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++; }
79 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
81 void resetNodeCounters();
82 void resetBetaCounters();
83 int64_t nodes_searched() const;
84 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { mp_score = 0; nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : mp_score <= m.mp_score;
134 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
135 Move pv[PLY_MAX_PLUS_2];
139 // The RootMoveList class is essentially an array of RootMove objects, with
140 // a handful of methods for accessing the data in the individual moves.
145 RootMoveList(Position& pos, Move searchMoves[]);
147 void set_mp_scores(const Position &pos);
149 int move_count() const { return count; }
150 Move get_move(int moveNum) const { return moves[moveNum].move; }
151 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
152 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
153 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
154 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
156 void set_move_nodes(int moveNum, int64_t nodes);
157 void set_beta_counters(int moveNum, int64_t our, int64_t their);
158 void set_move_pv(int moveNum, const Move pv[]);
160 void sort_multipv(int n);
163 static const int MaxRootMoves = 500;
164 RootMove moves[MaxRootMoves];
173 // Maximum depth for razoring
174 const Depth RazorDepth = 4 * ONE_PLY;
176 // Dynamic razoring margin based on depth
177 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
179 // Step 8. Null move search with verification search
181 // Null move margin. A null move search will not be done if the static
182 // evaluation of the position is more than NullMoveMargin below beta.
183 const Value NullMoveMargin = Value(0x200);
185 // Maximum depth for use of dynamic threat detection when null move fails low
186 const Depth ThreatDepth = 5 * ONE_PLY;
188 // Step 9. Internal iterative deepening
190 // Minimum depth for use of internal iterative deepening
191 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
193 // At Non-PV nodes we do an internal iterative deepening search
194 // when the static evaluation is bigger then beta - IIDMargin.
195 const Value IIDMargin = Value(0x100);
197 // Step 11. Decide the new search depth
199 // Extensions. Configurable UCI options
200 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
201 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
202 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
204 // Minimum depth for use of singular extension
205 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
207 // If the TT move is at least SingularExtensionMargin better then the
208 // remaining ones we will extend it.
209 const Value SingularExtensionMargin = Value(0x20);
211 // Step 12. Futility pruning
213 // Futility margin for quiescence search
214 const Value FutilityMarginQS = Value(0x80);
216 // Futility lookup tables (initialized at startup) and their getter functions
217 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
218 int FutilityMoveCountArray[32]; // [depth]
220 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
221 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
223 // Step 14. Reduced search
225 // Reduction lookup tables (initialized at startup) and their getter functions
226 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
228 template <NodeType PV>
229 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
231 // Common adjustments
233 // Search depth at iteration 1
234 const Depth InitialDepth = ONE_PLY;
236 // Easy move margin. An easy move candidate must be at least this much
237 // better than the second best move.
238 const Value EasyMoveMargin = Value(0x200);
246 // Scores and number of times the best move changed for each iteration
247 Value ValueByIteration[PLY_MAX_PLUS_2];
248 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
250 // Search window management
256 // Time managment variables
257 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
258 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
259 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
264 std::ofstream LogFile;
266 // Multi-threads related variables
267 Depth MinimumSplitDepth;
268 int MaxThreadsPerSplitPoint;
269 ThreadsManager ThreadsMgr;
271 // Node counters, used only by thread[0] but try to keep in different cache
272 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
274 int NodesBetweenPolls = 30000;
281 Value id_loop(const Position& pos, Move searchMoves[]);
282 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
284 template <NodeType PvNode>
285 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int 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 void sp_search(SplitPoint* sp, int threadID);
293 template <NodeType PvNode>
294 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
296 bool connected_moves(const Position& pos, Move m1, Move m2);
297 bool value_is_mate(Value value);
298 Value value_to_tt(Value v, int ply);
299 Value value_from_tt(Value v, int ply);
300 bool move_is_killer(Move m, SearchStack* ss);
301 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
302 bool connected_threat(const Position& pos, Move m, Move threat);
303 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
304 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
305 void update_killers(Move m, SearchStack* ss);
306 void update_gains(const Position& pos, Move move, Value before, Value after);
308 int current_search_time();
309 std::string value_to_uci(Value v);
313 void wait_for_stop_or_ponderhit();
314 void init_ss_array(SearchStack* ss, int size);
315 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
316 void insert_pv_in_tt(const Position& pos, Move pv[]);
317 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
319 #if !defined(_MSC_VER)
320 void *init_thread(void *threadID);
322 DWORD WINAPI init_thread(LPVOID threadID);
332 /// init_threads(), exit_threads() and nodes_searched() are helpers to
333 /// give accessibility to some TM methods from outside of current file.
335 void init_threads() { ThreadsMgr.init_threads(); }
336 void exit_threads() { ThreadsMgr.exit_threads(); }
337 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (ONE_PLY == 2)
345 int hd; // half depth (ONE_PLY == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
352 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
357 // Init futility margins array
358 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
367 /// perft() is our utility to verify move generation is bug free. All the legal
368 /// moves up to given depth are generated and counted and the sum returned.
370 int perft(Position& pos, Depth depth)
372 MoveStack mlist[256];
377 // Generate all legal moves
378 MoveStack* last = generate_moves(pos, mlist);
380 // If we are at the last ply we don't need to do and undo
381 // the moves, just to count them.
382 if (depth <= ONE_PLY)
383 return int(last - mlist);
385 // Loop through all legal moves
387 for (MoveStack* cur = mlist; cur != last; cur++)
390 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
391 sum += perft(pos, depth - ONE_PLY);
398 /// think() is the external interface to Stockfish's search, and is called when
399 /// the program receives the UCI 'go' command. It initializes various
400 /// search-related global variables, and calls root_search(). It returns false
401 /// when a quit command is received during the search.
403 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
404 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
406 // Initialize global search variables
407 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
409 ThreadsMgr.resetNodeCounters();
410 SearchStartTime = get_system_time();
411 ExactMaxTime = maxTime;
414 InfiniteSearch = infinite;
415 PonderSearch = ponder;
416 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
418 // Look for a book move, only during games, not tests
419 if (UseTimeManagement && get_option_value_bool("OwnBook"))
421 if (get_option_value_string("Book File") != OpeningBook.file_name())
422 OpeningBook.open(get_option_value_string("Book File"));
424 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
425 if (bookMove != MOVE_NONE)
428 wait_for_stop_or_ponderhit();
430 cout << "bestmove " << bookMove << endl;
435 // Read UCI option values
436 TT.set_size(get_option_value_int("Hash"));
437 if (button_was_pressed("Clear Hash"))
440 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
441 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
442 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
443 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
444 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
445 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
446 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
447 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
448 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
449 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
450 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
451 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
453 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
454 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
455 MultiPV = get_option_value_int("MultiPV");
456 Chess960 = get_option_value_bool("UCI_Chess960");
457 UseLogFile = get_option_value_bool("Use Search Log");
460 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
462 read_weights(pos.side_to_move());
464 // Set the number of active threads
465 int newActiveThreads = get_option_value_int("Threads");
466 if (newActiveThreads != ThreadsMgr.active_threads())
468 ThreadsMgr.set_active_threads(newActiveThreads);
469 init_eval(ThreadsMgr.active_threads());
472 // Wake up sleeping threads
473 ThreadsMgr.wake_sleeping_threads();
476 int myTime = time[pos.side_to_move()];
477 int myIncrement = increment[pos.side_to_move()];
478 if (UseTimeManagement)
479 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
481 // Set best NodesBetweenPolls interval to avoid lagging under
482 // heavy time pressure.
