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; }
79 bool available_thread_exists(int master) const;
80 bool thread_is_available(int slave, int master) const;
81 bool thread_should_stop(int threadID) const;
82 void wake_sleeping_thread(int threadID);
83 void idle_loop(int threadID, SplitPoint* sp);
86 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
91 volatile bool AllThreadsShouldExit;
92 Thread threads[MAX_THREADS];
94 WaitCondition WaitCond[MAX_THREADS];
98 // RootMove struct is used for moves at the root at the tree. For each
99 // root move, we store a score, a node count, and a PV (really a refutation
100 // in the case of moves which fail low).
104 RootMove() : mp_score(0), nodes(0) {}
106 // RootMove::operator<() is the comparison function used when
107 // sorting the moves. A move m1 is considered to be better
108 // than a move m2 if it has a higher score, or if the moves
109 // have equal score but m1 has the higher beta cut-off count.
110 bool operator<(const RootMove& m) const {
112 return score != m.score ? score < m.score : mp_score <= m.mp_score;
119 Move pv[PLY_MAX_PLUS_2];
123 // The RootMoveList class is essentially an array of RootMove objects, with
124 // a handful of methods for accessing the data in the individual moves.
129 RootMoveList(Position& pos, Move searchMoves[]);
131 Move move(int moveNum) const { return moves[moveNum].move; }
132 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
133 int move_count() const { return count; }
134 Value move_score(int moveNum) const { return moves[moveNum].score; }
135 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
136 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
137 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
139 void set_move_pv(int moveNum, const Move pv[]);
140 void score_moves(const Position& pos);
142 void sort_multipv(int n);
145 RootMove moves[MOVES_MAX];
150 // When formatting a move for std::cout we must know if we are in Chess960
151 // or not. To keep using the handy operator<<() on the move the trick is to
152 // embed this flag in the stream itself. Function-like named enum set960 is
153 // used as a custom manipulator and the stream internal general-purpose array,
154 // accessed through ios_base::iword(), is used to pass the flag to the move's
155 // operator<<() that will use it to properly format castling moves.
158 std::ostream& operator<< (std::ostream& os, const set960& m) {
160 os.iword(0) = int(m);
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * ONE_PLY;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Maximum depth for use of dynamic threat detection when null move fails low
176 const Depth ThreatDepth = 5 * ONE_PLY;
178 // Step 9. Internal iterative deepening
180 // Minimum depth for use of internal iterative deepening
181 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
183 // At Non-PV nodes we do an internal iterative deepening search
184 // when the static evaluation is bigger then beta - IIDMargin.
185 const Value IIDMargin = Value(0x100);
187 // Step 11. Decide the new search depth
189 // Extensions. Configurable UCI options
190 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
191 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
192 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
194 // Minimum depth for use of singular extension
195 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
197 // If the TT move is at least SingularExtensionMargin better then the
198 // remaining ones we will extend it.
199 const Value SingularExtensionMargin = Value(0x20);
201 // Step 12. Futility pruning
203 // Futility margin for quiescence search
204 const Value FutilityMarginQS = Value(0x80);
206 // Futility lookup tables (initialized at startup) and their getter functions
207 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
208 int FutilityMoveCountArray[32]; // [depth]
210 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
211 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
213 // Step 14. Reduced search
215 // Reduction lookup tables (initialized at startup) and their getter functions
216 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
218 template <NodeType PV>
219 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
221 // Common adjustments
223 // Search depth at iteration 1
224 const Depth InitialDepth = ONE_PLY;
226 // Easy move margin. An easy move candidate must be at least this much
227 // better than the second best move.
228 const Value EasyMoveMargin = Value(0x200);
231 /// Namespace variables
239 // Scores and number of times the best move changed for each iteration
240 Value ValueByIteration[PLY_MAX_PLUS_2];
241 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
243 // Search window management
249 // Time managment variables
250 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
251 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
252 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
257 std::ofstream LogFile;
259 // Multi-threads related variables
260 Depth MinimumSplitDepth;
261 int MaxThreadsPerSplitPoint;
262 bool UseSleepingMaster;
263 ThreadsManager ThreadsMgr;
265 // Node counters, used only by thread[0] but try to keep in different cache
266 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
268 int NodesBetweenPolls = 30000;
275 Value id_loop(Position& pos, Move searchMoves[]);
276 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
278 template <NodeType PvNode, bool SpNode>
279 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
281 template <NodeType PvNode>
282 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
287 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
288 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
291 template <NodeType PvNode>
292 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
294 bool connected_moves(const Position& pos, Move m1, Move m2);
295 bool value_is_mate(Value value);
296 Value value_to_tt(Value v, int ply);
297 Value value_from_tt(Value v, int ply);
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);
307 int nps(const Position& pos);
308 void poll(const Position& pos);
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() { ThreadsMgr.init_threads(); }
333 void exit_threads() { ThreadsMgr.exit_threads(); }
336 /// init_search() is called during startup. It initializes various lookup tables
340 int d; // depth (ONE_PLY == 2)
341 int hd; // half depth (ONE_PLY == 1)
344 // Init reductions array
345 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
347 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
348 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
349 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
350 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
353 // Init futility margins array
354 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
355 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
357 // Init futility move count array
358 for (d = 0; d < 32; d++)
359 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
363 /// perft() is our utility to verify move generation is bug free. All the legal
364 /// moves up to given depth are generated and counted and the sum returned.
366 int perft(Position& pos, Depth depth)
368 MoveStack mlist[MOVES_MAX];
373 // Generate all legal moves
374 MoveStack* last = generate_moves(pos, mlist);
376 // If we are at the last ply we don't need to do and undo
377 // the moves, just to count them.
378 if (depth <= ONE_PLY)
379 return int(last - mlist);
381 // Loop through all legal moves
383 for (MoveStack* cur = mlist; cur != last; cur++)
386 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
387 sum += perft(pos, depth - ONE_PLY);
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(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 SearchStartTime = get_system_time();
406 ExactMaxTime = maxTime;
409 InfiniteSearch = infinite;
410 PonderSearch = ponder;
411 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
413 // Look for a book move, only during games, not tests
414 if (UseTimeManagement && Options["OwnBook"].value<bool>())
416 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
417 OpeningBook.open(Options["Book File"].value<std::string>());
419 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
420 if (bookMove != MOVE_NONE)
423 wait_for_stop_or_ponderhit();
425 cout << "bestmove " << bookMove << endl;
430 // Read UCI option values
431 TT.set_size(Options["Hash"].value<int>());
432 if (Options["Clear Hash"].value<bool>())
434 Options["Clear Hash"].set_value("false");
438 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
439 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
440 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
441 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
442 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
443 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
444 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
445 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
446 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
447 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
448 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
449 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
451 MinimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
452 MaxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
453 MultiPV = Options["MultiPV"].value<int>();
454 UseLogFile = Options["Use Search Log"].value<bool>();
455 UseSleepingMaster = Options["Use Sleeping Master"].value<bool>();
458 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
460 read_weights(pos.side_to_move());
462 // Set the number of active threads
463 int newActiveThreads = Options["Threads"].value<int>();
464 if (newActiveThreads != ThreadsMgr.active_threads())
466 ThreadsMgr.set_active_threads(newActiveThreads);
467 init_eval(ThreadsMgr.active_threads());
471 int myTime = time[pos.side_to_move()];
472 int myIncrement = increment[pos.side_to_move()];
473 if (UseTimeManagement)
474 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
476 // Set best NodesBetweenPolls interval to avoid lagging under
477 // heavy time pressure.
