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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
79 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
81 void resetNodeCounters();
82 void resetBetaCounters();
83 int64_t nodes_searched() const;
84 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
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] = { 7 * 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, 1)][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);
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(const Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 void sp_search(SplitPoint* sp, int threadID);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool move_is_killer(Move m, SearchStack* ss);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 bool connected_threat(const Position& pos, Move m, Move threat);
300 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
301 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
302 void update_killers(Move m, SearchStack* ss);
303 void update_gains(const Position& pos, Move move, Value before, Value after);
305 int current_search_time();
306 std::string value_to_uci(Value v);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack* ss, int size);
312 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 void insert_pv_in_tt(const Position& pos, Move pv[]);
314 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
329 /// init_threads(), exit_threads() and nodes_searched() are helpers to
330 /// give accessibility to some TM methods from outside of current file.
332 void init_threads() { TM.init_threads(); }
333 void exit_threads() { TM.exit_threads(); }
334 int64_t nodes_searched() { return TM.nodes_searched(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (OnePly == 2)
342 int hd; // half depth (OnePly == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
372 MovePicker mp(pos, MOVE_NONE, depth, H);
374 // If we are at the last ply we don't need to do and undo
375 // the moves, just to count them.
376 if (depth <= OnePly) // Replace with '<' to test also qsearch
378 while (mp.get_next_move()) sum++;
382 // Loop through all legal moves
384 while ((move = mp.get_next_move()) != MOVE_NONE)
386 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
387 sum += perft(pos, depth - OnePly);
394 /// think() is the external interface to Stockfish's search, and is called when
395 /// the program receives the UCI 'go' command. It initializes various
396 /// search-related global variables, and calls root_search(). It returns false
397 /// when a quit command is received during the search.
399 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
400 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
402 // Initialize global search variables
403 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
405 TM.resetNodeCounters();
406 SearchStartTime = get_system_time();
407 ExactMaxTime = maxTime;
410 InfiniteSearch = infinite;
411 PonderSearch = ponder;
412 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
414 // Look for a book move, only during games, not tests
415 if (UseTimeManagement && get_option_value_bool("OwnBook"))
417 if (get_option_value_string("Book File") != OpeningBook.file_name())
418 OpeningBook.open(get_option_value_string("Book File"));
420 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
421 if (bookMove != MOVE_NONE)
424 wait_for_stop_or_ponderhit();
426 cout << "bestmove " << bookMove << endl;
431 // Read UCI option values
432 TT.set_size(get_option_value_int("Hash"));
433 if (button_was_pressed("Clear Hash"))
436 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
437 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
438 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
439 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
440 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
441 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
442 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
443 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
444 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
445 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
446 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
447 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
449 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
450 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
451 MultiPV = get_option_value_int("MultiPV");
452 Chess960 = get_option_value_bool("UCI_Chess960");
453 UseLogFile = get_option_value_bool("Use Search Log");
456 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
458 read_weights(pos.side_to_move());
460 // Set the number of active threads
461 int newActiveThreads = get_option_value_int("Threads");
462 if (newActiveThreads != TM.active_threads())
464 TM.set_active_threads(newActiveThreads);
465 init_eval(TM.active_threads());
468 // Wake up sleeping threads
469 TM.wake_sleeping_threads();
472 int myTime = time[pos.side_to_move()];
473 int myIncrement = increment[pos.side_to_move()];
474 if (UseTimeManagement)
475 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
477 // Set best NodesBetweenPolls interval to avoid lagging under
478 // heavy time pressure.
480 NodesBetweenPolls = Min(MaxNodes, 30000);
481 else if (myTime && myTime < 1000)
482 NodesBetweenPolls = 1000;
483 else if (myTime && myTime < 5000)
484 NodesBetweenPolls = 5000;
486 NodesBetweenPolls = 30000;
488 // Write search information to log file
490 LogFile << "Searching: " << pos.to_fen() << endl
491 << "infinite: " << infinite
492 << " ponder: " << ponder
493 << " time: " << myTime
494 << " increment: " << myIncrement
495 << " moves to go: " << movesToGo << endl;
497 // We're ready to start thinking. Call the iterative deepening loop function
498 id_loop(pos, searchMoves);
503 TM.put_threads_to_sleep();
511 // id_loop() is the main iterative deepening loop. It calls root_search
512 // repeatedly with increasing depth until the allocated thinking time has
513 // been consumed, the user stops the search, or the maximum search depth is
516 Value id_loop(const Position& pos, Move searchMoves[]) {
518 Position p(pos, pos.thread());
519 SearchStack ss[PLY_MAX_PLUS_2];
520 Move pv[PLY_MAX_PLUS_2];
521 Move EasyMove = MOVE_NONE;
522 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
524 // Moves to search are verified, copied, scored and sorted
525 RootMoveList rml(p, searchMoves);
527 // Handle special case of searching on a mate/stale position
528 if (rml.move_count() == 0)
531 wait_for_stop_or_ponderhit();
533 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
536 // Print RootMoveList startup scoring to the standard output,
537 // so to output information also for iteration 1.
538 cout << "info depth " << 1
539 << "\ninfo depth " << 1
540 << " score " << value_to_uci(rml.get_move_score(0))
541 << " time " << current_search_time()
542 << " nodes " << TM.nodes_searched()
544 << " pv " << rml.get_move(0) << "\n";
549 init_ss_array(ss, PLY_MAX_PLUS_2);
550 pv[0] = pv[1] = MOVE_NONE;
551 ValueByIteration[1] = rml.get_move_score(0);
554 // Is one move significantly better than others after initial scoring ?
555 if ( rml.move_count() == 1
556 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
557 EasyMove = rml.get_move(0);
559 // Iterative deepening loop
560 while (Iteration < PLY_MAX)
562 // Initialize iteration
564 BestMoveChangesByIteration[Iteration] = 0;
566 cout << "info depth " << Iteration << endl;
568 // Calculate dynamic aspiration window based on previous iterations
569 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
571 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
572 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
574 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
575 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
577 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
578 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
581 // Search to the current depth, rml is updated and sorted, alpha and beta could change
582 value = root_search(p, ss, pv, rml, &alpha, &beta);
584 // Write PV to transposition table, in case the relevant entries have
585 // been overwritten during the search.
586 insert_pv_in_tt(p, pv);
589 break; // Value cannot be trusted. Break out immediately!
591 //Save info about search result
592 ValueByIteration[Iteration] = value;
594 // Drop the easy move if differs from the new best move
595 if (pv[0] != EasyMove)
596 EasyMove = MOVE_NONE;
598 if (UseTimeManagement)
601 bool stopSearch = false;
603 // Stop search early if there is only a single legal move,
604 // we search up to Iteration 6 anyway to get a proper score.
605 if (Iteration >= 6 && rml.move_count() == 1)
608 // Stop search early when the last two iterations returned a mate score
610 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
611 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
614 // Stop search early if one move seems to be much better than the others
615 int64_t nodes = TM.nodes_searched();
618 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
619 && current_search_time() > TimeMgr.available_time() / 16)
620 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
621 && current_search_time() > TimeMgr.available_time() / 32)))
624 // Add some extra time if the best move has changed during the last two iterations
625 if (Iteration > 5 && Iteration <= 50)
626 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
627 BestMoveChangesByIteration[Iteration-1]);
629 // Stop search if most of MaxSearchTime is consumed at the end of the
630 // iteration. We probably don't have enough time to search the first
631 // move at the next iteration anyway.
