2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // Fast lookup table of sliding pieces indexed by Piece
63 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
64 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
66 // ThreadsManager class is used to handle all the threads related stuff in search,
67 // init, starting, parking and, the most important, launching a slave thread at a
68 // split point are what this class does. All the access to shared thread data is
69 // done through this class, so that we avoid using global variables instead.
71 class ThreadsManager {
72 /* As long as the single ThreadsManager object is defined as a global we don't
73 need to explicitly initialize to zero its data members because variables with
74 static storage duration are automatically set to zero before enter main()
80 int active_threads() const { return ActiveThreads; }
81 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
83 bool available_thread_exists(int master) const;
84 bool thread_is_available(int slave, int master) const;
85 bool thread_should_stop(int threadID) const;
86 void wake_sleeping_thread(int threadID);
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
95 volatile bool AllThreadsShouldExit;
96 Thread threads[MAX_THREADS];
98 WaitCondition WaitCond[MAX_THREADS];
102 // RootMove struct is used for moves at the root at the tree. For each
103 // root move, we store a score, a node count, and a PV (really a refutation
104 // in the case of moves which fail low).
108 RootMove() : mp_score(0), nodes(0) {}
110 // RootMove::operator<() is the comparison function used when
111 // sorting the moves. A move m1 is considered to be better
112 // than a move m2 if it has a higher score, or if the moves
113 // have equal score but m1 has the higher beta cut-off count.
114 bool operator<(const RootMove& m) const {
116 return score != m.score ? score < m.score : mp_score <= m.mp_score;
123 Move pv[PLY_MAX_PLUS_2];
127 // The RootMoveList class is essentially an array of RootMove objects, with
128 // a handful of methods for accessing the data in the individual moves.
133 RootMoveList(Position& pos, Move searchMoves[]);
135 Move move(int moveNum) const { return moves[moveNum].move; }
136 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
137 int move_count() const { return count; }
138 Value move_score(int moveNum) const { return moves[moveNum].score; }
139 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
140 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
141 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
143 void set_move_pv(int moveNum, const Move pv[]);
144 void score_moves(const Position& pos);
146 void sort_multipv(int n);
149 RootMove moves[MOVES_MAX];
154 // When formatting a move for std::cout we must know if we are in Chess960
155 // or not. To keep using the handy operator<<() on the move the trick is to
156 // embed this flag in the stream itself. Function-like named enum set960 is
157 // used as a custom manipulator and the stream internal general-purpose array,
158 // accessed through ios_base::iword(), is used to pass the flag to the move's
159 // operator<<() that will use it to properly format castling moves.
162 std::ostream& operator<< (std::ostream& os, const set960& m) {
164 os.iword(0) = int(m);
173 // Maximum depth for razoring
174 const Depth RazorDepth = 4 * ONE_PLY;
176 // Dynamic razoring margin based on depth
177 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
179 // Maximum depth for use of dynamic threat detection when null move fails low
180 const Depth ThreatDepth = 5 * ONE_PLY;
182 // Step 9. Internal iterative deepening
184 // Minimum depth for use of internal iterative deepening
185 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
187 // At Non-PV nodes we do an internal iterative deepening search
188 // when the static evaluation is bigger then beta - IIDMargin.
189 const Value IIDMargin = Value(0x100);
191 // Step 11. Decide the new search depth
193 // Extensions. Configurable UCI options
194 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
195 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
196 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
198 // Minimum depth for use of singular extension
199 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
201 // If the TT move is at least SingularExtensionMargin better then the
202 // remaining ones we will extend it.
203 const Value SingularExtensionMargin = Value(0x20);
205 // Step 12. Futility pruning
207 // Futility margin for quiescence search
208 const Value FutilityMarginQS = Value(0x80);
210 // Futility lookup tables (initialized at startup) and their getter functions
211 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
212 int FutilityMoveCountArray[32]; // [depth]
214 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
215 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
217 // Step 14. Reduced search
219 // Reduction lookup tables (initialized at startup) and their getter functions
220 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
222 template <NodeType PV>
223 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = ONE_PLY;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
235 /// Namespace variables
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
266 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode, bool SpNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
290 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
291 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
294 template <NodeType PvNode>
295 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
297 bool connected_moves(const Position& pos, Move m1, Move m2);
298 bool value_is_mate(Value value);
299 Value value_to_tt(Value v, int ply);
300 Value value_from_tt(Value v, int ply);
301 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
302 bool connected_threat(const Position& pos, Move m, Move threat);
303 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
304 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
305 void update_killers(Move m, SearchStack* ss);
306 void update_gains(const Position& pos, Move move, Value before, Value after);
308 int current_search_time();
309 std::string value_to_uci(Value v);
310 int nps(const Position& pos);
311 void poll(const Position& pos);
313 void wait_for_stop_or_ponderhit();
314 void init_ss_array(SearchStack* ss, int size);
315 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
316 void insert_pv_in_tt(const Position& pos, Move pv[]);
317 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
319 #if !defined(_MSC_VER)
320 void* init_thread(void* threadID);
322 DWORD WINAPI init_thread(LPVOID threadID);
332 /// init_threads(), exit_threads() and nodes_searched() are helpers to
333 /// give accessibility to some TM methods from outside of current file.
335 void init_threads() { ThreadsMgr.init_threads(); }
336 void exit_threads() { ThreadsMgr.exit_threads(); }
339 /// init_search() is called during startup. It initializes various lookup tables
343 int d; // depth (ONE_PLY == 2)
344 int hd; // half depth (ONE_PLY == 1)
347 // Init reductions array
348 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
350 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
351 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
352 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
353 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
356 // Init futility margins array
357 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
358 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
360 // Init futility move count array
361 for (d = 0; d < 32; d++)
362 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
366 /// perft() is our utility to verify move generation is bug free. All the legal
367 /// moves up to given depth are generated and counted and the sum returned.
369 int perft(Position& pos, Depth depth)
371 MoveStack mlist[MOVES_MAX];
376 // Generate all legal moves
377 MoveStack* last = generate_moves(pos, mlist);
379 // If we are at the last ply we don't need to do and undo
380 // the moves, just to count them.
381 if (depth <= ONE_PLY)
382 return int(last - mlist);
384 // Loop through all legal moves
386 for (MoveStack* cur = mlist; cur != last; cur++)
389 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
390 sum += perft(pos, depth - ONE_PLY);
397 /// think() is the external interface to Stockfish's search, and is called when
398 /// the program receives the UCI 'go' command. It initializes various
399 /// search-related global variables, and calls root_search(). It returns false
400 /// when a quit command is received during the search.
402 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
403 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
405 // Initialize global search variables
406 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
408 SearchStartTime = get_system_time();
409 ExactMaxTime = maxTime;
412 InfiniteSearch = infinite;
413 PonderSearch = ponder;
414 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
416 // Look for a book move, only during games, not tests
417 if (UseTimeManagement && Options["OwnBook"].value<bool>())
419 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
420 OpeningBook.open(Options["Book File"].value<std::string>());
422 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
423 if (bookMove != MOVE_NONE)
426 wait_for_stop_or_ponderhit();
428 cout << "bestmove " << bookMove << endl;
433 // Read UCI option values
434 TT.set_size(Options["Hash"].value<int>());
435 if (Options["Clear Hash"].value<bool>())
437 Options["Clear Hash"].set_value("false");
441 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
442 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
443 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
444 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
445 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
446 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
447 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
448 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
449 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
450 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
451 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
452 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
454 MinimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
455 MaxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
456 MultiPV = Options["MultiPV"].value<int>();
457 UseLogFile = Options["Use Search Log"].value<bool>();
460 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
462 read_weights(pos.side_to_move());
464 // Set the number of active threads
465 int newActiveThreads = Options["Threads"].value<int>();
466 if (newActiveThreads != ThreadsMgr.active_threads())
468 ThreadsMgr.set_active_threads(newActiveThreads);
469 init_eval(ThreadsMgr.active_threads());
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
476 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
478 // Set best NodesBetweenPolls interval to avoid lagging under
479 // heavy time pressure.
