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 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/>.
40 #include "ucioption.h"
44 //// Local definitions
51 // IterationInfoType stores search results for each iteration
53 // Because we use relatively small (dynamic) aspiration window,
54 // there happens many fail highs and fail lows in root. And
55 // because we don't do researches in those cases, "value" stored
56 // here is not necessarily exact. Instead in case of fail high/low
57 // we guess what the right value might be and store our guess
58 // as a "speculated value" and then move on. Speculated values are
59 // used just to calculate aspiration window width, so also if are
60 // not exact is not big a problem.
62 struct IterationInfoType {
64 IterationInfoType(Value v = Value(0), Value sv = Value(0))
65 : value(v), speculatedValue(sv) {}
67 Value value, speculatedValue;
71 // The BetaCounterType class is used to order moves at ply one.
72 // Apart for the first one that has its score, following moves
73 // normally have score -VALUE_INFINITE, so are ordered according
74 // to the number of beta cutoffs occurred under their subtree during
75 // the last iteration.
77 struct BetaCounterType {
81 void add(Color us, Depth d, int threadID);
82 void read(Color us, int64_t& our, int64_t& their);
84 int64_t hits[THREAD_MAX][2];
88 // The RootMove class is used for moves at the root at the tree. For each
89 // root move, we store a score, a node count, and a PV (really a refutation
90 // in the case of moves which fail low).
95 bool operator<(const RootMove&); // used to sort
99 int64_t nodes, cumulativeNodes;
100 Move pv[PLY_MAX_PLUS_2];
101 int64_t ourBeta, theirBeta;
105 // The RootMoveList class is essentially an array of RootMove objects, with
106 // a handful of methods for accessing the data in the individual moves.
111 RootMoveList(Position &pos, Move searchMoves[]);
112 inline Move get_move(int moveNum) const;
113 inline Value get_move_score(int moveNum) const;
114 inline void set_move_score(int moveNum, Value score);
115 inline void set_move_nodes(int moveNum, int64_t nodes);
116 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
117 void set_move_pv(int moveNum, const Move pv[]);
118 inline Move get_move_pv(int moveNum, int i) const;
119 inline int64_t get_move_cumulative_nodes(int moveNum) const;
120 inline int move_count() const;
121 Move scan_for_easy_move() const;
123 void sort_multipv(int n);
126 static const int MaxRootMoves = 500;
127 RootMove moves[MaxRootMoves];
132 /// Constants and variables initialized from UCI options
134 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
136 int LMRPVMoves, LMRNonPVMoves;
138 // Depth limit for use of dynamic threat detection
141 // Depth limit for selective search
142 Depth SelectiveDepth;
144 // Use internal iterative deepening?
145 const bool UseIIDAtPVNodes = true;
146 const bool UseIIDAtNonPVNodes = false;
148 // Internal iterative deepening margin. At Non-PV moves, when
149 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
150 // when the static evaluation is at most IIDMargin below beta.
151 const Value IIDMargin = Value(0x100);
153 // Easy move margin. An easy move candidate must be at least this much
154 // better than the second best move.
155 const Value EasyMoveMargin = Value(0x200);
157 // Problem margin. If the score of the first move at iteration N+1 has
158 // dropped by more than this since iteration N, the boolean variable
159 // "Problem" is set to true, which will make the program spend some extra
160 // time looking for a better move.
161 const Value ProblemMargin = Value(0x28);
163 // No problem margin. If the boolean "Problem" is true, and a new move
164 // is found at the root which is less than NoProblemMargin worse than the
165 // best move from the previous iteration, Problem is set back to false.
166 const Value NoProblemMargin = Value(0x14);
168 // Null move margin. A null move search will not be done if the approximate
169 // evaluation of the position is more than NullMoveMargin below beta.
170 const Value NullMoveMargin = Value(0x300);
172 // Pruning criterions. See the code and comments in ok_to_prune() to
173 // understand their precise meaning.
174 const bool PruneEscapeMoves = false;
175 const bool PruneDefendingMoves = false;
176 const bool PruneBlockingMoves = false;
178 // Use futility pruning?
179 bool UseQSearchFutilityPruning, UseFutilityPruning;
181 // Margins for futility pruning in the quiescence search, and at frontier
182 // and near frontier nodes
183 Value FutilityMarginQS;
184 Value FutilityMargins[6] = { Value(0x100), Value(0x200), Value(0x250),
185 Value(0x2A0), Value(0x340), Value(0x3A0) };
188 const bool RazorAtDepthOne = false;
192 // Last seconds noise filtering (LSN)
193 bool UseLSNFiltering;
194 bool looseOnTime = false;
195 int LSNTime; // In milliseconds
198 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
199 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
200 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
202 // Search depth at iteration 1
203 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
207 int NodesBetweenPolls = 30000;
209 // Iteration counters
211 BetaCounterType BetaCounter;
213 // Scores and number of times the best move changed for each iteration:
214 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
215 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
220 // Time managment variables
222 int MaxNodes, MaxDepth;
223 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
228 bool StopOnPonderhit;
234 bool PonderingEnabled;
237 // Show current line?
238 bool ShowCurrentLine;
242 std::ofstream LogFile;
244 // MP related variables
245 Depth MinimumSplitDepth;
246 int MaxThreadsPerSplitPoint;
247 Thread Threads[THREAD_MAX];
249 bool AllThreadsShouldExit = false;
250 const int MaxActiveSplitPoints = 8;
251 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
254 #if !defined(_MSC_VER)
255 pthread_cond_t WaitCond;
256 pthread_mutex_t WaitLock;
258 HANDLE SitIdleEvent[THREAD_MAX];
264 Value id_loop(const Position &pos, Move searchMoves[]);
265 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
266 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
267 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
268 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
269 void sp_search(SplitPoint *sp, int threadID);
270 void sp_search_pv(SplitPoint *sp, int threadID);
271 void init_node(SearchStack ss[], int ply, int threadID);
272 void update_pv(SearchStack ss[], int ply);
273 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
274 bool connected_moves(const Position &pos, Move m1, Move m2);
275 bool value_is_mate(Value value);
276 bool move_is_killer(Move m, const SearchStack& ss);
277 Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
278 bool ok_to_do_nullmove(const Position &pos);
279 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
280 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
281 bool ok_to_history(const Position &pos, Move m);
282 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
283 void update_killers(Move m, SearchStack& ss);
285 bool fail_high_ply_1();
286 int current_search_time();
290 void print_current_line(SearchStack ss[], int ply, int threadID);
291 void wait_for_stop_or_ponderhit();
293 void idle_loop(int threadID, SplitPoint *waitSp);
294 void init_split_point_stack();
295 void destroy_split_point_stack();
296 bool thread_should_stop(int threadID);
297 bool thread_is_available(int slave, int master);
298 bool idle_thread_exists(int master);
299 bool split(const Position &pos, SearchStack *ss, int ply,
300 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
301 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
302 void wake_sleeping_threads();
304 #if !defined(_MSC_VER)
305 void *init_thread(void *threadID);
307 DWORD WINAPI init_thread(LPVOID threadID);
314 //// Global variables
317 // The main transposition table
318 TranspositionTable TT = TranspositionTable(TTDefaultSize);
321 // Number of active threads:
322 int ActiveThreads = 1;
324 // Locks. In principle, there is no need for IOLock to be a global variable,
325 // but it could turn out to be useful for debugging.
328 History H; // Should be made local?
330 // The empty search stack
331 SearchStack EmptySearchStack;
334 // SearchStack::init() initializes a search stack. Used at the beginning of a
335 // new search from the root.