479 NodesBetweenPolls = Min(MaxNodes, 30000);
480 else if (myTime && myTime < 1000)
481 NodesBetweenPolls = 1000;
482 else if (myTime && myTime < 5000)
483 NodesBetweenPolls = 5000;
485 NodesBetweenPolls = 30000;
487 // Write search information to log file
489 LogFile << "Searching: " << pos.to_fen() << endl
490 << "infinite: " << infinite
491 << " ponder: " << ponder
492 << " time: " << myTime
493 << " increment: " << myIncrement
494 << " moves to go: " << movesToGo << endl;
496 // We're ready to start thinking. Call the iterative deepening loop function
497 id_loop(pos, searchMoves);
508 // id_loop() is the main iterative deepening loop. It calls root_search
509 // repeatedly with increasing depth until the allocated thinking time has
510 // been consumed, the user stops the search, or the maximum search depth is
513 Value id_loop(Position& pos, Move searchMoves[]) {
515 SearchStack ss[PLY_MAX_PLUS_2];
516 Move pv[PLY_MAX_PLUS_2];
517 Move EasyMove = MOVE_NONE;
518 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
520 // Moves to search are verified, copied, scored and sorted
521 RootMoveList rml(pos, searchMoves);
523 // Handle special case of searching on a mate/stale position
524 if (rml.move_count() == 0)
527 wait_for_stop_or_ponderhit();
529 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
532 // Print RootMoveList startup scoring to the standard output,
533 // so to output information also for iteration 1.
534 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
535 << "info depth " << 1
536 << "\ninfo depth " << 1
537 << " score " << value_to_uci(rml.move_score(0))
538 << " time " << current_search_time()
539 << " nodes " << pos.nodes_searched()
540 << " nps " << nps(pos)
541 << " pv " << rml.move(0) << "\n";
546 init_ss_array(ss, PLY_MAX_PLUS_2);
547 pv[0] = pv[1] = MOVE_NONE;
548 ValueByIteration[1] = rml.move_score(0);
551 // Is one move significantly better than others after initial scoring ?
552 if ( rml.move_count() == 1
553 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
554 EasyMove = rml.move(0);
556 // Iterative deepening loop
557 while (Iteration < PLY_MAX)
559 // Initialize iteration
561 BestMoveChangesByIteration[Iteration] = 0;
563 cout << "info depth " << Iteration << endl;
565 // Calculate dynamic aspiration window based on previous iterations
566 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
568 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
569 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
571 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
572 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
574 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
575 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
578 // Search to the current depth, rml is updated and sorted, alpha and beta could change
579 value = root_search(pos, ss, pv, rml, &alpha, &beta);
581 // Write PV to transposition table, in case the relevant entries have
582 // been overwritten during the search.
583 insert_pv_in_tt(pos, pv);
586 break; // Value cannot be trusted. Break out immediately!
588 //Save info about search result
589 ValueByIteration[Iteration] = value;
591 // Drop the easy move if differs from the new best move
592 if (pv[0] != EasyMove)
593 EasyMove = MOVE_NONE;
595 if (UseTimeManagement)
598 bool stopSearch = false;
600 // Stop search early if there is only a single legal move,
601 // we search up to Iteration 6 anyway to get a proper score.
602 if (Iteration >= 6 && rml.move_count() == 1)
605 // Stop search early when the last two iterations returned a mate score
607 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
608 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
611 // Stop search early if one move seems to be much better than the others
614 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
615 && current_search_time() > TimeMgr.available_time() / 16)
616 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
617 && current_search_time() > TimeMgr.available_time() / 32)))
620 // Add some extra time if the best move has changed during the last two iterations
621 if (Iteration > 5 && Iteration <= 50)
622 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
623 BestMoveChangesByIteration[Iteration-1]);
625 // Stop search if most of MaxSearchTime is consumed at the end of the
626 // iteration. We probably don't have enough time to search the first
627 // move at the next iteration anyway.
628 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
634 StopOnPonderhit = true;
640 if (MaxDepth && Iteration >= MaxDepth)
644 // If we are pondering or in infinite search, we shouldn't print the
645 // best move before we are told to do so.
646 if (!AbortSearch && (PonderSearch || InfiniteSearch))
647 wait_for_stop_or_ponderhit();
649 // Print final search statistics
650 cout << "info nodes " << pos.nodes_searched()
651 << " nps " << nps(pos)
652 << " time " << current_search_time() << endl;
654 // Print the best move and the ponder move to the standard output
655 if (pv[0] == MOVE_NONE)
661 assert(pv[0] != MOVE_NONE);
663 cout << "bestmove " << pv[0];
665 if (pv[1] != MOVE_NONE)
666 cout << " ponder " << pv[1];
673 dbg_print_mean(LogFile);
675 if (dbg_show_hit_rate)
676 dbg_print_hit_rate(LogFile);
678 LogFile << "\nNodes: " << pos.nodes_searched()
679 << "\nNodes/second: " << nps(pos)
680 << "\nBest move: " << move_to_san(pos, pv[0]);
683 pos.do_move(pv[0], st);
684 LogFile << "\nPonder move: "
685 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
688 return rml.move_score(0);
692 // root_search() is the function which searches the root node. It is
693 // similar to search_pv except that it uses a different move ordering
694 // scheme, prints some information to the standard output and handles
695 // the fail low/high loops.
697 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
703 Depth depth, ext, newDepth;
704 Value value, alpha, beta;
705 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
706 int researchCountFH, researchCountFL;
708 researchCountFH = researchCountFL = 0;
711 isCheck = pos.is_check();
712 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
714 // Step 1. Initialize node (polling is omitted at root)
715 ss->currentMove = ss->bestMove = MOVE_NONE;
717 // Step 2. Check for aborted search (omitted at root)
718 // Step 3. Mate distance pruning (omitted at root)
719 // Step 4. Transposition table lookup (omitted at root)
721 // Step 5. Evaluate the position statically
722 // At root we do this only to get reference value for child nodes
723 ss->evalMargin = VALUE_NONE;
724 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
726 // Step 6. Razoring (omitted at root)
727 // Step 7. Static null move pruning (omitted at root)
728 // Step 8. Null move search with verification search (omitted at root)
729 // Step 9. Internal iterative deepening (omitted at root)
731 // Step extra. Fail low loop
732 // We start with small aspiration window and in case of fail low, we research
733 // with bigger window until we are not failing low anymore.
736 // Sort the moves before to (re)search
737 rml.score_moves(pos);
740 // Step 10. Loop through all moves in the root move list
741 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
743 // This is used by time management
744 FirstRootMove = (i == 0);
746 // Save the current node count before the move is searched
747 nodes = pos.nodes_searched();
749 // Pick the next root move, and print the move and the move number to
750 // the standard output.
