2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_thread(int threadID);
86 void idle_loop(int threadID, SplitPoint* sp);
89 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
90 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
96 volatile bool AllThreadsShouldExit;
97 Thread threads[MAX_THREADS];
99 WaitCondition WaitCond[MAX_THREADS];
103 // RootMove struct is used for moves at the root at the tree. For each
104 // root move, we store a score, a node count, and a PV (really a refutation
105 // in the case of moves which fail low).
109 RootMove() : mp_score(0), nodes(0) {}
111 // RootMove::operator<() is the comparison function used when
112 // sorting the moves. A move m1 is considered to be better
113 // than a move m2 if it has a higher score, or if the moves
114 // have equal score but m1 has the higher beta cut-off count.
115 bool operator<(const RootMove& m) const {
117 return score != m.score ? score < m.score : mp_score <= m.mp_score;
124 Move pv[PLY_MAX_PLUS_2];
128 // The RootMoveList class is essentially an array of RootMove objects, with
129 // a handful of methods for accessing the data in the individual moves.
134 RootMoveList(Position& pos, Move searchMoves[]);
136 Move move(int moveNum) const { return moves[moveNum].move; }
137 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
138 int move_count() const { return count; }
139 Value move_score(int moveNum) const { return moves[moveNum].score; }
140 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
141 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
142 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 void set_move_pv(int moveNum, const Move pv[]);
145 void score_moves(const Position& pos);
147 void sort_multipv(int n);
150 RootMove moves[MOVES_MAX];
155 // When formatting a move for std::cout we must know if we are in Chess960
156 // or not. To keep using the handy operator<<() on the move the trick is to
157 // embed this flag in the stream itself. Function-like named enum set960 is
158 // used as a custom manipulator and the stream internal general-purpose array,
159 // accessed through ios_base::iword(), is used to pass the flag to the move's
160 // operator<<() that will use it to properly format castling moves.
163 std::ostream& operator<< (std::ostream& os, const set960& m) {
165 os.iword(0) = int(m);
174 // Maximum depth for razoring
175 const Depth RazorDepth = 4 * ONE_PLY;
177 // Dynamic razoring margin based on depth
178 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
180 // Maximum depth for use of dynamic threat detection when null move fails low
181 const Depth ThreatDepth = 5 * ONE_PLY;
183 // Step 9. Internal iterative deepening
185 // Minimum depth for use of internal iterative deepening
186 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
188 // At Non-PV nodes we do an internal iterative deepening search
189 // when the static evaluation is bigger then beta - IIDMargin.
190 const Value IIDMargin = Value(0x100);
192 // Step 11. Decide the new search depth
194 // Extensions. Configurable UCI options
195 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
196 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
197 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
199 // Minimum depth for use of singular extension
200 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
202 // If the TT move is at least SingularExtensionMargin better then the
203 // remaining ones we will extend it.
204 const Value SingularExtensionMargin = Value(0x20);
206 // Step 12. Futility pruning
208 // Futility margin for quiescence search
209 const Value FutilityMarginQS = Value(0x80);
211 // Futility lookup tables (initialized at startup) and their getter functions
212 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
213 int FutilityMoveCountArray[32]; // [depth]
215 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
216 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
218 // Step 14. Reduced search
220 // Reduction lookup tables (initialized at startup) and their getter functions
221 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
223 template <NodeType PV>
224 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
226 // Common adjustments
228 // Search depth at iteration 1
229 const Depth InitialDepth = ONE_PLY;
231 // Easy move margin. An easy move candidate must be at least this much
232 // better than the second best move.
233 const Value EasyMoveMargin = Value(0x200);
241 // Scores and number of times the best move changed for each iteration
242 Value ValueByIteration[PLY_MAX_PLUS_2];
243 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
245 // Search window management
251 // Time managment variables
252 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
253 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
254 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
259 std::ofstream LogFile;
261 // Multi-threads related variables
262 Depth MinimumSplitDepth;
263 int MaxThreadsPerSplitPoint;
264 ThreadsManager ThreadsMgr;
266 // Node counters, used only by thread[0] but try to keep in different cache
267 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
269 int NodesBetweenPolls = 30000;
276 Value id_loop(const Position& pos, Move searchMoves[]);
277 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
279 template <NodeType PvNode, bool SpNode>
280 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
282 template <NodeType PvNode>
283 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
285 template <NodeType PvNode>
286 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
288 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
289 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
292 template <NodeType PvNode>
293 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
295 bool connected_moves(const Position& pos, Move m1, Move m2);
296 bool value_is_mate(Value value);
297 Value value_to_tt(Value v, int ply);
298 Value value_from_tt(Value v, int ply);
299 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
300 bool connected_threat(const Position& pos, Move m, Move threat);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, SearchStack* ss);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
307 std::string value_to_uci(Value v);
311 void wait_for_stop_or_ponderhit();
312 void init_ss_array(SearchStack* ss, int size);
313 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
314 void insert_pv_in_tt(const Position& pos, Move pv[]);
315 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
317 #if !defined(_MSC_VER)
318 void *init_thread(void *threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
330 /// init_threads(), exit_threads() and nodes_searched() are helpers to
331 /// give accessibility to some TM methods from outside of current file.
333 void init_threads() { ThreadsMgr.init_threads(); }
334 void exit_threads() { ThreadsMgr.exit_threads(); }
335 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
338 /// init_search() is called during startup. It initializes various lookup tables
342 int d; // depth (ONE_PLY == 2)
343 int hd; // half depth (ONE_PLY == 1)
346 // Init reductions array
347 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
349 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
350 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
351 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
352 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
355 // Init futility margins array
356 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
357 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
359 // Init futility move count array
360 for (d = 0; d < 32; d++)
361 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
365 /// perft() is our utility to verify move generation is bug free. All the legal
366 /// moves up to given depth are generated and counted and the sum returned.
368 int perft(Position& pos, Depth depth)
370 MoveStack mlist[MOVES_MAX];
375 // Generate all legal moves
376 MoveStack* last = generate_moves(pos, mlist);
378 // If we are at the last ply we don't need to do and undo
379 // the moves, just to count them.
380 if (depth <= ONE_PLY)
381 return int(last - mlist);
383 // Loop through all legal moves
385 for (MoveStack* cur = mlist; cur != last; cur++)
388 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
389 sum += perft(pos, depth - ONE_PLY);
396 /// think() is the external interface to Stockfish's search, and is called when
397 /// the program receives the UCI 'go' command. It initializes various
398 /// search-related global variables, and calls root_search(). It returns false
399 /// when a quit command is received during the search.