484 NodesBetweenPolls = Min(MaxNodes, 30000);
485 else if (myTime && myTime < 1000)
486 NodesBetweenPolls = 1000;
487 else if (myTime && myTime < 5000)
488 NodesBetweenPolls = 5000;
490 NodesBetweenPolls = 30000;
492 // Write search information to log file
494 LogFile << "Searching: " << pos.to_fen() << endl
495 << "infinite: " << infinite
496 << " ponder: " << ponder
497 << " time: " << myTime
498 << " increment: " << myIncrement
499 << " moves to go: " << movesToGo << endl;
501 // We're ready to start thinking. Call the iterative deepening loop function
502 id_loop(pos, searchMoves);
507 ThreadsMgr.put_threads_to_sleep();
515 // id_loop() is the main iterative deepening loop. It calls root_search
516 // repeatedly with increasing depth until the allocated thinking time has
517 // been consumed, the user stops the search, or the maximum search depth is
520 Value id_loop(const Position& pos, Move searchMoves[]) {
522 Position p(pos, pos.thread());
523 SearchStack ss[PLY_MAX_PLUS_2];
524 Move pv[PLY_MAX_PLUS_2];
525 Move EasyMove = MOVE_NONE;
526 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
528 // Moves to search are verified, copied, scored and sorted
529 RootMoveList rml(p, searchMoves);
531 // Handle special case of searching on a mate/stale position
532 if (rml.move_count() == 0)
535 wait_for_stop_or_ponderhit();
537 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
540 // Print RootMoveList startup scoring to the standard output,
541 // so to output information also for iteration 1.
542 cout << "info depth " << 1
543 << "\ninfo depth " << 1
544 << " score " << value_to_uci(rml.get_move_score(0))
545 << " time " << current_search_time()
546 << " nodes " << ThreadsMgr.nodes_searched()
548 << " pv " << rml.get_move(0) << "\n";
553 init_ss_array(ss, PLY_MAX_PLUS_2);
554 pv[0] = pv[1] = MOVE_NONE;
555 ValueByIteration[1] = rml.get_move_score(0);
558 // Is one move significantly better than others after initial scoring ?
559 if ( rml.move_count() == 1
560 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
561 EasyMove = rml.get_move(0);
563 // Iterative deepening loop
564 while (Iteration < PLY_MAX)
566 // Initialize iteration
568 BestMoveChangesByIteration[Iteration] = 0;
570 cout << "info depth " << Iteration << endl;
572 // Calculate dynamic aspiration window based on previous iterations
573 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
575 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
576 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
578 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
579 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
581 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
582 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
585 // Search to the current depth, rml is updated and sorted, alpha and beta could change
586 value = root_search(p, ss, pv, rml, &alpha, &beta);
588 // Write PV to transposition table, in case the relevant entries have
589 // been overwritten during the search.
590 insert_pv_in_tt(p, pv);
593 break; // Value cannot be trusted. Break out immediately!
595 //Save info about search result
596 ValueByIteration[Iteration] = value;
598 // Drop the easy move if differs from the new best move
599 if (pv[0] != EasyMove)
600 EasyMove = MOVE_NONE;
602 if (UseTimeManagement)
605 bool stopSearch = false;
607 // Stop search early if there is only a single legal move,
608 // we search up to Iteration 6 anyway to get a proper score.
609 if (Iteration >= 6 && rml.move_count() == 1)
612 // Stop search early when the last two iterations returned a mate score
614 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
615 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
618 // Stop search early if one move seems to be much better than the others
619 int64_t nodes = ThreadsMgr.nodes_searched();
622 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
623 && current_search_time() > TimeMgr.available_time() / 16)
624 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
625 && current_search_time() > TimeMgr.available_time() / 32)))
628 // Add some extra time if the best move has changed during the last two iterations
629 if (Iteration > 5 && Iteration <= 50)
630 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
631 BestMoveChangesByIteration[Iteration-1]);
633 // Stop search if most of MaxSearchTime is consumed at the end of the
634 // iteration. We probably don't have enough time to search the first
635 // move at the next iteration anyway.
636 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
642 StopOnPonderhit = true;
648 if (MaxDepth && Iteration >= MaxDepth)
652 // If we are pondering or in infinite search, we shouldn't print the
653 // best move before we are told to do so.
654 if (!AbortSearch && (PonderSearch || InfiniteSearch))
655 wait_for_stop_or_ponderhit();
657 // Print final search statistics
658 cout << "info nodes " << ThreadsMgr.nodes_searched()
660 << " time " << current_search_time() << endl;
662 // Print the best move and the ponder move to the standard output
663 if (pv[0] == MOVE_NONE)
665 pv[0] = rml.get_move(0);
669 assert(pv[0] != MOVE_NONE);
671 cout << "bestmove " << pv[0];
673 if (pv[1] != MOVE_NONE)
674 cout << " ponder " << pv[1];
681 dbg_print_mean(LogFile);
683 if (dbg_show_hit_rate)
684 dbg_print_hit_rate(LogFile);
686 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
687 << "\nNodes/second: " << nps()
688 << "\nBest move: " << move_to_san(p, pv[0]);
691 p.do_move(pv[0], st);
692 LogFile << "\nPonder move: "
693 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
696 return rml.get_move_score(0);
700 // root_search() is the function which searches the root node. It is
701 // similar to search_pv except that it uses a different move ordering
702 // scheme, prints some information to the standard output and handles
703 // the fail low/high loops.
705 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
712 Depth depth, ext, newDepth;
713 Value value, alpha, beta;
714 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
715 int researchCountFH, researchCountFL;
717 researchCountFH = researchCountFL = 0;
720 isCheck = pos.is_check();
721 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
723 // Step 1. Initialize node (polling is omitted at root)
724 ss->currentMove = ss->bestMove = MOVE_NONE;
726 // Step 2. Check for aborted search (omitted at root)
727 // Step 3. Mate distance pruning (omitted at root)
728 // Step 4. Transposition table lookup (omitted at root)
730 // Step 5. Evaluate the position statically
731 // At root we do this only to get reference value for child nodes
732 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
734 // Step 6. Razoring (omitted at root)
735 // Step 7. Static null move pruning (omitted at root)
736 // Step 8. Null move search with verification search (omitted at root)
737 // Step 9. Internal iterative deepening (omitted at root)
739 // Step extra. Fail low loop
740 // We start with small aspiration window and in case of fail low, we research
741 // with bigger window until we are not failing low anymore.
744 // Sort the moves before to (re)search
745 rml.set_mp_scores(pos);
748 // Step 10. Loop through all moves in the root move list
749 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
751 // This is used by time management
752 FirstRootMove = (i == 0);
754 // Save the current node count before the move is searched
755 nodes = ThreadsMgr.nodes_searched();
757 // Reset beta cut-off counters
758 ThreadsMgr.resetBetaCounters();
760 // Pick the next root move, and print the move and the move number to
761 // the standard output.
762 move = ss->currentMove = rml.get_move(i);
764 if (current_search_time() >= 1000)
765 cout << "info currmove " << move
766 << " currmovenumber " << i + 1 << endl;
768 moveIsCheck = pos.move_is_check(move);
769 captureOrPromotion = pos.move_is_capture_or_promotion(move);
771 // Step 11. Decide the new search depth
772 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
773 newDepth = depth + ext;
775 // Step 12. Futility pruning (omitted at root)
777 // Step extra. Fail high loop
778 // If move fails high, we research with bigger window until we are not failing
780 value = - VALUE_INFINITE;
784 // Step 13. Make the move
785 pos.do_move(move, st, ci, moveIsCheck);
787 // Step extra. pv search
788 // We do pv search for first moves (i < MultiPV)
789 // and for fail high research (value > alpha)
790 if (i < MultiPV || value > alpha)
792 // Aspiration window is disabled in multi-pv case
794 alpha = -VALUE_INFINITE;
796 // Full depth PV search, done on first move or after a fail high
797 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
801 // Step 14. Reduced search
802 // if the move fails high will be re-searched at full depth
803 bool doFullDepthSearch = true;
805 if ( depth >= 3 * ONE_PLY
807 && !captureOrPromotion
808 && !move_is_castle(move))
810 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
813 assert(newDepth-ss->reduction >= ONE_PLY);
815 // Reduced depth non-pv search using alpha as upperbound
816 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
817 doFullDepthSearch = (value > alpha);
820 // The move failed high, but if reduction is very big we could
821 // face a false positive, retry with a less aggressive reduction,
822 // if the move fails high again then go with full depth search.
