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 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
230 int FutilityMoveCountArray[32]; // [depth]
232 inline Value futility_margin(Depth d, int mn) { return 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] = Value(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) {
723 Depth depth, ext, newDepth;
724 Value value, evalMargin, alpha, beta;
725 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
726 int researchCountFH, researchCountFL;
728 researchCountFH = researchCountFL = 0;
731 isCheck = pos.is_check();
732 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
734 // Step 1. Initialize node (polling is omitted at root)
735 ss->currentMove = ss->bestMove = MOVE_NONE;
737 // Step 2. Check for aborted search (omitted at root)
738 // Step 3. Mate distance pruning (omitted at root)
739 // Step 4. Transposition table lookup (omitted at root)
741 // Step 5. Evaluate the position statically
742 // At root we do this only to get reference value for child nodes
743 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
745 // Step 6. Razoring (omitted at root)
746 // Step 7. Static null move pruning (omitted at root)
747 // Step 8. Null move search with verification search (omitted at root)
748 // Step 9. Internal iterative deepening (omitted at root)
750 // Step extra. Fail low loop
751 // We start with small aspiration window and in case of fail low, we research
752 // with bigger window until we are not failing low anymore.
755 // Sort the moves before to (re)search
756 rml.score_moves(pos);
759 // Step 10. Loop through all moves in the root move list
760 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
762 // This is used by time management
763 FirstRootMove = (i == 0);
765 // Save the current node count before the move is searched
766 nodes = ThreadsMgr.nodes_searched();
768 // Pick the next root move, and print the move and the move number to
769 // the standard output.
770 move = ss->currentMove = rml.move(i);
772 if (current_search_time() >= 1000)
773 cout << "info currmove " << move
774 << " currmovenumber " << i + 1 << endl;
776 moveIsCheck = pos.move_is_check(move);
777 captureOrPromotion = pos.move_is_capture_or_promotion(move);
779 // Step 11. Decide the new search depth
780 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
781 newDepth = depth + ext;
783 // Step 12. Futility pruning (omitted at root)
785 // Step extra. Fail high loop
786 // If move fails high, we research with bigger window until we are not failing
788 value = - VALUE_INFINITE;
792 // Step 13. Make the move
793 pos.do_move(move, st, ci, moveIsCheck);
795 // Step extra. pv search
796 // We do pv search for first moves (i < MultiPV)
797 // and for fail high research (value > alpha)
798 if (i < MultiPV || value > alpha)
800 // Aspiration window is disabled in multi-pv case
802 alpha = -VALUE_INFINITE;
804 // Full depth PV search, done on first move or after a fail high
805 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
809 // Step 14. Reduced search
810 // if the move fails high will be re-searched at full depth
811 bool doFullDepthSearch = true;
813 if ( depth >= 3 * ONE_PLY
815 && !captureOrPromotion
816 && !move_is_castle(move))
818 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
821 assert(newDepth-ss->reduction >= ONE_PLY);
823 // Reduced depth non-pv search using alpha as upperbound
824 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
825 doFullDepthSearch = (value > alpha);
828 // The move failed high, but if reduction is very big we could
829 // face a false positive, retry with a less aggressive reduction,
830 // if the move fails high again then go with full depth search.
831 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
833 assert(newDepth - ONE_PLY >= ONE_PLY);
835 ss->reduction = ONE_PLY;
836 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
837 doFullDepthSearch = (value > alpha);
839 ss->reduction = DEPTH_ZERO; // Restore original reduction
842 // Step 15. Full depth search
843 if (doFullDepthSearch)
845 // Full depth non-pv search using alpha as upperbound
846 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
848 // If we are above alpha then research at same depth but as PV
849 // to get a correct score or eventually a fail high above beta.
851 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
855 // Step 16. Undo move
858 // Can we exit fail high loop ?
859 if (AbortSearch || value < beta)
862 // We are failing high and going to do a research. It's important to update
863 // the score before research in case we run out of time while researching.
