2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_thread(int threadID);
86 void idle_loop(int threadID, SplitPoint* sp);
89 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
90 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
96 volatile bool AllThreadsShouldExit;
97 Thread threads[MAX_THREADS];
99 WaitCondition WaitCond[MAX_THREADS];
103 // RootMove struct is used for moves at the root at the tree. For each
104 // root move, we store a score, a node count, and a PV (really a refutation
105 // in the case of moves which fail low).
109 RootMove() : mp_score(0), nodes(0) {}
111 // RootMove::operator<() is the comparison function used when
112 // sorting the moves. A move m1 is considered to be better
113 // than a move m2 if it has a higher score, or if the moves
114 // have equal score but m1 has the higher beta cut-off count.
115 bool operator<(const RootMove& m) const {
117 return score != m.score ? score < m.score : mp_score <= m.mp_score;
124 Move pv[PLY_MAX_PLUS_2];
128 // The RootMoveList class is essentially an array of RootMove objects, with
129 // a handful of methods for accessing the data in the individual moves.
134 RootMoveList(Position& pos, Move searchMoves[]);
136 Move move(int moveNum) const { return moves[moveNum].move; }
137 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
138 int move_count() const { return count; }
139 Value move_score(int moveNum) const { return moves[moveNum].score; }
140 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
141 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
142 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 void set_move_pv(int moveNum, const Move pv[]);
145 void score_moves(const Position& pos);
147 void sort_multipv(int n);
150 RootMove moves[MOVES_MAX];
155 // When formatting a move for std::cout we must know if we are in Chess960
156 // or not. To keep using the handy operator<<() on the move the trick is to
157 // embed this flag in the stream itself. Function-like named enum set960 is
158 // used as a custom manipulator and the stream internal general-purpose array,
159 // accessed through ios_base::iword(), is used to pass the flag to the move's
160 // operator<<() that will use it to properly format castling moves.
163 std::ostream& operator<< (std::ostream& os, const set960& m) {
165 os.iword(0) = int(m);
174 // Maximum depth for razoring
175 const Depth RazorDepth = 4 * ONE_PLY;
177 // Dynamic razoring margin based on depth
178 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
180 // Maximum depth for use of dynamic threat detection when null move fails low
181 const Depth ThreatDepth = 5 * ONE_PLY;
183 // Step 9. Internal iterative deepening
185 // Minimum depth for use of internal iterative deepening
186 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
188 // At Non-PV nodes we do an internal iterative deepening search
189 // when the static evaluation is bigger then beta - IIDMargin.
190 const Value IIDMargin = Value(0x100);
192 // Step 11. Decide the new search depth
194 // Extensions. Configurable UCI options
195 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
196 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
197 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
199 // Minimum depth for use of singular extension
200 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
202 // If the TT move is at least SingularExtensionMargin better then the
203 // remaining ones we will extend it.
204 const Value SingularExtensionMargin = Value(0x20);
206 // Step 12. Futility pruning
208 // Futility margin for quiescence search
209 const Value FutilityMarginQS = Value(0x80);
211 // Futility lookup tables (initialized at startup) and their getter functions
212 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
213 int FutilityMoveCountArray[32]; // [depth]
215 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
216 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
218 // Step 14. Reduced search
220 // Reduction lookup tables (initialized at startup) and their getter functions
221 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
223 template <NodeType PV>
224 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
226 // Common adjustments
228 // Search depth at iteration 1
229 const Depth InitialDepth = ONE_PLY;
231 // Easy move margin. An easy move candidate must be at least this much
232 // better than the second best move.
233 const Value EasyMoveMargin = Value(0x200);
241 // Scores and number of times the best move changed for each iteration
242 Value ValueByIteration[PLY_MAX_PLUS_2];
243 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
245 // Search window management
251 // Time managment variables
252 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
253 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
254 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
259 std::ofstream LogFile;
261 // Multi-threads related variables
262 Depth MinimumSplitDepth;
263 int MaxThreadsPerSplitPoint;
264 ThreadsManager ThreadsMgr;
266 // Node counters, used only by thread[0] but try to keep in different cache
267 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
269 int NodesBetweenPolls = 30000;
276 Value id_loop(const Position& pos, Move searchMoves[]);
277 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
279 template <NodeType PvNode, bool SpNode>
280 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
282 template <NodeType PvNode>
283 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());
468 int myTime = time[pos.side_to_move()];
469 int myIncrement = increment[pos.side_to_move()];
470 if (UseTimeManagement)
471 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
473 // Set best NodesBetweenPolls interval to avoid lagging under
474 // heavy time pressure.
476 NodesBetweenPolls = Min(MaxNodes, 30000);
477 else if (myTime && myTime < 1000)
478 NodesBetweenPolls = 1000;
479 else if (myTime && myTime < 5000)
480 NodesBetweenPolls = 5000;
482 NodesBetweenPolls = 30000;
484 // Write search information to log file
486 LogFile << "Searching: " << pos.to_fen() << endl
487 << "infinite: " << infinite
488 << " ponder: " << ponder
489 << " time: " << myTime
490 << " increment: " << myIncrement
491 << " moves to go: " << movesToGo << endl;
493 // We're ready to start thinking. Call the iterative deepening loop function
494 id_loop(pos, searchMoves);
505 // id_loop() is the main iterative deepening loop. It calls root_search
506 // repeatedly with increasing depth until the allocated thinking time has
507 // been consumed, the user stops the search, or the maximum search depth is
510 Value id_loop(const Position& pos, Move searchMoves[]) {
512 Position p(pos, pos.thread());
513 SearchStack ss[PLY_MAX_PLUS_2];
514 Move pv[PLY_MAX_PLUS_2];
515 Move EasyMove = MOVE_NONE;
516 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
518 // Moves to search are verified, copied, scored and sorted
519 RootMoveList rml(p, searchMoves);
521 // Handle special case of searching on a mate/stale position
522 if (rml.move_count() == 0)
525 wait_for_stop_or_ponderhit();
527 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
530 // Print RootMoveList startup scoring to the standard output,
531 // so to output information also for iteration 1.
532 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
533 << "info depth " << 1
534 << "\ninfo depth " << 1
535 << " score " << value_to_uci(rml.move_score(0))
536 << " time " << current_search_time()
537 << " nodes " << ThreadsMgr.nodes_searched()
539 << " pv " << rml.move(0) << "\n";
544 init_ss_array(ss, PLY_MAX_PLUS_2);
545 pv[0] = pv[1] = MOVE_NONE;
546 ValueByIteration[1] = rml.move_score(0);
549 // Is one move significantly better than others after initial scoring ?
