2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
42 #include "ucioption.h"
48 //// Local definitions
55 // IterationInfoType stores search results for each iteration
57 // Because we use relatively small (dynamic) aspiration window,
58 // there happens many fail highs and fail lows in root. And
59 // because we don't do researches in those cases, "value" stored
60 // here is not necessarily exact. Instead in case of fail high/low
61 // we guess what the right value might be and store our guess
62 // as a "speculated value" and then move on. Speculated values are
63 // used just to calculate aspiration window width, so also if are
64 // not exact is not big a problem.
66 struct IterationInfoType {
68 IterationInfoType(Value v = Value(0), Value sv = Value(0))
69 : value(v), speculatedValue(sv) {}
71 Value value, speculatedValue;
75 // The BetaCounterType class is used to order moves at ply one.
76 // Apart for the first one that has its score, following moves
77 // normally have score -VALUE_INFINITE, so are ordered according
78 // to the number of beta cutoffs occurred under their subtree during
79 // the last iteration. The counters are per thread variables to avoid
80 // concurrent accessing under SMP case.
82 struct BetaCounterType {
86 void add(Color us, Depth d, int threadID);
87 void read(Color us, int64_t& our, int64_t& their);
91 // The RootMove class is used for moves at the root at the tree. For each
92 // root move, we store a score, a node count, and a PV (really a refutation
93 // in the case of moves which fail low).
98 bool operator<(const RootMove&) const; // Used to sort
102 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
103 Move pv[PLY_MAX_PLUS_2];
107 // The RootMoveList class is essentially an array of RootMove objects, with
108 // a handful of methods for accessing the data in the individual moves.
113 RootMoveList(Position& pos, Move searchMoves[]);
114 inline Move get_move(int moveNum) const;
115 inline Value get_move_score(int moveNum) const;
116 inline void set_move_score(int moveNum, Value score);
117 inline void set_move_nodes(int moveNum, int64_t nodes);
118 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
119 void set_move_pv(int moveNum, const Move pv[]);
120 inline Move get_move_pv(int moveNum, int i) const;
121 inline int64_t get_move_cumulative_nodes(int moveNum) const;
122 inline int move_count() const;
124 void sort_multipv(int n);
127 static const int MaxRootMoves = 500;
128 RootMove moves[MaxRootMoves];
135 // Search depth at iteration 1
136 const Depth InitialDepth = OnePly;
138 // Depth limit for selective search
139 const Depth SelectiveDepth = 7 * OnePly;
141 // Use internal iterative deepening?
142 const bool UseIIDAtPVNodes = true;
143 const bool UseIIDAtNonPVNodes = true;
145 // Internal iterative deepening margin. At Non-PV moves, when
146 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
147 // search when the static evaluation is at most IIDMargin below beta.
148 const Value IIDMargin = Value(0x100);
150 // Easy move margin. An easy move candidate must be at least this much
151 // better than the second best move.
152 const Value EasyMoveMargin = Value(0x200);
154 // Problem margin. If the score of the first move at iteration N+1 has
155 // dropped by more than this since iteration N, the boolean variable
156 // "Problem" is set to true, which will make the program spend some extra
157 // time looking for a better move.
158 const Value ProblemMargin = Value(0x28);
160 // No problem margin. If the boolean "Problem" is true, and a new move
161 // is found at the root which is less than NoProblemMargin worse than the
162 // best move from the previous iteration, Problem is set back to false.
163 const Value NoProblemMargin = Value(0x14);
165 // Null move margin. A null move search will not be done if the approximate
166 // evaluation of the position is more than NullMoveMargin below beta.
167 const Value NullMoveMargin = Value(0x300);
169 // Pruning criterions. See the code and comments in ok_to_prune() to
170 // understand their precise meaning.
171 const bool PruneEscapeMoves = false;
172 const bool PruneDefendingMoves = false;
173 const bool PruneBlockingMoves = false;
175 // If the TT move is at least SingleReplyMargin better then the
176 // remaining ones we will extend it.
177 const Value SingleReplyMargin = Value(0x20);
179 // Margins for futility pruning in the quiescence search, and at frontier
180 // and near frontier nodes.
181 const Value FutilityMarginQS = Value(0x80);
183 // Each move futility margin is decreased
184 const Value IncrementalFutilityMargin = Value(0x8);
186 // Depth limit for razoring
187 const Depth RazorDepth = 4 * OnePly;
189 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
190 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
192 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
193 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
196 /// Variables initialized by UCI options
198 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
199 int LMRPVMoves, LMRNonPVMoves;
201 // Depth limit for use of dynamic threat detection
204 // Last seconds noise filtering (LSN)
205 const bool UseLSNFiltering = true;
206 const int LSNTime = 4000; // In milliseconds
207 const Value LSNValue = value_from_centipawns(200);
208 bool loseOnTime = false;
210 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
211 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
212 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
214 // Iteration counters
216 BetaCounterType BetaCounter;
218 // Scores and number of times the best move changed for each iteration
219 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
220 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
225 // Time managment variables
228 int MaxNodes, MaxDepth;
229 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
230 bool InfiniteSearch, PonderSearch, StopOnPonderhit;
231 bool AbortSearch, Quit;
232 bool FailHigh, FailLow, Problem;
234 // Show current line?
235 bool ShowCurrentLine;
239 std::ofstream LogFile;
241 // MP related variables
242 int ActiveThreads = 1;
243 Depth MinimumSplitDepth;
244 int MaxThreadsPerSplitPoint;
245 Thread Threads[THREAD_MAX];
248 bool AllThreadsShouldExit = false;
249 const int MaxActiveSplitPoints = 8; // FIXME, sync with UCI Option
250 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
253 #if !defined(_MSC_VER)
254 pthread_cond_t WaitCond;
255 pthread_mutex_t WaitLock;
257 HANDLE SitIdleEvent[THREAD_MAX];
260 // Node counters, used only by thread[0] but try to keep in different
261 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
263 int NodesBetweenPolls = 30000;
271 Value id_loop(const Position& pos, Move searchMoves[]);
272 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
273 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
274 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
275 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
276 void sp_search(SplitPoint* sp, int threadID);
277 void sp_search_pv(SplitPoint* sp, int threadID);
278 void init_node(SearchStack ss[], int ply, int threadID);
279 void update_pv(SearchStack ss[], int ply);
280 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
281 bool connected_moves(const Position& pos, Move m1, Move m2);
282 bool value_is_mate(Value value);
283 bool move_is_killer(Move m, const SearchStack& ss);
284 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
285 bool ok_to_do_nullmove(const Position& pos);
286 bool ok_to_prune(const Position& pos, Move m, Move threat);
287 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
288 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
289 void update_killers(Move m, SearchStack& ss);
291 bool fail_high_ply_1();
292 int current_search_time();
296 void print_current_line(SearchStack ss[], int ply, int threadID);
297 void wait_for_stop_or_ponderhit();
298 void init_ss_array(SearchStack ss[]);
300 void idle_loop(int threadID, SplitPoint* waitSp);
301 void init_split_point_stack();
302 void destroy_split_point_stack();
303 bool thread_should_stop(int threadID);
304 bool thread_is_available(int slave, int master);
305 bool idle_thread_exists(int master);
306 bool split(const Position& pos, SearchStack* ss, int ply,
307 Value *alpha, Value *beta, Value *bestValue,
308 const Value futilityValue, Depth depth, int *moves,
309 MovePicker *mp, int master, bool pvNode);
310 void wake_sleeping_threads();
312 #if !defined(_MSC_VER)
313 void *init_thread(void *threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
326 /// perft() is our utility to verify move generation is bug free. All the legal
327 /// moves up to given depth are generated and counted and the sum returned.
329 int perft(Position& pos, Depth depth)
333 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
335 // If we are at the last ply we don't need to do and undo
336 // the moves, just to count them.
337 if (depth <= OnePly) // Replace with '<' to test also qsearch
339 while (mp.get_next_move()) sum++;
343 // Loop through all legal moves
345 while ((move = mp.get_next_move()) != MOVE_NONE)
348 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
349 sum += perft(pos, depth - OnePly);
356 /// think() is the external interface to Stockfish's search, and is called when
357 /// the program receives the UCI 'go' command. It initializes various
358 /// search-related global variables, and calls root_search(). It returns false
359 /// when a quit command is received during the search.
