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 approximate
176 // evaluation of the position is more than NullMoveMargin below beta.
177 const Value NullMoveMargin = Value(0x300);
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 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
194 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
196 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
197 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
200 /// Variables initialized by UCI options
202 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
203 int LMRPVMoves, LMRNonPVMoves;
205 // Depth limit for use of dynamic threat detection
208 // Last seconds noise filtering (LSN)
209 const bool UseLSNFiltering = true;
210 const int LSNTime = 4000; // In milliseconds
211 const Value LSNValue = value_from_centipawns(200);
212 bool loseOnTime = false;
214 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
215 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
216 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
218 // Iteration counters
220 BetaCounterType BetaCounter;
222 // Scores and number of times the best move changed for each iteration
223 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
224 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
229 // Time managment variables
232 int MaxNodes, MaxDepth;
233 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
234 bool InfiniteSearch, PonderSearch, StopOnPonderhit;
235 bool AbortSearch, Quit;
236 bool FailHigh, FailLow, Problem;
238 // Show current line?
239 bool ShowCurrentLine;
243 std::ofstream LogFile;
245 // MP related variables
246 int ActiveThreads = 1;
247 Depth MinimumSplitDepth;
248 int MaxThreadsPerSplitPoint;
249 Thread Threads[THREAD_MAX];
252 bool AllThreadsShouldExit = false;
253 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
256 #if !defined(_MSC_VER)
257 pthread_cond_t WaitCond;
258 pthread_mutex_t WaitLock;
260 HANDLE SitIdleEvent[THREAD_MAX];
263 // Node counters, used only by thread[0] but try to keep in different
264 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
266 int NodesBetweenPolls = 30000;
274 Value id_loop(const Position& pos, Move searchMoves[]);
275 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
276 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
277 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
278 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
279 void sp_search(SplitPoint* sp, int threadID);
280 void sp_search_pv(SplitPoint* sp, int threadID);
281 void init_node(SearchStack ss[], int ply, int threadID);
282 void update_pv(SearchStack ss[], int ply);
283 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
284 bool connected_moves(const Position& pos, Move m1, Move m2);
285 bool value_is_mate(Value value);
286 bool move_is_killer(Move m, const SearchStack& ss);
287 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
288 bool ok_to_do_nullmove(const Position& pos);
289 bool ok_to_prune(const Position& pos, Move m, Move threat);
290 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
291 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
292 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
293 void update_killers(Move m, SearchStack& ss);
295 bool fail_high_ply_1();
296 int current_search_time();
300 void print_current_line(SearchStack ss[], int ply, int threadID);
301 void wait_for_stop_or_ponderhit();
302 void init_ss_array(SearchStack ss[]);
304 void idle_loop(int threadID, SplitPoint* waitSp);
305 void init_split_point_stack();
306 void destroy_split_point_stack();
307 bool thread_should_stop(int threadID);
308 bool thread_is_available(int slave, int master);
309 bool idle_thread_exists(int master);
310 bool split(const Position& pos, SearchStack* ss, int ply,
311 Value *alpha, Value *beta, Value *bestValue,
312 const Value futilityValue, Depth depth, int *moves,
313 MovePicker *mp, int master, bool pvNode);
314 void wake_sleeping_threads();
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
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 // Look for a book move
370 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
373 if (get_option_value_string("Book File") != OpeningBook.file_name())
374 OpeningBook.open(get_option_value_string("Book File"));
376 bookMove = OpeningBook.get_move(pos);
377 if (bookMove != MOVE_NONE)
379 cout << "bestmove " << bookMove << endl;
384 // Initialize global search variables
385 Idle = StopOnPonderhit = AbortSearch = Quit = false;
386 FailHigh = FailLow = Problem = false;
387 SearchStartTime = get_system_time();
388 ExactMaxTime = maxTime;
390 InfiniteSearch = infinite;
391 PonderSearch = ponder;
393 for (int i = 0; i < THREAD_MAX; i++)
395 Threads[i].nodes = 0ULL;
396 Threads[i].failHighPly1 = false;
399 if (button_was_pressed("New Game"))
400 loseOnTime = false; // Reset at the beginning of a new game
402 // Read UCI option values
403 TT.set_size(get_option_value_int("Hash"));
404 if (button_was_pressed("Clear Hash"))
407 bool PonderingEnabled = get_option_value_bool("Ponder");
408 MultiPV = get_option_value_int("MultiPV");
410 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
411 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
413 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
414 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
416 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
417 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
419 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
420 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
422 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
423 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
425 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
426 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
428 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
429 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
430 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
432 Chess960 = get_option_value_bool("UCI_Chess960");
433 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
434 UseLogFile = get_option_value_bool("Use Search Log");
436 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
438 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
439 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
441 read_weights(pos.side_to_move());
443 // Set the number of active threads
444 int newActiveThreads = get_option_value_int("Threads");
445 if (newActiveThreads != ActiveThreads)
447 ActiveThreads = newActiveThreads;
448 init_eval(ActiveThreads);
451 // Wake up sleeping threads
452 wake_sleeping_threads();
454 for (int i = 1; i < ActiveThreads; i++)
455 assert(thread_is_available(i, 0));
458 int myTime = time[side_to_move];
459 int myIncrement = increment[side_to_move];
461 if (!movesToGo) // Sudden death time control
465 MaxSearchTime = myTime / 30 + myIncrement;
466 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
468 else // Blitz game without increment
470 MaxSearchTime = myTime / 30;
471 AbsoluteMaxSearchTime = myTime / 8;
474 else // (x moves) / (y minutes)
478 MaxSearchTime = myTime / 2;
479 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
483 MaxSearchTime = myTime / Min(movesToGo, 20);
484 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
488 if (PonderingEnabled)
490 MaxSearchTime += MaxSearchTime / 4;
491 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
494 // Fixed depth or fixed number of nodes?
497 InfiniteSearch = true; // HACK
502 NodesBetweenPolls = Min(MaxNodes, 30000);
503 InfiniteSearch = true; // HACK
505 else if (myTime && myTime < 1000)
506 NodesBetweenPolls = 1000;
507 else if (myTime && myTime < 5000)
508 NodesBetweenPolls = 5000;
510 NodesBetweenPolls = 30000;
512 // Write information to search log file
514 LogFile << "Searching: " << pos.to_fen() << endl
515 << "infinite: " << infinite
516 << " ponder: " << ponder
517 << " time: " << myTime
518 << " increment: " << myIncrement
519 << " moves to go: " << movesToGo << endl;
521 // LSN filtering. Used only for developing purpose. Disabled by default.
525 // Step 2. If after last move we decided to lose on time, do it now!
526 while (SearchStartTime + myTime + 1000 > get_system_time())
530 // We're ready to start thinking. Call the iterative deepening loop function
531 Value v = id_loop(pos, searchMoves);
536 // Step 1. If this is sudden death game and our position is hopeless,
537 // decide to lose on time.
538 if ( !loseOnTime // If we already lost on time, go to step 3.
548 // Step 3. Now after stepping over the time limit, reset flag for next match.
561 /// init_threads() is called during startup. It launches all helper threads,
562 /// and initializes the split point stack and the global locks and condition
565 void init_threads() {
569 #if !defined(_MSC_VER)
570 pthread_t pthread[1];
573 for (i = 0; i < THREAD_MAX; i++)
574 Threads[i].activeSplitPoints = 0;
576 // Initialize global locks
577 lock_init(&MPLock, NULL);
578 lock_init(&IOLock, NULL);
580 init_split_point_stack();
582 #if !defined(_MSC_VER)
583 pthread_mutex_init(&WaitLock, NULL);
584 pthread_cond_init(&WaitCond, NULL);
586 for (i = 0; i < THREAD_MAX; i++)
587 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
590 // All threads except the main thread should be initialized to idle state
591 for (i = 1; i < THREAD_MAX; i++)
593 Threads[i].stop = false;
594 Threads[i].workIsWaiting = false;
595 Threads[i].idle = true;
596 Threads[i].running = false;
599 // Launch the helper threads
600 for (i = 1; i < THREAD_MAX; i++)
602 #if !defined(_MSC_VER)
603 pthread_create(pthread, NULL, init_thread, (void*)(&i));
606 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
609 // Wait until the thread has finished launching
610 while (!Threads[i].running);
615 /// stop_threads() is called when the program exits. It makes all the
616 /// helper threads exit cleanly.
