2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
39 #include "ucioption.h"
46 // Set to true to force running with one thread. Used for debugging
47 const bool FakeSplit = false;
49 // Different node types, used as template parameter
50 enum NodeType { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
52 // RootMove struct is used for moves at the root of the tree. For each root
53 // move, we store two scores, a node count, and a PV (really a refutation
54 // in the case of moves which fail low). Value pv_score is normally set at
55 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
56 // according to the order in which moves are returned by MovePicker.
60 RootMove(const RootMove& rm) { *this = rm; }
61 RootMove& operator=(const RootMove& rm);
63 // RootMove::operator<() is the comparison function used when
64 // sorting the moves. A move m1 is considered to be better
65 // than a move m2 if it has an higher pv_score, or if it has
66 // equal pv_score but m1 has the higher non_pv_score. In this way
67 // we are guaranteed that PV moves are always sorted as first.
68 bool operator<(const RootMove& m) const {
69 return pv_score != m.pv_score ? pv_score < m.pv_score
70 : non_pv_score < m.non_pv_score;
73 void extract_pv_from_tt(Position& pos);
74 void insert_pv_in_tt(Position& pos);
75 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
76 Value alpha, Value beta, int pvIdx);
80 Move pv[PLY_MAX_PLUS_2];
83 // RootMoveList struct is just a vector of RootMove objects,
84 // with an handful of methods above the standard ones.
85 struct RootMoveList : public std::vector<RootMove> {
87 typedef std::vector<RootMove> Base;
89 void init(Position& pos, Move searchMoves[]);
90 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
91 void sort_first(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
99 // Lookup table to check if a Piece is a slider and its access function
100 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
101 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
105 // Maximum depth for razoring
106 const Depth RazorDepth = 4 * ONE_PLY;
108 // Dynamic razoring margin based on depth
109 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
111 // Maximum depth for use of dynamic threat detection when null move fails low
112 const Depth ThreatDepth = 5 * ONE_PLY;
114 // Step 9. Internal iterative deepening
116 // Minimum depth for use of internal iterative deepening
117 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
119 // At Non-PV nodes we do an internal iterative deepening search
120 // when the static evaluation is bigger then beta - IIDMargin.
121 const Value IIDMargin = Value(0x100);
123 // Step 11. Decide the new search depth
125 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
126 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
127 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
128 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
129 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
131 // Minimum depth for use of singular extension
132 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
134 // Step 12. Futility pruning
136 // Futility margin for quiescence search
137 const Value FutilityMarginQS = Value(0x80);
139 // Futility lookup tables (initialized at startup) and their access functions
140 Value FutilityMargins[16][64]; // [depth][moveNumber]
141 int FutilityMoveCounts[32]; // [depth]
143 inline Value futility_margin(Depth d, int mn) {
145 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
146 : 2 * VALUE_INFINITE;
149 inline int futility_move_count(Depth d) {
151 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
154 // Step 14. Reduced search
156 // Reduction lookup tables (initialized at startup) and their access function
157 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
159 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
161 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
164 // Easy move margin. An easy move candidate must be at least this much
165 // better than the second best move.
166 const Value EasyMoveMargin = Value(0x200);
169 /// Namespace variables
175 int MultiPV, UCIMultiPV;
177 // Time management variables
178 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
183 std::ofstream LogFile;
185 // Skill level adjustment
187 bool SkillLevelEnabled;
189 // Node counters, used only by thread[0] but try to keep in different cache
190 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
191 bool SendSearchedNodes;
193 int NodesBetweenPolls = 30000;
201 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
203 template <NodeType NT>
204 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
206 template <NodeType NT>
207 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
209 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
210 bool connected_moves(const Position& pos, Move m1, Move m2);
211 Value value_to_tt(Value v, int ply);
212 Value value_from_tt(Value v, int ply);
213 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
214 bool connected_threat(const Position& pos, Move m, Move threat);
215 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
216 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
217 void update_gains(const Position& pos, Move move, Value before, Value after);
218 void do_skill_level(Move* best, Move* ponder);
220 int current_search_time(int set = 0);
221 std::string value_to_uci(Value v);
222 std::string speed_to_uci(int64_t nodes);
223 void poll(const Position& pos);
224 void wait_for_stop_or_ponderhit();
226 // MovePickerExt template class extends MovePicker and allows to choose at compile
227 // time the proper moves source according to the type of node. In the default case
228 // we simply create and use a standard MovePicker object.
229 template<NodeType> struct MovePickerExt : public MovePicker {
231 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
232 : MovePicker(p, ttm, d, h, ss, b) {}
234 RootMove& current() { assert(false); return Rml[0]; } // Dummy, needed to compile
237 // In case of a SpNode we use split point's shared MovePicker object as moves source
238 template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
240 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
241 : MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
243 Move get_next_move() { return mp->get_next_move(); }
247 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
249 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
250 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
253 // In case of a Root node we use RootMoveList as moves source
254 template<> struct MovePickerExt<Root> : public MovePicker {
256 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
257 RootMove& current() { return Rml[cur]; }
258 Move get_next_move() { return ++cur < (int)Rml.size() ? Rml[cur].pv[0] : MOVE_NONE; }
263 // Overload operator<<() to make it easier to print moves in a coordinate
264 // notation compatible with UCI protocol.
265 std::ostream& operator<<(std::ostream& os, Move m) {
267 bool chess960 = (os.iword(0) != 0); // See set960()
268 return os << move_to_uci(m, chess960);
271 // When formatting a move for std::cout we must know if we are in Chess960
272 // or not. To keep using the handy operator<<() on the move the trick is to
273 // embed this flag in the stream itself. Function-like named enum set960 is
274 // used as a custom manipulator and the stream internal general-purpose array,
275 // accessed through ios_base::iword(), is used to pass the flag to the move's
276 // operator<<() that will read it to properly format castling moves.
