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 Value FutilityMargins[2 * PLY_MAX_PLUS_2]; // Initialized at startup.
190 // Each move futility margin is decreased
191 const Value IncrementalFutilityMargin = Value(0x8);
193 // Depth limit for razoring
194 const Depth RazorDepth = 4 * OnePly;
196 /// Variables initialized by UCI options
198 // Depth limit for use of dynamic threat detection
201 // Last seconds noise filtering (LSN)
202 const bool UseLSNFiltering = true;
203 const int LSNTime = 4000; // In milliseconds
204 const Value LSNValue = value_from_centipawns(200);
205 bool loseOnTime = false;
207 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
208 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
209 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
211 // Iteration counters
213 BetaCounterType BetaCounter;
215 // Scores and number of times the best move changed for each iteration
216 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
217 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
219 // Search window management
225 // Time managment variables
228 int MaxNodes, MaxDepth;
229 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
230 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
231 bool AbortSearch, Quit;
232 bool FailHigh, FailLow, Problem;
234 // Show current line?
235 bool ShowCurrentLine;
239 std::ofstream LogFile;
241 // Natural logarithmic lookup table and its getter function
243 inline float ln(int i) { return lnArray[i]; }
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;
273 Value id_loop(const Position& pos, Move searchMoves[]);
274 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
275 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
276 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
277 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
278 void sp_search(SplitPoint* sp, int threadID);
279 void sp_search_pv(SplitPoint* sp, int threadID);
280 void init_node(SearchStack ss[], int ply, int threadID);
281 void update_pv(SearchStack ss[], int ply);
282 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
283 bool connected_moves(const Position& pos, Move m1, Move m2);
284 bool value_is_mate(Value value);
285 bool move_is_killer(Move m, const SearchStack& ss);
286 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
287 bool ok_to_do_nullmove(const Position& pos);
288 bool ok_to_prune(const Position& pos, Move m, Move threat);
289 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
290 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
291 void reduction_parameters(float base, float Inhibitor, Depth depth, float& logLimit, float& gradient);
292 Depth reduction(int moveCount, const float LogLimit, const float BaseRed, const float Gradient);
293 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
294 void update_killers(Move m, SearchStack& ss);
295 void update_gains(const Position& pos, Move move, Value before, Value after);
297 bool fail_high_ply_1();
298 int current_search_time();
302 void print_current_line(SearchStack ss[], int ply, int threadID);
303 void wait_for_stop_or_ponderhit();
304 void init_ss_array(SearchStack ss[]);
306 void idle_loop(int threadID, SplitPoint* waitSp);
307 void init_split_point_stack();
308 void destroy_split_point_stack();
309 bool thread_should_stop(int threadID);
310 bool thread_is_available(int slave, int master);
311 bool idle_thread_exists(int master);
312 bool split(const Position& pos, SearchStack* ss, int ply,
313 Value *alpha, Value *beta, Value *bestValue,
314 const Value futilityValue, Depth depth, int *moves,
315 MovePicker *mp, int master, bool pvNode);
316 void wake_sleeping_threads();
318 #if !defined(_MSC_VER)
319 void *init_thread(void *threadID);
321 DWORD WINAPI init_thread(LPVOID threadID);
332 /// perft() is our utility to verify move generation is bug free. All the legal
333 /// moves up to given depth are generated and counted and the sum returned.
335 int perft(Position& pos, Depth depth)
339 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
341 // If we are at the last ply we don't need to do and undo
342 // the moves, just to count them.
343 if (depth <= OnePly) // Replace with '<' to test also qsearch
345 while (mp.get_next_move()) sum++;
349 // Loop through all legal moves
351 while ((move = mp.get_next_move()) != MOVE_NONE)
354 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
355 sum += perft(pos, depth - OnePly);
362 /// think() is the external interface to Stockfish's search, and is called when
363 /// the program receives the UCI 'go' command. It initializes various
364 /// search-related global variables, and calls root_search(). It returns false
365 /// when a quit command is received during the search.
367 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
368 int time[], int increment[], int movesToGo, int maxDepth,
369 int maxNodes, int maxTime, Move searchMoves[]) {
371 // Initialize global search variables
372 Idle = StopOnPonderhit = AbortSearch = Quit = false;
373 FailHigh = FailLow = Problem = false;
375 SearchStartTime = get_system_time();
376 ExactMaxTime = maxTime;
379 InfiniteSearch = infinite;
380 PonderSearch = ponder;
381 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
383 // Look for a book move, only during games, not tests
384 if (UseTimeManagement && !ponder && get_option_value_bool("OwnBook"))
387 if (get_option_value_string("Book File") != OpeningBook.file_name())
388 OpeningBook.open(get_option_value_string("Book File"));
390 bookMove = OpeningBook.get_move(pos);
391 if (bookMove != MOVE_NONE)
393 cout << "bestmove " << bookMove << endl;
398 for (int i = 0; i < THREAD_MAX; i++)
400 Threads[i].nodes = 0ULL;
401 Threads[i].failHighPly1 = false;
404 if (button_was_pressed("New Game"))
405 loseOnTime = false; // Reset at the beginning of a new game
407 // Read UCI option values
408 TT.set_size(get_option_value_int("Hash"));
409 if (button_was_pressed("Clear Hash"))
412 bool PonderingEnabled = get_option_value_bool("Ponder");
413 MultiPV = get_option_value_int("MultiPV");
415 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
416 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
418 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
419 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
421 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
422 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
424 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
425 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
427 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
428 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
430 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
431 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
433 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
435 Chess960 = get_option_value_bool("UCI_Chess960");
436 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
437 UseLogFile = get_option_value_bool("Use Search Log");
439 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
441 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
442 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
444 read_weights(pos.side_to_move());
446 // Set the number of active threads
447 int newActiveThreads = get_option_value_int("Threads");
448 if (newActiveThreads != ActiveThreads)
450 ActiveThreads = newActiveThreads;
451 init_eval(ActiveThreads);
452 // HACK: init_eval() destroys the static castleRightsMask[] array in the
453 // Position class. The below line repairs the damage.
454 Position p(pos.to_fen());
458 // Wake up sleeping threads
459 wake_sleeping_threads();
461 for (int i = 1; i < ActiveThreads; i++)
462 assert(thread_is_available(i, 0));
465 int myTime = time[side_to_move];
466 int myIncrement = increment[side_to_move];
467 if (UseTimeManagement)
469 if (!movesToGo) // Sudden death time control
473 MaxSearchTime = myTime / 30 + myIncrement;
474 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
476 else // Blitz game without increment
478 MaxSearchTime = myTime / 30;
479 AbsoluteMaxSearchTime = myTime / 8;
482 else // (x moves) / (y minutes)
486 MaxSearchTime = myTime / 2;
487 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
491 MaxSearchTime = myTime / Min(movesToGo, 20);
492 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
496 if (PonderingEnabled)
498 MaxSearchTime += MaxSearchTime / 4;
499 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
503 // Set best NodesBetweenPolls interval
505 NodesBetweenPolls = Min(MaxNodes, 30000);
506 else if (myTime && myTime < 1000)
507 NodesBetweenPolls = 1000;
508 else if (myTime && myTime < 5000)
509 NodesBetweenPolls = 5000;
511 NodesBetweenPolls = 30000;
513 // Write information to search log file
515 LogFile << "Searching: " << pos.to_fen() << endl
516 << "infinite: " << infinite
517 << " ponder: " << ponder
518 << " time: " << myTime
519 << " increment: " << myIncrement
520 << " moves to go: " << movesToGo << endl;
522 // LSN filtering. Used only for developing purpose. Disabled by default.
526 // Step 2. If after last move we decided to lose on time, do it now!
527 while (SearchStartTime + myTime + 1000 > get_system_time())
531 // We're ready to start thinking. Call the iterative deepening loop function
532 Value v = id_loop(pos, searchMoves);
536 // Step 1. If this is sudden death game and our position is hopeless,
537 // decide to lose on time.
538 if ( !loseOnTime // If we already lost on time, go to step 3.
548 // Step 3. Now after stepping over the time limit, reset flag for next match.
561 /// init_threads() is called during startup. It launches all helper threads,
562 /// and initializes the split point stack and the global locks and condition
565 void init_threads() {
570 #if !defined(_MSC_VER)
571 pthread_t pthread[1];
574 // Init our logarithmic lookup table
575 for (i = 0; i < 512; i++)
576 lnArray[i] = float(log(double(i))); // log() returns base-e logarithm
578 for (i = 0; i < THREAD_MAX; i++)
579 Threads[i].activeSplitPoints = 0;
581 // Init futility margins array
582 FutilityMargins[0] = FutilityMargins[1] = Value(0);
584 for (i = 2; i < 2 * PLY_MAX_PLUS_2; i++)
586 FutilityMargins[i] = Value(112 * bitScanReverse32(i * i / 2)); // FIXME: test using log instead of BSR
589 // Initialize global locks
590 lock_init(&MPLock, NULL);
591 lock_init(&IOLock, NULL);
593 init_split_point_stack();
595 #if !defined(_MSC_VER)
596 pthread_mutex_init(&WaitLock, NULL);
597 pthread_cond_init(&WaitCond, NULL);
599 for (i = 0; i < THREAD_MAX; i++)
600 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
603 // All threads except the main thread should be initialized to idle state
604 for (i = 1; i < THREAD_MAX; i++)
606 Threads[i].stop = false;
607 Threads[i].workIsWaiting = false;
608 Threads[i].idle = true;
609 Threads[i].running = false;
612 // Launch the helper threads
613 for (i = 1; i < THREAD_MAX; i++)
615 #if !defined(_MSC_VER)
616 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
619 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
624 cout << "Failed to create thread number " << i << endl;
625 Application::exit_with_failure();
628 // Wait until the thread has finished launching
629 while (!Threads[i].running);
634 /// stop_threads() is called when the program exits. It makes all the
635 /// helper threads exit cleanly.
