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, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
242 // Scores and number of times the best move changed for each iteration
243 Value ValueByIteration[PLY_MAX_PLUS_2];
244 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
246 // Search window management
252 // Time managment variables
253 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
254 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
260 std::ofstream LogFile;
262 // Multi-threads related variables
263 Depth MinimumSplitDepth;
264 int MaxThreadsPerSplitPoint;
267 // Node counters, used only by thread[0] but try to keep in different cache
268 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
280 template <NodeType PvNode>
281 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 void sp_search(SplitPoint* sp, int threadID);
289 template <NodeType PvNode>
290 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 Value value_to_tt(Value v, int ply);
295 Value value_from_tt(Value v, int ply);
296 bool move_is_killer(Move m, SearchStack* ss);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
312 void insert_pv_in_tt(const Position& pos, Move pv[]);
313 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
315 #if !defined(_MSC_VER)
316 void *init_thread(void *threadID);
318 DWORD WINAPI init_thread(LPVOID threadID);
328 /// init_threads(), exit_threads() and nodes_searched() are helpers to
329 /// give accessibility to some TM methods from outside of current file.
331 void init_threads() { TM.init_threads(); }
332 void exit_threads() { TM.exit_threads(); }
333 int64_t nodes_searched() { return TM.nodes_searched(); }
336 /// init_search() is called during startup. It initializes various lookup tables
340 int d; // depth (OnePly == 2)
341 int hd; // half depth (OnePly == 1)
344 // Init reductions array
345 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
347 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
348 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
349 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
350 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
353 // Init futility margins array
354 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
355 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
357 // Init futility move count array
358 for (d = 0; d < 32; d++)
359 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
363 // SearchStack::init() initializes a search stack entry.
364 // Called at the beginning of search() when starting to examine a new node.
365 void SearchStack::init() {
367 currentMove = bestMove = MOVE_NONE;
370 // SearchStack::initKillers() initializes killers for a search stack entry
371 void SearchStack::initKillers() {
373 killers[0] = killers[1] = mateKiller = MOVE_NONE;
377 /// perft() is our utility to verify move generation is bug free. All the legal
378 /// moves up to given depth are generated and counted and the sum returned.
380 int perft(Position& pos, Depth depth)
385 MovePicker mp(pos, MOVE_NONE, depth, H);
387 // If we are at the last ply we don't need to do and undo
388 // the moves, just to count them.
389 if (depth <= OnePly) // Replace with '<' to test also qsearch
391 while (mp.get_next_move()) sum++;
395 // Loop through all legal moves
397 while ((move = mp.get_next_move()) != MOVE_NONE)
399 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
400 sum += perft(pos, depth - OnePly);
407 /// think() is the external interface to Stockfish's search, and is called when
408 /// the program receives the UCI 'go' command. It initializes various
409 /// search-related global variables, and calls root_search(). It returns false
410 /// when a quit command is received during the search.
412 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
413 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
415 // Initialize global search variables
416 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
417 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
419 TM.resetNodeCounters();
420 SearchStartTime = get_system_time();
421 ExactMaxTime = maxTime;
424 InfiniteSearch = infinite;
425 PonderSearch = ponder;
426 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
428 // Look for a book move, only during games, not tests
429 if (UseTimeManagement && get_option_value_bool("OwnBook"))
431 if (get_option_value_string("Book File") != OpeningBook.file_name())
432 OpeningBook.open(get_option_value_string("Book File"));
434 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
435 if (bookMove != MOVE_NONE)
438 wait_for_stop_or_ponderhit();
440 cout << "bestmove " << bookMove << endl;
445 // Read UCI option values
446 TT.set_size(get_option_value_int("Hash"));
447 if (button_was_pressed("Clear Hash"))
450 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
451 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
452 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
453 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
454 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
455 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
456 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
457 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
458 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
459 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
460 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
461 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
463 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
464 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
465 MultiPV = get_option_value_int("MultiPV");
466 Chess960 = get_option_value_bool("UCI_Chess960");
467 UseLogFile = get_option_value_bool("Use Search Log");
470 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
472 read_weights(pos.side_to_move());
474 // Set the number of active threads
475 int newActiveThreads = get_option_value_int("Threads");
476 if (newActiveThreads != TM.active_threads())
478 TM.set_active_threads(newActiveThreads);
479 init_eval(TM.active_threads());
482 // Wake up sleeping threads
483 TM.wake_sleeping_threads();
486 int myTime = time[pos.side_to_move()];
487 int myIncrement = increment[pos.side_to_move()];
488 if (UseTimeManagement)
490 if (!movesToGo) // Sudden death time control
494 MaxSearchTime = myTime / 30 + myIncrement;
495 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
497 else // Blitz game without increment
499 MaxSearchTime = myTime / 30;
500 AbsoluteMaxSearchTime = myTime / 8;
503 else // (x moves) / (y minutes)
507 MaxSearchTime = myTime / 2;
508 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
512 MaxSearchTime = myTime / Min(movesToGo, 20);
513 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
517 if (get_option_value_bool("Ponder"))
519 MaxSearchTime += MaxSearchTime / 4;
520 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
524 // Set best NodesBetweenPolls interval to avoid lagging under
525 // heavy time pressure.
527 NodesBetweenPolls = Min(MaxNodes, 30000);
528 else if (myTime && myTime < 1000)
529 NodesBetweenPolls = 1000;
530 else if (myTime && myTime < 5000)
531 NodesBetweenPolls = 5000;
533 NodesBetweenPolls = 30000;
535 // Write search information to log file
537 LogFile << "Searching: " << pos.to_fen() << endl
538 << "infinite: " << infinite
539 << " ponder: " << ponder
540 << " time: " << myTime
541 << " increment: " << myIncrement
542 << " moves to go: " << movesToGo << endl;
544 // We're ready to start thinking. Call the iterative deepening loop function
545 id_loop(pos, searchMoves);
550 TM.put_threads_to_sleep();
558 // id_loop() is the main iterative deepening loop. It calls root_search
559 // repeatedly with increasing depth until the allocated thinking time has
560 // been consumed, the user stops the search, or the maximum search depth is
563 Value id_loop(const Position& pos, Move searchMoves[]) {
565 Position p(pos, pos.thread());
566 SearchStack ss[PLY_MAX_PLUS_2];
567 Move pv[PLY_MAX_PLUS_2];
568 Move EasyMove = MOVE_NONE;
569 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
571 // Moves to search are verified, copied, scored and sorted
572 RootMoveList rml(p, searchMoves);
574 // Handle special case of searching on a mate/stale position
575 if (rml.move_count() == 0)
578 wait_for_stop_or_ponderhit();
580 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
583 // Print RootMoveList startup scoring to the standard output,
584 // so to output information also for iteration 1.
585 cout << "info depth " << 1
586 << "\ninfo depth " << 1
587 << " score " << value_to_uci(rml.get_move_score(0))
588 << " time " << current_search_time()
589 << " nodes " << TM.nodes_searched()
591 << " pv " << rml.get_move(0) << "\n";
596 init_ss_array(ss, PLY_MAX_PLUS_2);
597 pv[0] = pv[1] = MOVE_NONE;
598 ValueByIteration[1] = rml.get_move_score(0);
601 // Is one move significantly better than others after initial scoring ?
