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; }
79 bool available_thread_exists(int master) const;
80 bool thread_is_available(int slave, int master) const;
81 bool thread_should_stop(int threadID) const;
82 void wake_sleeping_thread(int threadID);
83 void idle_loop(int threadID, SplitPoint* sp);
86 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
91 volatile bool AllThreadsShouldExit;
92 Thread threads[MAX_THREADS];
94 WaitCondition WaitCond[MAX_THREADS];
98 // RootMove struct is used for moves at the root at the tree. For each
99 // root move, we store a score, a node count, and a PV (really a refutation
100 // in the case of moves which fail low).
104 RootMove() : mp_score(0), nodes(0) {}
106 // RootMove::operator<() is the comparison function used when
107 // sorting the moves. A move m1 is considered to be better
108 // than a move m2 if it has a higher score, or if the moves
109 // have equal score but m1 has the higher beta cut-off count.
110 bool operator<(const RootMove& m) const {
112 return score != m.score ? score < m.score : mp_score <= m.mp_score;
119 Move pv[PLY_MAX_PLUS_2];
123 // The RootMoveList class is essentially an array of RootMove objects, with
124 // a handful of methods for accessing the data in the individual moves.
129 RootMoveList(Position& pos, Move searchMoves[]);
131 Move move(int moveNum) const { return moves[moveNum].move; }
132 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
133 int move_count() const { return count; }
134 Value move_score(int moveNum) const { return moves[moveNum].score; }
135 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
136 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
137 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
139 void set_move_pv(int moveNum, const Move pv[]);
140 void score_moves(const Position& pos);
142 void sort_multipv(int n);
145 RootMove moves[MOVES_MAX];
150 // When formatting a move for std::cout we must know if we are in Chess960
151 // or not. To keep using the handy operator<<() on the move the trick is to
152 // embed this flag in the stream itself. Function-like named enum set960 is
153 // used as a custom manipulator and the stream internal general-purpose array,
154 // accessed through ios_base::iword(), is used to pass the flag to the move's
155 // operator<<() that will use it to properly format castling moves.
158 std::ostream& operator<< (std::ostream& os, const set960& m) {
160 os.iword(0) = int(m);
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * ONE_PLY;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Maximum depth for use of dynamic threat detection when null move fails low
176 const Depth ThreatDepth = 5 * ONE_PLY;
178 // Step 9. Internal iterative deepening
180 // Minimum depth for use of internal iterative deepening
181 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
183 // At Non-PV nodes we do an internal iterative deepening search
184 // when the static evaluation is bigger then beta - IIDMargin.
185 const Value IIDMargin = Value(0x100);
187 // Step 11. Decide the new search depth
189 // Extensions. Configurable UCI options
190 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
191 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
192 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
194 // Minimum depth for use of singular extension
195 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
197 // If the TT move is at least SingularExtensionMargin better then the
198 // remaining ones we will extend it.
199 const Value SingularExtensionMargin = Value(0x20);
201 // Step 12. Futility pruning
203 // Futility margin for quiescence search
204 const Value FutilityMarginQS = Value(0x80);
206 // Futility lookup tables (initialized at startup) and their getter functions
207 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
208 int FutilityMoveCountArray[32]; // [depth]
210 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
211 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
213 // Step 14. Reduced search
215 // Reduction lookup tables (initialized at startup) and their getter functions
216 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
218 template <NodeType PV>
219 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
221 // Common adjustments
223 // Search depth at iteration 1
224 const Depth InitialDepth = ONE_PLY;
226 // Easy move margin. An easy move candidate must be at least this much
227 // better than the second best move.
228 const Value EasyMoveMargin = Value(0x200);
236 // Scores and number of times the best move changed for each iteration
237 Value ValueByIteration[PLY_MAX_PLUS_2];
238 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
240 // Search window management
246 // Time managment variables
247 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
248 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
249 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
254 std::ofstream LogFile;
256 // Multi-threads related variables
257 Depth MinimumSplitDepth;
258 int MaxThreadsPerSplitPoint;
259 ThreadsManager ThreadsMgr;
261 // Node counters, used only by thread[0] but try to keep in different cache
262 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
264 int NodesBetweenPolls = 30000;
271 Value id_loop(Position& pos, Move searchMoves[]);
272 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
274 template <NodeType PvNode, bool SpNode>
275 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
277 template <NodeType PvNode>
278 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
280 template <NodeType PvNode>
281 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
283 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
284 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
287 template <NodeType PvNode>
288 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
290 bool connected_moves(const Position& pos, Move m1, Move m2);
291 bool value_is_mate(Value value);
292 Value value_to_tt(Value v, int ply);
293 Value value_from_tt(Value v, int ply);
294 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
295 bool connected_threat(const Position& pos, Move m, Move threat);
296 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
297 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
298 void update_killers(Move m, SearchStack* ss);
299 void update_gains(const Position& pos, Move move, Value before, Value after);
301 int current_search_time();
302 std::string value_to_uci(Value v);
303 int nps(const Position& pos);
304 void poll(const Position& pos);
306 void wait_for_stop_or_ponderhit();
307 void init_ss_array(SearchStack* ss, int size);
308 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
309 void insert_pv_in_tt(const Position& pos, Move pv[]);
310 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
312 #if !defined(_MSC_VER)
313 void* init_thread(void* threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
325 /// init_threads(), exit_threads() and nodes_searched() are helpers to
326 /// give accessibility to some TM methods from outside of current file.
328 void init_threads() { ThreadsMgr.init_threads(); }
329 void exit_threads() { ThreadsMgr.exit_threads(); }
332 /// init_search() is called during startup. It initializes various lookup tables
336 int d; // depth (ONE_PLY == 2)
337 int hd; // half depth (ONE_PLY == 1)
340 // Init reductions array
341 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
343 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
344 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
345 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
346 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
349 // Init futility margins array
350 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
351 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
353 // Init futility move count array
354 for (d = 0; d < 32; d++)
355 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
359 /// perft() is our utility to verify move generation is bug free. All the legal
360 /// moves up to given depth are generated and counted and the sum returned.
362 int perft(Position& pos, Depth depth)
364 MoveStack mlist[MOVES_MAX];
369 // Generate all legal moves
370 MoveStack* last = generate_moves(pos, mlist);
372 // If we are at the last ply we don't need to do and undo
373 // the moves, just to count them.
374 if (depth <= ONE_PLY)
375 return int(last - mlist);
377 // Loop through all legal moves
379 for (MoveStack* cur = mlist; cur != last; cur++)
382 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
383 sum += perft(pos, depth - ONE_PLY);
390 /// think() is the external interface to Stockfish's search, and is called when
391 /// the program receives the UCI 'go' command. It initializes various
392 /// search-related global variables, and calls root_search(). It returns false
393 /// when a quit command is received during the search.
