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_threads();
86 void put_threads_to_sleep();
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
98 Thread threads[MAX_THREADS];
100 Lock MPLock, WaitLock;
102 #if !defined(_MSC_VER)
103 pthread_cond_t WaitCond;
105 HANDLE SitIdleEvent[MAX_THREADS];
111 // RootMove struct is used for moves at the root at the tree. For each
112 // root move, we store a score, a node count, and a PV (really a refutation
113 // in the case of moves which fail low).
117 RootMove() : mp_score(0), nodes(0) {}
119 // RootMove::operator<() is the comparison function used when
120 // sorting the moves. A move m1 is considered to be better
121 // than a move m2 if it has a higher score, or if the moves
122 // have equal score but m1 has the higher beta cut-off count.
123 bool operator<(const RootMove& m) const {
125 return score != m.score ? score < m.score : mp_score <= m.mp_score;
132 Move pv[PLY_MAX_PLUS_2];
136 // The RootMoveList class is essentially an array of RootMove objects, with
137 // a handful of methods for accessing the data in the individual moves.
142 RootMoveList(Position& pos, Move searchMoves[]);
144 Move move(int moveNum) const { return moves[moveNum].move; }
145 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
146 int move_count() const { return count; }
147 Value move_score(int moveNum) const { return moves[moveNum].score; }
148 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
149 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
150 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
152 void set_move_pv(int moveNum, const Move pv[]);
153 void score_moves(const Position& pos);
155 void sort_multipv(int n);
158 RootMove moves[MOVES_MAX];
163 // When formatting a move for std::cout we must know if we are in Chess960
164 // or not. To keep using the handy operator<<() on the move the trick is to
165 // embed this flag in the stream itself. Function-like named enum set960 is
166 // used as a custom manipulator and the stream internal general-purpose array,
167 // accessed through ios_base::iword(), is used to pass the flag to the move's
168 // operator<<() that will use it to properly format castling moves.
171 std::ostream& operator<< (std::ostream& os, const set960& m) {
173 os.iword(0) = int(m);
182 // Maximum depth for razoring
183 const Depth RazorDepth = 4 * ONE_PLY;
185 // Dynamic razoring margin based on depth
186 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
188 // Maximum depth for use of dynamic threat detection when null move fails low
189 const Depth ThreatDepth = 5 * ONE_PLY;
191 // Step 9. Internal iterative deepening
193 // Minimum depth for use of internal iterative deepening
194 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
196 // At Non-PV nodes we do an internal iterative deepening search
197 // when the static evaluation is bigger then beta - IIDMargin.
198 const Value IIDMargin = Value(0x100);
200 // Step 11. Decide the new search depth
202 // Extensions. Configurable UCI options
203 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
204 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
205 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
207 // Minimum depth for use of singular extension
208 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
210 // If the TT move is at least SingularExtensionMargin better then the
211 // remaining ones we will extend it.
212 const Value SingularExtensionMargin = Value(0x20);
214 // Step 12. Futility pruning
216 // Futility margin for quiescence search
217 const Value FutilityMarginQS = Value(0x80);
219 // Futility lookup tables (initialized at startup) and their getter functions
220 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
221 int FutilityMoveCountArray[32]; // [depth]
223 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
224 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
226 // Step 14. Reduced search
228 // Reduction lookup tables (initialized at startup) and their getter functions
229 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
231 template <NodeType PV>
232 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
234 // Common adjustments
236 // Search depth at iteration 1
237 const Depth InitialDepth = ONE_PLY;
239 // Easy move margin. An easy move candidate must be at least this much
240 // better than the second best move.
241 const Value EasyMoveMargin = Value(0x200);
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
261 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
262 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
272 ThreadsManager ThreadsMgr;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode, bool SpNode>
288 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
292 return search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
298 template <NodeType PvNode>
299 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 Value value_to_tt(Value v, int ply);
304 Value value_from_tt(Value v, int ply);
305 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
306 bool connected_threat(const Position& pos, Move m, Move threat);
307 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
308 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
309 void update_killers(Move m, SearchStack* ss);
310 void update_gains(const Position& pos, Move move, Value before, Value after);
312 int current_search_time();
313 std::string value_to_uci(Value v);
317 void wait_for_stop_or_ponderhit();
318 void init_ss_array(SearchStack* ss, int size);
319 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
320 void insert_pv_in_tt(const Position& pos, Move pv[]);
321 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
323 #if !defined(_MSC_VER)
324 void *init_thread(void *threadID);
326 DWORD WINAPI init_thread(LPVOID threadID);
336 /// init_threads(), exit_threads() and nodes_searched() are helpers to
337 /// give accessibility to some TM methods from outside of current file.
339 void init_threads() { ThreadsMgr.init_threads(); }
340 void exit_threads() { ThreadsMgr.exit_threads(); }
341 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
344 /// init_search() is called during startup. It initializes various lookup tables
348 int d; // depth (ONE_PLY == 2)
349 int hd; // half depth (ONE_PLY == 1)
352 // Init reductions array
353 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
355 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
356 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
357 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
358 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
361 // Init futility margins array
362 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
363 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
365 // Init futility move count array
366 for (d = 0; d < 32; d++)
367 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
371 /// perft() is our utility to verify move generation is bug free. All the legal
372 /// moves up to given depth are generated and counted and the sum returned.
374 int perft(Position& pos, Depth depth)
376 MoveStack mlist[MOVES_MAX];
381 // Generate all legal moves
382 MoveStack* last = generate_moves(pos, mlist);
384 // If we are at the last ply we don't need to do and undo
385 // the moves, just to count them.
386 if (depth <= ONE_PLY)
387 return int(last - mlist);
389 // Loop through all legal moves
391 for (MoveStack* cur = mlist; cur != last; cur++)
394 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
395 sum += perft(pos, depth - ONE_PLY);
402 /// think() is the external interface to Stockfish's search, and is called when
403 /// the program receives the UCI 'go' command. It initializes various
404 /// search-related global variables, and calls root_search(). It returns false
405 /// when a quit command is received during the search.
407 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
408 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
410 // Initialize global search variables
411 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
413 ThreadsMgr.resetNodeCounters();
414 SearchStartTime = get_system_time();
415 ExactMaxTime = maxTime;
418 InfiniteSearch = infinite;
419 PonderSearch = ponder;
420 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
422 // Look for a book move, only during games, not tests
423 if (UseTimeManagement && get_option_value_bool("OwnBook"))
425 if (get_option_value_string("Book File") != OpeningBook.file_name())
426 OpeningBook.open(get_option_value_string("Book File"));
428 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
429 if (bookMove != MOVE_NONE)
432 wait_for_stop_or_ponderhit();
434 cout << "bestmove " << bookMove << endl;
439 // Read UCI option values
440 TT.set_size(get_option_value_int("Hash"));
441 if (button_was_pressed("Clear Hash"))
444 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
445 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
446 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
447 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
448 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
449 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
450 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
451 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
452 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
453 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
454 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
455 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
457 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
458 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
459 MultiPV = get_option_value_int("MultiPV");
460 UseLogFile = get_option_value_bool("Use Search Log");
463 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
465 read_weights(pos.side_to_move());
467 // Set the number of active threads
468 int newActiveThreads = get_option_value_int("Threads");
469 if (newActiveThreads != ThreadsMgr.active_threads())
471 ThreadsMgr.set_active_threads(newActiveThreads);
472 init_eval(ThreadsMgr.active_threads());
475 // Wake up sleeping threads
476 ThreadsMgr.wake_sleeping_threads();
479 int myTime = time[pos.side_to_move()];
480 int myIncrement = increment[pos.side_to_move()];
481 if (UseTimeManagement)
482 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
484 // Set best NodesBetweenPolls interval to avoid lagging under
485 // heavy time pressure.
