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
55 // Maximum number of allowed moves per position
56 const int MOVES_MAX = 256;
59 enum NodeType { NonPV, PV };
61 // Set to true to force running with one thread.
62 // Used for debugging SMP code.
63 const bool FakeSplit = false;
65 // ThreadsManager class is used to handle all the threads related stuff in search,
66 // init, starting, parking and, the most important, launching a slave thread at a
67 // split point are what this class does. All the access to shared thread data is
68 // done through this class, so that we avoid using global variables instead.
70 class ThreadsManager {
71 /* As long as the single ThreadsManager object is defined as a global we don't
72 need to explicitly initialize to zero its data members because variables with
73 static storage duration are automatically set to zero before enter main()
79 int active_threads() const { return ActiveThreads; }
80 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
81 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
83 void resetNodeCounters();
84 int64_t nodes_searched() 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(0) {}
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;
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 Move move(int moveNum) const { return moves[moveNum].move; }
148 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
149 int move_count() const { return count; }
150 Value move_score(int moveNum) const { return moves[moveNum].score; }
151 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
152 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
153 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
155 void set_move_pv(int moveNum, const Move pv[]);
156 void score_moves(const Position& pos);
158 void sort_multipv(int n);
161 RootMove moves[MOVES_MAX];
166 // When formatting a move for std::cout we must know if we are in Chess960
167 // or not. To keep using the handy operator<<() on the move the trick is to
168 // embed this flag in the stream itself. Function-like named enum set960 is
169 // used as a custom manipulator and the stream internal general-purpose array,
170 // accessed through ios_base::iword(), is used to pass the flag to the move's
171 // operator<<() that will use it to properly format castling moves.
174 std::ostream& operator<< (std::ostream& os, const set960& m) {
176 os.iword(0) = int(m);
185 // Maximum depth for razoring
186 const Depth RazorDepth = 4 * ONE_PLY;
188 // Dynamic razoring margin based on depth
189 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
191 // Step 8. Null move search with verification search
193 // Null move margin. A null move search will not be done if the static
194 // evaluation of the position is more than NullMoveMargin below beta.
195 const Value NullMoveMargin = Value(0x200);
197 // Maximum depth for use of dynamic threat detection when null move fails low
198 const Depth ThreatDepth = 5 * ONE_PLY;
200 // Step 9. Internal iterative deepening
202 // Minimum depth for use of internal iterative deepening
203 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
205 // At Non-PV nodes we do an internal iterative deepening search
206 // when the static evaluation is bigger then beta - IIDMargin.
207 const Value IIDMargin = Value(0x100);
209 // Step 11. Decide the new search depth
211 // Extensions. Configurable UCI options
212 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
213 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
214 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
216 // Minimum depth for use of singular extension
217 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
219 // If the TT move is at least SingularExtensionMargin better then the
220 // remaining ones we will extend it.
221 const Value SingularExtensionMargin = Value(0x20);
223 // Step 12. Futility pruning
225 // Futility margin for quiescence search
226 const Value FutilityMarginQS = Value(0x80);
228 // Futility lookup tables (initialized at startup) and their getter functions
229 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
230 int FutilityMoveCountArray[32]; // [depth]
232 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
233 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
235 // Step 14. Reduced search
237 // Reduction lookup tables (initialized at startup) and their getter functions
238 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
240 template <NodeType PV>
241 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
243 // Common adjustments
245 // Search depth at iteration 1
246 const Depth InitialDepth = ONE_PLY;
248 // Easy move margin. An easy move candidate must be at least this much
249 // better than the second best move.
250 const Value EasyMoveMargin = Value(0x200);
258 // Scores and number of times the best move changed for each iteration
259 Value ValueByIteration[PLY_MAX_PLUS_2];
260 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
262 // Search window management
268 // Time managment variables
269 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
270 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
271 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
276 std::ofstream LogFile;
278 // Multi-threads related variables
279 Depth MinimumSplitDepth;
280 int MaxThreadsPerSplitPoint;
281 ThreadsManager ThreadsMgr;
283 // Node counters, used only by thread[0] but try to keep in different cache
284 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
286 int NodesBetweenPolls = 30000;
293 Value id_loop(const Position& pos, Move searchMoves[]);
294 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
296 template <NodeType PvNode>
297 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
299 template <NodeType PvNode>
300 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
302 template <NodeType PvNode>
303 void sp_search(SplitPoint* sp, int threadID);
305 template <NodeType PvNode>
306 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
308 bool connected_moves(const Position& pos, Move m1, Move m2);
309 bool value_is_mate(Value value);
310 Value value_to_tt(Value v, int ply);
311 Value value_from_tt(Value v, int ply);
312 bool move_is_killer(Move m, SearchStack* ss);
313 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
314 bool connected_threat(const Position& pos, Move m, Move threat);
315 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
316 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
317 void update_killers(Move m, SearchStack* ss);
318 void update_gains(const Position& pos, Move move, Value before, Value after);
320 int current_search_time();
321 std::string value_to_uci(Value v);
325 void wait_for_stop_or_ponderhit();
326 void init_ss_array(SearchStack* ss, int size);
327 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
328 void insert_pv_in_tt(const Position& pos, Move pv[]);
329 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
331 #if !defined(_MSC_VER)
332 void *init_thread(void *threadID);
334 DWORD WINAPI init_thread(LPVOID threadID);
344 /// init_threads(), exit_threads() and nodes_searched() are helpers to
345 /// give accessibility to some TM methods from outside of current file.
347 void init_threads() { ThreadsMgr.init_threads(); }
348 void exit_threads() { ThreadsMgr.exit_threads(); }
349 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
352 /// init_search() is called during startup. It initializes various lookup tables
356 int d; // depth (ONE_PLY == 2)
357 int hd; // half depth (ONE_PLY == 1)
360 // Init reductions array
361 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
363 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
364 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
365 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
366 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
369 // Init futility margins array
370 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
371 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
373 // Init futility move count array
374 for (d = 0; d < 32; d++)
375 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
379 /// perft() is our utility to verify move generation is bug free. All the legal
380 /// moves up to given depth are generated and counted and the sum returned.
382 int perft(Position& pos, Depth depth)
384 MoveStack mlist[MOVES_MAX];
389 // Generate all legal moves
390 MoveStack* last = generate_moves(pos, mlist);
392 // If we are at the last ply we don't need to do and undo
393 // the moves, just to count them.
394 if (depth <= ONE_PLY)
395 return int(last - mlist);
397 // Loop through all legal moves
399 for (MoveStack* cur = mlist; cur != last; cur++)
402 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
403 sum += perft(pos, depth - ONE_PLY);
410 /// think() is the external interface to Stockfish's search, and is called when
411 /// the program receives the UCI 'go' command. It initializes various
412 /// search-related global variables, and calls root_search(). It returns false
413 /// when a quit command is received during the search.
415 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
416 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
418 // Initialize global search variables
419 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
421 ThreadsMgr.resetNodeCounters();
422 SearchStartTime = get_system_time();
423 ExactMaxTime = maxTime;
426 InfiniteSearch = infinite;
427 PonderSearch = ponder;
428 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
430 // Look for a book move, only during games, not tests
431 if (UseTimeManagement && get_option_value_bool("OwnBook"))
433 if (get_option_value_string("Book File") != OpeningBook.file_name())
434 OpeningBook.open(get_option_value_string("Book File"));
436 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
437 if (bookMove != MOVE_NONE)
440 wait_for_stop_or_ponderhit();
442 cout << "bestmove " << bookMove << endl;
447 // Read UCI option values
448 TT.set_size(get_option_value_int("Hash"));
449 if (button_was_pressed("Clear Hash"))
452 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
453 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
454 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
455 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
456 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
457 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
458 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
459 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
460 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
461 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
462 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
463 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
465 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
466 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
467 MultiPV = get_option_value_int("MultiPV");
468 UseLogFile = get_option_value_bool("Use Search Log");
471 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
473 read_weights(pos.side_to_move());
475 // Set the number of active threads
476 int newActiveThreads = get_option_value_int("Threads");
477 if (newActiveThreads != ThreadsMgr.active_threads())
479 ThreadsMgr.set_active_threads(newActiveThreads);
480 init_eval(ThreadsMgr.active_threads());
483 // Wake up sleeping threads
484 ThreadsMgr.wake_sleeping_threads();
487 int myTime = time[pos.side_to_move()];
488 int myIncrement = increment[pos.side_to_move()];
489 if (UseTimeManagement)
490 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
492 // Set best NodesBetweenPolls interval to avoid lagging under
493 // heavy time pressure.
