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/>.
39 #include "ucioption.h"
43 //// Local definitions
50 // The BetaCounterType class is used to order moves at ply one.
51 // Apart for the first one that has its score, following moves
52 // normally have score -VALUE_INFINITE, so are ordered according
53 // to the number of beta cutoffs occurred under their subtree during
54 // the last iteration.
56 struct BetaCounterType {
60 void add(Color us, Depth d, int threadID);
61 void read(Color us, int64_t& our, int64_t& their);
63 int64_t hits[THREAD_MAX][2];
67 // The RootMove class is used for moves at the root at the tree. For each
68 // root move, we store a score, a node count, and a PV (really a refutation
69 // in the case of moves which fail low).
74 bool operator<(const RootMove&); // used to sort
78 int64_t nodes, cumulativeNodes;
79 Move pv[PLY_MAX_PLUS_2];
80 int64_t ourBeta, theirBeta;
84 // The RootMoveList class is essentially an array of RootMove objects, with
85 // a handful of methods for accessing the data in the individual moves.
90 RootMoveList(Position &pos, Move searchMoves[]);
91 inline Move get_move(int moveNum) const;
92 inline Value get_move_score(int moveNum) const;
93 inline void set_move_score(int moveNum, Value score);
94 inline void set_move_nodes(int moveNum, int64_t nodes);
95 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
96 void set_move_pv(int moveNum, const Move pv[]);
97 inline Move get_move_pv(int moveNum, int i) const;
98 inline int64_t get_move_cumulative_nodes(int moveNum) const;
99 inline int move_count() const;
100 Move scan_for_easy_move() const;
102 void sort_multipv(int n);
105 static const int MaxRootMoves = 500;
106 RootMove moves[MaxRootMoves];
111 /// Constants and variables
113 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
116 int LMRNonPVMoves = 4;
118 // Depth limit for use of dynamic threat detection:
119 Depth ThreatDepth = 5*OnePly;
121 // Depth limit for selective search:
122 Depth SelectiveDepth = 7*OnePly;
124 // Use internal iterative deepening?
125 const bool UseIIDAtPVNodes = true;
126 const bool UseIIDAtNonPVNodes = false;
128 // Use null move driven internal iterative deepening?
129 bool UseNullDrivenIID = false;
131 // Internal iterative deepening margin. At Non-PV moves, when
132 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
133 // when the static evaluation is at most IIDMargin below beta.
134 const Value IIDMargin = Value(0x100);
137 const bool UseEasyMove = true;
139 // Easy move margin. An easy move candidate must be at least this much
140 // better than the second best move.
141 const Value EasyMoveMargin = Value(0x200);
143 // Problem margin. If the score of the first move at iteration N+1 has
144 // dropped by more than this since iteration N, the boolean variable
145 // "Problem" is set to true, which will make the program spend some extra
146 // time looking for a better move.
147 const Value ProblemMargin = Value(0x28);
149 // No problem margin. If the boolean "Problem" is true, and a new move
150 // is found at the root which is less than NoProblemMargin worse than the
151 // best move from the previous iteration, Problem is set back to false.
152 const Value NoProblemMargin = Value(0x14);
154 // Null move margin. A null move search will not be done if the approximate
155 // evaluation of the position is more than NullMoveMargin below beta.
156 const Value NullMoveMargin = Value(0x300);
158 // Pruning criterions. See the code and comments in ok_to_prune() to
159 // understand their precise meaning.
160 const bool PruneEscapeMoves = false;
161 const bool PruneDefendingMoves = false;
162 const bool PruneBlockingMoves = false;
164 // Use futility pruning?
165 bool UseQSearchFutilityPruning = true;
166 bool UseFutilityPruning = true;
168 // Margins for futility pruning in the quiescence search, at frontier
169 // nodes, and at pre-frontier nodes
170 Value FutilityMargin0 = Value(0x80);
171 Value FutilityMargin1 = Value(0x100);
172 Value FutilityMargin2 = Value(0x300);
175 Depth RazorDepth = 4*OnePly;
176 Value RazorMargin = Value(0x300);
178 // Last seconds noise filtering (LSN)
179 bool UseLSNFiltering = false;
180 bool looseOnTime = false;
181 int LSNTime = 4 * 1000; // In milliseconds
182 Value LSNValue = Value(0x200);
184 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
185 Depth CheckExtension[2] = {OnePly, OnePly};
186 Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
187 Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
188 Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
189 Depth PawnEndgameExtension[2] = {OnePly, OnePly};
190 Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
192 // Search depth at iteration 1
193 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
197 int NodesBetweenPolls = 30000;
199 // Iteration counters
202 BetaCounterType BetaCounter;
204 // Scores and number of times the best move changed for each iteration:
205 Value ValueByIteration[PLY_MAX_PLUS_2];
206 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
211 // Time managment variables
213 int MaxNodes, MaxDepth;
214 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
215 Move BestRootMove, PonderMove, EasyMove;
219 bool StopOnPonderhit;
224 bool PonderingEnabled;
227 // Show current line?
228 bool ShowCurrentLine = false;
231 bool UseLogFile = false;
232 std::ofstream LogFile;
234 // MP related variables
235 Depth MinimumSplitDepth = 4*OnePly;
236 int MaxThreadsPerSplitPoint = 4;
237 Thread Threads[THREAD_MAX];
239 bool AllThreadsShouldExit = false;
240 const int MaxActiveSplitPoints = 8;
241 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
244 #if !defined(_MSC_VER)
245 pthread_cond_t WaitCond;
246 pthread_mutex_t WaitLock;
248 HANDLE SitIdleEvent[THREAD_MAX];
254 Value id_loop(const Position &pos, Move searchMoves[]);
255 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
256 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
257 Depth depth, int ply, int threadID);
258 Value search(Position &pos, SearchStack ss[], Value beta,
259 Depth depth, int ply, bool allowNullmove, int threadID);
260 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
261 Depth depth, int ply, int threadID);
262 void sp_search(SplitPoint *sp, int threadID);
263 void sp_search_pv(SplitPoint *sp, int threadID);
264 void init_search_stack(SearchStack& ss);
265 void init_search_stack(SearchStack ss[]);
266 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
267 void update_pv(SearchStack ss[], int ply);
268 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
269 bool connected_moves(const Position &pos, Move m1, Move m2);
270 bool value_is_mate(Value value);
271 bool move_is_killer(Move m, const SearchStack& ss);
272 Depth extension(const Position &pos, Move m, bool pvNode, bool check, bool singleReply, bool mateThreat, bool* dangerous);
273 bool ok_to_do_nullmove(const Position &pos);
274 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
275 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
276 bool ok_to_history(const Position &pos, Move m);
277 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
278 void update_killers(Move m, SearchStack& ss);
280 bool fail_high_ply_1();
281 int current_search_time();
285 void print_current_line(SearchStack ss[], int ply, int threadID);
286 void wait_for_stop_or_ponderhit();
288 void idle_loop(int threadID, SplitPoint *waitSp);
289 void init_split_point_stack();
290 void destroy_split_point_stack();
291 bool thread_should_stop(int threadID);
292 bool thread_is_available(int slave, int master);
293 bool idle_thread_exists(int master);
294 bool split(const Position &pos, SearchStack *ss, int ply,
295 Value *alpha, Value *beta, Value *bestValue, Depth depth,
296 int *moves, MovePicker *mp, Bitboard dcCandidates, int master,
298 void wake_sleeping_threads();
300 #if !defined(_MSC_VER)
301 void *init_thread(void *threadID);
303 DWORD WINAPI init_thread(LPVOID threadID);
310 //// Global variables
313 // The main transposition table
314 TranspositionTable TT = TranspositionTable(TTDefaultSize);
317 // Number of active threads:
318 int ActiveThreads = 1;
320 // Locks. In principle, there is no need for IOLock to be a global variable,
321 // but it could turn out to be useful for debugging.
