2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
42 #include "ucioption.h"
48 //// Local definitions
55 // IterationInfoType stores search results for each iteration
57 // Because we use relatively small (dynamic) aspiration window,
58 // there happens many fail highs and fail lows in root. And
59 // because we don't do researches in those cases, "value" stored
60 // here is not necessarily exact. Instead in case of fail high/low
61 // we guess what the right value might be and store our guess
62 // as a "speculated value" and then move on. Speculated values are
63 // used just to calculate aspiration window width, so also if are
64 // not exact is not big a problem.
66 struct IterationInfoType {
68 IterationInfoType(Value v = Value(0), Value sv = Value(0))
69 : value(v), speculatedValue(sv) {}
71 Value value, speculatedValue;
75 // The BetaCounterType class is used to order moves at ply one.
76 // Apart for the first one that has its score, following moves
77 // normally have score -VALUE_INFINITE, so are ordered according
78 // to the number of beta cutoffs occurred under their subtree during
79 // the last iteration. The counters are per thread variables to avoid
80 // concurrent accessing under SMP case.
82 struct BetaCounterType {
86 void add(Color us, Depth d, int threadID);
87 void read(Color us, int64_t& our, int64_t& their);
91 // The RootMove class is used for moves at the root at the tree. For each
92 // root move, we store a score, a node count, and a PV (really a refutation
93 // in the case of moves which fail low).
97 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
99 // RootMove::operator<() is the comparison function used when
100 // sorting the moves. A move m1 is considered to be better
101 // than a move m2 if it has a higher score, or if the moves
102 // have equal score but m1 has the higher node count.
103 bool operator<(const RootMove& m) const {
105 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
110 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
111 Move pv[PLY_MAX_PLUS_2];
115 // The RootMoveList class is essentially an array of RootMove objects, with
116 // a handful of methods for accessing the data in the individual moves.
121 RootMoveList(Position& pos, Move searchMoves[]);
123 int move_count() const { return count; }
124 Move get_move(int moveNum) const { return moves[moveNum].move; }
125 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
126 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
127 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
128 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
130 void set_move_nodes(int moveNum, int64_t nodes);
131 void set_beta_counters(int moveNum, int64_t our, int64_t their);
132 void set_move_pv(int moveNum, const Move pv[]);
134 void sort_multipv(int n);
137 static const int MaxRootMoves = 500;
138 RootMove moves[MaxRootMoves];
145 // Search depth at iteration 1
146 const Depth InitialDepth = OnePly;
148 // Depth limit for selective search
149 const Depth SelectiveDepth = 7 * OnePly;
151 // Use internal iterative deepening?
152 const bool UseIIDAtPVNodes = true;
153 const bool UseIIDAtNonPVNodes = true;
155 // Internal iterative deepening margin. At Non-PV moves, when
156 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
157 // search when the static evaluation is at most IIDMargin below beta.
158 const Value IIDMargin = Value(0x100);
160 // Easy move margin. An easy move candidate must be at least this much
161 // better than the second best move.
162 const Value EasyMoveMargin = Value(0x200);
164 // Problem margin. If the score of the first move at iteration N+1 has
165 // dropped by more than this since iteration N, the boolean variable
166 // "Problem" is set to true, which will make the program spend some extra
167 // time looking for a better move.
168 const Value ProblemMargin = Value(0x28);
170 // No problem margin. If the boolean "Problem" is true, and a new move
171 // is found at the root which is less than NoProblemMargin worse than the
172 // best move from the previous iteration, Problem is set back to false.
173 const Value NoProblemMargin = Value(0x14);
175 // Null move margin. A null move search will not be done if the static
176 // evaluation of the position is more than NullMoveMargin below beta.
177 const Value NullMoveMargin = Value(0x200);
179 // If the TT move is at least SingleReplyMargin better then the
180 // remaining ones we will extend it.
181 const Value SingleReplyMargin = Value(0x20);
183 // Margins for futility pruning in the quiescence search, and at frontier
184 // and near frontier nodes.
185 const Value FutilityMarginQS = Value(0x80);
187 // Each move futility margin is decreased
188 const Value IncrementalFutilityMargin = Value(0x8);
190 // Depth limit for razoring
191 const Depth RazorDepth = 4 * OnePly;
193 /// Variables initialized by UCI options
195 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
196 int LMRPVMoves, LMRNonPVMoves;
198 // Depth limit for use of dynamic threat detection
201 // Last seconds noise filtering (LSN)
202 const bool UseLSNFiltering = true;
203 const int LSNTime = 4000; // In milliseconds
204 const Value LSNValue = value_from_centipawns(200);
205 bool loseOnTime = false;
207 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
208 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
209 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
211 // Iteration counters
213 BetaCounterType BetaCounter;
215 // Scores and number of times the best move changed for each iteration
216 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
217 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
222 // Time managment variables
225 int MaxNodes, MaxDepth;
226 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
227 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
228 bool AbortSearch, Quit;
229 bool FailHigh, FailLow, Problem;
231 // Show current line?
232 bool ShowCurrentLine;
236 std::ofstream LogFile;
238 // MP related variables
239 int ActiveThreads = 1;
240 Depth MinimumSplitDepth;
241 int MaxThreadsPerSplitPoint;
242 Thread Threads[THREAD_MAX];
245 bool AllThreadsShouldExit = false;
246 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
249 #if !defined(_MSC_VER)
250 pthread_cond_t WaitCond;
251 pthread_mutex_t WaitLock;
253 HANDLE SitIdleEvent[THREAD_MAX];
256 // Node counters, used only by thread[0] but try to keep in different
257 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
259 int NodesBetweenPolls = 30000;
267 Value id_loop(const Position& pos, Move searchMoves[]);
268 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
269 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
270 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
271 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 void sp_search(SplitPoint* sp, int threadID);
273 void sp_search_pv(SplitPoint* sp, int threadID);
274 void init_node(SearchStack ss[], int ply, int threadID);
275 void update_pv(SearchStack ss[], int ply);
276 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
277 bool connected_moves(const Position& pos, Move m1, Move m2);
278 bool value_is_mate(Value value);
279 bool move_is_killer(Move m, const SearchStack& ss);
280 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
281 bool ok_to_do_nullmove(const Position& pos);
282 bool ok_to_prune(const Position& pos, Move m, Move threat);
283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
284 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
285 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
286 void update_killers(Move m, SearchStack& ss);
288 bool fail_high_ply_1();
289 int current_search_time();
293 void print_current_line(SearchStack ss[], int ply, int threadID);
294 void wait_for_stop_or_ponderhit();
295 void init_ss_array(SearchStack ss[]);
297 void idle_loop(int threadID, SplitPoint* waitSp);
298 void init_split_point_stack();
299 void destroy_split_point_stack();
300 bool thread_should_stop(int threadID);
301 bool thread_is_available(int slave, int master);
302 bool idle_thread_exists(int master);
303 bool split(const Position& pos, SearchStack* ss, int ply,
304 Value *alpha, Value *beta, Value *bestValue,
305 const Value futilityValue, Depth depth, int *moves,
306 MovePicker *mp, int master, bool pvNode);
307 void wake_sleeping_threads();
309 #if !defined(_MSC_VER)
310 void *init_thread(void *threadID);
312 DWORD WINAPI init_thread(LPVOID threadID);
323 static double lnArray[512];
325 inline double ln(int i)
330 /// perft() is our utility to verify move generation is bug free. All the legal
331 /// moves up to given depth are generated and counted and the sum returned.
333 int perft(Position& pos, Depth depth)
337 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
339 // If we are at the last ply we don't need to do and undo
340 // the moves, just to count them.
341 if (depth <= OnePly) // Replace with '<' to test also qsearch
343 while (mp.get_next_move()) sum++;
347 // Loop through all legal moves
349 while ((move = mp.get_next_move()) != MOVE_NONE)
352 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
353 sum += perft(pos, depth - OnePly);
360 /// think() is the external interface to Stockfish's search, and is called when
361 /// the program receives the UCI 'go' command. It initializes various
362 /// search-related global variables, and calls root_search(). It returns false
363 /// when a quit command is received during the search.
