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 /// Lookup tables initialized at startup
155 // Reduction lookup tables and their getter functions
156 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
157 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
159 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
160 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
162 // Futility lookup tables and their getter functions
163 const Value FutilityMarginQS = Value(0x80);
164 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
165 int FutilityMoveCountArray[32]; // [depth]
167 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
168 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
170 /// Variables initialized by UCI options
172 // Depth limit for use of dynamic threat detection
175 // Last seconds noise filtering (LSN)
176 const bool UseLSNFiltering = true;
177 const int LSNTime = 4000; // In milliseconds
178 const Value LSNValue = value_from_centipawns(200);
179 bool loseOnTime = false;
181 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
182 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
183 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
185 // Iteration counters
187 BetaCounterType BetaCounter;
189 // Scores and number of times the best move changed for each iteration
190 Value ValueByIteration[PLY_MAX_PLUS_2];
191 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
193 // Search window management
199 // Time managment variables
202 int MaxNodes, MaxDepth;
203 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
204 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
205 bool AbortSearch, Quit;
206 bool AspirationFailLow;
208 // Show current line?
209 bool ShowCurrentLine;
213 std::ofstream LogFile;
215 // MP related variables
216 int ActiveThreads = 1;
217 Depth MinimumSplitDepth;
218 int MaxThreadsPerSplitPoint;
219 Thread Threads[THREAD_MAX];
222 bool AllThreadsShouldExit, AllThreadsShouldSleep;
223 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 AllThreadsShouldSleep = 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.
524 AllThreadsShouldSleep = true;
529 /// init_search() is called during startup. It initializes various lookup tables
533 // Init our reduction lookup tables
534 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
535 for (int j = 1; j < 64; j++) // j == moveNumber
537 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
538 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
539 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
540 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
543 // Init futility margins array
544 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
545 for (int j = 0; j < 64; j++) // j == moveNumber
547 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
550 // Init futility move count array
551 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
552 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
556 /// init_threads() is called during startup. It launches all helper threads,
557 /// and initializes the split point stack and the global locks and condition
560 void init_threads() {
565 #if !defined(_MSC_VER)
566 pthread_t pthread[1];
569 for (i = 0; i < THREAD_MAX; i++)
570 Threads[i].activeSplitPoints = 0;
572 // Initialize global locks
573 lock_init(&MPLock, NULL);
574 lock_init(&IOLock, NULL);
576 init_split_point_stack();
578 #if !defined(_MSC_VER)
579 pthread_mutex_init(&WaitLock, NULL);
580 pthread_cond_init(&WaitCond, NULL);
582 for (i = 0; i < THREAD_MAX; i++)
583 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
586 // Will be set just before program exits to properly end the threads
587 AllThreadsShouldExit = false;
589 // Threads will be put to sleep as soon as created
590 AllThreadsShouldSleep = true;
592 // All threads except the main thread should be initialized to idle state
593 for (i = 1; i < THREAD_MAX; i++)
595 Threads[i].stop = false;
596 Threads[i].workIsWaiting = false;
597 Threads[i].idle = true;
598 Threads[i].running = false;
601 // Launch the helper threads
602 for (i = 1; i < THREAD_MAX; i++)
604 #if !defined(_MSC_VER)
605 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
608 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
613 cout << "Failed to create thread number " << i << endl;
614 Application::exit_with_failure();
617 // Wait until the thread has finished launching
618 while (!Threads[i].running);
623 /// stop_threads() is called when the program exits. It makes all the
624 /// helper threads exit cleanly.
626 void stop_threads() {
628 ActiveThreads = THREAD_MAX; // HACK
629 AllThreadsShouldSleep = false; // HACK
630 wake_sleeping_threads();
631 AllThreadsShouldExit = true;
632 for (int i = 1; i < THREAD_MAX; i++)
634 Threads[i].stop = true;
635 while (Threads[i].running);
637 destroy_split_point_stack();
641 /// nodes_searched() returns the total number of nodes searched so far in
642 /// the current search.
644 int64_t nodes_searched() {
646 int64_t result = 0ULL;
647 for (int i = 0; i < ActiveThreads; i++)
648 result += Threads[i].nodes;
653 // SearchStack::init() initializes a search stack. Used at the beginning of a
654 // new search from the root.
655 void SearchStack::init(int ply) {
657 pv[ply] = pv[ply + 1] = MOVE_NONE;
658 currentMove = threatMove = MOVE_NONE;
659 reduction = Depth(0);
663 void SearchStack::initKillers() {
665 mateKiller = MOVE_NONE;
666 for (int i = 0; i < KILLER_MAX; i++)
667 killers[i] = MOVE_NONE;
672 // id_loop() is the main iterative deepening loop. It calls root_search
673 // repeatedly with increasing depth until the allocated thinking time has
674 // been consumed, the user stops the search, or the maximum search depth is
677 Value id_loop(const Position& pos, Move searchMoves[]) {
680 SearchStack ss[PLY_MAX_PLUS_2];
682 // searchMoves are verified, copied, scored and sorted
683 RootMoveList rml(p, searchMoves);
685 // Handle special case of searching on a mate/stale position
686 if (rml.move_count() == 0)
689 wait_for_stop_or_ponderhit();
691 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
694 // Print RootMoveList c'tor startup scoring to the standard output,
695 // so that we print information also for iteration 1.
696 cout << "info depth " << 1 << "\ninfo depth " << 1
697 << " score " << value_to_string(rml.get_move_score(0))
698 << " time " << current_search_time()
699 << " nodes " << nodes_searched()
701 << " pv " << rml.get_move(0) << "\n";
707 ValueByIteration[1] = rml.get_move_score(0);
710 // Is one move significantly better than others after initial scoring ?
711 Move EasyMove = MOVE_NONE;
712 if ( rml.move_count() == 1
713 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
714 EasyMove = rml.get_move(0);
716 // Iterative deepening loop
717 while (Iteration < PLY_MAX)
719 // Initialize iteration
722 BestMoveChangesByIteration[Iteration] = 0;
726 cout << "info depth " << Iteration << endl;
728 // Calculate dynamic search window based on previous iterations
731 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
733 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
734 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
736 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
737 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
739 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
740 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
744 alpha = - VALUE_INFINITE;
745 beta = VALUE_INFINITE;
748 // Search to the current depth
749 Value value = root_search(p, ss, rml, alpha, beta);
751 // Write PV to transposition table, in case the relevant entries have
752 // been overwritten during the search.
753 TT.insert_pv(p, ss[0].pv);
756 break; // Value cannot be trusted. Break out immediately!
758 //Save info about search result
759 ValueByIteration[Iteration] = value;
761 // Drop the easy move if it differs from the new best move
762 if (ss[0].pv[0] != EasyMove)
763 EasyMove = MOVE_NONE;
765 if (UseTimeManagement)
768 bool stopSearch = false;
770 // Stop search early if there is only a single legal move,
771 // we search up to Iteration 6 anyway to get a proper score.
772 if (Iteration >= 6 && rml.move_count() == 1)
775 // Stop search early when the last two iterations returned a mate score
777 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
778 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
781 // Stop search early if one move seems to be much better than the rest
782 int64_t nodes = nodes_searched();
784 && EasyMove == ss[0].pv[0]
785 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
786 && current_search_time() > MaxSearchTime / 16)
787 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
788 && current_search_time() > MaxSearchTime / 32)))
791 // Add some extra time if the best move has changed during the last two iterations
792 if (Iteration > 5 && Iteration <= 50)
793 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
794 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
796 // Stop search if most of MaxSearchTime is consumed at the end of the
797 // iteration. We probably don't have enough time to search the first
798 // move at the next iteration anyway.