487 NodesBetweenPolls = Min(MaxNodes, 30000);
488 else if (myTime && myTime < 1000)
489 NodesBetweenPolls = 1000;
490 else if (myTime && myTime < 5000)
491 NodesBetweenPolls = 5000;
493 NodesBetweenPolls = 30000;
495 // Write search information to log file
497 LogFile << "Searching: " << pos.to_fen() << endl
498 << "infinite: " << infinite
499 << " ponder: " << ponder
500 << " time: " << myTime
501 << " increment: " << myIncrement
502 << " moves to go: " << movesToGo << endl;
504 // We're ready to start thinking. Call the iterative deepening loop function
505 id_loop(pos, searchMoves);
510 ThreadsMgr.put_threads_to_sleep();
518 // id_loop() is the main iterative deepening loop. It calls root_search
519 // repeatedly with increasing depth until the allocated thinking time has
520 // been consumed, the user stops the search, or the maximum search depth is
523 Value id_loop(const Position& pos, Move searchMoves[]) {
525 Position p(pos, pos.thread());
526 SearchStack ss[PLY_MAX_PLUS_2];
527 Move pv[PLY_MAX_PLUS_2];
528 Move EasyMove = MOVE_NONE;
529 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
531 // Moves to search are verified, copied, scored and sorted
532 RootMoveList rml(p, searchMoves);
534 // Handle special case of searching on a mate/stale position
535 if (rml.move_count() == 0)
538 wait_for_stop_or_ponderhit();
540 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
543 // Print RootMoveList startup scoring to the standard output,
544 // so to output information also for iteration 1.
545 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
546 << "info depth " << 1
547 << "\ninfo depth " << 1
548 << " score " << value_to_uci(rml.move_score(0))
549 << " time " << current_search_time()
550 << " nodes " << ThreadsMgr.nodes_searched()
552 << " pv " << rml.move(0) << "\n";
557 init_ss_array(ss, PLY_MAX_PLUS_2);
558 pv[0] = pv[1] = MOVE_NONE;
559 ValueByIteration[1] = rml.move_score(0);
562 // Is one move significantly better than others after initial scoring ?
563 if ( rml.move_count() == 1
564 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
565 EasyMove = rml.move(0);
567 // Iterative deepening loop
568 while (Iteration < PLY_MAX)
570 // Initialize iteration
572 BestMoveChangesByIteration[Iteration] = 0;
574 cout << "info depth " << Iteration << endl;
576 // Calculate dynamic aspiration window based on previous iterations
577 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
579 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
580 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
582 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
583 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
585 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
586 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
589 // Search to the current depth, rml is updated and sorted, alpha and beta could change
590 value = root_search(p, ss, pv, rml, &alpha, &beta);
592 // Write PV to transposition table, in case the relevant entries have
593 // been overwritten during the search.
594 insert_pv_in_tt(p, pv);
597 break; // Value cannot be trusted. Break out immediately!
599 //Save info about search result
600 ValueByIteration[Iteration] = value;
602 // Drop the easy move if differs from the new best move
603 if (pv[0] != EasyMove)
604 EasyMove = MOVE_NONE;
606 if (UseTimeManagement)
609 bool stopSearch = false;
611 // Stop search early if there is only a single legal move,
612 // we search up to Iteration 6 anyway to get a proper score.
613 if (Iteration >= 6 && rml.move_count() == 1)
616 // Stop search early when the last two iterations returned a mate score
618 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
619 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
622 // Stop search early if one move seems to be much better than the others
623 int64_t nodes = ThreadsMgr.nodes_searched();
626 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
627 && current_search_time() > TimeMgr.available_time() / 16)
628 ||( rml.move_nodes(0) > (nodes * 98) / 100
629 && current_search_time() > TimeMgr.available_time() / 32)))
632 // Add some extra time if the best move has changed during the last two iterations
633 if (Iteration > 5 && Iteration <= 50)
634 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
635 BestMoveChangesByIteration[Iteration-1]);
637 // Stop search if most of MaxSearchTime is consumed at the end of the
638 // iteration. We probably don't have enough time to search the first
639 // move at the next iteration anyway.
640 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
646 StopOnPonderhit = true;
652 if (MaxDepth && Iteration >= MaxDepth)
656 // If we are pondering or in infinite search, we shouldn't print the
657 // best move before we are told to do so.
658 if (!AbortSearch && (PonderSearch || InfiniteSearch))
659 wait_for_stop_or_ponderhit();
661 // Print final search statistics
662 cout << "info nodes " << ThreadsMgr.nodes_searched()
664 << " time " << current_search_time() << endl;
666 // Print the best move and the ponder move to the standard output
667 if (pv[0] == MOVE_NONE)
673 assert(pv[0] != MOVE_NONE);
675 cout << "bestmove " << pv[0];
677 if (pv[1] != MOVE_NONE)
678 cout << " ponder " << pv[1];
685 dbg_print_mean(LogFile);
687 if (dbg_show_hit_rate)
688 dbg_print_hit_rate(LogFile);
690 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
691 << "\nNodes/second: " << nps()
692 << "\nBest move: " << move_to_san(p, pv[0]);
695 p.do_move(pv[0], st);
696 LogFile << "\nPonder move: "
697 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
700 return rml.move_score(0);
704 // root_search() is the function which searches the root node. It is
705 // similar to search_pv except that it uses a different move ordering
706 // scheme, prints some information to the standard output and handles
707 // the fail low/high loops.
709 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
715 Depth depth, ext, newDepth;
716 Value value, alpha, beta;
717 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
718 int researchCountFH, researchCountFL;
720 researchCountFH = researchCountFL = 0;
723 isCheck = pos.is_check();
724 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
726 // Step 1. Initialize node (polling is omitted at root)
727 ss->currentMove = ss->bestMove = MOVE_NONE;
729 // Step 2. Check for aborted search (omitted at root)
730 // Step 3. Mate distance pruning (omitted at root)
731 // Step 4. Transposition table lookup (omitted at root)
733 // Step 5. Evaluate the position statically
734 // At root we do this only to get reference value for child nodes
735 ss->evalMargin = VALUE_NONE;
736 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
738 // Step 6. Razoring (omitted at root)
739 // Step 7. Static null move pruning (omitted at root)
740 // Step 8. Null move search with verification search (omitted at root)
741 // Step 9. Internal iterative deepening (omitted at root)
743 // Step extra. Fail low loop
744 // We start with small aspiration window and in case of fail low, we research
745 // with bigger window until we are not failing low anymore.
748 // Sort the moves before to (re)search
749 rml.score_moves(pos);
752 // Step 10. Loop through all moves in the root move list
753 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
755 // This is used by time management
756 FirstRootMove = (i == 0);
758 // Save the current node count before the move is searched
759 nodes = ThreadsMgr.nodes_searched();
761 // Pick the next root move, and print the move and the move number to
762 // the standard output.
