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;
268 Value id_loop(const Position& pos, Move searchMoves[]);
269 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
270 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
271 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
272 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
273 void sp_search(SplitPoint* sp, int threadID);
274 void sp_search_pv(SplitPoint* sp, int threadID);
275 void init_node(SearchStack ss[], int ply, int threadID);
276 void update_pv(SearchStack ss[], int ply);
277 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
278 bool connected_moves(const Position& pos, Move m1, Move m2);
279 bool value_is_mate(Value value);
280 bool move_is_killer(Move m, const SearchStack& ss);
281 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
282 bool ok_to_do_nullmove(const Position& pos);
283 bool ok_to_prune(const Position& pos, Move m, Move threat);
284 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
285 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
286 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
287 void update_killers(Move m, SearchStack& ss);
288 void update_gains(const Position& pos, Move move, Value before, Value after);
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 && (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;
894 bool isCheck = pos.is_check();
896 // Evaluate the position statically
899 ss[0].eval = evaluate(pos, ei, 0);
901 ss[0].eval = VALUE_NONE;
903 // Loop through all the moves in the root move list
904 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
908 // We failed high, invalidate and skip next moves, leave node-counters
909 // and beta-counters as they are and quickly return, we will try to do
910 // a research at the next iteration with a bigger aspiration window.
911 rml.set_move_score(i, -VALUE_INFINITE);
917 Depth depth, ext, newDepth;
919 RootMoveNumber = i + 1;
922 // Save the current node count before the move is searched
923 nodes = nodes_searched();
925 // Reset beta cut-off counters
928 // Pick the next root move, and print the move and the move number to
929 // the standard output.
930 move = ss[0].currentMove = rml.get_move(i);
932 if (current_search_time() >= 1000)
933 cout << "info currmove " << move
934 << " currmovenumber " << RootMoveNumber << endl;
936 // Decide search depth for this move
937 bool moveIsCheck = pos.move_is_check(move);
938 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
940 depth = (Iteration - 2) * OnePly + InitialDepth;
941 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
942 newDepth = depth + ext;
944 // Make the move, and search it
945 pos.do_move(move, st, ci, moveIsCheck);
949 // Aspiration window is disabled in multi-pv case
951 alpha = -VALUE_INFINITE;
953 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
955 // If the value has dropped a lot compared to the last iteration,
956 // set the boolean variable Problem to true. This variable is used
957 // for time managment: When Problem is true, we try to complete the
958 // current iteration before playing a move.
959 Problem = ( Iteration >= 2
960 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
962 if (Problem && StopOnPonderhit)
963 StopOnPonderhit = false;
967 // Try to reduce non-pv search depth by one ply if move seems not problematic,
968 // if the move fails high will be re-searched at full depth.
969 bool doFullDepthSearch = true;
971 if ( depth >= 3*OnePly // FIXME was newDepth
973 && !captureOrPromotion
974 && !move_is_castle(move))
976 double red = 0.5 + ln(RootMoveNumber - MultiPV + 1) * ln(depth / 2) / 6.0;
979 ss[0].reduction = Depth(int(floor(red * int(OnePly))));
980 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
981 doFullDepthSearch = (value > alpha);
985 if (doFullDepthSearch)
987 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
991 // Fail high! Set the boolean variable FailHigh to true, and
992 // re-search the move using a PV search. The variable FailHigh
993 // is used for time managment: We try to avoid aborting the
994 // search prematurely during a fail high research.
996 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
1001 pos.undo_move(move);
1003 // Finished searching the move. If AbortSearch is true, the search
1004 // was aborted because the user interrupted the search or because we
1005 // ran out of time. In this case, the return value of the search cannot
1006 // be trusted, and we break out of the loop without updating the best
1011 // Remember beta-cutoff and searched nodes counts for this move. The
1012 // info is used to sort the root moves at the next iteration.
1014 BetaCounter.read(pos.side_to_move(), our, their);
1015 rml.set_beta_counters(i, our, their);
1016 rml.set_move_nodes(i, nodes_searched() - nodes);
1018 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1020 if (value <= alpha && i >= MultiPV)
1021 rml.set_move_score(i, -VALUE_INFINITE);
1024 // PV move or new best move!
1027 rml.set_move_score(i, value);
1029 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1030 rml.set_move_pv(i, ss[0].pv);
1034 // We record how often the best move has been changed in each
1035 // iteration. This information is used for time managment: When
1036 // the best move changes frequently, we allocate some more time.
1038 BestMoveChangesByIteration[Iteration]++;
1040 // Print search information to the standard output
1041 cout << "info depth " << Iteration
1042 << " score " << value_to_string(value)
1043 << ((value >= beta) ? " lowerbound" :
1044 ((value <= alpha)? " upperbound" : ""))
1045 << " time " << current_search_time()
1046 << " nodes " << nodes_searched()
1050 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1051 cout << ss[0].pv[j] << " ";
1057 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1058 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1060 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1061 nodes_searched(), value, type, ss[0].pv) << endl;
1066 // Reset the global variable Problem to false if the value isn't too
1067 // far below the final value from the last iteration.
1068 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1073 rml.sort_multipv(i);
1074 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1076 cout << "info multipv " << j + 1
1077 << " score " << value_to_string(rml.get_move_score(j))
1078 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1079 << " time " << current_search_time()
1080 << " nodes " << nodes_searched()
1084 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1085 cout << rml.get_move_pv(j, k) << " ";
1089 alpha = rml.get_move_score(Min(i, MultiPV-1));
1091 } // PV move or new best move
1093 assert(alpha >= oldAlpha);
1095 FailLow = (alpha == oldAlpha);
1101 // search_pv() is the main search function for PV nodes.
1103 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1104 Depth depth, int ply, int threadID) {
1106 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1107 assert(beta > alpha && beta <= VALUE_INFINITE);
1108 assert(ply >= 0 && ply < PLY_MAX);
1109 assert(threadID >= 0 && threadID < ActiveThreads);
1111 Move movesSearched[256];
1115 Depth ext, newDepth;
1116 Value oldAlpha, value;
1117 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1119 Value bestValue = value = -VALUE_INFINITE;
1122 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1124 // Initialize, and make an early exit in case of an aborted search,
1125 // an instant draw, maximum ply reached, etc.
1126 init_node(ss, ply, threadID);
1128 // After init_node() that calls poll()
1129 if (AbortSearch || thread_should_stop(threadID))
1132 if (pos.is_draw() || ply >= PLY_MAX - 1)
1135 // Mate distance pruning
1137 alpha = Max(value_mated_in(ply), alpha);
1138 beta = Min(value_mate_in(ply+1), beta);
1142 // Transposition table lookup. At PV nodes, we don't use the TT for
1143 // pruning, but only for move ordering. This is to avoid problems in
1144 // the following areas:
1146 // * Repetition draw detection
1147 // * Fifty move rule detection
1148 // * Searching for a mate
1149 // * Printing of full PV line
1151 tte = TT.retrieve(pos.get_key());
1152 ttMove = (tte ? tte->move() : MOVE_NONE);
1154 // Go with internal iterative deepening if we don't have a TT move
1155 if ( UseIIDAtPVNodes
1156 && depth >= 5*OnePly
1157 && ttMove == MOVE_NONE)
1159 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1160 ttMove = ss[ply].pv[ply];
1161 tte = TT.retrieve(pos.get_key());
1164 isCheck = pos.is_check();
1167 // Update gain statistics of the previous move that lead
1168 // us in this position.
