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);
79 Move pv[PLY_MAX_PLUS_2];
82 // RootMoveList struct is mainly a std::vector of RootMove objects
83 struct RootMoveList : public std::vector<RootMove> {
84 void init(Position& pos, Move searchMoves[]);
91 // Lookup table to check if a Piece is a slider and its access function
92 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
93 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
97 // Maximum depth for razoring
98 const Depth RazorDepth = 4 * ONE_PLY;
100 // Dynamic razoring margin based on depth
101 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
103 // Maximum depth for use of dynamic threat detection when null move fails low
104 const Depth ThreatDepth = 5 * ONE_PLY;
106 // Step 9. Internal iterative deepening
108 // Minimum depth for use of internal iterative deepening
109 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
111 // At Non-PV nodes we do an internal iterative deepening search
112 // when the static evaluation is bigger then beta - IIDMargin.
113 const Value IIDMargin = Value(0x100);
115 // Step 11. Decide the new search depth
117 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
118 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
119 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
120 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
121 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
123 // Minimum depth for use of singular extension
124 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
126 // Step 12. Futility pruning
128 // Futility margin for quiescence search
129 const Value FutilityMarginQS = Value(0x80);
131 // Futility lookup tables (initialized at startup) and their access functions
132 Value FutilityMargins[16][64]; // [depth][moveNumber]
133 int FutilityMoveCounts[32]; // [depth]
135 inline Value futility_margin(Depth d, int mn) {
137 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
138 : 2 * VALUE_INFINITE;
141 inline int futility_move_count(Depth d) {
143 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
146 // Step 14. Reduced search
148 // Reduction lookup tables (initialized at startup) and their access function
149 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
151 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
153 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
156 // Easy move margin. An easy move candidate must be at least this much
157 // better than the second best move.
158 const Value EasyMoveMargin = Value(0x200);
161 /// Namespace variables
167 int MultiPV, UCIMultiPV;
169 // Time management variables
170 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
175 std::ofstream LogFile;
177 // Skill level adjustment
179 bool SkillLevelEnabled;
181 // Node counters, used only by thread[0] but try to keep in different cache
182 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
183 bool SendSearchedNodes;
185 int NodesBetweenPolls = 30000;
193 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
195 template <NodeType NT>
196 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
198 template <NodeType NT>
199 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
201 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
202 bool connected_moves(const Position& pos, Move m1, Move m2);
203 Value value_to_tt(Value v, int ply);
204 Value value_from_tt(Value v, int ply);
205 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
206 bool connected_threat(const Position& pos, Move m, Move threat);
207 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
208 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
209 void update_gains(const Position& pos, Move move, Value before, Value after);
210 void do_skill_level(Move* best, Move* ponder);
212 int current_search_time(int set = 0);
213 std::string score_to_uci(Value v, Value alpha, Value beta);
214 std::string speed_to_uci(int64_t nodes);
215 std::string pv_to_uci(Move pv[], int pvNum);
216 std::string depth_to_uci(Depth depth);
217 void poll(const Position& pos);
218 void wait_for_stop_or_ponderhit();
220 // MovePickerExt template class extends MovePicker and allows to choose at compile
221 // time the proper moves source according to the type of node. In the default case
222 // we simply create and use a standard MovePicker object.
223 template<NodeType> struct MovePickerExt : public MovePicker {
225 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
226 : MovePicker(p, ttm, d, h, ss, b) {}
228 RootMove& current() { assert(false); return Rml[0]; } // Dummy, needed to compile
231 // In case of a SpNode we use split point's shared MovePicker object as moves source
232 template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
234 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
235 : MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
237 Move get_next_move() { return mp->get_next_move(); }
241 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
243 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
244 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
247 // In case of a Root node we use RootMoveList as moves source
248 template<> struct MovePickerExt<Root> : public MovePicker {
250 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
251 RootMove& current() { return Rml[cur]; }
252 Move get_next_move() { return ++cur < (int)Rml.size() ? Rml[cur].pv[0] : MOVE_NONE; }
257 // Overload operator<<() to make it easier to print moves in a coordinate
258 // notation compatible with UCI protocol.
259 std::ostream& operator<<(std::ostream& os, Move m) {
261 bool chess960 = (os.iword(0) != 0); // See set960()
262 return os << move_to_uci(m, chess960);
265 // When formatting a move for std::cout we must know if we are in Chess960
266 // or not. To keep using the handy operator<<() on the move the trick is to
267 // embed this flag in the stream itself. Function-like named enum set960 is
268 // used as a custom manipulator and the stream internal general-purpose array,
269 // accessed through ios_base::iword(), is used to pass the flag to the move's
270 // operator<<() that will read it to properly format castling moves.
273 std::ostream& operator<< (std::ostream& os, const set960& f) {
275 os.iword(0) = int(f);
279 // extension() decides whether a move should be searched with normal depth,
280 // or with extended depth. Certain classes of moves (checking moves, in
281 // particular) are searched with bigger depth than ordinary moves and in
282 // any case are marked as 'dangerous'. Note that also if a move is not
283 // extended, as example because the corresponding UCI option is set to zero,
284 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
285 template <bool PvNode>
286 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
287 bool moveIsCheck, bool* dangerous) {
288 assert(m != MOVE_NONE);
290 Depth result = DEPTH_ZERO;
291 *dangerous = moveIsCheck;
293 if (moveIsCheck && pos.see_sign(m) >= 0)
294 result += CheckExtension[PvNode];
296 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
298 Color c = pos.side_to_move();
299 if (relative_rank(c, move_to(m)) == RANK_7)
301 result += PawnPushTo7thExtension[PvNode];
304 if (pos.pawn_is_passed(c, move_to(m)))
306 result += PassedPawnExtension[PvNode];
311 if ( captureOrPromotion
312 && piece_type(pos.piece_on(move_to(m))) != PAWN
313 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
314 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
315 && !move_is_special(m))
317 result += PawnEndgameExtension[PvNode];
321 return Min(result, ONE_PLY);
327 /// init_search() is called during startup to initialize various lookup tables
331 int d; // depth (ONE_PLY == 2)
332 int hd; // half depth (ONE_PLY == 1)
335 // Init reductions array
336 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
338 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
339 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
340 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
341 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
344 // Init futility margins array
345 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
346 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
348 // Init futility move count array
349 for (d = 0; d < 32; d++)
350 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
354 /// perft() is our utility to verify move generation. All the leaf nodes up to
355 /// the given depth are generated and counted and the sum returned.