361 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
362 int time[], int increment[], int movesToGo, int maxDepth,
363 int maxNodes, int maxTime, Move searchMoves[]) {
365 // Look for a book move
366 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
369 if (get_option_value_string("Book File") != OpeningBook.file_name())
370 OpeningBook.open(get_option_value_string("Book File"));
372 bookMove = OpeningBook.get_move(pos);
373 if (bookMove != MOVE_NONE)
375 cout << "bestmove " << bookMove << endl;
380 // Initialize global search variables
381 Idle = StopOnPonderhit = AbortSearch = Quit = false;
382 FailHigh = FailLow = Problem = false;
383 SearchStartTime = get_system_time();
384 ExactMaxTime = maxTime;
386 InfiniteSearch = infinite;
387 PonderSearch = ponder;
389 for (int i = 0; i < THREAD_MAX; i++)
391 Threads[i].nodes = 0ULL;
392 Threads[i].failHighPly1 = false;
395 if (button_was_pressed("New Game"))
396 loseOnTime = false; // Reset at the beginning of a new game
398 // Read UCI option values
399 TT.set_size(get_option_value_int("Hash"));
400 if (button_was_pressed("Clear Hash"))
403 bool PonderingEnabled = get_option_value_bool("Ponder");
404 MultiPV = get_option_value_int("MultiPV");
406 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
407 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
409 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
410 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
412 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
413 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
415 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
416 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
418 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
419 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
421 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
422 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
424 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
425 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
426 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
428 Chess960 = get_option_value_bool("UCI_Chess960");
429 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
430 UseLogFile = get_option_value_bool("Use Search Log");
432 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
434 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
435 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
437 read_weights(pos.side_to_move());
439 // Set the number of active threads
440 int newActiveThreads = get_option_value_int("Threads");
441 if (newActiveThreads != ActiveThreads)
443 ActiveThreads = newActiveThreads;
444 init_eval(ActiveThreads);
447 // Wake up sleeping threads
448 wake_sleeping_threads();
450 for (int i = 1; i < ActiveThreads; i++)
451 assert(thread_is_available(i, 0));
454 int myTime = time[side_to_move];
455 int myIncrement = increment[side_to_move];
457 if (!movesToGo) // Sudden death time control
461 MaxSearchTime = myTime / 30 + myIncrement;
462 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
464 else // Blitz game without increment
466 MaxSearchTime = myTime / 30;
467 AbsoluteMaxSearchTime = myTime / 8;
470 else // (x moves) / (y minutes)
474 MaxSearchTime = myTime / 2;
475 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
479 MaxSearchTime = myTime / Min(movesToGo, 20);
480 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
484 if (PonderingEnabled)
486 MaxSearchTime += MaxSearchTime / 4;
487 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
490 // Fixed depth or fixed number of nodes?
493 InfiniteSearch = true; // HACK
498 NodesBetweenPolls = Min(MaxNodes, 30000);
499 InfiniteSearch = true; // HACK
501 else if (myTime && myTime < 1000)
502 NodesBetweenPolls = 1000;
503 else if (myTime && myTime < 5000)
504 NodesBetweenPolls = 5000;
506 NodesBetweenPolls = 30000;
508 // Write information to search log file
510 LogFile << "Searching: " << pos.to_fen() << endl
511 << "infinite: " << infinite
512 << " ponder: " << ponder
513 << " time: " << myTime
514 << " increment: " << myIncrement
515 << " moves to go: " << movesToGo << endl;
517 // LSN filtering. Used only for developing purpose. Disabled by default.
521 // Step 2. If after last move we decided to lose on time, do it now!
522 while (SearchStartTime + myTime + 1000 > get_system_time())
526 // We're ready to start thinking. Call the iterative deepening loop function
527 Value v = id_loop(pos, searchMoves);
532 // Step 1. If this is sudden death game and our position is hopeless,
533 // decide to lose on time.
534 if ( !loseOnTime // If we already lost on time, go to step 3.
544 // Step 3. Now after stepping over the time limit, reset flag for next match.
557 /// init_threads() is called during startup. It launches all helper threads,
558 /// and initializes the split point stack and the global locks and condition
561 void init_threads() {
565 #if !defined(_MSC_VER)
566 pthread_t pthread[1];
569 for (i = 0; i < THREAD_MAX; i++)
570 Threads[i].activeSplitPoints = 0;
572 // Initialize global locks
573 lock_init(&MPLock, NULL);
574 lock_init(&IOLock, NULL);
576 init_split_point_stack();
578 #if !defined(_MSC_VER)
579 pthread_mutex_init(&WaitLock, NULL);
580 pthread_cond_init(&WaitCond, NULL);
582 for (i = 0; i < THREAD_MAX; i++)
583 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
586 // All threads except the main thread should be initialized to idle state
587 for (i = 1; i < THREAD_MAX; i++)
589 Threads[i].stop = false;
590 Threads[i].workIsWaiting = false;
591 Threads[i].idle = true;
592 Threads[i].running = false;
595 // Launch the helper threads
596 for(i = 1; i < THREAD_MAX; i++)
598 #if !defined(_MSC_VER)
599 pthread_create(pthread, NULL, init_thread, (void*)(&i));
602 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
605 // Wait until the thread has finished launching
606 while (!Threads[i].running);
611 /// stop_threads() is called when the program exits. It makes all the
612 /// helper threads exit cleanly.
614 void stop_threads() {
616 ActiveThreads = THREAD_MAX; // HACK
617 Idle = false; // HACK
618 wake_sleeping_threads();
619 AllThreadsShouldExit = true;
620 for (int i = 1; i < THREAD_MAX; i++)
622 Threads[i].stop = true;
623 while(Threads[i].running);
625 destroy_split_point_stack();
629 /// nodes_searched() returns the total number of nodes searched so far in
630 /// the current search.
632 int64_t nodes_searched() {
634 int64_t result = 0ULL;
635 for (int i = 0; i < ActiveThreads; i++)
636 result += Threads[i].nodes;
641 // SearchStack::init() initializes a search stack. Used at the beginning of a
642 // new search from the root.
643 void SearchStack::init(int ply) {
645 pv[ply] = pv[ply + 1] = MOVE_NONE;
646 currentMove = threatMove = MOVE_NONE;
647 reduction = Depth(0);
650 void SearchStack::initKillers() {
652 mateKiller = MOVE_NONE;
653 for (int i = 0; i < KILLER_MAX; i++)
654 killers[i] = MOVE_NONE;
659 // id_loop() is the main iterative deepening loop. It calls root_search
660 // repeatedly with increasing depth until the allocated thinking time has
661 // been consumed, the user stops the search, or the maximum search depth is
664 Value id_loop(const Position& pos, Move searchMoves[]) {
667 SearchStack ss[PLY_MAX_PLUS_2];
669 // searchMoves are verified, copied, scored and sorted
670 RootMoveList rml(p, searchMoves);
672 if (rml.move_count() == 0)
675 wait_for_stop_or_ponderhit();
677 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
680 // Print RootMoveList c'tor startup scoring to the standard output,
681 // so that we print information also for iteration 1.
682 cout << "info depth " << 1 << "\ninfo depth " << 1
683 << " score " << value_to_string(rml.get_move_score(0))
684 << " time " << current_search_time()
685 << " nodes " << nodes_searched()
687 << " pv " << rml.get_move(0) << "\n";
693 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
696 // Is one move significantly better than others after initial scoring ?
697 Move EasyMove = MOVE_NONE;
698 if ( rml.move_count() == 1
699 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
700 EasyMove = rml.get_move(0);
702 // Iterative deepening loop
703 while (Iteration < PLY_MAX)
705 // Initialize iteration
708 BestMoveChangesByIteration[Iteration] = 0;
712 cout << "info depth " << Iteration << endl;
714 // Calculate dynamic search window based on previous iterations
717 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
719 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
720 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
722 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
724 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
725 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
729 alpha = - VALUE_INFINITE;
730 beta = VALUE_INFINITE;
733 // Search to the current depth
734 Value value = root_search(p, ss, rml, alpha, beta);
736 // Write PV to transposition table, in case the relevant entries have
737 // been overwritten during the search.
738 TT.insert_pv(p, ss[0].pv);
741 break; // Value cannot be trusted. Break out immediately!
743 //Save info about search result
744 Value speculatedValue;
747 Value delta = value - IterationInfo[Iteration - 1].value;
754 speculatedValue = value + delta;
755 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
757 else if (value <= alpha)
759 assert(value == alpha);
763 speculatedValue = value + delta;
764 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
766 speculatedValue = value;
768 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
769 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
771 // Drop the easy move if it differs from the new best move
772 if (ss[0].pv[0] != EasyMove)
773 EasyMove = MOVE_NONE;
780 bool stopSearch = false;
782 // Stop search early if there is only a single legal move,
783 // we search up to Iteration 6 anyway to get a proper score.
784 if (Iteration >= 6 && rml.move_count() == 1)
787 // Stop search early when the last two iterations returned a mate score
789 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
790 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
793 // Stop search early if one move seems to be much better than the rest
794 int64_t nodes = nodes_searched();
798 && EasyMove == ss[0].pv[0]
799 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
800 && current_search_time() > MaxSearchTime / 16)
801 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
802 && current_search_time() > MaxSearchTime / 32)))
805 // Add some extra time if the best move has changed during the last two iterations
806 if (Iteration > 5 && Iteration <= 50)
807 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
808 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
810 // Stop search if most of MaxSearchTime is consumed at the end of the
811 // iteration. We probably don't have enough time to search the first
812 // move at the next iteration anyway.