751 move = ss->currentMove = rml.move(i);
753 if (current_search_time() >= 1000)
754 cout << "info currmove " << move
755 << " currmovenumber " << i + 1 << endl;
757 moveIsCheck = pos.move_is_check(move);
758 captureOrPromotion = pos.move_is_capture_or_promotion(move);
760 // Step 11. Decide the new search depth
761 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
762 newDepth = depth + ext;
764 // Step 12. Futility pruning (omitted at root)
766 // Step extra. Fail high loop
767 // If move fails high, we research with bigger window until we are not failing
769 value = - VALUE_INFINITE;
773 // Step 13. Make the move
774 pos.do_move(move, st, ci, moveIsCheck);
776 // Step extra. pv search
777 // We do pv search for first moves (i < MultiPV)
778 // and for fail high research (value > alpha)
779 if (i < MultiPV || value > alpha)
781 // Aspiration window is disabled in multi-pv case
783 alpha = -VALUE_INFINITE;
785 // Full depth PV search, done on first move or after a fail high
786 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
790 // Step 14. Reduced search
791 // if the move fails high will be re-searched at full depth
792 bool doFullDepthSearch = true;
794 if ( depth >= 3 * ONE_PLY
796 && !captureOrPromotion
797 && !move_is_castle(move))
799 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
802 assert(newDepth-ss->reduction >= ONE_PLY);
804 // Reduced depth non-pv search using alpha as upperbound
805 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
806 doFullDepthSearch = (value > alpha);
809 // The move failed high, but if reduction is very big we could
810 // face a false positive, retry with a less aggressive reduction,
811 // if the move fails high again then go with full depth search.
812 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
814 assert(newDepth - ONE_PLY >= ONE_PLY);
816 ss->reduction = ONE_PLY;
817 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
818 doFullDepthSearch = (value > alpha);
820 ss->reduction = DEPTH_ZERO; // Restore original reduction
823 // Step 15. Full depth search
824 if (doFullDepthSearch)
826 // Full depth non-pv search using alpha as upperbound
827 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
829 // If we are above alpha then research at same depth but as PV
830 // to get a correct score or eventually a fail high above beta.
832 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
836 // Step 16. Undo move
839 // Can we exit fail high loop ?
840 if (AbortSearch || value < beta)
843 // We are failing high and going to do a research. It's important to update
844 // the score before research in case we run out of time while researching.
845 rml.set_move_score(i, value);
847 extract_pv_from_tt(pos, move, pv);
848 rml.set_move_pv(i, pv);
850 // Print information to the standard output
851 print_pv_info(pos, pv, alpha, beta, value);
853 // Prepare for a research after a fail high, each time with a wider window
854 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
857 } // End of fail high loop
859 // Finished searching the move. If AbortSearch is true, the search
860 // was aborted because the user interrupted the search or because we
861 // ran out of time. In this case, the return value of the search cannot
862 // be trusted, and we break out of the loop without updating the best
867 // Remember searched nodes counts for this move
868 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
870 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
871 assert(value < beta);
873 // Step 17. Check for new best move
874 if (value <= alpha && i >= MultiPV)
875 rml.set_move_score(i, -VALUE_INFINITE);
878 // PV move or new best move!
881 rml.set_move_score(i, value);
883 extract_pv_from_tt(pos, move, pv);
884 rml.set_move_pv(i, pv);
888 // We record how often the best move has been changed in each
889 // iteration. This information is used for time managment: When
890 // the best move changes frequently, we allocate some more time.
892 BestMoveChangesByIteration[Iteration]++;
894 // Print information to the standard output
895 print_pv_info(pos, pv, alpha, beta, value);
897 // Raise alpha to setup proper non-pv search upper bound
904 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
906 cout << "info multipv " << j + 1
907 << " score " << value_to_uci(rml.move_score(j))
908 << " depth " << (j <= i ? Iteration : Iteration - 1)
909 << " time " << current_search_time()
910 << " nodes " << pos.nodes_searched()
911 << " nps " << nps(pos)
914 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
915 cout << rml.move_pv(j, k) << " ";
919 alpha = rml.move_score(Min(i, MultiPV - 1));
921 } // PV move or new best move
923 assert(alpha >= *alphaPtr);
925 AspirationFailLow = (alpha == *alphaPtr);
927 if (AspirationFailLow && StopOnPonderhit)
928 StopOnPonderhit = false;
931 // Can we exit fail low loop ?
932 if (AbortSearch || !AspirationFailLow)
935 // Prepare for a research after a fail low, each time with a wider window
936 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
941 // Sort the moves before to return
948 // search<>() is the main search function for both PV and non-PV nodes and for
949 // normal and SplitPoint nodes. When called just after a split point the search
950 // is simpler because we have already probed the hash table, done a null move
951 // search, and searched the first move before splitting, we don't have to repeat
952 // all this work again. We also don't need to store anything to the hash table
953 // here: This is taken care of after we return from the split point.
955 template <NodeType PvNode, bool SpNode>
956 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
958 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
959 assert(beta > alpha && beta <= VALUE_INFINITE);
960 assert(PvNode || alpha == beta - 1);
961 assert(ply > 0 && ply < PLY_MAX);
962 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
964 Move movesSearched[MOVES_MAX];
968 Move ttMove, move, excludedMove, threatMove;
971 Value bestValue, value, oldAlpha;
972 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
973 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
974 bool mateThreat = false;
976 int threadID = pos.thread();
977 SplitPoint* sp = NULL;
978 refinedValue = bestValue = value = -VALUE_INFINITE;
980 isCheck = pos.is_check();
986 ttMove = excludedMove = MOVE_NONE;
987 threatMove = sp->threatMove;
988 mateThreat = sp->mateThreat;
989 goto split_point_start;
990 } else {} // Hack to fix icc's "statement is unreachable" warning
992 // Step 1. Initialize node and poll. Polling can abort search
993 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
994 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
996 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1002 // Step 2. Check for aborted search and immediate draw
1003 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1004 || pos.is_draw() || ply >= PLY_MAX - 1)
1007 // Step 3. Mate distance pruning
1008 alpha = Max(value_mated_in(ply), alpha);
1009 beta = Min(value_mate_in(ply+1), beta);
1013 // Step 4. Transposition table lookup
1015 // We don't want the score of a partial search to overwrite a previous full search
1016 // TT value, so we use a different position key in case of an excluded move exists.
1017 excludedMove = ss->excludedMove;
1018 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1020 tte = TT.retrieve(posKey);
1021 ttMove = tte ? tte->move() : MOVE_NONE;
1023 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1024 // This is to avoid problems in the following areas:
1026 // * Repetition draw detection
1027 // * Fifty move rule detection
1028 // * Searching for a mate
1029 // * Printing of full PV line
1030 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1033 ss->bestMove = ttMove; // Can be MOVE_NONE
1034 return value_from_tt(tte->value(), ply);
1037 // Step 5. Evaluate the position statically and
1038 // update gain statistics of parent move.
