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 /// perft() is our utility to verify move generation is bug free. All the legal
341 /// moves up to given depth are generated and counted and the sum returned.
343 int perft(Position& pos, Depth depth)
348 MovePicker mp(pos, MOVE_NONE, depth, H);
350 // If we are at the last ply we don't need to do and undo
351 // the moves, just to count them.
352 if (depth <= OnePly) // Replace with '<' to test also qsearch
354 while (mp.get_next_move()) sum++;
358 // Loop through all legal moves
360 while ((move = mp.get_next_move()) != MOVE_NONE)
362 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
363 sum += perft(pos, depth - OnePly);
370 /// think() is the external interface to Stockfish's search, and is called when
371 /// the program receives the UCI 'go' command. It initializes various
372 /// search-related global variables, and calls root_search(). It returns false
373 /// when a quit command is received during the search.
375 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
376 int time[], int increment[], int movesToGo, int maxDepth,
377 int maxNodes, int maxTime, Move searchMoves[]) {
379 // Initialize global search variables
380 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
381 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
383 TM.resetNodeCounters();
384 SearchStartTime = get_system_time();
385 ExactMaxTime = maxTime;
388 InfiniteSearch = infinite;
389 PonderSearch = ponder;
390 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
392 // Look for a book move, only during games, not tests
393 if (UseTimeManagement && get_option_value_bool("OwnBook"))
395 if (get_option_value_string("Book File") != OpeningBook.file_name())
396 OpeningBook.open(get_option_value_string("Book File"));
398 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
399 if (bookMove != MOVE_NONE)
402 wait_for_stop_or_ponderhit();
404 cout << "bestmove " << bookMove << endl;
409 // Reset loseOnTime flag at the beginning of a new game
410 if (button_was_pressed("New Game"))
413 // Read UCI option values
414 TT.set_size(get_option_value_int("Hash"));
415 if (button_was_pressed("Clear Hash"))
418 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
419 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
420 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
421 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
422 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
423 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
424 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
425 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
426 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
427 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
428 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
429 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
431 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
432 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
433 MultiPV = get_option_value_int("MultiPV");
434 Chess960 = get_option_value_bool("UCI_Chess960");
435 UseLogFile = get_option_value_bool("Use Search Log");
438 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
440 read_weights(pos.side_to_move());
442 // Set the number of active threads
443 int newActiveThreads = get_option_value_int("Threads");
444 if (newActiveThreads != TM.active_threads())
446 TM.set_active_threads(newActiveThreads);
447 init_eval(TM.active_threads());
450 // Wake up sleeping threads
451 TM.wake_sleeping_threads();
454 int myTime = time[side_to_move];
455 int myIncrement = increment[side_to_move];
456 if (UseTimeManagement)
458 if (!movesToGo) // Sudden death time control
462 MaxSearchTime = myTime / 30 + myIncrement;
463 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
465 else // Blitz game without increment
467 MaxSearchTime = myTime / 30;
468 AbsoluteMaxSearchTime = myTime / 8;
471 else // (x moves) / (y minutes)
475 MaxSearchTime = myTime / 2;
476 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
480 MaxSearchTime = myTime / Min(movesToGo, 20);
481 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
485 if (get_option_value_bool("Ponder"))
487 MaxSearchTime += MaxSearchTime / 4;
488 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
492 // Set best NodesBetweenPolls interval to avoid lagging under
493 // heavy time pressure.
495 NodesBetweenPolls = Min(MaxNodes, 30000);
496 else if (myTime && myTime < 1000)
497 NodesBetweenPolls = 1000;
498 else if (myTime && myTime < 5000)
499 NodesBetweenPolls = 5000;
501 NodesBetweenPolls = 30000;
503 // Write search information to log file
505 LogFile << "Searching: " << pos.to_fen() << endl
506 << "infinite: " << infinite
507 << " ponder: " << ponder
508 << " time: " << myTime
509 << " increment: " << myIncrement
510 << " moves to go: " << movesToGo << endl;
512 // LSN filtering. Used only for developing purposes, disabled by default
516 // Step 2. If after last move we decided to lose on time, do it now!