823 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
825 assert(newDepth - ONE_PLY >= ONE_PLY);
827 ss->reduction = ONE_PLY;
828 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
829 doFullDepthSearch = (value > alpha);
831 ss->reduction = DEPTH_ZERO; // Restore original reduction
834 // Step 15. Full depth search
835 if (doFullDepthSearch)
837 // Full depth non-pv search using alpha as upperbound
838 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
840 // If we are above alpha then research at same depth but as PV
841 // to get a correct score or eventually a fail high above beta.
843 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
847 // Step 16. Undo move
850 // Can we exit fail high loop ?
851 if (AbortSearch || value < beta)
854 // We are failing high and going to do a research. It's important to update
855 // the score before research in case we run out of time while researching.
856 rml.set_move_score(i, value);
858 extract_pv_from_tt(pos, move, pv);
859 rml.set_move_pv(i, pv);
861 // Print information to the standard output
862 print_pv_info(pos, pv, alpha, beta, value);
864 // Prepare for a research after a fail high, each time with a wider window
865 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
868 } // End of fail high loop
870 // Finished searching the move. If AbortSearch is true, the search
871 // was aborted because the user interrupted the search or because we
872 // ran out of time. In this case, the return value of the search cannot
873 // be trusted, and we break out of the loop without updating the best
878 // Remember beta-cutoff and searched nodes counts for this move. The
879 // info is used to sort the root moves for the next iteration.
881 ThreadsMgr.get_beta_counters(pos.side_to_move(), our, their);
882 rml.set_beta_counters(i, our, their);
883 rml.set_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
885 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
886 assert(value < beta);
888 // Step 17. Check for new best move
889 if (value <= alpha && i >= MultiPV)
890 rml.set_move_score(i, -VALUE_INFINITE);
893 // PV move or new best move!
896 rml.set_move_score(i, value);
898 extract_pv_from_tt(pos, move, pv);
899 rml.set_move_pv(i, pv);
903 // We record how often the best move has been changed in each
904 // iteration. This information is used for time managment: When
905 // the best move changes frequently, we allocate some more time.
907 BestMoveChangesByIteration[Iteration]++;
909 // Print information to the standard output
910 print_pv_info(pos, pv, alpha, beta, value);
912 // Raise alpha to setup proper non-pv search upper bound
919 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
921 cout << "info multipv " << j + 1
922 << " score " << value_to_uci(rml.get_move_score(j))
923 << " depth " << (j <= i ? Iteration : Iteration - 1)
924 << " time " << current_search_time()
925 << " nodes " << ThreadsMgr.nodes_searched()
929 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
930 cout << rml.get_move_pv(j, k) << " ";
934 alpha = rml.get_move_score(Min(i, MultiPV - 1));
936 } // PV move or new best move
938 assert(alpha >= *alphaPtr);
940 AspirationFailLow = (alpha == *alphaPtr);
942 if (AspirationFailLow && StopOnPonderhit)
943 StopOnPonderhit = false;
946 // Can we exit fail low loop ?
947 if (AbortSearch || !AspirationFailLow)
950 // Prepare for a research after a fail low, each time with a wider window
951 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
956 // Sort the moves before to return
963 // search<>() is the main search function for both PV and non-PV nodes
965 template <NodeType PvNode>
966 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
968 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
969 assert(beta > alpha && beta <= VALUE_INFINITE);
970 assert(PvNode || alpha == beta - 1);
971 assert(ply > 0 && ply < PLY_MAX);
972 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
974 Move movesSearched[256];
979 Move ttMove, move, excludedMove, threatMove;
981 Value bestValue, value, oldAlpha;
982 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
983 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
984 bool mateThreat = false;
986 int threadID = pos.thread();
987 refinedValue = bestValue = value = -VALUE_INFINITE;
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->king_danger());
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.
1043 isCheck = pos.is_check();
1045 ss->eval = VALUE_NONE;
1048 assert(tte->static_value() != VALUE_NONE);
1050 ss->eval = tte->static_value();
1051 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1052 refinedValue = refine_eval(tte, ss->eval, ply);
1056 refinedValue = ss->eval = evaluate(pos, ei);
1057 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1060 // Save gain for the parent non-capture move
1061 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1063 // Step 6. Razoring (is omitted in PV nodes)
1065 && depth < RazorDepth
1067 && refinedValue < beta - razor_margin(depth)
1068 && ttMove == MOVE_NONE
1069 && (ss-1)->currentMove != MOVE_NULL
1070 && !value_is_mate(beta)
1071 && !pos.has_pawn_on_7th(pos.side_to_move()))
1073 Value rbeta = beta - razor_margin(depth);
1074 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1076 // Logically we should return (v + razor_margin(depth)), but
1077 // surprisingly this did slightly weaker in tests.
1081 // Step 7. Static null move pruning (is omitted in PV nodes)
1082 // We're betting that the opponent doesn't have a move that will reduce
1083 // the score by more than futility_margin(depth) if we do a null move.
1085 && !ss->skipNullMove
1086 && depth < RazorDepth
1088 && refinedValue >= beta + futility_margin(depth, 0)
1089 && !value_is_mate(beta)
1090 && pos.non_pawn_material(pos.side_to_move()))
1091 return refinedValue - futility_margin(depth, 0);
1093 // Step 8. Null move search with verification search (is omitted in PV nodes)
1094 // When we jump directly to qsearch() we do a null move only if static value is
1095 // at least beta. Otherwise we do a null move if static value is not more than
1096 // NullMoveMargin under beta.
1098 && !ss->skipNullMove
1101 && refinedValue >= beta - (depth >= 4 * ONE_PLY ? NullMoveMargin : 0)
1102 && !value_is_mate(beta)
1103 && pos.non_pawn_material(pos.side_to_move()))
1105 ss->currentMove = MOVE_NULL;
1107 // Null move dynamic reduction based on depth
1108 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1110 // Null move dynamic reduction based on value
1111 if (refinedValue - beta > PawnValueMidgame)
1114 pos.do_null_move(st);
1115 (ss+1)->skipNullMove = true;
1117 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1118 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1119 (ss+1)->skipNullMove = false;
1120 pos.undo_null_move();
1122 if (nullValue >= beta)
1124 // Do not return unproven mate scores
1125 if (nullValue >= value_mate_in(PLY_MAX))
1128 if (depth < 6 * ONE_PLY)
1131 // Do verification search at high depths
1132 ss->skipNullMove = true;
1133 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1134 ss->skipNullMove = false;
1141 // The null move failed low, which means that we may be faced with
1142 // some kind of threat. If the previous move was reduced, check if
1143 // the move that refuted the null move was somehow connected to the
1144 // move which was reduced. If a connection is found, return a fail
1145 // low score (which will cause the reduced move to fail high in the
1146 // parent node, which will trigger a re-search with full depth).
