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/>.
43 #include "ucioption.h"
49 //// Local definitions
56 // IterationInfoType stores search results for each iteration
58 // Because we use relatively small (dynamic) aspiration window,
59 // there happens many fail highs and fail lows in root. And
60 // because we don't do researches in those cases, "value" stored
61 // here is not necessarily exact. Instead in case of fail high/low
62 // we guess what the right value might be and store our guess
63 // as a "speculated value" and then move on. Speculated values are
64 // used just to calculate aspiration window width, so also if are
65 // not exact is not big a problem.
67 struct IterationInfoType {
69 IterationInfoType(Value v = Value(0), Value sv = Value(0))
70 : value(v), speculatedValue(sv) {}
72 Value value, speculatedValue;
76 // The BetaCounterType class is used to order moves at ply one.
77 // Apart for the first one that has its score, following moves
78 // normally have score -VALUE_INFINITE, so are ordered according
79 // to the number of beta cutoffs occurred under their subtree during
80 // the last iteration. The counters are per thread variables to avoid
81 // concurrent accessing under SMP case.
83 struct BetaCounterType {
87 void add(Color us, Depth d, int threadID);
88 void read(Color us, int64_t& our, int64_t& their);
92 // The RootMove class is used for moves at the root at the tree. For each
93 // root move, we store a score, a node count, and a PV (really a refutation
94 // in the case of moves which fail low).
98 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
100 // RootMove::operator<() is the comparison function used when
101 // sorting the moves. A move m1 is considered to be better
102 // than a move m2 if it has a higher score, or if the moves
103 // have equal score but m1 has the higher node count.
104 bool operator<(const RootMove& m) const {
106 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
111 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
112 Move pv[PLY_MAX_PLUS_2];
116 // The RootMoveList class is essentially an array of RootMove objects, with
117 // a handful of methods for accessing the data in the individual moves.
122 RootMoveList(Position& pos, Move searchMoves[]);
124 int move_count() const { return count; }
125 Move get_move(int moveNum) const { return moves[moveNum].move; }
126 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
127 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
128 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
129 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
131 void set_move_nodes(int moveNum, int64_t nodes);
132 void set_beta_counters(int moveNum, int64_t our, int64_t their);
133 void set_move_pv(int moveNum, const Move pv[]);
135 void sort_multipv(int n);
138 static const int MaxRootMoves = 500;
139 RootMove moves[MaxRootMoves];
146 // Search depth at iteration 1
147 const Depth InitialDepth = OnePly;
149 // Depth limit for selective search
150 const Depth SelectiveDepth = 7 * OnePly;
152 // Use internal iterative deepening?
153 const bool UseIIDAtPVNodes = true;
154 const bool UseIIDAtNonPVNodes = true;
156 // Internal iterative deepening margin. At Non-PV moves, when
157 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
158 // search when the static evaluation is at most IIDMargin below beta.
159 const Value IIDMargin = Value(0x100);
161 // Easy move margin. An easy move candidate must be at least this much
162 // better than the second best move.
163 const Value EasyMoveMargin = Value(0x200);
165 // Problem margin. If the score of the first move at iteration N+1 has
166 // dropped by more than this since iteration N, the boolean variable
167 // "Problem" is set to true, which will make the program spend some extra
168 // time looking for a better move.
169 const Value ProblemMargin = Value(0x28);
171 // No problem margin. If the boolean "Problem" is true, and a new move
172 // is found at the root which is less than NoProblemMargin worse than the
173 // best move from the previous iteration, Problem is set back to false.
174 const Value NoProblemMargin = Value(0x14);
176 // Null move margin. A null move search will not be done if the static
177 // evaluation of the position is more than NullMoveMargin below beta.
178 const Value NullMoveMargin = Value(0x200);
180 // If the TT move is at least SingleReplyMargin better then the
181 // remaining ones we will extend it.
182 const Value SingleReplyMargin = Value(0x20);
184 // Margins for futility pruning in the quiescence search, and at frontier
185 // and near frontier nodes.
186 const Value FutilityMarginQS = Value(0x80);
188 // Each move futility margin is decreased
189 const Value IncrementalFutilityMargin = Value(0x8);
191 // Depth limit for razoring
192 const Depth RazorDepth = 4 * OnePly;
194 /// Variables initialized by UCI options
196 // Depth limit for use of dynamic threat detection
199 // Last seconds noise filtering (LSN)
200 const bool UseLSNFiltering = true;
201 const int LSNTime = 4000; // In milliseconds
202 const Value LSNValue = value_from_centipawns(200);
203 bool loseOnTime = false;
205 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
206 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
207 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
209 // Iteration counters
211 BetaCounterType BetaCounter;
213 // Scores and number of times the best move changed for each iteration
214 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
215 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
220 // Time managment variables
223 int MaxNodes, MaxDepth;
224 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
225 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
226 bool AbortSearch, Quit;
227 bool FailHigh, FailLow, Problem;
229 // Show current line?
230 bool ShowCurrentLine;
234 std::ofstream LogFile;
236 // Natural logarithmic lookup table and its getter function
238 inline double ln(int i) { return lnArray[i]; }
240 // MP related variables
241 int ActiveThreads = 1;
242 Depth MinimumSplitDepth;
243 int MaxThreadsPerSplitPoint;
244 Thread Threads[THREAD_MAX];
247 bool AllThreadsShouldExit = false;
248 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
251 #if !defined(_MSC_VER)
252 pthread_cond_t WaitCond;
253 pthread_mutex_t WaitLock;
255 HANDLE SitIdleEvent[THREAD_MAX];
258 // Node counters, used only by thread[0] but try to keep in different
259 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
261 int NodesBetweenPolls = 30000;
269 Value id_loop(const Position& pos, Move searchMoves[]);
270 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
271 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
273 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
274 void sp_search(SplitPoint* sp, int threadID);
275 void sp_search_pv(SplitPoint* sp, int threadID);
276 void init_node(SearchStack ss[], int ply, int threadID);
277 void update_pv(SearchStack ss[], int ply);
278 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
279 bool connected_moves(const Position& pos, Move m1, Move m2);
280 bool value_is_mate(Value value);
281 bool move_is_killer(Move m, const SearchStack& ss);
282 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
283 bool ok_to_do_nullmove(const Position& pos);
284 bool ok_to_prune(const Position& pos, Move m, Move threat);
285 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
286 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
287 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
288 void update_killers(Move m, SearchStack& ss);
290 bool fail_high_ply_1();
291 int current_search_time();
295 void print_current_line(SearchStack ss[], int ply, int threadID);
296 void wait_for_stop_or_ponderhit();
297 void init_ss_array(SearchStack ss[]);
299 void idle_loop(int threadID, SplitPoint* waitSp);
300 void init_split_point_stack();
301 void destroy_split_point_stack();
302 bool thread_should_stop(int threadID);
303 bool thread_is_available(int slave, int master);
304 bool idle_thread_exists(int master);
305 bool split(const Position& pos, SearchStack* ss, int ply,
306 Value *alpha, Value *beta, Value *bestValue,
307 const Value futilityValue, Depth depth, int *moves,
308 MovePicker *mp, int master, bool pvNode);
309 void wake_sleeping_threads();
311 #if !defined(_MSC_VER)
312 void *init_thread(void *threadID);
314 DWORD WINAPI init_thread(LPVOID threadID);
325 /// perft() is our utility to verify move generation is bug free. All the legal
326 /// moves up to given depth are generated and counted and the sum returned.
328 int perft(Position& pos, Depth depth)
332 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
334 // If we are at the last ply we don't need to do and undo
335 // the moves, just to count them.
336 if (depth <= OnePly) // Replace with '<' to test also qsearch
338 while (mp.get_next_move()) sum++;
342 // Loop through all legal moves
344 while ((move = mp.get_next_move()) != MOVE_NONE)
347 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
348 sum += perft(pos, depth - OnePly);
355 /// think() is the external interface to Stockfish's search, and is called when
356 /// the program receives the UCI 'go' command. It initializes various
357 /// search-related global variables, and calls root_search(). It returns false
358 /// when a quit command is received during the search.
