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/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
242 // Scores and number of times the best move changed for each iteration
243 Value ValueByIteration[PLY_MAX_PLUS_2];
244 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
246 // Search window management
252 // Time managment variables
253 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
254 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
260 std::ofstream LogFile;
262 // Multi-threads related variables
263 Depth MinimumSplitDepth;
264 int MaxThreadsPerSplitPoint;
267 // Node counters, used only by thread[0] but try to keep in different cache
268 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
280 template <NodeType PvNode>
281 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 void sp_search(SplitPoint* sp, int threadID);
289 template <NodeType PvNode>
290 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 Value value_to_tt(Value v, int ply);
295 Value value_from_tt(Value v, int ply);
296 bool move_is_killer(Move m, SearchStack* ss);
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() { TM.init_threads(); }
332 void exit_threads() { TM.exit_threads(); }
333 int64_t nodes_searched() { return TM.nodes_searched(); }
336 /// init_search() is called during startup. It initializes various lookup tables
340 int d; // depth (OnePly == 2)
341 int hd; // half depth (OnePly == 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(OnePly)) : 0);
350 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
353 // Init futility margins array
354 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
355 FutilityMarginsMatrix[d][mc] = 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] = 3 + (1 << (3 * d / 8));
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)
371 MovePicker mp(pos, MOVE_NONE, depth, H);
373 // If we are at the last ply we don't need to do and undo
374 // the moves, just to count them.
375 if (depth <= OnePly) // Replace with '<' to test also qsearch
377 while (mp.get_next_move()) sum++;
381 // Loop through all legal moves
383 while ((move = mp.get_next_move()) != MOVE_NONE)
385 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
386 sum += perft(pos, depth - OnePly);
393 /// think() is the external interface to Stockfish's search, and is called when
394 /// the program receives the UCI 'go' command. It initializes various
395 /// search-related global variables, and calls root_search(). It returns false
396 /// when a quit command is received during the search.
398 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
399 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
401 // Initialize global search variables
402 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
403 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
405 TM.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") * OnePly;
450 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
451 MultiPV = get_option_value_int("MultiPV");
452 Chess960 = get_option_value_bool("UCI_Chess960");
453 UseLogFile = get_option_value_bool("Use Search Log");
456 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
458 read_weights(pos.side_to_move());
460 // Set the number of active threads
461 int newActiveThreads = get_option_value_int("Threads");
462 if (newActiveThreads != TM.active_threads())
464 TM.set_active_threads(newActiveThreads);
465 init_eval(TM.active_threads());
468 // Wake up sleeping threads
469 TM.wake_sleeping_threads();
472 int myTime = time[pos.side_to_move()];
473 int myIncrement = increment[pos.side_to_move()];
474 if (UseTimeManagement)
476 if (!movesToGo) // Sudden death time control
480 MaxSearchTime = myTime / 30 + myIncrement;
481 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
483 else // Blitz game without increment
485 MaxSearchTime = myTime / 30;
486 AbsoluteMaxSearchTime = myTime / 8;
489 else // (x moves) / (y minutes)
493 MaxSearchTime = myTime / 2;
494 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
498 MaxSearchTime = myTime / Min(movesToGo, 20);
499 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
503 if (get_option_value_bool("Ponder"))
505 MaxSearchTime += MaxSearchTime / 4;
506 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
510 // Set best NodesBetweenPolls interval to avoid lagging under
511 // heavy time pressure.
513 NodesBetweenPolls = Min(MaxNodes, 30000);
514 else if (myTime && myTime < 1000)
515 NodesBetweenPolls = 1000;
516 else if (myTime && myTime < 5000)
517 NodesBetweenPolls = 5000;
519 NodesBetweenPolls = 30000;
521 // Write search information to log file
523 LogFile << "Searching: " << pos.to_fen() << endl
524 << "infinite: " << infinite
525 << " ponder: " << ponder
526 << " time: " << myTime
527 << " increment: " << myIncrement
528 << " moves to go: " << movesToGo << endl;
530 // We're ready to start thinking. Call the iterative deepening loop function
531 id_loop(pos, searchMoves);
536 TM.put_threads_to_sleep();
544 // id_loop() is the main iterative deepening loop. It calls root_search
545 // repeatedly with increasing depth until the allocated thinking time has
546 // been consumed, the user stops the search, or the maximum search depth is
549 Value id_loop(const Position& pos, Move searchMoves[]) {
551 Position p(pos, pos.thread());
552 SearchStack ss[PLY_MAX_PLUS_2];
553 Move pv[PLY_MAX_PLUS_2];
554 Move EasyMove = MOVE_NONE;
555 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
557 // Moves to search are verified, copied, scored and sorted
558 RootMoveList rml(p, searchMoves);
560 // Handle special case of searching on a mate/stale position
561 if (rml.move_count() == 0)
564 wait_for_stop_or_ponderhit();
566 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
569 // Print RootMoveList startup scoring to the standard output,
570 // so to output information also for iteration 1.
571 cout << "info depth " << 1
572 << "\ninfo depth " << 1
573 << " score " << value_to_uci(rml.get_move_score(0))
574 << " time " << current_search_time()
575 << " nodes " << TM.nodes_searched()
577 << " pv " << rml.get_move(0) << "\n";
582 init_ss_array(ss, PLY_MAX_PLUS_2);
583 pv[0] = pv[1] = MOVE_NONE;
584 ValueByIteration[1] = rml.get_move_score(0);
587 // Is one move significantly better than others after initial scoring ?
588 if ( rml.move_count() == 1
589 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
590 EasyMove = rml.get_move(0);
592 // Iterative deepening loop
593 while (Iteration < PLY_MAX)
595 // Initialize iteration
597 BestMoveChangesByIteration[Iteration] = 0;
599 cout << "info depth " << Iteration << endl;
601 // Calculate dynamic aspiration window based on previous iterations
602 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
604 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
605 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
607 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
608 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
610 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
611 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
614 // Search to the current depth, rml is updated and sorted, alpha and beta could change
615 value = root_search(p, ss, pv, rml, &alpha, &beta);
617 // Write PV to transposition table, in case the relevant entries have
618 // been overwritten during the search.
619 insert_pv_in_tt(p, pv);
622 break; // Value cannot be trusted. Break out immediately!
624 //Save info about search result
625 ValueByIteration[Iteration] = value;
627 // Drop the easy move if differs from the new best move
628 if (pv[0] != EasyMove)
629 EasyMove = MOVE_NONE;
631 if (UseTimeManagement)
634 bool stopSearch = false;
636 // Stop search early if there is only a single legal move,
637 // we search up to Iteration 6 anyway to get a proper score.
638 if (Iteration >= 6 && rml.move_count() == 1)
641 // Stop search early when the last two iterations returned a mate score
643 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
644 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
647 // Stop search early if one move seems to be much better than the others
648 int64_t nodes = TM.nodes_searched();
651 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
652 && current_search_time() > MaxSearchTime / 16)
653 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
654 && current_search_time() > MaxSearchTime / 32)))
657 // Add some extra time if the best move has changed during the last two iterations
658 if (Iteration > 5 && Iteration <= 50)
659 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
660 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
662 // Stop search if most of MaxSearchTime is consumed at the end of the
663 // iteration. We probably don't have enough time to search the first
664 // move at the next iteration anyway.
