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, bool allowNullmove, 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, false, 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, true, 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, true, 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, false, 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,
1035 bool allowNullmove, int threadID) {
1037 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1038 assert(beta > alpha && beta <= VALUE_INFINITE);
1039 assert(PvNode || alpha == beta - 1);
1040 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1041 assert(threadID >= 0 && threadID < TM.active_threads());
1043 Move movesSearched[256];
1048 Move ttMove, move, excludedMove;
1049 Depth ext, newDepth;
1050 Value bestValue, value, oldAlpha;
1051 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1052 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1053 bool mateThreat = false;
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 + 1)->excludedMove = MOVE_NONE;
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.
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.
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 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1182 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, false, threadID);
1183 pos.undo_null_move();
1185 if (nullValue >= beta)
1187 // Do not return unproven mate scores
1188 if (nullValue >= value_mate_in(PLY_MAX))
1191 // Do zugzwang verification search at high depths
1192 if ( depth < 6 * OnePly
1193 || search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID) >= beta)
1198 // The null move failed low, which means that we may be faced with
1199 // some kind of threat. If the previous move was reduced, check if
1200 // the move that refuted the null move was somehow connected to the
1201 // move which was reduced. If a connection is found, return a fail
1202 // low score (which will cause the reduced move to fail high in the
1203 // parent node, which will trigger a re-search with full depth).
1204 if (nullValue == value_mated_in(ply + 2))
1207 ss->threatMove = (ss+1)->currentMove;
1208 if ( depth < ThreatDepth
1209 && (ss-1)->reduction
1210 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1215 // Step 9. Internal iterative deepening
1216 if ( depth >= IIDDepth[PvNode]
1217 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1218 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1220 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1221 search<PvNode>(pos, ss, alpha, beta, d, false, threadID);
1222 ttMove = ss->pv[ply];
1223 tte = TT.retrieve(posKey);
1226 // Expensive mate threat detection (only for PV nodes)
1228 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1230 // Initialize a MovePicker object for the current position
1231 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1233 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1234 && tte && tte->move()
1235 && !excludedMove // Do not allow recursive singular extension search
1236 && is_lower_bound(tte->type())
1237 && tte->depth() >= depth - 3 * OnePly;
1239 // Step 10. Loop through moves
1240 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1241 while ( bestValue < beta
1242 && (move = mp.get_next_move()) != MOVE_NONE
1243 && !TM.thread_should_stop(threadID))
1245 assert(move_is_ok(move));
1247 if (move == excludedMove)
1250 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1251 moveIsCheck = pos.move_is_check(move, ci);
1252 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1254 // Step 11. Decide the new search depth
1255 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1257 // Singular extension search. We extend the TT move if its value is much better than
1258 // its siblings. To verify this we do a reduced search on all the other moves but the
1259 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1260 if ( singularExtensionNode
1261 && move == tte->move()
1264 Value ttValue = value_from_tt(tte->value(), ply);
1266 if (abs(ttValue) < VALUE_KNOWN_WIN)
1268 Value b = ttValue - SingularExtensionMargin;
1269 ss->excludedMove = move;
1270 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, false, threadID);
1271 ss->excludedMove = MOVE_NONE;
1273 if (v < ttValue - SingularExtensionMargin)
1278 newDepth = depth - OnePly + ext;
1280 // Update current move (this must be done after singular extension search)
1281 movesSearched[moveCount++] = ss->currentMove = move;
1283 // Step 12. Futility pruning (is omitted in PV nodes)
1285 && !captureOrPromotion
1289 && !move_is_castle(move))
1291 // Move count based pruning
1292 if ( moveCount >= futility_move_count(depth)
1293 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1294 && bestValue > value_mated_in(PLY_MAX))
1297 // Value based pruning
1298 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1299 // but fixing this made program slightly weaker.
1300 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1301 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1302 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1304 if (futilityValueScaled < beta)
1306 if (futilityValueScaled > bestValue)
1307 bestValue = futilityValueScaled;
1312 // Step 13. Make the move
1313 pos.do_move(move, st, ci, moveIsCheck);
1315 // Step extra. pv search (only in PV nodes)
1316 // The first move in list is the expected PV
1317 if (PvNode && moveCount == 1)
1318 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1319 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1322 // Step 14. Reduced depth search
1323 // If the move fails high will be re-searched at full depth.
1324 bool doFullDepthSearch = true;
1326 if ( depth >= 3 * OnePly
1327 && !captureOrPromotion
1329 && !move_is_castle(move)
1330 && !move_is_killer(move, ss))
1332 ss->reduction = reduction<PvNode>(depth, moveCount);
1335 Depth d = newDepth - ss->reduction;
1336 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1337 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, threadID);
1339 doFullDepthSearch = (value > alpha);
1342 // The move failed high, but if reduction is very big we could
1343 // face a false positive, retry with a less aggressive reduction,
1344 // if the move fails high again then go with full depth search.
