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, int ply);
300 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply);
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(int ply) {
371 pv[ply] = pv[ply + 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 // Reduced depth non-pv search using alpha as upperbound
896 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
897 doFullDepthSearch = (value > alpha);
901 // Step 15. Full depth search
902 if (doFullDepthSearch)
904 // Full depth non-pv search using alpha as upperbound
905 ss->reduction = Depth(0);
906 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
908 // If we are above alpha then research at same depth but as PV
909 // to get a correct score or eventually a fail high above beta.
911 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
915 // Step 16. Undo move
918 // Can we exit fail high loop ?
919 if (AbortSearch || value < beta)
922 // We are failing high and going to do a research. It's important to update
923 // the score before research in case we run out of time while researching.
924 rml.set_move_score(i, value);
926 TT.extract_pv(pos, ss->pv, PLY_MAX);
927 rml.set_move_pv(i, ss->pv);
929 // Print information to the standard output
930 print_pv_info(pos, ss, alpha, beta, value);
932 // Prepare for a research after a fail high, each time with a wider window
933 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
936 } // End of fail high loop
938 // Finished searching the move. If AbortSearch is true, the search
939 // was aborted because the user interrupted the search or because we
940 // ran out of time. In this case, the return value of the search cannot
941 // be trusted, and we break out of the loop without updating the best
946 // Remember beta-cutoff and searched nodes counts for this move. The
947 // info is used to sort the root moves for the next iteration.
949 TM.get_beta_counters(pos.side_to_move(), our, their);
950 rml.set_beta_counters(i, our, their);
951 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
953 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
954 assert(value < beta);
956 // Step 17. Check for new best move
957 if (value <= alpha && i >= MultiPV)
958 rml.set_move_score(i, -VALUE_INFINITE);
961 // PV move or new best move!
964 rml.set_move_score(i, value);
966 TT.extract_pv(pos, ss->pv, PLY_MAX);
967 rml.set_move_pv(i, ss->pv);
971 // We record how often the best move has been changed in each
972 // iteration. This information is used for time managment: When
973 // the best move changes frequently, we allocate some more time.
975 BestMoveChangesByIteration[Iteration]++;
977 // Print information to the standard output
978 print_pv_info(pos, ss, alpha, beta, value);
980 // Raise alpha to setup proper non-pv search upper bound
987 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
989 cout << "info multipv " << j + 1
990 << " score " << value_to_string(rml.get_move_score(j))
991 << " depth " << (j <= i ? Iteration : Iteration - 1)
992 << " time " << current_search_time()
993 << " nodes " << TM.nodes_searched()
997 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
998 cout << rml.get_move_pv(j, k) << " ";
1002 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1004 } // PV move or new best move
1006 assert(alpha >= *alphaPtr);
1008 AspirationFailLow = (alpha == *alphaPtr);
1010 if (AspirationFailLow && StopOnPonderhit)
1011 StopOnPonderhit = false;
1014 // Can we exit fail low loop ?
1015 if (AbortSearch || !AspirationFailLow)
1018 // Prepare for a research after a fail low, each time with a wider window
1019 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1024 // Sort the moves before to return
1031 // search<>() is the main search function for both PV and non-PV nodes
1033 template <NodeType PvNode>
1034 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1036 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1037 assert(beta > alpha && beta <= VALUE_INFINITE);
1038 assert(PvNode || alpha == beta - 1);
1039 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1040 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1042 Move movesSearched[256];
1047 Move ttMove, move, excludedMove;
1048 Depth ext, newDepth;
1049 Value bestValue, value, oldAlpha;
1050 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1051 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1052 bool mateThreat = false;
1054 int threadID = pos.thread();
1055 int ply = pos.ply();
1056 refinedValue = bestValue = value = -VALUE_INFINITE;
1059 // Step 1. Initialize node and poll. Polling can abort search
1060 TM.incrementNodeCounter(threadID);
1062 (ss + 2)->initKillers();
1064 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1070 // Step 2. Check for aborted search and immediate draw
1071 if (AbortSearch || TM.thread_should_stop(threadID))
1074 if (pos.is_draw() || ply >= PLY_MAX - 1)
1077 // Step 3. Mate distance pruning
1078 alpha = Max(value_mated_in(ply), alpha);
1079 beta = Min(value_mate_in(ply+1), beta);
1083 // Step 4. Transposition table lookup
1085 // We don't want the score of a partial search to overwrite a previous full search
1086 // TT value, so we use a different position key in case of an excluded move exists.
1087 excludedMove = ss->excludedMove;
1088 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1090 tte = TT.retrieve(posKey);
1091 ttMove = (tte ? tte->move() : MOVE_NONE);
1093 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1094 // This is to avoid problems in the following areas:
1096 // * Repetition draw detection
1097 // * Fifty move rule detection
1098 // * Searching for a mate
1099 // * Printing of full PV line
1101 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1103 // Refresh tte entry to avoid aging
1104 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1106 ss->currentMove = ttMove; // Can be MOVE_NONE
1107 return value_from_tt(tte->value(), ply);
1110 // Step 5. Evaluate the position statically
1111 // At PV nodes we do this only to update gain statistics
1112 isCheck = pos.is_check();
1115 if (tte && tte->static_value() != VALUE_NONE)
1117 ss->eval = tte->static_value();
1118 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1121 ss->eval = evaluate(pos, ei);
1123 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1124 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1127 // Step 6. Razoring (is omitted in PV nodes)
1129 && depth < RazorDepth
1131 && refinedValue < beta - razor_margin(depth)
1132 && ttMove == MOVE_NONE
1133 && (ss-1)->currentMove != MOVE_NULL
1134 && !value_is_mate(beta)
1135 && !pos.has_pawn_on_7th(pos.side_to_move()))
1137 Value rbeta = beta - razor_margin(depth);
1138 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0));
1140 // Logically we should return (v + razor_margin(depth)), but
1141 // surprisingly this did slightly weaker in tests.