481 NodesBetweenPolls = Min(MaxNodes, 30000);
482 else if (myTime && myTime < 1000)
483 NodesBetweenPolls = 1000;
484 else if (myTime && myTime < 5000)
485 NodesBetweenPolls = 5000;
487 NodesBetweenPolls = 30000;
489 // Write search information to log file
491 LogFile << "Searching: " << pos.to_fen() << endl
492 << "infinite: " << infinite
493 << " ponder: " << ponder
494 << " time: " << myTime
495 << " increment: " << myIncrement
496 << " moves to go: " << movesToGo << endl;
498 // We're ready to start thinking. Call the iterative deepening loop function
499 id_loop(pos, searchMoves);
510 // id_loop() is the main iterative deepening loop. It calls root_search
511 // repeatedly with increasing depth until the allocated thinking time has
512 // been consumed, the user stops the search, or the maximum search depth is
515 Value id_loop(Position& pos, Move searchMoves[]) {
517 SearchStack ss[PLY_MAX_PLUS_2];
518 Move pv[PLY_MAX_PLUS_2];
519 Move EasyMove = MOVE_NONE;
520 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
522 // Moves to search are verified, copied, scored and sorted
523 RootMoveList rml(pos, searchMoves);
525 // Handle special case of searching on a mate/stale position
526 if (rml.move_count() == 0)
529 wait_for_stop_or_ponderhit();
531 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
534 // Print RootMoveList startup scoring to the standard output,
535 // so to output information also for iteration 1.
536 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
537 << "info depth " << 1
538 << "\ninfo depth " << 1
539 << " score " << value_to_uci(rml.move_score(0))
540 << " time " << current_search_time()
541 << " nodes " << pos.nodes_searched()
542 << " nps " << nps(pos)
543 << " pv " << rml.move(0) << "\n";
548 init_ss_array(ss, PLY_MAX_PLUS_2);
549 pv[0] = pv[1] = MOVE_NONE;
550 ValueByIteration[1] = rml.move_score(0);
553 // Is one move significantly better than others after initial scoring ?
554 if ( rml.move_count() == 1
555 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
556 EasyMove = rml.move(0);
558 // Iterative deepening loop
559 while (Iteration < PLY_MAX)
561 // Initialize iteration
563 BestMoveChangesByIteration[Iteration] = 0;
565 cout << "info depth " << Iteration << endl;
567 // Calculate dynamic aspiration window based on previous iterations
568 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
570 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
571 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
573 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
574 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
576 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
577 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
580 // Search to the current depth, rml is updated and sorted, alpha and beta could change
581 value = root_search(pos, ss, pv, rml, &alpha, &beta);
583 // Write PV to transposition table, in case the relevant entries have
584 // been overwritten during the search.
585 insert_pv_in_tt(pos, pv);
588 break; // Value cannot be trusted. Break out immediately!
590 //Save info about search result
591 ValueByIteration[Iteration] = value;
593 // Drop the easy move if differs from the new best move
594 if (pv[0] != EasyMove)
595 EasyMove = MOVE_NONE;
597 if (UseTimeManagement)
600 bool stopSearch = false;
602 // Stop search early if there is only a single legal move,
603 // we search up to Iteration 6 anyway to get a proper score.
604 if (Iteration >= 6 && rml.move_count() == 1)
607 // Stop search early when the last two iterations returned a mate score
609 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
610 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
613 // Stop search early if one move seems to be much better than the others
616 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
617 && current_search_time() > TimeMgr.available_time() / 16)
618 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
619 && current_search_time() > TimeMgr.available_time() / 32)))
622 // Add some extra time if the best move has changed during the last two iterations
623 if (Iteration > 5 && Iteration <= 50)
624 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
625 BestMoveChangesByIteration[Iteration-1]);
627 // Stop search if most of MaxSearchTime is consumed at the end of the
628 // iteration. We probably don't have enough time to search the first
629 // move at the next iteration anyway.
630 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
636 StopOnPonderhit = true;
642 if (MaxDepth && Iteration >= MaxDepth)
646 // If we are pondering or in infinite search, we shouldn't print the
647 // best move before we are told to do so.
648 if (!AbortSearch && (PonderSearch || InfiniteSearch))
649 wait_for_stop_or_ponderhit();
651 // Print final search statistics
652 cout << "info nodes " << pos.nodes_searched()
653 << " nps " << nps(pos)
654 << " time " << current_search_time() << endl;
656 // Print the best move and the ponder move to the standard output
657 if (pv[0] == MOVE_NONE)
663 assert(pv[0] != MOVE_NONE);
665 cout << "bestmove " << pv[0];
667 if (pv[1] != MOVE_NONE)
668 cout << " ponder " << pv[1];
675 dbg_print_mean(LogFile);
677 if (dbg_show_hit_rate)
678 dbg_print_hit_rate(LogFile);
680 LogFile << "\nNodes: " << pos.nodes_searched()
681 << "\nNodes/second: " << nps(pos)
682 << "\nBest move: " << move_to_san(pos, pv[0]);
685 pos.do_move(pv[0], st);
686 LogFile << "\nPonder move: "
687 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
690 return rml.move_score(0);
694 // root_search() is the function which searches the root node. It is
695 // similar to search_pv except that it uses a different move ordering
696 // scheme, prints some information to the standard output and handles
697 // the fail low/high loops.
699 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
705 Depth depth, ext, newDepth;
706 Value value, alpha, beta;
707 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
708 int researchCountFH, researchCountFL;
710 researchCountFH = researchCountFL = 0;
713 isCheck = pos.is_check();
714 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
716 // Step 1. Initialize node (polling is omitted at root)
717 ss->currentMove = ss->bestMove = MOVE_NONE;
719 // Step 2. Check for aborted search (omitted at root)
720 // Step 3. Mate distance pruning (omitted at root)
721 // Step 4. Transposition table lookup (omitted at root)
723 // Step 5. Evaluate the position statically
724 // At root we do this only to get reference value for child nodes
725 ss->evalMargin = VALUE_NONE;
726 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
728 // Step 6. Razoring (omitted at root)
729 // Step 7. Static null move pruning (omitted at root)
730 // Step 8. Null move search with verification search (omitted at root)
731 // Step 9. Internal iterative deepening (omitted at root)
733 // Step extra. Fail low loop
734 // We start with small aspiration window and in case of fail low, we research
735 // with bigger window until we are not failing low anymore.
738 // Sort the moves before to (re)search
739 rml.score_moves(pos);
742 // Step 10. Loop through all moves in the root move list
743 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
745 // This is used by time management
746 FirstRootMove = (i == 0);
748 // Save the current node count before the move is searched
749 nodes = pos.nodes_searched();
751 // Pick the next root move, and print the move and the move number to
752 // the standard output.