517 while (SearchStartTime + myTime + 1000 > get_system_time())
521 // We're ready to start thinking. Call the iterative deepening loop function
522 Value v = id_loop(pos, searchMoves);
526 // Step 1. If this is sudden death game and our position is hopeless,
527 // decide to lose on time.
528 if ( !loseOnTime // If we already lost on time, go to step 3.
538 // Step 3. Now after stepping over the time limit, reset flag for next match.
546 TM.put_threads_to_sleep();
552 /// init_search() is called during startup. It initializes various lookup tables
556 // Init our reduction lookup tables
557 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
558 for (int j = 1; j < 64; j++) // j == moveNumber
560 double pvRed = log(double(i)) * log(double(j)) / 3.0;
561 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
562 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
563 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
566 // Init futility margins array
567 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
568 for (int j = 0; j < 64; j++) // j == moveNumber
570 // FIXME: test using log instead of BSR
571 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
574 // Init futility move count array
575 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
576 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
580 // SearchStack::init() initializes a search stack. Used at the beginning of a
581 // new search from the root.
582 void SearchStack::init(int ply) {
584 pv[ply] = pv[ply + 1] = MOVE_NONE;
585 currentMove = threatMove = MOVE_NONE;
586 reduction = Depth(0);
590 void SearchStack::initKillers() {
592 mateKiller = MOVE_NONE;
593 for (int i = 0; i < KILLER_MAX; i++)
594 killers[i] = MOVE_NONE;
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)
1678 && !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;
1713 && !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 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1722 doFullDepthSearch = (value > localAlpha);
1725 // The move failed high, but if reduction is very big we could
1726 // face a false positive, retry with a less aggressive reduction,
1727 // if the move fails high again then go with full depth search.
1728 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1730 ss->reduction = OnePly;
1731 Value localAlpha = sp->alpha;
1732 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1733 doFullDepthSearch = (value > localAlpha);
1737 // Step 15. Full depth search
1738 if (doFullDepthSearch)
1740 ss->reduction = Depth(0);
1741 Value localAlpha = sp->alpha;
1742 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, true, threadID);
1744 if (PvNode && value > localAlpha && value < sp->beta)
1745 value = -search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, false, threadID);
1748 // Step 16. Undo move
1749 pos.undo_move(move);
1751 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1753 // Step 17. Check for new best move
1754 lock_grab(&(sp->lock));
1756 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1758 sp->bestValue = value;
1760 if (sp->bestValue > sp->alpha)
1762 if (!PvNode || value >= sp->beta)
1763 sp->stopRequest = true;
1765 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1768 sp_update_pv(sp->parentSstack, ss, ply);
1773 /* Here we have the lock still grabbed */
1775 sp->slaves[threadID] = 0;
1777 lock_release(&(sp->lock));
1780 // update_pv() is called whenever a search returns a value > alpha.
1781 // It updates the PV in the SearchStack object corresponding to the
1784 void update_pv(SearchStack* ss, int ply) {
1786 assert(ply >= 0 && ply < PLY_MAX);
1790 ss->pv[ply] = ss->currentMove;
1792 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1793 ss->pv[p] = (ss+1)->pv[p];
1795 ss->pv[p] = MOVE_NONE;
1799 // sp_update_pv() is a variant of update_pv for use at split points. The
1800 // difference between the two functions is that sp_update_pv also updates
1801 // the PV at the parent node.
1803 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1805 assert(ply >= 0 && ply < PLY_MAX);
1809 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1811 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1812 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1814 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1818 // connected_moves() tests whether two moves are 'connected' in the sense
1819 // that the first move somehow made the second move possible (for instance
1820 // if the moving piece is the same in both moves). The first move is assumed
1821 // to be the move that was made to reach the current position, while the
1822 // second move is assumed to be a move from the current position.
