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 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 // Look for a book move
377 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
380 if (get_option_value_string("Book File") != OpeningBook.file_name())
381 OpeningBook.open(get_option_value_string("Book File"));
383 bookMove = OpeningBook.get_move(pos);
384 if (bookMove != MOVE_NONE)
386 cout << "bestmove " << bookMove << endl;
391 // Initialize global search variables
392 Idle = StopOnPonderhit = AbortSearch = Quit = false;
393 FailHigh = FailLow = Problem = false;
394 SearchStartTime = get_system_time();
395 ExactMaxTime = maxTime;
397 InfiniteSearch = infinite;
398 PonderSearch = ponder;
400 for (int i = 0; i < THREAD_MAX; i++)
402 Threads[i].nodes = 0ULL;
403 Threads[i].failHighPly1 = false;
406 if (button_was_pressed("New Game"))
407 loseOnTime = false; // Reset at the beginning of a new game
409 // Read UCI option values
410 TT.set_size(get_option_value_int("Hash"));
411 if (button_was_pressed("Clear Hash"))
414 bool PonderingEnabled = get_option_value_bool("Ponder");
415 MultiPV = get_option_value_int("MultiPV");
417 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
418 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
420 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
421 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
423 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
424 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
426 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
427 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
429 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
430 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
432 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
433 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
435 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
436 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
437 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
439 Chess960 = get_option_value_bool("UCI_Chess960");
440 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
441 UseLogFile = get_option_value_bool("Use Search Log");
443 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
445 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
446 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
448 read_weights(pos.side_to_move());
450 // Set the number of active threads
451 int newActiveThreads = get_option_value_int("Threads");
452 if (newActiveThreads != ActiveThreads)
454 ActiveThreads = newActiveThreads;
455 init_eval(ActiveThreads);
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];
468 if (!movesToGo) // Sudden death time control
472 MaxSearchTime = myTime / 30 + myIncrement;
473 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
475 else // Blitz game without increment
477 MaxSearchTime = myTime / 30;
478 AbsoluteMaxSearchTime = myTime / 8;
481 else // (x moves) / (y minutes)
485 MaxSearchTime = myTime / 2;
486 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
490 MaxSearchTime = myTime / Min(movesToGo, 20);
491 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
495 if (PonderingEnabled)
497 MaxSearchTime += MaxSearchTime / 4;
498 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
501 // Fixed depth or fixed number of nodes?
504 InfiniteSearch = true; // HACK
509 NodesBetweenPolls = Min(MaxNodes, 30000);
510 InfiniteSearch = true; // HACK
512 else if (myTime && myTime < 1000)
513 NodesBetweenPolls = 1000;
514 else if (myTime && myTime < 5000)
515 NodesBetweenPolls = 5000;
517 NodesBetweenPolls = 30000;
519 // Write information to search log file
521 LogFile << "Searching: " << pos.to_fen() << endl
522 << "infinite: " << infinite
523 << " ponder: " << ponder
524 << " time: " << myTime
525 << " increment: " << myIncrement
526 << " moves to go: " << movesToGo << endl;
528 // LSN filtering. Used only for developing purpose. Disabled by default.
532 // Step 2. If after last move we decided to lose on time, do it now!
533 while (SearchStartTime + myTime + 1000 > get_system_time())
537 // We're ready to start thinking. Call the iterative deepening loop function
538 Value v = id_loop(pos, searchMoves);
543 // Step 1. If this is sudden death game and our position is hopeless,
544 // decide to lose on time.
545 if ( !loseOnTime // If we already lost on time, go to step 3.
555 // Step 3. Now after stepping over the time limit, reset flag for next match.
568 /// init_threads() is called during startup. It launches all helper threads,
569 /// and initializes the split point stack and the global locks and condition
572 #include <cmath> //FIXME: HACK
574 void init_threads() {
577 for (int i = 0; i < 512; i++)
578 lnArray[i] = log(double(i));
582 #if !defined(_MSC_VER)
583 pthread_t pthread[1];
586 for (i = 0; i < THREAD_MAX; i++)
587 Threads[i].activeSplitPoints = 0;
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 pthread_create(pthread, NULL, init_thread, (void*)(&i));
619 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
622 // Wait until the thread has finished launching
623 while (!Threads[i].running);
628 /// stop_threads() is called when the program exits. It makes all the
629 /// helper threads exit cleanly.
631 void stop_threads() {
633 ActiveThreads = THREAD_MAX; // HACK
634 Idle = false; // HACK
635 wake_sleeping_threads();
636 AllThreadsShouldExit = true;
637 for (int i = 1; i < THREAD_MAX; i++)
639 Threads[i].stop = true;
640 while (Threads[i].running);
642 destroy_split_point_stack();
646 /// nodes_searched() returns the total number of nodes searched so far in
647 /// the current search.
649 int64_t nodes_searched() {
651 int64_t result = 0ULL;
652 for (int i = 0; i < ActiveThreads; i++)
653 result += Threads[i].nodes;
658 // SearchStack::init() initializes a search stack. Used at the beginning of a
659 // new search from the root.
660 void SearchStack::init(int ply) {
662 pv[ply] = pv[ply + 1] = MOVE_NONE;
663 currentMove = threatMove = MOVE_NONE;
664 reduction = Depth(0);
667 void SearchStack::initKillers() {
669 mateKiller = MOVE_NONE;
670 for (int i = 0; i < KILLER_MAX; i++)
671 killers[i] = MOVE_NONE;
676 // id_loop() is the main iterative deepening loop. It calls root_search
677 // repeatedly with increasing depth until the allocated thinking time has
678 // been consumed, the user stops the search, or the maximum search depth is
681 Value id_loop(const Position& pos, Move searchMoves[]) {
684 SearchStack ss[PLY_MAX_PLUS_2];
686 // searchMoves are verified, copied, scored and sorted
687 RootMoveList rml(p, searchMoves);
689 if (rml.move_count() == 0)
692 wait_for_stop_or_ponderhit();
694 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
697 // Print RootMoveList c'tor startup scoring to the standard output,
698 // so that we print information also for iteration 1.
699 cout << "info depth " << 1 << "\ninfo depth " << 1
700 << " score " << value_to_string(rml.get_move_score(0))
701 << " time " << current_search_time()
702 << " nodes " << nodes_searched()
704 << " pv " << rml.get_move(0) << "\n";
710 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
713 // Is one move significantly better than others after initial scoring ?
714 Move EasyMove = MOVE_NONE;
715 if ( rml.move_count() == 1
716 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
717 EasyMove = rml.get_move(0);
719 // Iterative deepening loop
720 while (Iteration < PLY_MAX)
722 // Initialize iteration
725 BestMoveChangesByIteration[Iteration] = 0;
729 cout << "info depth " << Iteration << endl;
731 // Calculate dynamic search window based on previous iterations
734 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
736 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
737 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
739 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
741 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
742 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
746 alpha = - VALUE_INFINITE;
747 beta = VALUE_INFINITE;
750 // Search to the current depth
751 Value value = root_search(p, ss, rml, alpha, beta);
753 // Write PV to transposition table, in case the relevant entries have
754 // been overwritten during the search.
755 TT.insert_pv(p, ss[0].pv);
758 break; // Value cannot be trusted. Break out immediately!
760 //Save info about search result
761 Value speculatedValue;
764 Value delta = value - IterationInfo[Iteration - 1].value;
771 speculatedValue = value + delta;
772 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
774 else if (value <= alpha)
776 assert(value == alpha);
780 speculatedValue = value + delta;
781 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
783 speculatedValue = value;
785 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
786 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
788 // Drop the easy move if it differs from the new best move
789 if (ss[0].pv[0] != EasyMove)
790 EasyMove = MOVE_NONE;
797 bool stopSearch = false;
799 // Stop search early if there is only a single legal move,
800 // we search up to Iteration 6 anyway to get a proper score.
