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, int master, 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, int threadID);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID);
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);
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[]) {
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";
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, 0);
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, 0);
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, 0);
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, 0);
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, 0);
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, int threadID) {
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(threadID >= 0 && threadID < 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 ply = pos.ply();
1055 refinedValue = bestValue = value = -VALUE_INFINITE;
1058 // Step 1. Initialize node and poll. Polling can abort search
1059 TM.incrementNodeCounter(threadID);
1061 (ss + 1)->excludedMove = MOVE_NONE;
1062 (ss + 1)->skipNullMove = false;
1063 (ss + 2)->initKillers();
1065 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1071 // Step 2. Check for aborted search and immediate draw
1072 if (AbortSearch || TM.thread_should_stop(threadID))
1075 if (pos.is_draw() || ply >= PLY_MAX - 1)
1078 // Step 3. Mate distance pruning
1079 alpha = Max(value_mated_in(ply), alpha);
1080 beta = Min(value_mate_in(ply+1), beta);
1084 // Step 4. Transposition table lookup
1086 // We don't want the score of a partial search to overwrite a previous full search
1087 // TT value, so we use a different position key in case of an excluded move exists.
1088 excludedMove = ss->excludedMove;
1089 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1091 tte = TT.retrieve(posKey);
1092 ttMove = (tte ? tte->move() : MOVE_NONE);
1094 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1095 // This is to avoid problems in the following areas:
1097 // * Repetition draw detection
1098 // * Fifty move rule detection
1099 // * Searching for a mate
1100 // * Printing of full PV line
1102 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1104 // Refresh tte entry to avoid aging
1105 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1107 ss->currentMove = ttMove; // Can be MOVE_NONE
1108 return value_from_tt(tte->value(), ply);
1111 // Step 5. Evaluate the position statically
1112 // At PV nodes we do this only to update gain statistics
1113 isCheck = pos.is_check();
1116 if (tte && tte->static_value() != VALUE_NONE)
1118 ss->eval = tte->static_value();
1119 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1122 ss->eval = evaluate(pos, ei, threadID);
1124 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1125 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1128 // Step 6. Razoring (is omitted in PV nodes)
1130 && depth < RazorDepth
1132 && refinedValue < beta - razor_margin(depth)
1133 && ttMove == MOVE_NONE
1134 && (ss-1)->currentMove != MOVE_NULL
1135 && !value_is_mate(beta)
1136 && !pos.has_pawn_on_7th(pos.side_to_move()))
1138 Value rbeta = beta - razor_margin(depth);
1139 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), threadID);
1141 // Logically we should return (v + razor_margin(depth)), but
1142 // surprisingly this did slightly weaker in tests.
1146 // Step 7. Static null move pruning (is omitted in PV nodes)
1147 // We're betting that the opponent doesn't have a move that will reduce
1148 // the score by more than futility_margin(depth) if we do a null move.
1150 && !ss->skipNullMove
1151 && depth < RazorDepth
1152 && refinedValue >= beta + futility_margin(depth, 0)
1154 && !value_is_mate(beta)
1155 && pos.non_pawn_material(pos.side_to_move()))
1156 return refinedValue - futility_margin(depth, 0);
1158 // Step 8. Null move search with verification search (is omitted in PV nodes)
1159 // When we jump directly to qsearch() we do a null move only if static value is
1160 // at least beta. Otherwise we do a null move if static value is not more than
1161 // NullMoveMargin under beta.
1163 && !ss->skipNullMove
1165 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1167 && !value_is_mate(beta)
1168 && pos.non_pawn_material(pos.side_to_move()))
1170 ss->currentMove = MOVE_NULL;
1172 // Null move dynamic reduction based on depth
1173 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1175 // Null move dynamic reduction based on value
1176 if (refinedValue - beta > PawnValueMidgame)
1179 pos.do_null_move(st);
1181 (ss+1)->skipNullMove = true;
1183 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1184 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, threadID);
1186 (ss+1)->skipNullMove = false;
1188 pos.undo_null_move();
1190 if (nullValue >= beta)
1192 // Do not return unproven mate scores
1193 if (nullValue >= value_mate_in(PLY_MAX))
1196 // Do zugzwang verification search at high depths
1197 if (depth < 6 * OnePly)
1200 ss->skipNullMove = true;
1201 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, threadID);
1202 ss->skipNullMove = false;
1209 // The null move failed low, which means that we may be faced with
1210 // some kind of threat. If the previous move was reduced, check if
1211 // the move that refuted the null move was somehow connected to the
1212 // move which was reduced. If a connection is found, return a fail
1213 // low score (which will cause the reduced move to fail high in the
1214 // parent node, which will trigger a re-search with full depth).