365 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
366 int time[], int increment[], int movesToGo, int maxDepth,
367 int maxNodes, int maxTime, Move searchMoves[]) {
369 // Initialize global search variables
370 Idle = StopOnPonderhit = AbortSearch = Quit = false;
371 FailHigh = FailLow = Problem = false;
373 SearchStartTime = get_system_time();
374 ExactMaxTime = maxTime;
377 InfiniteSearch = infinite;
378 PonderSearch = ponder;
379 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
381 // Look for a book move, only during games, not tests
382 if (UseTimeManagement && !ponder && get_option_value_bool("OwnBook"))
385 if (get_option_value_string("Book File") != OpeningBook.file_name())
386 OpeningBook.open(get_option_value_string("Book File"));
388 bookMove = OpeningBook.get_move(pos);
389 if (bookMove != MOVE_NONE)
391 cout << "bestmove " << bookMove << endl;
396 for (int i = 0; i < THREAD_MAX; i++)
398 Threads[i].nodes = 0ULL;
399 Threads[i].failHighPly1 = false;
402 if (button_was_pressed("New Game"))
403 loseOnTime = false; // Reset at the beginning of a new game
405 // Read UCI option values
406 TT.set_size(get_option_value_int("Hash"));
407 if (button_was_pressed("Clear Hash"))
410 bool PonderingEnabled = get_option_value_bool("Ponder");
411 MultiPV = get_option_value_int("MultiPV");
413 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
414 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
416 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
417 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
419 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
420 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
422 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
423 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
425 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
426 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
428 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
429 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
431 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
432 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
433 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
435 Chess960 = get_option_value_bool("UCI_Chess960");
436 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
437 UseLogFile = get_option_value_bool("Use Search Log");
439 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
441 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
442 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
444 read_weights(pos.side_to_move());
446 // Set the number of active threads
447 int newActiveThreads = get_option_value_int("Threads");
448 if (newActiveThreads != ActiveThreads)
450 ActiveThreads = newActiveThreads;
451 init_eval(ActiveThreads);
454 // Wake up sleeping threads
455 wake_sleeping_threads();
457 for (int i = 1; i < ActiveThreads; i++)
458 assert(thread_is_available(i, 0));
461 int myTime = time[side_to_move];
462 int myIncrement = increment[side_to_move];
463 if (UseTimeManagement)
465 if (!movesToGo) // Sudden death time control
469 MaxSearchTime = myTime / 30 + myIncrement;
470 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
472 else // Blitz game without increment
474 MaxSearchTime = myTime / 30;
475 AbsoluteMaxSearchTime = myTime / 8;
478 else // (x moves) / (y minutes)
482 MaxSearchTime = myTime / 2;
483 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
487 MaxSearchTime = myTime / Min(movesToGo, 20);
488 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
492 if (PonderingEnabled)
494 MaxSearchTime += MaxSearchTime / 4;
495 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
499 // Set best NodesBetweenPolls interval
501 NodesBetweenPolls = Min(MaxNodes, 30000);
502 else if (myTime && myTime < 1000)
503 NodesBetweenPolls = 1000;
504 else if (myTime && myTime < 5000)
505 NodesBetweenPolls = 5000;
507 NodesBetweenPolls = 30000;
509 // Write information to search log file
511 LogFile << "Searching: " << pos.to_fen() << endl
512 << "infinite: " << infinite
513 << " ponder: " << ponder
514 << " time: " << myTime
515 << " increment: " << myIncrement
516 << " moves to go: " << movesToGo << endl;
518 // LSN filtering. Used only for developing purpose. Disabled by default.
522 // Step 2. If after last move we decided to lose on time, do it now!
523 while (SearchStartTime + myTime + 1000 > get_system_time())
527 // We're ready to start thinking. Call the iterative deepening loop function
528 Value v = id_loop(pos, searchMoves);
533 // Step 1. If this is sudden death game and our position is hopeless,
534 // decide to lose on time.
535 if ( !loseOnTime // If we already lost on time, go to step 3.
545 // Step 3. Now after stepping over the time limit, reset flag for next match.
558 /// init_threads() is called during startup. It launches all helper threads,
559 /// and initializes the split point stack and the global locks and condition
562 #include <cmath> //FIXME: HACK
564 void init_threads() {
567 for (int i = 0; i < 512; i++)
568 lnArray[i] = log(double(i));
572 #if !defined(_MSC_VER)
573 pthread_t pthread[1];
576 for (i = 0; i < THREAD_MAX; i++)
577 Threads[i].activeSplitPoints = 0;
579 // Initialize global locks
580 lock_init(&MPLock, NULL);
581 lock_init(&IOLock, NULL);
583 init_split_point_stack();
585 #if !defined(_MSC_VER)
586 pthread_mutex_init(&WaitLock, NULL);
587 pthread_cond_init(&WaitCond, NULL);
589 for (i = 0; i < THREAD_MAX; i++)
590 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
593 // All threads except the main thread should be initialized to idle state
594 for (i = 1; i < THREAD_MAX; i++)
596 Threads[i].stop = false;
597 Threads[i].workIsWaiting = false;
598 Threads[i].idle = true;
599 Threads[i].running = false;
602 // Launch the helper threads
603 for (i = 1; i < THREAD_MAX; i++)
605 #if !defined(_MSC_VER)
606 pthread_create(pthread, NULL, init_thread, (void*)(&i));
609 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
612 // Wait until the thread has finished launching
613 while (!Threads[i].running);
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;
648 // SearchStack::init() initializes a search stack. Used at the beginning of a
649 // new search from the root.
650 void SearchStack::init(int ply) {
652 pv[ply] = pv[ply + 1] = MOVE_NONE;
653 currentMove = threatMove = MOVE_NONE;
654 reduction = Depth(0);
657 void SearchStack::initKillers() {
659 mateKiller = MOVE_NONE;
660 for (int i = 0; i < KILLER_MAX; i++)
661 killers[i] = MOVE_NONE;
666 // id_loop() is the main iterative deepening loop. It calls root_search
667 // repeatedly with increasing depth until the allocated thinking time has
668 // been consumed, the user stops the search, or the maximum search depth is
671 Value id_loop(const Position& pos, Move searchMoves[]) {
674 SearchStack ss[PLY_MAX_PLUS_2];
676 // searchMoves are verified, copied, scored and sorted
677 RootMoveList rml(p, searchMoves);
679 if (rml.move_count() == 0)
682 wait_for_stop_or_ponderhit();
684 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
687 // Print RootMoveList c'tor startup scoring to the standard output,
688 // so that we print information also for iteration 1.
689 cout << "info depth " << 1 << "\ninfo depth " << 1
690 << " score " << value_to_string(rml.get_move_score(0))
691 << " time " << current_search_time()
692 << " nodes " << nodes_searched()
694 << " pv " << rml.get_move(0) << "\n";
700 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
703 // Is one move significantly better than others after initial scoring ?
704 Move EasyMove = MOVE_NONE;
705 if ( rml.move_count() == 1
706 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
707 EasyMove = rml.get_move(0);
709 // Iterative deepening loop
710 while (Iteration < PLY_MAX)
712 // Initialize iteration
715 BestMoveChangesByIteration[Iteration] = 0;
719 cout << "info depth " << Iteration << endl;
721 // Calculate dynamic search window based on previous iterations
724 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
726 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
727 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
729 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
731 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
732 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
736 alpha = - VALUE_INFINITE;
737 beta = VALUE_INFINITE;
740 // Search to the current depth
741 Value value = root_search(p, ss, rml, alpha, beta);
743 // Write PV to transposition table, in case the relevant entries have
744 // been overwritten during the search.
745 TT.insert_pv(p, ss[0].pv);
748 break; // Value cannot be trusted. Break out immediately!
750 //Save info about search result
751 Value speculatedValue;
754 Value delta = value - IterationInfo[Iteration - 1].value;
761 speculatedValue = value + delta;
762 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
764 else if (value <= alpha)
766 assert(value == alpha);
770 speculatedValue = value + delta;
771 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
773 speculatedValue = value;
775 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
776 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
778 // Drop the easy move if it differs from the new best move
779 if (ss[0].pv[0] != EasyMove)
780 EasyMove = MOVE_NONE;
784 if (UseTimeManagement)
787 bool stopSearch = false;
789 // Stop search early if there is only a single legal move,
790 // we search up to Iteration 6 anyway to get a proper score.
791 if (Iteration >= 6 && rml.move_count() == 1)
794 // Stop search early when the last two iterations returned a mate score
796 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
797 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
800 // Stop search early if one move seems to be much better than the rest
801 int64_t nodes = nodes_searched();
805 && EasyMove == ss[0].pv[0]
806 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
807 && current_search_time() > MaxSearchTime / 16)
808 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
809 && current_search_time() > MaxSearchTime / 32)))
812 // Add some extra time if the best move has changed during the last two iterations
813 if (Iteration > 5 && Iteration <= 50)
814 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
815 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
817 // Stop search if most of MaxSearchTime is consumed at the end of the
818 // iteration. We probably don't have enough time to search the first
819 // move at the next iteration anyway.
820 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
828 StopOnPonderhit = true;
832 if (MaxDepth && Iteration >= MaxDepth)
838 // If we are pondering or in infinite search, we shouldn't print the
839 // best move before we are told to do so.