801 if (Iteration >= 6 && rml.move_count() == 1)
804 // Stop search early when the last two iterations returned a mate score
806 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
807 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
810 // Stop search early if one move seems to be much better than the rest
811 int64_t nodes = nodes_searched();
815 && EasyMove == ss[0].pv[0]
816 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
817 && current_search_time() > MaxSearchTime / 16)
818 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
819 && current_search_time() > MaxSearchTime / 32)))
822 // Add some extra time if the best move has changed during the last two iterations
823 if (Iteration > 5 && Iteration <= 50)
824 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
825 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
827 // Stop search if most of MaxSearchTime is consumed at the end of the
828 // iteration. We probably don't have enough time to search the first
829 // move at the next iteration anyway.
830 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
838 StopOnPonderhit = true;
842 if (MaxDepth && Iteration >= MaxDepth)
848 // If we are pondering, we shouldn't print the best move before we
851 wait_for_stop_or_ponderhit();
853 // Print final search statistics
854 cout << "info nodes " << nodes_searched()
856 << " time " << current_search_time()
857 << " hashfull " << TT.full() << endl;
859 // Print the best move and the ponder move to the standard output
860 if (ss[0].pv[0] == MOVE_NONE)
862 ss[0].pv[0] = rml.get_move(0);
863 ss[0].pv[1] = MOVE_NONE;
865 cout << "bestmove " << ss[0].pv[0];
866 if (ss[0].pv[1] != MOVE_NONE)
867 cout << " ponder " << ss[0].pv[1];
874 dbg_print_mean(LogFile);
876 if (dbg_show_hit_rate)
877 dbg_print_hit_rate(LogFile);
879 LogFile << "\nNodes: " << nodes_searched()
880 << "\nNodes/second: " << nps()
881 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
884 p.do_move(ss[0].pv[0], st);
885 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
887 return rml.get_move_score(0);
891 // root_search() is the function which searches the root node. It is
892 // similar to search_pv except that it uses a different move ordering
893 // scheme and prints some information to the standard output.
895 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta) {
897 Value oldAlpha = alpha;
901 // Loop through all the moves in the root move list
902 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
906 // We failed high, invalidate and skip next moves, leave node-counters
907 // and beta-counters as they are and quickly return, we will try to do
908 // a research at the next iteration with a bigger aspiration window.
909 rml.set_move_score(i, -VALUE_INFINITE);
917 RootMoveNumber = i + 1;
920 // Save the current node count before the move is searched
921 nodes = nodes_searched();
923 // Reset beta cut-off counters
926 // Pick the next root move, and print the move and the move number to
927 // the standard output.
928 move = ss[0].currentMove = rml.get_move(i);
930 if (current_search_time() >= 1000)
931 cout << "info currmove " << move
932 << " currmovenumber " << RootMoveNumber << endl;
934 // Decide search depth for this move
935 bool moveIsCheck = pos.move_is_check(move);
936 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
938 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
939 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
941 // Make the move, and search it
942 pos.do_move(move, st, ci, moveIsCheck);
946 // Aspiration window is disabled in multi-pv case
948 alpha = -VALUE_INFINITE;
950 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
952 // If the value has dropped a lot compared to the last iteration,
953 // set the boolean variable Problem to true. This variable is used
954 // for time managment: When Problem is true, we try to complete the
955 // current iteration before playing a move.
956 Problem = ( Iteration >= 2
957 && value <= IterationInfo[Iteration - 1].value - ProblemMargin);
959 if (Problem && StopOnPonderhit)
960 StopOnPonderhit = false;
964 // Try to reduce non-pv search depth by one ply if move seems not problematic,
965 // if the move fails high will be re-searched at full depth.
966 if ( newDepth >= 3*OnePly
967 && i >= MultiPV + LMRPVMoves
969 && !captureOrPromotion
970 && !move_is_castle(move))
972 ss[0].reduction = OnePly;
973 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
975 value = alpha + 1; // Just to trigger next condition
979 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
983 // Fail high! Set the boolean variable FailHigh to true, and
984 // re-search the move using a PV search. The variable FailHigh
985 // is used for time managment: We try to avoid aborting the
986 // search prematurely during a fail high research.
988 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
995 // Finished searching the move. If AbortSearch is true, the search
996 // was aborted because the user interrupted the search or because we
997 // ran out of time. In this case, the return value of the search cannot
998 // be trusted, and we break out of the loop without updating the best
1003 // Remember beta-cutoff and searched nodes counts for this move. The
1004 // info is used to sort the root moves at the next iteration.
1006 BetaCounter.read(pos.side_to_move(), our, their);
1007 rml.set_beta_counters(i, our, their);
1008 rml.set_move_nodes(i, nodes_searched() - nodes);
1010 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
1012 if (value <= alpha && i >= MultiPV)
1013 rml.set_move_score(i, -VALUE_INFINITE);
1016 // PV move or new best move!
1019 rml.set_move_score(i, value);
1021 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
1022 rml.set_move_pv(i, ss[0].pv);
1026 // We record how often the best move has been changed in each
1027 // iteration. This information is used for time managment: When
1028 // the best move changes frequently, we allocate some more time.
1030 BestMoveChangesByIteration[Iteration]++;
1032 // Print search information to the standard output
1033 cout << "info depth " << Iteration
1034 << " score " << value_to_string(value)
1035 << ((value >= beta) ? " lowerbound" :
1036 ((value <= alpha)? " upperbound" : ""))
1037 << " time " << current_search_time()
1038 << " nodes " << nodes_searched()
1042 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1043 cout << ss[0].pv[j] << " ";
1049 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
1050 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
1052 LogFile << pretty_pv(pos, current_search_time(), Iteration,
1053 nodes_searched(), value, type, ss[0].pv) << endl;
1058 // Reset the global variable Problem to false if the value isn't too
1059 // far below the final value from the last iteration.
1060 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1065 rml.sort_multipv(i);
1066 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1068 cout << "info multipv " << j + 1
1069 << " score " << value_to_string(rml.get_move_score(j))
1070 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1071 << " time " << current_search_time()
1072 << " nodes " << nodes_searched()
1076 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1077 cout << rml.get_move_pv(j, k) << " ";
1081 alpha = rml.get_move_score(Min(i, MultiPV-1));
1083 } // PV move or new best move
1085 assert(alpha >= oldAlpha);
1087 FailLow = (alpha == oldAlpha);
1093 // search_pv() is the main search function for PV nodes.
1095 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1096 Depth depth, int ply, int threadID) {
1098 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1099 assert(beta > alpha && beta <= VALUE_INFINITE);
1100 assert(ply >= 0 && ply < PLY_MAX);
1101 assert(threadID >= 0 && threadID < ActiveThreads);
1103 Move movesSearched[256];
1108 Depth ext, newDepth;
1109 Value oldAlpha, value;
1110 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1112 Value bestValue = -VALUE_INFINITE;
1115 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1117 // Initialize, and make an early exit in case of an aborted search,
1118 // an instant draw, maximum ply reached, etc.