550 if ( rml.move_count() == 1
551 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
552 EasyMove = rml.move(0);
554 // Iterative deepening loop
555 while (Iteration < PLY_MAX)
557 // Initialize iteration
559 BestMoveChangesByIteration[Iteration] = 0;
561 cout << "info depth " << Iteration << endl;
563 // Calculate dynamic aspiration window based on previous iterations
564 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
566 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
567 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
569 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
570 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
572 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
573 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
576 // Search to the current depth, rml is updated and sorted, alpha and beta could change
577 value = root_search(p, ss, pv, rml, &alpha, &beta);
579 // Write PV to transposition table, in case the relevant entries have
580 // been overwritten during the search.
581 insert_pv_in_tt(p, pv);
584 break; // Value cannot be trusted. Break out immediately!
586 //Save info about search result
587 ValueByIteration[Iteration] = value;
589 // Drop the easy move if differs from the new best move
590 if (pv[0] != EasyMove)
591 EasyMove = MOVE_NONE;
593 if (UseTimeManagement)
596 bool stopSearch = false;
598 // Stop search early if there is only a single legal move,
599 // we search up to Iteration 6 anyway to get a proper score.
600 if (Iteration >= 6 && rml.move_count() == 1)
603 // Stop search early when the last two iterations returned a mate score
605 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
606 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
609 // Stop search early if one move seems to be much better than the others
610 int64_t nodes = ThreadsMgr.nodes_searched();
613 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
614 && current_search_time() > TimeMgr.available_time() / 16)
615 ||( rml.move_nodes(0) > (nodes * 98) / 100
616 && current_search_time() > TimeMgr.available_time() / 32)))
619 // Add some extra time if the best move has changed during the last two iterations
620 if (Iteration > 5 && Iteration <= 50)
621 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
622 BestMoveChangesByIteration[Iteration-1]);
624 // Stop search if most of MaxSearchTime is consumed at the end of the
625 // iteration. We probably don't have enough time to search the first
626 // move at the next iteration anyway.
627 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
633 StopOnPonderhit = true;
639 if (MaxDepth && Iteration >= MaxDepth)
643 // If we are pondering or in infinite search, we shouldn't print the
644 // best move before we are told to do so.
645 if (!AbortSearch && (PonderSearch || InfiniteSearch))
646 wait_for_stop_or_ponderhit();
648 // Print final search statistics
649 cout << "info nodes " << ThreadsMgr.nodes_searched()
651 << " time " << current_search_time() << endl;
653 // Print the best move and the ponder move to the standard output
654 if (pv[0] == MOVE_NONE)
660 assert(pv[0] != MOVE_NONE);
662 cout << "bestmove " << pv[0];
664 if (pv[1] != MOVE_NONE)
665 cout << " ponder " << pv[1];
672 dbg_print_mean(LogFile);
674 if (dbg_show_hit_rate)
675 dbg_print_hit_rate(LogFile);
677 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
678 << "\nNodes/second: " << nps()
679 << "\nBest move: " << move_to_san(p, pv[0]);
682 p.do_move(pv[0], st);
683 LogFile << "\nPonder move: "
684 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
687 return rml.move_score(0);
691 // root_search() is the function which searches the root node. It is
692 // similar to search_pv except that it uses a different move ordering
693 // scheme, prints some information to the standard output and handles
694 // the fail low/high loops.
696 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
702 Depth depth, ext, newDepth;
703 Value value, evalMargin, alpha, beta;
704 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
705 int researchCountFH, researchCountFL;
707 researchCountFH = researchCountFL = 0;
710 isCheck = pos.is_check();
711 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
713 // Step 1. Initialize node (polling is omitted at root)
714 ss->currentMove = ss->bestMove = MOVE_NONE;
716 // Step 2. Check for aborted search (omitted at root)
717 // Step 3. Mate distance pruning (omitted at root)
718 // Step 4. Transposition table lookup (omitted at root)
720 // Step 5. Evaluate the position statically
721 // At root we do this only to get reference value for child nodes
722 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
724 // Step 6. Razoring (omitted at root)
725 // Step 7. Static null move pruning (omitted at root)
726 // Step 8. Null move search with verification search (omitted at root)
727 // Step 9. Internal iterative deepening (omitted at root)
729 // Step extra. Fail low loop
730 // We start with small aspiration window and in case of fail low, we research
731 // with bigger window until we are not failing low anymore.
734 // Sort the moves before to (re)search
735 rml.score_moves(pos);
738 // Step 10. Loop through all moves in the root move list
739 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
741 // This is used by time management
742 FirstRootMove = (i == 0);
744 // Save the current node count before the move is searched
745 nodes = ThreadsMgr.nodes_searched();
747 // Pick the next root move, and print the move and the move number to
748 // the standard output.
749 move = ss->currentMove = rml.move(i);
751 if (current_search_time() >= 1000)
752 cout << "info currmove " << move
753 << " currmovenumber " << i + 1 << endl;
755 moveIsCheck = pos.move_is_check(move);
756 captureOrPromotion = pos.move_is_capture_or_promotion(move);
758 // Step 11. Decide the new search depth
759 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
760 newDepth = depth + ext;
762 // Step 12. Futility pruning (omitted at root)
764 // Step extra. Fail high loop
765 // If move fails high, we research with bigger window until we are not failing
767 value = - VALUE_INFINITE;
771 // Step 13. Make the move
772 pos.do_move(move, st, ci, moveIsCheck);
774 // Step extra. pv search
775 // We do pv search for first moves (i < MultiPV)
776 // and for fail high research (value > alpha)
777 if (i < MultiPV || value > alpha)
779 // Aspiration window is disabled in multi-pv case
781 alpha = -VALUE_INFINITE;
783 // Full depth PV search, done on first move or after a fail high
784 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
788 // Step 14. Reduced search
789 // if the move fails high will be re-searched at full depth
790 bool doFullDepthSearch = true;
792 if ( depth >= 3 * ONE_PLY
794 && !captureOrPromotion
795 && !move_is_castle(move))
797 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
800 assert(newDepth-ss->reduction >= ONE_PLY);
802 // Reduced depth non-pv search using alpha as upperbound
803 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
804 doFullDepthSearch = (value > alpha);
807 // The move failed high, but if reduction is very big we could
808 // face a false positive, retry with a less aggressive reduction,
809 // if the move fails high again then go with full depth search.
810 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
812 assert(newDepth - ONE_PLY >= ONE_PLY);
814 ss->reduction = ONE_PLY;
815 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
816 doFullDepthSearch = (value > alpha);
818 ss->reduction = DEPTH_ZERO; // Restore original reduction
821 // Step 15. Full depth search
822 if (doFullDepthSearch)
824 // Full depth non-pv search using alpha as upperbound
825 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
827 // If we are above alpha then research at same depth but as PV
828 // to get a correct score or eventually a fail high above beta.
830 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
834 // Step 16. Undo move
837 // Can we exit fail high loop ?
838 if (AbortSearch || value < beta)
841 // We are failing high and going to do a research. It's important to update
842 // the score before research in case we run out of time while researching.
