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++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_threads();
86 void put_threads_to_sleep();
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
97 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
98 Thread threads[MAX_THREADS];
100 Lock MPLock, WaitLock;
102 #if !defined(_MSC_VER)
103 pthread_cond_t WaitCond;
105 HANDLE SitIdleEvent[MAX_THREADS];
111 // RootMove struct is used for moves at the root at the tree. For each
112 // root move, we store a score, a node count, and a PV (really a refutation
113 // in the case of moves which fail low).
117 RootMove() : mp_score(0), nodes(0), cumulativeNodes(0) {}
119 // RootMove::operator<() is the comparison function used when
120 // sorting the moves. A move m1 is considered to be better
121 // than a move m2 if it has a higher score, or if the moves
122 // have equal score but m1 has the higher beta cut-off count.
123 bool operator<(const RootMove& m) const {
125 return score != m.score ? score < m.score : mp_score <= m.mp_score;
131 int64_t nodes, cumulativeNodes;
132 Move pv[PLY_MAX_PLUS_2];
136 // The RootMoveList class is essentially an array of RootMove objects, with
137 // a handful of methods for accessing the data in the individual moves.
142 RootMoveList(Position& pos, Move searchMoves[]);
144 int move_count() const { return count; }
145 Move get_move(int moveNum) const { return moves[moveNum].move; }
146 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
147 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
148 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
149 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
150 void score_moves(const Position& pos);
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_move_pv(int moveNum, const Move pv[]);
155 void sort_multipv(int n);
158 static const int MaxRootMoves = 500;
159 RootMove moves[MaxRootMoves];
164 // When formatting a move for std::cout we must know if we are in Chess960
165 // or not. To keep using the handy operator<<() on the move the trick is to
166 // embed this flag in the stream itself. Function-like named enum set960 is
167 // used as a custom manipulator and the stream internal general-purpose array,
168 // accessed through ios_base::iword(), is used to pass the flag to the move's
169 // operator<<() that will use it to properly format castling moves.
172 std::ostream& operator<< (std::ostream& os, const set960& m) {
174 os.iword(0) = int(m);
183 // Maximum depth for razoring
184 const Depth RazorDepth = 4 * ONE_PLY;
186 // Dynamic razoring margin based on depth
187 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
189 // Step 8. Null move search with verification search
191 // Null move margin. A null move search will not be done if the static
192 // evaluation of the position is more than NullMoveMargin below beta.
193 const Value NullMoveMargin = Value(0x200);
195 // Maximum depth for use of dynamic threat detection when null move fails low
196 const Depth ThreatDepth = 5 * ONE_PLY;
198 // Step 9. Internal iterative deepening
200 // Minimum depth for use of internal iterative deepening
201 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
203 // At Non-PV nodes we do an internal iterative deepening search
204 // when the static evaluation is bigger then beta - IIDMargin.
205 const Value IIDMargin = Value(0x100);
207 // Step 11. Decide the new search depth
209 // Extensions. Configurable UCI options
210 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
211 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
212 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
214 // Minimum depth for use of singular extension
215 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
217 // If the TT move is at least SingularExtensionMargin better then the
218 // remaining ones we will extend it.
219 const Value SingularExtensionMargin = Value(0x20);
221 // Step 12. Futility pruning
223 // Futility margin for quiescence search
224 const Value FutilityMarginQS = Value(0x80);
226 // Futility lookup tables (initialized at startup) and their getter functions
227 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
228 int FutilityMoveCountArray[32]; // [depth]
230 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
231 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
233 // Step 14. Reduced search
235 // Reduction lookup tables (initialized at startup) and their getter functions
236 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
238 template <NodeType PV>
239 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
241 // Common adjustments
243 // Search depth at iteration 1
244 const Depth InitialDepth = ONE_PLY;
246 // Easy move margin. An easy move candidate must be at least this much
247 // better than the second best move.
248 const Value EasyMoveMargin = Value(0x200);
256 // Scores and number of times the best move changed for each iteration
257 Value ValueByIteration[PLY_MAX_PLUS_2];
258 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
260 // Search window management
266 // Time managment variables
267 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
268 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
269 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
274 std::ofstream LogFile;
276 // Multi-threads related variables
277 Depth MinimumSplitDepth;
278 int MaxThreadsPerSplitPoint;
279 ThreadsManager ThreadsMgr;
281 // Node counters, used only by thread[0] but try to keep in different cache
282 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
284 int NodesBetweenPolls = 30000;
291 Value id_loop(const Position& pos, Move searchMoves[]);
292 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
294 template <NodeType PvNode>
295 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
297 template <NodeType PvNode>
298 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
300 template <NodeType PvNode>
301 void sp_search(SplitPoint* sp, int threadID);
303 template <NodeType PvNode>
304 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
306 bool connected_moves(const Position& pos, Move m1, Move m2);
307 bool value_is_mate(Value value);
308 Value value_to_tt(Value v, int ply);
309 Value value_from_tt(Value v, int ply);
310 bool move_is_killer(Move m, SearchStack* ss);
311 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
312 bool connected_threat(const Position& pos, Move m, Move threat);
313 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
314 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
315 void update_killers(Move m, SearchStack* ss);
316 void update_gains(const Position& pos, Move move, Value before, Value after);
318 int current_search_time();
319 std::string value_to_uci(Value v);
323 void wait_for_stop_or_ponderhit();
324 void init_ss_array(SearchStack* ss, int size);
325 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
326 void insert_pv_in_tt(const Position& pos, Move pv[]);
327 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
329 #if !defined(_MSC_VER)
330 void *init_thread(void *threadID);
332 DWORD WINAPI init_thread(LPVOID threadID);
342 /// init_threads(), exit_threads() and nodes_searched() are helpers to
343 /// give accessibility to some TM methods from outside of current file.
345 void init_threads() { ThreadsMgr.init_threads(); }
346 void exit_threads() { ThreadsMgr.exit_threads(); }
347 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
350 /// init_search() is called during startup. It initializes various lookup tables
354 int d; // depth (ONE_PLY == 2)
355 int hd; // half depth (ONE_PLY == 1)
358 // Init reductions array
359 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
361 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
362 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
363 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
364 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
367 // Init futility margins array
368 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
369 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
371 // Init futility move count array
372 for (d = 0; d < 32; d++)
373 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
377 /// perft() is our utility to verify move generation is bug free. All the legal
378 /// moves up to given depth are generated and counted and the sum returned.
380 int perft(Position& pos, Depth depth)
382 MoveStack mlist[256];
387 // Generate all legal moves
388 MoveStack* last = generate_moves(pos, mlist);
390 // If we are at the last ply we don't need to do and undo
391 // the moves, just to count them.
392 if (depth <= ONE_PLY)
393 return int(last - mlist);
395 // Loop through all legal moves
397 for (MoveStack* cur = mlist; cur != last; cur++)
400 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
401 sum += perft(pos, depth - ONE_PLY);
408 /// think() is the external interface to Stockfish's search, and is called when
409 /// the program receives the UCI 'go' command. It initializes various
410 /// search-related global variables, and calls root_search(). It returns false
411 /// when a quit command is received during the search.
413 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
414 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
416 // Initialize global search variables
417 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
419 ThreadsMgr.resetNodeCounters();
420 SearchStartTime = get_system_time();
421 ExactMaxTime = maxTime;
424 InfiniteSearch = infinite;
425 PonderSearch = ponder;
426 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
428 // Look for a book move, only during games, not tests
429 if (UseTimeManagement && get_option_value_bool("OwnBook"))
431 if (get_option_value_string("Book File") != OpeningBook.file_name())
432 OpeningBook.open(get_option_value_string("Book File"));
434 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
435 if (bookMove != MOVE_NONE)
438 wait_for_stop_or_ponderhit();
440 cout << "bestmove " << bookMove << endl;
445 // Read UCI option values
446 TT.set_size(get_option_value_int("Hash"));
447 if (button_was_pressed("Clear Hash"))
450 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
451 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
452 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
453 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
454 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
455 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
456 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
457 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
458 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
459 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
460 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
461 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
463 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
464 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
465 MultiPV = get_option_value_int("MultiPV");
466 UseLogFile = get_option_value_bool("Use Search Log");
469 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
471 read_weights(pos.side_to_move());
473 // Set the number of active threads
474 int newActiveThreads = get_option_value_int("Threads");
475 if (newActiveThreads != ThreadsMgr.active_threads())
477 ThreadsMgr.set_active_threads(newActiveThreads);
478 init_eval(ThreadsMgr.active_threads());
481 // Wake up sleeping threads
482 ThreadsMgr.wake_sleeping_threads();
485 int myTime = time[pos.side_to_move()];
486 int myIncrement = increment[pos.side_to_move()];
487 if (UseTimeManagement)
488 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
490 // Set best NodesBetweenPolls interval to avoid lagging under
491 // heavy time pressure.