618 void stop_threads() {
620 ActiveThreads = THREAD_MAX; // HACK
621 Idle = false; // HACK
622 wake_sleeping_threads();
623 AllThreadsShouldExit = true;
624 for (int i = 1; i < THREAD_MAX; i++)
626 Threads[i].stop = true;
627 while (Threads[i].running);
629 destroy_split_point_stack();
633 /// nodes_searched() returns the total number of nodes searched so far in
634 /// the current search.
636 int64_t nodes_searched() {
638 int64_t result = 0ULL;
639 for (int i = 0; i < ActiveThreads; i++)
640 result += Threads[i].nodes;
645 // SearchStack::init() initializes a search stack. Used at the beginning of a
646 // new search from the root.
647 void SearchStack::init(int ply) {
649 pv[ply] = pv[ply + 1] = MOVE_NONE;
650 currentMove = threatMove = MOVE_NONE;
651 reduction = Depth(0);
654 void SearchStack::initKillers() {
656 mateKiller = MOVE_NONE;
657 for (int i = 0; i < KILLER_MAX; i++)
658 killers[i] = MOVE_NONE;
663 // id_loop() is the main iterative deepening loop. It calls root_search
664 // repeatedly with increasing depth until the allocated thinking time has
665 // been consumed, the user stops the search, or the maximum search depth is
668 Value id_loop(const Position& pos, Move searchMoves[]) {
671 SearchStack ss[PLY_MAX_PLUS_2];
673 // searchMoves are verified, copied, scored and sorted
674 RootMoveList rml(p, searchMoves);
676 if (rml.move_count() == 0)
679 wait_for_stop_or_ponderhit();
681 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
684 // Print RootMoveList c'tor startup scoring to the standard output,
685 // so that we print information also for iteration 1.
686 cout << "info depth " << 1 << "\ninfo depth " << 1
687 << " score " << value_to_string(rml.get_move_score(0))
688 << " time " << current_search_time()
689 << " nodes " << nodes_searched()
691 << " pv " << rml.get_move(0) << "\n";
697 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
700 // Is one move significantly better than others after initial scoring ?
701 Move EasyMove = MOVE_NONE;
702 if ( rml.move_count() == 1
703 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
704 EasyMove = rml.get_move(0);
706 // Iterative deepening loop
707 while (Iteration < PLY_MAX)
709 // Initialize iteration
712 BestMoveChangesByIteration[Iteration] = 0;
716 cout << "info depth " << Iteration << endl;
718 // Calculate dynamic search window based on previous iterations
721 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
723 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
724 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
726 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
728 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
729 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
733 alpha = - VALUE_INFINITE;
734 beta = VALUE_INFINITE;
737 // Search to the current depth
738 Value value = root_search(p, ss, rml, alpha, beta);
740 // Write PV to transposition table, in case the relevant entries have
741 // been overwritten during the search.
742 TT.insert_pv(p, ss[0].pv);
745 break; // Value cannot be trusted. Break out immediately!
747 //Save info about search result
748 Value speculatedValue;
751 Value delta = value - IterationInfo[Iteration - 1].value;
758 speculatedValue = value + delta;
759 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
761 else if (value <= alpha)
763 assert(value == alpha);
767 speculatedValue = value + delta;
768 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
770 speculatedValue = value;
772 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
773 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
775 // Drop the easy move if it differs from the new best move
776 if (ss[0].pv[0] != EasyMove)
777 EasyMove = MOVE_NONE;
784 bool stopSearch = false;
786 // Stop search early if there is only a single legal move,
787 // we search up to Iteration 6 anyway to get a proper score.
788 if (Iteration >= 6 && rml.move_count() == 1)
791 // Stop search early when the last two iterations returned a mate score
793 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
794 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
797 // Stop search early if one move seems to be much better than the rest
798 int64_t nodes = nodes_searched();
802 && EasyMove == ss[0].pv[0]
803 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
804 && current_search_time() > MaxSearchTime / 16)
805 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
806 && current_search_time() > MaxSearchTime / 32)))
809 // Add some extra time if the best move has changed during the last two iterations
810 if (Iteration > 5 && Iteration <= 50)
811 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
812 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
814 // Stop search if most of MaxSearchTime is consumed at the end of the
815 // iteration. We probably don't have enough time to search the first
816 // move at the next iteration anyway.
817 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
825 StopOnPonderhit = true;
829 if (MaxDepth && Iteration >= MaxDepth)
835 // If we are pondering, we shouldn't print the best move before we
838 wait_for_stop_or_ponderhit();
840 // Print final search statistics
841 cout << "info nodes " << nodes_searched()
843 << " time " << current_search_time()
844 << " hashfull " << TT.full() << endl;
846 // Print the best move and the ponder move to the standard output
847 if (ss[0].pv[0] == MOVE_NONE)
849 ss[0].pv[0] = rml.get_move(0);
850 ss[0].pv[1] = MOVE_NONE;
852 cout << "bestmove " << ss[0].pv[0];
853 if (ss[0].pv[1] != MOVE_NONE)
854 cout << " ponder " << ss[0].pv[1];
861 dbg_print_mean(LogFile);
863 if (dbg_show_hit_rate)
864 dbg_print_hit_rate(LogFile);
866 LogFile << "\nNodes: " << nodes_searched()
867 << "\nNodes/second: " << nps()
868 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
871 p.do_move(ss[0].pv[0], st);
872 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
874 return rml.get_move_score(0);
878 // root_search() is the function which searches the root node. It is
879 // similar to search_pv except that it uses a different move ordering
880 // scheme and prints some information to the standard output.
882 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
884 Value oldAlpha = alpha;
888 // Loop through all the moves in the root move list
889 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
893 // We failed high, invalidate and skip next moves, leave node-counters
894 // and beta-counters as they are and quickly return, we will try to do
895 // a research at the next iteration with a bigger aspiration window.
896 rml.set_move_score(i, -VALUE_INFINITE);
904 RootMoveNumber = i + 1;
907 // Save the current node count before the move is searched
908 nodes = nodes_searched();
910 // Reset beta cut-off counters
913 // Pick the next root move, and print the move and the move number to
914 // the standard output.
915 move = ss[0].currentMove = rml.get_move(i);
917 if (current_search_time() >= 1000)
918 cout << "info currmove " << move
919 << " currmovenumber " << RootMoveNumber << endl;
921 // Decide search depth for this move
922 bool moveIsCheck = pos.move_is_check(move);
923 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
925 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
926 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
928 // Make the move, and search it
929 pos.do_move(move, st, ci, moveIsCheck);
933 // Aspiration window is disabled in multi-pv case
935 alpha = -VALUE_INFINITE;
937 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
939 // If the value has dropped a lot compared to the last iteration,
940 // set the boolean variable Problem to true. This variable is used
941 // for time managment: When Problem is true, we try to complete the
942 // current iteration before playing a move.
943 Problem = ( Iteration >= 2
944 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
946 if (Problem && StopOnPonderhit)
947 StopOnPonderhit = false;
951 // Try to reduce non-pv search depth by one ply if move seems not problematic,
952 // if the move fails high will be re-searched at full depth.
953 if ( newDepth >= 3*OnePly
954 && i >= MultiPV + LMRPVMoves
956 && !captureOrPromotion
957 && !move_is_castle(move))
959 ss[0].reduction = OnePly;
960 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
962 value = alpha + 1; // Just to trigger next condition
966 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
970 // Fail high! Set the boolean variable FailHigh to true, and
971 // re-search the move using a PV search. The variable FailHigh
972 // is used for time managment: We try to avoid aborting the
973 // search prematurely during a fail high research.
975 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
982 // Finished searching the move. If AbortSearch is true, the search
983 // was aborted because the user interrupted the search or because we
984 // ran out of time. In this case, the return value of the search cannot
985 // be trusted, and we break out of the loop without updating the best
990 // Remember beta-cutoff and searched nodes counts for this move. The
991 // info is used to sort the root moves at the next iteration.
