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;
972 Value bestValue, value, oldAlpha;
973 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
974 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
975 bool mateThreat = false;
977 int threadID = pos.thread();
978 SplitPoint* sp = NULL;
979 refinedValue = bestValue = value = -VALUE_INFINITE;
981 isCheck = pos.is_check();
987 ttMove = excludedMove = MOVE_NONE;
988 threatMove = sp->threatMove;
989 mateThreat = sp->mateThreat;
990 goto split_point_start;
991 } else {} // Hack to fix icc's "statement is unreachable" warning
993 // Step 1. Initialize node and poll. Polling can abort search
994 ThreadsMgr.incrementNodeCounter(threadID);
995 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
996 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
998 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1004 // Step 2. Check for aborted search and immediate draw
1005 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1006 || pos.is_draw() || ply >= PLY_MAX - 1)
1009 // Step 3. Mate distance pruning
1010 alpha = Max(value_mated_in(ply), alpha);
1011 beta = Min(value_mate_in(ply+1), beta);
1015 // Step 4. Transposition table lookup
1017 // We don't want the score of a partial search to overwrite a previous full search
1018 // TT value, so we use a different position key in case of an excluded move exists.
1019 excludedMove = ss->excludedMove;
1020 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1022 tte = TT.retrieve(posKey);
1023 ttMove = tte ? tte->move() : MOVE_NONE;
1025 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1026 // This is to avoid problems in the following areas:
1028 // * Repetition draw detection
1029 // * Fifty move rule detection
1030 // * Searching for a mate
1031 // * Printing of full PV line
1032 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1035 ss->bestMove = ttMove; // Can be MOVE_NONE
1036 return value_from_tt(tte->value(), ply);
1039 // Step 5. Evaluate the position statically and
1040 // update gain statistics of parent move.
1042 ss->eval = ss->evalMargin = VALUE_NONE;
1045 assert(tte->static_value() != VALUE_NONE);
1047 ss->eval = tte->static_value();
1048 ss->evalMargin = tte->static_value_margin();
1049 refinedValue = refine_eval(tte, ss->eval, ply);
1053 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1054 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1057 // Save gain for the parent non-capture move
1058 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1060 // Step 6. Razoring (is omitted in PV nodes)
1062 && depth < RazorDepth
1064 && refinedValue < beta - razor_margin(depth)
1065 && ttMove == MOVE_NONE
1066 && (ss-1)->currentMove != MOVE_NULL
1067 && !value_is_mate(beta)
1068 && !pos.has_pawn_on_7th(pos.side_to_move()))
1070 Value rbeta = beta - razor_margin(depth);
1071 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1073 // Logically we should return (v + razor_margin(depth)), but
1074 // surprisingly this did slightly weaker in tests.
1078 // Step 7. Static null move pruning (is omitted in PV nodes)
1079 // We're betting that the opponent doesn't have a move that will reduce
1080 // the score by more than futility_margin(depth) if we do a null move.
1082 && !ss->skipNullMove
1083 && depth < RazorDepth
1085 && refinedValue >= beta + futility_margin(depth, 0)
1086 && !value_is_mate(beta)
1087 && pos.non_pawn_material(pos.side_to_move()))
1088 return refinedValue - futility_margin(depth, 0);
1090 // Step 8. Null move search with verification search (is omitted in PV nodes)
1092 && !ss->skipNullMove
1095 && refinedValue >= beta
1096 && !value_is_mate(beta)
1097 && pos.non_pawn_material(pos.side_to_move()))
1099 ss->currentMove = MOVE_NULL;
1101 // Null move dynamic reduction based on depth
1102 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1104 // Null move dynamic reduction based on value
1105 if (refinedValue - beta > PawnValueMidgame)
1108 pos.do_null_move(st);
1109 (ss+1)->skipNullMove = true;
1110 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1111 (ss+1)->skipNullMove = false;
1112 pos.undo_null_move();
1114 if (nullValue >= beta)
1116 // Do not return unproven mate scores
1117 if (nullValue >= value_mate_in(PLY_MAX))
1120 if (depth < 6 * ONE_PLY)
1123 // Do verification search at high depths
1124 ss->skipNullMove = true;
1125 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1126 ss->skipNullMove = false;
1133 // The null move failed low, which means that we may be faced with
1134 // some kind of threat. If the previous move was reduced, check if
1135 // the move that refuted the null move was somehow connected to the
1136 // move which was reduced. If a connection is found, return a fail
1137 // low score (which will cause the reduced move to fail high in the
1138 // parent node, which will trigger a re-search with full depth).