493 NodesBetweenPolls = Min(MaxNodes, 30000);
494 else if (myTime && myTime < 1000)
495 NodesBetweenPolls = 1000;
496 else if (myTime && myTime < 5000)
497 NodesBetweenPolls = 5000;
499 NodesBetweenPolls = 30000;
501 // Write search information to log file
503 LogFile << "Searching: " << pos.to_fen() << endl
504 << "infinite: " << infinite
505 << " ponder: " << ponder
506 << " time: " << myTime
507 << " increment: " << myIncrement
508 << " moves to go: " << movesToGo << endl;
510 // We're ready to start thinking. Call the iterative deepening loop function
511 id_loop(pos, searchMoves);
516 ThreadsMgr.put_threads_to_sleep();
524 // id_loop() is the main iterative deepening loop. It calls root_search
525 // repeatedly with increasing depth until the allocated thinking time has
526 // been consumed, the user stops the search, or the maximum search depth is
529 Value id_loop(const Position& pos, Move searchMoves[]) {
531 Position p(pos, pos.thread());
532 SearchStack ss[PLY_MAX_PLUS_2];
533 Move pv[PLY_MAX_PLUS_2];
534 Move EasyMove = MOVE_NONE;
535 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
537 // Moves to search are verified, copied, scored and sorted
538 RootMoveList rml(p, searchMoves);
540 // Handle special case of searching on a mate/stale position
541 if (rml.move_count() == 0)
544 wait_for_stop_or_ponderhit();
546 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
549 // Print RootMoveList startup scoring to the standard output,
550 // so to output information also for iteration 1.
551 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
552 << "info depth " << 1
553 << "\ninfo depth " << 1
554 << " score " << value_to_uci(rml.get_move_score(0))
555 << " time " << current_search_time()
556 << " nodes " << ThreadsMgr.nodes_searched()
558 << " pv " << rml.get_move(0) << "\n";
563 init_ss_array(ss, PLY_MAX_PLUS_2);
564 pv[0] = pv[1] = MOVE_NONE;
565 ValueByIteration[1] = rml.get_move_score(0);
568 // Is one move significantly better than others after initial scoring ?
569 if ( rml.move_count() == 1
570 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
571 EasyMove = rml.get_move(0);
573 // Iterative deepening loop
574 while (Iteration < PLY_MAX)
576 // Initialize iteration
578 BestMoveChangesByIteration[Iteration] = 0;
580 cout << "info depth " << Iteration << endl;
582 // Calculate dynamic aspiration window based on previous iterations
583 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
585 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
586 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
588 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
589 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
591 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
592 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
595 // Search to the current depth, rml is updated and sorted, alpha and beta could change
596 value = root_search(p, ss, pv, rml, &alpha, &beta);
598 // Write PV to transposition table, in case the relevant entries have
599 // been overwritten during the search.
600 insert_pv_in_tt(p, pv);
603 break; // Value cannot be trusted. Break out immediately!
605 //Save info about search result
606 ValueByIteration[Iteration] = value;
608 // Drop the easy move if differs from the new best move
609 if (pv[0] != EasyMove)
610 EasyMove = MOVE_NONE;
612 if (UseTimeManagement)
615 bool stopSearch = false;
617 // Stop search early if there is only a single legal move,
618 // we search up to Iteration 6 anyway to get a proper score.
619 if (Iteration >= 6 && rml.move_count() == 1)
622 // Stop search early when the last two iterations returned a mate score
624 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
625 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
628 // Stop search early if one move seems to be much better than the others
629 int64_t nodes = ThreadsMgr.nodes_searched();
632 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
633 && current_search_time() > TimeMgr.available_time() / 16)
634 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
635 && current_search_time() > TimeMgr.available_time() / 32)))
638 // Add some extra time if the best move has changed during the last two iterations
639 if (Iteration > 5 && Iteration <= 50)
640 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
641 BestMoveChangesByIteration[Iteration-1]);
643 // Stop search if most of MaxSearchTime is consumed at the end of the
644 // iteration. We probably don't have enough time to search the first
645 // move at the next iteration anyway.
646 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
652 StopOnPonderhit = true;
658 if (MaxDepth && Iteration >= MaxDepth)
662 // If we are pondering or in infinite search, we shouldn't print the
663 // best move before we are told to do so.
664 if (!AbortSearch && (PonderSearch || InfiniteSearch))
665 wait_for_stop_or_ponderhit();
667 // Print final search statistics
668 cout << "info nodes " << ThreadsMgr.nodes_searched()
670 << " time " << current_search_time() << endl;
672 // Print the best move and the ponder move to the standard output
673 if (pv[0] == MOVE_NONE)
675 pv[0] = rml.get_move(0);
679 assert(pv[0] != MOVE_NONE);
681 cout << "bestmove " << pv[0];
683 if (pv[1] != MOVE_NONE)
684 cout << " ponder " << pv[1];
691 dbg_print_mean(LogFile);
693 if (dbg_show_hit_rate)
694 dbg_print_hit_rate(LogFile);
696 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
697 << "\nNodes/second: " << nps()
698 << "\nBest move: " << move_to_san(p, pv[0]);
701 p.do_move(pv[0], st);
702 LogFile << "\nPonder move: "
703 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
706 return rml.get_move_score(0);
710 // root_search() is the function which searches the root node. It is
711 // similar to search_pv except that it uses a different move ordering
712 // scheme, prints some information to the standard output and handles
713 // the fail low/high loops.
715 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
722 Depth depth, ext, newDepth;
723 Value value, alpha, beta;
724 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
725 int researchCountFH, researchCountFL;
727 researchCountFH = researchCountFL = 0;
730 isCheck = pos.is_check();
731 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
733 // Step 1. Initialize node (polling is omitted at root)
734 ss->currentMove = ss->bestMove = MOVE_NONE;
736 // Step 2. Check for aborted search (omitted at root)
737 // Step 3. Mate distance pruning (omitted at root)
738 // Step 4. Transposition table lookup (omitted at root)
740 // Step 5. Evaluate the position statically
741 // At root we do this only to get reference value for child nodes
742 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, margins);
744 // Step 6. Razoring (omitted at root)
745 // Step 7. Static null move pruning (omitted at root)
746 // Step 8. Null move search with verification search (omitted at root)
747 // Step 9. Internal iterative deepening (omitted at root)
749 // Step extra. Fail low loop
750 // We start with small aspiration window and in case of fail low, we research
751 // with bigger window until we are not failing low anymore.
754 // Sort the moves before to (re)search
755 rml.score_moves(pos);
758 // Step 10. Loop through all moves in the root move list
759 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
761 // This is used by time management
762 FirstRootMove = (i == 0);
764 // Save the current node count before the move is searched
765 nodes = ThreadsMgr.nodes_searched();
767 // Pick the next root move, and print the move and the move number to
768 // the standard output.
