2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
42 #include "ucioption.h"
48 //// Local definitions
55 // IterationInfoType stores search results for each iteration
57 // Because we use relatively small (dynamic) aspiration window,
58 // there happens many fail highs and fail lows in root. And
59 // because we don't do researches in those cases, "value" stored
60 // here is not necessarily exact. Instead in case of fail high/low
61 // we guess what the right value might be and store our guess
62 // as a "speculated value" and then move on. Speculated values are
63 // used just to calculate aspiration window width, so also if are
64 // not exact is not big a problem.
66 struct IterationInfoType {
68 IterationInfoType(Value v = Value(0), Value sv = Value(0))
69 : value(v), speculatedValue(sv) {}
71 Value value, speculatedValue;
75 // The BetaCounterType class is used to order moves at ply one.
76 // Apart for the first one that has its score, following moves
77 // normally have score -VALUE_INFINITE, so are ordered according
78 // to the number of beta cutoffs occurred under their subtree during
79 // the last iteration. The counters are per thread variables to avoid
80 // concurrent accessing under SMP case.
82 struct BetaCounterType {
86 void add(Color us, Depth d, int threadID);
87 void read(Color us, int64_t& our, int64_t& their);
91 // The RootMove class is used for moves at the root at the tree. For each
92 // root move, we store a score, a node count, and a PV (really a refutation
93 // in the case of moves which fail low).
97 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
99 // RootMove::operator<() is the comparison function used when
100 // sorting the moves. A move m1 is considered to be better
101 // than a move m2 if it has a higher score, or if the moves
102 // have equal score but m1 has the higher node count.
103 bool operator<(const RootMove& m) const {
105 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
110 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
111 Move pv[PLY_MAX_PLUS_2];
115 // The RootMoveList class is essentially an array of RootMove objects, with
116 // a handful of methods for accessing the data in the individual moves.
121 RootMoveList(Position& pos, Move searchMoves[]);
123 int move_count() const { return count; }
124 Move get_move(int moveNum) const { return moves[moveNum].move; }
125 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
126 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
127 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
128 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
130 void set_move_nodes(int moveNum, int64_t nodes);
131 void set_beta_counters(int moveNum, int64_t our, int64_t their);
132 void set_move_pv(int moveNum, const Move pv[]);
134 void sort_multipv(int n);
137 static const int MaxRootMoves = 500;
138 RootMove moves[MaxRootMoves];
145 // Search depth at iteration 1
146 const Depth InitialDepth = OnePly;
148 // Depth limit for selective search
149 const Depth SelectiveDepth = 7 * OnePly;
151 // Use internal iterative deepening?
152 const bool UseIIDAtPVNodes = true;
153 const bool UseIIDAtNonPVNodes = true;
155 // Internal iterative deepening margin. At Non-PV moves, when
156 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
157 // search when the static evaluation is at most IIDMargin below beta.
158 const Value IIDMargin = Value(0x100);
160 // Easy move margin. An easy move candidate must be at least this much
161 // better than the second best move.
162 const Value EasyMoveMargin = Value(0x200);
164 // Problem margin. If the score of the first move at iteration N+1 has
165 // dropped by more than this since iteration N, the boolean variable
166 // "Problem" is set to true, which will make the program spend some extra
167 // time looking for a better move.
168 const Value ProblemMargin = Value(0x28);
170 // No problem margin. If the boolean "Problem" is true, and a new move
171 // is found at the root which is less than NoProblemMargin worse than the
172 // best move from the previous iteration, Problem is set back to false.
173 const Value NoProblemMargin = Value(0x14);
175 // Null move margin. A null move search will not be done if the approximate
176 // evaluation of the position is more than NullMoveMargin below beta.
177 const Value NullMoveMargin = Value(0x300);
179 // If the TT move is at least SingleReplyMargin better then the
180 // remaining ones we will extend it.
181 const Value SingleReplyMargin = Value(0x20);
183 // Margins for futility pruning in the quiescence search, and at frontier
184 // and near frontier nodes.
185 const Value FutilityMarginQS = Value(0x80);
187 // Each move futility margin is decreased
188 const Value IncrementalFutilityMargin = Value(0x8);
190 // Depth limit for razoring
191 const Depth RazorDepth = 4 * OnePly;
193 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
194 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
196 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
197 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
200 /// Variables initialized by UCI options
202 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
203 int LMRPVMoves, LMRNonPVMoves;
205 // Depth limit for use of dynamic threat detection
208 // Last seconds noise filtering (LSN)
209 const bool UseLSNFiltering = true;
210 const int LSNTime = 4000; // In milliseconds
211 const Value LSNValue = value_from_centipawns(200);
212 bool loseOnTime = false;
214 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
215 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
216 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
218 // Iteration counters
220 BetaCounterType BetaCounter;
222 // Scores and number of times the best move changed for each iteration
223 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
224 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
229 // Time managment variables
232 int MaxNodes, MaxDepth;
233 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
234 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
235 bool AbortSearch, Quit;
236 bool FailHigh, FailLow, Problem;
238 // Show current line?
239 bool ShowCurrentLine;
243 std::ofstream LogFile;
245 // MP related variables
246 int ActiveThreads = 1;
247 Depth MinimumSplitDepth;
248 int MaxThreadsPerSplitPoint;
249 Thread Threads[THREAD_MAX];
252 bool AllThreadsShouldExit = false;
253 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
256 #if !defined(_MSC_VER)
257 pthread_cond_t WaitCond;
258 pthread_mutex_t WaitLock;
260 HANDLE SitIdleEvent[THREAD_MAX];
263 // Node counters, used only by thread[0] but try to keep in different
264 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
266 int NodesBetweenPolls = 30000;
274 Value id_loop(const Position& pos, Move searchMoves[]);
275 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
276 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
277 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
278 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
279 void sp_search(SplitPoint* sp, int threadID);
280 void sp_search_pv(SplitPoint* sp, int threadID);
281 void init_node(SearchStack ss[], int ply, int threadID);
282 void update_pv(SearchStack ss[], int ply);
283 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
284 bool connected_moves(const Position& pos, Move m1, Move m2);
285 bool value_is_mate(Value value);
286 bool move_is_killer(Move m, const SearchStack& ss);
287 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
288 bool ok_to_do_nullmove(const Position& pos);
289 bool ok_to_prune(const Position& pos, Move m, Move threat);
290 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
291 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
292 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
293 void update_killers(Move m, SearchStack& ss);
295 bool fail_high_ply_1();
296 int current_search_time();
300 void print_current_line(SearchStack ss[], int ply, int threadID);
301 void wait_for_stop_or_ponderhit();
302 void init_ss_array(SearchStack ss[]);
304 void idle_loop(int threadID, SplitPoint* waitSp);
305 void init_split_point_stack();
306 void destroy_split_point_stack();
307 bool thread_should_stop(int threadID);
308 bool thread_is_available(int slave, int master);
309 bool idle_thread_exists(int master);
310 bool split(const Position& pos, SearchStack* ss, int ply,
311 Value *alpha, Value *beta, Value *bestValue,
312 const Value futilityValue, Depth depth, int *moves,
313 MovePicker *mp, int master, bool pvNode);
314 void wake_sleeping_threads();
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
330 static double lnArray[512];
332 inline double ln(int i)
337 /// perft() is our utility to verify move generation is bug free. All the legal
338 /// moves up to given depth are generated and counted and the sum returned.
340 int perft(Position& pos, Depth depth)
344 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
346 // If we are at the last ply we don't need to do and undo
347 // the moves, just to count them.
348 if (depth <= OnePly) // Replace with '<' to test also qsearch
350 while (mp.get_next_move()) sum++;
354 // Loop through all legal moves
356 while ((move = mp.get_next_move()) != MOVE_NONE)
359 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
360 sum += perft(pos, depth - OnePly);
367 /// think() is the external interface to Stockfish's search, and is called when
368 /// the program receives the UCI 'go' command. It initializes various
369 /// search-related global variables, and calls root_search(). It returns false
370 /// when a quit command is received during the search.
