_sleeping_threads();
455 int myTime = time[side_to_move];
456 int myIncrement = increment[side_to_move];
457 if (UseTimeManagement)
459 if (!movesToGo) // Sudden death time control
463 MaxSearchTime = myTime / 30 + myIncrement;
464 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
466 else // Blitz game without increment
468 MaxSearchTime = myTime / 30;
469 AbsoluteMaxSearchTime = myTime / 8;
472 else // (x moves) / (y minutes)
476 MaxSearchTime = myTime / 2;
477 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
481 MaxSearchTime = myTime / Min(movesToGo, 20);
482 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
486 if (get_option_value_bool("Ponder"))
488 MaxSearchTime += MaxSearchTime / 4;
489 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
493 // Set best NodesBetweenPolls interval to avoid lagging under
494 // heavy time pressure.
496 NodesBetweenPolls = Min(MaxNodes, 30000);
497 else if (myTime && myTime < 1000)
498 NodesBetweenPolls = 1000;
499 else if (myTime && myTime < 5000)
500 NodesBetweenPolls = 5000;
502 NodesBetweenPolls = 30000;
504 // Write search information to log file
506 LogFile << "Searching: " << pos.to_fen() << endl
507 << "infinite: " << infinite
508 << " ponder: " << ponder
509 << " time: " << myTime
510 << " increment: " << myIncrement
511 << " moves to go: " << movesToGo << endl;
513 // LSN filtering. Used only for developing purposes, disabled by default
517 // Step 2. If after last move we decided to lose on time, do it now!
518 while (SearchStartTime + myTime + 1000 > get_system_time())
522 // We're ready to start thinking. Call the iterative deepening loop function
523 Value v = id_loop(pos, searchMoves);
527 // Step 1. If this is sudden death game and our position is hopeless,
528 // decide to lose on time.
529 if ( !loseOnTime // If we already lost on time, go to step 3.
539 // Step 3. Now after stepping over the time limit, reset flag for next match.
547 TM.put_threads_to_sleep();
553 /// init_search() is called during startup. It initializes various lookup tables
557 // Init our reduction lookup tables
558 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
559 for (int j = 1; j < 64; j++) // j == moveNumber
561 double pvRed = log(double(i)) * log(double(j)) / 3.0;
562 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
563 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
564 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
567 // Init futility margins array
568 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
569 for (int j = 0; j < 64; j++) // j == moveNumber
571 // FIXME: test using log instead of BSR
572 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
575 // Init futility move count array
576 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
577 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
581 // SearchStack::init() initializes a search stack. Used at the beginning of a
582 // new search from the root.
583 void SearchStack::init(int ply) {
585 pv[ply] = pv[ply + 1] = MOVE_NONE;
586 currentMove = threatMove = MOVE_NONE;
587 reduction = Depth(0);
591 void SearchStack::initKillers() {
593 mateKiller = MOVE_NONE;
594 for (int i = 0; i < KILLER_MAX; i++)
595 killers[i] = MOVE_NONE;
600 // id_loop() is the main iterative deepening loop. It calls root_search
601 // repeatedly with increasing depth until the allocated thinking time has
602 // been consumed, the user stops the search, or the maximum search depth is
605 Value id_loop(const Position& pos, Move searchMoves[]) {
608 SearchStack ss[PLY_MAX_PLUS_2];
609 Move EasyMove = MOVE_NONE;
610 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
612 // Moves to search are verified, copied, scored and sorted
613 RootMoveList rml(p, searchMoves);
615 // Handle special case of searching on a mate/stale position
616 if (rml.move_count() == 0)
619 wait_for_stop_or_ponderhit();
621 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
624 // Print RootMoveList startup scoring to the standard output,
625 // so to output information also for iteration 1.
626 cout << "info depth " << 1
627 << "\ninfo depth " << 1
628 << " score " << value_to_string(rml.get_move_score(0))
629 << " time " << current_search_time()
630 << " nodes " << TM.nodes_searched()
632 << " pv " << rml.get_move(0) << "\n";
638 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->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->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->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->pv[0] == MOVE_NONE)
750 ss->pv[0] = rml.get_move(0);
751 ss->pv[1] = MOVE_NONE;
754 assert(ss->pv[0] != MOVE_NONE);
756 cout << "bestmove " << ss->pv[0];
758 if (ss->pv[1] != MOVE_NONE)
759 cout << " ponder " << ss->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->pv[0]);
776 p.do_move(ss->pv[0], st);
777 LogFile << "\nPonder move: "
778 << move_to_san(p, ss->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->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->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+1, -beta, -alpha, newDepth, 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->reduction = reduction<PV>(depth, i - MultiPV + 2);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 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->reduction = Depth(0);
907 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 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+1, -beta, -alpha, newDepth, 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->pv, PLY_MAX);
928 rml.set_move_pv(i, ss->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->pv, PLY_MAX);
968 rml.set_move_pv(i, ss->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 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(pos.ply() > 0 && pos.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 int ply = pos.ply();
1056 refinedValue = bestValue = value = -VALUE_INFINITE;
1059 // Step 1. Initialize node and poll. Polling can abort search
1060 TM.incrementNodeCounter(threadID);
1062 (ss + 2)->initKillers();
1064 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1070 // Step 2. Check for aborted search and immediate draw
1071 if (AbortSearch || TM.thread_should_stop(threadID))
1074 if (pos.is_draw() || ply >= PLY_MAX - 1)
1077 // Step 3. Mate distance pruning
1078 alpha = Max(value_mated_in(ply), alpha);
1079 beta = Min(value_mate_in(ply+1), beta);
1083 // Step 4. Transposition table lookup
1085 // We don't want the score of a partial search to overwrite a previous full search
1086 // TT value, so we use a different position key in case of an excluded move exists.
