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, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
101 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is bigger then beta - IIDMargin.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
218 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
220 // Step 14. Reduced search
222 // Reduction lookup tables (initialized at startup) and their getter functions
223 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
225 template <NodeType PV>
226 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
228 // Common adjustments
230 // Search depth at iteration 1
231 const Depth InitialDepth = OnePly;
233 // Easy move margin. An easy move candidate must be at least this much
234 // better than the second best move.
235 const Value EasyMoveMargin = Value(0x200);
237 // Last seconds noise filtering (LSN)
238 const bool UseLSNFiltering = true;
239 const int LSNTime = 4000; // In milliseconds
240 const Value LSNValue = value_from_centipawns(200);
241 bool loseOnTime = false;
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
261 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
262 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
263 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode>
288 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
293 template <NodeType PvNode>
294 void sp_search(SplitPoint* sp, int threadID);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 void update_pv(SearchStack* ss);
300 void sp_update_pv(SearchStack* pss, SearchStack* ss);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 bool move_is_killer(Move m, SearchStack* ss);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool connected_threat(const Position& pos, Move m, Move threat);
306 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
307 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
308 void update_killers(Move m, SearchStack* ss);
309 void update_gains(const Position& pos, Move move, Value before, Value after);
311 int current_search_time();
315 void wait_for_stop_or_ponderhit();
316 void init_ss_array(SearchStack* ss, int size);
317 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value);
319 #if !defined(_MSC_VER)
320 void *init_thread(void *threadID);
322 DWORD WINAPI init_thread(LPVOID threadID);
332 /// init_threads(), exit_threads() and nodes_searched() are helpers to
333 /// give accessibility to some TM methods from outside of current file.
335 void init_threads() { TM.init_threads(); }
336 void exit_threads() { TM.exit_threads(); }
337 int64_t nodes_searched() { return TM.nodes_searched(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (OnePly == 2)
345 int hd; // half depth (OnePly == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
352 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
357 // Init futility margins array
358 for (d = 0; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1) - 8 * mc + 45;
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
367 // SearchStack::init() initializes a search stack. Used at the beginning of a
368 // new search from the root.
369 void SearchStack::init() {
371 pv[0] = pv[1] = MOVE_NONE;
372 currentMove = threatMove = MOVE_NONE;
373 reduction = Depth(0);
377 void SearchStack::initKillers() {
379 mateKiller = MOVE_NONE;
380 for (int i = 0; i < KILLER_MAX; i++)
381 killers[i] = MOVE_NONE;
385 /// perft() is our utility to verify move generation is bug free. All the legal
386 /// moves up to given depth are generated and counted and the sum returned.
388 int perft(Position& pos, Depth depth)
393 MovePicker mp(pos, MOVE_NONE, depth, H);
395 // If we are at the last ply we don't need to do and undo
396 // the moves, just to count them.
397 if (depth <= OnePly) // Replace with '<' to test also qsearch
399 while (mp.get_next_move()) sum++;
403 // Loop through all legal moves
405 while ((move = mp.get_next_move()) != MOVE_NONE)
407 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
408 sum += perft(pos, depth - OnePly);
415 /// think() is the external interface to Stockfish's search, and is called when
416 /// the program receives the UCI 'go' command. It initializes various
417 /// search-related global variables, and calls root_search(). It returns false
418 /// when a quit command is received during the search.
420 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
421 int time[], int increment[], int movesToGo, int maxDepth,
422 int maxNodes, int maxTime, Move searchMoves[]) {
424 // Initialize global search variables
425 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
426 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
428 TM.resetNodeCounters();
429 SearchStartTime = get_system_time();
430 ExactMaxTime = maxTime;
433 InfiniteSearch = infinite;
434 PonderSearch = ponder;
435 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
437 // Look for a book move, only during games, not tests
438 if (UseTimeManagement && get_option_value_bool("OwnBook"))
440 if (get_option_value_string("Book File") != OpeningBook.file_name())
441 OpeningBook.open(get_option_value_string("Book File"));
443 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
444 if (bookMove != MOVE_NONE)
447 wait_for_stop_or_ponderhit();
449 cout << "bestmove " << bookMove << endl;
454 // Reset loseOnTime flag at the beginning of a new game
455 if (button_was_pressed("New Game"))
458 // Read UCI option values
459 TT.set_size(get_option_value_int("Hash"));
460 if (button_was_pressed("Clear Hash"))
463 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
464 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
465 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
466 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
467 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
468 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
469 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
470 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
471 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
472 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
473 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
474 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
476 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
477 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
478 MultiPV = get_option_value_int("MultiPV");
479 Chess960 = get_option_value_bool("UCI_Chess960");
480 UseLogFile = get_option_value_bool("Use Search Log");
483 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
485 read_weights(pos.side_to_move());
487 // Set the number of active threads
488 int newActiveThreads = get_option_value_int("Threads");
489 if (newActiveThreads != TM.active_threads())
491 TM.set_active_threads(newActiveThreads);
492 init_eval(TM.active_threads());
495 // Wake up sleeping threads
496 TM.wake_sleeping_threads();
499 int myTime = time[side_to_move];
500 int myIncrement = increment[side_to_move];
501 if (UseTimeManagement)
503 if (!movesToGo) // Sudden death time control
507 MaxSearchTime = myTime / 30 + myIncrement;
508 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
510 else // Blitz game without increment
512 MaxSearchTime = myTime / 30;
513 AbsoluteMaxSearchTime = myTime / 8;
516 else // (x moves) / (y minutes)
520 MaxSearchTime = myTime / 2;
521 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
525 MaxSearchTime = myTime / Min(movesToGo, 20);
526 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
530 if (get_option_value_bool("Ponder"))
532 MaxSearchTime += MaxSearchTime / 4;
533 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
537 // Set best NodesBetweenPolls interval to avoid lagging under
538 // heavy time pressure.
540 NodesBetweenPolls = Min(MaxNodes, 30000);
541 else if (myTime && myTime < 1000)
542 NodesBetweenPolls = 1000;
543 else if (myTime && myTime < 5000)
544 NodesBetweenPolls = 5000;
546 NodesBetweenPolls = 30000;
548 // Write search information to log file
550 LogFile << "Searching: " << pos.to_fen() << endl
551 << "infinite: " << infinite
552 << " ponder: " << ponder
553 << " time: " << myTime
554 << " increment: " << myIncrement
555 << " moves to go: " << movesToGo << endl;
557 // LSN filtering. Used only for developing purposes, disabled by default
561 // Step 2. If after last move we decided to lose on time, do it now!
562 while (SearchStartTime + myTime + 1000 > get_system_time())
566 // We're ready to start thinking. Call the iterative deepening loop function
567 Value v = id_loop(pos, searchMoves);
571 // Step 1. If this is sudden death game and our position is hopeless,
572 // decide to lose on time.
573 if ( !loseOnTime // If we already lost on time, go to step 3.
583 // Step 3. Now after stepping over the time limit, reset flag for next match.
591 TM.put_threads_to_sleep();
599 // id_loop() is the main iterative deepening loop. It calls root_search
600 // repeatedly with increasing depth until the allocated thinking time has
601 // been consumed, the user stops the search, or the maximum search depth is
604 Value id_loop(const Position& pos, Move searchMoves[]) {
606 Position p(pos, pos.thread());
607 SearchStack ss[PLY_MAX_PLUS_2];
608 Move EasyMove = MOVE_NONE;
609 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
611 // Moves to search are verified, copied, scored and sorted
612 RootMoveList rml(p, searchMoves);
614 // Handle special case of searching on a mate/stale position
615 if (rml.move_count() == 0)
618 wait_for_stop_or_ponderhit();
620 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
623 // Print RootMoveList startup scoring to the standard output,
624 // so to output information also for iteration 1.
