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];
98 Lock MPLock, WaitLock;
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 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
284 return search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
287 template <NodeType PvNode>
288 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
312 void insert_pv_in_tt(const Position& pos, Move pv[]);
313 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
315 #if !defined(_MSC_VER)
316 void *init_thread(void *threadID);
318 DWORD WINAPI init_thread(LPVOID threadID);
328 /// init_threads(), exit_threads() and nodes_searched() are helpers to
329 /// give accessibility to some TM methods from outside of current file.
331 void init_threads() { ThreadsMgr.init_threads(); }
332 void exit_threads() { ThreadsMgr.exit_threads(); }
333 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
336 /// init_search() is called during startup. It initializes various lookup tables
340 int d; // depth (ONE_PLY == 2)
341 int hd; // half depth (ONE_PLY == 1)
344 // Init reductions array
345 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
347 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
348 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
349 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
350 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
353 // Init futility margins array
354 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
355 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
357 // Init futility move count array
358 for (d = 0; d < 32; d++)
359 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
363 /// perft() is our utility to verify move generation is bug free. All the legal
364 /// moves up to given depth are generated and counted and the sum returned.
366 int perft(Position& pos, Depth depth)
368 MoveStack mlist[MOVES_MAX];
373 // Generate all legal moves
374 MoveStack* last = generate_moves(pos, mlist);
376 // If we are at the last ply we don't need to do and undo
377 // the moves, just to count them.
378 if (depth <= ONE_PLY)
379 return int(last - mlist);
381 // Loop through all legal moves
383 for (MoveStack* cur = mlist; cur != last; cur++)
386 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
387 sum += perft(pos, depth - ONE_PLY);
394 /// think() is the external interface to Stockfish's search, and is called when
395 /// the program receives the UCI 'go' command. It initializes various
396 /// search-related global variables, and calls root_search(). It returns false
397 /// when a quit command is received during the search.
399 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
400 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
402 // Initialize global search variables
403 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
405 ThreadsMgr.resetNodeCounters();
406 SearchStartTime = get_system_time();
407 ExactMaxTime = maxTime;
410 InfiniteSearch = infinite;
411 PonderSearch = ponder;
412 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
414 // Look for a book move, only during games, not tests
415 if (UseTimeManagement && get_option_value_bool("OwnBook"))
417 if (get_option_value_string("Book File") != OpeningBook.file_name())
418 OpeningBook.open(get_option_value_string("Book File"));
420 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
421 if (bookMove != MOVE_NONE)
424 wait_for_stop_or_ponderhit();
426 cout << "bestmove " << bookMove << endl;
431 // Read UCI option values
432 TT.set_size(get_option_value_int("Hash"));
433 if (button_was_pressed("Clear Hash"))
436 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
437 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
438 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
439 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
440 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
441 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
442 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
443 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
444 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
445 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
446 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
447 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
449 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
450 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
451 MultiPV = get_option_value_int("MultiPV");
452 UseLogFile = get_option_value_bool("Use Search Log");
455 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
457 read_weights(pos.side_to_move());
459 // Set the number of active threads
460 int newActiveThreads = get_option_value_int("Threads");
461 if (newActiveThreads != ThreadsMgr.active_threads())
463 ThreadsMgr.set_active_threads(newActiveThreads);
464 init_eval(ThreadsMgr.active_threads());
467 // Wake up needed threads
468 for (int i = 1; i < newActiveThreads; i++)
469 ThreadsMgr.wake_sleeping_thread(i);
472 int myTime = time[pos.side_to_move()];
473 int myIncrement = increment[pos.side_to_move()];
474 if (UseTimeManagement)
475 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
477 // Set best NodesBetweenPolls interval to avoid lagging under
478 // heavy time pressure.
480 NodesBetweenPolls = Min(MaxNodes, 30000);
481 else if (myTime && myTime < 1000)
482 NodesBetweenPolls = 1000;
483 else if (myTime && myTime < 5000)
484 NodesBetweenPolls = 5000;
486 NodesBetweenPolls = 30000;
488 // Write search information to log file
490 LogFile << "Searching: " << pos.to_fen() << endl
491 << "infinite: " << infinite
492 << " ponder: " << ponder
493 << " time: " << myTime
494 << " increment: " << myIncrement
495 << " moves to go: " << movesToGo << endl;
497 // We're ready to start thinking. Call the iterative deepening loop function
498 id_loop(pos, searchMoves);
503 // This makes all the threads to go to sleep
504 ThreadsMgr.set_active_threads(1);
512 // id_loop() is the main iterative deepening loop. It calls root_search
513 // repeatedly with increasing depth until the allocated thinking time has
514 // been consumed, the user stops the search, or the maximum search depth is
517 Value id_loop(const Position& pos, Move searchMoves[]) {
519 Position p(pos, pos.thread());
520 SearchStack ss[PLY_MAX_PLUS_2];
521 Move pv[PLY_MAX_PLUS_2];
522 Move EasyMove = MOVE_NONE;
523 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
525 // Moves to search are verified, copied, scored and sorted
526 RootMoveList rml(p, searchMoves);
528 // Handle special case of searching on a mate/stale position
529 if (rml.move_count() == 0)
532 wait_for_stop_or_ponderhit();
534 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
537 // Print RootMoveList startup scoring to the standard output,
538 // so to output information also for iteration 1.
539 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
540 << "info depth " << 1
541 << "\ninfo depth " << 1
542 << " score " << value_to_uci(rml.move_score(0))
543 << " time " << current_search_time()
544 << " nodes " << ThreadsMgr.nodes_searched()
546 << " pv " << rml.move(0) << "\n";
551 init_ss_array(ss, PLY_MAX_PLUS_2);
552 pv[0] = pv[1] = MOVE_NONE;
553 ValueByIteration[1] = rml.move_score(0);
556 // Is one move significantly better than others after initial scoring ?
557 if ( rml.move_count() == 1
558 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
559 EasyMove = rml.move(0);
561 // Iterative deepening loop
562 while (Iteration < PLY_MAX)
564 // Initialize iteration
566 BestMoveChangesByIteration[Iteration] = 0;
568 cout << "info depth " << Iteration << endl;
570 // Calculate dynamic aspiration window based on previous iterations
571 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
573 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
574 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
576 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
577 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
579 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
580 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
583 // Search to the current depth, rml is updated and sorted, alpha and beta could change
584 value = root_search(p, ss, pv, rml, &alpha, &beta);
586 // Write PV to transposition table, in case the relevant entries have
587 // been overwritten during the search.
588 insert_pv_in_tt(p, pv);
591 break; // Value cannot be trusted. Break out immediately!
593 //Save info about search result
594 ValueByIteration[Iteration] = value;
596 // Drop the easy move if differs from the new best move
597 if (pv[0] != EasyMove)
598 EasyMove = MOVE_NONE;
600 if (UseTimeManagement)
603 bool stopSearch = false;
605 // Stop search early if there is only a single legal move,
606 // we search up to Iteration 6 anyway to get a proper score.
