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, 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 = false;
239 const int LSNTime = 100; // 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, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode>
288 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
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 bool connected_moves(const Position& pos, Move m1, Move m2);
300 bool value_is_mate(Value value);
301 bool move_is_killer(Move m, SearchStack* ss);
302 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
303 bool connected_threat(const Position& pos, Move m, Move threat);
304 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
305 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
306 void update_killers(Move m, SearchStack* ss);
307 void update_gains(const Position& pos, Move move, Value before, Value after);
309 int current_search_time();
313 void wait_for_stop_or_ponderhit();
314 void init_ss_array(SearchStack* ss, int size);
315 void print_pv_info(const Position& pos, Move* ss, Value alpha, Value beta, Value value);
317 #if !defined(_MSC_VER)
318 void *init_thread(void *threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
330 /// init_threads(), exit_threads() and nodes_searched() are helpers to
331 /// give accessibility to some TM methods from outside of current file.
333 void init_threads() { TM.init_threads(); }
334 void exit_threads() { TM.exit_threads(); }
335 int64_t nodes_searched() { return TM.nodes_searched(); }
338 /// init_search() is called during startup. It initializes various lookup tables
342 int d; // depth (OnePly == 2)
343 int hd; // half depth (OnePly == 1)
346 // Init reductions array
347 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
349 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
350 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
351 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
352 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
355 // Init futility margins array
356 for (d = 0; d < 16; d++) for (mc = 0; mc < 64; mc++)
357 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
359 // Init futility move count array
360 for (d = 0; d < 32; d++)
361 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
365 // SearchStack::init() initializes a search stack entry.
366 // Called at the beginning of search() when starting to examine a new node.
367 void SearchStack::init() {
369 currentMove = threatMove = bestMove = MOVE_NONE;
370 reduction = Depth(0);
374 // SearchStack::initKillers() initializes killers for a search stack entry
375 void SearchStack::initKillers() {
377 mateKiller = MOVE_NONE;
378 for (int i = 0; i < KILLER_MAX; i++)
379 killers[i] = MOVE_NONE;
383 /// perft() is our utility to verify move generation is bug free. All the legal
384 /// moves up to given depth are generated and counted and the sum returned.
386 int perft(Position& pos, Depth depth)
391 MovePicker mp(pos, MOVE_NONE, depth, H);
393 // If we are at the last ply we don't need to do and undo
394 // the moves, just to count them.
395 if (depth <= OnePly) // Replace with '<' to test also qsearch
397 while (mp.get_next_move()) sum++;
401 // Loop through all legal moves
403 while ((move = mp.get_next_move()) != MOVE_NONE)
405 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
406 sum += perft(pos, depth - OnePly);
413 /// think() is the external interface to Stockfish's search, and is called when
414 /// the program receives the UCI 'go' command. It initializes various
415 /// search-related global variables, and calls root_search(). It returns false
416 /// when a quit command is received during the search.
418 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
419 int time[], int increment[], int movesToGo, int maxDepth,
420 int maxNodes, int maxTime, Move searchMoves[]) {
422 // Initialize global search variables
423 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
424 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
426 TM.resetNodeCounters();
427 SearchStartTime = get_system_time();
428 ExactMaxTime = maxTime;
431 InfiniteSearch = infinite;
432 PonderSearch = ponder;
433 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
435 // Look for a book move, only during games, not tests
436 if (UseTimeManagement && get_option_value_bool("OwnBook"))
438 if (get_option_value_string("Book File") != OpeningBook.file_name())
439 OpeningBook.open(get_option_value_string("Book File"));
441 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
442 if (bookMove != MOVE_NONE)
445 wait_for_stop_or_ponderhit();
447 cout << "bestmove " << bookMove << endl;
452 // Reset loseOnTime flag at the beginning of a new game
453 if (button_was_pressed("New Game"))
456 // Read UCI option values
457 TT.set_size(get_option_value_int("Hash"));
458 if (button_was_pressed("Clear Hash"))
461 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
462 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
463 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
464 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
465 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
466 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
467 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
468 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
469 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
470 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
471 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
472 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
474 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
475 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
476 MultiPV = get_option_value_int("MultiPV");
477 Chess960 = get_option_value_bool("UCI_Chess960");
478 UseLogFile = get_option_value_bool("Use Search Log");
481 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
483 read_weights(pos.side_to_move());
485 // Set the number of active threads
486 int newActiveThreads = get_option_value_int("Threads");
487 if (newActiveThreads != TM.active_threads())
489 TM.set_active_threads(newActiveThreads);
490 init_eval(TM.active_threads());
493 // Wake up sleeping threads
494 TM.wake_sleeping_threads();
497 int myTime = time[side_to_move];
498 int myIncrement = increment[side_to_move];
499 if (UseTimeManagement)
501 if (!movesToGo) // Sudden death time control
505 MaxSearchTime = myTime / 30 + myIncrement;
506 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
508 else // Blitz game without increment
510 MaxSearchTime = myTime / 30;
511 AbsoluteMaxSearchTime = myTime / 8;
514 else // (x moves) / (y minutes)
518 MaxSearchTime = myTime / 2;
519 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
523 MaxSearchTime = myTime / Min(movesToGo, 20);
524 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
528 if (get_option_value_bool("Ponder"))
530 MaxSearchTime += MaxSearchTime / 4;
531 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
535 // Set best NodesBetweenPolls interval to avoid lagging under
536 // heavy time pressure.
538 NodesBetweenPolls = Min(MaxNodes, 30000);
539 else if (myTime && myTime < 1000)
540 NodesBetweenPolls = 1000;
541 else if (myTime && myTime < 5000)
542 NodesBetweenPolls = 5000;
544 NodesBetweenPolls = 30000;
546 // Write search information to log file
548 LogFile << "Searching: " << pos.to_fen() << endl
549 << "infinite: " << infinite
550 << " ponder: " << ponder
551 << " time: " << myTime
552 << " increment: " << myIncrement
553 << " moves to go: " << movesToGo << endl;
555 // LSN filtering. Used only for developing purposes, disabled by default
559 // Step 2. If after last move we decided to lose on time, do it now!
560 while (SearchStartTime + myTime + 1000 > get_system_time())
564 // We're ready to start thinking. Call the iterative deepening loop function
565 Value v = id_loop(pos, searchMoves);
569 // Step 1. If this is sudden death game and our position is hopeless,
570 // decide to lose on time.
571 if ( !loseOnTime // If we already lost on time, go to step 3.
581 // Step 3. Now after stepping over the time limit, reset flag for next match.
589 TM.put_threads_to_sleep();
597 // id_loop() is the main iterative deepening loop. It calls root_search
598 // repeatedly with increasing depth until the allocated thinking time has
599 // been consumed, the user stops the search, or the maximum search depth is
602 Value id_loop(const Position& pos, Move searchMoves[]) {
604 Position p(pos, pos.thread());
605 SearchStack ss[PLY_MAX_PLUS_2];
606 Move pv[PLY_MAX_PLUS_2];
607 Move EasyMove = MOVE_NONE;
608 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
610 // Moves to search are verified, copied, scored and sorted
611 RootMoveList rml(p, searchMoves);
613 // Handle special case of searching on a mate/stale position
614 if (rml.move_count() == 0)
617 wait_for_stop_or_ponderhit();
619 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
622 // Print RootMoveList startup scoring to the standard output,
623 // so to output information also for iteration 1.