1824 bool connected_moves(const Position& pos, Move m1, Move m2) {
1826 Square f1, t1, f2, t2;
1829 assert(move_is_ok(m1));
1830 assert(move_is_ok(m2));
1832 if (m2 == MOVE_NONE)
1835 // Case 1: The moving piece is the same in both moves
1841 // Case 2: The destination square for m2 was vacated by m1
1847 // Case 3: Moving through the vacated square
1848 if ( piece_is_slider(pos.piece_on(f2))
1849 && bit_is_set(squares_between(f2, t2), f1))
1852 // Case 4: The destination square for m2 is defended by the moving piece in m1
1853 p = pos.piece_on(t1);
1854 if (bit_is_set(pos.attacks_from(p, t1), t2))
1857 // Case 5: Discovered check, checking piece is the piece moved in m1
1858 if ( piece_is_slider(p)
1859 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1860 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1862 // discovered_check_candidates() works also if the Position's side to
1863 // move is the opposite of the checking piece.
1864 Color them = opposite_color(pos.side_to_move());
1865 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1867 if (bit_is_set(dcCandidates, f2))
1874 // value_is_mate() checks if the given value is a mate one
1875 // eventually compensated for the ply.
1877 bool value_is_mate(Value value) {
1879 assert(abs(value) <= VALUE_INFINITE);
1881 return value <= value_mated_in(PLY_MAX)
1882 || value >= value_mate_in(PLY_MAX);
1886 // move_is_killer() checks if the given move is among the
1887 // killer moves of that ply.
1889 bool move_is_killer(Move m, SearchStack* ss) {
1891 const Move* k = ss->killers;
1892 for (int i = 0; i < KILLER_MAX; i++, k++)
1900 // extension() decides whether a move should be searched with normal depth,
1901 // or with extended depth. Certain classes of moves (checking moves, in
1902 // particular) are searched with bigger depth than ordinary moves and in
1903 // any case are marked as 'dangerous'. Note that also if a move is not
1904 // extended, as example because the corresponding UCI option is set to zero,
1905 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1906 template <NodeType PvNode>
1907 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1908 bool singleEvasion, bool mateThreat, bool* dangerous) {
1910 assert(m != MOVE_NONE);
1912 Depth result = Depth(0);
1913 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1918 result += CheckExtension[PvNode];
1921 result += SingleEvasionExtension[PvNode];
1924 result += MateThreatExtension[PvNode];
1927 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1929 Color c = pos.side_to_move();
1930 if (relative_rank(c, move_to(m)) == RANK_7)
1932 result += PawnPushTo7thExtension[PvNode];
1935 if (pos.pawn_is_passed(c, move_to(m)))
1937 result += PassedPawnExtension[PvNode];
1942 if ( captureOrPromotion
1943 && pos.type_of_piece_on(move_to(m)) != PAWN
1944 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1945 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1946 && !move_is_promotion(m)
1949 result += PawnEndgameExtension[PvNode];
1954 && captureOrPromotion
1955 && pos.type_of_piece_on(move_to(m)) != PAWN
1956 && pos.see_sign(m) >= 0)
1962 return Min(result, OnePly);
1966 // connected_threat() tests whether it is safe to forward prune a move or if
1967 // is somehow coonected to the threat move returned by null search.
1969 bool connected_threat(const Position& pos, Move m, Move threat) {
1971 assert(move_is_ok(m));
1972 assert(threat && move_is_ok(threat));
1973 assert(!pos.move_is_check(m));
1974 assert(!pos.move_is_capture_or_promotion(m));
1975 assert(!pos.move_is_passed_pawn_push(m));
1977 Square mfrom, mto, tfrom, tto;
1979 mfrom = move_from(m);
1981 tfrom = move_from(threat);
1982 tto = move_to(threat);
1984 // Case 1: Don't prune moves which move the threatened piece
1988 // Case 2: If the threatened piece has value less than or equal to the
1989 // value of the threatening piece, don't prune move which defend it.
