2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_thread(int threadID);
86 void idle_loop(int threadID, SplitPoint* sp);
89 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
90 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
96 volatile bool AllThreadsShouldExit;
97 Thread threads[MAX_THREADS];
99 WaitCondition WaitCond[MAX_THREADS];
103 // RootMove struct is used for moves at the root at the tree. For each
104 // root move, we store a score, a node count, and a PV (really a refutation
105 // in the case of moves which fail low).
109 RootMove() : mp_score(0), nodes(0) {}
111 // RootMove::operator<() is the comparison function used when
112 // sorting the moves. A move m1 is considered to be better
113 // than a move m2 if it has a higher score, or if the moves
114 // have equal score but m1 has the higher beta cut-off count.
115 bool operator<(const RootMove& m) const {
117 return score != m.score ? score < m.score : mp_score <= m.mp_score;
124 Move pv[PLY_MAX_PLUS_2];
128 // The RootMoveList class is essentially an array of RootMove objects, with
129 // a handful of methods for accessing the data in the individual moves.
134 RootMoveList(Position& pos, Move searchMoves[]);
136 Move move(int moveNum) const { return moves[moveNum].move; }
137 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
138 int move_count() const { return count; }
139 Value move_score(int moveNum) const { return moves[moveNum].score; }
140 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
141 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
142 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 void set_move_pv(int moveNum, const Move pv[]);
145 void score_moves(const Position& pos);
147 void sort_multipv(int n);
150 RootMove moves[MOVES_MAX];
155 // When formatting a move for std::cout we must know if we are in Chess960
156 // or not. To keep using the handy operator<<() on the move the trick is to
157 // embed this flag in the stream itself. Function-like named enum set960 is
158 // used as a custom manipulator and the stream internal general-purpose array,
159 // accessed through ios_base::iword(), is used to pass the flag to the move's
160 // operator<<() that will use it to properly format castling moves.
163 std::ostream& operator<< (std::ostream& os, const set960& m) {
165 os.iword(0) = int(m);
174 // Maximum depth for razoring
175 const Depth RazorDepth = 4 * ONE_PLY;
177 // Dynamic razoring margin based on depth
178 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
180 // Maximum depth for use of dynamic threat detection when null move fails low
181 const Depth ThreatDepth = 5 * ONE_PLY;
183 // Step 9. Internal iterative deepening
185 // Minimum depth for use of internal iterative deepening
186 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
188 // At Non-PV nodes we do an internal iterative deepening search
189 // when the static evaluation is bigger then beta - IIDMargin.
190 const Value IIDMargin = Value(0x100);
192 // Step 11. Decide the new search depth
194 // Extensions. Configurable UCI options
195 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
196 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
197 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
199 // Minimum depth for use of singular extension
200 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
202 // If the TT move is at least SingularExtensionMargin better then the
203 // remaining ones we will extend it.
204 const Value SingularExtensionMargin = Value(0x20);
206 // Step 12. Futility pruning
208 // Futility margin for quiescence search
209 const Value FutilityMarginQS = Value(0x80);
211 // Futility lookup tables (initialized at startup) and their getter functions
212 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
213 int FutilityMoveCountArray[32]; // [depth]
215 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
216 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
218 // Step 14. Reduced search
220 // Reduction lookup tables (initialized at startup) and their getter functions
221 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
223 template <NodeType PV>
224 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
226 // Common adjustments
228 // Search depth at iteration 1
229 const Depth InitialDepth = ONE_PLY;
231 // Easy move margin. An easy move candidate must be at least this much
232 // better than the second best move.
233 const Value EasyMoveMargin = Value(0x200);
241 // Scores and number of times the best move changed for each iteration
242 Value ValueByIteration[PLY_MAX_PLUS_2];
243 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
245 // Search window management
251 // Time managment variables
252 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
253 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
254 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
259 std::ofstream LogFile;
261 // Multi-threads related variables
262 Depth MinimumSplitDepth;
263 int MaxThreadsPerSplitPoint;
264 ThreadsManager ThreadsMgr;
266 // Node counters, used only by thread[0] but try to keep in different cache
267 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
269 int NodesBetweenPolls = 30000;
276 Value id_loop(const Position& pos, Move searchMoves[]);
277 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
279 template <NodeType PvNode, bool SpNode>
280 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
282 template <NodeType PvNode>
283 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
284 return search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
287 template <NodeType PvNode>
288 void sp_search(Position& pos, SearchStack* ss, Value, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
293 template <NodeType PvNode>
294 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
296 bool connected_moves(const Position& pos, Move m1, Move m2);
297 bool value_is_mate(Value value);
298 Value value_to_tt(Value v, int ply);
299 Value value_from_tt(Value v, int ply);
300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
301 bool connected_threat(const Position& pos, Move m, Move threat);
302 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
303 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
304 void update_killers(Move m, SearchStack* ss);
305 void update_gains(const Position& pos, Move move, Value before, Value after);
307 int current_search_time();
308 std::string value_to_uci(Value v);
312 void wait_for_stop_or_ponderhit();
313 void init_ss_array(SearchStack* ss, int size);
314 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
315 void insert_pv_in_tt(const Position& pos, Move pv[]);
316 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
318 #if !defined(_MSC_VER)
319 void *init_thread(void *threadID);
321 DWORD WINAPI init_thread(LPVOID threadID);
331 /// init_threads(), exit_threads() and nodes_searched() are helpers to
332 /// give accessibility to some TM methods from outside of current file.
334 void init_threads() { ThreadsMgr.init_threads(); }
335 void exit_threads() { ThreadsMgr.exit_threads(); }
336 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
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(const 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 ThreadsMgr.resetNodeCounters();
409 SearchStartTime = get_system_time();
410 ExactMaxTime = maxTime;
413 InfiniteSearch = infinite;
414 PonderSearch = ponder;
415 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
417 // Look for a book move, only during games, not tests
418 if (UseTimeManagement && get_option_value_bool("OwnBook"))
420 if (get_option_value_string("Book File") != OpeningBook.file_name())
421 OpeningBook.open(get_option_value_string("Book File"));
423 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
434 // Read UCI option values
435 TT.set_size(get_option_value_int("Hash"));
436 if (button_was_pressed("Clear Hash"))
439 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
440 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
441 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
442 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
443 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
444 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
445 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
446 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
447 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
448 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
449 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
450 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
452 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
453 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
454 MultiPV = get_option_value_int("MultiPV");
455 UseLogFile = get_option_value_bool("Use Search Log");
458 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
460 read_weights(pos.side_to_move());
462 // Set the number of active threads
463 int newActiveThreads = get_option_value_int("Threads");
464 if (newActiveThreads != ThreadsMgr.active_threads())
466 ThreadsMgr.set_active_threads(newActiveThreads);
467 init_eval(ThreadsMgr.active_threads());
471 int myTime = time[pos.side_to_move()];
472 int myIncrement = increment[pos.side_to_move()];
473 if (UseTimeManagement)
474 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
476 // Set best NodesBetweenPolls interval to avoid lagging under
477 // heavy time pressure.
