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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
79 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
81 void resetNodeCounters();
82 void resetBetaCounters();
83 int64_t nodes_searched() const;
84 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
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] = { 7 * 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, 1)][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);
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
255 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
256 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
257 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(const Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 void sp_search(SplitPoint* sp, int threadID);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool move_is_killer(Move m, SearchStack* ss);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 bool connected_threat(const Position& pos, Move m, Move threat);
300 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
301 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
302 void update_killers(Move m, SearchStack* ss);
303 void update_gains(const Position& pos, Move move, Value before, Value after);
305 int current_search_time();
306 std::string value_to_uci(Value v);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack* ss, int size);
312 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 void insert_pv_in_tt(const Position& pos, Move pv[]);
314 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
329 /// init_threads(), exit_threads() and nodes_searched() are helpers to
330 /// give accessibility to some TM methods from outside of current file.
332 void init_threads() { TM.init_threads(); }
333 void exit_threads() { TM.exit_threads(); }
334 int64_t nodes_searched() { return TM.nodes_searched(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (OnePly == 2)
342 int hd; // half depth (OnePly == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
372 MovePicker mp(pos, MOVE_NONE, depth, H);
374 // If we are at the last ply we don't need to do and undo
375 // the moves, just to count them.
376 if (depth <= OnePly) // Replace with '<' to test also qsearch
378 while (mp.get_next_move()) sum++;
382 // Loop through all legal moves
384 while ((move = mp.get_next_move()) != MOVE_NONE)
386 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
387 sum += perft(pos, depth - OnePly);
394 /// think() is the external interface to Stockfish's search, and is called when
395 /// the program receives the UCI 'go' command. It initializes various
396 /// search-related global variables, and calls root_search(). It returns false
397 /// when a quit command is received during the search.
399 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
400 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
402 // Initialize global search variables
403 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
404 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
406 TM.resetNodeCounters();
407 SearchStartTime = get_system_time();
408 ExactMaxTime = maxTime;
411 InfiniteSearch = infinite;
412 PonderSearch = ponder;
413 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
415 // Look for a book move, only during games, not tests
416 if (UseTimeManagement && get_option_value_bool("OwnBook"))
418 if (get_option_value_string("Book File") != OpeningBook.file_name())
419 OpeningBook.open(get_option_value_string("Book File"));
421 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
422 if (bookMove != MOVE_NONE)
425 wait_for_stop_or_ponderhit();
427 cout << "bestmove " << bookMove << endl;
432 // Read UCI option values
433 TT.set_size(get_option_value_int("Hash"));
434 if (button_was_pressed("Clear Hash"))
437 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
438 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
439 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
440 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
441 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
442 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
443 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
444 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
445 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
446 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
447 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
448 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
450 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
451 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
452 MultiPV = get_option_value_int("MultiPV");
453 Chess960 = get_option_value_bool("UCI_Chess960");
454 UseLogFile = get_option_value_bool("Use Search Log");
457 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
459 read_weights(pos.side_to_move());
461 // Set the number of active threads
462 int newActiveThreads = get_option_value_int("Threads");
463 if (newActiveThreads != TM.active_threads())
465 TM.set_active_threads(newActiveThreads);
466 init_eval(TM.active_threads());
469 // Wake up sleeping threads
470 TM.wake_sleeping_threads();
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
477 calc_search_times(myTime, myIncrement, movesToGo, pos.startpos_ply_counter(), MaxSearchTime, AbsoluteMaxSearchTime);
479 if (get_option_value_bool("Ponder"))
481 MaxSearchTime += MaxSearchTime / 4;
482 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
486 // Set best NodesBetweenPolls interval to avoid lagging under
487 // heavy time pressure.
489 NodesBetweenPolls = Min(MaxNodes, 30000);
490 else if (myTime && myTime < 1000)
491 NodesBetweenPolls = 1000;
492 else if (myTime && myTime < 5000)
493 NodesBetweenPolls = 5000;
495 NodesBetweenPolls = 30000;
497 // Write search information to log file
499 LogFile << "Searching: " << pos.to_fen() << endl
500 << "infinite: " << infinite
501 << " ponder: " << ponder
502 << " time: " << myTime
503 << " increment: " << myIncrement
504 << " moves to go: " << movesToGo << endl;
506 // We're ready to start thinking. Call the iterative deepening loop function
507 id_loop(pos, searchMoves);
512 TM.put_threads_to_sleep();
520 // id_loop() is the main iterative deepening loop. It calls root_search
521 // repeatedly with increasing depth until the allocated thinking time has
522 // been consumed, the user stops the search, or the maximum search depth is
525 Value id_loop(const Position& pos, Move searchMoves[]) {
527 Position p(pos, pos.thread());
528 SearchStack ss[PLY_MAX_PLUS_2];
529 Move pv[PLY_MAX_PLUS_2];
530 Move EasyMove = MOVE_NONE;
531 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
533 // Moves to search are verified, copied, scored and sorted
534 RootMoveList rml(p, searchMoves);
536 // Handle special case of searching on a mate/stale position
537 if (rml.move_count() == 0)
540 wait_for_stop_or_ponderhit();
542 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
545 // Print RootMoveList startup scoring to the standard output,
546 // so to output information also for iteration 1.
547 cout << "info depth " << 1
548 << "\ninfo depth " << 1
549 << " score " << value_to_uci(rml.get_move_score(0))
550 << " time " << current_search_time()
551 << " nodes " << TM.nodes_searched()
553 << " pv " << rml.get_move(0) << "\n";
558 init_ss_array(ss, PLY_MAX_PLUS_2);
559 pv[0] = pv[1] = MOVE_NONE;
560 ValueByIteration[1] = rml.get_move_score(0);
563 // Is one move significantly better than others after initial scoring ?
564 if ( rml.move_count() == 1
565 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
566 EasyMove = rml.get_move(0);
568 // Iterative deepening loop
569 while (Iteration < PLY_MAX)
571 // Initialize iteration
573 BestMoveChangesByIteration[Iteration] = 0;
575 cout << "info depth " << Iteration << endl;
577 // Calculate dynamic aspiration window based on previous iterations
578 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
580 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
581 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
583 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
584 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
586 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
587 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
590 // Search to the current depth, rml is updated and sorted, alpha and beta could change
591 value = root_search(p, ss, pv, rml, &alpha, &beta);
593 // Write PV to transposition table, in case the relevant entries have
594 // been overwritten during the search.
595 insert_pv_in_tt(p, pv);
598 break; // Value cannot be trusted. Break out immediately!
600 //Save info about search result
601 ValueByIteration[Iteration] = value;
603 // Drop the easy move if differs from the new best move
604 if (pv[0] != EasyMove)
605 EasyMove = MOVE_NONE;
607 if (UseTimeManagement)
610 bool stopSearch = false;
612 // Stop search early if there is only a single legal move,
613 // we search up to Iteration 6 anyway to get a proper score.
614 if (Iteration >= 6 && rml.move_count() == 1)
617 // Stop search early when the last two iterations returned a mate score
619 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
620 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
623 // Stop search early if one move seems to be much better than the others
624 int64_t nodes = TM.nodes_searched();
627 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
628 && current_search_time() > MaxSearchTime / 16)
629 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
630 && current_search_time() > MaxSearchTime / 32)))
633 // Add some extra time if the best move has changed during the last two iterations
634 if (Iteration > 5 && Iteration <= 50)
635 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
636 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
638 // Stop search if most of MaxSearchTime is consumed at the end of the
639 // iteration. We probably don't have enough time to search the first
640 // move at the next iteration anyway.
