2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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
56 // The BetaCounterType class is used to order moves at ply one.
57 // Apart for the first one that has its score, following moves
58 // normally have score -VALUE_INFINITE, so are ordered according
59 // to the number of beta cutoffs occurred under their subtree during
60 // the last iteration. The counters are per thread variables to avoid
61 // concurrent accessing under SMP case.
63 struct BetaCounterType {
67 void add(Color us, Depth d, int threadID);
68 void read(Color us, int64_t& our, int64_t& their);
72 // The RootMove class is used for moves at the root at the tree. For each
73 // root move, we store a score, a node count, and a PV (really a refutation
74 // in the case of moves which fail low).
78 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
80 // RootMove::operator<() is the comparison function used when
81 // sorting the moves. A move m1 is considered to be better
82 // than a move m2 if it has a higher score, or if the moves
83 // have equal score but m1 has the higher node count.
84 bool operator<(const RootMove& m) const {
86 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
91 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
92 Move pv[PLY_MAX_PLUS_2];
96 // The RootMoveList class is essentially an array of RootMove objects, with
97 // a handful of methods for accessing the data in the individual moves.
102 RootMoveList(Position& pos, Move searchMoves[]);
104 int move_count() const { return count; }
105 Move get_move(int moveNum) const { return moves[moveNum].move; }
106 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
107 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
108 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
109 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
111 void set_move_nodes(int moveNum, int64_t nodes);
112 void set_beta_counters(int moveNum, int64_t our, int64_t their);
113 void set_move_pv(int moveNum, const Move pv[]);
115 void sort_multipv(int n);
118 static const int MaxRootMoves = 500;
119 RootMove moves[MaxRootMoves];
126 // Search depth at iteration 1
127 const Depth InitialDepth = OnePly;
129 // Use internal iterative deepening?
130 const bool UseIIDAtPVNodes = true;
131 const bool UseIIDAtNonPVNodes = true;
133 // Internal iterative deepening margin. At Non-PV moves, when
134 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
135 // search when the static evaluation is at most IIDMargin below beta.
136 const Value IIDMargin = Value(0x100);
138 // Easy move margin. An easy move candidate must be at least this much
139 // better than the second best move.
140 const Value EasyMoveMargin = Value(0x200);
142 // Null move margin. A null move search will not be done if the static
143 // evaluation of the position is more than NullMoveMargin below beta.
144 const Value NullMoveMargin = Value(0x200);
146 // If the TT move is at least SingleReplyMargin better then the
147 // remaining ones we will extend it.
148 const Value SingleReplyMargin = Value(0x20);
150 // Depth limit for razoring
151 const Depth RazorDepth = 4 * OnePly;
153 /// Variables initialized by UCI options
155 // Depth limit for use of dynamic threat detection
158 // Last seconds noise filtering (LSN)
159 const bool UseLSNFiltering = true;
160 const int LSNTime = 4000; // In milliseconds
161 const Value LSNValue = value_from_centipawns(200);
162 bool loseOnTime = false;
164 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
165 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
166 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
168 // Iteration counters
170 BetaCounterType BetaCounter;
172 // Scores and number of times the best move changed for each iteration
173 Value ValueByIteration[PLY_MAX_PLUS_2];
174 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
176 // Search window management
182 // Time managment variables
185 int MaxNodes, MaxDepth;
186 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
187 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
188 bool AbortSearch, Quit;
189 bool AspirationFailLow;
191 // Show current line?
192 bool ShowCurrentLine;
196 std::ofstream LogFile;
198 // Futility lookup tables and their getter functions
199 const Value FutilityMarginQS = Value(0x80);
200 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
201 int FutilityMoveCountArray[32]; // [depth]
203 inline Value futility_margin(Depth d, int mn) { return (Value) (d < 14? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2*VALUE_INFINITE); }
204 inline int futility_move_count(Depth d) { return (d < 32? FutilityMoveCountArray[d] : 512); }
206 // Reduction lookup tables and their getter functions
207 // Initialized at startup
208 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
209 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
211 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
212 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
214 // MP related variables
215 int ActiveThreads = 1;
216 Depth MinimumSplitDepth;
217 int MaxThreadsPerSplitPoint;
218 Thread Threads[THREAD_MAX];
221 bool AllThreadsShouldExit = false;
222 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
225 #if !defined(_MSC_VER)
226 pthread_cond_t WaitCond;
227 pthread_mutex_t WaitLock;
229 HANDLE SitIdleEvent[THREAD_MAX];
232 // Node counters, used only by thread[0] but try to keep in different
233 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
235 int NodesBetweenPolls = 30000;
242 Value id_loop(const Position& pos, Move searchMoves[]);
243 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
244 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
245 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
246 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
247 void sp_search(SplitPoint* sp, int threadID);
248 void sp_search_pv(SplitPoint* sp, int threadID);
249 void init_node(SearchStack ss[], int ply, int threadID);
250 void update_pv(SearchStack ss[], int ply);
251 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
252 bool connected_moves(const Position& pos, Move m1, Move m2);
253 bool value_is_mate(Value value);
254 bool move_is_killer(Move m, const SearchStack& ss);
255 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
256 bool ok_to_do_nullmove(const Position& pos);
257 bool ok_to_prune(const Position& pos, Move m, Move threat);
258 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
259 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
260 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
261 void update_killers(Move m, SearchStack& ss);
262 void update_gains(const Position& pos, Move move, Value before, Value after);
264 int current_search_time();
268 void print_current_line(SearchStack ss[], int ply, int threadID);
269 void wait_for_stop_or_ponderhit();
270 void init_ss_array(SearchStack ss[]);
272 void idle_loop(int threadID, SplitPoint* waitSp);
273 void init_split_point_stack();
274 void destroy_split_point_stack();
275 bool thread_should_stop(int threadID);
276 bool thread_is_available(int slave, int master);
277 bool idle_thread_exists(int master);
278 bool split(const Position& pos, SearchStack* ss, int ply,
279 Value *alpha, Value *beta, Value *bestValue,
280 const Value futilityValue, Depth depth, int *moves,
281 MovePicker *mp, int master, bool pvNode);
282 void wake_sleeping_threads();
284 #if !defined(_MSC_VER)
285 void *init_thread(void *threadID);
287 DWORD WINAPI init_thread(LPVOID threadID);
298 /// perft() is our utility to verify move generation is bug free. All the legal
299 /// moves up to given depth are generated and counted and the sum returned.
301 int perft(Position& pos, Depth depth)
305 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
307 // If we are at the last ply we don't need to do and undo
308 // the moves, just to count them.
309 if (depth <= OnePly) // Replace with '<' to test also qsearch
311 while (mp.get_next_move()) sum++;
315 // Loop through all legal moves
317 while ((move = mp.get_next_move()) != MOVE_NONE)
320 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
321 sum += perft(pos, depth - OnePly);
328 /// think() is the external interface to Stockfish's search, and is called when
329 /// the program receives the UCI 'go' command. It initializes various
330 /// search-related global variables, and calls root_search(). It returns false
331 /// when a quit command is received during the search.
333 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
334 int time[], int increment[], int movesToGo, int maxDepth,
335 int maxNodes, int maxTime, Move searchMoves[]) {
337 // Initialize global search variables
338 Idle = StopOnPonderhit = AbortSearch = Quit = false;
339 AspirationFailLow = false;
341 SearchStartTime = get_system_time();
342 ExactMaxTime = maxTime;
345 InfiniteSearch = infinite;
346 PonderSearch = ponder;
347 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
349 // Look for a book move, only during games, not tests
350 if (UseTimeManagement && get_option_value_bool("OwnBook"))
353 if (get_option_value_string("Book File") != OpeningBook.file_name())
354 OpeningBook.open(get_option_value_string("Book File"));
356 bookMove = OpeningBook.get_move(pos);
357 if (bookMove != MOVE_NONE)
360 wait_for_stop_or_ponderhit();
362 cout << "bestmove " << bookMove << endl;
367 for (int i = 0; i < THREAD_MAX; i++)
369 Threads[i].nodes = 0ULL;
372 if (button_was_pressed("New Game"))
373 loseOnTime = false; // Reset at the beginning of a new game
375 // Read UCI option values
376 TT.set_size(get_option_value_int("Hash"));
377 if (button_was_pressed("Clear Hash"))
380 bool PonderingEnabled = get_option_value_bool("Ponder");
381 MultiPV = get_option_value_int("MultiPV");
383 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
384 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
386 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
387 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
389 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
390 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
392 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
393 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
395 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
396 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
398 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
399 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
401 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
403 Chess960 = get_option_value_bool("UCI_Chess960");
404 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
405 UseLogFile = get_option_value_bool("Use Search Log");
407 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
409 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
410 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
412 read_weights(pos.side_to_move());
414 // Set the number of active threads
415 int newActiveThreads = get_option_value_int("Threads");
416 if (newActiveThreads != ActiveThreads)
418 ActiveThreads = newActiveThreads;
419 init_eval(ActiveThreads);
420 // HACK: init_eval() destroys the static castleRightsMask[] array in the
421 // Position class. The below line repairs the damage.