763 move = ss->currentMove = rml.move(i);
765 if (current_search_time() >= 1000)
766 cout << "info currmove " << move
767 << " currmovenumber " << i + 1 << endl;
769 moveIsCheck = pos.move_is_check(move);
770 captureOrPromotion = pos.move_is_capture_or_promotion(move);
772 // Step 11. Decide the new search depth
773 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
774 newDepth = depth + ext;
776 // Step 12. Futility pruning (omitted at root)
778 // Step extra. Fail high loop
779 // If move fails high, we research with bigger window until we are not failing
781 value = - VALUE_INFINITE;
785 // Step 13. Make the move
786 pos.do_move(move, st, ci, moveIsCheck);
788 // Step extra. pv search
789 // We do pv search for first moves (i < MultiPV)
790 // and for fail high research (value > alpha)
791 if (i < MultiPV || value > alpha)
793 // Aspiration window is disabled in multi-pv case
795 alpha = -VALUE_INFINITE;
797 // Full depth PV search, done on first move or after a fail high
798 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
802 // Step 14. Reduced search
803 // if the move fails high will be re-searched at full depth
804 bool doFullDepthSearch = true;
806 if ( depth >= 3 * ONE_PLY
808 && !captureOrPromotion
809 && !move_is_castle(move))
811 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
814 assert(newDepth-ss->reduction >= ONE_PLY);
816 // Reduced depth non-pv search using alpha as upperbound
817 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
818 doFullDepthSearch = (value > alpha);
821 // The move failed high, but if reduction is very big we could
822 // face a false positive, retry with a less aggressive reduction,
823 // if the move fails high again then go with full depth search.
824 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
826 assert(newDepth - ONE_PLY >= ONE_PLY);
828 ss->reduction = ONE_PLY;
829 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
830 doFullDepthSearch = (value > alpha);
832 ss->reduction = DEPTH_ZERO; // Restore original reduction
835 // Step 15. Full depth search
836 if (doFullDepthSearch)
838 // Full depth non-pv search using alpha as upperbound
839 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
841 // If we are above alpha then research at same depth but as PV
842 // to get a correct score or eventually a fail high above beta.
844 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
848 // Step 16. Undo move
851 // Can we exit fail high loop ?
852 if (AbortSearch || value < beta)
855 // We are failing high and going to do a research. It's important to update
856 // the score before research in case we run out of time while researching.
857 rml.set_move_score(i, value);
859 extract_pv_from_tt(pos, move, pv);
860 rml.set_move_pv(i, pv);
862 // Print information to the standard output
863 print_pv_info(pos, pv, alpha, beta, value);
865 // Prepare for a research after a fail high, each time with a wider window
866 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
869 } // End of fail high loop
871 // Finished searching the move. If AbortSearch is true, the search
872 // was aborted because the user interrupted the search or because we
873 // ran out of time. In this case, the return value of the search cannot
874 // be trusted, and we break out of the loop without updating the best
879 // Remember searched nodes counts for this move
880 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
882 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
883 assert(value < beta);
885 // Step 17. Check for new best move
886 if (value <= alpha && i >= MultiPV)
887 rml.set_move_score(i, -VALUE_INFINITE);
890 // PV move or new best move!
893 rml.set_move_score(i, value);
895 extract_pv_from_tt(pos, move, pv);
896 rml.set_move_pv(i, pv);
900 // We record how often the best move has been changed in each
901 // iteration. This information is used for time managment: When
902 // the best move changes frequently, we allocate some more time.
904 BestMoveChangesByIteration[Iteration]++;
906 // Print information to the standard output
907 print_pv_info(pos, pv, alpha, beta, value);
909 // Raise alpha to setup proper non-pv search upper bound
916 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
918 cout << "info multipv " << j + 1
919 << " score " << value_to_uci(rml.move_score(j))
920 << " depth " << (j <= i ? Iteration : Iteration - 1)
921 << " time " << current_search_time()
922 << " nodes " << ThreadsMgr.nodes_searched()
926 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
927 cout << rml.move_pv(j, k) << " ";
931 alpha = rml.move_score(Min(i, MultiPV - 1));
933 } // PV move or new best move
935 assert(alpha >= *alphaPtr);
937 AspirationFailLow = (alpha == *alphaPtr);
939 if (AspirationFailLow && StopOnPonderhit)
940 StopOnPonderhit = false;
943 // Can we exit fail low loop ?
944 if (AbortSearch || !AspirationFailLow)
947 // Prepare for a research after a fail low, each time with a wider window
948 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
953 // Sort the moves before to return
960 // search<>() is the main search function for both PV and non-PV nodes and for
961 // normal and SplitPoint nodes. When called just after a split point the search
962 // is simpler because we have already probed the hash table, done a null move
963 // search, and searched the first move before splitting, we don't have to repeat
964 // all this work again. We also don't need to store anything to the hash table
965 // here: This is taken care of after we return from the split point.
967 template <NodeType PvNode, bool SpNode>
968 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
970 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
971 assert(beta > alpha && beta <= VALUE_INFINITE);
972 assert(PvNode || alpha == beta - 1);
973 assert(ply > 0 && ply < PLY_MAX);
974 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
976 Move movesSearched[MOVES_MAX];
980 Move ttMove, move, excludedMove, threatMove;
982 Value bestValue, value, oldAlpha;
983 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
984 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
985 bool mateThreat = false;
987 int threadID = pos.thread();
988 SplitPoint* sp = NULL;
989 refinedValue = bestValue = value = -VALUE_INFINITE;
991 isCheck = pos.is_check();
997 ttMove = excludedMove = MOVE_NONE;
998 threatMove = sp->threatMove;
999 mateThreat = sp->mateThreat;
1000 goto split_point_start;
1003 // Step 1. Initialize node and poll. Polling can abort search
1004 ThreadsMgr.incrementNodeCounter(threadID);
1005 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1006 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1008 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1014 // Step 2. Check for aborted search and immediate draw
1015 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1018 if (pos.is_draw() || ply >= PLY_MAX - 1)
1021 // Step 3. Mate distance pruning
1022 alpha = Max(value_mated_in(ply), alpha);
1023 beta = Min(value_mate_in(ply+1), beta);
1027 // Step 4. Transposition table lookup
1029 // We don't want the score of a partial search to overwrite a previous full search
1030 // TT value, so we use a different position key in case of an excluded move exists.
1031 excludedMove = ss->excludedMove;
1032 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1034 tte = TT.retrieve(posKey);
1035 ttMove = (tte ? tte->move() : MOVE_NONE);
1037 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1038 // This is to avoid problems in the following areas:
1040 // * Repetition draw detection
1041 // * Fifty move rule detection
1042 // * Searching for a mate
1043 // * Printing of full PV line
1045 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1047 // Refresh tte entry to avoid aging
1048 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1050 ss->bestMove = ttMove; // Can be MOVE_NONE
1051 return value_from_tt(tte->value(), ply);
1054 // Step 5. Evaluate the position statically and
1055 // update gain statistics of parent move.
1057 ss->eval = ss->evalMargin = VALUE_NONE;
1060 assert(tte->static_value() != VALUE_NONE);
1062 ss->eval = tte->static_value();
1063 ss->evalMargin = tte->static_value_margin();
1064 refinedValue = refine_eval(tte, ss->eval, ply);
1068 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1069 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1072 // Save gain for the parent non-capture move
1073 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1075 // Step 6. Razoring (is omitted in PV nodes)
1077 && depth < RazorDepth
1079 && refinedValue < beta - razor_margin(depth)
1080 && ttMove == MOVE_NONE
1081 && (ss-1)->currentMove != MOVE_NULL
1082 && !value_is_mate(beta)
1083 && !pos.has_pawn_on_7th(pos.side_to_move()))
1085 Value rbeta = beta - razor_margin(depth);
1086 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1088 // Logically we should return (v + razor_margin(depth)), but
1089 // surprisingly this did slightly weaker in tests.
