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, Move excludedMove = MOVE_NONE);
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, Move excludedMove) {
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 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 + 2)->initKillers();
1063 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1069 // Step 2. Check for aborted search and immediate draw
1070 if (AbortSearch || TM.thread_should_stop(threadID))
1073 if (pos.is_draw() || ply >= PLY_MAX - 1)
1076 // Step 3. Mate distance pruning
1077 alpha = Max(value_mated_in(ply), alpha);
1078 beta = Min(value_mate_in(ply+1), beta);
1082 // Step 4. Transposition table lookup
1084 // We don't want the score of a partial search to overwrite a previous full search
1085 // TT value, so we use a different position key in case of an excluded move exists.
1086 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1088 tte = TT.retrieve(posKey);
1089 ttMove = (tte ? tte->move() : MOVE_NONE);
1091 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1092 // This is to avoid problems in the following areas:
1094 // * Repetition draw detection
1095 // * Fifty move rule detection
1096 // * Searching for a mate
1097 // * Printing of full PV line
1099 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1101 // Refresh tte entry to avoid aging
1102 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1104 ss->currentMove = ttMove; // Can be MOVE_NONE
1105 return value_from_tt(tte->value(), ply);
1108 // Step 5. Evaluate the position statically
1109 // At PV nodes we do this only to update gain statistics
1110 isCheck = pos.is_check();
1113 if (tte && tte->static_value() != VALUE_NONE)
1115 ss->eval = tte->static_value();
1116 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1119 ss->eval = evaluate(pos, ei, threadID);
1121 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1122 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1125 // Step 6. Razoring (is omitted in PV nodes)
1127 && depth < RazorDepth
1129 && refinedValue < beta - razor_margin(depth)
1130 && ttMove == MOVE_NONE
1131 && (ss-1)->currentMove != MOVE_NULL
1132 && !value_is_mate(beta)
1133 && !pos.has_pawn_on_7th(pos.side_to_move()))
1135 Value rbeta = beta - razor_margin(depth);
1136 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), threadID);
1138 // Logically we should return (v + razor_margin(depth)), but
1139 // surprisingly this did slightly weaker in tests.
1143 // Step 7. Static null move pruning (is omitted in PV nodes)
1144 // We're betting that the opponent doesn't have a move that will reduce
1145 // the score by more than futility_margin(depth) if we do a null move.
1148 && depth < RazorDepth
1149 && refinedValue >= beta + futility_margin(depth, 0)
1151 && !value_is_mate(beta)
1152 && pos.non_pawn_material(pos.side_to_move()))
1153 return refinedValue - futility_margin(depth, 0);
1155 // Step 8. Null move search with verification search (is omitted in PV nodes)
1156 // When we jump directly to qsearch() we do a null move only if static value is
1157 // at least beta. Otherwise we do a null move if static value is not more than
1158 // NullMoveMargin under beta.
1162 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1164 && !value_is_mate(beta)
1165 && pos.non_pawn_material(pos.side_to_move()))
1167 ss->currentMove = MOVE_NULL;
1169 // Null move dynamic reduction based on depth
1170 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1172 // Null move dynamic reduction based on value
1173 if (refinedValue - beta > PawnValueMidgame)
1176 pos.do_null_move(st);
1178 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1179 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, false, threadID);
1180 pos.undo_null_move();
1182 if (nullValue >= beta)
1184 // Do not return unproven mate scores
1185 if (nullValue >= value_mate_in(PLY_MAX))
1188 // Do zugzwang verification search at high depths
1189 if ( depth < 6 * OnePly
1190 || search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID) >= beta)
1195 // The null move failed low, which means that we may be faced with
1196 // some kind of threat. If the previous move was reduced, check if
1197 // the move that refuted the null move was somehow connected to the
1198 // move which was reduced. If a connection is found, return a fail
1199 // low score (which will cause the reduced move to fail high in the
1200 // parent node, which will trigger a re-search with full depth).
1201 if (nullValue == value_mated_in(ply + 2))
1204 ss->threatMove = (ss+1)->currentMove;
1205 if ( depth < ThreatDepth
1206 && (ss-1)->reduction
1207 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1212 // Step 9. Internal iterative deepening
1213 if ( depth >= IIDDepth[PvNode]
1214 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1215 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1217 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1218 search<PvNode>(pos, ss, alpha, beta, d, false, threadID);
1219 ttMove = ss->pv[ply];
1220 tte = TT.retrieve(posKey);
1223 // Expensive mate threat detection (only for PV nodes)
1225 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1227 // Initialize a MovePicker object for the current position
1228 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1230 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1231 && tte && tte->move()
1232 && !excludedMove // Do not allow recursive singular extension search
1233 && is_lower_bound(tte->type())
1234 && tte->depth() >= depth - 3 * OnePly;
1236 // Step 10. Loop through moves
1237 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1238 while ( bestValue < beta
1239 && (move = mp.get_next_move()) != MOVE_NONE
1240 && !TM.thread_should_stop(threadID))
1242 assert(move_is_ok(move));
1244 if (move == excludedMove)
1247 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1248 moveIsCheck = pos.move_is_check(move, ci);
1249 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1251 // Step 11. Decide the new search depth
1252 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1254 // Singular extension search. We extend the TT move if its value is much better than
1255 // its siblings. To verify this we do a reduced search on all the other moves but the
1256 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1257 if ( singularExtensionNode
1258 && move == tte->move()
1261 Value ttValue = value_from_tt(tte->value(), ply);
1263 if (abs(ttValue) < VALUE_KNOWN_WIN)
1265 Value b = ttValue - SingularExtensionMargin;
1266 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, false, threadID, move);
1268 if (v < ttValue - SingularExtensionMargin)
1273 newDepth = depth - OnePly + ext;
1275 // Update current move (this must be done after singular extension search)
1276 movesSearched[moveCount++] = ss->currentMove = move;
1278 // Step 12. Futility pruning (is omitted in PV nodes)
1280 && !captureOrPromotion
1284 && !move_is_castle(move))
1286 // Move count based pruning
1287 if ( moveCount >= futility_move_count(depth)
1288 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1289 && bestValue > value_mated_in(PLY_MAX))
1292 // Value based pruning
1293 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1294 // but fixing this made program slightly weaker.