422 Position p(pos.to_fen());
426 // Wake up sleeping threads
427 wake_sleeping_threads();
429 for (int i = 1; i < ActiveThreads; i++)
430 assert(thread_is_available(i, 0));
433 int myTime = time[side_to_move];
434 int myIncrement = increment[side_to_move];
435 if (UseTimeManagement)
437 if (!movesToGo) // Sudden death time control
441 MaxSearchTime = myTime / 30 + myIncrement;
442 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
444 else // Blitz game without increment
446 MaxSearchTime = myTime / 30;
447 AbsoluteMaxSearchTime = myTime / 8;
450 else // (x moves) / (y minutes)
454 MaxSearchTime = myTime / 2;
455 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
459 MaxSearchTime = myTime / Min(movesToGo, 20);
460 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
464 if (PonderingEnabled)
466 MaxSearchTime += MaxSearchTime / 4;
467 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
471 // Set best NodesBetweenPolls interval
473 NodesBetweenPolls = Min(MaxNodes, 30000);
474 else if (myTime && myTime < 1000)
475 NodesBetweenPolls = 1000;
476 else if (myTime && myTime < 5000)
477 NodesBetweenPolls = 5000;
479 NodesBetweenPolls = 30000;
481 // Write information to search log file
483 LogFile << "Searching: " << pos.to_fen() << endl
484 << "infinite: " << infinite
485 << " ponder: " << ponder
486 << " time: " << myTime
487 << " increment: " << myIncrement
488 << " moves to go: " << movesToGo << endl;
490 // LSN filtering. Used only for developing purpose. Disabled by default.
494 // Step 2. If after last move we decided to lose on time, do it now!
495 while (SearchStartTime + myTime + 1000 > get_system_time())
499 // We're ready to start thinking. Call the iterative deepening loop function
500 Value v = id_loop(pos, searchMoves);
504 // Step 1. If this is sudden death game and our position is hopeless,
505 // decide to lose on time.
506 if ( !loseOnTime // If we already lost on time, go to step 3.
516 // Step 3. Now after stepping over the time limit, reset flag for next match.
529 /// init_threads() is called during startup. It launches all helper threads,
530 /// and initializes the split point stack and the global locks and condition
533 void init_threads() {
538 #if !defined(_MSC_VER)
539 pthread_t pthread[1];
542 // Init our reduction lookup tables
543 for (i = 1; i < 64; i++) // i == depth
544 for (int j = 1; j < 64; j++) // j == moveNumber
546 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
547 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
548 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
549 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
552 // Init futility margins array
553 for (i = 0; i < 14; i++) // i == depth (OnePly = 2)
554 for (int j = 0; j < 64; j++) // j == moveNumber
556 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
559 // Init futility move count array
560 for (i = 0; i < 32; i++) // i == depth (OnePly = 2)
561 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
563 for (i = 0; i < THREAD_MAX; i++)
564 Threads[i].activeSplitPoints = 0;
566 // Initialize global locks
567 lock_init(&MPLock, NULL);
568 lock_init(&IOLock, NULL);
570 init_split_point_stack();
572 #if !defined(_MSC_VER)
573 pthread_mutex_init(&WaitLock, NULL);
574 pthread_cond_init(&WaitCond, NULL);
576 for (i = 0; i < THREAD_MAX; i++)
577 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
580 // All threads except the main thread should be initialized to idle state
581 for (i = 1; i < THREAD_MAX; i++)
583 Threads[i].stop = false;
584 Threads[i].workIsWaiting = false;
585 Threads[i].idle = true;
586 Threads[i].running = false;
589 // Launch the helper threads
590 for (i = 1; i < THREAD_MAX; i++)
592 #if !defined(_MSC_VER)
593 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
596 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
601 cout << "Failed to create thread number " << i << endl;
602 Application::exit_with_failure();
605 // Wait until the thread has finished launching
606 while (!Threads[i].running);
611 /// stop_threads() is called when the program exits. It makes all the
612 /// helper threads exit cleanly.
614 void stop_threads() {
616 ActiveThreads = THREAD_MAX; // HACK
617 Idle = false; // HACK
618 wake_sleeping_threads();
619 AllThreadsShouldExit = true;
620 for (int i = 1; i < THREAD_MAX; i++)
622 Threads[i].stop = true;
623 while (Threads[i].running);
625 destroy_split_point_stack();
629 /// nodes_searched() returns the total number of nodes searched so far in
630 /// the current search.
632 int64_t nodes_searched() {
634 int64_t result = 0ULL;
635 for (int i = 0; i < ActiveThreads; i++)
636 result += Threads[i].nodes;
641 // SearchStack::init() initializes a search stack. Used at the beginning of a
642 // new search from the root.
643 void SearchStack::init(int ply) {
645 pv[ply] = pv[ply + 1] = MOVE_NONE;
646 currentMove = threatMove = MOVE_NONE;
647 reduction = Depth(0);
652 void SearchStack::initKillers() {
654 mateKiller = MOVE_NONE;
655 for (int i = 0; i < KILLER_MAX; i++)
656 killers[i] = MOVE_NONE;
661 // id_loop() is the main iterative deepening loop. It calls root_search
662 // repeatedly with increasing depth until the allocated thinking time has
663 // been consumed, the user stops the search, or the maximum search depth is
666 Value id_loop(const Position& pos, Move searchMoves[]) {
669 SearchStack ss[PLY_MAX_PLUS_2];
671 // searchMoves are verified, copied, scored and sorted
672 RootMoveList rml(p, searchMoves);
674 // Handle special case of searching on a mate/stale position
675 if (rml.move_count() == 0)
678 wait_for_stop_or_ponderhit();
680 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
683 // Print RootMoveList c'tor startup scoring to the standard output,
684 // so that we print information also for iteration 1.
685 cout << "info depth " << 1 << "\ninfo depth " << 1
686 << " score " << value_to_string(rml.get_move_score(0))
687 << " time " << current_search_time()
688 << " nodes " << nodes_searched()
690 << " pv " << rml.get_move(0) << "\n";
696 ValueByIteration[1] = rml.get_move_score(0);
699 // Is one move significantly better than others after initial scoring ?
700 Move EasyMove = MOVE_NONE;
701 if ( rml.move_count() == 1
702 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
703 EasyMove = rml.get_move(0);
705 // Iterative deepening loop
706 while (Iteration < PLY_MAX)
708 // Initialize iteration
711 BestMoveChangesByIteration[Iteration] = 0;
715 cout << "info depth " << Iteration << endl;
717 // Calculate dynamic search window based on previous iterations
720 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
722 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
723 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
725 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
726 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
728 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
729 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
733 alpha = - VALUE_INFINITE;
734 beta = VALUE_INFINITE;
737 // Search to the current depth
738 Value value = root_search(p, ss, rml, alpha, beta);
740 // Write PV to transposition table, in case the relevant entries have
741 // been overwritten during the search.
742 TT.insert_pv(p, ss[0].pv);
745 break; // Value cannot be trusted. Break out immediately!
747 //Save info about search result
748 ValueByIteration[Iteration] = value;
750 // Drop the easy move if it differs from the new best move
751 if (ss[0].pv[0] != EasyMove)
752 EasyMove = MOVE_NONE;
754 if (UseTimeManagement)
757 bool stopSearch = false;
759 // Stop search early if there is only a single legal move,
760 // we search up to Iteration 6 anyway to get a proper score.
761 if (Iteration >= 6 && rml.move_count() == 1)
764 // Stop search early when the last two iterations returned a mate score
766 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
767 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
770 // Stop search early if one move seems to be much better than the rest
771 int64_t nodes = nodes_searched();
773 && EasyMove == ss[0].pv[0]
774 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
775 && current_search_time() > MaxSearchTime / 16)
776 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
777 && current_search_time() > MaxSearchTime / 32)))
780 // Add some extra time if the best move has changed during the last two iterations
781 if (Iteration > 5 && Iteration <= 50)
782 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
783 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
785 // Stop search if most of MaxSearchTime is consumed at the end of the
786 // iteration. We probably don't have enough time to search the first
787 // move at the next iteration anyway.
788 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
796 StopOnPonderhit = true;
800 if (MaxDepth && Iteration >= MaxDepth)
806 // If we are pondering or in infinite search, we shouldn't print the
807 // best move before we are told to do so.
