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/>.
43 #include "ucioption.h"
49 //// Local definitions
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
107 // FIXME: document me
115 // RootMove struct is used for moves at the root at the tree. For each
116 // root move, we store a score, a node count, and a PV (really a refutation
117 // in the case of moves which fail low).
121 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
123 // RootMove::operator<() is the comparison function used when
124 // sorting the moves. A move m1 is considered to be better
125 // than a move m2 if it has a higher score, or if the moves
126 // have equal score but m1 has the higher node count.
127 bool operator<(const RootMove& m) const {
129 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
134 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
135 Move pv[PLY_MAX_PLUS_2];
139 // The RootMoveList class is essentially an array of RootMove objects, with
140 // a handful of methods for accessing the data in the individual moves.
145 RootMoveList(Position& pos, Move searchMoves[]);
147 int move_count() const { return count; }
148 Move get_move(int moveNum) const { return moves[moveNum].move; }
149 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
150 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
151 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
152 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
154 void set_move_nodes(int moveNum, int64_t nodes);
155 void set_beta_counters(int moveNum, int64_t our, int64_t their);
156 void set_move_pv(int moveNum, const Move pv[]);
158 void sort_multipv(int n);
161 static const int MaxRootMoves = 500;
162 RootMove moves[MaxRootMoves];
171 // Maximum depth for razoring
172 const Depth RazorDepth = 4 * OnePly;
174 // Dynamic razoring margin based on depth
175 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
177 // Step 8. Null move search with verification search
179 // Null move margin. A null move search will not be done if the static
180 // evaluation of the position is more than NullMoveMargin below beta.
181 const Value NullMoveMargin = Value(0x200);
183 // Maximum depth for use of dynamic threat detection when null move fails low
184 const Depth ThreatDepth = 5 * OnePly;
186 // Step 9. Internal iterative deepening
188 // Minimum depth for use of internal iterative deepening
189 const Depth IIDDepthAtPVNodes = 5 * OnePly;
190 const Depth IIDDepthAtNonPVNodes = 8 * OnePly;
192 // At Non-PV nodes we do an internal iterative deepening search
193 // when the static evaluation is at most IIDMargin below beta.
194 const Value IIDMargin = Value(0x100);
196 // Step 11. Decide the new search depth
198 // Extensions. Configurable UCI options
199 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
200 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
201 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
203 // Minimum depth for use of singular extension
204 const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly;
205 const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
207 // If the TT move is at least SingularExtensionMargin better then the
208 // remaining ones we will extend it.
209 const Value SingularExtensionMargin = Value(0x20);
211 // Step 12. Futility pruning
213 // Futility margin for quiescence search
214 const Value FutilityMarginQS = Value(0x80);
216 // Futility lookup tables (initialized at startup) and their getter functions
217 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
218 int FutilityMoveCountArray[32]; // [depth]
220 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
221 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
223 // Step 14. Reduced search
225 // Reduction lookup tables (initialized at startup) and their getter functions
226 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
227 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
229 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
230 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
232 // Common adjustments
234 // Search depth at iteration 1
235 const Depth InitialDepth = OnePly;
237 // Easy move margin. An easy move candidate must be at least this much
238 // better than the second best move.
239 const Value EasyMoveMargin = Value(0x200);
241 // Last seconds noise filtering (LSN)
242 const bool UseLSNFiltering = true;
243 const int LSNTime = 4000; // In milliseconds
244 const Value LSNValue = value_from_centipawns(200);
245 bool loseOnTime = false;
253 // Scores and number of times the best move changed for each iteration
254 Value ValueByIteration[PLY_MAX_PLUS_2];
255 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
257 // Search window management
263 // Time managment variables
264 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
265 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
266 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
267 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
271 std::ofstream LogFile;
273 // Multi-threads related variables
274 Depth MinimumSplitDepth;
275 int MaxThreadsPerSplitPoint;
278 // Node counters, used only by thread[0] but try to keep in different cache
279 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
281 int NodesBetweenPolls = 30000;
288 Value id_loop(const Position& pos, Move searchMoves[]);
289 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
290 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
291 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, NullStatus nullStatus, int threadID, Move excludedMove = MOVE_NONE);
292 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
293 void sp_search(SplitPoint* sp, int threadID);
294 void sp_search_pv(SplitPoint* sp, int threadID);
295 void init_node(SearchStack ss[], int ply, int threadID);
296 void update_pv(SearchStack ss[], int ply);
297 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 bool move_is_killer(Move m, const SearchStack& ss);
301 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
302 bool ok_to_do_nullmove(const Position& pos);
303 bool ok_to_prune(const Position& pos, Move m, Move threat);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove);
305 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
306 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
307 void update_killers(Move m, SearchStack& ss);
308 void update_gains(const Position& pos, Move move, Value before, Value after);
310 int current_search_time();
314 void wait_for_stop_or_ponderhit();
315 void init_ss_array(SearchStack ss[]);
316 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
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() { TM.init_threads(); }
335 void exit_threads() { TM.exit_threads(); }
336 int64_t nodes_searched() { return TM.nodes_searched(); }
339 /// perft() is our utility to verify move generation is bug free. All the legal
340 /// moves up to given depth are generated and counted and the sum returned.
342 int perft(Position& pos, Depth depth)
347 MovePicker mp(pos, MOVE_NONE, depth, H);
349 // If we are at the last ply we don't need to do and undo
350 // the moves, just to count them.
351 if (depth <= OnePly) // Replace with '<' to test also qsearch
353 while (mp.get_next_move()) sum++;
357 // Loop through all legal moves
359 while ((move = mp.get_next_move()) != MOVE_NONE)
361 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
362 sum += perft(pos, depth - OnePly);
369 /// think() is the external interface to Stockfish's search, and is called when
370 /// the program receives the UCI 'go' command. It initializes various
371 /// search-related global variables, and calls root_search(). It returns false
372 /// when a quit command is received during the search.
374 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
375 int time[], int increment[], int movesToGo, int maxDepth,
376 int maxNodes, int maxTime, Move searchMoves[]) {
378 // Initialize global search variables
379 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
380 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
382 TM.resetNodeCounters();
383 SearchStartTime = get_system_time();
384 ExactMaxTime = maxTime;
387 InfiniteSearch = infinite;
388 PonderSearch = ponder;
389 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
391 // Look for a book move, only during games, not tests
392 if (UseTimeManagement && get_option_value_bool("OwnBook"))
394 if (get_option_value_string("Book File") != OpeningBook.file_name())
395 OpeningBook.open(get_option_value_string("Book File"));
397 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
398 if (bookMove != MOVE_NONE)
401 wait_for_stop_or_ponderhit();
403 cout << "bestmove " << bookMove << endl;
408 // Reset loseOnTime flag at the beginning of a new game
409 if (button_was_pressed("New Game"))
412 // Read UCI option values
413 TT.set_size(get_option_value_int("Hash"));
414 if (button_was_pressed("Clear Hash"))
417 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
418 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
419 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
420 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
421 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
422 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
423 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
424 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
425 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
426 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
427 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
428 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
430 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
431 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
432 MultiPV = get_option_value_int("MultiPV");
433 Chess960 = get_option_value_bool("UCI_Chess960");
434 UseLogFile = get_option_value_bool("Use Search Log");
437 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
439 read_weights(pos.side_to_move());
441 // Set the number of active threads
442 int newActiveThreads = get_option_value_int("Threads");
443 if (newActiveThreads != TM.active_threads())
445 TM.set_active_threads(newActiveThreads);
446 init_eval(TM.active_threads());
449 // Wake up sleeping threads
450 TM.wake_sleeping_threads();
453 int myTime = time[side_to_move];
454 int myIncrement = increment[side_to_move];
455 if (UseTimeManagement)
457 if (!movesToGo) // Sudden death time control
461 MaxSearchTime = myTime / 30 + myIncrement;
462 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
464 else // Blitz game without increment
466 MaxSearchTime = myTime / 30;
467 AbsoluteMaxSearchTime = myTime / 8;
470 else // (x moves) / (y minutes)
474 MaxSearchTime = myTime / 2;
475 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
479 MaxSearchTime = myTime / Min(movesToGo, 20);
480 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
484 if (get_option_value_bool("Ponder"))
486 MaxSearchTime += MaxSearchTime / 4;
487 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
491 // Set best NodesBetweenPolls interval to avoid lagging under
492 // heavy time pressure.
494 NodesBetweenPolls = Min(MaxNodes, 30000);
495 else if (myTime && myTime < 1000)
496 NodesBetweenPolls = 1000;
497 else if (myTime && myTime < 5000)
498 NodesBetweenPolls = 5000;
500 NodesBetweenPolls = 30000;
502 // Write search information to log file
504 LogFile << "Searching: " << pos.to_fen() << endl
505 << "infinite: " << infinite
506 << " ponder: " << ponder
507 << " time: " << myTime
508 << " increment: " << myIncrement
509 << " moves to go: " << movesToGo << endl;
511 // LSN filtering. Used only for developing purposes, disabled by default
515 // Step 2. If after last move we decided to lose on time, do it now!