665 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
671 StopOnPonderhit = true;
677 if (MaxDepth && Iteration >= MaxDepth)
681 // If we are pondering or in infinite search, we shouldn't print the
682 // best move before we are told to do so.
683 if (!AbortSearch && (PonderSearch || InfiniteSearch))
684 wait_for_stop_or_ponderhit();
686 // Print final search statistics
687 cout << "info nodes " << TM.nodes_searched()
689 << " time " << current_search_time() << endl;
691 // Print the best move and the ponder move to the standard output
692 if (pv[0] == MOVE_NONE)
694 pv[0] = rml.get_move(0);
698 assert(pv[0] != MOVE_NONE);
700 cout << "bestmove " << pv[0];
702 if (pv[1] != MOVE_NONE)
703 cout << " ponder " << pv[1];
710 dbg_print_mean(LogFile);
712 if (dbg_show_hit_rate)
713 dbg_print_hit_rate(LogFile);
715 LogFile << "\nNodes: " << TM.nodes_searched()
716 << "\nNodes/second: " << nps()
717 << "\nBest move: " << move_to_san(p, pv[0]);
720 p.do_move(pv[0], st);
721 LogFile << "\nPonder move: "
722 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
725 return rml.get_move_score(0);
729 // root_search() is the function which searches the root node. It is
730 // similar to search_pv except that it uses a different move ordering
731 // scheme, prints some information to the standard output and handles
732 // the fail low/high loops.
734 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
741 Depth depth, ext, newDepth;
742 Value value, alpha, beta;
743 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
744 int researchCountFH, researchCountFL;
746 researchCountFH = researchCountFL = 0;
749 isCheck = pos.is_check();
751 // Step 1. Initialize node (polling is omitted at root)
752 ss->currentMove = ss->bestMove = MOVE_NONE;
754 // Step 2. Check for aborted search (omitted at root)
755 // Step 3. Mate distance pruning (omitted at root)
756 // Step 4. Transposition table lookup (omitted at root)
758 // Step 5. Evaluate the position statically
759 // At root we do this only to get reference value for child nodes
760 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
762 // Step 6. Razoring (omitted at root)
763 // Step 7. Static null move pruning (omitted at root)
764 // Step 8. Null move search with verification search (omitted at root)
765 // Step 9. Internal iterative deepening (omitted at root)
767 // Step extra. Fail low loop
768 // We start with small aspiration window and in case of fail low, we research
769 // with bigger window until we are not failing low anymore.
772 // Sort the moves before to (re)search
775 // Step 10. Loop through all moves in the root move list
776 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
778 // This is used by time management
779 FirstRootMove = (i == 0);
781 // Save the current node count before the move is searched
782 nodes = TM.nodes_searched();
784 // Reset beta cut-off counters
785 TM.resetBetaCounters();
787 // Pick the next root move, and print the move and the move number to
788 // the standard output.
789 move = ss->currentMove = rml.get_move(i);
791 if (current_search_time() >= 1000)
792 cout << "info currmove " << move
793 << " currmovenumber " << i + 1 << endl;
795 moveIsCheck = pos.move_is_check(move);
796 captureOrPromotion = pos.move_is_capture_or_promotion(move);
798 // Step 11. Decide the new search depth
799 depth = (Iteration - 2) * OnePly + InitialDepth;
800 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
801 newDepth = depth + ext;
803 // Step 12. Futility pruning (omitted at root)
805 // Step extra. Fail high loop
806 // If move fails high, we research with bigger window until we are not failing
808 value = - VALUE_INFINITE;
812 // Step 13. Make the move
813 pos.do_move(move, st, ci, moveIsCheck);
815 // Step extra. pv search
816 // We do pv search for first moves (i < MultiPV)
817 // and for fail high research (value > alpha)
818 if (i < MultiPV || value > alpha)
820 // Aspiration window is disabled in multi-pv case
822 alpha = -VALUE_INFINITE;
824 // Full depth PV search, done on first move or after a fail high
825 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
829 // Step 14. Reduced search
830 // if the move fails high will be re-searched at full depth
831 bool doFullDepthSearch = true;
833 if ( depth >= 3 * OnePly
835 && !captureOrPromotion
836 && !move_is_castle(move))
838 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
841 assert(newDepth-ss->reduction >= OnePly);
843 // Reduced depth non-pv search using alpha as upperbound
844 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
845 doFullDepthSearch = (value > alpha);
848 // The move failed high, but if reduction is very big we could
849 // face a false positive, retry with a less aggressive reduction,
850 // if the move fails high again then go with full depth search.
851 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
853 assert(newDepth - OnePly >= OnePly);
855 ss->reduction = OnePly;
856 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
857 doFullDepthSearch = (value > alpha);
859 ss->reduction = Depth(0); // Restore original reduction
862 // Step 15. Full depth search
863 if (doFullDepthSearch)
865 // Full depth non-pv search using alpha as upperbound
866 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
868 // If we are above alpha then research at same depth but as PV
869 // to get a correct score or eventually a fail high above beta.
871 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
875 // Step 16. Undo move
878 // Can we exit fail high loop ?
879 if (AbortSearch || value < beta)
882 // We are failing high and going to do a research. It's important to update
883 // the score before research in case we run out of time while researching.
884 rml.set_move_score(i, value);
886 extract_pv_from_tt(pos, move, pv);
887 rml.set_move_pv(i, pv);
889 // Print information to the standard output
890 print_pv_info(pos, pv, alpha, beta, value);
892 // Prepare for a research after a fail high, each time with a wider window
893 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
896 } // End of fail high loop
898 // Finished searching the move. If AbortSearch is true, the search
899 // was aborted because the user interrupted the search or because we
900 // ran out of time. In this case, the return value of the search cannot
901 // be trusted, and we break out of the loop without updating the best
906 // Remember beta-cutoff and searched nodes counts for this move. The
907 // info is used to sort the root moves for the next iteration.
909 TM.get_beta_counters(pos.side_to_move(), our, their);
910 rml.set_beta_counters(i, our, their);
911 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
913 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
914 assert(value < beta);
916 // Step 17. Check for new best move
917 if (value <= alpha && i >= MultiPV)
918 rml.set_move_score(i, -VALUE_INFINITE);
921 // PV move or new best move!
924 rml.set_move_score(i, value);
926 extract_pv_from_tt(pos, move, pv);
927 rml.set_move_pv(i, pv);
931 // We record how often the best move has been changed in each
932 // iteration. This information is used for time managment: When
933 // the best move changes frequently, we allocate some more time.
935 BestMoveChangesByIteration[Iteration]++;
937 // Print information to the standard output
938 print_pv_info(pos, pv, alpha, beta, value);
940 // Raise alpha to setup proper non-pv search upper bound
947 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
949 cout << "info multipv " << j + 1
950 << " score " << value_to_uci(rml.get_move_score(j))
951 << " depth " << (j <= i ? Iteration : Iteration - 1)
952 << " time " << current_search_time()
953 << " nodes " << TM.nodes_searched()
957 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
958 cout << rml.get_move_pv(j, k) << " ";
962 alpha = rml.get_move_score(Min(i, MultiPV - 1));
964 } // PV move or new best move
966 assert(alpha >= *alphaPtr);
968 AspirationFailLow = (alpha == *alphaPtr);
970 if (AspirationFailLow && StopOnPonderhit)
971 StopOnPonderhit = false;
974 // Can we exit fail low loop ?