1170 ss[ply].eval = evaluate(pos, ei, threadID);
1171 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1174 // Initialize a MovePicker object for the current position, and prepare
1175 // to search all moves
1176 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1178 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1180 // Loop through all legal moves until no moves remain or a beta cutoff
1182 while ( alpha < beta
1183 && (move = mp.get_next_move()) != MOVE_NONE
1184 && !thread_should_stop(threadID))
1186 assert(move_is_ok(move));
1188 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1189 moveIsCheck = pos.move_is_check(move, ci);
1190 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1192 // Decide the new search depth
1193 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1195 // Singular extension search. We extend the TT move if its value is much better than
1196 // its siblings. To verify this we do a reduced search on all the other moves but the
1197 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1198 if ( depth >= 6 * OnePly
1200 && move == tte->move()
1202 && is_lower_bound(tte->type())
1203 && tte->depth() >= depth - 3 * OnePly)
1205 Value ttValue = value_from_tt(tte->value(), ply);
1207 if (abs(ttValue) < VALUE_KNOWN_WIN)
1209 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1211 if (excValue < ttValue - SingleReplyMargin)
1216 newDepth = depth - OnePly + ext;
1218 // Update current move
1219 movesSearched[moveCount++] = ss[ply].currentMove = move;
1221 // Make and search the move
1222 pos.do_move(move, st, ci, moveIsCheck);
1224 if (moveCount == 1) // The first move in list is the PV
1225 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1228 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1229 // if the move fails high will be re-searched at full depth.
1230 bool doFullDepthSearch = true;
1232 if ( depth >= 3*OnePly
1234 && !captureOrPromotion
1235 && !move_is_castle(move)
1236 && !move_is_killer(move, ss[ply]))
1238 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 6.0;
1241 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1242 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1243 doFullDepthSearch = (value > alpha);
1247 if (doFullDepthSearch) // Go with full depth non-pv search
1249 ss[ply].reduction = Depth(0);
1250 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1251 if (value > alpha && value < beta)
1253 // When the search fails high at ply 1 while searching the first
1254 // move at the root, set the flag failHighPly1. This is used for
1255 // time managment: We don't want to stop the search early in
1256 // such cases, because resolving the fail high at ply 1 could
1257 // result in a big drop in score at the root.
1258 if (ply == 1 && RootMoveNumber == 1)
1259 Threads[threadID].failHighPly1 = true;
1261 // A fail high occurred. Re-search at full window (pv search)
1262 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1263 Threads[threadID].failHighPly1 = false;
1267 pos.undo_move(move);
1269 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1272 if (value > bestValue)
1279 if (value == value_mate_in(ply + 1))
1280 ss[ply].mateKiller = move;
1282 // If we are at ply 1, and we are searching the first root move at
1283 // ply 0, set the 'Problem' variable if the score has dropped a lot
1284 // (from the computer's point of view) since the previous iteration.
1287 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1292 if ( ActiveThreads > 1
1294 && depth >= MinimumSplitDepth
1296 && idle_thread_exists(threadID)
1298 && !thread_should_stop(threadID)
1299 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1300 depth, &moveCount, &mp, threadID, true))
1304 // All legal moves have been searched. A special case: If there were
1305 // no legal moves, it must be mate or stalemate.
1307 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1309 // If the search is not aborted, update the transposition table,
1310 // history counters, and killer moves.
1311 if (AbortSearch || thread_should_stop(threadID))
1314 if (bestValue <= oldAlpha)
1315 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1317 else if (bestValue >= beta)
1319 BetaCounter.add(pos.side_to_move(), depth, threadID);
1320 move = ss[ply].pv[ply];
1321 if (!pos.move_is_capture_or_promotion(move))
1323 update_history(pos, move, depth, movesSearched, moveCount);
1324 update_killers(move, ss[ply]);
1326 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1329 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1335 // search() is the search function for zero-width nodes.
1337 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1338 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1340 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1341 assert(ply >= 0 && ply < PLY_MAX);
1342 assert(threadID >= 0 && threadID < ActiveThreads);
1344 Move movesSearched[256];
1349 Depth ext, newDepth;
1350 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1351 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1352 bool mateThreat = false;
1354 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1357 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1359 // Initialize, and make an early exit in case of an aborted search,
1360 // an instant draw, maximum ply reached, etc.
1361 init_node(ss, ply, threadID);
1363 // After init_node() that calls poll()
1364 if (AbortSearch || thread_should_stop(threadID))
1367 if (pos.is_draw() || ply >= PLY_MAX - 1)
1370 // Mate distance pruning
1371 if (value_mated_in(ply) >= beta)
1374 if (value_mate_in(ply + 1) < beta)
1377 // We don't want the score of a partial search to overwrite a previous full search
1378 // TT value, so we use a different position key in case of an excluded move exsists.
1379 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1381 // Transposition table lookup
1382 tte = TT.retrieve(posKey);
1383 ttMove = (tte ? tte->move() : MOVE_NONE);
1385 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1387 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1388 return value_from_tt(tte->value(), ply);
1391 isCheck = pos.is_check();
1393 // Calculate depth dependant futility pruning parameters
1394 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1395 const int PostFutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1397 // Evaluate the position statically
1400 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1401 staticValue = value_from_tt(tte->value(), ply);
1404 staticValue = evaluate(pos, ei, threadID);
1405 ss[ply].evalInfo = &ei;
1408 ss[ply].eval = staticValue;
1409 futilityValue = staticValue + PostFutilityValueMargin; //FIXME: Remove me, only for split
1410 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1411 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1414 // Do a "stand pat". If we are above beta by a good margin then
1415 // return immediately.
1416 // FIXME: test with added condition 'allowNullmove || depth <= OnePly' and !value_is_mate(beta)
1417 // FIXME: test with modified condition 'depth < RazorDepth'
1419 && depth < SelectiveDepth
1420 && staticValue - PostFutilityValueMargin >= beta)
1421 return staticValue - PostFutilityValueMargin;
1427 && !value_is_mate(beta)
1428 && ok_to_do_nullmove(pos)
1429 && staticValue >= beta - NullMoveMargin)
1431 ss[ply].currentMove = MOVE_NULL;
1433 pos.do_null_move(st);
1435 // Null move dynamic reduction based on depth
1436 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1438 // Null move dynamic reduction based on value
1439 if (staticValue - beta > PawnValueMidgame)
1442 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1444 pos.undo_null_move();
1446 if (nullValue >= beta)
1448 if (depth < 6 * OnePly)
1451 // Do zugzwang verification search
1452 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1456 // The null move failed low, which means that we may be faced with
1457 // some kind of threat. If the previous move was reduced, check if
1458 // the move that refuted the null move was somehow connected to the
1459 // move which was reduced. If a connection is found, return a fail
1460 // low score (which will cause the reduced move to fail high in the
1461 // parent node, which will trigger a re-search with full depth).