1040 ss->eval = ss->evalMargin = VALUE_NONE;
1043 assert(tte->static_value() != VALUE_NONE);
1045 ss->eval = tte->static_value();
1046 ss->evalMargin = tte->static_value_margin();
1047 refinedValue = refine_eval(tte, ss->eval, ply);
1051 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1052 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
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_ZERO, 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)
1090 && !ss->skipNullMove
1093 && refinedValue >= beta
1094 && !value_is_mate(beta)
1095 && pos.non_pawn_material(pos.side_to_move()))
1097 ss->currentMove = MOVE_NULL;
1099 // Null move dynamic reduction based on depth
1100 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1102 // Null move dynamic reduction based on value
1103 if (refinedValue - beta > PawnValueMidgame)
1106 pos.do_null_move(st);
1107 (ss+1)->skipNullMove = true;
1108 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1109 (ss+1)->skipNullMove = false;
1110 pos.undo_null_move();
1112 if (nullValue >= beta)
1114 // Do not return unproven mate scores
1115 if (nullValue >= value_mate_in(PLY_MAX))
1118 if (depth < 6 * ONE_PLY)
1121 // Do verification search at high depths
1122 ss->skipNullMove = true;
1123 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1124 ss->skipNullMove = false;
1131 // The null move failed low, which means that we may be faced with
1132 // some kind of threat. If the previous move was reduced, check if
1133 // the move that refuted the null move was somehow connected to the
1134 // move which was reduced. If a connection is found, return a fail
1135 // low score (which will cause the reduced move to fail high in the
1136 // parent node, which will trigger a re-search with full depth).
1137 if (nullValue == value_mated_in(ply + 2))
1140 threatMove = (ss+1)->bestMove;
1141 if ( depth < ThreatDepth
1142 && (ss-1)->reduction
1143 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1148 // Step 9. Internal iterative deepening
1149 if ( depth >= IIDDepth[PvNode]
1150 && ttMove == MOVE_NONE
1151 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1153 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1155 ss->skipNullMove = true;
1156 search<PvNode>(pos, ss, alpha, beta, d, ply);
1157 ss->skipNullMove = false;
1159 ttMove = ss->bestMove;
1160 tte = TT.retrieve(posKey);
1163 // Expensive mate threat detection (only for PV nodes)
1165 mateThreat = pos.has_mate_threat();
1167 split_point_start: // At split points actual search starts from here
1169 // Initialize a MovePicker object for the current position
1170 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1171 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1172 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1174 ss->bestMove = MOVE_NONE;
1175 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1176 futilityBase = ss->eval + ss->evalMargin;
1177 singularExtensionNode = !SpNode
1178 && depth >= SingularExtensionDepth[PvNode]
1181 && !excludedMove // Do not allow recursive singular extension search
1182 && (tte->type() & VALUE_TYPE_LOWER)
1183 && tte->depth() >= depth - 3 * ONE_PLY;
1186 lock_grab(&(sp->lock));
1187 bestValue = sp->bestValue;
1190 // Step 10. Loop through moves
1191 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1192 while ( bestValue < beta
1193 && (move = mp.get_next_move()) != MOVE_NONE
1194 && !ThreadsMgr.thread_should_stop(threadID))
1196 assert(move_is_ok(move));
1200 moveCount = ++sp->moveCount;
1201 lock_release(&(sp->lock));
1203 else if (move == excludedMove)
1206 movesSearched[moveCount++] = move;
1208 moveIsCheck = pos.move_is_check(move, ci);
1209 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1211 // Step 11. Decide the new search depth
1212 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1214 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1215 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1216 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1217 // lower then ttValue minus a margin then we extend ttMove.
1218 if ( singularExtensionNode
1219 && move == tte->move()
1222 Value ttValue = value_from_tt(tte->value(), ply);
1224 if (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 // Update current move (this must be done after singular extension search)
1239 ss->currentMove = move;
1240 newDepth = depth - ONE_PLY + ext;
1242 // Step 12. Futility pruning (is omitted in PV nodes)
1244 && !captureOrPromotion
1248 && !move_is_castle(move))
1250 // Move count based pruning
1251 if ( moveCount >= futility_move_count(depth)
1252 && !(threatMove && connected_threat(pos, move, threatMove))
1253 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1256 lock_grab(&(sp->lock));
1261 // Value based pruning
1262 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1263 // but fixing this made program slightly weaker.
1264 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1265 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1266 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1268 if (futilityValueScaled < beta)
1272 lock_grab(&(sp->lock));
1273 if (futilityValueScaled > sp->bestValue)
1274 sp->bestValue = bestValue = futilityValueScaled;
1276 else if (futilityValueScaled > bestValue)
1277 bestValue = futilityValueScaled;
1283 // Step 13. Make the move
1284 pos.do_move(move, st, ci, moveIsCheck);
1286 // Step extra. pv search (only in PV nodes)
1287 // The first move in list is the expected PV
1288 if (!SpNode && PvNode && moveCount == 1)
1289 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1292 // Step 14. Reduced depth search
1293 // If the move fails high will be re-searched at full depth.
1294 bool doFullDepthSearch = true;
1296 if ( depth >= 3 * ONE_PLY
1297 && !captureOrPromotion
1299 && !move_is_castle(move)
1300 && !(ss->killers[0] == move || ss->killers[1] == move))
1302 ss->reduction = reduction<PvNode>(depth, moveCount);
1305 alpha = SpNode ? sp->alpha : alpha;
1306 Depth d = newDepth - ss->reduction;
1307 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1309 doFullDepthSearch = (value > alpha);
1312 // The move failed high, but if reduction is very big we could
1313 // face a false positive, retry with a less aggressive reduction,
1314 // if the move fails high again then go with full depth search.
1315 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1317 assert(newDepth - ONE_PLY >= ONE_PLY);
1319 ss->reduction = ONE_PLY;
1320 alpha = SpNode ? sp->alpha : alpha;
1321 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1322 doFullDepthSearch = (value > alpha);
1324 ss->reduction = DEPTH_ZERO; // Restore original reduction
1327 // Step 15. Full depth search
1328 if (doFullDepthSearch)
1330 alpha = SpNode ? sp->alpha : alpha;
1331 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1333 // Step extra. pv search (only in PV nodes)
1334 // Search only for possible new PV nodes, if instead value >= beta then
1335 // parent node fails low with value <= alpha and tries another move.
1336 if (PvNode && value > alpha && value < beta)
1337 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1341 // Step 16. Undo move
1342 pos.undo_move(move);
1344 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1346 // Step 17. Check for new best move
1349 lock_grab(&(sp->lock));
1350 bestValue = sp->bestValue;
1354 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1359 sp->bestValue = value;
1363 if (SpNode && (!PvNode || value >= beta))
1364 sp->stopRequest = true;
1366 if (PvNode && value < beta) // We want always alpha < beta
1373 if (value == value_mate_in(ply + 1))
1374 ss->mateKiller = move;
1376 ss->bestMove = move;
1379 sp->parentSstack->bestMove = move;
1383 // Step 18. Check for split
1385 && depth >= MinimumSplitDepth
1386 && ThreadsMgr.active_threads() > 1
1388 && ThreadsMgr.available_thread_exists(threadID)
1390 && !ThreadsMgr.thread_should_stop(threadID)
1392 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1393 threatMove, mateThreat, moveCount, &mp, PvNode);
1396 // Step 19. Check for mate and stalemate
1397 // All legal moves have been searched and if there are
1398 // no legal moves, it must be mate or stalemate.
1399 // If one move was excluded return fail low score.