607 if (Iteration >= 6 && rml.move_count() == 1)
610 // Stop search early when the last two iterations returned a mate score
612 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
613 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
616 // Stop search early if one move seems to be much better than the others
617 int64_t nodes = ThreadsMgr.nodes_searched();
620 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
621 && current_search_time() > TimeMgr.available_time() / 16)
622 ||( rml.move_nodes(0) > (nodes * 98) / 100
623 && current_search_time() > TimeMgr.available_time() / 32)))
626 // Add some extra time if the best move has changed during the last two iterations
627 if (Iteration > 5 && Iteration <= 50)
628 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
629 BestMoveChangesByIteration[Iteration-1]);
631 // Stop search if most of MaxSearchTime is consumed at the end of the
632 // iteration. We probably don't have enough time to search the first
633 // move at the next iteration anyway.
634 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
640 StopOnPonderhit = true;
646 if (MaxDepth && Iteration >= MaxDepth)
650 // If we are pondering or in infinite search, we shouldn't print the
651 // best move before we are told to do so.
652 if (!AbortSearch && (PonderSearch || InfiniteSearch))
653 wait_for_stop_or_ponderhit();
655 // Print final search statistics
656 cout << "info nodes " << ThreadsMgr.nodes_searched()
658 << " time " << current_search_time() << endl;
660 // Print the best move and the ponder move to the standard output
661 if (pv[0] == MOVE_NONE)
667 assert(pv[0] != MOVE_NONE);
669 cout << "bestmove " << pv[0];
671 if (pv[1] != MOVE_NONE)
672 cout << " ponder " << pv[1];
679 dbg_print_mean(LogFile);
681 if (dbg_show_hit_rate)
682 dbg_print_hit_rate(LogFile);
684 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
685 << "\nNodes/second: " << nps()
686 << "\nBest move: " << move_to_san(p, pv[0]);
689 p.do_move(pv[0], st);
690 LogFile << "\nPonder move: "
691 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
694 return rml.move_score(0);
698 // root_search() is the function which searches the root node. It is
699 // similar to search_pv except that it uses a different move ordering
700 // scheme, prints some information to the standard output and handles
701 // the fail low/high loops.
703 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
709 Depth depth, ext, newDepth;
710 Value value, alpha, beta;
711 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
712 int researchCountFH, researchCountFL;
714 researchCountFH = researchCountFL = 0;
717 isCheck = pos.is_check();
718 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
720 // Step 1. Initialize node (polling is omitted at root)
721 ss->currentMove = ss->bestMove = MOVE_NONE;
723 // Step 2. Check for aborted search (omitted at root)
724 // Step 3. Mate distance pruning (omitted at root)
725 // Step 4. Transposition table lookup (omitted at root)
727 // Step 5. Evaluate the position statically
728 // At root we do this only to get reference value for child nodes
729 ss->evalMargin = VALUE_NONE;
730 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
732 // Step 6. Razoring (omitted at root)
733 // Step 7. Static null move pruning (omitted at root)
734 // Step 8. Null move search with verification search (omitted at root)
735 // Step 9. Internal iterative deepening (omitted at root)
737 // Step extra. Fail low loop
738 // We start with small aspiration window and in case of fail low, we research
739 // with bigger window until we are not failing low anymore.
742 // Sort the moves before to (re)search
743 rml.score_moves(pos);
746 // Step 10. Loop through all moves in the root move list
747 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
749 // This is used by time management
750 FirstRootMove = (i == 0);
752 // Save the current node count before the move is searched
753 nodes = ThreadsMgr.nodes_searched();
755 // Pick the next root move, and print the move and the move number to
756 // the standard output.
757 move = ss->currentMove = rml.move(i);
759 if (current_search_time() >= 1000)
760 cout << "info currmove " << move
761 << " currmovenumber " << i + 1 << endl;
763 moveIsCheck = pos.move_is_check(move);
764 captureOrPromotion = pos.move_is_capture_or_promotion(move);
766 // Step 11. Decide the new search depth
767 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
768 newDepth = depth + ext;
770 // Step 12. Futility pruning (omitted at root)
772 // Step extra. Fail high loop
773 // If move fails high, we research with bigger window until we are not failing
775 value = - VALUE_INFINITE;
779 // Step 13. Make the move
780 pos.do_move(move, st, ci, moveIsCheck);
782 // Step extra. pv search
783 // We do pv search for first moves (i < MultiPV)
784 // and for fail high research (value > alpha)
785 if (i < MultiPV || value > alpha)
787 // Aspiration window is disabled in multi-pv case
789 alpha = -VALUE_INFINITE;
791 // Full depth PV search, done on first move or after a fail high
792 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
796 // Step 14. Reduced search
797 // if the move fails high will be re-searched at full depth
798 bool doFullDepthSearch = true;
800 if ( depth >= 3 * ONE_PLY
802 && !captureOrPromotion
803 && !move_is_castle(move))
805 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
808 assert(newDepth-ss->reduction >= ONE_PLY);
810 // Reduced depth non-pv search using alpha as upperbound
811 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
812 doFullDepthSearch = (value > alpha);
815 // The move failed high, but if reduction is very big we could
816 // face a false positive, retry with a less aggressive reduction,
817 // if the move fails high again then go with full depth search.
818 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
820 assert(newDepth - ONE_PLY >= ONE_PLY);
822 ss->reduction = ONE_PLY;
823 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
824 doFullDepthSearch = (value > alpha);
826 ss->reduction = DEPTH_ZERO; // Restore original reduction
829 // Step 15. Full depth search
830 if (doFullDepthSearch)
832 // Full depth non-pv search using alpha as upperbound
833 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
835 // If we are above alpha then research at same depth but as PV
836 // to get a correct score or eventually a fail high above beta.
838 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
842 // Step 16. Undo move
845 // Can we exit fail high loop ?
846 if (AbortSearch || value < beta)
849 // We are failing high and going to do a research. It's important to update
850 // the score before research in case we run out of time while researching.
851 rml.set_move_score(i, value);
853 extract_pv_from_tt(pos, move, pv);
854 rml.set_move_pv(i, pv);
856 // Print information to the standard output
857 print_pv_info(pos, pv, alpha, beta, value);
859 // Prepare for a research after a fail high, each time with a wider window
860 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
863 } // End of fail high loop
865 // Finished searching the move. If AbortSearch is true, the search
866 // was aborted because the user interrupted the search or because we
867 // ran out of time. In this case, the return value of the search cannot
868 // be trusted, and we break out of the loop without updating the best
873 // Remember searched nodes counts for this move
874 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
876 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
877 assert(value < beta);
879 // Step 17. Check for new best move
880 if (value <= alpha && i >= MultiPV)
881 rml.set_move_score(i, -VALUE_INFINITE);
884 // PV move or new best move!