336 void SearchStack::init(int ply) {
338 pv[ply] = pv[ply + 1] = MOVE_NONE;
339 currentMove = threatMove = MOVE_NONE;
340 reduction = Depth(0);
343 void SearchStack::initKillers() {
345 mateKiller = MOVE_NONE;
346 for (int i = 0; i < KILLER_MAX; i++)
347 killers[i] = MOVE_NONE;
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()
359 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
360 int time[], int increment[], int movesToGo, int maxDepth,
361 int maxNodes, int maxTime, Move searchMoves[]) {
363 // Look for a book move
364 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
367 if (get_option_value_string("Book File") != OpeningBook.file_name())
370 OpeningBook.open("book.bin");
372 bookMove = OpeningBook.get_move(pos);
373 if (bookMove != MOVE_NONE)
375 std::cout << "bestmove " << bookMove << std::endl;
380 // Initialize global search variables
382 SearchStartTime = get_system_time();
383 EasyMove = MOVE_NONE;
384 for (int i = 0; i < THREAD_MAX; i++)
386 Threads[i].nodes = 0ULL;
387 Threads[i].failHighPly1 = false;
390 InfiniteSearch = infinite;
391 PonderSearch = ponder;
392 StopOnPonderhit = false;
398 ExactMaxTime = maxTime;
400 // Read UCI option values
401 TT.set_size(get_option_value_int("Hash"));
402 if (button_was_pressed("Clear Hash"))
405 PonderingEnabled = get_option_value_bool("Ponder");
406 MultiPV = get_option_value_int("MultiPV");
408 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
409 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
411 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
412 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
414 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
415 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
417 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
418 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
427 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
428 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
429 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
431 Chess960 = get_option_value_bool("UCI_Chess960");
432 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
433 UseLogFile = get_option_value_bool("Use Search Log");
435 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
437 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
438 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
440 FutilityMarginQS = value_from_centipawns(get_option_value_int("Futility Margin (Quiescence Search)"));
441 int fmScale = get_option_value_int("Futility Margin Scale Factor (Main Search)");
442 for (int i = 0; i < 6; i++)
443 FutilityMargins[i] = (FutilityMargins[i] * fmScale) / 100;
445 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
446 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
448 UseLSNFiltering = get_option_value_bool("LSN filtering");
449 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
450 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
452 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
453 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
455 read_weights(pos.side_to_move());
457 int newActiveThreads = get_option_value_int("Threads");
458 if (newActiveThreads != ActiveThreads)
460 ActiveThreads = newActiveThreads;
461 init_eval(ActiveThreads);
464 // Wake up sleeping threads:
465 wake_sleeping_threads();
467 for (int i = 1; i < ActiveThreads; i++)
468 assert(thread_is_available(i, 0));
470 // Set thinking time:
471 int myTime = time[side_to_move];
472 int myIncrement = increment[side_to_move];
474 if (!movesToGo) // Sudden death time control
478 MaxSearchTime = myTime / 30 + myIncrement;
479 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
480 } else { // Blitz game without increment
481 MaxSearchTime = myTime / 30;
482 AbsoluteMaxSearchTime = myTime / 8;
485 else // (x moves) / (y minutes)
489 MaxSearchTime = myTime / 2;
490 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
492 MaxSearchTime = myTime / Min(movesToGo, 20);
493 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
497 if (PonderingEnabled)
499 MaxSearchTime += MaxSearchTime / 4;
500 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
503 // Fixed depth or fixed number of nodes?
506 InfiniteSearch = true; // HACK
511 NodesBetweenPolls = Min(MaxNodes, 30000);
512 InfiniteSearch = true; // HACK
515 NodesBetweenPolls = 30000;
518 // Write information to search log file:
520 LogFile << "Searching: " << pos.to_fen() << std::endl
521 << "infinite: " << infinite
522 << " ponder: " << ponder
523 << " time: " << myTime
524 << " increment: " << myIncrement
525 << " moves to go: " << movesToGo << std::endl;
528 // We're ready to start thinking. Call the iterative deepening loop
532 Value v = id_loop(pos, searchMoves);
533 looseOnTime = ( UseLSNFiltering
540 looseOnTime = false; // reset for next match
541 while (SearchStartTime + myTime + 1000 > get_system_time())
543 id_loop(pos, searchMoves); // to fail gracefully
560 /// init_threads() is called during startup. It launches all helper threads,
561 /// and initializes the split point stack and the global locks and condition
564 void init_threads() {
568 #if !defined(_MSC_VER)
569 pthread_t pthread[1];
572 for (i = 0; i < THREAD_MAX; i++)
573 Threads[i].activeSplitPoints = 0;
575 // Initialize global locks:
576 lock_init(&MPLock, NULL);
577 lock_init(&IOLock, NULL);
579 init_split_point_stack();
581 #if !defined(_MSC_VER)
582 pthread_mutex_init(&WaitLock, NULL);
583 pthread_cond_init(&WaitCond, NULL);
585 for (i = 0; i < THREAD_MAX; i++)
586 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
589 // All threads except the main thread should be initialized to idle state
590 for (i = 1; i < THREAD_MAX; i++)
592 Threads[i].stop = false;
593 Threads[i].workIsWaiting = false;
594 Threads[i].idle = true;
595 Threads[i].running = false;
598 // Launch the helper threads
599 for(i = 1; i < THREAD_MAX; i++)
601 #if !defined(_MSC_VER)
602 pthread_create(pthread, NULL, init_thread, (void*)(&i));
605 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
608 // Wait until the thread has finished launching:
609 while (!Threads[i].running);
612 // Init also the empty search stack
613 EmptySearchStack.init(0);
614 EmptySearchStack.initKillers();
618 /// stop_threads() is called when the program exits. It makes all the
619 /// helper threads exit cleanly.
621 void stop_threads() {
623 ActiveThreads = THREAD_MAX; // HACK
624 Idle = false; // HACK
625 wake_sleeping_threads();
626 AllThreadsShouldExit = true;
627 for (int i = 1; i < THREAD_MAX; i++)
629 Threads[i].stop = true;
630 while(Threads[i].running);
632 destroy_split_point_stack();
636 /// nodes_searched() returns the total number of nodes searched so far in
637 /// the current search.
639 int64_t nodes_searched() {
641 int64_t result = 0ULL;
642 for (int i = 0; i < ActiveThreads; i++)
643 result += Threads[i].nodes;
650 // id_loop() is the main iterative deepening loop. It calls root_search
651 // repeatedly with increasing depth until the allocated thinking time has
652 // been consumed, the user stops the search, or the maximum search depth is
655 Value id_loop(const Position &pos, Move searchMoves[]) {
658 SearchStack ss[PLY_MAX_PLUS_2];
660 // searchMoves are verified, copied, scored and sorted
661 RootMoveList rml(p, searchMoves);
666 for (int i = 0; i < 3; i++)
671 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
674 EasyMove = rml.scan_for_easy_move();
676 // Iterative deepening loop
677 while (Iteration < PLY_MAX)
679 // Initialize iteration
682 BestMoveChangesByIteration[Iteration] = 0;
686 std::cout << "info depth " << Iteration << std::endl;
688 // Calculate dynamic search window based on previous iterations
691 if (MultiPV == 1 && Iteration >= 6)
693 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
694 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
696 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
698 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
699 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
703 alpha = - VALUE_INFINITE;
704 beta = VALUE_INFINITE;
707 // Search to the current depth
708 Value value = root_search(p, ss, rml, alpha, beta);
710 // Write PV to transposition table, in case the relevant entries have
711 // been overwritten during the search.
712 TT.insert_pv(p, ss[0].pv);
715 break; // Value cannot be trusted. Break out immediately!
717 //Save info about search result
718 Value speculatedValue;
721 Value delta = value - IterationInfo[Iteration - 1].value;
728 speculatedValue = value + delta;
729 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
731 else if (value <= alpha)
733 assert(value == alpha);
737 speculatedValue = value + delta;
738 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
740 speculatedValue = value;
742 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
743 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
745 // Erase the easy move if it differs from the new best move
746 if (ss[0].pv[0] != EasyMove)
747 EasyMove = MOVE_NONE;
754 bool stopSearch = false;
756 // Stop search early if there is only a single legal move:
757 if (Iteration >= 6 && rml.move_count() == 1)
760 // Stop search early when the last two iterations returned a mate score
762 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
763 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
766 // Stop search early if one move seems to be much better than the rest
767 int64_t nodes = nodes_searched();
771 && EasyMove == ss[0].pv[0]
772 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
773 && current_search_time() > MaxSearchTime / 16)
774 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
775 && current_search_time() > MaxSearchTime / 32)))
778 // Add some extra time if the best move has changed during the last two iterations
779 if (Iteration > 5 && Iteration <= 50)
780 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
781 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
783 // Stop search if most of MaxSearchTime is consumed at the end of the
784 // iteration. We probably don't have enough time to search the first
785 // move at the next iteration anyway.