624 cout << "info depth " << 1
625 << "\ninfo depth " << 1
626 << " score " << value_to_string(rml.get_move_score(0))
627 << " time " << current_search_time()
628 << " nodes " << TM.nodes_searched()
630 << " pv " << rml.get_move(0) << "\n";
635 init_ss_array(ss, PLY_MAX_PLUS_2);
636 pv[0] = pv[1] = MOVE_NONE;
637 ValueByIteration[1] = rml.get_move_score(0);
640 // Is one move significantly better than others after initial scoring ?
641 if ( rml.move_count() == 1
642 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
643 EasyMove = rml.get_move(0);
645 // Iterative deepening loop
646 while (Iteration < PLY_MAX)
648 // Initialize iteration
650 BestMoveChangesByIteration[Iteration] = 0;
652 cout << "info depth " << Iteration << endl;
654 // Calculate dynamic aspiration window based on previous iterations
655 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
657 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
658 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
660 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
661 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
663 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
664 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
667 // Search to the current depth, rml is updated and sorted, alpha and beta could change
668 value = root_search(p, ss, pv, rml, &alpha, &beta);
670 // Write PV to transposition table, in case the relevant entries have
671 // been overwritten during the search.
675 break; // Value cannot be trusted. Break out immediately!
677 //Save info about search result
678 ValueByIteration[Iteration] = value;
680 // Drop the easy move if differs from the new best move
681 if (pv[0] != EasyMove)
682 EasyMove = MOVE_NONE;
684 if (UseTimeManagement)
687 bool stopSearch = false;
689 // Stop search early if there is only a single legal move,
690 // we search up to Iteration 6 anyway to get a proper score.
691 if (Iteration >= 6 && rml.move_count() == 1)
694 // Stop search early when the last two iterations returned a mate score
696 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
697 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
700 // Stop search early if one move seems to be much better than the others
701 int64_t nodes = TM.nodes_searched();
704 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
705 && current_search_time() > MaxSearchTime / 16)
706 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
707 && current_search_time() > MaxSearchTime / 32)))
710 // Add some extra time if the best move has changed during the last two iterations
711 if (Iteration > 5 && Iteration <= 50)
712 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
713 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
715 // Stop search if most of MaxSearchTime is consumed at the end of the
716 // iteration. We probably don't have enough time to search the first
717 // move at the next iteration anyway.
718 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
724 StopOnPonderhit = true;
730 if (MaxDepth && Iteration >= MaxDepth)
734 // If we are pondering or in infinite search, we shouldn't print the
735 // best move before we are told to do so.
736 if (!AbortSearch && (PonderSearch || InfiniteSearch))
737 wait_for_stop_or_ponderhit();
739 // Print final search statistics
740 cout << "info nodes " << TM.nodes_searched()
742 << " time " << current_search_time()
743 << " hashfull " << TT.full() << endl;
745 // Print the best move and the ponder move to the standard output
746 if (pv[0] == MOVE_NONE)
748 pv[0] = rml.get_move(0);
752 assert(pv[0] != MOVE_NONE);
754 cout << "bestmove " << pv[0];
756 if (pv[1] != MOVE_NONE)
757 cout << " ponder " << pv[1];
764 dbg_print_mean(LogFile);
766 if (dbg_show_hit_rate)
767 dbg_print_hit_rate(LogFile);
769 LogFile << "\nNodes: " << TM.nodes_searched()
770 << "\nNodes/second: " << nps()
771 << "\nBest move: " << move_to_san(p, pv[0]);
774 p.do_move(pv[0], st);
775 LogFile << "\nPonder move: "
776 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
779 return rml.get_move_score(0);
783 // root_search() is the function which searches the root node. It is
784 // similar to search_pv except that it uses a different move ordering
785 // scheme, prints some information to the standard output and handles
786 // the fail low/high loops.
788 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
795 Depth depth, ext, newDepth;
796 Value value, alpha, beta;
797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
798 int researchCountFH, researchCountFL;
800 researchCountFH = researchCountFL = 0;
803 isCheck = pos.is_check();
805 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
806 // Step 2. Check for aborted search (omitted at root)
807 // Step 3. Mate distance pruning (omitted at root)
808 // Step 4. Transposition table lookup (omitted at root)
810 // Step 5. Evaluate the position statically
811 // At root we do this only to get reference value for child nodes
813 ss->eval = evaluate(pos, ei);
815 // Step 6. Razoring (omitted at root)
816 // Step 7. Static null move pruning (omitted at root)
817 // Step 8. Null move search with verification search (omitted at root)
818 // Step 9. Internal iterative deepening (omitted at root)
820 // Step extra. Fail low loop
821 // We start with small aspiration window and in case of fail low, we research
822 // with bigger window until we are not failing low anymore.
825 // Sort the moves before to (re)search
828 // Step 10. Loop through all moves in the root move list
829 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
831 // This is used by time management
832 FirstRootMove = (i == 0);
834 // Save the current node count before the move is searched
835 nodes = TM.nodes_searched();
837 // Reset beta cut-off counters
838 TM.resetBetaCounters();
840 // Pick the next root move, and print the move and the move number to
841 // the standard output.
842 move = ss->currentMove = rml.get_move(i);
844 if (current_search_time() >= 1000)
845 cout << "info currmove " << move
846 << " currmovenumber " << i + 1 << endl;
848 moveIsCheck = pos.move_is_check(move);
849 captureOrPromotion = pos.move_is_capture_or_promotion(move);
851 // Step 11. Decide the new search depth
852 depth = (Iteration - 2) * OnePly + InitialDepth;
853 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
854 newDepth = depth + ext;
856 // Step 12. Futility pruning (omitted at root)
858 // Step extra. Fail high loop
859 // If move fails high, we research with bigger window until we are not failing
861 value = - VALUE_INFINITE;
865 // Step 13. Make the move
866 pos.do_move(move, st, ci, moveIsCheck);
868 // Step extra. pv search
869 // We do pv search for first moves (i < MultiPV)
870 // and for fail high research (value > alpha)
871 if (i < MultiPV || value > alpha)
873 // Aspiration window is disabled in multi-pv case
875 alpha = -VALUE_INFINITE;
877 // Full depth PV search, done on first move or after a fail high
878 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
882 // Step 14. Reduced search
883 // if the move fails high will be re-searched at full depth
884 bool doFullDepthSearch = true;
886 if ( depth >= 3 * OnePly
888 && !captureOrPromotion
889 && !move_is_castle(move))
891 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
894 assert(newDepth-ss->reduction >= OnePly);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
898 doFullDepthSearch = (value > alpha);
901 // The move failed high, but if reduction is very big we could
902 // face a false positive, retry with a less aggressive reduction,
903 // if the move fails high again then go with full depth search.
904 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
906 assert(newDepth - OnePly >= OnePly);
908 ss->reduction = OnePly;
909 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
910 doFullDepthSearch = (value > alpha);
912 ss->reduction = Depth(0); // Restore original reduction
915 // Step 15. Full depth search
916 if (doFullDepthSearch)
918 // Full depth non-pv search using alpha as upperbound
919 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
921 // If we are above alpha then research at same depth but as PV
922 // to get a correct score or eventually a fail high above beta.
924 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
928 // Step 16. Undo move
931 // Can we exit fail high loop ?
932 if (AbortSearch || value < beta)
935 // We are failing high and going to do a research. It's important to update
936 // the score before research in case we run out of time while researching.