1295 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1296 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1297 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1299 if (futilityValueScaled < beta)
1301 if (futilityValueScaled > bestValue)
1302 bestValue = futilityValueScaled;
1307 // Step 13. Make the move
1308 pos.do_move(move, st, ci, moveIsCheck);
1310 // Step extra. pv search (only in PV nodes)
1311 // The first move in list is the expected PV
1312 if (PvNode && moveCount == 1)
1313 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1314 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1317 // Step 14. Reduced depth search
1318 // If the move fails high will be re-searched at full depth.
1319 bool doFullDepthSearch = true;
1321 if ( depth >= 3 * OnePly
1322 && !captureOrPromotion
1324 && !move_is_castle(move)
1325 && !move_is_killer(move, ss))
1327 ss->reduction = reduction<PvNode>(depth, moveCount);
1330 Depth d = newDepth - ss->reduction;
1331 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1332 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, threadID);
1334 doFullDepthSearch = (value > alpha);
1337 // The move failed high, but if reduction is very big we could
1338 // face a false positive, retry with a less aggressive reduction,
1339 // if the move fails high again then go with full depth search.
1340 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1342 assert(newDepth - OnePly >= OnePly);
1344 ss->reduction = OnePly;
1345 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, threadID);
1346 doFullDepthSearch = (value > alpha);
1348 ss->reduction = Depth(0); // Restore original reduction
1351 // Step 15. Full depth search
1352 if (doFullDepthSearch)
1354 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), threadID)
1355 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, threadID);
1357 // Step extra. pv search (only in PV nodes)
1358 // Search only for possible new PV nodes, if instead value >= beta then
1359 // parent node fails low with value <= alpha and tries another move.
1360 if (PvNode && value > alpha && value < beta)
1361 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), threadID)
1362 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1366 // Step 16. Undo move
1367 pos.undo_move(move);
1369 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1371 // Step 17. Check for new best move
1372 if (value > bestValue)
1377 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1382 if (value == value_mate_in(ply + 1))
1383 ss->mateKiller = move;
1387 // Step 18. Check for split
1388 if ( depth >= MinimumSplitDepth
1389 && TM.active_threads() > 1
1391 && TM.available_thread_exists(threadID)
1393 && !TM.thread_should_stop(threadID)
1395 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1396 mateThreat, &moveCount, &mp, threadID, PvNode);
1399 // Step 19. Check for mate and stalemate
1400 // All legal moves have been searched and if there are
1401 // no legal moves, it must be mate or stalemate.
1402 // If one move was excluded return fail low score.
1404 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1406 // Step 20. Update tables
1407 // If the search is not aborted, update the transposition table,
1408 // history counters, and killer moves.
1409 if (AbortSearch || TM.thread_should_stop(threadID))
1412 if (bestValue <= oldAlpha)
1413 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1415 else if (bestValue >= beta)
1417 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1419 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1420 if (!pos.move_is_capture_or_promotion(move))
1422 update_history(pos, move, depth, movesSearched, moveCount);
1423 update_killers(move, ss);
1427 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1429 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1435 // qsearch() is the quiescence search function, which is called by the main
1436 // search function when the remaining depth is zero (or, to be more precise,
1437 // less than OnePly).
1439 template <NodeType PvNode>
1440 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID) {
1442 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1443 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1444 assert(PvNode || alpha == beta - 1);
1446 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1447 assert(threadID >= 0 && threadID < TM.active_threads());
1452 Value staticValue, bestValue, value, futilityBase, futilityValue;
1453 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1454 const TTEntry* tte = NULL;
1456 int ply = pos.ply();
1457 Value oldAlpha = alpha;
1459 TM.incrementNodeCounter(threadID);
1462 // Check for an instant draw or maximum ply reached
1463 if (pos.is_draw() || ply >= PLY_MAX - 1)
1466 // Transposition table lookup. At PV nodes, we don't use the TT for
1467 // pruning, but only for move ordering.