357 int64_t perft(Position& pos, Depth depth) {
362 // Generate all legal moves
363 MoveList<MV_LEGAL> ml(pos);
365 // If we are at the last ply we don't need to do and undo
366 // the moves, just to count them.
367 if (depth <= ONE_PLY)
370 // Loop through all legal moves
372 for ( ; !ml.end(); ++ml)
374 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
375 sum += perft(pos, depth - ONE_PLY);
376 pos.undo_move(ml.move());
382 /// think() is the external interface to Stockfish's search, and is called when
383 /// the program receives the UCI 'go' command. It initializes various global
384 /// variables, and calls id_loop(). It returns false when a "quit" command is
385 /// received during the search.
387 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
391 // Initialize global search-related variables
392 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
394 current_search_time(get_system_time());
396 TimeMgr.init(Limits, pos.startpos_ply_counter());
398 // Set output steram in normal or chess960 mode
399 cout << set960(pos.is_chess960());
401 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
403 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
404 else if (Limits.time && Limits.time < 1000)
405 NodesBetweenPolls = 1000;
406 else if (Limits.time && Limits.time < 5000)
407 NodesBetweenPolls = 5000;
409 NodesBetweenPolls = 30000;
411 // Look for a book move
412 if (Options["OwnBook"].value<bool>())
414 if (Options["Book File"].value<std::string>() != book.name())
415 book.open(Options["Book File"].value<std::string>());
417 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
418 if (bookMove != MOVE_NONE)
421 wait_for_stop_or_ponderhit();
423 cout << "bestmove " << bookMove << endl;
429 UCIMultiPV = Options["MultiPV"].value<int>();
430 SkillLevel = Options["Skill Level"].value<int>();
432 read_evaluation_uci_options(pos.side_to_move());
433 Threads.read_uci_options();
435 // If needed allocate pawn and material hash tables and adjust TT size
436 Threads.init_hash_tables();
437 TT.set_size(Options["Hash"].value<int>());
439 if (Options["Clear Hash"].value<bool>())
441 Options["Clear Hash"].set_value("false");
445 // Do we have to play with skill handicap? In this case enable MultiPV that
446 // we will use behind the scenes to retrieve a set of possible moves.
447 SkillLevelEnabled = (SkillLevel < 20);
448 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
450 // Wake up needed threads and reset maxPly counter
451 for (int i = 0; i < Threads.size(); i++)
453 Threads[i].wake_up();
454 Threads[i].maxPly = 0;
457 // Write to log file and keep it open to be accessed during the search
458 if (Options["Use Search Log"].value<bool>())
460 std::string name = Options["Search Log Filename"].value<std::string>();
461 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
463 if (LogFile.is_open())
464 LogFile << "\nSearching: " << pos.to_fen()
465 << "\ninfinite: " << Limits.infinite
466 << " ponder: " << Limits.ponder
467 << " time: " << Limits.time
468 << " increment: " << Limits.increment
469 << " moves to go: " << Limits.movesToGo
473 // We're ready to start thinking. Call the iterative deepening loop function
474 Move ponderMove = MOVE_NONE;
475 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
477 // Write final search statistics and close log file
478 if (LogFile.is_open())
480 int t = current_search_time();
482 LogFile << "Nodes: " << pos.nodes_searched()
483 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
484 << "\nBest move: " << move_to_san(pos, bestMove);
487 pos.do_move(bestMove, st);
488 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
489 pos.undo_move(bestMove); // Return from think() with unchanged position
493 // This makes all the threads to go to sleep
496 // If we are pondering or in infinite search, we shouldn't print the
497 // best move before we are told to do so.
498 if (!StopRequest && (Limits.ponder || Limits.infinite))
499 wait_for_stop_or_ponderhit();
501 // Could be MOVE_NONE when searching on a stalemate position
502 cout << "bestmove " << bestMove;
504 // UCI protol is not clear on allowing sending an empty ponder move, instead
505 // it is clear that ponder move is optional. So skip it if empty.
506 if (ponderMove != MOVE_NONE)
507 cout << " ponder " << ponderMove;
517 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
518 // with increasing depth until the allocated thinking time has been consumed,
519 // user stops the search, or the maximum search depth is reached.
521 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
523 SearchStack ss[PLY_MAX_PLUS_2];
524 Value bestValues[PLY_MAX_PLUS_2];
525 int bestMoveChanges[PLY_MAX_PLUS_2];
526 int depth, aspirationDelta;
527 Value value, alpha, beta;
528 Move bestMove, easyMove, skillBest, skillPonder;
530 // Initialize stuff before a new search
531 memset(ss, 0, 4 * sizeof(SearchStack));
534 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
535 depth = aspirationDelta = 0;
536 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
537 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
539 // Moves to search are verified and copied
540 Rml.init(pos, searchMoves);
542 // Handle special case of searching on a mate/stalemate position
545 cout << "info" << depth_to_uci(DEPTH_ZERO)
546 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
551 // Iterative deepening loop until requested to stop or target depth reached
552 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
554 Rml.bestMoveChanges = 0;
556 // Calculate dynamic aspiration window based on previous iterations
557 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
559 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
560 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
562 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
563 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
565 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
566 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
569 // Start with a small aspiration window and, in case of fail high/low,
570 // research with bigger window until not failing high/low anymore.
572 // Search starting from ss+1 to allow calling update_gains()
573 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
575 // Write PV back to transposition table in case the relevant entries
576 // have been overwritten during the search.
577 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
578 Rml[i].insert_pv_in_tt(pos);
580 // Value cannot be trusted. Break out immediately!
584 // Send full PV info to GUI if we are going to leave the loop or
585 // if we have a fail high/low and we are deep in the search.