1215 if (nullValue == value_mated_in(ply + 2))
1218 ss->threatMove = (ss+1)->currentMove;
1219 if ( depth < ThreatDepth
1220 && (ss-1)->reduction
1221 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1226 // Step 9. Internal iterative deepening
1227 if ( depth >= IIDDepth[PvNode]
1228 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1229 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1231 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1233 ss->skipNullMove = true;
1234 search<PvNode>(pos, ss, alpha, beta, d, threadID);
1235 ss->skipNullMove = false;
1237 ttMove = ss->pv[ply];
1238 tte = TT.retrieve(posKey);
1241 // Expensive mate threat detection (only for PV nodes)
1243 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1245 // Initialize a MovePicker object for the current position
1246 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1248 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1249 && tte && tte->move()
1250 && !excludedMove // Do not allow recursive singular extension search
1251 && is_lower_bound(tte->type())
1252 && tte->depth() >= depth - 3 * OnePly;
1254 // Step 10. Loop through moves
1255 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1256 while ( bestValue < beta
1257 && (move = mp.get_next_move()) != MOVE_NONE
1258 && !TM.thread_should_stop(threadID))
1260 assert(move_is_ok(move));
1262 if (move == excludedMove)
1265 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1266 moveIsCheck = pos.move_is_check(move, ci);
1267 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1269 // Step 11. Decide the new search depth
1270 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1272 // Singular extension search. We extend the TT move if its value is much better than
1273 // its siblings. To verify this we do a reduced search on all the other moves but the
1274 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1275 if ( singularExtensionNode
1276 && move == tte->move()
1279 Value ttValue = value_from_tt(tte->value(), ply);
1281 if (abs(ttValue) < VALUE_KNOWN_WIN)
1283 Value b = ttValue - SingularExtensionMargin;
1284 ss->excludedMove = move;
1285 ss->skipNullMove = true;
1286 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, threadID);
1287 ss->skipNullMove = false;
1288 ss->excludedMove = MOVE_NONE;
1290 if (v < ttValue - SingularExtensionMargin)
1295 newDepth = depth - OnePly + ext;
1297 // Update current move (this must be done after singular extension search)
1298 movesSearched[moveCount++] = ss->currentMove = move;
1300 // Step 12. Futility pruning (is omitted in PV nodes)
1302 && !captureOrPromotion
1306 && !move_is_castle(move))
1308 // Move count based pruning
1309 if ( moveCount >= futility_move_count(depth)
1310 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1311 && bestValue > value_mated_in(PLY_MAX))
1314 // Value based pruning
1315 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1316 // but fixing this made program slightly weaker.
1317 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1318 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1319 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1321 if (futilityValueScaled < beta)
1323 if (futilityValueScaled > bestValue)
1324 bestValue = futilityValueScaled;
1329 // Step 13. Make the move
1330 pos.do_move(move, st, ci, moveIsCheck);
1332 // Step extra. pv search (only in PV nodes)
1333 // The first move in list is the expected PV
1334 if (PvNode && moveCount == 1)
1335 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1336 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, threadID);
1339 // Step 14. Reduced depth search
1340 // If the move fails high will be re-searched at full depth.
1341 bool doFullDepthSearch = true;
1343 if ( depth >= 3 * OnePly
1344 && !captureOrPromotion
1346 && !move_is_castle(move)
1347 && !move_is_killer(move, ss))
1349 ss->reduction = reduction<PvNode>(depth, moveCount);
1352 Depth d = newDepth - ss->reduction;
1353 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1354 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, threadID);
1356 doFullDepthSearch = (value > alpha);
1359 // The move failed high, but if reduction is very big we could
1360 // face a false positive, retry with a less aggressive reduction,
1361 // if the move fails high again then go with full depth search.
1362 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1364 assert(newDepth - OnePly >= OnePly);
1366 ss->reduction = OnePly;
1367 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, threadID);
1368 doFullDepthSearch = (value > alpha);
1370 ss->reduction = Depth(0); // Restore original reduction
1373 // Step 15. Full depth search
1374 if (doFullDepthSearch)
1376 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1377 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, threadID);
1379 // Step extra. pv search (only in PV nodes)
1380 // Search only for possible new PV nodes, if instead value >= beta then
1381 // parent node fails low with value <= alpha and tries another move.
1382 if (PvNode && value > alpha && value < beta)
1383 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1384 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, threadID);
1388 // Step 16. Undo move
1389 pos.undo_move(move);
1391 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1393 // Step 17. Check for new best move
1394 if (value > bestValue)
1399 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1404 if (value == value_mate_in(ply + 1))
1405 ss->mateKiller = move;
1409 // Step 18. Check for split
1410 if ( depth >= MinimumSplitDepth
1411 && TM.active_threads() > 1
1413 && TM.available_thread_exists(threadID)
1415 && !TM.thread_should_stop(threadID)
1417 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1418 mateThreat, &moveCount, &mp, threadID, PvNode);
1421 // Step 19. Check for mate and stalemate
1422 // All legal moves have been searched and if there are
1423 // no legal moves, it must be mate or stalemate.
1424 // If one move was excluded return fail low score.
1426 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1428 // Step 20. Update tables
1429 // If the search is not aborted, update the transposition table,
1430 // history counters, and killer moves.
1431 if (AbortSearch || TM.thread_should_stop(threadID))
1434 if (bestValue <= oldAlpha)
1435 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1437 else if (bestValue >= beta)
1439 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1441 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1442 if (!pos.move_is_capture_or_promotion(move))
1444 update_history(pos, move, depth, movesSearched, moveCount);
1445 update_killers(move, ss);
1449 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1451 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1457 // qsearch() is the quiescence search function, which is called by the main
1458 // search function when the remaining depth is zero (or, to be more precise,
1459 // less than OnePly).