279 std::ostream& operator<< (std::ostream& os, const set960& f) {
281 os.iword(0) = int(f);
285 // extension() decides whether a move should be searched with normal depth,
286 // or with extended depth. Certain classes of moves (checking moves, in
287 // particular) are searched with bigger depth than ordinary moves and in
288 // any case are marked as 'dangerous'. Note that also if a move is not
289 // extended, as example because the corresponding UCI option is set to zero,
290 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
291 template <bool PvNode>
292 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
293 bool moveIsCheck, bool* dangerous) {
294 assert(m != MOVE_NONE);
296 Depth result = DEPTH_ZERO;
297 *dangerous = moveIsCheck;
299 if (moveIsCheck && pos.see_sign(m) >= 0)
300 result += CheckExtension[PvNode];
302 if (pos.type_of_piece_on(move_from(m)) == PAWN)
304 Color c = pos.side_to_move();
305 if (relative_rank(c, move_to(m)) == RANK_7)
307 result += PawnPushTo7thExtension[PvNode];
310 if (pos.pawn_is_passed(c, move_to(m)))
312 result += PassedPawnExtension[PvNode];
317 if ( captureOrPromotion
318 && pos.type_of_piece_on(move_to(m)) != PAWN
319 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
320 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
321 && !move_is_special(m))
323 result += PawnEndgameExtension[PvNode];
327 return Min(result, ONE_PLY);
333 /// init_search() is called during startup to initialize various lookup tables
337 int d; // depth (ONE_PLY == 2)
338 int hd; // half depth (ONE_PLY == 1)
341 // Init reductions array
342 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
344 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
345 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
346 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
347 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
350 // Init futility margins array
351 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
352 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
354 // Init futility move count array
355 for (d = 0; d < 32; d++)
356 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
360 /// perft() is our utility to verify move generation. All the leaf nodes up to
361 /// the given depth are generated and counted and the sum returned.
363 int64_t perft(Position& pos, Depth depth) {
365 MoveStack mlist[MAX_MOVES];
370 // Generate all legal moves
371 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
373 // If we are at the last ply we don't need to do and undo
374 // the moves, just to count them.
375 if (depth <= ONE_PLY)
376 return int(last - mlist);
378 // Loop through all legal moves
380 for (MoveStack* cur = mlist; cur != last; cur++)
383 pos.do_move(m, st, ci, pos.move_gives_check(m, ci));
384 sum += perft(pos, depth - ONE_PLY);
391 /// think() is the external interface to Stockfish's search, and is called when
392 /// the program receives the UCI 'go' command. It initializes various global
393 /// variables, and calls id_loop(). It returns false when a "quit" command is
394 /// received during the search.
396 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
400 // Initialize global search-related variables
401 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
403 current_search_time(get_system_time());
405 TimeMgr.init(Limits, pos.startpos_ply_counter());
407 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
409 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
410 else if (Limits.time && Limits.time < 1000)
411 NodesBetweenPolls = 1000;
412 else if (Limits.time && Limits.time < 5000)
413 NodesBetweenPolls = 5000;
415 NodesBetweenPolls = 30000;
417 // Look for a book move
418 if (Options["OwnBook"].value<bool>())
420 if (Options["Book File"].value<std::string>() != book.name())
421 book.open(Options["Book File"].value<std::string>());
423 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
435 UCIMultiPV = Options["MultiPV"].value<int>();
436 SkillLevel = Options["Skill Level"].value<int>();
438 read_evaluation_uci_options(pos.side_to_move());
439 Threads.read_uci_options();
441 // If needed allocate pawn and material hash tables and adjust TT size
442 Threads.init_hash_tables();
443 TT.set_size(Options["Hash"].value<int>());
445 if (Options["Clear Hash"].value<bool>())
447 Options["Clear Hash"].set_value("false");
451 // Do we have to play with skill handicap? In this case enable MultiPV that
452 // we will use behind the scenes to retrieve a set of possible moves.
453 SkillLevelEnabled = (SkillLevel < 20);
454 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
456 // Wake up needed threads and reset maxPly counter
457 for (int i = 0; i < Threads.size(); i++)
459 Threads[i].wake_up();
460 Threads[i].maxPly = 0;
463 // Write to log file and keep it open to be accessed during the search
464 if (Options["Use Search Log"].value<bool>())
466 std::string name = Options["Search Log Filename"].value<std::string>();
467 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
469 if (LogFile.is_open())
470 LogFile << "\nSearching: " << pos.to_fen()
471 << "\ninfinite: " << Limits.infinite
472 << " ponder: " << Limits.ponder
473 << " time: " << Limits.time
474 << " increment: " << Limits.increment
475 << " moves to go: " << Limits.movesToGo
479 // We're ready to start thinking. Call the iterative deepening loop function
480 Move ponderMove = MOVE_NONE;
481 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
483 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
485 // Write final search statistics and close log file
486 if (LogFile.is_open())
488 int t = current_search_time();
490 LogFile << "Nodes: " << pos.nodes_searched()
491 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
492 << "\nBest move: " << move_to_san(pos, bestMove);
495 pos.do_move(bestMove, st);
496 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
497 pos.undo_move(bestMove); // Return from think() with unchanged position
501 // This makes all the threads to go to sleep
504 // If we are pondering or in infinite search, we shouldn't print the
505 // best move before we are told to do so.
506 if (!StopRequest && (Limits.ponder || Limits.infinite))
507 wait_for_stop_or_ponderhit();
509 // Could be MOVE_NONE when searching on a stalemate position
510 cout << "bestmove " << bestMove;
512 // UCI protol is not clear on allowing sending an empty ponder move, instead
513 // it is clear that ponder move is optional. So skip it if empty.
514 if (ponderMove != MOVE_NONE)
515 cout << " ponder " << ponderMove;
525 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
526 // with increasing depth until the allocated thinking time has been consumed,
527 // user stops the search, or the maximum search depth is reached.
529 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
531 SearchStack ss[PLY_MAX_PLUS_2];
532 Value bestValues[PLY_MAX_PLUS_2];
533 int bestMoveChanges[PLY_MAX_PLUS_2];
534 int depth, selDepth, aspirationDelta;
535 Value value, alpha, beta;
536 Move bestMove, easyMove, skillBest, skillPonder;
538 // Initialize stuff before a new search
539 memset(ss, 0, 4 * sizeof(SearchStack));
542 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
543 depth = aspirationDelta = 0;
544 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
545 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
547 // Moves to search are verified and copied
548 Rml.init(pos, searchMoves);
550 // Handle special case of searching on a mate/stalemate position
553 cout << "info depth 0 score "
554 << value_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW)
560 // Iterative deepening loop until requested to stop or target depth reached
561 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
563 Rml.bestMoveChanges = 0;
564 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
566 // Calculate dynamic aspiration window based on previous iterations
567 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
569 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
570 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
572 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
573 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
575 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
576 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
579 // Start with a small aspiration window and, in case of fail high/low,
580 // research with bigger window until not failing high/low anymore.