632 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
638 StopOnPonderhit = true;
644 if (MaxDepth && Iteration >= MaxDepth)
648 // If we are pondering or in infinite search, we shouldn't print the
649 // best move before we are told to do so.
650 if (!AbortSearch && (PonderSearch || InfiniteSearch))
651 wait_for_stop_or_ponderhit();
653 // Print final search statistics
654 cout << "info nodes " << TM.nodes_searched()
656 << " time " << current_search_time() << endl;
658 // Print the best move and the ponder move to the standard output
659 if (pv[0] == MOVE_NONE)
661 pv[0] = rml.get_move(0);
665 assert(pv[0] != MOVE_NONE);
667 cout << "bestmove " << pv[0];
669 if (pv[1] != MOVE_NONE)
670 cout << " ponder " << pv[1];
677 dbg_print_mean(LogFile);
679 if (dbg_show_hit_rate)
680 dbg_print_hit_rate(LogFile);
682 LogFile << "\nNodes: " << TM.nodes_searched()
683 << "\nNodes/second: " << nps()
684 << "\nBest move: " << move_to_san(p, pv[0]);
687 p.do_move(pv[0], st);
688 LogFile << "\nPonder move: "
689 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
692 return rml.get_move_score(0);
696 // root_search() is the function which searches the root node. It is
697 // similar to search_pv except that it uses a different move ordering
698 // scheme, prints some information to the standard output and handles
699 // the fail low/high loops.
701 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
708 Depth depth, ext, newDepth;
709 Value value, alpha, beta;
710 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
711 int researchCountFH, researchCountFL;
713 researchCountFH = researchCountFL = 0;
716 isCheck = pos.is_check();
718 // Step 1. Initialize node (polling is omitted at root)
719 ss->currentMove = ss->bestMove = MOVE_NONE;
721 // Step 2. Check for aborted search (omitted at root)
722 // Step 3. Mate distance pruning (omitted at root)
723 // Step 4. Transposition table lookup (omitted at root)
725 // Step 5. Evaluate the position statically
726 // At root we do this only to get reference value for child nodes
727 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
729 // Step 6. Razoring (omitted at root)
730 // Step 7. Static null move pruning (omitted at root)
731 // Step 8. Null move search with verification search (omitted at root)
732 // Step 9. Internal iterative deepening (omitted at root)
734 // Step extra. Fail low loop
735 // We start with small aspiration window and in case of fail low, we research
736 // with bigger window until we are not failing low anymore.
739 // Sort the moves before to (re)search
742 // Step 10. Loop through all moves in the root move list
743 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
745 // This is used by time management
746 FirstRootMove = (i == 0);
748 // Save the current node count before the move is searched
749 nodes = TM.nodes_searched();
751 // Reset beta cut-off counters
752 TM.resetBetaCounters();
754 // Pick the next root move, and print the move and the move number to
755 // the standard output.
756 move = ss->currentMove = rml.get_move(i);
758 if (current_search_time() >= 1000)
759 cout << "info currmove " << move
760 << " currmovenumber " << i + 1 << endl;
762 moveIsCheck = pos.move_is_check(move);
763 captureOrPromotion = pos.move_is_capture_or_promotion(move);
765 // Step 11. Decide the new search depth
766 depth = (Iteration - 2) * OnePly + InitialDepth;
767 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
768 newDepth = depth + ext;
770 // Step 12. Futility pruning (omitted at root)
772 // Step extra. Fail high loop
773 // If move fails high, we research with bigger window until we are not failing
775 value = - VALUE_INFINITE;
779 // Step 13. Make the move
780 pos.do_move(move, st, ci, moveIsCheck);
782 // Step extra. pv search
783 // We do pv search for first moves (i < MultiPV)
784 // and for fail high research (value > alpha)
785 if (i < MultiPV || value > alpha)
787 // Aspiration window is disabled in multi-pv case
789 alpha = -VALUE_INFINITE;
791 // Full depth PV search, done on first move or after a fail high
792 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
796 // Step 14. Reduced search
797 // if the move fails high will be re-searched at full depth
798 bool doFullDepthSearch = true;
800 if ( depth >= 3 * OnePly
802 && !captureOrPromotion
803 && !move_is_castle(move))
805 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
808 assert(newDepth-ss->reduction >= OnePly);
810 // Reduced depth non-pv search using alpha as upperbound
811 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
812 doFullDepthSearch = (value > alpha);
815 // The move failed high, but if reduction is very big we could
816 // face a false positive, retry with a less aggressive reduction,
817 // if the move fails high again then go with full depth search.
818 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
820 assert(newDepth - OnePly >= OnePly);
822 ss->reduction = OnePly;
823 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
824 doFullDepthSearch = (value > alpha);
826 ss->reduction = Depth(0); // Restore original reduction
829 // Step 15. Full depth search
830 if (doFullDepthSearch)
832 // Full depth non-pv search using alpha as upperbound
833 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
835 // If we are above alpha then research at same depth but as PV
836 // to get a correct score or eventually a fail high above beta.
838 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
842 // Step 16. Undo move
845 // Can we exit fail high loop ?
846 if (AbortSearch || value < beta)
849 // We are failing high and going to do a research. It's important to update
850 // the score before research in case we run out of time while researching.
851 rml.set_move_score(i, value);
853 extract_pv_from_tt(pos, move, pv);
854 rml.set_move_pv(i, pv);
856 // Print information to the standard output
857 print_pv_info(pos, pv, alpha, beta, value);
859 // Prepare for a research after a fail high, each time with a wider window
860 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
863 } // End of fail high loop
865 // Finished searching the move. If AbortSearch is true, the search
866 // was aborted because the user interrupted the search or because we
867 // ran out of time. In this case, the return value of the search cannot
868 // be trusted, and we break out of the loop without updating the best
873 // Remember beta-cutoff and searched nodes counts for this move. The
874 // info is used to sort the root moves for the next iteration.
876 TM.get_beta_counters(pos.side_to_move(), our, their);
877 rml.set_beta_counters(i, our, their);
878 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
880 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
881 assert(value < beta);
883 // Step 17. Check for new best move
884 if (value <= alpha && i >= MultiPV)
885 rml.set_move_score(i, -VALUE_INFINITE);
888 // PV move or new best move!
891 rml.set_move_score(i, value);
893 extract_pv_from_tt(pos, move, pv);
894 rml.set_move_pv(i, pv);
898 // We record how often the best move has been changed in each
899 // iteration. This information is used for time managment: When
900 // the best move changes frequently, we allocate some more time.
902 BestMoveChangesByIteration[Iteration]++;
904 // Print information to the standard output
905 print_pv_info(pos, pv, alpha, beta, value);
907 // Raise alpha to setup proper non-pv search upper bound
914 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
916 cout << "info multipv " << j + 1
917 << " score " << value_to_uci(rml.get_move_score(j))
918 << " depth " << (j <= i ? Iteration : Iteration - 1)
919 << " time " << current_search_time()
920 << " nodes " << TM.nodes_searched()
924 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
925 cout << rml.get_move_pv(j, k) << " ";
929 alpha = rml.get_move_score(Min(i, MultiPV - 1));
931 } // PV move or new best move
933 assert(alpha >= *alphaPtr);
935 AspirationFailLow = (alpha == *alphaPtr);
937 if (AspirationFailLow && StopOnPonderhit)
938 StopOnPonderhit = false;
941 // Can we exit fail low loop ?
