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);
1398 TT.store(posKey, nullValue, VALUE_TYPE_NS_LO, depth, MOVE_NONE);
1402 // The null move failed low, which means that we may be faced with
1403 // some kind of threat. If the previous move was reduced, check if
1404 // the move that refuted the null move was somehow connected to the
1405 // move which was reduced. If a connection is found, return a fail
1406 // low score (which will cause the reduced move to fail high in the
1407 // parent node, which will trigger a re-search with full depth).
1408 if (nullValue == value_mated_in(ply + 2))
1411 ss[ply].threatMove = ss[ply + 1].currentMove;
1412 if ( depth < ThreatDepth
1413 && ss[ply - 1].reduction
1414 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1419 // Step 9. Internal iterative deepening
1420 if ( depth >= IIDDepthAtNonPVNodes
1421 && ttMove == MOVE_NONE
1423 && ss[ply].eval >= beta - IIDMargin)
1425 search(pos, ss, beta, depth/2, ply, FORBID_NULLMOVE, threadID);
1426 ttMove = ss[ply].pv[ply];
1427 tte = TT.retrieve(posKey);
1430 // Initialize a MovePicker object for the current position
1431 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1434 // Step 10. Loop through moves
1435 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1436 while ( bestValue < beta
1437 && (move = mp.get_next_move()) != MOVE_NONE
1438 && !TM.thread_should_stop(threadID))
1440 assert(move_is_ok(move));
1442 if (move == excludedMove)
1445 moveIsCheck = pos.move_is_check(move, ci);
1446 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1447 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1449 // Step 11. Decide the new search depth
1450 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1452 // Singular extension search. We extend the TT move if its value is much better than
1453 // its siblings. To verify this we do a reduced search on all the other moves but the
1454 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1455 if ( depth >= SingularExtensionDepthAtNonPVNodes
1457 && move == tte->move()
1458 && !excludedMove // Do not allow recursive singular extension search
1460 && is_lower_bound(tte->type())
1461 && tte->depth() >= depth - 3 * OnePly)
1463 Value ttValue = value_from_tt(tte->value(), ply);
1465 if (abs(ttValue) < VALUE_KNOWN_WIN)
1467 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, FORBID_NULLMOVE, threadID, move);
1469 if (excValue < ttValue - SingularExtensionMargin)
1474 newDepth = depth - OnePly + ext;
1476 // Update current move (this must be done after singular extension search)
1477 movesSearched[moveCount++] = ss[ply].currentMove = move;
1479 // Step 12. Futility pruning
1482 && !captureOrPromotion
1483 && !move_is_castle(move)
1486 // Move count based pruning
1487 if ( moveCount >= futility_move_count(depth)
1488 && ok_to_prune(pos, move, ss[ply].threatMove)
1489 && bestValue > value_mated_in(PLY_MAX))
1492 // Value based pruning
1493 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1494 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1495 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1497 if (futilityValueScaled < beta)
1499 if (futilityValueScaled > bestValue)
1500 bestValue = futilityValueScaled;
1505 // Step 13. Make the move
1506 pos.do_move(move, st, ci, moveIsCheck);
1508 // Step 14. Reduced search, if the move fails high
1509 // will be re-searched at full depth.
1510 bool doFullDepthSearch = true;
1512 if ( depth >= 3*OnePly
1514 && !captureOrPromotion
1515 && !move_is_castle(move)
1516 && !move_is_killer(move, ss[ply]))
1518 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1519 if (ss[ply].reduction)
1521 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, ALLOW_NULLMOVE, threadID);
1522 doFullDepthSearch = (value >= beta);
1526 // Step 15. Full depth search
1527 if (doFullDepthSearch)
1529 ss[ply].reduction = Depth(0);
1530 value = -search(pos, ss, -(beta-1), newDepth, ply+1, ALLOW_NULLMOVE, threadID);
1533 // Step 16. Undo move
1534 pos.undo_move(move);
1536 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1538 // Step 17. Check for new best move
1539 if (value > bestValue)
1545 if (value == value_mate_in(ply + 1))
1546 ss[ply].mateKiller = move;
1549 // Step 18. Check for split
1550 if ( TM.active_threads() > 1
1552 && depth >= MinimumSplitDepth
1554 && TM.available_thread_exists(threadID)
1556 && !TM.thread_should_stop(threadID)
1557 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1558 depth, mateThreat, &moveCount, &mp, threadID, false))
1562 // Step 19. Check for mate and stalemate
1563 // All legal moves have been searched and if there are
1564 // no legal moves, it must be mate or stalemate.
1565 // If one move was excluded return fail low score.
1567 return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1569 // Step 20. Update tables
1570 // If the search is not aborted, update the transposition table,
1571 // history counters, and killer moves.
1572 if (AbortSearch || TM.thread_should_stop(threadID))
1575 if (bestValue < beta)
1576 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1579 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1580 move = ss[ply].pv[ply];
1581 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1582 if (!pos.move_is_capture_or_promotion(move))
1584 update_history(pos, move, depth, movesSearched, moveCount);
1585 update_killers(move, ss[ply]);
1590 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1596 // qsearch() is the quiescence search function, which is called by the main
1597 // search function when the remaining depth is zero (or, to be more precise,
1598 // less than OnePly).