395 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
396 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
398 // Initialize global search variables
399 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
401 SearchStartTime = get_system_time();
402 ExactMaxTime = maxTime;
405 InfiniteSearch = infinite;
406 PonderSearch = ponder;
407 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
409 // Look for a book move, only during games, not tests
410 if (UseTimeManagement && get_option_value_bool("OwnBook"))
412 if (get_option_value_string("Book File") != OpeningBook.file_name())
413 OpeningBook.open(get_option_value_string("Book File"));
415 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
416 if (bookMove != MOVE_NONE)
419 wait_for_stop_or_ponderhit();
421 cout << "bestmove " << bookMove << endl;
426 // Read UCI option values
427 TT.set_size(get_option_value_int("Hash"));
428 if (get_option_value_bool("Clear Hash"))
430 set_option_value("Clear Hash", "false");
434 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
435 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
436 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
437 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
438 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
439 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
440 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
441 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
442 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
443 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
444 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
445 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
447 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
448 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
449 MultiPV = get_option_value_int("MultiPV");
450 UseLogFile = get_option_value_bool("Use Search Log");
453 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
455 read_weights(pos.side_to_move());
457 // Set the number of active threads
458 int newActiveThreads = get_option_value_int("Threads");
459 if (newActiveThreads != ThreadsMgr.active_threads())
461 ThreadsMgr.set_active_threads(newActiveThreads);
462 init_eval(ThreadsMgr.active_threads());
466 int myTime = time[pos.side_to_move()];
467 int myIncrement = increment[pos.side_to_move()];
468 if (UseTimeManagement)
469 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
471 // Set best NodesBetweenPolls interval to avoid lagging under
472 // heavy time pressure.
474 NodesBetweenPolls = Min(MaxNodes, 30000);
475 else if (myTime && myTime < 1000)
476 NodesBetweenPolls = 1000;
477 else if (myTime && myTime < 5000)
478 NodesBetweenPolls = 5000;
480 NodesBetweenPolls = 30000;
482 // Write search information to log file
484 LogFile << "Searching: " << pos.to_fen() << endl
485 << "infinite: " << infinite
486 << " ponder: " << ponder
487 << " time: " << myTime
488 << " increment: " << myIncrement
489 << " moves to go: " << movesToGo << endl;
491 // We're ready to start thinking. Call the iterative deepening loop function
492 id_loop(pos, searchMoves);
503 // id_loop() is the main iterative deepening loop. It calls root_search
504 // repeatedly with increasing depth until the allocated thinking time has
505 // been consumed, the user stops the search, or the maximum search depth is
508 Value id_loop(Position& pos, Move searchMoves[]) {
510 SearchStack ss[PLY_MAX_PLUS_2];
511 Move pv[PLY_MAX_PLUS_2];
512 Move EasyMove = MOVE_NONE;
513 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
515 // Moves to search are verified, copied, scored and sorted
516 RootMoveList rml(pos, searchMoves);
518 // Handle special case of searching on a mate/stale position
519 if (rml.move_count() == 0)
522 wait_for_stop_or_ponderhit();
524 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
527 // Print RootMoveList startup scoring to the standard output,
528 // so to output information also for iteration 1.
529 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
530 << "info depth " << 1
531 << "\ninfo depth " << 1
532 << " score " << value_to_uci(rml.move_score(0))
533 << " time " << current_search_time()
534 << " nodes " << pos.nodes_searched()
535 << " nps " << nps(pos)
536 << " pv " << rml.move(0) << "\n";
541 init_ss_array(ss, PLY_MAX_PLUS_2);
542 pv[0] = pv[1] = MOVE_NONE;
543 ValueByIteration[1] = rml.move_score(0);
546 // Is one move significantly better than others after initial scoring ?
547 if ( rml.move_count() == 1
548 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
549 EasyMove = rml.move(0);
551 // Iterative deepening loop
552 while (Iteration < PLY_MAX)
554 // Initialize iteration
556 BestMoveChangesByIteration[Iteration] = 0;
558 cout << "info depth " << Iteration << endl;
560 // Calculate dynamic aspiration window based on previous iterations
561 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
563 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
564 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
566 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
567 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
569 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
570 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
573 // Search to the current depth, rml is updated and sorted, alpha and beta could change
574 value = root_search(pos, ss, pv, rml, &alpha, &beta);
576 // Write PV to transposition table, in case the relevant entries have
577 // been overwritten during the search.
578 insert_pv_in_tt(pos, pv);
581 break; // Value cannot be trusted. Break out immediately!
583 //Save info about search result
584 ValueByIteration[Iteration] = value;
586 // Drop the easy move if differs from the new best move
587 if (pv[0] != EasyMove)
588 EasyMove = MOVE_NONE;
590 if (UseTimeManagement)
593 bool stopSearch = false;
595 // Stop search early if there is only a single legal move,
596 // we search up to Iteration 6 anyway to get a proper score.
597 if (Iteration >= 6 && rml.move_count() == 1)
600 // Stop search early when the last two iterations returned a mate score
602 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
603 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
606 // Stop search early if one move seems to be much better than the others
609 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
610 && current_search_time() > TimeMgr.available_time() / 16)
611 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
612 && current_search_time() > TimeMgr.available_time() / 32)))
615 // Add some extra time if the best move has changed during the last two iterations
616 if (Iteration > 5 && Iteration <= 50)
617 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
618 BestMoveChangesByIteration[Iteration-1]);
620 // Stop search if most of MaxSearchTime is consumed at the end of the
621 // iteration. We probably don't have enough time to search the first
622 // move at the next iteration anyway.
623 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
629 StopOnPonderhit = true;
635 if (MaxDepth && Iteration >= MaxDepth)
639 // If we are pondering or in infinite search, we shouldn't print the
640 // best move before we are told to do so.
641 if (!AbortSearch && (PonderSearch || InfiniteSearch))
642 wait_for_stop_or_ponderhit();
644 // Print final search statistics
645 cout << "info nodes " << pos.nodes_searched()
646 << " nps " << nps(pos)
647 << " time " << current_search_time() << endl;
649 // Print the best move and the ponder move to the standard output
650 if (pv[0] == MOVE_NONE)
656 assert(pv[0] != MOVE_NONE);
658 cout << "bestmove " << pv[0];
660 if (pv[1] != MOVE_NONE)
661 cout << " ponder " << pv[1];
668 dbg_print_mean(LogFile);
670 if (dbg_show_hit_rate)
671 dbg_print_hit_rate(LogFile);
673 LogFile << "\nNodes: " << pos.nodes_searched()
674 << "\nNodes/second: " << nps(pos)
675 << "\nBest move: " << move_to_san(pos, pv[0]);
678 pos.do_move(pv[0], st);
679 LogFile << "\nPonder move: "
680 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
683 return rml.move_score(0);
687 // root_search() is the function which searches the root node. It is
688 // similar to search_pv except that it uses a different move ordering
689 // scheme, prints some information to the standard output and handles
690 // the fail low/high loops.
692 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
698 Depth depth, ext, newDepth;
699 Value value, alpha, beta;
700 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
701 int researchCountFH, researchCountFL;
703 researchCountFH = researchCountFL = 0;
706 isCheck = pos.is_check();
707 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
709 // Step 1. Initialize node (polling is omitted at root)
710 ss->currentMove = ss->bestMove = MOVE_NONE;
712 // Step 2. Check for aborted search (omitted at root)
713 // Step 3. Mate distance pruning (omitted at root)
714 // Step 4. Transposition table lookup (omitted at root)
716 // Step 5. Evaluate the position statically
717 // At root we do this only to get reference value for child nodes
718 ss->evalMargin = VALUE_NONE;
719 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
721 // Step 6. Razoring (omitted at root)
722 // Step 7. Static null move pruning (omitted at root)
723 // Step 8. Null move search with verification search (omitted at root)
724 // Step 9. Internal iterative deepening (omitted at root)
726 // Step extra. Fail low loop
727 // We start with small aspiration window and in case of fail low, we research
728 // with bigger window until we are not failing low anymore.