864 rml.set_move_score(i, value);
866 extract_pv_from_tt(pos, move, pv);
867 rml.set_move_pv(i, pv);
869 // Print information to the standard output
870 print_pv_info(pos, pv, alpha, beta, value);
872 // Prepare for a research after a fail high, each time with a wider window
873 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
876 } // End of fail high loop
878 // Finished searching the move. If AbortSearch is true, the search
879 // was aborted because the user interrupted the search or because we
880 // ran out of time. In this case, the return value of the search cannot
881 // be trusted, and we break out of the loop without updating the best
886 // Remember searched nodes counts for this move
887 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
889 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
890 assert(value < beta);
892 // Step 17. Check for new best move
893 if (value <= alpha && i >= MultiPV)
894 rml.set_move_score(i, -VALUE_INFINITE);
897 // PV move or new best move!
900 rml.set_move_score(i, value);
902 extract_pv_from_tt(pos, move, pv);
903 rml.set_move_pv(i, pv);
907 // We record how often the best move has been changed in each
908 // iteration. This information is used for time managment: When
909 // the best move changes frequently, we allocate some more time.
911 BestMoveChangesByIteration[Iteration]++;
913 // Print information to the standard output
914 print_pv_info(pos, pv, alpha, beta, value);
916 // Raise alpha to setup proper non-pv search upper bound
923 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
925 cout << "info multipv " << j + 1
926 << " score " << value_to_uci(rml.move_score(j))
927 << " depth " << (j <= i ? Iteration : Iteration - 1)
928 << " time " << current_search_time()
929 << " nodes " << ThreadsMgr.nodes_searched()
933 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
934 cout << rml.move_pv(j, k) << " ";
938 alpha = rml.move_score(Min(i, MultiPV - 1));
940 } // PV move or new best move
942 assert(alpha >= *alphaPtr);
944 AspirationFailLow = (alpha == *alphaPtr);
946 if (AspirationFailLow && StopOnPonderhit)
947 StopOnPonderhit = false;
950 // Can we exit fail low loop ?
951 if (AbortSearch || !AspirationFailLow)
954 // Prepare for a research after a fail low, each time with a wider window
955 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
960 // Sort the moves before to return
967 // search<>() is the main search function for both PV and non-PV nodes
969 template <NodeType PvNode>
970 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
972 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
973 assert(beta > alpha && beta <= VALUE_INFINITE);
974 assert(PvNode || alpha == beta - 1);
975 assert(ply > 0 && ply < PLY_MAX);
976 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
978 Move movesSearched[MOVES_MAX];
982 Move ttMove, move, excludedMove, threatMove;
984 Value bestValue, value, evalMargin, oldAlpha;
985 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
986 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
987 bool mateThreat = false;
989 int threadID = pos.thread();
990 refinedValue = bestValue = value = -VALUE_INFINITE;
993 // Step 1. Initialize node and poll. Polling can abort search
994 ThreadsMgr.incrementNodeCounter(threadID);
995 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
996 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
998 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1004 // Step 2. Check for aborted search and immediate draw
1005 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1008 if (pos.is_draw() || ply >= PLY_MAX - 1)
1011 // Step 3. Mate distance pruning
1012 alpha = Max(value_mated_in(ply), alpha);
1013 beta = Min(value_mate_in(ply+1), beta);
1017 // Step 4. Transposition table lookup
1019 // We don't want the score of a partial search to overwrite a previous full search
1020 // TT value, so we use a different position key in case of an excluded move exists.
1021 excludedMove = ss->excludedMove;
1022 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1024 tte = TT.retrieve(posKey);
1025 ttMove = (tte ? tte->move() : MOVE_NONE);
1027 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1028 // This is to avoid problems in the following areas:
1030 // * Repetition draw detection
1031 // * Fifty move rule detection
1032 // * Searching for a mate
1033 // * Printing of full PV line
1035 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1037 // Refresh tte entry to avoid aging
1038 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1040 ss->bestMove = ttMove; // Can be MOVE_NONE
1041 return value_from_tt(tte->value(), ply);
1044 // Step 5. Evaluate the position statically and
1045 // update gain statistics of parent move.
