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/>.
42 #include "ucioption.h"
48 //// Local definitions
55 // IterationInfoType stores search results for each iteration
57 // Because we use relatively small (dynamic) aspiration window,
58 // there happens many fail highs and fail lows in root. And
59 // because we don't do researches in those cases, "value" stored
60 // here is not necessarily exact. Instead in case of fail high/low
61 // we guess what the right value might be and store our guess
62 // as a "speculated value" and then move on. Speculated values are
63 // used just to calculate aspiration window width, so also if are
64 // not exact is not big a problem.
66 struct IterationInfoType {
68 IterationInfoType(Value v = Value(0), Value sv = Value(0))
69 : value(v), speculatedValue(sv) {}
71 Value value, speculatedValue;
75 // The BetaCounterType class is used to order moves at ply one.
76 // Apart for the first one that has its score, following moves
77 // normally have score -VALUE_INFINITE, so are ordered according
78 // to the number of beta cutoffs occurred under their subtree during
79 // the last iteration. The counters are per thread variables to avoid
80 // concurrent accessing under SMP case.
82 struct BetaCounterType {
86 void add(Color us, Depth d, int threadID);
87 void read(Color us, int64_t& our, int64_t& their);
91 // The RootMove class is used for moves at the root at the tree. For each
92 // root move, we store a score, a node count, and a PV (really a refutation
93 // in the case of moves which fail low).
98 bool operator<(const RootMove&) const; // Used to sort
102 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
103 Move pv[PLY_MAX_PLUS_2];
107 // The RootMoveList class is essentially an array of RootMove objects, with
108 // a handful of methods for accessing the data in the individual moves.
113 RootMoveList(Position& pos, Move searchMoves[]);
114 inline Move get_move(int moveNum) const;
115 inline Value get_move_score(int moveNum) const;
116 inline void set_move_score(int moveNum, Value score);
117 inline void set_move_nodes(int moveNum, int64_t nodes);
118 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
119 void set_move_pv(int moveNum, const Move pv[]);
120 inline Move get_move_pv(int moveNum, int i) const;
121 inline int64_t get_move_cumulative_nodes(int moveNum) const;
122 inline int move_count() const;
124 void sort_multipv(int n);
127 static const int MaxRootMoves = 500;
128 RootMove moves[MaxRootMoves];
135 // Search depth at iteration 1
136 const Depth InitialDepth = OnePly;
138 // Depth limit for selective search
139 const Depth SelectiveDepth = 7 * OnePly;
141 // Use internal iterative deepening?
142 const bool UseIIDAtPVNodes = true;
143 const bool UseIIDAtNonPVNodes = true;
145 // Internal iterative deepening margin. At Non-PV moves, when
146 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
147 // search when the static evaluation is at most IIDMargin below beta.
148 const Value IIDMargin = Value(0x100);
150 // Easy move margin. An easy move candidate must be at least this much
151 // better than the second best move.
152 const Value EasyMoveMargin = Value(0x200);
154 // Problem margin. If the score of the first move at iteration N+1 has
155 // dropped by more than this since iteration N, the boolean variable
156 // "Problem" is set to true, which will make the program spend some extra
157 // time looking for a better move.
158 const Value ProblemMargin = Value(0x28);
160 // No problem margin. If the boolean "Problem" is true, and a new move
161 // is found at the root which is less than NoProblemMargin worse than the
162 // best move from the previous iteration, Problem is set back to false.
163 const Value NoProblemMargin = Value(0x14);
165 // Null move margin. A null move search will not be done if the approximate
166 // evaluation of the position is more than NullMoveMargin below beta.
167 const Value NullMoveMargin = Value(0x300);
169 // Pruning criterions. See the code and comments in ok_to_prune() to
170 // understand their precise meaning.
171 const bool PruneEscapeMoves = false;
172 const bool PruneDefendingMoves = false;
173 const bool PruneBlockingMoves = false;
175 // If the TT move is at least SingleReplyMargin better then the
176 // remaining ones we will extend it.
177 const Value SingleReplyMargin = Value(0x20);
179 // Margins for futility pruning in the quiescence search, and at frontier
180 // and near frontier nodes.
181 const Value FutilityMarginQS = Value(0x80);
183 // Each move futility margin is decreased
184 const Value IncrementalFutilityMargin = Value(0x8);
186 // Depth limit for razoring
187 const Depth RazorDepth = 4 * OnePly;
189 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
190 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
192 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
193 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
196 /// Variables initialized by UCI options
198 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
199 int LMRPVMoves, LMRNonPVMoves;
201 // Depth limit for use of dynamic threat detection
204 // Last seconds noise filtering (LSN)
205 const bool UseLSNFiltering = true;
206 const int LSNTime = 4000; // In milliseconds
207 const Value LSNValue = value_from_centipawns(200);
208 bool loseOnTime = false;
210 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
211 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
212 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
214 // Iteration counters
216 BetaCounterType BetaCounter;
218 // Scores and number of times the best move changed for each iteration
219 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
220 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
225 // Time managment variables
228 int MaxNodes, MaxDepth;
229 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
230 bool InfiniteSearch, PonderSearch, StopOnPonderhit;
231 bool AbortSearch, Quit;
232 bool FailHigh, FailLow, Problem;
234 // Show current line?
235 bool ShowCurrentLine;
239 std::ofstream LogFile;
241 // MP related variables
242 int ActiveThreads = 1;
243 Depth MinimumSplitDepth;
244 int MaxThreadsPerSplitPoint;
245 Thread Threads[THREAD_MAX];
248 bool AllThreadsShouldExit = false;
249 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
252 #if !defined(_MSC_VER)
253 pthread_cond_t WaitCond;
254 pthread_mutex_t WaitLock;
256 HANDLE SitIdleEvent[THREAD_MAX];
259 // Node counters, used only by thread[0] but try to keep in different
260 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
262 int NodesBetweenPolls = 30000;
270 Value id_loop(const Position& pos, Move searchMoves[]);
271 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
272 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
273 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
274 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
275 void sp_search(SplitPoint* sp, int threadID);
276 void sp_search_pv(SplitPoint* sp, int threadID);
277 void init_node(SearchStack ss[], int ply, int threadID);
278 void update_pv(SearchStack ss[], int ply);
279 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
280 bool connected_moves(const Position& pos, Move m1, Move m2);
281 bool value_is_mate(Value value);
282 bool move_is_killer(Move m, const SearchStack& ss);
283 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
284 bool ok_to_do_nullmove(const Position& pos);
285 bool ok_to_prune(const Position& pos, Move m, Move threat);
286 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
287 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
288 void update_killers(Move m, SearchStack& ss);
290 bool fail_high_ply_1();
291 int current_search_time();
295 void print_current_line(SearchStack ss[], int ply, int threadID);
296 void wait_for_stop_or_ponderhit();
297 void init_ss_array(SearchStack ss[]);
299 void idle_loop(int threadID, SplitPoint* waitSp);
300 void init_split_point_stack();
301 void destroy_split_point_stack();
302 bool thread_should_stop(int threadID);
303 bool thread_is_available(int slave, int master);
304 bool idle_thread_exists(int master);
305 bool split(const Position& pos, SearchStack* ss, int ply,
306 Value *alpha, Value *beta, Value *bestValue,
307 const Value futilityValue, Depth depth, int *moves,
308 MovePicker *mp, int master, bool pvNode);
309 void wake_sleeping_threads();
311 #if !defined(_MSC_VER)
312 void *init_thread(void *threadID);
314 DWORD WINAPI init_thread(LPVOID threadID);
325 /// perft() is our utility to verify move generation is bug free. All the legal
326 /// moves up to given depth are generated and counted and the sum returned.
328 int perft(Position& pos, Depth depth)
332 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
334 // If we are at the last ply we don't need to do and undo
335 // the moves, just to count them.
336 if (depth <= OnePly) // Replace with '<' to test also qsearch
338 while (mp.get_next_move()) sum++;
342 // Loop through all legal moves
344 while ((move = mp.get_next_move()) != MOVE_NONE)
347 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
348 sum += perft(pos, depth - OnePly);
355 /// think() is the external interface to Stockfish's search, and is called when
356 /// the program receives the UCI 'go' command. It initializes various
357 /// search-related global variables, and calls root_search(). It returns false
358 /// when a quit command is received during the search.