993 BetaCounter.read(pos.side_to_move(), our, their);
994 rml.set_beta_counters(i, our, their);
995 rml.set_move_nodes(i, nodes_searched() - nodes);
997 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
999 if (value <= alpha && i >= MultiPV)
1000 rml.set_move_score(i, -VALUE_INFINITE);
1003 // PV move or new best move!
1006 rml.set_move_score(i, value);
1008 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1009 rml.set_move_pv(i, ss[0].pv);
1013 // We record how often the best move has been changed in each
1014 // iteration. This information is used for time managment: When
1015 // the best move changes frequently, we allocate some more time.
1017 BestMoveChangesByIteration[Iteration]++;
1019 // Print search information to the standard output
1020 cout << "info depth " << Iteration
1021 << " score " << value_to_string(value)
1022 << ((value >= beta) ? " lowerbound" :
1023 ((value <= alpha)? " upperbound" : ""))
1024 << " time " << current_search_time()
1025 << " nodes " << nodes_searched()
1029 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1030 cout << ss[0].pv[j] << " ";
1036 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1037 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1039 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1040 nodes_searched(), value, type, ss[0].pv) << endl;
1045 // Reset the global variable Problem to false if the value isn't too
1046 // far below the final value from the last iteration.
1047 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1052 rml.sort_multipv(i);
1053 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1055 cout << "info multipv " << j + 1
1056 << " score " << value_to_string(rml.get_move_score(j))
1057 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1058 << " time " << current_search_time()
1059 << " nodes " << nodes_searched()
1063 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1064 cout << rml.get_move_pv(j, k) << " ";
1068 alpha = rml.get_move_score(Min(i, MultiPV-1));
1070 } // PV move or new best move
1072 assert(alpha >= oldAlpha);
1074 FailLow = (alpha == oldAlpha);
1080 // search_pv() is the main search function for PV nodes.
1082 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1083 Depth depth, int ply, int threadID) {
1085 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1086 assert(beta > alpha && beta <= VALUE_INFINITE);
1087 assert(ply >= 0 && ply < PLY_MAX);
1088 assert(threadID >= 0 && threadID < ActiveThreads);
1090 Move movesSearched[256];
1095 Depth ext, newDepth;
1096 Value oldAlpha, value;
1097 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1099 Value bestValue = -VALUE_INFINITE;
1102 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1104 // Initialize, and make an early exit in case of an aborted search,
1105 // an instant draw, maximum ply reached, etc.
1106 init_node(ss, ply, threadID);
1108 // After init_node() that calls poll()
1109 if (AbortSearch || thread_should_stop(threadID))
1115 if (ply >= PLY_MAX - 1)
1116 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1118 // Mate distance pruning
1120 alpha = Max(value_mated_in(ply), alpha);
1121 beta = Min(value_mate_in(ply+1), beta);
1125 // Transposition table lookup. At PV nodes, we don't use the TT for
1126 // pruning, but only for move ordering. This is to avoid problems in
1127 // the following areas:
1129 // * Repetition draw detection
1130 // * Fifty move rule detection
1131 // * Searching for a mate
1132 // * Printing of full PV line
1134 tte = TT.retrieve(pos.get_key());
1135 ttMove = (tte ? tte->move() : MOVE_NONE);
1137 // Go with internal iterative deepening if we don't have a TT move
1138 if ( UseIIDAtPVNodes
1139 && depth >= 5*OnePly
1140 && ttMove == MOVE_NONE)
1142 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1143 ttMove = ss[ply].pv[ply];
1144 tte = TT.retrieve(pos.get_key());
1147 // Initialize a MovePicker object for the current position, and prepare
1148 // to search all moves
1149 isCheck = pos.is_check();
1150 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1152 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1154 // Loop through all legal moves until no moves remain or a beta cutoff
1156 while ( alpha < beta
1157 && (move = mp.get_next_move()) != MOVE_NONE
1158 && !thread_should_stop(threadID))
1160 assert(move_is_ok(move));
1162 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1163 moveIsCheck = pos.move_is_check(move, ci);
1164 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1166 // Decide the new search depth
1167 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1169 // Singular extension search. We extend the TT move if its value is much better than
1170 // its siblings. To verify this we do a reduced search on all the other moves but the
1171 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1172 if ( depth >= 6 * OnePly
1174 && move == tte->move()
1176 && is_lower_bound(tte->type())
1177 && tte->depth() >= depth - 3 * OnePly)
1179 Value ttValue = value_from_tt(tte->value(), ply);
1181 if (abs(ttValue) < VALUE_KNOWN_WIN)
1183 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1185 if (excValue < ttValue - SingleReplyMargin)
1190 newDepth = depth - OnePly + ext;
1192 // Update current move
1193 movesSearched[moveCount++] = ss[ply].currentMove = move;
1195 // Make and search the move
1196 pos.do_move(move, st, ci, moveIsCheck);
1198 if (moveCount == 1) // The first move in list is the PV
1199 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1202 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1203 // if the move fails high will be re-searched at full depth.
1204 if ( depth >= 3*OnePly
1205 && moveCount >= LMRPVMoves
1207 && !captureOrPromotion
1208 && !move_is_castle(move)
1209 && !move_is_killer(move, ss[ply]))
1211 ss[ply].reduction = OnePly;
1212 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1215 value = alpha + 1; // Just to trigger next condition
1217 if (value > alpha) // Go with full depth non-pv search
1219 ss[ply].reduction = Depth(0);
1220 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1221 if (value > alpha && value < beta)
1223 // When the search fails high at ply 1 while searching the first
1224 // move at the root, set the flag failHighPly1. This is used for
1225 // time managment: We don't want to stop the search early in
1226 // such cases, because resolving the fail high at ply 1 could
1227 // result in a big drop in score at the root.
1228 if (ply == 1 && RootMoveNumber == 1)
1229 Threads[threadID].failHighPly1 = true;
1231 // A fail high occurred. Re-search at full window (pv search)
1232 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1233 Threads[threadID].failHighPly1 = false;
1237 pos.undo_move(move);
1239 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1242 if (value > bestValue)
1249 if (value == value_mate_in(ply + 1))
1250 ss[ply].mateKiller = move;
1252 // If we are at ply 1, and we are searching the first root move at
1253 // ply 0, set the 'Problem' variable if the score has dropped a lot
1254 // (from the computer's point of view) since the previous iteration.
1257 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1262 if ( ActiveThreads > 1
1264 && depth >= MinimumSplitDepth
1266 && idle_thread_exists(threadID)
1268 && !thread_should_stop(threadID)
1269 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1270 depth, &moveCount, &mp, threadID, true))
1274 // All legal moves have been searched. A special case: If there were
1275 // no legal moves, it must be mate or stalemate.
1277 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1279 // If the search is not aborted, update the transposition table,
1280 // history counters, and killer moves.
1281 if (AbortSearch || thread_should_stop(threadID))
1284 if (bestValue <= oldAlpha)
1285 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1287 else if (bestValue >= beta)
1289 BetaCounter.add(pos.side_to_move(), depth, threadID);
1290 move = ss[ply].pv[ply];
1291 if (!pos.move_is_capture_or_promotion(move))
1293 update_history(pos, move, depth, movesSearched, moveCount);
1294 update_killers(move, ss[ply]);
1296 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1299 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1305 // search() is the search function for zero-width nodes.
1307 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1308 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1310 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1311 assert(ply >= 0 && ply < PLY_MAX);
1312 assert(threadID >= 0 && threadID < ActiveThreads);
1314 Move movesSearched[256];
1319 Depth ext, newDepth;
1320 Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
1321 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1322 bool mateThreat = false;
1324 Value bestValue = -VALUE_INFINITE;
1327 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1329 // Initialize, and make an early exit in case of an aborted search,
1330 // an instant draw, maximum ply reached, etc.
1331 init_node(ss, ply, threadID);
1333 // After init_node() that calls poll()
1334 if (AbortSearch || thread_should_stop(threadID))
1340 if (ply >= PLY_MAX - 1)
1341 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1343 // Mate distance pruning
1344 if (value_mated_in(ply) >= beta)
1347 if (value_mate_in(ply + 1) < beta)
1350 // We don't want the score of a partial search to overwrite a previous full search
1351 // TT value, so we use a different position key in case of an excluded move exsists.