813 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
821 StopOnPonderhit = true;
825 if (MaxDepth && Iteration >= MaxDepth)
831 // If we are pondering, we shouldn't print the best move before we
834 wait_for_stop_or_ponderhit();
836 // Print final search statistics
837 cout << "info nodes " << nodes_searched()
839 << " time " << current_search_time()
840 << " hashfull " << TT.full() << endl;
842 // Print the best move and the ponder move to the standard output
843 if (ss[0].pv[0] == MOVE_NONE)
845 ss[0].pv[0] = rml.get_move(0);
846 ss[0].pv[1] = MOVE_NONE;
848 cout << "bestmove " << ss[0].pv[0];
849 if (ss[0].pv[1] != MOVE_NONE)
850 cout << " ponder " << ss[0].pv[1];
857 dbg_print_mean(LogFile);
859 if (dbg_show_hit_rate)
860 dbg_print_hit_rate(LogFile);
862 LogFile << "\nNodes: " << nodes_searched()
863 << "\nNodes/second: " << nps()
864 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
867 p.do_move(ss[0].pv[0], st);
868 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
870 return rml.get_move_score(0);
874 // root_search() is the function which searches the root node. It is
875 // similar to search_pv except that it uses a different move ordering
876 // scheme and prints some information to the standard output.
878 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
880 Value oldAlpha = alpha;
884 // Loop through all the moves in the root move list
885 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
889 // We failed high, invalidate and skip next moves, leave node-counters
890 // and beta-counters as they are and quickly return, we will try to do
891 // a research at the next iteration with a bigger aspiration window.
892 rml.set_move_score(i, -VALUE_INFINITE);
900 RootMoveNumber = i + 1;
903 // Save the current node count before the move is searched
904 nodes = nodes_searched();
906 // Reset beta cut-off counters
909 // Pick the next root move, and print the move and the move number to
910 // the standard output.
911 move = ss[0].currentMove = rml.get_move(i);
913 if (current_search_time() >= 1000)
914 cout << "info currmove " << move
915 << " currmovenumber " << RootMoveNumber << endl;
917 // Decide search depth for this move
918 bool moveIsCheck = pos.move_is_check(move);
919 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
921 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
922 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
924 // Make the move, and search it
925 pos.do_move(move, st, ci, moveIsCheck);
929 // Aspiration window is disabled in multi-pv case
931 alpha = -VALUE_INFINITE;
933 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
935 // If the value has dropped a lot compared to the last iteration,
936 // set the boolean variable Problem to true. This variable is used
937 // for time managment: When Problem is true, we try to complete the
938 // current iteration before playing a move.
939 Problem = ( Iteration >= 2
940 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
942 if (Problem && StopOnPonderhit)
943 StopOnPonderhit = false;
947 // Try to reduce non-pv search depth by one ply if move seems not problematic,
948 // if the move fails high will be re-searched at full depth.
949 if ( newDepth >= 3*OnePly
950 && i >= MultiPV + LMRPVMoves
952 && !captureOrPromotion
953 && !move_is_castle(move))
955 ss[0].reduction = OnePly;
956 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
958 value = alpha + 1; // Just to trigger next condition
962 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
966 // Fail high! Set the boolean variable FailHigh to true, and
967 // re-search the move using a PV search. The variable FailHigh
968 // is used for time managment: We try to avoid aborting the
969 // search prematurely during a fail high research.
971 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
978 // Finished searching the move. If AbortSearch is true, the search
979 // was aborted because the user interrupted the search or because we
980 // ran out of time. In this case, the return value of the search cannot
981 // be trusted, and we break out of the loop without updating the best
986 // Remember beta-cutoff and searched nodes counts for this move. The
987 // info is used to sort the root moves at the next iteration.
989 BetaCounter.read(pos.side_to_move(), our, their);
990 rml.set_beta_counters(i, our, their);
991 rml.set_move_nodes(i, nodes_searched() - nodes);
993 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
995 if (value <= alpha && i >= MultiPV)
996 rml.set_move_score(i, -VALUE_INFINITE);
999 // PV move or new best move!
1002 rml.set_move_score(i, value);
1004 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1005 rml.set_move_pv(i, ss[0].pv);
1009 // We record how often the best move has been changed in each
1010 // iteration. This information is used for time managment: When
1011 // the best move changes frequently, we allocate some more time.
1013 BestMoveChangesByIteration[Iteration]++;
1015 // Print search information to the standard output
1016 cout << "info depth " << Iteration
1017 << " score " << value_to_string(value)
1018 << ((value >= beta) ? " lowerbound" :
1019 ((value <= alpha)? " upperbound" : ""))
1020 << " time " << current_search_time()
1021 << " nodes " << nodes_searched()
1025 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1026 cout << ss[0].pv[j] << " ";
1032 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1033 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1035 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1036 nodes_searched(), value, type, ss[0].pv) << endl;
1041 // Reset the global variable Problem to false if the value isn't too
1042 // far below the final value from the last iteration.
1043 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1048 rml.sort_multipv(i);
1049 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1051 cout << "info multipv " << j + 1
1052 << " score " << value_to_string(rml.get_move_score(j))
1053 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1054 << " time " << current_search_time()
1055 << " nodes " << nodes_searched()
1059 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1060 cout << rml.get_move_pv(j, k) << " ";
1064 alpha = rml.get_move_score(Min(i, MultiPV-1));
1066 } // PV move or new best move
1068 assert(alpha >= oldAlpha);
1070 FailLow = (alpha == oldAlpha);
1076 // search_pv() is the main search function for PV nodes.
1078 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1079 Depth depth, int ply, int threadID) {
1081 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1082 assert(beta > alpha && beta <= VALUE_INFINITE);
1083 assert(ply >= 0 && ply < PLY_MAX);
1084 assert(threadID >= 0 && threadID < ActiveThreads);
1086 Move movesSearched[256];
1091 Depth ext, newDepth;
1092 Value oldAlpha, value;
1093 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1095 Value bestValue = -VALUE_INFINITE;
1098 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1100 // Initialize, and make an early exit in case of an aborted search,
1101 // an instant draw, maximum ply reached, etc.
1102 init_node(ss, ply, threadID);
1104 // After init_node() that calls poll()
1105 if (AbortSearch || thread_should_stop(threadID))
1111 if (ply >= PLY_MAX - 1)
1112 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1114 // Mate distance pruning
1116 alpha = Max(value_mated_in(ply), alpha);
1117 beta = Min(value_mate_in(ply+1), beta);
1121 // Transposition table lookup. At PV nodes, we don't use the TT for
1122 // pruning, but only for move ordering. This is to avoid problems in
1123 // the following areas:
1125 // * Repetition draw detection
1126 // * Fifty move rule detection
1127 // * Searching for a mate
1128 // * Printing of full PV line
1130 tte = TT.retrieve(pos.get_key());
1131 ttMove = (tte ? tte->move() : MOVE_NONE);
1133 // Go with internal iterative deepening if we don't have a TT move
1134 if ( UseIIDAtPVNodes
1135 && depth >= 5*OnePly
1136 && ttMove == MOVE_NONE)
1138 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1139 ttMove = ss[ply].pv[ply];
1140 tte = TT.retrieve(pos.get_key());
1143 // Initialize a MovePicker object for the current position, and prepare
1144 // to search all moves
1145 isCheck = pos.is_check();
1146 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1148 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1150 // Loop through all legal moves until no moves remain or a beta cutoff
1152 while ( alpha < beta
1153 && (move = mp.get_next_move()) != MOVE_NONE
1154 && !thread_should_stop(threadID))
1156 assert(move_is_ok(move));
1158 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1159 moveIsCheck = pos.move_is_check(move, ci);
1160 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1162 // Decide the new search depth
1163 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1165 // Singular extension search. We extend the TT move if its value is much better than
1166 // its siblings. To verify this we do a reduced search on all the other moves but the
1167 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1168 if ( depth >= 6 * OnePly
1170 && move == tte->move()
1172 && is_lower_bound(tte->type())
1173 && tte->depth() >= depth - 3 * OnePly)
1175 Value ttValue = value_from_tt(tte->value(), ply);
1177 if (abs(ttValue) < VALUE_KNOWN_WIN)
1179 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1181 if (excValue < ttValue - SingleReplyMargin)
1186 newDepth = depth - OnePly + ext;
1188 // Update current move
1189 movesSearched[moveCount++] = ss[ply].currentMove = move;
1191 // Make and search the move
1192 pos.do_move(move, st, ci, moveIsCheck);
1194 if (moveCount == 1) // The first move in list is the PV
1195 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1198 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1199 // if the move fails high will be re-searched at full depth.