637 void stop_threads() {
639 ActiveThreads = THREAD_MAX; // HACK
640 Idle = false; // HACK
641 wake_sleeping_threads();
642 AllThreadsShouldExit = true;
643 for (int i = 1; i < THREAD_MAX; i++)
645 Threads[i].stop = true;
646 while (Threads[i].running);
648 destroy_split_point_stack();
652 /// nodes_searched() returns the total number of nodes searched so far in
653 /// the current search.
655 int64_t nodes_searched() {
657 int64_t result = 0ULL;
658 for (int i = 0; i < ActiveThreads; i++)
659 result += Threads[i].nodes;
664 // SearchStack::init() initializes a search stack. Used at the beginning of a
665 // new search from the root.
666 void SearchStack::init(int ply) {
668 pv[ply] = pv[ply + 1] = MOVE_NONE;
669 currentMove = threatMove = MOVE_NONE;
670 reduction = Depth(0);
675 void SearchStack::initKillers() {
677 mateKiller = MOVE_NONE;
678 for (int i = 0; i < KILLER_MAX; i++)
679 killers[i] = MOVE_NONE;
684 // id_loop() is the main iterative deepening loop. It calls root_search
685 // repeatedly with increasing depth until the allocated thinking time has
686 // been consumed, the user stops the search, or the maximum search depth is
689 Value id_loop(const Position& pos, Move searchMoves[]) {
692 SearchStack ss[PLY_MAX_PLUS_2];
694 // searchMoves are verified, copied, scored and sorted
695 RootMoveList rml(p, searchMoves);
697 // Handle special case of searching on a mate/stale position
698 if (rml.move_count() == 0)
701 wait_for_stop_or_ponderhit();
703 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
706 // Print RootMoveList c'tor startup scoring to the standard output,
707 // so that we print information also for iteration 1.
708 cout << "info depth " << 1 << "\ninfo depth " << 1
709 << " score " << value_to_string(rml.get_move_score(0))
710 << " time " << current_search_time()
711 << " nodes " << nodes_searched()
713 << " pv " << rml.get_move(0) << "\n";
719 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
722 // Is one move significantly better than others after initial scoring ?
723 Move EasyMove = MOVE_NONE;
724 if ( rml.move_count() == 1
725 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
726 EasyMove = rml.get_move(0);
728 // Iterative deepening loop
729 while (Iteration < PLY_MAX)
731 // Initialize iteration
734 BestMoveChangesByIteration[Iteration] = 0;
738 cout << "info depth " << Iteration << endl;
740 // Calculate dynamic search window based on previous iterations
743 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
745 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
746 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
748 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
749 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
751 alpha = Max(IterationInfo[Iteration - 1].value - AspirationDelta, -VALUE_INFINITE);
752 beta = Min(IterationInfo[Iteration - 1].value + AspirationDelta, VALUE_INFINITE);
756 alpha = - VALUE_INFINITE;
757 beta = VALUE_INFINITE;
760 // Search to the current depth
761 Value value = root_search(p, ss, rml, alpha, beta);
763 // Write PV to transposition table, in case the relevant entries have
764 // been overwritten during the search.
765 TT.insert_pv(p, ss[0].pv);
768 break; // Value cannot be trusted. Break out immediately!
770 //Save info about search result
771 Value speculatedValue;
774 Value delta = value - IterationInfo[Iteration - 1].value;
781 speculatedValue = value + delta;
782 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
784 else if (value <= alpha)
786 assert(value == alpha);
790 speculatedValue = value + delta;
791 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
793 speculatedValue = value;
795 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
796 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
798 // Drop the easy move if it differs from the new best move
799 if (ss[0].pv[0] != EasyMove)
800 EasyMove = MOVE_NONE;
804 if (UseTimeManagement)
807 bool stopSearch = false;
809 // Stop search early if there is only a single legal move,
810 // we search up to Iteration 6 anyway to get a proper score.
811 if (Iteration >= 6 && rml.move_count() == 1)
814 // Stop search early when the last two iterations returned a mate score
816 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
817 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
820 // Stop search early if one move seems to be much better than the rest
821 int64_t nodes = nodes_searched();
825 && EasyMove == ss[0].pv[0]
826 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
827 && current_search_time() > MaxSearchTime / 16)
828 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
829 && current_search_time() > MaxSearchTime / 32)))
832 // Add some extra time if the best move has changed during the last two iterations
833 if (Iteration > 5 && Iteration <= 50)
834 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
835 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
837 // Stop search if most of MaxSearchTime is consumed at the end of the
838 // iteration. We probably don't have enough time to search the first
839 // move at the next iteration anyway.
840 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
848 StopOnPonderhit = true;
852 if (MaxDepth && Iteration >= MaxDepth)
858 // If we are pondering or in infinite search, we shouldn't print the
859 // best move before we are told to do so.
860 if (!AbortSearch && (PonderSearch || InfiniteSearch))
861 wait_for_stop_or_ponderhit();
863 // Print final search statistics
864 cout << "info nodes " << nodes_searched()
866 << " time " << current_search_time()
867 << " hashfull " << TT.full() << endl;
869 // Print the best move and the ponder move to the standard output
870 if (ss[0].pv[0] == MOVE_NONE)
872 ss[0].pv[0] = rml.get_move(0);
873 ss[0].pv[1] = MOVE_NONE;
875 cout << "bestmove " << ss[0].pv[0];
876 if (ss[0].pv[1] != MOVE_NONE)
877 cout << " ponder " << ss[0].pv[1];
884 dbg_print_mean(LogFile);
886 if (dbg_show_hit_rate)
887 dbg_print_hit_rate(LogFile);
889 LogFile << "\nNodes: " << nodes_searched()
890 << "\nNodes/second: " << nps()
891 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
894 p.do_move(ss[0].pv[0], st);
895 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
897 return rml.get_move_score(0);
901 // root_search() is the function which searches the root node. It is
902 // similar to search_pv except that it uses a different move ordering
903 // scheme and prints some information to the standard output.
905 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
910 Depth depth, ext, newDepth;
913 int researchCount = 0;
914 bool moveIsCheck, captureOrPromotion, dangerous;
915 Value alpha = oldAlpha;
916 bool isCheck = pos.is_check();
918 // Evaluate the position statically
920 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
922 while (1) // Fail low loop
925 // Loop through all the moves in the root move list
926 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
930 // We failed high, invalidate and skip next moves, leave node-counters
931 // and beta-counters as they are and quickly return, we will try to do
932 // a research at the next iteration with a bigger aspiration window.
933 rml.set_move_score(i, -VALUE_INFINITE);
937 RootMoveNumber = i + 1;
940 // Save the current node count before the move is searched
941 nodes = nodes_searched();
943 // Reset beta cut-off counters
946 // Pick the next root move, and print the move and the move number to
947 // the standard output.
948 move = ss[0].currentMove = rml.get_move(i);
950 if (current_search_time() >= 1000)
951 cout << "info currmove " << move
952 << " currmovenumber " << RootMoveNumber << endl;
954 // Decide search depth for this move
955 moveIsCheck = pos.move_is_check(move);
956 captureOrPromotion = pos.move_is_capture_or_promotion(move);
957 depth = (Iteration - 2) * OnePly + InitialDepth;
958 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
959 newDepth = depth + ext;
961 value = - VALUE_INFINITE;
963 // Precalculate reduction parameters
964 float LogLimit, Gradient, BaseReduction = 0.5;
965 reduction_parameters(BaseReduction, 6.0, depth, LogLimit, Gradient);
967 while (1) // Fail high loop
970 // Make the move, and search it
971 pos.do_move(move, st, ci, moveIsCheck);
973 if (i < MultiPV || value > alpha)
975 // Aspiration window is disabled in multi-pv case
977 alpha = -VALUE_INFINITE;
979 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
981 // If the value has dropped a lot compared to the last iteration,
982 // set the boolean variable Problem to true. This variable is used
983 // for time managment: When Problem is true, we try to complete the
984 // current iteration before playing a move.
985 Problem = ( Iteration >= 2
986 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
988 if (Problem && StopOnPonderhit)
989 StopOnPonderhit = false;
993 // Try to reduce non-pv search depth by one ply if move seems not problematic,
994 // if the move fails high will be re-searched at full depth.