1462 if (nullValue == value_mated_in(ply + 2))
1465 ss[ply].threatMove = ss[ply + 1].currentMove;
1466 if ( depth < ThreatDepth
1467 && ss[ply - 1].reduction
1468 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1472 // Null move search not allowed, try razoring
1473 else if ( !value_is_mate(beta)
1475 && depth < RazorDepth
1476 && staticValue < beta - (NullMoveMargin + 16 * depth)
1477 && ss[ply - 1].currentMove != MOVE_NULL
1478 && ttMove == MOVE_NONE
1479 && !pos.has_pawn_on_7th(pos.side_to_move()))
1481 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1482 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1487 // Go with internal iterative deepening if we don't have a TT move
1488 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1489 !isCheck && ss[ply].eval >= beta - IIDMargin)
1491 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1492 ttMove = ss[ply].pv[ply];
1493 tte = TT.retrieve(pos.get_key());
1496 // Initialize a MovePicker object for the current position, and prepare
1497 // to search all moves.
1498 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1501 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1502 while ( bestValue < beta
1503 && (move = mp.get_next_move()) != MOVE_NONE
1504 && !thread_should_stop(threadID))
1506 assert(move_is_ok(move));
1508 if (move == excludedMove)
1511 moveIsCheck = pos.move_is_check(move, ci);
1512 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1513 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1515 // Decide the new search depth
1516 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1518 // Singular extension search. We extend the TT move if its value is much better than
1519 // its siblings. To verify this we do a reduced search on all the other moves but the
1520 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1521 if ( depth >= 8 * OnePly
1523 && move == tte->move()
1524 && !excludedMove // Do not allow recursive single-reply search
1526 && is_lower_bound(tte->type())
1527 && tte->depth() >= depth - 3 * OnePly)
1529 Value ttValue = value_from_tt(tte->value(), ply);
1531 if (abs(ttValue) < VALUE_KNOWN_WIN)
1533 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1535 if (excValue < ttValue - SingleReplyMargin)
1540 newDepth = depth - OnePly + ext;
1542 // Update current move
1543 movesSearched[moveCount++] = ss[ply].currentMove = move;
1548 && !captureOrPromotion
1549 && !move_is_castle(move)
1552 // Move count based pruning
1553 if ( moveCount >= FutilityMoveCountMargin
1554 && ok_to_prune(pos, move, ss[ply].threatMove)
1555 && bestValue > value_mated_in(PLY_MAX))
1558 // Value based pruning
1559 Depth predictedDepth = newDepth;
1561 //FIXME HACK: awful code duplication
1562 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 3.0;
1564 predictedDepth -= int(floor(red * int(OnePly)));
1566 if (predictedDepth < SelectiveDepth)
1568 int preFutilityValueMargin = 0;
1569 if (predictedDepth >= OnePly)
1570 preFutilityValueMargin = 112 * bitScanReverse32(int(predictedDepth) * int(predictedDepth) / 2);
1572 preFutilityValueMargin += H.gain(pos.piece_on(move_from(move)), move_from(move), move_to(move)) + 45;
1574 futilityValueScaled = ss[ply].eval + preFutilityValueMargin - moveCount * IncrementalFutilityMargin;
1576 if (futilityValueScaled < beta)
1578 if (futilityValueScaled > bestValue)
1579 bestValue = futilityValueScaled;
1585 // Make and search the move
1586 pos.do_move(move, st, ci, moveIsCheck);
1588 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1589 // if the move fails high will be re-searched at full depth.
1590 bool doFullDepthSearch = true;
1592 if ( depth >= 3*OnePly
1594 && !captureOrPromotion
1595 && !move_is_castle(move)
1596 && !move_is_killer(move, ss[ply])
1597 /* && move != ttMove*/)
1599 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 3.0;
1602 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1603 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1604 doFullDepthSearch = (value >= beta);
1608 if (doFullDepthSearch) // Go with full depth non-pv search
1610 ss[ply].reduction = Depth(0);
1611 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1613 pos.undo_move(move);
1615 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1618 if (value > bestValue)
1624 if (value == value_mate_in(ply + 1))
1625 ss[ply].mateKiller = move;
1629 if ( ActiveThreads > 1
1631 && depth >= MinimumSplitDepth
1633 && idle_thread_exists(threadID)
1635 && !thread_should_stop(threadID)
1636 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1637 depth, &moveCount, &mp, threadID, false))
1641 // All legal moves have been searched. A special case: If there were
1642 // no legal moves, it must be mate or stalemate.
1644 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1646 // If the search is not aborted, update the transposition table,
1647 // history counters, and killer moves.
1648 if (AbortSearch || thread_should_stop(threadID))
1651 if (bestValue < beta)
1652 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1655 BetaCounter.add(pos.side_to_move(), depth, threadID);
1656 move = ss[ply].pv[ply];
1657 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1658 if (!pos.move_is_capture_or_promotion(move))
1660 update_history(pos, move, depth, movesSearched, moveCount);
1661 update_killers(move, ss[ply]);
1666 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1672 // qsearch() is the quiescence search function, which is called by the main
1673 // search function when the remaining depth is zero (or, to be more precise,
1674 // less than OnePly).
1676 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1677 Depth depth, int ply, int threadID) {
1679 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1680 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1682 assert(ply >= 0 && ply < PLY_MAX);
1683 assert(threadID >= 0 && threadID < ActiveThreads);
1688 Value staticValue, bestValue, value, futilityBase, futilityValue;
1689 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1690 const TTEntry* tte = NULL;
1692 bool pvNode = (beta - alpha != 1);
1694 // Initialize, and make an early exit in case of an aborted search,
1695 // an instant draw, maximum ply reached, etc.
1696 init_node(ss, ply, threadID);
1698 // After init_node() that calls poll()
1699 if (AbortSearch || thread_should_stop(threadID))
1702 if (pos.is_draw() || ply >= PLY_MAX - 1)
1705 // Transposition table lookup. At PV nodes, we don't use the TT for
1706 // pruning, but only for move ordering.