1093 // Step 7. Static null move pruning (is omitted in PV nodes)
1094 // We're betting that the opponent doesn't have a move that will reduce
1095 // the score by more than futility_margin(depth) if we do a null move.
1097 && !ss->skipNullMove
1098 && depth < RazorDepth
1100 && refinedValue >= beta + futility_margin(depth, 0)
1101 && !value_is_mate(beta)
1102 && pos.non_pawn_material(pos.side_to_move()))
1103 return refinedValue - futility_margin(depth, 0);
1105 // Step 8. Null move search with verification search (is omitted in PV nodes)
1107 && !ss->skipNullMove
1110 && refinedValue >= beta
1111 && !value_is_mate(beta)
1112 && pos.non_pawn_material(pos.side_to_move()))
1114 ss->currentMove = MOVE_NULL;
1116 // Null move dynamic reduction based on depth
1117 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1119 // Null move dynamic reduction based on value
1120 if (refinedValue - beta > PawnValueMidgame)
1123 pos.do_null_move(st);
1124 (ss+1)->skipNullMove = true;
1126 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1127 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1128 (ss+1)->skipNullMove = false;
1129 pos.undo_null_move();
1131 if (nullValue >= beta)
1133 // Do not return unproven mate scores
1134 if (nullValue >= value_mate_in(PLY_MAX))
1137 if (depth < 6 * ONE_PLY)
1140 // Do verification search at high depths
1141 ss->skipNullMove = true;
1142 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1143 ss->skipNullMove = false;
1150 // The null move failed low, which means that we may be faced with
1151 // some kind of threat. If the previous move was reduced, check if
1152 // the move that refuted the null move was somehow connected to the
1153 // move which was reduced. If a connection is found, return a fail
1154 // low score (which will cause the reduced move to fail high in the
1155 // parent node, which will trigger a re-search with full depth).
1156 if (nullValue == value_mated_in(ply + 2))
1159 threatMove = (ss+1)->bestMove;
1160 if ( depth < ThreatDepth
1161 && (ss-1)->reduction
1162 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1167 // Step 9. Internal iterative deepening
1168 if ( depth >= IIDDepth[PvNode]
1169 && ttMove == MOVE_NONE
1170 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1172 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1174 ss->skipNullMove = true;
1175 search<PvNode>(pos, ss, alpha, beta, d, ply);
1176 ss->skipNullMove = false;
1178 ttMove = ss->bestMove;
1179 tte = TT.retrieve(posKey);
1182 // Expensive mate threat detection (only for PV nodes)
1184 mateThreat = pos.has_mate_threat();
1186 split_point_start: // At split points actual search starts from here
1188 // Initialize a MovePicker object for the current position
1189 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1190 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1191 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1193 ss->bestMove = MOVE_NONE;
1194 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1195 futilityBase = ss->eval + ss->evalMargin;
1196 singularExtensionNode = !SpNode
1197 && depth >= SingularExtensionDepth[PvNode]
1200 && !excludedMove // Do not allow recursive singular extension search
1201 && (tte->type() & VALUE_TYPE_LOWER)
1202 && tte->depth() >= depth - 3 * ONE_PLY;
1205 lock_grab(&(sp->lock));
1206 bestValue = sp->bestValue;
1209 // Step 10. Loop through moves
1210 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1211 while ( bestValue < beta
1212 && (move = mp.get_next_move()) != MOVE_NONE
1213 && !ThreadsMgr.thread_should_stop(threadID))
1217 moveCount = ++sp->moveCount;
1218 lock_release(&(sp->lock));
1221 assert(move_is_ok(move));
1223 if (move == excludedMove)
1226 moveIsCheck = pos.move_is_check(move, ci);
1227 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1229 // Step 11. Decide the new search depth
1230 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1232 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1233 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1234 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1235 // lower then ttValue minus a margin then we extend ttMove.
1236 if ( singularExtensionNode
1237 && move == tte->move()
1240 Value ttValue = value_from_tt(tte->value(), ply);
1242 if (abs(ttValue) < VALUE_KNOWN_WIN)
1244 Value b = ttValue - SingularExtensionMargin;
1245 ss->excludedMove = move;
1246 ss->skipNullMove = true;
1247 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1248 ss->skipNullMove = false;
1249 ss->excludedMove = MOVE_NONE;
1250 ss->bestMove = MOVE_NONE;
1256 newDepth = depth - ONE_PLY + ext;
1258 // Update current move (this must be done after singular extension search)
1259 movesSearched[moveCount++] = ss->currentMove = move;
1261 // Step 12. Futility pruning (is omitted in PV nodes)
1263 && !captureOrPromotion
1267 && !move_is_castle(move))
1269 // Move count based pruning
1270 if ( moveCount >= futility_move_count(depth)
1271 && !(threatMove && connected_threat(pos, move, threatMove))
1272 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1275 lock_grab(&(sp->lock));
1280 // Value based pruning
1281 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1282 // but fixing this made program slightly weaker.
1283 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1284 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1285 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1287 if (futilityValueScaled < beta)
1291 lock_grab(&(sp->lock));
1292 if (futilityValueScaled > sp->bestValue)
1293 sp->bestValue = bestValue = futilityValueScaled;
1295 else if (futilityValueScaled > bestValue)
1296 bestValue = futilityValueScaled;
1302 // Step 13. Make the move
1303 pos.do_move(move, st, ci, moveIsCheck);
1305 // Step extra. pv search (only in PV nodes)
1306 // The first move in list is the expected PV
1307 if (!SpNode && PvNode && moveCount == 1)
1308 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1309 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1312 // Step 14. Reduced depth search
1313 // If the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * ONE_PLY
1317 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !(ss->killers[0] == move || ss->killers[1] == move))
1322 ss->reduction = reduction<PvNode>(depth, moveCount);
1325 alpha = SpNode ? sp->alpha : alpha;
1326 Depth d = newDepth - ss->reduction;
1327 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1328 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1330 doFullDepthSearch = (value > alpha);
1333 // The move failed high, but if reduction is very big we could
1334 // face a false positive, retry with a less aggressive reduction,
1335 // if the move fails high again then go with full depth search.
1336 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1338 assert(newDepth - ONE_PLY >= ONE_PLY);
1340 ss->reduction = ONE_PLY;
1341 alpha = SpNode ? sp->alpha : alpha;
1342 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1343 doFullDepthSearch = (value > alpha);
1345 ss->reduction = DEPTH_ZERO; // Restore original reduction
1348 // Step 15. Full depth search
1349 if (doFullDepthSearch)
1351 alpha = SpNode ? sp->alpha : alpha;
1352 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1353 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1355 // Step extra. pv search (only in PV nodes)
1356 // Search only for possible new PV nodes, if instead value >= beta then
1357 // parent node fails low with value <= alpha and tries another move.