602 if ( rml.move_count() == 1
603 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
604 EasyMove = rml.get_move(0);
606 // Iterative deepening loop
607 while (Iteration < PLY_MAX)
609 // Initialize iteration
611 BestMoveChangesByIteration[Iteration] = 0;
613 cout << "info depth " << Iteration << endl;
615 // Calculate dynamic aspiration window based on previous iterations
616 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
618 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
619 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
621 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
622 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
624 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
625 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
628 // Search to the current depth, rml is updated and sorted, alpha and beta could change
629 value = root_search(p, ss, pv, rml, &alpha, &beta);
631 // Write PV to transposition table, in case the relevant entries have
632 // been overwritten during the search.
633 insert_pv_in_tt(p, pv);
636 break; // Value cannot be trusted. Break out immediately!
638 //Save info about search result
639 ValueByIteration[Iteration] = value;
641 // Drop the easy move if differs from the new best move
642 if (pv[0] != EasyMove)
643 EasyMove = MOVE_NONE;
645 if (UseTimeManagement)
648 bool stopSearch = false;
650 // Stop search early if there is only a single legal move,
651 // we search up to Iteration 6 anyway to get a proper score.
652 if (Iteration >= 6 && rml.move_count() == 1)
655 // Stop search early when the last two iterations returned a mate score
657 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
658 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
661 // Stop search early if one move seems to be much better than the others
662 int64_t nodes = TM.nodes_searched();
665 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
666 && current_search_time() > MaxSearchTime / 16)
667 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
668 && current_search_time() > MaxSearchTime / 32)))
671 // Add some extra time if the best move has changed during the last two iterations
672 if (Iteration > 5 && Iteration <= 50)
673 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
674 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
676 // Stop search if most of MaxSearchTime is consumed at the end of the
677 // iteration. We probably don't have enough time to search the first
678 // move at the next iteration anyway.
679 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
685 StopOnPonderhit = true;
691 if (MaxDepth && Iteration >= MaxDepth)
695 // If we are pondering or in infinite search, we shouldn't print the
696 // best move before we are told to do so.
697 if (!AbortSearch && (PonderSearch || InfiniteSearch))
698 wait_for_stop_or_ponderhit();
700 // Print final search statistics
701 cout << "info nodes " << TM.nodes_searched()
703 << " time " << current_search_time() << endl;
705 // Print the best move and the ponder move to the standard output
706 if (pv[0] == MOVE_NONE)
708 pv[0] = rml.get_move(0);
712 assert(pv[0] != MOVE_NONE);
714 cout << "bestmove " << pv[0];
716 if (pv[1] != MOVE_NONE)
717 cout << " ponder " << pv[1];
724 dbg_print_mean(LogFile);
726 if (dbg_show_hit_rate)
727 dbg_print_hit_rate(LogFile);
729 LogFile << "\nNodes: " << TM.nodes_searched()
730 << "\nNodes/second: " << nps()
731 << "\nBest move: " << move_to_san(p, pv[0]);
734 p.do_move(pv[0], st);
735 LogFile << "\nPonder move: "
736 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
739 return rml.get_move_score(0);
743 // root_search() is the function which searches the root node. It is
744 // similar to search_pv except that it uses a different move ordering
745 // scheme, prints some information to the standard output and handles
746 // the fail low/high loops.
748 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
755 Depth depth, ext, newDepth;
756 Value value, alpha, beta;
757 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
758 int researchCountFH, researchCountFL;
760 researchCountFH = researchCountFL = 0;
763 isCheck = pos.is_check();
765 // Step 1. Initialize node (polling is omitted at root)
768 // Step 2. Check for aborted search (omitted at root)
769 // Step 3. Mate distance pruning (omitted at root)
770 // Step 4. Transposition table lookup (omitted at root)
772 // Step 5. Evaluate the position statically
773 // At root we do this only to get reference value for child nodes
774 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
776 // Step 6. Razoring (omitted at root)
777 // Step 7. Static null move pruning (omitted at root)
778 // Step 8. Null move search with verification search (omitted at root)
779 // Step 9. Internal iterative deepening (omitted at root)
781 // Step extra. Fail low loop
782 // We start with small aspiration window and in case of fail low, we research
783 // with bigger window until we are not failing low anymore.
786 // Sort the moves before to (re)search
789 // Step 10. Loop through all moves in the root move list
790 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
792 // This is used by time management
793 FirstRootMove = (i == 0);
795 // Save the current node count before the move is searched
796 nodes = TM.nodes_searched();
798 // Reset beta cut-off counters
799 TM.resetBetaCounters();
801 // Pick the next root move, and print the move and the move number to
802 // the standard output.
803 move = ss->currentMove = rml.get_move(i);
805 if (current_search_time() >= 1000)
806 cout << "info currmove " << move
807 << " currmovenumber " << i + 1 << endl;
809 moveIsCheck = pos.move_is_check(move);
810 captureOrPromotion = pos.move_is_capture_or_promotion(move);
812 // Step 11. Decide the new search depth
813 depth = (Iteration - 2) * OnePly + InitialDepth;
814 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
815 newDepth = depth + ext;
817 // Step 12. Futility pruning (omitted at root)
819 // Step extra. Fail high loop
820 // If move fails high, we research with bigger window until we are not failing
822 value = - VALUE_INFINITE;
826 // Step 13. Make the move
827 pos.do_move(move, st, ci, moveIsCheck);
829 // Step extra. pv search
830 // We do pv search for first moves (i < MultiPV)
831 // and for fail high research (value > alpha)
832 if (i < MultiPV || value > alpha)
834 // Aspiration window is disabled in multi-pv case
836 alpha = -VALUE_INFINITE;
838 // Full depth PV search, done on first move or after a fail high
839 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
843 // Step 14. Reduced search
844 // if the move fails high will be re-searched at full depth
845 bool doFullDepthSearch = true;
847 if ( depth >= 3 * OnePly
849 && !captureOrPromotion
850 && !move_is_castle(move))
852 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
855 assert(newDepth-ss->reduction >= OnePly);
857 // Reduced depth non-pv search using alpha as upperbound
858 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
859 doFullDepthSearch = (value > alpha);
862 // The move failed high, but if reduction is very big we could
863 // face a false positive, retry with a less aggressive reduction,
864 // if the move fails high again then go with full depth search.
865 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
867 assert(newDepth - OnePly >= OnePly);
869 ss->reduction = OnePly;
870 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
871 doFullDepthSearch = (value > alpha);
873 ss->reduction = Depth(0); // Restore original reduction
876 // Step 15. Full depth search
877 if (doFullDepthSearch)
879 // Full depth non-pv search using alpha as upperbound
880 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
882 // If we are above alpha then research at same depth but as PV
883 // to get a correct score or eventually a fail high above beta.
885 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
889 // Step 16. Undo move
892 // Can we exit fail high loop ?
893 if (AbortSearch || value < beta)
896 // We are failing high and going to do a research. It's important to update
897 // the score before research in case we run out of time while researching.
898 rml.set_move_score(i, value);
900 extract_pv_from_tt(pos, move, pv);
901 rml.set_move_pv(i, pv);
903 // Print information to the standard output
904 print_pv_info(pos, pv, alpha, beta, value);
906 // Prepare for a research after a fail high, each time with a wider window
907 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
910 } // End of fail high loop
912 // Finished searching the move. If AbortSearch is true, the search
913 // was aborted because the user interrupted the search or because we
914 // ran out of time. In this case, the return value of the search cannot
915 // be trusted, and we break out of the loop without updating the best
920 // Remember beta-cutoff and searched nodes counts for this move. The
921 // info is used to sort the root moves for the next iteration.
923 TM.get_beta_counters(pos.side_to_move(), our, their);
924 rml.set_beta_counters(i, our, their);
925 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
927 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
928 assert(value < beta);
930 // Step 17. Check for new best move
931 if (value <= alpha && i >= MultiPV)
932 rml.set_move_score(i, -VALUE_INFINITE);
935 // PV move or new best move!
