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 min_split_depth() const { return minimumSplitDepth; }
81 int active_threads() const { return activeThreads; }
82 void set_active_threads(int cnt) { activeThreads = cnt; }
84 void read_uci_options();
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_thread(int threadID);
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
96 Depth minimumSplitDepth;
97 int maxThreadsPerSplitPoint;
98 bool useSleepingThreads;
100 volatile bool allThreadsShouldExit;
101 Thread threads[MAX_THREADS];
102 Lock mpLock, sleepLock[MAX_THREADS];
103 WaitCondition sleepCond[MAX_THREADS];
107 // RootMove struct is used for moves at the root at the tree. For each
108 // root move, we store a score, a node count, and a PV (really a refutation
109 // in the case of moves which fail low).
113 RootMove() : mp_score(0), nodes(0) {}
115 // RootMove::operator<() is the comparison function used when
116 // sorting the moves. A move m1 is considered to be better
117 // than a move m2 if it has a higher score, or if the moves
118 // have equal score but m1 has the higher beta cut-off count.
119 bool operator<(const RootMove& m) const {
121 return score != m.score ? score < m.score : mp_score <= m.mp_score;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 Move move(int moveNum) const { return moves[moveNum].move; }
141 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
142 int move_count() const { return count; }
143 Value move_score(int moveNum) const { return moves[moveNum].score; }
144 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
145 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
146 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
148 void set_move_pv(int moveNum, const Move pv[]);
149 void score_moves(const Position& pos);
151 void sort_multipv(int n);
154 RootMove moves[MOVES_MAX];
159 // When formatting a move for std::cout we must know if we are in Chess960
160 // or not. To keep using the handy operator<<() on the move the trick is to
161 // embed this flag in the stream itself. Function-like named enum set960 is
162 // used as a custom manipulator and the stream internal general-purpose array,
163 // accessed through ios_base::iword(), is used to pass the flag to the move's
164 // operator<<() that will use it to properly format castling moves.
167 std::ostream& operator<< (std::ostream& os, const set960& m) {
169 os.iword(0) = int(m);
178 // Maximum depth for razoring
179 const Depth RazorDepth = 4 * ONE_PLY;
181 // Dynamic razoring margin based on depth
182 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
184 // Maximum depth for use of dynamic threat detection when null move fails low
185 const Depth ThreatDepth = 5 * ONE_PLY;
187 // Step 9. Internal iterative deepening
189 // Minimum depth for use of internal iterative deepening
190 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
192 // At Non-PV nodes we do an internal iterative deepening search
193 // when the static evaluation is bigger then beta - IIDMargin.
194 const Value IIDMargin = Value(0x100);
196 // Step 11. Decide the new search depth
198 // Extensions. Configurable UCI options
199 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
200 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
201 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
203 // Minimum depth for use of singular extension
204 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
206 // If the TT move is at least SingularExtensionMargin better then the
207 // remaining ones we will extend it.
208 const Value SingularExtensionMargin = Value(0x20);
210 // Step 12. Futility pruning
212 // Futility margin for quiescence search
213 const Value FutilityMarginQS = Value(0x80);
215 // Futility lookup tables (initialized at startup) and their getter functions
216 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
217 int FutilityMoveCountArray[32]; // [depth]
219 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
220 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
222 // Step 14. Reduced search
224 // Reduction lookup tables (initialized at startup) and their getter functions
225 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
227 template <NodeType PV>
228 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
230 // Common adjustments
232 // Search depth at iteration 1
233 const Depth InitialDepth = ONE_PLY;
235 // Easy move margin. An easy move candidate must be at least this much
236 // better than the second best move.
237 const Value EasyMoveMargin = Value(0x200);
240 /// Namespace variables
248 // Scores and number of times the best move changed for each iteration
249 Value ValueByIteration[PLY_MAX_PLUS_2];
250 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
252 // Search window management
258 // Time managment variables
259 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
260 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
261 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
266 std::ofstream LogFile;
268 // Multi-threads manager object
269 ThreadsManager ThreadsMgr;
271 // Node counters, used only by thread[0] but try to keep in different cache
272 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
274 int NodesBetweenPolls = 30000;
281 Value id_loop(Position& pos, Move searchMoves[]);
282 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
284 template <NodeType PvNode, bool SpNode>
285 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
293 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
294 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
297 template <NodeType PvNode>
298 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
300 bool check_is_useless(Position &pos, Move move, Value eval, Value futilityBase, Value beta, Value *bValue);
301 Bitboard attacks(const Piece P, const Square sq, const Bitboard occ);
302 bool connected_moves(const Position& pos, Move m1, Move m2);
303 bool value_is_mate(Value value);
304 Value value_to_tt(Value v, int ply);
305 Value value_from_tt(Value v, int ply);
306 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
307 bool connected_threat(const Position& pos, Move m, Move threat);
308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
309 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
310 void update_killers(Move m, SearchStack* ss);
311 void update_gains(const Position& pos, Move move, Value before, Value after);
313 int current_search_time();
314 std::string value_to_uci(Value v);
315 int nps(const Position& pos);
316 void poll(const Position& pos);
318 void wait_for_stop_or_ponderhit();
319 void init_ss_array(SearchStack* ss, int size);
320 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
321 void insert_pv_in_tt(const Position& pos, Move pv[]);
322 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
324 #if !defined(_MSC_VER)
325 void* init_thread(void* threadID);
327 DWORD WINAPI init_thread(LPVOID threadID);
337 /// init_threads(), exit_threads() and nodes_searched() are helpers to
338 /// give accessibility to some TM methods from outside of current file.
340 void init_threads() { ThreadsMgr.init_threads(); }
341 void exit_threads() { ThreadsMgr.exit_threads(); }
344 /// init_search() is called during startup. It initializes various lookup tables
348 int d; // depth (ONE_PLY == 2)
349 int hd; // half depth (ONE_PLY == 1)
352 // Init reductions array
353 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
355 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
356 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
357 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
358 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
361 // Init futility margins array
362 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
363 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
365 // Init futility move count array
366 for (d = 0; d < 32; d++)
367 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
371 /// perft() is our utility to verify move generation is bug free. All the legal
372 /// moves up to given depth are generated and counted and the sum returned.
374 int perft(Position& pos, Depth depth)
376 MoveStack mlist[MOVES_MAX];
381 // Generate all legal moves
382 MoveStack* last = generate_moves(pos, mlist);
384 // If we are at the last ply we don't need to do and undo
385 // the moves, just to count them.
386 if (depth <= ONE_PLY)
387 return int(last - mlist);
389 // Loop through all legal moves
391 for (MoveStack* cur = mlist; cur != last; cur++)
394 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
395 sum += perft(pos, depth - ONE_PLY);
402 /// think() is the external interface to Stockfish's search, and is called when
403 /// the program receives the UCI 'go' command. It initializes various
404 /// search-related global variables, and calls root_search(). It returns false
405 /// when a quit command is received during the search.
407 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
408 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
410 // Initialize global search variables
411 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
413 SearchStartTime = get_system_time();
414 ExactMaxTime = maxTime;
417 InfiniteSearch = infinite;
418 PonderSearch = ponder;
419 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
421 // Look for a book move, only during games, not tests
422 if (UseTimeManagement && Options["OwnBook"].value<bool>())
424 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
425 OpeningBook.open(Options["Book File"].value<std::string>());
427 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
428 if (bookMove != MOVE_NONE)
431 wait_for_stop_or_ponderhit();
433 cout << "bestmove " << bookMove << endl;
438 // Read UCI option values
439 TT.set_size(Options["Hash"].value<int>());
440 if (Options["Clear Hash"].value<bool>())
442 Options["Clear Hash"].set_value("false");
446 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
447 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
448 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
449 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
450 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
451 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
452 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
453 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
454 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
455 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
456 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
457 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
458 MultiPV = Options["MultiPV"].value<int>();
459 UseLogFile = Options["Use Search Log"].value<bool>();
462 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
464 read_weights(pos.side_to_move());
466 // Set the number of active threads
467 ThreadsMgr.read_uci_options();
468 init_eval(ThreadsMgr.active_threads());
470 // Wake up needed threads
471 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
472 ThreadsMgr.wake_sleeping_thread(i);
475 int myTime = time[pos.side_to_move()];
476 int myIncrement = increment[pos.side_to_move()];
477 if (UseTimeManagement)
478 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
480 // Set best NodesBetweenPolls interval to avoid lagging under
481 // heavy time pressure.