1461 template <NodeType PvNode>
1462 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID) {
1464 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1465 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1466 assert(PvNode || alpha == beta - 1);
1468 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1469 assert(threadID >= 0 && threadID < TM.active_threads());
1474 Value staticValue, bestValue, value, futilityBase, futilityValue;
1475 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1476 const TTEntry* tte = NULL;
1478 int ply = pos.ply();
1479 Value oldAlpha = alpha;
1481 TM.incrementNodeCounter(threadID);
1484 // Check for an instant draw or maximum ply reached
1485 if (pos.is_draw() || ply >= PLY_MAX - 1)
1488 // Transposition table lookup. At PV nodes, we don't use the TT for
1489 // pruning, but only for move ordering.
1490 tte = TT.retrieve(pos.get_key());
1491 ttMove = (tte ? tte->move() : MOVE_NONE);
1493 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1495 ss->currentMove = ttMove; // Can be MOVE_NONE
1496 return value_from_tt(tte->value(), ply);
1499 isCheck = pos.is_check();
1501 // Evaluate the position statically
1503 staticValue = -VALUE_INFINITE;
1504 else if (tte && tte->static_value() != VALUE_NONE)
1506 staticValue = tte->static_value();
1507 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1510 staticValue = evaluate(pos, ei, threadID);
1514 ss->eval = staticValue;
1515 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1518 // Initialize "stand pat score", and return it immediately if it is
1520 bestValue = staticValue;
1522 if (bestValue >= beta)
1524 // Store the score to avoid a future costly evaluation() call
1525 if (!isCheck && !tte)
1526 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()]);
1531 if (bestValue > alpha)
1534 // If we are near beta then try to get a cutoff pushing checks a bit further
1535 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1537 // Initialize a MovePicker object for the current position, and prepare
1538 // to search the moves. Because the depth is <= 0 here, only captures,
1539 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1540 // and we are near beta) will be generated.
1541 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1543 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1544 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1546 // Loop through the moves until no moves remain or a beta cutoff occurs
1547 while ( alpha < beta
1548 && (move = mp.get_next_move()) != MOVE_NONE)
1550 assert(move_is_ok(move));
1552 moveIsCheck = pos.move_is_check(move, ci);
1554 // Update current move
1556 ss->currentMove = move;
1564 && !move_is_promotion(move)
1565 && !pos.move_is_passed_pawn_push(move))
1567 futilityValue = futilityBase
1568 + pos.endgame_value_of_piece_on(move_to(move))
1569 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1571 if (futilityValue < alpha)
1573 if (futilityValue > bestValue)
1574 bestValue = futilityValue;
1579 // Detect blocking evasions that are candidate to be pruned
1580 evasionPrunable = isCheck
1581 && bestValue > value_mated_in(PLY_MAX)
1582 && !pos.move_is_capture(move)
1583 && pos.type_of_piece_on(move_from(move)) != KING
1584 && !pos.can_castle(pos.side_to_move());
1586 // Don't search moves with negative SEE values
1588 && (!isCheck || evasionPrunable)
1590 && !move_is_promotion(move)
1591 && pos.see_sign(move) < 0)
1594 // Make and search the move
1595 pos.do_move(move, st, ci, moveIsCheck);
1596 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, threadID);
1597 pos.undo_move(move);
1599 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1602 if (value > bestValue)
1613 // All legal moves have been searched. A special case: If we're in check
1614 // and no legal moves were found, it is checkmate.
1615 if (!moveCount && isCheck) // Mate!
1616 return value_mated_in(ply);
1618 // Update transposition table
1619 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1620 if (bestValue <= oldAlpha)
1622 // If bestValue isn't changed it means it is still the static evaluation
1623 // of the node, so keep this info to avoid a future evaluation() call.
1624 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1626 else if (bestValue >= beta)
1629 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1631 // Update killers only for good checking moves
1632 if (!pos.move_is_capture_or_promotion(move))
1633 update_killers(move, ss);
1636 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()]);
1638 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1644 // sp_search() is used to search from a split point. This function is called
1645 // by each thread working at the split point. It is similar to the normal
1646 // search() function, but simpler. Because we have already probed the hash
1647 // table, done a null move search, and searched the first move before
1648 // splitting, we don't have to repeat all this work in sp_search(). We
1649 // also don't need to store anything to the hash table here: This is taken
1650 // care of after we return from the split point.
1652 template <NodeType PvNode>
1653 void sp_search(SplitPoint* sp, int threadID) {
1655 assert(threadID >= 0 && threadID < TM.active_threads());
1656 assert(TM.active_threads() > 1);
1660 Depth ext, newDepth;
1662 Value futilityValueScaled; // NonPV specific
1663 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1665 value = -VALUE_INFINITE;
1667 Position pos(*sp->pos);
1669 int ply = pos.ply();
1670 SearchStack* ss = sp->sstack[threadID] + 1;
1671 isCheck = pos.is_check();
1673 // Step 10. Loop through moves
1674 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1675 lock_grab(&(sp->lock));
1677 while ( sp->bestValue < sp->beta
1678 && (move = sp->mp->get_next_move()) != MOVE_NONE
1679 && !TM.thread_should_stop(threadID))
1681 moveCount = ++sp->moveCount;
1682 lock_release(&(sp->lock));
1684 assert(move_is_ok(move));
1686 moveIsCheck = pos.move_is_check(move, ci);
1687 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1689 // Step 11. Decide the new search depth
1690 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1691 newDepth = sp->depth - OnePly + ext;
1693 // Update current move
1694 ss->currentMove = move;
1696 // Step 12. Futility pruning (is omitted in PV nodes)
1698 && !captureOrPromotion
1701 && !move_is_castle(move))
1703 // Move count based pruning
1704 if ( moveCount >= futility_move_count(sp->depth)
1705 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1706 && sp->bestValue > value_mated_in(PLY_MAX))
1708 lock_grab(&(sp->lock));
1712 // Value based pruning
1713 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1714 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1715 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1717 if (futilityValueScaled < sp->beta)
1719 lock_grab(&(sp->lock));
1721 if (futilityValueScaled > sp->bestValue)
1722 sp->bestValue = futilityValueScaled;
1727 // Step 13. Make the move
1728 pos.do_move(move, st, ci, moveIsCheck);
1730 // Step 14. Reduced search
1731 // If the move fails high will be re-searched at full depth.