937 rml.set_move_score(i, value);
939 TT.extract_pv(pos, move, pv, PLY_MAX);
940 rml.set_move_pv(i, pv);
942 // Print information to the standard output
943 print_pv_info(pos, pv, alpha, beta, value);
945 // Prepare for a research after a fail high, each time with a wider window
946 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
949 } // End of fail high loop
951 // Finished searching the move. If AbortSearch is true, the search
952 // was aborted because the user interrupted the search or because we
953 // ran out of time. In this case, the return value of the search cannot
954 // be trusted, and we break out of the loop without updating the best
959 // Remember beta-cutoff and searched nodes counts for this move. The
960 // info is used to sort the root moves for the next iteration.
962 TM.get_beta_counters(pos.side_to_move(), our, their);
963 rml.set_beta_counters(i, our, their);
964 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
966 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
967 assert(value < beta);
969 // Step 17. Check for new best move
970 if (value <= alpha && i >= MultiPV)
971 rml.set_move_score(i, -VALUE_INFINITE);
974 // PV move or new best move!
977 rml.set_move_score(i, value);
979 TT.extract_pv(pos, move, pv, PLY_MAX);
980 rml.set_move_pv(i, pv);
984 // We record how often the best move has been changed in each
985 // iteration. This information is used for time managment: When
986 // the best move changes frequently, we allocate some more time.
988 BestMoveChangesByIteration[Iteration]++;
990 // Print information to the standard output
991 print_pv_info(pos, pv, alpha, beta, value);
993 // Raise alpha to setup proper non-pv search upper bound
1000 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1002 cout << "info multipv " << j + 1
1003 << " score " << value_to_string(rml.get_move_score(j))
1004 << " depth " << (j <= i ? Iteration : Iteration - 1)
1005 << " time " << current_search_time()
1006 << " nodes " << TM.nodes_searched()
1010 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1011 cout << rml.get_move_pv(j, k) << " ";
1015 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1017 } // PV move or new best move
1019 assert(alpha >= *alphaPtr);
1021 AspirationFailLow = (alpha == *alphaPtr);
1023 if (AspirationFailLow && StopOnPonderhit)
1024 StopOnPonderhit = false;
1027 // Can we exit fail low loop ?
1028 if (AbortSearch || !AspirationFailLow)
1031 // Prepare for a research after a fail low, each time with a wider window
1032 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1037 // Sort the moves before to return
1044 // search<>() is the main search function for both PV and non-PV nodes
1046 template <NodeType PvNode>
1047 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1049 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1050 assert(beta > alpha && beta <= VALUE_INFINITE);
1051 assert(PvNode || alpha == beta - 1);
1052 assert(ply > 0 && ply < PLY_MAX);
1053 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1055 Move movesSearched[256];
1060 Move ttMove, move, excludedMove;
1061 Depth ext, newDepth;
1062 Value bestValue, value, oldAlpha;
1063 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1064 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1065 bool mateThreat = false;
1067 int threadID = pos.thread();
1068 refinedValue = bestValue = value = -VALUE_INFINITE;
1071 // Step 1. Initialize node and poll. Polling can abort search
1072 TM.incrementNodeCounter(threadID);
1074 (ss+2)->initKillers();
1076 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1082 // Step 2. Check for aborted search and immediate draw
1083 if (AbortSearch || TM.thread_should_stop(threadID))
1086 if (pos.is_draw() || ply >= PLY_MAX - 1)
1089 // Step 3. Mate distance pruning
1090 alpha = Max(value_mated_in(ply), alpha);
1091 beta = Min(value_mate_in(ply+1), beta);
1095 // Step 4. Transposition table lookup
1097 // We don't want the score of a partial search to overwrite a previous full search
1098 // TT value, so we use a different position key in case of an excluded move exists.
1099 excludedMove = ss->excludedMove;
1100 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1102 tte = TT.retrieve(posKey);
1103 ttMove = (tte ? tte->move() : MOVE_NONE);
1105 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1106 // This is to avoid problems in the following areas:
1108 // * Repetition draw detection
1109 // * Fifty move rule detection
1110 // * Searching for a mate
1111 // * Printing of full PV line
1113 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1115 // Refresh tte entry to avoid aging
1116 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1118 ss->currentMove = ttMove; // Can be MOVE_NONE
1119 return value_from_tt(tte->value(), ply);
1122 // Step 5. Evaluate the position statically
1123 // At PV nodes we do this only to update gain statistics
1124 isCheck = pos.is_check();
1127 if (tte && tte->static_value() != VALUE_NONE)
1129 ss->eval = tte->static_value();
1130 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1133 ss->eval = evaluate(pos, ei);
1135 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1136 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1139 // Step 6. Razoring (is omitted in PV nodes)
1141 && depth < RazorDepth
1143 && refinedValue < beta - razor_margin(depth)
1144 && ttMove == MOVE_NONE
1145 && (ss-1)->currentMove != MOVE_NULL
1146 && !value_is_mate(beta)
1147 && !pos.has_pawn_on_7th(pos.side_to_move()))
1149 // Pass ss->eval to qsearch() and avoid an evaluate call
1150 if (!tte || tte->static_value() == VALUE_NONE)
1151 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1153 Value rbeta = beta - razor_margin(depth);
1154 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1156 // Logically we should return (v + razor_margin(depth)), but
1157 // surprisingly this did slightly weaker in tests.
1161 // Step 7. Static null move pruning (is omitted in PV nodes)
1162 // We're betting that the opponent doesn't have a move that will reduce
1163 // the score by more than futility_margin(depth) if we do a null move.
1165 && !ss->skipNullMove
1166 && depth < RazorDepth
1167 && refinedValue >= beta + futility_margin(depth, 0)
1169 && !value_is_mate(beta)
1170 && pos.non_pawn_material(pos.side_to_move()))
1171 return refinedValue - futility_margin(depth, 0);
1173 // Step 8. Null move search with verification search (is omitted in PV nodes)
1174 // When we jump directly to qsearch() we do a null move only if static value is
1175 // at least beta. Otherwise we do a null move if static value is not more than
1176 // NullMoveMargin under beta.
1178 && !ss->skipNullMove
1180 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1182 && !value_is_mate(beta)
1183 && pos.non_pawn_material(pos.side_to_move()))
1185 ss->currentMove = MOVE_NULL;
1187 // Null move dynamic reduction based on depth
1188 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1190 // Null move dynamic reduction based on value
1191 if (refinedValue - beta > PawnValueMidgame)
1194 pos.do_null_move(st);
1195 (ss+1)->skipNullMove = true;
1197 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1198 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1199 (ss+1)->skipNullMove = false;
1200 pos.undo_null_move();
1202 if (nullValue >= beta)
1204 // Do not return unproven mate scores
1205 if (nullValue >= value_mate_in(PLY_MAX))
1208 // Do zugzwang verification search at high depths
1209 if (depth < 6 * OnePly)
1212 ss->skipNullMove = true;
1213 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
1214 ss->skipNullMove = false;
1221 // The null move failed low, which means that we may be faced with
1222 // some kind of threat. If the previous move was reduced, check if
1223 // the move that refuted the null move was somehow connected to the
1224 // move which was reduced. If a connection is found, return a fail
1225 // low score (which will cause the reduced move to fail high in the
1226 // parent node, which will trigger a re-search with full depth).