1119 init_node(ss, ply, threadID);
1121 // After init_node() that calls poll()
1122 if (AbortSearch || thread_should_stop(threadID))
1128 if (ply >= PLY_MAX - 1)
1129 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1131 // Mate distance pruning
1133 alpha = Max(value_mated_in(ply), alpha);
1134 beta = Min(value_mate_in(ply+1), beta);
1138 // Transposition table lookup. At PV nodes, we don't use the TT for
1139 // pruning, but only for move ordering. This is to avoid problems in
1140 // the following areas:
1142 // * Repetition draw detection
1143 // * Fifty move rule detection
1144 // * Searching for a mate
1145 // * Printing of full PV line
1147 tte = TT.retrieve(pos.get_key());
1148 ttMove = (tte ? tte->move() : MOVE_NONE);
1150 // Go with internal iterative deepening if we don't have a TT move
1151 if ( UseIIDAtPVNodes
1152 && depth >= 5*OnePly
1153 && ttMove == MOVE_NONE)
1155 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1156 ttMove = ss[ply].pv[ply];
1157 tte = TT.retrieve(pos.get_key());
1160 // Initialize a MovePicker object for the current position, and prepare
1161 // to search all moves
1162 isCheck = pos.is_check();
1163 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1165 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1167 // Loop through all legal moves until no moves remain or a beta cutoff
1169 while ( alpha < beta
1170 && (move = mp.get_next_move()) != MOVE_NONE
1171 && !thread_should_stop(threadID))
1173 assert(move_is_ok(move));
1175 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1176 moveIsCheck = pos.move_is_check(move, ci);
1177 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1179 // Decide the new search depth
1180 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1182 // Singular extension search. We extend the TT move if its value is much better than
1183 // its siblings. To verify this we do a reduced search on all the other moves but the
1184 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1185 if ( depth >= 6 * OnePly
1187 && move == tte->move()
1189 && is_lower_bound(tte->type())
1190 && tte->depth() >= depth - 3 * OnePly)
1192 Value ttValue = value_from_tt(tte->value(), ply);
1194 if (abs(ttValue) < VALUE_KNOWN_WIN)
1196 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1198 if (excValue < ttValue - SingleReplyMargin)
1203 newDepth = depth - OnePly + ext;
1205 // Update current move
1206 movesSearched[moveCount++] = ss[ply].currentMove = move;
1208 // Make and search the move
1209 pos.do_move(move, st, ci, moveIsCheck);
1211 if (moveCount == 1) // The first move in list is the PV
1212 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1215 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1216 // if the move fails high will be re-searched at full depth.
1217 if ( depth >= 3*OnePly
1219 && !captureOrPromotion
1220 && !move_is_castle(move)
1221 && !move_is_killer(move, ss[ply]))
1223 double red = ln(moveCount) * ln(depth / 2) / 3.0;
1226 ss[ply].reduction = Depth(floor(red * int(OnePly)));
1227 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1230 value = alpha + 1; // Just to trigger next condition
1233 value = alpha + 1; // Just to trigger next condition
1235 if (value > alpha) // Go with full depth non-pv search
1237 ss[ply].reduction = Depth(0);
1238 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1239 if (value > alpha && value < beta)
1241 // When the search fails high at ply 1 while searching the first
1242 // move at the root, set the flag failHighPly1. This is used for
1243 // time managment: We don't want to stop the search early in
1244 // such cases, because resolving the fail high at ply 1 could
1245 // result in a big drop in score at the root.
1246 if (ply == 1 && RootMoveNumber == 1)
1247 Threads[threadID].failHighPly1 = true;
1249 // A fail high occurred. Re-search at full window (pv search)
1250 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1251 Threads[threadID].failHighPly1 = false;
1255 pos.undo_move(move);
1257 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1260 if (value > bestValue)
1267 if (value == value_mate_in(ply + 1))
1268 ss[ply].mateKiller = move;
1270 // If we are at ply 1, and we are searching the first root move at
1271 // ply 0, set the 'Problem' variable if the score has dropped a lot
1272 // (from the computer's point of view) since the previous iteration.
1275 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1280 if ( ActiveThreads > 1
1282 && depth >= MinimumSplitDepth
1284 && idle_thread_exists(threadID)
1286 && !thread_should_stop(threadID)
1287 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1288 depth, &moveCount, &mp, threadID, true))
1292 // All legal moves have been searched. A special case: If there were
1293 // no legal moves, it must be mate or stalemate.
1295 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1297 // If the search is not aborted, update the transposition table,
1298 // history counters, and killer moves.
1299 if (AbortSearch || thread_should_stop(threadID))
1302 if (bestValue <= oldAlpha)
1303 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1305 else if (bestValue >= beta)
1307 BetaCounter.add(pos.side_to_move(), depth, threadID);
1308 move = ss[ply].pv[ply];
1309 if (!pos.move_is_capture_or_promotion(move))
1311 update_history(pos, move, depth, movesSearched, moveCount);
1312 update_killers(move, ss[ply]);
1314 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1317 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1323 // search() is the search function for zero-width nodes.
1325 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1326 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1328 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1329 assert(ply >= 0 && ply < PLY_MAX);
1330 assert(threadID >= 0 && threadID < ActiveThreads);
1332 Move movesSearched[256];
1337 Depth ext, newDepth;
1338 Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
1339 bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1340 bool mateThreat = false;
1342 Value bestValue = -VALUE_INFINITE;
1345 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1347 // Initialize, and make an early exit in case of an aborted search,
1348 // an instant draw, maximum ply reached, etc.
1349 init_node(ss, ply, threadID);
1351 // After init_node() that calls poll()
1352 if (AbortSearch || thread_should_stop(threadID))
1358 if (ply >= PLY_MAX - 1)
1359 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1361 // Mate distance pruning
1362 if (value_mated_in(ply) >= beta)
1365 if (value_mate_in(ply + 1) < beta)
1368 // We don't want the score of a partial search to overwrite a previous full search
1369 // TT value, so we use a different position key in case of an excluded move exsists.
1370 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1372 // Transposition table lookup
1373 tte = TT.retrieve(posKey);
1374 ttMove = (tte ? tte->move() : MOVE_NONE);
1376 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1378 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1379 return value_from_tt(tte->value(), ply);
1382 approximateEval = refine_eval(tte, quick_evaluate(pos), ply);
1383 isCheck = pos.is_check();
1389 && !value_is_mate(beta)
1390 && ok_to_do_nullmove(pos)
1391 && approximateEval >= beta - NullMoveMargin)
1393 ss[ply].currentMove = MOVE_NULL;
1395 pos.do_null_move(st);
1397 // Null move dynamic reduction based on depth
1398 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1400 // Null move dynamic reduction based on value
1401 if (approximateEval - beta > PawnValueMidgame)
1404 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1406 pos.undo_null_move();
1408 if (nullValue >= beta)
1410 if (depth < 6 * OnePly)
1413 // Do zugzwang verification search
1414 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1418 // The null move failed low, which means that we may be faced with
1419 // some kind of threat. If the previous move was reduced, check if
1420 // the move that refuted the null move was somehow connected to the
1421 // move which was reduced. If a connection is found, return a fail
1422 // low score (which will cause the reduced move to fail high in the
1423 // parent node, which will trigger a re-search with full depth).
1424 if (nullValue == value_mated_in(ply + 2))
1427 ss[ply].threatMove = ss[ply + 1].currentMove;
1428 if ( depth < ThreatDepth
1429 && ss[ply - 1].reduction
1430 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1434 // Null move search not allowed, try razoring
1435 else if ( !value_is_mate(beta)
1436 && depth < RazorDepth
1437 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1438 && ss[ply - 1].currentMove != MOVE_NULL
1439 && ttMove == MOVE_NONE
1440 && !pos.has_pawn_on_7th(pos.side_to_move()))
1442 Value rbeta = beta - RazorMargins[int(depth) - 2];
1443 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1448 // Go with internal iterative deepening if we don't have a TT move
1449 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1450 !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
1452 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1453 ttMove = ss[ply].pv[ply];
1454 tte = TT.retrieve(pos.get_key());
1457 // Initialize a MovePicker object for the current position, and prepare
1458 // to search all moves.
