2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, int master, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
101 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher 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 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 // Maximum number of moves to try before to split (strong YBWC)
238 const int MaximumSplitMove = 3;
240 // Last seconds noise filtering (LSN)
241 const bool UseLSNFiltering = true;
242 const int LSNTime = 4000; // In milliseconds
243 const Value LSNValue = value_from_centipawns(200);
244 bool loseOnTime = false;
252 // Scores and number of times the best move changed for each iteration
253 Value ValueByIteration[PLY_MAX_PLUS_2];
254 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
256 // Search window management
262 // Time managment variables
263 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
264 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
265 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
266 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
270 std::ofstream LogFile;
272 // Multi-threads related variables
273 Depth MinimumSplitDepth;
274 int MaxThreadsPerSplitPoint;
277 // Node counters, used only by thread[0] but try to keep in different cache
278 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
280 int NodesBetweenPolls = 30000;
287 Value id_loop(const Position& pos, Move searchMoves[]);
288 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
290 template <NodeType PvNode>
291 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
293 template <NodeType PvNode>
294 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
296 template <NodeType PvNode>
297 void sp_search(SplitPoint* sp, int threadID);
299 template <NodeType PvNode>
300 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
302 void init_node(SearchStack ss[], int ply, int threadID);
303 void update_pv(SearchStack ss[], int ply);
304 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
305 bool connected_moves(const Position& pos, Move m1, Move m2);
306 bool value_is_mate(Value value);
307 bool move_is_killer(Move m, const SearchStack& ss);
308 bool ok_to_do_nullmove(const Position& pos);
309 bool ok_to_prune(const Position& pos, Move m, Move threat);
310 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
311 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
312 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
313 void update_killers(Move m, SearchStack& ss);
314 void update_gains(const Position& pos, Move move, Value before, Value after);
316 int current_search_time();
320 void wait_for_stop_or_ponderhit();
321 void init_ss_array(SearchStack ss[]);
322 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
324 #if !defined(_MSC_VER)
325 void *init_thread(void *threadID);
327 DWORD WINAPI init_thread(LPVOID threadID);
337 /// init_threads(), exit_threads() and nodes_searched() are helpers to
338 /// give accessibility to some TM methods from outside of current file.
340 void init_threads() { TM.init_threads(); }
341 void exit_threads() { TM.exit_threads(); }
342 int64_t nodes_searched() { return TM.nodes_searched(); }
345 /// perft() is our utility to verify move generation is bug free. All the legal
346 /// moves up to given depth are generated and counted and the sum returned.
348 int perft(Position& pos, Depth depth)
353 MovePicker mp(pos, MOVE_NONE, depth, H);
355 // If we are at the last ply we don't need to do and undo
356 // the moves, just to count them.
357 if (depth <= OnePly) // Replace with '<' to test also qsearch
359 while (mp.get_next_move()) sum++;
363 // Loop through all legal moves
365 while ((move = mp.get_next_move()) != MOVE_NONE)
367 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
368 sum += perft(pos, depth - OnePly);
375 /// think() is the external interface to Stockfish's search, and is called when
376 /// the program receives the UCI 'go' command. It initializes various
377 /// search-related global variables, and calls root_search(). It returns false
378 /// when a quit command is received during the search.
380 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
381 int time[], int increment[], int movesToGo, int maxDepth,
382 int maxNodes, int maxTime, Move searchMoves[]) {
384 // Initialize global search variables
385 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
386 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
388 TM.resetNodeCounters();
389 SearchStartTime = get_system_time();
390 ExactMaxTime = maxTime;
393 InfiniteSearch = infinite;
394 PonderSearch = ponder;
395 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
397 // Look for a book move, only during games, not tests
398 if (UseTimeManagement && get_option_value_bool("OwnBook"))
400 if (get_option_value_string("Book File") != OpeningBook.file_name())
401 OpeningBook.open(get_option_value_string("Book File"));
403 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
404 if (bookMove != MOVE_NONE)
407 wait_for_stop_or_ponderhit();
409 cout << "bestmove " << bookMove << endl;
414 // Reset loseOnTime flag at the beginning of a new game
415 if (button_was_pressed("New Game"))
418 // Read UCI option values
419 TT.set_size(get_option_value_int("Hash"));
420 if (button_was_pressed("Clear Hash"))
423 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
424 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
425 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
426 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
427 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
428 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
429 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
430 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
431 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
432 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
433 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
434 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
436 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
437 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
438 MultiPV = get_option_value_int("MultiPV");
439 Chess960 = get_option_value_bool("UCI_Chess960");
440 UseLogFile = get_option_value_bool("Use Search Log");
443 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
445 read_weights(pos.side_to_move());
447 // Set the number of active threads
448 int newActiveThreads = get_option_value_int("Threads");
449 if (newActiveThreads != TM.active_threads())
451 TM.set_active_threads(newActiveThreads);
452 init_eval(TM.active_threads());
455 // Wake up sleeping threads
456 TM.wake_sleeping_threads();
459 int myTime = time[side_to_move];
460 int myIncrement = increment[side_to_move];
461 if (UseTimeManagement)
463 if (!movesToGo) // Sudden death time control
467 MaxSearchTime = myTime / 30 + myIncrement;
468 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
470 else // Blitz game without increment
472 MaxSearchTime = myTime / 30;
473 AbsoluteMaxSearchTime = myTime / 8;
476 else // (x moves) / (y minutes)
480 MaxSearchTime = myTime / 2;
481 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
485 MaxSearchTime = myTime / Min(movesToGo, 20);
486 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
490 if (get_option_value_bool("Ponder"))
492 MaxSearchTime += MaxSearchTime / 4;
493 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
497 // Set best NodesBetweenPolls interval to avoid lagging under
498 // heavy time pressure.