641 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
647 StopOnPonderhit = true;
653 if (MaxDepth && Iteration >= MaxDepth)
657 // If we are pondering or in infinite search, we shouldn't print the
658 // best move before we are told to do so.
659 if (!AbortSearch && (PonderSearch || InfiniteSearch))
660 wait_for_stop_or_ponderhit();
662 // Print final search statistics
663 cout << "info nodes " << TM.nodes_searched()
665 << " time " << current_search_time() << endl;
667 // Print the best move and the ponder move to the standard output
668 if (pv[0] == MOVE_NONE)
670 pv[0] = rml.get_move(0);
674 assert(pv[0] != MOVE_NONE);
676 cout << "bestmove " << pv[0];
678 if (pv[1] != MOVE_NONE)
679 cout << " ponder " << pv[1];
686 dbg_print_mean(LogFile);
688 if (dbg_show_hit_rate)
689 dbg_print_hit_rate(LogFile);
691 LogFile << "\nNodes: " << TM.nodes_searched()
692 << "\nNodes/second: " << nps()
693 << "\nBest move: " << move_to_san(p, pv[0]);
696 p.do_move(pv[0], st);
697 LogFile << "\nPonder move: "
698 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
701 return rml.get_move_score(0);
705 // root_search() is the function which searches the root node. It is
706 // similar to search_pv except that it uses a different move ordering
707 // scheme, prints some information to the standard output and handles
708 // the fail low/high loops.
710 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
717 Depth depth, ext, newDepth;
718 Value value, alpha, beta;
719 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
720 int researchCountFH, researchCountFL;
722 researchCountFH = researchCountFL = 0;
725 isCheck = pos.is_check();
727 // Step 1. Initialize node (polling is omitted at root)
728 ss->currentMove = ss->bestMove = MOVE_NONE;
730 // Step 2. Check for aborted search (omitted at root)
731 // Step 3. Mate distance pruning (omitted at root)
732 // Step 4. Transposition table lookup (omitted at root)
734 // Step 5. Evaluate the position statically
735 // At root we do this only to get reference value for child nodes
736 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
738 // Step 6. Razoring (omitted at root)
739 // Step 7. Static null move pruning (omitted at root)
740 // Step 8. Null move search with verification search (omitted at root)
741 // Step 9. Internal iterative deepening (omitted at root)
743 // Step extra. Fail low loop
744 // We start with small aspiration window and in case of fail low, we research
745 // with bigger window until we are not failing low anymore.
748 // Sort the moves before to (re)search
751 // Step 10. Loop through all moves in the root move list
752 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
754 // This is used by time management
755 FirstRootMove = (i == 0);
757 // Save the current node count before the move is searched
758 nodes = TM.nodes_searched();
760 // Reset beta cut-off counters
761 TM.resetBetaCounters();
763 // Pick the next root move, and print the move and the move number to
764 // the standard output.
765 move = ss->currentMove = rml.get_move(i);
767 if (current_search_time() >= 1000)
768 cout << "info currmove " << move
769 << " currmovenumber " << i + 1 << endl;
771 moveIsCheck = pos.move_is_check(move);
772 captureOrPromotion = pos.move_is_capture_or_promotion(move);
774 // Step 11. Decide the new search depth
775 depth = (Iteration - 2) * OnePly + InitialDepth;
776 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
777 newDepth = depth + ext;
779 // Step 12. Futility pruning (omitted at root)
781 // Step extra. Fail high loop
782 // If move fails high, we research with bigger window until we are not failing
784 value = - VALUE_INFINITE;
788 // Step 13. Make the move
789 pos.do_move(move, st, ci, moveIsCheck);
791 // Step extra. pv search
792 // We do pv search for first moves (i < MultiPV)
793 // and for fail high research (value > alpha)
794 if (i < MultiPV || value > alpha)
796 // Aspiration window is disabled in multi-pv case
798 alpha = -VALUE_INFINITE;
800 // Full depth PV search, done on first move or after a fail high
801 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
805 // Step 14. Reduced search
806 // if the move fails high will be re-searched at full depth
807 bool doFullDepthSearch = true;
809 if ( depth >= 3 * OnePly
811 && !captureOrPromotion
812 && !move_is_castle(move))
814 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
817 assert(newDepth-ss->reduction >= OnePly);
819 // Reduced depth non-pv search using alpha as upperbound
820 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
821 doFullDepthSearch = (value > alpha);
824 // The move failed high, but if reduction is very big we could
825 // face a false positive, retry with a less aggressive reduction,
826 // if the move fails high again then go with full depth search.
827 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
829 assert(newDepth - OnePly >= OnePly);
831 ss->reduction = OnePly;
832 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
833 doFullDepthSearch = (value > alpha);
835 ss->reduction = Depth(0); // Restore original reduction
838 // Step 15. Full depth search
839 if (doFullDepthSearch)
841 // Full depth non-pv search using alpha as upperbound
842 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
844 // If we are above alpha then research at same depth but as PV
845 // to get a correct score or eventually a fail high above beta.
847 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
851 // Step 16. Undo move
854 // Can we exit fail high loop ?
855 if (AbortSearch || value < beta)
858 // We are failing high and going to do a research. It's important to update
859 // the score before research in case we run out of time while researching.
860 rml.set_move_score(i, value);
862 extract_pv_from_tt(pos, move, pv);
863 rml.set_move_pv(i, pv);
865 // Print information to the standard output
866 print_pv_info(pos, pv, alpha, beta, value);
868 // Prepare for a research after a fail high, each time with a wider window
869 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
872 } // End of fail high loop
874 // Finished searching the move. If AbortSearch is true, the search
875 // was aborted because the user interrupted the search or because we
876 // ran out of time. In this case, the return value of the search cannot
877 // be trusted, and we break out of the loop without updating the best
882 // Remember beta-cutoff and searched nodes counts for this move. The
883 // info is used to sort the root moves for the next iteration.
885 TM.get_beta_counters(pos.side_to_move(), our, their);
886 rml.set_beta_counters(i, our, their);
887 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
889 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
890 assert(value < beta);
892 // Step 17. Check for new best move
893 if (value <= alpha && i >= MultiPV)
894 rml.set_move_score(i, -VALUE_INFINITE);
897 // PV move or new best move!
900 rml.set_move_score(i, value);
902 extract_pv_from_tt(pos, move, pv);
903 rml.set_move_pv(i, pv);
907 // We record how often the best move has been changed in each
908 // iteration. This information is used for time managment: When
909 // the best move changes frequently, we allocate some more time.
911 BestMoveChangesByIteration[Iteration]++;
913 // Print information to the standard output
914 print_pv_info(pos, pv, alpha, beta, value);
916 // Raise alpha to setup proper non-pv search upper bound
923 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
925 cout << "info multipv " << j + 1
926 << " score " << value_to_uci(rml.get_move_score(j))
927 << " depth " << (j <= i ? Iteration : Iteration - 1)
928 << " time " << current_search_time()
929 << " nodes " << TM.nodes_searched()
933 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
934 cout << rml.get_move_pv(j, k) << " ";
938 alpha = rml.get_move_score(Min(i, MultiPV - 1));
940 } // PV move or new best move
942 assert(alpha >= *alphaPtr);
944 AspirationFailLow = (alpha == *alphaPtr);
946 if (AspirationFailLow && StopOnPonderhit)
947 StopOnPonderhit = false;
950 // Can we exit fail low loop ?