942 if (AbortSearch || !AspirationFailLow)
945 // Prepare for a research after a fail low, each time with a wider window
946 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
951 // Sort the moves before to return
958 // search<>() is the main search function for both PV and non-PV nodes
960 template <NodeType PvNode>
961 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
963 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
964 assert(beta > alpha && beta <= VALUE_INFINITE);
965 assert(PvNode || alpha == beta - 1);
966 assert(ply > 0 && ply < PLY_MAX);
967 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
969 Move movesSearched[256];
972 const TTEntry *tte, *ttx;
974 Move ttMove, move, excludedMove, threatMove;
976 Value bestValue, value, oldAlpha;
977 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
978 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
979 bool mateThreat = false;
981 int threadID = pos.thread();
982 refinedValue = bestValue = value = -VALUE_INFINITE;
985 // Step 1. Initialize node and poll. Polling can abort search
986 TM.incrementNodeCounter(threadID);
987 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
988 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
990 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
996 // Step 2. Check for aborted search and immediate draw
997 if (AbortSearch || TM.thread_should_stop(threadID))
1000 if (pos.is_draw() || ply >= PLY_MAX - 1)
1003 // Step 3. Mate distance pruning
1004 alpha = Max(value_mated_in(ply), alpha);
1005 beta = Min(value_mate_in(ply+1), beta);
1009 // Step 4. Transposition table lookup
1011 // We don't want the score of a partial search to overwrite a previous full search
1012 // TT value, so we use a different position key in case of an excluded move exists.
1013 excludedMove = ss->excludedMove;
1014 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1016 tte = TT.retrieve(posKey);
1017 ttMove = (tte ? tte->move() : MOVE_NONE);
1019 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1020 // This is to avoid problems in the following areas:
1022 // * Repetition draw detection
1023 // * Fifty move rule detection
1024 // * Searching for a mate
1025 // * Printing of full PV line
1027 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1029 // Refresh tte entry to avoid aging
1030 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1032 ss->bestMove = ttMove; // Can be MOVE_NONE
1033 return value_from_tt(tte->value(), ply);
1036 // Step 5. Evaluate the position statically and
1037 // update gain statistics of parent move.
1038 isCheck = pos.is_check();
1040 ss->eval = VALUE_NONE;
1043 assert(tte->static_value() != VALUE_NONE);
1045 ss->eval = tte->static_value();
1046 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1047 refinedValue = refine_eval(tte, ss->eval, ply);
1051 refinedValue = ss->eval = evaluate(pos, ei);
1052 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1055 // Save gain for the parent non-capture move
1056 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1058 // Step 6. Razoring (is omitted in PV nodes)
1060 && depth < RazorDepth
1062 && refinedValue < beta - razor_margin(depth)
1063 && ttMove == MOVE_NONE
1064 && (ss-1)->currentMove != MOVE_NULL
1065 && !value_is_mate(beta)
1066 && !pos.has_pawn_on_7th(pos.side_to_move()))
1068 Value rbeta = beta - razor_margin(depth);
1069 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1071 // Logically we should return (v + razor_margin(depth)), but
1072 // surprisingly this did slightly weaker in tests.
1076 // Step 7. Static null move pruning (is omitted in PV nodes)
1077 // We're betting that the opponent doesn't have a move that will reduce
1078 // the score by more than futility_margin(depth) if we do a null move.
1080 && !ss->skipNullMove
1081 && depth < RazorDepth
1083 && refinedValue >= beta + futility_margin(depth, 0)
1084 && !value_is_mate(beta)
1085 && pos.non_pawn_material(pos.side_to_move()))
1086 return refinedValue - futility_margin(depth, 0);
1088 // Step 8. Null move search with verification search (is omitted in PV nodes)
1089 // When we jump directly to qsearch() we do a null move only if static value is
1090 // at least beta. Otherwise we do a null move if static value is not more than
1091 // NullMoveMargin under beta.
1093 && !ss->skipNullMove
1096 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1097 && !value_is_mate(beta)
1098 && pos.non_pawn_material(pos.side_to_move()))
1100 ss->currentMove = MOVE_NULL;
1102 // Null move dynamic reduction based on depth
1103 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1105 // Null move dynamic reduction based on value
1106 if (refinedValue - beta > PawnValueMidgame)
1109 pos.do_null_move(st);
1110 (ss+1)->skipNullMove = true;
1112 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1113 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1114 (ss+1)->skipNullMove = false;
1115 pos.undo_null_move();
1117 if (nullValue >= beta)
1119 // Do not return unproven mate scores
1120 if (nullValue >= value_mate_in(PLY_MAX))
1123 if (depth < 6 * OnePly)
1126 // Do verification search at high depths
1127 ss->skipNullMove = true;
1128 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1129 ss->skipNullMove = false;
1136 // The null move failed low, which means that we may be faced with
1137 // some kind of threat. If the previous move was reduced, check if
1138 // the move that refuted the null move was somehow connected to the
1139 // move which was reduced. If a connection is found, return a fail
1140 // low score (which will cause the reduced move to fail high in the
1141 // parent node, which will trigger a re-search with full depth).
1142 if (nullValue == value_mated_in(ply + 2))
1145 threatMove = (ss+1)->bestMove;
1146 if ( depth < ThreatDepth
1147 && (ss-1)->reduction
1148 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1153 // Step 9. Internal iterative deepening
1154 if ( depth >= IIDDepth[PvNode]
1155 && ttMove == MOVE_NONE
1156 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1158 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1160 ss->skipNullMove = true;
1161 search<PvNode>(pos, ss, alpha, beta, d, ply);
1162 ss->skipNullMove = false;
1164 ttMove = ss->bestMove;
1165 tte = TT.retrieve(posKey);
1168 // Expensive mate threat detection (only for PV nodes)
1170 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1172 // Initialize a MovePicker object for the current position
1173 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1175 ss->bestMove = MOVE_NONE;
1176 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1177 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1180 && !excludedMove // Do not allow recursive singular extension search
1181 && is_lower_bound(tte->type())
1182 && tte->depth() >= depth - 3 * OnePly;
1184 // Step 10. Loop through moves
1185 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1186 while ( bestValue < beta
1187 && (move = mp.get_next_move()) != MOVE_NONE
1188 && !TM.thread_should_stop(threadID))
1190 assert(move_is_ok(move));
1192 if (move == excludedMove)
1195 moveIsCheck = pos.move_is_check(move, ci);
1196 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1198 // Step 11. Decide the new search depth
1199 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1201 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1202 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1203 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1204 // lower then ttValue minus a margin then we extend ttMove.
1205 if ( singularExtensionNode
1206 && move == tte->move()
1209 // Avoid to do an expensive singular extension search on nodes where
1210 // such search have already been done in the past, so assume the last
1211 // singular extension search result is still valid.
1213 && depth < SingularExtensionDepth[PvNode] + 5 * OnePly
1214 && (ttx = TT.retrieve(pos.get_exclusion_key())) != NULL)
1216 if (is_upper_bound(ttx->type()))
1219 singularExtensionNode = false;
1222 Value ttValue = value_from_tt(tte->value(), ply);
1224 if (singularExtensionNode && abs(ttValue) < VALUE_KNOWN_WIN)
1226 Value b = ttValue - SingularExtensionMargin;
1227 ss->excludedMove = move;
1228 ss->skipNullMove = true;
1229 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1230 ss->skipNullMove = false;
1231 ss->excludedMove = MOVE_NONE;
1232 ss->bestMove = MOVE_NONE;
1238 newDepth = depth - OnePly + ext;
1240 // Update current move (this must be done after singular extension search)
1241 movesSearched[moveCount++] = ss->currentMove = move;
1243 // Step 12. Futility pruning (is omitted in PV nodes)
1245 && !captureOrPromotion
1249 && !move_is_castle(move))
1251 // Move count based pruning
1252 if ( moveCount >= futility_move_count(depth)
1253 && !(threatMove && connected_threat(pos, move, threatMove))
1254 && bestValue > value_mated_in(PLY_MAX))
1257 // Value based pruning
1258 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1259 // but fixing this made program slightly weaker.