500 NodesBetweenPolls = Min(MaxNodes, 30000);
501 else if (myTime && myTime < 1000)
502 NodesBetweenPolls = 1000;
503 else if (myTime && myTime < 5000)
504 NodesBetweenPolls = 5000;
506 NodesBetweenPolls = 30000;
508 // Write search information to log file
510 LogFile << "Searching: " << pos.to_fen() << endl
511 << "infinite: " << infinite
512 << " ponder: " << ponder
513 << " time: " << myTime
514 << " increment: " << myIncrement
515 << " moves to go: " << movesToGo << endl;
517 // LSN filtering. Used only for developing purposes, disabled by default
521 // Step 2. If after last move we decided to lose on time, do it now!
522 while (SearchStartTime + myTime + 1000 > get_system_time())
526 // We're ready to start thinking. Call the iterative deepening loop function
527 Value v = id_loop(pos, searchMoves);
531 // Step 1. If this is sudden death game and our position is hopeless,
532 // decide to lose on time.
533 if ( !loseOnTime // If we already lost on time, go to step 3.
543 // Step 3. Now after stepping over the time limit, reset flag for next match.
551 TM.put_threads_to_sleep();
557 /// init_search() is called during startup. It initializes various lookup tables
561 // Init our reduction lookup tables
562 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
563 for (int j = 1; j < 64; j++) // j == moveNumber
565 double pvRed = log(double(i)) * log(double(j)) / 3.0;
566 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
567 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
568 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
571 // Init futility margins array
572 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
573 for (int j = 0; j < 64; j++) // j == moveNumber
575 // FIXME: test using log instead of BSR
576 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
579 // Init futility move count array
580 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
581 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
585 // SearchStack::init() initializes a search stack. Used at the beginning of a
586 // new search from the root.
587 void SearchStack::init(int ply) {
589 pv[ply] = pv[ply + 1] = MOVE_NONE;
590 currentMove = threatMove = MOVE_NONE;
591 reduction = Depth(0);
595 void SearchStack::initKillers() {
597 mateKiller = MOVE_NONE;
598 for (int i = 0; i < KILLER_MAX; i++)
599 killers[i] = MOVE_NONE;
604 // id_loop() is the main iterative deepening loop. It calls root_search
605 // repeatedly with increasing depth until the allocated thinking time has
606 // been consumed, the user stops the search, or the maximum search depth is
609 Value id_loop(const Position& pos, Move searchMoves[]) {
612 SearchStack ss[PLY_MAX_PLUS_2];
613 Move EasyMove = MOVE_NONE;
614 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
616 // Moves to search are verified, copied, scored and sorted
617 RootMoveList rml(p, searchMoves);
619 // Handle special case of searching on a mate/stale position
620 if (rml.move_count() == 0)
623 wait_for_stop_or_ponderhit();
625 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
628 // Print RootMoveList startup scoring to the standard output,
629 // so to output information also for iteration 1.
630 cout << "info depth " << 1
631 << "\ninfo depth " << 1
632 << " score " << value_to_string(rml.get_move_score(0))
633 << " time " << current_search_time()
634 << " nodes " << TM.nodes_searched()
636 << " pv " << rml.get_move(0) << "\n";
642 ValueByIteration[1] = rml.get_move_score(0);
645 // Is one move significantly better than others after initial scoring ?
646 if ( rml.move_count() == 1
647 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
648 EasyMove = rml.get_move(0);
650 // Iterative deepening loop
651 while (Iteration < PLY_MAX)
653 // Initialize iteration
655 BestMoveChangesByIteration[Iteration] = 0;
657 cout << "info depth " << Iteration << endl;
659 // Calculate dynamic aspiration window based on previous iterations
660 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
662 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
663 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
665 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
666 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
668 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
669 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
672 // Search to the current depth, rml is updated and sorted, alpha and beta could change
673 value = root_search(p, ss, rml, &alpha, &beta);
675 // Write PV to transposition table, in case the relevant entries have
676 // been overwritten during the search.
677 TT.insert_pv(p, ss[0].pv);
680 break; // Value cannot be trusted. Break out immediately!
682 //Save info about search result
683 ValueByIteration[Iteration] = value;
685 // Drop the easy move if differs from the new best move
686 if (ss[0].pv[0] != EasyMove)
687 EasyMove = MOVE_NONE;
689 if (UseTimeManagement)
692 bool stopSearch = false;
694 // Stop search early if there is only a single legal move,
695 // we search up to Iteration 6 anyway to get a proper score.
696 if (Iteration >= 6 && rml.move_count() == 1)
699 // Stop search early when the last two iterations returned a mate score
701 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
702 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
705 // Stop search early if one move seems to be much better than the others
706 int64_t nodes = TM.nodes_searched();
708 && EasyMove == ss[0].pv[0]
709 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
710 && current_search_time() > MaxSearchTime / 16)
711 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
712 && current_search_time() > MaxSearchTime / 32)))
715 // Add some extra time if the best move has changed during the last two iterations
716 if (Iteration > 5 && Iteration <= 50)
717 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
718 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
720 // Stop search if most of MaxSearchTime is consumed at the end of the
721 // iteration. We probably don't have enough time to search the first
722 // move at the next iteration anyway.
723 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
729 StopOnPonderhit = true;
735 if (MaxDepth && Iteration >= MaxDepth)
739 // If we are pondering or in infinite search, we shouldn't print the
740 // best move before we are told to do so.