495 NodesBetweenPolls = Min(MaxNodes, 30000);
496 else if (myTime && myTime < 1000)
497 NodesBetweenPolls = 1000;
498 else if (myTime && myTime < 5000)
499 NodesBetweenPolls = 5000;
501 NodesBetweenPolls = 30000;
503 // Write search information to log file
505 LogFile << "Searching: " << pos.to_fen() << endl
506 << "infinite: " << infinite
507 << " ponder: " << ponder
508 << " time: " << myTime
509 << " increment: " << myIncrement
510 << " moves to go: " << movesToGo << endl;
512 // We're ready to start thinking. Call the iterative deepening loop function
513 id_loop(pos, searchMoves);
518 ThreadsMgr.put_threads_to_sleep();
526 // id_loop() is the main iterative deepening loop. It calls root_search
527 // repeatedly with increasing depth until the allocated thinking time has
528 // been consumed, the user stops the search, or the maximum search depth is
531 Value id_loop(const Position& pos, Move searchMoves[]) {
533 Position p(pos, pos.thread());
534 SearchStack ss[PLY_MAX_PLUS_2];
535 Move pv[PLY_MAX_PLUS_2];
536 Move EasyMove = MOVE_NONE;
537 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
539 // Moves to search are verified, copied, scored and sorted
540 RootMoveList rml(p, searchMoves);
542 // Handle special case of searching on a mate/stale position
543 if (rml.move_count() == 0)
546 wait_for_stop_or_ponderhit();
548 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
551 // Print RootMoveList startup scoring to the standard output,
552 // so to output information also for iteration 1.
553 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
554 << "info depth " << 1
555 << "\ninfo depth " << 1
556 << " score " << value_to_uci(rml.move_score(0))
557 << " time " << current_search_time()
558 << " nodes " << ThreadsMgr.nodes_searched()
560 << " pv " << rml.move(0) << "\n";
565 init_ss_array(ss, PLY_MAX_PLUS_2);
566 pv[0] = pv[1] = MOVE_NONE;
567 ValueByIteration[1] = rml.move_score(0);
570 // Is one move significantly better than others after initial scoring ?
571 if ( rml.move_count() == 1
572 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
573 EasyMove = rml.move(0);
575 // Iterative deepening loop
576 while (Iteration < PLY_MAX)
578 // Initialize iteration
580 BestMoveChangesByIteration[Iteration] = 0;
582 cout << "info depth " << Iteration << endl;
584 // Calculate dynamic aspiration window based on previous iterations
585 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
587 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
588 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
590 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
591 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
593 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
594 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
597 // Search to the current depth, rml is updated and sorted, alpha and beta could change
598 value = root_search(p, ss, pv, rml, &alpha, &beta);
600 // Write PV to transposition table, in case the relevant entries have
601 // been overwritten during the search.
602 insert_pv_in_tt(p, pv);
605 break; // Value cannot be trusted. Break out immediately!
607 //Save info about search result
608 ValueByIteration[Iteration] = value;
610 // Drop the easy move if differs from the new best move
611 if (pv[0] != EasyMove)
612 EasyMove = MOVE_NONE;
614 if (UseTimeManagement)
617 bool stopSearch = false;
619 // Stop search early if there is only a single legal move,
620 // we search up to Iteration 6 anyway to get a proper score.
621 if (Iteration >= 6 && rml.move_count() == 1)
624 // Stop search early when the last two iterations returned a mate score
626 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
627 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
630 // Stop search early if one move seems to be much better than the others
631 int64_t nodes = ThreadsMgr.nodes_searched();
634 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
635 && current_search_time() > TimeMgr.available_time() / 16)
636 ||( rml.move_nodes(0) > (nodes * 98) / 100
637 && current_search_time() > TimeMgr.available_time() / 32)))
640 // Add some extra time if the best move has changed during the last two iterations
641 if (Iteration > 5 && Iteration <= 50)
642 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
643 BestMoveChangesByIteration[Iteration-1]);
645 // Stop search if most of MaxSearchTime is consumed at the end of the
646 // iteration. We probably don't have enough time to search the first
647 // move at the next iteration anyway.
648 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
654 StopOnPonderhit = true;
660 if (MaxDepth && Iteration >= MaxDepth)
664 // If we are pondering or in infinite search, we shouldn't print the
665 // best move before we are told to do so.
666 if (!AbortSearch && (PonderSearch || InfiniteSearch))
667 wait_for_stop_or_ponderhit();
669 // Print final search statistics
670 cout << "info nodes " << ThreadsMgr.nodes_searched()
672 << " time " << current_search_time() << endl;
674 // Print the best move and the ponder move to the standard output
675 if (pv[0] == MOVE_NONE)
681 assert(pv[0] != MOVE_NONE);
683 cout << "bestmove " << pv[0];
685 if (pv[1] != MOVE_NONE)
686 cout << " ponder " << pv[1];
693 dbg_print_mean(LogFile);
695 if (dbg_show_hit_rate)
696 dbg_print_hit_rate(LogFile);
698 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
699 << "\nNodes/second: " << nps()
700 << "\nBest move: " << move_to_san(p, pv[0]);
703 p.do_move(pv[0], st);
704 LogFile << "\nPonder move: "
705 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
708 return rml.move_score(0);
712 // root_search() is the function which searches the root node. It is
713 // similar to search_pv except that it uses a different move ordering
714 // scheme, prints some information to the standard output and handles
715 // the fail low/high loops.
717 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
724 Depth depth, ext, newDepth;
725 Value value, alpha, beta;
726 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
727 int researchCountFH, researchCountFL;
729 researchCountFH = researchCountFL = 0;
732 isCheck = pos.is_check();
733 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
735 // Step 1. Initialize node (polling is omitted at root)
736 ss->currentMove = ss->bestMove = MOVE_NONE;
738 // Step 2. Check for aborted search (omitted at root)
739 // Step 3. Mate distance pruning (omitted at root)
740 // Step 4. Transposition table lookup (omitted at root)
742 // Step 5. Evaluate the position statically
743 // At root we do this only to get reference value for child nodes
744 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, margins);
746 // Step 6. Razoring (omitted at root)
747 // Step 7. Static null move pruning (omitted at root)
748 // Step 8. Null move search with verification search (omitted at root)
749 // Step 9. Internal iterative deepening (omitted at root)
751 // Step extra. Fail low loop
752 // We start with small aspiration window and in case of fail low, we research
753 // with bigger window until we are not failing low anymore.
756 // Sort the moves before to (re)search
757 rml.score_moves(pos);
760 // Step 10. Loop through all moves in the root move list
761 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
763 // This is used by time management
764 FirstRootMove = (i == 0);
766 // Save the current node count before the move is searched
767 nodes = ThreadsMgr.nodes_searched();
769 // Pick the next root move, and print the move and the move number to
770 // the standard output.
