2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
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 = threatMove = 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 refinedValue = bestValue = value = -VALUE_INFINITE;
1032 // Step 1. Initialize node and poll. Polling can abort search
1033 TM.incrementNodeCounter(threadID);
1035 (ss+2)->initKillers();
1037 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1043 // Step 2. Check for aborted search and immediate draw
1044 if (AbortSearch || TM.thread_should_stop(threadID))
1047 if (pos.is_draw() || ply >= PLY_MAX - 1)
1050 // Step 3. Mate distance pruning
1051 alpha = Max(value_mated_in(ply), alpha);
1052 beta = Min(value_mate_in(ply+1), beta);
1056 // Step 4. Transposition table lookup
1058 // We don't want the score of a partial search to overwrite a previous full search
1059 // TT value, so we use a different position key in case of an excluded move exists.
1060 excludedMove = ss->excludedMove;
1061 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1063 tte = TT.retrieve(posKey);
1064 ttMove = (tte ? tte->move() : MOVE_NONE);
1066 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1067 // This is to avoid problems in the following areas:
1069 // * Repetition draw detection
1070 // * Fifty move rule detection
1071 // * Searching for a mate
1072 // * Printing of full PV line
1074 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1076 // Refresh tte entry to avoid aging
1077 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1079 ss->currentMove = ttMove; // Can be MOVE_NONE
1080 return value_from_tt(tte->value(), ply);
1083 // Step 5. Evaluate the position statically
1084 // At PV nodes we do this only to update gain statistics
1085 isCheck = pos.is_check();
1090 assert(tte->static_value() != VALUE_NONE);
1091 ss->eval = tte->static_value();
1092 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1096 ss->eval = evaluate(pos, ei);
1097 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1100 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1101 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1104 ss->eval = VALUE_NONE;
1106 // Step 6. Razoring (is omitted in PV nodes)
1108 && depth < RazorDepth
1110 && refinedValue < beta - razor_margin(depth)
1111 && ttMove == MOVE_NONE
1112 && (ss-1)->currentMove != MOVE_NULL
1113 && !value_is_mate(beta)
1114 && !pos.has_pawn_on_7th(pos.side_to_move()))
1116 Value rbeta = beta - razor_margin(depth);
1117 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1119 // Logically we should return (v + razor_margin(depth)), but
1120 // surprisingly this did slightly weaker in tests.
1124 // Step 7. Static null move pruning (is omitted in PV nodes)
1125 // We're betting that the opponent doesn't have a move that will reduce
1126 // the score by more than futility_margin(depth) if we do a null move.
1128 && !ss->skipNullMove
1129 && depth < RazorDepth
1130 && refinedValue >= beta + futility_margin(depth, 0)
1132 && !value_is_mate(beta)
1133 && pos.non_pawn_material(pos.side_to_move()))
1134 return refinedValue - futility_margin(depth, 0);
1136 // Step 8. Null move search with verification search (is omitted in PV nodes)
1137 // When we jump directly to qsearch() we do a null move only if static value is
1138 // at least beta. Otherwise we do a null move if static value is not more than
1139 // NullMoveMargin under beta.
1141 && !ss->skipNullMove
1143 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1145 && !value_is_mate(beta)
1146 && pos.non_pawn_material(pos.side_to_move()))
1148 ss->currentMove = MOVE_NULL;
1150 // Null move dynamic reduction based on depth
1151 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1153 // Null move dynamic reduction based on value
1154 if (refinedValue - beta > PawnValueMidgame)
1157 pos.do_null_move(st);
1158 (ss+1)->skipNullMove = true;
1160 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1161 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1162 (ss+1)->skipNullMove = false;
1163 pos.undo_null_move();
1165 if (nullValue >= beta)
1167 // Do not return unproven mate scores
1168 if (nullValue >= value_mate_in(PLY_MAX))
1171 if (depth < 6 * OnePly)
1174 // Do verification search at high depths
1175 ss->skipNullMove = true;
1176 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1177 ss->skipNullMove = false;
1184 // The null move failed low, which means that we may be faced with
1185 // some kind of threat. If the previous move was reduced, check if
1186 // the move that refuted the null move was somehow connected to the
1187 // move which was reduced. If a connection is found, return a fail
1188 // low score (which will cause the reduced move to fail high in the
1189 // parent node, which will trigger a re-search with full depth).
1190 if (nullValue == value_mated_in(ply + 2))
1193 ss->threatMove = (ss+1)->currentMove;
1194 if ( depth < ThreatDepth
1195 && (ss-1)->reduction
1196 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1201 // Step 9. Internal iterative deepening
1202 if ( depth >= IIDDepth[PvNode]
1203 && ttMove == MOVE_NONE
1204 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1206 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1208 ss->skipNullMove = true;
1209 search<PvNode>(pos, ss, alpha, beta, d, ply);
1210 ss->skipNullMove = false;
1212 ttMove = ss->bestMove;
1213 tte = TT.retrieve(posKey);
1216 // Expensive mate threat detection (only for PV nodes)
1218 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1220 // Initialize a MovePicker object for the current position
1221 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1223 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1224 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1225 && tte && tte->move()
1226 && !excludedMove // Do not allow recursive singular extension search
1227 && is_lower_bound(tte->type())
1228 && tte->depth() >= depth - 3 * OnePly;
1230 // Step 10. Loop through moves
1231 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1232 while ( bestValue < beta
1233 && (move = mp.get_next_move()) != MOVE_NONE
1234 && !TM.thread_should_stop(threadID))
1236 assert(move_is_ok(move));
1238 if (move == excludedMove)
1241 moveIsCheck = pos.move_is_check(move, ci);
1242 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1244 // Step 11. Decide the new search depth
1245 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1247 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1248 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1249 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1250 // lower then ttValue minus a margin then we extend ttMove.