1600 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1601 Depth depth, int ply, int threadID) {
1603 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1604 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1606 assert(ply >= 0 && ply < PLY_MAX);
1607 assert(threadID >= 0 && threadID < TM.active_threads());
1612 Value staticValue, bestValue, value, futilityBase, futilityValue;
1613 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1614 const TTEntry* tte = NULL;
1616 bool pvNode = (beta - alpha != 1);
1617 Value oldAlpha = alpha;
1619 // Initialize, and make an early exit in case of an aborted search,
1620 // an instant draw, maximum ply reached, etc.
1621 init_node(ss, ply, threadID);
1623 // After init_node() that calls poll()
1624 if (AbortSearch || TM.thread_should_stop(threadID))
1627 if (pos.is_draw() || ply >= PLY_MAX - 1)
1630 // Transposition table lookup. At PV nodes, we don't use the TT for
1631 // pruning, but only for move ordering.
1632 tte = TT.retrieve(pos.get_key());
1633 ttMove = (tte ? tte->move() : MOVE_NONE);
1635 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply, true))
1637 assert(tte->type() != VALUE_TYPE_EVAL);
1639 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1640 return value_from_tt(tte->value(), ply);
1643 isCheck = pos.is_check();
1645 // Evaluate the position statically
1647 staticValue = -VALUE_INFINITE;
1648 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1649 staticValue = value_from_tt(tte->value(), ply);
1651 staticValue = evaluate(pos, ei, threadID);
1655 ss[ply].eval = staticValue;
1656 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1659 // Initialize "stand pat score", and return it immediately if it is
1661 bestValue = staticValue;
1663 if (bestValue >= beta)
1665 // Store the score to avoid a future costly evaluation() call
1666 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1667 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1672 if (bestValue > alpha)
1675 // If we are near beta then try to get a cutoff pushing checks a bit further
1676 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1678 // Initialize a MovePicker object for the current position, and prepare
1679 // to search the moves. Because the depth is <= 0 here, only captures,
1680 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1681 // and we are near beta) will be generated.
1682 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1684 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1685 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1687 // Loop through the moves until no moves remain or a beta cutoff occurs
1688 while ( alpha < beta
1689 && (move = mp.get_next_move()) != MOVE_NONE)
1691 assert(move_is_ok(move));
1693 moveIsCheck = pos.move_is_check(move, ci);
1695 // Update current move
1697 ss[ply].currentMove = move;
1705 && !move_is_promotion(move)
1706 && !pos.move_is_passed_pawn_push(move))
1708 futilityValue = futilityBase
1709 + pos.endgame_value_of_piece_on(move_to(move))
1710 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1712 if (futilityValue < alpha)
1714 if (futilityValue > bestValue)
1715 bestValue = futilityValue;
1720 // Detect blocking evasions that are candidate to be pruned
1721 evasionPrunable = isCheck
1722 && bestValue > value_mated_in(PLY_MAX)
1723 && !pos.move_is_capture(move)
1724 && pos.type_of_piece_on(move_from(move)) != KING
1725 && !pos.can_castle(pos.side_to_move());
1727 // Don't search moves with negative SEE values
1728 if ( (!isCheck || evasionPrunable)
1731 && !move_is_promotion(move)
1732 && pos.see_sign(move) < 0)
1735 // Make and search the move
1736 pos.do_move(move, st, ci, moveIsCheck);
1737 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1738 pos.undo_move(move);
1740 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1743 if (value > bestValue)
1754 // All legal moves have been searched. A special case: If we're in check
1755 // and no legal moves were found, it is checkmate.
1756 if (!moveCount && isCheck) // Mate!
1757 return value_mated_in(ply);
1759 // Update transposition table
1760 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1761 if (bestValue <= oldAlpha)
1763 // If bestValue isn't changed it means it is still the static evaluation
1764 // of the node, so keep this info to avoid a future evaluation() call.
1765 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1766 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1768 else if (bestValue >= beta)
1770 move = ss[ply].pv[ply];
1771 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1773 // Update killers only for good checking moves
1774 if (!pos.move_is_capture_or_promotion(move))
1775 update_killers(move, ss[ply]);
1778 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1780 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1786 // sp_search() is used to search from a split point. This function is called
1787 // by each thread working at the split point. It is similar to the normal
1788 // search() function, but simpler. Because we have already probed the hash
1789 // table, done a null move search, and searched the first move before
1790 // splitting, we don't have to repeat all this work in sp_search(). We
1791 // also don't need to store anything to the hash table here: This is taken
1792 // care of after we return from the split point.