843 rml.set_move_score(i, value);
845 extract_pv_from_tt(pos, move, pv);
846 rml.set_move_pv(i, pv);
848 // Print information to the standard output
849 print_pv_info(pos, pv, alpha, beta, value);
851 // Prepare for a research after a fail high, each time with a wider window
852 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
855 } // End of fail high loop
857 // Finished searching the move. If AbortSearch is true, the search
858 // was aborted because the user interrupted the search or because we
859 // ran out of time. In this case, the return value of the search cannot
860 // be trusted, and we break out of the loop without updating the best
865 // Remember searched nodes counts for this move
866 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
868 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
869 assert(value < beta);
871 // Step 17. Check for new best move
872 if (value <= alpha && i >= MultiPV)
873 rml.set_move_score(i, -VALUE_INFINITE);
876 // PV move or new best move!
879 rml.set_move_score(i, value);
881 extract_pv_from_tt(pos, move, pv);
882 rml.set_move_pv(i, pv);
886 // We record how often the best move has been changed in each
887 // iteration. This information is used for time managment: When
888 // the best move changes frequently, we allocate some more time.
890 BestMoveChangesByIteration[Iteration]++;
892 // Print information to the standard output
893 print_pv_info(pos, pv, alpha, beta, value);
895 // Raise alpha to setup proper non-pv search upper bound
902 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
904 cout << "info multipv " << j + 1
905 << " score " << value_to_uci(rml.move_score(j))
906 << " depth " << (j <= i ? Iteration : Iteration - 1)
907 << " time " << current_search_time()
908 << " nodes " << ThreadsMgr.nodes_searched()
912 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
913 cout << rml.move_pv(j, k) << " ";
917 alpha = rml.move_score(Min(i, MultiPV - 1));
919 } // PV move or new best move
921 assert(alpha >= *alphaPtr);
923 AspirationFailLow = (alpha == *alphaPtr);
925 if (AspirationFailLow && StopOnPonderhit)
926 StopOnPonderhit = false;
929 // Can we exit fail low loop ?
930 if (AbortSearch || !AspirationFailLow)
933 // Prepare for a research after a fail low, each time with a wider window
934 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
939 // Sort the moves before to return
946 // search<>() is the main search function for both PV and non-PV nodes and for
947 // normal and SplitPoint nodes. When called just after a split point the search
948 // is simpler because we have already probed the hash table, done a null move
949 // search, and searched the first move before splitting, we don't have to repeat
950 // all this work again. We also don't need to store anything to the hash table
951 // here: This is taken care of after we return from the split point.
953 template <NodeType PvNode, bool SpNode>
954 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
956 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
957 assert(beta > alpha && beta <= VALUE_INFINITE);
958 assert(PvNode || alpha == beta - 1);
959 assert(ply > 0 && ply < PLY_MAX);
960 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
962 Move movesSearched[MOVES_MAX];
966 Move ttMove, move, excludedMove, threatMove;
968 Value bestValue, value, evalMargin, oldAlpha;
969 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
970 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
971 bool mateThreat = false;
973 int threadID = pos.thread();
974 SplitPoint* sp = NULL;
975 refinedValue = bestValue = value = -VALUE_INFINITE;
977 isCheck = pos.is_check();
983 evalMargin = VALUE_ZERO;
984 ttMove = excludedMove = MOVE_NONE;
985 threatMove = sp->threatMove;
986 mateThreat = sp->mateThreat;
987 goto split_point_start;
990 // Step 1. Initialize node and poll. Polling can abort search
991 ThreadsMgr.incrementNodeCounter(threadID);
992 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
993 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
995 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1001 // Step 2. Check for aborted search and immediate draw
1002 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1005 if (pos.is_draw() || ply >= PLY_MAX - 1)
1008 // Step 3. Mate distance pruning
1009 alpha = Max(value_mated_in(ply), alpha);
1010 beta = Min(value_mate_in(ply+1), beta);
1014 // Step 4. Transposition table lookup
1016 // We don't want the score of a partial search to overwrite a previous full search
1017 // TT value, so we use a different position key in case of an excluded move exists.
1018 excludedMove = ss->excludedMove;
1019 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1021 tte = TT.retrieve(posKey);
1022 ttMove = (tte ? tte->move() : MOVE_NONE);
1024 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1025 // This is to avoid problems in the following areas:
1027 // * Repetition draw detection
1028 // * Fifty move rule detection
1029 // * Searching for a mate
1030 // * Printing of full PV line
1032 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1034 // Refresh tte entry to avoid aging
1035 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1037 ss->bestMove = ttMove; // Can be MOVE_NONE
1038 return value_from_tt(tte->value(), ply);
1041 // Step 5. Evaluate the position statically and
1042 // update gain statistics of parent move.
1044 ss->eval = evalMargin = VALUE_NONE;
1047 assert(tte->static_value() != VALUE_NONE);
1049 ss->eval = tte->static_value();
1050 evalMargin = tte->static_value_margin();
1051 refinedValue = refine_eval(tte, ss->eval, ply);
1055 refinedValue = ss->eval = evaluate(pos, evalMargin);
1056 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1059 // Save gain for the parent non-capture move
1060 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1062 // Step 6. Razoring (is omitted in PV nodes)
1064 && depth < RazorDepth
1066 && refinedValue < beta - razor_margin(depth)
1067 && ttMove == MOVE_NONE
1068 && (ss-1)->currentMove != MOVE_NULL
1069 && !value_is_mate(beta)
1070 && !pos.has_pawn_on_7th(pos.side_to_move()))
1072 Value rbeta = beta - razor_margin(depth);
1073 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1075 // Logically we should return (v + razor_margin(depth)), but
1076 // surprisingly this did slightly weaker in tests.
1080 // Step 7. Static null move pruning (is omitted in PV nodes)
1081 // We're betting that the opponent doesn't have a move that will reduce
1082 // the score by more than futility_margin(depth) if we do a null move.