799 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
807 StopOnPonderhit = true;
811 if (MaxDepth && Iteration >= MaxDepth)
817 // If we are pondering or in infinite search, we shouldn't print the
818 // best move before we are told to do so.
819 if (!AbortSearch && (PonderSearch || InfiniteSearch))
820 wait_for_stop_or_ponderhit();
822 // Print final search statistics
823 cout << "info nodes " << nodes_searched()
825 << " time " << current_search_time()
826 << " hashfull " << TT.full() << endl;
828 // Print the best move and the ponder move to the standard output
829 if (ss[0].pv[0] == MOVE_NONE)
831 ss[0].pv[0] = rml.get_move(0);
832 ss[0].pv[1] = MOVE_NONE;
834 cout << "bestmove " << ss[0].pv[0];
835 if (ss[0].pv[1] != MOVE_NONE)
836 cout << " ponder " << ss[0].pv[1];
843 dbg_print_mean(LogFile);
845 if (dbg_show_hit_rate)
846 dbg_print_hit_rate(LogFile);
848 LogFile << "\nNodes: " << nodes_searched()
849 << "\nNodes/second: " << nps()
850 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
853 p.do_move(ss[0].pv[0], st);
854 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
856 return rml.get_move_score(0);
860 // root_search() is the function which searches the root node. It is
861 // similar to search_pv except that it uses a different move ordering
862 // scheme and prints some information to the standard output.
864 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
869 Depth depth, ext, newDepth;
872 int researchCount = 0;
873 bool moveIsCheck, captureOrPromotion, dangerous;
874 Value alpha = oldAlpha;
875 bool isCheck = pos.is_check();
877 // Evaluate the position statically
879 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
881 while (1) // Fail low loop
884 // Loop through all the moves in the root move list
885 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
889 // We failed high, invalidate and skip next moves, leave node-counters
890 // and beta-counters as they are and quickly return, we will try to do
891 // a research at the next iteration with a bigger aspiration window.
892 rml.set_move_score(i, -VALUE_INFINITE);
896 RootMoveNumber = i + 1;
898 // Save the current node count before the move is searched
899 nodes = nodes_searched();
901 // Reset beta cut-off counters
904 // Pick the next root move, and print the move and the move number to
905 // the standard output.
906 move = ss[0].currentMove = rml.get_move(i);
908 if (current_search_time() >= 1000)
909 cout << "info currmove " << move
910 << " currmovenumber " << RootMoveNumber << endl;
912 // Decide search depth for this move
913 moveIsCheck = pos.move_is_check(move);
914 captureOrPromotion = pos.move_is_capture_or_promotion(move);
915 depth = (Iteration - 2) * OnePly + InitialDepth;
916 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
917 newDepth = depth + ext;
919 value = - VALUE_INFINITE;
921 while (1) // Fail high loop
924 // Make the move, and search it
925 pos.do_move(move, st, ci, moveIsCheck);
927 if (i < MultiPV || value > alpha)
929 // Aspiration window is disabled in multi-pv case
931 alpha = -VALUE_INFINITE;
933 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
937 // Try to reduce non-pv search depth by one ply if move seems not problematic,
938 // if the move fails high will be re-searched at full depth.
939 bool doFullDepthSearch = true;
941 if ( depth >= 3*OnePly // FIXME was newDepth
943 && !captureOrPromotion
944 && !move_is_castle(move))
946 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
949 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
950 doFullDepthSearch = (value > alpha);
954 if (doFullDepthSearch)
956 ss[0].reduction = Depth(0);
957 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
960 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
966 // Can we exit fail high loop ?
967 if (AbortSearch || value < beta)
970 // We are failing high and going to do a research. It's important to update score
971 // before research in case we run out of time while researching.
972 rml.set_move_score(i, value);
974 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
975 rml.set_move_pv(i, ss[0].pv);
977 // Print search information to the standard output
978 cout << "info depth " << Iteration
979 << " score " << value_to_string(value)
980 << ((value >= beta) ? " lowerbound" :
981 ((value <= alpha)? " upperbound" : ""))
982 << " time " << current_search_time()
983 << " nodes " << nodes_searched()
987 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
988 cout << ss[0].pv[j] << " ";
994 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
995 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
997 LogFile << pretty_pv(pos, current_search_time(), Iteration,
998 nodes_searched(), value, type, ss[0].pv) << endl;
1001 // Prepare for a research after a fail high, each time with a wider window
1003 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
1005 } // End of fail high loop
1007 // Finished searching the move. If AbortSearch is true, the search
1008 // was aborted because the user interrupted the search or because we
1009 // ran out of time. In this case, the return value of the search cannot
1010 // be trusted, and we break out of the loop without updating the best
1015 // Remember beta-cutoff and searched nodes counts for this move. The
1016 // info is used to sort the root moves at the next iteration.
1018 BetaCounter.read(pos.side_to_move(), our, their);
1019 rml.set_beta_counters(i, our, their);
1020 rml.set_move_nodes(i, nodes_searched() - nodes);
1022 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1024 if (value <= alpha && i >= MultiPV)
1025 rml.set_move_score(i, -VALUE_INFINITE);
1028 // PV move or new best move!
1031 rml.set_move_score(i, value);
1033 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1034 rml.set_move_pv(i, ss[0].pv);
1038 // We record how often the best move has been changed in each
1039 // iteration. This information is used for time managment: When
1040 // the best move changes frequently, we allocate some more time.
1042 BestMoveChangesByIteration[Iteration]++;
1044 // Print search information to the standard output
1045 cout << "info depth " << Iteration
1046 << " score " << value_to_string(value)
1047 << ((value >= beta) ? " lowerbound" :
1048 ((value <= alpha)? " upperbound" : ""))
1049 << " time " << current_search_time()
1050 << " nodes " << nodes_searched()
1054 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1055 cout << ss[0].pv[j] << " ";
1061 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1062 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1064 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1065 nodes_searched(), value, type, ss[0].pv) << endl;
1072 rml.sort_multipv(i);
1073 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1075 cout << "info multipv " << j + 1
1076 << " score " << value_to_string(rml.get_move_score(j))
1077 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1078 << " time " << current_search_time()
1079 << " nodes " << nodes_searched()
1083 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1084 cout << rml.get_move_pv(j, k) << " ";
1088 alpha = rml.get_move_score(Min(i, MultiPV-1));
1090 } // PV move or new best move
1092 assert(alpha >= oldAlpha);
1094 AspirationFailLow = (alpha == oldAlpha);
1096 if (AspirationFailLow && StopOnPonderhit)
1097 StopOnPonderhit = false;
1100 // Can we exit fail low loop ?
1101 if (AbortSearch || alpha > oldAlpha)
1104 // Prepare for a research after a fail low, each time with a wider window
1106 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1115 // search_pv() is the main search function for PV nodes.
1117 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1118 Depth depth, int ply, int threadID) {
1120 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1121 assert(beta > alpha && beta <= VALUE_INFINITE);
1122 assert(ply >= 0 && ply < PLY_MAX);
1123 assert(threadID >= 0 && threadID < ActiveThreads);
1125 Move movesSearched[256];
1129 Depth ext, newDepth;
1130 Value oldAlpha, value;
1131 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1133 Value bestValue = value = -VALUE_INFINITE;
1136 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1138 // Initialize, and make an early exit in case of an aborted search,
1139 // an instant draw, maximum ply reached, etc.