1139 if (nullValue == value_mated_in(ply + 2))
1142 threatMove = (ss+1)->bestMove;
1143 if ( depth < ThreatDepth
1144 && (ss-1)->reduction
1145 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1150 // Step 9. Internal iterative deepening
1151 if ( depth >= IIDDepth[PvNode]
1152 && ttMove == MOVE_NONE
1153 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1155 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1157 ss->skipNullMove = true;
1158 search<PvNode>(pos, ss, alpha, beta, d, ply);
1159 ss->skipNullMove = false;
1161 ttMove = ss->bestMove;
1162 tte = TT.retrieve(posKey);
1165 // Expensive mate threat detection (only for PV nodes)
1167 mateThreat = pos.has_mate_threat();
1169 split_point_start: // At split points actual search starts from here
1171 // Initialize a MovePicker object for the current position
1172 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1173 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1174 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1176 ss->bestMove = MOVE_NONE;
1177 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1178 futilityBase = ss->eval + ss->evalMargin;
1179 singularExtensionNode = !SpNode
1180 && depth >= SingularExtensionDepth[PvNode]
1183 && !excludedMove // Do not allow recursive singular extension search
1184 && (tte->type() & VALUE_TYPE_LOWER)
1185 && tte->depth() >= depth - 3 * ONE_PLY;
1188 lock_grab(&(sp->lock));
1189 bestValue = sp->bestValue;
1192 // Step 10. Loop through moves
1193 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1194 while ( bestValue < beta
1195 && (move = mp.get_next_move()) != MOVE_NONE
1196 && !ThreadsMgr.thread_should_stop(threadID))
1198 assert(move_is_ok(move));
1202 moveCount = ++sp->moveCount;
1203 lock_release(&(sp->lock));
1205 else if (move == excludedMove)
1208 movesSearched[moveCount++] = move;
1210 moveIsCheck = pos.move_is_check(move, ci);
1211 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1213 // Step 11. Decide the new search depth
1214 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1216 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1217 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1218 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1219 // lower then ttValue minus a margin then we extend ttMove.
1220 if ( singularExtensionNode
1221 && move == tte->move()
1224 Value ttValue = value_from_tt(tte->value(), ply);
1226 if (abs(ttValue) < VALUE_KNOWN_WIN)
1228 Value b = ttValue - SingularExtensionMargin;
1229 ss->excludedMove = move;
1230 ss->skipNullMove = true;
1231 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1232 ss->skipNullMove = false;
1233 ss->excludedMove = MOVE_NONE;
1234 ss->bestMove = MOVE_NONE;
1240 // Update current move (this must be done after singular extension search)
1241 ss->currentMove = move;
1242 newDepth = depth - ONE_PLY + ext;
1244 // Step 12. Futility pruning (is omitted in PV nodes)
1246 && !captureOrPromotion
1250 && !move_is_castle(move))
1252 // Move count based pruning
1253 if ( moveCount >= futility_move_count(depth)
1254 && !(threatMove && connected_threat(pos, move, threatMove))
1255 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1258 lock_grab(&(sp->lock));
1263 // Value based pruning
1264 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1265 // but fixing this made program slightly weaker.
1266 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1267 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1268 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1270 if (futilityValueScaled < beta)
1274 lock_grab(&(sp->lock));
1275 if (futilityValueScaled > sp->bestValue)
1276 sp->bestValue = bestValue = futilityValueScaled;
1278 else if (futilityValueScaled > bestValue)
1279 bestValue = futilityValueScaled;
1285 // Step 13. Make the move
1286 pos.do_move(move, st, ci, moveIsCheck);
1288 // Step extra. pv search (only in PV nodes)
1289 // The first move in list is the expected PV
1290 if (!SpNode && PvNode && moveCount == 1)
1291 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1294 // Step 14. Reduced depth search
1295 // If the move fails high will be re-searched at full depth.
1296 bool doFullDepthSearch = true;
1298 if ( depth >= 3 * ONE_PLY
1299 && !captureOrPromotion
1301 && !move_is_castle(move)
1302 && !(ss->killers[0] == move || ss->killers[1] == move))
1304 ss->reduction = reduction<PvNode>(depth, moveCount);
1307 alpha = SpNode ? sp->alpha : alpha;
1308 Depth d = newDepth - ss->reduction;
1309 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1311 doFullDepthSearch = (value > alpha);
1314 // The move failed high, but if reduction is very big we could
1315 // face a false positive, retry with a less aggressive reduction,
1316 // if the move fails high again then go with full depth search.
1317 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1319 assert(newDepth - ONE_PLY >= ONE_PLY);
1321 ss->reduction = ONE_PLY;
1322 alpha = SpNode ? sp->alpha : alpha;
1323 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1324 doFullDepthSearch = (value > alpha);
1326 ss->reduction = DEPTH_ZERO; // Restore original reduction
1329 // Step 15. Full depth search
1330 if (doFullDepthSearch)
1332 alpha = SpNode ? sp->alpha : alpha;
1333 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1335 // Step extra. pv search (only in PV nodes)
1336 // Search only for possible new PV nodes, if instead value >= beta then
1337 // parent node fails low with value <= alpha and tries another move.