1260 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1261 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1262 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1264 if (futilityValueScaled < beta)
1266 if (futilityValueScaled > bestValue)
1267 bestValue = futilityValueScaled;
1272 // Step 13. Make the move
1273 pos.do_move(move, st, ci, moveIsCheck);
1275 // Step extra. pv search (only in PV nodes)
1276 // The first move in list is the expected PV
1277 if (PvNode && moveCount == 1)
1278 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1279 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1282 // Step 14. Reduced depth search
1283 // If the move fails high will be re-searched at full depth.
1284 bool doFullDepthSearch = true;
1286 if ( depth >= 3 * OnePly
1287 && !captureOrPromotion
1289 && !move_is_castle(move)
1290 && !move_is_killer(move, ss))
1292 ss->reduction = reduction<PvNode>(depth, moveCount);
1295 Depth d = newDepth - ss->reduction;
1296 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1297 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1299 doFullDepthSearch = (value > alpha);
1302 // The move failed high, but if reduction is very big we could
1303 // face a false positive, retry with a less aggressive reduction,
1304 // if the move fails high again then go with full depth search.
1305 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1307 assert(newDepth - OnePly >= OnePly);
1309 ss->reduction = OnePly;
1310 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1311 doFullDepthSearch = (value > alpha);
1313 ss->reduction = Depth(0); // Restore original reduction
1316 // Step 15. Full depth search
1317 if (doFullDepthSearch)
1319 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1320 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1322 // Step extra. pv search (only in PV nodes)
1323 // Search only for possible new PV nodes, if instead value >= beta then
1324 // parent node fails low with value <= alpha and tries another move.
1325 if (PvNode && value > alpha && value < beta)
1326 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1327 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1331 // Step 16. Undo move
1332 pos.undo_move(move);
1334 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1336 // Step 17. Check for new best move
1337 if (value > bestValue)
1342 if (PvNode && value < beta) // We want always alpha < beta
1345 if (value == value_mate_in(ply + 1))
1346 ss->mateKiller = move;
1348 ss->bestMove = move;
1352 // Step 18. Check for split
1353 if ( depth >= MinimumSplitDepth
1354 && TM.active_threads() > 1
1356 && TM.available_thread_exists(threadID)
1358 && !TM.thread_should_stop(threadID)
1360 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1361 threatMove, mateThreat, &moveCount, &mp, PvNode);
1364 // Step 19. Check for mate and stalemate
1365 // All legal moves have been searched and if there are
1366 // no legal moves, it must be mate or stalemate.
1367 // If one move was excluded return fail low score.
1369 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1371 // Step 20. Update tables
1372 // If the search is not aborted, update the transposition table,
1373 // history counters, and killer moves.
1374 if (AbortSearch || TM.thread_should_stop(threadID))
1377 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1378 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1379 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1381 // Update killers and history only for non capture moves that fails high
1382 if (bestValue >= beta)
1384 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1385 if (!pos.move_is_capture_or_promotion(move))
1387 update_history(pos, move, depth, movesSearched, moveCount);
1388 update_killers(move, ss);
1392 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1398 // qsearch() is the quiescence search function, which is called by the main
1399 // search function when the remaining depth is zero (or, to be more precise,
1400 // less than OnePly).
1402 template <NodeType PvNode>
1403 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1405 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1406 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1407 assert(PvNode || alpha == beta - 1);
1409 assert(ply > 0 && ply < PLY_MAX);
1410 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1415 Value bestValue, value, futilityValue, futilityBase;
1416 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1418 Value oldAlpha = alpha;
1420 TM.incrementNodeCounter(pos.thread());
1421 ss->bestMove = ss->currentMove = MOVE_NONE;
1423 // Check for an instant draw or maximum ply reached
1424 if (pos.is_draw() || ply >= PLY_MAX - 1)
1427 // Transposition table lookup. At PV nodes, we don't use the TT for
1428 // pruning, but only for move ordering.
1429 tte = TT.retrieve(pos.get_key());
1430 ttMove = (tte ? tte->move() : MOVE_NONE);
1432 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1434 ss->bestMove = ttMove; // Can be MOVE_NONE
1435 return value_from_tt(tte->value(), ply);
1438 isCheck = pos.is_check();
1440 // Evaluate the position statically
1443 bestValue = futilityBase = -VALUE_INFINITE;
1444 ss->eval = VALUE_NONE;
1445 deepChecks = enoughMaterial = false;
1451 assert(tte->static_value() != VALUE_NONE);
1453 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1454 bestValue = tte->static_value();
1457 bestValue = evaluate(pos, ei);
1459 ss->eval = bestValue;
1460 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1462 // Stand pat. Return immediately if static value is at least beta
1463 if (bestValue >= beta)
1466 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1471 if (PvNode && bestValue > alpha)
1474 // If we are near beta then try to get a cutoff pushing checks a bit further
1475 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1477 // Futility pruning parameters, not needed when in check
1478 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1479 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1482 // Initialize a MovePicker object for the current position, and prepare
1483 // to search the moves. Because the depth is <= 0 here, only captures,
1484 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1485 // and we are near beta) will be generated.
1486 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1489 // Loop through the moves until no moves remain or a beta cutoff occurs
1490 while ( alpha < beta
1491 && (move = mp.get_next_move()) != MOVE_NONE)
1493 assert(move_is_ok(move));
1495 moveIsCheck = pos.move_is_check(move, ci);
1503 && !move_is_promotion(move)
1504 && !pos.move_is_passed_pawn_push(move))
1506 futilityValue = futilityBase
1507 + pos.endgame_value_of_piece_on(move_to(move))
1508 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1510 if (futilityValue < alpha)
1512 if (futilityValue > bestValue)
1513 bestValue = futilityValue;
1518 // Detect blocking evasions that are candidate to be pruned
1519 evasionPrunable = isCheck
1520 && bestValue > value_mated_in(PLY_MAX)
1521 && !pos.move_is_capture(move)
1522 && pos.type_of_piece_on(move_from(move)) != KING
1523 && !pos.can_castle(pos.side_to_move());
1525 // Don't search moves with negative SEE values
1527 && (!isCheck || evasionPrunable)
1529 && !move_is_promotion(move)
1530 && pos.see_sign(move) < 0)
1533 // Update current move
1534 ss->currentMove = move;
1536 // Make and search the move
1537 pos.do_move(move, st, ci, moveIsCheck);
1538 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1539 pos.undo_move(move);
1541 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1544 if (value > bestValue)
1550 ss->bestMove = move;
1555 // All legal moves have been searched. A special case: If we're in check
1556 // and no legal moves were found, it is checkmate.