975 if (AbortSearch || !AspirationFailLow)
978 // Prepare for a research after a fail low, each time with a wider window
979 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
984 // Sort the moves before to return
991 // search<>() is the main search function for both PV and non-PV nodes
993 template <NodeType PvNode>
994 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
996 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
997 assert(beta > alpha && beta <= VALUE_INFINITE);
998 assert(PvNode || alpha == beta - 1);
999 assert(ply > 0 && ply < PLY_MAX);
1000 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1002 Move movesSearched[256];
1007 Move ttMove, move, excludedMove, threatMove;
1008 Depth ext, newDepth;
1009 Value bestValue, value, oldAlpha;
1010 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1011 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1012 bool mateThreat = false;
1014 int threadID = pos.thread();
1015 refinedValue = bestValue = value = -VALUE_INFINITE;
1018 // Step 1. Initialize node and poll. Polling can abort search
1019 TM.incrementNodeCounter(threadID);
1020 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1021 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1023 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1029 // Step 2. Check for aborted search and immediate draw
1030 if (AbortSearch || TM.thread_should_stop(threadID))
1033 if (pos.is_draw() || ply >= PLY_MAX - 1)
1036 // Step 3. Mate distance pruning
1037 alpha = Max(value_mated_in(ply), alpha);
1038 beta = Min(value_mate_in(ply+1), beta);
1042 // Step 4. Transposition table lookup
1044 // We don't want the score of a partial search to overwrite a previous full search
1045 // TT value, so we use a different position key in case of an excluded move exists.
1046 excludedMove = ss->excludedMove;
1047 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1049 tte = TT.retrieve(posKey);
1050 ttMove = (tte ? tte->move() : MOVE_NONE);
1052 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1053 // This is to avoid problems in the following areas:
1055 // * Repetition draw detection
1056 // * Fifty move rule detection
1057 // * Searching for a mate
1058 // * Printing of full PV line
1060 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1062 // Refresh tte entry to avoid aging
1063 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1065 ss->currentMove = ttMove; // Can be MOVE_NONE
1066 return value_from_tt(tte->value(), ply);
1069 // Step 5. Evaluate the position statically
1070 // At PV nodes we do this only to update gain statistics
1071 isCheck = pos.is_check();
1076 assert(tte->static_value() != VALUE_NONE);
1077 ss->eval = tte->static_value();
1078 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1082 ss->eval = evaluate(pos, ei);
1083 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1086 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1087 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1090 ss->eval = VALUE_NONE;
1092 // Step 6. Razoring (is omitted in PV nodes)
1094 && depth < RazorDepth
1096 && refinedValue < beta - razor_margin(depth)
1097 && ttMove == MOVE_NONE
1098 && (ss-1)->currentMove != MOVE_NULL
1099 && !value_is_mate(beta)
1100 && !pos.has_pawn_on_7th(pos.side_to_move()))
1102 Value rbeta = beta - razor_margin(depth);
1103 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1105 // Logically we should return (v + razor_margin(depth)), but
1106 // surprisingly this did slightly weaker in tests.
1110 // Step 7. Static null move pruning (is omitted in PV nodes)
1111 // We're betting that the opponent doesn't have a move that will reduce
1112 // the score by more than futility_margin(depth) if we do a null move.
1114 && !ss->skipNullMove
1115 && depth < RazorDepth
1116 && refinedValue >= beta + futility_margin(depth, 0)
1118 && !value_is_mate(beta)
1119 && pos.non_pawn_material(pos.side_to_move()))
1120 return refinedValue - futility_margin(depth, 0);
1122 // Step 8. Null move search with verification search (is omitted in PV nodes)
1123 // When we jump directly to qsearch() we do a null move only if static value is
1124 // at least beta. Otherwise we do a null move if static value is not more than
1125 // NullMoveMargin under beta.
1127 && !ss->skipNullMove
1129 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1131 && !value_is_mate(beta)
1132 && pos.non_pawn_material(pos.side_to_move()))
1134 ss->currentMove = MOVE_NULL;
1136 // Null move dynamic reduction based on depth
1137 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1139 // Null move dynamic reduction based on value
1140 if (refinedValue - beta > PawnValueMidgame)
1143 pos.do_null_move(st);
1144 (ss+1)->skipNullMove = true;
1146 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1147 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1148 (ss+1)->skipNullMove = false;
1149 pos.undo_null_move();
1151 if (nullValue >= beta)
1153 // Do not return unproven mate scores
1154 if (nullValue >= value_mate_in(PLY_MAX))
1157 if (depth < 6 * OnePly)
1160 // Do verification search at high depths
1161 ss->skipNullMove = true;
1162 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1163 ss->skipNullMove = false;
1170 // The null move failed low, which means that we may be faced with
1171 // some kind of threat. If the previous move was reduced, check if
1172 // the move that refuted the null move was somehow connected to the
1173 // move which was reduced. If a connection is found, return a fail
1174 // low score (which will cause the reduced move to fail high in the
1175 // parent node, which will trigger a re-search with full depth).
1176 if (nullValue == value_mated_in(ply + 2))
1179 threatMove = (ss+1)->currentMove;
1180 if ( depth < ThreatDepth
1181 && (ss-1)->reduction
1182 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1187 // Step 9. Internal iterative deepening
1188 if ( depth >= IIDDepth[PvNode]
1189 && ttMove == MOVE_NONE
1190 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1192 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1194 ss->skipNullMove = true;
1195 search<PvNode>(pos, ss, alpha, beta, d, ply);
1196 ss->skipNullMove = false;
1198 ttMove = ss->bestMove;
1199 tte = TT.retrieve(posKey);
1202 // Expensive mate threat detection (only for PV nodes)
1204 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1206 // Initialize a MovePicker object for the current position
1207 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1209 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1210 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1211 && tte && tte->move()
1212 && !excludedMove // Do not allow recursive singular extension search
1213 && is_lower_bound(tte->type())
1214 && tte->depth() >= depth - 3 * OnePly;
1216 // Step 10. Loop through moves
1217 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1218 while ( bestValue < beta
1219 && (move = mp.get_next_move()) != MOVE_NONE
1220 && !TM.thread_should_stop(threadID))
1222 assert(move_is_ok(move));
1224 if (move == excludedMove)
1227 moveIsCheck = pos.move_is_check(move, ci);
1228 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1230 // Step 11. Decide the new search depth
1231 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1233 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1234 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1235 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1236 // lower then ttValue minus a margin then we extend ttMove.
1237 if ( singularExtensionNode
1238 && move == tte->move()
1241 Value ttValue = value_from_tt(tte->value(), ply);
1243 if (abs(ttValue) < VALUE_KNOWN_WIN)
1245 Value b = ttValue - SingularExtensionMargin;
1246 ss->excludedMove = move;
1247 ss->skipNullMove = true;
1248 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1249 ss->skipNullMove = false;
1250 ss->excludedMove = MOVE_NONE;
1256 newDepth = depth - OnePly + ext;
1258 // Update current move (this must be done after singular extension search)
1259 movesSearched[moveCount++] = ss->currentMove = move;
1261 // Step 12. Futility pruning (is omitted in PV nodes)
1263 && !captureOrPromotion
1267 && !move_is_castle(move))
1269 // Move count based pruning
1270 if ( moveCount >= futility_move_count(depth)
1271 && !(threatMove && connected_threat(pos, move, threatMove))
1272 && bestValue > value_mated_in(PLY_MAX))
1275 // Value based pruning
1276 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1277 // but fixing this made program slightly weaker.