1459 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1461 futilityValue = VALUE_NONE;
1462 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1464 // Calculate depth dependant futility pruning parameters
1465 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
1466 const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
1468 // Avoid calling evaluate() if we already have the score in TT
1469 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1470 futilityValue = value_from_tt(tte->value(), ply) + FutilityValueMargin;
1472 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1473 while ( bestValue < beta
1474 && (move = mp.get_next_move()) != MOVE_NONE
1475 && !thread_should_stop(threadID))
1477 assert(move_is_ok(move));
1479 if (move == excludedMove)
1482 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1483 moveIsCheck = pos.move_is_check(move, ci);
1484 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1486 // Decide the new search depth
1487 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1489 // Singular extension search. We extend the TT move if its value is much better than
1490 // its siblings. To verify this we do a reduced search on all the other moves but the
1491 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1492 if ( depth >= 8 * OnePly
1494 && move == tte->move()
1495 && !excludedMove // Do not allow recursive single-reply search
1497 && is_lower_bound(tte->type())
1498 && tte->depth() >= depth - 3 * OnePly)
1500 Value ttValue = value_from_tt(tte->value(), ply);
1502 if (abs(ttValue) < VALUE_KNOWN_WIN)
1504 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1506 if (excValue < ttValue - SingleReplyMargin)
1511 newDepth = depth - OnePly + ext;
1513 // Update current move
1514 movesSearched[moveCount++] = ss[ply].currentMove = move;
1517 if ( useFutilityPruning
1519 && !captureOrPromotion
1522 // Move count based pruning
1523 if ( moveCount >= FutilityMoveCountMargin
1524 && ok_to_prune(pos, move, ss[ply].threatMove)
1525 && bestValue > value_mated_in(PLY_MAX))
1528 // Value based pruning
1529 if (futilityValue == VALUE_NONE)
1530 futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1532 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1534 if (futilityValueScaled < beta)
1536 if (futilityValueScaled > bestValue)
1537 bestValue = futilityValueScaled;
1542 // Make and search the move
1543 pos.do_move(move, st, ci, moveIsCheck);
1545 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1546 // if the move fails high will be re-searched at full depth.
1547 if ( depth >= 3*OnePly
1549 && !captureOrPromotion
1550 && !move_is_castle(move)
1551 && !move_is_killer(move, ss[ply])
1552 /* && move != ttMove*/)
1554 double red = ln(moveCount) * ln(depth / 2) / 1.5;
1557 ss[ply].reduction = Depth(floor(red * int(OnePly)));
1558 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1561 value = beta; // Just to trigger next condition
1564 value = beta; // Just to trigger next condition
1566 if (value >= beta) // Go with full depth non-pv search
1568 ss[ply].reduction = Depth(0);
1569 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1571 pos.undo_move(move);
1573 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1576 if (value > bestValue)
1582 if (value == value_mate_in(ply + 1))
1583 ss[ply].mateKiller = move;
1587 if ( ActiveThreads > 1
1589 && depth >= MinimumSplitDepth
1591 && idle_thread_exists(threadID)
1593 && !thread_should_stop(threadID)
1594 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue,
1595 depth, &moveCount, &mp, threadID, false))
1599 // All legal moves have been searched. A special case: If there were
1600 // no legal moves, it must be mate or stalemate.
1602 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1604 // If the search is not aborted, update the transposition table,
1605 // history counters, and killer moves.
1606 if (AbortSearch || thread_should_stop(threadID))
1609 if (bestValue < beta)
1610 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1613 BetaCounter.add(pos.side_to_move(), depth, threadID);
1614 move = ss[ply].pv[ply];
1615 if (!pos.move_is_capture_or_promotion(move))
1617 update_history(pos, move, depth, movesSearched, moveCount);
1618 update_killers(move, ss[ply]);
1620 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1623 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1629 // qsearch() is the quiescence search function, which is called by the main
1630 // search function when the remaining depth is zero (or, to be more precise,
1631 // less than OnePly).
1633 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1634 Depth depth, int ply, int threadID) {
1636 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1637 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1639 assert(ply >= 0 && ply < PLY_MAX);
1640 assert(threadID >= 0 && threadID < ActiveThreads);
1645 Value staticValue, bestValue, value, futilityValue;
1646 bool isCheck, enoughMaterial, moveIsCheck;
1647 const TTEntry* tte = NULL;
1649 bool pvNode = (beta - alpha != 1);
1651 // Initialize, and make an early exit in case of an aborted search,
1652 // an instant draw, maximum ply reached, etc.
1653 init_node(ss, ply, threadID);
1655 // After init_node() that calls poll()
1656 if (AbortSearch || thread_should_stop(threadID))
1662 // Transposition table lookup, only when not in PV
1665 tte = TT.retrieve(pos.get_key());
1666 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1668 assert(tte->type() != VALUE_TYPE_EVAL);
1670 return value_from_tt(tte->value(), ply);
1673 ttMove = (tte ? tte->move() : MOVE_NONE);
1675 isCheck = pos.is_check();
1676 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1678 // Evaluate the position statically
1680 staticValue = -VALUE_INFINITE;
1682 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1684 // Use the cached evaluation score if possible
1685 assert(ei.futilityMargin == Value(0));
1687 staticValue = value_from_tt(tte->value(), ply);
1690 staticValue = evaluate(pos, ei, threadID);
1692 if (ply >= PLY_MAX - 1)
1693 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1695 // Initialize "stand pat score", and return it immediately if it is
1697 bestValue = staticValue;
1699 if (bestValue >= beta)
1701 // Store the score to avoid a future costly evaluation() call
1702 if (!isCheck && !tte && ei.futilityMargin == 0)
1703 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1708 if (bestValue > alpha)
1711 // Initialize a MovePicker object for the current position, and prepare
1712 // to search the moves. Because the depth is <= 0 here, only captures,
1713 // queen promotions and checks (only if depth == 0) will be generated.
1714 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1716 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1718 // Loop through the moves until no moves remain or a beta cutoff
1720 while ( alpha < beta
1721 && (move = mp.get_next_move()) != MOVE_NONE)
1723 assert(move_is_ok(move));
1726 ss[ply].currentMove = move;
1728 moveIsCheck = pos.move_is_check(move, ci);
1736 && !move_is_promotion(move)
1737 && !pos.move_is_passed_pawn_push(move))
1739 futilityValue = staticValue
1740 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1741 pos.endgame_value_of_piece_on(move_to(move)))
1742 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1744 + ei.futilityMargin;
1746 if (futilityValue < alpha)
1748 if (futilityValue > bestValue)
1749 bestValue = futilityValue;
1754 // Don't search captures and checks with negative SEE values
1757 && !move_is_promotion(move)
1758 && pos.see_sign(move) < 0)
1761 // Make and search the move
1762 pos.do_move(move, st, ci, moveIsCheck);
1763 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1764 pos.undo_move(move);
1766 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1769 if (value > bestValue)
1780 // All legal moves have been searched. A special case: If we're in check
1781 // and no legal moves were found, it is checkmate.
1782 if (!moveCount && pos.is_check()) // Mate!
1783 return value_mated_in(ply);
1785 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1787 // Update transposition table
1788 move = ss[ply].pv[ply];
1791 // If bestValue isn't changed it means it is still the static evaluation of
1792 // the node, so keep this info to avoid a future costly evaluation() call.
1793 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1794 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1796 if (bestValue < beta)
1797 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1799 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1802 // Update killers only for good check moves
1803 if (alpha >= beta && !pos.move_is_capture_or_promotion(move))
1804 update_killers(move, ss[ply]);
1810 // sp_search() is used to search from a split point. This function is called
1811 // by each thread working at the split point. It is similar to the normal
1812 // search() function, but simpler. Because we have already probed the hash
1813 // table, done a null move search, and searched the first move before
1814 // splitting, we don't have to repeat all this work in sp_search(). We
1815 // also don't need to store anything to the hash table here: This is taken
1816 // care of after we return from the split point.