808 if (!AbortSearch && (PonderSearch || InfiniteSearch))
809 wait_for_stop_or_ponderhit();
811 // Print final search statistics
812 cout << "info nodes " << nodes_searched()
814 << " time " << current_search_time()
815 << " hashfull " << TT.full() << endl;
817 // Print the best move and the ponder move to the standard output
818 if (ss[0].pv[0] == MOVE_NONE)
820 ss[0].pv[0] = rml.get_move(0);
821 ss[0].pv[1] = MOVE_NONE;
823 cout << "bestmove " << ss[0].pv[0];
824 if (ss[0].pv[1] != MOVE_NONE)
825 cout << " ponder " << ss[0].pv[1];
832 dbg_print_mean(LogFile);
834 if (dbg_show_hit_rate)
835 dbg_print_hit_rate(LogFile);
837 LogFile << "\nNodes: " << nodes_searched()
838 << "\nNodes/second: " << nps()
839 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
842 p.do_move(ss[0].pv[0], st);
843 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
845 return rml.get_move_score(0);
849 // root_search() is the function which searches the root node. It is
850 // similar to search_pv except that it uses a different move ordering
851 // scheme and prints some information to the standard output.
853 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
858 Depth depth, ext, newDepth;
861 int researchCount = 0;
862 bool moveIsCheck, captureOrPromotion, dangerous;
863 Value alpha = oldAlpha;
864 bool isCheck = pos.is_check();
866 // Evaluate the position statically
868 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
870 while (1) // Fail low loop
873 // Loop through all the moves in the root move list
874 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
878 // We failed high, invalidate and skip next moves, leave node-counters
879 // and beta-counters as they are and quickly return, we will try to do
880 // a research at the next iteration with a bigger aspiration window.
881 rml.set_move_score(i, -VALUE_INFINITE);
885 RootMoveNumber = i + 1;
887 // Save the current node count before the move is searched
888 nodes = nodes_searched();
890 // Reset beta cut-off counters
893 // Pick the next root move, and print the move and the move number to
894 // the standard output.
895 move = ss[0].currentMove = rml.get_move(i);
897 if (current_search_time() >= 1000)
898 cout << "info currmove " << move
899 << " currmovenumber " << RootMoveNumber << endl;
901 // Decide search depth for this move
902 moveIsCheck = pos.move_is_check(move);
903 captureOrPromotion = pos.move_is_capture_or_promotion(move);
904 depth = (Iteration - 2) * OnePly + InitialDepth;
905 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
906 newDepth = depth + ext;
908 value = - VALUE_INFINITE;
910 while (1) // Fail high loop
913 // Make the move, and search it
914 pos.do_move(move, st, ci, moveIsCheck);
916 if (i < MultiPV || value > alpha)
918 // Aspiration window is disabled in multi-pv case
920 alpha = -VALUE_INFINITE;
922 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
926 // Try to reduce non-pv search depth by one ply if move seems not problematic,
927 // if the move fails high will be re-searched at full depth.
928 bool doFullDepthSearch = true;
930 if ( depth >= 3*OnePly // FIXME was newDepth
932 && !captureOrPromotion
933 && !move_is_castle(move))
935 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
938 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
939 doFullDepthSearch = (value > alpha);
943 if (doFullDepthSearch)
945 ss[0].reduction = Depth(0);
946 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
949 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
955 // Can we exit fail high loop ?
956 if (AbortSearch || value < beta)
959 // We are failing high and going to do a research. It's important to update score
960 // before research in case we run out of time while researching.
961 rml.set_move_score(i, value);
963 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
964 rml.set_move_pv(i, ss[0].pv);
966 // Print search information to the standard output
967 cout << "info depth " << Iteration
968 << " score " << value_to_string(value)
969 << ((value >= beta) ? " lowerbound" :
970 ((value <= alpha)? " upperbound" : ""))
971 << " time " << current_search_time()
972 << " nodes " << nodes_searched()
976 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
977 cout << ss[0].pv[j] << " ";
983 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
984 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
986 LogFile << pretty_pv(pos, current_search_time(), Iteration,
987 nodes_searched(), value, type, ss[0].pv) << endl;
990 // Prepare for a research after a fail high, each time with a wider window
992 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
994 } // End of fail high loop
996 // Finished searching the move. If AbortSearch is true, the search
997 // was aborted because the user interrupted the search or because we
998 // ran out of time. In this case, the return value of the search cannot
999 // be trusted, and we break out of the loop without updating the best
1004 // Remember beta-cutoff and searched nodes counts for this move. The
1005 // info is used to sort the root moves at the next iteration.
1007 BetaCounter.read(pos.side_to_move(), our, their);
1008 rml.set_beta_counters(i, our, their);
1009 rml.set_move_nodes(i, nodes_searched() - nodes);
1011 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1013 if (value <= alpha && i >= MultiPV)
1014 rml.set_move_score(i, -VALUE_INFINITE);
1017 // PV move or new best move!
1020 rml.set_move_score(i, value);
1022 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1023 rml.set_move_pv(i, ss[0].pv);
1027 // We record how often the best move has been changed in each
1028 // iteration. This information is used for time managment: When
1029 // the best move changes frequently, we allocate some more time.
1031 BestMoveChangesByIteration[Iteration]++;
1033 // Print search information to the standard output
1034 cout << "info depth " << Iteration
1035 << " score " << value_to_string(value)
1036 << ((value >= beta) ? " lowerbound" :
1037 ((value <= alpha)? " upperbound" : ""))
1038 << " time " << current_search_time()
1039 << " nodes " << nodes_searched()
1043 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1044 cout << ss[0].pv[j] << " ";
1050 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1051 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1053 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1054 nodes_searched(), value, type, ss[0].pv) << endl;
1061 rml.sort_multipv(i);
1062 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1064 cout << "info multipv " << j + 1
1065 << " score " << value_to_string(rml.get_move_score(j))
1066 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1067 << " time " << current_search_time()
1068 << " nodes " << nodes_searched()
1072 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1073 cout << rml.get_move_pv(j, k) << " ";
1077 alpha = rml.get_move_score(Min(i, MultiPV-1));
1079 } // PV move or new best move
1081 assert(alpha >= oldAlpha);
1083 AspirationFailLow = (alpha == oldAlpha);
1085 if (AspirationFailLow && StopOnPonderhit)
1086 StopOnPonderhit = false;
1089 // Can we exit fail low loop ?
1090 if (AbortSearch || alpha > oldAlpha)
1093 // Prepare for a research after a fail low, each time with a wider window
1095 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1104 // search_pv() is the main search function for PV nodes.
1106 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1107 Depth depth, int ply, int threadID) {
1109 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1110 assert(beta > alpha && beta <= VALUE_INFINITE);
1111 assert(ply >= 0 && ply < PLY_MAX);
1112 assert(threadID >= 0 && threadID < ActiveThreads);
1114 Move movesSearched[256];
1118 Depth ext, newDepth;
1119 Value oldAlpha, value;
1120 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1122 Value bestValue = value = -VALUE_INFINITE;
1125 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1127 // Initialize, and make an early exit in case of an aborted search,
1128 // an instant draw, maximum ply reached, etc.
1129 init_node(ss, ply, threadID);
1131 // After init_node() that calls poll()
1132 if (AbortSearch || thread_should_stop(threadID))
1135 if (pos.is_draw() || ply >= PLY_MAX - 1)
1138 // Mate distance pruning
1140 alpha = Max(value_mated_in(ply), alpha);
1141 beta = Min(value_mate_in(ply+1), beta);
1145 // Transposition table lookup. At PV nodes, we don't use the TT for
1146 // pruning, but only for move ordering. This is to avoid problems in
1147 // the following areas:
1149 // * Repetition draw detection
1150 // * Fifty move rule detection
1151 // * Searching for a mate
1152 // * Printing of full PV line
1154 tte = TT.retrieve(pos.get_key());
1155 ttMove = (tte ? tte->move() : MOVE_NONE);
1157 // Go with internal iterative deepening if we don't have a TT move
1158 if ( UseIIDAtPVNodes
1159 && depth >= 5*OnePly
1160 && ttMove == MOVE_NONE)
1162 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1163 ttMove = ss[ply].pv[ply];
1164 tte = TT.retrieve(pos.get_key());
1167 isCheck = pos.is_check();
1170 // Update gain statistics of the previous move that lead
1171 // us in this position.
1173 ss[ply].eval = evaluate(pos, ei, threadID);
1174 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1177 // Initialize a MovePicker object for the current position, and prepare
1178 // to search all moves
1179 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1181 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1183 // Loop through all legal moves until no moves remain or a beta cutoff
1185 while ( alpha < beta
1186 && (move = mp.get_next_move()) != MOVE_NONE
1187 && !thread_should_stop(threadID))
1189 assert(move_is_ok(move));
1191 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1192 moveIsCheck = pos.move_is_check(move, ci);
1193 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1195 // Decide the new search depth
1196 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1198 // Singular extension search. We extend the TT move if its value is much better than
1199 // its siblings. To verify this we do a reduced search on all the other moves but the
1200 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1201 if ( depth >= 6 * OnePly
1203 && move == tte->move()
1205 && is_lower_bound(tte->type())
1206 && tte->depth() >= depth - 3 * OnePly)
1208 Value ttValue = value_from_tt(tte->value(), ply);
1210 if (abs(ttValue) < VALUE_KNOWN_WIN)
1212 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1214 if (excValue < ttValue - SingleReplyMargin)
1219 newDepth = depth - OnePly + ext;
1221 // Update current move
1222 movesSearched[moveCount++] = ss[ply].currentMove = move;
1224 // Make and search the move
1225 pos.do_move(move, st, ci, moveIsCheck);
1227 if (moveCount == 1) // The first move in list is the PV
1228 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1231 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1232 // if the move fails high will be re-searched at full depth.