1046 isCheck = pos.is_check();
1048 ss->eval = evalMargin = VALUE_NONE;
1051 assert(tte->static_value() != VALUE_NONE);
1053 ss->eval = tte->static_value();
1054 evalMargin = tte->static_value_margin();
1055 refinedValue = refine_eval(tte, ss->eval, ply);
1059 refinedValue = ss->eval = evaluate(pos, evalMargin);
1060 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1063 // Save gain for the parent non-capture move
1064 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1066 // Step 6. Razoring (is omitted in PV nodes)
1068 && depth < RazorDepth
1070 && refinedValue < beta - razor_margin(depth)
1071 && ttMove == MOVE_NONE
1072 && (ss-1)->currentMove != MOVE_NULL
1073 && !value_is_mate(beta)
1074 && !pos.has_pawn_on_7th(pos.side_to_move()))
1076 Value rbeta = beta - razor_margin(depth);
1077 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1079 // Logically we should return (v + razor_margin(depth)), but
1080 // surprisingly this did slightly weaker in tests.
1084 // Step 7. Static null move pruning (is omitted in PV nodes)
1085 // We're betting that the opponent doesn't have a move that will reduce
1086 // the score by more than futility_margin(depth) if we do a null move.
1088 && !ss->skipNullMove
1089 && depth < RazorDepth
1091 && refinedValue >= beta + futility_margin(depth, 0)
1092 && !value_is_mate(beta)
1093 && pos.non_pawn_material(pos.side_to_move()))
1094 return refinedValue - futility_margin(depth, 0);
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1097 // When we jump directly to qsearch() we do a null move only if static value is
1098 // at least beta. Otherwise we do a null move if static value is not more than
1099 // NullMoveMargin under beta.
1101 && !ss->skipNullMove
1104 && refinedValue >= beta - (depth >= 4 * ONE_PLY ? NullMoveMargin : 0)
1105 && !value_is_mate(beta)
1106 && pos.non_pawn_material(pos.side_to_move()))
1108 ss->currentMove = MOVE_NULL;
1110 // Null move dynamic reduction based on depth
1111 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1113 // Null move dynamic reduction based on value
1114 if (refinedValue - beta > PawnValueMidgame)
1117 pos.do_null_move(st);
1118 (ss+1)->skipNullMove = true;
1120 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1121 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1122 (ss+1)->skipNullMove = false;
1123 pos.undo_null_move();
1125 if (nullValue >= beta)
1127 // Do not return unproven mate scores
1128 if (nullValue >= value_mate_in(PLY_MAX))
1131 if (depth < 6 * ONE_PLY)
1134 // Do verification search at high depths
1135 ss->skipNullMove = true;
1136 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1137 ss->skipNullMove = false;
1144 // The null move failed low, which means that we may be faced with
1145 // some kind of threat. If the previous move was reduced, check if
1146 // the move that refuted the null move was somehow connected to the
1147 // move which was reduced. If a connection is found, return a fail
1148 // low score (which will cause the reduced move to fail high in the
1149 // parent node, which will trigger a re-search with full depth).
1150 if (nullValue == value_mated_in(ply + 2))
1153 threatMove = (ss+1)->bestMove;
1154 if ( depth < ThreatDepth
1155 && (ss-1)->reduction
1156 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1161 // Step 9. Internal iterative deepening
1162 if ( depth >= IIDDepth[PvNode]
1163 && ttMove == MOVE_NONE
1164 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1166 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1168 ss->skipNullMove = true;
1169 search<PvNode>(pos, ss, alpha, beta, d, ply);
1170 ss->skipNullMove = false;
1172 ttMove = ss->bestMove;
1173 tte = TT.retrieve(posKey);
1176 // Expensive mate threat detection (only for PV nodes)
1178 mateThreat = pos.has_mate_threat();
1180 // Initialize a MovePicker object for the current position
1181 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1183 ss->bestMove = MOVE_NONE;
1184 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1185 futilityBase = ss->eval + evalMargin;
1186 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1189 && !excludedMove // Do not allow recursive singular extension search
1190 && (tte->type() & VALUE_TYPE_LOWER)
1191 && tte->depth() >= depth - 3 * ONE_PLY;
1193 // Step 10. Loop through moves
1194 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1195 while ( bestValue < beta
1196 && (move = mp.get_next_move()) != MOVE_NONE
1197 && !ThreadsMgr.thread_should_stop(threadID))
1199 assert(move_is_ok(move));
1201 if (move == excludedMove)
1204 moveIsCheck = pos.move_is_check(move, ci);
1205 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1207 // Step 11. Decide the new search depth
1208 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1210 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1211 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1212 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1213 // lower then ttValue minus a margin then we extend ttMove.