1084 && !ss->skipNullMove
1085 && depth < RazorDepth
1087 && refinedValue >= beta + futility_margin(depth, 0)
1088 && !value_is_mate(beta)
1089 && pos.non_pawn_material(pos.side_to_move()))
1090 return refinedValue - futility_margin(depth, 0);
1092 // Step 8. Null move search with verification search (is omitted in PV nodes)
1094 && !ss->skipNullMove
1097 && refinedValue >= beta
1098 && !value_is_mate(beta)
1099 && pos.non_pawn_material(pos.side_to_move()))
1101 ss->currentMove = MOVE_NULL;
1103 // Null move dynamic reduction based on depth
1104 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1106 // Null move dynamic reduction based on value
1107 if (refinedValue - beta > PawnValueMidgame)
1110 pos.do_null_move(st);
1111 (ss+1)->skipNullMove = true;
1113 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1114 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * ONE_PLY)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1154 // Step 9. Internal iterative deepening
1155 if ( depth >= IIDDepth[PvNode]
1156 && ttMove == MOVE_NONE
1157 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1159 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1161 ss->skipNullMove = true;
1162 search<PvNode>(pos, ss, alpha, beta, d, ply);
1163 ss->skipNullMove = false;
1165 ttMove = ss->bestMove;
1166 tte = TT.retrieve(posKey);
1169 // Expensive mate threat detection (only for PV nodes)
1171 mateThreat = pos.has_mate_threat();
1173 split_point_start: // At split points actual search starts from here
1175 // Initialize a MovePicker object for the current position
1176 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1177 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1178 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1180 ss->bestMove = MOVE_NONE;
1181 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1182 futilityBase = ss->eval + evalMargin;
1183 singularExtensionNode = !SpNode
1184 && depth >= SingularExtensionDepth[PvNode]
1187 && !excludedMove // Do not allow recursive singular extension search
1188 && (tte->type() & VALUE_TYPE_LOWER)
1189 && tte->depth() >= depth - 3 * ONE_PLY;
1192 lock_grab(&(sp->lock));
1193 bestValue = sp->bestValue;
1196 // Step 10. Loop through moves
1197 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1198 while ( bestValue < beta
1199 && (move = mp.get_next_move()) != MOVE_NONE
1200 && !ThreadsMgr.thread_should_stop(threadID))
1204 moveCount = ++sp->moveCount;
1205 lock_release(&(sp->lock));
1208 assert(move_is_ok(move));
1210 if (move == excludedMove)
1213 moveIsCheck = pos.move_is_check(move, ci);
1214 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1216 // Step 11. Decide the new search depth
1217 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1219 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1220 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1221 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1222 // lower then ttValue minus a margin then we extend ttMove.
1223 if ( singularExtensionNode
1224 && move == tte->move()
1227 Value ttValue = value_from_tt(tte->value(), ply);
1229 if (abs(ttValue) < VALUE_KNOWN_WIN)
1231 Value b = ttValue - SingularExtensionMargin;
1232 ss->excludedMove = move;
1233 ss->skipNullMove = true;
1234 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1235 ss->skipNullMove = false;
1236 ss->excludedMove = MOVE_NONE;
1237 ss->bestMove = MOVE_NONE;
1243 newDepth = depth - ONE_PLY + ext;
1245 // Update current move (this must be done after singular extension search)
1246 movesSearched[moveCount++] = ss->currentMove = move;
1248 // Step 12. Futility pruning (is omitted in PV nodes)
1250 && !captureOrPromotion
1254 && !move_is_castle(move))
1256 // Move count based pruning
1257 if ( moveCount >= futility_move_count(depth)
1258 && !(threatMove && connected_threat(pos, move, threatMove))
1259 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1262 lock_grab(&(sp->lock));
1267 // Value based pruning
1268 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1269 // but fixing this made program slightly weaker.
1270 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1271 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1272 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1274 if (futilityValueScaled < beta)
1278 lock_grab(&(sp->lock));
1279 if (futilityValueScaled > sp->bestValue)
1280 sp->bestValue = bestValue = futilityValueScaled;
1282 else if (futilityValueScaled > bestValue)
1283 bestValue = futilityValueScaled;
1289 // Step 13. Make the move
1290 pos.do_move(move, st, ci, moveIsCheck);
1292 // Step extra. pv search (only in PV nodes)
1293 // The first move in list is the expected PV
1294 if (!SpNode && PvNode && moveCount == 1)
1295 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1296 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1299 // Step 14. Reduced depth search
1300 // If the move fails high will be re-searched at full depth.
1301 bool doFullDepthSearch = true;
1303 if ( depth >= 3 * ONE_PLY
1304 && !captureOrPromotion
1306 && !move_is_castle(move)
1307 && !(ss->killers[0] == move || ss->killers[1] == move))
1309 ss->reduction = reduction<PvNode>(depth, moveCount);
1312 alpha = SpNode ? sp->alpha : alpha;
1313 Depth d = newDepth - ss->reduction;
1314 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1315 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1317 doFullDepthSearch = (value > alpha);
1320 // The move failed high, but if reduction is very big we could
1321 // face a false positive, retry with a less aggressive reduction,
1322 // if the move fails high again then go with full depth search.
1323 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1325 assert(newDepth - ONE_PLY >= ONE_PLY);
1327 ss->reduction = ONE_PLY;
1328 alpha = SpNode ? sp->alpha : alpha;
1329 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1330 doFullDepthSearch = (value > alpha);
1332 ss->reduction = DEPTH_ZERO; // Restore original reduction
1335 // Step 15. Full depth search
1336 if (doFullDepthSearch)
1338 alpha = SpNode ? sp->alpha : alpha;
1339 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1340 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1342 // Step extra. pv search (only in PV nodes)
1343 // Search only for possible new PV nodes, if instead value >= beta then
1344 // parent node fails low with value <= alpha and tries another move.
1345 if (PvNode && value > alpha && value < beta)
1346 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1347 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1351 // Step 16. Undo move
1352 pos.undo_move(move);
1354 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1356 // Step 17. Check for new best move
1359 lock_grab(&(sp->lock));
1360 bestValue = sp->bestValue;
1364 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1369 if (SpNode && (!PvNode || value >= beta))
1370 sp->stopRequest = true;
1372 if (PvNode && value < beta) // We want always alpha < beta
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1382 sp->bestValue = bestValue;
1384 sp->parentSstack->bestMove = ss->bestMove;
1388 // Step 18. Check for split
1390 && depth >= MinimumSplitDepth
1391 && ThreadsMgr.active_threads() > 1
1393 && ThreadsMgr.available_thread_exists(threadID)
1395 && !ThreadsMgr.thread_should_stop(threadID)
1397 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1398 threatMove, mateThreat, moveCount, &mp, PvNode);
1403 /* Here we have the lock still grabbed */
1404 sp->slaves[threadID] = 0;
1405 lock_release(&(sp->lock));
1409 // Step 19. Check for mate and stalemate
1410 // All legal moves have been searched and if there are
1411 // no legal moves, it must be mate or stalemate.
1412 // If one move was excluded return fail low score.
1414 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1416 // Step 20. Update tables
1417 // If the search is not aborted, update the transposition table,
1418 // history counters, and killer moves.
1419 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1422 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1423 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1424 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
1426 // Update killers and history only for non capture moves that fails high
1427 if ( bestValue >= beta
1428 && !pos.move_is_capture_or_promotion(move))
1430 update_history(pos, move, depth, movesSearched, moveCount);
1431 update_killers(move, ss);
1434 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1440 // qsearch() is the quiescence search function, which is called by the main
1441 // search function when the remaining depth is zero (or, to be more precise,
1442 // less than ONE_PLY).