360 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
361 int time[], int increment[], int movesToGo, int maxDepth,
362 int maxNodes, int maxTime, Move searchMoves[]) {
364 // Look for a book move
365 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
368 if (get_option_value_string("Book File") != OpeningBook.file_name())
369 OpeningBook.open(get_option_value_string("Book File"));
371 bookMove = OpeningBook.get_move(pos);
372 if (bookMove != MOVE_NONE)
374 cout << "bestmove " << bookMove << endl;
379 // Initialize global search variables
380 Idle = StopOnPonderhit = AbortSearch = Quit = false;
381 FailHigh = FailLow = Problem = false;
382 SearchStartTime = get_system_time();
383 ExactMaxTime = maxTime;
385 InfiniteSearch = infinite;
386 PonderSearch = ponder;
388 for (int i = 0; i < THREAD_MAX; i++)
390 Threads[i].nodes = 0ULL;
391 Threads[i].failHighPly1 = false;
394 if (button_was_pressed("New Game"))
395 loseOnTime = false; // Reset at the beginning of a new game
397 // Read UCI option values
398 TT.set_size(get_option_value_int("Hash"));
399 if (button_was_pressed("Clear Hash"))
402 bool PonderingEnabled = get_option_value_bool("Ponder");
403 MultiPV = get_option_value_int("MultiPV");
405 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
406 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
408 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
409 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
411 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
412 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
414 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
415 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
417 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
418 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
420 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
421 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
423 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
424 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
425 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
427 Chess960 = get_option_value_bool("UCI_Chess960");
428 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
429 UseLogFile = get_option_value_bool("Use Search Log");
431 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
433 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
434 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
436 read_weights(pos.side_to_move());
438 // Set the number of active threads
439 int newActiveThreads = get_option_value_int("Threads");
440 if (newActiveThreads != ActiveThreads)
442 ActiveThreads = newActiveThreads;
443 init_eval(ActiveThreads);
446 // Wake up sleeping threads
447 wake_sleeping_threads();
449 for (int i = 1; i < ActiveThreads; i++)
450 assert(thread_is_available(i, 0));
453 int myTime = time[side_to_move];
454 int myIncrement = increment[side_to_move];
456 if (!movesToGo) // Sudden death time control
460 MaxSearchTime = myTime / 30 + myIncrement;
461 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
463 else // Blitz game without increment
465 MaxSearchTime = myTime / 30;
466 AbsoluteMaxSearchTime = myTime / 8;
469 else // (x moves) / (y minutes)
473 MaxSearchTime = myTime / 2;
474 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
478 MaxSearchTime = myTime / Min(movesToGo, 20);
479 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
483 if (PonderingEnabled)
485 MaxSearchTime += MaxSearchTime / 4;
486 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
489 // Fixed depth or fixed number of nodes?
492 InfiniteSearch = true; // HACK
497 NodesBetweenPolls = Min(MaxNodes, 30000);
498 InfiniteSearch = true; // HACK
500 else if (myTime && myTime < 1000)
501 NodesBetweenPolls = 1000;
502 else if (myTime && myTime < 5000)
503 NodesBetweenPolls = 5000;
505 NodesBetweenPolls = 30000;
507 // Write information to search log file
509 LogFile << "Searching: " << pos.to_fen() << endl
510 << "infinite: " << infinite
511 << " ponder: " << ponder
512 << " time: " << myTime
513 << " increment: " << myIncrement
514 << " moves to go: " << movesToGo << endl;
516 // LSN filtering. Used only for developing purpose. Disabled by default.
520 // Step 2. If after last move we decided to lose on time, do it now!
521 while (SearchStartTime + myTime + 1000 > get_system_time())
525 // We're ready to start thinking. Call the iterative deepening loop function
526 Value v = id_loop(pos, searchMoves);
531 // Step 1. If this is sudden death game and our position is hopeless,
532 // decide to lose on time.
533 if ( !loseOnTime // If we already lost on time, go to step 3.
543 // Step 3. Now after stepping over the time limit, reset flag for next match.
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() {
564 #if !defined(_MSC_VER)
565 pthread_t pthread[1];
568 for (i = 0; i < THREAD_MAX; i++)
569 Threads[i].activeSplitPoints = 0;
571 // Initialize global locks
572 lock_init(&MPLock, NULL);
573 lock_init(&IOLock, NULL);
575 init_split_point_stack();
577 #if !defined(_MSC_VER)
578 pthread_mutex_init(&WaitLock, NULL);
579 pthread_cond_init(&WaitCond, NULL);
581 for (i = 0; i < THREAD_MAX; i++)
582 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
585 // All threads except the main thread should be initialized to idle state
586 for (i = 1; i < THREAD_MAX; i++)
588 Threads[i].stop = false;
589 Threads[i].workIsWaiting = false;
590 Threads[i].idle = true;
591 Threads[i].running = false;
594 // Launch the helper threads
595 for (i = 1; i < THREAD_MAX; i++)
597 #if !defined(_MSC_VER)
598 pthread_create(pthread, NULL, init_thread, (void*)(&i));
601 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
604 // Wait until the thread has finished launching
605 while (!Threads[i].running);
610 /// stop_threads() is called when the program exits. It makes all the
611 /// helper threads exit cleanly.
613 void stop_threads() {
615 ActiveThreads = THREAD_MAX; // HACK
616 Idle = false; // HACK
617 wake_sleeping_threads();
618 AllThreadsShouldExit = true;
619 for (int i = 1; i < THREAD_MAX; i++)
621 Threads[i].stop = true;
622 while (Threads[i].running);
624 destroy_split_point_stack();
628 /// nodes_searched() returns the total number of nodes searched so far in
629 /// the current search.
631 int64_t nodes_searched() {
633 int64_t result = 0ULL;
634 for (int i = 0; i < ActiveThreads; i++)
635 result += Threads[i].nodes;
640 // SearchStack::init() initializes a search stack. Used at the beginning of a
641 // new search from the root.
642 void SearchStack::init(int ply) {
644 pv[ply] = pv[ply + 1] = MOVE_NONE;
645 currentMove = threatMove = MOVE_NONE;
646 reduction = Depth(0);
649 void SearchStack::initKillers() {
651 mateKiller = MOVE_NONE;
652 for (int i = 0; i < KILLER_MAX; i++)
653 killers[i] = MOVE_NONE;
658 // id_loop() is the main iterative deepening loop. It calls root_search
659 // repeatedly with increasing depth until the allocated thinking time has
660 // been consumed, the user stops the search, or the maximum search depth is
663 Value id_loop(const Position& pos, Move searchMoves[]) {
666 SearchStack ss[PLY_MAX_PLUS_2];
668 // searchMoves are verified, copied, scored and sorted
669 RootMoveList rml(p, searchMoves);
671 if (rml.move_count() == 0)
674 wait_for_stop_or_ponderhit();
676 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
679 // Print RootMoveList c'tor startup scoring to the standard output,
680 // so that we print information also for iteration 1.
681 cout << "info depth " << 1 << "\ninfo depth " << 1
682 << " score " << value_to_string(rml.get_move_score(0))
683 << " time " << current_search_time()
684 << " nodes " << nodes_searched()
686 << " pv " << rml.get_move(0) << "\n";
692 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
695 // Is one move significantly better than others after initial scoring ?
696 Move EasyMove = MOVE_NONE;
697 if ( rml.move_count() == 1
698 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
699 EasyMove = rml.get_move(0);
701 // Iterative deepening loop
702 while (Iteration < PLY_MAX)
704 // Initialize iteration
707 BestMoveChangesByIteration[Iteration] = 0;
711 cout << "info depth " << Iteration << endl;
713 // Calculate dynamic search window based on previous iterations
716 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
718 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
719 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
721 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
723 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
724 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
728 alpha = - VALUE_INFINITE;
729 beta = VALUE_INFINITE;
732 // Search to the current depth
733 Value value = root_search(p, ss, rml, alpha, beta);
735 // Write PV to transposition table, in case the relevant entries have
736 // been overwritten during the search.
737 TT.insert_pv(p, ss[0].pv);
740 break; // Value cannot be trusted. Break out immediately!
742 //Save info about search result
743 Value speculatedValue;
746 Value delta = value - IterationInfo[Iteration - 1].value;
753 speculatedValue = value + delta;
754 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
756 else if (value <= alpha)
758 assert(value == alpha);
762 speculatedValue = value + delta;
763 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
765 speculatedValue = value;
767 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
768 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
770 // Drop the easy move if it differs from the new best move
771 if (ss[0].pv[0] != EasyMove)
772 EasyMove = MOVE_NONE;
779 bool stopSearch = false;
781 // Stop search early if there is only a single legal move,
782 // we search up to Iteration 6 anyway to get a proper score.
783 if (Iteration >= 6 && rml.move_count() == 1)
786 // Stop search early when the last two iterations returned a mate score
788 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
789 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
792 // Stop search early if one move seems to be much better than the rest
793 int64_t nodes = nodes_searched();
797 && EasyMove == ss[0].pv[0]
798 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
799 && current_search_time() > MaxSearchTime / 16)
800 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
801 && current_search_time() > MaxSearchTime / 32)))
804 // Add some extra time if the best move has changed during the last two iterations
805 if (Iteration > 5 && Iteration <= 50)
806 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
807 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
809 // Stop search if most of MaxSearchTime is consumed at the end of the
810 // iteration. We probably don't have enough time to search the first
811 // move at the next iteration anyway.