1557 if (isCheck && bestValue == -VALUE_INFINITE)
1558 return value_mated_in(ply);
1560 // Update transposition table
1561 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1562 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1563 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1565 // Update killers only for checking moves that fails high
1566 if ( bestValue >= beta
1567 && !pos.move_is_capture_or_promotion(ss->bestMove))
1568 update_killers(ss->bestMove, ss);
1570 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1576 // sp_search() is used to search from a split point. This function is called
1577 // by each thread working at the split point. It is similar to the normal
1578 // search() function, but simpler. Because we have already probed the hash
1579 // table, done a null move search, and searched the first move before
1580 // splitting, we don't have to repeat all this work in sp_search(). We
1581 // also don't need to store anything to the hash table here: This is taken
1582 // care of after we return from the split point.
1584 template <NodeType PvNode>
1585 void sp_search(SplitPoint* sp, int threadID) {
1587 assert(threadID >= 0 && threadID < TM.active_threads());
1588 assert(TM.active_threads() > 1);
1592 Depth ext, newDepth;
1594 Value futilityValueScaled; // NonPV specific
1595 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1597 value = -VALUE_INFINITE;
1599 Position pos(*sp->pos, threadID);
1601 SearchStack* ss = sp->sstack[threadID] + 1;
1602 isCheck = pos.is_check();
1604 // Step 10. Loop through moves
1605 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1606 lock_grab(&(sp->lock));
1608 while ( sp->bestValue < sp->beta
1609 && (move = sp->mp->get_next_move()) != MOVE_NONE
1610 && !TM.thread_should_stop(threadID))
1612 moveCount = ++sp->moveCount;
1613 lock_release(&(sp->lock));
1615 assert(move_is_ok(move));
1617 moveIsCheck = pos.move_is_check(move, ci);
1618 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1620 // Step 11. Decide the new search depth
1621 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1622 newDepth = sp->depth - OnePly + ext;
1624 // Update current move
1625 ss->currentMove = move;
1627 // Step 12. Futility pruning (is omitted in PV nodes)
1629 && !captureOrPromotion
1632 && !move_is_castle(move))
1634 // Move count based pruning
1635 if ( moveCount >= futility_move_count(sp->depth)
1636 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1637 && sp->bestValue > value_mated_in(PLY_MAX))
1639 lock_grab(&(sp->lock));
1643 // Value based pruning
1644 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1645 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1646 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1648 if (futilityValueScaled < sp->beta)
1650 lock_grab(&(sp->lock));
1652 if (futilityValueScaled > sp->bestValue)
1653 sp->bestValue = futilityValueScaled;
1658 // Step 13. Make the move
1659 pos.do_move(move, st, ci, moveIsCheck);
1661 // Step 14. Reduced search
1662 // If the move fails high will be re-searched at full depth.
1663 bool doFullDepthSearch = true;
1665 if ( !captureOrPromotion
1667 && !move_is_castle(move)
1668 && !move_is_killer(move, ss))
1670 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1673 Value localAlpha = sp->alpha;
1674 Depth d = newDepth - ss->reduction;
1675 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1676 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1678 doFullDepthSearch = (value > localAlpha);
1681 // The move failed high, but if reduction is very big we could
1682 // face a false positive, retry with a less aggressive reduction,
1683 // if the move fails high again then go with full depth search.
1684 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1686 assert(newDepth - OnePly >= OnePly);
1688 ss->reduction = OnePly;
1689 Value localAlpha = sp->alpha;
1690 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1691 doFullDepthSearch = (value > localAlpha);
1693 ss->reduction = Depth(0); // Restore original reduction
1696 // Step 15. Full depth search
1697 if (doFullDepthSearch)
1699 Value localAlpha = sp->alpha;
1700 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1701 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1703 // Step extra. pv search (only in PV nodes)
1704 // Search only for possible new PV nodes, if instead value >= beta then
1705 // parent node fails low with value <= alpha and tries another move.
1706 if (PvNode && value > localAlpha && value < sp->beta)
1707 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1708 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1711 // Step 16. Undo move
1712 pos.undo_move(move);
1714 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1716 // Step 17. Check for new best move
1717 lock_grab(&(sp->lock));
1719 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1721 sp->bestValue = value;
1723 if (sp->bestValue > sp->alpha)
1725 if (!PvNode || value >= sp->beta)
1726 sp->stopRequest = true;
1728 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1731 sp->parentSstack->bestMove = ss->bestMove = move;
1736 /* Here we have the lock still grabbed */
1738 sp->slaves[threadID] = 0;
1740 lock_release(&(sp->lock));
1744 // connected_moves() tests whether two moves are 'connected' in the sense
1745 // that the first move somehow made the second move possible (for instance
1746 // if the moving piece is the same in both moves). The first move is assumed
1747 // to be the move that was made to reach the current position, while the
1748 // second move is assumed to be a move from the current position.
1750 bool connected_moves(const Position& pos, Move m1, Move m2) {
1752 Square f1, t1, f2, t2;
1755 assert(move_is_ok(m1));
1756 assert(move_is_ok(m2));
1758 if (m2 == MOVE_NONE)
1761 // Case 1: The moving piece is the same in both moves
1767 // Case 2: The destination square for m2 was vacated by m1
1773 // Case 3: Moving through the vacated square
1774 if ( piece_is_slider(pos.piece_on(f2))
1775 && bit_is_set(squares_between(f2, t2), f1))
1778 // Case 4: The destination square for m2 is defended by the moving piece in m1
1779 p = pos.piece_on(t1);
1780 if (bit_is_set(pos.attacks_from(p, t1), t2))
1783 // Case 5: Discovered check, checking piece is the piece moved in m1
1784 if ( piece_is_slider(p)
1785 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1786 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1788 // discovered_check_candidates() works also if the Position's side to
1789 // move is the opposite of the checking piece.
1790 Color them = opposite_color(pos.side_to_move());
1791 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1793 if (bit_is_set(dcCandidates, f2))
1800 // value_is_mate() checks if the given value is a mate one eventually
1801 // compensated for the ply.
1803 bool value_is_mate(Value value) {
1805 assert(abs(value) <= VALUE_INFINITE);
1807 return value <= value_mated_in(PLY_MAX)
1808 || value >= value_mate_in(PLY_MAX);
1812 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1813 // "plies to mate from the current ply". Non-mate scores are unchanged.
1814 // The function is called before storing a value to the transposition table.
1816 Value value_to_tt(Value v, int ply) {
1818 if (v >= value_mate_in(PLY_MAX))
1821 if (v <= value_mated_in(PLY_MAX))
1828 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1829 // the transposition table to a mate score corrected for the current ply.
1831 Value value_from_tt(Value v, int ply) {
1833 if (v >= value_mate_in(PLY_MAX))
1836 if (v <= value_mated_in(PLY_MAX))
1843 // move_is_killer() checks if the given move is among the killer moves
1845 bool move_is_killer(Move m, SearchStack* ss) {
1847 if (ss->killers[0] == m || ss->killers[1] == m)
1854 // extension() decides whether a move should be searched with normal depth,
1855 // or with extended depth. Certain classes of moves (checking moves, in
1856 // particular) are searched with bigger depth than ordinary moves and in
1857 // any case are marked as 'dangerous'. Note that also if a move is not
1858 // extended, as example because the corresponding UCI option is set to zero,
1859 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1860 template <NodeType PvNode>
1861 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1862 bool singleEvasion, bool mateThreat, bool* dangerous) {
1864 assert(m != MOVE_NONE);
1866 Depth result = Depth(0);
1867 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1871 if (moveIsCheck && pos.see_sign(m) >= 0)
1872 result += CheckExtension[PvNode];
1875 result += SingleEvasionExtension[PvNode];
1878 result += MateThreatExtension[PvNode];
1881 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1883 Color c = pos.side_to_move();
1884 if (relative_rank(c, move_to(m)) == RANK_7)
1886 result += PawnPushTo7thExtension[PvNode];
1889 if (pos.pawn_is_passed(c, move_to(m)))
1891 result += PassedPawnExtension[PvNode];
1896 if ( captureOrPromotion
1897 && pos.type_of_piece_on(move_to(m)) != PAWN
1898 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1899 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1900 && !move_is_promotion(m)
1903 result += PawnEndgameExtension[PvNode];
1908 && captureOrPromotion
1909 && pos.type_of_piece_on(move_to(m)) != PAWN
1910 && pos.see_sign(m) >= 0)
1916 return Min(result, OnePly);
1920 // connected_threat() tests whether it is safe to forward prune a move or if
1921 // is somehow coonected to the threat move returned by null search.