1352 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1354 // Transposition table lookup
1355 tte = TT.retrieve(posKey);
1356 ttMove = (tte ? tte->move() : MOVE_NONE);
1358 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1360 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1361 return value_from_tt(tte->value(), ply);
1364 approximateEval = refine_eval(tte, quick_evaluate(pos), ply);
1365 isCheck = pos.is_check();
1371 && !value_is_mate(beta)
1372 && ok_to_do_nullmove(pos)
1373 && approximateEval >= beta - NullMoveMargin)
1375 ss[ply].currentMove = MOVE_NULL;
1377 pos.do_null_move(st);
1379 // Null move dynamic reduction based on depth
1380 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1382 // Null move dynamic reduction based on value
1383 if (approximateEval - beta > PawnValueMidgame)
1386 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1388 pos.undo_null_move();
1390 if (nullValue >= beta)
1392 if (depth < 6 * OnePly)
1395 // Do zugzwang verification search
1396 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1400 // The null move failed low, which means that we may be faced with
1401 // some kind of threat. If the previous move was reduced, check if
1402 // the move that refuted the null move was somehow connected to the
1403 // move which was reduced. If a connection is found, return a fail
1404 // low score (which will cause the reduced move to fail high in the
1405 // parent node, which will trigger a re-search with full depth).
1406 if (nullValue == value_mated_in(ply + 2))
1409 ss[ply].threatMove = ss[ply + 1].currentMove;
1410 if ( depth < ThreatDepth
1411 && ss[ply - 1].reduction
1412 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1416 // Null move search not allowed, try razoring
1417 else if ( !value_is_mate(beta)
1418 && depth < RazorDepth
1419 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1420 && ss[ply - 1].currentMove != MOVE_NULL
1421 && ttMove == MOVE_NONE
1422 && !pos.has_pawn_on_7th(pos.side_to_move()))
1424 Value rbeta = beta - RazorMargins[int(depth) - 2];
1425 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1430 // Go with internal iterative deepening if we don't have a TT move
1431 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1432 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1434 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1435 ttMove = ss[ply].pv[ply];
1436 tte = TT.retrieve(pos.get_key());
1439 // Initialize a MovePicker object for the current position, and prepare
1440 // to search all moves.
1441 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1443 futilityValue = VALUE_NONE;
1444 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1446 // Calculate depth dependant futility pruning parameters
1447 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1448 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1450 // Avoid calling evaluate() if we already have the score in TT
1451 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1452 futilityValue = value_from_tt(tte->value(), ply) + FutilityValueMargin;
1454 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1455 while ( bestValue < beta
1456 && (move = mp.get_next_move()) != MOVE_NONE
1457 && !thread_should_stop(threadID))
1459 assert(move_is_ok(move));
1461 if (move == excludedMove)
1464 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1465 moveIsCheck = pos.move_is_check(move, ci);
1466 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1468 // Decide the new search depth
1469 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1471 // Singular extension search. We extend the TT move if its value is much better than
1472 // its siblings. To verify this we do a reduced search on all the other moves but the
1473 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1474 if ( depth >= 8 * OnePly
1476 && move == tte->move()
1477 && !excludedMove // Do not allow recursive single-reply search
1479 && is_lower_bound(tte->type())
1480 && tte->depth() >= depth - 3 * OnePly)
1482 Value ttValue = value_from_tt(tte->value(), ply);
1484 if (abs(ttValue) < VALUE_KNOWN_WIN)
1486 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1488 if (excValue < ttValue - SingleReplyMargin)
1493 newDepth = depth - OnePly + ext;
1495 // Update current move
1496 movesSearched[moveCount++] = ss[ply].currentMove = move;
1499 if ( useFutilityPruning
1501 && !captureOrPromotion
1504 // Move count based pruning
1505 if ( moveCount >= FutilityMoveCountMargin
1506 && ok_to_prune(pos, move, ss[ply].threatMove)
1507 && bestValue > value_mated_in(PLY_MAX))
1510 // Value based pruning
1511 if (futilityValue == VALUE_NONE)
1512 futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1514 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1516 if (futilityValueScaled < beta)
1518 if (futilityValueScaled > bestValue)
1519 bestValue = futilityValueScaled;
1524 // Make and search the move
1525 pos.do_move(move, st, ci, moveIsCheck);
1527 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1528 // if the move fails high will be re-searched at full depth.
1529 if ( depth >= 3*OnePly
1530 && moveCount >= LMRNonPVMoves
1532 && !captureOrPromotion
1533 && !move_is_castle(move)
1534 && !move_is_killer(move, ss[ply]))
1536 ss[ply].reduction = OnePly;
1537 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1540 value = beta; // Just to trigger next condition
1542 if (value >= beta) // Go with full depth non-pv search
1544 ss[ply].reduction = Depth(0);
1545 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1547 pos.undo_move(move);
1549 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1552 if (value > bestValue)
1558 if (value == value_mate_in(ply + 1))
1559 ss[ply].mateKiller = move;
1563 if ( ActiveThreads > 1
1565 && depth >= MinimumSplitDepth
1567 && idle_thread_exists(threadID)
1569 && !thread_should_stop(threadID)
1570 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1571 depth, &moveCount, &mp, threadID, false))
1575 // All legal moves have been searched. A special case: If there were
1576 // no legal moves, it must be mate or stalemate.
1578 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1580 // If the search is not aborted, update the transposition table,
1581 // history counters, and killer moves.
1582 if (AbortSearch || thread_should_stop(threadID))
1585 if (bestValue < beta)
1586 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1589 BetaCounter.add(pos.side_to_move(), depth, threadID);
1590 move = ss[ply].pv[ply];
1591 if (!pos.move_is_capture_or_promotion(move))
1593 update_history(pos, move, depth, movesSearched, moveCount);
1594 update_killers(move, ss[ply]);
1596 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1599 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1605 // qsearch() is the quiescence search function, which is called by the main
1606 // search function when the remaining depth is zero (or, to be more precise,
1607 // less than OnePly).
1609 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1610 Depth depth, int ply, int threadID) {
1612 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1613 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1615 assert(ply >= 0 && ply < PLY_MAX);
1616 assert(threadID >= 0 && threadID < ActiveThreads);
1621 Value staticValue, bestValue, value, futilityValue;
1622 bool isCheck, enoughMaterial, moveIsCheck;
1623 const TTEntry* tte = NULL;
1625 bool pvNode = (beta - alpha != 1);
1627 // Initialize, and make an early exit in case of an aborted search,
1628 // an instant draw, maximum ply reached, etc.
1629 init_node(ss, ply, threadID);
1631 // After init_node() that calls poll()
1632 if (AbortSearch || thread_should_stop(threadID))
1638 // Transposition table lookup, only when not in PV
1641 tte = TT.retrieve(pos.get_key());
1642 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1644 assert(tte->type() != VALUE_TYPE_EVAL);
1646 return value_from_tt(tte->value(), ply);
1649 ttMove = (tte ? tte->move() : MOVE_NONE);
1651 isCheck = pos.is_check();
1652 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1654 // Evaluate the position statically
1656 staticValue = -VALUE_INFINITE;
1658 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1660 // Use the cached evaluation score if possible
1661 assert(ei.futilityMargin == Value(0));
1663 staticValue = value_from_tt(tte->value(), ply);
1666 staticValue = evaluate(pos, ei, threadID);
1668 if (ply >= PLY_MAX - 1)
1669 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1671 // Initialize "stand pat score", and return it immediately if it is
1673 bestValue = staticValue;
1675 if (bestValue >= beta)
1677 // Store the score to avoid a future costly evaluation() call
1678 if (!isCheck && !tte && ei.futilityMargin == 0)
1679 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1684 if (bestValue > alpha)
1687 // Initialize a MovePicker object for the current position, and prepare
1688 // to search the moves. Because the depth is <= 0 here, only captures,
1689 // queen promotions and checks (only if depth == 0) will be generated.
