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 ThreadsManager ThreadsMgr;
264 // Node counters, used only by thread[0] but try to keep in different cache
265 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
267 int NodesBetweenPolls = 30000;
274 Value id_loop(Position& pos, Move searchMoves[]);
275 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
277 template <NodeType PvNode, bool SpNode>
278 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
280 template <NodeType PvNode>
281 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
286 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
287 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
306 int nps(const Position& pos);
307 void poll(const Position& pos);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
312 void insert_pv_in_tt(const Position& pos, Move pv[]);
313 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
315 #if !defined(_MSC_VER)
316 void* init_thread(void* threadID);
318 DWORD WINAPI init_thread(LPVOID threadID);
328 /// init_threads(), exit_threads() and nodes_searched() are helpers to
329 /// give accessibility to some TM methods from outside of current file.
331 void init_threads() { ThreadsMgr.init_threads(); }
332 void exit_threads() { ThreadsMgr.exit_threads(); }
335 /// init_search() is called during startup. It initializes various lookup tables
339 int d; // depth (ONE_PLY == 2)
340 int hd; // half depth (ONE_PLY == 1)
343 // Init reductions array
344 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
346 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
347 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
348 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
349 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
352 // Init futility margins array
353 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
354 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
356 // Init futility move count array
357 for (d = 0; d < 32; d++)
358 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
362 /// perft() is our utility to verify move generation is bug free. All the legal
363 /// moves up to given depth are generated and counted and the sum returned.
365 int perft(Position& pos, Depth depth)
367 MoveStack mlist[MOVES_MAX];
372 // Generate all legal moves
373 MoveStack* last = generate_moves(pos, mlist);
375 // If we are at the last ply we don't need to do and undo
376 // the moves, just to count them.
377 if (depth <= ONE_PLY)
378 return int(last - mlist);
380 // Loop through all legal moves
382 for (MoveStack* cur = mlist; cur != last; cur++)
385 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
386 sum += perft(pos, depth - ONE_PLY);
393 /// think() is the external interface to Stockfish's search, and is called when
394 /// the program receives the UCI 'go' command. It initializes various
395 /// search-related global variables, and calls root_search(). It returns false
396 /// when a quit command is received during the search.
398 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
399 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
401 // Initialize global search variables
402 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
404 SearchStartTime = get_system_time();
405 ExactMaxTime = maxTime;
408 InfiniteSearch = infinite;
409 PonderSearch = ponder;
410 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
412 // Look for a book move, only during games, not tests
413 if (UseTimeManagement && Options["OwnBook"].value<bool>())
415 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
416 OpeningBook.open(Options["Book File"].value<std::string>());
418 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
419 if (bookMove != MOVE_NONE)
422 wait_for_stop_or_ponderhit();
424 cout << "bestmove " << bookMove << endl;
429 // Read UCI option values
430 TT.set_size(Options["Hash"].value<int>());
431 if (Options["Clear Hash"].value<bool>())
433 Options["Clear Hash"].set_value("false");
437 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
438 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
439 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
440 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
441 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
442 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
443 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
444 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
445 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
446 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
447 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
448 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
450 MinimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
451 MaxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
452 MultiPV = Options["MultiPV"].value<int>();
453 UseLogFile = Options["Use Search Log"].value<bool>();
456 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
458 read_weights(pos.side_to_move());
460 // Set the number of active threads
461 int newActiveThreads = Options["Threads"].value<int>();
462 if (newActiveThreads != ThreadsMgr.active_threads())
464 ThreadsMgr.set_active_threads(newActiveThreads);
465 init_eval(ThreadsMgr.active_threads());
469 int myTime = time[pos.side_to_move()];
470 int myIncrement = increment[pos.side_to_move()];
471 if (UseTimeManagement)
472 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
474 // Set best NodesBetweenPolls interval to avoid lagging under
475 // heavy time pressure.
477 NodesBetweenPolls = Min(MaxNodes, 30000);
478 else if (myTime && myTime < 1000)
479 NodesBetweenPolls = 1000;
480 else if (myTime && myTime < 5000)
481 NodesBetweenPolls = 5000;
483 NodesBetweenPolls = 30000;
485 // Write search information to log file
487 LogFile << "Searching: " << pos.to_fen() << endl
488 << "infinite: " << infinite
489 << " ponder: " << ponder
490 << " time: " << myTime
491 << " increment: " << myIncrement
492 << " moves to go: " << movesToGo << endl;
494 // We're ready to start thinking. Call the iterative deepening loop function
495 id_loop(pos, searchMoves);
506 // id_loop() is the main iterative deepening loop. It calls root_search
507 // repeatedly with increasing depth until the allocated thinking time has
508 // been consumed, the user stops the search, or the maximum search depth is
511 Value id_loop(Position& pos, Move searchMoves[]) {
513 SearchStack ss[PLY_MAX_PLUS_2];
514 Move pv[PLY_MAX_PLUS_2];
515 Move EasyMove = MOVE_NONE;
516 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
518 // Moves to search are verified, copied, scored and sorted
519 RootMoveList rml(pos, searchMoves);
521 // Handle special case of searching on a mate/stale position
522 if (rml.move_count() == 0)
525 wait_for_stop_or_ponderhit();
527 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
530 // Print RootMoveList startup scoring to the standard output,
531 // so to output information also for iteration 1.
532 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
533 << "info depth " << 1
534 << "\ninfo depth " << 1
535 << " score " << value_to_uci(rml.move_score(0))
536 << " time " << current_search_time()
537 << " nodes " << pos.nodes_searched()
538 << " nps " << nps(pos)
539 << " pv " << rml.move(0) << "\n";
544 init_ss_array(ss, PLY_MAX_PLUS_2);
545 pv[0] = pv[1] = MOVE_NONE;
546 ValueByIteration[1] = rml.move_score(0);
549 // Is one move significantly better than others after initial scoring ?
550 if ( rml.move_count() == 1
551 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
552 EasyMove = rml.move(0);
554 // Iterative deepening loop
555 while (Iteration < PLY_MAX)
557 // Initialize iteration
559 BestMoveChangesByIteration[Iteration] = 0;
561 cout << "info depth " << Iteration << endl;
563 // Calculate dynamic aspiration window based on previous iterations
564 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
566 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
567 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
569 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
570 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
572 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
573 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
576 // Search to the current depth, rml is updated and sorted, alpha and beta could change
577 value = root_search(pos, ss, pv, rml, &alpha, &beta);
579 // Write PV to transposition table, in case the relevant entries have
580 // been overwritten during the search.
581 insert_pv_in_tt(pos, pv);
584 break; // Value cannot be trusted. Break out immediately!
586 //Save info about search result
587 ValueByIteration[Iteration] = value;
589 // Drop the easy move if differs from the new best move
590 if (pv[0] != EasyMove)
591 EasyMove = MOVE_NONE;
593 if (UseTimeManagement)
596 bool stopSearch = false;
598 // Stop search early if there is only a single legal move,
599 // we search up to Iteration 6 anyway to get a proper score.