479 NodesBetweenPolls = Min(MaxNodes, 30000);
480 else if (myTime && myTime < 1000)
481 NodesBetweenPolls = 1000;
482 else if (myTime && myTime < 5000)
483 NodesBetweenPolls = 5000;
485 NodesBetweenPolls = 30000;
487 // Write search information to log file
489 LogFile << "Searching: " << pos.to_fen() << endl
490 << "infinite: " << infinite
491 << " ponder: " << ponder
492 << " time: " << myTime
493 << " increment: " << myIncrement
494 << " moves to go: " << movesToGo << endl;
496 // We're ready to start thinking. Call the iterative deepening loop function
497 id_loop(pos, searchMoves);
508 // id_loop() is the main iterative deepening loop. It calls root_search
509 // repeatedly with increasing depth until the allocated thinking time has
510 // been consumed, the user stops the search, or the maximum search depth is
513 Value id_loop(const Position& pos, Move searchMoves[]) {
515 Position p(pos, pos.thread());
516 SearchStack ss[PLY_MAX_PLUS_2];
517 Move pv[PLY_MAX_PLUS_2];
518 Move EasyMove = MOVE_NONE;
519 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
521 // Moves to search are verified, copied, scored and sorted
522 RootMoveList rml(p, searchMoves);
524 // Handle special case of searching on a mate/stale position
525 if (rml.move_count() == 0)
528 wait_for_stop_or_ponderhit();
530 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
533 // Print RootMoveList startup scoring to the standard output,
534 // so to output information also for iteration 1.
535 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
536 << "info depth " << 1
537 << "\ninfo depth " << 1
538 << " score " << value_to_uci(rml.move_score(0))
539 << " time " << current_search_time()
540 << " nodes " << ThreadsMgr.nodes_searched()
542 << " pv " << rml.move(0) << "\n";
547 init_ss_array(ss, PLY_MAX_PLUS_2);
548 pv[0] = pv[1] = MOVE_NONE;
549 ValueByIteration[1] = rml.move_score(0);
552 // Is one move significantly better than others after initial scoring ?
553 if ( rml.move_count() == 1
554 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
555 EasyMove = rml.move(0);
557 // Iterative deepening loop
558 while (Iteration < PLY_MAX)
560 // Initialize iteration
562 BestMoveChangesByIteration[Iteration] = 0;
564 cout << "info depth " << Iteration << endl;
566 // Calculate dynamic aspiration window based on previous iterations
567 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
569 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
570 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
572 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
573 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
575 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
576 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
579 // Search to the current depth, rml is updated and sorted, alpha and beta could change
580 value = root_search(p, ss, pv, rml, &alpha, &beta);
582 // Write PV to transposition table, in case the relevant entries have
583 // been overwritten during the search.
584 insert_pv_in_tt(p, pv);
587 break; // Value cannot be trusted. Break out immediately!
589 //Save info about search result
590 ValueByIteration[Iteration] = value;
592 // Drop the easy move if differs from the new best move
593 if (pv[0] != EasyMove)
594 EasyMove = MOVE_NONE;
596 if (UseTimeManagement)
599 bool stopSearch = false;
601 // Stop search early if there is only a single legal move,
602 // we search up to Iteration 6 anyway to get a proper score.
603 if (Iteration >= 6 && rml.move_count() == 1)
606 // Stop search early when the last two iterations returned a mate score
608 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
609 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
612 // Stop search early if one move seems to be much better than the others
613 int64_t nodes = ThreadsMgr.nodes_searched();
616 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
617 && current_search_time() > TimeMgr.available_time() / 16)
618 ||( rml.move_nodes(0) > (nodes * 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 " << ThreadsMgr.nodes_searched()
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: " << ThreadsMgr.nodes_searched()
681 << "\nNodes/second: " << nps()
682 << "\nBest move: " << move_to_san(p, pv[0]);
685 p.do_move(pv[0], st);
686 LogFile << "\nPonder move: "
687 << move_to_san(p, 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, evalMargin, 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->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
727 // Step 6. Razoring (omitted at root)
728 // Step 7. Static null move pruning (omitted at root)
729 // Step 8. Null move search with verification search (omitted at root)
730 // Step 9. Internal iterative deepening (omitted at root)
732 // Step extra. Fail low loop
733 // We start with small aspiration window and in case of fail low, we research
734 // with bigger window until we are not failing low anymore.
737 // Sort the moves before to (re)search
738 rml.score_moves(pos);
741 // Step 10. Loop through all moves in the root move list
742 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
744 // This is used by time management
745 FirstRootMove = (i == 0);
747 // Save the current node count before the move is searched
748 nodes = ThreadsMgr.nodes_searched();
750 // Pick the next root move, and print the move and the move number to
751 // the standard output.
752 move = ss->currentMove = rml.move(i);
754 if (current_search_time() >= 1000)
755 cout << "info currmove " << move
756 << " currmovenumber " << i + 1 << endl;
758 moveIsCheck = pos.move_is_check(move);
759 captureOrPromotion = pos.move_is_capture_or_promotion(move);
761 // Step 11. Decide the new search depth
762 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
763 newDepth = depth + ext;
765 // Step 12. Futility pruning (omitted at root)
767 // Step extra. Fail high loop
768 // If move fails high, we research with bigger window until we are not failing
770 value = - VALUE_INFINITE;
774 // Step 13. Make the move
775 pos.do_move(move, st, ci, moveIsCheck);
777 // Step extra. pv search
778 // We do pv search for first moves (i < MultiPV)
779 // and for fail high research (value > alpha)
780 if (i < MultiPV || value > alpha)
782 // Aspiration window is disabled in multi-pv case
784 alpha = -VALUE_INFINITE;
786 // Full depth PV search, done on first move or after a fail high
787 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
791 // Step 14. Reduced search
792 // if the move fails high will be re-searched at full depth
793 bool doFullDepthSearch = true;
795 if ( depth >= 3 * ONE_PLY
797 && !captureOrPromotion
798 && !move_is_castle(move))
800 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
803 assert(newDepth-ss->reduction >= ONE_PLY);
805 // Reduced depth non-pv search using alpha as upperbound
806 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
807 doFullDepthSearch = (value > alpha);
810 // The move failed high, but if reduction is very big we could
811 // face a false positive, retry with a less aggressive reduction,
812 // if the move fails high again then go with full depth search.
813 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
815 assert(newDepth - ONE_PLY >= ONE_PLY);
817 ss->reduction = ONE_PLY;
818 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
819 doFullDepthSearch = (value > alpha);
821 ss->reduction = DEPTH_ZERO; // Restore original reduction
824 // Step 15. Full depth search
825 if (doFullDepthSearch)
827 // Full depth non-pv search using alpha as upperbound
828 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
830 // If we are above alpha then research at same depth but as PV
831 // to get a correct score or eventually a fail high above beta.
833 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
837 // Step 16. Undo move
840 // Can we exit fail high loop ?
841 if (AbortSearch || value < beta)
844 // We are failing high and going to do a research. It's important to update
845 // the score before research in case we run out of time while researching.
846 rml.set_move_score(i, value);
848 extract_pv_from_tt(pos, move, pv);
849 rml.set_move_pv(i, pv);
851 // Print information to the standard output
852 print_pv_info(pos, pv, alpha, beta, value);
854 // Prepare for a research after a fail high, each time with a wider window
855 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
858 } // End of fail high loop
860 // Finished searching the move. If AbortSearch is true, the search
861 // was aborted because the user interrupted the search or because we
862 // ran out of time. In this case, the return value of the search cannot
863 // be trusted, and we break out of the loop without updating the best
868 // Remember searched nodes counts for this move
869 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
871 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
872 assert(value < beta);
874 // Step 17. Check for new best move
875 if (value <= alpha && i >= MultiPV)
876 rml.set_move_score(i, -VALUE_INFINITE);
879 // PV move or new best move!
882 rml.set_move_score(i, value);
884 extract_pv_from_tt(pos, move, pv);
885 rml.set_move_pv(i, pv);
889 // We record how often the best move has been changed in each
890 // iteration. This information is used for time managment: When
891 // the best move changes frequently, we allocate some more time.