324 History H; // Should be made local?
326 // The empty search stack
327 SearchStack EmptySearchStack;
334 /// think() is the external interface to Stockfish's search, and is called when
335 /// the program receives the UCI 'go' command. It initializes various
336 /// search-related global variables, and calls root_search()
338 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
339 int time[], int increment[], int movesToGo, int maxDepth,
340 int maxNodes, int maxTime, Move searchMoves[]) {
342 // Look for a book move
343 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
346 if (get_option_value_string("Book File") != OpeningBook.file_name())
349 OpeningBook.open("book.bin");
351 bookMove = OpeningBook.get_move(pos);
352 if (bookMove != MOVE_NONE)
354 std::cout << "bestmove " << bookMove << std::endl;
359 // Initialize global search variables
361 SearchStartTime = get_system_time();
362 BestRootMove = MOVE_NONE;
363 PonderMove = MOVE_NONE;
364 EasyMove = MOVE_NONE;
365 for (int i = 0; i < THREAD_MAX; i++)
367 Threads[i].nodes = 0ULL;
368 Threads[i].failHighPly1 = false;
371 InfiniteSearch = infinite;
372 PonderSearch = ponder;
373 StopOnPonderhit = false;
378 ExactMaxTime = maxTime;
380 // Read UCI option values
381 TT.set_size(get_option_value_int("Hash"));
382 if (button_was_pressed("Clear Hash"))
385 PonderingEnabled = get_option_value_bool("Ponder");
386 MultiPV = get_option_value_int("MultiPV");
388 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
389 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
391 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
392 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
394 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
395 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
397 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
398 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
400 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
401 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
403 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
404 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
406 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
407 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
408 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
409 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
411 Chess960 = get_option_value_bool("UCI_Chess960");
412 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
413 UseLogFile = get_option_value_bool("Use Search Log");
415 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
417 UseNullDrivenIID = get_option_value_bool("Null driven IID");
418 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
419 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
421 FutilityMargin0 = value_from_centipawns(get_option_value_int("Futility Margin 0"));
422 FutilityMargin1 = value_from_centipawns(get_option_value_int("Futility Margin 1"));
423 FutilityMargin2 = value_from_centipawns(get_option_value_int("Futility Margin 2"));
425 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
426 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
428 UseLSNFiltering = get_option_value_bool("LSN filtering");
429 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
430 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
432 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
433 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
435 read_weights(pos.side_to_move());
437 int newActiveThreads = get_option_value_int("Threads");
438 if (newActiveThreads != ActiveThreads)
440 ActiveThreads = newActiveThreads;
441 init_eval(ActiveThreads);
444 // Wake up sleeping threads:
445 wake_sleeping_threads();
447 for (int i = 1; i < ActiveThreads; i++)
448 assert(thread_is_available(i, 0));
450 // Set thinking time:
451 int myTime = time[side_to_move];
452 int myIncrement = increment[side_to_move];
453 int oppTime = time[1 - side_to_move];
455 if (!movesToGo) // Sudden death time control
459 MaxSearchTime = myTime / 30 + myIncrement;
460 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
461 } else { // Blitz game without increment
462 MaxSearchTime = myTime / 30;
463 AbsoluteMaxSearchTime = myTime / 8;
466 else // (x moves) / (y minutes)
470 MaxSearchTime = myTime / 2;
471 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
473 MaxSearchTime = myTime / Min(movesToGo, 20);
474 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
478 if (PonderingEnabled)
480 MaxSearchTime += MaxSearchTime / 4;
481 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
484 // Fixed depth or fixed number of nodes?
487 InfiniteSearch = true; // HACK
492 NodesBetweenPolls = Min(MaxNodes, 30000);
493 InfiniteSearch = true; // HACK
496 NodesBetweenPolls = 30000;
499 // Write information to search log file:
501 LogFile << "Searching: " << pos.to_fen() << std::endl
502 << "infinite: " << infinite
503 << " ponder: " << ponder
504 << " time: " << myTime
505 << " increment: " << myIncrement
506 << " moves to go: " << movesToGo << std::endl;
509 // We're ready to start thinking. Call the iterative deepening loop
513 Value v = id_loop(pos, searchMoves);
514 looseOnTime = ( UseLSNFiltering
521 looseOnTime = false; // reset for next match
522 while (SearchStartTime + myTime + 1000 > get_system_time())
524 id_loop(pos, searchMoves); // to fail gracefully
541 /// init_threads() is called during startup. It launches all helper threads,
542 /// and initializes the split point stack and the global locks and condition
545 void init_threads() {
549 #if !defined(_MSC_VER)
550 pthread_t pthread[1];
553 for (i = 0; i < THREAD_MAX; i++)
554 Threads[i].activeSplitPoints = 0;
556 // Initialize global locks:
557 lock_init(&MPLock, NULL);
558 lock_init(&IOLock, NULL);
560 init_split_point_stack();
562 #if !defined(_MSC_VER)
563 pthread_mutex_init(&WaitLock, NULL);
564 pthread_cond_init(&WaitCond, NULL);
566 for (i = 0; i < THREAD_MAX; i++)
567 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
570 // All threads except the main thread should be initialized to idle state
571 for (i = 1; i < THREAD_MAX; i++)
573 Threads[i].stop = false;
574 Threads[i].workIsWaiting = false;
575 Threads[i].idle = true;
576 Threads[i].running = false;
579 // Launch the helper threads
580 for(i = 1; i < THREAD_MAX; i++)
582 #if !defined(_MSC_VER)
583 pthread_create(pthread, NULL, init_thread, (void*)(&i));
586 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
589 // Wait until the thread has finished launching:
590 while (!Threads[i].running);
593 // Init also the empty search stack
594 init_search_stack(EmptySearchStack);
598 /// stop_threads() is called when the program exits. It makes all the
599 /// helper threads exit cleanly.
601 void stop_threads() {
603 ActiveThreads = THREAD_MAX; // HACK
604 Idle = false; // HACK
605 wake_sleeping_threads();
606 AllThreadsShouldExit = true;
607 for (int i = 1; i < THREAD_MAX; i++)
609 Threads[i].stop = true;
610 while(Threads[i].running);
612 destroy_split_point_stack();
616 /// nodes_searched() returns the total number of nodes searched so far in
617 /// the current search.
619 int64_t nodes_searched() {
621 int64_t result = 0ULL;
622 for (int i = 0; i < ActiveThreads; i++)
623 result += Threads[i].nodes;
630 // id_loop() is the main iterative deepening loop. It calls root_search
631 // repeatedly with increasing depth until the allocated thinking time has
632 // been consumed, the user stops the search, or the maximum search depth is
635 Value id_loop(const Position &pos, Move searchMoves[]) {
638 SearchStack ss[PLY_MAX_PLUS_2];
640 // searchMoves are verified, copied, scored and sorted
641 RootMoveList rml(p, searchMoves);
646 init_search_stack(ss);
648 ValueByIteration[0] = Value(0);
649 ValueByIteration[1] = rml.get_move_score(0);
651 LastIterations = false;
653 EasyMove = rml.scan_for_easy_move();
655 // Iterative deepening loop
656 while (!AbortSearch && Iteration < PLY_MAX)
658 // Initialize iteration
661 BestMoveChangesByIteration[Iteration] = 0;
665 std::cout << "info depth " << Iteration << std::endl;
667 // Search to the current depth
668 ValueByIteration[Iteration] = root_search(p, ss, rml);
670 // Erase the easy move if it differs from the new best move
671 if (ss[0].pv[0] != EasyMove)
672 EasyMove = MOVE_NONE;
679 bool stopSearch = false;
681 // Stop search early if there is only a single legal move:
682 if (Iteration >= 6 && rml.move_count() == 1)
685 // Stop search early when the last two iterations returned a mate score
687 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
688 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
691 // Stop search early if one move seems to be much better than the rest
692 int64_t nodes = nodes_searched();
694 && EasyMove == ss[0].pv[0]
695 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
696 && current_search_time() > MaxSearchTime / 16)
697 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
698 && current_search_time() > MaxSearchTime / 32)))
701 // Add some extra time if the best move has changed during the last two iterations
702 if (Iteration > 5 && Iteration <= 50)
703 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
704 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
706 // Try to guess if the current iteration is the last one or the last two
707 LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
709 // Stop search if most of MaxSearchTime is consumed at the end of the
710 // iteration. We probably don't have enough time to search the first
711 // move at the next iteration anyway.
712 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
720 StopOnPonderhit = true;
723 // Write PV to transposition table, in case the relevant entries have
724 // been overwritten during the search:
725 TT.insert_pv(p, ss[0].pv);
727 if (MaxDepth && Iteration >= MaxDepth)
733 // If we are pondering, we shouldn't print the best move before we
736 wait_for_stop_or_ponderhit();
738 // Print final search statistics
739 std::cout << "info nodes " << nodes_searched()
741 << " time " << current_search_time()
742 << " hashfull " << TT.full() << std::endl;
744 // Print the best move and the ponder move to the standard output
745 std::cout << "bestmove " << ss[0].pv[0];
746 if (ss[0].pv[1] != MOVE_NONE)
747 std::cout << " ponder " << ss[0].pv[1];
749 std::cout << std::endl;
754 dbg_print_mean(LogFile);
756 if (dbg_show_hit_rate)
757 dbg_print_hit_rate(LogFile);
760 LogFile << "Nodes: " << nodes_searched() << std::endl
761 << "Nodes/second: " << nps() << std::endl
762 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
764 p.do_move(ss[0].pv[0], u);
765 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
766 << std::endl << std::endl;
768 return rml.get_move_score(0);
772 // root_search() is the function which searches the root node. It is
773 // similar to search_pv except that it uses a different move ordering
774 // scheme (perhaps we should try to use this at internal PV nodes, too?)