771 move = ss->currentMove = rml.move(i);
773 if (current_search_time() >= 1000)
774 cout << "info currmove " << move
775 << " currmovenumber " << i + 1 << endl;
777 moveIsCheck = pos.move_is_check(move);
778 captureOrPromotion = pos.move_is_capture_or_promotion(move);
780 // Step 11. Decide the new search depth
781 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
782 newDepth = depth + ext;
784 // Step 12. Futility pruning (omitted at root)
786 // Step extra. Fail high loop
787 // If move fails high, we research with bigger window until we are not failing
789 value = - VALUE_INFINITE;
793 // Step 13. Make the move
794 pos.do_move(move, st, ci, moveIsCheck);
796 // Step extra. pv search
797 // We do pv search for first moves (i < MultiPV)
798 // and for fail high research (value > alpha)
799 if (i < MultiPV || value > alpha)
801 // Aspiration window is disabled in multi-pv case
803 alpha = -VALUE_INFINITE;
805 // Full depth PV search, done on first move or after a fail high
806 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
810 // Step 14. Reduced search
811 // if the move fails high will be re-searched at full depth
812 bool doFullDepthSearch = true;
814 if ( depth >= 3 * ONE_PLY
816 && !captureOrPromotion
817 && !move_is_castle(move))
819 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
822 assert(newDepth-ss->reduction >= ONE_PLY);
824 // Reduced depth non-pv search using alpha as upperbound
825 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
826 doFullDepthSearch = (value > alpha);
829 // The move failed high, but if reduction is very big we could
830 // face a false positive, retry with a less aggressive reduction,
831 // if the move fails high again then go with full depth search.
832 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
834 assert(newDepth - ONE_PLY >= ONE_PLY);
836 ss->reduction = ONE_PLY;
837 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
838 doFullDepthSearch = (value > alpha);
840 ss->reduction = DEPTH_ZERO; // Restore original reduction
843 // Step 15. Full depth search
844 if (doFullDepthSearch)
846 // Full depth non-pv search using alpha as upperbound
847 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
849 // If we are above alpha then research at same depth but as PV
850 // to get a correct score or eventually a fail high above beta.
852 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
856 // Step 16. Undo move
859 // Can we exit fail high loop ?
860 if (AbortSearch || value < beta)
863 // We are failing high and going to do a research. It's important to update
864 // the score before research in case we run out of time while researching.
865 rml.set_move_score(i, value);
867 extract_pv_from_tt(pos, move, pv);
868 rml.set_move_pv(i, pv);
870 // Print information to the standard output
871 print_pv_info(pos, pv, alpha, beta, value);
873 // Prepare for a research after a fail high, each time with a wider window
874 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
877 } // End of fail high loop
879 // Finished searching the move. If AbortSearch is true, the search
880 // was aborted because the user interrupted the search or because we
881 // ran out of time. In this case, the return value of the search cannot
882 // be trusted, and we break out of the loop without updating the best
887 // Remember searched nodes counts for this move
888 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
890 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
891 assert(value < beta);
893 // Step 17. Check for new best move
894 if (value <= alpha && i >= MultiPV)
895 rml.set_move_score(i, -VALUE_INFINITE);
898 // PV move or new best move!
901 rml.set_move_score(i, value);
903 extract_pv_from_tt(pos, move, pv);
904 rml.set_move_pv(i, pv);
908 // We record how often the best move has been changed in each
909 // iteration. This information is used for time managment: When
910 // the best move changes frequently, we allocate some more time.
912 BestMoveChangesByIteration[Iteration]++;
914 // Print information to the standard output
915 print_pv_info(pos, pv, alpha, beta, value);
917 // Raise alpha to setup proper non-pv search upper bound
924 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
926 cout << "info multipv " << j + 1
927 << " score " << value_to_uci(rml.move_score(j))
928 << " depth " << (j <= i ? Iteration : Iteration - 1)
929 << " time " << current_search_time()
930 << " nodes " << ThreadsMgr.nodes_searched()
934 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
935 cout << rml.move_pv(j, k) << " ";
939 alpha = rml.move_score(Min(i, MultiPV - 1));
941 } // PV move or new best move
943 assert(alpha >= *alphaPtr);
945 AspirationFailLow = (alpha == *alphaPtr);
947 if (AspirationFailLow && StopOnPonderhit)
948 StopOnPonderhit = false;
951 // Can we exit fail low loop ?
952 if (AbortSearch || !AspirationFailLow)
955 // Prepare for a research after a fail low, each time with a wider window
956 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
961 // Sort the moves before to return
968 // search<>() is the main search function for both PV and non-PV nodes
970 template <NodeType PvNode>
971 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
973 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
974 assert(beta > alpha && beta <= VALUE_INFINITE);
975 assert(PvNode || alpha == beta - 1);
976 assert(ply > 0 && ply < PLY_MAX);
977 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
979 Move movesSearched[MOVES_MAX];
984 Move ttMove, move, excludedMove, threatMove;
986 Value bestValue, value, oldAlpha;
987 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
988 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
989 bool mateThreat = false;
991 int threadID = pos.thread();
992 refinedValue = bestValue = value = -VALUE_INFINITE;
995 // Step 1. Initialize node and poll. Polling can abort search
996 ThreadsMgr.incrementNodeCounter(threadID);
997 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
998 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1000 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1006 // Step 2. Check for aborted search and immediate draw
1007 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1010 if (pos.is_draw() || ply >= PLY_MAX - 1)
1013 // Step 3. Mate distance pruning
1014 alpha = Max(value_mated_in(ply), alpha);
1015 beta = Min(value_mate_in(ply+1), beta);
1019 // Step 4. Transposition table lookup
1021 // We don't want the score of a partial search to overwrite a previous full search
1022 // TT value, so we use a different position key in case of an excluded move exists.
1023 excludedMove = ss->excludedMove;
1024 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1026 tte = TT.retrieve(posKey);
1027 ttMove = (tte ? tte->move() : MOVE_NONE);
1029 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1030 // This is to avoid problems in the following areas:
1032 // * Repetition draw detection
1033 // * Fifty move rule detection
1034 // * Searching for a mate
1035 // * Printing of full PV line
1037 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1039 // Refresh tte entry to avoid aging
1040 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1042 ss->bestMove = ttMove; // Can be MOVE_NONE
1043 return value_from_tt(tte->value(), ply);
1046 // Step 5. Evaluate the position statically and
1047 // update gain statistics of parent move.
1048 isCheck = pos.is_check();
1050 ss->eval = VALUE_NONE;
1053 assert(tte->static_value() != VALUE_NONE);
1055 ss->eval = tte->static_value();
1056 margins[pos.side_to_move()] = tte->static_value_margin();
1057 refinedValue = refine_eval(tte, ss->eval, ply);
1061 refinedValue = ss->eval = evaluate(pos, margins);
1062 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1065 // Save gain for the parent non-capture move
1066 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1068 // Step 6. Razoring (is omitted in PV nodes)
1070 && depth < RazorDepth
1072 && refinedValue < beta - razor_margin(depth)
1073 && ttMove == MOVE_NONE
1074 && (ss-1)->currentMove != MOVE_NULL
1075 && !value_is_mate(beta)
1076 && !pos.has_pawn_on_7th(pos.side_to_move()))
1078 Value rbeta = beta - razor_margin(depth);
1079 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1081 // Logically we should return (v + razor_margin(depth)), but
1082 // surprisingly this did slightly weaker in tests.
1086 // Step 7. Static null move pruning (is omitted in PV nodes)
1087 // We're betting that the opponent doesn't have a move that will reduce
1088 // the score by more than futility_margin(depth) if we do a null move.
1090 && !ss->skipNullMove
1091 && depth < RazorDepth
1093 && refinedValue >= beta + futility_margin(depth, 0)
1094 && !value_is_mate(beta)
1095 && pos.non_pawn_material(pos.side_to_move()))
1096 return refinedValue - futility_margin(depth, 0);
1098 // Step 8. Null move search with verification search (is omitted in PV nodes)
1099 // When we jump directly to qsearch() we do a null move only if static value is
1100 // at least beta. Otherwise we do a null move if static value is not more than
1101 // NullMoveMargin under beta.