893 BestMoveChangesByIteration[Iteration]++;
895 // Print information to the standard output
896 print_pv_info(pos, pv, alpha, beta, value);
898 // Raise alpha to setup proper non-pv search upper bound
905 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
907 cout << "info multipv " << j + 1
908 << " score " << value_to_uci(rml.move_score(j))
909 << " depth " << (j <= i ? Iteration : Iteration - 1)
910 << " time " << current_search_time()
911 << " nodes " << ThreadsMgr.nodes_searched()
915 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
916 cout << rml.move_pv(j, k) << " ";
920 alpha = rml.move_score(Min(i, MultiPV - 1));
922 } // PV move or new best move
924 assert(alpha >= *alphaPtr);
926 AspirationFailLow = (alpha == *alphaPtr);
928 if (AspirationFailLow && StopOnPonderhit)
929 StopOnPonderhit = false;
932 // Can we exit fail low loop ?
933 if (AbortSearch || !AspirationFailLow)
936 // Prepare for a research after a fail low, each time with a wider window
937 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
942 // Sort the moves before to return
949 // search<>() is the main search function for both PV and non-PV nodes and for
950 // normal and SplitPoint nodes. When called just after a split point the search
951 // is simpler because we have already probed the hash table, done a null move
952 // search, and searched the first move before splitting, we don't have to repeat
953 // all this work again. We also don't need to store anything to the hash table
954 // here: This is taken care of after we return from the split point.
956 template <NodeType PvNode, bool SpNode>
957 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
959 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
960 assert(beta > alpha && beta <= VALUE_INFINITE);
961 assert(PvNode || alpha == beta - 1);
962 assert(ply > 0 && ply < PLY_MAX);
963 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
965 Move movesSearched[MOVES_MAX];
969 Move ttMove, move, excludedMove, threatMove;
971 Value bestValue, value, evalMargin, oldAlpha;
972 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
973 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
974 bool mateThreat = false;
976 int threadID = pos.thread();
977 SplitPoint* sp = NULL;
978 refinedValue = bestValue = value = -VALUE_INFINITE;
980 isCheck = pos.is_check();
986 evalMargin = VALUE_ZERO;
987 ttMove = excludedMove = MOVE_NONE;
988 threatMove = sp->threatMove;
989 mateThreat = sp->mateThreat;
990 goto split_point_start;
993 // Step 1. Initialize node and poll. Polling can abort search
994 ThreadsMgr.incrementNodeCounter(threadID);
995 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
996 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
998 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1004 // Step 2. Check for aborted search and immediate draw
1005 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1008 if (pos.is_draw() || ply >= PLY_MAX - 1)
1011 // Step 3. Mate distance pruning
1012 alpha = Max(value_mated_in(ply), alpha);
1013 beta = Min(value_mate_in(ply+1), beta);
1017 // Step 4. Transposition table lookup
1019 // We don't want the score of a partial search to overwrite a previous full search
1020 // TT value, so we use a different position key in case of an excluded move exists.
1021 excludedMove = ss->excludedMove;
1022 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1024 tte = TT.retrieve(posKey);
1025 ttMove = (tte ? tte->move() : MOVE_NONE);
1027 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1028 // This is to avoid problems in the following areas:
1030 // * Repetition draw detection
1031 // * Fifty move rule detection
1032 // * Searching for a mate
1033 // * Printing of full PV line
1035 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1037 // Refresh tte entry to avoid aging
1038 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1040 ss->bestMove = ttMove; // Can be MOVE_NONE
1041 return value_from_tt(tte->value(), ply);
1044 // Step 5. Evaluate the position statically and
1045 // update gain statistics of parent move.
1047 ss->eval = evalMargin = VALUE_NONE;
1050 assert(tte->static_value() != VALUE_NONE);
1052 ss->eval = tte->static_value();
1053 evalMargin = tte->static_value_margin();
1054 refinedValue = refine_eval(tte, ss->eval, ply);
1058 refinedValue = ss->eval = evaluate(pos, evalMargin);
1059 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, 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 && (ss-1)->currentMove != MOVE_NULL
1072 && !value_is_mate(beta)
1073 && !pos.has_pawn_on_7th(pos.side_to_move()))
1075 Value rbeta = beta - razor_margin(depth);
1076 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1078 // Logically we should return (v + razor_margin(depth)), but
1079 // surprisingly this did slightly weaker in tests.
1083 // Step 7. Static null move pruning (is omitted in PV nodes)
1084 // We're betting that the opponent doesn't have a move that will reduce
1085 // the score by more than futility_margin(depth) if we do a null move.
1087 && !ss->skipNullMove
1088 && depth < RazorDepth
1090 && refinedValue >= beta + futility_margin(depth, 0)
1091 && !value_is_mate(beta)
1092 && pos.non_pawn_material(pos.side_to_move()))
1093 return refinedValue - futility_margin(depth, 0);
1095 // Step 8. Null move search with verification search (is omitted in PV nodes)
1097 && !ss->skipNullMove
1100 && refinedValue >= beta
1101 && !value_is_mate(beta)
1102 && pos.non_pawn_material(pos.side_to_move()))
1104 ss->currentMove = MOVE_NULL;
1106 // Null move dynamic reduction based on depth
1107 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1109 // Null move dynamic reduction based on value
1110 if (refinedValue - beta > PawnValueMidgame)
1113 pos.do_null_move(st);
1114 (ss+1)->skipNullMove = true;
1116 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1117 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1118 (ss+1)->skipNullMove = false;
1119 pos.undo_null_move();
1121 if (nullValue >= beta)
1123 // Do not return unproven mate scores
1124 if (nullValue >= value_mate_in(PLY_MAX))
1127 if (depth < 6 * ONE_PLY)
1130 // Do verification search at high depths
1131 ss->skipNullMove = true;
1132 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1133 ss->skipNullMove = false;
1140 // The null move failed low, which means that we may be faced with
1141 // some kind of threat. If the previous move was reduced, check if
1142 // the move that refuted the null move was somehow connected to the
1143 // move which was reduced. If a connection is found, return a fail
1144 // low score (which will cause the reduced move to fail high in the
1145 // parent node, which will trigger a re-search with full depth).
1146 if (nullValue == value_mated_in(ply + 2))
1149 threatMove = (ss+1)->bestMove;
1150 if ( depth < ThreatDepth
1151 && (ss-1)->reduction
1152 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1157 // Step 9. Internal iterative deepening
1158 if ( depth >= IIDDepth[PvNode]
1159 && ttMove == MOVE_NONE
1160 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1162 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1164 ss->skipNullMove = true;
1165 search<PvNode>(pos, ss, alpha, beta, d, ply);
1166 ss->skipNullMove = false;
1168 ttMove = ss->bestMove;
1169 tte = TT.retrieve(posKey);
1172 // Expensive mate threat detection (only for PV nodes)
1174 mateThreat = pos.has_mate_threat();
1176 split_point_start: // At split points actual search starts from here
1178 // Initialize a MovePicker object for the current position
1179 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1180 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1181 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1183 ss->bestMove = MOVE_NONE;
1184 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1185 futilityBase = ss->eval + evalMargin;
1186 singularExtensionNode = !SpNode
1187 && depth >= SingularExtensionDepth[PvNode]
1190 && !excludedMove // Do not allow recursive singular extension search
1191 && (tte->type() & VALUE_TYPE_LOWER)
1192 && tte->depth() >= depth - 3 * ONE_PLY;
1195 lock_grab(&(sp->lock));
1196 bestValue = sp->bestValue;
1199 // Step 10. Loop through moves
1200 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1201 while ( bestValue < beta
1202 && (move = mp.get_next_move()) != MOVE_NONE
1203 && !ThreadsMgr.thread_should_stop(threadID))
1207 moveCount = ++sp->moveCount;
1208 lock_release(&(sp->lock));
1211 assert(move_is_ok(move));
1213 if (move == excludedMove)
1216 moveIsCheck = pos.move_is_check(move, ci);
1217 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1219 // Step 11. Decide the new search depth
1220 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1222 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1223 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1224 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1225 // lower then ttValue minus a margin then we extend ttMove.