1358 if (PvNode && value > alpha && value < beta)
1359 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1360 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1364 // Step 16. Undo move
1365 pos.undo_move(move);
1367 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1369 // Step 17. Check for new best move
1372 lock_grab(&(sp->lock));
1373 bestValue = sp->bestValue;
1377 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1382 if (SpNode && (!PvNode || value >= beta))
1383 sp->stopRequest = true;
1385 if (PvNode && value < beta) // We want always alpha < beta
1388 if (value == value_mate_in(ply + 1))
1389 ss->mateKiller = move;
1391 ss->bestMove = move;
1395 sp->bestValue = bestValue;
1397 sp->parentSstack->bestMove = ss->bestMove;
1401 // Step 18. Check for split
1403 && depth >= MinimumSplitDepth
1404 && ThreadsMgr.active_threads() > 1
1406 && ThreadsMgr.available_thread_exists(threadID)
1408 && !ThreadsMgr.thread_should_stop(threadID)
1410 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1411 threatMove, mateThreat, moveCount, &mp, PvNode);
1416 /* Here we have the lock still grabbed */
1417 sp->slaves[threadID] = 0;
1418 lock_release(&(sp->lock));
1422 // Step 19. Check for mate and stalemate
1423 // All legal moves have been searched and if there are
1424 // no legal moves, it must be mate or stalemate.
1425 // If one move was excluded return fail low score.
1427 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1429 // Step 20. Update tables
1430 // If the search is not aborted, update the transposition table,
1431 // history counters, and killer moves.
1432 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1435 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1436 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1437 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1439 // Update killers and history only for non capture moves that fails high
1440 if ( bestValue >= beta
1441 && !pos.move_is_capture_or_promotion(move))
1443 update_history(pos, move, depth, movesSearched, moveCount);
1444 update_killers(move, ss);
1447 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1453 // qsearch() is the quiescence search function, which is called by the main
1454 // search function when the remaining depth is zero (or, to be more precise,
1455 // less than ONE_PLY).
1457 template <NodeType PvNode>
1458 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1460 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1461 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1462 assert(PvNode || alpha == beta - 1);
1464 assert(ply > 0 && ply < PLY_MAX);
1465 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1469 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1470 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1472 Value oldAlpha = alpha;
1474 ThreadsMgr.incrementNodeCounter(pos.thread());
1475 ss->bestMove = ss->currentMove = MOVE_NONE;
1477 // Check for an instant draw or maximum ply reached
1478 if (pos.is_draw() || ply >= PLY_MAX - 1)
1481 // Transposition table lookup. At PV nodes, we don't use the TT for
1482 // pruning, but only for move ordering.
1483 tte = TT.retrieve(pos.get_key());
1484 ttMove = (tte ? tte->move() : MOVE_NONE);
1486 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1488 ss->bestMove = ttMove; // Can be MOVE_NONE
1489 return value_from_tt(tte->value(), ply);
1492 isCheck = pos.is_check();
1494 // Evaluate the position statically
1497 bestValue = futilityBase = -VALUE_INFINITE;
1498 ss->eval = evalMargin = VALUE_NONE;
1499 deepChecks = enoughMaterial = false;
1505 assert(tte->static_value() != VALUE_NONE);
1507 evalMargin = tte->static_value_margin();
1508 ss->eval = bestValue = tte->static_value();
1511 ss->eval = bestValue = evaluate(pos, evalMargin);
1513 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1515 // Stand pat. Return immediately if static value is at least beta
1516 if (bestValue >= beta)
1519 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1524 if (PvNode && bestValue > alpha)
1527 // If we are near beta then try to get a cutoff pushing checks a bit further
1528 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1530 // Futility pruning parameters, not needed when in check
1531 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1532 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1535 // Initialize a MovePicker object for the current position, and prepare
1536 // to search the moves. Because the depth is <= 0 here, only captures,
1537 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1538 // and we are near beta) will be generated.
1539 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1542 // Loop through the moves until no moves remain or a beta cutoff occurs
1543 while ( alpha < beta
1544 && (move = mp.get_next_move()) != MOVE_NONE)
1546 assert(move_is_ok(move));
1548 moveIsCheck = pos.move_is_check(move, ci);
1556 && !move_is_promotion(move)
1557 && !pos.move_is_passed_pawn_push(move))
1559 futilityValue = futilityBase
1560 + pos.endgame_value_of_piece_on(move_to(move))
1561 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1563 if (futilityValue < alpha)
1565 if (futilityValue > bestValue)
1566 bestValue = futilityValue;
1571 // Detect non-capture evasions that are candidate to be pruned
1572 evasionPrunable = isCheck
1573 && bestValue > value_mated_in(PLY_MAX)
1574 && !pos.move_is_capture(move)
1575 && !pos.can_castle(pos.side_to_move());
1577 // Don't search moves with negative SEE values
1579 && (!isCheck || evasionPrunable)
1581 && !move_is_promotion(move)
1582 && pos.see_sign(move) < 0)
1585 // Update current move
1586 ss->currentMove = move;
1588 // Make and search the move
1589 pos.do_move(move, st, ci, moveIsCheck);
1590 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1591 pos.undo_move(move);
1593 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1596 if (value > bestValue)
1602 ss->bestMove = move;
1607 // All legal moves have been searched. A special case: If we're in check
1608 // and no legal moves were found, it is checkmate.
1609 if (isCheck && bestValue == -VALUE_INFINITE)
1610 return value_mated_in(ply);
1612 // Update transposition table
1613 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1614 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1615 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1617 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1623 // connected_moves() tests whether two moves are 'connected' in the sense
1624 // that the first move somehow made the second move possible (for instance
1625 // if the moving piece is the same in both moves). The first move is assumed
1626 // to be the move that was made to reach the current position, while the
1627 // second move is assumed to be a move from the current position.
1629 bool connected_moves(const Position& pos, Move m1, Move m2) {
1631 Square f1, t1, f2, t2;
1634 assert(move_is_ok(m1));
1635 assert(move_is_ok(m2));
1637 if (m2 == MOVE_NONE)
1640 // Case 1: The moving piece is the same in both moves
1646 // Case 2: The destination square for m2 was vacated by m1
1652 // Case 3: Moving through the vacated square
1653 if ( piece_is_slider(pos.piece_on(f2))
1654 && bit_is_set(squares_between(f2, t2), f1))
1657 // Case 4: The destination square for m2 is defended by the moving piece in m1
1658 p = pos.piece_on(t1);
1659 if (bit_is_set(pos.attacks_from(p, t1), t2))
1662 // Case 5: Discovered check, checking piece is the piece moved in m1
1663 if ( piece_is_slider(p)
1664 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1665 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1667 // discovered_check_candidates() works also if the Position's side to
1668 // move is the opposite of the checking piece.
1669 Color them = opposite_color(pos.side_to_move());
1670 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1672 if (bit_is_set(dcCandidates, f2))
1679 // value_is_mate() checks if the given value is a mate one eventually
1680 // compensated for the ply.
1682 bool value_is_mate(Value value) {
1684 assert(abs(value) <= VALUE_INFINITE);
1686 return value <= value_mated_in(PLY_MAX)
1687 || value >= value_mate_in(PLY_MAX);
1691 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1692 // "plies to mate from the current ply". Non-mate scores are unchanged.
1693 // The function is called before storing a value to the transposition table.
1695 Value value_to_tt(Value v, int ply) {
1697 if (v >= value_mate_in(PLY_MAX))
1700 if (v <= value_mated_in(PLY_MAX))
1707 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1708 // the transposition table to a mate score corrected for the current ply.