1345 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1347 assert(newDepth - OnePly >= OnePly);
1349 ss->reduction = OnePly;
1350 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, threadID);
1351 doFullDepthSearch = (value > alpha);
1353 ss->reduction = Depth(0); // Restore original reduction
1356 // Step 15. Full depth search
1357 if (doFullDepthSearch)
1359 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1360 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, threadID);
1362 // Step extra. pv search (only in PV nodes)
1363 // Search only for possible new PV nodes, if instead value >= beta then
1364 // parent node fails low with value <= alpha and tries another move.
1365 if (PvNode && value > alpha && value < beta)
1366 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1367 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1371 // Step 16. Undo move
1372 pos.undo_move(move);
1374 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1376 // Step 17. Check for new best move
1377 if (value > bestValue)
1382 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1387 if (value == value_mate_in(ply + 1))
1388 ss->mateKiller = move;
1392 // Step 18. Check for split
1393 if ( depth >= MinimumSplitDepth
1394 && TM.active_threads() > 1
1396 && TM.available_thread_exists(threadID)
1398 && !TM.thread_should_stop(threadID)
1400 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1401 mateThreat, &moveCount, &mp, threadID, PvNode);
1404 // Step 19. Check for mate and stalemate
1405 // All legal moves have been searched and if there are
1406 // no legal moves, it must be mate or stalemate.
1407 // If one move was excluded return fail low score.
1409 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1411 // Step 20. Update tables
1412 // If the search is not aborted, update the transposition table,
1413 // history counters, and killer moves.
1414 if (AbortSearch || TM.thread_should_stop(threadID))
1417 if (bestValue <= oldAlpha)
1418 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1420 else if (bestValue >= beta)
1422 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1424 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1425 if (!pos.move_is_capture_or_promotion(move))
1427 update_history(pos, move, depth, movesSearched, moveCount);
1428 update_killers(move, ss);
1432 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1434 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1440 // qsearch() is the quiescence search function, which is called by the main
1441 // search function when the remaining depth is zero (or, to be more precise,
1442 // less than OnePly).
1444 template <NodeType PvNode>
1445 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID) {
1447 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1448 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1449 assert(PvNode || alpha == beta - 1);
1451 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1452 assert(threadID >= 0 && threadID < TM.active_threads());
1457 Value staticValue, bestValue, value, futilityBase, futilityValue;
1458 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1459 const TTEntry* tte = NULL;
1461 int ply = pos.ply();
1462 Value oldAlpha = alpha;
1464 TM.incrementNodeCounter(threadID);
1467 // Check for an instant draw or maximum ply reached
1468 if (pos.is_draw() || ply >= PLY_MAX - 1)
1471 // Transposition table lookup. At PV nodes, we don't use the TT for
1472 // pruning, but only for move ordering.
1473 tte = TT.retrieve(pos.get_key());
1474 ttMove = (tte ? tte->move() : MOVE_NONE);
1476 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1478 ss->currentMove = ttMove; // Can be MOVE_NONE
1479 return value_from_tt(tte->value(), ply);
1482 isCheck = pos.is_check();
1484 // Evaluate the position statically
1486 staticValue = -VALUE_INFINITE;
1487 else if (tte && tte->static_value() != VALUE_NONE)
1489 staticValue = tte->static_value();
1490 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1493 staticValue = evaluate(pos, ei, threadID);
1497 ss->eval = staticValue;
1498 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1501 // Initialize "stand pat score", and return it immediately if it is
1503 bestValue = staticValue;
1505 if (bestValue >= beta)
1507 // Store the score to avoid a future costly evaluation() call
1508 if (!isCheck && !tte)
1509 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()]);
1514 if (bestValue > alpha)
1517 // If we are near beta then try to get a cutoff pushing checks a bit further
1518 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1520 // Initialize a MovePicker object for the current position, and prepare
1521 // to search the moves. Because the depth is <= 0 here, only captures,
1522 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1523 // and we are near beta) will be generated.
1524 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1526 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1527 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1529 // Loop through the moves until no moves remain or a beta cutoff occurs
1530 while ( alpha < beta
1531 && (move = mp.get_next_move()) != MOVE_NONE)
1533 assert(move_is_ok(move));
1535 moveIsCheck = pos.move_is_check(move, ci);
1537 // Update current move
1539 ss->currentMove = move;
1547 && !move_is_promotion(move)
1548 && !pos.move_is_passed_pawn_push(move))
1550 futilityValue = futilityBase
1551 + pos.endgame_value_of_piece_on(move_to(move))
1552 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1554 if (futilityValue < alpha)
1556 if (futilityValue > bestValue)
1557 bestValue = futilityValue;
1562 // Detect blocking evasions that are candidate to be pruned
1563 evasionPrunable = isCheck
1564 && bestValue > value_mated_in(PLY_MAX)
1565 && !pos.move_is_capture(move)
1566 && pos.type_of_piece_on(move_from(move)) != KING
1567 && !pos.can_castle(pos.side_to_move());
1569 // Don't search moves with negative SEE values
1571 && (!isCheck || evasionPrunable)
1573 && !move_is_promotion(move)
1574 && pos.see_sign(move) < 0)
1577 // Make and search the move
1578 pos.do_move(move, st, ci, moveIsCheck);
1579 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, threadID);
1580 pos.undo_move(move);
1582 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1585 if (value > bestValue)
1596 // All legal moves have been searched. A special case: If we're in check
1597 // and no legal moves were found, it is checkmate.