1233 bool doFullDepthSearch = true;
1235 if ( depth >= 3*OnePly
1237 && !captureOrPromotion
1238 && !move_is_castle(move)
1239 && !move_is_killer(move, ss[ply]))
1241 ss[ply].reduction = pv_reduction(depth, moveCount);
1242 if (ss[ply].reduction)
1244 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1245 doFullDepthSearch = (value > alpha);
1249 if (doFullDepthSearch) // Go with full depth non-pv search
1251 ss[ply].reduction = Depth(0);
1252 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1253 if (value > alpha && value < beta)
1254 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1257 pos.undo_move(move);
1259 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1262 if (value > bestValue)
1269 if (value == value_mate_in(ply + 1))
1270 ss[ply].mateKiller = move;
1275 if ( ActiveThreads > 1
1277 && depth >= MinimumSplitDepth
1279 && idle_thread_exists(threadID)
1281 && !thread_should_stop(threadID)
1282 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1283 depth, &moveCount, &mp, threadID, true))
1287 // All legal moves have been searched. A special case: If there were
1288 // no legal moves, it must be mate or stalemate.
1290 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1292 // If the search is not aborted, update the transposition table,
1293 // history counters, and killer moves.
1294 if (AbortSearch || thread_should_stop(threadID))
1297 if (bestValue <= oldAlpha)
1298 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1300 else if (bestValue >= beta)
1302 BetaCounter.add(pos.side_to_move(), depth, threadID);
1303 move = ss[ply].pv[ply];
1304 if (!pos.move_is_capture_or_promotion(move))
1306 update_history(pos, move, depth, movesSearched, moveCount);
1307 update_killers(move, ss[ply]);
1309 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1312 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1318 // search() is the search function for zero-width nodes.
1320 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1321 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1323 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1324 assert(ply >= 0 && ply < PLY_MAX);
1325 assert(threadID >= 0 && threadID < ActiveThreads);
1327 Move movesSearched[256];
1332 Depth ext, newDepth;
1333 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1334 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1335 bool mateThreat = false;
1337 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1340 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1342 // Initialize, and make an early exit in case of an aborted search,
1343 // an instant draw, maximum ply reached, etc.
1344 init_node(ss, ply, threadID);
1346 // After init_node() that calls poll()
1347 if (AbortSearch || thread_should_stop(threadID))
1350 if (pos.is_draw() || ply >= PLY_MAX - 1)
1353 // Mate distance pruning
1354 if (value_mated_in(ply) >= beta)
1357 if (value_mate_in(ply + 1) < beta)
1360 // We don't want the score of a partial search to overwrite a previous full search
1361 // TT value, so we use a different position key in case of an excluded move exsists.
1362 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1364 // Transposition table lookup
1365 tte = TT.retrieve(posKey);
1366 ttMove = (tte ? tte->move() : MOVE_NONE);
1368 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1370 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1371 return value_from_tt(tte->value(), ply);
1374 isCheck = pos.is_check();
1376 // Evaluate the position statically
1379 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1380 staticValue = value_from_tt(tte->value(), ply);
1383 staticValue = evaluate(pos, ei, threadID);
1384 ss[ply].evalInfo = &ei;
1387 ss[ply].eval = staticValue;
1388 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1389 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1390 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1393 // Static null move pruning. We're betting that the opponent doesn't have
1394 // a move that will reduce the score by more than FutilityMargins[int(depth)]
1395 // if we do a null move.
1398 && depth < RazorDepth
1399 && staticValue - futility_margin(depth, 0) >= beta)
1400 return staticValue - futility_margin(depth, 0);
1406 && !value_is_mate(beta)
1407 && ok_to_do_nullmove(pos)
1408 && staticValue >= beta - NullMoveMargin)
1410 ss[ply].currentMove = MOVE_NULL;
1412 pos.do_null_move(st);
1414 // Null move dynamic reduction based on depth
1415 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1417 // Null move dynamic reduction based on value
1418 if (staticValue - beta > PawnValueMidgame)
1421 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1423 pos.undo_null_move();
1425 if (nullValue >= beta)
1427 if (depth < 6 * OnePly)
1430 // Do zugzwang verification search
1431 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1435 // The null move failed low, which means that we may be faced with
1436 // some kind of threat. If the previous move was reduced, check if
1437 // the move that refuted the null move was somehow connected to the
1438 // move which was reduced. If a connection is found, return a fail
1439 // low score (which will cause the reduced move to fail high in the
1440 // parent node, which will trigger a re-search with full depth).
1441 if (nullValue == value_mated_in(ply + 2))
1444 ss[ply].threatMove = ss[ply + 1].currentMove;
1445 if ( depth < ThreatDepth
1446 && ss[ply - 1].reduction
1447 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1451 // Null move search not allowed, try razoring
1452 else if ( !value_is_mate(beta)
1454 && depth < RazorDepth
1455 && staticValue < beta - (NullMoveMargin + 16 * depth)
1456 && ss[ply - 1].currentMove != MOVE_NULL
1457 && ttMove == MOVE_NONE
1458 && !pos.has_pawn_on_7th(pos.side_to_move()))
1460 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1461 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1466 // Go with internal iterative deepening if we don't have a TT move
1467 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1468 !isCheck && ss[ply].eval >= beta - IIDMargin)
1470 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1471 ttMove = ss[ply].pv[ply];
1472 tte = TT.retrieve(posKey);
1475 // Initialize a MovePicker object for the current position, and prepare
1476 // to search all moves.
1477 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1480 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1481 while ( bestValue < beta
1482 && (move = mp.get_next_move()) != MOVE_NONE
1483 && !thread_should_stop(threadID))
1485 assert(move_is_ok(move));
1487 if (move == excludedMove)
1490 moveIsCheck = pos.move_is_check(move, ci);
1491 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1492 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1494 // Decide the new search depth
1495 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1497 // Singular extension search. We extend the TT move if its value is much better than
1498 // its siblings. To verify this we do a reduced search on all the other moves but the
1499 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1500 if ( depth >= 8 * OnePly
1502 && move == tte->move()
1503 && !excludedMove // Do not allow recursive single-reply search
1505 && is_lower_bound(tte->type())
1506 && tte->depth() >= depth - 3 * OnePly)
1508 Value ttValue = value_from_tt(tte->value(), ply);
1510 if (abs(ttValue) < VALUE_KNOWN_WIN)
1512 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1514 if (excValue < ttValue - SingleReplyMargin)
1519 newDepth = depth - OnePly + ext;
1521 // Update current move
1522 movesSearched[moveCount++] = ss[ply].currentMove = move;
1527 && !captureOrPromotion
1528 && !move_is_castle(move)
1531 // Move count based pruning
1532 if ( moveCount >= futility_move_count(depth)
1533 && ok_to_prune(pos, move, ss[ply].threatMove)
1534 && bestValue > value_mated_in(PLY_MAX))
1537 // Value based pruning
1538 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1539 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount) + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1541 if (futilityValueScaled < beta)
1543 if (futilityValueScaled > bestValue)
1544 bestValue = futilityValueScaled;
1549 // Make and search the move
1550 pos.do_move(move, st, ci, moveIsCheck);
1552 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1553 // if the move fails high will be re-searched at full depth.
1554 bool doFullDepthSearch = true;
1556 if ( depth >= 3*OnePly
1558 && !captureOrPromotion
1559 && !move_is_castle(move)
1560 && !move_is_killer(move, ss[ply]))
1562 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1563 if (ss[ply].reduction)
1565 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1566 doFullDepthSearch = (value >= beta);
1570 if (doFullDepthSearch) // Go with full depth non-pv search
1572 ss[ply].reduction = Depth(0);
1573 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1575 pos.undo_move(move);
1577 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1580 if (value > bestValue)
1586 if (value == value_mate_in(ply + 1))
1587 ss[ply].mateKiller = move;
1591 if ( ActiveThreads > 1
1593 && depth >= MinimumSplitDepth
1595 && idle_thread_exists(threadID)
1597 && !thread_should_stop(threadID)
1598 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1599 depth, &moveCount, &mp, threadID, false))
1603 // All legal moves have been searched. A special case: If there were
1604 // no legal moves, it must be mate or stalemate.
1606 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1608 // If the search is not aborted, update the transposition table,
1609 // history counters, and killer moves.