1227 if (nullValue == value_mated_in(ply + 2))
1230 ss->threatMove = (ss+1)->currentMove;
1231 if ( depth < ThreatDepth
1232 && (ss-1)->reduction
1233 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1238 // Step 9. Internal iterative deepening
1239 if ( depth >= IIDDepth[PvNode]
1240 && ttMove == MOVE_NONE
1241 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1243 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1245 ss->skipNullMove = true;
1246 search<PvNode>(pos, ss, alpha, beta, d, ply);
1247 ss->skipNullMove = false;
1249 ttMove = ss->bestMove;
1250 tte = TT.retrieve(posKey);
1253 // Expensive mate threat detection (only for PV nodes)
1255 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1257 // Initialize a MovePicker object for the current position
1258 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1260 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1261 && tte && tte->move()
1262 && !excludedMove // Do not allow recursive singular extension search
1263 && is_lower_bound(tte->type())
1264 && tte->depth() >= depth - 3 * OnePly;
1266 // Step 10. Loop through moves
1267 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1268 while ( bestValue < beta
1269 && (move = mp.get_next_move()) != MOVE_NONE
1270 && !TM.thread_should_stop(threadID))
1272 assert(move_is_ok(move));
1274 if (move == excludedMove)
1277 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1278 moveIsCheck = pos.move_is_check(move, ci);
1279 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1281 // Step 11. Decide the new search depth
1282 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1284 // Singular extension search. We extend the TT move if its value is much better than
1285 // its siblings. To verify this we do a reduced search on all the other moves but the
1286 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1287 if ( singularExtensionNode
1288 && move == tte->move()
1291 Value ttValue = value_from_tt(tte->value(), ply);
1293 if (abs(ttValue) < VALUE_KNOWN_WIN)
1295 Value b = ttValue - SingularExtensionMargin;
1296 ss->excludedMove = move;
1297 ss->skipNullMove = true;
1298 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1299 ss->skipNullMove = false;
1300 ss->excludedMove = MOVE_NONE;
1301 if (v < ttValue - SingularExtensionMargin)
1306 newDepth = depth - OnePly + ext;
1308 // Update current move (this must be done after singular extension search)
1309 movesSearched[moveCount++] = ss->currentMove = move;
1311 // Step 12. Futility pruning (is omitted in PV nodes)
1313 && !captureOrPromotion
1317 && !move_is_castle(move))
1319 // Move count based pruning
1320 if ( moveCount >= futility_move_count(depth)
1321 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1322 && bestValue > value_mated_in(PLY_MAX))
1325 // Value based pruning
1326 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1327 // but fixing this made program slightly weaker.
1328 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1329 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1330 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1332 if (futilityValueScaled < beta)
1334 if (futilityValueScaled > bestValue)
1335 bestValue = futilityValueScaled;
1340 // Step 13. Make the move
1341 pos.do_move(move, st, ci, moveIsCheck);
1343 // Step extra. pv search (only in PV nodes)
1344 // The first move in list is the expected PV
1345 if (PvNode && moveCount == 1)
1346 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1347 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1350 // Step 14. Reduced depth search
1351 // If the move fails high will be re-searched at full depth.
1352 bool doFullDepthSearch = true;
1354 if ( depth >= 3 * OnePly
1355 && !captureOrPromotion
1357 && !move_is_castle(move)
1358 && !move_is_killer(move, ss))
1360 ss->reduction = reduction<PvNode>(depth, moveCount);
1363 Depth d = newDepth - ss->reduction;
1364 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1365 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1367 doFullDepthSearch = (value > alpha);
1370 // The move failed high, but if reduction is very big we could
1371 // face a false positive, retry with a less aggressive reduction,
1372 // if the move fails high again then go with full depth search.
1373 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1375 assert(newDepth - OnePly >= OnePly);
1377 ss->reduction = OnePly;
1378 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1379 doFullDepthSearch = (value > alpha);
1381 ss->reduction = Depth(0); // Restore original reduction
1384 // Step 15. Full depth search
1385 if (doFullDepthSearch)
1387 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1388 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1390 // Step extra. pv search (only in PV nodes)
1391 // Search only for possible new PV nodes, if instead value >= beta then
1392 // parent node fails low with value <= alpha and tries another move.
1393 if (PvNode && value > alpha && value < beta)
1394 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1395 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1399 // Step 16. Undo move
1400 pos.undo_move(move);
1402 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1404 // Step 17. Check for new best move
1405 if (value > bestValue)
1410 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1413 if (value == value_mate_in(ply + 1))
1414 ss->mateKiller = move;
1416 ss->bestMove = move;
1420 // Step 18. Check for split
1421 if ( depth >= MinimumSplitDepth
1422 && TM.active_threads() > 1
1424 && TM.available_thread_exists(threadID)
1426 && !TM.thread_should_stop(threadID)
1428 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1429 mateThreat, &moveCount, &mp, PvNode);
1432 // Step 19. Check for mate and stalemate
1433 // All legal moves have been searched and if there are
1434 // no legal moves, it must be mate or stalemate.
1435 // If one move was excluded return fail low score.
1437 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1439 // Step 20. Update tables
1440 // If the search is not aborted, update the transposition table,
1441 // history counters, and killer moves.
1442 if (AbortSearch || TM.thread_should_stop(threadID))
1445 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1446 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1447 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1449 // Update killers and history only for non capture moves that fails high
1450 if (bestValue >= beta)
1452 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1453 if (!pos.move_is_capture_or_promotion(move))
1455 update_history(pos, move, depth, movesSearched, moveCount);
1456 update_killers(move, ss);
1460 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1466 // qsearch() is the quiescence search function, which is called by the main
1467 // search function when the remaining depth is zero (or, to be more precise,
1468 // less than OnePly).
1470 template <NodeType PvNode>
1471 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1473 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1474 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1475 assert(PvNode || alpha == beta - 1);
1477 assert(ply > 0 && ply < PLY_MAX);
1478 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1483 Value bestValue, value, futilityValue, futilityBase;
1484 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1486 Value oldAlpha = alpha;
1488 TM.incrementNodeCounter(pos.thread());
1489 ss->bestMove = ss->currentMove = MOVE_NONE;
1490 ss->eval = VALUE_NONE;
1492 // Check for an instant draw or maximum ply reached
1493 if (pos.is_draw() || ply >= PLY_MAX - 1)
1496 // Transposition table lookup. At PV nodes, we don't use the TT for
1497 // pruning, but only for move ordering.
1498 tte = TT.retrieve(pos.get_key());
1499 ttMove = (tte ? tte->move() : MOVE_NONE);
1501 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1503 ss->currentMove = ttMove; // Can be MOVE_NONE
1504 return value_from_tt(tte->value(), ply);
1507 isCheck = pos.is_check();
1509 // Evaluate the position statically
1512 bestValue = futilityBase = -VALUE_INFINITE;
1513 deepChecks = enoughMaterial = false;
1517 if (tte && tte->static_value() != VALUE_NONE)
1519 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1520 bestValue = tte->static_value();
1523 bestValue = evaluate(pos, ei);
1525 ss->eval = bestValue;
1526 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1528 // Stand pat. Return immediately if static value is at least beta
1529 if (bestValue >= beta)
1532 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()]);
1537 if (PvNode && bestValue > alpha)
1540 // If we are near beta then try to get a cutoff pushing checks a bit further
1541 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1543 // Futility pruning parameters, not needed when in check
1544 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1545 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1548 // Initialize a MovePicker object for the current position, and prepare
1549 // to search the moves. Because the depth is <= 0 here, only captures,
1550 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1551 // and we are near beta) will be generated.