951 if (AbortSearch || !AspirationFailLow)
954 // Prepare for a research after a fail low, each time with a wider window
955 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
960 // Sort the moves before to return
967 // search<>() is the main search function for both PV and non-PV nodes
969 template <NodeType PvNode>
970 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
972 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
973 assert(beta > alpha && beta <= VALUE_INFINITE);
974 assert(PvNode || alpha == beta - 1);
975 assert(ply > 0 && ply < PLY_MAX);
976 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
978 Move movesSearched[256];
983 Move ttMove, move, excludedMove, threatMove;
985 Value bestValue, value, oldAlpha;
986 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
987 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
988 bool mateThreat = false;
990 int threadID = pos.thread();
991 refinedValue = bestValue = value = -VALUE_INFINITE;
994 // Step 1. Initialize node and poll. Polling can abort search
995 TM.incrementNodeCounter(threadID);
996 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
997 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
999 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1005 // Step 2. Check for aborted search and immediate draw
1006 if (AbortSearch || TM.thread_should_stop(threadID))
1009 if (pos.is_draw() || ply >= PLY_MAX - 1)
1012 // Step 3. Mate distance pruning
1013 alpha = Max(value_mated_in(ply), alpha);
1014 beta = Min(value_mate_in(ply+1), beta);
1018 // Step 4. Transposition table lookup
1020 // We don't want the score of a partial search to overwrite a previous full search
1021 // TT value, so we use a different position key in case of an excluded move exists.
1022 excludedMove = ss->excludedMove;
1023 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1025 tte = TT.retrieve(posKey);
1026 ttMove = (tte ? tte->move() : MOVE_NONE);
1028 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1029 // This is to avoid problems in the following areas:
1031 // * Repetition draw detection
1032 // * Fifty move rule detection
1033 // * Searching for a mate
1034 // * Printing of full PV line
1036 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1038 // Refresh tte entry to avoid aging
1039 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1041 ss->bestMove = ttMove; // Can be MOVE_NONE
1042 return value_from_tt(tte->value(), ply);
1045 // Step 5. Evaluate the position statically
1046 // At PV nodes we do this only to update gain statistics
1047 isCheck = pos.is_check();
1052 assert(tte->static_value() != VALUE_NONE);
1053 ss->eval = tte->static_value();
1054 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1058 ss->eval = evaluate(pos, ei);
1059 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1062 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1063 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1066 ss->eval = VALUE_NONE;
1068 // Step 6. Razoring (is omitted in PV nodes)
1070 && depth < RazorDepth
1072 && refinedValue < beta - razor_margin(depth)
1073 && ttMove == MOVE_NONE
1074 && (ss-1)->currentMove != MOVE_NULL
1075 && !value_is_mate(beta)
1076 && !pos.has_pawn_on_7th(pos.side_to_move()))
1078 Value rbeta = beta - razor_margin(depth);
1079 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1081 // Logically we should return (v + razor_margin(depth)), but
1082 // surprisingly this did slightly weaker in tests.
1086 // Step 7. Static null move pruning (is omitted in PV nodes)
1087 // We're betting that the opponent doesn't have a move that will reduce
1088 // the score by more than futility_margin(depth) if we do a null move.
1090 && !ss->skipNullMove
1091 && depth < RazorDepth
1092 && refinedValue >= beta + futility_margin(depth, 0)
1094 && !value_is_mate(beta)
1095 && pos.non_pawn_material(pos.side_to_move()))
1096 return refinedValue - futility_margin(depth, 0);
1098 // Step 8. Null move search with verification search (is omitted in PV nodes)
1099 // When we jump directly to qsearch() we do a null move only if static value is
1100 // at least beta. Otherwise we do a null move if static value is not more than
1101 // NullMoveMargin under beta.
1103 && !ss->skipNullMove
1105 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1107 && !value_is_mate(beta)
1108 && pos.non_pawn_material(pos.side_to_move()))
1110 ss->currentMove = MOVE_NULL;
1112 // Null move dynamic reduction based on depth
1113 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1115 // Null move dynamic reduction based on value
1116 if (refinedValue - beta > PawnValueMidgame)
1119 pos.do_null_move(st);
1120 (ss+1)->skipNullMove = true;
1122 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1123 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1124 (ss+1)->skipNullMove = false;
1125 pos.undo_null_move();
1127 if (nullValue >= beta)
1129 // Do not return unproven mate scores
1130 if (nullValue >= value_mate_in(PLY_MAX))
1133 if (depth < 6 * OnePly)
1136 // Do verification search at high depths
1137 ss->skipNullMove = true;
1138 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1139 ss->skipNullMove = false;
1146 // The null move failed low, which means that we may be faced with
1147 // some kind of threat. If the previous move was reduced, check if
1148 // the move that refuted the null move was somehow connected to the
1149 // move which was reduced. If a connection is found, return a fail
1150 // low score (which will cause the reduced move to fail high in the
1151 // parent node, which will trigger a re-search with full depth).
1152 if (nullValue == value_mated_in(ply + 2))
1155 threatMove = (ss+1)->bestMove;
1156 if ( depth < ThreatDepth
1157 && (ss-1)->reduction
1158 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1163 // Step 9. Internal iterative deepening
1164 if ( depth >= IIDDepth[PvNode]
1165 && ttMove == MOVE_NONE
1166 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1168 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1170 ss->skipNullMove = true;
1171 search<PvNode>(pos, ss, alpha, beta, d, ply);
1172 ss->skipNullMove = false;
1174 ttMove = ss->bestMove;
1175 tte = TT.retrieve(posKey);
1178 // Expensive mate threat detection (only for PV nodes)
1180 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1182 // Initialize a MovePicker object for the current position
1183 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1185 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1186 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1187 && tte && tte->move()
1188 && !excludedMove // Do not allow recursive singular extension search
1189 && is_lower_bound(tte->type())
1190 && tte->depth() >= depth - 3 * OnePly;
1192 // Avoid to do an expensive singular extension search on nodes where
1193 // such search had already failed in the past.
1195 && singularExtensionNode
1196 && depth < SingularExtensionDepth[PvNode] + 5 * OnePly)
1198 TTEntry* ttx = TT.retrieve(pos.get_exclusion_key());
1199 if (ttx && is_lower_bound(ttx->type()))
1200 singularExtensionNode = false;
1203 // Step 10. Loop through moves
1204 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1205 while ( bestValue < beta
1206 && (move = mp.get_next_move()) != MOVE_NONE
1207 && !TM.thread_should_stop(threadID))
1209 assert(move_is_ok(move));
1211 if (move == excludedMove)
1214 moveIsCheck = pos.move_is_check(move, ci);
1215 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1217 // Step 11. Decide the new search depth
1218 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1220 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1221 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1222 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1223 // lower then ttValue minus a margin then we extend ttMove.
1224 if ( singularExtensionNode
1225 && move == tte->move()
1228 Value ttValue = value_from_tt(tte->value(), ply);
1230 if (abs(ttValue) < VALUE_KNOWN_WIN)
1232 Value b = ttValue - SingularExtensionMargin;
1233 ss->excludedMove = move;
1234 ss->skipNullMove = true;
1235 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1236 ss->skipNullMove = false;
1237 ss->excludedMove = MOVE_NONE;
1243 newDepth = depth - OnePly + ext;
1245 // Update current move (this must be done after singular extension search)
1246 movesSearched[moveCount++] = ss->currentMove = move;
1248 // Step 12. Futility pruning (is omitted in PV nodes)
1250 && !captureOrPromotion
1254 && !move_is_castle(move))
1256 // Move count based pruning
1257 if ( moveCount >= futility_move_count(depth)
1258 && !(threatMove && connected_threat(pos, move, threatMove))
1259 && bestValue > value_mated_in(PLY_MAX))
1262 // Value based pruning
1263 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1264 // but fixing this made program slightly weaker.