775 // and prints some information to the standard output.
777 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
779 Value alpha = -VALUE_INFINITE;
780 Value beta = VALUE_INFINITE, value;
781 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
783 // Loop through all the moves in the root move list
784 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
791 RootMoveNumber = i + 1;
794 // Remember the node count before the move is searched. The node counts
795 // are used to sort the root moves at the next iteration.
796 nodes = nodes_searched();
798 // Reset beta cut-off counters
801 // Pick the next root move, and print the move and the move number to
802 // the standard output.
803 move = ss[0].currentMove = rml.get_move(i);
804 if (current_search_time() >= 1000)
805 std::cout << "info currmove " << move
806 << " currmovenumber " << i + 1 << std::endl;
808 // Decide search depth for this move
810 ext = extension(pos, move, true, pos.move_is_check(move), false, false, &dangerous);
811 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
813 // Make the move, and search it
814 pos.do_move(move, u, dcCandidates);
818 value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
819 // If the value has dropped a lot compared to the last iteration,
820 // set the boolean variable Problem to true. This variable is used
821 // for time managment: When Problem is true, we try to complete the
822 // current iteration before playing a move.
823 Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
825 if (Problem && StopOnPonderhit)
826 StopOnPonderhit = false;
830 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
833 // Fail high! Set the boolean variable FailHigh to true, and
834 // re-search the move with a big window. The variable FailHigh is
835 // used for time managment: We try to avoid aborting the search
836 // prematurely during a fail high research.
838 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
842 pos.undo_move(move, u);
844 // Finished searching the move. If AbortSearch is true, the search
845 // was aborted because the user interrupted the search or because we
846 // ran out of time. In this case, the return value of the search cannot
847 // be trusted, and we break out of the loop without updating the best
852 // Remember the node count for this move. The node counts are used to
853 // sort the root moves at the next iteration.
854 rml.set_move_nodes(i, nodes_searched() - nodes);
856 // Remember the beta-cutoff statistics
858 BetaCounter.read(pos.side_to_move(), our, their);
859 rml.set_beta_counters(i, our, their);
861 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
863 if (value <= alpha && i >= MultiPV)
864 rml.set_move_score(i, -VALUE_INFINITE);
870 rml.set_move_score(i, value);
872 rml.set_move_pv(i, ss[0].pv);
876 // We record how often the best move has been changed in each
877 // iteration. This information is used for time managment: When
878 // the best move changes frequently, we allocate some more time.
880 BestMoveChangesByIteration[Iteration]++;
882 // Print search information to the standard output:
883 std::cout << "info depth " << Iteration
884 << " score " << value_to_string(value)
885 << " time " << current_search_time()
886 << " nodes " << nodes_searched()
890 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
891 std::cout << ss[0].pv[j] << " ";
893 std::cout << std::endl;
896 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
901 // Reset the global variable Problem to false if the value isn't too
902 // far below the final value from the last iteration.
903 if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
909 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
912 std::cout << "info multipv " << j + 1
913 << " score " << value_to_string(rml.get_move_score(j))
914 << " depth " << ((j <= i)? Iteration : Iteration - 1)
915 << " time " << current_search_time()
916 << " nodes " << nodes_searched()
920 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
921 std::cout << rml.get_move_pv(j, k) << " ";
923 std::cout << std::endl;
925 alpha = rml.get_move_score(Min(i, MultiPV-1));
933 // search_pv() is the main search function for PV nodes.
935 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
936 Depth depth, int ply, int threadID) {
938 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
939 assert(beta > alpha && beta <= VALUE_INFINITE);
940 assert(ply >= 0 && ply < PLY_MAX);
941 assert(threadID >= 0 && threadID < ActiveThreads);
943 // Initialize, and make an early exit in case of an aborted search,
944 // an instant draw, maximum ply reached, etc.
945 if (AbortSearch || thread_should_stop(threadID))
949 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
951 init_node(pos, ss, ply, threadID);
958 if (ply >= PLY_MAX - 1)
959 return evaluate(pos, ei, threadID);
961 // Mate distance pruning
962 Value oldAlpha = alpha;
963 alpha = Max(value_mated_in(ply), alpha);
964 beta = Min(value_mate_in(ply+1), beta);
968 // Transposition table lookup. At PV nodes, we don't use the TT for
969 // pruning, but only for move ordering.
970 const TTEntry* tte = TT.retrieve(pos);
971 Move ttMove = (tte ? tte->move() : MOVE_NONE);
973 // Go with internal iterative deepening if we don't have a TT move
974 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
976 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
977 ttMove = ss[ply].pv[ply];
980 // Initialize a MovePicker object for the current position, and prepare
981 // to search all moves
982 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
984 Move move, movesSearched[256];
986 Value value, bestValue = -VALUE_INFINITE;
987 Bitboard dcCandidates = mp.discovered_check_candidates();
988 bool isCheck = pos.is_check();
989 bool mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
991 // Loop through all legal moves until no moves remain or a beta cutoff
994 && (move = mp.get_next_move()) != MOVE_NONE
995 && !thread_should_stop(threadID))
997 assert(move_is_ok(move));
999 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1000 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1001 bool moveIsCapture = pos.move_is_capture(move);
1003 movesSearched[moveCount++] = ss[ply].currentMove = move;
1006 ss[ply].currentMoveCaptureValue =
1007 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1009 ss[ply].currentMoveCaptureValue = Value(0);
1011 // Decide the new search depth
1013 Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat, &dangerous);
1014 Depth newDepth = depth - OnePly + ext;
1016 // Make and search the move
1018 pos.do_move(move, u, dcCandidates);
1020 if (moveCount == 1) // The first move in list is the PV
1021 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1024 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1025 // if the move fails high will be re-searched at full depth.
1026 if ( depth >= 2*OnePly
1027 && moveCount >= LMRPVMoves
1030 && !move_promotion(move)
1031 && !move_is_castle(move)
1032 && !move_is_killer(move, ss[ply]))
1034 ss[ply].reduction = OnePly;
1035 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1038 value = alpha + 1; // Just to trigger next condition
1040 if (value > alpha) // Go with full depth pv search
1042 ss[ply].reduction = Depth(0);
1043 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1044 if (value > alpha && value < beta)
1046 // When the search fails high at ply 1 while searching the first
1047 // move at the root, set the flag failHighPly1. This is used for
1048 // time managment: We don't want to stop the search early in
1049 // such cases, because resolving the fail high at ply 1 could
1050 // result in a big drop in score at the root.
1051 if (ply == 1 && RootMoveNumber == 1)
1052 Threads[threadID].failHighPly1 = true;
1054 // A fail high occurred. Re-search at full window (pv search)
1055 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1056 Threads[threadID].failHighPly1 = false;
1060 pos.undo_move(move, u);
1062 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1065 if (value > bestValue)
1072 if (value == value_mate_in(ply + 1))
1073 ss[ply].mateKiller = move;
1075 // If we are at ply 1, and we are searching the first root move at
1076 // ply 0, set the 'Problem' variable if the score has dropped a lot
1077 // (from the computer's point of view) since the previous iteration:
1078 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1083 if ( ActiveThreads > 1
1085 && depth >= MinimumSplitDepth
1087 && idle_thread_exists(threadID)
1089 && !thread_should_stop(threadID)
1090 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1091 &moveCount, &mp, dcCandidates, threadID, true))
1095 // All legal moves have been searched. A special case: If there were
1096 // no legal moves, it must be mate or stalemate:
1098 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1100 // If the search is not aborted, update the transposition table,
1101 // history counters, and killer moves.
1102 if (AbortSearch || thread_should_stop(threadID))
1105 if (bestValue <= oldAlpha)
1106 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1108 else if (bestValue >= beta)
1110 BetaCounter.add(pos.side_to_move(), depth, threadID);
1111 Move m = ss[ply].pv[ply];
1112 if (ok_to_history(pos, m)) // Only non capture moves are considered
1114 update_history(pos, m, depth, movesSearched, moveCount);
1115 update_killers(m, ss[ply]);
1117 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1120 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1126 // search() is the search function for zero-width nodes.
1128 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1129 int ply, bool allowNullmove, int threadID) {
1131 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1132 assert(ply >= 0 && ply < PLY_MAX);
1133 assert(threadID >= 0 && threadID < ActiveThreads);
1137 // Initialize, and make an early exit in case of an aborted search,
1138 // an instant draw, maximum ply reached, etc.