582 // Search starting from ss+1 to allow calling update_gains()
583 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
585 // Write PV back to transposition table in case the relevant entries
586 // have been overwritten during the search.
587 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
588 Rml[i].insert_pv_in_tt(pos);
590 // Value cannot be trusted. Break out immediately!
594 // In case of failing high/low increase aspiration window and research,
595 // otherwise exit the fail high/low loop.
598 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
599 aspirationDelta += aspirationDelta / 2;
601 else if (value <= alpha)
603 AspirationFailLow = true;
604 StopOnPonderhit = false;
606 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
607 aspirationDelta += aspirationDelta / 2;
612 } while (abs(value) < VALUE_KNOWN_WIN);
614 // Collect info about search result
615 bestMove = Rml[0].pv[0];
616 *ponderMove = Rml[0].pv[1];
617 bestValues[depth] = value;
618 bestMoveChanges[depth] = Rml.bestMoveChanges;
620 // Do we need to pick now the best and the ponder moves ?
621 if (SkillLevelEnabled && depth == 1 + SkillLevel)
622 do_skill_level(&skillBest, &skillPonder);
624 // Retrieve max searched depth among threads
626 for (int i = 0; i < Threads.size(); i++)
627 if (Threads[i].maxPly > selDepth)
628 selDepth = Threads[i].maxPly;
630 // Send PV line to GUI and to log file
631 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
632 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
634 if (LogFile.is_open())
635 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
637 // Init easyMove after first iteration or drop if differs from the best move
638 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
640 else if (bestMove != easyMove)
641 easyMove = MOVE_NONE;
643 // Check for some early stop condition
644 if (!StopRequest && Limits.useTimeManagement())
646 // Stop search early when the last two iterations returned a mate score
648 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
649 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
652 // Stop search early if one move seems to be much better than the
653 // others or if there is only a single legal move. Also in the latter
654 // case we search up to some depth anyway to get a proper score.
656 && easyMove == bestMove
658 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
659 && current_search_time() > TimeMgr.available_time() / 16)
660 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
661 && current_search_time() > TimeMgr.available_time() / 32)))
664 // Take in account some extra time if the best move has changed
665 if (depth > 4 && depth < 50)
666 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
668 // Stop search if most of available time is already consumed. We probably don't
669 // have enough time to search the first move at the next iteration anyway.
670 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
673 // If we are allowed to ponder do not stop the search now but keep pondering
674 if (StopRequest && Limits.ponder)
677 StopOnPonderhit = true;
682 // When using skills overwrite best and ponder moves with the sub-optimal ones
683 if (SkillLevelEnabled)
685 if (skillBest == MOVE_NONE) // Still unassigned ?
686 do_skill_level(&skillBest, &skillPonder);
688 bestMove = skillBest;
689 *ponderMove = skillPonder;
696 // search<>() is the main search function for both PV and non-PV nodes and for
697 // normal and SplitPoint nodes. When called just after a split point the search
698 // is simpler because we have already probed the hash table, done a null move
699 // search, and searched the first move before splitting, we don't have to repeat
700 // all this work again. We also don't need to store anything to the hash table
701 // here: This is taken care of after we return from the split point.
703 template <NodeType NT>
704 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
706 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
707 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
708 const bool RootNode = (NT == Root);
710 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
711 assert(beta > alpha && beta <= VALUE_INFINITE);
712 assert(PvNode || alpha == beta - 1);
713 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
715 Move movesSearched[MAX_MOVES];
720 Move ttMove, move, excludedMove, threatMove;
723 Value bestValue, value, oldAlpha;
724 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
725 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
726 int moveCount = 0, playedMoveCount = 0;
727 Thread& thread = Threads[pos.thread()];
728 SplitPoint* sp = NULL;
730 refinedValue = bestValue = value = -VALUE_INFINITE;
732 inCheck = pos.in_check();
733 ss->ply = (ss-1)->ply + 1;
735 // Used to send selDepth info to GUI
736 if (PvNode && thread.maxPly < ss->ply)
737 thread.maxPly = ss->ply;
743 ttMove = excludedMove = MOVE_NONE;
744 threatMove = sp->threatMove;
745 goto split_point_start;
748 // Step 1. Initialize node and poll. Polling can abort search
749 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
750 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
751 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
753 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
759 // Step 2. Check for aborted search and immediate draw
761 || pos.is_draw<false>()
762 || ss->ply > PLY_MAX) && !RootNode)
765 // Step 3. Mate distance pruning
768 alpha = Max(value_mated_in(ss->ply), alpha);
769 beta = Min(value_mate_in(ss->ply+1), beta);
774 // Step 4. Transposition table lookup
775 // We don't want the score of a partial search to overwrite a previous full search
776 // TT value, so we use a different position key in case of an excluded move.
777 excludedMove = ss->excludedMove;
778 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
780 tte = TT.probe(posKey);
781 ttMove = tte ? tte->move() : MOVE_NONE;
783 // At PV nodes we check for exact scores, while at non-PV nodes we check for
784 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
785 // smooth experience in analysis mode.
786 if (tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
787 : ok_to_use_TT(tte, depth, beta, ss->ply)))
790 ss->bestMove = ttMove; // Can be MOVE_NONE
791 return value_from_tt(tte->value(), ss->ply);
794 // Step 5. Evaluate the position statically and update parent's gain statistics
796 ss->eval = ss->evalMargin = VALUE_NONE;
799 assert(tte->static_value() != VALUE_NONE);
801 ss->eval = tte->static_value();
802 ss->evalMargin = tte->static_value_margin();
803 refinedValue = refine_eval(tte, ss->eval, ss->ply);
807 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
808 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
811 // Save gain for the parent non-capture move
812 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
814 // Step 6. Razoring (is omitted in PV nodes)
816 && depth < RazorDepth
818 && refinedValue + razor_margin(depth) < beta
819 && ttMove == MOVE_NONE
820 && abs(beta) < VALUE_MATE_IN_PLY_MAX
821 && !pos.has_pawn_on_7th(pos.side_to_move()))
823 Value rbeta = beta - razor_margin(depth);
824 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
826 // Logically we should return (v + razor_margin(depth)), but
827 // surprisingly this did slightly weaker in tests.
831 // Step 7. Static null move pruning (is omitted in PV nodes)
832 // We're betting that the opponent doesn't have a move that will reduce
833 // the score by more than futility_margin(depth) if we do a null move.