372 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
373 int time[], int increment[], int movesToGo, int maxDepth,
374 int maxNodes, int maxTime, Move searchMoves[]) {
376 // Initialize global search variables
377 Idle = StopOnPonderhit = AbortSearch = Quit = false;
378 FailHigh = FailLow = Problem = false;
380 SearchStartTime = get_system_time();
381 ExactMaxTime = maxTime;
384 InfiniteSearch = infinite;
385 PonderSearch = ponder;
386 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
388 // Look for a book move, only during games, not tests
389 if (UseTimeManagement && !ponder && get_option_value_bool("OwnBook"))
392 if (get_option_value_string("Book File") != OpeningBook.file_name())
393 OpeningBook.open(get_option_value_string("Book File"));
395 bookMove = OpeningBook.get_move(pos);
396 if (bookMove != MOVE_NONE)
398 cout << "bestmove " << bookMove << endl;
403 for (int i = 0; i < THREAD_MAX; i++)
405 Threads[i].nodes = 0ULL;
406 Threads[i].failHighPly1 = false;
409 if (button_was_pressed("New Game"))
410 loseOnTime = false; // Reset at the beginning of a new game
412 // Read UCI option values
413 TT.set_size(get_option_value_int("Hash"));
414 if (button_was_pressed("Clear Hash"))
417 bool PonderingEnabled = get_option_value_bool("Ponder");
418 MultiPV = get_option_value_int("MultiPV");
420 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
421 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
423 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
424 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
426 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
427 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
429 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
430 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
432 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
433 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
435 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
436 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
438 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
439 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
440 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
442 Chess960 = get_option_value_bool("UCI_Chess960");
443 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
444 UseLogFile = get_option_value_bool("Use Search Log");
446 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
448 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
449 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
451 read_weights(pos.side_to_move());
453 // Set the number of active threads
454 int newActiveThreads = get_option_value_int("Threads");
455 if (newActiveThreads != ActiveThreads)
457 ActiveThreads = newActiveThreads;
458 init_eval(ActiveThreads);
461 // Wake up sleeping threads
462 wake_sleeping_threads();
464 for (int i = 1; i < ActiveThreads; i++)
465 assert(thread_is_available(i, 0));
468 int myTime = time[side_to_move];
469 int myIncrement = increment[side_to_move];
470 if (UseTimeManagement)
472 if (!movesToGo) // Sudden death time control
476 MaxSearchTime = myTime / 30 + myIncrement;
477 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
479 else // Blitz game without increment
481 MaxSearchTime = myTime / 30;
482 AbsoluteMaxSearchTime = myTime / 8;
485 else // (x moves) / (y minutes)
489 MaxSearchTime = myTime / 2;
490 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
494 MaxSearchTime = myTime / Min(movesToGo, 20);
495 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
499 if (PonderingEnabled)
501 MaxSearchTime += MaxSearchTime / 4;
502 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
506 // Set best NodesBetweenPolls interval
508 NodesBetweenPolls = Min(MaxNodes, 30000);
509 else if (myTime && myTime < 1000)
510 NodesBetweenPolls = 1000;
511 else if (myTime && myTime < 5000)
512 NodesBetweenPolls = 5000;
514 NodesBetweenPolls = 30000;
516 // Write information to search log file
518 LogFile << "Searching: " << pos.to_fen() << endl
519 << "infinite: " << infinite
520 << " ponder: " << ponder
521 << " time: " << myTime
522 << " increment: " << myIncrement
523 << " moves to go: " << movesToGo << endl;
525 // LSN filtering. Used only for developing purpose. Disabled by default.
529 // Step 2. If after last move we decided to lose on time, do it now!
530 while (SearchStartTime + myTime + 1000 > get_system_time())
534 // We're ready to start thinking. Call the iterative deepening loop function
535 Value v = id_loop(pos, searchMoves);
540 // Step 1. If this is sudden death game and our position is hopeless,
541 // decide to lose on time.
542 if ( !loseOnTime // If we already lost on time, go to step 3.
552 // Step 3. Now after stepping over the time limit, reset flag for next match.
565 /// init_threads() is called during startup. It launches all helper threads,
566 /// and initializes the split point stack and the global locks and condition
569 #include <cmath> //FIXME: HACK
571 void init_threads() {
574 for (int i = 0; i < 512; i++)
575 lnArray[i] = log(double(i));
579 #if !defined(_MSC_VER)
580 pthread_t pthread[1];
583 for (i = 0; i < THREAD_MAX; i++)
584 Threads[i].activeSplitPoints = 0;
586 // Initialize global locks
587 lock_init(&MPLock, NULL);
588 lock_init(&IOLock, NULL);
590 init_split_point_stack();
592 #if !defined(_MSC_VER)
593 pthread_mutex_init(&WaitLock, NULL);
594 pthread_cond_init(&WaitCond, NULL);
596 for (i = 0; i < THREAD_MAX; i++)
597 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
600 // All threads except the main thread should be initialized to idle state
601 for (i = 1; i < THREAD_MAX; i++)
603 Threads[i].stop = false;
604 Threads[i].workIsWaiting = false;
605 Threads[i].idle = true;
606 Threads[i].running = false;
609 // Launch the helper threads
610 for (i = 1; i < THREAD_MAX; i++)
612 #if !defined(_MSC_VER)
613 pthread_create(pthread, NULL, init_thread, (void*)(&i));
616 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
619 // Wait until the thread has finished launching
620 while (!Threads[i].running);
625 /// stop_threads() is called when the program exits. It makes all the
626 /// helper threads exit cleanly.
628 void stop_threads() {
630 ActiveThreads = THREAD_MAX; // HACK
631 Idle = false; // HACK
632 wake_sleeping_threads();
633 AllThreadsShouldExit = true;
634 for (int i = 1; i < THREAD_MAX; i++)
636 Threads[i].stop = true;
637 while (Threads[i].running);
639 destroy_split_point_stack();
643 /// nodes_searched() returns the total number of nodes searched so far in
644 /// the current search.
646 int64_t nodes_searched() {
648 int64_t result = 0ULL;
649 for (int i = 0; i < ActiveThreads; i++)
650 result += Threads[i].nodes;
655 // SearchStack::init() initializes a search stack. Used at the beginning of a
656 // new search from the root.
657 void SearchStack::init(int ply) {
659 pv[ply] = pv[ply + 1] = MOVE_NONE;
660 currentMove = threatMove = MOVE_NONE;
661 reduction = Depth(0);
664 void SearchStack::initKillers() {
666 mateKiller = MOVE_NONE;
667 for (int i = 0; i < KILLER_MAX; i++)
668 killers[i] = MOVE_NONE;
673 // id_loop() is the main iterative deepening loop. It calls root_search
674 // repeatedly with increasing depth until the allocated thinking time has
675 // been consumed, the user stops the search, or the maximum search depth is
678 Value id_loop(const Position& pos, Move searchMoves[]) {
681 SearchStack ss[PLY_MAX_PLUS_2];
683 // searchMoves are verified, copied, scored and sorted
684 RootMoveList rml(p, searchMoves);
686 if (rml.move_count() == 0)
689 wait_for_stop_or_ponderhit();
691 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
694 // Print RootMoveList c'tor startup scoring to the standard output,
695 // so that we print information also for iteration 1.
696 cout << "info depth " << 1 << "\ninfo depth " << 1
697 << " score " << value_to_string(rml.get_move_score(0))
698 << " time " << current_search_time()
699 << " nodes " << nodes_searched()
701 << " pv " << rml.get_move(0) << "\n";
707 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
710 // Is one move significantly better than others after initial scoring ?
711 Move EasyMove = MOVE_NONE;
712 if ( rml.move_count() == 1
713 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
714 EasyMove = rml.get_move(0);
716 // Iterative deepening loop
717 while (Iteration < PLY_MAX)
719 // Initialize iteration
722 BestMoveChangesByIteration[Iteration] = 0;
726 cout << "info depth " << Iteration << endl;
728 // Calculate dynamic search window based on previous iterations
731 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
733 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
734 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
736 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
738 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
739 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
743 alpha = - VALUE_INFINITE;
744 beta = VALUE_INFINITE;
747 // Search to the current depth
748 Value value = root_search(p, ss, rml, alpha, beta);
750 // Write PV to transposition table, in case the relevant entries have
751 // been overwritten during the search.
752 TT.insert_pv(p, ss[0].pv);
755 break; // Value cannot be trusted. Break out immediately!
757 //Save info about search result
758 Value speculatedValue;
761 Value delta = value - IterationInfo[Iteration - 1].value;
768 speculatedValue = value + delta;
769 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
771 else if (value <= alpha)
773 assert(value == alpha);
777 speculatedValue = value + delta;
778 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
780 speculatedValue = value;
782 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
783 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
785 // Drop the easy move if it differs from the new best move
786 if (ss[0].pv[0] != EasyMove)
787 EasyMove = MOVE_NONE;
791 if (UseTimeManagement)
794 bool stopSearch = false;
796 // Stop search early if there is only a single legal move,
797 // we search up to Iteration 6 anyway to get a proper score.
798 if (Iteration >= 6 && rml.move_count() == 1)
801 // Stop search early when the last two iterations returned a mate score
803 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
804 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
807 // Stop search early if one move seems to be much better than the rest
808 int64_t nodes = nodes_searched();
812 && EasyMove == ss[0].pv[0]
813 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
814 && current_search_time() > MaxSearchTime / 16)
815 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
816 && current_search_time() > MaxSearchTime / 32)))
819 // Add some extra time if the best move has changed during the last two iterations
820 if (Iteration > 5 && Iteration <= 50)
821 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
822 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
824 // Stop search if most of MaxSearchTime is consumed at the end of the
825 // iteration. We probably don't have enough time to search the first
826 // move at the next iteration anyway.