812 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
820 StopOnPonderhit = true;
824 if (MaxDepth && Iteration >= MaxDepth)
830 // If we are pondering, we shouldn't print the best move before we
833 wait_for_stop_or_ponderhit();
835 // Print final search statistics
836 cout << "info nodes " << nodes_searched()
838 << " time " << current_search_time()
839 << " hashfull " << TT.full() << endl;
841 // Print the best move and the ponder move to the standard output
842 if (ss[0].pv[0] == MOVE_NONE)
844 ss[0].pv[0] = rml.get_move(0);
845 ss[0].pv[1] = MOVE_NONE;
847 cout << "bestmove " << ss[0].pv[0];
848 if (ss[0].pv[1] != MOVE_NONE)
849 cout << " ponder " << ss[0].pv[1];
856 dbg_print_mean(LogFile);
858 if (dbg_show_hit_rate)
859 dbg_print_hit_rate(LogFile);
861 LogFile << "\nNodes: " << nodes_searched()
862 << "\nNodes/second: " << nps()
863 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
866 p.do_move(ss[0].pv[0], st);
867 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
869 return rml.get_move_score(0);
873 // root_search() is the function which searches the root node. It is
874 // similar to search_pv except that it uses a different move ordering
875 // scheme and prints some information to the standard output.
877 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
879 Value oldAlpha = alpha;
883 // Loop through all the moves in the root move list
884 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
888 // We failed high, invalidate and skip next moves, leave node-counters
889 // and beta-counters as they are and quickly return, we will try to do
890 // a research at the next iteration with a bigger aspiration window.
891 rml.set_move_score(i, -VALUE_INFINITE);
899 RootMoveNumber = i + 1;
902 // Save the current node count before the move is searched
903 nodes = nodes_searched();
905 // Reset beta cut-off counters
908 // Pick the next root move, and print the move and the move number to
909 // the standard output.
910 move = ss[0].currentMove = rml.get_move(i);
912 if (current_search_time() >= 1000)
913 cout << "info currmove " << move
914 << " currmovenumber " << RootMoveNumber << endl;
916 // Decide search depth for this move
917 bool moveIsCheck = pos.move_is_check(move);
918 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
920 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
921 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
923 // Make the move, and search it
924 pos.do_move(move, st, ci, moveIsCheck);
928 // Aspiration window is disabled in multi-pv case
930 alpha = -VALUE_INFINITE;
932 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
934 // If the value has dropped a lot compared to the last iteration,
935 // set the boolean variable Problem to true. This variable is used
936 // for time managment: When Problem is true, we try to complete the
937 // current iteration before playing a move.
938 Problem = ( Iteration >= 2
939 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
941 if (Problem && StopOnPonderhit)
942 StopOnPonderhit = false;
946 // Try to reduce non-pv search depth by one ply if move seems not problematic,
947 // if the move fails high will be re-searched at full depth.
948 if ( newDepth >= 3*OnePly
949 && i >= MultiPV + LMRPVMoves
951 && !captureOrPromotion
952 && !move_is_castle(move))
954 ss[0].reduction = OnePly;
955 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
957 value = alpha + 1; // Just to trigger next condition
961 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
965 // Fail high! Set the boolean variable FailHigh to true, and
966 // re-search the move using a PV search. The variable FailHigh
967 // is used for time managment: We try to avoid aborting the
968 // search prematurely during a fail high research.
970 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
977 // Finished searching the move. If AbortSearch is true, the search
978 // was aborted because the user interrupted the search or because we
979 // ran out of time. In this case, the return value of the search cannot
980 // be trusted, and we break out of the loop without updating the best
985 // Remember beta-cutoff and searched nodes counts for this move. The
986 // info is used to sort the root moves at the next iteration.
988 BetaCounter.read(pos.side_to_move(), our, their);
989 rml.set_beta_counters(i, our, their);
990 rml.set_move_nodes(i, nodes_searched() - nodes);
992 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
994 if (value <= alpha && i >= MultiPV)
995 rml.set_move_score(i, -VALUE_INFINITE);
998 // PV move or new best move!
1001 rml.set_move_score(i, value);
1003 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1004 rml.set_move_pv(i, ss[0].pv);
1008 // We record how often the best move has been changed in each
1009 // iteration. This information is used for time managment: When
1010 // the best move changes frequently, we allocate some more time.
1012 BestMoveChangesByIteration[Iteration]++;
1014 // Print search information to the standard output
1015 cout << "info depth " << Iteration
1016 << " score " << value_to_string(value)
1017 << ((value >= beta) ? " lowerbound" :
1018 ((value <= alpha)? " upperbound" : ""))
1019 << " time " << current_search_time()
1020 << " nodes " << nodes_searched()
1024 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1025 cout << ss[0].pv[j] << " ";
1031 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1032 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1034 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1035 nodes_searched(), value, type, ss[0].pv) << endl;
1040 // Reset the global variable Problem to false if the value isn't too
1041 // far below the final value from the last iteration.
1042 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1047 rml.sort_multipv(i);
1048 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1050 cout << "info multipv " << j + 1
1051 << " score " << value_to_string(rml.get_move_score(j))
1052 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1053 << " time " << current_search_time()
1054 << " nodes " << nodes_searched()
1058 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1059 cout << rml.get_move_pv(j, k) << " ";
1063 alpha = rml.get_move_score(Min(i, MultiPV-1));
1065 } // PV move or new best move
1067 assert(alpha >= oldAlpha);
1069 FailLow = (alpha == oldAlpha);
1075 // search_pv() is the main search function for PV nodes.
1077 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1078 Depth depth, int ply, int threadID) {
1080 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1081 assert(beta > alpha && beta <= VALUE_INFINITE);
1082 assert(ply >= 0 && ply < PLY_MAX);
1083 assert(threadID >= 0 && threadID < ActiveThreads);
1085 Move movesSearched[256];
1090 Depth ext, newDepth;
1091 Value oldAlpha, value;
1092 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1094 Value bestValue = -VALUE_INFINITE;
1097 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1099 // Initialize, and make an early exit in case of an aborted search,
1100 // an instant draw, maximum ply reached, etc.
1101 init_node(ss, ply, threadID);
1103 // After init_node() that calls poll()
1104 if (AbortSearch || thread_should_stop(threadID))
1110 if (ply >= PLY_MAX - 1)
1111 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1113 // Mate distance pruning
1115 alpha = Max(value_mated_in(ply), alpha);
1116 beta = Min(value_mate_in(ply+1), beta);
1120 // Transposition table lookup. At PV nodes, we don't use the TT for
1121 // pruning, but only for move ordering. This is to avoid problems in
1122 // the following areas:
1124 // * Repetition draw detection
1125 // * Fifty move rule detection
1126 // * Searching for a mate
1127 // * Printing of full PV line
1129 tte = TT.retrieve(pos.get_key());
1130 ttMove = (tte ? tte->move() : MOVE_NONE);
1132 // Go with internal iterative deepening if we don't have a TT move
1133 if ( UseIIDAtPVNodes
1134 && depth >= 5*OnePly
1135 && ttMove == MOVE_NONE)
1137 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1138 ttMove = ss[ply].pv[ply];
1139 tte = TT.retrieve(pos.get_key());
1142 // Initialize a MovePicker object for the current position, and prepare
1143 // to search all moves
1144 isCheck = pos.is_check();
1145 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1147 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1149 // Loop through all legal moves until no moves remain or a beta cutoff
1151 while ( alpha < beta
1152 && (move = mp.get_next_move()) != MOVE_NONE
1153 && !thread_should_stop(threadID))
1155 assert(move_is_ok(move));
1157 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1158 moveIsCheck = pos.move_is_check(move, ci);
1159 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1161 // Decide the new search depth
1162 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1164 // Singular extension search. We extend the TT move if its value is much better than
1165 // its siblings. To verify this we do a reduced search on all the other moves but the
1166 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1167 if ( depth >= 6 * OnePly
1169 && move == tte->move()
1171 && is_lower_bound(tte->type())
1172 && tte->depth() >= depth - 3 * OnePly)
1174 Value ttValue = value_from_tt(tte->value(), ply);
1176 if (abs(ttValue) < VALUE_KNOWN_WIN)
1178 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1180 if (excValue < ttValue - SingleReplyMargin)
1185 newDepth = depth - OnePly + ext;
1187 // Update current move
1188 movesSearched[moveCount++] = ss[ply].currentMove = move;
1190 // Make and search the move
1191 pos.do_move(move, st, ci, moveIsCheck);
1193 if (moveCount == 1) // The first move in list is the PV
1194 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1197 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1198 // if the move fails high will be re-searched at full depth.