586 if ((value > alpha && value < beta) || current_search_time() > 2000)
587 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
589 << depth_to_uci(depth * ONE_PLY)
590 << score_to_uci(Rml[i].pv_score, alpha, beta)
591 << speed_to_uci(pos.nodes_searched())
592 << pv_to_uci(Rml[i].pv, i + 1) << endl;
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 if (LogFile.is_open())
625 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
627 // Init easyMove after first iteration or drop if differs from the best move
628 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
630 else if (bestMove != easyMove)
631 easyMove = MOVE_NONE;
633 // Check for some early stop condition
634 if (!StopRequest && Limits.useTimeManagement())
636 // Stop search early when the last two iterations returned a mate score
638 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
639 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
642 // Stop search early if one move seems to be much better than the
643 // others or if there is only a single legal move. Also in the latter
644 // case we search up to some depth anyway to get a proper score.
646 && easyMove == bestMove
648 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
649 && current_search_time() > TimeMgr.available_time() / 16)
650 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
651 && current_search_time() > TimeMgr.available_time() / 32)))
654 // Take in account some extra time if the best move has changed
655 if (depth > 4 && depth < 50)
656 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
658 // Stop search if most of available time is already consumed. We probably don't
659 // have enough time to search the first move at the next iteration anyway.
660 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
663 // If we are allowed to ponder do not stop the search now but keep pondering
664 if (StopRequest && Limits.ponder)
667 StopOnPonderhit = true;
672 // When using skills overwrite best and ponder moves with the sub-optimal ones
673 if (SkillLevelEnabled)
675 if (skillBest == MOVE_NONE) // Still unassigned ?
676 do_skill_level(&skillBest, &skillPonder);
678 bestMove = skillBest;
679 *ponderMove = skillPonder;
686 // search<>() is the main search function for both PV and non-PV nodes and for
687 // normal and SplitPoint nodes. When called just after a split point the search
688 // is simpler because we have already probed the hash table, done a null move
689 // search, and searched the first move before splitting, we don't have to repeat
690 // all this work again. We also don't need to store anything to the hash table
691 // here: This is taken care of after we return from the split point.
693 template <NodeType NT>
694 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
696 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
697 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
698 const bool RootNode = (NT == Root);
700 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
701 assert(beta > alpha && beta <= VALUE_INFINITE);
702 assert(PvNode || alpha == beta - 1);
703 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
705 Move movesSearched[MAX_MOVES];
710 Move ttMove, move, excludedMove, threatMove;
713 Value bestValue, value, oldAlpha;
714 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
715 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
716 int moveCount = 0, playedMoveCount = 0;
717 Thread& thread = Threads[pos.thread()];
718 SplitPoint* sp = NULL;
720 refinedValue = bestValue = value = -VALUE_INFINITE;
722 inCheck = pos.in_check();
723 ss->ply = (ss-1)->ply + 1;
725 // Used to send selDepth info to GUI
726 if (PvNode && thread.maxPly < ss->ply)
727 thread.maxPly = ss->ply;
729 // Step 1. Initialize node.
732 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
733 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
734 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
740 ttMove = excludedMove = MOVE_NONE;
741 threatMove = sp->threatMove;
742 goto split_point_start;
745 // Step 3. Mate distance pruning
748 alpha = Max(value_mated_in(ss->ply), alpha);
749 beta = Min(value_mate_in(ss->ply+1), beta);
754 // Step 4. Transposition table lookup
755 // We don't want the score of a partial search to overwrite a previous full search
756 // TT value, so we use a different position key in case of an excluded move.
757 excludedMove = ss->excludedMove;
758 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
759 tte = TT.probe(posKey);
760 ttMove = tte ? tte->move() : MOVE_NONE;
762 // At PV nodes we check for exact scores, while at non-PV nodes we check for
763 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
764 // smooth experience in analysis mode.
765 if (tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
766 : ok_to_use_TT(tte, depth, beta, ss->ply)))
769 ss->bestMove = ttMove; // Can be MOVE_NONE
770 return value_from_tt(tte->value(), ss->ply);
773 // Step 5. Evaluate the position statically and update parent's gain statistics
775 ss->eval = ss->evalMargin = VALUE_NONE;
778 assert(tte->static_value() != VALUE_NONE);
780 ss->eval = tte->static_value();
781 ss->evalMargin = tte->static_value_margin();
782 refinedValue = refine_eval(tte, ss->eval, ss->ply);
786 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
787 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
790 // Save gain for the parent non-capture move
791 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
793 // Step 6. Razoring (is omitted in PV nodes)
795 && depth < RazorDepth
797 && refinedValue + razor_margin(depth) < beta
798 && ttMove == MOVE_NONE
799 && abs(beta) < VALUE_MATE_IN_PLY_MAX
800 && !pos.has_pawn_on_7th(pos.side_to_move()))
802 Value rbeta = beta - razor_margin(depth);
803 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
805 // Logically we should return (v + razor_margin(depth)), but
806 // surprisingly this did slightly weaker in tests.
810 // Step 7. Static null move pruning (is omitted in PV nodes)
811 // We're betting that the opponent doesn't have a move that will reduce
812 // the score by more than futility_margin(depth) if we do a null move.
815 && depth < RazorDepth
817 && refinedValue - futility_margin(depth, 0) >= beta
818 && abs(beta) < VALUE_MATE_IN_PLY_MAX
819 && pos.non_pawn_material(pos.side_to_move()))
820 return refinedValue - futility_margin(depth, 0);
822 // Step 8. Null move search with verification search (is omitted in PV nodes)
827 && refinedValue >= beta
828 && abs(beta) < VALUE_MATE_IN_PLY_MAX
829 && pos.non_pawn_material(pos.side_to_move()))
831 ss->currentMove = MOVE_NULL;
833 // Null move dynamic reduction based on depth
834 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
836 // Null move dynamic reduction based on value
837 if (refinedValue - PawnValueMidgame > beta)
840 pos.do_null_move(st);
841 (ss+1)->skipNullMove = true;
842 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
843 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
844 (ss+1)->skipNullMove = false;
845 pos.undo_null_move();
847 if (nullValue >= beta)
849 // Do not return unproven mate scores
850 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
853 if (depth < 6 * ONE_PLY)
856 // Do verification search at high depths
857 ss->skipNullMove = true;
858 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
859 ss->skipNullMove = false;
866 // The null move failed low, which means that we may be faced with
867 // some kind of threat. If the previous move was reduced, check if
868 // the move that refuted the null move was somehow connected to the
869 // move which was reduced. If a connection is found, return a fail
870 // low score (which will cause the reduced move to fail high in the
871 // parent node, which will trigger a re-search with full depth).