827 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
835 StopOnPonderhit = true;
839 if (MaxDepth && Iteration >= MaxDepth)
845 // If we are pondering or in infinite search, we shouldn't print the
846 // best move before we are told to do so.
847 if (PonderSearch || InfiniteSearch)
848 wait_for_stop_or_ponderhit();
850 // Print final search statistics
851 cout << "info nodes " << nodes_searched()
853 << " time " << current_search_time()
854 << " hashfull " << TT.full() << endl;
856 // Print the best move and the ponder move to the standard output
857 if (ss[0].pv[0] == MOVE_NONE)
859 ss[0].pv[0] = rml.get_move(0);
860 ss[0].pv[1] = MOVE_NONE;
862 cout << "bestmove " << ss[0].pv[0];
863 if (ss[0].pv[1] != MOVE_NONE)
864 cout << " ponder " << ss[0].pv[1];
871 dbg_print_mean(LogFile);
873 if (dbg_show_hit_rate)
874 dbg_print_hit_rate(LogFile);
876 LogFile << "\nNodes: " << nodes_searched()
877 << "\nNodes/second: " << nps()
878 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
881 p.do_move(ss[0].pv[0], st);
882 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
884 return rml.get_move_score(0);
888 // root_search() is the function which searches the root node. It is
889 // similar to search_pv except that it uses a different move ordering
890 // scheme and prints some information to the standard output.
892 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
894 Value oldAlpha = alpha;
898 // Loop through all the moves in the root move list
899 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
903 // We failed high, invalidate and skip next moves, leave node-counters
904 // and beta-counters as they are and quickly return, we will try to do
905 // a research at the next iteration with a bigger aspiration window.
906 rml.set_move_score(i, -VALUE_INFINITE);
912 Depth depth, ext, newDepth;
914 RootMoveNumber = i + 1;
917 // Save the current node count before the move is searched
918 nodes = nodes_searched();
920 // Reset beta cut-off counters
923 // Pick the next root move, and print the move and the move number to
924 // the standard output.
925 move = ss[0].currentMove = rml.get_move(i);
927 if (current_search_time() >= 1000)
928 cout << "info currmove " << move
929 << " currmovenumber " << RootMoveNumber << endl;
931 // Decide search depth for this move
932 bool moveIsCheck = pos.move_is_check(move);
933 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
935 depth = (Iteration - 2) * OnePly + InitialDepth;
936 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
937 newDepth = depth + ext;
939 // Make the move, and search it
940 pos.do_move(move, st, ci, moveIsCheck);
944 // Aspiration window is disabled in multi-pv case
946 alpha = -VALUE_INFINITE;
948 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
950 // If the value has dropped a lot compared to the last iteration,
951 // set the boolean variable Problem to true. This variable is used
952 // for time managment: When Problem is true, we try to complete the
953 // current iteration before playing a move.
954 Problem = ( Iteration >= 2
955 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
957 if (Problem && StopOnPonderhit)
958 StopOnPonderhit = false;
962 // Try to reduce non-pv search depth by one ply if move seems not problematic,
963 // if the move fails high will be re-searched at full depth.
964 if ( depth >= 3*OnePly // FIXME was newDepth
966 && !captureOrPromotion
967 && !move_is_castle(move))
969 double red = 0.5 + ln(RootMoveNumber - MultiPV + 1) * ln(depth / 2) / 6.0;
972 ss[0].reduction = Depth(int(floor(red * int(OnePly))));
973 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
976 value = alpha + 1; // Just to trigger next condition
978 value = alpha + 1; // Just to trigger next condition
982 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
986 // Fail high! Set the boolean variable FailHigh to true, and
987 // re-search the move using a PV search. The variable FailHigh
988 // is used for time managment: We try to avoid aborting the
989 // search prematurely during a fail high research.
991 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
998 // Finished searching the move. If AbortSearch is true, the search
999 // was aborted because the user interrupted the search or because we
1000 // ran out of time. In this case, the return value of the search cannot
1001 // be trusted, and we break out of the loop without updating the best
1006 // Remember beta-cutoff and searched nodes counts for this move. The
1007 // info is used to sort the root moves at the next iteration.
1009 BetaCounter.read(pos.side_to_move(), our, their);
1010 rml.set_beta_counters(i, our, their);
1011 rml.set_move_nodes(i, nodes_searched() - nodes);
1013 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1015 if (value <= alpha && i >= MultiPV)
1016 rml.set_move_score(i, -VALUE_INFINITE);
1019 // PV move or new best move!
1022 rml.set_move_score(i, value);
1024 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1025 rml.set_move_pv(i, ss[0].pv);
1029 // We record how often the best move has been changed in each
1030 // iteration. This information is used for time managment: When
1031 // the best move changes frequently, we allocate some more time.
1033 BestMoveChangesByIteration[Iteration]++;
1035 // Print search information to the standard output
1036 cout << "info depth " << Iteration
1037 << " score " << value_to_string(value)
1038 << ((value >= beta) ? " lowerbound" :
1039 ((value <= alpha)? " upperbound" : ""))
1040 << " time " << current_search_time()
1041 << " nodes " << nodes_searched()
1045 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1046 cout << ss[0].pv[j] << " ";
1052 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1053 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1055 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1056 nodes_searched(), value, type, ss[0].pv) << endl;
1061 // Reset the global variable Problem to false if the value isn't too
1062 // far below the final value from the last iteration.
1063 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1068 rml.sort_multipv(i);
1069 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1071 cout << "info multipv " << j + 1
1072 << " score " << value_to_string(rml.get_move_score(j))
1073 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1074 << " time " << current_search_time()
1075 << " nodes " << nodes_searched()
1079 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1080 cout << rml.get_move_pv(j, k) << " ";
1084 alpha = rml.get_move_score(Min(i, MultiPV-1));
1086 } // PV move or new best move
1088 assert(alpha >= oldAlpha);
1090 FailLow = (alpha == oldAlpha);
1096 // search_pv() is the main search function for PV nodes.
1098 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1099 Depth depth, int ply, int threadID) {
1101 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1102 assert(beta > alpha && beta <= VALUE_INFINITE);
1103 assert(ply >= 0 && ply < PLY_MAX);
1104 assert(threadID >= 0 && threadID < ActiveThreads);
1106 Move movesSearched[256];
1111 Depth ext, newDepth;
1112 Value oldAlpha, value;
1113 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1115 Value bestValue = -VALUE_INFINITE;
1118 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1120 // Initialize, and make an early exit in case of an aborted search,
1121 // an instant draw, maximum ply reached, etc.
1122 init_node(ss, ply, threadID);
1124 // After init_node() that calls poll()
1125 if (AbortSearch || thread_should_stop(threadID))
1131 if (ply >= PLY_MAX - 1)
1132 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1134 // Mate distance pruning
1136 alpha = Max(value_mated_in(ply), alpha);
1137 beta = Min(value_mate_in(ply+1), beta);
1141 // Transposition table lookup. At PV nodes, we don't use the TT for
1142 // pruning, but only for move ordering. This is to avoid problems in
1143 // the following areas:
1145 // * Repetition draw detection
1146 // * Fifty move rule detection
1147 // * Searching for a mate
1148 // * Printing of full PV line
1150 tte = TT.retrieve(pos.get_key());
1151 ttMove = (tte ? tte->move() : MOVE_NONE);
1153 // Go with internal iterative deepening if we don't have a TT move
1154 if ( UseIIDAtPVNodes
1155 && depth >= 5*OnePly
1156 && ttMove == MOVE_NONE)
1158 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1159 ttMove = ss[ply].pv[ply];
1160 tte = TT.retrieve(pos.get_key());
1163 // Initialize a MovePicker object for the current position, and prepare
1164 // to search all moves
1165 isCheck = pos.is_check();
1166 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1168 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1170 // Loop through all legal moves until no moves remain or a beta cutoff
1172 while ( alpha < beta
1173 && (move = mp.get_next_move()) != MOVE_NONE
1174 && !thread_should_stop(threadID))
1176 assert(move_is_ok(move));
1178 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1179 moveIsCheck = pos.move_is_check(move, ci);
1180 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1182 // Decide the new search depth
1183 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1185 // Singular extension search. We extend the TT move if its value is much better than
1186 // its siblings. To verify this we do a reduced search on all the other moves but the
1187 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1188 if ( depth >= 6 * OnePly
1190 && move == tte->move()
1192 && is_lower_bound(tte->type())
1193 && tte->depth() >= depth - 3 * OnePly)
1195 Value ttValue = value_from_tt(tte->value(), ply);
1197 if (abs(ttValue) < VALUE_KNOWN_WIN)
1199 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1201 if (excValue < ttValue - SingleReplyMargin)
1206 newDepth = depth - OnePly + ext;
1208 // Update current move
1209 movesSearched[moveCount++] = ss[ply].currentMove = move;
1211 // Make and search the move
1212 pos.do_move(move, st, ci, moveIsCheck);
1214 if (moveCount == 1) // The first move in list is the PV
1215 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1218 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1219 // if the move fails high will be re-searched at full depth.