1145 // Step 7. Static null move pruning (is omitted in PV nodes)
1146 // We're betting that the opponent doesn't have a move that will reduce
1147 // the score by more than futility_margin(depth) if we do a null move.
1149 && !ss->skipNullMove
1150 && depth < RazorDepth
1151 && refinedValue >= beta + futility_margin(depth, 0)
1153 && !value_is_mate(beta)
1154 && pos.non_pawn_material(pos.side_to_move()))
1155 return refinedValue - futility_margin(depth, 0);
1157 // Step 8. Null move search with verification search (is omitted in PV nodes)
1158 // When we jump directly to qsearch() we do a null move only if static value is
1159 // at least beta. Otherwise we do a null move if static value is not more than
1160 // NullMoveMargin under beta.
1162 && !ss->skipNullMove
1164 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1166 && !value_is_mate(beta)
1167 && pos.non_pawn_material(pos.side_to_move()))
1169 ss->currentMove = MOVE_NULL;
1171 // Null move dynamic reduction based on depth
1172 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1174 // Null move dynamic reduction based on value
1175 if (refinedValue - beta > PawnValueMidgame)
1178 pos.do_null_move(st);
1179 (ss+1)->skipNullMove = true;
1181 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0))
1182 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly);
1183 (ss+1)->skipNullMove = false;
1184 pos.undo_null_move();
1186 if (nullValue >= beta)
1188 // Do not return unproven mate scores
1189 if (nullValue >= value_mate_in(PLY_MAX))
1192 // Do zugzwang verification search at high depths
1193 if (depth < 6 * OnePly)
1196 ss->skipNullMove = true;
1197 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly);
1198 ss->skipNullMove = false;
1205 // The null move failed low, which means that we may be faced with
1206 // some kind of threat. If the previous move was reduced, check if
1207 // the move that refuted the null move was somehow connected to the
1208 // move which was reduced. If a connection is found, return a fail
1209 // low score (which will cause the reduced move to fail high in the
1210 // parent node, which will trigger a re-search with full depth).
1211 if (nullValue == value_mated_in(ply + 2))
1214 ss->threatMove = (ss+1)->currentMove;
1215 if ( depth < ThreatDepth
1216 && (ss-1)->reduction
1217 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1222 // Step 9. Internal iterative deepening
1223 if ( depth >= IIDDepth[PvNode]
1224 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1225 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1227 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1229 ss->skipNullMove = true;
1230 search<PvNode>(pos, ss, alpha, beta, d);
1231 ss->skipNullMove = false;
1233 ttMove = ss->pv[ply];
1234 tte = TT.retrieve(posKey);
1237 // Expensive mate threat detection (only for PV nodes)
1239 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1241 // Initialize a MovePicker object for the current position
1242 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1244 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1245 && tte && tte->move()
1246 && !excludedMove // Do not allow recursive singular extension search
1247 && is_lower_bound(tte->type())
1248 && tte->depth() >= depth - 3 * OnePly;
1250 // Step 10. Loop through moves
1251 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1252 while ( bestValue < beta
1253 && (move = mp.get_next_move()) != MOVE_NONE
1254 && !TM.thread_should_stop(threadID))
1256 assert(move_is_ok(move));
1258 if (move == excludedMove)
1261 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1262 moveIsCheck = pos.move_is_check(move, ci);
1263 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1265 // Step 11. Decide the new search depth
1266 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1268 // Singular extension search. We extend the TT move if its value is much better than
1269 // its siblings. To verify this we do a reduced search on all the other moves but the
1270 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1271 if ( singularExtensionNode
1272 && move == tte->move()
1275 Value ttValue = value_from_tt(tte->value(), ply);
1277 if (abs(ttValue) < VALUE_KNOWN_WIN)
1279 Value b = ttValue - SingularExtensionMargin;
1280 ss->excludedMove = move;
1281 ss->skipNullMove = true;
1282 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2);
1283 ss->skipNullMove = false;
1284 ss->excludedMove = MOVE_NONE;
1286 if (v < ttValue - SingularExtensionMargin)
1291 newDepth = depth - OnePly + ext;
1293 // Update current move (this must be done after singular extension search)
1294 movesSearched[moveCount++] = ss->currentMove = move;
1296 // Step 12. Futility pruning (is omitted in PV nodes)
1298 && !captureOrPromotion
1302 && !move_is_castle(move))
1304 // Move count based pruning
1305 if ( moveCount >= futility_move_count(depth)
1306 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1307 && bestValue > value_mated_in(PLY_MAX))
1310 // Value based pruning
1311 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1312 // but fixing this made program slightly weaker.
1313 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1314 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1315 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1317 if (futilityValueScaled < beta)
1319 if (futilityValueScaled > bestValue)
1320 bestValue = futilityValueScaled;
1325 // Step 13. Make the move
1326 pos.do_move(move, st, ci, moveIsCheck);
1328 // Step extra. pv search (only in PV nodes)
1329 // The first move in list is the expected PV
1330 if (PvNode && moveCount == 1)
1331 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1332 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1335 // Step 14. Reduced depth search
1336 // If the move fails high will be re-searched at full depth.
1337 bool doFullDepthSearch = true;
1339 if ( depth >= 3 * OnePly
1340 && !captureOrPromotion
1342 && !move_is_castle(move)
1343 && !move_is_killer(move, ss))
1345 ss->reduction = reduction<PvNode>(depth, moveCount);
1348 Depth d = newDepth - ss->reduction;
1349 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1350 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1352 doFullDepthSearch = (value > alpha);
1355 // The move failed high, but if reduction is very big we could
1356 // face a false positive, retry with a less aggressive reduction,
1357 // if the move fails high again then go with full depth search.