995 bool doFullDepthSearch = true;
997 if ( depth >= 3*OnePly // FIXME was newDepth
999 && !captureOrPromotion
1000 && !move_is_castle(move))
1002 ss[0].reduction = reduction(RootMoveNumber - MultiPV + 1, LogLimit, BaseReduction, Gradient);
1003 if (ss[0].reduction)
1005 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
1006 doFullDepthSearch = (value > alpha);
1010 if (doFullDepthSearch)
1012 ss[0].reduction = Depth(0);
1013 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
1017 // Fail high! Set the boolean variable FailHigh to true, and
1018 // re-search the move using a PV search. The variable FailHigh
1019 // is used for time managment: We try to avoid aborting the
1020 // search prematurely during a fail high research.
1022 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
1027 pos.undo_move(move);
1029 // Can we exit fail high loop ?
1030 if (AbortSearch || value < beta)
1033 // We are failing high and going to do a research. It's important to update score
1034 // before research in case we run out of time while researching.
1035 rml.set_move_score(i, value);
1037 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1038 rml.set_move_pv(i, ss[0].pv);
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;
1064 // Prepare for a research after a fail high, each time with a wider window
1066 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
1068 } // End of fail high loop
1070 // Finished searching the move. If AbortSearch is true, the search
1071 // was aborted because the user interrupted the search or because we
1072 // ran out of time. In this case, the return value of the search cannot
1073 // be trusted, and we break out of the loop without updating the best
1078 // Remember beta-cutoff and searched nodes counts for this move. The
1079 // info is used to sort the root moves at the next iteration.
1081 BetaCounter.read(pos.side_to_move(), our, their);
1082 rml.set_beta_counters(i, our, their);
1083 rml.set_move_nodes(i, nodes_searched() - nodes);
1085 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1087 if (value <= alpha && i >= MultiPV)
1088 rml.set_move_score(i, -VALUE_INFINITE);
1091 // PV move or new best move!
1094 rml.set_move_score(i, value);
1096 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1097 rml.set_move_pv(i, ss[0].pv);
1101 // We record how often the best move has been changed in each
1102 // iteration. This information is used for time managment: When
1103 // the best move changes frequently, we allocate some more time.
1105 BestMoveChangesByIteration[Iteration]++;
1107 // Print search information to the standard output
1108 cout << "info depth " << Iteration
1109 << " score " << value_to_string(value)
1110 << ((value >= beta) ? " lowerbound" :
1111 ((value <= alpha)? " upperbound" : ""))
1112 << " time " << current_search_time()
1113 << " nodes " << nodes_searched()
1117 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1118 cout << ss[0].pv[j] << " ";
1124 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1125 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1127 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1128 nodes_searched(), value, type, ss[0].pv) << endl;
1133 // Reset the global variable Problem to false if the value isn't too
1134 // far below the final value from the last iteration.
1135 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1140 rml.sort_multipv(i);
1141 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1143 cout << "info multipv " << j + 1
1144 << " score " << value_to_string(rml.get_move_score(j))
1145 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1146 << " time " << current_search_time()
1147 << " nodes " << nodes_searched()
1151 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1152 cout << rml.get_move_pv(j, k) << " ";
1156 alpha = rml.get_move_score(Min(i, MultiPV-1));
1158 } // PV move or new best move
1160 assert(alpha >= oldAlpha);
1162 FailLow = (alpha == oldAlpha);
1165 // Can we exit fail low loop ?
1166 if (AbortSearch || alpha > oldAlpha)
1169 // Prepare for a research after a fail low, each time with a wider window
1171 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1180 // search_pv() is the main search function for PV nodes.
1182 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1183 Depth depth, int ply, int threadID) {
1185 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1186 assert(beta > alpha && beta <= VALUE_INFINITE);
1187 assert(ply >= 0 && ply < PLY_MAX);
1188 assert(threadID >= 0 && threadID < ActiveThreads);
1190 Move movesSearched[256];
1194 Depth ext, newDepth;
1195 Value oldAlpha, value;
1196 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1198 Value bestValue = value = -VALUE_INFINITE;
1201 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1203 // Initialize, and make an early exit in case of an aborted search,
1204 // an instant draw, maximum ply reached, etc.
1205 init_node(ss, ply, threadID);
1207 // After init_node() that calls poll()
1208 if (AbortSearch || thread_should_stop(threadID))
1211 if (pos.is_draw() || ply >= PLY_MAX - 1)
1214 // Mate distance pruning
1216 alpha = Max(value_mated_in(ply), alpha);
1217 beta = Min(value_mate_in(ply+1), beta);
1221 // Transposition table lookup. At PV nodes, we don't use the TT for
1222 // pruning, but only for move ordering. This is to avoid problems in
1223 // the following areas:
1225 // * Repetition draw detection
1226 // * Fifty move rule detection
1227 // * Searching for a mate
1228 // * Printing of full PV line
1230 tte = TT.retrieve(pos.get_key());
1231 ttMove = (tte ? tte->move() : MOVE_NONE);
1233 // Go with internal iterative deepening if we don't have a TT move
1234 if ( UseIIDAtPVNodes
1235 && depth >= 5*OnePly
1236 && ttMove == MOVE_NONE)
1238 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1239 ttMove = ss[ply].pv[ply];
1240 tte = TT.retrieve(pos.get_key());
1243 isCheck = pos.is_check();
1246 // Update gain statistics of the previous move that lead
1247 // us in this position.
1249 ss[ply].eval = evaluate(pos, ei, threadID);
1250 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1253 // Initialize a MovePicker object for the current position, and prepare
1254 // to search all moves
1255 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1257 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1259 // Precalculate reduction parameters
1260 float LogLimit, Gradient, BaseReduction = 0.5;
1261 reduction_parameters(BaseReduction, 6.0, depth, LogLimit, Gradient);
1263 // Loop through all legal moves until no moves remain or a beta cutoff
1265 while ( alpha < beta
1266 && (move = mp.get_next_move()) != MOVE_NONE
1267 && !thread_should_stop(threadID))
1269 assert(move_is_ok(move));
1271 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1272 moveIsCheck = pos.move_is_check(move, ci);
1273 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1275 // Decide the new search depth
1276 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1278 // Singular extension search. We extend the TT move if its value is much better than
1279 // its siblings. To verify this we do a reduced search on all the other moves but the
1280 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1281 if ( depth >= 6 * OnePly
1283 && move == tte->move()
1285 && is_lower_bound(tte->type())
1286 && tte->depth() >= depth - 3 * OnePly)
1288 Value ttValue = value_from_tt(tte->value(), ply);
1290 if (abs(ttValue) < VALUE_KNOWN_WIN)
1292 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1294 if (excValue < ttValue - SingleReplyMargin)
1299 newDepth = depth - OnePly + ext;
1301 // Update current move
1302 movesSearched[moveCount++] = ss[ply].currentMove = move;
1304 // Make and search the move
1305 pos.do_move(move, st, ci, moveIsCheck);
1307 if (moveCount == 1) // The first move in list is the PV
1308 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1311 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1312 // if the move fails high will be re-searched at full depth.
1313 bool doFullDepthSearch = true;
1315 if ( depth >= 3*OnePly
1317 && !captureOrPromotion
1318 && !move_is_castle(move)
1319 && !move_is_killer(move, ss[ply]))
1321 ss[ply].reduction = reduction(moveCount, LogLimit, BaseReduction, Gradient);
1322 if (ss[ply].reduction)
1324 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1325 doFullDepthSearch = (value > alpha);
1329 if (doFullDepthSearch) // Go with full depth non-pv search
1331 ss[ply].reduction = Depth(0);
1332 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1333 if (value > alpha && value < beta)
1335 // When the search fails high at ply 1 while searching the first
1336 // move at the root, set the flag failHighPly1. This is used for
1337 // time managment: We don't want to stop the search early in
1338 // such cases, because resolving the fail high at ply 1 could
1339 // result in a big drop in score at the root.
1340 if (ply == 1 && RootMoveNumber == 1)
1341 Threads[threadID].failHighPly1 = true;
1343 // A fail high occurred. Re-search at full window (pv search)
1344 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1345 Threads[threadID].failHighPly1 = false;
1349 pos.undo_move(move);
1351 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1354 if (value > bestValue)
1361 if (value == value_mate_in(ply + 1))
1362 ss[ply].mateKiller = move;
1364 // If we are at ply 1, and we are searching the first root move at
1365 // ply 0, set the 'Problem' variable if the score has dropped a lot
1366 // (from the computer's point of view) since the previous iteration.
1369 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1374 if ( ActiveThreads > 1
1376 && depth >= MinimumSplitDepth
1378 && idle_thread_exists(threadID)
1380 && !thread_should_stop(threadID)
1381 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1382 depth, &moveCount, &mp, threadID, true))
1386 // All legal moves have been searched. A special case: If there were
1387 // no legal moves, it must be mate or stalemate.
1389 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1391 // If the search is not aborted, update the transposition table,
1392 // history counters, and killer moves.
1393 if (AbortSearch || thread_should_stop(threadID))
1396 if (bestValue <= oldAlpha)
1397 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1399 else if (bestValue >= beta)
1401 BetaCounter.add(pos.side_to_move(), depth, threadID);
1402 move = ss[ply].pv[ply];
1403 if (!pos.move_is_capture_or_promotion(move))
1405 update_history(pos, move, depth, movesSearched, moveCount);
1406 update_killers(move, ss[ply]);
1408 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1411 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1417 // search() is the search function for zero-width nodes.