1400 if (!SpNode && !moveCount)
1401 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1403 // Step 20. Update tables
1404 // If the search is not aborted, update the transposition table,
1405 // history counters, and killer moves.
1406 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1408 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1409 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1410 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1412 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1414 // Update killers and history only for non capture moves that fails high
1415 if ( bestValue >= beta
1416 && !pos.move_is_capture_or_promotion(move))
1418 update_history(pos, move, depth, movesSearched, moveCount);
1419 update_killers(move, ss);
1425 // Here we have the lock still grabbed
1426 sp->slaves[threadID] = 0;
1427 sp->nodes += pos.nodes_searched();
1428 lock_release(&(sp->lock));
1431 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1437 // qsearch() is the quiescence search function, which is called by the main
1438 // search function when the remaining depth is zero (or, to be more precise,
1439 // less than ONE_PLY).
1441 template <NodeType PvNode>
1442 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1444 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1445 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1446 assert(PvNode || alpha == beta - 1);
1448 assert(ply > 0 && ply < PLY_MAX);
1449 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1453 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1454 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1456 Value oldAlpha = alpha;
1458 ss->bestMove = ss->currentMove = MOVE_NONE;
1460 // Check for an instant draw or maximum ply reached
1461 if (pos.is_draw() || ply >= PLY_MAX - 1)
1464 // Transposition table lookup. At PV nodes, we don't use the TT for
1465 // pruning, but only for move ordering.
1466 tte = TT.retrieve(pos.get_key());
1467 ttMove = (tte ? tte->move() : MOVE_NONE);
1469 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1471 ss->bestMove = ttMove; // Can be MOVE_NONE
1472 return value_from_tt(tte->value(), ply);
1475 isCheck = pos.is_check();
1477 // Evaluate the position statically
1480 bestValue = futilityBase = -VALUE_INFINITE;
1481 ss->eval = evalMargin = VALUE_NONE;
1482 deepChecks = enoughMaterial = false;
1488 assert(tte->static_value() != VALUE_NONE);
1490 evalMargin = tte->static_value_margin();
1491 ss->eval = bestValue = tte->static_value();
1494 ss->eval = bestValue = evaluate(pos, evalMargin);
1496 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1498 // Stand pat. Return immediately if static value is at least beta
1499 if (bestValue >= beta)
1502 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1507 if (PvNode && bestValue > alpha)
1510 // If we are near beta then try to get a cutoff pushing checks a bit further
1511 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1513 // Futility pruning parameters, not needed when in check
1514 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1515 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1518 // Initialize a MovePicker object for the current position, and prepare
1519 // to search the moves. Because the depth is <= 0 here, only captures,
1520 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1521 // and we are near beta) will be generated.
1522 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1525 // Loop through the moves until no moves remain or a beta cutoff occurs
1526 while ( alpha < beta
1527 && (move = mp.get_next_move()) != MOVE_NONE)
1529 assert(move_is_ok(move));
1531 moveIsCheck = pos.move_is_check(move, ci);
1539 && !move_is_promotion(move)
1540 && !pos.move_is_passed_pawn_push(move))
1542 futilityValue = futilityBase
1543 + pos.endgame_value_of_piece_on(move_to(move))
1544 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1546 if (futilityValue < alpha)
1548 if (futilityValue > bestValue)
1549 bestValue = futilityValue;
1554 // Detect non-capture evasions that are candidate to be pruned
1555 evasionPrunable = isCheck
1556 && bestValue > value_mated_in(PLY_MAX)
1557 && !pos.move_is_capture(move)
1558 && !pos.can_castle(pos.side_to_move());
1560 // Don't search moves with negative SEE values
1562 && (!isCheck || evasionPrunable)
1564 && !move_is_promotion(move)
1565 && pos.see_sign(move) < 0)
1568 // Update current move
1569 ss->currentMove = move;
1571 // Make and search the move
1572 pos.do_move(move, st, ci, moveIsCheck);
1573 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1574 pos.undo_move(move);
1576 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1579 if (value > bestValue)
1585 ss->bestMove = move;
1590 // All legal moves have been searched. A special case: If we're in check
1591 // and no legal moves were found, it is checkmate.
1592 if (isCheck && bestValue == -VALUE_INFINITE)
1593 return value_mated_in(ply);
1595 // Update transposition table
1596 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1597 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1598 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1600 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1606 // connected_moves() tests whether two moves are 'connected' in the sense
1607 // that the first move somehow made the second move possible (for instance
1608 // if the moving piece is the same in both moves). The first move is assumed
1609 // to be the move that was made to reach the current position, while the
1610 // second move is assumed to be a move from the current position.
1612 bool connected_moves(const Position& pos, Move m1, Move m2) {
1614 Square f1, t1, f2, t2;
1617 assert(move_is_ok(m1));
1618 assert(move_is_ok(m2));
1620 if (m2 == MOVE_NONE)
1623 // Case 1: The moving piece is the same in both moves
1629 // Case 2: The destination square for m2 was vacated by m1
1635 // Case 3: Moving through the vacated square
1636 if ( piece_is_slider(pos.piece_on(f2))
1637 && bit_is_set(squares_between(f2, t2), f1))
1640 // Case 4: The destination square for m2 is defended by the moving piece in m1
1641 p = pos.piece_on(t1);
1642 if (bit_is_set(pos.attacks_from(p, t1), t2))
1645 // Case 5: Discovered check, checking piece is the piece moved in m1
1646 if ( piece_is_slider(p)
1647 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1648 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1650 // discovered_check_candidates() works also if the Position's side to
1651 // move is the opposite of the checking piece.
1652 Color them = opposite_color(pos.side_to_move());
1653 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1655 if (bit_is_set(dcCandidates, f2))
1662 // value_is_mate() checks if the given value is a mate one eventually
1663 // compensated for the ply.
1665 bool value_is_mate(Value value) {
1667 assert(abs(value) <= VALUE_INFINITE);
1669 return value <= value_mated_in(PLY_MAX)
1670 || value >= value_mate_in(PLY_MAX);
1674 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1675 // "plies to mate from the current ply". Non-mate scores are unchanged.
1676 // The function is called before storing a value to the transposition table.
1678 Value value_to_tt(Value v, int ply) {
1680 if (v >= value_mate_in(PLY_MAX))
1683 if (v <= value_mated_in(PLY_MAX))
1690 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1691 // the transposition table to a mate score corrected for the current ply.