753 move = ss->currentMove = rml.move(i);
755 if (current_search_time() >= 1000)
756 cout << "info currmove " << move
757 << " currmovenumber " << i + 1 << endl;
759 moveIsCheck = pos.move_is_check(move);
760 captureOrPromotion = pos.move_is_capture_or_promotion(move);
762 // Step 11. Decide the new search depth
763 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
764 newDepth = depth + ext;
766 // Step 12. Futility pruning (omitted at root)
768 // Step extra. Fail high loop
769 // If move fails high, we research with bigger window until we are not failing
771 value = - VALUE_INFINITE;
775 // Step 13. Make the move
776 pos.do_move(move, st, ci, moveIsCheck);
778 // Step extra. pv search
779 // We do pv search for first moves (i < MultiPV)
780 // and for fail high research (value > alpha)
781 if (i < MultiPV || value > alpha)
783 // Aspiration window is disabled in multi-pv case
785 alpha = -VALUE_INFINITE;
787 // Full depth PV search, done on first move or after a fail high
788 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
792 // Step 14. Reduced search
793 // if the move fails high will be re-searched at full depth
794 bool doFullDepthSearch = true;
796 if ( depth >= 3 * ONE_PLY
798 && !captureOrPromotion
799 && !move_is_castle(move))
801 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
804 assert(newDepth-ss->reduction >= ONE_PLY);
806 // Reduced depth non-pv search using alpha as upperbound
807 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
808 doFullDepthSearch = (value > alpha);
811 // The move failed high, but if reduction is very big we could
812 // face a false positive, retry with a less aggressive reduction,
813 // if the move fails high again then go with full depth search.
814 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
816 assert(newDepth - ONE_PLY >= ONE_PLY);
818 ss->reduction = ONE_PLY;
819 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
820 doFullDepthSearch = (value > alpha);
822 ss->reduction = DEPTH_ZERO; // Restore original reduction
825 // Step 15. Full depth search
826 if (doFullDepthSearch)
828 // Full depth non-pv search using alpha as upperbound
829 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
831 // If we are above alpha then research at same depth but as PV
832 // to get a correct score or eventually a fail high above beta.
834 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
838 // Step 16. Undo move
841 // Can we exit fail high loop ?
842 if (AbortSearch || value < beta)
845 // We are failing high and going to do a research. It's important to update
846 // the score before research in case we run out of time while researching.
847 rml.set_move_score(i, value);
849 extract_pv_from_tt(pos, move, pv);
850 rml.set_move_pv(i, pv);
852 // Print information to the standard output
853 print_pv_info(pos, pv, alpha, beta, value);
855 // Prepare for a research after a fail high, each time with a wider window
856 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
859 } // End of fail high loop
861 // Finished searching the move. If AbortSearch is true, the search
862 // was aborted because the user interrupted the search or because we
863 // ran out of time. In this case, the return value of the search cannot
864 // be trusted, and we break out of the loop without updating the best
869 // Remember searched nodes counts for this move
870 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
872 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
873 assert(value < beta);
875 // Step 17. Check for new best move
876 if (value <= alpha && i >= MultiPV)
877 rml.set_move_score(i, -VALUE_INFINITE);
880 // PV move or new best move!
883 rml.set_move_score(i, value);
885 extract_pv_from_tt(pos, move, pv);
886 rml.set_move_pv(i, pv);
890 // We record how often the best move has been changed in each
891 // iteration. This information is used for time managment: When
892 // the best move changes frequently, we allocate some more time.
894 BestMoveChangesByIteration[Iteration]++;
896 // Print information to the standard output
897 print_pv_info(pos, pv, alpha, beta, value);
899 // Raise alpha to setup proper non-pv search upper bound
906 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
908 cout << "info multipv " << j + 1
909 << " score " << value_to_uci(rml.move_score(j))
910 << " depth " << (j <= i ? Iteration : Iteration - 1)
911 << " time " << current_search_time()
912 << " nodes " << pos.nodes_searched()
913 << " nps " << nps(pos)
916 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
917 cout << rml.move_pv(j, k) << " ";
921 alpha = rml.move_score(Min(i, MultiPV - 1));
923 } // PV move or new best move
925 assert(alpha >= *alphaPtr);
927 AspirationFailLow = (alpha == *alphaPtr);
929 if (AspirationFailLow && StopOnPonderhit)
930 StopOnPonderhit = false;
933 // Can we exit fail low loop ?
934 if (AbortSearch || !AspirationFailLow)
937 // Prepare for a research after a fail low, each time with a wider window
938 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
943 // Sort the moves before to return
950 // search<>() is the main search function for both PV and non-PV nodes and for
951 // normal and SplitPoint nodes. When called just after a split point the search
952 // is simpler because we have already probed the hash table, done a null move
953 // search, and searched the first move before splitting, we don't have to repeat
954 // all this work again. We also don't need to store anything to the hash table
955 // here: This is taken care of after we return from the split point.
957 template <NodeType PvNode, bool SpNode>
958 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
960 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
961 assert(beta > alpha && beta <= VALUE_INFINITE);
962 assert(PvNode || alpha == beta - 1);
963 assert(ply > 0 && ply < PLY_MAX);
964 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
966 Move movesSearched[MOVES_MAX];
970 Move ttMove, move, excludedMove, threatMove;
973 Value bestValue, value, oldAlpha;
974 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
975 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
976 bool mateThreat = false;
978 int threadID = pos.thread();
979 SplitPoint* sp = NULL;
980 refinedValue = bestValue = value = -VALUE_INFINITE;
982 isCheck = pos.is_check();
988 ttMove = excludedMove = MOVE_NONE;
989 threatMove = sp->threatMove;
990 mateThreat = sp->mateThreat;
991 goto split_point_start;
992 } else {} // Hack to fix icc's "statement is unreachable" warning
994 // Step 1. Initialize node and poll. Polling can abort search
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)
1006 || pos.is_draw() || ply >= PLY_MAX - 1)
1009 // Step 3. Mate distance pruning
1010 alpha = Max(value_mated_in(ply), alpha);
1011 beta = Min(value_mate_in(ply+1), beta);
1015 // Step 4. Transposition table lookup
1017 // We don't want the score of a partial search to overwrite a previous full search
1018 // TT value, so we use a different position key in case of an excluded move exists.
1019 excludedMove = ss->excludedMove;
1020 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1022 tte = TT.retrieve(posKey);
1023 ttMove = tte ? tte->move() : MOVE_NONE;
1025 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1026 // This is to avoid problems in the following areas:
1028 // * Repetition draw detection
1029 // * Fifty move rule detection
1030 // * Searching for a mate
1031 // * Printing of full PV line
1032 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1035 ss->bestMove = ttMove; // Can be MOVE_NONE
1036 return value_from_tt(tte->value(), ply);
1039 // Step 5. Evaluate the position statically and
1040 // update gain statistics of parent move.