1140 init_node(ss, ply, threadID);
1142 // After init_node() that calls poll()
1143 if (AbortSearch || thread_should_stop(threadID))
1146 if (pos.is_draw() || ply >= PLY_MAX - 1)
1149 // Mate distance pruning
1151 alpha = Max(value_mated_in(ply), alpha);
1152 beta = Min(value_mate_in(ply+1), beta);
1156 // Transposition table lookup. At PV nodes, we don't use the TT for
1157 // pruning, but only for move ordering. This is to avoid problems in
1158 // the following areas:
1160 // * Repetition draw detection
1161 // * Fifty move rule detection
1162 // * Searching for a mate
1163 // * Printing of full PV line
1165 tte = TT.retrieve(pos.get_key());
1166 ttMove = (tte ? tte->move() : MOVE_NONE);
1168 // Go with internal iterative deepening if we don't have a TT move
1169 if ( UseIIDAtPVNodes
1170 && depth >= 5*OnePly
1171 && ttMove == MOVE_NONE)
1173 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1174 ttMove = ss[ply].pv[ply];
1175 tte = TT.retrieve(pos.get_key());
1178 isCheck = pos.is_check();
1181 // Update gain statistics of the previous move that lead
1182 // us in this position.
1184 ss[ply].eval = evaluate(pos, ei, threadID);
1185 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1188 // Initialize a MovePicker object for the current position, and prepare
1189 // to search all moves
1190 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1192 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1194 // Loop through all legal moves until no moves remain or a beta cutoff
1196 while ( alpha < beta
1197 && (move = mp.get_next_move()) != MOVE_NONE
1198 && !thread_should_stop(threadID))
1200 assert(move_is_ok(move));
1202 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1203 moveIsCheck = pos.move_is_check(move, ci);
1204 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1206 // Decide the new search depth
1207 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1209 // Singular extension search. We extend the TT move if its value is much better than
1210 // its siblings. To verify this we do a reduced search on all the other moves but the
1211 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1212 if ( depth >= 6 * OnePly
1214 && move == tte->move()
1216 && is_lower_bound(tte->type())
1217 && tte->depth() >= depth - 3 * OnePly)
1219 Value ttValue = value_from_tt(tte->value(), ply);
1221 if (abs(ttValue) < VALUE_KNOWN_WIN)
1223 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1225 if (excValue < ttValue - SingleReplyMargin)
1230 newDepth = depth - OnePly + ext;
1232 // Update current move
1233 movesSearched[moveCount++] = ss[ply].currentMove = move;
1235 // Make and search the move
1236 pos.do_move(move, st, ci, moveIsCheck);
1238 if (moveCount == 1) // The first move in list is the PV
1239 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1242 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1243 // if the move fails high will be re-searched at full depth.
1244 bool doFullDepthSearch = true;
1246 if ( depth >= 3*OnePly
1248 && !captureOrPromotion
1249 && !move_is_castle(move)
1250 && !move_is_killer(move, ss[ply]))
1252 ss[ply].reduction = pv_reduction(depth, moveCount);
1253 if (ss[ply].reduction)
1255 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1256 doFullDepthSearch = (value > alpha);
1260 if (doFullDepthSearch) // Go with full depth non-pv search
1262 ss[ply].reduction = Depth(0);
1263 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1264 if (value > alpha && value < beta)
1265 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1268 pos.undo_move(move);
1270 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1273 if (value > bestValue)
1280 if (value == value_mate_in(ply + 1))
1281 ss[ply].mateKiller = move;
1286 if ( ActiveThreads > 1
1288 && depth >= MinimumSplitDepth
1290 && idle_thread_exists(threadID)
1292 && !thread_should_stop(threadID)
1293 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1294 depth, &moveCount, &mp, threadID, true))
1298 // All legal moves have been searched. A special case: If there were
1299 // no legal moves, it must be mate or stalemate.
1301 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1303 // If the search is not aborted, update the transposition table,
1304 // history counters, and killer moves.
1305 if (AbortSearch || thread_should_stop(threadID))
1308 if (bestValue <= oldAlpha)
1309 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1311 else if (bestValue >= beta)
1313 BetaCounter.add(pos.side_to_move(), depth, threadID);
1314 move = ss[ply].pv[ply];
1315 if (!pos.move_is_capture_or_promotion(move))
1317 update_history(pos, move, depth, movesSearched, moveCount);
1318 update_killers(move, ss[ply]);
1320 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1323 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1329 // search() is the search function for zero-width nodes.
1331 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1332 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1334 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1335 assert(ply >= 0 && ply < PLY_MAX);
1336 assert(threadID >= 0 && threadID < ActiveThreads);
1338 Move movesSearched[256];
1343 Depth ext, newDepth;
1344 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1345 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1346 bool mateThreat = false;
1348 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1351 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1353 // Initialize, and make an early exit in case of an aborted search,
1354 // an instant draw, maximum ply reached, etc.
1355 init_node(ss, ply, threadID);
1357 // After init_node() that calls poll()
1358 if (AbortSearch || thread_should_stop(threadID))
1361 if (pos.is_draw() || ply >= PLY_MAX - 1)
1364 // Mate distance pruning
1365 if (value_mated_in(ply) >= beta)
1368 if (value_mate_in(ply + 1) < beta)
1371 // We don't want the score of a partial search to overwrite a previous full search
1372 // TT value, so we use a different position key in case of an excluded move exsists.
1373 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1375 // Transposition table lookup
1376 tte = TT.retrieve(posKey);
1377 ttMove = (tte ? tte->move() : MOVE_NONE);
1379 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1381 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1382 return value_from_tt(tte->value(), ply);
1385 isCheck = pos.is_check();
1387 // Evaluate the position statically
1390 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1391 staticValue = value_from_tt(tte->value(), ply);
1393 staticValue = evaluate(pos, ei, threadID);
1395 ss[ply].eval = staticValue;
1396 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1397 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1398 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1401 // Static null move pruning. We're betting that the opponent doesn't have
1402 // a move that will reduce the score by more than FutilityMargins[int(depth)]
1403 // if we do a null move.
1406 && depth < RazorDepth
1407 && staticValue - futility_margin(depth, 0) >= beta)
1408 return staticValue - futility_margin(depth, 0);
1414 && !value_is_mate(beta)
1415 && ok_to_do_nullmove(pos)
1416 && staticValue >= beta - NullMoveMargin)
1418 ss[ply].currentMove = MOVE_NULL;
1420 pos.do_null_move(st);
1422 // Null move dynamic reduction based on depth
1423 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1425 // Null move dynamic reduction based on value
1426 if (staticValue - beta > PawnValueMidgame)
1429 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1431 pos.undo_null_move();
1433 if (nullValue >= beta)
1435 if (depth < 6 * OnePly)
1438 // Do zugzwang verification search
1439 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1443 // The null move failed low, which means that we may be faced with
1444 // some kind of threat. If the previous move was reduced, check if
1445 // the move that refuted the null move was somehow connected to the
1446 // move which was reduced. If a connection is found, return a fail
1447 // low score (which will cause the reduced move to fail high in the
1448 // parent node, which will trigger a re-search with full depth).
1449 if (nullValue == value_mated_in(ply + 2))
1452 ss[ply].threatMove = ss[ply + 1].currentMove;
1453 if ( depth < ThreatDepth
1454 && ss[ply - 1].reduction
1455 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1459 // Null move search not allowed, try razoring
1460 else if ( !value_is_mate(beta)
1462 && depth < RazorDepth
1463 && staticValue < beta - (NullMoveMargin + 16 * depth)
1464 && ss[ply - 1].currentMove != MOVE_NULL
1465 && ttMove == MOVE_NONE
1466 && !pos.has_pawn_on_7th(pos.side_to_move()))
1468 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1469 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1474 // Go with internal iterative deepening if we don't have a TT move
1475 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1476 !isCheck && ss[ply].eval >= beta - IIDMargin)
1478 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1479 ttMove = ss[ply].pv[ply];
1480 tte = TT.retrieve(posKey);
1483 // Initialize a MovePicker object for the current position, and prepare
1484 // to search all moves.