360 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
361 int time[], int increment[], int movesToGo, int maxDepth,
362 int maxNodes, int maxTime, Move searchMoves[]) {
364 // Initialize global search variables
365 Idle = StopOnPonderhit = AbortSearch = Quit = false;
366 FailHigh = FailLow = Problem = false;
368 SearchStartTime = get_system_time();
369 ExactMaxTime = maxTime;
372 InfiniteSearch = infinite;
373 PonderSearch = ponder;
374 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
376 // Look for a book move, only during games, not tests
377 if (UseTimeManagement && !ponder && get_option_value_bool("OwnBook"))
380 if (get_option_value_string("Book File") != OpeningBook.file_name())
381 OpeningBook.open(get_option_value_string("Book File"));
383 bookMove = OpeningBook.get_move(pos);
384 if (bookMove != MOVE_NONE)
386 cout << "bestmove " << bookMove << endl;
391 for (int i = 0; i < THREAD_MAX; i++)
393 Threads[i].nodes = 0ULL;
394 Threads[i].failHighPly1 = false;
397 if (button_was_pressed("New Game"))
398 loseOnTime = false; // Reset at the beginning of a new game
400 // Read UCI option values
401 TT.set_size(get_option_value_int("Hash"));
402 if (button_was_pressed("Clear Hash"))
405 bool PonderingEnabled = get_option_value_bool("Ponder");
406 MultiPV = get_option_value_int("MultiPV");
408 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
409 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
411 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
412 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
414 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
415 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
417 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
418 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 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);
445 // HACK: init_eval() destroys the static castleRightsMask[] array in the
446 // Position class. The below line repairs the damage.
447 Position p(pos.to_fen());
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];
460 if (UseTimeManagement)
462 if (!movesToGo) // Sudden death time control
466 MaxSearchTime = myTime / 30 + myIncrement;
467 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
469 else // Blitz game without increment
471 MaxSearchTime = myTime / 30;
472 AbsoluteMaxSearchTime = myTime / 8;
475 else // (x moves) / (y minutes)
479 MaxSearchTime = myTime / 2;
480 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
484 MaxSearchTime = myTime / Min(movesToGo, 20);
485 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
489 if (PonderingEnabled)
491 MaxSearchTime += MaxSearchTime / 4;
492 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
496 // Set best NodesBetweenPolls interval
498 NodesBetweenPolls = Min(MaxNodes, 30000);
499 else if (myTime && myTime < 1000)
500 NodesBetweenPolls = 1000;
501 else if (myTime && myTime < 5000)
502 NodesBetweenPolls = 5000;
504 NodesBetweenPolls = 30000;
506 // Write information to search log file
508 LogFile << "Searching: " << pos.to_fen() << endl
509 << "infinite: " << infinite
510 << " ponder: " << ponder
511 << " time: " << myTime
512 << " increment: " << myIncrement
513 << " moves to go: " << movesToGo << endl;
515 // LSN filtering. Used only for developing purpose. Disabled by default.
519 // Step 2. If after last move we decided to lose on time, do it now!
520 while (SearchStartTime + myTime + 1000 > get_system_time())
524 // We're ready to start thinking. Call the iterative deepening loop function
525 Value v = id_loop(pos, searchMoves);
530 // Step 1. If this is sudden death game and our position is hopeless,
531 // decide to lose on time.
532 if ( !loseOnTime // If we already lost on time, go to step 3.
542 // Step 3. Now after stepping over the time limit, reset flag for next match.
555 /// init_threads() is called during startup. It launches all helper threads,
556 /// and initializes the split point stack and the global locks and condition
559 void init_threads() {
564 #if !defined(_MSC_VER)
565 pthread_t pthread[1];
568 // Init our logarithmic lookup table
569 for (i = 0; i < 512; i++)
570 lnArray[i] = log(double(i)); // log() returns base-e logarithm
572 for (i = 0; i < THREAD_MAX; i++)
573 Threads[i].activeSplitPoints = 0;
575 // Initialize global locks
576 lock_init(&MPLock, NULL);
577 lock_init(&IOLock, NULL);
579 init_split_point_stack();
581 #if !defined(_MSC_VER)
582 pthread_mutex_init(&WaitLock, NULL);
583 pthread_cond_init(&WaitCond, NULL);
585 for (i = 0; i < THREAD_MAX; i++)
586 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
589 // All threads except the main thread should be initialized to idle state
590 for (i = 1; i < THREAD_MAX; i++)
592 Threads[i].stop = false;
593 Threads[i].workIsWaiting = false;
594 Threads[i].idle = true;
595 Threads[i].running = false;
598 // Launch the helper threads
599 for (i = 1; i < THREAD_MAX; i++)
601 #if !defined(_MSC_VER)
602 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
605 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
610 cout << "Failed to create thread number " << i << endl;
611 Application::exit_with_failure();
614 // Wait until the thread has finished launching
615 while (!Threads[i].running);
620 /// stop_threads() is called when the program exits. It makes all the
621 /// helper threads exit cleanly.
623 void stop_threads() {
625 ActiveThreads = THREAD_MAX; // HACK
626 Idle = false; // HACK
627 wake_sleeping_threads();
628 AllThreadsShouldExit = true;
629 for (int i = 1; i < THREAD_MAX; i++)
631 Threads[i].stop = true;
632 while (Threads[i].running);
634 destroy_split_point_stack();
638 /// nodes_searched() returns the total number of nodes searched so far in
639 /// the current search.
641 int64_t nodes_searched() {
643 int64_t result = 0ULL;
644 for (int i = 0; i < ActiveThreads; i++)
645 result += Threads[i].nodes;
650 // SearchStack::init() initializes a search stack. Used at the beginning of a
651 // new search from the root.
652 void SearchStack::init(int ply) {
654 pv[ply] = pv[ply + 1] = MOVE_NONE;
655 currentMove = threatMove = MOVE_NONE;
656 reduction = Depth(0);
661 void SearchStack::initKillers() {
663 mateKiller = MOVE_NONE;
664 for (int i = 0; i < KILLER_MAX; i++)
665 killers[i] = MOVE_NONE;
670 // id_loop() is the main iterative deepening loop. It calls root_search
671 // repeatedly with increasing depth until the allocated thinking time has
672 // been consumed, the user stops the search, or the maximum search depth is
675 Value id_loop(const Position& pos, Move searchMoves[]) {
678 SearchStack ss[PLY_MAX_PLUS_2];
680 // searchMoves are verified, copied, scored and sorted
681 RootMoveList rml(p, searchMoves);
683 if (rml.move_count() == 0)
686 wait_for_stop_or_ponderhit();
688 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
691 // Print RootMoveList c'tor startup scoring to the standard output,
692 // so that we print information also for iteration 1.
693 cout << "info depth " << 1 << "\ninfo depth " << 1
694 << " score " << value_to_string(rml.get_move_score(0))
695 << " time " << current_search_time()
696 << " nodes " << nodes_searched()
698 << " pv " << rml.get_move(0) << "\n";
704 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
707 // Is one move significantly better than others after initial scoring ?
708 Move EasyMove = MOVE_NONE;
709 if ( rml.move_count() == 1
710 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
711 EasyMove = rml.get_move(0);
713 // Iterative deepening loop
714 while (Iteration < PLY_MAX)
716 // Initialize iteration
719 BestMoveChangesByIteration[Iteration] = 0;
723 cout << "info depth " << Iteration << endl;
725 // Calculate dynamic search window based on previous iterations
728 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
730 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
731 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
733 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
735 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
736 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
740 alpha = - VALUE_INFINITE;
741 beta = VALUE_INFINITE;
744 // Search to the current depth
745 Value value = root_search(p, ss, rml, alpha, beta);
747 // Write PV to transposition table, in case the relevant entries have
748 // been overwritten during the search.
749 TT.insert_pv(p, ss[0].pv);
752 break; // Value cannot be trusted. Break out immediately!
754 //Save info about search result
755 Value speculatedValue;
758 Value delta = value - IterationInfo[Iteration - 1].value;
765 speculatedValue = value + delta;
766 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
768 else if (value <= alpha)
770 assert(value == alpha);
774 speculatedValue = value + delta;
775 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
777 speculatedValue = value;
779 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
780 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
782 // Drop the easy move if it differs from the new best move
783 if (ss[0].pv[0] != EasyMove)
784 EasyMove = MOVE_NONE;
788 if (UseTimeManagement)
791 bool stopSearch = false;
793 // Stop search early if there is only a single legal move,
794 // we search up to Iteration 6 anyway to get a proper score.
795 if (Iteration >= 6 && rml.move_count() == 1)
798 // Stop search early when the last two iterations returned a mate score
800 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
801 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
804 // Stop search early if one move seems to be much better than the rest
805 int64_t nodes = nodes_searched();
809 && EasyMove == ss[0].pv[0]
810 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
811 && current_search_time() > MaxSearchTime / 16)
812 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
813 && current_search_time() > MaxSearchTime / 32)))
816 // Add some extra time if the best move has changed during the last two iterations
817 if (Iteration > 5 && Iteration <= 50)
818 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
819 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
821 // Stop search if most of MaxSearchTime is consumed at the end of the
822 // iteration. We probably don't have enough time to search the first
823 // move at the next iteration anyway.