1147 if (nullValue == value_mated_in(ply + 2))
1150 threatMove = (ss+1)->bestMove;
1151 if ( depth < ThreatDepth
1152 && (ss-1)->reduction
1153 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1158 // Step 9. Internal iterative deepening
1159 if ( depth >= IIDDepth[PvNode]
1160 && ttMove == MOVE_NONE
1161 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1163 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1165 ss->skipNullMove = true;
1166 search<PvNode>(pos, ss, alpha, beta, d, ply);
1167 ss->skipNullMove = false;
1169 ttMove = ss->bestMove;
1170 tte = TT.retrieve(posKey);
1173 // Expensive mate threat detection (only for PV nodes)
1175 mateThreat = pos.has_mate_threat();
1177 // Initialize a MovePicker object for the current position
1178 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1180 ss->bestMove = MOVE_NONE;
1181 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1182 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1185 && !excludedMove // Do not allow recursive singular extension search
1186 && (tte->type() & VALUE_TYPE_LOWER)
1187 && tte->depth() >= depth - 3 * ONE_PLY;
1189 // Step 10. Loop through moves
1190 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1191 while ( bestValue < beta
1192 && (move = mp.get_next_move()) != MOVE_NONE
1193 && !ThreadsMgr.thread_should_stop(threadID))
1195 assert(move_is_ok(move));
1197 if (move == excludedMove)
1200 moveIsCheck = pos.move_is_check(move, ci);
1201 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1203 // Step 11. Decide the new search depth
1204 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1206 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1207 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1208 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1209 // lower then ttValue minus a margin then we extend ttMove.
1210 if ( singularExtensionNode
1211 && move == tte->move()
1214 Value ttValue = value_from_tt(tte->value(), ply);
1216 if (abs(ttValue) < VALUE_KNOWN_WIN)
1218 Value b = ttValue - SingularExtensionMargin;
1219 ss->excludedMove = move;
1220 ss->skipNullMove = true;
1221 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1222 ss->skipNullMove = false;
1223 ss->excludedMove = MOVE_NONE;
1224 ss->bestMove = MOVE_NONE;
1230 newDepth = depth - ONE_PLY + ext;
1232 // Update current move (this must be done after singular extension search)
1233 movesSearched[moveCount++] = ss->currentMove = move;
1235 // Step 12. Futility pruning (is omitted in PV nodes)
1237 && !captureOrPromotion
1241 && !move_is_castle(move))
1243 // Move count based pruning
1244 if ( moveCount >= futility_move_count(depth)
1245 && !(threatMove && connected_threat(pos, move, threatMove))
1246 && bestValue > value_mated_in(PLY_MAX))
1249 // Value based pruning
1250 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1251 // but fixing this made program slightly weaker.
1252 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1253 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1254 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1256 if (futilityValueScaled < beta)
1258 if (futilityValueScaled > bestValue)
1259 bestValue = futilityValueScaled;
1264 // Step 13. Make the move
1265 pos.do_move(move, st, ci, moveIsCheck);
1267 // Step extra. pv search (only in PV nodes)
1268 // The first move in list is the expected PV
1269 if (PvNode && moveCount == 1)
1270 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1271 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1274 // Step 14. Reduced depth search
1275 // If the move fails high will be re-searched at full depth.
1276 bool doFullDepthSearch = true;
1278 if ( depth >= 3 * ONE_PLY
1279 && !captureOrPromotion
1281 && !move_is_castle(move)
1282 && !move_is_killer(move, ss))
1284 ss->reduction = reduction<PvNode>(depth, moveCount);
1287 Depth d = newDepth - ss->reduction;
1288 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1289 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1291 doFullDepthSearch = (value > alpha);
1294 // The move failed high, but if reduction is very big we could
1295 // face a false positive, retry with a less aggressive reduction,
1296 // if the move fails high again then go with full depth search.
1297 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1299 assert(newDepth - ONE_PLY >= ONE_PLY);
1301 ss->reduction = ONE_PLY;
1302 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1303 doFullDepthSearch = (value > alpha);
1305 ss->reduction = DEPTH_ZERO; // Restore original reduction
1308 // Step 15. Full depth search
1309 if (doFullDepthSearch)
1311 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1312 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1314 // Step extra. pv search (only in PV nodes)
1315 // Search only for possible new PV nodes, if instead value >= beta then
1316 // parent node fails low with value <= alpha and tries another move.
1317 if (PvNode && value > alpha && value < beta)
1318 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1319 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1323 // Step 16. Undo move
1324 pos.undo_move(move);
1326 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1328 // Step 17. Check for new best move
1329 if (value > bestValue)
1334 if (PvNode && value < beta) // We want always alpha < beta
1337 if (value == value_mate_in(ply + 1))
1338 ss->mateKiller = move;
1340 ss->bestMove = move;
1344 // Step 18. Check for split
1345 if ( depth >= MinimumSplitDepth
1346 && ThreadsMgr.active_threads() > 1
1348 && ThreadsMgr.available_thread_exists(threadID)
1350 && !ThreadsMgr.thread_should_stop(threadID)
1352 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1353 threatMove, mateThreat, &moveCount, &mp, PvNode);
1356 // Step 19. Check for mate and stalemate
1357 // All legal moves have been searched and if there are
1358 // no legal moves, it must be mate or stalemate.
1359 // If one move was excluded return fail low score.
1361 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1363 // Step 20. Update tables
1364 // If the search is not aborted, update the transposition table,
1365 // history counters, and killer moves.
1366 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1369 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1370 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1371 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1373 // Update killers and history only for non capture moves that fails high
1374 if (bestValue >= beta)
1376 ThreadsMgr.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1377 if (!pos.move_is_capture_or_promotion(move))
1379 update_history(pos, move, depth, movesSearched, moveCount);
1380 update_killers(move, ss);
1384 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1390 // qsearch() is the quiescence search function, which is called by the main
1391 // search function when the remaining depth is zero (or, to be more precise,
1392 // less than ONE_PLY).
1394 template <NodeType PvNode>
1395 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1397 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1398 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1399 assert(PvNode || alpha == beta - 1);
1401 assert(ply > 0 && ply < PLY_MAX);
1402 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1407 Value bestValue, value, futilityValue, futilityBase;
1408 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1410 Value oldAlpha = alpha;
1412 ThreadsMgr.incrementNodeCounter(pos.thread());
1413 ss->bestMove = ss->currentMove = MOVE_NONE;
1415 // Check for an instant draw or maximum ply reached
1416 if (pos.is_draw() || ply >= PLY_MAX - 1)
1419 // Transposition table lookup. At PV nodes, we don't use the TT for
1420 // pruning, but only for move ordering.
1421 tte = TT.retrieve(pos.get_key());
1422 ttMove = (tte ? tte->move() : MOVE_NONE);
1424 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1426 ss->bestMove = ttMove; // Can be MOVE_NONE
1427 return value_from_tt(tte->value(), ply);
1430 isCheck = pos.is_check();
1432 // Evaluate the position statically
1435 bestValue = futilityBase = -VALUE_INFINITE;
1436 ss->eval = VALUE_NONE;
1437 deepChecks = enoughMaterial = false;
1443 assert(tte->static_value() != VALUE_NONE);
1445 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1446 bestValue = tte->static_value();
1449 bestValue = evaluate(pos, ei);
1451 ss->eval = bestValue;
1452 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1454 // Stand pat. Return immediately if static value is at least beta
1455 if (bestValue >= beta)
1458 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()]);
1463 if (PvNode && bestValue > alpha)
1466 // If we are near beta then try to get a cutoff pushing checks a bit further
1467 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1469 // Futility pruning parameters, not needed when in check
1470 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1471 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1474 // Initialize a MovePicker object for the current position, and prepare
1475 // to search the moves. Because the depth is <= 0 here, only captures,
1476 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1477 // and we are near beta) will be generated.