1358 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1360 assert(newDepth - OnePly >= OnePly);
1362 ss->reduction = OnePly;
1363 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
1364 doFullDepthSearch = (value > alpha);
1366 ss->reduction = Depth(0); // Restore original reduction
1369 // Step 15. Full depth search
1370 if (doFullDepthSearch)
1372 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1373 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1375 // Step extra. pv search (only in PV nodes)
1376 // Search only for possible new PV nodes, if instead value >= beta then
1377 // parent node fails low with value <= alpha and tries another move.
1378 if (PvNode && value > alpha && value < beta)
1379 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1380 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1384 // Step 16. Undo move
1385 pos.undo_move(move);
1387 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1389 // Step 17. Check for new best move
1390 if (value > bestValue)
1395 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1400 if (value == value_mate_in(ply + 1))
1401 ss->mateKiller = move;
1405 // Step 18. Check for split
1406 if ( depth >= MinimumSplitDepth
1407 && TM.active_threads() > 1
1409 && TM.available_thread_exists(threadID)
1411 && !TM.thread_should_stop(threadID)
1413 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1414 mateThreat, &moveCount, &mp, PvNode);
1417 // Step 19. Check for mate and stalemate
1418 // All legal moves have been searched and if there are
1419 // no legal moves, it must be mate or stalemate.
1420 // If one move was excluded return fail low score.
1422 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1424 // Step 20. Update tables
1425 // If the search is not aborted, update the transposition table,
1426 // history counters, and killer moves.
1427 if (AbortSearch || TM.thread_should_stop(threadID))
1430 if (bestValue <= oldAlpha)
1431 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1433 else if (bestValue >= beta)
1435 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1437 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1438 if (!pos.move_is_capture_or_promotion(move))
1440 update_history(pos, move, depth, movesSearched, moveCount);
1441 update_killers(move, ss);
1445 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1447 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1453 // qsearch() is the quiescence search function, which is called by the main
1454 // search function when the remaining depth is zero (or, to be more precise,
1455 // less than OnePly).
1457 template <NodeType PvNode>
1458 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1460 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1461 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1462 assert(PvNode || alpha == beta - 1);
1464 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1465 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1470 Value staticValue, bestValue, value, futilityBase;
1471 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1472 const TTEntry* tte = NULL;
1474 int ply = pos.ply();
1475 Value oldAlpha = alpha;
1476 Value futilityValue = VALUE_INFINITE;
1478 TM.incrementNodeCounter(pos.thread());
1481 // Check for an instant draw or maximum ply reached
1482 if (pos.is_draw() || ply >= PLY_MAX - 1)
1485 // Transposition table lookup. At PV nodes, we don't use the TT for
1486 // pruning, but only for move ordering.
1487 tte = TT.retrieve(pos.get_key());
1488 ttMove = (tte ? tte->move() : MOVE_NONE);
1490 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1492 ss->currentMove = ttMove; // Can be MOVE_NONE
1493 return value_from_tt(tte->value(), ply);
1496 isCheck = pos.is_check();
1498 // Evaluate the position statically
1500 staticValue = -VALUE_INFINITE;
1501 else if (tte && tte->static_value() != VALUE_NONE)
1503 staticValue = tte->static_value();
1504 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1507 staticValue = evaluate(pos, ei);
1511 ss->eval = staticValue;
1512 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1515 // Initialize "stand pat score", and return it immediately if it is
1517 bestValue = staticValue;
1519 if (bestValue >= beta)
1521 // Store the score to avoid a future costly evaluation() call
1522 if (!isCheck && !tte)
1523 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()]);
1528 if (PvNode && bestValue > alpha)
1531 // If we are near beta then try to get a cutoff pushing checks a bit further
1532 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1534 // Initialize a MovePicker object for the current position, and prepare
1535 // to search the moves. Because the depth is <= 0 here, only captures,
1536 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1537 // and we are near beta) will be generated.
1538 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1540 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1541 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1543 // Loop through the moves until no moves remain or a beta cutoff occurs
1544 while ( alpha < beta
1545 && (move = mp.get_next_move()) != MOVE_NONE)
1547 assert(move_is_ok(move));
1549 moveIsCheck = pos.move_is_check(move, ci);
1551 // Update current move
1553 ss->currentMove = move;
1561 && !move_is_promotion(move)
1562 && !pos.move_is_passed_pawn_push(move))
1564 // Can only decrease from previous move because of
1565 // MVV ordering so we don't need to recheck.
1566 if (futilityValue < alpha)
1569 futilityValue = futilityBase
1570 + pos.endgame_value_of_piece_on(move_to(move))
1571 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1573 if (futilityValue < alpha)
1575 if (futilityValue > bestValue)
1576 bestValue = futilityValue;
1581 // Detect blocking evasions that are candidate to be pruned
1582 evasionPrunable = isCheck
1583 && bestValue > value_mated_in(PLY_MAX)
1584 && !pos.move_is_capture(move)
1585 && pos.type_of_piece_on(move_from(move)) != KING
1586 && !pos.can_castle(pos.side_to_move());
1588 // Don't search moves with negative SEE values
1590 && (!isCheck || evasionPrunable)
1592 && !move_is_promotion(move)
1593 && pos.see_sign(move) < 0)
1596 // Make and search the move
1597 pos.do_move(move, st, ci, moveIsCheck);
1598 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly);
1599 pos.undo_move(move);
1601 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1604 if (value > bestValue)
1615 // All legal moves have been searched. A special case: If we're in check
1616 // and no legal moves were found, it is checkmate.
1617 if (!moveCount && isCheck) // Mate!
1618 return value_mated_in(ply);
1620 // Update transposition table
1621 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1622 if (bestValue <= oldAlpha)
1624 // If bestValue isn't changed it means it is still the static evaluation
1625 // of the node, so keep this info to avoid a future evaluation() call.