938 rml.set_move_score(i, value);
940 extract_pv_from_tt(pos, move, pv);
941 rml.set_move_pv(i, pv);
945 // We record how often the best move has been changed in each
946 // iteration. This information is used for time managment: When
947 // the best move changes frequently, we allocate some more time.
949 BestMoveChangesByIteration[Iteration]++;
951 // Print information to the standard output
952 print_pv_info(pos, pv, alpha, beta, value);
954 // Raise alpha to setup proper non-pv search upper bound
961 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
963 cout << "info multipv " << j + 1
964 << " score " << value_to_uci(rml.get_move_score(j))
965 << " depth " << (j <= i ? Iteration : Iteration - 1)
966 << " time " << current_search_time()
967 << " nodes " << TM.nodes_searched()
971 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
972 cout << rml.get_move_pv(j, k) << " ";
976 alpha = rml.get_move_score(Min(i, MultiPV - 1));
978 } // PV move or new best move
980 assert(alpha >= *alphaPtr);
982 AspirationFailLow = (alpha == *alphaPtr);
984 if (AspirationFailLow && StopOnPonderhit)
985 StopOnPonderhit = false;
988 // Can we exit fail low loop ?
989 if (AbortSearch || !AspirationFailLow)
992 // Prepare for a research after a fail low, each time with a wider window
993 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
998 // Sort the moves before to return
1005 // search<>() is the main search function for both PV and non-PV nodes
1007 template <NodeType PvNode>
1008 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1010 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1011 assert(beta > alpha && beta <= VALUE_INFINITE);
1012 assert(PvNode || alpha == beta - 1);
1013 assert(ply > 0 && ply < PLY_MAX);
1014 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1016 Move movesSearched[256];
1021 Move ttMove, move, excludedMove;
1022 Depth ext, newDepth;
1023 Value bestValue, value, oldAlpha;
1024 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1025 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1026 bool mateThreat = false;
1028 int threadID = pos.thread();
1029 Move threatMove = MOVE_NONE;
1030 refinedValue = bestValue = value = -VALUE_INFINITE;
1033 // Step 1. Initialize node and poll. Polling can abort search
1034 TM.incrementNodeCounter(threadID);
1036 (ss+2)->initKillers();
1038 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1044 // Step 2. Check for aborted search and immediate draw
1045 if (AbortSearch || TM.thread_should_stop(threadID))
1048 if (pos.is_draw() || ply >= PLY_MAX - 1)
1051 // Step 3. Mate distance pruning
1052 alpha = Max(value_mated_in(ply), alpha);
1053 beta = Min(value_mate_in(ply+1), beta);
1057 // Step 4. Transposition table lookup
1059 // We don't want the score of a partial search to overwrite a previous full search
1060 // TT value, so we use a different position key in case of an excluded move exists.
1061 excludedMove = ss->excludedMove;
1062 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1064 tte = TT.retrieve(posKey);
1065 ttMove = (tte ? tte->move() : MOVE_NONE);
1067 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1068 // This is to avoid problems in the following areas:
1070 // * Repetition draw detection
1071 // * Fifty move rule detection
1072 // * Searching for a mate
1073 // * Printing of full PV line
1075 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1077 // Refresh tte entry to avoid aging
1078 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1080 ss->currentMove = ttMove; // Can be MOVE_NONE
1081 return value_from_tt(tte->value(), ply);
1084 // Step 5. Evaluate the position statically
1085 // At PV nodes we do this only to update gain statistics
1086 isCheck = pos.is_check();
1091 assert(tte->static_value() != VALUE_NONE);
1092 ss->eval = tte->static_value();
1093 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1097 ss->eval = evaluate(pos, ei);
1098 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1101 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1102 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1105 ss->eval = VALUE_NONE;
1107 // Step 6. Razoring (is omitted in PV nodes)
1109 && depth < RazorDepth
1111 && refinedValue < beta - razor_margin(depth)
1112 && ttMove == MOVE_NONE
1113 && (ss-1)->currentMove != MOVE_NULL
1114 && !value_is_mate(beta)
1115 && !pos.has_pawn_on_7th(pos.side_to_move()))
1117 Value rbeta = beta - razor_margin(depth);
1118 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1120 // Logically we should return (v + razor_margin(depth)), but
1121 // surprisingly this did slightly weaker in tests.
1125 // Step 7. Static null move pruning (is omitted in PV nodes)
1126 // We're betting that the opponent doesn't have a move that will reduce
1127 // the score by more than futility_margin(depth) if we do a null move.
1129 && !ss->skipNullMove
1130 && depth < RazorDepth
1131 && refinedValue >= beta + futility_margin(depth, 0)
1133 && !value_is_mate(beta)
1134 && pos.non_pawn_material(pos.side_to_move()))
1135 return refinedValue - futility_margin(depth, 0);
1137 // Step 8. Null move search with verification search (is omitted in PV nodes)
1138 // When we jump directly to qsearch() we do a null move only if static value is
1139 // at least beta. Otherwise we do a null move if static value is not more than
1140 // NullMoveMargin under beta.
1142 && !ss->skipNullMove
1144 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1146 && !value_is_mate(beta)
1147 && pos.non_pawn_material(pos.side_to_move()))
1149 ss->currentMove = MOVE_NULL;
1151 // Null move dynamic reduction based on depth
1152 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1154 // Null move dynamic reduction based on value
1155 if (refinedValue - beta > PawnValueMidgame)
1158 pos.do_null_move(st);
1159 (ss+1)->skipNullMove = true;
1161 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1162 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1163 (ss+1)->skipNullMove = false;
1164 pos.undo_null_move();
1166 if (nullValue >= beta)
1168 // Do not return unproven mate scores
1169 if (nullValue >= value_mate_in(PLY_MAX))
1172 if (depth < 6 * OnePly)
1175 // Do verification search at high depths
1176 ss->skipNullMove = true;
1177 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1178 ss->skipNullMove = false;
1185 // The null move failed low, which means that we may be faced with
1186 // some kind of threat. If the previous move was reduced, check if
1187 // the move that refuted the null move was somehow connected to the
1188 // move which was reduced. If a connection is found, return a fail
1189 // low score (which will cause the reduced move to fail high in the
1190 // parent node, which will trigger a re-search with full depth).
1191 if (nullValue == value_mated_in(ply + 2))
1194 threatMove = (ss+1)->currentMove;
1195 if ( depth < ThreatDepth
1196 && (ss-1)->reduction
1197 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1202 // Step 9. Internal iterative deepening
1203 if ( depth >= IIDDepth[PvNode]
1204 && ttMove == MOVE_NONE
1205 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1207 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1209 ss->skipNullMove = true;
1210 search<PvNode>(pos, ss, alpha, beta, d, ply);
1211 ss->skipNullMove = false;
1213 ttMove = ss->bestMove;
1214 tte = TT.retrieve(posKey);
1217 // Expensive mate threat detection (only for PV nodes)
1219 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1221 // Initialize a MovePicker object for the current position
1222 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1224 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1225 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1226 && tte && tte->move()
1227 && !excludedMove // Do not allow recursive singular extension search
1228 && is_lower_bound(tte->type())
1229 && tte->depth() >= depth - 3 * OnePly;
1231 // Step 10. Loop through moves
1232 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1233 while ( bestValue < beta
1234 && (move = mp.get_next_move()) != MOVE_NONE
1235 && !TM.thread_should_stop(threadID))
1237 assert(move_is_ok(move));
1239 if (move == excludedMove)
1242 moveIsCheck = pos.move_is_check(move, ci);
1243 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1245 // Step 11. Decide the new search depth
1246 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1248 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1249 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1250 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1251 // lower then ttValue minus a margin then we extend ttMove.