1478 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1481 // Loop through the moves until no moves remain or a beta cutoff occurs
1482 while ( alpha < beta
1483 && (move = mp.get_next_move()) != MOVE_NONE)
1485 assert(move_is_ok(move));
1487 moveIsCheck = pos.move_is_check(move, ci);
1495 && !move_is_promotion(move)
1496 && !pos.move_is_passed_pawn_push(move))
1498 futilityValue = futilityBase
1499 + pos.endgame_value_of_piece_on(move_to(move))
1500 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1502 if (futilityValue < alpha)
1504 if (futilityValue > bestValue)
1505 bestValue = futilityValue;
1510 // Detect blocking evasions that are candidate to be pruned
1511 evasionPrunable = isCheck
1512 && bestValue > value_mated_in(PLY_MAX)
1513 && !pos.move_is_capture(move)
1514 && pos.type_of_piece_on(move_from(move)) != KING
1515 && !pos.can_castle(pos.side_to_move());
1517 // Don't search moves with negative SEE values
1519 && (!isCheck || evasionPrunable)
1521 && !move_is_promotion(move)
1522 && pos.see_sign(move) < 0)
1525 // Update current move
1526 ss->currentMove = move;
1528 // Make and search the move
1529 pos.do_move(move, st, ci, moveIsCheck);
1530 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1531 pos.undo_move(move);
1533 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1536 if (value > bestValue)
1542 ss->bestMove = move;
1547 // All legal moves have been searched. A special case: If we're in check
1548 // and no legal moves were found, it is checkmate.
1549 if (isCheck && bestValue == -VALUE_INFINITE)
1550 return value_mated_in(ply);
1552 // Update transposition table
1553 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1554 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1555 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1557 // Update killers only for checking moves that fails high
1558 if ( bestValue >= beta
1559 && !pos.move_is_capture_or_promotion(ss->bestMove))
1560 update_killers(ss->bestMove, ss);
1562 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1568 // sp_search() is used to search from a split point. This function is called
1569 // by each thread working at the split point. It is similar to the normal
1570 // search() function, but simpler. Because we have already probed the hash
1571 // table, done a null move search, and searched the first move before
1572 // splitting, we don't have to repeat all this work in sp_search(). We
1573 // also don't need to store anything to the hash table here: This is taken
1574 // care of after we return from the split point.
1576 template <NodeType PvNode>
1577 void sp_search(SplitPoint* sp, int threadID) {
1579 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1580 assert(ThreadsMgr.active_threads() > 1);
1584 Depth ext, newDepth;
1586 Value futilityValueScaled; // NonPV specific
1587 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1589 value = -VALUE_INFINITE;
1591 Position pos(*sp->pos, threadID);
1593 SearchStack* ss = sp->sstack[threadID] + 1;
1594 isCheck = pos.is_check();
1596 // Step 10. Loop through moves
1597 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1598 lock_grab(&(sp->lock));
1600 while ( sp->bestValue < sp->beta
1601 && (move = sp->mp->get_next_move()) != MOVE_NONE
1602 && !ThreadsMgr.thread_should_stop(threadID))
1604 moveCount = ++sp->moveCount;
1605 lock_release(&(sp->lock));
1607 assert(move_is_ok(move));
1609 moveIsCheck = pos.move_is_check(move, ci);
1610 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1612 // Step 11. Decide the new search depth
1613 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1614 newDepth = sp->depth - ONE_PLY + ext;
1616 // Update current move
1617 ss->currentMove = move;
1619 // Step 12. Futility pruning (is omitted in PV nodes)
1621 && !captureOrPromotion
1624 && !move_is_castle(move))
1626 // Move count based pruning
1627 if ( moveCount >= futility_move_count(sp->depth)
1628 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1629 && sp->bestValue > value_mated_in(PLY_MAX))
1631 lock_grab(&(sp->lock));
1635 // Value based pruning
1636 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1637 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1638 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1640 if (futilityValueScaled < sp->beta)
1642 lock_grab(&(sp->lock));
1644 if (futilityValueScaled > sp->bestValue)
1645 sp->bestValue = futilityValueScaled;
1650 // Step 13. Make the move
1651 pos.do_move(move, st, ci, moveIsCheck);
1653 // Step 14. Reduced search
1654 // If the move fails high will be re-searched at full depth.
1655 bool doFullDepthSearch = true;
1657 if ( !captureOrPromotion
1659 && !move_is_castle(move)
1660 && !move_is_killer(move, ss))
1662 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1665 Value localAlpha = sp->alpha;
1666 Depth d = newDepth - ss->reduction;
1667 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1668 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1670 doFullDepthSearch = (value > localAlpha);
1673 // The move failed high, but if reduction is very big we could
1674 // face a false positive, retry with a less aggressive reduction,
1675 // if the move fails high again then go with full depth search.
1676 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1678 assert(newDepth - ONE_PLY >= ONE_PLY);
1680 ss->reduction = ONE_PLY;
1681 Value localAlpha = sp->alpha;
1682 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1683 doFullDepthSearch = (value > localAlpha);
1685 ss->reduction = DEPTH_ZERO; // Restore original reduction
1688 // Step 15. Full depth search
1689 if (doFullDepthSearch)
1691 Value localAlpha = sp->alpha;
1692 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1693 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1695 // Step extra. pv search (only in PV nodes)
1696 // Search only for possible new PV nodes, if instead value >= beta then
1697 // parent node fails low with value <= alpha and tries another move.
1698 if (PvNode && value > localAlpha && value < sp->beta)
1699 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, DEPTH_ZERO, sp->ply+1)
1700 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1703 // Step 16. Undo move
1704 pos.undo_move(move);
1706 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1708 // Step 17. Check for new best move
1709 lock_grab(&(sp->lock));
1711 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1713 sp->bestValue = value;
1715 if (sp->bestValue > sp->alpha)
1717 if (!PvNode || value >= sp->beta)
1718 sp->stopRequest = true;
1720 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1723 sp->parentSstack->bestMove = ss->bestMove = move;
1728 /* Here we have the lock still grabbed */
1730 sp->slaves[threadID] = 0;
1732 lock_release(&(sp->lock));
1736 // connected_moves() tests whether two moves are 'connected' in the sense
1737 // that the first move somehow made the second move possible (for instance
1738 // if the moving piece is the same in both moves). The first move is assumed
1739 // to be the move that was made to reach the current position, while the
1740 // second move is assumed to be a move from the current position.
1742 bool connected_moves(const Position& pos, Move m1, Move m2) {
1744 Square f1, t1, f2, t2;
1747 assert(move_is_ok(m1));
1748 assert(move_is_ok(m2));
1750 if (m2 == MOVE_NONE)
1753 // Case 1: The moving piece is the same in both moves
1759 // Case 2: The destination square for m2 was vacated by m1
1765 // Case 3: Moving through the vacated square
1766 if ( piece_is_slider(pos.piece_on(f2))
1767 && bit_is_set(squares_between(f2, t2), f1))
1770 // Case 4: The destination square for m2 is defended by the moving piece in m1
1771 p = pos.piece_on(t1);
1772 if (bit_is_set(pos.attacks_from(p, t1), t2))
1775 // Case 5: Discovered check, checking piece is the piece moved in m1
1776 if ( piece_is_slider(p)
1777 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1778 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1780 // discovered_check_candidates() works also if the Position's side to
1781 // move is the opposite of the checking piece.
1782 Color them = opposite_color(pos.side_to_move());
1783 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1785 if (bit_is_set(dcCandidates, f2))
1792 // value_is_mate() checks if the given value is a mate one eventually
1793 // compensated for the ply.
1795 bool value_is_mate(Value value) {
1797 assert(abs(value) <= VALUE_INFINITE);
1799 return value <= value_mated_in(PLY_MAX)
1800 || value >= value_mate_in(PLY_MAX);
1804 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1805 // "plies to mate from the current ply". Non-mate scores are unchanged.
1806 // The function is called before storing a value to the transposition table.
1808 Value value_to_tt(Value v, int ply) {
1810 if (v >= value_mate_in(PLY_MAX))
1813 if (v <= value_mated_in(PLY_MAX))
1820 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1821 // the transposition table to a mate score corrected for the current ply.