1468 tte = TT.retrieve(pos.get_key());
1469 ttMove = (tte ? tte->move() : MOVE_NONE);
1471 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1473 ss->currentMove = ttMove; // Can be MOVE_NONE
1474 return value_from_tt(tte->value(), ply);
1477 isCheck = pos.is_check();
1479 // Evaluate the position statically
1481 staticValue = -VALUE_INFINITE;
1482 else if (tte && tte->static_value() != VALUE_NONE)
1484 staticValue = tte->static_value();
1485 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1488 staticValue = evaluate(pos, ei, threadID);
1492 ss->eval = staticValue;
1493 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1496 // Initialize "stand pat score", and return it immediately if it is
1498 bestValue = staticValue;
1500 if (bestValue >= beta)
1502 // Store the score to avoid a future costly evaluation() call
1503 if (!isCheck && !tte)
1504 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()]);
1509 if (bestValue > alpha)
1512 // If we are near beta then try to get a cutoff pushing checks a bit further
1513 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1515 // Initialize a MovePicker object for the current position, and prepare
1516 // to search the moves. Because the depth is <= 0 here, only captures,
1517 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1518 // and we are near beta) will be generated.
1519 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1521 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1522 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1524 // Loop through the moves until no moves remain or a beta cutoff occurs
1525 while ( alpha < beta
1526 && (move = mp.get_next_move()) != MOVE_NONE)
1528 assert(move_is_ok(move));
1530 moveIsCheck = pos.move_is_check(move, ci);
1532 // Update current move
1534 ss->currentMove = move;
1542 && !move_is_promotion(move)
1543 && !pos.move_is_passed_pawn_push(move))
1545 futilityValue = futilityBase
1546 + pos.endgame_value_of_piece_on(move_to(move))
1547 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1549 if (futilityValue < alpha)
1551 if (futilityValue > bestValue)
1552 bestValue = futilityValue;
1557 // Detect blocking evasions that are candidate to be pruned
1558 evasionPrunable = isCheck
1559 && bestValue > value_mated_in(PLY_MAX)
1560 && !pos.move_is_capture(move)
1561 && pos.type_of_piece_on(move_from(move)) != KING
1562 && !pos.can_castle(pos.side_to_move());
1564 // Don't search moves with negative SEE values
1566 && (!isCheck || evasionPrunable)
1568 && !move_is_promotion(move)
1569 && pos.see_sign(move) < 0)
1572 // Make and search the move
1573 pos.do_move(move, st, ci, moveIsCheck);
1574 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, threadID);
1575 pos.undo_move(move);
1577 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1580 if (value > bestValue)
1591 // All legal moves have been searched. A special case: If we're in check
1592 // and no legal moves were found, it is checkmate.
1593 if (!moveCount && isCheck) // Mate!
1594 return value_mated_in(ply);
1596 // Update transposition table
1597 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1598 if (bestValue <= oldAlpha)
1600 // If bestValue isn't changed it means it is still the static evaluation
1601 // of the node, so keep this info to avoid a future evaluation() call.
1602 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1604 else if (bestValue >= beta)
1607 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1609 // Update killers only for good checking moves
1610 if (!pos.move_is_capture_or_promotion(move))
1611 update_killers(move, ss);
1614 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()]);
1616 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1622 // sp_search() is used to search from a split point. This function is called
1623 // by each thread working at the split point. It is similar to the normal
1624 // search() function, but simpler. Because we have already probed the hash
1625 // table, done a null move search, and searched the first move before
1626 // splitting, we don't have to repeat all this work in sp_search(). We
1627 // also don't need to store anything to the hash table here: This is taken
1628 // care of after we return from the split point.
1630 template <NodeType PvNode>
1631 void sp_search(SplitPoint* sp, int threadID) {
1633 assert(threadID >= 0 && threadID < TM.active_threads());
1634 assert(TM.active_threads() > 1);
1638 Depth ext, newDepth;
1640 Value futilityValueScaled; // NonPV specific
1641 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1643 value = -VALUE_INFINITE;
1645 Position pos(*sp->pos);
1647 int ply = pos.ply();
1648 SearchStack* ss = sp->sstack[threadID] + 1;
1649 isCheck = pos.is_check();
1651 // Step 10. Loop through moves
1652 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1653 lock_grab(&(sp->lock));
1655 while ( sp->bestValue < sp->beta
1656 && (move = sp->mp->get_next_move()) != MOVE_NONE
1657 && !TM.thread_should_stop(threadID))
1659 moveCount = ++sp->moveCount;
1660 lock_release(&(sp->lock));
1662 assert(move_is_ok(move));
1664 moveIsCheck = pos.move_is_check(move, ci);
1665 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1667 // Step 11. Decide the new search depth
1668 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1669 newDepth = sp->depth - OnePly + ext;
1671 // Update current move
1672 ss->currentMove = move;
1674 // Step 12. Futility pruning (is omitted in PV nodes)
1676 && !captureOrPromotion
1679 && !move_is_castle(move))
1681 // Move count based pruning
1682 if ( moveCount >= futility_move_count(sp->depth)
1683 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1684 && sp->bestValue > value_mated_in(PLY_MAX))
1686 lock_grab(&(sp->lock));
1690 // Value based pruning
1691 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1692 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1693 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1695 if (futilityValueScaled < sp->beta)
1697 lock_grab(&(sp->lock));
1699 if (futilityValueScaled > sp->bestValue)
1700 sp->bestValue = futilityValueScaled;
1705 // Step 13. Make the move
1706 pos.do_move(move, st, ci, moveIsCheck);
1708 // Step 14. Reduced search
1709 // If the move fails high will be re-searched at full depth.