483 NodesBetweenPolls = Min(MaxNodes, 30000);
484 else if (myTime && myTime < 1000)
485 NodesBetweenPolls = 1000;
486 else if (myTime && myTime < 5000)
487 NodesBetweenPolls = 5000;
489 NodesBetweenPolls = 30000;
491 // Write search information to log file
493 LogFile << "Searching: " << pos.to_fen() << endl
494 << "infinite: " << infinite
495 << " ponder: " << ponder
496 << " time: " << myTime
497 << " increment: " << myIncrement
498 << " moves to go: " << movesToGo << endl;
500 // We're ready to start thinking. Call the iterative deepening loop function
501 id_loop(pos, searchMoves);
506 // This makes all the threads to go to sleep
507 ThreadsMgr.set_active_threads(1);
515 // id_loop() is the main iterative deepening loop. It calls root_search
516 // repeatedly with increasing depth until the allocated thinking time has
517 // been consumed, the user stops the search, or the maximum search depth is
520 Value id_loop(Position& pos, Move searchMoves[]) {
522 SearchStack ss[PLY_MAX_PLUS_2];
523 Move pv[PLY_MAX_PLUS_2];
524 Move EasyMove = MOVE_NONE;
525 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
527 // Moves to search are verified, copied, scored and sorted
528 RootMoveList rml(pos, searchMoves);
530 // Handle special case of searching on a mate/stale position
531 if (rml.move_count() == 0)
534 wait_for_stop_or_ponderhit();
536 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
539 // Print RootMoveList startup scoring to the standard output,
540 // so to output information also for iteration 1.
541 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
542 << "info depth " << 1
543 << "\ninfo depth " << 1
544 << " score " << value_to_uci(rml.move_score(0))
545 << " time " << current_search_time()
546 << " nodes " << pos.nodes_searched()
547 << " nps " << nps(pos)
548 << " pv " << rml.move(0) << "\n";
553 init_ss_array(ss, PLY_MAX_PLUS_2);
554 pv[0] = pv[1] = MOVE_NONE;
555 ValueByIteration[1] = rml.move_score(0);
558 // Is one move significantly better than others after initial scoring ?
559 if ( rml.move_count() == 1
560 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
561 EasyMove = rml.move(0);
563 // Iterative deepening loop
564 while (Iteration < PLY_MAX)
566 // Initialize iteration
568 BestMoveChangesByIteration[Iteration] = 0;
570 cout << "info depth " << Iteration << endl;
572 // Calculate dynamic aspiration window based on previous iterations
573 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
575 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
576 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
578 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
579 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
581 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
582 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
585 // Search to the current depth, rml is updated and sorted, alpha and beta could change
586 value = root_search(pos, ss, pv, rml, &alpha, &beta);
588 // Write PV to transposition table, in case the relevant entries have
589 // been overwritten during the search.
590 insert_pv_in_tt(pos, pv);
593 break; // Value cannot be trusted. Break out immediately!
595 //Save info about search result
596 ValueByIteration[Iteration] = value;
598 // Drop the easy move if differs from the new best move
599 if (pv[0] != EasyMove)
600 EasyMove = MOVE_NONE;
602 if (UseTimeManagement)
605 bool stopSearch = false;
607 // Stop search early if there is only a single legal move,
608 // we search up to Iteration 6 anyway to get a proper score.
609 if (Iteration >= 6 && rml.move_count() == 1)
612 // Stop search early when the last two iterations returned a mate score
614 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
615 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
618 // Stop search early if one move seems to be much better than the others
621 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
622 && current_search_time() > TimeMgr.available_time() / 16)
623 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
624 && current_search_time() > TimeMgr.available_time() / 32)))
627 // Add some extra time if the best move has changed during the last two iterations
628 if (Iteration > 5 && Iteration <= 50)
629 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
630 BestMoveChangesByIteration[Iteration-1]);
632 // Stop search if most of MaxSearchTime is consumed at the end of the
633 // iteration. We probably don't have enough time to search the first
634 // move at the next iteration anyway.
635 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
641 StopOnPonderhit = true;
647 if (MaxDepth && Iteration >= MaxDepth)
651 // If we are pondering or in infinite search, we shouldn't print the
652 // best move before we are told to do so.
653 if (!AbortSearch && (PonderSearch || InfiniteSearch))
654 wait_for_stop_or_ponderhit();
656 // Print final search statistics
657 cout << "info nodes " << pos.nodes_searched()
658 << " nps " << nps(pos)
659 << " time " << current_search_time() << endl;
661 // Print the best move and the ponder move to the standard output
662 if (pv[0] == MOVE_NONE || MultiPV > 1)
668 assert(pv[0] != MOVE_NONE);
670 cout << "bestmove " << pv[0];
672 if (pv[1] != MOVE_NONE)
673 cout << " ponder " << pv[1];
680 dbg_print_mean(LogFile);
682 if (dbg_show_hit_rate)
683 dbg_print_hit_rate(LogFile);
685 LogFile << "\nNodes: " << pos.nodes_searched()
686 << "\nNodes/second: " << nps(pos)
687 << "\nBest move: " << move_to_san(pos, pv[0]);
690 pos.do_move(pv[0], st);
691 LogFile << "\nPonder move: "
692 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
695 return rml.move_score(0);
699 // root_search() is the function which searches the root node. It is
700 // similar to search_pv except that it uses a different move ordering
701 // scheme, prints some information to the standard output and handles
702 // the fail low/high loops.
704 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
710 Depth depth, ext, newDepth;
711 Value value, alpha, beta;
712 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
713 int researchCountFH, researchCountFL;
715 researchCountFH = researchCountFL = 0;
718 isCheck = pos.is_check();
719 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
721 // Step 1. Initialize node (polling is omitted at root)
722 ss->currentMove = ss->bestMove = MOVE_NONE;
724 // Step 2. Check for aborted search (omitted at root)
725 // Step 3. Mate distance pruning (omitted at root)
726 // Step 4. Transposition table lookup (omitted at root)
728 // Step 5. Evaluate the position statically
729 // At root we do this only to get reference value for child nodes
730 ss->evalMargin = VALUE_NONE;
731 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
733 // Step 6. Razoring (omitted at root)
734 // Step 7. Static null move pruning (omitted at root)
735 // Step 8. Null move search with verification search (omitted at root)
736 // Step 9. Internal iterative deepening (omitted at root)
738 // Step extra. Fail low loop
739 // We start with small aspiration window and in case of fail low, we research
740 // with bigger window until we are not failing low anymore.
743 // Sort the moves before to (re)search
744 rml.score_moves(pos);
747 // Step 10. Loop through all moves in the root move list
748 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
750 // This is used by time management
751 FirstRootMove = (i == 0);
753 // Save the current node count before the move is searched
754 nodes = pos.nodes_searched();
756 // Pick the next root move, and print the move and the move number to
757 // the standard output.
