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, 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->evalMargin = VALUE_NONE;
723 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
725 // Step 6. Razoring (omitted at root)
726 // Step 7. Static null move pruning (omitted at root)
727 // Step 8. Null move search with verification search (omitted at root)
728 // Step 9. Internal iterative deepening (omitted at root)
730 // Step extra. Fail low loop
731 // We start with small aspiration window and in case of fail low, we research
732 // with bigger window until we are not failing low anymore.
735 // Sort the moves before to (re)search
736 rml.score_moves(pos);
739 // Step 10. Loop through all moves in the root move list
740 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
742 // This is used by time management
743 FirstRootMove = (i == 0);
745 // Save the current node count before the move is searched
746 nodes = ThreadsMgr.nodes_searched();
748 // Pick the next root move, and print the move and the move number to
749 // the standard output.
750 move = ss->currentMove = rml.move(i);
752 if (current_search_time() >= 1000)
753 cout << "info currmove " << move
754 << " currmovenumber " << i + 1 << endl;
756 moveIsCheck = pos.move_is_check(move);
757 captureOrPromotion = pos.move_is_capture_or_promotion(move);
759 // Step 11. Decide the new search depth
760 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
761 newDepth = depth + ext;
763 // Step 12. Futility pruning (omitted at root)
765 // Step extra. Fail high loop
766 // If move fails high, we research with bigger window until we are not failing
768 value = - VALUE_INFINITE;
772 // Step 13. Make the move
773 pos.do_move(move, st, ci, moveIsCheck);
775 // Step extra. pv search
776 // We do pv search for first moves (i < MultiPV)
777 // and for fail high research (value > alpha)
778 if (i < MultiPV || value > alpha)
780 // Aspiration window is disabled in multi-pv case
782 alpha = -VALUE_INFINITE;
784 // Full depth PV search, done on first move or after a fail high
785 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
789 // Step 14. Reduced search
790 // if the move fails high will be re-searched at full depth
791 bool doFullDepthSearch = true;
793 if ( depth >= 3 * ONE_PLY
795 && !captureOrPromotion
796 && !move_is_castle(move))
798 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
801 assert(newDepth-ss->reduction >= ONE_PLY);
803 // Reduced depth non-pv search using alpha as upperbound
804 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
805 doFullDepthSearch = (value > alpha);
808 // The move failed high, but if reduction is very big we could
809 // face a false positive, retry with a less aggressive reduction,
810 // if the move fails high again then go with full depth search.
811 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
813 assert(newDepth - ONE_PLY >= ONE_PLY);
815 ss->reduction = ONE_PLY;
816 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
817 doFullDepthSearch = (value > alpha);
819 ss->reduction = DEPTH_ZERO; // Restore original reduction
822 // Step 15. Full depth search
823 if (doFullDepthSearch)
825 // Full depth non-pv search using alpha as upperbound
826 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
828 // If we are above alpha then research at same depth but as PV
829 // to get a correct score or eventually a fail high above beta.
831 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
835 // Step 16. Undo move
838 // Can we exit fail high loop ?
839 if (AbortSearch || value < beta)
842 // We are failing high and going to do a research. It's important to update
843 // the score before research in case we run out of time while researching.
844 rml.set_move_score(i, value);
846 extract_pv_from_tt(pos, move, pv);
847 rml.set_move_pv(i, pv);
849 // Print information to the standard output
850 print_pv_info(pos, pv, alpha, beta, value);
852 // Prepare for a research after a fail high, each time with a wider window
853 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
856 } // End of fail high loop
858 // Finished searching the move. If AbortSearch is true, the search
859 // was aborted because the user interrupted the search or because we
860 // ran out of time. In this case, the return value of the search cannot
861 // be trusted, and we break out of the loop without updating the best
866 // Remember searched nodes counts for this move
867 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
869 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
870 assert(value < beta);
872 // Step 17. Check for new best move
873 if (value <= alpha && i >= MultiPV)
874 rml.set_move_score(i, -VALUE_INFINITE);
877 // PV move or new best move!
880 rml.set_move_score(i, value);
882 extract_pv_from_tt(pos, move, pv);
883 rml.set_move_pv(i, pv);
887 // We record how often the best move has been changed in each
888 // iteration. This information is used for time managment: When
889 // the best move changes frequently, we allocate some more time.
891 BestMoveChangesByIteration[Iteration]++;
893 // Print information to the standard output
894 print_pv_info(pos, pv, alpha, beta, value);
896 // Raise alpha to setup proper non-pv search upper bound
903 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
905 cout << "info multipv " << j + 1
906 << " score " << value_to_uci(rml.move_score(j))
907 << " depth " << (j <= i ? Iteration : Iteration - 1)
908 << " time " << current_search_time()
909 << " nodes " << ThreadsMgr.nodes_searched()
913 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
914 cout << rml.move_pv(j, k) << " ";
918 alpha = rml.move_score(Min(i, MultiPV - 1));
920 } // PV move or new best move
922 assert(alpha >= *alphaPtr);
924 AspirationFailLow = (alpha == *alphaPtr);
926 if (AspirationFailLow && StopOnPonderhit)
927 StopOnPonderhit = false;
930 // Can we exit fail low loop ?