1626 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1628 else if (bestValue >= beta)
1631 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1633 // Update killers only for good checking moves
1634 if (!pos.move_is_capture_or_promotion(move))
1635 update_killers(move, ss);
1638 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1640 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1646 // sp_search() is used to search from a split point. This function is called
1647 // by each thread working at the split point. It is similar to the normal
1648 // search() function, but simpler. Because we have already probed the hash
1649 // table, done a null move search, and searched the first move before
1650 // splitting, we don't have to repeat all this work in sp_search(). We
1651 // also don't need to store anything to the hash table here: This is taken
1652 // care of after we return from the split point.
1654 template <NodeType PvNode>
1655 void sp_search(SplitPoint* sp, int threadID) {
1657 assert(threadID >= 0 && threadID < TM.active_threads());
1658 assert(TM.active_threads() > 1);
1662 Depth ext, newDepth;
1664 Value futilityValueScaled; // NonPV specific
1665 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1667 value = -VALUE_INFINITE;
1669 Position pos(*sp->pos, threadID);
1671 int ply = pos.ply();
1672 SearchStack* ss = sp->sstack[threadID] + 1;
1673 isCheck = pos.is_check();
1675 // Step 10. Loop through moves
1676 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1677 lock_grab(&(sp->lock));
1679 while ( sp->bestValue < sp->beta
1680 && (move = sp->mp->get_next_move()) != MOVE_NONE
1681 && !TM.thread_should_stop(threadID))
1683 moveCount = ++sp->moveCount;
1684 lock_release(&(sp->lock));
1686 assert(move_is_ok(move));
1688 moveIsCheck = pos.move_is_check(move, ci);
1689 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1691 // Step 11. Decide the new search depth
1692 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1693 newDepth = sp->depth - OnePly + ext;
1695 // Update current move
1696 ss->currentMove = move;
1698 // Step 12. Futility pruning (is omitted in PV nodes)
1700 && !captureOrPromotion
1703 && !move_is_castle(move))
1705 // Move count based pruning
1706 if ( moveCount >= futility_move_count(sp->depth)
1707 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1708 && sp->bestValue > value_mated_in(PLY_MAX))
1710 lock_grab(&(sp->lock));
1714 // Value based pruning
1715 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1716 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1717 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1719 if (futilityValueScaled < sp->beta)
1721 lock_grab(&(sp->lock));
1723 if (futilityValueScaled > sp->bestValue)
1724 sp->bestValue = futilityValueScaled;
1729 // Step 13. Make the move
1730 pos.do_move(move, st, ci, moveIsCheck);
1732 // Step 14. Reduced search
1733 // If the move fails high will be re-searched at full depth.
1734 bool doFullDepthSearch = true;
1736 if ( !captureOrPromotion
1738 && !move_is_castle(move)
1739 && !move_is_killer(move, ss))
1741 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1744 Value localAlpha = sp->alpha;
1745 Depth d = newDepth - ss->reduction;
1746 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1747 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d);
1748 doFullDepthSearch = (value > localAlpha);
1751 // The move failed high, but if reduction is very big we could
1752 // face a false positive, retry with a less aggressive reduction,
1753 // if the move fails high again then go with full depth search.
1754 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1756 assert(newDepth - OnePly >= OnePly);
1758 ss->reduction = OnePly;
1759 Value localAlpha = sp->alpha;
1760 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction);
1761 doFullDepthSearch = (value > localAlpha);
1763 ss->reduction = Depth(0); // Restore original reduction
1766 // Step 15. Full depth search
1767 if (doFullDepthSearch)
1769 Value localAlpha = sp->alpha;
1770 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1771 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth);
1773 // Step extra. pv search (only in PV nodes)
1774 // Search only for possible new PV nodes, if instead value >= beta then
1775 // parent node fails low with value <= alpha and tries another move.
1776 if (PvNode && value > localAlpha && value < sp->beta)
1777 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0))
1778 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth);
1781 // Step 16. Undo move
1782 pos.undo_move(move);
1784 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1786 // Step 17. Check for new best move
1787 lock_grab(&(sp->lock));
1789 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1791 sp->bestValue = value;
1793 if (sp->bestValue > sp->alpha)
1795 if (!PvNode || value >= sp->beta)
1796 sp->stopRequest = true;
1798 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1801 sp_update_pv(sp->parentSstack, ss, ply);
1806 /* Here we have the lock still grabbed */
1808 sp->slaves[threadID] = 0;
1810 lock_release(&(sp->lock));
1813 // update_pv() is called whenever a search returns a value > alpha.
1814 // It updates the PV in the SearchStack object corresponding to the
1817 void update_pv(SearchStack* ss, int ply) {
1819 assert(ply >= 0 && ply < PLY_MAX);
1823 ss->pv[ply] = ss->currentMove;
1825 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1826 ss->pv[p] = (ss+1)->pv[p];
1828 ss->pv[p] = MOVE_NONE;
1832 // sp_update_pv() is a variant of update_pv for use at split points. The
1833 // difference between the two functions is that sp_update_pv also updates
1834 // the PV at the parent node.
1836 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1838 assert(ply >= 0 && ply < PLY_MAX);
1842 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1844 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1845 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1847 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1851 // connected_moves() tests whether two moves are 'connected' in the sense
1852 // that the first move somehow made the second move possible (for instance
1853 // if the moving piece is the same in both moves). The first move is assumed
1854 // to be the move that was made to reach the current position, while the
1855 // second move is assumed to be a move from the current position.