887 rml.set_move_score(i, value);
889 extract_pv_from_tt(pos, move, pv);
890 rml.set_move_pv(i, pv);
894 // We record how often the best move has been changed in each
895 // iteration. This information is used for time managment: When
896 // the best move changes frequently, we allocate some more time.
898 BestMoveChangesByIteration[Iteration]++;
900 // Print information to the standard output
901 print_pv_info(pos, pv, alpha, beta, value);
903 // Raise alpha to setup proper non-pv search upper bound
910 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
912 cout << "info multipv " << j + 1
913 << " score " << value_to_uci(rml.move_score(j))
914 << " depth " << (j <= i ? Iteration : Iteration - 1)
915 << " time " << current_search_time()
916 << " nodes " << ThreadsMgr.nodes_searched()
920 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
921 cout << rml.move_pv(j, k) << " ";
925 alpha = rml.move_score(Min(i, MultiPV - 1));
927 } // PV move or new best move
929 assert(alpha >= *alphaPtr);
931 AspirationFailLow = (alpha == *alphaPtr);
933 if (AspirationFailLow && StopOnPonderhit)
934 StopOnPonderhit = false;
937 // Can we exit fail low loop ?
938 if (AbortSearch || !AspirationFailLow)
941 // Prepare for a research after a fail low, each time with a wider window
942 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
947 // Sort the moves before to return
954 // search<>() is the main search function for both PV and non-PV nodes and for
955 // normal and SplitPoint nodes. When called just after a split point the search
956 // is simpler because we have already probed the hash table, done a null move
957 // search, and searched the first move before splitting, we don't have to repeat
958 // all this work again. We also don't need to store anything to the hash table
959 // here: This is taken care of after we return from the split point.
961 template <NodeType PvNode, bool SpNode>
962 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
964 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
965 assert(beta > alpha && beta <= VALUE_INFINITE);
966 assert(PvNode || alpha == beta - 1);
967 assert(ply > 0 && ply < PLY_MAX);
968 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
970 Move movesSearched[MOVES_MAX];
974 Move ttMove, move, excludedMove, threatMove;
976 Value bestValue, value, oldAlpha;
977 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
978 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
979 bool mateThreat = false;
981 int threadID = pos.thread();
982 SplitPoint* sp = NULL;
983 refinedValue = bestValue = value = -VALUE_INFINITE;
985 isCheck = pos.is_check();
991 ttMove = excludedMove = MOVE_NONE;
992 threatMove = sp->threatMove;
993 mateThreat = sp->mateThreat;
994 goto split_point_start;
997 // Step 1. Initialize node and poll. Polling can abort search
998 ThreadsMgr.incrementNodeCounter(threadID);
999 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1000 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1002 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1008 // Step 2. Check for aborted search and immediate draw
1009 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1012 if (pos.is_draw() || ply >= PLY_MAX - 1)
1015 // Step 3. Mate distance pruning
1016 alpha = Max(value_mated_in(ply), alpha);
1017 beta = Min(value_mate_in(ply+1), beta);
1021 // Step 4. Transposition table lookup
1023 // We don't want the score of a partial search to overwrite a previous full search
1024 // TT value, so we use a different position key in case of an excluded move exists.
1025 excludedMove = ss->excludedMove;
1026 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1028 tte = TT.retrieve(posKey);
1029 ttMove = (tte ? tte->move() : MOVE_NONE);
1031 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1032 // This is to avoid problems in the following areas:
1034 // * Repetition draw detection
1035 // * Fifty move rule detection
1036 // * Searching for a mate
1037 // * Printing of full PV line
1039 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1041 // Refresh tte entry to avoid aging
1042 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1044 ss->bestMove = ttMove; // Can be MOVE_NONE
1045 return value_from_tt(tte->value(), ply);
1048 // Step 5. Evaluate the position statically and
1049 // update gain statistics of parent move.
1051 ss->eval = ss->evalMargin = VALUE_NONE;
1054 assert(tte->static_value() != VALUE_NONE);
1056 ss->eval = tte->static_value();
1057 ss->evalMargin = tte->static_value_margin();
1058 refinedValue = refine_eval(tte, ss->eval, ply);
1062 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1063 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1066 // Save gain for the parent non-capture move
1067 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1069 // Step 6. Razoring (is omitted in PV nodes)
1071 && depth < RazorDepth
1073 && refinedValue < beta - razor_margin(depth)
1074 && ttMove == MOVE_NONE
1075 && (ss-1)->currentMove != MOVE_NULL
1076 && !value_is_mate(beta)
1077 && !pos.has_pawn_on_7th(pos.side_to_move()))
1079 Value rbeta = beta - razor_margin(depth);
1080 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1082 // Logically we should return (v + razor_margin(depth)), but
1083 // surprisingly this did slightly weaker in tests.
1087 // Step 7. Static null move pruning (is omitted in PV nodes)
1088 // We're betting that the opponent doesn't have a move that will reduce
1089 // the score by more than futility_margin(depth) if we do a null move.
1091 && !ss->skipNullMove
1092 && depth < RazorDepth
1094 && refinedValue >= beta + futility_margin(depth, 0)
1095 && !value_is_mate(beta)
1096 && pos.non_pawn_material(pos.side_to_move()))
1097 return refinedValue - futility_margin(depth, 0);
1099 // Step 8. Null move search with verification search (is omitted in PV nodes)
1101 && !ss->skipNullMove
1104 && refinedValue >= beta
1105 && !value_is_mate(beta)
1106 && pos.non_pawn_material(pos.side_to_move()))
1108 ss->currentMove = MOVE_NULL;
1110 // Null move dynamic reduction based on depth
1111 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1113 // Null move dynamic reduction based on value
1114 if (refinedValue - beta > PawnValueMidgame)
1117 pos.do_null_move(st);
1118 (ss+1)->skipNullMove = true;
1120 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1121 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1122 (ss+1)->skipNullMove = false;
1123 pos.undo_null_move();
1125 if (nullValue >= beta)
1127 // Do not return unproven mate scores
1128 if (nullValue >= value_mate_in(PLY_MAX))
1131 if (depth < 6 * ONE_PLY)
1134 // Do verification search at high depths
1135 ss->skipNullMove = true;
1136 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1137 ss->skipNullMove = false;
1144 // The null move failed low, which means that we may be faced with
1145 // some kind of threat. If the previous move was reduced, check if
1146 // the move that refuted the null move was somehow connected to the
1147 // move which was reduced. If a connection is found, return a fail
1148 // low score (which will cause the reduced move to fail high in the
1149 // parent node, which will trigger a re-search with full depth).