1732 bool doFullDepthSearch = true;
1734 if ( !captureOrPromotion
1736 && !move_is_castle(move)
1737 && !move_is_killer(move, ss))
1739 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1742 Value localAlpha = sp->alpha;
1743 Depth d = newDepth - ss->reduction;
1744 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1745 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, threadID);
1746 doFullDepthSearch = (value > localAlpha);
1749 // The move failed high, but if reduction is very big we could
1750 // face a false positive, retry with a less aggressive reduction,
1751 // if the move fails high again then go with full depth search.
1752 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1754 assert(newDepth - OnePly >= OnePly);
1756 ss->reduction = OnePly;
1757 Value localAlpha = sp->alpha;
1758 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, threadID);
1759 doFullDepthSearch = (value > localAlpha);
1761 ss->reduction = Depth(0); // Restore original reduction
1764 // Step 15. Full depth search
1765 if (doFullDepthSearch)
1767 Value localAlpha = sp->alpha;
1768 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1769 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, threadID);
1771 // Step extra. pv search (only in PV nodes)
1772 // Search only for possible new PV nodes, if instead value >= beta then
1773 // parent node fails low with value <= alpha and tries another move.
1774 if (PvNode && value > localAlpha && value < sp->beta)
1775 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), threadID)
1776 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, threadID);
1779 // Step 16. Undo move
1780 pos.undo_move(move);
1782 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1784 // Step 17. Check for new best move
1785 lock_grab(&(sp->lock));
1787 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1789 sp->bestValue = value;
1791 if (sp->bestValue > sp->alpha)
1793 if (!PvNode || value >= sp->beta)
1794 sp->stopRequest = true;
1796 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1799 sp_update_pv(sp->parentSstack, ss, ply);
1804 /* Here we have the lock still grabbed */
1806 sp->slaves[threadID] = 0;
1808 lock_release(&(sp->lock));
1811 // update_pv() is called whenever a search returns a value > alpha.
1812 // It updates the PV in the SearchStack object corresponding to the
1815 void update_pv(SearchStack* ss, int ply) {
1817 assert(ply >= 0 && ply < PLY_MAX);
1821 ss->pv[ply] = ss->currentMove;
1823 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1824 ss->pv[p] = (ss+1)->pv[p];
1826 ss->pv[p] = MOVE_NONE;
1830 // sp_update_pv() is a variant of update_pv for use at split points. The
1831 // difference between the two functions is that sp_update_pv also updates
1832 // the PV at the parent node.
1834 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1836 assert(ply >= 0 && ply < PLY_MAX);
1840 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1842 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1843 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1845 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1849 // connected_moves() tests whether two moves are 'connected' in the sense
1850 // that the first move somehow made the second move possible (for instance
1851 // if the moving piece is the same in both moves). The first move is assumed
1852 // to be the move that was made to reach the current position, while the
1853 // second move is assumed to be a move from the current position.
1855 bool connected_moves(const Position& pos, Move m1, Move m2) {
1857 Square f1, t1, f2, t2;
1860 assert(move_is_ok(m1));
1861 assert(move_is_ok(m2));
1863 if (m2 == MOVE_NONE)
1866 // Case 1: The moving piece is the same in both moves
1872 // Case 2: The destination square for m2 was vacated by m1
1878 // Case 3: Moving through the vacated square
1879 if ( piece_is_slider(pos.piece_on(f2))
1880 && bit_is_set(squares_between(f2, t2), f1))
1883 // Case 4: The destination square for m2 is defended by the moving piece in m1
1884 p = pos.piece_on(t1);
1885 if (bit_is_set(pos.attacks_from(p, t1), t2))
1888 // Case 5: Discovered check, checking piece is the piece moved in m1
1889 if ( piece_is_slider(p)
1890 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1891 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1893 // discovered_check_candidates() works also if the Position's side to
1894 // move is the opposite of the checking piece.
1895 Color them = opposite_color(pos.side_to_move());
1896 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1898 if (bit_is_set(dcCandidates, f2))
1905 // value_is_mate() checks if the given value is a mate one
1906 // eventually compensated for the ply.
1908 bool value_is_mate(Value value) {
1910 assert(abs(value) <= VALUE_INFINITE);
1912 return value <= value_mated_in(PLY_MAX)
1913 || value >= value_mate_in(PLY_MAX);
1917 // move_is_killer() checks if the given move is among the
1918 // killer moves of that ply.