1598 if (!moveCount && isCheck) // Mate!
1599 return value_mated_in(ply);
1601 // Update transposition table
1602 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1603 if (bestValue <= oldAlpha)
1605 // If bestValue isn't changed it means it is still the static evaluation
1606 // of the node, so keep this info to avoid a future evaluation() call.
1607 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1609 else if (bestValue >= beta)
1612 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1614 // Update killers only for good checking moves
1615 if (!pos.move_is_capture_or_promotion(move))
1616 update_killers(move, ss);
1619 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()]);
1621 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1627 // sp_search() is used to search from a split point. This function is called
1628 // by each thread working at the split point. It is similar to the normal
1629 // search() function, but simpler. Because we have already probed the hash
1630 // table, done a null move search, and searched the first move before
1631 // splitting, we don't have to repeat all this work in sp_search(). We
1632 // also don't need to store anything to the hash table here: This is taken
1633 // care of after we return from the split point.
1635 template <NodeType PvNode>
1636 void sp_search(SplitPoint* sp, int threadID) {
1638 assert(threadID >= 0 && threadID < TM.active_threads());
1639 assert(TM.active_threads() > 1);
1643 Depth ext, newDepth;
1645 Value futilityValueScaled; // NonPV specific
1646 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1648 value = -VALUE_INFINITE;
1650 Position pos(*sp->pos);
1652 int ply = pos.ply();
1653 SearchStack* ss = sp->sstack[threadID] + 1;
1654 isCheck = pos.is_check();
1656 // Step 10. Loop through moves
1657 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1658 lock_grab(&(sp->lock));
1660 while ( sp->bestValue < sp->beta
1661 && (move = sp->mp->get_next_move()) != MOVE_NONE
1662 && !TM.thread_should_stop(threadID))
1664 moveCount = ++sp->moveCount;
1665 lock_release(&(sp->lock));
1667 assert(move_is_ok(move));
1669 moveIsCheck = pos.move_is_check(move, ci);
1670 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1672 // Step 11. Decide the new search depth
1673 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1674 newDepth = sp->depth - OnePly + ext;
1676 // Update current move
1677 ss->currentMove = move;
1679 // Step 12. Futility pruning (is omitted in PV nodes)
1681 && !captureOrPromotion
1684 && !move_is_castle(move))
1686 // Move count based pruning
1687 if ( moveCount >= futility_move_count(sp->depth)
1688 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1689 && sp->bestValue > value_mated_in(PLY_MAX))
1691 lock_grab(&(sp->lock));
1695 // Value based pruning
1696 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1697 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1698 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1700 if (futilityValueScaled < sp->beta)
1702 lock_grab(&(sp->lock));
1704 if (futilityValueScaled > sp->bestValue)
1705 sp->bestValue = futilityValueScaled;
1710 // Step 13. Make the move
1711 pos.do_move(move, st, ci, moveIsCheck);
1713 // Step 14. Reduced search
1714 // If the move fails high will be re-searched at full depth.
1715 bool doFullDepthSearch = true;
1717 if ( !captureOrPromotion
1719 && !move_is_castle(move)
1720 && !move_is_killer(move, ss))
1722 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1725 Value localAlpha = sp->alpha;
1726 Depth d = newDepth - ss->reduction;
1727 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1728 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, true, threadID);
1729 doFullDepthSearch = (value > localAlpha);
1732 // The move failed high, but if reduction is very big we could
1733 // face a false positive, retry with a less aggressive reduction,
1734 // if the move fails high again then go with full depth search.
1735 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1737 assert(newDepth - OnePly >= OnePly);
1739 ss->reduction = OnePly;
1740 Value localAlpha = sp->alpha;
1741 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1742 doFullDepthSearch = (value > localAlpha);
1744 ss->reduction = Depth(0); // Restore original reduction
1747 // Step 15. Full depth search
1748 if (doFullDepthSearch)
1750 Value localAlpha = sp->alpha;
1751 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1752 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, true, threadID);
1754 // Step extra. pv search (only in PV nodes)
1755 // Search only for possible new PV nodes, if instead value >= beta then
1756 // parent node fails low with value <= alpha and tries another move.
1757 if (PvNode && value > localAlpha && value < sp->beta)
1758 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), threadID)
1759 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, false, threadID);
1762 // Step 16. Undo move
1763 pos.undo_move(move);
1765 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1767 // Step 17. Check for new best move
1768 lock_grab(&(sp->lock));
1770 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1772 sp->bestValue = value;
1774 if (sp->bestValue > sp->alpha)
1776 if (!PvNode || value >= sp->beta)
1777 sp->stopRequest = true;
1779 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1782 sp_update_pv(sp->parentSstack, ss, ply);
1787 /* Here we have the lock still grabbed */
1789 sp->slaves[threadID] = 0;
1791 lock_release(&(sp->lock));
1794 // update_pv() is called whenever a search returns a value > alpha.