1226 if ( singularExtensionNode
1227 && move == tte->move()
1230 Value ttValue = value_from_tt(tte->value(), ply);
1232 if (abs(ttValue) < VALUE_KNOWN_WIN)
1234 Value b = ttValue - SingularExtensionMargin;
1235 ss->excludedMove = move;
1236 ss->skipNullMove = true;
1237 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1238 ss->skipNullMove = false;
1239 ss->excludedMove = MOVE_NONE;
1240 ss->bestMove = MOVE_NONE;
1246 newDepth = depth - ONE_PLY + ext;
1248 // Update current move (this must be done after singular extension search)
1249 movesSearched[moveCount++] = ss->currentMove = move;
1251 // Step 12. Futility pruning (is omitted in PV nodes)
1253 && !captureOrPromotion
1257 && !move_is_castle(move))
1259 // Move count based pruning
1260 if ( moveCount >= futility_move_count(depth)
1261 && !(threatMove && connected_threat(pos, move, threatMove))
1262 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1265 lock_grab(&(sp->lock));
1270 // Value based pruning
1271 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1272 // but fixing this made program slightly weaker.
1273 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1274 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1275 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1277 if (futilityValueScaled < beta)
1281 lock_grab(&(sp->lock));
1282 if (futilityValueScaled > sp->bestValue)
1283 sp->bestValue = bestValue = futilityValueScaled;
1285 else if (futilityValueScaled > bestValue)
1286 bestValue = futilityValueScaled;
1292 // Step 13. Make the move
1293 pos.do_move(move, st, ci, moveIsCheck);
1295 // Step extra. pv search (only in PV nodes)
1296 // The first move in list is the expected PV
1297 if (!SpNode && PvNode && moveCount == 1)
1298 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1299 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1302 // Step 14. Reduced depth search
1303 // If the move fails high will be re-searched at full depth.
1304 bool doFullDepthSearch = true;
1306 if ( depth >= 3 * ONE_PLY
1307 && !captureOrPromotion
1309 && !move_is_castle(move)
1310 && !(ss->killers[0] == move || ss->killers[1] == move))
1312 ss->reduction = reduction<PvNode>(depth, moveCount);
1315 alpha = SpNode ? sp->alpha : alpha;
1316 Depth d = newDepth - ss->reduction;
1317 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1318 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1320 doFullDepthSearch = (value > alpha);
1323 // The move failed high, but if reduction is very big we could
1324 // face a false positive, retry with a less aggressive reduction,
1325 // if the move fails high again then go with full depth search.
1326 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1328 assert(newDepth - ONE_PLY >= ONE_PLY);
1330 ss->reduction = ONE_PLY;
1331 alpha = SpNode ? sp->alpha : alpha;
1332 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1333 doFullDepthSearch = (value > alpha);
1335 ss->reduction = DEPTH_ZERO; // Restore original reduction
1338 // Step 15. Full depth search
1339 if (doFullDepthSearch)
1341 alpha = SpNode ? sp->alpha : alpha;
1342 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1343 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1345 // Step extra. pv search (only in PV nodes)
1346 // Search only for possible new PV nodes, if instead value >= beta then
1347 // parent node fails low with value <= alpha and tries another move.
1348 if (PvNode && value > alpha && value < beta)
1349 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1350 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1354 // Step 16. Undo move
1355 pos.undo_move(move);
1357 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1359 // Step 17. Check for new best move
1362 lock_grab(&(sp->lock));
1363 bestValue = sp->bestValue;
1367 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1372 sp->bestValue = value;
1376 if (SpNode && (!PvNode || value >= beta))
1377 sp->stopRequest = true;
1379 if (PvNode && value < beta) // We want always alpha < beta
1386 if (value == value_mate_in(ply + 1))
1387 ss->mateKiller = move;
1389 ss->bestMove = move;
1392 sp->parentSstack->bestMove = move;
1396 // Step 18. Check for split
1398 && depth >= MinimumSplitDepth
1399 && ThreadsMgr.active_threads() > 1
1401 && ThreadsMgr.available_thread_exists(threadID)
1403 && !ThreadsMgr.thread_should_stop(threadID)
1405 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1406 threatMove, mateThreat, moveCount, &mp, PvNode);
1411 /* Here we have the lock still grabbed */
1412 sp->slaves[threadID] = 0;
1413 lock_release(&(sp->lock));
1417 // Step 19. Check for mate and stalemate
1418 // All legal moves have been searched and if there are
1419 // no legal moves, it must be mate or stalemate.
1420 // If one move was excluded return fail low score.
1422 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1424 // Step 20. Update tables
1425 // If the search is not aborted, update the transposition table,
1426 // history counters, and killer moves.
1427 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1430 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1431 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1432 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
1434 // Update killers and history only for non capture moves that fails high
1435 if ( bestValue >= beta
1436 && !pos.move_is_capture_or_promotion(move))
1438 update_history(pos, move, depth, movesSearched, moveCount);
1439 update_killers(move, ss);
1442 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1448 // qsearch() is the quiescence search function, which is called by the main
1449 // search function when the remaining depth is zero (or, to be more precise,
1450 // less than ONE_PLY).
1452 template <NodeType PvNode>
1453 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1455 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1456 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1457 assert(PvNode || alpha == beta - 1);
1459 assert(ply > 0 && ply < PLY_MAX);
1460 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1464 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1465 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1467 Value oldAlpha = alpha;
1469 ThreadsMgr.incrementNodeCounter(pos.thread());
1470 ss->bestMove = ss->currentMove = MOVE_NONE;
1472 // Check for an instant draw or maximum ply reached
1473 if (pos.is_draw() || ply >= PLY_MAX - 1)
1476 // Transposition table lookup. At PV nodes, we don't use the TT for
1477 // pruning, but only for move ordering.
1478 tte = TT.retrieve(pos.get_key());
1479 ttMove = (tte ? tte->move() : MOVE_NONE);
1481 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1483 ss->bestMove = ttMove; // Can be MOVE_NONE
1484 return value_from_tt(tte->value(), ply);
1487 isCheck = pos.is_check();
1489 // Evaluate the position statically
1492 bestValue = futilityBase = -VALUE_INFINITE;
1493 ss->eval = evalMargin = VALUE_NONE;
1494 deepChecks = enoughMaterial = false;
1500 assert(tte->static_value() != VALUE_NONE);
1502 evalMargin = tte->static_value_margin();
1503 ss->eval = bestValue = tte->static_value();
1506 ss->eval = bestValue = evaluate(pos, evalMargin);
1508 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1510 // Stand pat. Return immediately if static value is at least beta
1511 if (bestValue >= beta)
1514 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1519 if (PvNode && bestValue > alpha)
1522 // If we are near beta then try to get a cutoff pushing checks a bit further
1523 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1525 // Futility pruning parameters, not needed when in check
1526 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1527 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1530 // Initialize a MovePicker object for the current position, and prepare
1531 // to search the moves. Because the depth is <= 0 here, only captures,
1532 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1533 // and we are near beta) will be generated.