1485 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1488 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1489 while ( bestValue < beta
1490 && (move = mp.get_next_move()) != MOVE_NONE
1491 && !thread_should_stop(threadID))
1493 assert(move_is_ok(move));
1495 if (move == excludedMove)
1498 moveIsCheck = pos.move_is_check(move, ci);
1499 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1500 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1502 // Decide the new search depth
1503 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1505 // Singular extension search. We extend the TT move if its value is much better than
1506 // its siblings. To verify this we do a reduced search on all the other moves but the
1507 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1508 if ( depth >= 8 * OnePly
1510 && move == tte->move()
1511 && !excludedMove // Do not allow recursive single-reply search
1513 && is_lower_bound(tte->type())
1514 && tte->depth() >= depth - 3 * OnePly)
1516 Value ttValue = value_from_tt(tte->value(), ply);
1518 if (abs(ttValue) < VALUE_KNOWN_WIN)
1520 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1522 if (excValue < ttValue - SingleReplyMargin)
1527 newDepth = depth - OnePly + ext;
1529 // Update current move
1530 movesSearched[moveCount++] = ss[ply].currentMove = move;
1535 && !captureOrPromotion
1536 && !move_is_castle(move)
1539 // Move count based pruning
1540 if ( moveCount >= futility_move_count(depth)
1541 && ok_to_prune(pos, move, ss[ply].threatMove)
1542 && bestValue > value_mated_in(PLY_MAX))
1545 // Value based pruning
1546 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1547 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1548 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1550 if (futilityValueScaled < beta)
1552 if (futilityValueScaled > bestValue)
1553 bestValue = futilityValueScaled;
1558 // Make and search the move
1559 pos.do_move(move, st, ci, moveIsCheck);
1561 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1562 // if the move fails high will be re-searched at full depth.
1563 bool doFullDepthSearch = true;
1565 if ( depth >= 3*OnePly
1567 && !captureOrPromotion
1568 && !move_is_castle(move)
1569 && !move_is_killer(move, ss[ply]))
1571 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1572 if (ss[ply].reduction)
1574 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1575 doFullDepthSearch = (value >= beta);
1579 if (doFullDepthSearch) // Go with full depth non-pv search
1581 ss[ply].reduction = Depth(0);
1582 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1584 pos.undo_move(move);
1586 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1589 if (value > bestValue)
1595 if (value == value_mate_in(ply + 1))
1596 ss[ply].mateKiller = move;
1600 if ( ActiveThreads > 1
1602 && depth >= MinimumSplitDepth
1604 && idle_thread_exists(threadID)
1606 && !thread_should_stop(threadID)
1607 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1608 depth, &moveCount, &mp, threadID, false))
1612 // All legal moves have been searched. A special case: If there were
1613 // no legal moves, it must be mate or stalemate.
1615 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1617 // If the search is not aborted, update the transposition table,
1618 // history counters, and killer moves.
1619 if (AbortSearch || thread_should_stop(threadID))
1622 if (bestValue < beta)
1623 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1626 BetaCounter.add(pos.side_to_move(), depth, threadID);
1627 move = ss[ply].pv[ply];
1628 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1629 if (!pos.move_is_capture_or_promotion(move))
1631 update_history(pos, move, depth, movesSearched, moveCount);
1632 update_killers(move, ss[ply]);
1637 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1643 // qsearch() is the quiescence search function, which is called by the main
1644 // search function when the remaining depth is zero (or, to be more precise,
1645 // less than OnePly).
1647 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1648 Depth depth, int ply, int threadID) {
1650 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1651 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1653 assert(ply >= 0 && ply < PLY_MAX);
1654 assert(threadID >= 0 && threadID < ActiveThreads);
1659 Value staticValue, bestValue, value, futilityBase, futilityValue;
1660 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1661 const TTEntry* tte = NULL;
1663 bool pvNode = (beta - alpha != 1);
1664 Value oldAlpha = alpha;
1666 // Initialize, and make an early exit in case of an aborted search,
1667 // an instant draw, maximum ply reached, etc.
1668 init_node(ss, ply, threadID);
1670 // After init_node() that calls poll()
1671 if (AbortSearch || thread_should_stop(threadID))
1674 if (pos.is_draw() || ply >= PLY_MAX - 1)
1677 // Transposition table lookup. At PV nodes, we don't use the TT for
1678 // pruning, but only for move ordering.
1679 tte = TT.retrieve(pos.get_key());
1680 ttMove = (tte ? tte->move() : MOVE_NONE);
1682 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1684 assert(tte->type() != VALUE_TYPE_EVAL);
1686 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1687 return value_from_tt(tte->value(), ply);
1690 isCheck = pos.is_check();
1692 // Evaluate the position statically
1694 staticValue = -VALUE_INFINITE;
1695 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1696 staticValue = value_from_tt(tte->value(), ply);
1698 staticValue = evaluate(pos, ei, threadID);
1702 ss[ply].eval = staticValue;
1703 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1706 // Initialize "stand pat score", and return it immediately if it is
1708 bestValue = staticValue;
1710 if (bestValue >= beta)
1712 // Store the score to avoid a future costly evaluation() call
1713 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1714 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1719 if (bestValue > alpha)
1722 // If we are near beta then try to get a cutoff pushing checks a bit further
1723 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1725 // Initialize a MovePicker object for the current position, and prepare
1726 // to search the moves. Because the depth is <= 0 here, only captures,
1727 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1728 // and we are near beta) will be generated.
1729 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1731 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1732 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1734 // Loop through the moves until no moves remain or a beta cutoff
1736 while ( alpha < beta
1737 && (move = mp.get_next_move()) != MOVE_NONE)
1739 assert(move_is_ok(move));
1741 moveIsCheck = pos.move_is_check(move, ci);
1743 // Update current move
1745 ss[ply].currentMove = move;
1753 && !move_is_promotion(move)
1754 && !pos.move_is_passed_pawn_push(move))
1756 futilityValue = futilityBase
1757 + pos.endgame_value_of_piece_on(move_to(move))
1758 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1760 if (futilityValue < alpha)
1762 if (futilityValue > bestValue)
1763 bestValue = futilityValue;
1768 // Detect blocking evasions that are candidate to be pruned
1769 evasionPrunable = isCheck
1770 && bestValue != -VALUE_INFINITE
1771 && !pos.move_is_capture(move)
1772 && pos.type_of_piece_on(move_from(move)) != KING
1773 && !pos.can_castle(pos.side_to_move());
1775 // Don't search moves with negative SEE values
1776 if ( (!isCheck || evasionPrunable)
1778 && !move_is_promotion(move)
1779 && pos.see_sign(move) < 0)
1782 // Make and search the move
1783 pos.do_move(move, st, ci, moveIsCheck);
1784 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1785 pos.undo_move(move);
1787 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1790 if (value > bestValue)
1801 // All legal moves have been searched. A special case: If we're in check
1802 // and no legal moves were found, it is checkmate.
1803 if (!moveCount && pos.is_check()) // Mate!
1804 return value_mated_in(ply);
1806 // Update transposition table
1807 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1808 if (bestValue <= oldAlpha)
1810 // If bestValue isn't changed it means it is still the static evaluation
1811 // of the node, so keep this info to avoid a future evaluation() call.
1812 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1813 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1815 else if (bestValue >= beta)
1817 move = ss[ply].pv[ply];
1818 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1820 // Update killers only for good checking moves
1821 if (!pos.move_is_capture_or_promotion(move))
1822 update_killers(move, ss[ply]);
1825 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1827 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1833 // sp_search() is used to search from a split point. This function is called
1834 // by each thread working at the split point. It is similar to the normal
1835 // search() function, but simpler. Because we have already probed the hash
1836 // table, done a null move search, and searched the first move before
1837 // splitting, we don't have to repeat all this work in sp_search(). We
1838 // also don't need to store anything to the hash table here: This is taken
1839 // care of after we return from the split point.