1920 bool move_is_killer(Move m, SearchStack* ss) {
1922 const Move* k = ss->killers;
1923 for (int i = 0; i < KILLER_MAX; i++, k++)
1931 // extension() decides whether a move should be searched with normal depth,
1932 // or with extended depth. Certain classes of moves (checking moves, in
1933 // particular) are searched with bigger depth than ordinary moves and in
1934 // any case are marked as 'dangerous'. Note that also if a move is not
1935 // extended, as example because the corresponding UCI option is set to zero,
1936 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1937 template <NodeType PvNode>
1938 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1939 bool singleEvasion, bool mateThreat, bool* dangerous) {
1941 assert(m != MOVE_NONE);
1943 Depth result = Depth(0);
1944 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1949 result += CheckExtension[PvNode];
1952 result += SingleEvasionExtension[PvNode];
1955 result += MateThreatExtension[PvNode];
1958 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1960 Color c = pos.side_to_move();
1961 if (relative_rank(c, move_to(m)) == RANK_7)
1963 result += PawnPushTo7thExtension[PvNode];
1966 if (pos.pawn_is_passed(c, move_to(m)))
1968 result += PassedPawnExtension[PvNode];
1973 if ( captureOrPromotion
1974 && pos.type_of_piece_on(move_to(m)) != PAWN
1975 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1976 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1977 && !move_is_promotion(m)
1980 result += PawnEndgameExtension[PvNode];
1985 && captureOrPromotion
1986 && pos.type_of_piece_on(move_to(m)) != PAWN
1987 && pos.see_sign(m) >= 0)
1993 return Min(result, OnePly);
1997 // connected_threat() tests whether it is safe to forward prune a move or if
1998 // is somehow coonected to the threat move returned by null search.
2000 bool connected_threat(const Position& pos, Move m, Move threat) {
2002 assert(move_is_ok(m));
2003 assert(threat && move_is_ok(threat));
2004 assert(!pos.move_is_check(m));
2005 assert(!pos.move_is_capture_or_promotion(m));
2006 assert(!pos.move_is_passed_pawn_push(m));
2008 Square mfrom, mto, tfrom, tto;
2010 mfrom = move_from(m);
2012 tfrom = move_from(threat);
2013 tto = move_to(threat);
2015 // Case 1: Don't prune moves which move the threatened piece
2019 // Case 2: If the threatened piece has value less than or equal to the
2020 // value of the threatening piece, don't prune move which defend it.
2021 if ( pos.move_is_capture(threat)
2022 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2023 || pos.type_of_piece_on(tfrom) == KING)
2024 && pos.move_attacks_square(m, tto))
2027 // Case 3: If the moving piece in the threatened move is a slider, don't
2028 // prune safe moves which block its ray.
2029 if ( piece_is_slider(pos.piece_on(tfrom))
2030 && bit_is_set(squares_between(tfrom, tto), mto)
2031 && pos.see_sign(m) >= 0)
2038 // ok_to_use_TT() returns true if a transposition table score
2039 // can be used at a given point in search.
2041 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2043 Value v = value_from_tt(tte->value(), ply);
2045 return ( tte->depth() >= depth
2046 || v >= Max(value_mate_in(PLY_MAX), beta)
2047 || v < Min(value_mated_in(PLY_MAX), beta))
2049 && ( (is_lower_bound(tte->type()) && v >= beta)
2050 || (is_upper_bound(tte->type()) && v < beta));
2054 // refine_eval() returns the transposition table score if
2055 // possible otherwise falls back on static position evaluation.
2057 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2062 Value v = value_from_tt(tte->value(), ply);
2064 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2065 || (is_upper_bound(tte->type()) && v < defaultEval))
2072 // update_history() registers a good move that produced a beta-cutoff
2073 // in history and marks as failures all the other moves of that ply.
2075 void update_history(const Position& pos, Move move, Depth depth,
2076 Move movesSearched[], int moveCount) {
2080 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2082 for (int i = 0; i < moveCount - 1; i++)
2084 m = movesSearched[i];
2088 if (!pos.move_is_capture_or_promotion(m))
2089 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2094 // update_killers() add a good move that produced a beta-cutoff
2095 // among the killer moves of that ply.
2097 void update_killers(Move m, SearchStack* ss) {
2099 if (m == ss->killers[0])
2102 for (int i = KILLER_MAX - 1; i > 0; i--)
2103 ss->killers[i] = ss->killers[i - 1];
2109 // update_gains() updates the gains table of a non-capture move given
2110 // the static position evaluation before and after the move.
2112 void update_gains(const Position& pos, Move m, Value before, Value after) {
2115 && before != VALUE_NONE
2116 && after != VALUE_NONE
2117 && pos.captured_piece() == NO_PIECE_TYPE
2118 && !move_is_castle(m)
2119 && !move_is_promotion(m))
2120 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2124 // current_search_time() returns the number of milliseconds which have passed
2125 // since the beginning of the current search.
2127 int current_search_time() {
2129 return get_system_time() - SearchStartTime;
2133 // nps() computes the current nodes/second count.
2137 int t = current_search_time();
2138 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2142 // poll() performs two different functions: It polls for user input, and it
2143 // looks at the time consumed so far and decides if it's time to abort the
2148 static int lastInfoTime;
2149 int t = current_search_time();
2154 // We are line oriented, don't read single chars
2155 std::string command;
2157 if (!std::getline(std::cin, command))
2160 if (command == "quit")
2163 PonderSearch = false;
2167 else if (command == "stop")
2170 PonderSearch = false;
2172 else if (command == "ponderhit")
2176 // Print search information
2180 else if (lastInfoTime > t)
2181 // HACK: Must be a new search where we searched less than
2182 // NodesBetweenPolls nodes during the first second of search.