401 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
402 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
404 // Initialize global search variables
405 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
407 ThreadsMgr.resetNodeCounters();
408 SearchStartTime = get_system_time();
409 ExactMaxTime = maxTime;
412 InfiniteSearch = infinite;
413 PonderSearch = ponder;
414 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
416 // Look for a book move, only during games, not tests
417 if (UseTimeManagement && get_option_value_bool("OwnBook"))
419 if (get_option_value_string("Book File") != OpeningBook.file_name())
420 OpeningBook.open(get_option_value_string("Book File"));
422 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
423 if (bookMove != MOVE_NONE)
426 wait_for_stop_or_ponderhit();
428 cout << "bestmove " << bookMove << endl;
433 // Read UCI option values
434 TT.set_size(get_option_value_int("Hash"));
435 if (button_was_pressed("Clear Hash"))
438 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
439 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
440 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
441 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
442 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
443 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
444 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
445 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
446 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
447 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
448 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
449 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
451 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
452 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
453 MultiPV = get_option_value_int("MultiPV");
454 UseLogFile = get_option_value_bool("Use Search Log");
457 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
459 read_weights(pos.side_to_move());
461 // Set the number of active threads
462 int newActiveThreads = get_option_value_int("Threads");
463 if (newActiveThreads != ThreadsMgr.active_threads())
465 ThreadsMgr.set_active_threads(newActiveThreads);
466 init_eval(ThreadsMgr.active_threads());
470 int myTime = time[pos.side_to_move()];
471 int myIncrement = increment[pos.side_to_move()];
472 if (UseTimeManagement)
473 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
475 // Set best NodesBetweenPolls interval to avoid lagging under
476 // heavy time pressure.
478 NodesBetweenPolls = Min(MaxNodes, 30000);
479 else if (myTime && myTime < 1000)
480 NodesBetweenPolls = 1000;
481 else if (myTime && myTime < 5000)
482 NodesBetweenPolls = 5000;
484 NodesBetweenPolls = 30000;
486 // Write search information to log file
488 LogFile << "Searching: " << pos.to_fen() << endl
489 << "infinite: " << infinite
490 << " ponder: " << ponder
491 << " time: " << myTime
492 << " increment: " << myIncrement
493 << " moves to go: " << movesToGo << endl;
495 // We're ready to start thinking. Call the iterative deepening loop function
496 id_loop(pos, searchMoves);
507 // id_loop() is the main iterative deepening loop. It calls root_search
508 // repeatedly with increasing depth until the allocated thinking time has
509 // been consumed, the user stops the search, or the maximum search depth is
512 Value id_loop(const Position& pos, Move searchMoves[]) {
514 Position p(pos, pos.thread());
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(p, 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(p.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 " << ThreadsMgr.nodes_searched()
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(p, 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(p, 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
612 int64_t nodes = ThreadsMgr.nodes_searched();
615 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
616 && current_search_time() > TimeMgr.available_time() / 16)
617 ||( rml.move_nodes(0) > (nodes * 98) / 100
618 && current_search_time() > TimeMgr.available_time() / 32)))
621 // Add some extra time if the best move has changed during the last two iterations
622 if (Iteration > 5 && Iteration <= 50)
623 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
624 BestMoveChangesByIteration[Iteration-1]);
626 // Stop search if most of MaxSearchTime is consumed at the end of the
627 // iteration. We probably don't have enough time to search the first
628 // move at the next iteration anyway.
629 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
635 StopOnPonderhit = true;
641 if (MaxDepth && Iteration >= MaxDepth)
645 // If we are pondering or in infinite search, we shouldn't print the
646 // best move before we are told to do so.
647 if (!AbortSearch && (PonderSearch || InfiniteSearch))
648 wait_for_stop_or_ponderhit();
650 // Print final search statistics
651 cout << "info nodes " << ThreadsMgr.nodes_searched()
653 << " time " << current_search_time() << endl;
655 // Print the best move and the ponder move to the standard output
656 if (pv[0] == MOVE_NONE)
662 assert(pv[0] != MOVE_NONE);
664 cout << "bestmove " << pv[0];
666 if (pv[1] != MOVE_NONE)
667 cout << " ponder " << pv[1];
674 dbg_print_mean(LogFile);
676 if (dbg_show_hit_rate)
677 dbg_print_hit_rate(LogFile);
679 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
680 << "\nNodes/second: " << nps()
681 << "\nBest move: " << move_to_san(p, pv[0]);
684 p.do_move(pv[0], st);
685 LogFile << "\nPonder move: "
686 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
689 return rml.move_score(0);
693 // root_search() is the function which searches the root node. It is
694 // similar to search_pv except that it uses a different move ordering
695 // scheme, prints some information to the standard output and handles
696 // the fail low/high loops.
698 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
704 Depth depth, ext, newDepth;
705 Value value, alpha, beta;
706 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
707 int researchCountFH, researchCountFL;
709 researchCountFH = researchCountFL = 0;
712 isCheck = pos.is_check();
713 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
715 // Step 1. Initialize node (polling is omitted at root)
716 ss->currentMove = ss->bestMove = MOVE_NONE;
718 // Step 2. Check for aborted search (omitted at root)
719 // Step 3. Mate distance pruning (omitted at root)
720 // Step 4. Transposition table lookup (omitted at root)
722 // Step 5. Evaluate the position statically
723 // At root we do this only to get reference value for child nodes
724 ss->evalMargin = VALUE_NONE;
725 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
727 // Step 6. Razoring (omitted at root)
728 // Step 7. Static null move pruning (omitted at root)
729 // Step 8. Null move search with verification search (omitted at root)
730 // Step 9. Internal iterative deepening (omitted at root)
732 // Step extra. Fail low loop
733 // We start with small aspiration window and in case of fail low, we research
734 // with bigger window until we are not failing low anymore.
737 // Sort the moves before to (re)search
738 rml.score_moves(pos);
741 // Step 10. Loop through all moves in the root move list
742 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
744 // This is used by time management
745 FirstRootMove = (i == 0);
747 // Save the current node count before the move is searched
748 nodes = ThreadsMgr.nodes_searched();
750 // Pick the next root move, and print the move and the move number to
751 // the standard output.
752 move = ss->currentMove = rml.move(i);
754 if (current_search_time() >= 1000)
755 cout << "info currmove " << move
756 << " currmovenumber " << i + 1 << endl;
758 moveIsCheck = pos.move_is_check(move);
759 captureOrPromotion = pos.move_is_capture_or_promotion(move);
761 // Step 11. Decide the new search depth
762 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
763 newDepth = depth + ext;
765 // Step 12. Futility pruning (omitted at root)
767 // Step extra. Fail high loop
768 // If move fails high, we research with bigger window until we are not failing
770 value = - VALUE_INFINITE;
774 // Step 13. Make the move
775 pos.do_move(move, st, ci, moveIsCheck);
777 // Step extra. pv search
778 // We do pv search for first moves (i < MultiPV)
779 // and for fail high research (value > alpha)
780 if (i < MultiPV || value > alpha)
782 // Aspiration window is disabled in multi-pv case
784 alpha = -VALUE_INFINITE;
786 // Full depth PV search, done on first move or after a fail high
787 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
791 // Step 14. Reduced search
792 // if the move fails high will be re-searched at full depth
793 bool doFullDepthSearch = true;
795 if ( depth >= 3 * ONE_PLY
797 && !captureOrPromotion
798 && !move_is_castle(move))
800 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
803 assert(newDepth-ss->reduction >= ONE_PLY);
805 // Reduced depth non-pv search using alpha as upperbound
806 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
807 doFullDepthSearch = (value > alpha);
810 // The move failed high, but if reduction is very big we could
811 // face a false positive, retry with a less aggressive reduction,
812 // if the move fails high again then go with full depth search.