1220 if ( depth >= 3*OnePly
1222 && !captureOrPromotion
1223 && !move_is_castle(move)
1224 && !move_is_killer(move, ss[ply]))
1226 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 6.0;
1229 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1230 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1233 value = alpha + 1; // Just to trigger next condition
1236 value = alpha + 1; // Just to trigger next condition
1238 if (value > alpha) // Go with full depth non-pv search
1240 ss[ply].reduction = Depth(0);
1241 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1242 if (value > alpha && value < beta)
1244 // When the search fails high at ply 1 while searching the first
1245 // move at the root, set the flag failHighPly1. This is used for
1246 // time managment: We don't want to stop the search early in
1247 // such cases, because resolving the fail high at ply 1 could
1248 // result in a big drop in score at the root.
1249 if (ply == 1 && RootMoveNumber == 1)
1250 Threads[threadID].failHighPly1 = true;
1252 // A fail high occurred. Re-search at full window (pv search)
1253 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1254 Threads[threadID].failHighPly1 = false;
1258 pos.undo_move(move);
1260 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1263 if (value > bestValue)
1270 if (value == value_mate_in(ply + 1))
1271 ss[ply].mateKiller = move;
1273 // If we are at ply 1, and we are searching the first root move at
1274 // ply 0, set the 'Problem' variable if the score has dropped a lot
1275 // (from the computer's point of view) since the previous iteration.
1278 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1283 if ( ActiveThreads > 1
1285 && depth >= MinimumSplitDepth
1287 && idle_thread_exists(threadID)
1289 && !thread_should_stop(threadID)
1290 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1291 depth, &moveCount, &mp, threadID, true))
1295 // All legal moves have been searched. A special case: If there were
1296 // no legal moves, it must be mate or stalemate.
1298 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1300 // If the search is not aborted, update the transposition table,
1301 // history counters, and killer moves.
1302 if (AbortSearch || thread_should_stop(threadID))
1305 if (bestValue <= oldAlpha)
1306 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1308 else if (bestValue >= beta)
1310 BetaCounter.add(pos.side_to_move(), depth, threadID);
1311 move = ss[ply].pv[ply];
1312 if (!pos.move_is_capture_or_promotion(move))
1314 update_history(pos, move, depth, movesSearched, moveCount);
1315 update_killers(move, ss[ply]);
1317 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1320 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1326 // search() is the search function for zero-width nodes.
1328 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1329 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1331 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1332 assert(ply >= 0 && ply < PLY_MAX);
1333 assert(threadID >= 0 && threadID < ActiveThreads);
1335 Move movesSearched[256];
1340 Depth ext, newDepth;
1341 Value staticValue, nullValue, value, futilityValue, futilityValueScaled;
1342 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1343 bool mateThreat = false;
1345 Value bestValue = -VALUE_INFINITE;
1348 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1350 // Initialize, and make an early exit in case of an aborted search,
1351 // an instant draw, maximum ply reached, etc.
1352 init_node(ss, ply, threadID);
1354 // After init_node() that calls poll()
1355 if (AbortSearch || thread_should_stop(threadID))
1361 if (ply >= PLY_MAX - 1)
1362 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1364 // Mate distance pruning
1365 if (value_mated_in(ply) >= beta)
1368 if (value_mate_in(ply + 1) < beta)
1371 // We don't want the score of a partial search to overwrite a previous full search
1372 // TT value, so we use a different position key in case of an excluded move exsists.
1373 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1375 // Transposition table lookup
1376 tte = TT.retrieve(posKey);
1377 ttMove = (tte ? tte->move() : MOVE_NONE);
1379 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1381 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1382 return value_from_tt(tte->value(), ply);
1385 isCheck = pos.is_check();
1386 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1388 // Evaluate the position statically
1390 staticValue = quick_evaluate(pos);
1391 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1392 staticValue = value_from_tt(tte->value(), ply);
1394 staticValue = evaluate(pos, ei, threadID);
1396 // Calculate depth dependant futility pruning parameters
1397 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1398 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1400 // Enhance score accuracy with TT value if possible
1401 futilityValue = staticValue + FutilityValueMargin;
1402 staticValue = refine_eval(tte, staticValue, ply);
1408 && !value_is_mate(beta)
1409 && ok_to_do_nullmove(pos)
1410 && staticValue >= beta - NullMoveMargin)
1412 ss[ply].currentMove = MOVE_NULL;
1414 pos.do_null_move(st);
1416 // Null move dynamic reduction based on depth
1417 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1419 // Null move dynamic reduction based on value
1420 if (staticValue - beta > PawnValueMidgame)
1423 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1425 pos.undo_null_move();
1427 if (nullValue >= beta)
1429 if (depth < 6 * OnePly)
1432 // Do zugzwang verification search
1433 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1437 // The null move failed low, which means that we may be faced with
1438 // some kind of threat. If the previous move was reduced, check if
1439 // the move that refuted the null move was somehow connected to the
1440 // move which was reduced. If a connection is found, return a fail
1441 // low score (which will cause the reduced move to fail high in the
1442 // parent node, which will trigger a re-search with full depth).
1443 if (nullValue == value_mated_in(ply + 2))
1446 ss[ply].threatMove = ss[ply + 1].currentMove;
1447 if ( depth < ThreatDepth
1448 && ss[ply - 1].reduction
1449 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1453 // Null move search not allowed, try razoring
1454 else if ( !value_is_mate(beta)
1455 && depth < RazorDepth
1456 && staticValue < beta - RazorApprMargins[int(depth) - 2]
1457 && ss[ply - 1].currentMove != MOVE_NULL
1458 && ttMove == MOVE_NONE
1459 && !pos.has_pawn_on_7th(pos.side_to_move()))
1461 Value rbeta = beta - RazorMargins[int(depth) - 2];
1462 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1467 // Go with internal iterative deepening if we don't have a TT move
1468 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1469 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1471 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1472 ttMove = ss[ply].pv[ply];
1473 tte = TT.retrieve(pos.get_key());
1476 // Initialize a MovePicker object for the current position, and prepare
1477 // to search all moves.
1478 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1480 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1482 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1483 while ( bestValue < beta
1484 && (move = mp.get_next_move()) != MOVE_NONE
1485 && !thread_should_stop(threadID))
1487 assert(move_is_ok(move));
1489 if (move == excludedMove)
1492 moveIsCheck = pos.move_is_check(move, ci);
1493 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1494 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1496 // Decide the new search depth
1497 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1499 // Singular extension search. We extend the TT move if its value is much better than
1500 // its siblings. To verify this we do a reduced search on all the other moves but the
1501 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1502 if ( depth >= 8 * OnePly
1504 && move == tte->move()
1505 && !excludedMove // Do not allow recursive single-reply search
1507 && is_lower_bound(tte->type())
1508 && tte->depth() >= depth - 3 * OnePly)
1510 Value ttValue = value_from_tt(tte->value(), ply);
1512 if (abs(ttValue) < VALUE_KNOWN_WIN)
1514 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1516 if (excValue < ttValue - SingleReplyMargin)
1521 newDepth = depth - OnePly + ext;
1523 // Update current move
1524 movesSearched[moveCount++] = ss[ply].currentMove = move;
1527 if ( useFutilityPruning
1529 && !captureOrPromotion
1532 // Move count based pruning
1533 if ( moveCount >= FutilityMoveCountMargin
1534 && ok_to_prune(pos, move, ss[ply].threatMove)
1535 && bestValue > value_mated_in(PLY_MAX))
1538 // Value based pruning
1539 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1541 if (futilityValueScaled < beta)
1543 if (futilityValueScaled > bestValue)
1544 bestValue = futilityValueScaled;
1549 // Make and search the move
1550 pos.do_move(move, st, ci, moveIsCheck);
1552 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1553 // if the move fails high will be re-searched at full depth.
1554 if ( depth >= 3*OnePly
1556 && !captureOrPromotion
1557 && !move_is_castle(move)
1558 && !move_is_killer(move, ss[ply])
1559 /* && move != ttMove*/)
1561 double red = 0.5 + ln(moveCount) * ln(depth / 2) / 3.0;
1564 ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
1565 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1568 value = beta; // Just to trigger next condition
1571 value = beta; // Just to trigger next condition
1573 if (value >= beta) // Go with full depth non-pv search
1575 ss[ply].reduction = Depth(0);
1576 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1578 pos.undo_move(move);
1580 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1583 if (value > bestValue)
1589 if (value == value_mate_in(ply + 1))
1590 ss[ply].mateKiller = move;
1594 if ( ActiveThreads > 1
1596 && depth >= MinimumSplitDepth
1598 && idle_thread_exists(threadID)
1600 && !thread_should_stop(threadID)
1601 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1602 depth, &moveCount, &mp, threadID, false))
1606 // All legal moves have been searched. A special case: If there were
1607 // no legal moves, it must be mate or stalemate.