1278 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1279 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1280 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1282 if (futilityValueScaled < beta)
1284 if (futilityValueScaled > bestValue)
1285 bestValue = futilityValueScaled;
1290 // Step 13. Make the move
1291 pos.do_move(move, st, ci, moveIsCheck);
1293 // Step extra. pv search (only in PV nodes)
1294 // The first move in list is the expected PV
1295 if (PvNode && moveCount == 1)
1296 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1297 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1300 // Step 14. Reduced depth search
1301 // If the move fails high will be re-searched at full depth.
1302 bool doFullDepthSearch = true;
1304 if ( depth >= 3 * OnePly
1305 && !captureOrPromotion
1307 && !move_is_castle(move)
1308 && !move_is_killer(move, ss))
1310 ss->reduction = reduction<PvNode>(depth, moveCount);
1313 Depth d = newDepth - ss->reduction;
1314 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), 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 * OnePly)
1325 assert(newDepth - OnePly >= OnePly);
1327 ss->reduction = OnePly;
1328 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1329 doFullDepthSearch = (value > alpha);
1331 ss->reduction = Depth(0); // Restore original reduction
1334 // Step 15. Full depth search
1335 if (doFullDepthSearch)
1337 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1338 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1340 // Step extra. pv search (only in PV nodes)
1341 // Search only for possible new PV nodes, if instead value >= beta then
1342 // parent node fails low with value <= alpha and tries another move.
1343 if (PvNode && value > alpha && value < beta)
1344 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1345 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1349 // Step 16. Undo move
1350 pos.undo_move(move);
1352 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1354 // Step 17. Check for new best move
1355 if (value > bestValue)
1360 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1363 if (value == value_mate_in(ply + 1))
1364 ss->mateKiller = move;
1366 ss->bestMove = move;
1370 // Step 18. Check for split
1371 if ( depth >= MinimumSplitDepth
1372 && TM.active_threads() > 1
1374 && TM.available_thread_exists(threadID)
1376 && !TM.thread_should_stop(threadID)
1378 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1379 threatMove, mateThreat, &moveCount, &mp, PvNode);
1382 // Step 19. Check for mate and stalemate
1383 // All legal moves have been searched and if there are
1384 // no legal moves, it must be mate or stalemate.
1385 // If one move was excluded return fail low score.
1387 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1389 // Step 20. Update tables
1390 // If the search is not aborted, update the transposition table,
1391 // history counters, and killer moves.
1392 if (AbortSearch || TM.thread_should_stop(threadID))
1395 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1396 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1397 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1399 // Update killers and history only for non capture moves that fails high
1400 if (bestValue >= beta)
1402 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1403 if (!pos.move_is_capture_or_promotion(move))
1405 update_history(pos, move, depth, movesSearched, moveCount);
1406 update_killers(move, ss);
1410 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1416 // qsearch() is the quiescence search function, which is called by the main
1417 // search function when the remaining depth is zero (or, to be more precise,
1418 // less than OnePly).
1420 template <NodeType PvNode>
1421 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1423 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1424 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1425 assert(PvNode || alpha == beta - 1);
1427 assert(ply > 0 && ply < PLY_MAX);
1428 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1433 Value bestValue, value, futilityValue, futilityBase;
1434 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1436 Value oldAlpha = alpha;
1438 TM.incrementNodeCounter(pos.thread());
1439 ss->bestMove = ss->currentMove = MOVE_NONE;
1441 // Check for an instant draw or maximum ply reached
1442 if (pos.is_draw() || ply >= PLY_MAX - 1)
1445 // Transposition table lookup. At PV nodes, we don't use the TT for
1446 // pruning, but only for move ordering.
1447 tte = TT.retrieve(pos.get_key());
1448 ttMove = (tte ? tte->move() : MOVE_NONE);
1450 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1452 ss->currentMove = ttMove; // Can be MOVE_NONE
1453 return value_from_tt(tte->value(), ply);
1456 isCheck = pos.is_check();
1458 // Evaluate the position statically
1461 bestValue = futilityBase = -VALUE_INFINITE;
1462 ss->eval = VALUE_NONE;
1463 deepChecks = enoughMaterial = false;
1469 assert(tte->static_value() != VALUE_NONE);
1470 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1471 bestValue = tte->static_value();
1474 bestValue = evaluate(pos, ei);
1476 ss->eval = bestValue;
1477 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1479 // Stand pat. Return immediately if static value is at least beta
1480 if (bestValue >= beta)
1483 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1488 if (PvNode && bestValue > alpha)
1491 // If we are near beta then try to get a cutoff pushing checks a bit further
1492 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1494 // Futility pruning parameters, not needed when in check
1495 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1496 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1499 // Initialize a MovePicker object for the current position, and prepare
1500 // to search the moves. Because the depth is <= 0 here, only captures,
1501 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1502 // and we are near beta) will be generated.
1503 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1506 // Loop through the moves until no moves remain or a beta cutoff occurs
1507 while ( alpha < beta
1508 && (move = mp.get_next_move()) != MOVE_NONE)
1510 assert(move_is_ok(move));
1512 moveIsCheck = pos.move_is_check(move, ci);
1520 && !move_is_promotion(move)
1521 && !pos.move_is_passed_pawn_push(move))
1523 futilityValue = futilityBase
1524 + pos.endgame_value_of_piece_on(move_to(move))
1525 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1527 if (futilityValue < alpha)
1529 if (futilityValue > bestValue)
1530 bestValue = futilityValue;
1535 // Detect blocking evasions that are candidate to be pruned
1536 evasionPrunable = isCheck
1537 && bestValue > value_mated_in(PLY_MAX)
1538 && !pos.move_is_capture(move)
1539 && pos.type_of_piece_on(move_from(move)) != KING
1540 && !pos.can_castle(pos.side_to_move());
1542 // Don't search moves with negative SEE values
1544 && (!isCheck || evasionPrunable)
1546 && !move_is_promotion(move)
1547 && pos.see_sign(move) < 0)
1550 // Update current move
1551 ss->currentMove = move;
1553 // Make and search the move
1554 pos.do_move(move, st, ci, moveIsCheck);
1555 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1556 pos.undo_move(move);
1558 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1561 if (value > bestValue)
1567 ss->bestMove = move;
1572 // All legal moves have been searched. A special case: If we're in check
1573 // and no legal moves were found, it is checkmate.
1574 if (isCheck && bestValue == -VALUE_INFINITE)
1575 return value_mated_in(ply);
1577 // Update transposition table
1578 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1579 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1580 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1582 // Update killers only for checking moves that fails high
1583 if ( bestValue >= beta
1584 && !pos.move_is_capture_or_promotion(ss->bestMove))
1585 update_killers(ss->bestMove, ss);
1587 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1593 // sp_search() is used to search from a split point. This function is called
1594 // by each thread working at the split point. It is similar to the normal
1595 // search() function, but simpler. Because we have already probed the hash
1596 // table, done a null move search, and searched the first move before
1597 // splitting, we don't have to repeat all this work in sp_search(). We
1598 // also don't need to store anything to the hash table here: This is taken
1599 // care of after we return from the split point.