813 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
815 assert(newDepth - ONE_PLY >= ONE_PLY);
817 ss->reduction = ONE_PLY;
818 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
819 doFullDepthSearch = (value > alpha);
821 ss->reduction = DEPTH_ZERO; // Restore original reduction
824 // Step 15. Full depth search
825 if (doFullDepthSearch)
827 // Full depth non-pv search using alpha as upperbound
828 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
830 // If we are above alpha then research at same depth but as PV
831 // to get a correct score or eventually a fail high above beta.
833 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
837 // Step 16. Undo move
840 // Can we exit fail high loop ?
841 if (AbortSearch || value < beta)
844 // We are failing high and going to do a research. It's important to update
845 // the score before research in case we run out of time while researching.
846 rml.set_move_score(i, value);
848 extract_pv_from_tt(pos, move, pv);
849 rml.set_move_pv(i, pv);
851 // Print information to the standard output
852 print_pv_info(pos, pv, alpha, beta, value);
854 // Prepare for a research after a fail high, each time with a wider window
855 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
858 } // End of fail high loop
860 // Finished searching the move. If AbortSearch is true, the search
861 // was aborted because the user interrupted the search or because we
862 // ran out of time. In this case, the return value of the search cannot
863 // be trusted, and we break out of the loop without updating the best
868 // Remember searched nodes counts for this move
869 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
871 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
872 assert(value < beta);
874 // Step 17. Check for new best move
875 if (value <= alpha && i >= MultiPV)
876 rml.set_move_score(i, -VALUE_INFINITE);
879 // PV move or new best move!
882 rml.set_move_score(i, value);
884 extract_pv_from_tt(pos, move, pv);
885 rml.set_move_pv(i, pv);
889 // We record how often the best move has been changed in each
890 // iteration. This information is used for time managment: When
891 // the best move changes frequently, we allocate some more time.
893 BestMoveChangesByIteration[Iteration]++;
895 // Print information to the standard output
896 print_pv_info(pos, pv, alpha, beta, value);
898 // Raise alpha to setup proper non-pv search upper bound
905 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
907 cout << "info multipv " << j + 1
908 << " score " << value_to_uci(rml.move_score(j))
909 << " depth " << (j <= i ? Iteration : Iteration - 1)
910 << " time " << current_search_time()
911 << " nodes " << ThreadsMgr.nodes_searched()
915 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
916 cout << rml.move_pv(j, k) << " ";
920 alpha = rml.move_score(Min(i, MultiPV - 1));
922 } // PV move or new best move
924 assert(alpha >= *alphaPtr);
926 AspirationFailLow = (alpha == *alphaPtr);
928 if (AspirationFailLow && StopOnPonderhit)
929 StopOnPonderhit = false;
932 // Can we exit fail low loop ?
933 if (AbortSearch || !AspirationFailLow)
936 // Prepare for a research after a fail low, each time with a wider window
937 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
942 // Sort the moves before to return
949 // search<>() is the main search function for both PV and non-PV nodes and for
950 // normal and SplitPoint nodes. When called just after a split point the search
951 // is simpler because we have already probed the hash table, done a null move
952 // search, and searched the first move before splitting, we don't have to repeat
953 // all this work again. We also don't need to store anything to the hash table
954 // here: This is taken care of after we return from the split point.
956 template <NodeType PvNode, bool SpNode>
957 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
959 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
960 assert(beta > alpha && beta <= VALUE_INFINITE);
961 assert(PvNode || alpha == beta - 1);
962 assert(ply > 0 && ply < PLY_MAX);
963 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
965 Move movesSearched[MOVES_MAX];
969 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;
992 // Step 1. Initialize node and poll. Polling can abort search
993 ThreadsMgr.incrementNodeCounter(threadID);
994 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
995 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
997 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1003 // Step 2. Check for aborted search and immediate draw
1004 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1007 if (pos.is_draw() || ply >= PLY_MAX - 1)
1010 // Step 3. Mate distance pruning
1011 alpha = Max(value_mated_in(ply), alpha);
1012 beta = Min(value_mate_in(ply+1), beta);
1016 // Step 4. Transposition table lookup
1018 // We don't want the score of a partial search to overwrite a previous full search
1019 // TT value, so we use a different position key in case of an excluded move exists.
1020 excludedMove = ss->excludedMove;
1021 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1023 tte = TT.retrieve(posKey);
1024 ttMove = (tte ? tte->move() : MOVE_NONE);
1026 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1027 // This is to avoid problems in the following areas:
1029 // * Repetition draw detection
1030 // * Fifty move rule detection
1031 // * Searching for a mate
1032 // * Printing of full PV line
1034 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1036 // Refresh tte entry to avoid aging
1037 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1039 ss->bestMove = ttMove; // Can be MOVE_NONE
1040 return value_from_tt(tte->value(), ply);
1043 // Step 5. Evaluate the position statically and
1044 // update gain statistics of parent move.
1046 ss->eval = ss->evalMargin = VALUE_NONE;
1049 assert(tte->static_value() != VALUE_NONE);
1051 ss->eval = tte->static_value();
1052 ss->evalMargin = tte->static_value_margin();
1053 refinedValue = refine_eval(tte, ss->eval, ply);
1057 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1058 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1061 // Save gain for the parent non-capture move
1062 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1064 // Step 6. Razoring (is omitted in PV nodes)
1066 && depth < RazorDepth
1068 && refinedValue < beta - razor_margin(depth)
1069 && ttMove == MOVE_NONE
1070 && (ss-1)->currentMove != MOVE_NULL
1071 && !value_is_mate(beta)
1072 && !pos.has_pawn_on_7th(pos.side_to_move()))
1074 Value rbeta = beta - razor_margin(depth);
1075 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1077 // Logically we should return (v + razor_margin(depth)), but
1078 // surprisingly this did slightly weaker in tests.
1082 // Step 7. Static null move pruning (is omitted in PV nodes)
1083 // We're betting that the opponent doesn't have a move that will reduce
1084 // the score by more than futility_margin(depth) if we do a null move.