1794 void sp_search(SplitPoint* sp, int threadID) {
1796 assert(threadID >= 0 && threadID < TM.active_threads());
1797 assert(TM.active_threads() > 1);
1801 Depth ext, newDepth;
1802 Value value, futilityValueScaled;
1803 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1805 value = -VALUE_INFINITE;
1807 Position pos(*sp->pos);
1809 SearchStack* ss = sp->sstack[threadID];
1810 isCheck = pos.is_check();
1812 // Step 10. Loop through moves
1813 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1814 lock_grab(&(sp->lock));
1816 while ( sp->bestValue < sp->beta
1817 && !TM.thread_should_stop(threadID)
1818 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1820 moveCount = ++sp->moves;
1821 lock_release(&(sp->lock));
1823 assert(move_is_ok(move));
1825 moveIsCheck = pos.move_is_check(move, ci);
1826 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1828 // Step 11. Decide the new search depth
1829 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1830 newDepth = sp->depth - OnePly + ext;
1832 // Update current move
1833 ss[sp->ply].currentMove = move;
1835 // Step 12. Futility pruning
1838 && !captureOrPromotion
1839 && !move_is_castle(move))
1841 // Move count based pruning
1842 if ( moveCount >= futility_move_count(sp->depth)
1843 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1844 && sp->bestValue > value_mated_in(PLY_MAX))
1846 lock_grab(&(sp->lock));
1850 // Value based pruning
1851 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1852 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1853 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1855 if (futilityValueScaled < sp->beta)
1857 lock_grab(&(sp->lock));
1859 if (futilityValueScaled > sp->bestValue)
1860 sp->bestValue = futilityValueScaled;
1865 // Step 13. Make the move
1866 pos.do_move(move, st, ci, moveIsCheck);
1868 // Step 14. Reduced search
1869 // if the move fails high will be re-searched at full depth.
1870 bool doFullDepthSearch = true;
1873 && !captureOrPromotion
1874 && !move_is_castle(move)
1875 && !move_is_killer(move, ss[sp->ply]))
1877 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1878 if (ss[sp->ply].reduction)
1880 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, ALLOW_NULLMOVE, threadID);
1881 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1885 // Step 15. Full depth search
1886 if (doFullDepthSearch)
1888 ss[sp->ply].reduction = Depth(0);
1889 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, ALLOW_NULLMOVE, threadID);
1892 // Step 16. Undo move
1893 pos.undo_move(move);
1895 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1897 // Step 17. Check for new best move
1898 lock_grab(&(sp->lock));
1900 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1902 sp->bestValue = value;
1903 if (sp->bestValue >= sp->beta)
1905 sp->stopRequest = true;
1906 sp_update_pv(sp->parentSstack, ss, sp->ply);
1911 /* Here we have the lock still grabbed */
1913 sp->slaves[threadID] = 0;
1916 lock_release(&(sp->lock));
1920 // sp_search_pv() is used to search from a PV split point. This function
1921 // is called by each thread working at the split point. It is similar to
1922 // the normal search_pv() function, but simpler. Because we have already
1923 // probed the hash table and searched the first move before splitting, we
1924 // don't have to repeat all this work in sp_search_pv(). We also don't
1925 // need to store anything to the hash table here: This is taken care of
1926 // after we return from the split point.
1928 void sp_search_pv(SplitPoint* sp, int threadID) {
1930 assert(threadID >= 0 && threadID < TM.active_threads());
1931 assert(TM.active_threads() > 1);
1935 Depth ext, newDepth;
1937 bool moveIsCheck, captureOrPromotion, dangerous;
1939 value = -VALUE_INFINITE;
1941 Position pos(*sp->pos);
1943 SearchStack* ss = sp->sstack[threadID];
1945 // Step 10. Loop through moves
1946 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1947 lock_grab(&(sp->lock));
1949 while ( sp->alpha < sp->beta
1950 && !TM.thread_should_stop(threadID)
1951 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1953 moveCount = ++sp->moves;
1954 lock_release(&(sp->lock));
1956 assert(move_is_ok(move));
1958 moveIsCheck = pos.move_is_check(move, ci);
1959 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1961 // Step 11. Decide the new search depth
1962 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1963 newDepth = sp->depth - OnePly + ext;
1965 // Update current move
1966 ss[sp->ply].currentMove = move;
1968 // Step 12. Futility pruning (is omitted in PV nodes)
1970 // Step 13. Make the move
1971 pos.do_move(move, st, ci, moveIsCheck);
1973 // Step 14. Reduced search
1974 // if the move fails high will be re-searched at full depth.
1975 bool doFullDepthSearch = true;
1978 && !captureOrPromotion
1979 && !move_is_castle(move)
1980 && !move_is_killer(move, ss[sp->ply]))
1982 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1983 if (ss[sp->ply].reduction)
1985 Value localAlpha = sp->alpha;
1986 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, ALLOW_NULLMOVE, threadID);
1987 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1991 // Step 15. Full depth search
1992 if (doFullDepthSearch)
1994 Value localAlpha = sp->alpha;
1995 ss[sp->ply].reduction = Depth(0);
1996 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, ALLOW_NULLMOVE, threadID);
1998 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
2000 // If another thread has failed high then sp->alpha has been increased
2001 // to be higher or equal then beta, if so, avoid to start a PV search.
2002 localAlpha = sp->alpha;
2003 if (localAlpha < sp->beta)
2004 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2008 // Step 16. Undo move
2009 pos.undo_move(move);
2011 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2013 // Step 17. Check for new best move
2014 lock_grab(&(sp->lock));
2016 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2018 sp->bestValue = value;
2019 if (value > sp->alpha)
2021 // Ask threads to stop before to modify sp->alpha
2022 if (value >= sp->beta)
2023 sp->stopRequest = true;
2027 sp_update_pv(sp->parentSstack, ss, sp->ply);
2028 if (value == value_mate_in(sp->ply + 1))
2029 ss[sp->ply].mateKiller = move;
2034 /* Here we have the lock still grabbed */
2036 sp->slaves[threadID] = 0;
2039 lock_release(&(sp->lock));
2043 // init_node() is called at the beginning of all the search functions
2044 // (search(), search_pv(), qsearch(), and so on) and initializes the
2045 // search stack object corresponding to the current node. Once every
2046 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2047 // for user input and checks whether it is time to stop the search.