1087 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1089 tte = TT.retrieve(posKey);
1090 ttMove = (tte ? tte->move() : MOVE_NONE);
1092 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1093 // This is to avoid problems in the following areas:
1095 // * Repetition draw detection
1096 // * Fifty move rule detection
1097 // * Searching for a mate
1098 // * Printing of full PV line
1100 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1102 // Refresh tte entry to avoid aging
1103 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1105 ss->currentMove = ttMove; // Can be MOVE_NONE
1106 return value_from_tt(tte->value(), ply);
1109 // Step 5. Evaluate the position statically
1110 // At PV nodes we do this only to update gain statistics
1111 isCheck = pos.is_check();
1114 if (tte && tte->static_value() != VALUE_NONE)
1116 ss->eval = tte->static_value();
1117 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1120 ss->eval = evaluate(pos, ei, threadID);
1122 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1123 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1126 // Step 6. Razoring (is omitted in PV nodes)
1128 && refinedValue < beta - razor_margin(depth)
1129 && ttMove == MOVE_NONE
1130 && (ss-1)->currentMove != MOVE_NULL
1131 && depth < RazorDepth
1133 && !value_is_mate(beta)
1134 && !pos.has_pawn_on_7th(pos.side_to_move()))
1136 Value rbeta = beta - razor_margin(depth);
1137 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), threadID);
1139 // Logically we should return (v + razor_margin(depth)), but
1140 // surprisingly this did slightly weaker in tests.
1144 // Step 7. Static null move pruning (is omitted in PV nodes)
1145 // We're betting that the opponent doesn't have a move that will reduce
1146 // the score by more than futility_margin(depth) if we do a null move.
1149 && depth < RazorDepth
1151 && !value_is_mate(beta)
1152 && ok_to_do_nullmove(pos)
1153 && refinedValue >= beta + futility_margin(depth, 0))
1154 return refinedValue - futility_margin(depth, 0);
1156 // Step 8. Null move search with verification search (is omitted in PV nodes)
1157 // When we jump directly to qsearch() we do a null move only if static value is
1158 // at least beta. Otherwise we do a null move if static value is not more than
1159 // NullMoveMargin under beta.
1164 && !value_is_mate(beta)
1165 && ok_to_do_nullmove(pos)
1166 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1168 ss->currentMove = MOVE_NULL;
1170 // Null move dynamic reduction based on depth
1171 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1173 // Null move dynamic reduction based on value
1174 if (refinedValue - beta > PawnValueMidgame)
1177 pos.do_null_move(st);
1179 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1180 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, false, threadID);
1181 pos.undo_null_move();
1183 if (nullValue >= beta)
1185 // Do not return unproven mate scores
1186 if (nullValue >= value_mate_in(PLY_MAX))
1189 if (depth < 6 * OnePly)
1192 // Do zugzwang verification search
1193 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID);
1197 // The null move failed low, which means that we may be faced with
1198 // some kind of threat. If the previous move was reduced, check if
1199 // the move that refuted the null move was somehow connected to the
1200 // move which was reduced. If a connection is found, return a fail
1201 // low score (which will cause the reduced move to fail high in the
1202 // parent node, which will trigger a re-search with full depth).
1203 if (nullValue == value_mated_in(ply + 2))
1206 ss->threatMove = (ss+1)->currentMove;
1207 if ( depth < ThreatDepth
1208 && (ss-1)->reduction
1209 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1214 // Step 9. Internal iterative deepening
1215 if ( depth >= IIDDepth[PvNode]
1216 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1217 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1219 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1220 search<PvNode>(pos, ss, alpha, beta, d, false, threadID);
1221 ttMove = ss->pv[ply];
1222 tte = TT.retrieve(posKey);
1225 // Expensive mate threat detection (only for PV nodes)
1227 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1229 // Initialize a MovePicker object for the current position
1230 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1233 // Step 10. Loop through moves
1234 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1235 while ( bestValue < beta
1236 && (move = mp.get_next_move()) != MOVE_NONE
1237 && !TM.thread_should_stop(threadID))
1239 assert(move_is_ok(move));
1241 if (move == excludedMove)
1244 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1245 moveIsCheck = pos.move_is_check(move, ci);
1246 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1248 // Step 11. Decide the new search depth
1249 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1251 // Singular extension search. We extend the TT move if its value is much better than
1252 // its siblings. To verify this we do a reduced search on all the other moves but the
1253 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1254 if ( depth >= SingularExtensionDepth[PvNode]
1256 && move == tte->move()
1257 && !excludedMove // Do not allow recursive singular extension search
1259 && is_lower_bound(tte->type())
1260 && tte->depth() >= depth - 3 * OnePly)
1262 Value ttValue = value_from_tt(tte->value(), ply);
1264 if (abs(ttValue) < VALUE_KNOWN_WIN)
1266 Value b = ttValue - SingularExtensionMargin;
1267 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, false, threadID, move);
1269 if (v < ttValue - SingularExtensionMargin)
1274 newDepth = depth - OnePly + ext;
1276 // Update current move (this must be done after singular extension search)
1277 movesSearched[moveCount++] = ss->currentMove = move;
1279 // Step 12. Futility pruning (is omitted in PV nodes)
1283 && !captureOrPromotion
1284 && !move_is_castle(move)
1287 // Move count based pruning
1288 if ( moveCount >= futility_move_count(depth)
1289 && ok_to_prune(pos, move, ss->threatMove)
1290 && bestValue > value_mated_in(PLY_MAX))
1293 // Value based pruning
1294 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1295 // but fixing this made program slightly weaker.
1296 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1297 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1298 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1300 if (futilityValueScaled < beta)
1302 if (futilityValueScaled > bestValue)
1303 bestValue = futilityValueScaled;
1308 // Step 13. Make the move
1309 pos.do_move(move, st, ci, moveIsCheck);
1311 // Step extra. pv search (only in PV nodes)
1312 // The first move in list is the expected PV
1313 if (PvNode && moveCount == 1)
1314 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1315 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1318 // Step 14. Reduced depth search
1319 // If the move fails high will be re-searched at full depth.