625 cout << "info depth " << 1
626 << "\ninfo depth " << 1
627 << " score " << value_to_string(rml.get_move_score(0))
628 << " time " << current_search_time()
629 << " nodes " << TM.nodes_searched()
631 << " pv " << rml.get_move(0) << "\n";
636 init_ss_array(ss, PLY_MAX_PLUS_2);
637 ValueByIteration[1] = rml.get_move_score(0);
641 // Is one move significantly better than others after initial scoring ?
642 if ( rml.move_count() == 1
643 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
644 EasyMove = rml.get_move(0);
646 // Iterative deepening loop
647 while (Iteration < PLY_MAX)
649 // Initialize iteration
651 BestMoveChangesByIteration[Iteration] = 0;
653 cout << "info depth " << Iteration << endl;
655 // Calculate dynamic aspiration window based on previous iterations
656 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
658 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
659 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
661 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
662 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
664 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
665 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
668 // Search to the current depth, rml is updated and sorted, alpha and beta could change
669 value = root_search(p, ss, rml, &alpha, &beta);
671 // Write PV to transposition table, in case the relevant entries have
672 // been overwritten during the search.
673 TT.insert_pv(p, ss->pv);
676 break; // Value cannot be trusted. Break out immediately!
678 //Save info about search result
679 ValueByIteration[Iteration] = value;
681 // Drop the easy move if differs from the new best move
682 if (ss->pv[0] != EasyMove)
683 EasyMove = MOVE_NONE;
685 if (UseTimeManagement)
688 bool stopSearch = false;
690 // Stop search early if there is only a single legal move,
691 // we search up to Iteration 6 anyway to get a proper score.
692 if (Iteration >= 6 && rml.move_count() == 1)
695 // Stop search early when the last two iterations returned a mate score
697 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
698 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
701 // Stop search early if one move seems to be much better than the others
702 int64_t nodes = TM.nodes_searched();
704 && EasyMove == ss->pv[0]
705 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
706 && current_search_time() > MaxSearchTime / 16)
707 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
708 && current_search_time() > MaxSearchTime / 32)))
711 // Add some extra time if the best move has changed during the last two iterations
712 if (Iteration > 5 && Iteration <= 50)
713 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
714 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
716 // Stop search if most of MaxSearchTime is consumed at the end of the
717 // iteration. We probably don't have enough time to search the first
718 // move at the next iteration anyway.
719 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
725 StopOnPonderhit = true;
731 if (MaxDepth && Iteration >= MaxDepth)
735 // If we are pondering or in infinite search, we shouldn't print the
736 // best move before we are told to do so.
737 if (!AbortSearch && (PonderSearch || InfiniteSearch))
738 wait_for_stop_or_ponderhit();
740 // Print final search statistics
741 cout << "info nodes " << TM.nodes_searched()
743 << " time " << current_search_time()
744 << " hashfull " << TT.full() << endl;
746 // Print the best move and the ponder move to the standard output
747 if (ss->pv[0] == MOVE_NONE)
749 ss->pv[0] = rml.get_move(0);
750 ss->pv[1] = MOVE_NONE;
753 assert(ss->pv[0] != MOVE_NONE);
755 cout << "bestmove " << ss->pv[0];
757 if (ss->pv[1] != MOVE_NONE)
758 cout << " ponder " << ss->pv[1];
765 dbg_print_mean(LogFile);
767 if (dbg_show_hit_rate)
768 dbg_print_hit_rate(LogFile);
770 LogFile << "\nNodes: " << TM.nodes_searched()
771 << "\nNodes/second: " << nps()
772 << "\nBest move: " << move_to_san(p, ss->pv[0]);
775 p.do_move(ss->pv[0], st);
776 LogFile << "\nPonder move: "
777 << move_to_san(p, ss->pv[1]) // Works also with MOVE_NONE
780 return rml.get_move_score(0);
784 // root_search() is the function which searches the root node. It is
785 // similar to search_pv except that it uses a different move ordering
786 // scheme, prints some information to the standard output and handles
787 // the fail low/high loops.
789 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
796 Depth depth, ext, newDepth;
797 Value value, alpha, beta;
798 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
799 int researchCountFH, researchCountFL;
801 researchCountFH = researchCountFL = 0;
804 isCheck = pos.is_check();
806 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
807 // Step 2. Check for aborted search (omitted at root)
808 // Step 3. Mate distance pruning (omitted at root)
809 // Step 4. Transposition table lookup (omitted at root)
811 // Step 5. Evaluate the position statically
812 // At root we do this only to get reference value for child nodes
814 ss->eval = evaluate(pos, ei);
816 // Step 6. Razoring (omitted at root)
817 // Step 7. Static null move pruning (omitted at root)
818 // Step 8. Null move search with verification search (omitted at root)
819 // Step 9. Internal iterative deepening (omitted at root)
821 // Step extra. Fail low loop
822 // We start with small aspiration window and in case of fail low, we research
823 // with bigger window until we are not failing low anymore.
826 // Sort the moves before to (re)search
829 // Step 10. Loop through all moves in the root move list
830 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
832 // This is used by time management
833 FirstRootMove = (i == 0);
835 // Save the current node count before the move is searched
836 nodes = TM.nodes_searched();
838 // Reset beta cut-off counters
839 TM.resetBetaCounters();
841 // Pick the next root move, and print the move and the move number to
842 // the standard output.
843 move = ss->currentMove = rml.get_move(i);
845 if (current_search_time() >= 1000)
846 cout << "info currmove " << move
847 << " currmovenumber " << i + 1 << endl;
849 moveIsCheck = pos.move_is_check(move);
850 captureOrPromotion = pos.move_is_capture_or_promotion(move);
852 // Step 11. Decide the new search depth
853 depth = (Iteration - 2) * OnePly + InitialDepth;
854 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
855 newDepth = depth + ext;
857 // Step 12. Futility pruning (omitted at root)
859 // Step extra. Fail high loop
860 // If move fails high, we research with bigger window until we are not failing
862 value = - VALUE_INFINITE;
866 // Step 13. Make the move
867 pos.do_move(move, st, ci, moveIsCheck);
869 // Step extra. pv search
870 // We do pv search for first moves (i < MultiPV)
871 // and for fail high research (value > alpha)
872 if (i < MultiPV || value > alpha)
874 // Aspiration window is disabled in multi-pv case
876 alpha = -VALUE_INFINITE;
878 // Full depth PV search, done on first move or after a fail high
879 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
883 // Step 14. Reduced search
884 // if the move fails high will be re-searched at full depth
885 bool doFullDepthSearch = true;
887 if ( depth >= 3 * OnePly
889 && !captureOrPromotion
890 && !move_is_castle(move))
892 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
895 assert(newDepth-ss->reduction >= OnePly);
897 // Reduced depth non-pv search using alpha as upperbound
898 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
899 doFullDepthSearch = (value > alpha);
902 // The move failed high, but if reduction is very big we could
903 // face a false positive, retry with a less aggressive reduction,
904 // if the move fails high again then go with full depth search.
905 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
907 assert(newDepth - OnePly >= OnePly);
909 ss->reduction = OnePly;
910 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
911 doFullDepthSearch = (value > alpha);
913 ss->reduction = Depth(0); // Restore original reduction
916 // Step 15. Full depth search
917 if (doFullDepthSearch)
919 // Full depth non-pv search using alpha as upperbound
920 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
922 // If we are above alpha then research at same depth but as PV
923 // to get a correct score or eventually a fail high above beta.
925 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
929 // Step 16. Undo move
932 // Can we exit fail high loop ?