1200 if ( depth >= 3*OnePly
1201 && moveCount >= LMRPVMoves
1203 && !captureOrPromotion
1204 && !move_is_castle(move)
1205 && !move_is_killer(move, ss[ply]))
1207 ss[ply].reduction = OnePly;
1208 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1211 value = alpha + 1; // Just to trigger next condition
1213 if (value > alpha) // Go with full depth non-pv search
1215 ss[ply].reduction = Depth(0);
1216 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1217 if (value > alpha && value < beta)
1219 // When the search fails high at ply 1 while searching the first
1220 // move at the root, set the flag failHighPly1. This is used for
1221 // time managment: We don't want to stop the search early in
1222 // such cases, because resolving the fail high at ply 1 could
1223 // result in a big drop in score at the root.
1224 if (ply == 1 && RootMoveNumber == 1)
1225 Threads[threadID].failHighPly1 = true;
1227 // A fail high occurred. Re-search at full window (pv search)
1228 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1229 Threads[threadID].failHighPly1 = false;
1233 pos.undo_move(move);
1235 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1238 if (value > bestValue)
1245 if (value == value_mate_in(ply + 1))
1246 ss[ply].mateKiller = move;
1248 // If we are at ply 1, and we are searching the first root move at
1249 // ply 0, set the 'Problem' variable if the score has dropped a lot
1250 // (from the computer's point of view) since the previous iteration.
1253 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1258 if ( ActiveThreads > 1
1260 && depth >= MinimumSplitDepth
1262 && idle_thread_exists(threadID)
1264 && !thread_should_stop(threadID)
1265 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1266 depth, &moveCount, &mp, threadID, true))
1270 // All legal moves have been searched. A special case: If there were
1271 // no legal moves, it must be mate or stalemate.
1273 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1275 // If the search is not aborted, update the transposition table,
1276 // history counters, and killer moves.
1277 if (AbortSearch || thread_should_stop(threadID))
1280 if (bestValue <= oldAlpha)
1281 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1283 else if (bestValue >= beta)
1285 BetaCounter.add(pos.side_to_move(), depth, threadID);
1286 move = ss[ply].pv[ply];
1287 if (!pos.move_is_capture_or_promotion(move))
1289 update_history(pos, move, depth, movesSearched, moveCount);
1290 update_killers(move, ss[ply]);
1292 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1295 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1301 // search() is the search function for zero-width nodes.
1303 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1304 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1306 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1307 assert(ply >= 0 && ply < PLY_MAX);
1308 assert(threadID >= 0 && threadID < ActiveThreads);
1310 Move movesSearched[256];
1315 Depth ext, newDepth;
1316 Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
1317 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1318 bool mateThreat = false;
1320 Value bestValue = -VALUE_INFINITE;
1323 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1325 // Initialize, and make an early exit in case of an aborted search,
1326 // an instant draw, maximum ply reached, etc.
1327 init_node(ss, ply, threadID);
1329 // After init_node() that calls poll()
1330 if (AbortSearch || thread_should_stop(threadID))
1336 if (ply >= PLY_MAX - 1)
1337 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1339 // Mate distance pruning
1340 if (value_mated_in(ply) >= beta)
1343 if (value_mate_in(ply + 1) < beta)
1346 // We don't want the score of a partial search to overwrite a previous full search
1347 // TT value, so we use a different position key in case of an excluded move exsists.
1348 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1350 // Transposition table lookup
1351 tte = TT.retrieve(posKey);
1352 ttMove = (tte ? tte->move() : MOVE_NONE);
1354 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1356 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1357 return value_from_tt(tte->value(), ply);
1360 approximateEval = quick_evaluate(pos);
1361 isCheck = pos.is_check();
1367 && !value_is_mate(beta)
1368 && ok_to_do_nullmove(pos)
1369 && approximateEval >= beta - NullMoveMargin)
1371 ss[ply].currentMove = MOVE_NULL;
1373 pos.do_null_move(st);
1375 // Null move dynamic reduction based on depth
1376 int R = (depth >= 5 * OnePly ? 4 : 3);
1378 // Null move dynamic reduction based on value
1379 if (approximateEval - beta > PawnValueMidgame)
1382 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1384 pos.undo_null_move();
1386 if (nullValue >= beta)
1388 if (depth < 6 * OnePly)
1391 // Do zugzwang verification search
1392 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1396 // The null move failed low, which means that we may be faced with
1397 // some kind of threat. If the previous move was reduced, check if
1398 // the move that refuted the null move was somehow connected to the
1399 // move which was reduced. If a connection is found, return a fail
1400 // low score (which will cause the reduced move to fail high in the
1401 // parent node, which will trigger a re-search with full depth).
1402 if (nullValue == value_mated_in(ply + 2))
1405 ss[ply].threatMove = ss[ply + 1].currentMove;
1406 if ( depth < ThreatDepth
1407 && ss[ply - 1].reduction
1408 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1412 // Null move search not allowed, try razoring
1413 else if ( !value_is_mate(beta)
1414 && depth < RazorDepth
1415 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1416 && ss[ply - 1].currentMove != MOVE_NULL
1417 && ttMove == MOVE_NONE
1418 && !pos.has_pawn_on_7th(pos.side_to_move()))
1420 Value rbeta = beta - RazorMargins[int(depth) - 2];
1421 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1426 // Go with internal iterative deepening if we don't have a TT move
1427 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1428 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1430 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1431 ttMove = ss[ply].pv[ply];
1432 tte = TT.retrieve(pos.get_key());
1435 // Initialize a MovePicker object for the current position, and prepare
1436 // to search all moves.
1437 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1439 futilityValue = VALUE_NONE;
1440 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1442 // Calculate depth dependant futility pruning parameters
1443 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1444 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1446 // Avoid calling evaluate() if we already have the score in TT
1447 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1448 futilityValue = value_from_tt(tte->value(), ply) + FutilityValueMargin;
1450 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1451 while ( bestValue < beta
1452 && (move = mp.get_next_move()) != MOVE_NONE
1453 && !thread_should_stop(threadID))
1455 assert(move_is_ok(move));
1457 if (move == excludedMove)
1460 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1461 moveIsCheck = pos.move_is_check(move, ci);
1462 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1464 // Decide the new search depth
1465 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1467 // Singular extension search. We extend the TT move if its value is much better than
1468 // its siblings. To verify this we do a reduced search on all the other moves but the
1469 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1470 if ( depth >= 8 * OnePly
1472 && move == tte->move()
1473 && !excludedMove // Do not allow recursive single-reply search
1475 && is_lower_bound(tte->type())
1476 && tte->depth() >= depth - 3 * OnePly)
1478 Value ttValue = value_from_tt(tte->value(), ply);
1480 if (abs(ttValue) < VALUE_KNOWN_WIN)
1482 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1484 if (excValue < ttValue - SingleReplyMargin)
1489 newDepth = depth - OnePly + ext;
1491 // Update current move
1492 movesSearched[moveCount++] = ss[ply].currentMove = move;
1495 if ( useFutilityPruning
1497 && !captureOrPromotion
1500 // Move count based pruning
1501 if ( moveCount >= FutilityMoveCountMargin
1502 && ok_to_prune(pos, move, ss[ply].threatMove)
1503 && bestValue > value_mated_in(PLY_MAX))
1506 // Value based pruning
1507 if (futilityValue == VALUE_NONE)
1508 futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1510 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1512 if (futilityValueScaled < beta)
1514 if (futilityValueScaled > bestValue)
1515 bestValue = futilityValueScaled;
1520 // Make and search the move
1521 pos.do_move(move, st, ci, moveIsCheck);
1523 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1524 // if the move fails high will be re-searched at full depth.
1525 if ( depth >= 3*OnePly
1526 && moveCount >= LMRNonPVMoves
1528 && !captureOrPromotion
1529 && !move_is_castle(move)
1530 && !move_is_killer(move, ss[ply]))
1532 ss[ply].reduction = OnePly;
1533 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1536 value = beta; // Just to trigger next condition
1538 if (value >= beta) // Go with full depth non-pv search
1540 ss[ply].reduction = Depth(0);
1541 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1543 pos.undo_move(move);
1545 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1548 if (value > bestValue)
1554 if (value == value_mate_in(ply + 1))
1555 ss[ply].mateKiller = move;
1559 if ( ActiveThreads > 1
1561 && depth >= MinimumSplitDepth
1563 && idle_thread_exists(threadID)
1565 && !thread_should_stop(threadID)
1566 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1567 depth, &moveCount, &mp, threadID, false))
1571 // All legal moves have been searched. A special case: If there were
1572 // no legal moves, it must be mate or stalemate.
1574 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1576 // If the search is not aborted, update the transposition table,
1577 // history counters, and killer moves.