1534 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1537 // Loop through the moves until no moves remain or a beta cutoff occurs
1538 while ( alpha < beta
1539 && (move = mp.get_next_move()) != MOVE_NONE)
1541 assert(move_is_ok(move));
1543 moveIsCheck = pos.move_is_check(move, ci);
1551 && !move_is_promotion(move)
1552 && !pos.move_is_passed_pawn_push(move))
1554 futilityValue = futilityBase
1555 + pos.endgame_value_of_piece_on(move_to(move))
1556 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1558 if (futilityValue < alpha)
1560 if (futilityValue > bestValue)
1561 bestValue = futilityValue;
1566 // Detect non-capture evasions that are candidate to be pruned
1567 evasionPrunable = isCheck
1568 && bestValue > value_mated_in(PLY_MAX)
1569 && !pos.move_is_capture(move)
1570 && !pos.can_castle(pos.side_to_move());
1572 // Don't search moves with negative SEE values
1574 && (!isCheck || evasionPrunable)
1576 && !move_is_promotion(move)
1577 && pos.see_sign(move) < 0)
1580 // Update current move
1581 ss->currentMove = move;
1583 // Make and search the move
1584 pos.do_move(move, st, ci, moveIsCheck);
1585 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1586 pos.undo_move(move);
1588 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1591 if (value > bestValue)
1597 ss->bestMove = move;
1602 // All legal moves have been searched. A special case: If we're in check
1603 // and no legal moves were found, it is checkmate.
1604 if (isCheck && bestValue == -VALUE_INFINITE)
1605 return value_mated_in(ply);
1607 // Update transposition table
1608 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1609 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1610 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1612 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1618 // sp_search() is used to search from a split point. This function is called
1619 // by each thread working at the split point. It is similar to the normal
1620 // search() function, but simpler. Because we have already probed the hash
1621 // table, done a null move search, and searched the first move before
1622 // splitting, we don't have to repeat all this work in sp_search(). We
1623 // also don't need to store anything to the hash table here: This is taken
1624 // care of after we return from the split point.
1626 template <NodeType PvNode>
1627 void sp_search(Position& pos, SearchStack* ss, Value, Value beta, Depth depth, int ply) {
1631 Depth ext, newDepth;
1633 Value futilityValueScaled; // NonPV specific
1634 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1636 value = -VALUE_INFINITE;
1637 SplitPoint* sp = ss->sp;
1638 Move threatMove = sp->threatMove;
1639 MovePicker& mp = *sp->mp;
1640 int threadID = pos.thread();
1643 isCheck = pos.is_check();
1645 // Step 10. Loop through moves
1646 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1647 lock_grab(&(sp->lock));
1649 while ( sp->bestValue < beta
1650 && (move = mp.get_next_move()) != MOVE_NONE
1651 && !ThreadsMgr.thread_should_stop(threadID))
1653 moveCount = ++sp->moveCount;
1654 lock_release(&(sp->lock));
1656 assert(move_is_ok(move));
1658 moveIsCheck = pos.move_is_check(move, ci);
1659 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1661 // Step 11. Decide the new search depth
1662 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1663 newDepth = depth - ONE_PLY + ext;
1665 // Update current move
1666 ss->currentMove = move;
1668 // Step 12. Futility pruning (is omitted in PV nodes)
1670 && !captureOrPromotion
1673 && !move_is_castle(move))
1675 // Move count based pruning
1676 if ( moveCount >= futility_move_count(depth)
1677 && !(threatMove && connected_threat(pos, move, threatMove))
1678 && sp->bestValue > value_mated_in(PLY_MAX))
1680 lock_grab(&(sp->lock));
1684 // Value based pruning
1685 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1686 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1687 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1689 if (futilityValueScaled < beta)
1691 lock_grab(&(sp->lock));
1693 if (futilityValueScaled > sp->bestValue)
1694 sp->bestValue = futilityValueScaled;
1699 // Step 13. Make the move
1700 pos.do_move(move, st, ci, moveIsCheck);
1702 // Step 14. Reduced search
1703 // If the move fails high will be re-searched at full depth.
1704 bool doFullDepthSearch = true;
1706 if ( !captureOrPromotion
1708 && !move_is_castle(move)
1709 && !(ss->killers[0] == move || ss->killers[1] == move))
1711 ss->reduction = reduction<PvNode>(depth, moveCount);
1714 Value localAlpha = sp->alpha;
1715 Depth d = newDepth - ss->reduction;
1716 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, ply+1)
1717 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, ply+1);
1719 doFullDepthSearch = (value > localAlpha);
1722 // The move failed high, but if reduction is very big we could
1723 // face a false positive, retry with a less aggressive reduction,
1724 // if the move fails high again then go with full depth search.
1725 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1727 assert(newDepth - ONE_PLY >= ONE_PLY);
1729 ss->reduction = ONE_PLY;
1730 Value localAlpha = sp->alpha;
1731 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, ply+1);
1732 doFullDepthSearch = (value > localAlpha);
1734 ss->reduction = DEPTH_ZERO; // Restore original reduction
1737 // Step 15. Full depth search
1738 if (doFullDepthSearch)
1740 Value localAlpha = sp->alpha;
1741 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, ply+1)
1742 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, ply+1);
1744 // Step extra. pv search (only in PV nodes)
1745 // Search only for possible new PV nodes, if instead value >= beta then
1746 // parent node fails low with value <= alpha and tries another move.
1747 if (PvNode && value > localAlpha && value < beta)
1748 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -sp->alpha, DEPTH_ZERO, ply+1)
1749 : - search<PV>(pos, ss+1, -beta, -sp->alpha, newDepth, ply+1);
1752 // Step 16. Undo move
1753 pos.undo_move(move);
1755 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1757 // Step 17. Check for new best move
1758 lock_grab(&(sp->lock));
1760 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1762 sp->bestValue = value;
1763 if (value > sp->alpha)
1765 if (!PvNode || value >= beta)
1766 sp->stopRequest = true;
1768 if (PvNode && value < beta) // We want always sp->alpha < beta
1771 sp->parentSstack->bestMove = ss->bestMove = move;
1776 /* Here we have the lock still grabbed */
1778 sp->slaves[threadID] = 0;
1780 lock_release(&(sp->lock));
1784 // connected_moves() tests whether two moves are 'connected' in the sense
1785 // that the first move somehow made the second move possible (for instance
1786 // if the moving piece is the same in both moves). The first move is assumed
1787 // to be the move that was made to reach the current position, while the
1788 // second move is assumed to be a move from the current position.
1790 bool connected_moves(const Position& pos, Move m1, Move m2) {
1792 Square f1, t1, f2, t2;
1795 assert(move_is_ok(m1));
1796 assert(move_is_ok(m2));
1798 if (m2 == MOVE_NONE)
1801 // Case 1: The moving piece is the same in both moves
1807 // Case 2: The destination square for m2 was vacated by m1
1813 // Case 3: Moving through the vacated square
1814 if ( piece_is_slider(pos.piece_on(f2))
1815 && bit_is_set(squares_between(f2, t2), f1))
1818 // Case 4: The destination square for m2 is defended by the moving piece in m1
1819 p = pos.piece_on(t1);
1820 if (bit_is_set(pos.attacks_from(p, t1), t2))
1823 // Case 5: Discovered check, checking piece is the piece moved in m1
1824 if ( piece_is_slider(p)
1825 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1826 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1828 // discovered_check_candidates() works also if the Position's side to
1829 // move is the opposite of the checking piece.
1830 Color them = opposite_color(pos.side_to_move());
1831 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1833 if (bit_is_set(dcCandidates, f2))
1840 // value_is_mate() checks if the given value is a mate one eventually
1841 // compensated for the ply.