741 if (!AbortSearch && (PonderSearch || InfiniteSearch))
742 wait_for_stop_or_ponderhit();
744 // Print final search statistics
745 cout << "info nodes " << TM.nodes_searched()
747 << " time " << current_search_time()
748 << " hashfull " << TT.full() << endl;
750 // Print the best move and the ponder move to the standard output
751 if (ss[0].pv[0] == MOVE_NONE)
753 ss[0].pv[0] = rml.get_move(0);
754 ss[0].pv[1] = MOVE_NONE;
757 assert(ss[0].pv[0] != MOVE_NONE);
759 cout << "bestmove " << ss[0].pv[0];
761 if (ss[0].pv[1] != MOVE_NONE)
762 cout << " ponder " << ss[0].pv[1];
769 dbg_print_mean(LogFile);
771 if (dbg_show_hit_rate)
772 dbg_print_hit_rate(LogFile);
774 LogFile << "\nNodes: " << TM.nodes_searched()
775 << "\nNodes/second: " << nps()
776 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
779 p.do_move(ss[0].pv[0], st);
780 LogFile << "\nPonder move: "
781 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
784 return rml.get_move_score(0);
788 // root_search() is the function which searches the root node. It is
789 // similar to search_pv except that it uses a different move ordering
790 // scheme, prints some information to the standard output and handles
791 // the fail low/high loops.
793 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
800 Depth depth, ext, newDepth;
801 Value value, alpha, beta;
802 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
803 int researchCountFH, researchCountFL;
805 researchCountFH = researchCountFL = 0;
808 isCheck = pos.is_check();
810 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
811 // Step 2. Check for aborted search (omitted at root)
812 // Step 3. Mate distance pruning (omitted at root)
813 // Step 4. Transposition table lookup (omitted at root)
815 // Step 5. Evaluate the position statically
816 // At root we do this only to get reference value for child nodes
818 ss[0].eval = evaluate(pos, ei, 0);
820 // Step 6. Razoring (omitted at root)
821 // Step 7. Static null move pruning (omitted at root)
822 // Step 8. Null move search with verification search (omitted at root)
823 // Step 9. Internal iterative deepening (omitted at root)
825 // Step extra. Fail low loop
826 // We start with small aspiration window and in case of fail low, we research
827 // with bigger window until we are not failing low anymore.
830 // Sort the moves before to (re)search
833 // Step 10. Loop through all moves in the root move list
834 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
836 // This is used by time management
837 FirstRootMove = (i == 0);
839 // Save the current node count before the move is searched
840 nodes = TM.nodes_searched();
842 // Reset beta cut-off counters
843 TM.resetBetaCounters();
845 // Pick the next root move, and print the move and the move number to
846 // the standard output.
847 move = ss[0].currentMove = rml.get_move(i);
849 if (current_search_time() >= 1000)
850 cout << "info currmove " << move
851 << " currmovenumber " << i + 1 << endl;
853 moveIsCheck = pos.move_is_check(move);
854 captureOrPromotion = pos.move_is_capture_or_promotion(move);
856 // Step 11. Decide the new search depth
857 depth = (Iteration - 2) * OnePly + InitialDepth;
858 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
859 newDepth = depth + ext;
861 // Step 12. Futility pruning (omitted at root)
863 // Step extra. Fail high loop
864 // If move fails high, we research with bigger window until we are not failing
866 value = - VALUE_INFINITE;
870 // Step 13. Make the move
871 pos.do_move(move, st, ci, moveIsCheck);
873 // Step extra. pv search
874 // We do pv search for first moves (i < MultiPV)
875 // and for fail high research (value > alpha)
876 if (i < MultiPV || value > alpha)
878 // Aspiration window is disabled in multi-pv case
880 alpha = -VALUE_INFINITE;
882 // Full depth PV search, done on first move or after a fail high
883 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
887 // Step 14. Reduced search
888 // if the move fails high will be re-searched at full depth
889 bool doFullDepthSearch = true;
891 if ( depth >= 3 * OnePly
893 && !captureOrPromotion
894 && !move_is_castle(move))
896 ss[0].reduction = reduction<PV>(depth, i - MultiPV + 2);
899 // Reduced depth non-pv search using alpha as upperbound
900 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
901 doFullDepthSearch = (value > alpha);
905 // Step 15. Full depth search
906 if (doFullDepthSearch)
908 // Full depth non-pv search using alpha as upperbound
909 ss[0].reduction = Depth(0);
910 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
912 // If we are above alpha then research at same depth but as PV
913 // to get a correct score or eventually a fail high above beta.
915 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
919 // Step 16. Undo move
922 // Can we exit fail high loop ?
923 if (AbortSearch || value < beta)
926 // We are failing high and going to do a research. It's important to update
927 // the score before research in case we run out of time while researching.
928 rml.set_move_score(i, value);
930 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
931 rml.set_move_pv(i, ss[0].pv);
933 // Print information to the standard output
934 print_pv_info(pos, ss, alpha, beta, value);
936 // Prepare for a research after a fail high, each time with a wider window
937 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
940 } // End of fail high loop
942 // Finished searching the move. If AbortSearch is true, the search
943 // was aborted because the user interrupted the search or because we
944 // ran out of time. In this case, the return value of the search cannot
945 // be trusted, and we break out of the loop without updating the best
950 // Remember beta-cutoff and searched nodes counts for this move. The
951 // info is used to sort the root moves for the next iteration.
953 TM.get_beta_counters(pos.side_to_move(), our, their);
954 rml.set_beta_counters(i, our, their);
955 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
957 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
958 assert(value < beta);
960 // Step 17. Check for new best move
961 if (value <= alpha && i >= MultiPV)
962 rml.set_move_score(i, -VALUE_INFINITE);
965 // PV move or new best move!
968 rml.set_move_score(i, value);
970 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
971 rml.set_move_pv(i, ss[0].pv);
975 // We record how often the best move has been changed in each
976 // iteration. This information is used for time managment: When
977 // the best move changes frequently, we allocate some more time.