1214 if ( singularExtensionNode
1215 && move == tte->move()
1218 Value ttValue = value_from_tt(tte->value(), ply);
1220 if (abs(ttValue) < VALUE_KNOWN_WIN)
1222 Value b = ttValue - SingularExtensionMargin;
1223 ss->excludedMove = move;
1224 ss->skipNullMove = true;
1225 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1226 ss->skipNullMove = false;
1227 ss->excludedMove = MOVE_NONE;
1228 ss->bestMove = MOVE_NONE;
1234 newDepth = depth - ONE_PLY + ext;
1236 // Update current move (this must be done after singular extension search)
1237 movesSearched[moveCount++] = ss->currentMove = move;
1239 // Step 12. Futility pruning (is omitted in PV nodes)
1241 && !captureOrPromotion
1245 && !move_is_castle(move))
1247 // Move count based pruning
1248 if ( moveCount >= futility_move_count(depth)
1249 && !(threatMove && connected_threat(pos, move, threatMove))
1250 && bestValue > value_mated_in(PLY_MAX))
1253 // Value based pruning
1254 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1255 // but fixing this made program slightly weaker.
1256 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1257 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1258 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1260 if (futilityValueScaled < beta)
1262 if (futilityValueScaled > bestValue)
1263 bestValue = futilityValueScaled;
1268 // Step 13. Make the move
1269 pos.do_move(move, st, ci, moveIsCheck);
1271 // Step extra. pv search (only in PV nodes)
1272 // The first move in list is the expected PV
1273 if (PvNode && moveCount == 1)
1274 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1275 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1278 // Step 14. Reduced depth search
1279 // If the move fails high will be re-searched at full depth.
1280 bool doFullDepthSearch = true;
1282 if ( depth >= 3 * ONE_PLY
1283 && !captureOrPromotion
1285 && !move_is_castle(move)
1286 && !move_is_killer(move, ss))
1288 ss->reduction = reduction<PvNode>(depth, moveCount);
1291 Depth d = newDepth - ss->reduction;
1292 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1293 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1295 doFullDepthSearch = (value > alpha);
1298 // The move failed high, but if reduction is very big we could
1299 // face a false positive, retry with a less aggressive reduction,
1300 // if the move fails high again then go with full depth search.
1301 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1303 assert(newDepth - ONE_PLY >= ONE_PLY);
1305 ss->reduction = ONE_PLY;
1306 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1307 doFullDepthSearch = (value > alpha);
1309 ss->reduction = DEPTH_ZERO; // Restore original reduction
1312 // Step 15. Full depth search
1313 if (doFullDepthSearch)
1315 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1316 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1318 // Step extra. pv search (only in PV nodes)
1319 // Search only for possible new PV nodes, if instead value >= beta then
1320 // parent node fails low with value <= alpha and tries another move.
1321 if (PvNode && value > alpha && value < beta)
1322 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1323 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1327 // Step 16. Undo move
1328 pos.undo_move(move);
1330 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1332 // Step 17. Check for new best move
1333 if (value > bestValue)
1338 if (PvNode && value < beta) // We want always alpha < beta
1341 if (value == value_mate_in(ply + 1))
1342 ss->mateKiller = move;
1344 ss->bestMove = move;
1348 // Step 18. Check for split
1349 if ( depth >= MinimumSplitDepth
1350 && ThreadsMgr.active_threads() > 1
1352 && ThreadsMgr.available_thread_exists(threadID)
1354 && !ThreadsMgr.thread_should_stop(threadID)
1356 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1357 threatMove, mateThreat, &moveCount, &mp, PvNode);
1360 // Step 19. Check for mate and stalemate
1361 // All legal moves have been searched and if there are
1362 // no legal moves, it must be mate or stalemate.