1857 bool connected_moves(const Position& pos, Move m1, Move m2) {
1859 Square f1, t1, f2, t2;
1862 assert(move_is_ok(m1));
1863 assert(move_is_ok(m2));
1865 if (m2 == MOVE_NONE)
1868 // Case 1: The moving piece is the same in both moves
1874 // Case 2: The destination square for m2 was vacated by m1
1880 // Case 3: Moving through the vacated square
1881 if ( piece_is_slider(pos.piece_on(f2))
1882 && bit_is_set(squares_between(f2, t2), f1))
1885 // Case 4: The destination square for m2 is defended by the moving piece in m1
1886 p = pos.piece_on(t1);
1887 if (bit_is_set(pos.attacks_from(p, t1), t2))
1890 // Case 5: Discovered check, checking piece is the piece moved in m1
1891 if ( piece_is_slider(p)
1892 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1893 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1895 // discovered_check_candidates() works also if the Position's side to
1896 // move is the opposite of the checking piece.
1897 Color them = opposite_color(pos.side_to_move());
1898 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1900 if (bit_is_set(dcCandidates, f2))
1907 // value_is_mate() checks if the given value is a mate one
1908 // eventually compensated for the ply.
1910 bool value_is_mate(Value value) {
1912 assert(abs(value) <= VALUE_INFINITE);
1914 return value <= value_mated_in(PLY_MAX)
1915 || value >= value_mate_in(PLY_MAX);
1919 // move_is_killer() checks if the given move is among the
1920 // killer moves of that ply.
1922 bool move_is_killer(Move m, SearchStack* ss) {
1924 const Move* k = ss->killers;
1925 for (int i = 0; i < KILLER_MAX; i++, k++)
1933 // extension() decides whether a move should be searched with normal depth,
1934 // or with extended depth. Certain classes of moves (checking moves, in
1935 // particular) are searched with bigger depth than ordinary moves and in
1936 // any case are marked as 'dangerous'. Note that also if a move is not
1937 // extended, as example because the corresponding UCI option is set to zero,
1938 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1939 template <NodeType PvNode>
1940 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1941 bool singleEvasion, bool mateThreat, bool* dangerous) {
1943 assert(m != MOVE_NONE);
1945 Depth result = Depth(0);
1946 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1951 result += CheckExtension[PvNode];
1954 result += SingleEvasionExtension[PvNode];
1957 result += MateThreatExtension[PvNode];
1960 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1962 Color c = pos.side_to_move();
1963 if (relative_rank(c, move_to(m)) == RANK_7)
1965 result += PawnPushTo7thExtension[PvNode];
1968 if (pos.pawn_is_passed(c, move_to(m)))
1970 result += PassedPawnExtension[PvNode];
1975 if ( captureOrPromotion
1976 && pos.type_of_piece_on(move_to(m)) != PAWN
1977 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1978 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1979 && !move_is_promotion(m)
1982 result += PawnEndgameExtension[PvNode];
1987 && captureOrPromotion
1988 && pos.type_of_piece_on(move_to(m)) != PAWN
1989 && pos.see_sign(m) >= 0)
1995 return Min(result, OnePly);
1999 // connected_threat() tests whether it is safe to forward prune a move or if
2000 // is somehow coonected to the threat move returned by null search.
2002 bool connected_threat(const Position& pos, Move m, Move threat) {
2004 assert(move_is_ok(m));
2005 assert(threat && move_is_ok(threat));
2006 assert(!pos.move_is_check(m));
2007 assert(!pos.move_is_capture_or_promotion(m));
2008 assert(!pos.move_is_passed_pawn_push(m));
2010 Square mfrom, mto, tfrom, tto;
2012 mfrom = move_from(m);
2014 tfrom = move_from(threat);
2015 tto = move_to(threat);
2017 // Case 1: Don't prune moves which move the threatened piece
2021 // Case 2: If the threatened piece has value less than or equal to the
2022 // value of the threatening piece, don't prune move which defend it.
2023 if ( pos.move_is_capture(threat)
2024 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2025 || pos.type_of_piece_on(tfrom) == KING)
2026 && pos.move_attacks_square(m, tto))
2029 // Case 3: If the moving piece in the threatened move is a slider, don't
2030 // prune safe moves which block its ray.
2031 if ( piece_is_slider(pos.piece_on(tfrom))
2032 && bit_is_set(squares_between(tfrom, tto), mto)
2033 && pos.see_sign(m) >= 0)
2040 // ok_to_use_TT() returns true if a transposition table score
2041 // can be used at a given point in search.
2043 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2045 Value v = value_from_tt(tte->value(), ply);
2047 return ( tte->depth() >= depth
2048 || v >= Max(value_mate_in(PLY_MAX), beta)
2049 || v < Min(value_mated_in(PLY_MAX), beta))
2051 && ( (is_lower_bound(tte->type()) && v >= beta)
2052 || (is_upper_bound(tte->type()) && v < beta));
2056 // refine_eval() returns the transposition table score if
2057 // possible otherwise falls back on static position evaluation.
2059 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2064 Value v = value_from_tt(tte->value(), ply);
2066 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2067 || (is_upper_bound(tte->type()) && v < defaultEval))
2074 // update_history() registers a good move that produced a beta-cutoff
2075 // in history and marks as failures all the other moves of that ply.
2077 void update_history(const Position& pos, Move move, Depth depth,
2078 Move movesSearched[], int moveCount) {
2082 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2084 for (int i = 0; i < moveCount - 1; i++)
2086 m = movesSearched[i];
2090 if (!pos.move_is_capture_or_promotion(m))
2091 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2096 // update_killers() add a good move that produced a beta-cutoff
2097 // among the killer moves of that ply.
2099 void update_killers(Move m, SearchStack* ss) {
2101 if (m == ss->killers[0])
2104 for (int i = KILLER_MAX - 1; i > 0; i--)
2105 ss->killers[i] = ss->killers[i - 1];
2111 // update_gains() updates the gains table of a non-capture move given
2112 // the static position evaluation before and after the move.