1320 bool doFullDepthSearch = true;
1322 if ( depth >= 3 * OnePly
1324 && !captureOrPromotion
1325 && !move_is_castle(move)
1326 && !move_is_killer(move, ss))
1328 ss->reduction = reduction<PvNode>(depth, moveCount);
1331 Depth r = newDepth - ss->reduction;
1332 value = r < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1333 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, r, true, threadID);
1335 doFullDepthSearch = (value > alpha);
1338 // The move failed high, but if reduction is very big we could
1339 // face a false positive, retry with a less aggressive reduction,
1340 // if the move fails high again then go with full depth search.
1341 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1343 assert(newDepth - OnePly >= OnePly);
1345 ss->reduction = OnePly;
1346 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, threadID);
1347 doFullDepthSearch = (value > alpha);
1351 // Step 15. Full depth search
1352 if (doFullDepthSearch)
1354 ss->reduction = Depth(0);
1355 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1356 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, threadID);
1358 // Step extra. pv search (only in PV nodes)
1359 // Search only for possible new PV nodes, if instead value >= beta then
1360 // parent node fails low with value <= alpha and tries another move.
1361 if (PvNode && value > alpha && value < beta)
1362 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1363 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1367 // Step 16. Undo move
1368 pos.undo_move(move);
1370 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1372 // Step 17. Check for new best move
1373 if (value > bestValue)
1378 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1383 if (value == value_mate_in(ply + 1))
1384 ss->mateKiller = move;
1388 // Step 18. Check for split
1389 if ( TM.active_threads() > 1
1391 && depth >= MinimumSplitDepth
1393 && TM.available_thread_exists(threadID)
1395 && !TM.thread_should_stop(threadID))
1396 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1397 mateThreat, &moveCount, &mp, threadID, PvNode);
1400 // Step 19. Check for mate and stalemate
1401 // All legal moves have been searched and if there are
1402 // no legal moves, it must be mate or stalemate.
1403 // If one move was excluded return fail low score.
1405 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1407 // Step 20. Update tables
1408 // If the search is not aborted, update the transposition table,
1409 // history counters, and killer moves.
1410 if (AbortSearch || TM.thread_should_stop(threadID))
1413 if (bestValue <= oldAlpha)
1414 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1416 else if (bestValue >= beta)
1418 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1420 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1421 if (!pos.move_is_capture_or_promotion(move))
1423 update_history(pos, move, depth, movesSearched, moveCount);
1424 update_killers(move, ss);
1428 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1430 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1436 // qsearch() is the quiescence search function, which is called by the main
1437 // search function when the remaining depth is zero (or, to be more precise,
1438 // less than OnePly).
1440 template <NodeType PvNode>
1441 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID) {
1443 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1444 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1445 assert(PvNode || alpha == beta - 1);
1447 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1448 assert(threadID >= 0 && threadID < TM.active_threads());
1453 Value staticValue, bestValue, value, futilityBase, futilityValue;
1454 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1455 const TTEntry* tte = NULL;
1457 int ply = pos.ply();
1458 Value oldAlpha = alpha;
1460 TM.incrementNodeCounter(threadID);
1463 // Check for an instant draw or maximum ply reached
1464 if (pos.is_draw() || ply >= PLY_MAX - 1)
1467 // Transposition table lookup. At PV nodes, we don't use the TT for
1468 // pruning, but only for move ordering.
1469 tte = TT.retrieve(pos.get_key());
1470 ttMove = (tte ? tte->move() : MOVE_NONE);
1472 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1474 ss->currentMove = ttMove; // Can be MOVE_NONE
1475 return value_from_tt(tte->value(), ply);
1478 isCheck = pos.is_check();
1480 // Evaluate the position statically
1482 staticValue = -VALUE_INFINITE;
1483 else if (tte && tte->static_value() != VALUE_NONE)
1485 staticValue = tte->static_value();
1486 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1489 staticValue = evaluate(pos, ei, threadID);
1493 ss->eval = staticValue;
1494 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1497 // Initialize "stand pat score", and return it immediately if it is
1499 bestValue = staticValue;
1501 if (bestValue >= beta)
1503 // Store the score to avoid a future costly evaluation() call
1504 if (!isCheck && !tte)
1505 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1510 if (bestValue > alpha)
1513 // If we are near beta then try to get a cutoff pushing checks a bit further
1514 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1516 // Initialize a MovePicker object for the current position, and prepare
1517 // to search the moves. Because the depth is <= 0 here, only captures,
1518 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1519 // and we are near beta) will be generated.
1520 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1522 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1523 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1525 // Loop through the moves until no moves remain or a beta cutoff occurs
1526 while ( alpha < beta
1527 && (move = mp.get_next_move()) != MOVE_NONE)
1529 assert(move_is_ok(move));
1531 moveIsCheck = pos.move_is_check(move, ci);
1533 // Update current move
1535 ss->currentMove = move;
1543 && !move_is_promotion(move)
1544 && !pos.move_is_passed_pawn_push(move))
1546 futilityValue = futilityBase
1547 + pos.endgame_value_of_piece_on(move_to(move))
1548 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1550 if (futilityValue < alpha)
1552 if (futilityValue > bestValue)
1553 bestValue = futilityValue;
1558 // Detect blocking evasions that are candidate to be pruned
1559 evasionPrunable = isCheck
1560 && bestValue > value_mated_in(PLY_MAX)
1561 && !pos.move_is_capture(move)
1562 && pos.type_of_piece_on(move_from(move)) != KING
1563 && !pos.can_castle(pos.side_to_move());
1565 // Don't search moves with negative SEE values
1567 && (!isCheck || evasionPrunable)
1569 && !move_is_promotion(move)
1570 && pos.see_sign(move) < 0)
1573 // Make and search the move
1574 pos.do_move(move, st, ci, moveIsCheck);
1575 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, threadID);
1576 pos.undo_move(move);
1578 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1581 if (value > bestValue)
1592 // All legal moves have been searched. A special case: If we're in check
1593 // and no legal moves were found, it is checkmate.