1199 if ( depth >= 3*OnePly
1200 && moveCount >= LMRPVMoves
1202 && !captureOrPromotion
1203 && !move_is_castle(move)
1204 && !move_is_killer(move, ss[ply]))
1206 ss[ply].reduction = OnePly;
1207 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1210 value = alpha + 1; // Just to trigger next condition
1212 if (value > alpha) // Go with full depth non-pv search
1214 ss[ply].reduction = Depth(0);
1215 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1216 if (value > alpha && value < beta)
1218 // When the search fails high at ply 1 while searching the first
1219 // move at the root, set the flag failHighPly1. This is used for
1220 // time managment: We don't want to stop the search early in
1221 // such cases, because resolving the fail high at ply 1 could
1222 // result in a big drop in score at the root.
1223 if (ply == 1 && RootMoveNumber == 1)
1224 Threads[threadID].failHighPly1 = true;
1226 // A fail high occurred. Re-search at full window (pv search)
1227 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1228 Threads[threadID].failHighPly1 = false;
1232 pos.undo_move(move);
1234 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1237 if (value > bestValue)
1244 if (value == value_mate_in(ply + 1))
1245 ss[ply].mateKiller = move;
1247 // If we are at ply 1, and we are searching the first root move at
1248 // ply 0, set the 'Problem' variable if the score has dropped a lot
1249 // (from the computer's point of view) since the previous iteration.
1252 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1257 if ( ActiveThreads > 1
1259 && depth >= MinimumSplitDepth
1261 && idle_thread_exists(threadID)
1263 && !thread_should_stop(threadID)
1264 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1265 depth, &moveCount, &mp, threadID, true))
1269 // All legal moves have been searched. A special case: If there were
1270 // no legal moves, it must be mate or stalemate.
1272 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1274 // If the search is not aborted, update the transposition table,
1275 // history counters, and killer moves.
1276 if (AbortSearch || thread_should_stop(threadID))
1279 if (bestValue <= oldAlpha)
1280 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1282 else if (bestValue >= beta)
1284 BetaCounter.add(pos.side_to_move(), depth, threadID);
1285 move = ss[ply].pv[ply];
1286 if (!pos.move_is_capture_or_promotion(move))
1288 update_history(pos, move, depth, movesSearched, moveCount);
1289 update_killers(move, ss[ply]);
1291 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1294 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1300 // search() is the search function for zero-width nodes.
1302 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1303 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1305 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1306 assert(ply >= 0 && ply < PLY_MAX);
1307 assert(threadID >= 0 && threadID < ActiveThreads);
1309 Move movesSearched[256];
1314 Depth ext, newDepth;
1315 Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
1316 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1317 bool mateThreat = false;
1319 Value bestValue = -VALUE_INFINITE;
1322 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1324 // Initialize, and make an early exit in case of an aborted search,
1325 // an instant draw, maximum ply reached, etc.
1326 init_node(ss, ply, threadID);
1328 // After init_node() that calls poll()
1329 if (AbortSearch || thread_should_stop(threadID))
1335 if (ply >= PLY_MAX - 1)
1336 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1338 // Mate distance pruning
1339 if (value_mated_in(ply) >= beta)
1342 if (value_mate_in(ply + 1) < beta)
1345 // We don't want the score of a partial search to overwrite a previous full search
1346 // TT value, so we use a different position key in case of an excluded move exsists.
1347 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1349 // Transposition table lookup
1350 tte = TT.retrieve(posKey);
1351 ttMove = (tte ? tte->move() : MOVE_NONE);
1353 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1355 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1356 return value_from_tt(tte->value(), ply);
1359 approximateEval = quick_evaluate(pos);
1360 isCheck = pos.is_check();
1366 && !value_is_mate(beta)
1367 && ok_to_do_nullmove(pos)
1368 && approximateEval >= beta - NullMoveMargin)
1370 ss[ply].currentMove = MOVE_NULL;
1372 pos.do_null_move(st);
1374 // Null move dynamic reduction based on depth
1375 int R = (depth >= 5 * OnePly ? 4 : 3);
1377 // Null move dynamic reduction based on value
1378 if (approximateEval - beta > PawnValueMidgame)
1381 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1383 pos.undo_null_move();
1385 if (nullValue >= beta)
1387 if (depth < 6 * OnePly)
1390 // Do zugzwang verification search
1391 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1395 // The null move failed low, which means that we may be faced with
1396 // some kind of threat. If the previous move was reduced, check if
1397 // the move that refuted the null move was somehow connected to the
1398 // move which was reduced. If a connection is found, return a fail
1399 // low score (which will cause the reduced move to fail high in the
1400 // parent node, which will trigger a re-search with full depth).
1401 if (nullValue == value_mated_in(ply + 2))
1404 ss[ply].threatMove = ss[ply + 1].currentMove;
1405 if ( depth < ThreatDepth
1406 && ss[ply - 1].reduction
1407 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1411 // Null move search not allowed, try razoring
1412 else if ( !value_is_mate(beta)
1413 && depth < RazorDepth
1414 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1415 && ss[ply - 1].currentMove != MOVE_NULL
1416 && ttMove == MOVE_NONE
1417 && !pos.has_pawn_on_7th(pos.side_to_move()))
1419 Value rbeta = beta - RazorMargins[int(depth) - 2];
1420 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1425 // Go with internal iterative deepening if we don't have a TT move
1426 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1427 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1429 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1430 ttMove = ss[ply].pv[ply];
1431 tte = TT.retrieve(pos.get_key());
1434 // Initialize a MovePicker object for the current position, and prepare
1435 // to search all moves.
1436 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1438 futilityValue = VALUE_NONE;
1439 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1441 // Calculate depth dependant futility pruning parameters
1442 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1443 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1445 // Avoid calling evaluate() if we already have the score in TT
1446 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1447 futilityValue = value_from_tt(tte->value(), ply) + FutilityValueMargin;
1449 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1450 while ( bestValue < beta
1451 && (move = mp.get_next_move()) != MOVE_NONE
1452 && !thread_should_stop(threadID))
1454 assert(move_is_ok(move));
1456 if (move == excludedMove)
1459 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1460 moveIsCheck = pos.move_is_check(move, ci);
1461 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1463 // Decide the new search depth
1464 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1466 // Singular extension search. We extend the TT move if its value is much better than
1467 // its siblings. To verify this we do a reduced search on all the other moves but the
1468 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1469 if ( depth >= 8 * OnePly
1471 && move == tte->move()
1472 && !excludedMove // Do not allow recursive single-reply search
1474 && is_lower_bound(tte->type())
1475 && tte->depth() >= depth - 3 * OnePly)
1477 Value ttValue = value_from_tt(tte->value(), ply);
1479 if (abs(ttValue) < VALUE_KNOWN_WIN)
1481 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1483 if (excValue < ttValue - SingleReplyMargin)
1488 newDepth = depth - OnePly + ext;
1490 // Update current move
1491 movesSearched[moveCount++] = ss[ply].currentMove = move;
1494 if ( useFutilityPruning
1496 && !captureOrPromotion
1499 // Move count based pruning
1500 if ( moveCount >= FutilityMoveCountMargin
1501 && ok_to_prune(pos, move, ss[ply].threatMove)
1502 && bestValue > value_mated_in(PLY_MAX))
1505 // Value based pruning
1506 if (futilityValue == VALUE_NONE)
1507 futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1509 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1511 if (futilityValueScaled < beta)
1513 if (futilityValueScaled > bestValue)
1514 bestValue = futilityValueScaled;
1519 // Make and search the move
1520 pos.do_move(move, st, ci, moveIsCheck);
1522 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1523 // if the move fails high will be re-searched at full depth.
1524 if ( depth >= 3*OnePly
1525 && moveCount >= LMRNonPVMoves
1527 && !captureOrPromotion
1528 && !move_is_castle(move)
1529 && !move_is_killer(move, ss[ply]))
1531 ss[ply].reduction = OnePly;
1532 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1535 value = beta; // Just to trigger next condition
1537 if (value >= beta) // Go with full depth non-pv search
1539 ss[ply].reduction = Depth(0);
1540 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1542 pos.undo_move(move);
1544 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1547 if (value > bestValue)
1553 if (value == value_mate_in(ply + 1))
1554 ss[ply].mateKiller = move;
1558 if ( ActiveThreads > 1
1560 && depth >= MinimumSplitDepth
1562 && idle_thread_exists(threadID)
1564 && !thread_should_stop(threadID)
1565 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1566 depth, &moveCount, &mp, threadID, false))
1570 // All legal moves have been searched. A special case: If there were
1571 // no legal moves, it must be mate or stalemate.
1573 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1575 // If the search is not aborted, update the transposition table,
1576 // history counters, and killer moves.
1577 if (AbortSearch || thread_should_stop(threadID))
1580 if (bestValue < beta)
1581 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1584 BetaCounter.add(pos.side_to_move(), depth, threadID);
1585 move = ss[ply].pv[ply];
1586 if (!pos.move_is_capture_or_promotion(move))
1588 update_history(pos, move, depth, movesSearched, moveCount);
1589 update_killers(move, ss[ply]);
1591 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1594 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1600 // qsearch() is the quiescence search function, which is called by the main
1601 // search function when the remaining depth is zero (or, to be more precise,
1602 // less than OnePly).