836 && depth < RazorDepth
838 && refinedValue - futility_margin(depth, 0) >= beta
839 && abs(beta) < VALUE_MATE_IN_PLY_MAX
840 && pos.non_pawn_material(pos.side_to_move()))
841 return refinedValue - futility_margin(depth, 0);
843 // Step 8. Null move search with verification search (is omitted in PV nodes)
848 && refinedValue >= beta
849 && abs(beta) < VALUE_MATE_IN_PLY_MAX
850 && pos.non_pawn_material(pos.side_to_move()))
852 ss->currentMove = MOVE_NULL;
854 // Null move dynamic reduction based on depth
855 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
857 // Null move dynamic reduction based on value
858 if (refinedValue - PawnValueMidgame > beta)
861 pos.do_null_move(st);
862 (ss+1)->skipNullMove = true;
863 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
864 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
865 (ss+1)->skipNullMove = false;
866 pos.undo_null_move();
868 if (nullValue >= beta)
870 // Do not return unproven mate scores
871 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
874 if (depth < 6 * ONE_PLY)
877 // Do verification search at high depths
878 ss->skipNullMove = true;
879 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
880 ss->skipNullMove = false;
887 // The null move failed low, which means that we may be faced with
888 // some kind of threat. If the previous move was reduced, check if
889 // the move that refuted the null move was somehow connected to the
890 // move which was reduced. If a connection is found, return a fail
891 // low score (which will cause the reduced move to fail high in the
892 // parent node, which will trigger a re-search with full depth).
893 threatMove = (ss+1)->bestMove;
895 if ( depth < ThreatDepth
897 && threatMove != MOVE_NONE
898 && connected_moves(pos, (ss-1)->currentMove, threatMove))
903 // Step 9. ProbCut (is omitted in PV nodes)
904 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
905 // and a reduced search returns a value much above beta, we can (almost) safely
906 // prune the previous move.
908 && depth >= RazorDepth + ONE_PLY
911 && excludedMove == MOVE_NONE
912 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
914 Value rbeta = beta + 200;
915 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
917 assert(rdepth >= ONE_PLY);
919 MovePicker mp(pos, ttMove, H, Position::see_value(pos.captured_piece_type()));
922 while ((move = mp.get_next_move()) != MOVE_NONE)
923 if (pos.pl_move_is_legal(move, ci.pinned))
925 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
926 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
933 // Step 10. Internal iterative deepening
934 if ( depth >= IIDDepth[PvNode]
935 && ttMove == MOVE_NONE
936 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
938 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
940 ss->skipNullMove = true;
941 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
942 ss->skipNullMove = false;
944 tte = TT.probe(posKey);
945 ttMove = tte ? tte->move() : MOVE_NONE;
948 split_point_start: // At split points actual search starts from here
950 // Initialize a MovePicker object for the current position
951 MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
953 ss->bestMove = MOVE_NONE;
954 futilityBase = ss->eval + ss->evalMargin;
955 singularExtensionNode = !RootNode
957 && depth >= SingularExtensionDepth[PvNode]
958 && ttMove != MOVE_NONE
959 && !excludedMove // Do not allow recursive singular extension search
960 && (tte->type() & VALUE_TYPE_LOWER)
961 && tte->depth() >= depth - 3 * ONE_PLY;
964 lock_grab(&(sp->lock));
965 bestValue = sp->bestValue;
968 // Step 11. Loop through moves
969 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
970 while ( bestValue < beta
971 && (move = mp.get_next_move()) != MOVE_NONE
972 && !thread.cutoff_occurred())
974 assert(move_is_ok(move));
976 if (move == excludedMove)
979 // At PV and SpNode nodes we want the moves to be legal
980 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
985 moveCount = ++sp->moveCount;
986 lock_release(&(sp->lock));
993 // This is used by time management
994 FirstRootMove = (moveCount == 1);
996 // Save the current node count before the move is searched
997 nodes = pos.nodes_searched();
999 // If it's time to send nodes info, do it here where we have the
1000 // correct accumulated node counts searched by each thread.
1001 if (SendSearchedNodes)
1003 SendSearchedNodes = false;
1004 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1007 if (current_search_time() > 2000)
1008 cout << "info currmove " << move
1009 << " currmovenumber " << moveCount << endl;
1012 // At Root and at first iteration do a PV search on all the moves to score root moves
1013 isPvMove = (PvNode && moveCount <= (RootNode ? depth <= ONE_PLY ? MAX_MOVES : MultiPV : 1));
1014 givesCheck = pos.move_gives_check(move, ci);
1015 captureOrPromotion = pos.move_is_capture(move) || move_is_promotion(move);
1017 // Step 12. Decide the new search depth
1018 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1020 // Singular extension search. If all moves but one fail low on a search of
1021 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1022 // is singular and should be extended. To verify this we do a reduced search
1023 // on all the other moves but the ttMove, if result is lower than ttValue minus
1024 // a margin then we extend ttMove.
1025 if ( singularExtensionNode
1027 && pos.pl_move_is_legal(move, ci.pinned)
1030 Value ttValue = value_from_tt(tte->value(), ss->ply);
1032 if (abs(ttValue) < VALUE_KNOWN_WIN)
1034 Value rBeta = ttValue - int(depth);
1035 ss->excludedMove = move;
1036 ss->skipNullMove = true;
1037 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1038 ss->skipNullMove = false;
1039 ss->excludedMove = MOVE_NONE;
1040 ss->bestMove = MOVE_NONE;
1046 // Update current move (this must be done after singular extension search)
1047 newDepth = depth - ONE_PLY + ext;
1049 // Step 13. Futility pruning (is omitted in PV nodes)
1051 && !captureOrPromotion
1055 && !move_is_castle(move))
1057 // Move count based pruning
1058 if ( moveCount >= futility_move_count(depth)
1059 && (!threatMove || !connected_threat(pos, move, threatMove))
1060 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1063 lock_grab(&(sp->lock));
1068 // Value based pruning
1069 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1070 // but fixing this made program slightly weaker.