1042 ss->eval = ss->evalMargin = VALUE_NONE;
1045 assert(tte->static_value() != VALUE_NONE);
1047 ss->eval = tte->static_value();
1048 ss->evalMargin = tte->static_value_margin();
1049 refinedValue = refine_eval(tte, ss->eval, ply);
1053 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1054 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1057 // Save gain for the parent non-capture move
1058 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1060 // Step 6. Razoring (is omitted in PV nodes)
1062 && depth < RazorDepth
1064 && refinedValue < beta - razor_margin(depth)
1065 && ttMove == MOVE_NONE
1066 && (ss-1)->currentMove != MOVE_NULL
1067 && !value_is_mate(beta)
1068 && !pos.has_pawn_on_7th(pos.side_to_move()))
1070 Value rbeta = beta - razor_margin(depth);
1071 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1073 // Logically we should return (v + razor_margin(depth)), but
1074 // surprisingly this did slightly weaker in tests.
1078 // Step 7. Static null move pruning (is omitted in PV nodes)
1079 // We're betting that the opponent doesn't have a move that will reduce
1080 // the score by more than futility_margin(depth) if we do a null move.
1082 && !ss->skipNullMove
1083 && depth < RazorDepth
1085 && refinedValue >= beta + futility_margin(depth, 0)
1086 && !value_is_mate(beta)
1087 && pos.non_pawn_material(pos.side_to_move()))
1088 return refinedValue - futility_margin(depth, 0);
1090 // Step 8. Null move search with verification search (is omitted in PV nodes)
1092 && !ss->skipNullMove
1095 && refinedValue >= beta
1096 && !value_is_mate(beta)
1097 && pos.non_pawn_material(pos.side_to_move()))
1099 ss->currentMove = MOVE_NULL;
1101 // Null move dynamic reduction based on depth
1102 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1104 // Null move dynamic reduction based on value
1105 if (refinedValue - beta > PawnValueMidgame)
1108 pos.do_null_move(st);
1109 (ss+1)->skipNullMove = true;
1110 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1111 (ss+1)->skipNullMove = false;
1112 pos.undo_null_move();
1114 if (nullValue >= beta)
1116 // Do not return unproven mate scores
1117 if (nullValue >= value_mate_in(PLY_MAX))
1120 if (depth < 6 * ONE_PLY)
1123 // Do verification search at high depths
1124 ss->skipNullMove = true;
1125 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1126 ss->skipNullMove = false;
1133 // The null move failed low, which means that we may be faced with
1134 // some kind of threat. If the previous move was reduced, check if
1135 // the move that refuted the null move was somehow connected to the
1136 // move which was reduced. If a connection is found, return a fail
1137 // low score (which will cause the reduced move to fail high in the
1138 // parent node, which will trigger a re-search with full depth).
1139 if (nullValue == value_mated_in(ply + 2))
1142 threatMove = (ss+1)->bestMove;
1143 if ( depth < ThreatDepth
1144 && (ss-1)->reduction
1145 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1150 // Step 9. Internal iterative deepening
1151 if ( depth >= IIDDepth[PvNode]
1152 && ttMove == MOVE_NONE
1153 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1155 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1157 ss->skipNullMove = true;
1158 search<PvNode>(pos, ss, alpha, beta, d, ply);
1159 ss->skipNullMove = false;
1161 ttMove = ss->bestMove;
1162 tte = TT.retrieve(posKey);
1165 // Expensive mate threat detection (only for PV nodes)
1167 mateThreat = pos.has_mate_threat();
1169 split_point_start: // At split points actual search starts from here
1171 // Initialize a MovePicker object for the current position
1172 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1173 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1174 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1176 ss->bestMove = MOVE_NONE;
1177 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1178 futilityBase = ss->eval + ss->evalMargin;
1179 singularExtensionNode = !SpNode
1180 && depth >= SingularExtensionDepth[PvNode]
1183 && !excludedMove // Do not allow recursive singular extension search
1184 && (tte->type() & VALUE_TYPE_LOWER)
1185 && tte->depth() >= depth - 3 * ONE_PLY;
1188 lock_grab(&(sp->lock));
1189 bestValue = sp->bestValue;
1192 // Step 10. Loop through moves
1193 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1194 while ( bestValue < beta
1195 && (move = mp.get_next_move()) != MOVE_NONE
1196 && !ThreadsMgr.thread_should_stop(threadID))
1198 assert(move_is_ok(move));
1202 moveCount = ++sp->moveCount;
1203 lock_release(&(sp->lock));
1205 else if (move == excludedMove)
1208 movesSearched[moveCount++] = move;
1210 moveIsCheck = pos.move_is_check(move, ci);
1211 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1213 // Step 11. Decide the new search depth
1214 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1216 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1217 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1218 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1219 // lower then ttValue minus a margin then we extend ttMove.
1220 if ( singularExtensionNode
1221 && move == tte->move()
1224 Value ttValue = value_from_tt(tte->value(), ply);
1226 if (abs(ttValue) < VALUE_KNOWN_WIN)
1228 Value b = ttValue - SingularExtensionMargin;
1229 ss->excludedMove = move;
1230 ss->skipNullMove = true;
1231 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1232 ss->skipNullMove = false;
1233 ss->excludedMove = MOVE_NONE;
1234 ss->bestMove = MOVE_NONE;
1240 // Update current move (this must be done after singular extension search)
1241 ss->currentMove = move;
1242 newDepth = depth - ONE_PLY + ext;
1244 // Step 12. Futility pruning (is omitted in PV nodes)
1246 && !captureOrPromotion
1250 && !move_is_castle(move))
1252 // Move count based pruning
1253 if ( moveCount >= futility_move_count(depth)
1254 && !(threatMove && connected_threat(pos, move, threatMove))
1255 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1258 lock_grab(&(sp->lock));
1263 // Value based pruning
1264 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1265 // but fixing this made program slightly weaker.
1266 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1267 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1268 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1270 if (futilityValueScaled < beta)
1274 lock_grab(&(sp->lock));
1275 if (futilityValueScaled > sp->bestValue)
1276 sp->bestValue = bestValue = futilityValueScaled;
1278 else if (futilityValueScaled > bestValue)
1279 bestValue = futilityValueScaled;
1285 // Step 13. Make the move
1286 pos.do_move(move, st, ci, moveIsCheck);
1288 // Step extra. pv search (only in PV nodes)
1289 // The first move in list is the expected PV
1290 if (!SpNode && PvNode && moveCount == 1)
1291 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1294 // Step 14. Reduced depth search
1295 // If the move fails high will be re-searched at full depth.
1296 bool doFullDepthSearch = true;
1298 if ( depth >= 3 * ONE_PLY
1299 && !captureOrPromotion
1301 && !move_is_castle(move)
1302 && !(ss->killers[0] == move || ss->killers[1] == move))
1304 ss->reduction = reduction<PvNode>(depth, moveCount);
1307 alpha = SpNode ? sp->alpha : alpha;
1308 Depth d = newDepth - ss->reduction;
1309 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1311 doFullDepthSearch = (value > alpha);
1314 // The move failed high, but if reduction is very big we could
1315 // face a false positive, retry with a less aggressive reduction,
1316 // if the move fails high again then go with full depth search.
1317 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1319 assert(newDepth - ONE_PLY >= ONE_PLY);
1321 ss->reduction = ONE_PLY;
1322 alpha = SpNode ? sp->alpha : alpha;
1323 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1324 doFullDepthSearch = (value > alpha);
1326 ss->reduction = DEPTH_ZERO; // Restore original reduction
1329 // Step 15. Full depth search
1330 if (doFullDepthSearch)
1332 alpha = SpNode ? sp->alpha : alpha;
1333 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1335 // Step extra. pv search (only in PV nodes)
1336 // Search only for possible new PV nodes, if instead value >= beta then
1337 // parent node fails low with value <= alpha and tries another move.