769 move = ss->currentMove = rml.get_move(i);
771 if (current_search_time() >= 1000)
772 cout << "info currmove " << move
773 << " currmovenumber " << i + 1 << endl;
775 moveIsCheck = pos.move_is_check(move);
776 captureOrPromotion = pos.move_is_capture_or_promotion(move);
778 // Step 11. Decide the new search depth
779 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
780 newDepth = depth + ext;
782 // Step 12. Futility pruning (omitted at root)
784 // Step extra. Fail high loop
785 // If move fails high, we research with bigger window until we are not failing
787 value = - VALUE_INFINITE;
791 // Step 13. Make the move
792 pos.do_move(move, st, ci, moveIsCheck);
794 // Step extra. pv search
795 // We do pv search for first moves (i < MultiPV)
796 // and for fail high research (value > alpha)
797 if (i < MultiPV || value > alpha)
799 // Aspiration window is disabled in multi-pv case
801 alpha = -VALUE_INFINITE;
803 // Full depth PV search, done on first move or after a fail high
804 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
808 // Step 14. Reduced search
809 // if the move fails high will be re-searched at full depth
810 bool doFullDepthSearch = true;
812 if ( depth >= 3 * ONE_PLY
814 && !captureOrPromotion
815 && !move_is_castle(move))
817 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
820 assert(newDepth-ss->reduction >= ONE_PLY);
822 // Reduced depth non-pv search using alpha as upperbound
823 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
824 doFullDepthSearch = (value > alpha);
827 // The move failed high, but if reduction is very big we could
828 // face a false positive, retry with a less aggressive reduction,
829 // if the move fails high again then go with full depth search.
830 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
832 assert(newDepth - ONE_PLY >= ONE_PLY);
834 ss->reduction = ONE_PLY;
835 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
836 doFullDepthSearch = (value > alpha);
838 ss->reduction = DEPTH_ZERO; // Restore original reduction
841 // Step 15. Full depth search
842 if (doFullDepthSearch)
844 // Full depth non-pv search using alpha as upperbound
845 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
847 // If we are above alpha then research at same depth but as PV
848 // to get a correct score or eventually a fail high above beta.
850 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
854 // Step 16. Undo move
857 // Can we exit fail high loop ?
858 if (AbortSearch || value < beta)
861 // We are failing high and going to do a research. It's important to update
862 // the score before research in case we run out of time while researching.
863 rml.set_move_score(i, value);
865 extract_pv_from_tt(pos, move, pv);
866 rml.set_move_pv(i, pv);
868 // Print information to the standard output
869 print_pv_info(pos, pv, alpha, beta, value);
871 // Prepare for a research after a fail high, each time with a wider window
872 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
875 } // End of fail high loop
877 // Finished searching the move. If AbortSearch is true, the search
878 // was aborted because the user interrupted the search or because we
879 // ran out of time. In this case, the return value of the search cannot
880 // be trusted, and we break out of the loop without updating the best
885 // Remember searched nodes counts for this move
886 rml.set_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
888 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
889 assert(value < beta);
891 // Step 17. Check for new best move
892 if (value <= alpha && i >= MultiPV)
893 rml.set_move_score(i, -VALUE_INFINITE);
896 // PV move or new best move!
899 rml.set_move_score(i, value);
901 extract_pv_from_tt(pos, move, pv);
902 rml.set_move_pv(i, pv);
906 // We record how often the best move has been changed in each
907 // iteration. This information is used for time managment: When
908 // the best move changes frequently, we allocate some more time.
910 BestMoveChangesByIteration[Iteration]++;
912 // Print information to the standard output
913 print_pv_info(pos, pv, alpha, beta, value);
915 // Raise alpha to setup proper non-pv search upper bound
922 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
924 cout << "info multipv " << j + 1
925 << " score " << value_to_uci(rml.get_move_score(j))
926 << " depth " << (j <= i ? Iteration : Iteration - 1)
927 << " time " << current_search_time()
928 << " nodes " << ThreadsMgr.nodes_searched()
932 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
933 cout << rml.get_move_pv(j, k) << " ";
937 alpha = rml.get_move_score(Min(i, MultiPV - 1));
939 } // PV move or new best move
941 assert(alpha >= *alphaPtr);
943 AspirationFailLow = (alpha == *alphaPtr);
945 if (AspirationFailLow && StopOnPonderhit)
946 StopOnPonderhit = false;
949 // Can we exit fail low loop ?
950 if (AbortSearch || !AspirationFailLow)
953 // Prepare for a research after a fail low, each time with a wider window
954 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
959 // Sort the moves before to return
966 // search<>() is the main search function for both PV and non-PV nodes
968 template <NodeType PvNode>
969 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
971 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
972 assert(beta > alpha && beta <= VALUE_INFINITE);
973 assert(PvNode || alpha == beta - 1);
974 assert(ply > 0 && ply < PLY_MAX);
975 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
977 Move movesSearched[256];
982 Move ttMove, move, excludedMove, threatMove;
984 Value bestValue, value, oldAlpha;
985 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
986 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
987 bool mateThreat = false;
989 int threadID = pos.thread();
990 refinedValue = bestValue = value = -VALUE_INFINITE;
993 // Step 1. Initialize node and poll. Polling can abort search
994 ThreadsMgr.incrementNodeCounter(threadID);
995 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
996 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
998 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1004 // Step 2. Check for aborted search and immediate draw
1005 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1008 if (pos.is_draw() || ply >= PLY_MAX - 1)
1011 // Step 3. Mate distance pruning
1012 alpha = Max(value_mated_in(ply), alpha);
1013 beta = Min(value_mate_in(ply+1), beta);
1017 // Step 4. Transposition table lookup
1019 // We don't want the score of a partial search to overwrite a previous full search
1020 // TT value, so we use a different position key in case of an excluded move exists.
1021 excludedMove = ss->excludedMove;
1022 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1024 tte = TT.retrieve(posKey);
1025 ttMove = (tte ? tte->move() : MOVE_NONE);
1027 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1028 // This is to avoid problems in the following areas:
1030 // * Repetition draw detection
1031 // * Fifty move rule detection
1032 // * Searching for a mate
1033 // * Printing of full PV line
1035 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1037 // Refresh tte entry to avoid aging
1038 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1040 ss->bestMove = ttMove; // Can be MOVE_NONE
1041 return value_from_tt(tte->value(), ply);
1044 // Step 5. Evaluate the position statically and
1045 // update gain statistics of parent move.
1046 isCheck = pos.is_check();
1048 ss->eval = VALUE_NONE;
1051 assert(tte->static_value() != VALUE_NONE);
1053 ss->eval = tte->static_value();
1054 margins[pos.side_to_move()] = tte->static_value_margin();
1055 refinedValue = refine_eval(tte, ss->eval, ply);
1059 refinedValue = ss->eval = evaluate(pos, margins);
1060 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1063 // Save gain for the parent non-capture move
1064 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1066 // Step 6. Razoring (is omitted in PV nodes)
1068 && depth < RazorDepth
1070 && refinedValue < beta - razor_margin(depth)
1071 && ttMove == MOVE_NONE
1072 && (ss-1)->currentMove != MOVE_NULL
1073 && !value_is_mate(beta)
1074 && !pos.has_pawn_on_7th(pos.side_to_move()))
1076 Value rbeta = beta - razor_margin(depth);
1077 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1079 // Logically we should return (v + razor_margin(depth)), but
1080 // surprisingly this did slightly weaker in tests.
1084 // Step 7. Static null move pruning (is omitted in PV nodes)
1085 // We're betting that the opponent doesn't have a move that will reduce
1086 // the score by more than futility_margin(depth) if we do a null move.
1088 && !ss->skipNullMove
1089 && depth < RazorDepth
1091 && refinedValue >= beta + futility_margin(depth, 0)
1092 && !value_is_mate(beta)
1093 && pos.non_pawn_material(pos.side_to_move()))
1094 return refinedValue - futility_margin(depth, 0);
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1097 // When we jump directly to qsearch() we do a null move only if static value is
1098 // at least beta. Otherwise we do a null move if static value is not more than
1099 // NullMoveMargin under beta.