1710 bool doFullDepthSearch = true;
1712 if ( !captureOrPromotion
1714 && !move_is_castle(move)
1715 && !move_is_killer(move, ss))
1717 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1720 Value localAlpha = sp->alpha;
1721 Depth d = newDepth - ss->reduction;
1722 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1723 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, true, threadID);
1724 doFullDepthSearch = (value > localAlpha);
1727 // The move failed high, but if reduction is very big we could
1728 // face a false positive, retry with a less aggressive reduction,
1729 // if the move fails high again then go with full depth search.
1730 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1732 assert(newDepth - OnePly >= OnePly);
1734 ss->reduction = OnePly;
1735 Value localAlpha = sp->alpha;
1736 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1737 doFullDepthSearch = (value > localAlpha);
1741 // Step 15. Full depth search
1742 if (doFullDepthSearch)
1744 ss->reduction = Depth(0);
1745 Value localAlpha = sp->alpha;
1746 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), threadID)
1747 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, true, threadID);
1749 // Step extra. pv search (only in PV nodes)
1750 // Search only for possible new PV nodes, if instead value >= beta then
1751 // parent node fails low with value <= alpha and tries another move.
1752 if (PvNode && value > localAlpha && value < sp->beta)
1753 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), threadID)
1754 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, false, threadID);
1757 // Step 16. Undo move
1758 pos.undo_move(move);
1760 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1762 // Step 17. Check for new best move
1763 lock_grab(&(sp->lock));
1765 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1767 sp->bestValue = value;
1769 if (sp->bestValue > sp->alpha)
1771 if (!PvNode || value >= sp->beta)
1772 sp->stopRequest = true;
1774 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1777 sp_update_pv(sp->parentSstack, ss, ply);
1782 /* Here we have the lock still grabbed */
1784 sp->slaves[threadID] = 0;
1786 lock_release(&(sp->lock));
1789 // update_pv() is called whenever a search returns a value > alpha.
1790 // It updates the PV in the SearchStack object corresponding to the
1793 void update_pv(SearchStack* ss, int ply) {
1795 assert(ply >= 0 && ply < PLY_MAX);
1799 ss->pv[ply] = ss->currentMove;
1801 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1802 ss->pv[p] = (ss+1)->pv[p];
1804 ss->pv[p] = MOVE_NONE;
1808 // sp_update_pv() is a variant of update_pv for use at split points. The
1809 // difference between the two functions is that sp_update_pv also updates
1810 // the PV at the parent node.
1812 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1814 assert(ply >= 0 && ply < PLY_MAX);
1818 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1820 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1821 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1823 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1827 // connected_moves() tests whether two moves are 'connected' in the sense
1828 // that the first move somehow made the second move possible (for instance
1829 // if the moving piece is the same in both moves). The first move is assumed
1830 // to be the move that was made to reach the current position, while the
1831 // second move is assumed to be a move from the current position.
1833 bool connected_moves(const Position& pos, Move m1, Move m2) {
1835 Square f1, t1, f2, t2;
1838 assert(move_is_ok(m1));
1839 assert(move_is_ok(m2));
1841 if (m2 == MOVE_NONE)
1844 // Case 1: The moving piece is the same in both moves
1850 // Case 2: The destination square for m2 was vacated by m1
1856 // Case 3: Moving through the vacated square
1857 if ( piece_is_slider(pos.piece_on(f2))
1858 && bit_is_set(squares_between(f2, t2), f1))
1861 // Case 4: The destination square for m2 is defended by the moving piece in m1
1862 p = pos.piece_on(t1);
1863 if (bit_is_set(pos.attacks_from(p, t1), t2))
1866 // Case 5: Discovered check, checking piece is the piece moved in m1
1867 if ( piece_is_slider(p)
1868 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1869 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1871 // discovered_check_candidates() works also if the Position's side to
1872 // move is the opposite of the checking piece.
1873 Color them = opposite_color(pos.side_to_move());
1874 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1876 if (bit_is_set(dcCandidates, f2))
1883 // value_is_mate() checks if the given value is a mate one
1884 // eventually compensated for the ply.
1886 bool value_is_mate(Value value) {
1888 assert(abs(value) <= VALUE_INFINITE);
1890 return value <= value_mated_in(PLY_MAX)
1891 || value >= value_mate_in(PLY_MAX);
1895 // move_is_killer() checks if the given move is among the
1896 // killer moves of that ply.