1710 Value value_from_tt(Value v, int ply) {
1712 if (v >= value_mate_in(PLY_MAX))
1715 if (v <= value_mated_in(PLY_MAX))
1722 // extension() decides whether a move should be searched with normal depth,
1723 // or with extended depth. Certain classes of moves (checking moves, in
1724 // particular) are searched with bigger depth than ordinary moves and in
1725 // any case are marked as 'dangerous'. Note that also if a move is not
1726 // extended, as example because the corresponding UCI option is set to zero,
1727 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1728 template <NodeType PvNode>
1729 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1730 bool singleEvasion, bool mateThreat, bool* dangerous) {
1732 assert(m != MOVE_NONE);
1734 Depth result = DEPTH_ZERO;
1735 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1739 if (moveIsCheck && pos.see_sign(m) >= 0)
1740 result += CheckExtension[PvNode];
1743 result += SingleEvasionExtension[PvNode];
1746 result += MateThreatExtension[PvNode];
1749 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1751 Color c = pos.side_to_move();
1752 if (relative_rank(c, move_to(m)) == RANK_7)
1754 result += PawnPushTo7thExtension[PvNode];
1757 if (pos.pawn_is_passed(c, move_to(m)))
1759 result += PassedPawnExtension[PvNode];
1764 if ( captureOrPromotion
1765 && pos.type_of_piece_on(move_to(m)) != PAWN
1766 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1767 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1768 && !move_is_promotion(m)
1771 result += PawnEndgameExtension[PvNode];
1776 && captureOrPromotion
1777 && pos.type_of_piece_on(move_to(m)) != PAWN
1778 && pos.see_sign(m) >= 0)
1780 result += ONE_PLY / 2;
1784 return Min(result, ONE_PLY);
1788 // connected_threat() tests whether it is safe to forward prune a move or if
1789 // is somehow coonected to the threat move returned by null search.
1791 bool connected_threat(const Position& pos, Move m, Move threat) {
1793 assert(move_is_ok(m));
1794 assert(threat && move_is_ok(threat));
1795 assert(!pos.move_is_check(m));
1796 assert(!pos.move_is_capture_or_promotion(m));
1797 assert(!pos.move_is_passed_pawn_push(m));
1799 Square mfrom, mto, tfrom, tto;
1801 mfrom = move_from(m);
1803 tfrom = move_from(threat);
1804 tto = move_to(threat);
1806 // Case 1: Don't prune moves which move the threatened piece
1810 // Case 2: If the threatened piece has value less than or equal to the
1811 // value of the threatening piece, don't prune move which defend it.
1812 if ( pos.move_is_capture(threat)
1813 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1814 || pos.type_of_piece_on(tfrom) == KING)
1815 && pos.move_attacks_square(m, tto))
1818 // Case 3: If the moving piece in the threatened move is a slider, don't
1819 // prune safe moves which block its ray.
1820 if ( piece_is_slider(pos.piece_on(tfrom))
1821 && bit_is_set(squares_between(tfrom, tto), mto)
1822 && pos.see_sign(m) >= 0)
1829 // ok_to_use_TT() returns true if a transposition table score
1830 // can be used at a given point in search.
1832 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1834 Value v = value_from_tt(tte->value(), ply);
1836 return ( tte->depth() >= depth
1837 || v >= Max(value_mate_in(PLY_MAX), beta)
1838 || v < Min(value_mated_in(PLY_MAX), beta))
1840 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1841 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1845 // refine_eval() returns the transposition table score if
1846 // possible otherwise falls back on static position evaluation.
1848 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1852 Value v = value_from_tt(tte->value(), ply);
1854 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1855 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1862 // update_history() registers a good move that produced a beta-cutoff
1863 // in history and marks as failures all the other moves of that ply.
1865 void update_history(const Position& pos, Move move, Depth depth,
1866 Move movesSearched[], int moveCount) {
1869 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1871 for (int i = 0; i < moveCount - 1; i++)
1873 m = movesSearched[i];
1877 if (!pos.move_is_capture_or_promotion(m))
1878 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1883 // update_killers() add a good move that produced a beta-cutoff
1884 // among the killer moves of that ply.
1886 void update_killers(Move m, SearchStack* ss) {
1888 if (m == ss->killers[0])
1891 ss->killers[1] = ss->killers[0];
1896 // update_gains() updates the gains table of a non-capture move given
1897 // the static position evaluation before and after the move.
1899 void update_gains(const Position& pos, Move m, Value before, Value after) {
1902 && before != VALUE_NONE
1903 && after != VALUE_NONE
1904 && pos.captured_piece_type() == PIECE_TYPE_NONE
1905 && !move_is_special(m))
1906 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1910 // current_search_time() returns the number of milliseconds which have passed
1911 // since the beginning of the current search.
1913 int current_search_time() {
1915 return get_system_time() - SearchStartTime;
1919 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1921 std::string value_to_uci(Value v) {
1923 std::stringstream s;
1925 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1926 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1928 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1933 // nps() computes the current nodes/second count.
1937 int t = current_search_time();
1938 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1942 // poll() performs two different functions: It polls for user input, and it
1943 // looks at the time consumed so far and decides if it's time to abort the
1948 static int lastInfoTime;
1949 int t = current_search_time();
1954 // We are line oriented, don't read single chars
1955 std::string command;
1957 if (!std::getline(std::cin, command))
1960 if (command == "quit")
1963 PonderSearch = false;
1967 else if (command == "stop")
1970 PonderSearch = false;
1972 else if (command == "ponderhit")
1976 // Print search information
1980 else if (lastInfoTime > t)
1981 // HACK: Must be a new search where we searched less than
1982 // NodesBetweenPolls nodes during the first second of search.
1985 else if (t - lastInfoTime >= 1000)
1992 if (dbg_show_hit_rate)
1993 dbg_print_hit_rate();
1995 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1996 << " time " << t << endl;
1999 // Should we stop the search?
2003 bool stillAtFirstMove = FirstRootMove
2004 && !AspirationFailLow
2005 && t > TimeMgr.available_time();
2007 bool noMoreTime = t > TimeMgr.maximum_time()
2008 || stillAtFirstMove;
2010 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2011 || (ExactMaxTime && t >= ExactMaxTime)
2012 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2017 // ponderhit() is called when the program is pondering (i.e. thinking while
2018 // it's the opponent's turn to move) in order to let the engine know that
2019 // it correctly predicted the opponent's move.
2023 int t = current_search_time();
2024 PonderSearch = false;
2026 bool stillAtFirstMove = FirstRootMove
2027 && !AspirationFailLow
2028 && t > TimeMgr.available_time();
2030 bool noMoreTime = t > TimeMgr.maximum_time()
2031 || stillAtFirstMove;
2033 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2038 // init_ss_array() does a fast reset of the first entries of a SearchStack
2039 // array and of all the excludedMove and skipNullMove entries.
2041 void init_ss_array(SearchStack* ss, int size) {
2043 for (int i = 0; i < size; i++, ss++)
2045 ss->excludedMove = MOVE_NONE;
2046 ss->skipNullMove = false;
2047 ss->reduction = DEPTH_ZERO;
2051 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2056 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2057 // while the program is pondering. The point is to work around a wrinkle in
2058 // the UCI protocol: When pondering, the engine is not allowed to give a
2059 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2060 // We simply wait here until one of these commands is sent, and return,
2061 // after which the bestmove and pondermove will be printed (in id_loop()).
2063 void wait_for_stop_or_ponderhit() {
2065 std::string command;
2069 if (!std::getline(std::cin, command))
2072 if (command == "quit")
2077 else if (command == "ponderhit" || command == "stop")
2083 // print_pv_info() prints to standard output and eventually to log file information on
2084 // the current PV line. It is called at each iteration or after a new pv is found.