758 move = ss->currentMove = rml.move(i);
760 if (current_search_time() >= 1000)
761 cout << "info currmove " << move
762 << " currmovenumber " << i + 1 << endl;
764 moveIsCheck = pos.move_is_check(move);
765 captureOrPromotion = pos.move_is_capture_or_promotion(move);
767 // Step 11. Decide the new search depth
768 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
769 newDepth = depth + ext;
771 // Step 12. Futility pruning (omitted at root)
773 // Step extra. Fail high loop
774 // If move fails high, we research with bigger window until we are not failing
776 value = - VALUE_INFINITE;
780 // Step 13. Make the move
781 pos.do_move(move, st, ci, moveIsCheck);
783 // Step extra. pv search
784 // We do pv search for first moves (i < MultiPV)
785 // and for fail high research (value > alpha)
786 if (i < MultiPV || value > alpha)
788 // Aspiration window is disabled in multi-pv case
790 alpha = -VALUE_INFINITE;
792 // Full depth PV search, done on first move or after a fail high
793 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
797 // Step 14. Reduced search
798 // if the move fails high will be re-searched at full depth
799 bool doFullDepthSearch = true;
801 if ( depth >= 3 * ONE_PLY
803 && !captureOrPromotion
804 && !move_is_castle(move))
806 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
809 assert(newDepth-ss->reduction >= ONE_PLY);
811 // Reduced depth non-pv search using alpha as upperbound
812 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
813 doFullDepthSearch = (value > alpha);
816 // The move failed high, but if reduction is very big we could
817 // face a false positive, retry with a less aggressive reduction,
818 // if the move fails high again then go with full depth search.
819 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
821 assert(newDepth - ONE_PLY >= ONE_PLY);
823 ss->reduction = ONE_PLY;
824 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
825 doFullDepthSearch = (value > alpha);
827 ss->reduction = DEPTH_ZERO; // Restore original reduction
830 // Step 15. Full depth search
831 if (doFullDepthSearch)
833 // Full depth non-pv search using alpha as upperbound
834 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
836 // If we are above alpha then research at same depth but as PV
837 // to get a correct score or eventually a fail high above beta.
839 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
843 // Step 16. Undo move
846 // Can we exit fail high loop ?
847 if (AbortSearch || value < beta)
850 // We are failing high and going to do a research. It's important to update
851 // the score before research in case we run out of time while researching.
852 rml.set_move_score(i, value);
854 extract_pv_from_tt(pos, move, pv);
855 rml.set_move_pv(i, pv);
857 // Print information to the standard output
858 print_pv_info(pos, pv, alpha, beta, value);
860 // Prepare for a research after a fail high, each time with a wider window
861 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
864 } // End of fail high loop
866 // Finished searching the move. If AbortSearch is true, the search
867 // was aborted because the user interrupted the search or because we
868 // ran out of time. In this case, the return value of the search cannot
869 // be trusted, and we break out of the loop without updating the best
874 // Remember searched nodes counts for this move
875 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
877 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
878 assert(value < beta);
880 // Step 17. Check for new best move
881 if (value <= alpha && i >= MultiPV)
882 rml.set_move_score(i, -VALUE_INFINITE);
885 // PV move or new best move!
888 rml.set_move_score(i, value);
890 extract_pv_from_tt(pos, move, pv);
891 rml.set_move_pv(i, pv);
895 // We record how often the best move has been changed in each
896 // iteration. This information is used for time managment: When
897 // the best move changes frequently, we allocate some more time.
899 BestMoveChangesByIteration[Iteration]++;
901 // Print information to the standard output
902 print_pv_info(pos, pv, alpha, beta, value);
904 // Raise alpha to setup proper non-pv search upper bound
911 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
913 cout << "info multipv " << j + 1
914 << " score " << value_to_uci(rml.move_score(j))
915 << " depth " << (j <= i ? Iteration : Iteration - 1)
916 << " time " << current_search_time()
917 << " nodes " << pos.nodes_searched()
918 << " nps " << nps(pos)
921 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
922 cout << rml.move_pv(j, k) << " ";
926 alpha = rml.move_score(Min(i, MultiPV - 1));
928 } // PV move or new best move
930 assert(alpha >= *alphaPtr);
932 AspirationFailLow = (alpha == *alphaPtr);
934 if (AspirationFailLow && StopOnPonderhit)
935 StopOnPonderhit = false;
938 // Can we exit fail low loop ?
939 if (AbortSearch || !AspirationFailLow)
942 // Prepare for a research after a fail low, each time with a wider window
943 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
948 // Sort the moves before to return
955 // search<>() is the main search function for both PV and non-PV nodes and for
956 // normal and SplitPoint nodes. When called just after a split point the search
957 // is simpler because we have already probed the hash table, done a null move
958 // search, and searched the first move before splitting, we don't have to repeat
959 // all this work again. We also don't need to store anything to the hash table
960 // here: This is taken care of after we return from the split point.
962 template <NodeType PvNode, bool SpNode>
963 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
965 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
966 assert(beta > alpha && beta <= VALUE_INFINITE);
967 assert(PvNode || alpha == beta - 1);
968 assert(ply > 0 && ply < PLY_MAX);
969 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
971 Move movesSearched[MOVES_MAX];
975 Move ttMove, move, excludedMove, threatMove;
978 Value bestValue, value, oldAlpha;
979 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
980 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
981 bool mateThreat = false;
983 int threadID = pos.thread();
984 SplitPoint* sp = NULL;
985 refinedValue = bestValue = value = -VALUE_INFINITE;
987 isCheck = pos.is_check();
993 ttMove = excludedMove = MOVE_NONE;
994 threatMove = sp->threatMove;
995 mateThreat = sp->mateThreat;
996 goto split_point_start;
997 } else {} // Hack to fix icc's "statement is unreachable" warning
999 // Step 1. Initialize node and poll. Polling can abort search
1000 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1001 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1003 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1009 // Step 2. Check for aborted search and immediate draw
1010 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1011 || pos.is_draw() || ply >= PLY_MAX - 1)
1014 // Step 3. Mate distance pruning
1015 alpha = Max(value_mated_in(ply), alpha);
1016 beta = Min(value_mate_in(ply+1), beta);
1020 // Step 4. Transposition table lookup
1022 // We don't want the score of a partial search to overwrite a previous full search
1023 // TT value, so we use a different position key in case of an excluded move exists.
1024 excludedMove = ss->excludedMove;
1025 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1027 tte = TT.retrieve(posKey);
1028 ttMove = tte ? tte->move() : MOVE_NONE;
1030 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1031 // This is to avoid problems in the following areas:
1033 // * Repetition draw detection
1034 // * Fifty move rule detection
1035 // * Searching for a mate
1036 // * Printing of full PV line
1037 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
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.
1047 ss->eval = ss->evalMargin = VALUE_NONE;
1050 assert(tte->static_value() != VALUE_NONE);
1052 ss->eval = tte->static_value();
1053 ss->evalMargin = tte->static_value_margin();
1054 refinedValue = refine_eval(tte, ss->eval, ply);
1058 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1059 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1062 // Save gain for the parent non-capture move
1063 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1065 // Step 6. Razoring (is omitted in PV nodes)
1067 && depth < RazorDepth
1069 && refinedValue < beta - razor_margin(depth)
1070 && ttMove == MOVE_NONE
1071 && !value_is_mate(beta)
1072 && !pos.has_pawn_on_7th(pos.side_to_move()))
1074 Value rbeta = beta - razor_margin(depth);
1075 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1077 // Logically we should return (v + razor_margin(depth)), but
1078 // surprisingly this did slightly weaker in tests.
1082 // Step 7. Static null move pruning (is omitted in PV nodes)
1083 // We're betting that the opponent doesn't have a move that will reduce
1084 // the score by more than futility_margin(depth) if we do a null move.