1101 && !ss->skipNullMove
1104 && refinedValue >= beta - (depth >= 4 * ONE_PLY ? NullMoveMargin : 0)
1105 && !value_is_mate(beta)
1106 && pos.non_pawn_material(pos.side_to_move()))
1108 ss->currentMove = MOVE_NULL;
1110 // Null move dynamic reduction based on depth
1111 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1113 // Null move dynamic reduction based on value
1114 if (refinedValue - beta > PawnValueMidgame)
1117 pos.do_null_move(st);
1118 (ss+1)->skipNullMove = true;
1120 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1121 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1122 (ss+1)->skipNullMove = false;
1123 pos.undo_null_move();
1125 if (nullValue >= beta)
1127 // Do not return unproven mate scores
1128 if (nullValue >= value_mate_in(PLY_MAX))
1131 if (depth < 6 * ONE_PLY)
1134 // Do verification search at high depths
1135 ss->skipNullMove = true;
1136 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1137 ss->skipNullMove = false;
1144 // The null move failed low, which means that we may be faced with
1145 // some kind of threat. If the previous move was reduced, check if
1146 // the move that refuted the null move was somehow connected to the
1147 // move which was reduced. If a connection is found, return a fail
1148 // low score (which will cause the reduced move to fail high in the
1149 // parent node, which will trigger a re-search with full depth).
1150 if (nullValue == value_mated_in(ply + 2))
1153 threatMove = (ss+1)->bestMove;
1154 if ( depth < ThreatDepth
1155 && (ss-1)->reduction
1156 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1161 // Step 9. Internal iterative deepening
1162 if ( depth >= IIDDepth[PvNode]
1163 && ttMove == MOVE_NONE
1164 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1166 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1168 ss->skipNullMove = true;
1169 search<PvNode>(pos, ss, alpha, beta, d, ply);
1170 ss->skipNullMove = false;
1172 ttMove = ss->bestMove;
1173 tte = TT.retrieve(posKey);
1176 // Expensive mate threat detection (only for PV nodes)
1178 mateThreat = pos.has_mate_threat();
1180 // Initialize a MovePicker object for the current position
1181 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1183 ss->bestMove = MOVE_NONE;
1184 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1185 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1188 && !excludedMove // Do not allow recursive singular extension search
1189 && (tte->type() & VALUE_TYPE_LOWER)
1190 && tte->depth() >= depth - 3 * ONE_PLY;
1192 // Step 10. Loop through moves
1193 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1194 while ( bestValue < beta
1195 && (move = mp.get_next_move()) != MOVE_NONE
1196 && !ThreadsMgr.thread_should_stop(threadID))
1198 assert(move_is_ok(move));
1200 if (move == excludedMove)
1203 moveIsCheck = pos.move_is_check(move, ci);
1204 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1206 // Step 11. Decide the new search depth
1207 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1209 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1210 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1211 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1212 // lower then ttValue minus a margin then we extend ttMove.
1213 if ( singularExtensionNode
1214 && move == tte->move()
1217 Value ttValue = value_from_tt(tte->value(), ply);
1219 if (abs(ttValue) < VALUE_KNOWN_WIN)
1221 Value b = ttValue - SingularExtensionMargin;
1222 ss->excludedMove = move;
1223 ss->skipNullMove = true;
1224 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1225 ss->skipNullMove = false;
1226 ss->excludedMove = MOVE_NONE;
1227 ss->bestMove = MOVE_NONE;
1233 newDepth = depth - ONE_PLY + ext;
1235 // Update current move (this must be done after singular extension search)
1236 movesSearched[moveCount++] = ss->currentMove = move;
1238 // Step 12. Futility pruning (is omitted in PV nodes)
1240 && !captureOrPromotion
1244 && !move_is_castle(move))
1246 // Move count based pruning
1247 if ( moveCount >= futility_move_count(depth)
1248 && !(threatMove && connected_threat(pos, move, threatMove))
1249 && bestValue > value_mated_in(PLY_MAX))
1252 // Value based pruning
1253 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1254 // but fixing this made program slightly weaker.
1255 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1256 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1257 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1259 if (futilityValueScaled < beta)
1261 if (futilityValueScaled > bestValue)
1262 bestValue = futilityValueScaled;
1267 // Step 13. Make the move
1268 pos.do_move(move, st, ci, moveIsCheck);
1270 // Step extra. pv search (only in PV nodes)
1271 // The first move in list is the expected PV
1272 if (PvNode && moveCount == 1)
1273 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1274 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1277 // Step 14. Reduced depth search
1278 // If the move fails high will be re-searched at full depth.
1279 bool doFullDepthSearch = true;
1281 if ( depth >= 3 * ONE_PLY
1282 && !captureOrPromotion
1284 && !move_is_castle(move)
1285 && !move_is_killer(move, ss))
1287 ss->reduction = reduction<PvNode>(depth, moveCount);
1290 Depth d = newDepth - ss->reduction;
1291 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1292 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1294 doFullDepthSearch = (value > alpha);
1297 // The move failed high, but if reduction is very big we could
1298 // face a false positive, retry with a less aggressive reduction,
1299 // if the move fails high again then go with full depth search.
1300 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1302 assert(newDepth - ONE_PLY >= ONE_PLY);
1304 ss->reduction = ONE_PLY;
1305 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1306 doFullDepthSearch = (value > alpha);
1308 ss->reduction = DEPTH_ZERO; // Restore original reduction
1311 // Step 15. Full depth search
1312 if (doFullDepthSearch)
1314 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1315 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1317 // Step extra. pv search (only in PV nodes)
1318 // Search only for possible new PV nodes, if instead value >= beta then
1319 // parent node fails low with value <= alpha and tries another move.
1320 if (PvNode && value > alpha && value < beta)
1321 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1322 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1326 // Step 16. Undo move
1327 pos.undo_move(move);
1329 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1331 // Step 17. Check for new best move
1332 if (value > bestValue)
1337 if (PvNode && value < beta) // We want always alpha < beta
1340 if (value == value_mate_in(ply + 1))
1341 ss->mateKiller = move;
1343 ss->bestMove = move;
1347 // Step 18. Check for split
1348 if ( depth >= MinimumSplitDepth
1349 && ThreadsMgr.active_threads() > 1
1351 && ThreadsMgr.available_thread_exists(threadID)
1353 && !ThreadsMgr.thread_should_stop(threadID)
1355 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1356 threatMove, mateThreat, &moveCount, &mp, PvNode);
1359 // Step 19. Check for mate and stalemate
1360 // All legal moves have been searched and if there are
1361 // no legal moves, it must be mate or stalemate.
1362 // If one move was excluded return fail low score.
1364 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1366 // Step 20. Update tables
1367 // If the search is not aborted, update the transposition table,
1368 // history counters, and killer moves.
1369 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1372 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1373 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1374 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, margins[pos.side_to_move()]);
1376 // Update killers and history only for non capture moves that fails high
1377 if ( bestValue >= beta
1378 && !pos.move_is_capture_or_promotion(move))
1380 update_history(pos, move, depth, movesSearched, moveCount);
1381 update_killers(move, ss);
1384 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1390 // qsearch() is the quiescence search function, which is called by the main
1391 // search function when the remaining depth is zero (or, to be more precise,
1392 // less than ONE_PLY).
1394 template <NodeType PvNode>
1395 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1397 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1398 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1399 assert(PvNode || alpha == beta - 1);
1401 assert(ply > 0 && ply < PLY_MAX);
1402 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1407 Value bestValue, value, futilityValue, futilityBase;
1408 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1410 Value oldAlpha = alpha;
1412 ThreadsMgr.incrementNodeCounter(pos.thread());
1413 ss->bestMove = ss->currentMove = MOVE_NONE;
1415 // Check for an instant draw or maximum ply reached
1416 if (pos.is_draw() || ply >= PLY_MAX - 1)
1419 // Transposition table lookup. At PV nodes, we don't use the TT for
1420 // pruning, but only for move ordering.