1594 if (!moveCount && isCheck) // Mate!
1595 return value_mated_in(ply);
1597 // Update transposition table
1598 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1599 if (bestValue <= oldAlpha)
1601 // If bestValue isn't changed it means it is still the static evaluation
1602 // of the node, so keep this info to avoid a future evaluation() call.
1603 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1605 else if (bestValue >= beta)
1608 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1610 // Update killers only for good checking moves
1611 if (!pos.move_is_capture_or_promotion(move))
1612 update_killers(move, ss);
1615 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1617 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1623 // sp_search() is used to search from a split point. This function is called
1624 // by each thread working at the split point. It is similar to the normal
1625 // search() function, but simpler. Because we have already probed the hash
1626 // table, done a null move search, and searched the first move before
1627 // splitting, we don't have to repeat all this work in sp_search(). We
1628 // also don't need to store anything to the hash table here: This is taken
1629 // care of after we return from the split point.
1631 template <NodeType PvNode>
1632 void sp_search(SplitPoint* sp, int threadID) {
1634 assert(threadID >= 0 && threadID < TM.active_threads());
1635 assert(TM.active_threads() > 1);
1639 Depth ext, newDepth;
1641 Value futilityValueScaled; // NonPV specific
1642 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1644 value = -VALUE_INFINITE;
1646 Position pos(*sp->pos);
1648 int ply = pos.ply();
1649 SearchStack* ss = sp->sstack[threadID] + 1;
1650 isCheck = pos.is_check();
1652 // Step 10. Loop through moves
1653 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1654 lock_grab(&(sp->lock));
1656 while ( sp->bestValue < sp->beta
1657 && (move = sp->mp->get_next_move()) != MOVE_NONE
1658 && !TM.thread_should_stop(threadID))
1660 moveCount = ++sp->moveCount;
1661 lock_release(&(sp->lock));
1663 assert(move_is_ok(move));
1665 moveIsCheck = pos.move_is_check(move, ci);
1666 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1668 // Step 11. Decide the new search depth
1669 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1670 newDepth = sp->depth - OnePly + ext;
1672 // Update current move
1673 ss->currentMove = move;
1675 // Step 12. Futility pruning (is omitted in PV nodes)
1679 && !captureOrPromotion
1680 && !move_is_castle(move))
1682 // Move count based pruning
1683 if ( moveCount >= futility_move_count(sp->depth)
1684 && ok_to_prune(pos, move, ss->threatMove)
1685 && sp->bestValue > value_mated_in(PLY_MAX))
1687 lock_grab(&(sp->lock));
1691 // Value based pruning
1692 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1693 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1694 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1696 if (futilityValueScaled < sp->beta)
1698 lock_grab(&(sp->lock));
1700 if (futilityValueScaled > sp->bestValue)
1701 sp->bestValue = futilityValueScaled;
1706 // Step 13. Make the move
1707 pos.do_move(move, st, ci, moveIsCheck);
1709 // Step 14. Reduced search
1710 // If the move fails high will be re-searched at full depth.
1711 bool doFullDepthSearch = true;
1714 && !captureOrPromotion
1715 && !move_is_castle(move)
1716 && !move_is_killer(move, ss))
1718 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1721 Value localAlpha = sp->alpha;
1722 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1723 doFullDepthSearch = (value > localAlpha);
1726 // The move failed high, but if reduction is very big we could
1727 // face a false positive, retry with a less aggressive reduction,
1728 // if the move fails high again then go with full depth search.
1729 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1731 ss->reduction = OnePly;
1732 Value localAlpha = sp->alpha;
1733 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1734 doFullDepthSearch = (value > localAlpha);
1738 // Step 15. Full depth search
1739 if (doFullDepthSearch)
1741 ss->reduction = Depth(0);
1742 Value localAlpha = sp->alpha;
1743 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, true, threadID);
1745 if (PvNode && value > localAlpha && value < sp->beta)
1746 value = -search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, false, threadID);
1749 // Step 16. Undo move
1750 pos.undo_move(move);
1752 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1754 // Step 17. Check for new best move
1755 lock_grab(&(sp->lock));
1757 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1759 sp->bestValue = value;
1761 if (sp->bestValue > sp->alpha)
1763 if (!PvNode || value >= sp->beta)
1764 sp->stopRequest = true;
1766 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1769 sp_update_pv(sp->parentSstack, ss, ply);
1774 /* Here we have the lock still grabbed */
1776 sp->slaves[threadID] = 0;
1778 lock_release(&(sp->lock));
1781 // update_pv() is called whenever a search returns a value > alpha.
1782 // It updates the PV in the SearchStack object corresponding to the
1785 void update_pv(SearchStack* ss, int ply) {
1787 assert(ply >= 0 && ply < PLY_MAX);
1791 ss->pv[ply] = ss->currentMove;
1793 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1794 ss->pv[p] = (ss+1)->pv[p];
1796 ss->pv[p] = MOVE_NONE;
1800 // sp_update_pv() is a variant of update_pv for use at split points. The
1801 // difference between the two functions is that sp_update_pv also updates
1802 // the PV at the parent node.
1804 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1806 assert(ply >= 0 && ply < PLY_MAX);
1810 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1812 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1813 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1815 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1819 // connected_moves() tests whether two moves are 'connected' in the sense
1820 // that the first move somehow made the second move possible (for instance
1821 // if the moving piece is the same in both moves). The first move is assumed
1822 // to be the move that was made to reach the current position, while the
1823 // second move is assumed to be a move from the current position.