931 if (AbortSearch || !AspirationFailLow)
934 // Prepare for a research after a fail low, each time with a wider window
935 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
940 // Sort the moves before to return
947 // search<>() is the main search function for both PV and non-PV nodes and for
948 // normal and SplitPoint nodes. When called just after a split point the search
949 // is simpler because we have already probed the hash table, done a null move
950 // search, and searched the first move before splitting, we don't have to repeat
951 // all this work again. We also don't need to store anything to the hash table
952 // here: This is taken care of after we return from the split point.
954 template <NodeType PvNode, bool SpNode>
955 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
957 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
958 assert(beta > alpha && beta <= VALUE_INFINITE);
959 assert(PvNode || alpha == beta - 1);
960 assert(ply > 0 && ply < PLY_MAX);
961 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
963 Move movesSearched[MOVES_MAX];
967 Move ttMove, move, excludedMove, threatMove;
969 Value bestValue, value, oldAlpha;
970 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
971 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
972 bool mateThreat = false;
974 int threadID = pos.thread();
975 SplitPoint* sp = NULL;
976 refinedValue = bestValue = value = -VALUE_INFINITE;
978 isCheck = pos.is_check();
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 = ss->evalMargin = VALUE_NONE;
1047 assert(tte->static_value() != VALUE_NONE);
1049 ss->eval = tte->static_value();
1050 ss->evalMargin = tte->static_value_margin();
1051 refinedValue = refine_eval(tte, ss->eval, ply);
1055 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1056 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->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(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1178 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1180 ss->bestMove = MOVE_NONE;
1181 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1182 futilityBase = ss->eval + ss->evalMargin;
1183 singularExtensionNode = !SpNode
1184 && depth >= SingularExtensionDepth[PvNode]
1187 && !excludedMove // Do not allow recursive singular extension search
1188 && (tte->type() & VALUE_TYPE_LOWER)
1189 && tte->depth() >= depth - 3 * ONE_PLY;
1192 lock_grab(&(sp->lock));
1193 bestValue = sp->bestValue;
1196 // Step 10. Loop through moves
1197 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1198 while ( bestValue < beta
1199 && (move = mp.get_next_move()) != MOVE_NONE
1200 && !ThreadsMgr.thread_should_stop(threadID))
1204 moveCount = ++sp->moveCount;
1205 lock_release(&(sp->lock));
1208 assert(move_is_ok(move));
1210 if (move == excludedMove)
1213 moveIsCheck = pos.move_is_check(move, ci);
1214 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1216 // Step 11. Decide the new search depth
1217 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1219 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1220 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1221 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1222 // lower then ttValue minus a margin then we extend ttMove.
1223 if ( singularExtensionNode
1224 && move == tte->move()
1227 Value ttValue = value_from_tt(tte->value(), ply);
1229 if (abs(ttValue) < VALUE_KNOWN_WIN)
1231 Value b = ttValue - SingularExtensionMargin;
1232 ss->excludedMove = move;
1233 ss->skipNullMove = true;
1234 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1235 ss->skipNullMove = false;
1236 ss->excludedMove = MOVE_NONE;
1237 ss->bestMove = MOVE_NONE;
1243 newDepth = depth - ONE_PLY + ext;
1245 // Update current move (this must be done after singular extension search)
1246 movesSearched[moveCount] = ss->currentMove = move;
1251 // Step 12. Futility pruning (is omitted in PV nodes)
1253 && !captureOrPromotion
1257 && !move_is_castle(move))
1259 // Move count based pruning
1260 if ( moveCount >= futility_move_count(depth)
1261 && !(threatMove && connected_threat(pos, move, threatMove))
1262 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1265 lock_grab(&(sp->lock));
1270 // Value based pruning
1271 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1272 // but fixing this made program slightly weaker.
1273 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1274 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1275 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1277 if (futilityValueScaled < beta)
1281 lock_grab(&(sp->lock));
1282 if (futilityValueScaled > sp->bestValue)
1283 sp->bestValue = bestValue = futilityValueScaled;
1285 else if (futilityValueScaled > bestValue)
1286 bestValue = futilityValueScaled;
1292 // Step 13. Make the move
1293 pos.do_move(move, st, ci, moveIsCheck);
1295 // Step extra. pv search (only in PV nodes)
1296 // The first move in list is the expected PV
1297 if (!SpNode && PvNode && moveCount == 1)
1298 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1299 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1302 // Step 14. Reduced depth search
1303 // If the move fails high will be re-searched at full depth.
1304 bool doFullDepthSearch = true;
1306 if ( depth >= 3 * ONE_PLY
1307 && !captureOrPromotion
1309 && !move_is_castle(move)
1310 && !(ss->killers[0] == move || ss->killers[1] == move))
1312 ss->reduction = reduction<PvNode>(depth, moveCount);
1315 alpha = SpNode ? sp->alpha : alpha;
1316 Depth d = newDepth - ss->reduction;
1317 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1318 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1320 doFullDepthSearch = (value > alpha);
1323 // The move failed high, but if reduction is very big we could
1324 // face a false positive, retry with a less aggressive reduction,
1325 // if the move fails high again then go with full depth search.