1251 if ( singularExtensionNode
1252 && move == tte->move()
1255 Value ttValue = value_from_tt(tte->value(), ply);
1257 if (abs(ttValue) < VALUE_KNOWN_WIN)
1259 Value b = ttValue - SingularExtensionMargin;
1260 ss->excludedMove = move;
1261 ss->skipNullMove = true;
1262 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1263 ss->skipNullMove = false;
1264 ss->excludedMove = MOVE_NONE;
1270 newDepth = depth - OnePly + ext;
1272 // Update current move (this must be done after singular extension search)
1273 movesSearched[moveCount++] = ss->currentMove = move;
1275 // Step 12. Futility pruning (is omitted in PV nodes)
1277 && !captureOrPromotion
1281 && !move_is_castle(move))
1283 // Move count based pruning
1284 if ( moveCount >= futility_move_count(depth)
1285 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1286 && bestValue > value_mated_in(PLY_MAX))
1289 // Value based pruning
1290 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1291 // but fixing this made program slightly weaker.
1292 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1293 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1294 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1296 if (futilityValueScaled < beta)
1298 if (futilityValueScaled > bestValue)
1299 bestValue = futilityValueScaled;
1304 // Step 13. Make the move
1305 pos.do_move(move, st, ci, moveIsCheck);
1307 // Step extra. pv search (only in PV nodes)
1308 // The first move in list is the expected PV
1309 if (PvNode && moveCount == 1)
1310 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1311 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1314 // Step 14. Reduced depth search
1315 // If the move fails high will be re-searched at full depth.
1316 bool doFullDepthSearch = true;
1318 if ( depth >= 3 * OnePly
1319 && !captureOrPromotion
1321 && !move_is_castle(move)
1322 && !move_is_killer(move, ss))
1324 ss->reduction = reduction<PvNode>(depth, moveCount);
1327 Depth d = newDepth - ss->reduction;
1328 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1329 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1331 doFullDepthSearch = (value > alpha);
1334 // The move failed high, but if reduction is very big we could
1335 // face a false positive, retry with a less aggressive reduction,
1336 // if the move fails high again then go with full depth search.
1337 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1339 assert(newDepth - OnePly >= OnePly);
1341 ss->reduction = OnePly;
1342 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1343 doFullDepthSearch = (value > alpha);
1345 ss->reduction = Depth(0); // Restore original reduction
1348 // Step 15. Full depth search
1349 if (doFullDepthSearch)
1351 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1352 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1354 // Step extra. pv search (only in PV nodes)
1355 // Search only for possible new PV nodes, if instead value >= beta then
1356 // parent node fails low with value <= alpha and tries another move.
1357 if (PvNode && value > alpha && value < beta)
1358 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1359 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1363 // Step 16. Undo move
1364 pos.undo_move(move);
1366 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1368 // Step 17. Check for new best move
1369 if (value > bestValue)
1374 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1377 if (value == value_mate_in(ply + 1))
1378 ss->mateKiller = move;
1380 ss->bestMove = move;
1384 // Step 18. Check for split
1385 if ( depth >= MinimumSplitDepth
1386 && TM.active_threads() > 1
1388 && TM.available_thread_exists(threadID)
1390 && !TM.thread_should_stop(threadID)
1392 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1393 mateThreat, &moveCount, &mp, PvNode);
1396 // Step 19. Check for mate and stalemate
1397 // All legal moves have been searched and if there are
1398 // no legal moves, it must be mate or stalemate.
1399 // If one move was excluded return fail low score.
1401 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1403 // Step 20. Update tables
1404 // If the search is not aborted, update the transposition table,
1405 // history counters, and killer moves.
1406 if (AbortSearch || TM.thread_should_stop(threadID))
1409 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1410 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1411 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1413 // Update killers and history only for non capture moves that fails high
1414 if (bestValue >= beta)
1416 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1417 if (!pos.move_is_capture_or_promotion(move))
1419 update_history(pos, move, depth, movesSearched, moveCount);
1420 update_killers(move, ss);
1424 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1430 // qsearch() is the quiescence search function, which is called by the main
1431 // search function when the remaining depth is zero (or, to be more precise,
1432 // less than OnePly).
1434 template <NodeType PvNode>
1435 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1437 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1438 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1439 assert(PvNode || alpha == beta - 1);
1441 assert(ply > 0 && ply < PLY_MAX);
1442 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1447 Value bestValue, value, futilityValue, futilityBase;
1448 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1450 Value oldAlpha = alpha;
1452 TM.incrementNodeCounter(pos.thread());
1453 ss->bestMove = ss->currentMove = MOVE_NONE;
1455 // Check for an instant draw or maximum ply reached
1456 if (pos.is_draw() || ply >= PLY_MAX - 1)
1459 // Transposition table lookup. At PV nodes, we don't use the TT for
1460 // pruning, but only for move ordering.