1419 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1420 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1422 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1423 assert(ply >= 0 && ply < PLY_MAX);
1424 assert(threadID >= 0 && threadID < ActiveThreads);
1426 Move movesSearched[256];
1431 Depth ext, newDepth;
1432 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1433 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1434 bool mateThreat = false;
1436 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1439 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1441 // Initialize, and make an early exit in case of an aborted search,
1442 // an instant draw, maximum ply reached, etc.
1443 init_node(ss, ply, threadID);
1445 // After init_node() that calls poll()
1446 if (AbortSearch || thread_should_stop(threadID))
1449 if (pos.is_draw() || ply >= PLY_MAX - 1)
1452 // Mate distance pruning
1453 if (value_mated_in(ply) >= beta)
1456 if (value_mate_in(ply + 1) < beta)
1459 // We don't want the score of a partial search to overwrite a previous full search
1460 // TT value, so we use a different position key in case of an excluded move exsists.
1461 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1463 // Transposition table lookup
1464 tte = TT.retrieve(posKey);
1465 ttMove = (tte ? tte->move() : MOVE_NONE);
1467 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1469 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1470 return value_from_tt(tte->value(), ply);
1473 isCheck = pos.is_check();
1475 // Calculate depth dependant futility pruning parameters
1476 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1478 // Evaluate the position statically
1481 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1482 staticValue = value_from_tt(tte->value(), ply);
1485 staticValue = evaluate(pos, ei, threadID);
1486 ss[ply].evalInfo = &ei;
1489 ss[ply].eval = staticValue;
1490 futilityValue = staticValue + FutilityMargins[int(depth)]; //FIXME: Remove me, only for split
1491 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1492 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1495 // Do a "stand pat". If we are above beta by a good margin then
1496 // return immediately.
1499 && depth < RazorDepth
1500 && staticValue - FutilityMargins[int(depth)] >= beta)
1501 return staticValue - FutilityMargins[int(depth)];
1507 && !value_is_mate(beta)
1508 && ok_to_do_nullmove(pos)
1509 && staticValue >= beta - NullMoveMargin)
1511 ss[ply].currentMove = MOVE_NULL;
1513 pos.do_null_move(st);
1515 // Null move dynamic reduction based on depth
1516 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1518 // Null move dynamic reduction based on value
1519 if (staticValue - beta > PawnValueMidgame)
1522 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1524 pos.undo_null_move();
1526 if (nullValue >= beta)
1528 if (depth < 6 * OnePly)
1531 // Do zugzwang verification search
1532 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1536 // The null move failed low, which means that we may be faced with
1537 // some kind of threat. If the previous move was reduced, check if
1538 // the move that refuted the null move was somehow connected to the
1539 // move which was reduced. If a connection is found, return a fail
1540 // low score (which will cause the reduced move to fail high in the
1541 // parent node, which will trigger a re-search with full depth).
1542 if (nullValue == value_mated_in(ply + 2))
1545 ss[ply].threatMove = ss[ply + 1].currentMove;
1546 if ( depth < ThreatDepth
1547 && ss[ply - 1].reduction
1548 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1552 // Null move search not allowed, try razoring
1553 else if ( !value_is_mate(beta)
1555 && depth < RazorDepth
1556 && staticValue < beta - (NullMoveMargin + 16 * depth)
1557 && ss[ply - 1].currentMove != MOVE_NULL
1558 && ttMove == MOVE_NONE
1559 && !pos.has_pawn_on_7th(pos.side_to_move()))
1561 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1562 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1567 // Go with internal iterative deepening if we don't have a TT move
1568 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1569 !isCheck && ss[ply].eval >= beta - IIDMargin)
1571 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1572 ttMove = ss[ply].pv[ply];
1573 tte = TT.retrieve(pos.get_key());
1576 // Initialize a MovePicker object for the current position, and prepare
1577 // to search all moves.
1578 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1581 // Precalculate reduction parameters
1582 float LogLimit, Gradient, BaseReduction = 0.5;
1583 reduction_parameters(BaseReduction, 3.0, depth, LogLimit, Gradient);
1585 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1586 while ( bestValue < beta
1587 && (move = mp.get_next_move()) != MOVE_NONE
1588 && !thread_should_stop(threadID))
1590 assert(move_is_ok(move));
1592 if (move == excludedMove)
1595 moveIsCheck = pos.move_is_check(move, ci);
1596 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1597 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1599 // Decide the new search depth
1600 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1602 // Singular extension search. We extend the TT move if its value is much better than
1603 // its siblings. To verify this we do a reduced search on all the other moves but the
1604 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1605 if ( depth >= 8 * OnePly
1607 && move == tte->move()
1608 && !excludedMove // Do not allow recursive single-reply search
1610 && is_lower_bound(tte->type())
1611 && tte->depth() >= depth - 3 * OnePly)
1613 Value ttValue = value_from_tt(tte->value(), ply);
1615 if (abs(ttValue) < VALUE_KNOWN_WIN)
1617 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1619 if (excValue < ttValue - SingleReplyMargin)
1624 newDepth = depth - OnePly + ext;
1626 // Update current move
1627 movesSearched[moveCount++] = ss[ply].currentMove = move;
1632 && !captureOrPromotion
1633 && !move_is_castle(move)
1636 // Move count based pruning
1637 if ( moveCount >= FutilityMoveCountMargin
1638 && ok_to_prune(pos, move, ss[ply].threatMove)
1639 && bestValue > value_mated_in(PLY_MAX))
1642 // Value based pruning
1643 Depth predictedDepth = newDepth;
1645 //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1646 ss[ply].reduction = reduction(moveCount, LogLimit, BaseReduction, Gradient);
1647 if (ss[ply].reduction)
1648 predictedDepth -= ss[ply].reduction;
1650 if (predictedDepth < SelectiveDepth)
1652 int preFutilityValueMargin = 0;
1653 if (predictedDepth >= OnePly)
1654 preFutilityValueMargin = FutilityMargins[int(predictedDepth)];
1656 preFutilityValueMargin += H.gain(pos.piece_on(move_from(move)), move_from(move), move_to(move)) + 45;
1658 futilityValueScaled = ss[ply].eval + preFutilityValueMargin - moveCount * IncrementalFutilityMargin;
1660 if (futilityValueScaled < beta)
1662 if (futilityValueScaled > bestValue)
1663 bestValue = futilityValueScaled;
1669 // Make and search the move
1670 pos.do_move(move, st, ci, moveIsCheck);
1672 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1673 // if the move fails high will be re-searched at full depth.
1674 bool doFullDepthSearch = true;
1676 if ( depth >= 3*OnePly
1678 && !captureOrPromotion
1679 && !move_is_castle(move)
1680 && !move_is_killer(move, ss[ply]))
1682 ss[ply].reduction = reduction(moveCount, LogLimit, BaseReduction, Gradient);
1683 if (ss[ply].reduction)
1685 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1686 doFullDepthSearch = (value >= beta);
1690 if (doFullDepthSearch) // Go with full depth non-pv search
1692 ss[ply].reduction = Depth(0);
1693 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1695 pos.undo_move(move);
1697 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1700 if (value > bestValue)
1706 if (value == value_mate_in(ply + 1))
1707 ss[ply].mateKiller = move;
1711 if ( ActiveThreads > 1
1713 && depth >= MinimumSplitDepth
1715 && idle_thread_exists(threadID)
1717 && !thread_should_stop(threadID)
1718 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1719 depth, &moveCount, &mp, threadID, false))
1723 // All legal moves have been searched. A special case: If there were
1724 // no legal moves, it must be mate or stalemate.
1726 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1728 // If the search is not aborted, update the transposition table,
1729 // history counters, and killer moves.
1730 if (AbortSearch || thread_should_stop(threadID))
1733 if (bestValue < beta)
1734 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1737 BetaCounter.add(pos.side_to_move(), depth, threadID);
1738 move = ss[ply].pv[ply];
1739 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1740 if (!pos.move_is_capture_or_promotion(move))
1742 update_history(pos, move, depth, movesSearched, moveCount);
1743 update_killers(move, ss[ply]);
1748 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1754 // qsearch() is the quiescence search function, which is called by the main
1755 // search function when the remaining depth is zero (or, to be more precise,
1756 // less than OnePly).
1758 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1759 Depth depth, int ply, int threadID) {
1761 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1762 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1764 assert(ply >= 0 && ply < PLY_MAX);
1765 assert(threadID >= 0 && threadID < ActiveThreads);
1770 Value staticValue, bestValue, value, futilityBase, futilityValue;
1771 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1772 const TTEntry* tte = NULL;
1774 bool pvNode = (beta - alpha != 1);
1775 Value oldAlpha = alpha;
1777 // Initialize, and make an early exit in case of an aborted search,
1778 // an instant draw, maximum ply reached, etc.
1779 init_node(ss, ply, threadID);
1781 // After init_node() that calls poll()
1782 if (AbortSearch || thread_should_stop(threadID))
1785 if (pos.is_draw() || ply >= PLY_MAX - 1)
1788 // Transposition table lookup. At PV nodes, we don't use the TT for
1789 // pruning, but only for move ordering.