600 if (Iteration >= 6 && rml.move_count() == 1)
603 // Stop search early when the last two iterations returned a mate score
605 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
606 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
609 // Stop search early if one move seems to be much better than the others
612 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
613 && current_search_time() > TimeMgr.available_time() / 16)
614 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
615 && current_search_time() > TimeMgr.available_time() / 32)))
618 // Add some extra time if the best move has changed during the last two iterations
619 if (Iteration > 5 && Iteration <= 50)
620 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
621 BestMoveChangesByIteration[Iteration-1]);
623 // Stop search if most of MaxSearchTime is consumed at the end of the
624 // iteration. We probably don't have enough time to search the first
625 // move at the next iteration anyway.
626 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
632 StopOnPonderhit = true;
638 if (MaxDepth && Iteration >= MaxDepth)
642 // If we are pondering or in infinite search, we shouldn't print the
643 // best move before we are told to do so.
644 if (!AbortSearch && (PonderSearch || InfiniteSearch))
645 wait_for_stop_or_ponderhit();
647 // Print final search statistics
648 cout << "info nodes " << pos.nodes_searched()
649 << " nps " << nps(pos)
650 << " time " << current_search_time() << endl;
652 // Print the best move and the ponder move to the standard output
653 if (pv[0] == MOVE_NONE)
659 assert(pv[0] != MOVE_NONE);
661 cout << "bestmove " << pv[0];
663 if (pv[1] != MOVE_NONE)
664 cout << " ponder " << pv[1];
671 dbg_print_mean(LogFile);
673 if (dbg_show_hit_rate)
674 dbg_print_hit_rate(LogFile);
676 LogFile << "\nNodes: " << pos.nodes_searched()
677 << "\nNodes/second: " << nps(pos)
678 << "\nBest move: " << move_to_san(pos, pv[0]);
681 pos.do_move(pv[0], st);
682 LogFile << "\nPonder move: "
683 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
686 return rml.move_score(0);
690 // root_search() is the function which searches the root node. It is
691 // similar to search_pv except that it uses a different move ordering
692 // scheme, prints some information to the standard output and handles
693 // the fail low/high loops.
695 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
701 Depth depth, ext, newDepth;
702 Value value, alpha, beta;
703 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
704 int researchCountFH, researchCountFL;
706 researchCountFH = researchCountFL = 0;
709 isCheck = pos.is_check();
710 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
712 // Step 1. Initialize node (polling is omitted at root)
713 ss->currentMove = ss->bestMove = MOVE_NONE;
715 // Step 2. Check for aborted search (omitted at root)
716 // Step 3. Mate distance pruning (omitted at root)
717 // Step 4. Transposition table lookup (omitted at root)
719 // Step 5. Evaluate the position statically
720 // At root we do this only to get reference value for child nodes
721 ss->evalMargin = VALUE_NONE;
722 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
724 // Step 6. Razoring (omitted at root)
725 // Step 7. Static null move pruning (omitted at root)
726 // Step 8. Null move search with verification search (omitted at root)
727 // Step 9. Internal iterative deepening (omitted at root)
729 // Step extra. Fail low loop
730 // We start with small aspiration window and in case of fail low, we research
731 // with bigger window until we are not failing low anymore.
734 // Sort the moves before to (re)search
735 rml.score_moves(pos);
738 // Step 10. Loop through all moves in the root move list
739 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
741 // This is used by time management
742 FirstRootMove = (i == 0);
744 // Save the current node count before the move is searched
745 nodes = pos.nodes_searched();
747 // Pick the next root move, and print the move and the move number to
748 // the standard output.
749 move = ss->currentMove = rml.move(i);
751 if (current_search_time() >= 1000)
752 cout << "info currmove " << move
753 << " currmovenumber " << i + 1 << endl;
755 moveIsCheck = pos.move_is_check(move);
756 captureOrPromotion = pos.move_is_capture_or_promotion(move);
758 // Step 11. Decide the new search depth
759 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
760 newDepth = depth + ext;
762 // Step 12. Futility pruning (omitted at root)
764 // Step extra. Fail high loop
765 // If move fails high, we research with bigger window until we are not failing
767 value = - VALUE_INFINITE;
771 // Step 13. Make the move
772 pos.do_move(move, st, ci, moveIsCheck);
774 // Step extra. pv search
775 // We do pv search for first moves (i < MultiPV)
776 // and for fail high research (value > alpha)
777 if (i < MultiPV || value > alpha)
779 // Aspiration window is disabled in multi-pv case
781 alpha = -VALUE_INFINITE;
783 // Full depth PV search, done on first move or after a fail high
784 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
788 // Step 14. Reduced search
789 // if the move fails high will be re-searched at full depth
790 bool doFullDepthSearch = true;
792 if ( depth >= 3 * ONE_PLY
794 && !captureOrPromotion
795 && !move_is_castle(move))
797 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
800 assert(newDepth-ss->reduction >= ONE_PLY);
802 // Reduced depth non-pv search using alpha as upperbound
803 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
804 doFullDepthSearch = (value > alpha);
807 // The move failed high, but if reduction is very big we could
808 // face a false positive, retry with a less aggressive reduction,
809 // if the move fails high again then go with full depth search.
810 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
812 assert(newDepth - ONE_PLY >= ONE_PLY);
814 ss->reduction = ONE_PLY;
815 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
816 doFullDepthSearch = (value > alpha);
818 ss->reduction = DEPTH_ZERO; // Restore original reduction
821 // Step 15. Full depth search
822 if (doFullDepthSearch)
824 // Full depth non-pv search using alpha as upperbound
825 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
827 // If we are above alpha then research at same depth but as PV
828 // to get a correct score or eventually a fail high above beta.
830 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
834 // Step 16. Undo move
837 // Can we exit fail high loop ?
838 if (AbortSearch || value < beta)
841 // We are failing high and going to do a research. It's important to update
842 // the score before research in case we run out of time while researching.
843 rml.set_move_score(i, value);
845 extract_pv_from_tt(pos, move, pv);
846 rml.set_move_pv(i, pv);
848 // Print information to the standard output
849 print_pv_info(pos, pv, alpha, beta, value);
851 // Prepare for a research after a fail high, each time with a wider window
852 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
855 } // End of fail high loop
857 // Finished searching the move. If AbortSearch is true, the search
858 // was aborted because the user interrupted the search or because we
859 // ran out of time. In this case, the return value of the search cannot
860 // be trusted, and we break out of the loop without updating the best
865 // Remember searched nodes counts for this move
866 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
868 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
869 assert(value < beta);
871 // Step 17. Check for new best move
872 if (value <= alpha && i >= MultiPV)
873 rml.set_move_score(i, -VALUE_INFINITE);
876 // PV move or new best move!