1707 tte = TT.retrieve(pos.get_key());
1708 ttMove = (tte ? tte->move() : MOVE_NONE);
1710 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1712 assert(tte->type() != VALUE_TYPE_EVAL);
1714 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1715 return value_from_tt(tte->value(), ply);
1718 isCheck = pos.is_check();
1720 // Evaluate the position statically
1722 staticValue = -VALUE_INFINITE;
1723 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1724 staticValue = value_from_tt(tte->value(), ply);
1726 staticValue = evaluate(pos, ei, threadID);
1730 ss[ply].eval = staticValue;
1731 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1734 // Initialize "stand pat score", and return it immediately if it is
1736 bestValue = staticValue;
1738 if (bestValue >= beta)
1740 // Store the score to avoid a future costly evaluation() call
1741 if (!isCheck && !tte && ei.futilityMargin == 0)
1742 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1747 if (bestValue > alpha)
1750 // If we are near beta then try to get a cutoff pushing checks a bit further
1751 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1753 // Initialize a MovePicker object for the current position, and prepare
1754 // to search the moves. Because the depth is <= 0 here, only captures,
1755 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1756 // and we are near beta) will be generated.
1757 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1759 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1760 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;
1762 // Loop through the moves until no moves remain or a beta cutoff
1764 while ( alpha < beta
1765 && (move = mp.get_next_move()) != MOVE_NONE)
1767 assert(move_is_ok(move));
1769 moveIsCheck = pos.move_is_check(move, ci);
1771 // Update current move
1773 ss[ply].currentMove = move;
1781 && !move_is_promotion(move)
1782 && !pos.move_is_passed_pawn_push(move))
1784 futilityValue = futilityBase
1785 + pos.endgame_value_of_piece_on(move_to(move))
1786 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1788 if (futilityValue < alpha)
1790 if (futilityValue > bestValue)
1791 bestValue = futilityValue;
1796 // Detect blocking evasions that are candidate to be pruned
1797 evasionPrunable = isCheck
1798 && bestValue != -VALUE_INFINITE
1799 && !pos.move_is_capture(move)
1800 && pos.type_of_piece_on(move_from(move)) != KING
1801 && !pos.can_castle(pos.side_to_move());
1803 // Don't search moves with negative SEE values
1804 if ( (!isCheck || evasionPrunable)
1806 && !move_is_promotion(move)
1807 && pos.see_sign(move) < 0)
1810 // Make and search the move
1811 pos.do_move(move, st, ci, moveIsCheck);
1812 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1813 pos.undo_move(move);
1815 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1818 if (value > bestValue)
1829 // All legal moves have been searched. A special case: If we're in check
1830 // and no legal moves were found, it is checkmate.
1831 if (!moveCount && pos.is_check()) // Mate!
1832 return value_mated_in(ply);
1834 // Update transposition table
1835 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1836 if (bestValue < beta)
1838 // If bestValue isn't changed it means it is still the static evaluation
1839 // of the node, so keep this info to avoid a future evaluation() call.
1840 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1841 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1845 move = ss[ply].pv[ply];
1846 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1848 // Update killers only for good checking moves
1849 if (!pos.move_is_capture_or_promotion(move))
1850 update_killers(move, ss[ply]);
1853 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1859 // sp_search() is used to search from a split point. This function is called
1860 // by each thread working at the split point. It is similar to the normal
1861 // search() function, but simpler. Because we have already probed the hash
1862 // table, done a null move search, and searched the first move before
1863 // splitting, we don't have to repeat all this work in sp_search(). We
1864 // also don't need to store anything to the hash table here: This is taken
1865 // care of after we return from the split point.
1867 void sp_search(SplitPoint* sp, int threadID) {
1869 assert(threadID >= 0 && threadID < ActiveThreads);
1870 assert(ActiveThreads > 1);
1872 Position pos(*sp->pos);
1874 SearchStack* ss = sp->sstack[threadID];
1875 Value value = -VALUE_INFINITE;
1877 bool isCheck = pos.is_check();
1878 bool useFutilityPruning = sp->depth < SelectiveDepth
1881 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1883 while ( sp->bestValue < sp->beta
1884 && !thread_should_stop(threadID)
1885 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1887 assert(move_is_ok(move));
1889 bool moveIsCheck = pos.move_is_check(move, ci);
1890 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1892 lock_grab(&(sp->lock));
1893 int moveCount = ++sp->moves;
1894 lock_release(&(sp->lock));
1896 ss[sp->ply].currentMove = move;
1898 // Decide the new search depth.
1900 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1901 Depth newDepth = sp->depth - OnePly + ext;
1904 if ( useFutilityPruning
1906 && !captureOrPromotion)
1908 // Move count based pruning
1909 if ( moveCount >= FutilityMoveCountMargin
1910 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1911 && sp->bestValue > value_mated_in(PLY_MAX))
1914 // Value based pruning
1915 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1917 if (futilityValueScaled < sp->beta)
1919 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1921 lock_grab(&(sp->lock));
1922 if (futilityValueScaled > sp->bestValue)
1923 sp->bestValue = futilityValueScaled;
1924 lock_release(&(sp->lock));
1930 // Make and search the move.
1932 pos.do_move(move, st, ci, moveIsCheck);
1934 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1935 // if the move fails high will be re-searched at full depth.
1936 bool doFullDepthSearch = true;
1939 && !captureOrPromotion
1940 && !move_is_castle(move)
1941 && !move_is_killer(move, ss[sp->ply]))
1943 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 3.0;
1946 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
1947 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1948 doFullDepthSearch = (value >= sp->beta);
1952 if (doFullDepthSearch) // Go with full depth non-pv search
1954 ss[sp->ply].reduction = Depth(0);
1955 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1957 pos.undo_move(move);
1959 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1961 if (thread_should_stop(threadID))
1965 if (value > sp->bestValue) // Less then 2% of cases
1967 lock_grab(&(sp->lock));
1968 if (value > sp->bestValue && !thread_should_stop(threadID))
1970 sp->bestValue = value;
1971 if (sp->bestValue >= sp->beta)
1973 sp_update_pv(sp->parentSstack, ss, sp->ply);
1974 for (int i = 0; i < ActiveThreads; i++)
1975 if (i != threadID && (i == sp->master || sp->slaves[i]))
1976 Threads[i].stop = true;
1978 sp->finished = true;
1981 lock_release(&(sp->lock));
1985 lock_grab(&(sp->lock));
1987 // If this is the master thread and we have been asked to stop because of
1988 // a beta cutoff higher up in the tree, stop all slave threads.
1989 if (sp->master == threadID && thread_should_stop(threadID))
1990 for (int i = 0; i < ActiveThreads; i++)
1992 Threads[i].stop = true;
1995 sp->slaves[threadID] = 0;
1997 lock_release(&(sp->lock));
2001 // sp_search_pv() is used to search from a PV split point. This function
2002 // is called by each thread working at the split point. It is similar to
2003 // the normal search_pv() function, but simpler. Because we have already
2004 // probed the hash table and searched the first move before splitting, we
2005 // don't have to repeat all this work in sp_search_pv(). We also don't
2006 // need to store anything to the hash table here: This is taken care of
2007 // after we return from the split point.