1990 if ( pos.move_is_capture(threat)
1991 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1992 || pos.type_of_piece_on(tfrom) == KING)
1993 && pos.move_attacks_square(m, tto))
1996 // Case 3: If the moving piece in the threatened move is a slider, don't
1997 // prune safe moves which block its ray.
1998 if ( piece_is_slider(pos.piece_on(tfrom))
1999 && bit_is_set(squares_between(tfrom, tto), mto)
2000 && pos.see_sign(m) >= 0)
2007 // ok_to_use_TT() returns true if a transposition table score
2008 // can be used at a given point in search.
2010 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2012 Value v = value_from_tt(tte->value(), ply);
2014 return ( tte->depth() >= depth
2015 || v >= Max(value_mate_in(PLY_MAX), beta)
2016 || v < Min(value_mated_in(PLY_MAX), beta))
2018 && ( (is_lower_bound(tte->type()) && v >= beta)
2019 || (is_upper_bound(tte->type()) && v < beta));
2023 // refine_eval() returns the transposition table score if
2024 // possible otherwise falls back on static position evaluation.
2026 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2031 Value v = value_from_tt(tte->value(), ply);
2033 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2034 || (is_upper_bound(tte->type()) && v < defaultEval))
2041 // update_history() registers a good move that produced a beta-cutoff
2042 // in history and marks as failures all the other moves of that ply.
2044 void update_history(const Position& pos, Move move, Depth depth,
2045 Move movesSearched[], int moveCount) {
2049 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2051 for (int i = 0; i < moveCount - 1; i++)
2053 m = movesSearched[i];
2057 if (!pos.move_is_capture_or_promotion(m))
2058 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2063 // update_killers() add a good move that produced a beta-cutoff
2064 // among the killer moves of that ply.
2066 void update_killers(Move m, SearchStack* ss) {
2068 if (m == ss->killers[0])
2071 for (int i = KILLER_MAX - 1; i > 0; i--)
2072 ss->killers[i] = ss->killers[i - 1];
2078 // update_gains() updates the gains table of a non-capture move given
2079 // the static position evaluation before and after the move.
2081 void update_gains(const Position& pos, Move m, Value before, Value after) {
2084 && before != VALUE_NONE
2085 && after != VALUE_NONE
2086 && pos.captured_piece() == NO_PIECE_TYPE
2087 && !move_is_castle(m)
2088 && !move_is_promotion(m))
2089 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2093 // current_search_time() returns the number of milliseconds which have passed
2094 // since the beginning of the current search.
2096 int current_search_time() {
2098 return get_system_time() - SearchStartTime;
2102 // nps() computes the current nodes/second count.
2106 int t = current_search_time();
2107 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2111 // poll() performs two different functions: It polls for user input, and it
2112 // looks at the time consumed so far and decides if it's time to abort the
2117 static int lastInfoTime;
2118 int t = current_search_time();
2123 // We are line oriented, don't read single chars
2124 std::string command;
2126 if (!std::getline(std::cin, command))
2129 if (command == "quit")
2132 PonderSearch = false;
2136 else if (command == "stop")
2139 PonderSearch = false;
2141 else if (command == "ponderhit")
2145 // Print search information
2149 else if (lastInfoTime > t)
2150 // HACK: Must be a new search where we searched less than
2151 // NodesBetweenPolls nodes during the first second of search.
2154 else if (t - lastInfoTime >= 1000)
2161 if (dbg_show_hit_rate)
2162 dbg_print_hit_rate();
2164 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2165 << " time " << t << " hashfull " << TT.full() << endl;
2168 // Should we stop the search?