1578 if (AbortSearch || thread_should_stop(threadID))
1581 if (bestValue < beta)
1582 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1585 BetaCounter.add(pos.side_to_move(), depth, threadID);
1586 move = ss[ply].pv[ply];
1587 if (!pos.move_is_capture_or_promotion(move))
1589 update_history(pos, move, depth, movesSearched, moveCount);
1590 update_killers(move, ss[ply]);
1592 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1595 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1601 // qsearch() is the quiescence search function, which is called by the main
1602 // search function when the remaining depth is zero (or, to be more precise,
1603 // less than OnePly).
1605 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1606 Depth depth, int ply, int threadID) {
1608 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1609 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1611 assert(ply >= 0 && ply < PLY_MAX);
1612 assert(threadID >= 0 && threadID < ActiveThreads);
1617 Value staticValue, bestValue, value, futilityValue;
1618 bool isCheck, enoughMaterial, moveIsCheck;
1619 const TTEntry* tte = NULL;
1621 bool pvNode = (beta - alpha != 1);
1623 // Initialize, and make an early exit in case of an aborted search,
1624 // an instant draw, maximum ply reached, etc.
1625 init_node(ss, ply, threadID);
1627 // After init_node() that calls poll()
1628 if (AbortSearch || thread_should_stop(threadID))
1634 // Transposition table lookup, only when not in PV
1637 tte = TT.retrieve(pos.get_key());
1638 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1640 assert(tte->type() != VALUE_TYPE_EVAL);
1642 return value_from_tt(tte->value(), ply);
1645 ttMove = (tte ? tte->move() : MOVE_NONE);
1647 isCheck = pos.is_check();
1648 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1650 // Evaluate the position statically
1652 staticValue = -VALUE_INFINITE;
1654 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1656 // Use the cached evaluation score if possible
1657 assert(ei.futilityMargin == Value(0));
1659 staticValue = value_from_tt(tte->value(), ply);
1662 staticValue = evaluate(pos, ei, threadID);
1664 if (ply >= PLY_MAX - 1)
1665 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1667 // Initialize "stand pat score", and return it immediately if it is
1669 bestValue = staticValue;
1671 if (bestValue >= beta)
1673 // Store the score to avoid a future costly evaluation() call
1674 if (!isCheck && !tte && ei.futilityMargin == 0)
1675 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1680 if (bestValue > alpha)
1683 // Initialize a MovePicker object for the current position, and prepare
1684 // to search the moves. Because the depth is <= 0 here, only captures,
1685 // queen promotions and checks (only if depth == 0) will be generated.
1686 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1688 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1690 // Loop through the moves until no moves remain or a beta cutoff
1692 while ( alpha < beta
1693 && (move = mp.get_next_move()) != MOVE_NONE)
1695 assert(move_is_ok(move));
1698 ss[ply].currentMove = move;
1700 moveIsCheck = pos.move_is_check(move, ci);
1708 && !move_is_promotion(move)
1709 && !pos.move_is_passed_pawn_push(move))
1711 futilityValue = staticValue
1712 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1713 pos.endgame_value_of_piece_on(move_to(move)))
1714 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1716 + ei.futilityMargin;
1718 if (futilityValue < alpha)
1720 if (futilityValue > bestValue)
1721 bestValue = futilityValue;
1726 // Don't search captures and checks with negative SEE values
1729 && !move_is_promotion(move)
1730 && pos.see_sign(move) < 0)
1733 // Make and search the move
1734 pos.do_move(move, st, ci, moveIsCheck);
1735 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1736 pos.undo_move(move);
1738 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1741 if (value > bestValue)
1752 // All legal moves have been searched. A special case: If we're in check
1753 // and no legal moves were found, it is checkmate.
1754 if (!moveCount && pos.is_check()) // Mate!
1755 return value_mated_in(ply);
1757 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1759 // Update transposition table
1760 move = ss[ply].pv[ply];
1763 // If bestValue isn't changed it means it is still the static evaluation of
1764 // the node, so keep this info to avoid a future costly evaluation() call.
1765 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1766 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1768 if (bestValue < beta)
1769 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1771 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1774 // Update killers only for good check moves
1775 if (alpha >= beta && !pos.move_is_capture_or_promotion(move))
1776 update_killers(move, ss[ply]);
1782 // sp_search() is used to search from a split point. This function is called
1783 // by each thread working at the split point. It is similar to the normal
1784 // search() function, but simpler. Because we have already probed the hash
1785 // table, done a null move search, and searched the first move before
1786 // splitting, we don't have to repeat all this work in sp_search(). We
1787 // also don't need to store anything to the hash table here: This is taken
1788 // care of after we return from the split point.
1790 void sp_search(SplitPoint* sp, int threadID) {
1792 assert(threadID >= 0 && threadID < ActiveThreads);
1793 assert(ActiveThreads > 1);
1795 Position pos = Position(sp->pos);
1797 SearchStack* ss = sp->sstack[threadID];
1800 bool isCheck = pos.is_check();
1801 bool useFutilityPruning = sp->depth < SelectiveDepth
1804 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1805 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1807 while ( sp->bestValue < sp->beta
1808 && !thread_should_stop(threadID)
1809 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1811 assert(move_is_ok(move));
1813 bool moveIsCheck = pos.move_is_check(move, ci);
1814 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1816 lock_grab(&(sp->lock));
1817 int moveCount = ++sp->moves;
1818 lock_release(&(sp->lock));
1820 ss[sp->ply].currentMove = move;
1822 // Decide the new search depth.
1824 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1825 Depth newDepth = sp->depth - OnePly + ext;
1828 if ( useFutilityPruning
1830 && !captureOrPromotion)
1832 // Move count based pruning
1833 if ( moveCount >= FutilityMoveCountMargin
1834 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1835 && sp->bestValue > value_mated_in(PLY_MAX))
1838 // Value based pruning
1839 if (sp->futilityValue == VALUE_NONE)
1842 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1845 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1847 if (futilityValueScaled < sp->beta)
1849 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1851 lock_grab(&(sp->lock));
1852 if (futilityValueScaled > sp->bestValue)
1853 sp->bestValue = futilityValueScaled;
1854 lock_release(&(sp->lock));
1860 // Make and search the move.
1862 pos.do_move(move, st, ci, moveIsCheck);
1864 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1865 // if the move fails high will be re-searched at full depth.
1867 && moveCount >= LMRNonPVMoves
1868 && !captureOrPromotion
1869 && !move_is_castle(move)
1870 && !move_is_killer(move, ss[sp->ply]))
1872 ss[sp->ply].reduction = OnePly;
1873 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1876 value = sp->beta; // Just to trigger next condition
1878 if (value >= sp->beta) // Go with full depth non-pv search
1880 ss[sp->ply].reduction = Depth(0);
1881 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1883 pos.undo_move(move);
1885 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1887 if (thread_should_stop(threadID))
1891 if (value > sp->bestValue) // Less then 2% of cases
1893 lock_grab(&(sp->lock));
1894 if (value > sp->bestValue && !thread_should_stop(threadID))
1896 sp->bestValue = value;
1897 if (sp->bestValue >= sp->beta)
1899 sp_update_pv(sp->parentSstack, ss, sp->ply);
1900 for (int i = 0; i < ActiveThreads; i++)
1901 if (i != threadID && (i == sp->master || sp->slaves[i]))
1902 Threads[i].stop = true;
1904 sp->finished = true;
1907 lock_release(&(sp->lock));
1911 lock_grab(&(sp->lock));
1913 // If this is the master thread and we have been asked to stop because of
1914 // a beta cutoff higher up in the tree, stop all slave threads.
1915 if (sp->master == threadID && thread_should_stop(threadID))
1916 for (int i = 0; i < ActiveThreads; i++)
1918 Threads[i].stop = true;
1921 sp->slaves[threadID] = 0;
1923 lock_release(&(sp->lock));
1927 // sp_search_pv() is used to search from a PV split point. This function
1928 // is called by each thread working at the split point. It is similar to
1929 // the normal search_pv() function, but simpler. Because we have already
1930 // probed the hash table and searched the first move before splitting, we
1931 // don't have to repeat all this work in sp_search_pv(). We also don't
1932 // need to store anything to the hash table here: This is taken care of
1933 // after we return from the split point.
1935 void sp_search_pv(SplitPoint* sp, int threadID) {
1937 assert(threadID >= 0 && threadID < ActiveThreads);
1938 assert(ActiveThreads > 1);
1940 Position pos = Position(sp->pos);
1942 SearchStack* ss = sp->sstack[threadID];
1946 while ( sp->alpha < sp->beta
1947 && !thread_should_stop(threadID)
1948 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1950 bool moveIsCheck = pos.move_is_check(move, ci);
1951 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1953 assert(move_is_ok(move));
1955 lock_grab(&(sp->lock));
1956 int moveCount = ++sp->moves;
1957 lock_release(&(sp->lock));
1959 ss[sp->ply].currentMove = move;
1961 // Decide the new search depth.