1265 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1266 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1267 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1269 if (futilityValueScaled < beta)
1271 if (futilityValueScaled > bestValue)
1272 bestValue = futilityValueScaled;
1277 // Step 13. Make the move
1278 pos.do_move(move, st, ci, moveIsCheck);
1280 // Step extra. pv search (only in PV nodes)
1281 // The first move in list is the expected PV
1282 if (PvNode && moveCount == 1)
1283 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1284 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1287 // Step 14. Reduced depth search
1288 // If the move fails high will be re-searched at full depth.
1289 bool doFullDepthSearch = true;
1291 if ( depth >= 3 * OnePly
1292 && !captureOrPromotion
1294 && !move_is_castle(move)
1295 && !move_is_killer(move, ss))
1297 ss->reduction = reduction<PvNode>(depth, moveCount);
1300 Depth d = newDepth - ss->reduction;
1301 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1302 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1304 doFullDepthSearch = (value > alpha);
1307 // The move failed high, but if reduction is very big we could
1308 // face a false positive, retry with a less aggressive reduction,
1309 // if the move fails high again then go with full depth search.
1310 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1312 assert(newDepth - OnePly >= OnePly);
1314 ss->reduction = OnePly;
1315 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1316 doFullDepthSearch = (value > alpha);
1318 ss->reduction = Depth(0); // Restore original reduction
1321 // Step 15. Full depth search
1322 if (doFullDepthSearch)
1324 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1325 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1327 // Step extra. pv search (only in PV nodes)
1328 // Search only for possible new PV nodes, if instead value >= beta then
1329 // parent node fails low with value <= alpha and tries another move.
1330 if (PvNode && value > alpha && value < beta)
1331 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1332 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1336 // Step 16. Undo move
1337 pos.undo_move(move);
1339 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1341 // Step 17. Check for new best move
1342 if (value > bestValue)
1347 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1350 if (value == value_mate_in(ply + 1))
1351 ss->mateKiller = move;
1353 ss->bestMove = move;
1357 // Step 18. Check for split
1358 if ( depth >= MinimumSplitDepth
1359 && TM.active_threads() > 1
1361 && TM.available_thread_exists(threadID)
1363 && !TM.thread_should_stop(threadID)
1365 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1366 threatMove, mateThreat, &moveCount, &mp, PvNode);
1369 // Step 19. Check for mate and stalemate
1370 // All legal moves have been searched and if there are
1371 // no legal moves, it must be mate or stalemate.
1372 // If one move was excluded return fail low score.
1374 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1376 // Step 20. Update tables
1377 // If the search is not aborted, update the transposition table,
1378 // history counters, and killer moves.
1379 if (AbortSearch || TM.thread_should_stop(threadID))
1382 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1383 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1384 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1386 // Update killers and history only for non capture moves that fails high
1387 if (bestValue >= beta)
1389 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1390 if (!pos.move_is_capture_or_promotion(move))
1392 update_history(pos, move, depth, movesSearched, moveCount);
1393 update_killers(move, ss);
1397 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1403 // qsearch() is the quiescence search function, which is called by the main
1404 // search function when the remaining depth is zero (or, to be more precise,
1405 // less than OnePly).
1407 template <NodeType PvNode>
1408 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1410 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1411 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1412 assert(PvNode || alpha == beta - 1);
1414 assert(ply > 0 && ply < PLY_MAX);
1415 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1420 Value bestValue, value, futilityValue, futilityBase;
1421 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1423 Value oldAlpha = alpha;
1425 TM.incrementNodeCounter(pos.thread());
1426 ss->bestMove = ss->currentMove = MOVE_NONE;
1428 // Check for an instant draw or maximum ply reached
1429 if (pos.is_draw() || ply >= PLY_MAX - 1)
1432 // Transposition table lookup. At PV nodes, we don't use the TT for
1433 // pruning, but only for move ordering.
1434 tte = TT.retrieve(pos.get_key());
1435 ttMove = (tte ? tte->move() : MOVE_NONE);
1437 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1439 ss->bestMove = ttMove; // Can be MOVE_NONE
1440 return value_from_tt(tte->value(), ply);
1443 isCheck = pos.is_check();
1445 // Evaluate the position statically
1448 bestValue = futilityBase = -VALUE_INFINITE;
1449 ss->eval = VALUE_NONE;
1450 deepChecks = enoughMaterial = false;
1456 assert(tte->static_value() != VALUE_NONE);
1457 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1458 bestValue = tte->static_value();
1461 bestValue = evaluate(pos, ei);
1463 ss->eval = bestValue;
1464 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1466 // Stand pat. Return immediately if static value is at least beta
1467 if (bestValue >= beta)
1470 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1475 if (PvNode && bestValue > alpha)
1478 // If we are near beta then try to get a cutoff pushing checks a bit further
1479 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1481 // Futility pruning parameters, not needed when in check
1482 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1483 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1486 // Initialize a MovePicker object for the current position, and prepare
1487 // to search the moves. Because the depth is <= 0 here, only captures,
1488 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1489 // and we are near beta) will be generated.
1490 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1493 // Loop through the moves until no moves remain or a beta cutoff occurs
1494 while ( alpha < beta
1495 && (move = mp.get_next_move()) != MOVE_NONE)
1497 assert(move_is_ok(move));
1499 moveIsCheck = pos.move_is_check(move, ci);
1507 && !move_is_promotion(move)
1508 && !pos.move_is_passed_pawn_push(move))
1510 futilityValue = futilityBase
1511 + pos.endgame_value_of_piece_on(move_to(move))
1512 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1514 if (futilityValue < alpha)
1516 if (futilityValue > bestValue)
1517 bestValue = futilityValue;
1522 // Detect blocking evasions that are candidate to be pruned
1523 evasionPrunable = isCheck
1524 && bestValue > value_mated_in(PLY_MAX)
1525 && !pos.move_is_capture(move)
1526 && pos.type_of_piece_on(move_from(move)) != KING
1527 && !pos.can_castle(pos.side_to_move());
1529 // Don't search moves with negative SEE values
1531 && (!isCheck || evasionPrunable)
1533 && !move_is_promotion(move)
1534 && pos.see_sign(move) < 0)
1537 // Update current move
1538 ss->currentMove = move;
1540 // Make and search the move
1541 pos.do_move(move, st, ci, moveIsCheck);
1542 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1543 pos.undo_move(move);
1545 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1548 if (value > bestValue)
1554 ss->bestMove = move;
1559 // All legal moves have been searched. A special case: If we're in check
1560 // and no legal moves were found, it is checkmate.