731 // Sort the moves before to (re)search
732 rml.score_moves(pos);
735 // Step 10. Loop through all moves in the root move list
736 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
738 // This is used by time management
739 FirstRootMove = (i == 0);
741 // Save the current node count before the move is searched
742 nodes = pos.nodes_searched();
744 // Pick the next root move, and print the move and the move number to
745 // the standard output.
746 move = ss->currentMove = rml.move(i);
748 if (current_search_time() >= 1000)
749 cout << "info currmove " << move
750 << " currmovenumber " << i + 1 << endl;
752 moveIsCheck = pos.move_is_check(move);
753 captureOrPromotion = pos.move_is_capture_or_promotion(move);
755 // Step 11. Decide the new search depth
756 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
757 newDepth = depth + ext;
759 // Step 12. Futility pruning (omitted at root)
761 // Step extra. Fail high loop
762 // If move fails high, we research with bigger window until we are not failing
764 value = - VALUE_INFINITE;
768 // Step 13. Make the move
769 pos.do_move(move, st, ci, moveIsCheck);
771 // Step extra. pv search
772 // We do pv search for first moves (i < MultiPV)
773 // and for fail high research (value > alpha)
774 if (i < MultiPV || value > alpha)
776 // Aspiration window is disabled in multi-pv case
778 alpha = -VALUE_INFINITE;
780 // Full depth PV search, done on first move or after a fail high
781 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
785 // Step 14. Reduced search
786 // if the move fails high will be re-searched at full depth
787 bool doFullDepthSearch = true;
789 if ( depth >= 3 * ONE_PLY
791 && !captureOrPromotion
792 && !move_is_castle(move))
794 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
797 assert(newDepth-ss->reduction >= ONE_PLY);
799 // Reduced depth non-pv search using alpha as upperbound
800 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
801 doFullDepthSearch = (value > alpha);
804 // The move failed high, but if reduction is very big we could
805 // face a false positive, retry with a less aggressive reduction,
806 // if the move fails high again then go with full depth search.
807 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
809 assert(newDepth - ONE_PLY >= ONE_PLY);
811 ss->reduction = ONE_PLY;
812 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
813 doFullDepthSearch = (value > alpha);
815 ss->reduction = DEPTH_ZERO; // Restore original reduction
818 // Step 15. Full depth search
819 if (doFullDepthSearch)
821 // Full depth non-pv search using alpha as upperbound
822 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
824 // If we are above alpha then research at same depth but as PV
825 // to get a correct score or eventually a fail high above beta.
827 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
831 // Step 16. Undo move
834 // Can we exit fail high loop ?
835 if (AbortSearch || value < beta)
838 // We are failing high and going to do a research. It's important to update
839 // the score before research in case we run out of time while researching.
840 rml.set_move_score(i, value);
842 extract_pv_from_tt(pos, move, pv);
843 rml.set_move_pv(i, pv);
845 // Print information to the standard output
846 print_pv_info(pos, pv, alpha, beta, value);
848 // Prepare for a research after a fail high, each time with a wider window
849 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
852 } // End of fail high loop
854 // Finished searching the move. If AbortSearch is true, the search
855 // was aborted because the user interrupted the search or because we
856 // ran out of time. In this case, the return value of the search cannot
857 // be trusted, and we break out of the loop without updating the best
862 // Remember searched nodes counts for this move
863 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
865 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
866 assert(value < beta);
868 // Step 17. Check for new best move
869 if (value <= alpha && i >= MultiPV)
870 rml.set_move_score(i, -VALUE_INFINITE);
873 // PV move or new best move!
876 rml.set_move_score(i, value);
878 extract_pv_from_tt(pos, move, pv);
879 rml.set_move_pv(i, pv);
883 // We record how often the best move has been changed in each
884 // iteration. This information is used for time managment: When
885 // the best move changes frequently, we allocate some more time.
887 BestMoveChangesByIteration[Iteration]++;
889 // Print information to the standard output
890 print_pv_info(pos, pv, alpha, beta, value);
892 // Raise alpha to setup proper non-pv search upper bound
899 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
901 cout << "info multipv " << j + 1
902 << " score " << value_to_uci(rml.move_score(j))
903 << " depth " << (j <= i ? Iteration : Iteration - 1)
904 << " time " << current_search_time()
905 << " nodes " << pos.nodes_searched()
906 << " nps " << nps(pos)
909 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
910 cout << rml.move_pv(j, k) << " ";
914 alpha = rml.move_score(Min(i, MultiPV - 1));
916 } // PV move or new best move
918 assert(alpha >= *alphaPtr);
920 AspirationFailLow = (alpha == *alphaPtr);
922 if (AspirationFailLow && StopOnPonderhit)
923 StopOnPonderhit = false;
926 // Can we exit fail low loop ?
927 if (AbortSearch || !AspirationFailLow)
930 // Prepare for a research after a fail low, each time with a wider window
931 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
936 // Sort the moves before to return
943 // search<>() is the main search function for both PV and non-PV nodes and for
944 // normal and SplitPoint nodes. When called just after a split point the search
945 // is simpler because we have already probed the hash table, done a null move
946 // search, and searched the first move before splitting, we don't have to repeat
947 // all this work again. We also don't need to store anything to the hash table
948 // here: This is taken care of after we return from the split point.
950 template <NodeType PvNode, bool SpNode>
951 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
953 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
954 assert(beta > alpha && beta <= VALUE_INFINITE);
955 assert(PvNode || alpha == beta - 1);
956 assert(ply > 0 && ply < PLY_MAX);
957 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
959 Move movesSearched[MOVES_MAX];
963 Move ttMove, move, excludedMove, threatMove;
966 Value bestValue, value, oldAlpha;
967 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
968 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
969 bool mateThreat = false;
971 int threadID = pos.thread();
972 SplitPoint* sp = NULL;
973 refinedValue = bestValue = value = -VALUE_INFINITE;
975 isCheck = pos.is_check();
981 ttMove = excludedMove = MOVE_NONE;
982 threatMove = sp->threatMove;
983 mateThreat = sp->mateThreat;
984 goto split_point_start;
985 } else {} // Hack to fix icc's "statement is unreachable" warning
987 // Step 1. Initialize node and poll. Polling can abort search
988 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
989 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
991 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
997 // Step 2. Check for aborted search and immediate draw
998 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
999 || pos.is_draw() || ply >= PLY_MAX - 1)
1002 // Step 3. Mate distance pruning
1003 alpha = Max(value_mated_in(ply), alpha);
1004 beta = Min(value_mate_in(ply+1), beta);
1008 // Step 4. Transposition table lookup
1010 // We don't want the score of a partial search to overwrite a previous full search
1011 // TT value, so we use a different position key in case of an excluded move exists.
1012 excludedMove = ss->excludedMove;
1013 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1015 tte = TT.retrieve(posKey);
1016 ttMove = tte ? tte->move() : MOVE_NONE;
1018 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1019 // This is to avoid problems in the following areas:
1021 // * Repetition draw detection
1022 // * Fifty move rule detection
1023 // * Searching for a mate
1024 // * Printing of full PV line
1025 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1028 ss->bestMove = ttMove; // Can be MOVE_NONE
1029 return value_from_tt(tte->value(), ply);
1032 // Step 5. Evaluate the position statically and
1033 // update gain statistics of parent move.