979 BestMoveChangesByIteration[Iteration]++;
981 // Print information to the standard output
982 print_pv_info(pos, ss, alpha, beta, value);
984 // Raise alpha to setup proper non-pv search upper bound
991 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
993 cout << "info multipv " << j + 1
994 << " score " << value_to_string(rml.get_move_score(j))
995 << " depth " << (j <= i ? Iteration : Iteration - 1)
996 << " time " << current_search_time()
997 << " nodes " << TM.nodes_searched()
1001 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1002 cout << rml.get_move_pv(j, k) << " ";
1006 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1008 } // PV move or new best move
1010 assert(alpha >= *alphaPtr);
1012 AspirationFailLow = (alpha == *alphaPtr);
1014 if (AspirationFailLow && StopOnPonderhit)
1015 StopOnPonderhit = false;
1018 // Can we exit fail low loop ?
1019 if (AbortSearch || !AspirationFailLow)
1022 // Prepare for a research after a fail low, each time with a wider window
1023 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1028 // Sort the moves before to return
1035 // search<>() is the main search function for both PV and non-PV nodes
1037 template <NodeType PvNode>
1038 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth,
1039 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1041 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1042 assert(beta > alpha && beta <= VALUE_INFINITE);
1043 assert(PvNode || alpha == beta - 1);
1044 assert(ply >= 0 && ply < PLY_MAX);
1045 assert(threadID >= 0 && threadID < TM.active_threads());
1047 Move movesSearched[256];
1052 Depth ext, newDepth;
1053 Value bestValue, value, oldAlpha;
1054 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1055 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1056 bool mateThreat = false;
1058 refinedValue = bestValue = value = -VALUE_INFINITE;
1062 return qsearch<PvNode>(pos, ss, alpha, beta, Depth(0), ply, threadID);
1064 // Step 1. Initialize node and poll
1065 // Polling can abort search.
1066 init_node(ss, ply, threadID);
1068 // Step 2. Check for aborted search and immediate draw
1069 if (AbortSearch || TM.thread_should_stop(threadID))
1072 if (pos.is_draw() || ply >= PLY_MAX - 1)
1075 // Step 3. Mate distance pruning
1076 alpha = Max(value_mated_in(ply), alpha);
1077 beta = Min(value_mate_in(ply+1), beta);
1081 // Step 4. Transposition table lookup
1083 // We don't want the score of a partial search to overwrite a previous full search
1084 // TT value, so we use a different position key in case of an excluded move exists.
1085 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1087 tte = TT.retrieve(posKey);
1088 ttMove = (tte ? tte->move() : MOVE_NONE);
1090 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1091 // This is to avoid problems in the following areas:
1093 // * Repetition draw detection
1094 // * Fifty move rule detection
1095 // * Searching for a mate
1096 // * Printing of full PV line
1098 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1100 // Refresh tte entry to avoid aging
1101 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1103 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1104 return value_from_tt(tte->value(), ply);
1107 // Step 5. Evaluate the position statically
1108 // At PV nodes we do this only to update gain statistics
1109 isCheck = pos.is_check();
1112 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1113 ss[ply].eval = value_from_tt(tte->value(), ply);
1115 ss[ply].eval = evaluate(pos, ei, threadID);
1117 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1118 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1121 // Step 6. Razoring (is omitted in PV nodes)
1123 && refinedValue < beta - razor_margin(depth)
1124 && ttMove == MOVE_NONE
1125 && ss[ply - 1].currentMove != MOVE_NULL
1126 && depth < RazorDepth
1128 && !value_is_mate(beta)
1129 && !pos.has_pawn_on_7th(pos.side_to_move()))
1131 Value rbeta = beta - razor_margin(depth);
1132 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1134 // Logically we should return (v + razor_margin(depth)), but
1135 // surprisingly this did slightly weaker in tests.
1139 // Step 7. Static null move pruning (is omitted in PV nodes)
1140 // We're betting that the opponent doesn't have a move that will reduce
1141 // the score by more than futility_margin(depth) if we do a null move.
1144 && depth < RazorDepth
1146 && !value_is_mate(beta)
1147 && ok_to_do_nullmove(pos)
1148 && refinedValue >= beta + futility_margin(depth, 0))
1149 return refinedValue - futility_margin(depth, 0);
1151 // Step 8. Null move search with verification search (is omitted in PV nodes)
1152 // When we jump directly to qsearch() we do a null move only if static value is
1153 // at least beta. Otherwise we do a null move if static value is not more than
1154 // NullMoveMargin under beta.
1159 && !value_is_mate(beta)
1160 && ok_to_do_nullmove(pos)
1161 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1163 ss[ply].currentMove = MOVE_NULL;
1165 // Null move dynamic reduction based on depth
1166 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1168 // Null move dynamic reduction based on value
1169 if (refinedValue - beta > PawnValueMidgame)
1172 pos.do_null_move(st);
1174 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1176 pos.undo_null_move();
1178 if (nullValue >= beta)
1180 // Do not return unproven mate scores
1181 if (nullValue >= value_mate_in(PLY_MAX))
1184 if (depth < 6 * OnePly)
1187 // Do zugzwang verification search
1188 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1192 // The null move failed low, which means that we may be faced with
1193 // some kind of threat. If the previous move was reduced, check if
1194 // the move that refuted the null move was somehow connected to the
1195 // move which was reduced. If a connection is found, return a fail
1196 // low score (which will cause the reduced move to fail high in the
1197 // parent node, which will trigger a re-search with full depth).