1898 bool move_is_killer(Move m, SearchStack* ss) {
1900 const Move* k = ss->killers;
1901 for (int i = 0; i < KILLER_MAX; i++, k++)
1909 // extension() decides whether a move should be searched with normal depth,
1910 // or with extended depth. Certain classes of moves (checking moves, in
1911 // particular) are searched with bigger depth than ordinary moves and in
1912 // any case are marked as 'dangerous'. Note that also if a move is not
1913 // extended, as example because the corresponding UCI option is set to zero,
1914 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1915 template <NodeType PvNode>
1916 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1917 bool singleEvasion, bool mateThreat, bool* dangerous) {
1919 assert(m != MOVE_NONE);
1921 Depth result = Depth(0);
1922 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1927 result += CheckExtension[PvNode];
1930 result += SingleEvasionExtension[PvNode];
1933 result += MateThreatExtension[PvNode];
1936 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1938 Color c = pos.side_to_move();
1939 if (relative_rank(c, move_to(m)) == RANK_7)
1941 result += PawnPushTo7thExtension[PvNode];
1944 if (pos.pawn_is_passed(c, move_to(m)))
1946 result += PassedPawnExtension[PvNode];
1951 if ( captureOrPromotion
1952 && pos.type_of_piece_on(move_to(m)) != PAWN
1953 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1954 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1955 && !move_is_promotion(m)
1958 result += PawnEndgameExtension[PvNode];
1963 && captureOrPromotion
1964 && pos.type_of_piece_on(move_to(m)) != PAWN
1965 && pos.see_sign(m) >= 0)
1971 return Min(result, OnePly);
1975 // connected_threat() tests whether it is safe to forward prune a move or if
1976 // is somehow coonected to the threat move returned by null search.
1978 bool connected_threat(const Position& pos, Move m, Move threat) {
1980 assert(move_is_ok(m));
1981 assert(threat && move_is_ok(threat));
1982 assert(!pos.move_is_check(m));
1983 assert(!pos.move_is_capture_or_promotion(m));
1984 assert(!pos.move_is_passed_pawn_push(m));
1986 Square mfrom, mto, tfrom, tto;
1988 mfrom = move_from(m);
1990 tfrom = move_from(threat);
1991 tto = move_to(threat);
1993 // Case 1: Don't prune moves which move the threatened piece
1997 // Case 2: If the threatened piece has value less than or equal to the
1998 // value of the threatening piece, don't prune move which defend it.
1999 if ( pos.move_is_capture(threat)
2000 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2001 || pos.type_of_piece_on(tfrom) == KING)
2002 && pos.move_attacks_square(m, tto))
2005 // Case 3: If the moving piece in the threatened move is a slider, don't
2006 // prune safe moves which block its ray.
2007 if ( piece_is_slider(pos.piece_on(tfrom))
2008 && bit_is_set(squares_between(tfrom, tto), mto)
2009 && pos.see_sign(m) >= 0)
2016 // ok_to_use_TT() returns true if a transposition table score
2017 // can be used at a given point in search.
2019 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2021 Value v = value_from_tt(tte->value(), ply);
2023 return ( tte->depth() >= depth
2024 || v >= Max(value_mate_in(PLY_MAX), beta)
2025 || v < Min(value_mated_in(PLY_MAX), beta))
2027 && ( (is_lower_bound(tte->type()) && v >= beta)
2028 || (is_upper_bound(tte->type()) && v < beta));
2032 // refine_eval() returns the transposition table score if
2033 // possible otherwise falls back on static position evaluation.
2035 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2040 Value v = value_from_tt(tte->value(), ply);
2042 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2043 || (is_upper_bound(tte->type()) && v < defaultEval))
2050 // update_history() registers a good move that produced a beta-cutoff
2051 // in history and marks as failures all the other moves of that ply.
2053 void update_history(const Position& pos, Move move, Depth depth,
2054 Move movesSearched[], int moveCount) {
2058 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2060 for (int i = 0; i < moveCount - 1; i++)
2062 m = movesSearched[i];
2066 if (!pos.move_is_capture_or_promotion(m))
2067 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2072 // update_killers() add a good move that produced a beta-cutoff
2073 // among the killer moves of that ply.
2075 void update_killers(Move m, SearchStack* ss) {
2077 if (m == ss->killers[0])
2080 for (int i = KILLER_MAX - 1; i > 0; i--)
2081 ss->killers[i] = ss->killers[i - 1];
2087 // update_gains() updates the gains table of a non-capture move given
2088 // the static position evaluation before and after the move.
2090 void update_gains(const Position& pos, Move m, Value before, Value after) {
2093 && before != VALUE_NONE
2094 && after != VALUE_NONE
2095 && pos.captured_piece() == NO_PIECE_TYPE
2096 && !move_is_castle(m)
2097 && !move_is_promotion(m))
2098 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2102 // current_search_time() returns the number of milliseconds which have passed
2103 // since the beginning of the current search.
2105 int current_search_time() {
2107 return get_system_time() - SearchStartTime;
2111 // nps() computes the current nodes/second count.
2115 int t = current_search_time();
2116 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2120 // poll() performs two different functions: It polls for user input, and it
2121 // looks at the time consumed so far and decides if it's time to abort the
2126 static int lastInfoTime;
2127 int t = current_search_time();
2132 // We are line oriented, don't read single chars
2133 std::string command;
2135 if (!std::getline(std::cin, command))
2138 if (command == "quit")
2141 PonderSearch = false;
2145 else if (command == "stop")
2148 PonderSearch = false;
2150 else if (command == "ponderhit")
2154 // Print search information
2158 else if (lastInfoTime > t)
2159 // HACK: Must be a new search where we searched less than
2160 // NodesBetweenPolls nodes during the first second of search.
2163 else if (t - lastInfoTime >= 1000)
2170 if (dbg_show_hit_rate)
2171 dbg_print_hit_rate();
2173 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2174 << " time " << t << " hashfull " << TT.full() << endl;
2177 // Should we stop the search?