516 while (SearchStartTime + myTime + 1000 > get_system_time())
520 // We're ready to start thinking. Call the iterative deepening loop function
521 Value v = id_loop(pos, searchMoves);
525 // Step 1. If this is sudden death game and our position is hopeless,
526 // decide to lose on time.
527 if ( !loseOnTime // If we already lost on time, go to step 3.
537 // Step 3. Now after stepping over the time limit, reset flag for next match.
545 TM.put_threads_to_sleep();
551 /// init_search() is called during startup. It initializes various lookup tables
555 // Init our reduction lookup tables
556 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
557 for (int j = 1; j < 64; j++) // j == moveNumber
559 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
560 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
561 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
562 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
565 // Init futility margins array
566 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
567 for (int j = 0; j < 64; j++) // j == moveNumber
569 // FIXME: test using log instead of BSR
570 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
573 // Init futility move count array
574 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
575 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
579 // SearchStack::init() initializes a search stack. Used at the beginning of a
580 // new search from the root.
581 void SearchStack::init(int ply) {
583 pv[ply] = pv[ply + 1] = MOVE_NONE;
584 currentMove = threatMove = MOVE_NONE;
585 reduction = Depth(0);
589 void SearchStack::initKillers() {
591 mateKiller = MOVE_NONE;
592 for (int i = 0; i < KILLER_MAX; i++)
593 killers[i] = MOVE_NONE;
598 // id_loop() is the main iterative deepening loop. It calls root_search
599 // repeatedly with increasing depth until the allocated thinking time has
600 // been consumed, the user stops the search, or the maximum search depth is
603 Value id_loop(const Position& pos, Move searchMoves[]) {
606 SearchStack ss[PLY_MAX_PLUS_2];
607 Move EasyMove = MOVE_NONE;
608 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
610 // Moves to search are verified, copied, scored and sorted
611 RootMoveList rml(p, searchMoves);
613 // Handle special case of searching on a mate/stale position
614 if (rml.move_count() == 0)
617 wait_for_stop_or_ponderhit();
619 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
622 // Print RootMoveList startup scoring to the standard output,
623 // so to output information also for iteration 1.
624 cout << "info depth " << 1
625 << "\ninfo depth " << 1
626 << " score " << value_to_string(rml.get_move_score(0))
627 << " time " << current_search_time()
628 << " nodes " << TM.nodes_searched()
630 << " pv " << rml.get_move(0) << "\n";
636 ValueByIteration[1] = rml.get_move_score(0);
639 // Is one move significantly better than others after initial scoring ?
640 if ( rml.move_count() == 1
641 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
642 EasyMove = rml.get_move(0);
644 // Iterative deepening loop
645 while (Iteration < PLY_MAX)
647 // Initialize iteration
649 BestMoveChangesByIteration[Iteration] = 0;
651 cout << "info depth " << Iteration << endl;
653 // Calculate dynamic aspiration window based on previous iterations
654 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
656 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
657 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
659 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
660 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
662 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
663 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
666 // Search to the current depth, rml is updated and sorted, alpha and beta could change
667 value = root_search(p, ss, rml, &alpha, &beta);
669 // Write PV to transposition table, in case the relevant entries have
670 // been overwritten during the search.
671 TT.insert_pv(p, ss[0].pv);
674 break; // Value cannot be trusted. Break out immediately!
676 //Save info about search result
677 ValueByIteration[Iteration] = value;
679 // Drop the easy move if differs from the new best move
680 if (ss[0].pv[0] != EasyMove)
681 EasyMove = MOVE_NONE;
683 if (UseTimeManagement)
686 bool stopSearch = false;
688 // Stop search early if there is only a single legal move,
689 // we search up to Iteration 6 anyway to get a proper score.
690 if (Iteration >= 6 && rml.move_count() == 1)
693 // Stop search early when the last two iterations returned a mate score
695 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
696 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
699 // Stop search early if one move seems to be much better than the others
700 int64_t nodes = TM.nodes_searched();
702 && EasyMove == ss[0].pv[0]
703 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
704 && current_search_time() > MaxSearchTime / 16)
705 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
706 && current_search_time() > MaxSearchTime / 32)))
709 // Add some extra time if the best move has changed during the last two iterations
710 if (Iteration > 5 && Iteration <= 50)
711 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
712 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
714 // Stop search if most of MaxSearchTime is consumed at the end of the
715 // iteration. We probably don't have enough time to search the first
716 // move at the next iteration anyway.
717 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
723 StopOnPonderhit = true;
729 if (MaxDepth && Iteration >= MaxDepth)
733 // If we are pondering or in infinite search, we shouldn't print the
734 // best move before we are told to do so.
735 if (!AbortSearch && (PonderSearch || InfiniteSearch))
736 wait_for_stop_or_ponderhit();
738 // Print final search statistics
739 cout << "info nodes " << TM.nodes_searched()
741 << " time " << current_search_time()
742 << " hashfull " << TT.full() << endl;
744 // Print the best move and the ponder move to the standard output
745 if (ss[0].pv[0] == MOVE_NONE)
747 ss[0].pv[0] = rml.get_move(0);
748 ss[0].pv[1] = MOVE_NONE;
751 assert(ss[0].pv[0] != MOVE_NONE);
753 cout << "bestmove " << ss[0].pv[0];
755 if (ss[0].pv[1] != MOVE_NONE)
756 cout << " ponder " << ss[0].pv[1];
763 dbg_print_mean(LogFile);
765 if (dbg_show_hit_rate)
766 dbg_print_hit_rate(LogFile);
768 LogFile << "\nNodes: " << TM.nodes_searched()
769 << "\nNodes/second: " << nps()
770 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
773 p.do_move(ss[0].pv[0], st);
774 LogFile << "\nPonder move: "
775 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
778 return rml.get_move_score(0);
782 // root_search() is the function which searches the root node. It is
783 // similar to search_pv except that it uses a different move ordering
784 // scheme, prints some information to the standard output and handles
785 // the fail low/high loops.
787 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
794 Depth depth, ext, newDepth;
795 Value value, alpha, beta;
796 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
797 int researchCountFH, researchCountFL;
799 researchCountFH = researchCountFL = 0;
802 isCheck = pos.is_check();
804 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
805 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
806 // Step 3. Mate distance pruning (omitted at root)
807 // Step 4. Transposition table lookup (omitted at root)
809 // Step 5. Evaluate the position statically
810 // At root we do this only to get reference value for child nodes
812 ss[0].eval = evaluate(pos, ei, 0);
814 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
816 // Step 6. Razoring (omitted at root)
817 // Step 7. Static null move pruning (omitted at root)
818 // Step 8. Null move search with verification search (omitted at root)
819 // Step 9. Internal iterative deepening (omitted at root)
821 // Step extra. Fail low loop
822 // We start with small aspiration window and in case of fail low, we research
823 // with bigger window until we are not failing low anymore.
826 // Sort the moves before to (re)search
829 // Step 10. Loop through all moves in the root move list
830 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
832 // This is used by time management
833 FirstRootMove = (i == 0);
835 // Save the current node count before the move is searched
836 nodes = TM.nodes_searched();
838 // Reset beta cut-off counters
839 TM.resetBetaCounters();
841 // Pick the next root move, and print the move and the move number to
842 // the standard output.
843 move = ss[0].currentMove = rml.get_move(i);
845 if (current_search_time() >= 1000)
846 cout << "info currmove " << move
847 << " currmovenumber " << i + 1 << endl;
849 moveIsCheck = pos.move_is_check(move);
850 captureOrPromotion = pos.move_is_capture_or_promotion(move);
852 // Step 11. Decide the new search depth
853 depth = (Iteration - 2) * OnePly + InitialDepth;
854 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
855 newDepth = depth + ext;
857 // Step 12. Futility pruning (omitted at root)
859 // Step extra. Fail high loop
860 // If move fails high, we research with bigger window until we are not failing
862 value = - VALUE_INFINITE;
866 // Step 13. Make the move
867 pos.do_move(move, st, ci, moveIsCheck);
869 // Step extra. pv search
870 // We do pv search for first moves (i < MultiPV)
871 // and for fail high research (value > alpha)
872 if (i < MultiPV || value > alpha)
874 // Aspiration window is disabled in multi-pv case
876 alpha = -VALUE_INFINITE;
878 // Full depth PV search, done on first move or after a fail high
879 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
883 // Step 14. Reduced search
884 // if the move fails high will be re-searched at full depth
885 bool doFullDepthSearch = true;
887 if ( depth >= 3 * OnePly
889 && !captureOrPromotion
890 && !move_is_castle(move))
892 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
895 // Reduced depth non-pv search using alpha as upperbound
896 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, ALLOW_NULLMOVE, 0);
897 doFullDepthSearch = (value > alpha);
901 // Step 15. Full depth search
902 if (doFullDepthSearch)
904 // Full depth non-pv search using alpha as upperbound
905 ss[0].reduction = Depth(0);
906 value = -search(pos, ss, -alpha, newDepth, 1, ALLOW_NULLMOVE, 0);
908 // If we are above alpha then research at same depth but as PV
909 // to get a correct score or eventually a fail high above beta.