1601 template <NodeType PvNode>
1602 void sp_search(SplitPoint* sp, int threadID) {
1604 assert(threadID >= 0 && threadID < TM.active_threads());
1605 assert(TM.active_threads() > 1);
1609 Depth ext, newDepth;
1611 Value futilityValueScaled; // NonPV specific
1612 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1614 value = -VALUE_INFINITE;
1616 Position pos(*sp->pos, threadID);
1618 SearchStack* ss = sp->sstack[threadID] + 1;
1619 isCheck = pos.is_check();
1621 // Step 10. Loop through moves
1622 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1623 lock_grab(&(sp->lock));
1625 while ( sp->bestValue < sp->beta
1626 && (move = sp->mp->get_next_move()) != MOVE_NONE
1627 && !TM.thread_should_stop(threadID))
1629 moveCount = ++sp->moveCount;
1630 lock_release(&(sp->lock));
1632 assert(move_is_ok(move));
1634 moveIsCheck = pos.move_is_check(move, ci);
1635 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1637 // Step 11. Decide the new search depth
1638 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1639 newDepth = sp->depth - OnePly + ext;
1641 // Update current move
1642 ss->currentMove = move;
1644 // Step 12. Futility pruning (is omitted in PV nodes)
1646 && !captureOrPromotion
1649 && !move_is_castle(move))
1651 // Move count based pruning
1652 if ( moveCount >= futility_move_count(sp->depth)
1653 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1654 && sp->bestValue > value_mated_in(PLY_MAX))
1656 lock_grab(&(sp->lock));
1660 // Value based pruning
1661 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1662 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1663 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1665 if (futilityValueScaled < sp->beta)
1667 lock_grab(&(sp->lock));
1669 if (futilityValueScaled > sp->bestValue)
1670 sp->bestValue = futilityValueScaled;
1675 // Step 13. Make the move
1676 pos.do_move(move, st, ci, moveIsCheck);
1678 // Step 14. Reduced search
1679 // If the move fails high will be re-searched at full depth.
1680 bool doFullDepthSearch = true;
1682 if ( !captureOrPromotion
1684 && !move_is_castle(move)
1685 && !move_is_killer(move, ss))
1687 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1690 Value localAlpha = sp->alpha;
1691 Depth d = newDepth - ss->reduction;
1692 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1693 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1695 doFullDepthSearch = (value > localAlpha);
1698 // The move failed high, but if reduction is very big we could
1699 // face a false positive, retry with a less aggressive reduction,
1700 // if the move fails high again then go with full depth search.
1701 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1703 assert(newDepth - OnePly >= OnePly);
1705 ss->reduction = OnePly;
1706 Value localAlpha = sp->alpha;
1707 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1708 doFullDepthSearch = (value > localAlpha);
1710 ss->reduction = Depth(0); // Restore original reduction
1713 // Step 15. Full depth search
1714 if (doFullDepthSearch)
1716 Value localAlpha = sp->alpha;
1717 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1718 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1720 // Step extra. pv search (only in PV nodes)
1721 // Search only for possible new PV nodes, if instead value >= beta then
1722 // parent node fails low with value <= alpha and tries another move.
1723 if (PvNode && value > localAlpha && value < sp->beta)
1724 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1725 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1728 // Step 16. Undo move
1729 pos.undo_move(move);
1731 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1733 // Step 17. Check for new best move
1734 lock_grab(&(sp->lock));
1736 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1738 sp->bestValue = value;
1740 if (sp->bestValue > sp->alpha)
1742 if (!PvNode || value >= sp->beta)
1743 sp->stopRequest = true;
1745 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1748 sp->parentSstack->bestMove = ss->bestMove = move;
1753 /* Here we have the lock still grabbed */
1755 sp->slaves[threadID] = 0;
1757 lock_release(&(sp->lock));
1761 // connected_moves() tests whether two moves are 'connected' in the sense
1762 // that the first move somehow made the second move possible (for instance
1763 // if the moving piece is the same in both moves). The first move is assumed
1764 // to be the move that was made to reach the current position, while the
1765 // second move is assumed to be a move from the current position.
1767 bool connected_moves(const Position& pos, Move m1, Move m2) {
1769 Square f1, t1, f2, t2;
1772 assert(move_is_ok(m1));
1773 assert(move_is_ok(m2));
1775 if (m2 == MOVE_NONE)
1778 // Case 1: The moving piece is the same in both moves
1784 // Case 2: The destination square for m2 was vacated by m1
1790 // Case 3: Moving through the vacated square
1791 if ( piece_is_slider(pos.piece_on(f2))
1792 && bit_is_set(squares_between(f2, t2), f1))
1795 // Case 4: The destination square for m2 is defended by the moving piece in m1
1796 p = pos.piece_on(t1);
1797 if (bit_is_set(pos.attacks_from(p, t1), t2))
1800 // Case 5: Discovered check, checking piece is the piece moved in m1
1801 if ( piece_is_slider(p)
1802 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1803 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1805 // discovered_check_candidates() works also if the Position's side to
1806 // move is the opposite of the checking piece.
1807 Color them = opposite_color(pos.side_to_move());
1808 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1810 if (bit_is_set(dcCandidates, f2))
1817 // value_is_mate() checks if the given value is a mate one eventually
1818 // compensated for the ply.
1820 bool value_is_mate(Value value) {
1822 assert(abs(value) <= VALUE_INFINITE);
1824 return value <= value_mated_in(PLY_MAX)
1825 || value >= value_mate_in(PLY_MAX);
1829 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1830 // "plies to mate from the current ply". Non-mate scores are unchanged.
1831 // The function is called before storing a value to the transposition table.
1833 Value value_to_tt(Value v, int ply) {
1835 if (v >= value_mate_in(PLY_MAX))
1838 if (v <= value_mated_in(PLY_MAX))
1845 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1846 // the transposition table to a mate score corrected for the current ply.
1848 Value value_from_tt(Value v, int ply) {
1850 if (v >= value_mate_in(PLY_MAX))
1853 if (v <= value_mated_in(PLY_MAX))
1860 // move_is_killer() checks if the given move is among the killer moves
1862 bool move_is_killer(Move m, SearchStack* ss) {
1864 if (ss->killers[0] == m || ss->killers[1] == m)
1871 // extension() decides whether a move should be searched with normal depth,
1872 // or with extended depth. Certain classes of moves (checking moves, in
1873 // particular) are searched with bigger depth than ordinary moves and in
1874 // any case are marked as 'dangerous'. Note that also if a move is not
1875 // extended, as example because the corresponding UCI option is set to zero,
1876 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1877 template <NodeType PvNode>
1878 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1879 bool singleEvasion, bool mateThreat, bool* dangerous) {
1881 assert(m != MOVE_NONE);
1883 Depth result = Depth(0);
1884 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1888 if (moveIsCheck && pos.see_sign(m) >= 0)
1889 result += CheckExtension[PvNode];
1892 result += SingleEvasionExtension[PvNode];
1895 result += MateThreatExtension[PvNode];
1898 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1900 Color c = pos.side_to_move();
1901 if (relative_rank(c, move_to(m)) == RANK_7)
1903 result += PawnPushTo7thExtension[PvNode];
1906 if (pos.pawn_is_passed(c, move_to(m)))
1908 result += PassedPawnExtension[PvNode];
1913 if ( captureOrPromotion
1914 && pos.type_of_piece_on(move_to(m)) != PAWN
1915 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1916 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1917 && !move_is_promotion(m)
1920 result += PawnEndgameExtension[PvNode];
1925 && captureOrPromotion
1926 && pos.type_of_piece_on(move_to(m)) != PAWN
1927 && pos.see_sign(m) >= 0)
1933 return Min(result, OnePly);
1937 // connected_threat() tests whether it is safe to forward prune a move or if
1938 // is somehow coonected to the threat move returned by null search.