1035 ss->eval = ss->evalMargin = VALUE_NONE;
1038 assert(tte->static_value() != VALUE_NONE);
1040 ss->eval = tte->static_value();
1041 ss->evalMargin = tte->static_value_margin();
1042 refinedValue = refine_eval(tte, ss->eval, ply);
1046 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1047 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1050 // Save gain for the parent non-capture move
1051 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1053 // Step 6. Razoring (is omitted in PV nodes)
1055 && depth < RazorDepth
1057 && refinedValue < beta - razor_margin(depth)
1058 && ttMove == MOVE_NONE
1059 && (ss-1)->currentMove != MOVE_NULL
1060 && !value_is_mate(beta)
1061 && !pos.has_pawn_on_7th(pos.side_to_move()))
1063 Value rbeta = beta - razor_margin(depth);
1064 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1066 // Logically we should return (v + razor_margin(depth)), but
1067 // surprisingly this did slightly weaker in tests.
1071 // Step 7. Static null move pruning (is omitted in PV nodes)
1072 // We're betting that the opponent doesn't have a move that will reduce
1073 // the score by more than futility_margin(depth) if we do a null move.
1075 && !ss->skipNullMove
1076 && depth < RazorDepth
1078 && refinedValue >= beta + futility_margin(depth, 0)
1079 && !value_is_mate(beta)
1080 && pos.non_pawn_material(pos.side_to_move()))
1081 return refinedValue - futility_margin(depth, 0);
1083 // Step 8. Null move search with verification search (is omitted in PV nodes)
1085 && !ss->skipNullMove
1088 && refinedValue >= beta
1089 && !value_is_mate(beta)
1090 && pos.non_pawn_material(pos.side_to_move()))
1092 ss->currentMove = MOVE_NULL;
1094 // Null move dynamic reduction based on depth
1095 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1097 // Null move dynamic reduction based on value
1098 if (refinedValue - beta > PawnValueMidgame)
1101 pos.do_null_move(st);
1102 (ss+1)->skipNullMove = true;
1103 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1104 (ss+1)->skipNullMove = false;
1105 pos.undo_null_move();
1107 if (nullValue >= beta)
1109 // Do not return unproven mate scores
1110 if (nullValue >= value_mate_in(PLY_MAX))
1113 if (depth < 6 * ONE_PLY)
1116 // Do verification search at high depths
1117 ss->skipNullMove = true;
1118 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1119 ss->skipNullMove = false;
1126 // The null move failed low, which means that we may be faced with
1127 // some kind of threat. If the previous move was reduced, check if
1128 // the move that refuted the null move was somehow connected to the
1129 // move which was reduced. If a connection is found, return a fail
1130 // low score (which will cause the reduced move to fail high in the
1131 // parent node, which will trigger a re-search with full depth).
1132 if (nullValue == value_mated_in(ply + 2))
1135 threatMove = (ss+1)->bestMove;
1136 if ( depth < ThreatDepth
1137 && (ss-1)->reduction
1138 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1143 // Step 9. Internal iterative deepening
1144 if ( depth >= IIDDepth[PvNode]
1145 && ttMove == MOVE_NONE
1146 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1148 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1150 ss->skipNullMove = true;
1151 search<PvNode>(pos, ss, alpha, beta, d, ply);
1152 ss->skipNullMove = false;
1154 ttMove = ss->bestMove;
1155 tte = TT.retrieve(posKey);
1158 // Expensive mate threat detection (only for PV nodes)
1160 mateThreat = pos.has_mate_threat();
1162 split_point_start: // At split points actual search starts from here
1164 // Initialize a MovePicker object for the current position
1165 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1166 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1167 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1169 ss->bestMove = MOVE_NONE;
1170 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1171 futilityBase = ss->eval + ss->evalMargin;
1172 singularExtensionNode = !SpNode
1173 && depth >= SingularExtensionDepth[PvNode]
1176 && !excludedMove // Do not allow recursive singular extension search
1177 && (tte->type() & VALUE_TYPE_LOWER)
1178 && tte->depth() >= depth - 3 * ONE_PLY;
1181 lock_grab(&(sp->lock));
1182 bestValue = sp->bestValue;
1185 // Step 10. Loop through moves
1186 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1187 while ( bestValue < beta
1188 && (move = mp.get_next_move()) != MOVE_NONE
1189 && !ThreadsMgr.thread_should_stop(threadID))
1191 assert(move_is_ok(move));
1195 moveCount = ++sp->moveCount;
1196 lock_release(&(sp->lock));
1198 else if (move == excludedMove)
1201 movesSearched[moveCount++] = move;
1203 moveIsCheck = pos.move_is_check(move, ci);
1204 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1206 // Step 11. Decide the new search depth
1207 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1209 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1210 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1211 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1212 // lower then ttValue minus a margin then we extend ttMove.
1213 if ( singularExtensionNode
1214 && move == tte->move()
1217 Value ttValue = value_from_tt(tte->value(), ply);
1219 if (abs(ttValue) < VALUE_KNOWN_WIN)
1221 Value b = ttValue - SingularExtensionMargin;
1222 ss->excludedMove = move;
1223 ss->skipNullMove = true;
1224 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1225 ss->skipNullMove = false;
1226 ss->excludedMove = MOVE_NONE;
1227 ss->bestMove = MOVE_NONE;
1233 // Update current move (this must be done after singular extension search)
1234 ss->currentMove = move;
1235 newDepth = depth - ONE_PLY + ext;
1237 // Step 12. Futility pruning (is omitted in PV nodes)
1239 && !captureOrPromotion
1243 && !move_is_castle(move))
1245 // Move count based pruning
1246 if ( moveCount >= futility_move_count(depth)
1247 && !(threatMove && connected_threat(pos, move, threatMove))
1248 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1251 lock_grab(&(sp->lock));
1256 // Value based pruning
1257 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1258 // but fixing this made program slightly weaker.
1259 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1260 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1261 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1263 if (futilityValueScaled < beta)
1267 lock_grab(&(sp->lock));
1268 if (futilityValueScaled > sp->bestValue)
1269 sp->bestValue = bestValue = futilityValueScaled;
1271 else if (futilityValueScaled > bestValue)
1272 bestValue = futilityValueScaled;
1278 // Step 13. Make the move
1279 pos.do_move(move, st, ci, moveIsCheck);
1281 // Step extra. pv search (only in PV nodes)
1282 // The first move in list is the expected PV
1283 if (!SpNode && PvNode && moveCount == 1)
1284 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1287 // Step 14. Reduced depth search
1288 // If the move fails high will be re-searched at full depth.
1289 bool doFullDepthSearch = true;
1291 if ( depth >= 3 * ONE_PLY
1292 && !captureOrPromotion
1294 && !move_is_castle(move)
1295 && !(ss->killers[0] == move || ss->killers[1] == move))
1297 ss->reduction = reduction<PvNode>(depth, moveCount);
1300 alpha = SpNode ? sp->alpha : alpha;
1301 Depth d = newDepth - ss->reduction;
1302 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1304 doFullDepthSearch = (value > alpha);
1307 // The move failed high, but if reduction is very big we could
1308 // face a false positive, retry with a less aggressive reduction,
1309 // if the move fails high again then go with full depth search.
1310 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1312 assert(newDepth - ONE_PLY >= ONE_PLY);
1314 ss->reduction = ONE_PLY;
1315 alpha = SpNode ? sp->alpha : alpha;
1316 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1317 doFullDepthSearch = (value > alpha);
1319 ss->reduction = DEPTH_ZERO; // Restore original reduction
1322 // Step 15. Full depth search
1323 if (doFullDepthSearch)
1325 alpha = SpNode ? sp->alpha : alpha;
1326 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1328 // Step extra. pv search (only in PV nodes)
1329 // Search only for possible new PV nodes, if instead value >= beta then
1330 // parent node fails low with value <= alpha and tries another move.