1103 && !ss->skipNullMove
1106 && refinedValue >= beta - (depth >= 4 * ONE_PLY ? NullMoveMargin : 0)
1107 && !value_is_mate(beta)
1108 && pos.non_pawn_material(pos.side_to_move()))
1110 ss->currentMove = MOVE_NULL;
1112 // Null move dynamic reduction based on depth
1113 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1115 // Null move dynamic reduction based on value
1116 if (refinedValue - beta > PawnValueMidgame)
1119 pos.do_null_move(st);
1120 (ss+1)->skipNullMove = true;
1122 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1123 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1124 (ss+1)->skipNullMove = false;
1125 pos.undo_null_move();
1127 if (nullValue >= beta)
1129 // Do not return unproven mate scores
1130 if (nullValue >= value_mate_in(PLY_MAX))
1133 if (depth < 6 * ONE_PLY)
1136 // Do verification search at high depths
1137 ss->skipNullMove = true;
1138 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1139 ss->skipNullMove = false;
1146 // The null move failed low, which means that we may be faced with
1147 // some kind of threat. If the previous move was reduced, check if
1148 // the move that refuted the null move was somehow connected to the
1149 // move which was reduced. If a connection is found, return a fail
1150 // low score (which will cause the reduced move to fail high in the
1151 // parent node, which will trigger a re-search with full depth).
1152 if (nullValue == value_mated_in(ply + 2))
1155 threatMove = (ss+1)->bestMove;
1156 if ( depth < ThreatDepth
1157 && (ss-1)->reduction
1158 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1163 // Step 9. Internal iterative deepening
1164 if ( depth >= IIDDepth[PvNode]
1165 && ttMove == MOVE_NONE
1166 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1168 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1170 ss->skipNullMove = true;
1171 search<PvNode>(pos, ss, alpha, beta, d, ply);
1172 ss->skipNullMove = false;
1174 ttMove = ss->bestMove;
1175 tte = TT.retrieve(posKey);
1178 // Expensive mate threat detection (only for PV nodes)
1180 mateThreat = pos.has_mate_threat();
1182 // Initialize a MovePicker object for the current position
1183 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1185 ss->bestMove = MOVE_NONE;
1186 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1187 futilityBase = ss->eval + margins[pos.side_to_move()];
1188 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1191 && !excludedMove // Do not allow recursive singular extension search
1192 && (tte->type() & VALUE_TYPE_LOWER)
1193 && tte->depth() >= depth - 3 * ONE_PLY;
1195 // Step 10. Loop through moves
1196 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1197 while ( bestValue < beta
1198 && (move = mp.get_next_move()) != MOVE_NONE
1199 && !ThreadsMgr.thread_should_stop(threadID))
1201 assert(move_is_ok(move));
1203 if (move == excludedMove)
1206 moveIsCheck = pos.move_is_check(move, ci);
1207 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1209 // Step 11. Decide the new search depth
1210 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1212 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1213 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1214 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1215 // lower then ttValue minus a margin then we extend ttMove.
1216 if ( singularExtensionNode
1217 && move == tte->move()
1220 Value ttValue = value_from_tt(tte->value(), ply);
1222 if (abs(ttValue) < VALUE_KNOWN_WIN)
1224 Value b = ttValue - SingularExtensionMargin;
1225 ss->excludedMove = move;
1226 ss->skipNullMove = true;
1227 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1228 ss->skipNullMove = false;
1229 ss->excludedMove = MOVE_NONE;
1230 ss->bestMove = MOVE_NONE;
1236 newDepth = depth - ONE_PLY + ext;
1238 // Update current move (this must be done after singular extension search)
1239 movesSearched[moveCount++] = ss->currentMove = move;
1241 // Step 12. Futility pruning (is omitted in PV nodes)
1243 && !captureOrPromotion
1247 && !move_is_castle(move))
1249 // Move count based pruning
1250 if ( moveCount >= futility_move_count(depth)
1251 && !(threatMove && connected_threat(pos, move, threatMove))
1252 && bestValue > value_mated_in(PLY_MAX))
1255 // Value based pruning
1256 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1257 // but fixing this made program slightly weaker.
1258 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1259 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1260 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1262 if (futilityValueScaled < beta)
1264 if (futilityValueScaled > bestValue)
1265 bestValue = futilityValueScaled;
1270 // Step 13. Make the move
1271 pos.do_move(move, st, ci, moveIsCheck);
1273 // Step extra. pv search (only in PV nodes)
1274 // The first move in list is the expected PV
1275 if (PvNode && moveCount == 1)
1276 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1277 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1280 // Step 14. Reduced depth search
1281 // If the move fails high will be re-searched at full depth.
1282 bool doFullDepthSearch = true;
1284 if ( depth >= 3 * ONE_PLY
1285 && !captureOrPromotion
1287 && !move_is_castle(move)
1288 && !move_is_killer(move, ss))
1290 ss->reduction = reduction<PvNode>(depth, moveCount);
1293 Depth d = newDepth - ss->reduction;
1294 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1295 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1297 doFullDepthSearch = (value > alpha);
1300 // The move failed high, but if reduction is very big we could
1301 // face a false positive, retry with a less aggressive reduction,
1302 // if the move fails high again then go with full depth search.
1303 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1305 assert(newDepth - ONE_PLY >= ONE_PLY);
1307 ss->reduction = ONE_PLY;
1308 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1309 doFullDepthSearch = (value > alpha);
1311 ss->reduction = DEPTH_ZERO; // Restore original reduction
1314 // Step 15. Full depth search
1315 if (doFullDepthSearch)
1317 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1318 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1320 // Step extra. pv search (only in PV nodes)
1321 // Search only for possible new PV nodes, if instead value >= beta then
1322 // parent node fails low with value <= alpha and tries another move.
1323 if (PvNode && value > alpha && value < beta)
1324 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1325 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1329 // Step 16. Undo move
1330 pos.undo_move(move);
1332 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1334 // Step 17. Check for new best move
1335 if (value > bestValue)
1340 if (PvNode && value < beta) // We want always alpha < beta
1343 if (value == value_mate_in(ply + 1))
1344 ss->mateKiller = move;
1346 ss->bestMove = move;
1350 // Step 18. Check for split
1351 if ( depth >= MinimumSplitDepth
1352 && ThreadsMgr.active_threads() > 1
1354 && ThreadsMgr.available_thread_exists(threadID)
1356 && !ThreadsMgr.thread_should_stop(threadID)
1358 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1359 threatMove, mateThreat, &moveCount, &mp, PvNode);
1362 // Step 19. Check for mate and stalemate
1363 // All legal moves have been searched and if there are
1364 // no legal moves, it must be mate or stalemate.
1365 // If one move was excluded return fail low score.
1367 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1369 // Step 20. Update tables
1370 // If the search is not aborted, update the transposition table,
1371 // history counters, and killer moves.
1372 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1375 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1376 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1377 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, margins[pos.side_to_move()]);
1379 // Update killers and history only for non capture moves that fails high
1380 if ( bestValue >= beta
1381 && !pos.move_is_capture_or_promotion(move))
1383 update_history(pos, move, depth, movesSearched, moveCount);
1384 update_killers(move, ss);
1387 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1393 // qsearch() is the quiescence search function, which is called by the main
1394 // search function when the remaining depth is zero (or, to be more precise,
1395 // less than ONE_PLY).
1397 template <NodeType PvNode>
1398 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1400 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1401 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1402 assert(PvNode || alpha == beta - 1);
1404 assert(ply > 0 && ply < PLY_MAX);
1405 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1410 Value bestValue, value, futilityValue, futilityBase;
1411 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1413 Value oldAlpha = alpha;
1415 ThreadsMgr.incrementNodeCounter(pos.thread());
1416 ss->bestMove = ss->currentMove = MOVE_NONE;
1418 // Check for an instant draw or maximum ply reached
1419 if (pos.is_draw() || ply >= PLY_MAX - 1)
1422 // Transposition table lookup. At PV nodes, we don't use the TT for
1423 // pruning, but only for move ordering.