840 if (!AbortSearch && (PonderSearch || InfiniteSearch))
841 wait_for_stop_or_ponderhit();
843 // Print final search statistics
844 cout << "info nodes " << nodes_searched()
846 << " time " << current_search_time()
847 << " hashfull " << TT.full() << endl;
849 // Print the best move and the ponder move to the standard output
850 if (ss[0].pv[0] == MOVE_NONE)
852 ss[0].pv[0] = rml.get_move(0);
853 ss[0].pv[1] = MOVE_NONE;
855 cout << "bestmove " << ss[0].pv[0];
856 if (ss[0].pv[1] != MOVE_NONE)
857 cout << " ponder " << ss[0].pv[1];
864 dbg_print_mean(LogFile);
866 if (dbg_show_hit_rate)
867 dbg_print_hit_rate(LogFile);
869 LogFile << "\nNodes: " << nodes_searched()
870 << "\nNodes/second: " << nps()
871 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
874 p.do_move(ss[0].pv[0], st);
875 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
877 return rml.get_move_score(0);
881 // root_search() is the function which searches the root node. It is
882 // similar to search_pv except that it uses a different move ordering
883 // scheme and prints some information to the standard output.
885 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
887 Value oldAlpha = alpha;
891 // Loop through all the moves in the root move list
892 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
896 // We failed high, invalidate and skip next moves, leave node-counters
897 // and beta-counters as they are and quickly return, we will try to do
898 // a research at the next iteration with a bigger aspiration window.
899 rml.set_move_score(i, -VALUE_INFINITE);
905 Depth depth, ext, newDepth;
907 RootMoveNumber = i + 1;
910 // Save the current node count before the move is searched
911 nodes = nodes_searched();
913 // Reset beta cut-off counters
916 // Pick the next root move, and print the move and the move number to
917 // the standard output.
918 move = ss[0].currentMove = rml.get_move(i);
920 if (current_search_time() >= 1000)
921 cout << "info currmove " << move
922 << " currmovenumber " << RootMoveNumber << endl;
924 // Decide search depth for this move
925 bool moveIsCheck = pos.move_is_check(move);
926 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
928 depth = (Iteration - 2) * OnePly + InitialDepth;
929 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
930 newDepth = depth + ext;
932 // Make the move, and search it
933 pos.do_move(move, st, ci, moveIsCheck);
937 // Aspiration window is disabled in multi-pv case
939 alpha = -VALUE_INFINITE;
941 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
943 // If the value has dropped a lot compared to the last iteration,
944 // set the boolean variable Problem to true. This variable is used
945 // for time managment: When Problem is true, we try to complete the
946 // current iteration before playing a move.
947 Problem = ( Iteration >= 2
948 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
950 if (Problem && StopOnPonderhit)
951 StopOnPonderhit = false;
955 // Try to reduce non-pv search depth by one ply if move seems not problematic,
956 // if the move fails high will be re-searched at full depth.
957 if ( depth >= 3*OnePly // FIXME was newDepth
959 && !captureOrPromotion
960 && !move_is_castle(move))
962 double red = 0.5 + ln(RootMoveNumber - MultiPV + 1) * ln(depth / 2) / 6.0;
965 ss[0].reduction = Depth(int(floor(red * int(OnePly))));
966 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
969 value = alpha + 1; // Just to trigger next condition
971 value = alpha + 1; // Just to trigger next condition
975 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
979 // Fail high! Set the boolean variable FailHigh to true, and
980 // re-search the move using a PV search. The variable FailHigh
981 // is used for time managment: We try to avoid aborting the
982 // search prematurely during a fail high research.
984 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
991 // Finished searching the move. If AbortSearch is true, the search
992 // was aborted because the user interrupted the search or because we
993 // ran out of time. In this case, the return value of the search cannot
994 // be trusted, and we break out of the loop without updating the best
999 // Remember beta-cutoff and searched nodes counts for this move. The
1000 // info is used to sort the root moves at the next iteration.
1002 BetaCounter.read(pos.side_to_move(), our, their);
1003 rml.set_beta_counters(i, our, their);
1004 rml.set_move_nodes(i, nodes_searched() - nodes);
1006 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1008 if (value <= alpha && i >= MultiPV)
1009 rml.set_move_score(i, -VALUE_INFINITE);
1012 // PV move or new best move!
1015 rml.set_move_score(i, value);
1017 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1018 rml.set_move_pv(i, ss[0].pv);
1022 // We record how often the best move has been changed in each
1023 // iteration. This information is used for time managment: When
1024 // the best move changes frequently, we allocate some more time.
1026 BestMoveChangesByIteration[Iteration]++;
1028 // Print search information to the standard output
1029 cout << "info depth " << Iteration
1030 << " score " << value_to_string(value)
1031 << ((value >= beta) ? " lowerbound" :
1032 ((value <= alpha)? " upperbound" : ""))
1033 << " time " << current_search_time()
1034 << " nodes " << nodes_searched()
1038 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1039 cout << ss[0].pv[j] << " ";
1045 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1046 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1048 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1049 nodes_searched(), value, type, ss[0].pv) << endl;
1054 // Reset the global variable Problem to false if the value isn't too
1055 // far below the final value from the last iteration.
1056 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1061 rml.sort_multipv(i);
1062 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1064 cout << "info multipv " << j + 1
1065 << " score " << value_to_string(rml.get_move_score(j))
1066 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1067 << " time " << current_search_time()
1068 << " nodes " << nodes_searched()
1072 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1073 cout << rml.get_move_pv(j, k) << " ";
1077 alpha = rml.get_move_score(Min(i, MultiPV-1));
1079 } // PV move or new best move
1081 assert(alpha >= oldAlpha);
1083 FailLow = (alpha == oldAlpha);
1089 // search_pv() is the main search function for PV nodes.
1091 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1092 Depth depth, int ply, int threadID) {
1094 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1095 assert(beta > alpha && beta <= VALUE_INFINITE);
1096 assert(ply >= 0 && ply < PLY_MAX);
1097 assert(threadID >= 0 && threadID < ActiveThreads);
1099 Move movesSearched[256];
1104 Depth ext, newDepth;
1105 Value oldAlpha, value;
1106 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1108 Value bestValue = -VALUE_INFINITE;
1111 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1113 // Initialize, and make an early exit in case of an aborted search,
1114 // an instant draw, maximum ply reached, etc.
1115 init_node(ss, ply, threadID);
1117 // After init_node() that calls poll()
1118 if (AbortSearch || thread_should_stop(threadID))
1124 if (ply >= PLY_MAX - 1)
1125 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1127 // Mate distance pruning
1129 alpha = Max(value_mated_in(ply), alpha);
1130 beta = Min(value_mate_in(ply+1), beta);
1134 // Transposition table lookup. At PV nodes, we don't use the TT for
1135 // pruning, but only for move ordering. This is to avoid problems in
1136 // the following areas:
1138 // * Repetition draw detection
1139 // * Fifty move rule detection
1140 // * Searching for a mate
1141 // * Printing of full PV line
1143 tte = TT.retrieve(pos.get_key());
1144 ttMove = (tte ? tte->move() : MOVE_NONE);
1146 // Go with internal iterative deepening if we don't have a TT move
1147 if ( UseIIDAtPVNodes
1148 && depth >= 5*OnePly
1149 && ttMove == MOVE_NONE)
1151 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1152 ttMove = ss[ply].pv[ply];
1153 tte = TT.retrieve(pos.get_key());
1156 // Initialize a MovePicker object for the current position, and prepare
1157 // to search all moves
1158 isCheck = pos.is_check();
1159 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1161 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1163 // Loop through all legal moves until no moves remain or a beta cutoff
1165 while ( alpha < beta
1166 && (move = mp.get_next_move()) != MOVE_NONE
1167 && !thread_should_stop(threadID))
1169 assert(move_is_ok(move));
1171 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1172 moveIsCheck = pos.move_is_check(move, ci);
1173 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1175 // Decide the new search depth
1176 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1178 // Singular extension search. We extend the TT move if its value is much better than
1179 // its siblings. To verify this we do a reduced search on all the other moves but the
1180 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1181 if ( depth >= 6 * OnePly
1183 && move == tte->move()
1185 && is_lower_bound(tte->type())
1186 && tte->depth() >= depth - 3 * OnePly)
1188 Value ttValue = value_from_tt(tte->value(), ply);
1190 if (abs(ttValue) < VALUE_KNOWN_WIN)
1192 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1194 if (excValue < ttValue - SingleReplyMargin)
1199 newDepth = depth - OnePly + ext;
1201 // Update current move
1202 movesSearched[moveCount++] = ss[ply].currentMove = move;
1204 // Make and search the move
1205 pos.do_move(move, st, ci, moveIsCheck);
1207 if (moveCount == 1) // The first move in list is the PV
1208 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1211 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1212 // if the move fails high will be re-searched at full depth.