1790 tte = TT.retrieve(pos.get_key());
1791 ttMove = (tte ? tte->move() : MOVE_NONE);
1793 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1795 assert(tte->type() != VALUE_TYPE_EVAL);
1797 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1798 return value_from_tt(tte->value(), ply);
1801 isCheck = pos.is_check();
1803 // Evaluate the position statically
1805 staticValue = -VALUE_INFINITE;
1806 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1807 staticValue = value_from_tt(tte->value(), ply);
1809 staticValue = evaluate(pos, ei, threadID);
1813 ss[ply].eval = staticValue;
1814 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1817 // Initialize "stand pat score", and return it immediately if it is
1819 bestValue = staticValue;
1821 if (bestValue >= beta)
1823 // Store the score to avoid a future costly evaluation() call
1824 if (!isCheck && !tte && ei.futilityMargin == 0)
1825 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1830 if (bestValue > alpha)
1833 // If we are near beta then try to get a cutoff pushing checks a bit further
1834 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1836 // Initialize a MovePicker object for the current position, and prepare
1837 // to search the moves. Because the depth is <= 0 here, only captures,
1838 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1839 // and we are near beta) will be generated.
1840 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1842 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1843 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;
1845 // Loop through the moves until no moves remain or a beta cutoff
1847 while ( alpha < beta
1848 && (move = mp.get_next_move()) != MOVE_NONE)
1850 assert(move_is_ok(move));
1852 moveIsCheck = pos.move_is_check(move, ci);
1854 // Update current move
1856 ss[ply].currentMove = move;
1864 && !move_is_promotion(move)
1865 && !pos.move_is_passed_pawn_push(move))
1867 futilityValue = futilityBase
1868 + pos.endgame_value_of_piece_on(move_to(move))
1869 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1871 if (futilityValue < alpha)
1873 if (futilityValue > bestValue)
1874 bestValue = futilityValue;
1879 // Detect blocking evasions that are candidate to be pruned
1880 evasionPrunable = isCheck
1881 && bestValue != -VALUE_INFINITE
1882 && !pos.move_is_capture(move)
1883 && pos.type_of_piece_on(move_from(move)) != KING
1884 && !pos.can_castle(pos.side_to_move());
1886 // Don't search moves with negative SEE values
1887 if ( (!isCheck || evasionPrunable)
1889 && !move_is_promotion(move)
1890 && pos.see_sign(move) < 0)
1893 // Make and search the move
1894 pos.do_move(move, st, ci, moveIsCheck);
1895 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1896 pos.undo_move(move);
1898 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1901 if (value > bestValue)
1912 // All legal moves have been searched. A special case: If we're in check
1913 // and no legal moves were found, it is checkmate.
1914 if (!moveCount && pos.is_check()) // Mate!
1915 return value_mated_in(ply);
1917 // Update transposition table
1918 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1919 if (bestValue <= oldAlpha)
1921 // If bestValue isn't changed it means it is still the static evaluation
1922 // of the node, so keep this info to avoid a future evaluation() call.
1923 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1924 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1926 else if (bestValue >= beta)
1928 move = ss[ply].pv[ply];
1929 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1931 // Update killers only for good checking moves
1932 if (!pos.move_is_capture_or_promotion(move))
1933 update_killers(move, ss[ply]);
1936 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1938 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1944 // sp_search() is used to search from a split point. This function is called
1945 // by each thread working at the split point. It is similar to the normal
1946 // search() function, but simpler. Because we have already probed the hash
1947 // table, done a null move search, and searched the first move before
1948 // splitting, we don't have to repeat all this work in sp_search(). We
1949 // also don't need to store anything to the hash table here: This is taken
1950 // care of after we return from the split point.
1952 void sp_search(SplitPoint* sp, int threadID) {
1954 assert(threadID >= 0 && threadID < ActiveThreads);
1955 assert(ActiveThreads > 1);
1957 Position pos(*sp->pos);
1959 SearchStack* ss = sp->sstack[threadID];
1960 Value value = -VALUE_INFINITE;
1963 bool isCheck = pos.is_check();
1964 bool useFutilityPruning = sp->depth < SelectiveDepth
1967 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1969 // Precalculate reduction parameters
1970 float LogLimit, Gradient, BaseReduction = 0.5;
1971 reduction_parameters(BaseReduction, 3.0, sp->depth, LogLimit, Gradient);
1973 while ( lock_grab_bool(&(sp->lock))
1974 && sp->bestValue < sp->beta
1975 && !thread_should_stop(threadID)
1976 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1978 moveCount = ++sp->moves;
1979 lock_release(&(sp->lock));
1981 assert(move_is_ok(move));
1983 bool moveIsCheck = pos.move_is_check(move, ci);
1984 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1986 ss[sp->ply].currentMove = move;
1988 // Decide the new search depth
1990 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1991 Depth newDepth = sp->depth - OnePly + ext;
1994 if ( useFutilityPruning
1996 && !captureOrPromotion)
1998 // Move count based pruning
1999 if ( moveCount >= FutilityMoveCountMargin
2000 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
2001 && sp->bestValue > value_mated_in(PLY_MAX))
2004 // Value based pruning
2005 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
2007 if (futilityValueScaled < sp->beta)
2009 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
2011 lock_grab(&(sp->lock));
2012 if (futilityValueScaled > sp->bestValue)
2013 sp->bestValue = futilityValueScaled;
2014 lock_release(&(sp->lock));
2020 // Make and search the move.
2022 pos.do_move(move, st, ci, moveIsCheck);
2024 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2025 // if the move fails high will be re-searched at full depth.
2026 bool doFullDepthSearch = true;
2029 && !captureOrPromotion
2030 && !move_is_castle(move)
2031 && !move_is_killer(move, ss[sp->ply]))
2033 ss[sp->ply].reduction = reduction(moveCount, LogLimit, BaseReduction, Gradient);
2034 if (ss[sp->ply].reduction)
2036 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2037 doFullDepthSearch = (value >= sp->beta);
2041 if (doFullDepthSearch) // Go with full depth non-pv search
2043 ss[sp->ply].reduction = Depth(0);
2044 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
2046 pos.undo_move(move);
2048 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2050 if (thread_should_stop(threadID))
2052 lock_grab(&(sp->lock));
2057 if (value > sp->bestValue) // Less then 2% of cases
2059 lock_grab(&(sp->lock));
2060 if (value > sp->bestValue && !thread_should_stop(threadID))
2062 sp->bestValue = value;
2063 if (sp->bestValue >= sp->beta)
2065 sp_update_pv(sp->parentSstack, ss, sp->ply);
2066 for (int i = 0; i < ActiveThreads; i++)
2067 if (i != threadID && (i == sp->master || sp->slaves[i]))
2068 Threads[i].stop = true;
2070 sp->finished = true;
2073 lock_release(&(sp->lock));
2077 /* Here we have the lock still grabbed */
2079 // If this is the master thread and we have been asked to stop because of
2080 // a beta cutoff higher up in the tree, stop all slave threads.
2081 if (sp->master == threadID && thread_should_stop(threadID))
2082 for (int i = 0; i < ActiveThreads; i++)
2084 Threads[i].stop = true;
2087 sp->slaves[threadID] = 0;
2089 lock_release(&(sp->lock));
2093 // sp_search_pv() is used to search from a PV split point. This function
2094 // is called by each thread working at the split point. It is similar to
2095 // the normal search_pv() function, but simpler. Because we have already
2096 // probed the hash table and searched the first move before splitting, we
2097 // don't have to repeat all this work in sp_search_pv(). We also don't
2098 // need to store anything to the hash table here: This is taken care of
2099 // after we return from the split point.
2101 void sp_search_pv(SplitPoint* sp, int threadID) {
2103 assert(threadID >= 0 && threadID < ActiveThreads);
2104 assert(ActiveThreads > 1);
2106 Position pos(*sp->pos);
2108 SearchStack* ss = sp->sstack[threadID];
2109 Value value = -VALUE_INFINITE;
2113 // Precalculate reduction parameters
2114 float LogLimit, Gradient, BaseReduction = 0.5;
2115 reduction_parameters(BaseReduction, 6.0, sp->depth, LogLimit, Gradient);
2117 while ( lock_grab_bool(&(sp->lock))
2118 && sp->alpha < sp->beta
2119 && !thread_should_stop(threadID)
2120 && (move = sp->mp->get_next_move()) != MOVE_NONE)
2122 moveCount = ++sp->moves;
2123 lock_release(&(sp->lock));
2125 assert(move_is_ok(move));
2127 bool moveIsCheck = pos.move_is_check(move, ci);
2128 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
2130 ss[sp->ply].currentMove = move;
2132 // Decide the new search depth
2134 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
2135 Depth newDepth = sp->depth - OnePly + ext;
2137 // Make and search the move.
2139 pos.do_move(move, st, ci, moveIsCheck);
2141 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2142 // if the move fails high will be re-searched at full depth.