911 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
915 // Step 16. Undo move
918 // Can we exit fail high loop ?
919 if (AbortSearch || value < beta)
922 // We are failing high and going to do a research. It's important to update
923 // the score before research in case we run out of time while researching.
924 rml.set_move_score(i, value);
926 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
927 rml.set_move_pv(i, ss[0].pv);
929 // Print information to the standard output
930 print_pv_info(pos, ss, alpha, beta, value);
932 // Prepare for a research after a fail high, each time with a wider window
933 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
936 } // End of fail high loop
938 // Finished searching the move. If AbortSearch is true, the search
939 // was aborted because the user interrupted the search or because we
940 // ran out of time. In this case, the return value of the search cannot
941 // be trusted, and we break out of the loop without updating the best
946 // Remember beta-cutoff and searched nodes counts for this move. The
947 // info is used to sort the root moves for the next iteration.
949 TM.get_beta_counters(pos.side_to_move(), our, their);
950 rml.set_beta_counters(i, our, their);
951 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
953 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
954 assert(value < beta);
956 // Step 17. Check for new best move
957 if (value <= alpha && i >= MultiPV)
958 rml.set_move_score(i, -VALUE_INFINITE);
961 // PV move or new best move!
964 rml.set_move_score(i, value);
966 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
967 rml.set_move_pv(i, ss[0].pv);
971 // We record how often the best move has been changed in each
972 // iteration. This information is used for time managment: When
973 // the best move changes frequently, we allocate some more time.
975 BestMoveChangesByIteration[Iteration]++;
977 // Print information to the standard output
978 print_pv_info(pos, ss, alpha, beta, value);
980 // Raise alpha to setup proper non-pv search upper bound
987 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
989 cout << "info multipv " << j + 1
990 << " score " << value_to_string(rml.get_move_score(j))
991 << " depth " << (j <= i ? Iteration : Iteration - 1)
992 << " time " << current_search_time()
993 << " nodes " << TM.nodes_searched()
997 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
998 cout << rml.get_move_pv(j, k) << " ";
1002 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1004 } // PV move or new best move
1006 assert(alpha >= *alphaPtr);
1008 AspirationFailLow = (alpha == *alphaPtr);
1010 if (AspirationFailLow && StopOnPonderhit)
1011 StopOnPonderhit = false;
1014 // Can we exit fail low loop ?
1015 if (AbortSearch || !AspirationFailLow)
1018 // Prepare for a research after a fail low, each time with a wider window
1019 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1024 // Sort the moves before to return
1031 // search_pv() is the main search function for PV nodes.
1033 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1034 Depth depth, int ply, int threadID) {
1036 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1037 assert(beta > alpha && beta <= VALUE_INFINITE);
1038 assert(ply >= 0 && ply < PLY_MAX);
1039 assert(threadID >= 0 && threadID < TM.active_threads());
1041 Move movesSearched[256];
1046 Depth ext, newDepth;
1047 Value bestValue, value, oldAlpha;
1048 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1049 bool mateThreat = false;
1051 bestValue = value = -VALUE_INFINITE;
1054 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1056 // Step 1. Initialize node and poll
1057 // Polling can abort search.
1058 init_node(ss, ply, threadID);
1060 // Step 2. Check for aborted search and immediate draw
1061 if (AbortSearch || TM.thread_should_stop(threadID))
1064 if (pos.is_draw() || ply >= PLY_MAX - 1)
1067 // Step 3. Mate distance pruning
1069 alpha = Max(value_mated_in(ply), alpha);
1070 beta = Min(value_mate_in(ply+1), beta);
1074 // Step 4. Transposition table lookup
1075 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1076 // This is to avoid problems in the following areas:
1078 // * Repetition draw detection
1079 // * Fifty move rule detection
1080 // * Searching for a mate
1081 // * Printing of full PV line
1082 tte = TT.retrieve(pos.get_key());
1083 ttMove = (tte ? tte->move() : MOVE_NONE);
1085 // Step 5. Evaluate the position statically
1086 // At PV nodes we do this only to update gain statistics
1087 isCheck = pos.is_check();
1090 ss[ply].eval = evaluate(pos, ei, threadID);
1091 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1094 // Step 6. Razoring (is omitted in PV nodes)
1095 // Step 7. Static null move pruning (is omitted in PV nodes)
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1098 // Step 9. Internal iterative deepening
1099 if ( depth >= IIDDepthAtPVNodes
1100 && ttMove == MOVE_NONE)
1102 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1103 ttMove = ss[ply].pv[ply];
1104 tte = TT.retrieve(pos.get_key());
1107 // Initialize a MovePicker object for the current position
1108 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1109 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1112 // Step 10. Loop through moves
1113 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1114 while ( alpha < beta
1115 && (move = mp.get_next_move()) != MOVE_NONE
1116 && !TM.thread_should_stop(threadID))
1118 assert(move_is_ok(move));
1120 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1121 moveIsCheck = pos.move_is_check(move, ci);
1122 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1124 // Step 11. Decide the new search depth
1125 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1127 // Singular extension search. We extend the TT move if its value is much better than
1128 // its siblings. To verify this we do a reduced search on all the other moves but the
1129 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1130 if ( depth >= SingularExtensionDepthAtPVNodes
1132 && move == tte->move()
1134 && is_lower_bound(tte->type())
1135 && tte->depth() >= depth - 3 * OnePly)
1137 Value ttValue = value_from_tt(tte->value(), ply);
1139 if (abs(ttValue) < VALUE_KNOWN_WIN)
1141 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, FORBID_NULLMOVE, threadID, move);
1143 if (excValue < ttValue - SingularExtensionMargin)
1148 newDepth = depth - OnePly + ext;
1150 // Update current move (this must be done after singular extension search)
1151 movesSearched[moveCount++] = ss[ply].currentMove = move;
1153 // Step 12. Futility pruning (is omitted in PV nodes)
1155 // Step 13. Make the move
1156 pos.do_move(move, st, ci, moveIsCheck);
1158 // Step extra. pv search (only in PV nodes)
1159 // The first move in list is the expected PV
1161 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1164 // Step 14. Reduced search
1165 // if the move fails high will be re-searched at full depth.
1166 bool doFullDepthSearch = true;
1168 if ( depth >= 3 * OnePly
1170 && !captureOrPromotion
1171 && !move_is_castle(move)
1172 && !move_is_killer(move, ss[ply]))
1174 ss[ply].reduction = pv_reduction(depth, moveCount);
1175 if (ss[ply].reduction)
1177 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, ALLOW_NULLMOVE, threadID);
1178 doFullDepthSearch = (value > alpha);
1182 // Step 15. Full depth search
1183 if (doFullDepthSearch)
1185 ss[ply].reduction = Depth(0);
1186 value = -search(pos, ss, -alpha, newDepth, ply+1, ALLOW_NULLMOVE, threadID);
1188 // Step extra. pv search (only in PV nodes)
1189 if (value > alpha && value < beta)
1190 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1194 // Step 16. Undo move
1195 pos.undo_move(move);
1197 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1199 // Step 17. Check for new best move
1200 if (value > bestValue)
1207 if (value == value_mate_in(ply + 1))
1208 ss[ply].mateKiller = move;
1212 // Step 18. Check for split
1213 if ( TM.active_threads() > 1
1215 && depth >= MinimumSplitDepth
1217 && TM.available_thread_exists(threadID)
1219 && !TM.thread_should_stop(threadID)
1220 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1221 depth, mateThreat, &moveCount, &mp, threadID, true))
1225 // Step 19. Check for mate and stalemate
1226 // All legal moves have been searched and if there were
1227 // no legal moves, it must be mate or stalemate.
1229 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1231 // Step 20. Update tables
1232 // If the search is not aborted, update the transposition table,
1233 // history counters, and killer moves.
1234 if (AbortSearch || TM.thread_should_stop(threadID))
1237 if (bestValue <= oldAlpha)
1238 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1240 else if (bestValue >= beta)
1242 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1243 move = ss[ply].pv[ply];
1244 if (!pos.move_is_capture_or_promotion(move))
1246 update_history(pos, move, depth, movesSearched, moveCount);
1247 update_killers(move, ss[ply]);
1249 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1252 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1258 // search() is the search function for zero-width nodes.
1260 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1261 int ply, NullStatus nullStatus, int threadID, Move excludedMove) {
1263 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1264 assert(ply >= 0 && ply < PLY_MAX);
1265 assert(threadID >= 0 && threadID < TM.active_threads());
1267 Move movesSearched[256];
1272 Depth ext, newDepth;
1273 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1274 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1275 bool mateThreat = false;
1277 refinedValue = bestValue = value = -VALUE_INFINITE;
1280 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1282 // Step 1. Initialize node and poll
1283 // Polling can abort search.