1326 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1328 assert(newDepth - ONE_PLY >= ONE_PLY);
1330 ss->reduction = ONE_PLY;
1331 alpha = SpNode ? sp->alpha : alpha;
1332 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1333 doFullDepthSearch = (value > alpha);
1335 ss->reduction = DEPTH_ZERO; // Restore original reduction
1338 // Step 15. Full depth search
1339 if (doFullDepthSearch)
1341 alpha = SpNode ? sp->alpha : alpha;
1342 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1343 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1345 // Step extra. pv search (only in PV nodes)
1346 // Search only for possible new PV nodes, if instead value >= beta then
1347 // parent node fails low with value <= alpha and tries another move.
1348 if (PvNode && value > alpha && value < beta)
1349 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1350 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1354 // Step 16. Undo move
1355 pos.undo_move(move);
1357 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1359 // Step 17. Check for new best move
1362 lock_grab(&(sp->lock));
1363 bestValue = sp->bestValue;
1367 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1372 sp->bestValue = value;
1376 if (SpNode && (!PvNode || value >= beta))
1377 sp->stopRequest = true;
1379 if (PvNode && value < beta) // We want always alpha < beta
1386 if (value == value_mate_in(ply + 1))
1387 ss->mateKiller = move;
1389 ss->bestMove = move;
1392 sp->parentSstack->bestMove = move;
1396 // Step 18. Check for split
1398 && depth >= MinimumSplitDepth
1399 && ThreadsMgr.active_threads() > 1
1401 && ThreadsMgr.available_thread_exists(threadID)
1403 && !ThreadsMgr.thread_should_stop(threadID)
1405 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1406 threatMove, mateThreat, moveCount, &mp, PvNode);
1411 /* Here we have the lock still grabbed */
1412 sp->slaves[threadID] = 0;
1413 lock_release(&(sp->lock));
1417 // Step 19. Check for mate and stalemate
1418 // All legal moves have been searched and if there are
1419 // no legal moves, it must be mate or stalemate.
1420 // If one move was excluded return fail low score.
1422 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1424 // Step 20. Update tables
1425 // If the search is not aborted, update the transposition table,
1426 // history counters, and killer moves.
1427 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1430 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1431 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1432 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1434 // Update killers and history only for non capture moves that fails high
1435 if ( bestValue >= beta
1436 && !pos.move_is_capture_or_promotion(move))
1438 update_history(pos, move, depth, movesSearched, moveCount);
1439 update_killers(move, ss);
1442 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1448 // qsearch() is the quiescence search function, which is called by the main
1449 // search function when the remaining depth is zero (or, to be more precise,
1450 // less than ONE_PLY).
1452 template <NodeType PvNode>
1453 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1455 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1456 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1457 assert(PvNode || alpha == beta - 1);
1459 assert(ply > 0 && ply < PLY_MAX);
1460 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1464 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1465 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1467 Value oldAlpha = alpha;
1469 ThreadsMgr.incrementNodeCounter(pos.thread());
1470 ss->bestMove = ss->currentMove = MOVE_NONE;
1472 // Check for an instant draw or maximum ply reached
1473 if (pos.is_draw() || ply >= PLY_MAX - 1)
1476 // Transposition table lookup. At PV nodes, we don't use the TT for
1477 // pruning, but only for move ordering.
1478 tte = TT.retrieve(pos.get_key());
1479 ttMove = (tte ? tte->move() : MOVE_NONE);
1481 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1483 ss->bestMove = ttMove; // Can be MOVE_NONE
1484 return value_from_tt(tte->value(), ply);
1487 isCheck = pos.is_check();
1489 // Evaluate the position statically
1492 bestValue = futilityBase = -VALUE_INFINITE;
1493 ss->eval = evalMargin = VALUE_NONE;
1494 deepChecks = enoughMaterial = false;
1500 assert(tte->static_value() != VALUE_NONE);
1502 evalMargin = tte->static_value_margin();
1503 ss->eval = bestValue = tte->static_value();
1506 ss->eval = bestValue = evaluate(pos, evalMargin);
1508 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1510 // Stand pat. Return immediately if static value is at least beta
1511 if (bestValue >= beta)
1514 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1519 if (PvNode && bestValue > alpha)
1522 // If we are near beta then try to get a cutoff pushing checks a bit further
1523 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1525 // Futility pruning parameters, not needed when in check
1526 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1527 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1530 // Initialize a MovePicker object for the current position, and prepare
1531 // to search the moves. Because the depth is <= 0 here, only captures,
1532 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1533 // and we are near beta) will be generated.