1610 if (AbortSearch || thread_should_stop(threadID))
1613 if (bestValue < beta)
1614 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1617 BetaCounter.add(pos.side_to_move(), depth, threadID);
1618 move = ss[ply].pv[ply];
1619 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1620 if (!pos.move_is_capture_or_promotion(move))
1622 update_history(pos, move, depth, movesSearched, moveCount);
1623 update_killers(move, ss[ply]);
1628 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1634 // qsearch() is the quiescence search function, which is called by the main
1635 // search function when the remaining depth is zero (or, to be more precise,
1636 // less than OnePly).
1638 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1639 Depth depth, int ply, int threadID) {
1641 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1642 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1644 assert(ply >= 0 && ply < PLY_MAX);
1645 assert(threadID >= 0 && threadID < ActiveThreads);
1650 Value staticValue, bestValue, value, futilityBase, futilityValue;
1651 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1652 const TTEntry* tte = NULL;
1654 bool pvNode = (beta - alpha != 1);
1655 Value oldAlpha = alpha;
1657 // Initialize, and make an early exit in case of an aborted search,
1658 // an instant draw, maximum ply reached, etc.
1659 init_node(ss, ply, threadID);
1661 // After init_node() that calls poll()
1662 if (AbortSearch || thread_should_stop(threadID))
1665 if (pos.is_draw() || ply >= PLY_MAX - 1)
1668 // Transposition table lookup. At PV nodes, we don't use the TT for
1669 // pruning, but only for move ordering.
1670 tte = TT.retrieve(pos.get_key());
1671 ttMove = (tte ? tte->move() : MOVE_NONE);
1673 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1675 assert(tte->type() != VALUE_TYPE_EVAL);
1677 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1678 return value_from_tt(tte->value(), ply);
1681 isCheck = pos.is_check();
1683 // Evaluate the position statically
1685 staticValue = -VALUE_INFINITE;
1686 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1687 staticValue = value_from_tt(tte->value(), ply);
1689 staticValue = evaluate(pos, ei, threadID);
1693 ss[ply].eval = staticValue;
1694 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1697 // Initialize "stand pat score", and return it immediately if it is
1699 bestValue = staticValue;
1701 if (bestValue >= beta)
1703 // Store the score to avoid a future costly evaluation() call
1704 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1705 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1710 if (bestValue > alpha)
1713 // If we are near beta then try to get a cutoff pushing checks a bit further
1714 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1716 // Initialize a MovePicker object for the current position, and prepare
1717 // to search the moves. Because the depth is <= 0 here, only captures,
1718 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1719 // and we are near beta) will be generated.
1720 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1722 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1723 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1725 // Loop through the moves until no moves remain or a beta cutoff
1727 while ( alpha < beta
1728 && (move = mp.get_next_move()) != MOVE_NONE)
1730 assert(move_is_ok(move));
1732 moveIsCheck = pos.move_is_check(move, ci);
1734 // Update current move
1736 ss[ply].currentMove = move;
1744 && !move_is_promotion(move)
1745 && !pos.move_is_passed_pawn_push(move))
1747 futilityValue = futilityBase
1748 + pos.endgame_value_of_piece_on(move_to(move))
1749 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1751 if (futilityValue < alpha)
1753 if (futilityValue > bestValue)
1754 bestValue = futilityValue;
1759 // Detect blocking evasions that are candidate to be pruned
1760 evasionPrunable = isCheck
1761 && bestValue != -VALUE_INFINITE
1762 && !pos.move_is_capture(move)
1763 && pos.type_of_piece_on(move_from(move)) != KING
1764 && !pos.can_castle(pos.side_to_move());
1766 // Don't search moves with negative SEE values
1767 if ( (!isCheck || evasionPrunable)
1769 && !move_is_promotion(move)
1770 && pos.see_sign(move) < 0)
1773 // Make and search the move
1774 pos.do_move(move, st, ci, moveIsCheck);
1775 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1776 pos.undo_move(move);
1778 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1781 if (value > bestValue)
1792 // All legal moves have been searched. A special case: If we're in check
1793 // and no legal moves were found, it is checkmate.
1794 if (!moveCount && pos.is_check()) // Mate!
1795 return value_mated_in(ply);
1797 // Update transposition table
1798 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1799 if (bestValue <= oldAlpha)
1801 // If bestValue isn't changed it means it is still the static evaluation
1802 // of the node, so keep this info to avoid a future evaluation() call.
1803 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1804 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1806 else if (bestValue >= beta)
1808 move = ss[ply].pv[ply];
1809 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1811 // Update killers only for good checking moves
1812 if (!pos.move_is_capture_or_promotion(move))
1813 update_killers(move, ss[ply]);
1816 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1818 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1824 // sp_search() is used to search from a split point. This function is called
1825 // by each thread working at the split point. It is similar to the normal
1826 // search() function, but simpler. Because we have already probed the hash
1827 // table, done a null move search, and searched the first move before
1828 // splitting, we don't have to repeat all this work in sp_search(). We
1829 // also don't need to store anything to the hash table here: This is taken
1830 // care of after we return from the split point.
1832 void sp_search(SplitPoint* sp, int threadID) {
1834 assert(threadID >= 0 && threadID < ActiveThreads);
1835 assert(ActiveThreads > 1);
1837 Position pos(*sp->pos);
1839 SearchStack* ss = sp->sstack[threadID];
1840 Value value = -VALUE_INFINITE;
1843 bool isCheck = pos.is_check();
1844 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1847 while ( lock_grab_bool(&(sp->lock))
1848 && sp->bestValue < sp->beta
1849 && !thread_should_stop(threadID)
1850 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1852 moveCount = ++sp->moves;
1853 lock_release(&(sp->lock));
1855 assert(move_is_ok(move));
1857 bool moveIsCheck = pos.move_is_check(move, ci);
1858 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1860 ss[sp->ply].currentMove = move;
1862 // Decide the new search depth
1864 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1865 Depth newDepth = sp->depth - OnePly + ext;
1868 if ( useFutilityPruning
1870 && !captureOrPromotion)
1872 // Move count based pruning
1873 if ( moveCount >= futility_move_count(sp->depth)
1874 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1875 && sp->bestValue > value_mated_in(PLY_MAX))
1878 // Value based pruning
1879 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1881 if (futilityValueScaled < sp->beta)
1883 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1885 lock_grab(&(sp->lock));
1886 if (futilityValueScaled > sp->bestValue)
1887 sp->bestValue = futilityValueScaled;
1888 lock_release(&(sp->lock));
1894 // Make and search the move.
1896 pos.do_move(move, st, ci, moveIsCheck);
1898 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1899 // if the move fails high will be re-searched at full depth.
1900 bool doFullDepthSearch = true;
1903 && !captureOrPromotion
1904 && !move_is_castle(move)
1905 && !move_is_killer(move, ss[sp->ply]))
1907 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1908 if (ss[sp->ply].reduction)
1910 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1911 doFullDepthSearch = (value >= sp->beta);
1915 if (doFullDepthSearch) // Go with full depth non-pv search
1917 ss[sp->ply].reduction = Depth(0);
1918 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1920 pos.undo_move(move);
1922 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1924 if (thread_should_stop(threadID))
1926 lock_grab(&(sp->lock));
1931 if (value > sp->bestValue) // Less then 2% of cases
1933 lock_grab(&(sp->lock));
1934 if (value > sp->bestValue && !thread_should_stop(threadID))
1936 sp->bestValue = value;
1937 if (sp->bestValue >= sp->beta)
1939 sp_update_pv(sp->parentSstack, ss, sp->ply);
1940 for (int i = 0; i < ActiveThreads; i++)
1941 if (i != threadID && (i == sp->master || sp->slaves[i]))
1942 Threads[i].stop = true;
1944 sp->finished = true;
1947 lock_release(&(sp->lock));
1951 /* Here we have the lock still grabbed */
1953 // If this is the master thread and we have been asked to stop because of
1954 // a beta cutoff higher up in the tree, stop all slave threads.
1955 if (sp->master == threadID && thread_should_stop(threadID))
1956 for (int i = 0; i < ActiveThreads; i++)
1958 Threads[i].stop = true;
1961 sp->slaves[threadID] = 0;
1963 lock_release(&(sp->lock));
1967 // sp_search_pv() is used to search from a PV split point. This function
1968 // is called by each thread working at the split point. It is similar to
1969 // the normal search_pv() function, but simpler. Because we have already
1970 // probed the hash table and searched the first move before splitting, we
1971 // don't have to repeat all this work in sp_search_pv(). We also don't
1972 // need to store anything to the hash table here: This is taken care of
1973 // after we return from the split point.