872 threatMove = (ss+1)->bestMove;
874 if ( depth < ThreatDepth
876 && threatMove != MOVE_NONE
877 && connected_moves(pos, (ss-1)->currentMove, threatMove))
882 // Step 9. ProbCut (is omitted in PV nodes)
883 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
884 // and a reduced search returns a value much above beta, we can (almost) safely
885 // prune the previous move.
887 && depth >= RazorDepth + ONE_PLY
890 && excludedMove == MOVE_NONE
891 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
893 Value rbeta = beta + 200;
894 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
896 assert(rdepth >= ONE_PLY);
898 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
901 while ((move = mp.get_next_move()) != MOVE_NONE)
902 if (pos.pl_move_is_legal(move, ci.pinned))
904 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
906 if (pos.is_draw<false>() || ss->ply + 1 > PLY_MAX)
909 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
917 // Step 10. Internal iterative deepening
918 if ( depth >= IIDDepth[PvNode]
919 && ttMove == MOVE_NONE
920 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
922 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
924 ss->skipNullMove = true;
925 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
926 ss->skipNullMove = false;
928 tte = TT.probe(posKey);
929 ttMove = tte ? tte->move() : MOVE_NONE;
932 split_point_start: // At split points actual search starts from here
934 // Initialize a MovePicker object for the current position
935 MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
937 ss->bestMove = MOVE_NONE;
938 futilityBase = ss->eval + ss->evalMargin;
939 singularExtensionNode = !RootNode
941 && depth >= SingularExtensionDepth[PvNode]
942 && ttMove != MOVE_NONE
943 && !excludedMove // Do not allow recursive singular extension search
944 && (tte->type() & VALUE_TYPE_LOWER)
945 && tte->depth() >= depth - 3 * ONE_PLY;
948 lock_grab(&(sp->lock));
949 bestValue = sp->bestValue;
952 // Step 11. Loop through moves
953 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
954 while ( bestValue < beta
955 && (move = mp.get_next_move()) != MOVE_NONE
956 && !thread.cutoff_occurred())
958 assert(move_is_ok(move));
960 if (move == excludedMove)
963 // At PV and SpNode nodes we want all moves to be legal since the beginning
964 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
969 moveCount = ++sp->moveCount;
970 lock_release(&(sp->lock));
977 // This is used by time management
978 FirstRootMove = (moveCount == 1);
980 // Save the current node count before the move is searched
981 nodes = pos.nodes_searched();
983 // If it's time to send nodes info, do it here where we have the
984 // correct accumulated node counts searched by each thread.
985 if (SendSearchedNodes)
987 SendSearchedNodes = false;
988 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
991 // For long searches send current move info to GUI
992 if (current_search_time() > 2000)
993 cout << "info" << depth_to_uci(depth)
994 << " currmove " << move << " currmovenumber " << moveCount << endl;
997 // At Root and at first iteration do a PV search on all the moves to score root moves
998 isPvMove = (PvNode && moveCount <= (!RootNode ? 1 : depth <= ONE_PLY ? MAX_MOVES : MultiPV));
999 givesCheck = pos.move_gives_check(move, ci);
1000 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1002 // Step 12. Decide the new search depth
1003 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1005 // Singular extension search. If all moves but one fail low on a search of
1006 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1007 // is singular and should be extended. To verify this we do a reduced search
1008 // on all the other moves but the ttMove, if result is lower than ttValue minus
1009 // a margin then we extend ttMove.
1010 if ( singularExtensionNode
1012 && pos.pl_move_is_legal(move, ci.pinned)
1015 Value ttValue = value_from_tt(tte->value(), ss->ply);
1017 if (abs(ttValue) < VALUE_KNOWN_WIN)
1019 Value rBeta = ttValue - int(depth);
1020 ss->excludedMove = move;
1021 ss->skipNullMove = true;
1022 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1023 ss->skipNullMove = false;
1024 ss->excludedMove = MOVE_NONE;
1025 ss->bestMove = MOVE_NONE;
1031 // Update current move (this must be done after singular extension search)
1032 newDepth = depth - ONE_PLY + ext;
1034 // Step 13. Futility pruning (is omitted in PV nodes)
1036 && !captureOrPromotion
1040 && !move_is_castle(move))
1042 // Move count based pruning
1043 if ( moveCount >= futility_move_count(depth)
1044 && (!threatMove || !connected_threat(pos, move, threatMove))
1045 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1048 lock_grab(&(sp->lock));
1053 // Value based pruning
1054 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1055 // but fixing this made program slightly weaker.
1056 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1057 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1058 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1060 if (futilityValueScaled < beta)
1064 lock_grab(&(sp->lock));
1065 if (futilityValueScaled > sp->bestValue)
1066 sp->bestValue = bestValue = futilityValueScaled;
1068 else if (futilityValueScaled > bestValue)
1069 bestValue = futilityValueScaled;
1074 // Prune moves with negative SEE at low depths
1075 if ( predictedDepth < 2 * ONE_PLY
1076 && bestValue > VALUE_MATED_IN_PLY_MAX
1077 && pos.see_sign(move) < 0)
1080 lock_grab(&(sp->lock));
1086 // Check for legality only before to do the move
1087 if (!pos.pl_move_is_legal(move, ci.pinned))
1093 ss->currentMove = move;
1094 if (!SpNode && !captureOrPromotion)
1095 movesSearched[playedMoveCount++] = move;
1097 // Step 14. Make the move
1098 pos.do_move(move, st, ci, givesCheck);
1100 // Step XX. Poll. Check if search should be aborted.