1841 void sp_search(SplitPoint* sp, int threadID) {
1843 assert(threadID >= 0 && threadID < ActiveThreads);
1844 assert(ActiveThreads > 1);
1846 Position pos(*sp->pos);
1848 SearchStack* ss = sp->sstack[threadID];
1849 Value value = -VALUE_INFINITE;
1852 bool isCheck = pos.is_check();
1853 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1856 while ( lock_grab_bool(&(sp->lock))
1857 && sp->bestValue < sp->beta
1858 && !thread_should_stop(threadID)
1859 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1861 moveCount = ++sp->moves;
1862 lock_release(&(sp->lock));
1864 assert(move_is_ok(move));
1866 bool moveIsCheck = pos.move_is_check(move, ci);
1867 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1869 ss[sp->ply].currentMove = move;
1871 // Decide the new search depth
1873 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1874 Depth newDepth = sp->depth - OnePly + ext;
1877 if ( useFutilityPruning
1879 && !captureOrPromotion)
1881 // Move count based pruning
1882 if ( moveCount >= futility_move_count(sp->depth)
1883 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1884 && sp->bestValue > value_mated_in(PLY_MAX))
1887 // Value based pruning
1888 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1890 if (futilityValueScaled < sp->beta)
1892 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1894 lock_grab(&(sp->lock));
1895 if (futilityValueScaled > sp->bestValue)
1896 sp->bestValue = futilityValueScaled;
1897 lock_release(&(sp->lock));
1903 // Make and search the move.
1905 pos.do_move(move, st, ci, moveIsCheck);
1907 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1908 // if the move fails high will be re-searched at full depth.
1909 bool doFullDepthSearch = true;
1912 && !captureOrPromotion
1913 && !move_is_castle(move)
1914 && !move_is_killer(move, ss[sp->ply]))
1916 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1917 if (ss[sp->ply].reduction)
1919 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1920 doFullDepthSearch = (value >= sp->beta);
1924 if (doFullDepthSearch) // Go with full depth non-pv search
1926 ss[sp->ply].reduction = Depth(0);
1927 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1929 pos.undo_move(move);
1931 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1933 if (thread_should_stop(threadID))
1935 lock_grab(&(sp->lock));
1940 if (value > sp->bestValue) // Less then 2% of cases
1942 lock_grab(&(sp->lock));
1943 if (value > sp->bestValue && !thread_should_stop(threadID))
1945 sp->bestValue = value;
1946 if (sp->bestValue >= sp->beta)
1948 sp_update_pv(sp->parentSstack, ss, sp->ply);
1949 for (int i = 0; i < ActiveThreads; i++)
1950 if (i != threadID && (i == sp->master || sp->slaves[i]))
1951 Threads[i].stop = true;
1953 sp->finished = true;
1956 lock_release(&(sp->lock));
1960 /* Here we have the lock still grabbed */
1962 // If this is the master thread and we have been asked to stop because of
1963 // a beta cutoff higher up in the tree, stop all slave threads.
1964 if (sp->master == threadID && thread_should_stop(threadID))
1965 for (int i = 0; i < ActiveThreads; i++)
1967 Threads[i].stop = true;
1970 sp->slaves[threadID] = 0;
1972 lock_release(&(sp->lock));
1976 // sp_search_pv() is used to search from a PV split point. This function
1977 // is called by each thread working at the split point. It is similar to
1978 // the normal search_pv() function, but simpler. Because we have already
1979 // probed the hash table and searched the first move before splitting, we
1980 // don't have to repeat all this work in sp_search_pv(). We also don't
1981 // need to store anything to the hash table here: This is taken care of
1982 // after we return from the split point.
1984 void sp_search_pv(SplitPoint* sp, int threadID) {
1986 assert(threadID >= 0 && threadID < ActiveThreads);
1987 assert(ActiveThreads > 1);
1989 Position pos(*sp->pos);
1991 SearchStack* ss = sp->sstack[threadID];
1992 Value value = -VALUE_INFINITE;
1996 while ( lock_grab_bool(&(sp->lock))
1997 && sp->alpha < sp->beta
1998 && !thread_should_stop(threadID)
1999 && (move = sp->mp->get_next_move()) != MOVE_NONE)
2001 moveCount = ++sp->moves;
2002 lock_release(&(sp->lock));
2004 assert(move_is_ok(move));
2006 bool moveIsCheck = pos.move_is_check(move, ci);
2007 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
2009 ss[sp->ply].currentMove = move;
2011 // Decide the new search depth
2013 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
2014 Depth newDepth = sp->depth - OnePly + ext;
2016 // Make and search the move.
2018 pos.do_move(move, st, ci, moveIsCheck);
2020 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2021 // if the move fails high will be re-searched at full depth.
2022 bool doFullDepthSearch = true;
2025 && !captureOrPromotion
2026 && !move_is_castle(move)
2027 && !move_is_killer(move, ss[sp->ply]))
2029 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
2030 if (ss[sp->ply].reduction)
2032 Value localAlpha = sp->alpha;
2033 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2034 doFullDepthSearch = (value > localAlpha);
2038 if (doFullDepthSearch) // Go with full depth non-pv search
2040 Value localAlpha = sp->alpha;
2041 ss[sp->ply].reduction = Depth(0);
2042 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2044 if (value > localAlpha && value < sp->beta)
2046 // If another thread has failed high then sp->alpha has been increased
2047 // to be higher or equal then beta, if so, avoid to start a PV search.
2048 localAlpha = sp->alpha;
2049 if (localAlpha < sp->beta)
2050 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2052 assert(thread_should_stop(threadID));
2055 pos.undo_move(move);
2057 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2059 if (thread_should_stop(threadID))
2061 lock_grab(&(sp->lock));
2066 if (value > sp->bestValue) // Less then 2% of cases
2068 lock_grab(&(sp->lock));
2069 if (value > sp->bestValue && !thread_should_stop(threadID))
2071 sp->bestValue = value;
2072 if (value > sp->alpha)
2074 // Ask threads to stop before to modify sp->alpha
2075 if (value >= sp->beta)
2077 for (int i = 0; i < ActiveThreads; i++)
2078 if (i != threadID && (i == sp->master || sp->slaves[i]))
2079 Threads[i].stop = true;
2081 sp->finished = true;
2086 sp_update_pv(sp->parentSstack, ss, sp->ply);
2087 if (value == value_mate_in(sp->ply + 1))
2088 ss[sp->ply].mateKiller = move;
2091 lock_release(&(sp->lock));
2095 /* Here we have the lock still grabbed */
2097 // If this is the master thread and we have been asked to stop because of
2098 // a beta cutoff higher up in the tree, stop all slave threads.