2143 bool doFullDepthSearch = true;
2146 && !captureOrPromotion
2147 && !move_is_castle(move)
2148 && !move_is_killer(move, ss[sp->ply]))
2150 ss[sp->ply].reduction = reduction(moveCount, LogLimit, BaseReduction, Gradient);
2151 if (ss[sp->ply].reduction)
2153 Value localAlpha = sp->alpha;
2154 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2155 doFullDepthSearch = (value > localAlpha);
2159 if (doFullDepthSearch) // Go with full depth non-pv search
2161 Value localAlpha = sp->alpha;
2162 ss[sp->ply].reduction = Depth(0);
2163 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2165 if (value > localAlpha && value < sp->beta)
2167 // When the search fails high at ply 1 while searching the first
2168 // move at the root, set the flag failHighPly1. This is used for
2169 // time managment: We don't want to stop the search early in
2170 // such cases, because resolving the fail high at ply 1 could
2171 // result in a big drop in score at the root.
2172 if (sp->ply == 1 && RootMoveNumber == 1)
2173 Threads[threadID].failHighPly1 = true;
2175 // If another thread has failed high then sp->alpha has been increased
2176 // to be higher or equal then beta, if so, avoid to start a PV search.
2177 localAlpha = sp->alpha;
2178 if (localAlpha < sp->beta)
2179 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2181 assert(thread_should_stop(threadID));
2183 Threads[threadID].failHighPly1 = false;
2186 pos.undo_move(move);
2188 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2190 if (thread_should_stop(threadID))
2192 lock_grab(&(sp->lock));
2197 if (value > sp->bestValue) // Less then 2% of cases
2199 lock_grab(&(sp->lock));
2200 if (value > sp->bestValue && !thread_should_stop(threadID))
2202 sp->bestValue = value;
2203 if (value > sp->alpha)
2205 // Ask threads to stop before to modify sp->alpha
2206 if (value >= sp->beta)
2208 for (int i = 0; i < ActiveThreads; i++)
2209 if (i != threadID && (i == sp->master || sp->slaves[i]))
2210 Threads[i].stop = true;
2212 sp->finished = true;
2217 sp_update_pv(sp->parentSstack, ss, sp->ply);
2218 if (value == value_mate_in(sp->ply + 1))
2219 ss[sp->ply].mateKiller = move;
2221 // If we are at ply 1, and we are searching the first root move at
2222 // ply 0, set the 'Problem' variable if the score has dropped a lot
2223 // (from the computer's point of view) since the previous iteration.
2226 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2229 lock_release(&(sp->lock));
2233 /* Here we have the lock still grabbed */
2235 // If this is the master thread and we have been asked to stop because of
2236 // a beta cutoff higher up in the tree, stop all slave threads.
2237 if (sp->master == threadID && thread_should_stop(threadID))
2238 for (int i = 0; i < ActiveThreads; i++)
2240 Threads[i].stop = true;
2243 sp->slaves[threadID] = 0;
2245 lock_release(&(sp->lock));
2248 /// The BetaCounterType class
2250 BetaCounterType::BetaCounterType() { clear(); }
2252 void BetaCounterType::clear() {
2254 for (int i = 0; i < THREAD_MAX; i++)
2255 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2258 void BetaCounterType::add(Color us, Depth d, int threadID) {
2260 // Weighted count based on depth
2261 Threads[threadID].betaCutOffs[us] += unsigned(d);
2264 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2267 for (int i = 0; i < THREAD_MAX; i++)
2269 our += Threads[i].betaCutOffs[us];
2270 their += Threads[i].betaCutOffs[opposite_color(us)];
2275 /// The RootMoveList class
2277 // RootMoveList c'tor
2279 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2281 SearchStack ss[PLY_MAX_PLUS_2];
2282 MoveStack mlist[MaxRootMoves];
2284 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2286 // Generate all legal moves
2287 MoveStack* last = generate_moves(pos, mlist);
2289 // Add each move to the moves[] array
2290 for (MoveStack* cur = mlist; cur != last; cur++)
2292 bool includeMove = includeAllMoves;
2294 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2295 includeMove = (searchMoves[k] == cur->move);
2300 // Find a quick score for the move
2302 pos.do_move(cur->move, st);
2303 moves[count].move = cur->move;
2304 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2305 moves[count].pv[0] = cur->move;
2306 moves[count].pv[1] = MOVE_NONE;
2307 pos.undo_move(cur->move);
2314 // RootMoveList simple methods definitions
2316 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2318 moves[moveNum].nodes = nodes;
2319 moves[moveNum].cumulativeNodes += nodes;
2322 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2324 moves[moveNum].ourBeta = our;
2325 moves[moveNum].theirBeta = their;
2328 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2332 for (j = 0; pv[j] != MOVE_NONE; j++)
2333 moves[moveNum].pv[j] = pv[j];
2335 moves[moveNum].pv[j] = MOVE_NONE;
2339 // RootMoveList::sort() sorts the root move list at the beginning of a new
2342 void RootMoveList::sort() {
2344 sort_multipv(count - 1); // Sort all items
2348 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2349 // list by their scores and depths. It is used to order the different PVs
2350 // correctly in MultiPV mode.
2352 void RootMoveList::sort_multipv(int n) {
2356 for (i = 1; i <= n; i++)
2358 RootMove rm = moves[i];
2359 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2360 moves[j] = moves[j - 1];
2367 // init_node() is called at the beginning of all the search functions
2368 // (search(), search_pv(), qsearch(), and so on) and initializes the
2369 // search stack object corresponding to the current node. Once every
2370 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2371 // for user input and checks whether it is time to stop the search.
2373 void init_node(SearchStack ss[], int ply, int threadID) {
2375 assert(ply >= 0 && ply < PLY_MAX);
2376 assert(threadID >= 0 && threadID < ActiveThreads);
2378 Threads[threadID].nodes++;
2383 if (NodesSincePoll >= NodesBetweenPolls)
2390 ss[ply + 2].initKillers();
2392 if (Threads[threadID].printCurrentLine)
2393 print_current_line(ss, ply, threadID);
2397 // update_pv() is called whenever a search returns a value > alpha.
2398 // It updates the PV in the SearchStack object corresponding to the
2401 void update_pv(SearchStack ss[], int ply) {
2403 assert(ply >= 0 && ply < PLY_MAX);
2407 ss[ply].pv[ply] = ss[ply].currentMove;
2409 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2410 ss[ply].pv[p] = ss[ply + 1].pv[p];
2412 ss[ply].pv[p] = MOVE_NONE;
2416 // sp_update_pv() is a variant of update_pv for use at split points. The
2417 // difference between the two functions is that sp_update_pv also updates
2418 // the PV at the parent node.
2420 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2422 assert(ply >= 0 && ply < PLY_MAX);
2426 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2428 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2429 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2431 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2435 // connected_moves() tests whether two moves are 'connected' in the sense
2436 // that the first move somehow made the second move possible (for instance
2437 // if the moving piece is the same in both moves). The first move is assumed
2438 // to be the move that was made to reach the current position, while the
2439 // second move is assumed to be a move from the current position.
2441 bool connected_moves(const Position& pos, Move m1, Move m2) {
2443 Square f1, t1, f2, t2;
2446 assert(move_is_ok(m1));
2447 assert(move_is_ok(m2));
2449 if (m2 == MOVE_NONE)
2452 // Case 1: The moving piece is the same in both moves
2458 // Case 2: The destination square for m2 was vacated by m1
2464 // Case 3: Moving through the vacated square
2465 if ( piece_is_slider(pos.piece_on(f2))
2466 && bit_is_set(squares_between(f2, t2), f1))
2469 // Case 4: The destination square for m2 is defended by the moving piece in m1
2470 p = pos.piece_on(t1);
2471 if (bit_is_set(pos.attacks_from(p, t1), t2))
2474 // Case 5: Discovered check, checking piece is the piece moved in m1
2475 if ( piece_is_slider(p)
2476 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2477 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2479 // discovered_check_candidates() works also if the Position's side to
2480 // move is the opposite of the checking piece.
2481 Color them = opposite_color(pos.side_to_move());
2482 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2484 if (bit_is_set(dcCandidates, f2))
2491 // value_is_mate() checks if the given value is a mate one
2492 // eventually compensated for the ply.
2494 bool value_is_mate(Value value) {
2496 assert(abs(value) <= VALUE_INFINITE);
2498 return value <= value_mated_in(PLY_MAX)
2499 || value >= value_mate_in(PLY_MAX);
2503 // move_is_killer() checks if the given move is among the
2504 // killer moves of that ply.
2506 bool move_is_killer(Move m, const SearchStack& ss) {
2508 const Move* k = ss.killers;
2509 for (int i = 0; i < KILLER_MAX; i++, k++)
2517 // extension() decides whether a move should be searched with normal depth,
2518 // or with extended depth. Certain classes of moves (checking moves, in
2519 // particular) are searched with bigger depth than ordinary moves and in
2520 // any case are marked as 'dangerous'. Note that also if a move is not
2521 // extended, as example because the corresponding UCI option is set to zero,
2522 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2524 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2525 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2527 assert(m != MOVE_NONE);
2529 Depth result = Depth(0);
2530 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2535 result += CheckExtension[pvNode];
2538 result += SingleEvasionExtension[pvNode];
2541 result += MateThreatExtension[pvNode];
2544 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2546 Color c = pos.side_to_move();
2547 if (relative_rank(c, move_to(m)) == RANK_7)
2549 result += PawnPushTo7thExtension[pvNode];
2552 if (pos.pawn_is_passed(c, move_to(m)))
2554 result += PassedPawnExtension[pvNode];
2559 if ( captureOrPromotion
2560 && pos.type_of_piece_on(move_to(m)) != PAWN
2561 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2562 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2563 && !move_is_promotion(m)
2566 result += PawnEndgameExtension[pvNode];
2571 && captureOrPromotion
2572 && pos.type_of_piece_on(move_to(m)) != PAWN
2573 && pos.see_sign(m) >= 0)
2579 return Min(result, OnePly);
2583 // ok_to_do_nullmove() looks at the current position and decides whether
2584 // doing a 'null move' should be allowed. In order to avoid zugzwang
2585 // problems, null moves are not allowed when the side to move has very
2586 // little material left. Currently, the test is a bit too simple: Null
2587 // moves are avoided only when the side to move has only pawns left.