1101 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
1107 // Step XX. Check for aborted search and immediate draw
1109 || pos.is_draw<false>()
1110 || ss->ply + 1 > PLY_MAX)
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;
1127 if ( depth > 3 * ONE_PLY
1128 && !captureOrPromotion
1130 && !move_is_castle(move)
1131 && ss->killers[0] != move
1132 && ss->killers[1] != move
1133 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1135 Depth d = newDepth - ss->reduction;
1136 alpha = SpNode ? sp->alpha : alpha;
1138 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1139 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1141 ss->reduction = DEPTH_ZERO;
1142 doFullDepthSearch = (value > alpha);
1145 // Step 16. Full depth search
1146 if (doFullDepthSearch)
1148 alpha = SpNode ? sp->alpha : alpha;
1149 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1150 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1152 // Step extra. pv search (only in PV nodes)
1153 // Search only for possible new PV nodes, if instead value >= beta then
1154 // parent node fails low with value <= alpha and tries another move.
1155 if (PvNode && value > alpha && (RootNode || value < beta))
1156 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1157 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1161 // 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)
1178 ss->bestMove = move;
1183 && value < beta) // We want always alpha < beta
1186 if (SpNode && !thread.cutoff_occurred())
1188 sp->bestValue = value;
1189 sp->ss->bestMove = move;
1191 sp->is_betaCutoff = (value >= beta);
1197 // Finished searching the move. If StopRequest is true, the search
1198 // was aborted because the user interrupted the search or because we
1199 // ran out of time. In this case, the return value of the search cannot
1200 // be trusted, and we break out of the loop without updating the best
1205 // Remember searched nodes counts for this move
1206 mp.current().nodes += pos.nodes_searched() - nodes;
1208 // PV move or new best move ?
1209 if (isPvMove || value > alpha)
1212 mp.current().pv_score = value;
1213 mp.current().extract_pv_from_tt(pos);
1215 // We record how often the best move has been changed in each
1216 // iteration. This information is used for time management: When
1217 // the best move changes frequently, we allocate some more time.
1218 if (!isPvMove && MultiPV == 1)
1219 Rml.bestMoveChanges++;
1221 // It is critical that sorting is done with a stable algorithm
1222 // because all the values but the first are usually set to
1223 // -VALUE_INFINITE and we want to keep the same order for all
1224 // the moves but the new PV that goes to head.
1225 sort<RootMove>(Rml.begin(), Rml.begin() + moveCount);
1227 // Update alpha. In multi-pv we don't use aspiration window, so set
1228 // alpha equal to minimum score among the PV lines searched so far.
1230 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score;
1231 else if (value > alpha)
1235 // All other moves but the PV are set to the lowest value, this
1236 // is not a problem when sorting becuase sort is stable and move
1237 // position in the list is preserved, just the PV is pushed up.
1238 mp.current().pv_score = -VALUE_INFINITE;
1242 // Step 19. Check for split
1245 && depth >= Threads.min_split_depth()
1247 && Threads.available_slave_exists(pos.thread())
1249 && !thread.cutoff_occurred())
1250 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1251 threatMove, moveCount, &mp, PvNode);
1254 // Step 20. Check for mate and stalemate
1255 // All legal moves have been searched and if there are
1256 // no legal moves, it must be mate or stalemate.
1257 // If one move was excluded return fail low score.
1258 if (!SpNode && !moveCount)
1259 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1261 // Step 21. Update tables
1262 // If the search is not aborted, update the transposition table,
1263 // history counters, and killer moves.
1264 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1266 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1267 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1268 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1270 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1272 // Update killers and history only for non capture moves that fails high
1273 if ( bestValue >= beta
1274 && !pos.move_is_capture_or_promotion(move))
1276 if (move != ss->killers[0])
1278 ss->killers[1] = ss->killers[0];
1279 ss->killers[0] = move;
1281 update_history(pos, move, depth, movesSearched, playedMoveCount);
1287 // Here we have the lock still grabbed
1288 sp->is_slave[pos.thread()] = false;
1289 sp->nodes += pos.nodes_searched();
1290 lock_release(&(sp->lock));
1293 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1298 // qsearch() is the quiescence search function, which is called by the main
1299 // search function when the remaining depth is zero (or, to be more precise,
1300 // less than ONE_PLY).
1302 template <NodeType NT>
1303 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1305 const bool PvNode = (NT == PV);
1307 assert(NT == PV || NT == NonPV);
1308 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1309 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1310 assert(PvNode || alpha == beta - 1);
1312 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1316 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1317 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1320 Value oldAlpha = alpha;
1322 ss->bestMove = ss->currentMove = MOVE_NONE;
1323 ss->ply = (ss-1)->ply + 1;
1325 // Check for an instant draw or maximum ply reached
1326 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1329 // Decide whether or not to include checks, this fixes also the type of
1330 // TT entry depth that we are going to use. Note that in qsearch we use
1331 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1332 inCheck = pos.in_check();
1333 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1335 // Transposition table lookup. At PV nodes, we don't use the TT for
1336 // pruning, but only for move ordering.