786 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
791 //FIXME: Implement fail-low emergency measures
795 StopOnPonderhit = true;
799 if (MaxDepth && Iteration >= MaxDepth)
805 // If we are pondering, we shouldn't print the best move before we
808 wait_for_stop_or_ponderhit();
810 // Print final search statistics
811 std::cout << "info nodes " << nodes_searched()
813 << " time " << current_search_time()
814 << " hashfull " << TT.full() << std::endl;
816 // Print the best move and the ponder move to the standard output
817 if (ss[0].pv[0] == MOVE_NONE)
819 ss[0].pv[0] = rml.get_move(0);
820 ss[0].pv[1] = MOVE_NONE;
822 std::cout << "bestmove " << ss[0].pv[0];
823 if (ss[0].pv[1] != MOVE_NONE)
824 std::cout << " ponder " << ss[0].pv[1];
826 std::cout << std::endl;
831 dbg_print_mean(LogFile);
833 if (dbg_show_hit_rate)
834 dbg_print_hit_rate(LogFile);
837 LogFile << "Nodes: " << nodes_searched() << std::endl
838 << "Nodes/second: " << nps() << std::endl
839 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
841 p.do_move(ss[0].pv[0], st);
842 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
843 << std::endl << std::endl;
845 return rml.get_move_score(0);
849 // root_search() is the function which searches the root node. It is
850 // similar to search_pv except that it uses a different move ordering
851 // scheme (perhaps we should try to use this at internal PV nodes, too?)
852 // and prints some information to the standard output.
854 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
856 Value oldAlpha = alpha;
858 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
860 // Loop through all the moves in the root move list
861 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
865 // We failed high, invalidate and skip next moves, leave node-counters
866 // and beta-counters as they are and quickly return, we will try to do
867 // a research at the next iteration with a bigger aspiration window.
868 rml.set_move_score(i, -VALUE_INFINITE);
876 RootMoveNumber = i + 1;
879 // Remember the node count before the move is searched. The node counts
880 // are used to sort the root moves at the next iteration.
881 nodes = nodes_searched();
883 // Reset beta cut-off counters
886 // Pick the next root move, and print the move and the move number to
887 // the standard output.
888 move = ss[0].currentMove = rml.get_move(i);
889 if (current_search_time() >= 1000)
890 std::cout << "info currmove " << move
891 << " currmovenumber " << i + 1 << std::endl;
893 // Decide search depth for this move
895 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
896 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
898 // Make the move, and search it
899 pos.do_move(move, st, dcCandidates);
903 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
904 // If the value has dropped a lot compared to the last iteration,
905 // set the boolean variable Problem to true. This variable is used
906 // for time managment: When Problem is true, we try to complete the
907 // current iteration before playing a move.
908 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
910 if (Problem && StopOnPonderhit)
911 StopOnPonderhit = false;
915 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
918 // Fail high! Set the boolean variable FailHigh to true, and
919 // re-search the move with a big window. The variable FailHigh is
920 // used for time managment: We try to avoid aborting the search
921 // prematurely during a fail high research.
923 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
929 // Finished searching the move. If AbortSearch is true, the search
930 // was aborted because the user interrupted the search or because we
931 // ran out of time. In this case, the return value of the search cannot
932 // be trusted, and we break out of the loop without updating the best
937 // Remember the node count for this move. The node counts are used to
938 // sort the root moves at the next iteration.
939 rml.set_move_nodes(i, nodes_searched() - nodes);
941 // Remember the beta-cutoff statistics
943 BetaCounter.read(pos.side_to_move(), our, their);
944 rml.set_beta_counters(i, our, their);
946 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
948 if (value <= alpha && i >= MultiPV)
949 rml.set_move_score(i, -VALUE_INFINITE);
952 // PV move or new best move!
955 rml.set_move_score(i, value);
957 rml.set_move_pv(i, ss[0].pv);
961 // We record how often the best move has been changed in each
962 // iteration. This information is used for time managment: When
963 // the best move changes frequently, we allocate some more time.
965 BestMoveChangesByIteration[Iteration]++;
967 // Print search information to the standard output:
968 std::cout << "info depth " << Iteration
969 << " score " << value_to_string(value)
970 << " time " << current_search_time()
971 << " nodes " << nodes_searched()
975 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
976 std::cout << ss[0].pv[j] << " ";
978 std::cout << std::endl;
981 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
987 // Reset the global variable Problem to false if the value isn't too
988 // far below the final value from the last iteration.
989 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
995 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
998 std::cout << "info multipv " << j + 1
999 << " score " << value_to_string(rml.get_move_score(j))
1000 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1001 << " time " << current_search_time()
1002 << " nodes " << nodes_searched()
1006 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1007 std::cout << rml.get_move_pv(j, k) << " ";
1009 std::cout << std::endl;
1011 alpha = rml.get_move_score(Min(i, MultiPV-1));
1013 } // New best move case
1015 assert(alpha >= oldAlpha);
1017 FailLow = (alpha == oldAlpha);
1023 // search_pv() is the main search function for PV nodes.
1025 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
1026 Depth depth, int ply, int threadID) {
1028 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1029 assert(beta > alpha && beta <= VALUE_INFINITE);
1030 assert(ply >= 0 && ply < PLY_MAX);
1031 assert(threadID >= 0 && threadID < ActiveThreads);
1034 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1036 // Initialize, and make an early exit in case of an aborted search,
1037 // an instant draw, maximum ply reached, etc.
1038 init_node(ss, ply, threadID);
1040 // After init_node() that calls poll()
1041 if (AbortSearch || thread_should_stop(threadID))
1049 if (ply >= PLY_MAX - 1)
1050 return evaluate(pos, ei, threadID);
1052 // Mate distance pruning
1053 Value oldAlpha = alpha;
1054 alpha = Max(value_mated_in(ply), alpha);
1055 beta = Min(value_mate_in(ply+1), beta);
1059 // Transposition table lookup. At PV nodes, we don't use the TT for
1060 // pruning, but only for move ordering.
1061 const TTEntry* tte = TT.retrieve(pos);
1062 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1064 // Go with internal iterative deepening if we don't have a TT move
1065 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1067 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1068 ttMove = ss[ply].pv[ply];
1071 // Initialize a MovePicker object for the current position, and prepare
1072 // to search all moves
1073 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
1075 Move move, movesSearched[256];
1077 Value value, bestValue = -VALUE_INFINITE;
1078 Bitboard dcCandidates = mp.discovered_check_candidates();
1079 Color us = pos.side_to_move();
1080 bool isCheck = pos.is_check();
1081 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1083 // Loop through all legal moves until no moves remain or a beta cutoff
1085 while ( alpha < beta
1086 && (move = mp.get_next_move()) != MOVE_NONE
1087 && !thread_should_stop(threadID))
1089 assert(move_is_ok(move));
1091 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1092 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1093 bool moveIsCapture = pos.move_is_capture(move);
1095 movesSearched[moveCount++] = ss[ply].currentMove = move;
1097 // Decide the new search depth
1099 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1100 Depth newDepth = depth - OnePly + ext;
1102 // Make and search the move
1104 pos.do_move(move, st, dcCandidates);
1106 if (moveCount == 1) // The first move in list is the PV
1107 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1110 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1111 // if the move fails high will be re-searched at full depth.
1112 if ( depth >= 2*OnePly
1113 && moveCount >= LMRPVMoves
1116 && !move_promotion(move)
1117 && !move_is_castle(move)
1118 && !move_is_killer(move, ss[ply]))
1120 ss[ply].reduction = OnePly;
1121 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1124 value = alpha + 1; // Just to trigger next condition
1126 if (value > alpha) // Go with full depth non-pv search
1128 ss[ply].reduction = Depth(0);
1129 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1130 if (value > alpha && value < beta)
1132 // When the search fails high at ply 1 while searching the first
1133 // move at the root, set the flag failHighPly1. This is used for
1134 // time managment: We don't want to stop the search early in
1135 // such cases, because resolving the fail high at ply 1 could
1136 // result in a big drop in score at the root.
1137 if (ply == 1 && RootMoveNumber == 1)
1138 Threads[threadID].failHighPly1 = true;
1140 // A fail high occurred. Re-search at full window (pv search)
1141 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1142 Threads[threadID].failHighPly1 = false;
1146 pos.undo_move(move);
1148 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1151 if (value > bestValue)
1158 if (value == value_mate_in(ply + 1))
1159 ss[ply].mateKiller = move;
1161 // If we are at ply 1, and we are searching the first root move at
1162 // ply 0, set the 'Problem' variable if the score has dropped a lot
1163 // (from the computer's point of view) since the previous iteration:
1166 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1171 if ( ActiveThreads > 1
1173 && depth >= MinimumSplitDepth
1175 && idle_thread_exists(threadID)
1177 && !thread_should_stop(threadID)
1178 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1179 &moveCount, &mp, dcCandidates, threadID, true))
1183 // All legal moves have been searched. A special case: If there were
1184 // no legal moves, it must be mate or stalemate:
1186 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1188 // If the search is not aborted, update the transposition table,
1189 // history counters, and killer moves.