879 rml.set_move_score(i, value);
881 extract_pv_from_tt(pos, move, pv);
882 rml.set_move_pv(i, pv);
886 // We record how often the best move has been changed in each
887 // iteration. This information is used for time managment: When
888 // the best move changes frequently, we allocate some more time.
890 BestMoveChangesByIteration[Iteration]++;
892 // Print information to the standard output
893 print_pv_info(pos, pv, alpha, beta, value);
895 // Raise alpha to setup proper non-pv search upper bound
902 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
904 cout << "info multipv " << j + 1
905 << " score " << value_to_uci(rml.move_score(j))
906 << " depth " << (j <= i ? Iteration : Iteration - 1)
907 << " time " << current_search_time()
908 << " nodes " << pos.nodes_searched()
909 << " nps " << nps(pos)
912 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
913 cout << rml.move_pv(j, k) << " ";
917 alpha = rml.move_score(Min(i, MultiPV - 1));
919 } // PV move or new best move
921 assert(alpha >= *alphaPtr);
923 AspirationFailLow = (alpha == *alphaPtr);
925 if (AspirationFailLow && StopOnPonderhit)
926 StopOnPonderhit = false;
929 // Can we exit fail low loop ?
930 if (AbortSearch || !AspirationFailLow)
933 // Prepare for a research after a fail low, each time with a wider window
934 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
939 // Sort the moves before to return
946 // search<>() is the main search function for both PV and non-PV nodes and for
947 // normal and SplitPoint nodes. When called just after a split point the search
948 // is simpler because we have already probed the hash table, done a null move
949 // search, and searched the first move before splitting, we don't have to repeat
950 // all this work again. We also don't need to store anything to the hash table
951 // here: This is taken care of after we return from the split point.
953 template <NodeType PvNode, bool SpNode>
954 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
956 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
957 assert(beta > alpha && beta <= VALUE_INFINITE);
958 assert(PvNode || alpha == beta - 1);
959 assert(ply > 0 && ply < PLY_MAX);
960 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
962 Move movesSearched[MOVES_MAX];
966 Move ttMove, move, excludedMove, threatMove;
969 Value bestValue, value, oldAlpha;
970 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
971 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
972 bool mateThreat = false;
974 int threadID = pos.thread();
975 SplitPoint* sp = NULL;
976 refinedValue = bestValue = value = -VALUE_INFINITE;
978 isCheck = pos.is_check();
984 ttMove = excludedMove = MOVE_NONE;
985 threatMove = sp->threatMove;
986 mateThreat = sp->mateThreat;
987 goto split_point_start;
988 } else {} // Hack to fix icc's "statement is unreachable" warning
990 // Step 1. Initialize node and poll. Polling can abort search
991 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
992 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
994 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1000 // Step 2. Check for aborted search and immediate draw
1001 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1002 || pos.is_draw() || ply >= PLY_MAX - 1)
1005 // Step 3. Mate distance pruning
1006 alpha = Max(value_mated_in(ply), alpha);
1007 beta = Min(value_mate_in(ply+1), beta);
1011 // Step 4. Transposition table lookup
1013 // We don't want the score of a partial search to overwrite a previous full search
1014 // TT value, so we use a different position key in case of an excluded move exists.
1015 excludedMove = ss->excludedMove;
1016 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1018 tte = TT.retrieve(posKey);
1019 ttMove = tte ? tte->move() : MOVE_NONE;
1021 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1022 // This is to avoid problems in the following areas:
1024 // * Repetition draw detection
1025 // * Fifty move rule detection
1026 // * Searching for a mate
1027 // * Printing of full PV line
1028 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1031 ss->bestMove = ttMove; // Can be MOVE_NONE
1032 return value_from_tt(tte->value(), ply);
1035 // Step 5. Evaluate the position statically and
1036 // update gain statistics of parent move.
1038 ss->eval = ss->evalMargin = VALUE_NONE;
1041 assert(tte->static_value() != VALUE_NONE);
1043 ss->eval = tte->static_value();
1044 ss->evalMargin = tte->static_value_margin();
1045 refinedValue = refine_eval(tte, ss->eval, ply);
1049 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1050 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1053 // Save gain for the parent non-capture move
1054 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1056 // Step 6. Razoring (is omitted in PV nodes)
1058 && depth < RazorDepth
1060 && refinedValue < beta - razor_margin(depth)
1061 && ttMove == MOVE_NONE
1062 && (ss-1)->currentMove != MOVE_NULL
1063 && !value_is_mate(beta)
1064 && !pos.has_pawn_on_7th(pos.side_to_move()))
1066 Value rbeta = beta - razor_margin(depth);
1067 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1069 // Logically we should return (v + razor_margin(depth)), but
1070 // surprisingly this did slightly weaker in tests.
1074 // Step 7. Static null move pruning (is omitted in PV nodes)
1075 // We're betting that the opponent doesn't have a move that will reduce
1076 // the score by more than futility_margin(depth) if we do a null move.
1078 && !ss->skipNullMove
1079 && depth < RazorDepth
1081 && refinedValue >= beta + futility_margin(depth, 0)
1082 && !value_is_mate(beta)
1083 && pos.non_pawn_material(pos.side_to_move()))
1084 return refinedValue - futility_margin(depth, 0);
1086 // Step 8. Null move search with verification search (is omitted in PV nodes)
1088 && !ss->skipNullMove
1091 && refinedValue >= beta
1092 && !value_is_mate(beta)
1093 && pos.non_pawn_material(pos.side_to_move()))
1095 ss->currentMove = MOVE_NULL;
1097 // Null move dynamic reduction based on depth
1098 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1100 // Null move dynamic reduction based on value
1101 if (refinedValue - beta > PawnValueMidgame)
1104 pos.do_null_move(st);
1105 (ss+1)->skipNullMove = true;
1106 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1107 (ss+1)->skipNullMove = false;
1108 pos.undo_null_move();
1110 if (nullValue >= beta)
1112 // Do not return unproven mate scores
1113 if (nullValue >= value_mate_in(PLY_MAX))
1116 if (depth < 6 * ONE_PLY)
1119 // Do verification search at high depths
1120 ss->skipNullMove = true;
1121 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1122 ss->skipNullMove = false;
1129 // The null move failed low, which means that we may be faced with
1130 // some kind of threat. If the previous move was reduced, check if
1131 // the move that refuted the null move was somehow connected to the
1132 // move which was reduced. If a connection is found, return a fail
1133 // low score (which will cause the reduced move to fail high in the
1134 // parent node, which will trigger a re-search with full depth).