933 if (AbortSearch || value < beta)
936 // We are failing high and going to do a research. It's important to update
937 // the score before research in case we run out of time while researching.
938 rml.set_move_score(i, value);
940 TT.extract_pv(pos, ss->pv, PLY_MAX);
941 rml.set_move_pv(i, ss->pv);
943 // Print information to the standard output
944 print_pv_info(pos, ss, alpha, beta, value);
946 // Prepare for a research after a fail high, each time with a wider window
947 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
950 } // End of fail high loop
952 // Finished searching the move. If AbortSearch is true, the search
953 // was aborted because the user interrupted the search or because we
954 // ran out of time. In this case, the return value of the search cannot
955 // be trusted, and we break out of the loop without updating the best
960 // Remember beta-cutoff and searched nodes counts for this move. The
961 // info is used to sort the root moves for the next iteration.
963 TM.get_beta_counters(pos.side_to_move(), our, their);
964 rml.set_beta_counters(i, our, their);
965 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
967 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
968 assert(value < beta);
970 // Step 17. Check for new best move
971 if (value <= alpha && i >= MultiPV)
972 rml.set_move_score(i, -VALUE_INFINITE);
975 // PV move or new best move!
978 rml.set_move_score(i, value);
980 TT.extract_pv(pos, ss->pv, PLY_MAX);
981 rml.set_move_pv(i, ss->pv);
985 // We record how often the best move has been changed in each
986 // iteration. This information is used for time managment: When
987 // the best move changes frequently, we allocate some more time.
989 BestMoveChangesByIteration[Iteration]++;
991 // Print information to the standard output
992 print_pv_info(pos, ss, alpha, beta, value);
994 // Raise alpha to setup proper non-pv search upper bound
1000 rml.sort_multipv(i);
1001 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1003 cout << "info multipv " << j + 1
1004 << " score " << value_to_string(rml.get_move_score(j))
1005 << " depth " << (j <= i ? Iteration : Iteration - 1)
1006 << " time " << current_search_time()
1007 << " nodes " << TM.nodes_searched()
1011 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1012 cout << rml.get_move_pv(j, k) << " ";
1016 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1018 } // PV move or new best move
1020 assert(alpha >= *alphaPtr);
1022 AspirationFailLow = (alpha == *alphaPtr);
1024 if (AspirationFailLow && StopOnPonderhit)
1025 StopOnPonderhit = false;
1028 // Can we exit fail low loop ?
1029 if (AbortSearch || !AspirationFailLow)
1032 // Prepare for a research after a fail low, each time with a wider window
1033 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1038 // Sort the moves before to return
1045 // search<>() is the main search function for both PV and non-PV nodes
1047 template <NodeType PvNode>
1048 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1050 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1051 assert(beta > alpha && beta <= VALUE_INFINITE);
1052 assert(PvNode || alpha == beta - 1);
1053 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1054 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1056 Move movesSearched[256];
1061 Move ttMove, move, excludedMove;
1062 Depth ext, newDepth;
1063 Value bestValue, value, oldAlpha;
1064 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1065 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1066 bool mateThreat = false;
1068 int threadID = pos.thread();
1069 int ply = pos.ply();
1070 refinedValue = bestValue = value = -VALUE_INFINITE;
1073 // Step 1. Initialize node and poll. Polling can abort search
1074 TM.incrementNodeCounter(threadID);
1076 (ss+2)->initKillers();
1078 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1084 // Step 2. Check for aborted search and immediate draw
1085 if (AbortSearch || TM.thread_should_stop(threadID))
1088 if (pos.is_draw() || ply >= PLY_MAX - 1)
1091 // Step 3. Mate distance pruning
1092 alpha = Max(value_mated_in(ply), alpha);
1093 beta = Min(value_mate_in(ply+1), beta);
1097 // Step 4. Transposition table lookup
1099 // We don't want the score of a partial search to overwrite a previous full search
1100 // TT value, so we use a different position key in case of an excluded move exists.
1101 excludedMove = ss->excludedMove;
1102 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1104 tte = TT.retrieve(posKey);
1105 ttMove = (tte ? tte->move() : MOVE_NONE);
1107 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1108 // This is to avoid problems in the following areas:
1110 // * Repetition draw detection
1111 // * Fifty move rule detection
1112 // * Searching for a mate
1113 // * Printing of full PV line
1115 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1117 // Refresh tte entry to avoid aging
1118 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1120 ss->currentMove = ttMove; // Can be MOVE_NONE
1121 return value_from_tt(tte->value(), ply);
1124 // Step 5. Evaluate the position statically
1125 // At PV nodes we do this only to update gain statistics
1126 isCheck = pos.is_check();
1129 if (tte && tte->static_value() != VALUE_NONE)
1131 ss->eval = tte->static_value();
1132 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1135 ss->eval = evaluate(pos, ei);
1137 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1138 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1141 // Step 6. Razoring (is omitted in PV nodes)
1143 && depth < RazorDepth
1145 && refinedValue < beta - razor_margin(depth)
1146 && ttMove == MOVE_NONE
1147 && (ss-1)->currentMove != MOVE_NULL
1148 && !value_is_mate(beta)
1149 && !pos.has_pawn_on_7th(pos.side_to_move()))
1151 // Pass ss->eval to qsearch() and avoid an evaluate call
1152 if (!tte || tte->static_value() == VALUE_NONE)
1153 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1155 Value rbeta = beta - razor_margin(depth);
1156 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0));
1158 // Logically we should return (v + razor_margin(depth)), but
1159 // surprisingly this did slightly weaker in tests.
1163 // Step 7. Static null move pruning (is omitted in PV nodes)
1164 // We're betting that the opponent doesn't have a move that will reduce
1165 // the score by more than futility_margin(depth) if we do a null move.
1167 && !ss->skipNullMove
1168 && depth < RazorDepth
1169 && refinedValue >= beta + futility_margin(depth, 0)
1171 && !value_is_mate(beta)
1172 && pos.non_pawn_material(pos.side_to_move()))
1173 return refinedValue - futility_margin(depth, 0);
1175 // Step 8. Null move search with verification search (is omitted in PV nodes)
1176 // When we jump directly to qsearch() we do a null move only if static value is
1177 // at least beta. Otherwise we do a null move if static value is not more than
1178 // NullMoveMargin under beta.
1180 && !ss->skipNullMove
1182 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1184 && !value_is_mate(beta)
1185 && pos.non_pawn_material(pos.side_to_move()))
1187 ss->currentMove = MOVE_NULL;
1189 // Null move dynamic reduction based on depth
1190 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1192 // Null move dynamic reduction based on value
1193 if (refinedValue - beta > PawnValueMidgame)
1196 pos.do_null_move(st);
1197 (ss+1)->skipNullMove = true;
1199 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0))
1200 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly);
1201 (ss+1)->skipNullMove = false;
1202 pos.undo_null_move();
1204 if (nullValue >= beta)
1206 // Do not return unproven mate scores
1207 if (nullValue >= value_mate_in(PLY_MAX))
1210 // Do zugzwang verification search at high depths
1211 if (depth < 6 * OnePly)
1214 ss->skipNullMove = true;
1215 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly);
1216 ss->skipNullMove = false;
1223 // The null move failed low, which means that we may be faced with
1224 // some kind of threat. If the previous move was reduced, check if
1225 // the move that refuted the null move was somehow connected to the
1226 // move which was reduced. If a connection is found, return a fail
1227 // low score (which will cause the reduced move to fail high in the
1228 // parent node, which will trigger a re-search with full depth).