1843 bool value_is_mate(Value value) {
1845 assert(abs(value) <= VALUE_INFINITE);
1847 return value <= value_mated_in(PLY_MAX)
1848 || value >= value_mate_in(PLY_MAX);
1852 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1853 // "plies to mate from the current ply". Non-mate scores are unchanged.
1854 // The function is called before storing a value to the transposition table.
1856 Value value_to_tt(Value v, int ply) {
1858 if (v >= value_mate_in(PLY_MAX))
1861 if (v <= value_mated_in(PLY_MAX))
1868 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1869 // the transposition table to a mate score corrected for the current ply.
1871 Value value_from_tt(Value v, int ply) {
1873 if (v >= value_mate_in(PLY_MAX))
1876 if (v <= value_mated_in(PLY_MAX))
1883 // extension() decides whether a move should be searched with normal depth,
1884 // or with extended depth. Certain classes of moves (checking moves, in
1885 // particular) are searched with bigger depth than ordinary moves and in
1886 // any case are marked as 'dangerous'. Note that also if a move is not
1887 // extended, as example because the corresponding UCI option is set to zero,
1888 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1889 template <NodeType PvNode>
1890 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1891 bool singleEvasion, bool mateThreat, bool* dangerous) {
1893 assert(m != MOVE_NONE);
1895 Depth result = DEPTH_ZERO;
1896 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1900 if (moveIsCheck && pos.see_sign(m) >= 0)
1901 result += CheckExtension[PvNode];
1904 result += SingleEvasionExtension[PvNode];
1907 result += MateThreatExtension[PvNode];
1910 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1912 Color c = pos.side_to_move();
1913 if (relative_rank(c, move_to(m)) == RANK_7)
1915 result += PawnPushTo7thExtension[PvNode];
1918 if (pos.pawn_is_passed(c, move_to(m)))
1920 result += PassedPawnExtension[PvNode];
1925 if ( captureOrPromotion
1926 && pos.type_of_piece_on(move_to(m)) != PAWN
1927 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1928 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1929 && !move_is_promotion(m)
1932 result += PawnEndgameExtension[PvNode];
1937 && captureOrPromotion
1938 && pos.type_of_piece_on(move_to(m)) != PAWN
1939 && pos.see_sign(m) >= 0)
1941 result += ONE_PLY / 2;
1945 return Min(result, ONE_PLY);
1949 // connected_threat() tests whether it is safe to forward prune a move or if
1950 // is somehow coonected to the threat move returned by null search.
1952 bool connected_threat(const Position& pos, Move m, Move threat) {
1954 assert(move_is_ok(m));
1955 assert(threat && move_is_ok(threat));
1956 assert(!pos.move_is_check(m));
1957 assert(!pos.move_is_capture_or_promotion(m));
1958 assert(!pos.move_is_passed_pawn_push(m));
1960 Square mfrom, mto, tfrom, tto;
1962 mfrom = move_from(m);
1964 tfrom = move_from(threat);
1965 tto = move_to(threat);
1967 // Case 1: Don't prune moves which move the threatened piece
1971 // Case 2: If the threatened piece has value less than or equal to the
1972 // value of the threatening piece, don't prune move which defend it.
1973 if ( pos.move_is_capture(threat)
1974 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1975 || pos.type_of_piece_on(tfrom) == KING)
1976 && pos.move_attacks_square(m, tto))
1979 // Case 3: If the moving piece in the threatened move is a slider, don't
1980 // prune safe moves which block its ray.
1981 if ( piece_is_slider(pos.piece_on(tfrom))
1982 && bit_is_set(squares_between(tfrom, tto), mto)
1983 && pos.see_sign(m) >= 0)
1990 // ok_to_use_TT() returns true if a transposition table score
1991 // can be used at a given point in search.
1993 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1995 Value v = value_from_tt(tte->value(), ply);
1997 return ( tte->depth() >= depth
1998 || v >= Max(value_mate_in(PLY_MAX), beta)
1999 || v < Min(value_mated_in(PLY_MAX), beta))
2001 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
2002 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
2006 // refine_eval() returns the transposition table score if
2007 // possible otherwise falls back on static position evaluation.
2009 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2013 Value v = value_from_tt(tte->value(), ply);
2015 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
2016 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
2023 // update_history() registers a good move that produced a beta-cutoff
2024 // in history and marks as failures all the other moves of that ply.
2026 void update_history(const Position& pos, Move move, Depth depth,
2027 Move movesSearched[], int moveCount) {
2030 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2032 for (int i = 0; i < moveCount - 1; i++)
2034 m = movesSearched[i];
2038 if (!pos.move_is_capture_or_promotion(m))
2039 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2044 // update_killers() add a good move that produced a beta-cutoff
2045 // among the killer moves of that ply.
2047 void update_killers(Move m, SearchStack* ss) {
2049 if (m == ss->killers[0])
2052 ss->killers[1] = ss->killers[0];
2057 // update_gains() updates the gains table of a non-capture move given
2058 // the static position evaluation before and after the move.
2060 void update_gains(const Position& pos, Move m, Value before, Value after) {
2063 && before != VALUE_NONE
2064 && after != VALUE_NONE
2065 && pos.captured_piece_type() == PIECE_TYPE_NONE
2066 && !move_is_special(m))
2067 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2071 // current_search_time() returns the number of milliseconds which have passed
2072 // since the beginning of the current search.
2074 int current_search_time() {
2076 return get_system_time() - SearchStartTime;
2080 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2082 std::string value_to_uci(Value v) {
2084 std::stringstream s;
2086 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2087 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2089 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2094 // nps() computes the current nodes/second count.
2098 int t = current_search_time();
2099 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2103 // poll() performs two different functions: It polls for user input, and it
2104 // looks at the time consumed so far and decides if it's time to abort the
2109 static int lastInfoTime;
2110 int t = current_search_time();
2115 // We are line oriented, don't read single chars
2116 std::string command;
2118 if (!std::getline(std::cin, command))
2121 if (command == "quit")
2124 PonderSearch = false;
2128 else if (command == "stop")
2131 PonderSearch = false;
2133 else if (command == "ponderhit")
2137 // Print search information
2141 else if (lastInfoTime > t)
2142 // HACK: Must be a new search where we searched less than
2143 // NodesBetweenPolls nodes during the first second of search.
2146 else if (t - lastInfoTime >= 1000)
2153 if (dbg_show_hit_rate)
2154 dbg_print_hit_rate();
2156 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2157 << " time " << t << endl;
2160 // Should we stop the search?
2164 bool stillAtFirstMove = FirstRootMove
2165 && !AspirationFailLow
2166 && t > TimeMgr.available_time();
2168 bool noMoreTime = t > TimeMgr.maximum_time()
2169 || stillAtFirstMove;
2171 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2172 || (ExactMaxTime && t >= ExactMaxTime)
2173 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2178 // ponderhit() is called when the program is pondering (i.e. thinking while
2179 // it's the opponent's turn to move) in order to let the engine know that
2180 // it correctly predicted the opponent's move.
2184 int t = current_search_time();
2185 PonderSearch = false;
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > TimeMgr.available_time();
2191 bool noMoreTime = t > TimeMgr.maximum_time()
2192 || stillAtFirstMove;
2194 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2199 // init_ss_array() does a fast reset of the first entries of a SearchStack
2200 // array and of all the excludedMove and skipNullMove entries.