1461 tte = TT.retrieve(pos.get_key());
1462 ttMove = (tte ? tte->move() : MOVE_NONE);
1464 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1466 ss->currentMove = ttMove; // Can be MOVE_NONE
1467 return value_from_tt(tte->value(), ply);
1470 isCheck = pos.is_check();
1472 // Evaluate the position statically
1475 bestValue = futilityBase = -VALUE_INFINITE;
1476 ss->eval = VALUE_NONE;
1477 deepChecks = enoughMaterial = false;
1483 assert(tte->static_value() != VALUE_NONE);
1484 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1485 bestValue = tte->static_value();
1488 bestValue = evaluate(pos, ei);
1490 ss->eval = bestValue;
1491 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1493 // Stand pat. Return immediately if static value is at least beta
1494 if (bestValue >= beta)
1497 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()]);
1502 if (PvNode && bestValue > alpha)
1505 // If we are near beta then try to get a cutoff pushing checks a bit further
1506 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1508 // Futility pruning parameters, not needed when in check
1509 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1510 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1513 // Initialize a MovePicker object for the current position, and prepare
1514 // to search the moves. Because the depth is <= 0 here, only captures,
1515 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1516 // and we are near beta) will be generated.
1517 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1520 // Loop through the moves until no moves remain or a beta cutoff occurs
1521 while ( alpha < beta
1522 && (move = mp.get_next_move()) != MOVE_NONE)
1524 assert(move_is_ok(move));
1526 moveIsCheck = pos.move_is_check(move, ci);
1534 && !move_is_promotion(move)
1535 && !pos.move_is_passed_pawn_push(move))
1537 futilityValue = futilityBase
1538 + pos.endgame_value_of_piece_on(move_to(move))
1539 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1541 if (futilityValue < alpha)
1543 if (futilityValue > bestValue)
1544 bestValue = futilityValue;
1549 // Detect blocking evasions that are candidate to be pruned
1550 evasionPrunable = isCheck
1551 && bestValue > value_mated_in(PLY_MAX)
1552 && !pos.move_is_capture(move)
1553 && pos.type_of_piece_on(move_from(move)) != KING
1554 && !pos.can_castle(pos.side_to_move());
1556 // Don't search moves with negative SEE values
1558 && (!isCheck || evasionPrunable)
1560 && !move_is_promotion(move)
1561 && pos.see_sign(move) < 0)
1564 // Update current move
1565 ss->currentMove = move;
1567 // Make and search the move
1568 pos.do_move(move, st, ci, moveIsCheck);
1569 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1570 pos.undo_move(move);
1572 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1575 if (value > bestValue)
1581 ss->bestMove = move;
1586 // All legal moves have been searched. A special case: If we're in check
1587 // and no legal moves were found, it is checkmate.
1588 if (isCheck && bestValue == -VALUE_INFINITE)
1589 return value_mated_in(ply);
1591 // Update transposition table
1592 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1593 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1594 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1596 // Update killers only for checking moves that fails high
1597 if ( bestValue >= beta
1598 && !pos.move_is_capture_or_promotion(ss->bestMove))
1599 update_killers(ss->bestMove, ss);
1601 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1607 // sp_search() is used to search from a split point. This function is called
1608 // by each thread working at the split point. It is similar to the normal
1609 // search() function, but simpler. Because we have already probed the hash
1610 // table, done a null move search, and searched the first move before
1611 // splitting, we don't have to repeat all this work in sp_search(). We
1612 // also don't need to store anything to the hash table here: This is taken
1613 // care of after we return from the split point.
1615 template <NodeType PvNode>
1616 void sp_search(SplitPoint* sp, int threadID) {
1618 assert(threadID >= 0 && threadID < TM.active_threads());
1619 assert(TM.active_threads() > 1);
1623 Depth ext, newDepth;
1625 Value futilityValueScaled; // NonPV specific
1626 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1628 value = -VALUE_INFINITE;
1630 Position pos(*sp->pos, threadID);
1632 SearchStack* ss = sp->sstack[threadID] + 1;
1633 isCheck = pos.is_check();
1635 // Step 10. Loop through moves
1636 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1637 lock_grab(&(sp->lock));
1639 while ( sp->bestValue < sp->beta
1640 && (move = sp->mp->get_next_move()) != MOVE_NONE
1641 && !TM.thread_should_stop(threadID))
1643 moveCount = ++sp->moveCount;
1644 lock_release(&(sp->lock));
1646 assert(move_is_ok(move));
1648 moveIsCheck = pos.move_is_check(move, ci);
1649 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1651 // Step 11. Decide the new search depth
1652 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1653 newDepth = sp->depth - OnePly + ext;
1655 // Update current move
1656 ss->currentMove = move;
1658 // Step 12. Futility pruning (is omitted in PV nodes)
1660 && !captureOrPromotion
1663 && !move_is_castle(move))
1665 // Move count based pruning
1666 if ( moveCount >= futility_move_count(sp->depth)
1667 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1668 && sp->bestValue > value_mated_in(PLY_MAX))
1670 lock_grab(&(sp->lock));
1674 // Value based pruning
1675 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1676 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1677 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1679 if (futilityValueScaled < sp->beta)
1681 lock_grab(&(sp->lock));
1683 if (futilityValueScaled > sp->bestValue)
1684 sp->bestValue = futilityValueScaled;
1689 // Step 13. Make the move
1690 pos.do_move(move, st, ci, moveIsCheck);
1692 // Step 14. Reduced search
1693 // If the move fails high will be re-searched at full depth.