1421 tte = TT.retrieve(pos.get_key());
1422 ttMove = (tte ? tte->move() : MOVE_NONE);
1424 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1426 ss->bestMove = ttMove; // Can be MOVE_NONE
1427 return value_from_tt(tte->value(), ply);
1430 isCheck = pos.is_check();
1432 // Evaluate the position statically
1435 bestValue = futilityBase = -VALUE_INFINITE;
1436 ss->eval = VALUE_NONE;
1437 deepChecks = enoughMaterial = false;
1443 assert(tte->static_value() != VALUE_NONE);
1445 margins[pos.side_to_move()] = tte->static_value_margin();
1446 bestValue = tte->static_value();
1449 bestValue = evaluate(pos, margins);
1451 ss->eval = bestValue;
1452 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1454 // Stand pat. Return immediately if static value is at least beta
1455 if (bestValue >= beta)
1458 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1463 if (PvNode && bestValue > alpha)
1466 // If we are near beta then try to get a cutoff pushing checks a bit further
1467 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1469 // Futility pruning parameters, not needed when in check
1470 futilityBase = bestValue + FutilityMarginQS + margins[pos.side_to_move()];
1471 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1474 // Initialize a MovePicker object for the current position, and prepare
1475 // to search the moves. Because the depth is <= 0 here, only captures,
1476 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1477 // and we are near beta) will be generated.
1478 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1481 // Loop through the moves until no moves remain or a beta cutoff occurs
1482 while ( alpha < beta
1483 && (move = mp.get_next_move()) != MOVE_NONE)
1485 assert(move_is_ok(move));
1487 moveIsCheck = pos.move_is_check(move, ci);
1495 && !move_is_promotion(move)
1496 && !pos.move_is_passed_pawn_push(move))
1498 futilityValue = futilityBase
1499 + pos.endgame_value_of_piece_on(move_to(move))
1500 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1502 if (futilityValue < alpha)
1504 if (futilityValue > bestValue)
1505 bestValue = futilityValue;
1510 // Detect blocking evasions that are candidate to be pruned
1511 evasionPrunable = isCheck
1512 && bestValue > value_mated_in(PLY_MAX)
1513 && !pos.move_is_capture(move)
1514 && pos.type_of_piece_on(move_from(move)) != KING
1515 && !pos.can_castle(pos.side_to_move());
1517 // Don't search moves with negative SEE values
1519 && (!isCheck || evasionPrunable)
1521 && !move_is_promotion(move)
1522 && pos.see_sign(move) < 0)
1525 // Update current move
1526 ss->currentMove = move;
1528 // Make and search the move
1529 pos.do_move(move, st, ci, moveIsCheck);
1530 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1531 pos.undo_move(move);
1533 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1536 if (value > bestValue)
1542 ss->bestMove = move;
1547 // All legal moves have been searched. A special case: If we're in check
1548 // and no legal moves were found, it is checkmate.
1549 if (isCheck && bestValue == -VALUE_INFINITE)
1550 return value_mated_in(ply);
1552 // Update transposition table
1553 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1554 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1555 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, margins[pos.side_to_move()]);
1557 // Update killers only for checking moves that fails high
1558 if ( bestValue >= beta
1559 && !pos.move_is_capture_or_promotion(ss->bestMove))
1560 update_killers(ss->bestMove, ss);
1562 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1568 // sp_search() is used to search from a split point. This function is called
1569 // by each thread working at the split point. It is similar to the normal
1570 // search() function, but simpler. Because we have already probed the hash
1571 // table, done a null move search, and searched the first move before
1572 // splitting, we don't have to repeat all this work in sp_search(). We
1573 // also don't need to store anything to the hash table here: This is taken
1574 // care of after we return from the split point.
1576 template <NodeType PvNode>
1577 void sp_search(SplitPoint* sp, int threadID) {
1579 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1580 assert(ThreadsMgr.active_threads() > 1);
1584 Depth ext, newDepth;
1586 Value futilityValueScaled; // NonPV specific
1587 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1589 value = -VALUE_INFINITE;
1591 Position pos(*sp->pos, threadID);
1593 SearchStack* ss = sp->sstack[threadID] + 1;
1594 isCheck = pos.is_check();
1596 // Step 10. Loop through moves
1597 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1598 lock_grab(&(sp->lock));
1600 while ( sp->bestValue < sp->beta
1601 && (move = sp->mp->get_next_move()) != MOVE_NONE
1602 && !ThreadsMgr.thread_should_stop(threadID))
1604 moveCount = ++sp->moveCount;
1605 lock_release(&(sp->lock));
1607 assert(move_is_ok(move));
1609 moveIsCheck = pos.move_is_check(move, ci);
1610 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1612 // Step 11. Decide the new search depth
1613 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1614 newDepth = sp->depth - ONE_PLY + ext;
1616 // Update current move
1617 ss->currentMove = move;
1619 // Step 12. Futility pruning (is omitted in PV nodes)
1621 && !captureOrPromotion
1624 && !move_is_castle(move))
1626 // Move count based pruning
1627 if ( moveCount >= futility_move_count(sp->depth)
1628 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1629 && sp->bestValue > value_mated_in(PLY_MAX))
1631 lock_grab(&(sp->lock));
1635 // Value based pruning
1636 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1637 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1638 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1640 if (futilityValueScaled < sp->beta)
1642 lock_grab(&(sp->lock));
1644 if (futilityValueScaled > sp->bestValue)
1645 sp->bestValue = futilityValueScaled;
1650 // Step 13. Make the move
1651 pos.do_move(move, st, ci, moveIsCheck);
1653 // Step 14. Reduced search
1654 // If the move fails high will be re-searched at full depth.
1655 bool doFullDepthSearch = true;
1657 if ( !captureOrPromotion
1659 && !move_is_castle(move)
1660 && !move_is_killer(move, ss))
1662 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1665 Value localAlpha = sp->alpha;
1666 Depth d = newDepth - ss->reduction;
1667 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1668 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1670 doFullDepthSearch = (value > localAlpha);
1673 // The move failed high, but if reduction is very big we could
1674 // face a false positive, retry with a less aggressive reduction,
1675 // if the move fails high again then go with full depth search.
1676 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1678 assert(newDepth - ONE_PLY >= ONE_PLY);
1680 ss->reduction = ONE_PLY;
1681 Value localAlpha = sp->alpha;
1682 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1683 doFullDepthSearch = (value > localAlpha);
1685 ss->reduction = DEPTH_ZERO; // Restore original reduction
1688 // Step 15. Full depth search
1689 if (doFullDepthSearch)
1691 Value localAlpha = sp->alpha;
1692 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1693 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1695 // Step extra. pv search (only in PV nodes)
1696 // Search only for possible new PV nodes, if instead value >= beta then
1697 // parent node fails low with value <= alpha and tries another move.
1698 if (PvNode && value > localAlpha && value < sp->beta)
1699 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, DEPTH_ZERO, sp->ply+1)
1700 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1703 // Step 16. Undo move
1704 pos.undo_move(move);
1706 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1708 // Step 17. Check for new best move
1709 lock_grab(&(sp->lock));
1711 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1713 sp->bestValue = value;
1715 if (sp->bestValue > sp->alpha)
1717 if (!PvNode || value >= sp->beta)
1718 sp->stopRequest = true;
1720 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1723 sp->parentSstack->bestMove = ss->bestMove = move;
1728 /* Here we have the lock still grabbed */
1730 sp->slaves[threadID] = 0;
1732 lock_release(&(sp->lock));
1736 // connected_moves() tests whether two moves are 'connected' in the sense
1737 // that the first move somehow made the second move possible (for instance
1738 // if the moving piece is the same in both moves). The first move is assumed
1739 // to be the move that was made to reach the current position, while the
1740 // second move is assumed to be a move from the current position.
1742 bool connected_moves(const Position& pos, Move m1, Move m2) {
1744 Square f1, t1, f2, t2;
1747 assert(move_is_ok(m1));
1748 assert(move_is_ok(m2));
1750 if (m2 == MOVE_NONE)
1753 // Case 1: The moving piece is the same in both moves
1759 // Case 2: The destination square for m2 was vacated by m1
1765 // Case 3: Moving through the vacated square
1766 if ( piece_is_slider(pos.piece_on(f2))
1767 && bit_is_set(squares_between(f2, t2), f1))
1770 // Case 4: The destination square for m2 is defended by the moving piece in m1
1771 p = pos.piece_on(t1);
1772 if (bit_is_set(pos.attacks_from(p, t1), t2))
1775 // Case 5: Discovered check, checking piece is the piece moved in m1
1776 if ( piece_is_slider(p)
1777 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1778 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1780 // discovered_check_candidates() works also if the Position's side to
1781 // move is the opposite of the checking piece.