1213 if ( depth >= 3*OnePly
1215 && !captureOrPromotion
1216 && !move_is_castle(move)
1217 && !move_is_killer(move, ss[ply]))
1219 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 6.0;
1222 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1223 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1226 value = alpha + 1; // Just to trigger next condition
1229 value = alpha + 1; // Just to trigger next condition
1231 if (value > alpha) // Go with full depth non-pv search
1233 ss[ply].reduction = Depth(0);
1234 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1235 if (value > alpha && value < beta)
1237 // When the search fails high at ply 1 while searching the first
1238 // move at the root, set the flag failHighPly1. This is used for
1239 // time managment: We don't want to stop the search early in
1240 // such cases, because resolving the fail high at ply 1 could
1241 // result in a big drop in score at the root.
1242 if (ply == 1 && RootMoveNumber == 1)
1243 Threads[threadID].failHighPly1 = true;
1245 // A fail high occurred. Re-search at full window (pv search)
1246 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1247 Threads[threadID].failHighPly1 = false;
1251 pos.undo_move(move);
1253 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1256 if (value > bestValue)
1263 if (value == value_mate_in(ply + 1))
1264 ss[ply].mateKiller = move;
1266 // If we are at ply 1, and we are searching the first root move at
1267 // ply 0, set the 'Problem' variable if the score has dropped a lot
1268 // (from the computer's point of view) since the previous iteration.
1271 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1276 if ( ActiveThreads > 1
1278 && depth >= MinimumSplitDepth
1280 && idle_thread_exists(threadID)
1282 && !thread_should_stop(threadID)
1283 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1284 depth, &moveCount, &mp, threadID, true))
1288 // All legal moves have been searched. A special case: If there were
1289 // no legal moves, it must be mate or stalemate.
1291 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1293 // If the search is not aborted, update the transposition table,
1294 // history counters, and killer moves.
1295 if (AbortSearch || thread_should_stop(threadID))
1298 if (bestValue <= oldAlpha)
1299 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1301 else if (bestValue >= beta)
1303 BetaCounter.add(pos.side_to_move(), depth, threadID);
1304 move = ss[ply].pv[ply];
1305 if (!pos.move_is_capture_or_promotion(move))
1307 update_history(pos, move, depth, movesSearched, moveCount);
1308 update_killers(move, ss[ply]);
1310 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1313 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1319 // search() is the search function for zero-width nodes.
1321 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1322 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1324 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1325 assert(ply >= 0 && ply < PLY_MAX);
1326 assert(threadID >= 0 && threadID < ActiveThreads);
1328 Move movesSearched[256];
1333 Depth ext, newDepth;
1334 Value staticValue, nullValue, value, futilityValue, futilityValueScaled;
1335 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1336 bool mateThreat = false;
1338 Value bestValue = -VALUE_INFINITE;
1341 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1343 // Initialize, and make an early exit in case of an aborted search,
1344 // an instant draw, maximum ply reached, etc.
1345 init_node(ss, ply, threadID);
1347 // After init_node() that calls poll()
1348 if (AbortSearch || thread_should_stop(threadID))
1354 if (ply >= PLY_MAX - 1)
1355 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1357 // Mate distance pruning
1358 if (value_mated_in(ply) >= beta)
1361 if (value_mate_in(ply + 1) < beta)
1364 // We don't want the score of a partial search to overwrite a previous full search
1365 // TT value, so we use a different position key in case of an excluded move exsists.
1366 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1368 // Transposition table lookup
1369 tte = TT.retrieve(posKey);
1370 ttMove = (tte ? tte->move() : MOVE_NONE);
1372 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1374 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1375 return value_from_tt(tte->value(), ply);
1378 isCheck = pos.is_check();
1379 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1381 // Evaluate the position statically
1383 staticValue = quick_evaluate(pos);
1384 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1385 staticValue = value_from_tt(tte->value(), ply);
1387 staticValue = evaluate(pos, ei, threadID);
1389 // Calculate depth dependant futility pruning parameters
1390 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1391 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1393 // Enhance score accuracy with TT value if possible
1394 futilityValue = staticValue + FutilityValueMargin;
1395 staticValue = refine_eval(tte, staticValue, ply);
1401 && !value_is_mate(beta)
1402 && ok_to_do_nullmove(pos)
1403 && staticValue >= beta - NullMoveMargin)
1405 ss[ply].currentMove = MOVE_NULL;
1407 pos.do_null_move(st);
1409 // Null move dynamic reduction based on depth
1410 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1412 // Null move dynamic reduction based on value
1413 if (staticValue - beta > PawnValueMidgame)
1416 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1418 pos.undo_null_move();
1420 if (nullValue >= beta)
1422 if (depth < 6 * OnePly)
1425 // Do zugzwang verification search
1426 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1430 // The null move failed low, which means that we may be faced with
1431 // some kind of threat. If the previous move was reduced, check if
1432 // the move that refuted the null move was somehow connected to the
1433 // move which was reduced. If a connection is found, return a fail
1434 // low score (which will cause the reduced move to fail high in the
1435 // parent node, which will trigger a re-search with full depth).
1436 if (nullValue == value_mated_in(ply + 2))
1439 ss[ply].threatMove = ss[ply + 1].currentMove;
1440 if ( depth < ThreatDepth
1441 && ss[ply - 1].reduction
1442 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1446 // Null move search not allowed, try razoring
1447 else if ( !value_is_mate(beta)
1448 && depth < RazorDepth
1449 && staticValue < beta - (depth > OnePly ? NullMoveMargin + 16 * depth : 2*NullMoveMargin)
1450 && ss[ply - 1].currentMove != MOVE_NULL
1451 && ttMove == MOVE_NONE
1452 && !pos.has_pawn_on_7th(pos.side_to_move()))
1454 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1455 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1460 // Go with internal iterative deepening if we don't have a TT move
1461 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1462 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1464 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1465 ttMove = ss[ply].pv[ply];
1466 tte = TT.retrieve(pos.get_key());
1469 // Initialize a MovePicker object for the current position, and prepare
1470 // to search all moves.
1471 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1473 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1475 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1476 while ( bestValue < beta
1477 && (move = mp.get_next_move()) != MOVE_NONE
1478 && !thread_should_stop(threadID))
1480 assert(move_is_ok(move));
1482 if (move == excludedMove)
1485 moveIsCheck = pos.move_is_check(move, ci);
1486 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1487 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1489 // Decide the new search depth
1490 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1492 // Singular extension search. We extend the TT move if its value is much better than
1493 // its siblings. To verify this we do a reduced search on all the other moves but the
1494 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1495 if ( depth >= 8 * OnePly
1497 && move == tte->move()
1498 && !excludedMove // Do not allow recursive single-reply search
1500 && is_lower_bound(tte->type())
1501 && tte->depth() >= depth - 3 * OnePly)
1503 Value ttValue = value_from_tt(tte->value(), ply);
1505 if (abs(ttValue) < VALUE_KNOWN_WIN)
1507 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1509 if (excValue < ttValue - SingleReplyMargin)
1514 newDepth = depth - OnePly + ext;
1516 // Update current move
1517 movesSearched[moveCount++] = ss[ply].currentMove = move;
1520 if ( useFutilityPruning
1522 && !captureOrPromotion
1525 // Move count based pruning
1526 if ( moveCount >= FutilityMoveCountMargin
1527 && ok_to_prune(pos, move, ss[ply].threatMove)
1528 && bestValue > value_mated_in(PLY_MAX))
1531 // Value based pruning
1532 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1534 if (futilityValueScaled < beta)
1536 if (futilityValueScaled > bestValue)
1537 bestValue = futilityValueScaled;
1542 // Make and search the move
1543 pos.do_move(move, st, ci, moveIsCheck);
1545 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1546 // if the move fails high will be re-searched at full depth.
1547 if ( depth >= 3*OnePly
1549 && !captureOrPromotion
1550 && !move_is_castle(move)
1551 && !move_is_killer(move, ss[ply])
1552 /* && move != ttMove*/)
1554 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 3.0;
1557 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1558 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1561 value = beta; // Just to trigger next condition
1564 value = beta; // Just to trigger next condition
1566 if (value >= beta) // Go with full depth non-pv search
1568 ss[ply].reduction = Depth(0);
1569 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1571 pos.undo_move(move);
1573 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1576 if (value > bestValue)
1582 if (value == value_mate_in(ply + 1))
1583 ss[ply].mateKiller = move;
1587 if ( ActiveThreads > 1
1589 && depth >= MinimumSplitDepth
1591 && idle_thread_exists(threadID)
1593 && !thread_should_stop(threadID)
1594 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1595 depth, &moveCount, &mp, threadID, false))
1599 // All legal moves have been searched. A special case: If there were
1600 // no legal moves, it must be mate or stalemate.
1602 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1604 // If the search is not aborted, update the transposition table,
1605 // history counters, and killer moves.