1284 init_node(ss, ply, threadID);
1286 // Step 2. Check for aborted search and immediate draw
1287 if (AbortSearch || TM.thread_should_stop(threadID))
1290 if (pos.is_draw() || ply >= PLY_MAX - 1)
1293 // Step 3. Mate distance pruning
1294 if (value_mated_in(ply) >= beta)
1297 if (value_mate_in(ply + 1) < beta)
1300 // Step 4. Transposition table lookup
1302 // We don't want the score of a partial search to overwrite a previous full search
1303 // TT value, so we use a different position key in case of an excluded move exists.
1304 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1306 tte = TT.retrieve(posKey);
1307 ttMove = (tte ? tte->move() : MOVE_NONE);
1309 if (tte && ok_to_use_TT(tte, depth, beta, ply, nullStatus != VERIFY_NULLMOVE))
1311 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1312 return value_from_tt(tte->value(), ply);
1315 // Step 5. Evaluate the position statically
1316 isCheck = pos.is_check();
1320 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1321 ss[ply].eval = value_from_tt(tte->value(), ply);
1323 ss[ply].eval = evaluate(pos, ei, threadID);
1325 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1326 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1330 if ( refinedValue < beta - razor_margin(depth)
1331 && ttMove == MOVE_NONE
1332 && ss[ply - 1].currentMove != MOVE_NULL
1333 && depth < RazorDepth
1335 && !value_is_mate(beta)
1336 && !pos.has_pawn_on_7th(pos.side_to_move()))
1338 Value rbeta = beta - razor_margin(depth);
1339 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1341 // Logically we should return (v + razor_margin(depth)), but
1342 // surprisingly this did slightly weaker in tests.
1346 // Step 7. Static null move pruning
1347 // We're betting that the opponent doesn't have a move that will reduce
1348 // the score by more than futility_margin(depth) if we do a null move.
1349 if ( nullStatus == ALLOW_NULLMOVE
1350 && depth < RazorDepth
1352 && !value_is_mate(beta)
1353 && ok_to_do_nullmove(pos)
1354 && refinedValue >= beta + futility_margin(depth, 0))
1355 return refinedValue - futility_margin(depth, 0);
1357 // Step 8. Null move search with verification search
1358 // When we jump directly to qsearch() we do a null move only if static value is
1359 // at least beta. Otherwise we do a null move if static value is not more than
1360 // NullMoveMargin under beta.
1361 if ( nullStatus == ALLOW_NULLMOVE
1364 && !value_is_mate(beta)
1365 && ok_to_do_nullmove(pos)
1366 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1368 ss[ply].currentMove = MOVE_NULL;
1370 // Null move dynamic reduction based on depth
1371 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1373 // Null move dynamic reduction based on value
1374 if (refinedValue - beta > PawnValueMidgame)
1377 pos.do_null_move(st);
1379 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, FORBID_NULLMOVE, threadID);
1381 pos.undo_null_move();
1383 if (nullValue >= beta)
1385 // Do not return unproven mate scores
1386 if (nullValue >= value_mate_in(PLY_MAX))
1389 // Do zugzwang verification search for high depths, don't store in TT
1390 // if search was stopped.
1391 if ( ( depth < 6 * OnePly
1392 || search(pos, ss, beta, depth-5*OnePly, ply, VERIFY_NULLMOVE, threadID) >= beta)
1394 && !TM.thread_should_stop(threadID))
1396 assert(value_to_tt(nullValue, ply) == nullValue);
1399 TT.store(posKey, nullValue, VALUE_TYPE_NS_LO, depth, MOVE_NONE);
1404 // The null move failed low, which means that we may be faced with
1405 // some kind of threat. If the previous move was reduced, check if
1406 // the move that refuted the null move was somehow connected to the
1407 // move which was reduced. If a connection is found, return a fail
1408 // low score (which will cause the reduced move to fail high in the
1409 // parent node, which will trigger a re-search with full depth).
1410 if (nullValue == value_mated_in(ply + 2))
1413 ss[ply].threatMove = ss[ply + 1].currentMove;
1414 if ( depth < ThreatDepth
1415 && ss[ply - 1].reduction
1416 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1421 // Step 9. Internal iterative deepening
1422 if ( depth >= IIDDepthAtNonPVNodes
1423 && ttMove == MOVE_NONE
1425 && ss[ply].eval >= beta - IIDMargin)
1427 search(pos, ss, beta, depth/2, ply, FORBID_NULLMOVE, threadID);
1428 ttMove = ss[ply].pv[ply];
1429 tte = TT.retrieve(posKey);
1432 // Initialize a MovePicker object for the current position
1433 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1436 // Step 10. Loop through moves
1437 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1438 while ( bestValue < beta
1439 && (move = mp.get_next_move()) != MOVE_NONE
1440 && !TM.thread_should_stop(threadID))
1442 assert(move_is_ok(move));
1444 if (move == excludedMove)
1447 moveIsCheck = pos.move_is_check(move, ci);
1448 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1449 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1451 // Step 11. Decide the new search depth
1452 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1454 // Singular extension search. We extend the TT move if its value is much better than
1455 // its siblings. To verify this we do a reduced search on all the other moves but the
1456 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1457 if ( depth >= SingularExtensionDepthAtNonPVNodes
1459 && move == tte->move()
1460 && !excludedMove // Do not allow recursive singular extension search
1462 && is_lower_bound(tte->type())
1463 && tte->depth() >= depth - 3 * OnePly)
1465 Value ttValue = value_from_tt(tte->value(), ply);
1467 if (abs(ttValue) < VALUE_KNOWN_WIN)
1469 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, FORBID_NULLMOVE, threadID, move);
1471 if (excValue < ttValue - SingularExtensionMargin)
1476 newDepth = depth - OnePly + ext;
1478 // Update current move (this must be done after singular extension search)
1479 movesSearched[moveCount++] = ss[ply].currentMove = move;
1481 // Step 12. Futility pruning
1484 && !captureOrPromotion
1485 && !move_is_castle(move)
1488 // Move count based pruning
1489 if ( moveCount >= futility_move_count(depth)
1490 && ok_to_prune(pos, move, ss[ply].threatMove)
1491 && bestValue > value_mated_in(PLY_MAX))
1494 // Value based pruning
1495 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1496 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1497 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1499 if (futilityValueScaled < beta)
1501 if (futilityValueScaled > bestValue)
1502 bestValue = futilityValueScaled;
1507 // Step 13. Make the move
1508 pos.do_move(move, st, ci, moveIsCheck);
1510 // Step 14. Reduced search, if the move fails high
1511 // will be re-searched at full depth.
1512 bool doFullDepthSearch = true;
1514 if ( depth >= 3*OnePly
1516 && !captureOrPromotion
1517 && !move_is_castle(move)
1518 && !move_is_killer(move, ss[ply]))
1520 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1521 if (ss[ply].reduction)
1523 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, ALLOW_NULLMOVE, threadID);
1524 doFullDepthSearch = (value >= beta);
1528 // Step 15. Full depth search
1529 if (doFullDepthSearch)
1531 ss[ply].reduction = Depth(0);
1532 value = -search(pos, ss, -(beta-1), newDepth, ply+1, ALLOW_NULLMOVE, threadID);
1535 // Step 16. Undo move
1536 pos.undo_move(move);
1538 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1540 // Step 17. Check for new best move
1541 if (value > bestValue)
1547 if (value == value_mate_in(ply + 1))
1548 ss[ply].mateKiller = move;
1551 // Step 18. Check for split
1552 if ( TM.active_threads() > 1
1554 && depth >= MinimumSplitDepth
1556 && TM.available_thread_exists(threadID)
1558 && !TM.thread_should_stop(threadID)
1559 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1560 depth, mateThreat, &moveCount, &mp, threadID, false))
1564 // Step 19. Check for mate and stalemate
1565 // All legal moves have been searched and if there are
1566 // no legal moves, it must be mate or stalemate.
1567 // If one move was excluded return fail low score.
1569 return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1571 // Step 20. Update tables
1572 // If the search is not aborted, update the transposition table,
1573 // history counters, and killer moves.
1574 if (AbortSearch || TM.thread_should_stop(threadID))
1577 if (bestValue < beta)
1578 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1581 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1582 move = ss[ply].pv[ply];
1583 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1584 if (!pos.move_is_capture_or_promotion(move))
1586 update_history(pos, move, depth, movesSearched, moveCount);
1587 update_killers(move, ss[ply]);
1592 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1598 // qsearch() is the quiescence search function, which is called by the main
1599 // search function when the remaining depth is zero (or, to be more precise,
1600 // less than OnePly).
1602 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1603 Depth depth, int ply, int threadID) {
1605 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1606 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1608 assert(ply >= 0 && ply < PLY_MAX);
1609 assert(threadID >= 0 && threadID < TM.active_threads());
1614 Value staticValue, bestValue, value, futilityBase, futilityValue;
1615 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1616 const TTEntry* tte = NULL;
1618 bool pvNode = (beta - alpha != 1);
1619 Value oldAlpha = alpha;
1621 // Initialize, and make an early exit in case of an aborted search,
1622 // an instant draw, maximum ply reached, etc.