1782 Color them = opposite_color(pos.side_to_move());
1783 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1785 if (bit_is_set(dcCandidates, f2))
1792 // value_is_mate() checks if the given value is a mate one eventually
1793 // compensated for the ply.
1795 bool value_is_mate(Value value) {
1797 assert(abs(value) <= VALUE_INFINITE);
1799 return value <= value_mated_in(PLY_MAX)
1800 || value >= value_mate_in(PLY_MAX);
1804 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1805 // "plies to mate from the current ply". Non-mate scores are unchanged.
1806 // The function is called before storing a value to the transposition table.
1808 Value value_to_tt(Value v, int ply) {
1810 if (v >= value_mate_in(PLY_MAX))
1813 if (v <= value_mated_in(PLY_MAX))
1820 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1821 // the transposition table to a mate score corrected for the current ply.
1823 Value value_from_tt(Value v, int ply) {
1825 if (v >= value_mate_in(PLY_MAX))
1828 if (v <= value_mated_in(PLY_MAX))
1835 // move_is_killer() checks if the given move is among the killer moves
1837 bool move_is_killer(Move m, SearchStack* ss) {
1839 if (ss->killers[0] == m || ss->killers[1] == m)
1846 // extension() decides whether a move should be searched with normal depth,
1847 // or with extended depth. Certain classes of moves (checking moves, in
1848 // particular) are searched with bigger depth than ordinary moves and in
1849 // any case are marked as 'dangerous'. Note that also if a move is not
1850 // extended, as example because the corresponding UCI option is set to zero,
1851 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1852 template <NodeType PvNode>
1853 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1854 bool singleEvasion, bool mateThreat, bool* dangerous) {
1856 assert(m != MOVE_NONE);
1858 Depth result = DEPTH_ZERO;
1859 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1863 if (moveIsCheck && pos.see_sign(m) >= 0)
1864 result += CheckExtension[PvNode];
1867 result += SingleEvasionExtension[PvNode];
1870 result += MateThreatExtension[PvNode];
1873 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1875 Color c = pos.side_to_move();
1876 if (relative_rank(c, move_to(m)) == RANK_7)
1878 result += PawnPushTo7thExtension[PvNode];
1881 if (pos.pawn_is_passed(c, move_to(m)))
1883 result += PassedPawnExtension[PvNode];
1888 if ( captureOrPromotion
1889 && pos.type_of_piece_on(move_to(m)) != PAWN
1890 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1891 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1892 && !move_is_promotion(m)
1895 result += PawnEndgameExtension[PvNode];
1900 && captureOrPromotion
1901 && pos.type_of_piece_on(move_to(m)) != PAWN
1902 && pos.see_sign(m) >= 0)
1904 result += ONE_PLY / 2;
1908 return Min(result, ONE_PLY);
1912 // connected_threat() tests whether it is safe to forward prune a move or if
1913 // is somehow coonected to the threat move returned by null search.
1915 bool connected_threat(const Position& pos, Move m, Move threat) {
1917 assert(move_is_ok(m));
1918 assert(threat && move_is_ok(threat));
1919 assert(!pos.move_is_check(m));
1920 assert(!pos.move_is_capture_or_promotion(m));
1921 assert(!pos.move_is_passed_pawn_push(m));
1923 Square mfrom, mto, tfrom, tto;
1925 mfrom = move_from(m);
1927 tfrom = move_from(threat);
1928 tto = move_to(threat);
1930 // Case 1: Don't prune moves which move the threatened piece
1934 // Case 2: If the threatened piece has value less than or equal to the
1935 // value of the threatening piece, don't prune move which defend it.
1936 if ( pos.move_is_capture(threat)
1937 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1938 || pos.type_of_piece_on(tfrom) == KING)
1939 && pos.move_attacks_square(m, tto))
1942 // Case 3: If the moving piece in the threatened move is a slider, don't
1943 // prune safe moves which block its ray.
1944 if ( piece_is_slider(pos.piece_on(tfrom))
1945 && bit_is_set(squares_between(tfrom, tto), mto)
1946 && pos.see_sign(m) >= 0)
1953 // ok_to_use_TT() returns true if a transposition table score
1954 // can be used at a given point in search.
1956 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1958 Value v = value_from_tt(tte->value(), ply);
1960 return ( tte->depth() >= depth
1961 || v >= Max(value_mate_in(PLY_MAX), beta)
1962 || v < Min(value_mated_in(PLY_MAX), beta))
1964 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1965 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1969 // refine_eval() returns the transposition table score if
1970 // possible otherwise falls back on static position evaluation.
1972 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1976 Value v = value_from_tt(tte->value(), ply);
1978 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1979 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1986 // update_history() registers a good move that produced a beta-cutoff
1987 // in history and marks as failures all the other moves of that ply.
1989 void update_history(const Position& pos, Move move, Depth depth,
1990 Move movesSearched[], int moveCount) {
1994 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1996 for (int i = 0; i < moveCount - 1; i++)
1998 m = movesSearched[i];
2002 if (!pos.move_is_capture_or_promotion(m))
2003 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2008 // update_killers() add a good move that produced a beta-cutoff
2009 // among the killer moves of that ply.
2011 void update_killers(Move m, SearchStack* ss) {
2013 if (m == ss->killers[0])
2016 ss->killers[1] = ss->killers[0];
2021 // update_gains() updates the gains table of a non-capture move given
2022 // the static position evaluation before and after the move.
2024 void update_gains(const Position& pos, Move m, Value before, Value after) {
2027 && before != VALUE_NONE
2028 && after != VALUE_NONE
2029 && pos.captured_piece_type() == PIECE_TYPE_NONE
2030 && !move_is_special(m))
2031 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2035 // current_search_time() returns the number of milliseconds which have passed
2036 // since the beginning of the current search.
2038 int current_search_time() {
2040 return get_system_time() - SearchStartTime;
2044 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2046 std::string value_to_uci(Value v) {
2048 std::stringstream s;
2050 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2051 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2053 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2058 // nps() computes the current nodes/second count.
2062 int t = current_search_time();
2063 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2067 // poll() performs two different functions: It polls for user input, and it
2068 // looks at the time consumed so far and decides if it's time to abort the
2073 static int lastInfoTime;
2074 int t = current_search_time();
2079 // We are line oriented, don't read single chars
2080 std::string command;
2082 if (!std::getline(std::cin, command))
2085 if (command == "quit")
2088 PonderSearch = false;
2092 else if (command == "stop")
2095 PonderSearch = false;
2097 else if (command == "ponderhit")
2101 // Print search information
2105 else if (lastInfoTime > t)
2106 // HACK: Must be a new search where we searched less than
2107 // NodesBetweenPolls nodes during the first second of search.
2110 else if (t - lastInfoTime >= 1000)
2117 if (dbg_show_hit_rate)
2118 dbg_print_hit_rate();
2120 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2121 << " time " << t << endl;
2124 // Should we stop the search?
2128 bool stillAtFirstMove = FirstRootMove
2129 && !AspirationFailLow
2130 && t > TimeMgr.available_time();
2132 bool noMoreTime = t > TimeMgr.maximum_time()
2133 || stillAtFirstMove;
2135 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2136 || (ExactMaxTime && t >= ExactMaxTime)
2137 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2142 // ponderhit() is called when the program is pondering (i.e. thinking while
2143 // it's the opponent's turn to move) in order to let the engine know that
2144 // it correctly predicted the opponent's move.
2148 int t = current_search_time();
2149 PonderSearch = false;
2151 bool stillAtFirstMove = FirstRootMove
2152 && !AspirationFailLow
2153 && t > TimeMgr.available_time();
2155 bool noMoreTime = t > TimeMgr.maximum_time()
2156 || stillAtFirstMove;
2158 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2163 // init_ss_array() does a fast reset of the first entries of a SearchStack
2164 // array and of all the excludedMove and skipNullMove entries.