1795 // It updates the PV in the SearchStack object corresponding to the
1798 void update_pv(SearchStack* ss, int ply) {
1800 assert(ply >= 0 && ply < PLY_MAX);
1804 ss->pv[ply] = ss->currentMove;
1806 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1807 ss->pv[p] = (ss+1)->pv[p];
1809 ss->pv[p] = MOVE_NONE;
1813 // sp_update_pv() is a variant of update_pv for use at split points. The
1814 // difference between the two functions is that sp_update_pv also updates
1815 // the PV at the parent node.
1817 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1819 assert(ply >= 0 && ply < PLY_MAX);
1823 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1825 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1826 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1828 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1832 // connected_moves() tests whether two moves are 'connected' in the sense
1833 // that the first move somehow made the second move possible (for instance
1834 // if the moving piece is the same in both moves). The first move is assumed
1835 // to be the move that was made to reach the current position, while the
1836 // second move is assumed to be a move from the current position.
1838 bool connected_moves(const Position& pos, Move m1, Move m2) {
1840 Square f1, t1, f2, t2;
1843 assert(move_is_ok(m1));
1844 assert(move_is_ok(m2));
1846 if (m2 == MOVE_NONE)
1849 // Case 1: The moving piece is the same in both moves
1855 // Case 2: The destination square for m2 was vacated by m1
1861 // Case 3: Moving through the vacated square
1862 if ( piece_is_slider(pos.piece_on(f2))
1863 && bit_is_set(squares_between(f2, t2), f1))
1866 // Case 4: The destination square for m2 is defended by the moving piece in m1
1867 p = pos.piece_on(t1);
1868 if (bit_is_set(pos.attacks_from(p, t1), t2))
1871 // Case 5: Discovered check, checking piece is the piece moved in m1
1872 if ( piece_is_slider(p)
1873 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1874 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1876 // discovered_check_candidates() works also if the Position's side to
1877 // move is the opposite of the checking piece.
1878 Color them = opposite_color(pos.side_to_move());
1879 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1881 if (bit_is_set(dcCandidates, f2))
1888 // value_is_mate() checks if the given value is a mate one
1889 // eventually compensated for the ply.
1891 bool value_is_mate(Value value) {
1893 assert(abs(value) <= VALUE_INFINITE);
1895 return value <= value_mated_in(PLY_MAX)
1896 || value >= value_mate_in(PLY_MAX);
1900 // move_is_killer() checks if the given move is among the
1901 // killer moves of that ply.
1903 bool move_is_killer(Move m, SearchStack* ss) {
1905 const Move* k = ss->killers;
1906 for (int i = 0; i < KILLER_MAX; i++, k++)
1914 // extension() decides whether a move should be searched with normal depth,
1915 // or with extended depth. Certain classes of moves (checking moves, in
1916 // particular) are searched with bigger depth than ordinary moves and in
1917 // any case are marked as 'dangerous'. Note that also if a move is not
1918 // extended, as example because the corresponding UCI option is set to zero,
1919 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1920 template <NodeType PvNode>
1921 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1922 bool singleEvasion, bool mateThreat, bool* dangerous) {
1924 assert(m != MOVE_NONE);
1926 Depth result = Depth(0);
1927 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1932 result += CheckExtension[PvNode];
1935 result += SingleEvasionExtension[PvNode];
1938 result += MateThreatExtension[PvNode];
1941 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1943 Color c = pos.side_to_move();
1944 if (relative_rank(c, move_to(m)) == RANK_7)
1946 result += PawnPushTo7thExtension[PvNode];
1949 if (pos.pawn_is_passed(c, move_to(m)))
1951 result += PassedPawnExtension[PvNode];
1956 if ( captureOrPromotion
1957 && pos.type_of_piece_on(move_to(m)) != PAWN
1958 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1959 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1960 && !move_is_promotion(m)
1963 result += PawnEndgameExtension[PvNode];
1968 && captureOrPromotion
1969 && pos.type_of_piece_on(move_to(m)) != PAWN
1970 && pos.see_sign(m) >= 0)
1976 return Min(result, OnePly);
1980 // connected_threat() tests whether it is safe to forward prune a move or if
1981 // is somehow coonected to the threat move returned by null search.
1983 bool connected_threat(const Position& pos, Move m, Move threat) {
1985 assert(move_is_ok(m));
1986 assert(threat && move_is_ok(threat));
1987 assert(!pos.move_is_check(m));
1988 assert(!pos.move_is_capture_or_promotion(m));
1989 assert(!pos.move_is_passed_pawn_push(m));
1991 Square mfrom, mto, tfrom, tto;
1993 mfrom = move_from(m);
1995 tfrom = move_from(threat);
1996 tto = move_to(threat);
1998 // Case 1: Don't prune moves which move the threatened piece
2002 // Case 2: If the threatened piece has value less than or equal to the
2003 // value of the threatening piece, don't prune move which defend it.