1331 if (PvNode && value > alpha && value < beta)
1332 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1336 // Step 16. Undo move
1337 pos.undo_move(move);
1339 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1341 // Step 17. Check for new best move
1344 lock_grab(&(sp->lock));
1345 bestValue = sp->bestValue;
1349 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1354 sp->bestValue = value;
1358 if (SpNode && (!PvNode || value >= beta))
1359 sp->stopRequest = true;
1361 if (PvNode && value < beta) // We want always alpha < beta
1368 if (value == value_mate_in(ply + 1))
1369 ss->mateKiller = move;
1371 ss->bestMove = move;
1374 sp->parentSstack->bestMove = move;
1378 // Step 18. Check for split
1380 && depth >= MinimumSplitDepth
1381 && ThreadsMgr.active_threads() > 1
1383 && ThreadsMgr.available_thread_exists(threadID)
1385 && !ThreadsMgr.thread_should_stop(threadID)
1387 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1388 threatMove, mateThreat, moveCount, &mp, PvNode);
1391 // Step 19. Check for mate and stalemate
1392 // All legal moves have been searched and if there are
1393 // no legal moves, it must be mate or stalemate.
1394 // If one move was excluded return fail low score.
1395 if (!SpNode && !moveCount)
1396 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1398 // Step 20. Update tables
1399 // If the search is not aborted, update the transposition table,
1400 // history counters, and killer moves.
1401 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1403 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1404 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1405 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1407 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1409 // Update killers and history only for non capture moves that fails high
1410 if ( bestValue >= beta
1411 && !pos.move_is_capture_or_promotion(move))
1413 update_history(pos, move, depth, movesSearched, moveCount);
1414 update_killers(move, ss);
1420 // Here we have the lock still grabbed
1421 sp->slaves[threadID] = 0;
1422 sp->nodes += pos.nodes_searched();
1423 lock_release(&(sp->lock));
1426 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1432 // qsearch() is the quiescence search function, which is called by the main
1433 // search function when the remaining depth is zero (or, to be more precise,
1434 // less than ONE_PLY).
1436 template <NodeType PvNode>
1437 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1439 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1440 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1441 assert(PvNode || alpha == beta - 1);
1443 assert(ply > 0 && ply < PLY_MAX);
1444 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1448 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1449 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1451 Value oldAlpha = alpha;
1453 ss->bestMove = ss->currentMove = MOVE_NONE;
1455 // Check for an instant draw or maximum ply reached
1456 if (pos.is_draw() || ply >= PLY_MAX - 1)
1459 // Transposition table lookup. At PV nodes, we don't use the TT for
1460 // pruning, but only for move ordering.
1461 tte = TT.retrieve(pos.get_key());
1462 ttMove = (tte ? tte->move() : MOVE_NONE);
1464 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1466 ss->bestMove = ttMove; // Can be MOVE_NONE
1467 return value_from_tt(tte->value(), ply);
1470 isCheck = pos.is_check();
1472 // Evaluate the position statically
1475 bestValue = futilityBase = -VALUE_INFINITE;
1476 ss->eval = evalMargin = VALUE_NONE;
1477 deepChecks = enoughMaterial = false;
1483 assert(tte->static_value() != VALUE_NONE);
1485 evalMargin = tte->static_value_margin();
1486 ss->eval = bestValue = tte->static_value();
1489 ss->eval = bestValue = evaluate(pos, evalMargin);
1491 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1493 // Stand pat. Return immediately if static value is at least beta
1494 if (bestValue >= beta)
1497 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1502 if (PvNode && bestValue > alpha)
1505 // If we are near beta then try to get a cutoff pushing checks a bit further
1506 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1508 // Futility pruning parameters, not needed when in check
1509 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1510 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1513 // Initialize a MovePicker object for the current position, and prepare
1514 // to search the moves. Because the depth is <= 0 here, only captures,
1515 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1516 // and we are near beta) will be generated.
1517 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1520 // Loop through the moves until no moves remain or a beta cutoff occurs
1521 while ( alpha < beta
1522 && (move = mp.get_next_move()) != MOVE_NONE)
1524 assert(move_is_ok(move));
1526 moveIsCheck = pos.move_is_check(move, ci);
1534 && !move_is_promotion(move)
1535 && !pos.move_is_passed_pawn_push(move))
1537 futilityValue = futilityBase
1538 + pos.endgame_value_of_piece_on(move_to(move))
1539 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1541 if (futilityValue < alpha)
1543 if (futilityValue > bestValue)
1544 bestValue = futilityValue;
1549 // Detect non-capture evasions that are candidate to be pruned
1550 evasionPrunable = isCheck
1551 && bestValue > value_mated_in(PLY_MAX)
1552 && !pos.move_is_capture(move)
1553 && !pos.can_castle(pos.side_to_move());
1555 // Don't search moves with negative SEE values
1557 && (!isCheck || evasionPrunable)
1559 && !move_is_promotion(move)
1560 && pos.see_sign(move) < 0)
1563 // Update current move
1564 ss->currentMove = move;
1566 // Make and search the move
1567 pos.do_move(move, st, ci, moveIsCheck);
1568 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1569 pos.undo_move(move);
1571 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1574 if (value > bestValue)
1580 ss->bestMove = move;
1585 // All legal moves have been searched. A special case: If we're in check
1586 // and no legal moves were found, it is checkmate.
1587 if (isCheck && bestValue == -VALUE_INFINITE)
1588 return value_mated_in(ply);
1590 // Update transposition table
1591 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1592 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1593 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1595 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1601 // connected_moves() tests whether two moves are 'connected' in the sense
1602 // that the first move somehow made the second move possible (for instance
1603 // if the moving piece is the same in both moves). The first move is assumed
1604 // to be the move that was made to reach the current position, while the
1605 // second move is assumed to be a move from the current position.
1607 bool connected_moves(const Position& pos, Move m1, Move m2) {
1609 Square f1, t1, f2, t2;
1612 assert(move_is_ok(m1));
1613 assert(move_is_ok(m2));
1615 if (m2 == MOVE_NONE)
1618 // Case 1: The moving piece is the same in both moves
1624 // Case 2: The destination square for m2 was vacated by m1
1630 // Case 3: Moving through the vacated square
1631 if ( piece_is_slider(pos.piece_on(f2))
1632 && bit_is_set(squares_between(f2, t2), f1))
1635 // Case 4: The destination square for m2 is defended by the moving piece in m1
1636 p = pos.piece_on(t1);
1637 if (bit_is_set(pos.attacks_from(p, t1), t2))
1640 // Case 5: Discovered check, checking piece is the piece moved in m1
1641 if ( piece_is_slider(p)
1642 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1643 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1645 // discovered_check_candidates() works also if the Position's side to
1646 // move is the opposite of the checking piece.
1647 Color them = opposite_color(pos.side_to_move());
1648 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1650 if (bit_is_set(dcCandidates, f2))
1657 // value_is_mate() checks if the given value is a mate one eventually
1658 // compensated for the ply.