2009 void sp_search_pv(SplitPoint* sp, int threadID) {
2011 assert(threadID >= 0 && threadID < ActiveThreads);
2012 assert(ActiveThreads > 1);
2014 Position pos(*sp->pos);
2016 SearchStack* ss = sp->sstack[threadID];
2017 Value value = -VALUE_INFINITE;
2020 while ( sp->alpha < sp->beta
2021 && !thread_should_stop(threadID)
2022 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
2024 bool moveIsCheck = pos.move_is_check(move, ci);
2025 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
2027 assert(move_is_ok(move));
2029 lock_grab(&(sp->lock));
2030 int moveCount = ++sp->moves;
2031 lock_release(&(sp->lock));
2033 ss[sp->ply].currentMove = move;
2035 // Decide the new search depth.
2037 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
2038 Depth newDepth = sp->depth - OnePly + ext;
2040 // Make and search the move.
2042 pos.do_move(move, st, ci, moveIsCheck);
2044 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2045 // if the move fails high will be re-searched at full depth.
2046 bool doFullDepthSearch = true;
2049 && !captureOrPromotion
2050 && !move_is_castle(move)
2051 && !move_is_killer(move, ss[sp->ply]))
2053 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 6.0;
2056 Value localAlpha = sp->alpha;
2057 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
2058 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2059 doFullDepthSearch = (value > localAlpha);
2063 if (doFullDepthSearch) // Go with full depth non-pv search
2065 Value localAlpha = sp->alpha;
2066 ss[sp->ply].reduction = Depth(0);
2067 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2069 if (value > localAlpha && value < sp->beta)
2071 // When the search fails high at ply 1 while searching the first
2072 // move at the root, set the flag failHighPly1. This is used for
2073 // time managment: We don't want to stop the search early in
2074 // such cases, because resolving the fail high at ply 1 could
2075 // result in a big drop in score at the root.
2076 if (sp->ply == 1 && RootMoveNumber == 1)
2077 Threads[threadID].failHighPly1 = true;
2079 // If another thread has failed high then sp->alpha has been increased
2080 // to be higher or equal then beta, if so, avoid to start a PV search.
2081 localAlpha = sp->alpha;
2082 if (localAlpha < sp->beta)
2083 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2085 assert(thread_should_stop(threadID));
2087 Threads[threadID].failHighPly1 = false;
2090 pos.undo_move(move);
2092 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2094 if (thread_should_stop(threadID))
2098 if (value > sp->bestValue) // Less then 2% of cases
2100 lock_grab(&(sp->lock));
2101 if (value > sp->bestValue && !thread_should_stop(threadID))
2103 sp->bestValue = value;
2104 if (value > sp->alpha)
2106 // Ask threads to stop before to modify sp->alpha
2107 if (value >= sp->beta)
2109 for (int i = 0; i < ActiveThreads; i++)
2110 if (i != threadID && (i == sp->master || sp->slaves[i]))
2111 Threads[i].stop = true;
2113 sp->finished = true;
2118 sp_update_pv(sp->parentSstack, ss, sp->ply);
2119 if (value == value_mate_in(sp->ply + 1))
2120 ss[sp->ply].mateKiller = move;
2122 // If we are at ply 1, and we are searching the first root move at
2123 // ply 0, set the 'Problem' variable if the score has dropped a lot
2124 // (from the computer's point of view) since the previous iteration.
2127 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2130 lock_release(&(sp->lock));
2134 lock_grab(&(sp->lock));
2136 // If this is the master thread and we have been asked to stop because of
2137 // a beta cutoff higher up in the tree, stop all slave threads.
2138 if (sp->master == threadID && thread_should_stop(threadID))
2139 for (int i = 0; i < ActiveThreads; i++)
2141 Threads[i].stop = true;
2144 sp->slaves[threadID] = 0;
2146 lock_release(&(sp->lock));
2149 /// The BetaCounterType class
2151 BetaCounterType::BetaCounterType() { clear(); }
2153 void BetaCounterType::clear() {
2155 for (int i = 0; i < THREAD_MAX; i++)
2156 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2159 void BetaCounterType::add(Color us, Depth d, int threadID) {
2161 // Weighted count based on depth
2162 Threads[threadID].betaCutOffs[us] += unsigned(d);
2165 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2168 for (int i = 0; i < THREAD_MAX; i++)
2170 our += Threads[i].betaCutOffs[us];
2171 their += Threads[i].betaCutOffs[opposite_color(us)];
2176 /// The RootMoveList class
2178 // RootMoveList c'tor
2180 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2182 MoveStack mlist[MaxRootMoves];
2183 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2185 // Generate all legal moves
2186 MoveStack* last = generate_moves(pos, mlist);
2188 // Add each move to the moves[] array
2189 for (MoveStack* cur = mlist; cur != last; cur++)
2191 bool includeMove = includeAllMoves;
2193 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2194 includeMove = (searchMoves[k] == cur->move);
2199 // Find a quick score for the move
2201 SearchStack ss[PLY_MAX_PLUS_2];
2204 moves[count].move = cur->move;
2205 pos.do_move(moves[count].move, st);
2206 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2207 pos.undo_move(moves[count].move);
2208 moves[count].pv[0] = moves[count].move;
2209 moves[count].pv[1] = MOVE_NONE;
2216 // RootMoveList simple methods definitions
2218 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2220 moves[moveNum].nodes = nodes;
2221 moves[moveNum].cumulativeNodes += nodes;
2224 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2226 moves[moveNum].ourBeta = our;
2227 moves[moveNum].theirBeta = their;
2230 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2234 for (j = 0; pv[j] != MOVE_NONE; j++)
2235 moves[moveNum].pv[j] = pv[j];
2237 moves[moveNum].pv[j] = MOVE_NONE;
2241 // RootMoveList::sort() sorts the root move list at the beginning of a new
2244 void RootMoveList::sort() {
2246 sort_multipv(count - 1); // Sort all items
2250 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2251 // list by their scores and depths. It is used to order the different PVs
2252 // correctly in MultiPV mode.
2254 void RootMoveList::sort_multipv(int n) {
2258 for (i = 1; i <= n; i++)
2260 RootMove rm = moves[i];
2261 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2262 moves[j] = moves[j - 1];
2269 // init_node() is called at the beginning of all the search functions
2270 // (search(), search_pv(), qsearch(), and so on) and initializes the
2271 // search stack object corresponding to the current node. Once every
2272 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2273 // for user input and checks whether it is time to stop the search.
2275 void init_node(SearchStack ss[], int ply, int threadID) {
2277 assert(ply >= 0 && ply < PLY_MAX);
2278 assert(threadID >= 0 && threadID < ActiveThreads);
2280 Threads[threadID].nodes++;
2285 if (NodesSincePoll >= NodesBetweenPolls)
2292 ss[ply + 2].initKillers();
2294 if (Threads[threadID].printCurrentLine)
2295 print_current_line(ss, ply, threadID);
2299 // update_pv() is called whenever a search returns a value > alpha.