1604 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1605 Depth depth, int ply, int threadID) {
1607 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1608 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1610 assert(ply >= 0 && ply < PLY_MAX);
1611 assert(threadID >= 0 && threadID < ActiveThreads);
1616 Value staticValue, bestValue, value, futilityValue;
1617 bool isCheck, enoughMaterial, moveIsCheck;
1618 const TTEntry* tte = NULL;
1620 bool pvNode = (beta - alpha != 1);
1622 // Initialize, and make an early exit in case of an aborted search,
1623 // an instant draw, maximum ply reached, etc.
1624 init_node(ss, ply, threadID);
1626 // After init_node() that calls poll()
1627 if (AbortSearch || thread_should_stop(threadID))
1633 // Transposition table lookup, only when not in PV
1636 tte = TT.retrieve(pos.get_key());
1637 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1639 assert(tte->type() != VALUE_TYPE_EVAL);
1641 return value_from_tt(tte->value(), ply);
1644 ttMove = (tte ? tte->move() : MOVE_NONE);
1646 isCheck = pos.is_check();
1647 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1649 // Evaluate the position statically
1651 staticValue = -VALUE_INFINITE;
1653 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1655 // Use the cached evaluation score if possible
1656 assert(ei.futilityMargin == Value(0));
1658 staticValue = value_from_tt(tte->value(), ply);
1661 staticValue = evaluate(pos, ei, threadID);
1663 if (ply >= PLY_MAX - 1)
1664 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1666 // Initialize "stand pat score", and return it immediately if it is
1668 bestValue = staticValue;
1670 if (bestValue >= beta)
1672 // Store the score to avoid a future costly evaluation() call
1673 if (!isCheck && !tte && ei.futilityMargin == 0)
1674 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1679 if (bestValue > alpha)
1682 // Initialize a MovePicker object for the current position, and prepare
1683 // to search the moves. Because the depth is <= 0 here, only captures,
1684 // queen promotions and checks (only if depth == 0) will be generated.
1685 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1687 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1689 // Loop through the moves until no moves remain or a beta cutoff
1691 while ( alpha < beta
1692 && (move = mp.get_next_move()) != MOVE_NONE)
1694 assert(move_is_ok(move));
1697 ss[ply].currentMove = move;
1699 moveIsCheck = pos.move_is_check(move, ci);
1707 && !move_is_promotion(move)
1708 && !pos.move_is_passed_pawn_push(move))
1710 futilityValue = staticValue
1711 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1712 pos.endgame_value_of_piece_on(move_to(move)))
1713 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1715 + ei.futilityMargin;
1717 if (futilityValue < alpha)
1719 if (futilityValue > bestValue)
1720 bestValue = futilityValue;
1725 // Don't search captures and checks with negative SEE values
1728 && !move_is_promotion(move)
1729 && pos.see_sign(move) < 0)
1732 // Make and search the move
1733 pos.do_move(move, st, ci, moveIsCheck);
1734 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1735 pos.undo_move(move);
1737 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1740 if (value > bestValue)
1751 // All legal moves have been searched. A special case: If we're in check
1752 // and no legal moves were found, it is checkmate.
1753 if (!moveCount && pos.is_check()) // Mate!
1754 return value_mated_in(ply);
1756 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1758 // Update transposition table
1759 move = ss[ply].pv[ply];
1762 // If bestValue isn't changed it means it is still the static evaluation of
1763 // the node, so keep this info to avoid a future costly evaluation() call.
1764 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1765 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1767 if (bestValue < beta)
1768 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1770 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1773 // Update killers only for good check moves
1774 if (alpha >= beta && !pos.move_is_capture_or_promotion(move))
1775 update_killers(move, ss[ply]);
1781 // sp_search() is used to search from a split point. This function is called
1782 // by each thread working at the split point. It is similar to the normal
1783 // search() function, but simpler. Because we have already probed the hash
1784 // table, done a null move search, and searched the first move before
1785 // splitting, we don't have to repeat all this work in sp_search(). We
1786 // also don't need to store anything to the hash table here: This is taken
1787 // care of after we return from the split point.
1789 void sp_search(SplitPoint* sp, int threadID) {
1791 assert(threadID >= 0 && threadID < ActiveThreads);
1792 assert(ActiveThreads > 1);
1794 Position pos = Position(sp->pos);
1796 SearchStack* ss = sp->sstack[threadID];
1799 bool isCheck = pos.is_check();
1800 bool useFutilityPruning = sp->depth < SelectiveDepth
1803 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1804 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1806 while ( sp->bestValue < sp->beta
1807 && !thread_should_stop(threadID)
1808 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1810 assert(move_is_ok(move));
1812 bool moveIsCheck = pos.move_is_check(move, ci);
1813 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1815 lock_grab(&(sp->lock));
1816 int moveCount = ++sp->moves;
1817 lock_release(&(sp->lock));
1819 ss[sp->ply].currentMove = move;
1821 // Decide the new search depth.
1823 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1824 Depth newDepth = sp->depth - OnePly + ext;
1827 if ( useFutilityPruning
1829 && !captureOrPromotion)
1831 // Move count based pruning
1832 if ( moveCount >= FutilityMoveCountMargin
1833 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1834 && sp->bestValue > value_mated_in(PLY_MAX))
1837 // Value based pruning
1838 if (sp->futilityValue == VALUE_NONE)
1841 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1844 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1846 if (futilityValueScaled < sp->beta)
1848 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1850 lock_grab(&(sp->lock));
1851 if (futilityValueScaled > sp->bestValue)
1852 sp->bestValue = futilityValueScaled;
1853 lock_release(&(sp->lock));
1859 // Make and search the move.
1861 pos.do_move(move, st, ci, moveIsCheck);
1863 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1864 // if the move fails high will be re-searched at full depth.
1866 && moveCount >= LMRNonPVMoves
1867 && !captureOrPromotion
1868 && !move_is_castle(move)
1869 && !move_is_killer(move, ss[sp->ply]))
1871 ss[sp->ply].reduction = OnePly;
1872 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1875 value = sp->beta; // Just to trigger next condition
1877 if (value >= sp->beta) // Go with full depth non-pv search
1879 ss[sp->ply].reduction = Depth(0);
1880 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1882 pos.undo_move(move);
1884 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1886 if (thread_should_stop(threadID))
1890 if (value > sp->bestValue) // Less then 2% of cases
1892 lock_grab(&(sp->lock));
1893 if (value > sp->bestValue && !thread_should_stop(threadID))
1895 sp->bestValue = value;
1896 if (sp->bestValue >= sp->beta)
1898 sp_update_pv(sp->parentSstack, ss, sp->ply);
1899 for (int i = 0; i < ActiveThreads; i++)
1900 if (i != threadID && (i == sp->master || sp->slaves[i]))
1901 Threads[i].stop = true;
1903 sp->finished = true;
1906 lock_release(&(sp->lock));
1910 lock_grab(&(sp->lock));
1912 // If this is the master thread and we have been asked to stop because of
1913 // a beta cutoff higher up in the tree, stop all slave threads.
1914 if (sp->master == threadID && thread_should_stop(threadID))
1915 for (int i = 0; i < ActiveThreads; i++)
1917 Threads[i].stop = true;
1920 sp->slaves[threadID] = 0;
1922 lock_release(&(sp->lock));
1926 // sp_search_pv() is used to search from a PV split point. This function
1927 // is called by each thread working at the split point. It is similar to
1928 // the normal search_pv() function, but simpler. Because we have already
1929 // probed the hash table and searched the first move before splitting, we
1930 // don't have to repeat all this work in sp_search_pv(). We also don't
1931 // need to store anything to the hash table here: This is taken care of
1932 // after we return from the split point.
1934 void sp_search_pv(SplitPoint* sp, int threadID) {
1936 assert(threadID >= 0 && threadID < ActiveThreads);
1937 assert(ActiveThreads > 1);
1939 Position pos = Position(sp->pos);
1941 SearchStack* ss = sp->sstack[threadID];
1945 while ( sp->alpha < sp->beta
1946 && !thread_should_stop(threadID)
1947 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1949 bool moveIsCheck = pos.move_is_check(move, ci);
1950 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1952 assert(move_is_ok(move));
1954 lock_grab(&(sp->lock));
1955 int moveCount = ++sp->moves;
1956 lock_release(&(sp->lock));
1958 ss[sp->ply].currentMove = move;
1960 // Decide the new search depth.
1962 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1963 Depth newDepth = sp->depth - OnePly + ext;
1965 // Make and search the move.
1967 pos.do_move(move, st, ci, moveIsCheck);
1969 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1970 // if the move fails high will be re-searched at full depth.