1086 && !ss->skipNullMove
1087 && depth < RazorDepth
1089 && refinedValue >= beta + futility_margin(depth, 0)
1090 && !value_is_mate(beta)
1091 && pos.non_pawn_material(pos.side_to_move()))
1092 return refinedValue - futility_margin(depth, 0);
1094 // Step 8. Null move search with verification search (is omitted in PV nodes)
1096 && !ss->skipNullMove
1099 && refinedValue >= beta
1100 && !value_is_mate(beta)
1101 && pos.non_pawn_material(pos.side_to_move()))
1103 ss->currentMove = MOVE_NULL;
1105 // Null move dynamic reduction based on depth
1106 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1108 // Null move dynamic reduction based on value
1109 if (refinedValue - beta > PawnValueMidgame)
1112 pos.do_null_move(st);
1113 (ss+1)->skipNullMove = true;
1114 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * ONE_PLY)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1154 // Step 9. Internal iterative deepening
1155 if ( depth >= IIDDepth[PvNode]
1156 && ttMove == MOVE_NONE
1157 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1159 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1161 ss->skipNullMove = true;
1162 search<PvNode>(pos, ss, alpha, beta, d, ply);
1163 ss->skipNullMove = false;
1165 ttMove = ss->bestMove;
1166 tte = TT.retrieve(posKey);
1169 // Expensive mate threat detection (only for PV nodes)
1171 mateThreat = pos.has_mate_threat();
1173 split_point_start: // At split points actual search starts from here
1175 // Initialize a MovePicker object for the current position
1176 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1177 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1178 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1180 ss->bestMove = MOVE_NONE;
1181 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1182 futilityBase = ss->eval + ss->evalMargin;
1183 singularExtensionNode = !SpNode
1184 && depth >= SingularExtensionDepth[PvNode]
1187 && !excludedMove // Do not allow recursive singular extension search
1188 && (tte->type() & VALUE_TYPE_LOWER)
1189 && tte->depth() >= depth - 3 * ONE_PLY;
1192 lock_grab(&(sp->lock));
1193 bestValue = sp->bestValue;
1196 // Step 10. Loop through moves
1197 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1198 while ( bestValue < beta
1199 && (move = mp.get_next_move()) != MOVE_NONE
1200 && !ThreadsMgr.thread_should_stop(threadID))
1202 assert(move_is_ok(move));
1206 moveCount = ++sp->moveCount;
1207 lock_release(&(sp->lock));
1209 else if (move == excludedMove)
1212 movesSearched[moveCount++] = move;
1214 moveIsCheck = pos.move_is_check(move, ci);
1215 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1217 // Step 11. Decide the new search depth
1218 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1220 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1221 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1222 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1223 // lower then ttValue minus a margin then we extend ttMove.
1224 if ( singularExtensionNode
1225 && move == tte->move()
1228 Value ttValue = value_from_tt(tte->value(), ply);
1230 if (abs(ttValue) < VALUE_KNOWN_WIN)
1232 Value b = ttValue - SingularExtensionMargin;
1233 ss->excludedMove = move;
1234 ss->skipNullMove = true;
1235 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1236 ss->skipNullMove = false;
1237 ss->excludedMove = MOVE_NONE;
1238 ss->bestMove = MOVE_NONE;
1244 // Update current move (this must be done after singular extension search)
1245 ss->currentMove = move;
1246 newDepth = depth - ONE_PLY + ext;
1248 // Step 12. Futility pruning (is omitted in PV nodes)
1250 && !captureOrPromotion
1254 && !move_is_castle(move))
1256 // Move count based pruning
1257 if ( moveCount >= futility_move_count(depth)
1258 && !(threatMove && connected_threat(pos, move, threatMove))
1259 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1262 lock_grab(&(sp->lock));
1267 // Value based pruning
1268 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1269 // but fixing this made program slightly weaker.
1270 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1271 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1272 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1274 if (futilityValueScaled < beta)
1278 lock_grab(&(sp->lock));
1279 if (futilityValueScaled > sp->bestValue)
1280 sp->bestValue = bestValue = futilityValueScaled;
1282 else if (futilityValueScaled > bestValue)
1283 bestValue = futilityValueScaled;
1288 // Prune neg. see moves at low depths
1289 if ( predictedDepth < 2 * ONE_PLY
1290 && bestValue > value_mated_in(PLY_MAX)
1291 && pos.see_sign(move) < 0)
1294 lock_grab(&(sp->lock));
1300 // Step 13. Make the move
1301 pos.do_move(move, st, ci, moveIsCheck);
1303 // Step extra. pv search (only in PV nodes)
1304 // The first move in list is the expected PV
1305 if (!SpNode && PvNode && moveCount == 1)
1306 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1309 // Step 14. Reduced depth search
1310 // If the move fails high will be re-searched at full depth.
1311 bool doFullDepthSearch = true;
1313 if ( depth >= 3 * ONE_PLY
1314 && !captureOrPromotion
1316 && !move_is_castle(move)
1317 && !(ss->killers[0] == move || ss->killers[1] == move))
1319 ss->reduction = reduction<PvNode>(depth, moveCount);
1322 alpha = SpNode ? sp->alpha : alpha;
1323 Depth d = newDepth - ss->reduction;
1324 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1326 doFullDepthSearch = (value > alpha);
1329 // The move failed high, but if reduction is very big we could
1330 // face a false positive, retry with a less aggressive reduction,
1331 // if the move fails high again then go with full depth search.
1332 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1334 assert(newDepth - ONE_PLY >= ONE_PLY);
1336 ss->reduction = ONE_PLY;
1337 alpha = SpNode ? sp->alpha : alpha;
1338 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1339 doFullDepthSearch = (value > alpha);
1341 ss->reduction = DEPTH_ZERO; // Restore original reduction
1344 // Step 15. Full depth search
1345 if (doFullDepthSearch)
1347 alpha = SpNode ? sp->alpha : alpha;
1348 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1350 // Step extra. pv search (only in PV nodes)
1351 // Search only for possible new PV nodes, if instead value >= beta then
1352 // parent node fails low with value <= alpha and tries another move.
1353 if (PvNode && value > alpha && value < beta)
1354 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1358 // Step 16. Undo move
1359 pos.undo_move(move);
1361 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1363 // Step 17. Check for new best move
1366 lock_grab(&(sp->lock));
1367 bestValue = sp->bestValue;
1371 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1376 sp->bestValue = value;
1380 if (SpNode && (!PvNode || value >= beta))
1381 sp->stopRequest = true;
1383 if (PvNode && value < beta) // We want always alpha < beta
1390 if (value == value_mate_in(ply + 1))
1391 ss->mateKiller = move;
1393 ss->bestMove = move;
1396 sp->parentSstack->bestMove = move;
1400 // Step 18. Check for split
1402 && depth >= ThreadsMgr.min_split_depth()
1403 && ThreadsMgr.active_threads() > 1
1405 && ThreadsMgr.available_thread_exists(threadID)
1407 && !ThreadsMgr.thread_should_stop(threadID)
1409 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1410 threatMove, mateThreat, moveCount, &mp, PvNode);
1413 // Step 19. Check for mate and stalemate
1414 // All legal moves have been searched and if there are
1415 // no legal moves, it must be mate or stalemate.
1416 // If one move was excluded return fail low score.
1417 if (!SpNode && !moveCount)
1418 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1420 // Step 20. Update tables
1421 // If the search is not aborted, update the transposition table,
1422 // history counters, and killer moves.
1423 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1425 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1426 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1427 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1429 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1431 // Update killers and history only for non capture moves that fails high
1432 if ( bestValue >= beta
1433 && !pos.move_is_capture_or_promotion(move))
1435 update_history(pos, move, depth, movesSearched, moveCount);
1436 update_killers(move, ss);
1442 // Here we have the lock still grabbed
1443 sp->slaves[threadID] = 0;
1444 sp->nodes += pos.nodes_searched();
1445 lock_release(&(sp->lock));
1448 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1453 // qsearch() is the quiescence search function, which is called by the main
1454 // search function when the remaining depth is zero (or, to be more precise,
1455 // less than ONE_PLY).