2181 bool stillAtFirstMove = FirstRootMove
2182 && !AspirationFailLow
2183 && t > MaxSearchTime + ExtraSearchTime;
2185 bool noMoreTime = t > AbsoluteMaxSearchTime
2186 || stillAtFirstMove;
2188 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2189 || (ExactMaxTime && t >= ExactMaxTime)
2190 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2195 // ponderhit() is called when the program is pondering (i.e. thinking while
2196 // it's the opponent's turn to move) in order to let the engine know that
2197 // it correctly predicted the opponent's move.
2201 int t = current_search_time();
2202 PonderSearch = false;
2204 bool stillAtFirstMove = FirstRootMove
2205 && !AspirationFailLow
2206 && t > MaxSearchTime + ExtraSearchTime;
2208 bool noMoreTime = t > AbsoluteMaxSearchTime
2209 || stillAtFirstMove;
2211 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2216 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2218 void init_ss_array(SearchStack* ss) {
2220 for (int i = 0; i < 3; i++, ss++)
2228 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2229 // while the program is pondering. The point is to work around a wrinkle in
2230 // the UCI protocol: When pondering, the engine is not allowed to give a
2231 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2232 // We simply wait here until one of these commands is sent, and return,
2233 // after which the bestmove and pondermove will be printed (in id_loop()).
2235 void wait_for_stop_or_ponderhit() {
2237 std::string command;
2241 if (!std::getline(std::cin, command))
2244 if (command == "quit")
2249 else if (command == "ponderhit" || command == "stop")
2255 // print_pv_info() prints to standard output and eventually to log file information on
2256 // the current PV line. It is called at each iteration or after a new pv is found.
2258 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2260 cout << "info depth " << Iteration
2261 << " score " << value_to_string(value)
2262 << ((value >= beta) ? " lowerbound" :
2263 ((value <= alpha)? " upperbound" : ""))
2264 << " time " << current_search_time()
2265 << " nodes " << TM.nodes_searched()
2269 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2270 cout << ss->pv[j] << " ";
2276 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2277 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2279 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2280 TM.nodes_searched(), value, type, ss->pv) << endl;
2285 // init_thread() is the function which is called when a new thread is
2286 // launched. It simply calls the idle_loop() function with the supplied
2287 // threadID. There are two versions of this function; one for POSIX
2288 // threads and one for Windows threads.
2290 #if !defined(_MSC_VER)
2292 void* init_thread(void *threadID) {
2294 TM.idle_loop(*(int*)threadID, NULL);
2300 DWORD WINAPI init_thread(LPVOID threadID) {
2302 TM.idle_loop(*(int*)threadID, NULL);
2309 /// The ThreadsManager class
2311 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2312 // get_beta_counters() are getters/setters for the per thread
2313 // counters used to sort the moves at root.
2315 void ThreadsManager::resetNodeCounters() {
2317 for (int i = 0; i < MAX_THREADS; i++)
2318 threads[i].nodes = 0ULL;
2321 void ThreadsManager::resetBetaCounters() {
2323 for (int i = 0; i < MAX_THREADS; i++)
2324 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2327 int64_t ThreadsManager::nodes_searched() const {
2329 int64_t result = 0ULL;
2330 for (int i = 0; i < ActiveThreads; i++)
2331 result += threads[i].nodes;
2336 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2339 for (int i = 0; i < MAX_THREADS; i++)
2341 our += threads[i].betaCutOffs[us];
2342 their += threads[i].betaCutOffs[opposite_color(us)];
2347 // idle_loop() is where the threads are parked when they have no work to do.
2348 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2349 // object for which the current thread is the master.
2351 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2353 assert(threadID >= 0 && threadID < MAX_THREADS);
2357 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2358 // master should exit as last one.
2359 if (AllThreadsShouldExit)
2362 threads[threadID].state = THREAD_TERMINATED;
2366 // If we are not thinking, wait for a condition to be signaled
2367 // instead of wasting CPU time polling for work.
2368 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2371 assert(threadID != 0);
2372 threads[threadID].state = THREAD_SLEEPING;
2374 #if !defined(_MSC_VER)
2375 lock_grab(&WaitLock);
2376 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2377 pthread_cond_wait(&WaitCond, &WaitLock);
2378 lock_release(&WaitLock);
2380 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2384 // If thread has just woken up, mark it as available
2385 if (threads[threadID].state == THREAD_SLEEPING)
2386 threads[threadID].state = THREAD_AVAILABLE;
2388 // If this thread has been assigned work, launch a search
2389 if (threads[threadID].state == THREAD_WORKISWAITING)
2391 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2393 threads[threadID].state = THREAD_SEARCHING;
2395 if (threads[threadID].splitPoint->pvNode)
2396 sp_search<PV>(threads[threadID].splitPoint, threadID);
2398 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2400 assert(threads[threadID].state == THREAD_SEARCHING);
2402 threads[threadID].state = THREAD_AVAILABLE;
2405 // If this thread is the master of a split point and all slaves have
2406 // finished their work at this split point, return from the idle loop.
2408 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2410 if (i == ActiveThreads)
2412 // Because sp->slaves[] is reset under lock protection,
2413 // be sure sp->lock has been released before to return.