1252 if ( singularExtensionNode
1253 && move == tte->move()
1256 Value ttValue = value_from_tt(tte->value(), ply);
1258 if (abs(ttValue) < VALUE_KNOWN_WIN)
1260 Value b = ttValue - SingularExtensionMargin;
1261 ss->excludedMove = move;
1262 ss->skipNullMove = true;
1263 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1264 ss->skipNullMove = false;
1265 ss->excludedMove = MOVE_NONE;
1271 newDepth = depth - OnePly + ext;
1273 // Update current move (this must be done after singular extension search)
1274 movesSearched[moveCount++] = ss->currentMove = move;
1276 // Step 12. Futility pruning (is omitted in PV nodes)
1278 && !captureOrPromotion
1282 && !move_is_castle(move))
1284 // Move count based pruning
1285 if ( moveCount >= futility_move_count(depth)
1286 && !(threatMove && connected_threat(pos, move, threatMove))
1287 && bestValue > value_mated_in(PLY_MAX))
1290 // Value based pruning
1291 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1292 // but fixing this made program slightly weaker.
1293 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1294 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1295 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1297 if (futilityValueScaled < beta)
1299 if (futilityValueScaled > bestValue)
1300 bestValue = futilityValueScaled;
1305 // Step 13. Make the move
1306 pos.do_move(move, st, ci, moveIsCheck);
1308 // Step extra. pv search (only in PV nodes)
1309 // The first move in list is the expected PV
1310 if (PvNode && moveCount == 1)
1311 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1312 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1315 // Step 14. Reduced depth search
1316 // If the move fails high will be re-searched at full depth.
1317 bool doFullDepthSearch = true;
1319 if ( depth >= 3 * OnePly
1320 && !captureOrPromotion
1322 && !move_is_castle(move)
1323 && !move_is_killer(move, ss))
1325 ss->reduction = reduction<PvNode>(depth, moveCount);
1328 Depth d = newDepth - ss->reduction;
1329 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1330 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1332 doFullDepthSearch = (value > alpha);
1335 // The move failed high, but if reduction is very big we could
1336 // face a false positive, retry with a less aggressive reduction,
1337 // if the move fails high again then go with full depth search.
1338 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1340 assert(newDepth - OnePly >= OnePly);
1342 ss->reduction = OnePly;
1343 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1344 doFullDepthSearch = (value > alpha);
1346 ss->reduction = Depth(0); // Restore original reduction
1349 // Step 15. Full depth search
1350 if (doFullDepthSearch)
1352 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1353 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1355 // Step extra. pv search (only in PV nodes)
1356 // Search only for possible new PV nodes, if instead value >= beta then
1357 // parent node fails low with value <= alpha and tries another move.
1358 if (PvNode && value > alpha && value < beta)
1359 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1360 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1364 // Step 16. Undo move
1365 pos.undo_move(move);
1367 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1369 // Step 17. Check for new best move
1370 if (value > bestValue)
1375 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1378 if (value == value_mate_in(ply + 1))
1379 ss->mateKiller = move;
1381 ss->bestMove = move;
1385 // Step 18. Check for split
1386 if ( depth >= MinimumSplitDepth
1387 && TM.active_threads() > 1
1389 && TM.available_thread_exists(threadID)
1391 && !TM.thread_should_stop(threadID)
1393 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1394 threatMove, mateThreat, &moveCount, &mp, PvNode);
1397 // Step 19. Check for mate and stalemate
1398 // All legal moves have been searched and if there are
1399 // no legal moves, it must be mate or stalemate.
1400 // If one move was excluded return fail low score.
1402 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1404 // Step 20. Update tables
1405 // If the search is not aborted, update the transposition table,
1406 // history counters, and killer moves.
1407 if (AbortSearch || TM.thread_should_stop(threadID))
1410 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1411 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1412 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1414 // Update killers and history only for non capture moves that fails high
1415 if (bestValue >= beta)
1417 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1418 if (!pos.move_is_capture_or_promotion(move))
1420 update_history(pos, move, depth, movesSearched, moveCount);
1421 update_killers(move, ss);
1425 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1431 // qsearch() is the quiescence search function, which is called by the main
1432 // search function when the remaining depth is zero (or, to be more precise,
1433 // less than OnePly).
1435 template <NodeType PvNode>
1436 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1438 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1439 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1440 assert(PvNode || alpha == beta - 1);
1442 assert(ply > 0 && ply < PLY_MAX);
1443 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1448 Value bestValue, value, futilityValue, futilityBase;
1449 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1451 Value oldAlpha = alpha;
1453 TM.incrementNodeCounter(pos.thread());
1454 ss->bestMove = ss->currentMove = MOVE_NONE;
1456 // Check for an instant draw or maximum ply reached
1457 if (pos.is_draw() || ply >= PLY_MAX - 1)
1460 // Transposition table lookup. At PV nodes, we don't use the TT for
1461 // pruning, but only for move ordering.
1462 tte = TT.retrieve(pos.get_key());
1463 ttMove = (tte ? tte->move() : MOVE_NONE);
1465 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1467 ss->currentMove = ttMove; // Can be MOVE_NONE
1468 return value_from_tt(tte->value(), ply);
1471 isCheck = pos.is_check();
1473 // Evaluate the position statically
1476 bestValue = futilityBase = -VALUE_INFINITE;
1477 ss->eval = VALUE_NONE;
1478 deepChecks = enoughMaterial = false;
1484 assert(tte->static_value() != VALUE_NONE);
1485 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1486 bestValue = tte->static_value();
1489 bestValue = evaluate(pos, ei);
1491 ss->eval = bestValue;
1492 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1494 // Stand pat. Return immediately if static value is at least beta
1495 if (bestValue >= beta)
1498 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()]);
1503 if (PvNode && bestValue > alpha)
1506 // If we are near beta then try to get a cutoff pushing checks a bit further
1507 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1509 // Futility pruning parameters, not needed when in check
1510 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1511 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1514 // Initialize a MovePicker object for the current position, and prepare
1515 // to search the moves. Because the depth is <= 0 here, only captures,
1516 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1517 // and we are near beta) will be generated.
1518 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1521 // Loop through the moves until no moves remain or a beta cutoff occurs
1522 while ( alpha < beta
1523 && (move = mp.get_next_move()) != MOVE_NONE)
1525 assert(move_is_ok(move));
1527 moveIsCheck = pos.move_is_check(move, ci);
1535 && !move_is_promotion(move)
1536 && !pos.move_is_passed_pawn_push(move))
1538 futilityValue = futilityBase
1539 + pos.endgame_value_of_piece_on(move_to(move))
1540 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1542 if (futilityValue < alpha)
1544 if (futilityValue > bestValue)
1545 bestValue = futilityValue;
1550 // Detect blocking evasions that are candidate to be pruned
1551 evasionPrunable = isCheck
1552 && bestValue > value_mated_in(PLY_MAX)
1553 && !pos.move_is_capture(move)
1554 && pos.type_of_piece_on(move_from(move)) != KING
1555 && !pos.can_castle(pos.side_to_move());
1557 // Don't search moves with negative SEE values
1559 && (!isCheck || evasionPrunable)
1561 && !move_is_promotion(move)
1562 && pos.see_sign(move) < 0)
1565 // Update current move
1566 ss->currentMove = move;
1568 // Make and search the move
1569 pos.do_move(move, st, ci, moveIsCheck);
1570 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1571 pos.undo_move(move);
1573 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1576 if (value > bestValue)
1582 ss->bestMove = move;
1587 // All legal moves have been searched. A special case: If we're in check
1588 // and no legal moves were found, it is checkmate.