2588 // It's probably a good idea to avoid null moves in at least some more
2589 // complicated endgames, e.g. KQ vs KR. FIXME
2591 bool ok_to_do_nullmove(const Position& pos) {
2593 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2597 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2598 // non-tactical moves late in the move list close to the leaves are
2599 // candidates for pruning.
2601 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2603 assert(move_is_ok(m));
2604 assert(threat == MOVE_NONE || move_is_ok(threat));
2605 assert(!pos.move_is_check(m));
2606 assert(!pos.move_is_capture_or_promotion(m));
2607 assert(!pos.move_is_passed_pawn_push(m));
2609 Square mfrom, mto, tfrom, tto;
2611 // Prune if there isn't any threat move
2612 if (threat == MOVE_NONE)
2615 mfrom = move_from(m);
2617 tfrom = move_from(threat);
2618 tto = move_to(threat);
2620 // Case 1: Don't prune moves which move the threatened piece
2624 // Case 2: If the threatened piece has value less than or equal to the
2625 // value of the threatening piece, don't prune move which defend it.
2626 if ( pos.move_is_capture(threat)
2627 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2628 || pos.type_of_piece_on(tfrom) == KING)
2629 && pos.move_attacks_square(m, tto))
2632 // Case 3: If the moving piece in the threatened move is a slider, don't
2633 // prune safe moves which block its ray.
2634 if ( piece_is_slider(pos.piece_on(tfrom))
2635 && bit_is_set(squares_between(tfrom, tto), mto)
2636 && pos.see_sign(m) >= 0)
2643 // ok_to_use_TT() returns true if a transposition table score
2644 // can be used at a given point in search.
2646 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2648 Value v = value_from_tt(tte->value(), ply);
2650 return ( tte->depth() >= depth
2651 || v >= Max(value_mate_in(PLY_MAX), beta)
2652 || v < Min(value_mated_in(PLY_MAX), beta))
2654 && ( (is_lower_bound(tte->type()) && v >= beta)
2655 || (is_upper_bound(tte->type()) && v < beta));
2659 // refine_eval() returns the transposition table score if
2660 // possible otherwise falls back on static position evaluation.
2662 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2667 Value v = value_from_tt(tte->value(), ply);
2669 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2670 || (is_upper_bound(tte->type()) && v < defaultEval))
2677 // reduction_parameters() precalculates some parameters used later by reduction. Becasue
2678 // floating point operations are involved we try to recalculate reduction at each move, but
2679 // we do the most consuming computation only once per node.
2681 void reduction_parameters(float baseReduction, float reductionInhibitor, Depth depth, float& logLimit, float& gradient)
2683 // Precalculate some parameters to avoid to calculate the following formula for each move:
2685 // red = baseReduction + ln(moveCount) * ln(depth / 2) / reductionInhibitor;
2687 logLimit = depth > OnePly ? (1 - baseReduction) * reductionInhibitor / ln(depth / 2) : 1000;
2688 gradient = depth > OnePly ? ln(depth / 2) / reductionInhibitor : 0;
2692 // reduction() returns reduction in plies based on moveCount and depth.
2693 // Reduction is always at least one ply.
2695 Depth reduction(int moveCount, float logLimit, float baseReduction, float gradient) {
2697 if (ln(moveCount) < logLimit)
2700 float red = baseReduction + ln(moveCount) * gradient;
2701 return Depth(int(floor(red * int(OnePly))));
2705 // update_history() registers a good move that produced a beta-cutoff
2706 // in history and marks as failures all the other moves of that ply.
2708 void update_history(const Position& pos, Move move, Depth depth,
2709 Move movesSearched[], int moveCount) {
2713 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2715 for (int i = 0; i < moveCount - 1; i++)
2717 m = movesSearched[i];
2721 if (!pos.move_is_capture_or_promotion(m))
2722 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2727 // update_killers() add a good move that produced a beta-cutoff
2728 // among the killer moves of that ply.
2730 void update_killers(Move m, SearchStack& ss) {
2732 if (m == ss.killers[0])
2735 for (int i = KILLER_MAX - 1; i > 0; i--)
2736 ss.killers[i] = ss.killers[i - 1];
2742 // update_gains() updates the gains table of a non-capture move given
2743 // the static position evaluation before and after the move.
2745 void update_gains(const Position& pos, Move m, Value before, Value after) {
2748 && before != VALUE_NONE
2749 && after != VALUE_NONE
2750 && pos.captured_piece() == NO_PIECE_TYPE
2751 && !move_is_castle(m)
2752 && !move_is_promotion(m))
2753 H.set_gain(pos.piece_on(move_to(m)), move_from(m), move_to(m), -(before + after));
2757 // fail_high_ply_1() checks if some thread is currently resolving a fail
2758 // high at ply 1 at the node below the first root node. This information
2759 // is used for time management.
2761 bool fail_high_ply_1() {
2763 for (int i = 0; i < ActiveThreads; i++)
2764 if (Threads[i].failHighPly1)
2771 // current_search_time() returns the number of milliseconds which have passed
2772 // since the beginning of the current search.
2774 int current_search_time() {
2776 return get_system_time() - SearchStartTime;
2780 // nps() computes the current nodes/second count.
2784 int t = current_search_time();
2785 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2789 // poll() performs two different functions: It polls for user input, and it
2790 // looks at the time consumed so far and decides if it's time to abort the
2795 static int lastInfoTime;
2796 int t = current_search_time();
2801 // We are line oriented, don't read single chars
2802 std::string command;
2804 if (!std::getline(std::cin, command))
2807 if (command == "quit")
2810 PonderSearch = false;
2814 else if (command == "stop")
2817 PonderSearch = false;
2819 else if (command == "ponderhit")
2823 // Print search information
2827 else if (lastInfoTime > t)
2828 // HACK: Must be a new search where we searched less than
2829 // NodesBetweenPolls nodes during the first second of search.
2832 else if (t - lastInfoTime >= 1000)
2840 if (dbg_show_hit_rate)
2841 dbg_print_hit_rate();
2843 cout << "info nodes " << nodes_searched() << " nps " << nps()
2844 << " time " << t << " hashfull " << TT.full() << endl;
2846 lock_release(&IOLock);
2848 if (ShowCurrentLine)
2849 Threads[0].printCurrentLine = true;
2852 // Should we stop the search?
2856 bool stillAtFirstMove = RootMoveNumber == 1
2858 && t > MaxSearchTime + ExtraSearchTime;
2860 bool noProblemFound = !FailHigh
2862 && !fail_high_ply_1()
2864 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2866 bool noMoreTime = t > AbsoluteMaxSearchTime
2867 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2870 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2871 || (ExactMaxTime && t >= ExactMaxTime)
2872 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2877 // ponderhit() is called when the program is pondering (i.e. thinking while
2878 // it's the opponent's turn to move) in order to let the engine know that
2879 // it correctly predicted the opponent's move.
2883 int t = current_search_time();
2884 PonderSearch = false;
2886 bool stillAtFirstMove = RootMoveNumber == 1
2888 && t > MaxSearchTime + ExtraSearchTime;
2890 bool noProblemFound = !FailHigh
2892 && !fail_high_ply_1()
2894 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2896 bool noMoreTime = t > AbsoluteMaxSearchTime
2900 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2905 // print_current_line() prints the current line of search for a given
2906 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2908 void print_current_line(SearchStack ss[], int ply, int threadID) {
2910 assert(ply >= 0 && ply < PLY_MAX);
2911 assert(threadID >= 0 && threadID < ActiveThreads);
2913 if (!Threads[threadID].idle)
2916 cout << "info currline " << (threadID + 1);
2917 for (int p = 0; p < ply; p++)
2918 cout << " " << ss[p].currentMove;
2921 lock_release(&IOLock);
2923 Threads[threadID].printCurrentLine = false;
2924 if (threadID + 1 < ActiveThreads)
2925 Threads[threadID + 1].printCurrentLine = true;
2929 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2931 void init_ss_array(SearchStack ss[]) {
2933 for (int i = 0; i < 3; i++)
2936 ss[i].initKillers();
2941 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2942 // while the program is pondering. The point is to work around a wrinkle in
2943 // the UCI protocol: When pondering, the engine is not allowed to give a
2944 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2945 // We simply wait here until one of these commands is sent, and return,
2946 // after which the bestmove and pondermove will be printed (in id_loop()).
2948 void wait_for_stop_or_ponderhit() {
2950 std::string command;
2954 if (!std::getline(std::cin, command))
2957 if (command == "quit")
2962 else if (command == "ponderhit" || command == "stop")
2968 // idle_loop() is where the threads are parked when they have no work to do.