1660 bool value_is_mate(Value value) {
1662 assert(abs(value) <= VALUE_INFINITE);
1664 return value <= value_mated_in(PLY_MAX)
1665 || value >= value_mate_in(PLY_MAX);
1669 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1670 // "plies to mate from the current ply". Non-mate scores are unchanged.
1671 // The function is called before storing a value to the transposition table.
1673 Value value_to_tt(Value v, int ply) {
1675 if (v >= value_mate_in(PLY_MAX))
1678 if (v <= value_mated_in(PLY_MAX))
1685 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1686 // the transposition table to a mate score corrected for the current ply.
1688 Value value_from_tt(Value v, int ply) {
1690 if (v >= value_mate_in(PLY_MAX))
1693 if (v <= value_mated_in(PLY_MAX))
1700 // extension() decides whether a move should be searched with normal depth,
1701 // or with extended depth. Certain classes of moves (checking moves, in
1702 // particular) are searched with bigger depth than ordinary moves and in
1703 // any case are marked as 'dangerous'. Note that also if a move is not
1704 // extended, as example because the corresponding UCI option is set to zero,
1705 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1706 template <NodeType PvNode>
1707 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1708 bool singleEvasion, bool mateThreat, bool* dangerous) {
1710 assert(m != MOVE_NONE);
1712 Depth result = DEPTH_ZERO;
1713 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1717 if (moveIsCheck && pos.see_sign(m) >= 0)
1718 result += CheckExtension[PvNode];
1721 result += SingleEvasionExtension[PvNode];
1724 result += MateThreatExtension[PvNode];
1727 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1729 Color c = pos.side_to_move();
1730 if (relative_rank(c, move_to(m)) == RANK_7)
1732 result += PawnPushTo7thExtension[PvNode];
1735 if (pos.pawn_is_passed(c, move_to(m)))
1737 result += PassedPawnExtension[PvNode];
1742 if ( captureOrPromotion
1743 && pos.type_of_piece_on(move_to(m)) != PAWN
1744 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1745 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1746 && !move_is_promotion(m)
1749 result += PawnEndgameExtension[PvNode];
1754 && captureOrPromotion
1755 && pos.type_of_piece_on(move_to(m)) != PAWN
1756 && pos.see_sign(m) >= 0)
1758 result += ONE_PLY / 2;
1762 return Min(result, ONE_PLY);
1766 // connected_threat() tests whether it is safe to forward prune a move or if
1767 // is somehow coonected to the threat move returned by null search.
1769 bool connected_threat(const Position& pos, Move m, Move threat) {
1771 assert(move_is_ok(m));
1772 assert(threat && move_is_ok(threat));
1773 assert(!pos.move_is_check(m));
1774 assert(!pos.move_is_capture_or_promotion(m));
1775 assert(!pos.move_is_passed_pawn_push(m));
1777 Square mfrom, mto, tfrom, tto;
1779 mfrom = move_from(m);
1781 tfrom = move_from(threat);
1782 tto = move_to(threat);
1784 // Case 1: Don't prune moves which move the threatened piece
1788 // Case 2: If the threatened piece has value less than or equal to the
1789 // value of the threatening piece, don't prune move which defend it.
1790 if ( pos.move_is_capture(threat)
1791 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1792 || pos.type_of_piece_on(tfrom) == KING)
1793 && pos.move_attacks_square(m, tto))
1796 // Case 3: If the moving piece in the threatened move is a slider, don't
1797 // prune safe moves which block its ray.
1798 if ( piece_is_slider(pos.piece_on(tfrom))
1799 && bit_is_set(squares_between(tfrom, tto), mto)
1800 && pos.see_sign(m) >= 0)
1807 // ok_to_use_TT() returns true if a transposition table score
1808 // can be used at a given point in search.
1810 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1812 Value v = value_from_tt(tte->value(), ply);
1814 return ( tte->depth() >= depth
1815 || v >= Max(value_mate_in(PLY_MAX), beta)
1816 || v < Min(value_mated_in(PLY_MAX), beta))
1818 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1819 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1823 // refine_eval() returns the transposition table score if
1824 // possible otherwise falls back on static position evaluation.
1826 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1830 Value v = value_from_tt(tte->value(), ply);
1832 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1833 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1840 // update_history() registers a good move that produced a beta-cutoff
1841 // in history and marks as failures all the other moves of that ply.
1843 void update_history(const Position& pos, Move move, Depth depth,
1844 Move movesSearched[], int moveCount) {
1847 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1849 for (int i = 0; i < moveCount - 1; i++)
1851 m = movesSearched[i];
1855 if (!pos.move_is_capture_or_promotion(m))
1856 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1861 // update_killers() add a good move that produced a beta-cutoff
1862 // among the killer moves of that ply.
1864 void update_killers(Move m, SearchStack* ss) {
1866 if (m == ss->killers[0])
1869 ss->killers[1] = ss->killers[0];
1874 // update_gains() updates the gains table of a non-capture move given
1875 // the static position evaluation before and after the move.
1877 void update_gains(const Position& pos, Move m, Value before, Value after) {
1880 && before != VALUE_NONE
1881 && after != VALUE_NONE
1882 && pos.captured_piece_type() == PIECE_TYPE_NONE
1883 && !move_is_special(m))
1884 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1888 // current_search_time() returns the number of milliseconds which have passed
1889 // since the beginning of the current search.
1891 int current_search_time() {
1893 return get_system_time() - SearchStartTime;
1897 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1899 std::string value_to_uci(Value v) {
1901 std::stringstream s;
1903 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1904 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1906 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1911 // nps() computes the current nodes/second count.
1913 int nps(const Position& pos) {
1915 int t = current_search_time();
1916 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1920 // poll() performs two different functions: It polls for user input, and it
1921 // looks at the time consumed so far and decides if it's time to abort the
1924 void poll(const Position& pos) {
1926 static int lastInfoTime;
1927 int t = current_search_time();
1932 // We are line oriented, don't read single chars
1933 std::string command;
1935 if (!std::getline(std::cin, command))
1938 if (command == "quit")
1941 PonderSearch = false;
1945 else if (command == "stop")
1948 PonderSearch = false;
1950 else if (command == "ponderhit")
1954 // Print search information
1958 else if (lastInfoTime > t)
1959 // HACK: Must be a new search where we searched less than
1960 // NodesBetweenPolls nodes during the first second of search.
1963 else if (t - lastInfoTime >= 1000)
1970 if (dbg_show_hit_rate)
1971 dbg_print_hit_rate();
1973 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1974 << " time " << t << endl;
1977 // Should we stop the search?
1981 bool stillAtFirstMove = FirstRootMove
1982 && !AspirationFailLow
1983 && t > TimeMgr.available_time();
1985 bool noMoreTime = t > TimeMgr.maximum_time()
1986 || stillAtFirstMove;
1988 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1989 || (ExactMaxTime && t >= ExactMaxTime)
1990 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
1995 // ponderhit() is called when the program is pondering (i.e. thinking while
1996 // it's the opponent's turn to move) in order to let the engine know that
1997 // it correctly predicted the opponent's move.
2001 int t = current_search_time();
2002 PonderSearch = false;
2004 bool stillAtFirstMove = FirstRootMove
2005 && !AspirationFailLow
2006 && t > TimeMgr.available_time();
2008 bool noMoreTime = t > TimeMgr.maximum_time()
2009 || stillAtFirstMove;
2011 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2016 // init_ss_array() does a fast reset of the first entries of a SearchStack
2017 // array and of all the excludedMove and skipNullMove entries.