1534 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1537 // Loop through the moves until no moves remain or a beta cutoff occurs
1538 while ( alpha < beta
1539 && (move = mp.get_next_move()) != MOVE_NONE)
1541 assert(move_is_ok(move));
1543 moveIsCheck = pos.move_is_check(move, ci);
1551 && !move_is_promotion(move)
1552 && !pos.move_is_passed_pawn_push(move))
1554 futilityValue = futilityBase
1555 + pos.endgame_value_of_piece_on(move_to(move))
1556 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1558 if (futilityValue < alpha)
1560 if (futilityValue > bestValue)
1561 bestValue = futilityValue;
1566 // Detect non-capture evasions that are candidate to be pruned
1567 evasionPrunable = isCheck
1568 && bestValue > value_mated_in(PLY_MAX)
1569 && !pos.move_is_capture(move)
1570 && !pos.can_castle(pos.side_to_move());
1572 // Don't search moves with negative SEE values
1574 && (!isCheck || evasionPrunable)
1576 && !move_is_promotion(move)
1577 && pos.see_sign(move) < 0)
1580 // Update current move
1581 ss->currentMove = move;
1583 // Make and search the move
1584 pos.do_move(move, st, ci, moveIsCheck);
1585 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1586 pos.undo_move(move);
1588 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1591 if (value > bestValue)
1597 ss->bestMove = move;
1602 // All legal moves have been searched. A special case: If we're in check
1603 // and no legal moves were found, it is checkmate.
1604 if (isCheck && bestValue == -VALUE_INFINITE)
1605 return value_mated_in(ply);
1607 // Update transposition table
1608 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1609 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1610 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1612 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1618 // connected_moves() tests whether two moves are 'connected' in the sense
1619 // that the first move somehow made the second move possible (for instance
1620 // if the moving piece is the same in both moves). The first move is assumed
1621 // to be the move that was made to reach the current position, while the
1622 // second move is assumed to be a move from the current position.
1624 bool connected_moves(const Position& pos, Move m1, Move m2) {
1626 Square f1, t1, f2, t2;
1629 assert(move_is_ok(m1));
1630 assert(move_is_ok(m2));
1632 if (m2 == MOVE_NONE)
1635 // Case 1: The moving piece is the same in both moves
1641 // Case 2: The destination square for m2 was vacated by m1
1647 // Case 3: Moving through the vacated square
1648 if ( piece_is_slider(pos.piece_on(f2))
1649 && bit_is_set(squares_between(f2, t2), f1))
1652 // Case 4: The destination square for m2 is defended by the moving piece in m1
1653 p = pos.piece_on(t1);
1654 if (bit_is_set(pos.attacks_from(p, t1), t2))
1657 // Case 5: Discovered check, checking piece is the piece moved in m1
1658 if ( piece_is_slider(p)
1659 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1660 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1662 // discovered_check_candidates() works also if the Position's side to
1663 // move is the opposite of the checking piece.
1664 Color them = opposite_color(pos.side_to_move());
1665 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1667 if (bit_is_set(dcCandidates, f2))
1674 // value_is_mate() checks if the given value is a mate one eventually
1675 // compensated for the ply.
1677 bool value_is_mate(Value value) {
1679 assert(abs(value) <= VALUE_INFINITE);
1681 return value <= value_mated_in(PLY_MAX)
1682 || value >= value_mate_in(PLY_MAX);
1686 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1687 // "plies to mate from the current ply". Non-mate scores are unchanged.
1688 // The function is called before storing a value to the transposition table.
1690 Value value_to_tt(Value v, int ply) {
1692 if (v >= value_mate_in(PLY_MAX))
1695 if (v <= value_mated_in(PLY_MAX))
1702 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1703 // the transposition table to a mate score corrected for the current ply.
1705 Value value_from_tt(Value v, int ply) {
1707 if (v >= value_mate_in(PLY_MAX))
1710 if (v <= value_mated_in(PLY_MAX))
1717 // extension() decides whether a move should be searched with normal depth,
1718 // or with extended depth. Certain classes of moves (checking moves, in
1719 // particular) are searched with bigger depth than ordinary moves and in
1720 // any case are marked as 'dangerous'. Note that also if a move is not
1721 // extended, as example because the corresponding UCI option is set to zero,
1722 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1723 template <NodeType PvNode>
1724 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1725 bool singleEvasion, bool mateThreat, bool* dangerous) {
1727 assert(m != MOVE_NONE);
1729 Depth result = DEPTH_ZERO;
1730 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1734 if (moveIsCheck && pos.see_sign(m) >= 0)
1735 result += CheckExtension[PvNode];
1738 result += SingleEvasionExtension[PvNode];
1741 result += MateThreatExtension[PvNode];
1744 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1746 Color c = pos.side_to_move();
1747 if (relative_rank(c, move_to(m)) == RANK_7)
1749 result += PawnPushTo7thExtension[PvNode];
1752 if (pos.pawn_is_passed(c, move_to(m)))
1754 result += PassedPawnExtension[PvNode];
1759 if ( captureOrPromotion
1760 && pos.type_of_piece_on(move_to(m)) != PAWN
1761 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1762 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1763 && !move_is_promotion(m)
1766 result += PawnEndgameExtension[PvNode];
1771 && captureOrPromotion
1772 && pos.type_of_piece_on(move_to(m)) != PAWN
1773 && pos.see_sign(m) >= 0)
1775 result += ONE_PLY / 2;
1779 return Min(result, ONE_PLY);
1783 // connected_threat() tests whether it is safe to forward prune a move or if
1784 // is somehow coonected to the threat move returned by null search.