1338 if (PvNode && value > alpha && value < beta)
1339 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1343 // Step 16. Undo move
1344 pos.undo_move(move);
1346 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1348 // Step 17. Check for new best move
1351 lock_grab(&(sp->lock));
1352 bestValue = sp->bestValue;
1356 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1361 sp->bestValue = value;
1365 if (SpNode && (!PvNode || value >= beta))
1366 sp->stopRequest = true;
1368 if (PvNode && value < beta) // We want always alpha < beta
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1381 sp->parentSstack->bestMove = move;
1385 // Step 18. Check for split
1387 && depth >= MinimumSplitDepth
1388 && ThreadsMgr.active_threads() > 1
1390 && ThreadsMgr.available_thread_exists(threadID)
1392 && !ThreadsMgr.thread_should_stop(threadID)
1394 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1395 threatMove, mateThreat, moveCount, &mp, PvNode);
1398 // Step 19. Check for mate and stalemate
1399 // All legal moves have been searched and if there are
1400 // no legal moves, it must be mate or stalemate.
1401 // If one move was excluded return fail low score.
1402 if (!SpNode && !moveCount)
1403 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1405 // Step 20. Update tables
1406 // If the search is not aborted, update the transposition table,
1407 // history counters, and killer moves.
1408 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1410 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1411 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1412 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1414 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1416 // Update killers and history only for non capture moves that fails high
1417 if ( bestValue >= beta
1418 && !pos.move_is_capture_or_promotion(move))
1420 update_history(pos, move, depth, movesSearched, moveCount);
1421 update_killers(move, ss);
1427 // Here we have the lock still grabbed
1428 sp->slaves[threadID] = 0;
1429 lock_release(&(sp->lock));
1432 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1438 // qsearch() is the quiescence search function, which is called by the main
1439 // search function when the remaining depth is zero (or, to be more precise,
1440 // less than ONE_PLY).
1442 template <NodeType PvNode>
1443 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1445 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1446 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1447 assert(PvNode || alpha == beta - 1);
1449 assert(ply > 0 && ply < PLY_MAX);
1450 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1454 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1455 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1457 Value oldAlpha = alpha;
1459 ThreadsMgr.incrementNodeCounter(pos.thread());
1460 ss->bestMove = ss->currentMove = MOVE_NONE;
1462 // Check for an instant draw or maximum ply reached
1463 if (pos.is_draw() || ply >= PLY_MAX - 1)
1466 // Transposition table lookup. At PV nodes, we don't use the TT for
1467 // pruning, but only for move ordering.
1468 tte = TT.retrieve(pos.get_key());
1469 ttMove = (tte ? tte->move() : MOVE_NONE);
1471 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1473 ss->bestMove = ttMove; // Can be MOVE_NONE
1474 return value_from_tt(tte->value(), ply);
1477 isCheck = pos.is_check();
1479 // Evaluate the position statically
1482 bestValue = futilityBase = -VALUE_INFINITE;
1483 ss->eval = evalMargin = VALUE_NONE;
1484 deepChecks = enoughMaterial = false;
1490 assert(tte->static_value() != VALUE_NONE);
1492 evalMargin = tte->static_value_margin();
1493 ss->eval = bestValue = tte->static_value();
1496 ss->eval = bestValue = evaluate(pos, evalMargin);
1498 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1500 // Stand pat. Return immediately if static value is at least beta
1501 if (bestValue >= beta)
1504 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1509 if (PvNode && bestValue > alpha)
1512 // If we are near beta then try to get a cutoff pushing checks a bit further
1513 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1515 // Futility pruning parameters, not needed when in check
1516 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1517 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1520 // Initialize a MovePicker object for the current position, and prepare
1521 // to search the moves. Because the depth is <= 0 here, only captures,
1522 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1523 // and we are near beta) will be generated.
1524 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1527 // Loop through the moves until no moves remain or a beta cutoff occurs
1528 while ( alpha < beta
1529 && (move = mp.get_next_move()) != MOVE_NONE)
1531 assert(move_is_ok(move));
1533 moveIsCheck = pos.move_is_check(move, ci);
1541 && !move_is_promotion(move)
1542 && !pos.move_is_passed_pawn_push(move))
1544 futilityValue = futilityBase
1545 + pos.endgame_value_of_piece_on(move_to(move))
1546 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1548 if (futilityValue < alpha)
1550 if (futilityValue > bestValue)
1551 bestValue = futilityValue;
1556 // Detect non-capture evasions that are candidate to be pruned
1557 evasionPrunable = isCheck
1558 && bestValue > value_mated_in(PLY_MAX)
1559 && !pos.move_is_capture(move)
1560 && !pos.can_castle(pos.side_to_move());
1562 // Don't search moves with negative SEE values
1564 && (!isCheck || evasionPrunable)
1566 && !move_is_promotion(move)
1567 && pos.see_sign(move) < 0)
1570 // Update current move
1571 ss->currentMove = move;
1573 // Make and search the move
1574 pos.do_move(move, st, ci, moveIsCheck);
1575 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1576 pos.undo_move(move);
1578 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1581 if (value > bestValue)
1587 ss->bestMove = move;
1592 // All legal moves have been searched. A special case: If we're in check
1593 // and no legal moves were found, it is checkmate.