2019 void init_ss_array(SearchStack* ss, int size) {
2021 for (int i = 0; i < size; i++, ss++)
2023 ss->excludedMove = MOVE_NONE;
2024 ss->skipNullMove = false;
2025 ss->reduction = DEPTH_ZERO;
2029 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2034 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2035 // while the program is pondering. The point is to work around a wrinkle in
2036 // the UCI protocol: When pondering, the engine is not allowed to give a
2037 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2038 // We simply wait here until one of these commands is sent, and return,
2039 // after which the bestmove and pondermove will be printed (in id_loop()).
2041 void wait_for_stop_or_ponderhit() {
2043 std::string command;
2047 if (!std::getline(std::cin, command))
2050 if (command == "quit")
2055 else if (command == "ponderhit" || command == "stop")
2061 // print_pv_info() prints to standard output and eventually to log file information on
2062 // the current PV line. It is called at each iteration or after a new pv is found.
2064 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2066 cout << "info depth " << Iteration
2067 << " score " << value_to_uci(value)
2068 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2069 << " time " << current_search_time()
2070 << " nodes " << pos.nodes_searched()
2071 << " nps " << nps(pos)
2074 for (Move* m = pv; *m != MOVE_NONE; m++)
2081 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2082 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2084 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2089 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2090 // the PV back into the TT. This makes sure the old PV moves are searched
2091 // first, even if the old TT entries have been overwritten.
2093 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2097 Position p(pos, pos.thread());
2098 Value v, m = VALUE_NONE;
2100 for (int i = 0; pv[i] != MOVE_NONE; i++)
2102 tte = TT.retrieve(p.get_key());
2103 if (!tte || tte->move() != pv[i])
2105 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2106 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2108 p.do_move(pv[i], st);
2113 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2114 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2115 // allow to always have a ponder move even when we fail high at root and also a
2116 // long PV to print that is important for position analysis.
2118 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2122 Position p(pos, pos.thread());
2125 assert(bestMove != MOVE_NONE);
2128 p.do_move(pv[ply++], st);
2130 while ( (tte = TT.retrieve(p.get_key())) != NULL
2131 && tte->move() != MOVE_NONE
2132 && move_is_legal(p, tte->move())
2134 && (!p.is_draw() || ply < 2))
2136 pv[ply] = tte->move();
2137 p.do_move(pv[ply++], st);
2139 pv[ply] = MOVE_NONE;
2143 // init_thread() is the function which is called when a new thread is
2144 // launched. It simply calls the idle_loop() function with the supplied
2145 // threadID. There are two versions of this function; one for POSIX
2146 // threads and one for Windows threads.
2148 #if !defined(_MSC_VER)
2150 void* init_thread(void* threadID) {
2152 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2158 DWORD WINAPI init_thread(LPVOID threadID) {
2160 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2167 /// The ThreadsManager class
2170 // idle_loop() is where the threads are parked when they have no work to do.
2171 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2172 // object for which the current thread is the master.
2174 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2176 assert(threadID >= 0 && threadID < MAX_THREADS);
2180 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2181 // master should exit as last one.
2182 if (AllThreadsShouldExit)
2185 threads[threadID].state = THREAD_TERMINATED;
2189 // If we are not thinking, wait for a condition to be signaled
2190 // instead of wasting CPU time polling for work.
2191 while ( threadID >= ActiveThreads
2192 || threads[threadID].state == THREAD_INITIALIZING
2193 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2196 assert(threadID != 0);
2198 if (AllThreadsShouldExit)
2203 // Retest condition under lock protection
2204 if (!( threadID >= ActiveThreads
2205 || threads[threadID].state == THREAD_INITIALIZING
2206 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2208 lock_release(&MPLock);
2212 // Put thread to sleep
2213 threads[threadID].state = THREAD_AVAILABLE;
2214 cond_wait(&WaitCond[threadID], &MPLock);
2215 lock_release(&MPLock);
2218 // If this thread has been assigned work, launch a search
2219 if (threads[threadID].state == THREAD_WORKISWAITING)
2221 assert(!AllThreadsShouldExit);
2223 threads[threadID].state = THREAD_SEARCHING;
2225 // Here we call search() with SplitPoint template parameter set to true
2226 SplitPoint* tsp = threads[threadID].splitPoint;
2227 Position pos(*tsp->pos, threadID);
2228 SearchStack* ss = tsp->sstack[threadID] + 1;
2232 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2234 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2236 assert(threads[threadID].state == THREAD_SEARCHING);
2238 threads[threadID].state = THREAD_AVAILABLE;
2241 // If this thread is the master of a split point and all slaves have
2242 // finished their work at this split point, return from the idle loop.
2244 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2246 if (i == ActiveThreads)
2248 // Because sp->slaves[] is reset under lock protection,
2249 // be sure sp->lock has been released before to return.
2250 lock_grab(&(sp->lock));
2251 lock_release(&(sp->lock));
2253 // In helpful master concept a master can help only a sub-tree, and
2254 // because here is all finished is not possible master is booked.
2255 assert(threads[threadID].state == THREAD_AVAILABLE);
2257 threads[threadID].state = THREAD_SEARCHING;
2264 // init_threads() is called during startup. It launches all helper threads,
2265 // and initializes the split point stack and the global locks and condition
2268 void ThreadsManager::init_threads() {
2270 int i, arg[MAX_THREADS];
2273 // Initialize global locks
2276 for (i = 0; i < MAX_THREADS; i++)
2277 cond_init(&WaitCond[i]);
2279 // Initialize splitPoints[] locks
2280 for (i = 0; i < MAX_THREADS; i++)
2281 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2282 lock_init(&(threads[i].splitPoints[j].lock));
2284 // Will be set just before program exits to properly end the threads
2285 AllThreadsShouldExit = false;
2287 // Threads will be put all threads to sleep as soon as created
2290 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2291 threads[0].state = THREAD_SEARCHING;
2292 for (i = 1; i < MAX_THREADS; i++)
2293 threads[i].state = THREAD_INITIALIZING;
2295 // Launch the helper threads
2296 for (i = 1; i < MAX_THREADS; i++)
2300 #if !defined(_MSC_VER)
2301 pthread_t pthread[1];
2302 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2303 pthread_detach(pthread[0]);
2305 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2309 cout << "Failed to create thread number " << i << endl;
2310 Application::exit_with_failure();
2313 // Wait until the thread has finished launching and is gone to sleep
2314 while (threads[i].state == THREAD_INITIALIZING) {}
2319 // exit_threads() is called when the program exits. It makes all the
2320 // helper threads exit cleanly.
2322 void ThreadsManager::exit_threads() {
2324 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2326 // Wake up all the threads and waits for termination
2327 for (int i = 1; i < MAX_THREADS; i++)
2329 wake_sleeping_thread(i);
2330 while (threads[i].state != THREAD_TERMINATED) {}
2333 // Now we can safely destroy the locks
2334 for (int i = 0; i < MAX_THREADS; i++)
2335 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2336 lock_destroy(&(threads[i].splitPoints[j].lock));
2338 lock_destroy(&MPLock);
2340 // Now we can safely destroy the wait conditions
2341 for (int i = 0; i < MAX_THREADS; i++)
2342 cond_destroy(&WaitCond[i]);
2346 // thread_should_stop() checks whether the thread should stop its search.
2347 // This can happen if a beta cutoff has occurred in the thread's currently
2348 // active split point, or in some ancestor of the current split point.