2300 // It updates the PV in the SearchStack object corresponding to the
2303 void update_pv(SearchStack ss[], int ply) {
2305 assert(ply >= 0 && ply < PLY_MAX);
2309 ss[ply].pv[ply] = ss[ply].currentMove;
2311 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2312 ss[ply].pv[p] = ss[ply + 1].pv[p];
2314 ss[ply].pv[p] = MOVE_NONE;
2318 // sp_update_pv() is a variant of update_pv for use at split points. The
2319 // difference between the two functions is that sp_update_pv also updates
2320 // the PV at the parent node.
2322 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2324 assert(ply >= 0 && ply < PLY_MAX);
2328 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2330 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2331 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2333 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2337 // connected_moves() tests whether two moves are 'connected' in the sense
2338 // that the first move somehow made the second move possible (for instance
2339 // if the moving piece is the same in both moves). The first move is assumed
2340 // to be the move that was made to reach the current position, while the
2341 // second move is assumed to be a move from the current position.
2343 bool connected_moves(const Position& pos, Move m1, Move m2) {
2345 Square f1, t1, f2, t2;
2348 assert(move_is_ok(m1));
2349 assert(move_is_ok(m2));
2351 if (m2 == MOVE_NONE)
2354 // Case 1: The moving piece is the same in both moves
2360 // Case 2: The destination square for m2 was vacated by m1
2366 // Case 3: Moving through the vacated square
2367 if ( piece_is_slider(pos.piece_on(f2))
2368 && bit_is_set(squares_between(f2, t2), f1))
2371 // Case 4: The destination square for m2 is defended by the moving piece in m1
2372 p = pos.piece_on(t1);
2373 if (bit_is_set(pos.attacks_from(p, t1), t2))
2376 // Case 5: Discovered check, checking piece is the piece moved in m1
2377 if ( piece_is_slider(p)
2378 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2379 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2381 // discovered_check_candidates() works also if the Position's side to
2382 // move is the opposite of the checking piece.
2383 Color them = opposite_color(pos.side_to_move());
2384 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2386 if (bit_is_set(dcCandidates, f2))
2393 // value_is_mate() checks if the given value is a mate one
2394 // eventually compensated for the ply.
2396 bool value_is_mate(Value value) {
2398 assert(abs(value) <= VALUE_INFINITE);
2400 return value <= value_mated_in(PLY_MAX)
2401 || value >= value_mate_in(PLY_MAX);
2405 // move_is_killer() checks if the given move is among the
2406 // killer moves of that ply.
2408 bool move_is_killer(Move m, const SearchStack& ss) {
2410 const Move* k = ss.killers;
2411 for (int i = 0; i < KILLER_MAX; i++, k++)
2419 // extension() decides whether a move should be searched with normal depth,
2420 // or with extended depth. Certain classes of moves (checking moves, in
2421 // particular) are searched with bigger depth than ordinary moves and in
2422 // any case are marked as 'dangerous'. Note that also if a move is not
2423 // extended, as example because the corresponding UCI option is set to zero,
2424 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2426 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2427 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2429 assert(m != MOVE_NONE);
2431 Depth result = Depth(0);
2432 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2437 result += CheckExtension[pvNode];
2440 result += SingleEvasionExtension[pvNode];
2443 result += MateThreatExtension[pvNode];
2446 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2448 Color c = pos.side_to_move();
2449 if (relative_rank(c, move_to(m)) == RANK_7)
2451 result += PawnPushTo7thExtension[pvNode];
2454 if (pos.pawn_is_passed(c, move_to(m)))
2456 result += PassedPawnExtension[pvNode];
2461 if ( captureOrPromotion
2462 && pos.type_of_piece_on(move_to(m)) != PAWN
2463 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2464 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2465 && !move_is_promotion(m)
2468 result += PawnEndgameExtension[pvNode];
2473 && captureOrPromotion
2474 && pos.type_of_piece_on(move_to(m)) != PAWN
2475 && pos.see_sign(m) >= 0)
2481 return Min(result, OnePly);
2485 // ok_to_do_nullmove() looks at the current position and decides whether
2486 // doing a 'null move' should be allowed. In order to avoid zugzwang
2487 // problems, null moves are not allowed when the side to move has very
2488 // little material left. Currently, the test is a bit too simple: Null
2489 // moves are avoided only when the side to move has only pawns left.
2490 // It's probably a good idea to avoid null moves in at least some more
2491 // complicated endgames, e.g. KQ vs KR. FIXME
2493 bool ok_to_do_nullmove(const Position& pos) {
2495 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2499 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2500 // non-tactical moves late in the move list close to the leaves are
2501 // candidates for pruning.
2503 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2505 assert(move_is_ok(m));
2506 assert(threat == MOVE_NONE || move_is_ok(threat));
2507 assert(!pos.move_is_check(m));
2508 assert(!pos.move_is_capture_or_promotion(m));
2509 assert(!pos.move_is_passed_pawn_push(m));
2511 Square mfrom, mto, tfrom, tto;
2513 // Prune if there isn't any threat move
2514 if (threat == MOVE_NONE)
2517 mfrom = move_from(m);
2519 tfrom = move_from(threat);
2520 tto = move_to(threat);
2522 // Case 1: Don't prune moves which move the threatened piece
2526 // Case 2: If the threatened piece has value less than or equal to the
2527 // value of the threatening piece, don't prune move which defend it.
2528 if ( pos.move_is_capture(threat)
2529 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2530 || pos.type_of_piece_on(tfrom) == KING)
2531 && pos.move_attacks_square(m, tto))
2534 // Case 3: If the moving piece in the threatened move is a slider, don't
2535 // prune safe moves which block its ray.
2536 if ( piece_is_slider(pos.piece_on(tfrom))
2537 && bit_is_set(squares_between(tfrom, tto), mto)
2538 && pos.see_sign(m) >= 0)
2545 // ok_to_use_TT() returns true if a transposition table score
2546 // can be used at a given point in search.
2548 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2550 Value v = value_from_tt(tte->value(), ply);
2552 return ( tte->depth() >= depth
2553 || v >= Max(value_mate_in(PLY_MAX), beta)
2554 || v < Min(value_mated_in(PLY_MAX), beta))
2556 && ( (is_lower_bound(tte->type()) && v >= beta)
2557 || (is_upper_bound(tte->type()) && v < beta));
2561 // refine_eval() returns the transposition table score if
2562 // possible otherwise falls back on static position evaluation.
2564 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2569 Value v = value_from_tt(tte->value(), ply);
2571 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2572 || (is_upper_bound(tte->type()) && v < defaultEval))
2578 // update_history() registers a good move that produced a beta-cutoff
2579 // in history and marks as failures all the other moves of that ply.
2581 void update_history(const Position& pos, Move move, Depth depth,
2582 Move movesSearched[], int moveCount) {
2586 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2588 for (int i = 0; i < moveCount - 1; i++)
2590 m = movesSearched[i];
2594 if (!pos.move_is_capture_or_promotion(m))
2595 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2600 // update_killers() add a good move that produced a beta-cutoff
2601 // among the killer moves of that ply.