1139 if (AbortSearch || thread_should_stop(threadID))
1143 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1145 init_node(pos, ss, ply, threadID);
1150 if (ply >= PLY_MAX - 1)
1151 return evaluate(pos, ei, threadID);
1153 // Mate distance pruning
1154 if (value_mated_in(ply) >= beta)
1157 if (value_mate_in(ply + 1) < beta)
1160 // Transposition table lookup
1161 const TTEntry* tte = TT.retrieve(pos);
1162 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1164 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1166 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1167 return value_from_tt(tte->value(), ply);
1170 Value approximateEval = quick_evaluate(pos);
1171 bool mateThreat = false;
1172 bool nullDrivenIID = false;
1173 bool isCheck = pos.is_check();
1179 && !value_is_mate(beta)
1180 && ok_to_do_nullmove(pos)
1181 && approximateEval >= beta - NullMoveMargin)
1183 ss[ply].currentMove = MOVE_NULL;
1186 pos.do_null_move(u);
1187 int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
1189 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1191 // Check for a null capture artifact, if the value without the null capture
1192 // is above beta then there is a good possibility that this is a cut-node.
1193 // We will do an IID later to find a ttMove.
1194 if ( UseNullDrivenIID
1196 && depth > 6 * OnePly
1197 &&!value_is_mate(nullValue)
1198 && ttMove == MOVE_NONE
1199 && ss[ply + 1].currentMove != MOVE_NONE
1200 && pos.move_is_capture(ss[ply + 1].currentMove)
1201 && pos.see(ss[ply + 1].currentMove) + nullValue >= beta)
1202 nullDrivenIID = true;
1204 pos.undo_null_move(u);
1206 if (value_is_mate(nullValue))
1208 /* Do not return unproven mates */
1210 else if (nullValue >= beta)
1212 if (depth < 6 * OnePly)
1215 // Do zugzwang verification search
1216 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1220 // The null move failed low, which means that we may be faced with
1221 // some kind of threat. If the previous move was reduced, check if
1222 // the move that refuted the null move was somehow connected to the
1223 // move which was reduced. If a connection is found, return a fail
1224 // low score (which will cause the reduced move to fail high in the
1225 // parent node, which will trigger a re-search with full depth).
1226 if (nullValue == value_mated_in(ply + 2))
1229 nullDrivenIID = false;
1231 ss[ply].threatMove = ss[ply + 1].currentMove;
1232 if ( depth < ThreatDepth
1233 && ss[ply - 1].reduction
1234 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1238 // Null move search not allowed, try razoring
1239 else if ( !value_is_mate(beta)
1240 && ( (approximateEval < beta - RazorMargin && depth < RazorDepth)
1241 ||(approximateEval < beta - PawnValueMidgame && depth <= OnePly)))
1243 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1248 // Go with internal iterative deepening if we don't have a TT move
1249 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1250 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1252 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1253 ttMove = ss[ply].pv[ply];
1255 else if (nullDrivenIID)
1257 // The null move failed low due to a suspicious capture. Perhaps we
1258 // are facing a null capture artifact due to the side to move change
1259 // and this is a cut-node. So it's a good time to search for a ttMove.
1260 Move tm = ss[ply].threatMove;
1262 assert(tm != MOVE_NONE);
1263 assert(ttMove == MOVE_NONE);
1265 search(pos, ss, beta, depth/2, ply, false, threadID);
1266 ttMove = ss[ply].pv[ply];
1267 ss[ply].threatMove = tm;
1270 // Initialize a MovePicker object for the current position, and prepare
1271 // to search all moves:
1272 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1274 Move move, movesSearched[256];
1276 Value value, bestValue = -VALUE_INFINITE;
1277 Bitboard dcCandidates = mp.discovered_check_candidates();
1278 Value futilityValue = VALUE_NONE;
1279 bool useFutilityPruning = UseFutilityPruning
1280 && depth < SelectiveDepth
1283 // Loop through all legal moves until no moves remain or a beta cutoff
1285 while ( bestValue < beta
1286 && (move = mp.get_next_move()) != MOVE_NONE
1287 && !thread_should_stop(threadID))
1289 assert(move_is_ok(move));
1291 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1292 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1293 bool moveIsCapture = pos.move_is_capture(move);
1295 movesSearched[moveCount++] = ss[ply].currentMove = move;
1297 // Decide the new search depth
1299 Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat, &dangerous);
1300 Depth newDepth = depth - OnePly + ext;
1303 if ( useFutilityPruning
1306 && !move_promotion(move))
1308 // History pruning. See ok_to_prune() definition.
1309 if ( moveCount >= 2 + int(depth)
1310 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1313 // Value based pruning.
1314 if (depth < 3 * OnePly && approximateEval < beta)
1316 if (futilityValue == VALUE_NONE)
1317 futilityValue = evaluate(pos, ei, threadID)
1318 + (depth < 2 * OnePly ? FutilityMargin1 : FutilityMargin2);
1320 if (futilityValue < beta)
1322 if (futilityValue > bestValue)
1323 bestValue = futilityValue;
1329 // Make and search the move
1331 pos.do_move(move, u, dcCandidates);
1333 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1334 // if the move fails high will be re-searched at full depth.
1335 if ( depth >= 2*OnePly
1336 && moveCount >= LMRNonPVMoves
1339 && !move_promotion(move)
1340 && !move_is_castle(move)
1341 && !move_is_killer(move, ss[ply]))
1343 ss[ply].reduction = OnePly;
1344 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1347 value = beta; // Just to trigger next condition
1349 if (value >= beta) // Go with full depth non-pv search
1351 ss[ply].reduction = Depth(0);
1352 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1354 pos.undo_move(move, u);
1356 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1359 if (value > bestValue)
1365 if (value == value_mate_in(ply + 1))
1366 ss[ply].mateKiller = move;
1370 if ( ActiveThreads > 1
1372 && depth >= MinimumSplitDepth
1374 && idle_thread_exists(threadID)
1376 && !thread_should_stop(threadID)
1377 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1378 &mp, dcCandidates, threadID, false))
1382 // All legal moves have been searched. A special case: If there were
1383 // no legal moves, it must be mate or stalemate.
1385 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1387 // If the search is not aborted, update the transposition table,
1388 // history counters, and killer moves.
1389 if (AbortSearch || thread_should_stop(threadID))
1392 if (bestValue < beta)
1393 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1396 BetaCounter.add(pos.side_to_move(), depth, threadID);
1397 Move m = ss[ply].pv[ply];
1398 if (ok_to_history(pos, m)) // Only non capture moves are considered
1400 update_history(pos, m, depth, movesSearched, moveCount);
1401 update_killers(m, ss[ply]);
1403 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1409 // qsearch() is the quiescence search function, which is called by the main
1410 // search function when the remaining depth is zero (or, to be more precise,
1411 // less than OnePly).
1413 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1414 Depth depth, int ply, int threadID) {
1416 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1417 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1419 assert(ply >= 0 && ply < PLY_MAX);
1420 assert(threadID >= 0 && threadID < ActiveThreads);
1424 // Initialize, and make an early exit in case of an aborted search,
1425 // an instant draw, maximum ply reached, etc.
1426 if (AbortSearch || thread_should_stop(threadID))
1429 init_node(pos, ss, ply, threadID);
1434 // Transposition table lookup
1435 const TTEntry* tte = TT.retrieve(pos);
1436 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1437 return value_from_tt(tte->value(), ply);
1439 // Evaluate the position statically
1440 bool isCheck = pos.is_check();
1441 Value staticValue = (isCheck ? -VALUE_INFINITE : evaluate(pos, ei, threadID));
1443 if (ply == PLY_MAX - 1)
1444 return evaluate(pos, ei, threadID);
1446 // Initialize "stand pat score", and return it immediately if it is
1448 Value bestValue = staticValue;
1450 if (bestValue >= beta)
1453 if (bestValue > alpha)
1456 // Initialize a MovePicker object for the current position, and prepare
1457 // to search the moves. Because the depth is <= 0 here, only captures,
1458 // queen promotions and checks (only if depth == 0) will be generated.
1459 bool pvNode = (beta - alpha != 1);
1460 MovePicker mp = MovePicker(pos, pvNode, MOVE_NONE, EmptySearchStack, depth, isCheck ? NULL : &ei);
1463 Bitboard dcCandidates = mp.discovered_check_candidates();
1464 bool enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1466 // Loop through the moves until no moves remain or a beta cutoff
1468 while ( alpha < beta
1469 && (move = mp.get_next_move()) != MOVE_NONE)
1471 assert(move_is_ok(move));
1474 ss[ply].currentMove = move;
1477 if ( UseQSearchFutilityPruning
1481 && !move_promotion(move)
1482 && !pos.move_is_check(move, dcCandidates)
1483 && !pos.move_is_passed_pawn_push(move))
1485 Value futilityValue = staticValue
1486 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1487 pos.endgame_value_of_piece_on(move_to(move)))
1488 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1490 + ei.futilityMargin;
1492 if (futilityValue < alpha)
1494 if (futilityValue > bestValue)
1495 bestValue = futilityValue;
1500 // Don't search captures and checks with negative SEE values
1502 && !move_promotion(move)
1503 && (pos.midgame_value_of_piece_on(move_from(move)) >
1504 pos.midgame_value_of_piece_on(move_to(move)))
1505 && pos.see(move) < 0)
1508 // Make and search the move.