1071 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1072 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1073 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1075 if (futilityValueScaled < beta)
1079 lock_grab(&(sp->lock));
1080 if (futilityValueScaled > sp->bestValue)
1081 sp->bestValue = bestValue = futilityValueScaled;
1083 else if (futilityValueScaled > bestValue)
1084 bestValue = futilityValueScaled;
1089 // Prune moves with negative SEE at low depths
1090 if ( predictedDepth < 2 * ONE_PLY
1091 && bestValue > VALUE_MATED_IN_PLY_MAX
1092 && pos.see_sign(move) < 0)
1095 lock_grab(&(sp->lock));
1101 // Check for legality only before to do the move
1102 if (!pos.pl_move_is_legal(move, ci.pinned))
1108 ss->currentMove = move;
1110 // Step 14. Make the move
1111 pos.do_move(move, st, ci, givesCheck);
1113 if (!SpNode && !captureOrPromotion)
1114 movesSearched[playedMoveCount++] = move;
1116 // Step extra. pv search (only in PV nodes)
1117 // The first move in list is the expected PV
1119 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1120 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1123 // Step 15. Reduced depth search
1124 // If the move fails high will be re-searched at full depth.
1125 bool doFullDepthSearch = true;
1126 alpha = SpNode ? sp->alpha : alpha;
1128 if ( depth > 3 * ONE_PLY
1129 && !captureOrPromotion
1131 && !move_is_castle(move)
1132 && ss->killers[0] != move
1133 && ss->killers[1] != move)
1135 ss->reduction = reduction<PvNode>(depth, moveCount);
1138 Depth d = newDepth - ss->reduction;
1139 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1140 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1141 doFullDepthSearch = (value > alpha);
1143 ss->reduction = DEPTH_ZERO; // Restore original reduction
1146 // Step 16. Full depth search
1147 if (doFullDepthSearch)
1149 alpha = SpNode ? sp->alpha : alpha;
1150 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1151 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1153 // Step extra. pv search (only in PV nodes)
1154 // Search only for possible new PV nodes, if instead value >= beta then
1155 // parent node fails low with value <= alpha and tries another move.
1156 if (PvNode && value > alpha && (RootNode || value < beta))
1157 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1158 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1162 // Step 17. Undo move
1163 pos.undo_move(move);
1165 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1167 // Step 18. Check for new best move
1170 lock_grab(&(sp->lock));
1171 bestValue = sp->bestValue;
1175 if (value > bestValue && !(SpNode && thread.cutoff_occurred()))
1180 sp->bestValue = value;
1182 if (!RootNode && value > alpha)
1184 if (PvNode && value < beta) // We want always alpha < beta
1192 sp->is_betaCutoff = true;
1194 ss->bestMove = move;
1197 sp->ss->bestMove = move;
1203 // Finished searching the move. If StopRequest is true, the search
1204 // was aborted because the user interrupted the search or because we
1205 // ran out of time. In this case, the return value of the search cannot
1206 // be trusted, and we break out of the loop without updating the best
1211 // Remember searched nodes counts for this move
1212 mp.current().nodes += pos.nodes_searched() - nodes;
1214 // PV move or new best move ?
1215 if (isPvMove || value > alpha)
1218 ss->bestMove = move;
1219 mp.current().pv_score = value;
1220 mp.current().extract_pv_from_tt(pos);
1222 // We record how often the best move has been changed in each
1223 // iteration. This information is used for time management: When
1224 // the best move changes frequently, we allocate some more time.
1225 if (!isPvMove && MultiPV == 1)
1226 Rml.bestMoveChanges++;
1228 // It is critical that sorting is done with a stable algorithm
1229 // becuase all the values but the first are usually set to
1230 // -VALUE_INFINITE and we want to keep the same order for all
1231 // the moves but the new PV that goes to head.
1232 Rml.sort_first(moveCount);
1234 // Update alpha. In multi-pv we don't use aspiration window, so set
1235 // alpha equal to minimum score among the PV lines searched so far.
1237 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score;
1238 else if (value > alpha)
1242 // All other moves but the PV are set to the lowest value, this
1243 // is not a problem when sorting becuase sort is stable and move
1244 // position in the list is preserved, just the PV is pushed up.
1245 mp.current().pv_score = -VALUE_INFINITE;
1249 // Step 19. Check for split
1252 && depth >= Threads.min_split_depth()
1254 && Threads.available_slave_exists(pos.thread())
1256 && !thread.cutoff_occurred())
1257 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1258 threatMove, moveCount, &mp, PvNode);
1261 // Step 20. Check for mate and stalemate
1262 // All legal moves have been searched and if there are
1263 // no legal moves, it must be mate or stalemate.
1264 // If one move was excluded return fail low score.
1265 if (!SpNode && !moveCount)
1266 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1268 // Step 21. Update tables
1269 // If the search is not aborted, update the transposition table,
1270 // history counters, and killer moves.
1271 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1273 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1274 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1275 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1277 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1279 // Update killers and history only for non capture moves that fails high
1280 if ( bestValue >= beta
1281 && !pos.move_is_capture(move)
1282 && !move_is_promotion(move))
1284 if (move != ss->killers[0])
1286 ss->killers[1] = ss->killers[0];
1287 ss->killers[0] = move;
1289 update_history(pos, move, depth, movesSearched, playedMoveCount);
1295 // Here we have the lock still grabbed
1296 sp->is_slave[pos.thread()] = false;
1297 sp->nodes += pos.nodes_searched();
1298 lock_release(&(sp->lock));
1301 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1306 // qsearch() is the quiescence search function, which is called by the main
1307 // search function when the remaining depth is zero (or, to be more precise,
1308 // less than ONE_PLY).
1310 template <NodeType NT>
1311 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1313 const bool PvNode = (NT == PV);
1315 assert(NT == PV || NT == NonPV);
1316 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1317 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1318 assert(PvNode || alpha == beta - 1);
1320 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1324 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1325 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1328 Value oldAlpha = alpha;
1330 ss->bestMove = ss->currentMove = MOVE_NONE;
1331 ss->ply = (ss-1)->ply + 1;
1333 // Check for an instant draw or maximum ply reached
1334 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1337 // Decide whether or not to include checks, this fixes also the type of
1338 // TT entry depth that we are going to use. Note that in qsearch we use
1339 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1340 inCheck = pos.in_check();
1341 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1343 // Transposition table lookup. At PV nodes, we don't use the TT for
1344 // pruning, but only for move ordering.