2099 if (sp->master == threadID && thread_should_stop(threadID))
2100 for (int i = 0; i < ActiveThreads; i++)
2102 Threads[i].stop = true;
2105 sp->slaves[threadID] = 0;
2107 lock_release(&(sp->lock));
2110 /// The BetaCounterType class
2112 BetaCounterType::BetaCounterType() { clear(); }
2114 void BetaCounterType::clear() {
2116 for (int i = 0; i < THREAD_MAX; i++)
2117 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2120 void BetaCounterType::add(Color us, Depth d, int threadID) {
2122 // Weighted count based on depth
2123 Threads[threadID].betaCutOffs[us] += unsigned(d);
2126 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2129 for (int i = 0; i < THREAD_MAX; i++)
2131 our += Threads[i].betaCutOffs[us];
2132 their += Threads[i].betaCutOffs[opposite_color(us)];
2137 /// The RootMoveList class
2139 // RootMoveList c'tor
2141 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2143 SearchStack ss[PLY_MAX_PLUS_2];
2144 MoveStack mlist[MaxRootMoves];
2146 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2148 // Generate all legal moves
2149 MoveStack* last = generate_moves(pos, mlist);
2151 // Add each move to the moves[] array
2152 for (MoveStack* cur = mlist; cur != last; cur++)
2154 bool includeMove = includeAllMoves;
2156 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2157 includeMove = (searchMoves[k] == cur->move);
2162 // Find a quick score for the move
2164 pos.do_move(cur->move, st);
2165 moves[count].move = cur->move;
2166 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2167 moves[count].pv[0] = cur->move;
2168 moves[count].pv[1] = MOVE_NONE;
2169 pos.undo_move(cur->move);
2176 // RootMoveList simple methods definitions
2178 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2180 moves[moveNum].nodes = nodes;
2181 moves[moveNum].cumulativeNodes += nodes;
2184 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2186 moves[moveNum].ourBeta = our;
2187 moves[moveNum].theirBeta = their;
2190 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2194 for (j = 0; pv[j] != MOVE_NONE; j++)
2195 moves[moveNum].pv[j] = pv[j];
2197 moves[moveNum].pv[j] = MOVE_NONE;
2201 // RootMoveList::sort() sorts the root move list at the beginning of a new
2204 void RootMoveList::sort() {
2206 sort_multipv(count - 1); // Sort all items
2210 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2211 // list by their scores and depths. It is used to order the different PVs
2212 // correctly in MultiPV mode.
2214 void RootMoveList::sort_multipv(int n) {
2218 for (i = 1; i <= n; i++)
2220 RootMove rm = moves[i];
2221 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2222 moves[j] = moves[j - 1];
2229 // init_node() is called at the beginning of all the search functions
2230 // (search(), search_pv(), qsearch(), and so on) and initializes the
2231 // search stack object corresponding to the current node. Once every
2232 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2233 // for user input and checks whether it is time to stop the search.
2235 void init_node(SearchStack ss[], int ply, int threadID) {
2237 assert(ply >= 0 && ply < PLY_MAX);
2238 assert(threadID >= 0 && threadID < ActiveThreads);
2240 Threads[threadID].nodes++;
2245 if (NodesSincePoll >= NodesBetweenPolls)
2252 ss[ply + 2].initKillers();
2254 if (Threads[threadID].printCurrentLine)
2255 print_current_line(ss, ply, threadID);
2259 // update_pv() is called whenever a search returns a value > alpha.
2260 // It updates the PV in the SearchStack object corresponding to the
2263 void update_pv(SearchStack ss[], int ply) {
2265 assert(ply >= 0 && ply < PLY_MAX);
2269 ss[ply].pv[ply] = ss[ply].currentMove;
2271 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2272 ss[ply].pv[p] = ss[ply + 1].pv[p];
2274 ss[ply].pv[p] = MOVE_NONE;
2278 // sp_update_pv() is a variant of update_pv for use at split points. The
2279 // difference between the two functions is that sp_update_pv also updates
2280 // the PV at the parent node.
2282 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2284 assert(ply >= 0 && ply < PLY_MAX);
2288 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2290 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2291 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2293 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2297 // connected_moves() tests whether two moves are 'connected' in the sense
2298 // that the first move somehow made the second move possible (for instance
2299 // if the moving piece is the same in both moves). The first move is assumed
2300 // to be the move that was made to reach the current position, while the
2301 // second move is assumed to be a move from the current position.
2303 bool connected_moves(const Position& pos, Move m1, Move m2) {
2305 Square f1, t1, f2, t2;
2308 assert(move_is_ok(m1));
2309 assert(move_is_ok(m2));
2311 if (m2 == MOVE_NONE)
2314 // Case 1: The moving piece is the same in both moves
2320 // Case 2: The destination square for m2 was vacated by m1
2326 // Case 3: Moving through the vacated square
2327 if ( piece_is_slider(pos.piece_on(f2))
2328 && bit_is_set(squares_between(f2, t2), f1))
2331 // Case 4: The destination square for m2 is defended by the moving piece in m1
2332 p = pos.piece_on(t1);
2333 if (bit_is_set(pos.attacks_from(p, t1), t2))
2336 // Case 5: Discovered check, checking piece is the piece moved in m1
2337 if ( piece_is_slider(p)
2338 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2339 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2341 // discovered_check_candidates() works also if the Position's side to
2342 // move is the opposite of the checking piece.
2343 Color them = opposite_color(pos.side_to_move());
2344 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2346 if (bit_is_set(dcCandidates, f2))
2353 // value_is_mate() checks if the given value is a mate one
2354 // eventually compensated for the ply.
2356 bool value_is_mate(Value value) {
2358 assert(abs(value) <= VALUE_INFINITE);
2360 return value <= value_mated_in(PLY_MAX)
2361 || value >= value_mate_in(PLY_MAX);
2365 // move_is_killer() checks if the given move is among the
2366 // killer moves of that ply.
2368 bool move_is_killer(Move m, const SearchStack& ss) {
2370 const Move* k = ss.killers;
2371 for (int i = 0; i < KILLER_MAX; i++, k++)
2379 // extension() decides whether a move should be searched with normal depth,
2380 // or with extended depth. Certain classes of moves (checking moves, in
2381 // particular) are searched with bigger depth than ordinary moves and in
2382 // any case are marked as 'dangerous'. Note that also if a move is not
2383 // extended, as example because the corresponding UCI option is set to zero,
2384 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2386 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2387 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2389 assert(m != MOVE_NONE);
2391 Depth result = Depth(0);
2392 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2397 result += CheckExtension[pvNode];
2400 result += SingleEvasionExtension[pvNode];
2403 result += MateThreatExtension[pvNode];
2406 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2408 Color c = pos.side_to_move();
2409 if (relative_rank(c, move_to(m)) == RANK_7)
2411 result += PawnPushTo7thExtension[pvNode];
2414 if (pos.pawn_is_passed(c, move_to(m)))
2416 result += PassedPawnExtension[pvNode];
2421 if ( captureOrPromotion
2422 && pos.type_of_piece_on(move_to(m)) != PAWN
2423 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2424 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2425 && !move_is_promotion(m)
2428 result += PawnEndgameExtension[pvNode];
2433 && captureOrPromotion
2434 && pos.type_of_piece_on(move_to(m)) != PAWN
2435 && pos.see_sign(m) >= 0)
2441 return Min(result, OnePly);
2445 // ok_to_do_nullmove() looks at the current position and decides whether
2446 // doing a 'null move' should be allowed. In order to avoid zugzwang
2447 // problems, null moves are not allowed when the side to move has very
2448 // little material left. Currently, the test is a bit too simple: Null
2449 // moves are avoided only when the side to move has only pawns left.
2450 // It's probably a good idea to avoid null moves in at least some more
2451 // complicated endgames, e.g. KQ vs KR. FIXME
2453 bool ok_to_do_nullmove(const Position& pos) {
2455 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2459 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2460 // non-tactical moves late in the move list close to the leaves are
2461 // candidates for pruning.
2463 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2465 assert(move_is_ok(m));
2466 assert(threat == MOVE_NONE || move_is_ok(threat));
2467 assert(!pos.move_is_check(m));
2468 assert(!pos.move_is_capture_or_promotion(m));
2469 assert(!pos.move_is_passed_pawn_push(m));
2471 Square mfrom, mto, tfrom, tto;
2473 // Prune if there isn't any threat move
2474 if (threat == MOVE_NONE)
2477 mfrom = move_from(m);
2479 tfrom = move_from(threat);
2480 tto = move_to(threat);
2482 // Case 1: Don't prune moves which move the threatened piece
2486 // Case 2: If the threatened piece has value less than or equal to the
2487 // value of the threatening piece, don't prune move which defend it.