1606 if (AbortSearch || thread_should_stop(threadID))
1609 if (bestValue < beta)
1610 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1613 BetaCounter.add(pos.side_to_move(), depth, threadID);
1614 move = ss[ply].pv[ply];
1615 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1616 if (!pos.move_is_capture_or_promotion(move))
1618 update_history(pos, move, depth, movesSearched, moveCount);
1619 update_killers(move, ss[ply]);
1624 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1630 // qsearch() is the quiescence search function, which is called by the main
1631 // search function when the remaining depth is zero (or, to be more precise,
1632 // less than OnePly).
1634 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1635 Depth depth, int ply, int threadID) {
1637 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1638 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1640 assert(ply >= 0 && ply < PLY_MAX);
1641 assert(threadID >= 0 && threadID < ActiveThreads);
1646 Value staticValue, bestValue, value, futilityBase, futilityValue;
1647 bool isCheck, enoughMaterial, moveIsCheck;
1648 const TTEntry* tte = NULL;
1650 bool pvNode = (beta - alpha != 1);
1652 // Initialize, and make an early exit in case of an aborted search,
1653 // an instant draw, maximum ply reached, etc.
1654 init_node(ss, ply, threadID);
1656 // After init_node() that calls poll()
1657 if (AbortSearch || thread_should_stop(threadID))
1663 if (ply >= PLY_MAX - 1)
1664 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1666 // Transposition table lookup. At PV nodes, we don't use the TT for
1667 // pruning, but only for move ordering.
1668 tte = TT.retrieve(pos.get_key());
1669 ttMove = (tte ? tte->move() : MOVE_NONE);
1671 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1673 assert(tte->type() != VALUE_TYPE_EVAL);
1675 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1676 return value_from_tt(tte->value(), ply);
1679 isCheck = pos.is_check();
1680 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1682 // Evaluate the position statically
1684 staticValue = -VALUE_INFINITE;
1685 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1686 staticValue = value_from_tt(tte->value(), ply);
1688 staticValue = evaluate(pos, ei, threadID);
1690 // Initialize "stand pat score", and return it immediately if it is
1692 bestValue = staticValue;
1694 if (bestValue >= beta)
1696 // Store the score to avoid a future costly evaluation() call
1697 if (!isCheck && !tte && ei.futilityMargin == 0)
1698 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1703 if (bestValue > alpha)
1706 // Initialize a MovePicker object for the current position, and prepare
1707 // to search the moves. Because the depth is <= 0 here, only captures,
1708 // queen promotions and checks (only if depth == 0) will be generated.
1709 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1711 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1712 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;
1714 // Loop through the moves until no moves remain or a beta cutoff
1716 while ( alpha < beta
1717 && (move = mp.get_next_move()) != MOVE_NONE)
1719 assert(move_is_ok(move));
1721 moveIsCheck = pos.move_is_check(move, ci);
1723 // Update current move
1725 ss[ply].currentMove = move;
1733 && !move_is_promotion(move)
1734 && !pos.move_is_passed_pawn_push(move))
1736 futilityValue = futilityBase
1737 + pos.endgame_value_of_piece_on(move_to(move))
1738 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1740 if (futilityValue < alpha)
1742 if (futilityValue > bestValue)
1743 bestValue = futilityValue;
1748 // Don't search captures and checks with negative SEE values
1751 && !move_is_promotion(move)
1752 && pos.see_sign(move) < 0)
1755 // Make and search the move
1756 pos.do_move(move, st, ci, moveIsCheck);
1757 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1758 pos.undo_move(move);
1760 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1763 if (value > bestValue)
1774 // All legal moves have been searched. A special case: If we're in check
1775 // and no legal moves were found, it is checkmate.
1776 if (!moveCount && pos.is_check()) // Mate!
1777 return value_mated_in(ply);
1779 // Update transposition table
1780 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1781 if (bestValue < beta)
1783 // If bestValue isn't changed it means it is still the static evaluation
1784 // of the node, so keep this info to avoid a future evaluation() call.
1785 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1786 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1790 move = ss[ply].pv[ply];
1791 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1793 // Update killers only for good checking moves
1794 if (!pos.move_is_capture_or_promotion(move))
1795 update_killers(move, ss[ply]);
1798 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1804 // sp_search() is used to search from a split point. This function is called
1805 // by each thread working at the split point. It is similar to the normal
1806 // search() function, but simpler. Because we have already probed the hash
1807 // table, done a null move search, and searched the first move before
1808 // splitting, we don't have to repeat all this work in sp_search(). We
1809 // also don't need to store anything to the hash table here: This is taken
1810 // care of after we return from the split point.
1812 void sp_search(SplitPoint* sp, int threadID) {
1814 assert(threadID >= 0 && threadID < ActiveThreads);
1815 assert(ActiveThreads > 1);
1817 Position pos = Position(sp->pos);
1819 SearchStack* ss = sp->sstack[threadID];
1822 bool isCheck = pos.is_check();
1823 bool useFutilityPruning = sp->depth < SelectiveDepth
1826 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1827 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1829 while ( sp->bestValue < sp->beta
1830 && !thread_should_stop(threadID)
1831 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1833 assert(move_is_ok(move));
1835 bool moveIsCheck = pos.move_is_check(move, ci);
1836 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1838 lock_grab(&(sp->lock));
1839 int moveCount = ++sp->moves;
1840 lock_release(&(sp->lock));
1842 ss[sp->ply].currentMove = move;
1844 // Decide the new search depth.
1846 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1847 Depth newDepth = sp->depth - OnePly + ext;
1850 if ( useFutilityPruning
1852 && !captureOrPromotion)
1854 // Move count based pruning
1855 if ( moveCount >= FutilityMoveCountMargin
1856 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1857 && sp->bestValue > value_mated_in(PLY_MAX))
1860 // Value based pruning
1861 if (sp->futilityValue == VALUE_NONE)
1864 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1867 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1869 if (futilityValueScaled < sp->beta)
1871 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1873 lock_grab(&(sp->lock));
1874 if (futilityValueScaled > sp->bestValue)
1875 sp->bestValue = futilityValueScaled;
1876 lock_release(&(sp->lock));
1882 // Make and search the move.
1884 pos.do_move(move, st, ci, moveIsCheck);
1886 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1887 // if the move fails high will be re-searched at full depth.
1889 && !captureOrPromotion
1890 && !move_is_castle(move)
1891 && !move_is_killer(move, ss[sp->ply]))
1893 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 3.0;
1896 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
1897 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1900 value = sp->beta; // Just to trigger next condition
1903 value = sp->beta; // Just to trigger next condition
1905 if (value >= sp->beta) // Go with full depth non-pv search
1907 ss[sp->ply].reduction = Depth(0);
1908 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1910 pos.undo_move(move);
1912 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1914 if (thread_should_stop(threadID))
1918 if (value > sp->bestValue) // Less then 2% of cases
1920 lock_grab(&(sp->lock));
1921 if (value > sp->bestValue && !thread_should_stop(threadID))
1923 sp->bestValue = value;
1924 if (sp->bestValue >= sp->beta)
1926 sp_update_pv(sp->parentSstack, ss, sp->ply);
1927 for (int i = 0; i < ActiveThreads; i++)
1928 if (i != threadID && (i == sp->master || sp->slaves[i]))
1929 Threads[i].stop = true;
1931 sp->finished = true;
1934 lock_release(&(sp->lock));
1938 lock_grab(&(sp->lock));
1940 // If this is the master thread and we have been asked to stop because of
1941 // a beta cutoff higher up in the tree, stop all slave threads.
1942 if (sp->master == threadID && thread_should_stop(threadID))
1943 for (int i = 0; i < ActiveThreads; i++)
1945 Threads[i].stop = true;
1948 sp->slaves[threadID] = 0;
1950 lock_release(&(sp->lock));
1954 // sp_search_pv() is used to search from a PV split point. This function
1955 // is called by each thread working at the split point. It is similar to
1956 // the normal search_pv() function, but simpler. Because we have already
1957 // probed the hash table and searched the first move before splitting, we
1958 // don't have to repeat all this work in sp_search_pv(). We also don't
1959 // need to store anything to the hash table here: This is taken care of
1960 // after we return from the split point.
1962 void sp_search_pv(SplitPoint* sp, int threadID) {
1964 assert(threadID >= 0 && threadID < ActiveThreads);
1965 assert(ActiveThreads > 1);
1967 Position pos = Position(sp->pos);
1969 SearchStack* ss = sp->sstack[threadID];
1973 while ( sp->alpha < sp->beta
1974 && !thread_should_stop(threadID)
1975 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1977 bool moveIsCheck = pos.move_is_check(move, ci);
1978 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1980 assert(move_is_ok(move));
1982 lock_grab(&(sp->lock));
1983 int moveCount = ++sp->moves;
1984 lock_release(&(sp->lock));
1986 ss[sp->ply].currentMove = move;
1988 // Decide the new search depth.