1363 // If one move was excluded return fail low score.
1365 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1367 // Step 20. Update tables
1368 // If the search is not aborted, update the transposition table,
1369 // history counters, and killer moves.
1370 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1373 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1374 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1375 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
1377 // Update killers and history only for non capture moves that fails high
1378 if ( bestValue >= beta
1379 && !pos.move_is_capture_or_promotion(move))
1381 update_history(pos, move, depth, movesSearched, moveCount);
1382 update_killers(move, ss);
1385 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1391 // qsearch() is the quiescence search function, which is called by the main
1392 // search function when the remaining depth is zero (or, to be more precise,
1393 // less than ONE_PLY).
1395 template <NodeType PvNode>
1396 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1398 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1399 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1400 assert(PvNode || alpha == beta - 1);
1402 assert(ply > 0 && ply < PLY_MAX);
1403 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1407 Value bestValue, value, evalMargin, 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 = evalMargin = VALUE_NONE;
1437 deepChecks = enoughMaterial = false;
1443 assert(tte->static_value() != VALUE_NONE);
1445 evalMargin = tte->static_value_margin();
1446 bestValue = tte->static_value();
1449 bestValue = evaluate(pos, evalMargin);
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, evalMargin);
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 + evalMargin;
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, evalMargin);
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());
2245 Value v, m = VALUE_NONE;
2247 for (int i = 0; pv[i] != MOVE_NONE; i++)
2249 tte = TT.retrieve(p.get_key());
2250 if (!tte || tte->move() != pv[i])
2252 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2253 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2255 p.do_move(pv[i], st);
2260 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2261 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2262 // allow to always have a ponder move even when we fail high at root and also a
2263 // long PV to print that is important for position analysis.
2265 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2269 Position p(pos, pos.thread());
2272 assert(bestMove != MOVE_NONE);
2275 p.do_move(pv[ply++], st);
2277 while ( (tte = TT.retrieve(p.get_key())) != NULL
2278 && tte->move() != MOVE_NONE
2279 && move_is_legal(p, tte->move())
2281 && (!p.is_draw() || ply < 2))
2283 pv[ply] = tte->move();
2284 p.do_move(pv[ply++], st);
2286 pv[ply] = MOVE_NONE;
2290 // init_thread() is the function which is called when a new thread is
2291 // launched. It simply calls the idle_loop() function with the supplied
2292 // threadID. There are two versions of this function; one for POSIX
2293 // threads and one for Windows threads.
2295 #if !defined(_MSC_VER)
2297 void* init_thread(void *threadID) {
2299 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2305 DWORD WINAPI init_thread(LPVOID threadID) {
2307 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2314 /// The ThreadsManager class
2316 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2317 // get_beta_counters() are getters/setters for the per thread
2318 // counters used to sort the moves at root.
2320 void ThreadsManager::resetNodeCounters() {
2322 for (int i = 0; i < MAX_THREADS; i++)
2323 threads[i].nodes = 0ULL;
2326 int64_t ThreadsManager::nodes_searched() const {
2328 int64_t result = 0ULL;
2329 for (int i = 0; i < ActiveThreads; i++)
2330 result += threads[i].nodes;
2336 // idle_loop() is where the threads are parked when they have no work to do.
2337 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2338 // object for which the current thread is the master.
2340 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2342 assert(threadID >= 0 && threadID < MAX_THREADS);
2346 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2347 // master should exit as last one.
2348 if (AllThreadsShouldExit)
2351 threads[threadID].state = THREAD_TERMINATED;
2355 // If we are not thinking, wait for a condition to be signaled
2356 // instead of wasting CPU time polling for work.