2004 if ( pos.move_is_capture(threat)
2005 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2006 || pos.type_of_piece_on(tfrom) == KING)
2007 && pos.move_attacks_square(m, tto))
2010 // Case 3: If the moving piece in the threatened move is a slider, don't
2011 // prune safe moves which block its ray.
2012 if ( piece_is_slider(pos.piece_on(tfrom))
2013 && bit_is_set(squares_between(tfrom, tto), mto)
2014 && pos.see_sign(m) >= 0)
2021 // ok_to_use_TT() returns true if a transposition table score
2022 // can be used at a given point in search.
2024 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2026 Value v = value_from_tt(tte->value(), ply);
2028 return ( tte->depth() >= depth
2029 || v >= Max(value_mate_in(PLY_MAX), beta)
2030 || v < Min(value_mated_in(PLY_MAX), beta))
2032 && ( (is_lower_bound(tte->type()) && v >= beta)
2033 || (is_upper_bound(tte->type()) && v < beta));
2037 // refine_eval() returns the transposition table score if
2038 // possible otherwise falls back on static position evaluation.
2040 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2045 Value v = value_from_tt(tte->value(), ply);
2047 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2048 || (is_upper_bound(tte->type()) && v < defaultEval))
2055 // update_history() registers a good move that produced a beta-cutoff
2056 // in history and marks as failures all the other moves of that ply.
2058 void update_history(const Position& pos, Move move, Depth depth,
2059 Move movesSearched[], int moveCount) {
2063 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2065 for (int i = 0; i < moveCount - 1; i++)
2067 m = movesSearched[i];
2071 if (!pos.move_is_capture_or_promotion(m))
2072 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2077 // update_killers() add a good move that produced a beta-cutoff
2078 // among the killer moves of that ply.
2080 void update_killers(Move m, SearchStack* ss) {
2082 if (m == ss->killers[0])
2085 for (int i = KILLER_MAX - 1; i > 0; i--)
2086 ss->killers[i] = ss->killers[i - 1];
2092 // update_gains() updates the gains table of a non-capture move given
2093 // the static position evaluation before and after the move.
2095 void update_gains(const Position& pos, Move m, Value before, Value after) {
2098 && before != VALUE_NONE
2099 && after != VALUE_NONE
2100 && pos.captured_piece() == NO_PIECE_TYPE
2101 && !move_is_castle(m)
2102 && !move_is_promotion(m))
2103 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2107 // current_search_time() returns the number of milliseconds which have passed
2108 // since the beginning of the current search.
2110 int current_search_time() {
2112 return get_system_time() - SearchStartTime;
2116 // nps() computes the current nodes/second count.
2120 int t = current_search_time();
2121 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2125 // poll() performs two different functions: It polls for user input, and it
2126 // looks at the time consumed so far and decides if it's time to abort the
2131 static int lastInfoTime;
2132 int t = current_search_time();
2137 // We are line oriented, don't read single chars
2138 std::string command;
2140 if (!std::getline(std::cin, command))
2143 if (command == "quit")
2146 PonderSearch = false;
2150 else if (command == "stop")
2153 PonderSearch = false;
2155 else if (command == "ponderhit")
2159 // Print search information
2163 else if (lastInfoTime > t)
2164 // HACK: Must be a new search where we searched less than
2165 // NodesBetweenPolls nodes during the first second of search.
2168 else if (t - lastInfoTime >= 1000)
2175 if (dbg_show_hit_rate)
2176 dbg_print_hit_rate();
2178 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2179 << " time " << t << " hashfull " << TT.full() << endl;
2182 // Should we stop the search?
2186 bool stillAtFirstMove = FirstRootMove
2187 && !AspirationFailLow
2188 && t > MaxSearchTime + ExtraSearchTime;
2190 bool noMoreTime = t > AbsoluteMaxSearchTime
2191 || stillAtFirstMove;
2193 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2194 || (ExactMaxTime && t >= ExactMaxTime)
2195 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2200 // ponderhit() is called when the program is pondering (i.e. thinking while
2201 // it's the opponent's turn to move) in order to let the engine know that
2202 // it correctly predicted the opponent's move.
2206 int t = current_search_time();
2207 PonderSearch = false;
2209 bool stillAtFirstMove = FirstRootMove
2210 && !AspirationFailLow
2211 && t > MaxSearchTime + ExtraSearchTime;
2213 bool noMoreTime = t > AbsoluteMaxSearchTime
2214 || stillAtFirstMove;
2216 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2221 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2223 void init_ss_array(SearchStack* ss) {
2225 for (int i = 0; i < 3; i++, ss++)
2229 ss->excludedMove = MOVE_NONE;
2234 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2235 // while the program is pondering. The point is to work around a wrinkle in
2236 // the UCI protocol: When pondering, the engine is not allowed to give a
2237 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2238 // We simply wait here until one of these commands is sent, and return,
2239 // after which the bestmove and pondermove will be printed (in id_loop()).