1229 if (nullValue == value_mated_in(ply + 2))
1232 ss->threatMove = (ss+1)->currentMove;
1233 if ( depth < ThreatDepth
1234 && (ss-1)->reduction
1235 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1240 // Step 9. Internal iterative deepening
1241 if ( depth >= IIDDepth[PvNode]
1242 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1243 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1245 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1247 ss->skipNullMove = true;
1248 search<PvNode>(pos, ss, alpha, beta, d);
1249 ss->skipNullMove = false;
1252 tte = TT.retrieve(posKey);
1255 // Expensive mate threat detection (only for PV nodes)
1257 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1259 // Initialize a MovePicker object for the current position
1260 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1262 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1263 && tte && tte->move()
1264 && !excludedMove // Do not allow recursive singular extension search
1265 && is_lower_bound(tte->type())
1266 && tte->depth() >= depth - 3 * OnePly;
1268 // Step 10. Loop through moves
1269 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1270 while ( bestValue < beta
1271 && (move = mp.get_next_move()) != MOVE_NONE
1272 && !TM.thread_should_stop(threadID))
1274 assert(move_is_ok(move));
1276 if (move == excludedMove)
1279 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1280 moveIsCheck = pos.move_is_check(move, ci);
1281 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1283 // Step 11. Decide the new search depth
1284 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1286 // Singular extension search. We extend the TT move if its value is much better than
1287 // its siblings. To verify this we do a reduced search on all the other moves but the
1288 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1289 if ( singularExtensionNode
1290 && move == tte->move()
1293 Value ttValue = value_from_tt(tte->value(), ply);
1295 if (abs(ttValue) < VALUE_KNOWN_WIN)
1297 Value b = ttValue - SingularExtensionMargin;
1298 ss->excludedMove = move;
1299 ss->skipNullMove = true;
1300 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2);
1301 ss->skipNullMove = false;
1302 ss->excludedMove = MOVE_NONE;
1304 if (v < ttValue - SingularExtensionMargin)
1309 newDepth = depth - OnePly + ext;
1311 // Update current move (this must be done after singular extension search)
1312 movesSearched[moveCount++] = ss->currentMove = move;
1314 // Step 12. Futility pruning (is omitted in PV nodes)
1316 && !captureOrPromotion
1320 && !move_is_castle(move))
1322 // Move count based pruning
1323 if ( moveCount >= futility_move_count(depth)
1324 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1325 && bestValue > value_mated_in(PLY_MAX))
1328 // Value based pruning
1329 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1330 // but fixing this made program slightly weaker.
1331 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1332 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1333 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1335 if (futilityValueScaled < beta)
1337 if (futilityValueScaled > bestValue)
1338 bestValue = futilityValueScaled;
1343 // Step 13. Make the move
1344 pos.do_move(move, st, ci, moveIsCheck);
1346 // Step extra. pv search (only in PV nodes)
1347 // The first move in list is the expected PV
1348 if (PvNode && moveCount == 1)
1349 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1350 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1353 // Step 14. Reduced depth search
1354 // If the move fails high will be re-searched at full depth.
1355 bool doFullDepthSearch = true;
1357 if ( depth >= 3 * OnePly
1358 && !captureOrPromotion
1360 && !move_is_castle(move)
1361 && !move_is_killer(move, ss))
1363 ss->reduction = reduction<PvNode>(depth, moveCount);
1366 Depth d = newDepth - ss->reduction;
1367 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1368 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1370 doFullDepthSearch = (value > alpha);
1373 // The move failed high, but if reduction is very big we could
1374 // face a false positive, retry with a less aggressive reduction,
1375 // if the move fails high again then go with full depth search.
1376 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1378 assert(newDepth - OnePly >= OnePly);
1380 ss->reduction = OnePly;
1381 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
1382 doFullDepthSearch = (value > alpha);
1384 ss->reduction = Depth(0); // Restore original reduction
1387 // Step 15. Full depth search
1388 if (doFullDepthSearch)
1390 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1391 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1393 // Step extra. pv search (only in PV nodes)
1394 // Search only for possible new PV nodes, if instead value >= beta then
1395 // parent node fails low with value <= alpha and tries another move.
1396 if (PvNode && value > alpha && value < beta)
1397 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1398 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1402 // Step 16. Undo move
1403 pos.undo_move(move);
1405 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1407 // Step 17. Check for new best move
1408 if (value > bestValue)
1413 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1418 if (value == value_mate_in(ply + 1))
1419 ss->mateKiller = move;
1423 // Step 18. Check for split
1424 if ( depth >= MinimumSplitDepth
1425 && TM.active_threads() > 1
1427 && TM.available_thread_exists(threadID)
1429 && !TM.thread_should_stop(threadID)
1431 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1432 mateThreat, &moveCount, &mp, PvNode);
1435 // Step 19. Check for mate and stalemate
1436 // All legal moves have been searched and if there are
1437 // no legal moves, it must be mate or stalemate.
1438 // If one move was excluded return fail low score.
1440 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1442 // Step 20. Update tables
1443 // If the search is not aborted, update the transposition table,
1444 // history counters, and killer moves.
1445 if (AbortSearch || TM.thread_should_stop(threadID))
1448 if (bestValue <= oldAlpha)
1449 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1451 else if (bestValue >= beta)
1453 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1455 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1456 if (!pos.move_is_capture_or_promotion(move))
1458 update_history(pos, move, depth, movesSearched, moveCount);
1459 update_killers(move, ss);
1463 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[0], ss->eval, ei.kingDanger[pos.side_to_move()]);
1465 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1471 // qsearch() is the quiescence search function, which is called by the main
1472 // search function when the remaining depth is zero (or, to be more precise,
1473 // less than OnePly).
1475 template <NodeType PvNode>
1476 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1478 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1479 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1480 assert(PvNode || alpha == beta - 1);
1482 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1483 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1488 Value bestValue, value, futilityValue, futilityBase;
1489 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1491 Value oldAlpha = alpha;
1492 int ply = pos.ply();
1494 TM.incrementNodeCounter(pos.thread());
1495 ss->pv[0] = ss->pv[1] = ss->currentMove = MOVE_NONE;
1496 ss->eval = VALUE_NONE;
1498 // Check for an instant draw or maximum ply reached
1499 if (pos.is_draw() || ply >= PLY_MAX - 1)
1502 // Transposition table lookup. At PV nodes, we don't use the TT for
1503 // pruning, but only for move ordering.
1504 tte = TT.retrieve(pos.get_key());
1505 ttMove = (tte ? tte->move() : MOVE_NONE);
1507 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1509 ss->currentMove = ttMove; // Can be MOVE_NONE
1510 return value_from_tt(tte->value(), ply);
1513 isCheck = pos.is_check();
1515 // Evaluate the position statically
1518 bestValue = futilityBase = -VALUE_INFINITE;
1519 deepChecks = enoughMaterial = false;
1523 if (tte && tte->static_value() != VALUE_NONE)
1525 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1526 bestValue = tte->static_value();
1529 bestValue = evaluate(pos, ei);
1531 ss->eval = bestValue;
1532 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1534 // Stand pat. Return immediately if static value is at least beta
1535 if (bestValue >= beta)
1538 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1543 if (PvNode && bestValue > alpha)
1546 // If we are near beta then try to get a cutoff pushing checks a bit further
1547 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1549 // Futility pruning parameters, not needed when in check
1550 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1551 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1554 // Initialize a MovePicker object for the current position, and prepare
1555 // to search the moves. Because the depth is <= 0 here, only captures,
1556 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1557 // and we are near beta) will be generated.