1693 Value value_from_tt(Value v, int ply) {
1695 if (v >= value_mate_in(PLY_MAX))
1698 if (v <= value_mated_in(PLY_MAX))
1705 // extension() decides whether a move should be searched with normal depth,
1706 // or with extended depth. Certain classes of moves (checking moves, in
1707 // particular) are searched with bigger depth than ordinary moves and in
1708 // any case are marked as 'dangerous'. Note that also if a move is not
1709 // extended, as example because the corresponding UCI option is set to zero,
1710 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1711 template <NodeType PvNode>
1712 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1713 bool singleEvasion, bool mateThreat, bool* dangerous) {
1715 assert(m != MOVE_NONE);
1717 Depth result = DEPTH_ZERO;
1718 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1722 if (moveIsCheck && pos.see_sign(m) >= 0)
1723 result += CheckExtension[PvNode];
1726 result += SingleEvasionExtension[PvNode];
1729 result += MateThreatExtension[PvNode];
1732 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1734 Color c = pos.side_to_move();
1735 if (relative_rank(c, move_to(m)) == RANK_7)
1737 result += PawnPushTo7thExtension[PvNode];
1740 if (pos.pawn_is_passed(c, move_to(m)))
1742 result += PassedPawnExtension[PvNode];
1747 if ( captureOrPromotion
1748 && pos.type_of_piece_on(move_to(m)) != PAWN
1749 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1750 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1751 && !move_is_promotion(m)
1754 result += PawnEndgameExtension[PvNode];
1759 && captureOrPromotion
1760 && pos.type_of_piece_on(move_to(m)) != PAWN
1761 && pos.see_sign(m) >= 0)
1763 result += ONE_PLY / 2;
1767 return Min(result, ONE_PLY);
1771 // connected_threat() tests whether it is safe to forward prune a move or if
1772 // is somehow coonected to the threat move returned by null search.
1774 bool connected_threat(const Position& pos, Move m, Move threat) {
1776 assert(move_is_ok(m));
1777 assert(threat && move_is_ok(threat));
1778 assert(!pos.move_is_check(m));
1779 assert(!pos.move_is_capture_or_promotion(m));
1780 assert(!pos.move_is_passed_pawn_push(m));
1782 Square mfrom, mto, tfrom, tto;
1784 mfrom = move_from(m);
1786 tfrom = move_from(threat);
1787 tto = move_to(threat);
1789 // Case 1: Don't prune moves which move the threatened piece
1793 // Case 2: If the threatened piece has value less than or equal to the
1794 // value of the threatening piece, don't prune move which defend it.
1795 if ( pos.move_is_capture(threat)
1796 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1797 || pos.type_of_piece_on(tfrom) == KING)
1798 && pos.move_attacks_square(m, tto))
1801 // Case 3: If the moving piece in the threatened move is a slider, don't
1802 // prune safe moves which block its ray.
1803 if ( piece_is_slider(pos.piece_on(tfrom))
1804 && bit_is_set(squares_between(tfrom, tto), mto)
1805 && pos.see_sign(m) >= 0)
1812 // ok_to_use_TT() returns true if a transposition table score
1813 // can be used at a given point in search.
1815 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1817 Value v = value_from_tt(tte->value(), ply);
1819 return ( tte->depth() >= depth
1820 || v >= Max(value_mate_in(PLY_MAX), beta)
1821 || v < Min(value_mated_in(PLY_MAX), beta))
1823 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1824 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1828 // refine_eval() returns the transposition table score if
1829 // possible otherwise falls back on static position evaluation.
1831 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1835 Value v = value_from_tt(tte->value(), ply);
1837 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1838 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1845 // update_history() registers a good move that produced a beta-cutoff
1846 // in history and marks as failures all the other moves of that ply.
1848 void update_history(const Position& pos, Move move, Depth depth,
1849 Move movesSearched[], int moveCount) {
1852 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1854 for (int i = 0; i < moveCount - 1; i++)
1856 m = movesSearched[i];
1860 if (!pos.move_is_capture_or_promotion(m))
1861 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1866 // update_killers() add a good move that produced a beta-cutoff
1867 // among the killer moves of that ply.
1869 void update_killers(Move m, SearchStack* ss) {
1871 if (m == ss->killers[0])
1874 ss->killers[1] = ss->killers[0];
1879 // update_gains() updates the gains table of a non-capture move given
1880 // the static position evaluation before and after the move.
1882 void update_gains(const Position& pos, Move m, Value before, Value after) {
1885 && before != VALUE_NONE
1886 && after != VALUE_NONE
1887 && pos.captured_piece_type() == PIECE_TYPE_NONE
1888 && !move_is_special(m))
1889 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1893 // current_search_time() returns the number of milliseconds which have passed
1894 // since the beginning of the current search.
1896 int current_search_time() {
1898 return get_system_time() - SearchStartTime;
1902 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1904 std::string value_to_uci(Value v) {
1906 std::stringstream s;
1908 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1909 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1911 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1916 // nps() computes the current nodes/second count.
1918 int nps(const Position& pos) {
1920 int t = current_search_time();
1921 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1925 // poll() performs two different functions: It polls for user input, and it
1926 // looks at the time consumed so far and decides if it's time to abort the
1929 void poll(const Position& pos) {
1931 static int lastInfoTime;
1932 int t = current_search_time();
1937 // We are line oriented, don't read single chars
1938 std::string command;
1940 if (!std::getline(std::cin, command))
1943 if (command == "quit")
1946 PonderSearch = false;
1950 else if (command == "stop")
1953 PonderSearch = false;
1955 else if (command == "ponderhit")
1959 // Print search information
1963 else if (lastInfoTime > t)
1964 // HACK: Must be a new search where we searched less than
1965 // NodesBetweenPolls nodes during the first second of search.
1968 else if (t - lastInfoTime >= 1000)
1975 if (dbg_show_hit_rate)
1976 dbg_print_hit_rate();
1978 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1979 << " time " << t << endl;
1982 // Should we stop the search?
1986 bool stillAtFirstMove = FirstRootMove
1987 && !AspirationFailLow
1988 && t > TimeMgr.available_time();
1990 bool noMoreTime = t > TimeMgr.maximum_time()
1991 || stillAtFirstMove;
1993 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1994 || (ExactMaxTime && t >= ExactMaxTime)
1995 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2000 // ponderhit() is called when the program is pondering (i.e. thinking while
2001 // it's the opponent's turn to move) in order to let the engine know that
2002 // it correctly predicted the opponent's move.
2006 int t = current_search_time();
2007 PonderSearch = false;
2009 bool stillAtFirstMove = FirstRootMove
2010 && !AspirationFailLow
2011 && t > TimeMgr.available_time();
2013 bool noMoreTime = t > TimeMgr.maximum_time()
2014 || stillAtFirstMove;
2016 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2021 // init_ss_array() does a fast reset of the first entries of a SearchStack
2022 // array and of all the excludedMove and skipNullMove entries.
2024 void init_ss_array(SearchStack* ss, int size) {
2026 for (int i = 0; i < size; i++, ss++)
2028 ss->excludedMove = MOVE_NONE;
2029 ss->skipNullMove = false;
2030 ss->reduction = DEPTH_ZERO;
2034 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2039 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2040 // while the program is pondering. The point is to work around a wrinkle in
2041 // the UCI protocol: When pondering, the engine is not allowed to give a
2042 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2043 // We simply wait here until one of these commands is sent, and return,
2044 // after which the bestmove and pondermove will be printed (in id_loop()).
2046 void wait_for_stop_or_ponderhit() {
2048 std::string command;
2052 if (!std::getline(std::cin, command))
2055 if (command == "quit")
2060 else if (command == "ponderhit" || command == "stop")
2066 // print_pv_info() prints to standard output and eventually to log file information on
2067 // the current PV line. It is called at each iteration or after a new pv is found.