1338 if (PvNode && value > alpha && value < beta)
1339 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1343 // Step 16. Undo move
1344 pos.undo_move(move);
1346 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1348 // Step 17. Check for new best move
1351 lock_grab(&(sp->lock));
1352 bestValue = sp->bestValue;
1356 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1361 sp->bestValue = value;
1365 if (SpNode && (!PvNode || value >= beta))
1366 sp->stopRequest = true;
1368 if (PvNode && value < beta) // We want always alpha < beta
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1381 sp->parentSstack->bestMove = move;
1385 // Step 18. Check for split
1387 && depth >= MinimumSplitDepth
1388 && ThreadsMgr.active_threads() > 1
1390 && ThreadsMgr.available_thread_exists(threadID)
1392 && !ThreadsMgr.thread_should_stop(threadID)
1394 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1395 threatMove, mateThreat, moveCount, &mp, PvNode);
1398 // Step 19. Check for mate and stalemate
1399 // All legal moves have been searched and if there are
1400 // no legal moves, it must be mate or stalemate.
1401 // If one move was excluded return fail low score.
1402 if (!SpNode && !moveCount)
1403 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1405 // Step 20. Update tables
1406 // If the search is not aborted, update the transposition table,
1407 // history counters, and killer moves.
1408 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1410 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1411 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1412 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1414 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1416 // Update killers and history only for non capture moves that fails high
1417 if ( bestValue >= beta
1418 && !pos.move_is_capture_or_promotion(move))
1420 update_history(pos, move, depth, movesSearched, moveCount);
1421 update_killers(move, ss);
1427 // Here we have the lock still grabbed
1428 sp->slaves[threadID] = 0;
1429 sp->nodes += pos.nodes_searched();
1430 lock_release(&(sp->lock));
1433 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1439 // qsearch() is the quiescence search function, which is called by the main
1440 // search function when the remaining depth is zero (or, to be more precise,
1441 // less than ONE_PLY).
1443 template <NodeType PvNode>
1444 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1446 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1447 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1448 assert(PvNode || alpha == beta - 1);
1450 assert(ply > 0 && ply < PLY_MAX);
1451 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1455 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1456 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1458 Value oldAlpha = alpha;
1460 ss->bestMove = ss->currentMove = MOVE_NONE;
1462 // Check for an instant draw or maximum ply reached
1463 if (pos.is_draw() || ply >= PLY_MAX - 1)
1466 // Transposition table lookup. At PV nodes, we don't use the TT for
1467 // pruning, but only for move ordering.
1468 tte = TT.retrieve(pos.get_key());
1469 ttMove = (tte ? tte->move() : MOVE_NONE);
1471 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1473 ss->bestMove = ttMove; // Can be MOVE_NONE
1474 return value_from_tt(tte->value(), ply);
1477 isCheck = pos.is_check();
1479 // Evaluate the position statically
1482 bestValue = futilityBase = -VALUE_INFINITE;
1483 ss->eval = evalMargin = VALUE_NONE;
1484 deepChecks = enoughMaterial = false;
1490 assert(tte->static_value() != VALUE_NONE);
1492 evalMargin = tte->static_value_margin();
1493 ss->eval = bestValue = tte->static_value();
1496 ss->eval = bestValue = evaluate(pos, evalMargin);
1498 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1500 // Stand pat. Return immediately if static value is at least beta
1501 if (bestValue >= beta)
1504 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1509 if (PvNode && bestValue > alpha)
1512 // If we are near beta then try to get a cutoff pushing checks a bit further
1513 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1515 // Futility pruning parameters, not needed when in check
1516 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1517 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1520 // Initialize a MovePicker object for the current position, and prepare
1521 // to search the moves. Because the depth is <= 0 here, only captures,
1522 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1523 // and we are near beta) will be generated.
1524 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1527 // Loop through the moves until no moves remain or a beta cutoff occurs
1528 while ( alpha < beta
1529 && (move = mp.get_next_move()) != MOVE_NONE)
1531 assert(move_is_ok(move));
1533 moveIsCheck = pos.move_is_check(move, ci);
1541 && !move_is_promotion(move)
1542 && !pos.move_is_passed_pawn_push(move))
1544 futilityValue = futilityBase
1545 + pos.endgame_value_of_piece_on(move_to(move))
1546 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1548 if (futilityValue < alpha)
1550 if (futilityValue > bestValue)
1551 bestValue = futilityValue;
1556 // Detect non-capture evasions that are candidate to be pruned
1557 evasionPrunable = isCheck
1558 && bestValue > value_mated_in(PLY_MAX)
1559 && !pos.move_is_capture(move)
1560 && !pos.can_castle(pos.side_to_move());
1562 // Don't search moves with negative SEE values
1564 && (!isCheck || evasionPrunable)
1566 && !move_is_promotion(move)
1567 && pos.see_sign(move) < 0)
1570 // Update current move
1571 ss->currentMove = move;
1573 // Make and search the move
1574 pos.do_move(move, st, ci, moveIsCheck);
1575 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1576 pos.undo_move(move);
1578 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1581 if (value > bestValue)
1587 ss->bestMove = move;
1592 // All legal moves have been searched. A special case: If we're in check
1593 // and no legal moves were found, it is checkmate.
1594 if (isCheck && bestValue == -VALUE_INFINITE)
1595 return value_mated_in(ply);
1597 // Update transposition table
1598 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1599 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1600 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1602 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1608 // connected_moves() tests whether two moves are 'connected' in the sense
1609 // that the first move somehow made the second move possible (for instance
1610 // if the moving piece is the same in both moves). The first move is assumed
1611 // to be the move that was made to reach the current position, while the
1612 // second move is assumed to be a move from the current position.
1614 bool connected_moves(const Position& pos, Move m1, Move m2) {
1616 Square f1, t1, f2, t2;
1619 assert(move_is_ok(m1));
1620 assert(move_is_ok(m2));
1622 if (m2 == MOVE_NONE)
1625 // Case 1: The moving piece is the same in both moves
1631 // Case 2: The destination square for m2 was vacated by m1
1637 // Case 3: Moving through the vacated square
1638 if ( piece_is_slider(pos.piece_on(f2))
1639 && bit_is_set(squares_between(f2, t2), f1))
1642 // Case 4: The destination square for m2 is defended by the moving piece in m1
1643 p = pos.piece_on(t1);
1644 if (bit_is_set(pos.attacks_from(p, t1), t2))
1647 // Case 5: Discovered check, checking piece is the piece moved in m1
1648 if ( piece_is_slider(p)
1649 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1650 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1652 // discovered_check_candidates() works also if the Position's side to
1653 // move is the opposite of the checking piece.
1654 Color them = opposite_color(pos.side_to_move());
1655 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1657 if (bit_is_set(dcCandidates, f2))
1664 // value_is_mate() checks if the given value is a mate one eventually
1665 // compensated for the ply.
1667 bool value_is_mate(Value value) {
1669 assert(abs(value) <= VALUE_INFINITE);
1671 return value <= value_mated_in(PLY_MAX)
1672 || value >= value_mate_in(PLY_MAX);
1676 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1677 // "plies to mate from the current ply". Non-mate scores are unchanged.
1678 // The function is called before storing a value to the transposition table.