1558 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1561 // Loop through the moves until no moves remain or a beta cutoff occurs
1562 while ( alpha < beta
1563 && (move = mp.get_next_move()) != MOVE_NONE)
1565 assert(move_is_ok(move));
1567 moveIsCheck = pos.move_is_check(move, ci);
1575 && !move_is_promotion(move)
1576 && !pos.move_is_passed_pawn_push(move))
1578 futilityValue = futilityBase
1579 + pos.endgame_value_of_piece_on(move_to(move))
1580 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1582 if (futilityValue < alpha)
1584 if (futilityValue > bestValue)
1585 bestValue = futilityValue;
1590 // Detect blocking evasions that are candidate to be pruned
1591 evasionPrunable = isCheck
1592 && bestValue > value_mated_in(PLY_MAX)
1593 && !pos.move_is_capture(move)
1594 && pos.type_of_piece_on(move_from(move)) != KING
1595 && !pos.can_castle(pos.side_to_move());
1597 // Don't search moves with negative SEE values
1599 && (!isCheck || evasionPrunable)
1601 && !move_is_promotion(move)
1602 && pos.see_sign(move) < 0)
1605 // Update current move
1606 ss->currentMove = move;
1608 // Make and search the move
1609 pos.do_move(move, st, ci, moveIsCheck);
1610 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly);
1611 pos.undo_move(move);
1613 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1616 if (value > bestValue)
1627 // All legal moves have been searched. A special case: If we're in check
1628 // and no legal moves were found, it is checkmate.
1629 if (isCheck && bestValue == -VALUE_INFINITE)
1630 return value_mated_in(ply);
1632 // Update transposition table
1633 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1634 if (bestValue <= oldAlpha)
1635 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1636 else if (bestValue >= beta)
1639 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1641 // Update killers only for good checking moves
1642 if (!pos.move_is_capture_or_promotion(move))
1643 update_killers(move, ss);
1646 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[0], ss->eval, ei.kingDanger[pos.side_to_move()]);
1648 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1654 // sp_search() is used to search from a split point. This function is called
1655 // by each thread working at the split point. It is similar to the normal
1656 // search() function, but simpler. Because we have already probed the hash
1657 // table, done a null move search, and searched the first move before
1658 // splitting, we don't have to repeat all this work in sp_search(). We
1659 // also don't need to store anything to the hash table here: This is taken
1660 // care of after we return from the split point.
1662 template <NodeType PvNode>
1663 void sp_search(SplitPoint* sp, int threadID) {
1665 assert(threadID >= 0 && threadID < TM.active_threads());
1666 assert(TM.active_threads() > 1);
1670 Depth ext, newDepth;
1672 Value futilityValueScaled; // NonPV specific
1673 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1675 value = -VALUE_INFINITE;
1677 Position pos(*sp->pos, threadID);
1679 SearchStack* ss = sp->sstack[threadID] + 1;
1680 isCheck = pos.is_check();
1682 // Step 10. Loop through moves
1683 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1684 lock_grab(&(sp->lock));
1686 while ( sp->bestValue < sp->beta
1687 && (move = sp->mp->get_next_move()) != MOVE_NONE
1688 && !TM.thread_should_stop(threadID))
1690 moveCount = ++sp->moveCount;
1691 lock_release(&(sp->lock));
1693 assert(move_is_ok(move));
1695 moveIsCheck = pos.move_is_check(move, ci);
1696 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1698 // Step 11. Decide the new search depth
1699 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1700 newDepth = sp->depth - OnePly + ext;
1702 // Update current move
1703 ss->currentMove = move;
1705 // Step 12. Futility pruning (is omitted in PV nodes)
1707 && !captureOrPromotion
1710 && !move_is_castle(move))
1712 // Move count based pruning
1713 if ( moveCount >= futility_move_count(sp->depth)
1714 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1715 && sp->bestValue > value_mated_in(PLY_MAX))
1717 lock_grab(&(sp->lock));
1721 // Value based pruning
1722 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1723 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1724 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1726 if (futilityValueScaled < sp->beta)
1728 lock_grab(&(sp->lock));
1730 if (futilityValueScaled > sp->bestValue)
1731 sp->bestValue = futilityValueScaled;
1736 // Step 13. Make the move
1737 pos.do_move(move, st, ci, moveIsCheck);
1739 // Step 14. Reduced search
1740 // If the move fails high will be re-searched at full depth.
1741 bool doFullDepthSearch = true;
1743 if ( !captureOrPromotion
1745 && !move_is_castle(move)
1746 && !move_is_killer(move, ss))
1748 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1751 Value localAlpha = sp->alpha;
1752 Depth d = newDepth - ss->reduction;
1753 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1754 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d);
1755 doFullDepthSearch = (value > localAlpha);
1758 // The move failed high, but if reduction is very big we could
1759 // face a false positive, retry with a less aggressive reduction,
1760 // if the move fails high again then go with full depth search.
1761 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1763 assert(newDepth - OnePly >= OnePly);
1765 ss->reduction = OnePly;
1766 Value localAlpha = sp->alpha;
1767 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction);
1768 doFullDepthSearch = (value > localAlpha);
1770 ss->reduction = Depth(0); // Restore original reduction
1773 // Step 15. Full depth search
1774 if (doFullDepthSearch)
1776 Value localAlpha = sp->alpha;
1777 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1778 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth);
1780 // Step extra. pv search (only in PV nodes)
1781 // Search only for possible new PV nodes, if instead value >= beta then
1782 // parent node fails low with value <= alpha and tries another move.
1783 if (PvNode && value > localAlpha && value < sp->beta)
1784 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0))
1785 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth);
1788 // Step 16. Undo move
1789 pos.undo_move(move);
1791 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1793 // Step 17. Check for new best move
1794 lock_grab(&(sp->lock));
1796 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1798 sp->bestValue = value;
1800 if (sp->bestValue > sp->alpha)
1802 if (!PvNode || value >= sp->beta)
1803 sp->stopRequest = true;
1805 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1808 sp_update_pv(sp->parentSstack, ss);
1813 /* Here we have the lock still grabbed */
1815 sp->slaves[threadID] = 0;
1817 lock_release(&(sp->lock));
1820 // update_pv() is called whenever a search returns a value > alpha.
1821 // It updates the PV in the SearchStack object corresponding to the
1824 void update_pv(SearchStack* ss) {
1826 Move* src = (ss+1)->pv;
1829 *dst = ss->currentMove;
1833 while (*src++ != MOVE_NONE);
1837 // sp_update_pv() is a variant of update_pv for use at split points. The
1838 // difference between the two functions is that sp_update_pv also updates
1839 // the PV at the parent node.
1841 void sp_update_pv(SearchStack* pss, SearchStack* ss) {
1843 Move* src = (ss+1)->pv;
1845 Move* pdst = pss->pv;
1847 *dst = *pdst = ss->currentMove;
1850 *++dst = *++pdst = *src;
1851 while (*src++ != MOVE_NONE);
1855 // connected_moves() tests whether two moves are 'connected' in the sense
1856 // that the first move somehow made the second move possible (for instance
1857 // if the moving piece is the same in both moves). The first move is assumed
1858 // to be the move that was made to reach the current position, while the
1859 // second move is assumed to be a move from the current position.
1861 bool connected_moves(const Position& pos, Move m1, Move m2) {
1863 Square f1, t1, f2, t2;
1866 assert(move_is_ok(m1));
1867 assert(move_is_ok(m2));
1869 if (m2 == MOVE_NONE)
1872 // Case 1: The moving piece is the same in both moves
1878 // Case 2: The destination square for m2 was vacated by m1
1884 // Case 3: Moving through the vacated square
1885 if ( piece_is_slider(pos.piece_on(f2))
1886 && bit_is_set(squares_between(f2, t2), f1))
1889 // Case 4: The destination square for m2 is defended by the moving piece in m1
1890 p = pos.piece_on(t1);
1891 if (bit_is_set(pos.attacks_from(p, t1), t2))
1894 // Case 5: Discovered check, checking piece is the piece moved in m1
1895 if ( piece_is_slider(p)
1896 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1897 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1899 // discovered_check_candidates() works also if the Position's side to
1900 // move is the opposite of the checking piece.