2114 void update_gains(const Position& pos, Move m, Value before, Value after) {
2117 && before != VALUE_NONE
2118 && after != VALUE_NONE
2119 && pos.captured_piece() == NO_PIECE_TYPE
2120 && !move_is_castle(m)
2121 && !move_is_promotion(m))
2122 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2126 // current_search_time() returns the number of milliseconds which have passed
2127 // since the beginning of the current search.
2129 int current_search_time() {
2131 return get_system_time() - SearchStartTime;
2135 // nps() computes the current nodes/second count.
2139 int t = current_search_time();
2140 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2144 // poll() performs two different functions: It polls for user input, and it
2145 // looks at the time consumed so far and decides if it's time to abort the
2150 static int lastInfoTime;
2151 int t = current_search_time();
2156 // We are line oriented, don't read single chars
2157 std::string command;
2159 if (!std::getline(std::cin, command))
2162 if (command == "quit")
2165 PonderSearch = false;
2169 else if (command == "stop")
2172 PonderSearch = false;
2174 else if (command == "ponderhit")
2178 // Print search information
2182 else if (lastInfoTime > t)
2183 // HACK: Must be a new search where we searched less than
2184 // NodesBetweenPolls nodes during the first second of search.
2187 else if (t - lastInfoTime >= 1000)
2194 if (dbg_show_hit_rate)
2195 dbg_print_hit_rate();
2197 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2198 << " time " << t << " hashfull " << TT.full() << endl;
2201 // Should we stop the search?
2205 bool stillAtFirstMove = FirstRootMove
2206 && !AspirationFailLow
2207 && t > MaxSearchTime + ExtraSearchTime;
2209 bool noMoreTime = t > AbsoluteMaxSearchTime
2210 || stillAtFirstMove;
2212 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2213 || (ExactMaxTime && t >= ExactMaxTime)
2214 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2219 // ponderhit() is called when the program is pondering (i.e. thinking while
2220 // it's the opponent's turn to move) in order to let the engine know that
2221 // it correctly predicted the opponent's move.
2225 int t = current_search_time();
2226 PonderSearch = false;
2228 bool stillAtFirstMove = FirstRootMove
2229 && !AspirationFailLow
2230 && t > MaxSearchTime + ExtraSearchTime;
2232 bool noMoreTime = t > AbsoluteMaxSearchTime
2233 || stillAtFirstMove;
2235 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2240 // init_ss_array() does a fast reset of the first entries of a SearchStack
2241 // array and of all the excludedMove and skipNullMove entries.
2243 void init_ss_array(SearchStack* ss, int size) {
2245 for (int i = 0; i < size; i++, ss++)
2247 ss->excludedMove = MOVE_NONE;
2248 ss->skipNullMove = false;
2259 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2260 // while the program is pondering. The point is to work around a wrinkle in
2261 // the UCI protocol: When pondering, the engine is not allowed to give a
2262 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2263 // We simply wait here until one of these commands is sent, and return,
2264 // after which the bestmove and pondermove will be printed (in id_loop()).
2266 void wait_for_stop_or_ponderhit() {
2268 std::string command;
2272 if (!std::getline(std::cin, command))
2275 if (command == "quit")
2280 else if (command == "ponderhit" || command == "stop")
2286 // print_pv_info() prints to standard output and eventually to log file information on
2287 // the current PV line. It is called at each iteration or after a new pv is found.
2289 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2291 cout << "info depth " << Iteration
2292 << " score " << value_to_string(value)
2293 << ((value >= beta) ? " lowerbound" :
2294 ((value <= alpha)? " upperbound" : ""))
2295 << " time " << current_search_time()
2296 << " nodes " << TM.nodes_searched()
2300 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2301 cout << ss->pv[j] << " ";
2307 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2308 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2310 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2311 TM.nodes_searched(), value, type, ss->pv) << endl;
2316 // init_thread() is the function which is called when a new thread is
2317 // launched. It simply calls the idle_loop() function with the supplied
2318 // threadID. There are two versions of this function; one for POSIX
2319 // threads and one for Windows threads.
2321 #if !defined(_MSC_VER)
2323 void* init_thread(void *threadID) {
2325 TM.idle_loop(*(int*)threadID, NULL);
2331 DWORD WINAPI init_thread(LPVOID threadID) {
2333 TM.idle_loop(*(int*)threadID, NULL);
2340 /// The ThreadsManager class
2342 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2343 // get_beta_counters() are getters/setters for the per thread
2344 // counters used to sort the moves at root.
2346 void ThreadsManager::resetNodeCounters() {
2348 for (int i = 0; i < MAX_THREADS; i++)
2349 threads[i].nodes = 0ULL;
2352 void ThreadsManager::resetBetaCounters() {
2354 for (int i = 0; i < MAX_THREADS; i++)
2355 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2358 int64_t ThreadsManager::nodes_searched() const {
2360 int64_t result = 0ULL;
2361 for (int i = 0; i < ActiveThreads; i++)
2362 result += threads[i].nodes;
2367 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2370 for (int i = 0; i < MAX_THREADS; i++)
2372 our += threads[i].betaCutOffs[us];
2373 their += threads[i].betaCutOffs[opposite_color(us)];
2378 // idle_loop() is where the threads are parked when they have no work to do.
2379 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2380 // object for which the current thread is the master.
2382 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2384 assert(threadID >= 0 && threadID < MAX_THREADS);
2388 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2389 // master should exit as last one.
2390 if (AllThreadsShouldExit)
2393 threads[threadID].state = THREAD_TERMINATED;
2397 // If we are not thinking, wait for a condition to be signaled
2398 // instead of wasting CPU time polling for work.