1552 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1555 // Loop through the moves until no moves remain or a beta cutoff occurs
1556 while ( alpha < beta
1557 && (move = mp.get_next_move()) != MOVE_NONE)
1559 assert(move_is_ok(move));
1561 moveIsCheck = pos.move_is_check(move, ci);
1569 && !move_is_promotion(move)
1570 && !pos.move_is_passed_pawn_push(move))
1572 futilityValue = futilityBase
1573 + pos.endgame_value_of_piece_on(move_to(move))
1574 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1576 if (futilityValue < alpha)
1578 if (futilityValue > bestValue)
1579 bestValue = futilityValue;
1584 // Detect blocking evasions that are candidate to be pruned
1585 evasionPrunable = isCheck
1586 && bestValue > value_mated_in(PLY_MAX)
1587 && !pos.move_is_capture(move)
1588 && pos.type_of_piece_on(move_from(move)) != KING
1589 && !pos.can_castle(pos.side_to_move());
1591 // Don't search moves with negative SEE values
1593 && (!isCheck || evasionPrunable)
1595 && !move_is_promotion(move)
1596 && pos.see_sign(move) < 0)
1599 // Update current move
1600 ss->currentMove = move;
1602 // Make and search the move
1603 pos.do_move(move, st, ci, moveIsCheck);
1604 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1605 pos.undo_move(move);
1607 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1610 if (value > bestValue)
1616 ss->bestMove = move;
1621 // All legal moves have been searched. A special case: If we're in check
1622 // and no legal moves were found, it is checkmate.
1623 if (isCheck && bestValue == -VALUE_INFINITE)
1624 return value_mated_in(ply);
1626 // Update transposition table
1627 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1628 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1629 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1631 // Update killers only for checking moves that fails high
1632 if ( bestValue >= beta
1633 && !pos.move_is_capture_or_promotion(ss->bestMove))
1634 update_killers(ss->bestMove, ss);
1636 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1642 // sp_search() is used to search from a split point. This function is called
1643 // by each thread working at the split point. It is similar to the normal
1644 // search() function, but simpler. Because we have already probed the hash
1645 // table, done a null move search, and searched the first move before
1646 // splitting, we don't have to repeat all this work in sp_search(). We
1647 // also don't need to store anything to the hash table here: This is taken
1648 // care of after we return from the split point.
1650 template <NodeType PvNode>
1651 void sp_search(SplitPoint* sp, int threadID) {
1653 assert(threadID >= 0 && threadID < TM.active_threads());
1654 assert(TM.active_threads() > 1);
1658 Depth ext, newDepth;
1660 Value futilityValueScaled; // NonPV specific
1661 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1663 value = -VALUE_INFINITE;
1665 Position pos(*sp->pos, threadID);
1667 SearchStack* ss = sp->sstack[threadID] + 1;
1668 isCheck = pos.is_check();
1670 // Step 10. Loop through moves
1671 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1672 lock_grab(&(sp->lock));
1674 while ( sp->bestValue < sp->beta
1675 && (move = sp->mp->get_next_move()) != MOVE_NONE
1676 && !TM.thread_should_stop(threadID))
1678 moveCount = ++sp->moveCount;
1679 lock_release(&(sp->lock));
1681 assert(move_is_ok(move));
1683 moveIsCheck = pos.move_is_check(move, ci);
1684 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1686 // Step 11. Decide the new search depth
1687 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1688 newDepth = sp->depth - OnePly + ext;
1690 // Update current move
1691 ss->currentMove = move;
1693 // Step 12. Futility pruning (is omitted in PV nodes)
1695 && !captureOrPromotion
1698 && !move_is_castle(move))
1700 // Move count based pruning
1701 if ( moveCount >= futility_move_count(sp->depth)
1702 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1703 && sp->bestValue > value_mated_in(PLY_MAX))
1705 lock_grab(&(sp->lock));
1709 // Value based pruning
1710 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1711 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1712 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1714 if (futilityValueScaled < sp->beta)
1716 lock_grab(&(sp->lock));
1718 if (futilityValueScaled > sp->bestValue)
1719 sp->bestValue = futilityValueScaled;
1724 // Step 13. Make the move
1725 pos.do_move(move, st, ci, moveIsCheck);
1727 // Step 14. Reduced search
1728 // If the move fails high will be re-searched at full depth.
1729 bool doFullDepthSearch = true;
1731 if ( !captureOrPromotion
1733 && !move_is_castle(move)
1734 && !move_is_killer(move, ss))
1736 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1739 Value localAlpha = sp->alpha;
1740 Depth d = newDepth - ss->reduction;
1741 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1742 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1744 doFullDepthSearch = (value > localAlpha);
1747 // The move failed high, but if reduction is very big we could
1748 // face a false positive, retry with a less aggressive reduction,
1749 // if the move fails high again then go with full depth search.
1750 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1752 assert(newDepth - OnePly >= OnePly);
1754 ss->reduction = OnePly;
1755 Value localAlpha = sp->alpha;
1756 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1757 doFullDepthSearch = (value > localAlpha);
1759 ss->reduction = Depth(0); // Restore original reduction
1762 // Step 15. Full depth search
1763 if (doFullDepthSearch)
1765 Value localAlpha = sp->alpha;
1766 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1767 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1769 // Step extra. pv search (only in PV nodes)
1770 // Search only for possible new PV nodes, if instead value >= beta then
1771 // parent node fails low with value <= alpha and tries another move.
1772 if (PvNode && value > localAlpha && value < sp->beta)
1773 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1774 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1777 // Step 16. Undo move
1778 pos.undo_move(move);
1780 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1782 // Step 17. Check for new best move
1783 lock_grab(&(sp->lock));
1785 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1787 sp->bestValue = value;
1789 if (sp->bestValue > sp->alpha)
1791 if (!PvNode || value >= sp->beta)
1792 sp->stopRequest = true;
1794 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1797 sp->parentSstack->bestMove = ss->bestMove = move;
1802 /* Here we have the lock still grabbed */
1804 sp->slaves[threadID] = 0;
1806 lock_release(&(sp->lock));
1810 // connected_moves() tests whether two moves are 'connected' in the sense
1811 // that the first move somehow made the second move possible (for instance
1812 // if the moving piece is the same in both moves). The first move is assumed
1813 // to be the move that was made to reach the current position, while the
1814 // second move is assumed to be a move from the current position.
1816 bool connected_moves(const Position& pos, Move m1, Move m2) {
1818 Square f1, t1, f2, t2;
1821 assert(move_is_ok(m1));
1822 assert(move_is_ok(m2));
1824 if (m2 == MOVE_NONE)
1827 // Case 1: The moving piece is the same in both moves
1833 // Case 2: The destination square for m2 was vacated by m1
1839 // Case 3: Moving through the vacated square
1840 if ( piece_is_slider(pos.piece_on(f2))
1841 && bit_is_set(squares_between(f2, t2), f1))
1844 // Case 4: The destination square for m2 is defended by the moving piece in m1
1845 p = pos.piece_on(t1);
1846 if (bit_is_set(pos.attacks_from(p, t1), t2))
1849 // Case 5: Discovered check, checking piece is the piece moved in m1
1850 if ( piece_is_slider(p)
1851 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1852 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1854 // discovered_check_candidates() works also if the Position's side to
1855 // move is the opposite of the checking piece.
1856 Color them = opposite_color(pos.side_to_move());
1857 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1859 if (bit_is_set(dcCandidates, f2))
1866 // value_is_mate() checks if the given value is a mate one
1867 // eventually compensated for the ply.