1680 Value value_to_tt(Value v, int ply) {
1682 if (v >= value_mate_in(PLY_MAX))
1685 if (v <= value_mated_in(PLY_MAX))
1692 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1693 // the transposition table to a mate score corrected for the current ply.
1695 Value value_from_tt(Value v, int ply) {
1697 if (v >= value_mate_in(PLY_MAX))
1700 if (v <= value_mated_in(PLY_MAX))
1707 // extension() decides whether a move should be searched with normal depth,
1708 // or with extended depth. Certain classes of moves (checking moves, in
1709 // particular) are searched with bigger depth than ordinary moves and in
1710 // any case are marked as 'dangerous'. Note that also if a move is not
1711 // extended, as example because the corresponding UCI option is set to zero,
1712 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1713 template <NodeType PvNode>
1714 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1715 bool singleEvasion, bool mateThreat, bool* dangerous) {
1717 assert(m != MOVE_NONE);
1719 Depth result = DEPTH_ZERO;
1720 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1724 if (moveIsCheck && pos.see_sign(m) >= 0)
1725 result += CheckExtension[PvNode];
1728 result += SingleEvasionExtension[PvNode];
1731 result += MateThreatExtension[PvNode];
1734 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1736 Color c = pos.side_to_move();
1737 if (relative_rank(c, move_to(m)) == RANK_7)
1739 result += PawnPushTo7thExtension[PvNode];
1742 if (pos.pawn_is_passed(c, move_to(m)))
1744 result += PassedPawnExtension[PvNode];
1749 if ( captureOrPromotion
1750 && pos.type_of_piece_on(move_to(m)) != PAWN
1751 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1752 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1753 && !move_is_promotion(m)
1756 result += PawnEndgameExtension[PvNode];
1761 && captureOrPromotion
1762 && pos.type_of_piece_on(move_to(m)) != PAWN
1763 && pos.see_sign(m) >= 0)
1765 result += ONE_PLY / 2;
1769 return Min(result, ONE_PLY);
1773 // connected_threat() tests whether it is safe to forward prune a move or if
1774 // is somehow coonected to the threat move returned by null search.
1776 bool connected_threat(const Position& pos, Move m, Move threat) {
1778 assert(move_is_ok(m));
1779 assert(threat && move_is_ok(threat));
1780 assert(!pos.move_is_check(m));
1781 assert(!pos.move_is_capture_or_promotion(m));
1782 assert(!pos.move_is_passed_pawn_push(m));
1784 Square mfrom, mto, tfrom, tto;
1786 mfrom = move_from(m);
1788 tfrom = move_from(threat);
1789 tto = move_to(threat);
1791 // Case 1: Don't prune moves which move the threatened piece
1795 // Case 2: If the threatened piece has value less than or equal to the
1796 // value of the threatening piece, don't prune move which defend it.
1797 if ( pos.move_is_capture(threat)
1798 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1799 || pos.type_of_piece_on(tfrom) == KING)
1800 && pos.move_attacks_square(m, tto))
1803 // Case 3: If the moving piece in the threatened move is a slider, don't
1804 // prune safe moves which block its ray.
1805 if ( piece_is_slider(pos.piece_on(tfrom))
1806 && bit_is_set(squares_between(tfrom, tto), mto)
1807 && pos.see_sign(m) >= 0)
1814 // ok_to_use_TT() returns true if a transposition table score
1815 // can be used at a given point in search.
1817 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1819 Value v = value_from_tt(tte->value(), ply);
1821 return ( tte->depth() >= depth
1822 || v >= Max(value_mate_in(PLY_MAX), beta)
1823 || v < Min(value_mated_in(PLY_MAX), beta))
1825 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1826 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1830 // refine_eval() returns the transposition table score if
1831 // possible otherwise falls back on static position evaluation.
1833 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1837 Value v = value_from_tt(tte->value(), ply);
1839 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1840 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1847 // update_history() registers a good move that produced a beta-cutoff
1848 // in history and marks as failures all the other moves of that ply.
1850 void update_history(const Position& pos, Move move, Depth depth,
1851 Move movesSearched[], int moveCount) {
1854 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1856 for (int i = 0; i < moveCount - 1; i++)
1858 m = movesSearched[i];
1862 if (!pos.move_is_capture_or_promotion(m))
1863 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1868 // update_killers() add a good move that produced a beta-cutoff
1869 // among the killer moves of that ply.
1871 void update_killers(Move m, SearchStack* ss) {
1873 if (m == ss->killers[0])
1876 ss->killers[1] = ss->killers[0];
1881 // update_gains() updates the gains table of a non-capture move given
1882 // the static position evaluation before and after the move.
1884 void update_gains(const Position& pos, Move m, Value before, Value after) {
1887 && before != VALUE_NONE
1888 && after != VALUE_NONE
1889 && pos.captured_piece_type() == PIECE_TYPE_NONE
1890 && !move_is_special(m))
1891 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1895 // current_search_time() returns the number of milliseconds which have passed
1896 // since the beginning of the current search.
1898 int current_search_time() {
1900 return get_system_time() - SearchStartTime;
1904 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1906 std::string value_to_uci(Value v) {
1908 std::stringstream s;
1910 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1911 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1913 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1918 // nps() computes the current nodes/second count.
1920 int nps(const Position& pos) {
1922 int t = current_search_time();
1923 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1927 // poll() performs two different functions: It polls for user input, and it
1928 // looks at the time consumed so far and decides if it's time to abort the
1931 void poll(const Position& pos) {
1933 static int lastInfoTime;
1934 int t = current_search_time();
1937 if (data_available())
1939 // We are line oriented, don't read single chars
1940 std::string command;
1942 if (!std::getline(std::cin, command))
1945 if (command == "quit")
1948 PonderSearch = false;
1952 else if (command == "stop")
1955 PonderSearch = false;
1957 else if (command == "ponderhit")
1961 // Print search information
1965 else if (lastInfoTime > t)
1966 // HACK: Must be a new search where we searched less than
1967 // NodesBetweenPolls nodes during the first second of search.
1970 else if (t - lastInfoTime >= 1000)
1977 if (dbg_show_hit_rate)
1978 dbg_print_hit_rate();
1980 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1981 << " time " << t << endl;
1984 // Should we stop the search?
1988 bool stillAtFirstMove = FirstRootMove
1989 && !AspirationFailLow
1990 && t > TimeMgr.available_time();
1992 bool noMoreTime = t > TimeMgr.maximum_time()
1993 || stillAtFirstMove;
1995 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1996 || (ExactMaxTime && t >= ExactMaxTime)
1997 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2002 // ponderhit() is called when the program is pondering (i.e. thinking while
2003 // it's the opponent's turn to move) in order to let the engine know that
2004 // it correctly predicted the opponent's move.
2008 int t = current_search_time();
2009 PonderSearch = false;
2011 bool stillAtFirstMove = FirstRootMove
2012 && !AspirationFailLow
2013 && t > TimeMgr.available_time();
2015 bool noMoreTime = t > TimeMgr.maximum_time()
2016 || stillAtFirstMove;
2018 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2023 // init_ss_array() does a fast reset of the first entries of a SearchStack
2024 // array and of all the excludedMove and skipNullMove entries.