1694 bool doFullDepthSearch = true;
1696 if ( !captureOrPromotion
1698 && !move_is_castle(move)
1699 && !move_is_killer(move, ss))
1701 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1704 Value localAlpha = sp->alpha;
1705 Depth d = newDepth - ss->reduction;
1706 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1707 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1709 doFullDepthSearch = (value > localAlpha);
1712 // The move failed high, but if reduction is very big we could
1713 // face a false positive, retry with a less aggressive reduction,
1714 // if the move fails high again then go with full depth search.
1715 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1717 assert(newDepth - OnePly >= OnePly);
1719 ss->reduction = OnePly;
1720 Value localAlpha = sp->alpha;
1721 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1722 doFullDepthSearch = (value > localAlpha);
1724 ss->reduction = Depth(0); // Restore original reduction
1727 // Step 15. Full depth search
1728 if (doFullDepthSearch)
1730 Value localAlpha = sp->alpha;
1731 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1732 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1734 // Step extra. pv search (only in PV nodes)
1735 // Search only for possible new PV nodes, if instead value >= beta then
1736 // parent node fails low with value <= alpha and tries another move.
1737 if (PvNode && value > localAlpha && value < sp->beta)
1738 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1739 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1742 // Step 16. Undo move
1743 pos.undo_move(move);
1745 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1747 // Step 17. Check for new best move
1748 lock_grab(&(sp->lock));
1750 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1752 sp->bestValue = value;
1754 if (sp->bestValue > sp->alpha)
1756 if (!PvNode || value >= sp->beta)
1757 sp->stopRequest = true;
1759 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1762 sp->parentSstack->bestMove = ss->bestMove = move;
1767 /* Here we have the lock still grabbed */
1769 sp->slaves[threadID] = 0;
1771 lock_release(&(sp->lock));
1775 // connected_moves() tests whether two moves are 'connected' in the sense
1776 // that the first move somehow made the second move possible (for instance
1777 // if the moving piece is the same in both moves). The first move is assumed
1778 // to be the move that was made to reach the current position, while the
1779 // second move is assumed to be a move from the current position.
1781 bool connected_moves(const Position& pos, Move m1, Move m2) {
1783 Square f1, t1, f2, t2;
1786 assert(move_is_ok(m1));
1787 assert(move_is_ok(m2));
1789 if (m2 == MOVE_NONE)
1792 // Case 1: The moving piece is the same in both moves
1798 // Case 2: The destination square for m2 was vacated by m1
1804 // Case 3: Moving through the vacated square
1805 if ( piece_is_slider(pos.piece_on(f2))
1806 && bit_is_set(squares_between(f2, t2), f1))
1809 // Case 4: The destination square for m2 is defended by the moving piece in m1
1810 p = pos.piece_on(t1);
1811 if (bit_is_set(pos.attacks_from(p, t1), t2))
1814 // Case 5: Discovered check, checking piece is the piece moved in m1
1815 if ( piece_is_slider(p)
1816 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1817 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1819 // discovered_check_candidates() works also if the Position's side to
1820 // move is the opposite of the checking piece.
1821 Color them = opposite_color(pos.side_to_move());
1822 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1824 if (bit_is_set(dcCandidates, f2))
1831 // value_is_mate() checks if the given value is a mate one eventually
1832 // compensated for the ply.
1834 bool value_is_mate(Value value) {
1836 assert(abs(value) <= VALUE_INFINITE);
1838 return value <= value_mated_in(PLY_MAX)
1839 || value >= value_mate_in(PLY_MAX);
1843 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1844 // "plies to mate from the current ply". Non-mate scores are unchanged.
1845 // The function is called before storing a value to the transposition table.
1847 Value value_to_tt(Value v, int ply) {
1849 if (v >= value_mate_in(PLY_MAX))
1852 if (v <= value_mated_in(PLY_MAX))
1859 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1860 // the transposition table to a mate score corrected for the current ply.
1862 Value value_from_tt(Value v, int ply) {
1864 if (v >= value_mate_in(PLY_MAX))
1867 if (v <= value_mated_in(PLY_MAX))
1874 // move_is_killer() checks if the given move is among the killer moves
1876 bool move_is_killer(Move m, SearchStack* ss) {
1878 if (ss->killers[0] == m || ss->killers[1] == m)
1885 // extension() decides whether a move should be searched with normal depth,
1886 // or with extended depth. Certain classes of moves (checking moves, in
1887 // particular) are searched with bigger depth than ordinary moves and in
1888 // any case are marked as 'dangerous'. Note that also if a move is not
1889 // extended, as example because the corresponding UCI option is set to zero,
1890 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1891 template <NodeType PvNode>
1892 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1893 bool singleEvasion, bool mateThreat, bool* dangerous) {
1895 assert(m != MOVE_NONE);
1897 Depth result = Depth(0);
1898 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1902 if (moveIsCheck && pos.see_sign(m) >= 0)
1903 result += CheckExtension[PvNode];
1906 result += SingleEvasionExtension[PvNode];
1909 result += MateThreatExtension[PvNode];
1912 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1914 Color c = pos.side_to_move();
1915 if (relative_rank(c, move_to(m)) == RANK_7)
1917 result += PawnPushTo7thExtension[PvNode];
1920 if (pos.pawn_is_passed(c, move_to(m)))
1922 result += PassedPawnExtension[PvNode];
1927 if ( captureOrPromotion
1928 && pos.type_of_piece_on(move_to(m)) != PAWN
1929 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1930 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1931 && !move_is_promotion(m)
1934 result += PawnEndgameExtension[PvNode];
1939 && captureOrPromotion
1940 && pos.type_of_piece_on(move_to(m)) != PAWN
1941 && pos.see_sign(m) >= 0)
1947 return Min(result, OnePly);
1951 // connected_threat() tests whether it is safe to forward prune a move or if
1952 // is somehow coonected to the threat move returned by null search.