1198 if (nullValue == value_mated_in(ply + 2))
1201 ss[ply].threatMove = ss[ply + 1].currentMove;
1202 if ( depth < ThreatDepth
1203 && ss[ply - 1].reduction
1204 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1209 // Step 9. Internal iterative deepening
1210 if ( depth >= IIDDepth[PvNode]
1211 && ttMove == MOVE_NONE
1212 && (PvNode || (!isCheck && ss[ply].eval >= beta - IIDMargin)))
1214 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1215 search<PvNode>(pos, ss, alpha, beta, d, ply, false, threadID);
1216 ttMove = ss[ply].pv[ply];
1217 tte = TT.retrieve(posKey);
1220 // Expensive mate threat detection (only for PV nodes)
1222 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1224 // Initialize a MovePicker object for the current position
1225 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1228 // Step 10. Loop through moves
1229 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1230 while ( bestValue < beta
1231 && (move = mp.get_next_move()) != MOVE_NONE
1232 && !TM.thread_should_stop(threadID))
1234 assert(move_is_ok(move));
1236 if (move == excludedMove)
1239 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1240 moveIsCheck = pos.move_is_check(move, ci);
1241 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1243 // Step 11. Decide the new search depth
1244 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1246 // Singular extension search. We extend the TT move if its value is much better than
1247 // its siblings. To verify this we do a reduced search on all the other moves but the
1248 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1249 if ( depth >= SingularExtensionDepth[PvNode]
1251 && move == tte->move()
1252 && !excludedMove // Do not allow recursive singular extension search
1254 && is_lower_bound(tte->type())
1255 && tte->depth() >= depth - 3 * OnePly)
1257 Value ttValue = value_from_tt(tte->value(), ply);
1259 if (abs(ttValue) < VALUE_KNOWN_WIN)
1261 Value b = ttValue - SingularExtensionMargin;
1262 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply, false, threadID, move);
1264 if (v < ttValue - SingularExtensionMargin)
1269 newDepth = depth - OnePly + ext;
1271 // Update current move (this must be done after singular extension search)
1272 movesSearched[moveCount++] = ss[ply].currentMove = move;
1274 // Step 12. Futility pruning (is omitted in PV nodes)
1278 && !captureOrPromotion
1279 && !move_is_castle(move)
1282 // Move count based pruning
1283 if ( moveCount >= futility_move_count(depth)
1284 && ok_to_prune(pos, move, ss[ply].threatMove)
1285 && bestValue > value_mated_in(PLY_MAX))
1288 // Value based pruning
1289 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1290 // but fixing this made program slightly weaker.
1291 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1292 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1293 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1295 if (futilityValueScaled < beta)
1297 if (futilityValueScaled > bestValue)
1298 bestValue = futilityValueScaled;
1303 // Step 13. Make the move
1304 pos.do_move(move, st, ci, moveIsCheck);
1306 // Step extra. pv search (only in PV nodes)
1307 // The first move in list is the expected PV
1308 if (PvNode && moveCount == 1)
1309 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1312 // Step 14. Reduced search
1313 // if the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * OnePly
1318 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !move_is_killer(move, ss[ply]))
1322 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1323 if (ss[ply].reduction)
1325 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1326 doFullDepthSearch = (value > alpha);
1330 // Step 15. Full depth search
1331 if (doFullDepthSearch)
1333 ss[ply].reduction = Depth(0);
1334 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1336 // Step extra. pv search (only in PV nodes)
1337 // Search only for possible new PV nodes, if instead value >= beta then
1338 // parent node fails low with value <= alpha and tries another move.
1339 if (PvNode && value > alpha && value < beta)
1340 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1344 // Step 16. Undo move
1345 pos.undo_move(move);
1347 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1349 // Step 17. Check for new best move
1350 if (value > bestValue)
1355 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1360 if (value == value_mate_in(ply + 1))
1361 ss[ply].mateKiller = move;
1365 // Step 18. Check for split
1366 if ( TM.active_threads() > 1
1368 && depth >= MinimumSplitDepth
1369 && (PvNode || moveCount > MaximumSplitMove * MinimumSplitDepth / depth)
1371 && TM.available_thread_exists(threadID)
1373 && !TM.thread_should_stop(threadID))
1374 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1375 mateThreat, &moveCount, &mp, threadID, PvNode);
1378 // Step 19. Check for mate and stalemate
1379 // All legal moves have been searched and if there are
1380 // no legal moves, it must be mate or stalemate.
1381 // If one move was excluded return fail low score.
1383 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1385 // Step 20. Update tables
1386 // If the search is not aborted, update the transposition table,
1387 // history counters, and killer moves.
1388 if (AbortSearch || TM.thread_should_stop(threadID))
1391 if (bestValue <= oldAlpha)
1392 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1394 else if (bestValue >= beta)
1396 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1397 move = ss[ply].pv[ply];
1398 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1399 if (!pos.move_is_capture_or_promotion(move))
1401 update_history(pos, move, depth, movesSearched, moveCount);
1402 update_killers(move, ss[ply]);
1406 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1408 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1414 // qsearch() is the quiescence search function, which is called by the main
1415 // search function when the remaining depth is zero (or, to be more precise,
1416 // less than OnePly).
1418 template <NodeType PvNode>
1419 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1420 Depth depth, int ply, int threadID) {
1422 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1423 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1424 assert(PvNode || alpha == beta - 1);
1426 assert(ply >= 0 && ply < PLY_MAX);
1427 assert(threadID >= 0 && threadID < TM.active_threads());
1432 Value staticValue, bestValue, value, futilityBase, futilityValue;
1433 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1434 const TTEntry* tte = NULL;
1436 Value oldAlpha = alpha;
1438 // Initialize, and make an early exit in case of an aborted search,
1439 // an instant draw, maximum ply reached, etc.
1440 init_node(ss, ply, threadID);
1442 // After init_node() that calls poll()
1443 if (AbortSearch || TM.thread_should_stop(threadID))
1446 if (pos.is_draw() || ply >= PLY_MAX - 1)
1449 // Transposition table lookup. At PV nodes, we don't use the TT for
1450 // pruning, but only for move ordering.