1190 if (AbortSearch || thread_should_stop(threadID))
1193 if (bestValue <= oldAlpha)
1194 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1196 else if (bestValue >= beta)
1198 BetaCounter.add(pos.side_to_move(), depth, threadID);
1199 Move m = ss[ply].pv[ply];
1200 if (ok_to_history(pos, m)) // Only non capture moves are considered
1202 update_history(pos, m, depth, movesSearched, moveCount);
1203 update_killers(m, ss[ply]);
1205 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1208 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1214 // search() is the search function for zero-width nodes.
1216 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1217 int ply, bool allowNullmove, int threadID) {
1219 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1220 assert(ply >= 0 && ply < PLY_MAX);
1221 assert(threadID >= 0 && threadID < ActiveThreads);
1224 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1226 // Initialize, and make an early exit in case of an aborted search,
1227 // an instant draw, maximum ply reached, etc.
1228 init_node(ss, ply, threadID);
1230 // After init_node() that calls poll()
1231 if (AbortSearch || thread_should_stop(threadID))
1239 if (ply >= PLY_MAX - 1)
1240 return evaluate(pos, ei, threadID);
1242 // Mate distance pruning
1243 if (value_mated_in(ply) >= beta)
1246 if (value_mate_in(ply + 1) < beta)
1249 // Transposition table lookup
1250 const TTEntry* tte = TT.retrieve(pos);
1251 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1253 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1255 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1256 return value_from_tt(tte->value(), ply);
1259 Value approximateEval = quick_evaluate(pos);
1260 bool mateThreat = false;
1261 bool isCheck = pos.is_check();
1267 && !value_is_mate(beta)
1268 && ok_to_do_nullmove(pos)
1269 && approximateEval >= beta - NullMoveMargin)
1271 ss[ply].currentMove = MOVE_NULL;
1274 pos.do_null_move(st);
1275 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1277 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1279 pos.undo_null_move();
1281 if (value_is_mate(nullValue))
1283 /* Do not return unproven mates */
1285 else if (nullValue >= beta)
1287 if (depth < 6 * OnePly)
1290 // Do zugzwang verification search
1291 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1295 // The null move failed low, which means that we may be faced with
1296 // some kind of threat. If the previous move was reduced, check if
1297 // the move that refuted the null move was somehow connected to the
1298 // move which was reduced. If a connection is found, return a fail
1299 // low score (which will cause the reduced move to fail high in the
1300 // parent node, which will trigger a re-search with full depth).
1301 if (nullValue == value_mated_in(ply + 2))
1304 ss[ply].threatMove = ss[ply + 1].currentMove;
1305 if ( depth < ThreatDepth
1306 && ss[ply - 1].reduction
1307 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1311 // Null move search not allowed, try razoring
1312 else if ( !value_is_mate(beta)
1313 && approximateEval < beta - RazorMargin
1314 && depth < RazorDepth
1315 && (RazorAtDepthOne || depth > OnePly)
1316 && ttMove == MOVE_NONE
1317 && !pos.has_pawn_on_7th(pos.side_to_move()))
1319 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1320 if ( (v < beta - RazorMargin - RazorMargin / 4)
1321 || (depth <= 2*OnePly && v < beta - RazorMargin)
1322 || (depth <= OnePly && v < beta - RazorMargin / 2))
1326 // Go with internal iterative deepening if we don't have a TT move
1327 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1328 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1330 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1331 ttMove = ss[ply].pv[ply];
1334 // Initialize a MovePicker object for the current position, and prepare
1335 // to search all moves:
1336 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1338 Move move, movesSearched[256];
1340 Value value, bestValue = -VALUE_INFINITE;
1341 Bitboard dcCandidates = mp.discovered_check_candidates();
1342 Value futilityValue = VALUE_NONE;
1343 bool useFutilityPruning = UseFutilityPruning
1344 && depth < SelectiveDepth
1347 // Loop through all legal moves until no moves remain or a beta cutoff
1349 while ( bestValue < beta
1350 && (move = mp.get_next_move()) != MOVE_NONE
1351 && !thread_should_stop(threadID))
1353 assert(move_is_ok(move));
1355 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1356 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1357 bool moveIsCapture = pos.move_is_capture(move);
1359 movesSearched[moveCount++] = ss[ply].currentMove = move;
1361 // Decide the new search depth
1363 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1364 Depth newDepth = depth - OnePly + ext;
1367 if ( useFutilityPruning
1370 && !move_promotion(move))
1372 // History pruning. See ok_to_prune() definition
1373 if ( moveCount >= 2 + int(depth)
1374 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1377 // Value based pruning
1378 if (depth < 7 * OnePly && approximateEval < beta)
1380 if (futilityValue == VALUE_NONE)
1381 futilityValue = evaluate(pos, ei, threadID)
1382 + FutilityMargins[int(depth)/2 - 1]
1385 if (futilityValue < beta)
1387 if (futilityValue > bestValue)
1388 bestValue = futilityValue;
1394 // Make and search the move
1396 pos.do_move(move, st, dcCandidates);
1398 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1399 // if the move fails high will be re-searched at full depth.
1400 if ( depth >= 2*OnePly
1401 && moveCount >= LMRNonPVMoves
1404 && !move_promotion(move)
1405 && !move_is_castle(move)
1406 && !move_is_killer(move, ss[ply]))
1408 ss[ply].reduction = OnePly;
1409 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1412 value = beta; // Just to trigger next condition
1414 if (value >= beta) // Go with full depth non-pv search
1416 ss[ply].reduction = Depth(0);
1417 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1419 pos.undo_move(move);
1421 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1424 if (value > bestValue)
1430 if (value == value_mate_in(ply + 1))
1431 ss[ply].mateKiller = move;
1435 if ( ActiveThreads > 1
1437 && depth >= MinimumSplitDepth
1439 && idle_thread_exists(threadID)
1441 && !thread_should_stop(threadID)
1442 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1443 &mp, dcCandidates, threadID, false))
1447 // All legal moves have been searched. A special case: If there were
1448 // no legal moves, it must be mate or stalemate.
1450 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1452 // If the search is not aborted, update the transposition table,
1453 // history counters, and killer moves.
1454 if (AbortSearch || thread_should_stop(threadID))
1457 if (bestValue < beta)
1458 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1461 BetaCounter.add(pos.side_to_move(), depth, threadID);
1462 Move m = ss[ply].pv[ply];
1463 if (ok_to_history(pos, m)) // Only non capture moves are considered
1465 update_history(pos, m, depth, movesSearched, moveCount);
1466 update_killers(m, ss[ply]);
1468 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1471 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1477 // qsearch() is the quiescence search function, which is called by the main
1478 // search function when the remaining depth is zero (or, to be more precise,
1479 // less than OnePly).
1481 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1482 Depth depth, int ply, int threadID) {
1484 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1485 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1487 assert(ply >= 0 && ply < PLY_MAX);
1488 assert(threadID >= 0 && threadID < ActiveThreads);
1490 // Initialize, and make an early exit in case of an aborted search,
1491 // an instant draw, maximum ply reached, etc.
1492 init_node(ss, ply, threadID);
1494 // After init_node() that calls poll()
1495 if (AbortSearch || thread_should_stop(threadID))
1501 // Transposition table lookup, only when not in PV
1502 TTEntry* tte = NULL;
1503 bool pvNode = (beta - alpha != 1);
1506 tte = TT.retrieve(pos);
1507 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1509 assert(tte->type() != VALUE_TYPE_EVAL);
1511 return value_from_tt(tte->value(), ply);
1514 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1516 // Evaluate the position statically
1519 bool isCheck = pos.is_check();
1520 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1523 staticValue = -VALUE_INFINITE;
1525 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1527 // Use the cached evaluation score if possible
1528 assert(tte->value() == evaluate(pos, ei, threadID));
1529 assert(ei.futilityMargin == Value(0));
1531 staticValue = tte->value();
1534 staticValue = evaluate(pos, ei, threadID);
1536 if (ply == PLY_MAX - 1)
1537 return evaluate(pos, ei, threadID);
1539 // Initialize "stand pat score", and return it immediately if it is
1541 Value bestValue = staticValue;
1543 if (bestValue >= beta)
1545 // Store the score to avoid a future costly evaluation() call
1546 if (!isCheck && !tte && ei.futilityMargin == 0)
1547 TT.store(pos, value_to_tt(bestValue, ply), Depth(-127*OnePly), MOVE_NONE, VALUE_TYPE_EVAL);
1552 if (bestValue > alpha)
1555 // Initialize a MovePicker object for the current position, and prepare
1556 // to search the moves. Because the depth is <= 0 here, only captures,
1557 // queen promotions and checks (only if depth == 0) will be generated.