1901 Color them = opposite_color(pos.side_to_move());
1902 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1904 if (bit_is_set(dcCandidates, f2))
1911 // value_is_mate() checks if the given value is a mate one
1912 // eventually compensated for the ply.
1914 bool value_is_mate(Value value) {
1916 assert(abs(value) <= VALUE_INFINITE);
1918 return value <= value_mated_in(PLY_MAX)
1919 || value >= value_mate_in(PLY_MAX);
1923 // move_is_killer() checks if the given move is among the
1924 // killer moves of that ply.
1926 bool move_is_killer(Move m, SearchStack* ss) {
1928 const Move* k = ss->killers;
1929 for (int i = 0; i < KILLER_MAX; i++, k++)
1937 // extension() decides whether a move should be searched with normal depth,
1938 // or with extended depth. Certain classes of moves (checking moves, in
1939 // particular) are searched with bigger depth than ordinary moves and in
1940 // any case are marked as 'dangerous'. Note that also if a move is not
1941 // extended, as example because the corresponding UCI option is set to zero,
1942 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1943 template <NodeType PvNode>
1944 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1945 bool singleEvasion, bool mateThreat, bool* dangerous) {
1947 assert(m != MOVE_NONE);
1949 Depth result = Depth(0);
1950 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1955 result += CheckExtension[PvNode];
1958 result += SingleEvasionExtension[PvNode];
1961 result += MateThreatExtension[PvNode];
1964 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1966 Color c = pos.side_to_move();
1967 if (relative_rank(c, move_to(m)) == RANK_7)
1969 result += PawnPushTo7thExtension[PvNode];
1972 if (pos.pawn_is_passed(c, move_to(m)))
1974 result += PassedPawnExtension[PvNode];
1979 if ( captureOrPromotion
1980 && pos.type_of_piece_on(move_to(m)) != PAWN
1981 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1982 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1983 && !move_is_promotion(m)
1986 result += PawnEndgameExtension[PvNode];
1991 && captureOrPromotion
1992 && pos.type_of_piece_on(move_to(m)) != PAWN
1993 && pos.see_sign(m) >= 0)
1999 return Min(result, OnePly);
2003 // connected_threat() tests whether it is safe to forward prune a move or if
2004 // is somehow coonected to the threat move returned by null search.
2006 bool connected_threat(const Position& pos, Move m, Move threat) {
2008 assert(move_is_ok(m));
2009 assert(threat && move_is_ok(threat));
2010 assert(!pos.move_is_check(m));
2011 assert(!pos.move_is_capture_or_promotion(m));
2012 assert(!pos.move_is_passed_pawn_push(m));
2014 Square mfrom, mto, tfrom, tto;
2016 mfrom = move_from(m);
2018 tfrom = move_from(threat);
2019 tto = move_to(threat);
2021 // Case 1: Don't prune moves which move the threatened piece
2025 // Case 2: If the threatened piece has value less than or equal to the
2026 // value of the threatening piece, don't prune move which defend it.
2027 if ( pos.move_is_capture(threat)
2028 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2029 || pos.type_of_piece_on(tfrom) == KING)
2030 && pos.move_attacks_square(m, tto))
2033 // Case 3: If the moving piece in the threatened move is a slider, don't
2034 // prune safe moves which block its ray.
2035 if ( piece_is_slider(pos.piece_on(tfrom))
2036 && bit_is_set(squares_between(tfrom, tto), mto)
2037 && pos.see_sign(m) >= 0)
2044 // ok_to_use_TT() returns true if a transposition table score
2045 // can be used at a given point in search.
2047 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2049 Value v = value_from_tt(tte->value(), ply);
2051 return ( tte->depth() >= depth
2052 || v >= Max(value_mate_in(PLY_MAX), beta)
2053 || v < Min(value_mated_in(PLY_MAX), beta))
2055 && ( (is_lower_bound(tte->type()) && v >= beta)
2056 || (is_upper_bound(tte->type()) && v < beta));
2060 // refine_eval() returns the transposition table score if
2061 // possible otherwise falls back on static position evaluation.
2063 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2068 Value v = value_from_tt(tte->value(), ply);
2070 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2071 || (is_upper_bound(tte->type()) && v < defaultEval))
2078 // update_history() registers a good move that produced a beta-cutoff
2079 // in history and marks as failures all the other moves of that ply.
2081 void update_history(const Position& pos, Move move, Depth depth,
2082 Move movesSearched[], int moveCount) {
2086 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2088 for (int i = 0; i < moveCount - 1; i++)
2090 m = movesSearched[i];
2094 if (!pos.move_is_capture_or_promotion(m))
2095 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2100 // update_killers() add a good move that produced a beta-cutoff
2101 // among the killer moves of that ply.
2103 void update_killers(Move m, SearchStack* ss) {
2105 if (m == ss->killers[0])
2108 for (int i = KILLER_MAX - 1; i > 0; i--)
2109 ss->killers[i] = ss->killers[i - 1];
2115 // update_gains() updates the gains table of a non-capture move given
2116 // the static position evaluation before and after the move.
2118 void update_gains(const Position& pos, Move m, Value before, Value after) {
2121 && before != VALUE_NONE
2122 && after != VALUE_NONE
2123 && pos.captured_piece() == NO_PIECE_TYPE
2124 && !move_is_castle(m)
2125 && !move_is_promotion(m))
2126 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2130 // current_search_time() returns the number of milliseconds which have passed
2131 // since the beginning of the current search.
2133 int current_search_time() {
2135 return get_system_time() - SearchStartTime;
2139 // nps() computes the current nodes/second count.
2143 int t = current_search_time();
2144 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2148 // poll() performs two different functions: It polls for user input, and it
2149 // looks at the time consumed so far and decides if it's time to abort the
2154 static int lastInfoTime;
2155 int t = current_search_time();
2160 // We are line oriented, don't read single chars
2161 std::string command;
2163 if (!std::getline(std::cin, command))
2166 if (command == "quit")
2169 PonderSearch = false;
2173 else if (command == "stop")
2176 PonderSearch = false;
2178 else if (command == "ponderhit")
2182 // Print search information
2186 else if (lastInfoTime > t)
2187 // HACK: Must be a new search where we searched less than
2188 // NodesBetweenPolls nodes during the first second of search.
2191 else if (t - lastInfoTime >= 1000)
2198 if (dbg_show_hit_rate)
2199 dbg_print_hit_rate();
2201 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2202 << " time " << t << " hashfull " << TT.full() << endl;
2205 // Should we stop the search?
2209 bool stillAtFirstMove = FirstRootMove
2210 && !AspirationFailLow
2211 && t > MaxSearchTime + ExtraSearchTime;
2213 bool noMoreTime = t > AbsoluteMaxSearchTime
2214 || stillAtFirstMove;
2216 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2217 || (ExactMaxTime && t >= ExactMaxTime)
2218 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2223 // ponderhit() is called when the program is pondering (i.e. thinking while
2224 // it's the opponent's turn to move) in order to let the engine know that
2225 // it correctly predicted the opponent's move.