2488 if ( pos.move_is_capture(threat)
2489 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2490 || pos.type_of_piece_on(tfrom) == KING)
2491 && pos.move_attacks_square(m, tto))
2494 // Case 3: If the moving piece in the threatened move is a slider, don't
2495 // prune safe moves which block its ray.
2496 if ( piece_is_slider(pos.piece_on(tfrom))
2497 && bit_is_set(squares_between(tfrom, tto), mto)
2498 && pos.see_sign(m) >= 0)
2505 // ok_to_use_TT() returns true if a transposition table score
2506 // can be used at a given point in search.
2508 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2510 Value v = value_from_tt(tte->value(), ply);
2512 return ( tte->depth() >= depth
2513 || v >= Max(value_mate_in(PLY_MAX), beta)
2514 || v < Min(value_mated_in(PLY_MAX), beta))
2516 && ( (is_lower_bound(tte->type()) && v >= beta)
2517 || (is_upper_bound(tte->type()) && v < beta));
2521 // refine_eval() returns the transposition table score if
2522 // possible otherwise falls back on static position evaluation.
2524 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2529 Value v = value_from_tt(tte->value(), ply);
2531 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2532 || (is_upper_bound(tte->type()) && v < defaultEval))
2539 // update_history() registers a good move that produced a beta-cutoff
2540 // in history and marks as failures all the other moves of that ply.
2542 void update_history(const Position& pos, Move move, Depth depth,
2543 Move movesSearched[], int moveCount) {
2547 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2549 for (int i = 0; i < moveCount - 1; i++)
2551 m = movesSearched[i];
2555 if (!pos.move_is_capture_or_promotion(m))
2556 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2561 // update_killers() add a good move that produced a beta-cutoff
2562 // among the killer moves of that ply.
2564 void update_killers(Move m, SearchStack& ss) {
2566 if (m == ss.killers[0])
2569 for (int i = KILLER_MAX - 1; i > 0; i--)
2570 ss.killers[i] = ss.killers[i - 1];
2576 // update_gains() updates the gains table of a non-capture move given
2577 // the static position evaluation before and after the move.
2579 void update_gains(const Position& pos, Move m, Value before, Value after) {
2582 && before != VALUE_NONE
2583 && after != VALUE_NONE
2584 && pos.captured_piece() == NO_PIECE_TYPE
2585 && !move_is_castle(m)
2586 && !move_is_promotion(m))
2587 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2591 // current_search_time() returns the number of milliseconds which have passed
2592 // since the beginning of the current search.
2594 int current_search_time() {
2596 return get_system_time() - SearchStartTime;
2600 // nps() computes the current nodes/second count.
2604 int t = current_search_time();
2605 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2609 // poll() performs two different functions: It polls for user input, and it
2610 // looks at the time consumed so far and decides if it's time to abort the
2615 static int lastInfoTime;
2616 int t = current_search_time();
2621 // We are line oriented, don't read single chars
2622 std::string command;
2624 if (!std::getline(std::cin, command))
2627 if (command == "quit")
2630 PonderSearch = false;
2634 else if (command == "stop")
2637 PonderSearch = false;
2639 else if (command == "ponderhit")
2643 // Print search information
2647 else if (lastInfoTime > t)
2648 // HACK: Must be a new search where we searched less than
2649 // NodesBetweenPolls nodes during the first second of search.
2652 else if (t - lastInfoTime >= 1000)
2660 if (dbg_show_hit_rate)
2661 dbg_print_hit_rate();
2663 cout << "info nodes " << nodes_searched() << " nps " << nps()
2664 << " time " << t << " hashfull " << TT.full() << endl;
2666 lock_release(&IOLock);
2668 if (ShowCurrentLine)
2669 Threads[0].printCurrentLine = true;
2672 // Should we stop the search?
2676 bool stillAtFirstMove = RootMoveNumber == 1
2677 && !AspirationFailLow
2678 && t > MaxSearchTime + ExtraSearchTime;
2680 bool noMoreTime = t > AbsoluteMaxSearchTime
2681 || stillAtFirstMove;
2683 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2684 || (ExactMaxTime && t >= ExactMaxTime)
2685 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2690 // ponderhit() is called when the program is pondering (i.e. thinking while
2691 // it's the opponent's turn to move) in order to let the engine know that
2692 // it correctly predicted the opponent's move.
2696 int t = current_search_time();
2697 PonderSearch = false;
2699 bool stillAtFirstMove = RootMoveNumber == 1
2700 && !AspirationFailLow
2701 && t > MaxSearchTime + ExtraSearchTime;
2703 bool noMoreTime = t > AbsoluteMaxSearchTime
2704 || stillAtFirstMove;
2706 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2711 // print_current_line() prints the current line of search for a given
2712 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2714 void print_current_line(SearchStack ss[], int ply, int threadID) {
2716 assert(ply >= 0 && ply < PLY_MAX);
2717 assert(threadID >= 0 && threadID < ActiveThreads);
2719 if (!Threads[threadID].idle)
2722 cout << "info currline " << (threadID + 1);
2723 for (int p = 0; p < ply; p++)
2724 cout << " " << ss[p].currentMove;
2727 lock_release(&IOLock);
2729 Threads[threadID].printCurrentLine = false;
2730 if (threadID + 1 < ActiveThreads)
2731 Threads[threadID + 1].printCurrentLine = true;
2735 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2737 void init_ss_array(SearchStack ss[]) {
2739 for (int i = 0; i < 3; i++)
2742 ss[i].initKillers();
2747 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2748 // while the program is pondering. The point is to work around a wrinkle in
2749 // the UCI protocol: When pondering, the engine is not allowed to give a
2750 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2751 // We simply wait here until one of these commands is sent, and return,
2752 // after which the bestmove and pondermove will be printed (in id_loop()).
2754 void wait_for_stop_or_ponderhit() {
2756 std::string command;
2760 if (!std::getline(std::cin, command))
2763 if (command == "quit")
2768 else if (command == "ponderhit" || command == "stop")
2774 // idle_loop() is where the threads are parked when they have no work to do.
2775 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2776 // object for which the current thread is the master.
2778 void idle_loop(int threadID, SplitPoint* waitSp) {
2780 assert(threadID >= 0 && threadID < THREAD_MAX);
2782 Threads[threadID].running = true;
2784 while (!AllThreadsShouldExit || threadID == 0)
2786 // If we are not thinking, wait for a condition to be signaled
2787 // instead of wasting CPU time polling for work.
2788 while ( threadID != 0
2789 && !AllThreadsShouldExit
2790 && (AllThreadsShouldSleep || threadID >= ActiveThreads))
2793 Threads[threadID].sleeping = true;
2795 #if !defined(_MSC_VER)
2796 pthread_mutex_lock(&WaitLock);
2797 if (Idle || threadID >= ActiveThreads)
2798 pthread_cond_wait(&WaitCond, &WaitLock);
2800 pthread_mutex_unlock(&WaitLock);
2802 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2804 Threads[threadID].sleeping = false;
2807 // If this thread has been assigned work, launch a search
2808 if (Threads[threadID].workIsWaiting)
2810 assert(!Threads[threadID].idle);
2812 Threads[threadID].workIsWaiting = false;
2813 if (Threads[threadID].splitPoint->pvNode)
2814 sp_search_pv(Threads[threadID].splitPoint, threadID);
2816 sp_search(Threads[threadID].splitPoint, threadID);
2818 Threads[threadID].idle = true;
2821 // If this thread is the master of a split point and all threads have
2822 // finished their work at this split point, return from the idle loop.
2823 if (waitSp != NULL && waitSp->cpus == 0)
2827 Threads[threadID].running = false;
2831 // init_split_point_stack() is called during program initialization, and
2832 // initializes all split point objects.