1457 template <NodeType PvNode>
1458 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1460 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1461 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1462 assert(PvNode || alpha == beta - 1);
1464 assert(ply > 0 && ply < PLY_MAX);
1465 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1469 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1470 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1472 Value oldAlpha = alpha;
1474 ss->bestMove = ss->currentMove = MOVE_NONE;
1476 // Check for an instant draw or maximum ply reached
1477 if (pos.is_draw() || ply >= PLY_MAX - 1)
1480 // Decide whether or not to include checks
1481 isCheck = pos.is_check();
1484 if (isCheck || depth >= -ONE_PLY)
1487 d = DEPTH_ZERO - ONE_PLY;
1489 // Transposition table lookup. At PV nodes, we don't use the TT for
1490 // pruning, but only for move ordering.
1491 tte = TT.retrieve(pos.get_key());
1492 ttMove = (tte ? tte->move() : MOVE_NONE);
1494 if (!PvNode && tte && ok_to_use_TT(tte, d, beta, ply))
1496 ss->bestMove = ttMove; // Can be MOVE_NONE
1497 return value_from_tt(tte->value(), ply);
1500 // Evaluate the position statically
1503 bestValue = futilityBase = -VALUE_INFINITE;
1504 ss->eval = evalMargin = VALUE_NONE;
1505 enoughMaterial = false;
1511 assert(tte->static_value() != VALUE_NONE);
1513 evalMargin = tte->static_value_margin();
1514 ss->eval = bestValue = tte->static_value();
1517 ss->eval = bestValue = evaluate(pos, evalMargin);
1519 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1521 // Stand pat. Return immediately if static value is at least beta
1522 if (bestValue >= beta)
1525 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1530 if (PvNode && bestValue > alpha)
1533 // Futility pruning parameters, not needed when in check
1534 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1535 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1538 // Initialize a MovePicker object for the current position, and prepare
1539 // to search the moves. Because the depth is <= 0 here, only captures,
1540 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1541 // and we are near beta) will be generated.
1542 MovePicker mp = MovePicker(pos, ttMove, d, H);
1545 // Loop through the moves until no moves remain or a beta cutoff occurs
1546 while ( alpha < beta
1547 && (move = mp.get_next_move()) != MOVE_NONE)
1549 assert(move_is_ok(move));
1551 moveIsCheck = pos.move_is_check(move, ci);
1559 && !move_is_promotion(move)
1560 && !pos.move_is_passed_pawn_push(move))
1562 futilityValue = futilityBase
1563 + pos.endgame_value_of_piece_on(move_to(move))
1564 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1566 if (futilityValue < alpha)
1568 if (futilityValue > bestValue)
1569 bestValue = futilityValue;
1574 // Detect non-capture evasions that are candidate to be pruned
1575 evasionPrunable = isCheck
1576 && bestValue > value_mated_in(PLY_MAX)
1577 && !pos.move_is_capture(move)
1578 && !pos.can_castle(pos.side_to_move());
1580 // Don't search moves with negative SEE values
1582 && (!isCheck || evasionPrunable)
1584 && !move_is_promotion(move)
1585 && pos.see_sign(move) < 0)
1588 // Don't search useless checks
1593 && !pos.move_is_capture(move)
1594 && !move_is_promotion(move)
1595 && check_is_useless(pos, move, ss->eval, futilityBase, beta, &bestValue))
1598 // Update current move
1599 ss->currentMove = move;
1601 // Make and search the move
1602 pos.do_move(move, st, ci, moveIsCheck);
1603 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1604 pos.undo_move(move);
1606 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1609 if (value > bestValue)
1615 ss->bestMove = move;
1620 // All legal moves have been searched. A special case: If we're in check
1621 // and no legal moves were found, it is checkmate.
1622 if (isCheck && bestValue == -VALUE_INFINITE)
1623 return value_mated_in(ply);
1625 // Update transposition table
1626 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1627 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1629 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1634 // check_is_useless() tests if a checking move can be pruned in qsearch().
1635 // bestValue is updated when necesary.
1637 bool check_is_useless(Position &pos, Move move, Value eval, Value futilityBase, Value beta, Value *bValue)
1639 Value bestValue = *bValue;
1641 /// Rule 1. Using checks to reposition pieces when close to beta
1642 if (eval + PawnValueMidgame / 4 < beta)
1644 if (eval + PawnValueMidgame / 4 > bestValue)
1645 bestValue = eval + PawnValueMidgame / 4;
1650 Square from = move_from(move);
1651 Square to = move_to(move);
1652 Color oppColor = opposite_color(pos.side_to_move());
1653 Square oppKing = pos.king_square(oppColor);
1655 Bitboard occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL <<oppKing);
1656 Bitboard oppOcc = pos.pieces_of_color(oppColor) & ~(1ULL <<oppKing);
1657 Bitboard oldAtt = attacks(pos.piece_on(from), from, occ);
1658 Bitboard newAtt = attacks(pos.piece_on(from), to, occ);
1660 // Rule 2. Checks which give opponent's king at most one escape square are dangerous
1661 Bitboard escapeBB = attacks(WK, oppKing, 0) & ~oppOcc & ~newAtt & ~(1ULL << to);
1666 if (!(escapeBB & (escapeBB - 1)))
1669 /// Rule 3. Queen contact check is very dangerous
1670 if ( pos.type_of_piece_on(from) == QUEEN
1671 && bit_is_set(attacks(WK, oppKing, 0), to))
1674 /// Rule 4. Creating new double threats with checks
1675 Bitboard newVictims = oppOcc & ~oldAtt & newAtt;
1679 Square victimSq = pop_1st_bit(&newVictims);
1681 Value futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1683 // Note that here we generate illegal "double move"!
1684 if (futilityValue >= beta && pos.see_sign(make_move(from, victimSq)) >= 0)
1687 if (futilityValue > bestValue)
1688 bestValue = futilityValue;
1691 *bValue = bestValue;
1695 // attacks() returns attacked squares.
1697 Bitboard attacks(const Piece P, const Square sq, const Bitboard occ)
1707 return StepAttackBB[P][sq];
1710 return bishop_attacks_bb(sq, occ);
1713 return rook_attacks_bb(sq, occ);
1716 return bishop_attacks_bb(sq, occ) | rook_attacks_bb(sq, occ);
1723 // connected_moves() tests whether two moves are 'connected' in the sense
1724 // that the first move somehow made the second move possible (for instance
1725 // if the moving piece is the same in both moves). The first move is assumed
1726 // to be the move that was made to reach the current position, while the
1727 // second move is assumed to be a move from the current position.
1729 bool connected_moves(const Position& pos, Move m1, Move m2) {
1731 Square f1, t1, f2, t2;
1734 assert(move_is_ok(m1));
1735 assert(move_is_ok(m2));
1737 if (m2 == MOVE_NONE)
1740 // Case 1: The moving piece is the same in both moves
1746 // Case 2: The destination square for m2 was vacated by m1
1752 // Case 3: Moving through the vacated square
1753 if ( piece_is_slider(pos.piece_on(f2))
1754 && bit_is_set(squares_between(f2, t2), f1))
1757 // Case 4: The destination square for m2 is defended by the moving piece in m1
1758 p = pos.piece_on(t1);
1759 if (bit_is_set(pos.attacks_from(p, t1), t2))
1762 // Case 5: Discovered check, checking piece is the piece moved in m1
1763 if ( piece_is_slider(p)
1764 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1765 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1767 // discovered_check_candidates() works also if the Position's side to
1768 // move is the opposite of the checking piece.
1769 Color them = opposite_color(pos.side_to_move());
1770 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1772 if (bit_is_set(dcCandidates, f2))
1779 // value_is_mate() checks if the given value is a mate one eventually
1780 // compensated for the ply.