1135 if (nullValue == value_mated_in(ply + 2))
1138 threatMove = (ss+1)->bestMove;
1139 if ( depth < ThreatDepth
1140 && (ss-1)->reduction
1141 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1146 // Step 9. Internal iterative deepening
1147 if ( depth >= IIDDepth[PvNode]
1148 && ttMove == MOVE_NONE
1149 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1151 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1153 ss->skipNullMove = true;
1154 search<PvNode>(pos, ss, alpha, beta, d, ply);
1155 ss->skipNullMove = false;
1157 ttMove = ss->bestMove;
1158 tte = TT.retrieve(posKey);
1161 // Expensive mate threat detection (only for PV nodes)
1163 mateThreat = pos.has_mate_threat();
1165 split_point_start: // At split points actual search starts from here
1167 // Initialize a MovePicker object for the current position
1168 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1169 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1170 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1172 ss->bestMove = MOVE_NONE;
1173 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1174 futilityBase = ss->eval + ss->evalMargin;
1175 singularExtensionNode = !SpNode
1176 && depth >= SingularExtensionDepth[PvNode]
1179 && !excludedMove // Do not allow recursive singular extension search
1180 && (tte->type() & VALUE_TYPE_LOWER)
1181 && tte->depth() >= depth - 3 * ONE_PLY;
1184 lock_grab(&(sp->lock));
1185 bestValue = sp->bestValue;
1188 // Step 10. Loop through moves
1189 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1190 while ( bestValue < beta
1191 && (move = mp.get_next_move()) != MOVE_NONE
1192 && !ThreadsMgr.thread_should_stop(threadID))
1194 assert(move_is_ok(move));
1198 moveCount = ++sp->moveCount;
1199 lock_release(&(sp->lock));
1201 else if (move == excludedMove)
1204 movesSearched[moveCount++] = move;
1206 moveIsCheck = pos.move_is_check(move, ci);
1207 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1209 // Step 11. Decide the new search depth
1210 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1212 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1213 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1214 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1215 // lower then ttValue minus a margin then we extend ttMove.
1216 if ( singularExtensionNode
1217 && move == tte->move()
1220 Value ttValue = value_from_tt(tte->value(), ply);
1222 if (abs(ttValue) < VALUE_KNOWN_WIN)
1224 Value b = ttValue - SingularExtensionMargin;
1225 ss->excludedMove = move;
1226 ss->skipNullMove = true;
1227 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1228 ss->skipNullMove = false;
1229 ss->excludedMove = MOVE_NONE;
1230 ss->bestMove = MOVE_NONE;
1236 // Update current move (this must be done after singular extension search)
1237 ss->currentMove = move;
1238 newDepth = depth - ONE_PLY + ext;
1240 // Step 12. Futility pruning (is omitted in PV nodes)
1242 && !captureOrPromotion
1246 && !move_is_castle(move))
1248 // Move count based pruning
1249 if ( moveCount >= futility_move_count(depth)
1250 && !(threatMove && connected_threat(pos, move, threatMove))
1251 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1254 lock_grab(&(sp->lock));
1259 // Value based pruning
1260 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1261 // but fixing this made program slightly weaker.
1262 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1263 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1264 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1266 if (futilityValueScaled < beta)
1270 lock_grab(&(sp->lock));
1271 if (futilityValueScaled > sp->bestValue)
1272 sp->bestValue = bestValue = futilityValueScaled;
1274 else if (futilityValueScaled > bestValue)
1275 bestValue = futilityValueScaled;
1281 // Step 13. Make the move
1282 pos.do_move(move, st, ci, moveIsCheck);
1284 // Step extra. pv search (only in PV nodes)
1285 // The first move in list is the expected PV
1286 if (!SpNode && PvNode && moveCount == 1)
1287 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1290 // Step 14. Reduced depth search
1291 // If the move fails high will be re-searched at full depth.
1292 bool doFullDepthSearch = true;
1294 if ( depth >= 3 * ONE_PLY
1295 && !captureOrPromotion
1297 && !move_is_castle(move)
1298 && !(ss->killers[0] == move || ss->killers[1] == move))
1300 ss->reduction = reduction<PvNode>(depth, moveCount);
1303 alpha = SpNode ? sp->alpha : alpha;
1304 Depth d = newDepth - ss->reduction;
1305 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1307 doFullDepthSearch = (value > alpha);
1310 // The move failed high, but if reduction is very big we could
1311 // face a false positive, retry with a less aggressive reduction,
1312 // if the move fails high again then go with full depth search.
1313 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1315 assert(newDepth - ONE_PLY >= ONE_PLY);
1317 ss->reduction = ONE_PLY;
1318 alpha = SpNode ? sp->alpha : alpha;
1319 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1320 doFullDepthSearch = (value > alpha);
1322 ss->reduction = DEPTH_ZERO; // Restore original reduction
1325 // Step 15. Full depth search
1326 if (doFullDepthSearch)
1328 alpha = SpNode ? sp->alpha : alpha;
1329 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1331 // Step extra. pv search (only in PV nodes)
1332 // Search only for possible new PV nodes, if instead value >= beta then
1333 // parent node fails low with value <= alpha and tries another move.
1334 if (PvNode && value > alpha && value < beta)
1335 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1339 // Step 16. Undo move
1340 pos.undo_move(move);
1342 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1344 // Step 17. Check for new best move
1347 lock_grab(&(sp->lock));
1348 bestValue = sp->bestValue;
1352 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1357 sp->bestValue = value;
1361 if (SpNode && (!PvNode || value >= beta))
1362 sp->stopRequest = true;
1364 if (PvNode && value < beta) // We want always alpha < beta
1371 if (value == value_mate_in(ply + 1))
1372 ss->mateKiller = move;
1374 ss->bestMove = move;
1377 sp->parentSstack->bestMove = move;
1381 // Step 18. Check for split
1383 && depth >= MinimumSplitDepth
1384 && ThreadsMgr.active_threads() > 1
1386 && ThreadsMgr.available_thread_exists(threadID)
1388 && !ThreadsMgr.thread_should_stop(threadID)
1390 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1391 threatMove, mateThreat, moveCount, &mp, PvNode);
1394 // Step 19. Check for mate and stalemate
1395 // All legal moves have been searched and if there are
1396 // no legal moves, it must be mate or stalemate.
1397 // If one move was excluded return fail low score.
1398 if (!SpNode && !moveCount)
1399 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1401 // Step 20. Update tables
1402 // If the search is not aborted, update the transposition table,
1403 // history counters, and killer moves.
1404 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1406 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1407 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1408 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1410 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1412 // Update killers and history only for non capture moves that fails high
1413 if ( bestValue >= beta
1414 && !pos.move_is_capture_or_promotion(move))
1416 update_history(pos, move, depth, movesSearched, moveCount);
1417 update_killers(move, ss);
1423 // Here we have the lock still grabbed
1424 sp->slaves[threadID] = 0;
1425 sp->nodes += pos.nodes_searched();
1426 lock_release(&(sp->lock));
1429 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1435 // qsearch() is the quiescence search function, which is called by the main
1436 // search function when the remaining depth is zero (or, to be more precise,
1437 // less than ONE_PLY).