824 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
832 StopOnPonderhit = true;
836 if (MaxDepth && Iteration >= MaxDepth)
842 // If we are pondering or in infinite search, we shouldn't print the
843 // best move before we are told to do so.
844 if (!AbortSearch && !ExactMaxTime && (PonderSearch || InfiniteSearch))
845 wait_for_stop_or_ponderhit();
847 // Print final search statistics
848 cout << "info nodes " << nodes_searched()
850 << " time " << current_search_time()
851 << " hashfull " << TT.full() << endl;
853 // Print the best move and the ponder move to the standard output
854 if (ss[0].pv[0] == MOVE_NONE)
856 ss[0].pv[0] = rml.get_move(0);
857 ss[0].pv[1] = MOVE_NONE;
859 cout << "bestmove " << ss[0].pv[0];
860 if (ss[0].pv[1] != MOVE_NONE)
861 cout << " ponder " << ss[0].pv[1];
868 dbg_print_mean(LogFile);
870 if (dbg_show_hit_rate)
871 dbg_print_hit_rate(LogFile);
873 LogFile << "\nNodes: " << nodes_searched()
874 << "\nNodes/second: " << nps()
875 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
878 p.do_move(ss[0].pv[0], st);
879 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
881 return rml.get_move_score(0);
885 // root_search() is the function which searches the root node. It is
886 // similar to search_pv except that it uses a different move ordering
887 // scheme and prints some information to the standard output.
889 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
891 Value oldAlpha = alpha;
892 Value value = -VALUE_INFINITE;
895 // Loop through all the moves in the root move list
896 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
900 // We failed high, invalidate and skip next moves, leave node-counters
901 // and beta-counters as they are and quickly return, we will try to do
902 // a research at the next iteration with a bigger aspiration window.
903 rml.set_move_score(i, -VALUE_INFINITE);
909 Depth depth, ext, newDepth;
911 RootMoveNumber = i + 1;
914 // Save the current node count before the move is searched
915 nodes = nodes_searched();
917 // Reset beta cut-off counters
920 // Pick the next root move, and print the move and the move number to
921 // the standard output.
922 move = ss[0].currentMove = rml.get_move(i);
924 if (current_search_time() >= 1000)
925 cout << "info currmove " << move
926 << " currmovenumber " << RootMoveNumber << endl;
928 // Decide search depth for this move
929 bool moveIsCheck = pos.move_is_check(move);
930 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
932 depth = (Iteration - 2) * OnePly + InitialDepth;
933 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
934 newDepth = depth + ext;
936 // Make the move, and search it
937 pos.do_move(move, st, ci, moveIsCheck);
941 // Aspiration window is disabled in multi-pv case
943 alpha = -VALUE_INFINITE;
945 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
947 // If the value has dropped a lot compared to the last iteration,
948 // set the boolean variable Problem to true. This variable is used
949 // for time managment: When Problem is true, we try to complete the
950 // current iteration before playing a move.
951 Problem = ( Iteration >= 2
952 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
954 if (Problem && StopOnPonderhit)
955 StopOnPonderhit = false;
959 // Try to reduce non-pv search depth by one ply if move seems not problematic,
960 // if the move fails high will be re-searched at full depth.
961 bool doFullDepthSearch = true;
963 if ( depth >= 3*OnePly // FIXME was newDepth
965 && !captureOrPromotion
966 && !move_is_castle(move))
968 double red = 0.5 + ln(RootMoveNumber - MultiPV + 1) * ln(depth / 2) / 6.0;
971 ss[0].reduction = Depth(int(floor(red * int(OnePly))));
972 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
973 doFullDepthSearch = (value > alpha);
977 if (doFullDepthSearch)
979 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
983 // Fail high! Set the boolean variable FailHigh to true, and
984 // re-search the move using a PV search. The variable FailHigh
985 // is used for time managment: We try to avoid aborting the
986 // search prematurely during a fail high research.
988 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
995 // Finished searching the move. If AbortSearch is true, the search
996 // was aborted because the user interrupted the search or because we
997 // ran out of time. In this case, the return value of the search cannot
998 // be trusted, and we break out of the loop without updating the best
1003 // Remember beta-cutoff and searched nodes counts for this move. The
1004 // info is used to sort the root moves at the next iteration.
1006 BetaCounter.read(pos.side_to_move(), our, their);
1007 rml.set_beta_counters(i, our, their);
1008 rml.set_move_nodes(i, nodes_searched() - nodes);
1010 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1012 if (value <= alpha && i >= MultiPV)
1013 rml.set_move_score(i, -VALUE_INFINITE);
1016 // PV move or new best move!
1019 rml.set_move_score(i, value);
1021 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1022 rml.set_move_pv(i, ss[0].pv);
1026 // We record how often the best move has been changed in each
1027 // iteration. This information is used for time managment: When
1028 // the best move changes frequently, we allocate some more time.
1030 BestMoveChangesByIteration[Iteration]++;
1032 // Print search information to the standard output
1033 cout << "info depth " << Iteration
1034 << " score " << value_to_string(value)
1035 << ((value >= beta) ? " lowerbound" :
1036 ((value <= alpha)? " upperbound" : ""))
1037 << " time " << current_search_time()
1038 << " nodes " << nodes_searched()
1042 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1043 cout << ss[0].pv[j] << " ";
1049 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1050 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1052 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1053 nodes_searched(), value, type, ss[0].pv) << endl;
1058 // Reset the global variable Problem to false if the value isn't too
1059 // far below the final value from the last iteration.
1060 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1065 rml.sort_multipv(i);
1066 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1068 cout << "info multipv " << j + 1
1069 << " score " << value_to_string(rml.get_move_score(j))
1070 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1071 << " time " << current_search_time()
1072 << " nodes " << nodes_searched()
1076 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1077 cout << rml.get_move_pv(j, k) << " ";
1081 alpha = rml.get_move_score(Min(i, MultiPV-1));
1083 } // PV move or new best move
1085 assert(alpha >= oldAlpha);
1087 FailLow = (alpha == oldAlpha);
1093 // search_pv() is the main search function for PV nodes.
1095 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1096 Depth depth, int ply, int threadID) {
1098 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1099 assert(beta > alpha && beta <= VALUE_INFINITE);
1100 assert(ply >= 0 && ply < PLY_MAX);
1101 assert(threadID >= 0 && threadID < ActiveThreads);
1103 Move movesSearched[256];
1107 Depth ext, newDepth;
1108 Value oldAlpha, value;
1109 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1111 Value bestValue = value = -VALUE_INFINITE;
1114 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1116 // Initialize, and make an early exit in case of an aborted search,
1117 // an instant draw, maximum ply reached, etc.
1118 init_node(ss, ply, threadID);
1120 // After init_node() that calls poll()
1121 if (AbortSearch || thread_should_stop(threadID))
1124 if (pos.is_draw() || ply >= PLY_MAX - 1)
1127 // Mate distance pruning
1129 alpha = Max(value_mated_in(ply), alpha);
1130 beta = Min(value_mate_in(ply+1), beta);
1134 // Transposition table lookup. At PV nodes, we don't use the TT for
1135 // pruning, but only for move ordering. This is to avoid problems in
1136 // the following areas:
1138 // * Repetition draw detection
1139 // * Fifty move rule detection
1140 // * Searching for a mate
1141 // * Printing of full PV line
1143 tte = TT.retrieve(pos.get_key());
1144 ttMove = (tte ? tte->move() : MOVE_NONE);
1146 // Go with internal iterative deepening if we don't have a TT move
1147 if ( UseIIDAtPVNodes
1148 && depth >= 5*OnePly
1149 && ttMove == MOVE_NONE)
1151 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1152 ttMove = ss[ply].pv[ply];
1153 tte = TT.retrieve(pos.get_key());
1156 // Initialize a MovePicker object for the current position, and prepare
1157 // to search all moves
1158 isCheck = pos.is_check();
1159 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1161 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1163 // Loop through all legal moves until no moves remain or a beta cutoff
1165 while ( alpha < beta
1166 && (move = mp.get_next_move()) != MOVE_NONE
1167 && !thread_should_stop(threadID))
1169 assert(move_is_ok(move));
1171 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1172 moveIsCheck = pos.move_is_check(move, ci);
1173 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1175 // Decide the new search depth
1176 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1178 // Singular extension search. We extend the TT move if its value is much better than
1179 // its siblings. To verify this we do a reduced search on all the other moves but the
1180 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1181 if ( depth >= 6 * OnePly
1183 && move == tte->move()
1185 && is_lower_bound(tte->type())
1186 && tte->depth() >= depth - 3 * OnePly)
1188 Value ttValue = value_from_tt(tte->value(), ply);
1190 if (abs(ttValue) < VALUE_KNOWN_WIN)
1192 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1194 if (excValue < ttValue - SingleReplyMargin)
1199 newDepth = depth - OnePly + ext;
1201 // Update current move
1202 movesSearched[moveCount++] = ss[ply].currentMove = move;
1204 // Make and search the move
1205 pos.do_move(move, st, ci, moveIsCheck);
1207 if (moveCount == 1) // The first move in list is the PV
1208 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1211 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1212 // if the move fails high will be re-searched at full depth.