1786 bool connected_threat(const Position& pos, Move m, Move threat) {
1788 assert(move_is_ok(m));
1789 assert(threat && move_is_ok(threat));
1790 assert(!pos.move_is_check(m));
1791 assert(!pos.move_is_capture_or_promotion(m));
1792 assert(!pos.move_is_passed_pawn_push(m));
1794 Square mfrom, mto, tfrom, tto;
1796 mfrom = move_from(m);
1798 tfrom = move_from(threat);
1799 tto = move_to(threat);
1801 // Case 1: Don't prune moves which move the threatened piece
1805 // Case 2: If the threatened piece has value less than or equal to the
1806 // value of the threatening piece, don't prune move which defend it.
1807 if ( pos.move_is_capture(threat)
1808 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1809 || pos.type_of_piece_on(tfrom) == KING)
1810 && pos.move_attacks_square(m, tto))
1813 // Case 3: If the moving piece in the threatened move is a slider, don't
1814 // prune safe moves which block its ray.
1815 if ( piece_is_slider(pos.piece_on(tfrom))
1816 && bit_is_set(squares_between(tfrom, tto), mto)
1817 && pos.see_sign(m) >= 0)
1824 // ok_to_use_TT() returns true if a transposition table score
1825 // can be used at a given point in search.
1827 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1829 Value v = value_from_tt(tte->value(), ply);
1831 return ( tte->depth() >= depth
1832 || v >= Max(value_mate_in(PLY_MAX), beta)
1833 || v < Min(value_mated_in(PLY_MAX), beta))
1835 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1836 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1840 // refine_eval() returns the transposition table score if
1841 // possible otherwise falls back on static position evaluation.
1843 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1847 Value v = value_from_tt(tte->value(), ply);
1849 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1850 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1857 // update_history() registers a good move that produced a beta-cutoff
1858 // in history and marks as failures all the other moves of that ply.
1860 void update_history(const Position& pos, Move move, Depth depth,
1861 Move movesSearched[], int moveCount) {
1864 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1866 for (int i = 0; i < moveCount - 1; i++)
1868 m = movesSearched[i];
1872 if (!pos.move_is_capture_or_promotion(m))
1873 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1878 // update_killers() add a good move that produced a beta-cutoff
1879 // among the killer moves of that ply.
1881 void update_killers(Move m, SearchStack* ss) {
1883 if (m == ss->killers[0])
1886 ss->killers[1] = ss->killers[0];
1891 // update_gains() updates the gains table of a non-capture move given
1892 // the static position evaluation before and after the move.
1894 void update_gains(const Position& pos, Move m, Value before, Value after) {
1897 && before != VALUE_NONE
1898 && after != VALUE_NONE
1899 && pos.captured_piece_type() == PIECE_TYPE_NONE
1900 && !move_is_special(m))
1901 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1905 // current_search_time() returns the number of milliseconds which have passed
1906 // since the beginning of the current search.
1908 int current_search_time() {
1910 return get_system_time() - SearchStartTime;
1914 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1916 std::string value_to_uci(Value v) {
1918 std::stringstream s;
1920 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1921 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1923 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1928 // nps() computes the current nodes/second count.
1932 int t = current_search_time();
1933 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1937 // poll() performs two different functions: It polls for user input, and it
1938 // looks at the time consumed so far and decides if it's time to abort the
1943 static int lastInfoTime;
1944 int t = current_search_time();
1949 // We are line oriented, don't read single chars
1950 std::string command;
1952 if (!std::getline(std::cin, command))
1955 if (command == "quit")
1958 PonderSearch = false;
1962 else if (command == "stop")
1965 PonderSearch = false;
1967 else if (command == "ponderhit")
1971 // Print search information
1975 else if (lastInfoTime > t)
1976 // HACK: Must be a new search where we searched less than
1977 // NodesBetweenPolls nodes during the first second of search.
1980 else if (t - lastInfoTime >= 1000)
1987 if (dbg_show_hit_rate)
1988 dbg_print_hit_rate();
1990 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1991 << " time " << t << endl;
1994 // Should we stop the search?
1998 bool stillAtFirstMove = FirstRootMove
1999 && !AspirationFailLow
2000 && t > TimeMgr.available_time();
2002 bool noMoreTime = t > TimeMgr.maximum_time()
2003 || stillAtFirstMove;
2005 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2006 || (ExactMaxTime && t >= ExactMaxTime)
2007 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2012 // ponderhit() is called when the program is pondering (i.e. thinking while
2013 // it's the opponent's turn to move) in order to let the engine know that
2014 // it correctly predicted the opponent's move.
2018 int t = current_search_time();
2019 PonderSearch = false;
2021 bool stillAtFirstMove = FirstRootMove
2022 && !AspirationFailLow
2023 && t > TimeMgr.available_time();
2025 bool noMoreTime = t > TimeMgr.maximum_time()
2026 || stillAtFirstMove;
2028 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2033 // init_ss_array() does a fast reset of the first entries of a SearchStack
2034 // array and of all the excludedMove and skipNullMove entries.