1589 if (isCheck && bestValue == -VALUE_INFINITE)
1590 return value_mated_in(ply);
1592 // Update transposition table
1593 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1594 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1595 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1597 // Update killers only for checking moves that fails high
1598 if ( bestValue >= beta
1599 && !pos.move_is_capture_or_promotion(ss->bestMove))
1600 update_killers(ss->bestMove, ss);
1602 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1608 // sp_search() is used to search from a split point. This function is called
1609 // by each thread working at the split point. It is similar to the normal
1610 // search() function, but simpler. Because we have already probed the hash
1611 // table, done a null move search, and searched the first move before
1612 // splitting, we don't have to repeat all this work in sp_search(). We
1613 // also don't need to store anything to the hash table here: This is taken
1614 // care of after we return from the split point.
1616 template <NodeType PvNode>
1617 void sp_search(SplitPoint* sp, int threadID) {
1619 assert(threadID >= 0 && threadID < TM.active_threads());
1620 assert(TM.active_threads() > 1);
1624 Depth ext, newDepth;
1626 Value futilityValueScaled; // NonPV specific
1627 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1629 value = -VALUE_INFINITE;
1631 Position pos(*sp->pos, threadID);
1633 SearchStack* ss = sp->sstack[threadID] + 1;
1634 isCheck = pos.is_check();
1636 // Step 10. Loop through moves
1637 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1638 lock_grab(&(sp->lock));
1640 while ( sp->bestValue < sp->beta
1641 && (move = sp->mp->get_next_move()) != MOVE_NONE
1642 && !TM.thread_should_stop(threadID))
1644 moveCount = ++sp->moveCount;
1645 lock_release(&(sp->lock));
1647 assert(move_is_ok(move));
1649 moveIsCheck = pos.move_is_check(move, ci);
1650 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1652 // Step 11. Decide the new search depth
1653 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1654 newDepth = sp->depth - OnePly + ext;
1656 // Update current move
1657 ss->currentMove = move;
1659 // Step 12. Futility pruning (is omitted in PV nodes)
1661 && !captureOrPromotion
1664 && !move_is_castle(move))
1666 // Move count based pruning
1667 if ( moveCount >= futility_move_count(sp->depth)
1668 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1669 && sp->bestValue > value_mated_in(PLY_MAX))
1671 lock_grab(&(sp->lock));
1675 // Value based pruning
1676 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1677 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1678 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1680 if (futilityValueScaled < sp->beta)
1682 lock_grab(&(sp->lock));
1684 if (futilityValueScaled > sp->bestValue)
1685 sp->bestValue = futilityValueScaled;
1690 // Step 13. Make the move
1691 pos.do_move(move, st, ci, moveIsCheck);
1693 // Step 14. Reduced search
1694 // If the move fails high will be re-searched at full depth.
1695 bool doFullDepthSearch = true;
1697 if ( !captureOrPromotion
1699 && !move_is_castle(move)
1700 && !move_is_killer(move, ss))
1702 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1705 Value localAlpha = sp->alpha;
1706 Depth d = newDepth - ss->reduction;
1707 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1708 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1710 doFullDepthSearch = (value > localAlpha);
1713 // The move failed high, but if reduction is very big we could
1714 // face a false positive, retry with a less aggressive reduction,
1715 // if the move fails high again then go with full depth search.
1716 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1718 assert(newDepth - OnePly >= OnePly);
1720 ss->reduction = OnePly;
1721 Value localAlpha = sp->alpha;
1722 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1723 doFullDepthSearch = (value > localAlpha);
1725 ss->reduction = Depth(0); // Restore original reduction
1728 // Step 15. Full depth search
1729 if (doFullDepthSearch)
1731 Value localAlpha = sp->alpha;
1732 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1733 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1735 // Step extra. pv search (only in PV nodes)
1736 // Search only for possible new PV nodes, if instead value >= beta then
1737 // parent node fails low with value <= alpha and tries another move.
1738 if (PvNode && value > localAlpha && value < sp->beta)
1739 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1740 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1743 // Step 16. Undo move
1744 pos.undo_move(move);
1746 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1748 // Step 17. Check for new best move
1749 lock_grab(&(sp->lock));
1751 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1753 sp->bestValue = value;
1755 if (sp->bestValue > sp->alpha)
1757 if (!PvNode || value >= sp->beta)
1758 sp->stopRequest = true;
1760 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1763 sp->parentSstack->bestMove = ss->bestMove = move;
1768 /* Here we have the lock still grabbed */
1770 sp->slaves[threadID] = 0;
1772 lock_release(&(sp->lock));
1776 // connected_moves() tests whether two moves are 'connected' in the sense
1777 // that the first move somehow made the second move possible (for instance
1778 // if the moving piece is the same in both moves). The first move is assumed
1779 // to be the move that was made to reach the current position, while the
1780 // second move is assumed to be a move from the current position.
1782 bool connected_moves(const Position& pos, Move m1, Move m2) {
1784 Square f1, t1, f2, t2;
1787 assert(move_is_ok(m1));
1788 assert(move_is_ok(m2));
1790 if (m2 == MOVE_NONE)
1793 // Case 1: The moving piece is the same in both moves
1799 // Case 2: The destination square for m2 was vacated by m1
1805 // Case 3: Moving through the vacated square
1806 if ( piece_is_slider(pos.piece_on(f2))
1807 && bit_is_set(squares_between(f2, t2), f1))
1810 // Case 4: The destination square for m2 is defended by the moving piece in m1
1811 p = pos.piece_on(t1);
1812 if (bit_is_set(pos.attacks_from(p, t1), t2))
1815 // Case 5: Discovered check, checking piece is the piece moved in m1
1816 if ( piece_is_slider(p)
1817 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1818 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1820 // discovered_check_candidates() works also if the Position's side to
1821 // move is the opposite of the checking piece.
1822 Color them = opposite_color(pos.side_to_move());
1823 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1825 if (bit_is_set(dcCandidates, f2))
1832 // value_is_mate() checks if the given value is a mate one eventually
1833 // compensated for the ply.
1835 bool value_is_mate(Value value) {
1837 assert(abs(value) <= VALUE_INFINITE);
1839 return value <= value_mated_in(PLY_MAX)
1840 || value >= value_mate_in(PLY_MAX);
1844 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1845 // "plies to mate from the current ply". Non-mate scores are unchanged.
1846 // The function is called before storing a value to the transposition table.
1848 Value value_to_tt(Value v, int ply) {
1850 if (v >= value_mate_in(PLY_MAX))
1853 if (v <= value_mated_in(PLY_MAX))
1860 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1861 // the transposition table to a mate score corrected for the current ply.