1213 bool doFullDepthSearch = true;
1215 if ( depth >= 3*OnePly
1217 && !captureOrPromotion
1218 && !move_is_castle(move)
1219 && !move_is_killer(move, ss[ply]))
1221 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 6.0;
1224 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1225 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1226 doFullDepthSearch = (value > alpha);
1230 if (doFullDepthSearch) // Go with full depth non-pv search
1232 ss[ply].reduction = Depth(0);
1233 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1234 if (value > alpha && value < beta)
1236 // When the search fails high at ply 1 while searching the first
1237 // move at the root, set the flag failHighPly1. This is used for
1238 // time managment: We don't want to stop the search early in
1239 // such cases, because resolving the fail high at ply 1 could
1240 // result in a big drop in score at the root.
1241 if (ply == 1 && RootMoveNumber == 1)
1242 Threads[threadID].failHighPly1 = true;
1244 // A fail high occurred. Re-search at full window (pv search)
1245 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1246 Threads[threadID].failHighPly1 = false;
1250 pos.undo_move(move);
1252 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1255 if (value > bestValue)
1262 if (value == value_mate_in(ply + 1))
1263 ss[ply].mateKiller = move;
1265 // If we are at ply 1, and we are searching the first root move at
1266 // ply 0, set the 'Problem' variable if the score has dropped a lot
1267 // (from the computer's point of view) since the previous iteration.
1270 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1275 if ( ActiveThreads > 1
1277 && depth >= MinimumSplitDepth
1279 && idle_thread_exists(threadID)
1281 && !thread_should_stop(threadID)
1282 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1283 depth, &moveCount, &mp, threadID, true))
1287 // All legal moves have been searched. A special case: If there were
1288 // no legal moves, it must be mate or stalemate.
1290 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1292 // If the search is not aborted, update the transposition table,
1293 // history counters, and killer moves.
1294 if (AbortSearch || thread_should_stop(threadID))
1297 if (bestValue <= oldAlpha)
1298 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1300 else if (bestValue >= beta)
1302 BetaCounter.add(pos.side_to_move(), depth, threadID);
1303 move = ss[ply].pv[ply];
1304 if (!pos.move_is_capture_or_promotion(move))
1306 update_history(pos, move, depth, movesSearched, moveCount);
1307 update_killers(move, ss[ply]);
1309 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1312 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1318 // search() is the search function for zero-width nodes.
1320 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1321 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1323 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1324 assert(ply >= 0 && ply < PLY_MAX);
1325 assert(threadID >= 0 && threadID < ActiveThreads);
1327 Move movesSearched[256];
1332 Depth ext, newDepth;
1333 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1334 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1335 bool mateThreat = false;
1337 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1340 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1342 // Initialize, and make an early exit in case of an aborted search,
1343 // an instant draw, maximum ply reached, etc.
1344 init_node(ss, ply, threadID);
1346 // After init_node() that calls poll()
1347 if (AbortSearch || thread_should_stop(threadID))
1350 if (pos.is_draw() || ply >= PLY_MAX - 1)
1353 // Mate distance pruning
1354 if (value_mated_in(ply) >= beta)
1357 if (value_mate_in(ply + 1) < beta)
1360 // We don't want the score of a partial search to overwrite a previous full search
1361 // TT value, so we use a different position key in case of an excluded move exsists.
1362 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1364 // Transposition table lookup
1365 tte = TT.retrieve(posKey);
1366 ttMove = (tte ? tte->move() : MOVE_NONE);
1368 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1370 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1371 return value_from_tt(tte->value(), ply);
1374 isCheck = pos.is_check();
1376 // Calculate depth dependant futility pruning parameters
1377 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1378 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1380 // Evaluate the position statically
1383 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1384 staticValue = value_from_tt(tte->value(), ply);
1387 staticValue = evaluate(pos, ei, threadID);
1388 ss[ply].evalInfo = &ei;
1391 ss[ply].eval = staticValue;
1392 futilityValue = staticValue + FutilityValueMargin;
1393 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1400 && !value_is_mate(beta)
1401 && ok_to_do_nullmove(pos)
1402 && staticValue >= beta - NullMoveMargin)
1404 ss[ply].currentMove = MOVE_NULL;
1406 pos.do_null_move(st);
1408 // Null move dynamic reduction based on depth
1409 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1411 // Null move dynamic reduction based on value
1412 if (staticValue - beta > PawnValueMidgame)
1415 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1417 pos.undo_null_move();
1419 if (nullValue >= beta)
1421 if (depth < 6 * OnePly)
1424 // Do zugzwang verification search
1425 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1429 // The null move failed low, which means that we may be faced with
1430 // some kind of threat. If the previous move was reduced, check if
1431 // the move that refuted the null move was somehow connected to the
1432 // move which was reduced. If a connection is found, return a fail
1433 // low score (which will cause the reduced move to fail high in the
1434 // parent node, which will trigger a re-search with full depth).
1435 if (nullValue == value_mated_in(ply + 2))
1438 ss[ply].threatMove = ss[ply + 1].currentMove;
1439 if ( depth < ThreatDepth
1440 && ss[ply - 1].reduction
1441 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1445 // Null move search not allowed, try razoring
1446 else if ( !value_is_mate(beta)
1448 && depth < RazorDepth
1449 && staticValue < beta - (NullMoveMargin + 16 * depth)
1450 && ss[ply - 1].currentMove != MOVE_NULL
1451 && ttMove == MOVE_NONE
1452 && !pos.has_pawn_on_7th(pos.side_to_move()))
1454 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1455 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1460 // Go with internal iterative deepening if we don't have a TT move
1461 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1462 !isCheck && ss[ply].eval >= beta - IIDMargin)
1464 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1465 ttMove = ss[ply].pv[ply];
1466 tte = TT.retrieve(pos.get_key());
1469 // Initialize a MovePicker object for the current position, and prepare
1470 // to search all moves.
1471 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1473 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1475 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1476 while ( bestValue < beta
1477 && (move = mp.get_next_move()) != MOVE_NONE
1478 && !thread_should_stop(threadID))
1480 assert(move_is_ok(move));
1482 if (move == excludedMove)
1485 moveIsCheck = pos.move_is_check(move, ci);
1486 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1487 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1489 // Decide the new search depth
1490 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1492 // Singular extension search. We extend the TT move if its value is much better than
1493 // its siblings. To verify this we do a reduced search on all the other moves but the
1494 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1495 if ( depth >= 8 * OnePly
1497 && move == tte->move()
1498 && !excludedMove // Do not allow recursive single-reply search
1500 && is_lower_bound(tte->type())
1501 && tte->depth() >= depth - 3 * OnePly)
1503 Value ttValue = value_from_tt(tte->value(), ply);
1505 if (abs(ttValue) < VALUE_KNOWN_WIN)
1507 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1509 if (excValue < ttValue - SingleReplyMargin)
1514 newDepth = depth - OnePly + ext;
1516 // Update current move
1517 movesSearched[moveCount++] = ss[ply].currentMove = move;
1520 if ( useFutilityPruning
1522 && !captureOrPromotion
1525 // Move count based pruning
1526 if ( moveCount >= FutilityMoveCountMargin
1527 && ok_to_prune(pos, move, ss[ply].threatMove)
1528 && bestValue > value_mated_in(PLY_MAX))
1531 // Value based pruning
1532 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1534 if (futilityValueScaled < beta)
1536 if (futilityValueScaled > bestValue)
1537 bestValue = futilityValueScaled;
1542 // Make and search the move
1543 pos.do_move(move, st, ci, moveIsCheck);
1545 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1546 // if the move fails high will be re-searched at full depth.