1923 bool connected_threat(const Position& pos, Move m, Move threat) {
1925 assert(move_is_ok(m));
1926 assert(threat && move_is_ok(threat));
1927 assert(!pos.move_is_check(m));
1928 assert(!pos.move_is_capture_or_promotion(m));
1929 assert(!pos.move_is_passed_pawn_push(m));
1931 Square mfrom, mto, tfrom, tto;
1933 mfrom = move_from(m);
1935 tfrom = move_from(threat);
1936 tto = move_to(threat);
1938 // Case 1: Don't prune moves which move the threatened piece
1942 // Case 2: If the threatened piece has value less than or equal to the
1943 // value of the threatening piece, don't prune move which defend it.
1944 if ( pos.move_is_capture(threat)
1945 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1946 || pos.type_of_piece_on(tfrom) == KING)
1947 && pos.move_attacks_square(m, tto))
1950 // Case 3: If the moving piece in the threatened move is a slider, don't
1951 // prune safe moves which block its ray.
1952 if ( piece_is_slider(pos.piece_on(tfrom))
1953 && bit_is_set(squares_between(tfrom, tto), mto)
1954 && pos.see_sign(m) >= 0)
1961 // ok_to_use_TT() returns true if a transposition table score
1962 // can be used at a given point in search.
1964 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1966 Value v = value_from_tt(tte->value(), ply);
1968 return ( tte->depth() >= depth
1969 || v >= Max(value_mate_in(PLY_MAX), beta)
1970 || v < Min(value_mated_in(PLY_MAX), beta))
1972 && ( (is_lower_bound(tte->type()) && v >= beta)
1973 || (is_upper_bound(tte->type()) && v < beta));
1977 // refine_eval() returns the transposition table score if
1978 // possible otherwise falls back on static position evaluation.
1980 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1984 Value v = value_from_tt(tte->value(), ply);
1986 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1987 || (is_upper_bound(tte->type()) && v < defaultEval))
1994 // update_history() registers a good move that produced a beta-cutoff
1995 // in history and marks as failures all the other moves of that ply.
1997 void update_history(const Position& pos, Move move, Depth depth,
1998 Move movesSearched[], int moveCount) {
2002 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2004 for (int i = 0; i < moveCount - 1; i++)
2006 m = movesSearched[i];
2010 if (!pos.move_is_capture_or_promotion(m))
2011 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2016 // update_killers() add a good move that produced a beta-cutoff
2017 // among the killer moves of that ply.
2019 void update_killers(Move m, SearchStack* ss) {
2021 if (m == ss->killers[0])
2024 ss->killers[1] = ss->killers[0];
2029 // update_gains() updates the gains table of a non-capture move given
2030 // the static position evaluation before and after the move.
2032 void update_gains(const Position& pos, Move m, Value before, Value after) {
2035 && before != VALUE_NONE
2036 && after != VALUE_NONE
2037 && pos.captured_piece() == NO_PIECE_TYPE
2038 && !move_is_special(m))
2039 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2043 // current_search_time() returns the number of milliseconds which have passed
2044 // since the beginning of the current search.
2046 int current_search_time() {
2048 return get_system_time() - SearchStartTime;
2052 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2054 std::string value_to_uci(Value v) {
2056 std::stringstream s;
2058 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2059 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2061 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2066 // nps() computes the current nodes/second count.
2070 int t = current_search_time();
2071 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2075 // poll() performs two different functions: It polls for user input, and it
2076 // looks at the time consumed so far and decides if it's time to abort the
2081 static int lastInfoTime;
2082 int t = current_search_time();
2087 // We are line oriented, don't read single chars
2088 std::string command;
2090 if (!std::getline(std::cin, command))
2093 if (command == "quit")
2096 PonderSearch = false;
2100 else if (command == "stop")
2103 PonderSearch = false;
2105 else if (command == "ponderhit")
2109 // Print search information
2113 else if (lastInfoTime > t)
2114 // HACK: Must be a new search where we searched less than
2115 // NodesBetweenPolls nodes during the first second of search.
2118 else if (t - lastInfoTime >= 1000)
2125 if (dbg_show_hit_rate)
2126 dbg_print_hit_rate();
2128 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2129 << " time " << t << endl;
2132 // Should we stop the search?
2136 bool stillAtFirstMove = FirstRootMove
2137 && !AspirationFailLow
2138 && t > TimeMgr.available_time();
2140 bool noMoreTime = t > TimeMgr.maximum_time()
2141 || stillAtFirstMove;
2143 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2144 || (ExactMaxTime && t >= ExactMaxTime)
2145 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2150 // ponderhit() is called when the program is pondering (i.e. thinking while
2151 // it's the opponent's turn to move) in order to let the engine know that
2152 // it correctly predicted the opponent's move.
2156 int t = current_search_time();
2157 PonderSearch = false;
2159 bool stillAtFirstMove = FirstRootMove
2160 && !AspirationFailLow
2161 && t > TimeMgr.available_time();
2163 bool noMoreTime = t > TimeMgr.maximum_time()
2164 || stillAtFirstMove;
2166 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2171 // init_ss_array() does a fast reset of the first entries of a SearchStack
2172 // array and of all the excludedMove and skipNullMove entries.
2174 void init_ss_array(SearchStack* ss, int size) {
2176 for (int i = 0; i < size; i++, ss++)
2178 ss->excludedMove = MOVE_NONE;
2179 ss->skipNullMove = false;
2180 ss->reduction = Depth(0);
2183 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2188 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2189 // while the program is pondering. The point is to work around a wrinkle in
2190 // the UCI protocol: When pondering, the engine is not allowed to give a
2191 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2192 // We simply wait here until one of these commands is sent, and return,
2193 // after which the bestmove and pondermove will be printed (in id_loop()).
2195 void wait_for_stop_or_ponderhit() {
2197 std::string command;
2201 if (!std::getline(std::cin, command))
2204 if (command == "quit")
2209 else if (command == "ponderhit" || command == "stop")
2215 // print_pv_info() prints to standard output and eventually to log file information on
2216 // the current PV line. It is called at each iteration or after a new pv is found.
2218 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2220 cout << "info depth " << Iteration
2221 << " score " << value_to_uci(value)
2222 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2223 << " time " << current_search_time()
2224 << " nodes " << TM.nodes_searched()
2228 for (Move* m = pv; *m != MOVE_NONE; m++)
2235 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2236 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2238 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2239 TM.nodes_searched(), value, t, pv) << endl;
2244 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2245 // the PV back into the TT. This makes sure the old PV moves are searched
2246 // first, even if the old TT entries have been overwritten.