2185 else if (t - lastInfoTime >= 1000)
2192 if (dbg_show_hit_rate)
2193 dbg_print_hit_rate();
2195 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2196 << " time " << t << " hashfull " << TT.full() << endl;
2199 // Should we stop the search?
2203 bool stillAtFirstMove = FirstRootMove
2204 && !AspirationFailLow
2205 && t > MaxSearchTime + ExtraSearchTime;
2207 bool noMoreTime = t > AbsoluteMaxSearchTime
2208 || stillAtFirstMove;
2210 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2211 || (ExactMaxTime && t >= ExactMaxTime)
2212 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2217 // ponderhit() is called when the program is pondering (i.e. thinking while
2218 // it's the opponent's turn to move) in order to let the engine know that
2219 // it correctly predicted the opponent's move.
2223 int t = current_search_time();
2224 PonderSearch = false;
2226 bool stillAtFirstMove = FirstRootMove
2227 && !AspirationFailLow
2228 && t > MaxSearchTime + ExtraSearchTime;
2230 bool noMoreTime = t > AbsoluteMaxSearchTime
2231 || stillAtFirstMove;
2233 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2238 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2240 void init_ss_array(SearchStack* ss) {
2242 for (int i = 0; i < 3; i++, ss++)
2246 ss->excludedMove = MOVE_NONE;
2247 ss->skipNullMove = false;
2252 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2253 // while the program is pondering. The point is to work around a wrinkle in
2254 // the UCI protocol: When pondering, the engine is not allowed to give a
2255 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2256 // We simply wait here until one of these commands is sent, and return,
2257 // after which the bestmove and pondermove will be printed (in id_loop()).
2259 void wait_for_stop_or_ponderhit() {
2261 std::string command;
2265 if (!std::getline(std::cin, command))
2268 if (command == "quit")
2273 else if (command == "ponderhit" || command == "stop")
2279 // print_pv_info() prints to standard output and eventually to log file information on
2280 // the current PV line. It is called at each iteration or after a new pv is found.
2282 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2284 cout << "info depth " << Iteration
2285 << " score " << value_to_string(value)
2286 << ((value >= beta) ? " lowerbound" :
2287 ((value <= alpha)? " upperbound" : ""))
2288 << " time " << current_search_time()
2289 << " nodes " << TM.nodes_searched()
2293 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2294 cout << ss->pv[j] << " ";
2300 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2301 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2303 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2304 TM.nodes_searched(), value, type, ss->pv) << endl;
2309 // init_thread() is the function which is called when a new thread is
2310 // launched. It simply calls the idle_loop() function with the supplied
2311 // threadID. There are two versions of this function; one for POSIX
2312 // threads and one for Windows threads.
2314 #if !defined(_MSC_VER)
2316 void* init_thread(void *threadID) {
2318 TM.idle_loop(*(int*)threadID, NULL);
2324 DWORD WINAPI init_thread(LPVOID threadID) {
2326 TM.idle_loop(*(int*)threadID, NULL);
2333 /// The ThreadsManager class
2335 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2336 // get_beta_counters() are getters/setters for the per thread
2337 // counters used to sort the moves at root.
2339 void ThreadsManager::resetNodeCounters() {
2341 for (int i = 0; i < MAX_THREADS; i++)
2342 threads[i].nodes = 0ULL;
2345 void ThreadsManager::resetBetaCounters() {
2347 for (int i = 0; i < MAX_THREADS; i++)
2348 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2351 int64_t ThreadsManager::nodes_searched() const {
2353 int64_t result = 0ULL;
2354 for (int i = 0; i < ActiveThreads; i++)
2355 result += threads[i].nodes;
2360 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2363 for (int i = 0; i < MAX_THREADS; i++)
2365 our += threads[i].betaCutOffs[us];
2366 their += threads[i].betaCutOffs[opposite_color(us)];
2371 // idle_loop() is where the threads are parked when they have no work to do.
2372 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2373 // object for which the current thread is the master.
2375 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2377 assert(threadID >= 0 && threadID < MAX_THREADS);
2381 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2382 // master should exit as last one.
2383 if (AllThreadsShouldExit)
2386 threads[threadID].state = THREAD_TERMINATED;
2390 // If we are not thinking, wait for a condition to be signaled
2391 // instead of wasting CPU time polling for work.
2392 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2395 assert(threadID != 0);
2396 threads[threadID].state = THREAD_SLEEPING;
2398 #if !defined(_MSC_VER)
2399 lock_grab(&WaitLock);
2400 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2401 pthread_cond_wait(&WaitCond, &WaitLock);
2402 lock_release(&WaitLock);
2404 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2408 // If thread has just woken up, mark it as available
2409 if (threads[threadID].state == THREAD_SLEEPING)
2410 threads[threadID].state = THREAD_AVAILABLE;
2412 // If this thread has been assigned work, launch a search
2413 if (threads[threadID].state == THREAD_WORKISWAITING)
2415 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2417 threads[threadID].state = THREAD_SEARCHING;
2419 if (threads[threadID].splitPoint->pvNode)
2420 sp_search<PV>(threads[threadID].splitPoint, threadID);
2422 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2424 assert(threads[threadID].state == THREAD_SEARCHING);
2426 threads[threadID].state = THREAD_AVAILABLE;
2429 // If this thread is the master of a split point and all slaves have
2430 // finished their work at this split point, return from the idle loop.