1963 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1964 Depth newDepth = sp->depth - OnePly + ext;
1966 // Make and search the move.
1968 pos.do_move(move, st, ci, moveIsCheck);
1970 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1971 // if the move fails high will be re-searched at full depth.
1973 && moveCount >= LMRPVMoves
1974 && !captureOrPromotion
1975 && !move_is_castle(move)
1976 && !move_is_killer(move, ss[sp->ply]))
1978 ss[sp->ply].reduction = OnePly;
1979 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1982 value = sp->alpha + 1; // Just to trigger next condition
1984 if (value > sp->alpha) // Go with full depth non-pv search
1986 ss[sp->ply].reduction = Depth(0);
1987 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1989 if (value > sp->alpha && value < sp->beta)
1991 // When the search fails high at ply 1 while searching the first
1992 // move at the root, set the flag failHighPly1. This is used for
1993 // time managment: We don't want to stop the search early in
1994 // such cases, because resolving the fail high at ply 1 could
1995 // result in a big drop in score at the root.
1996 if (sp->ply == 1 && RootMoveNumber == 1)
1997 Threads[threadID].failHighPly1 = true;
1999 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
2000 Threads[threadID].failHighPly1 = false;
2003 pos.undo_move(move);
2005 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2007 if (thread_should_stop(threadID))
2011 lock_grab(&(sp->lock));
2012 if (value > sp->bestValue && !thread_should_stop(threadID))
2014 sp->bestValue = value;
2015 if (value > sp->alpha)
2018 sp_update_pv(sp->parentSstack, ss, sp->ply);
2019 if (value == value_mate_in(sp->ply + 1))
2020 ss[sp->ply].mateKiller = move;
2022 if (value >= sp->beta)
2024 for (int i = 0; i < ActiveThreads; i++)
2025 if (i != threadID && (i == sp->master || sp->slaves[i]))
2026 Threads[i].stop = true;
2028 sp->finished = true;
2031 // If we are at ply 1, and we are searching the first root move at
2032 // ply 0, set the 'Problem' variable if the score has dropped a lot
2033 // (from the computer's point of view) since the previous iteration.
2036 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2039 lock_release(&(sp->lock));
2042 lock_grab(&(sp->lock));
2044 // If this is the master thread and we have been asked to stop because of
2045 // a beta cutoff higher up in the tree, stop all slave threads.
2046 if (sp->master == threadID && thread_should_stop(threadID))
2047 for (int i = 0; i < ActiveThreads; i++)
2049 Threads[i].stop = true;
2052 sp->slaves[threadID] = 0;
2054 lock_release(&(sp->lock));
2057 /// The BetaCounterType class
2059 BetaCounterType::BetaCounterType() { clear(); }
2061 void BetaCounterType::clear() {
2063 for (int i = 0; i < THREAD_MAX; i++)
2064 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2067 void BetaCounterType::add(Color us, Depth d, int threadID) {
2069 // Weighted count based on depth
2070 Threads[threadID].betaCutOffs[us] += unsigned(d);
2073 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2076 for (int i = 0; i < THREAD_MAX; i++)
2078 our += Threads[i].betaCutOffs[us];
2079 their += Threads[i].betaCutOffs[opposite_color(us)];
2084 /// The RootMove class
2088 RootMove::RootMove() {
2089 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
2092 // RootMove::operator<() is the comparison function used when
2093 // sorting the moves. A move m1 is considered to be better
2094 // than a move m2 if it has a higher score, or if the moves
2095 // have equal score but m1 has the higher node count.
2097 bool RootMove::operator<(const RootMove& m) const {
2099 if (score != m.score)
2100 return (score < m.score);
2102 return theirBeta <= m.theirBeta;
2105 /// The RootMoveList class
2109 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2111 MoveStack mlist[MaxRootMoves];
2112 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2114 // Generate all legal moves
2115 MoveStack* last = generate_moves(pos, mlist);
2117 // Add each move to the moves[] array
2118 for (MoveStack* cur = mlist; cur != last; cur++)
2120 bool includeMove = includeAllMoves;
2122 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2123 includeMove = (searchMoves[k] == cur->move);
2128 // Find a quick score for the move
2130 SearchStack ss[PLY_MAX_PLUS_2];
2133 moves[count].move = cur->move;
2134 pos.do_move(moves[count].move, st);
2135 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2136 pos.undo_move(moves[count].move);
2137 moves[count].pv[0] = moves[count].move;
2138 moves[count].pv[1] = MOVE_NONE;
2145 // Simple accessor methods for the RootMoveList class
2147 inline Move RootMoveList::get_move(int moveNum) const {
2148 return moves[moveNum].move;
2151 inline Value RootMoveList::get_move_score(int moveNum) const {
2152 return moves[moveNum].score;
2155 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2156 moves[moveNum].score = score;
2159 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2160 moves[moveNum].nodes = nodes;
2161 moves[moveNum].cumulativeNodes += nodes;
2164 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2165 moves[moveNum].ourBeta = our;
2166 moves[moveNum].theirBeta = their;
2169 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2171 for(j = 0; pv[j] != MOVE_NONE; j++)
2172 moves[moveNum].pv[j] = pv[j];
2173 moves[moveNum].pv[j] = MOVE_NONE;
2176 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2177 return moves[moveNum].pv[i];
2180 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2181 return moves[moveNum].cumulativeNodes;
2184 inline int RootMoveList::move_count() const {
2189 // RootMoveList::sort() sorts the root move list at the beginning of a new
2192 inline void RootMoveList::sort() {
2194 sort_multipv(count - 1); // all items
2198 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2199 // list by their scores and depths. It is used to order the different PVs
2200 // correctly in MultiPV mode.
2202 void RootMoveList::sort_multipv(int n) {
2204 for (int i = 1; i <= n; i++)
2206 RootMove rm = moves[i];
2208 for (j = i; j > 0 && moves[j-1] < rm; j--)
2209 moves[j] = moves[j-1];
2215 // init_node() is called at the beginning of all the search functions
2216 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2217 // stack object corresponding to the current node. Once every
2218 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2219 // for user input and checks whether it is time to stop the search.
2221 void init_node(SearchStack ss[], int ply, int threadID) {
2223 assert(ply >= 0 && ply < PLY_MAX);
2224 assert(threadID >= 0 && threadID < ActiveThreads);
2226 Threads[threadID].nodes++;
2231 if (NodesSincePoll >= NodesBetweenPolls)
2238 ss[ply+2].initKillers();
2240 if (Threads[threadID].printCurrentLine)
2241 print_current_line(ss, ply, threadID);
2245 // update_pv() is called whenever a search returns a value > alpha. It
2246 // updates the PV in the SearchStack object corresponding to the current
2249 void update_pv(SearchStack ss[], int ply) {
2250 assert(ply >= 0 && ply < PLY_MAX);
2252 ss[ply].pv[ply] = ss[ply].currentMove;
2254 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2255 ss[ply].pv[p] = ss[ply+1].pv[p];
2256 ss[ply].pv[p] = MOVE_NONE;
2260 // sp_update_pv() is a variant of update_pv for use at split points. The
2261 // difference between the two functions is that sp_update_pv also updates
2262 // the PV at the parent node.
2264 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2265 assert(ply >= 0 && ply < PLY_MAX);
2267 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2269 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2270 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2271 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2275 // connected_moves() tests whether two moves are 'connected' in the sense
2276 // that the first move somehow made the second move possible (for instance
2277 // if the moving piece is the same in both moves). The first move is
2278 // assumed to be the move that was made to reach the current position, while
2279 // the second move is assumed to be a move from the current position.
2281 bool connected_moves(const Position& pos, Move m1, Move m2) {
2283 Square f1, t1, f2, t2;
2286 assert(move_is_ok(m1));
2287 assert(move_is_ok(m2));
2289 if (m2 == MOVE_NONE)
2292 // Case 1: The moving piece is the same in both moves
2298 // Case 2: The destination square for m2 was vacated by m1
2304 // Case 3: Moving through the vacated square
2305 if ( piece_is_slider(pos.piece_on(f2))
2306 && bit_is_set(squares_between(f2, t2), f1))
2309 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2310 p = pos.piece_on(t1);
2311 if (bit_is_set(pos.attacks_from(p, t1), t2))
2314 // Case 5: Discovered check, checking piece is the piece moved in m1
2315 if ( piece_is_slider(p)
2316 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2317 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2319 Bitboard occ = pos.occupied_squares();
2320 Color us = pos.side_to_move();
2321 Square ksq = pos.king_square(us);
2322 clear_bit(&occ, f2);
2323 if (type_of_piece(p) == BISHOP)
2325 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2328 else if (type_of_piece(p) == ROOK)
2330 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2335 assert(type_of_piece(p) == QUEEN);
2336 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2344 // value_is_mate() checks if the given value is a mate one
2345 // eventually compensated for the ply.