1150 if (nullValue == value_mated_in(ply + 2))
1153 threatMove = (ss+1)->bestMove;
1154 if ( depth < ThreatDepth
1155 && (ss-1)->reduction
1156 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1161 // Step 9. Internal iterative deepening
1162 if ( depth >= IIDDepth[PvNode]
1163 && ttMove == MOVE_NONE
1164 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1166 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1168 ss->skipNullMove = true;
1169 search<PvNode>(pos, ss, alpha, beta, d, ply);
1170 ss->skipNullMove = false;
1172 ttMove = ss->bestMove;
1173 tte = TT.retrieve(posKey);
1176 // Expensive mate threat detection (only for PV nodes)
1178 mateThreat = pos.has_mate_threat();
1180 split_point_start: // At split points actual search starts from here
1182 // Initialize a MovePicker object for the current position
1183 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1184 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1185 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1187 ss->bestMove = MOVE_NONE;
1188 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1189 futilityBase = ss->eval + ss->evalMargin;
1190 singularExtensionNode = !SpNode
1191 && depth >= SingularExtensionDepth[PvNode]
1194 && !excludedMove // Do not allow recursive singular extension search
1195 && (tte->type() & VALUE_TYPE_LOWER)
1196 && tte->depth() >= depth - 3 * ONE_PLY;
1199 lock_grab(&(sp->lock));
1200 bestValue = sp->bestValue;
1203 // Step 10. Loop through moves
1204 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1205 while ( bestValue < beta
1206 && (move = mp.get_next_move()) != MOVE_NONE
1207 && !ThreadsMgr.thread_should_stop(threadID))
1211 moveCount = ++sp->moveCount;
1212 lock_release(&(sp->lock));
1215 assert(move_is_ok(move));
1217 if (move == excludedMove)
1220 moveIsCheck = pos.move_is_check(move, ci);
1221 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1223 // Step 11. Decide the new search depth
1224 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1226 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1227 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1228 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1229 // lower then ttValue minus a margin then we extend ttMove.
1230 if ( singularExtensionNode
1231 && move == tte->move()
1234 Value ttValue = value_from_tt(tte->value(), ply);
1236 if (abs(ttValue) < VALUE_KNOWN_WIN)
1238 Value b = ttValue - SingularExtensionMargin;
1239 ss->excludedMove = move;
1240 ss->skipNullMove = true;
1241 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1242 ss->skipNullMove = false;
1243 ss->excludedMove = MOVE_NONE;
1244 ss->bestMove = MOVE_NONE;
1250 newDepth = depth - ONE_PLY + ext;
1252 // Update current move (this must be done after singular extension search)
1253 movesSearched[moveCount++] = ss->currentMove = move;
1255 // Step 12. Futility pruning (is omitted in PV nodes)
1257 && !captureOrPromotion
1261 && !move_is_castle(move))
1263 // Move count based pruning
1264 if ( moveCount >= futility_move_count(depth)
1265 && !(threatMove && connected_threat(pos, move, threatMove))
1266 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1269 lock_grab(&(sp->lock));
1274 // Value based pruning
1275 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1276 // but fixing this made program slightly weaker.
1277 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1278 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1279 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1281 if (futilityValueScaled < beta)
1285 lock_grab(&(sp->lock));
1286 if (futilityValueScaled > sp->bestValue)
1287 sp->bestValue = bestValue = futilityValueScaled;
1289 else if (futilityValueScaled > bestValue)
1290 bestValue = futilityValueScaled;
1296 // Step 13. Make the move
1297 pos.do_move(move, st, ci, moveIsCheck);
1299 // Step extra. pv search (only in PV nodes)
1300 // The first move in list is the expected PV
1301 if (!SpNode && PvNode && moveCount == 1)
1302 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1303 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1306 // Step 14. Reduced depth search
1307 // If the move fails high will be re-searched at full depth.
1308 bool doFullDepthSearch = true;
1310 if ( depth >= 3 * ONE_PLY
1311 && !captureOrPromotion
1313 && !move_is_castle(move)
1314 && !(ss->killers[0] == move || ss->killers[1] == move))
1316 ss->reduction = reduction<PvNode>(depth, moveCount);
1319 alpha = SpNode ? sp->alpha : alpha;
1320 Depth d = newDepth - ss->reduction;
1321 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1322 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1324 doFullDepthSearch = (value > alpha);
1327 // The move failed high, but if reduction is very big we could
1328 // face a false positive, retry with a less aggressive reduction,
1329 // if the move fails high again then go with full depth search.
1330 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1332 assert(newDepth - ONE_PLY >= ONE_PLY);
1334 ss->reduction = ONE_PLY;
1335 alpha = SpNode ? sp->alpha : alpha;
1336 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1337 doFullDepthSearch = (value > alpha);
1339 ss->reduction = DEPTH_ZERO; // Restore original reduction
1342 // Step 15. Full depth search
1343 if (doFullDepthSearch)
1345 alpha = SpNode ? sp->alpha : alpha;
1346 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1347 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1349 // Step extra. pv search (only in PV nodes)
1350 // Search only for possible new PV nodes, if instead value >= beta then
1351 // parent node fails low with value <= alpha and tries another move.
1352 if (PvNode && value > alpha && value < beta)
1353 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1354 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1358 // Step 16. Undo move
1359 pos.undo_move(move);
1361 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1363 // Step 17. Check for new best move
1366 lock_grab(&(sp->lock));
1367 bestValue = sp->bestValue;
1371 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1376 if (SpNode && (!PvNode || value >= beta))
1377 sp->stopRequest = true;
1379 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;
1389 sp->bestValue = bestValue;
1391 sp->parentSstack->bestMove = ss->bestMove;
1395 // Step 18. Check for split
1397 && depth >= MinimumSplitDepth
1398 && ThreadsMgr.active_threads() > 1
1400 && ThreadsMgr.available_thread_exists(threadID)
1402 && !ThreadsMgr.thread_should_stop(threadID)
1404 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1405 threatMove, mateThreat, moveCount, &mp, PvNode);
1410 /* Here we have the lock still grabbed */
1411 sp->slaves[threadID] = 0;
1412 lock_release(&(sp->lock));
1416 // Step 19. Check for mate and stalemate
1417 // All legal moves have been searched and if there are
1418 // no legal moves, it must be mate or stalemate.
1419 // If one move was excluded return fail low score.
1421 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1423 // Step 20. Update tables
1424 // If the search is not aborted, update the transposition table,
1425 // history counters, and killer moves.
1426 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1429 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1430 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1431 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1433 // Update killers and history only for non capture moves that fails high
1434 if ( bestValue >= beta
1435 && !pos.move_is_capture_or_promotion(move))
1437 update_history(pos, move, depth, movesSearched, moveCount);
1438 update_killers(move, ss);
1441 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1447 // qsearch() is the quiescence search function, which is called by the main
1448 // search function when the remaining depth is zero (or, to be more precise,
1449 // less than ONE_PLY).
1451 template <NodeType PvNode>
1452 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1454 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1455 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1456 assert(PvNode || alpha == beta - 1);
1458 assert(ply > 0 && ply < PLY_MAX);
1459 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1463 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1464 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1466 Value oldAlpha = alpha;
1468 ThreadsMgr.incrementNodeCounter(pos.thread());
1469 ss->bestMove = ss->currentMove = MOVE_NONE;
1471 // Check for an instant draw or maximum ply reached
1472 if (pos.is_draw() || ply >= PLY_MAX - 1)
1475 // Transposition table lookup. At PV nodes, we don't use the TT for
1476 // pruning, but only for move ordering.