2834 void init_split_point_stack() {
2836 for (int i = 0; i < THREAD_MAX; i++)
2837 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2839 SplitPointStack[i][j].parent = NULL;
2840 lock_init(&(SplitPointStack[i][j].lock), NULL);
2845 // destroy_split_point_stack() is called when the program exits, and
2846 // destroys all locks in the precomputed split point objects.
2848 void destroy_split_point_stack() {
2850 for (int i = 0; i < THREAD_MAX; i++)
2851 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2852 lock_destroy(&(SplitPointStack[i][j].lock));
2856 // thread_should_stop() checks whether the thread with a given threadID has
2857 // been asked to stop, directly or indirectly. This can happen if a beta
2858 // cutoff has occurred in the thread's currently active split point, or in
2859 // some ancestor of the current split point.
2861 bool thread_should_stop(int threadID) {
2863 assert(threadID >= 0 && threadID < ActiveThreads);
2867 if (Threads[threadID].stop)
2869 if (ActiveThreads <= 2)
2871 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2874 Threads[threadID].stop = true;
2881 // thread_is_available() checks whether the thread with threadID "slave" is
2882 // available to help the thread with threadID "master" at a split point. An
2883 // obvious requirement is that "slave" must be idle. With more than two
2884 // threads, this is not by itself sufficient: If "slave" is the master of
2885 // some active split point, it is only available as a slave to the other
2886 // threads which are busy searching the split point at the top of "slave"'s
2887 // split point stack (the "helpful master concept" in YBWC terminology).
2889 bool thread_is_available(int slave, int master) {
2891 assert(slave >= 0 && slave < ActiveThreads);
2892 assert(master >= 0 && master < ActiveThreads);
2893 assert(ActiveThreads > 1);
2895 if (!Threads[slave].idle || slave == master)
2898 // Make a local copy to be sure doesn't change under our feet
2899 int localActiveSplitPoints = Threads[slave].activeSplitPoints;
2901 if (localActiveSplitPoints == 0)
2902 // No active split points means that the thread is available as
2903 // a slave for any other thread.
2906 if (ActiveThreads == 2)
2909 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2910 // that is known to be > 0, instead of Threads[slave].activeSplitPoints that
2911 // could have been set to 0 by another thread leading to an out of bound access.
2912 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2919 // idle_thread_exists() tries to find an idle thread which is available as
2920 // a slave for the thread with threadID "master".
2922 bool idle_thread_exists(int master) {
2924 assert(master >= 0 && master < ActiveThreads);
2925 assert(ActiveThreads > 1);
2927 for (int i = 0; i < ActiveThreads; i++)
2928 if (thread_is_available(i, master))
2935 // split() does the actual work of distributing the work at a node between
2936 // several threads at PV nodes. If it does not succeed in splitting the
2937 // node (because no idle threads are available, or because we have no unused
2938 // split point objects), the function immediately returns false. If
2939 // splitting is possible, a SplitPoint object is initialized with all the
2940 // data that must be copied to the helper threads (the current position and
2941 // search stack, alpha, beta, the search depth, etc.), and we tell our
2942 // helper threads that they have been assigned work. This will cause them
2943 // to instantly leave their idle loops and call sp_search_pv(). When all
2944 // threads have returned from sp_search_pv (or, equivalently, when
2945 // splitPoint->cpus becomes 0), split() returns true.
2947 bool split(const Position& p, SearchStack* sstck, int ply,
2948 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2949 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2952 assert(sstck != NULL);
2953 assert(ply >= 0 && ply < PLY_MAX);
2954 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2955 assert(!pvNode || *alpha < *beta);
2956 assert(*beta <= VALUE_INFINITE);
2957 assert(depth > Depth(0));
2958 assert(master >= 0 && master < ActiveThreads);
2959 assert(ActiveThreads > 1);
2961 SplitPoint* splitPoint;
2965 // If no other thread is available to help us, or if we have too many
2966 // active split points, don't split.
2967 if ( !idle_thread_exists(master)
2968 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2970 lock_release(&MPLock);
2974 // Pick the next available split point object from the split point stack
2975 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2976 Threads[master].activeSplitPoints++;
2978 // Initialize the split point object
2979 splitPoint->parent = Threads[master].splitPoint;
2980 splitPoint->finished = false;
2981 splitPoint->ply = ply;
2982 splitPoint->depth = depth;
2983 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2984 splitPoint->beta = *beta;
2985 splitPoint->pvNode = pvNode;
2986 splitPoint->bestValue = *bestValue;
2987 splitPoint->futilityValue = futilityValue;
2988 splitPoint->master = master;
2989 splitPoint->mp = mp;
2990 splitPoint->moves = *moves;
2991 splitPoint->cpus = 1;
2992 splitPoint->pos = &p;
2993 splitPoint->parentSstack = sstck;
2994 for (int i = 0; i < ActiveThreads; i++)
2995 splitPoint->slaves[i] = 0;
2997 Threads[master].idle = false;
2998 Threads[master].stop = false;
2999 Threads[master].splitPoint = splitPoint;
3001 // Allocate available threads setting idle flag to false
3002 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
3003 if (thread_is_available(i, master))
3005 Threads[i].idle = false;
3006 Threads[i].stop = false;
3007 Threads[i].splitPoint = splitPoint;
3008 splitPoint->slaves[i] = 1;
3012 assert(splitPoint->cpus > 1);
3014 // We can release the lock because master and slave threads are already booked
3015 lock_release(&MPLock);
3017 // Tell the threads that they have work to do. This will make them leave
3018 // their idle loop. But before copy search stack tail for each thread.
3019 for (int i = 0; i < ActiveThreads; i++)
3020 if (i == master || splitPoint->slaves[i])
3022 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
3023 Threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
3026 // Everything is set up. The master thread enters the idle loop, from
3027 // which it will instantly launch a search, because its workIsWaiting
3028 // slot is 'true'. We send the split point as a second parameter to the
3029 // idle loop, which means that the main thread will return from the idle
3030 // loop when all threads have finished their work at this split point
3031 // (i.e. when splitPoint->cpus == 0).
3032 idle_loop(master, splitPoint);
3034 // We have returned from the idle loop, which means that all threads are
3035 // finished. Update alpha, beta and bestValue, and return.
3039 *alpha = splitPoint->alpha;
3041 *beta = splitPoint->beta;
3042 *bestValue = splitPoint->bestValue;
3043 Threads[master].stop = false;
3044 Threads[master].idle = false;
3045 Threads[master].activeSplitPoints--;
3046 Threads[master].splitPoint = splitPoint->parent;
3048 lock_release(&MPLock);
3053 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3054 // to start a new search from the root.
3056 void wake_sleeping_threads() {
3058 if (ActiveThreads > 1)
3060 for (int i = 1; i < ActiveThreads; i++)
3062 Threads[i].idle = true;
3063 Threads[i].workIsWaiting = false;
3066 #if !defined(_MSC_VER)
3067 pthread_mutex_lock(&WaitLock);
3068 pthread_cond_broadcast(&WaitCond);
3069 pthread_mutex_unlock(&WaitLock);
3071 for (int i = 1; i < THREAD_MAX; i++)
3072 SetEvent(SitIdleEvent[i]);
3078 // init_thread() is the function which is called when a new thread is
3079 // launched. It simply calls the idle_loop() function with the supplied
3080 // threadID. There are two versions of this function; one for POSIX
3081 // threads and one for Windows threads.
3083 #if !defined(_MSC_VER)
3085 void* init_thread(void *threadID) {
3087 idle_loop(*(int*)threadID, NULL);
3093 DWORD WINAPI init_thread(LPVOID threadID) {
3095 idle_loop(*(int*)threadID, NULL);