2069 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2071 cout << "info depth " << Iteration
2072 << " score " << value_to_uci(value)
2073 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2074 << " time " << current_search_time()
2075 << " nodes " << pos.nodes_searched()
2076 << " nps " << nps(pos)
2079 for (Move* m = pv; *m != MOVE_NONE; m++)
2086 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2087 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2089 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2094 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2095 // the PV back into the TT. This makes sure the old PV moves are searched
2096 // first, even if the old TT entries have been overwritten.
2098 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2102 Position p(pos, pos.thread());
2103 Value v, m = VALUE_NONE;
2105 for (int i = 0; pv[i] != MOVE_NONE; i++)
2107 tte = TT.retrieve(p.get_key());
2108 if (!tte || tte->move() != pv[i])
2110 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2111 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2113 p.do_move(pv[i], st);
2118 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2119 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2120 // allow to always have a ponder move even when we fail high at root and also a
2121 // long PV to print that is important for position analysis.
2123 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2127 Position p(pos, pos.thread());
2130 assert(bestMove != MOVE_NONE);
2133 p.do_move(pv[ply++], st);
2135 while ( (tte = TT.retrieve(p.get_key())) != NULL
2136 && tte->move() != MOVE_NONE
2137 && move_is_legal(p, tte->move())
2139 && (!p.is_draw() || ply < 2))
2141 pv[ply] = tte->move();
2142 p.do_move(pv[ply++], st);
2144 pv[ply] = MOVE_NONE;
2148 // init_thread() is the function which is called when a new thread is
2149 // launched. It simply calls the idle_loop() function with the supplied
2150 // threadID. There are two versions of this function; one for POSIX
2151 // threads and one for Windows threads.
2153 #if !defined(_MSC_VER)
2155 void* init_thread(void* threadID) {
2157 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2163 DWORD WINAPI init_thread(LPVOID threadID) {
2165 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2172 /// The ThreadsManager class
2175 // idle_loop() is where the threads are parked when they have no work to do.
2176 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2177 // object for which the current thread is the master.
2179 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2181 assert(threadID >= 0 && threadID < MAX_THREADS);
2184 bool allFinished = false;
2188 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2189 // master should exit as last one.
2190 if (AllThreadsShouldExit)
2193 threads[threadID].state = THREAD_TERMINATED;
2197 // If we are not thinking, wait for a condition to be signaled
2198 // instead of wasting CPU time polling for work.
2199 while ( threadID >= ActiveThreads
2200 || threads[threadID].state == THREAD_INITIALIZING
2201 || (threads[threadID].state == THREAD_AVAILABLE && (!sp || UseSleepingMaster)))
2205 // Test with lock held to avoid races with wake_sleeping_thread()
2206 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2207 allFinished = (i == ActiveThreads);
2209 // Retest sleep conditions under lock protection
2210 if ( AllThreadsShouldExit
2212 || !( threadID >= ActiveThreads
2213 || threads[threadID].state == THREAD_INITIALIZING
2214 || (threads[threadID].state == THREAD_AVAILABLE && (!sp || UseSleepingMaster))))
2216 lock_release(&MPLock);
2220 // Put thread to sleep
2221 threads[threadID].state = THREAD_AVAILABLE;
2222 cond_wait(&WaitCond[threadID], &MPLock);
2223 lock_release(&MPLock);
2226 // If this thread has been assigned work, launch a search
2227 if (threads[threadID].state == THREAD_WORKISWAITING)
2229 assert(!AllThreadsShouldExit);
2231 threads[threadID].state = THREAD_SEARCHING;
2233 // Here we call search() with SplitPoint template parameter set to true
2234 SplitPoint* tsp = threads[threadID].splitPoint;
2235 Position pos(*tsp->pos, threadID);
2236 SearchStack* ss = tsp->sstack[threadID] + 1;
2240 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2242 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2244 assert(threads[threadID].state == THREAD_SEARCHING);
2246 threads[threadID].state = THREAD_AVAILABLE;
2248 // Wake up master thread so to allow it to return from the idle loop in
2249 // case we are the last slave of the split point.
2250 if (UseSleepingMaster && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2251 wake_sleeping_thread(tsp->master);
2254 // If this thread is the master of a split point and all slaves have
2255 // finished their work at this split point, return from the idle loop.
2256 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2257 allFinished = (i == ActiveThreads);
2261 // Because sp->slaves[] is reset under lock protection,
2262 // be sure sp->lock has been released before to return.
2263 lock_grab(&(sp->lock));
2264 lock_release(&(sp->lock));
2266 // In helpful master concept a master can help only a sub-tree, and
2267 // because here is all finished is not possible master is booked.
2268 assert(threads[threadID].state == THREAD_AVAILABLE);
2270 threads[threadID].state = THREAD_SEARCHING;
2277 // init_threads() is called during startup. It launches all helper threads,
2278 // and initializes the split point stack and the global locks and condition
2281 void ThreadsManager::init_threads() {
2283 int i, arg[MAX_THREADS];
2286 // Initialize global locks
2289 for (i = 0; i < MAX_THREADS; i++)
2290 cond_init(&WaitCond[i]);
2292 // Initialize splitPoints[] locks
2293 for (i = 0; i < MAX_THREADS; i++)
2294 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2295 lock_init(&(threads[i].splitPoints[j].lock));
2297 // Will be set just before program exits to properly end the threads
2298 AllThreadsShouldExit = false;
2300 // Threads will be put all threads to sleep as soon as created
2303 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2304 threads[0].state = THREAD_SEARCHING;
2305 for (i = 1; i < MAX_THREADS; i++)
2306 threads[i].state = THREAD_INITIALIZING;
2308 // Launch the helper threads
2309 for (i = 1; i < MAX_THREADS; i++)
2313 #if !defined(_MSC_VER)
2314 pthread_t pthread[1];
2315 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2316 pthread_detach(pthread[0]);
2318 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2322 cout << "Failed to create thread number " << i << endl;
2323 Application::exit_with_failure();
2326 // Wait until the thread has finished launching and is gone to sleep
2327 while (threads[i].state == THREAD_INITIALIZING) {}
2332 // exit_threads() is called when the program exits. It makes all the
2333 // helper threads exit cleanly.
2335 void ThreadsManager::exit_threads() {
2337 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2339 // Wake up all the threads and waits for termination
2340 for (int i = 1; i < MAX_THREADS; i++)
2342 wake_sleeping_thread(i);
2343 while (threads[i].state != THREAD_TERMINATED) {}
2346 // Now we can safely destroy the locks
2347 for (int i = 0; i < MAX_THREADS; i++)
2348 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2349 lock_destroy(&(threads[i].splitPoints[j].lock));
2351 lock_destroy(&MPLock);
2353 // Now we can safely destroy the wait conditions
2354 for (int i = 0; i < MAX_THREADS; i++)
2355 cond_destroy(&WaitCond[i]);
2359 // thread_should_stop() checks whether the thread should stop its search.
2360 // This can happen if a beta cutoff has occurred in the thread's currently
2361 // active split point, or in some ancestor of the current split point.