1444 template <NodeType PvNode>
1445 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1447 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1448 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1449 assert(PvNode || alpha == beta - 1);
1451 assert(ply > 0 && ply < PLY_MAX);
1452 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1456 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1457 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1459 Value oldAlpha = alpha;
1461 ThreadsMgr.incrementNodeCounter(pos.thread());
1462 ss->bestMove = ss->currentMove = MOVE_NONE;
1464 // Check for an instant draw or maximum ply reached
1465 if (pos.is_draw() || ply >= PLY_MAX - 1)
1468 // Transposition table lookup. At PV nodes, we don't use the TT for
1469 // pruning, but only for move ordering.
1470 tte = TT.retrieve(pos.get_key());
1471 ttMove = (tte ? tte->move() : MOVE_NONE);
1473 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1475 ss->bestMove = ttMove; // Can be MOVE_NONE
1476 return value_from_tt(tte->value(), ply);
1479 isCheck = pos.is_check();
1481 // Evaluate the position statically
1484 bestValue = futilityBase = -VALUE_INFINITE;
1485 ss->eval = evalMargin = VALUE_NONE;
1486 deepChecks = enoughMaterial = false;
1492 assert(tte->static_value() != VALUE_NONE);
1494 evalMargin = tte->static_value_margin();
1495 ss->eval = bestValue = tte->static_value();
1498 ss->eval = bestValue = evaluate(pos, evalMargin);
1500 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1502 // Stand pat. Return immediately if static value is at least beta
1503 if (bestValue >= beta)
1506 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1511 if (PvNode && bestValue > alpha)
1514 // If we are near beta then try to get a cutoff pushing checks a bit further
1515 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1517 // Futility pruning parameters, not needed when in check
1518 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1519 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1522 // Initialize a MovePicker object for the current position, and prepare
1523 // to search the moves. Because the depth is <= 0 here, only captures,
1524 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1525 // and we are near beta) will be generated.
1526 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1529 // Loop through the moves until no moves remain or a beta cutoff occurs
1530 while ( alpha < beta
1531 && (move = mp.get_next_move()) != MOVE_NONE)
1533 assert(move_is_ok(move));
1535 moveIsCheck = pos.move_is_check(move, ci);
1543 && !move_is_promotion(move)
1544 && !pos.move_is_passed_pawn_push(move))
1546 futilityValue = futilityBase
1547 + pos.endgame_value_of_piece_on(move_to(move))
1548 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1550 if (futilityValue < alpha)
1552 if (futilityValue > bestValue)
1553 bestValue = futilityValue;
1558 // Detect non-capture evasions that are candidate to be pruned
1559 evasionPrunable = isCheck
1560 && bestValue > value_mated_in(PLY_MAX)
1561 && !pos.move_is_capture(move)
1562 && !pos.can_castle(pos.side_to_move());
1564 // Don't search moves with negative SEE values
1566 && (!isCheck || evasionPrunable)
1568 && !move_is_promotion(move)
1569 && pos.see_sign(move) < 0)
1572 // Update current move
1573 ss->currentMove = move;
1575 // Make and search the move
1576 pos.do_move(move, st, ci, moveIsCheck);
1577 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1578 pos.undo_move(move);
1580 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1583 if (value > bestValue)
1589 ss->bestMove = move;
1594 // All legal moves have been searched. A special case: If we're in check
1595 // and no legal moves were found, it is checkmate.
1596 if (isCheck && bestValue == -VALUE_INFINITE)
1597 return value_mated_in(ply);
1599 // Update transposition table
1600 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1601 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1602 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1604 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1610 // connected_moves() tests whether two moves are 'connected' in the sense
1611 // that the first move somehow made the second move possible (for instance
1612 // if the moving piece is the same in both moves). The first move is assumed
1613 // to be the move that was made to reach the current position, while the
1614 // second move is assumed to be a move from the current position.
1616 bool connected_moves(const Position& pos, Move m1, Move m2) {
1618 Square f1, t1, f2, t2;
1621 assert(move_is_ok(m1));
1622 assert(move_is_ok(m2));
1624 if (m2 == MOVE_NONE)
1627 // Case 1: The moving piece is the same in both moves
1633 // Case 2: The destination square for m2 was vacated by m1
1639 // Case 3: Moving through the vacated square
1640 if ( piece_is_slider(pos.piece_on(f2))
1641 && bit_is_set(squares_between(f2, t2), f1))
1644 // Case 4: The destination square for m2 is defended by the moving piece in m1
1645 p = pos.piece_on(t1);
1646 if (bit_is_set(pos.attacks_from(p, t1), t2))
1649 // Case 5: Discovered check, checking piece is the piece moved in m1
1650 if ( piece_is_slider(p)
1651 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1652 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1654 // discovered_check_candidates() works also if the Position's side to
1655 // move is the opposite of the checking piece.
1656 Color them = opposite_color(pos.side_to_move());
1657 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1659 if (bit_is_set(dcCandidates, f2))
1666 // value_is_mate() checks if the given value is a mate one eventually
1667 // compensated for the ply.
1669 bool value_is_mate(Value value) {
1671 assert(abs(value) <= VALUE_INFINITE);
1673 return value <= value_mated_in(PLY_MAX)
1674 || value >= value_mate_in(PLY_MAX);
1678 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1679 // "plies to mate from the current ply". Non-mate scores are unchanged.
1680 // The function is called before storing a value to the transposition table.
1682 Value value_to_tt(Value v, int ply) {
1684 if (v >= value_mate_in(PLY_MAX))
1687 if (v <= value_mated_in(PLY_MAX))
1694 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1695 // the transposition table to a mate score corrected for the current ply.
1697 Value value_from_tt(Value v, int ply) {
1699 if (v >= value_mate_in(PLY_MAX))
1702 if (v <= value_mated_in(PLY_MAX))
1709 // extension() decides whether a move should be searched with normal depth,
1710 // or with extended depth. Certain classes of moves (checking moves, in
1711 // particular) are searched with bigger depth than ordinary moves and in
1712 // any case are marked as 'dangerous'. Note that also if a move is not
1713 // extended, as example because the corresponding UCI option is set to zero,
1714 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1715 template <NodeType PvNode>
1716 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1717 bool singleEvasion, bool mateThreat, bool* dangerous) {
1719 assert(m != MOVE_NONE);
1721 Depth result = DEPTH_ZERO;
1722 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1726 if (moveIsCheck && pos.see_sign(m) >= 0)
1727 result += CheckExtension[PvNode];
1730 result += SingleEvasionExtension[PvNode];
1733 result += MateThreatExtension[PvNode];
1736 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1738 Color c = pos.side_to_move();
1739 if (relative_rank(c, move_to(m)) == RANK_7)
1741 result += PawnPushTo7thExtension[PvNode];
1744 if (pos.pawn_is_passed(c, move_to(m)))
1746 result += PassedPawnExtension[PvNode];
1751 if ( captureOrPromotion
1752 && pos.type_of_piece_on(move_to(m)) != PAWN
1753 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1754 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1755 && !move_is_promotion(m)
1758 result += PawnEndgameExtension[PvNode];
1763 && captureOrPromotion
1764 && pos.type_of_piece_on(move_to(m)) != PAWN
1765 && pos.see_sign(m) >= 0)
1767 result += ONE_PLY / 2;
1771 return Min(result, ONE_PLY);
1775 // connected_threat() tests whether it is safe to forward prune a move or if
1776 // is somehow coonected to the threat move returned by null search.