1690 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1692 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1694 // Loop through the moves until no moves remain or a beta cutoff
1696 while ( alpha < beta
1697 && (move = mp.get_next_move()) != MOVE_NONE)
1699 assert(move_is_ok(move));
1702 ss[ply].currentMove = move;
1704 moveIsCheck = pos.move_is_check(move, ci);
1712 && !move_is_promotion(move)
1713 && !pos.move_is_passed_pawn_push(move))
1715 futilityValue = staticValue
1716 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1717 pos.endgame_value_of_piece_on(move_to(move)))
1718 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1720 + ei.futilityMargin;
1722 if (futilityValue < alpha)
1724 if (futilityValue > bestValue)
1725 bestValue = futilityValue;
1730 // Don't search captures and checks with negative SEE values
1733 && !move_is_promotion(move)
1734 && pos.see_sign(move) < 0)
1737 // Make and search the move
1738 pos.do_move(move, st, ci, moveIsCheck);
1739 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1740 pos.undo_move(move);
1742 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1745 if (value > bestValue)
1756 // All legal moves have been searched. A special case: If we're in check
1757 // and no legal moves were found, it is checkmate.
1758 if (!moveCount && pos.is_check()) // Mate!
1759 return value_mated_in(ply);
1761 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1763 // Update transposition table
1764 move = ss[ply].pv[ply];
1767 // If bestValue isn't changed it means it is still the static evaluation of
1768 // the node, so keep this info to avoid a future costly evaluation() call.
1769 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1770 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1772 if (bestValue < beta)
1773 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1775 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1778 // Update killers only for good check moves
1779 if (alpha >= beta && !pos.move_is_capture_or_promotion(move))
1780 update_killers(move, ss[ply]);
1786 // sp_search() is used to search from a split point. This function is called
1787 // by each thread working at the split point. It is similar to the normal
1788 // search() function, but simpler. Because we have already probed the hash
1789 // table, done a null move search, and searched the first move before
1790 // splitting, we don't have to repeat all this work in sp_search(). We
1791 // also don't need to store anything to the hash table here: This is taken
1792 // care of after we return from the split point.
1794 void sp_search(SplitPoint* sp, int threadID) {
1796 assert(threadID >= 0 && threadID < ActiveThreads);
1797 assert(ActiveThreads > 1);
1799 Position pos = Position(sp->pos);
1801 SearchStack* ss = sp->sstack[threadID];
1804 bool isCheck = pos.is_check();
1805 bool useFutilityPruning = sp->depth < SelectiveDepth
1808 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1809 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1811 while ( sp->bestValue < sp->beta
1812 && !thread_should_stop(threadID)
1813 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1815 assert(move_is_ok(move));
1817 bool moveIsCheck = pos.move_is_check(move, ci);
1818 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1820 lock_grab(&(sp->lock));
1821 int moveCount = ++sp->moves;
1822 lock_release(&(sp->lock));
1824 ss[sp->ply].currentMove = move;
1826 // Decide the new search depth.
1828 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1829 Depth newDepth = sp->depth - OnePly + ext;
1832 if ( useFutilityPruning
1834 && !captureOrPromotion)
1836 // Move count based pruning
1837 if ( moveCount >= FutilityMoveCountMargin
1838 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1839 && sp->bestValue > value_mated_in(PLY_MAX))
1842 // Value based pruning
1843 if (sp->futilityValue == VALUE_NONE)
1846 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1849 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1851 if (futilityValueScaled < sp->beta)
1853 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1855 lock_grab(&(sp->lock));
1856 if (futilityValueScaled > sp->bestValue)
1857 sp->bestValue = futilityValueScaled;
1858 lock_release(&(sp->lock));
1864 // Make and search the move.
1866 pos.do_move(move, st, ci, moveIsCheck);
1868 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1869 // if the move fails high will be re-searched at full depth.
1871 && moveCount >= LMRNonPVMoves
1872 && !captureOrPromotion
1873 && !move_is_castle(move)
1874 && !move_is_killer(move, ss[sp->ply]))
1876 ss[sp->ply].reduction = OnePly;
1877 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1880 value = sp->beta; // Just to trigger next condition
1882 if (value >= sp->beta) // Go with full depth non-pv search
1884 ss[sp->ply].reduction = Depth(0);
1885 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1887 pos.undo_move(move);
1889 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1891 if (thread_should_stop(threadID))
1895 if (value > sp->bestValue) // Less then 2% of cases
1897 lock_grab(&(sp->lock));
1898 if (value > sp->bestValue && !thread_should_stop(threadID))
1900 sp->bestValue = value;
1901 if (sp->bestValue >= sp->beta)
1903 sp_update_pv(sp->parentSstack, ss, sp->ply);
1904 for (int i = 0; i < ActiveThreads; i++)
1905 if (i != threadID && (i == sp->master || sp->slaves[i]))
1906 Threads[i].stop = true;
1908 sp->finished = true;
1911 lock_release(&(sp->lock));
1915 lock_grab(&(sp->lock));
1917 // If this is the master thread and we have been asked to stop because of
1918 // a beta cutoff higher up in the tree, stop all slave threads.
1919 if (sp->master == threadID && thread_should_stop(threadID))
1920 for (int i = 0; i < ActiveThreads; i++)
1922 Threads[i].stop = true;
1925 sp->slaves[threadID] = 0;
1927 lock_release(&(sp->lock));
1931 // sp_search_pv() is used to search from a PV split point. This function
1932 // is called by each thread working at the split point. It is similar to
1933 // the normal search_pv() function, but simpler. Because we have already
1934 // probed the hash table and searched the first move before splitting, we
1935 // don't have to repeat all this work in sp_search_pv(). We also don't
1936 // need to store anything to the hash table here: This is taken care of
1937 // after we return from the split point.
1939 void sp_search_pv(SplitPoint* sp, int threadID) {
1941 assert(threadID >= 0 && threadID < ActiveThreads);
1942 assert(ActiveThreads > 1);
1944 Position pos = Position(sp->pos);
1946 SearchStack* ss = sp->sstack[threadID];
1950 while ( sp->alpha < sp->beta
1951 && !thread_should_stop(threadID)
1952 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1954 bool moveIsCheck = pos.move_is_check(move, ci);
1955 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1957 assert(move_is_ok(move));
1959 lock_grab(&(sp->lock));
1960 int moveCount = ++sp->moves;
1961 lock_release(&(sp->lock));
1963 ss[sp->ply].currentMove = move;
1965 // Decide the new search depth.
1967 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1968 Depth newDepth = sp->depth - OnePly + ext;
1970 // Make and search the move.
1972 pos.do_move(move, st, ci, moveIsCheck);
1974 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1975 // if the move fails high will be re-searched at full depth.
1977 && moveCount >= LMRPVMoves
1978 && !captureOrPromotion
1979 && !move_is_castle(move)
1980 && !move_is_killer(move, ss[sp->ply]))
1982 ss[sp->ply].reduction = OnePly;
1983 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1986 value = sp->alpha + 1; // Just to trigger next condition
1988 if (value > sp->alpha) // Go with full depth non-pv search
1990 ss[sp->ply].reduction = Depth(0);
1991 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1993 if (value > sp->alpha && value < sp->beta)
1995 // When the search fails high at ply 1 while searching the first
1996 // move at the root, set the flag failHighPly1. This is used for
1997 // time managment: We don't want to stop the search early in
1998 // such cases, because resolving the fail high at ply 1 could
1999 // result in a big drop in score at the root.
2000 if (sp->ply == 1 && RootMoveNumber == 1)
2001 Threads[threadID].failHighPly1 = true;
2003 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
2004 Threads[threadID].failHighPly1 = false;
2007 pos.undo_move(move);
2009 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2011 if (thread_should_stop(threadID))
2015 lock_grab(&(sp->lock));
2016 if (value > sp->bestValue && !thread_should_stop(threadID))
2018 sp->bestValue = value;
2019 if (value > sp->alpha)
2022 sp_update_pv(sp->parentSstack, ss, sp->ply);
2023 if (value == value_mate_in(sp->ply + 1))
2024 ss[sp->ply].mateKiller = move;
2026 if (value >= sp->beta)
2028 for (int i = 0; i < ActiveThreads; i++)
2029 if (i != threadID && (i == sp->master || sp->slaves[i]))
2030 Threads[i].stop = true;
2032 sp->finished = true;
2035 // If we are at ply 1, and we are searching the first root move at
2036 // ply 0, set the 'Problem' variable if the score has dropped a lot
2037 // (from the computer's point of view) since the previous iteration.