1972 && moveCount >= LMRPVMoves
1973 && !captureOrPromotion
1974 && !move_is_castle(move)
1975 && !move_is_killer(move, ss[sp->ply]))
1977 ss[sp->ply].reduction = OnePly;
1978 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1981 value = sp->alpha + 1; // Just to trigger next condition
1983 if (value > sp->alpha) // Go with full depth non-pv search
1985 ss[sp->ply].reduction = Depth(0);
1986 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1988 if (value > sp->alpha && value < sp->beta)
1990 // When the search fails high at ply 1 while searching the first
1991 // move at the root, set the flag failHighPly1. This is used for
1992 // time managment: We don't want to stop the search early in
1993 // such cases, because resolving the fail high at ply 1 could
1994 // result in a big drop in score at the root.
1995 if (sp->ply == 1 && RootMoveNumber == 1)
1996 Threads[threadID].failHighPly1 = true;
1998 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1999 Threads[threadID].failHighPly1 = false;
2002 pos.undo_move(move);
2004 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2006 if (thread_should_stop(threadID))
2010 lock_grab(&(sp->lock));
2011 if (value > sp->bestValue && !thread_should_stop(threadID))
2013 sp->bestValue = value;
2014 if (value > sp->alpha)
2017 sp_update_pv(sp->parentSstack, ss, sp->ply);
2018 if (value == value_mate_in(sp->ply + 1))
2019 ss[sp->ply].mateKiller = move;
2021 if (value >= sp->beta)
2023 for (int i = 0; i < ActiveThreads; i++)
2024 if (i != threadID && (i == sp->master || sp->slaves[i]))
2025 Threads[i].stop = true;
2027 sp->finished = true;
2030 // If we are at ply 1, and we are searching the first root move at
2031 // ply 0, set the 'Problem' variable if the score has dropped a lot
2032 // (from the computer's point of view) since the previous iteration.
2035 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2038 lock_release(&(sp->lock));
2041 lock_grab(&(sp->lock));
2043 // If this is the master thread and we have been asked to stop because of
2044 // a beta cutoff higher up in the tree, stop all slave threads.
2045 if (sp->master == threadID && thread_should_stop(threadID))
2046 for (int i = 0; i < ActiveThreads; i++)
2048 Threads[i].stop = true;
2051 sp->slaves[threadID] = 0;
2053 lock_release(&(sp->lock));
2056 /// The BetaCounterType class
2058 BetaCounterType::BetaCounterType() { clear(); }
2060 void BetaCounterType::clear() {
2062 for (int i = 0; i < THREAD_MAX; i++)
2063 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2066 void BetaCounterType::add(Color us, Depth d, int threadID) {
2068 // Weighted count based on depth
2069 Threads[threadID].betaCutOffs[us] += unsigned(d);
2072 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2075 for (int i = 0; i < THREAD_MAX; i++)
2077 our += Threads[i].betaCutOffs[us];
2078 their += Threads[i].betaCutOffs[opposite_color(us)];
2083 /// The RootMove class
2087 RootMove::RootMove() {
2088 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
2091 // RootMove::operator<() is the comparison function used when
2092 // sorting the moves. A move m1 is considered to be better
2093 // than a move m2 if it has a higher score, or if the moves
2094 // have equal score but m1 has the higher node count.
2096 bool RootMove::operator<(const RootMove& m) const {
2098 if (score != m.score)
2099 return (score < m.score);
2101 return theirBeta <= m.theirBeta;
2104 /// The RootMoveList class
2108 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2110 MoveStack mlist[MaxRootMoves];
2111 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2113 // Generate all legal moves
2114 MoveStack* last = generate_moves(pos, mlist);
2116 // Add each move to the moves[] array
2117 for (MoveStack* cur = mlist; cur != last; cur++)
2119 bool includeMove = includeAllMoves;
2121 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2122 includeMove = (searchMoves[k] == cur->move);
2127 // Find a quick score for the move
2129 SearchStack ss[PLY_MAX_PLUS_2];
2132 moves[count].move = cur->move;
2133 pos.do_move(moves[count].move, st);
2134 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2135 pos.undo_move(moves[count].move);
2136 moves[count].pv[0] = moves[count].move;
2137 moves[count].pv[1] = MOVE_NONE;
2144 // Simple accessor methods for the RootMoveList class
2146 inline Move RootMoveList::get_move(int moveNum) const {
2147 return moves[moveNum].move;
2150 inline Value RootMoveList::get_move_score(int moveNum) const {
2151 return moves[moveNum].score;
2154 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2155 moves[moveNum].score = score;
2158 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2159 moves[moveNum].nodes = nodes;
2160 moves[moveNum].cumulativeNodes += nodes;
2163 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2164 moves[moveNum].ourBeta = our;
2165 moves[moveNum].theirBeta = their;
2168 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2170 for (j = 0; pv[j] != MOVE_NONE; j++)
2171 moves[moveNum].pv[j] = pv[j];
2172 moves[moveNum].pv[j] = MOVE_NONE;
2175 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2176 return moves[moveNum].pv[i];
2179 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2180 return moves[moveNum].cumulativeNodes;
2183 inline int RootMoveList::move_count() const {
2188 // RootMoveList::sort() sorts the root move list at the beginning of a new
2191 inline void RootMoveList::sort() {
2193 sort_multipv(count - 1); // all items
2197 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2198 // list by their scores and depths. It is used to order the different PVs
2199 // correctly in MultiPV mode.
2201 void RootMoveList::sort_multipv(int n) {
2203 for (int i = 1; i <= n; i++)
2205 RootMove rm = moves[i];
2207 for (j = i; j > 0 && moves[j-1] < rm; j--)
2208 moves[j] = moves[j-1];
2214 // init_node() is called at the beginning of all the search functions
2215 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2216 // stack object corresponding to the current node. Once every
2217 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2218 // for user input and checks whether it is time to stop the search.
2220 void init_node(SearchStack ss[], int ply, int threadID) {
2222 assert(ply >= 0 && ply < PLY_MAX);
2223 assert(threadID >= 0 && threadID < ActiveThreads);
2225 Threads[threadID].nodes++;
2230 if (NodesSincePoll >= NodesBetweenPolls)
2237 ss[ply+2].initKillers();
2239 if (Threads[threadID].printCurrentLine)
2240 print_current_line(ss, ply, threadID);
2244 // update_pv() is called whenever a search returns a value > alpha. It
2245 // updates the PV in the SearchStack object corresponding to the current
2248 void update_pv(SearchStack ss[], int ply) {
2249 assert(ply >= 0 && ply < PLY_MAX);
2251 ss[ply].pv[ply] = ss[ply].currentMove;
2253 for (p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2254 ss[ply].pv[p] = ss[ply+1].pv[p];
2255 ss[ply].pv[p] = MOVE_NONE;
2259 // sp_update_pv() is a variant of update_pv for use at split points. The
2260 // difference between the two functions is that sp_update_pv also updates
2261 // the PV at the parent node.
2263 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2264 assert(ply >= 0 && ply < PLY_MAX);
2266 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2268 for (p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2269 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2270 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2274 // connected_moves() tests whether two moves are 'connected' in the sense
2275 // that the first move somehow made the second move possible (for instance
2276 // if the moving piece is the same in both moves). The first move is
2277 // assumed to be the move that was made to reach the current position, while
2278 // the second move is assumed to be a move from the current position.
2280 bool connected_moves(const Position& pos, Move m1, Move m2) {
2282 Square f1, t1, f2, t2;
2285 assert(move_is_ok(m1));
2286 assert(move_is_ok(m2));
2288 if (m2 == MOVE_NONE)
2291 // Case 1: The moving piece is the same in both moves
2297 // Case 2: The destination square for m2 was vacated by m1
2303 // Case 3: Moving through the vacated square
2304 if ( piece_is_slider(pos.piece_on(f2))
2305 && bit_is_set(squares_between(f2, t2), f1))
2308 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2309 p = pos.piece_on(t1);
2310 if (bit_is_set(pos.attacks_from(p, t1), t2))
2313 // Case 5: Discovered check, checking piece is the piece moved in m1
2314 if ( piece_is_slider(p)
2315 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2316 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2318 Bitboard occ = pos.occupied_squares();
2319 Color us = pos.side_to_move();
2320 Square ksq = pos.king_square(us);
2321 clear_bit(&occ, f2);
2322 if (type_of_piece(p) == BISHOP)
2324 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2327 else if (type_of_piece(p) == ROOK)
2329 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2334 assert(type_of_piece(p) == QUEEN);
2335 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2343 // value_is_mate() checks if the given value is a mate one
2344 // eventually compensated for the ply.
2346 bool value_is_mate(Value value) {
2348 assert(abs(value) <= VALUE_INFINITE);
2350 return value <= value_mated_in(PLY_MAX)
2351 || value >= value_mate_in(PLY_MAX);
2355 // move_is_killer() checks if the given move is among the
2356 // killer moves of that ply.