2172 bool stillAtFirstMove = FirstRootMove
2173 && !AspirationFailLow
2174 && t > MaxSearchTime + ExtraSearchTime;
2176 bool noMoreTime = t > AbsoluteMaxSearchTime
2177 || stillAtFirstMove;
2179 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2180 || (ExactMaxTime && t >= ExactMaxTime)
2181 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2186 // ponderhit() is called when the program is pondering (i.e. thinking while
2187 // it's the opponent's turn to move) in order to let the engine know that
2188 // it correctly predicted the opponent's move.
2192 int t = current_search_time();
2193 PonderSearch = false;
2195 bool stillAtFirstMove = FirstRootMove
2196 && !AspirationFailLow
2197 && t > MaxSearchTime + ExtraSearchTime;
2199 bool noMoreTime = t > AbsoluteMaxSearchTime
2200 || stillAtFirstMove;
2202 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2207 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2209 void init_ss_array(SearchStack* ss) {
2211 for (int i = 0; i < 3; i++, ss++)
2219 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2220 // while the program is pondering. The point is to work around a wrinkle in
2221 // the UCI protocol: When pondering, the engine is not allowed to give a
2222 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2223 // We simply wait here until one of these commands is sent, and return,
2224 // after which the bestmove and pondermove will be printed (in id_loop()).
2226 void wait_for_stop_or_ponderhit() {
2228 std::string command;
2232 if (!std::getline(std::cin, command))
2235 if (command == "quit")
2240 else if (command == "ponderhit" || command == "stop")
2246 // print_pv_info() prints to standard output and eventually to log file information on
2247 // the current PV line. It is called at each iteration or after a new pv is found.
2249 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2251 cout << "info depth " << Iteration
2252 << " score " << value_to_string(value)
2253 << ((value >= beta) ? " lowerbound" :
2254 ((value <= alpha)? " upperbound" : ""))
2255 << " time " << current_search_time()
2256 << " nodes " << TM.nodes_searched()
2260 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2261 cout << ss->pv[j] << " ";
2267 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2268 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2270 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2271 TM.nodes_searched(), value, type, ss->pv) << endl;
2276 // init_thread() is the function which is called when a new thread is
2277 // launched. It simply calls the idle_loop() function with the supplied
2278 // threadID. There are two versions of this function; one for POSIX
2279 // threads and one for Windows threads.
2281 #if !defined(_MSC_VER)
2283 void* init_thread(void *threadID) {
2285 TM.idle_loop(*(int*)threadID, NULL);
2291 DWORD WINAPI init_thread(LPVOID threadID) {
2293 TM.idle_loop(*(int*)threadID, NULL);
2300 /// The ThreadsManager class
2302 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2303 // get_beta_counters() are getters/setters for the per thread
2304 // counters used to sort the moves at root.
2306 void ThreadsManager::resetNodeCounters() {
2308 for (int i = 0; i < MAX_THREADS; i++)
2309 threads[i].nodes = 0ULL;
2312 void ThreadsManager::resetBetaCounters() {
2314 for (int i = 0; i < MAX_THREADS; i++)
2315 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2318 int64_t ThreadsManager::nodes_searched() const {
2320 int64_t result = 0ULL;
2321 for (int i = 0; i < ActiveThreads; i++)
2322 result += threads[i].nodes;
2327 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2330 for (int i = 0; i < MAX_THREADS; i++)
2332 our += threads[i].betaCutOffs[us];
2333 their += threads[i].betaCutOffs[opposite_color(us)];
2338 // idle_loop() is where the threads are parked when they have no work to do.
2339 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2340 // object for which the current thread is the master.
2342 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2344 assert(threadID >= 0 && threadID < MAX_THREADS);
2348 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2349 // master should exit as last one.
2350 if (AllThreadsShouldExit)
2353 threads[threadID].state = THREAD_TERMINATED;
2357 // If we are not thinking, wait for a condition to be signaled
2358 // instead of wasting CPU time polling for work.