2414 lock_grab(&(sp->lock));
2415 lock_release(&(sp->lock));
2417 assert(threads[threadID].state == THREAD_AVAILABLE);
2419 threads[threadID].state = THREAD_SEARCHING;
2426 // init_threads() is called during startup. It launches all helper threads,
2427 // and initializes the split point stack and the global locks and condition
2430 void ThreadsManager::init_threads() {
2435 #if !defined(_MSC_VER)
2436 pthread_t pthread[1];
2439 // Initialize global locks
2440 lock_init(&MPLock, NULL);
2441 lock_init(&WaitLock, NULL);
2443 #if !defined(_MSC_VER)
2444 pthread_cond_init(&WaitCond, NULL);
2446 for (i = 0; i < MAX_THREADS; i++)
2447 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2450 // Initialize SplitPointStack locks
2451 for (i = 0; i < MAX_THREADS; i++)
2452 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2453 lock_init(&(SplitPointStack[i][j].lock), NULL);
2455 // Will be set just before program exits to properly end the threads
2456 AllThreadsShouldExit = false;
2458 // Threads will be put to sleep as soon as created
2459 AllThreadsShouldSleep = true;
2461 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2463 threads[0].state = THREAD_SEARCHING;
2464 for (i = 1; i < MAX_THREADS; i++)
2465 threads[i].state = THREAD_AVAILABLE;
2467 // Launch the helper threads
2468 for (i = 1; i < MAX_THREADS; i++)
2471 #if !defined(_MSC_VER)
2472 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2474 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2479 cout << "Failed to create thread number " << i << endl;
2480 Application::exit_with_failure();
2483 // Wait until the thread has finished launching and is gone to sleep
2484 while (threads[i].state != THREAD_SLEEPING) {}
2489 // exit_threads() is called when the program exits. It makes all the
2490 // helper threads exit cleanly.
2492 void ThreadsManager::exit_threads() {
2494 ActiveThreads = MAX_THREADS; // HACK
2495 AllThreadsShouldSleep = true; // HACK
2496 wake_sleeping_threads();
2498 // This makes the threads to exit idle_loop()
2499 AllThreadsShouldExit = true;
2501 // Wait for thread termination
2502 for (int i = 1; i < MAX_THREADS; i++)
2503 while (threads[i].state != THREAD_TERMINATED) {}
2505 // Now we can safely destroy the locks
2506 for (int i = 0; i < MAX_THREADS; i++)
2507 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2508 lock_destroy(&(SplitPointStack[i][j].lock));
2510 lock_destroy(&WaitLock);
2511 lock_destroy(&MPLock);
2515 // thread_should_stop() checks whether the thread should stop its search.
2516 // This can happen if a beta cutoff has occurred in the thread's currently
2517 // active split point, or in some ancestor of the current split point.
2519 bool ThreadsManager::thread_should_stop(int threadID) const {
2521 assert(threadID >= 0 && threadID < ActiveThreads);
2525 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2530 // thread_is_available() checks whether the thread with threadID "slave" is
2531 // available to help the thread with threadID "master" at a split point. An
2532 // obvious requirement is that "slave" must be idle. With more than two
2533 // threads, this is not by itself sufficient: If "slave" is the master of
2534 // some active split point, it is only available as a slave to the other
2535 // threads which are busy searching the split point at the top of "slave"'s
2536 // split point stack (the "helpful master concept" in YBWC terminology).
2538 bool ThreadsManager::thread_is_available(int slave, int master) const {
2540 assert(slave >= 0 && slave < ActiveThreads);
2541 assert(master >= 0 && master < ActiveThreads);
2542 assert(ActiveThreads > 1);
2544 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2547 // Make a local copy to be sure doesn't change under our feet
2548 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2550 if (localActiveSplitPoints == 0)
2551 // No active split points means that the thread is available as
2552 // a slave for any other thread.
2555 if (ActiveThreads == 2)
2558 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2559 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2560 // could have been set to 0 by another thread leading to an out of bound access.
2561 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2568 // available_thread_exists() tries to find an idle thread which is available as
2569 // a slave for the thread with threadID "master".
2571 bool ThreadsManager::available_thread_exists(int master) const {
2573 assert(master >= 0 && master < ActiveThreads);
2574 assert(ActiveThreads > 1);
2576 for (int i = 0; i < ActiveThreads; i++)
2577 if (thread_is_available(i, master))
2584 // split() does the actual work of distributing the work at a node between
2585 // several available threads. If it does not succeed in splitting the
2586 // node (because no idle threads are available, or because we have no unused
2587 // split point objects), the function immediately returns. If splitting is
2588 // possible, a SplitPoint object is initialized with all the data that must be
2589 // copied to the helper threads and we tell our helper threads that they have
2590 // been assigned work. This will cause them to instantly leave their idle loops
2591 // and call sp_search(). When all threads have returned from sp_search() then
2594 template <bool Fake>
2595 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2596 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2597 MovePicker* mp, int master, bool pvNode) {
2599 assert(*bestValue >= -VALUE_INFINITE);
2600 assert(*bestValue <= *alpha);
2601 assert(*alpha < beta);
2602 assert(beta <= VALUE_INFINITE);
2603 assert(depth > Depth(0));
2604 assert(master >= 0 && master < ActiveThreads);
2605 assert(ActiveThreads > 1);
2609 // If no other thread is available to help us, or if we have too many
2610 // active split points, don't split.