1477 tte = TT.retrieve(pos.get_key());
1478 ttMove = (tte ? tte->move() : MOVE_NONE);
1480 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1482 ss->bestMove = ttMove; // Can be MOVE_NONE
1483 return value_from_tt(tte->value(), ply);
1486 isCheck = pos.is_check();
1488 // Evaluate the position statically
1491 bestValue = futilityBase = -VALUE_INFINITE;
1492 ss->eval = evalMargin = VALUE_NONE;
1493 deepChecks = enoughMaterial = false;
1499 assert(tte->static_value() != VALUE_NONE);
1501 evalMargin = tte->static_value_margin();
1502 ss->eval = bestValue = tte->static_value();
1505 ss->eval = bestValue = evaluate(pos, evalMargin);
1507 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1509 // Stand pat. Return immediately if static value is at least beta
1510 if (bestValue >= beta)
1513 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1518 if (PvNode && bestValue > alpha)
1521 // If we are near beta then try to get a cutoff pushing checks a bit further
1522 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1524 // Futility pruning parameters, not needed when in check
1525 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1526 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1529 // Initialize a MovePicker object for the current position, and prepare
1530 // to search the moves. Because the depth is <= 0 here, only captures,
1531 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1532 // and we are near beta) will be generated.
1533 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1536 // Loop through the moves until no moves remain or a beta cutoff occurs
1537 while ( alpha < beta
1538 && (move = mp.get_next_move()) != MOVE_NONE)
1540 assert(move_is_ok(move));
1542 moveIsCheck = pos.move_is_check(move, ci);
1550 && !move_is_promotion(move)
1551 && !pos.move_is_passed_pawn_push(move))
1553 futilityValue = futilityBase
1554 + pos.endgame_value_of_piece_on(move_to(move))
1555 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1557 if (futilityValue < alpha)
1559 if (futilityValue > bestValue)
1560 bestValue = futilityValue;
1565 // Detect non-capture evasions that are candidate to be pruned
1566 evasionPrunable = isCheck
1567 && bestValue > value_mated_in(PLY_MAX)
1568 && !pos.move_is_capture(move)
1569 && !pos.can_castle(pos.side_to_move());
1571 // Don't search moves with negative SEE values
1573 && (!isCheck || evasionPrunable)
1575 && !move_is_promotion(move)
1576 && pos.see_sign(move) < 0)
1579 // Update current move
1580 ss->currentMove = move;
1582 // Make and search the move
1583 pos.do_move(move, st, ci, moveIsCheck);
1584 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1585 pos.undo_move(move);
1587 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1590 if (value > bestValue)
1596 ss->bestMove = move;
1601 // All legal moves have been searched. A special case: If we're in check
1602 // and no legal moves were found, it is checkmate.
1603 if (isCheck && bestValue == -VALUE_INFINITE)
1604 return value_mated_in(ply);
1606 // Update transposition table
1607 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1608 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1609 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1611 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1617 // connected_moves() tests whether two moves are 'connected' in the sense
1618 // that the first move somehow made the second move possible (for instance
1619 // if the moving piece is the same in both moves). The first move is assumed
1620 // to be the move that was made to reach the current position, while the
1621 // second move is assumed to be a move from the current position.
1623 bool connected_moves(const Position& pos, Move m1, Move m2) {
1625 Square f1, t1, f2, t2;
1628 assert(move_is_ok(m1));
1629 assert(move_is_ok(m2));
1631 if (m2 == MOVE_NONE)
1634 // Case 1: The moving piece is the same in both moves
1640 // Case 2: The destination square for m2 was vacated by m1
1646 // Case 3: Moving through the vacated square
1647 if ( piece_is_slider(pos.piece_on(f2))
1648 && bit_is_set(squares_between(f2, t2), f1))
1651 // Case 4: The destination square for m2 is defended by the moving piece in m1
1652 p = pos.piece_on(t1);
1653 if (bit_is_set(pos.attacks_from(p, t1), t2))
1656 // Case 5: Discovered check, checking piece is the piece moved in m1
1657 if ( piece_is_slider(p)
1658 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1659 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1661 // discovered_check_candidates() works also if the Position's side to
1662 // move is the opposite of the checking piece.
1663 Color them = opposite_color(pos.side_to_move());
1664 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1666 if (bit_is_set(dcCandidates, f2))
1673 // value_is_mate() checks if the given value is a mate one eventually
1674 // compensated for the ply.
1676 bool value_is_mate(Value value) {
1678 assert(abs(value) <= VALUE_INFINITE);
1680 return value <= value_mated_in(PLY_MAX)
1681 || value >= value_mate_in(PLY_MAX);
1685 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1686 // "plies to mate from the current ply". Non-mate scores are unchanged.
1687 // The function is called before storing a value to the transposition table.
1689 Value value_to_tt(Value v, int ply) {
1691 if (v >= value_mate_in(PLY_MAX))
1694 if (v <= value_mated_in(PLY_MAX))
1701 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1702 // the transposition table to a mate score corrected for the current ply.
1704 Value value_from_tt(Value v, int ply) {
1706 if (v >= value_mate_in(PLY_MAX))
1709 if (v <= value_mated_in(PLY_MAX))
1716 // extension() decides whether a move should be searched with normal depth,
1717 // or with extended depth. Certain classes of moves (checking moves, in
1718 // particular) are searched with bigger depth than ordinary moves and in
1719 // any case are marked as 'dangerous'. Note that also if a move is not
1720 // extended, as example because the corresponding UCI option is set to zero,
1721 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1722 template <NodeType PvNode>
1723 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1724 bool singleEvasion, bool mateThreat, bool* dangerous) {
1726 assert(m != MOVE_NONE);
1728 Depth result = DEPTH_ZERO;
1729 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1733 if (moveIsCheck && pos.see_sign(m) >= 0)
1734 result += CheckExtension[PvNode];
1737 result += SingleEvasionExtension[PvNode];
1740 result += MateThreatExtension[PvNode];
1743 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1745 Color c = pos.side_to_move();
1746 if (relative_rank(c, move_to(m)) == RANK_7)
1748 result += PawnPushTo7thExtension[PvNode];
1751 if (pos.pawn_is_passed(c, move_to(m)))
1753 result += PassedPawnExtension[PvNode];
1758 if ( captureOrPromotion
1759 && pos.type_of_piece_on(move_to(m)) != PAWN
1760 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1761 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1762 && !move_is_promotion(m)
1765 result += PawnEndgameExtension[PvNode];
1770 && captureOrPromotion
1771 && pos.type_of_piece_on(move_to(m)) != PAWN
1772 && pos.see_sign(m) >= 0)
1774 result += ONE_PLY / 2;
1778 return Min(result, ONE_PLY);
1782 // connected_threat() tests whether it is safe to forward prune a move or if
1783 // is somehow coonected to the threat move returned by null search.