1863 Value value_from_tt(Value v, int ply) {
1865 if (v >= value_mate_in(PLY_MAX))
1868 if (v <= value_mated_in(PLY_MAX))
1875 // move_is_killer() checks if the given move is among the killer moves
1877 bool move_is_killer(Move m, SearchStack* ss) {
1879 if (ss->killers[0] == m || ss->killers[1] == m)
1886 // extension() decides whether a move should be searched with normal depth,
1887 // or with extended depth. Certain classes of moves (checking moves, in
1888 // particular) are searched with bigger depth than ordinary moves and in
1889 // any case are marked as 'dangerous'. Note that also if a move is not
1890 // extended, as example because the corresponding UCI option is set to zero,
1891 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1892 template <NodeType PvNode>
1893 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1894 bool singleEvasion, bool mateThreat, bool* dangerous) {
1896 assert(m != MOVE_NONE);
1898 Depth result = Depth(0);
1899 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1903 if (moveIsCheck && pos.see_sign(m) >= 0)
1904 result += CheckExtension[PvNode];
1907 result += SingleEvasionExtension[PvNode];
1910 result += MateThreatExtension[PvNode];
1913 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1915 Color c = pos.side_to_move();
1916 if (relative_rank(c, move_to(m)) == RANK_7)
1918 result += PawnPushTo7thExtension[PvNode];
1921 if (pos.pawn_is_passed(c, move_to(m)))
1923 result += PassedPawnExtension[PvNode];
1928 if ( captureOrPromotion
1929 && pos.type_of_piece_on(move_to(m)) != PAWN
1930 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1931 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1932 && !move_is_promotion(m)
1935 result += PawnEndgameExtension[PvNode];
1940 && captureOrPromotion
1941 && pos.type_of_piece_on(move_to(m)) != PAWN
1942 && pos.see_sign(m) >= 0)
1948 return Min(result, OnePly);
1952 // connected_threat() tests whether it is safe to forward prune a move or if
1953 // is somehow coonected to the threat move returned by null search.
1955 bool connected_threat(const Position& pos, Move m, Move threat) {
1957 assert(move_is_ok(m));
1958 assert(threat && move_is_ok(threat));
1959 assert(!pos.move_is_check(m));
1960 assert(!pos.move_is_capture_or_promotion(m));
1961 assert(!pos.move_is_passed_pawn_push(m));
1963 Square mfrom, mto, tfrom, tto;
1965 mfrom = move_from(m);
1967 tfrom = move_from(threat);
1968 tto = move_to(threat);
1970 // Case 1: Don't prune moves which move the threatened piece
1974 // Case 2: If the threatened piece has value less than or equal to the
1975 // value of the threatening piece, don't prune move which defend it.
1976 if ( pos.move_is_capture(threat)
1977 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1978 || pos.type_of_piece_on(tfrom) == KING)
1979 && pos.move_attacks_square(m, tto))
1982 // Case 3: If the moving piece in the threatened move is a slider, don't
1983 // prune safe moves which block its ray.
1984 if ( piece_is_slider(pos.piece_on(tfrom))
1985 && bit_is_set(squares_between(tfrom, tto), mto)
1986 && pos.see_sign(m) >= 0)
1993 // ok_to_use_TT() returns true if a transposition table score
1994 // can be used at a given point in search.
1996 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1998 Value v = value_from_tt(tte->value(), ply);
2000 return ( tte->depth() >= depth
2001 || v >= Max(value_mate_in(PLY_MAX), beta)
2002 || v < Min(value_mated_in(PLY_MAX), beta))
2004 && ( (is_lower_bound(tte->type()) && v >= beta)
2005 || (is_upper_bound(tte->type()) && v < beta));
2009 // refine_eval() returns the transposition table score if
2010 // possible otherwise falls back on static position evaluation.
2012 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2017 Value v = value_from_tt(tte->value(), ply);
2019 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2020 || (is_upper_bound(tte->type()) && v < defaultEval))
2027 // update_history() registers a good move that produced a beta-cutoff
2028 // in history and marks as failures all the other moves of that ply.
2030 void update_history(const Position& pos, Move move, Depth depth,
2031 Move movesSearched[], int moveCount) {
2035 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2037 for (int i = 0; i < moveCount - 1; i++)
2039 m = movesSearched[i];
2043 if (!pos.move_is_capture_or_promotion(m))
2044 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2049 // update_killers() add a good move that produced a beta-cutoff
2050 // among the killer moves of that ply.
2052 void update_killers(Move m, SearchStack* ss) {
2054 if (m == ss->killers[0])
2057 ss->killers[1] = ss->killers[0];
2062 // update_gains() updates the gains table of a non-capture move given
2063 // the static position evaluation before and after the move.
2065 void update_gains(const Position& pos, Move m, Value before, Value after) {
2068 && before != VALUE_NONE
2069 && after != VALUE_NONE
2070 && pos.captured_piece() == NO_PIECE_TYPE
2071 && !move_is_castle(m)
2072 && !move_is_promotion(m))
2073 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2077 // current_search_time() returns the number of milliseconds which have passed
2078 // since the beginning of the current search.
2080 int current_search_time() {
2082 return get_system_time() - SearchStartTime;
2086 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2088 std::string value_to_uci(Value v) {
2090 std::stringstream s;
2092 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2093 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2095 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2100 // nps() computes the current nodes/second count.
2104 int t = current_search_time();
2105 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2109 // poll() performs two different functions: It polls for user input, and it
2110 // looks at the time consumed so far and decides if it's time to abort the
2115 static int lastInfoTime;
2116 int t = current_search_time();
2121 // We are line oriented, don't read single chars
2122 std::string command;
2124 if (!std::getline(std::cin, command))
2127 if (command == "quit")
2130 PonderSearch = false;
2134 else if (command == "stop")
2137 PonderSearch = false;
2139 else if (command == "ponderhit")
2143 // Print search information
2147 else if (lastInfoTime > t)
2148 // HACK: Must be a new search where we searched less than
2149 // NodesBetweenPolls nodes during the first second of search.
2152 else if (t - lastInfoTime >= 1000)
2159 if (dbg_show_hit_rate)
2160 dbg_print_hit_rate();
2162 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2163 << " time " << t << endl;
2166 // Should we stop the search?
2170 bool stillAtFirstMove = FirstRootMove
2171 && !AspirationFailLow
2172 && t > MaxSearchTime + ExtraSearchTime;
2174 bool noMoreTime = t > AbsoluteMaxSearchTime
2175 || stillAtFirstMove;
2177 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2178 || (ExactMaxTime && t >= ExactMaxTime)
2179 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2184 // ponderhit() is called when the program is pondering (i.e. thinking while
2185 // it's the opponent's turn to move) in order to let the engine know that
2186 // it correctly predicted the opponent's move.
2190 int t = current_search_time();
2191 PonderSearch = false;
2193 bool stillAtFirstMove = FirstRootMove
2194 && !AspirationFailLow
2195 && t > MaxSearchTime + ExtraSearchTime;
2197 bool noMoreTime = t > AbsoluteMaxSearchTime
2198 || stillAtFirstMove;
2200 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2205 // init_ss_array() does a fast reset of the first entries of a SearchStack
2206 // array and of all the excludedMove and skipNullMove entries.
2208 void init_ss_array(SearchStack* ss, int size) {
2210 for (int i = 0; i < size; i++, ss++)
2212 ss->excludedMove = MOVE_NONE;
2213 ss->skipNullMove = false;
2214 ss->reduction = Depth(0);
2222 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2223 // while the program is pondering. The point is to work around a wrinkle in
2224 // the UCI protocol: When pondering, the engine is not allowed to give a
2225 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2226 // We simply wait here until one of these commands is sent, and return,
2227 // after which the bestmove and pondermove will be printed (in id_loop()).
2229 void wait_for_stop_or_ponderhit() {
2231 std::string command;
2235 if (!std::getline(std::cin, command))
2238 if (command == "quit")
2243 else if (command == "ponderhit" || command == "stop")
2249 // print_pv_info() prints to standard output and eventually to log file information on
2250 // the current PV line. It is called at each iteration or after a new pv is found.