2399 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2402 assert(threadID != 0);
2403 threads[threadID].state = THREAD_SLEEPING;
2405 #if !defined(_MSC_VER)
2406 lock_grab(&WaitLock);
2407 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2408 pthread_cond_wait(&WaitCond, &WaitLock);
2409 lock_release(&WaitLock);
2411 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2415 // If thread has just woken up, mark it as available
2416 if (threads[threadID].state == THREAD_SLEEPING)
2417 threads[threadID].state = THREAD_AVAILABLE;
2419 // If this thread has been assigned work, launch a search
2420 if (threads[threadID].state == THREAD_WORKISWAITING)
2422 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2424 threads[threadID].state = THREAD_SEARCHING;
2426 if (threads[threadID].splitPoint->pvNode)
2427 sp_search<PV>(threads[threadID].splitPoint, threadID);
2429 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2431 assert(threads[threadID].state == THREAD_SEARCHING);
2433 threads[threadID].state = THREAD_AVAILABLE;
2436 // If this thread is the master of a split point and all slaves have
2437 // finished their work at this split point, return from the idle loop.
2439 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2441 if (i == ActiveThreads)
2443 // Because sp->slaves[] is reset under lock protection,
2444 // be sure sp->lock has been released before to return.
2445 lock_grab(&(sp->lock));
2446 lock_release(&(sp->lock));
2448 assert(threads[threadID].state == THREAD_AVAILABLE);
2450 threads[threadID].state = THREAD_SEARCHING;
2457 // init_threads() is called during startup. It launches all helper threads,
2458 // and initializes the split point stack and the global locks and condition
2461 void ThreadsManager::init_threads() {
2466 #if !defined(_MSC_VER)
2467 pthread_t pthread[1];
2470 // Initialize global locks
2471 lock_init(&MPLock, NULL);
2472 lock_init(&WaitLock, NULL);
2474 #if !defined(_MSC_VER)
2475 pthread_cond_init(&WaitCond, NULL);
2477 for (i = 0; i < MAX_THREADS; i++)
2478 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2481 // Initialize SplitPointStack locks
2482 for (i = 0; i < MAX_THREADS; i++)
2483 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2484 lock_init(&(SplitPointStack[i][j].lock), NULL);
2486 // Will be set just before program exits to properly end the threads
2487 AllThreadsShouldExit = false;
2489 // Threads will be put to sleep as soon as created
2490 AllThreadsShouldSleep = true;
2492 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2494 threads[0].state = THREAD_SEARCHING;
2495 for (i = 1; i < MAX_THREADS; i++)
2496 threads[i].state = THREAD_AVAILABLE;
2498 // Launch the helper threads
2499 for (i = 1; i < MAX_THREADS; i++)
2502 #if !defined(_MSC_VER)
2503 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2505 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2510 cout << "Failed to create thread number " << i << endl;
2511 Application::exit_with_failure();
2514 // Wait until the thread has finished launching and is gone to sleep
2515 while (threads[i].state != THREAD_SLEEPING) {}
2520 // exit_threads() is called when the program exits. It makes all the
2521 // helper threads exit cleanly.
2523 void ThreadsManager::exit_threads() {
2525 ActiveThreads = MAX_THREADS; // HACK
2526 AllThreadsShouldSleep = true; // HACK
2527 wake_sleeping_threads();
2529 // This makes the threads to exit idle_loop()
2530 AllThreadsShouldExit = true;
2532 // Wait for thread termination
2533 for (int i = 1; i < MAX_THREADS; i++)
2534 while (threads[i].state != THREAD_TERMINATED) {}
2536 // Now we can safely destroy the locks
2537 for (int i = 0; i < MAX_THREADS; i++)
2538 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2539 lock_destroy(&(SplitPointStack[i][j].lock));
2541 lock_destroy(&WaitLock);
2542 lock_destroy(&MPLock);
2546 // thread_should_stop() checks whether the thread should stop its search.
2547 // This can happen if a beta cutoff has occurred in the thread's currently
2548 // active split point, or in some ancestor of the current split point.
2550 bool ThreadsManager::thread_should_stop(int threadID) const {
2552 assert(threadID >= 0 && threadID < ActiveThreads);
2556 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2561 // thread_is_available() checks whether the thread with threadID "slave" is
2562 // available to help the thread with threadID "master" at a split point. An
2563 // obvious requirement is that "slave" must be idle. With more than two
2564 // threads, this is not by itself sufficient: If "slave" is the master of
2565 // some active split point, it is only available as a slave to the other
2566 // threads which are busy searching the split point at the top of "slave"'s
2567 // split point stack (the "helpful master concept" in YBWC terminology).
2569 bool ThreadsManager::thread_is_available(int slave, int master) const {
2571 assert(slave >= 0 && slave < ActiveThreads);
2572 assert(master >= 0 && master < ActiveThreads);
2573 assert(ActiveThreads > 1);
2575 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2578 // Make a local copy to be sure doesn't change under our feet
2579 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2581 if (localActiveSplitPoints == 0)
2582 // No active split points means that the thread is available as
2583 // a slave for any other thread.
2586 if (ActiveThreads == 2)
2589 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2590 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2591 // could have been set to 0 by another thread leading to an out of bound access.
2592 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2599 // available_thread_exists() tries to find an idle thread which is available as
2600 // a slave for the thread with threadID "master".
2602 bool ThreadsManager::available_thread_exists(int master) const {
2604 assert(master >= 0 && master < ActiveThreads);
2605 assert(ActiveThreads > 1);
2607 for (int i = 0; i < ActiveThreads; i++)
2608 if (thread_is_available(i, master))
2615 // split() does the actual work of distributing the work at a node between
2616 // several available threads. If it does not succeed in splitting the
2617 // node (because no idle threads are available, or because we have no unused
2618 // split point objects), the function immediately returns. If splitting is
2619 // possible, a SplitPoint object is initialized with all the data that must be
2620 // copied to the helper threads and we tell our helper threads that they have
2621 // been assigned work. This will cause them to instantly leave their idle loops
2622 // and call sp_search(). When all threads have returned from sp_search() then
2625 template <bool Fake>
2626 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2627 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2628 MovePicker* mp, bool pvNode) {
2630 assert(*bestValue >= -VALUE_INFINITE);
2631 assert(*bestValue <= *alpha);
2632 assert(*alpha < beta);
2633 assert(beta <= VALUE_INFINITE);
2634 assert(depth > Depth(0));
2635 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2636 assert(ActiveThreads > 1);
2638 int master = p.thread();
2642 // If no other thread is available to help us, or if we have too many
2643 // active split points, don't split.