1954 bool connected_threat(const Position& pos, Move m, Move threat) {
1956 assert(move_is_ok(m));
1957 assert(threat && move_is_ok(threat));
1958 assert(!pos.move_is_check(m));
1959 assert(!pos.move_is_capture_or_promotion(m));
1960 assert(!pos.move_is_passed_pawn_push(m));
1962 Square mfrom, mto, tfrom, tto;
1964 mfrom = move_from(m);
1966 tfrom = move_from(threat);
1967 tto = move_to(threat);
1969 // Case 1: Don't prune moves which move the threatened piece
1973 // Case 2: If the threatened piece has value less than or equal to the
1974 // value of the threatening piece, don't prune move which defend it.
1975 if ( pos.move_is_capture(threat)
1976 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1977 || pos.type_of_piece_on(tfrom) == KING)
1978 && pos.move_attacks_square(m, tto))
1981 // Case 3: If the moving piece in the threatened move is a slider, don't
1982 // prune safe moves which block its ray.
1983 if ( piece_is_slider(pos.piece_on(tfrom))
1984 && bit_is_set(squares_between(tfrom, tto), mto)
1985 && pos.see_sign(m) >= 0)
1992 // ok_to_use_TT() returns true if a transposition table score
1993 // can be used at a given point in search.
1995 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1997 Value v = value_from_tt(tte->value(), ply);
1999 return ( tte->depth() >= depth
2000 || v >= Max(value_mate_in(PLY_MAX), beta)
2001 || v < Min(value_mated_in(PLY_MAX), beta))
2003 && ( (is_lower_bound(tte->type()) && v >= beta)
2004 || (is_upper_bound(tte->type()) && v < beta));
2008 // refine_eval() returns the transposition table score if
2009 // possible otherwise falls back on static position evaluation.
2011 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2016 Value v = value_from_tt(tte->value(), ply);
2018 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2019 || (is_upper_bound(tte->type()) && v < defaultEval))
2026 // update_history() registers a good move that produced a beta-cutoff
2027 // in history and marks as failures all the other moves of that ply.
2029 void update_history(const Position& pos, Move move, Depth depth,
2030 Move movesSearched[], int moveCount) {
2034 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2036 for (int i = 0; i < moveCount - 1; i++)
2038 m = movesSearched[i];
2042 if (!pos.move_is_capture_or_promotion(m))
2043 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2048 // update_killers() add a good move that produced a beta-cutoff
2049 // among the killer moves of that ply.
2051 void update_killers(Move m, SearchStack* ss) {
2053 if (m == ss->killers[0])
2056 ss->killers[1] = ss->killers[0];
2061 // update_gains() updates the gains table of a non-capture move given
2062 // the static position evaluation before and after the move.
2064 void update_gains(const Position& pos, Move m, Value before, Value after) {
2067 && before != VALUE_NONE
2068 && after != VALUE_NONE
2069 && pos.captured_piece() == NO_PIECE_TYPE
2070 && !move_is_castle(m)
2071 && !move_is_promotion(m))
2072 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2076 // current_search_time() returns the number of milliseconds which have passed
2077 // since the beginning of the current search.
2079 int current_search_time() {
2081 return get_system_time() - SearchStartTime;
2085 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2087 std::string value_to_uci(Value v) {
2089 std::stringstream s;
2091 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2092 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2094 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2099 // nps() computes the current nodes/second count.
2103 int t = current_search_time();
2104 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2108 // poll() performs two different functions: It polls for user input, and it
2109 // looks at the time consumed so far and decides if it's time to abort the
2114 static int lastInfoTime;
2115 int t = current_search_time();
2120 // We are line oriented, don't read single chars
2121 std::string command;
2123 if (!std::getline(std::cin, command))
2126 if (command == "quit")
2129 PonderSearch = false;
2133 else if (command == "stop")
2136 PonderSearch = false;
2138 else if (command == "ponderhit")
2142 // Print search information
2146 else if (lastInfoTime > t)
2147 // HACK: Must be a new search where we searched less than
2148 // NodesBetweenPolls nodes during the first second of search.
2151 else if (t - lastInfoTime >= 1000)
2158 if (dbg_show_hit_rate)
2159 dbg_print_hit_rate();
2161 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2162 << " time " << t << endl;
2165 // Should we stop the search?
2169 bool stillAtFirstMove = FirstRootMove
2170 && !AspirationFailLow
2171 && t > MaxSearchTime + ExtraSearchTime;
2173 bool noMoreTime = t > AbsoluteMaxSearchTime
2174 || stillAtFirstMove;
2176 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2177 || (ExactMaxTime && t >= ExactMaxTime)
2178 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2183 // ponderhit() is called when the program is pondering (i.e. thinking while
2184 // it's the opponent's turn to move) in order to let the engine know that
2185 // it correctly predicted the opponent's move.
2189 int t = current_search_time();
2190 PonderSearch = false;
2192 bool stillAtFirstMove = FirstRootMove
2193 && !AspirationFailLow
2194 && t > MaxSearchTime + ExtraSearchTime;
2196 bool noMoreTime = t > AbsoluteMaxSearchTime
2197 || stillAtFirstMove;
2199 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2204 // init_ss_array() does a fast reset of the first entries of a SearchStack
2205 // array and of all the excludedMove and skipNullMove entries.