1869 bool value_is_mate(Value value) {
1871 assert(abs(value) <= VALUE_INFINITE);
1873 return value <= value_mated_in(PLY_MAX)
1874 || value >= value_mate_in(PLY_MAX);
1878 // move_is_killer() checks if the given move is among the
1879 // killer moves of that ply.
1881 bool move_is_killer(Move m, SearchStack* ss) {
1883 const Move* k = ss->killers;
1884 for (int i = 0; i < KILLER_MAX; i++, k++)
1892 // extension() decides whether a move should be searched with normal depth,
1893 // or with extended depth. Certain classes of moves (checking moves, in
1894 // particular) are searched with bigger depth than ordinary moves and in
1895 // any case are marked as 'dangerous'. Note that also if a move is not
1896 // extended, as example because the corresponding UCI option is set to zero,
1897 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1898 template <NodeType PvNode>
1899 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1900 bool singleEvasion, bool mateThreat, bool* dangerous) {
1902 assert(m != MOVE_NONE);
1904 Depth result = Depth(0);
1905 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1909 if (moveIsCheck && pos.see_sign(m) >= 0)
1910 result += CheckExtension[PvNode];
1913 result += SingleEvasionExtension[PvNode];
1916 result += MateThreatExtension[PvNode];
1919 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1921 Color c = pos.side_to_move();
1922 if (relative_rank(c, move_to(m)) == RANK_7)
1924 result += PawnPushTo7thExtension[PvNode];
1927 if (pos.pawn_is_passed(c, move_to(m)))
1929 result += PassedPawnExtension[PvNode];
1934 if ( captureOrPromotion
1935 && pos.type_of_piece_on(move_to(m)) != PAWN
1936 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1937 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1938 && !move_is_promotion(m)
1941 result += PawnEndgameExtension[PvNode];
1946 && captureOrPromotion
1947 && pos.type_of_piece_on(move_to(m)) != PAWN
1948 && pos.see_sign(m) >= 0)
1954 return Min(result, OnePly);
1958 // connected_threat() tests whether it is safe to forward prune a move or if
1959 // is somehow coonected to the threat move returned by null search.
1961 bool connected_threat(const Position& pos, Move m, Move threat) {
1963 assert(move_is_ok(m));
1964 assert(threat && move_is_ok(threat));
1965 assert(!pos.move_is_check(m));
1966 assert(!pos.move_is_capture_or_promotion(m));
1967 assert(!pos.move_is_passed_pawn_push(m));
1969 Square mfrom, mto, tfrom, tto;
1971 mfrom = move_from(m);
1973 tfrom = move_from(threat);
1974 tto = move_to(threat);
1976 // Case 1: Don't prune moves which move the threatened piece
1980 // Case 2: If the threatened piece has value less than or equal to the
1981 // value of the threatening piece, don't prune move which defend it.
1982 if ( pos.move_is_capture(threat)
1983 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1984 || pos.type_of_piece_on(tfrom) == KING)
1985 && pos.move_attacks_square(m, tto))
1988 // Case 3: If the moving piece in the threatened move is a slider, don't
1989 // prune safe moves which block its ray.
1990 if ( piece_is_slider(pos.piece_on(tfrom))
1991 && bit_is_set(squares_between(tfrom, tto), mto)
1992 && pos.see_sign(m) >= 0)
1999 // ok_to_use_TT() returns true if a transposition table score
2000 // can be used at a given point in search.
2002 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2004 Value v = value_from_tt(tte->value(), ply);
2006 return ( tte->depth() >= depth
2007 || v >= Max(value_mate_in(PLY_MAX), beta)
2008 || v < Min(value_mated_in(PLY_MAX), beta))
2010 && ( (is_lower_bound(tte->type()) && v >= beta)
2011 || (is_upper_bound(tte->type()) && v < beta));
2015 // refine_eval() returns the transposition table score if
2016 // possible otherwise falls back on static position evaluation.
2018 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2023 Value v = value_from_tt(tte->value(), ply);
2025 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2026 || (is_upper_bound(tte->type()) && v < defaultEval))
2033 // update_history() registers a good move that produced a beta-cutoff
2034 // in history and marks as failures all the other moves of that ply.
2036 void update_history(const Position& pos, Move move, Depth depth,
2037 Move movesSearched[], int moveCount) {
2041 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2043 for (int i = 0; i < moveCount - 1; i++)
2045 m = movesSearched[i];
2049 if (!pos.move_is_capture_or_promotion(m))
2050 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2055 // update_killers() add a good move that produced a beta-cutoff
2056 // among the killer moves of that ply.
2058 void update_killers(Move m, SearchStack* ss) {
2060 if (m == ss->killers[0])
2063 for (int i = KILLER_MAX - 1; i > 0; i--)
2064 ss->killers[i] = ss->killers[i - 1];
2070 // update_gains() updates the gains table of a non-capture move given
2071 // the static position evaluation before and after the move.
2073 void update_gains(const Position& pos, Move m, Value before, Value after) {
2076 && before != VALUE_NONE
2077 && after != VALUE_NONE
2078 && pos.captured_piece() == NO_PIECE_TYPE
2079 && !move_is_castle(m)
2080 && !move_is_promotion(m))
2081 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2085 // current_search_time() returns the number of milliseconds which have passed
2086 // since the beginning of the current search.
2088 int current_search_time() {
2090 return get_system_time() - SearchStartTime;
2094 // nps() computes the current nodes/second count.
2098 int t = current_search_time();
2099 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2103 // poll() performs two different functions: It polls for user input, and it
2104 // looks at the time consumed so far and decides if it's time to abort the
2109 static int lastInfoTime;
2110 int t = current_search_time();
2115 // We are line oriented, don't read single chars
2116 std::string command;
2118 if (!std::getline(std::cin, command))
2121 if (command == "quit")
2124 PonderSearch = false;
2128 else if (command == "stop")
2131 PonderSearch = false;
2133 else if (command == "ponderhit")
2137 // Print search information
2141 else if (lastInfoTime > t)
2142 // HACK: Must be a new search where we searched less than
2143 // NodesBetweenPolls nodes during the first second of search.
2146 else if (t - lastInfoTime >= 1000)
2153 if (dbg_show_hit_rate)
2154 dbg_print_hit_rate();
2156 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2157 << " time " << t << " hashfull " << TT.full() << endl;
2160 // Should we stop the search?
2164 bool stillAtFirstMove = FirstRootMove
2165 && !AspirationFailLow
2166 && t > MaxSearchTime + ExtraSearchTime;
2168 bool noMoreTime = t > AbsoluteMaxSearchTime
2169 || stillAtFirstMove;
2171 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2172 || (ExactMaxTime && t >= ExactMaxTime)
2173 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2178 // ponderhit() is called when the program is pondering (i.e. thinking while
2179 // it's the opponent's turn to move) in order to let the engine know that
2180 // it correctly predicted the opponent's move.
2184 int t = current_search_time();
2185 PonderSearch = false;
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > MaxSearchTime + ExtraSearchTime;
2191 bool noMoreTime = t > AbsoluteMaxSearchTime
2192 || stillAtFirstMove;
2194 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2199 // init_ss_array() does a fast reset of the first entries of a SearchStack
2200 // array and of all the excludedMove and skipNullMove entries.
2202 void init_ss_array(SearchStack* ss, int size) {
2204 for (int i = 0; i < size; i++, ss++)
2206 ss->excludedMove = MOVE_NONE;
2207 ss->skipNullMove = false;
2218 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2219 // while the program is pondering. The point is to work around a wrinkle in
2220 // the UCI protocol: When pondering, the engine is not allowed to give a
2221 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2222 // We simply wait here until one of these commands is sent, and return,
2223 // after which the bestmove and pondermove will be printed (in id_loop()).