1345 tte = TT.probe(pos.get_key());
1346 ttMove = (tte ? tte->move() : MOVE_NONE);
1348 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1350 ss->bestMove = ttMove; // Can be MOVE_NONE
1351 return value_from_tt(tte->value(), ss->ply);
1354 // Evaluate the position statically
1357 bestValue = futilityBase = -VALUE_INFINITE;
1358 ss->eval = evalMargin = VALUE_NONE;
1359 enoughMaterial = false;
1365 assert(tte->static_value() != VALUE_NONE);
1367 evalMargin = tte->static_value_margin();
1368 ss->eval = bestValue = tte->static_value();
1371 ss->eval = bestValue = evaluate(pos, evalMargin);
1373 // Stand pat. Return immediately if static value is at least beta
1374 if (bestValue >= beta)
1377 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1382 if (PvNode && bestValue > alpha)
1385 // Futility pruning parameters, not needed when in check
1386 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1387 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1390 // Initialize a MovePicker object for the current position, and prepare
1391 // to search the moves. Because the depth is <= 0 here, only captures,
1392 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1394 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1397 // Loop through the moves until no moves remain or a beta cutoff occurs
1398 while ( alpha < beta
1399 && (move = mp.get_next_move()) != MOVE_NONE)
1401 assert(move_is_ok(move));
1403 givesCheck = pos.move_gives_check(move, ci);
1411 && !move_is_promotion(move)
1412 && !pos.move_is_passed_pawn_push(move))
1414 futilityValue = futilityBase
1415 + pos.endgame_value_of_piece_on(move_to(move))
1416 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1418 if (futilityValue < alpha)
1420 if (futilityValue > bestValue)
1421 bestValue = futilityValue;
1425 // Prune moves with negative or equal SEE
1426 if ( futilityBase < beta
1427 && depth < DEPTH_ZERO
1428 && pos.see(move) <= 0)
1432 // Detect non-capture evasions that are candidate to be pruned
1433 evasionPrunable = !PvNode
1435 && bestValue > VALUE_MATED_IN_PLY_MAX
1436 && !pos.move_is_capture(move)
1437 && !pos.can_castle(pos.side_to_move());
1439 // Don't search moves with negative SEE values
1441 && (!inCheck || evasionPrunable)
1443 && !move_is_promotion(move)
1444 && pos.see_sign(move) < 0)
1447 // Don't search useless checks
1452 && !pos.move_is_capture(move)
1453 && !move_is_promotion(move)
1454 && ss->eval + PawnValueMidgame / 4 < beta
1455 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1457 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1458 bestValue = ss->eval + PawnValueMidgame / 4;
1463 // Check for legality only before to do the move
1464 if (!pos.pl_move_is_legal(move, ci.pinned))
1467 // Update current move
1468 ss->currentMove = move;
1470 // Make and search the move
1471 pos.do_move(move, st, ci, givesCheck);
1472 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1473 pos.undo_move(move);
1475 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1478 if (value > bestValue)
1484 ss->bestMove = move;
1489 // All legal moves have been searched. A special case: If we're in check
1490 // and no legal moves were found, it is checkmate.
1491 if (inCheck && bestValue == -VALUE_INFINITE)
1492 return value_mated_in(ss->ply);
1494 // Update transposition table
1495 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1496 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1498 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1504 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1505 // bestValue is updated only when returning false because in that case move
1508 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1510 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1511 Square from, to, ksq, victimSq;
1514 Value futilityValue, bv = *bestValue;
1516 from = move_from(move);
1518 them = opposite_color(pos.side_to_move());
1519 ksq = pos.king_square(them);
1520 kingAtt = pos.attacks_from<KING>(ksq);
1521 pc = pos.piece_on(from);
1523 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1524 oldAtt = pos.attacks_from(pc, from, occ);
1525 newAtt = pos.attacks_from(pc, to, occ);
1527 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1528 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1530 if (!(b && (b & (b - 1))))
1533 // Rule 2. Queen contact check is very dangerous
1534 if ( type_of_piece(pc) == QUEEN
1535 && bit_is_set(kingAtt, to))
1538 // Rule 3. Creating new double threats with checks
1539 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1543 victimSq = pop_1st_bit(&b);
1544 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1546 // Note that here we generate illegal "double move"!
1547 if ( futilityValue >= beta
1548 && pos.see_sign(make_move(from, victimSq)) >= 0)
1551 if (futilityValue > bv)
1555 // Update bestValue only if check is not dangerous (because we will prune the move)
1561 // connected_moves() tests whether two moves are 'connected' in the sense
1562 // that the first move somehow made the second move possible (for instance
1563 // if the moving piece is the same in both moves). The first move is assumed
1564 // to be the move that was made to reach the current position, while the
1565 // second move is assumed to be a move from the current position.
1567 bool connected_moves(const Position& pos, Move m1, Move m2) {
1569 Square f1, t1, f2, t2;
1572 assert(m1 && move_is_ok(m1));
1573 assert(m2 && move_is_ok(m2));
1575 // Case 1: The moving piece is the same in both moves
1581 // Case 2: The destination square for m2 was vacated by m1
1587 // Case 3: Moving through the vacated square
1588 if ( piece_is_slider(pos.piece_on(f2))
1589 && bit_is_set(squares_between(f2, t2), f1))
1592 // Case 4: The destination square for m2 is defended by the moving piece in m1
1593 p = pos.piece_on(t1);
1594 if (bit_is_set(pos.attacks_from(p, t1), t2))
1597 // Case 5: Discovered check, checking piece is the piece moved in m1
1598 if ( piece_is_slider(p)
1599 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1600 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1602 // discovered_check_candidates() works also if the Position's side to
1603 // move is the opposite of the checking piece.
1604 Color them = opposite_color(pos.side_to_move());
1605 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1607 if (bit_is_set(dcCandidates, f2))
1614 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1615 // "plies to mate from the current ply". Non-mate scores are unchanged.
1616 // The function is called before storing a value to the transposition table.
1618 Value value_to_tt(Value v, int ply) {
1620 if (v >= VALUE_MATE_IN_PLY_MAX)
1623 if (v <= VALUE_MATED_IN_PLY_MAX)
1630 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1631 // the transposition table to a mate score corrected for the current ply.
1633 Value value_from_tt(Value v, int ply) {
1635 if (v >= VALUE_MATE_IN_PLY_MAX)
1638 if (v <= VALUE_MATED_IN_PLY_MAX)
1645 // connected_threat() tests whether it is safe to forward prune a move or if
1646 // is somehow connected to the threat move returned by null search.
1648 bool connected_threat(const Position& pos, Move m, Move threat) {
1650 assert(move_is_ok(m));
1651 assert(threat && move_is_ok(threat));
1652 assert(!pos.move_is_capture(m) && !move_is_promotion(m));
1653 assert(!pos.move_is_passed_pawn_push(m));
1655 Square mfrom, mto, tfrom, tto;
1657 mfrom = move_from(m);
1659 tfrom = move_from(threat);
1660 tto = move_to(threat);
1662 // Case 1: Don't prune moves which move the threatened piece
1666 // Case 2: If the threatened piece has value less than or equal to the
1667 // value of the threatening piece, don't prune moves which defend it.