2359 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2362 assert(threadID != 0);
2363 threads[threadID].state = THREAD_SLEEPING;
2365 #if !defined(_MSC_VER)
2366 lock_grab(&WaitLock);
2367 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2368 pthread_cond_wait(&WaitCond, &WaitLock);
2369 lock_release(&WaitLock);
2371 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2375 // If thread has just woken up, mark it as available
2376 if (threads[threadID].state == THREAD_SLEEPING)
2377 threads[threadID].state = THREAD_AVAILABLE;
2379 // If this thread has been assigned work, launch a search
2380 if (threads[threadID].state == THREAD_WORKISWAITING)
2382 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2384 threads[threadID].state = THREAD_SEARCHING;
2386 if (threads[threadID].splitPoint->pvNode)
2387 sp_search<PV>(threads[threadID].splitPoint, threadID);
2389 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2391 assert(threads[threadID].state == THREAD_SEARCHING);
2393 threads[threadID].state = THREAD_AVAILABLE;
2396 // If this thread is the master of a split point and all slaves have
2397 // finished their work at this split point, return from the idle loop.
2399 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2401 if (i == ActiveThreads)
2403 // Because sp->slaves[] is reset under lock protection,
2404 // be sure sp->lock has been released before to return.
2405 lock_grab(&(sp->lock));
2406 lock_release(&(sp->lock));
2408 assert(threads[threadID].state == THREAD_AVAILABLE);
2410 threads[threadID].state = THREAD_SEARCHING;
2417 // init_threads() is called during startup. It launches all helper threads,
2418 // and initializes the split point stack and the global locks and condition
2421 void ThreadsManager::init_threads() {
2426 #if !defined(_MSC_VER)
2427 pthread_t pthread[1];
2430 // Initialize global locks
2431 lock_init(&MPLock, NULL);
2432 lock_init(&WaitLock, NULL);
2434 #if !defined(_MSC_VER)
2435 pthread_cond_init(&WaitCond, NULL);
2437 for (i = 0; i < MAX_THREADS; i++)
2438 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2441 // Initialize SplitPointStack locks
2442 for (i = 0; i < MAX_THREADS; i++)
2443 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2444 lock_init(&(SplitPointStack[i][j].lock), NULL);
2446 // Will be set just before program exits to properly end the threads
2447 AllThreadsShouldExit = false;
2449 // Threads will be put to sleep as soon as created
2450 AllThreadsShouldSleep = true;
2452 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2454 threads[0].state = THREAD_SEARCHING;
2455 for (i = 1; i < MAX_THREADS; i++)
2456 threads[i].state = THREAD_AVAILABLE;
2458 // Launch the helper threads
2459 for (i = 1; i < MAX_THREADS; i++)
2462 #if !defined(_MSC_VER)
2463 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2465 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2470 cout << "Failed to create thread number " << i << endl;
2471 Application::exit_with_failure();
2474 // Wait until the thread has finished launching and is gone to sleep
2475 while (threads[i].state != THREAD_SLEEPING) {}
2480 // exit_threads() is called when the program exits. It makes all the
2481 // helper threads exit cleanly.
2483 void ThreadsManager::exit_threads() {
2485 ActiveThreads = MAX_THREADS; // HACK
2486 AllThreadsShouldSleep = true; // HACK
2487 wake_sleeping_threads();
2489 // This makes the threads to exit idle_loop()
2490 AllThreadsShouldExit = true;
2492 // Wait for thread termination
2493 for (int i = 1; i < MAX_THREADS; i++)
2494 while (threads[i].state != THREAD_TERMINATED) {}
2496 // Now we can safely destroy the locks
2497 for (int i = 0; i < MAX_THREADS; i++)
2498 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2499 lock_destroy(&(SplitPointStack[i][j].lock));
2501 lock_destroy(&WaitLock);
2502 lock_destroy(&MPLock);
2506 // thread_should_stop() checks whether the thread should stop its search.
2507 // This can happen if a beta cutoff has occurred in the thread's currently
2508 // active split point, or in some ancestor of the current split point.