2036 void init_ss_array(SearchStack* ss, int size) {
2038 for (int i = 0; i < size; i++, ss++)
2040 ss->excludedMove = MOVE_NONE;
2041 ss->skipNullMove = false;
2042 ss->reduction = DEPTH_ZERO;
2046 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2051 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2052 // while the program is pondering. The point is to work around a wrinkle in
2053 // the UCI protocol: When pondering, the engine is not allowed to give a
2054 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2055 // We simply wait here until one of these commands is sent, and return,
2056 // after which the bestmove and pondermove will be printed (in id_loop()).
2058 void wait_for_stop_or_ponderhit() {
2060 std::string command;
2064 if (!std::getline(std::cin, command))
2067 if (command == "quit")
2072 else if (command == "ponderhit" || command == "stop")
2078 // print_pv_info() prints to standard output and eventually to log file information on
2079 // the current PV line. It is called at each iteration or after a new pv is found.
2081 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2083 cout << "info depth " << Iteration
2084 << " score " << value_to_uci(value)
2085 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2086 << " time " << current_search_time()
2087 << " nodes " << ThreadsMgr.nodes_searched()
2091 for (Move* m = pv; *m != MOVE_NONE; m++)
2098 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2099 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2101 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2102 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2107 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2108 // the PV back into the TT. This makes sure the old PV moves are searched
2109 // first, even if the old TT entries have been overwritten.
2111 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2115 Position p(pos, pos.thread());
2116 Value v, m = VALUE_NONE;
2118 for (int i = 0; pv[i] != MOVE_NONE; i++)
2120 tte = TT.retrieve(p.get_key());
2121 if (!tte || tte->move() != pv[i])
2123 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2124 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2126 p.do_move(pv[i], st);
2131 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2132 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2133 // allow to always have a ponder move even when we fail high at root and also a
2134 // long PV to print that is important for position analysis.
2136 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2140 Position p(pos, pos.thread());
2143 assert(bestMove != MOVE_NONE);
2146 p.do_move(pv[ply++], st);
2148 while ( (tte = TT.retrieve(p.get_key())) != NULL
2149 && tte->move() != MOVE_NONE
2150 && move_is_legal(p, tte->move())
2152 && (!p.is_draw() || ply < 2))
2154 pv[ply] = tte->move();
2155 p.do_move(pv[ply++], st);
2157 pv[ply] = MOVE_NONE;
2161 // init_thread() is the function which is called when a new thread is
2162 // launched. It simply calls the idle_loop() function with the supplied
2163 // threadID. There are two versions of this function; one for POSIX
2164 // threads and one for Windows threads.
2166 #if !defined(_MSC_VER)
2168 void* init_thread(void *threadID) {
2170 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2176 DWORD WINAPI init_thread(LPVOID threadID) {
2178 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2185 /// The ThreadsManager class
2187 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2188 // get_beta_counters() are getters/setters for the per thread
2189 // counters used to sort the moves at root.
2191 void ThreadsManager::resetNodeCounters() {
2193 for (int i = 0; i < MAX_THREADS; i++)
2194 threads[i].nodes = 0ULL;
2197 int64_t ThreadsManager::nodes_searched() const {
2199 int64_t result = 0ULL;
2200 for (int i = 0; i < ActiveThreads; i++)
2201 result += threads[i].nodes;
2207 // idle_loop() is where the threads are parked when they have no work to do.
2208 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2209 // object for which the current thread is the master.
2211 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2213 assert(threadID >= 0 && threadID < MAX_THREADS);
2216 bool allFinished = false;
2220 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2221 // master should exit as last one.
2222 if (AllThreadsShouldExit)
2225 threads[threadID].state = THREAD_TERMINATED;
2229 // If we are not thinking, wait for a condition to be signaled
2230 // instead of wasting CPU time polling for work.
2231 while ( threadID >= ActiveThreads
2232 || threads[threadID].state == THREAD_INITIALIZING
2233 || threads[threadID].state == THREAD_AVAILABLE)
2237 // Test with lock held to avoid races with wake_sleeping_thread()
2238 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2239 allFinished = (i == ActiveThreads);
2241 // Retest sleep conditions under lock protection
2242 if ( AllThreadsShouldExit
2244 || !( threadID >= ActiveThreads
2245 || threads[threadID].state == THREAD_INITIALIZING
2246 || threads[threadID].state == THREAD_AVAILABLE))
2248 lock_release(&MPLock);
2252 // Put thread to sleep
2253 threads[threadID].state = THREAD_AVAILABLE;
2254 cond_wait(&WaitCond[threadID], &MPLock);
2255 lock_release(&MPLock);
2258 // If this thread has been assigned work, launch a search
2259 if (threads[threadID].state == THREAD_WORKISWAITING)
2261 assert(!AllThreadsShouldExit);
2263 threads[threadID].state = THREAD_SEARCHING;
2265 // Here we call search() with SplitPoint template parameter set to true
2266 SplitPoint* tsp = threads[threadID].splitPoint;
2267 Position pos(*tsp->pos, threadID);
2268 SearchStack* ss = tsp->sstack[threadID] + 1;
2272 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2274 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2276 assert(threads[threadID].state == THREAD_SEARCHING);
2278 threads[threadID].state = THREAD_AVAILABLE;
2280 // Wake up master thread so to allow it to return from the idle loop in
2281 // case we are the last slave of the split point.