1823 Value value_from_tt(Value v, int ply) {
1825 if (v >= value_mate_in(PLY_MAX))
1828 if (v <= value_mated_in(PLY_MAX))
1835 // move_is_killer() checks if the given move is among the killer moves
1837 bool move_is_killer(Move m, SearchStack* ss) {
1839 if (ss->killers[0] == m || ss->killers[1] == m)
1846 // extension() decides whether a move should be searched with normal depth,
1847 // or with extended depth. Certain classes of moves (checking moves, in
1848 // particular) are searched with bigger depth than ordinary moves and in
1849 // any case are marked as 'dangerous'. Note that also if a move is not
1850 // extended, as example because the corresponding UCI option is set to zero,
1851 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1852 template <NodeType PvNode>
1853 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1854 bool singleEvasion, bool mateThreat, bool* dangerous) {
1856 assert(m != MOVE_NONE);
1858 Depth result = DEPTH_ZERO;
1859 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1863 if (moveIsCheck && pos.see_sign(m) >= 0)
1864 result += CheckExtension[PvNode];
1867 result += SingleEvasionExtension[PvNode];
1870 result += MateThreatExtension[PvNode];
1873 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1875 Color c = pos.side_to_move();
1876 if (relative_rank(c, move_to(m)) == RANK_7)
1878 result += PawnPushTo7thExtension[PvNode];
1881 if (pos.pawn_is_passed(c, move_to(m)))
1883 result += PassedPawnExtension[PvNode];
1888 if ( captureOrPromotion
1889 && pos.type_of_piece_on(move_to(m)) != PAWN
1890 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1891 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1892 && !move_is_promotion(m)
1895 result += PawnEndgameExtension[PvNode];
1900 && captureOrPromotion
1901 && pos.type_of_piece_on(move_to(m)) != PAWN
1902 && pos.see_sign(m) >= 0)
1904 result += ONE_PLY / 2;
1908 return Min(result, ONE_PLY);
1912 // connected_threat() tests whether it is safe to forward prune a move or if
1913 // is somehow coonected to the threat move returned by null search.
1915 bool connected_threat(const Position& pos, Move m, Move threat) {
1917 assert(move_is_ok(m));
1918 assert(threat && move_is_ok(threat));
1919 assert(!pos.move_is_check(m));
1920 assert(!pos.move_is_capture_or_promotion(m));
1921 assert(!pos.move_is_passed_pawn_push(m));
1923 Square mfrom, mto, tfrom, tto;
1925 mfrom = move_from(m);
1927 tfrom = move_from(threat);
1928 tto = move_to(threat);
1930 // Case 1: Don't prune moves which move the threatened piece
1934 // Case 2: If the threatened piece has value less than or equal to the
1935 // value of the threatening piece, don't prune move which defend it.
1936 if ( pos.move_is_capture(threat)
1937 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1938 || pos.type_of_piece_on(tfrom) == KING)
1939 && pos.move_attacks_square(m, tto))
1942 // Case 3: If the moving piece in the threatened move is a slider, don't
1943 // prune safe moves which block its ray.
1944 if ( piece_is_slider(pos.piece_on(tfrom))
1945 && bit_is_set(squares_between(tfrom, tto), mto)
1946 && pos.see_sign(m) >= 0)
1953 // ok_to_use_TT() returns true if a transposition table score
1954 // can be used at a given point in search.
1956 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1958 Value v = value_from_tt(tte->value(), ply);
1960 return ( tte->depth() >= depth
1961 || v >= Max(value_mate_in(PLY_MAX), beta)
1962 || v < Min(value_mated_in(PLY_MAX), beta))
1964 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1965 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1969 // refine_eval() returns the transposition table score if
1970 // possible otherwise falls back on static position evaluation.
1972 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1976 Value v = value_from_tt(tte->value(), ply);
1978 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1979 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1986 // update_history() registers a good move that produced a beta-cutoff
1987 // in history and marks as failures all the other moves of that ply.
1989 void update_history(const Position& pos, Move move, Depth depth,
1990 Move movesSearched[], int moveCount) {
1994 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1996 for (int i = 0; i < moveCount - 1; i++)
1998 m = movesSearched[i];
2002 if (!pos.move_is_capture_or_promotion(m))
2003 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2008 // update_killers() add a good move that produced a beta-cutoff
2009 // among the killer moves of that ply.
2011 void update_killers(Move m, SearchStack* ss) {
2013 if (m == ss->killers[0])
2016 ss->killers[1] = ss->killers[0];
2021 // update_gains() updates the gains table of a non-capture move given
2022 // the static position evaluation before and after the move.
2024 void update_gains(const Position& pos, Move m, Value before, Value after) {
2027 && before != VALUE_NONE
2028 && after != VALUE_NONE
2029 && pos.captured_piece_type() == PIECE_TYPE_NONE
2030 && !move_is_special(m))
2031 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2035 // current_search_time() returns the number of milliseconds which have passed
2036 // since the beginning of the current search.
2038 int current_search_time() {
2040 return get_system_time() - SearchStartTime;
2044 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2046 std::string value_to_uci(Value v) {
2048 std::stringstream s;
2050 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2051 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2053 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2058 // nps() computes the current nodes/second count.
2062 int t = current_search_time();
2063 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2067 // poll() performs two different functions: It polls for user input, and it
2068 // looks at the time consumed so far and decides if it's time to abort the
2073 static int lastInfoTime;
2074 int t = current_search_time();
2079 // We are line oriented, don't read single chars
2080 std::string command;
2082 if (!std::getline(std::cin, command))
2085 if (command == "quit")
2088 PonderSearch = false;
2092 else if (command == "stop")
2095 PonderSearch = false;
2097 else if (command == "ponderhit")
2101 // Print search information
2105 else if (lastInfoTime > t)
2106 // HACK: Must be a new search where we searched less than
2107 // NodesBetweenPolls nodes during the first second of search.
2110 else if (t - lastInfoTime >= 1000)
2117 if (dbg_show_hit_rate)
2118 dbg_print_hit_rate();
2120 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2121 << " time " << t << endl;
2124 // Should we stop the search?
2128 bool stillAtFirstMove = FirstRootMove
2129 && !AspirationFailLow
2130 && t > TimeMgr.available_time();
2132 bool noMoreTime = t > TimeMgr.maximum_time()
2133 || stillAtFirstMove;
2135 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2136 || (ExactMaxTime && t >= ExactMaxTime)
2137 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2142 // ponderhit() is called when the program is pondering (i.e. thinking while
2143 // it's the opponent's turn to move) in order to let the engine know that
2144 // it correctly predicted the opponent's move.
2148 int t = current_search_time();
2149 PonderSearch = false;
2151 bool stillAtFirstMove = FirstRootMove
2152 && !AspirationFailLow
2153 && t > TimeMgr.available_time();
2155 bool noMoreTime = t > TimeMgr.maximum_time()
2156 || stillAtFirstMove;
2158 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2163 // init_ss_array() does a fast reset of the first entries of a SearchStack
2164 // array and of all the excludedMove and skipNullMove entries.
2166 void init_ss_array(SearchStack* ss, int size) {
2168 for (int i = 0; i < size; i++, ss++)
2170 ss->excludedMove = MOVE_NONE;
2171 ss->skipNullMove = false;
2172 ss->reduction = DEPTH_ZERO;
2175 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2180 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2181 // while the program is pondering. The point is to work around a wrinkle in
2182 // the UCI protocol: When pondering, the engine is not allowed to give a
2183 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2184 // We simply wait here until one of these commands is sent, and return,
2185 // after which the bestmove and pondermove will be printed (in id_loop()).
2187 void wait_for_stop_or_ponderhit() {
2189 std::string command;
2193 if (!std::getline(std::cin, command))
2196 if (command == "quit")
2201 else if (command == "ponderhit" || command == "stop")
2207 // print_pv_info() prints to standard output and eventually to log file information on
2208 // the current PV line. It is called at each iteration or after a new pv is found.