1668 if ( pos.move_is_capture(threat)
1669 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1670 || pos.type_of_piece_on(tfrom) == KING)
1671 && pos.move_attacks_square(m, tto))
1674 // Case 3: If the moving piece in the threatened move is a slider, don't
1675 // prune safe moves which block its ray.
1676 if ( piece_is_slider(pos.piece_on(tfrom))
1677 && bit_is_set(squares_between(tfrom, tto), mto)
1678 && pos.see_sign(m) >= 0)
1685 // ok_to_use_TT() returns true if a transposition table score
1686 // can be used at a given point in search.
1688 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1690 Value v = value_from_tt(tte->value(), ply);
1692 return ( tte->depth() >= depth
1693 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1694 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1696 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1697 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1701 // refine_eval() returns the transposition table score if
1702 // possible otherwise falls back on static position evaluation.
1704 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1708 Value v = value_from_tt(tte->value(), ply);
1710 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1711 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1718 // update_history() registers a good move that produced a beta-cutoff
1719 // in history and marks as failures all the other moves of that ply.
1721 void update_history(const Position& pos, Move move, Depth depth,
1722 Move movesSearched[], int moveCount) {
1724 Value bonus = Value(int(depth) * int(depth));
1726 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1728 for (int i = 0; i < moveCount - 1; i++)
1730 m = movesSearched[i];
1734 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1739 // update_gains() updates the gains table of a non-capture move given
1740 // the static position evaluation before and after the move.
1742 void update_gains(const Position& pos, Move m, Value before, Value after) {
1745 && before != VALUE_NONE
1746 && after != VALUE_NONE
1747 && pos.captured_piece_type() == PIECE_TYPE_NONE
1748 && !move_is_special(m))
1749 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1753 // current_search_time() returns the number of milliseconds which have passed
1754 // since the beginning of the current search.
1756 int current_search_time(int set) {
1758 static int searchStartTime;
1761 searchStartTime = set;
1763 return get_system_time() - searchStartTime;
1767 // value_to_uci() converts a value to a string suitable for use with the UCI
1768 // protocol specifications:
1770 // cp <x> The score from the engine's point of view in centipawns.
1771 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1772 // use negative values for y.
1774 std::string value_to_uci(Value v) {
1776 std::stringstream s;
1778 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1779 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1781 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1787 // speed_to_uci() returns a string with time stats of current search suitable
1788 // to be sent to UCI gui.
1790 std::string speed_to_uci(int64_t nodes) {
1792 std::stringstream s;
1793 int t = current_search_time();
1795 s << " nodes " << nodes
1796 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1803 // poll() performs two different functions: It polls for user input, and it
1804 // looks at the time consumed so far and decides if it's time to abort the
1807 void poll(const Position& pos) {
1809 static int lastInfoTime;
1810 int t = current_search_time();
1813 if (input_available())
1815 // We are line oriented, don't read single chars
1816 std::string command;
1818 if (!std::getline(std::cin, command) || command == "quit")
1820 // Quit the program as soon as possible
1821 Limits.ponder = false;
1822 QuitRequest = StopRequest = true;
1825 else if (command == "stop")
1827 // Stop calculating as soon as possible, but still send the "bestmove"
1828 // and possibly the "ponder" token when finishing the search.
1829 Limits.ponder = false;
1832 else if (command == "ponderhit")
1834 // The opponent has played the expected move. GUI sends "ponderhit" if
1835 // we were told to ponder on the same move the opponent has played. We
1836 // should continue searching but switching from pondering to normal search.
1837 Limits.ponder = false;
1839 if (StopOnPonderhit)
1844 // Print search information
1848 else if (lastInfoTime > t)
1849 // HACK: Must be a new search where we searched less than
1850 // NodesBetweenPolls nodes during the first second of search.
1853 else if (t - lastInfoTime >= 1000)
1858 dbg_print_hit_rate();
1860 // Send info on searched nodes as soon as we return to root
1861 SendSearchedNodes = true;
1864 // Should we stop the search?
1868 bool stillAtFirstMove = FirstRootMove
1869 && !AspirationFailLow
1870 && t > TimeMgr.available_time();
1872 bool noMoreTime = t > TimeMgr.maximum_time()
1873 || stillAtFirstMove;
1875 if ( (Limits.useTimeManagement() && noMoreTime)
1876 || (Limits.maxTime && t >= Limits.maxTime)
1877 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1882 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1883 // while the program is pondering. The point is to work around a wrinkle in
1884 // the UCI protocol: When pondering, the engine is not allowed to give a
1885 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1886 // We simply wait here until one of these commands is sent, and return,
1887 // after which the bestmove and pondermove will be printed.
1889 void wait_for_stop_or_ponderhit() {
1891 std::string command;
1893 // Wait for a command from stdin
1894 while ( std::getline(std::cin, command)
1895 && command != "ponderhit" && command != "stop" && command != "quit") {};
1897 if (command != "ponderhit" && command != "stop")
1898 QuitRequest = true; // Must be "quit" or getline() returned false
1902 // When playing with strength handicap choose best move among the MultiPV set
1903 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1904 void do_skill_level(Move* best, Move* ponder) {
1906 assert(MultiPV > 1);
1910 // Rml list is already sorted by pv_score in descending order
1912 int max_s = -VALUE_INFINITE;
1913 int size = Min(MultiPV, (int)Rml.size());
1914 int max = Rml[0].pv_score;
1915 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1916 int wk = 120 - 2 * SkillLevel;
1918 // PRNG sequence should be non deterministic
1919 for (int i = abs(get_system_time() % 50); i > 0; i--)
1920 rk.rand<unsigned>();
1922 // Choose best move. For each move's score we add two terms both dependent
1923 // on wk, one deterministic and bigger for weaker moves, and one random,
1924 // then we choose the move with the resulting highest score.