2026 void init_ss_array(SearchStack* ss, int size) {
2028 for (int i = 0; i < size; i++, ss++)
2030 ss->excludedMove = MOVE_NONE;
2031 ss->skipNullMove = false;
2032 ss->reduction = DEPTH_ZERO;
2036 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2041 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2042 // while the program is pondering. The point is to work around a wrinkle in
2043 // the UCI protocol: When pondering, the engine is not allowed to give a
2044 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2045 // We simply wait here until one of these commands is sent, and return,
2046 // after which the bestmove and pondermove will be printed (in id_loop()).
2048 void wait_for_stop_or_ponderhit() {
2050 std::string command;
2054 if (!std::getline(std::cin, command))
2057 if (command == "quit")
2062 else if (command == "ponderhit" || command == "stop")
2068 // print_pv_info() prints to standard output and eventually to log file information on
2069 // the current PV line. It is called at each iteration or after a new pv is found.
2071 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2073 cout << "info depth " << Iteration
2074 << " score " << value_to_uci(value)
2075 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2076 << " time " << current_search_time()
2077 << " nodes " << pos.nodes_searched()
2078 << " nps " << nps(pos)
2081 for (Move* m = pv; *m != MOVE_NONE; m++)
2088 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2089 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2091 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2096 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2097 // the PV back into the TT. This makes sure the old PV moves are searched
2098 // first, even if the old TT entries have been overwritten.
2100 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2104 Position p(pos, pos.thread());
2105 Value v, m = VALUE_NONE;
2107 for (int i = 0; pv[i] != MOVE_NONE; i++)
2109 tte = TT.retrieve(p.get_key());
2110 if (!tte || tte->move() != pv[i])
2112 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2113 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2115 p.do_move(pv[i], st);
2120 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2121 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2122 // allow to always have a ponder move even when we fail high at root and also a
2123 // long PV to print that is important for position analysis.
2125 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2129 Position p(pos, pos.thread());
2132 assert(bestMove != MOVE_NONE);
2135 p.do_move(pv[ply++], st);
2137 while ( (tte = TT.retrieve(p.get_key())) != NULL
2138 && tte->move() != MOVE_NONE
2139 && move_is_legal(p, tte->move())
2141 && (!p.is_draw() || ply < 2))
2143 pv[ply] = tte->move();
2144 p.do_move(pv[ply++], st);
2146 pv[ply] = MOVE_NONE;
2150 // init_thread() is the function which is called when a new thread is
2151 // launched. It simply calls the idle_loop() function with the supplied
2152 // threadID. There are two versions of this function; one for POSIX
2153 // threads and one for Windows threads.
2155 #if !defined(_MSC_VER)
2157 void* init_thread(void* threadID) {
2159 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2165 DWORD WINAPI init_thread(LPVOID threadID) {
2167 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2174 /// The ThreadsManager class
2177 // idle_loop() is where the threads are parked when they have no work to do.
2178 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2179 // object for which the current thread is the master.
2181 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2183 assert(threadID >= 0 && threadID < MAX_THREADS);
2187 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2188 // master should exit as last one.
2189 if (AllThreadsShouldExit)
2192 threads[threadID].state = THREAD_TERMINATED;
2196 // If we are not thinking, wait for a condition to be signaled
2197 // instead of wasting CPU time polling for work.
2198 while ( threadID >= ActiveThreads
2199 || threads[threadID].state == THREAD_INITIALIZING
2200 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2203 assert(threadID != 0);
2205 if (AllThreadsShouldExit)
2210 // Retest condition under lock protection
2211 if (!( threadID >= ActiveThreads
2212 || threads[threadID].state == THREAD_INITIALIZING
2213 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2215 lock_release(&MPLock);
2219 // Put thread to sleep
2220 threads[threadID].state = THREAD_AVAILABLE;
2221 cond_wait(&WaitCond[threadID], &MPLock);
2222 lock_release(&MPLock);
2225 // If this thread has been assigned work, launch a search
2226 if (threads[threadID].state == THREAD_WORKISWAITING)
2228 assert(!AllThreadsShouldExit);
2230 threads[threadID].state = THREAD_SEARCHING;
2232 // Here we call search() with SplitPoint template parameter set to true
2233 SplitPoint* tsp = threads[threadID].splitPoint;
2234 Position pos(*tsp->pos, threadID);
2235 SearchStack* ss = tsp->sstack[threadID] + 1;
2239 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2241 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2243 assert(threads[threadID].state == THREAD_SEARCHING);
2245 threads[threadID].state = THREAD_AVAILABLE;
2248 // If this thread is the master of a split point and all slaves have
2249 // finished their work at this split point, return from the idle loop.
2251 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2253 if (i == ActiveThreads)
2255 // Because sp->slaves[] is reset under lock protection,
2256 // be sure sp->lock has been released before to return.
2257 lock_grab(&(sp->lock));
2258 lock_release(&(sp->lock));
2260 // In helpful master concept a master can help only a sub-tree, and
2261 // because here is all finished is not possible master is booked.
2262 assert(threads[threadID].state == THREAD_AVAILABLE);
2264 threads[threadID].state = THREAD_SEARCHING;
2271 // init_threads() is called during startup. It launches all helper threads,
2272 // and initializes the split point stack and the global locks and condition
2275 void ThreadsManager::init_threads() {
2277 int i, arg[MAX_THREADS];
2280 // Initialize global locks
2283 for (i = 0; i < MAX_THREADS; i++)
2284 cond_init(&WaitCond[i]);
2286 // Initialize splitPoints[] locks
2287 for (i = 0; i < MAX_THREADS; i++)
2288 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2289 lock_init(&(threads[i].splitPoints[j].lock));
2291 // Will be set just before program exits to properly end the threads
2292 AllThreadsShouldExit = false;
2294 // Threads will be put all threads to sleep as soon as created
2297 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2298 threads[0].state = THREAD_SEARCHING;
2299 for (i = 1; i < MAX_THREADS; i++)
2300 threads[i].state = THREAD_INITIALIZING;
2302 // Launch the helper threads
2303 for (i = 1; i < MAX_THREADS; i++)
2307 #if !defined(_MSC_VER)
2308 pthread_t pthread[1];
2309 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2310 pthread_detach(pthread[0]);
2312 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2316 cout << "Failed to create thread number " << i << endl;
2320 // Wait until the thread has finished launching and is gone to sleep
2321 while (threads[i].state == THREAD_INITIALIZING) {}
2326 // exit_threads() is called when the program exits. It makes all the
2327 // helper threads exit cleanly.
2329 void ThreadsManager::exit_threads() {
2331 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2333 // Wake up all the threads and waits for termination
2334 for (int i = 1; i < MAX_THREADS; i++)
2336 wake_sleeping_thread(i);
2337 while (threads[i].state != THREAD_TERMINATED) {}
2340 // Now we can safely destroy the locks
2341 for (int i = 0; i < MAX_THREADS; i++)
2342 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2343 lock_destroy(&(threads[i].splitPoints[j].lock));
2345 lock_destroy(&MPLock);
2347 // Now we can safely destroy the wait conditions
2348 for (int i = 0; i < MAX_THREADS; i++)
2349 cond_destroy(&WaitCond[i]);
2353 // thread_should_stop() checks whether the thread should stop its search.
2354 // This can happen if a beta cutoff has occurred in the thread's currently
2355 // active split point, or in some ancestor of the current split point.