1424 tte = TT.retrieve(pos.get_key());
1425 ttMove = (tte ? tte->move() : MOVE_NONE);
1427 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1429 ss->bestMove = ttMove; // Can be MOVE_NONE
1430 return value_from_tt(tte->value(), ply);
1433 isCheck = pos.is_check();
1435 // Evaluate the position statically
1438 bestValue = futilityBase = -VALUE_INFINITE;
1439 ss->eval = VALUE_NONE;
1440 deepChecks = enoughMaterial = false;
1446 assert(tte->static_value() != VALUE_NONE);
1448 margins[pos.side_to_move()] = tte->static_value_margin();
1449 bestValue = tte->static_value();
1452 bestValue = evaluate(pos, margins);
1454 ss->eval = bestValue;
1455 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1457 // Stand pat. Return immediately if static value is at least beta
1458 if (bestValue >= beta)
1461 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1466 if (PvNode && bestValue > alpha)
1469 // If we are near beta then try to get a cutoff pushing checks a bit further
1470 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1472 // Futility pruning parameters, not needed when in check
1473 futilityBase = bestValue + FutilityMarginQS + margins[pos.side_to_move()];
1474 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1477 // Initialize a MovePicker object for the current position, and prepare
1478 // to search the moves. Because the depth is <= 0 here, only captures,
1479 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1480 // and we are near beta) will be generated.
1481 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1484 // Loop through the moves until no moves remain or a beta cutoff occurs
1485 while ( alpha < beta
1486 && (move = mp.get_next_move()) != MOVE_NONE)
1488 assert(move_is_ok(move));
1490 moveIsCheck = pos.move_is_check(move, ci);
1498 && !move_is_promotion(move)
1499 && !pos.move_is_passed_pawn_push(move))
1501 futilityValue = futilityBase
1502 + pos.endgame_value_of_piece_on(move_to(move))
1503 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1505 if (futilityValue < alpha)
1507 if (futilityValue > bestValue)
1508 bestValue = futilityValue;
1513 // Detect blocking evasions that are candidate to be pruned
1514 evasionPrunable = isCheck
1515 && bestValue > value_mated_in(PLY_MAX)
1516 && !pos.move_is_capture(move)
1517 && pos.type_of_piece_on(move_from(move)) != KING
1518 && !pos.can_castle(pos.side_to_move());
1520 // Don't search moves with negative SEE values
1522 && (!isCheck || evasionPrunable)
1524 && !move_is_promotion(move)
1525 && pos.see_sign(move) < 0)
1528 // Update current move
1529 ss->currentMove = move;
1531 // Make and search the move
1532 pos.do_move(move, st, ci, moveIsCheck);
1533 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1534 pos.undo_move(move);
1536 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1539 if (value > bestValue)
1545 ss->bestMove = move;
1550 // All legal moves have been searched. A special case: If we're in check
1551 // and no legal moves were found, it is checkmate.
1552 if (isCheck && bestValue == -VALUE_INFINITE)
1553 return value_mated_in(ply);
1555 // Update transposition table
1556 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1557 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1558 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, margins[pos.side_to_move()]);
1560 // Update killers only for checking moves that fails high
1561 if ( bestValue >= beta
1562 && !pos.move_is_capture_or_promotion(ss->bestMove))
1563 update_killers(ss->bestMove, ss);
1565 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1571 // sp_search() is used to search from a split point. This function is called
1572 // by each thread working at the split point. It is similar to the normal
1573 // search() function, but simpler. Because we have already probed the hash
1574 // table, done a null move search, and searched the first move before
1575 // splitting, we don't have to repeat all this work in sp_search(). We
1576 // also don't need to store anything to the hash table here: This is taken
1577 // care of after we return from the split point.
1579 template <NodeType PvNode>
1580 void sp_search(SplitPoint* sp, int threadID) {
1582 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1583 assert(ThreadsMgr.active_threads() > 1);
1587 Depth ext, newDepth;
1589 Value futilityValueScaled; // NonPV specific
1590 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1592 value = -VALUE_INFINITE;
1594 Position pos(*sp->pos, threadID);
1596 SearchStack* ss = sp->sstack[threadID] + 1;
1597 isCheck = pos.is_check();
1599 // Step 10. Loop through moves
1600 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1601 lock_grab(&(sp->lock));
1603 while ( sp->bestValue < sp->beta
1604 && (move = sp->mp->get_next_move()) != MOVE_NONE
1605 && !ThreadsMgr.thread_should_stop(threadID))
1607 moveCount = ++sp->moveCount;
1608 lock_release(&(sp->lock));
1610 assert(move_is_ok(move));
1612 moveIsCheck = pos.move_is_check(move, ci);
1613 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1615 // Step 11. Decide the new search depth
1616 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1617 newDepth = sp->depth - ONE_PLY + ext;
1619 // Update current move
1620 ss->currentMove = move;
1622 // Step 12. Futility pruning (is omitted in PV nodes)
1624 && !captureOrPromotion
1627 && !move_is_castle(move))
1629 // Move count based pruning
1630 if ( moveCount >= futility_move_count(sp->depth)
1631 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1632 && sp->bestValue > value_mated_in(PLY_MAX))
1634 lock_grab(&(sp->lock));
1638 // Value based pruning
1639 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1640 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1641 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1643 if (futilityValueScaled < sp->beta)
1645 lock_grab(&(sp->lock));
1647 if (futilityValueScaled > sp->bestValue)
1648 sp->bestValue = futilityValueScaled;
1653 // Step 13. Make the move
1654 pos.do_move(move, st, ci, moveIsCheck);
1656 // Step 14. Reduced search
1657 // If the move fails high will be re-searched at full depth.
1658 bool doFullDepthSearch = true;
1660 if ( !captureOrPromotion
1662 && !move_is_castle(move)
1663 && !move_is_killer(move, ss))
1665 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1668 Value localAlpha = sp->alpha;
1669 Depth d = newDepth - ss->reduction;
1670 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1671 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1673 doFullDepthSearch = (value > localAlpha);
1676 // The move failed high, but if reduction is very big we could
1677 // face a false positive, retry with a less aggressive reduction,
1678 // if the move fails high again then go with full depth search.
1679 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1681 assert(newDepth - ONE_PLY >= ONE_PLY);
1683 ss->reduction = ONE_PLY;
1684 Value localAlpha = sp->alpha;
1685 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1686 doFullDepthSearch = (value > localAlpha);
1688 ss->reduction = DEPTH_ZERO; // Restore original reduction
1691 // Step 15. Full depth search
1692 if (doFullDepthSearch)
1694 Value localAlpha = sp->alpha;
1695 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1696 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1698 // Step extra. pv search (only in PV nodes)
1699 // Search only for possible new PV nodes, if instead value >= beta then
1700 // parent node fails low with value <= alpha and tries another move.
1701 if (PvNode && value > localAlpha && value < sp->beta)
1702 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, DEPTH_ZERO, sp->ply+1)
1703 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1706 // Step 16. Undo move
1707 pos.undo_move(move);
1709 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1711 // Step 17. Check for new best move
1712 lock_grab(&(sp->lock));
1714 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1716 sp->bestValue = value;
1718 if (sp->bestValue > sp->alpha)
1720 if (!PvNode || value >= sp->beta)
1721 sp->stopRequest = true;
1723 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1726 sp->parentSstack->bestMove = ss->bestMove = move;
1731 /* Here we have the lock still grabbed */
1733 sp->slaves[threadID] = 0;
1735 lock_release(&(sp->lock));
1739 // connected_moves() tests whether two moves are 'connected' in the sense
1740 // that the first move somehow made the second move possible (for instance
1741 // if the moving piece is the same in both moves). The first move is assumed
1742 // to be the move that was made to reach the current position, while the
1743 // second move is assumed to be a move from the current position.
1745 bool connected_moves(const Position& pos, Move m1, Move m2) {
1747 Square f1, t1, f2, t2;
1750 assert(move_is_ok(m1));
1751 assert(move_is_ok(m2));
1753 if (m2 == MOVE_NONE)
1756 // Case 1: The moving piece is the same in both moves
1762 // Case 2: The destination square for m2 was vacated by m1
1768 // Case 3: Moving through the vacated square
1769 if ( piece_is_slider(pos.piece_on(f2))
1770 && bit_is_set(squares_between(f2, t2), f1))
1773 // Case 4: The destination square for m2 is defended by the moving piece in m1
1774 p = pos.piece_on(t1);
1775 if (bit_is_set(pos.attacks_from(p, t1), t2))
1778 // Case 5: Discovered check, checking piece is the piece moved in m1
1779 if ( piece_is_slider(p)
1780 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1781 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1783 // discovered_check_candidates() works also if the Position's side to
1784 // move is the opposite of the checking piece.