1594 if (isCheck && bestValue == -VALUE_INFINITE)
1595 return value_mated_in(ply);
1597 // Update transposition table
1598 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1599 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1600 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1602 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1608 // connected_moves() tests whether two moves are 'connected' in the sense
1609 // that the first move somehow made the second move possible (for instance
1610 // if the moving piece is the same in both moves). The first move is assumed
1611 // to be the move that was made to reach the current position, while the
1612 // second move is assumed to be a move from the current position.
1614 bool connected_moves(const Position& pos, Move m1, Move m2) {
1616 Square f1, t1, f2, t2;
1619 assert(move_is_ok(m1));
1620 assert(move_is_ok(m2));
1622 if (m2 == MOVE_NONE)
1625 // Case 1: The moving piece is the same in both moves
1631 // Case 2: The destination square for m2 was vacated by m1
1637 // Case 3: Moving through the vacated square
1638 if ( piece_is_slider(pos.piece_on(f2))
1639 && bit_is_set(squares_between(f2, t2), f1))
1642 // Case 4: The destination square for m2 is defended by the moving piece in m1
1643 p = pos.piece_on(t1);
1644 if (bit_is_set(pos.attacks_from(p, t1), t2))
1647 // Case 5: Discovered check, checking piece is the piece moved in m1
1648 if ( piece_is_slider(p)
1649 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1650 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1652 // discovered_check_candidates() works also if the Position's side to
1653 // move is the opposite of the checking piece.
1654 Color them = opposite_color(pos.side_to_move());
1655 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1657 if (bit_is_set(dcCandidates, f2))
1664 // value_is_mate() checks if the given value is a mate one eventually
1665 // compensated for the ply.
1667 bool value_is_mate(Value value) {
1669 assert(abs(value) <= VALUE_INFINITE);
1671 return value <= value_mated_in(PLY_MAX)
1672 || value >= value_mate_in(PLY_MAX);
1676 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1677 // "plies to mate from the current ply". Non-mate scores are unchanged.
1678 // The function is called before storing a value to the transposition table.
1680 Value value_to_tt(Value v, int ply) {
1682 if (v >= value_mate_in(PLY_MAX))
1685 if (v <= value_mated_in(PLY_MAX))
1692 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1693 // the transposition table to a mate score corrected for the current ply.
1695 Value value_from_tt(Value v, int ply) {
1697 if (v >= value_mate_in(PLY_MAX))
1700 if (v <= value_mated_in(PLY_MAX))
1707 // extension() decides whether a move should be searched with normal depth,
1708 // or with extended depth. Certain classes of moves (checking moves, in
1709 // particular) are searched with bigger depth than ordinary moves and in
1710 // any case are marked as 'dangerous'. Note that also if a move is not
1711 // extended, as example because the corresponding UCI option is set to zero,
1712 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1713 template <NodeType PvNode>
1714 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1715 bool singleEvasion, bool mateThreat, bool* dangerous) {
1717 assert(m != MOVE_NONE);
1719 Depth result = DEPTH_ZERO;
1720 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1724 if (moveIsCheck && pos.see_sign(m) >= 0)
1725 result += CheckExtension[PvNode];
1728 result += SingleEvasionExtension[PvNode];
1731 result += MateThreatExtension[PvNode];
1734 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1736 Color c = pos.side_to_move();
1737 if (relative_rank(c, move_to(m)) == RANK_7)
1739 result += PawnPushTo7thExtension[PvNode];
1742 if (pos.pawn_is_passed(c, move_to(m)))
1744 result += PassedPawnExtension[PvNode];
1749 if ( captureOrPromotion
1750 && pos.type_of_piece_on(move_to(m)) != PAWN
1751 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1752 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1753 && !move_is_promotion(m)
1756 result += PawnEndgameExtension[PvNode];
1761 && captureOrPromotion
1762 && pos.type_of_piece_on(move_to(m)) != PAWN
1763 && pos.see_sign(m) >= 0)
1765 result += ONE_PLY / 2;
1769 return Min(result, ONE_PLY);
1773 // connected_threat() tests whether it is safe to forward prune a move or if
1774 // is somehow coonected to the threat move returned by null search.
1776 bool connected_threat(const Position& pos, Move m, Move threat) {
1778 assert(move_is_ok(m));
1779 assert(threat && move_is_ok(threat));
1780 assert(!pos.move_is_check(m));
1781 assert(!pos.move_is_capture_or_promotion(m));
1782 assert(!pos.move_is_passed_pawn_push(m));
1784 Square mfrom, mto, tfrom, tto;
1786 mfrom = move_from(m);
1788 tfrom = move_from(threat);
1789 tto = move_to(threat);
1791 // Case 1: Don't prune moves which move the threatened piece
1795 // Case 2: If the threatened piece has value less than or equal to the
1796 // value of the threatening piece, don't prune move which defend it.