1439 template <NodeType PvNode>
1440 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1442 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1443 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1444 assert(PvNode || alpha == beta - 1);
1446 assert(ply > 0 && ply < PLY_MAX);
1447 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1451 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1452 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1454 Value oldAlpha = alpha;
1456 ss->bestMove = ss->currentMove = MOVE_NONE;
1458 // Check for an instant draw or maximum ply reached
1459 if (pos.is_draw() || ply >= PLY_MAX - 1)
1462 // Transposition table lookup. At PV nodes, we don't use the TT for
1463 // pruning, but only for move ordering.
1464 tte = TT.retrieve(pos.get_key());
1465 ttMove = (tte ? tte->move() : MOVE_NONE);
1467 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1469 ss->bestMove = ttMove; // Can be MOVE_NONE
1470 return value_from_tt(tte->value(), ply);
1473 isCheck = pos.is_check();
1475 // Evaluate the position statically
1478 bestValue = futilityBase = -VALUE_INFINITE;
1479 ss->eval = evalMargin = VALUE_NONE;
1480 deepChecks = enoughMaterial = false;
1486 assert(tte->static_value() != VALUE_NONE);
1488 evalMargin = tte->static_value_margin();
1489 ss->eval = bestValue = tte->static_value();
1492 ss->eval = bestValue = evaluate(pos, evalMargin);
1494 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1496 // Stand pat. Return immediately if static value is at least beta
1497 if (bestValue >= beta)
1500 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1505 if (PvNode && bestValue > alpha)
1508 // If we are near beta then try to get a cutoff pushing checks a bit further
1509 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1511 // Futility pruning parameters, not needed when in check
1512 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1513 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1516 // Initialize a MovePicker object for the current position, and prepare
1517 // to search the moves. Because the depth is <= 0 here, only captures,
1518 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1519 // and we are near beta) will be generated.
1520 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1523 // Loop through the moves until no moves remain or a beta cutoff occurs
1524 while ( alpha < beta
1525 && (move = mp.get_next_move()) != MOVE_NONE)
1527 assert(move_is_ok(move));
1529 moveIsCheck = pos.move_is_check(move, ci);
1537 && !move_is_promotion(move)
1538 && !pos.move_is_passed_pawn_push(move))
1540 futilityValue = futilityBase
1541 + pos.endgame_value_of_piece_on(move_to(move))
1542 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1544 if (futilityValue < alpha)
1546 if (futilityValue > bestValue)
1547 bestValue = futilityValue;
1552 // Detect non-capture evasions that are candidate to be pruned
1553 evasionPrunable = isCheck
1554 && bestValue > value_mated_in(PLY_MAX)
1555 && !pos.move_is_capture(move)
1556 && !pos.can_castle(pos.side_to_move());
1558 // Don't search moves with negative SEE values
1560 && (!isCheck || evasionPrunable)
1562 && !move_is_promotion(move)
1563 && pos.see_sign(move) < 0)
1566 // Update current move
1567 ss->currentMove = move;
1569 // Make and search the move
1570 pos.do_move(move, st, ci, moveIsCheck);
1571 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1572 pos.undo_move(move);
1574 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1577 if (value > bestValue)
1583 ss->bestMove = move;
1588 // All legal moves have been searched. A special case: If we're in check
1589 // and no legal moves were found, it is checkmate.
1590 if (isCheck && bestValue == -VALUE_INFINITE)
1591 return value_mated_in(ply);
1593 // Update transposition table
1594 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1595 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1596 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1598 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1604 // connected_moves() tests whether two moves are 'connected' in the sense
1605 // that the first move somehow made the second move possible (for instance
1606 // if the moving piece is the same in both moves). The first move is assumed
1607 // to be the move that was made to reach the current position, while the
1608 // second move is assumed to be a move from the current position.
1610 bool connected_moves(const Position& pos, Move m1, Move m2) {
1612 Square f1, t1, f2, t2;
1615 assert(move_is_ok(m1));
1616 assert(move_is_ok(m2));
1618 if (m2 == MOVE_NONE)
1621 // Case 1: The moving piece is the same in both moves
1627 // Case 2: The destination square for m2 was vacated by m1
1633 // Case 3: Moving through the vacated square
1634 if ( piece_is_slider(pos.piece_on(f2))
1635 && bit_is_set(squares_between(f2, t2), f1))
1638 // Case 4: The destination square for m2 is defended by the moving piece in m1
1639 p = pos.piece_on(t1);
1640 if (bit_is_set(pos.attacks_from(p, t1), t2))
1643 // Case 5: Discovered check, checking piece is the piece moved in m1
1644 if ( piece_is_slider(p)
1645 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1646 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1648 // discovered_check_candidates() works also if the Position's side to
1649 // move is the opposite of the checking piece.
1650 Color them = opposite_color(pos.side_to_move());
1651 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1653 if (bit_is_set(dcCandidates, f2))
1660 // value_is_mate() checks if the given value is a mate one eventually
1661 // compensated for the ply.
1663 bool value_is_mate(Value value) {
1665 assert(abs(value) <= VALUE_INFINITE);
1667 return value <= value_mated_in(PLY_MAX)
1668 || value >= value_mate_in(PLY_MAX);
1672 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1673 // "plies to mate from the current ply". Non-mate scores are unchanged.
1674 // The function is called before storing a value to the transposition table.
1676 Value value_to_tt(Value v, int ply) {
1678 if (v >= value_mate_in(PLY_MAX))
1681 if (v <= value_mated_in(PLY_MAX))
1688 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1689 // the transposition table to a mate score corrected for the current ply.
1691 Value value_from_tt(Value v, int ply) {
1693 if (v >= value_mate_in(PLY_MAX))
1696 if (v <= value_mated_in(PLY_MAX))
1703 // extension() decides whether a move should be searched with normal depth,
1704 // or with extended depth. Certain classes of moves (checking moves, in
1705 // particular) are searched with bigger depth than ordinary moves and in
1706 // any case are marked as 'dangerous'. Note that also if a move is not
1707 // extended, as example because the corresponding UCI option is set to zero,
1708 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1709 template <NodeType PvNode>
1710 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1711 bool singleEvasion, bool mateThreat, bool* dangerous) {
1713 assert(m != MOVE_NONE);
1715 Depth result = DEPTH_ZERO;
1716 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1720 if (moveIsCheck && pos.see_sign(m) >= 0)
1721 result += CheckExtension[PvNode];
1724 result += SingleEvasionExtension[PvNode];
1727 result += MateThreatExtension[PvNode];
1730 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1732 Color c = pos.side_to_move();
1733 if (relative_rank(c, move_to(m)) == RANK_7)
1735 result += PawnPushTo7thExtension[PvNode];
1738 if (pos.pawn_is_passed(c, move_to(m)))
1740 result += PassedPawnExtension[PvNode];
1745 if ( captureOrPromotion
1746 && pos.type_of_piece_on(move_to(m)) != PAWN
1747 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1748 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1749 && !move_is_promotion(m)
1752 result += PawnEndgameExtension[PvNode];
1757 && captureOrPromotion
1758 && pos.type_of_piece_on(move_to(m)) != PAWN
1759 && pos.see_sign(m) >= 0)
1761 result += ONE_PLY / 2;
1765 return Min(result, ONE_PLY);
1769 // connected_threat() tests whether it is safe to forward prune a move or if
1770 // is somehow coonected to the threat move returned by null search.