2040 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2043 lock_release(&(sp->lock));
2046 lock_grab(&(sp->lock));
2048 // If this is the master thread and we have been asked to stop because of
2049 // a beta cutoff higher up in the tree, stop all slave threads.
2050 if (sp->master == threadID && thread_should_stop(threadID))
2051 for (int i = 0; i < ActiveThreads; i++)
2053 Threads[i].stop = true;
2056 sp->slaves[threadID] = 0;
2058 lock_release(&(sp->lock));
2061 /// The BetaCounterType class
2063 BetaCounterType::BetaCounterType() { clear(); }
2065 void BetaCounterType::clear() {
2067 for (int i = 0; i < THREAD_MAX; i++)
2068 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2071 void BetaCounterType::add(Color us, Depth d, int threadID) {
2073 // Weighted count based on depth
2074 Threads[threadID].betaCutOffs[us] += unsigned(d);
2077 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2080 for (int i = 0; i < THREAD_MAX; i++)
2082 our += Threads[i].betaCutOffs[us];
2083 their += Threads[i].betaCutOffs[opposite_color(us)];
2088 /// The RootMoveList class
2090 // RootMoveList c'tor
2092 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2094 MoveStack mlist[MaxRootMoves];
2095 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2097 // Generate all legal moves
2098 MoveStack* last = generate_moves(pos, mlist);
2100 // Add each move to the moves[] array
2101 for (MoveStack* cur = mlist; cur != last; cur++)
2103 bool includeMove = includeAllMoves;
2105 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2106 includeMove = (searchMoves[k] == cur->move);
2111 // Find a quick score for the move
2113 SearchStack ss[PLY_MAX_PLUS_2];
2116 moves[count].move = cur->move;
2117 pos.do_move(moves[count].move, st);
2118 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2119 pos.undo_move(moves[count].move);
2120 moves[count].pv[0] = moves[count].move;
2121 moves[count].pv[1] = MOVE_NONE;
2128 // RootMoveList simple methods definitions
2130 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2132 moves[moveNum].nodes = nodes;
2133 moves[moveNum].cumulativeNodes += nodes;
2136 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2138 moves[moveNum].ourBeta = our;
2139 moves[moveNum].theirBeta = their;
2142 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2146 for (j = 0; pv[j] != MOVE_NONE; j++)
2147 moves[moveNum].pv[j] = pv[j];
2149 moves[moveNum].pv[j] = MOVE_NONE;
2153 // RootMoveList::sort() sorts the root move list at the beginning of a new
2156 void RootMoveList::sort() {
2158 sort_multipv(count - 1); // Sort all items
2162 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2163 // list by their scores and depths. It is used to order the different PVs
2164 // correctly in MultiPV mode.
2166 void RootMoveList::sort_multipv(int n) {
2170 for (i = 1; i <= n; i++)
2172 RootMove rm = moves[i];
2173 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2174 moves[j] = moves[j - 1];
2181 // init_node() is called at the beginning of all the search functions
2182 // (search(), search_pv(), qsearch(), and so on) and initializes the
2183 // search stack object corresponding to the current node. Once every
2184 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2185 // for user input and checks whether it is time to stop the search.
2187 void init_node(SearchStack ss[], int ply, int threadID) {
2189 assert(ply >= 0 && ply < PLY_MAX);
2190 assert(threadID >= 0 && threadID < ActiveThreads);
2192 Threads[threadID].nodes++;
2197 if (NodesSincePoll >= NodesBetweenPolls)
2204 ss[ply + 2].initKillers();
2206 if (Threads[threadID].printCurrentLine)
2207 print_current_line(ss, ply, threadID);
2211 // update_pv() is called whenever a search returns a value > alpha.
2212 // It updates the PV in the SearchStack object corresponding to the
2215 void update_pv(SearchStack ss[], int ply) {
2217 assert(ply >= 0 && ply < PLY_MAX);
2221 ss[ply].pv[ply] = ss[ply].currentMove;
2223 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2224 ss[ply].pv[p] = ss[ply + 1].pv[p];
2226 ss[ply].pv[p] = MOVE_NONE;
2230 // sp_update_pv() is a variant of update_pv for use at split points. The
2231 // difference between the two functions is that sp_update_pv also updates
2232 // the PV at the parent node.
2234 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2236 assert(ply >= 0 && ply < PLY_MAX);
2240 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2242 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2243 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2245 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2249 // connected_moves() tests whether two moves are 'connected' in the sense
2250 // that the first move somehow made the second move possible (for instance
2251 // if the moving piece is the same in both moves). The first move is assumed
2252 // to be the move that was made to reach the current position, while the
2253 // second move is assumed to be a move from the current position.
2255 bool connected_moves(const Position& pos, Move m1, Move m2) {
2257 Square f1, t1, f2, t2;
2260 assert(move_is_ok(m1));
2261 assert(move_is_ok(m2));
2263 if (m2 == MOVE_NONE)
2266 // Case 1: The moving piece is the same in both moves
2272 // Case 2: The destination square for m2 was vacated by m1
2278 // Case 3: Moving through the vacated square
2279 if ( piece_is_slider(pos.piece_on(f2))
2280 && bit_is_set(squares_between(f2, t2), f1))
2283 // Case 4: The destination square for m2 is defended by the moving piece in m1
2284 p = pos.piece_on(t1);
2285 if (bit_is_set(pos.attacks_from(p, t1), t2))
2288 // Case 5: Discovered check, checking piece is the piece moved in m1
2289 if ( piece_is_slider(p)
2290 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2291 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2293 // discovered_check_candidates() works also if the Position's side to
2294 // move is the opposite of the checking piece.
2295 Color them = opposite_color(pos.side_to_move());
2296 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2298 if (bit_is_set(dcCandidates, f2))
2305 // value_is_mate() checks if the given value is a mate one
2306 // eventually compensated for the ply.
2308 bool value_is_mate(Value value) {
2310 assert(abs(value) <= VALUE_INFINITE);
2312 return value <= value_mated_in(PLY_MAX)
2313 || value >= value_mate_in(PLY_MAX);
2317 // move_is_killer() checks if the given move is among the
2318 // killer moves of that ply.
2320 bool move_is_killer(Move m, const SearchStack& ss) {
2322 const Move* k = ss.killers;
2323 for (int i = 0; i < KILLER_MAX; i++, k++)
2331 // extension() decides whether a move should be searched with normal depth,
2332 // or with extended depth. Certain classes of moves (checking moves, in
2333 // particular) are searched with bigger depth than ordinary moves and in
2334 // any case are marked as 'dangerous'. Note that also if a move is not
2335 // extended, as example because the corresponding UCI option is set to zero,
2336 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2338 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2339 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2341 assert(m != MOVE_NONE);
2343 Depth result = Depth(0);
2344 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2349 result += CheckExtension[pvNode];
2352 result += SingleEvasionExtension[pvNode];
2355 result += MateThreatExtension[pvNode];
2358 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2360 Color c = pos.side_to_move();
2361 if (relative_rank(c, move_to(m)) == RANK_7)
2363 result += PawnPushTo7thExtension[pvNode];
2366 if (pos.pawn_is_passed(c, move_to(m)))
2368 result += PassedPawnExtension[pvNode];
2373 if ( captureOrPromotion
2374 && pos.type_of_piece_on(move_to(m)) != PAWN
2375 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2376 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2377 && !move_is_promotion(m)
2380 result += PawnEndgameExtension[pvNode];
2385 && captureOrPromotion
2386 && pos.type_of_piece_on(move_to(m)) != PAWN
2387 && pos.see_sign(m) >= 0)
2393 return Min(result, OnePly);
2397 // ok_to_do_nullmove() looks at the current position and decides whether
2398 // doing a 'null move' should be allowed. In order to avoid zugzwang
2399 // problems, null moves are not allowed when the side to move has very
2400 // little material left. Currently, the test is a bit too simple: Null
2401 // moves are avoided only when the side to move has only pawns left.