1510 pos.do_move(move, u, dcCandidates);
1511 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1512 pos.undo_move(move, u);
1514 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1517 if (value > bestValue)
1528 // All legal moves have been searched. A special case: If we're in check
1529 // and no legal moves were found, it is checkmate:
1530 if (pos.is_check() && moveCount == 0) // Mate!
1531 return value_mated_in(ply);
1533 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1535 // Update transposition table
1536 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
1538 // Update killers only for good check moves
1539 Move m = ss[ply].currentMove;
1540 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1542 // Wrong to update history when depth is <= 0
1543 update_killers(m, ss[ply]);
1549 // sp_search() is used to search from a split point. This function is called
1550 // by each thread working at the split point. It is similar to the normal
1551 // search() function, but simpler. Because we have already probed the hash
1552 // table, done a null move search, and searched the first move before
1553 // splitting, we don't have to repeat all this work in sp_search(). We
1554 // also don't need to store anything to the hash table here: This is taken
1555 // care of after we return from the split point.
1557 void sp_search(SplitPoint *sp, int threadID) {
1559 assert(threadID >= 0 && threadID < ActiveThreads);
1560 assert(ActiveThreads > 1);
1562 Position pos = Position(sp->pos);
1563 SearchStack *ss = sp->sstack[threadID];
1566 bool isCheck = pos.is_check();
1567 bool useFutilityPruning = UseFutilityPruning
1568 && sp->depth < SelectiveDepth
1571 while ( sp->bestValue < sp->beta
1572 && !thread_should_stop(threadID)
1573 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1575 assert(move_is_ok(move));
1577 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1578 bool moveIsCapture = pos.move_is_capture(move);
1580 lock_grab(&(sp->lock));
1581 int moveCount = ++sp->moves;
1582 lock_release(&(sp->lock));
1584 ss[sp->ply].currentMove = move;
1586 // Decide the new search depth.
1588 Depth ext = extension(pos, move, false, moveIsCheck, false, false, &dangerous);
1589 Depth newDepth = sp->depth - OnePly + ext;
1592 if ( useFutilityPruning
1595 && !move_promotion(move)
1596 && moveCount >= 2 + int(sp->depth)
1597 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1600 // Make and search the move.
1602 pos.do_move(move, u, sp->dcCandidates);
1604 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1605 // if the move fails high will be re-searched at full depth.
1607 && moveCount >= LMRNonPVMoves
1609 && !move_promotion(move)
1610 && !move_is_castle(move)
1611 && !move_is_killer(move, ss[sp->ply]))
1613 ss[sp->ply].reduction = OnePly;
1614 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1617 value = sp->beta; // Just to trigger next condition
1619 if (value >= sp->beta) // Go with full depth non-pv search
1621 ss[sp->ply].reduction = Depth(0);
1622 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1624 pos.undo_move(move, u);
1626 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1628 if (thread_should_stop(threadID))
1632 lock_grab(&(sp->lock));
1633 if (value > sp->bestValue && !thread_should_stop(threadID))
1635 sp->bestValue = value;
1636 if (sp->bestValue >= sp->beta)
1638 sp_update_pv(sp->parentSstack, ss, sp->ply);
1639 for (int i = 0; i < ActiveThreads; i++)
1640 if (i != threadID && (i == sp->master || sp->slaves[i]))
1641 Threads[i].stop = true;
1643 sp->finished = true;
1646 lock_release(&(sp->lock));
1649 lock_grab(&(sp->lock));
1651 // If this is the master thread and we have been asked to stop because of
1652 // a beta cutoff higher up in the tree, stop all slave threads:
1653 if (sp->master == threadID && thread_should_stop(threadID))
1654 for (int i = 0; i < ActiveThreads; i++)
1656 Threads[i].stop = true;
1659 sp->slaves[threadID] = 0;
1661 lock_release(&(sp->lock));
1665 // sp_search_pv() is used to search from a PV split point. This function
1666 // is called by each thread working at the split point. It is similar to
1667 // the normal search_pv() function, but simpler. Because we have already
1668 // probed the hash table and searched the first move before splitting, we
1669 // don't have to repeat all this work in sp_search_pv(). We also don't
1670 // need to store anything to the hash table here: This is taken care of
1671 // after we return from the split point.
1673 void sp_search_pv(SplitPoint *sp, int threadID) {
1675 assert(threadID >= 0 && threadID < ActiveThreads);
1676 assert(ActiveThreads > 1);
1678 Position pos = Position(sp->pos);
1679 SearchStack *ss = sp->sstack[threadID];
1683 while ( sp->alpha < sp->beta
1684 && !thread_should_stop(threadID)
1685 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1687 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1688 bool moveIsCapture = pos.move_is_capture(move);
1690 assert(move_is_ok(move));
1693 ss[sp->ply].currentMoveCaptureValue =
1694 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1696 ss[sp->ply].currentMoveCaptureValue = Value(0);
1698 lock_grab(&(sp->lock));
1699 int moveCount = ++sp->moves;
1700 lock_release(&(sp->lock));
1702 ss[sp->ply].currentMove = move;
1704 // Decide the new search depth.
1706 Depth ext = extension(pos, move, true, moveIsCheck, false, false, &dangerous);
1707 Depth newDepth = sp->depth - OnePly + ext;
1709 // Make and search the move.
1711 pos.do_move(move, u, sp->dcCandidates);
1713 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1714 // if the move fails high will be re-searched at full depth.
1716 && moveCount >= LMRPVMoves
1718 && !move_promotion(move)
1719 && !move_is_castle(move)
1720 && !move_is_killer(move, ss[sp->ply]))
1722 ss[sp->ply].reduction = OnePly;
1723 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1726 value = sp->alpha + 1; // Just to trigger next condition
1728 if (value > sp->alpha) // Go with full depth non-pv search
1730 ss[sp->ply].reduction = Depth(0);
1731 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1733 if (value > sp->alpha && value < sp->beta)
1735 // When the search fails high at ply 1 while searching the first
1736 // move at the root, set the flag failHighPly1. This is used for
1737 // time managment: We don't want to stop the search early in
1738 // such cases, because resolving the fail high at ply 1 could
1739 // result in a big drop in score at the root.
1740 if (sp->ply == 1 && RootMoveNumber == 1)
1741 Threads[threadID].failHighPly1 = true;
1743 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1744 Threads[threadID].failHighPly1 = false;
1747 pos.undo_move(move, u);
1749 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1751 if (thread_should_stop(threadID))
1755 lock_grab(&(sp->lock));
1756 if (value > sp->bestValue && !thread_should_stop(threadID))
1758 sp->bestValue = value;
1759 if (value > sp->alpha)
1762 sp_update_pv(sp->parentSstack, ss, sp->ply);
1763 if (value == value_mate_in(sp->ply + 1))
1764 ss[sp->ply].mateKiller = move;
1766 if(value >= sp->beta)
1768 for(int i = 0; i < ActiveThreads; i++)
1769 if(i != threadID && (i == sp->master || sp->slaves[i]))
1770 Threads[i].stop = true;
1772 sp->finished = true;
1775 // If we are at ply 1, and we are searching the first root move at
1776 // ply 0, set the 'Problem' variable if the score has dropped a lot
1777 // (from the computer's point of view) since the previous iteration:
1778 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1781 lock_release(&(sp->lock));
1784 lock_grab(&(sp->lock));
1786 // If this is the master thread and we have been asked to stop because of
1787 // a beta cutoff higher up in the tree, stop all slave threads:
1788 if (sp->master == threadID && thread_should_stop(threadID))
1789 for (int i = 0; i < ActiveThreads; i++)
1791 Threads[i].stop = true;
1794 sp->slaves[threadID] = 0;
1796 lock_release(&(sp->lock));
1799 /// The BetaCounterType class
1801 BetaCounterType::BetaCounterType() { clear(); }
1803 void BetaCounterType::clear() {
1805 for (int i = 0; i < THREAD_MAX; i++)
1806 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1809 void BetaCounterType::add(Color us, Depth d, int threadID) {
1811 // Weighted count based on depth
1812 hits[threadID][us] += int(d);
1815 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1818 for (int i = 0; i < THREAD_MAX; i++)
1821 their += hits[i][opposite_color(us)];
1826 /// The RootMove class
1830 RootMove::RootMove() {
1831 nodes = cumulativeNodes = 0ULL;
1834 // RootMove::operator<() is the comparison function used when
1835 // sorting the moves. A move m1 is considered to be better
1836 // than a move m2 if it has a higher score, or if the moves
1837 // have equal score but m1 has the higher node count.