2049 void init_node(SearchStack ss[], int ply, int threadID) {
2051 assert(ply >= 0 && ply < PLY_MAX);
2052 assert(threadID >= 0 && threadID < TM.active_threads());
2054 TM.incrementNodeCounter(threadID);
2059 if (NodesSincePoll >= NodesBetweenPolls)
2066 ss[ply + 2].initKillers();
2070 // update_pv() is called whenever a search returns a value > alpha.
2071 // It updates the PV in the SearchStack object corresponding to the
2074 void update_pv(SearchStack ss[], int ply) {
2076 assert(ply >= 0 && ply < PLY_MAX);
2080 ss[ply].pv[ply] = ss[ply].currentMove;
2082 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2083 ss[ply].pv[p] = ss[ply + 1].pv[p];
2085 ss[ply].pv[p] = MOVE_NONE;
2089 // sp_update_pv() is a variant of update_pv for use at split points. The
2090 // difference between the two functions is that sp_update_pv also updates
2091 // the PV at the parent node.
2093 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2095 assert(ply >= 0 && ply < PLY_MAX);
2099 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2101 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2102 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2104 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2108 // connected_moves() tests whether two moves are 'connected' in the sense
2109 // that the first move somehow made the second move possible (for instance
2110 // if the moving piece is the same in both moves). The first move is assumed
2111 // to be the move that was made to reach the current position, while the
2112 // second move is assumed to be a move from the current position.
2114 bool connected_moves(const Position& pos, Move m1, Move m2) {
2116 Square f1, t1, f2, t2;
2119 assert(move_is_ok(m1));
2120 assert(move_is_ok(m2));
2122 if (m2 == MOVE_NONE)
2125 // Case 1: The moving piece is the same in both moves
2131 // Case 2: The destination square for m2 was vacated by m1
2137 // Case 3: Moving through the vacated square
2138 if ( piece_is_slider(pos.piece_on(f2))
2139 && bit_is_set(squares_between(f2, t2), f1))
2142 // Case 4: The destination square for m2 is defended by the moving piece in m1
2143 p = pos.piece_on(t1);
2144 if (bit_is_set(pos.attacks_from(p, t1), t2))
2147 // Case 5: Discovered check, checking piece is the piece moved in m1
2148 if ( piece_is_slider(p)
2149 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2150 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2152 // discovered_check_candidates() works also if the Position's side to
2153 // move is the opposite of the checking piece.
2154 Color them = opposite_color(pos.side_to_move());
2155 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2157 if (bit_is_set(dcCandidates, f2))
2164 // value_is_mate() checks if the given value is a mate one
2165 // eventually compensated for the ply.
2167 bool value_is_mate(Value value) {
2169 assert(abs(value) <= VALUE_INFINITE);
2171 return value <= value_mated_in(PLY_MAX)
2172 || value >= value_mate_in(PLY_MAX);
2176 // move_is_killer() checks if the given move is among the
2177 // killer moves of that ply.
2179 bool move_is_killer(Move m, const SearchStack& ss) {
2181 const Move* k = ss.killers;
2182 for (int i = 0; i < KILLER_MAX; i++, k++)
2190 // extension() decides whether a move should be searched with normal depth,
2191 // or with extended depth. Certain classes of moves (checking moves, in
2192 // particular) are searched with bigger depth than ordinary moves and in
2193 // any case are marked as 'dangerous'. Note that also if a move is not
2194 // extended, as example because the corresponding UCI option is set to zero,
2195 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2197 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2198 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2200 assert(m != MOVE_NONE);
2202 Depth result = Depth(0);
2203 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2208 result += CheckExtension[pvNode];
2211 result += SingleEvasionExtension[pvNode];
2214 result += MateThreatExtension[pvNode];
2217 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2219 Color c = pos.side_to_move();
2220 if (relative_rank(c, move_to(m)) == RANK_7)
2222 result += PawnPushTo7thExtension[pvNode];
2225 if (pos.pawn_is_passed(c, move_to(m)))
2227 result += PassedPawnExtension[pvNode];
2232 if ( captureOrPromotion
2233 && pos.type_of_piece_on(move_to(m)) != PAWN
2234 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2235 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2236 && !move_is_promotion(m)
2239 result += PawnEndgameExtension[pvNode];
2244 && captureOrPromotion
2245 && pos.type_of_piece_on(move_to(m)) != PAWN
2246 && pos.see_sign(m) >= 0)
2252 return Min(result, OnePly);
2256 // ok_to_do_nullmove() looks at the current position and decides whether
2257 // doing a 'null move' should be allowed. In order to avoid zugzwang
2258 // problems, null moves are not allowed when the side to move has very
2259 // little material left. Currently, the test is a bit too simple: Null
2260 // moves are avoided only when the side to move has only pawns left.