1451 tte = TT.retrieve(pos.get_key());
1452 ttMove = (tte ? tte->move() : MOVE_NONE);
1454 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1456 assert(tte->type() != VALUE_TYPE_EVAL);
1458 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1459 return value_from_tt(tte->value(), ply);
1462 isCheck = pos.is_check();
1464 // Evaluate the position statically
1466 staticValue = -VALUE_INFINITE;
1467 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1468 staticValue = value_from_tt(tte->value(), ply);
1470 staticValue = evaluate(pos, ei, threadID);
1474 ss[ply].eval = staticValue;
1475 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1478 // Initialize "stand pat score", and return it immediately if it is
1480 bestValue = staticValue;
1482 if (bestValue >= beta)
1484 // Store the score to avoid a future costly evaluation() call
1485 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1486 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1491 if (bestValue > alpha)
1494 // If we are near beta then try to get a cutoff pushing checks a bit further
1495 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1497 // Initialize a MovePicker object for the current position, and prepare
1498 // to search the moves. Because the depth is <= 0 here, only captures,
1499 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1500 // and we are near beta) will be generated.
1501 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1503 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1504 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1506 // Loop through the moves until no moves remain or a beta cutoff occurs
1507 while ( alpha < beta
1508 && (move = mp.get_next_move()) != MOVE_NONE)
1510 assert(move_is_ok(move));
1512 moveIsCheck = pos.move_is_check(move, ci);
1514 // Update current move
1516 ss[ply].currentMove = move;
1524 && !move_is_promotion(move)
1525 && !pos.move_is_passed_pawn_push(move))
1527 futilityValue = futilityBase
1528 + pos.endgame_value_of_piece_on(move_to(move))
1529 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1531 if (futilityValue < alpha)
1533 if (futilityValue > bestValue)
1534 bestValue = futilityValue;
1539 // Detect blocking evasions that are candidate to be pruned
1540 evasionPrunable = isCheck
1541 && bestValue > value_mated_in(PLY_MAX)
1542 && !pos.move_is_capture(move)
1543 && pos.type_of_piece_on(move_from(move)) != KING
1544 && !pos.can_castle(pos.side_to_move());
1546 // Don't search moves with negative SEE values
1548 && (!isCheck || evasionPrunable)
1550 && !move_is_promotion(move)
1551 && pos.see_sign(move) < 0)
1554 // Make and search the move
1555 pos.do_move(move, st, ci, moveIsCheck);
1556 value = -qsearch<PvNode>(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1557 pos.undo_move(move);
1559 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1562 if (value > bestValue)
1573 // All legal moves have been searched. A special case: If we're in check
1574 // and no legal moves were found, it is checkmate.
1575 if (!moveCount && isCheck) // Mate!
1576 return value_mated_in(ply);
1578 // Update transposition table
1579 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1580 if (bestValue <= oldAlpha)
1582 // If bestValue isn't changed it means it is still the static evaluation
1583 // of the node, so keep this info to avoid a future evaluation() call.
1584 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1585 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1587 else if (bestValue >= beta)
1589 move = ss[ply].pv[ply];
1590 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1592 // Update killers only for good checking moves
1593 if (!pos.move_is_capture_or_promotion(move))
1594 update_killers(move, ss[ply]);
1597 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1599 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1605 // sp_search() is used to search from a split point. This function is called
1606 // by each thread working at the split point. It is similar to the normal
1607 // search() function, but simpler. Because we have already probed the hash
1608 // table, done a null move search, and searched the first move before
1609 // splitting, we don't have to repeat all this work in sp_search(). We
1610 // also don't need to store anything to the hash table here: This is taken
1611 // care of after we return from the split point.
1613 template <NodeType PvNode>
1614 void sp_search(SplitPoint* sp, int threadID) {
1616 assert(threadID >= 0 && threadID < TM.active_threads());
1617 assert(TM.active_threads() > 1);
1621 Depth ext, newDepth;
1623 Value futilityValueScaled; // NonPV specific
1624 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1626 value = -VALUE_INFINITE;
1628 Position pos(*sp->pos);
1630 SearchStack* ss = sp->sstack[threadID];
1631 isCheck = pos.is_check();
1633 // Step 10. Loop through moves
1634 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1635 lock_grab(&(sp->lock));
1637 while ( sp->bestValue < sp->beta
1638 && (move = sp->mp->get_next_move()) != MOVE_NONE
1639 && !TM.thread_should_stop(threadID))
1641 moveCount = ++sp->moveCount;
1642 lock_release(&(sp->lock));
1644 assert(move_is_ok(move));
1646 moveIsCheck = pos.move_is_check(move, ci);
1647 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1649 // Step 11. Decide the new search depth
1650 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1651 newDepth = sp->depth - OnePly + ext;
1653 // Update current move
1654 ss[sp->ply].currentMove = move;
1656 // Step 12. Futility pruning (is omitted in PV nodes)
1660 && !captureOrPromotion
1661 && !move_is_castle(move))
1663 // Move count based pruning
1664 if ( moveCount >= futility_move_count(sp->depth)
1665 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1666 && sp->bestValue > value_mated_in(PLY_MAX))
1668 lock_grab(&(sp->lock));
1672 // Value based pruning
1673 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1674 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1675 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1677 if (futilityValueScaled < sp->beta)
1679 lock_grab(&(sp->lock));
1681 if (futilityValueScaled > sp->bestValue)
1682 sp->bestValue = futilityValueScaled;
1687 // Step 13. Make the move
1688 pos.do_move(move, st, ci, moveIsCheck);
1690 // Step 14. Reduced search
1691 // if the move fails high will be re-searched at full depth.
1692 bool doFullDepthSearch = true;
1695 && !captureOrPromotion
1696 && !move_is_castle(move)
1697 && !move_is_killer(move, ss[sp->ply]))
1699 ss[sp->ply].reduction = reduction<PvNode>(sp->depth, moveCount);
1700 if (ss[sp->ply].reduction)
1702 Value localAlpha = sp->alpha;
1703 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1704 doFullDepthSearch = (value > localAlpha);
1708 // Step 15. Full depth search
1709 if (doFullDepthSearch)
1711 ss[sp->ply].reduction = Depth(0);
1712 Value localAlpha = sp->alpha;
1713 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1715 if (PvNode && value > localAlpha && value < sp->beta)
1716 value = -search<PV>(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, false, threadID);
1719 // Step 16. Undo move
1720 pos.undo_move(move);
1722 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1724 // Step 17. Check for new best move
1725 lock_grab(&(sp->lock));
1727 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1729 sp->bestValue = value;
1731 if (sp->bestValue > sp->alpha)
1733 if (!PvNode || value >= sp->beta)
1734 sp->stopRequest = true;
1736 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1739 sp_update_pv(sp->parentSstack, ss, sp->ply);
1744 /* Here we have the lock still grabbed */
1746 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 slaves have
2413 // finished their work at this split point, return from the idle loop.