1561 if (isCheck && bestValue == -VALUE_INFINITE)
1562 return value_mated_in(ply);
1564 // Update transposition table
1565 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1566 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1567 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1569 // Update killers only for checking moves that fails high
1570 if ( bestValue >= beta
1571 && !pos.move_is_capture_or_promotion(ss->bestMove))
1572 update_killers(ss->bestMove, ss);
1574 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1580 // sp_search() is used to search from a split point. This function is called
1581 // by each thread working at the split point. It is similar to the normal
1582 // search() function, but simpler. Because we have already probed the hash
1583 // table, done a null move search, and searched the first move before
1584 // splitting, we don't have to repeat all this work in sp_search(). We
1585 // also don't need to store anything to the hash table here: This is taken
1586 // care of after we return from the split point.
1588 template <NodeType PvNode>
1589 void sp_search(SplitPoint* sp, int threadID) {
1591 assert(threadID >= 0 && threadID < TM.active_threads());
1592 assert(TM.active_threads() > 1);
1596 Depth ext, newDepth;
1598 Value futilityValueScaled; // NonPV specific
1599 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1601 value = -VALUE_INFINITE;
1603 Position pos(*sp->pos, threadID);
1605 SearchStack* ss = sp->sstack[threadID] + 1;
1606 isCheck = pos.is_check();
1608 // Step 10. Loop through moves
1609 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1610 lock_grab(&(sp->lock));
1612 while ( sp->bestValue < sp->beta
1613 && (move = sp->mp->get_next_move()) != MOVE_NONE
1614 && !TM.thread_should_stop(threadID))
1616 moveCount = ++sp->moveCount;
1617 lock_release(&(sp->lock));
1619 assert(move_is_ok(move));
1621 moveIsCheck = pos.move_is_check(move, ci);
1622 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1624 // Step 11. Decide the new search depth
1625 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1626 newDepth = sp->depth - OnePly + ext;
1628 // Update current move
1629 ss->currentMove = move;
1631 // Step 12. Futility pruning (is omitted in PV nodes)
1633 && !captureOrPromotion
1636 && !move_is_castle(move))
1638 // Move count based pruning
1639 if ( moveCount >= futility_move_count(sp->depth)
1640 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1641 && sp->bestValue > value_mated_in(PLY_MAX))
1643 lock_grab(&(sp->lock));
1647 // Value based pruning
1648 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1649 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1650 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1652 if (futilityValueScaled < sp->beta)
1654 lock_grab(&(sp->lock));
1656 if (futilityValueScaled > sp->bestValue)
1657 sp->bestValue = futilityValueScaled;
1662 // Step 13. Make the move
1663 pos.do_move(move, st, ci, moveIsCheck);
1665 // Step 14. Reduced search
1666 // If the move fails high will be re-searched at full depth.
1667 bool doFullDepthSearch = true;
1669 if ( !captureOrPromotion
1671 && !move_is_castle(move)
1672 && !move_is_killer(move, ss))
1674 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1677 Value localAlpha = sp->alpha;
1678 Depth d = newDepth - ss->reduction;
1679 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1680 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1682 doFullDepthSearch = (value > localAlpha);
1685 // The move failed high, but if reduction is very big we could
1686 // face a false positive, retry with a less aggressive reduction,
1687 // if the move fails high again then go with full depth search.
1688 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1690 assert(newDepth - OnePly >= OnePly);
1692 ss->reduction = OnePly;
1693 Value localAlpha = sp->alpha;
1694 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1695 doFullDepthSearch = (value > localAlpha);
1697 ss->reduction = Depth(0); // Restore original reduction
1700 // Step 15. Full depth search
1701 if (doFullDepthSearch)
1703 Value localAlpha = sp->alpha;
1704 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1705 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1707 // Step extra. pv search (only in PV nodes)
1708 // Search only for possible new PV nodes, if instead value >= beta then
1709 // parent node fails low with value <= alpha and tries another move.
1710 if (PvNode && value > localAlpha && value < sp->beta)
1711 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1712 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1715 // Step 16. Undo move
1716 pos.undo_move(move);
1718 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1720 // Step 17. Check for new best move
1721 lock_grab(&(sp->lock));
1723 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1725 sp->bestValue = value;
1727 if (sp->bestValue > sp->alpha)
1729 if (!PvNode || value >= sp->beta)
1730 sp->stopRequest = true;
1732 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1735 sp->parentSstack->bestMove = ss->bestMove = move;
1740 /* Here we have the lock still grabbed */
1742 sp->slaves[threadID] = 0;
1744 lock_release(&(sp->lock));
1748 // connected_moves() tests whether two moves are 'connected' in the sense
1749 // that the first move somehow made the second move possible (for instance
1750 // if the moving piece is the same in both moves). The first move is assumed
1751 // to be the move that was made to reach the current position, while the
1752 // second move is assumed to be a move from the current position.
1754 bool connected_moves(const Position& pos, Move m1, Move m2) {
1756 Square f1, t1, f2, t2;
1759 assert(move_is_ok(m1));
1760 assert(move_is_ok(m2));
1762 if (m2 == MOVE_NONE)
1765 // Case 1: The moving piece is the same in both moves
1771 // Case 2: The destination square for m2 was vacated by m1
1777 // Case 3: Moving through the vacated square
1778 if ( piece_is_slider(pos.piece_on(f2))
1779 && bit_is_set(squares_between(f2, t2), f1))
1782 // Case 4: The destination square for m2 is defended by the moving piece in m1
1783 p = pos.piece_on(t1);
1784 if (bit_is_set(pos.attacks_from(p, t1), t2))
1787 // Case 5: Discovered check, checking piece is the piece moved in m1
1788 if ( piece_is_slider(p)
1789 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1790 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1792 // discovered_check_candidates() works also if the Position's side to
1793 // move is the opposite of the checking piece.
1794 Color them = opposite_color(pos.side_to_move());
1795 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1797 if (bit_is_set(dcCandidates, f2))
1804 // value_is_mate() checks if the given value is a mate one eventually
1805 // compensated for the ply.
1807 bool value_is_mate(Value value) {
1809 assert(abs(value) <= VALUE_INFINITE);
1811 return value <= value_mated_in(PLY_MAX)
1812 || value >= value_mate_in(PLY_MAX);
1816 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1817 // "plies to mate from the current ply". Non-mate scores are unchanged.
1818 // The function is called before storing a value to the transposition table.
1820 Value value_to_tt(Value v, int ply) {
1822 if (v >= value_mate_in(PLY_MAX))
1825 if (v <= value_mated_in(PLY_MAX))
1832 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1833 // the transposition table to a mate score corrected for the current ply.
1835 Value value_from_tt(Value v, int ply) {
1837 if (v >= value_mate_in(PLY_MAX))
1840 if (v <= value_mated_in(PLY_MAX))
1847 // move_is_killer() checks if the given move is among the killer moves
1849 bool move_is_killer(Move m, SearchStack* ss) {
1851 if (ss->killers[0] == m || ss->killers[1] == m)
1858 // extension() decides whether a move should be searched with normal depth,
1859 // or with extended depth. Certain classes of moves (checking moves, in
1860 // particular) are searched with bigger depth than ordinary moves and in
1861 // any case are marked as 'dangerous'. Note that also if a move is not
1862 // extended, as example because the corresponding UCI option is set to zero,
1863 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1864 template <NodeType PvNode>
1865 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1866 bool singleEvasion, bool mateThreat, bool* dangerous) {
1868 assert(m != MOVE_NONE);
1870 Depth result = Depth(0);
1871 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1875 if (moveIsCheck && pos.see_sign(m) >= 0)
1876 result += CheckExtension[PvNode];
1879 result += SingleEvasionExtension[PvNode];
1882 result += MateThreatExtension[PvNode];
1885 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1887 Color c = pos.side_to_move();
1888 if (relative_rank(c, move_to(m)) == RANK_7)
1890 result += PawnPushTo7thExtension[PvNode];
1893 if (pos.pawn_is_passed(c, move_to(m)))
1895 result += PassedPawnExtension[PvNode];
1900 if ( captureOrPromotion
1901 && pos.type_of_piece_on(move_to(m)) != PAWN
1902 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1903 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1904 && !move_is_promotion(m)
1907 result += PawnEndgameExtension[PvNode];
1912 && captureOrPromotion
1913 && pos.type_of_piece_on(move_to(m)) != PAWN
1914 && pos.see_sign(m) >= 0)
1920 return Min(result, OnePly);
1924 // connected_threat() tests whether it is safe to forward prune a move or if
1925 // is somehow coonected to the threat move returned by null search.