2086 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2088 cout << "info depth " << Iteration
2089 << " score " << value_to_uci(value)
2090 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2091 << " time " << current_search_time()
2092 << " nodes " << ThreadsMgr.nodes_searched()
2096 for (Move* m = pv; *m != MOVE_NONE; m++)
2103 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2104 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2106 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2107 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2112 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2113 // the PV back into the TT. This makes sure the old PV moves are searched
2114 // first, even if the old TT entries have been overwritten.
2116 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2120 Position p(pos, pos.thread());
2121 Value v, m = VALUE_NONE;
2123 for (int i = 0; pv[i] != MOVE_NONE; i++)
2125 tte = TT.retrieve(p.get_key());
2126 if (!tte || tte->move() != pv[i])
2128 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2129 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2131 p.do_move(pv[i], st);
2136 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2137 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2138 // allow to always have a ponder move even when we fail high at root and also a
2139 // long PV to print that is important for position analysis.
2141 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2145 Position p(pos, pos.thread());
2148 assert(bestMove != MOVE_NONE);
2151 p.do_move(pv[ply++], st);
2153 while ( (tte = TT.retrieve(p.get_key())) != NULL
2154 && tte->move() != MOVE_NONE
2155 && move_is_legal(p, tte->move())
2157 && (!p.is_draw() || ply < 2))
2159 pv[ply] = tte->move();
2160 p.do_move(pv[ply++], st);
2162 pv[ply] = MOVE_NONE;
2166 // init_thread() is the function which is called when a new thread is
2167 // launched. It simply calls the idle_loop() function with the supplied
2168 // threadID. There are two versions of this function; one for POSIX
2169 // threads and one for Windows threads.
2171 #if !defined(_MSC_VER)
2173 void* init_thread(void *threadID) {
2175 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2181 DWORD WINAPI init_thread(LPVOID threadID) {
2183 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2190 /// The ThreadsManager class
2192 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2193 // get_beta_counters() are getters/setters for the per thread
2194 // counters used to sort the moves at root.
2196 void ThreadsManager::resetNodeCounters() {
2198 for (int i = 0; i < MAX_THREADS; i++)
2199 threads[i].nodes = 0ULL;
2202 int64_t ThreadsManager::nodes_searched() const {
2204 int64_t result = 0ULL;
2205 for (int i = 0; i < ActiveThreads; i++)
2206 result += threads[i].nodes;
2212 // idle_loop() is where the threads are parked when they have no work to do.
2213 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2214 // object for which the current thread is the master.
2216 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2218 assert(threadID >= 0 && threadID < MAX_THREADS);
2222 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2223 // master should exit as last one.
2224 if (AllThreadsShouldExit)
2227 threads[threadID].state = THREAD_TERMINATED;
2231 // If we are not thinking, wait for a condition to be signaled
2232 // instead of wasting CPU time polling for work.
2233 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2236 assert(threadID != 0);
2237 threads[threadID].state = THREAD_SLEEPING;
2239 #if !defined(_MSC_VER)
2240 lock_grab(&WaitLock);
2241 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2242 pthread_cond_wait(&WaitCond, &WaitLock);
2243 lock_release(&WaitLock);
2245 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2249 // If thread has just woken up, mark it as available
2250 if (threads[threadID].state == THREAD_SLEEPING)
2251 threads[threadID].state = THREAD_AVAILABLE;
2253 // If this thread has been assigned work, launch a search
2254 if (threads[threadID].state == THREAD_WORKISWAITING)
2256 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2258 threads[threadID].state = THREAD_SEARCHING;
2260 // Here we call search() with SplitPoint template parameter set to true
2261 SplitPoint* tsp = threads[threadID].splitPoint;
2262 Position pos(*tsp->pos, threadID);
2263 SearchStack* ss = tsp->sstack[threadID] + 1;
2267 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2269 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2271 assert(threads[threadID].state == THREAD_SEARCHING);
2273 threads[threadID].state = THREAD_AVAILABLE;
2276 // If this thread is the master of a split point and all slaves have
2277 // finished their work at this split point, return from the idle loop.
2279 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2281 if (i == ActiveThreads)
2283 // Because sp->slaves[] is reset under lock protection,
2284 // be sure sp->lock has been released before to return.
2285 lock_grab(&(sp->lock));
2286 lock_release(&(sp->lock));
2288 // In helpful master concept a master can help only a sub-tree, and
2289 // because here is all finished is not possible master is booked.
2290 assert(threads[threadID].state == THREAD_AVAILABLE);
2292 threads[threadID].state = THREAD_SEARCHING;
2299 // init_threads() is called during startup. It launches all helper threads,
2300 // and initializes the split point stack and the global locks and condition
2303 void ThreadsManager::init_threads() {
2308 #if !defined(_MSC_VER)
2309 pthread_t pthread[1];
2312 // Initialize global locks
2314 lock_init(&WaitLock);
2316 #if !defined(_MSC_VER)
2317 pthread_cond_init(&WaitCond, NULL);
2319 for (i = 0; i < MAX_THREADS; i++)
2320 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2323 // Initialize splitPoints[] locks
2324 for (i = 0; i < MAX_THREADS; i++)
2325 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2326 lock_init(&(threads[i].splitPoints[j].lock));
2328 // Will be set just before program exits to properly end the threads
2329 AllThreadsShouldExit = false;
2331 // Threads will be put to sleep as soon as created
2332 AllThreadsShouldSleep = true;
2334 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2336 threads[0].state = THREAD_SEARCHING;
2337 for (i = 1; i < MAX_THREADS; i++)
2338 threads[i].state = THREAD_AVAILABLE;
2340 // Launch the helper threads
2341 for (i = 1; i < MAX_THREADS; i++)
2344 #if !defined(_MSC_VER)
2345 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2347 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2352 cout << "Failed to create thread number " << i << endl;
2353 Application::exit_with_failure();
2356 // Wait until the thread has finished launching and is gone to sleep
2357 while (threads[i].state != THREAD_SLEEPING) {}
2362 // exit_threads() is called when the program exits. It makes all the
2363 // helper threads exit cleanly.
2365 void ThreadsManager::exit_threads() {
2367 ActiveThreads = MAX_THREADS; // Wake up all the threads
2368 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2369 AllThreadsShouldSleep = true; // Avoid an assert in wake_sleeping_threads()
2370 wake_sleeping_threads();
2372 // Wait for thread termination
2373 for (int i = 1; i < MAX_THREADS; i++)
2374 while (threads[i].state != THREAD_TERMINATED) {}
2376 // Now we can safely destroy the locks
2377 for (int i = 0; i < MAX_THREADS; i++)
2378 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2379 lock_destroy(&(threads[i].splitPoints[j].lock));
2381 lock_destroy(&WaitLock);
2382 lock_destroy(&MPLock);
2386 // thread_should_stop() checks whether the thread should stop its search.
2387 // This can happen if a beta cutoff has occurred in the thread's currently
2388 // active split point, or in some ancestor of the current split point.
2390 bool ThreadsManager::thread_should_stop(int threadID) const {
2392 assert(threadID >= 0 && threadID < ActiveThreads);
2394 SplitPoint* sp = threads[threadID].splitPoint;
2396 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2401 // thread_is_available() checks whether the thread with threadID "slave" is
2402 // available to help the thread with threadID "master" at a split point. An
2403 // obvious requirement is that "slave" must be idle. With more than two
2404 // threads, this is not by itself sufficient: If "slave" is the master of
2405 // some active split point, it is only available as a slave to the other
2406 // threads which are busy searching the split point at the top of "slave"'s
2407 // split point stack (the "helpful master concept" in YBWC terminology).