2358 bool move_is_killer(Move m, const SearchStack& ss) {
2360 const Move* k = ss.killers;
2361 for (int i = 0; i < KILLER_MAX; i++, k++)
2369 // extension() decides whether a move should be searched with normal depth,
2370 // or with extended depth. Certain classes of moves (checking moves, in
2371 // particular) are searched with bigger depth than ordinary moves and in
2372 // any case are marked as 'dangerous'. Note that also if a move is not
2373 // extended, as example because the corresponding UCI option is set to zero,
2374 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2376 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2377 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2379 assert(m != MOVE_NONE);
2381 Depth result = Depth(0);
2382 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2387 result += CheckExtension[pvNode];
2390 result += SingleEvasionExtension[pvNode];
2393 result += MateThreatExtension[pvNode];
2396 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2398 Color c = pos.side_to_move();
2399 if (relative_rank(c, move_to(m)) == RANK_7)
2401 result += PawnPushTo7thExtension[pvNode];
2404 if (pos.pawn_is_passed(c, move_to(m)))
2406 result += PassedPawnExtension[pvNode];
2411 if ( captureOrPromotion
2412 && pos.type_of_piece_on(move_to(m)) != PAWN
2413 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2414 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2415 && !move_is_promotion(m)
2418 result += PawnEndgameExtension[pvNode];
2423 && captureOrPromotion
2424 && pos.type_of_piece_on(move_to(m)) != PAWN
2425 && pos.see_sign(m) >= 0)
2431 return Min(result, OnePly);
2435 // ok_to_do_nullmove() looks at the current position and decides whether
2436 // doing a 'null move' should be allowed. In order to avoid zugzwang
2437 // problems, null moves are not allowed when the side to move has very
2438 // little material left. Currently, the test is a bit too simple: Null
2439 // moves are avoided only when the side to move has only pawns left. It's
2440 // probably a good idea to avoid null moves in at least some more
2441 // complicated endgames, e.g. KQ vs KR. FIXME
2443 bool ok_to_do_nullmove(const Position& pos) {
2445 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2449 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2450 // non-tactical moves late in the move list close to the leaves are
2451 // candidates for pruning.
2453 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2455 assert(move_is_ok(m));
2456 assert(threat == MOVE_NONE || move_is_ok(threat));
2457 assert(!pos.move_is_check(m));
2458 assert(!pos.move_is_capture_or_promotion(m));
2459 assert(!pos.move_is_passed_pawn_push(m));
2461 Square mfrom, mto, tfrom, tto;
2463 mfrom = move_from(m);
2465 tfrom = move_from(threat);
2466 tto = move_to(threat);
2468 // Case 1: Castling moves are never pruned
2469 if (move_is_castle(m))
2472 // Case 2: Don't prune moves which move the threatened piece
2473 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2476 // Case 3: If the threatened piece has value less than or equal to the
2477 // value of the threatening piece, don't prune move which defend it.
2478 if ( !PruneDefendingMoves
2479 && threat != MOVE_NONE
2480 && pos.move_is_capture(threat)
2481 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2482 || pos.type_of_piece_on(tfrom) == KING)
2483 && pos.move_attacks_square(m, tto))
2486 // Case 4: If the moving piece in the threatened move is a slider, don't
2487 // prune safe moves which block its ray.
2488 if ( !PruneBlockingMoves
2489 && threat != MOVE_NONE
2490 && piece_is_slider(pos.piece_on(tfrom))
2491 && bit_is_set(squares_between(tfrom, tto), mto)
2492 && pos.see_sign(m) >= 0)
2499 // ok_to_use_TT() returns true if a transposition table score
2500 // can be used at a given point in search.
2502 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2504 Value v = value_from_tt(tte->value(), ply);
2506 return ( tte->depth() >= depth
2507 || v >= Max(value_mate_in(PLY_MAX), beta)
2508 || v < Min(value_mated_in(PLY_MAX), beta))
2510 && ( (is_lower_bound(tte->type()) && v >= beta)
2511 || (is_upper_bound(tte->type()) && v < beta));
2515 // update_history() registers a good move that produced a beta-cutoff
2516 // in history and marks as failures all the other moves of that ply.
2518 void update_history(const Position& pos, Move m, Depth depth,
2519 Move movesSearched[], int moveCount) {
2521 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2523 for (int i = 0; i < moveCount - 1; i++)
2525 assert(m != movesSearched[i]);
2526 if (!pos.move_is_capture_or_promotion(movesSearched[i]))
2527 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]), depth);
2532 // update_killers() add a good move that produced a beta-cutoff
2533 // among the killer moves of that ply.
2535 void update_killers(Move m, SearchStack& ss) {
2537 if (m == ss.killers[0])
2540 for (int i = KILLER_MAX - 1; i > 0; i--)
2541 ss.killers[i] = ss.killers[i - 1];
2547 // fail_high_ply_1() checks if some thread is currently resolving a fail
2548 // high at ply 1 at the node below the first root node. This information
2549 // is used for time managment.
2551 bool fail_high_ply_1() {
2553 for (int i = 0; i < ActiveThreads; i++)
2554 if (Threads[i].failHighPly1)
2561 // current_search_time() returns the number of milliseconds which have passed
2562 // since the beginning of the current search.
2564 int current_search_time() {
2566 return get_system_time() - SearchStartTime;
2570 // nps() computes the current nodes/second count.
2574 int t = current_search_time();
2575 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2579 // poll() performs two different functions: It polls for user input, and it
2580 // looks at the time consumed so far and decides if it's time to abort the
2585 static int lastInfoTime;
2586 int t = current_search_time();
2591 // We are line oriented, don't read single chars
2592 std::string command;
2594 if (!std::getline(std::cin, command))
2597 if (command == "quit")
2600 PonderSearch = false;
2604 else if (command == "stop")
2607 PonderSearch = false;
2609 else if (command == "ponderhit")
2613 // Print search information
2617 else if (lastInfoTime > t)
2618 // HACK: Must be a new search where we searched less than
2619 // NodesBetweenPolls nodes during the first second of search.
2622 else if (t - lastInfoTime >= 1000)
2630 if (dbg_show_hit_rate)
2631 dbg_print_hit_rate();
2633 cout << "info nodes " << nodes_searched() << " nps " << nps()
2634 << " time " << t << " hashfull " << TT.full() << endl;
2636 lock_release(&IOLock);
2638 if (ShowCurrentLine)
2639 Threads[0].printCurrentLine = true;
2642 // Should we stop the search?
2646 bool stillAtFirstMove = RootMoveNumber == 1
2648 && t > MaxSearchTime + ExtraSearchTime;
2650 bool noProblemFound = !FailHigh
2652 && !fail_high_ply_1()
2654 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2656 bool noMoreTime = t > AbsoluteMaxSearchTime
2657 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2660 if ( (Iteration >= 3 && !InfiniteSearch && noMoreTime)
2661 || (ExactMaxTime && t >= ExactMaxTime)
2662 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2667 // ponderhit() is called when the program is pondering (i.e. thinking while
2668 // it's the opponent's turn to move) in order to let the engine know that
2669 // it correctly predicted the opponent's move.
2673 int t = current_search_time();
2674 PonderSearch = false;
2676 bool stillAtFirstMove = RootMoveNumber == 1
2678 && t > MaxSearchTime + ExtraSearchTime;
2680 bool noProblemFound = !FailHigh
2682 && !fail_high_ply_1()
2684 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2686 bool noMoreTime = t > AbsoluteMaxSearchTime
2690 if (Iteration >= 3 && !InfiniteSearch && (noMoreTime || StopOnPonderhit))
2695 // print_current_line() prints the current line of search for a given
2696 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2698 void print_current_line(SearchStack ss[], int ply, int threadID) {
2700 assert(ply >= 0 && ply < PLY_MAX);
2701 assert(threadID >= 0 && threadID < ActiveThreads);
2703 if (!Threads[threadID].idle)
2706 cout << "info currline " << (threadID + 1);
2707 for (int p = 0; p < ply; p++)
2708 cout << " " << ss[p].currentMove;
2711 lock_release(&IOLock);
2713 Threads[threadID].printCurrentLine = false;
2714 if (threadID + 1 < ActiveThreads)
2715 Threads[threadID + 1].printCurrentLine = true;
2719 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2721 void init_ss_array(SearchStack ss[]) {
2723 for (int i = 0; i < 3; i++)
2726 ss[i].initKillers();
2731 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2732 // while the program is pondering. The point is to work around a wrinkle in
2733 // the UCI protocol: When pondering, the engine is not allowed to give a
2734 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2735 // We simply wait here until one of these commands is sent, and return,
2736 // after which the bestmove and pondermove will be printed (in id_loop()).
2738 void wait_for_stop_or_ponderhit() {
2740 std::string command;
2744 if (!std::getline(std::cin, command))
2747 if (command == "quit")
2752 else if (command == "ponderhit" || command == "stop")
2758 // idle_loop() is where the threads are parked when they have no work to do.
2759 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2760 // object for which the current thread is the master.