2202 void init_ss_array(SearchStack* ss, int size) {
2204 for (int i = 0; i < size; i++, ss++)
2206 ss->excludedMove = MOVE_NONE;
2207 ss->skipNullMove = false;
2208 ss->reduction = DEPTH_ZERO;
2212 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2217 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2218 // while the program is pondering. The point is to work around a wrinkle in
2219 // the UCI protocol: When pondering, the engine is not allowed to give a
2220 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2221 // We simply wait here until one of these commands is sent, and return,
2222 // after which the bestmove and pondermove will be printed (in id_loop()).
2224 void wait_for_stop_or_ponderhit() {
2226 std::string command;
2230 if (!std::getline(std::cin, command))
2233 if (command == "quit")
2238 else if (command == "ponderhit" || command == "stop")
2244 // print_pv_info() prints to standard output and eventually to log file information on
2245 // the current PV line. It is called at each iteration or after a new pv is found.
2247 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2249 cout << "info depth " << Iteration
2250 << " score " << value_to_uci(value)
2251 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2252 << " time " << current_search_time()
2253 << " nodes " << ThreadsMgr.nodes_searched()
2257 for (Move* m = pv; *m != MOVE_NONE; m++)
2264 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2265 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2267 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2268 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2273 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2274 // the PV back into the TT. This makes sure the old PV moves are searched
2275 // first, even if the old TT entries have been overwritten.
2277 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2281 Position p(pos, pos.thread());
2282 Value v, m = VALUE_NONE;
2284 for (int i = 0; pv[i] != MOVE_NONE; i++)
2286 tte = TT.retrieve(p.get_key());
2287 if (!tte || tte->move() != pv[i])
2289 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2290 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2292 p.do_move(pv[i], st);
2297 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2298 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2299 // allow to always have a ponder move even when we fail high at root and also a
2300 // long PV to print that is important for position analysis.
2302 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2306 Position p(pos, pos.thread());
2309 assert(bestMove != MOVE_NONE);
2312 p.do_move(pv[ply++], st);
2314 while ( (tte = TT.retrieve(p.get_key())) != NULL
2315 && tte->move() != MOVE_NONE
2316 && move_is_legal(p, tte->move())
2318 && (!p.is_draw() || ply < 2))
2320 pv[ply] = tte->move();
2321 p.do_move(pv[ply++], st);
2323 pv[ply] = MOVE_NONE;
2327 // init_thread() is the function which is called when a new thread is
2328 // launched. It simply calls the idle_loop() function with the supplied
2329 // threadID. There are two versions of this function; one for POSIX
2330 // threads and one for Windows threads.
2332 #if !defined(_MSC_VER)
2334 void* init_thread(void *threadID) {
2336 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2342 DWORD WINAPI init_thread(LPVOID threadID) {
2344 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2351 /// The ThreadsManager class
2353 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2354 // get_beta_counters() are getters/setters for the per thread
2355 // counters used to sort the moves at root.
2357 void ThreadsManager::resetNodeCounters() {
2359 for (int i = 0; i < MAX_THREADS; i++)
2360 threads[i].nodes = 0ULL;
2363 int64_t ThreadsManager::nodes_searched() const {
2365 int64_t result = 0ULL;
2366 for (int i = 0; i < ActiveThreads; i++)
2367 result += threads[i].nodes;
2373 // idle_loop() is where the threads are parked when they have no work to do.
2374 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2375 // object for which the current thread is the master.
2377 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2379 assert(threadID >= 0 && threadID < MAX_THREADS);
2383 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2384 // master should exit as last one.
2385 if (AllThreadsShouldExit)
2388 threads[threadID].state = THREAD_TERMINATED;
2392 // If we are not thinking, wait for a condition to be signaled
2393 // instead of wasting CPU time polling for work.
2394 while ( threadID >= ActiveThreads
2395 || threads[threadID].state == THREAD_INITIALIZING
2396 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2399 assert(threadID != 0);
2401 if (AllThreadsShouldExit)
2406 // Retest condition under lock protection
2407 if (!( threadID >= ActiveThreads
2408 || threads[threadID].state == THREAD_INITIALIZING
2409 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2411 lock_release(&MPLock);
2415 // Put thread to sleep
2416 threads[threadID].state = THREAD_AVAILABLE;
2417 cond_wait(&WaitCond[threadID], &MPLock);
2418 lock_release(&MPLock);
2421 // If this thread has been assigned work, launch a search
2422 if (threads[threadID].state == THREAD_WORKISWAITING)
2424 assert(!AllThreadsShouldExit);
2426 threads[threadID].state = THREAD_SEARCHING;
2428 // Here we call search() with SplitPoint template parameter set to true
2429 SplitPoint* tsp = threads[threadID].splitPoint;
2430 Position pos(*tsp->pos, threadID);
2431 SearchStack* ss = tsp->sstack[threadID] + 1;
2435 //search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2436 sp_search<PV>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2438 //search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2439 sp_search<NonPV>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2441 assert(threads[threadID].state == THREAD_SEARCHING);
2443 threads[threadID].state = THREAD_AVAILABLE;
2446 // If this thread is the master of a split point and all slaves have
2447 // finished their work at this split point, return from the idle loop.
2449 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2451 if (i == ActiveThreads)
2453 // Because sp->slaves[] is reset under lock protection,
2454 // be sure sp->lock has been released before to return.
2455 lock_grab(&(sp->lock));
2456 lock_release(&(sp->lock));
2458 // In helpful master concept a master can help only a sub-tree, and
2459 // because here is all finished is not possible master is booked.
2460 assert(threads[threadID].state == THREAD_AVAILABLE);
2462 threads[threadID].state = THREAD_SEARCHING;
2469 // init_threads() is called during startup. It launches all helper threads,
2470 // and initializes the split point stack and the global locks and condition
2473 void ThreadsManager::init_threads() {
2478 // Initialize global locks
2481 for (i = 0; i < MAX_THREADS; i++)
2482 cond_init(&WaitCond[i]);
2484 // Initialize splitPoints[] locks
2485 for (i = 0; i < MAX_THREADS; i++)
2486 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2487 lock_init(&(threads[i].splitPoints[j].lock));
2489 // Will be set just before program exits to properly end the threads
2490 AllThreadsShouldExit = false;
2492 // Threads will be put all threads to sleep as soon as created
2495 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2496 threads[0].state = THREAD_SEARCHING;
2497 for (i = 1; i < MAX_THREADS; i++)
2498 threads[i].state = THREAD_INITIALIZING;
2500 // Launch the helper threads
2501 for (i = 1; i < MAX_THREADS; i++)
2504 #if !defined(_MSC_VER)
2505 pthread_t pthread[1];
2506 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2508 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2513 cout << "Failed to create thread number " << i << endl;
2514 Application::exit_with_failure();
2517 // Wait until the thread has finished launching and is gone to sleep
2518 while (threads[i].state == THREAD_INITIALIZING) {}
2523 // exit_threads() is called when the program exits. It makes all the
2524 // helper threads exit cleanly.
2526 void ThreadsManager::exit_threads() {
2528 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2530 // Wake up all the threads and waits for termination
2531 for (int i = 1; i < MAX_THREADS; i++)
2533 wake_sleeping_thread(i);
2534 while (threads[i].state != THREAD_TERMINATED) {}
2537 // Now we can safely destroy the locks
2538 for (int i = 0; i < MAX_THREADS; i++)
2539 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2540 lock_destroy(&(threads[i].splitPoints[j].lock));
2542 lock_destroy(&MPLock);
2544 // Now we can safely destroy the wait conditions
2545 for (int i = 0; i < MAX_THREADS; i++)
2546 cond_destroy(&WaitCond[i]);
2550 // thread_should_stop() checks whether the thread should stop its search.