1839 bool RootMove::operator<(const RootMove& m) {
1841 if (score != m.score)
1842 return (score < m.score);
1844 return theirBeta <= m.theirBeta;
1847 /// The RootMoveList class
1851 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1853 MoveStack mlist[MaxRootMoves];
1854 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1856 // Generate all legal moves
1857 int lm_count = generate_legal_moves(pos, mlist);
1859 // Add each move to the moves[] array
1860 for (int i = 0; i < lm_count; i++)
1862 bool includeMove = includeAllMoves;
1864 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1865 includeMove = (searchMoves[k] == mlist[i].move);
1869 // Find a quick score for the move
1871 SearchStack ss[PLY_MAX_PLUS_2];
1873 moves[count].move = mlist[i].move;
1874 moves[count].nodes = 0ULL;
1875 pos.do_move(moves[count].move, u);
1876 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1878 pos.undo_move(moves[count].move, u);
1879 moves[count].pv[0] = moves[i].move;
1880 moves[count].pv[1] = MOVE_NONE; // FIXME
1888 // Simple accessor methods for the RootMoveList class
1890 inline Move RootMoveList::get_move(int moveNum) const {
1891 return moves[moveNum].move;
1894 inline Value RootMoveList::get_move_score(int moveNum) const {
1895 return moves[moveNum].score;
1898 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1899 moves[moveNum].score = score;
1902 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1903 moves[moveNum].nodes = nodes;
1904 moves[moveNum].cumulativeNodes += nodes;
1907 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
1908 moves[moveNum].ourBeta = our;
1909 moves[moveNum].theirBeta = their;
1912 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1914 for(j = 0; pv[j] != MOVE_NONE; j++)
1915 moves[moveNum].pv[j] = pv[j];
1916 moves[moveNum].pv[j] = MOVE_NONE;
1919 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1920 return moves[moveNum].pv[i];
1923 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1924 return moves[moveNum].cumulativeNodes;
1927 inline int RootMoveList::move_count() const {
1932 // RootMoveList::scan_for_easy_move() is called at the end of the first
1933 // iteration, and is used to detect an "easy move", i.e. a move which appears
1934 // to be much bester than all the rest. If an easy move is found, the move
1935 // is returned, otherwise the function returns MOVE_NONE. It is very
1936 // important that this function is called at the right moment: The code
1937 // assumes that the first iteration has been completed and the moves have
1938 // been sorted. This is done in RootMoveList c'tor.
1940 Move RootMoveList::scan_for_easy_move() const {
1947 // moves are sorted so just consider the best and the second one
1948 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
1954 // RootMoveList::sort() sorts the root move list at the beginning of a new
1957 inline void RootMoveList::sort() {
1959 sort_multipv(count - 1); // all items
1963 // RootMoveList::sort_multipv() sorts the first few moves in the root move
1964 // list by their scores and depths. It is used to order the different PVs
1965 // correctly in MultiPV mode.
1967 void RootMoveList::sort_multipv(int n) {
1969 for (int i = 1; i <= n; i++)
1971 RootMove rm = moves[i];
1973 for (j = i; j > 0 && moves[j-1] < rm; j--)
1974 moves[j] = moves[j-1];
1980 // init_search_stack() initializes a search stack at the beginning of a
1981 // new search from the root.
1982 void init_search_stack(SearchStack& ss) {
1984 ss.pv[0] = MOVE_NONE;
1985 ss.pv[1] = MOVE_NONE;
1986 ss.currentMove = MOVE_NONE;
1987 ss.threatMove = MOVE_NONE;
1988 ss.reduction = Depth(0);
1989 for (int j = 0; j < KILLER_MAX; j++)
1990 ss.killers[j] = MOVE_NONE;
1993 void init_search_stack(SearchStack ss[]) {
1995 for (int i = 0; i < 3; i++)
1997 ss[i].pv[i] = MOVE_NONE;
1998 ss[i].pv[i+1] = MOVE_NONE;
1999 ss[i].currentMove = MOVE_NONE;
2000 ss[i].threatMove = MOVE_NONE;
2001 ss[i].reduction = Depth(0);
2002 for (int j = 0; j < KILLER_MAX; j++)
2003 ss[i].killers[j] = MOVE_NONE;
2008 // init_node() is called at the beginning of all the search functions
2009 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2010 // stack object corresponding to the current node. Once every
2011 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2012 // for user input and checks whether it is time to stop the search.
2014 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID) {
2015 assert(ply >= 0 && ply < PLY_MAX);
2016 assert(threadID >= 0 && threadID < ActiveThreads);
2018 Threads[threadID].nodes++;
2022 if(NodesSincePoll >= NodesBetweenPolls) {
2027 ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE;
2028 ss[ply+2].mateKiller = MOVE_NONE;
2029 ss[ply].threatMove = MOVE_NONE;
2030 ss[ply].reduction = Depth(0);
2031 ss[ply].currentMoveCaptureValue = Value(0);
2032 for (int j = 0; j < KILLER_MAX; j++)
2033 ss[ply+2].killers[j] = MOVE_NONE;
2035 if(Threads[threadID].printCurrentLine)
2036 print_current_line(ss, ply, threadID);
2040 // update_pv() is called whenever a search returns a value > alpha. It
2041 // updates the PV in the SearchStack object corresponding to the current
2044 void update_pv(SearchStack ss[], int ply) {
2045 assert(ply >= 0 && ply < PLY_MAX);
2047 ss[ply].pv[ply] = ss[ply].currentMove;
2049 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2050 ss[ply].pv[p] = ss[ply+1].pv[p];
2051 ss[ply].pv[p] = MOVE_NONE;
2055 // sp_update_pv() is a variant of update_pv for use at split points. The
2056 // difference between the two functions is that sp_update_pv also updates
2057 // the PV at the parent node.
2059 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2060 assert(ply >= 0 && ply < PLY_MAX);
2062 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2064 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2065 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2066 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2070 // connected_moves() tests whether two moves are 'connected' in the sense
2071 // that the first move somehow made the second move possible (for instance
2072 // if the moving piece is the same in both moves). The first move is
2073 // assumed to be the move that was made to reach the current position, while
2074 // the second move is assumed to be a move from the current position.
2076 bool connected_moves(const Position &pos, Move m1, Move m2) {
2077 Square f1, t1, f2, t2;
2079 assert(move_is_ok(m1));
2080 assert(move_is_ok(m2));
2085 // Case 1: The moving piece is the same in both moves.
2091 // Case 2: The destination square for m2 was vacated by m1.
2097 // Case 3: Moving through the vacated square:
2098 if(piece_is_slider(pos.piece_on(f2)) &&
2099 bit_is_set(squares_between(f2, t2), f1))
2102 // Case 4: The destination square for m2 is attacked by the moving piece
2104 if(pos.piece_attacks_square(t1, t2))
2107 // Case 5: Discovered check, checking piece is the piece moved in m1:
2108 if(piece_is_slider(pos.piece_on(t1)) &&
2109 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2111 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2113 Bitboard occ = pos.occupied_squares();
2114 Color us = pos.side_to_move();
2115 Square ksq = pos.king_square(us);
2116 clear_bit(&occ, f2);
2117 if(pos.type_of_piece_on(t1) == BISHOP) {
2118 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2121 else if(pos.type_of_piece_on(t1) == ROOK) {
2122 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2126 assert(pos.type_of_piece_on(t1) == QUEEN);
2127 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2136 // value_is_mate() checks if the given value is a mate one
2137 // eventually compensated for the ply.
2139 bool value_is_mate(Value value) {
2141 assert(abs(value) <= VALUE_INFINITE);
2143 return value <= value_mated_in(PLY_MAX)
2144 || value >= value_mate_in(PLY_MAX);
2148 // move_is_killer() checks if the given move is among the
2149 // killer moves of that ply.