1818 void sp_search(SplitPoint* sp, int threadID) {
1820 assert(threadID >= 0 && threadID < ActiveThreads);
1821 assert(ActiveThreads > 1);
1823 Position pos = Position(sp->pos);
1825 SearchStack* ss = sp->sstack[threadID];
1828 bool isCheck = pos.is_check();
1829 bool useFutilityPruning = sp->depth < SelectiveDepth
1832 const int FutilityMoveCountMargin = 3 + (1 << (3 * int(sp->depth) / 8));
1833 const int FutilityValueMargin = 112 * bitScanReverse32(int(sp->depth) * int(sp->depth) / 2);
1835 while ( sp->bestValue < sp->beta
1836 && !thread_should_stop(threadID)
1837 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1839 assert(move_is_ok(move));
1841 bool moveIsCheck = pos.move_is_check(move, ci);
1842 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1844 lock_grab(&(sp->lock));
1845 int moveCount = ++sp->moves;
1846 lock_release(&(sp->lock));
1848 ss[sp->ply].currentMove = move;
1850 // Decide the new search depth.
1852 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1853 Depth newDepth = sp->depth - OnePly + ext;
1856 if ( useFutilityPruning
1858 && !captureOrPromotion)
1860 // Move count based pruning
1861 if ( moveCount >= FutilityMoveCountMargin
1862 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1863 && sp->bestValue > value_mated_in(PLY_MAX))
1866 // Value based pruning
1867 if (sp->futilityValue == VALUE_NONE)
1870 sp->futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
1873 Value futilityValueScaled = sp->futilityValue - moveCount * IncrementalFutilityMargin;
1875 if (futilityValueScaled < sp->beta)
1877 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1879 lock_grab(&(sp->lock));
1880 if (futilityValueScaled > sp->bestValue)
1881 sp->bestValue = futilityValueScaled;
1882 lock_release(&(sp->lock));
1888 // Make and search the move.
1890 pos.do_move(move, st, ci, moveIsCheck);
1892 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1893 // if the move fails high will be re-searched at full depth.
1895 && !captureOrPromotion
1896 && !move_is_castle(move)
1897 && !move_is_killer(move, ss[sp->ply]))
1899 double red = ln(moveCount) * ln(sp->depth / 2) / 1.5;
1902 ss[sp->ply].reduction = Depth(floor(red * int(OnePly)));
1903 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1906 value = sp->beta; // Just to trigger next condition
1909 value = sp->beta; // Just to trigger next condition
1911 if (value >= sp->beta) // Go with full depth non-pv search
1913 ss[sp->ply].reduction = Depth(0);
1914 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1916 pos.undo_move(move);
1918 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1920 if (thread_should_stop(threadID))
1924 if (value > sp->bestValue) // Less then 2% of cases
1926 lock_grab(&(sp->lock));
1927 if (value > sp->bestValue && !thread_should_stop(threadID))
1929 sp->bestValue = value;
1930 if (sp->bestValue >= sp->beta)
1932 sp_update_pv(sp->parentSstack, ss, sp->ply);
1933 for (int i = 0; i < ActiveThreads; i++)
1934 if (i != threadID && (i == sp->master || sp->slaves[i]))
1935 Threads[i].stop = true;
1937 sp->finished = true;
1940 lock_release(&(sp->lock));
1944 lock_grab(&(sp->lock));
1946 // If this is the master thread and we have been asked to stop because of
1947 // a beta cutoff higher up in the tree, stop all slave threads.
1948 if (sp->master == threadID && thread_should_stop(threadID))
1949 for (int i = 0; i < ActiveThreads; i++)
1951 Threads[i].stop = true;
1954 sp->slaves[threadID] = 0;
1956 lock_release(&(sp->lock));
1960 // sp_search_pv() is used to search from a PV split point. This function
1961 // is called by each thread working at the split point. It is similar to
1962 // the normal search_pv() function, but simpler. Because we have already
1963 // probed the hash table and searched the first move before splitting, we
1964 // don't have to repeat all this work in sp_search_pv(). We also don't
1965 // need to store anything to the hash table here: This is taken care of
1966 // after we return from the split point.
1968 void sp_search_pv(SplitPoint* sp, int threadID) {
1970 assert(threadID >= 0 && threadID < ActiveThreads);
1971 assert(ActiveThreads > 1);
1973 Position pos = Position(sp->pos);
1975 SearchStack* ss = sp->sstack[threadID];
1979 while ( sp->alpha < sp->beta
1980 && !thread_should_stop(threadID)
1981 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1983 bool moveIsCheck = pos.move_is_check(move, ci);
1984 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1986 assert(move_is_ok(move));
1988 lock_grab(&(sp->lock));
1989 int moveCount = ++sp->moves;
1990 lock_release(&(sp->lock));
1992 ss[sp->ply].currentMove = move;
1994 // Decide the new search depth.
1996 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1997 Depth newDepth = sp->depth - OnePly + ext;
1999 // Make and search the move.
2001 pos.do_move(move, st, ci, moveIsCheck);
2003 // Try to reduce non-pv search depth by one ply if move seems not problematic,
2004 // if the move fails high will be re-searched at full depth.
2006 && !captureOrPromotion
2007 && !move_is_castle(move)
2008 && !move_is_killer(move, ss[sp->ply]))
2010 double red = ln(moveCount) * ln(sp->depth / 2) / 3.0;
2013 ss[sp->ply].reduction = Depth(floor(red * int(OnePly)));
2014 value = -search(pos, ss, -sp->alpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
2017 value = sp->alpha + 1; // Just to trigger next condition
2020 value = sp->alpha + 1; // Just to trigger next condition
2022 if (value > sp->alpha) // Go with full depth non-pv search
2024 ss[sp->ply].reduction = Depth(0);
2025 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
2027 if (value > sp->alpha && value < sp->beta)
2029 // When the search fails high at ply 1 while searching the first
2030 // move at the root, set the flag failHighPly1. This is used for
2031 // time managment: We don't want to stop the search early in
2032 // such cases, because resolving the fail high at ply 1 could
2033 // result in a big drop in score at the root.
2034 if (sp->ply == 1 && RootMoveNumber == 1)
2035 Threads[threadID].failHighPly1 = true;
2037 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
2038 Threads[threadID].failHighPly1 = false;
2041 pos.undo_move(move);
2043 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2045 if (thread_should_stop(threadID))
2049 lock_grab(&(sp->lock));
2050 if (value > sp->bestValue && !thread_should_stop(threadID))
2052 sp->bestValue = value;
2053 if (value > sp->alpha)
2056 sp_update_pv(sp->parentSstack, ss, sp->ply);
2057 if (value == value_mate_in(sp->ply + 1))
2058 ss[sp->ply].mateKiller = move;
2060 if (value >= sp->beta)
2062 for (int i = 0; i < ActiveThreads; i++)
2063 if (i != threadID && (i == sp->master || sp->slaves[i]))
2064 Threads[i].stop = true;
2066 sp->finished = true;
2069 // If we are at ply 1, and we are searching the first root move at
2070 // ply 0, set the 'Problem' variable if the score has dropped a lot
2071 // (from the computer's point of view) since the previous iteration.
2074 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2077 lock_release(&(sp->lock));
2080 lock_grab(&(sp->lock));
2082 // If this is the master thread and we have been asked to stop because of
2083 // a beta cutoff higher up in the tree, stop all slave threads.