2261 // It's probably a good idea to avoid null moves in at least some more
2262 // complicated endgames, e.g. KQ vs KR. FIXME
2264 bool ok_to_do_nullmove(const Position& pos) {
2266 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2270 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2271 // non-tactical moves late in the move list close to the leaves are
2272 // candidates for pruning.
2274 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2276 assert(move_is_ok(m));
2277 assert(threat == MOVE_NONE || move_is_ok(threat));
2278 assert(!pos.move_is_check(m));
2279 assert(!pos.move_is_capture_or_promotion(m));
2280 assert(!pos.move_is_passed_pawn_push(m));
2282 Square mfrom, mto, tfrom, tto;
2284 // Prune if there isn't any threat move
2285 if (threat == MOVE_NONE)
2288 mfrom = move_from(m);
2290 tfrom = move_from(threat);
2291 tto = move_to(threat);
2293 // Case 1: Don't prune moves which move the threatened piece
2297 // Case 2: If the threatened piece has value less than or equal to the
2298 // value of the threatening piece, don't prune move which defend it.
2299 if ( pos.move_is_capture(threat)
2300 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2301 || pos.type_of_piece_on(tfrom) == KING)
2302 && pos.move_attacks_square(m, tto))
2305 // Case 3: If the moving piece in the threatened move is a slider, don't
2306 // prune safe moves which block its ray.
2307 if ( piece_is_slider(pos.piece_on(tfrom))
2308 && bit_is_set(squares_between(tfrom, tto), mto)
2309 && pos.see_sign(m) >= 0)
2316 // ok_to_use_TT() returns true if a transposition table score can be used at a
2317 // given point in search. To avoid zugzwang issues TT cutoffs at the root node
2318 // of a null move verification search are not allowed if the TT value was found
2319 // by a null search, this is implemented testing allowNullmove and TT entry type.
2321 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove) {
2323 Value v = value_from_tt(tte->value(), ply);
2325 return (allowNullmove || !(tte->type() & VALUE_TYPE_NULL))
2327 && ( tte->depth() >= depth
2328 || v >= Max(value_mate_in(PLY_MAX), beta)
2329 || v < Min(value_mated_in(PLY_MAX), beta))
2331 && ( (is_lower_bound(tte->type()) && v >= beta)
2332 || (is_upper_bound(tte->type()) && v < beta));
2336 // refine_eval() returns the transposition table score if
2337 // possible otherwise falls back on static position evaluation.
2339 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2344 Value v = value_from_tt(tte->value(), ply);
2346 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2347 || (is_upper_bound(tte->type()) && v < defaultEval))
2354 // update_history() registers a good move that produced a beta-cutoff
2355 // in history and marks as failures all the other moves of that ply.
2357 void update_history(const Position& pos, Move move, Depth depth,
2358 Move movesSearched[], int moveCount) {
2362 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2364 for (int i = 0; i < moveCount - 1; i++)
2366 m = movesSearched[i];
2370 if (!pos.move_is_capture_or_promotion(m))
2371 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2376 // update_killers() add a good move that produced a beta-cutoff
2377 // among the killer moves of that ply.
2379 void update_killers(Move m, SearchStack& ss) {
2381 if (m == ss.killers[0])
2384 for (int i = KILLER_MAX - 1; i > 0; i--)
2385 ss.killers[i] = ss.killers[i - 1];
2391 // update_gains() updates the gains table of a non-capture move given
2392 // the static position evaluation before and after the move.
2394 void update_gains(const Position& pos, Move m, Value before, Value after) {
2397 && before != VALUE_NONE
2398 && after != VALUE_NONE
2399 && pos.captured_piece() == NO_PIECE_TYPE
2400 && !move_is_castle(m)
2401 && !move_is_promotion(m))
2402 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2406 // current_search_time() returns the number of milliseconds which have passed
2407 // since the beginning of the current search.
2409 int current_search_time() {
2411 return get_system_time() - SearchStartTime;
2415 // nps() computes the current nodes/second count.
2419 int t = current_search_time();
2420 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2424 // poll() performs two different functions: It polls for user input, and it
2425 // looks at the time consumed so far and decides if it's time to abort the
2430 static int lastInfoTime;
2431 int t = current_search_time();
2436 // We are line oriented, don't read single chars
2437 std::string command;
2439 if (!std::getline(std::cin, command))
2442 if (command == "quit")
2445 PonderSearch = false;
2449 else if (command == "stop")
2452 PonderSearch = false;
2454 else if (command == "ponderhit")
2458 // Print search information
2462 else if (lastInfoTime > t)
2463 // HACK: Must be a new search where we searched less than
2464 // NodesBetweenPolls nodes during the first second of search.
2467 else if (t - lastInfoTime >= 1000)
2474 if (dbg_show_hit_rate)
2475 dbg_print_hit_rate();
2477 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2478 << " time " << t << " hashfull " << TT.full() << endl;
2481 // Should we stop the search?
2485 bool stillAtFirstMove = FirstRootMove
2486 && !AspirationFailLow
2487 && t > MaxSearchTime + ExtraSearchTime;
2489 bool noMoreTime = t > AbsoluteMaxSearchTime
2490 || stillAtFirstMove;
2492 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2493 || (ExactMaxTime && t >= ExactMaxTime)
2494 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2499 // ponderhit() is called when the program is pondering (i.e. thinking while
2500 // it's the opponent's turn to move) in order to let the engine know that
2501 // it correctly predicted the opponent's move.