2151 bool move_is_killer(Move m, const SearchStack& ss) {
2153 const Move* k = ss.killers;
2154 for (int i = 0; i < KILLER_MAX; i++, k++)
2162 // extension() decides whether a move should be searched with normal depth,
2163 // or with extended depth. Certain classes of moves (checking moves, in
2164 // particular) are searched with bigger depth than ordinary moves and in
2165 // any case are marked as 'dangerous'. Note that also if a move is not
2166 // extended, as example because the corresponding UCI option is set to zero,
2167 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2169 Depth extension(const Position &pos, Move m, bool pvNode, bool check,
2170 bool singleReply, bool mateThreat, bool* dangerous) {
2172 assert(m != MOVE_NONE);
2174 Depth result = Depth(0);
2175 *dangerous = check || singleReply || mateThreat;
2178 result += CheckExtension[pvNode];
2181 result += SingleReplyExtension[pvNode];
2184 result += MateThreatExtension[pvNode];
2186 if (pos.move_is_pawn_push_to_7th(m))
2188 result += PawnPushTo7thExtension[pvNode];
2191 if (pos.move_is_passed_pawn_push(m))
2193 result += PassedPawnExtension[pvNode];
2197 if ( pos.move_is_capture(m)
2198 && pos.type_of_piece_on(move_to(m)) != PAWN
2199 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2200 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2201 && !move_promotion(m)
2204 result += PawnEndgameExtension[pvNode];
2209 && pos.move_is_capture(m)
2210 && pos.type_of_piece_on(move_to(m)) != PAWN
2217 return Min(result, OnePly);
2221 // ok_to_do_nullmove() looks at the current position and decides whether
2222 // doing a 'null move' should be allowed. In order to avoid zugzwang
2223 // problems, null moves are not allowed when the side to move has very
2224 // little material left. Currently, the test is a bit too simple: Null
2225 // moves are avoided only when the side to move has only pawns left. It's
2226 // probably a good idea to avoid null moves in at least some more
2227 // complicated endgames, e.g. KQ vs KR. FIXME
2229 bool ok_to_do_nullmove(const Position &pos) {
2230 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2236 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2237 // non-tactical moves late in the move list close to the leaves are
2238 // candidates for pruning.
2240 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2241 Square mfrom, mto, tfrom, tto;
2243 assert(move_is_ok(m));
2244 assert(threat == MOVE_NONE || move_is_ok(threat));
2245 assert(!move_promotion(m));
2246 assert(!pos.move_is_check(m));
2247 assert(!pos.move_is_capture(m));
2248 assert(!pos.move_is_passed_pawn_push(m));
2249 assert(d >= OnePly);
2251 mfrom = move_from(m);
2253 tfrom = move_from(threat);
2254 tto = move_to(threat);
2256 // Case 1: Castling moves are never pruned.
2257 if (move_is_castle(m))
2260 // Case 2: Don't prune moves which move the threatened piece
2261 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2264 // Case 3: If the threatened piece has value less than or equal to the
2265 // value of the threatening piece, don't prune move which defend it.
2266 if ( !PruneDefendingMoves
2267 && threat != MOVE_NONE
2268 && pos.move_is_capture(threat)
2269 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2270 || pos.type_of_piece_on(tfrom) == KING)
2271 && pos.move_attacks_square(m, tto))
2274 // Case 4: Don't prune moves with good history.
2275 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2278 // Case 5: If the moving piece in the threatened move is a slider, don't
2279 // prune safe moves which block its ray.
2280 if ( !PruneBlockingMoves
2281 && threat != MOVE_NONE
2282 && piece_is_slider(pos.piece_on(tfrom))
2283 && bit_is_set(squares_between(tfrom, tto), mto) && pos.see(m) >= 0)
2290 // ok_to_use_TT() returns true if a transposition table score
2291 // can be used at a given point in search.
2293 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2295 Value v = value_from_tt(tte->value(), ply);
2297 return ( tte->depth() >= depth
2298 || v >= Max(value_mate_in(100), beta)
2299 || v < Min(value_mated_in(100), beta))
2301 && ( (is_lower_bound(tte->type()) && v >= beta)
2302 || (is_upper_bound(tte->type()) && v < beta));
2306 // ok_to_history() returns true if a move m can be stored
2307 // in history. Should be a non capturing move nor a promotion.
2309 bool ok_to_history(const Position& pos, Move m) {
2311 return !pos.move_is_capture(m) && !move_promotion(m);
2315 // update_history() registers a good move that produced a beta-cutoff
2316 // in history and marks as failures all the other moves of that ply.
2318 void update_history(const Position& pos, Move m, Depth depth,
2319 Move movesSearched[], int moveCount) {
2321 H.success(pos.piece_on(move_from(m)), m, depth);
2323 for (int i = 0; i < moveCount - 1; i++)
2325 assert(m != movesSearched[i]);
2326 if (ok_to_history(pos, movesSearched[i]))
2327 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2332 // update_killers() add a good move that produced a beta-cutoff
2333 // among the killer moves of that ply.
2335 void update_killers(Move m, SearchStack& ss) {
2337 if (m == ss.killers[0])
2340 for (int i = KILLER_MAX - 1; i > 0; i--)
2341 ss.killers[i] = ss.killers[i - 1];
2346 // fail_high_ply_1() checks if some thread is currently resolving a fail
2347 // high at ply 1 at the node below the first root node. This information
2348 // is used for time managment.
2350 bool fail_high_ply_1() {
2351 for(int i = 0; i < ActiveThreads; i++)
2352 if(Threads[i].failHighPly1)
2358 // current_search_time() returns the number of milliseconds which have passed
2359 // since the beginning of the current search.
2361 int current_search_time() {
2362 return get_system_time() - SearchStartTime;
2366 // nps() computes the current nodes/second count.
2369 int t = current_search_time();
2370 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2374 // poll() performs two different functions: It polls for user input, and it
2375 // looks at the time consumed so far and decides if it's time to abort the
2380 static int lastInfoTime;
2381 int t = current_search_time();
2386 // We are line oriented, don't read single chars
2387 std::string command;
2388 if (!std::getline(std::cin, command))
2391 if (command == "quit")
2394 PonderSearch = false;
2397 else if(command == "stop")
2400 PonderSearch = false;
2402 else if(command == "ponderhit")
2405 // Print search information
2409 else if (lastInfoTime > t)
2410 // HACK: Must be a new search where we searched less than
2411 // NodesBetweenPolls nodes during the first second of search.
2414 else if (t - lastInfoTime >= 1000)
2421 if (dbg_show_hit_rate)
2422 dbg_print_hit_rate();
2424 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2425 << " time " << t << " hashfull " << TT.full() << std::endl;
2426 lock_release(&IOLock);
2427 if (ShowCurrentLine)
2428 Threads[0].printCurrentLine = true;
2430 // Should we stop the search?
2434 bool overTime = t > AbsoluteMaxSearchTime
2435 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
2436 || ( !FailHigh && !fail_high_ply_1() && !Problem
2437 && t > 6*(MaxSearchTime + ExtraSearchTime));
2439 if ( (Iteration >= 2 && (!InfiniteSearch && overTime))
2440 || (ExactMaxTime && t >= ExactMaxTime)
2441 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2446 // ponderhit() is called when the program is pondering (i.e. thinking while
2447 // it's the opponent's turn to move) in order to let the engine know that
2448 // it correctly predicted the opponent's move.
2451 int t = current_search_time();
2452 PonderSearch = false;
2453 if(Iteration >= 2 &&
2454 (!InfiniteSearch && (StopOnPonderhit ||
2455 t > AbsoluteMaxSearchTime ||
2456 (RootMoveNumber == 1 &&
2457 t > MaxSearchTime + ExtraSearchTime) ||
2458 (!FailHigh && !fail_high_ply_1() && !Problem &&
2459 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2464 // print_current_line() prints the current line of search for a given
2465 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2467 void print_current_line(SearchStack ss[], int ply, int threadID) {
2468 assert(ply >= 0 && ply < PLY_MAX);
2469 assert(threadID >= 0 && threadID < ActiveThreads);
2471 if(!Threads[threadID].idle) {
2473 std::cout << "info currline " << (threadID + 1);
2474 for(int p = 0; p < ply; p++)
2475 std::cout << " " << ss[p].currentMove;
2476 std::cout << std::endl;
2477 lock_release(&IOLock);
2479 Threads[threadID].printCurrentLine = false;
2480 if(threadID + 1 < ActiveThreads)
2481 Threads[threadID + 1].printCurrentLine = true;
2485 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2486 // while the program is pondering. The point is to work around a wrinkle in
2487 // the UCI protocol: When pondering, the engine is not allowed to give a
2488 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2489 // We simply wait here until one of these commands is sent, and return,
2490 // after which the bestmove and pondermove will be printed (in id_loop()).
2492 void wait_for_stop_or_ponderhit() {
2493 std::string command;
2496 if(!std::getline(std::cin, command))
2499 if(command == "quit") {
2500 OpeningBook.close();
2505 else if(command == "ponderhit" || command == "stop")
2511 // idle_loop() is where the threads are parked when they have no work to do.
2512 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2513 // object for which the current thread is the master.