2210 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2212 cout << "info depth " << Iteration
2213 << " score " << value_to_uci(value)
2214 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2215 << " time " << current_search_time()
2216 << " nodes " << ThreadsMgr.nodes_searched()
2220 for (Move* m = pv; *m != MOVE_NONE; m++)
2227 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2228 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2230 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2231 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2236 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2237 // the PV back into the TT. This makes sure the old PV moves are searched
2238 // first, even if the old TT entries have been overwritten.
2240 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2244 Position p(pos, pos.thread());
2248 for (int i = 0; pv[i] != MOVE_NONE; i++)
2250 tte = TT.retrieve(p.get_key());
2251 if (!tte || tte->move() != pv[i])
2253 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2254 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2256 p.do_move(pv[i], st);
2261 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2262 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2263 // allow to always have a ponder move even when we fail high at root and also a
2264 // long PV to print that is important for position analysis.
2266 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2270 Position p(pos, pos.thread());
2273 assert(bestMove != MOVE_NONE);
2276 p.do_move(pv[ply++], st);
2278 while ( (tte = TT.retrieve(p.get_key())) != NULL
2279 && tte->move() != MOVE_NONE
2280 && move_is_legal(p, tte->move())
2282 && (!p.is_draw() || ply < 2))
2284 pv[ply] = tte->move();
2285 p.do_move(pv[ply++], st);
2287 pv[ply] = MOVE_NONE;
2291 // init_thread() is the function which is called when a new thread is
2292 // launched. It simply calls the idle_loop() function with the supplied
2293 // threadID. There are two versions of this function; one for POSIX
2294 // threads and one for Windows threads.
2296 #if !defined(_MSC_VER)
2298 void* init_thread(void *threadID) {
2300 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2306 DWORD WINAPI init_thread(LPVOID threadID) {
2308 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2315 /// The ThreadsManager class
2317 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2318 // get_beta_counters() are getters/setters for the per thread
2319 // counters used to sort the moves at root.
2321 void ThreadsManager::resetNodeCounters() {
2323 for (int i = 0; i < MAX_THREADS; i++)
2324 threads[i].nodes = 0ULL;
2327 void ThreadsManager::resetBetaCounters() {
2329 for (int i = 0; i < MAX_THREADS; i++)
2330 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2333 int64_t ThreadsManager::nodes_searched() const {
2335 int64_t result = 0ULL;
2336 for (int i = 0; i < ActiveThreads; i++)
2337 result += threads[i].nodes;
2342 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2345 for (int i = 0; i < MAX_THREADS; i++)
2347 our += threads[i].betaCutOffs[us];
2348 their += threads[i].betaCutOffs[opposite_color(us)];
2353 // idle_loop() is where the threads are parked when they have no work to do.
2354 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2355 // object for which the current thread is the master.
2357 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2359 assert(threadID >= 0 && threadID < MAX_THREADS);
2363 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2364 // master should exit as last one.
2365 if (AllThreadsShouldExit)
2368 threads[threadID].state = THREAD_TERMINATED;
2372 // If we are not thinking, wait for a condition to be signaled
2373 // instead of wasting CPU time polling for work.
2374 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2377 assert(threadID != 0);
2378 threads[threadID].state = THREAD_SLEEPING;
2380 #if !defined(_MSC_VER)
2381 lock_grab(&WaitLock);
2382 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2383 pthread_cond_wait(&WaitCond, &WaitLock);
2384 lock_release(&WaitLock);
2386 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2390 // If thread has just woken up, mark it as available
2391 if (threads[threadID].state == THREAD_SLEEPING)
2392 threads[threadID].state = THREAD_AVAILABLE;
2394 // If this thread has been assigned work, launch a search
2395 if (threads[threadID].state == THREAD_WORKISWAITING)
2397 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2399 threads[threadID].state = THREAD_SEARCHING;
2401 if (threads[threadID].splitPoint->pvNode)
2402 sp_search<PV>(threads[threadID].splitPoint, threadID);
2404 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2406 assert(threads[threadID].state == THREAD_SEARCHING);
2408 threads[threadID].state = THREAD_AVAILABLE;
2411 // If this thread is the master of a split point and all slaves have
2412 // finished their work at this split point, return from the idle loop.
2414 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2416 if (i == ActiveThreads)
2418 // Because sp->slaves[] is reset under lock protection,
2419 // be sure sp->lock has been released before to return.
2420 lock_grab(&(sp->lock));
2421 lock_release(&(sp->lock));
2423 assert(threads[threadID].state == THREAD_AVAILABLE);
2425 threads[threadID].state = THREAD_SEARCHING;
2432 // init_threads() is called during startup. It launches all helper threads,
2433 // and initializes the split point stack and the global locks and condition
2436 void ThreadsManager::init_threads() {
2441 #if !defined(_MSC_VER)
2442 pthread_t pthread[1];
2445 // Initialize global locks
2447 lock_init(&WaitLock);
2449 #if !defined(_MSC_VER)
2450 pthread_cond_init(&WaitCond, NULL);
2452 for (i = 0; i < MAX_THREADS; i++)
2453 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2456 // Initialize splitPoints[] locks
2457 for (i = 0; i < MAX_THREADS; i++)
2458 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2459 lock_init(&(threads[i].splitPoints[j].lock));
2461 // Will be set just before program exits to properly end the threads
2462 AllThreadsShouldExit = false;
2464 // Threads will be put to sleep as soon as created
2465 AllThreadsShouldSleep = true;
2467 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2469 threads[0].state = THREAD_SEARCHING;
2470 for (i = 1; i < MAX_THREADS; i++)
2471 threads[i].state = THREAD_AVAILABLE;
2473 // Launch the helper threads
2474 for (i = 1; i < MAX_THREADS; i++)
2477 #if !defined(_MSC_VER)
2478 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2480 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2485 cout << "Failed to create thread number " << i << endl;
2486 Application::exit_with_failure();
2489 // Wait until the thread has finished launching and is gone to sleep
2490 while (threads[i].state != THREAD_SLEEPING) {}
2495 // exit_threads() is called when the program exits. It makes all the
2496 // helper threads exit cleanly.
2498 void ThreadsManager::exit_threads() {
2500 ActiveThreads = MAX_THREADS; // HACK
2501 AllThreadsShouldSleep = true; // HACK
2502 wake_sleeping_threads();
2504 // This makes the threads to exit idle_loop()
2505 AllThreadsShouldExit = true;
2507 // Wait for thread termination
2508 for (int i = 1; i < MAX_THREADS; i++)
2509 while (threads[i].state != THREAD_TERMINATED) {}
2511 // Now we can safely destroy the locks
2512 for (int i = 0; i < MAX_THREADS; i++)
2513 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2514 lock_destroy(&(threads[i].splitPoints[j].lock));
2516 lock_destroy(&WaitLock);
2517 lock_destroy(&MPLock);
2521 // thread_should_stop() checks whether the thread should stop its search.
2522 // This can happen if a beta cutoff has occurred in the thread's currently
2523 // active split point, or in some ancestor of the current split point.
2525 bool ThreadsManager::thread_should_stop(int threadID) const {
2527 assert(threadID >= 0 && threadID < ActiveThreads);
2531 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2536 // thread_is_available() checks whether the thread with threadID "slave" is
2537 // available to help the thread with threadID "master" at a split point. An
2538 // obvious requirement is that "slave" must be idle. With more than two
2539 // threads, this is not by itself sufficient: If "slave" is the master of
2540 // some active split point, it is only available as a slave to the other
2541 // threads which are busy searching the split point at the top of "slave"'s
2542 // split point stack (the "helpful master concept" in YBWC terminology).