1825 bool connected_moves(const Position& pos, Move m1, Move m2) {
1827 Square f1, t1, f2, t2;
1830 assert(move_is_ok(m1));
1831 assert(move_is_ok(m2));
1833 if (m2 == MOVE_NONE)
1836 // Case 1: The moving piece is the same in both moves
1842 // Case 2: The destination square for m2 was vacated by m1
1848 // Case 3: Moving through the vacated square
1849 if ( piece_is_slider(pos.piece_on(f2))
1850 && bit_is_set(squares_between(f2, t2), f1))
1853 // Case 4: The destination square for m2 is defended by the moving piece in m1
1854 p = pos.piece_on(t1);
1855 if (bit_is_set(pos.attacks_from(p, t1), t2))
1858 // Case 5: Discovered check, checking piece is the piece moved in m1
1859 if ( piece_is_slider(p)
1860 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1861 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1863 // discovered_check_candidates() works also if the Position's side to
1864 // move is the opposite of the checking piece.
1865 Color them = opposite_color(pos.side_to_move());
1866 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1868 if (bit_is_set(dcCandidates, f2))
1875 // value_is_mate() checks if the given value is a mate one
1876 // eventually compensated for the ply.
1878 bool value_is_mate(Value value) {
1880 assert(abs(value) <= VALUE_INFINITE);
1882 return value <= value_mated_in(PLY_MAX)
1883 || value >= value_mate_in(PLY_MAX);
1887 // move_is_killer() checks if the given move is among the
1888 // killer moves of that ply.
1890 bool move_is_killer(Move m, SearchStack* ss) {
1892 const Move* k = ss->killers;
1893 for (int i = 0; i < KILLER_MAX; i++, k++)
1901 // extension() decides whether a move should be searched with normal depth,
1902 // or with extended depth. Certain classes of moves (checking moves, in
1903 // particular) are searched with bigger depth than ordinary moves and in
1904 // any case are marked as 'dangerous'. Note that also if a move is not
1905 // extended, as example because the corresponding UCI option is set to zero,
1906 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1907 template <NodeType PvNode>
1908 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1909 bool singleEvasion, bool mateThreat, bool* dangerous) {
1911 assert(m != MOVE_NONE);
1913 Depth result = Depth(0);
1914 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1919 result += CheckExtension[PvNode];
1922 result += SingleEvasionExtension[PvNode];
1925 result += MateThreatExtension[PvNode];
1928 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1930 Color c = pos.side_to_move();
1931 if (relative_rank(c, move_to(m)) == RANK_7)
1933 result += PawnPushTo7thExtension[PvNode];
1936 if (pos.pawn_is_passed(c, move_to(m)))
1938 result += PassedPawnExtension[PvNode];
1943 if ( captureOrPromotion
1944 && pos.type_of_piece_on(move_to(m)) != PAWN
1945 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1946 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1947 && !move_is_promotion(m)
1950 result += PawnEndgameExtension[PvNode];
1955 && captureOrPromotion
1956 && pos.type_of_piece_on(move_to(m)) != PAWN
1957 && pos.see_sign(m) >= 0)
1963 return Min(result, OnePly);
1967 // ok_to_do_nullmove() looks at the current position and decides whether
1968 // doing a 'null move' should be allowed. In order to avoid zugzwang
1969 // problems, null moves are not allowed when the side to move has very
1970 // little material left. Currently, the test is a bit too simple: Null
1971 // moves are avoided only when the side to move has only pawns left.
1972 // It's probably a good idea to avoid null moves in at least some more
1973 // complicated endgames, e.g. KQ vs KR. FIXME
1975 bool ok_to_do_nullmove(const Position& pos) {
1977 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1981 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1982 // non-tactical moves late in the move list close to the leaves are
1983 // candidates for pruning.
1985 bool ok_to_prune(const Position& pos, Move m, Move threat) {
1987 assert(move_is_ok(m));
1988 assert(threat == MOVE_NONE || move_is_ok(threat));
1989 assert(!pos.move_is_check(m));
1990 assert(!pos.move_is_capture_or_promotion(m));
1991 assert(!pos.move_is_passed_pawn_push(m));
1993 Square mfrom, mto, tfrom, tto;
1995 // Prune if there isn't any threat move
1996 if (threat == MOVE_NONE)
1999 mfrom = move_from(m);
2001 tfrom = move_from(threat);
2002 tto = move_to(threat);
2004 // Case 1: Don't prune moves which move the threatened piece
2008 // Case 2: If the threatened piece has value less than or equal to the
2009 // value of the threatening piece, don't prune move which defend it.
2010 if ( pos.move_is_capture(threat)
2011 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2012 || pos.type_of_piece_on(tfrom) == KING)
2013 && pos.move_attacks_square(m, tto))
2016 // Case 3: If the moving piece in the threatened move is a slider, don't
2017 // prune safe moves which block its ray.
2018 if ( piece_is_slider(pos.piece_on(tfrom))
2019 && bit_is_set(squares_between(tfrom, tto), mto)
2020 && pos.see_sign(m) >= 0)
2027 // ok_to_use_TT() returns true if a transposition table score
2028 // can be used at a given point in search.
2030 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2032 Value v = value_from_tt(tte->value(), ply);
2034 return ( tte->depth() >= depth
2035 || v >= Max(value_mate_in(PLY_MAX), beta)
2036 || v < Min(value_mated_in(PLY_MAX), beta))
2038 && ( (is_lower_bound(tte->type()) && v >= beta)
2039 || (is_upper_bound(tte->type()) && v < beta));
2043 // refine_eval() returns the transposition table score if
2044 // possible otherwise falls back on static position evaluation.
2046 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2051 Value v = value_from_tt(tte->value(), ply);
2053 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2054 || (is_upper_bound(tte->type()) && v < defaultEval))
2061 // update_history() registers a good move that produced a beta-cutoff
2062 // in history and marks as failures all the other moves of that ply.