1623 init_node(ss, ply, threadID);
1625 // After init_node() that calls poll()
1626 if (AbortSearch || TM.thread_should_stop(threadID))
1629 if (pos.is_draw() || ply >= PLY_MAX - 1)
1632 // Transposition table lookup. At PV nodes, we don't use the TT for
1633 // pruning, but only for move ordering.
1634 tte = TT.retrieve(pos.get_key());
1635 ttMove = (tte ? tte->move() : MOVE_NONE);
1637 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply, true))
1639 assert(tte->type() != VALUE_TYPE_EVAL);
1641 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1642 return value_from_tt(tte->value(), ply);
1645 isCheck = pos.is_check();
1647 // Evaluate the position statically
1649 staticValue = -VALUE_INFINITE;
1650 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1651 staticValue = value_from_tt(tte->value(), ply);
1653 staticValue = evaluate(pos, ei, threadID);
1657 ss[ply].eval = staticValue;
1658 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1661 // Initialize "stand pat score", and return it immediately if it is
1663 bestValue = staticValue;
1665 if (bestValue >= beta)
1667 // Store the score to avoid a future costly evaluation() call
1668 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1669 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1674 if (bestValue > alpha)
1677 // If we are near beta then try to get a cutoff pushing checks a bit further
1678 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1680 // Initialize a MovePicker object for the current position, and prepare
1681 // to search the moves. Because the depth is <= 0 here, only captures,
1682 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1683 // and we are near beta) will be generated.
1684 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1686 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1687 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1689 // Loop through the moves until no moves remain or a beta cutoff occurs
1690 while ( alpha < beta
1691 && (move = mp.get_next_move()) != MOVE_NONE)
1693 assert(move_is_ok(move));
1695 moveIsCheck = pos.move_is_check(move, ci);
1697 // Update current move
1699 ss[ply].currentMove = move;
1707 && !move_is_promotion(move)
1708 && !pos.move_is_passed_pawn_push(move))
1710 futilityValue = futilityBase
1711 + pos.endgame_value_of_piece_on(move_to(move))
1712 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1714 if (futilityValue < alpha)
1716 if (futilityValue > bestValue)
1717 bestValue = futilityValue;
1722 // Detect blocking evasions that are candidate to be pruned
1723 evasionPrunable = isCheck
1724 && bestValue > value_mated_in(PLY_MAX)
1725 && !pos.move_is_capture(move)
1726 && pos.type_of_piece_on(move_from(move)) != KING
1727 && !pos.can_castle(pos.side_to_move());
1729 // Don't search moves with negative SEE values
1730 if ( (!isCheck || evasionPrunable)
1733 && !move_is_promotion(move)
1734 && pos.see_sign(move) < 0)
1737 // Make and search the move
1738 pos.do_move(move, st, ci, moveIsCheck);
1739 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1740 pos.undo_move(move);
1742 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1745 if (value > bestValue)
1756 // All legal moves have been searched. A special case: If we're in check
1757 // and no legal moves were found, it is checkmate.
1758 if (!moveCount && isCheck) // Mate!
1759 return value_mated_in(ply);
1761 // Update transposition table
1762 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1763 if (bestValue <= oldAlpha)
1765 // If bestValue isn't changed it means it is still the static evaluation
1766 // of the node, so keep this info to avoid a future evaluation() call.
1767 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1768 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1770 else if (bestValue >= beta)
1772 move = ss[ply].pv[ply];
1773 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1775 // Update killers only for good checking moves
1776 if (!pos.move_is_capture_or_promotion(move))
1777 update_killers(move, ss[ply]);
1780 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1782 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1788 // sp_search() is used to search from a split point. This function is called
1789 // by each thread working at the split point. It is similar to the normal
1790 // search() function, but simpler. Because we have already probed the hash
1791 // table, done a null move search, and searched the first move before
1792 // splitting, we don't have to repeat all this work in sp_search(). We
1793 // also don't need to store anything to the hash table here: This is taken
1794 // care of after we return from the split point.
1796 void sp_search(SplitPoint* sp, int threadID) {
1798 assert(threadID >= 0 && threadID < TM.active_threads());
1799 assert(TM.active_threads() > 1);
1803 Depth ext, newDepth;
1804 Value value, futilityValueScaled;
1805 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1807 value = -VALUE_INFINITE;
1809 Position pos(*sp->pos);
1811 SearchStack* ss = sp->sstack[threadID];
1812 isCheck = pos.is_check();
1814 // Step 10. Loop through moves
1815 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1816 lock_grab(&(sp->lock));
1818 while ( sp->bestValue < sp->beta
1819 && !TM.thread_should_stop(threadID)
1820 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1822 moveCount = ++sp->moves;
1823 lock_release(&(sp->lock));
1825 assert(move_is_ok(move));
1827 moveIsCheck = pos.move_is_check(move, ci);
1828 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1830 // Step 11. Decide the new search depth
1831 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1832 newDepth = sp->depth - OnePly + ext;
1834 // Update current move
1835 ss[sp->ply].currentMove = move;
1837 // Step 12. Futility pruning
1840 && !captureOrPromotion
1841 && !move_is_castle(move))
1843 // Move count based pruning
1844 if ( moveCount >= futility_move_count(sp->depth)
1845 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1846 && sp->bestValue > value_mated_in(PLY_MAX))
1848 lock_grab(&(sp->lock));
1852 // Value based pruning
1853 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1854 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1855 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1857 if (futilityValueScaled < sp->beta)
1859 lock_grab(&(sp->lock));
1861 if (futilityValueScaled > sp->bestValue)
1862 sp->bestValue = futilityValueScaled;
1867 // Step 13. Make the move
1868 pos.do_move(move, st, ci, moveIsCheck);
1870 // Step 14. Reduced search
1871 // if the move fails high will be re-searched at full depth.
1872 bool doFullDepthSearch = true;
1875 && !captureOrPromotion
1876 && !move_is_castle(move)
1877 && !move_is_killer(move, ss[sp->ply]))
1879 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1880 if (ss[sp->ply].reduction)
1882 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, ALLOW_NULLMOVE, threadID);
1883 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1887 // Step 15. Full depth search
1888 if (doFullDepthSearch)
1890 ss[sp->ply].reduction = Depth(0);
1891 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, ALLOW_NULLMOVE, threadID);
1894 // Step 16. Undo move
1895 pos.undo_move(move);
1897 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1899 // Step 17. Check for new best move
1900 lock_grab(&(sp->lock));
1902 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1904 sp->bestValue = value;
1905 if (sp->bestValue >= sp->beta)
1907 sp->stopRequest = true;
1908 sp_update_pv(sp->parentSstack, ss, sp->ply);
1913 /* Here we have the lock still grabbed */
1915 sp->slaves[threadID] = 0;
1918 lock_release(&(sp->lock));
1922 // sp_search_pv() is used to search from a PV split point. This function
1923 // is called by each thread working at the split point. It is similar to
1924 // the normal search_pv() function, but simpler. Because we have already
1925 // probed the hash table and searched the first move before splitting, we
1926 // don't have to repeat all this work in sp_search_pv(). We also don't
1927 // need to store anything to the hash table here: This is taken care of
1928 // after we return from the split point.
1930 void sp_search_pv(SplitPoint* sp, int threadID) {
1932 assert(threadID >= 0 && threadID < TM.active_threads());
1933 assert(TM.active_threads() > 1);
1937 Depth ext, newDepth;
1939 bool moveIsCheck, captureOrPromotion, dangerous;
1941 value = -VALUE_INFINITE;
1943 Position pos(*sp->pos);
1945 SearchStack* ss = sp->sstack[threadID];
1947 // Step 10. Loop through moves
1948 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1949 lock_grab(&(sp->lock));
1951 while ( sp->alpha < sp->beta
1952 && !TM.thread_should_stop(threadID)
1953 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1955 moveCount = ++sp->moves;
1956 lock_release(&(sp->lock));
1958 assert(move_is_ok(move));
1960 moveIsCheck = pos.move_is_check(move, ci);
1961 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1963 // Step 11. Decide the new search depth
1964 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1965 newDepth = sp->depth - OnePly + ext;
1967 // Update current move
1968 ss[sp->ply].currentMove = move;
1970 // Step 12. Futility pruning (is omitted in PV nodes)
1972 // Step 13. Make the move
1973 pos.do_move(move, st, ci, moveIsCheck);
1975 // Step 14. Reduced search
1976 // if the move fails high will be re-searched at full depth.
1977 bool doFullDepthSearch = true;
1980 && !captureOrPromotion
1981 && !move_is_castle(move)
1982 && !move_is_killer(move, ss[sp->ply]))
1984 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1985 if (ss[sp->ply].reduction)
1987 Value localAlpha = sp->alpha;
1988 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, ALLOW_NULLMOVE, threadID);
1989 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1993 // Step 15. Full depth search
1994 if (doFullDepthSearch)
1996 Value localAlpha = sp->alpha;
1997 ss[sp->ply].reduction = Depth(0);
1998 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, ALLOW_NULLMOVE, threadID);
2000 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
2002 // If another thread has failed high then sp->alpha has been increased
2003 // to be higher or equal then beta, if so, avoid to start a PV search.