1337 tte = TT.probe(pos.get_key());
1338 ttMove = (tte ? tte->move() : MOVE_NONE);
1340 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1342 ss->bestMove = ttMove; // Can be MOVE_NONE
1343 return value_from_tt(tte->value(), ss->ply);
1346 // Evaluate the position statically
1349 bestValue = futilityBase = -VALUE_INFINITE;
1350 ss->eval = evalMargin = VALUE_NONE;
1351 enoughMaterial = false;
1357 assert(tte->static_value() != VALUE_NONE);
1359 evalMargin = tte->static_value_margin();
1360 ss->eval = bestValue = tte->static_value();
1363 ss->eval = bestValue = evaluate(pos, evalMargin);
1365 // Stand pat. Return immediately if static value is at least beta
1366 if (bestValue >= beta)
1369 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1374 if (PvNode && bestValue > alpha)
1377 // Futility pruning parameters, not needed when in check
1378 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1379 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1382 // Initialize a MovePicker object for the current position, and prepare
1383 // to search the moves. Because the depth is <= 0 here, only captures,
1384 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1386 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1389 // Loop through the moves until no moves remain or a beta cutoff occurs
1390 while ( alpha < beta
1391 && (move = mp.get_next_move()) != MOVE_NONE)
1393 assert(move_is_ok(move));
1395 givesCheck = pos.move_gives_check(move, ci);
1403 && !move_is_promotion(move)
1404 && !pos.move_is_passed_pawn_push(move))
1406 futilityValue = futilityBase
1407 + piece_value_endgame(pos.piece_on(move_to(move)))
1408 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1410 if (futilityValue < alpha)
1412 if (futilityValue > bestValue)
1413 bestValue = futilityValue;
1417 // Prune moves with negative or equal SEE
1418 if ( futilityBase < beta
1419 && depth < DEPTH_ZERO
1420 && pos.see(move) <= 0)
1424 // Detect non-capture evasions that are candidate to be pruned
1425 evasionPrunable = !PvNode
1427 && bestValue > VALUE_MATED_IN_PLY_MAX
1428 && !pos.move_is_capture(move)
1429 && !pos.can_castle(pos.side_to_move());
1431 // Don't search moves with negative SEE values
1433 && (!inCheck || evasionPrunable)
1435 && !move_is_promotion(move)
1436 && pos.see_sign(move) < 0)
1439 // Don't search useless checks
1444 && !pos.move_is_capture_or_promotion(move)
1445 && ss->eval + PawnValueMidgame / 4 < beta
1446 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1448 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1449 bestValue = ss->eval + PawnValueMidgame / 4;
1454 // Check for legality only before to do the move
1455 if (!pos.pl_move_is_legal(move, ci.pinned))
1458 // Update current move
1459 ss->currentMove = move;
1461 // Make and search the move
1462 pos.do_move(move, st, ci, givesCheck);
1463 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1464 pos.undo_move(move);
1466 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1469 if (value > bestValue)
1475 ss->bestMove = move;
1480 // All legal moves have been searched. A special case: If we're in check
1481 // and no legal moves were found, it is checkmate.
1482 if (inCheck && bestValue == -VALUE_INFINITE)
1483 return value_mated_in(ss->ply);
1485 // Update transposition table
1486 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1487 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1489 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1495 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1496 // bestValue is updated only when returning false because in that case move
1499 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1501 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1502 Square from, to, ksq, victimSq;
1505 Value futilityValue, bv = *bestValue;
1507 from = move_from(move);
1509 them = opposite_color(pos.side_to_move());
1510 ksq = pos.king_square(them);
1511 kingAtt = pos.attacks_from<KING>(ksq);
1512 pc = pos.piece_on(from);
1514 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1515 oldAtt = pos.attacks_from(pc, from, occ);
1516 newAtt = pos.attacks_from(pc, to, occ);
1518 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1519 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1521 if (!(b && (b & (b - 1))))
1524 // Rule 2. Queen contact check is very dangerous
1525 if ( piece_type(pc) == QUEEN
1526 && bit_is_set(kingAtt, to))
1529 // Rule 3. Creating new double threats with checks
1530 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1534 victimSq = pop_1st_bit(&b);
1535 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1537 // Note that here we generate illegal "double move"!
1538 if ( futilityValue >= beta
1539 && pos.see_sign(make_move(from, victimSq)) >= 0)
1542 if (futilityValue > bv)
1546 // Update bestValue only if check is not dangerous (because we will prune the move)
1552 // connected_moves() tests whether two moves are 'connected' in the sense
1553 // that the first move somehow made the second move possible (for instance
1554 // if the moving piece is the same in both moves). The first move is assumed
1555 // to be the move that was made to reach the current position, while the
1556 // second move is assumed to be a move from the current position.
1558 bool connected_moves(const Position& pos, Move m1, Move m2) {
1560 Square f1, t1, f2, t2;
1564 assert(m1 && move_is_ok(m1));
1565 assert(m2 && move_is_ok(m2));
1567 // Case 1: The moving piece is the same in both moves
1573 // Case 2: The destination square for m2 was vacated by m1
1579 // Case 3: Moving through the vacated square
1580 p2 = pos.piece_on(f2);
1581 if ( piece_is_slider(p2)
1582 && bit_is_set(squares_between(f2, t2), f1))
1585 // Case 4: The destination square for m2 is defended by the moving piece in m1
1586 p1 = pos.piece_on(t1);
1587 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1590 // Case 5: Discovered check, checking piece is the piece moved in m1
1591 ksq = pos.king_square(pos.side_to_move());
1592 if ( piece_is_slider(p1)
1593 && bit_is_set(squares_between(t1, ksq), f2))
1595 Bitboard occ = pos.occupied_squares();
1596 clear_bit(&occ, f2);
1597 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1604 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1605 // "plies to mate from the current ply". Non-mate scores are unchanged.
1606 // The function is called before storing a value to the transposition table.
1608 Value value_to_tt(Value v, int ply) {
1610 if (v >= VALUE_MATE_IN_PLY_MAX)
1613 if (v <= VALUE_MATED_IN_PLY_MAX)
1620 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1621 // the transposition table to a mate score corrected for the current ply.
1623 Value value_from_tt(Value v, int ply) {
1625 if (v >= VALUE_MATE_IN_PLY_MAX)
1628 if (v <= VALUE_MATED_IN_PLY_MAX)
1635 // connected_threat() tests whether it is safe to forward prune a move or if
1636 // is somehow connected to the threat move returned by null search.
1638 bool connected_threat(const Position& pos, Move m, Move threat) {
1640 assert(move_is_ok(m));
1641 assert(threat && move_is_ok(threat));
1642 assert(!pos.move_is_capture_or_promotion(m));
1643 assert(!pos.move_is_passed_pawn_push(m));
1645 Square mfrom, mto, tfrom, tto;
1647 mfrom = move_from(m);
1649 tfrom = move_from(threat);
1650 tto = move_to(threat);
1652 // Case 1: Don't prune moves which move the threatened piece
1656 // Case 2: If the threatened piece has value less than or equal to the
1657 // value of the threatening piece, don't prune moves which defend it.
1658 if ( pos.move_is_capture(threat)
1659 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1660 || piece_type(pos.piece_on(tfrom)) == KING)
1661 && pos.move_attacks_square(m, tto))
1664 // Case 3: If the moving piece in the threatened move is a slider, don't
1665 // prune safe moves which block its ray.