1990 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1991 Depth newDepth = sp->depth - OnePly + ext;
1993 // Make and search the move.
1995 pos.do_move(move, st, ci, moveIsCheck);
1997 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1998 // if the move fails high will be re-searched at full depth.
2000 && !captureOrPromotion
2001 && !move_is_castle(move)
2002 && !move_is_killer(move, ss[sp->ply]))
2004 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 6.0;
2007 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
2008 value = -search(pos, ss, -sp->alpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2011 value = sp->alpha + 1; // Just to trigger next condition
2014 value = sp->alpha + 1; // Just to trigger next condition
2016 if (value > sp->alpha) // Go with full depth non-pv search
2018 ss[sp->ply].reduction = Depth(0);
2019 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
2021 if (value > sp->alpha && value < sp->beta)
2023 // When the search fails high at ply 1 while searching the first
2024 // move at the root, set the flag failHighPly1. This is used for
2025 // time managment: We don't want to stop the search early in
2026 // such cases, because resolving the fail high at ply 1 could
2027 // result in a big drop in score at the root.
2028 if (sp->ply == 1 && RootMoveNumber == 1)
2029 Threads[threadID].failHighPly1 = true;
2031 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
2032 Threads[threadID].failHighPly1 = false;
2035 pos.undo_move(move);
2037 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2039 if (thread_should_stop(threadID))
2043 lock_grab(&(sp->lock));
2044 if (value > sp->bestValue && !thread_should_stop(threadID))
2046 sp->bestValue = value;
2047 if (value > sp->alpha)
2050 sp_update_pv(sp->parentSstack, ss, sp->ply);
2051 if (value == value_mate_in(sp->ply + 1))
2052 ss[sp->ply].mateKiller = move;
2054 if (value >= sp->beta)
2056 for (int i = 0; i < ActiveThreads; i++)
2057 if (i != threadID && (i == sp->master || sp->slaves[i]))
2058 Threads[i].stop = true;
2060 sp->finished = true;
2063 // If we are at ply 1, and we are searching the first root move at
2064 // ply 0, set the 'Problem' variable if the score has dropped a lot
2065 // (from the computer's point of view) since the previous iteration.
2068 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2071 lock_release(&(sp->lock));
2074 lock_grab(&(sp->lock));
2076 // If this is the master thread and we have been asked to stop because of
2077 // a beta cutoff higher up in the tree, stop all slave threads.
2078 if (sp->master == threadID && thread_should_stop(threadID))
2079 for (int i = 0; i < ActiveThreads; i++)
2081 Threads[i].stop = true;
2084 sp->slaves[threadID] = 0;
2086 lock_release(&(sp->lock));
2089 /// The BetaCounterType class
2091 BetaCounterType::BetaCounterType() { clear(); }
2093 void BetaCounterType::clear() {
2095 for (int i = 0; i < THREAD_MAX; i++)
2096 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2099 void BetaCounterType::add(Color us, Depth d, int threadID) {
2101 // Weighted count based on depth
2102 Threads[threadID].betaCutOffs[us] += unsigned(d);
2105 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2108 for (int i = 0; i < THREAD_MAX; i++)
2110 our += Threads[i].betaCutOffs[us];
2111 their += Threads[i].betaCutOffs[opposite_color(us)];
2116 /// The RootMoveList class
2118 // RootMoveList c'tor
2120 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2122 MoveStack mlist[MaxRootMoves];
2123 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2125 // Generate all legal moves
2126 MoveStack* last = generate_moves(pos, mlist);
2128 // Add each move to the moves[] array
2129 for (MoveStack* cur = mlist; cur != last; cur++)
2131 bool includeMove = includeAllMoves;
2133 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2134 includeMove = (searchMoves[k] == cur->move);
2139 // Find a quick score for the move
2141 SearchStack ss[PLY_MAX_PLUS_2];
2144 moves[count].move = cur->move;
2145 pos.do_move(moves[count].move, st);
2146 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2147 pos.undo_move(moves[count].move);
2148 moves[count].pv[0] = moves[count].move;
2149 moves[count].pv[1] = MOVE_NONE;
2156 // RootMoveList simple methods definitions
2158 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2160 moves[moveNum].nodes = nodes;
2161 moves[moveNum].cumulativeNodes += nodes;
2164 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2166 moves[moveNum].ourBeta = our;
2167 moves[moveNum].theirBeta = their;
2170 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2174 for (j = 0; pv[j] != MOVE_NONE; j++)
2175 moves[moveNum].pv[j] = pv[j];
2177 moves[moveNum].pv[j] = MOVE_NONE;
2181 // RootMoveList::sort() sorts the root move list at the beginning of a new
2184 void RootMoveList::sort() {
2186 sort_multipv(count - 1); // Sort all items
2190 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2191 // list by their scores and depths. It is used to order the different PVs
2192 // correctly in MultiPV mode.
2194 void RootMoveList::sort_multipv(int n) {
2198 for (i = 1; i <= n; i++)
2200 RootMove rm = moves[i];
2201 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2202 moves[j] = moves[j - 1];
2209 // init_node() is called at the beginning of all the search functions
2210 // (search(), search_pv(), qsearch(), and so on) and initializes the
2211 // search stack object corresponding to the current node. Once every
2212 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2213 // for user input and checks whether it is time to stop the search.
2215 void init_node(SearchStack ss[], int ply, int threadID) {
2217 assert(ply >= 0 && ply < PLY_MAX);
2218 assert(threadID >= 0 && threadID < ActiveThreads);
2220 Threads[threadID].nodes++;
2225 if (NodesSincePoll >= NodesBetweenPolls)
2232 ss[ply + 2].initKillers();
2234 if (Threads[threadID].printCurrentLine)
2235 print_current_line(ss, ply, threadID);
2239 // update_pv() is called whenever a search returns a value > alpha.
2240 // It updates the PV in the SearchStack object corresponding to the
2243 void update_pv(SearchStack ss[], int ply) {
2245 assert(ply >= 0 && ply < PLY_MAX);
2249 ss[ply].pv[ply] = ss[ply].currentMove;
2251 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2252 ss[ply].pv[p] = ss[ply + 1].pv[p];
2254 ss[ply].pv[p] = MOVE_NONE;
2258 // sp_update_pv() is a variant of update_pv for use at split points. The
2259 // difference between the two functions is that sp_update_pv also updates
2260 // the PV at the parent node.
2262 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2264 assert(ply >= 0 && ply < PLY_MAX);
2268 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2270 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2271 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2273 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2277 // connected_moves() tests whether two moves are 'connected' in the sense
2278 // that the first move somehow made the second move possible (for instance
2279 // if the moving piece is the same in both moves). The first move is assumed
2280 // to be the move that was made to reach the current position, while the
2281 // second move is assumed to be a move from the current position.
2283 bool connected_moves(const Position& pos, Move m1, Move m2) {
2285 Square f1, t1, f2, t2;
2288 assert(move_is_ok(m1));
2289 assert(move_is_ok(m2));
2291 if (m2 == MOVE_NONE)
2294 // Case 1: The moving piece is the same in both moves
2300 // Case 2: The destination square for m2 was vacated by m1
2306 // Case 3: Moving through the vacated square
2307 if ( piece_is_slider(pos.piece_on(f2))
2308 && bit_is_set(squares_between(f2, t2), f1))
2311 // Case 4: The destination square for m2 is defended by the moving piece in m1
2312 p = pos.piece_on(t1);
2313 if (bit_is_set(pos.attacks_from(p, t1), t2))
2316 // Case 5: Discovered check, checking piece is the piece moved in m1
2317 if ( piece_is_slider(p)
2318 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2319 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2321 // discovered_check_candidates() works also if the Position's side to
2322 // move is the opposite of the checking piece.
2323 Color them = opposite_color(pos.side_to_move());
2324 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2326 if (bit_is_set(dcCandidates, f2))
2333 // value_is_mate() checks if the given value is a mate one
2334 // eventually compensated for the ply.
2336 bool value_is_mate(Value value) {
2338 assert(abs(value) <= VALUE_INFINITE);
2340 return value <= value_mated_in(PLY_MAX)
2341 || value >= value_mate_in(PLY_MAX);
2345 // move_is_killer() checks if the given move is among the
2346 // killer moves of that ply.