2644 if ( !available_thread_exists(master)
2645 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2647 lock_release(&MPLock);
2651 // Pick the next available split point object from the split point stack
2652 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2654 // Initialize the split point object
2655 splitPoint->parent = threads[master].splitPoint;
2656 splitPoint->stopRequest = false;
2657 splitPoint->depth = depth;
2658 splitPoint->mateThreat = mateThreat;
2659 splitPoint->alpha = *alpha;
2660 splitPoint->beta = beta;
2661 splitPoint->pvNode = pvNode;
2662 splitPoint->bestValue = *bestValue;
2663 splitPoint->mp = mp;
2664 splitPoint->moveCount = *moveCount;
2665 splitPoint->pos = &p;
2666 splitPoint->parentSstack = ss;
2667 for (int i = 0; i < ActiveThreads; i++)
2668 splitPoint->slaves[i] = 0;
2670 threads[master].splitPoint = splitPoint;
2671 threads[master].activeSplitPoints++;
2673 // If we are here it means we are not available
2674 assert(threads[master].state != THREAD_AVAILABLE);
2676 int workersCnt = 1; // At least the master is included
2678 // Allocate available threads setting state to THREAD_BOOKED
2679 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2680 if (thread_is_available(i, master))
2682 threads[i].state = THREAD_BOOKED;
2683 threads[i].splitPoint = splitPoint;
2684 splitPoint->slaves[i] = 1;
2688 assert(Fake || workersCnt > 1);
2690 // We can release the lock because slave threads are already booked and master is not available
2691 lock_release(&MPLock);
2693 // Tell the threads that they have work to do. This will make them leave
2694 // their idle loop. But before copy search stack tail for each thread.
2695 for (int i = 0; i < ActiveThreads; i++)
2696 if (i == master || splitPoint->slaves[i])
2698 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2700 assert(i == master || threads[i].state == THREAD_BOOKED);
2702 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2705 // Everything is set up. The master thread enters the idle loop, from
2706 // which it will instantly launch a search, because its state is
2707 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2708 // idle loop, which means that the main thread will return from the idle
2709 // loop when all threads have finished their work at this split point.
2710 idle_loop(master, splitPoint);
2712 // We have returned from the idle loop, which means that all threads are
2713 // finished. Update alpha and bestValue, and return.
2716 *alpha = splitPoint->alpha;
2717 *bestValue = splitPoint->bestValue;
2718 threads[master].activeSplitPoints--;
2719 threads[master].splitPoint = splitPoint->parent;
2721 lock_release(&MPLock);
2725 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2726 // to start a new search from the root.
2728 void ThreadsManager::wake_sleeping_threads() {
2730 assert(AllThreadsShouldSleep);
2731 assert(ActiveThreads > 0);
2733 AllThreadsShouldSleep = false;
2735 if (ActiveThreads == 1)
2738 #if !defined(_MSC_VER)
2739 pthread_mutex_lock(&WaitLock);
2740 pthread_cond_broadcast(&WaitCond);
2741 pthread_mutex_unlock(&WaitLock);
2743 for (int i = 1; i < MAX_THREADS; i++)
2744 SetEvent(SitIdleEvent[i]);
2750 // put_threads_to_sleep() makes all the threads go to sleep just before
2751 // to leave think(), at the end of the search. Threads should have already
2752 // finished the job and should be idle.
2754 void ThreadsManager::put_threads_to_sleep() {
2756 assert(!AllThreadsShouldSleep);
2758 // This makes the threads to go to sleep
2759 AllThreadsShouldSleep = true;
2762 /// The RootMoveList class
2764 // RootMoveList c'tor
2766 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2768 SearchStack ss[PLY_MAX_PLUS_2];
2769 MoveStack mlist[MaxRootMoves];
2771 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2773 // Generate all legal moves
2774 MoveStack* last = generate_moves(pos, mlist);
2776 // Add each move to the moves[] array
2777 for (MoveStack* cur = mlist; cur != last; cur++)
2779 bool includeMove = includeAllMoves;
2781 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2782 includeMove = (searchMoves[k] == cur->move);
2787 // Find a quick score for the move
2788 init_ss_array(ss, PLY_MAX_PLUS_2);
2789 pos.do_move(cur->move, st);
2790 moves[count].move = cur->move;
2791 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0));
2792 moves[count].pv[0] = cur->move;
2793 moves[count].pv[1] = MOVE_NONE;
2794 pos.undo_move(cur->move);
2801 // RootMoveList simple methods definitions
2803 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2805 moves[moveNum].nodes = nodes;
2806 moves[moveNum].cumulativeNodes += nodes;
2809 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2811 moves[moveNum].ourBeta = our;
2812 moves[moveNum].theirBeta = their;
2815 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2819 for (j = 0; pv[j] != MOVE_NONE; j++)
2820 moves[moveNum].pv[j] = pv[j];
2822 moves[moveNum].pv[j] = MOVE_NONE;
2826 // RootMoveList::sort() sorts the root move list at the beginning of a new
2829 void RootMoveList::sort() {
2831 sort_multipv(count - 1); // Sort all items
2835 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2836 // list by their scores and depths. It is used to order the different PVs
2837 // correctly in MultiPV mode.
2839 void RootMoveList::sort_multipv(int n) {
2843 for (i = 1; i <= n; i++)
2845 RootMove rm = moves[i];
2846 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2847 moves[j] = moves[j - 1];