1086 && !ss->skipNullMove
1087 && depth < RazorDepth
1089 && refinedValue >= beta + futility_margin(depth, 0)
1090 && !value_is_mate(beta)
1091 && pos.non_pawn_material(pos.side_to_move()))
1092 return refinedValue - futility_margin(depth, 0);
1094 // Step 8. Null move search with verification search (is omitted in PV nodes)
1096 && !ss->skipNullMove
1099 && refinedValue >= beta
1100 && !value_is_mate(beta)
1101 && pos.non_pawn_material(pos.side_to_move()))
1103 ss->currentMove = MOVE_NULL;
1105 // Null move dynamic reduction based on depth
1106 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1108 // Null move dynamic reduction based on value
1109 if (refinedValue - beta > PawnValueMidgame)
1112 pos.do_null_move(st);
1113 (ss+1)->skipNullMove = true;
1114 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * ONE_PLY)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1154 // Step 9. Internal iterative deepening
1155 if ( depth >= IIDDepth[PvNode]
1156 && ttMove == MOVE_NONE
1157 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1159 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1161 ss->skipNullMove = true;
1162 search<PvNode>(pos, ss, alpha, beta, d, ply);
1163 ss->skipNullMove = false;
1165 ttMove = ss->bestMove;
1166 tte = TT.retrieve(posKey);
1169 // Expensive mate threat detection (only for PV nodes)
1171 mateThreat = pos.has_mate_threat();
1173 split_point_start: // At split points actual search starts from here
1175 // Initialize a MovePicker object for the current position
1176 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1177 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1178 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1180 ss->bestMove = MOVE_NONE;
1181 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1182 futilityBase = ss->eval + ss->evalMargin;
1183 singularExtensionNode = !SpNode
1184 && depth >= SingularExtensionDepth[PvNode]
1187 && !excludedMove // Do not allow recursive singular extension search
1188 && (tte->type() & VALUE_TYPE_LOWER)
1189 && tte->depth() >= depth - 3 * ONE_PLY;
1192 lock_grab(&(sp->lock));
1193 bestValue = sp->bestValue;
1196 // Step 10. Loop through moves
1197 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1198 while ( bestValue < beta
1199 && (move = mp.get_next_move()) != MOVE_NONE
1200 && !ThreadsMgr.thread_should_stop(threadID))
1204 moveCount = ++sp->moveCount;
1205 lock_release(&(sp->lock));
1208 assert(move_is_ok(move));
1210 if (move == excludedMove)
1213 moveIsCheck = pos.move_is_check(move, ci);
1214 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1216 // Step 11. Decide the new search depth
1217 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1219 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1220 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1221 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1222 // lower then ttValue minus a margin then we extend ttMove.
1223 if ( singularExtensionNode
1224 && move == tte->move()
1227 Value ttValue = value_from_tt(tte->value(), ply);
1229 if (abs(ttValue) < VALUE_KNOWN_WIN)
1231 Value b = ttValue - SingularExtensionMargin;
1232 ss->excludedMove = move;
1233 ss->skipNullMove = true;
1234 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1235 ss->skipNullMove = false;
1236 ss->excludedMove = MOVE_NONE;
1237 ss->bestMove = MOVE_NONE;
1243 newDepth = depth - ONE_PLY + ext;
1245 // Update current move (this must be done after singular extension search)
1246 movesSearched[moveCount] = ss->currentMove = move;
1251 // Step 12. Futility pruning (is omitted in PV nodes)
1253 && !captureOrPromotion
1257 && !move_is_castle(move))
1259 // Move count based pruning
1260 if ( moveCount >= futility_move_count(depth)
1261 && !(threatMove && connected_threat(pos, move, threatMove))
1262 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1265 lock_grab(&(sp->lock));
1270 // Value based pruning
1271 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1272 // but fixing this made program slightly weaker.
1273 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1274 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1275 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1277 if (futilityValueScaled < beta)
1281 lock_grab(&(sp->lock));
1282 if (futilityValueScaled > sp->bestValue)
1283 sp->bestValue = bestValue = futilityValueScaled;
1285 else if (futilityValueScaled > bestValue)
1286 bestValue = futilityValueScaled;
1292 // Step 13. Make the move
1293 pos.do_move(move, st, ci, moveIsCheck);
1295 // Step extra. pv search (only in PV nodes)
1296 // The first move in list is the expected PV
1297 if (!SpNode && PvNode && moveCount == 1)
1298 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1301 // Step 14. Reduced depth search
1302 // If the move fails high will be re-searched at full depth.
1303 bool doFullDepthSearch = true;
1305 if ( depth >= 3 * ONE_PLY
1306 && !captureOrPromotion
1308 && !move_is_castle(move)
1309 && !(ss->killers[0] == move || ss->killers[1] == move))
1311 ss->reduction = reduction<PvNode>(depth, moveCount);
1314 alpha = SpNode ? sp->alpha : alpha;
1315 Depth d = newDepth - ss->reduction;
1316 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1318 doFullDepthSearch = (value > alpha);
1321 // The move failed high, but if reduction is very big we could
1322 // face a false positive, retry with a less aggressive reduction,
1323 // if the move fails high again then go with full depth search.
1324 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1326 assert(newDepth - ONE_PLY >= ONE_PLY);
1328 ss->reduction = ONE_PLY;
1329 alpha = SpNode ? sp->alpha : alpha;
1330 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1331 doFullDepthSearch = (value > alpha);
1333 ss->reduction = DEPTH_ZERO; // Restore original reduction
1336 // Step 15. Full depth search
1337 if (doFullDepthSearch)
1339 alpha = SpNode ? sp->alpha : alpha;
1340 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1342 // Step extra. pv search (only in PV nodes)
1343 // Search only for possible new PV nodes, if instead value >= beta then
1344 // parent node fails low with value <= alpha and tries another move.
1345 if (PvNode && value > alpha && value < beta)
1346 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1350 // Step 16. Undo move
1351 pos.undo_move(move);
1353 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1355 // Step 17. Check for new best move
1358 lock_grab(&(sp->lock));
1359 bestValue = sp->bestValue;
1363 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1368 sp->bestValue = value;
1372 if (SpNode && (!PvNode || value >= beta))
1373 sp->stopRequest = true;
1375 if (PvNode && value < beta) // We want always alpha < beta
1382 if (value == value_mate_in(ply + 1))
1383 ss->mateKiller = move;
1385 ss->bestMove = move;
1388 sp->parentSstack->bestMove = move;
1392 // Step 18. Check for split
1394 && depth >= MinimumSplitDepth
1395 && ThreadsMgr.active_threads() > 1
1397 && ThreadsMgr.available_thread_exists(threadID)
1399 && !ThreadsMgr.thread_should_stop(threadID)
1401 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1402 threatMove, mateThreat, moveCount, &mp, PvNode);
1407 /* Here we have the lock still grabbed */
1408 sp->slaves[threadID] = 0;
1409 lock_release(&(sp->lock));
1413 // Step 19. Check for mate and stalemate
1414 // All legal moves have been searched and if there are
1415 // no legal moves, it must be mate or stalemate.
1416 // If one move was excluded return fail low score.
1418 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1420 // Step 20. Update tables
1421 // If the search is not aborted, update the transposition table,
1422 // history counters, and killer moves.
1423 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1426 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1427 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1428 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1430 // Update killers and history only for non capture moves that fails high
1431 if ( bestValue >= beta
1432 && !pos.move_is_capture_or_promotion(move))
1434 update_history(pos, move, depth, movesSearched, moveCount);
1435 update_killers(move, ss);
1438 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1444 // qsearch() is the quiescence search function, which is called by the main
1445 // search function when the remaining depth is zero (or, to be more precise,
1446 // less than ONE_PLY).