2350 bool ThreadsManager::thread_should_stop(int threadID) const {
2352 assert(threadID >= 0 && threadID < ActiveThreads);
2354 SplitPoint* sp = threads[threadID].splitPoint;
2356 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2361 // thread_is_available() checks whether the thread with threadID "slave" is
2362 // available to help the thread with threadID "master" at a split point. An
2363 // obvious requirement is that "slave" must be idle. With more than two
2364 // threads, this is not by itself sufficient: If "slave" is the master of
2365 // some active split point, it is only available as a slave to the other
2366 // threads which are busy searching the split point at the top of "slave"'s
2367 // split point stack (the "helpful master concept" in YBWC terminology).
2369 bool ThreadsManager::thread_is_available(int slave, int master) const {
2371 assert(slave >= 0 && slave < ActiveThreads);
2372 assert(master >= 0 && master < ActiveThreads);
2373 assert(ActiveThreads > 1);
2375 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2378 // Make a local copy to be sure doesn't change under our feet
2379 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2381 // No active split points means that the thread is available as
2382 // a slave for any other thread.
2383 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2386 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2387 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2388 // could have been set to 0 by another thread leading to an out of bound access.
2389 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2396 // available_thread_exists() tries to find an idle thread which is available as
2397 // a slave for the thread with threadID "master".
2399 bool ThreadsManager::available_thread_exists(int master) const {
2401 assert(master >= 0 && master < ActiveThreads);
2402 assert(ActiveThreads > 1);
2404 for (int i = 0; i < ActiveThreads; i++)
2405 if (thread_is_available(i, master))
2412 // split() does the actual work of distributing the work at a node between
2413 // several available threads. If it does not succeed in splitting the
2414 // node (because no idle threads are available, or because we have no unused
2415 // split point objects), the function immediately returns. If splitting is
2416 // possible, a SplitPoint object is initialized with all the data that must be
2417 // copied to the helper threads and we tell our helper threads that they have
2418 // been assigned work. This will cause them to instantly leave their idle loops and
2419 // call search().When all threads have returned from search() then split() returns.
2421 template <bool Fake>
2422 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2423 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2424 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2425 assert(pos.is_ok());
2426 assert(ply > 0 && ply < PLY_MAX);
2427 assert(*bestValue >= -VALUE_INFINITE);
2428 assert(*bestValue <= *alpha);
2429 assert(*alpha < beta);
2430 assert(beta <= VALUE_INFINITE);
2431 assert(depth > DEPTH_ZERO);
2432 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2433 assert(ActiveThreads > 1);
2435 int i, master = pos.thread();
2436 Thread& masterThread = threads[master];
2440 // If no other thread is available to help us, or if we have too many
2441 // active split points, don't split.
2442 if ( !available_thread_exists(master)
2443 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2445 lock_release(&MPLock);
2449 // Pick the next available split point object from the split point stack
2450 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2452 // Initialize the split point object
2453 splitPoint.parent = masterThread.splitPoint;
2454 splitPoint.stopRequest = false;
2455 splitPoint.ply = ply;
2456 splitPoint.depth = depth;
2457 splitPoint.threatMove = threatMove;
2458 splitPoint.mateThreat = mateThreat;
2459 splitPoint.alpha = *alpha;
2460 splitPoint.beta = beta;
2461 splitPoint.pvNode = pvNode;
2462 splitPoint.bestValue = *bestValue;
2464 splitPoint.moveCount = moveCount;
2465 splitPoint.pos = &pos;
2466 splitPoint.nodes = 0;
2467 splitPoint.parentSstack = ss;
2468 for (i = 0; i < ActiveThreads; i++)
2469 splitPoint.slaves[i] = 0;
2471 masterThread.splitPoint = &splitPoint;
2473 // If we are here it means we are not available
2474 assert(masterThread.state != THREAD_AVAILABLE);
2476 int workersCnt = 1; // At least the master is included
2478 // Allocate available threads setting state to THREAD_BOOKED
2479 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2480 if (thread_is_available(i, master))
2482 threads[i].state = THREAD_BOOKED;
2483 threads[i].splitPoint = &splitPoint;
2484 splitPoint.slaves[i] = 1;
2488 assert(Fake || workersCnt > 1);
2490 // We can release the lock because slave threads are already booked and master is not available
2491 lock_release(&MPLock);
2493 // Tell the threads that they have work to do. This will make them leave
2494 // their idle loop. But before copy search stack tail for each thread.
2495 for (i = 0; i < ActiveThreads; i++)
2496 if (i == master || splitPoint.slaves[i])
2498 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2500 assert(i == master || threads[i].state == THREAD_BOOKED);
2502 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2504 wake_sleeping_thread(i);
2507 // Everything is set up. The master thread enters the idle loop, from
2508 // which it will instantly launch a search, because its state is
2509 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2510 // idle loop, which means that the main thread will return from the idle
2511 // loop when all threads have finished their work at this split point.
2512 idle_loop(master, &splitPoint);
2514 // We have returned from the idle loop, which means that all threads are
2515 // finished. Update alpha and bestValue, and return.
2518 *alpha = splitPoint.alpha;
2519 *bestValue = splitPoint.bestValue;
2520 masterThread.activeSplitPoints--;
2521 masterThread.splitPoint = splitPoint.parent;
2522 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2524 lock_release(&MPLock);
2528 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2529 // to start a new search from the root.
2531 void ThreadsManager::wake_sleeping_thread(int threadID) {
2534 cond_signal(&WaitCond[threadID]);
2535 lock_release(&MPLock);
2539 /// The RootMoveList class
2541 // RootMoveList c'tor
2543 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2545 SearchStack ss[PLY_MAX_PLUS_2];
2546 MoveStack mlist[MOVES_MAX];
2548 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2550 // Initialize search stack
2551 init_ss_array(ss, PLY_MAX_PLUS_2);
2552 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2555 // Generate all legal moves
2556 MoveStack* last = generate_moves(pos, mlist);
2558 // Add each move to the moves[] array
2559 for (MoveStack* cur = mlist; cur != last; cur++)
2561 bool includeMove = includeAllMoves;
2563 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2564 includeMove = (searchMoves[k] == cur->move);
2569 // Find a quick score for the move
2570 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2571 moves[count].pv[1] = MOVE_NONE;
2572 pos.do_move(cur->move, st);
2573 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2574 pos.undo_move(cur->move);
2580 // Score root moves using the standard way used in main search, the moves
2581 // are scored according to the order in which are returned by MovePicker.
2583 void RootMoveList::score_moves(const Position& pos)
2587 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2589 while ((move = mp.get_next_move()) != MOVE_NONE)
2590 for (int i = 0; i < count; i++)
2591 if (moves[i].move == move)
2593 moves[i].mp_score = score--;
2598 // RootMoveList simple methods definitions
2600 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2604 for (j = 0; pv[j] != MOVE_NONE; j++)
2605 moves[moveNum].pv[j] = pv[j];
2607 moves[moveNum].pv[j] = MOVE_NONE;
2611 // RootMoveList::sort() sorts the root move list at the beginning of a new
2614 void RootMoveList::sort() {
2616 sort_multipv(count - 1); // Sort all items
2620 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2621 // list by their scores and depths. It is used to order the different PVs
2622 // correctly in MultiPV mode.
2624 void RootMoveList::sort_multipv(int n) {
2628 for (i = 1; i <= n; i++)
2630 RootMove rm = moves[i];
2631 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2632 moves[j] = moves[j - 1];