1940 bool connected_threat(const Position& pos, Move m, Move threat) {
1942 assert(move_is_ok(m));
1943 assert(threat && move_is_ok(threat));
1944 assert(!pos.move_is_check(m));
1945 assert(!pos.move_is_capture_or_promotion(m));
1946 assert(!pos.move_is_passed_pawn_push(m));
1948 Square mfrom, mto, tfrom, tto;
1950 mfrom = move_from(m);
1952 tfrom = move_from(threat);
1953 tto = move_to(threat);
1955 // Case 1: Don't prune moves which move the threatened piece
1959 // Case 2: If the threatened piece has value less than or equal to the
1960 // value of the threatening piece, don't prune move which defend it.
1961 if ( pos.move_is_capture(threat)
1962 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1963 || pos.type_of_piece_on(tfrom) == KING)
1964 && pos.move_attacks_square(m, tto))
1967 // Case 3: If the moving piece in the threatened move is a slider, don't
1968 // prune safe moves which block its ray.
1969 if ( piece_is_slider(pos.piece_on(tfrom))
1970 && bit_is_set(squares_between(tfrom, tto), mto)
1971 && pos.see_sign(m) >= 0)
1978 // ok_to_use_TT() returns true if a transposition table score
1979 // can be used at a given point in search.
1981 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1983 Value v = value_from_tt(tte->value(), ply);
1985 return ( tte->depth() >= depth
1986 || v >= Max(value_mate_in(PLY_MAX), beta)
1987 || v < Min(value_mated_in(PLY_MAX), beta))
1989 && ( (is_lower_bound(tte->type()) && v >= beta)
1990 || (is_upper_bound(tte->type()) && v < beta));
1994 // refine_eval() returns the transposition table score if
1995 // possible otherwise falls back on static position evaluation.
1997 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2002 Value v = value_from_tt(tte->value(), ply);
2004 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2005 || (is_upper_bound(tte->type()) && v < defaultEval))
2012 // update_history() registers a good move that produced a beta-cutoff
2013 // in history and marks as failures all the other moves of that ply.
2015 void update_history(const Position& pos, Move move, Depth depth,
2016 Move movesSearched[], int moveCount) {
2020 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2022 for (int i = 0; i < moveCount - 1; i++)
2024 m = movesSearched[i];
2028 if (!pos.move_is_capture_or_promotion(m))
2029 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2034 // update_killers() add a good move that produced a beta-cutoff
2035 // among the killer moves of that ply.
2037 void update_killers(Move m, SearchStack* ss) {
2039 if (m == ss->killers[0])
2042 ss->killers[1] = ss->killers[0];
2047 // update_gains() updates the gains table of a non-capture move given
2048 // the static position evaluation before and after the move.
2050 void update_gains(const Position& pos, Move m, Value before, Value after) {
2053 && before != VALUE_NONE
2054 && after != VALUE_NONE
2055 && pos.captured_piece() == NO_PIECE_TYPE
2056 && !move_is_castle(m)
2057 && !move_is_promotion(m))
2058 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2062 // current_search_time() returns the number of milliseconds which have passed
2063 // since the beginning of the current search.
2065 int current_search_time() {
2067 return get_system_time() - SearchStartTime;
2071 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2073 std::string value_to_uci(Value v) {
2075 std::stringstream s;
2077 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2078 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2080 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2085 // nps() computes the current nodes/second count.
2089 int t = current_search_time();
2090 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2094 // poll() performs two different functions: It polls for user input, and it
2095 // looks at the time consumed so far and decides if it's time to abort the
2100 static int lastInfoTime;
2101 int t = current_search_time();
2106 // We are line oriented, don't read single chars
2107 std::string command;
2109 if (!std::getline(std::cin, command))
2112 if (command == "quit")
2115 PonderSearch = false;
2119 else if (command == "stop")
2122 PonderSearch = false;
2124 else if (command == "ponderhit")
2128 // Print search information
2132 else if (lastInfoTime > t)
2133 // HACK: Must be a new search where we searched less than
2134 // NodesBetweenPolls nodes during the first second of search.
2137 else if (t - lastInfoTime >= 1000)
2144 if (dbg_show_hit_rate)
2145 dbg_print_hit_rate();
2147 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2148 << " time " << t << endl;
2151 // Should we stop the search?
2155 bool stillAtFirstMove = FirstRootMove
2156 && !AspirationFailLow
2157 && t > MaxSearchTime + ExtraSearchTime;
2159 bool noMoreTime = t > AbsoluteMaxSearchTime
2160 || stillAtFirstMove;
2162 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2163 || (ExactMaxTime && t >= ExactMaxTime)
2164 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2169 // ponderhit() is called when the program is pondering (i.e. thinking while
2170 // it's the opponent's turn to move) in order to let the engine know that
2171 // it correctly predicted the opponent's move.
2175 int t = current_search_time();
2176 PonderSearch = false;
2178 bool stillAtFirstMove = FirstRootMove
2179 && !AspirationFailLow
2180 && t > MaxSearchTime + ExtraSearchTime;
2182 bool noMoreTime = t > AbsoluteMaxSearchTime
2183 || stillAtFirstMove;
2185 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2190 // init_ss_array() does a fast reset of the first entries of a SearchStack
2191 // array and of all the excludedMove and skipNullMove entries.
2193 void init_ss_array(SearchStack* ss, int size) {
2195 for (int i = 0; i < size; i++, ss++)
2197 ss->excludedMove = MOVE_NONE;
2198 ss->skipNullMove = false;
2199 ss->reduction = Depth(0);
2202 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2207 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2208 // while the program is pondering. The point is to work around a wrinkle in
2209 // the UCI protocol: When pondering, the engine is not allowed to give a
2210 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2211 // We simply wait here until one of these commands is sent, and return,
2212 // after which the bestmove and pondermove will be printed (in id_loop()).
2214 void wait_for_stop_or_ponderhit() {
2216 std::string command;
2220 if (!std::getline(std::cin, command))
2223 if (command == "quit")
2228 else if (command == "ponderhit" || command == "stop")
2234 // print_pv_info() prints to standard output and eventually to log file information on
2235 // the current PV line. It is called at each iteration or after a new pv is found.
2237 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2239 cout << "info depth " << Iteration
2240 << " score " << value_to_uci(value)
2241 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2242 << " time " << current_search_time()
2243 << " nodes " << TM.nodes_searched()
2247 for (Move* m = pv; *m != MOVE_NONE; m++)
2254 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2255 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2257 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2258 TM.nodes_searched(), value, t, pv) << endl;
2263 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2264 // the PV back into the TT. This makes sure the old PV moves are searched
2265 // first, even if the old TT entries have been overwritten.