2347 bool value_is_mate(Value value) {
2349 assert(abs(value) <= VALUE_INFINITE);
2351 return value <= value_mated_in(PLY_MAX)
2352 || value >= value_mate_in(PLY_MAX);
2356 // move_is_killer() checks if the given move is among the
2357 // killer moves of that ply.
2359 bool move_is_killer(Move m, const SearchStack& ss) {
2361 const Move* k = ss.killers;
2362 for (int i = 0; i < KILLER_MAX; i++, k++)
2370 // extension() decides whether a move should be searched with normal depth,
2371 // or with extended depth. Certain classes of moves (checking moves, in
2372 // particular) are searched with bigger depth than ordinary moves and in
2373 // any case are marked as 'dangerous'. Note that also if a move is not
2374 // extended, as example because the corresponding UCI option is set to zero,
2375 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2377 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2378 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2380 assert(m != MOVE_NONE);
2382 Depth result = Depth(0);
2383 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2388 result += CheckExtension[pvNode];
2391 result += SingleEvasionExtension[pvNode];
2394 result += MateThreatExtension[pvNode];
2397 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2399 Color c = pos.side_to_move();
2400 if (relative_rank(c, move_to(m)) == RANK_7)
2402 result += PawnPushTo7thExtension[pvNode];
2405 if (pos.pawn_is_passed(c, move_to(m)))
2407 result += PassedPawnExtension[pvNode];
2412 if ( captureOrPromotion
2413 && pos.type_of_piece_on(move_to(m)) != PAWN
2414 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2415 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2416 && !move_is_promotion(m)
2419 result += PawnEndgameExtension[pvNode];
2424 && captureOrPromotion
2425 && pos.type_of_piece_on(move_to(m)) != PAWN
2426 && pos.see_sign(m) >= 0)
2432 return Min(result, OnePly);
2436 // ok_to_do_nullmove() looks at the current position and decides whether
2437 // doing a 'null move' should be allowed. In order to avoid zugzwang
2438 // problems, null moves are not allowed when the side to move has very
2439 // little material left. Currently, the test is a bit too simple: Null
2440 // moves are avoided only when the side to move has only pawns left. It's
2441 // probably a good idea to avoid null moves in at least some more
2442 // complicated endgames, e.g. KQ vs KR. FIXME
2444 bool ok_to_do_nullmove(const Position& pos) {
2446 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2450 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2451 // non-tactical moves late in the move list close to the leaves are
2452 // candidates for pruning.
2454 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2456 assert(move_is_ok(m));
2457 assert(threat == MOVE_NONE || move_is_ok(threat));
2458 assert(!pos.move_is_check(m));
2459 assert(!pos.move_is_capture_or_promotion(m));
2460 assert(!pos.move_is_passed_pawn_push(m));
2462 Square mfrom, mto, tfrom, tto;
2464 mfrom = move_from(m);
2466 tfrom = move_from(threat);
2467 tto = move_to(threat);
2469 // Case 1: Castling moves are never pruned
2470 if (move_is_castle(m))
2473 // Case 2: Don't prune moves which move the threatened piece
2474 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2477 // Case 3: If the threatened piece has value less than or equal to the
2478 // value of the threatening piece, don't prune move which defend it.
2479 if ( !PruneDefendingMoves
2480 && threat != MOVE_NONE
2481 && pos.move_is_capture(threat)
2482 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2483 || pos.type_of_piece_on(tfrom) == KING)
2484 && pos.move_attacks_square(m, tto))
2487 // Case 4: If the moving piece in the threatened move is a slider, don't
2488 // prune safe moves which block its ray.
2489 if ( !PruneBlockingMoves
2490 && threat != MOVE_NONE
2491 && piece_is_slider(pos.piece_on(tfrom))
2492 && bit_is_set(squares_between(tfrom, tto), mto)
2493 && pos.see_sign(m) >= 0)
2500 // ok_to_use_TT() returns true if a transposition table score
2501 // can be used at a given point in search.
2503 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2505 Value v = value_from_tt(tte->value(), ply);
2507 return ( tte->depth() >= depth
2508 || v >= Max(value_mate_in(PLY_MAX), beta)
2509 || v < Min(value_mated_in(PLY_MAX), beta))
2511 && ( (is_lower_bound(tte->type()) && v >= beta)
2512 || (is_upper_bound(tte->type()) && v < beta));
2516 // update_history() registers a good move that produced a beta-cutoff
2517 // in history and marks as failures all the other moves of that ply.
2519 void update_history(const Position& pos, Move m, Depth depth,
2520 Move movesSearched[], int moveCount) {
2522 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2524 for (int i = 0; i < moveCount - 1; i++)
2526 assert(m != movesSearched[i]);
2527 if (!pos.move_is_capture_or_promotion(movesSearched[i]))
2528 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]), depth);
2533 // update_killers() add a good move that produced a beta-cutoff
2534 // among the killer moves of that ply.
2536 void update_killers(Move m, SearchStack& ss) {
2538 if (m == ss.killers[0])
2541 for (int i = KILLER_MAX - 1; i > 0; i--)
2542 ss.killers[i] = ss.killers[i - 1];
2548 // fail_high_ply_1() checks if some thread is currently resolving a fail
2549 // high at ply 1 at the node below the first root node. This information
2550 // is used for time managment.
2552 bool fail_high_ply_1() {
2554 for(int i = 0; i < ActiveThreads; i++)
2555 if (Threads[i].failHighPly1)
2562 // current_search_time() returns the number of milliseconds which have passed
2563 // since the beginning of the current search.
2565 int current_search_time() {
2566 return get_system_time() - SearchStartTime;
2570 // nps() computes the current nodes/second count.
2573 int t = current_search_time();
2574 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2578 // poll() performs two different functions: It polls for user input, and it
2579 // looks at the time consumed so far and decides if it's time to abort the
2584 static int lastInfoTime;
2585 int t = current_search_time();
2590 // We are line oriented, don't read single chars
2591 std::string command;
2592 if (!std::getline(std::cin, command))
2595 if (command == "quit")
2598 PonderSearch = false;
2602 else if (command == "stop")
2605 PonderSearch = false;
2607 else if (command == "ponderhit")
2610 // Print search information
2614 else if (lastInfoTime > t)
2615 // HACK: Must be a new search where we searched less than
2616 // NodesBetweenPolls nodes during the first second of search.
2619 else if (t - lastInfoTime >= 1000)
2626 if (dbg_show_hit_rate)
2627 dbg_print_hit_rate();
2629 cout << "info nodes " << nodes_searched() << " nps " << nps()
2630 << " time " << t << " hashfull " << TT.full() << endl;
2631 lock_release(&IOLock);
2632 if (ShowCurrentLine)
2633 Threads[0].printCurrentLine = true;
2635 // Should we stop the search?
2639 bool overTime = t > AbsoluteMaxSearchTime
2640 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2641 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2642 && t > 6*(MaxSearchTime + ExtraSearchTime));
2644 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2645 || (ExactMaxTime && t >= ExactMaxTime)
2646 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2651 // ponderhit() is called when the program is pondering (i.e. thinking while
2652 // it's the opponent's turn to move) in order to let the engine know that
2653 // it correctly predicted the opponent's move.
2657 int t = current_search_time();
2658 PonderSearch = false;
2659 if (Iteration >= 3 &&
2660 (!InfiniteSearch && (StopOnPonderhit ||
2661 t > AbsoluteMaxSearchTime ||
2662 (RootMoveNumber == 1 &&
2663 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2664 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2665 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2670 // print_current_line() prints the current line of search for a given
2671 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2673 void print_current_line(SearchStack ss[], int ply, int threadID) {
2675 assert(ply >= 0 && ply < PLY_MAX);
2676 assert(threadID >= 0 && threadID < ActiveThreads);
2678 if (!Threads[threadID].idle)
2681 cout << "info currline " << (threadID + 1);
2682 for (int p = 0; p < ply; p++)
2683 cout << " " << ss[p].currentMove;
2686 lock_release(&IOLock);
2688 Threads[threadID].printCurrentLine = false;
2689 if (threadID + 1 < ActiveThreads)
2690 Threads[threadID + 1].printCurrentLine = true;
2694 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2696 void init_ss_array(SearchStack ss[]) {
2698 for (int i = 0; i < 3; i++)
2701 ss[i].initKillers();
2706 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2707 // while the program is pondering. The point is to work around a wrinkle in
2708 // the UCI protocol: When pondering, the engine is not allowed to give a
2709 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2710 // We simply wait here until one of these commands is sent, and return,
2711 // after which the bestmove and pondermove will be printed (in id_loop()).
2713 void wait_for_stop_or_ponderhit() {
2715 std::string command;
2719 if (!std::getline(std::cin, command))
2722 if (command == "quit")
2727 else if (command == "ponderhit" || command == "stop")
2733 // idle_loop() is where the threads are parked when they have no work to do.