1797 if ( pos.move_is_capture(threat)
1798 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1799 || pos.type_of_piece_on(tfrom) == KING)
1800 && pos.move_attacks_square(m, tto))
1803 // Case 3: If the moving piece in the threatened move is a slider, don't
1804 // prune safe moves which block its ray.
1805 if ( piece_is_slider(pos.piece_on(tfrom))
1806 && bit_is_set(squares_between(tfrom, tto), mto)
1807 && pos.see_sign(m) >= 0)
1814 // ok_to_use_TT() returns true if a transposition table score
1815 // can be used at a given point in search.
1817 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1819 Value v = value_from_tt(tte->value(), ply);
1821 return ( tte->depth() >= depth
1822 || v >= Max(value_mate_in(PLY_MAX), beta)
1823 || v < Min(value_mated_in(PLY_MAX), beta))
1825 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1826 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1830 // refine_eval() returns the transposition table score if
1831 // possible otherwise falls back on static position evaluation.
1833 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1837 Value v = value_from_tt(tte->value(), ply);
1839 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1840 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1847 // update_history() registers a good move that produced a beta-cutoff
1848 // in history and marks as failures all the other moves of that ply.
1850 void update_history(const Position& pos, Move move, Depth depth,
1851 Move movesSearched[], int moveCount) {
1854 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1856 for (int i = 0; i < moveCount - 1; i++)
1858 m = movesSearched[i];
1862 if (!pos.move_is_capture_or_promotion(m))
1863 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1868 // update_killers() add a good move that produced a beta-cutoff
1869 // among the killer moves of that ply.
1871 void update_killers(Move m, SearchStack* ss) {
1873 if (m == ss->killers[0])
1876 ss->killers[1] = ss->killers[0];
1881 // update_gains() updates the gains table of a non-capture move given
1882 // the static position evaluation before and after the move.
1884 void update_gains(const Position& pos, Move m, Value before, Value after) {
1887 && before != VALUE_NONE
1888 && after != VALUE_NONE
1889 && pos.captured_piece_type() == PIECE_TYPE_NONE
1890 && !move_is_special(m))
1891 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1895 // current_search_time() returns the number of milliseconds which have passed
1896 // since the beginning of the current search.
1898 int current_search_time() {
1900 return get_system_time() - SearchStartTime;
1904 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1906 std::string value_to_uci(Value v) {
1908 std::stringstream s;
1910 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1911 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1913 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1918 // nps() computes the current nodes/second count.
1922 int t = current_search_time();
1923 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1927 // poll() performs two different functions: It polls for user input, and it
1928 // looks at the time consumed so far and decides if it's time to abort the
1933 static int lastInfoTime;
1934 int t = current_search_time();
1939 // We are line oriented, don't read single chars
1940 std::string command;
1942 if (!std::getline(std::cin, command))
1945 if (command == "quit")
1948 PonderSearch = false;
1952 else if (command == "stop")
1955 PonderSearch = false;
1957 else if (command == "ponderhit")
1961 // Print search information
1965 else if (lastInfoTime > t)
1966 // HACK: Must be a new search where we searched less than
1967 // NodesBetweenPolls nodes during the first second of search.
1970 else if (t - lastInfoTime >= 1000)
1977 if (dbg_show_hit_rate)
1978 dbg_print_hit_rate();
1980 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1981 << " time " << t << endl;
1984 // Should we stop the search?
1988 bool stillAtFirstMove = FirstRootMove
1989 && !AspirationFailLow
1990 && t > TimeMgr.available_time();
1992 bool noMoreTime = t > TimeMgr.maximum_time()
1993 || stillAtFirstMove;
1995 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1996 || (ExactMaxTime && t >= ExactMaxTime)
1997 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2002 // ponderhit() is called when the program is pondering (i.e. thinking while
2003 // it's the opponent's turn to move) in order to let the engine know that
2004 // it correctly predicted the opponent's move.
2008 int t = current_search_time();
2009 PonderSearch = false;
2011 bool stillAtFirstMove = FirstRootMove
2012 && !AspirationFailLow
2013 && t > TimeMgr.available_time();
2015 bool noMoreTime = t > TimeMgr.maximum_time()
2016 || stillAtFirstMove;
2018 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2023 // init_ss_array() does a fast reset of the first entries of a SearchStack
2024 // array and of all the excludedMove and skipNullMove entries.
2026 void init_ss_array(SearchStack* ss, int size) {
2028 for (int i = 0; i < size; i++, ss++)
2030 ss->excludedMove = MOVE_NONE;
2031 ss->skipNullMove = false;
2032 ss->reduction = DEPTH_ZERO;
2036 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2041 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2042 // while the program is pondering. The point is to work around a wrinkle in
2043 // the UCI protocol: When pondering, the engine is not allowed to give a
2044 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2045 // We simply wait here until one of these commands is sent, and return,
2046 // after which the bestmove and pondermove will be printed (in id_loop()).