2084 if (sp->master == threadID && thread_should_stop(threadID))
2085 for (int i = 0; i < ActiveThreads; i++)
2087 Threads[i].stop = true;
2090 sp->slaves[threadID] = 0;
2092 lock_release(&(sp->lock));
2095 /// The BetaCounterType class
2097 BetaCounterType::BetaCounterType() { clear(); }
2099 void BetaCounterType::clear() {
2101 for (int i = 0; i < THREAD_MAX; i++)
2102 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2105 void BetaCounterType::add(Color us, Depth d, int threadID) {
2107 // Weighted count based on depth
2108 Threads[threadID].betaCutOffs[us] += unsigned(d);
2111 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2114 for (int i = 0; i < THREAD_MAX; i++)
2116 our += Threads[i].betaCutOffs[us];
2117 their += Threads[i].betaCutOffs[opposite_color(us)];
2122 /// The RootMoveList class
2124 // RootMoveList c'tor
2126 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2128 MoveStack mlist[MaxRootMoves];
2129 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2131 // Generate all legal moves
2132 MoveStack* last = generate_moves(pos, mlist);
2134 // Add each move to the moves[] array
2135 for (MoveStack* cur = mlist; cur != last; cur++)
2137 bool includeMove = includeAllMoves;
2139 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2140 includeMove = (searchMoves[k] == cur->move);
2145 // Find a quick score for the move
2147 SearchStack ss[PLY_MAX_PLUS_2];
2150 moves[count].move = cur->move;
2151 pos.do_move(moves[count].move, st);
2152 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2153 pos.undo_move(moves[count].move);
2154 moves[count].pv[0] = moves[count].move;
2155 moves[count].pv[1] = MOVE_NONE;
2162 // RootMoveList simple methods definitions
2164 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2166 moves[moveNum].nodes = nodes;
2167 moves[moveNum].cumulativeNodes += nodes;
2170 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2172 moves[moveNum].ourBeta = our;
2173 moves[moveNum].theirBeta = their;
2176 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2180 for (j = 0; pv[j] != MOVE_NONE; j++)
2181 moves[moveNum].pv[j] = pv[j];
2183 moves[moveNum].pv[j] = MOVE_NONE;
2187 // RootMoveList::sort() sorts the root move list at the beginning of a new
2190 void RootMoveList::sort() {
2192 sort_multipv(count - 1); // Sort all items
2196 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2197 // list by their scores and depths. It is used to order the different PVs
2198 // correctly in MultiPV mode.
2200 void RootMoveList::sort_multipv(int n) {
2204 for (i = 1; i <= n; i++)
2206 RootMove rm = moves[i];
2207 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2208 moves[j] = moves[j - 1];
2215 // init_node() is called at the beginning of all the search functions
2216 // (search(), search_pv(), qsearch(), and so on) and initializes the
2217 // search stack object corresponding to the current node. Once every
2218 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2219 // for user input and checks whether it is time to stop the search.
2221 void init_node(SearchStack ss[], int ply, int threadID) {
2223 assert(ply >= 0 && ply < PLY_MAX);
2224 assert(threadID >= 0 && threadID < ActiveThreads);
2226 Threads[threadID].nodes++;
2231 if (NodesSincePoll >= NodesBetweenPolls)
2238 ss[ply + 2].initKillers();
2240 if (Threads[threadID].printCurrentLine)
2241 print_current_line(ss, ply, threadID);
2245 // update_pv() is called whenever a search returns a value > alpha.
2246 // It updates the PV in the SearchStack object corresponding to the
2249 void update_pv(SearchStack ss[], int ply) {
2251 assert(ply >= 0 && ply < PLY_MAX);
2255 ss[ply].pv[ply] = ss[ply].currentMove;
2257 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2258 ss[ply].pv[p] = ss[ply + 1].pv[p];
2260 ss[ply].pv[p] = MOVE_NONE;
2264 // sp_update_pv() is a variant of update_pv for use at split points. The
2265 // difference between the two functions is that sp_update_pv also updates
2266 // the PV at the parent node.
2268 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2270 assert(ply >= 0 && ply < PLY_MAX);
2274 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2276 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2277 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2279 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2283 // connected_moves() tests whether two moves are 'connected' in the sense
2284 // that the first move somehow made the second move possible (for instance
2285 // if the moving piece is the same in both moves). The first move is assumed
2286 // to be the move that was made to reach the current position, while the
2287 // second move is assumed to be a move from the current position.
2289 bool connected_moves(const Position& pos, Move m1, Move m2) {
2291 Square f1, t1, f2, t2;
2294 assert(move_is_ok(m1));
2295 assert(move_is_ok(m2));
2297 if (m2 == MOVE_NONE)
2300 // Case 1: The moving piece is the same in both moves
2306 // Case 2: The destination square for m2 was vacated by m1
2312 // Case 3: Moving through the vacated square
2313 if ( piece_is_slider(pos.piece_on(f2))
2314 && bit_is_set(squares_between(f2, t2), f1))
2317 // Case 4: The destination square for m2 is defended by the moving piece in m1
2318 p = pos.piece_on(t1);
2319 if (bit_is_set(pos.attacks_from(p, t1), t2))
2322 // Case 5: Discovered check, checking piece is the piece moved in m1
2323 if ( piece_is_slider(p)
2324 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2325 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2327 // discovered_check_candidates() works also if the Position's side to
2328 // move is the opposite of the checking piece.
2329 Color them = opposite_color(pos.side_to_move());
2330 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2332 if (bit_is_set(dcCandidates, f2))
2339 // value_is_mate() checks if the given value is a mate one
2340 // eventually compensated for the ply.
2342 bool value_is_mate(Value value) {
2344 assert(abs(value) <= VALUE_INFINITE);
2346 return value <= value_mated_in(PLY_MAX)
2347 || value >= value_mate_in(PLY_MAX);
2351 // move_is_killer() checks if the given move is among the
2352 // killer moves of that ply.
2354 bool move_is_killer(Move m, const SearchStack& ss) {
2356 const Move* k = ss.killers;
2357 for (int i = 0; i < KILLER_MAX; i++, k++)
2365 // extension() decides whether a move should be searched with normal depth,
2366 // or with extended depth. Certain classes of moves (checking moves, in
2367 // particular) are searched with bigger depth than ordinary moves and in
2368 // any case are marked as 'dangerous'. Note that also if a move is not
2369 // extended, as example because the corresponding UCI option is set to zero,
2370 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2372 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2373 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2375 assert(m != MOVE_NONE);
2377 Depth result = Depth(0);
2378 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2383 result += CheckExtension[pvNode];
2386 result += SingleEvasionExtension[pvNode];
2389 result += MateThreatExtension[pvNode];
2392 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2394 Color c = pos.side_to_move();
2395 if (relative_rank(c, move_to(m)) == RANK_7)
2397 result += PawnPushTo7thExtension[pvNode];
2400 if (pos.pawn_is_passed(c, move_to(m)))
2402 result += PassedPawnExtension[pvNode];
2407 if ( captureOrPromotion
2408 && pos.type_of_piece_on(move_to(m)) != PAWN
2409 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2410 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2411 && !move_is_promotion(m)
2414 result += PawnEndgameExtension[pvNode];
2419 && captureOrPromotion
2420 && pos.type_of_piece_on(move_to(m)) != PAWN
2421 && pos.see_sign(m) >= 0)
2427 return Min(result, OnePly);
2431 // ok_to_do_nullmove() looks at the current position and decides whether
2432 // doing a 'null move' should be allowed. In order to avoid zugzwang
2433 // problems, null moves are not allowed when the side to move has very
2434 // little material left. Currently, the test is a bit too simple: Null
2435 // moves are avoided only when the side to move has only pawns left.
2436 // It's probably a good idea to avoid null moves in at least some more
2437 // complicated endgames, e.g. KQ vs KR. FIXME
2439 bool ok_to_do_nullmove(const Position& pos) {
2441 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2445 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2446 // non-tactical moves late in the move list close to the leaves are
2447 // candidates for pruning.
2449 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2451 assert(move_is_ok(m));
2452 assert(threat == MOVE_NONE || move_is_ok(threat));
2453 assert(!pos.move_is_check(m));
2454 assert(!pos.move_is_capture_or_promotion(m));
2455 assert(!pos.move_is_passed_pawn_push(m));
2457 Square mfrom, mto, tfrom, tto;
2459 // Prune if there isn't any threat move and
2460 // is not a castling move (common case).
2461 if (threat == MOVE_NONE && !move_is_castle(m))
2464 mfrom = move_from(m);
2466 tfrom = move_from(threat);
2467 tto = move_to(threat);
2469 // Case 1: Castling moves are never pruned
2470 if (move_is_castle(m))
2473 // Case 2: Don't prune moves which move the threatened piece
2477 // Case 3: If the threatened piece has value less than or equal to the
2478 // value of the threatening piece, don't prune move which defend it.