2267 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2271 Position p(pos, pos.thread());
2275 for (int i = 0; pv[i] != MOVE_NONE; i++)
2277 tte = TT.retrieve(p.get_key());
2278 if (!tte || tte->move() != pv[i])
2280 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2281 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2283 p.do_move(pv[i], st);
2288 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2289 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2290 // allow to always have a ponder move even when we fail high at root and also a
2291 // long PV to print that is important for position analysis.
2293 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2297 Position p(pos, pos.thread());
2300 assert(bestMove != MOVE_NONE);
2303 p.do_move(pv[ply++], st);
2305 while ( (tte = TT.retrieve(p.get_key())) != NULL
2306 && tte->move() != MOVE_NONE
2307 && move_is_legal(p, tte->move())
2309 && (!p.is_draw() || ply < 2))
2311 pv[ply] = tte->move();
2312 p.do_move(pv[ply++], st);
2314 pv[ply] = MOVE_NONE;
2318 // init_thread() is the function which is called when a new thread is
2319 // launched. It simply calls the idle_loop() function with the supplied
2320 // threadID. There are two versions of this function; one for POSIX
2321 // threads and one for Windows threads.
2323 #if !defined(_MSC_VER)
2325 void* init_thread(void *threadID) {
2327 TM.idle_loop(*(int*)threadID, NULL);
2333 DWORD WINAPI init_thread(LPVOID threadID) {
2335 TM.idle_loop(*(int*)threadID, NULL);
2342 /// The ThreadsManager class
2344 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2345 // get_beta_counters() are getters/setters for the per thread
2346 // counters used to sort the moves at root.
2348 void ThreadsManager::resetNodeCounters() {
2350 for (int i = 0; i < MAX_THREADS; i++)
2351 threads[i].nodes = 0ULL;
2354 void ThreadsManager::resetBetaCounters() {
2356 for (int i = 0; i < MAX_THREADS; i++)
2357 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2360 int64_t ThreadsManager::nodes_searched() const {
2362 int64_t result = 0ULL;
2363 for (int i = 0; i < ActiveThreads; i++)
2364 result += threads[i].nodes;
2369 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2372 for (int i = 0; i < MAX_THREADS; i++)
2374 our += threads[i].betaCutOffs[us];
2375 their += threads[i].betaCutOffs[opposite_color(us)];
2380 // idle_loop() is where the threads are parked when they have no work to do.
2381 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2382 // object for which the current thread is the master.
2384 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2386 assert(threadID >= 0 && threadID < MAX_THREADS);
2390 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2391 // master should exit as last one.
2392 if (AllThreadsShouldExit)
2395 threads[threadID].state = THREAD_TERMINATED;
2399 // If we are not thinking, wait for a condition to be signaled
2400 // instead of wasting CPU time polling for work.
2401 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2404 assert(threadID != 0);
2405 threads[threadID].state = THREAD_SLEEPING;
2407 #if !defined(_MSC_VER)
2408 lock_grab(&WaitLock);
2409 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2410 pthread_cond_wait(&WaitCond, &WaitLock);
2411 lock_release(&WaitLock);
2413 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2417 // If thread has just woken up, mark it as available
2418 if (threads[threadID].state == THREAD_SLEEPING)
2419 threads[threadID].state = THREAD_AVAILABLE;
2421 // If this thread has been assigned work, launch a search
2422 if (threads[threadID].state == THREAD_WORKISWAITING)
2424 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2426 threads[threadID].state = THREAD_SEARCHING;
2428 if (threads[threadID].splitPoint->pvNode)
2429 sp_search<PV>(threads[threadID].splitPoint, threadID);
2431 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2433 assert(threads[threadID].state == THREAD_SEARCHING);
2435 threads[threadID].state = THREAD_AVAILABLE;
2438 // If this thread is the master of a split point and all slaves have
2439 // finished their work at this split point, return from the idle loop.
2441 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2443 if (i == ActiveThreads)
2445 // Because sp->slaves[] is reset under lock protection,
2446 // be sure sp->lock has been released before to return.
2447 lock_grab(&(sp->lock));
2448 lock_release(&(sp->lock));
2450 assert(threads[threadID].state == THREAD_AVAILABLE);
2452 threads[threadID].state = THREAD_SEARCHING;
2459 // init_threads() is called during startup. It launches all helper threads,
2460 // and initializes the split point stack and the global locks and condition
2463 void ThreadsManager::init_threads() {
2468 #if !defined(_MSC_VER)
2469 pthread_t pthread[1];
2472 // Initialize global locks
2473 lock_init(&MPLock, NULL);
2474 lock_init(&WaitLock, NULL);
2476 #if !defined(_MSC_VER)
2477 pthread_cond_init(&WaitCond, NULL);
2479 for (i = 0; i < MAX_THREADS; i++)
2480 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2483 // Initialize splitPoints[] locks
2484 for (i = 0; i < MAX_THREADS; i++)
2485 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2486 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2488 // Will be set just before program exits to properly end the threads
2489 AllThreadsShouldExit = false;
2491 // Threads will be put to sleep as soon as created
2492 AllThreadsShouldSleep = true;
2494 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2496 threads[0].state = THREAD_SEARCHING;
2497 for (i = 1; i < MAX_THREADS; i++)
2498 threads[i].state = THREAD_AVAILABLE;
2500 // Launch the helper threads
2501 for (i = 1; i < MAX_THREADS; i++)
2504 #if !defined(_MSC_VER)
2505 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2507 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2512 cout << "Failed to create thread number " << i << endl;
2513 Application::exit_with_failure();
2516 // Wait until the thread has finished launching and is gone to sleep
2517 while (threads[i].state != THREAD_SLEEPING) {}
2522 // exit_threads() is called when the program exits. It makes all the
2523 // helper threads exit cleanly.
2525 void ThreadsManager::exit_threads() {
2527 ActiveThreads = MAX_THREADS; // HACK
2528 AllThreadsShouldSleep = true; // HACK
2529 wake_sleeping_threads();
2531 // This makes the threads to exit idle_loop()
2532 AllThreadsShouldExit = true;
2534 // Wait for thread termination
2535 for (int i = 1; i < MAX_THREADS; i++)
2536 while (threads[i].state != THREAD_TERMINATED) {}
2538 // Now we can safely destroy the locks
2539 for (int i = 0; i < MAX_THREADS; i++)
2540 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2541 lock_destroy(&(threads[i].splitPoints[j].lock));
2543 lock_destroy(&WaitLock);
2544 lock_destroy(&MPLock);
2548 // thread_should_stop() checks whether the thread should stop its search.
2549 // This can happen if a beta cutoff has occurred in the thread's currently
2550 // active split point, or in some ancestor of the current split point.
2552 bool ThreadsManager::thread_should_stop(int threadID) const {
2554 assert(threadID >= 0 && threadID < ActiveThreads);
2558 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2563 // thread_is_available() checks whether the thread with threadID "slave" is
2564 // available to help the thread with threadID "master" at a split point. An
2565 // obvious requirement is that "slave" must be idle. With more than two
2566 // threads, this is not by itself sufficient: If "slave" is the master of
2567 // some active split point, it is only available as a slave to the other
2568 // threads which are busy searching the split point at the top of "slave"'s
2569 // split point stack (the "helpful master concept" in YBWC terminology).