2229 int t = current_search_time();
2230 PonderSearch = false;
2232 bool stillAtFirstMove = FirstRootMove
2233 && !AspirationFailLow
2234 && t > MaxSearchTime + ExtraSearchTime;
2236 bool noMoreTime = t > AbsoluteMaxSearchTime
2237 || stillAtFirstMove;
2239 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2244 // init_ss_array() does a fast reset of the first entries of a SearchStack
2245 // array and of all the excludedMove and skipNullMove entries.
2247 void init_ss_array(SearchStack* ss, int size) {
2249 for (int i = 0; i < size; i++, ss++)
2251 ss->excludedMove = MOVE_NONE;
2252 ss->skipNullMove = false;
2263 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2264 // while the program is pondering. The point is to work around a wrinkle in
2265 // the UCI protocol: When pondering, the engine is not allowed to give a
2266 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2267 // We simply wait here until one of these commands is sent, and return,
2268 // after which the bestmove and pondermove will be printed (in id_loop()).
2270 void wait_for_stop_or_ponderhit() {
2272 std::string command;
2276 if (!std::getline(std::cin, command))
2279 if (command == "quit")
2284 else if (command == "ponderhit" || command == "stop")
2290 // print_pv_info() prints to standard output and eventually to log file information on
2291 // the current PV line. It is called at each iteration or after a new pv is found.
2293 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2295 cout << "info depth " << Iteration
2296 << " score " << value_to_string(value)
2297 << ((value >= beta) ? " lowerbound" :
2298 ((value <= alpha)? " upperbound" : ""))
2299 << " time " << current_search_time()
2300 << " nodes " << TM.nodes_searched()
2304 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2305 cout << ss->pv[j] << " ";
2311 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2312 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2314 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2315 TM.nodes_searched(), value, type, ss->pv) << endl;
2320 // init_thread() is the function which is called when a new thread is
2321 // launched. It simply calls the idle_loop() function with the supplied
2322 // threadID. There are two versions of this function; one for POSIX
2323 // threads and one for Windows threads.
2325 #if !defined(_MSC_VER)
2327 void* init_thread(void *threadID) {
2329 TM.idle_loop(*(int*)threadID, NULL);
2335 DWORD WINAPI init_thread(LPVOID threadID) {
2337 TM.idle_loop(*(int*)threadID, NULL);
2344 /// The ThreadsManager class
2346 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2347 // get_beta_counters() are getters/setters for the per thread
2348 // counters used to sort the moves at root.
2350 void ThreadsManager::resetNodeCounters() {
2352 for (int i = 0; i < MAX_THREADS; i++)
2353 threads[i].nodes = 0ULL;
2356 void ThreadsManager::resetBetaCounters() {
2358 for (int i = 0; i < MAX_THREADS; i++)
2359 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2362 int64_t ThreadsManager::nodes_searched() const {
2364 int64_t result = 0ULL;
2365 for (int i = 0; i < ActiveThreads; i++)
2366 result += threads[i].nodes;
2371 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2374 for (int i = 0; i < MAX_THREADS; i++)
2376 our += threads[i].betaCutOffs[us];
2377 their += threads[i].betaCutOffs[opposite_color(us)];
2382 // idle_loop() is where the threads are parked when they have no work to do.
2383 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2384 // object for which the current thread is the master.
2386 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2388 assert(threadID >= 0 && threadID < MAX_THREADS);
2392 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2393 // master should exit as last one.
2394 if (AllThreadsShouldExit)
2397 threads[threadID].state = THREAD_TERMINATED;
2401 // If we are not thinking, wait for a condition to be signaled
2402 // instead of wasting CPU time polling for work.
2403 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2406 assert(threadID != 0);
2407 threads[threadID].state = THREAD_SLEEPING;
2409 #if !defined(_MSC_VER)
2410 lock_grab(&WaitLock);
2411 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2412 pthread_cond_wait(&WaitCond, &WaitLock);
2413 lock_release(&WaitLock);
2415 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2419 // If thread has just woken up, mark it as available
2420 if (threads[threadID].state == THREAD_SLEEPING)
2421 threads[threadID].state = THREAD_AVAILABLE;
2423 // If this thread has been assigned work, launch a search
2424 if (threads[threadID].state == THREAD_WORKISWAITING)
2426 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2428 threads[threadID].state = THREAD_SEARCHING;
2430 if (threads[threadID].splitPoint->pvNode)
2431 sp_search<PV>(threads[threadID].splitPoint, threadID);
2433 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2435 assert(threads[threadID].state == THREAD_SEARCHING);
2437 threads[threadID].state = THREAD_AVAILABLE;
2440 // If this thread is the master of a split point and all slaves have
2441 // finished their work at this split point, return from the idle loop.
2443 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2445 if (i == ActiveThreads)
2447 // Because sp->slaves[] is reset under lock protection,
2448 // be sure sp->lock has been released before to return.
2449 lock_grab(&(sp->lock));
2450 lock_release(&(sp->lock));
2452 assert(threads[threadID].state == THREAD_AVAILABLE);
2454 threads[threadID].state = THREAD_SEARCHING;
2461 // init_threads() is called during startup. It launches all helper threads,
2462 // and initializes the split point stack and the global locks and condition
2465 void ThreadsManager::init_threads() {
2470 #if !defined(_MSC_VER)
2471 pthread_t pthread[1];
2474 // Initialize global locks
2475 lock_init(&MPLock, NULL);
2476 lock_init(&WaitLock, NULL);
2478 #if !defined(_MSC_VER)
2479 pthread_cond_init(&WaitCond, NULL);
2481 for (i = 0; i < MAX_THREADS; i++)
2482 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2485 // Initialize SplitPointStack locks
2486 for (i = 0; i < MAX_THREADS; i++)
2487 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2488 lock_init(&(SplitPointStack[i][j].lock), NULL);
2490 // Will be set just before program exits to properly end the threads
2491 AllThreadsShouldExit = false;
2493 // Threads will be put to sleep as soon as created
2494 AllThreadsShouldSleep = true;
2496 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2498 threads[0].state = THREAD_SEARCHING;
2499 for (i = 1; i < MAX_THREADS; i++)
2500 threads[i].state = THREAD_AVAILABLE;
2502 // Launch the helper threads
2503 for (i = 1; i < MAX_THREADS; i++)
2506 #if !defined(_MSC_VER)
2507 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2509 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2514 cout << "Failed to create thread number " << i << endl;
2515 Application::exit_with_failure();
2518 // Wait until the thread has finished launching and is gone to sleep
2519 while (threads[i].state != THREAD_SLEEPING) {}
2524 // exit_threads() is called when the program exits. It makes all the
2525 // helper threads exit cleanly.
2527 void ThreadsManager::exit_threads() {
2529 ActiveThreads = MAX_THREADS; // HACK
2530 AllThreadsShouldSleep = true; // HACK
2531 wake_sleeping_threads();
2533 // This makes the threads to exit idle_loop()
2534 AllThreadsShouldExit = true;
2536 // Wait for thread termination
2537 for (int i = 1; i < MAX_THREADS; i++)
2538 while (threads[i].state != THREAD_TERMINATED) {}
2540 // Now we can safely destroy the locks
2541 for (int i = 0; i < MAX_THREADS; i++)
2542 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2543 lock_destroy(&(SplitPointStack[i][j].lock));
2545 lock_destroy(&WaitLock);
2546 lock_destroy(&MPLock);
2550 // thread_should_stop() checks whether the thread should stop its search.
2551 // This can happen if a beta cutoff has occurred in the thread's currently
2552 // active split point, or in some ancestor of the current split point.