1448 template <NodeType PvNode>
1449 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1451 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1452 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1453 assert(PvNode || alpha == beta - 1);
1455 assert(ply > 0 && ply < PLY_MAX);
1456 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1460 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1461 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1463 Value oldAlpha = alpha;
1465 ThreadsMgr.incrementNodeCounter(pos.thread());
1466 ss->bestMove = ss->currentMove = MOVE_NONE;
1468 // Check for an instant draw or maximum ply reached
1469 if (pos.is_draw() || ply >= PLY_MAX - 1)
1472 // Transposition table lookup. At PV nodes, we don't use the TT for
1473 // pruning, but only for move ordering.
1474 tte = TT.retrieve(pos.get_key());
1475 ttMove = (tte ? tte->move() : MOVE_NONE);
1477 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1479 ss->bestMove = ttMove; // Can be MOVE_NONE
1480 return value_from_tt(tte->value(), ply);
1483 isCheck = pos.is_check();
1485 // Evaluate the position statically
1488 bestValue = futilityBase = -VALUE_INFINITE;
1489 ss->eval = evalMargin = VALUE_NONE;
1490 deepChecks = enoughMaterial = false;
1496 assert(tte->static_value() != VALUE_NONE);
1498 evalMargin = tte->static_value_margin();
1499 ss->eval = bestValue = tte->static_value();
1502 ss->eval = bestValue = evaluate(pos, evalMargin);
1504 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1506 // Stand pat. Return immediately if static value is at least beta
1507 if (bestValue >= beta)
1510 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1515 if (PvNode && bestValue > alpha)
1518 // If we are near beta then try to get a cutoff pushing checks a bit further
1519 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1521 // Futility pruning parameters, not needed when in check
1522 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1523 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1526 // Initialize a MovePicker object for the current position, and prepare
1527 // to search the moves. Because the depth is <= 0 here, only captures,
1528 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1529 // and we are near beta) will be generated.
1530 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1533 // Loop through the moves until no moves remain or a beta cutoff occurs
1534 while ( alpha < beta
1535 && (move = mp.get_next_move()) != MOVE_NONE)
1537 assert(move_is_ok(move));
1539 moveIsCheck = pos.move_is_check(move, ci);
1547 && !move_is_promotion(move)
1548 && !pos.move_is_passed_pawn_push(move))
1550 futilityValue = futilityBase
1551 + pos.endgame_value_of_piece_on(move_to(move))
1552 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1554 if (futilityValue < alpha)
1556 if (futilityValue > bestValue)
1557 bestValue = futilityValue;
1562 // Detect non-capture evasions that are candidate to be pruned
1563 evasionPrunable = isCheck
1564 && bestValue > value_mated_in(PLY_MAX)
1565 && !pos.move_is_capture(move)
1566 && !pos.can_castle(pos.side_to_move());
1568 // Don't search moves with negative SEE values
1570 && (!isCheck || evasionPrunable)
1572 && !move_is_promotion(move)
1573 && pos.see_sign(move) < 0)
1576 // Update current move
1577 ss->currentMove = move;
1579 // Make and search the move
1580 pos.do_move(move, st, ci, moveIsCheck);
1581 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1582 pos.undo_move(move);
1584 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1587 if (value > bestValue)
1593 ss->bestMove = move;
1598 // All legal moves have been searched. A special case: If we're in check
1599 // and no legal moves were found, it is checkmate.
1600 if (isCheck && bestValue == -VALUE_INFINITE)
1601 return value_mated_in(ply);
1603 // Update transposition table
1604 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1605 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1606 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1608 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1614 // connected_moves() tests whether two moves are 'connected' in the sense
1615 // that the first move somehow made the second move possible (for instance
1616 // if the moving piece is the same in both moves). The first move is assumed
1617 // to be the move that was made to reach the current position, while the
1618 // second move is assumed to be a move from the current position.
1620 bool connected_moves(const Position& pos, Move m1, Move m2) {
1622 Square f1, t1, f2, t2;
1625 assert(move_is_ok(m1));
1626 assert(move_is_ok(m2));
1628 if (m2 == MOVE_NONE)
1631 // Case 1: The moving piece is the same in both moves
1637 // Case 2: The destination square for m2 was vacated by m1
1643 // Case 3: Moving through the vacated square
1644 if ( piece_is_slider(pos.piece_on(f2))
1645 && bit_is_set(squares_between(f2, t2), f1))
1648 // Case 4: The destination square for m2 is defended by the moving piece in m1
1649 p = pos.piece_on(t1);
1650 if (bit_is_set(pos.attacks_from(p, t1), t2))
1653 // Case 5: Discovered check, checking piece is the piece moved in m1
1654 if ( piece_is_slider(p)
1655 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1656 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1658 // discovered_check_candidates() works also if the Position's side to
1659 // move is the opposite of the checking piece.
1660 Color them = opposite_color(pos.side_to_move());
1661 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1663 if (bit_is_set(dcCandidates, f2))
1670 // value_is_mate() checks if the given value is a mate one eventually
1671 // compensated for the ply.
1673 bool value_is_mate(Value value) {
1675 assert(abs(value) <= VALUE_INFINITE);
1677 return value <= value_mated_in(PLY_MAX)
1678 || value >= value_mate_in(PLY_MAX);
1682 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1683 // "plies to mate from the current ply". Non-mate scores are unchanged.
1684 // The function is called before storing a value to the transposition table.
1686 Value value_to_tt(Value v, int ply) {
1688 if (v >= value_mate_in(PLY_MAX))
1691 if (v <= value_mated_in(PLY_MAX))
1698 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1699 // the transposition table to a mate score corrected for the current ply.
1701 Value value_from_tt(Value v, int ply) {
1703 if (v >= value_mate_in(PLY_MAX))
1706 if (v <= value_mated_in(PLY_MAX))
1713 // extension() decides whether a move should be searched with normal depth,
1714 // or with extended depth. Certain classes of moves (checking moves, in
1715 // particular) are searched with bigger depth than ordinary moves and in
1716 // any case are marked as 'dangerous'. Note that also if a move is not
1717 // extended, as example because the corresponding UCI option is set to zero,
1718 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1719 template <NodeType PvNode>
1720 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1721 bool singleEvasion, bool mateThreat, bool* dangerous) {
1723 assert(m != MOVE_NONE);
1725 Depth result = DEPTH_ZERO;
1726 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1730 if (moveIsCheck && pos.see_sign(m) >= 0)
1731 result += CheckExtension[PvNode];
1734 result += SingleEvasionExtension[PvNode];
1737 result += MateThreatExtension[PvNode];
1740 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1742 Color c = pos.side_to_move();
1743 if (relative_rank(c, move_to(m)) == RANK_7)
1745 result += PawnPushTo7thExtension[PvNode];
1748 if (pos.pawn_is_passed(c, move_to(m)))
1750 result += PassedPawnExtension[PvNode];
1755 if ( captureOrPromotion
1756 && pos.type_of_piece_on(move_to(m)) != PAWN
1757 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1758 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1759 && !move_is_promotion(m)
1762 result += PawnEndgameExtension[PvNode];
1767 && captureOrPromotion
1768 && pos.type_of_piece_on(move_to(m)) != PAWN
1769 && pos.see_sign(m) >= 0)
1771 result += ONE_PLY / 2;
1775 return Min(result, ONE_PLY);
1779 // connected_threat() tests whether it is safe to forward prune a move or if
1780 // is somehow coonected to the threat move returned by null search.