2064 void update_history(const Position& pos, Move move, Depth depth,
2065 Move movesSearched[], int moveCount) {
2069 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2071 for (int i = 0; i < moveCount - 1; i++)
2073 m = movesSearched[i];
2077 if (!pos.move_is_capture_or_promotion(m))
2078 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2083 // update_killers() add a good move that produced a beta-cutoff
2084 // among the killer moves of that ply.
2086 void update_killers(Move m, SearchStack* ss) {
2088 if (m == ss->killers[0])
2091 for (int i = KILLER_MAX - 1; i > 0; i--)
2092 ss->killers[i] = ss->killers[i - 1];
2098 // update_gains() updates the gains table of a non-capture move given
2099 // the static position evaluation before and after the move.
2101 void update_gains(const Position& pos, Move m, Value before, Value after) {
2104 && before != VALUE_NONE
2105 && after != VALUE_NONE
2106 && pos.captured_piece() == NO_PIECE_TYPE
2107 && !move_is_castle(m)
2108 && !move_is_promotion(m))
2109 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2113 // current_search_time() returns the number of milliseconds which have passed
2114 // since the beginning of the current search.
2116 int current_search_time() {
2118 return get_system_time() - SearchStartTime;
2122 // nps() computes the current nodes/second count.
2126 int t = current_search_time();
2127 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2131 // poll() performs two different functions: It polls for user input, and it
2132 // looks at the time consumed so far and decides if it's time to abort the
2137 static int lastInfoTime;
2138 int t = current_search_time();
2143 // We are line oriented, don't read single chars
2144 std::string command;
2146 if (!std::getline(std::cin, command))
2149 if (command == "quit")
2152 PonderSearch = false;
2156 else if (command == "stop")
2159 PonderSearch = false;
2161 else if (command == "ponderhit")
2165 // Print search information
2169 else if (lastInfoTime > t)
2170 // HACK: Must be a new search where we searched less than
2171 // NodesBetweenPolls nodes during the first second of search.
2174 else if (t - lastInfoTime >= 1000)
2181 if (dbg_show_hit_rate)
2182 dbg_print_hit_rate();
2184 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2185 << " time " << t << " hashfull " << TT.full() << endl;
2188 // Should we stop the search?
2192 bool stillAtFirstMove = FirstRootMove
2193 && !AspirationFailLow
2194 && t > MaxSearchTime + ExtraSearchTime;
2196 bool noMoreTime = t > AbsoluteMaxSearchTime
2197 || stillAtFirstMove;
2199 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2200 || (ExactMaxTime && t >= ExactMaxTime)
2201 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2206 // ponderhit() is called when the program is pondering (i.e. thinking while
2207 // it's the opponent's turn to move) in order to let the engine know that
2208 // it correctly predicted the opponent's move.
2212 int t = current_search_time();
2213 PonderSearch = false;
2215 bool stillAtFirstMove = FirstRootMove
2216 && !AspirationFailLow
2217 && t > MaxSearchTime + ExtraSearchTime;
2219 bool noMoreTime = t > AbsoluteMaxSearchTime
2220 || stillAtFirstMove;
2222 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2227 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2229 void init_ss_array(SearchStack* ss) {
2231 for (int i = 0; i < 3; i++, ss++)
2239 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2240 // while the program is pondering. The point is to work around a wrinkle in
2241 // the UCI protocol: When pondering, the engine is not allowed to give a
2242 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2243 // We simply wait here until one of these commands is sent, and return,
2244 // after which the bestmove and pondermove will be printed (in id_loop()).
2246 void wait_for_stop_or_ponderhit() {
2248 std::string command;
2252 if (!std::getline(std::cin, command))
2255 if (command == "quit")
2260 else if (command == "ponderhit" || command == "stop")
2266 // print_pv_info() prints to standard output and eventually to log file information on
2267 // the current PV line. It is called at each iteration or after a new pv is found.
2269 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2271 cout << "info depth " << Iteration
2272 << " score " << value_to_string(value)
2273 << ((value >= beta) ? " lowerbound" :
2274 ((value <= alpha)? " upperbound" : ""))
2275 << " time " << current_search_time()
2276 << " nodes " << TM.nodes_searched()
2280 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2281 cout << ss->pv[j] << " ";
2287 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2288 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2290 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2291 TM.nodes_searched(), value, type, ss->pv) << endl;
2296 // init_thread() is the function which is called when a new thread is
2297 // launched. It simply calls the idle_loop() function with the supplied
2298 // threadID. There are two versions of this function; one for POSIX
2299 // threads and one for Windows threads.
2301 #if !defined(_MSC_VER)
2303 void* init_thread(void *threadID) {
2305 TM.idle_loop(*(int*)threadID, NULL);
2311 DWORD WINAPI init_thread(LPVOID threadID) {
2313 TM.idle_loop(*(int*)threadID, NULL);
2320 /// The ThreadsManager class
2322 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2323 // get_beta_counters() are getters/setters for the per thread
2324 // counters used to sort the moves at root.
2326 void ThreadsManager::resetNodeCounters() {
2328 for (int i = 0; i < MAX_THREADS; i++)
2329 threads[i].nodes = 0ULL;
2332 void ThreadsManager::resetBetaCounters() {
2334 for (int i = 0; i < MAX_THREADS; i++)
2335 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2338 int64_t ThreadsManager::nodes_searched() const {
2340 int64_t result = 0ULL;
2341 for (int i = 0; i < ActiveThreads; i++)
2342 result += threads[i].nodes;
2347 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2350 for (int i = 0; i < MAX_THREADS; i++)
2352 our += threads[i].betaCutOffs[us];
2353 their += threads[i].betaCutOffs[opposite_color(us)];
2358 // idle_loop() is where the threads are parked when they have no work to do.
2359 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2360 // object for which the current thread is the master.
2362 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2364 assert(threadID >= 0 && threadID < MAX_THREADS);
2368 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2369 // master should exit as last one.