2357 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2360 assert(threadID != 0);
2361 threads[threadID].state = THREAD_SLEEPING;
2363 #if !defined(_MSC_VER)
2364 lock_grab(&WaitLock);
2365 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2366 pthread_cond_wait(&WaitCond, &WaitLock);
2367 lock_release(&WaitLock);
2369 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2373 // If thread has just woken up, mark it as available
2374 if (threads[threadID].state == THREAD_SLEEPING)
2375 threads[threadID].state = THREAD_AVAILABLE;
2377 // If this thread has been assigned work, launch a search
2378 if (threads[threadID].state == THREAD_WORKISWAITING)
2380 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2382 threads[threadID].state = THREAD_SEARCHING;
2384 if (threads[threadID].splitPoint->pvNode)
2385 sp_search<PV>(threads[threadID].splitPoint, threadID);
2387 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2389 assert(threads[threadID].state == THREAD_SEARCHING);
2391 threads[threadID].state = THREAD_AVAILABLE;
2394 // If this thread is the master of a split point and all slaves have
2395 // finished their work at this split point, return from the idle loop.
2397 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2399 if (i == ActiveThreads)
2401 // Because sp->slaves[] is reset under lock protection,
2402 // be sure sp->lock has been released before to return.
2403 lock_grab(&(sp->lock));
2404 lock_release(&(sp->lock));
2406 assert(threads[threadID].state == THREAD_AVAILABLE);
2408 threads[threadID].state = THREAD_SEARCHING;
2415 // init_threads() is called during startup. It launches all helper threads,
2416 // and initializes the split point stack and the global locks and condition
2419 void ThreadsManager::init_threads() {
2424 #if !defined(_MSC_VER)
2425 pthread_t pthread[1];
2428 // Initialize global locks
2430 lock_init(&WaitLock);
2432 #if !defined(_MSC_VER)
2433 pthread_cond_init(&WaitCond, NULL);
2435 for (i = 0; i < MAX_THREADS; i++)
2436 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2439 // Initialize splitPoints[] locks
2440 for (i = 0; i < MAX_THREADS; i++)
2441 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2442 lock_init(&(threads[i].splitPoints[j].lock));
2444 // Will be set just before program exits to properly end the threads
2445 AllThreadsShouldExit = false;
2447 // Threads will be put to sleep as soon as created
2448 AllThreadsShouldSleep = true;
2450 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2452 threads[0].state = THREAD_SEARCHING;
2453 for (i = 1; i < MAX_THREADS; i++)
2454 threads[i].state = THREAD_AVAILABLE;
2456 // Launch the helper threads
2457 for (i = 1; i < MAX_THREADS; i++)
2460 #if !defined(_MSC_VER)
2461 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2463 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2468 cout << "Failed to create thread number " << i << endl;
2469 Application::exit_with_failure();
2472 // Wait until the thread has finished launching and is gone to sleep
2473 while (threads[i].state != THREAD_SLEEPING) {}
2478 // exit_threads() is called when the program exits. It makes all the
2479 // helper threads exit cleanly.
2481 void ThreadsManager::exit_threads() {
2483 ActiveThreads = MAX_THREADS; // HACK
2484 AllThreadsShouldSleep = true; // HACK
2485 wake_sleeping_threads();
2487 // This makes the threads to exit idle_loop()
2488 AllThreadsShouldExit = true;
2490 // Wait for thread termination
2491 for (int i = 1; i < MAX_THREADS; i++)
2492 while (threads[i].state != THREAD_TERMINATED) {}
2494 // Now we can safely destroy the locks
2495 for (int i = 0; i < MAX_THREADS; i++)
2496 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2497 lock_destroy(&(threads[i].splitPoints[j].lock));
2499 lock_destroy(&WaitLock);
2500 lock_destroy(&MPLock);
2504 // thread_should_stop() checks whether the thread should stop its search.
2505 // This can happen if a beta cutoff has occurred in the thread's currently
2506 // active split point, or in some ancestor of the current split point.