1785 Color them = opposite_color(pos.side_to_move());
1786 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1788 if (bit_is_set(dcCandidates, f2))
1795 // value_is_mate() checks if the given value is a mate one eventually
1796 // compensated for the ply.
1798 bool value_is_mate(Value value) {
1800 assert(abs(value) <= VALUE_INFINITE);
1802 return value <= value_mated_in(PLY_MAX)
1803 || value >= value_mate_in(PLY_MAX);
1807 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1808 // "plies to mate from the current ply". Non-mate scores are unchanged.
1809 // The function is called before storing a value to the transposition table.
1811 Value value_to_tt(Value v, int ply) {
1813 if (v >= value_mate_in(PLY_MAX))
1816 if (v <= value_mated_in(PLY_MAX))
1823 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1824 // the transposition table to a mate score corrected for the current ply.
1826 Value value_from_tt(Value v, int ply) {
1828 if (v >= value_mate_in(PLY_MAX))
1831 if (v <= value_mated_in(PLY_MAX))
1838 // move_is_killer() checks if the given move is among the killer moves
1840 bool move_is_killer(Move m, SearchStack* ss) {
1842 if (ss->killers[0] == m || ss->killers[1] == m)
1849 // extension() decides whether a move should be searched with normal depth,
1850 // or with extended depth. Certain classes of moves (checking moves, in
1851 // particular) are searched with bigger depth than ordinary moves and in
1852 // any case are marked as 'dangerous'. Note that also if a move is not
1853 // extended, as example because the corresponding UCI option is set to zero,
1854 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1855 template <NodeType PvNode>
1856 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1857 bool singleEvasion, bool mateThreat, bool* dangerous) {
1859 assert(m != MOVE_NONE);
1861 Depth result = DEPTH_ZERO;
1862 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1866 if (moveIsCheck && pos.see_sign(m) >= 0)
1867 result += CheckExtension[PvNode];
1870 result += SingleEvasionExtension[PvNode];
1873 result += MateThreatExtension[PvNode];
1876 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1878 Color c = pos.side_to_move();
1879 if (relative_rank(c, move_to(m)) == RANK_7)
1881 result += PawnPushTo7thExtension[PvNode];
1884 if (pos.pawn_is_passed(c, move_to(m)))
1886 result += PassedPawnExtension[PvNode];
1891 if ( captureOrPromotion
1892 && pos.type_of_piece_on(move_to(m)) != PAWN
1893 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1894 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1895 && !move_is_promotion(m)
1898 result += PawnEndgameExtension[PvNode];
1903 && captureOrPromotion
1904 && pos.type_of_piece_on(move_to(m)) != PAWN
1905 && pos.see_sign(m) >= 0)
1907 result += ONE_PLY / 2;
1911 return Min(result, ONE_PLY);
1915 // connected_threat() tests whether it is safe to forward prune a move or if
1916 // is somehow coonected to the threat move returned by null search.
1918 bool connected_threat(const Position& pos, Move m, Move threat) {
1920 assert(move_is_ok(m));
1921 assert(threat && move_is_ok(threat));
1922 assert(!pos.move_is_check(m));
1923 assert(!pos.move_is_capture_or_promotion(m));
1924 assert(!pos.move_is_passed_pawn_push(m));
1926 Square mfrom, mto, tfrom, tto;
1928 mfrom = move_from(m);
1930 tfrom = move_from(threat);
1931 tto = move_to(threat);
1933 // Case 1: Don't prune moves which move the threatened piece
1937 // Case 2: If the threatened piece has value less than or equal to the
1938 // value of the threatening piece, don't prune move which defend it.
1939 if ( pos.move_is_capture(threat)
1940 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1941 || pos.type_of_piece_on(tfrom) == KING)
1942 && pos.move_attacks_square(m, tto))
1945 // Case 3: If the moving piece in the threatened move is a slider, don't
1946 // prune safe moves which block its ray.
1947 if ( piece_is_slider(pos.piece_on(tfrom))
1948 && bit_is_set(squares_between(tfrom, tto), mto)
1949 && pos.see_sign(m) >= 0)
1956 // ok_to_use_TT() returns true if a transposition table score
1957 // can be used at a given point in search.
1959 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1961 Value v = value_from_tt(tte->value(), ply);
1963 return ( tte->depth() >= depth
1964 || v >= Max(value_mate_in(PLY_MAX), beta)
1965 || v < Min(value_mated_in(PLY_MAX), beta))
1967 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1968 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1972 // refine_eval() returns the transposition table score if
1973 // possible otherwise falls back on static position evaluation.
1975 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1979 Value v = value_from_tt(tte->value(), ply);
1981 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1982 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1989 // update_history() registers a good move that produced a beta-cutoff
1990 // in history and marks as failures all the other moves of that ply.
1992 void update_history(const Position& pos, Move move, Depth depth,
1993 Move movesSearched[], int moveCount) {
1997 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1999 for (int i = 0; i < moveCount - 1; i++)
2001 m = movesSearched[i];
2005 if (!pos.move_is_capture_or_promotion(m))
2006 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2011 // update_killers() add a good move that produced a beta-cutoff
2012 // among the killer moves of that ply.
2014 void update_killers(Move m, SearchStack* ss) {
2016 if (m == ss->killers[0])
2019 ss->killers[1] = ss->killers[0];
2024 // update_gains() updates the gains table of a non-capture move given
2025 // the static position evaluation before and after the move.
2027 void update_gains(const Position& pos, Move m, Value before, Value after) {
2030 && before != VALUE_NONE
2031 && after != VALUE_NONE
2032 && pos.captured_piece_type() == PIECE_TYPE_NONE
2033 && !move_is_special(m))
2034 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2038 // current_search_time() returns the number of milliseconds which have passed
2039 // since the beginning of the current search.
2041 int current_search_time() {
2043 return get_system_time() - SearchStartTime;
2047 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2049 std::string value_to_uci(Value v) {
2051 std::stringstream s;
2053 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2054 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2056 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2061 // nps() computes the current nodes/second count.
2065 int t = current_search_time();
2066 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2070 // poll() performs two different functions: It polls for user input, and it
2071 // looks at the time consumed so far and decides if it's time to abort the
2076 static int lastInfoTime;
2077 int t = current_search_time();
2082 // We are line oriented, don't read single chars
2083 std::string command;
2085 if (!std::getline(std::cin, command))
2088 if (command == "quit")
2091 PonderSearch = false;
2095 else if (command == "stop")
2098 PonderSearch = false;
2100 else if (command == "ponderhit")
2104 // Print search information
2108 else if (lastInfoTime > t)
2109 // HACK: Must be a new search where we searched less than
2110 // NodesBetweenPolls nodes during the first second of search.
2113 else if (t - lastInfoTime >= 1000)
2120 if (dbg_show_hit_rate)
2121 dbg_print_hit_rate();
2123 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2124 << " time " << t << endl;
2127 // Should we stop the search?
2131 bool stillAtFirstMove = FirstRootMove
2132 && !AspirationFailLow
2133 && t > TimeMgr.available_time();
2135 bool noMoreTime = t > TimeMgr.maximum_time()
2136 || stillAtFirstMove;
2138 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2139 || (ExactMaxTime && t >= ExactMaxTime)
2140 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2145 // ponderhit() is called when the program is pondering (i.e. thinking while
2146 // it's the opponent's turn to move) in order to let the engine know that
2147 // it correctly predicted the opponent's move.
2151 int t = current_search_time();
2152 PonderSearch = false;
2154 bool stillAtFirstMove = FirstRootMove
2155 && !AspirationFailLow
2156 && t > TimeMgr.available_time();
2158 bool noMoreTime = t > TimeMgr.maximum_time()
2159 || stillAtFirstMove;
2161 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2166 // init_ss_array() does a fast reset of the first entries of a SearchStack
2167 // array and of all the excludedMove and skipNullMove entries.