2225 void wait_for_stop_or_ponderhit() {
2227 std::string command;
2231 if (!std::getline(std::cin, command))
2234 if (command == "quit")
2239 else if (command == "ponderhit" || command == "stop")
2245 // print_pv_info() prints to standard output and eventually to log file information on
2246 // the current PV line. It is called at each iteration or after a new pv is found.
2248 void print_pv_info(const Position& pos, Move* pv, Value alpha, Value beta, Value value) {
2250 cout << "info depth " << Iteration
2251 << " score " << value_to_string(value)
2252 << ((value >= beta) ? " lowerbound" :
2253 ((value <= alpha)? " upperbound" : ""))
2254 << " time " << current_search_time()
2255 << " nodes " << TM.nodes_searched()
2259 for (int j = 0; pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2260 cout << pv[j] << " ";
2266 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2267 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2269 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2270 TM.nodes_searched(), value, type, pv) << endl;
2275 // init_thread() is the function which is called when a new thread is
2276 // launched. It simply calls the idle_loop() function with the supplied
2277 // threadID. There are two versions of this function; one for POSIX
2278 // threads and one for Windows threads.
2280 #if !defined(_MSC_VER)
2282 void* init_thread(void *threadID) {
2284 TM.idle_loop(*(int*)threadID, NULL);
2290 DWORD WINAPI init_thread(LPVOID threadID) {
2292 TM.idle_loop(*(int*)threadID, NULL);
2299 /// The ThreadsManager class
2301 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2302 // get_beta_counters() are getters/setters for the per thread
2303 // counters used to sort the moves at root.
2305 void ThreadsManager::resetNodeCounters() {
2307 for (int i = 0; i < MAX_THREADS; i++)
2308 threads[i].nodes = 0ULL;
2311 void ThreadsManager::resetBetaCounters() {
2313 for (int i = 0; i < MAX_THREADS; i++)
2314 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2317 int64_t ThreadsManager::nodes_searched() const {
2319 int64_t result = 0ULL;
2320 for (int i = 0; i < ActiveThreads; i++)
2321 result += threads[i].nodes;
2326 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2329 for (int i = 0; i < MAX_THREADS; i++)
2331 our += threads[i].betaCutOffs[us];
2332 their += threads[i].betaCutOffs[opposite_color(us)];
2337 // idle_loop() is where the threads are parked when they have no work to do.
2338 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2339 // object for which the current thread is the master.
2341 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2343 assert(threadID >= 0 && threadID < MAX_THREADS);
2347 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2348 // master should exit as last one.
2349 if (AllThreadsShouldExit)
2352 threads[threadID].state = THREAD_TERMINATED;
2356 // If we are not thinking, wait for a condition to be signaled
2357 // instead of wasting CPU time polling for work.
2358 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2361 assert(threadID != 0);
2362 threads[threadID].state = THREAD_SLEEPING;
2364 #if !defined(_MSC_VER)
2365 lock_grab(&WaitLock);
2366 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2367 pthread_cond_wait(&WaitCond, &WaitLock);
2368 lock_release(&WaitLock);
2370 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2374 // If thread has just woken up, mark it as available
2375 if (threads[threadID].state == THREAD_SLEEPING)
2376 threads[threadID].state = THREAD_AVAILABLE;
2378 // If this thread has been assigned work, launch a search
2379 if (threads[threadID].state == THREAD_WORKISWAITING)
2381 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2383 threads[threadID].state = THREAD_SEARCHING;
2385 if (threads[threadID].splitPoint->pvNode)
2386 sp_search<PV>(threads[threadID].splitPoint, threadID);
2388 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2390 assert(threads[threadID].state == THREAD_SEARCHING);
2392 threads[threadID].state = THREAD_AVAILABLE;
2395 // If this thread is the master of a split point and all slaves have
2396 // finished their work at this split point, return from the idle loop.
2398 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2400 if (i == ActiveThreads)
2402 // Because sp->slaves[] is reset under lock protection,
2403 // be sure sp->lock has been released before to return.
2404 lock_grab(&(sp->lock));
2405 lock_release(&(sp->lock));
2407 assert(threads[threadID].state == THREAD_AVAILABLE);
2409 threads[threadID].state = THREAD_SEARCHING;
2416 // init_threads() is called during startup. It launches all helper threads,
2417 // and initializes the split point stack and the global locks and condition
2420 void ThreadsManager::init_threads() {
2425 #if !defined(_MSC_VER)
2426 pthread_t pthread[1];
2429 // Initialize global locks
2430 lock_init(&MPLock, NULL);
2431 lock_init(&WaitLock, NULL);
2433 #if !defined(_MSC_VER)
2434 pthread_cond_init(&WaitCond, NULL);
2436 for (i = 0; i < MAX_THREADS; i++)
2437 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2440 // Initialize SplitPointStack locks
2441 for (i = 0; i < MAX_THREADS; i++)
2442 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2443 lock_init(&(SplitPointStack[i][j].lock), NULL);
2445 // Will be set just before program exits to properly end the threads
2446 AllThreadsShouldExit = false;
2448 // Threads will be put to sleep as soon as created
2449 AllThreadsShouldSleep = true;
2451 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2453 threads[0].state = THREAD_SEARCHING;
2454 for (i = 1; i < MAX_THREADS; i++)
2455 threads[i].state = THREAD_AVAILABLE;
2457 // Launch the helper threads
2458 for (i = 1; i < MAX_THREADS; i++)
2461 #if !defined(_MSC_VER)
2462 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2464 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2469 cout << "Failed to create thread number " << i << endl;
2470 Application::exit_with_failure();
2473 // Wait until the thread has finished launching and is gone to sleep
2474 while (threads[i].state != THREAD_SLEEPING) {}
2479 // exit_threads() is called when the program exits. It makes all the
2480 // helper threads exit cleanly.
2482 void ThreadsManager::exit_threads() {
2484 ActiveThreads = MAX_THREADS; // HACK
2485 AllThreadsShouldSleep = true; // HACK
2486 wake_sleeping_threads();
2488 // This makes the threads to exit idle_loop()
2489 AllThreadsShouldExit = true;
2491 // Wait for thread termination
2492 for (int i = 1; i < MAX_THREADS; i++)
2493 while (threads[i].state != THREAD_TERMINATED) {}
2495 // Now we can safely destroy the locks
2496 for (int i = 0; i < MAX_THREADS; i++)
2497 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2498 lock_destroy(&(SplitPointStack[i][j].lock));
2500 lock_destroy(&WaitLock);
2501 lock_destroy(&MPLock);
2505 // thread_should_stop() checks whether the thread should stop its search.
2506 // This can happen if a beta cutoff has occurred in the thread's currently
2507 // active split point, or in some ancestor of the current split point.
2509 bool ThreadsManager::thread_should_stop(int threadID) const {
2511 assert(threadID >= 0 && threadID < ActiveThreads);
2515 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2520 // thread_is_available() checks whether the thread with threadID "slave" is
2521 // available to help the thread with threadID "master" at a split point. An
2522 // obvious requirement is that "slave" must be idle. With more than two
2523 // threads, this is not by itself sufficient: If "slave" is the master of
2524 // some active split point, it is only available as a slave to the other
2525 // threads which are busy searching the split point at the top of "slave"'s
2526 // split point stack (the "helpful master concept" in YBWC terminology).