2252 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2254 cout << "info depth " << Iteration
2255 << " score " << value_to_uci(value)
2256 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2257 << " time " << current_search_time()
2258 << " nodes " << TM.nodes_searched()
2262 for (Move* m = pv; *m != MOVE_NONE; m++)
2269 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2270 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2272 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2273 TM.nodes_searched(), value, t, pv) << endl;
2278 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2279 // the PV back into the TT. This makes sure the old PV moves are searched
2280 // first, even if the old TT entries have been overwritten.
2282 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2286 Position p(pos, pos.thread());
2290 for (int i = 0; pv[i] != MOVE_NONE; i++)
2292 tte = TT.retrieve(p.get_key());
2293 if (!tte || tte->move() != pv[i])
2295 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2296 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2298 p.do_move(pv[i], st);
2303 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2304 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2305 // allow to always have a ponder move even when we fail high at root and also a
2306 // long PV to print that is important for position analysis.
2308 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2312 Position p(pos, pos.thread());
2315 assert(bestMove != MOVE_NONE);
2318 p.do_move(pv[ply++], st);
2320 while ( (tte = TT.retrieve(p.get_key())) != NULL
2321 && tte->move() != MOVE_NONE
2322 && move_is_legal(p, tte->move())
2324 && (!p.is_draw() || ply < 2))
2326 pv[ply] = tte->move();
2327 p.do_move(pv[ply++], st);
2329 pv[ply] = MOVE_NONE;
2333 // init_thread() is the function which is called when a new thread is
2334 // launched. It simply calls the idle_loop() function with the supplied
2335 // threadID. There are two versions of this function; one for POSIX
2336 // threads and one for Windows threads.
2338 #if !defined(_MSC_VER)
2340 void* init_thread(void *threadID) {
2342 TM.idle_loop(*(int*)threadID, NULL);
2348 DWORD WINAPI init_thread(LPVOID threadID) {
2350 TM.idle_loop(*(int*)threadID, NULL);
2357 /// The ThreadsManager class
2359 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2360 // get_beta_counters() are getters/setters for the per thread
2361 // counters used to sort the moves at root.
2363 void ThreadsManager::resetNodeCounters() {
2365 for (int i = 0; i < MAX_THREADS; i++)
2366 threads[i].nodes = 0ULL;
2369 void ThreadsManager::resetBetaCounters() {
2371 for (int i = 0; i < MAX_THREADS; i++)
2372 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2375 int64_t ThreadsManager::nodes_searched() const {
2377 int64_t result = 0ULL;
2378 for (int i = 0; i < ActiveThreads; i++)
2379 result += threads[i].nodes;
2384 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2387 for (int i = 0; i < MAX_THREADS; i++)
2389 our += threads[i].betaCutOffs[us];
2390 their += threads[i].betaCutOffs[opposite_color(us)];
2395 // idle_loop() is where the threads are parked when they have no work to do.
2396 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2397 // object for which the current thread is the master.
2399 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2401 assert(threadID >= 0 && threadID < MAX_THREADS);
2405 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2406 // master should exit as last one.
2407 if (AllThreadsShouldExit)
2410 threads[threadID].state = THREAD_TERMINATED;
2414 // If we are not thinking, wait for a condition to be signaled
2415 // instead of wasting CPU time polling for work.
2416 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2419 assert(threadID != 0);
2420 threads[threadID].state = THREAD_SLEEPING;
2422 #if !defined(_MSC_VER)
2423 lock_grab(&WaitLock);
2424 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2425 pthread_cond_wait(&WaitCond, &WaitLock);
2426 lock_release(&WaitLock);
2428 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2432 // If thread has just woken up, mark it as available
2433 if (threads[threadID].state == THREAD_SLEEPING)
2434 threads[threadID].state = THREAD_AVAILABLE;
2436 // If this thread has been assigned work, launch a search
2437 if (threads[threadID].state == THREAD_WORKISWAITING)
2439 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2441 threads[threadID].state = THREAD_SEARCHING;
2443 if (threads[threadID].splitPoint->pvNode)
2444 sp_search<PV>(threads[threadID].splitPoint, threadID);
2446 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2448 assert(threads[threadID].state == THREAD_SEARCHING);
2450 threads[threadID].state = THREAD_AVAILABLE;
2453 // If this thread is the master of a split point and all slaves have
2454 // finished their work at this split point, return from the idle loop.
2456 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2458 if (i == ActiveThreads)
2460 // Because sp->slaves[] is reset under lock protection,
2461 // be sure sp->lock has been released before to return.
2462 lock_grab(&(sp->lock));
2463 lock_release(&(sp->lock));
2465 assert(threads[threadID].state == THREAD_AVAILABLE);
2467 threads[threadID].state = THREAD_SEARCHING;
2474 // init_threads() is called during startup. It launches all helper threads,
2475 // and initializes the split point stack and the global locks and condition
2478 void ThreadsManager::init_threads() {
2483 #if !defined(_MSC_VER)
2484 pthread_t pthread[1];
2487 // Initialize global locks
2488 lock_init(&MPLock, NULL);
2489 lock_init(&WaitLock, NULL);
2491 #if !defined(_MSC_VER)
2492 pthread_cond_init(&WaitCond, NULL);
2494 for (i = 0; i < MAX_THREADS; i++)
2495 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2498 // Initialize splitPoints[] locks
2499 for (i = 0; i < MAX_THREADS; i++)
2500 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2501 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2503 // Will be set just before program exits to properly end the threads
2504 AllThreadsShouldExit = false;
2506 // Threads will be put to sleep as soon as created
2507 AllThreadsShouldSleep = true;
2509 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2511 threads[0].state = THREAD_SEARCHING;
2512 for (i = 1; i < MAX_THREADS; i++)
2513 threads[i].state = THREAD_AVAILABLE;
2515 // Launch the helper threads
2516 for (i = 1; i < MAX_THREADS; i++)
2519 #if !defined(_MSC_VER)
2520 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2522 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2527 cout << "Failed to create thread number " << i << endl;
2528 Application::exit_with_failure();
2531 // Wait until the thread has finished launching and is gone to sleep
2532 while (threads[i].state != THREAD_SLEEPING) {}
2537 // exit_threads() is called when the program exits. It makes all the
2538 // helper threads exit cleanly.
2540 void ThreadsManager::exit_threads() {
2542 ActiveThreads = MAX_THREADS; // HACK
2543 AllThreadsShouldSleep = true; // HACK
2544 wake_sleeping_threads();
2546 // This makes the threads to exit idle_loop()
2547 AllThreadsShouldExit = true;
2549 // Wait for thread termination
2550 for (int i = 1; i < MAX_THREADS; i++)
2551 while (threads[i].state != THREAD_TERMINATED) {}
2553 // Now we can safely destroy the locks
2554 for (int i = 0; i < MAX_THREADS; i++)
2555 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2556 lock_destroy(&(threads[i].splitPoints[j].lock));
2558 lock_destroy(&WaitLock);
2559 lock_destroy(&MPLock);
2563 // thread_should_stop() checks whether the thread should stop its search.
2564 // This can happen if a beta cutoff has occurred in the thread's currently
2565 // active split point, or in some ancestor of the current split point.
2567 bool ThreadsManager::thread_should_stop(int threadID) const {
2569 assert(threadID >= 0 && threadID < ActiveThreads);
2573 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2578 // thread_is_available() checks whether the thread with threadID "slave" is
2579 // available to help the thread with threadID "master" at a split point. An
2580 // obvious requirement is that "slave" must be idle. With more than two
2581 // threads, this is not by itself sufficient: If "slave" is the master of
2582 // some active split point, it is only available as a slave to the other
2583 // threads which are busy searching the split point at the top of "slave"'s
2584 // split point stack (the "helpful master concept" in YBWC terminology).