1609 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1611 // If the search is not aborted, update the transposition table,
1612 // history counters, and killer moves.
1613 if (AbortSearch || thread_should_stop(threadID))
1616 if (bestValue < beta)
1617 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1620 BetaCounter.add(pos.side_to_move(), depth, threadID);
1621 move = ss[ply].pv[ply];
1622 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1623 if (!pos.move_is_capture_or_promotion(move))
1625 update_history(pos, move, depth, movesSearched, moveCount);
1626 update_killers(move, ss[ply]);
1631 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1637 // qsearch() is the quiescence search function, which is called by the main
1638 // search function when the remaining depth is zero (or, to be more precise,
1639 // less than OnePly).
1641 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1642 Depth depth, int ply, int threadID) {
1644 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1645 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1647 assert(ply >= 0 && ply < PLY_MAX);
1648 assert(threadID >= 0 && threadID < ActiveThreads);
1653 Value staticValue, bestValue, value, futilityBase, futilityValue;
1654 bool isCheck, enoughMaterial, moveIsCheck;
1655 const TTEntry* tte = NULL;
1657 bool pvNode = (beta - alpha != 1);
1659 // Initialize, and make an early exit in case of an aborted search,
1660 // an instant draw, maximum ply reached, etc.
1661 init_node(ss, ply, threadID);
1663 // After init_node() that calls poll()
1664 if (AbortSearch || thread_should_stop(threadID))
1670 if (ply >= PLY_MAX - 1)
1671 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1673 // Transposition table lookup. At PV nodes, we don't use the TT for
1674 // pruning, but only for move ordering.
1675 tte = TT.retrieve(pos.get_key());
1676 ttMove = (tte ? tte->move() : MOVE_NONE);
1678 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1680 assert(tte->type() != VALUE_TYPE_EVAL);
1682 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1683 return value_from_tt(tte->value(), ply);
1686 isCheck = pos.is_check();
1687 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1689 // Evaluate the position statically
1691 staticValue = -VALUE_INFINITE;
1692 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1693 staticValue = value_from_tt(tte->value(), ply);
1695 staticValue = evaluate(pos, ei, threadID);
1697 // Initialize "stand pat score", and return it immediately if it is
1699 bestValue = staticValue;
1701 if (bestValue >= beta)
1703 // Store the score to avoid a future costly evaluation() call
1704 if (!isCheck && !tte && ei.futilityMargin == 0)
1705 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1710 if (bestValue > alpha)
1713 // Initialize a MovePicker object for the current position, and prepare
1714 // to search the moves. Because the depth is <= 0 here, only captures,
1715 // queen promotions and checks (only if depth == 0) will be generated.
1716 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1718 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1719 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;
1721 // Loop through the moves until no moves remain or a beta cutoff
1723 while ( alpha < beta
1724 && (move = mp.get_next_move()) != MOVE_NONE)
1726 assert(move_is_ok(move));
1728 moveIsCheck = pos.move_is_check(move, ci);
1730 // Update current move
1732 ss[ply].currentMove = move;
1740 && !move_is_promotion(move)
1741 && !pos.move_is_passed_pawn_push(move))
1743 futilityValue = futilityBase
1744 + pos.endgame_value_of_piece_on(move_to(move))
1745 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1747 if (futilityValue < alpha)
1749 if (futilityValue > bestValue)
1750 bestValue = futilityValue;
1755 // Don't search captures and checks with negative SEE values
1758 && !move_is_promotion(move)
1759 && pos.see_sign(move) < 0)
1762 // Make and search the move
1763 pos.do_move(move, st, ci, moveIsCheck);
1764 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1765 pos.undo_move(move);
1767 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1770 if (value > bestValue)
1781 // All legal moves have been searched. A special case: If we're in check
1782 // and no legal moves were found, it is checkmate.
1783 if (!moveCount && pos.is_check()) // Mate!
1784 return value_mated_in(ply);
1786 // Update transposition table
1787 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1788 if (bestValue < beta)
1790 // If bestValue isn't changed it means it is still the static evaluation
1791 // of the node, so keep this info to avoid a future evaluation() call.
1792 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1793 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1797 move = ss[ply].pv[ply];
1798 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1800 // Update killers only for good checking moves
1801 if (!pos.move_is_capture_or_promotion(move))
1802 update_killers(move, ss[ply]);
1805 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1811 // sp_search() is used to search from a split point. This function is called
1812 // by each thread working at the split point. It is similar to the normal
1813 // search() function, but simpler. Because we have already probed the hash
1814 // table, done a null move search, and searched the first move before
1815 // splitting, we don't have to repeat all this work in sp_search(). We
1816 // also don't need to store anything to the hash table here: This is taken
1817 // care of after we return from the split point.
1819 void sp_search(SplitPoint* sp, int threadID) {
1821 assert(threadID >= 0 && threadID < ActiveThreads);
1822 assert(ActiveThreads > 1);
1824 Position pos = Position(sp->pos);
1826 SearchStack* ss = sp->sstack[threadID];
1829 bool isCheck = pos.is_check();
1830 bool useFutilityPruning = sp->depth < SelectiveDepth
1833 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1834 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1836 while ( sp->bestValue < sp->beta
1837 && !thread_should_stop(threadID)
1838 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1840 assert(move_is_ok(move));
1842 bool moveIsCheck = pos.move_is_check(move, ci);
1843 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1845 lock_grab(&(sp->lock));
1846 int moveCount = ++sp->moves;
1847 lock_release(&(sp->lock));
1849 ss[sp->ply].currentMove = move;
1851 // Decide the new search depth.
1853 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1854 Depth newDepth = sp->depth - OnePly + ext;
1857 if ( useFutilityPruning
1859 && !captureOrPromotion)
1861 // Move count based pruning
1862 if ( moveCount >= FutilityMoveCountMargin
1863 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1864 && sp->bestValue > value_mated_in(PLY_MAX))
1867 // Value based pruning
1868 if (sp->futilityValue == VALUE_NONE)
1871 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1874 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1876 if (futilityValueScaled < sp->beta)
1878 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1880 lock_grab(&(sp->lock));
1881 if (futilityValueScaled > sp->bestValue)
1882 sp->bestValue = futilityValueScaled;
1883 lock_release(&(sp->lock));
1889 // Make and search the move.
1891 pos.do_move(move, st, ci, moveIsCheck);
1893 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1894 // if the move fails high will be re-searched at full depth.
1896 && !captureOrPromotion
1897 && !move_is_castle(move)
1898 && !move_is_killer(move, ss[sp->ply]))
1900 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 3.0;
1903 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
1904 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1907 value = sp->beta; // Just to trigger next condition
1910 value = sp->beta; // Just to trigger next condition
1912 if (value >= sp->beta) // Go with full depth non-pv search
1914 ss[sp->ply].reduction = Depth(0);
1915 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1917 pos.undo_move(move);
1919 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1921 if (thread_should_stop(threadID))
1925 if (value > sp->bestValue) // Less then 2% of cases
1927 lock_grab(&(sp->lock));
1928 if (value > sp->bestValue && !thread_should_stop(threadID))
1930 sp->bestValue = value;
1931 if (sp->bestValue >= sp->beta)
1933 sp_update_pv(sp->parentSstack, ss, sp->ply);
1934 for (int i = 0; i < ActiveThreads; i++)
1935 if (i != threadID && (i == sp->master || sp->slaves[i]))
1936 Threads[i].stop = true;
1938 sp->finished = true;
1941 lock_release(&(sp->lock));
1945 lock_grab(&(sp->lock));
1947 // If this is the master thread and we have been asked to stop because of
1948 // a beta cutoff higher up in the tree, stop all slave threads.
1949 if (sp->master == threadID && thread_should_stop(threadID))
1950 for (int i = 0; i < ActiveThreads; i++)
1952 Threads[i].stop = true;
1955 sp->slaves[threadID] = 0;
1957 lock_release(&(sp->lock));
1961 // sp_search_pv() is used to search from a PV split point. This function
1962 // is called by each thread working at the split point. It is similar to
1963 // the normal search_pv() function, but simpler. Because we have already
1964 // probed the hash table and searched the first move before splitting, we
1965 // don't have to repeat all this work in sp_search_pv(). We also don't
1966 // need to store anything to the hash table here: This is taken care of
1967 // after we return from the split point.
1969 void sp_search_pv(SplitPoint* sp, int threadID) {
1971 assert(threadID >= 0 && threadID < ActiveThreads);
1972 assert(ActiveThreads > 1);
1974 Position pos = Position(sp->pos);
1976 SearchStack* ss = sp->sstack[threadID];
1980 while ( sp->alpha < sp->beta
1981 && !thread_should_stop(threadID)
1982 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1984 bool moveIsCheck = pos.move_is_check(move, ci);
1985 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1987 assert(move_is_ok(move));
1989 lock_grab(&(sp->lock));
1990 int moveCount = ++sp->moves;
1991 lock_release(&(sp->lock));
1993 ss[sp->ply].currentMove = move;
1995 // Decide the new search depth.