2048 void wait_for_stop_or_ponderhit() {
2050 std::string command;
2054 if (!std::getline(std::cin, command))
2057 if (command == "quit")
2062 else if (command == "ponderhit" || command == "stop")
2068 // print_pv_info() prints to standard output and eventually to log file information on
2069 // the current PV line. It is called at each iteration or after a new pv is found.
2071 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2073 cout << "info depth " << Iteration
2074 << " score " << value_to_uci(value)
2075 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2076 << " time " << current_search_time()
2077 << " nodes " << ThreadsMgr.nodes_searched()
2081 for (Move* m = pv; *m != MOVE_NONE; m++)
2088 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2089 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2091 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2092 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2097 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2098 // the PV back into the TT. This makes sure the old PV moves are searched
2099 // first, even if the old TT entries have been overwritten.
2101 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2105 Position p(pos, pos.thread());
2106 Value v, m = VALUE_NONE;
2108 for (int i = 0; pv[i] != MOVE_NONE; i++)
2110 tte = TT.retrieve(p.get_key());
2111 if (!tte || tte->move() != pv[i])
2113 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2114 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2116 p.do_move(pv[i], st);
2121 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2122 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2123 // allow to always have a ponder move even when we fail high at root and also a
2124 // long PV to print that is important for position analysis.
2126 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2130 Position p(pos, pos.thread());
2133 assert(bestMove != MOVE_NONE);
2136 p.do_move(pv[ply++], st);
2138 while ( (tte = TT.retrieve(p.get_key())) != NULL
2139 && tte->move() != MOVE_NONE
2140 && move_is_legal(p, tte->move())
2142 && (!p.is_draw() || ply < 2))
2144 pv[ply] = tte->move();
2145 p.do_move(pv[ply++], st);
2147 pv[ply] = MOVE_NONE;
2151 // init_thread() is the function which is called when a new thread is
2152 // launched. It simply calls the idle_loop() function with the supplied
2153 // threadID. There are two versions of this function; one for POSIX
2154 // threads and one for Windows threads.
2156 #if !defined(_MSC_VER)
2158 void* init_thread(void *threadID) {
2160 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2166 DWORD WINAPI init_thread(LPVOID threadID) {
2168 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2175 /// The ThreadsManager class
2177 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2178 // get_beta_counters() are getters/setters for the per thread
2179 // counters used to sort the moves at root.
2181 void ThreadsManager::resetNodeCounters() {
2183 for (int i = 0; i < MAX_THREADS; i++)
2184 threads[i].nodes = 0ULL;
2187 int64_t ThreadsManager::nodes_searched() const {
2189 int64_t result = 0ULL;
2190 for (int i = 0; i < ActiveThreads; i++)
2191 result += threads[i].nodes;
2197 // idle_loop() is where the threads are parked when they have no work to do.
2198 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2199 // object for which the current thread is the master.
2201 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2203 assert(threadID >= 0 && threadID < MAX_THREADS);
2207 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2208 // master should exit as last one.
2209 if (AllThreadsShouldExit)
2212 threads[threadID].state = THREAD_TERMINATED;
2216 // If we are not thinking, wait for a condition to be signaled
2217 // instead of wasting CPU time polling for work.
2218 while ( threadID >= ActiveThreads
2219 || threads[threadID].state == THREAD_INITIALIZING
2220 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2223 assert(threadID != 0);
2225 if (AllThreadsShouldExit)
2230 // Retest condition under lock protection
2231 if (!( threadID >= ActiveThreads
2232 || threads[threadID].state == THREAD_INITIALIZING
2233 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2235 lock_release(&MPLock);
2239 // Put thread to sleep
2240 threads[threadID].state = THREAD_AVAILABLE;
2241 cond_wait(&WaitCond[threadID], &MPLock);
2242 lock_release(&MPLock);
2245 // If this thread has been assigned work, launch a search
2246 if (threads[threadID].state == THREAD_WORKISWAITING)
2248 assert(!AllThreadsShouldExit);
2250 threads[threadID].state = THREAD_SEARCHING;
2252 // Here we call search() with SplitPoint template parameter set to true
2253 SplitPoint* tsp = threads[threadID].splitPoint;
2254 Position pos(*tsp->pos, threadID);
2255 SearchStack* ss = tsp->sstack[threadID] + 1;
2259 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2261 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2263 assert(threads[threadID].state == THREAD_SEARCHING);
2265 threads[threadID].state = THREAD_AVAILABLE;
2268 // If this thread is the master of a split point and all slaves have
2269 // finished their work at this split point, return from the idle loop.
2271 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2273 if (i == ActiveThreads)
2275 // Because sp->slaves[] is reset under lock protection,
2276 // be sure sp->lock has been released before to return.
2277 lock_grab(&(sp->lock));
2278 lock_release(&(sp->lock));
2280 // In helpful master concept a master can help only a sub-tree, and
2281 // because here is all finished is not possible master is booked.