2207 void init_ss_array(SearchStack* ss, int size) {
2209 for (int i = 0; i < size; i++, ss++)
2211 ss->excludedMove = MOVE_NONE;
2212 ss->skipNullMove = false;
2213 ss->reduction = Depth(0);
2221 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2222 // while the program is pondering. The point is to work around a wrinkle in
2223 // the UCI protocol: When pondering, the engine is not allowed to give a
2224 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2225 // We simply wait here until one of these commands is sent, and return,
2226 // after which the bestmove and pondermove will be printed (in id_loop()).
2228 void wait_for_stop_or_ponderhit() {
2230 std::string command;
2234 if (!std::getline(std::cin, command))
2237 if (command == "quit")
2242 else if (command == "ponderhit" || command == "stop")
2248 // print_pv_info() prints to standard output and eventually to log file information on
2249 // the current PV line. It is called at each iteration or after a new pv is found.
2251 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2253 cout << "info depth " << Iteration
2254 << " score " << value_to_uci(value)
2255 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2256 << " time " << current_search_time()
2257 << " nodes " << TM.nodes_searched()
2261 for (Move* m = pv; *m != MOVE_NONE; m++)
2268 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2269 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2271 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2272 TM.nodes_searched(), value, t, pv) << endl;
2277 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2278 // the PV back into the TT. This makes sure the old PV moves are searched
2279 // first, even if the old TT entries have been overwritten.
2281 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2285 Position p(pos, pos.thread());
2289 for (int i = 0; pv[i] != MOVE_NONE; i++)
2291 tte = TT.retrieve(p.get_key());
2292 if (!tte || tte->move() != pv[i])
2294 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2295 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2297 p.do_move(pv[i], st);
2302 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2303 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2304 // allow to always have a ponder move even when we fail high at root and also a
2305 // long PV to print that is important for position analysis.
2307 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2311 Position p(pos, pos.thread());
2314 assert(bestMove != MOVE_NONE);
2317 p.do_move(pv[ply++], st);
2319 while ( (tte = TT.retrieve(p.get_key())) != NULL
2320 && tte->move() != MOVE_NONE
2321 && move_is_legal(p, tte->move())
2323 && (!p.is_draw() || ply < 2))
2325 pv[ply] = tte->move();
2326 p.do_move(pv[ply++], st);
2328 pv[ply] = MOVE_NONE;
2332 // init_thread() is the function which is called when a new thread is
2333 // launched. It simply calls the idle_loop() function with the supplied
2334 // threadID. There are two versions of this function; one for POSIX
2335 // threads and one for Windows threads.
2337 #if !defined(_MSC_VER)
2339 void* init_thread(void *threadID) {
2341 TM.idle_loop(*(int*)threadID, NULL);
2347 DWORD WINAPI init_thread(LPVOID threadID) {
2349 TM.idle_loop(*(int*)threadID, NULL);
2356 /// The ThreadsManager class
2358 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2359 // get_beta_counters() are getters/setters for the per thread
2360 // counters used to sort the moves at root.
2362 void ThreadsManager::resetNodeCounters() {
2364 for (int i = 0; i < MAX_THREADS; i++)
2365 threads[i].nodes = 0ULL;
2368 void ThreadsManager::resetBetaCounters() {
2370 for (int i = 0; i < MAX_THREADS; i++)
2371 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2374 int64_t ThreadsManager::nodes_searched() const {
2376 int64_t result = 0ULL;
2377 for (int i = 0; i < ActiveThreads; i++)
2378 result += threads[i].nodes;
2383 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2386 for (int i = 0; i < MAX_THREADS; i++)
2388 our += threads[i].betaCutOffs[us];
2389 their += threads[i].betaCutOffs[opposite_color(us)];
2394 // idle_loop() is where the threads are parked when they have no work to do.
2395 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2396 // object for which the current thread is the master.
2398 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2400 assert(threadID >= 0 && threadID < MAX_THREADS);
2404 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2405 // master should exit as last one.
2406 if (AllThreadsShouldExit)
2409 threads[threadID].state = THREAD_TERMINATED;
2413 // If we are not thinking, wait for a condition to be signaled
2414 // instead of wasting CPU time polling for work.
2415 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2418 assert(threadID != 0);
2419 threads[threadID].state = THREAD_SLEEPING;
2421 #if !defined(_MSC_VER)
2422 lock_grab(&WaitLock);
2423 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2424 pthread_cond_wait(&WaitCond, &WaitLock);
2425 lock_release(&WaitLock);
2427 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2431 // If thread has just woken up, mark it as available
2432 if (threads[threadID].state == THREAD_SLEEPING)
2433 threads[threadID].state = THREAD_AVAILABLE;
2435 // If this thread has been assigned work, launch a search
2436 if (threads[threadID].state == THREAD_WORKISWAITING)
2438 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2440 threads[threadID].state = THREAD_SEARCHING;
2442 if (threads[threadID].splitPoint->pvNode)
2443 sp_search<PV>(threads[threadID].splitPoint, threadID);
2445 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2447 assert(threads[threadID].state == THREAD_SEARCHING);
2449 threads[threadID].state = THREAD_AVAILABLE;
2452 // If this thread is the master of a split point and all slaves have
2453 // finished their work at this split point, return from the idle loop.
2455 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2457 if (i == ActiveThreads)
2459 // Because sp->slaves[] is reset under lock protection,
2460 // be sure sp->lock has been released before to return.