1558 MovePicker mp = MovePicker(pos, pvNode, ttMove, EmptySearchStack, depth);
1561 Bitboard dcCandidates = mp.discovered_check_candidates();
1562 Color us = pos.side_to_move();
1563 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1565 // Loop through the moves until no moves remain or a beta cutoff
1567 while ( alpha < beta
1568 && (move = mp.get_next_move()) != MOVE_NONE)
1570 assert(move_is_ok(move));
1573 ss[ply].currentMove = move;
1576 if ( UseQSearchFutilityPruning
1580 && !move_promotion(move)
1581 && !pos.move_is_check(move, dcCandidates)
1582 && !pos.move_is_passed_pawn_push(move))
1584 Value futilityValue = staticValue
1585 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1586 pos.endgame_value_of_piece_on(move_to(move)))
1587 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1589 + ei.futilityMargin;
1591 if (futilityValue < alpha)
1593 if (futilityValue > bestValue)
1594 bestValue = futilityValue;
1599 // Don't search captures and checks with negative SEE values
1601 && !move_promotion(move)
1602 && (pos.midgame_value_of_piece_on(move_from(move)) >
1603 pos.midgame_value_of_piece_on(move_to(move)))
1604 && pos.see(move) < 0)
1607 // Make and search the move.
1609 pos.do_move(move, st, dcCandidates);
1610 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1611 pos.undo_move(move);
1613 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1616 if (value > bestValue)
1627 // All legal moves have been searched. A special case: If we're in check
1628 // and no legal moves were found, it is checkmate:
1629 if (pos.is_check() && moveCount == 0) // Mate!
1630 return value_mated_in(ply);
1632 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1634 // Update transposition table
1635 Move m = ss[ply].pv[ply];
1638 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1639 if (bestValue < beta)
1640 TT.store(pos, value_to_tt(bestValue, ply), d, MOVE_NONE, VALUE_TYPE_UPPER);
1642 TT.store(pos, value_to_tt(bestValue, ply), d, m, VALUE_TYPE_LOWER);
1645 // Update killers only for good check moves
1646 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1647 update_killers(m, ss[ply]);
1653 // sp_search() is used to search from a split point. This function is called
1654 // by each thread working at the split point. It is similar to the normal
1655 // search() function, but simpler. Because we have already probed the hash
1656 // table, done a null move search, and searched the first move before
1657 // splitting, we don't have to repeat all this work in sp_search(). We
1658 // also don't need to store anything to the hash table here: This is taken
1659 // care of after we return from the split point.
1661 void sp_search(SplitPoint *sp, int threadID) {
1663 assert(threadID >= 0 && threadID < ActiveThreads);
1664 assert(ActiveThreads > 1);
1666 Position pos = Position(sp->pos);
1667 SearchStack *ss = sp->sstack[threadID];
1670 bool isCheck = pos.is_check();
1671 bool useFutilityPruning = UseFutilityPruning
1672 && sp->depth < SelectiveDepth
1675 while ( sp->bestValue < sp->beta
1676 && !thread_should_stop(threadID)
1677 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1679 assert(move_is_ok(move));
1681 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1682 bool moveIsCapture = pos.move_is_capture(move);
1684 lock_grab(&(sp->lock));
1685 int moveCount = ++sp->moves;
1686 lock_release(&(sp->lock));
1688 ss[sp->ply].currentMove = move;
1690 // Decide the new search depth.
1692 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1693 Depth newDepth = sp->depth - OnePly + ext;
1696 if ( useFutilityPruning
1699 && !move_promotion(move)
1700 && moveCount >= 2 + int(sp->depth)
1701 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1704 // Make and search the move.
1706 pos.do_move(move, st, sp->dcCandidates);
1708 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1709 // if the move fails high will be re-searched at full depth.
1711 && moveCount >= LMRNonPVMoves
1713 && !move_promotion(move)
1714 && !move_is_castle(move)
1715 && !move_is_killer(move, ss[sp->ply]))
1717 ss[sp->ply].reduction = OnePly;
1718 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1721 value = sp->beta; // Just to trigger next condition
1723 if (value >= sp->beta) // Go with full depth non-pv search
1725 ss[sp->ply].reduction = Depth(0);
1726 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1728 pos.undo_move(move);
1730 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1732 if (thread_should_stop(threadID))
1736 lock_grab(&(sp->lock));
1737 if (value > sp->bestValue && !thread_should_stop(threadID))
1739 sp->bestValue = value;
1740 if (sp->bestValue >= sp->beta)
1742 sp_update_pv(sp->parentSstack, ss, sp->ply);
1743 for (int i = 0; i < ActiveThreads; i++)
1744 if (i != threadID && (i == sp->master || sp->slaves[i]))
1745 Threads[i].stop = true;
1747 sp->finished = true;
1750 lock_release(&(sp->lock));
1753 lock_grab(&(sp->lock));
1755 // If this is the master thread and we have been asked to stop because of
1756 // a beta cutoff higher up in the tree, stop all slave threads:
1757 if (sp->master == threadID && thread_should_stop(threadID))
1758 for (int i = 0; i < ActiveThreads; i++)
1760 Threads[i].stop = true;
1763 sp->slaves[threadID] = 0;
1765 lock_release(&(sp->lock));
1769 // sp_search_pv() is used to search from a PV split point. This function
1770 // is called by each thread working at the split point. It is similar to
1771 // the normal search_pv() function, but simpler. Because we have already
1772 // probed the hash table and searched the first move before splitting, we
1773 // don't have to repeat all this work in sp_search_pv(). We also don't
1774 // need to store anything to the hash table here: This is taken care of
1775 // after we return from the split point.
1777 void sp_search_pv(SplitPoint *sp, int threadID) {
1779 assert(threadID >= 0 && threadID < ActiveThreads);
1780 assert(ActiveThreads > 1);
1782 Position pos = Position(sp->pos);
1783 SearchStack *ss = sp->sstack[threadID];
1787 while ( sp->alpha < sp->beta
1788 && !thread_should_stop(threadID)
1789 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1791 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1792 bool moveIsCapture = pos.move_is_capture(move);
1794 assert(move_is_ok(move));
1796 lock_grab(&(sp->lock));
1797 int moveCount = ++sp->moves;
1798 lock_release(&(sp->lock));
1800 ss[sp->ply].currentMove = move;
1802 // Decide the new search depth.
1804 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1805 Depth newDepth = sp->depth - OnePly + ext;
1807 // Make and search the move.
1809 pos.do_move(move, st, sp->dcCandidates);
1811 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1812 // if the move fails high will be re-searched at full depth.
1814 && moveCount >= LMRPVMoves
1816 && !move_promotion(move)
1817 && !move_is_castle(move)
1818 && !move_is_killer(move, ss[sp->ply]))
1820 ss[sp->ply].reduction = OnePly;
1821 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1824 value = sp->alpha + 1; // Just to trigger next condition
1826 if (value > sp->alpha) // Go with full depth non-pv search
1828 ss[sp->ply].reduction = Depth(0);
1829 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1831 if (value > sp->alpha && value < sp->beta)
1833 // When the search fails high at ply 1 while searching the first
1834 // move at the root, set the flag failHighPly1. This is used for
1835 // time managment: We don't want to stop the search early in
1836 // such cases, because resolving the fail high at ply 1 could
1837 // result in a big drop in score at the root.
1838 if (sp->ply == 1 && RootMoveNumber == 1)
1839 Threads[threadID].failHighPly1 = true;
1841 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1842 Threads[threadID].failHighPly1 = false;
1845 pos.undo_move(move);
1847 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1849 if (thread_should_stop(threadID))
1853 lock_grab(&(sp->lock));
1854 if (value > sp->bestValue && !thread_should_stop(threadID))
1856 sp->bestValue = value;
1857 if (value > sp->alpha)
1860 sp_update_pv(sp->parentSstack, ss, sp->ply);
1861 if (value == value_mate_in(sp->ply + 1))
1862 ss[sp->ply].mateKiller = move;
1864 if(value >= sp->beta)
1866 for(int i = 0; i < ActiveThreads; i++)
1867 if(i != threadID && (i == sp->master || sp->slaves[i]))
1868 Threads[i].stop = true;
1870 sp->finished = true;
1873 // If we are at ply 1, and we are searching the first root move at
1874 // ply 0, set the 'Problem' variable if the score has dropped a lot
1875 // (from the computer's point of view) since the previous iteration.