1782 bool value_is_mate(Value value) {
1784 assert(abs(value) <= VALUE_INFINITE);
1786 return value <= value_mated_in(PLY_MAX)
1787 || value >= value_mate_in(PLY_MAX);
1791 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1792 // "plies to mate from the current ply". Non-mate scores are unchanged.
1793 // The function is called before storing a value to the transposition table.
1795 Value value_to_tt(Value v, int ply) {
1797 if (v >= value_mate_in(PLY_MAX))
1800 if (v <= value_mated_in(PLY_MAX))
1807 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1808 // the transposition table to a mate score corrected for the current ply.
1810 Value value_from_tt(Value v, int ply) {
1812 if (v >= value_mate_in(PLY_MAX))
1815 if (v <= value_mated_in(PLY_MAX))
1822 // extension() decides whether a move should be searched with normal depth,
1823 // or with extended depth. Certain classes of moves (checking moves, in
1824 // particular) are searched with bigger depth than ordinary moves and in
1825 // any case are marked as 'dangerous'. Note that also if a move is not
1826 // extended, as example because the corresponding UCI option is set to zero,
1827 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1828 template <NodeType PvNode>
1829 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1830 bool singleEvasion, bool mateThreat, bool* dangerous) {
1832 assert(m != MOVE_NONE);
1834 Depth result = DEPTH_ZERO;
1835 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1839 if (moveIsCheck && pos.see_sign(m) >= 0)
1840 result += CheckExtension[PvNode];
1843 result += SingleEvasionExtension[PvNode];
1846 result += MateThreatExtension[PvNode];
1849 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1851 Color c = pos.side_to_move();
1852 if (relative_rank(c, move_to(m)) == RANK_7)
1854 result += PawnPushTo7thExtension[PvNode];
1857 if (pos.pawn_is_passed(c, move_to(m)))
1859 result += PassedPawnExtension[PvNode];
1864 if ( captureOrPromotion
1865 && pos.type_of_piece_on(move_to(m)) != PAWN
1866 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1867 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1868 && !move_is_promotion(m)
1871 result += PawnEndgameExtension[PvNode];
1876 && captureOrPromotion
1877 && pos.type_of_piece_on(move_to(m)) != PAWN
1878 && pos.see_sign(m) >= 0)
1880 result += ONE_PLY / 2;
1884 return Min(result, ONE_PLY);
1888 // connected_threat() tests whether it is safe to forward prune a move or if
1889 // is somehow coonected to the threat move returned by null search.
1891 bool connected_threat(const Position& pos, Move m, Move threat) {
1893 assert(move_is_ok(m));
1894 assert(threat && move_is_ok(threat));
1895 assert(!pos.move_is_check(m));
1896 assert(!pos.move_is_capture_or_promotion(m));
1897 assert(!pos.move_is_passed_pawn_push(m));
1899 Square mfrom, mto, tfrom, tto;
1901 mfrom = move_from(m);
1903 tfrom = move_from(threat);
1904 tto = move_to(threat);
1906 // Case 1: Don't prune moves which move the threatened piece
1910 // Case 2: If the threatened piece has value less than or equal to the
1911 // value of the threatening piece, don't prune move which defend it.
1912 if ( pos.move_is_capture(threat)
1913 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1914 || pos.type_of_piece_on(tfrom) == KING)
1915 && pos.move_attacks_square(m, tto))
1918 // Case 3: If the moving piece in the threatened move is a slider, don't
1919 // prune safe moves which block its ray.
1920 if ( piece_is_slider(pos.piece_on(tfrom))
1921 && bit_is_set(squares_between(tfrom, tto), mto)
1922 && pos.see_sign(m) >= 0)
1929 // ok_to_use_TT() returns true if a transposition table score
1930 // can be used at a given point in search.
1932 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1934 Value v = value_from_tt(tte->value(), ply);
1936 return ( tte->depth() >= depth
1937 || v >= Max(value_mate_in(PLY_MAX), beta)
1938 || v < Min(value_mated_in(PLY_MAX), beta))
1940 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1941 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1945 // refine_eval() returns the transposition table score if
1946 // possible otherwise falls back on static position evaluation.
1948 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1952 Value v = value_from_tt(tte->value(), ply);
1954 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1955 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1962 // update_history() registers a good move that produced a beta-cutoff
1963 // in history and marks as failures all the other moves of that ply.
1965 void update_history(const Position& pos, Move move, Depth depth,
1966 Move movesSearched[], int moveCount) {
1969 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1971 for (int i = 0; i < moveCount - 1; i++)
1973 m = movesSearched[i];
1977 if (!pos.move_is_capture_or_promotion(m))
1978 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1983 // update_killers() add a good move that produced a beta-cutoff
1984 // among the killer moves of that ply.
1986 void update_killers(Move m, SearchStack* ss) {
1988 if (m == ss->killers[0])
1991 ss->killers[1] = ss->killers[0];
1996 // update_gains() updates the gains table of a non-capture move given
1997 // the static position evaluation before and after the move.
1999 void update_gains(const Position& pos, Move m, Value before, Value after) {
2002 && before != VALUE_NONE
2003 && after != VALUE_NONE
2004 && pos.captured_piece_type() == PIECE_TYPE_NONE
2005 && !move_is_special(m))
2006 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2010 // current_search_time() returns the number of milliseconds which have passed
2011 // since the beginning of the current search.
2013 int current_search_time() {
2015 return get_system_time() - SearchStartTime;
2019 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2021 std::string value_to_uci(Value v) {
2023 std::stringstream s;
2025 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2026 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2028 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2033 // nps() computes the current nodes/second count.
2035 int nps(const Position& pos) {
2037 int t = current_search_time();
2038 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2042 // poll() performs two different functions: It polls for user input, and it
2043 // looks at the time consumed so far and decides if it's time to abort the
2046 void poll(const Position& pos) {
2048 static int lastInfoTime;
2049 int t = current_search_time();
2052 if (data_available())
2054 // We are line oriented, don't read single chars
2055 std::string command;
2057 if (!std::getline(std::cin, command))
2060 if (command == "quit")
2063 PonderSearch = false;
2067 else if (command == "stop")
2070 PonderSearch = false;
2072 else if (command == "ponderhit")
2076 // Print search information
2080 else if (lastInfoTime > t)
2081 // HACK: Must be a new search where we searched less than
2082 // NodesBetweenPolls nodes during the first second of search.
2085 else if (t - lastInfoTime >= 1000)
2092 if (dbg_show_hit_rate)
2093 dbg_print_hit_rate();
2095 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2096 << " time " << t << endl;
2099 // Should we stop the search?
2103 bool stillAtFirstMove = FirstRootMove
2104 && !AspirationFailLow
2105 && t > TimeMgr.available_time();
2107 bool noMoreTime = t > TimeMgr.maximum_time()
2108 || stillAtFirstMove;
2110 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2111 || (ExactMaxTime && t >= ExactMaxTime)
2112 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2117 // ponderhit() is called when the program is pondering (i.e. thinking while
2118 // it's the opponent's turn to move) in order to let the engine know that
2119 // it correctly predicted the opponent's move.
2123 int t = current_search_time();
2124 PonderSearch = false;
2126 bool stillAtFirstMove = FirstRootMove
2127 && !AspirationFailLow
2128 && t > TimeMgr.available_time();
2130 bool noMoreTime = t > TimeMgr.maximum_time()
2131 || stillAtFirstMove;
2133 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2138 // init_ss_array() does a fast reset of the first entries of a SearchStack
2139 // array and of all the excludedMove and skipNullMove entries.