2282 assert(threads[threadID].state == THREAD_AVAILABLE);
2284 threads[threadID].state = THREAD_SEARCHING;
2291 // init_threads() is called during startup. It launches all helper threads,
2292 // and initializes the split point stack and the global locks and condition
2295 void ThreadsManager::init_threads() {
2300 // Initialize global locks
2303 for (i = 0; i < MAX_THREADS; i++)
2304 cond_init(&WaitCond[i]);
2306 // Initialize splitPoints[] locks
2307 for (i = 0; i < MAX_THREADS; i++)
2308 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2309 lock_init(&(threads[i].splitPoints[j].lock));
2311 // Will be set just before program exits to properly end the threads
2312 AllThreadsShouldExit = false;
2314 // Threads will be put all threads to sleep as soon as created
2317 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2318 threads[0].state = THREAD_SEARCHING;
2319 for (i = 1; i < MAX_THREADS; i++)
2320 threads[i].state = THREAD_INITIALIZING;
2322 // Launch the helper threads
2323 for (i = 1; i < MAX_THREADS; i++)
2326 #if !defined(_MSC_VER)
2327 pthread_t pthread[1];
2328 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2329 pthread_detach(pthread[0]);
2331 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2336 cout << "Failed to create thread number " << i << endl;
2337 Application::exit_with_failure();
2340 // Wait until the thread has finished launching and is gone to sleep
2341 while (threads[i].state == THREAD_INITIALIZING) {}
2346 // exit_threads() is called when the program exits. It makes all the
2347 // helper threads exit cleanly.
2349 void ThreadsManager::exit_threads() {
2351 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2353 // Wake up all the threads and waits for termination
2354 for (int i = 1; i < MAX_THREADS; i++)
2356 wake_sleeping_thread(i);
2357 while (threads[i].state != THREAD_TERMINATED) {}
2360 // Now we can safely destroy the locks
2361 for (int i = 0; i < MAX_THREADS; i++)
2362 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2363 lock_destroy(&(threads[i].splitPoints[j].lock));
2365 lock_destroy(&MPLock);
2367 // Now we can safely destroy the wait conditions
2368 for (int i = 0; i < MAX_THREADS; i++)
2369 cond_destroy(&WaitCond[i]);
2373 // thread_should_stop() checks whether the thread should stop its search.
2374 // This can happen if a beta cutoff has occurred in the thread's currently
2375 // active split point, or in some ancestor of the current split point.
2377 bool ThreadsManager::thread_should_stop(int threadID) const {
2379 assert(threadID >= 0 && threadID < ActiveThreads);
2381 SplitPoint* sp = threads[threadID].splitPoint;
2383 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2388 // thread_is_available() checks whether the thread with threadID "slave" is
2389 // available to help the thread with threadID "master" at a split point. An
2390 // obvious requirement is that "slave" must be idle. With more than two
2391 // threads, this is not by itself sufficient: If "slave" is the master of
2392 // some active split point, it is only available as a slave to the other
2393 // threads which are busy searching the split point at the top of "slave"'s
2394 // split point stack (the "helpful master concept" in YBWC terminology).
2396 bool ThreadsManager::thread_is_available(int slave, int master) const {
2398 assert(slave >= 0 && slave < ActiveThreads);
2399 assert(master >= 0 && master < ActiveThreads);
2400 assert(ActiveThreads > 1);
2402 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2405 // Make a local copy to be sure doesn't change under our feet
2406 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2408 // No active split points means that the thread is available as
2409 // a slave for any other thread.
2410 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2413 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2414 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2415 // could have been set to 0 by another thread leading to an out of bound access.
2416 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2423 // available_thread_exists() tries to find an idle thread which is available as
2424 // a slave for the thread with threadID "master".
2426 bool ThreadsManager::available_thread_exists(int master) const {
2428 assert(master >= 0 && master < ActiveThreads);
2429 assert(ActiveThreads > 1);
2431 for (int i = 0; i < ActiveThreads; i++)
2432 if (thread_is_available(i, master))
2439 // split() does the actual work of distributing the work at a node between
2440 // several available threads. If it does not succeed in splitting the
2441 // node (because no idle threads are available, or because we have no unused
2442 // split point objects), the function immediately returns. If splitting is
2443 // possible, a SplitPoint object is initialized with all the data that must be
2444 // copied to the helper threads and we tell our helper threads that they have
2445 // been assigned work. This will cause them to instantly leave their idle loops and
2446 // call search().When all threads have returned from search() then split() returns.
2448 template <bool Fake>
2449 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2450 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2451 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2453 assert(ply > 0 && ply < PLY_MAX);
2454 assert(*bestValue >= -VALUE_INFINITE);
2455 assert(*bestValue <= *alpha);
2456 assert(*alpha < beta);
2457 assert(beta <= VALUE_INFINITE);
2458 assert(depth > DEPTH_ZERO);
2459 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2460 assert(ActiveThreads > 1);
2462 int i, master = p.thread();
2463 Thread& masterThread = threads[master];
2467 // If no other thread is available to help us, or if we have too many
2468 // active split points, don't split.