2554 bool ThreadsManager::thread_should_stop(int threadID) const {
2556 assert(threadID >= 0 && threadID < ActiveThreads);
2560 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2565 // thread_is_available() checks whether the thread with threadID "slave" is
2566 // available to help the thread with threadID "master" at a split point. An
2567 // obvious requirement is that "slave" must be idle. With more than two
2568 // threads, this is not by itself sufficient: If "slave" is the master of
2569 // some active split point, it is only available as a slave to the other
2570 // threads which are busy searching the split point at the top of "slave"'s
2571 // split point stack (the "helpful master concept" in YBWC terminology).
2573 bool ThreadsManager::thread_is_available(int slave, int master) const {
2575 assert(slave >= 0 && slave < ActiveThreads);
2576 assert(master >= 0 && master < ActiveThreads);
2577 assert(ActiveThreads > 1);
2579 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2582 // Make a local copy to be sure doesn't change under our feet
2583 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2585 if (localActiveSplitPoints == 0)
2586 // No active split points means that the thread is available as
2587 // a slave for any other thread.
2590 if (ActiveThreads == 2)
2593 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2594 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2595 // could have been set to 0 by another thread leading to an out of bound access.
2596 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2603 // available_thread_exists() tries to find an idle thread which is available as
2604 // a slave for the thread with threadID "master".
2606 bool ThreadsManager::available_thread_exists(int master) const {
2608 assert(master >= 0 && master < ActiveThreads);
2609 assert(ActiveThreads > 1);
2611 for (int i = 0; i < ActiveThreads; i++)
2612 if (thread_is_available(i, master))
2619 // split() does the actual work of distributing the work at a node between
2620 // several available threads. If it does not succeed in splitting the
2621 // node (because no idle threads are available, or because we have no unused
2622 // split point objects), the function immediately returns. If splitting is
2623 // possible, a SplitPoint object is initialized with all the data that must be
2624 // copied to the helper threads and we tell our helper threads that they have
2625 // been assigned work. This will cause them to instantly leave their idle loops
2626 // and call sp_search(). When all threads have returned from sp_search() then
2629 template <bool Fake>
2630 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2631 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2632 MovePicker* mp, bool pvNode) {
2634 assert(*bestValue >= -VALUE_INFINITE);
2635 assert(*bestValue <= *alpha);
2636 assert(*alpha < beta);
2637 assert(beta <= VALUE_INFINITE);
2638 assert(depth > Depth(0));
2639 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2640 assert(ActiveThreads > 1);
2642 int master = p.thread();
2646 // If no other thread is available to help us, or if we have too many
2647 // active split points, don't split.
2648 if ( !available_thread_exists(master)
2649 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2651 lock_release(&MPLock);
2655 // Pick the next available split point object from the split point stack
2656 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2658 // Initialize the split point object
2659 splitPoint->parent = threads[master].splitPoint;
2660 splitPoint->stopRequest = false;
2661 splitPoint->depth = depth;
2662 splitPoint->mateThreat = mateThreat;
2663 splitPoint->alpha = *alpha;
2664 splitPoint->beta = beta;
2665 splitPoint->pvNode = pvNode;
2666 splitPoint->bestValue = *bestValue;
2667 splitPoint->mp = mp;
2668 splitPoint->moveCount = *moveCount;
2669 splitPoint->pos = &p;
2670 splitPoint->parentSstack = ss;
2671 for (int i = 0; i < ActiveThreads; i++)
2672 splitPoint->slaves[i] = 0;
2674 threads[master].splitPoint = splitPoint;
2675 threads[master].activeSplitPoints++;
2677 // If we are here it means we are not available
2678 assert(threads[master].state != THREAD_AVAILABLE);
2680 int workersCnt = 1; // At least the master is included
2682 // Allocate available threads setting state to THREAD_BOOKED
2683 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2684 if (thread_is_available(i, master))
2686 threads[i].state = THREAD_BOOKED;
2687 threads[i].splitPoint = splitPoint;
2688 splitPoint->slaves[i] = 1;
2692 assert(Fake || workersCnt > 1);
2694 // We can release the lock because slave threads are already booked and master is not available
2695 lock_release(&MPLock);
2697 // Tell the threads that they have work to do. This will make them leave
2698 // their idle loop. But before copy search stack tail for each thread.
2699 for (int i = 0; i < ActiveThreads; i++)
2700 if (i == master || splitPoint->slaves[i])
2702 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2704 assert(i == master || threads[i].state == THREAD_BOOKED);
2706 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2709 // Everything is set up. The master thread enters the idle loop, from
2710 // which it will instantly launch a search, because its state is
2711 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2712 // idle loop, which means that the main thread will return from the idle
2713 // loop when all threads have finished their work at this split point.
2714 idle_loop(master, splitPoint);
2716 // We have returned from the idle loop, which means that all threads are
2717 // finished. Update alpha and bestValue, and return.
2720 *alpha = splitPoint->alpha;
2721 *bestValue = splitPoint->bestValue;
2722 threads[master].activeSplitPoints--;
2723 threads[master].splitPoint = splitPoint->parent;
2725 lock_release(&MPLock);
2729 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2730 // to start a new search from the root.
2732 void ThreadsManager::wake_sleeping_threads() {
2734 assert(AllThreadsShouldSleep);
2735 assert(ActiveThreads > 0);
2737 AllThreadsShouldSleep = false;
2739 if (ActiveThreads == 1)
2742 #if !defined(_MSC_VER)
2743 pthread_mutex_lock(&WaitLock);
2744 pthread_cond_broadcast(&WaitCond);
2745 pthread_mutex_unlock(&WaitLock);
2747 for (int i = 1; i < MAX_THREADS; i++)
2748 SetEvent(SitIdleEvent[i]);
2754 // put_threads_to_sleep() makes all the threads go to sleep just before
2755 // to leave think(), at the end of the search. Threads should have already
2756 // finished the job and should be idle.
2758 void ThreadsManager::put_threads_to_sleep() {
2760 assert(!AllThreadsShouldSleep);
2762 // This makes the threads to go to sleep
2763 AllThreadsShouldSleep = true;
2766 /// The RootMoveList class
2768 // RootMoveList c'tor
2770 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2772 SearchStack ss[PLY_MAX_PLUS_2];
2773 MoveStack mlist[MaxRootMoves];
2775 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2777 // Generate all legal moves
2778 MoveStack* last = generate_moves(pos, mlist);
2780 // Add each move to the moves[] array
2781 for (MoveStack* cur = mlist; cur != last; cur++)
2783 bool includeMove = includeAllMoves;
2785 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2786 includeMove = (searchMoves[k] == cur->move);
2791 // Find a quick score for the move
2792 init_ss_array(ss, PLY_MAX_PLUS_2);
2793 pos.do_move(cur->move, st);
2794 moves[count].move = cur->move;
2795 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0));
2796 moves[count].pv[0] = cur->move;
2797 moves[count].pv[1] = MOVE_NONE;
2798 pos.undo_move(cur->move);
2805 // RootMoveList simple methods definitions
2807 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2809 moves[moveNum].nodes = nodes;
2810 moves[moveNum].cumulativeNodes += nodes;
2813 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2815 moves[moveNum].ourBeta = our;
2816 moves[moveNum].theirBeta = their;
2819 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2823 for (j = 0; pv[j] != MOVE_NONE; j++)
2824 moves[moveNum].pv[j] = pv[j];
2826 moves[moveNum].pv[j] = MOVE_NONE;
2830 // RootMoveList::sort() sorts the root move list at the beginning of a new
2833 void RootMoveList::sort() {
2835 sort_multipv(count - 1); // Sort all items
2839 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2840 // list by their scores and depths. It is used to order the different PVs
2841 // correctly in MultiPV mode.
2843 void RootMoveList::sort_multipv(int n) {
2847 for (i = 1; i <= n; i++)
2849 RootMove rm = moves[i];
2850 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2851 moves[j] = moves[j - 1];