2528 bool ThreadsManager::thread_is_available(int slave, int master) const {
2530 assert(slave >= 0 && slave < ActiveThreads);
2531 assert(master >= 0 && master < ActiveThreads);
2532 assert(ActiveThreads > 1);
2534 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2537 // Make a local copy to be sure doesn't change under our feet
2538 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2540 if (localActiveSplitPoints == 0)
2541 // No active split points means that the thread is available as
2542 // a slave for any other thread.
2545 if (ActiveThreads == 2)
2548 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2549 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2550 // could have been set to 0 by another thread leading to an out of bound access.
2551 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2558 // available_thread_exists() tries to find an idle thread which is available as
2559 // a slave for the thread with threadID "master".
2561 bool ThreadsManager::available_thread_exists(int master) const {
2563 assert(master >= 0 && master < ActiveThreads);
2564 assert(ActiveThreads > 1);
2566 for (int i = 0; i < ActiveThreads; i++)
2567 if (thread_is_available(i, master))
2574 // split() does the actual work of distributing the work at a node between
2575 // several available threads. If it does not succeed in splitting the
2576 // node (because no idle threads are available, or because we have no unused
2577 // split point objects), the function immediately returns. If splitting is
2578 // possible, a SplitPoint object is initialized with all the data that must be
2579 // copied to the helper threads and we tell our helper threads that they have
2580 // been assigned work. This will cause them to instantly leave their idle loops
2581 // and call sp_search(). When all threads have returned from sp_search() then
2584 template <bool Fake>
2585 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2586 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2587 int* moveCount, MovePicker* mp, bool pvNode) {
2589 assert(ply > 0 && ply < PLY_MAX);
2590 assert(*bestValue >= -VALUE_INFINITE);
2591 assert(*bestValue <= *alpha);
2592 assert(*alpha < beta);
2593 assert(beta <= VALUE_INFINITE);
2594 assert(depth > Depth(0));
2595 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2596 assert(ActiveThreads > 1);
2598 int master = p.thread();
2602 // If no other thread is available to help us, or if we have too many
2603 // active split points, don't split.
2604 if ( !available_thread_exists(master)
2605 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2607 lock_release(&MPLock);
2611 // Pick the next available split point object from the split point stack
2612 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2614 // Initialize the split point object
2615 splitPoint->parent = threads[master].splitPoint;
2616 splitPoint->stopRequest = false;
2617 splitPoint->ply = ply;
2618 splitPoint->depth = depth;
2619 splitPoint->mateThreat = mateThreat;
2620 splitPoint->alpha = *alpha;
2621 splitPoint->beta = beta;
2622 splitPoint->pvNode = pvNode;
2623 splitPoint->bestValue = *bestValue;
2624 splitPoint->mp = mp;
2625 splitPoint->moveCount = *moveCount;
2626 splitPoint->pos = &p;
2627 splitPoint->parentSstack = ss;
2628 for (int i = 0; i < ActiveThreads; i++)
2629 splitPoint->slaves[i] = 0;
2631 threads[master].splitPoint = splitPoint;
2632 threads[master].activeSplitPoints++;
2634 // If we are here it means we are not available
2635 assert(threads[master].state != THREAD_AVAILABLE);
2637 int workersCnt = 1; // At least the master is included
2639 // Allocate available threads setting state to THREAD_BOOKED
2640 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2641 if (thread_is_available(i, master))
2643 threads[i].state = THREAD_BOOKED;
2644 threads[i].splitPoint = splitPoint;
2645 splitPoint->slaves[i] = 1;
2649 assert(Fake || workersCnt > 1);
2651 // We can release the lock because slave threads are already booked and master is not available
2652 lock_release(&MPLock);
2654 // Tell the threads that they have work to do. This will make them leave
2655 // their idle loop. But before copy search stack tail for each thread.
2656 for (int i = 0; i < ActiveThreads; i++)
2657 if (i == master || splitPoint->slaves[i])
2659 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2661 assert(i == master || threads[i].state == THREAD_BOOKED);
2663 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2666 // Everything is set up. The master thread enters the idle loop, from
2667 // which it will instantly launch a search, because its state is
2668 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2669 // idle loop, which means that the main thread will return from the idle
2670 // loop when all threads have finished their work at this split point.
2671 idle_loop(master, splitPoint);
2673 // We have returned from the idle loop, which means that all threads are
2674 // finished. Update alpha and bestValue, and return.
2677 *alpha = splitPoint->alpha;
2678 *bestValue = splitPoint->bestValue;
2679 threads[master].activeSplitPoints--;
2680 threads[master].splitPoint = splitPoint->parent;
2682 lock_release(&MPLock);
2686 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2687 // to start a new search from the root.
2689 void ThreadsManager::wake_sleeping_threads() {
2691 assert(AllThreadsShouldSleep);
2692 assert(ActiveThreads > 0);
2694 AllThreadsShouldSleep = false;
2696 if (ActiveThreads == 1)
2699 #if !defined(_MSC_VER)
2700 pthread_mutex_lock(&WaitLock);
2701 pthread_cond_broadcast(&WaitCond);
2702 pthread_mutex_unlock(&WaitLock);
2704 for (int i = 1; i < MAX_THREADS; i++)
2705 SetEvent(SitIdleEvent[i]);
2711 // put_threads_to_sleep() makes all the threads go to sleep just before
2712 // to leave think(), at the end of the search. Threads should have already
2713 // finished the job and should be idle.
2715 void ThreadsManager::put_threads_to_sleep() {
2717 assert(!AllThreadsShouldSleep);
2719 // This makes the threads to go to sleep
2720 AllThreadsShouldSleep = true;
2723 /// The RootMoveList class
2725 // RootMoveList c'tor
2727 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2729 SearchStack ss[PLY_MAX_PLUS_2];
2730 MoveStack mlist[MaxRootMoves];
2732 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2734 // Generate all legal moves
2735 MoveStack* last = generate_moves(pos, mlist);
2737 // Add each move to the moves[] array
2738 for (MoveStack* cur = mlist; cur != last; cur++)
2740 bool includeMove = includeAllMoves;
2742 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2743 includeMove = (searchMoves[k] == cur->move);
2748 // Find a quick score for the move
2749 init_ss_array(ss, PLY_MAX_PLUS_2);
2750 pos.do_move(cur->move, st);
2751 moves[count].move = cur->move;
2752 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2753 moves[count].pv[0] = cur->move;
2754 moves[count].pv[1] = MOVE_NONE;
2755 pos.undo_move(cur->move);
2762 // RootMoveList simple methods definitions
2764 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2766 moves[moveNum].nodes = nodes;
2767 moves[moveNum].cumulativeNodes += nodes;
2770 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2772 moves[moveNum].ourBeta = our;
2773 moves[moveNum].theirBeta = their;
2776 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2780 for (j = 0; pv[j] != MOVE_NONE; j++)
2781 moves[moveNum].pv[j] = pv[j];
2783 moves[moveNum].pv[j] = MOVE_NONE;
2787 // RootMoveList::sort() sorts the root move list at the beginning of a new
2790 void RootMoveList::sort() {
2792 sort_multipv(count - 1); // Sort all items
2796 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2797 // list by their scores and depths. It is used to order the different PVs
2798 // correctly in MultiPV mode.
2800 void RootMoveList::sort_multipv(int n) {
2804 for (i = 1; i <= n; i++)
2806 RootMove rm = moves[i];
2807 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2808 moves[j] = moves[j - 1];