2348 bool move_is_killer(Move m, const SearchStack& ss) {
2350 const Move* k = ss.killers;
2351 for (int i = 0; i < KILLER_MAX; i++, k++)
2359 // extension() decides whether a move should be searched with normal depth,
2360 // or with extended depth. Certain classes of moves (checking moves, in
2361 // particular) are searched with bigger depth than ordinary moves and in
2362 // any case are marked as 'dangerous'. Note that also if a move is not
2363 // extended, as example because the corresponding UCI option is set to zero,
2364 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2366 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2367 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2369 assert(m != MOVE_NONE);
2371 Depth result = Depth(0);
2372 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2377 result += CheckExtension[pvNode];
2380 result += SingleEvasionExtension[pvNode];
2383 result += MateThreatExtension[pvNode];
2386 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2388 Color c = pos.side_to_move();
2389 if (relative_rank(c, move_to(m)) == RANK_7)
2391 result += PawnPushTo7thExtension[pvNode];
2394 if (pos.pawn_is_passed(c, move_to(m)))
2396 result += PassedPawnExtension[pvNode];
2401 if ( captureOrPromotion
2402 && pos.type_of_piece_on(move_to(m)) != PAWN
2403 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2404 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2405 && !move_is_promotion(m)
2408 result += PawnEndgameExtension[pvNode];
2413 && captureOrPromotion
2414 && pos.type_of_piece_on(move_to(m)) != PAWN
2415 && pos.see_sign(m) >= 0)
2421 return Min(result, OnePly);
2425 // ok_to_do_nullmove() looks at the current position and decides whether
2426 // doing a 'null move' should be allowed. In order to avoid zugzwang
2427 // problems, null moves are not allowed when the side to move has very
2428 // little material left. Currently, the test is a bit too simple: Null
2429 // moves are avoided only when the side to move has only pawns left.
2430 // It's probably a good idea to avoid null moves in at least some more
2431 // complicated endgames, e.g. KQ vs KR. FIXME
2433 bool ok_to_do_nullmove(const Position& pos) {
2435 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2439 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2440 // non-tactical moves late in the move list close to the leaves are
2441 // candidates for pruning.
2443 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2445 assert(move_is_ok(m));
2446 assert(threat == MOVE_NONE || move_is_ok(threat));
2447 assert(!pos.move_is_check(m));
2448 assert(!pos.move_is_capture_or_promotion(m));
2449 assert(!pos.move_is_passed_pawn_push(m));
2451 Square mfrom, mto, tfrom, tto;
2453 // Prune if there isn't any threat move and
2454 // is not a castling move (common case).
2455 if (threat == MOVE_NONE && !move_is_castle(m))
2458 mfrom = move_from(m);
2460 tfrom = move_from(threat);
2461 tto = move_to(threat);
2463 // Case 1: Castling moves are never pruned
2464 if (move_is_castle(m))
2467 // Case 2: Don't prune moves which move the threatened piece
2471 // Case 3: If the threatened piece has value less than or equal to the
2472 // value of the threatening piece, don't prune move which defend it.
2473 if ( pos.move_is_capture(threat)
2474 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2475 || pos.type_of_piece_on(tfrom) == KING)
2476 && pos.move_attacks_square(m, tto))
2479 // Case 4: If the moving piece in the threatened move is a slider, don't
2480 // prune safe moves which block its ray.
2481 if ( piece_is_slider(pos.piece_on(tfrom))
2482 && bit_is_set(squares_between(tfrom, tto), mto)
2483 && pos.see_sign(m) >= 0)
2490 // ok_to_use_TT() returns true if a transposition table score
2491 // can be used at a given point in search.
2493 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2495 Value v = value_from_tt(tte->value(), ply);
2497 return ( tte->depth() >= depth
2498 || v >= Max(value_mate_in(PLY_MAX), beta)
2499 || v < Min(value_mated_in(PLY_MAX), beta))
2501 && ( (is_lower_bound(tte->type()) && v >= beta)
2502 || (is_upper_bound(tte->type()) && v < beta));
2506 // refine_eval() returns the transposition table score if
2507 // possible otherwise falls back on static position evaluation.
2509 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2514 Value v = value_from_tt(tte->value(), ply);
2516 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2517 || (is_upper_bound(tte->type()) && v < defaultEval))
2523 // update_history() registers a good move that produced a beta-cutoff
2524 // in history and marks as failures all the other moves of that ply.
2526 void update_history(const Position& pos, Move move, Depth depth,
2527 Move movesSearched[], int moveCount) {
2531 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2533 for (int i = 0; i < moveCount - 1; i++)
2535 m = movesSearched[i];
2539 if (!pos.move_is_capture_or_promotion(m))
2540 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2545 // update_killers() add a good move that produced a beta-cutoff
2546 // among the killer moves of that ply.
2548 void update_killers(Move m, SearchStack& ss) {
2550 if (m == ss.killers[0])
2553 for (int i = KILLER_MAX - 1; i > 0; i--)
2554 ss.killers[i] = ss.killers[i - 1];
2560 // fail_high_ply_1() checks if some thread is currently resolving a fail
2561 // high at ply 1 at the node below the first root node. This information
2562 // is used for time management.
2564 bool fail_high_ply_1() {
2566 for (int i = 0; i < ActiveThreads; i++)
2567 if (Threads[i].failHighPly1)
2574 // current_search_time() returns the number of milliseconds which have passed
2575 // since the beginning of the current search.
2577 int current_search_time() {
2579 return get_system_time() - SearchStartTime;
2583 // nps() computes the current nodes/second count.
2587 int t = current_search_time();
2588 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2592 // poll() performs two different functions: It polls for user input, and it
2593 // looks at the time consumed so far and decides if it's time to abort the
2598 static int lastInfoTime;
2599 int t = current_search_time();
2604 // We are line oriented, don't read single chars
2605 std::string command;
2607 if (!std::getline(std::cin, command))
2610 if (command == "quit")
2613 PonderSearch = false;
2617 else if (command == "stop")
2620 PonderSearch = false;
2622 else if (command == "ponderhit")
2626 // Print search information
2630 else if (lastInfoTime > t)
2631 // HACK: Must be a new search where we searched less than
2632 // NodesBetweenPolls nodes during the first second of search.
2635 else if (t - lastInfoTime >= 1000)
2643 if (dbg_show_hit_rate)
2644 dbg_print_hit_rate();
2646 cout << "info nodes " << nodes_searched() << " nps " << nps()
2647 << " time " << t << " hashfull " << TT.full() << endl;
2649 lock_release(&IOLock);
2651 if (ShowCurrentLine)
2652 Threads[0].printCurrentLine = true;
2655 // Should we stop the search?
2659 bool stillAtFirstMove = RootMoveNumber == 1
2661 && t > MaxSearchTime + ExtraSearchTime;
2663 bool noProblemFound = !FailHigh
2665 && !fail_high_ply_1()
2667 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2669 bool noMoreTime = t > AbsoluteMaxSearchTime
2670 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2673 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2674 || (ExactMaxTime && t >= ExactMaxTime)
2675 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2680 // ponderhit() is called when the program is pondering (i.e. thinking while
2681 // it's the opponent's turn to move) in order to let the engine know that
2682 // it correctly predicted the opponent's move.
2686 int t = current_search_time();
2687 PonderSearch = false;
2689 bool stillAtFirstMove = RootMoveNumber == 1
2691 && t > MaxSearchTime + ExtraSearchTime;
2693 bool noProblemFound = !FailHigh
2695 && !fail_high_ply_1()
2697 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2699 bool noMoreTime = t > AbsoluteMaxSearchTime
2703 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2708 // print_current_line() prints the current line of search for a given
2709 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2711 void print_current_line(SearchStack ss[], int ply, int threadID) {
2713 assert(ply >= 0 && ply < PLY_MAX);
2714 assert(threadID >= 0 && threadID < ActiveThreads);
2716 if (!Threads[threadID].idle)
2719 cout << "info currline " << (threadID + 1);
2720 for (int p = 0; p < ply; p++)
2721 cout << " " << ss[p].currentMove;
2724 lock_release(&IOLock);
2726 Threads[threadID].printCurrentLine = false;
2727 if (threadID + 1 < ActiveThreads)
2728 Threads[threadID + 1].printCurrentLine = true;
2732 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2734 void init_ss_array(SearchStack ss[]) {
2736 for (int i = 0; i < 3; i++)
2739 ss[i].initKillers();
2744 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2745 // while the program is pondering. The point is to work around a wrinkle in
2746 // the UCI protocol: When pondering, the engine is not allowed to give a
2747 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2748 // We simply wait here until one of these commands is sent, and return,
2749 // after which the bestmove and pondermove will be printed (in id_loop()).
2751 void wait_for_stop_or_ponderhit() {
2753 std::string command;
2757 if (!std::getline(std::cin, command))
2760 if (command == "quit")
2765 else if (command == "ponderhit" || command == "stop")
2771 // idle_loop() is where the threads are parked when they have no work to do.
2772 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2773 // object for which the current thread is the master.