2505 int t = current_search_time();
2506 PonderSearch = false;
2508 bool stillAtFirstMove = FirstRootMove
2509 && !AspirationFailLow
2510 && t > MaxSearchTime + ExtraSearchTime;
2512 bool noMoreTime = t > AbsoluteMaxSearchTime
2513 || stillAtFirstMove;
2515 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2520 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2522 void init_ss_array(SearchStack ss[]) {
2524 for (int i = 0; i < 3; i++)
2527 ss[i].initKillers();
2532 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2533 // while the program is pondering. The point is to work around a wrinkle in
2534 // the UCI protocol: When pondering, the engine is not allowed to give a
2535 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2536 // We simply wait here until one of these commands is sent, and return,
2537 // after which the bestmove and pondermove will be printed (in id_loop()).
2539 void wait_for_stop_or_ponderhit() {
2541 std::string command;
2545 if (!std::getline(std::cin, command))
2548 if (command == "quit")
2553 else if (command == "ponderhit" || command == "stop")
2559 // print_pv_info() prints to standard output and eventually to log file information on
2560 // the current PV line. It is called at each iteration or after a new pv is found.
2562 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2564 cout << "info depth " << Iteration
2565 << " score " << value_to_string(value)
2566 << ((value >= beta) ? " lowerbound" :
2567 ((value <= alpha)? " upperbound" : ""))
2568 << " time " << current_search_time()
2569 << " nodes " << TM.nodes_searched()
2573 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2574 cout << ss[0].pv[j] << " ";
2580 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2581 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2583 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2584 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2589 // init_thread() is the function which is called when a new thread is
2590 // launched. It simply calls the idle_loop() function with the supplied
2591 // threadID. There are two versions of this function; one for POSIX
2592 // threads and one for Windows threads.
2594 #if !defined(_MSC_VER)
2596 void* init_thread(void *threadID) {
2598 TM.idle_loop(*(int*)threadID, NULL);
2604 DWORD WINAPI init_thread(LPVOID threadID) {
2606 TM.idle_loop(*(int*)threadID, NULL);
2613 /// The ThreadsManager class
2615 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2616 // get_beta_counters() are getters/setters for the per thread
2617 // counters used to sort the moves at root.
2619 void ThreadsManager::resetNodeCounters() {
2621 for (int i = 0; i < MAX_THREADS; i++)
2622 threads[i].nodes = 0ULL;
2625 void ThreadsManager::resetBetaCounters() {
2627 for (int i = 0; i < MAX_THREADS; i++)
2628 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2631 int64_t ThreadsManager::nodes_searched() const {
2633 int64_t result = 0ULL;
2634 for (int i = 0; i < ActiveThreads; i++)
2635 result += threads[i].nodes;
2640 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2643 for (int i = 0; i < MAX_THREADS; i++)
2645 our += threads[i].betaCutOffs[us];
2646 their += threads[i].betaCutOffs[opposite_color(us)];
2651 // idle_loop() is where the threads are parked when they have no work to do.
2652 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2653 // object for which the current thread is the master.
2655 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2657 assert(threadID >= 0 && threadID < MAX_THREADS);
2661 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2662 // master should exit as last one.
2663 if (AllThreadsShouldExit)
2666 threads[threadID].state = THREAD_TERMINATED;
2670 // If we are not thinking, wait for a condition to be signaled
2671 // instead of wasting CPU time polling for work.
2672 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2675 assert(threadID != 0);
2676 threads[threadID].state = THREAD_SLEEPING;
2678 #if !defined(_MSC_VER)
2679 lock_grab(&WaitLock);
2680 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2681 pthread_cond_wait(&WaitCond, &WaitLock);
2682 lock_release(&WaitLock);
2684 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2688 // If thread has just woken up, mark it as available
2689 if (threads[threadID].state == THREAD_SLEEPING)
2690 threads[threadID].state = THREAD_AVAILABLE;
2692 // If this thread has been assigned work, launch a search
2693 if (threads[threadID].state == THREAD_WORKISWAITING)
2695 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2697 threads[threadID].state = THREAD_SEARCHING;
2699 if (threads[threadID].splitPoint->pvNode)
2700 sp_search_pv(threads[threadID].splitPoint, threadID);
2702 sp_search(threads[threadID].splitPoint, threadID);
2704 assert(threads[threadID].state == THREAD_SEARCHING);
2706 threads[threadID].state = THREAD_AVAILABLE;
2709 // If this thread is the master of a split point and all threads have
2710 // finished their work at this split point, return from the idle loop.