2141 void init_ss_array(SearchStack* ss, int size) {
2143 for (int i = 0; i < size; i++, ss++)
2145 ss->excludedMove = MOVE_NONE;
2146 ss->skipNullMove = false;
2147 ss->reduction = DEPTH_ZERO;
2151 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2156 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2157 // while the program is pondering. The point is to work around a wrinkle in
2158 // the UCI protocol: When pondering, the engine is not allowed to give a
2159 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2160 // We simply wait here until one of these commands is sent, and return,
2161 // after which the bestmove and pondermove will be printed (in id_loop()).
2163 void wait_for_stop_or_ponderhit() {
2165 std::string command;
2169 if (!std::getline(std::cin, command))
2172 if (command == "quit")
2177 else if (command == "ponderhit" || command == "stop")
2183 // print_pv_info() prints to standard output and eventually to log file information on
2184 // the current PV line. It is called at each iteration or after a new pv is found.
2186 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2188 cout << "info depth " << Iteration
2189 << " score " << value_to_uci(value)
2190 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2191 << " time " << current_search_time()
2192 << " nodes " << pos.nodes_searched()
2193 << " nps " << nps(pos)
2196 for (Move* m = pv; *m != MOVE_NONE; m++)
2203 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2204 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2206 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2211 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2212 // the PV back into the TT. This makes sure the old PV moves are searched
2213 // first, even if the old TT entries have been overwritten.
2215 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2219 Position p(pos, pos.thread());
2220 Value v, m = VALUE_NONE;
2222 for (int i = 0; pv[i] != MOVE_NONE; i++)
2224 tte = TT.retrieve(p.get_key());
2225 if (!tte || tte->move() != pv[i])
2227 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2228 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2230 p.do_move(pv[i], st);
2235 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2236 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2237 // allow to always have a ponder move even when we fail high at root and also a
2238 // long PV to print that is important for position analysis.
2240 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2244 Position p(pos, pos.thread());
2247 assert(bestMove != MOVE_NONE);
2250 p.do_move(pv[ply++], st);
2252 while ( (tte = TT.retrieve(p.get_key())) != NULL
2253 && tte->move() != MOVE_NONE
2254 && move_is_legal(p, tte->move())
2256 && (!p.is_draw() || ply < 2))
2258 pv[ply] = tte->move();
2259 p.do_move(pv[ply++], st);
2261 pv[ply] = MOVE_NONE;
2265 // init_thread() is the function which is called when a new thread is
2266 // launched. It simply calls the idle_loop() function with the supplied
2267 // threadID. There are two versions of this function; one for POSIX
2268 // threads and one for Windows threads.
2270 #if !defined(_MSC_VER)
2272 void* init_thread(void* threadID) {
2274 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2280 DWORD WINAPI init_thread(LPVOID threadID) {
2282 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2289 /// The ThreadsManager class
2292 // read_uci_options() updates number of active threads and other internal
2293 // parameters according to the UCI options values. It is called before
2294 // to start a new search.
2296 void ThreadsManager::read_uci_options() {
2298 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2299 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2300 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2301 activeThreads = Options["Threads"].value<int>();
2305 // idle_loop() is where the threads are parked when they have no work to do.
2306 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2307 // object for which the current thread is the master.
2309 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2311 assert(threadID >= 0 && threadID < MAX_THREADS);
2314 bool allFinished = false;
2318 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2319 // master should exit as last one.
2320 if (allThreadsShouldExit)
2323 threads[threadID].state = THREAD_TERMINATED;
2327 // If we are not thinking, wait for a condition to be signaled
2328 // instead of wasting CPU time polling for work.
2329 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2330 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2332 assert(!sp || useSleepingThreads);
2333 assert(threadID != 0 || useSleepingThreads);
2335 if (threads[threadID].state == THREAD_INITIALIZING)
2336 threads[threadID].state = THREAD_AVAILABLE;
2338 // Grab the lock to avoid races with wake_sleeping_thread()
2339 lock_grab(&sleepLock[threadID]);
2341 // If we are master and all slaves have finished do not go to sleep
2342 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2343 allFinished = (i == activeThreads);
2345 if (allFinished || allThreadsShouldExit)
2347 lock_release(&sleepLock[threadID]);
2351 // Do sleep here after retesting sleep conditions
2352 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2353 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2355 lock_release(&sleepLock[threadID]);
2358 // If this thread has been assigned work, launch a search
2359 if (threads[threadID].state == THREAD_WORKISWAITING)
2361 assert(!allThreadsShouldExit);
2363 threads[threadID].state = THREAD_SEARCHING;
2365 // Here we call search() with SplitPoint template parameter set to true
2366 SplitPoint* tsp = threads[threadID].splitPoint;
2367 Position pos(*tsp->pos, threadID);
2368 SearchStack* ss = tsp->sstack[threadID] + 1;
2372 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2374 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2376 assert(threads[threadID].state == THREAD_SEARCHING);
2378 threads[threadID].state = THREAD_AVAILABLE;
2380 // Wake up master thread so to allow it to return from the idle loop in
2381 // case we are the last slave of the split point.
2382 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2383 wake_sleeping_thread(tsp->master);
2386 // If this thread is the master of a split point and all slaves have
2387 // finished their work at this split point, return from the idle loop.
2388 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2389 allFinished = (i == activeThreads);
2393 // Because sp->slaves[] is reset under lock protection,
2394 // be sure sp->lock has been released before to return.
2395 lock_grab(&(sp->lock));
2396 lock_release(&(sp->lock));
2398 // In helpful master concept a master can help only a sub-tree, and
2399 // because here is all finished is not possible master is booked.
2400 assert(threads[threadID].state == THREAD_AVAILABLE);
2402 threads[threadID].state = THREAD_SEARCHING;
2409 // init_threads() is called during startup. It launches all helper threads,
2410 // and initializes the split point stack and the global locks and condition
2413 void ThreadsManager::init_threads() {
2415 int i, arg[MAX_THREADS];
2418 // Initialize global locks
2421 for (i = 0; i < MAX_THREADS; i++)
2423 lock_init(&sleepLock[i]);
2424 cond_init(&sleepCond[i]);
2427 // Initialize splitPoints[] locks
2428 for (i = 0; i < MAX_THREADS; i++)
2429 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2430 lock_init(&(threads[i].splitPoints[j].lock));
2432 // Will be set just before program exits to properly end the threads
2433 allThreadsShouldExit = false;
2435 // Threads will be put all threads to sleep as soon as created
2438 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2439 threads[0].state = THREAD_SEARCHING;
2440 for (i = 1; i < MAX_THREADS; i++)
2441 threads[i].state = THREAD_INITIALIZING;
2443 // Launch the helper threads
2444 for (i = 1; i < MAX_THREADS; i++)
2448 #if !defined(_MSC_VER)
2449 pthread_t pthread[1];
2450 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2451 pthread_detach(pthread[0]);
2453 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2457 cout << "Failed to create thread number " << i << endl;
2461 // Wait until the thread has finished launching and is gone to sleep
2462 while (threads[i].state == THREAD_INITIALIZING) {}
2467 // exit_threads() is called when the program exits. It makes all the
2468 // helper threads exit cleanly.
2470 void ThreadsManager::exit_threads() {
2472 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2474 // Wake up all the threads and waits for termination
2475 for (int i = 1; i < MAX_THREADS; i++)
2477 wake_sleeping_thread(i);
2478 while (threads[i].state != THREAD_TERMINATED) {}
2481 // Now we can safely destroy the locks
2482 for (int i = 0; i < MAX_THREADS; i++)
2483 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2484 lock_destroy(&(threads[i].splitPoints[j].lock));
2486 lock_destroy(&mpLock);
2488 // Now we can safely destroy the wait conditions
2489 for (int i = 0; i < MAX_THREADS; i++)
2491 lock_destroy(&sleepLock[i]);
2492 cond_destroy(&sleepCond[i]);
2497 // thread_should_stop() checks whether the thread should stop its search.