2402 // It's probably a good idea to avoid null moves in at least some more
2403 // complicated endgames, e.g. KQ vs KR. FIXME
2405 bool ok_to_do_nullmove(const Position& pos) {
2407 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2411 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2412 // non-tactical moves late in the move list close to the leaves are
2413 // candidates for pruning.
2415 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2417 assert(move_is_ok(m));
2418 assert(threat == MOVE_NONE || move_is_ok(threat));
2419 assert(!pos.move_is_check(m));
2420 assert(!pos.move_is_capture_or_promotion(m));
2421 assert(!pos.move_is_passed_pawn_push(m));
2423 Square mfrom, mto, tfrom, tto;
2425 // Prune if there isn't any threat move and
2426 // is not a castling move (common case).
2427 if (threat == MOVE_NONE && !move_is_castle(m))
2430 mfrom = move_from(m);
2432 tfrom = move_from(threat);
2433 tto = move_to(threat);
2435 // Case 1: Castling moves are never pruned
2436 if (move_is_castle(m))
2439 // Case 2: Don't prune moves which move the threatened piece
2443 // Case 3: If the threatened piece has value less than or equal to the
2444 // value of the threatening piece, don't prune move which defend it.
2445 if ( pos.move_is_capture(threat)
2446 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2447 || pos.type_of_piece_on(tfrom) == KING)
2448 && pos.move_attacks_square(m, tto))
2451 // Case 4: If the moving piece in the threatened move is a slider, don't
2452 // prune safe moves which block its ray.
2453 if ( piece_is_slider(pos.piece_on(tfrom))
2454 && bit_is_set(squares_between(tfrom, tto), mto)
2455 && pos.see_sign(m) >= 0)
2462 // ok_to_use_TT() returns true if a transposition table score
2463 // can be used at a given point in search.
2465 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2467 Value v = value_from_tt(tte->value(), ply);
2469 return ( tte->depth() >= depth
2470 || v >= Max(value_mate_in(PLY_MAX), beta)
2471 || v < Min(value_mated_in(PLY_MAX), beta))
2473 && ( (is_lower_bound(tte->type()) && v >= beta)
2474 || (is_upper_bound(tte->type()) && v < beta));
2478 // refine_eval() returns the transposition table score if
2479 // possible otherwise falls back on static position evaluation.
2481 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2486 Value v = value_from_tt(tte->value(), ply);
2488 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2489 || (is_upper_bound(tte->type()) && v < defaultEval))
2495 // update_history() registers a good move that produced a beta-cutoff
2496 // in history and marks as failures all the other moves of that ply.
2498 void update_history(const Position& pos, Move move, Depth depth,
2499 Move movesSearched[], int moveCount) {
2503 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2505 for (int i = 0; i < moveCount - 1; i++)
2507 m = movesSearched[i];
2511 if (!pos.move_is_capture_or_promotion(m))
2512 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2517 // update_killers() add a good move that produced a beta-cutoff
2518 // among the killer moves of that ply.
2520 void update_killers(Move m, SearchStack& ss) {
2522 if (m == ss.killers[0])
2525 for (int i = KILLER_MAX - 1; i > 0; i--)
2526 ss.killers[i] = ss.killers[i - 1];
2532 // fail_high_ply_1() checks if some thread is currently resolving a fail
2533 // high at ply 1 at the node below the first root node. This information
2534 // is used for time management.
2536 bool fail_high_ply_1() {
2538 for (int i = 0; i < ActiveThreads; i++)
2539 if (Threads[i].failHighPly1)
2546 // current_search_time() returns the number of milliseconds which have passed
2547 // since the beginning of the current search.
2549 int current_search_time() {
2551 return get_system_time() - SearchStartTime;
2555 // nps() computes the current nodes/second count.
2559 int t = current_search_time();
2560 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2564 // poll() performs two different functions: It polls for user input, and it
2565 // looks at the time consumed so far and decides if it's time to abort the
2570 static int lastInfoTime;
2571 int t = current_search_time();
2576 // We are line oriented, don't read single chars
2577 std::string command;
2579 if (!std::getline(std::cin, command))
2582 if (command == "quit")
2585 PonderSearch = false;
2589 else if (command == "stop")
2592 PonderSearch = false;
2594 else if (command == "ponderhit")
2598 // Print search information
2602 else if (lastInfoTime > t)
2603 // HACK: Must be a new search where we searched less than
2604 // NodesBetweenPolls nodes during the first second of search.
2607 else if (t - lastInfoTime >= 1000)
2615 if (dbg_show_hit_rate)
2616 dbg_print_hit_rate();
2618 cout << "info nodes " << nodes_searched() << " nps " << nps()
2619 << " time " << t << " hashfull " << TT.full() << endl;
2621 lock_release(&IOLock);
2623 if (ShowCurrentLine)
2624 Threads[0].printCurrentLine = true;
2627 // Should we stop the search?
2631 bool stillAtFirstMove = RootMoveNumber == 1
2633 && t > MaxSearchTime + ExtraSearchTime;
2635 bool noProblemFound = !FailHigh
2637 && !fail_high_ply_1()
2639 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2641 bool noMoreTime = t > AbsoluteMaxSearchTime
2642 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2645 if ( (Iteration >= 3 && !InfiniteSearch && noMoreTime)
2646 || (ExactMaxTime && t >= ExactMaxTime)
2647 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2652 // ponderhit() is called when the program is pondering (i.e. thinking while
2653 // it's the opponent's turn to move) in order to let the engine know that
2654 // it correctly predicted the opponent's move.
2658 int t = current_search_time();
2659 PonderSearch = false;
2661 bool stillAtFirstMove = RootMoveNumber == 1
2663 && t > MaxSearchTime + ExtraSearchTime;
2665 bool noProblemFound = !FailHigh
2667 && !fail_high_ply_1()
2669 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2671 bool noMoreTime = t > AbsoluteMaxSearchTime
2675 if (Iteration >= 3 && !InfiniteSearch && (noMoreTime || StopOnPonderhit))
2680 // print_current_line() prints the current line of search for a given
2681 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2683 void print_current_line(SearchStack ss[], int ply, int threadID) {
2685 assert(ply >= 0 && ply < PLY_MAX);
2686 assert(threadID >= 0 && threadID < ActiveThreads);
2688 if (!Threads[threadID].idle)
2691 cout << "info currline " << (threadID + 1);
2692 for (int p = 0; p < ply; p++)
2693 cout << " " << ss[p].currentMove;
2696 lock_release(&IOLock);
2698 Threads[threadID].printCurrentLine = false;
2699 if (threadID + 1 < ActiveThreads)
2700 Threads[threadID + 1].printCurrentLine = true;
2704 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2706 void init_ss_array(SearchStack ss[]) {
2708 for (int i = 0; i < 3; i++)
2711 ss[i].initKillers();
2716 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2717 // while the program is pondering. The point is to work around a wrinkle in
2718 // the UCI protocol: When pondering, the engine is not allowed to give a
2719 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2720 // We simply wait here until one of these commands is sent, and return,
2721 // after which the bestmove and pondermove will be printed (in id_loop()).
2723 void wait_for_stop_or_ponderhit() {
2725 std::string command;
2729 if (!std::getline(std::cin, command))
2732 if (command == "quit")
2737 else if (command == "ponderhit" || command == "stop")
2743 // idle_loop() is where the threads are parked when they have no work to do.
2744 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2745 // object for which the current thread is the master.
2747 void idle_loop(int threadID, SplitPoint* waitSp) {
2749 assert(threadID >= 0 && threadID < THREAD_MAX);
2751 Threads[threadID].running = true;
2755 if (AllThreadsShouldExit && threadID != 0)
2758 // If we are not thinking, wait for a condition to be signaled
2759 // instead of wasting CPU time polling for work.
2760 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2763 #if !defined(_MSC_VER)
2764 pthread_mutex_lock(&WaitLock);
2765 if (Idle || threadID >= ActiveThreads)
2766 pthread_cond_wait(&WaitCond, &WaitLock);
2768 pthread_mutex_unlock(&WaitLock);
2770 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2774 // If this thread has been assigned work, launch a search
2775 if (Threads[threadID].workIsWaiting)
2777 Threads[threadID].workIsWaiting = false;
2778 if (Threads[threadID].splitPoint->pvNode)
2779 sp_search_pv(Threads[threadID].splitPoint, threadID);
2781 sp_search(Threads[threadID].splitPoint, threadID);
2783 Threads[threadID].idle = true;
2786 // If this thread is the master of a split point and all threads have
2787 // finished their work at this split point, return from the idle loop.