1878 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1881 lock_release(&(sp->lock));
1884 lock_grab(&(sp->lock));
1886 // If this is the master thread and we have been asked to stop because of
1887 // a beta cutoff higher up in the tree, stop all slave threads.
1888 if (sp->master == threadID && thread_should_stop(threadID))
1889 for (int i = 0; i < ActiveThreads; i++)
1891 Threads[i].stop = true;
1894 sp->slaves[threadID] = 0;
1896 lock_release(&(sp->lock));
1899 /// The BetaCounterType class
1901 BetaCounterType::BetaCounterType() { clear(); }
1903 void BetaCounterType::clear() {
1905 for (int i = 0; i < THREAD_MAX; i++)
1906 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1909 void BetaCounterType::add(Color us, Depth d, int threadID) {
1911 // Weighted count based on depth
1912 hits[threadID][us] += int(d);
1915 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1918 for (int i = 0; i < THREAD_MAX; i++)
1921 their += hits[i][opposite_color(us)];
1926 /// The RootMove class
1930 RootMove::RootMove() {
1931 nodes = cumulativeNodes = 0ULL;
1934 // RootMove::operator<() is the comparison function used when
1935 // sorting the moves. A move m1 is considered to be better
1936 // than a move m2 if it has a higher score, or if the moves
1937 // have equal score but m1 has the higher node count.
1939 bool RootMove::operator<(const RootMove& m) {
1941 if (score != m.score)
1942 return (score < m.score);
1944 return theirBeta <= m.theirBeta;
1947 /// The RootMoveList class
1951 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1953 MoveStack mlist[MaxRootMoves];
1954 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1956 // Generate all legal moves
1957 int lm_count = generate_legal_moves(pos, mlist);
1959 // Add each move to the moves[] array
1960 for (int i = 0; i < lm_count; i++)
1962 bool includeMove = includeAllMoves;
1964 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1965 includeMove = (searchMoves[k] == mlist[i].move);
1969 // Find a quick score for the move
1971 SearchStack ss[PLY_MAX_PLUS_2];
1973 moves[count].move = mlist[i].move;
1974 moves[count].nodes = 0ULL;
1975 pos.do_move(moves[count].move, st);
1976 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1978 pos.undo_move(moves[count].move);
1979 moves[count].pv[0] = moves[i].move;
1980 moves[count].pv[1] = MOVE_NONE; // FIXME
1988 // Simple accessor methods for the RootMoveList class
1990 inline Move RootMoveList::get_move(int moveNum) const {
1991 return moves[moveNum].move;
1994 inline Value RootMoveList::get_move_score(int moveNum) const {
1995 return moves[moveNum].score;
1998 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1999 moves[moveNum].score = score;
2002 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2003 moves[moveNum].nodes = nodes;
2004 moves[moveNum].cumulativeNodes += nodes;
2007 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2008 moves[moveNum].ourBeta = our;
2009 moves[moveNum].theirBeta = their;
2012 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2014 for(j = 0; pv[j] != MOVE_NONE; j++)
2015 moves[moveNum].pv[j] = pv[j];
2016 moves[moveNum].pv[j] = MOVE_NONE;
2019 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2020 return moves[moveNum].pv[i];
2023 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2024 return moves[moveNum].cumulativeNodes;
2027 inline int RootMoveList::move_count() const {
2032 // RootMoveList::scan_for_easy_move() is called at the end of the first
2033 // iteration, and is used to detect an "easy move", i.e. a move which appears
2034 // to be much bester than all the rest. If an easy move is found, the move
2035 // is returned, otherwise the function returns MOVE_NONE. It is very
2036 // important that this function is called at the right moment: The code
2037 // assumes that the first iteration has been completed and the moves have
2038 // been sorted. This is done in RootMoveList c'tor.
2040 Move RootMoveList::scan_for_easy_move() const {
2047 // moves are sorted so just consider the best and the second one
2048 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2054 // RootMoveList::sort() sorts the root move list at the beginning of a new
2057 inline void RootMoveList::sort() {
2059 sort_multipv(count - 1); // all items
2063 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2064 // list by their scores and depths. It is used to order the different PVs
2065 // correctly in MultiPV mode.
2067 void RootMoveList::sort_multipv(int n) {
2069 for (int i = 1; i <= n; i++)
2071 RootMove rm = moves[i];
2073 for (j = i; j > 0 && moves[j-1] < rm; j--)
2074 moves[j] = moves[j-1];
2080 // init_node() is called at the beginning of all the search functions
2081 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2082 // stack object corresponding to the current node. Once every
2083 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2084 // for user input and checks whether it is time to stop the search.
2086 void init_node(SearchStack ss[], int ply, int threadID) {
2087 assert(ply >= 0 && ply < PLY_MAX);
2088 assert(threadID >= 0 && threadID < ActiveThreads);
2090 Threads[threadID].nodes++;
2094 if(NodesSincePoll >= NodesBetweenPolls) {
2101 ss[ply+2].initKillers();
2103 if(Threads[threadID].printCurrentLine)
2104 print_current_line(ss, ply, threadID);
2108 // update_pv() is called whenever a search returns a value > alpha. It
2109 // updates the PV in the SearchStack object corresponding to the current
2112 void update_pv(SearchStack ss[], int ply) {
2113 assert(ply >= 0 && ply < PLY_MAX);
2115 ss[ply].pv[ply] = ss[ply].currentMove;
2117 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2118 ss[ply].pv[p] = ss[ply+1].pv[p];
2119 ss[ply].pv[p] = MOVE_NONE;
2123 // sp_update_pv() is a variant of update_pv for use at split points. The
2124 // difference between the two functions is that sp_update_pv also updates
2125 // the PV at the parent node.
2127 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2128 assert(ply >= 0 && ply < PLY_MAX);
2130 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2132 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2133 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2134 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2138 // connected_moves() tests whether two moves are 'connected' in the sense
2139 // that the first move somehow made the second move possible (for instance
2140 // if the moving piece is the same in both moves). The first move is
2141 // assumed to be the move that was made to reach the current position, while
2142 // the second move is assumed to be a move from the current position.
2144 bool connected_moves(const Position &pos, Move m1, Move m2) {
2145 Square f1, t1, f2, t2;
2147 assert(move_is_ok(m1));
2148 assert(move_is_ok(m2));
2153 // Case 1: The moving piece is the same in both moves.
2159 // Case 2: The destination square for m2 was vacated by m1.
2165 // Case 3: Moving through the vacated square:
2166 if(piece_is_slider(pos.piece_on(f2)) &&
2167 bit_is_set(squares_between(f2, t2), f1))
2170 // Case 4: The destination square for m2 is attacked by the moving piece
2172 if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2175 // Case 5: Discovered check, checking piece is the piece moved in m1:
2176 if(piece_is_slider(pos.piece_on(t1)) &&
2177 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2179 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2181 Bitboard occ = pos.occupied_squares();
2182 Color us = pos.side_to_move();
2183 Square ksq = pos.king_square(us);
2184 clear_bit(&occ, f2);
2185 if(pos.type_of_piece_on(t1) == BISHOP) {
2186 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2189 else if(pos.type_of_piece_on(t1) == ROOK) {
2190 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2194 assert(pos.type_of_piece_on(t1) == QUEEN);
2195 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2204 // value_is_mate() checks if the given value is a mate one
2205 // eventually compensated for the ply.
2207 bool value_is_mate(Value value) {
2209 assert(abs(value) <= VALUE_INFINITE);
2211 return value <= value_mated_in(PLY_MAX)
2212 || value >= value_mate_in(PLY_MAX);
2216 // move_is_killer() checks if the given move is among the
2217 // killer moves of that ply.