1782 bool connected_threat(const Position& pos, Move m, Move threat) {
1784 assert(move_is_ok(m));
1785 assert(threat && move_is_ok(threat));
1786 assert(!pos.move_is_check(m));
1787 assert(!pos.move_is_capture_or_promotion(m));
1788 assert(!pos.move_is_passed_pawn_push(m));
1790 Square mfrom, mto, tfrom, tto;
1792 mfrom = move_from(m);
1794 tfrom = move_from(threat);
1795 tto = move_to(threat);
1797 // Case 1: Don't prune moves which move the threatened piece
1801 // Case 2: If the threatened piece has value less than or equal to the
1802 // value of the threatening piece, don't prune move which defend it.
1803 if ( pos.move_is_capture(threat)
1804 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1805 || pos.type_of_piece_on(tfrom) == KING)
1806 && pos.move_attacks_square(m, tto))
1809 // Case 3: If the moving piece in the threatened move is a slider, don't
1810 // prune safe moves which block its ray.
1811 if ( piece_is_slider(pos.piece_on(tfrom))
1812 && bit_is_set(squares_between(tfrom, tto), mto)
1813 && pos.see_sign(m) >= 0)
1820 // ok_to_use_TT() returns true if a transposition table score
1821 // can be used at a given point in search.
1823 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1825 Value v = value_from_tt(tte->value(), ply);
1827 return ( tte->depth() >= depth
1828 || v >= Max(value_mate_in(PLY_MAX), beta)
1829 || v < Min(value_mated_in(PLY_MAX), beta))
1831 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1832 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1836 // refine_eval() returns the transposition table score if
1837 // possible otherwise falls back on static position evaluation.
1839 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1843 Value v = value_from_tt(tte->value(), ply);
1845 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1846 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1853 // update_history() registers a good move that produced a beta-cutoff
1854 // in history and marks as failures all the other moves of that ply.
1856 void update_history(const Position& pos, Move move, Depth depth,
1857 Move movesSearched[], int moveCount) {
1860 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1862 for (int i = 0; i < moveCount - 1; i++)
1864 m = movesSearched[i];
1868 if (!pos.move_is_capture_or_promotion(m))
1869 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1874 // update_killers() add a good move that produced a beta-cutoff
1875 // among the killer moves of that ply.
1877 void update_killers(Move m, SearchStack* ss) {
1879 if (m == ss->killers[0])
1882 ss->killers[1] = ss->killers[0];
1887 // update_gains() updates the gains table of a non-capture move given
1888 // the static position evaluation before and after the move.
1890 void update_gains(const Position& pos, Move m, Value before, Value after) {
1893 && before != VALUE_NONE
1894 && after != VALUE_NONE
1895 && pos.captured_piece_type() == PIECE_TYPE_NONE
1896 && !move_is_special(m))
1897 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1901 // current_search_time() returns the number of milliseconds which have passed
1902 // since the beginning of the current search.
1904 int current_search_time() {
1906 return get_system_time() - SearchStartTime;
1910 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1912 std::string value_to_uci(Value v) {
1914 std::stringstream s;
1916 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1917 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1919 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1924 // nps() computes the current nodes/second count.
1928 int t = current_search_time();
1929 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1933 // poll() performs two different functions: It polls for user input, and it
1934 // looks at the time consumed so far and decides if it's time to abort the
1939 static int lastInfoTime;
1940 int t = current_search_time();
1945 // We are line oriented, don't read single chars
1946 std::string command;
1948 if (!std::getline(std::cin, command))
1951 if (command == "quit")
1954 PonderSearch = false;
1958 else if (command == "stop")
1961 PonderSearch = false;
1963 else if (command == "ponderhit")
1967 // Print search information
1971 else if (lastInfoTime > t)
1972 // HACK: Must be a new search where we searched less than
1973 // NodesBetweenPolls nodes during the first second of search.
1976 else if (t - lastInfoTime >= 1000)
1983 if (dbg_show_hit_rate)
1984 dbg_print_hit_rate();
1986 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1987 << " time " << t << endl;
1990 // Should we stop the search?
1994 bool stillAtFirstMove = FirstRootMove
1995 && !AspirationFailLow
1996 && t > TimeMgr.available_time();
1998 bool noMoreTime = t > TimeMgr.maximum_time()
1999 || stillAtFirstMove;
2001 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2002 || (ExactMaxTime && t >= ExactMaxTime)
2003 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2008 // ponderhit() is called when the program is pondering (i.e. thinking while
2009 // it's the opponent's turn to move) in order to let the engine know that
2010 // it correctly predicted the opponent's move.
2014 int t = current_search_time();
2015 PonderSearch = false;
2017 bool stillAtFirstMove = FirstRootMove
2018 && !AspirationFailLow
2019 && t > TimeMgr.available_time();
2021 bool noMoreTime = t > TimeMgr.maximum_time()
2022 || stillAtFirstMove;
2024 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2029 // init_ss_array() does a fast reset of the first entries of a SearchStack
2030 // array and of all the excludedMove and skipNullMove entries.
2032 void init_ss_array(SearchStack* ss, int size) {
2034 for (int i = 0; i < size; i++, ss++)
2036 ss->excludedMove = MOVE_NONE;
2037 ss->skipNullMove = false;
2038 ss->reduction = DEPTH_ZERO;
2042 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2047 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2048 // while the program is pondering. The point is to work around a wrinkle in
2049 // the UCI protocol: When pondering, the engine is not allowed to give a
2050 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2051 // We simply wait here until one of these commands is sent, and return,
2052 // after which the bestmove and pondermove will be printed (in id_loop()).
2054 void wait_for_stop_or_ponderhit() {
2056 std::string command;
2060 if (!std::getline(std::cin, command))
2063 if (command == "quit")
2068 else if (command == "ponderhit" || command == "stop")
2074 // print_pv_info() prints to standard output and eventually to log file information on
2075 // the current PV line. It is called at each iteration or after a new pv is found.
2077 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2079 cout << "info depth " << Iteration
2080 << " score " << value_to_uci(value)
2081 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2082 << " time " << current_search_time()
2083 << " nodes " << ThreadsMgr.nodes_searched()
2087 for (Move* m = pv; *m != MOVE_NONE; m++)
2094 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2095 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2097 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2098 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2103 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2104 // the PV back into the TT. This makes sure the old PV moves are searched
2105 // first, even if the old TT entries have been overwritten.