2461 lock_grab(&(sp->lock));
2462 lock_release(&(sp->lock));
2464 assert(threads[threadID].state == THREAD_AVAILABLE);
2466 threads[threadID].state = THREAD_SEARCHING;
2473 // init_threads() is called during startup. It launches all helper threads,
2474 // and initializes the split point stack and the global locks and condition
2477 void ThreadsManager::init_threads() {
2482 #if !defined(_MSC_VER)
2483 pthread_t pthread[1];
2486 // Initialize global locks
2487 lock_init(&MPLock, NULL);
2488 lock_init(&WaitLock, NULL);
2490 #if !defined(_MSC_VER)
2491 pthread_cond_init(&WaitCond, NULL);
2493 for (i = 0; i < MAX_THREADS; i++)
2494 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2497 // Initialize splitPoints[] locks
2498 for (i = 0; i < MAX_THREADS; i++)
2499 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2500 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2502 // Will be set just before program exits to properly end the threads
2503 AllThreadsShouldExit = false;
2505 // Threads will be put to sleep as soon as created
2506 AllThreadsShouldSleep = true;
2508 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2510 threads[0].state = THREAD_SEARCHING;
2511 for (i = 1; i < MAX_THREADS; i++)
2512 threads[i].state = THREAD_AVAILABLE;
2514 // Launch the helper threads
2515 for (i = 1; i < MAX_THREADS; i++)
2518 #if !defined(_MSC_VER)
2519 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2521 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2526 cout << "Failed to create thread number " << i << endl;
2527 Application::exit_with_failure();
2530 // Wait until the thread has finished launching and is gone to sleep
2531 while (threads[i].state != THREAD_SLEEPING) {}
2536 // exit_threads() is called when the program exits. It makes all the
2537 // helper threads exit cleanly.
2539 void ThreadsManager::exit_threads() {
2541 ActiveThreads = MAX_THREADS; // HACK
2542 AllThreadsShouldSleep = true; // HACK
2543 wake_sleeping_threads();
2545 // This makes the threads to exit idle_loop()
2546 AllThreadsShouldExit = true;
2548 // Wait for thread termination
2549 for (int i = 1; i < MAX_THREADS; i++)
2550 while (threads[i].state != THREAD_TERMINATED) {}
2552 // Now we can safely destroy the locks
2553 for (int i = 0; i < MAX_THREADS; i++)
2554 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2555 lock_destroy(&(threads[i].splitPoints[j].lock));
2557 lock_destroy(&WaitLock);
2558 lock_destroy(&MPLock);
2562 // thread_should_stop() checks whether the thread should stop its search.
2563 // This can happen if a beta cutoff has occurred in the thread's currently
2564 // active split point, or in some ancestor of the current split point.
2566 bool ThreadsManager::thread_should_stop(int threadID) const {
2568 assert(threadID >= 0 && threadID < ActiveThreads);
2572 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2577 // thread_is_available() checks whether the thread with threadID "slave" is
2578 // available to help the thread with threadID "master" at a split point. An
2579 // obvious requirement is that "slave" must be idle. With more than two
2580 // threads, this is not by itself sufficient: If "slave" is the master of
2581 // some active split point, it is only available as a slave to the other
2582 // threads which are busy searching the split point at the top of "slave"'s
2583 // split point stack (the "helpful master concept" in YBWC terminology).
2585 bool ThreadsManager::thread_is_available(int slave, int master) const {
2587 assert(slave >= 0 && slave < ActiveThreads);
2588 assert(master >= 0 && master < ActiveThreads);
2589 assert(ActiveThreads > 1);
2591 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2594 // Make a local copy to be sure doesn't change under our feet
2595 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2597 if (localActiveSplitPoints == 0)
2598 // No active split points means that the thread is available as
2599 // a slave for any other thread.
2602 if (ActiveThreads == 2)
2605 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2606 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2607 // could have been set to 0 by another thread leading to an out of bound access.
2608 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2615 // available_thread_exists() tries to find an idle thread which is available as
2616 // a slave for the thread with threadID "master".
2618 bool ThreadsManager::available_thread_exists(int master) const {
2620 assert(master >= 0 && master < ActiveThreads);
2621 assert(ActiveThreads > 1);
2623 for (int i = 0; i < ActiveThreads; i++)
2624 if (thread_is_available(i, master))
2631 // split() does the actual work of distributing the work at a node between
2632 // several available threads. If it does not succeed in splitting the
2633 // node (because no idle threads are available, or because we have no unused
2634 // split point objects), the function immediately returns. If splitting is
2635 // possible, a SplitPoint object is initialized with all the data that must be
2636 // copied to the helper threads and we tell our helper threads that they have
2637 // been assigned work. This will cause them to instantly leave their idle loops
2638 // and call sp_search(). When all threads have returned from sp_search() then
2641 template <bool Fake>
2642 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2643 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2644 int* moveCount, MovePicker* mp, bool pvNode) {
2646 assert(ply > 0 && ply < PLY_MAX);
2647 assert(*bestValue >= -VALUE_INFINITE);
2648 assert(*bestValue <= *alpha);
2649 assert(*alpha < beta);
2650 assert(beta <= VALUE_INFINITE);
2651 assert(depth > Depth(0));
2652 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2653 assert(ActiveThreads > 1);
2655 int i, master = p.thread();
2656 Thread& masterThread = threads[master];
2660 // If no other thread is available to help us, or if we have too many
2661 // active split points, don't split.