2508 bool ThreadsManager::thread_should_stop(int threadID) const {
2510 assert(threadID >= 0 && threadID < ActiveThreads);
2514 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2519 // thread_is_available() checks whether the thread with threadID "slave" is
2520 // available to help the thread with threadID "master" at a split point. An
2521 // obvious requirement is that "slave" must be idle. With more than two
2522 // threads, this is not by itself sufficient: If "slave" is the master of
2523 // some active split point, it is only available as a slave to the other
2524 // threads which are busy searching the split point at the top of "slave"'s
2525 // split point stack (the "helpful master concept" in YBWC terminology).
2527 bool ThreadsManager::thread_is_available(int slave, int master) const {
2529 assert(slave >= 0 && slave < ActiveThreads);
2530 assert(master >= 0 && master < ActiveThreads);
2531 assert(ActiveThreads > 1);
2533 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2536 // Make a local copy to be sure doesn't change under our feet
2537 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2539 if (localActiveSplitPoints == 0)
2540 // No active split points means that the thread is available as
2541 // a slave for any other thread.
2544 if (ActiveThreads == 2)
2547 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2548 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2549 // could have been set to 0 by another thread leading to an out of bound access.
2550 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2557 // available_thread_exists() tries to find an idle thread which is available as
2558 // a slave for the thread with threadID "master".
2560 bool ThreadsManager::available_thread_exists(int master) const {
2562 assert(master >= 0 && master < ActiveThreads);
2563 assert(ActiveThreads > 1);
2565 for (int i = 0; i < ActiveThreads; i++)
2566 if (thread_is_available(i, master))
2573 // split() does the actual work of distributing the work at a node between
2574 // several available threads. If it does not succeed in splitting the
2575 // node (because no idle threads are available, or because we have no unused
2576 // split point objects), the function immediately returns. If splitting is
2577 // possible, a SplitPoint object is initialized with all the data that must be
2578 // copied to the helper threads and we tell our helper threads that they have
2579 // been assigned work. This will cause them to instantly leave their idle loops
2580 // and call sp_search(). When all threads have returned from sp_search() then
2583 template <bool Fake>
2584 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2585 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2586 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2588 assert(ply > 0 && ply < PLY_MAX);
2589 assert(*bestValue >= -VALUE_INFINITE);
2590 assert(*bestValue <= *alpha);
2591 assert(*alpha < beta);
2592 assert(beta <= VALUE_INFINITE);
2593 assert(depth > DEPTH_ZERO);
2594 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2595 assert(ActiveThreads > 1);
2597 int i, master = p.thread();
2598 Thread& masterThread = threads[master];
2602 // If no other thread is available to help us, or if we have too many
2603 // active split points, don't split.
2604 if ( !available_thread_exists(master)
2605 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2607 lock_release(&MPLock);
2611 // Pick the next available split point object from the split point stack
2612 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2614 // Initialize the split point object
2615 splitPoint.parent = masterThread.splitPoint;
2616 splitPoint.stopRequest = false;
2617 splitPoint.ply = ply;
2618 splitPoint.depth = depth;
2619 splitPoint.threatMove = threatMove;
2620 splitPoint.mateThreat = mateThreat;
2621 splitPoint.alpha = *alpha;
2622 splitPoint.beta = beta;
2623 splitPoint.pvNode = pvNode;
2624 splitPoint.bestValue = *bestValue;
2626 splitPoint.moveCount = *moveCount;
2627 splitPoint.pos = &p;
2628 splitPoint.parentSstack = ss;
2629 for (i = 0; i < ActiveThreads; i++)
2630 splitPoint.slaves[i] = 0;
2632 masterThread.splitPoint = &splitPoint;
2634 // If we are here it means we are not available
2635 assert(masterThread.state != THREAD_AVAILABLE);
2637 int workersCnt = 1; // At least the master is included
2639 // Allocate available threads setting state to THREAD_BOOKED
2640 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2641 if (thread_is_available(i, master))
2643 threads[i].state = THREAD_BOOKED;
2644 threads[i].splitPoint = &splitPoint;
2645 splitPoint.slaves[i] = 1;
2649 assert(Fake || workersCnt > 1);
2651 // We can release the lock because slave threads are already booked and master is not available
2652 lock_release(&MPLock);
2654 // Tell the threads that they have work to do. This will make them leave
2655 // their idle loop. But before copy search stack tail for each thread.