2107 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2111 Position p(pos, pos.thread());
2112 Value v, m = VALUE_NONE;
2114 for (int i = 0; pv[i] != MOVE_NONE; i++)
2116 tte = TT.retrieve(p.get_key());
2117 if (!tte || tte->move() != pv[i])
2119 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2120 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2122 p.do_move(pv[i], st);
2127 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2128 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2129 // allow to always have a ponder move even when we fail high at root and also a
2130 // long PV to print that is important for position analysis.
2132 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2136 Position p(pos, pos.thread());
2139 assert(bestMove != MOVE_NONE);
2142 p.do_move(pv[ply++], st);
2144 while ( (tte = TT.retrieve(p.get_key())) != NULL
2145 && tte->move() != MOVE_NONE
2146 && move_is_legal(p, tte->move())
2148 && (!p.is_draw() || ply < 2))
2150 pv[ply] = tte->move();
2151 p.do_move(pv[ply++], st);
2153 pv[ply] = MOVE_NONE;
2157 // init_thread() is the function which is called when a new thread is
2158 // launched. It simply calls the idle_loop() function with the supplied
2159 // threadID. There are two versions of this function; one for POSIX
2160 // threads and one for Windows threads.
2162 #if !defined(_MSC_VER)
2164 void* init_thread(void *threadID) {
2166 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2172 DWORD WINAPI init_thread(LPVOID threadID) {
2174 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2181 /// The ThreadsManager class
2183 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2184 // get_beta_counters() are getters/setters for the per thread
2185 // counters used to sort the moves at root.
2187 void ThreadsManager::resetNodeCounters() {
2189 for (int i = 0; i < MAX_THREADS; i++)
2190 threads[i].nodes = 0ULL;
2193 int64_t ThreadsManager::nodes_searched() const {
2195 int64_t result = 0ULL;
2196 for (int i = 0; i < ActiveThreads; i++)
2197 result += threads[i].nodes;
2203 // idle_loop() is where the threads are parked when they have no work to do.
2204 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2205 // object for which the current thread is the master.
2207 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2209 assert(threadID >= 0 && threadID < MAX_THREADS);
2213 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2214 // master should exit as last one.
2215 if (AllThreadsShouldExit)
2218 threads[threadID].state = THREAD_TERMINATED;
2222 // If we are not thinking, wait for a condition to be signaled
2223 // instead of wasting CPU time polling for work.
2224 while ( threadID >= ActiveThreads
2225 || threads[threadID].state == THREAD_INITIALIZING
2226 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2229 assert(threadID != 0);
2231 if (AllThreadsShouldExit)
2236 // Retest condition under lock protection
2237 if (!( threadID >= ActiveThreads
2238 || threads[threadID].state == THREAD_INITIALIZING
2239 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2241 lock_release(&MPLock);
2245 // Put thread to sleep
2246 threads[threadID].state = THREAD_AVAILABLE;
2247 cond_wait(&WaitCond[threadID], &MPLock);
2248 lock_release(&MPLock);
2251 // If this thread has been assigned work, launch a search
2252 if (threads[threadID].state == THREAD_WORKISWAITING)
2254 assert(!AllThreadsShouldExit);
2256 threads[threadID].state = THREAD_SEARCHING;
2258 // Here we call search() with SplitPoint template parameter set to true
2259 SplitPoint* tsp = threads[threadID].splitPoint;
2260 Position pos(*tsp->pos, threadID);
2261 SearchStack* ss = tsp->sstack[threadID] + 1;
2265 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2267 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2269 assert(threads[threadID].state == THREAD_SEARCHING);
2271 threads[threadID].state = THREAD_AVAILABLE;
2274 // If this thread is the master of a split point and all slaves have
2275 // finished their work at this split point, return from the idle loop.
2277 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2279 if (i == ActiveThreads)
2281 // Because sp->slaves[] is reset under lock protection,
2282 // be sure sp->lock has been released before to return.
2283 lock_grab(&(sp->lock));
2284 lock_release(&(sp->lock));
2286 // In helpful master concept a master can help only a sub-tree, and
2287 // because here is all finished is not possible master is booked.
2288 assert(threads[threadID].state == THREAD_AVAILABLE);
2290 threads[threadID].state = THREAD_SEARCHING;
2297 // init_threads() is called during startup. It launches all helper threads,
2298 // and initializes the split point stack and the global locks and condition
2301 void ThreadsManager::init_threads() {
2306 // Initialize global locks
2309 for (i = 0; i < MAX_THREADS; i++)
2310 cond_init(&WaitCond[i]);
2312 // Initialize splitPoints[] locks
2313 for (i = 0; i < MAX_THREADS; i++)
2314 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2315 lock_init(&(threads[i].splitPoints[j].lock));
2317 // Will be set just before program exits to properly end the threads
2318 AllThreadsShouldExit = false;
2320 // Threads will be put all threads to sleep as soon as created
2323 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2324 threads[0].state = THREAD_SEARCHING;
2325 for (i = 1; i < MAX_THREADS; i++)
2326 threads[i].state = THREAD_INITIALIZING;
2328 // Launch the helper threads
2329 for (i = 1; i < MAX_THREADS; i++)
2332 #if !defined(_MSC_VER)
2333 pthread_t pthread[1];
2334 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2335 pthread_detach(pthread[0]);
2337 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2342 cout << "Failed to create thread number " << i << endl;
2343 Application::exit_with_failure();
2346 // Wait until the thread has finished launching and is gone to sleep
2347 while (threads[i].state == THREAD_INITIALIZING) {}
2352 // exit_threads() is called when the program exits. It makes all the
2353 // helper threads exit cleanly.
2355 void ThreadsManager::exit_threads() {
2357 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2359 // Wake up all the threads and waits for termination
2360 for (int i = 1; i < MAX_THREADS; i++)
2362 wake_sleeping_thread(i);
2363 while (threads[i].state != THREAD_TERMINATED) {}
2366 // Now we can safely destroy the locks
2367 for (int i = 0; i < MAX_THREADS; i++)
2368 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2369 lock_destroy(&(threads[i].splitPoints[j].lock));
2371 lock_destroy(&MPLock);
2373 // Now we can safely destroy the wait conditions
2374 for (int i = 0; i < MAX_THREADS; i++)
2375 cond_destroy(&WaitCond[i]);
2379 // thread_should_stop() checks whether the thread should stop its search.
2380 // This can happen if a beta cutoff has occurred in the thread's currently
2381 // active split point, or in some ancestor of the current split point.
2383 bool ThreadsManager::thread_should_stop(int threadID) const {
2385 assert(threadID >= 0 && threadID < ActiveThreads);
2387 SplitPoint* sp = threads[threadID].splitPoint;
2389 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2394 // thread_is_available() checks whether the thread with threadID "slave" is
2395 // available to help the thread with threadID "master" at a split point. An
2396 // obvious requirement is that "slave" must be idle. With more than two
2397 // threads, this is not by itself sufficient: If "slave" is the master of
2398 // some active split point, it is only available as a slave to the other
2399 // threads which are busy searching the split point at the top of "slave"'s
2400 // split point stack (the "helpful master concept" in YBWC terminology).