1772 bool connected_threat(const Position& pos, Move m, Move threat) {
1774 assert(move_is_ok(m));
1775 assert(threat && move_is_ok(threat));
1776 assert(!pos.move_is_check(m));
1777 assert(!pos.move_is_capture_or_promotion(m));
1778 assert(!pos.move_is_passed_pawn_push(m));
1780 Square mfrom, mto, tfrom, tto;
1782 mfrom = move_from(m);
1784 tfrom = move_from(threat);
1785 tto = move_to(threat);
1787 // Case 1: Don't prune moves which move the threatened piece
1791 // Case 2: If the threatened piece has value less than or equal to the
1792 // value of the threatening piece, don't prune move which defend it.
1793 if ( pos.move_is_capture(threat)
1794 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1795 || pos.type_of_piece_on(tfrom) == KING)
1796 && pos.move_attacks_square(m, tto))
1799 // Case 3: If the moving piece in the threatened move is a slider, don't
1800 // prune safe moves which block its ray.
1801 if ( piece_is_slider(pos.piece_on(tfrom))
1802 && bit_is_set(squares_between(tfrom, tto), mto)
1803 && pos.see_sign(m) >= 0)
1810 // ok_to_use_TT() returns true if a transposition table score
1811 // can be used at a given point in search.
1813 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1815 Value v = value_from_tt(tte->value(), ply);
1817 return ( tte->depth() >= depth
1818 || v >= Max(value_mate_in(PLY_MAX), beta)
1819 || v < Min(value_mated_in(PLY_MAX), beta))
1821 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1822 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1826 // refine_eval() returns the transposition table score if
1827 // possible otherwise falls back on static position evaluation.
1829 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1833 Value v = value_from_tt(tte->value(), ply);
1835 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1836 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1843 // update_history() registers a good move that produced a beta-cutoff
1844 // in history and marks as failures all the other moves of that ply.
1846 void update_history(const Position& pos, Move move, Depth depth,
1847 Move movesSearched[], int moveCount) {
1850 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1852 for (int i = 0; i < moveCount - 1; i++)
1854 m = movesSearched[i];
1858 if (!pos.move_is_capture_or_promotion(m))
1859 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1864 // update_killers() add a good move that produced a beta-cutoff
1865 // among the killer moves of that ply.
1867 void update_killers(Move m, SearchStack* ss) {
1869 if (m == ss->killers[0])
1872 ss->killers[1] = ss->killers[0];
1877 // update_gains() updates the gains table of a non-capture move given
1878 // the static position evaluation before and after the move.
1880 void update_gains(const Position& pos, Move m, Value before, Value after) {
1883 && before != VALUE_NONE
1884 && after != VALUE_NONE
1885 && pos.captured_piece_type() == PIECE_TYPE_NONE
1886 && !move_is_special(m))
1887 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1891 // current_search_time() returns the number of milliseconds which have passed
1892 // since the beginning of the current search.
1894 int current_search_time() {
1896 return get_system_time() - SearchStartTime;
1900 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1902 std::string value_to_uci(Value v) {
1904 std::stringstream s;
1906 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1907 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1909 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1914 // nps() computes the current nodes/second count.
1916 int nps(const Position& pos) {
1918 int t = current_search_time();
1919 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1923 // poll() performs two different functions: It polls for user input, and it
1924 // looks at the time consumed so far and decides if it's time to abort the
1927 void poll(const Position& pos) {
1929 static int lastInfoTime;
1930 int t = current_search_time();
1935 // We are line oriented, don't read single chars
1936 std::string command;
1938 if (!std::getline(std::cin, command))
1941 if (command == "quit")
1944 PonderSearch = false;
1948 else if (command == "stop")
1951 PonderSearch = false;
1953 else if (command == "ponderhit")
1957 // Print search information
1961 else if (lastInfoTime > t)
1962 // HACK: Must be a new search where we searched less than
1963 // NodesBetweenPolls nodes during the first second of search.
1966 else if (t - lastInfoTime >= 1000)
1973 if (dbg_show_hit_rate)
1974 dbg_print_hit_rate();
1976 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1977 << " time " << t << endl;
1980 // Should we stop the search?
1984 bool stillAtFirstMove = FirstRootMove
1985 && !AspirationFailLow
1986 && t > TimeMgr.available_time();
1988 bool noMoreTime = t > TimeMgr.maximum_time()
1989 || stillAtFirstMove;
1991 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1992 || (ExactMaxTime && t >= ExactMaxTime)
1993 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
1998 // ponderhit() is called when the program is pondering (i.e. thinking while
1999 // it's the opponent's turn to move) in order to let the engine know that
2000 // it correctly predicted the opponent's move.
2004 int t = current_search_time();
2005 PonderSearch = false;
2007 bool stillAtFirstMove = FirstRootMove
2008 && !AspirationFailLow
2009 && t > TimeMgr.available_time();
2011 bool noMoreTime = t > TimeMgr.maximum_time()
2012 || stillAtFirstMove;
2014 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2019 // init_ss_array() does a fast reset of the first entries of a SearchStack
2020 // array and of all the excludedMove and skipNullMove entries.
2022 void init_ss_array(SearchStack* ss, int size) {
2024 for (int i = 0; i < size; i++, ss++)
2026 ss->excludedMove = MOVE_NONE;
2027 ss->skipNullMove = false;
2028 ss->reduction = DEPTH_ZERO;
2032 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2037 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2038 // while the program is pondering. The point is to work around a wrinkle in
2039 // the UCI protocol: When pondering, the engine is not allowed to give a
2040 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2041 // We simply wait here until one of these commands is sent, and return,
2042 // after which the bestmove and pondermove will be printed (in id_loop()).
2044 void wait_for_stop_or_ponderhit() {
2046 std::string command;
2050 if (!std::getline(std::cin, command))
2053 if (command == "quit")
2058 else if (command == "ponderhit" || command == "stop")
2064 // print_pv_info() prints to standard output and eventually to log file information on
2065 // the current PV line. It is called at each iteration or after a new pv is found.
2067 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2069 cout << "info depth " << Iteration
2070 << " score " << value_to_uci(value)
2071 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2072 << " time " << current_search_time()
2073 << " nodes " << pos.nodes_searched()
2074 << " nps " << nps(pos)
2077 for (Move* m = pv; *m != MOVE_NONE; m++)
2084 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2085 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2087 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2092 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2093 // the PV back into the TT. This makes sure the old PV moves are searched
2094 // first, even if the old TT entries have been overwritten.