2515 void idle_loop(int threadID, SplitPoint *waitSp) {
2516 assert(threadID >= 0 && threadID < THREAD_MAX);
2518 Threads[threadID].running = true;
2521 if(AllThreadsShouldExit && threadID != 0)
2524 // If we are not thinking, wait for a condition to be signaled instead
2525 // of wasting CPU time polling for work:
2526 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2527 #if !defined(_MSC_VER)
2528 pthread_mutex_lock(&WaitLock);
2529 if(Idle || threadID >= ActiveThreads)
2530 pthread_cond_wait(&WaitCond, &WaitLock);
2531 pthread_mutex_unlock(&WaitLock);
2533 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2537 // If this thread has been assigned work, launch a search:
2538 if(Threads[threadID].workIsWaiting) {
2539 Threads[threadID].workIsWaiting = false;
2540 if(Threads[threadID].splitPoint->pvNode)
2541 sp_search_pv(Threads[threadID].splitPoint, threadID);
2543 sp_search(Threads[threadID].splitPoint, threadID);
2544 Threads[threadID].idle = true;
2547 // If this thread is the master of a split point and all threads have
2548 // finished their work at this split point, return from the idle loop:
2549 if(waitSp != NULL && waitSp->cpus == 0)
2553 Threads[threadID].running = false;
2557 // init_split_point_stack() is called during program initialization, and
2558 // initializes all split point objects.
2560 void init_split_point_stack() {
2561 for(int i = 0; i < THREAD_MAX; i++)
2562 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2563 SplitPointStack[i][j].parent = NULL;
2564 lock_init(&(SplitPointStack[i][j].lock), NULL);
2569 // destroy_split_point_stack() is called when the program exits, and
2570 // destroys all locks in the precomputed split point objects.
2572 void destroy_split_point_stack() {
2573 for(int i = 0; i < THREAD_MAX; i++)
2574 for(int j = 0; j < MaxActiveSplitPoints; j++)
2575 lock_destroy(&(SplitPointStack[i][j].lock));
2579 // thread_should_stop() checks whether the thread with a given threadID has
2580 // been asked to stop, directly or indirectly. This can happen if a beta
2581 // cutoff has occured in thre thread's currently active split point, or in
2582 // some ancestor of the current split point.
2584 bool thread_should_stop(int threadID) {
2585 assert(threadID >= 0 && threadID < ActiveThreads);
2589 if(Threads[threadID].stop)
2591 if(ActiveThreads <= 2)
2593 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2595 Threads[threadID].stop = true;
2602 // thread_is_available() checks whether the thread with threadID "slave" is
2603 // available to help the thread with threadID "master" at a split point. An
2604 // obvious requirement is that "slave" must be idle. With more than two
2605 // threads, this is not by itself sufficient: If "slave" is the master of
2606 // some active split point, it is only available as a slave to the other
2607 // threads which are busy searching the split point at the top of "slave"'s
2608 // split point stack (the "helpful master concept" in YBWC terminology).
2610 bool thread_is_available(int slave, int master) {
2611 assert(slave >= 0 && slave < ActiveThreads);
2612 assert(master >= 0 && master < ActiveThreads);
2613 assert(ActiveThreads > 1);
2615 if(!Threads[slave].idle || slave == master)
2618 if(Threads[slave].activeSplitPoints == 0)
2619 // No active split points means that the thread is available as a slave
2620 // for any other thread.
2623 if(ActiveThreads == 2)
2626 // Apply the "helpful master" concept if possible.
2627 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2634 // idle_thread_exists() tries to find an idle thread which is available as
2635 // a slave for the thread with threadID "master".
2637 bool idle_thread_exists(int master) {
2638 assert(master >= 0 && master < ActiveThreads);
2639 assert(ActiveThreads > 1);
2641 for(int i = 0; i < ActiveThreads; i++)
2642 if(thread_is_available(i, master))
2648 // split() does the actual work of distributing the work at a node between
2649 // several threads at PV nodes. If it does not succeed in splitting the
2650 // node (because no idle threads are available, or because we have no unused
2651 // split point objects), the function immediately returns false. If
2652 // splitting is possible, a SplitPoint object is initialized with all the
2653 // data that must be copied to the helper threads (the current position and
2654 // search stack, alpha, beta, the search depth, etc.), and we tell our
2655 // helper threads that they have been assigned work. This will cause them
2656 // to instantly leave their idle loops and call sp_search_pv(). When all
2657 // threads have returned from sp_search_pv (or, equivalently, when
2658 // splitPoint->cpus becomes 0), split() returns true.
2660 bool split(const Position &p, SearchStack *sstck, int ply,
2661 Value *alpha, Value *beta, Value *bestValue,
2662 Depth depth, int *moves,
2663 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2665 assert(sstck != NULL);
2666 assert(ply >= 0 && ply < PLY_MAX);
2667 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2668 assert(!pvNode || *alpha < *beta);
2669 assert(*beta <= VALUE_INFINITE);
2670 assert(depth > Depth(0));
2671 assert(master >= 0 && master < ActiveThreads);
2672 assert(ActiveThreads > 1);
2674 SplitPoint *splitPoint;
2679 // If no other thread is available to help us, or if we have too many
2680 // active split points, don't split:
2681 if(!idle_thread_exists(master) ||
2682 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2683 lock_release(&MPLock);
2687 // Pick the next available split point object from the split point stack:
2688 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2689 Threads[master].activeSplitPoints++;
2691 // Initialize the split point object:
2692 splitPoint->parent = Threads[master].splitPoint;
2693 splitPoint->finished = false;
2694 splitPoint->ply = ply;
2695 splitPoint->depth = depth;
2696 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2697 splitPoint->beta = *beta;
2698 splitPoint->pvNode = pvNode;
2699 splitPoint->dcCandidates = dcCandidates;
2700 splitPoint->bestValue = *bestValue;
2701 splitPoint->master = master;
2702 splitPoint->mp = mp;
2703 splitPoint->moves = *moves;
2704 splitPoint->cpus = 1;
2705 splitPoint->pos.copy(p);
2706 splitPoint->parentSstack = sstck;
2707 for(i = 0; i < ActiveThreads; i++)
2708 splitPoint->slaves[i] = 0;
2710 // Copy the current position and the search stack to the master thread:
2711 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2712 Threads[master].splitPoint = splitPoint;
2714 // Make copies of the current position and search stack for each thread:
2715 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2717 if(thread_is_available(i, master)) {
2718 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2719 Threads[i].splitPoint = splitPoint;
2720 splitPoint->slaves[i] = 1;
2724 // Tell the threads that they have work to do. This will make them leave
2726 for(i = 0; i < ActiveThreads; i++)
2727 if(i == master || splitPoint->slaves[i]) {
2728 Threads[i].workIsWaiting = true;
2729 Threads[i].idle = false;
2730 Threads[i].stop = false;
2733 lock_release(&MPLock);
2735 // Everything is set up. The master thread enters the idle loop, from
2736 // which it will instantly launch a search, because its workIsWaiting
2737 // slot is 'true'. We send the split point as a second parameter to the
2738 // idle loop, which means that the main thread will return from the idle
2739 // loop when all threads have finished their work at this split point
2740 // (i.e. when // splitPoint->cpus == 0).
2741 idle_loop(master, splitPoint);
2743 // We have returned from the idle loop, which means that all threads are
2744 // finished. Update alpha, beta and bestvalue, and return:
2746 if(pvNode) *alpha = splitPoint->alpha;
2747 *beta = splitPoint->beta;
2748 *bestValue = splitPoint->bestValue;
2749 Threads[master].stop = false;
2750 Threads[master].idle = false;
2751 Threads[master].activeSplitPoints--;
2752 Threads[master].splitPoint = splitPoint->parent;
2753 lock_release(&MPLock);
2759 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2760 // to start a new search from the root.
2762 void wake_sleeping_threads() {
2763 if(ActiveThreads > 1) {
2764 for(int i = 1; i < ActiveThreads; i++) {
2765 Threads[i].idle = true;
2766 Threads[i].workIsWaiting = false;
2768 #if !defined(_MSC_VER)
2769 pthread_mutex_lock(&WaitLock);
2770 pthread_cond_broadcast(&WaitCond);
2771 pthread_mutex_unlock(&WaitLock);
2773 for(int i = 1; i < THREAD_MAX; i++)
2774 SetEvent(SitIdleEvent[i]);
2780 // init_thread() is the function which is called when a new thread is
2781 // launched. It simply calls the idle_loop() function with the supplied
2782 // threadID. There are two versions of this function; one for POSIX threads
2783 // and one for Windows threads.
2785 #if !defined(_MSC_VER)
2787 void *init_thread(void *threadID) {
2788 idle_loop(*(int *)threadID, NULL);
2794 DWORD WINAPI init_thread(LPVOID threadID) {
2795 idle_loop(*(int *)threadID, NULL);