2711 if (waitSp != NULL && waitSp->cpus == 0)
2713 assert(threads[threadID].state == THREAD_AVAILABLE);
2715 threads[threadID].state = THREAD_SEARCHING;
2722 // init_threads() is called during startup. It launches all helper threads,
2723 // and initializes the split point stack and the global locks and condition
2726 void ThreadsManager::init_threads() {
2731 #if !defined(_MSC_VER)
2732 pthread_t pthread[1];
2735 // Initialize global locks
2736 lock_init(&MPLock, NULL);
2737 lock_init(&WaitLock, NULL);
2739 #if !defined(_MSC_VER)
2740 pthread_cond_init(&WaitCond, NULL);
2742 for (i = 0; i < MAX_THREADS; i++)
2743 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2746 // Initialize SplitPointStack locks
2747 for (i = 0; i < MAX_THREADS; i++)
2748 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2750 SplitPointStack[i][j].parent = NULL;
2751 lock_init(&(SplitPointStack[i][j].lock), NULL);
2754 // Will be set just before program exits to properly end the threads
2755 AllThreadsShouldExit = false;
2757 // Threads will be put to sleep as soon as created
2758 AllThreadsShouldSleep = true;
2760 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2762 threads[0].state = THREAD_SEARCHING;
2763 for (i = 1; i < MAX_THREADS; i++)
2764 threads[i].state = THREAD_AVAILABLE;
2766 // Launch the helper threads
2767 for (i = 1; i < MAX_THREADS; i++)
2770 #if !defined(_MSC_VER)
2771 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2773 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2778 cout << "Failed to create thread number " << i << endl;
2779 Application::exit_with_failure();
2782 // Wait until the thread has finished launching and is gone to sleep
2783 while (threads[i].state != THREAD_SLEEPING) {}
2788 // exit_threads() is called when the program exits. It makes all the
2789 // helper threads exit cleanly.
2791 void ThreadsManager::exit_threads() {
2793 ActiveThreads = MAX_THREADS; // HACK
2794 AllThreadsShouldSleep = true; // HACK
2795 wake_sleeping_threads();
2797 // This makes the threads to exit idle_loop()
2798 AllThreadsShouldExit = true;
2800 // Wait for thread termination
2801 for (int i = 1; i < MAX_THREADS; i++)
2802 while (threads[i].state != THREAD_TERMINATED);
2804 // Now we can safely destroy the locks
2805 for (int i = 0; i < MAX_THREADS; i++)
2806 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2807 lock_destroy(&(SplitPointStack[i][j].lock));
2809 lock_destroy(&WaitLock);
2810 lock_destroy(&MPLock);
2814 // thread_should_stop() checks whether the thread should stop its search.
2815 // This can happen if a beta cutoff has occurred in the thread's currently
2816 // active split point, or in some ancestor of the current split point.
2818 bool ThreadsManager::thread_should_stop(int threadID) const {
2820 assert(threadID >= 0 && threadID < ActiveThreads);
2824 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2829 // thread_is_available() checks whether the thread with threadID "slave" is
2830 // available to help the thread with threadID "master" at a split point. An
2831 // obvious requirement is that "slave" must be idle. With more than two
2832 // threads, this is not by itself sufficient: If "slave" is the master of
2833 // some active split point, it is only available as a slave to the other
2834 // threads which are busy searching the split point at the top of "slave"'s
2835 // split point stack (the "helpful master concept" in YBWC terminology).
2837 bool ThreadsManager::thread_is_available(int slave, int master) const {
2839 assert(slave >= 0 && slave < ActiveThreads);
2840 assert(master >= 0 && master < ActiveThreads);
2841 assert(ActiveThreads > 1);
2843 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2846 // Make a local copy to be sure doesn't change under our feet
2847 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2849 if (localActiveSplitPoints == 0)
2850 // No active split points means that the thread is available as
2851 // a slave for any other thread.
2854 if (ActiveThreads == 2)
2857 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2858 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2859 // could have been set to 0 by another thread leading to an out of bound access.
2860 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2867 // available_thread_exists() tries to find an idle thread which is available as
2868 // a slave for the thread with threadID "master".
2870 bool ThreadsManager::available_thread_exists(int master) const {
2872 assert(master >= 0 && master < ActiveThreads);
2873 assert(ActiveThreads > 1);
2875 for (int i = 0; i < ActiveThreads; i++)
2876 if (thread_is_available(i, master))
2883 // split() does the actual work of distributing the work at a node between
2884 // several threads at PV nodes. If it does not succeed in splitting the
2885 // node (because no idle threads are available, or because we have no unused
2886 // split point objects), the function immediately returns false. If
2887 // splitting is possible, a SplitPoint object is initialized with all the
2888 // data that must be copied to the helper threads (the current position and
2889 // search stack, alpha, beta, the search depth, etc.), and we tell our
2890 // helper threads that they have been assigned work. This will cause them
2891 // to instantly leave their idle loops and call sp_search_pv(). When all
2892 // threads have returned from sp_search_pv (or, equivalently, when
2893 // splitPoint->cpus becomes 0), split() returns true.
2895 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2896 Value* alpha, const Value beta, Value* bestValue,
2897 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2900 assert(sstck != NULL);
2901 assert(ply >= 0 && ply < PLY_MAX);
2902 assert(*bestValue >= -VALUE_INFINITE);
2903 assert( ( pvNode && *bestValue <= *alpha)
2904 || (!pvNode && *bestValue < beta ));
2905 assert(!pvNode || *alpha < beta);
2906 assert(beta <= VALUE_INFINITE);
2907 assert(depth > Depth(0));
2908 assert(master >= 0 && master < ActiveThreads);
2909 assert(ActiveThreads > 1);
2911 SplitPoint* splitPoint;
2915 // If no other thread is available to help us, or if we have too many
2916 // active split points, don't split.