1778 bool connected_threat(const Position& pos, Move m, Move threat) {
1780 assert(move_is_ok(m));
1781 assert(threat && move_is_ok(threat));
1782 assert(!pos.move_is_check(m));
1783 assert(!pos.move_is_capture_or_promotion(m));
1784 assert(!pos.move_is_passed_pawn_push(m));
1786 Square mfrom, mto, tfrom, tto;
1788 mfrom = move_from(m);
1790 tfrom = move_from(threat);
1791 tto = move_to(threat);
1793 // Case 1: Don't prune moves which move the threatened piece
1797 // Case 2: If the threatened piece has value less than or equal to the
1798 // value of the threatening piece, don't prune move which defend it.
1799 if ( pos.move_is_capture(threat)
1800 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1801 || pos.type_of_piece_on(tfrom) == KING)
1802 && pos.move_attacks_square(m, tto))
1805 // Case 3: If the moving piece in the threatened move is a slider, don't
1806 // prune safe moves which block its ray.
1807 if ( piece_is_slider(pos.piece_on(tfrom))
1808 && bit_is_set(squares_between(tfrom, tto), mto)
1809 && pos.see_sign(m) >= 0)
1816 // ok_to_use_TT() returns true if a transposition table score
1817 // can be used at a given point in search.
1819 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1821 Value v = value_from_tt(tte->value(), ply);
1823 return ( tte->depth() >= depth
1824 || v >= Max(value_mate_in(PLY_MAX), beta)
1825 || v < Min(value_mated_in(PLY_MAX), beta))
1827 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1828 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1832 // refine_eval() returns the transposition table score if
1833 // possible otherwise falls back on static position evaluation.
1835 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1839 Value v = value_from_tt(tte->value(), ply);
1841 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1842 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1849 // update_history() registers a good move that produced a beta-cutoff
1850 // in history and marks as failures all the other moves of that ply.
1852 void update_history(const Position& pos, Move move, Depth depth,
1853 Move movesSearched[], int moveCount) {
1856 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1858 for (int i = 0; i < moveCount - 1; i++)
1860 m = movesSearched[i];
1864 if (!pos.move_is_capture_or_promotion(m))
1865 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1870 // update_killers() add a good move that produced a beta-cutoff
1871 // among the killer moves of that ply.
1873 void update_killers(Move m, SearchStack* ss) {
1875 if (m == ss->killers[0])
1878 ss->killers[1] = ss->killers[0];
1883 // update_gains() updates the gains table of a non-capture move given
1884 // the static position evaluation before and after the move.
1886 void update_gains(const Position& pos, Move m, Value before, Value after) {
1889 && before != VALUE_NONE
1890 && after != VALUE_NONE
1891 && pos.captured_piece_type() == PIECE_TYPE_NONE
1892 && !move_is_special(m))
1893 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1897 // current_search_time() returns the number of milliseconds which have passed
1898 // since the beginning of the current search.
1900 int current_search_time() {
1902 return get_system_time() - SearchStartTime;
1906 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1908 std::string value_to_uci(Value v) {
1910 std::stringstream s;
1912 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1913 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1915 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1920 // nps() computes the current nodes/second count.
1924 int t = current_search_time();
1925 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1929 // poll() performs two different functions: It polls for user input, and it
1930 // looks at the time consumed so far and decides if it's time to abort the
1935 static int lastInfoTime;
1936 int t = current_search_time();
1941 // We are line oriented, don't read single chars
1942 std::string command;
1944 if (!std::getline(std::cin, command))
1947 if (command == "quit")
1950 PonderSearch = false;
1954 else if (command == "stop")
1957 PonderSearch = false;
1959 else if (command == "ponderhit")
1963 // Print search information
1967 else if (lastInfoTime > t)
1968 // HACK: Must be a new search where we searched less than
1969 // NodesBetweenPolls nodes during the first second of search.
1972 else if (t - lastInfoTime >= 1000)
1979 if (dbg_show_hit_rate)
1980 dbg_print_hit_rate();
1982 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1983 << " time " << t << endl;
1986 // Should we stop the search?
1990 bool stillAtFirstMove = FirstRootMove
1991 && !AspirationFailLow
1992 && t > TimeMgr.available_time();
1994 bool noMoreTime = t > TimeMgr.maximum_time()
1995 || stillAtFirstMove;
1997 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1998 || (ExactMaxTime && t >= ExactMaxTime)
1999 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2004 // ponderhit() is called when the program is pondering (i.e. thinking while
2005 // it's the opponent's turn to move) in order to let the engine know that
2006 // it correctly predicted the opponent's move.
2010 int t = current_search_time();
2011 PonderSearch = false;
2013 bool stillAtFirstMove = FirstRootMove
2014 && !AspirationFailLow
2015 && t > TimeMgr.available_time();
2017 bool noMoreTime = t > TimeMgr.maximum_time()
2018 || stillAtFirstMove;
2020 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2025 // init_ss_array() does a fast reset of the first entries of a SearchStack
2026 // array and of all the excludedMove and skipNullMove entries.
2028 void init_ss_array(SearchStack* ss, int size) {
2030 for (int i = 0; i < size; i++, ss++)
2032 ss->excludedMove = MOVE_NONE;
2033 ss->skipNullMove = false;
2034 ss->reduction = DEPTH_ZERO;
2038 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2043 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2044 // while the program is pondering. The point is to work around a wrinkle in
2045 // the UCI protocol: When pondering, the engine is not allowed to give a
2046 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2047 // We simply wait here until one of these commands is sent, and return,
2048 // after which the bestmove and pondermove will be printed (in id_loop()).
2050 void wait_for_stop_or_ponderhit() {
2052 std::string command;
2056 if (!std::getline(std::cin, command))
2059 if (command == "quit")
2064 else if (command == "ponderhit" || command == "stop")
2070 // print_pv_info() prints to standard output and eventually to log file information on
2071 // the current PV line. It is called at each iteration or after a new pv is found.
2073 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2075 cout << "info depth " << Iteration
2076 << " score " << value_to_uci(value)
2077 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2078 << " time " << current_search_time()
2079 << " nodes " << ThreadsMgr.nodes_searched()
2083 for (Move* m = pv; *m != MOVE_NONE; m++)
2090 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2091 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2093 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2094 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2099 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2100 // the PV back into the TT. This makes sure the old PV moves are searched
2101 // first, even if the old TT entries have been overwritten.