2656 for (i = 0; i < ActiveThreads; i++)
2657 if (i == master || splitPoint.slaves[i])
2659 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2661 assert(i == master || threads[i].state == THREAD_BOOKED);
2663 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2666 // Everything is set up. The master thread enters the idle loop, from
2667 // which it will instantly launch a search, because its state is
2668 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2669 // idle loop, which means that the main thread will return from the idle
2670 // loop when all threads have finished their work at this split point.
2671 idle_loop(master, &splitPoint);
2673 // We have returned from the idle loop, which means that all threads are
2674 // finished. Update alpha and bestValue, and return.
2677 *alpha = splitPoint.alpha;
2678 *bestValue = splitPoint.bestValue;
2679 masterThread.activeSplitPoints--;
2680 masterThread.splitPoint = splitPoint.parent;
2682 lock_release(&MPLock);
2686 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2687 // to start a new search from the root.
2689 void ThreadsManager::wake_sleeping_threads() {
2691 assert(AllThreadsShouldSleep);
2692 assert(ActiveThreads > 0);
2694 AllThreadsShouldSleep = false;
2696 if (ActiveThreads == 1)
2699 #if !defined(_MSC_VER)
2700 pthread_mutex_lock(&WaitLock);
2701 pthread_cond_broadcast(&WaitCond);
2702 pthread_mutex_unlock(&WaitLock);
2704 for (int i = 1; i < MAX_THREADS; i++)
2705 SetEvent(SitIdleEvent[i]);
2711 // put_threads_to_sleep() makes all the threads go to sleep just before
2712 // to leave think(), at the end of the search. Threads should have already
2713 // finished the job and should be idle.
2715 void ThreadsManager::put_threads_to_sleep() {
2717 assert(!AllThreadsShouldSleep);
2719 // This makes the threads to go to sleep
2720 AllThreadsShouldSleep = true;
2723 /// The RootMoveList class
2725 // RootMoveList c'tor
2727 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2729 SearchStack ss[PLY_MAX_PLUS_2];
2730 MoveStack mlist[MOVES_MAX];
2732 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2734 // Initialize search stack
2735 init_ss_array(ss, PLY_MAX_PLUS_2);
2736 ss[0].eval = VALUE_NONE;
2739 // Generate all legal moves
2740 MoveStack* last = generate_moves(pos, mlist);
2742 // Add each move to the moves[] array
2743 for (MoveStack* cur = mlist; cur != last; cur++)
2745 bool includeMove = includeAllMoves;
2747 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2748 includeMove = (searchMoves[k] == cur->move);
2753 // Find a quick score for the move
2754 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2755 moves[count].pv[1] = MOVE_NONE;
2756 pos.do_move(cur->move, st);
2757 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2758 pos.undo_move(cur->move);
2764 // Score root moves using the standard way used in main search, the moves
2765 // are scored according to the order in which are returned by MovePicker.
2767 void RootMoveList::score_moves(const Position& pos)
2771 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2773 while ((move = mp.get_next_move()) != MOVE_NONE)
2774 for (int i = 0; i < count; i++)
2775 if (moves[i].move == move)
2777 moves[i].mp_score = score--;
2782 // RootMoveList simple methods definitions
2784 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2788 for (j = 0; pv[j] != MOVE_NONE; j++)
2789 moves[moveNum].pv[j] = pv[j];
2791 moves[moveNum].pv[j] = MOVE_NONE;
2795 // RootMoveList::sort() sorts the root move list at the beginning of a new
2798 void RootMoveList::sort() {
2800 sort_multipv(count - 1); // Sort all items
2804 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2805 // list by their scores and depths. It is used to order the different PVs
2806 // correctly in MultiPV mode.
2808 void RootMoveList::sort_multipv(int n) {
2812 for (i = 1; i <= n; i++)
2814 RootMove rm = moves[i];
2815 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2816 moves[j] = moves[j - 1];