2166 void init_ss_array(SearchStack* ss, int size) {
2168 for (int i = 0; i < size; i++, ss++)
2170 ss->excludedMove = MOVE_NONE;
2171 ss->skipNullMove = false;
2172 ss->reduction = DEPTH_ZERO;
2175 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2180 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2181 // while the program is pondering. The point is to work around a wrinkle in
2182 // the UCI protocol: When pondering, the engine is not allowed to give a
2183 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2184 // We simply wait here until one of these commands is sent, and return,
2185 // after which the bestmove and pondermove will be printed (in id_loop()).
2187 void wait_for_stop_or_ponderhit() {
2189 std::string command;
2193 if (!std::getline(std::cin, command))
2196 if (command == "quit")
2201 else if (command == "ponderhit" || command == "stop")
2207 // print_pv_info() prints to standard output and eventually to log file information on
2208 // the current PV line. It is called at each iteration or after a new pv is found.
2210 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2212 cout << "info depth " << Iteration
2213 << " score " << value_to_uci(value)
2214 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2215 << " time " << current_search_time()
2216 << " nodes " << ThreadsMgr.nodes_searched()
2220 for (Move* m = pv; *m != MOVE_NONE; m++)
2227 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2228 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2230 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2231 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2236 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2237 // the PV back into the TT. This makes sure the old PV moves are searched
2238 // first, even if the old TT entries have been overwritten.
2240 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2244 Position p(pos, pos.thread());
2248 for (int i = 0; pv[i] != MOVE_NONE; i++)
2250 tte = TT.retrieve(p.get_key());
2251 if (!tte || tte->move() != pv[i])
2253 v = (p.is_check() ? VALUE_NONE : evaluate(p, margins));
2254 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, margins[pos.side_to_move()]);
2256 p.do_move(pv[i], st);
2261 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2262 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2263 // allow to always have a ponder move even when we fail high at root and also a
2264 // long PV to print that is important for position analysis.
2266 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2270 Position p(pos, pos.thread());
2273 assert(bestMove != MOVE_NONE);
2276 p.do_move(pv[ply++], st);
2278 while ( (tte = TT.retrieve(p.get_key())) != NULL
2279 && tte->move() != MOVE_NONE
2280 && move_is_legal(p, tte->move())
2282 && (!p.is_draw() || ply < 2))
2284 pv[ply] = tte->move();
2285 p.do_move(pv[ply++], st);
2287 pv[ply] = MOVE_NONE;
2291 // init_thread() is the function which is called when a new thread is
2292 // launched. It simply calls the idle_loop() function with the supplied
2293 // threadID. There are two versions of this function; one for POSIX
2294 // threads and one for Windows threads.
2296 #if !defined(_MSC_VER)
2298 void* init_thread(void *threadID) {
2300 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2306 DWORD WINAPI init_thread(LPVOID threadID) {
2308 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2315 /// The ThreadsManager class
2317 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2318 // get_beta_counters() are getters/setters for the per thread
2319 // counters used to sort the moves at root.
2321 void ThreadsManager::resetNodeCounters() {
2323 for (int i = 0; i < MAX_THREADS; i++)
2324 threads[i].nodes = 0ULL;
2327 int64_t ThreadsManager::nodes_searched() const {
2329 int64_t result = 0ULL;
2330 for (int i = 0; i < ActiveThreads; i++)
2331 result += threads[i].nodes;
2337 // idle_loop() is where the threads are parked when they have no work to do.
2338 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2339 // object for which the current thread is the master.
2341 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2343 assert(threadID >= 0 && threadID < MAX_THREADS);
2347 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2348 // master should exit as last one.
2349 if (AllThreadsShouldExit)
2352 threads[threadID].state = THREAD_TERMINATED;
2356 // If we are not thinking, wait for a condition to be signaled
2357 // instead of wasting CPU time polling for work.
2358 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2361 assert(threadID != 0);
2362 threads[threadID].state = THREAD_SLEEPING;
2364 #if !defined(_MSC_VER)
2365 lock_grab(&WaitLock);
2366 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2367 pthread_cond_wait(&WaitCond, &WaitLock);
2368 lock_release(&WaitLock);
2370 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2374 // If thread has just woken up, mark it as available
2375 if (threads[threadID].state == THREAD_SLEEPING)
2376 threads[threadID].state = THREAD_AVAILABLE;
2378 // If this thread has been assigned work, launch a search
2379 if (threads[threadID].state == THREAD_WORKISWAITING)
2381 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2383 threads[threadID].state = THREAD_SEARCHING;
2385 if (threads[threadID].splitPoint->pvNode)
2386 sp_search<PV>(threads[threadID].splitPoint, threadID);
2388 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2390 assert(threads[threadID].state == THREAD_SEARCHING);
2392 threads[threadID].state = THREAD_AVAILABLE;
2395 // If this thread is the master of a split point and all slaves have
2396 // finished their work at this split point, return from the idle loop.
2398 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2400 if (i == ActiveThreads)
2402 // Because sp->slaves[] is reset under lock protection,
2403 // be sure sp->lock has been released before to return.
2404 lock_grab(&(sp->lock));
2405 lock_release(&(sp->lock));
2407 assert(threads[threadID].state == THREAD_AVAILABLE);
2409 threads[threadID].state = THREAD_SEARCHING;
2416 // init_threads() is called during startup. It launches all helper threads,
2417 // and initializes the split point stack and the global locks and condition
2420 void ThreadsManager::init_threads() {
2425 #if !defined(_MSC_VER)
2426 pthread_t pthread[1];
2429 // Initialize global locks
2431 lock_init(&WaitLock);
2433 #if !defined(_MSC_VER)
2434 pthread_cond_init(&WaitCond, NULL);
2436 for (i = 0; i < MAX_THREADS; i++)
2437 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2440 // Initialize splitPoints[] locks
2441 for (i = 0; i < MAX_THREADS; i++)
2442 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2443 lock_init(&(threads[i].splitPoints[j].lock));
2445 // Will be set just before program exits to properly end the threads
2446 AllThreadsShouldExit = false;
2448 // Threads will be put to sleep as soon as created
2449 AllThreadsShouldSleep = true;
2451 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2453 threads[0].state = THREAD_SEARCHING;
2454 for (i = 1; i < MAX_THREADS; i++)
2455 threads[i].state = THREAD_AVAILABLE;
2457 // Launch the helper threads
2458 for (i = 1; i < MAX_THREADS; i++)
2461 #if !defined(_MSC_VER)
2462 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2464 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2469 cout << "Failed to create thread number " << i << endl;
2470 Application::exit_with_failure();
2473 // Wait until the thread has finished launching and is gone to sleep
2474 while (threads[i].state != THREAD_SLEEPING) {}
2479 // exit_threads() is called when the program exits. It makes all the
2480 // helper threads exit cleanly.
2482 void ThreadsManager::exit_threads() {
2484 ActiveThreads = MAX_THREADS; // HACK
2485 AllThreadsShouldSleep = true; // HACK
2486 wake_sleeping_threads();
2488 // This makes the threads to exit idle_loop()
2489 AllThreadsShouldExit = true;
2491 // Wait for thread termination
2492 for (int i = 1; i < MAX_THREADS; i++)
2493 while (threads[i].state != THREAD_TERMINATED) {}
2495 // Now we can safely destroy the locks
2496 for (int i = 0; i < MAX_THREADS; i++)
2497 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2498 lock_destroy(&(threads[i].splitPoints[j].lock));
2500 lock_destroy(&WaitLock);
2501 lock_destroy(&MPLock);
2505 // thread_should_stop() checks whether the thread should stop its search.
2506 // This can happen if a beta cutoff has occurred in the thread's currently
2507 // active split point, or in some ancestor of the current split point.
2509 bool ThreadsManager::thread_should_stop(int threadID) const {
2511 assert(threadID >= 0 && threadID < ActiveThreads);
2515 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2520 // thread_is_available() checks whether the thread with threadID "slave" is
2521 // available to help the thread with threadID "master" at a split point. An
2522 // obvious requirement is that "slave" must be idle. With more than two
2523 // threads, this is not by itself sufficient: If "slave" is the master of
2524 // some active split point, it is only available as a slave to the other
2525 // threads which are busy searching the split point at the top of "slave"'s
2526 // split point stack (the "helpful master concept" in YBWC terminology).