2103 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2107 Position p(pos, pos.thread());
2108 Value v, m = VALUE_NONE;
2110 for (int i = 0; pv[i] != MOVE_NONE; i++)
2112 tte = TT.retrieve(p.get_key());
2113 if (!tte || tte->move() != pv[i])
2115 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2116 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2118 p.do_move(pv[i], st);
2123 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2124 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2125 // allow to always have a ponder move even when we fail high at root and also a
2126 // long PV to print that is important for position analysis.
2128 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2132 Position p(pos, pos.thread());
2135 assert(bestMove != MOVE_NONE);
2138 p.do_move(pv[ply++], st);
2140 while ( (tte = TT.retrieve(p.get_key())) != NULL
2141 && tte->move() != MOVE_NONE
2142 && move_is_legal(p, tte->move())
2144 && (!p.is_draw() || ply < 2))
2146 pv[ply] = tte->move();
2147 p.do_move(pv[ply++], st);
2149 pv[ply] = MOVE_NONE;
2153 // init_thread() is the function which is called when a new thread is
2154 // launched. It simply calls the idle_loop() function with the supplied
2155 // threadID. There are two versions of this function; one for POSIX
2156 // threads and one for Windows threads.
2158 #if !defined(_MSC_VER)
2160 void* init_thread(void *threadID) {
2162 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2168 DWORD WINAPI init_thread(LPVOID threadID) {
2170 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2177 /// The ThreadsManager class
2179 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2180 // get_beta_counters() are getters/setters for the per thread
2181 // counters used to sort the moves at root.
2183 void ThreadsManager::resetNodeCounters() {
2185 for (int i = 0; i < MAX_THREADS; i++)
2186 threads[i].nodes = 0ULL;
2189 int64_t ThreadsManager::nodes_searched() const {
2191 int64_t result = 0ULL;
2192 for (int i = 0; i < ActiveThreads; i++)
2193 result += threads[i].nodes;
2199 // idle_loop() is where the threads are parked when they have no work to do.
2200 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2201 // object for which the current thread is the master.
2203 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2205 assert(threadID >= 0 && threadID < MAX_THREADS);
2209 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2210 // master should exit as last one.
2211 if (AllThreadsShouldExit)
2214 threads[threadID].state = THREAD_TERMINATED;
2218 // If we are not thinking, wait for a condition to be signaled
2219 // instead of wasting CPU time polling for work.
2220 while ( threadID >= ActiveThreads
2221 || threads[threadID].state == THREAD_INITIALIZING
2222 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2225 assert(threadID != 0);
2227 if (AllThreadsShouldExit)
2232 // Retest condition under lock protection
2233 if (!( threadID >= ActiveThreads
2234 || threads[threadID].state == THREAD_INITIALIZING
2235 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2237 lock_release(&MPLock);
2241 // Put thread to sleep
2242 threads[threadID].state = THREAD_AVAILABLE;
2243 cond_wait(&WaitCond[threadID], &MPLock);
2244 lock_release(&MPLock);
2247 // If this thread has been assigned work, launch a search
2248 if (threads[threadID].state == THREAD_WORKISWAITING)
2250 assert(!AllThreadsShouldExit);
2252 threads[threadID].state = THREAD_SEARCHING;
2254 // Here we call search() with SplitPoint template parameter set to true
2255 SplitPoint* tsp = threads[threadID].splitPoint;
2256 Position pos(*tsp->pos, threadID);
2257 SearchStack* ss = tsp->sstack[threadID] + 1;
2261 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2263 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2265 assert(threads[threadID].state == THREAD_SEARCHING);
2267 threads[threadID].state = THREAD_AVAILABLE;
2270 // If this thread is the master of a split point and all slaves have
2271 // finished their work at this split point, return from the idle loop.
2273 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2275 if (i == ActiveThreads)
2277 // Because sp->slaves[] is reset under lock protection,
2278 // be sure sp->lock has been released before to return.
2279 lock_grab(&(sp->lock));
2280 lock_release(&(sp->lock));
2282 // In helpful master concept a master can help only a sub-tree, and
2283 // because here is all finished is not possible master is booked.
2284 assert(threads[threadID].state == THREAD_AVAILABLE);
2286 threads[threadID].state = THREAD_SEARCHING;
2293 // init_threads() is called during startup. It launches all helper threads,
2294 // and initializes the split point stack and the global locks and condition
2297 void ThreadsManager::init_threads() {
2302 // Initialize global locks
2305 for (i = 0; i < MAX_THREADS; i++)
2306 cond_init(&WaitCond[i]);
2308 // Initialize splitPoints[] locks
2309 for (i = 0; i < MAX_THREADS; i++)
2310 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2311 lock_init(&(threads[i].splitPoints[j].lock));
2313 // Will be set just before program exits to properly end the threads
2314 AllThreadsShouldExit = false;
2316 // Threads will be put all threads to sleep as soon as created
2319 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2320 threads[0].state = THREAD_SEARCHING;
2321 for (i = 1; i < MAX_THREADS; i++)
2322 threads[i].state = THREAD_INITIALIZING;
2324 // Launch the helper threads
2325 for (i = 1; i < MAX_THREADS; i++)
2328 #if !defined(_MSC_VER)
2329 pthread_t pthread[1];
2330 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2332 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2337 cout << "Failed to create thread number " << i << endl;
2338 Application::exit_with_failure();
2341 // Wait until the thread has finished launching and is gone to sleep
2342 while (threads[i].state == THREAD_INITIALIZING) {}
2347 // exit_threads() is called when the program exits. It makes all the
2348 // helper threads exit cleanly.
2350 void ThreadsManager::exit_threads() {
2352 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2354 // Wake up all the threads and waits for termination
2355 for (int i = 1; i < MAX_THREADS; i++)
2357 wake_sleeping_thread(i);
2358 while (threads[i].state != THREAD_TERMINATED) {}
2361 // Now we can safely destroy the locks
2362 for (int i = 0; i < MAX_THREADS; i++)
2363 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2364 lock_destroy(&(threads[i].splitPoints[j].lock));
2366 lock_destroy(&MPLock);
2368 // Now we can safely destroy the wait conditions
2369 for (int i = 0; i < MAX_THREADS; i++)
2370 cond_destroy(&WaitCond[i]);
2374 // thread_should_stop() checks whether the thread should stop its search.
2375 // This can happen if a beta cutoff has occurred in the thread's currently
2376 // active split point, or in some ancestor of the current split point.
2378 bool ThreadsManager::thread_should_stop(int threadID) const {
2380 assert(threadID >= 0 && threadID < ActiveThreads);
2382 SplitPoint* sp = threads[threadID].splitPoint;
2384 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2389 // thread_is_available() checks whether the thread with threadID "slave" is
2390 // available to help the thread with threadID "master" at a split point. An
2391 // obvious requirement is that "slave" must be idle. With more than two
2392 // threads, this is not by itself sufficient: If "slave" is the master of
2393 // some active split point, it is only available as a slave to the other
2394 // threads which are busy searching the split point at the top of "slave"'s
2395 // split point stack (the "helpful master concept" in YBWC terminology).