1666 if ( piece_is_slider(pos.piece_on(tfrom))
1667 && bit_is_set(squares_between(tfrom, tto), mto)
1668 && pos.see_sign(m) >= 0)
1675 // ok_to_use_TT() returns true if a transposition table score
1676 // can be used at a given point in search.
1678 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1680 Value v = value_from_tt(tte->value(), ply);
1682 return ( tte->depth() >= depth
1683 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1684 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1686 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1687 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1691 // refine_eval() returns the transposition table score if
1692 // possible otherwise falls back on static position evaluation.
1694 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1698 Value v = value_from_tt(tte->value(), ply);
1700 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1701 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1708 // update_history() registers a good move that produced a beta-cutoff
1709 // in history and marks as failures all the other moves of that ply.
1711 void update_history(const Position& pos, Move move, Depth depth,
1712 Move movesSearched[], int moveCount) {
1714 Value bonus = Value(int(depth) * int(depth));
1716 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1718 for (int i = 0; i < moveCount - 1; i++)
1720 m = movesSearched[i];
1724 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1729 // update_gains() updates the gains table of a non-capture move given
1730 // the static position evaluation before and after the move.
1732 void update_gains(const Position& pos, Move m, Value before, Value after) {
1735 && before != VALUE_NONE
1736 && after != VALUE_NONE
1737 && pos.captured_piece_type() == PIECE_TYPE_NONE
1738 && !move_is_special(m))
1739 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1743 // current_search_time() returns the number of milliseconds which have passed
1744 // since the beginning of the current search.
1746 int current_search_time(int set) {
1748 static int searchStartTime;
1751 searchStartTime = set;
1753 return get_system_time() - searchStartTime;
1757 // score_to_uci() converts a value to a string suitable for use with the UCI
1758 // protocol specifications:
1760 // cp <x> The score from the engine's point of view in centipawns.
1761 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1762 // use negative values for y.
1764 std::string score_to_uci(Value v, Value alpha, Value beta) {
1766 std::stringstream s;
1768 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1769 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1771 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1773 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1779 // speed_to_uci() returns a string with time stats of current search suitable
1780 // to be sent to UCI gui.
1782 std::string speed_to_uci(int64_t nodes) {
1784 std::stringstream s;
1785 int t = current_search_time();
1787 s << " nodes " << nodes
1788 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1794 // pv_to_uci() returns a string with information on the current PV line
1795 // formatted according to UCI specification.
1797 std::string pv_to_uci(Move pv[], int pvNum) {
1799 std::stringstream s;
1801 s << " multipv " << pvNum << " pv ";
1803 for ( ; *pv != MOVE_NONE; pv++)
1809 // depth_to_uci() returns a string with information on the current depth and
1810 // seldepth formatted according to UCI specification.
1812 std::string depth_to_uci(Depth depth) {
1814 std::stringstream s;
1816 // Retrieve max searched depth among threads
1818 for (int i = 0; i < Threads.size(); i++)
1819 if (Threads[i].maxPly > selDepth)
1820 selDepth = Threads[i].maxPly;
1822 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1828 // poll() performs two different functions: It polls for user input, and it
1829 // looks at the time consumed so far and decides if it's time to abort the
1832 void poll(const Position& pos) {
1834 static int lastInfoTime;
1835 int t = current_search_time();
1838 if (input_available())
1840 // We are line oriented, don't read single chars
1841 std::string command;
1843 if (!std::getline(std::cin, command) || command == "quit")
1845 // Quit the program as soon as possible
1846 Limits.ponder = false;
1847 QuitRequest = StopRequest = true;
1850 else if (command == "stop")
1852 // Stop calculating as soon as possible, but still send the "bestmove"
1853 // and possibly the "ponder" token when finishing the search.
1854 Limits.ponder = false;
1857 else if (command == "ponderhit")
1859 // The opponent has played the expected move. GUI sends "ponderhit" if
1860 // we were told to ponder on the same move the opponent has played. We
1861 // should continue searching but switching from pondering to normal search.
1862 Limits.ponder = false;
1864 if (StopOnPonderhit)
1869 // Print search information
1873 else if (lastInfoTime > t)
1874 // HACK: Must be a new search where we searched less than
1875 // NodesBetweenPolls nodes during the first second of search.
1878 else if (t - lastInfoTime >= 1000)
1883 dbg_print_hit_rate();
1885 // Send info on searched nodes as soon as we return to root
1886 SendSearchedNodes = true;
1889 // Should we stop the search?
1893 bool stillAtFirstMove = FirstRootMove
1894 && !AspirationFailLow
1895 && t > TimeMgr.available_time();
1897 bool noMoreTime = t > TimeMgr.maximum_time()
1898 || stillAtFirstMove;
1900 if ( (Limits.useTimeManagement() && noMoreTime)
1901 || (Limits.maxTime && t >= Limits.maxTime)
1902 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1907 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1908 // while the program is pondering. The point is to work around a wrinkle in
1909 // the UCI protocol: When pondering, the engine is not allowed to give a
1910 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1911 // We simply wait here until one of these commands is sent, and return,
1912 // after which the bestmove and pondermove will be printed.
1914 void wait_for_stop_or_ponderhit() {
1916 std::string command;
1918 // Wait for a command from stdin
1919 while ( std::getline(std::cin, command)
1920 && command != "ponderhit" && command != "stop" && command != "quit") {};
1922 if (command != "ponderhit" && command != "stop")
1923 QuitRequest = true; // Must be "quit" or getline() returned false
1927 // When playing with strength handicap choose best move among the MultiPV set
1928 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1929 void do_skill_level(Move* best, Move* ponder) {
1931 assert(MultiPV > 1);
1935 // Rml list is already sorted by pv_score in descending order
1937 int max_s = -VALUE_INFINITE;
1938 int size = Min(MultiPV, (int)Rml.size());
1939 int max = Rml[0].pv_score;
1940 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1941 int wk = 120 - 2 * SkillLevel;
1943 // PRNG sequence should be non deterministic
1944 for (int i = abs(get_system_time() % 50); i > 0; i--)
1945 rk.rand<unsigned>();
1947 // Choose best move. For each move's score we add two terms both dependent
1948 // on wk, one deterministic and bigger for weaker moves, and one random,
1949 // then we choose the move with the resulting highest score.