2788 if (waitSp != NULL && waitSp->cpus == 0)
2792 Threads[threadID].running = false;
2796 // init_split_point_stack() is called during program initialization, and
2797 // initializes all split point objects.
2799 void init_split_point_stack() {
2801 for (int i = 0; i < THREAD_MAX; i++)
2802 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2804 SplitPointStack[i][j].parent = NULL;
2805 lock_init(&(SplitPointStack[i][j].lock), NULL);
2810 // destroy_split_point_stack() is called when the program exits, and
2811 // destroys all locks in the precomputed split point objects.
2813 void destroy_split_point_stack() {
2815 for (int i = 0; i < THREAD_MAX; i++)
2816 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2817 lock_destroy(&(SplitPointStack[i][j].lock));
2821 // thread_should_stop() checks whether the thread with a given threadID has
2822 // been asked to stop, directly or indirectly. This can happen if a beta
2823 // cutoff has occurred in the thread's currently active split point, or in
2824 // some ancestor of the current split point.
2826 bool thread_should_stop(int threadID) {
2828 assert(threadID >= 0 && threadID < ActiveThreads);
2832 if (Threads[threadID].stop)
2834 if (ActiveThreads <= 2)
2836 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2839 Threads[threadID].stop = true;
2846 // thread_is_available() checks whether the thread with threadID "slave" is
2847 // available to help the thread with threadID "master" at a split point. An
2848 // obvious requirement is that "slave" must be idle. With more than two
2849 // threads, this is not by itself sufficient: If "slave" is the master of
2850 // some active split point, it is only available as a slave to the other
2851 // threads which are busy searching the split point at the top of "slave"'s
2852 // split point stack (the "helpful master concept" in YBWC terminology).
2854 bool thread_is_available(int slave, int master) {
2856 assert(slave >= 0 && slave < ActiveThreads);
2857 assert(master >= 0 && master < ActiveThreads);
2858 assert(ActiveThreads > 1);
2860 if (!Threads[slave].idle || slave == master)
2863 if (Threads[slave].activeSplitPoints == 0)
2864 // No active split points means that the thread is available as
2865 // a slave for any other thread.
2868 if (ActiveThreads == 2)
2871 // Apply the "helpful master" concept if possible
2872 if (SplitPointStack[slave][Threads[slave].activeSplitPoints - 1].slaves[master])
2879 // idle_thread_exists() tries to find an idle thread which is available as
2880 // a slave for the thread with threadID "master".
2882 bool idle_thread_exists(int master) {
2884 assert(master >= 0 && master < ActiveThreads);
2885 assert(ActiveThreads > 1);
2887 for (int i = 0; i < ActiveThreads; i++)
2888 if (thread_is_available(i, master))
2895 // split() does the actual work of distributing the work at a node between
2896 // several threads at PV nodes. If it does not succeed in splitting the
2897 // node (because no idle threads are available, or because we have no unused
2898 // split point objects), the function immediately returns false. If
2899 // splitting is possible, a SplitPoint object is initialized with all the
2900 // data that must be copied to the helper threads (the current position and
2901 // search stack, alpha, beta, the search depth, etc.), and we tell our
2902 // helper threads that they have been assigned work. This will cause them
2903 // to instantly leave their idle loops and call sp_search_pv(). When all
2904 // threads have returned from sp_search_pv (or, equivalently, when
2905 // splitPoint->cpus becomes 0), split() returns true.
2907 bool split(const Position& p, SearchStack* sstck, int ply,
2908 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2909 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2912 assert(sstck != NULL);
2913 assert(ply >= 0 && ply < PLY_MAX);
2914 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2915 assert(!pvNode || *alpha < *beta);
2916 assert(*beta <= VALUE_INFINITE);
2917 assert(depth > Depth(0));
2918 assert(master >= 0 && master < ActiveThreads);
2919 assert(ActiveThreads > 1);
2921 SplitPoint* splitPoint;
2926 // If no other thread is available to help us, or if we have too many
2927 // active split points, don't split.
2928 if ( !idle_thread_exists(master)
2929 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2931 lock_release(&MPLock);
2935 // Pick the next available split point object from the split point stack
2936 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2937 Threads[master].activeSplitPoints++;
2939 // Initialize the split point object and copy current position
2940 splitPoint->parent = Threads[master].splitPoint;
2941 splitPoint->finished = false;
2942 splitPoint->ply = ply;
2943 splitPoint->depth = depth;
2944 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2945 splitPoint->beta = *beta;
2946 splitPoint->pvNode = pvNode;
2947 splitPoint->bestValue = *bestValue;
2948 splitPoint->futilityValue = futilityValue;
2949 splitPoint->master = master;
2950 splitPoint->mp = mp;
2951 splitPoint->moves = *moves;
2952 splitPoint->cpus = 1;
2953 splitPoint->pos.copy(p);
2954 splitPoint->parentSstack = sstck;
2955 for (i = 0; i < ActiveThreads; i++)
2956 splitPoint->slaves[i] = 0;
2958 // Copy the current search stack to the master thread
2959 memcpy(splitPoint->sstack[master], sstck, (ply+1) * sizeof(SearchStack));
2960 Threads[master].splitPoint = splitPoint;
2962 // Make copies of the current position and search stack for each thread
2963 for (i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2964 if (thread_is_available(i, master))
2966 memcpy(splitPoint->sstack[i], sstck, (ply+1) * sizeof(SearchStack));
2967 Threads[i].splitPoint = splitPoint;
2968 splitPoint->slaves[i] = 1;
2972 // Tell the threads that they have work to do. This will make them leave
2974 for (i = 0; i < ActiveThreads; i++)
2975 if (i == master || splitPoint->slaves[i])
2977 Threads[i].workIsWaiting = true;
2978 Threads[i].idle = false;
2979 Threads[i].stop = false;
2982 lock_release(&MPLock);
2984 // Everything is set up. The master thread enters the idle loop, from
2985 // which it will instantly launch a search, because its workIsWaiting
2986 // slot is 'true'. We send the split point as a second parameter to the
2987 // idle loop, which means that the main thread will return from the idle
2988 // loop when all threads have finished their work at this split point
2989 // (i.e. when splitPoint->cpus == 0).
2990 idle_loop(master, splitPoint);
2992 // We have returned from the idle loop, which means that all threads are
2993 // finished. Update alpha, beta and bestValue, and return.
2997 *alpha = splitPoint->alpha;
2999 *beta = splitPoint->beta;
3000 *bestValue = splitPoint->bestValue;
3001 Threads[master].stop = false;
3002 Threads[master].idle = false;
3003 Threads[master].activeSplitPoints--;
3004 Threads[master].splitPoint = splitPoint->parent;
3006 lock_release(&MPLock);
3011 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3012 // to start a new search from the root.
3014 void wake_sleeping_threads() {
3016 if (ActiveThreads > 1)
3018 for (int i = 1; i < ActiveThreads; i++)
3020 Threads[i].idle = true;
3021 Threads[i].workIsWaiting = false;
3024 #if !defined(_MSC_VER)
3025 pthread_mutex_lock(&WaitLock);
3026 pthread_cond_broadcast(&WaitCond);
3027 pthread_mutex_unlock(&WaitLock);
3029 for (int i = 1; i < THREAD_MAX; i++)
3030 SetEvent(SitIdleEvent[i]);
3036 // init_thread() is the function which is called when a new thread is
3037 // launched. It simply calls the idle_loop() function with the supplied
3038 // threadID. There are two versions of this function; one for POSIX
3039 // threads and one for Windows threads.
3041 #if !defined(_MSC_VER)
3043 void* init_thread(void *threadID) {
3045 idle_loop(*(int*)threadID, NULL);
3051 DWORD WINAPI init_thread(LPVOID threadID) {
3053 idle_loop(*(int*)threadID, NULL);