2402 bool ThreadsManager::thread_is_available(int slave, int master) const {
2404 assert(slave >= 0 && slave < ActiveThreads);
2405 assert(master >= 0 && master < ActiveThreads);
2406 assert(ActiveThreads > 1);
2408 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2411 // Make a local copy to be sure doesn't change under our feet
2412 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2414 // No active split points means that the thread is available as
2415 // a slave for any other thread.
2416 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2419 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2420 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2421 // could have been set to 0 by another thread leading to an out of bound access.
2422 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2429 // available_thread_exists() tries to find an idle thread which is available as
2430 // a slave for the thread with threadID "master".
2432 bool ThreadsManager::available_thread_exists(int master) const {
2434 assert(master >= 0 && master < ActiveThreads);
2435 assert(ActiveThreads > 1);
2437 for (int i = 0; i < ActiveThreads; i++)
2438 if (thread_is_available(i, master))
2445 // split() does the actual work of distributing the work at a node between
2446 // several available threads. If it does not succeed in splitting the
2447 // node (because no idle threads are available, or because we have no unused
2448 // split point objects), the function immediately returns. If splitting is
2449 // possible, a SplitPoint object is initialized with all the data that must be
2450 // copied to the helper threads and we tell our helper threads that they have
2451 // been assigned work. This will cause them to instantly leave their idle loops and
2452 // call search().When all threads have returned from search() then split() returns.
2454 template <bool Fake>
2455 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2456 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2457 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2459 assert(ply > 0 && ply < PLY_MAX);
2460 assert(*bestValue >= -VALUE_INFINITE);
2461 assert(*bestValue <= *alpha);
2462 assert(*alpha < beta);
2463 assert(beta <= VALUE_INFINITE);
2464 assert(depth > DEPTH_ZERO);
2465 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2466 assert(ActiveThreads > 1);
2468 int i, master = p.thread();
2469 Thread& masterThread = threads[master];
2473 // If no other thread is available to help us, or if we have too many
2474 // active split points, don't split.
2475 if ( !available_thread_exists(master)
2476 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2478 lock_release(&MPLock);
2482 // Pick the next available split point object from the split point stack
2483 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2485 // Initialize the split point object
2486 splitPoint.parent = masterThread.splitPoint;
2487 splitPoint.stopRequest = false;
2488 splitPoint.ply = ply;
2489 splitPoint.depth = depth;
2490 splitPoint.threatMove = threatMove;
2491 splitPoint.mateThreat = mateThreat;
2492 splitPoint.alpha = *alpha;
2493 splitPoint.beta = beta;
2494 splitPoint.pvNode = pvNode;
2495 splitPoint.bestValue = *bestValue;
2497 splitPoint.moveCount = moveCount;
2498 splitPoint.pos = &p;
2499 splitPoint.parentSstack = ss;
2500 for (i = 0; i < ActiveThreads; i++)
2501 splitPoint.slaves[i] = 0;
2503 masterThread.splitPoint = &splitPoint;
2505 // If we are here it means we are not available
2506 assert(masterThread.state != THREAD_AVAILABLE);
2508 int workersCnt = 1; // At least the master is included
2510 // Allocate available threads setting state to THREAD_BOOKED
2511 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2512 if (thread_is_available(i, master))
2514 threads[i].state = THREAD_BOOKED;
2515 threads[i].splitPoint = &splitPoint;
2516 splitPoint.slaves[i] = 1;
2520 assert(Fake || workersCnt > 1);
2522 // We can release the lock because slave threads are already booked and master is not available
2523 lock_release(&MPLock);
2525 // Tell the threads that they have work to do. This will make them leave
2526 // their idle loop. But before copy search stack tail for each thread.
2527 for (i = 0; i < ActiveThreads; i++)
2528 if (i == master || splitPoint.slaves[i])
2530 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2532 assert(i == master || threads[i].state == THREAD_BOOKED);
2534 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2536 wake_sleeping_thread(i);
2539 // Everything is set up. The master thread enters the idle loop, from
2540 // which it will instantly launch a search, because its state is
2541 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2542 // idle loop, which means that the main thread will return from the idle
2543 // loop when all threads have finished their work at this split point.
2544 idle_loop(master, &splitPoint);
2546 // We have returned from the idle loop, which means that all threads are
2547 // finished. Update alpha and bestValue, and return.
2550 *alpha = splitPoint.alpha;
2551 *bestValue = splitPoint.bestValue;
2552 masterThread.activeSplitPoints--;
2553 masterThread.splitPoint = splitPoint.parent;
2555 lock_release(&MPLock);
2559 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2560 // to start a new search from the root.
2562 void ThreadsManager::wake_sleeping_thread(int threadID) {
2565 cond_signal(&WaitCond[threadID]);
2566 lock_release(&MPLock);
2570 /// The RootMoveList class
2572 // RootMoveList c'tor
2574 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2576 SearchStack ss[PLY_MAX_PLUS_2];
2577 MoveStack mlist[MOVES_MAX];
2579 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2581 // Initialize search stack
2582 init_ss_array(ss, PLY_MAX_PLUS_2);
2583 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2586 // Generate all legal moves
2587 MoveStack* last = generate_moves(pos, mlist);
2589 // Add each move to the moves[] array
2590 for (MoveStack* cur = mlist; cur != last; cur++)
2592 bool includeMove = includeAllMoves;
2594 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2595 includeMove = (searchMoves[k] == cur->move);
2600 // Find a quick score for the move
2601 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2602 moves[count].pv[1] = MOVE_NONE;
2603 pos.do_move(cur->move, st);
2604 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2605 pos.undo_move(cur->move);
2611 // Score root moves using the standard way used in main search, the moves
2612 // are scored according to the order in which are returned by MovePicker.
2614 void RootMoveList::score_moves(const Position& pos)
2618 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2620 while ((move = mp.get_next_move()) != MOVE_NONE)
2621 for (int i = 0; i < count; i++)
2622 if (moves[i].move == move)
2624 moves[i].mp_score = score--;
2629 // RootMoveList simple methods definitions
2631 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2635 for (j = 0; pv[j] != MOVE_NONE; j++)
2636 moves[moveNum].pv[j] = pv[j];
2638 moves[moveNum].pv[j] = MOVE_NONE;
2642 // RootMoveList::sort() sorts the root move list at the beginning of a new
2645 void RootMoveList::sort() {
2647 sort_multipv(count - 1); // Sort all items
2651 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2652 // list by their scores and depths. It is used to order the different PVs
2653 // correctly in MultiPV mode.
2655 void RootMoveList::sort_multipv(int n) {
2659 for (i = 1; i <= n; i++)
2661 RootMove rm = moves[i];
2662 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2663 moves[j] = moves[j - 1];