2510 bool ThreadsManager::thread_should_stop(int threadID) const {
2512 assert(threadID >= 0 && threadID < ActiveThreads);
2516 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2521 // thread_is_available() checks whether the thread with threadID "slave" is
2522 // available to help the thread with threadID "master" at a split point. An
2523 // obvious requirement is that "slave" must be idle. With more than two
2524 // threads, this is not by itself sufficient: If "slave" is the master of
2525 // some active split point, it is only available as a slave to the other
2526 // threads which are busy searching the split point at the top of "slave"'s
2527 // split point stack (the "helpful master concept" in YBWC terminology).
2529 bool ThreadsManager::thread_is_available(int slave, int master) const {
2531 assert(slave >= 0 && slave < ActiveThreads);
2532 assert(master >= 0 && master < ActiveThreads);
2533 assert(ActiveThreads > 1);
2535 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2538 // Make a local copy to be sure doesn't change under our feet
2539 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2541 if (localActiveSplitPoints == 0)
2542 // No active split points means that the thread is available as
2543 // a slave for any other thread.
2546 if (ActiveThreads == 2)
2549 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2550 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2551 // could have been set to 0 by another thread leading to an out of bound access.
2552 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2559 // available_thread_exists() tries to find an idle thread which is available as
2560 // a slave for the thread with threadID "master".
2562 bool ThreadsManager::available_thread_exists(int master) const {
2564 assert(master >= 0 && master < ActiveThreads);
2565 assert(ActiveThreads > 1);
2567 for (int i = 0; i < ActiveThreads; i++)
2568 if (thread_is_available(i, master))
2575 // split() does the actual work of distributing the work at a node between
2576 // several available threads. If it does not succeed in splitting the
2577 // node (because no idle threads are available, or because we have no unused
2578 // split point objects), the function immediately returns. If splitting is
2579 // possible, a SplitPoint object is initialized with all the data that must be
2580 // copied to the helper threads and we tell our helper threads that they have
2581 // been assigned work. This will cause them to instantly leave their idle loops
2582 // and call sp_search(). When all threads have returned from sp_search() then
2585 template <bool Fake>
2586 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2587 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2588 MovePicker* mp, int master, bool pvNode) {
2590 assert(*bestValue >= -VALUE_INFINITE);
2591 assert(*bestValue <= *alpha);
2592 assert(*alpha < beta);
2593 assert(beta <= VALUE_INFINITE);
2594 assert(depth > Depth(0));
2595 assert(master >= 0 && master < ActiveThreads);
2596 assert(ActiveThreads > 1);
2600 // If no other thread is available to help us, or if we have too many
2601 // active split points, don't split.
2602 if ( !available_thread_exists(master)
2603 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2605 lock_release(&MPLock);
2609 // Pick the next available split point object from the split point stack
2610 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2612 // Initialize the split point object
2613 splitPoint->parent = threads[master].splitPoint;
2614 splitPoint->stopRequest = false;
2615 splitPoint->depth = depth;
2616 splitPoint->mateThreat = mateThreat;
2617 splitPoint->alpha = *alpha;
2618 splitPoint->beta = beta;
2619 splitPoint->pvNode = pvNode;
2620 splitPoint->bestValue = *bestValue;
2621 splitPoint->mp = mp;
2622 splitPoint->moveCount = *moveCount;
2623 splitPoint->pos = &p;
2624 splitPoint->parentSstack = ss;
2625 for (int i = 0; i < ActiveThreads; i++)
2626 splitPoint->slaves[i] = 0;
2628 threads[master].splitPoint = splitPoint;
2629 threads[master].activeSplitPoints++;
2631 // If we are here it means we are not available
2632 assert(threads[master].state != THREAD_AVAILABLE);
2634 int workersCnt = 1; // At least the master is included
2636 // Allocate available threads setting state to THREAD_BOOKED
2637 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2638 if (thread_is_available(i, master))
2640 threads[i].state = THREAD_BOOKED;
2641 threads[i].splitPoint = splitPoint;
2642 splitPoint->slaves[i] = 1;
2646 assert(Fake || workersCnt > 1);
2648 // We can release the lock because slave threads are already booked and master is not available
2649 lock_release(&MPLock);
2651 // Tell the threads that they have work to do. This will make them leave
2652 // their idle loop. But before copy search stack tail for each thread.