2586 bool ThreadsManager::thread_is_available(int slave, int master) const {
2588 assert(slave >= 0 && slave < ActiveThreads);
2589 assert(master >= 0 && master < ActiveThreads);
2590 assert(ActiveThreads > 1);
2592 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2595 // Make a local copy to be sure doesn't change under our feet
2596 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2598 if (localActiveSplitPoints == 0)
2599 // No active split points means that the thread is available as
2600 // a slave for any other thread.
2603 if (ActiveThreads == 2)
2606 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2607 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2608 // could have been set to 0 by another thread leading to an out of bound access.
2609 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2616 // available_thread_exists() tries to find an idle thread which is available as
2617 // a slave for the thread with threadID "master".
2619 bool ThreadsManager::available_thread_exists(int master) const {
2621 assert(master >= 0 && master < ActiveThreads);
2622 assert(ActiveThreads > 1);
2624 for (int i = 0; i < ActiveThreads; i++)
2625 if (thread_is_available(i, master))
2632 // split() does the actual work of distributing the work at a node between
2633 // several available threads. If it does not succeed in splitting the
2634 // node (because no idle threads are available, or because we have no unused
2635 // split point objects), the function immediately returns. If splitting is
2636 // possible, a SplitPoint object is initialized with all the data that must be
2637 // copied to the helper threads and we tell our helper threads that they have
2638 // been assigned work. This will cause them to instantly leave their idle loops
2639 // and call sp_search(). When all threads have returned from sp_search() then
2642 template <bool Fake>
2643 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2644 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2645 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2647 assert(ply > 0 && ply < PLY_MAX);
2648 assert(*bestValue >= -VALUE_INFINITE);
2649 assert(*bestValue <= *alpha);
2650 assert(*alpha < beta);
2651 assert(beta <= VALUE_INFINITE);
2652 assert(depth > Depth(0));
2653 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2654 assert(ActiveThreads > 1);
2656 int i, master = p.thread();
2657 Thread& masterThread = threads[master];
2661 // If no other thread is available to help us, or if we have too many
2662 // active split points, don't split.
2663 if ( !available_thread_exists(master)
2664 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2666 lock_release(&MPLock);
2670 // Pick the next available split point object from the split point stack
2671 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2673 // Initialize the split point object
2674 splitPoint.parent = masterThread.splitPoint;
2675 splitPoint.stopRequest = false;
2676 splitPoint.ply = ply;
2677 splitPoint.depth = depth;
2678 splitPoint.threatMove = threatMove;
2679 splitPoint.mateThreat = mateThreat;
2680 splitPoint.alpha = *alpha;
2681 splitPoint.beta = beta;
2682 splitPoint.pvNode = pvNode;
2683 splitPoint.bestValue = *bestValue;
2685 splitPoint.moveCount = *moveCount;
2686 splitPoint.pos = &p;
2687 splitPoint.parentSstack = ss;
2688 for (i = 0; i < ActiveThreads; i++)
2689 splitPoint.slaves[i] = 0;
2691 masterThread.splitPoint = &splitPoint;
2693 // If we are here it means we are not available
2694 assert(masterThread.state != THREAD_AVAILABLE);
2696 int workersCnt = 1; // At least the master is included
2698 // Allocate available threads setting state to THREAD_BOOKED
2699 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2700 if (thread_is_available(i, master))
2702 threads[i].state = THREAD_BOOKED;
2703 threads[i].splitPoint = &splitPoint;
2704 splitPoint.slaves[i] = 1;
2708 assert(Fake || workersCnt > 1);
2710 // We can release the lock because slave threads are already booked and master is not available
2711 lock_release(&MPLock);
2713 // Tell the threads that they have work to do. This will make them leave
2714 // their idle loop. But before copy search stack tail for each thread.
2715 for (i = 0; i < ActiveThreads; i++)
2716 if (i == master || splitPoint.slaves[i])
2718 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2720 assert(i == master || threads[i].state == THREAD_BOOKED);
2722 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2725 // Everything is set up. The master thread enters the idle loop, from
2726 // which it will instantly launch a search, because its state is
2727 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2728 // idle loop, which means that the main thread will return from the idle
2729 // loop when all threads have finished their work at this split point.
2730 idle_loop(master, &splitPoint);
2732 // We have returned from the idle loop, which means that all threads are
2733 // finished. Update alpha and bestValue, and return.
2736 *alpha = splitPoint.alpha;
2737 *bestValue = splitPoint.bestValue;
2738 masterThread.activeSplitPoints--;
2739 masterThread.splitPoint = splitPoint.parent;
2741 lock_release(&MPLock);
2745 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2746 // to start a new search from the root.
2748 void ThreadsManager::wake_sleeping_threads() {
2750 assert(AllThreadsShouldSleep);
2751 assert(ActiveThreads > 0);
2753 AllThreadsShouldSleep = false;
2755 if (ActiveThreads == 1)
2758 #if !defined(_MSC_VER)
2759 pthread_mutex_lock(&WaitLock);
2760 pthread_cond_broadcast(&WaitCond);
2761 pthread_mutex_unlock(&WaitLock);
2763 for (int i = 1; i < MAX_THREADS; i++)
2764 SetEvent(SitIdleEvent[i]);
2770 // put_threads_to_sleep() makes all the threads go to sleep just before
2771 // to leave think(), at the end of the search. Threads should have already
2772 // finished the job and should be idle.
2774 void ThreadsManager::put_threads_to_sleep() {
2776 assert(!AllThreadsShouldSleep);
2778 // This makes the threads to go to sleep
2779 AllThreadsShouldSleep = true;
2782 /// The RootMoveList class
2784 // RootMoveList c'tor
2786 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2788 SearchStack ss[PLY_MAX_PLUS_2];
2789 MoveStack mlist[MaxRootMoves];
2791 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2793 // Initialize search stack
2794 init_ss_array(ss, PLY_MAX_PLUS_2);
2796 ss[0].eval = VALUE_NONE;
2798 // Generate all legal moves
2799 MoveStack* last = generate_moves(pos, mlist);
2801 // Add each move to the moves[] array
2802 for (MoveStack* cur = mlist; cur != last; cur++)
2804 bool includeMove = includeAllMoves;
2806 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2807 includeMove = (searchMoves[k] == cur->move);
2812 // Find a quick score for the move
2813 pos.do_move(cur->move, st);
2814 ss[0].currentMove = cur->move;
2815 moves[count].move = cur->move;
2816 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2817 moves[count].pv[0] = cur->move;
2818 moves[count].pv[1] = MOVE_NONE;
2819 pos.undo_move(cur->move);
2826 // RootMoveList simple methods definitions
2828 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2830 moves[moveNum].nodes = nodes;
2831 moves[moveNum].cumulativeNodes += nodes;
2834 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2836 moves[moveNum].ourBeta = our;
2837 moves[moveNum].theirBeta = their;
2840 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2844 for (j = 0; pv[j] != MOVE_NONE; j++)
2845 moves[moveNum].pv[j] = pv[j];
2847 moves[moveNum].pv[j] = MOVE_NONE;
2851 // RootMoveList::sort() sorts the root move list at the beginning of a new
2854 void RootMoveList::sort() {
2856 sort_multipv(count - 1); // Sort all items
2860 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2861 // list by their scores and depths. It is used to order the different PVs
2862 // correctly in MultiPV mode.
2864 void RootMoveList::sort_multipv(int n) {
2868 for (i = 1; i <= n; i++)
2870 RootMove rm = moves[i];
2871 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2872 moves[j] = moves[j - 1];