2219 bool move_is_killer(Move m, const SearchStack& ss) {
2221 const Move* k = ss.killers;
2222 for (int i = 0; i < KILLER_MAX; i++, k++)
2230 // extension() decides whether a move should be searched with normal depth,
2231 // or with extended depth. Certain classes of moves (checking moves, in
2232 // particular) are searched with bigger depth than ordinary moves and in
2233 // any case are marked as 'dangerous'. Note that also if a move is not
2234 // extended, as example because the corresponding UCI option is set to zero,
2235 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2237 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2238 bool singleReply, bool mateThreat, bool* dangerous) {
2240 assert(m != MOVE_NONE);
2242 Depth result = Depth(0);
2243 *dangerous = check || singleReply || mateThreat;
2246 result += CheckExtension[pvNode];
2249 result += SingleReplyExtension[pvNode];
2252 result += MateThreatExtension[pvNode];
2254 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2256 if (pos.move_is_pawn_push_to_7th(m))
2258 result += PawnPushTo7thExtension[pvNode];
2261 if (pos.move_is_passed_pawn_push(m))
2263 result += PassedPawnExtension[pvNode];
2269 && pos.type_of_piece_on(move_to(m)) != PAWN
2270 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2271 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2272 && !move_promotion(m)
2275 result += PawnEndgameExtension[pvNode];
2281 && pos.type_of_piece_on(move_to(m)) != PAWN
2288 return Min(result, OnePly);
2292 // ok_to_do_nullmove() looks at the current position and decides whether
2293 // doing a 'null move' should be allowed. In order to avoid zugzwang
2294 // problems, null moves are not allowed when the side to move has very
2295 // little material left. Currently, the test is a bit too simple: Null
2296 // moves are avoided only when the side to move has only pawns left. It's
2297 // probably a good idea to avoid null moves in at least some more
2298 // complicated endgames, e.g. KQ vs KR. FIXME
2300 bool ok_to_do_nullmove(const Position &pos) {
2301 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2307 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2308 // non-tactical moves late in the move list close to the leaves are
2309 // candidates for pruning.
2311 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2312 Square mfrom, mto, tfrom, tto;
2314 assert(move_is_ok(m));
2315 assert(threat == MOVE_NONE || move_is_ok(threat));
2316 assert(!move_promotion(m));
2317 assert(!pos.move_is_check(m));
2318 assert(!pos.move_is_capture(m));
2319 assert(!pos.move_is_passed_pawn_push(m));
2320 assert(d >= OnePly);
2322 mfrom = move_from(m);
2324 tfrom = move_from(threat);
2325 tto = move_to(threat);
2327 // Case 1: Castling moves are never pruned.
2328 if (move_is_castle(m))
2331 // Case 2: Don't prune moves which move the threatened piece
2332 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2335 // Case 3: If the threatened piece has value less than or equal to the
2336 // value of the threatening piece, don't prune move which defend it.
2337 if ( !PruneDefendingMoves
2338 && threat != MOVE_NONE
2339 && pos.move_is_capture(threat)
2340 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2341 || pos.type_of_piece_on(tfrom) == KING)
2342 && pos.move_attacks_square(m, tto))
2345 // Case 4: Don't prune moves with good history.
2346 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2349 // Case 5: If the moving piece in the threatened move is a slider, don't
2350 // prune safe moves which block its ray.
2351 if ( !PruneBlockingMoves
2352 && threat != MOVE_NONE
2353 && piece_is_slider(pos.piece_on(tfrom))
2354 && bit_is_set(squares_between(tfrom, tto), mto)
2362 // ok_to_use_TT() returns true if a transposition table score
2363 // can be used at a given point in search.
2365 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2367 Value v = value_from_tt(tte->value(), ply);
2369 return ( tte->depth() >= depth
2370 || v >= Max(value_mate_in(100), beta)
2371 || v < Min(value_mated_in(100), beta))
2373 && ( (is_lower_bound(tte->type()) && v >= beta)
2374 || (is_upper_bound(tte->type()) && v < beta));
2378 // ok_to_history() returns true if a move m can be stored
2379 // in history. Should be a non capturing move nor a promotion.
2381 bool ok_to_history(const Position& pos, Move m) {
2383 return !pos.move_is_capture(m) && !move_promotion(m);
2387 // update_history() registers a good move that produced a beta-cutoff
2388 // in history and marks as failures all the other moves of that ply.
2390 void update_history(const Position& pos, Move m, Depth depth,
2391 Move movesSearched[], int moveCount) {
2393 H.success(pos.piece_on(move_from(m)), m, depth);
2395 for (int i = 0; i < moveCount - 1; i++)
2397 assert(m != movesSearched[i]);
2398 if (ok_to_history(pos, movesSearched[i]))
2399 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2404 // update_killers() add a good move that produced a beta-cutoff
2405 // among the killer moves of that ply.
2407 void update_killers(Move m, SearchStack& ss) {
2409 if (m == ss.killers[0])
2412 for (int i = KILLER_MAX - 1; i > 0; i--)
2413 ss.killers[i] = ss.killers[i - 1];
2418 // fail_high_ply_1() checks if some thread is currently resolving a fail
2419 // high at ply 1 at the node below the first root node. This information
2420 // is used for time managment.
2422 bool fail_high_ply_1() {
2423 for(int i = 0; i < ActiveThreads; i++)
2424 if(Threads[i].failHighPly1)
2430 // current_search_time() returns the number of milliseconds which have passed
2431 // since the beginning of the current search.
2433 int current_search_time() {
2434 return get_system_time() - SearchStartTime;
2438 // nps() computes the current nodes/second count.
2441 int t = current_search_time();
2442 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2446 // poll() performs two different functions: It polls for user input, and it
2447 // looks at the time consumed so far and decides if it's time to abort the
2452 static int lastInfoTime;
2453 int t = current_search_time();
2458 // We are line oriented, don't read single chars
2459 std::string command;
2460 if (!std::getline(std::cin, command))
2463 if (command == "quit")
2466 PonderSearch = false;
2469 else if(command == "stop")
2472 PonderSearch = false;
2474 else if(command == "ponderhit")
2477 // Print search information
2481 else if (lastInfoTime > t)
2482 // HACK: Must be a new search where we searched less than
2483 // NodesBetweenPolls nodes during the first second of search.
2486 else if (t - lastInfoTime >= 1000)
2493 if (dbg_show_hit_rate)
2494 dbg_print_hit_rate();
2496 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2497 << " time " << t << " hashfull " << TT.full() << std::endl;
2498 lock_release(&IOLock);
2499 if (ShowCurrentLine)
2500 Threads[0].printCurrentLine = true;
2502 // Should we stop the search?
2506 bool overTime = t > AbsoluteMaxSearchTime
2507 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2508 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2509 && t > 6*(MaxSearchTime + ExtraSearchTime));
2511 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2512 || (ExactMaxTime && t >= ExactMaxTime)
2513 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2518 // ponderhit() is called when the program is pondering (i.e. thinking while
2519 // it's the opponent's turn to move) in order to let the engine know that
2520 // it correctly predicted the opponent's move.
2523 int t = current_search_time();
2524 PonderSearch = false;
2525 if(Iteration >= 3 &&
2526 (!InfiniteSearch && (StopOnPonderhit ||
2527 t > AbsoluteMaxSearchTime ||
2528 (RootMoveNumber == 1 &&
2529 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2530 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2531 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2536 // print_current_line() prints the current line of search for a given
2537 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2539 void print_current_line(SearchStack ss[], int ply, int threadID) {
2540 assert(ply >= 0 && ply < PLY_MAX);
2541 assert(threadID >= 0 && threadID < ActiveThreads);
2543 if(!Threads[threadID].idle) {
2545 std::cout << "info currline " << (threadID + 1);
2546 for(int p = 0; p < ply; p++)
2547 std::cout << " " << ss[p].currentMove;
2548 std::cout << std::endl;
2549 lock_release(&IOLock);
2551 Threads[threadID].printCurrentLine = false;
2552 if(threadID + 1 < ActiveThreads)
2553 Threads[threadID + 1].printCurrentLine = true;
2557 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2558 // while the program is pondering. The point is to work around a wrinkle in
2559 // the UCI protocol: When pondering, the engine is not allowed to give a
2560 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2561 // We simply wait here until one of these commands is sent, and return,
2562 // after which the bestmove and pondermove will be printed (in id_loop()).
2564 void wait_for_stop_or_ponderhit() {
2565 std::string command;
2568 if(!std::getline(std::cin, command))
2571 if(command == "quit") {
2572 OpeningBook.close();
2577 else if(command == "ponderhit" || command == "stop")
2583 // idle_loop() is where the threads are parked when they have no work to do.
2584 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2585 // object for which the current thread is the master.