2662 if ( !available_thread_exists(master)
2663 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2665 lock_release(&MPLock);
2669 // Pick the next available split point object from the split point stack
2670 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2672 // Initialize the split point object
2673 splitPoint.parent = masterThread.splitPoint;
2674 splitPoint.stopRequest = false;
2675 splitPoint.ply = ply;
2676 splitPoint.depth = depth;
2677 splitPoint.mateThreat = mateThreat;
2678 splitPoint.alpha = *alpha;
2679 splitPoint.beta = beta;
2680 splitPoint.pvNode = pvNode;
2681 splitPoint.bestValue = *bestValue;
2683 splitPoint.moveCount = *moveCount;
2684 splitPoint.pos = &p;
2685 splitPoint.parentSstack = ss;
2686 for (i = 0; i < ActiveThreads; i++)
2687 splitPoint.slaves[i] = 0;
2689 masterThread.splitPoint = &splitPoint;
2691 // If we are here it means we are not available
2692 assert(masterThread.state != THREAD_AVAILABLE);
2694 int workersCnt = 1; // At least the master is included
2696 // Allocate available threads setting state to THREAD_BOOKED
2697 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2698 if (thread_is_available(i, master))
2700 threads[i].state = THREAD_BOOKED;
2701 threads[i].splitPoint = &splitPoint;
2702 splitPoint.slaves[i] = 1;
2706 assert(Fake || workersCnt > 1);
2708 // We can release the lock because slave threads are already booked and master is not available
2709 lock_release(&MPLock);
2711 // Tell the threads that they have work to do. This will make them leave
2712 // their idle loop. But before copy search stack tail for each thread.
2713 for (i = 0; i < ActiveThreads; i++)
2714 if (i == master || splitPoint.slaves[i])
2716 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2718 assert(i == master || threads[i].state == THREAD_BOOKED);
2720 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2723 // Everything is set up. The master thread enters the idle loop, from
2724 // which it will instantly launch a search, because its state is
2725 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2726 // idle loop, which means that the main thread will return from the idle
2727 // loop when all threads have finished their work at this split point.
2728 idle_loop(master, &splitPoint);
2730 // We have returned from the idle loop, which means that all threads are
2731 // finished. Update alpha and bestValue, and return.
2734 *alpha = splitPoint.alpha;
2735 *bestValue = splitPoint.bestValue;
2736 masterThread.activeSplitPoints--;
2737 masterThread.splitPoint = splitPoint.parent;
2739 lock_release(&MPLock);
2743 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2744 // to start a new search from the root.
2746 void ThreadsManager::wake_sleeping_threads() {
2748 assert(AllThreadsShouldSleep);
2749 assert(ActiveThreads > 0);
2751 AllThreadsShouldSleep = false;
2753 if (ActiveThreads == 1)
2756 #if !defined(_MSC_VER)
2757 pthread_mutex_lock(&WaitLock);
2758 pthread_cond_broadcast(&WaitCond);
2759 pthread_mutex_unlock(&WaitLock);
2761 for (int i = 1; i < MAX_THREADS; i++)
2762 SetEvent(SitIdleEvent[i]);
2768 // put_threads_to_sleep() makes all the threads go to sleep just before
2769 // to leave think(), at the end of the search. Threads should have already
2770 // finished the job and should be idle.
2772 void ThreadsManager::put_threads_to_sleep() {
2774 assert(!AllThreadsShouldSleep);
2776 // This makes the threads to go to sleep
2777 AllThreadsShouldSleep = true;
2780 /// The RootMoveList class
2782 // RootMoveList c'tor
2784 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2786 SearchStack ss[PLY_MAX_PLUS_2];
2787 MoveStack mlist[MaxRootMoves];
2789 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2791 // Initialize search stack
2792 init_ss_array(ss, PLY_MAX_PLUS_2);
2794 ss[0].eval = VALUE_NONE;
2796 // Generate all legal moves
2797 MoveStack* last = generate_moves(pos, mlist);
2799 // Add each move to the moves[] array
2800 for (MoveStack* cur = mlist; cur != last; cur++)
2802 bool includeMove = includeAllMoves;
2804 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2805 includeMove = (searchMoves[k] == cur->move);
2810 // Find a quick score for the move
2811 pos.do_move(cur->move, st);
2812 ss[0].currentMove = cur->move;
2813 moves[count].move = cur->move;
2814 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2815 moves[count].pv[0] = cur->move;
2816 moves[count].pv[1] = MOVE_NONE;
2817 pos.undo_move(cur->move);
2824 // RootMoveList simple methods definitions
2826 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2828 moves[moveNum].nodes = nodes;
2829 moves[moveNum].cumulativeNodes += nodes;
2832 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2834 moves[moveNum].ourBeta = our;
2835 moves[moveNum].theirBeta = their;
2838 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2842 for (j = 0; pv[j] != MOVE_NONE; j++)
2843 moves[moveNum].pv[j] = pv[j];
2845 moves[moveNum].pv[j] = MOVE_NONE;
2849 // RootMoveList::sort() sorts the root move list at the beginning of a new
2852 void RootMoveList::sort() {
2854 sort_multipv(count - 1); // Sort all items
2858 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2859 // list by their scores and depths. It is used to order the different PVs
2860 // correctly in MultiPV mode.
2862 void RootMoveList::sort_multipv(int n) {
2866 for (i = 1; i <= n; i++)
2868 RootMove rm = moves[i];
2869 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2870 moves[j] = moves[j - 1];