2409 bool ThreadsManager::thread_is_available(int slave, int master) const {
2411 assert(slave >= 0 && slave < ActiveThreads);
2412 assert(master >= 0 && master < ActiveThreads);
2413 assert(ActiveThreads > 1);
2415 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2418 // Make a local copy to be sure doesn't change under our feet
2419 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2421 // No active split points means that the thread is available as
2422 // a slave for any other thread.
2423 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2426 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2427 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2428 // could have been set to 0 by another thread leading to an out of bound access.
2429 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2436 // available_thread_exists() tries to find an idle thread which is available as
2437 // a slave for the thread with threadID "master".
2439 bool ThreadsManager::available_thread_exists(int master) const {
2441 assert(master >= 0 && master < ActiveThreads);
2442 assert(ActiveThreads > 1);
2444 for (int i = 0; i < ActiveThreads; i++)
2445 if (thread_is_available(i, master))
2452 // split() does the actual work of distributing the work at a node between
2453 // several available threads. If it does not succeed in splitting the
2454 // node (because no idle threads are available, or because we have no unused
2455 // split point objects), the function immediately returns. If splitting is
2456 // possible, a SplitPoint object is initialized with all the data that must be
2457 // copied to the helper threads and we tell our helper threads that they have
2458 // been assigned work. This will cause them to instantly leave their idle loops
2459 // and call sp_search(). When all threads have returned from sp_search() then
2462 template <bool Fake>
2463 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2464 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2465 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2467 assert(ply > 0 && ply < PLY_MAX);
2468 assert(*bestValue >= -VALUE_INFINITE);
2469 assert(*bestValue <= *alpha);
2470 assert(*alpha < beta);
2471 assert(beta <= VALUE_INFINITE);
2472 assert(depth > DEPTH_ZERO);
2473 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2474 assert(ActiveThreads > 1);
2476 int i, master = p.thread();
2477 Thread& masterThread = threads[master];
2481 // If no other thread is available to help us, or if we have too many
2482 // active split points, don't split.
2483 if ( !available_thread_exists(master)
2484 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2486 lock_release(&MPLock);
2490 // Pick the next available split point object from the split point stack
2491 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2493 // Initialize the split point object
2494 splitPoint.parent = masterThread.splitPoint;
2495 splitPoint.stopRequest = false;
2496 splitPoint.ply = ply;
2497 splitPoint.depth = depth;
2498 splitPoint.threatMove = threatMove;
2499 splitPoint.mateThreat = mateThreat;
2500 splitPoint.alpha = *alpha;
2501 splitPoint.beta = beta;
2502 splitPoint.pvNode = pvNode;
2503 splitPoint.bestValue = *bestValue;
2505 splitPoint.moveCount = moveCount;
2506 splitPoint.pos = &p;
2507 splitPoint.parentSstack = ss;
2508 for (i = 0; i < ActiveThreads; i++)
2509 splitPoint.slaves[i] = 0;
2511 masterThread.splitPoint = &splitPoint;
2513 // If we are here it means we are not available
2514 assert(masterThread.state != THREAD_AVAILABLE);
2516 int workersCnt = 1; // At least the master is included
2518 // Allocate available threads setting state to THREAD_BOOKED
2519 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2520 if (thread_is_available(i, master))
2522 threads[i].state = THREAD_BOOKED;
2523 threads[i].splitPoint = &splitPoint;
2524 splitPoint.slaves[i] = 1;
2528 assert(Fake || workersCnt > 1);
2530 // We can release the lock because slave threads are already booked and master is not available
2531 lock_release(&MPLock);
2533 // Tell the threads that they have work to do. This will make them leave
2534 // their idle loop. But before copy search stack tail for each thread.
2535 for (i = 0; i < ActiveThreads; i++)
2536 if (i == master || splitPoint.slaves[i])
2538 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2540 assert(i == master || threads[i].state == THREAD_BOOKED);
2542 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2545 // Everything is set up. The master thread enters the idle loop, from
2546 // which it will instantly launch a search, because its state is
2547 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2548 // idle loop, which means that the main thread will return from the idle
2549 // loop when all threads have finished their work at this split point.
2550 idle_loop(master, &splitPoint);
2552 // We have returned from the idle loop, which means that all threads are
2553 // finished. Update alpha and bestValue, and return.
2556 *alpha = splitPoint.alpha;
2557 *bestValue = splitPoint.bestValue;
2558 masterThread.activeSplitPoints--;
2559 masterThread.splitPoint = splitPoint.parent;
2561 lock_release(&MPLock);
2565 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2566 // to start a new search from the root.
2568 void ThreadsManager::wake_sleeping_threads() {
2570 assert(AllThreadsShouldSleep);
2571 assert(ActiveThreads > 0);
2573 AllThreadsShouldSleep = false;
2575 if (ActiveThreads == 1)
2578 #if !defined(_MSC_VER)
2579 pthread_mutex_lock(&WaitLock);
2580 pthread_cond_broadcast(&WaitCond);
2581 pthread_mutex_unlock(&WaitLock);
2583 for (int i = 1; i < MAX_THREADS; i++)
2584 SetEvent(SitIdleEvent[i]);
2590 // put_threads_to_sleep() makes all the threads go to sleep just before
2591 // to leave think(), at the end of the search. Threads should have already
2592 // finished the job and should be idle.
2594 void ThreadsManager::put_threads_to_sleep() {
2596 assert(!AllThreadsShouldSleep);
2598 // This makes the threads to go to sleep
2599 AllThreadsShouldSleep = true;
2602 /// The RootMoveList class
2604 // RootMoveList c'tor
2606 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2608 SearchStack ss[PLY_MAX_PLUS_2];
2609 MoveStack mlist[MOVES_MAX];
2611 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2613 // Initialize search stack
2614 init_ss_array(ss, PLY_MAX_PLUS_2);
2615 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2618 // Generate all legal moves
2619 MoveStack* last = generate_moves(pos, mlist);
2621 // Add each move to the moves[] array
2622 for (MoveStack* cur = mlist; cur != last; cur++)
2624 bool includeMove = includeAllMoves;
2626 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2627 includeMove = (searchMoves[k] == cur->move);
2632 // Find a quick score for the move
2633 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2634 moves[count].pv[1] = MOVE_NONE;
2635 pos.do_move(cur->move, st);
2636 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2637 pos.undo_move(cur->move);
2643 // Score root moves using the standard way used in main search, the moves
2644 // are scored according to the order in which are returned by MovePicker.
2646 void RootMoveList::score_moves(const Position& pos)
2650 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2652 while ((move = mp.get_next_move()) != MOVE_NONE)
2653 for (int i = 0; i < count; i++)
2654 if (moves[i].move == move)
2656 moves[i].mp_score = score--;
2661 // RootMoveList simple methods definitions
2663 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2667 for (j = 0; pv[j] != MOVE_NONE; j++)
2668 moves[moveNum].pv[j] = pv[j];
2670 moves[moveNum].pv[j] = MOVE_NONE;
2674 // RootMoveList::sort() sorts the root move list at the beginning of a new
2677 void RootMoveList::sort() {
2679 sort_multipv(count - 1); // Sort all items
2683 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2684 // list by their scores and depths. It is used to order the different PVs
2685 // correctly in MultiPV mode.
2687 void RootMoveList::sort_multipv(int n) {
2691 for (i = 1; i <= n; i++)
2693 RootMove rm = moves[i];
2694 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2695 moves[j] = moves[j - 1];