2917 if ( !available_thread_exists(master)
2918 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2920 lock_release(&MPLock);
2924 // Pick the next available split point object from the split point stack
2925 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2927 // Initialize the split point object
2928 splitPoint->parent = threads[master].splitPoint;
2929 splitPoint->stopRequest = false;
2930 splitPoint->ply = ply;
2931 splitPoint->depth = depth;
2932 splitPoint->mateThreat = mateThreat;
2933 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2934 splitPoint->beta = beta;
2935 splitPoint->pvNode = pvNode;
2936 splitPoint->bestValue = *bestValue;
2937 splitPoint->master = master;
2938 splitPoint->mp = mp;
2939 splitPoint->moves = *moves;
2940 splitPoint->cpus = 1;
2941 splitPoint->pos = &p;
2942 splitPoint->parentSstack = sstck;
2943 for (int i = 0; i < ActiveThreads; i++)
2944 splitPoint->slaves[i] = 0;
2946 threads[master].splitPoint = splitPoint;
2947 threads[master].activeSplitPoints++;
2949 // If we are here it means we are not available
2950 assert(threads[master].state != THREAD_AVAILABLE);
2952 // Allocate available threads setting state to THREAD_BOOKED
2953 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2954 if (thread_is_available(i, master))
2956 threads[i].state = THREAD_BOOKED;
2957 threads[i].splitPoint = splitPoint;
2958 splitPoint->slaves[i] = 1;
2962 assert(splitPoint->cpus > 1);
2964 // We can release the lock because slave threads are already booked and master is not available
2965 lock_release(&MPLock);
2967 // Tell the threads that they have work to do. This will make them leave
2968 // their idle loop. But before copy search stack tail for each thread.
2969 for (int i = 0; i < ActiveThreads; i++)
2970 if (i == master || splitPoint->slaves[i])
2972 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2974 assert(i == master || threads[i].state == THREAD_BOOKED);
2976 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2979 // Everything is set up. The master thread enters the idle loop, from
2980 // which it will instantly launch a search, because its state is
2981 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2982 // idle loop, which means that the main thread will return from the idle
2983 // loop when all threads have finished their work at this split point
2984 // (i.e. when splitPoint->cpus == 0).
2985 idle_loop(master, splitPoint);
2987 // We have returned from the idle loop, which means that all threads are
2988 // finished. Update alpha, beta and bestValue, and return.
2992 *alpha = splitPoint->alpha;
2994 *bestValue = splitPoint->bestValue;
2995 threads[master].activeSplitPoints--;
2996 threads[master].splitPoint = splitPoint->parent;
2998 lock_release(&MPLock);
3003 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3004 // to start a new search from the root.
3006 void ThreadsManager::wake_sleeping_threads() {
3008 assert(AllThreadsShouldSleep);
3009 assert(ActiveThreads > 0);
3011 AllThreadsShouldSleep = false;
3013 if (ActiveThreads == 1)
3016 #if !defined(_MSC_VER)
3017 pthread_mutex_lock(&WaitLock);
3018 pthread_cond_broadcast(&WaitCond);
3019 pthread_mutex_unlock(&WaitLock);
3021 for (int i = 1; i < MAX_THREADS; i++)
3022 SetEvent(SitIdleEvent[i]);
3028 // put_threads_to_sleep() makes all the threads go to sleep just before
3029 // to leave think(), at the end of the search. Threads should have already
3030 // finished the job and should be idle.
3032 void ThreadsManager::put_threads_to_sleep() {
3034 assert(!AllThreadsShouldSleep);
3036 // This makes the threads to go to sleep
3037 AllThreadsShouldSleep = true;
3040 /// The RootMoveList class
3042 // RootMoveList c'tor
3044 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3046 SearchStack ss[PLY_MAX_PLUS_2];
3047 MoveStack mlist[MaxRootMoves];
3049 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3051 // Generate all legal moves
3052 MoveStack* last = generate_moves(pos, mlist);
3054 // Add each move to the moves[] array
3055 for (MoveStack* cur = mlist; cur != last; cur++)
3057 bool includeMove = includeAllMoves;
3059 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3060 includeMove = (searchMoves[k] == cur->move);
3065 // Find a quick score for the move
3067 pos.do_move(cur->move, st);
3068 moves[count].move = cur->move;
3069 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3070 moves[count].pv[0] = cur->move;
3071 moves[count].pv[1] = MOVE_NONE;
3072 pos.undo_move(cur->move);
3079 // RootMoveList simple methods definitions
3081 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3083 moves[moveNum].nodes = nodes;
3084 moves[moveNum].cumulativeNodes += nodes;
3087 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3089 moves[moveNum].ourBeta = our;
3090 moves[moveNum].theirBeta = their;
3093 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3097 for (j = 0; pv[j] != MOVE_NONE; j++)
3098 moves[moveNum].pv[j] = pv[j];
3100 moves[moveNum].pv[j] = MOVE_NONE;
3104 // RootMoveList::sort() sorts the root move list at the beginning of a new
3107 void RootMoveList::sort() {
3109 sort_multipv(count - 1); // Sort all items
3113 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3114 // list by their scores and depths. It is used to order the different PVs
3115 // correctly in MultiPV mode.
3117 void RootMoveList::sort_multipv(int n) {
3121 for (i = 1; i <= n; i++)
3123 RootMove rm = moves[i];
3124 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3125 moves[j] = moves[j - 1];