2544 bool ThreadsManager::thread_is_available(int slave, int master) const {
2546 assert(slave >= 0 && slave < ActiveThreads);
2547 assert(master >= 0 && master < ActiveThreads);
2548 assert(ActiveThreads > 1);
2550 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2553 // Make a local copy to be sure doesn't change under our feet
2554 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2556 if (localActiveSplitPoints == 0)
2557 // No active split points means that the thread is available as
2558 // a slave for any other thread.
2561 if (ActiveThreads == 2)
2564 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2565 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2566 // could have been set to 0 by another thread leading to an out of bound access.
2567 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2574 // available_thread_exists() tries to find an idle thread which is available as
2575 // a slave for the thread with threadID "master".
2577 bool ThreadsManager::available_thread_exists(int master) const {
2579 assert(master >= 0 && master < ActiveThreads);
2580 assert(ActiveThreads > 1);
2582 for (int i = 0; i < ActiveThreads; i++)
2583 if (thread_is_available(i, master))
2590 // split() does the actual work of distributing the work at a node between
2591 // several available threads. If it does not succeed in splitting the
2592 // node (because no idle threads are available, or because we have no unused
2593 // split point objects), the function immediately returns. If splitting is
2594 // possible, a SplitPoint object is initialized with all the data that must be
2595 // copied to the helper threads and we tell our helper threads that they have
2596 // been assigned work. This will cause them to instantly leave their idle loops
2597 // and call sp_search(). When all threads have returned from sp_search() then
2600 template <bool Fake>
2601 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2602 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2603 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2605 assert(ply > 0 && ply < PLY_MAX);
2606 assert(*bestValue >= -VALUE_INFINITE);
2607 assert(*bestValue <= *alpha);
2608 assert(*alpha < beta);
2609 assert(beta <= VALUE_INFINITE);
2610 assert(depth > DEPTH_ZERO);
2611 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2612 assert(ActiveThreads > 1);
2614 int i, master = p.thread();
2615 Thread& masterThread = threads[master];
2619 // If no other thread is available to help us, or if we have too many
2620 // active split points, don't split.
2621 if ( !available_thread_exists(master)
2622 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2624 lock_release(&MPLock);
2628 // Pick the next available split point object from the split point stack
2629 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2631 // Initialize the split point object
2632 splitPoint.parent = masterThread.splitPoint;
2633 splitPoint.stopRequest = false;
2634 splitPoint.ply = ply;
2635 splitPoint.depth = depth;
2636 splitPoint.threatMove = threatMove;
2637 splitPoint.mateThreat = mateThreat;
2638 splitPoint.alpha = *alpha;
2639 splitPoint.beta = beta;
2640 splitPoint.pvNode = pvNode;
2641 splitPoint.bestValue = *bestValue;
2643 splitPoint.moveCount = *moveCount;
2644 splitPoint.pos = &p;
2645 splitPoint.parentSstack = ss;
2646 for (i = 0; i < ActiveThreads; i++)
2647 splitPoint.slaves[i] = 0;
2649 masterThread.splitPoint = &splitPoint;
2651 // If we are here it means we are not available
2652 assert(masterThread.state != THREAD_AVAILABLE);
2654 int workersCnt = 1; // At least the master is included
2656 // Allocate available threads setting state to THREAD_BOOKED
2657 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2658 if (thread_is_available(i, master))
2660 threads[i].state = THREAD_BOOKED;
2661 threads[i].splitPoint = &splitPoint;
2662 splitPoint.slaves[i] = 1;
2666 assert(Fake || workersCnt > 1);
2668 // We can release the lock because slave threads are already booked and master is not available
2669 lock_release(&MPLock);
2671 // Tell the threads that they have work to do. This will make them leave
2672 // their idle loop. But before copy search stack tail for each thread.
2673 for (i = 0; i < ActiveThreads; i++)
2674 if (i == master || splitPoint.slaves[i])
2676 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2678 assert(i == master || threads[i].state == THREAD_BOOKED);
2680 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2683 // Everything is set up. The master thread enters the idle loop, from
2684 // which it will instantly launch a search, because its state is
2685 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2686 // idle loop, which means that the main thread will return from the idle
2687 // loop when all threads have finished their work at this split point.
2688 idle_loop(master, &splitPoint);
2690 // We have returned from the idle loop, which means that all threads are
2691 // finished. Update alpha and bestValue, and return.
2694 *alpha = splitPoint.alpha;
2695 *bestValue = splitPoint.bestValue;
2696 masterThread.activeSplitPoints--;
2697 masterThread.splitPoint = splitPoint.parent;
2699 lock_release(&MPLock);
2703 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2704 // to start a new search from the root.
2706 void ThreadsManager::wake_sleeping_threads() {
2708 assert(AllThreadsShouldSleep);
2709 assert(ActiveThreads > 0);
2711 AllThreadsShouldSleep = false;
2713 if (ActiveThreads == 1)
2716 #if !defined(_MSC_VER)
2717 pthread_mutex_lock(&WaitLock);
2718 pthread_cond_broadcast(&WaitCond);
2719 pthread_mutex_unlock(&WaitLock);
2721 for (int i = 1; i < MAX_THREADS; i++)
2722 SetEvent(SitIdleEvent[i]);
2728 // put_threads_to_sleep() makes all the threads go to sleep just before
2729 // to leave think(), at the end of the search. Threads should have already
2730 // finished the job and should be idle.
2732 void ThreadsManager::put_threads_to_sleep() {
2734 assert(!AllThreadsShouldSleep);
2736 // This makes the threads to go to sleep
2737 AllThreadsShouldSleep = true;
2740 /// The RootMoveList class
2742 // RootMoveList c'tor
2744 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2746 SearchStack ss[PLY_MAX_PLUS_2];
2747 MoveStack mlist[MaxRootMoves];
2749 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2751 // Initialize search stack
2752 init_ss_array(ss, PLY_MAX_PLUS_2);
2753 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2754 ss[0].eval = VALUE_NONE;
2756 // Generate all legal moves
2757 MoveStack* last = generate_moves(pos, mlist);
2759 // Add each move to the moves[] array
2760 for (MoveStack* cur = mlist; cur != last; cur++)
2762 bool includeMove = includeAllMoves;
2764 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2765 includeMove = (searchMoves[k] == cur->move);
2770 // Find a quick score for the move
2771 pos.do_move(cur->move, st);
2772 ss[0].currentMove = cur->move;
2773 moves[count].move = cur->move;
2774 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2775 moves[count].pv[0] = cur->move;
2776 moves[count].pv[1] = MOVE_NONE;
2777 pos.undo_move(cur->move);
2784 void RootMoveList::set_mp_scores(const Position &pos)
2786 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2790 while ((move = mp.get_next_move()) != MOVE_NONE)
2793 for (int i = 0; i < count; i++)
2795 if (moves[i].move == move)
2797 moves[i].mp_score = 512 - moveCount;
2804 // RootMoveList simple methods definitions
2806 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2808 moves[moveNum].nodes = nodes;
2809 moves[moveNum].cumulativeNodes += nodes;
2812 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2814 moves[moveNum].ourBeta = our;
2815 moves[moveNum].theirBeta = their;
2818 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2822 for (j = 0; pv[j] != MOVE_NONE; j++)
2823 moves[moveNum].pv[j] = pv[j];
2825 moves[moveNum].pv[j] = MOVE_NONE;
2829 // RootMoveList::sort() sorts the root move list at the beginning of a new
2832 void RootMoveList::sort() {
2834 sort_multipv(count - 1); // Sort all items
2838 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2839 // list by their scores and depths. It is used to order the different PVs
2840 // correctly in MultiPV mode.
2842 void RootMoveList::sort_multipv(int n) {
2846 for (i = 1; i <= n; i++)
2848 RootMove rm = moves[i];
2849 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2850 moves[j] = moves[j - 1];