1785 bool connected_threat(const Position& pos, Move m, Move threat) {
1787 assert(move_is_ok(m));
1788 assert(threat && move_is_ok(threat));
1789 assert(!pos.move_is_check(m));
1790 assert(!pos.move_is_capture_or_promotion(m));
1791 assert(!pos.move_is_passed_pawn_push(m));
1793 Square mfrom, mto, tfrom, tto;
1795 mfrom = move_from(m);
1797 tfrom = move_from(threat);
1798 tto = move_to(threat);
1800 // Case 1: Don't prune moves which move the threatened piece
1804 // Case 2: If the threatened piece has value less than or equal to the
1805 // value of the threatening piece, don't prune move which defend it.
1806 if ( pos.move_is_capture(threat)
1807 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1808 || pos.type_of_piece_on(tfrom) == KING)
1809 && pos.move_attacks_square(m, tto))
1812 // Case 3: If the moving piece in the threatened move is a slider, don't
1813 // prune safe moves which block its ray.
1814 if ( piece_is_slider(pos.piece_on(tfrom))
1815 && bit_is_set(squares_between(tfrom, tto), mto)
1816 && pos.see_sign(m) >= 0)
1823 // ok_to_use_TT() returns true if a transposition table score
1824 // can be used at a given point in search.
1826 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1828 Value v = value_from_tt(tte->value(), ply);
1830 return ( tte->depth() >= depth
1831 || v >= Max(value_mate_in(PLY_MAX), beta)
1832 || v < Min(value_mated_in(PLY_MAX), beta))
1834 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1835 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1839 // refine_eval() returns the transposition table score if
1840 // possible otherwise falls back on static position evaluation.
1842 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1846 Value v = value_from_tt(tte->value(), ply);
1848 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1849 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1856 // update_history() registers a good move that produced a beta-cutoff
1857 // in history and marks as failures all the other moves of that ply.
1859 void update_history(const Position& pos, Move move, Depth depth,
1860 Move movesSearched[], int moveCount) {
1863 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1865 for (int i = 0; i < moveCount - 1; i++)
1867 m = movesSearched[i];
1871 if (!pos.move_is_capture_or_promotion(m))
1872 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1877 // update_killers() add a good move that produced a beta-cutoff
1878 // among the killer moves of that ply.
1880 void update_killers(Move m, SearchStack* ss) {
1882 if (m == ss->killers[0])
1885 ss->killers[1] = ss->killers[0];
1890 // update_gains() updates the gains table of a non-capture move given
1891 // the static position evaluation before and after the move.
1893 void update_gains(const Position& pos, Move m, Value before, Value after) {
1896 && before != VALUE_NONE
1897 && after != VALUE_NONE
1898 && pos.captured_piece_type() == PIECE_TYPE_NONE
1899 && !move_is_special(m))
1900 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1904 // current_search_time() returns the number of milliseconds which have passed
1905 // since the beginning of the current search.
1907 int current_search_time() {
1909 return get_system_time() - SearchStartTime;
1913 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1915 std::string value_to_uci(Value v) {
1917 std::stringstream s;
1919 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1920 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1922 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1927 // nps() computes the current nodes/second count.
1931 int t = current_search_time();
1932 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1936 // poll() performs two different functions: It polls for user input, and it
1937 // looks at the time consumed so far and decides if it's time to abort the
1942 static int lastInfoTime;
1943 int t = current_search_time();
1948 // We are line oriented, don't read single chars
1949 std::string command;
1951 if (!std::getline(std::cin, command))
1954 if (command == "quit")
1957 PonderSearch = false;
1961 else if (command == "stop")
1964 PonderSearch = false;
1966 else if (command == "ponderhit")
1970 // Print search information
1974 else if (lastInfoTime > t)
1975 // HACK: Must be a new search where we searched less than
1976 // NodesBetweenPolls nodes during the first second of search.
1979 else if (t - lastInfoTime >= 1000)
1986 if (dbg_show_hit_rate)
1987 dbg_print_hit_rate();
1989 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1990 << " time " << t << endl;
1993 // Should we stop the search?
1997 bool stillAtFirstMove = FirstRootMove
1998 && !AspirationFailLow
1999 && t > TimeMgr.available_time();
2001 bool noMoreTime = t > TimeMgr.maximum_time()
2002 || stillAtFirstMove;
2004 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2005 || (ExactMaxTime && t >= ExactMaxTime)
2006 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2011 // ponderhit() is called when the program is pondering (i.e. thinking while
2012 // it's the opponent's turn to move) in order to let the engine know that
2013 // it correctly predicted the opponent's move.
2017 int t = current_search_time();
2018 PonderSearch = false;
2020 bool stillAtFirstMove = FirstRootMove
2021 && !AspirationFailLow
2022 && t > TimeMgr.available_time();
2024 bool noMoreTime = t > TimeMgr.maximum_time()
2025 || stillAtFirstMove;
2027 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2032 // init_ss_array() does a fast reset of the first entries of a SearchStack
2033 // array and of all the excludedMove and skipNullMove entries.
2035 void init_ss_array(SearchStack* ss, int size) {
2037 for (int i = 0; i < size; i++, ss++)
2039 ss->excludedMove = MOVE_NONE;
2040 ss->skipNullMove = false;
2041 ss->reduction = DEPTH_ZERO;
2045 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2050 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2051 // while the program is pondering. The point is to work around a wrinkle in
2052 // the UCI protocol: When pondering, the engine is not allowed to give a
2053 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2054 // We simply wait here until one of these commands is sent, and return,
2055 // after which the bestmove and pondermove will be printed (in id_loop()).
2057 void wait_for_stop_or_ponderhit() {
2059 std::string command;
2063 if (!std::getline(std::cin, command))
2066 if (command == "quit")
2071 else if (command == "ponderhit" || command == "stop")
2077 // print_pv_info() prints to standard output and eventually to log file information on
2078 // the current PV line. It is called at each iteration or after a new pv is found.
2080 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2082 cout << "info depth " << Iteration
2083 << " score " << value_to_uci(value)
2084 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2085 << " time " << current_search_time()
2086 << " nodes " << ThreadsMgr.nodes_searched()
2090 for (Move* m = pv; *m != MOVE_NONE; m++)
2097 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2098 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2100 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2101 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2106 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2107 // the PV back into the TT. This makes sure the old PV moves are searched
2108 // first, even if the old TT entries have been overwritten.
2110 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2114 Position p(pos, pos.thread());
2115 Value v, m = VALUE_NONE;
2117 for (int i = 0; pv[i] != MOVE_NONE; i++)
2119 tte = TT.retrieve(p.get_key());
2120 if (!tte || tte->move() != pv[i])
2122 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2123 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2125 p.do_move(pv[i], st);
2130 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2131 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2132 // allow to always have a ponder move even when we fail high at root and also a
2133 // long PV to print that is important for position analysis.