1997 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1998 Depth newDepth = sp->depth - OnePly + ext;
2000 // Make and search the move.
2002 pos.do_move(move, st, ci, moveIsCheck);
2004 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2005 // if the move fails high will be re-searched at full depth.
2007 && !captureOrPromotion
2008 && !move_is_castle(move)
2009 && !move_is_killer(move, ss[sp->ply]))
2011 double red = 0.5 + ln(moveCount) * ln(sp->depth / 2) / 6.0;
2014 ss[sp->ply].reduction = Depth(int(floor(red * int(OnePly))));
2015 value = -search(pos, ss, -sp->alpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2018 value = sp->alpha + 1; // Just to trigger next condition
2021 value = sp->alpha + 1; // Just to trigger next condition
2023 if (value > sp->alpha) // Go with full depth non-pv search
2025 ss[sp->ply].reduction = Depth(0);
2026 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
2028 if (value > sp->alpha && value < sp->beta)
2030 // When the search fails high at ply 1 while searching the first
2031 // move at the root, set the flag failHighPly1. This is used for
2032 // time managment: We don't want to stop the search early in
2033 // such cases, because resolving the fail high at ply 1 could
2034 // result in a big drop in score at the root.
2035 if (sp->ply == 1 && RootMoveNumber == 1)
2036 Threads[threadID].failHighPly1 = true;
2038 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
2039 Threads[threadID].failHighPly1 = false;
2042 pos.undo_move(move);
2044 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2046 if (thread_should_stop(threadID))
2050 lock_grab(&(sp->lock));
2051 if (value > sp->bestValue && !thread_should_stop(threadID))
2053 sp->bestValue = value;
2054 if (value > sp->alpha)
2057 sp_update_pv(sp->parentSstack, ss, sp->ply);
2058 if (value == value_mate_in(sp->ply + 1))
2059 ss[sp->ply].mateKiller = move;
2061 if (value >= sp->beta)
2063 for (int i = 0; i < ActiveThreads; i++)
2064 if (i != threadID && (i == sp->master || sp->slaves[i]))
2065 Threads[i].stop = true;
2067 sp->finished = true;
2070 // If we are at ply 1, and we are searching the first root move at
2071 // ply 0, set the 'Problem' variable if the score has dropped a lot
2072 // (from the computer's point of view) since the previous iteration.
2075 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2078 lock_release(&(sp->lock));
2081 lock_grab(&(sp->lock));
2083 // If this is the master thread and we have been asked to stop because of
2084 // a beta cutoff higher up in the tree, stop all slave threads.
2085 if (sp->master == threadID && thread_should_stop(threadID))
2086 for (int i = 0; i < ActiveThreads; i++)
2088 Threads[i].stop = true;
2091 sp->slaves[threadID] = 0;
2093 lock_release(&(sp->lock));
2096 /// The BetaCounterType class
2098 BetaCounterType::BetaCounterType() { clear(); }
2100 void BetaCounterType::clear() {
2102 for (int i = 0; i < THREAD_MAX; i++)
2103 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2106 void BetaCounterType::add(Color us, Depth d, int threadID) {
2108 // Weighted count based on depth
2109 Threads[threadID].betaCutOffs[us] += unsigned(d);
2112 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2115 for (int i = 0; i < THREAD_MAX; i++)
2117 our += Threads[i].betaCutOffs[us];
2118 their += Threads[i].betaCutOffs[opposite_color(us)];
2123 /// The RootMoveList class
2125 // RootMoveList c'tor
2127 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2129 MoveStack mlist[MaxRootMoves];
2130 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2132 // Generate all legal moves
2133 MoveStack* last = generate_moves(pos, mlist);
2135 // Add each move to the moves[] array
2136 for (MoveStack* cur = mlist; cur != last; cur++)
2138 bool includeMove = includeAllMoves;
2140 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2141 includeMove = (searchMoves[k] == cur->move);
2146 // Find a quick score for the move
2148 SearchStack ss[PLY_MAX_PLUS_2];
2151 moves[count].move = cur->move;
2152 pos.do_move(moves[count].move, st);
2153 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2154 pos.undo_move(moves[count].move);
2155 moves[count].pv[0] = moves[count].move;
2156 moves[count].pv[1] = MOVE_NONE;
2163 // RootMoveList simple methods definitions
2165 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2167 moves[moveNum].nodes = nodes;
2168 moves[moveNum].cumulativeNodes += nodes;
2171 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2173 moves[moveNum].ourBeta = our;
2174 moves[moveNum].theirBeta = their;
2177 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2181 for (j = 0; pv[j] != MOVE_NONE; j++)
2182 moves[moveNum].pv[j] = pv[j];
2184 moves[moveNum].pv[j] = MOVE_NONE;
2188 // RootMoveList::sort() sorts the root move list at the beginning of a new
2191 void RootMoveList::sort() {
2193 sort_multipv(count - 1); // Sort all items
2197 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2198 // list by their scores and depths. It is used to order the different PVs
2199 // correctly in MultiPV mode.
2201 void RootMoveList::sort_multipv(int n) {
2205 for (i = 1; i <= n; i++)
2207 RootMove rm = moves[i];
2208 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2209 moves[j] = moves[j - 1];
2216 // init_node() is called at the beginning of all the search functions
2217 // (search(), search_pv(), qsearch(), and so on) and initializes the
2218 // search stack object corresponding to the current node. Once every
2219 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2220 // for user input and checks whether it is time to stop the search.
2222 void init_node(SearchStack ss[], int ply, int threadID) {
2224 assert(ply >= 0 && ply < PLY_MAX);
2225 assert(threadID >= 0 && threadID < ActiveThreads);
2227 Threads[threadID].nodes++;
2232 if (NodesSincePoll >= NodesBetweenPolls)
2239 ss[ply + 2].initKillers();
2241 if (Threads[threadID].printCurrentLine)
2242 print_current_line(ss, ply, threadID);
2246 // update_pv() is called whenever a search returns a value > alpha.
2247 // It updates the PV in the SearchStack object corresponding to the
2250 void update_pv(SearchStack ss[], int ply) {
2252 assert(ply >= 0 && ply < PLY_MAX);
2256 ss[ply].pv[ply] = ss[ply].currentMove;
2258 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2259 ss[ply].pv[p] = ss[ply + 1].pv[p];
2261 ss[ply].pv[p] = MOVE_NONE;
2265 // sp_update_pv() is a variant of update_pv for use at split points. The
2266 // difference between the two functions is that sp_update_pv also updates
2267 // the PV at the parent node.
2269 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2271 assert(ply >= 0 && ply < PLY_MAX);
2275 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2277 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2278 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2280 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2284 // connected_moves() tests whether two moves are 'connected' in the sense
2285 // that the first move somehow made the second move possible (for instance
2286 // if the moving piece is the same in both moves). The first move is assumed
2287 // to be the move that was made to reach the current position, while the
2288 // second move is assumed to be a move from the current position.
2290 bool connected_moves(const Position& pos, Move m1, Move m2) {
2292 Square f1, t1, f2, t2;
2295 assert(move_is_ok(m1));
2296 assert(move_is_ok(m2));
2298 if (m2 == MOVE_NONE)
2301 // Case 1: The moving piece is the same in both moves
2307 // Case 2: The destination square for m2 was vacated by m1
2313 // Case 3: Moving through the vacated square
2314 if ( piece_is_slider(pos.piece_on(f2))
2315 && bit_is_set(squares_between(f2, t2), f1))
2318 // Case 4: The destination square for m2 is defended by the moving piece in m1
2319 p = pos.piece_on(t1);
2320 if (bit_is_set(pos.attacks_from(p, t1), t2))
2323 // Case 5: Discovered check, checking piece is the piece moved in m1
2324 if ( piece_is_slider(p)
2325 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2326 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2328 // discovered_check_candidates() works also if the Position's side to
2329 // move is the opposite of the checking piece.
2330 Color them = opposite_color(pos.side_to_move());
2331 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2333 if (bit_is_set(dcCandidates, f2))
2340 // value_is_mate() checks if the given value is a mate one
2341 // eventually compensated for the ply.
2343 bool value_is_mate(Value value) {
2345 assert(abs(value) <= VALUE_INFINITE);
2347 return value <= value_mated_in(PLY_MAX)
2348 || value >= value_mate_in(PLY_MAX);
2352 // move_is_killer() checks if the given move is among the
2353 // killer moves of that ply.