2969 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2970 // object for which the current thread is the master.
2972 void idle_loop(int threadID, SplitPoint* waitSp) {
2974 assert(threadID >= 0 && threadID < THREAD_MAX);
2976 Threads[threadID].running = true;
2980 if (AllThreadsShouldExit && threadID != 0)
2983 // If we are not thinking, wait for a condition to be signaled
2984 // instead of wasting CPU time polling for work.
2985 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2988 #if !defined(_MSC_VER)
2989 pthread_mutex_lock(&WaitLock);
2990 if (Idle || threadID >= ActiveThreads)
2991 pthread_cond_wait(&WaitCond, &WaitLock);
2993 pthread_mutex_unlock(&WaitLock);
2995 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2999 // If this thread has been assigned work, launch a search
3000 if (Threads[threadID].workIsWaiting)
3002 assert(!Threads[threadID].idle);
3004 Threads[threadID].workIsWaiting = false;
3005 if (Threads[threadID].splitPoint->pvNode)
3006 sp_search_pv(Threads[threadID].splitPoint, threadID);
3008 sp_search(Threads[threadID].splitPoint, threadID);
3010 Threads[threadID].idle = true;
3013 // If this thread is the master of a split point and all threads have
3014 // finished their work at this split point, return from the idle loop.
3015 if (waitSp != NULL && waitSp->cpus == 0)
3019 Threads[threadID].running = false;
3023 // init_split_point_stack() is called during program initialization, and
3024 // initializes all split point objects.
3026 void init_split_point_stack() {
3028 for (int i = 0; i < THREAD_MAX; i++)
3029 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
3031 SplitPointStack[i][j].parent = NULL;
3032 lock_init(&(SplitPointStack[i][j].lock), NULL);
3037 // destroy_split_point_stack() is called when the program exits, and
3038 // destroys all locks in the precomputed split point objects.
3040 void destroy_split_point_stack() {
3042 for (int i = 0; i < THREAD_MAX; i++)
3043 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
3044 lock_destroy(&(SplitPointStack[i][j].lock));
3048 // thread_should_stop() checks whether the thread with a given threadID has
3049 // been asked to stop, directly or indirectly. This can happen if a beta
3050 // cutoff has occurred in the thread's currently active split point, or in
3051 // some ancestor of the current split point.
3053 bool thread_should_stop(int threadID) {
3055 assert(threadID >= 0 && threadID < ActiveThreads);
3059 if (Threads[threadID].stop)
3061 if (ActiveThreads <= 2)
3063 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
3066 Threads[threadID].stop = true;
3073 // thread_is_available() checks whether the thread with threadID "slave" is
3074 // available to help the thread with threadID "master" at a split point. An
3075 // obvious requirement is that "slave" must be idle. With more than two
3076 // threads, this is not by itself sufficient: If "slave" is the master of
3077 // some active split point, it is only available as a slave to the other
3078 // threads which are busy searching the split point at the top of "slave"'s
3079 // split point stack (the "helpful master concept" in YBWC terminology).
3081 bool thread_is_available(int slave, int master) {
3083 assert(slave >= 0 && slave < ActiveThreads);
3084 assert(master >= 0 && master < ActiveThreads);
3085 assert(ActiveThreads > 1);
3087 if (!Threads[slave].idle || slave == master)
3090 // Make a local copy to be sure doesn't change under our feet
3091 int localActiveSplitPoints = Threads[slave].activeSplitPoints;
3093 if (localActiveSplitPoints == 0)
3094 // No active split points means that the thread is available as
3095 // a slave for any other thread.
3098 if (ActiveThreads == 2)
3101 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
3102 // that is known to be > 0, instead of Threads[slave].activeSplitPoints that
3103 // could have been set to 0 by another thread leading to an out of bound access.
3104 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
3111 // idle_thread_exists() tries to find an idle thread which is available as
3112 // a slave for the thread with threadID "master".
3114 bool idle_thread_exists(int master) {
3116 assert(master >= 0 && master < ActiveThreads);
3117 assert(ActiveThreads > 1);
3119 for (int i = 0; i < ActiveThreads; i++)
3120 if (thread_is_available(i, master))
3127 // split() does the actual work of distributing the work at a node between
3128 // several threads at PV nodes. If it does not succeed in splitting the
3129 // node (because no idle threads are available, or because we have no unused
3130 // split point objects), the function immediately returns false. If
3131 // splitting is possible, a SplitPoint object is initialized with all the
3132 // data that must be copied to the helper threads (the current position and
3133 // search stack, alpha, beta, the search depth, etc.), and we tell our
3134 // helper threads that they have been assigned work. This will cause them
3135 // to instantly leave their idle loops and call sp_search_pv(). When all
3136 // threads have returned from sp_search_pv (or, equivalently, when
3137 // splitPoint->cpus becomes 0), split() returns true.
3139 bool split(const Position& p, SearchStack* sstck, int ply,
3140 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
3141 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
3144 assert(sstck != NULL);
3145 assert(ply >= 0 && ply < PLY_MAX);
3146 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
3147 assert(!pvNode || *alpha < *beta);
3148 assert(*beta <= VALUE_INFINITE);
3149 assert(depth > Depth(0));
3150 assert(master >= 0 && master < ActiveThreads);
3151 assert(ActiveThreads > 1);
3153 SplitPoint* splitPoint;
3157 // If no other thread is available to help us, or if we have too many
3158 // active split points, don't split.
3159 if ( !idle_thread_exists(master)
3160 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
3162 lock_release(&MPLock);
3166 // Pick the next available split point object from the split point stack
3167 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
3168 Threads[master].activeSplitPoints++;
3170 // Initialize the split point object
3171 splitPoint->parent = Threads[master].splitPoint;
3172 splitPoint->finished = false;
3173 splitPoint->ply = ply;
3174 splitPoint->depth = depth;
3175 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
3176 splitPoint->beta = *beta;
3177 splitPoint->pvNode = pvNode;
3178 splitPoint->bestValue = *bestValue;
3179 splitPoint->futilityValue = futilityValue;
3180 splitPoint->master = master;
3181 splitPoint->mp = mp;
3182 splitPoint->moves = *moves;
3183 splitPoint->cpus = 1;
3184 splitPoint->pos = &p;
3185 splitPoint->parentSstack = sstck;
3186 for (int i = 0; i < ActiveThreads; i++)
3187 splitPoint->slaves[i] = 0;
3189 Threads[master].idle = false;
3190 Threads[master].stop = false;
3191 Threads[master].splitPoint = splitPoint;
3193 // Allocate available threads setting idle flag to false
3194 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
3195 if (thread_is_available(i, master))
3197 Threads[i].idle = false;
3198 Threads[i].stop = false;
3199 Threads[i].splitPoint = splitPoint;
3200 splitPoint->slaves[i] = 1;
3204 assert(splitPoint->cpus > 1);
3206 // We can release the lock because master and slave threads are already booked
3207 lock_release(&MPLock);
3209 // Tell the threads that they have work to do. This will make them leave
3210 // their idle loop. But before copy search stack tail for each thread.
3211 for (int i = 0; i < ActiveThreads; i++)
3212 if (i == master || splitPoint->slaves[i])
3214 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 3 * sizeof(SearchStack));
3215 Threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
3218 // Everything is set up. The master thread enters the idle loop, from
3219 // which it will instantly launch a search, because its workIsWaiting
3220 // slot is 'true'. We send the split point as a second parameter to the
3221 // idle loop, which means that the main thread will return from the idle
3222 // loop when all threads have finished their work at this split point
3223 // (i.e. when splitPoint->cpus == 0).
3224 idle_loop(master, splitPoint);
3226 // We have returned from the idle loop, which means that all threads are
3227 // finished. Update alpha, beta and bestValue, and return.
3231 *alpha = splitPoint->alpha;
3233 *beta = splitPoint->beta;
3234 *bestValue = splitPoint->bestValue;
3235 Threads[master].stop = false;
3236 Threads[master].idle = false;
3237 Threads[master].activeSplitPoints--;
3238 Threads[master].splitPoint = splitPoint->parent;
3240 lock_release(&MPLock);
3245 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3246 // to start a new search from the root.
3248 void wake_sleeping_threads() {
3250 if (ActiveThreads > 1)
3252 for (int i = 1; i < ActiveThreads; i++)
3254 Threads[i].idle = true;
3255 Threads[i].workIsWaiting = false;
3258 #if !defined(_MSC_VER)
3259 pthread_mutex_lock(&WaitLock);
3260 pthread_cond_broadcast(&WaitCond);
3261 pthread_mutex_unlock(&WaitLock);
3263 for (int i = 1; i < THREAD_MAX; i++)
3264 SetEvent(SitIdleEvent[i]);
3270 // init_thread() is the function which is called when a new thread is
3271 // launched. It simply calls the idle_loop() function with the supplied
3272 // threadID. There are two versions of this function; one for POSIX
3273 // threads and one for Windows threads.
3275 #if !defined(_MSC_VER)
3277 void* init_thread(void *threadID) {
3279 idle_loop(*(int*)threadID, NULL);
3285 DWORD WINAPI init_thread(LPVOID threadID) {
3287 idle_loop(*(int*)threadID, NULL);