1547 bool doFullDepthSearch = true;
1549 if ( depth >= 3*OnePly
1551 && !captureOrPromotion
1552 && !move_is_castle(move)
1553 && !move_is_killer(move, ss[ply])
1554 /* && move != ttMove*/)
1556 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 3.0;
1559 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1560 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1561 doFullDepthSearch = (value >= beta);
1565 if (doFullDepthSearch) // Go with full depth non-pv search
1567 ss[ply].reduction = Depth(0);
1568 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1570 pos.undo_move(move);
1572 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1575 if (value > bestValue)
1581 if (value == value_mate_in(ply + 1))
1582 ss[ply].mateKiller = move;
1586 if ( ActiveThreads > 1
1588 && depth >= MinimumSplitDepth
1590 && idle_thread_exists(threadID)
1592 && !thread_should_stop(threadID)
1593 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1594 depth, &moveCount, &mp, threadID, false))
1598 // All legal moves have been searched. A special case: If there were
1599 // no legal moves, it must be mate or stalemate.
1601 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1603 // If the search is not aborted, update the transposition table,
1604 // history counters, and killer moves.
1605 if (AbortSearch || thread_should_stop(threadID))
1608 if (bestValue < beta)
1609 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1612 BetaCounter.add(pos.side_to_move(), depth, threadID);
1613 move = ss[ply].pv[ply];
1614 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1615 if (!pos.move_is_capture_or_promotion(move))
1617 update_history(pos, move, depth, movesSearched, moveCount);
1618 update_killers(move, ss[ply]);
1623 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1629 // qsearch() is the quiescence search function, which is called by the main
1630 // search function when the remaining depth is zero (or, to be more precise,
1631 // less than OnePly).
1633 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1634 Depth depth, int ply, int threadID) {
1636 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1637 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1639 assert(ply >= 0 && ply < PLY_MAX);
1640 assert(threadID >= 0 && threadID < ActiveThreads);
1645 Value staticValue, bestValue, value, futilityBase, futilityValue;
1646 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1647 const TTEntry* tte = NULL;
1649 bool pvNode = (beta - alpha != 1);
1651 // Initialize, and make an early exit in case of an aborted search,
1652 // an instant draw, maximum ply reached, etc.
1653 init_node(ss, ply, threadID);
1655 // After init_node() that calls poll()
1656 if (AbortSearch || thread_should_stop(threadID))
1659 if (pos.is_draw() || ply >= PLY_MAX - 1)
1662 // Transposition table lookup. At PV nodes, we don't use the TT for
1663 // pruning, but only for move ordering.
1664 tte = TT.retrieve(pos.get_key());
1665 ttMove = (tte ? tte->move() : MOVE_NONE);
1667 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1669 assert(tte->type() != VALUE_TYPE_EVAL);
1671 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1672 return value_from_tt(tte->value(), ply);
1675 isCheck = pos.is_check();
1677 // Evaluate the position statically
1679 staticValue = -VALUE_INFINITE;
1680 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1681 staticValue = value_from_tt(tte->value(), ply);
1683 staticValue = evaluate(pos, ei, threadID);
1685 // Initialize "stand pat score", and return it immediately if it is
1687 bestValue = staticValue;
1689 if (bestValue >= beta)
1691 // Store the score to avoid a future costly evaluation() call
1692 if (!isCheck && !tte && ei.futilityMargin == 0)
1693 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1698 if (bestValue > alpha)
1701 // If we are near beta then try to get a cutoff pushing checks a bit further
1702 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1704 // Initialize a MovePicker object for the current position, and prepare
1705 // to search the moves. Because the depth is <= 0 here, only captures,
1706 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1707 // and we are near beta) will be generated.
1708 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1710 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1711 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;
1713 // Loop through the moves until no moves remain or a beta cutoff
1715 while ( alpha < beta
1716 && (move = mp.get_next_move()) != MOVE_NONE)
1718 assert(move_is_ok(move));
1720 moveIsCheck = pos.move_is_check(move, ci);
1722 // Update current move
1724 ss[ply].currentMove = move;
1732 && !move_is_promotion(move)
1733 && !pos.move_is_passed_pawn_push(move))
1735 futilityValue = futilityBase
1736 + pos.endgame_value_of_piece_on(move_to(move))
1737 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1739 if (futilityValue < alpha)
1741 if (futilityValue > bestValue)
1742 bestValue = futilityValue;
1747 // Detect blocking evasions that are candidate to be pruned
1748 evasionPrunable = isCheck
1749 && bestValue != -VALUE_INFINITE
1750 && !pos.move_is_capture(move)
1751 && pos.type_of_piece_on(move_from(move)) != KING
1752 && !pos.can_castle(pos.side_to_move());
1754 // Don't search moves with negative SEE values
1755 if ( (!isCheck || evasionPrunable)
1757 && !move_is_promotion(move)
1758 && pos.see_sign(move) < 0)
1761 // Make and search the move
1762 pos.do_move(move, st, ci, moveIsCheck);
1763 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1764 pos.undo_move(move);
1766 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1769 if (value > bestValue)
1780 // All legal moves have been searched. A special case: If we're in check
1781 // and no legal moves were found, it is checkmate.
1782 if (!moveCount && pos.is_check()) // Mate!
1783 return value_mated_in(ply);
1785 // Update transposition table
1786 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1787 if (bestValue < beta)
1789 // If bestValue isn't changed it means it is still the static evaluation
1790 // of the node, so keep this info to avoid a future evaluation() call.
1791 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1792 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1796 move = ss[ply].pv[ply];
1797 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1799 // Update killers only for good checking moves
1800 if (!pos.move_is_capture_or_promotion(move))
1801 update_killers(move, ss[ply]);
1804 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1810 // sp_search() is used to search from a split point. This function is called
1811 // by each thread working at the split point. It is similar to the normal
1812 // search() function, but simpler. Because we have already probed the hash
1813 // table, done a null move search, and searched the first move before
1814 // splitting, we don't have to repeat all this work in sp_search(). We
1815 // also don't need to store anything to the hash table here: This is taken
1816 // care of after we return from the split point.
1818 void sp_search(SplitPoint* sp, int threadID) {
1820 assert(threadID >= 0 && threadID < ActiveThreads);
1821 assert(ActiveThreads > 1);
1823 Position pos(*sp->pos);
1825 SearchStack* ss = sp->sstack[threadID];
1826 Value value = -VALUE_INFINITE;
1828 bool isCheck = pos.is_check();
1829 bool useFutilityPruning = sp->depth < SelectiveDepth
1832 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1834 while ( sp->bestValue < sp->beta
1835 && !thread_should_stop(threadID)
1836 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1838 assert(move_is_ok(move));
1840 bool moveIsCheck = pos.move_is_check(move, ci);
1841 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1843 lock_grab(&(sp->lock));
1844 int moveCount = ++sp->moves;
1845 lock_release(&(sp->lock));
1847 ss[sp->ply].currentMove = move;
1849 // Decide the new search depth.
1851 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1852 Depth newDepth = sp->depth - OnePly + ext;
1855 if ( useFutilityPruning
1857 && !captureOrPromotion)
1859 // Move count based pruning
1860 if ( moveCount >= FutilityMoveCountMargin
1861 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1862 && sp->bestValue > value_mated_in(PLY_MAX))
1865 // Value based pruning
1866 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1868 if (futilityValueScaled < sp->beta)
1870 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1872 lock_grab(&(sp->lock));
1873 if (futilityValueScaled > sp->bestValue)
1874 sp->bestValue = futilityValueScaled;
1875 lock_release(&(sp->lock));
1881 // Make and search the move.
1883 pos.do_move(move, st, ci, moveIsCheck);
1885 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1886 // if the move fails high will be re-searched at full depth.
1887 bool doFullDepthSearch = true;
1890 && !captureOrPromotion
1891 && !move_is_castle(move)
1892 && !move_is_killer(move, ss[sp->ply]))
1894 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 3.0;
1897 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
1898 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1899 doFullDepthSearch = (value >= sp->beta);
1903 if (doFullDepthSearch) // Go with full depth non-pv search
1905 ss[sp->ply].reduction = Depth(0);
1906 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1908 pos.undo_move(move);
1910 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1912 if (thread_should_stop(threadID))
1916 if (value > sp->bestValue) // Less then 2% of cases
1918 lock_grab(&(sp->lock));
1919 if (value > sp->bestValue && !thread_should_stop(threadID))
1921 sp->bestValue = value;
1922 if (sp->bestValue >= sp->beta)
1924 sp_update_pv(sp->parentSstack, ss, sp->ply);
1925 for (int i = 0; i < ActiveThreads; i++)
1926 if (i != threadID && (i == sp->master || sp->slaves[i]))
1927 Threads[i].stop = true;
1929 sp->finished = true;
1932 lock_release(&(sp->lock));
1936 lock_grab(&(sp->lock));
1938 // If this is the master thread and we have been asked to stop because of
1939 // a beta cutoff higher up in the tree, stop all slave threads.