2603 void update_killers(Move m, SearchStack& ss) {
2605 if (m == ss.killers[0])
2608 for (int i = KILLER_MAX - 1; i > 0; i--)
2609 ss.killers[i] = ss.killers[i - 1];
2615 // update_gains() updates the gains table of a non-capture move given
2616 // the static position evaluation before and after the move.
2618 void update_gains(const Position& pos, Move m, Value before, Value after) {
2621 && before != VALUE_NONE
2622 && after != VALUE_NONE
2623 && pos.captured_piece() == NO_PIECE_TYPE
2624 && !move_is_castle(m)
2625 && !move_is_promotion(m))
2626 H.set_gain(pos.piece_on(move_to(m)), move_from(m), move_to(m), -(before + after));
2630 // fail_high_ply_1() checks if some thread is currently resolving a fail
2631 // high at ply 1 at the node below the first root node. This information
2632 // is used for time management.
2634 bool fail_high_ply_1() {
2636 for (int i = 0; i < ActiveThreads; i++)
2637 if (Threads[i].failHighPly1)
2644 // current_search_time() returns the number of milliseconds which have passed
2645 // since the beginning of the current search.
2647 int current_search_time() {
2649 return get_system_time() - SearchStartTime;
2653 // nps() computes the current nodes/second count.
2657 int t = current_search_time();
2658 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2662 // poll() performs two different functions: It polls for user input, and it
2663 // looks at the time consumed so far and decides if it's time to abort the
2668 static int lastInfoTime;
2669 int t = current_search_time();
2674 // We are line oriented, don't read single chars
2675 std::string command;
2677 if (!std::getline(std::cin, command))
2680 if (command == "quit")
2683 PonderSearch = false;
2687 else if (command == "stop")
2690 PonderSearch = false;
2692 else if (command == "ponderhit")
2696 // Print search information
2700 else if (lastInfoTime > t)
2701 // HACK: Must be a new search where we searched less than
2702 // NodesBetweenPolls nodes during the first second of search.
2705 else if (t - lastInfoTime >= 1000)
2713 if (dbg_show_hit_rate)
2714 dbg_print_hit_rate();
2716 cout << "info nodes " << nodes_searched() << " nps " << nps()
2717 << " time " << t << " hashfull " << TT.full() << endl;
2719 lock_release(&IOLock);
2721 if (ShowCurrentLine)
2722 Threads[0].printCurrentLine = true;
2725 // Should we stop the search?
2729 bool stillAtFirstMove = RootMoveNumber == 1
2731 && t > MaxSearchTime + ExtraSearchTime;
2733 bool noProblemFound = !FailHigh
2735 && !fail_high_ply_1()
2737 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2739 bool noMoreTime = t > AbsoluteMaxSearchTime
2740 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2743 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2744 || (ExactMaxTime && t >= ExactMaxTime)
2745 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2750 // ponderhit() is called when the program is pondering (i.e. thinking while
2751 // it's the opponent's turn to move) in order to let the engine know that
2752 // it correctly predicted the opponent's move.
2756 int t = current_search_time();
2757 PonderSearch = false;
2759 bool stillAtFirstMove = RootMoveNumber == 1
2761 && t > MaxSearchTime + ExtraSearchTime;
2763 bool noProblemFound = !FailHigh
2765 && !fail_high_ply_1()
2767 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2769 bool noMoreTime = t > AbsoluteMaxSearchTime
2773 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2778 // print_current_line() prints the current line of search for a given
2779 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2781 void print_current_line(SearchStack ss[], int ply, int threadID) {
2783 assert(ply >= 0 && ply < PLY_MAX);
2784 assert(threadID >= 0 && threadID < ActiveThreads);
2786 if (!Threads[threadID].idle)
2789 cout << "info currline " << (threadID + 1);
2790 for (int p = 0; p < ply; p++)
2791 cout << " " << ss[p].currentMove;
2794 lock_release(&IOLock);
2796 Threads[threadID].printCurrentLine = false;
2797 if (threadID + 1 < ActiveThreads)
2798 Threads[threadID + 1].printCurrentLine = true;
2802 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2804 void init_ss_array(SearchStack ss[]) {
2806 for (int i = 0; i < 3; i++)
2809 ss[i].initKillers();
2814 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2815 // while the program is pondering. The point is to work around a wrinkle in
2816 // the UCI protocol: When pondering, the engine is not allowed to give a
2817 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2818 // We simply wait here until one of these commands is sent, and return,
2819 // after which the bestmove and pondermove will be printed (in id_loop()).
2821 void wait_for_stop_or_ponderhit() {
2823 std::string command;
2827 if (!std::getline(std::cin, command))
2830 if (command == "quit")
2835 else if (command == "ponderhit" || command == "stop")
2841 // idle_loop() is where the threads are parked when they have no work to do.
2842 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2843 // object for which the current thread is the master.
2845 void idle_loop(int threadID, SplitPoint* waitSp) {
2847 assert(threadID >= 0 && threadID < THREAD_MAX);
2849 Threads[threadID].running = true;
2853 if (AllThreadsShouldExit && threadID != 0)
2856 // If we are not thinking, wait for a condition to be signaled
2857 // instead of wasting CPU time polling for work.
2858 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2861 #if !defined(_MSC_VER)
2862 pthread_mutex_lock(&WaitLock);
2863 if (Idle || threadID >= ActiveThreads)
2864 pthread_cond_wait(&WaitCond, &WaitLock);
2866 pthread_mutex_unlock(&WaitLock);
2868 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2872 // If this thread has been assigned work, launch a search
2873 if (Threads[threadID].workIsWaiting)
2875 assert(!Threads[threadID].idle);
2877 Threads[threadID].workIsWaiting = false;
2878 if (Threads[threadID].splitPoint->pvNode)
2879 sp_search_pv(Threads[threadID].splitPoint, threadID);
2881 sp_search(Threads[threadID].splitPoint, threadID);
2883 Threads[threadID].idle = true;
2886 // If this thread is the master of a split point and all threads have
2887 // finished their work at this split point, return from the idle loop.
2888 if (waitSp != NULL && waitSp->cpus == 0)
2892 Threads[threadID].running = false;
2896 // init_split_point_stack() is called during program initialization, and
2897 // initializes all split point objects.
2899 void init_split_point_stack() {
2901 for (int i = 0; i < THREAD_MAX; i++)
2902 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2904 SplitPointStack[i][j].parent = NULL;
2905 lock_init(&(SplitPointStack[i][j].lock), NULL);
2910 // destroy_split_point_stack() is called when the program exits, and
2911 // destroys all locks in the precomputed split point objects.
2913 void destroy_split_point_stack() {
2915 for (int i = 0; i < THREAD_MAX; i++)
2916 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2917 lock_destroy(&(SplitPointStack[i][j].lock));
2921 // thread_should_stop() checks whether the thread with a given threadID has
2922 // been asked to stop, directly or indirectly. This can happen if a beta
2923 // cutoff has occurred in the thread's currently active split point, or in
2924 // some ancestor of the current split point.