2135 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2139 Position p(pos, pos.thread());
2142 assert(bestMove != MOVE_NONE);
2145 p.do_move(pv[ply++], st);
2147 while ( (tte = TT.retrieve(p.get_key())) != NULL
2148 && tte->move() != MOVE_NONE
2149 && move_is_legal(p, tte->move())
2151 && (!p.is_draw() || ply < 2))
2153 pv[ply] = tte->move();
2154 p.do_move(pv[ply++], st);
2156 pv[ply] = MOVE_NONE;
2160 // init_thread() is the function which is called when a new thread is
2161 // launched. It simply calls the idle_loop() function with the supplied
2162 // threadID. There are two versions of this function; one for POSIX
2163 // threads and one for Windows threads.
2165 #if !defined(_MSC_VER)
2167 void* init_thread(void *threadID) {
2169 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2175 DWORD WINAPI init_thread(LPVOID threadID) {
2177 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2184 /// The ThreadsManager class
2186 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2187 // get_beta_counters() are getters/setters for the per thread
2188 // counters used to sort the moves at root.
2190 void ThreadsManager::resetNodeCounters() {
2192 for (int i = 0; i < MAX_THREADS; i++)
2193 threads[i].nodes = 0ULL;
2196 int64_t ThreadsManager::nodes_searched() const {
2198 int64_t result = 0ULL;
2199 for (int i = 0; i < ActiveThreads; i++)
2200 result += threads[i].nodes;
2206 // idle_loop() is where the threads are parked when they have no work to do.
2207 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2208 // object for which the current thread is the master.
2210 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2212 assert(threadID >= 0 && threadID < MAX_THREADS);
2216 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2217 // master should exit as last one.
2218 if (AllThreadsShouldExit)
2221 threads[threadID].state = THREAD_TERMINATED;
2225 // If we are not thinking, wait for a condition to be signaled
2226 // instead of wasting CPU time polling for work.
2227 while ( threadID >= ActiveThreads
2228 || threads[threadID].state == THREAD_INITIALIZING)
2231 assert(threadID != 0);
2233 if (AllThreadsShouldExit)
2236 threads[threadID].state = THREAD_AVAILABLE;
2238 #if !defined(_MSC_VER)
2239 lock_grab(&WaitLock);
2240 if (threadID >= ActiveThreads)
2241 pthread_cond_wait(&WaitCond[threadID], &WaitLock);
2242 lock_release(&WaitLock);
2244 WaitForSingleObject(WaitCond[threadID], INFINITE);
2248 // If this thread has been assigned work, launch a search
2249 if (threads[threadID].state == THREAD_WORKISWAITING)
2251 assert(!AllThreadsShouldExit);
2253 threads[threadID].state = THREAD_SEARCHING;
2255 // Here we call search() with SplitPoint template parameter set to true
2256 SplitPoint* tsp = threads[threadID].splitPoint;
2257 Position pos(*tsp->pos, threadID);
2258 SearchStack* ss = tsp->sstack[threadID] + 1;
2262 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2264 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2266 assert(threads[threadID].state == THREAD_SEARCHING);
2268 threads[threadID].state = THREAD_AVAILABLE;
2271 // If this thread is the master of a split point and all slaves have
2272 // finished their work at this split point, return from the idle loop.
2274 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2276 if (i == ActiveThreads)
2278 // Because sp->slaves[] is reset under lock protection,
2279 // be sure sp->lock has been released before to return.
2280 lock_grab(&(sp->lock));
2281 lock_release(&(sp->lock));
2283 // In helpful master concept a master can help only a sub-tree, and
2284 // because here is all finished is not possible master is booked.
2285 assert(threads[threadID].state == THREAD_AVAILABLE);
2287 threads[threadID].state = THREAD_SEARCHING;
2294 // init_threads() is called during startup. It launches all helper threads,
2295 // and initializes the split point stack and the global locks and condition
2298 void ThreadsManager::init_threads() {
2303 // Initialize global locks
2305 lock_init(&WaitLock);
2307 for (i = 0; i < MAX_THREADS; i++)
2308 #if !defined(_MSC_VER)
2309 pthread_cond_init(&WaitCond[i], NULL);
2311 WaitCond[i] = CreateEvent(0, FALSE, FALSE, 0);
2314 // Initialize splitPoints[] locks
2315 for (i = 0; i < MAX_THREADS; i++)
2316 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2317 lock_init(&(threads[i].splitPoints[j].lock));
2319 // Will be set just before program exits to properly end the threads
2320 AllThreadsShouldExit = false;
2322 // Threads will be put all threads to sleep as soon as created
2325 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2326 threads[0].state = THREAD_SEARCHING;
2327 for (i = 1; i < MAX_THREADS; i++)
2328 threads[i].state = THREAD_INITIALIZING;
2330 // Launch the helper threads
2331 for (i = 1; i < MAX_THREADS; i++)
2334 #if !defined(_MSC_VER)
2335 pthread_t pthread[1];
2336 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2338 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2343 cout << "Failed to create thread number " << i << endl;
2344 Application::exit_with_failure();
2347 // Wait until the thread has finished launching and is gone to sleep
2348 while (threads[i].state == THREAD_INITIALIZING) {}
2353 // exit_threads() is called when the program exits. It makes all the
2354 // helper threads exit cleanly.
2356 void ThreadsManager::exit_threads() {
2358 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2360 // Wake up all the threads and waits for termination
2361 for (int i = 1; i < MAX_THREADS; i++)
2363 wake_sleeping_thread(i);
2364 while (threads[i].state != THREAD_TERMINATED) {}
2367 // Now we can safely destroy the locks
2368 for (int i = 0; i < MAX_THREADS; i++)
2369 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2370 lock_destroy(&(threads[i].splitPoints[j].lock));
2372 lock_destroy(&WaitLock);
2373 lock_destroy(&MPLock);
2375 // Now we can safely destroy the wait conditions
2376 for (int i = 0; i < MAX_THREADS; i++)
2377 cond_destroy(&WaitCond[i]);
2381 // thread_should_stop() checks whether the thread should stop its search.
2382 // This can happen if a beta cutoff has occurred in the thread's currently
2383 // active split point, or in some ancestor of the current split point.
2385 bool ThreadsManager::thread_should_stop(int threadID) const {
2387 assert(threadID >= 0 && threadID < ActiveThreads);
2389 SplitPoint* sp = threads[threadID].splitPoint;
2391 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2396 // thread_is_available() checks whether the thread with threadID "slave" is
2397 // available to help the thread with threadID "master" at a split point. An
2398 // obvious requirement is that "slave" must be idle. With more than two
2399 // threads, this is not by itself sufficient: If "slave" is the master of
2400 // some active split point, it is only available as a slave to the other
2401 // threads which are busy searching the split point at the top of "slave"'s
2402 // split point stack (the "helpful master concept" in YBWC terminology).