2432 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2434 if (i == ActiveThreads)
2436 // Because sp->slaves[] is reset under lock protection,
2437 // be sure sp->lock has been released before to return.
2438 lock_grab(&(sp->lock));
2439 lock_release(&(sp->lock));
2441 assert(threads[threadID].state == THREAD_AVAILABLE);
2443 threads[threadID].state = THREAD_SEARCHING;
2450 // init_threads() is called during startup. It launches all helper threads,
2451 // and initializes the split point stack and the global locks and condition
2454 void ThreadsManager::init_threads() {
2459 #if !defined(_MSC_VER)
2460 pthread_t pthread[1];
2463 // Initialize global locks
2464 lock_init(&MPLock, NULL);
2465 lock_init(&WaitLock, NULL);
2467 #if !defined(_MSC_VER)
2468 pthread_cond_init(&WaitCond, NULL);
2470 for (i = 0; i < MAX_THREADS; i++)
2471 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2474 // Initialize SplitPointStack locks
2475 for (i = 0; i < MAX_THREADS; i++)
2476 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2477 lock_init(&(SplitPointStack[i][j].lock), NULL);
2479 // Will be set just before program exits to properly end the threads
2480 AllThreadsShouldExit = false;
2482 // Threads will be put to sleep as soon as created
2483 AllThreadsShouldSleep = true;
2485 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2487 threads[0].state = THREAD_SEARCHING;
2488 for (i = 1; i < MAX_THREADS; i++)
2489 threads[i].state = THREAD_AVAILABLE;
2491 // Launch the helper threads
2492 for (i = 1; i < MAX_THREADS; i++)
2495 #if !defined(_MSC_VER)
2496 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2498 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2503 cout << "Failed to create thread number " << i << endl;
2504 Application::exit_with_failure();
2507 // Wait until the thread has finished launching and is gone to sleep
2508 while (threads[i].state != THREAD_SLEEPING) {}
2513 // exit_threads() is called when the program exits. It makes all the
2514 // helper threads exit cleanly.
2516 void ThreadsManager::exit_threads() {
2518 ActiveThreads = MAX_THREADS; // HACK
2519 AllThreadsShouldSleep = true; // HACK
2520 wake_sleeping_threads();
2522 // This makes the threads to exit idle_loop()
2523 AllThreadsShouldExit = true;
2525 // Wait for thread termination
2526 for (int i = 1; i < MAX_THREADS; i++)
2527 while (threads[i].state != THREAD_TERMINATED) {}
2529 // Now we can safely destroy the locks
2530 for (int i = 0; i < MAX_THREADS; i++)
2531 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2532 lock_destroy(&(SplitPointStack[i][j].lock));
2534 lock_destroy(&WaitLock);
2535 lock_destroy(&MPLock);
2539 // thread_should_stop() checks whether the thread should stop its search.
2540 // This can happen if a beta cutoff has occurred in the thread's currently
2541 // active split point, or in some ancestor of the current split point.
2543 bool ThreadsManager::thread_should_stop(int threadID) const {
2545 assert(threadID >= 0 && threadID < ActiveThreads);
2549 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2554 // thread_is_available() checks whether the thread with threadID "slave" is
2555 // available to help the thread with threadID "master" at a split point. An
2556 // obvious requirement is that "slave" must be idle. With more than two
2557 // threads, this is not by itself sufficient: If "slave" is the master of
2558 // some active split point, it is only available as a slave to the other
2559 // threads which are busy searching the split point at the top of "slave"'s
2560 // split point stack (the "helpful master concept" in YBWC terminology).
2562 bool ThreadsManager::thread_is_available(int slave, int master) const {
2564 assert(slave >= 0 && slave < ActiveThreads);
2565 assert(master >= 0 && master < ActiveThreads);
2566 assert(ActiveThreads > 1);
2568 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2571 // Make a local copy to be sure doesn't change under our feet
2572 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2574 if (localActiveSplitPoints == 0)
2575 // No active split points means that the thread is available as
2576 // a slave for any other thread.
2579 if (ActiveThreads == 2)
2582 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2583 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2584 // could have been set to 0 by another thread leading to an out of bound access.
2585 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2592 // available_thread_exists() tries to find an idle thread which is available as
2593 // a slave for the thread with threadID "master".
2595 bool ThreadsManager::available_thread_exists(int master) const {
2597 assert(master >= 0 && master < ActiveThreads);
2598 assert(ActiveThreads > 1);
2600 for (int i = 0; i < ActiveThreads; i++)
2601 if (thread_is_available(i, master))
2608 // split() does the actual work of distributing the work at a node between
2609 // several available threads. If it does not succeed in splitting the
2610 // node (because no idle threads are available, or because we have no unused
2611 // split point objects), the function immediately returns. If splitting is
2612 // possible, a SplitPoint object is initialized with all the data that must be
2613 // copied to the helper threads and we tell our helper threads that they have
2614 // been assigned work. This will cause them to instantly leave their idle loops
2615 // and call sp_search(). When all threads have returned from sp_search() then
2618 template <bool Fake>
2619 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2620 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2621 MovePicker* mp, int master, bool pvNode) {
2623 assert(*bestValue >= -VALUE_INFINITE);
2624 assert(*bestValue <= *alpha);
2625 assert(*alpha < beta);
2626 assert(beta <= VALUE_INFINITE);
2627 assert(depth > Depth(0));
2628 assert(master >= 0 && master < ActiveThreads);
2629 assert(ActiveThreads > 1);
2633 // If no other thread is available to help us, or if we have too many
2634 // active split points, don't split.