2926 bool thread_should_stop(int threadID) {
2928 assert(threadID >= 0 && threadID < ActiveThreads);
2932 if (Threads[threadID].stop)
2934 if (ActiveThreads <= 2)
2936 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2939 Threads[threadID].stop = true;
2946 // thread_is_available() checks whether the thread with threadID "slave" is
2947 // available to help the thread with threadID "master" at a split point. An
2948 // obvious requirement is that "slave" must be idle. With more than two
2949 // threads, this is not by itself sufficient: If "slave" is the master of
2950 // some active split point, it is only available as a slave to the other
2951 // threads which are busy searching the split point at the top of "slave"'s
2952 // split point stack (the "helpful master concept" in YBWC terminology).
2954 bool thread_is_available(int slave, int master) {
2956 assert(slave >= 0 && slave < ActiveThreads);
2957 assert(master >= 0 && master < ActiveThreads);
2958 assert(ActiveThreads > 1);
2960 if (!Threads[slave].idle || slave == master)
2963 // Make a local copy to be sure doesn't change under our feet
2964 int localActiveSplitPoints = Threads[slave].activeSplitPoints;
2966 if (localActiveSplitPoints == 0)
2967 // No active split points means that the thread is available as
2968 // a slave for any other thread.
2971 if (ActiveThreads == 2)
2974 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2975 // that is known to be > 0, instead of Threads[slave].activeSplitPoints that
2976 // could have been set to 0 by another thread leading to an out of bound access.
2977 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2984 // idle_thread_exists() tries to find an idle thread which is available as
2985 // a slave for the thread with threadID "master".
2987 bool idle_thread_exists(int master) {
2989 assert(master >= 0 && master < ActiveThreads);
2990 assert(ActiveThreads > 1);
2992 for (int i = 0; i < ActiveThreads; i++)
2993 if (thread_is_available(i, master))
3000 // split() does the actual work of distributing the work at a node between
3001 // several threads at PV nodes. If it does not succeed in splitting the
3002 // node (because no idle threads are available, or because we have no unused
3003 // split point objects), the function immediately returns false. If
3004 // splitting is possible, a SplitPoint object is initialized with all the
3005 // data that must be copied to the helper threads (the current position and
3006 // search stack, alpha, beta, the search depth, etc.), and we tell our
3007 // helper threads that they have been assigned work. This will cause them
3008 // to instantly leave their idle loops and call sp_search_pv(). When all
3009 // threads have returned from sp_search_pv (or, equivalently, when
3010 // splitPoint->cpus becomes 0), split() returns true.
3012 bool split(const Position& p, SearchStack* sstck, int ply,
3013 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
3014 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
3017 assert(sstck != NULL);
3018 assert(ply >= 0 && ply < PLY_MAX);
3019 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
3020 assert(!pvNode || *alpha < *beta);
3021 assert(*beta <= VALUE_INFINITE);
3022 assert(depth > Depth(0));
3023 assert(master >= 0 && master < ActiveThreads);
3024 assert(ActiveThreads > 1);
3026 SplitPoint* splitPoint;
3030 // If no other thread is available to help us, or if we have too many
3031 // active split points, don't split.
3032 if ( !idle_thread_exists(master)
3033 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
3035 lock_release(&MPLock);
3039 // Pick the next available split point object from the split point stack
3040 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
3041 Threads[master].activeSplitPoints++;
3043 // Initialize the split point object
3044 splitPoint->parent = Threads[master].splitPoint;
3045 splitPoint->finished = false;
3046 splitPoint->ply = ply;
3047 splitPoint->depth = depth;
3048 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
3049 splitPoint->beta = *beta;
3050 splitPoint->pvNode = pvNode;
3051 splitPoint->bestValue = *bestValue;
3052 splitPoint->futilityValue = futilityValue;
3053 splitPoint->master = master;
3054 splitPoint->mp = mp;
3055 splitPoint->moves = *moves;
3056 splitPoint->cpus = 1;
3057 splitPoint->pos = &p;
3058 splitPoint->parentSstack = sstck;
3059 for (int i = 0; i < ActiveThreads; i++)
3060 splitPoint->slaves[i] = 0;
3062 Threads[master].idle = false;
3063 Threads[master].stop = false;
3064 Threads[master].splitPoint = splitPoint;
3066 // Allocate available threads setting idle flag to false
3067 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
3068 if (thread_is_available(i, master))
3070 Threads[i].idle = false;
3071 Threads[i].stop = false;
3072 Threads[i].splitPoint = splitPoint;
3073 splitPoint->slaves[i] = 1;
3077 assert(splitPoint->cpus > 1);
3079 // We can release the lock because master and slave threads are already booked
3080 lock_release(&MPLock);
3082 // Tell the threads that they have work to do. This will make them leave
3083 // their idle loop. But before copy search stack tail for each thread.
3084 for (int i = 0; i < ActiveThreads; i++)
3085 if (i == master || splitPoint->slaves[i])
3087 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 3 * sizeof(SearchStack));
3088 Threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
3091 // Everything is set up. The master thread enters the idle loop, from
3092 // which it will instantly launch a search, because its workIsWaiting
3093 // slot is 'true'. We send the split point as a second parameter to the
3094 // idle loop, which means that the main thread will return from the idle
3095 // loop when all threads have finished their work at this split point
3096 // (i.e. when splitPoint->cpus == 0).
3097 idle_loop(master, splitPoint);
3099 // We have returned from the idle loop, which means that all threads are
3100 // finished. Update alpha, beta and bestValue, and return.
3104 *alpha = splitPoint->alpha;
3106 *beta = splitPoint->beta;
3107 *bestValue = splitPoint->bestValue;
3108 Threads[master].stop = false;
3109 Threads[master].idle = false;
3110 Threads[master].activeSplitPoints--;
3111 Threads[master].splitPoint = splitPoint->parent;
3113 lock_release(&MPLock);
3118 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3119 // to start a new search from the root.
3121 void wake_sleeping_threads() {
3123 if (ActiveThreads > 1)
3125 for (int i = 1; i < ActiveThreads; i++)
3127 Threads[i].idle = true;
3128 Threads[i].workIsWaiting = false;
3131 #if !defined(_MSC_VER)
3132 pthread_mutex_lock(&WaitLock);
3133 pthread_cond_broadcast(&WaitCond);
3134 pthread_mutex_unlock(&WaitLock);
3136 for (int i = 1; i < THREAD_MAX; i++)
3137 SetEvent(SitIdleEvent[i]);
3143 // init_thread() is the function which is called when a new thread is
3144 // launched. It simply calls the idle_loop() function with the supplied
3145 // threadID. There are two versions of this function; one for POSIX
3146 // threads and one for Windows threads.
3148 #if !defined(_MSC_VER)
3150 void* init_thread(void *threadID) {
3152 idle_loop(*(int*)threadID, NULL);
3158 DWORD WINAPI init_thread(LPVOID threadID) {
3160 idle_loop(*(int*)threadID, NULL);