2415 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2417 if (i == ActiveThreads)
2419 // Because sp->slaves[] is reset under lock protection,
2420 // be sure sp->lock has been released before to return.
2421 lock_grab(&(sp->lock));
2422 lock_release(&(sp->lock));
2424 assert(threads[threadID].state == THREAD_AVAILABLE);
2426 threads[threadID].state = THREAD_SEARCHING;
2433 // init_threads() is called during startup. It launches all helper threads,
2434 // and initializes the split point stack and the global locks and condition
2437 void ThreadsManager::init_threads() {
2442 #if !defined(_MSC_VER)
2443 pthread_t pthread[1];
2446 // Initialize global locks
2447 lock_init(&MPLock, NULL);
2448 lock_init(&WaitLock, NULL);
2450 #if !defined(_MSC_VER)
2451 pthread_cond_init(&WaitCond, NULL);
2453 for (i = 0; i < MAX_THREADS; i++)
2454 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2457 // Initialize SplitPointStack locks
2458 for (i = 0; i < MAX_THREADS; i++)
2459 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2461 SplitPointStack[i][j].parent = NULL;
2462 lock_init(&(SplitPointStack[i][j].lock), NULL);
2465 // Will be set just before program exits to properly end the threads
2466 AllThreadsShouldExit = false;
2468 // Threads will be put to sleep as soon as created
2469 AllThreadsShouldSleep = true;
2471 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2473 threads[0].state = THREAD_SEARCHING;
2474 for (i = 1; i < MAX_THREADS; i++)
2475 threads[i].state = THREAD_AVAILABLE;
2477 // Launch the helper threads
2478 for (i = 1; i < MAX_THREADS; i++)
2481 #if !defined(_MSC_VER)
2482 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2484 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2489 cout << "Failed to create thread number " << i << endl;
2490 Application::exit_with_failure();
2493 // Wait until the thread has finished launching and is gone to sleep
2494 while (threads[i].state != THREAD_SLEEPING) {}
2499 // exit_threads() is called when the program exits. It makes all the
2500 // helper threads exit cleanly.
2502 void ThreadsManager::exit_threads() {
2504 ActiveThreads = MAX_THREADS; // HACK
2505 AllThreadsShouldSleep = true; // HACK
2506 wake_sleeping_threads();
2508 // This makes the threads to exit idle_loop()
2509 AllThreadsShouldExit = true;
2511 // Wait for thread termination
2512 for (int i = 1; i < MAX_THREADS; i++)
2513 while (threads[i].state != THREAD_TERMINATED);
2515 // Now we can safely destroy the locks
2516 for (int i = 0; i < MAX_THREADS; i++)
2517 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2518 lock_destroy(&(SplitPointStack[i][j].lock));
2520 lock_destroy(&WaitLock);
2521 lock_destroy(&MPLock);
2525 // thread_should_stop() checks whether the thread should stop its search.
2526 // This can happen if a beta cutoff has occurred in the thread's currently
2527 // active split point, or in some ancestor of the current split point.
2529 bool ThreadsManager::thread_should_stop(int threadID) const {
2531 assert(threadID >= 0 && threadID < ActiveThreads);
2535 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2540 // thread_is_available() checks whether the thread with threadID "slave" is
2541 // available to help the thread with threadID "master" at a split point. An
2542 // obvious requirement is that "slave" must be idle. With more than two
2543 // threads, this is not by itself sufficient: If "slave" is the master of
2544 // some active split point, it is only available as a slave to the other
2545 // threads which are busy searching the split point at the top of "slave"'s
2546 // split point stack (the "helpful master concept" in YBWC terminology).
2548 bool ThreadsManager::thread_is_available(int slave, int master) const {
2550 assert(slave >= 0 && slave < ActiveThreads);
2551 assert(master >= 0 && master < ActiveThreads);
2552 assert(ActiveThreads > 1);
2554 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2557 // Make a local copy to be sure doesn't change under our feet
2558 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2560 if (localActiveSplitPoints == 0)
2561 // No active split points means that the thread is available as
2562 // a slave for any other thread.
2565 if (ActiveThreads == 2)
2568 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2569 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2570 // could have been set to 0 by another thread leading to an out of bound access.
2571 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2578 // available_thread_exists() tries to find an idle thread which is available as
2579 // a slave for the thread with threadID "master".
2581 bool ThreadsManager::available_thread_exists(int master) const {
2583 assert(master >= 0 && master < ActiveThreads);
2584 assert(ActiveThreads > 1);
2586 for (int i = 0; i < ActiveThreads; i++)
2587 if (thread_is_available(i, master))
2594 // split() does the actual work of distributing the work at a node between
2595 // several available threads. If it does not succeed in splitting the
2596 // node (because no idle threads are available, or because we have no unused
2597 // split point objects), the function immediately returns. If splitting is
2598 // possible, a SplitPoint object is initialized with all the data that must be
2599 // copied to the helper threads and we tell our helper threads that they have
2600 // been assigned work. This will cause them to instantly leave their idle loops
2601 // and call sp_search(). When all threads have returned from sp_search() then
2604 template <bool Fake>
2605 void ThreadsManager::split(const Position& p, SearchStack* sstck, int ply, Value* alpha,
2606 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2607 int* moveCount, MovePicker* mp, int master, bool pvNode) {
2609 assert(sstck != NULL);
2610 assert(ply >= 0 && ply < PLY_MAX);
2611 assert(*bestValue >= -VALUE_INFINITE);
2612 assert(*bestValue <= *alpha);
2613 assert(*alpha < beta);
2614 assert(beta <= VALUE_INFINITE);
2615 assert(depth > Depth(0));
2616 assert(master >= 0 && master < ActiveThreads);
2617 assert(ActiveThreads > 1);
2621 // If no other thread is available to help us, or if we have too many
2622 // active split points, don't split.