1975 void sp_search_pv(SplitPoint* sp, int threadID) {
1977 assert(threadID >= 0 && threadID < ActiveThreads);
1978 assert(ActiveThreads > 1);
1980 Position pos(*sp->pos);
1982 SearchStack* ss = sp->sstack[threadID];
1983 Value value = -VALUE_INFINITE;
1987 while ( lock_grab_bool(&(sp->lock))
1988 && sp->alpha < sp->beta
1989 && !thread_should_stop(threadID)
1990 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1992 moveCount = ++sp->moves;
1993 lock_release(&(sp->lock));
1995 assert(move_is_ok(move));
1997 bool moveIsCheck = pos.move_is_check(move, ci);
1998 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
2000 ss[sp->ply].currentMove = move;
2002 // Decide the new search depth
2004 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
2005 Depth newDepth = sp->depth - OnePly + ext;
2007 // Make and search the move.
2009 pos.do_move(move, st, ci, moveIsCheck);
2011 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2012 // if the move fails high will be re-searched at full depth.
2013 bool doFullDepthSearch = true;
2016 && !captureOrPromotion
2017 && !move_is_castle(move)
2018 && !move_is_killer(move, ss[sp->ply]))
2020 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
2021 if (ss[sp->ply].reduction)
2023 Value localAlpha = sp->alpha;
2024 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2025 doFullDepthSearch = (value > localAlpha);
2029 if (doFullDepthSearch) // Go with full depth non-pv search
2031 Value localAlpha = sp->alpha;
2032 ss[sp->ply].reduction = Depth(0);
2033 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2035 if (value > localAlpha && value < sp->beta)
2037 // If another thread has failed high then sp->alpha has been increased
2038 // to be higher or equal then beta, if so, avoid to start a PV search.
2039 localAlpha = sp->alpha;
2040 if (localAlpha < sp->beta)
2041 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2043 assert(thread_should_stop(threadID));
2046 pos.undo_move(move);
2048 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2050 if (thread_should_stop(threadID))
2052 lock_grab(&(sp->lock));
2057 if (value > sp->bestValue) // Less then 2% of cases
2059 lock_grab(&(sp->lock));
2060 if (value > sp->bestValue && !thread_should_stop(threadID))
2062 sp->bestValue = value;
2063 if (value > sp->alpha)
2065 // Ask threads to stop before to modify sp->alpha
2066 if (value >= sp->beta)
2068 for (int i = 0; i < ActiveThreads; i++)
2069 if (i != threadID && (i == sp->master || sp->slaves[i]))
2070 Threads[i].stop = true;
2072 sp->finished = true;
2077 sp_update_pv(sp->parentSstack, ss, sp->ply);
2078 if (value == value_mate_in(sp->ply + 1))
2079 ss[sp->ply].mateKiller = move;
2082 lock_release(&(sp->lock));
2086 /* Here we have the lock still grabbed */
2088 // If this is the master thread and we have been asked to stop because of
2089 // a beta cutoff higher up in the tree, stop all slave threads.
2090 if (sp->master == threadID && thread_should_stop(threadID))
2091 for (int i = 0; i < ActiveThreads; i++)
2093 Threads[i].stop = true;
2096 sp->slaves[threadID] = 0;
2098 lock_release(&(sp->lock));
2101 /// The BetaCounterType class
2103 BetaCounterType::BetaCounterType() { clear(); }
2105 void BetaCounterType::clear() {
2107 for (int i = 0; i < THREAD_MAX; i++)
2108 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2111 void BetaCounterType::add(Color us, Depth d, int threadID) {
2113 // Weighted count based on depth
2114 Threads[threadID].betaCutOffs[us] += unsigned(d);
2117 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2120 for (int i = 0; i < THREAD_MAX; i++)
2122 our += Threads[i].betaCutOffs[us];
2123 their += Threads[i].betaCutOffs[opposite_color(us)];
2128 /// The RootMoveList class
2130 // RootMoveList c'tor
2132 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2134 SearchStack ss[PLY_MAX_PLUS_2];
2135 MoveStack mlist[MaxRootMoves];
2137 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2139 // Generate all legal moves
2140 MoveStack* last = generate_moves(pos, mlist);
2142 // Add each move to the moves[] array
2143 for (MoveStack* cur = mlist; cur != last; cur++)
2145 bool includeMove = includeAllMoves;
2147 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2148 includeMove = (searchMoves[k] == cur->move);
2153 // Find a quick score for the move
2155 pos.do_move(cur->move, st);
2156 moves[count].move = cur->move;
2157 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2158 moves[count].pv[0] = cur->move;
2159 moves[count].pv[1] = MOVE_NONE;
2160 pos.undo_move(cur->move);
2167 // RootMoveList simple methods definitions
2169 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2171 moves[moveNum].nodes = nodes;
2172 moves[moveNum].cumulativeNodes += nodes;
2175 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2177 moves[moveNum].ourBeta = our;
2178 moves[moveNum].theirBeta = their;
2181 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2185 for (j = 0; pv[j] != MOVE_NONE; j++)
2186 moves[moveNum].pv[j] = pv[j];
2188 moves[moveNum].pv[j] = MOVE_NONE;
2192 // RootMoveList::sort() sorts the root move list at the beginning of a new
2195 void RootMoveList::sort() {
2197 sort_multipv(count - 1); // Sort all items
2201 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2202 // list by their scores and depths. It is used to order the different PVs
2203 // correctly in MultiPV mode.
2205 void RootMoveList::sort_multipv(int n) {
2209 for (i = 1; i <= n; i++)
2211 RootMove rm = moves[i];
2212 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2213 moves[j] = moves[j - 1];
2220 // init_node() is called at the beginning of all the search functions
2221 // (search(), search_pv(), qsearch(), and so on) and initializes the
2222 // search stack object corresponding to the current node. Once every
2223 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2224 // for user input and checks whether it is time to stop the search.
2226 void init_node(SearchStack ss[], int ply, int threadID) {
2228 assert(ply >= 0 && ply < PLY_MAX);
2229 assert(threadID >= 0 && threadID < ActiveThreads);
2231 Threads[threadID].nodes++;
2236 if (NodesSincePoll >= NodesBetweenPolls)
2243 ss[ply + 2].initKillers();
2245 if (Threads[threadID].printCurrentLine)
2246 print_current_line(ss, ply, threadID);
2250 // update_pv() is called whenever a search returns a value > alpha.
2251 // It updates the PV in the SearchStack object corresponding to the
2254 void update_pv(SearchStack ss[], int ply) {
2256 assert(ply >= 0 && ply < PLY_MAX);
2260 ss[ply].pv[ply] = ss[ply].currentMove;
2262 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2263 ss[ply].pv[p] = ss[ply + 1].pv[p];
2265 ss[ply].pv[p] = MOVE_NONE;
2269 // sp_update_pv() is a variant of update_pv for use at split points. The
2270 // difference between the two functions is that sp_update_pv also updates
2271 // the PV at the parent node.
2273 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2275 assert(ply >= 0 && ply < PLY_MAX);
2279 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2281 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2282 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2284 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2288 // connected_moves() tests whether two moves are 'connected' in the sense
2289 // that the first move somehow made the second move possible (for instance
2290 // if the moving piece is the same in both moves). The first move is assumed
2291 // to be the move that was made to reach the current position, while the
2292 // second move is assumed to be a move from the current position.
2294 bool connected_moves(const Position& pos, Move m1, Move m2) {
2296 Square f1, t1, f2, t2;
2299 assert(move_is_ok(m1));
2300 assert(move_is_ok(m2));
2302 if (m2 == MOVE_NONE)
2305 // Case 1: The moving piece is the same in both moves
2311 // Case 2: The destination square for m2 was vacated by m1
2317 // Case 3: Moving through the vacated square
2318 if ( piece_is_slider(pos.piece_on(f2))
2319 && bit_is_set(squares_between(f2, t2), f1))
2322 // Case 4: The destination square for m2 is defended by the moving piece in m1
2323 p = pos.piece_on(t1);
2324 if (bit_is_set(pos.attacks_from(p, t1), t2))
2327 // Case 5: Discovered check, checking piece is the piece moved in m1
2328 if ( piece_is_slider(p)
2329 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2330 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2332 // discovered_check_candidates() works also if the Position's side to
2333 // move is the opposite of the checking piece.
2334 Color them = opposite_color(pos.side_to_move());
2335 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2337 if (bit_is_set(dcCandidates, f2))
2344 // value_is_mate() checks if the given value is a mate one
2345 // eventually compensated for the ply.
2347 bool value_is_mate(Value value) {
2349 assert(abs(value) <= VALUE_INFINITE);
2351 return value <= value_mated_in(PLY_MAX)
2352 || value >= value_mate_in(PLY_MAX);
2356 // move_is_killer() checks if the given move is among the
2357 // killer moves of that ply.