1927 bool connected_threat(const Position& pos, Move m, Move threat) {
1929 assert(move_is_ok(m));
1930 assert(threat && move_is_ok(threat));
1931 assert(!pos.move_is_check(m));
1932 assert(!pos.move_is_capture_or_promotion(m));
1933 assert(!pos.move_is_passed_pawn_push(m));
1935 Square mfrom, mto, tfrom, tto;
1937 mfrom = move_from(m);
1939 tfrom = move_from(threat);
1940 tto = move_to(threat);
1942 // Case 1: Don't prune moves which move the threatened piece
1946 // Case 2: If the threatened piece has value less than or equal to the
1947 // value of the threatening piece, don't prune move which defend it.
1948 if ( pos.move_is_capture(threat)
1949 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1950 || pos.type_of_piece_on(tfrom) == KING)
1951 && pos.move_attacks_square(m, tto))
1954 // Case 3: If the moving piece in the threatened move is a slider, don't
1955 // prune safe moves which block its ray.
1956 if ( piece_is_slider(pos.piece_on(tfrom))
1957 && bit_is_set(squares_between(tfrom, tto), mto)
1958 && pos.see_sign(m) >= 0)
1965 // ok_to_use_TT() returns true if a transposition table score
1966 // can be used at a given point in search.
1968 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1970 Value v = value_from_tt(tte->value(), ply);
1972 return ( tte->depth() >= depth
1973 || v >= Max(value_mate_in(PLY_MAX), beta)
1974 || v < Min(value_mated_in(PLY_MAX), beta))
1976 && ( (is_lower_bound(tte->type()) && v >= beta)
1977 || (is_upper_bound(tte->type()) && v < beta));
1981 // refine_eval() returns the transposition table score if
1982 // possible otherwise falls back on static position evaluation.
1984 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1989 Value v = value_from_tt(tte->value(), ply);
1991 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1992 || (is_upper_bound(tte->type()) && v < defaultEval))
1999 // update_history() registers a good move that produced a beta-cutoff
2000 // in history and marks as failures all the other moves of that ply.
2002 void update_history(const Position& pos, Move move, Depth depth,
2003 Move movesSearched[], int moveCount) {
2007 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2009 for (int i = 0; i < moveCount - 1; i++)
2011 m = movesSearched[i];
2015 if (!pos.move_is_capture_or_promotion(m))
2016 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2021 // update_killers() add a good move that produced a beta-cutoff
2022 // among the killer moves of that ply.
2024 void update_killers(Move m, SearchStack* ss) {
2026 if (m == ss->killers[0])
2029 ss->killers[1] = ss->killers[0];
2034 // update_gains() updates the gains table of a non-capture move given
2035 // the static position evaluation before and after the move.
2037 void update_gains(const Position& pos, Move m, Value before, Value after) {
2040 && before != VALUE_NONE
2041 && after != VALUE_NONE
2042 && pos.captured_piece() == NO_PIECE_TYPE
2043 && !move_is_castle(m)
2044 && !move_is_promotion(m))
2045 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2049 // current_search_time() returns the number of milliseconds which have passed
2050 // since the beginning of the current search.
2052 int current_search_time() {
2054 return get_system_time() - SearchStartTime;
2058 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2060 std::string value_to_uci(Value v) {
2062 std::stringstream s;
2064 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2065 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2067 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2072 // nps() computes the current nodes/second count.
2076 int t = current_search_time();
2077 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2081 // poll() performs two different functions: It polls for user input, and it
2082 // looks at the time consumed so far and decides if it's time to abort the
2087 static int lastInfoTime;
2088 int t = current_search_time();
2093 // We are line oriented, don't read single chars
2094 std::string command;
2096 if (!std::getline(std::cin, command))
2099 if (command == "quit")
2102 PonderSearch = false;
2106 else if (command == "stop")
2109 PonderSearch = false;
2111 else if (command == "ponderhit")
2115 // Print search information
2119 else if (lastInfoTime > t)
2120 // HACK: Must be a new search where we searched less than
2121 // NodesBetweenPolls nodes during the first second of search.
2124 else if (t - lastInfoTime >= 1000)
2131 if (dbg_show_hit_rate)
2132 dbg_print_hit_rate();
2134 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2135 << " time " << t << endl;
2138 // Should we stop the search?
2142 bool stillAtFirstMove = FirstRootMove
2143 && !AspirationFailLow
2144 && t > MaxSearchTime + ExtraSearchTime;
2146 bool noMoreTime = t > AbsoluteMaxSearchTime
2147 || stillAtFirstMove;
2149 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2150 || (ExactMaxTime && t >= ExactMaxTime)
2151 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2156 // ponderhit() is called when the program is pondering (i.e. thinking while
2157 // it's the opponent's turn to move) in order to let the engine know that
2158 // it correctly predicted the opponent's move.
2162 int t = current_search_time();
2163 PonderSearch = false;
2165 bool stillAtFirstMove = FirstRootMove
2166 && !AspirationFailLow
2167 && t > MaxSearchTime + ExtraSearchTime;
2169 bool noMoreTime = t > AbsoluteMaxSearchTime
2170 || stillAtFirstMove;
2172 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2177 // init_ss_array() does a fast reset of the first entries of a SearchStack
2178 // array and of all the excludedMove and skipNullMove entries.
2180 void init_ss_array(SearchStack* ss, int size) {
2182 for (int i = 0; i < size; i++, ss++)
2184 ss->excludedMove = MOVE_NONE;
2185 ss->skipNullMove = false;
2186 ss->reduction = Depth(0);
2189 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2194 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2195 // while the program is pondering. The point is to work around a wrinkle in
2196 // the UCI protocol: When pondering, the engine is not allowed to give a
2197 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2198 // We simply wait here until one of these commands is sent, and return,
2199 // after which the bestmove and pondermove will be printed (in id_loop()).
2201 void wait_for_stop_or_ponderhit() {
2203 std::string command;
2207 if (!std::getline(std::cin, command))
2210 if (command == "quit")
2215 else if (command == "ponderhit" || command == "stop")
2221 // print_pv_info() prints to standard output and eventually to log file information on
2222 // the current PV line. It is called at each iteration or after a new pv is found.
2224 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2226 cout << "info depth " << Iteration
2227 << " score " << value_to_uci(value)
2228 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2229 << " time " << current_search_time()
2230 << " nodes " << TM.nodes_searched()
2234 for (Move* m = pv; *m != MOVE_NONE; m++)
2241 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2242 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2244 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2245 TM.nodes_searched(), value, t, pv) << endl;
2250 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2251 // the PV back into the TT. This makes sure the old PV moves are searched
2252 // first, even if the old TT entries have been overwritten.