2587 void idle_loop(int threadID, SplitPoint *waitSp) {
2588 assert(threadID >= 0 && threadID < THREAD_MAX);
2590 Threads[threadID].running = true;
2593 if(AllThreadsShouldExit && threadID != 0)
2596 // If we are not thinking, wait for a condition to be signaled instead
2597 // of wasting CPU time polling for work:
2598 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2599 #if !defined(_MSC_VER)
2600 pthread_mutex_lock(&WaitLock);
2601 if(Idle || threadID >= ActiveThreads)
2602 pthread_cond_wait(&WaitCond, &WaitLock);
2603 pthread_mutex_unlock(&WaitLock);
2605 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2609 // If this thread has been assigned work, launch a search:
2610 if(Threads[threadID].workIsWaiting) {
2611 Threads[threadID].workIsWaiting = false;
2612 if(Threads[threadID].splitPoint->pvNode)
2613 sp_search_pv(Threads[threadID].splitPoint, threadID);
2615 sp_search(Threads[threadID].splitPoint, threadID);
2616 Threads[threadID].idle = true;
2619 // If this thread is the master of a split point and all threads have
2620 // finished their work at this split point, return from the idle loop:
2621 if(waitSp != NULL && waitSp->cpus == 0)
2625 Threads[threadID].running = false;
2629 // init_split_point_stack() is called during program initialization, and
2630 // initializes all split point objects.
2632 void init_split_point_stack() {
2633 for(int i = 0; i < THREAD_MAX; i++)
2634 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2635 SplitPointStack[i][j].parent = NULL;
2636 lock_init(&(SplitPointStack[i][j].lock), NULL);
2641 // destroy_split_point_stack() is called when the program exits, and
2642 // destroys all locks in the precomputed split point objects.
2644 void destroy_split_point_stack() {
2645 for(int i = 0; i < THREAD_MAX; i++)
2646 for(int j = 0; j < MaxActiveSplitPoints; j++)
2647 lock_destroy(&(SplitPointStack[i][j].lock));
2651 // thread_should_stop() checks whether the thread with a given threadID has
2652 // been asked to stop, directly or indirectly. This can happen if a beta
2653 // cutoff has occured in thre thread's currently active split point, or in
2654 // some ancestor of the current split point.
2656 bool thread_should_stop(int threadID) {
2657 assert(threadID >= 0 && threadID < ActiveThreads);
2661 if(Threads[threadID].stop)
2663 if(ActiveThreads <= 2)
2665 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2667 Threads[threadID].stop = true;
2674 // thread_is_available() checks whether the thread with threadID "slave" is
2675 // available to help the thread with threadID "master" at a split point. An
2676 // obvious requirement is that "slave" must be idle. With more than two
2677 // threads, this is not by itself sufficient: If "slave" is the master of
2678 // some active split point, it is only available as a slave to the other
2679 // threads which are busy searching the split point at the top of "slave"'s
2680 // split point stack (the "helpful master concept" in YBWC terminology).
2682 bool thread_is_available(int slave, int master) {
2683 assert(slave >= 0 && slave < ActiveThreads);
2684 assert(master >= 0 && master < ActiveThreads);
2685 assert(ActiveThreads > 1);
2687 if(!Threads[slave].idle || slave == master)
2690 if(Threads[slave].activeSplitPoints == 0)
2691 // No active split points means that the thread is available as a slave
2692 // for any other thread.
2695 if(ActiveThreads == 2)
2698 // Apply the "helpful master" concept if possible.
2699 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2706 // idle_thread_exists() tries to find an idle thread which is available as
2707 // a slave for the thread with threadID "master".
2709 bool idle_thread_exists(int master) {
2710 assert(master >= 0 && master < ActiveThreads);
2711 assert(ActiveThreads > 1);
2713 for(int i = 0; i < ActiveThreads; i++)
2714 if(thread_is_available(i, master))
2720 // split() does the actual work of distributing the work at a node between
2721 // several threads at PV nodes. If it does not succeed in splitting the
2722 // node (because no idle threads are available, or because we have no unused
2723 // split point objects), the function immediately returns false. If
2724 // splitting is possible, a SplitPoint object is initialized with all the
2725 // data that must be copied to the helper threads (the current position and
2726 // search stack, alpha, beta, the search depth, etc.), and we tell our
2727 // helper threads that they have been assigned work. This will cause them
2728 // to instantly leave their idle loops and call sp_search_pv(). When all
2729 // threads have returned from sp_search_pv (or, equivalently, when
2730 // splitPoint->cpus becomes 0), split() returns true.
2732 bool split(const Position &p, SearchStack *sstck, int ply,
2733 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
2734 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2737 assert(sstck != NULL);
2738 assert(ply >= 0 && ply < PLY_MAX);
2739 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2740 assert(!pvNode || *alpha < *beta);
2741 assert(*beta <= VALUE_INFINITE);
2742 assert(depth > Depth(0));
2743 assert(master >= 0 && master < ActiveThreads);
2744 assert(ActiveThreads > 1);
2746 SplitPoint *splitPoint;
2751 // If no other thread is available to help us, or if we have too many
2752 // active split points, don't split:
2753 if(!idle_thread_exists(master) ||
2754 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2755 lock_release(&MPLock);
2759 // Pick the next available split point object from the split point stack:
2760 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2761 Threads[master].activeSplitPoints++;
2763 // Initialize the split point object:
2764 splitPoint->parent = Threads[master].splitPoint;
2765 splitPoint->finished = false;
2766 splitPoint->ply = ply;
2767 splitPoint->depth = depth;
2768 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2769 splitPoint->beta = *beta;
2770 splitPoint->pvNode = pvNode;
2771 splitPoint->dcCandidates = dcCandidates;
2772 splitPoint->bestValue = *bestValue;
2773 splitPoint->master = master;
2774 splitPoint->mp = mp;
2775 splitPoint->moves = *moves;
2776 splitPoint->cpus = 1;
2777 splitPoint->pos.copy(p);
2778 splitPoint->parentSstack = sstck;
2779 for(i = 0; i < ActiveThreads; i++)
2780 splitPoint->slaves[i] = 0;
2782 // Copy the current position and the search stack to the master thread:
2783 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2784 Threads[master].splitPoint = splitPoint;
2786 // Make copies of the current position and search stack for each thread:
2787 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2789 if(thread_is_available(i, master)) {
2790 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2791 Threads[i].splitPoint = splitPoint;
2792 splitPoint->slaves[i] = 1;
2796 // Tell the threads that they have work to do. This will make them leave
2798 for(i = 0; i < ActiveThreads; i++)
2799 if(i == master || splitPoint->slaves[i]) {
2800 Threads[i].workIsWaiting = true;
2801 Threads[i].idle = false;
2802 Threads[i].stop = false;
2805 lock_release(&MPLock);
2807 // Everything is set up. The master thread enters the idle loop, from
2808 // which it will instantly launch a search, because its workIsWaiting
2809 // slot is 'true'. We send the split point as a second parameter to the
2810 // idle loop, which means that the main thread will return from the idle
2811 // loop when all threads have finished their work at this split point
2812 // (i.e. when // splitPoint->cpus == 0).
2813 idle_loop(master, splitPoint);
2815 // We have returned from the idle loop, which means that all threads are
2816 // finished. Update alpha, beta and bestvalue, and return:
2818 if(pvNode) *alpha = splitPoint->alpha;
2819 *beta = splitPoint->beta;
2820 *bestValue = splitPoint->bestValue;
2821 Threads[master].stop = false;
2822 Threads[master].idle = false;
2823 Threads[master].activeSplitPoints--;
2824 Threads[master].splitPoint = splitPoint->parent;
2825 lock_release(&MPLock);
2831 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2832 // to start a new search from the root.
2834 void wake_sleeping_threads() {
2835 if(ActiveThreads > 1) {
2836 for(int i = 1; i < ActiveThreads; i++) {
2837 Threads[i].idle = true;
2838 Threads[i].workIsWaiting = false;
2840 #if !defined(_MSC_VER)
2841 pthread_mutex_lock(&WaitLock);
2842 pthread_cond_broadcast(&WaitCond);
2843 pthread_mutex_unlock(&WaitLock);
2845 for(int i = 1; i < THREAD_MAX; i++)
2846 SetEvent(SitIdleEvent[i]);
2852 // init_thread() is the function which is called when a new thread is
2853 // launched. It simply calls the idle_loop() function with the supplied
2854 // threadID. There are two versions of this function; one for POSIX threads
2855 // and one for Windows threads.
2857 #if !defined(_MSC_VER)
2859 void *init_thread(void *threadID) {
2860 idle_loop(*(int *)threadID, NULL);
2866 DWORD WINAPI init_thread(LPVOID threadID) {
2867 idle_loop(*(int *)threadID, NULL);