2004 localAlpha = sp->alpha;
2005 if (localAlpha < sp->beta)
2006 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2010 // Step 16. Undo move
2011 pos.undo_move(move);
2013 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2015 // Step 17. Check for new best move
2016 lock_grab(&(sp->lock));
2018 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2020 sp->bestValue = value;
2021 if (value > sp->alpha)
2023 // Ask threads to stop before to modify sp->alpha
2024 if (value >= sp->beta)
2025 sp->stopRequest = true;
2029 sp_update_pv(sp->parentSstack, ss, sp->ply);
2030 if (value == value_mate_in(sp->ply + 1))
2031 ss[sp->ply].mateKiller = move;
2036 /* Here we have the lock still grabbed */
2038 sp->slaves[threadID] = 0;
2041 lock_release(&(sp->lock));
2045 // init_node() is called at the beginning of all the search functions
2046 // (search(), search_pv(), qsearch(), and so on) and initializes the
2047 // search stack object corresponding to the current node. Once every
2048 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2049 // for user input and checks whether it is time to stop the search.
2051 void init_node(SearchStack ss[], int ply, int threadID) {
2053 assert(ply >= 0 && ply < PLY_MAX);
2054 assert(threadID >= 0 && threadID < TM.active_threads());
2056 TM.incrementNodeCounter(threadID);
2061 if (NodesSincePoll >= NodesBetweenPolls)
2068 ss[ply + 2].initKillers();
2072 // update_pv() is called whenever a search returns a value > alpha.
2073 // It updates the PV in the SearchStack object corresponding to the
2076 void update_pv(SearchStack ss[], int ply) {
2078 assert(ply >= 0 && ply < PLY_MAX);
2082 ss[ply].pv[ply] = ss[ply].currentMove;
2084 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2085 ss[ply].pv[p] = ss[ply + 1].pv[p];
2087 ss[ply].pv[p] = MOVE_NONE;
2091 // sp_update_pv() is a variant of update_pv for use at split points. The
2092 // difference between the two functions is that sp_update_pv also updates
2093 // the PV at the parent node.
2095 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2097 assert(ply >= 0 && ply < PLY_MAX);
2101 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2103 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2104 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2106 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2110 // connected_moves() tests whether two moves are 'connected' in the sense
2111 // that the first move somehow made the second move possible (for instance
2112 // if the moving piece is the same in both moves). The first move is assumed
2113 // to be the move that was made to reach the current position, while the
2114 // second move is assumed to be a move from the current position.
2116 bool connected_moves(const Position& pos, Move m1, Move m2) {
2118 Square f1, t1, f2, t2;
2121 assert(move_is_ok(m1));
2122 assert(move_is_ok(m2));
2124 if (m2 == MOVE_NONE)
2127 // Case 1: The moving piece is the same in both moves
2133 // Case 2: The destination square for m2 was vacated by m1
2139 // Case 3: Moving through the vacated square
2140 if ( piece_is_slider(pos.piece_on(f2))
2141 && bit_is_set(squares_between(f2, t2), f1))
2144 // Case 4: The destination square for m2 is defended by the moving piece in m1
2145 p = pos.piece_on(t1);
2146 if (bit_is_set(pos.attacks_from(p, t1), t2))
2149 // Case 5: Discovered check, checking piece is the piece moved in m1
2150 if ( piece_is_slider(p)
2151 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2152 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2154 // discovered_check_candidates() works also if the Position's side to
2155 // move is the opposite of the checking piece.
2156 Color them = opposite_color(pos.side_to_move());
2157 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2159 if (bit_is_set(dcCandidates, f2))
2166 // value_is_mate() checks if the given value is a mate one
2167 // eventually compensated for the ply.
2169 bool value_is_mate(Value value) {
2171 assert(abs(value) <= VALUE_INFINITE);
2173 return value <= value_mated_in(PLY_MAX)
2174 || value >= value_mate_in(PLY_MAX);
2178 // move_is_killer() checks if the given move is among the
2179 // killer moves of that ply.
2181 bool move_is_killer(Move m, const SearchStack& ss) {
2183 const Move* k = ss.killers;
2184 for (int i = 0; i < KILLER_MAX; i++, k++)
2192 // extension() decides whether a move should be searched with normal depth,
2193 // or with extended depth. Certain classes of moves (checking moves, in
2194 // particular) are searched with bigger depth than ordinary moves and in
2195 // any case are marked as 'dangerous'. Note that also if a move is not
2196 // extended, as example because the corresponding UCI option is set to zero,
2197 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2199 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2200 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2202 assert(m != MOVE_NONE);
2204 Depth result = Depth(0);
2205 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2210 result += CheckExtension[pvNode];
2213 result += SingleEvasionExtension[pvNode];
2216 result += MateThreatExtension[pvNode];
2219 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2221 Color c = pos.side_to_move();
2222 if (relative_rank(c, move_to(m)) == RANK_7)
2224 result += PawnPushTo7thExtension[pvNode];
2227 if (pos.pawn_is_passed(c, move_to(m)))
2229 result += PassedPawnExtension[pvNode];
2234 if ( captureOrPromotion
2235 && pos.type_of_piece_on(move_to(m)) != PAWN
2236 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2237 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2238 && !move_is_promotion(m)
2241 result += PawnEndgameExtension[pvNode];
2246 && captureOrPromotion
2247 && pos.type_of_piece_on(move_to(m)) != PAWN
2248 && pos.see_sign(m) >= 0)
2254 return Min(result, OnePly);
2258 // ok_to_do_nullmove() looks at the current position and decides whether
2259 // doing a 'null move' should be allowed. In order to avoid zugzwang
2260 // problems, null moves are not allowed when the side to move has very
2261 // little material left. Currently, the test is a bit too simple: Null
2262 // moves are avoided only when the side to move has only pawns left.
2263 // It's probably a good idea to avoid null moves in at least some more
2264 // complicated endgames, e.g. KQ vs KR. FIXME
2266 bool ok_to_do_nullmove(const Position& pos) {
2268 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2272 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2273 // non-tactical moves late in the move list close to the leaves are
2274 // candidates for pruning.
2276 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2278 assert(move_is_ok(m));
2279 assert(threat == MOVE_NONE || move_is_ok(threat));
2280 assert(!pos.move_is_check(m));
2281 assert(!pos.move_is_capture_or_promotion(m));
2282 assert(!pos.move_is_passed_pawn_push(m));
2284 Square mfrom, mto, tfrom, tto;
2286 // Prune if there isn't any threat move
2287 if (threat == MOVE_NONE)
2290 mfrom = move_from(m);
2292 tfrom = move_from(threat);
2293 tto = move_to(threat);
2295 // Case 1: Don't prune moves which move the threatened piece
2299 // Case 2: If the threatened piece has value less than or equal to the
2300 // value of the threatening piece, don't prune move which defend it.
2301 if ( pos.move_is_capture(threat)
2302 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2303 || pos.type_of_piece_on(tfrom) == KING)
2304 && pos.move_attacks_square(m, tto))
2307 // Case 3: If the moving piece in the threatened move is a slider, don't
2308 // prune safe moves which block its ray.
2309 if ( piece_is_slider(pos.piece_on(tfrom))
2310 && bit_is_set(squares_between(tfrom, tto), mto)
2311 && pos.see_sign(m) >= 0)
2318 // ok_to_use_TT() returns true if a transposition table score can be used at a
2319 // given point in search. To avoid zugzwang issues TT cutoffs at the root node
2320 // of a null move verification search are not allowed if the TT value was found
2321 // by a null search, this is implemented testing allowNullmove and TT entry type.
2323 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove) {
2325 Value v = value_from_tt(tte->value(), ply);
2327 return (allowNullmove || !(tte->type() & VALUE_TYPE_NULL))
2329 && ( tte->depth() >= depth
2330 || v >= Max(value_mate_in(PLY_MAX), beta)
2331 || v < Min(value_mated_in(PLY_MAX), beta))
2333 && ( (is_lower_bound(tte->type()) && v >= beta)
2334 || (is_upper_bound(tte->type()) && v < beta));
2338 // refine_eval() returns the transposition table score if
2339 // possible otherwise falls back on static position evaluation.
2341 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2346 Value v = value_from_tt(tte->value(), ply);
2348 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2349 || (is_upper_bound(tte->type()) && v < defaultEval))
2356 // update_history() registers a good move that produced a beta-cutoff
2357 // in history and marks as failures all the other moves of that ply.
2359 void update_history(const Position& pos, Move move, Depth depth,
2360 Move movesSearched[], int moveCount) {
2364 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2366 for (int i = 0; i < moveCount - 1; i++)
2368 m = movesSearched[i];
2372 if (!pos.move_is_capture_or_promotion(m))
2373 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2378 // update_killers() add a good move that produced a beta-cutoff
2379 // among the killer moves of that ply.