2359 bool move_is_killer(Move m, const SearchStack& ss) {
2361 const Move* k = ss.killers;
2362 for (int i = 0; i < KILLER_MAX; i++, k++)
2370 // extension() decides whether a move should be searched with normal depth,
2371 // or with extended depth. Certain classes of moves (checking moves, in
2372 // particular) are searched with bigger depth than ordinary moves and in
2373 // any case are marked as 'dangerous'. Note that also if a move is not
2374 // extended, as example because the corresponding UCI option is set to zero,
2375 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2377 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2378 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2380 assert(m != MOVE_NONE);
2382 Depth result = Depth(0);
2383 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2388 result += CheckExtension[pvNode];
2391 result += SingleEvasionExtension[pvNode];
2394 result += MateThreatExtension[pvNode];
2397 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2399 Color c = pos.side_to_move();
2400 if (relative_rank(c, move_to(m)) == RANK_7)
2402 result += PawnPushTo7thExtension[pvNode];
2405 if (pos.pawn_is_passed(c, move_to(m)))
2407 result += PassedPawnExtension[pvNode];
2412 if ( captureOrPromotion
2413 && pos.type_of_piece_on(move_to(m)) != PAWN
2414 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2415 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2416 && !move_is_promotion(m)
2419 result += PawnEndgameExtension[pvNode];
2424 && captureOrPromotion
2425 && pos.type_of_piece_on(move_to(m)) != PAWN
2426 && pos.see_sign(m) >= 0)
2432 return Min(result, OnePly);
2436 // ok_to_do_nullmove() looks at the current position and decides whether
2437 // doing a 'null move' should be allowed. In order to avoid zugzwang
2438 // problems, null moves are not allowed when the side to move has very
2439 // little material left. Currently, the test is a bit too simple: Null
2440 // moves are avoided only when the side to move has only pawns left.
2441 // It's probably a good idea to avoid null moves in at least some more
2442 // complicated endgames, e.g. KQ vs KR. FIXME
2444 bool ok_to_do_nullmove(const Position& pos) {
2446 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2450 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2451 // non-tactical moves late in the move list close to the leaves are
2452 // candidates for pruning.
2454 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2456 assert(move_is_ok(m));
2457 assert(threat == MOVE_NONE || move_is_ok(threat));
2458 assert(!pos.move_is_check(m));
2459 assert(!pos.move_is_capture_or_promotion(m));
2460 assert(!pos.move_is_passed_pawn_push(m));
2462 Square mfrom, mto, tfrom, tto;
2464 // Prune if there isn't any threat move
2465 if (threat == MOVE_NONE)
2468 mfrom = move_from(m);
2470 tfrom = move_from(threat);
2471 tto = move_to(threat);
2473 // Case 1: Don't prune moves which move the threatened piece
2477 // Case 2: If the threatened piece has value less than or equal to the
2478 // value of the threatening piece, don't prune move which defend it.
2479 if ( pos.move_is_capture(threat)
2480 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2481 || pos.type_of_piece_on(tfrom) == KING)
2482 && pos.move_attacks_square(m, tto))
2485 // Case 3: If the moving piece in the threatened move is a slider, don't
2486 // prune safe moves which block its ray.
2487 if ( piece_is_slider(pos.piece_on(tfrom))
2488 && bit_is_set(squares_between(tfrom, tto), mto)
2489 && pos.see_sign(m) >= 0)
2496 // ok_to_use_TT() returns true if a transposition table score
2497 // can be used at a given point in search.
2499 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2501 Value v = value_from_tt(tte->value(), ply);
2503 return ( tte->depth() >= depth
2504 || v >= Max(value_mate_in(PLY_MAX), beta)
2505 || v < Min(value_mated_in(PLY_MAX), beta))
2507 && ( (is_lower_bound(tte->type()) && v >= beta)
2508 || (is_upper_bound(tte->type()) && v < beta));
2512 // refine_eval() returns the transposition table score if
2513 // possible otherwise falls back on static position evaluation.
2515 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2520 Value v = value_from_tt(tte->value(), ply);
2522 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2523 || (is_upper_bound(tte->type()) && v < defaultEval))
2530 // update_history() registers a good move that produced a beta-cutoff
2531 // in history and marks as failures all the other moves of that ply.
2533 void update_history(const Position& pos, Move move, Depth depth,
2534 Move movesSearched[], int moveCount) {
2538 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2540 for (int i = 0; i < moveCount - 1; i++)
2542 m = movesSearched[i];
2546 if (!pos.move_is_capture_or_promotion(m))
2547 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2552 // update_killers() add a good move that produced a beta-cutoff
2553 // among the killer moves of that ply.
2555 void update_killers(Move m, SearchStack& ss) {
2557 if (m == ss.killers[0])
2560 for (int i = KILLER_MAX - 1; i > 0; i--)
2561 ss.killers[i] = ss.killers[i - 1];
2567 // update_gains() updates the gains table of a non-capture move given
2568 // the static position evaluation before and after the move.
2570 void update_gains(const Position& pos, Move m, Value before, Value after) {
2573 && before != VALUE_NONE
2574 && after != VALUE_NONE
2575 && pos.captured_piece() == NO_PIECE_TYPE
2576 && !move_is_castle(m)
2577 && !move_is_promotion(m))
2578 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2582 // current_search_time() returns the number of milliseconds which have passed
2583 // since the beginning of the current search.
2585 int current_search_time() {
2587 return get_system_time() - SearchStartTime;
2591 // nps() computes the current nodes/second count.
2595 int t = current_search_time();
2596 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2600 // poll() performs two different functions: It polls for user input, and it
2601 // looks at the time consumed so far and decides if it's time to abort the
2606 static int lastInfoTime;
2607 int t = current_search_time();
2612 // We are line oriented, don't read single chars
2613 std::string command;
2615 if (!std::getline(std::cin, command))
2618 if (command == "quit")
2621 PonderSearch = false;
2625 else if (command == "stop")
2628 PonderSearch = false;
2630 else if (command == "ponderhit")
2634 // Print search information
2638 else if (lastInfoTime > t)
2639 // HACK: Must be a new search where we searched less than
2640 // NodesBetweenPolls nodes during the first second of search.
2643 else if (t - lastInfoTime >= 1000)
2651 if (dbg_show_hit_rate)
2652 dbg_print_hit_rate();
2654 cout << "info nodes " << nodes_searched() << " nps " << nps()
2655 << " time " << t << " hashfull " << TT.full() << endl;
2657 lock_release(&IOLock);
2659 if (ShowCurrentLine)
2660 Threads[0].printCurrentLine = true;
2663 // Should we stop the search?
2667 bool stillAtFirstMove = RootMoveNumber == 1
2668 && !AspirationFailLow
2669 && t > MaxSearchTime + ExtraSearchTime;
2671 bool noMoreTime = t > AbsoluteMaxSearchTime
2672 || stillAtFirstMove;
2674 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2675 || (ExactMaxTime && t >= ExactMaxTime)
2676 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2681 // ponderhit() is called when the program is pondering (i.e. thinking while
2682 // it's the opponent's turn to move) in order to let the engine know that
2683 // it correctly predicted the opponent's move.
2687 int t = current_search_time();
2688 PonderSearch = false;
2690 bool stillAtFirstMove = RootMoveNumber == 1
2691 && !AspirationFailLow
2692 && t > MaxSearchTime + ExtraSearchTime;
2694 bool noMoreTime = t > AbsoluteMaxSearchTime
2695 || stillAtFirstMove;
2697 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2702 // print_current_line() prints the current line of search for a given
2703 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2705 void print_current_line(SearchStack ss[], int ply, int threadID) {
2707 assert(ply >= 0 && ply < PLY_MAX);
2708 assert(threadID >= 0 && threadID < ActiveThreads);
2710 if (!Threads[threadID].idle)
2713 cout << "info currline " << (threadID + 1);
2714 for (int p = 0; p < ply; p++)
2715 cout << " " << ss[p].currentMove;
2718 lock_release(&IOLock);
2720 Threads[threadID].printCurrentLine = false;
2721 if (threadID + 1 < ActiveThreads)
2722 Threads[threadID + 1].printCurrentLine = true;
2726 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2728 void init_ss_array(SearchStack ss[]) {
2730 for (int i = 0; i < 3; i++)
2733 ss[i].initKillers();
2738 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2739 // while the program is pondering. The point is to work around a wrinkle in
2740 // the UCI protocol: When pondering, the engine is not allowed to give a
2741 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2742 // We simply wait here until one of these commands is sent, and return,
2743 // after which the bestmove and pondermove will be printed (in id_loop()).
2745 void wait_for_stop_or_ponderhit() {
2747 std::string command;
2751 if (!std::getline(std::cin, command))
2754 if (command == "quit")
2759 else if (command == "ponderhit" || command == "stop")
2765 // idle_loop() is where the threads are parked when they have no work to do.
2766 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2767 // object for which the current thread is the master.
2769 void idle_loop(int threadID, SplitPoint* waitSp) {
2771 assert(threadID >= 0 && threadID < THREAD_MAX);
2773 Threads[threadID].running = true;
2777 if (AllThreadsShouldExit && threadID != 0)
2780 // If we are not thinking, wait for a condition to be signaled
2781 // instead of wasting CPU time polling for work.