2775 void idle_loop(int threadID, SplitPoint* waitSp) {
2777 assert(threadID >= 0 && threadID < THREAD_MAX);
2779 Threads[threadID].running = true;
2783 if (AllThreadsShouldExit && threadID != 0)
2786 // If we are not thinking, wait for a condition to be signaled
2787 // instead of wasting CPU time polling for work.
2788 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2791 #if !defined(_MSC_VER)
2792 pthread_mutex_lock(&WaitLock);
2793 if (Idle || threadID >= ActiveThreads)
2794 pthread_cond_wait(&WaitCond, &WaitLock);
2796 pthread_mutex_unlock(&WaitLock);
2798 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2802 // If this thread has been assigned work, launch a search
2803 if (Threads[threadID].workIsWaiting)
2805 Threads[threadID].workIsWaiting = false;
2806 if (Threads[threadID].splitPoint->pvNode)
2807 sp_search_pv(Threads[threadID].splitPoint, threadID);
2809 sp_search(Threads[threadID].splitPoint, threadID);
2811 Threads[threadID].idle = true;
2814 // If this thread is the master of a split point and all threads have
2815 // finished their work at this split point, return from the idle loop.
2816 if (waitSp != NULL && waitSp->cpus == 0)
2820 Threads[threadID].running = false;
2824 // init_split_point_stack() is called during program initialization, and
2825 // initializes all split point objects.
2827 void init_split_point_stack() {
2829 for (int i = 0; i < THREAD_MAX; i++)
2830 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2832 SplitPointStack[i][j].parent = NULL;
2833 lock_init(&(SplitPointStack[i][j].lock), NULL);
2838 // destroy_split_point_stack() is called when the program exits, and
2839 // destroys all locks in the precomputed split point objects.
2841 void destroy_split_point_stack() {
2843 for (int i = 0; i < THREAD_MAX; i++)
2844 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2845 lock_destroy(&(SplitPointStack[i][j].lock));
2849 // thread_should_stop() checks whether the thread with a given threadID has
2850 // been asked to stop, directly or indirectly. This can happen if a beta
2851 // cutoff has occurred in the thread's currently active split point, or in
2852 // some ancestor of the current split point.
2854 bool thread_should_stop(int threadID) {
2856 assert(threadID >= 0 && threadID < ActiveThreads);
2860 if (Threads[threadID].stop)
2862 if (ActiveThreads <= 2)
2864 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2867 Threads[threadID].stop = true;
2874 // thread_is_available() checks whether the thread with threadID "slave" is
2875 // available to help the thread with threadID "master" at a split point. An
2876 // obvious requirement is that "slave" must be idle. With more than two
2877 // threads, this is not by itself sufficient: If "slave" is the master of
2878 // some active split point, it is only available as a slave to the other
2879 // threads which are busy searching the split point at the top of "slave"'s
2880 // split point stack (the "helpful master concept" in YBWC terminology).
2882 bool thread_is_available(int slave, int master) {
2884 assert(slave >= 0 && slave < ActiveThreads);
2885 assert(master >= 0 && master < ActiveThreads);
2886 assert(ActiveThreads > 1);
2888 if (!Threads[slave].idle || slave == master)
2891 if (Threads[slave].activeSplitPoints == 0)
2892 // No active split points means that the thread is available as
2893 // a slave for any other thread.
2896 if (ActiveThreads == 2)
2899 // Apply the "helpful master" concept if possible
2900 if (SplitPointStack[slave][Threads[slave].activeSplitPoints - 1].slaves[master])
2907 // idle_thread_exists() tries to find an idle thread which is available as
2908 // a slave for the thread with threadID "master".
2910 bool idle_thread_exists(int master) {
2912 assert(master >= 0 && master < ActiveThreads);
2913 assert(ActiveThreads > 1);
2915 for (int i = 0; i < ActiveThreads; i++)
2916 if (thread_is_available(i, master))
2923 // split() does the actual work of distributing the work at a node between
2924 // several threads at PV nodes. If it does not succeed in splitting the
2925 // node (because no idle threads are available, or because we have no unused
2926 // split point objects), the function immediately returns false. If
2927 // splitting is possible, a SplitPoint object is initialized with all the
2928 // data that must be copied to the helper threads (the current position and
2929 // search stack, alpha, beta, the search depth, etc.), and we tell our
2930 // helper threads that they have been assigned work. This will cause them
2931 // to instantly leave their idle loops and call sp_search_pv(). When all
2932 // threads have returned from sp_search_pv (or, equivalently, when
2933 // splitPoint->cpus becomes 0), split() returns true.
2935 bool split(const Position& p, SearchStack* sstck, int ply,
2936 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2937 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2940 assert(sstck != NULL);
2941 assert(ply >= 0 && ply < PLY_MAX);
2942 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2943 assert(!pvNode || *alpha < *beta);
2944 assert(*beta <= VALUE_INFINITE);
2945 assert(depth > Depth(0));
2946 assert(master >= 0 && master < ActiveThreads);
2947 assert(ActiveThreads > 1);
2949 SplitPoint* splitPoint;
2954 // If no other thread is available to help us, or if we have too many
2955 // active split points, don't split.
2956 if ( !idle_thread_exists(master)
2957 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2959 lock_release(&MPLock);
2963 // Pick the next available split point object from the split point stack
2964 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2965 Threads[master].activeSplitPoints++;
2967 // Initialize the split point object and copy current position
2968 splitPoint->parent = Threads[master].splitPoint;
2969 splitPoint->finished = false;
2970 splitPoint->ply = ply;
2971 splitPoint->depth = depth;
2972 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2973 splitPoint->beta = *beta;
2974 splitPoint->pvNode = pvNode;
2975 splitPoint->bestValue = *bestValue;
2976 splitPoint->futilityValue = futilityValue;
2977 splitPoint->master = master;
2978 splitPoint->mp = mp;
2979 splitPoint->moves = *moves;
2980 splitPoint->cpus = 1;
2981 splitPoint->pos.copy(p);
2982 splitPoint->parentSstack = sstck;
2983 for (i = 0; i < ActiveThreads; i++)
2984 splitPoint->slaves[i] = 0;
2986 // Copy the current search stack to the master thread
2987 memcpy(splitPoint->sstack[master], sstck, (ply+1) * sizeof(SearchStack));
2988 Threads[master].splitPoint = splitPoint;
2990 // Make copies of the current position and search stack for each thread
2991 for (i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2992 if (thread_is_available(i, master))
2994 memcpy(splitPoint->sstack[i], sstck, (ply+1) * sizeof(SearchStack));
2995 Threads[i].splitPoint = splitPoint;
2996 splitPoint->slaves[i] = 1;
3000 // Tell the threads that they have work to do. This will make them leave
3002 for (i = 0; i < ActiveThreads; i++)
3003 if (i == master || splitPoint->slaves[i])
3005 Threads[i].workIsWaiting = true;
3006 Threads[i].idle = false;
3007 Threads[i].stop = false;
3010 lock_release(&MPLock);
3012 // Everything is set up. The master thread enters the idle loop, from
3013 // which it will instantly launch a search, because its workIsWaiting
3014 // slot is 'true'. We send the split point as a second parameter to the
3015 // idle loop, which means that the main thread will return from the idle
3016 // loop when all threads have finished their work at this split point
3017 // (i.e. when splitPoint->cpus == 0).
3018 idle_loop(master, splitPoint);
3020 // We have returned from the idle loop, which means that all threads are
3021 // finished. Update alpha, beta and bestValue, and return.
3025 *alpha = splitPoint->alpha;
3027 *beta = splitPoint->beta;
3028 *bestValue = splitPoint->bestValue;
3029 Threads[master].stop = false;
3030 Threads[master].idle = false;
3031 Threads[master].activeSplitPoints--;
3032 Threads[master].splitPoint = splitPoint->parent;
3034 lock_release(&MPLock);
3039 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3040 // to start a new search from the root.
3042 void wake_sleeping_threads() {
3044 if (ActiveThreads > 1)
3046 for (int i = 1; i < ActiveThreads; i++)
3048 Threads[i].idle = true;
3049 Threads[i].workIsWaiting = false;
3052 #if !defined(_MSC_VER)
3053 pthread_mutex_lock(&WaitLock);
3054 pthread_cond_broadcast(&WaitCond);
3055 pthread_mutex_unlock(&WaitLock);
3057 for (int i = 1; i < THREAD_MAX; i++)
3058 SetEvent(SitIdleEvent[i]);
3064 // init_thread() is the function which is called when a new thread is
3065 // launched. It simply calls the idle_loop() function with the supplied
3066 // threadID. There are two versions of this function; one for POSIX
3067 // threads and one for Windows threads.
3069 #if !defined(_MSC_VER)
3071 void* init_thread(void *threadID) {
3073 idle_loop(*(int*)threadID, NULL);
3079 DWORD WINAPI init_thread(LPVOID threadID) {
3081 idle_loop(*(int*)threadID, NULL);