2254 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2258 Position p(pos, pos.thread());
2262 for (int i = 0; pv[i] != MOVE_NONE; i++)
2264 tte = TT.retrieve(p.get_key());
2265 if (!tte || tte->move() != pv[i])
2267 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2268 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2270 p.do_move(pv[i], st);
2275 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2276 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2277 // allow to always have a ponder move even when we fail high at root and also a
2278 // long PV to print that is important for position analysis.
2280 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2284 Position p(pos, pos.thread());
2287 assert(bestMove != MOVE_NONE);
2290 p.do_move(pv[ply++], st);
2292 while ( (tte = TT.retrieve(p.get_key())) != NULL
2293 && tte->move() != MOVE_NONE
2294 && move_is_legal(p, tte->move())
2296 && (!p.is_draw() || ply < 2))
2298 pv[ply] = tte->move();
2299 p.do_move(pv[ply++], st);
2301 pv[ply] = MOVE_NONE;
2305 // init_thread() is the function which is called when a new thread is
2306 // launched. It simply calls the idle_loop() function with the supplied
2307 // threadID. There are two versions of this function; one for POSIX
2308 // threads and one for Windows threads.
2310 #if !defined(_MSC_VER)
2312 void* init_thread(void *threadID) {
2314 TM.idle_loop(*(int*)threadID, NULL);
2320 DWORD WINAPI init_thread(LPVOID threadID) {
2322 TM.idle_loop(*(int*)threadID, NULL);
2329 /// The ThreadsManager class
2331 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2332 // get_beta_counters() are getters/setters for the per thread
2333 // counters used to sort the moves at root.
2335 void ThreadsManager::resetNodeCounters() {
2337 for (int i = 0; i < MAX_THREADS; i++)
2338 threads[i].nodes = 0ULL;
2341 void ThreadsManager::resetBetaCounters() {
2343 for (int i = 0; i < MAX_THREADS; i++)
2344 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2347 int64_t ThreadsManager::nodes_searched() const {
2349 int64_t result = 0ULL;
2350 for (int i = 0; i < ActiveThreads; i++)
2351 result += threads[i].nodes;
2356 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2359 for (int i = 0; i < MAX_THREADS; i++)
2361 our += threads[i].betaCutOffs[us];
2362 their += threads[i].betaCutOffs[opposite_color(us)];
2367 // idle_loop() is where the threads are parked when they have no work to do.
2368 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2369 // object for which the current thread is the master.
2371 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2373 assert(threadID >= 0 && threadID < MAX_THREADS);
2377 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2378 // master should exit as last one.
2379 if (AllThreadsShouldExit)
2382 threads[threadID].state = THREAD_TERMINATED;
2386 // If we are not thinking, wait for a condition to be signaled
2387 // instead of wasting CPU time polling for work.
2388 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2391 assert(threadID != 0);
2392 threads[threadID].state = THREAD_SLEEPING;
2394 #if !defined(_MSC_VER)
2395 lock_grab(&WaitLock);
2396 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2397 pthread_cond_wait(&WaitCond, &WaitLock);
2398 lock_release(&WaitLock);
2400 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2404 // If thread has just woken up, mark it as available
2405 if (threads[threadID].state == THREAD_SLEEPING)
2406 threads[threadID].state = THREAD_AVAILABLE;
2408 // If this thread has been assigned work, launch a search
2409 if (threads[threadID].state == THREAD_WORKISWAITING)
2411 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2413 threads[threadID].state = THREAD_SEARCHING;
2415 if (threads[threadID].splitPoint->pvNode)
2416 sp_search<PV>(threads[threadID].splitPoint, threadID);
2418 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2420 assert(threads[threadID].state == THREAD_SEARCHING);
2422 threads[threadID].state = THREAD_AVAILABLE;
2425 // If this thread is the master of a split point and all slaves have
2426 // finished their work at this split point, return from the idle loop.
2428 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2430 if (i == ActiveThreads)
2432 // Because sp->slaves[] is reset under lock protection,
2433 // be sure sp->lock has been released before to return.
2434 lock_grab(&(sp->lock));
2435 lock_release(&(sp->lock));
2437 assert(threads[threadID].state == THREAD_AVAILABLE);
2439 threads[threadID].state = THREAD_SEARCHING;
2446 // init_threads() is called during startup. It launches all helper threads,
2447 // and initializes the split point stack and the global locks and condition
2450 void ThreadsManager::init_threads() {
2455 #if !defined(_MSC_VER)
2456 pthread_t pthread[1];
2459 // Initialize global locks
2461 lock_init(&WaitLock);
2463 #if !defined(_MSC_VER)
2464 pthread_cond_init(&WaitCond, NULL);
2466 for (i = 0; i < MAX_THREADS; i++)
2467 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2470 // Initialize splitPoints[] locks
2471 for (i = 0; i < MAX_THREADS; i++)
2472 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2473 lock_init(&(threads[i].splitPoints[j].lock));
2475 // Will be set just before program exits to properly end the threads
2476 AllThreadsShouldExit = false;
2478 // Threads will be put to sleep as soon as created
2479 AllThreadsShouldSleep = true;
2481 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2483 threads[0].state = THREAD_SEARCHING;
2484 for (i = 1; i < MAX_THREADS; i++)
2485 threads[i].state = THREAD_AVAILABLE;
2487 // Launch the helper threads
2488 for (i = 1; i < MAX_THREADS; i++)
2491 #if !defined(_MSC_VER)
2492 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2494 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2499 cout << "Failed to create thread number " << i << endl;
2500 Application::exit_with_failure();
2503 // Wait until the thread has finished launching and is gone to sleep
2504 while (threads[i].state != THREAD_SLEEPING) {}
2509 // exit_threads() is called when the program exits. It makes all the
2510 // helper threads exit cleanly.
2512 void ThreadsManager::exit_threads() {
2514 ActiveThreads = MAX_THREADS; // HACK
2515 AllThreadsShouldSleep = true; // HACK
2516 wake_sleeping_threads();
2518 // This makes the threads to exit idle_loop()
2519 AllThreadsShouldExit = true;
2521 // Wait for thread termination
2522 for (int i = 1; i < MAX_THREADS; i++)
2523 while (threads[i].state != THREAD_TERMINATED) {}
2525 // Now we can safely destroy the locks
2526 for (int i = 0; i < MAX_THREADS; i++)
2527 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2528 lock_destroy(&(threads[i].splitPoints[j].lock));
2530 lock_destroy(&WaitLock);
2531 lock_destroy(&MPLock);
2535 // thread_should_stop() checks whether the thread should stop its search.
2536 // This can happen if a beta cutoff has occurred in the thread's currently
2537 // active split point, or in some ancestor of the current split point.
2539 bool ThreadsManager::thread_should_stop(int threadID) const {
2541 assert(threadID >= 0 && threadID < ActiveThreads);
2545 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2550 // thread_is_available() checks whether the thread with threadID "slave" is
2551 // available to help the thread with threadID "master" at a split point. An
2552 // obvious requirement is that "slave" must be idle. With more than two
2553 // threads, this is not by itself sufficient: If "slave" is the master of
2554 // some active split point, it is only available as a slave to the other
2555 // threads which are busy searching the split point at the top of "slave"'s
2556 // split point stack (the "helpful master concept" in YBWC terminology).