1925 for (int i = 0; i < size; i++)
1927 s = Rml[i].pv_score;
1929 // Don't allow crazy blunders even at very low skills
1930 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1933 // This is our magical formula
1934 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1939 *best = Rml[i].pv[0];
1940 *ponder = Rml[i].pv[1];
1946 /// RootMove and RootMoveList method's definitions
1948 RootMove::RootMove() {
1951 pv_score = non_pv_score = -VALUE_INFINITE;
1955 RootMove& RootMove::operator=(const RootMove& rm) {
1957 const Move* src = rm.pv;
1960 // Avoid a costly full rm.pv[] copy
1961 do *dst++ = *src; while (*src++ != MOVE_NONE);
1964 pv_score = rm.pv_score;
1965 non_pv_score = rm.non_pv_score;
1969 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1971 MoveStack mlist[MAX_MOVES];
1975 bestMoveChanges = 0;
1977 // Generate all legal moves and add them to RootMoveList
1978 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
1979 for (MoveStack* cur = mlist; cur != last; cur++)
1981 // If we have a searchMoves[] list then verify cur->move
1982 // is in the list before to add it.
1983 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
1985 if (searchMoves[0] && *sm != cur->move)
1989 rm.pv[0] = cur->move;
1990 rm.pv[1] = MOVE_NONE;
1991 rm.pv_score = -VALUE_INFINITE;
1996 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
1997 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
1998 // allow to always have a ponder move even when we fail high at root and also a
1999 // long PV to print that is important for position analysis.
2001 void RootMove::extract_pv_from_tt(Position& pos) {
2003 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2007 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2009 pos.do_move(pv[0], *st++);
2011 while ( (tte = TT.probe(pos.get_key())) != NULL
2012 && tte->move() != MOVE_NONE
2013 && pos.move_is_pl(tte->move())
2014 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces(pos.side_to_move()))
2016 && (!pos.is_draw<false>() || ply < 2))
2018 pv[ply] = tte->move();
2019 pos.do_move(pv[ply++], *st++);
2021 pv[ply] = MOVE_NONE;
2023 do pos.undo_move(pv[--ply]); while (ply);
2026 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2027 // the PV back into the TT. This makes sure the old PV moves are searched
2028 // first, even if the old TT entries have been overwritten.
2030 void RootMove::insert_pv_in_tt(Position& pos) {
2032 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2035 Value v, m = VALUE_NONE;
2038 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2044 // Don't overwrite existing correct entries
2045 if (!tte || tte->move() != pv[ply])
2047 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2048 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2050 pos.do_move(pv[ply], *st++);
2052 } while (pv[++ply] != MOVE_NONE);
2054 do pos.undo_move(pv[--ply]); while (ply);
2057 // pv_info_to_uci() returns a string with information on the current PV line
2058 // formatted according to UCI specification.
2060 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2061 Value beta, int pvIdx) {
2062 std::stringstream s;
2064 s << "info depth " << depth
2065 << " seldepth " << selDepth
2066 << " multipv " << pvIdx + 1
2067 << " score " << value_to_uci(pv_score)
2068 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2069 << speed_to_uci(pos.nodes_searched())
2072 for (Move* m = pv; *m != MOVE_NONE; m++)
2078 // Specializations for MovePickerExt in case of Root node
2079 MovePickerExt<Root>::MovePickerExt(const Position& p, Move ttm, Depth d,
2080 const History& h, SearchStack* ss, Value b)
2081 : MovePicker(p, ttm, d, h, ss, b), cur(-1) {
2083 Value score = VALUE_ZERO;
2085 // Score root moves using standard ordering used in main search, the moves
2086 // are scored according to the order in which they are returned by MovePicker.
2087 // This is the second order score that is used to compare the moves when
2088 // the first orders pv_score of both moves are equal.
2089 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2090 for (RootMoveList::iterator rm = Rml.begin(); rm != Rml.end(); ++rm)
2091 if (rm->pv[0] == move)
2093 rm->non_pv_score = score--;
2103 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2104 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2105 // object for which the current thread is the master.
2107 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2109 assert(threadID >= 0 && threadID < MAX_THREADS);
2116 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2117 // master should exit as last one.
2118 if (allThreadsShouldExit)
2121 threads[threadID].state = Thread::TERMINATED;
2125 // If we are not thinking, wait for a condition to be signaled
2126 // instead of wasting CPU time polling for work.
2127 while ( threadID >= activeThreads
2128 || threads[threadID].state == Thread::INITIALIZING
2129 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2131 assert(!sp || useSleepingThreads);
2132 assert(threadID != 0 || useSleepingThreads);
2134 if (threads[threadID].state == Thread::INITIALIZING)
2135 threads[threadID].state = Thread::AVAILABLE;
2137 // Grab the lock to avoid races with Thread::wake_up()
2138 lock_grab(&threads[threadID].sleepLock);
2140 // If we are master and all slaves have finished do not go to sleep
2141 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2142 allFinished = (i == activeThreads);
2144 if (allFinished || allThreadsShouldExit)
2146 lock_release(&threads[threadID].sleepLock);
2150 // Do sleep here after retesting sleep conditions
2151 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2152 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2154 lock_release(&threads[threadID].sleepLock);
2157 // If this thread has been assigned work, launch a search
2158 if (threads[threadID].state == Thread::WORKISWAITING)
2160 assert(!allThreadsShouldExit);
2162 threads[threadID].state = Thread::SEARCHING;
2164 // Copy split point position and search stack and call search()
2165 // with SplitPoint template parameter set to true.
2166 SearchStack ss[PLY_MAX_PLUS_2];
2167 SplitPoint* tsp = threads[threadID].splitPoint;
2168 Position pos(*tsp->pos, threadID);
2170 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2174 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2176 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2178 assert(threads[threadID].state == Thread::SEARCHING);
2180 threads[threadID].state = Thread::AVAILABLE;
2182 // Wake up master thread so to allow it to return from the idle loop in
2183 // case we are the last slave of the split point.
2184 if ( useSleepingThreads
2185 && threadID != tsp->master
2186 && threads[tsp->master].state == Thread::AVAILABLE)
2187 threads[tsp->master].wake_up();
2190 // If this thread is the master of a split point and all slaves have
2191 // finished their work at this split point, return from the idle loop.
2192 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2193 allFinished = (i == activeThreads);
2197 // Because sp->slaves[] is reset under lock protection,
2198 // be sure sp->lock has been released before to return.
2199 lock_grab(&(sp->lock));
2200 lock_release(&(sp->lock));
2202 // In helpful master concept a master can help only a sub-tree, and
2203 // because here is all finished is not possible master is booked.
2204 assert(threads[threadID].state == Thread::AVAILABLE);
2206 threads[threadID].state = Thread::SEARCHING;