2381 void update_killers(Move m, SearchStack& ss) {
2383 if (m == ss.killers[0])
2386 for (int i = KILLER_MAX - 1; i > 0; i--)
2387 ss.killers[i] = ss.killers[i - 1];
2393 // update_gains() updates the gains table of a non-capture move given
2394 // the static position evaluation before and after the move.
2396 void update_gains(const Position& pos, Move m, Value before, Value after) {
2399 && before != VALUE_NONE
2400 && after != VALUE_NONE
2401 && pos.captured_piece() == NO_PIECE_TYPE
2402 && !move_is_castle(m)
2403 && !move_is_promotion(m))
2404 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2408 // current_search_time() returns the number of milliseconds which have passed
2409 // since the beginning of the current search.
2411 int current_search_time() {
2413 return get_system_time() - SearchStartTime;
2417 // nps() computes the current nodes/second count.
2421 int t = current_search_time();
2422 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2426 // poll() performs two different functions: It polls for user input, and it
2427 // looks at the time consumed so far and decides if it's time to abort the
2432 static int lastInfoTime;
2433 int t = current_search_time();
2438 // We are line oriented, don't read single chars
2439 std::string command;
2441 if (!std::getline(std::cin, command))
2444 if (command == "quit")
2447 PonderSearch = false;
2451 else if (command == "stop")
2454 PonderSearch = false;
2456 else if (command == "ponderhit")
2460 // Print search information
2464 else if (lastInfoTime > t)
2465 // HACK: Must be a new search where we searched less than
2466 // NodesBetweenPolls nodes during the first second of search.
2469 else if (t - lastInfoTime >= 1000)
2476 if (dbg_show_hit_rate)
2477 dbg_print_hit_rate();
2479 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2480 << " time " << t << " hashfull " << TT.full() << endl;
2483 // Should we stop the search?
2487 bool stillAtFirstMove = FirstRootMove
2488 && !AspirationFailLow
2489 && t > MaxSearchTime + ExtraSearchTime;
2491 bool noMoreTime = t > AbsoluteMaxSearchTime
2492 || stillAtFirstMove;
2494 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2495 || (ExactMaxTime && t >= ExactMaxTime)
2496 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2501 // ponderhit() is called when the program is pondering (i.e. thinking while
2502 // it's the opponent's turn to move) in order to let the engine know that
2503 // it correctly predicted the opponent's move.
2507 int t = current_search_time();
2508 PonderSearch = false;
2510 bool stillAtFirstMove = FirstRootMove
2511 && !AspirationFailLow
2512 && t > MaxSearchTime + ExtraSearchTime;
2514 bool noMoreTime = t > AbsoluteMaxSearchTime
2515 || stillAtFirstMove;
2517 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2522 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2524 void init_ss_array(SearchStack ss[]) {
2526 for (int i = 0; i < 3; i++)
2529 ss[i].initKillers();
2534 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2535 // while the program is pondering. The point is to work around a wrinkle in
2536 // the UCI protocol: When pondering, the engine is not allowed to give a
2537 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2538 // We simply wait here until one of these commands is sent, and return,
2539 // after which the bestmove and pondermove will be printed (in id_loop()).
2541 void wait_for_stop_or_ponderhit() {
2543 std::string command;
2547 if (!std::getline(std::cin, command))
2550 if (command == "quit")
2555 else if (command == "ponderhit" || command == "stop")
2561 // print_pv_info() prints to standard output and eventually to log file information on
2562 // the current PV line. It is called at each iteration or after a new pv is found.
2564 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2566 cout << "info depth " << Iteration
2567 << " score " << value_to_string(value)
2568 << ((value >= beta) ? " lowerbound" :
2569 ((value <= alpha)? " upperbound" : ""))
2570 << " time " << current_search_time()
2571 << " nodes " << TM.nodes_searched()
2575 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2576 cout << ss[0].pv[j] << " ";
2582 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2583 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2585 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2586 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2591 // init_thread() is the function which is called when a new thread is
2592 // launched. It simply calls the idle_loop() function with the supplied
2593 // threadID. There are two versions of this function; one for POSIX
2594 // threads and one for Windows threads.
2596 #if !defined(_MSC_VER)
2598 void* init_thread(void *threadID) {
2600 TM.idle_loop(*(int*)threadID, NULL);
2606 DWORD WINAPI init_thread(LPVOID threadID) {
2608 TM.idle_loop(*(int*)threadID, NULL);
2615 /// The ThreadsManager class
2617 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2618 // get_beta_counters() are getters/setters for the per thread
2619 // counters used to sort the moves at root.
2621 void ThreadsManager::resetNodeCounters() {
2623 for (int i = 0; i < MAX_THREADS; i++)
2624 threads[i].nodes = 0ULL;
2627 void ThreadsManager::resetBetaCounters() {
2629 for (int i = 0; i < MAX_THREADS; i++)
2630 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2633 int64_t ThreadsManager::nodes_searched() const {
2635 int64_t result = 0ULL;
2636 for (int i = 0; i < ActiveThreads; i++)
2637 result += threads[i].nodes;
2642 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2645 for (int i = 0; i < MAX_THREADS; i++)
2647 our += threads[i].betaCutOffs[us];
2648 their += threads[i].betaCutOffs[opposite_color(us)];
2653 // idle_loop() is where the threads are parked when they have no work to do.
2654 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2655 // object for which the current thread is the master.
2657 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2659 assert(threadID >= 0 && threadID < MAX_THREADS);
2663 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2664 // master should exit as last one.
2665 if (AllThreadsShouldExit)
2668 threads[threadID].state = THREAD_TERMINATED;
2672 // If we are not thinking, wait for a condition to be signaled
2673 // instead of wasting CPU time polling for work.
2674 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2677 assert(threadID != 0);
2678 threads[threadID].state = THREAD_SLEEPING;
2680 #if !defined(_MSC_VER)
2681 lock_grab(&WaitLock);
2682 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2683 pthread_cond_wait(&WaitCond, &WaitLock);
2684 lock_release(&WaitLock);
2686 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2690 // If thread has just woken up, mark it as available
2691 if (threads[threadID].state == THREAD_SLEEPING)
2692 threads[threadID].state = THREAD_AVAILABLE;
2694 // If this thread has been assigned work, launch a search
2695 if (threads[threadID].state == THREAD_WORKISWAITING)
2697 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2699 threads[threadID].state = THREAD_SEARCHING;
2701 if (threads[threadID].splitPoint->pvNode)
2702 sp_search_pv(threads[threadID].splitPoint, threadID);
2704 sp_search(threads[threadID].splitPoint, threadID);
2706 assert(threads[threadID].state == THREAD_SEARCHING);
2708 threads[threadID].state = THREAD_AVAILABLE;
2711 // If this thread is the master of a split point and all threads have
2712 // finished their work at this split point, return from the idle loop.
2713 if (waitSp != NULL && waitSp->cpus == 0)
2715 assert(threads[threadID].state == THREAD_AVAILABLE);
2717 threads[threadID].state = THREAD_SEARCHING;
2724 // init_threads() is called during startup. It launches all helper threads,
2725 // and initializes the split point stack and the global locks and condition
2728 void ThreadsManager::init_threads() {
2733 #if !defined(_MSC_VER)
2734 pthread_t pthread[1];
2737 // Initialize global locks
2738 lock_init(&MPLock, NULL);
2739 lock_init(&WaitLock, NULL);
2741 #if !defined(_MSC_VER)
2742 pthread_cond_init(&WaitCond, NULL);
2744 for (i = 0; i < MAX_THREADS; i++)
2745 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2748 // Initialize SplitPointStack locks
2749 for (i = 0; i < MAX_THREADS; i++)
2750 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2752 SplitPointStack[i][j].parent = NULL;
2753 lock_init(&(SplitPointStack[i][j].lock), NULL);
2756 // Will be set just before program exits to properly end the threads
2757 AllThreadsShouldExit = false;
2759 // Threads will be put to sleep as soon as created
2760 AllThreadsShouldSleep = true;
2762 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2764 threads[0].state = THREAD_SEARCHING;
2765 for (i = 1; i < MAX_THREADS; i++)
2766 threads[i].state = THREAD_AVAILABLE;
2768 // Launch the helper threads
2769 for (i = 1; i < MAX_THREADS; i++)
2772 #if !defined(_MSC_VER)
2773 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2775 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2780 cout << "Failed to create thread number " << i << endl;
2781 Application::exit_with_failure();
2784 // Wait until the thread has finished launching and is gone to sleep
2785 while (threads[i].state != THREAD_SLEEPING) {}
2790 // exit_threads() is called when the program exits. It makes all the
2791 // helper threads exit cleanly.