2558 bool ThreadsManager::thread_is_available(int slave, int master) const {
2560 assert(slave >= 0 && slave < ActiveThreads);
2561 assert(master >= 0 && master < ActiveThreads);
2562 assert(ActiveThreads > 1);
2564 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2567 // Make a local copy to be sure doesn't change under our feet
2568 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2570 if (localActiveSplitPoints == 0)
2571 // No active split points means that the thread is available as
2572 // a slave for any other thread.
2575 if (ActiveThreads == 2)
2578 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2579 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2580 // could have been set to 0 by another thread leading to an out of bound access.
2581 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2588 // available_thread_exists() tries to find an idle thread which is available as
2589 // a slave for the thread with threadID "master".
2591 bool ThreadsManager::available_thread_exists(int master) const {
2593 assert(master >= 0 && master < ActiveThreads);
2594 assert(ActiveThreads > 1);
2596 for (int i = 0; i < ActiveThreads; i++)
2597 if (thread_is_available(i, master))
2604 // split() does the actual work of distributing the work at a node between
2605 // several available threads. If it does not succeed in splitting the
2606 // node (because no idle threads are available, or because we have no unused
2607 // split point objects), the function immediately returns. If splitting is
2608 // possible, a SplitPoint object is initialized with all the data that must be
2609 // copied to the helper threads and we tell our helper threads that they have
2610 // been assigned work. This will cause them to instantly leave their idle loops
2611 // and call sp_search(). When all threads have returned from sp_search() then
2614 template <bool Fake>
2615 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2616 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2617 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2619 assert(ply > 0 && ply < PLY_MAX);
2620 assert(*bestValue >= -VALUE_INFINITE);
2621 assert(*bestValue <= *alpha);
2622 assert(*alpha < beta);
2623 assert(beta <= VALUE_INFINITE);
2624 assert(depth > Depth(0));
2625 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2626 assert(ActiveThreads > 1);
2628 int i, master = p.thread();
2629 Thread& masterThread = threads[master];
2633 // If no other thread is available to help us, or if we have too many
2634 // active split points, don't split.
2635 if ( !available_thread_exists(master)
2636 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2638 lock_release(&MPLock);
2642 // Pick the next available split point object from the split point stack
2643 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2645 // Initialize the split point object
2646 splitPoint.parent = masterThread.splitPoint;
2647 splitPoint.stopRequest = false;
2648 splitPoint.ply = ply;
2649 splitPoint.depth = depth;
2650 splitPoint.threatMove = threatMove;
2651 splitPoint.mateThreat = mateThreat;
2652 splitPoint.alpha = *alpha;
2653 splitPoint.beta = beta;
2654 splitPoint.pvNode = pvNode;
2655 splitPoint.bestValue = *bestValue;
2657 splitPoint.moveCount = *moveCount;
2658 splitPoint.pos = &p;
2659 splitPoint.parentSstack = ss;
2660 for (i = 0; i < ActiveThreads; i++)
2661 splitPoint.slaves[i] = 0;
2663 masterThread.splitPoint = &splitPoint;
2665 // If we are here it means we are not available
2666 assert(masterThread.state != THREAD_AVAILABLE);
2668 int workersCnt = 1; // At least the master is included
2670 // Allocate available threads setting state to THREAD_BOOKED
2671 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2672 if (thread_is_available(i, master))
2674 threads[i].state = THREAD_BOOKED;
2675 threads[i].splitPoint = &splitPoint;
2676 splitPoint.slaves[i] = 1;
2680 assert(Fake || workersCnt > 1);
2682 // We can release the lock because slave threads are already booked and master is not available
2683 lock_release(&MPLock);
2685 // Tell the threads that they have work to do. This will make them leave
2686 // their idle loop. But before copy search stack tail for each thread.
2687 for (i = 0; i < ActiveThreads; i++)
2688 if (i == master || splitPoint.slaves[i])
2690 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2692 assert(i == master || threads[i].state == THREAD_BOOKED);
2694 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2697 // Everything is set up. The master thread enters the idle loop, from
2698 // which it will instantly launch a search, because its state is
2699 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2700 // idle loop, which means that the main thread will return from the idle
2701 // loop when all threads have finished their work at this split point.
2702 idle_loop(master, &splitPoint);
2704 // We have returned from the idle loop, which means that all threads are
2705 // finished. Update alpha and bestValue, and return.
2708 *alpha = splitPoint.alpha;
2709 *bestValue = splitPoint.bestValue;
2710 masterThread.activeSplitPoints--;
2711 masterThread.splitPoint = splitPoint.parent;
2713 lock_release(&MPLock);
2717 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2718 // to start a new search from the root.
2720 void ThreadsManager::wake_sleeping_threads() {
2722 assert(AllThreadsShouldSleep);
2723 assert(ActiveThreads > 0);
2725 AllThreadsShouldSleep = false;
2727 if (ActiveThreads == 1)
2730 #if !defined(_MSC_VER)
2731 pthread_mutex_lock(&WaitLock);
2732 pthread_cond_broadcast(&WaitCond);
2733 pthread_mutex_unlock(&WaitLock);
2735 for (int i = 1; i < MAX_THREADS; i++)
2736 SetEvent(SitIdleEvent[i]);
2742 // put_threads_to_sleep() makes all the threads go to sleep just before
2743 // to leave think(), at the end of the search. Threads should have already
2744 // finished the job and should be idle.
2746 void ThreadsManager::put_threads_to_sleep() {
2748 assert(!AllThreadsShouldSleep);
2750 // This makes the threads to go to sleep
2751 AllThreadsShouldSleep = true;
2754 /// The RootMoveList class
2756 // RootMoveList c'tor
2758 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2760 SearchStack ss[PLY_MAX_PLUS_2];
2761 MoveStack mlist[MaxRootMoves];
2763 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2765 // Initialize search stack
2766 init_ss_array(ss, PLY_MAX_PLUS_2);
2767 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2768 ss[0].eval = VALUE_NONE;
2770 // Generate all legal moves
2771 MoveStack* last = generate_moves(pos, mlist);
2773 // Add each move to the moves[] array
2774 for (MoveStack* cur = mlist; cur != last; cur++)
2776 bool includeMove = includeAllMoves;
2778 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2779 includeMove = (searchMoves[k] == cur->move);
2784 // Find a quick score for the move
2785 pos.do_move(cur->move, st);
2786 ss[0].currentMove = cur->move;
2787 moves[count].move = cur->move;
2788 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2789 moves[count].pv[0] = cur->move;
2790 moves[count].pv[1] = MOVE_NONE;
2791 pos.undo_move(cur->move);
2798 // RootMoveList simple methods definitions
2800 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2802 moves[moveNum].nodes = nodes;
2803 moves[moveNum].cumulativeNodes += nodes;
2806 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2808 moves[moveNum].ourBeta = our;
2809 moves[moveNum].theirBeta = their;
2812 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2816 for (j = 0; pv[j] != MOVE_NONE; j++)
2817 moves[moveNum].pv[j] = pv[j];
2819 moves[moveNum].pv[j] = MOVE_NONE;
2823 // RootMoveList::sort() sorts the root move list at the beginning of a new
2826 void RootMoveList::sort() {
2828 sort_multipv(count - 1); // Sort all items
2832 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2833 // list by their scores and depths. It is used to order the different PVs
2834 // correctly in MultiPV mode.
2836 void RootMoveList::sort_multipv(int n) {
2840 for (i = 1; i <= n; i++)
2842 RootMove rm = moves[i];
2843 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2844 moves[j] = moves[j - 1];