2357 bool ThreadsManager::thread_should_stop(int threadID) const {
2359 assert(threadID >= 0 && threadID < ActiveThreads);
2361 SplitPoint* sp = threads[threadID].splitPoint;
2363 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2368 // thread_is_available() checks whether the thread with threadID "slave" is
2369 // available to help the thread with threadID "master" at a split point. An
2370 // obvious requirement is that "slave" must be idle. With more than two
2371 // threads, this is not by itself sufficient: If "slave" is the master of
2372 // some active split point, it is only available as a slave to the other
2373 // threads which are busy searching the split point at the top of "slave"'s
2374 // split point stack (the "helpful master concept" in YBWC terminology).
2376 bool ThreadsManager::thread_is_available(int slave, int master) const {
2378 assert(slave >= 0 && slave < ActiveThreads);
2379 assert(master >= 0 && master < ActiveThreads);
2380 assert(ActiveThreads > 1);
2382 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2385 // Make a local copy to be sure doesn't change under our feet
2386 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2388 // No active split points means that the thread is available as
2389 // a slave for any other thread.
2390 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2393 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2394 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2395 // could have been set to 0 by another thread leading to an out of bound access.
2396 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2403 // available_thread_exists() tries to find an idle thread which is available as
2404 // a slave for the thread with threadID "master".
2406 bool ThreadsManager::available_thread_exists(int master) const {
2408 assert(master >= 0 && master < ActiveThreads);
2409 assert(ActiveThreads > 1);
2411 for (int i = 0; i < ActiveThreads; i++)
2412 if (thread_is_available(i, master))
2419 // split() does the actual work of distributing the work at a node between
2420 // several available threads. If it does not succeed in splitting the
2421 // node (because no idle threads are available, or because we have no unused
2422 // split point objects), the function immediately returns. If splitting is
2423 // possible, a SplitPoint object is initialized with all the data that must be
2424 // copied to the helper threads and we tell our helper threads that they have
2425 // been assigned work. This will cause them to instantly leave their idle loops and
2426 // call search().When all threads have returned from search() then split() returns.
2428 template <bool Fake>
2429 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2430 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2431 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2432 assert(pos.is_ok());
2433 assert(ply > 0 && ply < PLY_MAX);
2434 assert(*bestValue >= -VALUE_INFINITE);
2435 assert(*bestValue <= *alpha);
2436 assert(*alpha < beta);
2437 assert(beta <= VALUE_INFINITE);
2438 assert(depth > DEPTH_ZERO);
2439 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2440 assert(ActiveThreads > 1);
2442 int i, master = pos.thread();
2443 Thread& masterThread = threads[master];
2447 // If no other thread is available to help us, or if we have too many
2448 // active split points, don't split.
2449 if ( !available_thread_exists(master)
2450 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2452 lock_release(&MPLock);
2456 // Pick the next available split point object from the split point stack
2457 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2459 // Initialize the split point object
2460 splitPoint.parent = masterThread.splitPoint;
2461 splitPoint.stopRequest = false;
2462 splitPoint.ply = ply;
2463 splitPoint.depth = depth;
2464 splitPoint.threatMove = threatMove;
2465 splitPoint.mateThreat = mateThreat;
2466 splitPoint.alpha = *alpha;
2467 splitPoint.beta = beta;
2468 splitPoint.pvNode = pvNode;
2469 splitPoint.bestValue = *bestValue;
2471 splitPoint.moveCount = moveCount;
2472 splitPoint.pos = &pos;
2473 splitPoint.nodes = 0;
2474 splitPoint.parentSstack = ss;
2475 for (i = 0; i < ActiveThreads; i++)
2476 splitPoint.slaves[i] = 0;
2478 masterThread.splitPoint = &splitPoint;
2480 // If we are here it means we are not available
2481 assert(masterThread.state != THREAD_AVAILABLE);
2483 int workersCnt = 1; // At least the master is included
2485 // Allocate available threads setting state to THREAD_BOOKED
2486 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2487 if (thread_is_available(i, master))
2489 threads[i].state = THREAD_BOOKED;
2490 threads[i].splitPoint = &splitPoint;
2491 splitPoint.slaves[i] = 1;
2495 assert(Fake || workersCnt > 1);
2497 // We can release the lock because slave threads are already booked and master is not available
2498 lock_release(&MPLock);
2500 // Tell the threads that they have work to do. This will make them leave
2501 // their idle loop. But before copy search stack tail for each thread.
2502 for (i = 0; i < ActiveThreads; i++)
2503 if (i == master || splitPoint.slaves[i])
2505 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2507 assert(i == master || threads[i].state == THREAD_BOOKED);
2509 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2511 wake_sleeping_thread(i);
2514 // Everything is set up. The master thread enters the idle loop, from
2515 // which it will instantly launch a search, because its state is
2516 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2517 // idle loop, which means that the main thread will return from the idle
2518 // loop when all threads have finished their work at this split point.
2519 idle_loop(master, &splitPoint);
2521 // We have returned from the idle loop, which means that all threads are
2522 // finished. Update alpha and bestValue, and return.
2525 *alpha = splitPoint.alpha;
2526 *bestValue = splitPoint.bestValue;
2527 masterThread.activeSplitPoints--;
2528 masterThread.splitPoint = splitPoint.parent;
2529 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2531 lock_release(&MPLock);
2535 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2536 // to start a new search from the root.
2538 void ThreadsManager::wake_sleeping_thread(int threadID) {
2541 cond_signal(&WaitCond[threadID]);
2542 lock_release(&MPLock);
2546 /// The RootMoveList class
2548 // RootMoveList c'tor
2550 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2552 SearchStack ss[PLY_MAX_PLUS_2];
2553 MoveStack mlist[MOVES_MAX];
2555 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2557 // Initialize search stack
2558 init_ss_array(ss, PLY_MAX_PLUS_2);
2559 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2562 // Generate all legal moves
2563 MoveStack* last = generate_moves(pos, mlist);
2565 // Add each move to the moves[] array
2566 for (MoveStack* cur = mlist; cur != last; cur++)
2568 bool includeMove = includeAllMoves;
2570 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2571 includeMove = (searchMoves[k] == cur->move);
2576 // Find a quick score for the move
2577 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2578 moves[count].pv[1] = MOVE_NONE;
2579 pos.do_move(cur->move, st);
2580 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2581 pos.undo_move(cur->move);
2587 // Score root moves using the standard way used in main search, the moves
2588 // are scored according to the order in which are returned by MovePicker.
2590 void RootMoveList::score_moves(const Position& pos)
2594 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2596 while ((move = mp.get_next_move()) != MOVE_NONE)
2597 for (int i = 0; i < count; i++)
2598 if (moves[i].move == move)
2600 moves[i].mp_score = score--;
2605 // RootMoveList simple methods definitions
2607 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2611 for (j = 0; pv[j] != MOVE_NONE; j++)
2612 moves[moveNum].pv[j] = pv[j];
2614 moves[moveNum].pv[j] = MOVE_NONE;
2618 // RootMoveList::sort() sorts the root move list at the beginning of a new
2621 void RootMoveList::sort() {
2623 sort_multipv(count - 1); // Sort all items
2627 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2628 // list by their scores and depths. It is used to order the different PVs
2629 // correctly in MultiPV mode.
2631 void RootMoveList::sort_multipv(int n) {
2635 for (i = 1; i <= n; i++)
2637 RootMove rm = moves[i];
2638 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2639 moves[j] = moves[j - 1];