2479 if ( pos.move_is_capture(threat)
2480 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2481 || pos.type_of_piece_on(tfrom) == KING)
2482 && pos.move_attacks_square(m, tto))
2485 // Case 4: If the moving piece in the threatened move is a slider, don't
2486 // prune safe moves which block its ray.
2487 if ( piece_is_slider(pos.piece_on(tfrom))
2488 && bit_is_set(squares_between(tfrom, tto), mto)
2489 && pos.see_sign(m) >= 0)
2496 // ok_to_use_TT() returns true if a transposition table score
2497 // can be used at a given point in search.
2499 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2501 Value v = value_from_tt(tte->value(), ply);
2503 return ( tte->depth() >= depth
2504 || v >= Max(value_mate_in(PLY_MAX), beta)
2505 || v < Min(value_mated_in(PLY_MAX), beta))
2507 && ( (is_lower_bound(tte->type()) && v >= beta)
2508 || (is_upper_bound(tte->type()) && v < beta));
2512 // refine_eval() returns the transposition table score if
2513 // possible otherwise falls back on static position evaluation.
2515 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2520 Value v = value_from_tt(tte->value(), ply);
2522 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2523 || (is_upper_bound(tte->type()) && v < defaultEval))
2529 // update_history() registers a good move that produced a beta-cutoff
2530 // in history and marks as failures all the other moves of that ply.
2532 void update_history(const Position& pos, Move move, Depth depth,
2533 Move movesSearched[], int moveCount) {
2537 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2539 for (int i = 0; i < moveCount - 1; i++)
2541 m = movesSearched[i];
2545 if (!pos.move_is_capture_or_promotion(m))
2546 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2551 // update_killers() add a good move that produced a beta-cutoff
2552 // among the killer moves of that ply.
2554 void update_killers(Move m, SearchStack& ss) {
2556 if (m == ss.killers[0])
2559 for (int i = KILLER_MAX - 1; i > 0; i--)
2560 ss.killers[i] = ss.killers[i - 1];
2566 // fail_high_ply_1() checks if some thread is currently resolving a fail
2567 // high at ply 1 at the node below the first root node. This information
2568 // is used for time management.
2570 bool fail_high_ply_1() {
2572 for (int i = 0; i < ActiveThreads; i++)
2573 if (Threads[i].failHighPly1)
2580 // current_search_time() returns the number of milliseconds which have passed
2581 // since the beginning of the current search.
2583 int current_search_time() {
2585 return get_system_time() - SearchStartTime;
2589 // nps() computes the current nodes/second count.
2593 int t = current_search_time();
2594 return (t > 0 ? int((nodes_searched() * 1000) / t) : 0);
2598 // poll() performs two different functions: It polls for user input, and it
2599 // looks at the time consumed so far and decides if it's time to abort the
2604 static int lastInfoTime;
2605 int t = current_search_time();
2610 // We are line oriented, don't read single chars
2611 std::string command;
2613 if (!std::getline(std::cin, command))
2616 if (command == "quit")
2619 PonderSearch = false;
2623 else if (command == "stop")
2626 PonderSearch = false;
2628 else if (command == "ponderhit")
2632 // Print search information
2636 else if (lastInfoTime > t)
2637 // HACK: Must be a new search where we searched less than
2638 // NodesBetweenPolls nodes during the first second of search.
2641 else if (t - lastInfoTime >= 1000)
2649 if (dbg_show_hit_rate)
2650 dbg_print_hit_rate();
2652 cout << "info nodes " << nodes_searched() << " nps " << nps()
2653 << " time " << t << " hashfull " << TT.full() << endl;
2655 lock_release(&IOLock);
2657 if (ShowCurrentLine)
2658 Threads[0].printCurrentLine = true;
2661 // Should we stop the search?
2665 bool stillAtFirstMove = RootMoveNumber == 1
2667 && t > MaxSearchTime + ExtraSearchTime;
2669 bool noProblemFound = !FailHigh
2671 && !fail_high_ply_1()
2673 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2675 bool noMoreTime = t > AbsoluteMaxSearchTime
2676 || stillAtFirstMove //FIXME: We are not checking any problem flags, BUG?
2679 if ( (Iteration >= 3 && !InfiniteSearch && noMoreTime)
2680 || (ExactMaxTime && t >= ExactMaxTime)
2681 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2686 // ponderhit() is called when the program is pondering (i.e. thinking while
2687 // it's the opponent's turn to move) in order to let the engine know that
2688 // it correctly predicted the opponent's move.
2692 int t = current_search_time();
2693 PonderSearch = false;
2695 bool stillAtFirstMove = RootMoveNumber == 1
2697 && t > MaxSearchTime + ExtraSearchTime;
2699 bool noProblemFound = !FailHigh
2701 && !fail_high_ply_1()
2703 && t > 6 * (MaxSearchTime + ExtraSearchTime);
2705 bool noMoreTime = t > AbsoluteMaxSearchTime
2709 if (Iteration >= 3 && !InfiniteSearch && (noMoreTime || StopOnPonderhit))
2714 // print_current_line() prints the current line of search for a given
2715 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2717 void print_current_line(SearchStack ss[], int ply, int threadID) {
2719 assert(ply >= 0 && ply < PLY_MAX);
2720 assert(threadID >= 0 && threadID < ActiveThreads);
2722 if (!Threads[threadID].idle)
2725 cout << "info currline " << (threadID + 1);
2726 for (int p = 0; p < ply; p++)
2727 cout << " " << ss[p].currentMove;
2730 lock_release(&IOLock);
2732 Threads[threadID].printCurrentLine = false;
2733 if (threadID + 1 < ActiveThreads)
2734 Threads[threadID + 1].printCurrentLine = true;
2738 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2740 void init_ss_array(SearchStack ss[]) {
2742 for (int i = 0; i < 3; i++)
2745 ss[i].initKillers();
2750 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2751 // while the program is pondering. The point is to work around a wrinkle in
2752 // the UCI protocol: When pondering, the engine is not allowed to give a
2753 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2754 // We simply wait here until one of these commands is sent, and return,
2755 // after which the bestmove and pondermove will be printed (in id_loop()).
2757 void wait_for_stop_or_ponderhit() {
2759 std::string command;
2763 if (!std::getline(std::cin, command))
2766 if (command == "quit")
2771 else if (command == "ponderhit" || command == "stop")
2777 // idle_loop() is where the threads are parked when they have no work to do.
2778 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2779 // object for which the current thread is the master.
2781 void idle_loop(int threadID, SplitPoint* waitSp) {
2783 assert(threadID >= 0 && threadID < THREAD_MAX);
2785 Threads[threadID].running = true;
2789 if (AllThreadsShouldExit && threadID != 0)
2792 // If we are not thinking, wait for a condition to be signaled
2793 // instead of wasting CPU time polling for work.
2794 while (threadID != 0 && (Idle || threadID >= ActiveThreads))
2797 #if !defined(_MSC_VER)
2798 pthread_mutex_lock(&WaitLock);
2799 if (Idle || threadID >= ActiveThreads)
2800 pthread_cond_wait(&WaitCond, &WaitLock);
2802 pthread_mutex_unlock(&WaitLock);
2804 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2808 // If this thread has been assigned work, launch a search
2809 if (Threads[threadID].workIsWaiting)
2811 Threads[threadID].workIsWaiting = false;
2812 if (Threads[threadID].splitPoint->pvNode)
2813 sp_search_pv(Threads[threadID].splitPoint, threadID);
2815 sp_search(Threads[threadID].splitPoint, threadID);
2817 Threads[threadID].idle = true;
2820 // If this thread is the master of a split point and all threads have
2821 // finished their work at this split point, return from the idle loop.