2096 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2100 Position p(pos, pos.thread());
2101 Value v, m = VALUE_NONE;
2103 for (int i = 0; pv[i] != MOVE_NONE; i++)
2105 tte = TT.retrieve(p.get_key());
2106 if (!tte || tte->move() != pv[i])
2108 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2109 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2111 p.do_move(pv[i], st);
2116 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2117 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2118 // allow to always have a ponder move even when we fail high at root and also a
2119 // long PV to print that is important for position analysis.
2121 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2125 Position p(pos, pos.thread());
2128 assert(bestMove != MOVE_NONE);
2131 p.do_move(pv[ply++], st);
2133 while ( (tte = TT.retrieve(p.get_key())) != NULL
2134 && tte->move() != MOVE_NONE
2135 && move_is_legal(p, tte->move())
2137 && (!p.is_draw() || ply < 2))
2139 pv[ply] = tte->move();
2140 p.do_move(pv[ply++], st);
2142 pv[ply] = MOVE_NONE;
2146 // init_thread() is the function which is called when a new thread is
2147 // launched. It simply calls the idle_loop() function with the supplied
2148 // threadID. There are two versions of this function; one for POSIX
2149 // threads and one for Windows threads.
2151 #if !defined(_MSC_VER)
2153 void* init_thread(void* threadID) {
2155 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2161 DWORD WINAPI init_thread(LPVOID threadID) {
2163 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2170 /// The ThreadsManager class
2173 // idle_loop() is where the threads are parked when they have no work to do.
2174 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2175 // object for which the current thread is the master.
2177 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2179 assert(threadID >= 0 && threadID < MAX_THREADS);
2183 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2184 // master should exit as last one.
2185 if (AllThreadsShouldExit)
2188 threads[threadID].state = THREAD_TERMINATED;
2192 // If we are not thinking, wait for a condition to be signaled
2193 // instead of wasting CPU time polling for work.
2194 while ( threadID >= ActiveThreads
2195 || threads[threadID].state == THREAD_INITIALIZING
2196 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2199 assert(threadID != 0);
2201 if (AllThreadsShouldExit)
2206 // Retest condition under lock protection
2207 if (!( threadID >= ActiveThreads
2208 || threads[threadID].state == THREAD_INITIALIZING
2209 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2211 lock_release(&MPLock);
2215 // Put thread to sleep
2216 threads[threadID].state = THREAD_AVAILABLE;
2217 cond_wait(&WaitCond[threadID], &MPLock);
2218 lock_release(&MPLock);
2221 // If this thread has been assigned work, launch a search
2222 if (threads[threadID].state == THREAD_WORKISWAITING)
2224 assert(!AllThreadsShouldExit);
2226 threads[threadID].state = THREAD_SEARCHING;
2228 // Here we call search() with SplitPoint template parameter set to true
2229 SplitPoint* tsp = threads[threadID].splitPoint;
2230 Position pos(*tsp->pos, threadID);
2231 SearchStack* ss = tsp->sstack[threadID] + 1;
2235 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2237 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2239 assert(threads[threadID].state == THREAD_SEARCHING);
2241 threads[threadID].state = THREAD_AVAILABLE;
2244 // If this thread is the master of a split point and all slaves have
2245 // finished their work at this split point, return from the idle loop.
2247 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2249 if (i == ActiveThreads)
2251 // Because sp->slaves[] is reset under lock protection,
2252 // be sure sp->lock has been released before to return.
2253 lock_grab(&(sp->lock));
2254 lock_release(&(sp->lock));
2256 // In helpful master concept a master can help only a sub-tree, and
2257 // because here is all finished is not possible master is booked.
2258 assert(threads[threadID].state == THREAD_AVAILABLE);
2260 threads[threadID].state = THREAD_SEARCHING;
2267 // init_threads() is called during startup. It launches all helper threads,
2268 // and initializes the split point stack and the global locks and condition
2271 void ThreadsManager::init_threads() {
2273 int i, arg[MAX_THREADS];
2276 // Initialize global locks
2279 for (i = 0; i < MAX_THREADS; i++)
2280 cond_init(&WaitCond[i]);
2282 // Initialize splitPoints[] locks
2283 for (i = 0; i < MAX_THREADS; i++)
2284 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2285 lock_init(&(threads[i].splitPoints[j].lock));
2287 // Will be set just before program exits to properly end the threads
2288 AllThreadsShouldExit = false;
2290 // Threads will be put all threads to sleep as soon as created
2293 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2294 threads[0].state = THREAD_SEARCHING;
2295 for (i = 1; i < MAX_THREADS; i++)
2296 threads[i].state = THREAD_INITIALIZING;
2298 // Launch the helper threads
2299 for (i = 1; i < MAX_THREADS; i++)
2303 #if !defined(_MSC_VER)
2304 pthread_t pthread[1];
2305 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2306 pthread_detach(pthread[0]);
2308 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2312 cout << "Failed to create thread number " << i << endl;
2313 Application::exit_with_failure();
2316 // Wait until the thread has finished launching and is gone to sleep
2317 while (threads[i].state == THREAD_INITIALIZING) {}
2322 // exit_threads() is called when the program exits. It makes all the
2323 // helper threads exit cleanly.
2325 void ThreadsManager::exit_threads() {
2327 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2329 // Wake up all the threads and waits for termination
2330 for (int i = 1; i < MAX_THREADS; i++)
2332 wake_sleeping_thread(i);
2333 while (threads[i].state != THREAD_TERMINATED) {}
2336 // Now we can safely destroy the locks
2337 for (int i = 0; i < MAX_THREADS; i++)
2338 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2339 lock_destroy(&(threads[i].splitPoints[j].lock));
2341 lock_destroy(&MPLock);
2343 // Now we can safely destroy the wait conditions
2344 for (int i = 0; i < MAX_THREADS; i++)
2345 cond_destroy(&WaitCond[i]);
2349 // thread_should_stop() checks whether the thread should stop its search.
2350 // This can happen if a beta cutoff has occurred in the thread's currently
2351 // active split point, or in some ancestor of the current split point.
2353 bool ThreadsManager::thread_should_stop(int threadID) const {
2355 assert(threadID >= 0 && threadID < ActiveThreads);
2357 SplitPoint* sp = threads[threadID].splitPoint;
2359 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2364 // thread_is_available() checks whether the thread with threadID "slave" is
2365 // available to help the thread with threadID "master" at a split point. An
2366 // obvious requirement is that "slave" must be idle. With more than two
2367 // threads, this is not by itself sufficient: If "slave" is the master of
2368 // some active split point, it is only available as a slave to the other
2369 // threads which are busy searching the split point at the top of "slave"'s
2370 // split point stack (the "helpful master concept" in YBWC terminology).