2241 void wait_for_stop_or_ponderhit() {
2243 std::string command;
2247 if (!std::getline(std::cin, command))
2250 if (command == "quit")
2255 else if (command == "ponderhit" || command == "stop")
2261 // print_pv_info() prints to standard output and eventually to log file information on
2262 // the current PV line. It is called at each iteration or after a new pv is found.
2264 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2266 cout << "info depth " << Iteration
2267 << " score " << value_to_string(value)
2268 << ((value >= beta) ? " lowerbound" :
2269 ((value <= alpha)? " upperbound" : ""))
2270 << " time " << current_search_time()
2271 << " nodes " << TM.nodes_searched()
2275 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2276 cout << ss->pv[j] << " ";
2282 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2283 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2285 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2286 TM.nodes_searched(), value, type, ss->pv) << endl;
2291 // init_thread() is the function which is called when a new thread is
2292 // launched. It simply calls the idle_loop() function with the supplied
2293 // threadID. There are two versions of this function; one for POSIX
2294 // threads and one for Windows threads.
2296 #if !defined(_MSC_VER)
2298 void* init_thread(void *threadID) {
2300 TM.idle_loop(*(int*)threadID, NULL);
2306 DWORD WINAPI init_thread(LPVOID threadID) {
2308 TM.idle_loop(*(int*)threadID, NULL);
2315 /// The ThreadsManager class
2317 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2318 // get_beta_counters() are getters/setters for the per thread
2319 // counters used to sort the moves at root.
2321 void ThreadsManager::resetNodeCounters() {
2323 for (int i = 0; i < MAX_THREADS; i++)
2324 threads[i].nodes = 0ULL;
2327 void ThreadsManager::resetBetaCounters() {
2329 for (int i = 0; i < MAX_THREADS; i++)
2330 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2333 int64_t ThreadsManager::nodes_searched() const {
2335 int64_t result = 0ULL;
2336 for (int i = 0; i < ActiveThreads; i++)
2337 result += threads[i].nodes;
2342 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2345 for (int i = 0; i < MAX_THREADS; i++)
2347 our += threads[i].betaCutOffs[us];
2348 their += threads[i].betaCutOffs[opposite_color(us)];
2353 // idle_loop() is where the threads are parked when they have no work to do.
2354 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2355 // object for which the current thread is the master.
2357 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2359 assert(threadID >= 0 && threadID < MAX_THREADS);
2363 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2364 // master should exit as last one.
2365 if (AllThreadsShouldExit)
2368 threads[threadID].state = THREAD_TERMINATED;
2372 // If we are not thinking, wait for a condition to be signaled
2373 // instead of wasting CPU time polling for work.
2374 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2377 assert(threadID != 0);
2378 threads[threadID].state = THREAD_SLEEPING;
2380 #if !defined(_MSC_VER)
2381 lock_grab(&WaitLock);
2382 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2383 pthread_cond_wait(&WaitCond, &WaitLock);
2384 lock_release(&WaitLock);
2386 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2390 // If thread has just woken up, mark it as available
2391 if (threads[threadID].state == THREAD_SLEEPING)
2392 threads[threadID].state = THREAD_AVAILABLE;
2394 // If this thread has been assigned work, launch a search
2395 if (threads[threadID].state == THREAD_WORKISWAITING)
2397 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2399 threads[threadID].state = THREAD_SEARCHING;
2401 if (threads[threadID].splitPoint->pvNode)
2402 sp_search<PV>(threads[threadID].splitPoint, threadID);
2404 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2406 assert(threads[threadID].state == THREAD_SEARCHING);
2408 threads[threadID].state = THREAD_AVAILABLE;
2411 // If this thread is the master of a split point and all slaves have
2412 // finished their work at this split point, return from the idle loop.
2414 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2416 if (i == ActiveThreads)
2418 // Because sp->slaves[] is reset under lock protection,
2419 // be sure sp->lock has been released before to return.