2397 bool ThreadsManager::thread_is_available(int slave, int master) const {
2399 assert(slave >= 0 && slave < ActiveThreads);
2400 assert(master >= 0 && master < ActiveThreads);
2401 assert(ActiveThreads > 1);
2403 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2406 // Make a local copy to be sure doesn't change under our feet
2407 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2409 // No active split points means that the thread is available as
2410 // a slave for any other thread.
2411 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2414 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2415 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2416 // could have been set to 0 by another thread leading to an out of bound access.
2417 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2424 // available_thread_exists() tries to find an idle thread which is available as
2425 // a slave for the thread with threadID "master".
2427 bool ThreadsManager::available_thread_exists(int master) const {
2429 assert(master >= 0 && master < ActiveThreads);
2430 assert(ActiveThreads > 1);
2432 for (int i = 0; i < ActiveThreads; i++)
2433 if (thread_is_available(i, master))
2440 // split() does the actual work of distributing the work at a node between
2441 // several available threads. If it does not succeed in splitting the
2442 // node (because no idle threads are available, or because we have no unused
2443 // split point objects), the function immediately returns. If splitting is
2444 // possible, a SplitPoint object is initialized with all the data that must be
2445 // copied to the helper threads and we tell our helper threads that they have
2446 // been assigned work. This will cause them to instantly leave their idle loops
2447 // and call sp_search(). When all threads have returned from sp_search() then
2450 template <bool Fake>
2451 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2452 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2453 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2455 assert(ply > 0 && ply < PLY_MAX);
2456 assert(*bestValue >= -VALUE_INFINITE);
2457 assert(*bestValue <= *alpha);
2458 assert(*alpha < beta);
2459 assert(beta <= VALUE_INFINITE);
2460 assert(depth > DEPTH_ZERO);
2461 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2462 assert(ActiveThreads > 1);
2464 int i, master = p.thread();
2465 Thread& masterThread = threads[master];
2469 // If no other thread is available to help us, or if we have too many
2470 // active split points, don't split.
2471 if ( !available_thread_exists(master)
2472 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2474 lock_release(&MPLock);
2478 // Pick the next available split point object from the split point stack
2479 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2481 // Initialize the split point object
2482 splitPoint.parent = masterThread.splitPoint;
2483 splitPoint.stopRequest = false;
2484 splitPoint.ply = ply;
2485 splitPoint.depth = depth;
2486 splitPoint.threatMove = threatMove;
2487 splitPoint.mateThreat = mateThreat;
2488 splitPoint.alpha = *alpha;
2489 splitPoint.beta = beta;
2490 splitPoint.pvNode = pvNode;
2491 splitPoint.bestValue = *bestValue;
2493 splitPoint.moveCount = moveCount;
2494 splitPoint.pos = &p;
2495 splitPoint.parentSstack = ss;
2496 for (i = 0; i < ActiveThreads; i++)
2497 splitPoint.slaves[i] = 0;
2499 masterThread.splitPoint = &splitPoint;
2501 // If we are here it means we are not available
2502 assert(masterThread.state != THREAD_AVAILABLE);
2504 int workersCnt = 1; // At least the master is included
2506 // Allocate available threads setting state to THREAD_BOOKED
2507 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2508 if (thread_is_available(i, master))
2510 threads[i].state = THREAD_BOOKED;
2511 threads[i].splitPoint = &splitPoint;
2512 splitPoint.slaves[i] = 1;
2516 assert(Fake || workersCnt > 1);
2518 // We can release the lock because slave threads are already booked and master is not available
2519 lock_release(&MPLock);
2521 // Tell the threads that they have work to do. This will make them leave
2522 // their idle loop. But before copy search stack tail for each thread.
2523 for (i = 0; i < ActiveThreads; i++)
2524 if (i == master || splitPoint.slaves[i])
2526 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2528 assert(i == master || threads[i].state == THREAD_BOOKED);
2530 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2532 wake_sleeping_thread(i);
2535 // Everything is set up. The master thread enters the idle loop, from
2536 // which it will instantly launch a search, because its state is
2537 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2538 // idle loop, which means that the main thread will return from the idle
2539 // loop when all threads have finished their work at this split point.
2540 idle_loop(master, &splitPoint);
2542 // We have returned from the idle loop, which means that all threads are
2543 // finished. Update alpha and bestValue, and return.
2546 *alpha = splitPoint.alpha;
2547 *bestValue = splitPoint.bestValue;
2548 masterThread.activeSplitPoints--;
2549 masterThread.splitPoint = splitPoint.parent;
2551 lock_release(&MPLock);
2555 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2556 // to start a new search from the root.
2558 void ThreadsManager::wake_sleeping_thread(int threadID) {
2561 cond_signal(&WaitCond[threadID]);
2562 lock_release(&MPLock);
2566 /// The RootMoveList class
2568 // RootMoveList c'tor
2570 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2572 SearchStack ss[PLY_MAX_PLUS_2];
2573 MoveStack mlist[MOVES_MAX];
2575 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2577 // Initialize search stack
2578 init_ss_array(ss, PLY_MAX_PLUS_2);
2579 ss[0].eval = VALUE_NONE;
2582 // Generate all legal moves
2583 MoveStack* last = generate_moves(pos, mlist);
2585 // Add each move to the moves[] array
2586 for (MoveStack* cur = mlist; cur != last; cur++)
2588 bool includeMove = includeAllMoves;
2590 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2591 includeMove = (searchMoves[k] == cur->move);
2596 // Find a quick score for the move
2597 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2598 moves[count].pv[1] = MOVE_NONE;
2599 pos.do_move(cur->move, st);
2600 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2601 pos.undo_move(cur->move);
2607 // Score root moves using the standard way used in main search, the moves
2608 // are scored according to the order in which are returned by MovePicker.
2610 void RootMoveList::score_moves(const Position& pos)
2614 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2616 while ((move = mp.get_next_move()) != MOVE_NONE)
2617 for (int i = 0; i < count; i++)
2618 if (moves[i].move == move)
2620 moves[i].mp_score = score--;
2625 // RootMoveList simple methods definitions
2627 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2631 for (j = 0; pv[j] != MOVE_NONE; j++)
2632 moves[moveNum].pv[j] = pv[j];
2634 moves[moveNum].pv[j] = MOVE_NONE;
2638 // RootMoveList::sort() sorts the root move list at the beginning of a new
2641 void RootMoveList::sort() {
2643 sort_multipv(count - 1); // Sort all items
2647 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2648 // list by their scores and depths. It is used to order the different PVs
2649 // correctly in MultiPV mode.
2651 void RootMoveList::sort_multipv(int n) {
2655 for (i = 1; i <= n; i++)
2657 RootMove rm = moves[i];
2658 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2659 moves[j] = moves[j - 1];