2404 bool ThreadsManager::thread_is_available(int slave, int master) const {
2406 assert(slave >= 0 && slave < ActiveThreads);
2407 assert(master >= 0 && master < ActiveThreads);
2408 assert(ActiveThreads > 1);
2410 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2413 // Make a local copy to be sure doesn't change under our feet
2414 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2416 // No active split points means that the thread is available as
2417 // a slave for any other thread.
2418 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2421 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2422 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2423 // could have been set to 0 by another thread leading to an out of bound access.
2424 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2431 // available_thread_exists() tries to find an idle thread which is available as
2432 // a slave for the thread with threadID "master".
2434 bool ThreadsManager::available_thread_exists(int master) const {
2436 assert(master >= 0 && master < ActiveThreads);
2437 assert(ActiveThreads > 1);
2439 for (int i = 0; i < ActiveThreads; i++)
2440 if (thread_is_available(i, master))
2447 // split() does the actual work of distributing the work at a node between
2448 // several available threads. If it does not succeed in splitting the
2449 // node (because no idle threads are available, or because we have no unused
2450 // split point objects), the function immediately returns. If splitting is
2451 // possible, a SplitPoint object is initialized with all the data that must be
2452 // copied to the helper threads and we tell our helper threads that they have
2453 // been assigned work. This will cause them to instantly leave their idle loops
2454 // and call sp_search(). When all threads have returned from sp_search() then
2457 template <bool Fake>
2458 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2459 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2460 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2462 assert(ply > 0 && ply < PLY_MAX);
2463 assert(*bestValue >= -VALUE_INFINITE);
2464 assert(*bestValue <= *alpha);
2465 assert(*alpha < beta);
2466 assert(beta <= VALUE_INFINITE);
2467 assert(depth > DEPTH_ZERO);
2468 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2469 assert(ActiveThreads > 1);
2471 int i, master = p.thread();
2472 Thread& masterThread = threads[master];
2476 // If no other thread is available to help us, or if we have too many
2477 // active split points, don't split.
2478 if ( !available_thread_exists(master)
2479 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2481 lock_release(&MPLock);
2485 // Pick the next available split point object from the split point stack
2486 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2488 // Initialize the split point object
2489 splitPoint.parent = masterThread.splitPoint;
2490 splitPoint.stopRequest = false;
2491 splitPoint.ply = ply;
2492 splitPoint.depth = depth;
2493 splitPoint.threatMove = threatMove;
2494 splitPoint.mateThreat = mateThreat;
2495 splitPoint.alpha = *alpha;
2496 splitPoint.beta = beta;
2497 splitPoint.pvNode = pvNode;
2498 splitPoint.bestValue = *bestValue;
2500 splitPoint.moveCount = moveCount;
2501 splitPoint.pos = &p;
2502 splitPoint.parentSstack = ss;
2503 for (i = 0; i < ActiveThreads; i++)
2504 splitPoint.slaves[i] = 0;
2506 masterThread.splitPoint = &splitPoint;
2508 // If we are here it means we are not available
2509 assert(masterThread.state != THREAD_AVAILABLE);
2511 int workersCnt = 1; // At least the master is included
2513 // Allocate available threads setting state to THREAD_BOOKED
2514 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2515 if (thread_is_available(i, master))
2517 threads[i].state = THREAD_BOOKED;
2518 threads[i].splitPoint = &splitPoint;
2519 splitPoint.slaves[i] = 1;
2523 assert(Fake || workersCnt > 1);
2525 // We can release the lock because slave threads are already booked and master is not available
2526 lock_release(&MPLock);
2528 // Tell the threads that they have work to do. This will make them leave
2529 // their idle loop. But before copy search stack tail for each thread.
2530 for (i = 0; i < ActiveThreads; i++)
2531 if (i == master || splitPoint.slaves[i])
2533 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2535 assert(i == master || threads[i].state == THREAD_BOOKED);
2537 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2540 // Everything is set up. The master thread enters the idle loop, from
2541 // which it will instantly launch a search, because its state is
2542 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2543 // idle loop, which means that the main thread will return from the idle
2544 // loop when all threads have finished their work at this split point.
2545 idle_loop(master, &splitPoint);
2547 // We have returned from the idle loop, which means that all threads are
2548 // finished. Update alpha and bestValue, and return.
2551 *alpha = splitPoint.alpha;
2552 *bestValue = splitPoint.bestValue;
2553 masterThread.activeSplitPoints--;
2554 masterThread.splitPoint = splitPoint.parent;
2556 lock_release(&MPLock);
2560 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2561 // to start a new search from the root.
2563 void ThreadsManager::wake_sleeping_thread(int threadID) {
2565 assert(threadID > 0);
2566 assert(threads[threadID].state == THREAD_AVAILABLE);
2568 #if !defined(_MSC_VER)
2569 pthread_mutex_lock(&WaitLock);
2570 pthread_cond_signal(&WaitCond[threadID]);
2571 pthread_mutex_unlock(&WaitLock);
2573 SetEvent(WaitCond[threadID]);
2578 /// The RootMoveList class
2580 // RootMoveList c'tor
2582 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2584 SearchStack ss[PLY_MAX_PLUS_2];
2585 MoveStack mlist[MOVES_MAX];
2587 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2589 // Initialize search stack
2590 init_ss_array(ss, PLY_MAX_PLUS_2);
2591 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2594 // Generate all legal moves
2595 MoveStack* last = generate_moves(pos, mlist);
2597 // Add each move to the moves[] array
2598 for (MoveStack* cur = mlist; cur != last; cur++)
2600 bool includeMove = includeAllMoves;
2602 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2603 includeMove = (searchMoves[k] == cur->move);
2608 // Find a quick score for the move
2609 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2610 moves[count].pv[1] = MOVE_NONE;
2611 pos.do_move(cur->move, st);
2612 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2613 pos.undo_move(cur->move);
2619 // Score root moves using the standard way used in main search, the moves
2620 // are scored according to the order in which are returned by MovePicker.
2622 void RootMoveList::score_moves(const Position& pos)
2626 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2628 while ((move = mp.get_next_move()) != MOVE_NONE)
2629 for (int i = 0; i < count; i++)
2630 if (moves[i].move == move)
2632 moves[i].mp_score = score--;
2637 // RootMoveList simple methods definitions
2639 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2643 for (j = 0; pv[j] != MOVE_NONE; j++)
2644 moves[moveNum].pv[j] = pv[j];
2646 moves[moveNum].pv[j] = MOVE_NONE;
2650 // RootMoveList::sort() sorts the root move list at the beginning of a new
2653 void RootMoveList::sort() {
2655 sort_multipv(count - 1); // Sort all items
2659 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2660 // list by their scores and depths. It is used to order the different PVs
2661 // correctly in MultiPV mode.
2663 void RootMoveList::sort_multipv(int n) {
2667 for (i = 1; i <= n; i++)
2669 RootMove rm = moves[i];
2670 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2671 moves[j] = moves[j - 1];