2370 if (AllThreadsShouldExit)
2373 threads[threadID].state = THREAD_TERMINATED;
2377 // If we are not thinking, wait for a condition to be signaled
2378 // instead of wasting CPU time polling for work.
2379 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2382 assert(threadID != 0);
2383 threads[threadID].state = THREAD_SLEEPING;
2385 #if !defined(_MSC_VER)
2386 lock_grab(&WaitLock);
2387 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2388 pthread_cond_wait(&WaitCond, &WaitLock);
2389 lock_release(&WaitLock);
2391 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2395 // If thread has just woken up, mark it as available
2396 if (threads[threadID].state == THREAD_SLEEPING)
2397 threads[threadID].state = THREAD_AVAILABLE;
2399 // If this thread has been assigned work, launch a search
2400 if (threads[threadID].state == THREAD_WORKISWAITING)
2402 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2404 threads[threadID].state = THREAD_SEARCHING;
2406 if (threads[threadID].splitPoint->pvNode)
2407 sp_search<PV>(threads[threadID].splitPoint, threadID);
2409 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2411 assert(threads[threadID].state == THREAD_SEARCHING);
2413 threads[threadID].state = THREAD_AVAILABLE;
2416 // If this thread is the master of a split point and all slaves have
2417 // finished their work at this split point, return from the idle loop.
2419 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2421 if (i == ActiveThreads)
2423 // Because sp->slaves[] is reset under lock protection,
2424 // be sure sp->lock has been released before to return.
2425 lock_grab(&(sp->lock));
2426 lock_release(&(sp->lock));
2428 assert(threads[threadID].state == THREAD_AVAILABLE);
2430 threads[threadID].state = THREAD_SEARCHING;
2437 // init_threads() is called during startup. It launches all helper threads,
2438 // and initializes the split point stack and the global locks and condition
2441 void ThreadsManager::init_threads() {
2446 #if !defined(_MSC_VER)
2447 pthread_t pthread[1];
2450 // Initialize global locks
2451 lock_init(&MPLock, NULL);
2452 lock_init(&WaitLock, NULL);
2454 #if !defined(_MSC_VER)
2455 pthread_cond_init(&WaitCond, NULL);
2457 for (i = 0; i < MAX_THREADS; i++)
2458 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2461 // Initialize SplitPointStack locks
2462 for (i = 0; i < MAX_THREADS; i++)
2463 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2464 lock_init(&(SplitPointStack[i][j].lock), NULL);
2466 // Will be set just before program exits to properly end the threads
2467 AllThreadsShouldExit = false;
2469 // Threads will be put to sleep as soon as created
2470 AllThreadsShouldSleep = true;
2472 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2474 threads[0].state = THREAD_SEARCHING;
2475 for (i = 1; i < MAX_THREADS; i++)
2476 threads[i].state = THREAD_AVAILABLE;
2478 // Launch the helper threads
2479 for (i = 1; i < MAX_THREADS; i++)
2482 #if !defined(_MSC_VER)
2483 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2485 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2490 cout << "Failed to create thread number " << i << endl;
2491 Application::exit_with_failure();
2494 // Wait until the thread has finished launching and is gone to sleep
2495 while (threads[i].state != THREAD_SLEEPING) {}
2500 // exit_threads() is called when the program exits. It makes all the
2501 // helper threads exit cleanly.
2503 void ThreadsManager::exit_threads() {
2505 ActiveThreads = MAX_THREADS; // HACK
2506 AllThreadsShouldSleep = true; // HACK
2507 wake_sleeping_threads();
2509 // This makes the threads to exit idle_loop()
2510 AllThreadsShouldExit = true;
2512 // Wait for thread termination
2513 for (int i = 1; i < MAX_THREADS; i++)
2514 while (threads[i].state != THREAD_TERMINATED) {}
2516 // Now we can safely destroy the locks
2517 for (int i = 0; i < MAX_THREADS; i++)
2518 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2519 lock_destroy(&(SplitPointStack[i][j].lock));
2521 lock_destroy(&WaitLock);
2522 lock_destroy(&MPLock);
2526 // thread_should_stop() checks whether the thread should stop its search.
2527 // This can happen if a beta cutoff has occurred in the thread's currently
2528 // active split point, or in some ancestor of the current split point.
2530 bool ThreadsManager::thread_should_stop(int threadID) const {
2532 assert(threadID >= 0 && threadID < ActiveThreads);
2536 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2541 // thread_is_available() checks whether the thread with threadID "slave" is
2542 // available to help the thread with threadID "master" at a split point. An
2543 // obvious requirement is that "slave" must be idle. With more than two
2544 // threads, this is not by itself sufficient: If "slave" is the master of
2545 // some active split point, it is only available as a slave to the other
2546 // threads which are busy searching the split point at the top of "slave"'s
2547 // split point stack (the "helpful master concept" in YBWC terminology).
2549 bool ThreadsManager::thread_is_available(int slave, int master) const {
2551 assert(slave >= 0 && slave < ActiveThreads);
2552 assert(master >= 0 && master < ActiveThreads);
2553 assert(ActiveThreads > 1);
2555 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2558 // Make a local copy to be sure doesn't change under our feet
2559 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2561 if (localActiveSplitPoints == 0)
2562 // No active split points means that the thread is available as
2563 // a slave for any other thread.
2566 if (ActiveThreads == 2)
2569 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2570 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2571 // could have been set to 0 by another thread leading to an out of bound access.
2572 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2579 // available_thread_exists() tries to find an idle thread which is available as
2580 // a slave for the thread with threadID "master".