2762 void idle_loop(int threadID, SplitPoint* waitSp) {
2764 assert(threadID >= 0 && threadID < THREAD_MAX);
2766 Threads[threadID].running = true;
2770 if (AllThreadsShouldExit && threadID != 0)
2773 // If we are not thinking, wait for a condition to be signaled instead
2774 // of wasting CPU time polling for work.
2775 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2778 #if !defined(_MSC_VER)
2779 pthread_mutex_lock(&WaitLock);
2780 if (Idle || threadID >= ActiveThreads)
2781 pthread_cond_wait(&WaitCond, &WaitLock);
2783 pthread_mutex_unlock(&WaitLock);
2785 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2789 // If this thread has been assigned work, launch a search
2790 if (Threads[threadID].workIsWaiting)
2792 Threads[threadID].workIsWaiting = false;
2793 if (Threads[threadID].splitPoint->pvNode)
2794 sp_search_pv(Threads[threadID].splitPoint, threadID);
2796 sp_search(Threads[threadID].splitPoint, threadID);
2798 Threads[threadID].idle = true;
2801 // If this thread is the master of a split point and all threads have
2802 // finished their work at this split point, return from the idle loop.
2803 if (waitSp != NULL && waitSp->cpus == 0)
2807 Threads[threadID].running = false;
2811 // init_split_point_stack() is called during program initialization, and
2812 // initializes all split point objects.
2814 void init_split_point_stack() {
2816 for (int i = 0; i < THREAD_MAX; i++)
2817 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2819 SplitPointStack[i][j].parent = NULL;
2820 lock_init(&(SplitPointStack[i][j].lock), NULL);
2825 // destroy_split_point_stack() is called when the program exits, and
2826 // destroys all locks in the precomputed split point objects.
2828 void destroy_split_point_stack() {
2830 for (int i = 0; i < THREAD_MAX; i++)
2831 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2832 lock_destroy(&(SplitPointStack[i][j].lock));
2836 // thread_should_stop() checks whether the thread with a given threadID has
2837 // been asked to stop, directly or indirectly. This can happen if a beta
2838 // cutoff has occured in the thread's currently active split point, or in
2839 // some ancestor of the current split point.
2841 bool thread_should_stop(int threadID) {
2843 assert(threadID >= 0 && threadID < ActiveThreads);
2847 if (Threads[threadID].stop)
2849 if (ActiveThreads <= 2)
2851 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2854 Threads[threadID].stop = true;
2861 // thread_is_available() checks whether the thread with threadID "slave" is
2862 // available to help the thread with threadID "master" at a split point. An
2863 // obvious requirement is that "slave" must be idle. With more than two
2864 // threads, this is not by itself sufficient: If "slave" is the master of
2865 // some active split point, it is only available as a slave to the other
2866 // threads which are busy searching the split point at the top of "slave"'s
2867 // split point stack (the "helpful master concept" in YBWC terminology).
2869 bool thread_is_available(int slave, int master) {
2871 assert(slave >= 0 && slave < ActiveThreads);
2872 assert(master >= 0 && master < ActiveThreads);
2873 assert(ActiveThreads > 1);
2875 if (!Threads[slave].idle || slave == master)
2878 if (Threads[slave].activeSplitPoints == 0)
2879 // No active split points means that the thread is available as
2880 // a slave for any other thread.
2883 if (ActiveThreads == 2)
2886 // Apply the "helpful master" concept if possible.
2887 if (SplitPointStack[slave][Threads[slave].activeSplitPoints - 1].slaves[master])
2894 // idle_thread_exists() tries to find an idle thread which is available as
2895 // a slave for the thread with threadID "master".
2897 bool idle_thread_exists(int master) {
2899 assert(master >= 0 && master < ActiveThreads);
2900 assert(ActiveThreads > 1);
2902 for (int i = 0; i < ActiveThreads; i++)
2903 if (thread_is_available(i, master))
2910 // split() does the actual work of distributing the work at a node between
2911 // several threads at PV nodes. If it does not succeed in splitting the
2912 // node (because no idle threads are available, or because we have no unused
2913 // split point objects), the function immediately returns false. If
2914 // splitting is possible, a SplitPoint object is initialized with all the
2915 // data that must be copied to the helper threads (the current position and
2916 // search stack, alpha, beta, the search depth, etc.), and we tell our
2917 // helper threads that they have been assigned work. This will cause them
2918 // to instantly leave their idle loops and call sp_search_pv(). When all
2919 // threads have returned from sp_search_pv (or, equivalently, when
2920 // splitPoint->cpus becomes 0), split() returns true.
2922 bool split(const Position& p, SearchStack* sstck, int ply,
2923 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2924 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2927 assert(sstck != NULL);
2928 assert(ply >= 0 && ply < PLY_MAX);
2929 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2930 assert(!pvNode || *alpha < *beta);
2931 assert(*beta <= VALUE_INFINITE);
2932 assert(depth > Depth(0));
2933 assert(master >= 0 && master < ActiveThreads);
2934 assert(ActiveThreads > 1);
2936 SplitPoint* splitPoint;
2941 // If no other thread is available to help us, or if we have too many
2942 // active split points, don't split.
2943 if ( !idle_thread_exists(master)
2944 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2946 lock_release(&MPLock);
2950 // Pick the next available split point object from the split point stack
2951 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2952 Threads[master].activeSplitPoints++;
2954 // Initialize the split point object and copy current position
2955 splitPoint->parent = Threads[master].splitPoint;
2956 splitPoint->finished = false;
2957 splitPoint->ply = ply;
2958 splitPoint->depth = depth;
2959 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2960 splitPoint->beta = *beta;
2961 splitPoint->pvNode = pvNode;
2962 splitPoint->bestValue = *bestValue;
2963 splitPoint->futilityValue = futilityValue;
2964 splitPoint->master = master;
2965 splitPoint->mp = mp;
2966 splitPoint->moves = *moves;
2967 splitPoint->cpus = 1;
2968 splitPoint->pos.copy(p);
2969 splitPoint->parentSstack = sstck;
2970 for (i = 0; i < ActiveThreads; i++)
2971 splitPoint->slaves[i] = 0;
2973 // Copy the current search stack to the master thread
2974 memcpy(splitPoint->sstack[master], sstck, (ply+1) * sizeof(SearchStack));
2975 Threads[master].splitPoint = splitPoint;
2977 // Make copies of the current position and search stack for each thread
2978 for (i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2979 if (thread_is_available(i, master))
2981 memcpy(splitPoint->sstack[i], sstck, (ply+1) * sizeof(SearchStack));
2982 Threads[i].splitPoint = splitPoint;
2983 splitPoint->slaves[i] = 1;
2987 // Tell the threads that they have work to do. This will make them leave
2989 for (i = 0; i < ActiveThreads; i++)
2990 if (i == master || splitPoint->slaves[i])
2992 Threads[i].workIsWaiting = true;
2993 Threads[i].idle = false;
2994 Threads[i].stop = false;
2997 lock_release(&MPLock);
2999 // Everything is set up. The master thread enters the idle loop, from
3000 // which it will instantly launch a search, because its workIsWaiting
3001 // slot is 'true'. We send the split point as a second parameter to the
3002 // idle loop, which means that the main thread will return from the idle
3003 // loop when all threads have finished their work at this split point
3004 // (i.e. when splitPoint->cpus == 0).
3005 idle_loop(master, splitPoint);
3007 // We have returned from the idle loop, which means that all threads are
3008 // finished. Update alpha, beta and bestValue, and return.
3012 *alpha = splitPoint->alpha;
3014 *beta = splitPoint->beta;
3015 *bestValue = splitPoint->bestValue;
3016 Threads[master].stop = false;
3017 Threads[master].idle = false;
3018 Threads[master].activeSplitPoints--;
3019 Threads[master].splitPoint = splitPoint->parent;
3021 lock_release(&MPLock);
3026 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3027 // to start a new search from the root.
3029 void wake_sleeping_threads() {
3031 if (ActiveThreads > 1)
3033 for (int i = 1; i < ActiveThreads; i++)
3035 Threads[i].idle = true;
3036 Threads[i].workIsWaiting = false;
3039 #if !defined(_MSC_VER)
3040 pthread_mutex_lock(&WaitLock);
3041 pthread_cond_broadcast(&WaitCond);
3042 pthread_mutex_unlock(&WaitLock);
3044 for (int i = 1; i < THREAD_MAX; i++)
3045 SetEvent(SitIdleEvent[i]);
3051 // init_thread() is the function which is called when a new thread is
3052 // launched. It simply calls the idle_loop() function with the supplied
3053 // threadID. There are two versions of this function; one for POSIX
3054 // threads and one for Windows threads.
3056 #if !defined(_MSC_VER)
3058 void* init_thread(void *threadID) {
3060 idle_loop(*(int*)threadID, NULL);
3066 DWORD WINAPI init_thread(LPVOID threadID) {
3068 idle_loop(*(int*)threadID, NULL);