2653 for (int i = 0; i < ActiveThreads; i++)
2654 if (i == master || splitPoint->slaves[i])
2656 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2658 assert(i == master || threads[i].state == THREAD_BOOKED);
2660 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2663 // Everything is set up. The master thread enters the idle loop, from
2664 // which it will instantly launch a search, because its state is
2665 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2666 // idle loop, which means that the main thread will return from the idle
2667 // loop when all threads have finished their work at this split point.
2668 idle_loop(master, splitPoint);
2670 // We have returned from the idle loop, which means that all threads are
2671 // finished. Update alpha and bestValue, and return.
2674 *alpha = splitPoint->alpha;
2675 *bestValue = splitPoint->bestValue;
2676 threads[master].activeSplitPoints--;
2677 threads[master].splitPoint = splitPoint->parent;
2679 lock_release(&MPLock);
2683 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2684 // to start a new search from the root.
2686 void ThreadsManager::wake_sleeping_threads() {
2688 assert(AllThreadsShouldSleep);
2689 assert(ActiveThreads > 0);
2691 AllThreadsShouldSleep = false;
2693 if (ActiveThreads == 1)
2696 #if !defined(_MSC_VER)
2697 pthread_mutex_lock(&WaitLock);
2698 pthread_cond_broadcast(&WaitCond);
2699 pthread_mutex_unlock(&WaitLock);
2701 for (int i = 1; i < MAX_THREADS; i++)
2702 SetEvent(SitIdleEvent[i]);
2708 // put_threads_to_sleep() makes all the threads go to sleep just before
2709 // to leave think(), at the end of the search. Threads should have already
2710 // finished the job and should be idle.
2712 void ThreadsManager::put_threads_to_sleep() {
2714 assert(!AllThreadsShouldSleep);
2716 // This makes the threads to go to sleep
2717 AllThreadsShouldSleep = true;
2720 /// The RootMoveList class
2722 // RootMoveList c'tor
2724 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2726 SearchStack ss[PLY_MAX_PLUS_2];
2727 MoveStack mlist[MaxRootMoves];
2729 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2731 // Generate all legal moves
2732 MoveStack* last = generate_moves(pos, mlist);
2734 // Add each move to the moves[] array
2735 for (MoveStack* cur = mlist; cur != last; cur++)
2737 bool includeMove = includeAllMoves;
2739 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2740 includeMove = (searchMoves[k] == cur->move);
2745 // Find a quick score for the move
2747 pos.do_move(cur->move, st);
2748 moves[count].move = cur->move;
2749 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2750 moves[count].pv[0] = cur->move;
2751 moves[count].pv[1] = MOVE_NONE;
2752 pos.undo_move(cur->move);
2759 // RootMoveList simple methods definitions
2761 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2763 moves[moveNum].nodes = nodes;
2764 moves[moveNum].cumulativeNodes += nodes;
2767 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2769 moves[moveNum].ourBeta = our;
2770 moves[moveNum].theirBeta = their;
2773 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2777 for (j = 0; pv[j] != MOVE_NONE; j++)
2778 moves[moveNum].pv[j] = pv[j];
2780 moves[moveNum].pv[j] = MOVE_NONE;
2784 // RootMoveList::sort() sorts the root move list at the beginning of a new
2787 void RootMoveList::sort() {
2789 sort_multipv(count - 1); // Sort all items
2793 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2794 // list by their scores and depths. It is used to order the different PVs
2795 // correctly in MultiPV mode.
2797 void RootMoveList::sort_multipv(int n) {
2801 for (i = 1; i <= n; i++)
2803 RootMove rm = moves[i];
2804 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2805 moves[j] = moves[j - 1];