2420 lock_grab(&(sp->lock));
2421 lock_release(&(sp->lock));
2423 assert(threads[threadID].state == THREAD_AVAILABLE);
2425 threads[threadID].state = THREAD_SEARCHING;
2432 // init_threads() is called during startup. It launches all helper threads,
2433 // and initializes the split point stack and the global locks and condition
2436 void ThreadsManager::init_threads() {
2441 #if !defined(_MSC_VER)
2442 pthread_t pthread[1];
2445 // Initialize global locks
2446 lock_init(&MPLock, NULL);
2447 lock_init(&WaitLock, NULL);
2449 #if !defined(_MSC_VER)
2450 pthread_cond_init(&WaitCond, NULL);
2452 for (i = 0; i < MAX_THREADS; i++)
2453 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2456 // Initialize SplitPointStack locks
2457 for (i = 0; i < MAX_THREADS; i++)
2458 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2459 lock_init(&(SplitPointStack[i][j].lock), NULL);
2461 // Will be set just before program exits to properly end the threads
2462 AllThreadsShouldExit = false;
2464 // Threads will be put to sleep as soon as created
2465 AllThreadsShouldSleep = true;
2467 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2469 threads[0].state = THREAD_SEARCHING;
2470 for (i = 1; i < MAX_THREADS; i++)
2471 threads[i].state = THREAD_AVAILABLE;
2473 // Launch the helper threads
2474 for (i = 1; i < MAX_THREADS; i++)
2477 #if !defined(_MSC_VER)
2478 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2480 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2485 cout << "Failed to create thread number " << i << endl;
2486 Application::exit_with_failure();
2489 // Wait until the thread has finished launching and is gone to sleep
2490 while (threads[i].state != THREAD_SLEEPING) {}
2495 // exit_threads() is called when the program exits. It makes all the
2496 // helper threads exit cleanly.
2498 void ThreadsManager::exit_threads() {
2500 ActiveThreads = MAX_THREADS; // HACK
2501 AllThreadsShouldSleep = true; // HACK
2502 wake_sleeping_threads();
2504 // This makes the threads to exit idle_loop()
2505 AllThreadsShouldExit = true;
2507 // Wait for thread termination
2508 for (int i = 1; i < MAX_THREADS; i++)
2509 while (threads[i].state != THREAD_TERMINATED) {}
2511 // Now we can safely destroy the locks
2512 for (int i = 0; i < MAX_THREADS; i++)
2513 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2514 lock_destroy(&(SplitPointStack[i][j].lock));
2516 lock_destroy(&WaitLock);
2517 lock_destroy(&MPLock);
2521 // thread_should_stop() checks whether the thread should stop its search.
2522 // This can happen if a beta cutoff has occurred in the thread's currently
2523 // active split point, or in some ancestor of the current split point.
2525 bool ThreadsManager::thread_should_stop(int threadID) const {
2527 assert(threadID >= 0 && threadID < ActiveThreads);
2531 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2536 // thread_is_available() checks whether the thread with threadID "slave" is
2537 // available to help the thread with threadID "master" at a split point. An
2538 // obvious requirement is that "slave" must be idle. With more than two
2539 // threads, this is not by itself sufficient: If "slave" is the master of
2540 // some active split point, it is only available as a slave to the other
2541 // threads which are busy searching the split point at the top of "slave"'s
2542 // split point stack (the "helpful master concept" in YBWC terminology).
2544 bool ThreadsManager::thread_is_available(int slave, int master) const {
2546 assert(slave >= 0 && slave < ActiveThreads);
2547 assert(master >= 0 && master < ActiveThreads);
2548 assert(ActiveThreads > 1);
2550 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2553 // Make a local copy to be sure doesn't change under our feet
2554 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2556 if (localActiveSplitPoints == 0)
2557 // No active split points means that the thread is available as
2558 // a slave for any other thread.
2561 if (ActiveThreads == 2)
2564 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2565 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2566 // could have been set to 0 by another thread leading to an out of bound access.
2567 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2574 // available_thread_exists() tries to find an idle thread which is available as
2575 // a slave for the thread with threadID "master".
2577 bool ThreadsManager::available_thread_exists(int master) const {
2579 assert(master >= 0 && master < ActiveThreads);
2580 assert(ActiveThreads > 1);
2582 for (int i = 0; i < ActiveThreads; i++)
2583 if (thread_is_available(i, master))
2590 // split() does the actual work of distributing the work at a node between
2591 // several available threads. If it does not succeed in splitting the
2592 // node (because no idle threads are available, or because we have no unused
2593 // split point objects), the function immediately returns. If splitting is
2594 // possible, a SplitPoint object is initialized with all the data that must be
2595 // copied to the helper threads and we tell our helper threads that they have
2596 // been assigned work. This will cause them to instantly leave their idle loops
2597 // and call sp_search(). When all threads have returned from sp_search() then
2600 template <bool Fake>
2601 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2602 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2603 MovePicker* mp, int master, bool pvNode) {
2605 assert(*bestValue >= -VALUE_INFINITE);
2606 assert(*bestValue <= *alpha);
2607 assert(*alpha < beta);
2608 assert(beta <= VALUE_INFINITE);
2609 assert(depth > Depth(0));
2610 assert(master >= 0 && master < ActiveThreads);
2611 assert(ActiveThreads > 1);
2615 // If no other thread is available to help us, or if we have too many
2616 // active split points, don't split.