1950 for (int i = 0; i < size; i++)
1952 s = Rml[i].pv_score;
1954 // Don't allow crazy blunders even at very low skills
1955 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1958 // This is our magical formula
1959 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1964 *best = Rml[i].pv[0];
1965 *ponder = Rml[i].pv[1];
1971 /// RootMove and RootMoveList method's definitions
1973 RootMove::RootMove() {
1976 pv_score = non_pv_score = -VALUE_INFINITE;
1980 RootMove& RootMove::operator=(const RootMove& rm) {
1982 const Move* src = rm.pv;
1985 // Avoid a costly full rm.pv[] copy
1986 do *dst++ = *src; while (*src++ != MOVE_NONE);
1989 pv_score = rm.pv_score;
1990 non_pv_score = rm.non_pv_score;
1994 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1997 bestMoveChanges = 0;
2000 // Generate all legal moves and add them to RootMoveList
2001 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2003 // If we have a searchMoves[] list then verify the move
2004 // is in the list before to add it.
2005 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2007 if (sm != searchMoves && *sm != ml.move())
2011 rm.pv[0] = ml.move();
2012 rm.pv[1] = MOVE_NONE;
2013 rm.pv_score = -VALUE_INFINITE;
2018 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2019 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2020 // allow to always have a ponder move even when we fail high at root and also a
2021 // long PV to print that is important for position analysis.
2023 void RootMove::extract_pv_from_tt(Position& pos) {
2025 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2029 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2031 pos.do_move(pv[0], *st++);
2033 while ( (tte = TT.probe(pos.get_key())) != NULL
2034 && tte->move() != MOVE_NONE
2035 && pos.move_is_pl(tte->move())
2036 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2038 && (!pos.is_draw<false>() || ply < 2))
2040 pv[ply] = tte->move();
2041 pos.do_move(pv[ply++], *st++);
2043 pv[ply] = MOVE_NONE;
2045 do pos.undo_move(pv[--ply]); while (ply);
2048 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2049 // the PV back into the TT. This makes sure the old PV moves are searched
2050 // first, even if the old TT entries have been overwritten.
2052 void RootMove::insert_pv_in_tt(Position& pos) {
2054 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2057 Value v, m = VALUE_NONE;
2060 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2066 // Don't overwrite existing correct entries
2067 if (!tte || tte->move() != pv[ply])
2069 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2070 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2072 pos.do_move(pv[ply], *st++);
2074 } while (pv[++ply] != MOVE_NONE);
2076 do pos.undo_move(pv[--ply]); while (ply);
2079 // Specializations for MovePickerExt in case of Root node
2080 MovePickerExt<Root>::MovePickerExt(const Position& p, Move ttm, Depth d,
2081 const History& h, SearchStack* ss, Value b)
2082 : MovePicker(p, ttm, d, h, ss, b), cur(-1) {
2084 Value score = VALUE_ZERO;
2086 // Score root moves using standard ordering used in main search, the moves
2087 // are scored according to the order in which they are returned by MovePicker.
2088 // This is the second order score that is used to compare the moves when
2089 // the first orders pv_score of both moves are equal.
2090 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2091 for (RootMoveList::iterator rm = Rml.begin(); rm != Rml.end(); ++rm)
2092 if (rm->pv[0] == move)
2094 rm->non_pv_score = score--;
2098 sort<RootMove>(Rml.begin(), Rml.end());
2104 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2105 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2106 // object for which the current thread is the master.
2108 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2110 assert(threadID >= 0 && threadID < MAX_THREADS);
2117 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2118 // master should exit as last one.
2119 if (allThreadsShouldExit)
2122 threads[threadID].state = Thread::TERMINATED;
2126 // If we are not thinking, wait for a condition to be signaled
2127 // instead of wasting CPU time polling for work.
2128 while ( threadID >= activeThreads
2129 || threads[threadID].state == Thread::INITIALIZING
2130 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2132 assert(!sp || useSleepingThreads);
2133 assert(threadID != 0 || useSleepingThreads);
2135 if (threads[threadID].state == Thread::INITIALIZING)
2136 threads[threadID].state = Thread::AVAILABLE;
2138 // Grab the lock to avoid races with Thread::wake_up()
2139 lock_grab(&threads[threadID].sleepLock);
2141 // If we are master and all slaves have finished do not go to sleep
2142 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2143 allFinished = (i == activeThreads);
2145 if (allFinished || allThreadsShouldExit)
2147 lock_release(&threads[threadID].sleepLock);
2151 // Do sleep here after retesting sleep conditions
2152 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2153 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2155 lock_release(&threads[threadID].sleepLock);
2158 // If this thread has been assigned work, launch a search
2159 if (threads[threadID].state == Thread::WORKISWAITING)
2161 assert(!allThreadsShouldExit);
2163 threads[threadID].state = Thread::SEARCHING;
2165 // Copy split point position and search stack and call search()
2166 // with SplitPoint template parameter set to true.
2167 SearchStack ss[PLY_MAX_PLUS_2];
2168 SplitPoint* tsp = threads[threadID].splitPoint;
2169 Position pos(*tsp->pos, threadID);
2171 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2175 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2177 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2179 assert(threads[threadID].state == Thread::SEARCHING);
2181 threads[threadID].state = Thread::AVAILABLE;
2183 // Wake up master thread so to allow it to return from the idle loop in
2184 // case we are the last slave of the split point.
2185 if ( useSleepingThreads
2186 && threadID != tsp->master
2187 && threads[tsp->master].state == Thread::AVAILABLE)
2188 threads[tsp->master].wake_up();
2191 // If this thread is the master of a split point and all slaves have
2192 // finished their work at this split point, return from the idle loop.
2193 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2194 allFinished = (i == activeThreads);
2198 // Because sp->slaves[] is reset under lock protection,
2199 // be sure sp->lock has been released before to return.
2200 lock_grab(&(sp->lock));
2201 lock_release(&(sp->lock));
2203 // In helpful master concept a master can help only a sub-tree, and
2204 // because here is all finished is not possible master is booked.
2205 assert(threads[threadID].state == Thread::AVAILABLE);
2207 threads[threadID].state = Thread::SEARCHING;