2528 bool ThreadsManager::thread_is_available(int slave, int master) const {
2530 assert(slave >= 0 && slave < ActiveThreads);
2531 assert(master >= 0 && master < ActiveThreads);
2532 assert(ActiveThreads > 1);
2534 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2537 // Make a local copy to be sure doesn't change under our feet
2538 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2540 if (localActiveSplitPoints == 0)
2541 // No active split points means that the thread is available as
2542 // a slave for any other thread.
2545 if (ActiveThreads == 2)
2548 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2549 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2550 // could have been set to 0 by another thread leading to an out of bound access.
2551 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2558 // available_thread_exists() tries to find an idle thread which is available as
2559 // a slave for the thread with threadID "master".
2561 bool ThreadsManager::available_thread_exists(int master) const {
2563 assert(master >= 0 && master < ActiveThreads);
2564 assert(ActiveThreads > 1);
2566 for (int i = 0; i < ActiveThreads; i++)
2567 if (thread_is_available(i, master))
2574 // split() does the actual work of distributing the work at a node between
2575 // several available threads. If it does not succeed in splitting the
2576 // node (because no idle threads are available, or because we have no unused
2577 // split point objects), the function immediately returns. If splitting is
2578 // possible, a SplitPoint object is initialized with all the data that must be
2579 // copied to the helper threads and we tell our helper threads that they have
2580 // been assigned work. This will cause them to instantly leave their idle loops
2581 // and call sp_search(). When all threads have returned from sp_search() then
2584 template <bool Fake>
2585 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2586 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2587 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2589 assert(ply > 0 && ply < PLY_MAX);
2590 assert(*bestValue >= -VALUE_INFINITE);
2591 assert(*bestValue <= *alpha);
2592 assert(*alpha < beta);
2593 assert(beta <= VALUE_INFINITE);
2594 assert(depth > DEPTH_ZERO);
2595 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2596 assert(ActiveThreads > 1);
2598 int i, master = p.thread();
2599 Thread& masterThread = threads[master];
2603 // If no other thread is available to help us, or if we have too many
2604 // active split points, don't split.
2605 if ( !available_thread_exists(master)
2606 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2608 lock_release(&MPLock);
2612 // Pick the next available split point object from the split point stack
2613 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2615 // Initialize the split point object
2616 splitPoint.parent = masterThread.splitPoint;
2617 splitPoint.stopRequest = false;
2618 splitPoint.ply = ply;
2619 splitPoint.depth = depth;
2620 splitPoint.threatMove = threatMove;
2621 splitPoint.mateThreat = mateThreat;
2622 splitPoint.alpha = *alpha;
2623 splitPoint.beta = beta;
2624 splitPoint.pvNode = pvNode;
2625 splitPoint.bestValue = *bestValue;
2627 splitPoint.moveCount = *moveCount;
2628 splitPoint.pos = &p;
2629 splitPoint.parentSstack = ss;
2630 for (i = 0; i < ActiveThreads; i++)
2631 splitPoint.slaves[i] = 0;
2633 masterThread.splitPoint = &splitPoint;
2635 // If we are here it means we are not available
2636 assert(masterThread.state != THREAD_AVAILABLE);
2638 int workersCnt = 1; // At least the master is included
2640 // Allocate available threads setting state to THREAD_BOOKED
2641 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2642 if (thread_is_available(i, master))
2644 threads[i].state = THREAD_BOOKED;
2645 threads[i].splitPoint = &splitPoint;
2646 splitPoint.slaves[i] = 1;
2650 assert(Fake || workersCnt > 1);
2652 // We can release the lock because slave threads are already booked and master is not available
2653 lock_release(&MPLock);
2655 // Tell the threads that they have work to do. This will make them leave
2656 // their idle loop. But before copy search stack tail for each thread.
2657 for (i = 0; i < ActiveThreads; i++)
2658 if (i == master || splitPoint.slaves[i])
2660 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2662 assert(i == master || threads[i].state == THREAD_BOOKED);
2664 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2667 // Everything is set up. The master thread enters the idle loop, from
2668 // which it will instantly launch a search, because its state is
2669 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2670 // idle loop, which means that the main thread will return from the idle
2671 // loop when all threads have finished their work at this split point.
2672 idle_loop(master, &splitPoint);
2674 // We have returned from the idle loop, which means that all threads are
2675 // finished. Update alpha and bestValue, and return.
2678 *alpha = splitPoint.alpha;
2679 *bestValue = splitPoint.bestValue;
2680 masterThread.activeSplitPoints--;
2681 masterThread.splitPoint = splitPoint.parent;
2683 lock_release(&MPLock);
2687 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2688 // to start a new search from the root.
2690 void ThreadsManager::wake_sleeping_threads() {
2692 assert(AllThreadsShouldSleep);
2693 assert(ActiveThreads > 0);
2695 AllThreadsShouldSleep = false;
2697 if (ActiveThreads == 1)
2700 #if !defined(_MSC_VER)
2701 pthread_mutex_lock(&WaitLock);
2702 pthread_cond_broadcast(&WaitCond);
2703 pthread_mutex_unlock(&WaitLock);
2705 for (int i = 1; i < MAX_THREADS; i++)
2706 SetEvent(SitIdleEvent[i]);
2712 // put_threads_to_sleep() makes all the threads go to sleep just before
2713 // to leave think(), at the end of the search. Threads should have already
2714 // finished the job and should be idle.
2716 void ThreadsManager::put_threads_to_sleep() {
2718 assert(!AllThreadsShouldSleep);
2720 // This makes the threads to go to sleep
2721 AllThreadsShouldSleep = true;
2724 /// The RootMoveList class
2726 // RootMoveList c'tor
2728 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2730 SearchStack ss[PLY_MAX_PLUS_2];
2731 MoveStack mlist[MaxRootMoves];
2733 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2735 // Initialize search stack
2736 init_ss_array(ss, PLY_MAX_PLUS_2);
2737 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2738 ss[0].eval = VALUE_NONE;
2740 // Generate all legal moves
2741 MoveStack* last = generate_moves(pos, mlist);
2743 // Add each move to the moves[] array
2744 for (MoveStack* cur = mlist; cur != last; cur++)
2746 bool includeMove = includeAllMoves;
2748 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2749 includeMove = (searchMoves[k] == cur->move);
2754 // Find a quick score for the move
2755 pos.do_move(cur->move, st);
2756 ss[0].currentMove = cur->move;
2757 moves[count].move = cur->move;
2758 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2759 moves[count].pv[0] = cur->move;
2760 moves[count].pv[1] = MOVE_NONE;
2761 pos.undo_move(cur->move);
2767 // Score root moves using the standard way used in main search, the moves
2768 // are scored according to the order in which are returned by MovePicker.
2770 void RootMoveList::score_moves(const Position& pos)
2774 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2776 while ((move = mp.get_next_move()) != MOVE_NONE)
2777 for (int i = 0; i < count; i++)
2778 if (moves[i].move == move)
2780 moves[i].mp_score = score--;
2785 // RootMoveList simple methods definitions
2787 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2789 moves[moveNum].nodes = nodes;
2790 moves[moveNum].cumulativeNodes += nodes;
2793 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2797 for (j = 0; pv[j] != MOVE_NONE; j++)
2798 moves[moveNum].pv[j] = pv[j];
2800 moves[moveNum].pv[j] = MOVE_NONE;
2804 // RootMoveList::sort() sorts the root move list at the beginning of a new
2807 void RootMoveList::sort() {
2809 sort_multipv(count - 1); // Sort all items
2813 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2814 // list by their scores and depths. It is used to order the different PVs
2815 // correctly in MultiPV mode.
2817 void RootMoveList::sort_multipv(int n) {
2821 for (i = 1; i <= n; i++)
2823 RootMove rm = moves[i];
2824 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2825 moves[j] = moves[j - 1];