2372 bool ThreadsManager::thread_is_available(int slave, int master) const {
2374 assert(slave >= 0 && slave < ActiveThreads);
2375 assert(master >= 0 && master < ActiveThreads);
2376 assert(ActiveThreads > 1);
2378 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2381 // Make a local copy to be sure doesn't change under our feet
2382 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2384 // No active split points means that the thread is available as
2385 // a slave for any other thread.
2386 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2389 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2390 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2391 // could have been set to 0 by another thread leading to an out of bound access.
2392 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2399 // available_thread_exists() tries to find an idle thread which is available as
2400 // a slave for the thread with threadID "master".
2402 bool ThreadsManager::available_thread_exists(int master) const {
2404 assert(master >= 0 && master < ActiveThreads);
2405 assert(ActiveThreads > 1);
2407 for (int i = 0; i < ActiveThreads; i++)
2408 if (thread_is_available(i, master))
2415 // split() does the actual work of distributing the work at a node between
2416 // several available threads. If it does not succeed in splitting the
2417 // node (because no idle threads are available, or because we have no unused
2418 // split point objects), the function immediately returns. If splitting is
2419 // possible, a SplitPoint object is initialized with all the data that must be
2420 // copied to the helper threads and we tell our helper threads that they have
2421 // been assigned work. This will cause them to instantly leave their idle loops and
2422 // call search().When all threads have returned from search() then split() returns.
2424 template <bool Fake>
2425 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2426 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2427 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2428 assert(pos.is_ok());
2429 assert(ply > 0 && ply < PLY_MAX);
2430 assert(*bestValue >= -VALUE_INFINITE);
2431 assert(*bestValue <= *alpha);
2432 assert(*alpha < beta);
2433 assert(beta <= VALUE_INFINITE);
2434 assert(depth > DEPTH_ZERO);
2435 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2436 assert(ActiveThreads > 1);
2438 int i, master = pos.thread();
2439 Thread& masterThread = threads[master];
2443 // If no other thread is available to help us, or if we have too many
2444 // active split points, don't split.
2445 if ( !available_thread_exists(master)
2446 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2448 lock_release(&MPLock);
2452 // Pick the next available split point object from the split point stack
2453 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2455 // Initialize the split point object
2456 splitPoint.parent = masterThread.splitPoint;
2457 splitPoint.stopRequest = false;
2458 splitPoint.ply = ply;
2459 splitPoint.depth = depth;
2460 splitPoint.threatMove = threatMove;
2461 splitPoint.mateThreat = mateThreat;
2462 splitPoint.alpha = *alpha;
2463 splitPoint.beta = beta;
2464 splitPoint.pvNode = pvNode;
2465 splitPoint.bestValue = *bestValue;
2467 splitPoint.moveCount = moveCount;
2468 splitPoint.pos = &pos;
2469 splitPoint.nodes = 0;
2470 splitPoint.parentSstack = ss;
2471 for (i = 0; i < ActiveThreads; i++)
2472 splitPoint.slaves[i] = 0;
2474 masterThread.splitPoint = &splitPoint;
2476 // If we are here it means we are not available
2477 assert(masterThread.state != THREAD_AVAILABLE);
2479 int workersCnt = 1; // At least the master is included
2481 // Allocate available threads setting state to THREAD_BOOKED
2482 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2483 if (thread_is_available(i, master))
2485 threads[i].state = THREAD_BOOKED;
2486 threads[i].splitPoint = &splitPoint;
2487 splitPoint.slaves[i] = 1;
2491 assert(Fake || workersCnt > 1);
2493 // We can release the lock because slave threads are already booked and master is not available
2494 lock_release(&MPLock);
2496 // Tell the threads that they have work to do. This will make them leave
2497 // their idle loop. But before copy search stack tail for each thread.
2498 for (i = 0; i < ActiveThreads; i++)
2499 if (i == master || splitPoint.slaves[i])
2501 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2503 assert(i == master || threads[i].state == THREAD_BOOKED);
2505 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2507 wake_sleeping_thread(i);
2510 // Everything is set up. The master thread enters the idle loop, from
2511 // which it will instantly launch a search, because its state is
2512 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2513 // idle loop, which means that the main thread will return from the idle
2514 // loop when all threads have finished their work at this split point.
2515 idle_loop(master, &splitPoint);
2517 // We have returned from the idle loop, which means that all threads are
2518 // finished. Update alpha and bestValue, and return.
2521 *alpha = splitPoint.alpha;
2522 *bestValue = splitPoint.bestValue;
2523 masterThread.activeSplitPoints--;
2524 masterThread.splitPoint = splitPoint.parent;
2525 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2527 lock_release(&MPLock);
2531 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2532 // to start a new search from the root.
2534 void ThreadsManager::wake_sleeping_thread(int threadID) {
2537 cond_signal(&WaitCond[threadID]);
2538 lock_release(&MPLock);
2542 /// The RootMoveList class
2544 // RootMoveList c'tor
2546 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2548 SearchStack ss[PLY_MAX_PLUS_2];
2549 MoveStack mlist[MOVES_MAX];
2551 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2553 // Initialize search stack
2554 init_ss_array(ss, PLY_MAX_PLUS_2);
2555 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2558 // Generate all legal moves
2559 MoveStack* last = generate_moves(pos, mlist);
2561 // Add each move to the moves[] array
2562 for (MoveStack* cur = mlist; cur != last; cur++)
2564 bool includeMove = includeAllMoves;
2566 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2567 includeMove = (searchMoves[k] == cur->move);
2572 // Find a quick score for the move
2573 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2574 moves[count].pv[1] = MOVE_NONE;
2575 pos.do_move(cur->move, st);
2576 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2577 pos.undo_move(cur->move);
2583 // Score root moves using the standard way used in main search, the moves
2584 // are scored according to the order in which are returned by MovePicker.
2586 void RootMoveList::score_moves(const Position& pos)
2590 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2592 while ((move = mp.get_next_move()) != MOVE_NONE)
2593 for (int i = 0; i < count; i++)
2594 if (moves[i].move == move)
2596 moves[i].mp_score = score--;
2601 // RootMoveList simple methods definitions
2603 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2607 for (j = 0; pv[j] != MOVE_NONE; j++)
2608 moves[moveNum].pv[j] = pv[j];
2610 moves[moveNum].pv[j] = MOVE_NONE;
2614 // RootMoveList::sort() sorts the root move list at the beginning of a new
2617 void RootMoveList::sort() {
2619 sort_multipv(count - 1); // Sort all items
2623 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2624 // list by their scores and depths. It is used to order the different PVs
2625 // correctly in MultiPV mode.
2627 void RootMoveList::sort_multipv(int n) {
2631 for (i = 1; i <= n; i++)
2633 RootMove rm = moves[i];
2634 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2635 moves[j] = moves[j - 1];