2623 if ( !available_thread_exists(master)
2624 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2626 lock_release(&MPLock);
2630 // Pick the next available split point object from the split point stack
2631 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2633 // Initialize the split point object
2634 splitPoint->parent = threads[master].splitPoint;
2635 splitPoint->stopRequest = false;
2636 splitPoint->ply = ply;
2637 splitPoint->depth = depth;
2638 splitPoint->mateThreat = mateThreat;
2639 splitPoint->alpha = *alpha;
2640 splitPoint->beta = beta;
2641 splitPoint->pvNode = pvNode;
2642 splitPoint->bestValue = *bestValue;
2643 splitPoint->mp = mp;
2644 splitPoint->moveCount = *moveCount;
2645 splitPoint->pos = &p;
2646 splitPoint->parentSstack = sstck;
2647 for (int i = 0; i < ActiveThreads; i++)
2648 splitPoint->slaves[i] = 0;
2650 threads[master].splitPoint = splitPoint;
2651 threads[master].activeSplitPoints++;
2653 // If we are here it means we are not available
2654 assert(threads[master].state != THREAD_AVAILABLE);
2656 int workersCnt = 1; // At least the master is included
2658 // Allocate available threads setting state to THREAD_BOOKED
2659 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2660 if (thread_is_available(i, master))
2662 threads[i].state = THREAD_BOOKED;
2663 threads[i].splitPoint = splitPoint;
2664 splitPoint->slaves[i] = 1;
2668 assert(Fake || workersCnt > 1);
2670 // We can release the lock because slave threads are already booked and master is not available
2671 lock_release(&MPLock);
2673 // Tell the threads that they have work to do. This will make them leave
2674 // their idle loop. But before copy search stack tail for each thread.
2675 for (int i = 0; i < ActiveThreads; i++)
2676 if (i == master || splitPoint->slaves[i])
2678 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2680 assert(i == master || threads[i].state == THREAD_BOOKED);
2682 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2685 // Everything is set up. The master thread enters the idle loop, from
2686 // which it will instantly launch a search, because its state is
2687 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2688 // idle loop, which means that the main thread will return from the idle
2689 // loop when all threads have finished their work at this split point.
2690 idle_loop(master, splitPoint);
2692 // We have returned from the idle loop, which means that all threads are
2693 // finished. Update alpha and bestValue, and return.
2696 *alpha = splitPoint->alpha;
2697 *bestValue = splitPoint->bestValue;
2698 threads[master].activeSplitPoints--;
2699 threads[master].splitPoint = splitPoint->parent;
2701 lock_release(&MPLock);
2705 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2706 // to start a new search from the root.
2708 void ThreadsManager::wake_sleeping_threads() {
2710 assert(AllThreadsShouldSleep);
2711 assert(ActiveThreads > 0);
2713 AllThreadsShouldSleep = false;
2715 if (ActiveThreads == 1)
2718 #if !defined(_MSC_VER)
2719 pthread_mutex_lock(&WaitLock);
2720 pthread_cond_broadcast(&WaitCond);
2721 pthread_mutex_unlock(&WaitLock);
2723 for (int i = 1; i < MAX_THREADS; i++)
2724 SetEvent(SitIdleEvent[i]);
2730 // put_threads_to_sleep() makes all the threads go to sleep just before
2731 // to leave think(), at the end of the search. Threads should have already
2732 // finished the job and should be idle.
2734 void ThreadsManager::put_threads_to_sleep() {
2736 assert(!AllThreadsShouldSleep);
2738 // This makes the threads to go to sleep
2739 AllThreadsShouldSleep = true;
2742 /// The RootMoveList class
2744 // RootMoveList c'tor
2746 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2748 SearchStack ss[PLY_MAX_PLUS_2];
2749 MoveStack mlist[MaxRootMoves];
2751 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2753 // Generate all legal moves
2754 MoveStack* last = generate_moves(pos, mlist);
2756 // Add each move to the moves[] array
2757 for (MoveStack* cur = mlist; cur != last; cur++)
2759 bool includeMove = includeAllMoves;
2761 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2762 includeMove = (searchMoves[k] == cur->move);
2767 // Find a quick score for the move
2769 pos.do_move(cur->move, st);
2770 moves[count].move = cur->move;
2771 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2772 moves[count].pv[0] = cur->move;
2773 moves[count].pv[1] = MOVE_NONE;
2774 pos.undo_move(cur->move);
2781 // RootMoveList simple methods definitions
2783 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2785 moves[moveNum].nodes = nodes;
2786 moves[moveNum].cumulativeNodes += nodes;
2789 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2791 moves[moveNum].ourBeta = our;
2792 moves[moveNum].theirBeta = their;
2795 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2799 for (j = 0; pv[j] != MOVE_NONE; j++)
2800 moves[moveNum].pv[j] = pv[j];
2802 moves[moveNum].pv[j] = MOVE_NONE;
2806 // RootMoveList::sort() sorts the root move list at the beginning of a new
2809 void RootMoveList::sort() {
2811 sort_multipv(count - 1); // Sort all items
2815 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2816 // list by their scores and depths. It is used to order the different PVs
2817 // correctly in MultiPV mode.
2819 void RootMoveList::sort_multipv(int n) {
2823 for (i = 1; i <= n; i++)
2825 RootMove rm = moves[i];
2826 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2827 moves[j] = moves[j - 1];