2282 if (threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2283 wake_sleeping_thread(tsp->master);
2286 // If this thread is the master of a split point and all slaves have
2287 // finished their work at this split point, return from the idle loop.
2288 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2289 allFinished = (i == ActiveThreads);
2293 // Because sp->slaves[] is reset under lock protection,
2294 // be sure sp->lock has been released before to return.
2295 lock_grab(&(sp->lock));
2296 lock_release(&(sp->lock));
2298 // In helpful master concept a master can help only a sub-tree, and
2299 // because here is all finished is not possible master is booked.
2300 assert(threads[threadID].state == THREAD_AVAILABLE);
2302 threads[threadID].state = THREAD_SEARCHING;
2309 // init_threads() is called during startup. It launches all helper threads,
2310 // and initializes the split point stack and the global locks and condition
2313 void ThreadsManager::init_threads() {
2318 // Initialize global locks
2321 for (i = 0; i < MAX_THREADS; i++)
2322 cond_init(&WaitCond[i]);
2324 // Initialize splitPoints[] locks
2325 for (i = 0; i < MAX_THREADS; i++)
2326 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2327 lock_init(&(threads[i].splitPoints[j].lock));
2329 // Will be set just before program exits to properly end the threads
2330 AllThreadsShouldExit = false;
2332 // Threads will be put all threads to sleep as soon as created
2335 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2336 threads[0].state = THREAD_SEARCHING;
2337 for (i = 1; i < MAX_THREADS; i++)
2338 threads[i].state = THREAD_INITIALIZING;
2340 // Launch the helper threads
2341 for (i = 1; i < MAX_THREADS; i++)
2344 #if !defined(_MSC_VER)
2345 pthread_t pthread[1];
2346 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2348 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2353 cout << "Failed to create thread number " << i << endl;
2354 Application::exit_with_failure();
2357 // Wait until the thread has finished launching and is gone to sleep
2358 while (threads[i].state == THREAD_INITIALIZING) {}
2363 // exit_threads() is called when the program exits. It makes all the
2364 // helper threads exit cleanly.
2366 void ThreadsManager::exit_threads() {
2368 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2370 // Wake up all the threads and waits for termination
2371 for (int i = 1; i < MAX_THREADS; i++)
2373 wake_sleeping_thread(i);
2374 while (threads[i].state != THREAD_TERMINATED) {}
2377 // Now we can safely destroy the locks
2378 for (int i = 0; i < MAX_THREADS; i++)
2379 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2380 lock_destroy(&(threads[i].splitPoints[j].lock));
2382 lock_destroy(&MPLock);
2384 // Now we can safely destroy the wait conditions
2385 for (int i = 0; i < MAX_THREADS; i++)
2386 cond_destroy(&WaitCond[i]);
2390 // thread_should_stop() checks whether the thread should stop its search.
2391 // This can happen if a beta cutoff has occurred in the thread's currently
2392 // active split point, or in some ancestor of the current split point.
2394 bool ThreadsManager::thread_should_stop(int threadID) const {
2396 assert(threadID >= 0 && threadID < ActiveThreads);
2398 SplitPoint* sp = threads[threadID].splitPoint;
2400 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2405 // thread_is_available() checks whether the thread with threadID "slave" is
2406 // available to help the thread with threadID "master" at a split point. An
2407 // obvious requirement is that "slave" must be idle. With more than two
2408 // threads, this is not by itself sufficient: If "slave" is the master of
2409 // some active split point, it is only available as a slave to the other
2410 // threads which are busy searching the split point at the top of "slave"'s
2411 // split point stack (the "helpful master concept" in YBWC terminology).
2413 bool ThreadsManager::thread_is_available(int slave, int master) const {
2415 assert(slave >= 0 && slave < ActiveThreads);
2416 assert(master >= 0 && master < ActiveThreads);
2417 assert(ActiveThreads > 1);
2419 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2422 // Make a local copy to be sure doesn't change under our feet
2423 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2425 // No active split points means that the thread is available as
2426 // a slave for any other thread.
2427 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2430 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2431 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2432 // could have been set to 0 by another thread leading to an out of bound access.
2433 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2440 // available_thread_exists() tries to find an idle thread which is available as
2441 // a slave for the thread with threadID "master".
2443 bool ThreadsManager::available_thread_exists(int master) const {
2445 assert(master >= 0 && master < ActiveThreads);
2446 assert(ActiveThreads > 1);
2448 for (int i = 0; i < ActiveThreads; i++)
2449 if (thread_is_available(i, master))
2456 // split() does the actual work of distributing the work at a node between
2457 // several available threads. If it does not succeed in splitting the
2458 // node (because no idle threads are available, or because we have no unused
2459 // split point objects), the function immediately returns. If splitting is
2460 // possible, a SplitPoint object is initialized with all the data that must be
2461 // copied to the helper threads and we tell our helper threads that they have
2462 // been assigned work. This will cause them to instantly leave their idle loops and
2463 // call search().When all threads have returned from search() then split() returns.