2169 void init_ss_array(SearchStack* ss, int size) {
2171 for (int i = 0; i < size; i++, ss++)
2173 ss->excludedMove = MOVE_NONE;
2174 ss->skipNullMove = false;
2175 ss->reduction = DEPTH_ZERO;
2178 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2183 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2184 // while the program is pondering. The point is to work around a wrinkle in
2185 // the UCI protocol: When pondering, the engine is not allowed to give a
2186 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2187 // We simply wait here until one of these commands is sent, and return,
2188 // after which the bestmove and pondermove will be printed (in id_loop()).
2190 void wait_for_stop_or_ponderhit() {
2192 std::string command;
2196 if (!std::getline(std::cin, command))
2199 if (command == "quit")
2204 else if (command == "ponderhit" || command == "stop")
2210 // print_pv_info() prints to standard output and eventually to log file information on
2211 // the current PV line. It is called at each iteration or after a new pv is found.
2213 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2215 cout << "info depth " << Iteration
2216 << " score " << value_to_uci(value)
2217 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2218 << " time " << current_search_time()
2219 << " nodes " << ThreadsMgr.nodes_searched()
2223 for (Move* m = pv; *m != MOVE_NONE; m++)
2230 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2231 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2233 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2234 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2239 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2240 // the PV back into the TT. This makes sure the old PV moves are searched
2241 // first, even if the old TT entries have been overwritten.
2243 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2247 Position p(pos, pos.thread());
2251 for (int i = 0; pv[i] != MOVE_NONE; i++)
2253 tte = TT.retrieve(p.get_key());
2254 if (!tte || tte->move() != pv[i])
2256 v = (p.is_check() ? VALUE_NONE : evaluate(p, margins));
2257 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, margins[pos.side_to_move()]);
2259 p.do_move(pv[i], st);
2264 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2265 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2266 // allow to always have a ponder move even when we fail high at root and also a
2267 // long PV to print that is important for position analysis.
2269 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2273 Position p(pos, pos.thread());
2276 assert(bestMove != MOVE_NONE);
2279 p.do_move(pv[ply++], st);
2281 while ( (tte = TT.retrieve(p.get_key())) != NULL
2282 && tte->move() != MOVE_NONE
2283 && move_is_legal(p, tte->move())
2285 && (!p.is_draw() || ply < 2))
2287 pv[ply] = tte->move();
2288 p.do_move(pv[ply++], st);
2290 pv[ply] = MOVE_NONE;
2294 // init_thread() is the function which is called when a new thread is
2295 // launched. It simply calls the idle_loop() function with the supplied
2296 // threadID. There are two versions of this function; one for POSIX
2297 // threads and one for Windows threads.
2299 #if !defined(_MSC_VER)
2301 void* init_thread(void *threadID) {
2303 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2309 DWORD WINAPI init_thread(LPVOID threadID) {
2311 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2318 /// The ThreadsManager class
2320 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2321 // get_beta_counters() are getters/setters for the per thread
2322 // counters used to sort the moves at root.
2324 void ThreadsManager::resetNodeCounters() {
2326 for (int i = 0; i < MAX_THREADS; i++)
2327 threads[i].nodes = 0ULL;
2330 int64_t ThreadsManager::nodes_searched() const {
2332 int64_t result = 0ULL;
2333 for (int i = 0; i < ActiveThreads; i++)
2334 result += threads[i].nodes;
2340 // idle_loop() is where the threads are parked when they have no work to do.
2341 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2342 // object for which the current thread is the master.
2344 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2346 assert(threadID >= 0 && threadID < MAX_THREADS);
2350 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2351 // master should exit as last one.
2352 if (AllThreadsShouldExit)
2355 threads[threadID].state = THREAD_TERMINATED;
2359 // If we are not thinking, wait for a condition to be signaled
2360 // instead of wasting CPU time polling for work.
2361 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2364 assert(threadID != 0);
2365 threads[threadID].state = THREAD_SLEEPING;
2367 #if !defined(_MSC_VER)
2368 lock_grab(&WaitLock);
2369 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2370 pthread_cond_wait(&WaitCond, &WaitLock);
2371 lock_release(&WaitLock);
2373 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2377 // If thread has just woken up, mark it as available
2378 if (threads[threadID].state == THREAD_SLEEPING)
2379 threads[threadID].state = THREAD_AVAILABLE;
2381 // If this thread has been assigned work, launch a search
2382 if (threads[threadID].state == THREAD_WORKISWAITING)
2384 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2386 threads[threadID].state = THREAD_SEARCHING;
2388 if (threads[threadID].splitPoint->pvNode)
2389 sp_search<PV>(threads[threadID].splitPoint, threadID);
2391 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2393 assert(threads[threadID].state == THREAD_SEARCHING);
2395 threads[threadID].state = THREAD_AVAILABLE;
2398 // If this thread is the master of a split point and all slaves have
2399 // finished their work at this split point, return from the idle loop.
2401 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2403 if (i == ActiveThreads)
2405 // Because sp->slaves[] is reset under lock protection,
2406 // be sure sp->lock has been released before to return.
2407 lock_grab(&(sp->lock));
2408 lock_release(&(sp->lock));
2410 assert(threads[threadID].state == THREAD_AVAILABLE);
2412 threads[threadID].state = THREAD_SEARCHING;
2419 // init_threads() is called during startup. It launches all helper threads,
2420 // and initializes the split point stack and the global locks and condition
2423 void ThreadsManager::init_threads() {
2428 #if !defined(_MSC_VER)
2429 pthread_t pthread[1];
2432 // Initialize global locks
2434 lock_init(&WaitLock);
2436 #if !defined(_MSC_VER)
2437 pthread_cond_init(&WaitCond, NULL);
2439 for (i = 0; i < MAX_THREADS; i++)
2440 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2443 // Initialize splitPoints[] locks
2444 for (i = 0; i < MAX_THREADS; i++)
2445 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2446 lock_init(&(threads[i].splitPoints[j].lock));
2448 // Will be set just before program exits to properly end the threads
2449 AllThreadsShouldExit = false;
2451 // Threads will be put to sleep as soon as created
2452 AllThreadsShouldSleep = true;
2454 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2456 threads[0].state = THREAD_SEARCHING;
2457 for (i = 1; i < MAX_THREADS; i++)
2458 threads[i].state = THREAD_AVAILABLE;
2460 // Launch the helper threads
2461 for (i = 1; i < MAX_THREADS; i++)
2464 #if !defined(_MSC_VER)
2465 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2467 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2472 cout << "Failed to create thread number " << i << endl;
2473 Application::exit_with_failure();
2476 // Wait until the thread has finished launching and is gone to sleep
2477 while (threads[i].state != THREAD_SLEEPING) {}
2482 // exit_threads() is called when the program exits. It makes all the
2483 // helper threads exit cleanly.
2485 void ThreadsManager::exit_threads() {
2487 ActiveThreads = MAX_THREADS; // HACK
2488 AllThreadsShouldSleep = true; // HACK
2489 wake_sleeping_threads();
2491 // This makes the threads to exit idle_loop()
2492 AllThreadsShouldExit = true;
2494 // Wait for thread termination
2495 for (int i = 1; i < MAX_THREADS; i++)
2496 while (threads[i].state != THREAD_TERMINATED) {}
2498 // Now we can safely destroy the locks
2499 for (int i = 0; i < MAX_THREADS; i++)
2500 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2501 lock_destroy(&(threads[i].splitPoints[j].lock));
2503 lock_destroy(&WaitLock);
2504 lock_destroy(&MPLock);
2508 // thread_should_stop() checks whether the thread should stop its search.
2509 // This can happen if a beta cutoff has occurred in the thread's currently
2510 // active split point, or in some ancestor of the current split point.