2355 bool move_is_killer(Move m, const SearchStack& ss) {
2357 const Move* k = ss.killers;
2358 for (int i = 0; i < KILLER_MAX; i++, k++)
2366 // extension() decides whether a move should be searched with normal depth,
2367 // or with extended depth. Certain classes of moves (checking moves, in
2368 // particular) are searched with bigger depth than ordinary moves and in
2369 // any case are marked as 'dangerous'. Note that also if a move is not
2370 // extended, as example because the corresponding UCI option is set to zero,
2371 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2373 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2374 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2376 assert(m != MOVE_NONE);
2378 Depth result = Depth(0);
2379 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2384 result += CheckExtension[pvNode];
2387 result += SingleEvasionExtension[pvNode];
2390 result += MateThreatExtension[pvNode];
2393 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2395 Color c = pos.side_to_move();
2396 if (relative_rank(c, move_to(m)) == RANK_7)
2398 result += PawnPushTo7thExtension[pvNode];
2401 if (pos.pawn_is_passed(c, move_to(m)))
2403 result += PassedPawnExtension[pvNode];
2408 if ( captureOrPromotion
2409 && pos.type_of_piece_on(move_to(m)) != PAWN
2410 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2411 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2412 && !move_is_promotion(m)
2415 result += PawnEndgameExtension[pvNode];
2420 && captureOrPromotion
2421 && pos.type_of_piece_on(move_to(m)) != PAWN
2422 && pos.see_sign(m) >= 0)
2428 return Min(result, OnePly);
2432 // ok_to_do_nullmove() looks at the current position and decides whether
2433 // doing a 'null move' should be allowed. In order to avoid zugzwang
2434 // problems, null moves are not allowed when the side to move has very
2435 // little material left. Currently, the test is a bit too simple: Null
2436 // moves are avoided only when the side to move has only pawns left.
2437 // It's probably a good idea to avoid null moves in at least some more
2438 // complicated endgames, e.g. KQ vs KR. FIXME
2440 bool ok_to_do_nullmove(const Position& pos) {
2442 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2446 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2447 // non-tactical moves late in the move list close to the leaves are
2448 // candidates for pruning.
2450 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2452 assert(move_is_ok(m));
2453 assert(threat == MOVE_NONE || move_is_ok(threat));
2454 assert(!pos.move_is_check(m));
2455 assert(!pos.move_is_capture_or_promotion(m));
2456 assert(!pos.move_is_passed_pawn_push(m));
2458 Square mfrom, mto, tfrom, tto;
2460 // Prune if there isn't any threat move and
2461 // is not a castling move (common case).
2462 if (threat == MOVE_NONE && !move_is_castle(m))
2465 mfrom = move_from(m);
2467 tfrom = move_from(threat);
2468 tto = move_to(threat);
2470 // Case 1: Castling moves are never pruned
2471 if (move_is_castle(m))
2474 // Case 2: Don't prune moves which move the threatened piece
2478 // Case 3: If the threatened piece has value less than or equal to the
2479 // value of the threatening piece, don't prune move which defend it.
2480 if ( pos.move_is_capture(threat)
2481 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2482 || pos.type_of_piece_on(tfrom) == KING)
2483 && pos.move_attacks_square(m, tto))
2486 // Case 4: If the moving piece in the threatened move is a slider, don't
2487 // prune safe moves which block its ray.
2488 if ( piece_is_slider(pos.piece_on(tfrom))
2489 && bit_is_set(squares_between(tfrom, tto), mto)
2490 && pos.see_sign(m) >= 0)
2497 // ok_to_use_TT() returns true if a transposition table score
2498 // can be used at a given point in search.
2500 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2502 Value v = value_from_tt(tte->value(), ply);
2504 return ( tte->depth() >= depth
2505 || v >= Max(value_mate_in(PLY_MAX), beta)
2506 || v < Min(value_mated_in(PLY_MAX), beta))
2508 && ( (is_lower_bound(tte->type()) && v >= beta)
2509 || (is_upper_bound(tte->type()) && v < beta));
2513 // refine_eval() returns the transposition table score if
2514 // possible otherwise falls back on static position evaluation.
2516 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2521 Value v = value_from_tt(tte->value(), ply);
2523 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2524 || (is_upper_bound(tte->type()) && v < defaultEval))
2530 // update_history() registers a good move that produced a beta-cutoff
2531 // in history and marks as failures all the other moves of that ply.
2533 void update_history(const Position& pos, Move move, Depth depth,
2534 Move movesSearched[], int moveCount) {
2538 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2540 for (int i = 0; i < moveCount - 1; i++)
2542 m = movesSearched[i];
2546 if (!pos.move_is_capture_or_promotion(m))
2547 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2552 // update_killers() add a good move that produced a beta-cutoff
2553 // among the killer moves of that ply.
2555 void update_killers(Move m, SearchStack& ss) {
2557 if (m == ss.killers[0])
2560 for (int i = KILLER_MAX - 1; i > 0; i--)
2561 ss.killers[i] = ss.killers[i - 1];
2567 // fail_high_ply_1() checks if some thread is currently resolving a fail
2568 // high at ply 1 at the node below the first root node. This information
2569 // is used for time management.
2571 bool fail_high_ply_1() {
2573 for (int i = 0; i < ActiveThreads; i++)
2574 if (Threads[i].failHighPly1)
2581 // current_search_time() returns the number of milliseconds which have passed
2582 // since the beginning of the current search.
2584 int current_search_time() {
2586 return get_system_time() - SearchStartTime;
2590 // nps() computes the current nodes/second count.
2594 int t = current_search_time();
2595 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2599 // poll() performs two different functions: It polls for user input, and it
2600 // looks at the time consumed so far and decides if it's time to abort the
2605 static int lastInfoTime;
2606 int t = current_search_time();
2611 // We are line oriented, don't read single chars
2612 std::string command;
2614 if (!std::getline(std::cin, command))
2617 if (command == "quit")
2620 PonderSearch = false;
2624 else if (command == "stop")
2627 PonderSearch = false;
2629 else if (command == "ponderhit")
2633 // Print search information
2637 else if (lastInfoTime > t)
2638 // HACK: Must be a new search where we searched less than
2639 // NodesBetweenPolls nodes during the first second of search.
2642 else if (t - lastInfoTime >= 1000)
2650 if (dbg_show_hit_rate)
2651 dbg_print_hit_rate();
2653 cout << "info nodes " << nodes_searched() << " nps " << nps()
2654 << " time " << t << " hashfull " << TT.full() << endl;
2656 lock_release(&IOLock);
2658 if (ShowCurrentLine)
2659 Threads[0].printCurrentLine = true;
2662 // Should we stop the search?
2666 bool stillAtFirstMove = RootMoveNumber == 1
2668 && t > MaxSearchTime + ExtraSearchTime;
2670 bool noProblemFound = !FailHigh
2672 && !fail_high_ply_1()
2674 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2676 bool noMoreTime = t > AbsoluteMaxSearchTime
2677 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2680 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2681 || (ExactMaxTime && t >= ExactMaxTime)
2682 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2687 // ponderhit() is called when the program is pondering (i.e. thinking while
2688 // it's the opponent's turn to move) in order to let the engine know that
2689 // it correctly predicted the opponent's move.
2693 int t = current_search_time();
2694 PonderSearch = false;
2696 bool stillAtFirstMove = RootMoveNumber == 1
2698 && t > MaxSearchTime + ExtraSearchTime;
2700 bool noProblemFound = !FailHigh
2702 && !fail_high_ply_1()
2704 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2706 bool noMoreTime = t > AbsoluteMaxSearchTime
2710 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2715 // print_current_line() prints the current line of search for a given
2716 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2718 void print_current_line(SearchStack ss[], int ply, int threadID) {
2720 assert(ply >= 0 && ply < PLY_MAX);
2721 assert(threadID >= 0 && threadID < ActiveThreads);
2723 if (!Threads[threadID].idle)
2726 cout << "info currline " << (threadID + 1);
2727 for (int p = 0; p < ply; p++)
2728 cout << " " << ss[p].currentMove;
2731 lock_release(&IOLock);
2733 Threads[threadID].printCurrentLine = false;
2734 if (threadID + 1 < ActiveThreads)
2735 Threads[threadID + 1].printCurrentLine = true;
2739 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2741 void init_ss_array(SearchStack ss[]) {
2743 for (int i = 0; i < 3; i++)
2746 ss[i].initKillers();
2751 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2752 // while the program is pondering. The point is to work around a wrinkle in
2753 // the UCI protocol: When pondering, the engine is not allowed to give a
2754 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2755 // We simply wait here until one of these commands is sent, and return,
2756 // after which the bestmove and pondermove will be printed (in id_loop()).
2758 void wait_for_stop_or_ponderhit() {
2760 std::string command;
2764 if (!std::getline(std::cin, command))
2767 if (command == "quit")
2772 else if (command == "ponderhit" || command == "stop")
2778 // idle_loop() is where the threads are parked when they have no work to do.
2779 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2780 // object for which the current thread is the master.