2734 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2735 // object for which the current thread is the master.
2737 void idle_loop(int threadID, SplitPoint* waitSp) {
2738 assert(threadID >= 0 && threadID < THREAD_MAX);
2740 Threads[threadID].running = true;
2743 if(AllThreadsShouldExit && threadID != 0)
2746 // If we are not thinking, wait for a condition to be signaled instead
2747 // of wasting CPU time polling for work:
2748 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2749 #if !defined(_MSC_VER)
2750 pthread_mutex_lock(&WaitLock);
2751 if(Idle || threadID >= ActiveThreads)
2752 pthread_cond_wait(&WaitCond, &WaitLock);
2753 pthread_mutex_unlock(&WaitLock);
2755 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2759 // If this thread has been assigned work, launch a search
2760 if(Threads[threadID].workIsWaiting) {
2761 Threads[threadID].workIsWaiting = false;
2762 if(Threads[threadID].splitPoint->pvNode)
2763 sp_search_pv(Threads[threadID].splitPoint, threadID);
2765 sp_search(Threads[threadID].splitPoint, threadID);
2766 Threads[threadID].idle = true;
2769 // If this thread is the master of a split point and all threads have
2770 // finished their work at this split point, return from the idle loop.
2771 if(waitSp != NULL && waitSp->cpus == 0)
2775 Threads[threadID].running = false;
2779 // init_split_point_stack() is called during program initialization, and
2780 // initializes all split point objects.
2782 void init_split_point_stack() {
2783 for(int i = 0; i < THREAD_MAX; i++)
2784 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2785 SplitPointStack[i][j].parent = NULL;
2786 lock_init(&(SplitPointStack[i][j].lock), NULL);
2791 // destroy_split_point_stack() is called when the program exits, and
2792 // destroys all locks in the precomputed split point objects.
2794 void destroy_split_point_stack() {
2795 for(int i = 0; i < THREAD_MAX; i++)
2796 for(int j = 0; j < MaxActiveSplitPoints; j++)
2797 lock_destroy(&(SplitPointStack[i][j].lock));
2801 // thread_should_stop() checks whether the thread with a given threadID has
2802 // been asked to stop, directly or indirectly. This can happen if a beta
2803 // cutoff has occured in thre thread's currently active split point, or in
2804 // some ancestor of the current split point.
2806 bool thread_should_stop(int threadID) {
2807 assert(threadID >= 0 && threadID < ActiveThreads);
2811 if(Threads[threadID].stop)
2813 if(ActiveThreads <= 2)
2815 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2817 Threads[threadID].stop = true;
2824 // thread_is_available() checks whether the thread with threadID "slave" is
2825 // available to help the thread with threadID "master" at a split point. An
2826 // obvious requirement is that "slave" must be idle. With more than two
2827 // threads, this is not by itself sufficient: If "slave" is the master of
2828 // some active split point, it is only available as a slave to the other
2829 // threads which are busy searching the split point at the top of "slave"'s
2830 // split point stack (the "helpful master concept" in YBWC terminology).
2832 bool thread_is_available(int slave, int master) {
2833 assert(slave >= 0 && slave < ActiveThreads);
2834 assert(master >= 0 && master < ActiveThreads);
2835 assert(ActiveThreads > 1);
2837 if(!Threads[slave].idle || slave == master)
2840 if(Threads[slave].activeSplitPoints == 0)
2841 // No active split points means that the thread is available as a slave
2842 // for any other thread.
2845 if(ActiveThreads == 2)
2848 // Apply the "helpful master" concept if possible.
2849 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2856 // idle_thread_exists() tries to find an idle thread which is available as
2857 // a slave for the thread with threadID "master".
2859 bool idle_thread_exists(int master) {
2860 assert(master >= 0 && master < ActiveThreads);
2861 assert(ActiveThreads > 1);
2863 for(int i = 0; i < ActiveThreads; i++)
2864 if(thread_is_available(i, master))
2870 // split() does the actual work of distributing the work at a node between
2871 // several threads at PV nodes. If it does not succeed in splitting the
2872 // node (because no idle threads are available, or because we have no unused
2873 // split point objects), the function immediately returns false. If
2874 // splitting is possible, a SplitPoint object is initialized with all the
2875 // data that must be copied to the helper threads (the current position and
2876 // search stack, alpha, beta, the search depth, etc.), and we tell our
2877 // helper threads that they have been assigned work. This will cause them
2878 // to instantly leave their idle loops and call sp_search_pv(). When all
2879 // threads have returned from sp_search_pv (or, equivalently, when
2880 // splitPoint->cpus becomes 0), split() returns true.
2882 bool split(const Position& p, SearchStack* sstck, int ply,
2883 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2884 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2887 assert(sstck != NULL);
2888 assert(ply >= 0 && ply < PLY_MAX);
2889 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2890 assert(!pvNode || *alpha < *beta);
2891 assert(*beta <= VALUE_INFINITE);
2892 assert(depth > Depth(0));
2893 assert(master >= 0 && master < ActiveThreads);
2894 assert(ActiveThreads > 1);
2896 SplitPoint* splitPoint;
2901 // If no other thread is available to help us, or if we have too many
2902 // active split points, don't split.
2903 if(!idle_thread_exists(master) ||
2904 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2905 lock_release(&MPLock);
2909 // Pick the next available split point object from the split point stack
2910 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2911 Threads[master].activeSplitPoints++;
2913 // Initialize the split point object
2914 splitPoint->parent = Threads[master].splitPoint;
2915 splitPoint->finished = false;
2916 splitPoint->ply = ply;
2917 splitPoint->depth = depth;
2918 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2919 splitPoint->beta = *beta;
2920 splitPoint->pvNode = pvNode;
2921 splitPoint->bestValue = *bestValue;
2922 splitPoint->futilityValue = futilityValue;
2923 splitPoint->master = master;
2924 splitPoint->mp = mp;
2925 splitPoint->moves = *moves;
2926 splitPoint->cpus = 1;
2927 splitPoint->pos.copy(p);
2928 splitPoint->parentSstack = sstck;
2929 for(i = 0; i < ActiveThreads; i++)
2930 splitPoint->slaves[i] = 0;
2932 // Copy the current position and the search stack to the master thread
2933 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2934 Threads[master].splitPoint = splitPoint;
2936 // Make copies of the current position and search stack for each thread
2937 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2939 if(thread_is_available(i, master)) {
2940 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2941 Threads[i].splitPoint = splitPoint;
2942 splitPoint->slaves[i] = 1;
2946 // Tell the threads that they have work to do. This will make them leave
2948 for(i = 0; i < ActiveThreads; i++)
2949 if(i == master || splitPoint->slaves[i]) {
2950 Threads[i].workIsWaiting = true;
2951 Threads[i].idle = false;
2952 Threads[i].stop = false;
2955 lock_release(&MPLock);
2957 // Everything is set up. The master thread enters the idle loop, from
2958 // which it will instantly launch a search, because its workIsWaiting
2959 // slot is 'true'. We send the split point as a second parameter to the
2960 // idle loop, which means that the main thread will return from the idle
2961 // loop when all threads have finished their work at this split point
2962 // (i.e. when // splitPoint->cpus == 0).
2963 idle_loop(master, splitPoint);
2965 // We have returned from the idle loop, which means that all threads are
2966 // finished. Update alpha, beta and bestvalue, and return.
2968 if(pvNode) *alpha = splitPoint->alpha;
2969 *beta = splitPoint->beta;
2970 *bestValue = splitPoint->bestValue;
2971 Threads[master].stop = false;
2972 Threads[master].idle = false;
2973 Threads[master].activeSplitPoints--;
2974 Threads[master].splitPoint = splitPoint->parent;
2975 lock_release(&MPLock);
2981 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2982 // to start a new search from the root.
2984 void wake_sleeping_threads() {
2985 if(ActiveThreads > 1) {
2986 for(int i = 1; i < ActiveThreads; i++) {
2987 Threads[i].idle = true;
2988 Threads[i].workIsWaiting = false;
2990 #if !defined(_MSC_VER)
2991 pthread_mutex_lock(&WaitLock);
2992 pthread_cond_broadcast(&WaitCond);
2993 pthread_mutex_unlock(&WaitLock);
2995 for(int i = 1; i < THREAD_MAX; i++)
2996 SetEvent(SitIdleEvent[i]);
3002 // init_thread() is the function which is called when a new thread is
3003 // launched. It simply calls the idle_loop() function with the supplied
3004 // threadID. There are two versions of this function; one for POSIX threads
3005 // and one for Windows threads.
3007 #if !defined(_MSC_VER)
3009 void *init_thread(void *threadID) {
3010 idle_loop(*(int *)threadID, NULL);
3016 DWORD WINAPI init_thread(LPVOID threadID) {
3017 idle_loop(*(int *)threadID, NULL);