2248 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2252 Position p(pos, pos.thread());
2256 for (int i = 0; pv[i] != MOVE_NONE; i++)
2258 tte = TT.retrieve(p.get_key());
2259 if (!tte || tte->move() != pv[i])
2261 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2262 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2264 p.do_move(pv[i], st);
2269 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2270 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2271 // allow to always have a ponder move even when we fail high at root and also a
2272 // long PV to print that is important for position analysis.
2274 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2278 Position p(pos, pos.thread());
2281 assert(bestMove != MOVE_NONE);
2284 p.do_move(pv[ply++], st);
2286 while ( (tte = TT.retrieve(p.get_key())) != NULL
2287 && tte->move() != MOVE_NONE
2288 && move_is_legal(p, tte->move())
2290 && (!p.is_draw() || ply < 2))
2292 pv[ply] = tte->move();
2293 p.do_move(pv[ply++], st);
2295 pv[ply] = MOVE_NONE;
2299 // init_thread() is the function which is called when a new thread is
2300 // launched. It simply calls the idle_loop() function with the supplied
2301 // threadID. There are two versions of this function; one for POSIX
2302 // threads and one for Windows threads.
2304 #if !defined(_MSC_VER)
2306 void* init_thread(void *threadID) {
2308 TM.idle_loop(*(int*)threadID, NULL);
2314 DWORD WINAPI init_thread(LPVOID threadID) {
2316 TM.idle_loop(*(int*)threadID, NULL);
2323 /// The ThreadsManager class
2325 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2326 // get_beta_counters() are getters/setters for the per thread
2327 // counters used to sort the moves at root.
2329 void ThreadsManager::resetNodeCounters() {
2331 for (int i = 0; i < MAX_THREADS; i++)
2332 threads[i].nodes = 0ULL;
2335 void ThreadsManager::resetBetaCounters() {
2337 for (int i = 0; i < MAX_THREADS; i++)
2338 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2341 int64_t ThreadsManager::nodes_searched() const {
2343 int64_t result = 0ULL;
2344 for (int i = 0; i < ActiveThreads; i++)
2345 result += threads[i].nodes;
2350 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2353 for (int i = 0; i < MAX_THREADS; i++)
2355 our += threads[i].betaCutOffs[us];
2356 their += threads[i].betaCutOffs[opposite_color(us)];
2361 // idle_loop() is where the threads are parked when they have no work to do.
2362 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2363 // object for which the current thread is the master.
2365 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2367 assert(threadID >= 0 && threadID < MAX_THREADS);
2371 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2372 // master should exit as last one.
2373 if (AllThreadsShouldExit)
2376 threads[threadID].state = THREAD_TERMINATED;
2380 // If we are not thinking, wait for a condition to be signaled
2381 // instead of wasting CPU time polling for work.
2382 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2385 assert(threadID != 0);
2386 threads[threadID].state = THREAD_SLEEPING;
2388 #if !defined(_MSC_VER)
2389 lock_grab(&WaitLock);
2390 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2391 pthread_cond_wait(&WaitCond, &WaitLock);
2392 lock_release(&WaitLock);
2394 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2398 // If thread has just woken up, mark it as available
2399 if (threads[threadID].state == THREAD_SLEEPING)
2400 threads[threadID].state = THREAD_AVAILABLE;
2402 // If this thread has been assigned work, launch a search
2403 if (threads[threadID].state == THREAD_WORKISWAITING)
2405 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2407 threads[threadID].state = THREAD_SEARCHING;
2409 if (threads[threadID].splitPoint->pvNode)
2410 sp_search<PV>(threads[threadID].splitPoint, threadID);
2412 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2414 assert(threads[threadID].state == THREAD_SEARCHING);
2416 threads[threadID].state = THREAD_AVAILABLE;
2419 // If this thread is the master of a split point and all slaves have
2420 // finished their work at this split point, return from the idle loop.
2422 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2424 if (i == ActiveThreads)
2426 // Because sp->slaves[] is reset under lock protection,
2427 // be sure sp->lock has been released before to return.
2428 lock_grab(&(sp->lock));
2429 lock_release(&(sp->lock));
2431 assert(threads[threadID].state == THREAD_AVAILABLE);
2433 threads[threadID].state = THREAD_SEARCHING;
2440 // init_threads() is called during startup. It launches all helper threads,
2441 // and initializes the split point stack and the global locks and condition
2444 void ThreadsManager::init_threads() {
2449 #if !defined(_MSC_VER)
2450 pthread_t pthread[1];
2453 // Initialize global locks
2455 lock_init(&WaitLock);
2457 #if !defined(_MSC_VER)
2458 pthread_cond_init(&WaitCond, NULL);
2460 for (i = 0; i < MAX_THREADS; i++)
2461 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2464 // Initialize splitPoints[] locks
2465 for (i = 0; i < MAX_THREADS; i++)
2466 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2467 lock_init(&(threads[i].splitPoints[j].lock));
2469 // Will be set just before program exits to properly end the threads
2470 AllThreadsShouldExit = false;
2472 // Threads will be put to sleep as soon as created
2473 AllThreadsShouldSleep = true;
2475 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2477 threads[0].state = THREAD_SEARCHING;
2478 for (i = 1; i < MAX_THREADS; i++)
2479 threads[i].state = THREAD_AVAILABLE;
2481 // Launch the helper threads
2482 for (i = 1; i < MAX_THREADS; i++)
2485 #if !defined(_MSC_VER)
2486 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2488 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2493 cout << "Failed to create thread number " << i << endl;
2494 Application::exit_with_failure();
2497 // Wait until the thread has finished launching and is gone to sleep
2498 while (threads[i].state != THREAD_SLEEPING) {}
2503 // exit_threads() is called when the program exits. It makes all the
2504 // helper threads exit cleanly.
2506 void ThreadsManager::exit_threads() {
2508 ActiveThreads = MAX_THREADS; // HACK
2509 AllThreadsShouldSleep = true; // HACK
2510 wake_sleeping_threads();
2512 // This makes the threads to exit idle_loop()
2513 AllThreadsShouldExit = true;
2515 // Wait for thread termination
2516 for (int i = 1; i < MAX_THREADS; i++)
2517 while (threads[i].state != THREAD_TERMINATED) {}
2519 // Now we can safely destroy the locks
2520 for (int i = 0; i < MAX_THREADS; i++)
2521 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2522 lock_destroy(&(threads[i].splitPoints[j].lock));
2524 lock_destroy(&WaitLock);
2525 lock_destroy(&MPLock);
2529 // thread_should_stop() checks whether the thread should stop its search.
2530 // This can happen if a beta cutoff has occurred in the thread's currently
2531 // active split point, or in some ancestor of the current split point.
2533 bool ThreadsManager::thread_should_stop(int threadID) const {
2535 assert(threadID >= 0 && threadID < ActiveThreads);
2539 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2544 // thread_is_available() checks whether the thread with threadID "slave" is
2545 // available to help the thread with threadID "master" at a split point. An
2546 // obvious requirement is that "slave" must be idle. With more than two
2547 // threads, this is not by itself sufficient: If "slave" is the master of
2548 // some active split point, it is only available as a slave to the other
2549 // threads which are busy searching the split point at the top of "slave"'s
2550 // split point stack (the "helpful master concept" in YBWC terminology).