2782 void idle_loop(int threadID, SplitPoint* waitSp) {
2784 assert(threadID >= 0 && threadID < THREAD_MAX);
2786 Threads[threadID].running = true;
2790 if (AllThreadsShouldExit && threadID != 0)
2793 // If we are not thinking, wait for a condition to be signaled
2794 // instead of wasting CPU time polling for work.
2795 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2798 #if !defined(_MSC_VER)
2799 pthread_mutex_lock(&WaitLock);
2800 if (Idle || threadID >= ActiveThreads)
2801 pthread_cond_wait(&WaitCond, &WaitLock);
2803 pthread_mutex_unlock(&WaitLock);
2805 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2809 // If this thread has been assigned work, launch a search
2810 if (Threads[threadID].workIsWaiting)
2812 Threads[threadID].workIsWaiting = false;
2813 if (Threads[threadID].splitPoint->pvNode)
2814 sp_search_pv(Threads[threadID].splitPoint, threadID);
2816 sp_search(Threads[threadID].splitPoint, threadID);
2818 Threads[threadID].idle = true;
2821 // If this thread is the master of a split point and all threads have
2822 // finished their work at this split point, return from the idle loop.
2823 if (waitSp != NULL && waitSp->cpus == 0)
2827 Threads[threadID].running = false;
2831 // init_split_point_stack() is called during program initialization, and
2832 // initializes all split point objects.
2834 void init_split_point_stack() {
2836 for (int i = 0; i < THREAD_MAX; i++)
2837 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2839 SplitPointStack[i][j].parent = NULL;
2840 lock_init(&(SplitPointStack[i][j].lock), NULL);
2845 // destroy_split_point_stack() is called when the program exits, and
2846 // destroys all locks in the precomputed split point objects.
2848 void destroy_split_point_stack() {
2850 for (int i = 0; i < THREAD_MAX; i++)
2851 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2852 lock_destroy(&(SplitPointStack[i][j].lock));
2856 // thread_should_stop() checks whether the thread with a given threadID has
2857 // been asked to stop, directly or indirectly. This can happen if a beta
2858 // cutoff has occurred in the thread's currently active split point, or in
2859 // some ancestor of the current split point.
2861 bool thread_should_stop(int threadID) {
2863 assert(threadID >= 0 && threadID < ActiveThreads);
2867 if (Threads[threadID].stop)
2869 if (ActiveThreads <= 2)
2871 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2874 Threads[threadID].stop = true;
2881 // thread_is_available() checks whether the thread with threadID "slave" is
2882 // available to help the thread with threadID "master" at a split point. An
2883 // obvious requirement is that "slave" must be idle. With more than two
2884 // threads, this is not by itself sufficient: If "slave" is the master of
2885 // some active split point, it is only available as a slave to the other
2886 // threads which are busy searching the split point at the top of "slave"'s
2887 // split point stack (the "helpful master concept" in YBWC terminology).
2889 bool thread_is_available(int slave, int master) {
2891 assert(slave >= 0 && slave < ActiveThreads);
2892 assert(master >= 0 && master < ActiveThreads);
2893 assert(ActiveThreads > 1);
2895 if (!Threads[slave].idle || slave == master)
2898 if (Threads[slave].activeSplitPoints == 0)
2899 // No active split points means that the thread is available as
2900 // a slave for any other thread.
2903 if (ActiveThreads == 2)
2906 // Apply the "helpful master" concept if possible
2907 if (SplitPointStack[slave][Threads[slave].activeSplitPoints - 1].slaves[master])
2914 // idle_thread_exists() tries to find an idle thread which is available as
2915 // a slave for the thread with threadID "master".
2917 bool idle_thread_exists(int master) {
2919 assert(master >= 0 && master < ActiveThreads);
2920 assert(ActiveThreads > 1);
2922 for (int i = 0; i < ActiveThreads; i++)
2923 if (thread_is_available(i, master))
2930 // split() does the actual work of distributing the work at a node between
2931 // several threads at PV nodes. If it does not succeed in splitting the
2932 // node (because no idle threads are available, or because we have no unused
2933 // split point objects), the function immediately returns false. If
2934 // splitting is possible, a SplitPoint object is initialized with all the
2935 // data that must be copied to the helper threads (the current position and
2936 // search stack, alpha, beta, the search depth, etc.), and we tell our
2937 // helper threads that they have been assigned work. This will cause them
2938 // to instantly leave their idle loops and call sp_search_pv(). When all
2939 // threads have returned from sp_search_pv (or, equivalently, when
2940 // splitPoint->cpus becomes 0), split() returns true.
2942 bool split(const Position& p, SearchStack* sstck, int ply,
2943 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2944 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2947 assert(sstck != NULL);
2948 assert(ply >= 0 && ply < PLY_MAX);
2949 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2950 assert(!pvNode || *alpha < *beta);
2951 assert(*beta <= VALUE_INFINITE);
2952 assert(depth > Depth(0));
2953 assert(master >= 0 && master < ActiveThreads);
2954 assert(ActiveThreads > 1);
2956 SplitPoint* splitPoint;
2961 // If no other thread is available to help us, or if we have too many
2962 // active split points, don't split.
2963 if ( !idle_thread_exists(master)
2964 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2966 lock_release(&MPLock);
2970 // Pick the next available split point object from the split point stack
2971 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2972 Threads[master].activeSplitPoints++;
2974 // Initialize the split point object and copy current position
2975 splitPoint->parent = Threads[master].splitPoint;
2976 splitPoint->finished = false;
2977 splitPoint->ply = ply;
2978 splitPoint->depth = depth;
2979 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2980 splitPoint->beta = *beta;
2981 splitPoint->pvNode = pvNode;
2982 splitPoint->bestValue = *bestValue;
2983 splitPoint->futilityValue = futilityValue;
2984 splitPoint->master = master;
2985 splitPoint->mp = mp;
2986 splitPoint->moves = *moves;
2987 splitPoint->cpus = 1;
2988 splitPoint->pos.copy(p);
2989 splitPoint->parentSstack = sstck;
2990 for (i = 0; i < ActiveThreads; i++)
2991 splitPoint->slaves[i] = 0;
2993 // Copy the current search stack to the master thread
2994 memcpy(splitPoint->sstack[master], sstck, (ply+1) * sizeof(SearchStack));
2995 Threads[master].splitPoint = splitPoint;
2997 // Make copies of the current position and search stack for each thread
2998 for (i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2999 if (thread_is_available(i, master))
3001 memcpy(splitPoint->sstack[i], sstck, (ply+1) * sizeof(SearchStack));
3002 Threads[i].splitPoint = splitPoint;
3003 splitPoint->slaves[i] = 1;
3007 // Tell the threads that they have work to do. This will make them leave
3009 for (i = 0; i < ActiveThreads; i++)
3010 if (i == master || splitPoint->slaves[i])
3012 Threads[i].workIsWaiting = true;
3013 Threads[i].idle = false;
3014 Threads[i].stop = false;
3017 lock_release(&MPLock);
3019 // Everything is set up. The master thread enters the idle loop, from
3020 // which it will instantly launch a search, because its workIsWaiting
3021 // slot is 'true'. We send the split point as a second parameter to the
3022 // idle loop, which means that the main thread will return from the idle
3023 // loop when all threads have finished their work at this split point
3024 // (i.e. when splitPoint->cpus == 0).
3025 idle_loop(master, splitPoint);
3027 // We have returned from the idle loop, which means that all threads are
3028 // finished. Update alpha, beta and bestValue, and return.
3032 *alpha = splitPoint->alpha;
3034 *beta = splitPoint->beta;
3035 *bestValue = splitPoint->bestValue;
3036 Threads[master].stop = false;
3037 Threads[master].idle = false;
3038 Threads[master].activeSplitPoints--;
3039 Threads[master].splitPoint = splitPoint->parent;
3041 lock_release(&MPLock);
3046 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3047 // to start a new search from the root.
3049 void wake_sleeping_threads() {
3051 if (ActiveThreads > 1)
3053 for (int i = 1; i < ActiveThreads; i++)
3055 Threads[i].idle = true;
3056 Threads[i].workIsWaiting = false;
3059 #if !defined(_MSC_VER)
3060 pthread_mutex_lock(&WaitLock);
3061 pthread_cond_broadcast(&WaitCond);
3062 pthread_mutex_unlock(&WaitLock);
3064 for (int i = 1; i < THREAD_MAX; i++)
3065 SetEvent(SitIdleEvent[i]);
3071 // init_thread() is the function which is called when a new thread is
3072 // launched. It simply calls the idle_loop() function with the supplied
3073 // threadID. There are two versions of this function; one for POSIX
3074 // threads and one for Windows threads.
3076 #if !defined(_MSC_VER)
3078 void* init_thread(void *threadID) {
3080 idle_loop(*(int*)threadID, NULL);
3086 DWORD WINAPI init_thread(LPVOID threadID) {
3088 idle_loop(*(int*)threadID, NULL);