2498 // This can happen if a beta cutoff has occurred in the thread's currently
2499 // active split point, or in some ancestor of the current split point.
2501 bool ThreadsManager::thread_should_stop(int threadID) const {
2503 assert(threadID >= 0 && threadID < activeThreads);
2505 SplitPoint* sp = threads[threadID].splitPoint;
2507 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2512 // thread_is_available() checks whether the thread with threadID "slave" is
2513 // available to help the thread with threadID "master" at a split point. An
2514 // obvious requirement is that "slave" must be idle. With more than two
2515 // threads, this is not by itself sufficient: If "slave" is the master of
2516 // some active split point, it is only available as a slave to the other
2517 // threads which are busy searching the split point at the top of "slave"'s
2518 // split point stack (the "helpful master concept" in YBWC terminology).
2520 bool ThreadsManager::thread_is_available(int slave, int master) const {
2522 assert(slave >= 0 && slave < activeThreads);
2523 assert(master >= 0 && master < activeThreads);
2524 assert(activeThreads > 1);
2526 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2529 // Make a local copy to be sure doesn't change under our feet
2530 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2532 // No active split points means that the thread is available as
2533 // a slave for any other thread.
2534 if (localActiveSplitPoints == 0 || activeThreads == 2)
2537 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2538 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2539 // could have been set to 0 by another thread leading to an out of bound access.
2540 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2547 // available_thread_exists() tries to find an idle thread which is available as
2548 // a slave for the thread with threadID "master".
2550 bool ThreadsManager::available_thread_exists(int master) const {
2552 assert(master >= 0 && master < activeThreads);
2553 assert(activeThreads > 1);
2555 for (int i = 0; i < activeThreads; i++)
2556 if (thread_is_available(i, master))
2563 // split() does the actual work of distributing the work at a node between
2564 // several available threads. If it does not succeed in splitting the
2565 // node (because no idle threads are available, or because we have no unused
2566 // split point objects), the function immediately returns. If splitting is
2567 // possible, a SplitPoint object is initialized with all the data that must be
2568 // copied to the helper threads and we tell our helper threads that they have
2569 // been assigned work. This will cause them to instantly leave their idle loops and
2570 // call search().When all threads have returned from search() then split() returns.
2572 template <bool Fake>
2573 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2574 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2575 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2576 assert(pos.is_ok());
2577 assert(ply > 0 && ply < PLY_MAX);
2578 assert(*bestValue >= -VALUE_INFINITE);
2579 assert(*bestValue <= *alpha);
2580 assert(*alpha < beta);
2581 assert(beta <= VALUE_INFINITE);
2582 assert(depth > DEPTH_ZERO);
2583 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2584 assert(activeThreads > 1);
2586 int i, master = pos.thread();
2587 Thread& masterThread = threads[master];
2591 // If no other thread is available to help us, or if we have too many
2592 // active split points, don't split.
2593 if ( !available_thread_exists(master)
2594 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2596 lock_release(&mpLock);
2600 // Pick the next available split point object from the split point stack
2601 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2603 // Initialize the split point object
2604 splitPoint.parent = masterThread.splitPoint;
2605 splitPoint.master = master;
2606 splitPoint.stopRequest = false;
2607 splitPoint.ply = ply;
2608 splitPoint.depth = depth;
2609 splitPoint.threatMove = threatMove;
2610 splitPoint.mateThreat = mateThreat;
2611 splitPoint.alpha = *alpha;
2612 splitPoint.beta = beta;
2613 splitPoint.pvNode = pvNode;
2614 splitPoint.bestValue = *bestValue;
2616 splitPoint.moveCount = moveCount;
2617 splitPoint.pos = &pos;
2618 splitPoint.nodes = 0;
2619 splitPoint.parentSstack = ss;
2620 for (i = 0; i < activeThreads; i++)
2621 splitPoint.slaves[i] = 0;
2623 masterThread.splitPoint = &splitPoint;
2625 // If we are here it means we are not available
2626 assert(masterThread.state != THREAD_AVAILABLE);
2628 int workersCnt = 1; // At least the master is included
2630 // Allocate available threads setting state to THREAD_BOOKED
2631 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2632 if (thread_is_available(i, master))
2634 threads[i].state = THREAD_BOOKED;
2635 threads[i].splitPoint = &splitPoint;
2636 splitPoint.slaves[i] = 1;
2640 assert(Fake || workersCnt > 1);
2642 // We can release the lock because slave threads are already booked and master is not available
2643 lock_release(&mpLock);
2645 // Tell the threads that they have work to do. This will make them leave
2646 // their idle loop. But before copy search stack tail for each thread.
2647 for (i = 0; i < activeThreads; i++)
2648 if (i == master || splitPoint.slaves[i])
2650 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2652 assert(i == master || threads[i].state == THREAD_BOOKED);
2654 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2656 if (useSleepingThreads && i != master)
2657 wake_sleeping_thread(i);
2660 // Everything is set up. The master thread enters the idle loop, from
2661 // which it will instantly launch a search, because its state is
2662 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2663 // idle loop, which means that the main thread will return from the idle
2664 // loop when all threads have finished their work at this split point.
2665 idle_loop(master, &splitPoint);
2667 // We have returned from the idle loop, which means that all threads are
2668 // finished. Update alpha and bestValue, and return.
2671 *alpha = splitPoint.alpha;
2672 *bestValue = splitPoint.bestValue;
2673 masterThread.activeSplitPoints--;
2674 masterThread.splitPoint = splitPoint.parent;
2675 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2677 lock_release(&mpLock);
2681 // wake_sleeping_thread() wakes up the thread with the given threadID
2682 // when it is time to start a new search.
2684 void ThreadsManager::wake_sleeping_thread(int threadID) {
2686 lock_grab(&sleepLock[threadID]);
2687 cond_signal(&sleepCond[threadID]);
2688 lock_release(&sleepLock[threadID]);
2692 /// The RootMoveList class
2694 // RootMoveList c'tor
2696 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2698 SearchStack ss[PLY_MAX_PLUS_2];
2699 MoveStack mlist[MOVES_MAX];
2701 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2703 // Initialize search stack
2704 init_ss_array(ss, PLY_MAX_PLUS_2);
2705 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2708 // Generate all legal moves
2709 MoveStack* last = generate_moves(pos, mlist);
2711 // Add each move to the moves[] array
2712 for (MoveStack* cur = mlist; cur != last; cur++)
2714 bool includeMove = includeAllMoves;
2716 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2717 includeMove = (searchMoves[k] == cur->move);
2722 // Find a quick score for the move
2723 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2724 moves[count].pv[1] = MOVE_NONE;
2725 pos.do_move(cur->move, st);
2726 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2727 pos.undo_move(cur->move);
2733 // Score root moves using the standard way used in main search, the moves
2734 // are scored according to the order in which are returned by MovePicker.
2736 void RootMoveList::score_moves(const Position& pos)
2740 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2742 while ((move = mp.get_next_move()) != MOVE_NONE)
2743 for (int i = 0; i < count; i++)
2744 if (moves[i].move == move)
2746 moves[i].mp_score = score--;
2751 // RootMoveList simple methods definitions
2753 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2757 for (j = 0; pv[j] != MOVE_NONE; j++)
2758 moves[moveNum].pv[j] = pv[j];
2760 moves[moveNum].pv[j] = MOVE_NONE;
2764 // RootMoveList::sort() sorts the root move list at the beginning of a new
2767 void RootMoveList::sort() {
2769 sort_multipv(count - 1); // Sort all items
2773 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2774 // list by their scores and depths. It is used to order the different PVs
2775 // correctly in MultiPV mode.
2777 void RootMoveList::sort_multipv(int n) {
2781 for (i = 1; i <= n; i++)
2783 RootMove rm = moves[i];
2784 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2785 moves[j] = moves[j - 1];