2793 void ThreadsManager::exit_threads() {
2795 ActiveThreads = MAX_THREADS; // HACK
2796 AllThreadsShouldSleep = true; // HACK
2797 wake_sleeping_threads();
2799 // This makes the threads to exit idle_loop()
2800 AllThreadsShouldExit = true;
2802 // Wait for thread termination
2803 for (int i = 1; i < MAX_THREADS; i++)
2804 while (threads[i].state != THREAD_TERMINATED);
2806 // Now we can safely destroy the locks
2807 for (int i = 0; i < MAX_THREADS; i++)
2808 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2809 lock_destroy(&(SplitPointStack[i][j].lock));
2811 lock_destroy(&WaitLock);
2812 lock_destroy(&MPLock);
2816 // thread_should_stop() checks whether the thread should stop its search.
2817 // This can happen if a beta cutoff has occurred in the thread's currently
2818 // active split point, or in some ancestor of the current split point.
2820 bool ThreadsManager::thread_should_stop(int threadID) const {
2822 assert(threadID >= 0 && threadID < ActiveThreads);
2826 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2831 // thread_is_available() checks whether the thread with threadID "slave" is
2832 // available to help the thread with threadID "master" at a split point. An
2833 // obvious requirement is that "slave" must be idle. With more than two
2834 // threads, this is not by itself sufficient: If "slave" is the master of
2835 // some active split point, it is only available as a slave to the other
2836 // threads which are busy searching the split point at the top of "slave"'s
2837 // split point stack (the "helpful master concept" in YBWC terminology).
2839 bool ThreadsManager::thread_is_available(int slave, int master) const {
2841 assert(slave >= 0 && slave < ActiveThreads);
2842 assert(master >= 0 && master < ActiveThreads);
2843 assert(ActiveThreads > 1);
2845 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2848 // Make a local copy to be sure doesn't change under our feet
2849 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2851 if (localActiveSplitPoints == 0)
2852 // No active split points means that the thread is available as
2853 // a slave for any other thread.
2856 if (ActiveThreads == 2)
2859 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2860 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2861 // could have been set to 0 by another thread leading to an out of bound access.
2862 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2869 // available_thread_exists() tries to find an idle thread which is available as
2870 // a slave for the thread with threadID "master".
2872 bool ThreadsManager::available_thread_exists(int master) const {
2874 assert(master >= 0 && master < ActiveThreads);
2875 assert(ActiveThreads > 1);
2877 for (int i = 0; i < ActiveThreads; i++)
2878 if (thread_is_available(i, master))
2885 // split() does the actual work of distributing the work at a node between
2886 // several threads at PV nodes. If it does not succeed in splitting the
2887 // node (because no idle threads are available, or because we have no unused
2888 // split point objects), the function immediately returns false. If
2889 // splitting is possible, a SplitPoint object is initialized with all the
2890 // data that must be copied to the helper threads (the current position and
2891 // search stack, alpha, beta, the search depth, etc.), and we tell our
2892 // helper threads that they have been assigned work. This will cause them
2893 // to instantly leave their idle loops and call sp_search_pv(). When all
2894 // threads have returned from sp_search_pv (or, equivalently, when
2895 // splitPoint->cpus becomes 0), split() returns true.
2897 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2898 Value* alpha, const Value beta, Value* bestValue,
2899 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2902 assert(sstck != NULL);
2903 assert(ply >= 0 && ply < PLY_MAX);
2904 assert(*bestValue >= -VALUE_INFINITE);
2905 assert( ( pvNode && *bestValue <= *alpha)
2906 || (!pvNode && *bestValue < beta ));
2907 assert(!pvNode || *alpha < beta);
2908 assert(beta <= VALUE_INFINITE);
2909 assert(depth > Depth(0));
2910 assert(master >= 0 && master < ActiveThreads);
2911 assert(ActiveThreads > 1);
2913 SplitPoint* splitPoint;
2917 // If no other thread is available to help us, or if we have too many
2918 // active split points, don't split.
2919 if ( !available_thread_exists(master)
2920 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2922 lock_release(&MPLock);
2926 // Pick the next available split point object from the split point stack
2927 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2929 // Initialize the split point object
2930 splitPoint->parent = threads[master].splitPoint;
2931 splitPoint->stopRequest = false;
2932 splitPoint->ply = ply;
2933 splitPoint->depth = depth;
2934 splitPoint->mateThreat = mateThreat;
2935 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2936 splitPoint->beta = beta;
2937 splitPoint->pvNode = pvNode;
2938 splitPoint->bestValue = *bestValue;
2939 splitPoint->master = master;
2940 splitPoint->mp = mp;
2941 splitPoint->moves = *moves;
2942 splitPoint->cpus = 1;
2943 splitPoint->pos = &p;
2944 splitPoint->parentSstack = sstck;
2945 for (int i = 0; i < ActiveThreads; i++)
2946 splitPoint->slaves[i] = 0;
2948 threads[master].splitPoint = splitPoint;
2949 threads[master].activeSplitPoints++;
2951 // If we are here it means we are not available
2952 assert(threads[master].state != THREAD_AVAILABLE);
2954 // Allocate available threads setting state to THREAD_BOOKED
2955 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2956 if (thread_is_available(i, master))
2958 threads[i].state = THREAD_BOOKED;
2959 threads[i].splitPoint = splitPoint;
2960 splitPoint->slaves[i] = 1;
2964 assert(splitPoint->cpus > 1);
2966 // We can release the lock because slave threads are already booked and master is not available
2967 lock_release(&MPLock);
2969 // Tell the threads that they have work to do. This will make them leave
2970 // their idle loop. But before copy search stack tail for each thread.
2971 for (int i = 0; i < ActiveThreads; i++)
2972 if (i == master || splitPoint->slaves[i])
2974 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2976 assert(i == master || threads[i].state == THREAD_BOOKED);
2978 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2981 // Everything is set up. The master thread enters the idle loop, from
2982 // which it will instantly launch a search, because its state is
2983 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2984 // idle loop, which means that the main thread will return from the idle
2985 // loop when all threads have finished their work at this split point
2986 // (i.e. when splitPoint->cpus == 0).
2987 idle_loop(master, splitPoint);
2989 // We have returned from the idle loop, which means that all threads are
2990 // finished. Update alpha, beta and bestValue, and return.
2994 *alpha = splitPoint->alpha;
2996 *bestValue = splitPoint->bestValue;
2997 threads[master].activeSplitPoints--;
2998 threads[master].splitPoint = splitPoint->parent;
3000 lock_release(&MPLock);
3005 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3006 // to start a new search from the root.
3008 void ThreadsManager::wake_sleeping_threads() {
3010 assert(AllThreadsShouldSleep);
3011 assert(ActiveThreads > 0);
3013 AllThreadsShouldSleep = false;
3015 if (ActiveThreads == 1)
3018 #if !defined(_MSC_VER)
3019 pthread_mutex_lock(&WaitLock);
3020 pthread_cond_broadcast(&WaitCond);
3021 pthread_mutex_unlock(&WaitLock);
3023 for (int i = 1; i < MAX_THREADS; i++)
3024 SetEvent(SitIdleEvent[i]);
3030 // put_threads_to_sleep() makes all the threads go to sleep just before
3031 // to leave think(), at the end of the search. Threads should have already
3032 // finished the job and should be idle.
3034 void ThreadsManager::put_threads_to_sleep() {
3036 assert(!AllThreadsShouldSleep);
3038 // This makes the threads to go to sleep
3039 AllThreadsShouldSleep = true;
3042 /// The RootMoveList class
3044 // RootMoveList c'tor
3046 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3048 SearchStack ss[PLY_MAX_PLUS_2];
3049 MoveStack mlist[MaxRootMoves];
3051 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3053 // Generate all legal moves
3054 MoveStack* last = generate_moves(pos, mlist);
3056 // Add each move to the moves[] array
3057 for (MoveStack* cur = mlist; cur != last; cur++)
3059 bool includeMove = includeAllMoves;
3061 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3062 includeMove = (searchMoves[k] == cur->move);
3067 // Find a quick score for the move
3069 pos.do_move(cur->move, st);
3070 moves[count].move = cur->move;
3071 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3072 moves[count].pv[0] = cur->move;
3073 moves[count].pv[1] = MOVE_NONE;
3074 pos.undo_move(cur->move);
3081 // RootMoveList simple methods definitions
3083 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3085 moves[moveNum].nodes = nodes;
3086 moves[moveNum].cumulativeNodes += nodes;
3089 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3091 moves[moveNum].ourBeta = our;
3092 moves[moveNum].theirBeta = their;
3095 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3099 for (j = 0; pv[j] != MOVE_NONE; j++)
3100 moves[moveNum].pv[j] = pv[j];
3102 moves[moveNum].pv[j] = MOVE_NONE;
3106 // RootMoveList::sort() sorts the root move list at the beginning of a new
3109 void RootMoveList::sort() {
3111 sort_multipv(count - 1); // Sort all items
3115 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3116 // list by their scores and depths. It is used to order the different PVs
3117 // correctly in MultiPV mode.
3119 void RootMoveList::sort_multipv(int n) {
3123 for (i = 1; i <= n; i++)
3125 RootMove rm = moves[i];
3126 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3127 moves[j] = moves[j - 1];