2571 bool ThreadsManager::thread_is_available(int slave, int master) const {
2573 assert(slave >= 0 && slave < ActiveThreads);
2574 assert(master >= 0 && master < ActiveThreads);
2575 assert(ActiveThreads > 1);
2577 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2580 // Make a local copy to be sure doesn't change under our feet
2581 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2583 if (localActiveSplitPoints == 0)
2584 // No active split points means that the thread is available as
2585 // a slave for any other thread.
2588 if (ActiveThreads == 2)
2591 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2592 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2593 // could have been set to 0 by another thread leading to an out of bound access.
2594 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2601 // available_thread_exists() tries to find an idle thread which is available as
2602 // a slave for the thread with threadID "master".
2604 bool ThreadsManager::available_thread_exists(int master) const {
2606 assert(master >= 0 && master < ActiveThreads);
2607 assert(ActiveThreads > 1);
2609 for (int i = 0; i < ActiveThreads; i++)
2610 if (thread_is_available(i, master))
2617 // split() does the actual work of distributing the work at a node between
2618 // several available threads. If it does not succeed in splitting the
2619 // node (because no idle threads are available, or because we have no unused
2620 // split point objects), the function immediately returns. If splitting is
2621 // possible, a SplitPoint object is initialized with all the data that must be
2622 // copied to the helper threads and we tell our helper threads that they have
2623 // been assigned work. This will cause them to instantly leave their idle loops
2624 // and call sp_search(). When all threads have returned from sp_search() then
2627 template <bool Fake>
2628 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2629 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2630 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2632 assert(ply > 0 && ply < PLY_MAX);
2633 assert(*bestValue >= -VALUE_INFINITE);
2634 assert(*bestValue <= *alpha);
2635 assert(*alpha < beta);
2636 assert(beta <= VALUE_INFINITE);
2637 assert(depth > Depth(0));
2638 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2639 assert(ActiveThreads > 1);
2641 int i, master = p.thread();
2642 Thread& masterThread = threads[master];
2646 // If no other thread is available to help us, or if we have too many
2647 // active split points, don't split.
2648 if ( !available_thread_exists(master)
2649 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2651 lock_release(&MPLock);
2655 // Pick the next available split point object from the split point stack
2656 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2658 // Initialize the split point object
2659 splitPoint.parent = masterThread.splitPoint;
2660 splitPoint.stopRequest = false;
2661 splitPoint.ply = ply;
2662 splitPoint.depth = depth;
2663 splitPoint.threatMove = threatMove;
2664 splitPoint.mateThreat = mateThreat;
2665 splitPoint.alpha = *alpha;
2666 splitPoint.beta = beta;
2667 splitPoint.pvNode = pvNode;
2668 splitPoint.bestValue = *bestValue;
2670 splitPoint.moveCount = *moveCount;
2671 splitPoint.pos = &p;
2672 splitPoint.parentSstack = ss;
2673 for (i = 0; i < ActiveThreads; i++)
2674 splitPoint.slaves[i] = 0;
2676 masterThread.splitPoint = &splitPoint;
2678 // If we are here it means we are not available
2679 assert(masterThread.state != THREAD_AVAILABLE);
2681 int workersCnt = 1; // At least the master is included
2683 // Allocate available threads setting state to THREAD_BOOKED
2684 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2685 if (thread_is_available(i, master))
2687 threads[i].state = THREAD_BOOKED;
2688 threads[i].splitPoint = &splitPoint;
2689 splitPoint.slaves[i] = 1;
2693 assert(Fake || workersCnt > 1);
2695 // We can release the lock because slave threads are already booked and master is not available
2696 lock_release(&MPLock);
2698 // Tell the threads that they have work to do. This will make them leave
2699 // their idle loop. But before copy search stack tail for each thread.
2700 for (i = 0; i < ActiveThreads; i++)
2701 if (i == master || splitPoint.slaves[i])
2703 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2705 assert(i == master || threads[i].state == THREAD_BOOKED);
2707 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2710 // Everything is set up. The master thread enters the idle loop, from
2711 // which it will instantly launch a search, because its state is
2712 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2713 // idle loop, which means that the main thread will return from the idle
2714 // loop when all threads have finished their work at this split point.
2715 idle_loop(master, &splitPoint);
2717 // We have returned from the idle loop, which means that all threads are
2718 // finished. Update alpha and bestValue, and return.
2721 *alpha = splitPoint.alpha;
2722 *bestValue = splitPoint.bestValue;
2723 masterThread.activeSplitPoints--;
2724 masterThread.splitPoint = splitPoint.parent;
2726 lock_release(&MPLock);
2730 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2731 // to start a new search from the root.
2733 void ThreadsManager::wake_sleeping_threads() {
2735 assert(AllThreadsShouldSleep);
2736 assert(ActiveThreads > 0);
2738 AllThreadsShouldSleep = false;
2740 if (ActiveThreads == 1)
2743 #if !defined(_MSC_VER)
2744 pthread_mutex_lock(&WaitLock);
2745 pthread_cond_broadcast(&WaitCond);
2746 pthread_mutex_unlock(&WaitLock);
2748 for (int i = 1; i < MAX_THREADS; i++)
2749 SetEvent(SitIdleEvent[i]);
2755 // put_threads_to_sleep() makes all the threads go to sleep just before
2756 // to leave think(), at the end of the search. Threads should have already
2757 // finished the job and should be idle.
2759 void ThreadsManager::put_threads_to_sleep() {
2761 assert(!AllThreadsShouldSleep);
2763 // This makes the threads to go to sleep
2764 AllThreadsShouldSleep = true;
2767 /// The RootMoveList class
2769 // RootMoveList c'tor
2771 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2773 SearchStack ss[PLY_MAX_PLUS_2];
2774 MoveStack mlist[MaxRootMoves];
2776 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2778 // Initialize search stack
2779 init_ss_array(ss, PLY_MAX_PLUS_2);
2780 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2781 ss[0].eval = VALUE_NONE;
2783 // Generate all legal moves
2784 MoveStack* last = generate_moves(pos, mlist);
2786 // Add each move to the moves[] array
2787 for (MoveStack* cur = mlist; cur != last; cur++)
2789 bool includeMove = includeAllMoves;
2791 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2792 includeMove = (searchMoves[k] == cur->move);
2797 // Find a quick score for the move
2798 pos.do_move(cur->move, st);
2799 ss[0].currentMove = cur->move;
2800 moves[count].move = cur->move;
2801 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2802 moves[count].pv[0] = cur->move;
2803 moves[count].pv[1] = MOVE_NONE;
2804 pos.undo_move(cur->move);
2811 // RootMoveList simple methods definitions
2813 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2815 moves[moveNum].nodes = nodes;
2816 moves[moveNum].cumulativeNodes += nodes;
2819 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2821 moves[moveNum].ourBeta = our;
2822 moves[moveNum].theirBeta = their;
2825 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2829 for (j = 0; pv[j] != MOVE_NONE; j++)
2830 moves[moveNum].pv[j] = pv[j];
2832 moves[moveNum].pv[j] = MOVE_NONE;
2836 // RootMoveList::sort() sorts the root move list at the beginning of a new
2839 void RootMoveList::sort() {
2841 sort_multipv(count - 1); // Sort all items
2845 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2846 // list by their scores and depths. It is used to order the different PVs
2847 // correctly in MultiPV mode.
2849 void RootMoveList::sort_multipv(int n) {
2853 for (i = 1; i <= n; i++)
2855 RootMove rm = moves[i];
2856 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2857 moves[j] = moves[j - 1];