2465 template <bool Fake>
2466 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2467 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2468 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2470 assert(ply > 0 && ply < PLY_MAX);
2471 assert(*bestValue >= -VALUE_INFINITE);
2472 assert(*bestValue <= *alpha);
2473 assert(*alpha < beta);
2474 assert(beta <= VALUE_INFINITE);
2475 assert(depth > DEPTH_ZERO);
2476 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2477 assert(ActiveThreads > 1);
2479 int i, master = p.thread();
2480 Thread& masterThread = threads[master];
2484 // If no other thread is available to help us, or if we have too many
2485 // active split points, don't split.
2486 if ( !available_thread_exists(master)
2487 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2489 lock_release(&MPLock);
2493 // Pick the next available split point object from the split point stack
2494 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2496 // Initialize the split point object
2497 splitPoint.parent = masterThread.splitPoint;
2498 splitPoint.master = master;
2499 splitPoint.stopRequest = false;
2500 splitPoint.ply = ply;
2501 splitPoint.depth = depth;
2502 splitPoint.threatMove = threatMove;
2503 splitPoint.mateThreat = mateThreat;
2504 splitPoint.alpha = *alpha;
2505 splitPoint.beta = beta;
2506 splitPoint.pvNode = pvNode;
2507 splitPoint.bestValue = *bestValue;
2509 splitPoint.moveCount = moveCount;
2510 splitPoint.pos = &p;
2511 splitPoint.parentSstack = ss;
2512 for (i = 0; i < ActiveThreads; i++)
2513 splitPoint.slaves[i] = 0;
2515 masterThread.splitPoint = &splitPoint;
2517 // If we are here it means we are not available
2518 assert(masterThread.state != THREAD_AVAILABLE);
2520 int workersCnt = 1; // At least the master is included
2522 // Allocate available threads setting state to THREAD_BOOKED
2523 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2524 if (thread_is_available(i, master))
2526 threads[i].state = THREAD_BOOKED;
2527 threads[i].splitPoint = &splitPoint;
2528 splitPoint.slaves[i] = 1;
2532 assert(Fake || workersCnt > 1);
2534 // We can release the lock because slave threads are already booked and master is not available
2535 lock_release(&MPLock);
2537 // Tell the threads that they have work to do. This will make them leave
2538 // their idle loop. But before copy search stack tail for each thread.
2539 for (i = 0; i < ActiveThreads; i++)
2540 if (i == master || splitPoint.slaves[i])
2542 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2544 assert(i == master || threads[i].state == THREAD_BOOKED);
2546 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2548 wake_sleeping_thread(i);
2551 // Everything is set up. The master thread enters the idle loop, from
2552 // which it will instantly launch a search, because its state is
2553 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2554 // idle loop, which means that the main thread will return from the idle
2555 // loop when all threads have finished their work at this split point.
2556 idle_loop(master, &splitPoint);
2558 // We have returned from the idle loop, which means that all threads are
2559 // finished. Update alpha and bestValue, and return.
2562 *alpha = splitPoint.alpha;
2563 *bestValue = splitPoint.bestValue;
2564 masterThread.activeSplitPoints--;
2565 masterThread.splitPoint = splitPoint.parent;
2567 lock_release(&MPLock);
2571 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2572 // to start a new search from the root.
2574 void ThreadsManager::wake_sleeping_thread(int threadID) {
2577 cond_signal(&WaitCond[threadID]);
2578 lock_release(&MPLock);
2582 /// The RootMoveList class
2584 // RootMoveList c'tor
2586 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2588 SearchStack ss[PLY_MAX_PLUS_2];
2589 MoveStack mlist[MOVES_MAX];
2591 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2593 // Initialize search stack
2594 init_ss_array(ss, PLY_MAX_PLUS_2);
2595 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2598 // Generate all legal moves
2599 MoveStack* last = generate_moves(pos, mlist);
2601 // Add each move to the moves[] array
2602 for (MoveStack* cur = mlist; cur != last; cur++)
2604 bool includeMove = includeAllMoves;
2606 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2607 includeMove = (searchMoves[k] == cur->move);
2612 // Find a quick score for the move
2613 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2614 moves[count].pv[1] = MOVE_NONE;
2615 pos.do_move(cur->move, st);
2616 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2617 pos.undo_move(cur->move);
2623 // Score root moves using the standard way used in main search, the moves
2624 // are scored according to the order in which are returned by MovePicker.
2626 void RootMoveList::score_moves(const Position& pos)
2630 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2632 while ((move = mp.get_next_move()) != MOVE_NONE)
2633 for (int i = 0; i < count; i++)
2634 if (moves[i].move == move)
2636 moves[i].mp_score = score--;
2641 // RootMoveList simple methods definitions
2643 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2647 for (j = 0; pv[j] != MOVE_NONE; j++)
2648 moves[moveNum].pv[j] = pv[j];
2650 moves[moveNum].pv[j] = MOVE_NONE;
2654 // RootMoveList::sort() sorts the root move list at the beginning of a new
2657 void RootMoveList::sort() {
2659 sort_multipv(count - 1); // Sort all items
2663 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2664 // list by their scores and depths. It is used to order the different PVs
2665 // correctly in MultiPV mode.
2667 void RootMoveList::sort_multipv(int n) {
2671 for (i = 1; i <= n; i++)
2673 RootMove rm = moves[i];
2674 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2675 moves[j] = moves[j - 1];