2611 if ( !available_thread_exists(master)
2612 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2614 lock_release(&MPLock);
2618 // Pick the next available split point object from the split point stack
2619 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2621 // Initialize the split point object
2622 splitPoint->parent = threads[master].splitPoint;
2623 splitPoint->stopRequest = false;
2624 splitPoint->depth = depth;
2625 splitPoint->mateThreat = mateThreat;
2626 splitPoint->alpha = *alpha;
2627 splitPoint->beta = beta;
2628 splitPoint->pvNode = pvNode;
2629 splitPoint->bestValue = *bestValue;
2630 splitPoint->mp = mp;
2631 splitPoint->moveCount = *moveCount;
2632 splitPoint->pos = &p;
2633 splitPoint->parentSstack = ss;
2634 for (int i = 0; i < ActiveThreads; i++)
2635 splitPoint->slaves[i] = 0;
2637 threads[master].splitPoint = splitPoint;
2638 threads[master].activeSplitPoints++;
2640 // If we are here it means we are not available
2641 assert(threads[master].state != THREAD_AVAILABLE);
2643 int workersCnt = 1; // At least the master is included
2645 // Allocate available threads setting state to THREAD_BOOKED
2646 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2647 if (thread_is_available(i, master))
2649 threads[i].state = THREAD_BOOKED;
2650 threads[i].splitPoint = splitPoint;
2651 splitPoint->slaves[i] = 1;
2655 assert(Fake || workersCnt > 1);
2657 // We can release the lock because slave threads are already booked and master is not available
2658 lock_release(&MPLock);
2660 // Tell the threads that they have work to do. This will make them leave
2661 // their idle loop. But before copy search stack tail for each thread.
2662 for (int i = 0; i < ActiveThreads; i++)
2663 if (i == master || splitPoint->slaves[i])
2665 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2667 assert(i == master || threads[i].state == THREAD_BOOKED);
2669 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2672 // Everything is set up. The master thread enters the idle loop, from
2673 // which it will instantly launch a search, because its state is
2674 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2675 // idle loop, which means that the main thread will return from the idle
2676 // loop when all threads have finished their work at this split point.
2677 idle_loop(master, splitPoint);
2679 // We have returned from the idle loop, which means that all threads are
2680 // finished. Update alpha and bestValue, and return.
2683 *alpha = splitPoint->alpha;
2684 *bestValue = splitPoint->bestValue;
2685 threads[master].activeSplitPoints--;
2686 threads[master].splitPoint = splitPoint->parent;
2688 lock_release(&MPLock);
2692 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2693 // to start a new search from the root.
2695 void ThreadsManager::wake_sleeping_threads() {
2697 assert(AllThreadsShouldSleep);
2698 assert(ActiveThreads > 0);
2700 AllThreadsShouldSleep = false;
2702 if (ActiveThreads == 1)
2705 #if !defined(_MSC_VER)
2706 pthread_mutex_lock(&WaitLock);
2707 pthread_cond_broadcast(&WaitCond);
2708 pthread_mutex_unlock(&WaitLock);
2710 for (int i = 1; i < MAX_THREADS; i++)
2711 SetEvent(SitIdleEvent[i]);
2717 // put_threads_to_sleep() makes all the threads go to sleep just before
2718 // to leave think(), at the end of the search. Threads should have already
2719 // finished the job and should be idle.
2721 void ThreadsManager::put_threads_to_sleep() {
2723 assert(!AllThreadsShouldSleep);
2725 // This makes the threads to go to sleep
2726 AllThreadsShouldSleep = true;
2729 /// The RootMoveList class
2731 // RootMoveList c'tor
2733 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2735 SearchStack ss[PLY_MAX_PLUS_2];
2736 MoveStack mlist[MaxRootMoves];
2738 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2740 // Generate all legal moves
2741 MoveStack* last = generate_moves(pos, mlist);
2743 // Add each move to the moves[] array
2744 for (MoveStack* cur = mlist; cur != last; cur++)
2746 bool includeMove = includeAllMoves;
2748 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2749 includeMove = (searchMoves[k] == cur->move);
2754 // Find a quick score for the move
2756 pos.do_move(cur->move, st);
2757 moves[count].move = cur->move;
2758 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2759 moves[count].pv[0] = cur->move;
2760 moves[count].pv[1] = MOVE_NONE;
2761 pos.undo_move(cur->move);
2768 // RootMoveList simple methods definitions
2770 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2772 moves[moveNum].nodes = nodes;
2773 moves[moveNum].cumulativeNodes += nodes;
2776 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2778 moves[moveNum].ourBeta = our;
2779 moves[moveNum].theirBeta = their;
2782 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2786 for (j = 0; pv[j] != MOVE_NONE; j++)
2787 moves[moveNum].pv[j] = pv[j];
2789 moves[moveNum].pv[j] = MOVE_NONE;
2793 // RootMoveList::sort() sorts the root move list at the beginning of a new
2796 void RootMoveList::sort() {
2798 sort_multipv(count - 1); // Sort all items
2802 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2803 // list by their scores and depths. It is used to order the different PVs
2804 // correctly in MultiPV mode.
2806 void RootMoveList::sort_multipv(int n) {
2810 for (i = 1; i <= n; i++)
2812 RootMove rm = moves[i];
2813 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2814 moves[j] = moves[j - 1];