2512 bool ThreadsManager::thread_should_stop(int threadID) const {
2514 assert(threadID >= 0 && threadID < ActiveThreads);
2518 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2523 // thread_is_available() checks whether the thread with threadID "slave" is
2524 // available to help the thread with threadID "master" at a split point. An
2525 // obvious requirement is that "slave" must be idle. With more than two
2526 // threads, this is not by itself sufficient: If "slave" is the master of
2527 // some active split point, it is only available as a slave to the other
2528 // threads which are busy searching the split point at the top of "slave"'s
2529 // split point stack (the "helpful master concept" in YBWC terminology).
2531 bool ThreadsManager::thread_is_available(int slave, int master) const {
2533 assert(slave >= 0 && slave < ActiveThreads);
2534 assert(master >= 0 && master < ActiveThreads);
2535 assert(ActiveThreads > 1);
2537 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2540 // Make a local copy to be sure doesn't change under our feet
2541 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2543 if (localActiveSplitPoints == 0)
2544 // No active split points means that the thread is available as
2545 // a slave for any other thread.
2548 if (ActiveThreads == 2)
2551 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2552 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2553 // could have been set to 0 by another thread leading to an out of bound access.
2554 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2561 // available_thread_exists() tries to find an idle thread which is available as
2562 // a slave for the thread with threadID "master".
2564 bool ThreadsManager::available_thread_exists(int master) const {
2566 assert(master >= 0 && master < ActiveThreads);
2567 assert(ActiveThreads > 1);
2569 for (int i = 0; i < ActiveThreads; i++)
2570 if (thread_is_available(i, master))
2577 // split() does the actual work of distributing the work at a node between
2578 // several available threads. If it does not succeed in splitting the
2579 // node (because no idle threads are available, or because we have no unused
2580 // split point objects), the function immediately returns. If splitting is
2581 // possible, a SplitPoint object is initialized with all the data that must be
2582 // copied to the helper threads and we tell our helper threads that they have
2583 // been assigned work. This will cause them to instantly leave their idle loops
2584 // and call sp_search(). When all threads have returned from sp_search() then
2587 template <bool Fake>
2588 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2589 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2590 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2592 assert(ply > 0 && ply < PLY_MAX);
2593 assert(*bestValue >= -VALUE_INFINITE);
2594 assert(*bestValue <= *alpha);
2595 assert(*alpha < beta);
2596 assert(beta <= VALUE_INFINITE);
2597 assert(depth > DEPTH_ZERO);
2598 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2599 assert(ActiveThreads > 1);
2601 int i, master = p.thread();
2602 Thread& masterThread = threads[master];
2606 // If no other thread is available to help us, or if we have too many
2607 // active split points, don't split.
2608 if ( !available_thread_exists(master)
2609 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2611 lock_release(&MPLock);
2615 // Pick the next available split point object from the split point stack
2616 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2618 // Initialize the split point object
2619 splitPoint.parent = masterThread.splitPoint;
2620 splitPoint.stopRequest = false;
2621 splitPoint.ply = ply;
2622 splitPoint.depth = depth;
2623 splitPoint.threatMove = threatMove;
2624 splitPoint.mateThreat = mateThreat;
2625 splitPoint.alpha = *alpha;
2626 splitPoint.beta = beta;
2627 splitPoint.pvNode = pvNode;
2628 splitPoint.bestValue = *bestValue;
2630 splitPoint.moveCount = *moveCount;
2631 splitPoint.pos = &p;
2632 splitPoint.parentSstack = ss;
2633 for (i = 0; i < ActiveThreads; i++)
2634 splitPoint.slaves[i] = 0;
2636 masterThread.splitPoint = &splitPoint;
2638 // If we are here it means we are not available
2639 assert(masterThread.state != THREAD_AVAILABLE);
2641 int workersCnt = 1; // At least the master is included
2643 // Allocate available threads setting state to THREAD_BOOKED
2644 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2645 if (thread_is_available(i, master))
2647 threads[i].state = THREAD_BOOKED;
2648 threads[i].splitPoint = &splitPoint;
2649 splitPoint.slaves[i] = 1;
2653 assert(Fake || workersCnt > 1);
2655 // We can release the lock because slave threads are already booked and master is not available
2656 lock_release(&MPLock);
2658 // Tell the threads that they have work to do. This will make them leave
2659 // their idle loop. But before copy search stack tail for each thread.
2660 for (i = 0; i < ActiveThreads; i++)
2661 if (i == master || splitPoint.slaves[i])
2663 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2665 assert(i == master || threads[i].state == THREAD_BOOKED);
2667 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2670 // Everything is set up. The master thread enters the idle loop, from
2671 // which it will instantly launch a search, because its state is
2672 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2673 // idle loop, which means that the main thread will return from the idle
2674 // loop when all threads have finished their work at this split point.
2675 idle_loop(master, &splitPoint);
2677 // We have returned from the idle loop, which means that all threads are
2678 // finished. Update alpha and bestValue, and return.
2681 *alpha = splitPoint.alpha;
2682 *bestValue = splitPoint.bestValue;
2683 masterThread.activeSplitPoints--;
2684 masterThread.splitPoint = splitPoint.parent;
2686 lock_release(&MPLock);
2690 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2691 // to start a new search from the root.
2693 void ThreadsManager::wake_sleeping_threads() {
2695 assert(AllThreadsShouldSleep);
2696 assert(ActiveThreads > 0);
2698 AllThreadsShouldSleep = false;
2700 if (ActiveThreads == 1)
2703 #if !defined(_MSC_VER)
2704 pthread_mutex_lock(&WaitLock);
2705 pthread_cond_broadcast(&WaitCond);
2706 pthread_mutex_unlock(&WaitLock);
2708 for (int i = 1; i < MAX_THREADS; i++)
2709 SetEvent(SitIdleEvent[i]);
2715 // put_threads_to_sleep() makes all the threads go to sleep just before
2716 // to leave think(), at the end of the search. Threads should have already
2717 // finished the job and should be idle.
2719 void ThreadsManager::put_threads_to_sleep() {
2721 assert(!AllThreadsShouldSleep);
2723 // This makes the threads to go to sleep
2724 AllThreadsShouldSleep = true;
2727 /// The RootMoveList class
2729 // RootMoveList c'tor
2731 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2733 SearchStack ss[PLY_MAX_PLUS_2];
2734 MoveStack mlist[MOVES_MAX];
2736 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2738 // Initialize search stack
2739 init_ss_array(ss, PLY_MAX_PLUS_2);
2740 ss[0].eval = VALUE_NONE;
2743 // Generate all legal moves
2744 MoveStack* last = generate_moves(pos, mlist);
2746 // Add each move to the moves[] array
2747 for (MoveStack* cur = mlist; cur != last; cur++)
2749 bool includeMove = includeAllMoves;
2751 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2752 includeMove = (searchMoves[k] == cur->move);
2757 // Find a quick score for the move
2758 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2759 moves[count].pv[1] = MOVE_NONE;
2760 pos.do_move(cur->move, st);
2761 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2762 pos.undo_move(cur->move);
2768 // Score root moves using the standard way used in main search, the moves
2769 // are scored according to the order in which are returned by MovePicker.
2771 void RootMoveList::score_moves(const Position& pos)
2775 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2777 while ((move = mp.get_next_move()) != MOVE_NONE)
2778 for (int i = 0; i < count; i++)
2779 if (moves[i].move == move)
2781 moves[i].mp_score = score--;
2786 // RootMoveList simple methods definitions
2788 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2792 for (j = 0; pv[j] != MOVE_NONE; j++)
2793 moves[moveNum].pv[j] = pv[j];
2795 moves[moveNum].pv[j] = MOVE_NONE;
2799 // RootMoveList::sort() sorts the root move list at the beginning of a new
2802 void RootMoveList::sort() {
2804 sort_multipv(count - 1); // Sort all items
2808 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2809 // list by their scores and depths. It is used to order the different PVs
2810 // correctly in MultiPV mode.
2812 void RootMoveList::sort_multipv(int n) {
2816 for (i = 1; i <= n; i++)
2818 RootMove rm = moves[i];
2819 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2820 moves[j] = moves[j - 1];