2363 bool ThreadsManager::thread_should_stop(int threadID) const {
2365 assert(threadID >= 0 && threadID < ActiveThreads);
2367 SplitPoint* sp = threads[threadID].splitPoint;
2369 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2374 // thread_is_available() checks whether the thread with threadID "slave" is
2375 // available to help the thread with threadID "master" at a split point. An
2376 // obvious requirement is that "slave" must be idle. With more than two
2377 // threads, this is not by itself sufficient: If "slave" is the master of
2378 // some active split point, it is only available as a slave to the other
2379 // threads which are busy searching the split point at the top of "slave"'s
2380 // split point stack (the "helpful master concept" in YBWC terminology).
2382 bool ThreadsManager::thread_is_available(int slave, int master) const {
2384 assert(slave >= 0 && slave < ActiveThreads);
2385 assert(master >= 0 && master < ActiveThreads);
2386 assert(ActiveThreads > 1);
2388 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2391 // Make a local copy to be sure doesn't change under our feet
2392 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2394 // No active split points means that the thread is available as
2395 // a slave for any other thread.
2396 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2399 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2400 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2401 // could have been set to 0 by another thread leading to an out of bound access.
2402 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2409 // available_thread_exists() tries to find an idle thread which is available as
2410 // a slave for the thread with threadID "master".
2412 bool ThreadsManager::available_thread_exists(int master) const {
2414 assert(master >= 0 && master < ActiveThreads);
2415 assert(ActiveThreads > 1);
2417 for (int i = 0; i < ActiveThreads; i++)
2418 if (thread_is_available(i, master))
2425 // split() does the actual work of distributing the work at a node between
2426 // several available threads. If it does not succeed in splitting the
2427 // node (because no idle threads are available, or because we have no unused
2428 // split point objects), the function immediately returns. If splitting is
2429 // possible, a SplitPoint object is initialized with all the data that must be
2430 // copied to the helper threads and we tell our helper threads that they have
2431 // been assigned work. This will cause them to instantly leave their idle loops and
2432 // call search().When all threads have returned from search() then split() returns.
2434 template <bool Fake>
2435 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2436 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2437 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2438 assert(pos.is_ok());
2439 assert(ply > 0 && ply < PLY_MAX);
2440 assert(*bestValue >= -VALUE_INFINITE);
2441 assert(*bestValue <= *alpha);
2442 assert(*alpha < beta);
2443 assert(beta <= VALUE_INFINITE);
2444 assert(depth > DEPTH_ZERO);
2445 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2446 assert(ActiveThreads > 1);
2448 int i, master = pos.thread();
2449 Thread& masterThread = threads[master];
2453 // If no other thread is available to help us, or if we have too many
2454 // active split points, don't split.
2455 if ( !available_thread_exists(master)
2456 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2458 lock_release(&MPLock);
2462 // Pick the next available split point object from the split point stack
2463 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2465 // Initialize the split point object
2466 splitPoint.parent = masterThread.splitPoint;
2467 splitPoint.master = master;
2468 splitPoint.stopRequest = false;
2469 splitPoint.ply = ply;
2470 splitPoint.depth = depth;
2471 splitPoint.threatMove = threatMove;
2472 splitPoint.mateThreat = mateThreat;
2473 splitPoint.alpha = *alpha;
2474 splitPoint.beta = beta;
2475 splitPoint.pvNode = pvNode;
2476 splitPoint.bestValue = *bestValue;
2478 splitPoint.moveCount = moveCount;
2479 splitPoint.pos = &pos;
2480 splitPoint.nodes = 0;
2481 splitPoint.parentSstack = ss;
2482 for (i = 0; i < ActiveThreads; i++)
2483 splitPoint.slaves[i] = 0;
2485 masterThread.splitPoint = &splitPoint;
2487 // If we are here it means we are not available
2488 assert(masterThread.state != THREAD_AVAILABLE);
2490 int workersCnt = 1; // At least the master is included
2492 // Allocate available threads setting state to THREAD_BOOKED
2493 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2494 if (thread_is_available(i, master))
2496 threads[i].state = THREAD_BOOKED;
2497 threads[i].splitPoint = &splitPoint;
2498 splitPoint.slaves[i] = 1;
2502 assert(Fake || workersCnt > 1);
2504 // We can release the lock because slave threads are already booked and master is not available
2505 lock_release(&MPLock);
2507 // Tell the threads that they have work to do. This will make them leave
2508 // their idle loop. But before copy search stack tail for each thread.
2509 for (i = 0; i < ActiveThreads; i++)
2510 if (i == master || splitPoint.slaves[i])
2512 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2514 assert(i == master || threads[i].state == THREAD_BOOKED);
2516 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2518 wake_sleeping_thread(i);
2521 // Everything is set up. The master thread enters the idle loop, from
2522 // which it will instantly launch a search, because its state is
2523 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2524 // idle loop, which means that the main thread will return from the idle
2525 // loop when all threads have finished their work at this split point.
2526 idle_loop(master, &splitPoint);
2528 // We have returned from the idle loop, which means that all threads are
2529 // finished. Update alpha and bestValue, and return.
2532 *alpha = splitPoint.alpha;
2533 *bestValue = splitPoint.bestValue;
2534 masterThread.activeSplitPoints--;
2535 masterThread.splitPoint = splitPoint.parent;
2536 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2538 lock_release(&MPLock);
2542 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2543 // to start a new search from the root.
2545 void ThreadsManager::wake_sleeping_thread(int threadID) {
2548 cond_signal(&WaitCond[threadID]);
2549 lock_release(&MPLock);
2553 /// The RootMoveList class
2555 // RootMoveList c'tor
2557 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2559 SearchStack ss[PLY_MAX_PLUS_2];
2560 MoveStack mlist[MOVES_MAX];
2562 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2564 // Initialize search stack
2565 init_ss_array(ss, PLY_MAX_PLUS_2);
2566 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2569 // Generate all legal moves
2570 MoveStack* last = generate_moves(pos, mlist);
2572 // Add each move to the moves[] array
2573 for (MoveStack* cur = mlist; cur != last; cur++)
2575 bool includeMove = includeAllMoves;
2577 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2578 includeMove = (searchMoves[k] == cur->move);
2583 // Find a quick score for the move
2584 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2585 moves[count].pv[1] = MOVE_NONE;
2586 pos.do_move(cur->move, st);
2587 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2588 pos.undo_move(cur->move);
2594 // Score root moves using the standard way used in main search, the moves
2595 // are scored according to the order in which are returned by MovePicker.
2597 void RootMoveList::score_moves(const Position& pos)
2601 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2603 while ((move = mp.get_next_move()) != MOVE_NONE)
2604 for (int i = 0; i < count; i++)
2605 if (moves[i].move == move)
2607 moves[i].mp_score = score--;
2612 // RootMoveList simple methods definitions
2614 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2618 for (j = 0; pv[j] != MOVE_NONE; j++)
2619 moves[moveNum].pv[j] = pv[j];
2621 moves[moveNum].pv[j] = MOVE_NONE;
2625 // RootMoveList::sort() sorts the root move list at the beginning of a new
2628 void RootMoveList::sort() {
2630 sort_multipv(count - 1); // Sort all items
2634 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2635 // list by their scores and depths. It is used to order the different PVs
2636 // correctly in MultiPV mode.
2638 void RootMoveList::sort_multipv(int n) {
2642 for (i = 1; i <= n; i++)
2644 RootMove rm = moves[i];
2645 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2646 moves[j] = moves[j - 1];