2782 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2785 #if !defined(_MSC_VER)
2786 pthread_mutex_lock(&WaitLock);
2787 if (Idle || threadID >= ActiveThreads)
2788 pthread_cond_wait(&WaitCond, &WaitLock);
2790 pthread_mutex_unlock(&WaitLock);
2792 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2796 // If this thread has been assigned work, launch a search
2797 if (Threads[threadID].workIsWaiting)
2799 assert(!Threads[threadID].idle);
2801 Threads[threadID].workIsWaiting = false;
2802 if (Threads[threadID].splitPoint->pvNode)
2803 sp_search_pv(Threads[threadID].splitPoint, threadID);
2805 sp_search(Threads[threadID].splitPoint, threadID);
2807 Threads[threadID].idle = true;
2810 // If this thread is the master of a split point and all threads have
2811 // finished their work at this split point, return from the idle loop.
2812 if (waitSp != NULL && waitSp->cpus == 0)
2816 Threads[threadID].running = false;
2820 // init_split_point_stack() is called during program initialization, and
2821 // initializes all split point objects.
2823 void init_split_point_stack() {
2825 for (int i = 0; i < THREAD_MAX; i++)
2826 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2828 SplitPointStack[i][j].parent = NULL;
2829 lock_init(&(SplitPointStack[i][j].lock), NULL);
2834 // destroy_split_point_stack() is called when the program exits, and
2835 // destroys all locks in the precomputed split point objects.
2837 void destroy_split_point_stack() {
2839 for (int i = 0; i < THREAD_MAX; i++)
2840 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2841 lock_destroy(&(SplitPointStack[i][j].lock));
2845 // thread_should_stop() checks whether the thread with a given threadID has
2846 // been asked to stop, directly or indirectly. This can happen if a beta
2847 // cutoff has occurred in the thread's currently active split point, or in
2848 // some ancestor of the current split point.
2850 bool thread_should_stop(int threadID) {
2852 assert(threadID >= 0 && threadID < ActiveThreads);
2856 if (Threads[threadID].stop)
2858 if (ActiveThreads <= 2)
2860 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2863 Threads[threadID].stop = true;
2870 // thread_is_available() checks whether the thread with threadID "slave" is
2871 // available to help the thread with threadID "master" at a split point. An
2872 // obvious requirement is that "slave" must be idle. With more than two
2873 // threads, this is not by itself sufficient: If "slave" is the master of
2874 // some active split point, it is only available as a slave to the other
2875 // threads which are busy searching the split point at the top of "slave"'s
2876 // split point stack (the "helpful master concept" in YBWC terminology).
2878 bool thread_is_available(int slave, int master) {
2880 assert(slave >= 0 && slave < ActiveThreads);
2881 assert(master >= 0 && master < ActiveThreads);
2882 assert(ActiveThreads > 1);
2884 if (!Threads[slave].idle || slave == master)
2887 // Make a local copy to be sure doesn't change under our feet
2888 int localActiveSplitPoints = Threads[slave].activeSplitPoints;
2890 if (localActiveSplitPoints == 0)
2891 // No active split points means that the thread is available as
2892 // a slave for any other thread.
2895 if (ActiveThreads == 2)
2898 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2899 // that is known to be > 0, instead of Threads[slave].activeSplitPoints that
2900 // could have been set to 0 by another thread leading to an out of bound access.
2901 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2908 // idle_thread_exists() tries to find an idle thread which is available as
2909 // a slave for the thread with threadID "master".
2911 bool idle_thread_exists(int master) {
2913 assert(master >= 0 && master < ActiveThreads);
2914 assert(ActiveThreads > 1);
2916 for (int i = 0; i < ActiveThreads; i++)
2917 if (thread_is_available(i, master))
2924 // split() does the actual work of distributing the work at a node between
2925 // several threads at PV nodes. If it does not succeed in splitting the
2926 // node (because no idle threads are available, or because we have no unused
2927 // split point objects), the function immediately returns false. If
2928 // splitting is possible, a SplitPoint object is initialized with all the
2929 // data that must be copied to the helper threads (the current position and
2930 // search stack, alpha, beta, the search depth, etc.), and we tell our
2931 // helper threads that they have been assigned work. This will cause them
2932 // to instantly leave their idle loops and call sp_search_pv(). When all
2933 // threads have returned from sp_search_pv (or, equivalently, when
2934 // splitPoint->cpus becomes 0), split() returns true.
2936 bool split(const Position& p, SearchStack* sstck, int ply,
2937 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2938 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2941 assert(sstck != NULL);
2942 assert(ply >= 0 && ply < PLY_MAX);
2943 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2944 assert(!pvNode || *alpha < *beta);
2945 assert(*beta <= VALUE_INFINITE);
2946 assert(depth > Depth(0));
2947 assert(master >= 0 && master < ActiveThreads);
2948 assert(ActiveThreads > 1);
2950 SplitPoint* splitPoint;
2954 // If no other thread is available to help us, or if we have too many
2955 // active split points, don't split.
2956 if ( !idle_thread_exists(master)
2957 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2959 lock_release(&MPLock);
2963 // Pick the next available split point object from the split point stack
2964 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2965 Threads[master].activeSplitPoints++;
2967 // Initialize the split point object
2968 splitPoint->parent = Threads[master].splitPoint;
2969 splitPoint->finished = false;
2970 splitPoint->ply = ply;
2971 splitPoint->depth = depth;
2972 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2973 splitPoint->beta = *beta;
2974 splitPoint->pvNode = pvNode;
2975 splitPoint->bestValue = *bestValue;
2976 splitPoint->futilityValue = futilityValue;
2977 splitPoint->master = master;
2978 splitPoint->mp = mp;
2979 splitPoint->moves = *moves;
2980 splitPoint->cpus = 1;
2981 splitPoint->pos = &p;
2982 splitPoint->parentSstack = sstck;
2983 for (int i = 0; i < ActiveThreads; i++)
2984 splitPoint->slaves[i] = 0;
2986 Threads[master].idle = false;
2987 Threads[master].stop = false;
2988 Threads[master].splitPoint = splitPoint;
2990 // Allocate available threads setting idle flag to false
2991 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2992 if (thread_is_available(i, master))
2994 Threads[i].idle = false;
2995 Threads[i].stop = false;
2996 Threads[i].splitPoint = splitPoint;
2997 splitPoint->slaves[i] = 1;
3001 assert(splitPoint->cpus > 1);
3003 // We can release the lock because master and slave threads are already booked
3004 lock_release(&MPLock);
3006 // Tell the threads that they have work to do. This will make them leave
3007 // their idle loop. But before copy search stack tail for each thread.
3008 for (int i = 0; i < ActiveThreads; i++)
3009 if (i == master || splitPoint->slaves[i])
3011 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
3012 Threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
3015 // Everything is set up. The master thread enters the idle loop, from
3016 // which it will instantly launch a search, because its workIsWaiting
3017 // slot is 'true'. We send the split point as a second parameter to the
3018 // idle loop, which means that the main thread will return from the idle
3019 // loop when all threads have finished their work at this split point
3020 // (i.e. when splitPoint->cpus == 0).
3021 idle_loop(master, splitPoint);
3023 // We have returned from the idle loop, which means that all threads are
3024 // finished. Update alpha, beta and bestValue, and return.
3028 *alpha = splitPoint->alpha;
3030 *beta = splitPoint->beta;
3031 *bestValue = splitPoint->bestValue;
3032 Threads[master].stop = false;
3033 Threads[master].idle = false;
3034 Threads[master].activeSplitPoints--;
3035 Threads[master].splitPoint = splitPoint->parent;
3037 lock_release(&MPLock);
3042 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3043 // to start a new search from the root.
3045 void wake_sleeping_threads() {
3047 if (ActiveThreads > 1)
3049 for (int i = 1; i < ActiveThreads; i++)
3051 Threads[i].idle = true;
3052 Threads[i].workIsWaiting = false;
3055 #if !defined(_MSC_VER)
3056 pthread_mutex_lock(&WaitLock);
3057 pthread_cond_broadcast(&WaitCond);
3058 pthread_mutex_unlock(&WaitLock);
3060 for (int i = 1; i < THREAD_MAX; i++)
3061 SetEvent(SitIdleEvent[i]);
3067 // init_thread() is the function which is called when a new thread is
3068 // launched. It simply calls the idle_loop() function with the supplied
3069 // threadID. There are two versions of this function; one for POSIX
3070 // threads and one for Windows threads.
3072 #if !defined(_MSC_VER)
3074 void* init_thread(void *threadID) {
3076 idle_loop(*(int*)threadID, NULL);
3082 DWORD WINAPI init_thread(LPVOID threadID) {
3084 idle_loop(*(int*)threadID, NULL);