2617 if ( !available_thread_exists(master)
2618 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2620 lock_release(&MPLock);
2624 // Pick the next available split point object from the split point stack
2625 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2627 // Initialize the split point object
2628 splitPoint->parent = threads[master].splitPoint;
2629 splitPoint->stopRequest = false;
2630 splitPoint->depth = depth;
2631 splitPoint->mateThreat = mateThreat;
2632 splitPoint->alpha = *alpha;
2633 splitPoint->beta = beta;
2634 splitPoint->pvNode = pvNode;
2635 splitPoint->bestValue = *bestValue;
2636 splitPoint->mp = mp;
2637 splitPoint->moveCount = *moveCount;
2638 splitPoint->pos = &p;
2639 splitPoint->parentSstack = ss;
2640 for (int i = 0; i < ActiveThreads; i++)
2641 splitPoint->slaves[i] = 0;
2643 threads[master].splitPoint = splitPoint;
2644 threads[master].activeSplitPoints++;
2646 // If we are here it means we are not available
2647 assert(threads[master].state != THREAD_AVAILABLE);
2649 int workersCnt = 1; // At least the master is included
2651 // Allocate available threads setting state to THREAD_BOOKED
2652 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2653 if (thread_is_available(i, master))
2655 threads[i].state = THREAD_BOOKED;
2656 threads[i].splitPoint = splitPoint;
2657 splitPoint->slaves[i] = 1;
2661 assert(Fake || workersCnt > 1);
2663 // We can release the lock because slave threads are already booked and master is not available
2664 lock_release(&MPLock);
2666 // Tell the threads that they have work to do. This will make them leave
2667 // their idle loop. But before copy search stack tail for each thread.
2668 for (int i = 0; i < ActiveThreads; i++)
2669 if (i == master || splitPoint->slaves[i])
2671 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2673 assert(i == master || threads[i].state == THREAD_BOOKED);
2675 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2678 // Everything is set up. The master thread enters the idle loop, from
2679 // which it will instantly launch a search, because its state is
2680 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2681 // idle loop, which means that the main thread will return from the idle
2682 // loop when all threads have finished their work at this split point.
2683 idle_loop(master, splitPoint);
2685 // We have returned from the idle loop, which means that all threads are
2686 // finished. Update alpha and bestValue, and return.
2689 *alpha = splitPoint->alpha;
2690 *bestValue = splitPoint->bestValue;
2691 threads[master].activeSplitPoints--;
2692 threads[master].splitPoint = splitPoint->parent;
2694 lock_release(&MPLock);
2698 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2699 // to start a new search from the root.
2701 void ThreadsManager::wake_sleeping_threads() {
2703 assert(AllThreadsShouldSleep);
2704 assert(ActiveThreads > 0);
2706 AllThreadsShouldSleep = false;
2708 if (ActiveThreads == 1)
2711 #if !defined(_MSC_VER)
2712 pthread_mutex_lock(&WaitLock);
2713 pthread_cond_broadcast(&WaitCond);
2714 pthread_mutex_unlock(&WaitLock);
2716 for (int i = 1; i < MAX_THREADS; i++)
2717 SetEvent(SitIdleEvent[i]);
2723 // put_threads_to_sleep() makes all the threads go to sleep just before
2724 // to leave think(), at the end of the search. Threads should have already
2725 // finished the job and should be idle.
2727 void ThreadsManager::put_threads_to_sleep() {
2729 assert(!AllThreadsShouldSleep);
2731 // This makes the threads to go to sleep
2732 AllThreadsShouldSleep = true;
2735 /// The RootMoveList class
2737 // RootMoveList c'tor
2739 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2741 SearchStack ss[PLY_MAX_PLUS_2];
2742 MoveStack mlist[MaxRootMoves];
2744 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2746 // Generate all legal moves
2747 MoveStack* last = generate_moves(pos, mlist);
2749 // Add each move to the moves[] array
2750 for (MoveStack* cur = mlist; cur != last; cur++)
2752 bool includeMove = includeAllMoves;
2754 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2755 includeMove = (searchMoves[k] == cur->move);
2760 // Find a quick score for the move
2762 pos.do_move(cur->move, st);
2763 moves[count].move = cur->move;
2764 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2765 moves[count].pv[0] = cur->move;
2766 moves[count].pv[1] = MOVE_NONE;
2767 pos.undo_move(cur->move);
2774 // RootMoveList simple methods definitions
2776 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2778 moves[moveNum].nodes = nodes;
2779 moves[moveNum].cumulativeNodes += nodes;
2782 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2784 moves[moveNum].ourBeta = our;
2785 moves[moveNum].theirBeta = their;
2788 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2792 for (j = 0; pv[j] != MOVE_NONE; j++)
2793 moves[moveNum].pv[j] = pv[j];
2795 moves[moveNum].pv[j] = MOVE_NONE;
2799 // RootMoveList::sort() sorts the root move list at the beginning of a new
2802 void RootMoveList::sort() {
2804 sort_multipv(count - 1); // Sort all items
2808 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2809 // list by their scores and depths. It is used to order the different PVs
2810 // correctly in MultiPV mode.
2812 void RootMoveList::sort_multipv(int n) {
2816 for (i = 1; i <= n; i++)
2818 RootMove rm = moves[i];
2819 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2820 moves[j] = moves[j - 1];