2582 bool ThreadsManager::available_thread_exists(int master) const {
2584 assert(master >= 0 && master < ActiveThreads);
2585 assert(ActiveThreads > 1);
2587 for (int i = 0; i < ActiveThreads; i++)
2588 if (thread_is_available(i, master))
2595 // split() does the actual work of distributing the work at a node between
2596 // several available threads. If it does not succeed in splitting the
2597 // node (because no idle threads are available, or because we have no unused
2598 // split point objects), the function immediately returns. If splitting is
2599 // possible, a SplitPoint object is initialized with all the data that must be
2600 // copied to the helper threads and we tell our helper threads that they have
2601 // been assigned work. This will cause them to instantly leave their idle loops
2602 // and call sp_search(). When all threads have returned from sp_search() then
2605 template <bool Fake>
2606 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2607 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2608 MovePicker* mp, int master, bool pvNode) {
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);
2620 // If no other thread is available to help us, or if we have too many
2621 // active split points, don't split.
2622 if ( !available_thread_exists(master)
2623 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2625 lock_release(&MPLock);
2629 // Pick the next available split point object from the split point stack
2630 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2632 // Initialize the split point object
2633 splitPoint->parent = threads[master].splitPoint;
2634 splitPoint->stopRequest = false;
2635 splitPoint->depth = depth;
2636 splitPoint->mateThreat = mateThreat;
2637 splitPoint->alpha = *alpha;
2638 splitPoint->beta = beta;
2639 splitPoint->pvNode = pvNode;
2640 splitPoint->bestValue = *bestValue;
2641 splitPoint->mp = mp;
2642 splitPoint->moveCount = *moveCount;
2643 splitPoint->pos = &p;
2644 splitPoint->parentSstack = ss;
2645 for (int i = 0; i < ActiveThreads; i++)
2646 splitPoint->slaves[i] = 0;
2648 threads[master].splitPoint = splitPoint;
2649 threads[master].activeSplitPoints++;
2651 // If we are here it means we are not available
2652 assert(threads[master].state != THREAD_AVAILABLE);
2654 int workersCnt = 1; // At least the master is included
2656 // Allocate available threads setting state to THREAD_BOOKED
2657 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2658 if (thread_is_available(i, master))
2660 threads[i].state = THREAD_BOOKED;
2661 threads[i].splitPoint = splitPoint;
2662 splitPoint->slaves[i] = 1;
2666 assert(Fake || workersCnt > 1);
2668 // We can release the lock because slave threads are already booked and master is not available
2669 lock_release(&MPLock);
2671 // Tell the threads that they have work to do. This will make them leave
2672 // their idle loop. But before copy search stack tail for each thread.
2673 for (int i = 0; i < ActiveThreads; i++)
2674 if (i == master || splitPoint->slaves[i])
2676 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2678 assert(i == master || threads[i].state == THREAD_BOOKED);
2680 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2683 // Everything is set up. The master thread enters the idle loop, from
2684 // which it will instantly launch a search, because its state is
2685 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2686 // idle loop, which means that the main thread will return from the idle
2687 // loop when all threads have finished their work at this split point.
2688 idle_loop(master, splitPoint);
2690 // We have returned from the idle loop, which means that all threads are
2691 // finished. Update alpha and bestValue, and return.
2694 *alpha = splitPoint->alpha;
2695 *bestValue = splitPoint->bestValue;
2696 threads[master].activeSplitPoints--;
2697 threads[master].splitPoint = splitPoint->parent;
2699 lock_release(&MPLock);
2703 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2704 // to start a new search from the root.
2706 void ThreadsManager::wake_sleeping_threads() {
2708 assert(AllThreadsShouldSleep);
2709 assert(ActiveThreads > 0);
2711 AllThreadsShouldSleep = false;
2713 if (ActiveThreads == 1)
2716 #if !defined(_MSC_VER)
2717 pthread_mutex_lock(&WaitLock);
2718 pthread_cond_broadcast(&WaitCond);
2719 pthread_mutex_unlock(&WaitLock);
2721 for (int i = 1; i < MAX_THREADS; i++)
2722 SetEvent(SitIdleEvent[i]);
2728 // put_threads_to_sleep() makes all the threads go to sleep just before
2729 // to leave think(), at the end of the search. Threads should have already
2730 // finished the job and should be idle.
2732 void ThreadsManager::put_threads_to_sleep() {
2734 assert(!AllThreadsShouldSleep);
2736 // This makes the threads to go to sleep
2737 AllThreadsShouldSleep = true;
2740 /// The RootMoveList class
2742 // RootMoveList c'tor
2744 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2746 SearchStack ss[PLY_MAX_PLUS_2];
2747 MoveStack mlist[MaxRootMoves];
2749 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2751 // Generate all legal moves
2752 MoveStack* last = generate_moves(pos, mlist);
2754 // Add each move to the moves[] array
2755 for (MoveStack* cur = mlist; cur != last; cur++)
2757 bool includeMove = includeAllMoves;
2759 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2760 includeMove = (searchMoves[k] == cur->move);
2765 // Find a quick score for the move
2767 pos.do_move(cur->move, st);
2768 moves[count].move = cur->move;
2769 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2770 moves[count].pv[0] = cur->move;
2771 moves[count].pv[1] = MOVE_NONE;
2772 pos.undo_move(cur->move);
2779 // RootMoveList simple methods definitions
2781 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2783 moves[moveNum].nodes = nodes;
2784 moves[moveNum].cumulativeNodes += nodes;
2787 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2789 moves[moveNum].ourBeta = our;
2790 moves[moveNum].theirBeta = their;
2793 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2797 for (j = 0; pv[j] != MOVE_NONE; j++)
2798 moves[moveNum].pv[j] = pv[j];
2800 moves[moveNum].pv[j] = MOVE_NONE;
2804 // RootMoveList::sort() sorts the root move list at the beginning of a new
2807 void RootMoveList::sort() {
2809 sort_multipv(count - 1); // Sort all items
2813 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2814 // list by their scores and depths. It is used to order the different PVs
2815 // correctly in MultiPV mode.
2817 void RootMoveList::sort_multipv(int n) {
2821 for (i = 1; i <= n; i++)
2823 RootMove rm = moves[i];
2824 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2825 moves[j] = moves[j - 1];