2551 // This can happen if a beta cutoff has occurred in the thread's currently
2552 // active split point, or in some ancestor of the current split point.
2554 bool ThreadsManager::thread_should_stop(int threadID) const {
2556 assert(threadID >= 0 && threadID < ActiveThreads);
2558 SplitPoint* sp = threads[threadID].splitPoint;
2560 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2565 // thread_is_available() checks whether the thread with threadID "slave" is
2566 // available to help the thread with threadID "master" at a split point. An
2567 // obvious requirement is that "slave" must be idle. With more than two
2568 // threads, this is not by itself sufficient: If "slave" is the master of
2569 // some active split point, it is only available as a slave to the other
2570 // threads which are busy searching the split point at the top of "slave"'s
2571 // split point stack (the "helpful master concept" in YBWC terminology).
2573 bool ThreadsManager::thread_is_available(int slave, int master) const {
2575 assert(slave >= 0 && slave < ActiveThreads);
2576 assert(master >= 0 && master < ActiveThreads);
2577 assert(ActiveThreads > 1);
2579 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2582 // Make a local copy to be sure doesn't change under our feet
2583 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2585 // No active split points means that the thread is available as
2586 // a slave for any other thread.
2587 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2590 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2591 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2592 // could have been set to 0 by another thread leading to an out of bound access.
2593 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2600 // available_thread_exists() tries to find an idle thread which is available as
2601 // a slave for the thread with threadID "master".
2603 bool ThreadsManager::available_thread_exists(int master) const {
2605 assert(master >= 0 && master < ActiveThreads);
2606 assert(ActiveThreads > 1);
2608 for (int i = 0; i < ActiveThreads; i++)
2609 if (thread_is_available(i, master))
2616 // split() does the actual work of distributing the work at a node between
2617 // several available threads. If it does not succeed in splitting the
2618 // node (because no idle threads are available, or because we have no unused
2619 // split point objects), the function immediately returns. If splitting is
2620 // possible, a SplitPoint object is initialized with all the data that must be
2621 // copied to the helper threads and we tell our helper threads that they have
2622 // been assigned work. This will cause them to instantly leave their idle loops
2623 // and call sp_search(). When all threads have returned from sp_search() then
2626 template <bool Fake>
2627 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2628 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2629 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2631 assert(ply > 0 && ply < PLY_MAX);
2632 assert(*bestValue >= -VALUE_INFINITE);
2633 assert(*bestValue <= *alpha);
2634 assert(*alpha < beta);
2635 assert(beta <= VALUE_INFINITE);
2636 assert(depth > DEPTH_ZERO);
2637 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2638 assert(ActiveThreads > 1);
2640 int i, master = p.thread();
2641 Thread& masterThread = threads[master];
2645 // If no other thread is available to help us, or if we have too many
2646 // active split points, don't split.
2647 if ( !available_thread_exists(master)
2648 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2650 lock_release(&MPLock);
2654 // Pick the next available split point object from the split point stack
2655 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2657 // Initialize the split point object
2658 splitPoint.parent = masterThread.splitPoint;
2659 splitPoint.stopRequest = false;
2660 splitPoint.ply = ply;
2661 splitPoint.depth = depth;
2662 splitPoint.threatMove = threatMove;
2663 splitPoint.mateThreat = mateThreat;
2664 splitPoint.alpha = *alpha;
2665 splitPoint.beta = beta;
2666 splitPoint.pvNode = pvNode;
2667 splitPoint.bestValue = *bestValue;
2669 splitPoint.moveCount = moveCount;
2670 splitPoint.pos = &p;
2671 splitPoint.parentSstack = ss;
2672 for (i = 0; i < ActiveThreads; i++)
2673 splitPoint.slaves[i] = 0;
2675 masterThread.splitPoint = &splitPoint;
2677 // If we are here it means we are not available
2678 assert(masterThread.state != THREAD_AVAILABLE);
2680 int workersCnt = 1; // At least the master is included
2682 // Allocate available threads setting state to THREAD_BOOKED
2683 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2684 if (thread_is_available(i, master))
2686 threads[i].state = THREAD_BOOKED;
2687 threads[i].splitPoint = &splitPoint;
2688 splitPoint.slaves[i] = 1;
2692 assert(Fake || workersCnt > 1);
2694 // We can release the lock because slave threads are already booked and master is not available
2695 lock_release(&MPLock);
2697 // Tell the threads that they have work to do. This will make them leave
2698 // their idle loop. But before copy search stack tail for each thread.
2699 for (i = 0; i < ActiveThreads; i++)
2700 if (i == master || splitPoint.slaves[i])
2702 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2704 assert(i == master || threads[i].state == THREAD_BOOKED);
2706 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2708 wake_sleeping_thread(i);
2711 // Everything is set up. The master thread enters the idle loop, from
2712 // which it will instantly launch a search, because its state is
2713 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2714 // idle loop, which means that the main thread will return from the idle
2715 // loop when all threads have finished their work at this split point.
2716 idle_loop(master, &splitPoint);
2718 // We have returned from the idle loop, which means that all threads are
2719 // finished. Update alpha and bestValue, and return.
2722 *alpha = splitPoint.alpha;
2723 *bestValue = splitPoint.bestValue;
2724 masterThread.activeSplitPoints--;
2725 masterThread.splitPoint = splitPoint.parent;
2727 lock_release(&MPLock);
2731 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2732 // to start a new search from the root.
2734 void ThreadsManager::wake_sleeping_thread(int threadID) {
2737 cond_signal(&WaitCond[threadID]);
2738 lock_release(&MPLock);
2742 /// The RootMoveList class
2744 // RootMoveList c'tor
2746 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2748 SearchStack ss[PLY_MAX_PLUS_2];
2749 MoveStack mlist[MOVES_MAX];
2751 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2753 // Initialize search stack
2754 init_ss_array(ss, PLY_MAX_PLUS_2);
2755 ss[0].eval = VALUE_NONE;
2758 // Generate all legal moves
2759 MoveStack* last = generate_moves(pos, mlist);
2761 // Add each move to the moves[] array
2762 for (MoveStack* cur = mlist; cur != last; cur++)
2764 bool includeMove = includeAllMoves;
2766 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2767 includeMove = (searchMoves[k] == cur->move);
2772 // Find a quick score for the move
2773 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2774 moves[count].pv[1] = MOVE_NONE;
2775 pos.do_move(cur->move, st);
2776 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2777 pos.undo_move(cur->move);
2783 // Score root moves using the standard way used in main search, the moves
2784 // are scored according to the order in which are returned by MovePicker.
2786 void RootMoveList::score_moves(const Position& pos)
2790 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2792 while ((move = mp.get_next_move()) != MOVE_NONE)
2793 for (int i = 0; i < count; i++)
2794 if (moves[i].move == move)
2796 moves[i].mp_score = score--;
2801 // RootMoveList simple methods definitions
2803 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2807 for (j = 0; pv[j] != MOVE_NONE; j++)
2808 moves[moveNum].pv[j] = pv[j];
2810 moves[moveNum].pv[j] = MOVE_NONE;
2814 // RootMoveList::sort() sorts the root move list at the beginning of a new
2817 void RootMoveList::sort() {
2819 sort_multipv(count - 1); // Sort all items
2823 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2824 // list by their scores and depths. It is used to order the different PVs
2825 // correctly in MultiPV mode.
2827 void RootMoveList::sort_multipv(int n) {
2831 for (i = 1; i <= n; i++)
2833 RootMove rm = moves[i];
2834 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2835 moves[j] = moves[j - 1];