1940 if (sp->master == threadID && thread_should_stop(threadID))
1941 for (int i = 0; i < ActiveThreads; i++)
1943 Threads[i].stop = true;
1946 sp->slaves[threadID] = 0;
1948 lock_release(&(sp->lock));
1952 // sp_search_pv() is used to search from a PV split point. This function
1953 // is called by each thread working at the split point. It is similar to
1954 // the normal search_pv() function, but simpler. Because we have already
1955 // probed the hash table and searched the first move before splitting, we
1956 // don't have to repeat all this work in sp_search_pv(). We also don't
1957 // need to store anything to the hash table here: This is taken care of
1958 // after we return from the split point.
1960 void sp_search_pv(SplitPoint* sp, int threadID) {
1962 assert(threadID >= 0 && threadID < ActiveThreads);
1963 assert(ActiveThreads > 1);
1965 Position pos(*sp->pos);
1967 SearchStack* ss = sp->sstack[threadID];
1968 Value value = -VALUE_INFINITE;
1971 while ( sp->alpha < sp->beta
1972 && !thread_should_stop(threadID)
1973 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1975 bool moveIsCheck = pos.move_is_check(move, ci);
1976 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1978 assert(move_is_ok(move));
1980 lock_grab(&(sp->lock));
1981 int moveCount = ++sp->moves;
1982 lock_release(&(sp->lock));
1984 ss[sp->ply].currentMove = move;
1986 // Decide the new search depth.
1988 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1989 Depth newDepth = sp->depth - OnePly + ext;
1991 // Make and search the move.
1993 pos.do_move(move, st, ci, moveIsCheck);
1995 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1996 // if the move fails high will be re-searched at full depth.
1997 bool doFullDepthSearch = true;
2000 && !captureOrPromotion
2001 && !move_is_castle(move)
2002 && !move_is_killer(move, ss[sp->ply]))
2004 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 6.0;
2007 Value localAlpha = sp->alpha;
2008 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
2009 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2010 doFullDepthSearch = (value > localAlpha);
2014 if (doFullDepthSearch) // Go with full depth non-pv search
2016 Value localAlpha = sp->alpha;
2017 ss[sp->ply].reduction = Depth(0);
2018 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2020 if (value > localAlpha && value < sp->beta)
2022 // When the search fails high at ply 1 while searching the first
2023 // move at the root, set the flag failHighPly1. This is used for
2024 // time managment: We don't want to stop the search early in
2025 // such cases, because resolving the fail high at ply 1 could
2026 // result in a big drop in score at the root.
2027 if (sp->ply == 1 && RootMoveNumber == 1)
2028 Threads[threadID].failHighPly1 = true;
2030 // If another thread has failed high then sp->alpha has been increased
2031 // to be higher or equal then beta, if so, avoid to start a PV search.
2032 localAlpha = sp->alpha;
2033 if (localAlpha < sp->beta)
2034 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2036 assert(thread_should_stop(threadID));
2038 Threads[threadID].failHighPly1 = false;
2041 pos.undo_move(move);
2043 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2045 if (thread_should_stop(threadID))
2049 if (value > sp->bestValue) // Less then 2% of cases
2051 lock_grab(&(sp->lock));
2052 if (value > sp->bestValue && !thread_should_stop(threadID))
2054 sp->bestValue = value;
2055 if (value > sp->alpha)
2057 // Ask threads to stop before to modify sp->alpha
2058 if (value >= sp->beta)
2060 for (int i = 0; i < ActiveThreads; i++)
2061 if (i != threadID && (i == sp->master || sp->slaves[i]))
2062 Threads[i].stop = true;
2064 sp->finished = true;
2069 sp_update_pv(sp->parentSstack, ss, sp->ply);
2070 if (value == value_mate_in(sp->ply + 1))
2071 ss[sp->ply].mateKiller = move;
2073 // If we are at ply 1, and we are searching the first root move at
2074 // ply 0, set the 'Problem' variable if the score has dropped a lot
2075 // (from the computer's point of view) since the previous iteration.
2078 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2081 lock_release(&(sp->lock));
2085 lock_grab(&(sp->lock));
2087 // If this is the master thread and we have been asked to stop because of
2088 // a beta cutoff higher up in the tree, stop all slave threads.
2089 if (sp->master == threadID && thread_should_stop(threadID))
2090 for (int i = 0; i < ActiveThreads; i++)
2092 Threads[i].stop = true;
2095 sp->slaves[threadID] = 0;
2097 lock_release(&(sp->lock));
2100 /// The BetaCounterType class
2102 BetaCounterType::BetaCounterType() { clear(); }
2104 void BetaCounterType::clear() {
2106 for (int i = 0; i < THREAD_MAX; i++)
2107 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2110 void BetaCounterType::add(Color us, Depth d, int threadID) {
2112 // Weighted count based on depth
2113 Threads[threadID].betaCutOffs[us] += unsigned(d);
2116 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2119 for (int i = 0; i < THREAD_MAX; i++)
2121 our += Threads[i].betaCutOffs[us];
2122 their += Threads[i].betaCutOffs[opposite_color(us)];
2127 /// The RootMoveList class
2129 // RootMoveList c'tor
2131 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2133 MoveStack mlist[MaxRootMoves];
2134 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2136 // Generate all legal moves
2137 MoveStack* last = generate_moves(pos, mlist);
2139 // Add each move to the moves[] array
2140 for (MoveStack* cur = mlist; cur != last; cur++)
2142 bool includeMove = includeAllMoves;
2144 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2145 includeMove = (searchMoves[k] == cur->move);
2150 // Find a quick score for the move
2152 SearchStack ss[PLY_MAX_PLUS_2];
2155 moves[count].move = cur->move;
2156 pos.do_move(moves[count].move, st);
2157 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2158 pos.undo_move(moves[count].move);
2159 moves[count].pv[0] = moves[count].move;
2160 moves[count].pv[1] = MOVE_NONE;
2167 // RootMoveList simple methods definitions
2169 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2171 moves[moveNum].nodes = nodes;
2172 moves[moveNum].cumulativeNodes += nodes;
2175 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2177 moves[moveNum].ourBeta = our;
2178 moves[moveNum].theirBeta = their;
2181 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2185 for (j = 0; pv[j] != MOVE_NONE; j++)
2186 moves[moveNum].pv[j] = pv[j];
2188 moves[moveNum].pv[j] = MOVE_NONE;
2192 // RootMoveList::sort() sorts the root move list at the beginning of a new
2195 void RootMoveList::sort() {
2197 sort_multipv(count - 1); // Sort all items
2201 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2202 // list by their scores and depths. It is used to order the different PVs
2203 // correctly in MultiPV mode.
2205 void RootMoveList::sort_multipv(int n) {
2209 for (i = 1; i <= n; i++)
2211 RootMove rm = moves[i];
2212 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2213 moves[j] = moves[j - 1];
2220 // init_node() is called at the beginning of all the search functions
2221 // (search(), search_pv(), qsearch(), and so on) and initializes the
2222 // search stack object corresponding to the current node. Once every
2223 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2224 // for user input and checks whether it is time to stop the search.
2226 void init_node(SearchStack ss[], int ply, int threadID) {
2228 assert(ply >= 0 && ply < PLY_MAX);
2229 assert(threadID >= 0 && threadID < ActiveThreads);
2231 Threads[threadID].nodes++;
2236 if (NodesSincePoll >= NodesBetweenPolls)
2243 ss[ply + 2].initKillers();
2245 if (Threads[threadID].printCurrentLine)
2246 print_current_line(ss, ply, threadID);
2250 // update_pv() is called whenever a search returns a value > alpha.
2251 // It updates the PV in the SearchStack object corresponding to the
2254 void update_pv(SearchStack ss[], int ply) {
2256 assert(ply >= 0 && ply < PLY_MAX);
2260 ss[ply].pv[ply] = ss[ply].currentMove;
2262 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2263 ss[ply].pv[p] = ss[ply + 1].pv[p];
2265 ss[ply].pv[p] = MOVE_NONE;
2269 // sp_update_pv() is a variant of update_pv for use at split points. The
2270 // difference between the two functions is that sp_update_pv also updates
2271 // the PV at the parent node.