2552 bool ThreadsManager::thread_is_available(int slave, int master) const {
2554 assert(slave >= 0 && slave < ActiveThreads);
2555 assert(master >= 0 && master < ActiveThreads);
2556 assert(ActiveThreads > 1);
2558 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2561 // Make a local copy to be sure doesn't change under our feet
2562 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2564 if (localActiveSplitPoints == 0)
2565 // No active split points means that the thread is available as
2566 // a slave for any other thread.
2569 if (ActiveThreads == 2)
2572 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2573 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2574 // could have been set to 0 by another thread leading to an out of bound access.
2575 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2582 // available_thread_exists() tries to find an idle thread which is available as
2583 // a slave for the thread with threadID "master".
2585 bool ThreadsManager::available_thread_exists(int master) const {
2587 assert(master >= 0 && master < ActiveThreads);
2588 assert(ActiveThreads > 1);
2590 for (int i = 0; i < ActiveThreads; i++)
2591 if (thread_is_available(i, master))
2598 // split() does the actual work of distributing the work at a node between
2599 // several available threads. If it does not succeed in splitting the
2600 // node (because no idle threads are available, or because we have no unused
2601 // split point objects), the function immediately returns. If splitting is
2602 // possible, a SplitPoint object is initialized with all the data that must be
2603 // copied to the helper threads and we tell our helper threads that they have
2604 // been assigned work. This will cause them to instantly leave their idle loops
2605 // and call sp_search(). When all threads have returned from sp_search() then
2608 template <bool Fake>
2609 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2610 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2611 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2613 assert(ply > 0 && ply < PLY_MAX);
2614 assert(*bestValue >= -VALUE_INFINITE);
2615 assert(*bestValue <= *alpha);
2616 assert(*alpha < beta);
2617 assert(beta <= VALUE_INFINITE);
2618 assert(depth > Depth(0));
2619 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2620 assert(ActiveThreads > 1);
2622 int i, master = p.thread();
2623 Thread& masterThread = threads[master];
2627 // If no other thread is available to help us, or if we have too many
2628 // active split points, don't split.
2629 if ( !available_thread_exists(master)
2630 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2632 lock_release(&MPLock);
2636 // Pick the next available split point object from the split point stack
2637 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2639 // Initialize the split point object
2640 splitPoint.parent = masterThread.splitPoint;
2641 splitPoint.stopRequest = false;
2642 splitPoint.ply = ply;
2643 splitPoint.depth = depth;
2644 splitPoint.threatMove = threatMove;
2645 splitPoint.mateThreat = mateThreat;
2646 splitPoint.alpha = *alpha;
2647 splitPoint.beta = beta;
2648 splitPoint.pvNode = pvNode;
2649 splitPoint.bestValue = *bestValue;
2651 splitPoint.moveCount = *moveCount;
2652 splitPoint.pos = &p;
2653 splitPoint.parentSstack = ss;
2654 for (i = 0; i < ActiveThreads; i++)
2655 splitPoint.slaves[i] = 0;
2657 masterThread.splitPoint = &splitPoint;
2659 // If we are here it means we are not available
2660 assert(masterThread.state != THREAD_AVAILABLE);
2662 int workersCnt = 1; // At least the master is included
2664 // Allocate available threads setting state to THREAD_BOOKED
2665 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2666 if (thread_is_available(i, master))
2668 threads[i].state = THREAD_BOOKED;
2669 threads[i].splitPoint = &splitPoint;
2670 splitPoint.slaves[i] = 1;
2674 assert(Fake || workersCnt > 1);
2676 // We can release the lock because slave threads are already booked and master is not available
2677 lock_release(&MPLock);
2679 // Tell the threads that they have work to do. This will make them leave
2680 // their idle loop. But before copy search stack tail for each thread.
2681 for (i = 0; i < ActiveThreads; i++)
2682 if (i == master || splitPoint.slaves[i])
2684 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2686 assert(i == master || threads[i].state == THREAD_BOOKED);
2688 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2691 // Everything is set up. The master thread enters the idle loop, from
2692 // which it will instantly launch a search, because its state is
2693 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2694 // idle loop, which means that the main thread will return from the idle
2695 // loop when all threads have finished their work at this split point.
2696 idle_loop(master, &splitPoint);
2698 // We have returned from the idle loop, which means that all threads are
2699 // finished. Update alpha and bestValue, and return.
2702 *alpha = splitPoint.alpha;
2703 *bestValue = splitPoint.bestValue;
2704 masterThread.activeSplitPoints--;
2705 masterThread.splitPoint = splitPoint.parent;
2707 lock_release(&MPLock);
2711 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2712 // to start a new search from the root.
2714 void ThreadsManager::wake_sleeping_threads() {
2716 assert(AllThreadsShouldSleep);
2717 assert(ActiveThreads > 0);
2719 AllThreadsShouldSleep = false;
2721 if (ActiveThreads == 1)
2724 #if !defined(_MSC_VER)
2725 pthread_mutex_lock(&WaitLock);
2726 pthread_cond_broadcast(&WaitCond);
2727 pthread_mutex_unlock(&WaitLock);
2729 for (int i = 1; i < MAX_THREADS; i++)
2730 SetEvent(SitIdleEvent[i]);
2736 // put_threads_to_sleep() makes all the threads go to sleep just before
2737 // to leave think(), at the end of the search. Threads should have already
2738 // finished the job and should be idle.
2740 void ThreadsManager::put_threads_to_sleep() {
2742 assert(!AllThreadsShouldSleep);
2744 // This makes the threads to go to sleep
2745 AllThreadsShouldSleep = true;
2748 /// The RootMoveList class
2750 // RootMoveList c'tor
2752 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2754 SearchStack ss[PLY_MAX_PLUS_2];
2755 MoveStack mlist[MaxRootMoves];
2757 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2759 // Initialize search stack
2760 init_ss_array(ss, PLY_MAX_PLUS_2);
2761 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2762 ss[0].eval = VALUE_NONE;
2764 // Generate all legal moves
2765 MoveStack* last = generate_moves(pos, mlist);
2767 // Add each move to the moves[] array
2768 for (MoveStack* cur = mlist; cur != last; cur++)
2770 bool includeMove = includeAllMoves;
2772 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2773 includeMove = (searchMoves[k] == cur->move);
2778 // Find a quick score for the move
2779 pos.do_move(cur->move, st);
2780 ss[0].currentMove = cur->move;
2781 moves[count].move = cur->move;
2782 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2783 moves[count].pv[0] = cur->move;
2784 moves[count].pv[1] = MOVE_NONE;
2785 pos.undo_move(cur->move);
2792 // RootMoveList simple methods definitions
2794 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2796 moves[moveNum].nodes = nodes;
2797 moves[moveNum].cumulativeNodes += nodes;
2800 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2802 moves[moveNum].ourBeta = our;
2803 moves[moveNum].theirBeta = their;
2806 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2810 for (j = 0; pv[j] != MOVE_NONE; j++)
2811 moves[moveNum].pv[j] = pv[j];
2813 moves[moveNum].pv[j] = MOVE_NONE;
2817 // RootMoveList::sort() sorts the root move list at the beginning of a new
2820 void RootMoveList::sort() {
2822 sort_multipv(count - 1); // Sort all items
2826 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2827 // list by their scores and depths. It is used to order the different PVs
2828 // correctly in MultiPV mode.
2830 void RootMoveList::sort_multipv(int n) {
2834 for (i = 1; i <= n; i++)
2836 RootMove rm = moves[i];
2837 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2838 moves[j] = moves[j - 1];