2822 if (waitSp != NULL && waitSp->cpus == 0)
2826 Threads[threadID].running = false;
2830 // init_split_point_stack() is called during program initialization, and
2831 // initializes all split point objects.
2833 void init_split_point_stack() {
2835 for (int i = 0; i < THREAD_MAX; i++)
2836 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2838 SplitPointStack[i][j].parent = NULL;
2839 lock_init(&(SplitPointStack[i][j].lock), NULL);
2844 // destroy_split_point_stack() is called when the program exits, and
2845 // destroys all locks in the precomputed split point objects.
2847 void destroy_split_point_stack() {
2849 for (int i = 0; i < THREAD_MAX; i++)
2850 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2851 lock_destroy(&(SplitPointStack[i][j].lock));
2855 // thread_should_stop() checks whether the thread with a given threadID has
2856 // been asked to stop, directly or indirectly. This can happen if a beta
2857 // cutoff has occurred in the thread's currently active split point, or in
2858 // some ancestor of the current split point.
2860 bool thread_should_stop(int threadID) {
2862 assert(threadID >= 0 && threadID < ActiveThreads);
2866 if (Threads[threadID].stop)
2868 if (ActiveThreads <= 2)
2870 for (sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2873 Threads[threadID].stop = true;
2880 // thread_is_available() checks whether the thread with threadID "slave" is
2881 // available to help the thread with threadID "master" at a split point. An
2882 // obvious requirement is that "slave" must be idle. With more than two
2883 // threads, this is not by itself sufficient: If "slave" is the master of
2884 // some active split point, it is only available as a slave to the other
2885 // threads which are busy searching the split point at the top of "slave"'s
2886 // split point stack (the "helpful master concept" in YBWC terminology).
2888 bool thread_is_available(int slave, int master) {
2890 assert(slave >= 0 && slave < ActiveThreads);
2891 assert(master >= 0 && master < ActiveThreads);
2892 assert(ActiveThreads > 1);
2894 if (!Threads[slave].idle || slave == master)
2897 if (Threads[slave].activeSplitPoints == 0)
2898 // No active split points means that the thread is available as
2899 // a slave for any other thread.
2902 if (ActiveThreads == 2)
2905 // Apply the "helpful master" concept if possible
2906 if (SplitPointStack[slave][Threads[slave].activeSplitPoints - 1].slaves[master])
2913 // idle_thread_exists() tries to find an idle thread which is available as
2914 // a slave for the thread with threadID "master".
2916 bool idle_thread_exists(int master) {
2918 assert(master >= 0 && master < ActiveThreads);
2919 assert(ActiveThreads > 1);
2921 for (int i = 0; i < ActiveThreads; i++)
2922 if (thread_is_available(i, master))
2929 // split() does the actual work of distributing the work at a node between
2930 // several threads at PV nodes. If it does not succeed in splitting the
2931 // node (because no idle threads are available, or because we have no unused
2932 // split point objects), the function immediately returns false. If
2933 // splitting is possible, a SplitPoint object is initialized with all the
2934 // data that must be copied to the helper threads (the current position and
2935 // search stack, alpha, beta, the search depth, etc.), and we tell our
2936 // helper threads that they have been assigned work. This will cause them
2937 // to instantly leave their idle loops and call sp_search_pv(). When all
2938 // threads have returned from sp_search_pv (or, equivalently, when
2939 // splitPoint->cpus becomes 0), split() returns true.
2941 bool split(const Position& p, SearchStack* sstck, int ply,
2942 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2943 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2946 assert(sstck != NULL);
2947 assert(ply >= 0 && ply < PLY_MAX);
2948 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2949 assert(!pvNode || *alpha < *beta);
2950 assert(*beta <= VALUE_INFINITE);
2951 assert(depth > Depth(0));
2952 assert(master >= 0 && master < ActiveThreads);
2953 assert(ActiveThreads > 1);
2955 SplitPoint* splitPoint;
2960 // If no other thread is available to help us, or if we have too many
2961 // active split points, don't split.
2962 if ( !idle_thread_exists(master)
2963 || Threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2965 lock_release(&MPLock);
2969 // Pick the next available split point object from the split point stack
2970 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2971 Threads[master].activeSplitPoints++;
2973 // Initialize the split point object and copy current position
2974 splitPoint->parent = Threads[master].splitPoint;
2975 splitPoint->finished = false;
2976 splitPoint->ply = ply;
2977 splitPoint->depth = depth;
2978 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2979 splitPoint->beta = *beta;
2980 splitPoint->pvNode = pvNode;
2981 splitPoint->bestValue = *bestValue;
2982 splitPoint->futilityValue = futilityValue;
2983 splitPoint->master = master;
2984 splitPoint->mp = mp;
2985 splitPoint->moves = *moves;
2986 splitPoint->cpus = 1;
2987 splitPoint->pos.copy(p);
2988 splitPoint->parentSstack = sstck;
2989 for (i = 0; i < ActiveThreads; i++)
2990 splitPoint->slaves[i] = 0;
2992 // Copy the current search stack to the master thread
2993 memcpy(splitPoint->sstack[master], sstck, (ply+1) * sizeof(SearchStack));
2994 Threads[master].splitPoint = splitPoint;
2996 // Make copies of the current position and search stack for each thread
2997 for (i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2998 if (thread_is_available(i, master))
3000 memcpy(splitPoint->sstack[i], sstck, (ply+1) * sizeof(SearchStack));
3001 Threads[i].splitPoint = splitPoint;
3002 splitPoint->slaves[i] = 1;
3006 // Tell the threads that they have work to do. This will make them leave
3008 for (i = 0; i < ActiveThreads; i++)
3009 if (i == master || splitPoint->slaves[i])
3011 Threads[i].workIsWaiting = true;
3012 Threads[i].idle = false;
3013 Threads[i].stop = false;
3016 lock_release(&MPLock);
3018 // Everything is set up. The master thread enters the idle loop, from
3019 // which it will instantly launch a search, because its workIsWaiting
3020 // slot is 'true'. We send the split point as a second parameter to the
3021 // idle loop, which means that the main thread will return from the idle
3022 // loop when all threads have finished their work at this split point
3023 // (i.e. when splitPoint->cpus == 0).
3024 idle_loop(master, splitPoint);
3026 // We have returned from the idle loop, which means that all threads are
3027 // finished. Update alpha, beta and bestValue, and return.
3031 *alpha = splitPoint->alpha;
3033 *beta = splitPoint->beta;
3034 *bestValue = splitPoint->bestValue;
3035 Threads[master].stop = false;
3036 Threads[master].idle = false;
3037 Threads[master].activeSplitPoints--;
3038 Threads[master].splitPoint = splitPoint->parent;
3040 lock_release(&MPLock);
3045 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3046 // to start a new search from the root.
3048 void wake_sleeping_threads() {
3050 if (ActiveThreads > 1)
3052 for (int i = 1; i < ActiveThreads; i++)
3054 Threads[i].idle = true;
3055 Threads[i].workIsWaiting = false;
3058 #if !defined(_MSC_VER)
3059 pthread_mutex_lock(&WaitLock);
3060 pthread_cond_broadcast(&WaitCond);
3061 pthread_mutex_unlock(&WaitLock);
3063 for (int i = 1; i < THREAD_MAX; i++)
3064 SetEvent(SitIdleEvent[i]);
3070 // init_thread() is the function which is called when a new thread is
3071 // launched. It simply calls the idle_loop() function with the supplied
3072 // threadID. There are two versions of this function; one for POSIX
3073 // threads and one for Windows threads.
3075 #if !defined(_MSC_VER)
3077 void* init_thread(void *threadID) {
3079 idle_loop(*(int*)threadID, NULL);
3085 DWORD WINAPI init_thread(LPVOID threadID) {
3087 idle_loop(*(int*)threadID, NULL);