2273 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2275 assert(ply >= 0 && ply < PLY_MAX);
2279 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2281 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2282 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2284 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2288 // connected_moves() tests whether two moves are 'connected' in the sense
2289 // that the first move somehow made the second move possible (for instance
2290 // if the moving piece is the same in both moves). The first move is assumed
2291 // to be the move that was made to reach the current position, while the
2292 // second move is assumed to be a move from the current position.
2294 bool connected_moves(const Position& pos, Move m1, Move m2) {
2296 Square f1, t1, f2, t2;
2299 assert(move_is_ok(m1));
2300 assert(move_is_ok(m2));
2302 if (m2 == MOVE_NONE)
2305 // Case 1: The moving piece is the same in both moves
2311 // Case 2: The destination square for m2 was vacated by m1
2317 // Case 3: Moving through the vacated square
2318 if ( piece_is_slider(pos.piece_on(f2))
2319 && bit_is_set(squares_between(f2, t2), f1))
2322 // Case 4: The destination square for m2 is defended by the moving piece in m1
2323 p = pos.piece_on(t1);
2324 if (bit_is_set(pos.attacks_from(p, t1), t2))
2327 // Case 5: Discovered check, checking piece is the piece moved in m1
2328 if ( piece_is_slider(p)
2329 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2330 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2332 // discovered_check_candidates() works also if the Position's side to
2333 // move is the opposite of the checking piece.
2334 Color them = opposite_color(pos.side_to_move());
2335 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2337 if (bit_is_set(dcCandidates, f2))
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.
2441 // It's 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 // Prune if there isn't any threat move and
2465 // is not a castling move (common case).
2466 if (threat == MOVE_NONE && !move_is_castle(m))
2469 mfrom = move_from(m);
2471 tfrom = move_from(threat);
2472 tto = move_to(threat);
2474 // Case 1: Castling moves are never pruned
2475 if (move_is_castle(m))
2478 // Case 2: Don't prune moves which move the threatened piece
2482 // Case 3: If the threatened piece has value less than or equal to the
2483 // value of the threatening piece, don't prune move which defend it.
2484 if ( pos.move_is_capture(threat)
2485 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2486 || pos.type_of_piece_on(tfrom) == KING)
2487 && pos.move_attacks_square(m, tto))
2490 // Case 4: If the moving piece in the threatened move is a slider, don't
2491 // prune safe moves which block its ray.
2492 if ( piece_is_slider(pos.piece_on(tfrom))
2493 && bit_is_set(squares_between(tfrom, tto), mto)
2494 && pos.see_sign(m) >= 0)
2501 // ok_to_use_TT() returns true if a transposition table score
2502 // can be used at a given point in search.
2504 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2506 Value v = value_from_tt(tte->value(), ply);
2508 return ( tte->depth() >= depth
2509 || v >= Max(value_mate_in(PLY_MAX), beta)
2510 || v < Min(value_mated_in(PLY_MAX), beta))
2512 && ( (is_lower_bound(tte->type()) && v >= beta)
2513 || (is_upper_bound(tte->type()) && v < beta));
2517 // refine_eval() returns the transposition table score if
2518 // possible otherwise falls back on static position evaluation.
2520 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2525 Value v = value_from_tt(tte->value(), ply);
2527 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2528 || (is_upper_bound(tte->type()) && v < defaultEval))
2534 // update_history() registers a good move that produced a beta-cutoff
2535 // in history and marks as failures all the other moves of that ply.
2537 void update_history(const Position& pos, Move move, Depth depth,
2538 Move movesSearched[], int moveCount) {
2542 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2544 for (int i = 0; i < moveCount - 1; i++)
2546 m = movesSearched[i];
2550 if (!pos.move_is_capture_or_promotion(m))
2551 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2556 // update_killers() add a good move that produced a beta-cutoff
2557 // among the killer moves of that ply.
2559 void update_killers(Move m, SearchStack& ss) {
2561 if (m == ss.killers[0])
2564 for (int i = KILLER_MAX - 1; i > 0; i--)
2565 ss.killers[i] = ss.killers[i - 1];
2571 // fail_high_ply_1() checks if some thread is currently resolving a fail
2572 // high at ply 1 at the node below the first root node. This information
2573 // is used for time management.
2575 bool fail_high_ply_1() {
2577 for (int i = 0; i < ActiveThreads; i++)
2578 if (Threads[i].failHighPly1)
2585 // current_search_time() returns the number of milliseconds which have passed
2586 // since the beginning of the current search.
2588 int current_search_time() {
2590 return get_system_time() - SearchStartTime;
2594 // nps() computes the current nodes/second count.
2598 int t = current_search_time();
2599 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2603 // poll() performs two different functions: It polls for user input, and it
2604 // looks at the time consumed so far and decides if it's time to abort the
2609 static int lastInfoTime;
2610 int t = current_search_time();
2615 // We are line oriented, don't read single chars
2616 std::string command;
2618 if (!std::getline(std::cin, command))
2621 if (command == "quit")
2624 PonderSearch = false;
2628 else if (command == "stop")
2631 PonderSearch = false;
2633 else if (command == "ponderhit")
2637 // Print search information
2641 else if (lastInfoTime > t)
2642 // HACK: Must be a new search where we searched less than
2643 // NodesBetweenPolls nodes during the first second of search.
2646 else if (t - lastInfoTime >= 1000)
2654 if (dbg_show_hit_rate)
2655 dbg_print_hit_rate();
2657 cout << "info nodes " << nodes_searched() << " nps " << nps()
2658 << " time " << t << " hashfull " << TT.full() << endl;
2660 lock_release(&IOLock);
2662 if (ShowCurrentLine)
2663 Threads[0].printCurrentLine = true;
2666 // Should we stop the search?
2670 bool stillAtFirstMove = RootMoveNumber == 1
2672 && t > MaxSearchTime + ExtraSearchTime;
2674 bool noProblemFound = !FailHigh
2676 && !fail_high_ply_1()
2678 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2680 bool noMoreTime = t > AbsoluteMaxSearchTime
2681 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2684 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2685 || (ExactMaxTime && t >= ExactMaxTime)
2686 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2691 // ponderhit() is called when the program is pondering (i.e. thinking while
2692 // it's the opponent's turn to move) in order to let the engine know that
2693 // it correctly predicted the opponent's move.
2697 int t = current_search_time();
2698 PonderSearch = false;
2700 bool stillAtFirstMove = RootMoveNumber == 1
2702 && t > MaxSearchTime + ExtraSearchTime;
2704 bool noProblemFound = !FailHigh
2706 && !fail_high_ply_1()
2708 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2710 bool noMoreTime = t > AbsoluteMaxSearchTime
2714 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2719 // print_current_line() prints the current line of search for a given
2720 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2722 void print_current_line(SearchStack ss[], int ply, int threadID) {
2724 assert(ply >= 0 && ply < PLY_MAX);
2725 assert(threadID >= 0 && threadID < ActiveThreads);
2727 if (!Threads[threadID].idle)
2730 cout << "info currline " << (threadID + 1);
2731 for (int p = 0; p < ply; p++)
2732 cout << " " << ss[p].currentMove;
2735 lock_release(&IOLock);
2737 Threads[threadID].printCurrentLine = false;
2738 if (threadID + 1 < ActiveThreads)
2739 Threads[threadID + 1].printCurrentLine = true;
2743 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2745 void init_ss_array(SearchStack ss[]) {
2747 for (int i = 0; i < 3; i++)
2750 ss[i].initKillers();
2755 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2756 // while the program is pondering. The point is to work around a wrinkle in
2757 // the UCI protocol: When pondering, the engine is not allowed to give a
2758 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2759 // We simply wait here until one of these commands is sent, and return,
2760 // after which the bestmove and pondermove will be printed (in id_loop()).
2762 void wait_for_stop_or_ponderhit() {
2764 std::string command;
2768 if (!std::getline(std::cin, command))
2771 if (command == "quit")
2776 else if (command == "ponderhit" || command == "stop")
2782 // idle_loop() is where the threads are parked when they have no work to do.
2783 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2784 // object for which the current thread is the master.
2786 void idle_loop(int threadID, SplitPoint* waitSp) {
2788 assert(threadID >= 0 && threadID < THREAD_MAX);
2790 Threads[threadID].running = true;
2794 if (AllThreadsShouldExit && threadID != 0)
2797 // If we are not thinking, wait for a condition to be signaled
2798 // instead of wasting CPU time polling for work.