2635 if ( !available_thread_exists(master)
2636 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2638 lock_release(&MPLock);
2642 // Pick the next available split point object from the split point stack
2643 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2645 // Initialize the split point object
2646 splitPoint->parent = threads[master].splitPoint;
2647 splitPoint->stopRequest = false;
2648 splitPoint->depth = depth;
2649 splitPoint->mateThreat = mateThreat;
2650 splitPoint->alpha = *alpha;
2651 splitPoint->beta = beta;
2652 splitPoint->pvNode = pvNode;
2653 splitPoint->bestValue = *bestValue;
2654 splitPoint->mp = mp;
2655 splitPoint->moveCount = *moveCount;
2656 splitPoint->pos = &p;
2657 splitPoint->parentSstack = ss;
2658 for (int i = 0; i < ActiveThreads; i++)
2659 splitPoint->slaves[i] = 0;
2661 threads[master].splitPoint = splitPoint;
2662 threads[master].activeSplitPoints++;
2664 // If we are here it means we are not available
2665 assert(threads[master].state != THREAD_AVAILABLE);
2667 int workersCnt = 1; // At least the master is included
2669 // Allocate available threads setting state to THREAD_BOOKED
2670 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2671 if (thread_is_available(i, master))
2673 threads[i].state = THREAD_BOOKED;
2674 threads[i].splitPoint = splitPoint;
2675 splitPoint->slaves[i] = 1;
2679 assert(Fake || workersCnt > 1);
2681 // We can release the lock because slave threads are already booked and master is not available
2682 lock_release(&MPLock);
2684 // Tell the threads that they have work to do. This will make them leave
2685 // their idle loop. But before copy search stack tail for each thread.
2686 for (int i = 0; i < ActiveThreads; i++)
2687 if (i == master || splitPoint->slaves[i])
2689 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2691 assert(i == master || threads[i].state == THREAD_BOOKED);
2693 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2696 // Everything is set up. The master thread enters the idle loop, from
2697 // which it will instantly launch a search, because its state is
2698 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2699 // idle loop, which means that the main thread will return from the idle
2700 // loop when all threads have finished their work at this split point.
2701 idle_loop(master, splitPoint);
2703 // We have returned from the idle loop, which means that all threads are
2704 // finished. Update alpha and bestValue, and return.
2707 *alpha = splitPoint->alpha;
2708 *bestValue = splitPoint->bestValue;
2709 threads[master].activeSplitPoints--;
2710 threads[master].splitPoint = splitPoint->parent;
2712 lock_release(&MPLock);
2716 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2717 // to start a new search from the root.
2719 void ThreadsManager::wake_sleeping_threads() {
2721 assert(AllThreadsShouldSleep);
2722 assert(ActiveThreads > 0);
2724 AllThreadsShouldSleep = false;
2726 if (ActiveThreads == 1)
2729 #if !defined(_MSC_VER)
2730 pthread_mutex_lock(&WaitLock);
2731 pthread_cond_broadcast(&WaitCond);
2732 pthread_mutex_unlock(&WaitLock);
2734 for (int i = 1; i < MAX_THREADS; i++)
2735 SetEvent(SitIdleEvent[i]);
2741 // put_threads_to_sleep() makes all the threads go to sleep just before
2742 // to leave think(), at the end of the search. Threads should have already
2743 // finished the job and should be idle.
2745 void ThreadsManager::put_threads_to_sleep() {
2747 assert(!AllThreadsShouldSleep);
2749 // This makes the threads to go to sleep
2750 AllThreadsShouldSleep = true;
2753 /// The RootMoveList class
2755 // RootMoveList c'tor
2757 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2759 SearchStack ss[PLY_MAX_PLUS_2];
2760 MoveStack mlist[MaxRootMoves];
2762 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2764 // Generate all legal moves
2765 MoveStack* last = generate_moves(pos, mlist);
2767 // Add each move to the moves[] array
2768 for (MoveStack* cur = mlist; cur != last; cur++)
2770 bool includeMove = includeAllMoves;
2772 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2773 includeMove = (searchMoves[k] == cur->move);
2778 // Find a quick score for the move
2780 pos.do_move(cur->move, st);
2781 moves[count].move = cur->move;
2782 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2783 moves[count].pv[0] = cur->move;
2784 moves[count].pv[1] = MOVE_NONE;
2785 pos.undo_move(cur->move);
2792 // RootMoveList simple methods definitions
2794 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2796 moves[moveNum].nodes = nodes;
2797 moves[moveNum].cumulativeNodes += nodes;
2800 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2802 moves[moveNum].ourBeta = our;
2803 moves[moveNum].theirBeta = their;
2806 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2810 for (j = 0; pv[j] != MOVE_NONE; j++)
2811 moves[moveNum].pv[j] = pv[j];
2813 moves[moveNum].pv[j] = MOVE_NONE;
2817 // RootMoveList::sort() sorts the root move list at the beginning of a new
2820 void RootMoveList::sort() {
2822 sort_multipv(count - 1); // Sort all items
2826 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2827 // list by their scores and depths. It is used to order the different PVs
2828 // correctly in MultiPV mode.
2830 void RootMoveList::sort_multipv(int n) {
2834 for (i = 1; i <= n; i++)
2836 RootMove rm = moves[i];
2837 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2838 moves[j] = moves[j - 1];