2469 if ( !available_thread_exists(master)
2470 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2472 lock_release(&MPLock);
2476 // Pick the next available split point object from the split point stack
2477 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2479 // Initialize the split point object
2480 splitPoint.parent = masterThread.splitPoint;
2481 splitPoint.stopRequest = false;
2482 splitPoint.ply = ply;
2483 splitPoint.depth = depth;
2484 splitPoint.threatMove = threatMove;
2485 splitPoint.mateThreat = mateThreat;
2486 splitPoint.alpha = *alpha;
2487 splitPoint.beta = beta;
2488 splitPoint.pvNode = pvNode;
2489 splitPoint.bestValue = *bestValue;
2491 splitPoint.moveCount = moveCount;
2492 splitPoint.pos = &p;
2493 splitPoint.parentSstack = ss;
2494 for (i = 0; i < ActiveThreads; i++)
2495 splitPoint.slaves[i] = 0;
2497 masterThread.splitPoint = &splitPoint;
2499 // If we are here it means we are not available
2500 assert(masterThread.state != THREAD_AVAILABLE);
2502 int workersCnt = 1; // At least the master is included
2504 // Allocate available threads setting state to THREAD_BOOKED
2505 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2506 if (thread_is_available(i, master))
2508 threads[i].state = THREAD_BOOKED;
2509 threads[i].splitPoint = &splitPoint;
2510 splitPoint.slaves[i] = 1;
2514 assert(Fake || workersCnt > 1);
2516 // We can release the lock because slave threads are already booked and master is not available
2517 lock_release(&MPLock);
2519 // Tell the threads that they have work to do. This will make them leave
2520 // their idle loop. But before copy search stack tail for each thread.
2521 for (i = 0; i < ActiveThreads; i++)
2522 if (i == master || splitPoint.slaves[i])
2524 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2526 assert(i == master || threads[i].state == THREAD_BOOKED);
2528 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2530 wake_sleeping_thread(i);
2533 // Everything is set up. The master thread enters the idle loop, from
2534 // which it will instantly launch a search, because its state is
2535 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2536 // idle loop, which means that the main thread will return from the idle
2537 // loop when all threads have finished their work at this split point.
2538 idle_loop(master, &splitPoint);
2540 // We have returned from the idle loop, which means that all threads are
2541 // finished. Update alpha and bestValue, and return.
2544 *alpha = splitPoint.alpha;
2545 *bestValue = splitPoint.bestValue;
2546 masterThread.activeSplitPoints--;
2547 masterThread.splitPoint = splitPoint.parent;
2549 lock_release(&MPLock);
2553 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2554 // to start a new search from the root.
2556 void ThreadsManager::wake_sleeping_thread(int threadID) {
2559 cond_signal(&WaitCond[threadID]);
2560 lock_release(&MPLock);
2564 /// The RootMoveList class
2566 // RootMoveList c'tor
2568 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2570 SearchStack ss[PLY_MAX_PLUS_2];
2571 MoveStack mlist[MOVES_MAX];
2573 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2575 // Initialize search stack
2576 init_ss_array(ss, PLY_MAX_PLUS_2);
2577 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2580 // Generate all legal moves
2581 MoveStack* last = generate_moves(pos, mlist);
2583 // Add each move to the moves[] array
2584 for (MoveStack* cur = mlist; cur != last; cur++)
2586 bool includeMove = includeAllMoves;
2588 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2589 includeMove = (searchMoves[k] == cur->move);
2594 // Find a quick score for the move
2595 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2596 moves[count].pv[1] = MOVE_NONE;
2597 pos.do_move(cur->move, st);
2598 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2599 pos.undo_move(cur->move);
2605 // Score root moves using the standard way used in main search, the moves
2606 // are scored according to the order in which are returned by MovePicker.
2608 void RootMoveList::score_moves(const Position& pos)
2612 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2614 while ((move = mp.get_next_move()) != MOVE_NONE)
2615 for (int i = 0; i < count; i++)
2616 if (moves[i].move == move)
2618 moves[i].mp_score = score--;
2623 // RootMoveList simple methods definitions
2625 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2629 for (j = 0; pv[j] != MOVE_NONE; j++)
2630 moves[moveNum].pv[j] = pv[j];
2632 moves[moveNum].pv[j] = MOVE_NONE;
2636 // RootMoveList::sort() sorts the root move list at the beginning of a new
2639 void RootMoveList::sort() {
2641 sort_multipv(count - 1); // Sort all items
2645 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2646 // list by their scores and depths. It is used to order the different PVs
2647 // correctly in MultiPV mode.
2649 void RootMoveList::sort_multipv(int n) {
2653 for (i = 1; i <= n; i++)
2655 RootMove rm = moves[i];
2656 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2657 moves[j] = moves[j - 1];