2799 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2802 #if !defined(_MSC_VER)
2803 pthread_mutex_lock(&WaitLock);
2804 if (Idle || threadID >= ActiveThreads)
2805 pthread_cond_wait(&WaitCond, &WaitLock);
2807 pthread_mutex_unlock(&WaitLock);
2809 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2813 // If this thread has been assigned work, launch a search
2814 if (Threads[threadID].workIsWaiting)
2816 assert(!Threads[threadID].idle);
2818 Threads[threadID].workIsWaiting = false;
2819 if (Threads[threadID].splitPoint->pvNode)
2820 sp_search_pv(Threads[threadID].splitPoint, threadID);
2822 sp_search(Threads[threadID].splitPoint, threadID);
2824 Threads[threadID].idle = true;
2827 // If this thread is the master of a split point and all threads have
2828 // finished their work at this split point, return from the idle loop.
2829 if (waitSp != NULL && waitSp->cpus == 0)
2833 Threads[threadID].running = false;
2837 // init_split_point_stack() is called during program initialization, and
2838 // initializes all split point objects.
2840 void init_split_point_stack() {
2842 for (int i = 0; i < THREAD_MAX; i++)
2843 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2845 SplitPointStack[i][j].parent = NULL;
2846 lock_init(&(SplitPointStack[i][j].lock), NULL);
2851 // destroy_split_point_stack() is called when the program exits, and
2852 // destroys all locks in the precomputed split point objects.
2854 void destroy_split_point_stack() {
2856 for (int i = 0; i < THREAD_MAX; i++)
2857 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2858 lock_destroy(&(SplitPointStack[i][j].lock));
2862 // thread_should_stop() checks whether the thread with a given threadID has
2863 // been asked to stop, directly or indirectly. This can happen if a beta
2864 // cutoff has occurred in the thread's currently active split point, or in
2865 // some ancestor of the current split point.
2867 bool thread_should_stop(int threadID) {
2869 assert(threadID >= 0 && threadID < ActiveThreads);
2873 if (Threads[threadID].stop)
2875 if (ActiveThreads <= 2)
2877 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2880 Threads[threadID].stop = true;
2887 // thread_is_available() checks whether the thread with threadID "slave" is
2888 // available to help the thread with threadID "master" at a split point. An
2889 // obvious requirement is that "slave" must be idle. With more than two
2890 // threads, this is not by itself sufficient: If "slave" is the master of
2891 // some active split point, it is only available as a slave to the other
2892 // threads which are busy searching the split point at the top of "slave"'s
2893 // split point stack (the "helpful master concept" in YBWC terminology).
2895 bool thread_is_available(int slave, int master) {
2897 assert(slave >= 0 && slave < ActiveThreads);
2898 assert(master >= 0 && master < ActiveThreads);
2899 assert(ActiveThreads > 1);
2901 if (!Threads[slave].idle || slave == master)
2904 // Make a local copy to be sure doesn't change under our feet
2905 int localActiveSplitPoints = Threads[slave].activeSplitPoints;
2907 if (localActiveSplitPoints == 0)
2908 // No active split points means that the thread is available as
2909 // a slave for any other thread.
2912 if (ActiveThreads == 2)
2915 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2916 // that is known to be > 0, instead of Threads[slave].activeSplitPoints that
2917 // could have been set to 0 by another thread leading to an out of bound access.
2918 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2925 // idle_thread_exists() tries to find an idle thread which is available as
2926 // a slave for the thread with threadID "master".
2928 bool idle_thread_exists(int master) {
2930 assert(master >= 0 && master < ActiveThreads);
2931 assert(ActiveThreads > 1);
2933 for (int i = 0; i < ActiveThreads; i++)
2934 if (thread_is_available(i, master))
2941 // split() does the actual work of distributing the work at a node between
2942 // several threads at PV nodes. If it does not succeed in splitting the
2943 // node (because no idle threads are available, or because we have no unused
2944 // split point objects), the function immediately returns false. If
2945 // splitting is possible, a SplitPoint object is initialized with all the
2946 // data that must be copied to the helper threads (the current position and
2947 // search stack, alpha, beta, the search depth, etc.), and we tell our
2948 // helper threads that they have been assigned work. This will cause them
2949 // to instantly leave their idle loops and call sp_search_pv(). When all
2950 // threads have returned from sp_search_pv (or, equivalently, when
2951 // splitPoint->cpus becomes 0), split() returns true.
2953 bool split(const Position& p, SearchStack* sstck, int ply,
2954 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2955 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2958 assert(sstck != NULL);
2959 assert(ply >= 0 && ply < PLY_MAX);
2960 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2961 assert(!pvNode || *alpha < *beta);
2962 assert(*beta <= VALUE_INFINITE);
2963 assert(depth > Depth(0));
2964 assert(master >= 0 && master < ActiveThreads);
2965 assert(ActiveThreads > 1);
2967 SplitPoint* splitPoint;
2971 // If no other thread is available to help us, or if we have too many
2972 // active split points, don't split.
2973 if ( !idle_thread_exists(master)
2974 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2976 lock_release(&MPLock);
2980 // Pick the next available split point object from the split point stack
2981 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2982 Threads[master].activeSplitPoints++;
2984 // Initialize the split point object
2985 splitPoint->parent = Threads[master].splitPoint;
2986 splitPoint->finished = false;
2987 splitPoint->ply = ply;
2988 splitPoint->depth = depth;
2989 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2990 splitPoint->beta = *beta;
2991 splitPoint->pvNode = pvNode;
2992 splitPoint->bestValue = *bestValue;
2993 splitPoint->futilityValue = futilityValue;
2994 splitPoint->master = master;
2995 splitPoint->mp = mp;
2996 splitPoint->moves = *moves;
2997 splitPoint->cpus = 1;
2998 splitPoint->pos = &p;
2999 splitPoint->parentSstack = sstck;
3000 for (int i = 0; i < ActiveThreads; i++)
3001 splitPoint->slaves[i] = 0;
3003 Threads[master].idle = false;
3004 Threads[master].stop = false;
3005 Threads[master].splitPoint = splitPoint;
3007 // Allocate available threads setting idle flag to false
3008 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
3009 if (thread_is_available(i, master))
3011 Threads[i].idle = false;
3012 Threads[i].stop = false;
3013 Threads[i].splitPoint = splitPoint;
3014 splitPoint->slaves[i] = 1;
3018 assert(splitPoint->cpus > 1);
3020 // We can release the lock because master and slave threads are already booked
3021 lock_release(&MPLock);
3023 // Tell the threads that they have work to do. This will make them leave
3024 // their idle loop. But before copy search stack tail for each thread.
3025 for (int i = 0; i < ActiveThreads; i++)
3026 if (i == master || splitPoint->slaves[i])
3028 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 3 * sizeof(SearchStack));
3029 Threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
3032 // Everything is set up. The master thread enters the idle loop, from
3033 // which it will instantly launch a search, because its workIsWaiting
3034 // slot is 'true'. We send the split point as a second parameter to the
3035 // idle loop, which means that the main thread will return from the idle
3036 // loop when all threads have finished their work at this split point
3037 // (i.e. when splitPoint->cpus == 0).
3038 idle_loop(master, splitPoint);
3040 // We have returned from the idle loop, which means that all threads are
3041 // finished. Update alpha, beta and bestValue, and return.
3045 *alpha = splitPoint->alpha;
3047 *beta = splitPoint->beta;
3048 *bestValue = splitPoint->bestValue;
3049 Threads[master].stop = false;
3050 Threads[master].idle = false;
3051 Threads[master].activeSplitPoints--;
3052 Threads[master].splitPoint = splitPoint->parent;
3054 lock_release(&MPLock);
3059 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3060 // to start a new search from the root.
3062 void wake_sleeping_threads() {
3064 if (ActiveThreads > 1)
3066 for (int i = 1; i < ActiveThreads; i++)
3068 Threads[i].idle = true;
3069 Threads[i].workIsWaiting = false;
3072 #if !defined(_MSC_VER)
3073 pthread_mutex_lock(&WaitLock);
3074 pthread_cond_broadcast(&WaitCond);
3075 pthread_mutex_unlock(&WaitLock);
3077 for (int i = 1; i < THREAD_MAX; i++)
3078 SetEvent(SitIdleEvent[i]);
3084 // init_thread() is the function which is called when a new thread is
3085 // launched. It simply calls the idle_loop() function with the supplied
3086 // threadID. There are two versions of this function; one for POSIX
3087 // threads and one for Windows threads.
3089 #if !defined(_MSC_VER)
3091 void* init_thread(void *threadID) {
3093 idle_loop(*(int*)threadID, NULL);
3099 DWORD WINAPI init_thread(LPVOID threadID) {
3101 idle_loop(*(int*)threadID, NULL);